Aqueous polymer dispersion for paper with a copolymer of vinyl acetate and an acrylate monomer prepared in the presence of a starch derivative

Abstract

The invention relates to an aqueous dispersion of a polymer P, which comprises the emulsion polymerization of vinyl acetate, an acrylate monomer, which is a C.sub.1-C.sub.10 alkyl acrylate or a C.sub.1-C.sub.10 methacrylate, an ,-ethylenically unsaturated C.sub.3-C.sub.8 carboxylic acid and at least one out of glycidyl methacrylate, glycidyl acrylate, allyl methacrylate and allyl acrylate, in the presence of a starch derivative. Optionally, an additional monomer is an ethylenically unsaturated sulfonic acid, an ethylenically unsaturated other monomer or both of them. The aqueous polymer dispersion and a powder form thereof are useful for a paper coating slip containing one of the aforementioned forms. A paper or a cardboard, which is coated with the paper coating slip, shows surface strength, which is expressed by a good dry pick resistance, a good wet pick resistance or good offset test results. The aqueous polymer dispersion or the powder form thereof is furthermore useful as a binder.

Claims

1. A paper coating slip, comprising: an inorganic pigment, and an aqueous dispersion comprising a polymer P, which is obtained by a process comprising: emulsifying a mixture comprising monomers in an aqueous medium, and polymerizing the monomers in the presence of a free-radical initiator and a starch derivative, wherein the monomer mixture consists of: vinyl acetate, as a monomer (a), at least one acrylate monomer, which is selected from the group consisting of a C.sub.1-C.sub.10 alkyl acrylate and a C.sub.1-C.sub.10 alkyl methacrylate, as a monomer (b), at least one a,-ethylenically unsaturated C.sub.3-C.sub.6 carboxylic acid, as a monomer (c), at least one monomer selected from the group consisting of glycidyl methacrylate and glycidyl acrylate, as a monomer (d), optionally at least one ethylenically unsaturated sulfonic acid, as a monomer (e), and optionally at least one ethylenically unsaturated other monomer, which is different from the monomers (a), (b), (c), (d) and (e), as a monomer (f), and wherein the content of the vinyl acetate monomer (a) is from 70 to 94.7 parts by weight of the monomers, the content of the at least one acrylate monomer (b) is from 5 to 25 parts by weight of the monomers, the content of the at least one a,-ethylenically unsaturated C.sub.3-C.sub.6 carboxylic acid monomer (c) is from 0.1 to 10 parts by weight of the monomers, the content of the at least one monomer (d) selected from the group consisting of glycidyl methacrylate and glycidyl acrylate from 0.1 to 10 parts by weight of the monomers, the optional content of the at least one ethylenically unsaturated sulfonic acid monomer (e) is from 0.1 to 5 parts by weight of the monomers, the optional content of the at least one other ethylenically unsaturated monomer (f) is from 0.1 to 15 parts by weight of the monomers, and the sum total of the parts by weight of the monomers (a), (b), (c), (d), (e) and (l) is 100.

2. The paper coating slip according to claim 1, wherein the content of the vinyl acetate is from 70 to 85 parts by weight of the monomers.

3. The paper coating slip according to claim 1, wherein the content of the starch derivative is from 10 to 65 parts by weight of the sum total of the parts by weight of the monomers (a), (b), (c), (d), (e) and (f).

4. The paper coating slip according to claim 1, wherein the starch derivative is a degraded starch having an intrinsic viscosity i of less than 0.07 dl/g.

5. The paper coating slip according to claim 1, wherein the at least one acrylate monomer (b) is selected from the group consisting of n-butyl acrylate and ethylhexyl acrylate, and the at least one a,-ethylenically unsaturated C.sub.3-C.sub.6 carboxylic acid monomer (c) is selected from the group consisting of acrylic acid, methacrylic acid, crotonic acid, fumaric acid, maleic acid, maleic acid anhydride, 2-methyl maleic acid, 2-methyl maleic acid anhydride and itaconic acid.

