Translucent coating systems, manufacturing process for the coating systems and their use

Abstract

The invention relates to a translucent, multi-layered structure for surface coating, comprising a laser-engravable primer layer, a translucent base layer, and a clear varnish layer. The coating system according to the invention is particularly suitable for indicating and actuating buttons on the surface of a substrate backlit by a light source. The resulting coating systems are particularly suitable for surfaces with integrated lighting, such as those used, for example, in displays or instrument panels.

Description

[0001] The invention relates to a translucent, multilayer structure for coating surfaces. The coating system according to the invention is particularly suitable for displaying and operating buttons on the surface of a substrate that is backlit by a light source. Furthermore, the invention relates to coating materials and their compositions for producing backlit and translucent coating systems. The resulting coating systems are particularly suitable for surfaces with integrated lighting, such as those used, for example, in displays or dashboards.

[0002] Coating systems comprising primer, basecoat, and clearcoat layers are known. For example, WO 2018 / 138253 A1 describes basecoat-clearcoat systems for coating concrete surfaces with a clearcoat layer and at least one basecoat layer, and WO 2017 / 160398 A1 describes coating systems for metal substrates with a basecoat and a clearcoat layer, applied using a wet-on-wet process and subsequently cured. Translucent trim components for motor vehicles are known from EP 3632749 A1. They consist of a translucent or transparent substrate onto which a lacquer film is applied, containing perforations in selected areas. Light from a light source located behind or beneath the substrate can shine through these perforations. The lacquer film is sealed with a clearcoat layer in such a way that the perforations are not visible.Backlighting creates a glow that matches the size and shape of the perforated area. The color of the light is determined by the light source used. Applying films to uneven surfaces, such as curved or textured surfaces, is known to be problematic. Furthermore, heat and humidity negatively affect adhesion, causing the films to detach from the substrate. The films and plastics commonly used are also susceptible to scratches.

[0003] The object of the present invention is therefore to provide improved back- and through-the-air coating systems which overcome the known disadvantages.

[0004] The problem is solved by methods for producing coating systems comprising a laser-engravable primer layer, a first clearcoat layer, a translucent basecoat layer, and a second clearcoat layer. The problem is further solved by using these coating systems to manufacture backlit components.

[0005] In the following, the term coating system refers to a paint finish or coating structure consisting of several layers. The individual layers are applied by applying and curing coating materials. In the following, the term translucency refers to the partial light transmittance of a body.

[0006] The primer layer according to the invention comprises one or more coatings obtained by applying and curing suitable coating materials on a substrate surface. The term primer refers both to the coating materials and to the coatings obtained therefrom, which are applied directly to the substrate surface and perform specific functions, such as improving the adhesion between the substrate and the coating.

[0007] The primer compositions usable according to the invention are opaque and laser engravable. Laser engraving is an engraving technique in which material is heated so intensely by an incident laser beam that it vaporizes or burns. To obtain sharp contours and clear, transparent surfaces in the engraving, the material must vaporize or burn without leaving any residue.

[0008] Suitable primer coatings are polyurethane-based, consisting of two-component compositions with a polyol component as a binder and an isocyanate component as a hardener. The primer compositions usable according to the invention contain, in the binder component, 10 to 80 wt.% of at least one polyol, 5 to 30 wt.% of at least one pigment, and 3 to 25 wt.% of at least one filler.

[0009] Suitable polyols are those commonly used in the production of polyurethanes and familiar to those skilled in the art, such as polyether polyols, polycaprolactone polyols, polyester polyols, polycarbonate polyols, polyacrylate polyols, polyols based on dimeric fatty acids, and mixtures thereof. Polycarbonate polyols, polyacrylate polyols, and mixtures thereof are preferred.

[0010] Suitable pigments are the usual inorganic and organic pigments familiar to those skilled in the art, such as carbon black, titanium dioxide, iron oxides, perylene pigments, and mixtures thereof. The use of carbon black, perylene pigments, and mixtures thereof is preferred.

