|1.||A procesε for the manufacture of paper, board an other wet-laid products under pH conditions ranging from 4. to 12.0, from aqueous furniεheε comprising at least one kin of fibers εelected from the group conεiεting of celluloεi fiberε, εynthetic organic fiberε and inorganic fiberε, εai furnishes being treated with in-situ-εyntheεized complex func tional microgel cementε, retained in εaid productε in propor tionε of from 0.4 to 10.0%, by weight, aε determined by aεh ing, compriεing the εteps of: (a) preparing, in situ, a transient chemically reactiv subcolloidal hydrosol by blending with said furnishes two sep arate εolutionε, one of which compriεeε at leaεt one reagen selected from the group consisting of alkali-metal silicate and quaternary ammonium εilicateε, employed in proportionε o from 0.2% to 5.0%, by weight, of furniεh εolidε, and the othe of which compriεeε at leaεt one reagent εelected from th group conεiεting of alkali-metal aluminates and alkali-meta zincates, employed in proportionε of from 0.2% to 5.0%, b weight, of furniεh εolidε, wherein the ratio of εaid -εilicate to said aluminates, zincates or blends thereof is from 1:10 t 10:1, by weight; (b) blending an aqueous solution comprising at least on crosε-linking agent εelected from a firεt group conεiεting o bivalent and multivalent inorganic salts, employed in propor tions of from 0.4% to 10.0%, by weight, of furnish solidε εaid aqueous solution optionally comprising one or more addi tional crosε-linking agent(ε) εelected from a εecond grou conεiεting of organic, cationically active chemical compound with at least two reactive groups in each molecule, employe in a proportion of up to 0.5%, by weight, of furnish solidε with the furniεheε reεulting from step (a) to cross-link sai in-situ-formed transient chemically reactive subcolloidal hy drosol and synthesize in situ said complex functional microge cements, whereupon said furnishes flocculate instantaneously indiscriminately and completely; (c) optionally purging εaid flocculated furniεhes re suiting from εtep (b) of diεεolved contaminantε; and (d) recovering εaid flocculated furniεhes resulting fro steps (b) and (c) to form paper, board or other wet-laid prod ucts on a paper machine.|
|2.||The process according to Claim 1, wherein said fur nisheε optionally compriεe one or more one of the followin materialε in proportionε εpecified below in relation to fur niεh εolidε: (a) filler pigmentε, up to more than 50%, by weight; (b) color dyeε, up to 5.0%, by weight; (c) carbon black, deagglo erated by the maεter-batc method, up to 0.1%, by weight; (d) latex adhesives with an average particle diamete larger than 70 nm, up to 5.0%, by weight; (e) ultrafine acrylic polymer-emulsion adhesiveε with a average particle diameter εmaller than 55 nm and a glaεs-tran sition temperature ranging from -60°C to +20°C, up to 5.0%, b weight; (f) waterborne acrylic rubber cements, up to 5.0%, b weight; (g) waterborne disperεe thermoplastic adhesives, up t 20.0%, by weight; (h) water-soluble adhesiveε, up to 2.0%, by weight; (i) εynthetic microfibrilε, up to 2.0%, by weight; (j) celluloεic microfibrilε with a length of from 10 μ to 200 μm, prepared extraneouεly by the cascade microfibrilla tion process, up to 2.0%, by weight; and (k) ultrafine electroconductive and/or magnetic cerami and/or metallic powders with particle diametersε finer tha 0.2 μm, up to 20%, by weight.|
|3.||The proceεε according to Claim 1, wherein aqueou εolutions of said organic, cationically active chemical com pounds with at least two reactive groups in each molecule ar employed as an aftertreatment, by blending said aqueous solu tions with furnishes already flocculated by said in-situ sy thesized complex functional microgel cements.|
|4.||The process according to Claim 1, wherein said least one reagent εelected from the group consisting of sodi and potasεium εilicateε and quaternary ammonium εilicateε employed in εaid furniεheε at a concentration of from 0.01% 2.0%, by weight.|
|5.||The process according to Claim 1, wherein said least one reagent selected from the group consisting of sodi and potaεεium aluminates and εodium and potaεεiu zincateε employed in εaid furniεheε at a concentration of from 0.01% 2.0%, by weight.|
|6.||The proceεε according to Claim 1, wherein εaid least one bivalent or multivalent inorganic cross-linking sa selected from the group consiεting of water-εoluble, esse tially colorleεs saltε of calcium, magnesium, barium, alum num, zinc and zirconium is employed in εaid furniεheε at concentration of from 0.02% to 4.0%, by weight.|
|7.||The process according to Claim 1, wherein said least one organic cationically active chemical compound wi at least two reactive groups in each molecule, selected fr the group consisting of cationic surface active agents, org nometallic Werner complexes and cationic polyelectrolyteε, employed in εaid furnishes at a concentration of up to 0.15 by weight.|
|8.||The procesε according to Claim 2, wherein εaid extr neously prepared cellulosic microfibrils with a length of fr 10 μm to 200 μm are made from cellulosic fibers by the casca microfibrillation process comprising the steps of: (a) chopping said cellulosic fibers to a length preven ing hydraulic spinning in the subsequent refining operation (b) refining an aqueous dispersion of said chopped f berε from εtep (a) at a solids concentration of up to 35%, b weight; (c) additionally refining said aqueous dispersion of o fibers resulting from εtep (b) with the aid of centrifuga comminutorε; and (d) finalizing said cascade microfibrillation proceε with the aid of homogenizers in which εaid aqueouε diεperεio of refined fiberε reεulting from εtep (c) is compresεed a very high preεsures and then rapidly decompressed, by pasεin through a nozzle, cauεing the residual bundles of fibrilε t exploεively εeparate into individual microfibrils.|
|9.||The procesε for the manufacture of paper, board an other wet-laid productε from aqueouε furnishes according t Claim 1, wherein the process is performed in a continuous mod in which step (a) is performed by injecting two separate stream of aqueouε εolutions of subcolloidal-hydroεol-forming reagent into an in-line-agitated εtream of εaid furniεhes, to for said tranεient chemically reactive εubcolloidal hydroεolε εaid one εtream compriεing at least one reagent selected fro the group consisting of alkali-metal silicates and quaternar ammonium silicates and said other stream comprising at leas one reagent selected from the group consisting of alkali-meta aluminates and alkali-metal zincates; step (b) iε performed by injecting into the in-line agitated εtream of εaid furniεheε reεulting from εtep (a) a aqueous solution of at least one crosε-linking agent εelecte from a firεt group consiεting of bivalent and multivalen inorganic salts, said aqueouε εolution optionally compriεin one or more additional croεε-linking agent selected from second group conεisting of organic cationically active chemi cal compounds with at least two reactive groups in each mole cule, to cross-link said subcolloidal hydrosol and synthesize in situ, εaid complex functional microgel cements, whereupo said furnishes become flocculated instantaneously, indiscrimi nately and completely; optional step (c) is performed by purging said floccu lated furnisheε resulting from step (b) of diεsolved contami nants; and εtep (d) is performed by recovering said flocculated fur nisheε resulting from stepε (b) and (c) to form paper, boar and other wet-laid productε on a paper machine.|
|10.||A proceεs for the manufacture of paper, board an other wet-laid products under pH conditions ranging from 4. to 12.0, from aqueous furnishes comprising fibers selecte from the group consisting of cellulosic fibers, syntheti organic fibers and inorganic fibers, said furnisheε bein treated with in-εitu-εyntheεized complex functional microge cementε, retained in εaid productε in proportions of from 0.4 to 10%, by weight, as determined by ashing, comprising th stepε of: (a) blending into εaid furniεheε an aqueouε εolutio compriεing at leaεt one croεε-linking agent εelected from firεt group consisting of bivalent and multivalent inorgani saltε, uεed in proportionε of from 0.4% to 10.0%, by weight of furniεh solids, said aqueous solution comprising optionall at least one additional cross-linking agent selected from εecond group conεisting of organic cationically active com pounds with at least two reactive groups in each molecule employed in a proportion of up to 0.5%, by weight, of furnis solidε; (b) preparing, εeparately, a transient chemically reac tive subcolloidal hydroεol by blending an aqueous solution o at least one reagent selected from the group consisting o alkali-metal silicates and quaternary ammonium silicates employed in a proportion of from 0.2% to 5%, by weight, o furnish εolids, with an aqueous solution of at least on reagent εelected from the group consisting of alkali-meta aluminates and alkali-metal zincates, employed in a propor tion of from 0.2% to 5.0%, by weight, of furnish solidε wherein the ratio of said silicates to said aluminates, zinc ates or blends thereof is from 1:10 to 10:1; (c) blending said furnisheε resulting from step (a) wit said transient chemically reactive subcolloidal hydroso resulting from step (b) to synthesize, in situ, said comple functional microgel cementε, whereupon εaid furniεhes floccu late instantaneouεly, indiεcriminately and completely; (d) optionally purging εaid flocculated furniεhe reεulting from εtep (c) of diεsolved contaminants; and (e) recovering said flocculated furnishes resulting fro steps (c) and (d) to form paper, board and other wet-lai products on a paper machine.|
BACKGROUND OF THE INVENTION
l. Field of the Invention
This invention relates to a fundamentally new papermakin process, based on a fundamentally new flocculation mechanis different from charge-neutralization or polymer-bridging know in the prior art. Specifically, this invention relates to a process for th manufacture of novel and improved paper, board and other wet laid products from furnishes comprising cellulosic and/or syn thetic fibers, optionally also comprising inorganic and organ ic filler pigments, water-soluble and water-disperse polyme adhesives, color dyes and other adjuvants, treated with com plex functional microgel cements.
The complex functional microgel cements are synthesize in situ (in the furnish) from transient, chemically reactiv subcolloidal sodium-silico-aluminate or similar hydrosol cross-linked with bivalent and/or multivalent inorganic salts optionally also using organic, cationically active chemica compounds having at least two reactive groups in each molecul as auxiliary (additional) cross-linking agents.
2. Discussion of the Relevant Art
Paper, as a web of cellulosic fibers, is made in princi ple by dewatering aqueous suspensions (furnishes) of partiall crushed (refined) cellulosic fibers on stationary or movin screens and drying the resultant screen residue.
The quality of paper products made in the above manne would obviously be unacceptable for most of today\'s applica tions; hence, modern papermaking furnishes usually consist o blends of selected species of cellulosic fibers, refined t
precisely defined standards; mineral and/or plastic fille pigments; dyes; sizing agents; strength-enhancing polymers and so forth, the resultant webs being appropriately finished To obtain satisfactory retention of solids from such comple furnishes on rapidly moving and vibrating forming screens o modern paper machines, these furnishes must be flocculated i a controlled manner with the aid of appropriate colloid-chem ical mechanisms. The type of flocculation-controlling mecha nism depends on the system of chemical agents ("wet-end che icals") specific to the papermaking process employed.
As is readily understood by those skilled in the art there can be only as many principal, fundamentally differen papermaking processes as there are principal, fundamentall different flocculation mechanisms, the only two such floccula tion mechanisms known in the prior art being based on eithe charge neutralization or polymer bridging. Accordingly, th two principal papermaking processes at the foundation of th entire contemporary papermaking industry, depending on tw fundamentally different colloid-chemical mechanisms (wet-en chemistries) for furnish flocculation, are the "acidic" pro cess, known since ancient times, and the "alkaline" process known for just a few decades.
The flocculation of furnish ingredients in the acidi papermaking process is induced with the aid of papermaker alu (aluminum sulfate) , which requires that the pH level in th furnish be maintained below 5.3. It is only below the pH o 5.3 that alum dissociates into trivalent cations, Al 3+ , whic effectively suppress the negative charges on furnish particu lates causing their flocculation. To maintain a precise con trol of the pH level in the furnish, alum is often used i combination with sulfuric acid. A dose of about 20-30 lbs. o alum per ton of furnish solids is usually sufficient to floc culate the latter and obtain satisfactory solids retention o the forming wire. High-molecular-weight organic cationi polymers are often employed as auxiliary flocculants, i proportions of from 1 to 4 lbs. per ton of furnish solids, t increase the efficiency of solids retention.
To counter the inherent drawbacks of the acidic paper¬ making process, an alkaline version of the papermaking process was developed in the past few decades and is now replacing the former to an ever growing extent. The most pronounced draw- backs of the acidic papermaking process traditionally have been manifested in the low mechanical strength and poor aging characteristic of paper products, along with severe adverse environmental side effects. The alkaline papermaking process, whose wet-end chemistry relies upon the use of special func- tional high-molecular-weight polymers (retention aids) , is carried out as a rule at a furnish pH ranging from about 7 to 8, although somewhat higher or lower pH levels are not uncom¬ mon. The fundamental colloid-chemical mechanism employed for furnish flocculation in the latter process is based on "poly- er bridging," according to which the relatively long macro- molecular chains of the above-mentioned high-molecular-weight polymeric retention aids become attached directly to receptive sites on the surface of cellulosic fibers and/or filler parti¬ cles. As the effect of polymer bridging, manifested by the "tying" of adjacent particulates with polymer chains, ensem¬ bles of flocculated matter are formed which can be retained efficiently on the forming wire of a paper machine.
Although the alkaline papermaking process is free of the major drawbacks of the acidic process, it nevertheless has some serious drawbacks of its own. A most serious one is the former\'s inherent inability to cope with the emerging techno¬ logical trends and advancements taking foothold in the paper industry. These new trends and advancements aim, among other things, toward vastly increased paper machine speeds, on the order of 6,000-8,000 ft/min; formation of webs from signifi¬ cantly more concentrated furnishes than those presently used; total closure of process-water streams on paper machines; manufacture of "high-ash" printing papers with filler-loading levels ranging from 25% to more than 50%, by weight; manufac- ture of high-quality on-machine-coated papers; as well as manufacture of ultraopaque papers (having opacities of at least 98%) for two sided, high-resolution computer printout
and office reproduction. It is thus fair to state that th alkaline papermaking process of the prior art, although relatively very recent newcomer to the paper industry, ha been "born senile" at the very onset as far as its techno logical growth potential is concerned.
The papermaking process of the present invention relie on an instantaneous (for all practical purposes) , indiscrimi nate and complete flocculation of any and all particulate present in papermaking furnishes with the aid of in-sit synthesized multicomponent, functional complex microgel disclosed by the applicant in the co-pending Patent Applica tion Serial No. 07/775,025 ("Functional Complex Microgel with Rapid Formation Kinetics") , Filed October 11, 1991, incorporated herein by reference. The complex microgels i question are synthesized in principle by cross-linking in situ-formed transient, chemically reactive sodium-silico aluminate and similar subcolloidal hydrosols with the aid o bivalent and/or multivalent inorganic salts.
The above in-situ (in the papermaking furnish) synthe sized complex functional microgels used in practicing th present invention are believed to represent the most powerfu and versatile colloid-chemical systems known in the colloi science and technology. Although many thousands of seemingl analogous colloidal systems were described and/or patente during the past 150 years, the applicant is not aware of an even remotely resembling the complex functional microgel under discussion with regard to either the chemical composi tion, ultrarapid formation kinetics, colloid-chemical natur or application versatility. The inescapable deficiency of all paper products made b the prior-art acidic and alkaline papermaking processes is th lack of a truly uniform distribution of the highly diversifie particulate matter present in papermaking furnishes used fo these products\' manufacture. As is readily understood b those skilled in the art, paper products with a unifor structure (statistically uniform spatial distribution of al particulate components) can be obtained only if all of th
following conditions are fulfilled:
(a) starting with papermaking furnishes in which al particulate ingredients (fibers, fiber fines, fillers) ar optimally (for all practical purposes) dispersed, th statistically uniform distribution of the particulates i question being sustained intact prior to flocculation;
(b) flocculating the optimally dispersed particulat components of papermaking furnishes from step (a) instantane ously (for all practical purposes) , indiscriminately and com pletely to retain an equivalent statistically uniform distri bution of furnish particulates in the resultant floes; and
(c) providing an adequate mechanical integrity to th resultant floes, enabling the latter to effectively withstan the shearing forces to which they may be exposed while th flocculated furnish is conveyed to the headbox or applied ont the forming wire of a paper machine.
