CA2235151A1 - Stabilized calcium carbonate composition using sodium carbonate and mixtures of acids and uses therefor - Google Patents
Stabilized calcium carbonate composition using sodium carbonate and mixtures of acids and uses therefor Download PDFInfo
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Abstract
An improved form of calcium carbonate which is acid resistant to enable its use as a filler material in the making of neutral to weakly acid paper, and a process for producing this acid resistant calcium carbonate are provided. This acid resistant calcium carbonate comprises a mixture of at least about 0.1 percent, based on the dry weight of the calcium carbonate of sodium carbonate, together with at least 0.1 percent, based on the dry weight of the calcium carbonate, of a mixture of weak acids in admixture with the calcium carbonate.
The figure exemplifies the composition by teaching the weak acids are polyacrylate acid and phosphoric acid.
The figure exemplifies the composition by teaching the weak acids are polyacrylate acid and phosphoric acid.
Description
CA 0223~1~1 1998-04-16 WO97/14651 PCT~S96/16610 STABILIZED CALCIUM CARBONATE COMPOSITION
USING SODIUM CARBONATE AND ~l~l~K~S OF ACIDS
AND USES THEREFOR
BACKGROUND OF TH~ INVENTION
This invention relates generally to calcium carbonate for use in papermaking, and related industries, and more particularly to a calcium carbonate having acid resistant properties.
Titanium dioxide and calcined clay have traditionally been utilized as filler materials in the preparation of neutral to weakly acidic paper in order to improve the optical properties, especially the brightness, of the resultant product. These materials, however, especially titanium dioxide, have the disadvantage of being very expensive, resulting in higher manufacturing costs and an uncompetitively priced paper product.
Calcium carbonate, particularly precipitated calcium carbonate, has been used as a filler material in the making of alkaline paper. Such usage results in a paper with enhanced optical properties, without the expense incurred in using titanium oxide ~illers, resulting in a much less expensive product. Calcium carbonate, however, cannot generally be used as a filler in acidic paper because it decomposes in an acidic environment.
Consequently, there has long been a need to develop a calcium carbonate composition which is acid stabilized and resistant to decomposition at low pH, so that it can be utilized as a ~iller material in the manufacture of acidic paper, such as groundwood paper, where the use o~
an alkaline filler would have a negative impact on the final paper properties.
~ Paper made from mechanical pulps has been traditionally produced under acidic papermaking conditions because o~ "~iber alkaline darkening" that occurs as pH rises. This means that ther~ is a reduction CA 0223~1~1 1998-04-16 WO97/14651 PCT~S96/16610 ln brightness o~ the paper (brightness reversion) when the pH is raised ~rom acid to alkaline in wood-containing systems. Alkaline darkening will occur to some degree ln any wood pulps with significant lignin content. The degree o~ darkening depends on the particular pulps, pH, and water quality. In general, ground calcium carbonate and precipitated calcium carbonate ~illers bu~er wet end in the 7.5-8.2 pH range. Acid-resistant calcium carbonate compositions thus provide a means ~or reducing the degree o~ ~iber alkaline darkening and brightness reversion due to their ability to maintain a stabilized pH.
U. S. Patent 5,0~3,017 discloses and claims an acid-stable calcium carbonate resistant to degradation in a mildly acidic environment which comprises a mixture o~ a calcium-chelating agent or a conjugate base, and a weak acid, such that calcium carbonate is coated by, and is in equilibrium with, the calcium-chelating agent or conjugate base and the weak acid. Pre~erred calcium carbonate compositions contain sodium hexametaphosphate and phosphoric acid.
ORJi~CTS OF T~ INVENTION
It is an object o~ the present invention to provide stabilized and acid resistant calcium carbonate composition especially suitable ~or use in papermaking applications.
It is a ~urther object o~ the present invention to provide a process ~or the preparation o~ the a~oresaid calcium carbonate compositions.
A still ~urther object of the present invention is to provide a paper having enhanced optical q~ualities prepared using the calcium carbonate compositions o~ the present invention.
eCIlUS 96/ 166 IP~.J~O OCT t9~7 m~king of neutral to weakly acid paper, and a process for producing this acid reeietslnt calcium carbonate. More particularly, this invention concerns an acid r~eiet~nt calcium carbonate comprising a mixture of at least about 0.1 percent, based on the dry weight of the calcium ca,l,oll~Le, of sodium carbonate together with at least about 0.1 percent, based on the dry weight of the calcium carbonate, of a ~ of two or moreweak acids, in ~ ; X ~ e with the calciwn carbonate. It has surprisingly been found that the inclusion of the sodium cAIbo~le and the nlLxlul~, of two or more weak acids confers a higher degree of stability and acid reeiet~noe for calcium ca.l,o~ in the presence of fiber slurry, and a longer term of pH stability than the prior art acid-stabilized calcium carbonate compositions. ~ ~
RRTFF DF.~CR~PTION OF T~F T~R~wI~Gs FIGURE 1 is a graph co. ~ ' ;ng the 24 hours ageing of scalenohedral prc;~ iL~l~d calcium carbonate compositions of the present invention using 1-2% sodium carbonate, 1% polyacrylic acid and various concentrations of phosphoric acid.
FIGURE2isagraphco-- ~pA.;Il~ thepHofascal~nch~ lp,ecipiL~L~dcalcium carbonate composition of the present invention using 1% sodium carbonate/1%
polyacrylic acid/6% phnsphoric acid, to the pH of a composition using 1% sodium c~l ollatel7% phosph~ric acid, or 1% sodium ca 1,oll~le/7% polyacrylic acid.
FIGURE 3 is a graph co",p~;"g the pH of a scalenohedral ~..,ci~ilaled calcium c~L-bol,~le composition of the present invention using 2% sodium carbonate/1%
polyacrylic acid/6% phosphoric acid, to the pH of a composition using 2% sodium c~l~oll~le/7% phosphoric acid.
FIGURE 4 is a graph showing the 24 hours ageing of rhombic ~l~,cipil~led calciumcarbonate compositions of the present invention using 0.5% sodium c~bollale/1%
phosphoric acid, with various conc~n~tions of polyacrylic acid.
CA 02235151 1998-04-16 P.CT¦IJS 9 6/ 1 6 6 1 t IP~AnJSl O OCT 199 FIGURE 5 is a graph comr~ring the pH of a rhombic precipitated calcium carbonatecomposition co.~ g 0.5% sodium carbonate/4% polyacrylic acid/1% phosphoric acid, to the pH of a composition co,~ 0.5% sodium carbonate/5% phosphoric acid, or 0.5% sodium carbonate/5% polyacrylic acid.
