METHOD FOR COATING PLASTICS SUBSTRATES

Abstract

The present invention relates to a method for coating plastics substrates with an aqueous coating composition (A) comprising at least one organic polymer as binder, said coating composition being applied to at least one surface (O) of the plastics substrate and being subsequently cured, wherein (i) the application of the coating composition (A) is preceded by the application of a carbene-forming compound (C) of the formula (I) below

##STR00001##

where
R.sub.1=(CX.sub.2).sub.nX, where X=F or Cl, and n=0 or 1,
R.sub.2=

##STR00002##

where
R.sub.3 and R.sub.4 independently of one another =H, (CH.sub.2).sub.mY,
where Y=OH, CO.sub.2H, NH.sub.2, or Br, and m=0 to 4,
with the exception of R.sub.3=R.sub.4=H,
directly to the surface (O) and its activation to carbene formation, and/or (ii) the coating composition (A) comprises the carbene-forming compound (C), which is activated to carbene formation following application of the coating composition (A). The invention also relates to coatings produced by means of the method, and to coated plastics substrates.

Claims

1. A method for coating plastics substrates with an aqueous coating composition (A) comprising at least one organic polymer as binder, said coating composition being applied to at least one surface (O) of the plastics substrate and being subsequently cured, wherein (i) the application of the coating composition (A) is preceded by the application of a carbene-forming compound (C) of the formula (I) below ##STR00007## where R.sub.1=(CX.sub.2).sub.nX, where X=F or Cl, and n=0 or 1, R.sub.2= ##STR00008## where R.sub.3 and R.sub.4 independently of one another =H, (CH.sub.2).sub.mY, where Y=OH, CO.sub.2H, NH.sub.2, or Br, and m=0 to 4, with the exception of R.sub.3=R.sub.4=H, directly to the surface (O) and its activation to carbene formation, and/or (ii) the coating composition (A) comprises the carbene-forming compound (C), which is activated to carbene formation following application of the coating composition (A).

2. The method as claimed in claim 1, wherein the aqueous coating composition comprises a total fraction of 15 to 60 wt %, based on the total amount of the coating composition, of at least one organic, OH-functional polymer as binder and at least one crosslinker selected from the group of fully etherified and/or partially etherified amino resins, monomeric and/or polymeric polyamines and/or monomeric and/or polymeric, blocked and/or free polyisocyanates.

3. The method as claimed in claim 1, wherein the aqueous coating composition comprises at least 20 wt % of water, based on the total amount of the coating composition.

4. The method as claimed in claim 1, wherein the aqueous coating composition is a pigmented basecoat material.

5. The method as claimed in claim 1, wherein the plastics substrate comprises plastics selected from the group consisting of polystyrene (PS), polyvinyl chloride (PVC), polyurethane (PU), glass fiber-reinforced unsaturated polyesters, polymethyl methacrylate (PMMA), polyphenylene sulfide (PPS), polyoxymethylene (POM), polyphenylene ethers (PPE), polyphenylene oxide (PPO), polyurea, polybutadiene terephthalate (PBT), polycarbonate (PC), acrylonitrile-butadiene-styrene copolymers (ABS), polyolefins such as polypropylene (PP), optionally modified with ethylene-propylene-diene copolymers (EPDM), and also mixtures of these plastics.

6. The method as claimed in claim 1, wherein for the compound (C) of the formula (I) it is the case that R.sub.1=CF.sub.3, R.sub.3=OH, CO.sub.2H, CH.sub.2OH, CH.sub.2CO.sub.2H, and R.sub.4=H.

7. The method as claimed in claim 1, wherein for the compound (C) of the formula (I) it is the case that R.sub.1=CF.sub.3, R.sub.3=CO.sub.2H or CH.sub.2OH, and R.sub.4=H.

8. The method as claimed in claim 1, wherein the activation of the compound (C) to carbene formation comprises exposing the compound (C) to UV radiation.

9. The method as claimed in claim 1, wherein the application of the coating composition (A) is preceded by the application of the carbene-forming compound (C) directly to the surface (O) of the substrate and its activation to carbene formation.

10. The method as claimed in claim 9, wherein the compound (C) is applied in the form of a solution in an organic solvent.

11. The method as claimed in claim 1, wherein following the application of the aqueous coating composition (A), at least one further coating composition is applied and is cured jointly with the applied coating composition (A), at least one of the further coating compositions being a clearcoat material.

12. A coating produced by a method as claimed in claim 1.

13. A coated plastics substrate which has been coated by the method as claimed in claim 1.

14. The coated plastics substrate as claimed in claim 13, which is coated with a multicoat coating system comprising a basecoat and a clearcoat.

