High wear resistant composite structure, preparation and use thereof

Abstract

A composite structure comprising a finishing layer disposed on a base layer wherein the finishing layer is based on a cured polymer and is obtainable by a process comprising radiation curing a topcoat applied on the base layer and comprising a radiation curable compound to obtain a cured polymer; a method of making a composite structure; and the use of the composite structure for the interior of a vehicle.

Description

Technical Field

[0001] The present invention relates to a composite structure having high wear resistance, a method for preparing the composite structure and the use of the composite structure, in particular as artificial leather in touch interface applications in vehicles. Background Art

[0002] EP 3 575 121 A1 discloses a composite structure comprising a translucent layer, an opaque layer containing a translucent area and a touch sensor, and is used for hidden-until-lit applications. The translucent layer may be coated with a translucent lacquer layer.

[0003] EP 3 723 981 A1 discloses a component with a decorative surface and with a signal or operating element arranged in the surface, wherein the component comprises a component carrier as a supporting structure and a multilayer film arranged on its exterior, wherein the layers forming the film consist of a flexible, elastomeric and reversibly deformable polymer, and wherein the component carrier comprises means acting on the film for regional deformation of the film, and means for regional transillumination of the film. The multilayer film can be coated with a lacquer layer.

[0004] Problems to be solved by the present invention

[0005] Touch interfaces need to have high wear resistance. Since the paint layers used in the prior art do not adequately meet this requirement, the problem underlying the present invention is to provide a composite structure for touch interface applications that has high wear resistance. Another problem to be solved is to provide a composite structure with increased wear resistance while keeping other properties such as translucency, gloss and color unaffected. Summary of the invention

[0006] The problem underlying the present invention is solved by providing a new composite structure coated with a finishing layer having high wear resistance.The present application covers the following aspects [1] to

[15] .

[0007] [1] A composite structure comprising a finishing layer arranged on a substrate layer and a touch sensor below the substrate layer, wherein the finishing layer is based on a cured polymer and can be obtained by a process comprising radiation curing a topcoat to obtain the cured polymer, the topcoat being applied on the substrate layer and containing a radiation curable compound.

[0008] [1-1] The composite structure according to aspect [1], wherein the base layer has a thickness of 30 μm to 3000 μm, preferably 50 μm to 1000 μm.

[0009] [1-2] The composite structure according to aspect [1] or [1-1], wherein the finishing layer has a thickness of 5 μm to 100 μm, preferably 5 μm to 50 μm.

[0010] [1-3] The composite structure according to any one of the preceding aspects, wherein the radiation curable compound contains radiation curable carbon-carbon double bonds.

[0011] [1-4] The composite structure according to any one of the preceding aspects, wherein the finishing layer consists of two or more layers, preferably each layer contains a radiation curable compound. The two or more layers may have the same composition or different compositions.

[0012] [1-5] The composite structure according to any one of the preceding aspects, wherein the cured polymer is a cross-linked polyurethane.

[0013] [1-6] A composite structure according to any one of the preceding aspects, which contains the following structural elements beneath the base layer: an opaque area or an opaque layer having an opaque area and a translucent area; a touch sensor contained in a touch sensor area or a sensor layer including a touch sensor area; an optional light source; an optional supporting layer; and an optional soft layer.

[0014] [1-7] A composite structure according to any one of the preceding aspects, wherein the base layer has a light transmittance of 1% to 50% and includes an opaque layer containing a translucent area and a touch sensor area, and the touch sensor area is at least partially arranged in, above or below the translucent area of ​​the opaque layer.

[0015] [1-8] The composite structure according to aspect [1-6], wherein the opaque layer containing the semi-transparent area is a mask layer.

[0016] [1-9] A composite structure according to any one of aspects [1-6] to [1-8], comprising a sensor layer, wherein the sensor layer includes the touch sensor area and at least an electrical conductor connected thereto.

[0017] [1-10] A composite structure according to any one of aspects [1-6] to [1-9], wherein the touch sensor area contains the touch sensor completely arranged below the opaque area of ​​the opaque layer, and a translucent area at least partially arranged below the translucent area of ​​the opaque layer.

[0018] [1-11] A composite structure according to any one of aspects [1-6] to [1-10], comprising the base layer, the opaque layer containing the translucent area, the touch sensor and an optional support layer in this order, wherein the support layer is translucent or at least partially translucent.

