Technical Field

The present invention is directed to an aqueous solution suitable for bonding fibers, comprising a linear structure of polymer prepared by polymerization of ethylenically unsaturated monomers comprising acrylic acid, and optionally at least one functional monomer other than acrylic acid. Moreover, the present invention is directed to a method for preparing a binder composition comprising at least one step of mixing the aqueous solution according to the present invention with saccharide compound or dispersion, use of the aqueous solution according to the present invention for preparing a binder composition, and a binder composition comprising the aqueous solution according to the present invention, and saccharide compound or dispersion.

Background

In fiber bonding applications, binder is used to increase the strength, durability and functions of the resulted product, i.e., substrates, such as paper, nonwoven martial and so on. Water born formaldehyde emitting binder is used in this application, such as melamine formaldehyde resin, phenolic resin and urea resin, which show good performance. However, formaldehyde is hazardous to the health and thus has been regulated in many applications.

Several formaldehyde-free binder compositions have been developed in recent times. One of such binder compositions is based on polyester chemistry, more particularly curable aqueous binder compositions comprising a polyacid component or anhydride or salt derivatives thereof, and a polyhydroxy component. To be specific, polyacid based aqueous solution is optionally blended with dispersions (for example, styrene-acrylic dispersion, PVAc dispersion) or starch and other component (additive, pigment and so on) to form a formulation. Then the formulation is applied to a substrate by soaking the raw substrate into the formulation and then removing the excess formulation. After the application, the saturated substrate is passed through a drying device to remove water and the polymer bonds to the fiber. Finally, the substrate becomes strong, water resistant and possesses also other properties.

Polyacid based binder is formaldehyde-free and environment friendly, but its strength is not as good as formaldehyde emitting binder under the same application condition.

EP0338115 disclosed a dissolved polyacrylic acid binding agent. But the cross-linked molecular structure of the binding agent cannot provide desirable dispersibility to prepare an aqueous solution for fiber bonding application.

LIS2011028371 disclosed a hybrid copolymer of polyacrylic acid. But it does not address how to improve its strength to make it suitable for use in fiber bonding application.

Therefore, how to increase the performance of polyacid based binder, especially the strength is quite critical. Summary description

The object of the present invention is to provide a binder composition suitable for bonding fibers, which could improve the strength of the fibrous product and at the same time provide water resistance.

It has been surprisingly found that the object is achieved by an aqueous solution, comprising a linear structure of polymer prepared by polymerization of ethylenically unsaturated monomers comprising acrylic acid, and optionally at least one functional monomer other than acrylic acid; wherein the polymer has a weight average molecular weight between 300,000 g/mol and 2,000,000 g/mol, preferable between 450,000 g/mol and 1 ,000,000 g/mol; more preferable between 500,000 g/mol and 1 ,000,000 g/mol.

In one aspect, the present invention is directed to an aqueous solution, comprising a linear structure of polymer prepared by polymerization of ethylenically unsaturated monomers comprising acrylic acid, and optionally at least one functional monomer other than acrylic acid; wherein the polymer has a weight average molecular weight between 300,000 g/mol and 2,000,000 g/mol, preferably between 450,000 g/mol and 1,000,000 g/mol; more preferably between 500,000 g/mol and 1 ,000,000 g/mol.

In another aspect, the present invention is directed to a method for preparing a binder composition, comprising at least one step of mixing the aqueous solution according to the present invention with saccharide compound or dispersion.

In another aspect, the present invention is directed to use of the aqueous solution according to the present invention for preparing a binder composition.

In another aspect, the present invention is directed to a binder composition comprising the aqueous solution according to the present invention, and saccharide compound or dispersion.

Detailed description

The present invention would be illustrated in a detailed way hereinafter.

In one aspect, the present invention is directed to an aqueous solution, comprising a linear structure of polymer prepared by polymerization of ethylenically unsaturated monomers comprising acrylic acid, and optionally at least one functional monomer other than acrylic acid; wherein the polymer has a weight average molecular weight between 300,000 g/mol and 2,000,000 g/mol, preferably between 450,000 g/mol and 1,000,000 g/mol; more preferably between 500,000 g/mol and 1 ,000,000 g/mol. Linear structure of polymer means the backbone of the polymer chain consists of monomers that attach to each other forming a straight linear structure. There can be side groups or pendant groups in this linear structure but no branches (side chains). According to the arrangement of the pendant groups, there can be three forms of linear polymers as isotactic, atactic and syndiotactic, Together, it is called tacticity of the polymer. Isotactic polymers have pendant groups on the same side of the polymer chain. Syndiotactic polymers have the pendant groups in an alternating pattern. Atactic polymers have pendant groups in a random manner.

It is surprisingly found that linear structure would give the polymer better dispersibility than crosslinked structure.

