EP0828568B1 - Multi-coat painting process - Google Patents

Abstract

PCT No. PCT/EP96/02233 Sec. 371 Date Nov. 25, 1997 Sec. 102(e) Date Nov. 25, 1997 PCT Filed May 24, 1996 PCT Pub. No. WO96/38234 PCT Pub. Date Dec. 5, 1996Process for producing a multilayer lacquer coating, in which a primer of an electrophoretically depositable aqueous coating agent (1) is electrophoretically applied on to an electrically conductive substrate and is then stoved, whereupon a color-giving and/or effect-producing base lacquer coat of an aqueous coating agent (II) is applied and stoved and this coat is then provided with one or more clear lacquer coatings, in which process a) as the coating agent (I), a coating agent which, in the stoved state, will produce an electrically conductive primary coat is used, b) the base lacquer coat is formed by an electrophoretically depositable aqueous coating agent (II) by a process of electrophoretical deposition, c) the overall dry layer thickness of the dry lacquer coat or dry lacquer coats is about 40 and 80 mu m, and d) the overall dry layer thickness of the multilayer lacquer coating is about 80 to 110 mu m.

Description

The invention relates to a method for producing a multi-layer paint conductive, especially metallic Substrates that are particularly suitable for automotive painting.

Today's, high-quality automotive OEM coatings exist in generally from an electrophoretically applied against corrosion protective primer and subsequently by spray painting applied subsequent layers consisting of a filler layer and one subsequently applied decorative purposes Painting from color and / or effect basecoat and one the surface sealing protective clear coat.

The total layer thickness of such automotive paintwork is in practice between 90 and 130 µm, which is the sum of 15 to 25 µm Layer thickness for the primer, 30 to 40 µm for the filler layer, 10 to 25 µm for the basecoat and 30 to 40 µm for the Clear coat results. These layer thicknesses become significant exceeded if paintwork with particularly good optical Appearance, i.e. with outstanding gloss and top coat for example in the painting of motor vehicles of the upper and Luxury class should be achieved. In DE-A-42 15 070, in DE-A-38 39 905 or in US-A-5203975 For example, the application of several layers of clear lacquer described on a basecoat film. It then results Layer thicknesses of 120 µm and above, e.g. up to 170 µm, what from Saving material and saving weight on the finished Vehicle is undesirable.

The object of the invention is to provide multi-layer coatings, in particular automotive paintwork, the Requirements of an outstanding gloss and topcoat level are sufficient, without the normal measure of the total layer thickness of automotive paintwork to exceed and without disadvantages in To have to accept overall property level.

a) als Überzugsmittel (I) ein solches verwendet, das zu einer im eingebrannten Zustand elektrisch leitfähigen Grundierungsschicht führt,

b) die Basislackschicht aus einem elektrophoretisch abscheidbaren wäßrigen Überzugsmittel (II) durch elektrophoretische Abscheidung gebildet wird,

c) die Gesamttrockenschichtdicke der Klarlackschicht oder Klarlackschichten bei 40 bis 80µm liegt und

d) die Gesamttrockenschichtdicke der Mehrschichtlackierung bei 80 bis 110 µm liegt.

It has been shown that this object can surprisingly be achieved by a process for producing a multi-layer coating, in which a primer from an electrophoretically separable aqueous coating agent (1) is applied electrophoretically and then baked on an electrically conductive substrate, whereupon a color and / or effect basecoat is applied from an aqueous coating agent (II) and baked and this is provided with one or more clearcoat coatings, which is characterized in that

a) the coating agent (I) used is one which leads to a primer layer which is electrically conductive when baked,

b) the basecoat film is formed from an electrophoretically depositable aqueous coating composition (II) by electrophoretic deposition,

c) the total dry layer thickness of the clear lacquer layer or clear lacquer layers is 40 to 80 μm and

d) the total dry layer thickness of the multi-layer coating is 80 to 110 µm.

