EP0764475B1 - Process for making an effect laquer on a grained plastic substrate - Google Patents

Abstract

A process for the decorative painting of polar plastics with a grained surface, comprising (a) applying a first coat contg. no decorative pigments or modified polyolefins, which is based on physically drying binders (I) contg. polyurethane (PU) resin(s) and/or oligomeric urethanes which do not undergo chemical crosslinking at the temps. used in stage (f), in a dry film thickness of 5-40 microns, (b) drying at 20-80 degrees C to a residual volatiles content of 3-20 wt% based on the amt. of volatiles in the film at the temp. used in stage (a), (c) applying a decorative base-coat wet-in-wet, (d) drying at 20-80 degrees C to a residual volatiles content of 3-20 wt% (as above), (e) overcoating with a liq. clear-coat which undergoes covalent chemical crosslinking at the temp. used in stage (f), and (f) drying/hardening the three coats together at 60-110 degrees C.

Description

The invention relates to a method for producing Effect coatings on polar, grained plastic parts.

In the automotive industry, plastic parts such as e.g. Bumpers, spoilers, hubcaps or mirror housings to the Metal body attached. Are the plastic parts made of non-polar Polyolefin plastics such as polypropylene or the like Blends and these should be painted, so it is necessary to the to prepare non-polar plastic surfaces for painting, to ensure the necessary adhesion of the paint layer. So are different methods have become known that serve to to create a polar surface for subsequent painting. Examples of such methods are physical and chemical Treatment methods, such as flaming or UV irradiation of the Plastic surfaces or chemical modification with aggressive ones Agents such as sulfonation. But it can also adhesion-promoting primer layers are applied. In practice Primers, the chlorinated polyolefins (CPO), have proven particularly effective contain.

Are you working with polar plastics such as Polycarbonate, can on the labor-intensive preparation of the plastic surface before No painting by physical and chemical methods become. It is also not necessary to apply a primer.

Ideally, the plastic parts to be painted have a smooth, shiny surface. However, depending on the vehicle model or equipment, the same plastic part is often painted or unpainted for reasons of a rational workflow in an assembly line. For visual reasons, the unpainted plastic part must have a surface that appears matt to the viewer in order to visually conceal scratches or points of deposit. This is done by graining the surface of the plastic parts. The fineness of the grain is given in μ m, and particularly suitable for vehicle mounting parts are common plastic parts with a grain of ≥ 10 μ m, in particular, for example, with a between 20 and 50 μ m underlying grain. For reasons of simple storage and rational production, plastic parts with only one type of surface structure are preferably used, for example only parts with 40 μm grain.

The overpainting of such grained plastic parts is however problematic in terms of effects training and Color matching the color of the body, especially in the Case of effect painting. Before applying the effect paint layer an effect basecoat on the grained plastic part is therefore applied a smooth primer coat. However, with the Painting of polar plastic parts due to the use of organically bound chlorine contained in them is not harmless Primers are dispensed with, the primer layer can be made of harmless materials. For this purpose, in the Practice chemically crosslinking paint systems used according to the Application for one to be applied below Top coat suitable primer under Drying at temperatures between 60 and 100 ° C, for example be cured. Examples of chemically crosslinking for the Lacquer systems suitable for plastic priming are two-component Epoxy / amine systems and two-component polyurethane systems. To Application and curing of these primers can be the decorative im general from color and / or effect basecoat and protective clearcoat can be applied.

The object of the invention is to provide a method for Production of effect coatings on grained plastic parts, the the problems of lack of effect formation and color matching with the color of the other body parts and can be carried out in an energy-saving manner.

a) eine von Effektpigmenten und modifizierten Polyolefinen freie erste Überzugsschicht aus einem Überzugsmittel auf der Basis physikalisch trocknender, ein oder mehrere Polyurethanharze und/oder oligomere Urethane enthaltender Bindemittelsysteme, die bei den im Verfahrensschritt f) angewendeten Temperaturen nicht chemisch vernetzen, in einer Trockenschichtdicke von 5 bis 40 µm aufträgt,

b) bei 20 bis 80°C bis zu einem Restgehalt von 3 bis 20 Gew.-% der bei der angewandten Temperatur im aufgetragenen Überzugsfilm enthaltenen flüchtigen Anteile antrocknet,

c) naß-in-naß mit einem Effektbasislack überlackiert,

d) bei 20 bis 80°C bis zu einem Restgehalt von 3 bis 20 Gew.-% der bei der angewandten Temperatur im aufgetragenen Überzugsfilm enthaltenen flüchtigen Anteile antrocknet,

e) naß-in-naß mit einem flüssigen Klarlack, der bei den in Verfahrensschritt f) angewendeten Trocknungstemperaturen unter Ausbildung kovalenter Bindungen chemisch vernetzt, überlackiert und

f) die erhaltenen drei Überzugsschichten bei Temperaturen von 60 bis 110°C gemeinsam trocknet bzw. härtet.

