UV- and thermally curing clearcoat composition for automotive refinishing

Abstract

An UV- and thermally curable, solventborne clearcoat material suitable for automotive refinishing comprises: (A) at least one polyhydroxy-functional poly(meth)acrylate having grafted-on unsaturated (meth)acrylate side groups, (B) at least one polyisocyanate-functional, poly(meth)acrylate-functional aliphatic urethane, (C) at least one (meth)acrylate-functional aliphatic urethane free from isocyanate groups, (D) at least one hydroxy-functional, (meth)acrylate-functional aliphatic component free from isocyanate groups and from urethane groups and having a molecular weight of not more than 1000 g/mol and a (meth)acrylate functionality of at least 4, (E) at least one aliphatic polymercaptan, (F) at least one phosphoric acid or phosphonic acid blocked with an amine, the amine possessing a pK.sub.b of 3 and a boiling point under atmospheric pressure of >100 C., and (G) at least one photoinitiator selected from the group consisting of -hydroxyalkyl phenyl ketones and monoacylphosphine oxides. Component (A) may be an intermediate in the production of the clearcoat material.

Claims

1. An UV- and thermally curable, solventborne clearcoat material comprising (A) at least one polyhydroxy-functional poly(meth)acrylate having grafted-on unsaturated (meth)acrylate side groups, (B) at least one polyisocyanate-functional aliphatic urethane containing at least two (meth)acrylate groups, (C) at least one (meth)acrylate-functional aliphatic urethane free from isocyanate groups, (D) at least one hydroxy-functional, (meth)acrylate-functional aliphatic component free from isocyanate groups and from urethane groups and having a molecular weight of not more than 1000 g/mol and a (meth)acrylate functionality of at least 4, (E) at least one aliphatic polymercaptan, (F) at least one phosphoric acid or phosphonic acid blocked with an amine, the amine possessing a pKb of 3 and a boiling point under atmospheric pressure of >100 C., and (G) at least one photoinitiator selected from the group consisting of hydroxyalkyl phenyl ketones and monoacylphosphine oxides.

2. The UV- and thermally curable, solventborne clearcoat material according to claim 1, wherein component (A) is a (meth)acrylate copolymer of: (a) one or more monounsaturated acrylate and/or methacrylate monomers, (b) one or more monoethylenically unsaturated aromatic monomers, and optionally (c) one or more ethylenically unsaturated monomers different from (a) and (b), where a portion of the monomers (a) carry hydroxyl groups and a further portion of the monomers (a) carry epoxy groups, and where, after polymerization reaction has taken place, some or all, preferably all, of the epoxy groups have been reacted with acrylic acid and/or methacrylic acid, with retention of the carbon-carbon double bonds in the acrylic acid and/or methacrylic acid.

3. The UV- and thermally curable, solventborne clearcoat material according to claim 2, wherein the fraction of the monomers (a) is 50% to 70% by weight and the fraction of the monomers (b) is 30% to 50% by weight, based in each case on the total weight of the monomers constituting the main chain.

4. The UV- and thermally curable, solventborne clearcoat material according to claim 1, wherein the glass transition temperature of (A) is at least 10 C., preferably 20 to 60 C.

5. The UV- and thermally curable, solventborne clearcoat material according to claim 1, wherein (B) contains 2 to 6 unsaturated (meth)acrylate groups.

6. The UV- and thermally curable, solventborne clearcoat material according to claim 1, characterized in that (C) contains 2 to 6 unsaturated (meth)acrylate groups.

7. The UV- and thermally curable, solventborne clearcoat material according to claim 1, wherein (D) is selected from the group consisting of dipentaerythritol tetraacrylate and dipentaerythritol pentaacrylate.

8. The UV- and thermally curable, solventborne clearcoat material according to claim 7, wherein (D) is dipentaerythritol pentaacrylate.

9. The UV- and thermally curable, solventborne clearcoat material according to claim 1, wherein the aliphatic polymercaptan (E) is mono- or polyalkoxylated, has a number-average molecular weight of 200 to 2500 g/mol, and contains 2 to 6 thiol groups.

10. The UV- and thermally curable, solventborne clearcoat material according to claim 1, wherein the amine of component (F) is triethylenediamine and the phosphoric acid is a di(2-ethylhexyl)phosphoric acid.

11. The UV- and thermally curable, solventborne clearcoat material according to claim 1, wherein the photoinitiator (G) comprises an hydroxyalkyl phenyl ketone and a monoacylphosphine oxide.