In the multi-layer coating according to the invention, a Clear coat with a high thickness of 40 to 80 microns, preferably from 50 to 60 µm provided. This is applied to the baked basecoat be applied. The clear coat can consist of one or more Layers exist, the first clear lacquer layer preferably before Application of the further layers of clear lacquer is baked. Several Clearcoat layers can be the same or different Clear coating agents are created.

In the method according to the invention can be used as electrophoretic separable but different coating agents (I) and (II) known anodically or cathodically separable Electrodeposition paints (ETL) are used to produce the first and second coating layer, the electrophoretic separable coating agent (I) contains components that the first Coating layer in the baked state one for electrophoretic Depositing another coating layer from one of (I) various electrophoretically depositable coating agents (II) give sufficiently low resistivity, and that the electrophoretically depositable coating agent (II) color and / or contains effect pigments.

The coating agents (I) and (II) are aqueous Coating agents with a solids content of, for example, 10 to 20% by weight. This consists of conventional binders, with at least a part the binder ionic and / or convertible into ionic groups Substituents and possibly capable of chemical crosslinking Groups carries, as well as any existing crosslinkers, electrically conductive components, fillers, pigments and paint Additives.

The ionic groups or groups of the binders which can be converted into ionic groups can be anionic or groups which can be converted into anionic groups, for example acidic groups such as -COOH, -SO ₃ H and / or -PO ₃ H ₂ and the corresponding anionic groups neutralized with bases . They can also be cationic or convertible into cationic groups, for example basic groups, preferably nitrogen-containing basic groups; these groups can be quaternized or they are converted into ionic groups using a conventional neutralizing agent, for example an organic monocarboxylic acid, such as, for example, formic acid or acetic acid. Examples are amino, ammonium, for example quaternary ammonium, phosphonium and / or sulfonium groups.

In the process according to the invention, the usual anionic group-containing anodically depositable electrocoat binders and paints (ATL) can be used to produce the first and / or second coating layer. Examples are those as described in DE-A-28 24 418. These are, for example, binders based on polyesters, epoxy resin esters, (meth) acrylic copolymer resins, maleate oils or polybutadiene oils with a weight average molecular weight (Mw) of, for example, 300-10000 and an acid number of 35-300 mg KOH / g. In particular for the production of the second coating layer, binders based on polyesters or (meth) acrylic copolymer resins are preferably used as anodically depositable binders. The binders carry -COOH, -SO ₃ H and / or -PO ₃ H ₂ groups. After neutralization of at least some of the acidic groups, the resins can be converted into the water phase. The binders can be self-crosslinking or externally crosslinking. The lacquers can therefore also contain customary crosslinking agents, for example triazine resins, crosslinking agents which contain groups capable of transesterification or blocked polyisocyanates.

Can also be used in the process according to the invention for producing the The first and / or second coating layers are the usual cathodic ones Electrophoretic coatings (KTL) based on cationic or basic Binder. Such basic resins are, for example, primary, resins containing secondary and / or tertiary amino groups, the Amine numbers e.g. are 20 to 250 mg KOH / g. The weight average of the Molar mass (Mw) of the base resins is preferably 300 to 10,000. Examples of such base resins are amino epoxy resins, amino epoxy resins with terminal double bonds, amino epoxy resins with primary OH groups, Aminopolyurethane resins, amino group-containing polybutadiene resins or modified epoxy resin-carbon dioxide-amine reaction products as well which is preferred in the production of the second coating layer Amino (meth) acrylate resins used. These base resins can be self-crosslinking or they are used with known crosslinkers Mixture used. Examples of such crosslinkers are Aminoplast resins, blocked polyisocyanates, crosslinkers with terminal Double bonds, polyepoxide compounds or crosslinkers Contain transesterifiable groups.

