BINDER COMPOSITION FOR BOARD COATING SLIPS

Abstract

The invention relates to a coating slip comprising (i) an aqueous dispersion of one or more vinyl acetate polymers, obtainable by free-radically initiated emulsion polymerization of 77% to 99% by weight of vinyl acetate, 1% to 13% by weight of ethylene and 0% to 10% by weight of one or more monoethylenically unsaturated monomers that are neither vinyl acetate nor ethylene, where the amounts of the monomers add up to 100% by weight, (ii) an aqueous dispersion of one or more styrene copolymers, obtainable by free-radically initiated emulsion polymerization of a monomer composition comprising 35% to 70% by weight of styrene, 20% to 60% by weight of one or more esters of acrylic and/or methacrylic acid with alkanols having 1 to 12 carbon atoms, or of one or more conjugated aliphatic dienes, 1% to 10% by weight of one or more monomers comprising acid groups, where the amounts of the monomers add up to 100% by weight, (iii) inorganic pigments and (iv) optionally further auxiliaries, where the total amount of emulsion polymers (i) and (ii) is 10 to 30 parts by weight based on 100 parts by weight of inorganic pigment (iii) and where the weight ratio of the styrene copolymer to the vinyl acetate polymer is 77:23 to 93:7, and to a method of producing the coating slip, to the use thereof for coating board, to a method of coating board with the coating slip and to the board coated thereby.

Claims

1.-13. (canceled)

14. A coating slip comprising (i) an aqueous dispersion of one or more vinyl acetate polymers, obtained by free-radically initiated emulsion polymerization of 77% to 99% by weight of vinyl acetate, 1% to 13% by weight of ethylene and 0% to 10% by weight of one or more monoethylenically unsaturated monomers that are neither vinyl acetate nor ethylene, (ii) an aqueous dispersion of one or more styrene copolymers, obtained by free-radically initiated emulsion polymerization of a monomer composition comprising 35% to 70% by weight of styrene, 20% to 60% by weight of one or more esters of acrylic and/or methacrylic acid with alkanols having 1 to 12 carbon atoms, or of one or more conjugated aliphatic dienes, 1% to 10% by weight of one or more monomers comprising acid groups, (iii) inorganic pigments and (iv) optionally further auxiliaries, where the total amount of emulsion polymers (i) and (ii) is 10 to 30 parts by weight based on 100 parts by weight of inorganic pigment (iii) and where the weight ratio of the styrene copolymer to the vinyl acetate polymer is 77:23 to 93:7.

15. The coating slip according to claim 14, wherein the vinyl acetate polymer has a glass transition temperature T.sub.g in the range from 10 to 30° C., measured to DIN EN ISO 11357-2 (2013-09).

16. The coating slip according to claim 14, wherein the one or more vinyl acetate polymer(s) is/are obtained by free-radically initiated emulsion polymerization of 82% to 98% by weight of vinyl acetate, 1% to 13% by weight of ethylene and 1% to 5% by weight of one or more monoethylenically unsaturated monomers selected from vinyl esters of α-branched monocarboxylic acids having 9 to 11 carbon atoms, vinyl laurate or vinyl esters of an α-branched carboxylic acid having 9 to 11 carbon atoms, (meth)acrylic esters of alcohols having 1 to 15 carbon atoms that also comprise 1 to 40% by weight of ethylene.

17. The coating slip according to claim 14, wherein the styrene copolymer is obtained by free-radically initiated emulsion polymerization of a monomer composition comprising 40% to 59% by weight of styrene, 40% to 59% by weight of one or more esters of acrylic and/or methacrylic acid with alkanols having 1 to 12 carbon atoms, and 1% to 10% by weight of a monomer comprising acid groups.

18. The coating slip according to claim 14, wherein the styrene copolymer is obtained by free-radically initiated emulsion polymerization in the presence of 10% to 80% by weight, based on total monomers of the styrene copolymer, of a degraded starch.

19. The coating slip according to claim 14, wherein the weight ratio of the styrene copolymer to the vinyl acetate polymer is 80:20 to 90:10.

20. The coating slip according to claim 14, wherein at least 80% by weight of the total solids content of the coating slip is inorganic pigment.