The object is achieved by a process for painting polar plastic parts with a grained surface, which is characterized in that

a) a first coating layer free of effect pigments and modified polyolefins and consisting of a coating agent based on physically drying binder systems containing one or more polyurethane resins and / or oligomeric urethanes, which do not chemically crosslink at the temperatures used in process step f), in a dry layer thickness of 5 applying to 40 μ m,

b) drying at 20 to 80 ° C. to a residual content of 3 to 20% by weight of the volatile constituents contained in the applied coating film at the temperature used,

c) wet-on-wet overcoated with an effect basecoat,

d) drying at 20 to 80 ° C. to a residual content of 3 to 20% by weight of the volatile constituents contained in the applied coating film at the temperature used,

e) wet-on-wet with a liquid clear lacquer which chemically crosslinks, overpaints and chemically crosslinks at the drying temperatures used in process step f) to form covalent bonds

f) drying or curing the three coating layers obtained at temperatures of 60 to 110 ° C.

Drying in process stages b) and d) can be done in this way, for example be carried out that the drying time is 1 to 3 minutes is. Up to a residual content of 5 to 15% by weight is preferred, particularly preferably from 5 to 10% by weight of that used Temperature in the applied coating film contains volatile components dried on. It is generally worked so that the Drying of the first two layers, i.e. process steps b) and d), takes place under temperature and time conditions, which under those the joint drying or hardening of the three layers in Process stage f) are. If necessary, after the order of the Clear coats and before drying or hardening the three together Coating layers, i.e. between process stages e) and f) be ventilated. The ventilation can, for example, at 20 to 30 ° C, be carried out for 1 to 3 minutes.

In the process according to the invention, polar plastics other than pure olefin or diene polymers, such as, for example, polyamide, polyurethane, polycarbonate or polyester, such as, for example, polybutylene terephthalate, and corresponding blends are used as the substrate. Plastic parts made of polyolefin plastics are unsuitable. In particular, they are plastic parts that are used as motor vehicle add-on parts, such as bumpers or spoilers. The plastic parts used in the present process have a grained surface, for example, with a 10 to 50 μ m-grain, preferably a greater than 20 μ m underlying grain.

In the method according to the invention, a lacquer layer is first made a pigment- and filler-free or plain-colored pigmented Coating agent applied, the binder base is physically drying binder systems. It can happen also about binders / crosslinking systems which are covalently crosslinkable per se act under the conditions of drying or Hardening step f) of the method according to the invention however, do not suffer from chemical crosslinking. Especially in The binder systems do not develop a temperature range below 110 ° C chemical reactivity. The crosslinkers that can be used are among these Conditions of physically dryable, film-forming systems, e.g. Melamine resins. The coating agent is preferably known per se derived color and / or effect basecoat coating agents. The Coating agents can be formulated on the basis of solvents, however, it is preferably an aqueous coating agent whose Binder systems in a suitable manner, e.g. anionic, cationic or are non-ionic, stabilized.

In the process step a) of the process according to the invention, e.g. usable basecoat coating agents are customary Lacquer systems that use one or more common base resins as film-forming Contain binders. Although they can contain crosslinkers, these however, unfold under the conditions of drying or hardening of the Process step f) no crosslinking effect compared to Binders. The basecoat contains film-forming binders (Base resins) one or more polyurethane resins and / or oligomers Urethanes (oligourethanes), preferably with a content of at least 15 % By weight, based on the solid resin content of the basecoat. As an additional Film-forming binders are preferably polyester and / or (Meth) acrylic copolymer resins.

