COATING MATERIAL COMBINATION CONSISTING OF SURFACER AND TOPCOAT

Abstract

Coating material combination consisting of a coating material for forming a surfacer coat and a coating material for forming a topcoat, and use thereof for producing a coating system consisting of a surfacer coat and topcoat on a substrate. The substrate preferably comprises the body or the cabin of a motor vehicle, or a constituent thereof. The coating material combination of the invention is suitable especially for producing coatings consisting of a cured surfacer coat and a cured topcoat on automobiles and commercial vehicles, such as trucks, vans, or buses.

Claims

1. A coating material combination, comprising: a coating material comprising at least one coloring pigment and at least one externally crosslinking binder as main binder for forming a surface coat on a substrate; a coating material comprising at least one coloring pigment and at least one externally crosslinking binder as main binder for forming a topcoat on the surfacer coat, wherein: the coating material for forming the surfacer coat and the coating material for forming the top coat are compatible according to DIN EN ISO 12944-5:2008-1; the coating material for forming the topcoat can be applied to the surfacer coat before the surfacer coat has reached drying stage 1 according to DIN 53150:2002-09, the drying stage being determined according to EN ISO 9117-3:2010; the coating material for forming the surfacer coat comprises organic solvents; and the coating material for forming the topcoat comprises organic solvents.

2. The coating material combination as claimed in claim 1, wherein the main binder of the coating material for forming the surfacer coat and the main binder for forming the topcoat are compatible according to DIN EN ISO 12944-5:2008-01.

3. The coating material combination as claimed in claim 1, wherein the main binder of the coating material for forming the surfacer coat and the main binder of the coating material for forming the topcoat belong to the same binder class.

4. The coating material combination as claimed in claim 1, wherein the main hinder of the coating material for forming the surfacer coat and the main binder of the coating material for forming the topcoat are identical.

5. The coating material combination as claimed in claim 1, wherein the organic solvents of the coating material for forming the surfacer coat and the organic solvents of the coating material for forming the topcoat belong to the same solvent class.

6. The coating material combination as claimed in claim 5, wherein the organic solvents of the coating material for forming the surfacer coat and the organic solvents of the coating material for forming the topcoat are identical.

7. The coating material combination as claimed in claim 1, wherein the main binder and the organic solvents of the coating material for forming the surfacer coat and the main binder and the organic solvents of the coating material for forming the topcoat are identical.

8. The coating material combination as claimed in claim 1, wherein the coating materials for forming the surfacer coat and for forming the topcoat have a solids fraction of at least 40 wt %.

9. The coating material combination as claimed in claim 1, wherein: the main binder of the coating materials for forming the surfacer coat is selected from the group consisting of isocyanate-crosslinking, polyhydroxyl group-containing polyester and polyacrylate resins and mixtures thereof; and the main binder of the coating materials for forming the topcoat is selected from the group consisting of isocyanate-crosslinking, polyhydroxyl group-containing polyester and polyacrylate resins and mixtures thereof.

10. A process for producing a coating system on a substrate, the process comprising applying the coating material combination of claim 1 to a substrate to obtain a coating system consisting of a surfacer coat and a topcoat, wherein: i-a) the coating material for forming the surfacer coat is applied to the substrate to form a surfacer coat; and i-b) the coating material for forming the topcoat is applied to the surfacer coat to form a topcoat, the application of the coating material to form the topcoat in i-b) taking place before the coating material for forming the surfacer coat in i-a) has reached drying stage 1 according to DIN 53150:2002-09, the drying stage being determined according to EN ISO 9117-3:2010.

11. The process as claimed in claim 10, further comprising curing the coating system to obtain a coating consisting of a cured surfacer coat and cured topcoat.

12. The coating material combination of claim 1, wherein the costing material combination consists of: the coating material comprising at least one coloring pigment and at least one externally crosslinking binder as main binder for forming the surface coat on the substrate; and the coating material comprising at least one coloring pigment and at least one externally crosslinking binder as main binder for forming the topcoat on the surfacer coat.

Description

ABBREVIATIONS AND STARTING MATERIALS

[0079] TNP 1,1,1tris(hydroxymethyl)propane

[0080] HHPAn hexahydrophthalic anhydride

[0081] Cardura E10? glycidyl ester of neodecanoic acids; manufacturer: Momentive

[0082] HDI hexamethylene diisocyanate

[0083] IPDI isophorone diisocyanate

[0084] The nonvolatile fraction, i.e., the solids content (solids fraction), of the coating materials is determined according to DIN EN ISO 3251 (date: June 2008). The test duration for this is 60 minutes at a temperature of 130? C. The nonvolatile fraction which remains after drying is expressed in relation to the initial mass, and indicates the percentage solids content of the coating material composition.

