Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
  • C09D7/40—Additives
  • C09D7/60—Additives non-macromolecular
  • C09D7/61—Additives non-macromolecular inorganic
  • C09D7/62—Additives non-macromolecular inorganic modified by treatment with other compounds
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
  • C09D7/40—Additives
  • C09D7/70—Additives characterised by shape, e.g. fibres, flakes or microspheres
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
  • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
  • C09C1/0015—Pigments exhibiting interference colours, e.g. transparent platelets of appropriate thinness or flaky substrates, e.g. mica, bearing appropriate thin transparent coatings
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
  • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
  • C09C1/0015—Pigments exhibiting interference colours, e.g. transparent platelets of appropriate thinness or flaky substrates, e.g. mica, bearing appropriate thin transparent coatings
  • C09C1/0024—Pigments exhibiting interference colours, e.g. transparent platelets of appropriate thinness or flaky substrates, e.g. mica, bearing appropriate thin transparent coatings comprising a stack of coating layers with alternating high and low refractive indices, wherein the first coating layer on the core surface has the high refractive index
  • C09C1/003—Pigments exhibiting interference colours, e.g. transparent platelets of appropriate thinness or flaky substrates, e.g. mica, bearing appropriate thin transparent coatings comprising a stack of coating layers with alternating high and low refractive indices, wherein the first coating layer on the core surface has the high refractive index comprising at least one light-absorbing layer
  • C09C1/0039—Pigments exhibiting interference colours, e.g. transparent platelets of appropriate thinness or flaky substrates, e.g. mica, bearing appropriate thin transparent coatings comprising a stack of coating layers with alternating high and low refractive indices, wherein the first coating layer on the core surface has the high refractive index comprising at least one light-absorbing layer consisting of at least one coloured inorganic material
  • C09C1/0042—Sub-stoichiometric inorganic materials
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D1/00—Coating compositions, e.g. paints, varnishes or lacquers, based on inorganic substances
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
  • C09D5/29—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes for multicolour effects
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
  • C09D5/32—Radiation-absorbing paints
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values
  • C01P2006/62—L* (lightness axis)
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/34—Silicon-containing compounds
  • C08K3/346—Clay
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K9/00—Use of pretreated ingredients
  • C08K9/02—Ingredients treated with inorganic substances
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
  • C09C2200/00—Compositional and structural details of pigments exhibiting interference colours
  • C09C2200/10—Interference pigments characterized by the core material
  • C09C2200/1004—Interference pigments characterized by the core material the core comprising at least one inorganic oxide, e.g. Al2O3, TiO2 or SiO2
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
  • C09C2200/00—Compositional and structural details of pigments exhibiting interference colours
  • C09C2200/10—Interference pigments characterized by the core material
  • C09C2200/102—Interference pigments characterized by the core material the core consisting of glass or silicate material like mica or clays, e.g. kaolin

Definitions

• the present invention relates to a metal effect pigment-free, radar-capable coating with a metallic character on a substrate, to a method for producing such a coating and to the use of such a coating on a substrate, in particular in vehicle construction.
• radar devices With the increase in vehicles that enable autonomous driving, it is necessary to integrate radar devices into the corresponding automobile parts on a previously unimagined scale, which enable both the distance measurement to other vehicles or traffic obstacles and the measurement of the speed of other road users.
• Such radar devices are usually installed behind the bumpers of vehicles in order not to adversely affect the visual appearance of the vehicle.
• Metallic paints preferably silver-colored metallic paints
• these metallic paints pose a major challenge with regard to the visual design of paneling parts for radar devices installed inside such vehicles, because the usual metallic paints, which contain aluminum-based metal effect pigments, the radar waves, which are usually in the frequency range of 76-81 GHz , can reflect, dampen or absorb to such an extent that the use of previously customary metallic vehicle paints for cladding parts of radar devices in vehicles would lead to an undesirable reduction in the functionality of the radar devices.
• Corresponding trim parts which are designed, for example, as radiator grilles or company emblems and largely have sub-areas that are transparent to radar waves and metalized struts, often have layers of vapour-deposited metals such as indium. Such components usually show a chrome-like visual appearance.
• Such coatings are not suitable for vehicle parts which, although they are in the beam path of a radar device, are intended to give the viewer the visual impression of a conventional silver-colored metallic paint.