[0019] [1-12] A composite structure according to any one of aspects [1-6] to [1-11], which contains a light source, which is arranged in or attached to at least one of the layers selected from the opaque layer containing the translucent area, the translucent sensor layer and the support layer.

[0020] [1-13] A composite structure according to any one of aspects [1-6] to [1-12], comprising a soft layer, which is contained in the base layer below one or more dense layers or arranged between the base layer and the opaque layer or between the opaque layer or the sensor layer if present and the support layer.

[0021] [1-14] According to any one of aspects [1-6] to [1-13], the composite structure can be obtained by a method comprising the following steps: a step of printing an opaque mask layer on the base layer, and a subsequent step of printing the touch sensor (preferably in the form of a sensor layer) on the mask layer.

[0022] [1-15] A composite structure according to any one of the preceding aspects, wherein the finish layer is the visible side of the composite structure, and the base layer is a translucent layer, the translucent layer being selected so that other elements of the composite structure are not visible in the absence of light emitted from a light source, the light source being arranged in or at the rear side of the composite structure.

[0023] [1-16] A composite structure according to aspect [1-15], wherein the translucent elements of the composite structure are selected to allow transmission of visible light emitted from a light source, and the opaque areas of the composite structure are selected to suppress transmission of visible light emitted from a light source, wherein the light source is arranged in or at the rear side of the composite structure.

[0024] [2] A composite structure according to any one of the preceding aspects, wherein the composite structure is a flexible film.

[0025] [2-1] The composite structure according to aspect [2], wherein the finishing layer, the base layer, and the touch sensor are flexible.

[0026] [2-2] The composite structure according to aspect [2] or [2-1], wherein if it contains a support layer, the composite structure is flexible in the absence of the support layer.

[0027] [3] A composite structure according to any one of the preceding aspects, wherein the radiation curing comprises excimer curing.

[0028] [3-1] The composite structure according to aspect [3], wherein the excimer curing is a first curing step in the radiation curing of the topcoat.

[0029] [4] A composite structure according to any one of the preceding aspects, wherein the first step of radiation curing is a step of excimer curing the surface of the topcoat composition, and the second step of radiation curing is a step of UV curing the entire topcoat composition; preferably, the radiation curing consists of the first step and the second step.

[0030] [4-1] The composite structure according to any one of the preceding aspects, wherein the finishing layer has a nanostructure on its surface.

[0031] [4-2] A composite structure according to aspect [4-1], wherein the surface of the composite structure has a texture and surface folds on the texture, wherein the depth of the depressions of the textured surface structure is in the range of 10 μm to 1000 μm, and the depth of the depressions of the surface folds is in the range of 10 nm to 5000 nm, preferably 10 nm to 1000 nm.

[0032] [4-3] The composite structure according to any one of aspects [4] to [4-2], wherein the finishing layer contains a photoinitiator.

[0033] [5] The composite structure according to any one of the preceding aspects, wherein the finishing layer contains depressions and protrusions on its surface, wherein the depth of the depressions is 10 nm to 1000 nm.

[0034] [6] A composite structure according to any of the preceding aspects, in particular according to aspects [4], [4-1], [4-2] or [4-3], wherein a sample of the composite structure shows only slight matting after 10,000 cycles, preferably after 40,000 cycles, at 5 N in an abrasion test according to DIN EN 60068-2-70 and has an unchanged overall structure.

[0035] [7] A composite structure according to any of the preceding aspects, wherein the touch sensor is a printed structure.

[0036] [8] The composite structure according to any one of the preceding aspects, wherein the base layer is a semi-transparent layer having a light transmittance of 1 to 50%.

[0037] [8-1] The composite structure according to aspect [8], wherein the composite structure has a light transmittance of 1 to 50%.

[0038] [8-2] The composite structure according to aspect [8] or [8-1], wherein the base layer, the finishing layer and the composite structure are translucent.

[0039] [9] A method for preparing a composite structure comprising a substrate layer and a finishing layer comprising a cured polymer disposed on the substrate, the method comprising the following steps:

[0040] (i) providing a substrate comprising a substrate layer as a top layer or consisting of a substrate layer;

[0041] (ii) providing a liquid topcoat comprising a radiation curable compound;

[0042] (iii) applying a liquid topcoat on the base layer to obtain a topcoat layer;

[0043] (iv) radiation curing the radiation curable compound of the topcoat layer to produce a cured polymer and obtain the composite structure, wherein the radiation curing comprises or consists of a first step of excimer curing and a second step of UV curing.