The functional monomer is selected from the group consisting of unsaturated carboxylic acids and their salts, esters, and derivatives; ethylenically unsaturated dicarboxylic acids and their salts, esters, anhydrides and derivatives; ethylenically unsaturated alcohols; ethylenically unsaturated amines; ethylenically unsaturated pyrrols, vinyl ethers; alkyl acrylates; alkenyl carboxylalkyl ethers; viny esters of carboxylic acids; alkenyl aryls; alkenyl aldehydes; acrylonitrile; methacrylonitrile; olefins and furans; wherein the functional monomer does not comprise acrylic acid. Surprisingly, it was found that the use of the functional monomer would improve the strength.

The functional monomer is present in an amount of 0% to 50% by weight, preferable 1 to 35% by weight, and more preferable 10 to 30% by weight, based on the total amount of the monomers.

In the polymer, the mole ratio of acrylic acid to the functional monomer is 1 :0 to 1 :1 ; preferable 1 :0.01 to 1 :0.5; most perferable1 :0.1 to 1 :0.3.

The unsaturated carboxylic acids and their salts, esters, and derivatives may be

(i) methacrylic acid, and its salts, more particularly water-soluble salts, such as the corresponding alkali metal, alkaline earth metal and ammonium salts, which are prepared by partial or complete neutralization of the free acid groups with bases; for example, sodium hydroxide solution, potassium hydroxide solution, magnesium oxide, ammonia or amines, such as triethanolamine, ethanolamine, morpholine, triethylamine or butylamine, are used for the neutralization;

(ii) (meth)acrylate alkyl esters, such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, sec-butyl acrylate, sec-butyl methacrylate, n- pentyl acrylate, n-pentyl methacrylate, neopentyl acrylate, neopentyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, 2-hexyl acrylate, 2-hexyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, n-octyl acrylate, n-octyl methacrylate, isooctyl acrylate, isooctyl methacrylate, decyl acrylate and decyl methacrylate, dodecyl acrylate, dodecyl methacrylate, 2-propylheptyl acrylate and 2-propylheptyl methacrylate. Preferably used monomers of this group are esters of acrylic acid and methacrylic acid with C1-C8-alcohols, such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, sec-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate and 2-ethylhexyl methacrylate, among those, acrylic acid with C1-C4-alcohols, such as n-butyl acrylate, sec-butyl acrylate, isobutyl acrylate and tert-butyl acrylate are very particularly preferred;

(iii) hydroxyalkyl (meth)acrylate, such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxyethyl ethacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3- hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 3-hydroxybutyl acrylate, 3- hydroxybutyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, 6- hydroxyhexyl acrylate, 6-hydroxyhexyl methacrylate, 3-hydroxy-2-ethylhexyl acrylate, 3- hydroxy-2-ethylhexyl methacrylate, neopentyl glycol mono(meth)acrylate, 1,5-pentanediol mono(meth)acrylate, 1,6-hexanediol mono(meth)acrylate and mixtures thereof;

(iv) acrylamide, methacrylamide, dimethylaminoethylacrylamide, dimethylaminoethylmethacrylamide, dimethylaminopropylacrylamide, dimethylaminopropylmethacrylamide; or

(v) a-halogen substituted (meth)acrylic acid, in which the halogen may be fluorine, chlorine or iodine.

The ethylenically unsaturated dicarboxylic acids and their salts, esters, anhydrides and derivatives may be ethylenically unsaturated dicarboxylic acids, such as maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, aconitic acid and mixtures thereof; their salts, especially their water-soluble salts, such as alkali metal, alkaline earth metal and ammonium salts; their esters, preferably mono- or di-alkyl ester, more preferably mono- or di-Ci to Cs alkyl ester, such as mono- or di-methyl ester, mono- or di-ethyl ester, mono- or di-propyl ester, mono- or di-butyl ester; their anhydrides, such as maleic anhydride, fumaric anhydride, itaconic anhydride, preferably maleic anhydride. The derivatives may be, for example, maleic amide, fumaric amide, itaconic amide.

The ethylenically unsaturated alcohols may be vinyl alcohol or allyl alcohol.

The ethylenically unsaturated amines may be vinyl amine, allyl amine, vinylpyridine, alkylvi- nylpyridine, or mono- or di-alkylaminoalkyl (meth)acrylate such as dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylyate, dimethylaminopropyl methacrylate, dimethylaminopropyl acrylate, diethylaminopropyl methacrylate, or diethylaminopropyl acrylate.

The ethylenically unsaturated pyrrols may be vinyl pyrrol or allyl pyrrol. The vinyl ethers may be Ci to Cs alkyl vinyl ethers, such as methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, pentyl vinyl ether, hexyl vinyl ether, heptyl vinyl ether or octyl vinyl ether.

