Composition for modifying rheology of coating color, its use and a coating color

Abstract

The invention relates to a composition for modifying rheology of coating colour and its use. The composition comprises an aqueous polymer dispersion, comprising a copolymer of monomer (a), which is at least one optionally substituted styrene, and monomer (b), which is at least one C1-C4-alkyl (meth)acrylate. The copolymer has a particle size D50<100 nm. Composition comprises also degraded starch having an average molecular weight Mn<1000 g/mol.

Claims

1. A coating color for coating of paper or board, the coating color comprising inorganic mineral particles and a composition for modifying rheology of the coating color, wherein the composition is a mixture of an aqueous polymer dispersion and an aqueous solution of degraded starch, the composition comprising: 30-99 weight-% of the aqueous polymer dispersion, calculated from a total dry solids content of the composition, the polymer dispersion comprising a copolymer of: 0.1-75 weight-% of a monomer (a), which is at least one optionally substituted styrene, and 25-99.9 weight-% of a monomer (b), which is at least one C1-C4-alkyl (meth)acrylate, wherein the weight-% is calculated from a total dry solids content of the monomers (a) and (b), and wherein the copolymer has a particle size D50<100 nm; and 1-70 weight-% of the degraded starch having an average molecular weight Mn<1000 g/mol, calculated from the total dry solids content of the composition.

2. The coating color according to claim 1, wherein the amount of the degraded starch in the composition is in a range of 3-60 weight-%, calculated from the total dry solids content of the composition.

3. The coating color according to claim 1, wherein the amount of the polymer dispersion in the composition is in a range of 40-97 weight-%, calculated from the total dry solids content of the composition.

4. The coating color according to claim 1, wherein the degraded starch has an average molecular weight Mn<800 g/mol.

5. The coating color according to claim 1, wherein the degraded starch has an average molecular weight Mn in a range of 50-990 g/mol.

6. The coating color according to claim 1, wherein the degraded starch is non-ionic or the degraded starch has a net anionic charge.

7. The coating color according to claim 6, wherein the degraded starch is degraded anionic potato or degraded tapioca starch.

8. The coating color according to claim 1, wherein the monomer (a) is selected from a group comprising styrene, substituted styrenes, and any mixtures thereof.

9. The coating color according to claim 1, wherein the monomer (b) is selected from butyl (meth)acrylates.

10. The coating color according to claim 1, wherein the copolymer is obtained by copolymerization of the monomers (a) and (b), as well as at least one monomer (c), which is ethylenically unsaturated and different from the monomers (a) and (b).

11. The coating color according to claim 10, wherein the monomer (c) is selected from a group consisting of ethylhexyl acrylate; stearyl acrylate; stearyl methacrylate; esters of acrylic and methacrylic acid with alcohols which have more than four C atoms; acrylonitrile; methacrylonitrile; acrylamide; vinyl acetate; and anionic co-monomers selected from acrylic acid, methacrylic acid, itaconic acid, maleic acid and styrene sulphonic acid.

12. The coating color according to claim 1, wherein the copolymer has a particle size D50<85 nm.

13. The coating color according to claim 1, wherein the polymer dispersion comprising the copolymer is obtained by free radical emulsion polymerization of at least the monomers (a) and (b) in the presence of a polysaccharide.

14. The coating color according to claim 13, wherein the polysaccharide is starch or dextrin.

15. The coating color according to claim 14, wherein the polysaccharide is degraded starch which has an average molecular weight in a range of 100-990 g/mol.

16. The coating color according to claim 1, wherein the inorganic mineral particles are selected from a group consisting of calcium carbonate, kaolin, calcinated kaolin, talc, titanium dioxide, gypsum, chalk, satine white, barium sulphate, sodium aluminum silicate, aluminum hydroxide and any of their mixtures.

17. The coating color according to claim 2, wherein the amount of the degraded starch in the composition is in a range of 5-50 weight-%, calculated from the total dry solids content of the composition.

18. The coating color according to claim 8, wherein the monomer (a) is selected from a group comprising styrene, -methylstyrene or vinyltoluene, and any mixtures thereof.

19. The coating color according to claim 15, wherein the polysaccharide is degraded starch which has an average molecular weight in a range of 100-790 g/mol.

20. The coating color according to claim 15, wherein the polysaccharide is degraded starch which has an average molecular weight in a range of 100-490 g/mol.