21. The coating slip according to claim 14, having a solids content of 30% to 80% by weight.

22. A process for producing the coating slip according to claim 14 by mixing (i) the aqueous dispersion of one or more vinyl acetate polymers, (ii) the aqueous dispersion of one or more styrene copolymers, (iii) inorganic pigments and (iv) optionally further auxiliaries, (v) optionally water, where the total amount of emulsion polymers (i) and (ii) is 10 to 30 parts by weight based on 100 parts by weight of inorganic pigment (iii) and where the weight ratio of the styrene copolymer (ii) to the vinyl acetate polymer (i) is 77:23 to 93:7.

23. The use of the coating slip according to claim 14 for production of a coated board having a basis weight in the range from 150 to 600 g/m.sup.2.

24. A method of producing a coated board by providing a multilayer board having a basis weight in the range from 150 to 600 g/m.sup.2, applying a coating slip according to claim 14 to at least one surface of said board such that the coatweight of the coating slip as dry weight on a surface of the substrate is 5 to 30 g/m.sup.2 and then drying the coated board.

25. The coated board obtainable by the method according to claim 24.

26. A binder composition comprising (i) an aqueous dispersion of one or more vinyl acetate polymers, obtained by free-radically initiated emulsion polymerization of TABLE-US-00009 77% to 99% by weight of vinyl acetate,  1% to 13% by weight of ethylene and  0% to 10% by weight of one or more monoethylenically unsaturated monomers that are neither vinyl acetate nor ethylene, (ii) an aqueous dispersion of one or more styrene copolymers, obtained by free-radically initiated emulsion polymerization of a monomer composition comprising TABLE-US-00010 35% to 70% by weight of styrene, 20% to 60% by weight of one or more esters of acrylic and/or methacrylic acid with alkanols having 1 to 12 carbon atoms, or of one or more conjugated aliphatic dienes,  1% to 10% by weight of one or more monomers comprising acid groups.

Description

EXAMPLES

[0126] Unless the context indicates otherwise, percentages always signify weight percent.

[0127] Contents reported relate to the content in an aqueous solution or dispersion.

[0128] Where water was used in the context of the examples, demineralized water was used.

[0129] Measurement Methods

[0130] Glass transition temperature:

[0131] The glass transition temperature T.sub.g of a dispersion was generally determined with the aid of a TA Instruments Q 2000 differential calorimeter. The heating rate was 10 K per minute.

[0132] Determination of the viscosity of the coating slip:

[0133] The viscosity of the dispersion was determined to ASTM D2196 with a Brookfield viscometer with RV spindle 4 at 100 rpm and at a temperature of 23° C.

[0134] Solids Content:

[0135] The solids content of a coating slip or dispersion was determined by distributing 0.5 to 1.5 g of the coating slip/dispersion in a sheet metal lid of diameter 4 cm and then drying in an air circulation drying cabinet at 140° C. for 30 minutes. The ratio of the mass of the sample after drying under the above conditions to the mass of the sample taken gives the solids content.

[0136] General Production of the Coating Slips:

[0137] The coating slip was prepared in a stirring apparatus into which the individual components were fed one after the other. The pigments were initially charged in predispersed form as a slurry. Subsequently, the rheology aid was first added, then adjusted to a pH of 9 with sodium hydroxide solution, and then the emulsion polymer was added. The final solids content was set by the addition of water.

[0138] The stated amounts are each based on solids.

TABLE-US-00001 100 parts by weight of calcium carbonate (Hydrocarb 90 Slurry from OMYA, solids content 78.6% by weight) 0.11 part by weight of rheology aid (Sterocoll FS from BASF SE) 16 parts by weight of emulsion polymer from the respective example

[0139] A 3-ply uncoated raw board having a basis weight of 225 g/m.sup.2 (residual moisture content 4.5% by weight) was coated with the coating slip. The coating slip was applied to one side of the raw board using a laboratory coating machine and dried to 4.5% by weight of residual moisture by means of an IR lamp. The coating was effected by the blade coating method. One ply was applied. The coatweight was 10 g/m.sup.2 (in solid form).