The alkenyl carboxylalkyl ethers may be methyl vinyloxyacetate, methyl vinyloxypropionate, methyl vinyloxybutanoate, methyl vinyloxypentanoate, vinyl 3,3-dicarboxymethylpropyl ether, or vinyl 3,3,3-tricarboxymethylpropyl ether.

The viny esters of carboxylic acids may be vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, vinyl hexoate or vinyl neodecanoate.

The alkenyl aryls may be styrene, a-methylstyrene, tert-butylstyrene and vinyltoluene.

The alkenyl aldehydes may be acrolein or methacrolein.

The olefins may be ethylene, propylene, butylene, pentene, or hexene.

The furans may be furan or a furan compound in which the furan ring is substituted by one or more (for example, 2-4) substituents selected from the C1-C12 alkyl and C1-C12 hydroxyalkyl, such as furfuryl alcohol; or the furan ring may further fuse with an aromatic ring (such as benzene ring), such as methylbenzofuran.

Among the functional monomers, unsaturated carboxylic acids and their salts, ethylenically unsaturated dicarboxylic acids and their salts or anhydrides are preferable, ethylenically unsaturated dicarboxylic acids and their salts or anhydrides are more preferable, and maleic anhydride is most preferable.

According to the invention, the polymer is obtained by free radical polymerization in water, especially in deionized water, in the presence of initiator. The amount of water is selected such that it is >40 and < 900% by weight, advantageously > 60 and < 700% by weight and especially advantageously > 80 and < 500% by weight, based in each case on the total amount of monomers.

The polymerization may be carried out by firstly adding the total amount of monomers and the initiator before initiating the polymerization. However, it is also possible to charge the monomers and the initiator into the aqueous reaction medium continuously at a constant or varying flow rate. The monomers can be metered in as individual streams, as a homogeneous or heterogeneous (partial) mixture. Advantageously, the monomers are metered in as individual streams.

The polymerization is carried out in a way of solution polymerization, which is familiar to those skilled in the art (see, for example, C. Erbil et al., Polymer 41, 2000, pages 1391 ff).

The polymerization is carried out in the presence of initiator which forms radicals under the reaction conditions. The initiator may be peroxides or else azo compounds. Redox initiator systems are also contemplated, of course.

Peroxides used may in principle be inorganic peroxides and/or organic peroxides. Examples of suitable inorganic peroxides include hydrogen peroxide and also persulfates, such as the mono- or di-alkali metal or -ammonium salts of persulfuric acid, examples being its mono- and disodium, -potassium or -ammonium salts, such as sodium persulfate, potassium persulfate and ammonium persulfate. Examples of suitable organic peroxides are alkyl hydroperoxides such as tert-butyl hydroperoxide, aryl hydroperoxides such as cumene hydroperoxide, dialkyl or diaryl peroxides, such as di-(tert-butyl) peroxide, and benzoyl peroxide or di-cumene peroxide, and peroxy esters, such as tert-butyl peracetate or tert-butyl perbenzoate.

Azo compounds used are essentially 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2- methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(N,N'- dimethyleneisobutyroamidine) dihydrochloride and 2,2'-azobis(amidinopropyl) dihydrochloride.

Redox initiator systems are combined systems composed of at least one organic or inorganic reducing agent and at least one oxidizing agent. Oxidizing agents contemplated for redox initiator systems are essentially the peroxides stated above. As corresponding reducing agents it is possible to use compounds of sulfur in a low oxidation state, such as alkali metal sulfites, as for example potassium and/or sodium sulfite, alkali metal hydrogensulfites, as for example potassium and/or sodium hydrogensulfite, alkali metal metabisulfites, as for example potassium and/or sodium metabisulfite, acetone bisulfite, alkali metal salts, especially potassium and/or sodium salts, of aliphatic sulfonic acids, and alkali metal hydrogensulfides, such as potassium and/or sodium hydrogensulfide, for example, salts of polyvalent metals, such as iron(ll) sulfate, iron(ll) ammonium sulfate, iron(ll) phosphate, enediols, such as dihydroxymaleic acid, benzoin and/or ascorbic acid, and also reducing saccharides, such as sorbose, glucose, fructose and/or dihydroxyacetone.

Preferred initiators are peroxy type initiators such as hydrogen peroxide, tert-butyl hydroperoxide, di-(tert-butyl) peroxide, benzoyl peroxide, peroxy esters; and persulfates such as sodium persulfate, potassium persulfate and ammonium persulfate; and azo type initiators. The polymerization takes place in general by using 0.01 to 5% by weight of the radical initiator, preferably 0.1 to 2% by weight of the radical initiator, based in each case on the total amount of the monomers.