• the difficulty here is to achieve the strong brightness flop that is usual with metallic paints containing metal pigments (clear change from light to dark with changing lighting or viewing angles), to achieve the hiding power of such metallic paints, and to reduce the attenuation of the radar waves to such an extent that the transmission of the radar waves is sufficient to be able to operate a built-in radar device fully functionally.
• JP 2004-244516 A discloses a shiny product with high permeability to electromagnetic radiation, which can be used as a radiator grille, but also as part of another vehicle part, for example a tailgate.
• a layer on a polycarbonate panel may contain metal particles such as zinc, tin or indium, but may instead be pigmented with interference pigments such as mica coated with titanium dioxide.
• the particles are applied to the panel in a concentration of 3 to 8% by weight in a polyurethane-containing layer.
• a black base coat is then applied as a rear coating.
• the resulting glossy multilayer product is said to have high transmittance to electromagnetic radiation and high gloss.
• interference pigments made of titanium dioxide-coated mica in such coatings it is possible to achieve good transparency of radar waves, but the hiding power of metallic paints containing metal pigments and the strong metallic brightness flop that can be achieved with the latter is with such simple, transparent and colorless mica-based interference pigments not available alone.
• JP 2006-282886 A is a coating for a vehicle part which is transparent to radar waves and which contains interference pigments in a layer on a plastic substrate and dispenses with metallic effect pigments.
• the interference pigments should be based on particularly smooth substrate particles in order to enable a color variance in the coating. Silicon dioxide or alumina substrate wafers are suggested as suitable substrate wafers.
• the visual impression of a metallic finish cannot be achieved with a layer containing such interference pigments on a plastic substrate to be coated either.
• the object of the present invention is to provide a coating on a substrate which is permeable to radar waves and which is suitable for use in covering parts of radar devices, in particular in vehicle construction, and which dispenses with conventional metallic effect pigments, in particular aluminum pigments, and preferably differs visually from conventional ones differs as little as possible from silver-colored vehicle metallic paintwork and, in particular, has a silver-colored metallic appearance, high hiding power and a strong brightness flop with good transparency of radar waves.
• Another object of the present invention is to provide a method for producing the above coating.
• Another object of the present invention is to show the use of such a coating on a substrate.
• the object of the present invention is achieved by a radar-capable coating containing platelet-shaped effect pigments on a substrate, the coating being free from metallic effect pigments and having at least two layers, in this order, on the substrate:
• the object of the present invention is also achieved by a method for producing such a radar-capable coating containing no metal effect pigments and containing platelet-shaped effect pigments on a substrate, with an optionally precoated substrate consisting of a plastic plate or plastic film
• a first layer is applied as a base layer, which contains at least one absorbent pigment and is free from platelet-shaped effect pigments, and below
• a second layer is applied to the first layer, which contains platelet-shaped effect pigments with absorbent properties in an amount of at least 10% by weight, based on the weight of the solid layer, the second layer being a single layer or two or more layers one above the other arranged partial layers is applied and drying takes place after the application of each layer.
• the object of the invention is also achieved through the use of a coating as described above on a substrate as a radar-capable vehicle coating on a vehicle part.
• the present inventors have surprisingly found that it is possible to provide covering parts of radar devices in vehicle construction with coatings that have a layer containing platelet-shaped effect pigments, the coating being free of metal effect pigments overall but optically having a silver-colored metallic character.
• flake-form effect pigments which have no metal layers do not generally result in strong attenuation of the radar signal in coatings, they usually exhibit little or no intrinsic absorption and only low hiding power. These properties mean that an opaque, silver-colored coating with high gloss and a strong brightness flop, as is characteristic of metallic finishes, cannot be achieved with the usual flake-form effect pigments, which are mostly interference pigments. It was therefore necessary to find out under which conditions coatings can be obtained on cladding parts for radar devices in vehicle construction that meet the requirements for hiding power, brightness flop and radar capability without metallic effect pigments in the coating are included, but the visual appearance of a metallic finish can be imitated to a sufficient extent.
• the present inventors have found a layer structure on a substrate that satisfies the stated conditions well.