[0085] Determination of the OH number: The OH number is calculated via the stoichiometry of the components used. The OH number is calculated from the OH-functional components employed minus the acid number attained, plus the further OH groups arising from the ring-opening reaction.

[0086] Determination of the acid number: The acid number is determined by titration with a KGH solution according to DIN EN ISO 2114. The acid number here indicates the amount of potassium hydroxide in mg which is consumed in the neutralization of 1 g of the respective compound.

[0087] The reported OH numbers and acid numbers relate in each case to the solids fraction of the coating material.

[0088] Determination of the molecular weight: Molecular weight determinations are carried out by means of gel permeation chromatography (GPC) at 40? C. using a high-pressure liquid chromatography pump and a refractive index detector. Eluent used is tetrahydrofuran, with an elution rate of 1 ml/min. Calibration is carried out using a polyMMA standard. The number-average molecular weight Mn, the weight-average molecular weight Mw, and Mp are determined, with the polymolecularity index Mp being calculated from Mp=Mw/Mn.

[0089] Determination of the glass transition temperature T.sub.g is carried out according to DIN 53765.

[0090] The measurement of the viscosity was carried out at 23? C. using a rotational viscometer from Brookfield, model cap 2000+, spindle 3 with a shear rate of 1250 s.sup.?1.

[0091] In the working examples below, application took place in each case by ESTA to cathodically electrocoated substrate; dry film thicknesses: surfacer 30 ?m in each case, topcoat 50 ?m in each case.

[0092] Prior art: Comparative example sample 1 with a commercial surfacer (surfacer 1) and a commercial white two-component topcoat (topcoat 1) (both from BASF Coatings GmbH M?nster):

[0093] Surfacer 1 is a solventborne one-component (1-K) surfacer based on a polyester, crosslinked with a melamine resin. An alternative possibility is to also use other commercial solventborne fillers, such as polyamine-crosslinked epoxy resins or oligoisocyanate-crosslinked OH-functional acrylate resins, for example, and also aqueous surfacers.

[0094] Topcoat 1 is a two-component (2-K) topcoat (white) based on an OH-functional acrylate resin which has been crosslinked with oligoisocyanate (similar in composition to the topcoat composition of topcoat 2).

[0095] Filler and topcoat of the inventive coating material combination: solventborne 2-K surfacer (surfacer 2) and solventborne 2-K topcoat (white) (topcoat 2)

Description of the Individual Syntheses for Producing the Inventive Coating Material Combination:

Polyester:

[0096] Analogous: reference: Research Disclosure (2006), 505 (May), P520-P521 (No. 505044; CODEN: RSDSBB; ISSN; 0374-4353

[0097] In analogy to example A from the literature reference identified above, 1 mol of TNP is reacted with 2 mol of HHPAn, and then the resulting product is reacted in a second stage with 2 mol of Cardura E-10? at 120? C. After a further 2 hours at this; temperature, the product is cooled and diluted with a mixture of 2 parts xylene and 1 part SOLVENTNAPHTHA 160/180 to a solids content of 84?1%. This gives a viscous solution having a viscosity of 3400-4800 mPas.

OH-Functional Acrylate 1:

[0098] OH-functional acrylate polymerized in SOLVENTNAPHTHA 160/180 with an OH number of 115-125 mg KOH/g, a T.sub.g of 33? C., an acid number of 5-8 mg KOH/g, a number-average molecular weight of 1200-2000 daltons, and a weight-average molecular weight of 3300-5100 daltons (measured against polymethyl methacrylate as standard), and a solids content of 65?1%. The polymerization temperature is 160? C. under superatmospheric pressure (3 bar abs.).

[0099] The solvent is a mixture of SOLVENTNAPHTHA 160/180 and n-butyl acetate in a ratio of 4:1. The OH acrylate has a viscosity of 650-1000 mPas. The monomer composition is composed of approximately equal parts of styrene, hydroxyethyl methacrylate, methyl methacrylate, and isodecyl methacrylate.

OH-Functional Acrylate 2:

[0100] OH-functional acrylate polymerized in butyl acetate with an OH number of 152-160 mg KOH/g, a T.sub.g of 55? C., an acid number of 8-10 mg KOH/g, a number-average molecular weight of 1600-2200 daltons, and a weight-average molecular weight of 3900-4500 daltons (measured against polymethyl methacrylate as standard), and a solids content of 55?1%. The solvent is a mixture of SOLVENTNAPHTHA 160/180 arid n-butyl acetate in a ratio of 7:1.

[0101] The OH acrylate has a viscosity of 900-1300 mPas. The monomer composition consists of equal parts of styrene, butyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and also cyclohexyl methacrylate and a small fraction of acrylic acid.