[0044] [9-1] The method according to aspect [9], wherein the topcoat contains a solvent and / or water, and the method includes drying the topcoat layer before step (iv).

[0045] [9-2] The method according to aspect [9], wherein the topcoat is an aqueous dispersion of the radiation curable compound.

[0046] [9-3] The method according to any one of aspects [9] to [9-2], wherein step (iii) is performed in a roll-to-roll process.

[0047] [9-4] The method according to any one of aspects [9] to [9-3], wherein the radiation curable compound is a polymer containing radiation curable carbon-carbon double bonds such as polyurethane.

[0048]

[10] A method according to any one of aspects [9] to [9-2], wherein the radiation-curable compound of the topcoat contains polymerizable groups that cannot be polymerized by radiation curing, and step (iv) includes a step (iv-1) of subjecting the topcoat layer to polymerization of the polymerizable groups and a step (iv-2) of irradiating to crosslink the radiation-curable compound, wherein the step (iv-1) is carried out before, after or simultaneously with the step (iv-2).

[0049] [10-1]A method according to aspect

[10] , wherein the polymerization in step (iv-1) is a reaction of a prepolymer with a chain extender, and the reaction optionally uses a catalyst.

[0050]

[11] A method according to aspect [9] or

[10] , wherein the topcoat contains a diisocyanate, a polyol and a photoinitiator, wherein the diisocyanate is a radiation-curable compound and / or the polyol is a radiation-curable compound.

[0051] [11-1]A method according to aspect

[11] , wherein the diisocyanate and / or the polyol contains radiation-curable carbon-carbon double bonds, preferably (meth)acrylate groups.

[0052]

[12] A method according to any one of aspects [9] to

[11] , wherein the first step of radiation curing is a step of excimer curing the surface of the topcoat composition, and the second step of radiation curing is a step of UV curing the entire topcoat composition.

[0053]

[13] A method according to any one of aspects [9]-

[12] , wherein the step of excimer curing forms a nanostructure on the surface of the finish layer.

[0054]

[14] A composite structure obtainable by a method according to any one of aspects [9] to

[13] .

[0055]

[15] Use of a composite structure according to any one of aspects [1] to [8] or

[14] as a material for vehicle interiors.

[0056] Advantages of the present invention

[0057] The finishing lacquer imparts high abrasion resistance to the composite structure of the present invention. The composite structure retains its structure and gloss after standard wear tests.

[0058] The composite structure with high abrasion resistance can be used in touch interface applications. A combination with seamless and matte hiding applications is possible. The finish layer can combine the properties of high abrasion resistance and translucency.

[0059] The composite structure can be used in vehicle interiors and can be artificial leather. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 The production of a composite structure according to the invention by a method according to an embodiment of the invention is shown. Figure 1 (A): A topcoat (2) is applied to a base layer (1). Figure 1 (B): The topcoat is exposed to excimer radiation. The parameters of the excimer radiation are adjusted so that only the upper part (3) of the topcoat layer is cured. Curing conditions such as a high curing speed lead to the formation of a structured surface containing peaks and valleys. Figure 1 (C): The topcoat is exposed to UV radiation to fully cure the topcoat, thereby obtaining a final finish (4). DETAILED DESCRIPTION

[0061] The composite structure of the invention is preferably a flexible film. In this context, a flexible structure such as a flexible film is a non-self-supporting structure; in particular, it is dimensionally unstable and bends without a dimensionally stable support, such as a support layer, and such a support may be required to be suitable for the intended use as a material for vehicle interiors. The finishing layer and the base layer preferably have a total thickness of 30 μm to 3000 μm, more preferably 50 μm to 2000 μm.

[0062] The composite structure includes a layer structure and is itself a layer structure. The plane of the layer of the composite structure is sometimes referred to as the "layer plane" in the present invention. The composite structure can be defined by its visible side, that is, the upper side of the finish layer disposed on the base layer that may have a texture. This side is also referred to as the A side. The lower side is referred to as the B side. These names apply to all layers of the composite structure. This means that the side facing the base layer is the A side of the layer, and the back side is the B side of the layer. The direction within the same layer plane is referred to as the horizontal direction, and the direction from one layer plane to another layer plane, in particular the direction perpendicular to the layer plane, is referred to as the vertical direction within the composite structure. The terms "above" and "below" refer to positions perpendicular to the layer plane. In the composite structure of the present invention, the finish layer, the base layer and the touch sensor are arranged in sequence from the A side to the B side.