The mechanical integrity in question is attainable b generating floes with an adequate inherent tenacity or impart ing to these floes the ability to reform (reconstitute) afte a transient breakup. It should be further emphasized in th above context that the use of well-dispersed, let alone opti mally dispersed, furnishes in the acidic and alkaline paper making processes of the prior art, required by condition (a above, is technically infeasible for all practical purposes i that the flocculation mechanisms at the foundations of both o the above processes are too weak to override the action of th powerful modern dispersants. Moreover, the wet-end chemistr of an "ideal" papermaking procesε should also provide, in ad dition to the flocculating action, an intrinsic mechanism fo enhancing the resultant paper products\' mechanical strength and even for imparting desirable functional properties. As i well known to those skilled in the art, however, the wet-en chemistries of the acidic and alkaline papermaking processe of the prior art have, for all practical purposes, none of th above-mentioned "ideal" features which represent but a few o the many attractive and important benefits provided by th versatile papermaking process of the present invention.
Although there is no direct prior art whatsoever relatin to the acid-to-alkaline papermaking process of the present in vention, to the best of the applicant\'s knowledge, reference will be made hereinafter to any even indirectly related tech nical and patent literature deemed helpful to elucidating th subject matter under discussion.
In accordance with the foregoing and disclosures t follow, it is an object of the present invention to provide working description of a fundamentally novel acid-to-alkalin papermaking process, based on a fundamentally new, hithert unknown flocculation mechanism, allowing one to manufactur improved or entirely novel paper, board and wet-laid nonwove products from furnishes treated with in-situ synthesize complex functional microgels having intrinsic cementing an surface-chemistry-modifying properties.
In particular, it iε an object of the invention t provide a working description of the wet-end chemistry of th papermaking process under discussion, relying on the use o the complex functional microgelε disclosed in the co-pendin Patent Application Serial No. 07/775,025 ("Functional Comple Microgels with Rapid Formation Kinetics") , Filed October 11 1991, applicable to a whole spectrum of tasks extending fro laboratory-scale handsheet making up to full-fledged produc tion runs on even the fastest paper machines. It is a further object of the invention to provide nove approaches to the manufacture of paper, board and wet-lai nonwoven products on paper machines utilizing essentially 100 of the particulate matter, such as fibers or fillers, presen in the starting furnishes, thus obtaining effluent stream free of particulate contaminants.
It is a still further object of the invention to provid novel approaches to manufacturing more uniform webs at faste paper machine speeds than is possible with the aid of th acidic and alkaline processes of the prior art. It is a yet further object of the invention to provid novel approaches to manufacturing very uniform webs on pape machines, using considerably more concentrated furnishes tha
can be employed in the acidic and alkaline papermaking proces ses of the prior art, hence, greatly reducing the enormou water demand inherent to the latter processes.
It is a yet further object of the invention to provid novel approaches to attaining the environmentally most desir able goal of a total closure of process-water streams on pape machines.
It is a still further object of the invention to provid novel approaches to the manufacture of cellulosic webs with superior resistance to aging.
It is a further object of the invention to provide nove approaches to the manufacture of high-temperature-resistan wet-laid ("nonwoven") products.
It is a yet further object of the invention to provid novel methods of "intrinεic" sizing of cellulosic webs.
It is a still further object of the invention to provid novel approaches to attaining filler-retention efficiencie exceeding those presently feasible with the aid of the acidi and alkaline papermaking processes of the prior art. It is a yet further object of the invention to provid novel approaches to manufacturing "very-high-ash" papers wit filler-loading levels even exceeding 50%, by weight.
It is a yet further object of the invention to provid novel approaches to manufacturing colored cellulosic and wet laid nonwoven webs, while utilizing essentially 100% of th color dyes employed.
It is a still further object of the invention to provid novel approaches to the manufacture of webs readily acceptin (dissipating) both water and organic liquids. A yet further object of the invention is to provide nove approaches to the manufacture of cellulosic webs whose dry an wet strengths surpass those attainable with similar webs mad with the aid of the acidic or alkaline papermaking processe of the prior art. A still further object of the invention is to provid novel approaches to manufacturing extra-high-strength cellu losic and other wet-laid products from furnishes optionall
comprising, besides cellulosic and/or synthetic fibers, one or more of additional ingredients such as synthetic microfibrils, extraneously prepared novel cellulosic microfibrils, novel ultrafine polymer-emulsion adhesives and novel waterborne rub- ber cements.
It is a yet further object of the invention to provid novel approaches to manufacturing under alkaline conditions groundwood-containing paper products, including newsprint, of a quality not attainable with the aid of the papermakin processes of the prior art.
It is a εtill further object of the invention to provide novel approaches for manufacturing ultraopaque paper (with an opacity of at least 98%) for high-resolution, two-sided com¬ puter printout and office reproduction. A yet further object of the invention is to provide a general blueprint for custom designing novel approaches to the manufacture of a variety of paper, board and other wet-lai products on a paper machine, having better quality and/or being made faεter and more economically than analogous prod- ucts made with the aid of the acidic and alkaline processes of the prior art, as well as to provide novel approaches to mak¬ ing entirely new types of paper, board and other wet-laid products whose manufacture was hitherto not feasible with the aid of the technologies and materials known in the prior art.
SUMMARY OF THE INVENTION
The present invention relates to a fundamentally ne acid-to-alkaline process for manufacturing paper, board and other wet-laid products on a paper machine, from aqueous fur¬ nishes having a pH of from 4.5 to 12 (the alkaline and near- εubalkaline pH range being preferred for practicing the pres¬ ent invention) , wherein said process comprises the following steps: (a) blending an aqueous solution of an alkali-metal or quaternary ammonium silicate, and a second aqueous solution of an alkali-metal aluminate and/or alkali-metal zincate, with a
paper, board or wet-laid-nonwoven furnish to form in situ transient, chemically reactive subcolloidal hydrosol, wherei each of said solutions is employed in said furnish at a con centration of from 0.01% to 2.0%, by weight; (b) blending an aqueous solution of at leaεt one cross linking agent selected from the group consisting of bivalen and/or multivalent inorganic salts, said aqueous solution op tionally containing at least one additional (auxiliary) cross linking agent selected from the group consisting of organi cationically active chemical compounds with at least tw reactive groups in each molecule, with the resultant furnis from step (a) , εaid cross-linking agent(s) being employed i said furnish at a concentration of from 0.02% to 4.0%, b weight, to cross-link said transient chemically reactiv subcolloidal hydrosol and syntheεize in situ a complex func tional microgel cement, whereupon all particulate component of said furnish become flocculated instantaneously, indis criminately and completely;
(c) optionally purging said furnishes resulting fro step (b) of dissolved contaminants, e.g., with the aid of fil tration and rinsing; and
(d) recovering said furnishes resulting from steps (b) and/or (c) to manufacture paper, board or other wet-laid (non woven) products on a paper machine. The in-situ-synthesized microgels from εtep (b) , furthe in the εpecification and in the claims to follow referred t in the generic terms, regardless of their specific chemica compoεition, as complex functional microgels or microge cements, are employed in proportions of from 0.4% to 10%, b weight, as determined by aεhing, in relation to the mass o the resultant paper, board or wet-laid nonwoven products wherein the constituents of said microgel cements are
(a) from 0.4% to 10%, by weight, in relation to th total mass of paper, board or wet-laid-nonwove furnish solids, of transient, chemically reactiv subcolloidal hydrosols formed of (1) at least one reagent selected from the grou
consisting of alkali-metal silicates and qua ternary ammonium silicates; and (2) at least one reagent selected from the grou consisting of alkali-metal aluminates an alkali-metal zincates, the ratio of the rea gents of (1) to the reagents of (2) being fro 1:10 to 10:1, by weight; cross-linked by
(b) at least one cross-linking agent selected from first group consisting of bivalent and multivalen inorganic salts, employed in a proportion of fro 0.4% to 10.0%, by weight, in relation to the tota mass of paper, board or other wet-laid products and, optionally, at leaεt one auxiliary cross-link ing agent selected from a second group consisting o organic, cationically active chemical compounds hav ing at least two reactive groups in each molecule employed in a proportion of up to 0.5%, by weight in relation to the total mass of paper, board o other wet-laid products, the ratio of said cross linking agents to said chemically reactive, subcol loidal hydrosols being from 1:10 to 10:1. In addition to cellulosic and/or synthetic fibers an customary disperse and/or water-soluble functional adjuvant used in papermaking, the above-mentioned furnisheε for makin paper, board and other wet-laid productε optionally compris at least one of the following materials in proportions speci fied below in relation to furnish solids:
(a) filler pigments, up to more than 50%, by weight; (b) color dyes, up to 5.0%, by weight;
(c) carbon black, deagglomerated by the master-batc method, up to 0.1%, by weight;
(d) commercial latex adhesives with an average particl diameter larger than 70 nm, up to 5.0%, by weight; (e) novel ultrafine acrylic polymer-emulsion adheεive with an average particle diameter smaller than 55 nm and glass-transition temperature ranging from -60°C to +20°C, u
to 5.0%, by weight;
(f) novel waterborne acrylic rubber cements, up to 5.0% by weight;
(g) waterborne disperse thermoplastic adhesives, up t 20.0%, by weight;
(h) commercial water-soluble wet-end adhesives, up t 2.0%, by weight;
(i) synthetic microfibrils, up to 2.0%, by weight; (j) cellulosic microfibrilε with a length of from 10 μ to 200 μm, prepared extraneously by the cascade microfibrilla tion process, up to 2.0%, by weight; and
(k) ultrafine electroconductive and/or magnetic cerami and/or metallic powders with particle diameters finer tha 0.2 μm, up to 20.0%, by weight.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the preferred mode of practicing the present inven tion, novel and improved paper, board and other wet-laid prod ucts are manufactured on paper machines from aqueous furnishe comprising cellulosic and/or synthetic fibers, optionally als comprising at least one functional ingredient such as inorgan ic and organic pigments, organic polymer adhesiveε, color dye and other adjuvantε uεeful in papermaking, diεperεed and/o dissolved in said furnishes, by flocculating all particulat furnish ingredients instantaneously, indiscriminately and com pletely with the aid of the above-mentioned, in-situ-synthe sized complex functional microgels which, in terms of second ary functions, also contribute (by virtue of their cementin properties) to the dry and wet strengths of the resultan cellulosic or wet-laid nonwoven webs. The microgelε (microge cementε) in queεtion, disclosed in the previously mentione co-pending Patent Application Serial No. 07/775,025, File October 11, 1991, are formed in two distinct process stages a different polymerization mechanism being active in each stage
In the first process stage, two separate reagent solu¬ tions are introduced into an aqueous furnish comprising cellu¬ losic and/or synthetic fibers, optionally also containing fil¬ ler pigments, water-disperse and/or water-soluble adhesives, dyes and other water-disperse and/or water-soluble adjuvants (auxiliary functional materials) . One of these reagent solu¬ tions contains an alkali-metal or quaternary ammonium sili¬ cate, preferably sodium silicate. The other reagent solution contains an alkali-metal aluminate and/or alkali-metal zinc- ate, preferably εodium aluminate. An immediately commencing addition polymerization of the above "primary" subcolloidal- hydrosol-forming reagents leads to the formation of sodium- silico-aluminate (zincate) dimers, trimers and higher-rank oligomers. These transient, chemically reactive anionic polymer precursors remain, for a limited period, in a very specific state of solution, for which the objectively fitting term "subcolloidal hydrosolε" haε been employed herein.
In the second process stage, an aqueous solution contain¬ ing at least one cross-linking agent selected from the group consiεting of eεsentially colorless, bivalent and/or multi- valent salts of calcium, magnesium, barium, aluminum, zinc and zirconium, preferably calcium chloride or nitrate, iε intro¬ duced into the above-mentioned furnish containing the subcol¬ loidal hydrosol formed in the first process stage. The poly- condensation reaction taking place between the transient, chemically reactive subcolloidal εodium-εilico-aluminate (zincate) hydroεolε and the inorganic croεs-linking εalts leads to an ultrarapid formation of complex (multicomponent) calcium-silico-aluminate (zincate) or similar microgel cements, made up of networks of macromolecules of a polymer- polycondensate type.
The colloidal consequence of synthesizing the complex microgel cements used in practicing the present invention in in-εitu, in the furniεh, is an instantaneous, indiscriminate and complete flocculation (coflocculation) of any and all par¬ ticulates present in the furnish. The tenacity of the evolv¬ ing floes can often be enhanced, improving the efficiency of
fines retention on the forming wire, by incorporating sma proportions of cationic polyelectrolytes into the solutions the above-mentioned inorganic bivalent and/or multivale cross-linking salts. It should be emphasized that the primary reagents used the firεt stage of the process of the formation of the compl microgels, i.e., sodium silicate and sodium aluminate (zin ate) , must first react with each other to form the transien chemically reactive εubcolloidal εodium-silico-alumina (zincate) hydrosols before any complex microgelε can be εy theεized (in the second stage of the process) by cross-linki the subcolloidal hydrosolε in queεtion with bivalent or mult valent inorganic salts. Hence, the subcolloidal sodium-εilic aluminate (zincate) hydroεolε which, along with the inorgan crosε-linking salts, are the factual microgel-forming agent muεt be conεidered as "higher-rank" reagents synthesized situ from the primary, lower-rank reagents, i.e., sodium sil cate and sodium aluminate (zincate) . If the latter individu reagents reacted directly (on their own) with a crosε-linki εalt, e.g., calcium chloride, the productε of εuch reactio would be merely εuεpenεionε, or precipitateε, of εolid, mo or less crystalline particles of bico ponent calcium silica and calcium aluminate (zincate) , respectively, but not micr gels, let alone complex microgels which, by definition, mu contain at leaεt three different chemical building blocks their macromolecular make-up.
The complex functional microgels used in practicing t present invention are formed virtually instantaneously, t chemical reaction of polycondensation between the above-me tioned low-molecular-weight subcolloidal hydroεols and t bivalent and multivalent inorganic salts being estimated occur in less than one microsecond. The consequences of th polycondenεation are further manifeεted in a very rapid prop gation of aεεociation between calcium-εilico-aluminate (pol mer-polycondenεate) macromoleculeε, bringing about, within couple of milliεecondε, the development of colloidal form tions with useful molecular weights that may reach billion
It iε primarily thiε rapid continuous growth of the molecula weights acroεε such an enormouεly broad range, "εweeping through the entire reaction εpace, which iε deemed reεponεibl for the instantaneous, indiscriminate and complete floccula tion of even the most heterodiεperεe and polydisperse colloi dal syεtemε known in the art, regardleεε of these syεtemε phyεical, chemical or colloidal make-up.
The quantitative aεpectε of the unique flocculating powe of the in-εitu-εyntheεized complex microgelε under discussio can be readily underεtood conεidering that the efficiency o organic polymeric flocculantε, εuch aε are routinely employe in the acidic and alkaline papermaking procesεeε of the prio art, increases markedly with the increaεing molecular weight Aε iε well known to thoεe εkilled in the art, however, the uε of polymeric flocculants with a molecular weight higher tha about 15,000,000 iε often difficult, if not impoεεible, due t their limited εolubility in water. Moreover, all organi polymeric flocculantε have relatively narrow molecular-weigh diεtributionε and are thuε incapable of εatiεfying "acrόsε the-board" the highly differentiated flocculation requirement inherent to εuch pronouncedly heterodiεperεe and polydiεperε εystems aε the contemporary furniεhes for making paper an other wet-laid products. On the other hand, the complex micro gelε under diεcuεεion poεεess εuch an across-the-board (uni versal) flocculating ability in that, being εynthesized i situ and growing continuouεly from the very εmalleεt dimen sions, they sweep through an enormously broad molecular-weigh range. It would obviously be imposεible to introduce analo gouε extraneouε high-molecular-weight polymeric flocculant into a paper (nonwoven) furnish becauεe of insolubility.