12. The UV- and thermally curable, solventborne clearcoat material according to claim 1, wherein: component (A) is a (meth)acrylate copolymer of: (a) one or more monounsaturated acrylate and/or methacrylate monomers, (b) one or more monoethylenically unsaturated aromatic monomers, and optionally (c) one or more ethylenically unsaturated monomers different from (a) and (b), where a portion of the monomers (a) carry hydroxyl groups and a further portion of the monomers (a) carry epoxy groups, and where, after the polymerization reaction has taken place, some or all, preferably all, of the epoxy groups have been reacted with acrylic acid and/or methacrylic acid, with retention of the carbon-carbon double bonds in the acrylic acid and/or methacrylic acid, components (B) and (C) each contain 2 to 6 unsaturated (meth)acrylate groups, component (D) is selected from the group consisting of dipentaerythritol tetraacrylate and dipentaerythritol pentaacrylate, component (E) is mono- or polyalkoxylated, has a number-average molecular weight of 200 to 2500 g/mol, and contains 2 to 6, preferably 3, thiol groups, and component (G) comprises an -hydroxyalkyl phenyl ketone and a monoacylphosphine oxide.

13. The UV- and thermally curable, solventborne clearcoat material according to claim 1 comprising: 15% to 33% by weight of component (A), 5% to 30% by weight of component (B), 1% to 9% by weight of component (C), 3% to 16% by weight of component (D), 0.5% to 25% by weight of component (E), 0.009% to 0.1% by weight of component (F), and 0.03% to 3.1% by weight of component (G), based in each case on the total weight of the clearcoat material.

14. A modular system for producing the UV- and thermally curable, solvent-based clearcoat material according claim 1, comprising: a module (I) comprising components (A), (C), (D), (F), and (G), a module (II) comprising component (E), and a module (III) comprising component (B).

15. A method for producing a coating system comprising (i) singly or repeatedly applying the clearcoat material of claim 1 to a precoated or uncoated substrate; (ii) irradiating the applied clearcoat film or films with UV radiation for a time of 3 to 10 minutes at a temperature between 10 and 120 C.; (iii) optionally subsequently polishing the irradiated and heat-treated and thus cured clearcoat film.

16. The method for producing a coating system according to claim 15, where the UV radiation possesses a fraction of UV-A radiation and a fraction of UV-B radiation, and the fraction of UV-B radiation is smaller than the fraction of UV A radiation.

17. The method for producing a coating system according to claim 15, wherein the energy flux density of the UV-A radiation is 500 to 1000 microwatts/cm.sup.2 as measured from a distance of 200 cm, and the energy flux density of the UV-B radiation is 100 to 300 microwatts/cm.sup.2 as measured from a distance of 200 cm.

18. The method of claim 15, wherein the substrate is a curved substrate.

19. The method of claim 15, wherein the substrate is an automotive substrate.

Description

EXAMPLES

Example A

Preparation of Component (A)

(1) In a first step a glycidyl-functionalized copolymer was prepared. This was done by introducing 1165.6 g of butyl acetate into a standard stirring vessel and heating it to 164 C. under a nitrogen atmosphere at 3.5 bar. A mixture of 14 g of butyl acetate and 81.8 g of DTAP peroxide was added dropwise over the course of 15 minutes. 15 minutes later the dropwise addition of a mixture of 720.6 g of styrene, 394.7 g of methyl methacrylate, 171.6 g of butyl methacrylate, 103 g of hydroxyethyl acrylate, 68.6 g of hydroxybutyl acrylate and 257.4 g of glycidyl methacrylate was commenced, this mixture being metered in at a uniform rate over 460 minutes. Further initiator was metered in after 30 minutes, giving a total initiator feed time of 285 minutes. After the end of the metered addition, stirring was continued for 1 hour more at 150 C. and 3.5 bar. The result was a polymer solution having a solids content of 57.9% by weight (on drying for 1 hour at 130 C.) and a viscosity at 23 C. of 253 mPas at 750 revolutions per minute using spindle 3 (Brookfield CAP cone/plate viscosimeter; the samples were temperature-conditioned for 10 seconds beforehand, and the measurement was carried out over a period of 30 seconds, with the reading after 30 seconds being the measurement value reported).

(2) In a second step, 62.2 g of acrylic acid was metered in over the course of 1 hour to a mixture of 1478.1 g of the polymer solution obtained in the first step, 0.92 g of zinc acetylacetonate (0.1% by weight based on solids), 0.6 g of Doverphos S 9228 (0.065% by weight based on solids) and 0.3 g of methylhydroquinone (0.04% by weight based on solids) under lean air at 120 C. The mixture was held at 120 C. until the acid number fell below a level of 2 mg KOH/g. The result was a clear, 61.8% strength by weight polymer solution of component (A), the polymer possessing an OH number of 97 mg KOH/g, a weight-average molecular weight of 4485 g/mol, a number-average molecular weight of 1618 g/mol, and a double bond content of 2.65% by weight, based on the total weight of the monomers incorporated in the polymer, including the grafted-on acrylic acid. The polymer possesses a glass transition temperature of 35 C. as measured by differential scanning calorimetry (DSC) with a heating rate of 10 C./min (sample preparation as per DIN EN ISO 16805, with a glass plate as substrate and a sample applied by knife coating: 100 micrometers, dried at 130 C. for 60 minutes) and a Gardner color number of 0.5 (in accordance with DIN EN ISO 4630-2).