It can be conventional plain-colored basecoat coating agents, such as they are used in automotive painting to manufacture Two-coat paint of the basecoat / clearcoat type or it is a pigment - and filler - free coating agent based on the Binder system or the binder / crosslinker system one Basecoat coating agent. It is crucial that the Process step a) according to the invention used none Effect pigments and no modified polyolefins, such as contain chlorinated polyolefins.

The coating agent applied in process step a) is preferred uni-colored pigmented, i.e. it is preferably a Basecoat, in addition to the usual physically drying and / or chemically crosslinkable binders and crosslinkers inorganic and / or organic colored pigments, such as e.g. Titanium dioxide, Iron oxide pigments, carbon black, azo pigments, phthalocyanine pigments, however contains no effect pigments.

An example of a solvent-based basecoat system, which in Process step a) of the process according to the invention can be used can be found in EP-A-0 302 296.

Examples of the preferred water-based paint systems or Waterborne paint binder systems which in process step a) of can be used can be found in DE-A-36 28 124, DE-A-40 25 264, EP-A-0 089 497, EP-A-0 379 158, EP-A-0 427 979, EP-A-0 512 524, EP-A-0 581 211, EP-A-0 584 818 and WO 95/16004.

In process step a) of the process according to the invention, the first coating layer microns in a dry film thickness of 5 to 40, preferably 20 and 30 μ administered m interlocutory, zBdurch syringes. It is advisable to choose the dry layer thickness of the first coating layer in the upper range of values for larger grain of the plastic substrate to be painted. In process step b), the first coating layer is dried at 20 to 80 ° C. to a residual content of 3 to 20% by weight of the volatile constituents contained in the applied coating film at the temperature used, for example within 1 to 3 minutes. Thereafter, c in process step c) of the inventive method with a known effect base paint based on organic solvents or, preferably, of water to a dry film thickness of for example 10 to 30 μ m, preferably 15-25 μ m, in the wet-on-wet Process painted over eg by spraying.

The effect basecoats known per se are effect and in general also color Basecoat coating agents, such as those used for the production of Basecoat / clearcoat two-coat coatings are used and in large numbers are known for example from the patent literature.

The effect basecoats can be formulated on the basis of solvents , but it is preferably aqueous effect basecoats, their binder systems in a suitable manner, e.g. anionic, are stabilized cationically or non-ionically. It can be for example, physically drying binder systems or are covalently crosslinkable binder / crosslinker systems that under the conditions of forced drying of the process step f) the method according to the invention, however, no chemical crosslinking suffer. Especially in the temperature range below 110 ° C Binder systems no chemical reactivity. It is a matter of usual coating systems, which as one or more common base resins contain film-forming binders. You can use crosslinkers included, but unfold under the conditions of drying of process step f) no crosslinking effect compared to Binders. Can be used as film-forming binders (base resins) for example polyester, polyurethane and / or (Meth) acrylic copolymer resins can be used. In the case of the preferred Effect waterborne basecoats preferably contain polyurethane resins, particularly preferably at least in a proportion of 15% by weight on the solid resin content of the aqueous effect basecoat.

The process step c) of the method according to the invention Effect basecoats used contain in addition to the usual physical drying and / or chemically crosslinking binder systems Effect pigments, e.g. Metal pigments, e.g. made of titanium, aluminum or Copper, interference pigments, e.g. titanium dioxide coated Aluminum, coated mica, graphite effect pigments, platelet-shaped iron oxide, platelet-shaped Copper phthalocyanine pigments. Generally they also contain coloring inorganic and / or organic colored pigments, e.g. Titanium dioxide, iron oxide pigments, carbon black, azo pigments, Phthalocyanine pigments.

In addition, the effect basecoats can contain customary auxiliaries included, such as Fillers, catalysts, leveling agents, Anti-cratering agent, light stabilizer, if necessary in combination with Antioxidants.

Examples of effect basecoats or effect basecoat systems Solvent base, which in process step c) of the invention Process can be used can be found in DE-A-29 24 632, DE-A-42 18 106, EP-A-0 302 296, WO-91 00 895 and WO-95 05 425.

Examples of the process step c) of the invention Aqueous effect basecoat systems preferably used in the process in DE-A-38 41 540, DE-A-41 22 266, EP-A-0 089 497, EP-A-0 287 144, EP-A-0 427 979.

Examples of in process step c) of the process according to the invention aqueous effect basecoat systems used with particular preference in DE-A-36 28 124, DE-A-40 25 264, EP-A-0 379 158, EP-A-0 512 524, EP-A-0 581 211 and EP-A-0 584 818.

