Method for improving rheological properties of an aqueous pigment slurry and a dispersion agent

Abstract

The invention relates to a method for improving rheological properties of an aqueous pigment slurry. In the method dispersion agent is added to an aqueous phase of a slurry comprising pigment particles or to the aqueous phase into which the pigment particles are to be added. The dispersion agent comprises styrene acrylate copolymer. The invention also relates to a dispersion agent for a pigment slurry comprising a first component comprising styrene acrylate copolymer and a second component comprising a conventional dispersion agent, such as a straight-chain polyacrylate.

Claims

1. A method for improving .Iadd.the .Iaddend.rheological high shear properties of an aqueous pigment slurry comprising calcium carbonate, kaolin, calcinated kaolin, talc, titanium dioxide, gypsum, chalk, satine white, barium sulphate, sodium aluminium silicate, aluminium hydroxide or any of their mixture, the aqueous pigment slurry having a solids content .Iadd.of .Iaddend.about 68%, the method comprising adding a dispersion agent to an aqueous phase of a slurry comprising pigment particles or to the aqueous phase into which the pigment particles are to be added, the dispersion agent comprising styrene acrylate copolymer, wherein the styrene acrylate copolymer comprises starch, wherein the dispersion agent improves the rheological properties of the slurry, and wherein the dispersion agent decreases the high shear viscosity of the slurry, and further comprising adding also a conventional dispersion agent comprising straight-chain polyacrylate to the aqueous phase.

2. The method according to claim 1, comprising adding at least 0.1 parts dispersion agent comprising styrene acrylate copolymer per 100 parts pigment in the slurry.

3. The method according to claim 1, wherein the dispersion agent comprising the styrene acrylate copolymer is used in the form of an aqueous polymer dispersion having a solids content of 10-50%.

4. The method according to claim 1, wherein the proportion .[.first component: second component.]. .Iadd.of the dispersion agent:the conventional dispersion agent .Iaddend.is in the range .Iadd.of .Iaddend.50:50-99:1.

5. A dispersion agent for a pigment slurry, where the pigment slurry comprises calcium carbonate, kaolin, calcinated kaolin, talc, titanium dioxide, gypsum, chalk, satine white, barium sulphate, sodium aluminium silicate, aluminium hydroxide or any of their mixture, comprising a first component comprising styrene acrylate copolymer wherein the styrene acrylate copolymer decreases the high shear viscosity of the slurry, wherein the styrene acrylate copolymer comprises starch, the aqueous pigment slurry having a solids content of about 68%, a second component comprising .Iadd.a .Iaddend.conventional dispersion agent comprising straight-chain polyacrylate.

6. The dispersion agent according to claim 5, wherein the proportion .Iadd.of .Iaddend.first component:second component is in the range .Iadd.of .Iaddend.50:50-99:1.

7. The dispersion agent according to claim 5, wherein the mean particle size of the styrene acrylate copolymer is 20-300 nm.

Description

EXAMPLE

(1) 100 parts of dried undispersed PCC (precipitated calcium carbonate, 95%<1 m) is added into water with 0.55 pph (parts per 100) conventional Na-polyacrylate dispersant, Colloid 220 (trademark) by Kemira, to the solid content of the slurry 68%. The pH is adjusted to the value 9.9 or 9.5 (sample 4) using 10% sodium hydroxide. The slurry is mixed 10 minutes at ambient temperature in Diaf-mixer at 3000 rpm, after which 1 pph of dispersion agent according to the present invention is added for formulations 2 to 4. The mixing of the slurry is continued for further 5 minutes. From the prepared slurries viscosities are measured using Brookfield viscometer, type DV-II, with speeds 100 and 50 rpm and using spindle 3. The sample size was 500 g of dry pigment, solid content of the slurry ca 68%. High shear viscosity at shear blocking is measured using Hercules Hi-Shear DV-10 rotational viscometer. The test procedure of evaluating the viscosity of slurry pigments is as outlined by TAPPI (Technical Association of the Pulp and Paper Industry) test method T-648 (valid in September 2008). Results are shown in table 1.

(2) Dispersion agent in the samples is as follows:

(3) Reference: pigment slurry with 0.55 pph Na-polyacrylate

(4) Sample 2: pigment slurry with 0.55 pph Na-polyacrylate+1 pph styrene acrylate copolymer

(5) Sample 3: pigment slurry with 0.55 pph Na-polyacrylate+1 pph 90/10 styrene acrylate copolymer/Na-polyacrylate

(6) Sample 4: pigment slurry with 0.55 pph Na-polyacrylate+1 pph Na-polyacrylate

(7) In other words, samples 2 and 3 are according to the present invention, in reference sample and sample 4 employ conventional dispersion agent in different amounts.

(8) TABLE-US-00001 TABLE 1 Results of viscosity measurements Sample Measured Property Unit Reference Sample 2 Sample 3 4 Viscosity, mPas 115 103 124 131 Brookfield 100 rpm Viscosity, mPas 132 141 164 173 Brookfield 50 rpm High shear viscosity mPas 95 85 63 101 at shear blocking Solids content % 68.2 68.1 68.1 68.3 pH 9.9 9.9 9.9 9.5 Temperature C. 24 24 24 24 Density g/cm.sup.3 1.84 1.84 1.84 1.84

(9) From the results it can be seen that when a dispersion agent according to the present invention comprising styrene acrylate copolymer is used, the high shear viscosity at shear blocking decreases compared to slurries with conventional Na-polyacrylate dispersant.

(10) Even if the invention was described with reference to what at present seems to be the most practical and preferred embodiments, it is appreciated that the invention shall not be limited to the embodiments described above, but the invention is intended to cover also different modifications and equivalent technical solutions within the scope of the enclosed claims.