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EP0568967A2 - Method for preparing multilayer coatings - Google Patents

Method for preparing multilayer coatings Download PDF

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Publication number
EP0568967A2
EP0568967A2 EP93107182A EP93107182A EP0568967A2 EP 0568967 A2 EP0568967 A2 EP 0568967A2 EP 93107182 A EP93107182 A EP 93107182A EP 93107182 A EP93107182 A EP 93107182A EP 0568967 A2 EP0568967 A2 EP 0568967A2
Authority
EP
European Patent Office
Prior art keywords
radiation
clear lacquer
layer
curing
curable
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.)
Granted
Application number
EP93107182A
Other languages
German (de)
French (fr)
Other versions
EP0568967B1 (en
EP0568967A3 (en
Inventor
Edgar Dr. Lahrmann
Stefan Dr. Drüeke
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
Priority date (The priority date 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 date listed.)
Filing date
Publication date
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Publication of EP0568967A2 publication Critical patent/EP0568967A2/en
Publication of EP0568967A3 publication Critical patent/EP0568967A3/en
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Publication of EP0568967B1 publication Critical patent/EP0568967B1/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
    • 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
    • B05D7/56—Three layers or more
    • B05D7/57—Three layers or more the last layer being a clear coat
    • B05D7/576—Three layers or more the last layer being a clear coat 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
    • B05D3/06—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
    • B05D3/068—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 ionising radiations (gamma, X, electrons)

