Aqueous pigment dispersion

Abstract

The present invention relates to a stable aqueous pigment dispersion including: an aqueous medium, pigment particles, and from 0.1% to 15%, by weight based on the weight of pigment, of a certain first water-soluble polymer; and 2) a certain second water-soluble polymer; wherein the dispersant comprises a proportion of the first polymer to the second polymer of from 0.1:1 to 10:1 on a solids basis, and the first polymer and the second polymer are miscible in those proportions; and wherein the dispersant is substantially free of structural units of phosphorus acid monomers and their salts. The invention also relates to a method for forming the stable aqueous dispersion and a dry coating formed from the aqueous dispersion. The stable aqueous dispersion is useful, inter alia, for forming certain composite particles.

Claims

1. A stable aqueous pigment dispersion comprising: a pigment particle and a dispersant comprising: (1) a first water-soluble polymer having an acid number of from 0 to 80 and a calculated Mn of from 450 Daltons to 10,000 Daltons; and 2) a second water-soluble polymer comprising, as copolymerized units, from 30% to 100% by weight, based on the weight of said second polymer, sulfonic acid monomer, or a salt thereof; and from 0% to 10% by weight, based on the weight of said second polymer, carboxylic acid monomer, or a salt thereof; wherein said second polymer has a calculated Mn of from 1000 to 25,000 Daltons; wherein said dispersant comprises a proportion of said first polymer to said second polymer of from 0.1:1 to 10:1 on a solids basis, and said first polymer and said second polymer are miscible in said proportions; and wherein said dispersant is substantially free of structural units of phosphorus acid monomers and salts thereof.

2. The stable aqueous dispersion of claim 1 wherein said pigment particle is an inorganic pigment particle comprising TiO.sub.2, said pigment particle having an average particle diameter of from 0.05 microns to 10 microns.

3. The stable aqueous dispersion of claim 1 wherein the acid number of said first water-soluble polymer is from 0 to 40.

4. The stable aqueous dispersion of claim 1 wherein said pigment particle has disposed thereon a plurality of water-insoluble polymer particles in an amount of from 2% to 50% by weight, based on the weight of the resultant composite particles.

5. A method comprising: dispersing a pigment particle in an aqueous medium in the presence of from 0.1% to 15%, by weight based on the weight of pigment, of a dispersant comprising: (1) a first water-soluble polymer having an acid number of from 0 to 80 and a calculated Mn of from 450 Daltons to 10,000 Daltons; and 2) a second water-soluble polymer comprising, as copolymerized units, from 30% to 100% by weight, based on the weight of said second polymer sulfonic acid monomer, or a salt thereof and from 0% to 10% by weight, based on the weight of said second polymer, carboxylic acid monomer, or a salt thereof; wherein said second polymer has a calculated Mn of from 1000 to 25,000 Daltons; wherein said dispersant comprises a proportion of said first polymer to said second polymer of from 0.1:1 to 10:1 on a solids basis, and said first polymer and said second polymer are miscible in said proportions; wherein said dispersant is substantially free of structural units of phosphorus acid monomers and salts thereof.

6. The method of claim 5 further comprising: contacting said dispersed pigment particle with an aqueous dispersion of water-insoluble polymer particles in an amount of from 2% to 300% by weight, based on the weight of the resultant composite particles.

7. The method of claim 6 wherein said contacting is conducted for a period of less than 60 minutes at a temperature of from 5 C. to 50 C.

8. The method of claim 5 wherein the acid number of said first water-soluble polymer is from 0 to 40.

9. The method of claim 6 wherein the acid number of said first water-soluble polymer is from 0 to 40.

10. A dry coating formed by the method comprising: a) forming an aqueous coating composition comprising the stable aqueous dispersion of claim 1 or claim 2 or claim 3 or claim 4; b) applying said aqueous coating composition to a substrate; and c) drying, or allowing to dry, said aqueous coating composition.

Description

EXAMPLE 1 AND COMPARATIVE EXAMPLES A-C

(1) Samples of DuPont TiPure R-706 TiO.sub.2 slurry at 75.0%w/w were prepared using the following dispersants.

Example 1

(2) Dispersant a: second polymer, AMPS/HPA/AA copolymer (Dispersant b)+12% w/w with first polymer, MPEG 550 (calculated Mn=550) 28% w/w (total solids 40% w/w). The first polymer and the second polymer were miscible together in all proportions; they formed a clear solution with no phase separation or sediment after 6 months at 25 C.

