FIELD OF INVENTION This invention relates to papermaking systems, particularly systems containing neutral pH rosin sizing and mineral fillers and/or coatings, such as calcium carbonate. In one aspect, the invention further relates to methods to achieve such systems by the providing of certain agents to such systems. In another aspect, the invention relates to rosin type papers having increased amounts of fillers and/or coatings.

BACKGROUND During the papermaking process, paper can be made with a rosin size to inhibit the penetrability of liquids into the paper sheet. Neutral pH rosin size systems have been developed which utilize a dispersed rosin size and a source of aluminum ions. The aluminum ions acts to fix the rosin to the cellulose fibers of the paper. Typically, such systems use a dispersed rosin size which has been modified to limit ionization in a neutral pH range. Typical sources of aluminum ions in such systems include aluminum sulfate and polyaluminum chloride.

Certain metal salts can be used in paper systems as a filling or coating material. A problem can arise when a metal salt is used due to the presence of divalent cations. Free divalent cations can be present due to a number of causes. Such ions may be present since certain chemical compounds, such as aluminum sulfate or polyaluminum chloride, liberate divalent cations from other certain compounds. For example, calcium ions can be liberated from calcium carbonates. A further example is the release of ions from precipitated calcium carbonate through a buffering action. Such divalent cations can react with the rosin to form metal rosinate soaps, such as calcium rosinate soaps when calcium ions are the divalent cations. Such soap formation interferes with the formation of a desired aluminum - rosin complex and competes with the sizing-fiber fixing of the rosin by the available aluminum ions.

Attempts have been made to address the rosin sizing problems created by the presence of calcium ions in paper systems. Such efforts have been to modify the sources of aluminum ions or the rosin molecules. In particular, attempts have been made to increase the amount of calcium carbonate filler material in papers having rosin sizing. However, increasing the amount of calcium carbonate can also increase the

^" amount of divalent cations present further creating problems in the sizing process. Improved methods and compositions are needed to improve neutral pH rosin sizing in systems having divalent ions present. An object of the present invention is to provide improved papermaking systems having neutral pH rosin size fixed to cellulose fibers when a metal salt, such as calcium carbonate, is present as filler or coating material. Another object is to provide methods for achieving such systems. Yet another object is to provide a novel paper composition having an enhanced amount of filler and sizing material. Yet another object is to provide a novel composition to achieve the above results. These and other objects will be apparent in the description of the inventions hereinafter.

RELATED ART In Strazdins, E., "Chemistry and Application of Rosin Size," The Sizing of Paper 2nd Edition, TAPPI Press, 1989, the problem in rosin systems of the presence of free calcium ions from calcium carbonate is recognized. In Liu J., Paper Technology. 36(5) :20 (1995), the use of Polyaluminum chloride in place of aluminum sulfate to attempt improvement of neutral pH rosin sizing is described.

SUMMARY According to the present invention, the foregoing and other objects are attained by a papermaking method using a specified amount of an effective chelating or precipitating agent to remove divalent cations so as to avoid the formation of undesired soaps in rosin-sized paper systems.

In accordance with one aspect of the invention, the method is performed where a calcium carbonate is used as a paper filling and/or coating and a sodium phosphate compound is used to scavenge divalent cations, such as calcium ions, so as to prevent the formation of calcium rosinates which interfere with rosin sizing of the paper formed. Other or broader aspects are presented as well.

The objects are further attained by novel paper compositions made with paper stock having in novel combination at least enhanced amounts of rosin-reactive coating and/or filling materials and a desired range of the amount of rosin. Additionally, the objectives are achieved with a paper filler composition for rosin-sized paper comprising a calcium carbonate material having in association therewith a precipitating or chelating agent effective to reduce the presence of calcium

ions when the filler composition is added to a papermaking slurry so as to prevent the formation of soap.

Such novel methods and compositions afford the advantage of making paper with higher contents of fillers or coatings and rosin sizing not heretofore available.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION One embodiment of the present invention is a method of making paper comprising (1) admixing a first amount of chelating or precipitating agent and a second amount of a slurry comprising a third amount of a metal salt, preferably a calcium carbonate, and a fourth amount of divalent cations, the admixing and first amount of chelating or precipitating agent being effective to produce a fifth amount of slurry having at least a substantial reduction of the amount of free divalent cations, and (2) admixing the fifth amount of slurry and a sixth amount of a paper furnish comprising rosin, said admixing performed at about an alkaline or neutral pH. The chelating or precipitating agent used is one which is effective to remove the divalent cations from solution without creating substantial problems in the papermaking process. If need be, the chelated or precipitated divalent cations can be removed before introduction of the fifth amount of slurry to the paper furnish. The preferred chelating or precipitating agent comprises one or more phosphate moiety. A phosphate moiety contains phosphorous and oxygen atoms and has a negative charge. Non-limiting examples are PO ₄ and P ₃ O _IO ^"5 . Additional atoms, such as hydrogen among others, can be present.