OH-Functional Acrylate 3:

[0102] OH-functional acrylate polymerized in butyl acetate with an OH number of 115-125 mg KOH/g, a T.sub.g of 33? C., an acid number of 5-8 mg KOH/g, a number-average molecular weight of 1300-1500 daltons, and a weight-average molecular weight of 3700-4500 daltons (measured against polymethyl methacrylate as standard), and a solids content of 78?1% in butyl acetate. The polymerization temperature is 160? C. under superatmospheric pressure (3 bar abs.).

[0103] This gives a viscous solution having a viscosity of 5800-6300 mPas. The monomer composition is composed of approximately equal parts of styrene, hydroxyethyl methacrylate, methyl methacrylate, and isodecyl methacrylate.

Working Example of a Surfacer Formulation and a Topcoat Formulation for the Inventive Coating Material Combination (Surfacer 2 with Topcoat 2)

TABLE-US-00001 Surfacer 2 Topcoat 2 Polyester (solid) 15.5 16 OH acrylate resin 1 and 2 (solid) 10 13.1 OH acrylate resin 3 (solid) 11 9.4 Commercial dispersing additives 1 0.8 (Disperbyk from Byk) Filler 1 5 0 Talc Filler 2 16 0 Chalk Filler 3 12 0 Zinc oxide Pigment 1 3 33.7 Titanium dioxide Pigment 2 0.01 0.2 Carbon black Additives (light stabilizer, UV 0 0.5 absorber, HALS) Thixotropic additive 1 0.1 0.2 Aerosil Thixotropic additive 2 0.3 0.2 Bentone Catalyst 0.02 0.02 Solvents 25 25.83 Acetates, ketones, aromatics, aliphatics Additives (flow control, wetting) 0.07 0.05 100 100

[0104] Both surfacer and topcoat were crosslinked with a commercial aliphatic oligoisocyanate based on hexamethylene diisocyanate (HDI). Alternatively, crosslinking can also be carried out with isophorone diisocyanate (IPDI).

[0105] The application itself was made in each case under identical conditions, with ESTA (electrostatic application), from the same distance, with the same delivery rates, drawing speeds, rotary speed of the bell, etc.

Inventive Samples:

[0106] In inventive examples 2, 3 and 4, the coating material for forming the topcoat is applied before the coating material for forming the surfacer coat has reached drying stage 1 according to DIN 53150:2002-09. The samples differ in the flash-off time of the surfacer coat.

[0107] Comparative samples with surfacer 1 or surfacer 2: The topcoat was applied, after curing of the surfacer, to the respective cured surfacer coat.

[0108] Sample 1: Surfacer 1 cured thermally before topcoat application

[0109] Sample 5: Surfacer 2 cured thermally before topcoat application

TABLE-US-00002 Sample 1* 2 3 4 5* Surfacer Surfacer 1 Surfacer 2 Surfacer 2 Surfacer 2 Surfacer 2 Flash- 240 sec 480 sec 600 sec off time of surfacer coat Curing x x of surfacer coat Topcoat Topcoat 1 Topcoat 2 Topcoat 2 Topcoat 2 Topcoat 2 LW 23.6 3.4 5.4 7.2 17.5 SW 6.2 5.4 6.5 6.9 2.3 N1 8.4 3.6 4.8 5.5 8 N3 8.4 3.8 5.1 5.8 8.3 CF 43.3 70.2 64.4 60.6 44.6 DOI 92.4 93.3 93.2 93 93.6 *not inventive

[0110] With noninventive combination of surfacer 1 with topcoat 1 or 2 (not listed in the table) and with application of the topcoats to the surfacer coat before the latter has achieved dust dryness, after the flash-off times reported in the table, matt topcoat surfaces were obtained. This represents an unwanted side effect. The surface properties of a matt surface cannot be measured using a wave-scan instrument.

[0111] The optical properties were measured using a commercial wave-scan dual instrument from Byk Gardner. The values obtained therewith on glossy surfaces were converted, by the accompanying software, into the following values: [0112] Longwave (LW), shortwave (SW) [0113] N1 and N3 (according to BMW scales, which represent the surface as viewed from a distance of 1 m and 3 m respectively) [0114] CP (according to FORD scales, which are made up of luster, sharpness, and orange peel) [0115] DOI (corresponding approximately to the gloss at a 20? viewing angle)

[0116] With regard to the evaluation of the optical result, better optical properties are present when [0117] LW and SW are smaller and/or when LW<SW [0118] N1 and N3 are smaller [0119] CF is greater

[0120] The results table shows that sample 2 (inventive coating material combination of surfacer 2 and topcoat 2 with the shortest flash-off time) exhibits the best optical properties. An extension to the flash-off time causes deterioration in the optical properties, contrary to the existing experience with known coating material combinations from the prior art. Overall it is found that all inventive samples exhibit good optical properties. In particular, the coatings produced from the coating material combinations of the invention display the best results in terms of gloss and leveling.