AQUEOUS SURFACE-COATING AGENT FOR PAPER AND PAPERBOARD

Abstract

The present invention relates to an aqueous surface coating composition for paper and board with a solids content of 1 to 55 wt % comprising (A) 0 to 20 parts by weight of starch (solids), (B) 0.01 to 20 parts by weight of a zirconium carbonate compound, (C) 0.01 to 40 parts by weight of water-soluble synthetic polymer (solids) containing in copolymerized form one or more monomers having monoethylenic double bonds,
and also to a method for producing paper and board using the aqueous surface coating composition, and to corrugated boards produced from this paper.

Claims

1. An aqueous surface coating composition for paper and board with a solids content of 1 to 55 wt %, the coating composition comprising: (A) 0 to 20 parts by weight of a starch; (B) 0.01 to 20 parts by weight of a zirconium carbonate compound; and (C) 0.01 to 40 parts by weight of a water-soluble synthetic polymer comprising in copolymerized form at least one monomer comprising at least one monoethylenic double bond.

2. The aqueous surface coating composition according to claim 1, wherein the water-soluble synthetic polymer has an average molecular weight M.sub.w1 million daltons.

3. The aqueous surface coating composition according to claim 1, wherein the water-soluble synthetic polymer comprises at least one monomer in copolymerized form selected from the group consisting of an acrylamide, a vinyl alcohol, a vinyl acetate, and an N-vinylcarboxamide of the formula (I): ##STR00006## in which R.sup.1, R.sup.2H or C.sub.1 to C.sub.6 alkyl.

4. The aqueous surface coating composition according to claim 1, wherein the water-soluble synthetic polymer is an anionic polymer.

5. The aqueous surface coating composition according to claim 1, wherein the water-soluble synthetic polymer is obtainable by copolymerizing a monomer mixture comprising: (a) at least one monomer selected from the group consisting of an acrylamide and an N-vinylcarboxamide of the formula (I): ##STR00007## in which R.sup.1, R.sup.2H or C.sub.1 to C.sub.6 alkyl; (b) at least one monoethylenically unsaturated monomer comprising an acid group, an alkali metal salt of an acid group, an alkaline earth metal salt of an acid group, and an ammonium salt of an acid group, or a mixture thereof; (c) optionally at least one monoethylenically unsaturated monomer which is different from the monomers (a) and (b); and (d) optionally at least one compound having at least two ethylenically unsaturated double bonds in the molecule.

6. The aqueous surface coating composition according to claim 1, wherein the water-soluble synthetic polymer is a copolymer or terpolymer comprising in copolymerized form monomers acrylic acid and vinylformamide.

7. The aqueous surface coating composition according to claim 1, wherein the aqueous surface coating composition has a viscosity in the range from 1 to 200 mPa.Math.s.

8. The aqueous surface coating composition according to claim 1, comprising: (A) 1 to 20 parts by weight of the starch; (B) 0.01 to 20 parts by weight of the zirconium carbonate compound; and (C) 0.01 to 40 parts by weight of the water-soluble synthetic polymer.

9. A method for producing paper and board, the method comprising: a) treating a paper stock with a paper auxiliary, a filler, or both, to obtain a treated paper stock; b) draining the treated paper stock with sheet formation, to obtain a paper web; and c) coating the paper web with the surface coating composition of claim 1, to obtain a coated paper web; and d) drying the coated paper web.

10. A paper or board obtained by the method according to claim 9.

11. A method for producing corrugated board, the method comprising corrugating the board of claim 10 to obtain a corrugated board.

12. A corrugated board obtained by the method of claim 11.

Description

EXAMPLES

[0151] The examples which follow illustrate the present invention. The percentages in the examples are by weight, unless otherwise stated.

[0152] The K value of the polymers was determined according to Fikentscher, Cellulose-Chemie, Volume 13, 58-64 and 71-74 (1932) at a temperature of 20 C. In this connection, K=k.Math.1000.

[0153] The solids content was ascertained by temperature-conditioning a sample of the product (approximately 3 g)that is, drying it to constant weightin a preheated forced air drying cabinet at 120 C.

[0154] Polymers used in the inventive and comparative examples were as follows.