FIGURE 6 is a graph COl"p~ ;"g the pH of a ground calcium carbonate composition co~ g 0.5% sodium carbonate/1% polyacrylic acid/3% phosphoric acid, to the pH
of a composition co~ .;"i~-g 0.5% sodium carbonate/4% phosphoric acid, or 0.5%
sodium carbonate/4% polyacrylic acid.
FIGURE 7 is a graph COlll~u~g the pH of a ground calcium carbonate composition of the present invention using 3% sodium c~bol~ /1% polyacrylic acid/5% phosphoric acid, to the pH of a composition co"~ 3% sodium carbonat~J 6% phosphoric acid.
FIGURE 8 is a graph co. . .~ the pH of a ground calcium carbonate composition ofthe present invention using 1% sodium carbonate/4% polymaleic acid/1% phosphoricacld to the pH of a composition co. .l~ 1% sodium carbonate with 5% ph~sphnric acld.
FIGUR~ 9 is a graph co. . .p~ g the pH of a scalenohedral precipitated c~lcil~n~c~G~lc composition of the present invention using 0.5% sodium carbonate/1%
polyacrylic acid/6% phosphoric acid, to the pH of a prior art composition which COnt~lil S 0.5% sodium h~met~rhosph~tP/7% phosphoric acid.
DFTATT Fn nF~c~TpTIoN OF THF. T~VF~TION
The in~loved form of calcium c~l/oll~le y~ d by the instant invention is stabilized, and thus, acid resi~t~nt to enable its use as a filler m~teri~l in the m~king of neutral to weakly acid paper. While not wishing to be bound by any particulartheory as to the operability of the present invention, it is believed that the acid AM~DED 8~ET
IPEA~U&~L O OCT 1997 resistance conferred upon the calcium carbonate compositions of the present invention is a result of the inactivation of the surface of the calcium carbonate by the addition of the sodium carbonate and the mixtures of the two weak acids. The combination of the two weak acids a~p~.llLly results in a synergistic relationship since the results shown in the FIGURES in(1ir.5~tes that a greater stability and acid resi~t~nce is afforded by the use of two acids when col,lpaL~d to the same weight percent of a single acid.
In the practice of the present invention, the calcium carbonate compositions arerendered acid ~ L~l by the inclusion of at least about 0. l percent, based on the dry weight of the calcium carbonate, of sodium c~l~l~l~ together with at least about 0.l ~ ~
percent, based on the dry weight of the calciurn carbonate, of a n,i~L~e of two or more weak acids. Especially pleL~ d as one component of the l~ of weak acids is an organic, polymeric weak acid, such as polyacrylic or polymaleic acid.
While not wishing to be bound by any theory, it is believed that the capability of tbe acid-stabilized calcium c~l,ollate ofthe present invention to resist ~1ic~oCi~tion in an acidic en~dlullme.ll is due to the polymer adsorption on the surface of the calcium c~l)ol~LL~, absorption of polymer functional groups on the calcium carbonate surface, and the formation of a b~ ; . .p system between anionic functional groups of thepolymer and a weak acid, or the polymeric acid and the weak base. This me~h~ni~mof polymer adsorption is distinct from absorption or reaction of the prior art sodium k~,....r~ph~sphate on the surface of calcillm carbonate. Polymer adsorption can provide a barrier coating on the surface of calcium carbonate which reduces the dissolution reaction of calcium carbonate. On the other hand, the absorption or reaction of sodium h~xs.. el;.phosphate is limited to the surface of the calcium carbonate.
The sodium carbonate utilized in the compositions of the present invention is commercially available in forms suitable for direct inclusion into the calcium ~NOED s~Er CA 0223~1~1 1998-04-16 ~CTII~S 9 6 / 1 6 6 1 ~
IP~JS~ O OCT 1997 carbonate llliXlUl~. The amount of the sodillm carbonate utilized is at least 0.1 percent, based on the dry weight of the calcium carbonate, and is preferably about 1 to about 6 percent, based on the dry weight of calcium carbonate.
The weak acids utilized in the compositions of the present invention are preferably weak acids selected from the group conei.etin~ of phosphoric acid, metaphosphoric acid, h~mçt~ph~sphoric acid, ethylene~lih...i,.cltil.~acetic acid (EDTA), citric acid, sulfurous acid, boric acid, acetic acid, and weak acids derived from organic polymeric acids, such as polyacrylic acid, polymaleic acid and polycarboxylic acid. As noted hereinbefore, the lnixlule of weak acids preferably colll~il,s at least one weak acid - -which is derived from an organic, polymeric acid. These organic polymeric acids are typically an organic polymer having a weight average molecular weight, M~v, in the range of 750-1,000,000, coneieting of regularly lcpe~ g units or chemic~lly similar units, connecte~l by primary covalent bonds. The total amount of the weak acids utilized is at least 0.1 percent, based on the dry weight of the calcium carbonate, and is preferably about 1 to about 8 percent, based on the dry weight of the c~lcillm carbonate.
Ple~ ;d combin~tione of sodium carbonate and weak acids for use in the present invention include sodium c~l,o~ /polyacrylic acid/phosph~ ric acid and sodium ch bo~le/polymaleic acid/ph~-sph-~ric acid.
The c~lr,illm carbonate utilized is preferably finely divided and it can be either a precipitated calcium carbonate or a natural ground limestone.
The process for producing this acid resistant calcium carbonate involves first forming a m,xlu-~, of calcium c~bo"~lt; with at least about 0.1 percent, based on the dry weight of the calcium carbonate, of the sodium carbonate to be l~tili7Pfl Then, at least about 0.1 percent, based on the dry weight of the c~lcil-m c~l,onate, of the mixture of weak acids is added to this reslllt~nt mixture.
~OED~
CA 0223~1~1 1998-04-16 WO97/14651 PCT~S96/16610 1 to about 8 percent, based on the dry weight o~ the calcium carbonate.
Preferred combinations of sodium carbonate and weak acids for use in the present invention include sodium carbonate/polyacrylate acid/phosphoric acid and sodium carbonate/polymaleic acid/phosphorlc acid.
The calcium carbonate utllized is preferably ~inely divided and it can be either a precipitated calcium carbonate or a natural ground limestone.
The process for producing this acid resistant calcium carbonate involves first forming a mixture of calcium carbonate with at least about 0.1 percent, based on the dry weight of the calcium carbonate, of the sodium carbonate to be utilized. Then, at least about 0.1 percent, based on the dry weight of the calcium carbonate, of the mixture of weak acids is added to this resultant mixture. Finally, the resultant mixture is blended for a sufficiently long period of time to ensure uniform mixing of the ingredients.
The calcium carbonate can be utillzed in the above-described process either as a dry powder or an aqueous slurry with up to about 60 percent by weight solids content.
The sodium carbonate can be utilized in the instant process either as a dry solid or as an aqueous solution.