Definitions

  • the invention relates to a process for the production of multi-layer coatings with a multi-layer clear lacquer coating, the top clear lacquer layer being based on a radiation-curing clear lacquer.
  • Today's automotive OEM coatings mostly consist of a clear coat / basecoat top coat, which is applied to an electrophoretically primed body and coated with a filler.
  • Basecoat and clearcoat are preferably applied wet-on-wet, i.e. after a flash-off time, if necessary with heating, and after subsequent application of a clear coat, the basecoat is baked together with it, e.g. in EP-A-0 038 127 and 0 402 772.
  • Suitable clear coats in this context are e.g. in EP-A-0 038 127 and 0 184 761.
  • These are systems based on binders that crosslink via addition or condensation reactions, e.g. binders crosslinking via melamine resins or isocyanate derivatives.
  • EP-A-0 402 181 describes the production of a multi-layer coating by applying several layers of clear lacquer to a basecoat.
  • Thermosetting clearcoats are described based on hydroxy-functional acrylate resins as binders and melamine resins or isocyanates as crosslinkers.
  • thermosetting clear lacquers are in need of improvement with regard to their chemical resistance and the mechanical strength, for example the scratch resistance.
  • DE-A-41 33 290 describes a process for producing a multilayer coating by applying a radiation-curing clearcoat to a dried basecoat.
  • These clear lacquer layers are characterized by improved chemical resistance.
  • the clear lacquer coatings must be coated in a total layer thickness of at least 50 ⁇ m.
  • the problem with these high layer thicknesses is the high volume shrinkage of radiation-curing lacquers during curing.
  • high layer thicknesses there are tensions in the film and a deterioration in adhesion to the underlying base coat or edge alignment is observed.
  • Such a procedure is uneconomical because of the high price of radiation-curing coating agents compared to conventional thermosetting lacquers.
  • the object of the invention was to provide a process for the production of multilayer coatings with high chemical resistance and the fulfillment of increased demands on the optical quality.
  • thermosetting clear coat is applied to a pigmented basecoat and crosslinked in the heat, and which is characterized in that a further clear coat based on radiation-curing coating agents is applied to the clear coat and then crosslinked with actinic radiation.
  • the generally known basecoats can serve as basecoats. Examples of these are solvent-based, aqueous or powder base coats. Water-dilutable basecoats are preferred.
  • the basecoats contain conventional physically drying and / or chemical crosslinking binders, inorganic and / or organic colored pigments and / or effect pigments, such as e.g. B. metallic or pearlescent pigments and other customary auxiliaries, such as. B. catalysts, leveling agents or anti-cratering agents. Polyester, polyurethane or acrylate resins are preferably used as the binder base of the basecoat. These binders can optionally be crosslinked, e.g. B. melamine or isocyanate derivatives.
  • the basecoats are applied to conventional substrates either directly or to precoated substrates in a layer thickness of 10-30 ⁇ m, preferably less than 20 ⁇ m.
  • 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.
  • thermosetting clearcoat All customary thermosetting clear lacquer coating compositions which cannot be hardened by actinic radiation can be used as clear lacquers. Examples are powder clearcoats, clearcoats dissolved in solvents, low-solvent or solvent-free clearcoats and water-dilutable clearcoats. They can be one or more components, self-or externally cross-linking. As a binder base of these clear coats serve z.
  • the layer formed is dried or baked at elevated temperature to form a basecoat / clearcoat two-layer lacquer.
  • the basecoat may have previously been dried at temperatures up to 150 ° C. or, as a preferred embodiment of the process according to the invention, the clearcoat layer is applied wet-on-wet to the basecoat layer, whereupon it is dried or baked together.
  • the drying or stoving process of the base and thermosetting clear lacquer layer is carried out in the process according to the invention in such a way that the lower lacquer layers obtained contain only small proportions of volatile substances. Especially at the time of the radiation-induced crosslinking reaction of the further clear lacquer coating layer, none should substantial parts of volatile constituents are more contained in the underlying lacquer layers. Such components can cause gloss and adhesion problems in the upper radiation-curing clear lacquer film.
  • the underlying clear coat can be sanded before applying the radiation-curing clear coat. If necessary, further thermosetting clear lacquer layers can be applied between the first thermosetting clear lacquer layer and the top radiation-curing clear lacquer layer. If desired, special optical effects can be achieved via these additional layers.
  • a radiation-curing coating agent is applied to the dried and crosslinked base and clear lacquer layers. These are known free-radically and / or cationically polymerizing clearcoats, which can be mixed with conventional additives. These are networked by radiation.
  • 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 spray.
  • B. compressed air spraying airless spraying, high rotation, electrostatic spray application (ESTA)
  • hot spray application such as. B. Hot air hot spray.
  • This can be carried out at temperatures of a maximum of 70-80 ° C., so that suitable application viscosities are achieved and there is no change in the coating material and in the overspray, which may need to be reprocessed, in the event of a brief thermal load.
  • hot spraying can be designed in such a way that the paint material is only heated briefly in or shortly before the spray nozzle.
  • the spray booth can be operated, for example, with a circulation that can be tempered, if necessary, which is equipped with a suitable absorption medium for the overspray, e.g. B. the paint material is operated.
  • the spray booth consists of materials that prevent contamination of the material and are not attacked by the circulating medium. Such measures can support reprocessing of the overspray.
  • the coating process is preferably carried out when illuminated with visible light of a wavelength of over 550 nm or with exclusion of light.
  • 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 necessary, a mixing device for keeping volatile constituents constant, such as. B. the organic solvent or water, necessary.
  • the radiation-curing clear lacquer is preferably applied in such a way that dry layer thicknesses of 10-50 ⁇ m, particularly preferably 15-35 ⁇ m, are preferably achieved. If desired, the radiation-curing clear lacquer can be applied in several layers.
  • the coated substrate is subjected to the crosslinking process, if appropriate 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, for example, with supercritical carbon dioxide as a solvent, such as. B. described in EP-A-0 321 607. It is also possible to support the resting time by increasing 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 adding CO2, N2 or by using a mixture of both directly to the substrate surface.
  • Radiation curing can be carried out using customary radiation sources, optical auxiliary measures for carrying out, customary periods of time and customary measures for controlling the radiation process, and using customary arrangements of the radiation sources under conditions familiar to the person skilled in the art.
  • UV lamps and electron beam sources are preferably used.
  • the radiation can be carried out in such a way that the radiation-curing 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.
  • a problem in the coating of complex shaped bodies, such as. B. automotive bodies with radiation-curing paint systems is in the curing in areas not directly accessible to the radiation (shadow areas), such as. 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.
  • thermal activation it is possible to use thermal activation to crosslink the coating agent.
  • thermally activatable radical initiators it may be advantageous 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.
  • the coating systems which can be used according to the invention for the upper clear lacquer layer are customary radiation-curing coating compositions which crosslink 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% lacquer systems that can be applied without solvents and without water.
  • the radiation-curing clearcoats can be formulated as unpigmented or transparent pigmented topcoats, colored with soluble dyes if desired.
  • 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 generates radicals which then trigger the crosslinking reaction, or it is a matter of cationic curing systems in which Lewis acids are formed by radiation from initiators and serve to trigger the crosslinking reaction.
  • the radical 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 agents of this type can also contain, for example, customary initiators, light stabilizers, transparent pigments, soluble dyes and / or other coating aids.
  • 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 Mn) 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 generally used in amounts of 1-70% by weight, preferably 5-40% 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, N-vinylpyrrolidone, vinyl acetate, vinyl ether, substituted vinyl ureas.
  • Photoinitiators for radical curing systems can e.g. B. in amounts of 0.1-5% by weight, preferably 0.5-4% by weight, based on the sum of free-radically polymerizable prepolymers, reactive diluents and initiators. It is favorable if their absorption is in the wavelength range of 260-450nm.
  • Conventional photoinitiators known to those skilled in the art can be used. Examples of photoinitiators are benzoin and derivatives, benzil and derivatives, benzophenone and derivatives, acetophenone and derivatives, e.g. B.
  • the photoinitiators can be used alone or in combination.
  • other synergistic components e.g. B. tertiary amines can be used.
  • conventional sensitizers such as. B. anthracene can be used in the usual amounts.
  • conventional thermally activatable free radical initiators can also be used, if appropriate. These form radicals from 80-120 ° C, which then start the crosslinking reaction.
  • 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 gaseous decomposition products are formed during thermal cleavage, which can lead to faults in the lacquer layer.
  • the preferred amounts are between 0.1-5% 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-A-36 15 790. These are, 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. reactive liquid compounds
  • reactive liquid compounds e.g. B. reactive monomers such as cyclohexene oxide, butene oxide, butanediol divinyl ether, 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 sum of cationically polymerizable prepolymers, reactive diluents and initiators. They are substances known as onium salts that release Lewis acids photolytically under radiation. Examples of this are diazonium salts, sulfonium salts or iodonium salts. Triarylsulfonium salts are particularly preferred.
  • the radiation-curable binders can contain further functional groups in the molecule, such as. B. hydroxyl, oxirane or isocyanate groups, which are accessible for chemical crosslinking.
  • the radiation-curable clearcoats external crosslinkers such.
  • suitable crosslinking agents are polyamine hardeners, polyamidoamine hardeners, moisture-cleavable ketimine crosslinkers, CH-acidic compounds which can have a crosslinking action in the sense of a Michael addition.
  • Examples are the radiation-induced curable clearcoats described in EP-A-0 247 563, which additionally contain OH-functional binder and a polyisocyanate hardener and thus crosslink by means of two combined curing mechanisms. These can also be used by the process according to the invention.
  • Non-reactive solvents for free-radically and cationically curing systems are conventional paint solvents, such as esters, ethers, ketones, for example butyl acetate, ethylene glycol ether, methyl ethyl ketone, methyl isobutyl ketone and aromatic hydrocarbons.
  • paint solvents such as esters, ethers, ketones, for example butyl acetate, ethylene glycol ether, methyl ethyl ketone, methyl isobutyl ketone and aromatic hydrocarbons.
  • C2-C4 alkanols for radical polymerizable systems
  • water preferably water as a solvent.
  • Light stabilizers are preferably added to the clearcoats used according to the invention.
  • these are phenylsalicylates, benzotriazole and derivatives, HALS compounds and oxalanilide derivatives, as well as combinations thereof.
  • 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, optical brighteners and adhesive additives, such as. B. phosphoric acid esters and / or silanes.
  • 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 oxides, 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.
  • Manufacturing processes for suitable radiation-curing clear lacquer coating compositions are known. It is possible to combine systems with different radiation-induced chemical cross-linking mechanisms. These can be different radically curing crosslinking systems or cationically curing crosslinking systems or radically and cationically curing crosslinking combined.
  • the radiation-curing clearcoats can, for. B. also advantageously contain such components that allow an additional curing mechanism to the radiation-induced radical and / or cationic crosslinking mechanism already described. This procedure allows a combined hardening of the upper clear lacquer layer applied according to the invention by running in parallel or in succession radiation-induced and non-radiation-induced crosslinking reactions.
  • the non-radiation-induced crosslinking reaction serves for additional crosslinking or postcrosslinking, which can be advantageous.
  • Examples of such non-radiation-induced mechanisms are polyaddition and polycondensation reactions. These additional curing reactions can e.g. B. at elevated temperature up to 180 ° C.
  • the radiation-curable clearcoats used according to the invention can have one or two components, depending on the additional crosslinking mechanism chosen. Care should be taken to choose the composition so that the radiation-curable clearcoat or the components of a multi-component radiation-curable clearcoat are stable in storage. Likewise, different reaction initiation processes, for example UV with UV curing, UV with thermal initiation or electron beam curing with UV curing, can be combined.
  • the various crosslinking reactions can be started with mixtures of the corresponding initiators.
  • mixtures of photoinitiators 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, e.g. B. also spatially separate.
  • the radiation sources used can be the same or different.
  • thermoly cleaving initiators it is possible first to carry out a radiation-induced crosslinking reaction and then or simultaneously to carry out a thermally induced crosslinking reaction.
  • one or more thermally cleaving initiators can also be used for this purpose, if desired.
  • photoinitiators is not necessary for electron beam curing.
  • the two-stage or multi-stage mode of operation can be favorable in order to initially achieve, for example, a gelation.
  • B. Avoid runners on painted vertical surfaces. The hinge is too cheap for solvent-based systems to allow evaporation of the solvent.
  • the photoinitiators are preferably chosen so that they do not disintegrate when exposed to visible 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 so 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 multi-layer coating obtained by the process according to the invention shows good adhesion of the individual layers to one another.
  • An increased total layer thickness of the clear lacquer coating is possible, and clear lacquers with different properties can also be used. This also has special optical properties, e.g. better gloss, better structure-free surface.
  • the possible rapid crosslinking reaction of the outer clear lacquer layer also results in advantages in sensitivity to external influences, e.g. Inclusions of dust, in the paint.
  • the process according to the invention gives yellowing-free multi-layer coatings with high chemical resistance, good scratch resistance and high optical quality (fullness, gloss). In particular structure-free surfaces achieved. This results, for example, from the following examples, which show particularly high DOI values for the coatings according to the invention.
  • the overspray of the radiation-curing coating agent used in the process according to the invention is suitable for direct recycling.
  • the method according to the invention is particularly suitable for use in automotive OEM painting.
  • Metal or plastic parts are particularly suitable as substrates, e.g. Automotive bodies and their parts.
  • a radiation-curable and thermosetting clear lacquer coating composition was prepared from 52 parts of a 60% strength solution of a difunctional polyester acrylate with a molecular weight of 1300 in dipropylene glycol diacrylate with an acid number of 18 mg KOH / g based on the solution and a hydroxyl number based on the solution of 150 mg KOH / g, 35 parts of phenoxyethyl acrylate, 4 parts of 2-hydroxy-2-methyl-1-phenylpropan-1-one, 0.2 part of a commercially available leveling agent (BYK 310 from BYK) and 8.8 parts of hexamethoxymethylmelamine.
  • BYK 310 from BYK
  • Comparative experiment A was repeated analogously, with the difference that instead of a second clearcoat layer based on the 1K clearcoat, the radiation-curable clearcoat from example 1 was applied by spraying in a 35 ⁇ m dry film thickness.
  • the horizontal sample sheet was then irradiated for curing at a belt speed of 1 m / min using 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 approx. 10 sec). When looking at the high-gloss surface, no structure was perceptible.
  • a KTL-primed (20 ⁇ m) and pre-coated with commercially available filler (35 ⁇ m) was spray-coated with a standard plain-colored water-based paint in a dry film thickness of 15 ⁇ m; after flashing off at 60 ° C. for 5 minutes, followed by flashing off at 100 ° C. for 5 minutes, the reaction was carried out with conventional solvent-based 1-component clear lacquer based on acrylic resin / melamine resin wet-on-wet overcoated in a dry layer thickness of 35 ⁇ m and baked at 140 ° C for 10 min. The same 1-component clearcoat was then spray-coated in a 35 ⁇ m dry film thickness and baked at 140 ° C. for 20 minutes. When looking at the glossy surface, a structure was seen.
  • Comparative experiment B was repeated analogously, with the difference that instead of a second clear lacquer layer based on the 1-component clear lacquer, one was prepared by mixing 90 parts of the radiation-curable clear lacquer from Example 2 and 10 parts of a polyisocyanate hardener (Desmodur N / 75 from Bayer) Clear coat in 35 ⁇ m dry film thickness was applied by hot spraying at 60 ° C to the test sheet preheated to 60 ° C. The lying sample sheet was then irradiated for curing at a belt speed of 1 m / min with two medium-pressure mercury lamps of 100 W / cm each at a distance of 30 cm from the surface to be hardened (irradiation time approx. 10 sec). The mixture was then cured at 140 ° C. for 20 minutes. A high-gloss surface with no perceptible structure was obtained.
  • a polyisocyanate hardener Desmodur N / 75 from Bayer
  • Comparative experiment B was repeated analogously, with the difference that after application of the first 1K clearcoat layer, curing was carried out at 140 ° C. for 20 minutes and then, instead of a second clearcoat layer based on the 1K clearcoat, the radiation-curable clearcoat from Example 3 was applied in a 35 ⁇ m dry film thickness Hot spraying at 60 ° C was applied to the test sheet preheated to 60 ° C. The radiation was then cured as described in Example 6. Thermal post-curing as in Example 6 was not carried out. A high-gloss surface with no perceptible structure was obtained.
  • Comparative experiment B was repeated analogously, with the difference that instead of a second clearcoat layer based on the 1K clearcoat, the radiation-curable clearcoat from Example 4 was applied in 35 ⁇ m dry film thickness by hot spraying at 60 ° C. to the sample sheet preheated to 60 ° C. The radiation curing and subsequent thermal post-curing was performed as described in Example 6. The high-gloss surface obtained was free of any noticeable structure.
  • Comparative experiment A was repeated with the difference that instead of the two clearcoat layers based on the 1K clearcoat, the radiation-curable clearcoat from example 1 was applied by spraying to a thickness of 35 ⁇ m.
  • the lying test sheet was then hardened at 1 m / min.
  • Belt speed irradiated with two medium pressure mercury lamps each with a power of 100 W / cm at a distance of 10 cm from the surface to be hardened irradiation time thus approx. 10 sec.
  • Comparative experiment C was repeated analogously.
  • another layer based on the radiation-curable clear lacquer from Example 1 was also applied in a 35 ⁇ m dry layer thickness by spraying.
  • the radiation curing was carried out analogously.
  • no structure was perceptible, but yellowing was perceptible in comparison with the multilayer structures obtained in Example 5 and in Comparative Experiments A and C.