[0155] Polymer (1) Vinylformamide/Acrylic Acid Copolymer (90/10 mol/mol)

[0156] In the initial charge, in 46.8 kg of water, the pH was adjusted to 6.6 using 0.35 kg of 85 wt % strength aqueous phosphoric acid and 0.65 kg of 25 wt % strength sodium hydroxide. 200 g of Afranil T (liquid) (defoamer) were added. The initial charge was then flushed with nitrogen and heated to 80 C., and a pressure of 450 mbar was established. The appearance of distillate was the cue for metered addition over 4 hours, from a feed, of 32.5 kg of vinylformamide (99% form), 14.8 kg of 32% strength aqueous sodium acrylate solution, and 8.9 kg of water. Concurrently, 7.4 kg of a 10 wt % strength aqueous solution of 2,2-azobis(2-amidinopropane) hydrochloride were metered in over 4 hours.

[0157] After the end of the feeds, polymerization was continued for a further hour, after which a further 7.4 kg of 10 wt % strength aqueous 2,2-azobis(2-amidinopropane) hydrochloride solution were metered in over a period of 15 minutes, followed by polymerization for 2 hours more. During the polymerization, 8.9 kg of water were distilled off. The product obtained accordingly may be characterized as follows:

[0158] K value 50.2 (determined in a 5 wt % strength aqueous sodium chloride solution at a pH of 7 and a polymer concentration of 1%)

[0159] Solids content (SC): 36 wt %

[0160] Polymer (2) Polyvinylformamide

[0161] With 62.7 kg of water, a pH of 65 was adjusted in the initial charge using 0.36 kg of 85 wt % strength aqueous phosphoric acid and 0.59 kg of 25 wt % strength sodium hydroxide. The initial charge was then flushed with nitrogen and heated to 80 C., and a pressure of 450 mbar was established. Appearance of distillate was the cue for metered addition over 3 hours of 38.0 kg of vinylformamide (99% form).

[0162] Concurrently, 0.83 kg of a 10 wt % strength aqueous solution of 2,2-azobis(2-amidinopropane) hydrochloride were metered in from a feed over a period of 3 hours. 30 minutes after the start of the two feeds, the feed of 15.7 kg of water was commenced, over 3 hours 30 minutes. After the end of the monomer feed, the reaction mixture was held at 80 C. for 3 hours more. During the whole polymerization, 15.7 kg of water were distilled off. The product obtained accordingly may be characterized as follows:

[0163] K value: 42.9 (determined in water at a pH of 7 and a polymer concentration of 1%)

[0164] SC: 34.33%

[0165] Polymer (3) Hydrolyzed Copolymer of Vinyl Acetate/Crotonic Acid (90/10)

[0166] Included in the initial charge were 70 kg of water and 40 kg of 25 wt % strength sodium hydroxide. Dissolved with stirring over 60 minutes were, in portions, 21.6 kg of Luviset CA 66 (from BASF, VAc/crotonic acid 90/10 mol/mol).

[0167] After the end of the addition, the solution was heated at an internal temperature of 80 C. and held at the temperature for a further 5 hours. The solution was then cooled and a pH of 6 was set by addition of 2.2 kg of 32% strength hydrochloric acid. The product obtained accordingly may be characterized as follows:

[0168] Degree of hydrolysis of VAc: 68%.

[0169] 22.5% nonvolatile fraction (NVF); polymer content 18.0 wt %

[0170] Polymer (4) Copolymer of Acrylamide and Acrylic Acid (90:10 mol:mol)

[0171] In the initial charge, 80 kg of water, 1.38 kg of a dilute solution of Trilon C (from BASF, diluted to 1 wt % solids content), and 375 g of sodium hypophosphite monohydrate (solid) were heated to 60 C., during which nitrogen was passed through the charge. 9.8 kg of 32 wt % strength aqueous sodium acrylate solution (33.34 mol) and 42.5 kg of 50 wt % strength aqueous acrylamide (301.07 mol) were metered in over a period of 2 hours 20 minutes. Concurrently, 12.6 kg of a 4 wt % strength aqueous solution of 2,2-azobis(2-amidinopropane) hydrochloride were metered in over 2 hours 20 minutes. An hour after the end of the feeds, 2.76 kg of 4 wt % strength aqueous 2,2-azobis(2-amidinopropane) hydrochloride solution were metered in over 5 minutes, after which the mixture was heated to an internal temperature of 80 C., thereby initiating the postpolymerization. The mixture was held at 80 C. for 2 hours. Then the pH was set to 6.3 by addition of 0.36 kg of 32% strength hydrochloric acid. The product obtained accordingly may be characterized as follows:

[0172] K value: 28.8 (determined in 5 wt % strength aqueous sodium chloride solution at a pH of 7 and a polymer concentration of 2%)

[0173] AM/AA ratio in the polymer: 90/10 mol/mol

[0174] SC: 17%

[0175] Polymer (5) Hydrolyzed Copolymer of Vinyl Acetate (VAc) and Vinylformamide (VFA)

[0176] In the initial charge, with 31.7 kg of water, a pH of 6.5 was set with 0.22 kg of 85 wt % strength phosphoric acid and 0.42 kg of 25 wt % strength sodium hydroxide. 2.33 kg of a 10% strength aqueous solution of Mowiol 40-88 (from Kuraray) were added.

[0177] The initial charge was then flushed with nitrogen and heated to 65 C.

[0178] 8.35 kg of vinylformamide (99%) were metered in over 3 hours. Commenced concurrently was the supply of 15.0 kg of vinyl acetate over 0.5 hour, and of 8.18 kg of a 2 wt % strength aqueous solution of 2,2-azobis(2-amidinopropane) hydrochloride, over 8 hours.

[0179] After the end of the initiator feed, 5.0 kg of water were added and polymerization was continued for an hour. Then 10.5 kg of 2 wt % strength aqueous 2,2-azobis(2-amidinopropane) hydrochloride solution were metered in over 15 minutes and, after the end of the feed, 5.0 kg of water were added. The batch was heated to an internal temperature of 70 C. and polymerization was continued for 2 hours, after which 25 kg of water were added. The pressure was lowered slightly, and 15 kg of water were distilled off. This gave a copolymer of vinyl acetate and VFA (47.6/52.4 mol:mol). The product mixture may be characterized as follows:

[0180] K value: 54.6 (determined in formamide with a polymer concentration of 1%)

[0181] SC: 22.8%

[0182] The product mixture obtained was then heated to an internal temperature of 80 C. Thereafter 0.6 kg of sodium bisulfate solution (40% in water) was added. When 80 C. had been reached, 3.2 kg of 25 wt % strength sodium hydroxide are added over 15 minutes. The mixture was hydrolyzed at this temperature for 3 hours and then cooled and adjusted to a pH of 8.2 using 8.7 kg of 32 wt % strength aqueous hydrochloric acid. This gave an end product with a polyvinyl alcohol content of 45.7%, a polyvinyl acetate content of 6.7%, a polyvinylformamide content of 27.8%, and a polyvinylformamide content of 19.8%. NVF: 22.4% WS: 15.8% polymer content: 9.8%

[0183] Polymer (6) Copolymer of Vinyl Acetate and VFA (50/50)

[0184] In the initial charge, with 31.7 kg of water, a pH of 6.5 was set with 0.22 kg of 85 wt % strength phosphoric acid and 0.42 kg of 25 wt % strength sodium hydroxide. 2.33 kg of a 10% strength aqueous solution of Mowiol 40-88 (from Kuraray) were added. The initial charge was then flushed with nitrogen and heated to 65 C. 8.35 kg of vinylformamide (99%) were metered in over 3 hours; concurrently, the supply of 15.0 kg of vinyl acetate commenced, over 0.5 hour, and of 8.18 kg of a 2 wt % strength aqueous solution of 2,2-azobis(2-amidinopropane) hydrochloride, over 8 hours. After the end of the initiator feed, 5.0 kg of water were added and polymerization was continued for an hour. Then 10.5 kg of 2 wt % strength aqueous 2,2-azobis(2-amidinopropane) hydrochloride solution were metered in over 15 minutes and, after the end of the feed, 5.0 kg of water were added. The batch was heated to an internal temperature of 70 C. and polymerization was continued for 2 hours, after which 25 kg of water were added. The pressure was lowered slightly and 15 kg of water were distilled off.

[0185] K value: 54.6 (determined in formamide with a polymer concentration of 1%).

[0186] SC: 22.8%

[0187] Ratio in the polymer: 47.6/52.4

[0188] Polymer (7)

[0189] Polymer 7 used was a polyacrylic acid having an average molecular weight (by GPC) of about 4000 g/mol and a degree of neutralization of 50.