• the layer structure according to the invention therefore consists of at least one layer system of two successive layers on a substrate, with the first layer, which is located directly on the substrate or optionally also on a precoated substrate, in particular on a substrate precoated with a base layer (primer layer), contains absorbing pigments and has an achromatic colour.
• white, gray or black are not referred to as colors in professional circles, because these are achromatic optical phenomena that only describe the amount of light absorbed by the respective surface.
• white, gray and black shall be referred to as colors, deviating from this.
• the first layer of the coating according to the invention contains no flake-form effect pigments, i.e. neither metallic effect pigments nor other flake-form effect pigments such as, for example, interference pigments.
• the first layer has a solid, effect-free, neutral coloring. It completely covers the substrate or, if present, the pre-coating on the substrate.
• Organic or inorganic pigments with absorbent properties can be used as absorbent pigments for the first layer. These are essentially the classic ones Organic absorption pigments or inorganic absorption pigments All absorption pigments commonly used in various industrial coatings can be used for this. These are preferably present with a particle diameter in the range from 10 to 500 nm, in particular from 10 to ⁇ 100 nm. Preparations of absorption pigments are generally commercially available.
• systems such as Heucotint® W (Heubach, DE), Heucotint® UN (Heubach, DE), MIPA WBC (Mipa, DE), Standoblue® (Standox GmbH, DE), Standohyd® (Standox GmbH, DE), Vocaflex® (Anchemie, DE), Vocaplast® (Anchemie, DE), or others.
• absorption pigments examples include isoindolidones, benzimidazoles, quinacridones, copper phthalocyanines, perylenes, carbon black and/or titanium dioxide, to name just a few.
• Colored absorption pigments can be used in suitable mixtures in order to obtain a neutral, achromatic coloring of the first layer.
• the absorbing pigments are contained in the first layer in an amount of 1 to 50% by weight, preferably in the range of 20 to 40% by weight, based on the weight of the first layer. They can be used individually or in a mixture of two or more. Mixtures are preferably used, particularly in the case of the gray tones. The information relates to the weight of the solid layer.
• the layer thickness of the first layer is not critical to the success of the present invention.
• a layer thickness is set which completely covers the substrate or the pre-coating which may be present on the substrate and which is economically sensible.
• Customary layer thicknesses of the first layer are in the range from 5 to 15 ⁇ m, but can deviate from this if necessary.
• the layer thickness of the first layer and the concentration of the absorbing pigments in the first layer are adjusted according to the invention within the above limits such that the first layer, if it is applied as a single layer over the entire surface on a standardized black-and-white background and in L*,a *,b* color space is measured spectrophotometrically at an illumination angle of 45° and at an observation angle of 75°, a color difference AE* between the coated black background and the coated white background in the range from 0 to 5, preferably from 0 to ⁇ 2 and in particular from 0 to ⁇ 1.
• the first layer represents the base layer of the coating according to the invention on the substrate.
• a second layer is arranged directly on the first layer.
• the second layer is pigmented with platelet-shaped effect pigments, but does not contain any metal effect pigments or any other metal pigments.
• the platelet-shaped effect pigments in the second layer have absorbent properties.
• They are preferably platelet-shaped interference pigments which have a silver-grey absorption color.
• the optical effect of platelet-shaped interference pigments generally consists of a combination of reflection and transmission phenomena of light on a sequence of thin layers of which such effect pigments usually consist, usually on a platelet-shaped carrier material.
• a platelet-shaped carrier material usually consist, usually on a platelet-shaped carrier material.
• colorless materials that are largely transparent to visible light are used here, such as platelet-shaped mica pigments that are coated with titanium dioxide.
• Such pigments can have a silver interference color or colored interference colors, but are transparent overall and have no body color.
• Interference pigments acquire absorbing properties and thus a body color if either the platelet-shaped carrier or at least one of the layers located on the platelet-shaped carrier consists of a material which has its own color, ie an absorption color.
• These can be colored metal oxides, metal suboxides, mixed metal oxides or oxygen-deficient metal oxides or metal oxide hydrates.
• Interference pigments also acquire absorbing properties from layers that contain organic color pigments.
• interference pigments are preferably used in the second layer, which have at least one layer on a platelet-shaped, transparent carrier material that contains an iron oxide, a mixed oxide of iron oxide and titanium oxide, or a titanium suboxide, or have a layer that consists of carbon .