In addition to the above components, a chain transfer agent may optionally be used during the solution polymerization to reduce/correct the molecular weight of the polymer obtainable by the polymerization. It is possible to use predominantly aliphatic and/or araliphatic halogen compounds, for example halogenated hydrocarbons, such as n-butyl chloride, n-butyl bromide, n- butyl iodide, methylene chloride, ethylene chloride, chloroform, bromoform, bromotrichloromethane, dibromomethylene chloride, carbon tetrachloride, carbon tetrabromide, benzyl chloride, benzyl bromide, organosulfur compounds, such as aliphatic primary, secondary or tertiary mercaptans, for example ethylmercaptan, n-propylmercaptan, 2-propylmercaptan, n- butylmercaptan, 2-methyl-2-propylmercaptan, n-pentylmercaptan, 2-pentylmercaptan, 3- pentylmercaptan, 2-methyl-2-butylmercaptan, 3-methyl-2-butylmercaptan, n-hexylmercaptan, 2- hexylmercaptan, 3-hexylmercaptan, 2-methyl-2-pentylmercaptan, 3-methyl-2-pentylmercaptan, 4-methyl-2-pentylmercaptan, 2-methyl-3-pentylmercaptan, 3-methyl-3-pentylmercaptan, 2- ethylbutylmercaptan, 2-ethyl-2-butylmercaptan, n-heptylmercaptan and its isomer compounds, n-octylmercaptan and its isomer compounds, n-nonylmercaptan and its isomer compounds, n- decylmercaptan and its isomer compounds, n-undecylmercaptan and its isomer compounds, n- dodecylmercaptan and its isomer compounds, n-tridecylmercaptan and its isomer compounds, substituted mercaptans, e.g. 2-hydroxyethylmercaptan, tertiododecylmercaptan, aromatic mercaptans such as benzenethiol, o-benzenethiol, m-or p-methylbenzenethiol, and all others described in Polymerhandbook, 3rd edition, 1989, J. Brandrup and E. H. Immergut, John Wiley & Sons, section II, sulfur compounds from pages 133 to 141, as well as aliphatic and/or aromatic aldehydes such as acetaldehyde, propionaldehyde and/or benzaldehyde, unsaturated fatty acids such as oleic acid, dienes with nonconjugated double bonds such as divinylmethane or vi- nylcyclohexane, olefns such as cyclohexene, alpha-methyl styrene and its dimer, or hydrocarbons with readily removable hydrogen atoms such as toluene.

The total amount of chain transfer agent used during the solution polymerization is generally 5% by weight or less, often 3% by weight or less and often 1 % by weight or less, based on the total monomers. In an embodiment, the total amount of chain transfer agent used during the solution polymerization is in the range from 0.1% to 5% by weight, or 0.2 to 3% by weight, based on the total monomers.

The polymerization usually takes place under atmospheric pressure, although it can also proceed under reduced or increased pressure. A suitable pressure range is between 1 and 10 bar (absolute).

The polymerization reaction may be carried out at a temperature of 60°C to 125°C, preferably from 70°C to 110°C, more preferably from 80°C to 100°C for a period of 1 to 10 hours, preferably 2 to 8 hours, more preferably 4 to 6 hours. After the polymerization, the residual content of the monomers is generally removed in order to deodorize, such as by chemical and/or physical processes. The typical chemical and/or physical deodorization processes are known to the person skilled in the art [see, for example, EP- A771328, DE-A19624299, DE-A19621027, DE-A19741184, DE-A19741187, DE-A19805122, DE-A19828183, DE-A19839199, DE-A19840586 and 19847115], The chemical deodorization process may be carried out by adding a further radical initiator from the group of the abovementioned initiators to the reaction mixture, or to prolong the addition thereof, and carrying out what is called an “after-polymerization”, in other words a polymerization for achieving a conversion of 95 to 99.9%. It is sufficient in the majority of cases for the reaction mixture to be stirred for 0.1 to 3 hours, preferably 0.5 to 2 hours, more preferably 0.5 to 1 hour, at the polymerization temperature, after the end of the addition of monomer. The physical deodorization process may be carried out by stripping with steam or inert gas, in order to reduce the content of the monomers.

The polymer according to the present invention has a weight-averaged molecular weight (Mw) between 300,000 g/mol and 2,000,000 g/mol, preferably between 450,000 g/mol and 1,000,000 g/mol; more preferably between 500,000 g/mol and 1 ,000,000 g/mol. The determination of Mw is found in the Example section. Surprisingly, it was found that the when the Mw of the polymer is within the above range, the strength of the substrate would be improved.

After the polymerization, the resultant polymer is present in form of aqueous solution. Certain amount of aqueous solution is blended with dispersion or saccharide compound, then diluted to a suitable solid content, such as 0.6 to 80 % by weight, preferably 1 to 40% by weight, more preferably 5 to 20% by weight, in each case based on the total weight of the binder composition, thus obtaining the binder composition.

