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EP0540884B1 - Process for making multilayer coatings using a radially or cationnically polymerisable clear coat - Google Patents

Process for making multilayer coatings using a radially or cationnically polymerisable clear coat Download PDF

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Publication number
EP0540884B1
EP0540884B1 EP92116937A EP92116937A EP0540884B1 EP 0540884 B1 EP0540884 B1 EP 0540884B1 EP 92116937 A EP92116937 A EP 92116937A EP 92116937 A EP92116937 A EP 92116937A EP 0540884 B1 EP0540884 B1 EP 0540884B1
Authority
EP
European Patent Office
Prior art keywords
curing
process according
coating
coating composition
radiation
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP92116937A
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German (de)
French (fr)
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EP0540884A1 (en
Inventor
Udo Dr. Bastian
Manfred Dr. Stein
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Axalta Coating Systems Germany GmbH and Co KG
Original Assignee
Herberts GmbH
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Publication date
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Publication of EP0540884A1 publication Critical patent/EP0540884A1/en
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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D1/00—Processes for applying liquids or other fluent materials
    • B05D1/36—Successively applying liquids or other fluent materials, e.g. without intermediate treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
    • B05D7/50—Multilayers
    • B05D7/52—Two layers
    • B05D7/53—Base coat plus clear coat type
    • B05D7/536—Base coat plus clear coat type each layer being cured, at least partially, separately
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
    • B05D3/06—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by exposure to radiation
    • B05D3/061—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by exposure to radiation using U.V.
    • B05D3/065—After-treatment
    • B05D3/067—Curing or cross-linking the coating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
    • B05D3/02—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by baking
    • B05D3/0254—After-treatment