• a platelet-shaped, transparent carrier material that contains an iron oxide, a mixed oxide of iron oxide and titanium oxide, or a titanium suboxide, or have a layer that consists of carbon .
• One or more other layers of colorless, transparent materials can also be located on the platelet-shaped carrier material.
• Fe2O3 , FeO, Fe3O4 or FeOOH can be considered as iron oxides.
• Mixed oxides of iron oxide and titanium oxide are often ilmenite (FeTiO 3 ) or pseudobrookite (Fe2TiOs).
• TiO, Ti 2 O 3 , Ti 3 Os, Ti 4 O 7 , Ti 2 O, Ti 3 O or TisO can be used as titanium suboxides.
• the layer thicknesses of the absorbing layers which contain an iron oxide, a mixed oxide of iron oxide and titanium oxide, or a titanium suboxide, or of the layer consisting of carbon, are set in such a way that the interference pigment has a silver-grey absorption color. All other layers that may be present on the carrier material, on the other hand, make no contribution to the absorption color.
• colorless transparent layers on the platelet-shaped carrier material are in particular layers of colorless metal oxides or Metal oxide hydrates suitable, such as tin oxide, titanium dioxide, zirconium oxide, silicon dioxide, silicon oxide hydrate, aluminum oxide or aluminum oxide hydrate.
• Natural or synthetic mica, kaolin, talc or sericite, as well as glass, calcium aluminum borosilicate, SiO 2 , TiO 2 or Al 2 O 3 can be considered as platelet-shaped carrier materials. Preference is given to using natural or synthetic mica or A ⁇ Os flakes as platelet-shaped carrier materials.
• Interference pigments of the type mentioned are commercially available. They are available, for example, from Merck KGaA under the trade names Iriodin® 9602 Silver-Grey SW or Iriodin® 9605 Blue Shade Silver SW. These are based on mica flakes and have at least one layer containing an iron oxide or a titanium suboxide.
• interference pigments which have one or more interference layers on a transparent carrier plate and, as the final layer, a very thin, light-transmissive layer which consists of carbon.
• Such pigments have been described, for example, in the patent application EP 3795645 A1 of the present patent applicant.
• interference pigments with a silver-grey absorption color are particularly well suited for use as effect pigments with absorbing properties in the second layer, since the overall coating should have a silver-metallic appearance. Due to the pigment structure in the form of successions of thin layers on platelet-shaped substrates, such interference pigments exhibit an optically perceptible luster when incident light falls on them. The silver-grey absorption color causes a sufficiently high brightness with direct incidence of light.
• These interference pigments with absorbing properties generally have particle sizes in the range from 1 to 100 ⁇ m, in particular from 2 to 70 ⁇ m and particularly preferably in the range from 3 to 50 ⁇ m. The thickness of the interference pigments is in the range from 0.1 to 2 ⁇ m.
• the particle size of the effect pigments with absorbing properties can be determined using laser diffractometry.
• the particle size and the particle size distribution are preferably determined volume-related using a device from Malvern (Malvern Mastersizer 3000, APA300, product from Malvern Instruments Ltd., UK) in standard operation.
• the minimum amount of platelet-shaped effect pigments with absorbent properties in the second layer is 10% by weight, based on the weight of the (solid) second layer.
• the maximum amount of platelet-shaped effect pigments with absorbent properties in the second layer is 40% by weight, based on the weight of the second layer.
• These effect pigments are preferably used in the second layer in a concentration of from 15 to 35% by weight, based on their weight.
• the layer thickness of the second layer is in the range from 3 to 25 ⁇ m, preferably in the range from 5 to 20 ⁇ m.
• the second layer may also contain one or more of the absorption pigments described above for the first layer included, as long as the optical measured values for the opacity (AE*), the brightness (L*15) and the brightness flop (flop index) remain within the specified limits.
• the hiding power is determined using the AE* values, which can be determined by spectrophotometric measurement of coated substrates in the L*,a*,b* color space.