[0140] Determination of Delamination [0141] Principle: The delamination characteristics of a coating slip are determined by printing a coated board sample with a pick oil test ink using an IGT AIC 2-5 printability tester. The tensile force of the pick oil test ink damages the surface to a greater or lesser degree (formation of corrugation). The lower the level of damage, the lower the level of delamination shown by the coating slip. [0142] Preparation: 5 strips are cut out of the coated board samples to be tested in running direction of the board web in 340 mm×40 mm format. [0143] The polyurethane rolls are inserted into the roll mill. To the left-hand roll is applied 1.3 ml (+/−0.01 ml), and to the right-hand roll 0.93 ml (+/−0.01 ml), of the chosen IGT test pick oil (Standard IGT Testing System IGT pick oil, moderate viscosity, no. 404.004.020). The comminution time is 45 minutes. Then 2 metal print wheels are inked on the left-hand roll for 90 seconds, and then on the right-hand roll for a further 90 seconds. The print speed is set to a value of 200 cm/s (standard) with rising speed; the linear pressure is 700 N(=350 N/cm). [0144] Test: A strip of board is clipped to the circular segment, and the print operation is started. [0145] Evaluation: The printed strip of board is then viewed under light and in a standardized manner, and the commencement of formation of corrugation on the print side is marked with a dash. The distance from the commencement of printing up to the marks is used to determine delamination. 5 strips are tested per data point.

[0146] Measurement of dry pick resistance with IGT test printer (IGT dry):

[0147] Strips of the coated board to be tested were cut and printed with the IGT test printer. The printing inks used are specific test inks from Lorilleux that transmit different tensile forces. The test strips are guided through the press with continuously rising speed (maximum speed 200 cm/s). The result is evaluated by determining the point on the printed specimen strip at which 10 pick points have occurred on the paper surface after commencement of printing. The measure of dry pick resistance mentioned is the speed in cm/s that exists at this juncture during printing, and the test ink used. The higher this print speed at the tenth pick point, the better the assessment of the quality of the paper surface.

[0148] In the examples, the following aqueous binder dispersions were used as feedstocks: [0149] SA1: Bimodal styrene/n-butyl acrylate/acrylic acid dispersion with a solids content (SC) of 50% by weight and a glass transition temperature T.sub.g of 20° C. [0150] SA2: Monomodal styrene/n-butyl acrylate/acrylic acid dispersion with SC 50% by weight and T.sub.g of 20° C. [0151] SA3: Monomodal styrene/n-butyl acrylate/acrylic acid dispersion with SC 50% by weight and produced in the presence of 10 parts by weight of maltodextrin (dextrose equivalent DE=18, M.sub.w of 11 000 and an intrinsic viscosity of ηi 0.052 dl/g) based on 100 parts by weight of monomer.

[0152] The monomer composition of the styrene/butyl acrylate/acrylic acid polymers for all three dispersions was 46/50/4. [0153] SB1: Styrene/butadiene/acrylic acid dispersion with SC 50% by weight and T.sub.g of 20° C. [0154] SB2: Styrene/butadiene/acrylic acid dispersion with SC 50% by weight and T.sub.g of 6° C., produced in the presence of 60 parts by weight of maltodextrin (DE=18, Mw of 11 000 and an intrinsic viscosity of ηi 0.052 dl/g) based on 100 parts by weight of monomer.

[0155] The monomer composition of the styrene/butadiene/acrylic acid polymers was 65/30/5 (SB1) or 57/39/4 (SB2). [0156] D1: Vinyl acetate/ethylene copolymer dispersion (89.5/10.5 vinyl acetate/ethylene) with SC 60% by weight and T.sub.g of 10° C. [0157] D2: Vinyl acetate/ethylene copolymer (87/13 vinyl acetate/ethylene) dispersion with SC 55% by weight and T.sub.g of 5° C. [0158] D3: Vinyl acetate/ethylene copolymer dispersion (93.3/6.7 vinyl acetate/ethylene) with SC 58% by weight and Tg of 18° C. [0159] D4: Vinyl acetate homopolymer dispersion with SC 50% by weight and T.sub.g of 33° C.