Example B

Preparation of an Inventive Clearcoat Material Using Component (A) from Example A

(3) A millbase module (I), comprising components (A), (C), (D), (F), and (G), a standardizing additive module (II), comprising component (E), and a curing agent module (III), comprising component (B), were produced. The compositions of each of the modules can be seen from Table 1. Shortly before application, the modules (I), (II), and (III) were mixed with one another to form the inventive clearcoat material.

(4) TABLE-US-00001 TABLE 1 Amount used in parts by weight per 100 Module parts by weight of clearcoat material Millbase module (I) Component (A) from 41.74 Example A (61.8% strength by weight) Component (C).sup.1 9.21 Component (D).sup.2 6.14 Component (F).sup.3 0.09 Component (G).sup.4 0.77 Flow control agent.sup.5 0.24 Light stabilizers.sup.6 1.1 Dibutyltin dilaurate 0.09 Additive solvents.sup.7 2.0 Standardizing module (II) Component (E).sup.8 4.51 Defoamer/Flow control agent.sup.9 0.27 Standardizing additive.sup.10 13.24 Curing agent module (III) Component (B).sup.11 15.45 Butyl acetate 5.15 (I) + (II) + (III) 100.00 .sup.1Unsaturated aliphatic urethane acrylate (58% in butyl acetate) .sup.2Dipentaerythritol pentaacrylate (100% form) .sup.3Di-(C.sub.8 alkyl ester) of phosphoric acid, blocked with triethylenediamine (50% in isopropanol) .sup.4Photoinitiator mixture of an -hydroxyalkyl phenyl ketone and a monoacyl- phosphine oxide .sup.5Mixture of two polyether-modified polydimethylsiloxanes (56%) .sup.6Mixture of two light stabilizers .sup.7Mixture of butyl acetate and methyl isobutyl ketone .sup.8Ethoxylated trimethylpropane tri(3-mercaptopropionate); M.sub.n = 708 g/mol; Functionality: 3 .sup.9Silicone-free, nonionic, high molecular mass defoamer/flow control agent (50%) .sup.10Glassodur standardizing additive, containing about 22.5% alkylbenzenes and about 77.5% different acetic esters (product of BASF Coatings GmbH) .sup.11Aliphatic urethane acrylate formed from hydroxyethyl acrylate and hexamethylene diisocyanate oligomers
Polishability:

(5) To investigate the polishability of the inventive clearcoat material, it is applied to a DIN A4 steel panel already coated with a 2-component PU primer-surfacer and a waterborne basecoat material. Application took place in two spray passes with a 1-minute intermediate flash-off time and a 5-minute final flash-off time in the spray booth. Drying took place over a time of 9 minutes under UV irradiation from a distance of 180 cm from angle of 90 to the panel, with a temperature of 23 C. and an atmospheric humidity of 50% (+5%). The characteristics of the UV radiation source are as follows (determined using Belt Radiometer ILT 390 C):

(6) TABLE-US-00002 Distance in cm Dose in mJ/cm.sup.2 50 18742 100 5731 180 1662 200 1437

(7) The measurement range of the instrument is located between 225 and 425 nm.

(8) After drying, the inventive UV clearcoat material was matted in the middle of the test panel over an area of approximately 1010 cm, using a Festo eccentric sanding machine and P2000 abrasive paper from 3M. It was subsequently polished up with a polishing machine (from Rupes) in the following 2 stages:

(9) In the first stage, polishing foam (pimpled) was used along with 3M Plus Abrasive Paste for 30 seconds for polishing. The second polishing stage used a polishing pad along with a high-gloss machine polish from 3M, again for 30 seconds.

(10) Immediately thereafter the polished surface was inspected for the following parameters:

(11) 1. Abrasion scars in daylight

(12) 2. Gloss (to DIN EN ISO 2813; measured at the receiver aperture angle of 20)

(13) 3. Shade shift (visual in daylight) and

(14) 4. Marginal zones (visibility of marginal zones around the polished site)

(15) Drying Recorder

(16) In accordance with ASTM D 5895-03 (Reapproved 2008)

(17) For assessment using the drying recorder, glass strips were painted using a Sata RP 1.3 NR gravity-fed cup gun in 2 spray passes (resulting in a dry film thickness of 40-45 m). There was a 1-minute flash-off between the spray passes. Subsequently, over a test duration of 12 hours at 23 C. and 50% relative humidity, determinations were made, by analogy with ASTM D 5895-03, of the set-to-touch time, tack-free time, dry-hard time and dry-through time.

