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
  • B05D7/52—Two layers
  • B05D7/53—Base coat plus clear coat type
  • B05D7/536—Base coat plus clear coat type each layer being cured, at least partially, separately
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
  • B05D3/12—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 mechanical means
• • 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
  • B05D5/00—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures
  • B05D5/06—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain multicolour or other optical effects
• • 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
  • B05D5/00—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures
  • B05D5/06—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain multicolour or other optical effects
  • B05D5/067—Metallic effect
  • B05D5/068—Metallic effect achieved by multilayers
• • 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
  • B05D2202/00—Metallic substrate
• • 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
  • B05D2350/00—Pretreatment of the substrate
  • B05D2350/20—Chromatation
• • 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
  • B05D2451/00—Type of carrier, type of coating (Multilayers)

Definitions

• the invention relates to a method for painting and mechanical processing of workpieces made of chromatable metals, such as aluminum, magnesium and their alloys, which is particularly suitable for the production of motor vehicle parts, for example rims.
• chromatable metals such as aluminum, magnesium and their alloys
• lacquers there are metal surfaces covered by pigment-containing lacquers in addition to freely visible metal surfaces coated by clear lacquers.
• non-ferrous metals are increasingly being used as substrates, e.g. Aluminum or magnesium.
• the parts are generally provided with a coating.
• multi-layer coatings have been used so far.
• the metal part is first chromated, then a primer is applied and then a color or effect basecoat is applied.
• a clear coat is applied to the basecoat. After the two layers of paint have been applied and baked, the workpiece can be machined.
• Coating agents for the production of multilayer coatings e.g. Metallic paints have already been described in the literature.
• DE-A-19 49 372 and EP-B-0 052 776 describe processes for producing multi-layer coatings which consist of a metallic basecoat and a clearcoat coating agent, the metallic basecoats being made from polyacrylates or polyesters as well as cross-linking agents.
• these basecoat coating compositions have the disadvantage that they contain considerable amounts of organic solvents. Subsequent processing of parts, e.g. by couping, not described.
• the object of the invention is therefore to provide a method for the mechanical processing of painted metallic workpieces, which can be carried out in a simplified manner, in which processing damage to the coating is avoided and a uniform optical appearance is achieved.
• the method is intended to enable the production of painted metal surfaces which have partial areas with freely visible metal surfaces in addition to surface areas covered with pigment-containing paints.
• this object can be achieved by the process forming the subject of the invention for the production of coatings on chromatable metals, in which partial areas of the metal surface covered by pigmented lacquers and visible, only coated with clear lacquer, are present side by side, initially with one Painting the optionally pretreated entire metal surface with a basecoat with a solids content of 15 to 45% by weight, a binder based on one or more polyesters and / or polymers made from free-radically polymerizable monomers, crosslinking agents, Pigments and / or fillers, one or more rheological additives, organic solvents, and optionally other paint additives, are applied and crosslinked in the heat, whereupon a mechanical treatment is carried out without the prior application of a clear coat, exposing part of the metal surface, the exposed metal surface chromated and then a clear coat is applied to the entire surface using a powder coating.
• the further painting takes place after the mechanical treatment with a powder car paint.
• the solids content of the basecoat coating composition applied according to the invention is 15-45% by weight, since it does not require painting with a clearcoat before mechanical processing.
• the powder coating adheres directly to the high-solids basecoat without an adhesion promoter.
• the metal substrates for using the method according to the invention are customary chromatable metals. These are preferably light metals, such as aluminum, magnesium or alloys thereof. However, other metals are also suitable, such as zinc, cadmium or alloys, which contain such metals.
• the workpieces are essentially in their final shape before coating. However, in order to achieve high technical requirements or certain optical properties, it is still necessary later to carry out a further mechanical processing step, in particular machining, such as couping
• the substrate can be subjected to chromating. It is also possible to apply a primer layer. Layers can also be applied to improve adhesion.
• a powder primer is preferably used.
• This primer layer can be based on known polymer powder binders, for example polyepoxides, polyester, polyurethane or polyamide.
