Method for coating a metal or plastic substrate, coating that can be obtained therefrom, and coated substrate

Abstract

A method for coating an uncoated or precoated metallic or plastics substrate by (a) applying an aqueous coating composition (W) whose constituents are free or substantially free from blocked isocyanate groups, which comprises an aqueous dispersion of an epoxide-amine adduct, and which comprises either no crosslinking agent or one or more nonblocked polyisocyanate crosslinking agents, to the substrate, (b) optionally applying one or more further coating compositions, and (c) curing the coating composition (W) and, where appropriate, the further coating composition(s) at temperatures of below 90 C.

Claims

1. A method for coating an uncoated or precoated metallic or plastic substrate, comprising: (a) applying an aqueous coating composition (W) to the substrate, wherein constituents of the aqueous coating composition are free or substantially free of blocked isocyanate groups, the aqueous coating composition (W) comprising i) a cationically stabilized aqueous dispersion of an epoxide-amine adduct which is the reaction product of at least one polyepoxide and at least one amine, wherein the aqueous coating composition (W) comprises 1% to 60% by weight, based on the overall aqueous coating composition (W), of the epoxide-amine adduct, and ii) one or more nonblocked polyisocyanate crosslinking agents, wherein no crosslinking agent other than the one or more nonblocked polyisocyanate crosslinking agents is present in coating composition (W), and; (b) applying one or more further coating compositions; and (c) completely thermally curing the coating composition (W) and, where appropriate, the further coating composition(s), at temperatures of below 90 C.

2. The method of claim 1, wherein said curing takes place at temperatures of below 70 C.

3. The method of claim 1, wherein the aqueous coating composition comprises 1% to 30% by weight, based on the overall aqueous coating composition (W), of the one or more nonblocked polyisocyanates.

4. The method of claim 1, wherein the aqueous coating composition (W) comprises 5% to 40% by weight, based on the overall aqueous coating composition (W), of the epoxide-amine adduct.

5. The method of claim 1, wherein the aqueous dispersion is cationically stabilized by 0.1% to 4.0% by weight, based on the overall aqueous coating composition (W), of phosphoric acid.

6. The method of claim 1, wherein the fraction of organic solvents in the aqueous coating composition (W) is less than 30%, by weight, based on the overall aqueous coating composition (W).

7. The method of claim 1, wherein the aqueous coating composition (W) is applied to the substrate by spraying.

8. The method of claim 7, wherein the spraying step comprises electrostatically assisted spraying.

9. The method of claim 1, wherein the substrate comprises an uncoated or precoated metallic substrate made of aluminum, steel, or galvanized steel.

10. The method of claim 1, wherein the substrate is part of an automobile body.

11. The method of claim 1, wherein the substrate has an existing paint finish.

12. The method of claim 1, wherein the coating composition (W) and the further coating composition(s) are completely thermally cured at temperatures of below 90 C.

13. The method of claim 1, wherein the at least one amine is selected from the group consisting of alkanolamines, aminoalkoxy alcohols and dialkylaminoalkylamines.

14. The method of claim 13, wherein the at least one amine is an aminoalkoxy alcohol.

15. A method for providing corrosion control to an uncoated or precoated metallic substrate, comprising: (a) applying an aqueous coating composition (W) to the substrate, wherein constituents of the aqueous coating composition are free or substantially free of blocked isocyanate groups, the aqueous coating composition (W) comprising i) a cationically stabilized aqueous dispersion of an epoxide-amine adduct which is the reaction product of at least one polyepoxide and at least one amine, wherein the aqueous coating composition (W) comprises 1% to 60% by weight, based on the overall aqueous coating composition (W), of the epoxide-amine adduct, and ii) one or more nonblocked polyisocyanate crosslinking agents, wherein no crosslinking agent other than the one or more nonblocked polyisocyanate crosslinking agents is present in coating composition (W), and; (b) applying one or more further coating compositions; and (c) completely thermally curing the coating composition (W) and, where appropriate, the further coating composition(s), at temperatures of below 90 C.

Description

EXAMPLES

(1) The quantity figures are in parts by weight unless indicated otherwise.