15. The use of a compound (C) of the formula (I) below ##STR00009## where R.sub.1=(CX.sub.2).sub.nX, where X=F or Cl, and n=0 or 1, R.sub.2= ##STR00010## where R.sub.3 and R.sub.4 independently of one another =H, (CH.sub.2).sub.mY, where Y=OH, CO.sub.2H, NH.sub.2, or Br, and m=0 to 4, with the exception of R.sub.3=R.sub.4=H, for improving the adhesion of coatings on plastics substrates that have been produced by means of aqueous coating compositions.

Description

EXAMPLES

[0079] Various plastics substrates, in each case in the form of test plaques having a size of 10100.3 cm or 1001003 cm, were coated with different aqueous coating compositions. The plastics materials used were PP sheets (Daplen EE103AE (Borealis)).

A) Coating of Plastics Substrates

[0080] A plastics substrate was coated using the coating compositions identified in tables 1 and 2 (see also associated explanations). Prior to application with these coating compositions, the substrate was treated as described below with a solution of 4-[3-(trifluoromethyl)-3H-diazirin-3-yl]benzoic acid (compound (C), where R.sub.1=CF.sub.3 and in R.sub.2 the following is the case: R.sub.3=COOH, R.sub.4=H) (0.005 mol/l in methyl ethyl ketone).

[0081] The aqueous coating composition (A) used for coating was the aqueous basecoat material having the composition according to table 1. The basecoat material was prepared by combining and intimately mixing the components indicated in table 1, in a dissolver.

TABLE-US-00001 TABLE 1 Composition of the aqueous basecoat material used Parts by Component weight used Commercial thixotropic agent 18.2 (Laponite RD) Commercial dispersion of an OH- 31.9 functional polyurethane resin (water content: 66.0% by weight, organic solvents: 6.3% by weight) TMDD BG 52 (commercial wetting 0.5 agent) Commercial dispersion of an OH- 3.0 functional polyester resin (water content: 17.7% by weight, organic solvents: 20.0% by weight) Butoxypropanol 2.0 Cymel 327 (commercial melamine- 4.2 formaldehyde resin) Neutralizing solution 0.7 (dimethylethanolamine, 10% in water) Commercial dispersion of an OH- 5.1 functional acrylate resin (water content: 49.5% by weight, organic solvents: 13.0% by weight) Water 2.1 Foamstar MF324 (commercial 0.5 defoamer) Ethylhexanol 3.9 BYK 347 (commercial wetting 0.5 agent) Pluriol P900 (commercial 2.0 polyethylene glycol) Butyldiglycol 4.7 Isopropanol 2.1 Water 1.8 Neutralizing solution 0.8 (dimethylethanolamine, 10% in water) Water 2.2 Viscalex HV 30 (commercial 0.4 rheological agent) Water 2.0 Tinting paste 1 (10% dispersion 10.1 of Monarch 1400 carbon black pigment in water) Tinting paste 2 (50% dispersion 0.1 of titanium rutile 2310 pigment in water) Water 1.2

[0082] Additionally used was a commercial clearcoat material (see table 2), which was produced by combining and intimately mixing the components specified in table 2, in a dissolver.

TABLE-US-00002 TABLE 2 Composition of the clearcoat material used Amount (in % Component by weight) Commercial dispersion of an OH-functional 50.9 acrylate resin in organic solvents Setal 82166 SS-55 25.5 Cyclohexanone 3.9 Solvent Naphtha 230/290 2.0 Commercial dispersion of an OH-functional 9.8 acrylate resin in organic solvents Disolucion de Silicona F-2 1.5 5% strength solution of Baysilon OL44 0.5 Tinuvin 292 (commercial light stabilizer) 0.9 Tinuvin 1130 (commercial UV absorber) 0.9 1% strength solution of dibutyltin 0.6 laurate Cumyl hydroperoxide (80% form) 0.4 1-Methoxyprop-2-yl acetate 3.1

[0083] The actual production of coatings took place as follows.

[0084] First of all, by means of spray application, the solution comprising the diaziridine-containing compound (C) was applied directly to a plastics substrate.

[0085] This was followed initially by matt flashing (5 minutes at 20 C.), after which the applied diaziridine-containing compound was treated or activated with UV radiation (2837 mJ per cm.sup.2 of plastics substrate). Activation took place using a UV curing apparatus from IST Strahlentechnik Metz GmbH (model type M-40-2*1-R-Ir-SLC-So-inert, UV lamp type (mercury vapor lamp type) M 400 U 2 H with a typical UV emission line spectrum with spectral lines from 184 to 365 nanometers.

