Adhesion promoter for solventborne clearcoat materials

Abstract

The present invention relates to a solventborne clearcoat material which comprises at least one additive preparable by reacting at least one alpha,omega-hydroxy-functionalized oligoester which has an OH number of 30 to 160 mg KOH/g, a theoretical carbon-carbon double bond content of 1 to 2.5 mmol/g, a number-average molecular weight of 1000 to 3000 g/mol, and a weight-average molecular weight of 2800 to 10 000 g/mol, and at least one alkoxysilane which possesses an OH-reactive functional group, the sum of the weight percentage fractions of all additives of the invention being 0.5 to 10 wt %, based on the total amount of the solventborne clearcoat material. The present invention further relates to a process for producing multicoat paint systems, and to multicoat paint systems producible by means of said process. The invention further relates to the use of the above-identified additive in solventborne clearcoat materials for the purpose of improving adhesion.

Claims

1. A solventborne clearcoat material, comprising at least one additive prepared by reacting (a) at least one alpha,omega-hydroxy-functionalized oligoester which possesses an OH number of 30 to 160 mg KOH/g, a theoretical carbon-carbon double bond content of 1 to 2.5 mmol/g, a number-average molecular weight of 1000 to 3000 g/mol, and a weight-average molecular weight of 2800 to 10000 g/mol, and (b) at least one alkoxysilane of the structural formula (II)
A-RSi(R).sub.x(OR).sub.3x wherein A is an OH-reactive functional group, R is an aliphatic radical having 2 to 12 carbon atoms, a cycloaliphatic radical having 3 to 12 carbon atoms, an aromatic radical having 6 to 12 carbon atoms, or an araliphatic radical having 7 to 18 carbon atoms, the radical R is selected from the group of C1 to C12 alkyl radical, R is a methyl or ethyl radical, and x is 0 to 2, with the proviso that at least 90 mol % of all the OH groups of the alpha,omega-hydroxy-functionalized oligoester have been reacted with the OH-reactive functional group A, and, in addition, the amount by weight of the at least one additive is 0.5 to 10 wt %, based on the total amount of the solventborne clearcoat material.

2. The solventborne clearcoat material of claim 1, wherein the amount by weight of the at least one additive is 1.5 to 7.5 wt %, based on the total amount of the solventborne clearcoat material.

3. The solventborne clearcoat material of claim 1, wherein the alpha,omega-hydroxy-functionalized oligoester possesses the following structural formula (I): ##STR00004## where the radicals R1 independently of one another are selected from the group consisting of a linear alkylene radical and a cyclic alkylene radical, the radicals R2 independently of one another are selected from the group consisting of an alkylene radical and an alkenylene radical, the ratio of alkylene to alkenylene radicals being selected specifically such that the alpha,omega-hydroxy-functionalized oligoester of the structural formula (I) possesses a theoretical carbon-carbon double bond content of 1 to 2.5 mmol/g, and the index m is selected such that the number-average molecular weight of the alpha,omega-hydroxy-functionalized oligoester of the structural formula (I) is 1000 to 3000 g/mol.

4. The solventborne clearcoat material of claim 3, wherein the radicals R.sub.1 are linear alkylene radicals having 6 to 10 carbon atoms.

5. The solventborne clearcoat material of claim 3, wherein the radicals R.sub.2 are linear alkylene radicals having 4 to 8 carbon atoms or linear alkenylene radicals having 2 to 4 carbon atoms.

6. The solventborne clearcoat material of claim 3, wherein the alkoxysilane possesses the general structural formula (II. 1)
OCNR.sub.1Si(R).sub.x(OR).sub.3x wherein R1 is a C2 to C12 alkylene radical, a C2 to C12 alkenylene radical, or a a C4 to C12 polyalkenylene radical, the radical R is a C1 to C12 alkyl radical, R is a methyl or ethyl radical, and x is 0 to 2.

7. The solventborne clearcoat material of claim 6, wherein R.sub.1 is a C.sub.2 to C.sub.6 alkylene radical.

8. The solventborne clearcoat material of claim 7, wherein x=0.

9. A process for producing a multicoat paint system on a substrate, the process comprising (A) applying a basecoat material, (B) applying the solventborne clearcoat material of claim 1, and (C) jointly curing the basecoat material and the clearcoat material.