Definitions

  • the invention relates to a method for producing a multi-layer coating with a mechanically stable, fast-drying clear lacquer coating based on radiation-curing systems.
  • Today's automotive OEM paints mostly consist of a clear coat / basecoat top coat, which is applied to an electrophoretically primed body coated with a filler.
  • Basecoat and clearcoat are preferably applied wet-on-wet, i.e. after a flash-off time, the basecoat is optionally baked with heating and after subsequent application of a clearcoat, e.g. is described in EP-A 38 127 and 402 772.
  • Suitable clear coats in this context are e.g. in EP-A-38 127 and 184 761.
  • the baking process in industrial serial painting requires long dryer sections, naturally it takes a certain amount of time until the paint is no longer tacky, so that special measures must be taken to avoid dust inclusions on the surface.
  • JP-A-6213 2570 describes UV clearcoats which serve to protect electrical instruments for the household and automotive industry. They are applied in a thin layer, there is no multiple pre-coating.
  • EP-A-0 118 705 and GB-A-2 226 566 describe UV-curable layers for the automotive underbody area as stone chip protection.
  • the Layers are applied up to 180 »m thick. They are soft and elastic and cannot be sanded.
  • EP-A-0 247 563 describes coatings which, as a topcoat, have a coating which, in addition to an isocyanate-hydroxyl group crosslinking reaction, is additionally crosslinked by UV radiation. Due to the chemical reaction, the overspray of the coating agent that occurs during application can no longer be subjected to recycling.
  • the object of the invention is to provide a painting process for a multi-layer coating, in particular for the motor vehicle industry, in which a clear coat is used as the top coat, which allows rapid crosslinking, in which the overspray is recyclable after application, and in which the obtained coating on the substrate gives a glossy or matt hard clear top coat.
  • this goal can be achieved by a process for producing a multi-layer coating, in which a liquid clear lacquer is applied to a previously dried basecoat layer (basecoat layer) and can only be crosslinked via radical and / or cationic polymerization.
  • the clear lacquer is applied with the shielding of daylight, if necessary with illumination with visible light with a wavelength above 550 nm.
  • the overspray accumulated when the clear lacquer is applied is collected and can be used again for repainting after reprocessing.
  • the clearcoat film is then cured by irradiation with high-energy radiation or is initiated by irradiation with high-energy radiation.
  • An advantage of the method according to the invention is that even temperature-sensitive substrates can be provided with a permanent top coat. Contamination of the freshly painted surface can also be avoided by short reaction and drying times. The surfaces obtained in this way have good optical behavior and high scratch resistance.
  • the coating systems which can be used according to the invention are radiation-curing coating compositions which crosslink exclusively via free-radical or cationic polymerization or combinations thereof.
  • a preferred embodiment are high-solids aqueous systems which are present as an emulsion.
  • Solvent-based coating agents can also be used. It is particularly preferred to use 100% paint systems that can be applied without solvents and without water.
  • the radiation-curing clearcoats can be formulated as unpigmented or transparent pigmented topcoats, optionally colored with soluble dyes.
  • the clear lacquer coatings can be applied to standard basecoats. These can be solvent-based, aqueous or powder base coats.
  • the basecoats contain conventional physically drying and / or chemically crosslinking binders, inorganic and / or organic colored pigments and / or effect pigments, such as. B. metallic or pearlescent pigments as well as other paint additives, such as. B. catalysts, leveling agents or anti-cratering agents.
  • These basecoats are applied to common substrates either directly or to pre-coated substrates.
  • the substrates can be z. B. with conventional primer, filler and intermediate layers, such as z. B. are common for multi-layer coatings in the motor vehicle sector. Metal or plastic parts are suitable as substrates.
  • the background layers are dried or baked under conditions such that they contain only a small proportion of volatile substances. Particularly at the time of the radiation-induced crosslinking reaction of the clear lacquer coating layer, no substantial proportions of volatile constituents should be contained in the base layer. Such constituents can cause gloss and adhesion problems in the clear lacquer film.
  • the base layer can be dried at ambient temperature or at temperatures up to 150 ° C. A chemical cross-linking reaction is not excluded.
  • the process according to the invention is based on metallic basecoats to achieve a particularly good metal effect formation as a base layer.
  • the workpiece After applying and drying the basecoat, the workpiece is coated with the radiation-curing topcoat.
  • the coating process until the workpiece emerges from the coating unit is carried out under illumination with visible light of a wavelength of over 550 nm or with exclusion of light.
  • necessary measures to shield other light sources are used, e.g. B. light locks at the entrances and exits of the painting systems, filters in front of light sources or anti-reflective measures. Only light sources are used whose emission spectrum begins above 550 nm. There are e.g. B. lamps equipped with UV filters or yellow filters. If necessary, the lighting can also be provided through windows from the outside.
  • the application of the radiation-curable lacquer can be carried out by all usual spray application methods, such as. B. compressed air spraying, airless spraying, high rotation, electrostatic spray application (ESTA), optionally coupled with hot spray application, such as. B. hot-air hot spraying, at temperatures of maximum 70 - 80 ° C, so that suitable application viscosities are achieved and no change in the coating material and the overspray to be reprocessed occurs during the briefly acting thermal load.
  • hot spraying can be designed in such a way that the paint material is only briefly heated in or shortly before the spray nozzle.
  • the spray booth is operated with an optionally temperature-controlled circulation, which is equipped with a suitable absorption medium for the overspray, e.g. B. the paint material is operated.
  • a suitable absorption medium for the overspray e.g. B. the paint material is operated.
  • the spray booth is made of materials that contaminate the recyclable material exclude and are not attacked by the circulating medium. Examples of this are stainless steel or suitable plastics.
  • the recycling unit essentially comprises a filtration unit and a mixing device which maintains a controllable ratio of fresh paint material to refurbished and possibly rotating paint material. Storage tanks and pumps as well as control devices are also available. If non-100% lacquer material is used, an admixing device is also necessary to keep volatile constituents, such as the organic solvent components or water, constant.
  • the application is such that preferably dry layer thicknesses of 10-80 »m, particularly preferably 30-60» m, are achieved.
  • the clear coat can optionally be applied in several layers.
  • the coated substrate is optionally subjected to the crosslinking process after a rest period.
  • the rest time is used, for example, for the course, for degassing the paint film or for evaporating volatile constituents, such as solvents, water or CO2, if the paint material has been applied with supercritical carbon dioxide as a solvent, such as. B. described in EP-A-321 607. If necessary, it can also be supported by elevated temperatures up to 80 ° C., preferably up to 60 ° C.
  • the actual radiation curing process can be carried out either with UV rays or electron beams or with actinic radiation emanating from other radiation sources.
  • work is preferably carried out under an inert gas atmosphere. This can be done, for example, by supplying CO2, N2 or by using a mixture of both directly on the substrate surface.
  • UV sources or electron beam sources are preferred as the radiation source.
  • UV radiation sources with emissions in the wavelength range of 180-420 nm, preferably 200-400 nm, are for example: optionally doped high-pressure, medium-pressure and low-pressure mercury lamps, gas discharge tubes, e.g. Xenon low pressure lamps, pulsed and non-pulsed UV lasers, UV spot lamps, such as. B. UV emitting diodes. So-called black light tubes are suitable as radiation sources emitting particularly in the long-wave UV range. If necessary, measures can be taken against the heat of the radiation source, e.g. B. by water or air cooling.
  • Electron beam sources are e.g. B. spot radiators working according to the cathode ray principle (e.g. from Polymerphysik, Tübingen) or linear cathodes working according to the Elektrocurtain R principle (e.g. from Energy Science Inc.). They have a radiation power of 100 keV to 1 MeV. Combinations of these radiation sources are also possible.
  • Both the electron sources and the UV radiation sources can also be designed to operate discontinuously. Laser light sources or electron sources are then particularly suitable. Another possibility for temporarily switching on and off (clockable) UV sources is by connecting z. B. movable shutters.
  • auxiliary elements conventional lighting control systems used in technical optics, such as. B. absorption filters, reflectors, mirrors, lens systems, or optical fibers can be used.
  • the irradiation can be carried out in such a way that the clear lacquer layer is continuously crosslinked in one step.
  • the arrangement of the radiation source is known in principle, it can be adapted to the conditions of the workpiece and the process parameters.
  • the workpiece as a whole can be irradiated, or a radiation curtain can be used that moves relative to the workpiece.
  • a punctiform radiation source can be guided over the substrate via an automatic device and initiate the crosslinking process.
  • the distance of the radiation source can be fixed or it is adjusted to a desired value of the substrate shape.
  • the distances between the radiation sources are preferably in the range of 2-25 cm, particularly preferably 5-10 cm, from the wet lacquer surface. If a UV laser is used, a larger distance is possible.
  • the radiation duration is, for example, in the range from 0.1 seconds to 30 minutes, depending on the coating system and radiation source. A time of less than 5 minutes is preferred.
  • the irradiation time is chosen so that complete curing is achieved, i. H. the formation of the required technological properties is guaranteed.
  • the inventive method can be particularly advantageous for the production of multi-layer coatings in the automotive sector, for. B. of automobile bodies or parts thereof.
  • thermal activation for crosslinking the coating agent on surfaces which can only be subjected to the radiation crosslinking process in an insufficient manner.
  • thermally activatable radical initiators it may be expedient to use thermally activatable radical initiators so that a thermally activated radical polymerization can be carried out after the irradiation or simultaneously with the irradiation.
  • cationically polymerizable coating agents it is not necessary to use special thermally activatable initiators.
  • the cationic polymerization initiated by the radiation energy also plants itself in the shadow areas e.g. B. not or only little irradiated areas. In this case, too, however, it is advantageous to heat to support the polymerization in the shadow areas.
  • radiation-curing clear lacquer coating compositions can be used which are known in principle and are described in the literature. They are either radical curing systems, i. H. The action of radiation on the coating agent gives rise to radicals which then trigger the crosslinking reaction, or it is a matter of cationically curing systems in which Lewis acids are formed by radiation from initiators and serve to trigger the crosslinking reaction.
  • the radically curing systems are e.g. B. prepolymers, such as poly- or oligomers, which have olefinic double bonds in the molecule. These prepolymers can optionally in reactive diluents, i.e. H. reactive liquid monomers.
  • coating compositions of this type can also contain customary initiators, light stabilizers, optionally transparent pigments, soluble dyes, and other coating assistants.
  • prepolymers or oligomers are (meth) acrylic-functional (meth) acrylic copolymers, epoxy resin (meth) acrylates that are free from aromatic structural units, polyester (meth) acrylates, polyether (meth) acrylates, polyurethane (meth) acrylates, unsaturated polyesters , Amino (meth) acrylates, melamine (meth) acrylates, unsaturated polyurethanes or silicone (meth) acrylates.
  • the molecular weight (Number average M n ) is preferably in the range from 200 to 10,000, particularly preferably from 500 to 2000.
  • (Meth) acrylic here and hereinafter means acrylic and / or methacrylic.
  • reactive diluents are used, they are generally used between 1-50% by weight, preferably 5-30% by weight, based on the total weight of prepolymers and reactive diluents. They can be mono-, di- or poly-unsaturated.
  • reactive diluents are: (meth) acrylic acid and its esters, maleic acid and its half esters, vinyl acetate, vinyl ether, substituted vinyl ureas, alkylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, 1,3-butanediol di ( meth) acrylate, vinyl (meth) acrylate, allyl (meth) acrylate, glycerol tri- (meth) acrylate, trimethylolpropane tri- (meth) acrylate, styrene, vinyl toluene, divinylbenzene, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipropylene glycol di (meth) acrylate and hexanediol di (meth) acrylate, and mixtures thereof. They serve to influence the viscosity and
  • Photoinitiators for radical curing systems can e.g. B. in amounts of 0.1-5% by weight, preferably 0.5-3% by weight, based on the sum of free-radically polymerizable prepolymers, reactive diluents and initiators. It is advantageous if their absorption is in the wavelength range from 260 -450 nm.
  • photoinitiators are benzoin and derivatives, benzil and derivatives, benzophenone and derivatives, acetophenone and derivatives, for example 2,2-diethoxyacetophenone, thioxanthone and derivatives, anthraquinone, 1-benzoylcyclohexanol, organophosphorus compounds, such as, for. B. acylphosphine oxides.
  • the photoinitiators can be used alone or in combination.
  • other synergistic components e.g. B. tertiary amines can be used.
  • thermolabile radicals Initiators are: organic peroxides, organic azo compounds or CC-cleaving initiators, such as dialkyl peroxides, peroxocarboxylic acids, peroxodicarbonates, peroxide esters, hydroperoxides, ketone peroxides, azodinitriles or benzpinacol silyl ethers.
  • CC-cleaving initiators are particularly preferred, since no thermal decomposition products are formed during thermal cleavage, which can lead to faults in the lacquer layer.
  • the preferred amounts are between 0.1 and 5% by weight, based on the sum of free-radically polymerizable prepolymers, reactive diluents and initiators.
  • the initiators can also be used in a mixture.
  • Binding agents for cationically polymerizable coating agents are, for example, polyfunctional epoxy oligomers which contain more than two epoxy groups in the molecule. It is advantageous if the binders are free from aromatic structures.
  • epoxy oligomers are described for example in DE-OS 36 15 790. It is, for example, polyalkylene glycol diglycidyl ether, hydrogenated bisphenol A glycidyl ether, epoxy urethane resins, glycerol triglycidyl ether, diglycidyl hexahydrophthalate, diglycidyl ester of dimer acids, epoxidized derivatives of (methyl) cyclohexene, such as, for. B.
  • the number average molecular weight of the polyepoxide compounds is preferably less than 10,000.
  • reactive thinners i.e. H. reactive liquid compounds, such as. B. cyclohexene oxide, butene oxide, butanediol diglycidyl ether or hexanediol diglycidyl ether.
  • reactive solvents are alcohols, polyalkylene glycols, polyalcohols, hydroxy-functional polymers, cyclic carbonates or water. These can also contain solid components, such as solid polyalcohols, such as trimethylolpropane.
  • Photoinitiators for cationically curing systems are used in amounts of 0.5-5% by weight, alone or in combination, based on the total of cationically polymerizable prepolymers, reactive diluents and initiators.
  • onium salts that Release Lewis acids photolytically under irradiation. Examples include diazonium salts, sulfonium salts or iodonium salts. Triarylsulfonium salts are particularly preferred.
  • Non-reactive solvents for free-radically and cationically curing systems are customary paint solvents, such as esters, ethers, ketones, for example butyl acetate, ethylene glycol ether, methyl ethyl ketone, methyl isobutyl ketone and aromatic hydrocarbons.
  • esters, ethers, ketones for example butyl acetate, ethylene glycol ether, methyl ethyl ketone, methyl isobutyl ketone and aromatic hydrocarbons.
  • C2-C2 alkanols and preferably water are also suitable as solvents.
  • Light stabilizers are preferably added to the clearcoats used according to the invention.
  • these are phenyl salicylates, benzotriazole and derivatives, HALS compounds and oxalanilide derivatives, if appropriate also in combination.
  • Usual concentrations are 0.5-5% by weight, preferably 1-2% by weight, based on the total clearcoat.
  • additives are, for example, elastifying agents, polymerization inhibitors, defoamers, leveling agents, antioxidants, transparent dyes or optical brighteners.
  • transparent colorless fillers and / or pigments can be added to the coating agent.
  • the amount is up to 10% by weight, based on the total clear coat. Examples are silicon dioxide, mica, magnesium oxide, titanium dioxide or barium sulfate.
  • the particle size is preferably less than 200 nm. In the case of UV-curable systems, care must be taken that the coating film remains transparent to UV radiation in the layer thickness used.
  • Other additives that can be used are, for example, conventional matting agents of an inorganic or organic type. These can be added in conventional amounts, for example up to 10% by weight.
  • matting agents are silicates, pyrogenic silicas, such as Aerosil, Bentone, or condensed and crosslinked urea-formaldehyde resins, natural and synthetic waxes.
  • the particle sizes Such matting agents are generally up to 100 »m, preferably up to 30» m.
  • the various crosslinking reactions can be started with mixtures of the corresponding initiators.
  • mixtures of UV initiators with different absorption maximums are possible.
  • different emission maxima of one or more radiation sources can be used. This can be done simultaneously or one after the other.
  • curing can be initiated with the radiation from one radiation source and continued with that of another.
  • the reaction can then be carried out in two or more stages, if appropriate also spatially separated.
  • the radiation sources used can be the same or different.
  • thermoly cleaving initiators can optionally be used in addition to one or more photoinitiators.
  • photoinitiators is not necessary for electron beam curing.
  • the two-stage or multi-stage mode of operation can be favorable in order to first achieve, for example, a gelation.
  • B. Avoid running on painted vertical surfaces.
  • the gelation is also favorable in solvent-containing systems in order to allow the solvent to be sealed off.
  • the photoinitiators are preferably chosen so that they do not disintegrate in light with a wavelength of over 550 nm. If thermally splitting initiators are used, they should be selected so that they do not disintegrate under the application conditions of the coating material. In this way it is possible to reprocess and use the overspray of the coating agent directly since a chemical reaction during the application is avoided.
  • the crosslinking density of the paint film can be adjusted via the functionality of the binder components used. The selection can be made in such a way that the crosslinked clear lacquer coating has sufficient hardness and an excessive degree of crosslinking is avoided in order to prevent films which are too brittle.
  • the process according to the invention gives multilayer coatings which comprise a clear lacquer coating with high scratch resistance and high gloss and with high mechanical resistance.
  • the overspray of the coating agent to be applied can be directly recycled on the basis of the process parameters and the chosen crosslinking mechanism.
  • the method according to the invention is particularly suitable for use in automotive serial painting, for example for painting automobile bodies and their parts.
  • the radiation-curing clearcoats were applied in a room illuminated exclusively by red light sources (light wavelength greater than 600 nm).
  • a radiation-curable clear lacquer coating agent was formulated by mixing the following components: Parts by weight 44.5 Novacure 3200 (aliphatic epoxy acrylate from Interorgana) 32.2 Ebecryl 264 (aliphatic urethane acrylate from UCB) 3.0 Irgacure 184 (photoinitiator from CIBA) 10.0 dipropylene glycol diacrylate 10.0 trimethylolpropane triacrylate 0.3 Ebecryl 350 (silicone acrylate from UCB)
  • a lacquer structure was then produced as follows: A KTL-primed (20 »m) and pre-coated with a commercially available filler (35» m) was coated once with conventional water-based paint, in a second case with solvent-based paint (15 »m dry film thickness) and then in both cases for 20 min at 140 ° C branded. The above lacquer system was then applied in a layer thickness of 35 »m.
  • the horizontal sample sheet was irradiated for curing at a belt speed of 9 m / min with two medium pressure mercury lamps of 100 W / cm each at a distance of 10 cm from the surface to be hardened (irradiation time thus 1 - 2 sec).
  • a well-adhering, glossy and hard surface was obtained both on water-based coat and on conventional base-coat.
  • the sticky back which was only partially cross-linked by radiation, was baked for 15 minutes at 110 ° C. in a forced air oven.
  • Example 1 was repeated with the same painting result. Only the basecoat layers were baked here at 120 ° C for 30 minutes and pre-coated polycarbonate sheets were used.
  • Example 1 To 100 parts of the clear lacquer coating agent from Example 1, 2 parts of anthracene were added as a sensitizer. The application was carried out as described in Example 1. Subsequently, at a belt speed of 1 m / min, lying was irradiated with 10 black light tubes at a distance of 10 cm from the wet lacquer surface (irradiation time thus 90-120 sec). A sticky, partially cross-linked surface was obtained. The sample sheet was then suspended for 5 minutes and then irradiated freely suspended by uniformly moving the still sticky surface at a distance of 10 cm within 5 seconds on a medium-pressure mercury lamp as mentioned in Example 1. A painting result as mentioned in Example 1 was obtained. The surface was run-free.

