Aqueous binders

Abstract

A process for preparing an aqueous polymer dispersion, the process including forming a copolymer A from at least one α,β-monoethylenically unsaturated C.sub.3 to C.sub.6 monocarboxylic acid (monomers A1) and at least one other monoethylenically unsaturated compound (monomers A2); reacting the copolymer A with a metal compound M in an aqueous medium; and conducting free-radical polymerization of at least one ethylenically unsaturated compound (monomer P) in the presence of the copolymer A in an aqueous medium.

Claims

1. A process for preparing an aqueous polymer dispersion, the process comprising: forming a copolymer A from at least one α,β-monoethylenically unsaturated C.sub.3 to C.sub.6 monocarboxylic acid (monomers A1) and at least one other monoethylenically unsaturated compound (monomers A2); reacting the copolymer A with a metal compound M in an aqueous medium to modify copolymer A; and conducting free-radical polymerization of at least one ethylenically unsaturated compound (monomer P) in the presence of the modified copolymer A in an aqueous medium, wherein a) the copolymer A is formed in copolymerized form from ≥10% and ≤50% by weight of the monomers A1, and ≥50% and ≤90% by weight of the monomers A2, wherein amounts of monomers A1 and A2 add up to 100% by weight (total amount of monomers A) and wherein the copolymer A has a weight-average molecular weight in a range of ≥5000 and ≤20 000 g/mol, the monomers A1 and A2 are chosen such that the copolymer A has a glass transition temperature Tg measured according to DIN EN ISO 11357-2 (2013-09) in a range of ≥70° C. and wherein the metal compound M is selected from the group consisting of an oxide, a hydroxide, a carbonate or a hydrogen carbonate of magnesium, calcium or zinc, and used in combination with a base B that differs from the metal compound M, such that ≥50 mol % of carboxyl groups present in the copolymer A are neutralized by the base B, and an amount of the metal compound M is 0.01% to 5% by weight based on an amount of the copolymer A, b) the at least one monomer P is chosen such that the dispersion polymer P has a glass transition temperature Tg measured in accordance with DIN EN ISO 11357-2 (2013-09) in a range of ≥−30 and ≤90° C., and wherein c) a ratio of the amounts by weight of copolymer A to the at least one monomer P used to prepare the dispersion polymer P is in a range of ≥15 and ≤60 to ≥40 and ≤85.

2. The process according to claim 1, wherein the copolymer A comprises in copolymerized form as monomers A2: ≥25% and ≤90% by weight of at least one monoethylenically unsaturated aromatic compound (monomers A2-1) and ≥0% and ≤65% by weight of at least one other monoethylenically unsaturated compound that differs from monomers A1 and A2-1 (monomers A2-2), based on the total amount of monomers A, wherein amounts of monomers A2-1 and A2-2 add up to a minimum of 50% by weight and a maximum of 90% by weight of the total amount of monomers A.

3. The process according to claim 2, wherein the copolymer A comprises in copolymerized form acrylic acid and/or methacrylic acid as monomers A1, styrene and/or α-methylstyrene as monomers A2-1, and methyl methacrylate, n-butyl acrylate and/or 2-ethylhexyl acrylate as monomers A2-2.

4. The process for preparing an aqueous polymer dispersion according to claim 1, wherein the copolymer A comprises in copolymerized form: ≥10% and ≤45% by weight of acrylic acid, ≥25% and ≤65% by weight of styrene, ≥0% and ≤40% by weight of α-methylstyrene, and ≥0% and ≤65% by weight of methyl methacrylate, n-butyl acrylate and/or 2-ethylhexyl acrylate.

5. The process according to claim 1, wherein the base B is an organic or inorganic basic compound having a boiling point ≤110° C. at 1.013 bar (absolute).

6. The process according to claim 1, wherein the base B is ammonium hydroxide and/or an organic amine.

7. The process according to claim 1, wherein the metal compound M is calcium hydroxide and/or zinc oxide.

8. The process according to any claim 1, the process furtherer comprising neutralizing ≥70 mol-% of the carboxyl groups present in the copolymer A by the base B.

9. The process according to claim 1, wherein the amount of the metal compound M is 0.1% to 1.0% by weight based on the amount of copolymer A.

10. The process according to claim 1, wherein no dispersing aids (surfactants and/or protective colloids) are used.

11. An aqueous polymer dispersion obtained by the process according to claim 1.

12. A polymer powder obtained by drying an aqueous polymer dispersion according to claim 11.

13. An article comprising the aqueous polymer dispersion according to claim 11 wherein the article is selected from the group consisting of an adhesive, a sealant, a synthetic resin render, a paper coating slip, a fiber nonwoven, a flexible roof coating, a printing ink, a coating material, a textile or leather auxiliary, an impact modifier, a mineral binder and a plastic.

14. An aqueous formulation comprising: the aqueous polymer dispersion according to claim 11 and at least one pigment and/or filler.

15. The aqueous formulation according to claim 14 having a pigment volume concentration in a range of ≥1% and ≤60%.

Description

EXAMPLES

(1) The aqueous coating formulation was prepared using a copolymer A prepared in accordance with the procedure disclosed in U.S. Pat. No. 4,529,787 from a mixture of the following monomers A1 and A2: 10.8% by weight of acrylic acid, 27.8% by weight of styrene, 47.3% by weight of methyl methacrylate, and 14.1% by weight of n-butyl acrylate. The copolymer A obtained in the form of powder flakes had a weight-average molecular weight of 9150 g/mol, a glass transition temperature of 81° C., and an acid value of 77 mg KOH/g of polymer.

(2) The weight-average molecular weight thereof was determined by gel-permeation chromatography. The eluent used was a mixture of tetrahydrofuran and 0.1% by weight of trifluoroacetic acid. Separation was on a “PLgel MIXED-B” column from Agilent. Calibration was performed using narrowly distributed polystyrene standards from Polymer Laboratories having molecular weights from M=580 to M 6 870 000 g/mol and hexylbenzene (M=162 g/mol). Values outside this elution range were extrapolated. Detection was at 254 nm using the “DRI Agilent 1100 UV Agilent 1100 VWD” detector from Agilent.

(3) In the context of this document, the glass transition temperature Tg was generally determined in accordance with DIN EN ISO 11357-2 (2013-09) by differential scanning calorimetry (DSC) with a heating rate of 20 K/min using a DSC 02000 instrument from TA Instruments. The determination here was based on the midpoint temperatures.

(4) The acid value of the copolymer A was calculated taking into account the corresponding molar masses of the monomers and the theoretical composition of the polymer.

(5) Preparation of the Copolymer A Solutions

(6) Inventive Copolymer A Solution (Copolymer A Solution)

(7) A reaction vessel was initially charged at room temperature with 680.2 parts by weight of deionized water, 0.62 parts by weight of powdered calcium hydroxide, and 300.0 parts by weight of powdered copolymer A and then 23.44 parts by weight of a 25% by weight aqueous ammonia solution was metered in over a period of 10 minutes with stirring. The reaction mixture obtained was stirred at room temperature for a further 30 minutes, then heated to 80° C. with stirring and stirred at this temperature for 2 hours, resulting in the complete dissolution of the copolymer A. The copolymer A solution, which showed only slight turbidity, was then cooled to room temperature. The copolymer A solution obtained had a solids content of 29.7% by weight and a pH of 7.9.

(8) In the context of this document, the solids contents were generally determined by drying a defined amount of the aqueous polymer dispersion (about 0.8 g) to constant weight at a temperature of 130° C. using a Mettler Toledo HR73 moisture analyzer. Two measurements are in each case carried out and the average of these two measurements is reported.

(9) In the context of this document, the pH is generally determined at room temperature using a calibrated InPro® 325X pH electrode from Mettler-Toledo GmbH.

(10) Comparative Copolymer A Solution (Copolymer CA Solution)

(11) The copolymer CA solution was prepared in completely analogous manner to the preparation of the copolymer A solution, except that no calcium hydroxide was used. The copolymer CA solution obtained had a solids content of 29.9% by weight and a pH of 7.7.

(12) Preparation of Aqueous Polymer Dispersions

(13) Inventive Aqueous Polymer Dispersion P

(14) A polymerization vessel equipped with metering devices and temperature control was initially charged at room temperature under a nitrogen atmosphere with

(15) TABLE-US-00010 317.9 g deionized water 480.5 g copolymer solution
and heated to 80° C. with stirring. On reaching this temperature,

(16) TABLE-US-00011 30.9 g of a 7% by weight aqueous solution of ammonium peroxodisulfate
was added and the mixture was stirred for 5 minutes while maintaining this temperature. Feed 1 was then metered in continuously over a period of 120 minutes at a uniform addition rate. At the end of feed 1, feed 2 was added (rinsing the feed line with feed 2) and the resulting reaction mixture subjected to further polymerization for 60 minutes.
Feed 1 (Homogeneous Mixture of):

(17) TABLE-US-00012 216.2 g styrene  62.5 g n-butyl acrylate  57.7 g 2-ethylhexyl acrylate
Feed 2:

(18) TABLE-US-00013 25.00 g deionized water

(19) At the end of the further polymerization time, the aqueous polymer dispersion obtained was cooled to room temperature, 0.5 g of a 5% by weight aqueous solution of Acticid® MBS (a biocide from Thor GmbH), 14.8 g of deionized water, and 2.9 g of a 25% by weight aqueous ammonia solution were added, and the mixture was filtered through a 125 μm filter.

(20) The aqueous polymer dispersion obtained had a solids content of 40.2% by weight and a pH of 8.3. The weight-average particle diameter was 53 nm. Filtration through the 125 μm filter afforded an amount of coagulate corresponding to 0.01% by weight based on the solids content of the aqueous polymer dispersion obtained. No gel formation was observed in the reaction vessel either.

(21) In the context of this document, the weight-average particle diameter was generally determined in accordance with ISO 13321 using a Malvern High Performance Particle Sizer at 22° C. and a wavelength of 633 nm.

(22) Comparative Aqueous Polymer Dispersion CP1

(23) The comparative polymer dispersion CP1 was prepared in completely analogous manner to the preparation of the aqueous polymer dispersion P of the invention, except that the same amount of copolymer CA solution was used instead of the copolymer A solution.

(24) The resulting aqueous comparative polymer dispersion CP1 had a solids content of 40.2% by weight and a pH of 8.2. The weight-average particle diameter was 51 nm. Filtration through the 125 μm filter afforded an amount of coagulate corresponding to 0.01% by weight based on the solids content of the aqueous polymer dispersion obtained. No gel formation was observed in the reaction vessel either.

(25) Aqueous Comparative Polymer Dispersion CP2

(26) 100.0 g of a comparative polymer dispersion CP1 filtered through a 45 μm filter was mixed at room temperature in a glass vessel, with stirring, with 0.12 g of a 20% by weight aqueous calcium hydroxide slurry over a period of 10 minutes and stirring was continued for a further 30 minutes. The resulting comparative polymer dispersion CP2 was then filtered through a 45 μm filter, affording 0.6 g of coagulate (corresponding to 1.5% by weight based on the total solids content). The formation of coagulate or gel particles was also observed on the stirrer and on the surface of the glass vessel.

(27) Preparation and Performance Testing of the Varnish Formulations

(28) For the preparation of the varnish formulations, the aqueous polymer dispersion P and the comparative dispersions CP1 and CP2 were adjusted to a solids content of 39.0% by weight through addition of deionized water to the stirred dispersions.

(29) In each case, 150 g of the aqueous (comparative) polymer dispersions thus obtained was then initially charged at room temperature. To the initially charged aqueous (comparative) polymer dispersions were then in each case successively added, with stirring, 0.7 g of FoamStar® SI 2180 from BASF SE as defoamer and 0.4 g of Rheovis® PU 1250 from BASF SE as thickener.

(30) To these mixtures was then in each case added, with stirring, 12.2 g of ethylene glycol butyl ether as a film-forming aid. Where necessary, the respective varnish formulations were then adjusted to a pH of 8.0 to 8.2 with a 10% by weight aqueous ammonia solution. The varnish formulations thus obtained were stirred for a further 5 minutes. Before undergoing the performance tests, the varnish formulations thus obtained were left to stand for at least 1 hour. The aqueous coating formulations thus obtained from the aqueous polymer dispersion P and from the comparative polymer dispersions CP1 and CP2 are referred to hereinbelow as varnishes VP (inventive) and CVP1 and CVP2 (non-inventive).

(31) Performance Tests:

(32) Testing of chemical resistances and resistance to staining was carried out on test boards that had been coated with the varnishes prepared. For this purpose, beech test boards (veneered) were coated with the respective varnish VP and also CVP1 and CVP2 using a bar applicator in a layer thickness of 150 μm (wet). The test boards were then dried under standard climatic conditions (23° C. and 50% relative humidity) for 30 days. Testing of chemical resistances and resistance to staining was carried out in accordance with DIN 68861-1. This was done by placing filter papers (diameter: 3 cm; basis weight: 500 g/m.sup.2) soaked in the test liquids on the surface to be tested. To suppress evaporation, small plastic beakers having an internal diameter of 3.5 cm and a height of 1.5 cm were placed over the filter papers. The test liquids used were acetone, blackcurrant juice, and deionized water. The filter papers soaked in deionized water, blackcurrant juice, and acetone were then applied to the varnished test boards at room temperature. The exposure time of the filter paper soaked in acetone was 10 seconds, whereas that of the filter paper soaked in deionized water and in blackcurrant juice was 16 hours. For each varnish, 3 filter papers soaked in the different test liquids were in each case used. The change in the respective varnish was visually assessed after removing the soaked filter paper. The visual assessment was based on the following assessment/grading system:

(33) TABLE-US-00014 No visible changes in gloss and color; Grade 5 the structure of the test area is un- changed: Changes in gloss and color just about Grade 4 detectable; the structure of the test area is unchanged: Slight changes in gloss and color; the Grade 3 structure of the test area is unchanged: Significant changes in gloss and color; Grade 2 the structure of the test area is un- changed: Significant changes in gloss and color; Grade 1 the structure of the test area is changed: Significant changes in gloss and color; Grade 0 the structure of the test area is signifi- cantly changed:

(34) The results obtained with the respective varnishes VP, CVP1, and CVP2 are summarized in Table 1 below.

(35) In a further experiment, the respective varnishes VP, CVP1, and CVP2 were applied with a bar applicator to a glass plate in a layer thickness of 150 μm (wet) and dried for 48 hours at room temperature. The number of defects, termed “specks”, on an area of 9 cm.sup.2 was then counted visually (against a white background). For this, three independent assessments were in each case carried out. The corresponding results—obtained as the mean of the three assessments—are also shown in Table 1. The lower the number of specks, the better the assessment of a varnish.

(36) TABLE-US-00015 TABLE 1 Results of the performance tests Staining Number of Varnish Water Blackcurrant juice Acetone specks VP 4 4 2  17 CVP1 3 3 0  11 CVP2 3 2 2 150

(37) The results show clearly that the varnish formulation VP prepared from the aqueous polymer dispersion P of the invention has good to very good resistance to staining and a low number of specks. By contrast, although the calcium hydroxide-free varnish formulation has good resistance to staining by water and blackcurrant juice and a low number of specks, resistance to staining by acetone declines sharply. The coating formulation CVP2, in which the calcium ions are added after preparation of the aqueous comparative polymer dispersion CP1, also shows good or acceptable resistance to staining by water, blackcurrant juice, and acetone, but the number of specks is not acceptable. Moreover, coagulate formation caused by addition of calcium hydroxide to the aqueous polymer dispersion after the polymerization is not acceptable.