While the complex (multicomponent) microgels used i practicing the present invention were completely unknown here tofore, the transient, chemically reactive subcolloidal hydro sols used for syntheεizing theεe microgelε need some elabora tion to distinguish them from other, deceptively similar εys temε of the prior art. In view of the confuεion and lack o εtandardization in the present colloid-chemical terminology
a fundamental treatment of the subject matter of the preεen invention and a brief chronological review of the prior ar related to this subject matter is deemed necessary.
It is esεential to point out in the above context that a active worldwide intereεt in natural and εynthetic εilica an εilico-aluminateε commenced with the key discoveries of
1) water-soluble sodium εilicates ("water glass") b Johann Nepomuk von Fuchs (1774-1856) , who εuggeεted numerou practical applications for these intereεting chemicalε, e.g. in application to the formulation of adheεives, cements, flam retardants for paintε, detergentε, εoap builders, dyeing adju vants, metal fluxes and fertilizerε;
2) metallic aluminum in 1825 by Oerstedt and Woehler with most of the inorganic chemical compounds of this elemen known today having been described in the profeεεional litera ture by countless scientists within the next few decades; an
3) the phenomena of ion exchange in soilε (natural alu mino-εilicateε) by J. T. Way in 1850.
The rapidly following diεcoverieε of many other commer cially valuable propertieε of silica and alumino-εilicat mineralε, e.g., in the application to the deεiccation o gaseε, clarification of water, removal of color impuritie from edible and mineral oilε, or manufacture of pigments an catalystε, triggered intenεive reεearch efforts in the fiel of silica and alumino-εilicateε. These efforts were directe both towards improving the performance properties of naturall occurring materials as well aε producing analogouε or ye unknown εynthetic materialε with yet more improved or eve entirely novel propertieε. Due to the similar dimensions of ionic radii of Si 4+ an Al 3+ (0.41 k and 0.50 A, respectively), as well aε an over whelming abundance of theεe two elementε in the lithoεphere a large variety of alumino-εilicate mineralε have been εyn theεized in nature by geochemical processes. In contrast, th more complex (comprising three or more components) mineral related to alumino-εilicateε, exemplified by the previousl mentioned calcium-alumino-silicates, are relatively uncommo
in nature. The reason for the rare occurrence of calcium alumino-εilicate mineralε, εuch as anorthite, Ca[Al 2 Si 2 0 8 ] , o margarite, CaAl 2 [Al 2 Si 2 O 10 ] [OH] 2 , is readily understood con sidering that Ca ++ , with an ionic radiuε of 0.99 A, iε rathe εtrongly rejected from an evolving alumino-εilicate matrix making the formation of such complex minerals by the exceed ingly slow geochemical procesεeε difficult.
Since no significant practical applications have yet bee found for calcium-alumino-silicate mineralε, an in-depth ex ploration or εyntheεiε of the latter generated thuε far onl a limited interest from the standpoint of academic or indus trial research. On the other hand, a great number of alumino εilicate preparationε and productε were εyntheεized in th past 150 yearε becauεe of the latterε\' highly diverεified com ercial applications. That such an enormous variety of chemi cal compounds, characterized by diεtinct phyεical and colloid chemical propertieε, can be εynthesized using juεt one or tw of the four simple, eaεily available reagents, i.e., εodiu εilicate, εilicic acid, εodium aluminate and alum, has abεo lutely no precedent in the inorganic chemiεtry. The almos countless patents issued in the past 150 years for a broa variety of synthetic silica and alu ino-silicate product obtained with the aid of the above-mentioned reagents relat esεentially to only three principal colloidal εystems, namely continuous gels and discrete sols and precipitates.
The incredible diversification of the forms and proper ties of products εyntheεized with the aid of the εame fe reagentε may be explained by accepting the hypotheεiε tha colloidε are the loweεt-rank εyεtems known in nature equippe with "memory." It is the latter which makes the colloid "remember" their history in chronological detail and reac accordingly, as manifested in terms of their resultant materi al properties and functional behavior. Hence, any intention al, or even accidental, deviation from established syntheεi procedureε or reaction conditions will bring about inescapabl certain differences, mostly quantitative but sometimes pro foundly qualitative, in the constitution and/or functiona
propertieε of the reεultant colloidal εyεte ε. Indeed, eεεen- tially all εimilar, or even virtually identical, patented εyn¬ thetic εilica and alumino-εilicate productε differ among eac other merely with reεpect to relatively minor quantitativ compoεitional variationε, procedural modificationε (such a may pertain to the rates, order of addition and concentration of reagents, pH ranges, as well as thermal and aging regimes) , or with respect to the resultant products\' modified physica and physicochemical propertieε and new areaε of application. How even a minor proceεεing detail may be deciεive to th very uεefulneεε of a εynthetic alumino-silicate product may b illustrated, for example, by U.S. Patent No. 2,757,085 t Paquin. Aε diεcloεed therein, εatiεfactory color-reactiv alumino-εilicate pigmentε, synthesized in situ in a papermak ing furniεh, were obtained only if sodium aluminate waε intro duced into the furnish firεt, followed by the addition o sodium silicate, but not vice-verεa. Similarly, U.S. Paten No. 4,213,874 to Williamε et al. teaches that it was posεibl to εynthesize satisfactory amorphous sodium aluminosilicat baεe exchange materialε only if, among other things, th proper sequence and rate of addition of the reactants wer maintained during the precipitation procesε.
The critical dependence of a εucceεεful preparation o colloidal εyεtemε on maintaining εtrictly defined proces parameters and conditionε iε perhapε beεt summarized by S. Voyutsky in his textbook of COLLOID CHEMISTRY (Page 269, secon paragraph) , Mir Publishers, Moscow, translated into English i 1978: "Colloidal systemε can be obtained by variouε chemica reactionε: exchange, reduction, oxidation, hydrolysis, and s forth. But colloidal systems are not always formed in reac tions capable of producing sols; they are formed only (under lining added by the applicant) at definite concentrations o the initial substances, at definite order of their mixing an temperature, and when some other conditionε are met." The preferred tranεient, chemically reactive εubcolloida hydroεolε used in practicing the present invention are solubl εodium-alumino-εilicates which form εpontaneously when solu
tionε of sodium silicate and sodium aluminate are blended int aqueouε εlurrieε of particulate raw materialε (furnishes) use for the manufacture of celluloεic or wet-laid nonwoven prod uctε by the papermaking process under discussion. As the re εult of an immediately commencing addition polymerization, dimerε, trimerε and higher-rank oligomers (polymer precursors) evolve sequentially and continuously into very-low-molecular weight sodium-alumino-silicate macromoleculeε of an anioni polyelectrolyte type. Due to the relatively low concentration of the reagentε employed, but moεtly due to the prompt croεε linking of the transient subcolloidal hydroεolε (terminatin their further molecular growth) , the evolving εodium-alumino silicate macromolecules are very εmall, their eεtimated dimen εionε being at moεt only εlightly larger than 1 nm (10 A) . Such highly diεperse syεtemε represent special borderlin solutionε claεεified dimenεionally above εolutionε of cryεtal loidε (εimple moleculeε or ionε) , but below colloidal εolu tionε, e.g., those of starch, protein or polyacrylamides. εcientifically appropriate term "εubcolloidal hydroεolε" ha been systematically used herein in referring to the above εyε temε, which εhould be diεtinguiεhed from aquaεolε (hydroεolε) of the prior art which are aqueous suspensions of solid par ticles with diameters of from about 5 nm to 100-200 nm.
Historically, the terminology uεed in colloid εcience an technology evolved in connection with the baεic investigativ tools available at the inception of colloidal research, name ly, the conventional light microεcope and ultramicroεcope. Colloidal particleε with diameterε εmaller than 200 nm coul hardly be reεolved with the aid of old-faεhioned light micro εcopes equipped with low-aperture objectives; hence, they wer referred to as "submicroscopic." On the other hand, ultra microεcopeε, utilizing the Tyndall effect, made it poεεible t obεerve, though not resolve, particleε aε εmall aε 5 nm i diameter. Conεequently, colloidal εyεtemε became traditional ly the domain of ultramicroεcopical inveεtigationε and thei clasεification as "ultramicroscopic," with particle dimenεion ranging from 5 nm to 200 nm, still has a great deal of valid
ity for most practical applications. Regrettably, some les rigorous colloid textbooks still routinely list the colloida dimensions as extending from 1 nm to 500 nm, or even 1000 nm. Modern scientific research has establiεhed unequivocally, however, that the traditional delineation between "colloidal and "noncolloidal" (crystalloid) syεtemε, eεtabliεhed εolel on the baεiε of the dimensions of particles of the disperε phaεe, haε no εcientific foundation. Hence, contemporary doc trineε refute the concept of "colloidε" and "cryεtalloidε, interpreted in the past in a rather absolute senεe, acceptin inεtead the existence of a very specific "colloidal state asεociated with diεperse systems conforming to the establishe criteria of "colloid-like" behavior. The reasons for this ca be illuεtrated rather clearly uεing the example of εodiu chloride which behaveε aε a typical cryεtalloid in aqueou solutions and a typical colloid in benzene εolutionε, numerou other εuch syεtemε already having been identified.
Many experimental findingε made during εtudieε of-highl disperse syεtemε atteεt particularly clearly to the uniqueneε of the particle-dimenεion interval extending from 1 nm to 5 n (10-50 A) , in which the colloidal and crystalloid stateε over lap and deficiencies of the imperfect colloid-chemical nomen clature are most evident. Hence, an unambiguous treatment o disperse systems of the above type frequently makes definin them in fundamental terms virtually mandatory, aε haε bee eεtabliεhed in dealing with many extremely important medi εuch aε εurfactants, dyeε, toxinε and antitoxinε. For exam ple, the dimenεions of individual moleculeε of εome of th above-mentioned materialε are larger than 1 nm (10 A) , con εidered aε the conventional upper limit of cryεtalloid par ticles, but smaller than 5 nm (50 A) , considered as a prac tical lower limit for typical colloidal particles. Since th behavior of such syεtemε overlaps the domains of both crystal loidε and colloidε, εome authors have introduced the rathe artificial term "semicolloids" to deal with these unusua solutions. Still other authors refer to such highly dispers syεtems, with particle dimensions ranging from l nm to 5 nm,
as "amicronε" (εubcolloidε) , to be diεtinguiεhed from "submi- cronε" applying to systemε with particleε larger than 5 nm in diameter.
Perhapε the most unfortunate aspect of the traditional colloid-chemical terminology is that the term "aquasol," an the equivalent term "hydroεol," in which the εuffix "εol" εtandε for "solution," are used in referring to suεpenεionε of ultramicroεcopic solid particles in water. Although aqua- εolε (hydrosols) do indeed appear as translucent (opalescent) solutionε to an unaided eye, the latter, fundamentally incor¬ rect, termε complicate the clarity of the iεεue when the εci- entific diεcourεe revolveε around boundary εyεtems of overlap¬ ping behavior (e.g., crystalloid/εubcolloid or εubcolloid/col- loid) or extendε beyond professional circles. It should b pointed out, though, that many rigorous colloid scientiεt εyεtematically employ the εcientifically correct term "εuεpen- soids" in referring to aquasolε (hydroεolε) of the prior art.
The above-mentioned, nomenclature-relatedproblemε becom even more complicated in dealing with novel subject matter, such as the subcolloidal sodium-silico-aluminate or εimila hydroεolε used to synthesize the complex microgels at th foundation of the present invention. The latter subcolloidal hydrosolε conεtitute borderline solutions of transient, chemi¬ cally reactive polyanionic molecules. As solutions, they hav the appearance of completely clear, plain water, are totall devoid of any solid particles and do not exhibit the Tyndal effect.
The tranεient character of theεe continuouεly changin subcolloidal sodium-alumino-εilicate hydrosolε renderε th underlying oligomers and macromoleculeε fundamentally unde finable in terms of the exact phyεical dimensionε or chemica compoεition. Thiε iε understood best when considering tha the reaction of addition polymerization, commencing with th moment the εolutionε of εodium εilicate and εodium aluminat become introduced into a reactor (furnish) , proceeds continu ously. Hence, even if it were possible to determine, at an given instant, the dimensions, molecular weights, or chemica
composition of the evolving macromolecules, εuch informatio would become obsolete in the very subsequent instant.
It is poεεible, however, to objectively define the unique εyεtemε mentioned above employing criteria of the philosoph of science used in formulating εcientific definitionε. Accord ing to theεe criteria, the continuously changing, transient, subcolloidal hydrosols cannot be claεsified as "materials" i a conventional sense in that they have no definite (fixed) form, masε or propertieε by which a material iε conventionall described or defined, e.g., in textbooks of material science. Instead, the latter subcolloidal syεtemε, repreεenting a ver εpecific "material εtate. " are defined in terms of
(a) a detailed description of the reaction medium an conditions at the onεet of the εyntheεiε of the εubcolloida hydroεolε in question, i.e., at the point of time (t) wher t = 0; and
(b) an arbitrary subεequent fixed point of time (t = c) . The latter means that if the in-situ synthesis of an arbitrar transient subcolloidal hydroεol iε initiated at a time t = 0, uεing identical reagentε, reagent proportionε and concentra tionε, sequences and rates of reagent addition, temperature, pH and all other effective reaction conditions and proces parameterε, then, and only then, the reεultant transient sub colloidal hydroεol will be exactly the same each time it pas εes through a subεequent fixed point of time t = x (x = c) .
While the above-discuεεed continuouεly evolving (in stat nascendi) subcolloidal εyεtemε, e.g., the transient subcolloida sodium-alumino-silicate hydroεols under discussion, are unde finable in conventional terms used in material sciences, it i also completely certain that they are different from an existing natural or εynthetic substances of the same nomina chemical compositionε. By contraεt, all traditional sols ar claεsified aε "phaεeal" colloids, the latter term indicatin that the disperεe phaεe iε identical to an analogouε phaε exiεting on a macro scale and could, in principle, be obtaine from the latter with the aid of mechanical comminution o other preparatory methods.
The transient aspects of the subcolloidal sodium-alumino εilicate hydroεolε used in practicing the present inventio must be particularly εtrongly emphaεized εince the process o addition polymerization between sodium silicate and sodiu aluminate is a continuous one. Hence, at some advanced stag of polymerization (aging) , particles of the above-mentione subcolloidal hydroεolε acquire εufficiently high molecula weightε to exceed the εolubility limits, whereupon the subcol loidal hydrosolε in queεtion transform into conventiona (prior-art) aquasolε, i.e., colloidal εuspensionε of εoli particleε. The period of aging neceεεary to initiate εuch tranεformation may extend from less than a second up to sever al days, or even weeks or months, depending on the concentra tion of εodium εilicate and sodium aluminate (zincate) in th reaction medium (furnish) , and iε manifeεted by the appearanc of the Tyndall effect.
Aε iε readily understood by thoεe εkilled in the art, th chemical reactivity of the tranεient εubcolloidal hydroεolε i question, i.e., the ability to form the complex microgels a the foundation of the present invention by a process of chemi cal cross-linking carried out with the aid of bivalent (multi valent) inorganic saltε, decayε with the increaεing degree o polymerization (aging) . The chemical reactivity iε loεt almos completely when the εolute particles of the above subcolloida hydrosolε polymerize beyond the εolubility limitε transformin into solid colloidal particles of conventional sols. It i important, therefore, that the second εtage of the in-εit syntheεiε of complex microgelε, in which the above-mentione subcolloidal sodium-alumino-εilicate or similar hydrosols ar chemically cross-linked with the aid of bivalent and/or multi valent inorganic salts, be carried out before the advent o the Tyndall effect.