[0063] The composite structure may be textured. The texture may be geometric or may be intended to imitate natural leather. The textured surface structure contains depressions and protrusions. The depth of the depressions of the textured surface structure is generally in the range of greater than 10 μm to 2000 μm, preferably greater than 10 μm to 1000 μm. Therefore, the textured surface structure is preferably a microstructure. In any case, the size of the textured surface structure is greater than the size of the surface folds obtained by radiation curing. Radiation curing may result in surface folds on the finishing layer. The surface folds contain depressions and protrusions. The depth of the depressions of the surface folds is preferably in the range of 10 nm to 1000 nm. Therefore, the surface folds produce nanostructures. In one embodiment, nanostructured surface folds may be present on the microstructured texture of the finishing layer. In the present invention, the depth of the depression can be determined by microscopically detecting the depressions and protrusions in the cross-sectional view of the sample, measuring the height of the peaks of two adjacent protrusions, determining the average of the two heights, and taking the difference between the average height and the height of the bottom of the depression as the depth of the depression.

[0064] The composite structure can be translucent. Therefore, the base layer, the finishing layer and the optionally included additional structural elements can be translucent. When light is emitted from the same light source and hits the structure, a "translucent" structure allows more visible light to be transmitted than an "opaque" structure. In the present invention, the meaning of the term "translucency" covers the meaning of "transparency". In general, transparency is a physical property that allows light to pass through a material without being scattered. Translucency is a superset of transparency and allows light to pass through and allows scattering. In other words, a translucent medium allows light transmission, while a transparent medium allows not only light transmission but also image formation. Transparent materials appear transparent. Since the value of transmittance is affected by absorption, scattering, reflection, etc., the exact transmittance values ​​of different parts of the composite structure may vary depending on the type of light source, the composition and thickness of each layer. For different wavelength ranges, the transmittance is also different.

[0065] In one embodiment, the semi-transparent structure is defined as a lighting system with relatively low luminous power, such as a light source, such as a 0.5 watt LED, so as to achieve between 2 and 4 cd / m 2 (cd = candela) or even between 2 and 5 cd / m 2 The brightness of the composite structure between the two thus achieves a suitable background lighting, wherein the elements arranged under the translucent layer are not noticeable as long as the lighting system is deactivated. This type of lighting is also called dark hidden lighting.

[0066] The various semi-transparent layers of the composite structure may differ in their respective light transmittances. For example, the light transmittance of the composite structure in the vertical direction from the B side to the A side or from the light source to the A side through the semi-transparent region may be 1% to 50%, preferably 1% to 30%, more preferably 2% to 20%, and even more preferably 5% to 10% in the wavelength range of 400nm to 700nm.

[0067] The opposite property of translucency is opacity. The light transmittance of the opaque part of the composite structure can be less than 1%, preferably less than 0.1%, and preferably 0%. The values ​​preferably relate to the wavelength range of 400 to 700 nm. In a preferred embodiment, the term "opaque" means that the light transmittance in the wavelength range of 400 to 700 nm is less than 1%. In any case, the light transmittance of the opaque layer is lower than the light transmittance of the semi-transparent layer. For example, if the light transmittance of the semi-transparent layer is at least 2%, the light transmittance of the layer contained in the same composite structure and referred to as "opaque" is less than 2%.

[0068] The light transmittance of the composite structure is ultimately determined by the composite structure of the material, wherein the light transmittance of the base layer can be low to achieve the desired property of hiding other elements when the light source is deactivated, i.e., the other elements are hidden by the absence of light. When the light source is deactivated, the upper side of the composite structure has the appearance of a conventional structure, such as the appearance of conventional artificial leather. In order to be able to hide the properties of the elements arranged below the translucent layer, the light transmittance of the base layer is preferably 1 to 50%, more preferably 1 to 30%, still more preferably 2 to 20% or 5 to 10% in the wavelength range of 400 to 700 nm.

[0069] The translucent element and the light source can be adjusted to each other in such a way that a light intensity of 1 to 20 cd / m 2 , preferably 2 to 20 cd / m 2 , more preferably 2 to 10 cd / m 2 or 2 to 8cd / m 2 brightness.

[0070] The light transmittance of the layer structures described in this application (i.e., individual layers or any composite structure) was determined as follows: Equipment: Datacolor, Model 850; Lamp: Xenon lamp. The total transmittance was measured according to the user guide provided by the manufacturer. A white plate (e.g. The white plate is used as an optical standard for transmission calibration and measurement. The white plate is placed at the front aperture plate. The sample to be measured is placed against the sphere. At the wavelength λ of the maximum transmittance peak of the sample max The transmittance [%] of a sample is defined as 100% x (in the presence of a layer structure at λ max Transmittance value measured at λ) / (transmittance value measured at λ in the absence of a layer structure max The transmittance value measured at ).