• This coating contains the known additives, catalysts and pigments, in particular also anti-corrosion pigments.
• This coating agent is applied by customary methods, such as electrostatic powder spraying. Then the powder primer is made to flow and chemically crosslink by heating. Chromating is particularly preferably carried out before priming. Chromating can be carried out under customary conditions familiar to the person skilled in the art.
• the basecoat which can be used according to the invention is applied, for example to the crosslinked primer layer.
• the application can be carried out by customary spraying methods, for example by electrostatic spraying methods or by compressed air spraying methods.
• the basecoat layer applied in this way is crosslinked by heating, if appropriate after a rest, which can optionally be carried out at an elevated temperature at which the coating agent can flow.
• the baking temperature is, for example, 80-200 ° C, preferably 90-160 ° C.
• the layer thickness of the basecoat layer is preferably 5-40 ⁇ m, particularly preferably 5-25 ⁇ m.
• the coating agent used for the production of the basecoat contains in particular: 10 - 35% by weight of one or more OH group-containing binders based on one or more radical polymers of one or more unsaturated monomers or of polyesters, each with a number average molecular weight of 2000 - 100000 and an OH number of 20 - 300, 2 to 20% by weight of one or more crosslinking agents based on one or more blocked polyisocyanates and / or melamine resins, 0.5 to 10% by weight of one or more pigments and / or fillers, 1 - 12% by weight of one or more rheological additives (which can be plasticizer resins, for example), 0.1 - 5 wt .-% of one or more other paint additives, and 55-85% by weight of one or more organic solvents.
• 10 - 35% by weight of one or more OH group-containing binders based on one or more radical polymers of one or more unsaturated monomers or of polyesters each with a number average molecular
• the solids content of the coating composition is 15-45% by weight.
• the coating agents which can be used according to the invention can, if desired, be adjusted to a suitable application viscosity before application with solvent.
• the basecoat coating composition used according to the invention contains one or more polymers of polyfinically unsaturated monomers. These can be homo- and copolymers; the term "polymer” is used for simplification and is intended to include both.
• binders containing OH groups which can be used according to the invention are described in EP-A-0 358 979. These are polyol components based on olefinically unsaturated compounds.
• the reactive OH groups can be introduced into the binder molecule via the polymerization of appropriately functioning unsaturated monomers.
• the binder should contain reactive hydroxyl groups with an OH number between 20 to 300, preferably 40 to 200 mg KOH / g solid resin.
• the acid number is below 20, preferably below 10 mg KOH / g solid resin.
• the molecular weight is from 500 to 100,000, preferably from 2,000 to 20,000 (gel permeation chromatography, GPC, with polystyrene standard).
• the number of reactive hydroxyl groups must be large enough to ensure adequate crosslinking. If there are too few OH groups, the film does not crosslink sufficiently and its mechanical stability is poor. If the proportion is too high, brittle films are formed which no longer have sufficient flexibility and adhesion.
• the preparation of the hydroxyl-containing polymers from olefinic unsaturated monomers are known in principle.
• the usual unsaturated monomers can be used.
• examples of such monomers are styrene, vinyl acetate, (meth) acrylonitrile, (the term (meth) acrylic used here and in the following refers to acrylic and / or methacrylic), esters of acrylic acid or methacrylic acid with 1 to 12 carbon atoms in the alcohol radical, such as eg methyl acrylate, isopropyl acrylate, butyl acrylate. Mixtures of such monomers can also be used.
• Monomers with functional groups are, for example, hydroxyalkyl esters of acrylic acid or methacrylic acid with 2 to 4 carbon atoms in the alkyl radical, such as 2-hydroxyethyl acrylate or hydroxybutyl acrylate, and allyl alcohol.
• suitable monomers are those which have epoxy groups in the side chain. such as glycidyl (meth) acrylate.
• Other functionalized monomers are, for example, N-methoxymethyl (meth) acrylamide.
• the preparation is preferably carried out in organic solution using continuous or discontinuous polymerization processes.