[0190] Preparation of Starch Solution:

[0191] Merizet 120 maize starch (from Tate & Lyle) was used, and was enzymatically degraded as follows: a 12% slurry of Merizet 120 was prepared in hot water at 65 C. under agitation in a 1000 L vessel, and 0.012% of PL 120 enzyme from Novozyme was added. After 20 minutes, 100 ml of acetic acid were metered into the starch solution to terminate the process of starch degradation. The starch solution had a viscosity of 55 mPas at 100 rpm (spindle 2).

[0192] Determination of the Mass Average (M.sub.w) of the Starch Solution

[0193] The aqueous starch solutions were diluted with DMSO and thereby stabilized. The molar mass distribution was determined by GPC-MALLS (gel chromatography with multiangle laser light scattering). The GPC-MALLS consists of a Waters 515 pump module, devolatilizer, Waters 717 Autosampler, GPC column heating (Jet Stream). The MALLS detector is a Dawn-Heleos (Wyatt Technology, Santa Barbara, USA) equipped with a K5 flow cell and a HeNe laser m from 10 to 658 nm and equipped with 16 detectors with an angle of 15 to 162 . The following GPC columns were used in series: Suprema S 30000, S 1000, and S 10 (PSS, Mainz, Germany). The samples were eluted with a DMSO-containing 0.09 M NaNO.sub.3 solution with a flow rate of 0.5 ml/min and a temperature of 70 C. in the GPC columns. For software analysis, ASTRA 5.3.0.18 was used.

[0194] Determination of the Mass Average (M.sub.w) of the Polymers

[0195] The molar mass distribution was determined by means of GPC-UV (gel chromatography with UV and fluorescence detector). The GPC consists of a Waters 515 pump module, devolatilizer, Waters 717 Autosampler, GPC column heating (Jet Stream). The UV detector is an Agilent (DRI 1200 UV) and the equipment also includes a fluorescence detector from Agilent (1200 VWD-260 nm). The following GPC columns were used in series: TSKgel GMPWXL. The samples were eluted with a 0.01 M NaN.sub.3 solution with a flow rate of 0.8 ml/min and a temperature of 35 C. in the GPC columns. Prior to injection, the polymer solutions were filtered through a 0.2 micrometer Millipore filter. The concentration of the polymer solution was 1.5%.

[0196] Further compounds, used as auxiliaries:

[0197] Bacote 20 (from Zirconium Chemicals) is an alkaline solution of ammonium zirconium carbonate (Zirconate (2),bis[carbonato(2)-0]dihydroxydiammonium) with a solids content of 20%.

[0198] Production of Surface Coating Compositions

[0199] Using the polymers 1-7 and the above-prepared 12 wt % strength starch solution, surface coating compositions were produced. For this purpose, the starch solution was introduced first, and the polymer solution and Bacote 20 were metered in. The constitution of the surface coating composition was selected so as to achieve the amounts indicated in the table in parts by weight of starch (solids), parts by weight of polymer (solids), and parts by weight of Bacote 20. Each of the compositions was made up with water so as to give a solids content of 12 wt %. 2 parts by weight of Bacote 20 were used in each case, corresponding after conversion to 0.4 part by weight of ammonium zirconium carbonate.

TABLE-US-00001 Surface coating Starch composition [parts by weight] Polymer Bacote 20 1 (comparative) 12 2 n.i. 8 4 pbw Polymer 1 3 8 4 pbw Polymer 1 2 pbw 4 n.i. 8 4 pbw Polymer 2 5 8 4 pbw Polymer 2 2 pbw 6 n.i. 8 4 pbw Polymer 3 7 8 4 pbw Polymer 3 2 pbw 8 n.i. 8 4 pbw Polymer 4 9 8 4 pbw Polymer 4 2 pbw 11 n.i. 8 4 pbw Polymer 5 12 8 4 pbw Polymer 5 2 pbw 13 n.i. 8 4 pbw Polymer 6 14 8 4 pbw Polymer 6 2 pbw 15 n.i. 8 4 pbw Polymer 7 16 8 4 pbw Polymer 7 2 pbw n.i.: not inventive pbw: parts by weight

[0200] Paper Coating

[0201] Since no large-scale pilot experiment was carried out, dry base paper was coated with the surface coating composition. Since the paper is subsequently dried again, the effect on the paper properties is negligible. The base paper used was composed 100% of waste paper (mixture of the following grades: 1.02, 1.04, 4.01) with a grammage of 100 g/m2, possessing no surface starch.