Comparative Example A

(3) Dispersant b: AMPS/HPA/AA copolymer; less than 10 wt % copolymerized carboxylic acid monomer; from 30 wt % to 100 wt % copolymerized sulfonic acid monomer; Acid No. =193 mg KOH/g polymer.

Comparative Example B

(4) Dispersant c: copolymer of AMPS/Dibutylamino-polyethyleneoxide(4)-methacrylate

Comparative Example C

(5) Dispersant d: copolymer of AMPS/Dibutylamino-polyethyleneoxide(4)-methacrylate (Mw=480) of the same mole ratios as Dispersant b, replacing HPA with PEGMA.

(6) TABLE-US-00001 TABLE 1.1 Pigment Dispersion Compositions Ex. 1 Comp. A Comp. B Comp. C Material Name grams grams grams grams Water 16.86 17.86 15.86 17.86 Dispersant a 2.53 Dispersant b 0.75 Dispersant c 1.07 Dispersant d 1.07 AMP-95 0.20 0.20 0.20 0.20 Ti-Pure R-706 75.00 75.00 75.00 75.00 Water 5.41 6.19 7.87 5.87 Totals 100.00 100.00 100.00 100.00
The pigment was dispersed with SpeedMixer (FlackTek Inc.) DAC 150 FVZ at 2,200 rpm for 4 minutes. The samples were equilibrated to 25 C. overnight and viscosity measured on a Brookfield viscometer at selected rpm.

(7) The aqueous dispersions were stable according to the test method herein. Further, the dispersions of Example 1 and Comparative Example A were stable to greater than 6 months at 25 C.

(8) TABLE-US-00002 TABLE 1.2 Determination of Thixotropic Index Sample 4/6* 4/12* 4/60* T.I. Ex. 1 8900 4750 1140 7.8 Comp. A 7200 3050 780 9.2 Comp. B 10100 4900 1220 8.3 Comp. C 25300 13100 3030 8.3 *Brookfield DV II spindle # and rpm. Measurements shown in cP T.I is the thixotropic index, the ratio of cP at 6 divided by the cP at 60 rpm. Repeated batches and repeated measurements found that the error is +/0.1

(9) Composite formation by contacting the dispersed pigment particles with an aqueous dispersion of water-insoluble polymer particles in an amount of from 5% to 300% by weight, based on the weight of the composite particles provided a viscosity increase in the composite premix and the hiding via S/mil of the coatings were equivalent within experimental error.

(10) Example 1 of the invention provides a desirably lower thixotropic index relative to that of Comparative Examples A-C

EXAMPLE 2 and COMPARATIVE EXAMPLE D

(11) TiPure R-706 TiO.sub.2 was dispersed at 73 wt % pigment with either Dispersant a (Example 2) or with Dispersant b (Comparative Example D), as identified in Example 1 above, and contacted with three different aqueous dispersions of water-insoluble polymer particles at PVC=40. The low shear (Brookfield) viscosity (Spindle 4, 6 rpm) was measured at each time point. In addition, aliquots of each premix were diluted and centrifuged to determine the amount of latex adsorbed to TiO.sub.2 according to the Adsorption Centrifugation Test Method for Degree of Composite Formation test method provided herein.

(12) TABLE-US-00003 TABLE 2.1 degree of composite formation BF Viscosity Composite (cP) Free Latex Formation Time (min) Disp. b Disp. a Disp. b Disp. a Disp. b Disp. a PRIMAL 10 310 246 75.88% 81.10% 25.15% 19.71% AC-6501 45 826 692 63.17% 69.38% 38.39% 31.92% 240 4210 3600 51.62% 53.72% 50.44% 48.25% 1440 10000 10000 40.06% 41.79% 62.49% 60.68% RHOPLEX 10 404 350 90.47% 93.08% 6.37% 4.63% SG-30 45 640 576 86.36% 90.63% 9.12% 6.26% 240 1020 1220 79.94% 81.27% 13.41% 12.52% 1440 1310 1210 69.66% 64.88% 20.28% 23.48% RHOPLEX 10 850 818 87.08% 88.13% 14.49% 13.31% VSR-50 45 1460 1140 84.30% 85.76% 17.60% 15.96% 240 3430 2320 79.95% 81.83% 22.47% 20.37% 1440 3860 2020 70.33% 72.86% 33.26% 30.42% PRIMAL and RHOPLEX are trademarks of the The Dow Chemical Company
Example 2 of the invention provides a substantially equivalent degree of composite formation relative to that of Comparative Example D.