Examples for use in cathodic dip lacquer (KTL) baths Base resins and crosslinkers are described in EP-A-0 082 291, EP-A-0 234 395, EP-A-0 227 975, EP-A-0 178 531, EP-A-0 333 327, EP-A-0 310 971, EP-A-0 456 270, US 3 922 253, EP-A-0 261 385, EP-A-0 245 786, DE-A-33 24 211, EP-A-0 414 199, EP-A-0 476 514. These resins can work alone or used in a mixture. So-called "non-yellowing" CTL systems are preferred used a yellowing or discoloration of those produced by the process according to the invention Avoid multi-layer painting when baking. For example it is blocked by means of specially selected KTL systems crosslinking polyisocyanates, such as in EP-A-0 265,363.

The electrocoat (ETL) coating agent (I) contains components that impart electrical conductivity. They should give the first coating layer in the baked state a resistivity which is sufficiently low for the electrophoretic deposition of a further coating layer from the electrophoretically depositable coating agent (II), for example between 10 ³ and 10 ⁸ Ohm.cm. Examples of such constituents are particulate inorganic or organic electrical conductors or semiconductors, such as, for example, iron oxide black, graphite, carbon black, metal powder, for example made of aluminum, copper or stainless steel, molybdenum disulfide or polymers with electrical conductivity, such as, for example, preferably polyaniline. Examples of electrodeposition paints containing such constituents, which can be used according to the invention, can be found in US Pat. No. 3,674,671, GB 2,129,807, EP-A-0 409 821 and EP-A-0 426 327. The constituents imparting electrical conductivity are described in US Pat Contain ETL coating agent (I) in such an amount that the desired resistivity of the deposited coating layer is achieved in the baked state. Based on the solids content of the ETL coating agent (I), the proportion of the constituent or components imparting electrical conductivity is, for example, between 1 and 30% by weight. The proportion can easily be determined by a specialist; it depends, for example, on the specific weight, the specific electrical conductivity and the particle size of the components imparting electrical conductivity. One or more of these components can be present in combination.

In addition to the base resins and any crosslinking agents present and the first one contained in the ETL coating agent (I) Coating layer in the baked state, electrical conductivity components and in the case of the ETL coating agent (II) Color and / or effect pigments contained in the ETL coating agents (I) and (II) fillers and / or additives customary in paint contain. Of course, the ETL coating agent (I) Pigments included. The usual pigments are used, for example inorganic and / or organic colored pigments and / or Effect pigments, e.g. Titanium dioxide, iron oxide pigments, Phthalocyanine pigments, quinacridone pigments, metal pigments, e.g. out Titanium, aluminum or copper, interference pigments, such as e.g. titanium dioxide coated aluminum, coated mica, Graphite effect pigments, platelet-shaped iron oxide, platelet-shaped Copper phthalocyanine pigments in question. Examples of black pigments are coarse coal, generated by incomplete combustion carbon black, by catalytic or thermal decomposition of coarse particles obtained from liquid or gaseous hydrocarbons Soot. Examples of fillers are kaolin, talc or silicon dioxide.

The pigments can be dispersed into pigment pastes, e.g. under Use of known paste resins. Such resins are known to the person skilled in the art common. Examples of paste resins that can be used in KTL baths are in EP-A-0 183 025 and EP-A-0 469 497. Especially preferred in the case of producing the second coating layer ATL coating agents used, it is possible to add pigment pastes use as in the known to those skilled in the manufacture of Suitable for two-coat finishes of the basecoat / clearcoat type Waterborne basecoats are used. Such pigment pastes can are obtained by grinding the pigments in a special water-thinnable paste resin. An example of such preferred paste resin based on an anionic Stabilized polyurethane resin can be found in DE-A-40 00 889.

The usual additives, in particular, are possible as additives are known for ETL coating agents. Examples include wetting agents, Neutralizing agents, leveling agents, catalysts, Corrosion inhibitors, anti-foaming agents, solvents, in particular however, light protection agents if necessary in combination with Antioxidants.