In typical paper mill installations working in a continu ous proceεε mode, the above croεε-linking can be carried ou within a period ranging from εeveral εecondε to a couple o minuteε, counting from the moment the solutions of sodiu silicate and sodium aluminate are added to furnishes fo
making paper, board and other wet-laid productε.
The primary purpoεe of the in-εitu εyntheεized comple functional microgels under discussion is to induce an instan taneous, indiscriminate and complete flocculation (cofloccula tion) of all diεperεe raw materialε preεent in paper, board o wet-laid-nonwoven furniεheε. Flocculation phenomena play fundamental role in the manufacture of celluloεic and wet-lai nonwoven productε; however, the flocculation proceεεeε uεe in the acidic and alkaline papermaking proceεεeε of the prio art are εlow, detrimentally εelective (rather than indiscrimi nate) and incomplete. Accordingly, theεe proceεseε are no well εuited for the manufacture of advanced paper, board an wet-laid nonwoven productε (especially at high paper machin speedε) that are free of detrimental conεequenceε of a εelec tive flocculation and fractionation of furniεh component according to specieε and size, manifested in more or les pronounced performance deficiencies of the resultant productε. Aε a matter of fact, many potentially uεeful ultrafine colloi dal materials cannot, for all practical purposeε, be floccu lated (precipitated) with the aid of the inefficient floccula tion processes and agents used in prior-art acidic and alka line papermaking processes, thus being effectively eliminate as viable raw materials for manufacturing the above-mentione advanced paper, board and wet-laid nonwoven products. Typical contemporary paper furniεheε are highly hetero diεperεe and polydiεperεe waterborne εyεtemε containing cellu loεic fiberε and fiber fines, inorganic and organic fillers water-soluble adhesiveε, εizing agentε, dyes, and other adju vants. All of the above furnish ingredientε muεt be uniforml coflocculated to be efficiently retained on the forming wir of a paper machine and yield εatiεfactory (uniform) webs. A iε well known, however, each diεperεe component of a hetero disperse εystem has different surface-chemical properties electrical-charge density, dispersion stability, and εo forth hence, alεo a different reεistance to flocculation. Moreover virtually all particulate specieε uεed in paper furniεheε ar more or leεs polydisperse in their own right, the proceεs o
flocculation of dimensionally different component fractions o these εpecies being controlled by different colloid-chemica and other mechanismε. Conεiderable difficultieε are encoun tered in particular when flocculating inherently polydiεperε mineral fillers whose particle dimenεions may range from abou 0.1 μm to 20 μm e.s.d. (equivalent εpherical diameter). Hence, coarεe filler fractions, e.g., those with an equivalent spher ical diameter larger than 2 μm, are relatively resistant t colloid-chemical flocculation their retention in the web bein affected primarily by mechanical factors εuch as turbulence, gravitational settling, or filtration. The flocculation o intermediate-size fractions, on the other hand, is effecte mainly by the neutralization of electrical charges on fille particles and by polymer bridging. The ultrafine filler frac tions, i.e., those with an equivalent εpherical diameter εmal ler than 0.1 μm, are hardly affected by the flocculation mech aniεmε employed in the acidic and alkaline papermaking proceε ses of the prior art. Similarly, many ultrafine particulateε, such as color dyeε or polymer-emulεion adheεiveε, are largel immune to flocculation by alum or organic polymerε.
Another detrimental εide effect of the slow and selectiv flocculation of heterodisperεe and polydisperse furniεh compo nentε in the acidic and alkaline papermaking proceεεes of th prior art is the formation of aggregates of the undesirabl εegregated [...fiber/fiber...] or [...filler/filler...] typeε. The latter εegregation, in turn, iε the reaεon for a reduce retention of filler particleε on the forming wire, deteriora tion of web-formation quality, and reduction of the optical performance efficacy of filler particleε retained in the web. The slow and selective flocculation is particularly detrimen tal to the optical-performance efficacy of the expensiv titanium dioxide (Ti0 2 ) pigments, which are virtually alway employed in combination with less expensive, low-refractive index extender pigments intended to function as phyεica εpacerε. The reaεon for this reduced optical-performanc efficacy of Ti0 2 is that, because of the inefficient (slow an selective) flocculation proceεses of the prior art, the pre
dominantly formed filler-particle aggregates are of the opti cally inferior [...Ti0 2 /Ti0 2 ...] and [...extender/extender... types instead of the deεirable, optically far more efficien [...extender/Ti0 2 /extender...] type. It εhould alεo be borne in mind that a εubεtantial pro portion of furniεh ingredientε diεpenεed from the headbox ont the forming wire is not retained in the first pass and must b recycled a couple of times through the papermaking proceεε Since the flocculation of furniεh ingredientε in the conven tional (prior-art) acidic and alkaline papermaking proceεse iε also incomplete, the detrimental effects of fractionatio and selective aggregation (flocculation) of the individua furnish components are continuously amplified during th above-mentioned recycling. The instantaneouε, indiεcriminate and complete flocculat ing action of the in-εitu (in the furniεh) εyntheεized comple functional microgelε uεed in practicing the preεent inventio totally eliminateε the drawbackε normally aεεociated with th uεe of highly heterodiεperεe and polydiεperεe paper, board an wet-laid-nonwoven furniεheε. Hence, novel and unuεual type of paper, board and nonwoven productε can be prepared fro even the moεt exotic, extremely heterodisperse and polydiε perεe furnishes, without incurring even a trace of selectivit (fractionation) or incomplete flocculation. As iε readil underεtood by those skilled in the art, furniεhes of th above-mentioned type could not be used in the papermakin proceεεes of the prior art without incurring unacceptabl material losses and operational difficulties, not to mentio potentially diεastrous ecological conεequenceε. The exotic furniεheε under discusεion may contain, amon other thingε, cellulosic fibers; synthetic organic fibers inorganic fibers; reinforcing synthetic microfibrils an extraneously prepared celluloεic microfibrils; magnetic an electroconductive metal powders; mineral as well as plasti filler pigments with particle dimensions ranging from abou 0.1 μm up to 20 μm e.s.d.; non-film-forming (nonfuεing, o fuεing only at elevated temperatures) emulsion polymers wit
particles as small aε 30 nm in diameter; novel ultrafin polymer-e ulεion adhesives with particles smaller than 55 n in diameter and glass-transition temperatures ranging betwee -60°C and +20°C; novel waterborne rubber cements; commer cial water-soluble paper adhesiveε; microparticulate thermo plaεtic adheεiveε; color pigments; and carbon black wit particles even εmaller than 10 nm in diameter. Moreover, th above particulateε may have relative denεitieε ranging fro about 1 g/cm 3 for organic polymerε up to 4.2 g/cm 3 for titaniu dioxide pigmentε, or yet conεiderably higher for metal pow derε, while their εurface-chemical propertieε may range fro very hydrophilic to extremely hydrophobic.
Virtually no limits to potential furnish diversitieε, hence alεo to the diverεity and verεatility of the reεultan paper, board and wet-laid nonwoven productε, are enviεage with the papermaking proceεε of the present invention since, in the applicant\'s extenεive inveεtigationε, no waterborn diεperεion or colloidal system, regardlesε of how fine, com plex or difficult, had yet been encountered able to reεiεt th overpowering instantaneous, indiscriminate and complete floc culating action of the in-εitu synthesized complex functiona microgels under diεcuεεion.
The εecondary purpose of the complex functional microgel is to provide, by virtue of their inherent cementing proper ties, an increased level of mechanical εtrength to paper, board and wet-laid nonwoven productε made by the proceεε o the present invention. The adhesive action of theεe microgel can be controlled by both the dosage employed and a purposefu optimization of their chemical composition, much in the sam way as iε cuεtomary in optimizing the bonding εtrength o contemporary induεtrial inorganic cementε. With cellulosi webs, the principal mechanical εtrength is derived fro hydrogen bonds formed between functional groupε exposed at th surface of fibrillated (refined) cellulosic fibers, the actin range of εuch bondε extending merely over a diεtance of a fe of Angstroms. A secondary reinforcement of cellulosic web made by the prior-art papermaking processes is presentl
obtained with the aid of water-εoluble polymerε, main εtarch, added directly to the papermaking furniεh.
While the concept of cementing εynthetic organic a inorganic fiberε by the complex functional microgels used practicing the present invention is rather straightforward, analogous cementing of cellulosic fiberε iε unique a warrantε further elaboration. Aε iε obviouε from elementa chemical conεiderationε, the in-εitu (in the furniεh) synth sized complex microgels of calcium-silico-aluminate or simil types leave, upon drying, an inorganic residue embedded in t reεultant celluloεic-web εtructure. According to prior-art\' teachings and experience, however, any and all inorganic pa ticulates embedded between cellulosic fibers invariably i hibit the formation of cloεe-range hydrogen bondε by phyεical ly εeparating the fiberε, thus weakening the resultant webε To effectively "glue" celluloεic fibers to each oth with the aid of the microgels in question, three obvious co ditions must thus be met. Firεt of all, the microgel part cles must be extremely εmall (ultrafine) , εuch aε are inde obtained with the aid of the high εhearing forceε uεed in εy theεizing these microgels, in εitu, in paper, board and we laid-nonwoven furniεheε. Secondly, the ultrafine microg particles must be "strategically" depoεited at the very co tact areaε between adjacent fiberε. Thirdly, the microg particleε muεt have an inherent deformability to εpread in t form of diεcrete, ultrathin layerε between the adjacent fibe to be cemented. Needless to say, only true microgel particle but not solid aquasol particleε or precipitateε, εuch aε pi ments, are capable of such a deformation. Some quantitati aspects of the adhesive action of the complex microgel cemen in celluloεic webε will be discuεεed in the context of t exampleε to follow.
An additional interfiber bonding of a hitherto unkno kind can be obtained by coflocculating, with the aid of t complex microgelε, novel ultrafine polymer-emulεion adheεiv added directly to the papermaking furnish. The subject matt of this novel class of adhesives, developed by the applica
εpecially for icroadhesive applications, is disclosed in the co-pending Patent Application Serial No. 07/333/435 ("Ultra fine Polymer-Emulsion Adhesives for Microadhesion") , File April 4, 1989, incorporated herein by reference. The latte adheεiveε, encompaεεing primarily acrylic polymerε and co polymers, have average particle diameters smaller than 55 n and glasε-tranεition temperatureε (T g ) ranging from -60°C t +20°C. In comparison, the average particle diameters of eve the finest conventional (commercially available) polymer emulsion adhesiveε, known in the trade as "latexeε," ar εignificantly coarser, e.g., in excess of about 70 nm.
It should be pointed out in the above context that poly¬ mer-emulsion adheεiveε have found thus far no application as direct furniεh additiveε in the prior-art acidic and alkalin papermaking proceεs, since they cannot be acceptably floccu lated (retained with furnish solidε) by the latter. Moreover, even the fineεt conventional latexeε, uεed aε wet-end addi tiveε, are too coarεe to provide any meaεurable interfibe bonding until the relative weight-content of latex in the we exceedε about 15%. Aε a consequence, commercial latexes are used only to saturate paper or wet-laid nonwoven webs tha have already been preformed.
The interfiber bonding of cellulosic webs by the above- mentioned ultrafine polymer-emulsion adhesiveε repreεentε a fundamentally new diεcovery, which, for all practical pur- poεeε, applieε excluεively to the papermaking proceεs of th present invention but not to the acidic or alkaline paper making procesεeε of the prior art. It εhould be pointed out, however, that the interfiber bonding in question is observe only when the above-mentioned ultrafine polymer-emulsion adhe¬ siveε have average particle diameters smaller than 55 nm an their content in cellulosic webs doeε not exceed 2% of th webs\' masε (the interfiber-bonding action of the latter adhe¬ sives stops increasing perceptibly beyond the 2% level until substantially higher adhesive contents in the web, on the order of about 10-20%, are reached) .
The ternary function of the in-situ syntheεized comple
functional microgelε iε to impart deεirable functional charac teriεticε to the resultant paper, board and wet-laid nonwove products, important from the standpoint of the latters\' en uεe applicationε. Theεe functional characteriεticε ar derived from the microgelε\' own highly diversified physica and surface-chemical properties, which can be controlled to large extent by a purpoεeful modification of the microgels chemical composition to εuit the intended end-uεe application of the reεultant paper or wet-laid nonwoven productε. Fo example, intrinεically εized paper can be manufactured i accordance with the preεent invention by incorporating mino proportions of organic, cationically active chemical compound with at least two reactive groups in each molecule into th solutionε of bivalent and multivalent inorganic croεε-linkin salts. The resultant complex microgels, made up of hybri macromoleculeε of an inorganic/organic polymer-polycondenεat type, are interεpersed throughout the consolidated celluloεi webε in a statistically uniform fashion, providing a εteri matrix of diεcrete hydrophobic εiteε, thus also a controlle level of intrinsic sizing.
The surface-chemical properties of the resultant webs ca also be modified indirectly with the aid of the complex func tional microgels under discuεsion, by coflocculating wit other furnish ingredients εuch powerful εurface-chemiεtry modifying agents in their own right as polymer-emulsion adhe siveε (having a dual organophilic/hydrophilic character) organophilic or even hydrophobic organic dyeε, polar minera pigmentε, or organic polymerε of controlled polarity.
The principal reagentε of commercial significance for th syntheεiε of the complex (multicomponent) functional microgel uεed in practicing the present invention are as follows:
(1) alkali-metal silicateε and quaternary ammonium εili cateε, preferably εodium or potaεεium εilicateε;
(2) alkali-metal aluminateε, alkali-metal zincateε an blendε thereof in any proportions, preferably sodium or potas εium aluminateε and/or εodium or potassium zincates; an
(3) water-εoluble, eεεentially colorless, bivalent an
multivalent εaltε of calcium, magnesium, barium, aluminum zinc, and zirconium, preferably calcium chloride or calciu nitrate. The use of calcium nitrate, alone or in blends wit calcium chloride, iε beneficial during hot εeaεonε when man paper millε encounter problemε of aggravated bacterial conta mination and εlime growth.
The pH of microgel-flocculated paper, board and wet-laid nonwoven furniεheε uεually rangeε from about 8 to 12, depend ing to a large extent on the initial acidity of the proceε water employed. The use of aluminum sulfate, alone or in combination with calcium chloride and/or other equivalen crosε-linking εaltε, may be advantageouε in thoεe inεtanceε i which it iε deεirable to lower the pH of a flocculated pape furniεh, particularly one containing groundwood fibers. I addition to, or instead of aluminum sulfate, sulfuric acid an other common acidifying agents can also be uεed for the abov purpoεe. The proportionε of acidifying agentε needed to lowe the furniεh pH to a deεired level muεt be aεεessed beforehand e.g., by flocculating an aliquot εample of the furniεh with a unadulterated (alkaline) complex microgel and then titratin the resultant flocculated furnish with a solution of the acid ifying agent(s) to be employed.
Since the primary functions of the complex functiona microgels uεed in practicing the preεent invention are limite to flocculation, cementation, and εurface-chemical modifica tion of particulate ingredientε of paper, board and wet-laid nonwoven furniεheε, theεe microgels are used aε a rule only i proportionε neceεεary to accomplish the intended tasks. I general, a microgel content ranging from about 0.4% to 10%, b weight, aε determined by aεhing, waε found to be adequate fo many typeε of paper, board and wet-laid nonwoven productε The preferred microgel contents for most commercial paper board and wet-laid nonwoven products range from about 4% t 10%, by weight, as determined by aεhing after waεhing out th electrolyte byproducts of the crosε-linking reaction, εuch a NaCl, NaN0 3 , or Na 2 S0 4 .
