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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• 1992
  • 1992-05-07 DE DE4215070A patent/DE4215070A1/de not_active Withdrawn
• 1993
  • 1993-05-04 DE DE59307302T patent/DE59307302D1/de not_active Expired - Fee Related
  • 1993-05-04 EP EP93107182A patent/EP0568967B1/fr not_active Expired - Lifetime
  • 1993-05-06 US US08/058,481 patent/US5425970A/en not_active Expired - Fee Related
  • 1993-05-07 JP JP10648093A patent/JP3282881B2/ja not_active Expired - Fee Related

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