POLYMER AND METHODS FOR MANUFACTURING IT

Abstract

The invention relates to a polymer having a main chain which is obtained by free radical emulsion polymerisation of a monomer mixture, which comprises at least one optionally substituted styrene, at least one C1-C4 alkyl (meth) acrylate and at least one ethylenically unsaturated monomer. The monomer mixture is polymerised in a reaction mixture comprising a natural and/or synthetic polymeric stabilator. According to the invention the polymer main chain further comprises a reaction product of silica sol and an unsaturated organosilicon compound. The invention relates also to methods of making such polymer.

Claims

1. A polymer having a main chain and being obtained by free radical emulsion polymerization of a monomer mixture comprising: at least one optionally substituted styrene; at least one C1-C4 alkyl (meth)acrylate; and at least one ethylenically unsaturated monomer; wherein the polymerization is conducted in a reaction mixture comprising a natural and/or synthetic polymeric stabilator, and wherein the main chain comprises a reaction product of silica sol and an unsaturated organosilicon compound.

2. The polymer according to claim 1, wherein the monomer mixture further comprises the reaction product of silica sol and an unsaturated organosilicon compound.

3. The polymer according to claim 1, wherein the polymer is obtained by a) polymerizing by free radical emulsion polymerisation polymerization the monomer mixture comprising: at least one optionally substituted styrene, at least one C1-C4 alkyl (meth)acrylate, at least one ethylenically unsaturated monomer, and at least one unsaturated organosilicon compound, in the reaction mixture comprising a natural and/or synthetic polymeric stabilator for obtaining an intermediate, and b) reacting the intermediate obtained in step a) with silica sol.

4. The polymer according to claim 1, wherein the unsaturated organosilicon compound is an alkenyl siloxane.

5. The polymer according to claim 4, wherein the alkenyl siloxane is selected from vinyl siloxane or 3-trimethoxysilylpropylmethacrylate.

6. The polymer according to claim 1, wherein the reaction product is obtained by reacting an alkenyl siloxane and tetraethoxysilane.

7. The polymer according to claim 1, wherein the main chain comprises 0.3-6 weight-%, preferably 0.5-5 weight-%, of the unsaturated organosilicon compound.

8. The polymer according to claim 1, wherein the monomer mixture comprises 10-40 weight-%, preferably 20-35 weight-%, of at least one optionally substituted styrene, 10-20 weight-%, preferably 12-18 weight-%, of at least one C1-C4 alkyl (meth)acrylate, and 10-30 weight-%, preferably 15-25 weight-%, of at least one ethylenically unsaturated monomer.

9. The polymer according to claim 1, wherein the ethylenically unsaturated monomer is selected from the group consisting of ethylhexyl acrylate, stearyl acrylate, stearyl methacrylate, esters of acrylic and methacrylic acid with alcohols having more than four C atoms, acrylonitrile, methacrylonitrile, acrylamide, vinyl acetate, and anionic comonomers, such as acrylic acid, methacrylic acid, styrene sulphonic acid.

10. The polymer according claim 1, wherein the natural polymeric stabilator is a polysaccharide stabilator, such as degraded starch or dextrin.

11. The polymer according to claim 1, wherein the synthetic polymeric stabilator is a synthetic polymer, such as polyvinyl alcohol.

12. The polymer according to claim 1, wherein the polymer is in form of a dispersion, where the polymer particles have D(50) value <110 nm, preferably <100 nm, more preferably <80 nm, and/or D(90) value <200 nm, preferably <170 nm, more preferably <150 nm.

13. The polymer according to claim 12, wherein the solids content of the polymer dispersion is >25 weight-%, more typically >30%, based on the weight of the total dispersion.

14. (canceled)

15. A method to prepare a dispersion of the polymer of claim 1, which method comprises a) allowing silica sol and an unsaturated organosilicon compound to react with each other and to form a reaction product, b) polymerizing by free radical emulsion polymerization in a solution of a natural and/or synthetic polymeric stabilator a mixture comprising at least one optionally substituted styrene, at least one C1-C4 alkyl (meth)acrylate, at least one ethylenically unsaturated monomer, and the reaction product obtained in step a).

16. The method according to claim 15, wherein the silica sol and the unsaturated organosilicon compound are reacted with each other in a temperature range of 50-70° C., preferably 55-65° C.

17. The method according to claim 15, wherein the silica sol and the unsaturated organosilicon compound are reacted with each other in pH in the range of 3.5-5.5, preferably 4-5.