6. The paper coating slip according to claim 1, wherein the at least one ethylenically unsaturated sulfonic acid monomer (e) is present and is selected from the group consisting of vinyl sulfonic acid and 2-acrylamido-2-methylpropane sulfonic acid.

7. The paper coating slip according to claim 1, wherein the at least one acrylate monomer (b) is n-butyl acrylate the at least one a,-ethylenically unsaturated C.sub.3-C.sub.6 carboxylic acid monomer (c) is selected from the group consisting of acrylic acid and methacrylic acid, and the at least one ethylenically unsaturated sulfonic acid monomer (e) is present and is vinyl sulfonic acid.

8. The paper coating slip according to claim 1, wherein the content of the vinyl acetate monomer (a) is from 75 to 85 parts by weight of the monomers, the content of the at least one acrylate monomer (b) is from 7 to 19 parts by weight of the monomers, the content of the at least one a,-ethylenically unsaturated C.sub.3-C.sub.6 carboxylic acid monomer (c) is from 0.5 to 5 parts by weight of the monomers, the content of at least one monomer (d) selected from the group consisting of glycidyl methacrylate and glycidyl acrylate is from 0.5 to 8 parts by weight of the monomers, the optional content of the at least one ethylenically unsaturated sulfonic acid monomer (e) is from 0.1 to 2 parts by weigh of the monomers, the optional content of the at least one other ethylenically unsaturated monomer (f) is from 0.1 to 10 parts by weight of the monomers, and the sum total of the parts by weight of the monomers (a), (b), (c), (d), (e) and (f) is 100.

9. The paper coating slip according to claim 1, wherein the at least one ethylenically unsaturated monomer, which is different from the monomers (a), (b), (c), (d) and (e) is present and is selected from the group consisting of an alkene, a cycloalkane, a conjugated aliphatic C.sub.4-C.sub.9 diene, an ester of vinyl alcohol and a C.sub.2-C.sub.15 monocarboxylic acid, a C.sub.5-C.sub.10 cycloalkyl acrylate, a C.sub.5-C.sub.10 cycloalkyl methacrylate, di(C.sub.1-C.sub.10 alkyl) maleinate, di(C.sub.1-C.sub.10 alkyl) fumarate, a vinylaromatic compound, an ethylenically unsaturated C.sub.3-C.sub.8-monocarbonitrile, an ethylenically unsaturated C.sub.4-C.sub.8-dicarbonitrile, an ethylenically unsaturated C.sub.3-C.sub.8 monocarboxamide, an ethylenically unsaturated C.sub.4-C.sub.8 dicarboxamide, ureido methacrylate or ureido acrylate.

10. The paper coating slip according to claim 1, wherein a polymer seed is present during the polymerizing of the monomers in the presence of a free-radical initiator and a starch derivative.

11. A process for coating a paper or a cardboard, comprising: preparing a paper coating slip according to claim 1, from an inorganic pigment and optionally from an auxiliary ingredient, applying the prepared coating slip to at least one surface of the paper or the cardboard, and drying the at least one surface of the paper or the cardboard.

12. A paper or a cardboard, which is obtained by the process according to claim 11.

13. The paper coating slip according to claim 1, wherein the monomer d is glycidyl acrylate.

14. The paper coating slip according to claim 1, wherein the monomer d is glycidyl methacrylate.

15. The paper coating slip according to claim 1, further comprising: an auxiliary ingredient, which is different from the polymer P and which is selected from the group consisting of a thickener, a further polymeric binder, an optical brightener, a flow control agent, a further dispersant, a surfactant, a lubricant, a further neutralizing agent, a defoamer, a deaerator, a preservative and a dye.