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Abstract

A process for making a multilayer coating by applying a clear coat varnish exclusively comprising coating compositions which can be cured by means of free-radical and/or cationic polymerisation to a dried or crosslinked, colour-providing and/or effect-providing base coat, under illumination with light having a wavelength of greater than 550 nm or in the absence of light, and subsequently initiating or carrying out the curing of the clear coat by means of high-energy radiation. The process is particularly suitable for making multilayer coatings in the automotive sector.

Description

Die Erfindung betrifft ein Verfahren zur Herstellung einer Mehrschichtlackierung mit einem mechanisch stabilen schnelltrocknenden Klarlacküberzug auf Basis von strahlenhärtenden Systemen.The invention relates to a method for producing a multi-layer coating with a mechanically stable, fast-drying clear lacquer coating based on radiation-curing systems.

Heutige Automobilserienlackierungen bestehen meist aus einer Klarlack/Basislack-Decklackierung, die auf eine elektrophoretisch grundierte und mit Füller beschichtete Karosse aufgebracht wird. Dabei werden Basislack und Klarlack bevorzugt naß-in-naß appliziert, d.h. der Basislack wird nach einer Ablüftzeit gegebenenfalls unter Erwärmen und nach anschließender Applikation eines Klarlackes gemeinsam mit diesem eingebrannt, wie z.B. in EP-A 38 127 und 402 772 beschrieben wird. In diesem Zusammenhang geeignete Klarlacke sind z.B. in den EP-A-38 127 und 184 761 beschrieben. Der Einbrennvorgang in der industriellen Serienlackierung erfordert lange Trocknerstrecken, naturgemäß vergeht ein gewisser Zeitraum bis die Klebfreiheit des Lackes erreicht ist, so daß besondere Maßnahmen ergriffen werden müssen, um Staubeinschlüsse auf der Oberfläche zu vermeiden.Today's automotive OEM paints mostly consist of a clear coat / basecoat top coat, which is applied to an electrophoretically primed body coated with a filler. Basecoat and clearcoat are preferably applied wet-on-wet, i.e. after a flash-off time, the basecoat is optionally baked with heating and after subsequent application of a clearcoat, e.g. is described in EP-A 38 127 and 402 772. Suitable clear coats in this context are e.g. in EP-A-38 127 and 184 761. The baking process in industrial serial painting requires long dryer sections, naturally it takes a certain amount of time until the paint is no longer tacky, so that special measures must be taken to avoid dust inclusions on the surface.

Sowohl im Falle der Verwendung von einkomponentigen (1K) als auch von zweikomponentigen (2K) Klarlacken ist der Lackiervorgang mit Emissionen von umweltschädlichen Lösemitteln oder Spaltprodukten aus der Vernetzungsreaktion verbunden. Im Falle von beispielsweise isocyanatvernetzenden 2K-Klarlacken z.B. nach DE-OS 33 22 037 oder DE-PS 36 00 425 ist ein Overspray-Recycling naturgemäß nicht möglich.In the case of the use of one-component (1K) as well as two-component (2K) clearcoats, the painting process is associated with emissions of environmentally harmful solvents or fission products from the crosslinking reaction. In the case of, for example, isocyanate-crosslinking two-component clearcoats, e.g. According to DE-OS 33 22 037 or DE-PS 36 00 425, overspray recycling is naturally not possible.

In der JP-A-6213 2570 werden UV-Klarlacke beschrieben, die zum Schutz von elektrischen Instrumenten für die Haushalts- und Automobilindustrie dienen. Sie werden in dünner Schicht aufgetragen, eine mehrfache Vorbeschichtung findet nicht statt.JP-A-6213 2570 describes UV clearcoats which serve to protect electrical instruments for the household and automotive industry. They are applied in a thin layer, there is no multiple pre-coating.

In den EP-A-0 118 705 und GB-A-2 226 566 werden UV-härtbare Schichten für den Automobilunterbodenbereich als Steinschlagschutz beschrieben. Die Schichten werden bis zum 180 »m dick aufgetragen. Sie sind weich und elastisch eingestellt und nicht schleifbar.EP-A-0 118 705 and GB-A-2 226 566 describe UV-curable layers for the automotive underbody area as stone chip protection. The Layers are applied up to 180 »m thick. They are soft and elastic and cannot be sanded.

In der EP-A-0 247 563 werden Beschichtungen beschrieben, die als Decklack einen Überzug aufweisen, der parallel zu einer Isocyanat-Hydroxylgruppen-Vernetzungsreaktion zusätzlich durch UV-Bestrahlung vernetzt wird. Der bei der Applikation anfallende Overspray des Überzugsmittels ist aufgrund der chemischen Reaktion nicht mehr einem Recycling zu unterziehen.EP-A-0 247 563 describes coatings which, as a topcoat, have a coating which, in addition to an isocyanate-hydroxyl group crosslinking reaction, is additionally crosslinked by UV radiation. Due to the chemical reaction, the overspray of the coating agent that occurs during application can no longer be subjected to recycling.

Aufgabe der Erfindung ist es, ein Lackierverfahren für eine Mehrschichtlackierung, insbesondere für die Kraftfahrzeugindustrie zur Verfügung zu stellen, bei dem als Decklacküberzug ein Klarlack eingesetzt wird, der eine schnelle Vernetzung erlaubt, bei dem der Overspray nach der Applikation recyclisierbar ist, und bei dem der erhaltene Überzug auf dem Substrat eine glänzende oder matte harte klare Decklackierung ergibt.The object of the invention is to provide a painting process for a multi-layer coating, in particular for the motor vehicle industry, in which a clear coat is used as the top coat, which allows rapid crosslinking, in which the overspray is recyclable after application, and in which the obtained coating on the substrate gives a glossy or matt hard clear top coat.

Es hat sich gezeigt, daß dieses Ziel erreicht werden kann durch ein Verfahren zur Herstellung einer Mehrschichtlackierung, bei dem auf eine vorher getrocknete Basecoatschicht (Basislackschicht) ein flüssiger Klarlack aufgebracht wird, der ausschließlich über radikalische und/oder kationische Polymerisation vernetzt werden kann. Die Applikation des Klarlacks erfolgt unter Abschirmung des Tageslichts, gegebenenfalls bei Beleuchtung mit sichtbaren Licht mit einer Wellenlänge über 550 nm. Der beim Auftrag des Klarlacks anfallende Overspray wird gesammelt und kann gegebenenfalls nach Wiederaufbereitung erneut zur Lackierung eingesetzt werden. Die Härtung der Klarlackschicht erfolgt anschließend durch Bestrahlen mit energiereicher Strahlung oder wird durch Bestrahlen mit energiereicher Strahlung eingeleitet.It has been shown that this goal can be achieved by a process for producing a multi-layer coating, in which a liquid clear lacquer is applied to a previously dried basecoat layer (basecoat layer) and can only be crosslinked via radical and / or cationic polymerization. The clear lacquer is applied with the shielding of daylight, if necessary with illumination with visible light with a wavelength above 550 nm. The overspray accumulated when the clear lacquer is applied is collected and can be used again for repainting after reprocessing. The clearcoat film is then cured by irradiation with high-energy radiation or is initiated by irradiation with high-energy radiation.

Ein Vorteil des erfindungsgemäßen Verfahrens besteht darin, daß auch temperaturempfindliche Substrate mit einer beständigen Decklackschicht versehen werden können. Ebenso können durch kurze Reaktions- und Trockenzeiten Verunreinigungen der frisch lackierten Oberfläche vermieden werden. Die so erhaltenen Oberflächen weisen ein gutes optisches Verhalten und eine hohe Kratzbeständigkeit auf.An advantage of the method according to the invention is that even temperature-sensitive substrates can be provided with a permanent top coat. Contamination of the freshly painted surface can also be avoided by short reaction and drying times. The surfaces obtained in this way have good optical behavior and high scratch resistance.

Bei den erfindungsgemäß verwendbaren Lacksystemen handelt es sich um strahlenhärtende Überzugsmittel, die ausschließlich über radikalische oder kationische Polymerisation oder Kombinationen davon vernetzen. Eine bevorzugte Ausführungsform sind festkörperreiche wäßrige Systeme, die als Emulsion vorliegen. Es können aber auch lösemittelhaltige Überzugsmittel eingesetzt werden. Besonders bevorzugt handelt es sich um 100%-Lacksysteme, die ohne Lösungsmittel und ohne Wasser appliziert werden können. Die strahlenhärtenden Klarlacke können als unpigmentierte oder transparent pigmentierte gegebenenfalls mit löslichen Farbstoffen gefärbte Decklacke formuliert sein.The coating systems which can be used according to the invention are radiation-curing coating compositions which crosslink exclusively via free-radical or cationic polymerization or combinations thereof. A preferred embodiment are high-solids aqueous systems which are present as an emulsion. Solvent-based coating agents can also be used. It is particularly preferred to use 100% paint systems that can be applied without solvents and without water. The radiation-curing clearcoats can be formulated as unpigmented or transparent pigmented topcoats, optionally colored with soluble dyes.

Die Klarlacküberzüge können auf übliche Basecoats aufgebracht werden. Diese können lösemittelbasierende, wäßrige oder Pulver-Basecoats sein. Die Basecoats enthalten übliche physikalisch trocknende und/oder chemisch vernetzende Bindemittel, anorganische und/oder organische Buntpigmente und/oder Effektpigmente, wie z. B. Metallic- oder Perlglanzpigmente sowie weiter lackübliche Hilfsstoffe, wie z. B. Katalysatoren, Verlaufsmittel oder Antikratermittel. Diese Basecoats werden auf übliche Substrate entweder direkt oder auf vorbeschichtete Substrate aufgebracht. Die Substrate können vor dem Aufbringen des Basecoats z. B. mit üblichen Grundierungs-, Füller- und Zwischenschichten versehen werden, wie sie z. B. für Mehrschichtlackierungen auf dem Kraftfahrzeugsektor üblich sind. Als Substrate sind Metall oder Kunststoffteile geeignet.The clear lacquer coatings can be applied to standard basecoats. These can be solvent-based, aqueous or powder base coats. The basecoats contain conventional physically drying and / or chemically crosslinking binders, inorganic and / or organic colored pigments and / or effect pigments, such as. B. metallic or pearlescent pigments as well as other paint additives, such as. B. catalysts, leveling agents or anti-cratering agents. These basecoats are applied to common substrates either directly or to pre-coated substrates. The substrates can be z. B. with conventional primer, filler and intermediate layers, such as z. B. are common for multi-layer coatings in the motor vehicle sector. Metal or plastic parts are suitable as substrates.