• the variable AE* is defined as the color distance of samples in the L*a*b* color space over a standardized black and white background with an illumination angle of 45° and an observation angle of 75° and is determined using the formula:
• the second layer used in the coating according to the invention has an AE* value in the range from 0 to 20, preferably in the range from 5 to 20, when the second layer with a layer thickness in the range of 14 ⁇ 2 ⁇ m is applied to the black-and-white substrate is applied and measured under the above measurement conditions. These values indicate sufficient hiding power of the second layer for the purposes of the present invention.
• the L*15 value of a coating which is photometrically in the L*,a*,b* color space on a standardized basis, is the measure of the brightness of a layer black and white background with an illumination angle of 45°. In order to be suitable as a coating according to the invention, it should have a minimum brightness that is obtained both over a white and over a black base layer.
• a second layer is obtained which, if it is applied over the entire surface to a black-and-white background with a layer thickness of 14 ⁇ 2 ⁇ m and in the L*,a*,b* color space is measured spectrophotometrically at an illumination angle of 45° and an observation angle of 15°, has a brightness L*15 of at least 105 on the coated white background and on the coated black background.
• the flop index is in the range of at least 10 both on a white and on a black-coated background if the second layer, if it is applied over the entire surface to a black-and-white background with a layer thickness of 14 ⁇ 2 ⁇ m and is in the L*, a*,b* color space is measured spectrophotometrically under an illumination angle of 45° and at observation angles of 45°: as15°, 45°: as45° and 45°: as110°.
• the flop index is a measure of the brightness flop at changing viewing angles and is determined using the formula: Specifying upper limit values does not make sense either for the brightness L*15 or for the flop index, since both variables have open upper limits and measurement results that are above the specified minimum values always have a positive effect if the opacity is maintained in the specified range affect the overall visual result.
• the lightness flop of the coating according to the invention can be significantly improved, especially on a gray or black first base layer on a substrate, if the second layer consists of two or more, preferably three or four partial layers arranged one on top of the other, without having to accept any significant deterioration in the hiding power or the brightness of the overall coating.
• the total dry layer thickness of the second layer in these cases is preferably only in the range from 5 to 15 ⁇ m.
• At least one of the sub-layers preferably two or three of the sub-layers, has a dry layer thickness of ⁇ 5 ⁇ m.
• the dry layer thickness of at least one of the partial layers is ⁇ 4 ⁇ m or ⁇ 3 ⁇ m, particularly preferably about 2 ⁇ m. These extremely small layer thicknesses can preferably also be present in two or three of the partial layers.
• smooth surfaces of the individual sub-layers are required. These result from interfaces between the individual sub-layers of the second layer, which are largely parallel to the base layer or to the coated substrate are arranged.
• the interfaces are obtained by intermediate drying after the application of each of the individual sub-layers.
• the intermediate drying aligns the platelet-shaped effect pigments with absorbing properties in each of the sub-layers with their main axes approximately parallel to the surface of the first layer (and the substrate) and thus achieve good reflection of the incident light in each of the sub-layers.
• the pigment loading of the individual partial layers is likewise at least 10% by weight of platelet-shaped effect pigments with absorbent properties and is at most 40% by weight, based in each case on the weight of the individual partial layer. Preference is given to using 15 to 35% by weight of flake-form effect pigments with absorbent properties in each of the partial layers.
• Radar-capable in the context of the present invention is understood to mean a coating that has a permittivity of ⁇ 30 when exposed to electromagnetic waves with a peak frequency of 76.5 GHz. Furthermore, it is required that the coating on a 350 ⁇ m PET substrate has a one-way transmission loss of ⁇ 2 dB when exposed to electromagnetic waves with a peak frequency of 76.5 GHz.
• the measurement of the permittivity of the coating and the one-way transmission attenuation of the coating on the substrate are carried out using a device of the type RMS-D-77/79G from devisns GmbH, Germany, in standard operation.
• binders and binder systems which appear transparent in the solidified state can be used as binders for the first and second layer of the coating according to the invention. All common types of binders can be used here, which are usual coating processes are used and are compatible with the pigments used. Solvent-based binder systems, water-based binder systems and radiation-curing binder systems can all be used, provided that the usual special features are taken into account when selecting the pigment and with regard to the coating process.
• Both the first and the second layer of the coating according to the invention can contain other customary additives such as fillers, inhibitors, flame retardants, lubricants, rheological aids, dispersants, redispersants, defoamers, leveling agents, film formers, adhesion promoters, drying accelerators, photoinitiators, etc.