16. The paper coating slip according to claim 1, wherein the content of the inorganic pigment is from 80 to 95 parts by weight based on the total solids content of the paper coating slip, and the content of the polymer P is from 0.5 to 20 parts by weight based on the total solids content of the paper coating slip.

17. An aqueous dispersion comprising a polymer P, which is obtained by the process comprising: emulsifying a mixture comprising monomers in an aqueous medium, and polymerizing the monomers in the presence of a free-radical initiator and a starch derivative, wherein the monomer mixture consists of: vinyl acetate, as a monomer (a), at least one acrylate monomer, which is selected from the group consisting of a C.sub.1-C.sub.10 alkyl acrylate and a C.sub.1-C.sub.10 alkyl methacrylate, as a monomer (b), at least one a,-ethylenically unsaturated C.sub.3-C.sub.6 carboxylic acid, as a monomer (c), at least one monomer selected from the group consisting of glycidyl methacrylate and glycidyl acrylate, as a monomer (d), optionally at least one ethylenically unsaturated sulfonic acid, as a monomer (e), and optionally at least one ethylenically unsaturated other monomer, which is different from the monomers (a), (b), (c), (d) and (e), as a monomer (f), and wherein the content of the vinyl acetate monomer (a) is from 70 to 94.7 parts by weight of the monomers, the content of the at least one acrylate monomer (b) is from 5 to 25 parts by weight of the monomers, the content of the at least one a,-ethylenically unsaturated C.sub.3-C.sub.6 carboxylic acid monomer (c) is from 0.1 to 10 parts by weight of the monomers, the content of the at least one monomer (d) selected from the group consisting of glycidyl methacrylate and glycidyl acrylate is from 0.1 to 10 parts by weight of the monomers, the optional content of the at least one ethylenically unsaturated sulfonic acid monomer (e) is from 0.1 to 5 parts by weight of the monomers, the optional content of the at least one other ethylenically unsaturated monomer (f) is from 0.1 to 15 parts by weight of the monomers, and the sum total of the parts by weight of the monomers (a), (b), (c), (d), (e) and (l) is 100.

18. A binder, comprising: the aqueous dispersion comprising a polymer P according to claim 17.

19. A powder comprising a polymer P, which is obtained by drying of an aqueous dispersion comprising the polymer P obtained by a process comprising: emulsifying a mixture comprising monomers in an aqueous medium, and polymerizing the monomers in the presence of a free-radical initiator and a starch derivative, wherein the monomer mixture consists of: vinyl acetate, as a monomer (a), at least one acrylate monomer, which is selected from the group consisting of a C.sub.1-C.sub.10 alkyl acrylate and a C.sub.1-C.sub.10 alkyl methacrylate, as a monomer (b), at least one a,-ethylenically unsaturated C.sub.3-C.sub.6 carboxylic acid, as a monomer (c), at least one monomer selected from the group consisting of glycidyl methacrylate and glycidyl acrylate, as a monomer (d), optionally at least one ethylenically unsaturated sulfonic acid, as a monomer (e), and optionally at least one ethylenically unsaturated other monomer, which is different from the monomers (a), (b), (c), (d) and (e), as a monomer (f), and wherein the content of the vinyl acetate monomer (a) is from 70 to 94.7 parts by weight of the monomers, the content of the at least one acrylate monomer (b) is from 5 to 25 parts by weight of the monomers, the content of the at least one a,-ethylenically unsaturated C.sub.3-C.sub.6 carboxylic acid monomer (c) is from 0.1 to 10 parts by weight of the monomers, the content of the at least one monomer (d) selected from the group consisting of glycidyl methacrylate and glycidyl acrylate is from 0.1 to 10 parts by weight of the monomers, the optional content of the at least one ethylenically unsaturated sulfonic acid monomer (e) is from 0.1 to 5 parts by weight of the monomers, the optional content of the at least one other ethylenically unsaturated monomer (f) is from 0.1 to 15 parts by weight of the monomers, and the sum total of the parts by weight of the monomers (a), (b), (c), (d), (e) and (f) is 100.