(2) 1. Primers, Primer-Surfacers or Fillers in Multicoat Systems with Additional Basecoat and Clearcoat

(3) Mixture 1 was prepared by mixing the constituents according to table 1 in a dissolver for 15 minutes and then dispersing the mixture in a stirred mill for 30 minutes.

(4) TABLE-US-00001 TABLE 1 Mixture 1 Epoxide-amine adduct (I), 63% in 24.2 butyl glycol/water/glacial acetic acid DI water 29.8 Phosphoric acid, 8.5% in water 2.0 Aerosil R 972 1.0 Blanc Fixe powder N 10.8 Titanium dioxide (Tiona 595) 10.0 Talc (Luzenac 10 MO) 8.0 Zinc phosphate (PZ 10) 6.0 Bayferrox 3910 3.0 Bayferrox 130 BM 0.1 Lamp black (Flamm 101) 0.1 Butyl glycol 5

(5) The epoxide-amine adduct (I) in table 1 is the reaction product prepared in example 3 (epoxide-amine adduct, 63% in butyl glycol/water/glacial acetic acid).

(6) Adjustment of Filler/Primer-Surfacer/Primer before Spray Application

(7) Before spray application, 100 parts of mixture 1 were admixed with an additional 15 parts of dilute phosphoric acid (8.5% in DI water), as indicated in table 2. This gave mixture 2.

(8) TABLE-US-00002 TABLE 2 Mixture 2 Mixture 1 100 Phosphoric acid, 8.5% 15

(9) Subsequently, 115 parts of mixture 2 were mixed with 10 parts of a polyisocyanate curing agent (SC20-030F, hexamethylene diisocyanate trimer, 78% in butyl acetate/xylene) and then adjusted with 12.5 parts of DI water to spray viscosity (65 sec. ISO 4/EN ISO 2431).

(10) The resulting mixture was used as a primer, as a primer-surfacer, as a wet-on-wet filler, and as a sanding filler, as described below.

(11) 1.1 Application as a Primer in Combination with a Conventional Sanding Filler

(12) The primer was applied in each case to substrates of aluminum, steel, and galvanized steel, and to plastic (GRP). Prior to application, the substrates were sanded and cleaned. Application was made by spraying in a dry film thickness of approximately 10 m. The layer was flashed off on the substrate at room temperature for 30 minutes, and then a 2K [2-component] polyurethane filler was applied in a film thickness of approximately 60 m. Primer and filler were cured jointly at 60 C. for 30 minutes.

(13) After the cured filler surface had been sanded, a commercial aqueous basecoat was applied in a film thickness of approximately 10 m. After a 20-minute flash-off time, a commercial 2K polyurethane clearcoat was applied thereto wet-on-wet in a film thickness of approximately 60 m. Aqueous basecoat and clearcoat were cured jointly at 60 C. for 30 minutes.

(14) 1.2 Application as a Primer-Surfacer

(15) The primer-surfacer was applied in each case to substrates of aluminum, steel, and galvanized steel, and to plastic (GRP). Prior to application, the substrates were sanded and cleaned. Application was made by spraying in a dry film thickness of approximately 60 m. The layer was flashed off on the substrate at room temperature for 30 minutes and cured at 60 C. for 30 minutes. After cooling had taken place, the primer-surfacer was sanded, and a commercial aqueous basecoat was applied in a film thickness of approximately 10 m. After a 20-minute flash-off time, a commercial 2K polyurethane clearcoat was applied thereto wet-on-wet in a film thickness of approximately 60 m. Aqueous basecoat and clearcoat were cured jointly at 60 C. for 30 minutes.

(16) 1.3 Application as a Wet-On-Wet (Non-Sanding) Filler

(17) The aqueous filler was applied to a cathodically electrocoated steel panel (roughened by abrasion, and cleaned) in a dry film thickness of approximately 40 m. After a 30-minute flash-off time at room temperature and subsequent curing at 60 C. for 30 minutes, a commercial aqueous basecoat was applied in a film thickness of approximately 10 m and, after a 20-minute flash-off time, a commercial 2K polyurethane clearcoat was applied thereto wet-on-wet in a film thickness of approximately 60 m. The system was cured at 60 C. for 30 minutes.