[0160] Production of Coating Slips S1 to S4 (Styrene/Acrylate Polymer (SA1) and Vinyl Acetate/Ethylene Polymer (D1))

[0161] The above-detailed binder dispersions were used to produce coating slips consisting of [0162] 100 parts by weight of pigment (Omya Hydrocarb 90) [0163] 0.11 part by weight of rheology aid (Sterocoll FS) [0164] 16 parts by weight of binder (total).

[0165] All weight figures are based on the respective solids content of the components. The ratio of the two binder polymers (solid styrene-acrylate polymer/vinyl acetate/solid ethylene polymer) can be found in table 1. The solids content of the coating slip was 65% by weight; the pH was 8.8.

TABLE-US-00002 TABLE 1 Delamination values depending on different compositions of SA1 and D1 SA1 [% by D1 [% Delamination % based on Ex. wt.] by wt.] [cm/s] ex. 1 1 n.i. 100 0 116 0 2 90 10 126 8.6 3 80 20 131 12.9 4 n.i. 70 30  135* 16.4 n.i.: not according to the invention *delamination of the board layers and additionally even picking of the coating were observed

[0166] It can be inferred from the examples that the binder compositions of examples 2 and 3 formulated as coating slips and applied to board lead to delamination only at relatively high tensile forces, with no observation of picking. These two coating slips are thus better than the coating slip with straight styrene-acrylate from example 1. Although example 4 shows a good denomination value, significant picking is already observed. Picking means that the slip is poor and there is poor surface cohesion.

[0167] Production of Coating Slips S5 to S9 (Styrene/Acrylate Polymer (SA2) and Various Vinyl Acetate Polymers)

[0168] The above-detailed binder dispersions were used to produce coating slips consisting of 100 parts by weight of pigment (Omya Hydrocarb 90), 0.11 part by weight of rheology aid (Sterocoll FS) and 16 parts by weight of binder (total binder in solid form). Components chosen in the binder compositions were the styrene/acrylate copolymer SA2 and various vinyl acetate/ethylene copolymers, the latter having different glass transition temperatures. The respective compositions of the two binder components can be found in table 2 (likewise based on the respective solids content).

[0169] All weight figures are based on the respective solids content of the components. The solids content of the coating slip was 65% by weight; the pH was 8.8.

TABLE-US-00003 TABLE 2 Delamination values depending on compositions comprising different vinyl acetate polymers having different glass transition temperatures 20% by weight of Tg of the SA2 [% vinyl acetate vinyl acetate Delamination % based Ex. by wt.] polymer polymer [° C.] [cm/s] on ex. 9 5 80 D1 10 111 12.1 6 n.i. 80 D2 5 106 7.0 7 80 D3 18 123 24.2 8 n.i. 80 D4* 33 97 −2.1 9 n.i. 100 — — 99 0 *a vinyl acetate homopolymer was used in place of the vinyl acetate/ethylene polymer n.i.: not according to the invention

[0170] It can be inferred from the examples that binder compositions comprising vinyl acetate/ethylene polymers with a T.sub.g in the range from 10 to 25° C. formulated as a coating slip and applied to board lead to better delamination values of the board than a straight styrene-acrylate as binder in the coating slip.

[0171] Production of Coating Slips S10 to S15 (Styrene/Acrylate Polymers (SA1) or (SA2), Each with Vinyl Acetate/Ethylene Polymer (D3))

[0172] The above-detailed binder dispersions were used to produce coating slips consisting of

TABLE-US-00004 100 parts by weight of pigment (80 parts by weight of calcium carbonate and 20 parts by weight of kaolin) 0.9 part by weight of BF-05 polyvinyl alcohol 0.12 part by weight of rheology aid (Sterocoll FS (SC: 40%)) 15.5 parts by weight of binder polymer

[0173] The solids content of the coating slip was 65% by weight; the pH was 9. The addition was effected in this tabular sequence.

[0174] This coating slip was applied with a bent blade pilot plant (manufacturer: Voith) to singly primer-coated raw board (primer coatweight was 10 g/m.sup.2 in solid form). The coatweight was 10 g/m.sup.2 (in solid form). All weight figures are based on the respective solids content of the components. The ratio of the two binder polymers (solid styrene/acrylate polymer/solid vinyl acetate polymer) can be found in table 3.