10. A multicoat paint system produced by the process of claim 9.

11. The process of claim 9, wherein, atop the clearcoat film as per step (C), i. a basecoat film is applied, ii. a clearcoat film is applied, and iii. the basecoat film and the clearcoat film are jointly cured.

12. A multicoat paint system produced by the process of claim 11.

13. The process of claim 9, wherein, atop the cured clearcoat film as per step (C), a sealant is applied.

14. A multicoat paint system produced by the process of claim 13.

15. A process for improving the adhesion properties of a clearcoat, the process comprising formulating a solventborne clearcoat material with at least one additive prepared by reacting (a) at least one alpha,omega-hydroxy-functionalized oligoester which possesses an OH number of 30 to 160 mg KOH/g, a theoretical carbon-carbon double bond content of 1 to 2.5 mmol/g, a number-average molecular weight of 1000 to 3000 g/mol, and a weight-average molecular weight of 2800 to 10000 g/mol, and (b) at least one alkoxysilane of the structural formula (II)
A-RSi(R).sub.x(OR).sub.3x wherein A is an OH-reactive functional group, R is an aliphatic radical having 2 to 12 carbon atoms, a cycloaliphatic radical having 3 to 12 carbon atoms, an aromatic radical having 6 to 12 carbon atoms, or an araliphatic radical having 7 to 18 carbon atoms, the radical R is a C1 to C12 alkyl radical, R is a methyl or ethyl radical, and x is 0 to 2, with the proviso that at least 90 mol % of all the OH groups of the alpha,omega-hydroxy-functionalized oligoester have been reacted with the OH-reactive functional group A, and, in addition, the amount by weight of the at least one additive is 0.5 to 10 wt %, based on the total amount of the solventborne clearcoat material.

Description

EXAMPLES

Preparation Example

Example A

Preparation of the Alpha,Omega-Hydroxy-Functionalized Oligoester

(1) The reactants identified in table 1 are reacted as set out below in the molar proportions indicated therein. First of all, maleic anhydride (MAn), adipic acid (AD), and 1,6-hexanediol (HD) are charged to a 4-liter reactor made from stainless steel and equipped with a column, a condenser, and a water separator. This is followed by addition of 3% of xylene as azeotrope former and of 0.1% of methylhydroquinone (the percentage figures are based on the amount of the MAn, AD, and HD used). The resulting reaction mixture is heated under lean air over the course of 5 minutes. Throughout the reaction time, the temperature of the reaction mixture does not exceed 230 C. When an acid number of 2 mg KOH/g is reached, the reaction mixture is cooled to 80 C. The characteristic data for the resulting alpha,omega-hydroxy-functionalized oligoesters are as follows:

(2) OH number: 65 mg KOH/g

(3) Number-average molecular weight: 1412 g/mol

(4) Weight-average molecular weight: 3313 g/mol

(5) Theoretical carbon-carbon double bond content: 1.86 mmol/g

(6) TABLE-US-00001 TABLE 1 Amounts of substance of the reactants for use, in mol. Raw Amount of material substance 1 MAn 5.05 2 AD 5.53 3 HD 14.46 Solids content 97 [%]

Example B

Preparation of an Inventive Additive (A1)

(7) A steel reactor equipped with a reflux condenser and a thermometer is charged with 27.4 parts of 3-isocyanatopropyltriethoxysilane from ABCR GmbH & Co. KG (European dispatch of Gelest INC. products), 9.4 parts of butyl acetate, 0.2 part of 1,4-diaza-bicyclo[2.2.2]octane, and 2.2 parts of triethyl orthoformate. Via a dropping funnel, subsequently, a mixture of 46.3 parts of the alpha,omega-hydroxy-functionalized oligoester (example A) and 14.5 parts of butyl acetate is added dropwise under a nitrogen atmosphere and with stirring. After 6-hour stirring at 70-80 C., the NCO value is verified by titrimetry according to DIN EN ISO 11909 (date: May 2007) and the reaction is continued until an NCO value of 0 is found. The inventive additive A1 has a nonvolatiles content of 71.8 wt %.