Therefore, in another aspect, the present invention is directed to a method for preparing a binder composition, comprising at least one step of mixing the aqueous solution according to the present invention with saccharide compound or dispersion.

In another aspect, the present invention is directed to use of the aqueous solution according to the present invention for preparing a binder composition.

In a further aspect, the present invention is directed to a binder composition comprising the aqueous solution according to the present invention, and saccharide compound or dispersion.

The polymer according to the present invention is present in an amount of 0.5 to 40 % by weight, preferably 1 to 20% by weight, more preferably 1.5 to 10% by weight, in each case based on the solid content of the binder composition. The dispersion or the saccharide compound is present in an amount of 0.5 to 40 % by weight, preferably 5 to 20% by weight, more preferably 5 to 10% by weight, in each case based on the solid content of the binder composition.

The dispersion used herein may be styrene-acrylic dispersion, acrylic dispersion, poly (acrylic- co-vinyl acetate) dispersion, poly vinyl acetate dispersion, ethylene vinyl acetate dispersion and carboxylated styrene-butadiene dispersion. The dispersion and its preparation are well known in the art and is available commercially.

In a preferred embodiment, the dispersion used herein is styrene-acrylic dispersion. Preferred acrylic monomers used in the styrene-acrylic dispersion includes acrylic acid and its esters such as methyl acrylate, butyl acrylate, ethyl acrylate, and 2-ethylhexyl acrylate. The weight ratio of styrene and acrylic monomers in the styrene-acrylic dispersion is in the range from 85:15 to 45:55, preferably from 75:25 to 55:45, more preferably from 70:30 to 60:40.

Saccharide compound, also called carbohydrates, are polyhydroxy aldehydes, ketones, alcohols, acids, their simple derivatives and their polymers having linkages of the acetal type. They may be classified according to their degree of polymerization, and may be divided initially into four principal groups, namely monosaccharides, disaccharides, oligosaccharides and polysaccharides.

Monosaccharides contain a single polyhydroxy aldehyde or ketone unit. Examples of monosaccharides include glucose, galactose, fructose and xylose.

Disaccharides consist of two monosaccharide units linked together by a covalent bond. Examples of disaccharides include sucrose, lactose, maltose, isomaltulose and trehalose.

Oligosaccharides contain from 3 to 9 monosaccharide units. Examples of oligosaccharides include maltodextrins, raffinose, stachyose and fructo-oligosaccharides.

Polysaccharides contain more than 9 monosaccharide units, which may be either in straight or branched chains, Examples of polysaccharides include starch, glycogen, cellulose, hemicellulose, pectins and hydrocolloids.

The saccharide compound used herein is preferred starch and derivatives and/or substitution products thereof. The starch used herein may be all starch types, for example starches from potatoes, corn, wheat, rice, tapioca, peas, sorghum or wax starch. The starch may be anionically and/or cationically modified, esterified, etherified and/or crosslinked. Anionic starches are preferred.

In the case of anionically modified starches, these are obtained, for example, by oxidative reaction of the native starch with a suitable oxidizing agent, such as sodium hypochlorite or periodate.

In the case of cationically modified starches, these are prepared, for example, by reacting native starch with at least one quaternizing agent, such as 2,3-epoxypropyltrimethyl-ammonium chloride. The cationically modified starches comprise quaternary ammonium groups.

The proportion of cationic or anionic groups in the modified starch is stated with the aid of the degree of substitution (DS). It is, for example, from 0.005 to 1.0, preferably from 0.01 to 0.4.

The starch may be degraded starch which has a molar mass M _w of from 1000 to 65 000 g/mol. The degradation of starch may be carried out enzymatically and/or oxidatively.

The binder composition may comprise inorganic pigment. Preferably, the content of an inorganic pigment is from 1 to 10% by weight, based on the total solid content of the binder composition

The inorganic pigment is for example a metal salt, in particular a calcium sulfate, a barium sulfate, a magnesium carbonate, a calcium carbonate, an aluminate, a silicate, an aluminum oxide, a titanium dioxide, a zinc oxide, a zinc sulfide, a silicon dioxide or an argillaceous earth. A mixture of inorganic pigments is also suitable. Preferred is a white inorganic pigment. A white pigment is understood herein as a pigment, which has no significant absorption of light at a wavelength of from 400 nm to around 800 nm. Accordingly, a human being perceives the white pigment as colorless. There are several inorganic pigments, which are metal salts, which comprise two or more anionic groups, two or more cationic metals, or both of them. An example thereof is a calcium aluminate sulfate or a two- or three-layered phyllosilicate such as kaolinite, halloysite, talc, montmorillonite, hectorite, nontronite or saponite. Preferred is an inorganic pigment, which is a calcium sulfate, a barium sulfate, a magnesium carbonate, a calcium carbonate, an aluminate, a silicate, an aluminum oxide, a titanium dioxide, a zinc oxide, a zinc sulfide or a silicon dioxide. Especially preferred is an inorganic pigment, which is a calcium sulfate, a calcium aluminate sulfate, a barium sulfate, a magnesium carbonate, a calcium carbonate, a silica, an alumina, an aluminum hydrate, a silicate, a titanium dioxide, a zinc oxide, a kaolin, a talc or a silicon dioxide. The calcium carbonate may be a natural ground calcium carbonate (GCC), a precipitated calcium carbonate (PCC), a lime or a chalk. Suitable calcium carbonate pigments are available, for example as Covercarb 60 (RTM Omya), Hydrocarb 60 (RTM Omya) or Hydrocarb 90 ME. Other suitable inorganic pigments are also available, for example as Hydrogloss 90 (clay, RTM KaMin) or Finntalc C10 (talc, RTM Mondo Minerals).