TABLE-US-00005 TABLE 3 Delamination values depending on compositions comprising vinyl acetate/ethylene copolymers with different Tg SA1 [% by SA2 [% by D3 [% Delamination.sup.1) IGT length Ex. wt] wt.] by wt.] [cm/s] (cm/s) 10 n.i. 100 0 0 131 >400* 11 90 0 10 292 >400* 12 80 0 20 326 >400* 13 n.i. 0 100 0 103 >400* 14 0 90 10 335 >400* 15 0 80 20 372 >400* n.i.: not according to the invent ion *no picking observed .sup.1)Delamination was determined by cutting the 5 board samples in cross direction of the board web in 340 mm × 40 mm format.

[0175] Production of Coating Slips S16 to S19 (Styrene/Butadiene Polymer (SB1) or (SB2) and Vinyl Acetate/Ethylene Polymer (D3))

[0176] The above-detailed binder dispersions were used to produce coating slips consisting of [0177] 100 parts by weight of pigment (Omya Hydrocarb 90) [0178] 0.11 part by weight of rheology aid (Sterocoll FS) [0179] 16 parts by weight of binder (total).

[0180] All weight figures are based on the respective solids content of the components. The ratio of the two binder polymers (solid styrene/butadiene polymer/vinyl acetate/solid ethylene polymer) can be found in table 4. The solids content of the coating slip was 65% by weight; the pH was 8.8.

TABLE-US-00006 TABLE 4 Delamination values with the same monomer composition of the styrene/butadiene/acrylic acid polymer depending on the production thereof in the presence of degraded starch SB1 SB2 % based [% by [% by Delamination on ex. Ex. wt] wt.] D3 [% by wt.] [cm/s] 16 or 18 16 n.i. 100 0 0 125 0 17 80 0 20 152 21.6 18 n.i. 0 100 0 138 0 19 0 80 20 182 37.8 n.i.: not according to the invention

[0181] Production of Coating Slips S20 to S23 (Styrene/Butadiene Polymer (SA2) or (SA3) and Vinyl Acetate/Ethylene Polymer (D3))

[0182] The above-detailed binder dispersions were used to produce coating slips consisting of [0183] 100 parts by weight of pigment (Omya Hydrocarb 90) [0184] 0.11 part by weight of rheology aid (Sterocoll FS) [0185] 16 parts by weight of binder (total).

[0186] All weight figures are based on the respective solids content of the components. The ratio of the two binder polymers (solid styrene/acrylate polymer/vinyl acetate/solid ethylene polymer) can be found in table 5. The solids content of the coating slip was 66% by weight; the pH was 8.8.

TABLE-US-00007 TABLE 5 Delamination values with the same monomer composition of the styrene/acrylate polymer depending on the production thereof in the presence of degraded starch SA2 SA3 [% by D3 [% Delamination % based on ex. Ex. [% by wt.] wt.] by wt.] (cm/s) 20 or 22 20 n.i. 100 0 0 103 0 21 80 0 20 126 22.3 22 n.i. 0 100 0 105 0 23 0 80 20 129 22.8 n.i.: not according to the invention

Ex. 24 and 25: Comparative Experiments with SA2 and D3

[0187] The above-detailed binder dispersions were used to produce coating slips consisting of [0188] 100 parts by weight of pigment (Omya Hydrocarb 90) [0189] 0.11 part by weight of rheology aid (Sterocoll FS) [0190] 16 parts by weight of binder (total).

TABLE-US-00008 TABLE 6 Delamination values for the coating slips comprising SA2 or D3 as binder SA2 Delamination Ex. [% by wt] D3 [% by wt.] (cm/s) 24 n.i. 100 0 103 25 n.i. 0 100  104* *: The strips show additional picking

[0191] Board coated with the coating slip from example 24 or example 25 gives comparable delamination values. However, the board coated with the coating slip with D3 as binder additionally has poorer surface cohesion, since picking is also observed. The inventive mixture of the two polymers SA2 and D3 (example 21) demonstrates the existence of synergism since both an improved delamination value and good surface cohesion are observed (no picking).