[0011] Suitable fillers include, for example, oxide, carbonate, sulfate, and silicate fillers with alkali or alkaline earth cations, as well as cations from groups 3 and 4 of the periodic table as counterions. Barium sulfate, talc, calcium carbonate, silicon dioxide, and mixtures thereof are preferred.

[0012] Furthermore, the primer-binder components usable according to the invention can contain at least one solvent, preferably in proportions of 0.01 to 82 wt.%. Suitable solvents are the usual solvents known to those skilled in the art, such as aliphatic hydrocarbons, aromatic hydrocarbons, and mixtures thereof. Acetic acid esters, aromatic hydrocarbons such as xylenes, and mixtures thereof are preferred. n-Butyl acetate, methoxypropyl acetate, i-Butyl acetate, and mixtures thereof are particularly preferred.

[0013] Furthermore, the primer-binder components usable according to the invention can comprise at least one additive, preferably in proportions of 0.1 to 20 wt.%. Suitable additives are those commonly used and known to those skilled in the art, in particular wetting agents, defoamers, leveling agents and adhesion promoters.

[0014] The primer compositions usable according to the invention contain at least one isocyanate in the hardener component. Suitable isocyanates are those commonly used in the production of polyurethane and familiar to those skilled in the art, such as oligomers or prepolymers based on toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 4,4'-diisocyanato-dicyclohexylmethane (HMDI), 1,6-diisocyanatotrimethylhexane (TMDI), and mixtures thereof. Aliphatic isocyanates, in particular oligomers based on hexamethylene diisocyanate (HDI), are preferred.

[0015] Furthermore, the hardener components can contain at least one solvent, preferably in proportions of 0.01 to 70 wt.%. Suitable solvents are the usual solvents familiar to those skilled in the art, such as aliphatic hydrocarbons, aromatic hydrocarbons, and mixtures thereof. Acetic acid esters, aromatic hydrocarbons, and mixtures thereof are preferred. Butyl acetates, xylenes, and mixtures thereof are particularly preferred.

[0016] The binder component and the hardener component of the primer composition are used in a molar ratio of the OH groups of the binder to the NCO groups of the hardener in the range of 1 : 0.5 to 1 : 2, preferably from 1 : 0.8 to 1 : 1.3, particularly preferably 1 : 0.9 to 1 : 1.1.

[0017] The primer compositions have a high degree of opacity. They can therefore form layers with very low dry film thicknesses without impairing the desired properties. The dry film thicknesses according to the invention are between 2 and 40 µm, preferably between 2 and 20 µm, and particularly preferably between 2 and 10 µm.

[0018] In addition, the primer compositions usable according to the invention comprise electrically conductive particles. The primer compositions usable according to the invention contain conductive particles in amounts of 1 to 40 wt.%, preferably 10 to 30 wt.%, and particularly preferably 15 to 25 wt.%. Suitable substances are conductive carbon black, silver nanowires, electrically conductive polymers, indium tin oxide, silver, indium tin oxide-doped mica, conductive titanium dioxide, graphene, antimony tin oxide, antimony tin oxide-doped mica, aluminum-doped tin oxide, and mixtures thereof. Conductive carbon black is preferred. The conductive particles are preferably contained in the primer binder component.

[0019] The addition of conductive particles creates an electrically conductive primer layer. This allows electrical signals to be generated by touching the surface of the coating system with a conductive material, such as a hand or finger, which can then be used for operation or switching functions.

[0020] The basecoat layer usable according to the invention comprises one or more coatings, which are obtained by the application and curing of suitable coating materials. In the following, the term basecoat or base lacquer refers to a colored coating or finish within a coating system.

[0021] Suitable basecoats are polyurethane-based coatings obtained from two-component compositions with a polyol component as a binder and an isocyanate component as a hardener. The basecoat compositions usable according to the invention contain, in the binder component, 1 to 90 wt.% of at least one polyol, 0.1 to 5 wt.% of at least one catalyst, 0.5 to 60 wt.% of a mixture containing at least one pigment and at least one filler, and 0.5 to 50 wt.% of at least one additive. Suitable polyols are those commonly used in the production of polyurethanes and familiar to those skilled in the art, such as polyether polyols, polycaprolactone polyols, polyester polyols, polycarbonate polyols, polyacrylate polyols, polyols based on dimeric fatty acids, and mixtures thereof. Polycaprolactone polyols, polycarbonate polyols, polyester polyols, and mixtures thereof are preferred.