[0086] Applied pneumatically directly atop the substrate thus precoated was the aqueous basecoat material (table 1), followed by flashing at 20 C. for 5 minutes. Thereafter the clearcoat material (table 2) was pneumatically applied directly and flashed at 20 C. for 10 minutes. Curing was carried out subsequently at a temperature of 80 C. over a duration of 30 minutes. The dry film thicknesses of the individual coats in the multicoat coating system (E1) produced in accordance with the invention were 2 micrometers (coat based on the diaziridine-containing compound), 15 micrometers (basecoat), and 42 micrometers (clearcoat).

[0087] In addition to the multicoat coating system (E1), further multicoat coating systems were produced by analogy with the instructions given above. In the multicoat coating system (E2), however, a different compound (C) was used, namely 4-[3-(trifluoromethyl)-3H-diazirin-3-yl]benzyl alcohol (compound (C), where R.sub.1=CF.sub.3 and in R.sub.2 the following is the case: R.sub.3=CH.sub.2OH, R.sub.4=H). In the comparative multicoat coating system (V1), no compound (C) was used, the carbene instead being 3-phenyl-3-(trifluoromethyl)-3H-diaziridine (compound similar to formula (I), but with R.sub.1=CF.sub.3 and the following being the case in R.sub.2: R.sub.3=R.sub.4=H). In the case of the production of the multicoat coating systems (V2) and (V3), the application and activation of a compound (C) was likewise omitted. However, no carbene at all was used (the steps of the corresponding application and activation were therefore dropped). Whereas in the case of (V2) merely the stated steps were dropped, the plastics substrate in the case of the multicoat coating system (V3), instead of the application and activation of the aforementioned diaziridine-containing compound (C), was pretreated, prior to the application of the basecoat material (A), by customary flaming (by means of a commercial automatic flaming device from Kirchgssner Elektrotechnik).

[0088] Table 3 shows an overview of the multicoat coating systems produced. All multicoat coating systems comprise a basecoat and a clearcoat.

TABLE-US-00003 TABLE 3 Multicoat coating systems Multicoat coating system Specification (E1) 4-[3-(Trifluoromethyl)-3H-diazirin-3- yl]benzoic acid (compound (C), where R.sub.1 = CF.sub.3 and in R.sub.2: R.sub.3 = COOH, R.sub.4 = H) (E2) 4-[3-(Trifluoromethyl)-3H-diazirin-3- yl]benzyl alcohol (compound (C), where R.sub.1 = CF.sub.3 and in R.sub.2: R.sub.3 = CH.sub.2OH, R.sub.4 = H) (V1) 3-Phenyl-3-(trifluoromethyl)-3H- diaziridine (compound similar to formula (I), but where R.sub.1 = CF.sub.3 and in R.sub.2: R.sub.3 = R.sub.4 = H) (V2) No carbene (V3) No carbene, but flaming

B) Investigation of the Adhesion Properties of Coatings

[0089] The adhesion properties of the coatings produced were investigated by way of a widely known steam jet test (DIN 55662:2009-12, 1 minute of steam jetting at 60 C., pressure 67 bar, vertical distance from test specimen 10 cm).

[0090] The adhesion was evaluated using a whole-number rating system with ratings of 0-5, the rating 0 being awarded for coatings which had no visible traces after steam jet treatment (very good adhesion), and the rating 5 being awarded for coatings which after the steam jet test had very comprehensively detached regions (insufficient adhesion).

[0091] Table 4 shows the adhesion properties of the coatings produced in relation to the plastics substrates used and their pretreatment.

TABLE-US-00004 TABLE 4 Adhesion properties of the multicoat coating systems Multicoat coating system Adhesion result (E1) 0 (E2) 0 (V1) 5 (V2) 5 (V3) 2

[0092] The results show that the multicoat coating systems constructed in accordance with the method of the invention have a significantly better adhesion than is the case for the multicoat coating systems (V1) and (V2) (omission of the use of a compound (C) or of any carbene at all). The comparison with the results for the multicoat coating system (V3), moreover, also demonstrates the surprising advantage of the method of the invention in the context in particular of the coating of nonpolar plastics substrates (in this case, PP). In spite of the substitution of conventional flaming for application and activation of a compound (C), the adhesion of the multicoat coating system (V3) is significantly poorer than is the case for the very effectively adhering multicoat coating systems (E1) and (E2).