In the majority of laboratory and pilot-plant trial
carried out with papermaking furnishes comprising cellulos fibers, conventional inorganic fillers, and/or novel aggrega filler pigments (to be dealt with in more detail hereinafter) two different dosageε of the microgel-forming reagents we employed. With furniεheε having a εolidε content in excess 5%, by weight, the reagent dosageε encompaεεed 2 g of εodi εilicate, 2 g of εodium aluminate, and 4 g of calcium chlori per 100 g of dry furniεh maεε. With furniεheε having a εoli content of less than 5%, the reagent dosageε encompaεεed 3 of εodium silicate, 3 g of sodium aluminate and 6 g of calci chloride per 100 g of dry furnish masε. From the standpoi of both lowering the reagent-consumption requirementε a attaining better end reεultε, it iε advantageous to use t highest posεible furniεh-εolidε concentrations, e.g., of up 20% or even 30%, by weight. Furniεheε with a εolidε conce tration appreciably lower than 2%, by weight, may requi higher microgel dosageε than those recommended above.
There is a great latitude with regard to the quantitati and qualitative composition of both the (intermediate) tra sient, chemically reactive subcolloidal sodium-εilico-alum nate or εimilar hydroεolε, on the one hand, and the (fina complex microgelε, used in practicing the present inventio on the other, without detriment to their intended function For example, the acceptable ratio of sodium silicate to sodi aluminate, sodium silicate to sodium zincate, or sodi silicate to the combined masε of εodium aluminate and εodi zincate employed in forming the above εubcolloidal hydroεo can be varied from 1:10 to 10:1, by weight. Aε had be eεtabliεhed in numerous trials pertaining to the manufactu of paper, board and wet-laid nonwoven products, a preferr such ratio iε 1:1.
The preferred concentration of sodium silicate in t furniεh ranges from 0.01% to 2.0%, by weight, the same ran of concentrationε being preferred with εodium aluminat εodium zincate or combinationε thereof. When concentratio of the above reagentε in the furniεh exceed 2%, by weight, accelerated molecular-weight growth of εodium-silico-alumina
(zincate) macro olecules sets in, reducing the latters\' chemi cal reactivity toward the inorganic croεε-linking salts. T sustain a sufficient level of chemical reactivity necessar for syntheεizing complex functional microgels with adequat flocculating and cementing properties, the transient εubcollo idal hydroεols evolving from εuch concentrated reagent solu tions should be crosε-linked within a period of a few εecondε which, in turn, neceεεitateε the use of special, extra-effi cient in-line mixerε/reactorε. The ratio of calcium chloride or equivalent inorgani croεε-linking εalt(s) to the combined masε of the tranεient chemically reactive εubcolloidal hydroεolε to be cross-linke can vary from 1:10 to 10:1, by weight, but the simple ratio o 1:1 waε found to be most satiεfactory for εyntheεizing in sit complex functional microgels with adequate flocculating effi cacieε and for providing a subsequent marked enhancement o the dry and wet strength of the resultant webs. While the in organic crosε-linking εaltε can be uεed in proportionε rangin from 0.4% to 10%, by weight, of furniεh solids, the amount o calcium or equivalent bivalent and multivalent ions present i the reaction medium should optimally exceed by at least 50 the quantity of εuch ions bound chemically by the above-men tioned transient subcolloidal hydroεols. As was determined b a chemical analysiε of filtrateε from complex microgels syn theεized in plain water, the above-mentioned excess of croεε linking ionε reduceε the reεidual concentration of unreacte εilicate and aluminate (zincate) moleculeε to juεt a few part per million. For moεt practical purpoεes, it is adequate t employ the bivalent (multivalent) inorganic crosε-linkin εaltε at a concentration of from 0.02% to 4.0%, by weight, i the paper, board and wet-laid-nonwoven furniεheε.
Although many organic, cationically active chemical com pounds with at least two reactive groups in each molecule ar themselveε capable of croεs-linking the tranεient, chemicall reactive εubcolloidal εodium-εilico-aluminate and εimila hydroεolε, their uεe as the sole cross-linking agents is no recommended for most practical purposes. Instead, the latte
organic compounds, εelected from the group comprising cationi surfactantε, organometallic Werner complexes and cationi polyelectrolytes, εhould be added in only relatively mino proportionε to the εolutions of inorganic cross-linking salt to the extent needed for imparting the deεired εurface-chemi cal modification to the in-εitu εynthesized complex microgels thus indirectly also to the reεultant paper, board and wet laid nonwoven products. It is important, however, to monito the cementing efficacy of the evolving hybrid inorganic/or ganic microgels, in that the former deteriorates perceptibl with the increasing levels of organic cationic compounds buil into the macromolecules making up the microgels in question. The quantitative levelε of the organic, cationicall active croεs-linking agents with at least two. reactive group in each molecule, neceεεary for a particular functional pur poεe, e.g., εurface-chemical modification of paper, board o wet-laid nonwoven webs, must be determined empirically fo each individual agent and the intended end-product applica tion, e.g., with the aid of contact angle determinations εizing teεtε, and εo forth. According to the preεent find ings, a pronounced modification of surface-chemical propertie of fibrouε productε made with the aid of complex microgelε o an inorganic/organic type waε observed when the organic cross linking agents were preεent in paper, board or wet-laid non woven furnishes at concentrations of from 0.0003% to 0.15%, b weight. The practically useful proportions of these agents i the reεultant celluloεic or wet-laid nonwoven webε range fro about 0.001% to 0.5%, by weight.
It εhould be emphaεized that the formation of both th (intermediate) tranεient, chemically reactive subcolloida sodium-εilico-aluminate or similar hydrosols and the (final complex functional microgel cements uεed in practicing th present invention are not stoichiometric. Identical tranεien εubcolloidal hydrosols and final complex microgel cements ar syntheεized each time, however, when the same compoεitionε concentrations, proportionε, doεages, rateε and εequences o addition of the reagents, as well as the specified reactio
conditionε, are maintained during the εynthesis proceεε.
Aε iε typical of ultrafaεt chemical reactions in aqueou media, the in-situ formation of complex functional microgel used in practicing the preεent invention iε practicall independent of the temperature of the reaction medium. I principle, therefore, the above microgels can be formed withi the entire temperature interval in which water remainε fluid provided that the εtability of the reagentε iε not affected a elevated reaction temperatureε. A εpecial conεideration, fo example, εhould be given to the limited thermal εtability o εolutionε of εodium aluminate.
The above virtual independence of the εynthesis proces from thermal conditions and regimeε iε a unique feature of th above complex microgelε, which becomeε readily apparent whe compariεonε are made with the methodε of preparation of eve much εimpler εingle-component or bicomponent colloidal εyε temε, εuch aε εilica and alumino-silicate gels or aquaεol (colloidal εuεpenεionε of εolid particleε) known in the prio art. For example, numerouε patentε diεcloεing various method of manufacturing pharmaceutical preparations, ion exchangers, catalyεtε and other productε baεed on extraneouεly or in-sit prepared gels, aquasolε or precipitates, sometimeε of an iden tical chemical compoεition, often differ merely with respec to some εeemingly minor (though critical to these products succeεεful εyntheεis) variations in the thermal regimes.
The broad latitudes with regard to concentrations an chemical compositionε of the reagentε, or to reaction condi tionε tolerable in εyntheεizing the complex functional micro gelε under diεcuεεion, are indicative of the enormouε potenc of the general colloid-chemical εyεtem uεed in practicing th preεent invention. It iε worth noting that εimilar latitude are virtually unheard-of with analogouε proceεεeε of the prio art, according to which even oεt εimple monocomponent and bi component colloidal systems based on silica or alumino-sili cates muεt always be syntheεized under rigorouεly maintaine procedural and thermal regimeε as well as strictly define concentrations, proportions and types of reagents and pH con
ditionε in the reaction medium.
A εtill more detailed diεcuεsion of the subject matter the above complex functional microgels is provided in t specification to the previously mentioned co-pending Pate Application Serial No. 07/775,025 ("Functional Complex Micr gels with Rapid Formation Kinetics"), Filed October 11, 199
The alkaline version of the papermaking procesε of t present invention iε illuεtrated in the example to follow.
A εet of handsheets waε prepared by treating a chemic pulp conεiεting of a 50:50 softwood/hardwood blend with brightnesε of 86%, uεing the previouεly deεcribed in-εitu ( the furniεh) εyntheεized calcium-εilico-aluminate microgelε the papermaking (wet-end) chemicalε. The handεheetε, havi dimenεionε of 20 cm x 20 cm and a baεiε weight of 60 g/m 2 were prepared with the aid of a εheet mold, uεing a procedu developed specifically for laboratory applications of t papermaking process of the present invention.
According to the latter procedure, a "minibatch" of pu with a conεiεtency of 3%, in an amount εufficient for t preparation of just a single handsheet, was introduced into Waring blender with a capacity of 500 cm 3 . Aqueous 5%-soli solutionε of sodium silicate and εodium aluminate were injec ed simultaneouεly into the εtrongly agitated furnish usi plastic εyringeε poεitioned at diametrically oppoεite εideε the blender, avoiding a direct contact between the ejecti streams of reagent solutionε. After about 20 seconds, the 5 solidε aqueous solution of calcium chloride was injected in the same strongly agitated furnish. The proportions of acti reagents used per 100 g of pulp were 3 g of sodium silicat 3 g of sodium aluminate and 6 g of calcium chloride.
The minibatch of flocculated furnish was transferred fr the blender into a 2-liter beaker and, after an aging peri ranging from a few minutes to about 2 hours, diluted wi water (under stirring) to the full capacity of the beaker a
poured into the mold to form a handsheet. The wet handsheet were firεt pressed to a solidε level of about 35% and the dried on a rotating heated drum covered with a felt. Th relative weight content of mineral residue (discrete calciu εilico-aluminate microgel depoεitε) retained in the hand sheets, further called the "principal handsheetε," waε equa to about 7%, aε determined with the aid of εtandard gravi metric methodε.
Analogous handsheets, further called "control han sheets," were prepared with the aid of a typical acidic paper making procesε using alum and Percol 292 (a high-molecular weight cationic polyacrylamide flocculant) in proportions 20 lbs. and l lb., respectively, per ton of pulp. Some of th control handεheetε were prepared from a furniεh containin only fiberε while εome additional control handεheets were pre pared from the same furnish to which increaεing proportionε o starch were being added.
The principal handsheetε were characterized by a vastl better formation quality, significantly higher dry and we strengths as well as stiffneεε, more pronounced "rattle" an εlightly higher brightneεε and opacity than analogouε contro handεheetε made without the use of web-strength-reinforcin εtarch. Since a legitimate comparative aεsessment of th optical properties of paper products requires that the system under evaluation alwayε be of equal mechanical strength, th principal handsheets were additionally evaluated agains appropriately matched, starch-reinforced control handsheetε Since wet-end εtarch markedly reduces handsheetε\' brightneε and opacity, the principal handsheetε (devoid of starch) were in the final balance, both brighter and more opaque by abou 1.5 to 2 percentage pointε than the correεponding εtarch containing control handεheetε of equal mechanical εtrength.
It iε important to point out that the rather εubεtantia content (i.e., about 7%, by weight) of the microgel reεidue i the principal handsheets only slightly increaεed the latterε brightneεs and opacity, which is clearly indicative of th extremely εmall dimensions of microgel particles (depositε
retained in the εheets. In general, the undersized pigmen fractionε with particles smaller than about 0.1 μm e.s.d. ar referred to in the trade aε ultrafine. or subpigmentary. sinc their inadequate light-scattering efficacy disqualifieε the as pigments in the conventional (commercial) senεe. The diε crete microgel reεidueε embedded in the handεheetε, however are dimenεionally yet much εmaller than typical εubpigmentar particleε. Aε is well known to those skilled in the art, th principal handεheetε would be automatically brighter by abou 3-4 percentage points and more opaque by about 8-10 percentag points if the microgel residue in the εheetε were replace with an equivalent proportion (i.e., 7%, by weight) of a extraneouε εynthetic filler pigment, εuch aε precipitate calcium εilicate or an in-εitu (in the furnish) precipitate alumino-silicate filler pigment of the type diεcloεed in U.S Patent No. 2,757,085 to Paquin.
It iε worth pointing out that reεults identical to thos reported above were also obtained when εodium aluminate, a the constituent of the transient subcolloidal hydroεolε, wa partially or totally replaced with sodium zincate, or whe calcium chloride, as the cross-linking agent, was partially o totally replaced with calcium nitrate.
In analyzing the findingε diεcussed in the above example the foremost emphaεiε εhould be placed on the unique εheet εtrength-reinforcing action of the in-εitu-εyntheεized comple microgels used in practicing the present invention. Numerou other beneficial and unique propertieε of the complex micro gelε notwithstanding, the hitherto unheard-of reinforcement o εheet εtrength by embedded inorganic particleε unmiεtakabl diεtinguisheε the above microgels from all seemingly relate inorganic colloid-chemical εyεte s known in the prior art. Another important finding made in evaluating pape sampleε prepared in Example I was the enormous magnitude o "wet strength" imparted to the principal handsheets by th calcium-silico-aluminate microgels. The above performanc
property common to the complex microgels under discussion i particularly attractive from a commercial standpoint in tha the practical means for increasing the wet strength of paper known in the prior art, are quite limited. Hence, the we strength of handsheetε dried according to the procedure deε cribed in Example 1 waε found to be about 100% higher with th principal εample than with analogouε control εampleε. However after an additional heating for 30 εecondε at a temperature o 204°C (400°F) , the wet εtrength of handεheetε waε found to b 600% higher with the principal εample than with the correε ponding control εampleε.
The above εpectacular wet-εtrength increaεe of microgel containing handεheetε can be explained, in principle, by th fact that calcium-silico-aluminate microgels become eεεential ly fully cured, thuε alεo water reεiεtant, when heated at temperature of about 218°C. As is readily underεtood, th high-wet-εtrength propertieε can be imparted to celluloεi webε by the in-εitu εyntheεized complex microgelε only becauε the diεcrete microgel depoεitε, interεperεed throughout th fibrouε εtructure, are both ultrathin. causing no interferenc with the formation of close-range hydrogen bonds betwee cellulosic fibers, and strategically located at the intimat fiber-to-fiber contact areas. In comparison, the only practi cally feasible ways of increasing the dry or wet strength o cellulosic webε known in the prior art are through the addi tion of organic water-εoluble "glueε" to the fiber furniεh.
An outεtanding feature of the papermaking proceεε of th preεent invention, inherently related to the inεtantaneous indiscriminate and complete flocculation mechanism, iε tha all particulate furniεh ingredients become coflocculated in statiεtically oεt uniform faεhion, regardleεε of theεe parti culateε\' dimenεionε, morphology, relative densities, surfac chemistry or colloidal characteristicε. As a consequence, th detrimental fractionation, segregation and εelective aggrega tion (flocculation) of particulate ingredientε contained i heterodiεperεe and polydisperse papermaking furniεheε, such a cannot be avoided in the papermaking processes of the prio
art, iε, for all practical purposes, totally eliminated in th papermaking procesε of the preεent invention.
Some of the inεtant aε well as potential benefits derive from the flocculation mechanism inherent to the papermakin procesε of the present invention become apparent by way of th following example:
Three laboratory batches of identical furnish, each con taining 80%, by weight, of a 50:50 hardwood/εoftwood blend an 20%, by weight, of a delaminated clay filler, were prepared a an initial conεiεtency of 3%, by weight.