(18) 1.4 Application as a Sanding Filler

(19) The aqueous filler was applied to a cathodically electrocoated steel panel (roughened by abrasion, and cleaned) in a dry film thickness of approximately 60 m. After a 30-minute flash-off time at room temperature, the filler was cured in an oven at 60 C. for 30 minutes. After it had cooled, the filler was sanded using commercial sandpaper. After subsequent cleaning, a commercial aqueous basecoat was applied in a film thickness of approximately 10 m, and, after a 20-minute flash-off time, a commercial 2K polyurethane clearcoat was applied thereto wet-on-wet in a film thickness of approximately 60 m. Aqueous basecoat and clearcoat were cured jointly at 60 C. for 30 minutes.

(20) The properties of the resultant coatings were tested after aging for 7 days at room temperature as follows.

(21) All Substrates

(22) Adhesion test using the cross-cut instrument (DIN EN ISO 2409) and subsequent tape removal (Tesaband from Beiersdorf, Tesa 4651) MB scratch sample (PBO DC 371) Stonechip test (DIN 55996-1)

(23) The codes indicated are defined as follows:

(24) Code 0=excellent

(25) Code 1=very good

(26) Code 2=good.

(27) TABLE-US-00003 TABLE 3 Scratch System Cross-cut sample Stonechip 1.1 on steel code 0 code 1 code 2 1.1 on galvanized steel code 0 code 1 code 2 1.1 on aluminum code 0 code 1 code 2 1.1 on plastic code 0 code 1 code 2 1.2 on steel code 0 code 0 code 1.5 1.2 on galvanized steel code 0 code 0 code 1.5 1.2 on aluminum code 0 code 0 code 1.5 1.2 on plastic code 0 code 1 code 1.5 1.3 on cathodic electrocoat code 0 code 0 code 1.5 1.4 on cathodic electrocoat code 0 code 0 code 1.5

(28) The results in table 3 show that the coatings according to 1.1, 1.2, 1.3, and 1.4 exhibit excellent adhesion on different substrates, even in the scratch sample, and good stonechip resistance.

(29) Additionally determined were the corrosion control effect on steel, on galvanized steel, and on aluminum of the resultant coatings from 1.1 and 1.2 after aging for 7 days at room temperature, by means of the DIN 50021 salt spray test (480 h; for steel and galvanized steel: pH 6.5-7.2; for aluminum: pH 3.1-3.3). The sample panels for this purpose were scored with an Erichsen scorer, type 463. The results of the corrosion control tests are shown in table 4 in the form of the visible subfilm migration at the scoring mark [mm].

(30) TABLE-US-00004 TABLE 4 Aluminum Galvanized steel Steel Coatings 1.1 0.4 1.8 2.5 Coatings 1.2 0 2.2 3.0

(31) The results in table 4 show that the coatings of systems 1.1 and 1.2 im part very good corrosion control to all three substrates.

(32) 2. Basecoats, Topcoats

(33) 2.1 Color RAL 9010 (White)

(34) Mixture W1 was prepared by mixing the constituents according to table 5 in a dissolver for 15 minutes and then dispersing the mixture in a stirred mill for 45 minutes.

(35) TABLE-US-00005 TABLE 5 Mixture W1 Epoxide-amine adduct (I), 63% in 25 butyl glycol/water/glacial acetic acid DI water 25 Phosphoric acid, 8.5% in water 4 Aerosil R 972 0.7 Titanium dioxide (Tiona 595) 20.0 Bayferrox 3920 0.06 Lamp black (Flamm 101) 0.001 Blanc Fixe powder N 12.939 Zinc phosphate (PZ 20) 6.0 Butyl glycol 5 Tinuvin 5941 R 1 Byk 331 0.3

(36) The epoxide-amine adduct (I) in table 5 is the reaction product prepared in example 3 (epoxide-amine adduct, 63% in butyl glycol/water/glacial acetic acid).