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Abstract

The invention relates to a method for preparing multilayer coatings (finishes) in which at least one thermocurable clear coat is applied to a substrate provided with a pigmented base coat and is fully cured at elevated temperature, after which at least one further clear coat based on radiation-curable coating compositions is applied and fully cured under the action of actinic radiation. Finishes of particularly good visual quality are obtained.

Description

Die Erfindung betrifft ein Verfahren zur Herstellung von Mehrschichtlackierungen mit einem mehrschichtigen Klarlacküberzug, wobei die oben liegende Klarlackschicht auf einem strahlenhärtenden Klarlack basiert.The invention relates to a process for the production of multi-layer coatings with a multi-layer clear lacquer coating, the top clear lacquer layer being based on a radiation-curing clear lacquer.

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-0 038 127 und 0 402 772 beschrieben wird. In diesem Zusammenhang geeignete Klarlacke sind z.B. in den EP-A-0 038 127 und 0 184 761 beschrieben. Es handelt sich um Systeme auf Basis von Bindemitteln, die über Additions- oder Kondensationsreaktionen vernetzen, z.B. über Melaminharze oder Isocyanatderivate vernetzende Bindemittel.Today's automotive OEM coatings mostly consist of a clear coat / basecoat top coat, which is applied to an electrophoretically primed body and coated with a filler. Basecoat and clearcoat are preferably applied wet-on-wet, i.e. after a flash-off time, if necessary with heating, and after subsequent application of a clear coat, the basecoat is baked together with it, e.g. in EP-A-0 038 127 and 0 402 772. Suitable clear coats in this context are e.g. in EP-A-0 038 127 and 0 184 761. These are systems based on binders that crosslink via addition or condensation reactions, e.g. binders crosslinking via melamine resins or isocyanate derivatives.

In neuerer Zeit sind Mehrschichtlackierungen mit mehreren Klarlackschichten beschrieben worden. Eine solche Verfahrensweise erlaubt die Herstellung von Lackierungen mit besseren optischen Eigenschaften.In recent times, multi-layer coatings with several layers of clear lacquer have been described. Such a procedure allows the production of coatings with better optical properties.

In der DE 38 39 905 C2 werden Mehrschichtlackierungen beschrieben, bei denen auf eine pigmenthaltige Schicht zwei Klarlackschichten auf Lösemittelbasis aufgebracht werden. Es hat sich gezeigt, daß derartige Lackierungen hinsichtlich ihrer chemischen Beständigkeit, sowie ihres optischen Eindrucks verbesserungsbedürftig sind.DE 38 39 905 C2 describes multi-layer coatings in which two solvent-based clear lacquer layers are applied to a pigment-containing layer. It has been shown that such coatings are in need of improvement with regard to their chemical resistance and their visual impression.

Die EP-A-0 402 181 beschreibt die Herstellung einer Mehrschichtlackierung durch Aufbringen mehrerer Klarlackschichten auf einen Basislack. Es werden wärmehärtende Klarlacke beschrieben auf Basis von hydroxyfunktionellen Acrylatharzen als Bindemittel und Melaminharzen bzw. Isocyanaten als Vernetzer.EP-A-0 402 181 describes the production of a multi-layer coating by applying several layers of clear lacquer to a basecoat. Thermosetting clearcoats are described based on hydroxy-functional acrylate resins as binders and melamine resins or isocyanates as crosslinkers.

Die auf Basis von wärmehärtenden Klarlacken hergestellten Klarlackschichten sind jedoch verbesserungsbedürftig hinsichtlich ihrer Chemikalienfestigkeit und der mechanischen Festigkeit, z.B. der Kratzfestigkeit.However, the clear lacquer layers produced on the basis of thermosetting clear lacquers are in need of improvement with regard to their chemical resistance and the mechanical strength, for example the scratch resistance.

So beschreibt die DE-A-41 33 290 ein Verfahren zur Herstellung einer Mehrschichtlackierung durch Auftrag eines strahlenhärtenden Klarlackes auf einen getrockneten Basislack. Diese Klarlackschichten zeichnen sich aus durch verbesserte Chemikalienbeständigkeit.For example, DE-A-41 33 290 describes a process for producing a multilayer coating by applying a radiation-curing clearcoat to a dried basecoat. These clear lacquer layers are characterized by improved chemical resistance.

Werden an die optische Qualität (Fülle, hohe DOI-Werte) die eingangs erwähnten erhöhten Maßstäbe angelegt, so müssen die Klarlacküberzüge in Gesamtschichtdicken von mindestens 50 µm lackiert werden. Problematisch bei diesen hohen Schichtstärken ist der hohe Volumenschrumpf strahlenhärtender Lacke bei der Aushärtung. Bei hohen Schichtstärken ergeben sich Spannungen im Film und man beobachtet eine Haftungsverschlechterung zum darunter befindlichen Basislack bzw. Kantenflucht. Außerdem ist an senkrechten Flächen bei hoher Schichtstärke eine erhöhte Ablaufneigung festzustellen. Ein derartiges Vorgehen ist unwirtschaftlich aufgrund des hohen Preises strahlenhärtender Beschichtungsmittel im Vergleich zu üblichen wärmehärtenden Lacken.If the higher standards mentioned at the outset are applied to the optical quality (fullness, high DOI values), the clear lacquer coatings must be coated in a total layer thickness of at least 50 µm. The problem with these high layer thicknesses is the high volume shrinkage of radiation-curing lacquers during curing. At high layer thicknesses, there are tensions in the film and a deterioration in adhesion to the underlying base coat or edge alignment is observed. In addition, there is an increased tendency to run off on vertical surfaces with a thick layer. Such a procedure is uneconomical because of the high price of radiation-curing coating agents compared to conventional thermosetting lacquers.

Aufgabe der Erfindung war es, ein Verfahren zur Herstellung von Mehrschichtüberzügen mit hoher Chemikalienfestigkeit und der Erfüllung erhöhter Anforderungen an die optische Qualität zur Verfügung zu stellen.The object of the invention was to provide a process for the production of multilayer coatings with high chemical resistance and the fulfillment of increased demands on the optical quality.

Diese Aufgabe wird gelöst durch ein Verfahren zur Herstellung von Mehrschichtlackierungen, bei dem auf eine pigmentierte Basislackschicht mindestens eine wärmehärtbare Klarlackschicht aufgebracht und in der Wärme vernetzt wird, und das dadurch gekennzeichnet ist, daß auf die Klarlackschicht eine weitere Klarlackschicht auf Basis von strahlenhärtenden Überzugsmitteln aufgetragen wird und danach mit aktinischer Strahlung vernetzt wird.This object is achieved by a process for the production of multi-layer coatings, in which at least one thermosetting clear coat is applied to a pigmented basecoat and crosslinked in the heat, and which is characterized in that a further clear coat based on radiation-curing coating agents is applied to the clear coat and then crosslinked with actinic radiation.

Es ist gegebenenfalls möglich, die Strahlenhärtung in Stufen durchzuführen. Ebenfalls ist es bevorzugt möglich, eine thermische Vernetzung zusätzlich zur strahleninduzierten Vernetzung durchzuführen.It may be possible to carry out radiation curing in stages. It is also preferably possible to carry out thermal crosslinking in addition to radiation-induced crosslinking.

Als Basislacke können die allgemein bekannten Basislacke dienen. Beispiele dafür sind lösemittelbasierende, wäßrige oder Pulver-Basecoats. Bevorzugt sind wasserverdünnbare Basislacke. Die Basecoats enthalten übliche physikalisch trocknende und/oder chemische vernetzende Bindemittel, anorganische und/oder organisch Buntpigmente und/oder Effektpigmente, wie z. B. Metallic- oder Perlglanzpigmente sowie weitere lackübliche Hilfsstoffe, wie z. B. Katalysatoren, Verlaufsmittel oder Antikratermittel. Als Bindemittelbasis des Basislacks werden bevorzugt Polyester-, Polyurethan- oder Acrylatharze eingesetzt. Diese Bindemittel können gegebenenfalls über Vernetzer, z. B. Melamin- oder Isocyanatderivate vernetzt werden. Die Basecoats werden auf übliche Substrate entweder direkt oder auf vorbeschichtete Substrate in einer Schichtdicke von 10 - 30 µm, bevorzugt unter 20 µm, 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.The generally known basecoats can serve as basecoats. Examples of these are solvent-based, aqueous or powder base coats. Water-dilutable basecoats are preferred. The basecoats contain conventional physically drying and / or chemical crosslinking binders, inorganic and / or organic colored pigments and / or effect pigments, such as e.g. B. metallic or pearlescent pigments and other customary auxiliaries, such as. B. catalysts, leveling agents or anti-cratering agents. Polyester, polyurethane or acrylate resins are preferably used as the binder base of the basecoat. These binders can optionally be crosslinked, e.g. B. melamine or isocyanate derivatives. The basecoats are applied to conventional substrates either directly or to precoated substrates in a layer thickness of 10-30 μm, preferably less than 20 μm. 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.