Optionally, the binder composition may comprise further auxiliary ingredients, for example, a thickener, an optical brightener, a flow control agent, a lubricant, a neutralizing agent, a defoamer, a deaerator, a preservative or a dye in conventional amounts. A thickener helps to further optimize viscosity and water retention of the binder composition. A thickener is for example a cross-linked polyacrylate or a cellulose derivative such as carboxymethylcellulose. A thickener is preferably used in an amount of from 0.05 to 5% by weight, in particular from 0.1 to 2 % by weight, based on 100 % by weight of the inorganic pigment. An optical brightener is for example a stilbene derivative, in particular a di-, tetra- or hexasulfonate bistriazinyl-substituted 4,4’-diaminostilbene. A lubricant is for example a stearate such as calcium stearate or a wax. A neutralizing agent is used to adjust the pH value of the binder composition and is for example sodium hydroxide or ammonium hydroxide. A preservative is for example a biocide which can be added to the binder composition to inhibit microbial activity. A biocide is for example 1 ,2- benzisothiazol-3(2H)-one, 2-methyl-4-isothiazolin-3-one or 5-chloro-2-methyl-4-isothiazolin-3- one. A dye for is example an organic pigment with a strong absorption at a wavelength between 400 nm and 800 nm or a soluble compound with a strong absorption at a wavelength between 400 nm and 800 nm. A preferred dye is a soluble compound or a combination of a soluble dye with an organic pigment.

The binder composition of the invention may be used to bond a collection of loosely assembled matter. The collection of matter includes any collection of matter which comprises fibers selected from mineral fibers, including but not limited to slag wool fibers, stone wool fibers, glass fibers, aramid fibers, ceramic fibers, metal fibers, carbon fibers, polyimide fibers, polyester fibers, rayon fibers, and cellulosic fibers. Further examples of collection of matter include particulates such as coal, sand, cellulosic fibers, wood shavings, saw dust, wood pulp, ground wood, wood chips, wood strands, wood layers, other natural fibers, such as jute, flax, hemp, straw, wood veneers, facings and other particles, woven or non-woven materials. The collection of matter to be treated by the binder composition of the invention hereinafter also referred as substrate.

In one embodiment, the binder composition of the invention may be used to prepare nonwovens. The nonwovens may be formed in accordance with any of the known methods, for example, dry-laid processing and wet-laid processing. In a dry-laid process, fibers are chopped and air blown onto a conveyor and the binder composition is then applied and dried and/or cured to form a mat. Dry-laid processes may be particularly suitable for the production of highly porous mats having bundles of glass fibers. In a wet-laid process, a water slurry, so-called “white water”, is provided into which fibers are dispersed. The white water may contain dispersants, viscosity modifiers, defoaming agents, or other chemical agents. The slurry containing the fibers is then deposited onto a moving screen and a substantial amount of the water is removed therefrom. The binder composition may then be applied to the deposited fibers, after which heat is applied to remove any remaining water and to cure the binder thereby forming a non-woven mat. In another embodiment, the binder composition of the invention may be used to make insulation products, comprising mineral fibers. In such an application, the fibers are bonded together such that they become organized in a mat, and the binder composition is then applied and dried and/or cured to form the insulation products.

In another embodiment, the binder composition of the invention may be used to bond cellulosic particles, such as cellulosic fibers, wood shavings, wood pulp and other materials commonly used to manufacture composite wood boards, including fiber boards, particle boards, oriented strand boards etc. In such applications, the cellulosic particles are soaked or spray by the binder composition, put into a heatable press or mold, and is subsequently dried and/or cured in a manner familiar to the skilled worker.