• additives such as fillers, inhibitors, flame retardants, lubricants, rheological aids, dispersants, redispersants, defoamers, leveling agents, film formers, adhesion promoters, drying accelerators, photoinitiators, etc.
• the second layer consists of two or more sub-layers
• rheological aids are usually indicated.
• Substances such as BaSC, polyamide powder, silicates or other rheology aids familiar to the person skilled in the art, but in particular nanofibers based on cellulose, come into consideration as rheological aids. The latter are used with particular preference.
• the coating compositions used to produce the first and second layer of the coating may also contain organic solvents and/or water, which, however, are no longer present in the coating according to the invention after the two layers have solidified.
• the customary solvent systems can be used without restrictions.
• Corresponding compositions for binder systems, including solvents and additives, are well known to those skilled in the art and some are also commercially available in the unpigmented state as finished products. A person skilled in the art can make a corresponding selection on the basis of the particular pigmentation to be used and the desired coating method. Plates or foils made of plastic can be used as the substrate on which the coating according to the invention made up of the first and second layer is applied if the coating is to be radar-capable.
• plastics commonly used in automotive construction can be used, for example substrates made of polycarbonate (PC), polypropylene (PP), polyurethane (PUR), polymethyl methacrylate (PMMA), acrylonitrile butadiene styrene (ABS) or acrylonitrile ethylene styrene ( AES) just to name a few.
• Such plastic plates or plastic foils have a certain basic attenuation of the radar signal, which should only increase slightly as a result of the coating on them.
• the value of the basic attenuation of the radar signal with regard to the one-way transmission, which is present through the respective substrate is contained in the measured values.
• the basic attenuation of the one-way transmission of the radar signal caused solely by the substrate is listed separately in Example 4. A measurement of the attenuation of the radar signal caused solely by the coating is not possible for technical reasons.
• the coating according to the invention is to be applied to substrates for purely optical reasons and if the focus is not on the radar capability of the coating, metallic or metal-containing substrates can of course also be used.
• the substrates can be shaped three-dimensionally depending on the intended use, ie can have a three-dimensional external shape.
• a plastic plate that is intended to form part of a tailgate of a vehicle naturally has a different three-dimensional external shape than a plastic plate provided as a shock absorber.
• the three-dimensional shape of the substrate is produced by means of customary shaping methods before the coating according to the invention is applied.
• An indispensable core element of the coating according to the invention on a substrate is the package made up of the first and second layers described above, with the second layer being arranged directly on the first layer, viewed from the substrate.
• further layers can optionally be located between the substrate and the first layer and/or above the second layer, which can also be part of the coating according to the invention.
• the coating according to the present invention can have a base coat (primer coat) and/or a clear coat coat. According to the invention, all the customary materials that are widely used industrially and therefore do not require any further discussion can be used here.
• the coating according to the invention on a substrate can be used to advantage wherever radar devices are to be provided with panels that visually have a silver-colored effect coating, without the functionality of the radar devices being adversely affected. Of course, this applies in particular to trim parts that are used in vehicle construction.
• the coating according to the invention is therefore preferably a vehicle paint finish. Due to its good optical properties, this can of course also be used for all types of paintwork that should look as similar as possible to a standard silver-colored metallic paintwork.
• the existing radar wave permeability can also play a subordinate role and the corresponding areas of application are not limited to vehicle construction.
• the present invention also relates to a method for producing a radar-capable coating which is free of metal effect pigments and contains flake-form effect pigments on a substrate as described above, wherein a first layer is applied as a base layer to an optionally precoated substrate made of a plastic plate or plastic film, said first layer being at least contains an absorbent pigment and is free of platelet-shaped effect pigments, and a second layer is subsequently applied to the first layer, which layer contains platelet-shaped effect pigments with absorbent properties in an amount of at least 10% by weight, based on the weight of the solid layer, wherein the second layer is applied as a single layer or in two or more partial layers arranged one on top of the other and drying takes place after the application of each layer.
• the two layers of the coating can be applied to the substrate by means of customary coating methods, for example by spraying methods, brushing methods, inmold methods, roller coating methods, coil coating methods or curtain coating methods.
• Such coating processes are common on an industrial scale and can be used in a skilled manner.