(8) I) Window Bonding Adhesion

(9) I.1) Preparation of a Solventborne 2K Clearcoat Material Comprising Additive (A1)

(10) A commercial solventborne 2-component clearcoat material was used. The composition of the two millbase and curing agent components is shown in table 2. Both the millbase and the curing agent were each admixed with 4 wt % of the additive (A1), based on the total amount of the 2-component clearcoat material. A laboratory stirrer was used for the additization (260-1820 rpm). The millbase and curing agent components are used in a ratio of 100:36, the ratio being based on the weight of the components.

(11) TABLE-US-00002 TABLE 2 Composition of the clearcoat material used (millbase, curing agent). The weight percentage figures are based in each case on the total weight of the millbase or of the curing agent, respectively. Millbase Curing agent Component wt % Component wt % Hydroxy-functional acrylate (I) 35 Butyl acetate 3.2 Hydroxy-functional acrylate (II) 26 Isophorone diisocyanate 15.2 Antisettling agent 13 Desmodur N3390 78.2 Thixotropic agent 2 Solvent naphtha 3.4 Cymel 202 (82% form), 8 (melamine-formaldehyde resin) Solvent naphtha 4 Tinuvin 384 (light stabilizer) 1.1 Tinuvin 292 (light stabilizer) 0.9 Butyl acetate 3.7 Byk 325 (surface additive) 0.2 Dipropylene glycol methyl ether 7 Butanol 1
I.2) Production of a Coated Substrate

(12) The clearcoat material is applied to a substrate coated successively with an electrocoat material, a primer surfacer, and a basecoat material. The electrocoat is produced using the commercially available product CathoGuard 500 from BASF Coatings. The primer surface coat is produced using the commercially available product SecuBloc from BASF Coatings. The substrate coated with the primer surfacer is coated with the basecoat material so as to give a dry basecoat film thickness of 10-15 micrometers. The basecoat is produced using a commercially available aqueous basecoat material, this being the commercially available product Colorbrite from BASF Coatings. This is followed by drying at 80 C. for 7 minutes. To produce the clearcoat material, millbase and curing agent as per table 2, and also the additive (A1) present in the millbase component, are stirred together homogeneously using a wooden spatula, the millbase and curing agent components being used in a ratio of 100:36, the ratio being based on the weight of the components, and the mixture is subsequently applied pneumatically. At this point the clearcoat is dried to start with at 135 C. for 20 minutes, and the applied coatings are subsequently baked at 135 C. for 30 minutes. The baking step is repeated twice more. The resulting clearcoat has a dry film thickness of 40-45 micrometers.

(13) I.3) Investigation of the Adhesion Properties

(14) An adhesive (EFBOND DA 293) was applied as sealant to the cured clearcoat. This adhesive is used to bond the clearcoat to a glass sheet. The adhesion properties of the layer of adhesive on the clearcoat are investigated by means of the window bonding test (peel test of glazing adhesives) in accordance with the method described above.

(15) The failure mode is evaluated according to the scheme below, with the abbreviation OK standing for satisfactory, and the abbreviation nOK standing for unsatisfactory:

(16) TABLE-US-00003 Cohesive component Rating Evaluation of fracture 1 OK >95% 2 OK >75% to 95% 3 nOK >25% to 75% 4 nOK <25%

(17) It follows from the results set out in table 3 that using the additive allows a significant improvement to be obtained in the adhesion between the layer of adhesive and the clearcoat.

(18) TABLE-US-00004 TABLE 3 Adhesion properties of the unadditized and the additized clearcoat materials. Formulation Adhesion (rating) no additive 4 4 wt % of additive in millbase 1 4 wt % of additive in curing agent 1
II) Refinishing of an OEM Finish
II.1) Preparation of a Solventborne 2-Component Clearcoat Material Comprising Additive (A1)

(19) A commercial solventborne 2-component clearcoat material is used. The composition of the two millbase and curing agent components used in preparing the clearcoat material has already been shown in table 2. The millbase was admixed with 4 wt % or with 2 wt % of the additive (A1), based on the total amount of the 2-component clearcoat material. A laboratory stirrer was used for the additization (260-1820 rpm).