Die Basislackschicht wird mit wärmehärtendem Klarlack überlackiert. Als Klarlacke können alle üblichen wärmehärtbaren Klarlacküberzugsmittel, die durch aktinische Strahlung nicht härtbar sind, eingesetzt werden. Beispiele sind Pulverklarlacke, in Lösemitteln gelöste Klarlacke, lösemittelarme oder lösemittelfreie Klarlacke und wasserverdünnbare Klarlacke. Sie können ein- oder mehrkomponentig, selbst- oder fremdvernetzend sein. Als Bindemittelbasis dieser Klarlacke dienen z. B. Polyester, Polyurethane und (Meth)acrylcopolymere.The basecoat is overcoated with thermosetting clearcoat. All customary thermosetting clear lacquer coating compositions which cannot be hardened by actinic radiation can be used as clear lacquers. Examples are powder clearcoats, clearcoats dissolved in solvents, low-solvent or solvent-free clearcoats and water-dilutable clearcoats. They can be one or more components, self-or externally cross-linking. As a binder base of these clear coats serve z. B. polyester, polyurethane and (meth) acrylic copolymers.

Beispiele für derartige Klarlacküberzugsmittel sind in den DE-A-39 10 829, DE-A-37 40 774, EP-A-0 038 127 zu finden.Examples of such clear lacquer coating compositions can be found in DE-A-39 10 829, DE-A-37 40 774, EP-A-0 038 127.

Nach Auftrag des Klarlacküberzugsmittels in einer Schichtdicke von 20-80 µm, bevorzugt 25-50 µm, wird die gebildete Schicht bei erhöhter Temperatur getrocknet bzw. eingebrannt unter Ausbildung einer Basislack/Klarlack-Zweischichtlackierung. Dabei kann der Basislack zuvor bei Temperaturen bis zu 150°C getrocknet worden sein oder als bevorzugte Ausführungsform des erfindungsgemäßen Verfahrens erfolgt der Auftrag der Klarlackschicht naß-in-naß auf die Basislackschicht, worauf gemeinsam getrocknet bzw. eingebrannt wird.After application of the clear lacquer coating agent in a layer thickness of 20-80 μm, preferably 25-50 μm, the layer formed is dried or baked at elevated temperature to form a basecoat / clearcoat two-layer lacquer. The basecoat may have previously been dried at temperatures up to 150 ° C. or, as a preferred embodiment of the process according to the invention, the clearcoat layer is applied wet-on-wet to the basecoat layer, whereupon it is dried or baked together.

Die Trocknung bzw. der Einbrennprozeß von Basis- und wärmehärtender Klarlackschicht wird bei dem erfindungsgemäßen Verfahren so durchgeführt, daß die erhaltenen unteren Lackschichten nur geringe Anteile von flüchtigen Substanzen enthalten. Besonders zum Zeitpunkt der strahleninduzierten Vernetzungsreaktion der weiteren Klarlacküberzugsschicht sollen keine wesentlichen Anteile an flüchtigen Bestandteilen mehr in den darunter liegenden Lackschichten enthalten sein. Solche Bestandteile können Glanz- und Haftungsstörung im oberen strahlenhärtenden Klarlackfilm bewirken.The drying or stoving process of the base and thermosetting clear lacquer layer is carried out in the process according to the invention in such a way that the lower lacquer layers obtained contain only small proportions of volatile substances. Especially at the time of the radiation-induced crosslinking reaction of the further clear lacquer coating layer, none should substantial parts of volatile constituents are more contained in the underlying lacquer layers. Such components can cause gloss and adhesion problems in the upper radiation-curing clear lacquer film.

Vor Auftrag der strahlenhärtenden Klarlackschicht kann, falls gewünscht, die darunter liegende Klarlackschicht geschliffen werden. Gegebenenfalls können zwischen erster wärmehärtender Klarlackschicht und oben liegender strahlenhärtender Klarlackschicht weitere wärmehärtende Klarlackschichten aufgebracht werden. Über diese zusätzlichen Schichten können falls gewünscht besondere optische Effekte erzielt werden.If desired, the underlying clear coat can be sanded before applying the radiation-curing clear coat. If necessary, further thermosetting clear lacquer layers can be applied between the first thermosetting clear lacquer layer and the top radiation-curing clear lacquer layer. If desired, special optical effects can be achieved via these additional layers.

Auf die getrockneten und vernetzten Basis- und Klarlackschichten wird ein strahlenhärtendes Überzugsmittel aufgetragen. Es handelt sich um bekannte radikalisch oder/und kationisch polymerisierende Klarlacke, die mit üblichen Additiven versetzt sein können. Diese werden strahleninduziert vernetzt.A radiation-curing coating agent is applied to the dried and crosslinked base and clear lacquer layers. These are known free-radically and / or cationically polymerizing clearcoats, which can be mixed with conventional additives. These are networked by radiation.

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. Das kann bei Temperaturen von maximal 70-80°C durchgeführt werden, so daß geeignete Applikationsviskositäten erreicht werden und bei der kurzzeitig einwirkenden thermischen Belastung keine Veränderung des Lackmaterials und des gegebenenfalls wiederaufzubereitenden Oversprays eintritt. So kann beispielsweise 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 spray. This can be carried out at temperatures of a maximum of 70-80 ° C., so that suitable application viscosities are achieved and there is no change in the coating material and in the overspray, which may need to be reprocessed, in the event of a brief thermal load. For example, hot spraying can be designed in such a way that the paint material is only heated briefly in or shortly before the spray nozzle.

Die Spritzkabine kann beispielsweise mit einem gegebenenfalls temperierbaren Umlauf betrieben werden, der mit einem geeigneten Absorptionsmedium für das Overspray, z. B. dem Lackmaterial, betrieben wird. Die Spritzkabine besteht aus Materialien, die eine Kontamination des Materials ausschließen und vom umlaufenden Medium nicht angegriffen werden. Mit solchen Maßnahmen kann eine Wiederaufbereitung des Oversprays unterstützt werden.The spray booth can be operated, for example, with a circulation that can be tempered, if necessary, which is equipped with a suitable absorption medium for the overspray, e.g. B. the paint material is operated. The spray booth consists of materials that prevent contamination of the material and are not attacked by the circulating medium. Such measures can support reprocessing of the overspray.

Bevorzugt wird der Beschichtungsvorgang bei Beleuchtung mit sichtbarem Licht einer Wellenlänge von über 550 nm oder unter Lichtausschluß durchgeführt.The coating process is preferably carried out when illuminated with visible light of a wavelength of over 550 nm or with exclusion of light.

Durch Vermeidung von Licht einer Wellenlänge von unter 550 nm werden das eingesetzte Lackmaterial und der Overspray nicht beeinflußt. Es ist also gegebenenfalls 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 umlaufendem Lackmaterial einhält. Weiterhin sind Vorratsbehälter und Pumpen sowie Steuereinrichtungen vorhanden. Gegebenenfalls ist noch eine Zumischvorrichtung für ein Konstanthalten von flüchtigen Bestandteilen, wie z. B. 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. If necessary, direct reprocessing is 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 necessary, a mixing device for keeping volatile constituents constant, such as. B. the organic solvent or water, necessary.

Der strahlenhärtende Klarlack wird bevorzugt so appliziert, daß bevorzugt Trockenschichtdicken von 10-50 µm, besonders bevorzugt 15-35 µm, erreicht werden. Der Auftrag des strahlenhärtenden Klarlacks kann falls gewünscht in mehreren Schichten erfolgen.The radiation-curing clear lacquer is preferably applied in such a way that dry layer thicknesses of 10-50 μm, particularly preferably 15-35 μm, are preferably achieved. If desired, the radiation-curing clear lacquer can be applied in several layers.

Nach dem Auftragen des strahlenhärtenden 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 beispielsweise mit überkritischem Kohlendioxid als Lösungsmittel appliziert worden ist wie z. B. in EP-A-0 321 607 beschrieben. Es ist auch möglich, die Ruhezeit durch erhöhte Temperaturen bis 80°C, bevorzugt bis 60°C, zu unterstützen.After the application of the radiation-curing clear lacquer coating agent, the coated substrate is subjected to the crosslinking process, if appropriate 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, for example, with supercritical carbon dioxide as a solvent, such as. B. described in EP-A-0 321 607. It is also possible to support the resting time by increasing 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 Zuführen 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 adding CO₂, N₂ or by using a mixture of both directly to 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 auch 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 also be removed, for example, by suction.

Die Strahlenhärtung kann unter Anwendung üblicher Strahlenquellen, optischer Hilfsmaßnahmen zur Durchführung, üblicher Zeitdauern und üblicher Maßnahmen zur Steuerung des Bestrahlungsprozesses, sowie unter Verwendung üblicher Anordnungen der Bestrahlungsquellen unter dem Fachmann geläufigen Bedingungen durchgeführt werden. Bevorzugt werden UV-Strahler und Elektronenstrahlquellen eingesetzt.Radiation curing can be carried out using customary radiation sources, optical auxiliary measures for carrying out, customary periods of time and customary measures for controlling the radiation process, and using customary arrangements of the radiation sources under conditions familiar to the person skilled in the art. UV lamps and electron beam sources are preferably used.