[0022] Suitable catalysts are those commonly used in the production of polyurethanes and familiar to those skilled in the art, such as organometallic complexes with tin, zirconium, titanium, or bismuth as the central atom, tertiary amines, and mixtures thereof. Dibutyltin dilaureate is preferred.

[0023] Suitable pigments are the usual inorganic and organic pigments familiar to those skilled in the art. Suitable inorganic pigments include, for example, titanium dioxide, iron oxides, chromium oxides, chromium titanates, bismuth vanadate, cobalt blue, carbon blacks, and mixtures thereof. Suitable organic pigments include, for example, Pigment Yellow 151, Pigment Yellow 213, Pigment Yellow 83, Pigment Orange 67, Pigment Orange 62, Pigment Orange 36, Pigment Red 170, Pigment Violet 19, Pigment Violet 23, Pigment Blue 15:3, Pigment Blue 15:6, Pigment Green 7, and mixtures thereof.

[0024] Suitable fillers include, for example, oxide, carbonate, sulfate, and silicate fillers with alkali or alkaline earth cations, as well as cations from groups 3 and 4 of the periodic table as counterions. Barium sulfate, talc, calcium carbonate, silicon dioxide, and mixtures thereof are preferred.

[0025] Suitable additives include, for example, light stabilizers, dispersants, rheology additives, defoamers, leveling agents, wetting agents, and mixtures thereof. Light stabilizers, dispersants, rheology additives, defoamers, and mixtures thereof are preferred.

[0026] Furthermore, the basecoat binder components usable according to the invention can contain at least one matting agent, preferably in proportions of 0.1 to 20 wt.%. Suitable

[0027] Matting agents include, for example, silicates (salts and esters of orthosilicic acid and their condensates), amorphous silicas, precipitated silicas, micronized waxes such as polyethylene waxes, polypropylene waxes, polyamide waxes, PTFE waxes, micronized polymers such as ureaaldehyde resins, beeswaxes, carnauba waxes, and mixtures thereof. Silicates, silicas, polyethylene waxes, polypropylene waxes, polyamide waxes, and mixtures thereof are preferred.

[0028] Furthermore, the basecoat binder components usable according to the invention can contain at least one solvent, preferably in proportions of 1 to 83 wt.%. Suitable solvents are aromatic hydrocarbons, aliphatic hydrocarbons, carboxylic acid esters, ethers, and mixtures thereof. Aromatic hydrocarbons, acetic acid esters, and mixtures thereof are preferred. Xylene, butyl acetates, and mixtures thereof are particularly preferred.

[0029] The basecoat compositions usable according to the invention contain at least one isocyanate in the hardener component. Suitable isocyanates are those commonly used in the production of polyurethane and familiar to those skilled in the art, such as oligomers and prepolymers based on hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 4,4'-diisocyanato-dicyclohexylmethane (HMDI), 1,6-diisocyanatotrimethylhexane (TMDI), and mixtures thereof. Oligomers based on hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI) and mixtures thereof are preferred.

[0030] Furthermore, the hardener components may contain at least one solvent, preferably in proportions of 0.01 to 50 wt.%. Suitable solvents are the usual solvents familiar to those skilled in the art, such as aliphatic hydrocarbons, aromatic hydrocarbons and mixtures thereof.

[0031] The binder component and the hardener component of the basecoat composition are used in a molar ratio of the OH groups of the binder to the NCO groups of the hardener in the range of 1 : 0.5 to 1 : 2, preferably from 1 : 0.8 to 1 : 1.3, particularly preferably 1 : 0.9 to 1 : 1.1.

[0032] The clearcoat layer usable according to the invention comprises one or more coatings, which are obtained by the application and curing of suitable coating materials. In the following, the term clearcoat or clear lacquer refers to a transparent coating or lacquer with protective, decorative, or specific technical properties.