(18) Type: The B.K. Drying Recorder

(19) Company: The Mickle Laboratory Engineering Co. Ltd GB

(20) Sample Preparation:

(21) Substrate material: Glass strips

(22) Spray gun: Sata RP 1.3 NR gun, used as per technical information sheet

(23) Spray passes: 2

(24) Intermediate flash-off time: 1 minute

(25) Test duration: 12 hours

(26) Temperature: 23 C.

(27) Atmospheric humidity: 50%

(28) Dry film thickness: 40-45 m

(29) The color numbers were determined in accordance with DIN EN ISO 4630-2, using a Dr. Lange LICO 200 instrument for color number determination.

(30) TABLE-US-00003 Millbase 1 Millbase C1 Millbase C2 Millbase C3 Millbase module (inventive) (comparative) (comparative) (comparative) Component (A).sup.a 65 65 Component (A) from 68 Example A Component (C).sup.b 15 Component (D).sup.c 10 24 24 Component (F).sup.d 0.15 Component (G).sup.e 1.25 1.5 1.5 1.5 Flow control agent.sup.f 0.4 0.4 0.4 0.4 Defoamer/Leveling 0.5 0.5 agent.sup.g Light stabilizers.sup.h 1.8 1.8 1.8 1.8 Dibutyltin dilaurate 0.15 0.15 0.15 0.15 Butyl acetate 1.25 6.15 2.65 2.65 Methyl isobutyl ketone 2 4 4 4 Triallyl isocyanurate 62 24 Standardizing Standardizing Standardizing additive module additive 1 additive 2 Standardizing additive.sup.i 73.50 65.000 Component (E).sup.j 35.000 Component (E).sup.k 25.00 Defoamer/Flow control agent.sup.g 1.50 Curing agent module Curing agent 1 Curing agent C1 Component (B).sup.l 75.00 Butyl acetate 25.00 TDI-based polyisocyanate 100 (75% in butyl acetate) 13.3% NCO content .sup.aParocryl VP 56017 (a polyhydroxy-functionalized poly(meth)acrylate with grafted-on unsaturated (meth)acrylate sidegroups) .sup.bUnsaturated aliphatic urethane acrylate (58% in butyl acetate) .sup.cDipentaerythritol pentaacrylate (100% form) .sup.dDi-(C.sub.8 alkyl ester) of phosphoric acid, blocked with triethylene diamine (50% in isopropanol) .sup.ePhotoinitiator mixture of an -hydroxyalkyl phenyl ketone and a monoacyl-phosphine oxide .sup.fMixture of two polyether-modified polydimethylsiloxanes (56%) .sup.gSilicone-free, nonionic, high molecular mass defoamer/flow control agent (50%) .sup.hMixture of two light stabilizers .sup.iGlassodur standardizing additive, containing about 22.5% alkylbenzenes and about 77.5% different acetic esters (product of BASF Coatings GmbH) .sup.jPentaerythritol tetra(3-mercaptopropionate) Functionality: 4 .sup.kEthoxylated trimethylpropane tri(3-mercaptopropionate); M.sub.n = 708 g/mol; Functionality: 3 .sup.lAliphatic urethane acrylate made from hydroxyethyl acrylate and hexamethylene diisocyanate oligomers

(31) TABLE-US-00004 Working examples Modules Parts by volume Example 1 Example C1 Example C2 Example C3 Example C4 Example C5 Millbase 3 Millbase 1 Millbase C1 Millbase C2 Millbase C3 Millbase C1 Millbase C3 Curing agent 1 Curing agent 1 Curing agent 1 Curing agent 1 Curing agent C1 Curing agent C1 Curing agent 1 Standardizing 1 Standardizing Standardizing Standardizing Standardizing Standardizing Standardizing additive additive 1 additive 2 additive 2 additive 2 additive 2 additive 2 Drying at room temperature Example 1 Example C1 Example C2 Example C3 Example C4 Example C5 Drying Recorder 12 h Set-to-touch time after start in h 0.25 2 0.5 0.5 12 1 Tack-free time after start in h 0.75 12 2 1 2 Dry-hard time after start in h 1.25 6.5 2 7 Dry-through time after start in h 1.5 11 7 11.5 dry, firm to Notes/Assessment: dry, firm to no drying, very dry, firm to no drying, sticky Drying at room temperature touch, good wet sticky, touch, wet surface, after 24h topcoat hold clearcoat pinholes pinholes, clearcoat fine down blushing pinholes Polishability 1. Abrasion scars in daylight none visible visible visible visible none 2. Gloss (to DIN EN ISO 2813; 89 75 80 78 73 89 measured at the receiver aperture angle of 20) 3. Shade shift (visual in daylight) none distinct slight severe severe none 4. Marginal zones (visibility of none visible visible visible visible slight marginal zones around the marking polished site)