In a preferable embodiment, the binder composition of the invention may be used to coat paper. The paper may be uncoated base paper or coated paper, preferably uncoated base paper. The amount of the binder composition applied is in general from 1 to 50 g per square meter, preferably from 5 to 30 g per square meter, based on the solid content of the binder composition. The binder composition can be applied by a customary application method, for example by means of a size press, a film press, a blade coater, an air brush, a knife coater, a curtain coater or a spray coater. After coating, the excess binder composition and water may be removed, such as by roller. The coated paper is then dried/cured. Drying/curing may be conducted for example by IR. The surface temperature of the paper surface during the drying/curing step has to enable a film formation from the polymer. Preferably, the surface temperature during the drying/curing step exceeds the glass transition temperature of the polymer, for example by at least 25°C. Frequently, the drying or curing of the coated paper is effected in two temperature stages, in which case the drying stage is effected at a temperature of < 120°C, preferably = 20°C and = 110°C and especially preferably > 40°C and < 110°C, and the curing stage at a temperature of > 110°C, frequently > 130°C and < 250°C or > 160°C and < 220°C. It will be appreciated that it is also possible that the drying stage and the curing stage of the mouldings are effected in one step, for example in a mould press. The coated paper can be readily printed on in a common printing process, for example a relief printing, a gravure printing, an offset printing, an ink jet printing, a flexographic printing, a newspaper printing, a letterpress printing, a sublimation printing or a laser printing, an electrophotographic printing or a combination of these printing processes.

The coated paper or the coated cardboard shows good strength, for example good dry burst strength and wet burst strength. For a certain binder, if the wet burst strength is high, the speed of production line can be increased, or the dry/curing temperature can be decreased. It is surprisingly found that using the binder composition of the current disclosure can increase paper production capacity or decrease the energy cost, respectively.

The present invention is further illustrated by the following embodiments and combinations of embodiments as indicated by the respective dependencies and back-references. In particular, it is noted that in each instance where a range of embodiments is mentioned, for example in the con-text of a term such as "The process of any of embodiments 1 to 4", every embodiment in this range is meant to be explicitly disclosed for the skilled person, i.e. the wording of this term is to be understood by the skilled person as being synonymous to "The process of any of embodiments 1 , 2, 3, and 4".

1 . An aqueous solution, comprising a linear structure of polymer prepared by polymerization of ethylenically unsaturated monomers comprising acrylic acid, and optionally at least one functional monomer other than acrylic acid; wherein the polymer has a weight average molecular weight between 300,000 g/mol and 2,000,000 g/mol, preferably between 450,000 g/mol and 1 ,000,000 g/mol; more preferably between 500,000 g/mol and 1 ,000,000 g/mol.

2. The aqueous solution as defined according to embodiment 1 , wherein the functional monomer is selected from the group consisting of unsaturated carboxylic acids and their salts, esters, and derivatives; ethylenically unsaturated dicarboxylic acids and their salts, esters, anhydrides and derivatives; ethylenically unsaturated alcohols; ethylenically unsaturated amines; ethylenically unsaturated pyrrols, vinyl ethers; alkenyl carboxylalkyl ethers; viny esters of carboxylic acids; alkenyl aryls; alkenyl aldehydes; acrylonitrile; methacrylonitrile; olefins and furans; wherein the functional monomer does not comprise acrylic acid.

3. The aqueous solution as defined according to embodiment 1 or 2, wherein the functional monomer is selected from the group consisting of maleic acid, maleic anhydride, fumaric acid, itaconic acid, methacrylic acid, acrylamide, methacrylamide, 2-hydroxylethyl acrylate, 2- hydroxy I propyl acrylate, and 2-hydroxylethyl methacrylate.

4. The aqueous solution as defined according to any one of embodiments 1 or 3, wherein the functional monomer is in an amount of 0% to 50%, preferable 1 to 35%, and more preferable 10 to 30% by weight, based on the total amount of the polymer.

5. The aqueous solution as defined according to any one of embodiments 1 to 4, wherein the polymer is obtained by free radical polymerization in water or other solvent in the presence of initiator.

6. The aqueous solution as defined according to embodiment 5, wherein the initiator is selected from the group consisting of peroxy type initiators such as hydrogen peroxide, tert-butyl hydroperoxide, di-(tert-butyl) peroxide, benzoyl peroxide, peroxy esters; and persulfates such as sodium persulfate, potassium persulfate and ammonium persulfate; and azo type initiators.

7. A method for preparing a binder composition, comprising at least one step of mixing the aqueous solution as embodimented in any one of embodiments 1 to 6 with saccharide compound or dispersion.

8. A method according to embodiment 7, wherein the dispersion comprises styrene-acrylic dispersion, acrylic dispersion, poly (acrylic-co-vinyl acetate) dispersion, poly vinyl acetate dispersion, ethylene vinyl acetate dispersion and carboxylated styrene-butadiene dispersion.

9. Use of the aqueous solution as claimed in any one of embodiments 1 to 6 for preparing binder composition. 10. A binder composition comprising the aqueous solution as defined according to any one of embodiments 1 to 6, and saccharide compound or dispersion.