When the calcium carbonate is used in dry powder ~orm, it is preferable to utilize an aqueous solution o~ the sodium carbonate in order to facilitate homogeneous mixing. Where a slurry of the calcium carbonate is utilized, the solid form of the sodium carbonate readily dissolves therein so that an aqueous solution is unnecessary.
PCrlUS 9 6/.16610 tP~~WSi 0 OCT 1997 The invention will be filrther ill--~tr~tç(l by the following F~mplçs, which are to be considered illu~Lldlive of the invention, and not limited to the precise embo~1iment~
shown.
FX~MPT.F.
S- ~lton- hedral P.ec~i~ ;d Calci -m Carbon~t~
Acid stabilized sc~l~noh~ral ~.eci~ A calcium carbonate slurry can be obtained by the addition of a weak base such as sodium c~bo-l~Le, followed by the addition of a weak acid such as phosphoric acid and a polymeric acid such as polyacrylic acid.Initially, 1% or 2% sodium carbonate, based on the dry weight of calcium call,ollate, was added into 19.7% solids slully of scalenohedral pLe~ A calcium carbonate.
The pH of untreated scalenohedral ~re~ ted calcium carbonate slurry was 8.83.
After mi~rin~ 6% phosphoric acid and 1% polyacrylic acid, based on the dry weight of calcium carbonate, were added. A plot of the pH was measured for each sample after 24 hours ageing as shown in Figure 1. A composition co..~ g 1% sodium carbonate, based on the dry weight of G~Tcillm c~bon~le, and 6% phosphoric acid and 1% of polyacrylic acid, based on the dry weight of calcium carbonate was found to have an initial pH 5.35, and a pH of 6.19 after 24 hours ageing.
F,~A~fPT F. 2 Scalen~ h~-lral P.~,ci~,i~l~d Calciu~Carbonate Acid stabilized scalenohedral plcci~i~led c~lcillm carbonate slurry can be obtained by the addition of a weak acid such as sodium carbonate, followed by the addition of a mixture of weak acids such as phr~sphnric acid and a polymeric acid such as polyacrylic acid. In addition, acid stabilized calcium carbonate can be ~.~p~d A~DEO ~
eCTlus 9 6/ 16 6 1 ~
tKA/~JSl O OCT 1997 with a weak base such as sodium carbonate and a weak acid such as phosphoric acid.
Initially, 1% sodium calbollaLt;, based on the dry weight of calcium carbonate, was added into 19.7% solids slurry of scalenohedral precipit~te~ calcium carbonate. The pH of the u~LIG~l~d scalenohedral precipitated calcium carbonate slurry was 8.83.
After mixin~, 7% phosphoric acid, 7% polyacrylic acid or 6% phosphoric acid/1%
polyacrylic acid, based on the dry weight of c~lci-lm carbonate, were added. The pHs of the calcium carbonate slurries are measured over a period of 120 hours ageing and shown ~phic~lly in Figure 2. The initial pH of the slurry with 1%Na2COJ6%H3PO~,/1% polyacrylate acid tre~tm~nt was measured and found to be 5.35, and then measured after 115 hours ageing and found to be 6.47. On the other - ~
hand, the initial pH of the c~lcillnl carbonate slurry co..l~ 1%Na2CO3/7%H3PO~
was measured and found to be 6.30, and, after 115 hours ageing was found to be 7.45.
The pH di~elellce was thus 0.98 unit after 115 hours ageing, which is significantly di~ele,.~. In addition, the pH of calcium carbonate treated with 1~/ONa2CO3/7%
polyacrylic acid was 1.24 unit higher than that treated with 1%Na2CO3/6%H3PO41%
polyacrylic acid after 115 hours ageing.
FX~ F 3 S~len<)hedral Pl~eci~i~led Calci -m Carbonate Acid stabilized scalenohedral ~le~ iLal~d calcium c~bol.~.le slurry can be obtained by the addition of sodium c~l,on~le, followed by the addition of a weak acid such as phosphoric acid and a polymeric acid such as polyacrylic acid. For co~ ~;son, anacid stabilized calcium carbonate composition can be ~repal~d using sodiurn carbonate and a weak acid such as phosphoric acid. Initially, 2% sodiurn carbonate, based on the dry weight of calcium carbonate, was added into 19.7% solids slurry of scalenohedral pl'~ d calcium carbonate. The pH of Ullll~ c.led scalenohedral ~,reci~ led calciurn carbonate slurry was 8.83. After mi~cin~, 7% phosphoric acid, or 6% phosphoric acid~l% polyacrylic acid, based on the dry weight of c~lcillm carbonate, were added. The results indicated that the pHs of calcium c~l,ol.ate OED ~ItEET
eC~LUS 96/1661 O OCT l997 slurries treated with 2%Na2CO3l6%H3PO4/1% polyacrylic acid were lower than the pHs of calcium c~l,ollate slurry treated with 2%Na2CO3/7%H3PO4 after 90 hours ageing, as shown in Figure 3. The initial pH of the calcium carbonate slurry with 2%Na2CO3/6%H3PO4/1% polyacrylic acid tre~tment was measured and found to be 5.82, and, after 88 hours ageing was again measured and found to be 6.88. In comparison, the initial pH of the slurry cont~ining 2%Na2CO3/7%H3PO4 was measured and found to be 6.41, and 88 hours ageing was reme~llred and found to be 7.56. The pH diLL'~.cnce was thus 0.68 unit after 88 hours ageing, which is ~i~nific~ntly diLL'~rcnt.
pchornhic Prec~ ed Calcium Carbonate The initial pH of rhombic pre~ cd calcium carbonate was 8.79. First, 0.5%
sodium c~l~.~le, based on the dry weight of calcium c~l,o.l~le, was added into l8.2% solids slurry of rhombic ple~i~i~lcd c~lcillm carbonate. After blen~1ing, l%
phosphoric acid and 2%-6% polyacrylic acid, based on the dry welght of calciurn ca.l~le, were added. The pH me~u~clllent was monitored for 24 hours ageing and the results are as shown in Figure 4. One of the examples showed that the initial pH
of rhombic ~ i~led calcium call,oll~le slurry treated with 0.5%Na2CO3tl%H3PO4/4% polyacrylic acid was 6.03, and the pH of the slurry was found to be 6.50 after 24 hours ageing.
'M~WED 8HEET
F~CTIUS 9 6 / 16 6 1 0 IPEAJlJ~ o OCT 1997 F,~MPr,F, S
l~homhic P,~ici~ led Calcillm Carbonate The initial pH of rhombic plccipilalcd calcium carbonate was 8.79. First, 0.5%
sodiurn carbonate, based on the dry weight of calcium carbonate, was added into 18.2% solids slurry of rhombic pl~cipil~led calcium carbonate. After blending 1%phosphoric acid/4% polyacrylic acid, 5% polyacrylic acid or 5% phosphoric acid, - based on the dry weight of c~lcillm carbonate, was added. The initial pH of the slurry with 0.5~/ONa2CO3/1%H3PO~/4% polyacrylic acid tre~tm-ont was measured and found ~ -to be 6.03, and, upon remea~u~cm~,ll 90 hours ageing, was found to be 6.80, as shown in Figure S. On the other hand, the initial pH of the slurry cont~inin~
0.5~/ONa2CO3/5%H3PO4 was measured and found to be 6.59, and after 90 hours ageing was f~und to be 7.43 Thç pH cl; rr"l~lce was thus Q.63 unit af er 90 hours a~eing, which is significantly ~ lL Also, the pH of c~lcilmn carbonate slurry treated with 0.5%Na2CO3/5% polyacrylic acid was 0.57 unit higher than that treated with 0.5%Na2CO3/1%H3PO~/4% polyacrylic acid after 90 hours ageing.
FXA~PT F. 6 Grollncl C~lcium Carbonate The initial pH of ground calcium carbonate was 8.01. Initially, 0.5% sodium c~l,on~le, based on the dry weight of calcium carbonate, was added into 20% solid slurry of ground calciurn c~l,onate. After blending, 4% phosphoric acid, 4%
polyacrylic acid or 3% phosphoric acid/1% polyacrylic acid, based on the dry weight of calcium carbonate, was added. The initial pH of the slurry con~ ~;, . i, .~
0.5%Na2CO3/3%H3PO4/1% polyacrylic acid was measured and found to be 5.24, and after 9S hours ageing was found to be 5.86, as shown gr~phic~lly in Figure 6. In P~ S ~6/1661C
IP~AJllS!~ O OCT 1997 comparison, the initial pH of the slurry with 0.5~/ONa2CO3/4%H3PO4 and 0.5~/ONa2CO3/4~/O polyacrylic acid was measured and found to be 6.31 and 6.47, and, after 9S hours ageing, was measured and found to be 7.17 and 7.40. The pH
diL~l~l,ce was thus 1.31 and 1.54 unit after 9S hours ageing, which is ~iFnifi~n~ly different.
FXA~rPT F 7 Grol-nti Calcillm Carbonate The initial pH of ground calcium carbonate was 8.01. Initially, 3% sodium carbonate, based on the dry weight of c~lcillm carbonate, was added into a 20% solids slurry of ground calcium c~l,ol~Le. After blen~iing~ 6% phosphoric acid or 5% phosphoric acid/1% polyacrylic acid, based on dry weight of calcium carbonate, was added. The initial pH of slurry with 3%Na2CO3/5%H3PO4/1% polyacrylic acid tre~tment was measured and found to be 6.25, and, when reme-S3ellred after 24 hours ageing wasfound to be 6.37 as shown graphically in Figure 7. On the other hand, the initial pH of the slurry 3%Na2CO3/6%H3PO4 LIC;~ L~I~ was measured and found to be 7.12, and, when r~m~llred after 24 hours ageing was found to be 7.89. The pH di~e.lce was thus 1.52 units after 24 hours ageing, which is significantly different.
Fx~Pr F 8 Grolm~l Calcium Carbonate The initial pH of ground calcium carbonate was 8.01. Initially, 1% sodiurn carbonate, based on the dry weight of calcium carbonate, was added into a 20% solids slurry of ground calcium call,onate. After blen~ling, 5% phosphoric acid or 1% phosphoric acid~4% polymaleic acid, based on the dry weight of calcium carbonate, was added.
eCTlJS 96/ 1661C
The initial pH ofthe slurry with 1%Na2CO3/1%H3PO4/4% polymaleic acid tre~tment was measured and found to be 6.08, and, when rçm~el-red 40 hours ageing was found to have a pH of 6.30 as shown graphically in Figure 8. In comparison, the initial pH
ofthe slurry co,,~ g 1%Na2CO3/5%H3PO~ was measured and found to be 6.87, and, when remeasured after 40 hours ageing was found to be 7.50. The pH di~erellce was thus 1.20 unit after 40 hours ageing, which is ci~nific~ntly different.
FXAMPT F g Com~p~ricoll with Prior Art Acid stabilized scalenohedral preci~ ed calciurn carbonate slurry can be obtained by the addition of sodium carbonate, followed by the addition of a mixture of weak acids 1 5 such as phosphoric acid and polyacrylic acid. Initially, 0.5% sodium call,oll~le, based on the dry weight of calcium carbonate, was added into 19.7% solids slurry of scalenohedral p~ e~1 calciurn c~l,o~L~. The pH of ul~ aled scalenohedral precirit~tecl calciurn carbonate slurry was 8.83. After mixin~, 6% phosrhoric acid/1%
polyacrylic acid, based on the dry weight of calcium carbonate, was added. A similar composition, based on the te~c hinpc of the U.S. Patent No. 51567i 9, was pLepaled using 0.5% sodiurn hrx~metaphosphate and 7% ph~sph~ric acid. The initial pH of the slurry co..li.i..;..g 0.5% sodium he~metaphosphate/7% phosphoric acid was 4.91, and was found to be 6.41 after 75 hours ageing, as shown graphically in Figure 9. Incomr~ricon, the initial pH of the slurry co~t ~ g 0.5% sodium carbonate/6%
phosphoric acid/1% polyacrylic acid was 5.15, and was found to be 6.17, after 75hours ageing. These results indicate that the compositions of the present invention are - superiortothoseofthepriorartU.S. PatentNo. 5156719.
'~OED ~#E~T
USING SODIUM CARBONATE AND ~l~l~K~S OF ACIDS
AND USES THEREFOR
BACKGROUND OF TH~ INVENTION
This invention relates generally to calcium carbonate for use in papermaking, and related industries, and more particularly to a calcium carbonate having acid resistant properties.
Titanium dioxide and calcined clay have traditionally been utilized as filler materials in the preparation of neutral to weakly acidic paper in order to improve the optical properties, especially the brightness, of the resultant product. These materials, however, especially titanium dioxide, have the disadvantage of being very expensive, resulting in higher manufacturing costs and an uncompetitively priced paper product.
Calcium carbonate, particularly precipitated calcium carbonate, has been used as a filler material in the making of alkaline paper. Such usage results in a paper with enhanced optical properties, without the expense incurred in using titanium oxide ~illers, resulting in a much less expensive product. Calcium carbonate, however, cannot generally be used as a filler in acidic paper because it decomposes in an acidic environment.
Consequently, there has long been a need to develop a calcium carbonate composition which is acid stabilized and resistant to decomposition at low pH, so that it can be utilized as a ~iller material in the manufacture of acidic paper, such as groundwood paper, where the use o~
an alkaline filler would have a negative impact on the final paper properties.
~ Paper made from mechanical pulps has been traditionally produced under acidic papermaking conditions because o~ "~iber alkaline darkening" that occurs as pH rises. This means that ther~ is a reduction CA 0223~1~1 1998-04-16 WO97/14651 PCT~S96/16610 ln brightness o~ the paper (brightness reversion) when the pH is raised ~rom acid to alkaline in wood-containing systems. Alkaline darkening will occur to some degree ln any wood pulps with significant lignin content. The degree o~ darkening depends on the particular pulps, pH, and water quality. In general, ground calcium carbonate and precipitated calcium carbonate ~illers bu~er wet end in the 7.5-8.2 pH range. Acid-resistant calcium carbonate compositions thus provide a means ~or reducing the degree o~ ~iber alkaline darkening and brightness reversion due to their ability to maintain a stabilized pH.
U. S. Patent 5,0~3,017 discloses and claims an acid-stable calcium carbonate resistant to degradation in a mildly acidic environment which comprises a mixture o~ a calcium-chelating agent or a conjugate base, and a weak acid, such that calcium carbonate is coated by, and is in equilibrium with, the calcium-chelating agent or conjugate base and the weak acid. Pre~erred calcium carbonate compositions contain sodium hexametaphosphate and phosphoric acid.
ORJi~CTS OF T~ INVENTION
It is an object o~ the present invention to provide stabilized and acid resistant calcium carbonate composition especially suitable ~or use in papermaking applications.
It is a ~urther object o~ the present invention to provide a process ~or the preparation o~ the a~oresaid calcium carbonate compositions.
A still ~urther object of the present invention is to provide a paper having enhanced optical q~ualities prepared using the calcium carbonate compositions o~ the present invention.
eCIlUS 96/ 166 IP~.J~O OCT t9~7 m~king of neutral to weakly acid paper, and a process for producing this acid reeietslnt calcium carbonate. More particularly, this invention concerns an acid r~eiet~nt calcium carbonate comprising a mixture of at least about 0.1 percent, based on the dry weight of the calcium ca,l,oll~Le, of sodium carbonate together with at least about 0.1 percent, based on the dry weight of the calcium carbonate, of a ~ of two or moreweak acids, in ~ ; X ~ e with the calciwn carbonate. It has surprisingly been found that the inclusion of the sodium cAIbo~le and the nlLxlul~, of two or more weak acids confers a higher degree of stability and acid reeiet~noe for calcium ca.l,o~ in the presence of fiber slurry, and a longer term of pH stability than the prior art acid-stabilized calcium carbonate compositions. ~ ~
RRTFF DF.~CR~PTION OF T~F T~R~wI~Gs FIGURE 1 is a graph co. ~ ' ;ng the 24 hours ageing of scalenohedral prc;~ iL~l~d calcium carbonate compositions of the present invention using 1-2% sodium carbonate, 1% polyacrylic acid and various concentrations of phosphoric acid.
FIGURE2isagraphco-- ~pA.;Il~ thepHofascal~nch~ lp,ecipiL~L~dcalcium carbonate composition of the present invention using 1% sodium carbonate/1%
polyacrylic acid/6% phnsphoric acid, to the pH of a composition using 1% sodium c~l ollatel7% phosph~ric acid, or 1% sodium ca 1,oll~le/7% polyacrylic acid.
FIGURE 3 is a graph co",p~;"g the pH of a scalenohedral ~..,ci~ilaled calcium c~L-bol,~le composition of the present invention using 2% sodium carbonate/1%
polyacrylic acid/6% phosphoric acid, to the pH of a composition using 2% sodium c~l~oll~le/7% phosphoric acid.
FIGURE 4 is a graph showing the 24 hours ageing of rhombic ~l~,cipil~led calciumcarbonate compositions of the present invention using 0.5% sodium c~bollale/1%
phosphoric acid, with various conc~n~tions of polyacrylic acid.
CA 02235151 1998-04-16 P.CT¦IJS 9 6/ 1 6 6 1 t IP~AnJSl O OCT 199 FIGURE 5 is a graph comr~ring the pH of a rhombic precipitated calcium carbonatecomposition co.~ g 0.5% sodium carbonate/4% polyacrylic acid/1% phosphoric acid, to the pH of a composition co,~ 0.5% sodium carbonate/5% phosphoric acid, or 0.5% sodium carbonate/5% polyacrylic acid.
FIGURE 6 is a graph COl"p~ ;"g the pH of a ground calcium carbonate composition co~ g 0.5% sodium carbonate/1% polyacrylic acid/3% phosphoric acid, to the pH
of a composition co~ .;"i~-g 0.5% sodium carbonate/4% phosphoric acid, or 0.5%
sodium carbonate/4% polyacrylic acid.
FIGURE 7 is a graph COlll~u~g the pH of a ground calcium carbonate composition of the present invention using 3% sodium c~bol~ /1% polyacrylic acid/5% phosphoric acid, to the pH of a composition co"~ 3% sodium carbonat~J 6% phosphoric acid.
FIGURE 8 is a graph co. . .~ the pH of a ground calcium carbonate composition ofthe present invention using 1% sodium carbonate/4% polymaleic acid/1% phosphoricacld to the pH of a composition co. .l~ 1% sodium carbonate with 5% ph~sphnric acld.
FIGUR~ 9 is a graph co. . .p~ g the pH of a scalenohedral precipitated c~lcil~n~c~G~lc composition of the present invention using 0.5% sodium carbonate/1%
polyacrylic acid/6% phosphoric acid, to the pH of a prior art composition which COnt~lil S 0.5% sodium h~met~rhosph~tP/7% phosphoric acid.
DFTATT Fn nF~c~TpTIoN OF THF. T~VF~TION
The in~loved form of calcium c~l/oll~le y~ d by the instant invention is stabilized, and thus, acid resi~t~nt to enable its use as a filler m~teri~l in the m~king of neutral to weakly acid paper. While not wishing to be bound by any particulartheory as to the operability of the present invention, it is believed that the acid AM~DED 8~ET
IPEA~U&~L O OCT 1997 resistance conferred upon the calcium carbonate compositions of the present invention is a result of the inactivation of the surface of the calcium carbonate by the addition of the sodium carbonate and the mixtures of the two weak acids. The combination of the two weak acids a~p~.llLly results in a synergistic relationship since the results shown in the FIGURES in(1ir.5~tes that a greater stability and acid resi~t~nce is afforded by the use of two acids when col,lpaL~d to the same weight percent of a single acid.
In the practice of the present invention, the calcium carbonate compositions arerendered acid ~ L~l by the inclusion of at least about 0. l percent, based on the dry weight of the calcium carbonate, of sodium c~l~l~l~ together with at least about 0.l ~ ~
percent, based on the dry weight of the calciurn carbonate, of a n,i~L~e of two or more weak acids. Especially pleL~ d as one component of the l~ of weak acids is an organic, polymeric weak acid, such as polyacrylic or polymaleic acid.
While not wishing to be bound by any theory, it is believed that the capability of tbe acid-stabilized calcium c~l,ollate ofthe present invention to resist ~1ic~oCi~tion in an acidic en~dlullme.ll is due to the polymer adsorption on the surface of the calcium c~l)ol~LL~, absorption of polymer functional groups on the calcium carbonate surface, and the formation of a b~ ; . .p system between anionic functional groups of thepolymer and a weak acid, or the polymeric acid and the weak base. This me~h~ni~mof polymer adsorption is distinct from absorption or reaction of the prior art sodium k~,....r~ph~sphate on the surface of calcillm carbonate. Polymer adsorption can provide a barrier coating on the surface of calcium carbonate which reduces the dissolution reaction of calcium carbonate. On the other hand, the absorption or reaction of sodium h~xs.. el;.phosphate is limited to the surface of the calcium carbonate.
The sodium carbonate utilized in the compositions of the present invention is commercially available in forms suitable for direct inclusion into the calcium ~NOED s~Er CA 0223~1~1 1998-04-16 ~CTII~S 9 6 / 1 6 6 1 ~
IP~JS~ O OCT 1997 carbonate llliXlUl~. The amount of the sodillm carbonate utilized is at least 0.1 percent, based on the dry weight of the calcium carbonate, and is preferably about 1 to about 6 percent, based on the dry weight of calcium carbonate.
The weak acids utilized in the compositions of the present invention are preferably weak acids selected from the group conei.etin~ of phosphoric acid, metaphosphoric acid, h~mçt~ph~sphoric acid, ethylene~lih...i,.cltil.~acetic acid (EDTA), citric acid, sulfurous acid, boric acid, acetic acid, and weak acids derived from organic polymeric acids, such as polyacrylic acid, polymaleic acid and polycarboxylic acid. As noted hereinbefore, the lnixlule of weak acids preferably colll~il,s at least one weak acid - -which is derived from an organic, polymeric acid. These organic polymeric acids are typically an organic polymer having a weight average molecular weight, M~v, in the range of 750-1,000,000, coneieting of regularly lcpe~ g units or chemic~lly similar units, connecte~l by primary covalent bonds. The total amount of the weak acids utilized is at least 0.1 percent, based on the dry weight of the calcium carbonate, and is preferably about 1 to about 8 percent, based on the dry weight of the c~lcillm carbonate.
Ple~ ;d combin~tione of sodium carbonate and weak acids for use in the present invention include sodium c~l,o~ /polyacrylic acid/phosph~ ric acid and sodium ch bo~le/polymaleic acid/ph~-sph-~ric acid.
The c~lr,illm carbonate utilized is preferably finely divided and it can be either a precipitated calcium carbonate or a natural ground limestone.
The process for producing this acid resistant calcium carbonate involves first forming a m,xlu-~, of calcium c~bo"~lt; with at least about 0.1 percent, based on the dry weight of the calcium carbonate, of the sodium carbonate to be l~tili7Pfl Then, at least about 0.1 percent, based on the dry weight of the c~lcil-m c~l,onate, of the mixture of weak acids is added to this reslllt~nt mixture.
~OED~
CA 0223~1~1 1998-04-16 WO97/14651 PCT~S96/16610 1 to about 8 percent, based on the dry weight o~ the calcium carbonate.
Preferred combinations of sodium carbonate and weak acids for use in the present invention include sodium carbonate/polyacrylate acid/phosphoric acid and sodium carbonate/polymaleic acid/phosphorlc acid.
The calcium carbonate utllized is preferably ~inely divided and it can be either a precipitated calcium carbonate or a natural ground limestone.
The process for producing this acid resistant calcium carbonate involves first forming a mixture of calcium carbonate with at least about 0.1 percent, based on the dry weight of the calcium carbonate, of the sodium carbonate to be utilized. Then, at least about 0.1 percent, based on the dry weight of the calcium carbonate, of the mixture of weak acids is added to this resultant mixture. Finally, the resultant mixture is blended for a sufficiently long period of time to ensure uniform mixing of the ingredients.
The calcium carbonate can be utillzed in the above-described process either as a dry powder or an aqueous slurry with up to about 60 percent by weight solids content.
The sodium carbonate can be utilized in the instant process either as a dry solid or as an aqueous solution.
When the calcium carbonate is used in dry powder ~orm, it is preferable to utilize an aqueous solution o~ the sodium carbonate in order to facilitate homogeneous mixing. Where a slurry of the calcium carbonate is utilized, the solid form of the sodium carbonate readily dissolves therein so that an aqueous solution is unnecessary.
PCrlUS 9 6/.16610 tP~~WSi 0 OCT 1997 The invention will be filrther ill--~tr~tç(l by the following F~mplçs, which are to be considered illu~Lldlive of the invention, and not limited to the precise embo~1iment~
shown.
FX~MPT.F.
S- ~lton- hedral P.ec~i~ ;d Calci -m Carbon~t~
Acid stabilized sc~l~noh~ral ~.eci~ A calcium carbonate slurry can be obtained by the addition of a weak base such as sodium c~bo-l~Le, followed by the addition of a weak acid such as phosphoric acid and a polymeric acid such as polyacrylic acid.Initially, 1% or 2% sodium carbonate, based on the dry weight of calcium call,ollate, was added into 19.7% solids slully of scalenohedral pLe~ A calcium carbonate.
The pH of untreated scalenohedral ~re~ ted calcium carbonate slurry was 8.83.
After mi~rin~ 6% phosphoric acid and 1% polyacrylic acid, based on the dry weight of calcium carbonate, were added. A plot of the pH was measured for each sample after 24 hours ageing as shown in Figure 1. A composition co..~ g 1% sodium carbonate, based on the dry weight of G~Tcillm c~bon~le, and 6% phosphoric acid and 1% of polyacrylic acid, based on the dry weight of calcium carbonate was found to have an initial pH 5.35, and a pH of 6.19 after 24 hours ageing.
F,~A~fPT F. 2 Scalen~ h~-lral P.~,ci~,i~l~d Calciu~Carbonate Acid stabilized scalenohedral plcci~i~led c~lcillm carbonate slurry can be obtained by the addition of a weak acid such as sodium carbonate, followed by the addition of a mixture of weak acids such as phr~sphnric acid and a polymeric acid such as polyacrylic acid. In addition, acid stabilized calcium carbonate can be ~.~p~d A~DEO ~
eCTlus 9 6/ 16 6 1 ~
tKA/~JSl O OCT 1997 with a weak base such as sodium carbonate and a weak acid such as phosphoric acid.
Initially, 1% sodium calbollaLt;, based on the dry weight of calcium carbonate, was added into 19.7% solids slurry of scalenohedral precipit~te~ calcium carbonate. The pH of the u~LIG~l~d scalenohedral precipitated calcium carbonate slurry was 8.83.
After mixin~, 7% phosphoric acid, 7% polyacrylic acid or 6% phosphoric acid/1%
polyacrylic acid, based on the dry weight of c~lci-lm carbonate, were added. The pHs of the calcium carbonate slurries are measured over a period of 120 hours ageing and shown ~phic~lly in Figure 2. The initial pH of the slurry with 1%Na2COJ6%H3PO~,/1% polyacrylate acid tre~tm~nt was measured and found to be 5.35, and then measured after 115 hours ageing and found to be 6.47. On the other - ~
hand, the initial pH of the c~lcillnl carbonate slurry co..l~ 1%Na2CO3/7%H3PO~
was measured and found to be 6.30, and, after 115 hours ageing was found to be 7.45.
The pH di~elellce was thus 0.98 unit after 115 hours ageing, which is significantly di~ele,.~. In addition, the pH of calcium carbonate treated with 1~/ONa2CO3/7%
polyacrylic acid was 1.24 unit higher than that treated with 1%Na2CO3/6%H3PO41%
polyacrylic acid after 115 hours ageing.
FX~ F 3 S~len<)hedral Pl~eci~i~led Calci -m Carbonate Acid stabilized scalenohedral ~le~ iLal~d calcium c~bol.~.le slurry can be obtained by the addition of sodium c~l,on~le, followed by the addition of a weak acid such as phosphoric acid and a polymeric acid such as polyacrylic acid. For co~ ~;son, anacid stabilized calcium carbonate composition can be ~repal~d using sodiurn carbonate and a weak acid such as phosphoric acid. Initially, 2% sodiurn carbonate, based on the dry weight of calcium carbonate, was added into 19.7% solids slurry of scalenohedral pl'~ d calcium carbonate. The pH of Ullll~ c.led scalenohedral ~,reci~ led calciurn carbonate slurry was 8.83. After mi~cin~, 7% phosphoric acid, or 6% phosphoric acid~l% polyacrylic acid, based on the dry weight of c~lcillm carbonate, were added. The results indicated that the pHs of calcium c~l,ol.ate OED ~ItEET
eC~LUS 96/1661 O OCT l997 slurries treated with 2%Na2CO3l6%H3PO4/1% polyacrylic acid were lower than the pHs of calcium c~l,ollate slurry treated with 2%Na2CO3/7%H3PO4 after 90 hours ageing, as shown in Figure 3. The initial pH of the calcium carbonate slurry with 2%Na2CO3/6%H3PO4/1% polyacrylic acid tre~tment was measured and found to be 5.82, and, after 88 hours ageing was again measured and found to be 6.88. In comparison, the initial pH of the slurry cont~ining 2%Na2CO3/7%H3PO4 was measured and found to be 6.41, and 88 hours ageing was reme~llred and found to be 7.56. The pH diLL'~.cnce was thus 0.68 unit after 88 hours ageing, which is ~i~nific~ntly diLL'~rcnt.
pchornhic Prec~ ed Calcium Carbonate The initial pH of rhombic pre~ cd calcium carbonate was 8.79. First, 0.5%
sodium c~l~.~le, based on the dry weight of calcium c~l,o.l~le, was added into l8.2% solids slurry of rhombic ple~i~i~lcd c~lcillm carbonate. After blen~1ing, l%
phosphoric acid and 2%-6% polyacrylic acid, based on the dry welght of calciurn ca.l~le, were added. The pH me~u~clllent was monitored for 24 hours ageing and the results are as shown in Figure 4. One of the examples showed that the initial pH
of rhombic ~ i~led calcium call,oll~le slurry treated with 0.5%Na2CO3tl%H3PO4/4% polyacrylic acid was 6.03, and the pH of the slurry was found to be 6.50 after 24 hours ageing.
'M~WED 8HEET
F~CTIUS 9 6 / 16 6 1 0 IPEAJlJ~ o OCT 1997 F,~MPr,F, S
l~homhic P,~ici~ led Calcillm Carbonate The initial pH of rhombic plccipilalcd calcium carbonate was 8.79. First, 0.5%
sodiurn carbonate, based on the dry weight of calcium carbonate, was added into 18.2% solids slurry of rhombic pl~cipil~led calcium carbonate. After blending 1%phosphoric acid/4% polyacrylic acid, 5% polyacrylic acid or 5% phosphoric acid, - based on the dry weight of c~lcillm carbonate, was added. The initial pH of the slurry with 0.5~/ONa2CO3/1%H3PO~/4% polyacrylic acid tre~tm-ont was measured and found ~ -to be 6.03, and, upon remea~u~cm~,ll 90 hours ageing, was found to be 6.80, as shown in Figure S. On the other hand, the initial pH of the slurry cont~inin~
0.5~/ONa2CO3/5%H3PO4 was measured and found to be 6.59, and after 90 hours ageing was f~und to be 7.43 Thç pH cl; rr"l~lce was thus Q.63 unit af er 90 hours a~eing, which is significantly ~ lL Also, the pH of c~lcilmn carbonate slurry treated with 0.5%Na2CO3/5% polyacrylic acid was 0.57 unit higher than that treated with 0.5%Na2CO3/1%H3PO~/4% polyacrylic acid after 90 hours ageing.
FXA~PT F. 6 Grollncl C~lcium Carbonate The initial pH of ground calcium carbonate was 8.01. Initially, 0.5% sodium c~l,on~le, based on the dry weight of calcium carbonate, was added into 20% solid slurry of ground calciurn c~l,onate. After blending, 4% phosphoric acid, 4%
polyacrylic acid or 3% phosphoric acid/1% polyacrylic acid, based on the dry weight of calcium carbonate, was added. The initial pH of the slurry con~ ~;, . i, .~
0.5%Na2CO3/3%H3PO4/1% polyacrylic acid was measured and found to be 5.24, and after 9S hours ageing was found to be 5.86, as shown gr~phic~lly in Figure 6. In P~ S ~6/1661C
IP~AJllS!~ O OCT 1997 comparison, the initial pH of the slurry with 0.5~/ONa2CO3/4%H3PO4 and 0.5~/ONa2CO3/4~/O polyacrylic acid was measured and found to be 6.31 and 6.47, and, after 9S hours ageing, was measured and found to be 7.17 and 7.40. The pH
diL~l~l,ce was thus 1.31 and 1.54 unit after 9S hours ageing, which is ~iFnifi~n~ly different.
