AQUEOUS COATING COMPOSITIONS

Abstract

The invention relates to an aqueous pigmented coating composition containing at least one polymer P1 in the form of an aqueous polymer dispersion, and at least one water-soluble polymer P2 that is composed of ethylenically unsaturated monomers M and contains at least 30% by weight of polymerized N-vinylpyrrolidone in relation to the total amount of monomers M. The invention further relates to the use of the aqueous pigmented coating compositions of the invention for coating tannin-containing substrates, a coating method, and the coated substrates.

Claims

1. An aqueous, pigment-containing coating composition, comprising: a) at least one polymer P1 in the form of an aqueous polymer dispersion; and b) at least one water-soluble polymer P2 which comprises an ethylenically unsaturated monomer M and which comprises in copolymerized form at least 30 wt %, based on a total amount of the monomers M, of N-vinylpyrrolidone.

2. The aqueous, pigment-containing coating composition according to claim 1, wherein the water-soluble polymer P2 is selected from the group consisting of homopolymers of N-vinylpyrrolidone.

3. The aqueous, pigment-containing coating composition according to claim 1, wherein the water-soluble polymer P2 is selected from the group consisting of copolymers which comprise in copolymerized form a) 30 to 90 wt % of N-vinylpyrrolidone as monomer A, b) 10 to 70 wt % of at least one neutral, monoethylenically unsaturated monomer as monomer B, and c) optionally, 0 to 20 wt % of a cationic monomer as monomer C, the values in wt % being based on the total mass of the monomers M, and the monomers A and B making up at least 80 wt %, based on the total mass of the monomers M.

4. The aqueous, pigment-containing composition according to claim 3, wherein the monomers B are selected from the group consisting of b1) vinyl esters of saturated C.sub.2-C.sub.12 monocarboxylic acids, b2) primary amides of monoethylenically unsaturated C.sub.3-C.sub.6 monocarboxylic acids b3) N-vinyl lactams having 7 to 10C atoms, b4) vinyl-substituted nitrogen heteroaromatics, b5) N—C.sub.1-C.sub.4 alkyl amides and N,N-di-C.sub.1-C.sub.4 alkyl amides of monoethylenically unsaturated C.sub.3-C.sub.6 monocarboxylic acids, b6) N-vinyl amides of saturated C.sub.1-C.sub.6 monocarboxylic acids, b7) C.sub.1-C.sub.3 alkyl acrylates and methyl methacrylate; and mixtures thereof.

5. The aqueous, pigment-containing coating composition according to claim 3, the polymer P2 being selected from the group consisting of copolymers of N-vinylpyrrolidone with N-vinyl acetate, copolymers of N-vinylpyrrolidone with methacrylamide, terpolymers of N-vinylpyrrolidone with N-vinyl acetate and vinyl ester of a branched aliphatic monocarboxylic acid having 9C atoms, terpolymers of N-vinylpyrrolidone with methacrylamide and N-vinylcaprolactam, terpolymers of N-vinylpyrrolidone with methacrylamide and N-vinylimidazole, terpolymers of N-vinylpyrrolidone with methacrylamide and quaternized N-vinylimidazole, terpolymers of N-vinylpyrrolidone with N-vinylcaprolactam and N-vinylimidazole, quaterpolymers of N-vinylpyrrolidone with methacrylamide, N-vinylimidazole, and quaternized N-vinylimidazole, quaterpolymers of N-vinylpyrrolidone with N-vinylcaprolactam, N-vinylimidazole and quaternized N-vinylimidazole, and mixtures thereof.

6. The aqueous, pigment-containing coating composition according to claim 1, comprising the water-soluble polymer P2 in an amount of 0 5 to 10 wt %, based on the polymer P1.

7. The aqueous, pigment-containing coating composition according to claim 1, wherein the water-soluble polymer has a number-average molecular weight M.sub.n of 5000 to 200 000 g/mol, determined by means of gel permeation chromatography (GPC), or a K value in the range from 10 to 100.