18. A method to prepare a polymer according to claim 1, which method comprises a) producing an intermediate dispersion by polymerizing by free radical emulsion polymerization in a solution of a natural and/or synthetic polymeric stabilator a mixture comprising at least one optionally substituted styrene, at least one C1-C4 alkyl (meth)acrylate, at least one ethylenically unsaturated monomer, and at least one unsaturated organosilicon compound, and b) allowing the intermediate dispersion produced in step a) to react with silica sol.

19. The method according to claim 18, wherein the intermediate dispersion and silica sol are reacted with each other in a temperature range of 65-95° C., preferably 70-90° C.

20. The method according to claim 18, wherein the intermediate dispersion and silica sol are reacted with each other in pH in the range of 3.5-5.5, preferably 4-5.

21. The method according to claim 18, wherein the ratio intermediate dispersion:silica sol is 25:1-3:1, preferably 18:1-5:1, calculated from total dry monomers and silica sol.

Description

EXPERIMENTAL

Preparation of the Polymer

[0043] Polymer used in the experiments was prepared as follows:

[0044] 82.98 g starch and an amount of water were added into a reactor under stirring, heated up to 80° C., and kept in this temperature for 30 min. After this 0.53 g ferrous sulphate and 15.89 g silica sol were added, and the reaction mixture was heated up to 85° C. A mixture comprising 99.57 g styrene, 49.79 g butyl acrylate, 49.79 g tert-butyl acrylate and 5.30 g 3-trimethoxysilyl-propyl-methacrylate was formed and added to the reaction mixture simultaneously with a mixture of 25.25 g hydrogen peroxide and water. The addition was completed in 4 hours. After the addition was completed the reaction mixture was kept at 85° C. under stirring for 1 h, whereafter it was cooled down to room temperature.

[0045] The total amount of water in the reaction mixture was 670.89 g.

Preparation of Surface Size Solution Comprising a Polymer

[0046] 80 g oxidatively degraded tapioca starch and 920 g water were added into a glass beaker under stirring and heated up to 95° C. When the temperature reached 95° C., the starch mixture was kept in this temperature 30 min, and then cooled down to 70° C. For obtaining the used surface size solution, 6.0 g of the polymer solution prepared above was added into warm (70° C.) starch solution, under effective stirring.

Sizing Experiments

[0047] Sizing experiments were generally performed as follows:

[0048] 200 g of a surface size solution was weighed and poured it in the middle of two rolls of size press. The size press was opened, the rollers started to rotate, a paper was put in the middle of the two rollers, so that the surface size solution evenly coated the surface of the paper. Pick-up was 2.2 g/m.sup.2 (two sides). The paper was removed and dried by using a heating plate. The sized paper was liner paper, weight 180 g/m.sup.2.

[0049] Three surface size solutions were prepared:

[0050] Ref 1 (reference): surface size solution comprising a commercial

[0051] Ref 2 (reference): starch solution comprising 7.1% of starch LS-2

[0052] Solution 1: surface size solution comprising polymer according to the invention, prepared as described above.

[0053] The results of the sizing experiments are shown in Tables 1 and 2.

TABLE-US-00001 TABLE 1 Cobb120 (g/m.sup.2) results obtained in sizing experiments. Size dosage, kg/t 0.5 1 1.5 Ref 1 45 39 26 Solution 1 67.6 39 31

[0054] Cobb120 values describe the water absorbance of the paper. The higher the value, the more water the paper absorbs. It is seen from Table 1 that the surface size solution comprising the polymer according to the invention provides weaker resistance for water absorption at lower size dosage than a commercial reference. At higher dosages the results are similar with the results obtained with a commercial reference.

TABLE-US-00002 TABLE 2 Ring Crush (Nm/g) results obtained in sizing experiments. Ring crush (Nm/g) Dosage Ref 2 Ref 1 Solution 1 (kg/t) L-CRT T-CRT L-CRT T-CRT L-CRT T-CRT 2 9.0 7.0 8.93 7.86 10.36 8.14 4 10.36 8.14 10.21 8.0 6 10.5 7.5 10.5 7.71 L-CRT = Longitudinal ring crush strength T-CRT = Transverse ring crush strength

[0055] Ring crush test gives a measure of the edgewise compression of paper. In the test a short cylinder is inserted into an annular groove and axially loaded to failure. It is seen from the results in Table 2 that the surface size solution comprising the polymer according to the invention provides better results as starch alone, and as good or better results than the commercial reference. Especially at low dosage the results show unexpected improvement.

[0056] 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.