FXA~rPT F 7 Grol-nti Calcillm Carbonate The initial pH of ground calcium carbonate was 8.01. Initially, 3% sodium carbonate, based on the dry weight of c~lcillm carbonate, was added into a 20% solids slurry of ground calcium c~l,ol~Le. After blen~iing~ 6% phosphoric acid or 5% phosphoric acid/1% polyacrylic acid, based on dry weight of calcium carbonate, was added. The initial pH of slurry with 3%Na2CO3/5%H3PO4/1% polyacrylic acid tre~tment was measured and found to be 6.25, and, when reme-S3ellred after 24 hours ageing wasfound to be 6.37 as shown graphically in Figure 7. On the other hand, the initial pH of the slurry 3%Na2CO3/6%H3PO4 LIC;~ L~I~ was measured and found to be 7.12, and, when r~m~llred after 24 hours ageing was found to be 7.89. The pH di~e.lce was thus 1.52 units after 24 hours ageing, which is significantly different.
Fx~Pr F 8 Grolm~l Calcium Carbonate The initial pH of ground calcium carbonate was 8.01. Initially, 1% sodiurn carbonate, based on the dry weight of calcium carbonate, was added into a 20% solids slurry of ground calcium call,onate. After blen~ling, 5% phosphoric acid or 1% phosphoric acid~4% polymaleic acid, based on the dry weight of calcium carbonate, was added.
eCTlJS 96/ 1661C
The initial pH ofthe slurry with 1%Na2CO3/1%H3PO4/4% polymaleic acid tre~tment was measured and found to be 6.08, and, when rçm~el-red 40 hours ageing was found to have a pH of 6.30 as shown graphically in Figure 8. In comparison, the initial pH
ofthe slurry co,,~ g 1%Na2CO3/5%H3PO~ was measured and found to be 6.87, and, when remeasured after 40 hours ageing was found to be 7.50. The pH di~erellce was thus 1.20 unit after 40 hours ageing, which is ci~nific~ntly different.
FXAMPT F g Com~p~ricoll with Prior Art Acid stabilized scalenohedral preci~ ed calciurn carbonate slurry can be obtained by the addition of sodium carbonate, followed by the addition of a mixture of weak acids 1 5 such as phosphoric acid and polyacrylic acid. Initially, 0.5% sodium call,oll~le, based on the dry weight of calcium carbonate, was added into 19.7% solids slurry of scalenohedral p~ e~1 calciurn c~l,o~L~. The pH of ul~ aled scalenohedral precirit~tecl calciurn carbonate slurry was 8.83. After mixin~, 6% phosrhoric acid/1%
polyacrylic acid, based on the dry weight of calcium carbonate, was added. A similar composition, based on the te~c hinpc of the U.S. Patent No. 51567i 9, was pLepaled using 0.5% sodiurn hrx~metaphosphate and 7% ph~sph~ric acid. The initial pH of the slurry co..li.i..;..g 0.5% sodium he~metaphosphate/7% phosphoric acid was 4.91, and was found to be 6.41 after 75 hours ageing, as shown graphically in Figure 9. Incomr~ricon, the initial pH of the slurry co~t ~ g 0.5% sodium carbonate/6%
phosphoric acid/1% polyacrylic acid was 5.15, and was found to be 6.17, after 75hours ageing. These results indicate that the compositions of the present invention are - superiortothoseofthepriorartU.S. PatentNo. 5156719.
'~OED ~#E~T
Claims (11)
1. An acid resistant calcium carbonate comprising a mixture of about 1 to about 6 percent, based on the dry weight of the calcium carbonate, of sodium carbonate together with at least about 0.1 percent, based on the dry weight of the calciumcarbonate, of a mixture of two or more weak acids, in admixture with the calciumcarbonate.
2. The acid resistant calcium carbonate of claim 1 wherein the weak acids are selected from the group consisting of polyacrylic acid, polymaleic acid and phosphoric acid.
3. The acid resistant calcium carbonate of claim 2 wherein the mixture of weak acids is comprised of polyacrylic acid and phosphoric acid.
4. The acid resistant calcium carbonate of claim 2 wherein the mixture of weak acids is comprised of polymaleic acid and phosphoric acid.
5. The acid resistant calcium carbonate of claim 1 wherein the mixture of weak acids is present in an amount of about 1 to about 8 percent, based on the dry weight of the calcium carbonate.
6. A process for the preparation of an acid resistant calcium carbonate which comprises:
a) forming a mixture of calcium carbonate with at least about 1 to about 6 percent, based on the dry weight of the calcium carbonate, of sodium carbonate;
b) adding at least about 0.1 percent, based on the dry weight of the calcium carbonate, of a mixture of two or more weak acids to the mixture; and c) blending the resultant mixture to ensure uniform mixing.
a) forming a mixture of calcium carbonate with at least about 1 to about 6 percent, based on the dry weight of the calcium carbonate, of sodium carbonate;
b) adding at least about 0.1 percent, based on the dry weight of the calcium carbonate, of a mixture of two or more weak acids to the mixture; and c) blending the resultant mixture to ensure uniform mixing.
7. The process according to claim 6 wherein the weak acids of the mixture are selected from the group consisting of polyacrylic acid, polymaleic acid and phosphoric acid.
8. The process according to claim 7 wherein the mixture of weak acids is comprised of polyacrylic acid and phosphoric acid.
9. The process according to claim 7 wherein the mixture of weak acids is comprised of polymaleic acid and phosphoric acid.
10. The process according to claim 7 wherein the sodium carbonate is present in an amount of about 1 to about 8 per cent, based on the dry weight of the calciumcarbonate.
11. A method of improving the optical properties of neutral to weakly acidic paper by the addition of an acid resistant calcium carbonate comprising a mixture of at least about 0.1 percent, based on the dry weight of the calcium carbonate of sodium carbonate together with at least about 0.1 percent, based on the dry weight of the calcium carbonate, of a mixture of two or more weak acids, in admixture with thecalcium carbonate.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/546,493 | 1995-10-20 | ||
| US08/546,493 US5647902A (en) | 1995-10-20 | 1995-10-20 | Stabilized calcium carbonate composition using sodium carbonate and mixtures of acids and uses therefor |
| PCT/US1996/016610 WO1997014651A1 (en) | 1995-10-20 | 1996-10-18 | Stabilized calcium carbonate composition using sodium carbonate and mixtures of acids and uses therefor |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2235151A1 true CA2235151A1 (en) | 1997-04-24 |
Family
ID=29405984
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2235151 Abandoned CA2235151A1 (en) | 1995-10-20 | 1996-10-18 | Stabilized calcium carbonate composition using sodium carbonate and mixtures of acids and uses therefor |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2235151A1 (en) |
-
1996
- 1996-10-18 CA CA 2235151 patent/CA2235151A1/en not_active Abandoned
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