(37) Prior to spray application, 100 parts of mixture W1 were admixed with a further 10 parts of dilute phosphoric acid (8.5% in DI water), as indicated in table 6. This gave mixture W2.

(38) TABLE-US-00006 TABLE 6 Mixture W2 Mixture W1 100 Phosphoric acid, 8.5% 10

(39) Then 110 parts of mixture W2 were mixed with 20 parts of a polyisocyanate curing agent (Desmodur N 3600, hexamethylene diisocyanate trimer, 78%) and then adjusted to spray viscosity with 15 parts of DI water (20 sec. ISO 4/EN ISO 2431).

(40) The characteristics of the resulting mixture were as follows:

(41) TABLE-US-00007 nonvolatiles content (solids) 49.4% by weight VOC 285 g/L pH 5.0

(42) The resulting mixture was used

(43) 1.) as a white primer-surfacer without further coat system (i.e. as a white topcoat) and

(44) 2.) as a white primer-surfacer beneath a clearcoat as described below.

(45) Substrates: aluminum, steel, galvanized steel, in each case sanded and cleaned System 1.) 2 spray passes with 5-minute flash-off in between, film thickness approximately 50-60 m, curing at 60 C. for 30 minutes System 2.) 2 spray passes with 5-minute flash-off in between, film thickness approximately 50-60 m, curing at 60 C. for 30 minutes coating with commercial 2K clearcoat curing at 60 C. for 30 minutes

(46) The resulting systems (coatings) showed good processing properties, good adhesion, and good stonechip protection on all three substrates.

(47) 2.2 Clearcoat

(48) Mixture K1 was prepared by mixing the constituents according to table 7 in a dissolver for 10 minutes.

(49) TABLE-US-00008 TABLE 7 Mixture K1 Epoxide-amine adduct (I), 63% in 44 butyl glycol/water/glacial acetic acid DI water 47.6 Phosphoric acid, 8.5% in water 2.5 Butyl glycol 4.6 Tinuvin 59-41 R 1 Byk 331 0.3

(50) The epoxide-amine adduct (I) in table 7 is the reaction product prepared in example 3 (epoxide-amine adduct, 63% in butyl glycol/water/glacial acetic acid).

(51) Prior to spray application, 100 parts of mixture K1 were admixed with a further 10 parts of dilute phosphoric acid (8.5% in DI water), as indicated in table 8. This gave mixture K2.

(52) TABLE-US-00009 TABLE 8 Mixture K2 Mixture K1 100 Phosphoric acid, 8.5% 10

(53) Then 110 parts of mixture K2 were mixed with 20 parts of a polyisocyanate curing agent (Desmodur N 3600, hexamethylene diisocyanate trimer, 78%) and then adjusted to spray viscosity with 12 parts of DI water (20 sec. ISO 4/EN ISO 2431).

(54) The characteristics of the resulting mixture were as follows:

(55) TABLE-US-00010 nonvolatiles content (solids) 31% by weight VOC 290 g/L pH 5.0

(56) The resulting mixture was used

(57) 1.) as a clear primer-surfacer without further coat system (i.e. as a clear topcoat) and

(58) 2.) as a clear primer-surfacer beneath a clearcoat as described below.

(59) Substrates: aluminum, steel, galvanized steel, in each case sanded and cleaned System 1.) 2 spray passes with 5-minute flash-off in between, film thickness approximately 30-40 m, curing at 60 C. for 30 minutes System 2.) 2 spray passes with 5-minute flash-off in between, film thickness approximately 30-40 m, curing at 60 C. for 30 minutes coating with commercial 2K clearcoat curing at 60 C. for 30 minutes

(60) The resulting systems (coatings) showed very good adhesion on all three substrates.

(61) 2.3 Silver Metallic Color

(62) Mixture M1 was prepared by mixing the constituents according to table 9 in a dissolver for 10 minutes.

(63) TABLE-US-00011 TABLE 9 Mixture M1 Epoxide-amine adduct (I), 63% in 39 butyl glycol/water/glacial acetic acid Phosphoric acid, 8.5% in water 2.5 Tinuvin 59-41 R 1 Byk 331 0.3 Butyl glycol 4.6 Alu Stapa Hydrolux 8154, 65% 10

(64) The epoxide-amine adduct (I) in table 9 is the reaction product prepared in example 3 (epoxide-amine adduct, 63% in butyl glycol/water/glacial acetic acid).