Preferably the chelating or precipitating agent is selected from sodium phosphate compounds, preferably sodium hydrogen phosphate (Na ₃ HPO ₄ ), also referred to as dibasic sodium phosphate, and sodium tripolyphosphate (Na ₅ P ₃ O ₎₀ ). Other non- limiting examples are tribasic sodium phosphate (Na ₃ PO ₄ ), tetrasodium pyrophosphate (Na ₄ PO ₇ ), and sodium metaphosphates, (NaPO) _n where n is a small integer greater than three (3).

The slurry comprising the metal salt is a slurry compatible with the papermaking process. The metal salt is used as an intended paper filler or coating or both. A preferred metal salt is calcium carbonate. The calcium carbonate can be present as a precipitated calcium carbonate (PCC), ground calcium carbonate (GCC) or

a lime derivative, preferably as PCC or GCC, more preferably as PCC. Another metal salt is magnesium sulphate.

The divalent cations can be any divalent cations which would react with rosin to create a rosinate soap, typically a metal rosinate soap. Typically, a source of the divalent cations could be the metal salt. Such cations can be compounds, but are typically single atom ions such as calcium ions or magnesium ions.

The method of admixing and the amount of the chelating or precipitating agent should be effective to produce a fifth amount of slurry having at least a substantial reduction of the amount of divalent cations initially present in the second amount of slurry. A substantial reductions is at least a reduction of about fifteen percent, preferably at least about fifty percent, more preferably essentially all of the free divalent ions. In a preferred embodiment, the produced slurry has a reduction of calcium ions in these stated amounts.

In another preferred embodiment the fifth amount of slurry comprises at least about fifteen percent by weight calcium carbonate and at most about one part per million (ppm) by weight free calcium ions.

The present invention of making paper is effective to prevent formation of a substantial amount of divalent metal rosinate soaps, particularly calcium rosinates among others. Such rosinates are formed in the reaction of divalent cations and the rosin in the sixth amount of paper furnish. The amount of rosinates is deemed substantial when the amount is sufficient to substantially interfere with the reaction between aluminum and rosin which creates sizing in paper. Such competition is deemed substantial when the rosinate formed is at least about one-fourth percent by weight of the paper stock. The admixing of the fifth amount of slurry and the sixth amount of a paper furnish is performed in conditions at about an alkaline or neutral pH, preferably from about 6.5 pH to about 8.0 pH, more preferably about 7 pH.

In another embodiment, the present invention is a rosin type paper composition comprising paper stock; at least about ten percent by weight coating and/or filler material, the material having a moiety which is rosin-reactive when in an ionic form; and less than a substantial amount of rosin soap. A "rosin type paper" is a paper containing an effective amount of rosin, preferably from at least about 0.05

^■ percent, more preferably from about 0.05 percent to at about 1.0 percent by weight rosin. Preferably the coating and/or filler material is a calcium salt, more preferably calcium carbonate or calcium sulphate. The rosin preferably has aluminum ions associated with the rosin to facilitate the sizing phenomenon. A substantial amount of rosin soap is that amount which would make the paper commercially unattractive. Such unattractiveness would not permit using an amount of coating and/or filler material in a substantial amount, such as at least about 10 percent for example, because of the formation of undesired soap in the absence of the use of the use chelating or precipitating agent in the present invention. In another preferred embodiment the paper described is an alkaline or neutral paper, the coating and/or filler material is precipitated calcium carbonate, the rosin aluminum complex originates from a dispersed rosin or a rosin soap, and the filler in the paper stock is effectively treated or pretreated with a sodium phosphate, preferably dibasic sodium phosphate or sodium tripolyphosphate, to prevent formation of a substantial amount of divalent metal rosinate soap. In a more preferred embodiment, the divalent metal rosinate soap is calcium rosinate soap.