[0033] Suitable clearcoat coatings are polyurethane-based, consisting of two-component compositions with a polyol component as a binder and an isocyanate component as a hardener. The clearcoat compositions usable according to the invention contain at least one polyol in the binder component in 20 to 70 wt.% and at least one additive in 5 to 30 wt.%.

[0034] Suitable polyols are those commonly used in the production of polyurethanes and familiar to those skilled in the art, such as polyether polyols, polycaprolactone polyols, polyester polyols, polycarbonate polyols, polyacrylate polyols, polyols based on dimeric fatty acids, and mixtures thereof. Polyester polyols are preferred.

[0035] Suitable additives are the usual additives known to the skilled person, such as light stabilizers, dispersants, rheology additives, defoamers, leveling agents, wetting agents and their mixtures.

[0036] Additionally, the clearcoat binder components may contain at least one matting agent, preferably in proportions of 8 to 14 wt.%.

[0037] Suitable matting agents include, for example, silicates (salts and esters of orthosilicic acid and their condensates), amorphous silicas, precipitated silicas, micronized waxes such as polyethylene waxes, polypropylene waxes, polyamide waxes, PTFE waxes, micronized polymers such as ureaaldehyde resins, beeswaxes, carnauba waxes, and mixtures thereof. Silicates, silicas, polyethylene waxes, polypropylene waxes, polyamide waxes, and mixtures thereof are preferred.

[0038] Furthermore, the clearcoat binder components usable according to the invention can contain at least one solvent, preferably in proportions of 0.3 to 75 wt.%. Suitable solvents are aromatic hydrocarbons, aliphatic hydrocarbons, carboxylic acid esters, ethers, and mixtures thereof. Aromatic hydrocarbons, acetic acid esters, and mixtures thereof are preferred. Xylenes, butyl acetates, and mixtures thereof are particularly preferred.

[0039] The clearcoat compositions usable according to the invention contain at least one isocyanate in the hardener component. Suitable isocyanates are those commonly used in the production of polyurethane and familiar to those skilled in the art, such as oligomers and prepolymers based on hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 4,4'-diisocyanato-dicyclohexylmethane (HMDI), 1,6-diisocyanatotrimethylhexane (TMDI), and mixtures thereof. Oligomers based on hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI) and mixtures thereof are preferred.

[0040] Furthermore, the hardener components can contain at least one solvent, preferably in proportions of 0.01 to 30 wt.%. Suitable solvents are aromatic hydrocarbons, aliphatic hydrocarbons, carboxylic acid esters, ethers, and mixtures thereof. Aromatic hydrocarbons, acetic acid esters, and mixtures thereof are preferred. Xylenes, butyl acetates, and mixtures thereof are particularly preferred.

[0041] The binder component and the hardener component of the clearcoat composition are used in a molar ratio of the OH groups of the binder to the NCO groups of the hardener in the range of 1 : 0.5 to 1 : 2, preferably from 1 : 0.8 to 1 : 1.3, particularly preferably 1 : 0.9 to 1 : 1.1.

[0042] The coating system according to the invention is produced by a process which comprises at least the following steps: (a) Applying at least one primer coating to a translucent or transparent substrate to produce an opaque primer layer, (b) partially removing the primer layer from the substrate surface by laser engraving, (e) applying at least one clearcoat coating to the engraved primer layer to produce a first clearcoat layer, (c) applying at least one translucent basecoat coating to the first clearcoat layer to produce the basecoat layer, and (5) applying at least one clearcoat coating to the basecoat layer to produce the second clearcoat layer.

[0043] Preferably, clearcoat compositions containing matting agents are used in step (3).

[0044] The coating systems according to the invention, with their combination of primer, basecoat, and clearcoat layers, are particularly well-suited for producing smooth surfaces on backlit components. When illuminated by a light source positioned behind the component (from the viewer's perspective), only those sections where the opaque primer layer has been removed by laser engraving illuminate. Without illumination, the components coated according to the invention exhibit a smooth, painted surface. Unlike previously used films, the coatings according to the invention can also be applied to components with highly curved surfaces and to small components such as control knobs or dials. By using an electrically conductive primer layer, these surfaces can also perform operating or switching functions, since the primer layer has been removed by laser engraving in the illuminated sections.