8. The aqueous, pigment-containing coating composition according to claim 1, wherein the polymer P1 has a glass transition temperature Tg, determined by DSC to ISO 11357-2, in the range from −30 to +60° C.

9. The aqueous, pigment-containing coating composition according to claim 1, wherein the polymer P1 comprises i) 90 to 99.9 wt % of at least one monomer M1 which has a water-solubility of not more than 40 g/l at 20° C. and 1 bar; and ii) 0.1 to 10 wt % of at least one monomer M2 which has a water-solubility of at least 50 g/l at 20° C. and 1 bar.

10. The aqueous, pigment-containing composition according to claim 1, in the form of a formulation containing white pigment.

11. A method for coating a substrate containing tannin, said method comprising: coating said surface with a pigment-containing coating composition according to claim 1.

12. A method for improving a tannin blocking effect of an aqueous coating composition, said method comprising: adding to said aqueous coating composition a water-soluble polymer which comprises an ethylenically unsaturated monomer M and which comprises in copolymerized form at least 30 wt %, based on the monomer M, of N-vinylpyrrolidone.

13. A method for coating a substrate containing tannin, comprising: first coating the substrate with a pigment-containing coating composition according to claim 1 and subsequently, subjecting the aqueous coating to a drying step.

14. The method according to claim 13, wherein the amount of coating formulation is selected such that the amount of water-soluble polymer is in the range from 0.001 to 100 g/m.sup.2 of substrate.

15. A coated substrate containing tannin, obtainable by a method according to claim 13.

Description

EXAMPLES

[0147] 1. Analysis

[0148] The solids content was determined by drying a defined amount of the aqueous polymer dispersion (approximately 2 g) to constant weight in a drying cabinet (approximately 2 hours) in an aluminum crucible having an internal diameter of approximately 5 cm, at 120° C. Two separate measurements were conducted. The value reported in the example represents the average value of the two results.

[0149] The average particle diameter of the polymer particles was determined by dynamic light scattering of an aqueous polymer dispersion diluted with deionized water to 0.005 to 0.01 wt %, at 23° C., by means of a High Performance Particle Sizer (HPPS) from Malvern Instruments, England. The figure reported is the average diameter of the cumulant evaluation (cumulant z.sub.average) of the measured autocorrelation function (ISO standard 13321).

[0150] The glass transition temperature was determined by the DSC method (differential scanning calorimetry, 20 K/min, midpoint measurement, DIN 53765) by means of a DSC 822 instrument (series TA 8000) from Mettler-Toledo.

[0151] 2. Ingredients:

[0152] 2.1. Preparation of an Aqueous Polymer Dispersion (Polymer P1)

[0153] A reaction vessel equipped with stirrer, thermometer, reflux condenser, and feed vessels was charged at room temperature under a nitrogen atmosphere with a mixture of 2900 g of deionized water, 24 g of a 15 wt % strength aqueous solution of sodium lauryl sulfate, 150 g of a 20 wt % strength aqueous solution of a C.sub.16C.sub.18 fatty alcohol polyethoxylate, 37.2 g of a 6 wt % strength aqueous solution of sodium bicarbonate, and 314 g of feed 1.

[0154] Feed 1 consisted of 1945 g of deionized water, 140 g of a 15 wt % strength aqueous solution of sodium lauryl sulfate, 113 g of a 32 wt % strength aqueous solution of a C.sub.12C.sub.14 fatty alcohol polyethoxysulfate sodium salt (Disponil FES 77; commercial product from Cognis), 150 g of a 20 wt % strength aqueous solution of a C.sub.16C.sub.18 fatty alcohol polyethoxylate, 67 g of acrylic acid, 170 g of a 50 wt % strength aqueous solution of acrylamide, 3060 g of n-butyl acrylate, and 2370 g of methyl methacrylate in homogeneous emulsion.

[0155] The initial charge was heated to 90° C. with stirring. Subsequently, with this temperature maintained, 32 g of a 7 wt % strength aqueous solution of sodium peroxodisulfate were added and the resulting mixture was stirred for 5 minutes. Thereafter, beginning simultaneously, the remainder of feed 1 and 185 g of a 7 wt % strength aqueous solution of sodium peroxodisulfate were metered in continuously over the course of 3 hours at constant volume flow rates, via separate feed lines.

[0156] After the end of the feeds, postpolymerization took place for 15 minutes, after which the aqueous polymer dispersion obtained was admixed with 40 g of a 25 wt % strength aqueous solution of ammonia. After the aqueous polymer dispersion obtained had been cooled to 85° C., it was admixed with, beginning simultaneously, 76 g of a 10 wt % strength aqueous solution of tert-butyl hydroperoxide and 101 g of a 13.1 wt % strength aqueous solution of acetone bisulfite (1:1 adduct of acetone and sodium bisulfite) over the course of 1 hour, continuously, with constant volume flow rates. After the end of the additions, the aqueous polymer dispersion was further admixed with 80 g of deionized water and 36 g of Acticid® MBS (commercial product from Thor Chemie GmbH). Subsequently the aqueous polymer dispersion was cooled to room temperature and filtered through a 125 μm filter.

[0157] The aqueous polymer dispersion obtained had a solids content of 50.2 wt % and a glass transition temperature of 17° C. The average particle diameter was 115 nm.

[0158] 2.2 Polymers P2

[0159] Polymer P2.1: terpolymer of 40 wt % N-vinylpyrrolidone, 50 wt % N-vinylcaprolactam, and 10 wt % N-vinyl-3-methylimidazolium chloride.

[0160] Polymer P2.2: quaterpolymer of 55 wt % N-vinylpyrrolidone, 29 wt % methacrylamide, 10 wt % N-vinylimidazole, and 6 wt % N-vinyl-3-methylimidazolium methosulfate.

[0161] Polymer P2.3: terpolymer of 65 wt % N-vinylpyrrolidone, 30 wt % methacrylamide, and 5 wt % N-vinylimidazole.

[0162] Polymer P2.4: copolymer of 61 wt % N-vinylpyrrolidone, 39 wt % vinyl acetate, having a K value, determined on a 1 wt % strength aqueous solution, of 24.9, prepared as per example 1 of EP 418721.

[0163] Polymer P2.5: terpolymer of 60 wt % N-vinylpyrrolidone, 37 wt % vinyl acetate, and 3 wt % VeoVA 9* having a K value, determined on a 1 wt % strength aqueous solution, of 63, prepared as per example 1 of DE 19950229.

[0164] *Vinyl ester of a Versatic acid with 9C atoms (CAS 54423-67-5)

[0165] Polymer P2.6: commercially customary homopolymer of N-vinylpyrrolidone, with a K value of 30, e.g., Kollidon 30.

[0166] 3. Preparation of the Modified Aqueous Polymer Dispersions

[0167] The compositions of the invention were prepared by adding the respective polymer P2 to a portion of the aqueous polymer dispersion prepared under 2.1, at room temperature, with stirring. The amounts of the polymers P2 here were calculated so as to give the values indicated in table 1 below. The figure reported is the amount of polymer P2 in parts by weight, based on 100 parts by weight of polymer P1 in the aqueous polymer dispersion used (solid/solid). The corresponding designation of the modified aqueous polymer dispersion obtained is likewise reported in table 1.

TABLE-US-00001 TABLE 1 Preparation of the aqueous polymer dispersions modified with the polymers P2 Amount [per 100 parts by weight solid of the Designation of the modified Polymer P2: aqueous polymer dispersion] aqueous polymer dispersion — 0 dispersion D0 P2.1 3.0 dispersion D1 P2.2 3.0 dispersion D2 P2.3 3.0 dispersion D3 P2.4 3.0 dispersion D4 P2.5 3.0 dispersion D5 P2.6 3.0 dispersion D6

[0168] 4. Production of a Paint Formulation

[0169] In order to produce the corresponding paint formulations, the components listed in tables 2 and 3 below were mixed homogeneously in the stated amount and in the stated order, at room temperature, using a toothed disk stirrer, to form color pastes.

TABLE-US-00002 TABLE 2 Components of color paste F1 Constituent Parts by weight [g] Deionized water 102.5 Thickener.sup.1) 8.2 Pigment dispersant.sup.2) 2.0 Dispersant.sup.3) 4.1 Biocide.sup.4) 2.0 Defoamer.sup.5) 5.1 Film-forming assistant.sup.6) 20.5 Pigment.sup.7) 204.9 Filler.sup.8) 82.0 Filler.sup.9) 30.7 Solvent.sup.10) 15.4 Thickener.sup.11) 4.6 .sup.1)Coapur ® XS 73 from Omya GmbH, Germany .sup.2)Pigmentverteiler ® MD 20 from BASF SE, Germany .sup.3)25 wt % strength aqueous solution of sodium polyphosphate from Sigma Aldrich Chemie GmbH, Germany .sup.4)Parmetol ® A 26 from Schülke & Mayr GmbH, Germany .sup.5)Byk ® 024 from Byk-Chemie GmbH, Germany .sup.6)Lusolvan ® PP from BASF SE, Germany .sup.7)Titanium dioxide; Kronos ® 2056 from Kronos Titan GmbH, Germany .sup.8)Calcium carbonate; Omyacarb ® 5 GU from Omya GmbH, Germany .sup.9)Talc; Finntalc ® M 30 SL from Mondo Minerals, Netherlands .sup.10)Butyl diglycol from BASF SE, Germany .sup.11)Collacral ® LR 8990 from BASF SE, Germany

TABLE-US-00003 TABLE 3 Components of color paste F2 Constituent Parts by weight [g] Deionized water 119.5 Solvent.sup.12) 33.5 Dispersant.sup.13) 13.7 Biocide.sup.14) 1.0 Emulsifier.sup.15) 1.5 Thickener 1 .sup.16) 6.4 Thickener 2 .sup.17) 7.0 Defoamer.sup.18) 3.4 Pigment.sup.19) 228.8 Filler.sup.20) 81.6 Thickener 3 .sup.21) 38.3 Film-forming assistant.sup.22) 6.7 .sup.12)Propylene Glycol from BASF SE, Germany .sup.13)Sokalan ® CP9 from BASF SE, Germany .sup.14)Acticide ® MBS from Thor, Germany .sup.15)Lutensol ® XL 80 from BASF SE, Germany .sup.16) Collacral ® LR 8990 from BASF SE, Germany .sup.17) Collacral ® LR 8989 from BASF SE, Germany .sup.18)Che Coat DF 6682 from C. H. Erbslöh, Germany .sup.19)Tiona ®595 from Millenium Chemicals (Lyondell Company), Belgium .sup.20)Omyacarb ® 5 GU from Omya GmbH, Germany .sup.21) Natrosol plus ®, 2% strength from Hercules, Belgium .sup.22)Texanol ® from Krahn-Chemie GmbH, Germany

[0170] The color pastes, prepared freshly in accordance with the procedure described above, were filtered through a 125 μm filter, with reduced pressure applied, in order to remove air bubbles and larger pigment agglomerates. After that, the color pastes F1 were admixed homogeneously with 438.5 g of the dispersions and 79.4 g of deionized water, and the color pastes F2 with 393.5 g of the dispersions and 64.9 g of deionized water. The paint formulations obtained accordingly were then stored at rest for one day at room temperature.

[0171] 5. Performance Investigations

[0172] The performance investigations were carried out with untreated merbau, cedar, and oak. For this purpose, boards of the various woods were used, with dimensions of 150×50×5 mm, which had been freed from adhering dust using a dry cotton cloth. In order to minimize deviations and ensure compatibility, the test series were conducted on one board in each case. The procedure here was that first of all areas on the respective board of 130×40 mm were coated uniformly with 0.46 g of one each of the formulations, and the coated boards were then dried in a conditioned chamber at 23° C. and 50% relative humidity for two hours (coat 1). After that 0.32 g of the respective formulation was applied uniformly to each of these coatings over an area of 90×40 mm, with drying as for the first coat (coat 2). Thereafter, 0.18 g of the respective formulation was applied uniformly to this second coat over an area of 50×40 mm (coat 3), after which the correspondingly coated boards were stored for 24 hours in a conditioned chamber at 23° C. and 50% relative humidity. Since each of the coating operations was started at one side edge, congruently, the respective paint films had a 40×40 mm area which had been coated only once (coat 1), a 40×40 mm area which had been coated twice (coat 1 plus coat 2), and a 50×40 mm area which had been coated three times (coat 1 plus coat 2 plus coat 3). As a reference, each of the corresponding paint formulations was applied to grease-free glass plates and dried.

[0173] Discoloration was measured by two different methods. With method 1, the extent of discoloration resulting from the application of each of the aqueous paint formulations and its drying was ascertained (“early tannin blocking”). Method 2 measured the extent of discoloration resulting from the effect of water on the respective dried paint film (“late tannin blocking”).

[0174] Method 1

[0175] Using a photospectrometer (Minolta CM-508i spectrometer), at least two points on coat 3 of the respective paint films on the wooden boards and glass plates were used for measuring the so-called L, a and b values, and subsequently the respective average was formed. After that, the differences between the averaged L, a and b values of the respective paint films on the wooden boards and glass plates were ascertained (ΔL, Δa and Δb). One measure of the respective deviation in color is the ΔE value, which was determined as follows:

ΔE=√{square root over ((ΔL).sup.2+(Δa).sup.2+(Δb).sup.2)}

[0176] The smaller the ΔE value, the smaller the deviation in color (and hence the less the “bleeding” of the wood in question). This means that the lower the ΔE value of each of the paint films, the less colored substances have been leached from the wood in question in the course of the application and drying of the respective paint formulation. The results obtained from the various measurement series are listed in table 4.

[0177] Note: the so-called CIE-Lab color space is formed from the lightness axis L, the red/green axis a, and the yellow/blue axis b. Corresponding color deviations are indicated by the ΔE value (as defined above).

[0178] Method 2

[0179] In each case, one drop of deionized water was applied to coat 3 of each of the paint films on the wooden boards, and the paint films thus treated were dried in a conditioned chamber for 12 hours at 23° C. and 50% relative humidity. After that, the locations with the dried water drops were evaluated in accordance with the following scale of ratings:

[0180] Rating Evaluation [0181] 0 the full ring of water is clearly apparent and dark brown in color [0182] 1 the full ring of water is clearly apparent and light brown in color [0183] 2 the outer ring of water can be seen [0184] 3 parts of the outer ring of water can be seen [0185] 4 the ring of water is still perceptible, but not colored [0186] 5 it is impossible to tell where the drop of water was

[0187] At least two measurements were carried out on each paint film. The values reported in table 3 represent the averages of these assessments.

TABLE-US-00004 TABLE 4 Results of the performance investigations Measurement Modified polymer Color series dispersion paste ΔE.sup.1) Rating.sup.2) 1 (merbau) D0 F1 1.318 2 D1 F1 0.788 2 D2 F1 0.783 2 D3 F1 1.120 2 D4 F1 0.680 3 D5 F1 0.994 2 D6 F1 0.539 2 2 (cedar) D0 F1 1.058 2 D2 F1 0.861 2 D3 F1 0.579 2 D4 F1 0.659 2 D5 F1 0.573 2 D6 F1 0.441 2 3 (merbau) D0 F2 1.775 2 D4 F2 0.801 3 4 (cedar) D0 F2 2.128 1 D4 F2 1.676 2

[0188] The results described above have shown that the addition of polymers P2 in polymer dispersions leads to an improved tannin blocking effect (especially “early tannin blocking”) of the resulting coatings.