For the first and second basecoat, different basecoats may be preferred however, similar basecoats are used as in the following is explained.

For example, a can be used to generate the first coating layer solvent-based basecoat or preferably a water-dilutable Basecoat can be used. The same choice exists for the second coating layer, but it is preferred for both Coating layers are either solvent-based Basecoat or particularly preferably a waterborne basecoat use. It is particularly preferred if the solid resin composition that for the production of the first and second coating layers the basecoats used are essentially the same, i.e. the qualitative has the same solid resin composition (the same binders and crosslinkers may be present) and in the quantitative Solid resin composition only a fluctuation range of less than 30 % By weight, preferably below 20% by weight, particularly preferably below 15% by weight, each based on the relative weight proportion of each Has binder and any crosslinker present. In addition, it is preferred if the to generate the first The basecoat used a neutral color shade or one Hue has that of that for producing the second coating layer effect basecoat used.

The effect layer applied in process step c) of the process according to the invention is in process step d) at 20 to 80 ° C. to a residual content of 3 to 20% by weight of the volatile constituents contained in the applied coating film at the applied temperature, for example within 1 to 3 Minutes dried. Then in process step e), with a known clear lacquer coating agent, for example in a dry layer thickness of 25 to 50 μm in the wet-on-wet process, for example by spraying.

As a clear coat for the production of the third The coating layer is basically suitable for all known clearcoats, the chemical under the temperature conditions of step f) network. This can be one or preferably act multi-component clear lacquer coating agents. It can be Act systems based on solvents or are water-borne clear varnishes, the binder systems of which are suitable Manner, e.g. are anionically, cationically or non-ionically stabilized. The waterborne clearcoat systems can be water-soluble or water-dispersed systems, especially Act emulsion systems. The clear lacquer coating agents are in Method step f) of the method according to the invention with training chemically cross-linked covalent bonds.

The clear lacquers which can be used in the process according to the invention are concerned it is usual clearcoat coating agents, the one or more usual Contain base resins as film-forming binders. They contain if the base resins which are not self-crosslinking are also crosslinkers. Both the Base resin component and the crosslinker component are subject no restriction, except that it is under the conditions of step f) must be chemically crosslinkable. As film-forming binders (base resins), for example Polyester, polyurethane and / or poly (meth) acrylate resins are used become. The selection of the crosslinkers that may be included not critical, it depends on the functionality of the base resins, i.e. the crosslinkers are selected so that they are one for Functionality of the base resins complementary, reactive functionality exhibit. Preferred examples of such complementary Functionalities between base resin and crosslinker are: Carboxyl / epoxy, (meth) acryloyl / CH-acidic group and preferred Hydroxyl / free isocyanate. If compatible with one another, too several such complementary functionalities in one clear coat coexist. The possibly in the clear coats contained crosslinkers can be present individually or in a mixture.

In addition to the chemically crosslinking binders and, if appropriate Crosslinkers can be used in the process according to the invention Clear varnishes auxiliary materials, such as Catalysts, Contain leveling agents and light stabilizers.

Examples of non-aqueous clearcoat systems used in the invention Processes which can preferably be used as clear lacquer can be found in DE-A-40 17 075, DE-A-41 24 167, EP-A-0 318 800, EP-A-0 327 031 and EP-A-0 355 959.

Examples of water clearcoat systems used in the process according to the invention can preferably be used as clear lacquer, can be found in DE-A-41 01 696, DE-A-42 03 510, EP-A-0 496 205, EP-A-0 469 210, EP-A-0 626 401 and EP-A-0 626 432.

The wet-on-wet in process step e) of the process according to the invention applied clear coat can optionally between 1 and 3 Minutes at 20 to 30 ° C flash off. In the following Process step f) the three coating layers under chemical Crosslinking of the outer clear lacquer layer dried together Temperatures between 60 and 110 ° C.

The method according to the invention allows the production of Effect coatings on grained plastic parts in the sense of a wet-on-wet application three coating layers, the three Coating layers are dried together. The outer Clear coat chemically forming covalent bonds networked. A good result is obtained by the process according to the invention Effects training. The grain of the plastic surface is balanced, color deviations between the after Effect-painted process according to the invention Plastic parts and one painted in the same effect color Body do not occur. The method also has the advantage that it has few drying steps so that it is not necessary several energy-intensive drying and curing steps perform.