The main batch, deεignated aε the "principal" batch, wa flocculated with the aid of the in-εitu εyntheεized calcium εilico-aluminate microgelε according to the procedure deε cribed in Example I and then diluted to a conεiεtency of 0.7 typically used in commercial paper machine operations. Th first control batch, designated "AC" (acidic) , waε dilute right away to a conεiεtency of 0.7% and then flocculated i accordance with typical prior-art acidic-papermaking proce dureε, uεing alum and Percol 292 in proportions of 20 lbs. an 1 lb., respectively, per ton of furniεh εolidε. Similarly the εecond control batch, designated "ALK" (alkaline) , wa diluted to a consistency of 0.7% and then flocculated i accordance with typical prior-art alkaline papermaking proce dures using a pair of organic polymeric retention aids (Calgo Polymer H-7392 and Calgon Polymer H-7736 EZ) , each in a pro portion of 2 lbs. per ton of furnish solids. The pH of th furnish was adjuεted to a level of 8 uεing εodium hydroxide Each of the above flocculated furnish sampleε waε tranε ferred into separate sealed glasε jarε for further obεerva tion. Both control batcheε, "AC" and "ALK," were character ized by decidedly nonuniform, coarεely grained floe εtruc tureε, the carrier medium (water) being permanently cloud with a εubεtantial proportion of εolid matter εettling rathe promptly to the bottom of each jar. Unlike both contro
batches, the principal batch settled to the bottom of the ja in the form of a εingle floe ("monofloc") reεembling a large fluffy cotton ball εurrounded by a cryεtal-clear εupernatant the monofloc in question being characterized by an extremel uniform micrograin structure.
After some period of aging, each of the above-mentione jarε waε rapidly inverted. Both of the jarε containing th control batcheε revealed a layer of a densified tacky residue conεiεting predominantly of filler particleε firmly adherin to the bottom of the jar. The above εeparation of furniεh in gredientε, of courεe, provideε clear evidence that the floccu lation mechanisms inherent to the acidic and alkaline paper making procesεeε of the prior art are εlow, εelective, an incomplete, leading to a predominant formation of aggregate of the undeεirable segregated [...filler/filler...] an [...fiber/fiber...] types, instead of the desirable hetero aggregateε of a [...fiber/filler...] type. In contraεt, th bottom of the inverted jar containing the principal batch wa completely clear, indicative of the fact that the entir filler content of the furniεh waε firmly and intimatel coflocculated with the cellulosic fibers.
Aε is readily understood by those skilled in the art, th potential practical consequenceε of the above findingε ar enormous. In accordance with the prior art, for example, pa per and board are made from very dilute furnishes, containin only about 0.5-0.7%, by weight, of solid matter. The latte cumbersome dilution requiring vaεt amountε of water iε indiε penεable in that the web-formation quality deteriorateε rapid ly aε the εolidε concentration in the furnish is increased In contraεt, the inherent, extremely uniform micrograin εtruc ture of furniεhes flocculated with the aid of the in-situ-syn thesized complex microgels makes it possible to use furnishe with significantly higher solids concentrations than ar feasible in the papermaking procesεes of the prior art withou detriment to the resultant web-formation quality. Accordin
to preεent indicationε, εolids concentrations in the furnis (furnish consistencieε) could be increaεed 2 or 3 timeε abov the cuεtomary levelε with only minor modificationε of the con temporary headbox deεignε. Yet higher furniεh conεiεtencies e.g., of up to 4 or 5 times higher than those currently uεed are likely to be feaεible with εomewhat more radically modi fied headbox deεignε.
The ineεcapable deterioration of web-formation qualit resulting from attempts to increase paper machine speedε be yond the current practical limits is also well known to thos εkilled in the art. Again, due to the extremely uniform in trinεic micrograin structure of fiber/fiber floes (in filler leεε furniεheε) and fiber/filler flocε (in filler-containin furniεheε) generated by the action of the in-situ-syntheεize complex microgelε, it iε now possible to greatly increase th paper machine speeds without detriment to the resultant web formation quality. It is also poεεible to combine increaεe furniεh conεistencies with higher paper machine εpeedε t manufacture well-formed paper, board and wet-laid nonwove webε uεing the papermaking process of the present invention
The total coflocculation of cellulosic fibers and minera filler particles by the in-situ εynthesized complex microgel is another important finding made in Example II. Aε iε wel known to those skilled in the art, the uniformity of web for mation in the acidic and alkaline papermaking procesεeε of th prior art improves with increasing filler-loading levels, u to about 20%, by weight. As the filler-loading levels ar still further increased, however, the papermaking furniεhe muεt be exceεsively flocculated to obtain an adequate first paεε retention of pigment particles in the web, the unavoid able consequence of this "overflocculation" often bein manifested in an excesεive deterioration of the web-formatio quality. In a radical contraεt, the intrinεic micrograi εtructure of high-aεh furniεhes flocculated with the in-sit εyntheεized complex microgelε under diεcuεεion, as well as th quality of formation of the resultant webs, steadily improve with the increasing filler-loading level, even if the latte
exceeds 50%, by weight. As shall be discussed in more detai hereinafter, the latter repeatedly verified finding now make possible to manufacture very-high-ash paper products with web-formation quality not attainable hitherto with the aid o the papermaking processes of the prior art.
As is also well known to those skilled in the art, signi ficant proportions of valuable furnish ingredients are syεte matically and irretrievably paεεed into waεte-water εtream when the acidic or alkaline papermaking proceεses of the prio art are employed, cauεing εubεtantial material loεεeε aε wel aε εeriouε ecological problemε. On the other hand, the tota (100% complete) flocculation of particulate furniεh ingre dientε attained with the aid of the papermaking proceεs of th present invention enables one to recover 100% of the particu late matter from spent furniεhes before the latter are pasεe to waεte-water streamε. The complete elimination of particu late contaminantε from waεte-water streams, using filtration cycloning and other easy methods for separating εolidε fro liquidε, provideε a clear economical and ecological advantag over the papermaking proceεεeε of the prior art.
The total coflocculation of fiberε and filler particle by the in-situ-synthesized complex functional microgels offer the attractive possibility of attaining a true "self-extin guishing" process loop on a paper machine. Such a self-extin guishing loop can be realized preferably by replacing th conventional water-εoluble εtarch adhesives in papermakin furnisheε with particulate (polymer-emulεion) adheεiveε an flocculating these furnishes at very-high solidε, e.g., of u to 10-30%, by weight, with the aid of the in-εitu synthesize complex functional microgels. By purging the resultant syε temε of salt byproducts of microgel formation and other εolut contaminantε, e.g., by using a vacuum filtration combined wit spray rinsing, eεεentially solute-free and electrolyte-fre papermaking furnisheε can be obtained. The above contaminant free furniεhes, diluted subεequently with water to a deεirabl headbox consistency, can be recirculated on a paper machin until their solids are totally depleted, the portion of fur
niεh εolidε retained on the forming wire being continuousl replenished with a new portion of a (virgin) purified furnish Thus, the customary heavily polluted waεte-water εtreams fro paper machines can be eliminated completely, with enormou quantities of water being saved aε an additional benefit. Th εole waεte εtream reεulting from εuch a cloεed-loop papermak ing proceεε iε a low-volume, relatively concentrated cryεtal clear filtrate containing sodium and calcium saltε, diεper εantε (e.g., from fillerε and adheεiveε) and εimilar solute extracted from the flocculated high-conεiεtency papermakin furnishes before using them on a paper machine.
It should be emphasized that the cuεtomary laborator procedureε for making handεheetε, which rely on furniεheε tha are 25-50 timeε leεε concentrated than analogouε furnishe used on paper machineε, do not alwayε provide a correct indi cation of the filler-retention efficiencieε to be obtained i commercial operationε. For example, εlightly lower filler retention efficiencieε were sometimes observed when laborator handsheets were prepared from such highly dilute furnishe with the aid of the papermaking process of the present inven tion, using all-inorganic (calciu -silico-aluminate) micro gels, than were obtained when similar handsheets were prepare with the aid of the acidic and alkaline processes of the prio art. However, when analogous large-scale papermaking trial were carried out with the aid of a pilot-plant paper machine using typical commercial furnish-solidε concentrationε of 0.5 0.7%, by weight, the reεultant filler retention efficiencie were conεistently higher with the papermaking proceεε of th preεent invention than with the acidic and alkaline paper making proceεεeε of the prior art.
The reaεon for the above-mentioned reverεal of filler retention trendε (from preliminary laboratory indicationε t the actual full-εcale results on a paper machine) is a bette utilization of the fiber fines generated during refining o cellulosic pulps. The discrete cellulosic fiber fines gener ated by refining are "short-lived," reattaching themselve readily to the comparatively much larger full-fledged fiber
after a relatively εhort period of aging, or, particularly during the courεe of furniεh flocculation by the slow an inefficient flocculation mechanismε of the acidic and alkalin papermaking proceεεeε of the prior art. Aε a conεequence, th latter fiber fineε contribute little or nothing to reinforcin the reεultant fibrouε networkε or to facilitating the reten tion of filler particleε. However, when freεhly refined fibe furniεhes (still containing freely floating, unattached fibe fines) are treated with the in-situ syntheεized complex micro gelε inducing an inεtantaneouε flocculation of all particu lateε preεent in the furniεh, the numerically abundant fibe fineε become intricately coflocculated with full-fledge fiberε, εignificantly contributing to the reinforcement of th reεultant fibrouε networkε. Moεt of all, however, the unattached fiber fineε cofloc culate predominantly, in accordance with the laws of statiε ticε, with the numerically yet more abundant filler particle preεent in the furniεh. The filler-laden fiber fineε ar obviouεly heavy in relation to their geometrical dimension and have a low buoyancy. Hence, bearing in mind that th principal mechanism of filler-particle retention on th forming wire is filtration (a fibrouε mat iε firεt formed o the forming wire, which then "filters out" the flocculate filler particles) , it is readily understood that filler-lade fiber fines are difficult to retain on the forming screen whe making laboratory handsheets from highly dilute furnisheε. O the other hand, the fact that filler-laden fibers fines ar efficiently retained on a paper machine when typical commer cial furnisheε with a εolidε content of 0.5-0.7% are bein employed clearly pointε to an additional, hitherto unknow filler-retention mechaniεm baεed on the "entanglement" o filler-laden fiber fineε with conεolidating fibrous networks
As was establiεhed in numerous trials, extremely hig filler-retention efficiencies, unmatched by those typical o the prior-art acidic and alkaline papermaking processes, wer consiεtently obtained, regardless of whether the furnishe were dilute or concentrated, when relatively minor proportion
of organic cationic polyelectrolytes were added beforehand t the εolutionε of inorganic croεs-linking salts. For example by incorporating Percol 292 or Hydraid 777 in proportions o from 0.5 to 0.75 lbε. per ton of furniεh εolidε directly int the solution of cross-linking salt (calcium chloride) , th reεulting filler-retention efficiencieε were increaεed b εeveral percentage pointε relative to thoεe obtained unde εimilar conditionε with the acidic and alkaline papermakin proceεεeε of the prior art. It iε worth noting, though, tha the above-mentioned or similar polymeric agents are custom arily employed in the conventional paper-making processes i much higher proportions, usually ranging from about 2 lbε. t 4 lbε. per ton of furnish solids. Moreover, the formatio quality of sheetε obtained with the aid of the above-mentione hybrid inorganic/organic complex functional microgelε waε in variably vaεtly εuperior to even the beεt commercial standard known to the applicant.
One of the most important taskε f cing the paper induεtr at the preεent time iε to develop new lineε of high-qualit printing paperε in which a major portion of celluloεic fiber iε replaced with mineral fillerε. Paper productε of th latter type, e.g., those having a relative filler content i excesε of 25%, by weight, are referred to in the trade a "high-aεh" papers. Regardlesε of the obviouε ecological an economical benefitε offered by high-ash paper products, how ever, tangible technological advances in implementing routin maεε production of the latter are εtill in the εtate of rela tive infancy. The moεt important reaεons for the abov apparent lack of succeεε are the exceεεive deterioration o εheet εtrength at high levelε of filler loading, relativel high abraεivity of the conventional filler pigments, as wel as the deterioration of εheet-formation quality aεεociate with the harεh colloid-chemical meaεureε which muεt be under taken to effectively flocculate, retain and affix the maεεiv proportionε of fillerε contained in high-aεh paperε. Theε harεh measures pertain, most of all, to employing high dosage of polymeric flocculants to obtain an adequate flocculation o
filler particles in high-ash furnishes along with employin high proportions of water-soluble adhesives to compensate fo the excesεive fiber debonding resulting from high filler loading levels. Aε iε well known to thoεe εkilled in the art, the increaεed levelε of flocculantε and adheεiveε required i connection with high-aεh furniεheε complicate the delicat balanceε of wet-end chemiεtrieε of the acidic and alkalin papermaking proceεεeε of the prior art to a point exceedin the limitε of theεe proceεεeε\' objective performance capabi litieε. Aε the conεequence, the web-formation quality o high-ash paper products as well as the optical-performanc efficacy of both the filler pigments and cellulosic fibers i adverεely affected.
Bearing in mind that the potential, aε well aε th inherent limitationε, of the prior-art acidic and alkalin papermaking proceεεeε have already been thoroughly explored, it iε highly unlikely that the vast array of difficultie associated with the manufacture of high-ash paper will b resolved in the foreεeeable future with the aid of material and technologies known in the prior art.
Novel promiεing approaches applicable to the manufactur of high-ash paper products have been opened, however, by th papermaking procesε of the present invention. One suc approach is applicable to the manufacture of moderately-high- ash paper, containing up to 25%, by weight, of conventional mineral filler pigments in combination with the novel ultra fine polymer-emulsion adheεiveε diεcuεεed previouεly. Inter εperεed uniformly among the flocculated furniεh ingredientε, the ultrafine polymer particleε form, upon drying and ho calendering of the reεultant filled webε, microadheεive jointε between individual filler particleε aε well as between indivi¬ dual filler particles or filler aggregateε, on the one hand, and celluloεic fiberε, on the other. It was indeed posεibl to make filled paper of εatiεfactory mechanical strengt containing up to 25%, by weight, delaminated clay and 1-2%, b weight, novel ultrafine polymer-emulsion adhesives using th papermaking process of the present invention.
The papermaking proceεs of the present invention is als suitable for manufacturing very-high-ash paper with filler loading levels ranging from 25% to more than 50%, by weight The manufacture of the above paper grades requireε, however that both the previouεly mentioned novel functional fille pigmentε and ultrafine polymer-emulεion adheεiveε be εimulta neouεly employed. For filler-loading levelε approaching o exceeding 50%, by weight, synthetic microfibrils and/or nove celluloεic microfibrilε (to be diεcuεεed in more detail here inafter) εhould alεo be employed in the papermaking furniεh The εubject matter of the above novel aggregate fille pigmentε iε diεcloεed in detail by Kaliεki in U.S. Paten Application Serial No.07/811,623 (Low-Refractive-Index Aggre gate Pigment Productε), Filed December 23, 1991 and in U.S Patent No. 5,116,418 ("Proceεε for Making Structural Aggregat Pigmentε") , incorporated herein by reference. The fille pigmentε in queεtion are made in principle by a controlle aggregation of very-fine-particle-εize kaolin clayε (ofte referred to in the trade aε high-gloεεing clayε) combined wit other functional ingredientε, such as the novel ultrafin polymer-emulsion adheεiveε, for reducing fiber debonding i paper-filling applicationε, and/or with εynthetic and/o cellulosic microfibrils, for reducing fiber debonding an increasing filler-retention efficiency. The latter fille pigmentε are uniquely qualified for very-high-aεh fillin applicationε in that, among other thingε, theεe pigmentε optical-performance efficacy doeε not decay at even th higheεt filler-loading levelε and their unuεually low abra εivity rarely approacheε 0.5 mg on the Einlehner teεter. The unique εuitability of the novel ultrafine polymer emulεion adheεiveε for the manufacture of high-ash papers ca be understood readily conεidering that their average particl diameterε are εmaller than 55 nm. In contrast, the averag particle diameters of the overwhelming majority of polymer emulεion adheεives (latexes) used in the paper industry rang from about 150 to 200 nm. Hence, at any given adhesive maεε at leaεt 60 times more microadhesive joints (involving singl
adhesive particles) can potentially be formed with the nove ultrafine polymer-emulεion adhesives than with conventiona latexes. Moreover, as is well known in the art, the dimen εionε of the "glue line" (adheεive between two adhintε) εhoul be conεiderably εmaller than the dimenεions of the adhint themεelveε, particleε of conventional latexes being as a rul too large to form proper microadheεive jointε of fiber/fille or filler/filler typeε. Aε waε found in numerouε trialε, εignificant and εteady web-strength increase of paper and wet laid nonwoven products was obtained by increaεing the doεag of the novel ultrafine polymer-emulsion adhesiveε up to 2%, b weight, of the web maεs, whereas no correεponding web-εtrengt increaεe waε observed with conventional latexes.