Vor der Beschichtung mit strahlenhärtenden Lacken werden die Untergrundschichten unter solchen Bedingungen getrocknet oder eingebrannt, daß sie nur geringe Anteile von flüchtigen Substanzen enthalten. Besonders zum Zeitpunkt der strahleninduzierten Vernetzungsreaktion der Klarlacküberzugsschicht sollen keine wesentlichen Anteile an flüchtigen Bestandteilen mehr in der Basisschicht enthalten sein. Solche Bestandteile können Glanz -und Haftungsstörung im Klarlackfilm bewirken. Die Trocknung der Basisschicht kann bei Umgebungstemperatur oder Temperaturen bis zu 150°C erfolgen. Dabei ist eine chemische Vernetzungsreaktion nicht ausgeschlossen.Before coating with radiation-curing lacquers, the background layers are dried or baked under conditions such that they contain only a small proportion of volatile substances. Particularly at the time of the radiation-induced crosslinking reaction of the clear lacquer coating layer, no substantial proportions of volatile constituents should be contained in the base layer. Such constituents can cause gloss and adhesion problems in the clear lacquer film. The base layer can be dried at ambient temperature or at temperatures up to 150 ° C. A chemical cross-linking reaction is not excluded.

Im besonders bevorzugten Fall von lösungsmittelfreien strahlenhärtenden Klarlack-Systemen ist bei dem erfindungsgemäßen Verfahren auf Metallic-Basecoats als Basisschicht eine besonders gute Metalleffektausbildung zu erreichen.In the particularly preferred case of solvent-free radiation-curing clear lacquer systems, the process according to the invention is based on metallic basecoats to achieve a particularly good metal effect formation as a base layer.

Nach dem Auftragen und Trocknen des Basislacks wird das Werkstück mit dem strahlenhärtenden Decklack versehen. Das Beschichtungsverfahren bis zum Austritt des Werkstücks aus der Beschichtungseinheit wird unter Beleuchtung mit sichtbarem Licht einer Wellenlänge von über 550 nm oder unter Lichtausschluß durchgeführt. Dazu werden gegebenenfalls notwendige Maßnahmen zur Abschirmung von anderen Lichtquellen eingesetzt, z. B. Lichtschleusen an Ein- und Ausgängen der Lackieranlagen, Filter vor Lichtquellen oder reflexverhindernde Maßnahmen. Es werden nur Lichtquellen eingesetzt, deren Emissionsspektrum oberhalb 550 nm beginnt. Es sind z. B. mit UV- Filtern oder Gelbfiltern versehene Lampen. Die Beleuchtung kann gegebenenfalls auch durch Fenster von außen erfolgen. In Verfahrensschritten, die automatisch ablaufen und keiner optischen Kontrolle bedürfen, kann selbstverständlich auch unter Lichtausschluß gearbeitet werden, so daß die vorstehend genannten Lichtquellen nur im Falle einer auftretenden Störung eingeschaltet werden müssen. Im Fall einer reinen Elektronenstrahlhärtung mit angepaßten Lacksystemen kann auch unter üblichen Lichtbedingungen gearbeitet werden.After applying and drying the basecoat, the workpiece is coated with the radiation-curing topcoat. The coating process until the workpiece emerges from the coating unit is carried out under illumination with visible light of a wavelength of over 550 nm or with exclusion of light. For this purpose, necessary measures to shield other light sources are used, e.g. B. light locks at the entrances and exits of the painting systems, filters in front of light sources or anti-reflective measures. Only light sources are used whose emission spectrum begins above 550 nm. There are e.g. B. lamps equipped with UV filters or yellow filters. If necessary, the lighting can also be provided through windows from the outside. In process steps that run automatically and do not require any optical control, work can of course also be carried out with the exclusion of light, so that the aforementioned light sources only have to be switched on in the event of a malfunction. In the case of pure electron beam curing with adapted coating systems, it is also possible to work under normal lighting conditions.

Die Applikation des strahlenhärtbaren Lackes kann durch alle üblichen Spritzapplikationsmethoden durchgeführt werden, wie z. B. Druckluftspritzen, Airless-Spritzen, Hochrotation, elektrostatischen Sprühauftrag (ESTA), gegebenenfalls gekoppelt mit Heißspritzapplikation, wie z. B. Hot-Air-Heißspritzen, bei Temperaturen von maximal 70 - 80°C, so daß geeignete Applikationsviskositäten erreicht werden und bei der kurzzeitig einwirkenden thermischen Belastung keine Veränderung des Lackmaterials und des wiederaufzubereitenden Oversprays eintritt. So kann das Heißspritzen so ausgestaltet sein, daß das Lackmaterial nur kurzzeitig in der oder kurz vor der Spritzdüse erhitzt wird.The application of the radiation-curable lacquer can be carried out by all usual spray application methods, such as. B. compressed air spraying, airless spraying, high rotation, electrostatic spray application (ESTA), optionally coupled with hot spray application, such as. B. hot-air hot spraying, at temperatures of maximum 70 - 80 ° C, so that suitable application viscosities are achieved and no change in the coating material and the overspray to be reprocessed occurs during the briefly acting thermal load. For example, hot spraying can be designed in such a way that the paint material is only briefly heated in or shortly before the spray nozzle.

Die Spritzkabine wird mit einem gegebenenfalls temperierbaren Umlauf betrieben, der mit einem geeigneten Absorptionsmedium für das Overspray, z. B. dem Lackmaterial, betrieben wird. Die Spritzkabine besteht aus Materialien, die eine Kontamination des recyclisierbaren Materials ausschließen und vom umlaufenden Medium nicht angegriffen werden. Beispiele dafür sind Edelstahl oder geeignete Kunststoffe.The spray booth is operated with an optionally temperature-controlled circulation, which is equipped with a suitable absorption medium for the overspray, e.g. B. the paint material is operated. The spray booth is made of materials that contaminate the recyclable material exclude and are not attacked by the circulating medium. Examples of this are stainless steel or suitable plastics.

Durch die Vermeidung von Licht einer Wellenlänge von unter 550 nm werden das eingesetzte Lackmaterial und der Overspray nicht beeinflußt. Es ist also eine direkte Wiederaufbereitung möglich. Die Recycling-Einheit umfaßt im wesentlichen eine Filtrationseinheit sowie eine Mischvorrichtung, die ein regelbares Verhältnis von frischem Lackmaterial zu aufgearbeitetem und gegebenenfalls umlaufenden Lackmaterial einhält. Weiterhin sind Vorratsbehälter und Pumpen sowie Steuereinrichtungen vorhanden. Bei Verwendung von nicht 100%igem Lackmaterial ist noch eine Zumischvorrichtung für ein Konstanthalten von flüchtigen Bestandteilen, wie der organischen Lösungsmittelanteile oder des Wassers, notwendig.By avoiding light with a wavelength of less than 550 nm, the paint material and the overspray are not affected. Direct reprocessing is therefore possible. The recycling unit essentially comprises a filtration unit and a mixing device which maintains a controllable ratio of fresh paint material to refurbished and possibly rotating paint material. Storage tanks and pumps as well as control devices are also available. If non-100% lacquer material is used, an admixing device is also necessary to keep volatile constituents, such as the organic solvent components or water, constant.

Appliziert wird so, daß bevorzugt Trockenschichtdicken von 10 - 80 »m, besonders bevorzugt 30 - 60 »m, erreicht werden. Der Klarlackauftrag kann gegebenenfalls in mehreren Schichten erfolgen.The application is such that preferably dry layer thicknesses of 10-80 »m, particularly preferably 30-60» m, are achieved. The clear coat can optionally be applied in several layers.

Nach dem Auftragen des Klarlacküberzugsmittels wird das beschichtete Substrat gegebenenfalls nach einer Ruhezeit dem Vernetzungsprozeß unterworfen. Die Ruhezeit dient beispielsweise zum Verlauf, zur Entgasung des Lackfilms oder zum Verdunsten von flüchtigen Bestandteilen, wie Lösungsmittel, Wasser oder CO₂, wenn das Lackmaterial mit überkritischen Kohlendioxid als Lösemittel appliziert worden ist, wie z. B. in EP-A-321 607 beschrieben. Sie kann gegebenenfalls auch durch erhöhte Temperaturen bis 80°C, bevorzugt bis 60°C, unterstützt werden.After the application of the clear lacquer coating agent, the coated substrate is optionally subjected to the crosslinking process after a rest period. The rest time is used, for example, for the course, for degassing the paint film or for evaporating volatile constituents, such as solvents, water or CO₂, if the paint material has been applied with supercritical carbon dioxide as a solvent, such as. B. described in EP-A-321 607. If necessary, it can also be supported by elevated temperatures up to 80 ° C., preferably up to 60 ° C.

Der eigentliche Strahlenhärtungsprozeß kann entweder mit UV-Strahlen oder Elektronenstrahlen oder mit von anderen Strahlenquellen ausgehender aktinischer Strahlung durchgeführt werden. Im Falle von Elektronenstrahlen wird bevorzugt unter Inertgasatmosphäre gearbeitet. Das kann beispielsweise durch Zufuhren von CO₂, N₂ oder durch Einsatz eines Gemischs aus beiden direkt an die Substratoberfläche geschehen.The actual radiation curing process can be carried out either with UV rays or electron beams or with actinic radiation emanating from other radiation sources. In the case of electron beams, work is preferably carried out under an inert gas atmosphere. This can be done, for example, by supplying CO₂, N₂ or by using a mixture of both directly on the substrate surface.

Es kann auch im Falle der UV-Härtung unter Inertgas gearbeitet werden. Wird nicht unter Schutzgas gearbeitet, kann Ozon entstehen. Dieses kann beispielsweise durch Absaugen entfernt werden.It is also possible to work under inert gas in the case of UV curing. If you do not work under protective gas, ozone can develop. This can be removed, for example, by suction.

Als Strahlenquelle sind UV-Strahler oder Elektronenstrahlquellen bevorzugt. UV-Strahlenquellen mit Emissionen im Wellenlängenbereich von 180 - 420 nm, bevorzugt 200 - 400 nm, sind beispielsweise: gegebenenfalls dotierte Quecksilberhochdruck-, -mitteldruck- und -niederdruckstrahler, Gasentladungsröhren, wie z.B. Xenonniederdrucklampen, gepulste und ungepulste UV-Laser, UV-Punktstrahler, wie z. B. UV-emittierende Dioden. Als besonders im langwelligen UV-Bereich emittierende Strahlenquellen sind sogenannte Schwarzlichtröhren geeignet. Gegebenenfalls können Maßnahmen gegen die Wärme der Strahlungsquelle getroffen werden, z. B. durch Wasser- oder Luftkühlung.UV sources or electron beam sources are preferred as the radiation source. UV radiation sources with emissions in the wavelength range of 180-420 nm, preferably 200-400 nm, are for example: optionally doped high-pressure, medium-pressure and low-pressure mercury lamps, gas discharge tubes, e.g. Xenon low pressure lamps, pulsed and non-pulsed UV lasers, UV spot lamps, such as. B. UV emitting diodes. So-called black light tubes are suitable as radiation sources emitting particularly in the long-wave UV range. If necessary, measures can be taken against the heat of the radiation source, e.g. B. by water or air cooling.