Description

EXAMPLES

(1) Unless the context suggests otherwise, percentages are always by weight. A reported content is based on the content in aqueous solution or dispersion if not stated otherwise.

(2) Solids contents are determined by drying a defined amount of the particular aqueous polymer dispersion (about 5 g) at 140 C. in a drying cabinet to constant weight. Two separate measurements are carried out in each case and averaged.

(3) The glass transition temperature Tg is determined in accordance with the norm ISO 11357-2 by differential scanning calorimetry using a TA8000 series DSC820 instrument from Mettler-Toledo Int. Inc.

(4) The average particle diameters of the polymer particles are determined by dynamic light scattering on a 0.005 to 0.01 wt % aqueous polymer dispersion at 23 C. by means of an Autosizer IIC from Malvern Instruments, England. The cumulant z-average diameter of the measured autocorrelation function (ISO standard 13321) is reported.

(5) Materials Used:

(6) VA vinyl acetate

(7) nBA n-butyl acrylate

(8) AA acrylic acid

(9) VS vinyl sulfonate

(10) GMA glycidyl methacrylate (=2,3-epoxypropyl methacrylate)

(11) AMA allyl methacrylate

(12) Amol N-methylolacrylamide (=N-hydroxymethyl acrylamide)

(13) BDDA 1,4-butandiol diacrylate

(14) DVB para-divinylbenzene

(15) tDMK tert-dodecylmercaptan

(16) MD Roquette Maltodextrin fluessig 1967 (B) (Roquette, maltodextrin in form of an aqueous solution of saccharides obtained from starch, D.E. of 18-20)

(17) GS C-Star-Sweet 01403 (Cargill, glucose sirup in form of an aqeous solution of saccharides obtained by hydrolysis of starch, D.E. of 26-32)

(18) Seed latex polystyrene dispersion in water with an average diameter of 30 nm

(19) The materials are commercially available for example from Aldrich Inc. except for Roquette Maltodextrin fluessig 1967 (B), which is available from Roquette GmbH, Frankfurt, Germany; C-Star-Sweet 01403, which is available from Cargill Inc.; and the seed latex, which is prepared using a standard procedure.

(20) Emulsion Polymerization Procedure for Polymer Dispersion No. D2

(21) A pressure reactor equipped with a stirrer and dosing devices is initially charged with 290.76 g of water, 85.00 g of 20 wt % aqueous emulsifier solution of Lutensol AT 18 (BASF, a polyethoxylated fatty alcohol), 171.14 g of polystyrene seed latex and 1020.00 g of 50 wt % aqueous solution of maltodextrin (Roquette Maltodextrin fluessig 1967 (B) diluted with water for a solids content of 50 wt %). The mixture is heated to 75 C. under agitation. Then a shot of initiator, 97.14 g of a 7 wt % aqueous solution of sodium persulfate, is added to the reactor and after 10 minutes the emulsion feed is added in 3 hours. The emulsion feed is composed of 800.00 g of water, 63.76 g of 20 wt % aqueous emulsifier solution of Lutensol AT 18, 39.84 g of 32 wt % aqueous emulsifier solution of Disponil FES 77 (BASF, an alkyl polyglycol ethersulfate), 34.00 g of 25 wt % aqueous solution of VS, 42.50 g AA, 17.00 g GMA, 289.00 g nBA and 1343.00 g VA. After the end of the emulsion feed, the reaction mixture is stirred for another 30 min and then cooled to 70 C. At 70 C., 34.00 g of 10 wt % aqueous solution of tert.-butyl hydroperoxide and 44.12 g of a 13 wt % aqueous solution of sodium acetone bisulfite are fed during 1 hour. The reactor contents are then cooled down to room temperature and 22.67 g of a 1.5 wt % solution of Acticid MV (Thor, 5-chloro-2-methyl-4-isothiazolin-3-one/2-methyl-4-isothiazolin-3-one (CIT/MIT)) is added and the dispersion is adjusted to pH of approximately 6.5 using a 10 wt % aqueous solution of sodium hydroxide.