(20) II.2) Production of a Coated Substrate

(21) The clearcoat material is applied to a substrate coated successively with an electrocoat material, a primer surfacer, and a basecoat material. This multiple coating takes place in accordance with the procedure described in section I.2). To produce the clearcoat material, millbase and curing agent as per table 2, and also the additive (A1) present in the millbase component, are stirred together homogeneously using a wooden spatula, the millbase and curing agent components being used in a ratio of 100:36, the ratio being based on the weight of the components, and the mixture is subsequently applied pneumatically. At this point the clearcoat is dried to start with at 135 C. for 20 minutes, and the applied coatings are subsequently baked at 135 C. for 30 minutes. The baking step is repeated twice more. The resulting clearcoat has a dry film thickness of 40-45 micrometers. Applied pneumatically atop the overbaked additized clearcoat is a refinish basecoat, in such a way that the refinish basecoat dry film thickness is 10-15 micrometers. The resulting coat is dried at 18-23 C. for 10 minutes. The refinish basecoat material used is the basecoat composition according to table 4. A refinish clearcoat material is subsequently applied by pneumatic spray application. The resulting basecoat-clearcoat system is first dried at room temperature for 10 minutes and then cured in a forced air oven at 60 C. for 10 minutes. The refinish clearcoat material used is the 2-component clearcoat composition according to table 2, with the difference that it contains no additive (A1).

(22) TABLE-US-00005 TABLE 4 Basecoat composition used for preparing the refinish basecoat material Component wt % Commercial thixotropic agent (Laponite 18.2 RD) Water 9.3 Commercial dispersion of an OH 31.2 functional polyurethane resin (water content: 66.0 wt %, organic solvents: 6.3 wt %) Commercial dispersion of an OH 3.0 functional polyester resin (water content: 17.7 wt %, organic solvents: 20.0 wt %) Butoxypropanol 2.0 Cymel 327 (commercial melamine- 4.2 formaldehyde resin) TMDD BG 52 (commercial wetting agent) 0.5 DMEA, 10% strength in water 1.5 Commercial dispersion of an OH 5.1 functional acrylate resin (water content: 49.5 wt %, organic solvents: 13.0 wt %) Foamstar MF324 (commercial defoamer) 0.5 Ethylhexanol 4.0 BYK 347 (commercial wetting agent) 0.5 Pluriol P900 (commercial polyethylene 2.0 glycol) Isopropanol 2.2 Viscalex HV 30 (commercial rheological 0.4 agent) ABC tinting paste (10% dispersion of 10.1 Monarch 1400 carbon black pigment in water ABC tinting paste (50% dispersion of 0.04 Titanrutil 2310 pigment in water
II.3) Investigation of the Adhesion Properties

(23) The adhesion properties of the coatings produced are investigated by means of the cross-cut test in accordance with DIN EN ISO 2409 (date: April 2010). The adhesion was investigated for a coating system overbaked three times and five times (see table 5).

(24) TABLE-US-00006 TABLE 5 Adhesion properties of the unadditized and additized clearcoats of a correspondingly coated substrate in refinishing Cross-cut Cross-cut test to DIN test to DIN Gloss EN ISO 2409 EN ISO 2409 measurement (3 times (5 times according to clearcoat overbaked)/ overbaked)/ DIN EN ISO material used rating rating 2813 no additive 5 5 (A1) 2 wt % of 1 1 + additive (A1), based on the total amount of the 2-component clearcoat 4 wt % of 1 1 + additive (A1), based on the total amount of the 2-component clearcoat

(25) The determination of gloss is used to ascertain the surface gloss of painted areas, and is carried out from an angle of 60 in accordance with DIN EN ISO 2813 (date: October 2012). The assessment is made by determining the gloss value (GU) between 0 and 100. A gloss of less than 35 GU is given as , and a gloss >50 is given as +.