• Spraying methods are preferably used. Customary spraying technologies, in which dry layer thicknesses in the range from 5 to 25 ⁇ m can be obtained with a single spraying process, are suitable for producing the coating according to the invention.
• two coating processes are sufficient here, in which after the application of the first layer, with or without intermediate drying, the second layer is applied immediately, the layer(s) are dried and both layers are cured in the composite .
• spray methods are particularly suitable which allow successive partial layers to be applied to the first layer of the coating according to the invention in several work steps with a very small dry layer thickness of the individual partial layers.
• the preferably two to four sub-layers are each dried after the application of each individual sub-layer, so that interfaces between the individual sub-layers are formed.
• the temperature for drying the individual layers depends on the respective binder system and the solvents used and is at least 20°C. Temperatures up to 150°C, preferably up to 100°C, can be used.
• the amount of platelet-shaped effect pigments with absorbent properties in the second layer is at least 10% by weight for each of the individual partial layers, based on the weight of the dry layer, but can be in the range from 10 to 40% by weight, in particular in the range from 15 to 35% by weight.
• the dry layer thickness of at least one of the partial layers is ⁇ 5 ⁇ m, preferably ⁇ 4 ⁇ m and in particular ⁇ 3 ⁇ m or approx. 2 ⁇ m. Two or three partial layers preferably have such small layer thicknesses.
• the high pigment concentration in the respective sub-layers with a very low dry layer thickness of the sub-layers can be adjusted by the proportion of binders in the respective coating composition greatly reduced (approx. 6 to 7% by weight solids content) and the proportion of solvent (preferably water) is greatly increased. So that such a highly diluted coating composition can form a continuous coating film on the substrate, various auxiliaries, in particular rheology auxiliaries, are added, which ensure that the coating composition has a suitable viscosity, so that it can be applied to the substrate by means of a spraying process and shows good leveling properties .
• cellulose-based nanofibers are preferably added as rheological aids in an amount of 5 to 20% by weight, based on the weight of the coating composition.
• the multiple application of partial layers arranged one on top of the other and the respective intermediate drying of the partial layers allows the platelet-shaped effect pigments in the second layer to be oriented particularly well, so that a high level of reflection of incident light is obtained at the surface of the second layer.
• the brightness flop of the overall coating in particular improves without there being any significant limitations in terms of hiding power or the brightness of the entire layer structure.
• a particularly preferred embodiment of the coating according to the invention can thus be obtained on a substrate with platelet-shaped effect pigments with absorbent properties in the second layer and without the use of metal pigments of all kinds in the overall coating, which optically has a silver color Similar to metallic paint, but with good radar capability when applied to a plastic substrate.
• the plastic substrates used which have predefined radar properties, can optionally be pre-coated, for example with one or more primer and/or coloring layers.
• the entire coating is to have a radar-capable character, it must be ensured that none of the optionally additionally present layers on the respective substrate contain metallic effect pigments or other components that could interfere with the necessary radar wave permeability of the entire coating.
• primer layer Pre-coating the plastic substrate with a primer layer (primer layer) is advantageous because such primer layers improve, among other things, the mechanical stability of the overall coating and the adhesion of the first layer of the stack of layers on the substrate.
• outermost layers of clear lacquer which are generally colorless and transparent to visible light, are advantageous in particular for the mechanical stability and weathering resistance of coatings. In the present invention, too, they are preferably applied to the upper layer of the layered composite of the first and second layers as the outermost layer of the overall coating.
• the overall coating is subjected to at least one curing process, which takes place either after the application and drying of the second layer on the substrate and/or after the application of the clear coat.
• the curing of coatings on substrates, especially in the automotive sector, is a common practice and does not need to be described in more detail.
• the present invention also relates to the use of the coating described above, which is free of metallic effect pigments, as a radar-capable coating Vehicle painting on a vehicle part. It can be applied to all vehicle parts that are based on base bodies (substrates) made of plastic. Metal substrates are not suitable because they cannot guarantee the desired radar capability.
• the coating can be applied to outer body parts that are intended as outer covering or facing parts for radar devices installed in the vehicle interior, or it can also be applied to the full surface of suitable body parts. Bumpers, tailgates, radiator grilles, fenders or parts of these are to be mentioned in particular as body parts.