• suitable solvents are aromatics such as toluene or xylene, esters such as butyl acetate or methoxypropyl acetate, esters such as butyl glycol, tetrahydrofuran or ethyl glycol ether, ketones such as acetone or methyl ethyl ketone.
• the solvent content can be reduced by distillation, preferably in vacuo before further processing. Solvents are preferred which do not lead to malfunctions when the binders are subsequently used in the coating agent.
• the copolymerization is carried out in a known manner with the addition of free radical initiators, optionally also regulators, at temperatures of, for example, 50 to 160.degree. It takes place in a liquid in which monomers and polymers dissolve together.
• Initiators which are soluble in organic solvents are, for example, 0.1 to 5% by weight, based on the amount of monomers used, of peroxides and / or azo compounds.
• Peroxides, peresters or azo compounds which break down thermally into radicals can be used as initiators.
• the additives can be added continuously or in stages.
• the molecular weight can be reduced in a known manner by using regulators.
• Mercaptans, halogen-containing compounds and other radical-transferring substances are preferably used for this purpose.
• N- or tertiary dodecyl mercaptan, tetrakismercaptoacetylpentaerythritol are particularly preferred. They are added in amounts of at most 3% by weight based on the monomer mixture.
• Binders based on polyesters can be used as a further polyol component. These are linear or branched, oil-free polyesters based on di- or polyvalent aliphatic and / or cycloaliphatic saturated polyalcohols, as well as aliphatic, cycloaliphatic or aromatic di- or polybasic carboxylic acids, which can optionally be polycondensed with linear or branched monoalcohols. Polyesters with a corresponding composition are described, for example, in DE-A-26 29 930 or DE-A-22 53 300.
• the alcohols preferably contain 2 to 21 C atoms, the dicarboxylic acids preferably 5 to 10 C atoms.
• the dicarboxylic acids preferably 5 to 10 C atoms.
• examples of alcohols are hexanediol-2,5, neopentyl glycol, heptanediol-1,7, 2,2,4-trimethyl-pentanediol-1,3 or 1,4-bis (hydroxymethyl) cyclohexane.
• Examples of carboxylic acids are isophthalic acid, terephthalic acid, 1,3-cyclo-hexanedicarboxylic acid, succinic acid, adipic acid, azelaic acid, decanedicarboxylic acid or butyl isophthalic acid.
• Small amounts of tricarboxylic acids or tri- or polyalcohols can also be used to achieve branches in the molecular structure.
• polyesters can also be increased in molecular weight by reaction with diisocyanates. If necessary, further modifications can be carried out via reactive groups, for example OH groups or COOH groups. It is also possible to introduce polar groups into the molecular structure by reacting diols containing ionic groups. These can affect adhesion properties. Examples of such compounds are, for example, dihydroxypropionic acid.
• the polyesters which can be used according to the invention have a molar mass (number average, Mn) of 500-15000, preferably 1500-5000.
• the OH number is between 20 and 300, preferably between 40 and 200.
• the acid number is preferably below 15.
• the polyesters are produced by known processes. A stepwise reaction is preferred. For example, they can be produced azeotropically or in the melt. The reaction temperature is e.g. at 150 to 240 ° C. After reaching the final values, the polyester can be diluted with solvents if necessary to achieve a good processing viscosity.
• the properties of the polyesters can be influenced by the dicarboxylic acids or polyalcohols that can be used.
• Higher-chain aliphatic alcohols increase the flexibility of the polyester, aromatic dicarboxylic acids reduce the elasticity.
• the degree of branching is influenced by the amount of tri- or polycarboxylic acids or tri- or polyalcohols.
• the number of polar groups, e.g. OH groups, ether groups, urethane groups increased the polarity of the crosslinked lacquer layer and influenced the adhesion.
• Rheological additives can also be used in the coating agent used according to the invention.
• plasticizers or additional binders are suitable.