Example 1 (comparative example)

A plastic plate made of polycarbonate with a grain of 40 μ m is spray painted in 20 μ m dry film thickness with a silver metallic aqueous basecoat material according to DE-A-42 24 617th After drying for three minutes at 20 ° C., a commercially available two-component clear varnish based on acrylate resin is overpainted in a dry layer thickness of 35 μm by spraying. After forced drying at 80 ° C for 30 minutes, a metallic coating with a disrupted flop is obtained.

Example 2 (comparative example)

A plastic plate made of polycarbonate with a grain of 40 μ m is spray painted in 20 μ m dry film thickness with the silver metallic base coat from Example. 1 After drying for three minutes at 20 ° C., a further layer of the same metallic basecoat is also applied in a 20 μm dry layer thickness by spraying. After drying for three minutes at 20 ° C., a commercially available two-component clear lacquer based on acrylate resin is overcoated in a dry layer thickness of 35 μm by spraying. After forced drying at 80 ° C for 30 minutes, a metallic coating with a disrupted flop is obtained.

Example 3

A plastic plate made of polycarbonate with a grain of 40 μ m is spray painted in 20 μ m dry film thickness with a single-color water-based coating according to WO 95/16004, Example 4.2. After drying for three minutes at 20 ° C., the silver-colored metallic basecoat from Example 1 is applied in a 20 μm dry layer thickness by spraying. After drying for three minutes at 20 ° C., a commercially available two-component clear lacquer based on acrylate resin is overcoated in a dry layer thickness of 35 μm by spraying. After forced drying at 80 ° C for 30 minutes, a metallic coating with a good metallic effect and a good flop is obtained.

Claims (11)

1. Process for making an effect lacquer on polar plastic parts with a grained surface, wherein

   a) a first coating layer free from effect pigments and modified polyolefins, consisting of a coating compound based on physically drying binder systems containing one or more polyurethane resins and/or oligomeric urethanes, which do not cure chemically at the temperatures used in process step f), is applied in a dry film thickness of 5 to 40 µm,

   b) the coating is touch-dried at 20 to 80°C to a residual content of 3 to 20 wt.% of the volatiles contained in the coating applied at the temperature used,

   c) this is overlacquered wet-in-wet with an effect basecoat,

   d) the coating is touch-dried at 20 to 80°C to a residual content of 3 to 20 wt.% of the volatiles contained in the coating applied at the temperature used,

   e) this is overlacquered wet-in-wet with a liquid clear lacquer which cures chemically at the drying temperatures used in process step f) to form covalent bonds, and

   f) the three coating layers obtained are dried or cured jointly at temperatures of 60 to 110°C.
2. Process according to claim 1, characterised in that a coating compound is used to form the first coating layer in process step a), which is a conventional coating compound for the formation of basecoats.
3. Process according to claim 1 or 2, characterised in that the grained surface possesses a grain of 10 to 50 µm.
4. Process according to claims 1 to 3, characterised in that a solvent-based coating compound is used to make the first coating layer in process step a).
5. Process according to claim 4, characterised in that a coating compound is used which, in addition to polyurethane resins and/or oligomeric urethanes, also contains polyester and/or (meth)acrylic copolymer resins as binders.
6. Process according to one of claims 1 to 3, characterised in that a water-based coating compound is used to make the first coating layer in process step a).
7. Process according to claims 1 to 3, characterised in that the coating compound contains at least 15 wt.% of one or more polyurethane resins and/or oligomeric urethanes, based on the solid resin content of the coating compound, as binder.
8. Process according to claim 6, characterised in that a coating compound is used which contains polyester and/or (meth)acrylic copolymer resins as binder in addition to polyurethane resins and/or oligomeric urethanes.
9. Process according to one of the above claims, characterised in that the solid resin compositions of binders and/or curing agents for the first coating layer made in process step a) and the second coating layer made in process step c) are qualitatively the same.
10. Process according to one of the above claims, characterised in that the touch drying of the first two coats in process steps b) and d) takes place under temperature and time conditions which are below those of the joint drying or curing of the two coats in process step f).
11. Process according to one of the above claims, characterised in that it is carried out for the lacquering of motor vehicle parts made of polar plastics with a grained surface.