Elektronenstrahlquellen sind z. B. nach dem Kathodenstrahlprinzip arbeitende Punktstrahler (z. B. der Fa. Polymerphysik, Tübingen) oder Linearkathoden, die nach dem ElektrocurtainR-Prinzip arbeiten (z. B. von Fa. Energie Science Inc.). Sie haben eine Strahlungsleistung von 100 keV bis 1 MeV. Auch Kombinationen dieser Strahlenquellen sind möglich.Electron beam sources are e.g. B. spot radiators working according to the cathode ray principle (e.g. from Polymerphysik, Tübingen) or linear cathodes working according to the Elektrocurtain R principle (e.g. from Energie Science Inc.). They have a radiation power of 100 keV to 1 MeV. Combinations of these radiation sources are also possible.

Sowohl die Elektronenquellen als auch die UV-Strahlenquellen können auch diskontinuierlich arbeitend ausgelegt sein. Besonders geeignet sind dann Laserlichtquellen oder Elektronenquellen. Eine andere Möglichkeit für kurzzeitig an- und ausschaltbare (taktbare) UV-Quellen besteht durch Vorschaltung von z. B. beweglichen Blenden (Shutter).Both the electron sources and the UV radiation sources can also be designed to operate discontinuously. Laser light sources or electron sources are then particularly suitable. Another possibility for temporarily switching on and off (clockable) UV sources is by connecting z. B. movable shutters.

Als Hilfselemente können übliche in der technischen Optik verwendete Lichtsteuersysteme, wie z. B. Absorptionsfilter, Reflektoren, Spiegel, Linsensysteme, oder Lichtwellenleiter eingesetzt werden.As auxiliary elements, conventional lighting control systems used in technical optics, such as. B. absorption filters, reflectors, mirrors, lens systems, or optical fibers can be used.

Erfindungsgemäß kann die Bestrahlung so durchgeführt werden, daß in einer Stufe eine durchgehende Vernetzung der Klarlackschicht erfolgt. Es kann jedoch auch günstig sein, zunächst eine Vorgelierung des Überzugsfilms durch UV-induzierte Vernetzung, z. B. in einer ersten Zone mit Schwarzlichtbestrahlung durchzuführen und anschließend weiter in einer zweiten oder mehreren Stufen zu vernetzen, beispielsweise durch erneute UV-Bestrahlung oder Bestrahlung mit Elektronenstrahlen.According to the invention, the irradiation can be carried out in such a way that the clear lacquer layer is continuously crosslinked in one step. However, it may also be advantageous to first pre-gel the coating film by UV-induced crosslinking, e.g. B. in a first zone with black light irradiation and then further crosslinked in a second or more stages, for example by renewed UV irradiation or irradiation with electron beams.

Die Anordnung der Strahlenquelle ist im Prinzip bekannt, sie kann den Gegebenheiten des Werkstücks und der Verfahrensparameter angepaßt werden.The arrangement of the radiation source is known in principle, it can be adapted to the conditions of the workpiece and the process parameters.

Beispielsweise kann das Werkstück im Ganzen bestrahlt werden, oder es kann ein Strahlungsvorhang verwendet werden, der sich relativ zum Werkstück bewegt. Außerdem kann über eine automatische Vorrichtung eine punktförmige Strahlenquelle über das Substrat geführt werden und den Vernetzungsprozeß einleiten. Um eine Vernetzungsreaktion auf allen Seiten des Werkstückes zu erreichen, ist auch gegebenenfalls ein Bewegen des Substrats vor den Strahlenquellen um Längs- oder Querachsen möglich.For example, the workpiece as a whole can be irradiated, or a radiation curtain can be used that moves relative to the workpiece. In addition, a punctiform radiation source can be guided over the substrate via an automatic device and initiate the crosslinking process. In order to achieve a crosslinking reaction on all sides of the workpiece, it is also possible, if necessary, to move the substrate in front of the radiation sources about longitudinal or transverse axes.

Der Abstand der Strahlenquelle kann fest sein oder er wird auf einen gewünschten Wert der Substratform angepaßt. Die Abstände der Strahlenquellen liegen bevorzugt im Bereich von 2 - 25 cm, besonders bevorzugt 5 - 10 cm, zur Naßlackoberfläche. Im Falle der Verwendung eines UV-Lasers ist ein größerer Abstand möglich.The distance of the radiation source can be fixed or it is adjusted to a desired value of the substrate shape. The distances between the radiation sources are preferably in the range of 2-25 cm, particularly preferably 5-10 cm, from the wet lacquer surface. If a UV laser is used, a larger distance is possible.

Selbstverständlich können die als Beispiele aufgezählten Verfahrensmaßnahmen auch kombiniert werden. Das kann in einem einzigen Prozeßschritt erfolgen oder in zeitlich oder räumlich voneinander getrennten Prozeßschritten.Of course, the procedural measures listed as examples can also be combined. This can take place in a single process step or in process steps that are separated from one another in time or space.

Die Bestrahlungsdauer liegt beispielsweise im Bereich von 0,1 Sekunden bis 30 Minuten, je nach Lacksystem und Strahlenquelle. Bevorzugt ist eine Zeit von unter 5 Minuten. Die Bestrahlungsdauer wird so gewählt, daß eine vollständige Aushärtung erreicht wird, d. h. die Ausbildung der geforderten technologischen Eigenschaften gewährleistet ist.The radiation duration is, for example, in the range from 0.1 seconds to 30 minutes, depending on the coating system and radiation source. A time of less than 5 minutes is preferred. The irradiation time is chosen so that complete curing is achieved, i. H. the formation of the required technological properties is guaranteed.

Das erfindungsgemäße Verfahren läßt sich besonders vorteilhaft zur Herstellung von Mehrschichtlackierungen auf dem Kraftfahrzeugsektor, z. B. von Automobilkarossen oder deren Teilen verwenden.The inventive method can be particularly advantageous for the production of multi-layer coatings in the automotive sector, for. B. of automobile bodies or parts thereof.

Ein Problem bei der Beschichtung von Automobilkarossen mit strahlenhärtenden Lacksystemen liegt in der Aushärtung in nicht direkt der Strahlung zugänglichen Bereichen (Schattenbereichen), wie z. B. Hohlräumen, Falzen und anderen konstruktionsbedingten Hinterschneidungen. Dieses Problem kann z. B. durch Einsatz von Punkt-, Kleinflächen- oder Rundumstrahlern unter Verwendung einer automatischen Bewegungseinrichtung für das Bestrahlen von Innen-, Motor-, Hohlräumen oder Kanten gelöst werden.One problem with the coating of automobile bodies with radiation-curing paint systems is the curing in areas that are not directly accessible to the radiation (shadow areas), such as, for example, B. cavities, folds and other design-related undercuts. This problem can e.g. B. can be solved by using point, small area or omnidirectional emitters using an automatic movement device for irradiating interior, motor, cavities or edges.

Zusätzlich ist es möglich, eine thermische Aktivierung zur Vernetzung des Überzugsmittels auf solchen Flächen anzuwenden, die nur in nicht ausreichender Weise dem Strahlungsvernetzungsprozeß unterworfen werden können. Beim Einsatz von radikalisch polymerisierbaren Überzugsmitteln kann es hierzu günstig sein, thermisch aktivierbare Radikalinitiatoren zu verwenden, so daß im Anschluß an die Bestrahlung oder gleichzeitig mit der Bestrahlung eine thermisch aktivierte radikalische Polymerisation durchgeführt werden kann. Beim Einsatz von kationisch polymerisierbaren Überzugsmitteln ist es nicht notwendig, spezielle thermisch aktivierbare Initiatoren zu verwenden. Die durch die Strahlungsenergie eingeleitete kationische Polymerisation pflanzt sich auch in die Schattenbereiche z. B. nicht oder nur wenig bestrahlter Flächen, fort. Es ist allerdings auch in diesem Falle günstig zu erwärmen, um die Polymerisation in den Schattenbereichen zu unterstützen.In addition, it is possible to use thermal activation for crosslinking the coating agent on surfaces which can only be subjected to the radiation crosslinking process in an insufficient manner. When using radically polymerizable coating agents, it may be expedient to use thermally activatable radical initiators so that a thermally activated radical polymerization can be carried out after the irradiation or simultaneously with the irradiation. When using cationically polymerizable coating agents, it is not necessary to use special thermally activatable initiators. The cationic polymerization initiated by the radiation energy also plants itself in the shadow areas e.g. B. not or only little irradiated areas. In this case, too, however, it is advantageous to heat to support the polymerization in the shadow areas.

Erfindungsgemäß können strahlenhärtende Klarlack-Überzugsmittel eingesetzt werden, die im Prinzip bekannt und in der Literatur beschrieben sind. Es handelt sich entweder um radikalisch härtende Systeme, d. h. durch Einwirkung von Strahlung auf das Überzugsmittel entstehen Radikale, die dann die Vernetzungsreaktion auslösen, oder es handelt sich um kationisch härtende Systeme, bei denen durch Bestrahlung aus Initiatoren Lewis-Säuren gebildet werden, die zum Auslösen der Vernetzungsreaktion dienen.According to the invention, radiation-curing clear lacquer coating compositions can be used which are known in principle and are described in the literature. They are either radical curing systems, i. H. The action of radiation on the coating agent gives rise to radicals which then trigger the crosslinking reaction, or it is a matter of cationically curing systems in which Lewis acids are formed by radiation from initiators and serve to trigger the crosslinking reaction.

Bei den radikalisch härtenden Systemen handelt es sich z. B. um Prepolymere, wie Poly- oder Oligomere, die olefinische Doppelbindungen im Molekül aufweisen. Diese Prepolymere können gegebenenfalls in Reaktivverdünnern, d. h. reaktiven flüssigen Monomeren, gelöst sein. Zusätzlich können Überzugsmittel dieser Art noch übliche Initiatoren, Lichtschutzmittel, gegebenenfalls transparente Pigmente, lösliche Farbstoffe, sowie weitere lacktechnische Hilfsmittel enthalten.The radically curing systems are e.g. B. prepolymers, such as poly- or oligomers, which have olefinic double bonds in the molecule. These prepolymers can optionally in reactive diluents, i.e. H. reactive liquid monomers. In addition, coating compositions of this type can also contain customary initiators, light stabilizers, optionally transparent pigments, soluble dyes, and other coating assistants.

Beispiele für Prepolymere oder Oligomere sind (meth)acrylfunktionelle (Meth)Acryl-Copolymere, Epoxidharz(meth)acrylate, die frei von aromatischen Struktureinheiten sind, Polyester(meth)acrylate, Polyether(meth)acrylate, Polyurethan(meth)acrylate, ungesättigte Polyester, Amino(meth)acrylate, Melamin(meth)acrylate, ungesättigte Polyurethane oder Silikon(meth)acrylate. Das Molekulargewicht (Zahlenmittel Mn) liegt bevorzugt im Bereich von 200 bis 10000, besonders bevorzugt von 500 bis 2000. (Meth)Acryl bedeutet hier und im folgenden dabei Acryl und/oder Methacryl.Examples of prepolymers or oligomers are (meth) acrylic-functional (meth) acrylic copolymers, epoxy resin (meth) acrylates that are free from aromatic structural units, polyester (meth) acrylates, polyether (meth) acrylates, polyurethane (meth) acrylates, unsaturated polyesters , Amino (meth) acrylates, melamine (meth) acrylates, unsaturated polyurethanes or silicone (meth) acrylates. The molecular weight (Number average M n ) is preferably in the range from 200 to 10,000, particularly preferably from 500 to 2000. (Meth) acrylic here and hereinafter means acrylic and / or methacrylic.

Werden Reaktivverdünner verwendet, so werden sie im allgemeinen zwischen 1 - 50 Gew.% eingesetzt, bevorzugt 5 - 30 Gew.%., bezogen auf das Gesamtgewicht von Prepolymeren und Reaktivverdünnern. Sie können mono-, di- oder polyungesättigt sein. Beispiele für solche Reaktivverdünner sind: (Meth)Acrylsäure und deren Ester, Maleinsäure und deren Halbester, Vinylacetat, Vinylether, substituierte Vinylharnstoffe, Alkylenglykol-di(meth)acrylat, Polyethylenglykol-di(meth)acrylat, 1,3-Butandiol-di(meth)acrylat, Vinyl(meth)acrylat, Allyl(meth)acrylat, Glycerin-tri-(meth)acrylat, Trimethylolpropan-tri-(meth)acrylat, Styrol, Vinyltoluol, Divinylbenzol, Pentaerythrittri(meth)acrylat, Pentaerythrittetra(meth)acrylat, Dipropylenglykol-di-(meth)acrylat und Hexandiol-di-(meth)acrylat, sowie deren Gemische. Sie dienen zur Beeinflussung der Viskosität und von lacktechnischen Eigenschaften, wie z. B. der Vernetzungsdichte.If reactive diluents are used, they are generally used between 1-50% by weight, preferably 5-30% by weight, based on the total weight of prepolymers and reactive diluents. They can be mono-, di- or poly-unsaturated. Examples of such reactive diluents are: (meth) acrylic acid and its esters, maleic acid and its half esters, vinyl acetate, vinyl ether, substituted vinyl ureas, alkylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, 1,3-butanediol di ( meth) acrylate, vinyl (meth) acrylate, allyl (meth) acrylate, glycerol tri- (meth) acrylate, trimethylolpropane tri- (meth) acrylate, styrene, vinyl toluene, divinylbenzene, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipropylene glycol di (meth) acrylate and hexanediol di (meth) acrylate, and mixtures thereof. They serve to influence the viscosity and paint properties, such as. B. the crosslink density.

Photoinitiatoren für radikalisch härtende Systeme können z. B. in Mengen von 0,1 - 5 Gew.% eingesetzt werden, bevorzugt 0,5 - 3 Gew.%, bezogen auf die Summe von radikalisch polymerisierbaren Prepolymeren, Reaktivverdünnern und Initiatoren. Es ist günstig, wenn ihre Absorption im Wellenlängenbereich von 260 -450 nm liegt. Beispiele für Photoinitiatoren sind Benzoin und Derivate, Benzil und Derivate, Benzophenon und Derivate, Acetophenon und Derivate, z B. 2,2-Diethoxyacetophenon, Thioxanthon und Derivate, Anthrachinon, 1-Benzoylcyclohexanol, phosphororganische Verbindungen, wie z. B. Acylphosphinoxide. Die Photoinitiatoren können allein oder in Kombination eingesetzt werden. Außerdem können weitere synergistische Komponenten, z. B. tertiäre Amine, eingesetzt werden.Photoinitiators for radical curing systems can e.g. B. in amounts of 0.1-5% by weight, preferably 0.5-3% by weight, based on the sum of free-radically polymerizable prepolymers, reactive diluents and initiators. It is advantageous if their absorption is in the wavelength range from 260 -450 nm. Examples of photoinitiators are benzoin and derivatives, benzil and derivatives, benzophenone and derivatives, acetophenone and derivatives, for example 2,2-diethoxyacetophenone, thioxanthone and derivatives, anthraquinone, 1-benzoylcyclohexanol, organophosphorus compounds, such as, for. B. acylphosphine oxides. The photoinitiators can be used alone or in combination. In addition, other synergistic components, e.g. B. tertiary amines can be used.

Neben den Photoinitiatoren können im Bedarfsfall, beispielsweise für die Bestrahlung mit Schwarzlichtröhren, übliche Sensibilisatoren, wie Anthracen in üblichen Mengen mitverwendet werden. Zusätzlich können gegebenenfalls thermisch aktivierbare radikalische Initiatoren eingesetzt werden. Diese bilden ab 80 - 120°C Radikale, die dann die Vernetzungsreaktion starten. Beispiele für thermolabile radikalische Initiatoren sind: organische Peroxide, organische Azoverbindungen oder C-C-spaltende Initiatoren, wie Dialkylperoxide, Peroxocarbonsäuren, Peroxodicarbonate, Peroxidester, Hydroperoxide, Ketonperoxide, Azodinitrile oder Benzpinakolsilylether. C-C-spaltende Initiatoren sind besonders bevorzugt, da bei der thermischen Spaltung keine gasförmigen Zersetzungsprodukte gebildet werden, die zu Störungen in der Lackschicht führen können. Die bevorzugten Einsatzmengen liegen zwischen 0,1 - 5 Gew.%, bezogen auf die Summe von radikalisch polymerisierbaren Prepolymeren, Reaktivverdünnern und Initiatoren. Die Initiatoren können auch im Gemisch eingesetzt werden.In addition to the photoinitiators, if necessary, for example for irradiation with black light tubes, customary sensitizers, such as anthracene, can also be used in customary amounts. In addition, thermally activatable free radical initiators can optionally be used. From 80 - 120 ° C, these form radicals, which then start the crosslinking reaction. Examples of thermolabile radicals Initiators are: organic peroxides, organic azo compounds or CC-cleaving initiators, such as dialkyl peroxides, peroxocarboxylic acids, peroxodicarbonates, peroxide esters, hydroperoxides, ketone peroxides, azodinitriles or benzpinacol silyl ethers. CC-cleaving initiators are particularly preferred, since no thermal decomposition products are formed during thermal cleavage, which can lead to faults in the lacquer layer. The preferred amounts are between 0.1 and 5% by weight, based on the sum of free-radically polymerizable prepolymers, reactive diluents and initiators. The initiators can also be used in a mixture.

Bindemittel für kationisch polymerisierbare Überzugsmittel sind beispielsweise polyfunktionelle Epoxyoligomere, die mehr als zwei Epoxygruppen im Molekül enthalten. Es ist günstig, wenn die Bindemittel frei von aromatischen Strukturen sind. Solche Epoxyoligomere sind beispielsweise in der DE-OS 36 15 790 beschrieben. Es handelt sich beispielsweise um Polyalkylenglykoldiglycidylether, hydrierte Bisphenol-A-Glycidylether, Epoxyurethanharze, Glycerintriglycidylether, Diglycidylhexahydrophthalat, Diglycidylester von Dimersäuren, epoxidierte Derivate des (Methyl)cyclohexens, wie z. B. 3,4-Epoxycyclohexyl-methyl-(3,4-epoxycyclohexan)carboxylat oder epoxidiertes Polybutadien. Das Zahlenmittel des Molekulargewichts der Polyepoxidverbindungen liegt bevorzugt unter 10000.Binding agents for cationically polymerizable coating agents are, for example, polyfunctional epoxy oligomers which contain more than two epoxy groups in the molecule. It is advantageous if the binders are free from aromatic structures. Such epoxy oligomers are described for example in DE-OS 36 15 790. It is, for example, polyalkylene glycol diglycidyl ether, hydrogenated bisphenol A glycidyl ether, epoxy urethane resins, glycerol triglycidyl ether, diglycidyl hexahydrophthalate, diglycidyl ester of dimer acids, epoxidized derivatives of (methyl) cyclohexene, such as, for. B. 3,4-Epoxycyclohexyl-methyl- (3,4-epoxycyclohexane) carboxylate or epoxidized polybutadiene. The number average molecular weight of the polyepoxide compounds is preferably less than 10,000.

Sind zur Applikation niedrige Viskositäten notwendig, so können diese durch Reaktivverdünner, d. h. reaktive flüssige Verbindungen, wie z. B. Cyclohexenoxid, Butenoxid, Butandioldiglycidylether oder Hexandioldiglycidylether eingestellt werden. Weitere reaktive Lösungsmittel als Beispiel sind Alkohole, Polyalkylenglykole, Polyalkohole, hydroxyfunktionelle Polymere, cyclische Carbonate oder Wasser. Diese können auch feste Bestandteile gelöst enthalten, wie beispielsweise feste Polyalkohole, wie Trimethylolpropan.If low viscosities are required for application, these can be reduced by reactive thinners, i.e. H. reactive liquid compounds, such as. B. cyclohexene oxide, butene oxide, butanediol diglycidyl ether or hexanediol diglycidyl ether. Examples of other reactive solvents are alcohols, polyalkylene glycols, polyalcohols, hydroxy-functional polymers, cyclic carbonates or water. These can also contain solid components, such as solid polyalcohols, such as trimethylolpropane.

Photoinitiatoren für kationisch härtende Systeme werden in Mengen von 0,5 - 5 Gew.% allein oder in Kombination eingesetzt, bezogen auf die Summe von kationisch polymerisierbaren Prepolymeren, Reaktivverdünnern und Initiatoren. Es sind Substanzen, die als Onium-Salze bekannt sind, die unter Bestrahlung photolytisch Lewis-Säuren freisetzen. Beispiele dafür sind Diazoniumsalze, Sulfoniumsalze oder Jodoniumsalze. Besonders bevorzugt sind Triarylsulfoniumsalze.Photoinitiators for cationically curing systems are used in amounts of 0.5-5% by weight, alone or in combination, based on the total of cationically polymerizable prepolymers, reactive diluents and initiators. There are substances known as onium salts that Release Lewis acids photolytically under irradiation. Examples include diazonium salts, sulfonium salts or iodonium salts. Triarylsulfonium salts are particularly preferred.