It is worth pointing out in the above context that bot conventional latexeε aε well aε the novel ultrafine polymer emulεion adhesives are for all practical purposes unsuitabl aε wet-end additiveε in the acidic and alkaline papermakin proceεεeε of the prior art. Since the inefficient floccula tion mechaniεmε at the foundation of prior-art papermakin proceεεeε are incapable of totally flocculating polymer emulεion adhesiveε of any kind, uεing the latter aε wet-en additiveε would result in many serious runnability problem such as plugging of paper machine felts, εurface picking o paper during calendering or printing, and contamination o waεte-water εtreams. In contrast, both commercial latexes an the novel ultrafine polymer-emulεion adheεives are totall (100%) flocculated by the in-situ-εyntheεized complex func tional microgelε used in practicing the present invention, th use of such adhesives as wet-end additiveε preεenting none o the above-mentioned runnability problemε.
The manufacture of very-high-aεh, ultraopaque color-code paper for two-εided, high-reεolution computer printout o office reproduction, using paper furnisheε containing th previouεly mentioned aggregate (functional) filler pigmentε organic color dyeε and the novel ultrafine polymer-emulεio adhesives, shall be demonstrated in the example to follow Ultraopaque printing paper is understood herein as having a
opacity of at least 98.0%, necessary to eliminate the dis turbing show-through of high-optical-density laser prints fro the opposite sheet side.
To comprehend the enormous magnitude of practical diffi culties in obtaining a conventionally machine-calendered εhee of paper with an opacity of 98% one εhould conεider, for exam ple, that a stack of three sheets of a typical white "xerox paper used for office reproduction or computer printout, or stack of two sheets of color-coded computer printout paper will not always attain an opacity of 98%.
The ultraopaque, color-coded handsheets under discuεεio were prepared using the procedures and fiber-furnish compo εition deεcribed in Example I, except that Hydraid 777 ( commercial polyelectrolyte retention aid) in a proportion o 0.75 lbε. per ton of furniεh εolidε waε added directly to th εolution of calcium chloride uεed aε the croεs-1inking salt In addition to cellulosic fibers, the furniεh for makin handεheetε alεo contained the previouεly mentioned ultrafin polymer-emulεion adheεive in a proportion of 1.5 g per 100 of furniεh εolidε; a blue dye (Victoria blue) in a proportio of 0.075 g per 100 g of furniεh εolids (equivalent to 2 lbs of dye per ton of furnish εolids) ; and the previously men tioned aggregate filler pigment, used in εuch proportionε a to obtain a filler-loading level of at leaεt 35%, by weight in the reεultant handεheetε.
All furniεh componentε, including the polymer-emulεio adheεive and dye, were coflocculated uniformly and completel by the in-εitu-εyntheεized hybrid inorganic/organic comple microgelε, the εupernatant (filtrate) being completely clea and colorleεε. The handεheetε had a baεiε weight of 51.9 lbε per 3000 ft 2 ; a filler-loading level of 35.0%, by weight; a opacity of 98.0%.; a brightneεε of 82.3%; and a lightneεε o 85.0%. The handεheets had satisfactory strength, handling an rattle, a very light pastel blue color, and a most attractiv
εurface appearance reεembling that of a coated paper.
The extra-high opacity of the above very-high-ash hand¬ εheetε made it poεεible to print high-optical-density images on both sides, using a laεer printer, without any print εhow- through from the oppoεite side being noticeable. Moreover, due to the high brightnesε and lightneεε, the handεheetε were also found to be most suitable for desktop-publiεhing applica¬ tions requiring high-resolution, high-fidelity, high-contraεt reproduction of delicate halftone εcaleε.
Similar very-high-ash handsheetε aε thoεe deεcribed in the above example were alεo prepared uεing Hydraid 777, in a proportion equal to 1.5 lbε. per ton of furniεh εolidε, by adding it by itεelf (aε an aftertreatment) to furniεheε that were already flocculated by an in-εitu synthesized all-inor¬ ganic calcium-silico-aluminate microgel. Although the hand¬ εheetε in queεtion had the εame filler content and optical performance aε the handεheets from Example III, their sheet- formation quality waε markedly poorer. The reason for the poorer sheet-formation quality waε that the polymeric reten¬ tion aid, added to an already flocculated furnish, induced a secondary, coarse flocculation pattern εuperimpoεed upon the original, very uniform microflocculation pattern. While the overall resultε, εuch aε filler retention, optical performance or color uniformity of the above handεheetε (made with Hydraid 777 uεed as an aftertreatment) were still better than can be obtained with analogouε handsheets prepared with the aid of the acidic and alkaline papermaking procesεeε of the prior art, the overwhelmingly preferred approach iε uεing the paper¬ making proceεε of the preεent invention in which the auxiliary organic retention aidε are incorporated directly into the εolutions of calcium chloride or equivalent cross-linking saltε prior to the flocculation of the furniεh. The following example, pertaining to the preparation of filled groundwood handsheets, illustrateε particularly clearly the benefitε of adding the auxiliary organic polymeric reten-
tion aidε directly to the εolutions of the inorganic crosε linking salts used in practicing the present invention.
A εample of a typical groundwood furnish uεed for news print manufacture, additionally containing a typical low leve of a mineral filler (mechanically delaminated clay) , waε age for εeveral hourε to intentionally deteriorate the formatio quality of the handεheetε to be prepared from thiε furniεh.
A εet of newεprint handεheetε, further called principa handεheetε, waε prepared with the aid of procedureε outline in Example I, except that Percol 292, uεed in a proportion o
0.5 lbε. per ton of furnish solidε, waε added directly to th εolution of calcium chloride. Two similar setε of contro handεheets were prepared from the same aged furnish using th acidic papermaking proceεε outlined in Example I, Percol 29 being employed in a proportion of 1 lb. per ton of furniε εolidε in the firεt εet of control handεheetε and in a pro portion of 2 lbε. per ton of furniεh εolidε in the second se of control handsheetε.
Despite of the intentional furnish aging, such as lead invariably to a deterioration of the web-formation quality o handsheetε made by any prior-art papermaking process, th principal newsprint handεheetε were characterized by a virtu ally perfect web-formation quality. Aε a matter of fact, comparable web-formation quality iε, to the beεt of the appli cant\'ε knowledge, impoεsible to attain with the aid of an laboratory or commercial newsprint-making procesεeε of th prior art. In contraεt, the web-formation quality of bot sets of control newsprint handsheetε waε extremely poor coarεe unεightly flocε, undiεperεed clumpε of fiberε and othe defectε being clearly viεible in the handsheet surface, and viewed in a transmitted light, alεo in the handεheet interior Aε waε anticipated, the brightneεε of the principa groundwood handεheetε made under alkaline conditionε (pH o about 9.5) was lower by about 3 percentage points than th
brightneεs of control handsheetε made by the prior-art acidi papermaking proceεε. The above brightness reversal can b reduced, or even eliminated, by partially or totally replacin calcium chloride (as the crosε-linking agent) with alum and/o adding a predetermined proportion of acid to the solution o the cross-linking agent(s) .
From the standpoint of the overall resultε, however, i iε still preferable to employ the alkaline version of th papermaking proceεε of the preεent invention, combined wit adding hydrogen peroxide directly into the newεprint furniε in proportionε cuεtomarily employed in groundwood bleaching By adding the hydrogen peroxide into the newεprint furnis prior to, or simultaneouεly with, the addition of the εolu tionε of εodium silicate and sodium aluminate, the brightneε reverεal of groundwood fiberε can be fully eliminated.
Some of the potential benefits of making newsprint unde alkaline conditions are best evidenced by the fact that th brightnesε of the principal (alkaline) newεprint handsheet from Example IV remained unchanged even after a prolonge period of aging. In contrast, the originally brighter contro newsprint handsheetε, made by the acidic papermaking proceεε became progreεsively more yellow and brittle with increasin aging. It should be emphasized that while attempts have con tinuously been made worldwide to manufacture newεprint unde alkaline conditionε, tangible εucceεεeε have thuε far not bee attained to the beεt of the applicant\'ε knowledge.
Additional obεervationε made in connection with the pre ceding example revealed that the filler-retention efficienc obtained with the control newεprint handεheets increased whe the proportion of Percol 292 was increased from 1 to 2 lbs per ton of furnish solids. The highest filler-retention effi ciency was obtained, however, with the principal newsprin handsheetε made from a furniεh treated with the in-εitu-syn thesized hybrid inorganic/organic complex functional microgel with Percol 292, in a proportion of 0.5 lb. per ton of furnis solidε, added directly to the εolution of calcium chloride.
Another important benefit derived from the instantaneous indiscriminate and complete flocculation of all particulate preεent in paper, board and wet-laid-nonwoven furniεheε i manifeεted in the formation of bulky, uniformly diεtribute εteric configurationε of filler-particle aggregateε with vaεtly enhanced light-scattering efficacy. As is well under εtood by thoεe εkilled in the art, it would be impoεεible t obtain an opacity of 98.0% with a 51.9 lbε./3000 ft 2 εhee from Example III, containing excluεively low-refractive-inde fillerε, if an abundance of εuch optically favorable aggre gate-pigment configurationε had not been formed within the we εtructure.
Still another important benefit of the papermaking pro ceεs under discuεεion iε a complete and extremely uniform co flocculation of organic dyeε with the particulate ingredient of paper, board and wet-laid-nonwoven furnishes. The extra ordinarily high level of opacity of handsheetε obtained i Example III, of a magnitude hitherto imposεible to attain wit the aid of low-refractive-index fillerε, iε largely the reεul of an intrinεic interplay of light εcattering and light ab εorption between the uniformly and intimately interεperεe filler particleε and dyeε. It should also be emphasized tha the entire dosage of the relatively low-color-intensit Victoria Blue dye used in Example III was equivalent to onl 2 lbs. per ton of furnish solidε. To obtain handsheets wit a comparable level of color intensity with the aid of th acidic or alkaline papermaking procesεeε of the prior art, th dye concentration in the furniεh would have to be, aε a rule at leaεt 10 timeε higher than in Example III due to the noto riouεly poor retention and unfavorable flocculation character iεtic of virtually all organic dyeε in both latter proceεεeε
Intenεely colored paperε can alεo be obtained with th aid of the papermaking proceεs of the present invention b εimply increaεing the proportionε of dyeε added to th furniεh. Analogous intensely colored paperε can not be mad by the acidic or alkaline papermaking processeε of the prio art without εevere dye loεεeε and the accompanying unavoidabl
εerious contamination of waste-water streamε. Moreover, th εevere degradation of εtrength of intenεely colored paper mad by the papermaking proceεεeε of the prior art can be curtaile or even eliminated with the papermaking proceεε of the preεen invention by incorporating the highly efficient novel ultra fine polymer-emulεion adheεiveε and/or novel waterborne rubbe cementε into the εtarting furniεheε.
By far the moεt attractive colored papers are obtained, without exception, by combining the addition of dyes wit high-ash filling. The surface of colored paperε εo obtained, particularly after εupercalendering, haε a unique, extremel pleaεant εilky appearance that iε virtually impoεεible t duplicate by any other method known in the art. Moreover, th color uniformity of the reεultant productε iε virtuall perfect, reεembling the uniformity of colored glaεε or cerami tileε. In contraεt, a more or leεs pronounced color uneven ness and color two-sidedneεε typical of eεεentially all colo paperε made by the papermaking proceεεeε of the prior art ca readily be detected by even caεual evaluatorε. The papermaking proceεε of the preεent invention iε alε particularly well-εuited for a complete coflocculation o carbon black with celluloεic fiberε and filler particle present in a paper furniεh. The need for carbon black i preεent-day papermaking becomeε increaεingly more acute i that very εubεtantial opacity incrementε can be obtained moε economically uεing extremely low doεageε of thiε material. While it iε neceεεary to forfeit some sheet brightness to gai an increment of the far more valuable and costly shee opacity, the most favorable brightnesε-for-opacity trade of is obtained using carbon black disperεions prepared by th method discloεed in U.S. Patent No. 5,116,418 to Kaliεk ("Process for Making Structural Aggregate Pigments") . Th above method, referred to hereinafter and in the claimε t follow aε the " aεter-batch" method, makeε it poεεible t vaεtly increaεe the opacifying power of prior-art commercia carbon-black diεperεionε. In accordance with the presen industrial experience, the opacifying power of carbon blac
obtained from εuch dispersions is about 100-150 times highe than the opacifying power of titanium dioxide. An additiona procesεing of the commercial carbon-black diεperεionε with th aid of the maεter-batch method in queεtion εtill furthe increases the above-mentioned opacifying power by a factor o 20 to 50.
To suεtain a total immobilization of carbon black in th reεultant paper or wet-laid nonwoven productε (a releaεe o even traceε of carbon black, e.g., on the order of partε pe billion, would be unacceptable in the papermaking induεtry) the former muεt be employed in combination with latexeε o ultrafine polymer-emulεion adheεiveε, or with novel waterborn rubber cementε obtained by underpolymerization of the latte ultrafine emulεion adheεiveε. In contraεt, aε iε well know to thoεe εkilled in the art, the prior-art papermaking proceε εeε are incapable of a complete flocculation and immobiliza tion of either carbon black or polymer-emulεion adheεiveε.
The papermaking proceεε of the preεent invention can alε be uεed for the manufacture of very-high-aεh printing paper with filler-loading levelε approaching or even εurpaεεing 50% by weight, while conεiderably reducing these papers\' basi weight and preεerving the neceεεary εheet εtrength. The lat ter taεk can be realized by incorporating up to 2%, by weight of εynthetic microfibrilε and/or extraneouεly prepared nove celluloεic microfibrilε with a length ranging from about 10 μ to 200 μm in combination with 1-5%, by weight, of the nove ultrafine polymer-emulsion adhesiveε and/or waterborne rubbe cements into furnisheε for making the above-mentioned very high-ash paper products. The novel (extraneouε) celluloεic microfibrils should b distinguiεhed from ordinary fiber fineε generated (in εitu during mechanical refining of celluloεic pulpε, the latte fineε being defined aε miniature fibers paεεing through a 200 meεh εcreen. The extraneouε cellulosic microfibrils, whoε aεpect ratio (the ratio of length to diameter) is 10 to 100 times higher than that of fiber fines, can be obtained exclu sively by the process referred to hereinafter as well as i
the claims to follow as the "cascade-microfibrillation" pro ceεε. According to the latter, cellulosic fibers derive preferably from cotton or well-fibrillating cellulosic pulp undergo the following consecutive proceεεing εteps: (a) dry or wet chopping of fibers to a length preventin a hydraulic εpinning during the εubεequent wet refining, th reεultant length being dependent upon both the furniεh εolid and type of refining equipment to be employed in εubεequen proceεεing; (b) preliminary refining of chopped fibers resultin from εtep (a) at the higheεt practically feaεible εolids con centrationε, e.g., of up to 30-35%, by weight, preferably i the preεence of εodium εilicate, Congo red and/or other inor ganic and organic fibrillation-enhancing agents; (c) additional refining of the fiberε reεulting fro εtep (b) with the aid of centrifugal comminuterε (exemplifie by the well-known colloidal millε) ; and
(d) finalizing of the fibrillation attained in εtep (c with the aid of Gmolin homogenizers or equivalent equipment i which the fibrous furniεh iε compressed at very high presεure and then rapidly decompreεεed by paεsing through a nozzle causing the residual bundles of fibrils to "explosively separate into individual microfibrils.