(22) The dispersion thus produced has a solids content of 49.4%, a pH of 6.6, a particle diameter of 286 nm and a Tg of 28 C.

(23) The polymer dispersions No. D1 and D3 to D10 are prepared in analogy.

(24) Tables 1-A and 1-B show the employed amounts of monomers and maltodextrin/glucose sirup for the polymer dispersions No. D1 to D10.

(25) TABLE-US-00001 TABLE 1-A monomer/ polymer dispersion-No. MD D1.sup.a) D2.sup.b) D3.sup.b) D4.sup.b) D5.sup.b) D6.sup.a) VA 80 79 78 80 79.5 79 nBA 17 17 17 12 17 17 GMA 0.0 1.0 2.0 5.0 0.0 0.0 AA 2.5 2.5 2.5 2.5 2.5 2.5 VS 0.5 0.5 0.5 0.5 0.5 0.5 AMA 0.0 0.0 0.0 0.0 0.5 0.0 Amol 0.0 0.0 0.0 0.0 0.0 1.0 BDDA 0.0 0.0 0.0 0.0 0.0 0.0 DVB 0.0 0.0 0.0 0.0 0.0 0.0 MD 30.0 30.0 30.0 30.0 30.0 30.0 GS 0.0 0.0 0.0 0.0 0.0 0.0

(26) TABLE-US-00002 TABLE 1-B monomer/ polymer dispersion No. MD D7.sup.a) D8.sup.a) D9.sup.b) D10.sup.b) VA 79 79 78 80 nBA 17 17 16.5 14 GMA 0.0 0.0 3.0 3.0 AA 2.5 2.5 2.5 2.5 VS 0.5 0.5 0.0 0.5 AMA 0.0 0.0 0.0 0.0 Amol 0.0 0.0 0.0 0.0 BDDA 1.0 0.0 0.0 0.0 DVB 0.0 1.0 0.0 0.0 MD 30.0 30.0 30.0 0.0 GS 0.0 0.0 0.0 30.0 a): comparative b): according to the invention

(27) The desired polymer dispersion No. D8 could not be obtained due to the strong inhibition of the DVB on the polymerization reaction.

(28) Procedure for a Paper Coating Slip Containing a Polymer Dispersion

(29) In a stirred assembly, the individual components are fed in succession. The pigments are added in pre-dispersed slurry form. The other components are added after the pigments, the order corresponding to the order in the reported coating slip formulation. Final solids content is set by adding water.

(30) Composition of the Paper Coating Slip Formulation Based on Solids Content of the Components: 100 parts of finely divided calcium carbonate (Hydrocarb 60, Omya) 7 parts of one of the polymer dispersions No. D1 to D7 or D9 to D10 as binder 0.25 parts of thickener (Sterocoll FS)

(31) The solids content of the paper coating slip is 64 wt % and its pH is about 9.

(32) Paper Coated with a Coating Slip Containing a Polymer Dispersion and its Surface Strength

(33) The paper coating slip containing a polymer dispersion, i.e. one of the polymer dispersion No. D1 to D7 or D9 to D10, is applied to one side of uncoated base paper (wood-free, 70 g/m.sup.2) using a laboratory coating machine and dried via IR radiator. The weight of the coat applied is about 10 g/m.sup.2 determined by gravimetric measurement. The paper is cut into sheets and calendered on a lab calendar to give even and flat sheets. Before conducting the surface strength tests, the paper sheets are conditioned for at least 15 hours at 23 C. and 50% relative humidity.

(34) The received coated paper is tested for surface strength using the test methods IGT dry pick resistance, IGT wet pick resistance and Offset test, which are known to a person skilled in the art.