[0045] This four-layer structure of the coating system according to the invention produces very homogeneous and smooth surfaces, which are particularly suitable for high-gloss and metallic finishes. High-gloss surfaces and / or surfaces with a metallic effect can be created on a component, revealing differently colored sections only when backlit. These surfaces can also incorporate operating or switching functions.

[0046] The coating systems according to the invention are particularly resistant to moisture, chemicals and mechanical stresses, making them especially suitable for coating components in vehicles, aircraft and ships, for example for coating exterior and interior panels with integrated lighting.

[0047] The coating systems according to the invention are suitable for use on backlit components that only illuminate in selected areas of their surface. In a further embodiment, the illuminated areas have operating or switching functions.

[0048] The coating systems according to the invention are particularly suitable for use on automotive components in the exterior and interior areas, as they meet the requirements with regard to adhesion, aging, hydrolysis resistance, cream resistance, chemical resistance, abrasion behavior, scratch resistance and scrub resistance. Examples Compositions of the coating materials Example 1: laser-engravable primer

[0049] ingredient Percentage [wt.%) Main component Acrylate polyol (OH number 6 to 12 mg KOH / g) 18 Carbonate diol (OH number 118 to 132 mg KOH / g) 3 Precipitated barium sulfate 17 soot 16 Surface additive 0,5 Wetting agent 14,5 Butyl acetate 31 Harder Aliphatic polyisocyanate (90% in butyl acetate and solvent naphtha with NCO content 19.6%) 84 Butyl acetate 10 Xylene 6 Example 2: conductive, laser-engravable primer

[0050] ingredient Percentage [wt.%) Main component Acrylate polyol (OH number 6 to 12 mg KOH / g) 18 Carbonate diol (OH number 118 to 132 mg KOH / g) 3 Precipitated barium sulfate 17 Conductivity carbon black 16 Surface additive 0,5 Wetting agent 14,5 Butyl acetate 31 Hardener component Aliphatic polyisocyanate (90% in butyl acetate and solvent naphtha with NCO content 19.6%) 84 Butyl acetate 10 Xylene 6 Example 3: Base coat

[0051] ingredient Percentage [wt.%) Main component Hydroxyl group-containing polyester resin (OH number 185 to 205 mg KOH / g) 19 Aliphatic polycarbonate polyester (OH number 56 mg KOH / g) 8,5 Precipitated barium sulfate 28 talc 4 pigment 0,8 Matting agent 5,8 Rheology additives 1,5 Surface additive 3 Wetting agent 0,2 catalyst 0,1 Butyl acetate 17 Xylene 10,7 Methoxypropyl acetate 0,1 Butyl glycol 0,4 test gasoline 0,4 Propyl carbonate 0,5 Hardener component Aliphatic polyisocyanate (75% in butyl acetate with NCO content 16.5%) 100 Example 4: Clearcoat, glossy

[0052] ingredient Percentage [wt.%) Main component Acrylate polyol (OH number 4 to 9 mg KOH / g) 20 Acrylate polyol (OH number 4 to 8 mg KOH / g) 10 Acrylate polyol (OH number 3 to 5 mg KOH / g) 20 Polyester resin containing hydroxyl groups (OH number 5 to 10 mg KOH / g) 20 Butyl glycol acetate 3,5 sunscreen 1,5 Surface additive 0,5 catalyst 0,1 Xylene 13,4 Solvent Naphtha 11 Hardener component Aliphatic polyisocyanate (90% in butyl acetate and solvent naphtha with NCO content 19.6%) 84 Butyl acetate 10 Xylene 6 Example 5: Clearcoat, matt