• the additional binders present are, for example, non-reactive binders or those which contain functional groups. e.g. OH groups. Examples of these are OH-containing polyurethane resins, polyurea resins or cellulose esters. Examples of non-reactive additional resins are polyurethane resins, caramide resins or low molecular weight polyesters. These binders should have an OH number of up to 150 mg KOH / g solid resin and a molar mass of 500 to 100,000.
• the resins used must be compatible with the binder and must not migrate from the coating agent even after crosslinking. Otherwise, this can lead to film and adhesion problems in the adjacent layers.
• the properties of the coating agent can be influenced, for example rheology, elasticity, adhesion or the glass transition temperature. Care should be taken to ensure that the crosslinking density is not reduced too much by the additional resins, since otherwise coatings which are too soft are formed and do not result in a mechanically stable multi-layer coating.
• crosslinking agents which can be used in the coating compositions used according to the invention are crosslinking agents based on melamine resins or based on blocked polyisocyanates. These crosslinkers are commercially available and have already been described in the literature.
• Suitable amine resins include, for example, alkylated condensates which are prepared by reacting aminotriazines and amidotriazines with aldehydes.
• amines or amino group-bearing compounds such as melamine, guanamine, acetoguanamine, benzoguanamine, dicyandiamide or urea in the presence of alcohols, such as methanol, ethanol, propanol, butanol or hexanol, with aldehydes, in particular formaldehyde.
• alcohols such as methanol, ethanol, propanol, butanol or hexanol
• aldehydes in particular formaldehyde.
• aldehydes in particular formaldehyde.
• polyisocyanate crosslinkers are customary lacquer polyisocyanates such as, for example, aliphatic, cycloaliphatic and aromatic polyisocyanates, e.g. hexamethylene diisocyanate, isophorone diisocyanate, tolylene-2,4-diisocyanate, 4-diisocyanatodiphenylmethane.
• diisocyanates can be polymerized by reaction and then have biuret, allophanate, urethane or isocyanurate groups. It is also possible to react with polyols, e.g. Trimethylolpropane to produce NCO-containing oligomers.
• the isocyanate groups are capped using conventional capping agents.
• ketoximes examples include ketoximes, cyclic lactams, low molecular weight aliphatic alcohols or low molecular weight aliphatic amines.
• Processes for capping and oligomerizing the isocyanates are known to the person skilled in the art.
• the quantitative ratio of crosslinkable binders to crosslinkers is preferably 80:20 to 50:50, in each case based on the solid resin weight.
• the reactivity of the crosslinking agents can optionally be increased by adding catalysts.
• the pigments and fillers which can be used according to the invention comprise organic and inorganic effect and color pigments and fillers.
• organic and inorganic effect and color pigments and fillers examples of this are transparent or opaque color pigments, e.g. Titanium dioxide, iron oxide and organic color pigments; Effect pigments, e.g. finely divided metal pigments or pearlescent pigments; Fillers such as aluminum silicate, barium sulfate or mica.
• transparent inorganic or organic pigments e.g. highly disperse silica, highly disperse titanium dioxide. If necessary, finely divided crosslinked polymer microparticles can be used. Finely divided aluminum pigments are preferably used.
• the coating agent may also contain paint additives, for example other agents influencing the rheology, such as highly disperse silica, layered silicates or polymeric urea compounds; Anti-settling agents, leveling agents, anti-foaming agents, such as, for example, silicone-containing compounds; Wetting agents and substances for influencing the conductivity. Wetting agents are also understood to mean known paste resins, such as those e.g. are described in EP-A-0 260 447, which can be used for better dispersing and grinding of the pigments. Catalysts such as amines or heavy metal salts can be used to accelerate the reaction, but it is also possible to harden by thermal energy without using a catalyst.
• paint additives for example other agents influencing the rheology, such as highly disperse silica, layered silicates or polymeric urea compounds; Anti-settling agents, leveling agents, anti-foaming agents, such as, for example, silicone-containing compounds; Wetting agents and substances for influencing the conduct
• solvents are suitable as solvents; these can come from the production of the binders.