It is preferred in the process according to the invention as an ETL coating agent (I) a KTL coating agent and as an ETL coating agent (II) an ATL coating agent to use.

As a clear coat for the production of the third and any additional coating layers are in principle all usual clear coats or transparent colored or colorless pigmented Coating agent suitable. It can be one or act multi-component clear lacquer coating agents. You can be solvent-free (liquid or as a powder clear coat), or it can are systems based on solvents or are are water-thinnable clear coats, whose binder systems in suitably, e.g. anionic, cationic or non-ionic, are stabilized. With the water-borne clear lacquer systems it can are water-soluble or water-dispersed systems, act, for example, emulsion systems or powder slurry systems. The Clear lacquer coating agents harden during baking under training covalent bonds due to chemical cross-linking.

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. You can if the base resins are not self-crosslinking, if necessary also Crosslinker included. Both the base resin component and the Crosslinker components are not subject to any restrictions. As Film-forming binders (base resins) can, for example, be polyester, Polyurethane and / or (meth) acrylic copolymer resins can be used. The Selection of any crosslinker that is included is not critical to them depends on the functionality of the base resins, i.e. the crosslinker are selected so that they are one for the functionality of the base resins have complementary, reactive functionality. Examples of such Complementary functionalities between base resin and crosslinker are: Carboxyl / epoxy, directly bound to carbon or silicon Hydroxyl / methylol ether, directly bound to carbon or silicon Hydroxyl / free and / or blocked isocyanate, (meth) acryloyl / CH-acidic Group. In this context, are directly bound to silicon Hydroxyl groups also latent silanol groups, e.g. Alkoxysilane groups to understand. If compatible with each other, can also combine several such complementary functionalities in one Clear varnish side by side. The possibly in the clear coats Crosslinkers used 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 varnish additives, such as Catalysts, leveling agents, Dyes, but especially rheology control agents such as microgels, NAD (= non-aqueous dispersions), disubstituted ureas ("sagging control agents "), and light protection agents, if necessary in combination contain with antioxidants.

Examples of one (1K) and two-component (2K) non-aqueous Clear lacquer systems used as clear lacquer in the process according to the invention can be used can be found in DE-A-38 26 693, DE-A-40 17 075, DE-A-41 24 167, DE-A-41 33 704, DE-A-42 04 518, DE-A-42 04 611, EP-A-0 257 513, EP-A-0 408 858, EP-A-0 523 267, EP-A-0 557 822, WO-92 11 327.

Examples of one (1K) or two-component (2K) Water-clear lacquer systems used as clear lacquer in the process according to the invention can be used can be found in DE-A-39 10 829, DE-A-40 09 931, DE-A-40 09 932, DE-A-41 01 696, DE-A-41 32 430, DE-A-41 34 290, DE-A-42 03 510, EP-A-0 365 098, EP-A-0 365 775, EP-A-0 496 079, EP-A-0 546 640.

Examples of the in the inventive method for generating the transparent coating layer preferably used Powder clearcoat systems can be found in EP-A-0 509 392, EP-A-0 509 393, EP-A-0 522 648, EP-A-0 544 206, EP-A-0 555 705, DE-A-42 22 194, DE-A-42 27 580.

The transparent coating can be in a single layer or in shape of multiple layers from the same or from several different transparent coating agents can be applied. The is expedient transparent coating layer, however, as a third layer of only one Clear coating agent applied. Those are preferred Clear varnish coating agent used, the lowest possible Have a tendency to run off, for example with high-solids clear coats according to adjusted rheological behavior. Particularly preferred are powder clear coats.

As a substrate for the method according to the invention are electrical conductive materials, such as metals. Particularly suitable are e.g. Automobile bodies or parts of them, them can be made of pretreated or untreated metal or electrical conductive or provided with an electrically conductive layer Plastic. The first coating layer is applied to these substrates from the aqueous coating agent (I) electrophoretically in a conventional manner in a dry layer thickness of, for example, 5 to 15 µm deposited and for example at temperatures between 130 and 180 ° C. branded.