(65) With stirring, 42.6 parts of DI water were added to mixture M1. The 100 parts of the resultant mixture were admixed with 10 parts of dilute phosphoric acid (8.5% in DI water). This gave mixture M2.

(66) Then 110 parts of mixture M2 were mixed with 20 parts of a polyisocyanate curing agent (Desmodur N 3600, hexamethylene diisocyanate trimer, 78%) and then adjusted to spray viscosity with 12 parts of DI water (20 sec. ISO 4/EN ISO 2431).

(67) The resulting mixture was used

(68) 1.) as a metallic coating without further coat system (i.e. as a metallic topcoat) and

(69) 2.) as a metallic coating beneath a clearcoat as described below.

(70) Substrates: aluminum, steel, galvanized steel, in each case sanded and cleaned System 1.) 2 spray passes with 5-minute flash-off in between, and 1 misting pass for effect alignment, film thickness approximately 30-40 m, curing at 60 C. for 30 minutes System 2.) 2 spray passes with 5-minute flash-off in between, and 1 misting pass for effect alignment, film thickness approximately 30-40 m, curing at 60 C. for 30 minutes coating with commercial 2K clearcoat curing at 60 C. for 30 minutes

(71) The metallic coating had excellent processing properties. In particular, the spray mist assimilation, the substrate wetting, and the flow were excellent.

(72) The resultant systems (coatings) showed a good metallic effect, good adhesion, and good stonechip protection on all three substrates.

(73) 2.4 Color VWL Y 3D (Tornado Red)

(74) Mixture R1 was prepared by mixing the constituents according to table 10 in a dissolver for 15 minutes and then dispersing the mixture in a stirred mill for 120 minutes.

(75) TABLE-US-00012 TABLE 10 Mixture R1 Epoxide-amine adduct (I), 63% in 27.29 butyl glycol/water/glacial acetic acid DI water 30 Phosphoric acid, 8.5% in water 5 Butyl glycol 5 Irgazin DPP red BO 9 Quindo violet RV 6902/R 1.6 Chromophtal red A2B 0.8 Novoperm orange HL-70 0.8 Color black FW-2 0.01 Titanium rutile 2310 0.8 Aerosil R 972 0.7 Blanc Fixe powder N 13 Zinc phosphate (PZ 20) 6.0

(76) The epoxide-amine adduct (I) in table 10 is the reaction product prepared in example 3 (epoxide-amine adduct, 63% in butyl glycol/water/glacial acetic acid).

(77) Prior to spray application, 100 parts of mixture R1 were admixed with a further 10 parts of dilute phosphoric acid (8.5% in DI water), as indicated in table 11. This gave mixture R2.

(78) TABLE-US-00013 TABLE 11 Mixture R2 Mixture R1 100 Phosphoric acid, 8.5% 10

(79) Then 110 parts of mixture R2 were mixed with 20 parts of a polyisocyanate curing agent (Desmodur N 3600, hexamethylene diisocyanate trimer, 78%) and then adjusted to spray viscosity with 15 parts of DI water (20 sec. ISO 4/EN ISO 2431).

(80) The resulting mixture was used

(81) 1.) as a tornado red primer-surfacer without further coat system (i.e. as a tornado red topcoat) and

(82) 2.) as a tornado red primer-surfacer beneath a clearcoat as described below.

(83) Substrates: aluminum, steel, galvanized steel, in each case sanded and cleaned System 1.) 2 spray passes with 5-minute flash-off in between, film thickness approximately 50-60 m, curing at 60 C. for 30 minutes System 2.) 2 spray passes with 5-minute flash-off in between, film thickness approximately 50-60 m, curing at 60 C. for 30 minutes coating with commercial 2K clearcoat curing at 60 C. for 30 minutes

(84) The resulting systems (coatings) showed good adhesion, and good stonechip protection on all three substrates.