[0053] ingredient Percentage [wt.%) Main component Polyester resin containing hydroxyl groups (OH number 50 to 65 mg KOH / g) 31,4 Polyester resin containing hydroxyl groups (OH number 120 to 140 mg KOH / g) 5,4 Hydroxyl group-containing polyester resin (OH number 280 mg KOH / g) 6,4 Matting agent 11 Rheology additives 0,4 Surface additive 2,4 sunscreen 0,8 catalyst 0,1 Butyl acetate 12,5 Ethyl acetate 2,5 Diacetone alcohol 25,2 Butyl glycol 0,6 Xylene 0,75 test gasoline 0,5 Methoxypropyl acetate 0,05 Hardener component Aliphatic polyisocyanate (90% in butyl acetate and solvent naphtha with NCO content 19.6%) 84 Butyl acetate 10 Xylene 6

[0054] The production of coating materials from the above-mentioned compositions is carried out according to known methods familiar to those skilled in the art. Preparation of the test specimens Test specimen 3 (four-layer structure):

[0055] Substrate: Makrolon AG 2405 polycarbonate. First layer: Laser primer (Example 1), pneumatic application, oven drying at 80 °C, dry film thickness 2 to 6 µm. Second layer: Clearcoat (Example 4), application technique: pneumatic application, oven drying at 80 °C, dry film thickness 40 to 50 µm. Third layer: Basecoat (Example 3), pneumatic application, oven drying at 80 °C, dry film thickness 40 to 50 µm. Fourth layer: Clearcoat (Example 4), pneumatic application, oven drying at 80 °C, dry film thickness 40 to 50 µm. Testing methods: Determination of liability (cross-section):

[0056] Six parallel cuts are made with a utility knife on the coating of the test specimens. The cuts are deep enough to reach the substrate surface without damaging it. Six more parallel cuts are then made perpendicular to the first, forming a uniform square or grid. The grid spacing is 1 mm. A strip of clear film or masking tape with an adhesive strength of 8 to 10 N / 25 mm is applied to the resulting square. This tape is then peeled off at an angle of 60° within 0.5 to 1 second. The grid or coating is then visually evaluated. The results of the cross-cut test are visually assessed according to the following scheme: GT 0 Smooth cut edges, no chipping. GT 1 Up to 5% of the sections have chipped off. GT2 Up to 15% of the sections have chipped off. GT3 Up to 35% of the sections have chipped off. GT 4 Over 65% of the sections have chipped off.

[0057] The cross-cut strength value Gt 0 corresponds to very good adhesion, while the value Gt 5 corresponds to very poor adhesion. Determination of scratch resistance (Erichsen scratch hardness):

[0058] A weighted scribing tool is placed vertically with its tip on the coating to be tested and, while standing upright, drawn across the surface. The test is then visually assessed to determine if the coating shows any scratch marks. The maximum weight the scribing tool can bear without damaging the coating is given as a measure of the coating's scratch resistance. An Erichsen hardness tester type 318 with a Bosch test needle, whose engraving tip has a diameter of 0.75 mm, is used for this test. Determination of hydrolysis resistance:

[0059] The coated specimens are stored in a climate chamber for 72 hours at 90 °C ± 2 °C and ≥ 93% relative humidity. They are then conditioned for 30 minutes at room temperature (18 °C to 28 °C) and subsequently visually evaluated. After a further 30 minutes of conditioning, a cross-cut test is performed. Determination of cream stability:

[0060] A gauze bandage is placed on the coated surface of the specimens, and test cream (test creams A and B from Thierry GmbH, Stuttgart) is applied to it. The cream is pressed through the gauze bandage onto the surface and spread so that the spaces between the meshes are filled with cream. Excess cream is wiped off. The prepared specimen is then stored in a circulating air oven at 80 °C for 24 hours. After this time, the gauze bandage is removed, and the remaining cream is wiped off with a cloth. The specimen is then conditioned for 4 hours at room temperature (+18 °C to +28 °C). A cross-cut test is then performed. Determination of chemical resistance:

[0061] Droplets of different chemical solutions are successively applied to the coated surface of the test specimens. These solutions include a surfactant-based aqueous solution (commercial dishwashing liquid), an ammoniacal alcoholic cleaning solution (commercial glass cleaner), ethanol denatured with 1 wt% methyl ethyl ketone, and cleaning naphtha (boiling range 80–100°C). After 10 minutes of evaporation at room temperature, the test specimens are heated in a convection oven at 60°C for 30 minutes and then cooled to room temperature for 30 minutes. After 24 hours of storage at room temperature, the test specimens are cleaned with distilled water. The changes in color and surface quality are then visually assessed. Determination of conductivity (layer resistance):

[0062] The layer resistance Rs is determined using a standard measuring probe (Ken MR-1 from Schütz Messtechnik) in a 4-point measurement method. It is usually given in Ω / sq. Typical values ​​for the layer resistance of touch panel surfaces are in the range of 10–1000 Ω / sq. Determination of transmission:

[0063] A polycarbonate plastic sheet made of Makrolon 2405 is coated with the coating system to be tested. Using a standard spectrophotometer (CM.36dGV from Konica Minolta), the transmission of visible light in the range of 400 to 700 nm is determined and averaged over all wavelength ranges. Determination of visual concealment:

[0064] In the following, visual opacity refers to the coverage of the laser engravings on the coating or coating system by the overlying layers. The coated specimens are examined without backlighting. The coating surface is first evaluated in daylight. In the second step, the surface is illuminated frontally with a flashlight, and the visibility of the laser-engraved areas is visually assessed according to the following scheme: 0 Engravings are very visible in daylight and can be felt with a finger. 1 Engravings are very visible in daylight, but not perceptible with a finger. 2 Engravings are faintly visible in daylight. 3 Engravings are not visible in daylight, only when illuminated with a flashlight. 4 Engravings are not visible in daylight or when illuminated with a flashlight. Results

[0065] The following table shows the test results obtained. The coating systems according to the invention exhibit significantly higher light transmission and better lamination on the engraved sections in comparison. Table of test results

[0066] Test specimen 3 Cross-cut GT 0 Erichsen scratch hardness 20 N Hydrolysis resistance (cross-section) Gt ≤ 1 Cream resistance (cross-cut) Gt ≤ 1 Chemical resistance (surface) no change transmission 10% conductivity <1 masking value 3

Claims

1. Method for producing a translucent coating system, comprising the steps of (a) applying at least one primer coating on a translucent or transparent substrate to produce a primer layer which is impermeable to light, (b) the partial removal of the primer layer from the substrate surface by means of laser engraving, (e) applying at least one clear coating on the engraved primer layer to produce a first clear coating layer, (c) applying at least one translucent base coating to produce a base coat layer and (d) applying at least one further clear coating to produce a second clear coating layer.

2. Procedure according to claim 1, characterised in that the primer layer is electrically conductive.

3. Procedure according claim 1 or 2, characterised in that the primer coatings are made of components including a binder component comprising 10 to 80 weight % of at least one polyol, 5 to 30 weight % of at least one pigment, 2 to 25 weight % of at least one filler as well as a hardener component comprising at least one isocyanate.

4. Procedure according to claim 2, characterised in that the applied primer compositions further contain 1 to 40 weight % of conductive particles.

5. Procedure according to one of the foregoing claims, characterised in that the base coat layers are made of compositions containing a binder component comprising 1 to 90 weight % of at least one polyol, 0.5 to 5 weight % of at least one catalyst, 0.5 to 60 weight % of a mixture containing at least one pigment and at least one filler, 0.5 to 50 weight % of at least one additive as well as one hardener component comprising at least one isocyanate.

6. Procedure according to one of the foregoing claims, characterised in that the base coat layers are made of compositions containing one binder component comprising 20 to 70 weight % of at least one polyol, 5 to 30 weight % of at least one additive as well as one hardener component comprising at least one isocyanate.

7. Procedure according to claim 6, characterised in that the clear coat compositions applied further comprise 8 to 14 weight % of mattifying agent.

8. Procedure according to claim 7, characterised in that the clear coat compositions comprising the matting agent are applied in step (e).

9. Use of the coating system made according to one of the claims 1 to 8 for backlit components.

10. Use of the system of coating layers according to claim 9, characterised in that the components have an operating function.