Erfindungsgemäß kann die Bestrahlung so durchgeführt werden, daß in einer Stufe eine durchgehende Vernetzung der strahlenhärtenden Klarlackschicht erfolgt. Es kann jedoch auch günstig sein, zunächst ein 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 radiation can be carried out in such a way that the radiation-curing 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.

Ein Problem bei der Beschichtung von kompliziert geformten Körpern, wie z. B. 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.A problem in the coating of complex shaped bodies, such as. B. automotive bodies with radiation-curing paint systems is in the curing in areas not directly accessible to the radiation (shadow areas), such as. 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 anzuwenden. 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.In addition, it is possible to use thermal activation to crosslink the coating agent. When using radically polymerizable coating agents, it may be advantageous 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.

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 fort. Es kann allerdings auch in diesem Falle günstig sein zu erwärmen.When using cationically polymerizable coating agents, it is not necessary to use special thermally activatable initiators. The cationic polymerization initiated by the radiation energy propagates. However, it can also be beneficial to heat in this case.

Bei den erfindungsgemäß für die obere Klarlackschicht verwendbaren Lacksystemem handelt es sich um übliche strahlenhärtende Überzugsmittel, die 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, falls gewünscht, mit löslichen Farbstoffen gefärbte Decklacke formuliert sein.The coating systems which can be used according to the invention for the upper clear lacquer layer are customary radiation-curing coating compositions which crosslink 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% lacquer systems that can be applied without solvents and without water. The radiation-curing clearcoats can be formulated as unpigmented or transparent pigmented topcoats, colored with soluble dyes if desired.

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 generates radicals which then trigger the crosslinking reaction, or it is a matter of cationic 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 beispielsweise noch übliche Initiatoren, Lichtschutzmittel, transparente Pigmente, lösliche Farbstoffe und/oder weitere lacktechnische Hilfsmittel enthalten.The radical 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 agents of this type can also contain, for example, customary initiators, light stabilizers, transparent pigments, soluble dyes and / or other coating aids.

Beispiele für Prepolymere oder Oligomere sind (meth)acrylfunktionelle (Meth)Acrylcopolymere, 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 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 Mn) 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 in Mengen von 1-70 Gew.% eingesetzt, bevorzugt 5-40 Gew.%, bezogen auf das Gesamtgewicht von Prepolymeren und Reaktivverdünnern. Sie können mono-, di- oder polyungesättigt sein. Beispiele für solche Reakivverdünner sind: (Meth)acrylsäure und deren Ester, Maleinsäure und deren Halbester, N-Vinylpyrrolidon, 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 in amounts of 1-70% by weight, preferably 5-40% 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, N-vinylpyrrolidone, 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 radikalische härtende Systeme können z. B. in Mengen von 0,1-5 Gew.% eingesetzt werden, bevorzugt 0,5-4 Gew.%, bezogen auf die Summe von radikalisch polymerisierbaren Prepolymeren, Reaktivverdünnern und Initiatoren. Es ist günstig, wenn ihre Absorption im Wellenlängenbereich von 260-450nm liegt. Es können übliche, dem Fachmann geläufige Photoinitiatoren verwendet werden. 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 0.5-4% by weight, based on the sum of free-radically polymerizable prepolymers, reactive diluents and initiators. It is favorable if their absorption is in the wavelength range of 260-450nm. Conventional photoinitiators known to those skilled in the art can be used. Examples of photoinitiators are benzoin and derivatives, benzil and derivatives, benzophenone and derivatives, acetophenone and derivatives, e.g. B. 2,2-diethoxyacetophenone, thioxanthone and derivatives, anthraquinone, 1-benzoylcyclohexanol, organophosphorus compounds, such as. 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 z. B. Anthracen in üblichen Mengen mitverwendet werden. Zusätzlich können gegebenenfalls auch übliche 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, conventional sensitizers, such as. B. anthracene can be used in the usual amounts. In addition, conventional thermally activatable free radical initiators can also be used, if appropriate. These form radicals from 80-120 ° C, 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 gaseous decomposition products are formed during thermal cleavage, which can lead to faults in the lacquer layer. The preferred amounts are between 0.1-5% 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-A-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-A-36 15 790. These are, 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, z. B. reaktive Monomere, wie Cyclohexenoxid, Butenoxid, Butandioldivinylether, 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. reactive liquid compounds, e.g. B. reactive monomers such as cyclohexene oxide, butene oxide, butanediol divinyl ether, 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 sum of cationically polymerizable prepolymers, reactive diluents and initiators. They are substances known as onium salts that release Lewis acids photolytically under radiation. Examples of this are diazonium salts, sulfonium salts or iodonium salts. Triarylsulfonium salts are particularly preferred.

Die strahleninduziert härtbaren Bindemittel können außer den für sie typischen funktionellen Gruppen weitere funktionelle Gruppen im Molekül enthalten, wie z. B. Hydroxyl-, Oxiran- oder Isocyanatgruppen, die einer chemischen Vernetzung zugänglich sind. In diesen Fällen werden den strahlenhärtbaren Klarlacken externe Vernetzer, wie z. B. Aminoplastvernetzer, gegebenenfalls blockierte Polyisocyanate, carboxylgruppenhaltige Härter, bei Zutritt von Luftfeuchtigkeit spaltende Ketiminvernetzer, Polyamin- oder Polyamidoaminhärter in geeigneter Menge zugesetzt. Die schon erwähnten, für strahlenhärtbare Bindemittel typischen, funktionellen Gruppen - Oxirangruppen, polymerisierbare C=C-Doppelbindungen - können durch Zusatz geeigneter Vernetzer, ebenfalls im Sinne einer Polyadditionsreaktion, zusätzlich zur strahleninduzierten Härtungsreaktion herangezogen werden. Beispiele für solche Vernetzer sind Polyaminhärter, Polyamidoaminhärter, feuchtigkeitsspaltbare Ketiminvernetzer, CH-acide Verbindungen, die im Sinne einer Michael-Addition vernetzend wirken können.In addition to the functional groups that are typical for them, the radiation-curable binders can contain further functional groups in the molecule, such as. B. hydroxyl, oxirane or isocyanate groups, which are accessible for chemical crosslinking. In these cases, the radiation-curable clearcoats external crosslinkers such. B. aminoplast crosslinking agent, optionally blocked polyisocyanates, carboxyl group-containing hardener, upon entry of humidity-splitting ketimine crosslinker, polyamine or polyamidoamine hardener added in a suitable amount. The functional groups already mentioned, typical of radiation-curable binders - oxirane groups, polymerizable C = C double bonds - can be used in addition to the radiation-induced curing reaction by adding suitable crosslinking agents, also in the sense of a polyaddition reaction. Examples of such crosslinkers are polyamine hardeners, polyamidoamine hardeners, moisture-cleavable ketimine crosslinkers, CH-acidic compounds which can have a crosslinking action in the sense of a Michael addition.

Ebenso können außer den genannten Vernetzern den strahlenhärtbaren Klarlacken nicht strahleninduziert härtbare Bindemittel zugesetzt werden, die aufgrund geeigneter funktioneller Gruppen eine nicht strahleninduzierte zusätzliche Härtungsreaktion, wie schon vorstehend erwähnt, erlauben. Beispiele für derartige funktionelle Gruppen sind die schon vorstehend erwähnten im Molekül der strahlenhärtbaren Bindemittel enthaltenen weiteren funktionellen Gruppen.In addition to the crosslinking agents mentioned, it is also possible to add radiation-curable binders to the radiation-curable clearcoats, which, because of suitable functional groups, permit a non-radiation-induced additional curing reaction, as already mentioned above. Examples of such functional groups are the further functional groups already mentioned above in the molecule of the radiation-curable binders.

Beispiele sind die in der EP-A-0 247 563 beschriebenen strahleninduziert härtbaren Klarlacke, die zusätzlich OH-funktionelles Bindemittel und einen Polyisocyanathärter enthalten und somit durch zwei kombinierte Härtungsmechanismen vernetzen. Diese können auch nach dem erfindungsgemäßen Verfahren eingesetzt werden.Examples are the radiation-induced curable clearcoats described in EP-A-0 247 563, which additionally contain OH-functional binder and a polyisocyanate hardener and thus crosslink by means of two combined curing mechanisms. These can also be used by the process according to the invention.

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 conventional 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 are also suitable C₂-C₄ alkanols and preferably water as a solvent.

Den erfindungsgemäß verwendeten Klarlacken werden bevorzugt Lichtschutzmittel zugesetzt. Beispiele dafür sind Phenylsalicylate, Benzotriazol und Derivate, HALS-Verbindungen sowie Oxalanilid-Derivate, sowie auch Kombinationen davon. 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 im Strahlenhärtungsprozeß eingesetzte Strahlung stabil sind.Light stabilizers are preferably added to the clearcoats used according to the invention. Examples of these are phenylsalicylates, benzotriazole and derivatives, HALS compounds and oxalanilide derivatives, as well as combinations thereof. 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 crosslinking is not impaired by the light stabilizers and that the light stabilizers used are stable against the radiation used in the radiation curing process.

Weitere Additive sind beispielsweise Elastifizierungsmittel, Polymerisations-Inhibitoren, Entschäumer, Verlaufsmittel, Antioxidationsmittel, transparente Farbstoffe, optische Aufheller sowie Haftzusätze, wie z. B. Phosphorsäureester und/oder Silane.Other additives are, for example, elastifying agents, polymerization inhibitors, defoamers, leveling agents, antioxidants, transparent dyes, optical brighteners and adhesive additives, such as. B. phosphoric acid esters and / or silanes.