11. A binder composition according to embodiment 10, wherein the dispersion comprises sty- rene-acrylic dispersion, acrylic dispersion, poly (acrylic-co-vinyl acetate) dispersion, poly vinyl acetate dispersion, ethylene vinyl acetate dispersion and carboxylated styrene-butadiene dispersion.

12. A binder composition according to embodiment 10, wherein the saccharide compound is starch or its derivatives.

13. Use of the binder composition as claimed in any one of embodiments 10 to 12 for fiber bonding.

The present invention would be further explained by the following examples. These, however, would not be construed to further limit the scopes set forth in the following claims.

Examples

Determination method

Determination of weight-averaged molecular weight Mw

The molecular weight of the polymer is characterized by water phase Gel Permeation Chromatography (GPC). The sample is dissolved in an eluent (H2O + 0.01 M Phosphate Buffer (P5244 from Sigma) + 0.1 M NaCI (pH=7.4)) at 1.5mg/mL for 2h at room temperature. After filtration (pore size 0.22 pm), 100 pL of this solution are injected into the GPC system. The GPC system is operated at a flow rate of 0.8 mL per min. A DRI Agilent 1100 is used as the detector. The standard calibration curve was based on narrow dispersity polyacrylic acids, molecular weights ranging from 1 ,250 to 1 ,100,000 g/mol.

Determination of wet burst strength and dry burst strength

The wet burst strength and dry burst strength are tested according to the test method of GB/T 454-2020 (ISO 2758: 2014, MOD).

The materials used in the examples are present below.

Acrylic acid: BASF, 99.5 % purity sodium persulfate: BASF, 99.5 % purity

Maleic anhydride: BASF, 99.5 % purity

Filtration base paper: cellulosic filtration paper, lab hand sheet, air permeability is 170 or 120 L/m ² /s Examples 1-6:

The components for Example 1 through 5 are shown in Table 1. All values listed in Table 1 refer to grams. Example 6 is comparative example using a commercialized poly acrylic acid with a molecular weight of 275,700 g/mol.

Table 1

Procedure

For Examples 1, poly acrylic acid was synthesized as below: 230 g water was first charge into the reactor and heated up to 95 °C under nitrogen; then acrylic acid, 660 g water and 7% sodium persulfate aqueous solution were fed into the reactor over 150 min, 195 min and 210 min with constant feeding rates, respectively. After the feeding completed, the reactant was kept stirring for another 90 min at 95 °C. Then the reaction mixture is cooled down to 60°C. 60 g water is dosed over 15 min with a constant dosing rate. The reaction mixture was stirred for another 30 min at 60°C before cooling down to room temperature.

Example 2 was prepared in the same manner as Example 1, with the exception that acrylic acid was fed over 180min, instead of 150 min.

For Examples 3-5, poly (acrylic acid-co-maleic anhydride) was synthesized as below: 500 g water and maleic anhydride (MAH) was first charge into reactor and heated up to 95 °C under nitrogen; then acrylic acid, 450 g water and 7% sodium persulfate aqueous solution were fed into the reactor over 180 min, 180 min and 270 min with constant feeding rates, respectively. After all the feeding, the reactant was kept stirring for another 120 min at 95 °C. Then the reaction mixture is cooled down to 60 °C. 60 g water is dosed over 15 min with a constant dosing rate. The reaction mixture was stirred for another 30 min at 60°C before cooling down to room temperature.

For Example 6, the comparative polymer used was a 35% by weight water solution of a poly acrylic acid with a molecular weight of 275,700 g/mol. After the solution polymerization, a polymer solution is formed. For each Example 1 to 6, the polymer solution was first blended with styrene-acrylic dispersion (Acronal® 7216 from BASF), where the solid ratio of polymer solution to dispersion is 5:100, and then diluted to 15% solid content. The prepared aqueous dispersion was fed into the pinch area of horizontal placed two rollers. Raw filtration base paper pass though the two rollers, where the base paper was first saturated by the prepared aqueous dispersion and the excess aqueous was remove by the roller immediately. The saturated paper was placed into oven to dry at 110°C for 5 minutes and to cure at 150°C for 10 minutes. After the curing, the paper was sent to burst strength test.

Results

The Mw, dry burst strength and wet burst strength were shown in Table 2.

Table 2

It is evident that with polyacrylic acid as crosslinker in the formulation (Example 1, 2 and 6) the higher the molecular weight, the higher the strength of the samples can be achieved. At the same molecular weight level, incorporating MAH into polyacrylic acid backbone can increase the wet burst strength (Example 4 compared to Example 1). At the same MAH% level in the backbone (Example 3 and 5), the higher the molecular weight, the higher the strength of the samples can be achieved.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. Thus, it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents.