Use of multi-stage polymerizate dispersions to coat metal sheets

Abstract

The present invention relates to the use of aqueous multistage polymer dispersions obtainable by free-radically initiated aqueous emulsion polymerization, having a soft phase and a hard phase and having a hard-to-soft stage ratio of 25% to 95% by weight to 75% to 5% by weight, the glass transition temperature (Tg) of the soft phase, as first stage, being 30 to 0 C. and that of the hard phase, as second stage, being 20 to 60 C., comprising at least one monomer of the general formula I ##STR00001##
in which the variables have the following definitions:
n=0 to 2,
R1, R2, R3=independently of one another hydrogen or methyl group,
XO or NH,
YH, alkali metal or NH.sub.4,
to coat metal sheets.

Claims

1. A method of coating a metal sheet, comprising: coating the surface of the metal sheet with an aqueous multistage polymer dispersion obtained by free-radically initiated aqueous emulsion polymerization, wherein the aqueous multistage polymer dispersion comprises a soft phase, a hard phase and a hard-to-soft stage ratio of 25% to 95% by weight to 75% to 5% by weight, wherein the soft phase, as a first stage has a glass transition temperature (Tg) of 30 to 0 C., wherein the hard phase, as a second stage, has a glass transition temperature of 20 to 60 C., and wherein the aqueous multistage polymer dispersion comprises at least one monomer of the general formula I: ##STR00004## in which: n=0 to 2, R1, R2, R3=independently of one another hydrogen or methyl group, XO or NH, and YH, alkali metal, NH.sub.4.

2. The method according to claim 1, wherein the aqueous polymer dispersion is present on a profiled metal roofing element.

3. The method according to claim 1, wherein the aqueous polymer dispersion is present as a basecoat and/or a topcoat on a metal sheet.

4. The method according to claim 1, wherein the hard-to-soft stage ratio is 25-95:75-5.

5. The method according to claim 1, wherein the first stage is a copolymer which (i) is present in an amount of 5% to 50% by weight, based on 100 parts by weight of the total monomers to be polymerized in the first and second stages, (ii) comprises 80% to 99% by weight of principal monomers selected from the group consisting of C1 to C10 alkyl(meth)acrylates, amides and hydroxyalkyl esters of ,-unsaturated C.sub.3-C.sub.6 carboxylic acids, and mixtures thereof, and (iii) comprises 0.1% to 5% by weight of the monomer of the general formula I.

6. A metal sheet comprising on at least one surface thereof, the aqueous multistage polymer dispersion according to claim 1.

7. The metal sheet according to claim 6, wherein the sheet is granulated.

8. The metal sheet according to claim 6, wherein the metal sheet comprises aluminum, zinc, copper or steel.

9. The metal sheet according to claim 6, wherein the metal sheet is a profiled metal roofing element.

10. The metal sheet according to claim 6, wherein the metal sheet is a roof covering or a wall cladding.

11. The metal sheet according to claim 6, wherein the aqueous polymer dispersion is present as a basecoat and/or a topcoat on the metal sheet.

12. A method for coating a granulated metal sheet, the method comprising: coating the surface of the granulated metal sheet with a first paint layer of 100 to 800 m thick comprising a polymer dispersion comprising at least one monomer of the formula I, scattering a layer of granules into the first paint layer while the first paint layer is still wet, and coating the layer of granules with a second paint layer comprising a polymer dispersion comprising at least one monomer of the formula I or with a transparent clearcoat, ##STR00005## wherein: n=0 to 2, R1, R2, R3 each independently is hydrogen or a methyl group, X is O or NH, and Y is H, alkali metal, or NH.sub.4, wherein the polymer dispersions of the first and second paint e same or different, wherein the polymer dispersions of the first and second paint layers comprise a soft phase, a hard phase and a hard-to-soft stage ratio of 25% to 95% by weight to 75% to 5% by weight, wherein the soft phase, as a first stage has a glass transition temperature (Tg) of 30 to 0 C., and wherein the hard phase, as a second stage, has a glass transition temperature of 20 to 60 C.

13. A method for coating an ungranulated metal sheet, comprising: coating the surface of the ungranulated metal sheet with a paint layer of 100 to 800 m thick comprising the polymer dispersion according to claim 1.

Description

EXAMPLES

1) Comparative Dispersion Tg(theo.)=44 C.

(1) The components below were introduced into a polymerization vessel equipped with metering means and temperature regulation:

(2) Initial charge:

(3) 402.1 g water 13.26 g 20% aqueous solution of C.sub.16-18 fatty alcohol polyethoxylate 8.71 g 45% aqueous solution of dodecyl diphenyl ether disulfonic acid sodium salt

(4) In a feed vessel, an emulsion was prepared from the following components: 560.2 g water 19.89 g 20% aqueous solution of C.sub.16-18 fatty alcohol polyethoxylate 34.85 g 45% aqueous solution of dodecyl diphenyl ether disulfonic acid sodium salt 5.23 g 50% aqueous solution of 2-acrylamido-2-methylpropanesulfonic acid 13.07 g 50% aqueous solution of acrylamide 392.0 g n-butyl acrylate 908.2 g methyl methacrylate

(5) In a third feed vessel the following feed was prepared:

(6) Feed 3

(7) 56.00 g 7% aqueous solution of sodium peroxodisulfate

(8) The initial charge was heated without the 50% aqueous solution of 2-acrylamido-2-methylpropanesulfonic acid to 95 C. (external temperature; polymerization temperature 90 C., stirring speed 150 rpm). The 50% aqueous solution of 2-acrylamido-2-methylpropanesulfonic acid was added and the mixture was stirred for 15 minutes. Then feed 1 and feed 2 were commenced. Feed 1 was metered in over 3 hours, feed 2 over 3.5 hours. The stirring speed was reduced back to 100 rpm, and stirring continued for 30 minutes.

(9) Over the course of 30 minutes, 11.7 g of a 10% aqueous solution of tert-butyl hydroperoxide and 9.1 g of a 10% aqueous solution of hydroxymethanesulfinic acid were metered in. 2.61 of a 5% aqueous hydrogen peroxide solution were added, and the mixture was stirred for 10 minutes. After cooling, neutralization was carried out with 1.57 g of 25% aqueous NH.sub.3, and 161.77 of water were added. This gave 2620 g of a 51.6% aqueous dispersion.

2) Comparative Dispersion (Two-Stage)(without Inventive Monomers I)

(10) The components below were introduced into a polymerization vessel equipped with metering means and temperature regulation:

(11) Initial Charge: 389.7 g water 51.07 g polystyrene seed latex (33% in water)

(12) In a first feed vessel, an emulsion was prepared from the following components:

(13) Feed 1

(14) 323.9 g water 9.7 g 20% aqueous solution of C.sub.16-18 fatty alcohol polyethoxylate 23.15 g 28% aqueous solution of sodium lauryl polyethoxysulfate 9.07 g 50% aqueous solution of acrylic acid 462.3 g n-butyl acrylate 178.8 g methyl methacrylate

(15) In a second feed vessel, an emulsion was prepared from the following components:

(16) Feed 2

(17) 320.7 g water 9.7 g 20% aqueous solution of C.sub.16-18 fatty alcohol polyethoxylate 23.15 g 28% aqueous solution of sodium lauryl polyethoxysulfate 10.37 g 50% aqueous solution of acrylamide 9.07 g 50% aqueous solution of acrylic acid 210.0 g n-butyl acrylate 431.0 g methyl methacrylate

(18) In a third feed vessel the following feed was prepared:

(19) Feed 3

(20) 55.6 g 7% aqueous solution of sodium peroxodisulfate

(21) The initial charge was heated (external temperature: 90 C., polymerization temperature: 83 C., stirring speed: 150 rpm). Feeds 1 and 3 were commenced simultaneously. Feed 1 was metered in over 1.5 hours, and then feed 2 over 1.5 hours. Feed 3 was metered in over 3 hours. This was followed by stirring for 30 minutes, after which, over the course of 1 hour, 11.7 g of a 10% aqueous solution of tert-butyl hydroperoxide and 9.1 g of a 10% aqueous solution of hydroxymethanesulfinic acid were metered in. This was followed by neutralization with 55.09 g of 2% aqueous NaOH, stirring for 10 minutes, reduction in the stirring speed to 100 rpm, and cooling. Thereafter 2.6 g of a 5% aqueous hydrogen peroxide solution and 78.78 g of water were added. This gave 2674 g of a 49.9% dispersion.

3) Exemplary Dispersion (Two-Stage), Inventive, with Monomers I

(22) The components below were introduced into a polymerization vessel equipped with metering means and temperature regulation:

(23) Initial Charge:

(24) 389.7 g water 51.07 g polystyrene seed latex (33% in water)

(25) In a first feed vessel, an emulsion was prepared from the following components:

(26) Feed 1

(27) 323.9 g water 9.7 g 20% aqueous solution of C.sub.16-18 fatty alcohol polyethoxylate 23.15 g 28% aqueous solution of sodium lauryl polyethoxysulfate 9.07 g 50% aqueous solution of 2-acrylamido-2-methylpropanesulfonic acid 462.3 g n-butyl acrylate 178.8 g methyl methacrylate

(28) In a second feed vessel, an emulsion was prepared from the following components:

(29) Feed 2

(30) 320.7 g water 9.7 g 20% aqueous solution of C.sub.16-18 fatty alcohol polyethoxylate 23.15 g 28% aqueous solution of sodium lauryl polyethoxysulfate 10.37 g 50% aqueous solution of acrylamide 9.07 g 50% aqueous solution of 2-acrylamido-2-methylpropanesulfonic acid 210.0 g n-butyl acrylate 431.0 g methyl methacrylate

(31) In a third feed vessel the following feed was prepared:

(32) Feed 3

(33) 55.6 g 7% aqueous solution of sodium peroxodisulfate

(34) The initial charge was heated (external temperature: 90 C., polymerization temperature: 83 C., stirring speed: 150 rpm). Feeds 1 and 3 were commenced simultaneously. Feed 1 was metered in over 1.5 hours, and then feed 2 over 1.5 hours. Feed 3 was metered in over 3 hours. This was followed by stirring for 30 minutes, after which, over the course of 1 hour, 11.7 g of a 10% aqueous solution of tert-butyl hydroperoxide and 9.1 g of a 10% aqueous solution of hydroxymethanesulfinic acid were metered in. This was followed by neutralization with 55.09 g of 2% aqueous NaOH, stirring for 10 minutes, reduction in the stirring speed to 100 rpm, and cooling. Thereafter 2.6 g of a 5% aqueous hydrogen peroxide solution and 78.78 g of water were added. This gave 2674 g of a 49.9% dispersion.

4) Exemplary Dispersion (Two-Stage), Inventive, with Monomers I, More Hard Phase

(35) The components below were introduced into a polymerization vessel equipped with metering means and temperature regulation:

(36) Initial Charge:

(37) 389.7 g water 51.07 g polystyrene seed latex (33% in water)

(38) In a first feed vessel, an emulsion was prepared from the following components:

(39) Feed 1

(40) 129.6 g water 3.89 g 20% aqueous solution of C.sub.16-18 fatty alcohol polyethoxylate 9.26 g 28% aqueous solution of sodium lauryl polyethoxysulfate 3.63 g 50% aqueous solution of 2-acrylamido-2-methylpropanesulfonic acid 184.9 g n-butyl acrylate 71.50 g methyl methacrylate

(41) In a second feed vessel, an emulsion was prepared from the following components:

(42) Feed 2

(43) 515.0 g water 15.56 g 20% aqueous solution of C.sub.16-18 fatty alcohol polyethoxylate 37.04 g 28% aqueous solution of sodium lauryl polyethoxysulfate 10.37 g 50% aqueous solution of acrylamide 14.52 g 50% aqueous solution of 2-acrylamido-2-methylpropanesulfonic acid 336.0 g n-butyl acrylate 689.6 g methyl methacrylate

(44) In a third feed vessel the following feed was prepared:

(45) Feed 3

(46) 55.6 g 7% aqueous solution of sodium peroxodisulfate

(47) The initial charge was heated (external temperature: 90 C., polymerization temperature: 83 C., stirring speed: 150 rpm). Feeds 1 and 3 were commenced simultaneously. Feed 1 was metered in over 36 minutes, and then feed 2 over 2 hours 24 minutes. Feed 3 was metered in over 3 hours. This was followed by stirring for 30 minutes, after which, over the course of 1 hour, 11.7 g of a 10% aqueous solution of tert-butyl hydroperoxide and 9.1 g of a 10% aqueous solution of hydroxymethanesulfinic acid were metered in. This was followed by neutralization with 55.09 g of 2% aqueous NaOH, stirring for 10 minutes, reduction in the stirring speed to 100 rpm, and cooling. Thereafter 2.6 g of a 5% aqueous hydrogen peroxide solution and 78.78 g of water were added. This gave 2674 g of a 49.7% dispersion.

5) Exemplary Dispersion (Two-Stage), Inventive, with Monomers I, with Chain Transfer Agent and Crosslinker

(48) The components below were introduced into a polymerization vessel equipped with metering means and temperature regulation:

(49) Initial Charge:

(50) 389.7 g water 51.07 g polystyrene seed latex (33% in water)

(51) In a first feed vessel, an emulsion was prepared from the following components:

(52) Feed 1

(53) 327.2 g water 9.7 g 20% aqueous solution of C.sub.16-18 fatty alcohol polyethoxylate 23.15 g 28% aqueous solution of sodium lauryl polyethoxysulfate 5.19 g 50% aqueous solution of acrylamide 9.07 g 50% aqueous solution of 2-acrylamido-2-methylpropanesulfonic acid 3.24 g 3-methacryloyloxypropyltrimethoxysilane 465.4 g n-butyl acrylate 175.7 g methyl methacrylate

(54) In a second feed vessel, an emulsion was prepared from the following components:

(55) Feed 2

(56) 331.7 g water 9.7 g 20% aqueous solution of C.sub.16-18 fatty alcohol polyethoxylate 23.15 g 28% aqueous solution of sodium lauryl polyethoxysulfate 5.19 g 50% aqueous solution of acrylamide 9.07 g 50% aqueous solution of 2-acrylamido-2-methylpropanesulfonic acid 7.78 g tert-dodecyl mercaptan 1.30 g allyl methacrylate 3.24 g 3-methacryloyloxypropyltrimethoxysilane 207.5 g n-butyl acrylate 432.2 g methyl methacrylate

(57) In a third feed vessel the following feed was prepared:

(58) Feed 3

(59) 55.6 g 7% aqueous solution of sodium peroxodisulfate

(60) The initial charge was heated (external temperature: 90 C., polymerization temperature: 83 C., stirring speed: 150 rpm). Feeds 1 and 3 were commenced simultaneously. Feed 1 was metered in over 1.5 hours, and then feed 2 over 1.5 hours. Feed 3 was metered in over 3 hours. This was followed by stirring for 30 minutes, after which, over the course of 1 hour, 11.7 g of a 10% aqueous solution of tert-butyl hydroperoxide and 9.1 g of a 10% aqueous solution of hydroxymethanesulfinic acid were metered in. This was followed by neutralization with 55.09 g of 2% aqueous NaOH, stirring for 10 minutes, reduction in the stirring speed to 100 rpm, and cooling. Thereafter 2.6 g of a 5% aqueous hydrogen peroxide solution and 69.18 g of water were added. This gave 2703 g of a 49.9% dispersion.

6) Standard, Comparative Dispersion, Single-Stage Tg(Theo.)=28 C.

(61) The components below were introduced in a polymerization vessel equipped with metering means and temperature regulation:

(62) Initial charge:

(63) 200 g water 35 g polystyrene seed latex (33% in water) 3.4 g 7% aqueous solution of sodium peroxodisulfate

(64) In a feed vessel, an emulsion was prepared from the following components:

(65) Feed 1.

(66) 269.4 g water 43.3 g 15% aqueous solution of sodium lauryl sulfate 26 g 20% aqueous solution of C.sub.12-14 fatty alcohol polyethoxylate 19.5 g acrylic acid 19.5 g 50% aqueous solution of acrylamide 319.3.0 g n-butyl acrylate 294.7 g styrene

(67) In a second feed vessel the following feed was prepared:

(68) Feed 2

(69) 46.00 g 7% aqueous solution of sodium peroxodisulfate

(70) The initial charge was heated to 95 C. (external temperature; polymerization temperature 90 C., stirring speed 150 rpm). After 5 minutes, feed 1 and feed 2 were commenced and were both metered in over 2.5 hours, with stirring for 30 minutes thereafter. The batch was neutralized with 54 g of 10% aqueous sodium hydroxide solution.

(71) Performance Testing:

(72) Testing takes place with sheets only with the first paint coating, and also with the complete system (basecoat, granules, and final coat). Following application of the coating, the steel sheet, which is coated with an epoxy primer, is cured at room temperature (RT) for at least 24 hours. This is followed by testing of the adhesion at RT and after 24 hours of water storage. After brief drying, the samples are frozen at 20 C. for 24 hours. This is followed immediately by a hammer blow test and by the flexural test with 180 bending.

(73) The adhesion is evaluated using a scale of 1-5, with 1 representing optimum adhesion, with no conspicuities, and 5 representing detachment without further mechanical influence. In the case of the flexure and the hammer blow test, the cracking and delamination are likewise evaluated with a scale of 1-5. The rating 1 here denotes virtually no delamination and cracking, and rating 5 denotes complete delamination at the test point.

(74) Flexural Test

(75) The flexural test takes place at 10 C. It involves bending the metal sheet by 180 C. with the coating outward. Thereafter the adhesion of the coating to the substrate, particularly in the region of the bending, is evaluated.

(76) Hammer blow test (along the lines of the notched impact flexural test according to EN1004b, but without a notch and only manually with a hammer).

(77) In the hammer blow test, a sheet at a temperature of 10 C. receives a blow on its reverse face with a pointed hammer. The coating is subsequently inspected for the quality of its adhesion on the front face in the region of the deformation.