[0071] In some examples, graphic designs, images, patterns, etc. are provided in the composite structure. In this specification, the elements may be collectively referred to as graphics. For example, decorative patterns or indicative patterns may be applied. The pattern may be colored, such as red, to simplify the user's orientation when the light source is activated or to draw the user's attention to the illuminated area. Examples of applying graphics are inkjet printing and screen printing.

[0072] Whenever it is mentioned in the context of this specification that an individual component or element is based on or made of a certain material, this should be interpreted as the corresponding material forming the main component of the component, wherein small amounts of other components may also be present. In an embodiment, the term "based on" or "made of" a certain material means a content of more than 50%, preferably 90%, more preferably 95%.

[0073] In this specification, compounds, elements and components are often described in the singular form, such as "a" or "the" compound. It is emphasized that, unless otherwise stated, these formulations do not in any way exclude the presence of more than one of the indicated compounds, components or elements.

[0074] The terms "comprises," "comprising," "including," and "having" are inclusive and thus specify the presence of stated features, components, layers, elements, and / or steps, but do not preclude the presence or addition of one or more other features, components, layers, elements, steps, and / or groups thereof. Unless specifically noted as an order of execution, the method steps, processes, and operations described herein should not be construed as necessarily requiring their execution in the particular order discussed or illustrated. It should also be understood that additional steps may be employed.

[0075] The term "and / or" includes any and all combinations of one or more of the associated listed items.

[0076] In the present invention, unless otherwise stated, the standards and specifications mentioned refer to the latest versions available at the time of filing this application.

[0077] In the present invention, unless otherwise specifically stated, percentage (%) is mass percentage (mass %).

[0078] Basal layer

[0079] The substrate layer covers all other layers and elements of the composite structure of the present invention except the finishing layer. The substrate layer can be a single layer or a multilayer structure and can be composed of or include one or more dense layers and / or one or more foam layers. Preferably, the substrate layer comprises two or more layers. These layers can differ in composition, thickness, translucency and any other properties. In particular, the uppermost layer, i.e. the layer in contact with the finishing layer, can be a primer. The primer is a primer that provides good adhesion of the finishing layer to the substrate and provides a barrier to prevent substances (e.g., plasticizers in the case of PVC) from migrating from the substrate.

[0080] The substrate layer can be a single layer structure, such as a film. It can be composed of or include a film, for example, composed of or include the following film: TPO, polylactic acid (PLA), thermoplastic elastomer (TPE), polyamide (PA), polybutadiene (PB), polyurethane (PUR), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), polyvinyl chloride (PVC) or a combination thereof. Preferred materials are TPO, TPU, PUR or PVC. The film can be coated with a primer. In this case, the substrate layer is a primer or a composite structure of a film and a primer, respectively.

[0081] The substrate layer may be flexible and soft. In one embodiment, the translucent layer has a soft touch, such as a Shore A hardness in the range of 60 to 80, for example about 70. The Shore A hardness referred to in the present invention is defined in DIN 53505.

[0082] The base layer is coated with a finishing layer, ie the uppermost component at the A side of the base layer, and / or may have a textured surface structure to simulate natural leather.Additives may be included in the base layer.

[0083] The additives contained in the base layer may be additives that make it resistant to UV and / or high temperatures. Two types of light stabilizers can be used, namely ultraviolet light absorbers (UVA) and hindered amine light stabilizers (HALS). Several types of UVA are commercially available, such as benzotriazole, which provides the widest spectrum coverage. Triazine is also an option. HALS captures free radicals to maintain surface properties such as gloss and prevent paint cracking and chalking. When combined, UVA and HALS provide a synergistic effect and provide the simplicity of the formulation. Regarding thermal degradation, suitable products are, for example, N, N'-1,6-hexanediylbis[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenylpropanamide, antioxidants and tris(2,4-di-tert-butylphenyl)phosphite.

[0084] The base layer may be opaque or translucent. The light transmittance of the base layer may be 0% to 100%. The finishing layer and the base layer may have the same or different light transmittance. For matte hidden applications, the light transmittance may be 1% to 50%, preferably 1% to 30%, more preferably 2% to 20%, even more preferably 5% to 10% in the wavelength range of 400nm to 700nm.