(85) 2.5 Basecoat Color VWL Y 3D (Tornado Red)

(86) Mixture B1 was prepared by mixing the constituents according to table 12 in a dissolver for 15 minutes and then dispersing the mixture in a stirred mill for 120 minutes.

(87) TABLE-US-00014 TABLE 12 Mixture B1 Epoxide-amine adduct (I), 63% in 36.89 butyl glycol/water/glacial acetic acid DI water 39.8 Acetic acid, 10% in water 2.9 Butyl glycol 7.4 Irgazin DPP red BO 9 Quindo violet RV 6902/R 1.6 Chromophtal red A2B 0.8 Novoperm orange HL-70 0.8 Color black FW-2 0.01 Titanium rutile 2310 0.8

(88) The epoxide-amine adduct (I) in table 12 is the reaction product prepared in example 3 (epoxide-amine adduct, 63% in butyl glycol/water/glacial acetic acid).

(89) 100 parts of mixture B1 were mixed with 20 parts of a polyisocyanate curing agent (Desmodur N 3600, hexamethylene diisocyanate trimer, 78%) and then adjusted to spray viscosity with 20 parts of DI water (20 sec. ISO 4/EN ISO 2431).

(90) The resulting mixture was used as a tornado red basecoat atop a primer-surfacer and beneath a clearcoat. Substrates: aluminum, steel, galvanized steel, in each case sanded and cleaned System: 2 spray passes of white primer-surfacer from example 2.1 with 5-minute flash-off in between, film thickness approximately 50-60 m, curing at 60 C. for 30 minutes, 2 spray passes of tornado red basecoat with 5-minute flash-off in between, film thickness approximately 30 m, after approximately 30 minutes at room temperature, coating with commercial 2K clearcoat, film thickness approximately 60 m curing at 60 C. for 30 minutes

(91) The resulting systems (coatings) showed good adhesion, and good stonechip protection on all three substrates.

(92) 3. Preparation of the Epoxide-Amine Adduct (I)

(93) In a reactor equipped with a stirrer, reflux condenser, internal thermometer, and inert-gas inlet, 1099.2 parts of epoxide resin based on bisphenol A, with an epoxy equivalent weight (EEW) of 186 g/eq, are heated, together with 336.9 parts of bisphenol A, 193.6 parts of dodecylphenol, and 84.1 parts of xylene, to 125 C. under a nitrogen atmosphere, and stirred for 10 minutes. Heating then takes place to 130 C. and 1.6 parts of triphenylphosphine (from BASF SE) are added. After a brief exotherm to 150 C., the reaction mixture is held at 130 C. until the EEW has reached a value of 738 g/eq.

(94) At that point 412.7 parts of butyl glycol and 997.3 parts of a polypropylene glycol glycidyl ether having an EEW of 392 (Araldit DY 3601; Huntsman) are added and the temperature is allowed to drop to 90 C.

(95) At 90 C., 165.5 parts of 2,2-aminoethoxyethanol (from BASF SE) and, 10 minutes later, 40 parts of N,N-dimethylaminopropylamine (from BASF SE) are added. An exothermic reaction occurs and the temperature climbs to 120 C. It is then held at 110 C. for 2 hours until the viscosity remains constant at 359 mPas (85% resin solution, diluted with propylene glycol methyl ether to 45%; measured on Brookfield CAP 2000 viscometer at 23 C.). The resin solution is then cooled to 80 C. and discharged.

(96) 2946.8 parts of the resin solution are transferred to a dispersing vessel, into which 573.1 parts of deionized water, 462.2 parts of butyl glycol and 17.9 parts of glacial acetic acid have been introduced. The mixture is stirred and homogenized for an hour and then the resin solution is allowed to cool to room temperature. This produces a semitransparent whitish solution possessing the following characteristics:

(97) TABLE-US-00015 Solids content: 63.3% (1 h at 130 C., initial mass 1.0 g) Base content: 0.79 milliequivalents/g solids Acid content: 0.11 milliequivalents/g solids pH: 7.6 Conductivity: 0.33 mS (as 10% strength aqueous solution) Hydroxyl number: 138.5 mg KOH/g