• the coating according to the invention can also be applied to vehicle parts other than those mentioned and in particular also to metal-containing substrates if only the visual appearance of a metallic coating is of interest and radar capability is not required.
• the field of application of the invention is not limited to vehicle construction.
• black and white coated Leneta sheets (white and black base layer already present on the respective partial area) are coated with a second layer.
• the coating is carried out as a pneumatic spray coating.
• the preparation WBC 000 from MIPA SE, DE, is used as the binder.
• all samples are coated with a standard 2K clear coat.
• the second layer is pigmented with interference pigments with a silver-grey absorption color in the amounts indicated in the tables.
• Effect pigment A Mica-based interference pigment with coating of SnC, TiO2 and carbon (C content 1.14%), particle size 5-25 pm;
• Effect pigment B Interference pigment based on aluminum oxide flakes with a coating of SnO2, TiC>2 and carbon (C content 0.44%), particle size 5-30 pm;
• Effect pigment C Mica-based interference pigment with a coating of SnO2, TiO2, titanium suboxide and additives, particle size 5-40 pm
• coating compositions containing pigments A, B and C with a pigment mass concentration of 18% by weight, based on the weight of the solid second layer are applied in a single coating operation to the standardized black and white coated Sheets applied and dried at 80 ° C for 5 minutes.
• the second layer is applied in four partial layers (each 18% by weight PMK, layer thicknesses 9, 2, 2, 2 ⁇ m, drying 5 minutes each at 80°C), there are only slight changes in the hiding power compared to the single-layer process.
• Table 1 Hiding power Sublayers: Number of sublayers of the second layer of the coating
• PMK pigment mass concentration of effect pigment in each of the partial layers
• TSD dry layer thickness of the entire second layer, consisting of x
• L* Brightness value L* in the L*a*b* color space at observation angle 15°, illumination angle 45°
• AE* Color distance of samples in the L*a*b* color space over a standardized black and white background (illumination angle 45°, observation angle 75°), determined according to the formula:
• Flop index Measure of the brightness flop at changing viewing angles (illumination angle 45°, viewing angle 45°: as15°, 45°: as45°, 45°: as110°), determined using the formula:
• the effect pigments A, B and C are applied as in Example 1 to the respective black or white background.
• the same pigments are applied to the black or white coated substrate with a pigment mass concentration of 30% by weight, based on the weight of each partial layer, in a three-stage process in a layer thickness of approx. 2 ⁇ m per partial layer (drying after each Application: 80°C, 5 min.).
• Customary silver metallic coatings which generally contain aluminum pigments, have flop indices in the range from about 12 to 17.
• the colorimetric measurement of the samples is carried out using a BYKMac i color measuring device (from Byk-Gardner) in SMC5 mode.
• the black-and-white sheets used here as a substrate meet the ASTM E 1347 standard and are marketed by the Leneta company under the name Metopac T12G sheets. From the tables it can be seen that the coatings according to the invention with each of the interference pigments used with silver-grey absorption color and each of the variants of the coating process used achieve good brightness and a strong brightness flop with satisfactory hiding power and are therefore able to metallic coatings containing aluminum pigments , to imitate optically in a good to very good way. Since the coatings do not contain any metal pigments, a significant attenuation of radar waves by the respective coating on a substrate is not to be expected.
• a 350 ⁇ m thick PET film (Hostaphan RN 350, Mitsubishi Polyester Film GmbH, DE) is used as the substrate.
• the coating is carried out as a pneumatic spray coating.
• the preparation WBC 000 from MIPA SE, DE, is used as the binder.
• a completely covering layer in RAL color 7037 (dusty grey) is applied as the first layer.
• a layer with the interference pigments listed in Table 4 with a silver-grey absorption color is applied as the second layer in each case in one or four partial layers and dried as described in Example 1.
• Table 4 shows the dielectric constant (permittivity) of the respective layer structure and the attenuation of the radar signal in dB for a single beam passage (76.5 GHz) (device: RMS-D-77/79G from devisns GmbH, DE, standard operation)
• the uncoated PET substrate has a permittivity of about 3.2 and a radar wave attenuation of 1.05 dB.

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• 2021
  • 2021-09-27 KR KR1020237014151A patent/KR20230074789A/ko unknown
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