[0202] The base paper was coated in the formulations described in table 1 using a film press at 800 m/min on an experimental coater unit with IR dryers. The coatweights were determined gravimetrically. The coatweight reported is based on the dried amount of coating after departure from the IR dryer. The strength of the example papers was then investigated. Coating took place with different amounts of surface coating composition.

[0203] Performance Testing of the Base Papers

[0204] Prior to the testing of the paper, it was stored at 50% humidity for 24 hours, and the following strength investigations were conducted: [0205] CMT according to DIN EN 23035 (Corona medium test)

[0206] The results of coating with a coatweight of 2 g/m.sup.2 can be seen in table 2. This corresponds to an application quantity of 0.7 g/m.sup.2 polymer (solids) and 1.3 g/m.sup.2 starch (solids) with the addition in the inventive examples of Barcote 20.

TABLE-US-00002 TABLE 2 Performance results of the paper with the surface coating compositions of examples 2-16 at a coatweight of 2 g/m.sup.2 Example CMT factor Increase.sup.1) Paper formulation Polymer [N .Math. m2/g] [%] 1 1 1.97 6 2a 2 n.i. 1 2.16 16 3a 3 1 2.19 19 4a 4 n.i. 2 2.00 8 5a 5 2 2.09 13 6a 6 n.i. 3 7a 7 3 8a 8 n.i. 4 2.00 9 9a 9 4 2.09 14 11a 11 n.i. 5 2.04 11 12a 12 5 2.11 15 13a 13 n.i. 6 2.00 13 14a 14 6 2.10 16 15a 15 n.i. 7 2.01 10 16a 16 7 2.08 15 .sup.1)Increase in % by comparison with the uncoated base paper

[0207] The results of coating with a coatweight of 4 g/m.sup.2 can be seen in table 3. This corresponds to an application quantity of 1.3 g/m.sup.2 polymer (solids) and 2.7 g/m.sup.2 starch (solids) with the addition in the inventive examples of Barcote 20.

TABLE-US-00003 TABLE 3 Performance results of the paper with the surface coating compositions of examples 2-16 at a coatweight of 4 g/m.sup.2 Example CMT factor Increase.sup.1) Paper formulation Polymer [N .Math. m2/g] [%] 1 comparative 1 2.20 19 2b 2 n.i. 1 2.25 22 3b 3 1 2.43 31 4b 4 n.i. 2 2.25 22 5b 5 2 2.50 35 6b 6 n.i. 3 7b 7 3 8b 8 n.i. 4 2.24 22 9b 9 4 2.29 25 11b 11 n.i. 5 2.23 21 12b 12 5 2.43 32 13b 13 n.i. 6 2.11 19 14b 14 6 2.22 21 15b 15 n.i. 7 2.23 21 16b 16 7 2.40 31 .sup.1)Increase in % by comparison with the uncoated base paper

[0208] The results of coating with a coatweight of 6 g/m.sup.2 can be seen in table 4. This corresponds to an application quantity of 2 g/m.sup.2 polymer (solids) and 4 g/m.sup.2 starch (solids) with the addition in the inventive examples of Barcote 20.

TABLE-US-00004 TABLE 4 Performance results of the paper with the surface coating compositions of examples 2-16 at a coatweight of 6 g/m.sup.2 Example GMT factor Increase.sup.1) Paper formulation Polymer [N . m.sup.2/g] [%] 1 1 2.36 28 2c 2 n.i. 1 2.34 27 3c 3 1 2.50 37 4c 4 n.i. 2 2.31 26 5c 5 2 2.57 40 6c 6 n.i. 3 7c 7 3 8c 8 n.i. 4 2.22 21 9c 9 4 2.27 24 11c 11 n.i. 5 2.23 21 12c 12 5 2.62 42 13c 13 n.i. 6 2.23 21 14c 14 6 2.26 27 15c 15 n.i. 7 2.23 21 16c 16 7 2.42 32 .sup.1)Increase in % by comparison with the uncoated base paper