Description

EXAMPLE 1

Preparation of Composition

(1) 70.4 g of an oxidatively degraded potato starch (Perfectamyl A 4692) was dispersed with stirring in 266 g of demineralizer water in a 1 l glass reactor with a cooling/heating jacket under a nitrogen atmosphere. The starch was dissolved by heating the mixture to 95 C. during 60 minutes. After the dissolution of starch, pH was adjusted to 2 with sulphuric acid. After 5 min mixing, 2.17 g of 1.0% strength aqueous solution of ferrous(II)sulphate heptahydrate was added in to the reactor. After 5 minutes 3.47 g of 30% strength hydrogen peroxide was added. After 30 minutes, the starch degradation was complete. The chemical feeds were started.

(2) Monomers were fed as a mixture: 210.8 g of mixture of n-butyl acrylate and styrene (1:1 weight) was fed during 200 minutes. 41.0 g of 4.5% solution of hydrogen peroxide was fed simultaneously with the monomer feeds during 205 min. The reactor temperature was kept at 95 C. during the feeds and 15 minutes after for postpolymerization. Then the mixture was cooled to 60 C. and 0.57 g of 70% strength tert-butyl hydroperoxide solution was added into the reactor. The temperature was kept at 60 C. for further 60 min. Thereafter, cooling was effected to 40 C. and 2.2 g of 10% strength ethylenediaminetetraacetic acid sodium salt (EDTA-Na) solution was added, followed by pH adjustment to 6.2 with 50% strength sodium hydroxide solution and cooling to room temperature. Filtration was performed using a 100 m filter cloth. A finely divided dispersion with a solid content of 45.6%, particle size 66 nm, viscosity 148 mPas, was obtained.

(3) In a separate 1 l glass reactor with a cooling/heating jacket under a nitrogen atmosphere 148.3 g of an oxidatively degraded potato starch (Perfectamyl A 4692) was dispersed with stirring in 276 g of demineralizer water. The starch was dissolved by heating the mixture to 95 C. during 60 minutes. After the dissolution of starch, pH was adjusted to 2 with sulphuric acid. After 5 min mixing, 1.52 g of 1.0% strength aqueous solution of ferrous (II) sulphate heptahydrate was added in to the reactor. After 5 minutes 7.27 g of 30% strength hydrogen peroxide was added. After 120 minutes, the starch degradation was complete, and it was cooled to room temperature. A starch solution with a solid content of 28.1% was obtained. The solution of degraded starch was mixed with the polymer dispersion in the ratio 10:90 weight-%.

Example 2

Preparation of Coating Color and Experiments

(4) The following procedure is used for coating color make down for coating color 1:

(5) 100 parts of ground calcium carbonate (GCC), 75%, particle size <2 m, and 4.5 parts styrene-butadiene latex is mixed together. 7 parts of cooked native starch, at solids content 28 weight-% is added to the mixture of GCC and latex. Water is added in order to obtain a coating color with target solids content of 60 weight-%. pH of the coating color is adjusted to pH 9.2 by using 10% sodium hydroxide. The coating color batch size is 500 g of dry inorganic mineral pigment.

(6) Low shear viscosity is measured from the prepared coating color with Brookfield viscometer, type DV-II with speed 100 rpm using spindle 3. High shear viscosity is measured using Hercules Hi-Shear DV-10 rational viscometer. Static water retention is measured with bo Akademi Gravimetric Water Retention device.

(7) Coating color 2 is prepared in similar manner as coating color 1, but 4.5 parts of styrene butadiene latex is replaced with 4.5 parts of polymer dispersion and 0.5 parts of degraded starch is added after native starch. Polymer dispersion corresponds to that prepared in Example 1 and degraded starch corresponds to that prepared in Example 1.

(8) Coating color 3 is prepared in similar manner as coating color 1, but 0.5 parts of degraded starch is added after native starch. Used degraded starch corresponds to that prepared in Example 1.

(9) Coating color compositions are given in Table 1 and the obtained measurement results in Table 2.

(10) TABLE-US-00001 TABLE 1 Coating color compositions used in Example 1. Coating color 1 Coating color 2 Coating color 3 GCC 100 100 100 Styrene 4.5 4.5 Butadiene Latex Polymer 4.5 dispersion Native 7 7 7 starch Degraded 0.5 0.5 starch

(11) TABLE-US-00002 TABLE 2 Measurement results for coating colors studied in Example 1. Property Coating color 1 Coating color 2 Coating color 3 pH 9.2 9.2 9.2 Solids Content 60 60 60 [weight-%] Temperature 23.1 23.1 23.1 [ C.] Low Shear 304 290 290 Viscosity [mPas] High Shear 37 36 36 Viscosity [mPas] Water 68 28 71 Retention [g/m.sup.3]

(12) From Table 2 it can be seen that when strongly degraded starch is added to the coating composition, the static water retention of the coating color has improved without increase in coating color high shear viscosity.

(13) 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.