Nicht-reaktive Lösungsmittel für radikalisch und kationisch härtende Systeme sind übliche Lacklösemittel, wie Ester, Ether, Ketone, beispielsweise Butylacetat, Ethylenglykolether, Methylethylketon, Methylisobutylketon sowie aromatische Kohlenwasserstoffe. Für radikalisch polymerisierbare Systeme sind auch C₂-C₄-Alkanole und bevorzugt Wasser als Lösungsmittel geeignet.Non-reactive solvents for free-radically and cationically curing systems are customary paint solvents, such as esters, ethers, ketones, for example butyl acetate, ethylene glycol ether, methyl ethyl ketone, methyl isobutyl ketone and aromatic hydrocarbons. For radical polymerizable systems, C₂-C₂ alkanols and preferably water are also suitable as solvents.

Den erfindungsgemäß verwendeten Klarlacken werden bevorzugt Lichtschutzmittel zugesetzt. Beispiele dafür sind Phenylsalicylate, Benzotriazol und Derivate, HALS-Verbindungen sowie Oxalanilid-Derivate, gegebenenfalls auch in Kombination. Übliche Konzentrationen betragen 0,5 - 5 Gew.%, bevorzugt 1 - 2 Gew.%, bezogen auf den gesamten Klarlack. Es muß bei der Auswahl der Lichtschutzmittel darauf geachtet werden, daß die Initiierung der Vernetzung durch die Lichtschutzmittel nicht beeinträchtigt wird und daß die verwendeten Lichtschutzmittel gegen die Strahlung des Strahlenhärtungsprozesses stabil sind.Light stabilizers are preferably added to the clearcoats used according to the invention. Examples of these are phenyl salicylates, benzotriazole and derivatives, HALS compounds and oxalanilide derivatives, if appropriate also in combination. Usual concentrations are 0.5-5% by weight, preferably 1-2% by weight, based on the total clearcoat. When selecting the light stabilizers, care must be taken to ensure that the initiation of the crosslinking is not impaired by the light stabilizers and that the light stabilizers used are stable against the radiation from the radiation curing process.

Weitere Additive sind beispielsweise Elastifizierungsmittel, Polymerisations-Inhibitoren, Entschäumer, Verlaufsmittel, Antioxidationsmittel, transparente Farbstoffe oder optische Aufheller.Other additives are, for example, elastifying agents, polymerization inhibitors, defoamers, leveling agents, antioxidants, transparent dyes or optical brighteners.

Gegebenenfalls können dem Überzugsmittel transparente farblose Füllstoffe und/oder Pigmente zugegeben werden. Die Menge beträgt bis zu 10 Gew.%, bezogen auf den gesamten Klarlack. Beispiele sind Siliciumdioxid, Glimmer, Magnesiumoxid, Titandioxid oder Bariumsulfat. Die Teilchengröße liegt bevorzugt unter 200 nm. Bei UV-härtbaren Systemen ist darauf zu achten, daß der Überzugsfilm in der verwendeten Schichtdicke noch für UV-Strahlung transparent bleibt. Weitere verwendbare Additive sind beispielsweise übliche Mattierungsmittel anorganischer oder organischer Art. Diese können in üblichen Mengen beispielsweise bis zu 10 Gew.% zugesetzt werden. Beispiele für Mattierungsmittel sind Silikate, pyrogene Kieselsäuren, wie Aerosil, Bentone, oder auskondensierte und vernetzte Harnstoff-Formaldehydharze, natürliche und synthetische Wachse. Die Teilchengrößen derartiger Mattierungsmittel liegen im allgemeinen bis zu 100 »m, bevorzugt bis zu 30 »m.If necessary, transparent colorless fillers and / or pigments can be added to the coating agent. The amount is up to 10% by weight, based on the total clear coat. Examples are silicon dioxide, mica, magnesium oxide, titanium dioxide or barium sulfate. The particle size is preferably less than 200 nm. In the case of UV-curable systems, care must be taken that the coating film remains transparent to UV radiation in the layer thickness used. Other additives that can be used are, for example, conventional matting agents of an inorganic or organic type. These can be added in conventional amounts, for example up to 10% by weight. Examples of matting agents are silicates, pyrogenic silicas, such as Aerosil, Bentone, or condensed and crosslinked urea-formaldehyde resins, natural and synthetic waxes. The particle sizes Such matting agents are generally up to 100 »m, preferably up to 30» m.

Die verfahrenstechnischen Maßnahmen zur Herstellung von geeigneten strahlenhärtenden Klarlack-Überzugsmitteln sind bekannt. Es ist möglich, Systeme mit unterschiedlichem strahleninduziertem chemischem Vernetzungsmechanismus zu kombinieren. Dies können verschiedene radikalisch härtende Vernetzungssysteme oder kationisch härtende Vernetzungssysteme oder radikalisch und kationisch härtende Vernetzung miteinander kombiniert sein. Es sollte darauf geachtet werden, die Zusammensetzung so zu wählen, daß Lagerstabilität gegeben ist. Ebenso können unterschiedliche Reaktionsinitiierungsverfahren beispielsweise UV mit UV-Härtung, UV mit thermischer Initiierung oder Elektronenstrahlenhärtung mit UV-Härtung kombiniert werden.The procedural measures for the production of suitable radiation-curing clear lacquer coating compositions are known. It is possible to combine systems with different radiation-induced chemical cross-linking mechanisms. This can be combined with different free-radically curing crosslinking systems or cationically curing crosslinking systems or free-radically and cationically curing crosslinking. Care should be taken to choose the composition so that there is storage stability. Different reaction initiation processes, for example UV with UV curing, UV with thermal initiation or electron beam curing with UV curing, can also be combined.

Die verschiedenen Vernetzungsreaktionen können mit Gemischen der entsprechenden Initiatoren gestartet werden. Beispielsweise sind Gemische von UV-Initiatoren mit unterschiedlichem Absorptionsmaximum möglich. Auf diese Weise können unterschiedliche Emissionsmaxima einer oder mehrerer Strahlenquellen ausgenutzt werden. Dies kann gleichzeitig oder nacheinander erfolgen. So kann beispielsweise mit der Strahlung einer Strahlenquelle die Härtung eingeleitet und mit der einer anderen weitergeführt werden. Die Reaktion läßt sich dann zwei- oder mehrstufig, gegebenenfalls auch räumlich getrennt, durchführen. Die verwendeten Strahlenquellen können gleich oder verschieden sein.The various crosslinking reactions can be started with mixtures of the corresponding initiators. For example, mixtures of UV initiators with different absorption maximums are possible. In this way, different emission maxima of one or more radiation sources can be used. This can be done simultaneously or one after the other. For example, curing can be initiated with the radiation from one radiation source and continued with that of another. The reaction can then be carried out in two or more stages, if appropriate also spatially separated. The radiation sources used can be the same or different.

Erfindungsgemäß ist es möglich, zuerst eine strahleninduzierte und anschließend oder gleichzeitig eine thermisch induzierte Vernetzungsreaktion durchzuführen. Dazu können gegebenenfalls neben einem oder mehreren Photoinitiatoren ein oder mehrere thermisch spaltende Initiatoren verwendet werden. Die Verwendung von Photoinitiatoren ist bei der Elektronenstrahlhärtung nicht notwendig.According to the invention, it is possible to first carry out a radiation-induced crosslinking reaction and then or simultaneously a thermally induced crosslinking reaction. For this purpose, one or more thermally cleaving initiators can optionally be used in addition to one or more photoinitiators. The use of photoinitiators is not necessary for electron beam curing.

Die zwei- oder mehrstufige Arbeitsweise kann günstig sein um zunächst beispielsweise eine Angelierung zu erzielen, wodurch sich z. B. Läufer auf lackierten senkrechten Flächen vermeiden lassen. Die Angelierung ist auch bei lösemittelhaltigen Systemen günstig, um eine Abduristung des Lösungsmittels zu gestatten.The two-stage or multi-stage mode of operation can be favorable in order to first achieve, for example, a gelation. B. Avoid running on painted vertical surfaces. The gelation is also favorable in solvent-containing systems in order to allow the solvent to be sealed off.

Die Photoinitiatoren werden bevorzugt so gewählt, daß sie bei Licht mit einer Wellenlänge von über 550 nm nicht zerfallen. Bei Einsatz von thermisch spaltenden Initiatoren sind diese so zu wählen, daß sie unter Applikations-Bedingungen des Lackmaterials nicht zerfallen. Auf diese Art und Weise ist es möglich, den Overspray des Überzugsmittels direkt wieder aufzuarbeiten und einzusetzen, da eine chemische Reaktion während der Applikation vermieden wird.The photoinitiators are preferably chosen so that they do not disintegrate in light with a wavelength of over 550 nm. If thermally splitting initiators are used, they should be selected so that they do not disintegrate under the application conditions of the coating material. In this way it is possible to reprocess and use the overspray of the coating agent directly since a chemical reaction during the application is avoided.

Die Vernetzungsdichte des Lackfilms kann über die Funktionalität der eingesetzten Bindemittelbestandteile eingestellt werden. Die Auswahl kann so getroffen werden, daß der vernetzte Klarlacküberzug eine ausreichende Härte besitzt und ein zu hoher Vernetzungsgrad vermieden wird, um zu spröde Filme zu verhindern.The crosslinking density of the paint film can be adjusted via the functionality of the binder components used. The selection can be made in such a way that the crosslinked clear lacquer coating has sufficient hardness and an excessive degree of crosslinking is avoided in order to prevent films which are too brittle.

Durch das erfindungsgemäße Verfahren erhält man Mehrschichtüberzüge, die einen Klarlacküberzug hoher Kratzfestigkeit und mit hohem Glanz umfassen sowie mit einer hohen mechanischen Beständigkeit. Dabei kann der Overspray des zu applizierenden Überzugsmittels aufgrund der Verfahrensparameter und des gewählten Vernetzungsmechanismus einer direkten Wiederverwertung zugeführt werden. Das erfindungsgemäße Verfahren eignet sich besonders zur Anwendung in der Kraftfahrzeug-Serienlackierung, beispielsweise zur Lackierung von Automobilkarossen und deren Teilen.The process according to the invention gives multilayer coatings which comprise a clear lacquer coating with high scratch resistance and high gloss and with high mechanical resistance. The overspray of the coating agent to be applied can be directly recycled on the basis of the process parameters and the chosen crosslinking mechanism. The method according to the invention is particularly suitable for use in automotive serial painting, for example for painting automobile bodies and their parts.

In allen nachfolgend beschriebenen Beispielen wurde die Applikation der strahlenhärtenden Klarlacke in einem ausschließlich durch Rotlichtquellen beleuchteten Raum (Lichtwellenlänge größer 600 nm) durchgeführt.In all of the examples described below, the radiation-curing clearcoats were applied in a room illuminated exclusively by red light sources (light wavelength greater than 600 nm).