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, Magnesiumoxide, 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.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 oxides, 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.

Herstellungsverfahren für geeignete strahlenhärtende Klarlack-Überzugsmittel sind bekannt. Es ist möglich, Systeme mit unterschiedlichen strahleninduziertem chemischem Vernetzungsmechanismus zu kombinieren. Dies können verschiedene radikalisch härtende Vernetzungssysteme oder kationisch härtende Vernetzungssysteme oder radikalisch und kationisch härtende Vernetzung miteinander kombiniert sein. Die strahlenhärtenden Klarlacke können z. B. auch vorteilhaft solche Bestandteile enthalten, die einen zusätzlichen Aushärtungsmechanismus zu dem schon beschriebenen strahleninduzierbaren radikalischen und/oder kationischen Vernetzungsmechanismus erlauben. Diese Verfahrensweise erlaubt eine kombinierte Härtung der erfindungsgemäß aufgebrachten oberen Klarlackschicht durch parallel oder nacheinander ablaufende strahleninduzierte und nicht strahleninduzierte Vernetzungsreaktionen. Die nicht strahleninduzierte Vernetzungsreaktion dient dabei einer zusätzlichen Vernetzung oder Nachvernetzung, die vorteilhaft sein kann. Beispiele für solche nicht strahleninduzierten Mechanismen sind Polyadditions- und Polykondensationsreaktionen. Diese zusätzlichen Härtungsreaktionen können z. B. bei erhöhter Temperatur bis zu 180°C durchgeführt werden.Manufacturing processes for suitable radiation-curing clear lacquer coating compositions are known. It is possible to combine systems with different radiation-induced chemical cross-linking mechanisms. These can be different radically curing crosslinking systems or cationically curing crosslinking systems or radically and cationically curing crosslinking combined. The radiation-curing clearcoats can, for. B. also advantageously contain such components that allow an additional curing mechanism to the radiation-induced radical and / or cationic crosslinking mechanism already described. This procedure allows a combined hardening of the upper clear lacquer layer applied according to the invention by running in parallel or in succession radiation-induced and non-radiation-induced crosslinking reactions. The non-radiation-induced crosslinking reaction serves for additional crosslinking or postcrosslinking, which can be advantageous. Examples of such non-radiation-induced mechanisms are polyaddition and polycondensation reactions. These additional curing reactions can e.g. B. at elevated temperature up to 180 ° C.

Die erfindungsgemäß eingesetzten strahlenhärtbaren Klarlacke können je nach gewähltem zusätzlichen Vernetzungsmechanismus ein- oder zweikomponentig sein. Es sollte darauf geachtet werden, die Zusammensetzung so zu wählen, daß Lagerstabilität des strahlenhärtbaren Klarlacks oder der Komponenten eines mehrkomponentigen strahlenhärtbaren Klarlackes gegeben ist. Ebenso können unterschiedliche Reaktionsinitiierungsverfahren beispielsweise UV mit UV-Härtung, UV mit thermischer Initiierung oder Elektronenstrahlhärtung mit UV-Härtung kombiniert werden.The radiation-curable clearcoats used according to the invention can have one or two components, depending on the additional crosslinking mechanism chosen. Care should be taken to choose the composition so that the radiation-curable clearcoat or the components of a multi-component radiation-curable clearcoat are stable in storage. Likewise, different reaction initiation processes, for example UV with UV curing, UV with thermal initiation or electron beam curing with UV curing, can be combined.

Die verschiedenen Vernetzungsreaktionen können mit Gemischen der entsprechenden Initiatoren gestartet werden. Beispielsweise sind Gemische von Photoinitiatoren 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, z. B. 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 photoinitiators 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, e.g. B. also spatially separate. 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, falls gewünscht, neben einem oder mehreren Photoinitiatoren zusätzlich 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 first to carry out a radiation-induced crosslinking reaction and then or simultaneously to carry out a thermally induced crosslinking reaction. If desired, one or more thermally cleaving initiators can also be used for this purpose, if desired. 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 Abdunstung des Lösemittels zu gestatten.The two-stage or multi-stage mode of operation can be favorable in order to initially achieve, for example, a gelation. B. Avoid runners on painted vertical surfaces. The hinge is too cheap for solvent-based systems to allow evaporation of the solvent.

Die Photoinitiatoren werden bevorzugt so gewählt, daß sie bei Einwirkung von sichtbarem Licht mit einer Wellenlänge von über 550 nm nicht zerfallen. Bei Einsatz von thermisch spaltenden Initiatoren sind diese so zu wählen, daß sie unter den Applikationsbedingungen 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 when exposed to visible 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 so 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.

Die durch das erfindungsgemäße Verfahren erhaltene Mehrschichtlackierung zeigt eine gute Haftung der einzelnen Schichten untereinander. Es ist eine erhöhte Gesamtschichtdicke des Klarlacküberzugs möglich, ebenso können unterschiedliche Eigenschaften aufweisende Klarlacke verwendet werden. Damit sind auch besondere optische Eigenschaften, z.B. besserer Glanz, bessere strukturfreie Oberfläche zu erzielen. Mittels des vorliegenden Verfahrens ist es auch möglich, zwei Klarlackschichten zu kombinieren, die unterschiedliche, miteinander unverträgliche Additive enthalten. Beispiele für solche Kombinationen sind eine basische Additive (beispielsweise Lichtschutzmittel) enthaltende Klarlackschicht als untere Klarlackschicht in Kombination mit einer saure Additive (beispielsweise ebenfalls Lichtschutzmittel) enthaltenden oberen Klarlackschicht bzw. die umgekehrte Kombination. Durch die mögliche schnelle Vernetzungsreaktion der äußeren Klarlackschicht ergeben sich außerdem Vorteile in der Empfindlichkeit gegen äußere Einflüsse, z.B. Staubeinschlüsse, im Lack.The multi-layer coating obtained by the process according to the invention shows good adhesion of the individual layers to one another. An increased total layer thickness of the clear lacquer coating is possible, and clear lacquers with different properties can also be used. This also has special optical properties, e.g. better gloss, better structure-free surface. By means of the present method it is also possible to combine two clear lacquer layers which contain different additives which are incompatible with one another. Examples of such combinations are a clear lacquer layer containing basic additives (for example light stabilizers) as the lower clear lacquer layer in combination with an upper clear lacquer layer containing acid additives (for example likewise light stabilizers) or the reverse combination. The possible rapid crosslinking reaction of the outer clear lacquer layer also results in advantages in sensitivity to external influences, e.g. Inclusions of dust, in the paint.

Durch das erfindungsgemäße Verfahren erhält man vergilbungsfreie Mehrschichtüberzüge mit hoher Chemikalienbeständigkeit, guter Kratzbeständigkeit und hoher optischer Qualität (Fülle, Glanz). Insbesondere werden strukturfreie Oberflächen erzielt. Dies ergibt sich beispielsweise aus den folgenden Beispielen, die für die erfindungsgemäßen Lackierungen besonders hohe DOI-Werte zeigen. Das Overspray des im erfindungsgemäßen Verfahren verwendeten strahlenhärtenden Überzugsmittels eignet sich für eine direkte Wiederverwertung.The process according to the invention gives yellowing-free multi-layer coatings with high chemical resistance, good scratch resistance and high optical quality (fullness, gloss). In particular structure-free surfaces achieved. This results, for example, from the following examples, which show particularly high DOI values for the coatings according to the invention. The overspray of the radiation-curing coating agent used in the process according to the invention is suitable for direct recycling.

Das erfindungsgemäße Verfahren eignet sich besonders zur Anwendung in der Kraftfahrzeug-Serienlackierung. Als Substrate sind besonders Metall- oder Kunststoffteile geeignet, wie z.B. Automobilkarossen und deren Teile.The method according to the invention is particularly suitable for use in automotive OEM painting. Metal or plastic parts are particularly suitable as substrates, e.g. Automotive bodies and their parts.

Die folgenden Beispiele erläutern die Erfindung.The following examples illustrate the invention.

Herstellung strahlenhärtbarer KlarlackeProduction of radiation-curable clear coats (Beispiele 1 - 4)(Examples 1-4) Beispiel 1:Example 1:

Durch Vermischen von 3124 g eines ethoxylierten Trimethylolpropantriacrylats, 616 g eines aliphatischen Urethanacrylats mit einer Doppelbindungsfunktionalität von 2 und einem Gehalt von 1 mol polymerisierbaren C=C-Doppelbindungen pro kg, 3790 g eines Polyesteracrylats mit einer Doppelbindungsfunktionalität von 3,5 und einem Gehalt von 3,9 mol polymerisierbaren C=C-Doppelbindungen pro kg, 332 g Tripropylenglykoldiacrylat, 332 g 2-Hydroxy-2-methyl-1-phenyl-propan-1on, 8 g eines Silikondiacrylats, 966 g Nonylacrylat und 832 g Hexylacrylat wurde ein strahlenhärtbares Klarlacküberzugsmittel hergestellt.By mixing 3124 g of an ethoxylated trimethylolpropane triacrylate, 616 g of an aliphatic urethane acrylate with a double bond functionality of 2 and a content of 1 mol of polymerizable C = C double bonds per kg, 3790 g of a polyester acrylate with a double bond functionality of 3.5 and a content of 3 , 9 mol of polymerizable C = C double bonds per kg, 332 g of tripropylene glycol diacrylate, 332 g of 2-hydroxy-2-methyl-1-phenyl-propan-1one, 8 g of a silicone diacrylate, 966 g of nonylacrylate and 832 g of hexyl acrylate became a radiation-curable clear lacquer coating agent produced.

