Process for preparing an aqueous polymer dispersion having high chemical resistance

Abstract

A process for producing aqueous polymer dispersions and the use thereof as binder for coatings having high solvent stability and a low tendency to soiling.

Claims

1. A process for producing an aqueous polymer dispersion by free-radically initiated aqueous emulsion polymerization, the process comprising: free-radically polymerizing, in an aqueous medium, in the presence of at least one polymer 1, 5.0% by weight of monomer A2, which is at least one ,-monoethylenically unsaturated C.sub.3 to C.sub.6 mono- or dicarboxylic acid, and 95% and 100% by weight of monomer B2, which is at least one ethylenically unsaturated compound other than the monomer A2, where the amounts of monomers A2 and B2 add up to 100% by weight, thereby obtaining polymer 2, wherein the monomers A2 and B2 are chosen such that the polymer 2 obtained therefrom has a Hansch parameter 2.80 and a glass transition temperature 20 C., the at least one polymer 1 comprises, in copolymerized form, 3.0% and 35% by weight of monomer A1, which is at least one ,-monoethylenically unsaturated C.sub.3 to C.sub.6 mono- or dicarboxylic acid, and 65% and 97.0% by weight of monomer B1, which is at least one ethylenically unsaturated compound other than the monomers A1, where the amounts of monomers A1 and B1 add up to 100% by weight, the monomers A1 and B1 are chosen such that the at least one polymer 1 has a Hansch parameter >1.35 to 2.00, and a weight ratio of the at least one polymer 1 to a total amounts of monomers A2 and B2 is in the range of 15:85 to 60:40.

2. The process according to claim 1, wherein the monomers A1 and B1 are chosen such that the at least one polymer 1 has a Hansch parameter in the range of 1.40 to 2.00.

3. The process according to claim 1, wherein the monomers A2 and B2 are chosen such that the polymer 2 obtained therefrom has a Hansch parameter in the range of 2.80 to 3.20.

4. The process according to claim 1, wherein the at least one polymer 1 comprises, in copolymerized form, 4.0% and 25% by weight of at least one monomer A1, and 75% and 96.0% by weight of at least one monomer B1.

5. The process according to claim 1, wherein the monomers A2 and B2 are chosen such that the polymer 2 obtained has a glass transition temperature of 20 C. to 60 C.

6. The process according to claim 1, wherein no monomers A2 are used.

7. The process according to claim 1, wherein the at least one polymer 1 comprises, in copolymerized form, acrylic acid and/or methacrylic acid as the monomers A1, and styrene, -methylstyrene, methyl methacrylate, n-butyl acrylate and/or 2-ethylhexyl acrylate as the monomers B1.

8. The process according to claim 1, wherein the monomers B2 are styrene, a-methylstyrene, methyl methacrylate, n-butyl acrylate, ethylhexyl acrylate, or a combination thereof.

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

10. A polymer powder, obtained by drying the aqueous polymer dispersion according to claim 9.

11. An aqueous formulation, comprising the aqueous polymer dispersion according to claim 9 and/or a polymer powder obtained by drying the aqueous polymer dispersion and at least one pigment.

12. The aqueous formulation according to claim 11, having a pigment volume concentration in the range of 1% to 60%.

13. The aqueous formulation according to claim 11, comprising titanium dioxide as the at least one pigment.

14. A method for producing a coating, the method comprising: preparing the coating using the aqueous formulation according to claim 11.

Description

EXAMPLES

1 Preparation of Aqueous Polymer 1 Solutions

(1) The inventive acid-rich polymers P1-A to P1-C and the noninventive acid-rich polymers P1-V were prepared analogously to the procedure described in U.S. Pat. No. 4,529,787.

(2) The monomer compositions of the polymers P1 and the characterization thereof are listed in table 1.

(3) TABLE-US-00004 TABLE 1 Monomer composition, molar mass, Hansch parameter and Tg of the polymers P1 Methyl alpha- Acrylic meth- n-Butyl Ethylhexyl Molar Styrene Methylstyrene acid [% by acrylate acrylate acrylate mass Mw Hansch Tg Polymer [% by wt.] [% by wt.] wt.] [% by wt.] [% by wt.] [% by wt.] [g/mol] parameter [ C.] P1-A 27.5 0 10.6 47.9 14.0 0 9000 1.46 81 P1-B 31.7 37.1 31.2 0 0 0 8500 1.43 127 P1-C 15.4 39.0 20.2 0 25.4 0 7000 1.86 72 P1-V 22.7 35.2 36.2 0 0 5.9 9200 1.23 117

(4) Polymers P1-A to P1-V were used to prepare ammoniacal aqueous solutions as follows: For this purpose, at room temperature (20 to 25 C.), a stirred vessel was initially charged with 700 g of deionized water, and 300 g of the respective solid polymer P1 in powder form were added in portions. Subsequently, the amounts of 25% by weight aqueous ammonia solution specified in table 2 were added gradually to the polymer suspension and the aqueous polymer mixture was stirred at room temperature for 30 min. Subsequently, the aqueous polymer mixtures thus obtained were heated to 80 C. and stirred at this temperature for 2 hours. After cooling to room temperature and filtration through a 125 m filter, slightly cloudy to clear solutions were obtained. The aqueous polymer solutions obtained are called PL1-A to PL1-C and PL1-V.

(5) TABLE-US-00005 TABLE 2 Preparation of the polymer solutions Amount of 25% by weight aqueous ammonia solution Solids content Polymer added [g] [% by wt.] Name P1-A 18.8 29.6 PL1-A P1-B 65.2 29.8 PL1-B P1-C 37.1 29.7 PL1-C P1-V 73.5 29.5 PL1-V

2 Preparation of the Aqueous Polymer Dispersions

Aqueous Polymer Dispersion 1 (B1)

(6) A glass polymerization vessel equipped with metering devices and closed-loop temperature control was initially charged at room temperature under a nitrogen atmosphere with

(7) TABLE-US-00006 357.1 g deionized water 533.9 g polymer solution PL1-A
and heated to 80 C. while stirring. On attainment of this temperature, 34.0 g a 7% by weight aqueous solution of sodium peroxodisulfate
were added within one minute and then the mixture was stirred while maintaining this temperature for 5 minutes. Thereafter, feed 1 was metered in continuously at constant metering rate over the course of 120 minutes. After feed 1 had ended, feed 2 was added all at once, then polymerization was continued for 60 minutes.

Feed 1 (Homogeneous Monomer Mixture of)

(8) TABLE-US-00007 269.1 g styrene 104.6 g 2-ethylhexyl acrylate

Feed 2

(9) TABLE-US-00008 25.0 g deionized water

(10) After the further polymerization time had ended, the aqueous polymer dispersion obtained was cooled down to room temperature, 0.6 g of a 5% by weight aqueous solution of Acticid MBS (a biocide from Thor GmbH) and 16.4 g of deionized water were added, and the mixture was filtered through a 125 m filter.

(11) The aqueous polymer dispersion 1 obtained had a solids content of 40.0% by weight and a pH of 7.3. The weight-average particle diameter was 58 nm. The Hansch parameter of polymer 2 formed from feed 1 was calculated as 3.23. The glass transition temperature of polymer 2 was determined as 39 C.

(12) 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 conducted in each case, and the average of these two measurements is reported.

(13) The weight-average particle sizes were generally determined to ISO 13321 with a High Performance Particle Sizer from Malvern at 22 C. and a wavelength of 633 nm.

(14) The pH was generally determined by means of a calibrated InPro 325X pH electrode from Mettler-Toledo GmbH.

(15) The glass transition temperatures were generally determined to DIN EN ISO 11357-2 (2013-09) via differential scanning calorimetry (DSC) with a heating rate of 20 K/min by means of a DSC Q2000 from TA Instruments. The midpoint temperatures were used here for the determination.

Aqueous Polymer Dispersion 2 (B2)

(16) The aqueous polymer dispersion 2 was prepared entirely analogously to the preparation of the aqueous polymer dispersion 1, except that the following initial charge, amount of sodium peroxodisulfate, feeds 1 and 2, biocide solution and deionized water were used:

Initial Charge

(17) TABLE-US-00009 143.2 g deionized water 571.7 g polymer solution PL1-A

(18) Amount of 7% by weight aqueous solution of sodium peroxodisulfate: 29.0 g

Feed 1 (Homogeneous Mixture of)

(19) TABLE-US-00010 203.8 g styrene 57.3 g 2-ethylhexyl acrylate 57.3 g n-butyl acrylate

Feed 2

(20) TABLE-US-00011 22.9 g deionized water

(21) Amount of 5% by weight aqueous solution of Acticid MBS: 0.6 g

(22) Amount of deionized water: 15.1 g

(23) The aqueous polymer dispersion 2 obtained had a solids content of 44.6% by weight and a pH of 7.4. The weight-average particle diameter was 80 nm. The Hansch parameter of polymer 2 formed from feed 1 was calculated as 2.98. The glass transition temperature of polymer 2 was determined as 29 C.

Aqueous Polymer Dispersion 3 (B3)

(24) The aqueous polymer dispersion 3 was prepared entirely analogously to the preparation of the aqueous polymer dispersion 1, except that the following initial charge, amount of sodium peroxodisulfate, feeds 1 and 2, biocide solution and deionized water were used:

Initial Charge

(25) TABLE-US-00012 87.9 g deionized water 653.3 g polymer solution PL1-A

(26) Amount of 7% by weight aqueous solution of sodium peroxodisulfate: 26.7 g

Feed 1 (Homogeneous Mixture of)

(27) TABLE-US-00013 188.2 g styrene 52.9 g 2-ethylhexyl acrylate 52.9 g n-butyl acrylate

Feed 2

(28) TABLE-US-00014 22.9 g deionized water

(29) Amount of 5% by weight aqueous solution of Acticid MBS: 0.6 g

(30) Amount of deionized water: 15.1 g

(31) The aqueous polymer dispersion 3 obtained had a solids content of 44.8% by weight and a pH of 7.6. The weight-average particle diameter was 83 nm. The Hansch parameter of polymer 2 formed from feed 1 was calculated as 2.98. The glass transition temperature of polymer 2 was determined as 29 C.

Aqueous Polymer Dispersion 4 (B4)

(32) The aqueous polymer dispersion 3 was prepared entirely analogously to the preparation of the aqueous polymer dispersion 1, except that the following initial charge, amount of sodium peroxodisulfate, feeds 1 and 2, biocide solution and deionized water were used:

Initial Charge

(33) TABLE-US-00015 226.0 g deionized water 641.0 g polymer solution PL1-C

(34) Amount of 7% by weight aqueous solution of sodium peroxodisulfate: 54.0 g

Feed 1 (Homogeneous Mixture of)

(35) TABLE-US-00016 239.2 g styrene 67.3 g 2-ethylhexyl acrylate 67.3 g n-butyl acrylate

Feed 2

(36) TABLE-US-00017 25.0 g deionized water

(37) Amount of 5% by weight aqueous solution of Acticid MBS: 0.6 g

(38) Amount of deionized water: 16.4 g

(39) The aqueous polymer dispersion 3 obtained had a solids content of 39.5% by weight and a pH of 7.7. The weight-average particle diameter was 70 nm. The Hansch parameter of polymer 2 formed from feed 1 was calculated as 2.98. The glass transition temperature of polymer 2 was determined as 29 C.

Aqueous Polymer Dispersion 5 (B5)

(40) The aqueous polymer dispersion 5 was prepared entirely analogously to the preparation of the aqueous polymer dispersion 1, except that the following initial charge, amount of sodium peroxodisulfate, feeds 1 and 2, biocide solution and deionized water were used:

Initial Charge

(41) TABLE-US-00018 216.3 g deionized water 533.9 g polymer solution PL1-A

(42) Amount of 7% by weight aqueous solution of sodium peroxodisulfate: 34.0 g

Feed 1 (Homogeneous Mixture of)

(43) TABLE-US-00019 263.8 g styrene 52.3 g 2-ethylhexyl acrylate 52.3 g n-butyl acrylate 5.3 g hexane-1,6-diol diacrylate

Feed 2

(44) TABLE-US-00020 25.0 g deionized water

(45) Amount of 5% by weight aqueous solution of Acticid MBS: 0.6 g

(46) Amount of deionized water: 16.4 g

(47) The aqueous polymer dispersion 5 obtained had a solids content of 44.4% by weight and a pH of 7.6. The weight-average particle diameter was 77 nm. The Hansch parameter of polymer 2 formed from feed 1 was calculated as 2.98. The glass transition temperature of polymer 2 was determined as 42 C.

Aqueous Polymer Dispersion 6 (B6)

(48) The aqueous polymer dispersion 6 was prepared entirely analogously to the preparation of the aqueous polymer dispersion 1, except that the following initial charge, amount of sodium peroxodisulfate, feeds 1 and 2, biocide solution and deionized water were used:

Initial Charge

(49) TABLE-US-00021 325.1 g deionized water 480.5 g polymer solution PL1-A

(50) Amount of 7% by weight aqueous solution of sodium peroxodisulfate: 30.9 g

Feed 1 (Homogeneous Mixture of)

(51) TABLE-US-00022 216.2 g styrene 57.7 g 2-ethylhexyl acrylate 62.5 g n-butyl acrylate

Feed 2

(52) TABLE-US-00023 22.5 g deionized water

(53) Amount of 5% by weight aqueous solution of Acticid MBS: 0.6 g

(54) Amount of deionized water: 14.8 g

(55) and an additional 1.2 g of a 25% by weight aqueous ammonia solution

(56) The aqueous polymer dispersion 6 obtained had a solids content of 39.6% by weight and a pH of 8.0. The weight-average particle diameter was 94 nm. The Hansch parameter of polymer 2 formed from feed 1 was calculated as 3.07. The glass transition temperature of polymer 2 was determined as 30 C.

Aqueous Comparative Dispersion 1 (VB1)

(57) The aqueous comparative dispersion 1 was prepared entirely analogously to the preparation of the aqueous polymer dispersion 1, except that the following initial charge, amount of sodium peroxodisulfate, feeds 1 and 2, biocide solution and deionized water were used:

Initial Charge

(58) TABLE-US-00024 316.2 g deionized water 478.9 g polymer solution PL1-V

(59) Amount of 7% by weight aqueous solution of sodium peroxodisulfate: 38.3 g

Feed 1 (Homogeneous Mixture of)

(60) TABLE-US-00025 269.1 g styrene 104.6 g 2-ethylhexyl acrylate

Feed 2

(61) TABLE-US-00026 22.5 g deionized water

(62) Amount of 5% by weight aqueous solution of Acticid MBS: 0.6 g

(63) mount of deionized water: 14.8 g

(64) The aqueous comparative dispersion 1 obtained had a solids content of 41.5% by weight and a pH of 7.9. The weight-average particle diameter was 350 nm. The Hansch parameter of polymer 2 formed from feed 1 was calculated as 3.23. The glass transition temperature of polymer 2 was determined as 39 C.

Aqueous Comparative Dispersion 2 (VB2)

(65) The aqueous comparative dispersion 2 was prepared entirely analogously to the preparation of the aqueous polymer dispersion 1, except that the following initial charge, amount of sodium peroxodisulfate, feeds 1 and 2, biocide solution and deionized water were used:

Initial Charge

(66) TABLE-US-00027 216.3 g deionized water 533.9 g polymer solution PL1-A

(67) Amount of 7% by weight aqueous solution of sodium peroxodisulfate: 34.0 g

Feed 1 (Homogeneous Mixture of)

(68) TABLE-US-00028 261.6 g methyl methacrylate 112.1 g n-butyl acrylate

Feed 2

(69) TABLE-US-00029 25.0 g deionized water

(70) Amount of 5% by weight aqueous solution of Acticid MBS: 0.6 g

(71) Amount of deionized water: 16.4 g

(72) The aqueous comparative dispersion 2 obtained had a solids content of 44.5% by weight and a pH of 7.6. The weight-average particle diameter was 78 nm. The Hansch parameter of polymer 2 formed from feed 1 was calculated as 1.56. The glass transition temperature of polymer 2 was determined as 44 C.

Aqueous Comparative Dispersion 3 (VB3)

(73) The aqueous comparative dispersion 3 was prepared entirely analogously to the preparation of the aqueous polymer dispersion 1, except that the following initial charge, amount of sodium peroxodisulfate, feeds 1 and 2, biocide solution and deionized water were used:

Initial Charge

(74) TABLE-US-00030 227.9 g deionized water 608.6 g polymer solution PL1-A

(75) Amount of 7% by weight aqueous solution of sodium peroxodisulfate: 34.3 g

Feed 1 (Homogeneous Mixture of)

(76) TABLE-US-00031 115.3 g methyl methacrylate 67.3 g styrene 62.5 g 2-ethylhexyl acrylate 52.9 g n-butyl acrylate

Feed 2

(77) TABLE-US-00032 22.5 g deionized water

(78) Amount of 5% by weight aqueous solution of Acticid MBS: 0.6 g

(79) Amount of deionized water: 14.8 g

(80) and additionally 1.9 g of a 25% by weight aqueous ammonia solution

(81) The aqueous comparative dispersion 3 obtained had a solids content of 39.5% by weight and a pH of 7.6. The weight-average particle diameter was 65 nm. The Hansch parameter of polymer 2 formed from feed 1 was calculated as 2.40. The glass transition temperature of polymer 2 was determined as 24 C.

Aqueous Comparative Dispersion 4 (VB4)

(82) The aqueous comparative dispersion 4 was prepared entirely analogously to the preparation of the aqueous polymer dispersion 1, except that the following initial charge, amount of sodium peroxodisulfate, feeds 1 and 2, biocide solution and deionized water were used:

Initial Charge

(83) TABLE-US-00033 295.8 g deionized water 497.1 g polymer solution PL1-B

(84) Amount of 7% by weight aqueous solution of sodium peroxodisulfate: 38.3 g

Feed 1 (Homogeneous Mixture of)

(85) TABLE-US-00034 134.5 g styrene 100.9 g 2-ethylhexyl acrylate 100.9 g n-butyl acrylate

Feed 2

(86) TABLE-US-00035 25.0 g deionized water

(87) Amount of 5% by weight aqueous solution of Acticid MBS: 0.6 g

(88) Amount of deionized water: 14.8 g

(89) and additionally 1.4 g of a 25% by weight aqueous ammonia solution

(90) The aqueous comparative dispersion 4 obtained had a solids content of 40.3% by weight and a pH of 7.6. The weight-average particle diameter was 61 nm. The Hansch parameter of polymer 2 formed from feed 1 was calculated as 3.04. The glass transition temperature of polymer 2 was determined as 7 C.

Aqueous Comparative Dispersion 5 (VB5)

(91) The aqueous comparative dispersion 5 was prepared entirely analogously to the preparation of the aqueous polymer dispersion 1, except that the following initial charge, amount of sodium peroxodisulfate, feeds 1 and 2, biocide solution and deionized water were used:

Initial Charge

(92) TABLE-US-00036 216.3 g deionized water 533.9 g polymer solution PL1-A

(93) Amount of 7% by weight aqueous solution of sodium peroxodisulfate: 34.0 g

Feed 1 (Homogeneous Mixture of)

(94) TABLE-US-00037 129.2 g methyl methacrylate 129.2 g styrene 57.7 g 2-ethylhexyl acrylate 57.7 g n-butyl acrylate

Feed 2

(95) TABLE-US-00038 25.0 g deionized water

(96) Amount of 5% by weight aqueous solution of Acticid MBS: 0.6 g

(97) Amount of deionized water: 16.4 g

(98) The aqueous comparative dispersion 5 obtained had a solids content of 44.6% by weight and a pH of 7.5. The weight-average particle diameter was 99 nm. The Hansch parameter of polymer 2 formed from feed 1 was calculated as 2.41. The glass transition temperature of polymer 2 was determined as 38 C.

3 Production of the Varnish Formulations

(99) For production of the varnish formulations, the aqueous polymer dispersions B1 to B6 and VB1 to VB5 were adjusted to a solids content of 39.0% by weight while stirring and with addition of deionized water.

(100) Subsequently, 60 g in each case of these aqueous polymer dispersions thus obtained formed an initial charge at room temperature in a plastic container of capacity 0.5 L that had a diameter of 80 mm. The following were added successively in each case to the initial charges of aqueous polymer dispersions thus formed: 2.0 g of Joncryl HPD 296 from BASF as dispersant, 0.7 g of FoamStar SI 2180 from BASF as defoamer, 44.0 g of Kronos 2190 from Kronos International as titanium dioxide pigment and 0.4 g of Rheovis PU 1250 from BASF as thickener.

(101) Subsequently, 320 g of dispersing beads having a diameter of 3 mm made of soda-lime glass were added to the formulations thus obtained, and the mixtures thus obtained were stirred with a Teflon disk having a diameter of 60 mm having a circumferential speed of 7 m/s for 10 min.

(102) The following were then added to these mixtures with further stirring: 78 g of the respective aqueous polymer dispersion diluted to 39.0% by weight, 12.2 g of ethylene glycol butyl ether as film-forming auxiliary, 0.8 g of Rheovis PU 1250 and 1.9 g of deionized water. Subsequently, the respective varnish formulations were adjusted to a pH of 8.0 to 8.2 with a 10% by weight aqueous ammonia solution. Stirring of the varnish formulations thus obtained was continued for another 5 minutes, and then the dispersing beads were filtered off. Prior to the performance tests, the varnish formulations thus obtained were left to stand for at least 1 hour.

(103) The aqueous varnish formulations thus obtained from the aqueous polymer dispersions B1 to B6 and VB1 to VB5 are referred to hereinafter as varnishes LB1 to LB6 (inventive) and LVB1 to LVB5 (noninventive).

4 Performance Tests

(104) Testing of chemical resistances or resistance to staining was effected on test boards that had been coated with the varnishes produced. For this purpose, beech test boards (veneered) were coated by means of an applicator frame with the respective varnish LB1 to LB6 and LVB1 to LVB5 in a layer thickness of 150 m (wet). Subsequently, the test boards were dried under standard climatic conditions (23 C. and 50% relative air humidity) for 30 days. The testing for chemical resistances or resistance to staining was effected to DIN 68861-1. This involved placing filter papers (diameter: 3 cm; basis weight: 500 g/m.sup.2) soaked with the test liquids onto 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. Test liquids used were a 48% by volume aqueous ethanol solution and a coffee solution, cooled to room temperature, prepared by dissolving 2.0 g of the instant coffee Nescafe Gold in 100 mL of boiling tap water. The filter papers soaked with the alcohol solution or the coffee were then placed onto the varnished test boards at room temperature, the plastic beakers were placed over them, and the change in the respective varnishes was visually assessed after 1 hour in the case of the alcohol solution and after 16 hours in the case of the coffee solution (after removal of the soaked filter papers). The visual assessment was made by the following rating/grade system:

(105) TABLE-US-00039 No visible changes in gloss and color; the structure of the test Grade 5 area is unchanged Changes just apparent in gloss and color; the structure of the Grade 4 test area is unchanged Slight changes in gloss and color; the structure of the test area is Grade 3 unchanged Significant changes in gloss and color; the structure of the test Grade 2 area is unchanged Significant changes in gloss and color; the structure of the test Grade 1 area is changed Significant changes in gloss and color; the structure of the test Grade 0 area is significantly changed

(106) 3 soaked filter papers with alcohol solution and coffee solution were used for each varnish. The results reported in table 3 are the averages from these 3 visual assessments.

(107) TABLE-US-00040 TABLE 3 Results from the visual assessments of varnishes LB1 to LVB5 Varnish Coffee Ethanol 5 LB1 5 4 LB2 5 4 LB3 5 4 LB4 5 4 LB5 5 4 LB6 5 4 LVB1 3 2 LVB2 3 1 LVB3 3 1 LVB4 2 2 LVB5 3 2

(108) It is clearly apparent from the results that the varnishes produced with the aqueous polymer dispersions of the invention have excellent resistances to coffee with simultaneously very good resistances to aqueous ethanol.