(35) Measurement of Dry Pick Resistance with IGT Test Printer (IGT Dry):

(36) Strips were cut out of the in-test papers and printed with the IGT test printer. The printing inks used are specific test inks from Lorilleux, which transmit different tensile forces. The test strips are fed through the press at continuously increasing speed (maximum speed 200 cm/s). To evaluate the result, the point at which 10 picks have occurred on the paper surface after the start of printing is determined on the sample printing strip. The measure reported for dry pick resistance is the speed in cm/sec present at this point during printing and also the test ink used. The higher this printing speed at the tenth pick point, the better the quality rating of the paper surface.

(37) Measurement of Wet Pick Resistance with IGT Test Printer (IGT Wet):

(38) Strips were cut out of the in-test papers and printed with the IGT test printer. The printer was set up such that the test strips are moistened with water prior to the printing operation. The printing inks used are specific test inks from Lorilleux (No. 3807), which transmit different tensile forces. Printing is done at a constant speed of 0.6 cm/s. Picks out of the paper surface are visible as unprinted spots. To determine wet pick resistance, a color densitometer is used to determine color density in % compared with the full hue. The higher the reported color density, the better the wet pick resistance.

(39) Offset Test:

(40) Samples having a size of 24046 mm are cut out of the in-test papers in the longitudinal direction. An appropriate amount of printing ink is applied to the inking roll and left to run for 1 minute. A printing disk is then inserted and inked for 30 s. The printing speed is 1 m/s. A paper strip is brought back to the starting position on a printing test support with the printed paper strip. After a specified time interval, the printing process is started again without replacing the printing disk. This operation is repeated more than once. After each printing cycle, the pick on the printed side of the paper strip is assessed by visual inspection. The table reports the number of cycles before picking occurred for the first time. The higher the number of cycles up to the occurrence of picking, the better is the suitability of the papers for offset printing.

(41) The surface strength results of the papers coated with one of the polymer dispersions No. D1 to D7 or D9 to D10 are summarized in table 2.

(42) TABLE-US-00003 TABLE 2 Paper applied dry pick wet pick offset No. dispersion No. resistance [cm/s] resistance [cm/s] cycles P-1.sup.a) D1.sup.a) 32 10.4 2.25 P-2.sup.b) D2.sup.b) 67 18.8 3.75 P-3.sup.b) D3.sup.b) 77 15.7 4.75 P-4.sup.b) D4.sup.b) 79 10.8 3.25 P-5.sup.b) D5.sup.b) 45 5.5 3.25 P-6.sup.a) D6.sup.a) 38 12.9 2.75 P-7.sup.a) D7.sup.a) 28 8.0 1.25 P-9.sup.b) D9.sup.b) 78 22.5 3.50 P-10.sup.b) D10.sup.b) 90 10.5 3.50 .sup.a)comparative .sup.b)according to the invention

(43) The measured results of the papers P-1 to P-7 or P-9 to P-10 produced with paper coating slips containing one of the polymer dispersion No. D1 to D7 or D9 to D10 show that a content of glycidyl methacrylate leads to improved results by comparison of P-2 to P-4 versus P-1; that a content of glycidyl methacrylate leads to better results than a content of N-methylolacrylaminde by comparison of P-2 versus P-6; that a content of glycidyl methacrylate leads to better results than a content of 1,4-butandiol diacrylate by comparison of P-2 versus P-7; that a content of allyl methacrylate leads to better results in regard to dry pick resistance and offset cycles than a content of N-methylolacrylaminde by comparison of P-5 versus P-6; that a content of allyl methacrylate leads to better results than a content of 1,4-butandiol diacrylate by comparison of P-5 versus P-7; that a content of vinyl sulfonate or an absence of vinyl sulfonate leads to similar results by comparison of P-3 and P-4 versus P-9; that glucose sirup instead of maltodextrin leads to comparable results by comparison of P-3 and P-4 versus P-10.