Beispiel 2:Example 2:

Analog zu Beispiel 1 wurde ein strahlenhärtbares Klarlacküberzugsmittel hergestellt aus 28 Teilen eines mehrfunktionellen Urethanacrylats mit einer Molmasse von 4500, einem Gehalt an polymerisierbaren C=C-Doppelbindungen von 2,5 mol pro kg und einer Hydroxylzahl von 150 mg KOH/g, 19 Teilen Dipropylenglykoldiacrylat, 48 Teilen Tripropylenglykoldiacrylat, 4 Teilen 2-Hydroxy-2-methyl-1-phenyl-propan-1-on und 1 Teil einer 10 %igen Lösung eines Silikonöls in Toluol (Silikonöl "OL" der Fa. Bayer).Analogously to Example 1, a radiation-curable clear lacquer coating composition was prepared from 28 parts of a multifunctional urethane acrylate with a molecular weight of 4500, a content of polymerizable C = C double bonds of 2.5 mol per kg and a hydroxyl number of 150 mg KOH / g, 19 parts of dipropylene glycol diacrylate , 48 parts tripropylene glycol diacrylate, 4 parts 2-hydroxy-2-methyl-1-phenyl-propan-1-one and 1 part of a 10% solution of a silicone oil in toluene (silicone oil "OL" from Bayer).

Beispiel 3:Example 3:

Analog zu Beispiel 1 wurde ein strahlenhärtbares Klarlacküberzugsmittel hergestellt aus 24 Teilen des mehrfunktionellen Urethanacrylats aus Beispiel 2, 16 Teilen eines mehrfunktionellen Melaminacrylats mit einer Molmasse von 900 und einem Gehalt an polymerisierbaren C=C-Doppelbindungen von 5,5 mol pro kg, 16 Teilen Dipropylenglykoldiacrylat, 39 Teilen Tripropylenglykoldiacrylat, 4 Teilen 2-Hydroxy-2-methyl-1-phenyl-propan-1-on und 1 Teil der Silikonöl-Lösung aus Beispiel 2.Analogously to Example 1, a radiation-curable clear lacquer coating composition was prepared from 24 parts of the polyfunctional urethane acrylate from Example 2, 16 parts of a polyfunctional melamine acrylate with a molecular weight of 900 and a content of polymerizable C = C double bonds of 5.5 mol per kg, 16 parts of dipropylene glycol diacrylate , 39 parts of tripropylene glycol diacrylate, 4 parts of 2-hydroxy-2-methyl-1-phenyl-propan-1-one and 1 part of the silicone oil solution from Example 2.

Beispiel 4:Example 4:

Analog zu Beispiel 1 wurde ein strahlen- und wärmehärtbares Klarlacküberzugsmittel hergestellt aus 52 Teilen einer 60 %igen Lösung eines difunktionellen Polyesteracrylats mit einer Molmasse von 1300 in Dipropylenglykoldiacrylat mit einer auf die Lösung bezogenen Säurezahl von 18 mg KOH/g und einer auf die Lösung bezogenen Hydroxylzahl von 150 mg KOH/g, 35 Teilen Phenoxyethylacrylat, 4 Teilen 2-Hydroxy-2-methyl-1-phenylpropan-1-on, 0,2 Teilen eines handelsüblichen Verlaufsmittels (BYK 310 der Firma BYK) und 8,8 Teilen Hexamethoxymethylmelamin.Analogously to Example 1, a radiation-curable and thermosetting clear lacquer coating composition was prepared from 52 parts of a 60% strength solution of a difunctional polyester acrylate with a molecular weight of 1300 in dipropylene glycol diacrylate with an acid number of 18 mg KOH / g based on the solution and a hydroxyl number based on the solution of 150 mg KOH / g, 35 parts of phenoxyethyl acrylate, 4 parts of 2-hydroxy-2-methyl-1-phenylpropan-1-one, 0.2 part of a commercially available leveling agent (BYK 310 from BYK) and 8.8 parts of hexamethoxymethylmelamine.

Herstellung von Mehrschichtlackierungen:Production of multi-layer coatings: (Beispiele 5-8 und Vergleichsversuche A und B)(Examples 5-8 and Comparative Experiments A and B) Vergleichsversuch A:Comparative experiment A:

Ein KTL-grundiertes (20 µm) und mit handelsüblichem Füller (35 µm vorbeschichtetes Blech wurde mit üblichem lösemittelhaltigem Metallicbasislack in einer Trockenfilmdicke von 10 µm spritzlackiert, nach 5-minütigem Ablüften bei 20°C mit einem üblichen lösemittelhaltigen 1K-Klarlack auf Basis Acrylatharz/Melaminharz naß-in-naß in einer Trockenschichtdicke von 35 µm überlackiert und 25 min bei 135°C eingebrannt. Anschließend wurde der gleiche 1K-Klarlack in 35 µm Trockenschichtdicke durch Spritzen auflackiert und 25 min bei 135°C eingebrannt. Bei Betrachtung der glänzenden Oberfläche war eine Struktur zu erkennen.
KTL = Kathodische Tauchlackierung
1K = EinkomponentenA KTL-primed (20 µm) and with commercially available filler (35 µm pre-coated sheet was spray-coated with a conventional solvent-based metallic basecoat in a dry film thickness of 10 µm, after 5 minutes flashing at 20 ° C with a conventional solvent-based 1K clearcoat based on acrylic resin / Melamine resin wet-on-wet overcoated in a dry layer thickness of 35 µm and baked for 25 min at 135 ° C. Then the same 1-component clear coat in 35 µm dry layer thickness was spray-coated and baked for 25 minutes at 135 ° C. When looking at the glossy surface a structure was recognizable.
KTL = cathodic dip painting
1K = one-component

Beispiel 5:Example 5:

Der Vergleichsversuch A wurde analog wiederholt, mit dem Unterschied, daß anstelle einer zweiten Klarlackschicht auf Basis des 1K-Klarlackes der strahlenhärtbare Klarlack aus Beispiel 1 in 35 µm Trockenfilmdicke durch Spritzen aufgetragen wurde. Anschließend wurde das liegende Probeblech zur Härtung bei 1 m/min Bandgeschwindigkeit mit zwei Quecksilbermitteldruckstrahlern von je 100 W/cm Leistung im Abstand von 10 cm zur auszuhärtenden Oberfläche (Bestrahlungsdauer somit ca. 10 sec) bestrahlt. Bei Betrachtung der hochglänzenden Oberfläche war keinerlei Struktur wahrnehmbar.Comparative experiment A was repeated analogously, with the difference that instead of a second clearcoat layer based on the 1K clearcoat, the radiation-curable clearcoat from example 1 was applied by spraying in a 35 μm dry film thickness. The horizontal sample sheet was then irradiated for curing at a belt speed of 1 m / min using 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 approx. 10 sec). When looking at the high-gloss surface, no structure was perceptible.

Vergleichsversuch B:Comparative experiment B:

Ein KTL-grundiertes (20 µm) und mit handelsüblichem Füller (35 µm) vorbeschichtetes Blech wurde mit üblichem unifarbenem Wasserbasislack in einer Trockenfilmdicke von 15 µm spritzlackiert; nach 5-minütigem Ablüften bei 60°C gefolgt von 5-minütigem Ablüften bei 100°C wurde mit üblichem lösemittelhaltigem 1K-Klarlack auf Basis Acrylatharz/Melaminharz naß-in-naß in einer Trockenschichtdicke von 35 µm überlackiert und 10 min bei 140°C eingebrannt. Anschließend wurde der gleiche 1K-Klarlack in 35 µm Trockenschichtdicke durch Spritzen auflackiert und 20 min bei 140°C eingebrannt. Bei Betrachtung der glänzenden Oberfläche war eine Struktur zu erkennen.A KTL-primed (20 µm) and pre-coated with commercially available filler (35 µm) was spray-coated with a standard plain-colored water-based paint in a dry film thickness of 15 µm; after flashing off at 60 ° C. for 5 minutes, followed by flashing off at 100 ° C. for 5 minutes, the reaction was carried out with conventional solvent-based 1-component clear lacquer based on acrylic resin / melamine resin wet-on-wet overcoated in a dry layer thickness of 35 µm and baked at 140 ° C for 10 min. The same 1-component clearcoat was then spray-coated in a 35 μm dry film thickness and baked at 140 ° C. for 20 minutes. When looking at the glossy surface, a structure was seen.