The second coating layer made of a second color and / or effect coating agent (II) which is different from (I) and which can be deposited electrophoretically is applied to the substrate thus obtained, which has an ETL layer having a specific resistance of in particular 10 ³ to 10 ⁸ ohm.cm. a dry layer thickness of, for example, 10 to 45 μm, preferably applied between 15 and 30 μm and likewise baked, for example, at temperatures between 130 and 180 ° C. The second coating layer generally has practically no electrical conductivity, ie it has a specific resistance of more than 10 ⁹ ohm.cm in the baked state.

The one obtained by electrodeposition from the coating agent (I) Coating serves in particular to protect against chemical and corrosive attack, so it is advantageous to try the whole Surface of a three-dimensional substrate, for example one To coat the body.

The one obtained by electrodeposition from the coating agent (II) color and / or effect and in the baked state electrical Insulating coating can, but does not have to cover the entire surface extend across the three-dimensional substrate; a possible Accordingly, double coating is, for example, an entire surface first coating by electrocoating from the coating agent (I) and a color and / or effect coating from the Coating agent (II) by electrocoating, for example in essential only on outer areas, especially visible surfaces a three-dimensional substrate, i.e. for example not in narrow Cavities in a body.

Then the clear coat is applied. The third Coating layer is made from a common liquid or powder clear coat applied and for example at temperatures of 80 to 160 ° C. branded. If necessary, further layers of clear lacquer from the the same or different clear lacquer coating agents applied become. According to the invention is preferably carried out so that the Layer thickness of the transparent coating layer or the Total layer thickness of several transparent coating layers between 40 and 80 microns, particularly preferably between 50 and 60 microns.

The method according to the invention allows the production of Multi-layer paintwork, in particular of automotive paintwork with comparable to the prior art Overall property level as well as improved gloss and top coat level. It has been shown that excellent properties through the Procedure according to the invention can be achieved, although the Elimination of filler layers enables. Despite the high layer thickness at Clear coat application is the total layer thickness after the Multi-layer coatings produced according to the method of the invention low. They are in particular 80 to 110 µm and below comparable to the area of usual automotive OEM paintwork high clear coat thickness.

Claims (6)

1. A process for producing a multi-layer lacquer coating, wherein a primer comprising an electrophoretically depositable aqueous coating medium (I) is electrophoretically deposited on an electrically conductive substrate and is subsequently stoved, whereupon a colour- and/or effect-imparting base lacquer coat of an aqueous coating medium (II) is applied and stoved and the latter is provided with one or more clear lacquer coats, characterised in that

   a) a coating medium which results in an electrically conductive primer coat in its stoved state is used as coating medium (I),

   b) the base lacquer coat is formed from an electrophoretically depositable aqueous coating medium (II) by electrophoretic deposition,

   c) the total dry coat thickness of the clear lacquer coat or clear lacquer coats is 40 to 80 µm, and

   d) the total dry coat thickness of the multi-layer lacquer coating is 80 to 110 µm.
2. A process according to claim 1, characterised in that the total dry coat thickness of the clear lacquer coat or clear lacquer coats is 50 to 60 µm.
3. A process according to claim 1 or 2, characterised in that it is carried out for the lacquer coating of motor vehicles and motor vehicle parts.
4. A process according to any one of the preceding claims, characterised in that an anodically depositable coating medium is used as coating medium (II) for producing the base lacquer coat.
5. A process according to any one of the preceding claims, characterised in the primer coat is applied to give a dry coat thickness of 5 to 15 µm and the base lacquer coat is applied to give a dry coat thickness of 10 to 45 µm.
6. A process according to any one of the preceding claims, characterised in that the clear lacquer coat or clear lacquer coats are produced using a powder coating.