The process of the present invention iε also most suit able for the manufacture of advanced wet-laid nonwoven prod uctε on a paper machine. Contemporary nonwovens, as a clas of materialε, are manufactured in two conεecutive proceεsin stepε. The firεt εtep involveε preforming of unbounded fibe webs (mats) uεing either a wet-laid approach or the currentl predominant dry-forming approach. Since the preformed webε made up mainly of εynthetic fiberε, have no coheεive εtrength εuitable adheεiveε muεt be incorporated into the webε in th εecond proceεεing εtep to eεtabliεh adheεive joints betwee adjacent fibers. The principal method of imparting the desired level o cohesive εtrength to the preformed webs is by saturating the with acrylic latexes to attain an adhesive content of up t
20%, by weight, followed by drying. Another method relies o "blowing" a relatively coarse thermoplaεtic adheεive powder εuεpended in air, into the preformed mat uεing electrostati asεiεt, followed by a thermal fuεing of adheεive particle depoεited between the fiberε.
Aε is well known to those skilled in the art, the above described approaches to making nonwoven products have man inherent disadvantageε. Firstly, the preforming of both wet laid and dry-formed nonwoven webs iε εeveral times slower tha making of analogouε celluloεic webε of εimilar baεiε weight on paper machineε. Secondly, the fiber lay of raw (unbounded nonwoven webε iε relatively poor to begin with, deterioratin εtill further when webs are treated with strength-reinforcin adhesiveε in the subεequent proceεεing εtep. Thirdly, th compoεition of furniεheε for making both wet-laid and dry formed nonwoven webε iε limited mainly to fiberε, no uεe bein made of many valuable functional additiveε routinely employe in papermaking furniεheε. Fourthly, the latex and thermo plaεtic-powder adheεiveε uεed for imparting coheεive εtrengt to nonwoven productε are utilized rather waεtefully. Fo example, adequate mechanical εtrength with latex-εaturate nonwoven webε iε obtained first when the latex content in th mat reaches about 15-20%, by weight, the powdered adhesive not faring much better. The above waεteful uεe of adhesives is readily understoo conεidering that neither the wet εaturation with latex nor th electroεtatically aided incorporation of adhesive powders i amenable to directing the adhesive particles effectively int εtrategic locationε into, or cloεe to, the fiber/fiber contac areaε. Aε a consequence, the overwhelming proportion of late iε paεted uεeleεεly around the fiberε themεelveε while εimilarly, a major proportion of adheεive-powder particleε i located too far from the fiber/fiber contact areaε to for adheεive jointε. Some unique problemε are alεo aεsociate with the use of dry adhesive powderε inaεmuch aε virtually al very fine powderε are agglomerating ("sticking") easily, thei flow properties being adversely affected. Moreover, as
general rule, very fine particles are not readily amenable to electroεtatic deposition. As a consequence, adhesive-powder particles must be much larger (e.g., 20-25 μm e.s.d.) than is necessary for establishing individual adhesive joints between the relatively thin synthetic fibers whose diameters typically range between 10 and 15 μm.
In contraεt, the method of the papermaking proceεε of the present invention makes it posεible to manufacture novel and improved wet-laid nonwoven productε with unique functional propertieε and material characteriεticε, not attainable with the aid of the nonwoven-manufacturing technologieε of the prior art. The latter advancementε are realized by floccu¬ lating εpecially deεigned multico ponent nonwoven furniεheε with the in-εitu synthesized complex functional microgels and forming wet-laid nonwoven webs on a paper machine. The above multicomponent furnishes can be incomparably more diversified and complex than furnisheε uεed in the nonwoven-manufacturing technologieε of the prior art, comprising, among other things, synthetic fibers; εynthetic reinforcing microfibrils; polymer- emulεion adheεiveε, particularly the previously mentioned novel acrylic ultrafine polymer-emulsion adhesives; novel waterborne rubber cements; aqueouε dispersions of fine- particle-size thermoplastic adhesive powders with a preferred average particle diameter of about 0.5 μm; organic dyes; and bioactive materialε; the advantageε of the above functional additiveε being explained in more detail hereinafter.
Although, aε is readily understood by those skilled in the art, a uniform mat can be made only from a well-disperεed fiber furniεh, the inefficient flocculation mechaniεms at the foundation of the papermaking processes of the prior art are incapable of overwhelming the action of the powerful modern disperεantε. As a consequence, wet-laid nonwoven webs made of more or less nonpolar synthetic fibers, crudely (mechanically) dispersed in aqueous furnishes, are much less uniform than comparable webs (paper) made of distinctly polar cellulosic fibers. Moreover, the inherently poor web-formation quality of prior-art wet-laid nonwovens makes it difficult to increase
the present low paper machine speeds, or use longer fiber (yielding stronger webs) , in making the latter nonwovens.
In contraεt, the overpowering flocculation mechaniεm a the foundation of the papermaking proceεs of the presen invention allows one to uεe well-diεperεed, highly diverεifie furniεh compoεitionε, invariably generating extremely unifor micrograin εtructureε in the flocculated furniεheε. Conεe quently, very uniform wet-laid nonwoven webε can be preforme at considerably higher paper machine speedε, uεing longe fiberε, than are feaεible in the nonwoven-making technologie of the prior art.
The manufacture of raw wet-laid nonwoven webs is greatl facilitated by incorporating into the furnish up to 5%, b weight, in relation to furnish solidε, of the novel ultrafin polymer-emulεion adheεiveε and/or novel waterborne rubbe cementε with pronounced wet-tack propertieε. The latter adhe εiveε, along with the in-εitu εyntheεized complex functiona microgel cementε, impart a certain level of inεtant εtrengt to the raw nonwoven webε, protecting the initial uniform fibe lay from damage during the εubsequent latex saturation o blowing-in of thermoplastic adhesive powders.
Since both the polymer-emulsion adhesives and waterborn rubber cements are coflocculated and retained primarily wit the discrete deposits of the complex functional microgel embedded strategically between adjacent fibers, the overal adhesive demand in the subsequent latex saturation o incorporation of adhesive powderε iε substantially reduced. Regardless of the complete flocculation of all particulates however, it would be impractical to incorporate more tha about 5%, by weight, of the novel polymer-emulsion adhesive and/or novel waterborne rubber cements into the furniεh i that an excessive concentration of tacky aggregates present i raw wet-laid nonwoven webs could lead to a contamination o paper-machine felts. The logical consequence of the above i that the customary second process stage in making wet-lai nonwoven webs cannot be eliminated as long as latex saturatio is the principal vehicle of providing the web strength.
The second process stage in making wet-laid nonwovens ca be eliminated completely with the papermaking process of th present invention by incorporating thermoplastic adhesive pow ders directly into nonwoven furnisheε. The adhesive powder in queεtion, employed in the form of fine-particle-εiz aqueouε diεperεionε, are retained in raw wet-laid nonwove webε on the forming εcreen in exactly the εame manner a ordinary filler pigmentε are retained in paper webs, withou contaminating paper-machine felts. In addition to eliminating a second processing step, th principal advantages of the above approach are a bette overall material and process economy as well as strategicall favorable placement of adhesive particleε at the fiber/fibe contact areas. The economic advantage in question is readil apparent considering that about 125,000 particles with a dia meter of 0.5 μm, being potentially able of forming 125,00 microadhesive jointε, can be obtained from just a single adhe εive-powder particle with a diameter of 25 μm. Moreover, adhe εive joints between the relatively thin synthetic fibers ca be formed more readily with commensurately fine adhesive par ticles than with excesεively coarse ones.
The above-mentioned strategic placement of adhesive par ticles coaggregated with microgel particles occurs because th aggregates in question migrate with the receding water durin the dehydration (drying) of raw wet-laid nonwoven webs. Sinc the very last pockets of water within dehydrating webε ar confined to capillarieε formed by fiber/fiber interεectionε, adheεive jointε are automatically eεtabliεhed after an appro priate heat treatment of the dehydrated webs. Another advantage of applying the papermaking process o the present invention to the manufacture of wet-laid nonwove webs is that uniformly colored nonwoven products can b obtained economically by incorporating organic dyes directl into wet-laid-nonwoven furnishes. It is important, however, to simultaneously incorporate the novel ultrafine acryli polymer-emulsion adhesives and/or waterborne rubber cement into the latter furnishes to effectively immobilize the dye
retained in nonwoven webs. On the other hand, as is wel known to those skilled in the art, the flocculation and reten tion of organic dyes iε largely impractical in prior-art pro ceεεeε for making wet-laid nonwoven productε. Attractive, novel, uniquely εtrong nonwoven productε ca be obtained with the aid of the papermaking proceεε of t preεent invention from furniεheε containing well-diεperε εynthetic fiberε, reinforcing εynthetic microfibrilε, ultra fine acrylic polymer-diεperεion adheεiveε and/or waterbor rubber cementε, aε well aε the previouεly mentioned aqueo dispersions of fine-particle-size thermoplaεtic adheεi powderε. Freεhly formed (raw) nonwoven webs formulated in t above manner, unlike raw nonwoven webs of the prior art, ha a considerable "green" strength (the latter term, borrow from the ceramic technology, referε to the εtrength of a y unbounded, or only partially bounded, raw mat) , thuε can readily laminated with the aid of cylinder-board machineε multiple-Fourdrinier machineε to yield even εtronger, mo verεatile novel nonwoven productε capable of εucceεεfull competing with a broad range of conventional woven fabrics The lamination process can be facilitated by applying spra of aqueous disperεionε of thermoplastic adhesive powders on the surface of freshly formed individual raw wet-laid nonwov webs before the latter are wound into multilayer composites As is well known to thoεe εkilled in the art, hygroεcopi propertieε are most desirable with nonwoven products intende for body contact, while intrinsic biostatic or biocidal pr pertieε are deεirable with many nonwoven productε intended f uεe in hoεpitalε, biological laboratories and for related a plicationε. In making the above productε in accordance wi the prior art, the functional propertieε under diεcuεεion mu be imparted to nonwoven productε by way of εpecial, εepara aftertreatmentε. In contrast, a certain level of intrins hygroεcopic properties is imparted automatically to wet-la nonwoven products made with the aid of the in-situ synthesiz complex microgels, by virtue of these microgels\' pronounced polar nature, while yet higher levels of hygroscopic prope
ties are obtained by adding hydrophilic anionic or nonioni polymers directly to wet-laid-nonwoven furnishes or by addin hydrophilic cationic polymers to the solutionε of calciu chloride or equivalent croεε-linking εalts. Bioεtatic and/o biocidal propertieε can εimilarly be imparted to wet-laid non woven productε by adding εuitable bioεtatic and/or biocida materialε into wet-laid-nonwoven furniεheε.
The papermaking proceεε of the preεent invention iε alε uniquely εuitable for manufacturing wet-laid nonwoven web reεiεtant to high temperatureε, uεing furnishes comprisin thermally reεiεtant inorganic fiberε. In making the abov productε it is often advantageous to simultaneouεly emplo polymer-emulεion adheεiveε in the furniεh to improve the gree εtrength of the reεultant raw wet-laid nonwoven webε and the burn off the adheεiveε by way of calcining.
The papermaking proceεε of the preεent invention iε alε uniquely εuited for the manufacture of novel electroconductiv and/or magnetic paper, board and wet-laid nonwoven productε b incorporating aqueous dispersions of ultrafine powders (wit particles finer than 0.2 μm e.s.d.) of metallic or cerami electroconductive materials, or ceramic or metallic (alloyed magnetic materials (e.g., super alloy or permalloy), int paper, board and wet-laid-nonwoven furnishes, in proportion of from 0.1% to 20% (active), by weight, of furnish solidε For example, paper and wet-laid nonwoven webs containin intrinsically deposited magnetic powders are uniquely suite for printing of counterfeit-proof, virtually indeεtructibl (when made of nonwovenε) banknotes, the magnetic responεe o εuch banknoteε being measurable quickly and conveniently wit the aid of inexpensive countertop detectors.
The paper (nonwoven) process of the present invention ma be executed in actual paper mill operations in several differ ent fashions. In a preferred approach, paper, board or wet laid-nonwoven furnishes are flocculated with the aid of in situ synthesized complex functional microgels immediatel before entering the chest or after leaving the chest on th way to the headbox. To manufacture groundwood-containin
paper, hydrogen peroxide is preferably incorporated into th furnish prior to, or εimultaneouεly with, the addition of th highly alkaline solutions of sodium silicate and sodium alumi nate (zincate) . The most preferable approach is to carry out the furnis flocculation in a fully continuous mode, using in-line mixers reactors, exemplified by the following consecutive εtepε:
(a) continuouεly injecting, in the firεt proceεεing sta tion, εeparate εtreamε of aqueouε εolutionε of εodium εilicat and εodium aluminate (εodium zincate or blendε of εodium alu minate and εodium zincate) into an in-line-agitated εtream o paper, board or wet-laid-nonwoven furniεheε to form, in εitu a tranεient chemically reactive εubcolloidal hydroεol;
(b) continuouεly injecting, in the εecond processing sta tion, an aqueous solution of calcium chloride or equivalen bivalent or multivalent crosε-linking εalt(ε) , optionally con taining organic cationically active compound(s) with at leas two reactive groups in each molecule aε the auxiliary croεε linking εalt(ε), into the furniεh εtream reεulting from ste (a) to cross-link said subcolloidal hydrosol and synthesize in situ, complex functional microgel cements, whereupon sai paper, board or wet-laid-nonwoven furnish becomes flocculate instantaneouεly, indiscriminately and completely;
(c) optionally, continuously purging the flocculated fur niεh reεulting from εtep (b) of diεsolved contaminants; an
(d) continuously recovering the flocculated furniεh re εulting from εtepε (b) and (c) to manufacture paper, board an other wet-laid productε on a paper machine.
In another verεion of the above continuouε proceεε mod the εtream of furniεh iε firεt divided into two εeparate half εtreamε, the εolution of εodium εilicate being injected int one halfεtream and the εolution of εodium aluminate, εodiu zincate or blends thereof into the other. Both above half εtreamε are recombined in the εubsequent processing statio (in-line mixer-reactor) to form, in situ, the transient chemi cally reactive subcolloidal hydrosol, the solution of t cross-linking agent(s) being injected into the recombine
halfstreams in the subsequent processing station to form, i situ, the complex functional microgel cements.
As is understood readily by those skilled in the art, th sequence of the individual procesεing steps in the genera procesε of the preεent invention may be reverεed by addin εolutionε of bivalent and/or multivalent inorganic croεε linking εaltε to the furniεh in εtep (a) ; separately pre paring the transient reactive εubcolloidal εodium-εilico aluminate or εimilar hydrosols in step (b) ; and blending i εtep (c) the εyεtemε reεulting from εtepε (a) and (b) to for in εitu a complex functional calcium-εilico-aluminate or εimi lar microgel cement and flocculate the furniεh instantaneous ly, indiscriminately and completely, thus obtaining a mediu suitable for making paper, board and other wet-laid product on a paper machine. Such a reversal of the sequence of th procesεing εtepε is recommended only in such inεtanceε, how ever, in which the colloidal εtability of paper, board or wet laid-nonwoven furniεheε iε not intolerably impaired by th action of the bivalent and/or multivalent inorganic cross linking εaltε during the interval preceding the introductio of the previouεly mentioned, separately prepared transien chemically reactive subcolloidal hydrosol into the furnish Although the overall results obtained by the above approac are as a rule better than can be obtained with the aid o prior-art acidic and alkaline papermaking procesεes, the prin cipal procesε verεion of the preεent invention, in which th εubcolloidal hydroεolε are formed in εitu (in the furniεh) i the firεt εtep and then cross-linked in the second step, i decidedly εuperior and preferable. While certain preferred practiceε and embodimentε of thi invention have been set forth in the foregoing εpecification it iε underεtood by those skilled in the art that other vari ations and modifications may be employed within the scope o the teachings of the present invention. The detailed descrip tion iε, therefore, not to be taken in a limiting sense an the scope of the present invention is best defined by th claims to follow.