Beispiel 6:Example 6:

Der Vergleichsversuch B wurde analog wiederholt, mit dem Unterschied, daß anstelle einer zweiten Klarlackschicht auf Basis des 1K-Klarlacks ein durch Mischen von 90 Teilen des strahlenhärtbaren Klarlackes aus Beispiel 2 und 10 Teilen eines Polyisocyanathärters (Desmodur N/75 der Fa. Bayer) hergestellter Klarlack in 35 µm Trockenschichtdicke durch Heißspritzen bei 60°C auf das auf 60°C vorgewärmte Prüfblech aufgetragen wurde. Anschließend wurde das liegende Probeblech zur Härtung bei 1m/min Bandgeschwindigkeit mit zwei Quecksilbermitteldruckstrahlern von je 100 W/cm Leistung im Abstand von 30 cm zur auszuhärtenden Oberfläche (Bestrahlungsdauer ca. 10 sec) bestrahlt. Anschließend wurde 20 min bei 140°C nachgehärtet. Man erhielt eine hochglänzende Oberfläche ohne wahrnehmbare Struktur.Comparative experiment B was repeated analogously, with the difference that instead of a second clear lacquer layer based on the 1-component clear lacquer, one was prepared by mixing 90 parts of the radiation-curable clear lacquer from Example 2 and 10 parts of a polyisocyanate hardener (Desmodur N / 75 from Bayer) Clear coat in 35 µm dry film thickness was applied by hot spraying at 60 ° C to the test sheet preheated to 60 ° C. The lying sample sheet was then irradiated for curing at a belt speed of 1 m / min with two medium-pressure mercury lamps of 100 W / cm each at a distance of 30 cm from the surface to be hardened (irradiation time approx. 10 sec). The mixture was then cured at 140 ° C. for 20 minutes. A high-gloss surface with no perceptible structure was obtained.

Beispiel 7:Example 7:

Der Vergleichsversuch B wurde analog wiederholt, mit dem Unterschied, daß nach Auftragen der ersten 1K-Klarlackschicht 20 min bei 140°C gehärtet wurde und anschließend anstelle einer zweiten Klarlackschicht auf Basis des 1K-Klarlacks der strahlenhärtbare Klarlack aus Beispiel 3 in 35 µm Trockenfilmdicke durch Heißspritzen bei 60°C auf das auf 60°C vorgewärmte Prüfblech aufgetragen wurde. Anschließend wurde wie in Beispiel 6 beschrieben strahlengehärtet. Eine thermische Nachhärtung wie in Beispiel 6 wurde nicht durchgeführt. Man erhielt eine hochglänzende Oberfläche ohne wahrnehmbare Struktur.Comparative experiment B was repeated analogously, with the difference that after application of the first 1K clearcoat layer, curing was carried out at 140 ° C. for 20 minutes and then, instead of a second clearcoat layer based on the 1K clearcoat, the radiation-curable clearcoat from Example 3 was applied in a 35 μm dry film thickness Hot spraying at 60 ° C was applied to the test sheet preheated to 60 ° C. The radiation was then cured as described in Example 6. Thermal post-curing as in Example 6 was not carried out. A high-gloss surface with no perceptible structure was obtained.

Beispiel 8:Example 8:

Der Vergleichsversuch B wurde analog wiederholt, mit dem Unterschied, daß anstelle einer zweiten Klarlackschicht auf Basis des 1K-Klarlackes der strahlenhärtbare Klarlack aus Beispiel 4 in 35 µm Trockenfilmdicke durch Heißspritzen bei 60°C auf das auf 60°C vorgewärmte Probeblech aufgetragen wurde. Die Strahlenhärtung und nachfolgende thermische Nachhärtung wurde wie in Beispiel 6 beschrieben durchgeführt. Die erhaltene hochglänzende Oberfläche war frei von wahrnehmbarer Struktur.Comparative experiment B was repeated analogously, with the difference that instead of a second clearcoat layer based on the 1K clearcoat, the radiation-curable clearcoat from Example 4 was applied in 35 μm dry film thickness by hot spraying at 60 ° C. to the sample sheet preheated to 60 ° C. The radiation curing and subsequent thermal post-curing was performed as described in Example 6. The high-gloss surface obtained was free of any noticeable structure.

Vergleichsversuch C:Comparative experiment C:

Der Vergleichsversuch A wurde wiederholt mit dem Unterschied, daß anstelle der zwei Klarlackschichten auf Basis des 1K-Klarlacks der strahlenhärtbare Klarlack aus Beispiel 1 in 35 µm Trockenschichtdicke durch Spritzen aufgetragen wurde.
Anschließend wurde das liegende Probeblech zur Härtung bei 1 m/min. Bandgeschwindigkeit mit zwei Quecksilbermitteldruckstrahlern von je 100 W/cm Leistung im Abstand von 10 cm zur auszuhärtenden Oberfläche (Bestrahlungsdauer somit ca. 10 sec.) bestrahlt. Bei Betrachtung der hochglänzenden Oberfläche war eine leichte Struktur wahrnehmbar.Comparative experiment A was repeated with the difference that instead of the two clearcoat layers based on the 1K clearcoat, the radiation-curable clearcoat from example 1 was applied by spraying to a thickness of 35 μm.
The lying test sheet was then hardened at 1 m / min. Belt speed irradiated with two medium pressure mercury lamps each with a power of 100 W / cm at a distance of 10 cm from the surface to be hardened (irradiation time thus approx. 10 sec.). When looking at the high-gloss surface, a slight structure was perceptible.

Vergleichsversuch D:Comparative experiment D:

Vergleichsversuch C wurde analog wiederholt. Zusätzlich wurde eine weitere Schicht auf Basis des strahlenhärtbaren Klarlacks aus Beispiel 1 ebenfalls in 35 µm Trockenschichtdicke durch Spritzen aufgetragen. Die Strahlenhärtung wurde analog durchgeführt. Bei Betrachtung der hochglänzenden Oberfläche war keine Struktur wahrnehmbar, jedoch war eine Vergilbung im Vergleich zu den in Beispiel 5 und in den Vergleichsversuchen A und C erhaltenen Mehrschichtaufbauten wahrnehmbar.Comparative experiment C was repeated analogously. In addition, another layer based on the radiation-curable clear lacquer from Example 1 was also applied in a 35 μm dry layer thickness by spraying. The radiation curing was carried out analogously. When looking at the high-gloss surface, no structure was perceptible, but yellowing was perceptible in comparison with the multilayer structures obtained in Example 5 and in Comparative Experiments A and C.

Tabelle 1 stellt die Prüfergebnisse zusammen.

Figure imgb0001
Figure imgb0002
 Table 1 summarizes the test results.
Figure imgb0001
Figure imgb0002

Claims (8)

Verfahren zur Herstellung von Mehrschichtlackierungen durch Auftrag einer Klarlackschicht auf ein mit einer pigmentierten Basislackschicht versehenes Substrat und anschließendes Aushärten der Klarlackschicht dadurch gekennzeichnet,
daß man auf die Basislackschicht mindestens eine wärmehärtbare Klarlackschicht aufbringt, in der Wärme aushärtet, und ansschließend mindestens eine weitere Klarlackschicht auf der Basis von strahlenhärtbaren Überzugsmitteln aufträgt und diese unter Einwirkung von aktinischer Strahlung aushärtet.Process for the production of multi-layer coatings by applying a clear lacquer layer to a substrate provided with a pigmented basecoat layer and then curing the clear lacquer layer ,
that at least one thermosetting clear lacquer layer is applied to the basecoat, hardened in the heat, and then at least one further clear lacquer layer is applied on the basis of radiation-curable coating agents and cured under the action of actinic radiation. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß man die Härtung mit aktinischer Strahlung unter Verwendung von UV-Strahlung oder Elektronenstrahlung durchführt.Process according to Claim 1, characterized in that the curing is carried out using actinic radiation using UV radiation or electron beams. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß man die Klarlackschicht auf der Basis strahlenhärtbarer Überzugsmittel unter zusätzlich unterstützendem Erwärmen aushärtet.A method according to claim 1 or 2, characterized in that the clear lacquer layer is cured on the basis of radiation-curable coating agents with additional heating. Verfahren nach Anspruch 2 oder 3, dadurch gekennzeichnet, daß man zur Härtung mit UV-Strahlung ein Klarlacküberzugsmittel verwendet, das mindestens einen Photoinitiator enthält.Process according to Claim 2 or 3, characterized in that a clear lacquer coating composition which contains at least one photoinitiator is used for curing with UV radiation. Verfahren nach Anspruch 3, dadurch gekennzeichnet, daß man ein strahlenhärtbares Klarlacküberzugsmittel verwendet, das zusätzlich mindestens einen thermisch aktivierbaren Radikalinitiator enthält.Process according to Claim 3, characterized in that a radiation-curable clear lacquer coating composition is used which additionally contains at least one thermally activatable radical initiator. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß man es zur Lackierung von Kraftfahrzeug-Karrossen und deren Teilen verwendet.Method according to one of the preceding claims, characterized in that it is used for painting motor vehicle bodies and their parts. Verwendung von Klarlacken auf der Basis von strahlenhärtbaren Überzugsmitteln zur Herstellung von Klarlackschichten auf Substraten, die bereits eine ausgehärtete pigmentierte Basislackschicht und darüber mindestens eine thermisch ausgehärtete Klarlackschicht aus einem nicht strahlenhärtbaren Klarlack aufweisen.Use of clear lacquers based on radiation-curable coating compositions for the production of clear lacquer layers on substrates which already have a hardened pigmented basecoat layer and above that at least one thermally hardened clear lacquer layer made of a non-radiation-curable clear lacquer. Verwendung nach Anspruch 7 bei der Herstellung von Mehrschichtlackierungen von Kraftfahrzeugen und deren Teilen.Use according to claim 7 in the production of multi-layer coatings for motor vehicles and their parts.
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EP0568967B1 (en) 1997-09-10
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JP3282881B2 (en) 2002-05-20
DE4215070A1 (en) 1993-11-11
DE59307302D1 (en) 1997-10-16
US5425970A (en) 1995-06-20

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