Beispiel 1example 1

Durch Mischen folgender Bestandteile wurde ein strahlenhärtbares Klarlacküberzugsmittel formuliert:
Gew.-Teile
44,5 Novacure 3200 (aliphatisches Epoxyacrylat von Interorgana)
32,2 Ebecryl 264 (aliphatisches Urethanacrylat von UCB)
3,0 Irgacure 184 (Photoinitiator von CIBA)
10,0 Dipropylenglycoldiacrylat
10,0 Trimethylolpropantriacrylat
0,3 Ebecryl 350 (Siliconacrylat von UCB)
Anschließend wurde, wie folgt, ein Lackaufbau hergestellt:
Ein KTL-grundiertes (20 »m) und mit handelsüblichem Füller (35 »m) vorbeschichtetes Blech wurde einmal mit üblichem Wasserbasislack, in einem zweiten Falle mit lösemittelhaltigem Basislack (15 »m Trockenschichtdicke) beschichtet und danach in beiden Fällen 20 min bei 140°C eingebrannt. Anschließend wurde obiges Lacksystem in einer Schichtdicke von 35 »m appliziert.A radiation-curable clear lacquer coating agent was formulated by mixing the following components:
Parts by weight
44.5 Novacure 3200 (aliphatic epoxy acrylate from Interorgana)
32.2 Ebecryl 264 (aliphatic urethane acrylate from UCB)
3.0 Irgacure 184 (photoinitiator from CIBA)
10.0 dipropylene glycol diacrylate
10.0 trimethylolpropane triacrylate
0.3 Ebecryl 350 (silicone acrylate from UCB)
A lacquer structure was then produced as follows:
A KTL-primed (20 »m) and pre-coated with a commercially available filler (35» m) was coated once with conventional water-based paint, in a second case with solvent-based paint (15 »m dry film thickness) and then in both cases for 20 min at 140 ° C branded. The above lacquer system was then applied in a layer thickness of 35 »m.

Das liegende Probeblech wurde zur Härtung bei 9 m/min Bandgeschwindigkeit mit zwei Quecksilbermitteldruckstrahlern von je 100 W/cm Leistung im Abstand von 10 cm zur auszuhärtenden Oberfläche (Bestrahlungsdauer somit 1 - 2 sec) bestrahlt. Man erhielt eine gut haftende, glänzende und harte Oberfläche sowohl auf Wasserbasecoat als auch auf konventionellem Basecoat.The horizontal sample sheet was irradiated for curing at a belt speed of 9 m / min with two medium pressure mercury lamps of 100 W / cm each at a distance of 10 cm from the surface to be hardened (irradiation time thus 1 - 2 sec). A well-adhering, glossy and hard surface was obtained both on water-based coat and on conventional base-coat.

Beispiel 2Example 2

Gew.-Teile:
40,5 Novacure 3200
27,5 Ebecryl 264
2,0 C-C-spaltender Initiator (Tetraphenylethanderivat gem. DE-A-1219224)
2,0 Irgacure 184
10,0 Dipropylenglycoldiacrylat
10,0 Tripropylenglycoldiacrylat
0,3 Ebecryl 350
7,7 Vinyltoluol
In analoger Weise wie in Beispiel 1 wurde ein in diesem Falle jedoch beidseitig beschichtetes Probeblech hergestellt und nach Applikation des obenstehenden strahlenhärtbaren Klarlackes freihängend nur von einer Seite bestrahlt, indem die zu bestrahlende Seite mit einem Abstand von 10 cm innerhalb 5 sec an einem wie in Beispiel 1 genannten Quecksilbermitteldruckstrahler gleichförmig entlang bewegt wurde.Parts by weight:
40.5 Novacure 3200
27.5 Ebecryl 264
2.0 CC-cleaving initiator (tetraphenylethane derivative according to DE-A-1219224)
2.0 Irgacure 184
10.0 dipropylene glycol diacrylate
10.0 tripropylene glycol diacrylate
0.3 Ebecryl 350
7.7 vinyl toluene
In a manner analogous to that in Example 1, in this case, however, a sample sheet coated on both sides was produced and, after application of the above radiation-curable clearcoat, exposed to radiation from one side only, by exposing the side to be irradiated with a distance of 10 cm within 5 seconds on one as in Example 1 mentioned medium pressure mercury lamp was moved uniformly along.

Die durch Strahlung nur teilvernetzte klebrige Rückseite wurde 15 min bei 110°C im Umluftofen eingebrannt.The sticky back, which was only partially cross-linked by radiation, was baked for 15 minutes at 110 ° C. in a forced air oven.

Auf beiden Seiten des Probebleches erhielt man Oberflächen mit wie in Beispiel 1 beschriebenen Eigenschaften.Surfaces with properties as described in Example 1 were obtained on both sides of the test sheet.

Beispiel 3Example 3 (Strahlungsinduziert kationisch härtender Klarlack)(Radiation-induced cationically curing clear coat)

Gew.-Teile
60,0 Degacure K 126 (cycloaliphatisches Epoxid von DEGUSSA)
25,0 Araldit DY 026 (Hexandioldiglycidylether von CIBA)
4,5 Degacure KI 85 (Sulfoniumsalz von DEGUSSA)
0,5 Dynasilan Glymo (glycidylfunktionelles Silan von Dynamit Nobel)
10,0 Cyclohexanol
Unter Verwendung dieser Formulierung wurde völlig analog Beispiel 1 gearbeitet. Man erhielt ein gleichartiges Lackierergebnis.Parts by weight
60.0 Degacure K 126 (cycloaliphatic epoxy from DEGUSSA)
25.0 araldite DY 026 (hexanediol diglycidyl ether from CIBA)
4.5 Degacure KI 85 (sulfonium salt from DEGUSSA)
0.5 Dynasilan Glymo (glycidyl functional silane from Dynamit Nobel)
10.0 cyclohexanol
Using this formulation, the procedure was completely analogous to Example 1. A similar painting result was obtained.

Beispiel 4Example 4

Beispiel 1 wurde mit gleichem Lackierergebnis wiederholt.
Lediglich wurden die Basislackschichten hier 30 min bei 120°C eingebrannt und vorbeschichtete Polycarbonatplatten verwendet.Example 1 was repeated with the same painting result.
Only the basecoat layers were baked here at 120 ° C for 30 minutes and pre-coated polycarbonate sheets were used.

Beispiel 5Example 5

Zu 100 Teilen des Klarlacküberzugsmittels aus Beispiel 1 wurden 2 Teile Anthracen als Sensibilisator hinzugefügt. Die Applikation erfolgte wie in Beispiel 1 beschrieben. Anschließend wurde bei 1m/min Bandgeschwindigkeit liegend mit 10 Schwarzlichtröhren im Abstand von 10 cm zur Naßlackoberfläche (Bestrahlungszeit somit 90 - 120 sec) bestrahlt. Man erhielt eine klebrige, teilvernetzte Oberfläche. Danach wurde das Probeblech 5 min aufgehängt und anschließend freihängend bestrahlt, indem die noch klebrige Oberfläche mit einem Abstand von 10 cm innerhalb 5 sec an einem wie in Beispiel 1 genannten Quecksilbermitteldruckstrahler gleichförmig entlang bewegt wurde. Man erhielt ein wie in Beispiel 1 genanntes Lackierergebnis. Die Oberfläche war läuferfrei.To 100 parts of the clear lacquer coating agent from Example 1, 2 parts of anthracene were added as a sensitizer. The application was carried out as described in Example 1. Subsequently, at a belt speed of 1 m / min, lying was irradiated with 10 black light tubes at a distance of 10 cm from the wet lacquer surface (irradiation time thus 90-120 sec). A sticky, partially cross-linked surface was obtained. The sample sheet was then suspended for 5 minutes and then irradiated freely suspended by uniformly moving the still sticky surface at a distance of 10 cm within 5 seconds on a medium-pressure mercury lamp as mentioned in Example 1. A painting result as mentioned in Example 1 was obtained. The surface was run-free.

Claims (13)

  1. Process for the production of a multilayer lacquer coating by applying a clear lacquer coating onto a dried or crosslinked, coloured and/or effect base coat lacquer layer, characterised in that the clear lacquer coating is produced using a coating composition which may be cured exclusively by free-radical and/or cationic polymerisation, the coating composition is applied with illumination with light having a wavelength of above 550 nm or with exclusion of light, whereupon curing is initiated and/or effected by high-energy radiation.
  2. Process according to claim 1, characterised in that curing is initiated and/or effected by UV radiation in a wavelength range of 180 to 420 nm.
  3. Process according to one of the preceding claims, characterised in that curing is initiated and/or effected by electron beams.
  4. Process according to one of the preceding claims, characterised in that curing is performed sequentially in two or more stages with two or more sources of high-energy radiation.
  5. Process according to one of the preceding claims, characterised in that, after initial curing by high-energy radiation, curing additionally proceeds thermally or is continued thermally.
  6. Process according to claim 5, characterised in that it is performed with a coating composition curable by free-radical polymerisation, which coating composition contains one or more photoinitiators and one or more thermally activatable free-radical initiators.
  7. Process according to claim 5, characterised in that it is performed with a coating composition curable by cationic polymerisation, which coating composition contains one or more photoinitiators.
  8. Process according to one of the preceding claims, characterised in that it is performed with a coating composition which contains transparent pigments and/or soluble dyes.
  9. Process according to one of the preceding claims, characterised in that a coating composition is used which contains substantially no solvents or which contains water as the solvent.
  10. Process according to one of the preceding claims, characterised in that the clear lacquer coating is applied to a dry film thickness of 10 to 80 »m.
  11. Process according to one of the preceding claims, characterised in that the coating composition is applied by spraying and any overspray is recycled for spray application, optionally after supplementing any volatile constituents.
  12. Use of transparent coating compositions curable by free-radical and/or cationic polymerisation optionally containing transparent pigments and/or soluble dyes as clear lacquers in the production of multilayer lacquer coatings.
  13. Use according to claim 12 in the production of multilayer lacquer coatings in the automotive sector.
EP92116937A 1991-10-08 1992-10-03 Process for making multilayer coatings using a radially or cationnically polymerisable clear coat Expired - Lifetime EP0540884B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE4133290 1991-10-08
DE4133290A DE4133290A1 (en) 1991-10-08 1991-10-08 METHOD FOR PRODUCING MULTILAYER LACQUERING USING RADICALLY AND / OR CATIONICALLY POLYMERIZABLE CLEAR VARNISHES

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EP0540884B1 true EP0540884B1 (en) 1995-06-28

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EP (1) EP0540884B1 (en)
JP (1) JPH05222319A (en)
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DE59202711D1 (en) 1995-08-03
JPH05222319A (en) 1993-08-31
EP0540884A1 (en) 1993-05-12
US5486384A (en) 1996-01-23
ATE124299T1 (en) 1995-07-15
CA2079498A1 (en) 1993-04-09
DE4133290A1 (en) 1993-04-15
ES2076643T3 (en) 1995-11-01
KR930007519A (en) 1993-05-20

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