In another embodiment, the present invention is a paper filler composition for rosin-sized paper. The composition contains a calcium carbonate material, preferably precipitated calcium carbonate, having in association therewith a precipitating or chelating agent effective to reduce the presence of calcium ions when the filler composition is added to a papermaking slurry. The chelating or precipitating agent is one of those described hereinabove. The agent is associated with the calcium carbonate material in being intimately mixed therewith or affixed to the calcium carbonate material itself, such as in a pretreatment step before the introduction of the calcium carbonate to the papermaking process. When the calcium carbonate is added to the papermaking slurry, the agent already associated with the calcium carbonate is present in an amount effective to prevent any generated calcium ions, such as from buffering activity in solution, from interfering substantially with the subsequent rosin sizing process. Such agent can be, but need not be, confined to the superficial surface of the calcium carbonate material. Alternatively, the agent may be provided within the superficial boundaries of the calcium carbonate material, such as in the pores or cracks of the material. The agent is provided in an amount sufficient to prevent the formation

of soap which interferes substantially with the rosin sizing process.

The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent in the following illustrative examples, which are not intended to limit the scope of the invention. EXAMPLES

Example 1 : Calcium Ion Removal

A calcium selective electrode was standardized. Then the electrode was placed in a 100 gram slurry containing 22 dry grams of Minerals Technologies Inc. produced precipitated calcium carbonate. Two milliliters of ISA was added. The precipitating agents identified in Table 1 were added as a solution in 0.5 percent by weight increments and the readings recorded.

TABLE 1 EFFECTS OF CHELATING AGENTS ON CALCIUM CONCENTRATION

* by weight of an ion ** ppm - parts per million

Examples Handsheet Preparations

For Examples 2, 3 and 4, the following methodology was used to prepare handsheets: Handsheets were prepared using four inch Turbulent Pulse apparatus, and a 75/25 Prince Albert northern hardwood/softwood pulp blend refined to 400 + 25 Canadian Standard Freeness. Neutros Extra rosin (manufactured by Akzo-

Nobel), alum (manufactured by General Chemical) and starch (cationic potato starch manufactured by Akzo-Nobel) were added to enough thick stock (1.5 weight percent) to make four sheets. The pulp was stirred and after 10 seconds dilution water was added and 500 mL of diluted pulp (0.12 weight percent) was added to the turbulent pulse jar. The filler was then added followed ten seconds later by the addition of cationic polyacrylamide retention aid (0.5 pound per ton Percol 175 polymer manufactured by Allied Colloids) and drained an additional ten seconds later. The sheet of paper was then pressed at 20 pound per square inch and dried on a drum dryer at 1 15 degrees Centigrade. The sheets were then conditioned at 23 degrees Centigrade and 50 percent relative humidity for 24 hours. Sizing evaluations were performed using a Hercules Sizing Test (HST), TAPPI Method T-530PM-89 (revised 1989). Example 2: Effect of Free Calcium Ion on Sizing Performance in a Neutral Rosin Svstem For this Example the following amount were used: Rosin 9 pounds per ton

Alum 13.5 pounds per ton

Starch 15 pounds per ton

Four handsheets were prepared. In the Control handsheet precipitated calcium carbonate was used as filler and no attempt was made to reduce the calcium ion concentration. In the LC (Low Calcium) handsheet same type filler was used and the calcium ion concentration reduced by filtering the slurry, washing with deionized waster, drying and then reslurrying with deionized water. The Hydrogen Phosphate and Tripolyphosphate handsheets respectively had the calcium ion concentration reduced by treatment with hydrogen phosphate and tripolyphosphate agents at a concentration of one weight percent each. The results of testing with a Hercules Sizing Test (HST) are shown in Table 2.

TABLE 2 NEUTRAL ROSIN SIZING

Example 3: Effect of Size Addition Level on Sizing Performance in a Neutral Rosin

Svstem

For this Example the following amounts were used:

Rosin Level varied, see Table

Alum 1.5 times the sizing level

Starch 15 pounds per ton

Hercules Sizing Tests (HST) were performed on handsheets prepared using size levels of 9, 7.5, and 6 pounds per tons. All sheets were prepared at 20 weight percent filler level. The results are shown in Table 3:

TABLE 3 NEUTRAL ROSIN SIZING

Example 4: Effect of Precipitant Treatment Level on Sizing Performance in a Neutral Rosin Svstem

For this Example the following amounts were used: Rosin 6 and 9 pounds per ton (see Table)

Alum 9 and 13.5 pound per ton (see Table) Starch 15 pounds per ton

Hercules Sizing Tests (HST) were performed on handsheets treated with varying amounts of treatment agents and sizing. All sheets prepared at 20 weight percent filler level. The results are shown in Table 4:

TABLE 4 NEUTRAL ROSIN SIZING - EFFECT OF ADDITIVE LEVEL

Although the present invention has been described in detail, it is clearly understood that the same is by way of example only and is not to be taken by way of limitation.