• solvents are glycol ethers, for example diethylene glycol dimethyl ether, ethoxypropanol, butyl glycol; Alcohol, for example isopropanol or n-butanol, glycols, for example ethylene glycol; N-methylpyrrolidone and ketones such as methyl ethyl ketone; aromatic or aliphatic hydrocarbons, for example xylene or C6 - C12 linear or branched aliphatic hydrocarbons.
• the course and the viscosity of the coating agent can be selected by selecting the solvent to be influenced.
• the evaporation process can be influenced via the boiling point of the solvent mixture used.
• the methods for producing the coating agent are known.
• the pigments and / or fillers can be dispersed and ground in part of the binders.
• Special paste resins can also be used.
• the viscosity can be adjusted to a suitable value by adding solvent components.
• the other paint components for example further binders, crosslinking agents, rheology-influencing agents, defoamers, anti-cratering agents, leveling agents, catalysts or solvents can be added. Care must be taken that the components used are compatible with one another and give a coating composition which is stable in storage.
• the workpiece After the base layer has been applied, the workpiece is heated.
• the applied basecoat cross-links to form a dense, tough, elastic film.
• the workpiece can be processed without an additional intermediate layer (especially without a clear lacquer layer).
• Mechanical processing can be carried out, in particular machining treatments, e.g. Coup. The resulting chips no longer damage the surface and the surface quality is not impaired.
• the surface Upon completion of the machining operations, the surface is contaminated, e.g. Particles, cleaned.
• chromating takes place, after which further painting can be carried out, e.g. by applying a clear coat. Chromating improves the properties of the multilayer structure, e.g. the adhesion or corrosion behavior.
• the chromating is dried before the additional layer of lacquer is applied. Chromating is in particular clear or colorless chromating.
• Conventional powder coatings can be used to produce the clear coat. These can contain, for example, polyurethane powder or polyester powder as a binder base, as well as the usual pigments and / or additives.
• the clear lacquer coating material is melted and crosslinked by heating.
• the resulting clear coat layer thickness is preferably 10 to 100 microns.
• the invention further relates to a multi-layer coating, produced by applying a color or effect-imparting base layer to an optionally chromated and primed substrate, crosslinking the coating by heating, subsequent mechanical processing, chromating and then applying a powder clearcoat coating.
• the substrate is optionally subjected to a pretreatment comprising chromating and / or subsequent priming.
• the multilayer coating obtained in accordance with the invention has a good surface and good corrosion protection.
• the adhesion between the layers is good and shows no delamination disorders even when exposed to damp conditions.
• the method according to the invention is particularly suitable for coating parts for the motor vehicle industry. Rims, for example aluminum rims, are particularly suitable as parts or workpieces.
• the method according to the invention simplifies the method of operation by saving an additional coating process, namely a clear lacquer coating, as is required in the prior art before mechanical processing of the painted workpiece.
• the parts machined according to the invention show a reduced error rate, in particular reduced liability disorders of the coated parts.
• the surface of the workpieces machined according to the invention has a good visual appearance and good corrosion properties.
• 32% of a commercially available polyester (OH number 80, acid number 10; 50% solids) are mixed with 12% of a high-methanol etherified melamine resin (55% solids), 6% of a plasticizer based on carbamic acid. 18% xylene and 3.5% isobutanol are added and 2% of a cellulose acetobutyrate and 1% of a magnesium silicate are mixed in. 6% of a commercially available aluminum bronze are mixed in and 0.5% of a commercially available thickener (acrylic acid base) are added and thoroughly homogenized. It is diluted to a suitable solid with approx. 19% butyl acetate.
• the test for moisture resistance (DIN 50 017 condensation test climates; interlayer adhesion Cass test DIN 50 021) shows a good result.
• the structure is scratch-resistant and shows good optical behavior.

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• Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Wood Science & Technology (AREA)
• Mechanical Engineering (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Paints Or Removers (AREA)

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Cited By (5)

Citations (8)

• 1993
  • 1993-09-07 EP EP93114294A patent/EP0587099A1/fr not_active Ceased

Patent Citations (8)

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