(78) Weathering Stability

(79) To test the weathering stability of the paints on the metal sheets, a Xenon test is carried out for paints in accordance with DIN EN ISO 11341 (cycle A), and inspection takes place after 500 hours in each case. In this Xenon test, coated metal sheets with a size of 5*13 cm are each illuminated in alternation for 102 minutes dry and for 18 minutes during which the sheets are dampened with a fine water mist. The relative humidity is set at 50% and the black standard temperature is 65 C. The irradiation power corresponds to 60 W UV light at 300-400 nm or 0.51 W/(m.sup.2.Math.nm) at a 340 nm light wavelength.

(80) Damage criteria assessed are visible paint damage, such as cracks or delamination, color changes, and loss of gloss. The paint's gloss is measured with a gloss meter at a 60 angle before and after the weathering test.

(81) In order to determine the performance properties of the dispersions of the invention, paints were produced to the following formula:

(82) TABLE-US-00001 TABLE 1 Formulation Standard (Example 6) Example 5 Water 68.61 80 Standard (Example 6) 39.13 Pigmentverteiler NL BASF SE 2.45 3.0 Tego Airex 902 W Defoamer from 2.94 4.0 Evonik; DPnB/BDG, 1:1 Dow Chemical (dipropylene glycol n- butyl ether (Solvenon DPnB, BASF) and BDG Calcilit Extra Alpha Calcit 216.38 215 Bayferrox black 318 Lanxess, Krefeld 71.91 70 LusolvanFBH BASF SE 23.48 Diethylhexyl phthalate BASF SE 20.54 Standard (Example 6) 550.65 Example 5 585 Tego Airex902W 3.91 3 DPnB/BDG, 1:1 30 ViscalexHV30 BASF SE, thickener 10 1000 1000 PVC: 25.25 25.22 SC: 58.3 57.8

(83) The paints were knife-coated onto primed metal sheets, with a wet film thickness of 300 m. The sheets had been primed with an epoxy coating. One cohort of the sheets is dried for 3 hours in a drying cabinet at 40 C. and then for 3 days at room temperature, and subsequently tested. The second cohort of the sheets is subjected directly to further processing. The granules are scattered into the paint while it is still wet, and the sheet is tapped to remove excess granules. This is followed immediately by coating with a clearcoat (130-180 g/m.sup.2) based on a crosslinked straight acrylic (Acronal8974). Drying then takes place likewise, in the same way.

(84) Sheet Testing without Granules Example 6 Example 5

(85) TABLE-US-00002 Adhesion RT 3 1 Adhesion after 24 h water 4 2.5 Hammer blow after 24 h 20 C. 2 2 Flexural test after 24 h 20 C. 1 1
Sheet Testing with Granules and Clearcoat Example 6 Example 5

(86) TABLE-US-00003 Adhesion RT 2 1 Adhesion after 24 h water 4 2 Hammer blow after 24 h 20 C. 2 2 Flexural test after 24 h 20 C. 5 2
Sheet Testing without Granules Example 6 Example 5

(87) TABLE-US-00004 Adhesion RT 3.5 1 Adhesion after 24 h water 4.5 2.5 Hammer blow after 24 h 20 C. 3 2 Flexural test after 24 h 20 C. 4 1.5
Weathering Test

(88) After 2600 hours of Xenotest: no differences are perceptible. The weather resistance is comparable with that of the current market systems (valid for the entire system construction).

(89) Pendulum Hardness

(90) The coating under test was knife-coated using an Erichsen film-drawing apparatus (200 m wet) onto a 387 cm glass plate. After 1 day of drying at room temperature or 30 minutes at 60 C. and 1 day of room temperature, three pendulum test measurements were conducted at three points on the glass plate. Measurement took place by the method of Knig (DIN EN ISO 1522).

(91) Measurements were performed after 1 day, 4 days, 6 days, and 14 days. The results found correspond to the average value from each of the 3 measurements.

(92) The test shows that with the new binder, it is possible to produce coatings which are significantly less soft and tacky, despite high flexibility and good adhesion.

(93) TABLE-US-00005 1 d 4 d 6 d 14 d Pendulum hardness (in sec.) Standard (Example 6) 9.3 9.4 9.4 9.8 New binder (Example 5) 15.4 19.1 22.9 27.1 Film on glass 200 drying at room temperature Standard (Example 6) 9.8 9.8 9.8 9.8 New binder (Example 5) 15.4 19.1 22.4 27.5 Film on glass 200 drying for 30 min at 60 C., further drying at room temperature