[0085] In another embodiment, the base layer contains one or more soft layers, preferably one soft layer, and a dense layer as the uppermost layer coated by the finishing layer. In particular, the base layer may contain one soft layer and two or three dense layers and have a texture. The soft layer is preferably a foam layer. In the present invention, the dense layer has a density greater than 0.80 g / cm 3 The density of the foam layer is less than 0.80 g / cm 3 density.

[0086] Final coating

[0087] The finishing layer is disposed on the base layer and determines the wear resistance and other surface properties such as slip, sound reduction and surface feel. The finishing layer is obtained by radiation curing of the liquid topcoat. The finishing layer can be opaque or translucent.

[0088] The topcoat contains raw material compounds to obtain a cured polymer of the final finish by radiation curing. The raw material compounds include monomers, oligomers and / or prepolymers capable of forming a cured polymer. In this document, the term "oligomer" is used to refer to 2 to 5 consecutive related structural units; molecular structures with 6 or more such structural units are called "polymers". In particular, the topcoat contains radiation-curable compounds. In particular, the compounds are curable by UV or excimer radiation. Curing by other means is not excluded, for example by light of other wavelengths or electron beams.

[0089] The radiation curable compound may contain a free radical polymerizable C=C double bond. Examples of free radical polymerizable groups are non-aromatic C=C double bonds, such as vinyl, allyl or norbornene groups. The compound may be selected from vinyl ethers, allyl ethers, propyl ethers, alkenes, diesters, unsaturated esters, allyl triazines, allyl isocyanates and N-vinylamides. Preferred UV curable compounds are (meth)acrylates and their derivatives. Unless otherwise stated, the expression "(meth)acrylate" means "acrylate and / or methacrylate". The same applies to the expressions "(meth)acrylic acid" and "(meth)acrylate". Examples of (meth)acrylates are 1,4-butanediol dimethacrylate (BDDMA), hexanediol dimethacrylate (HDDMA), 1,3-butanediol dimethacrylate (1,3-BGDMA), ethylene glycol dimethacrylate (EGDMA), dodecanediol dimethacrylate (DDDMA), trimethylolpropane trimethacrylate (TMPTMA), trimethacrylate (TMA ester), wherein these monomers may be used alone or in combination of two or more.

[0090] In addition to UV-curable compounds with C=C double bonds, the topcoat may also contain monomers with at least two thiol groups, such as ethylene glycol di(3-mercaptopropionate) (GDMP). The reaction of a thiol group with a carbon-carbon double bond is a thiol-ene reaction. Other examples of monomeric structural units with at least two thiol groups are 3-mercaptopropionate, 3-mercaptoacetate, mercaptoacetate and alkylthiols. The topcoat may contain, for example, monomers with at least two thiol groups in an amount of 1% to 50%, in particular 5% to 30%, monomers or oligomers with at least one polymerizable double bond in an amount of 1% to 90%, in particular 10% to 50%.

[0091] Preferably, the radiation curable compound comprises at least one ester of an alcohol with a C=C double bond and an acid. More preferably, the UV curable compound is an alcohol esterified with one or two or more, preferably two, (meth)acrylate groups.

[0092] The radiation-curable compound can be a prepolymer (sometimes simply referred to as "prepolymer" herein) and preferably contains at least one polymerizable carbon-carbon double bond. The prepolymer can be an oligomer or polymer having a weight-average molecular weight Mw of at least 2000 g / mol or even greater than 5000 g / mol. A lower Mw results in a lower viscosity. The prepolymer is preferably an oligomer having at least two, more preferably at least five or at least ten repeating units. The monomer units can be structurally the same or similar, or they can be different from each other. The prepolymer can be cured, i.e., polymerized, to produce a cured polymer. The topcoat can contain the prepolymer as the sole polymerizable component and thus may not contain polymerizable components other than the prepolymer. Alternatively, the topcoat can contain the prepolymer and other copolymerizable components that can be monomers, such as chain extenders. In this case, the final polymer is obtained, for example, by chain extension and by curing the polymerizable C-C double bonds. For example, a urethane acrylate prepolymer containing terminal hydroxyl groups can be chain-extended by reacting with a diisocyanate and optionally using a reaction catalyst such as a mixture of bismuth neodecanoate and zinc neodecanoate. The chain extension can be carried out before curing and can be independent of curing. Preferably, the chain extension and curing are carried out simultaneously. The radiation-curable compound can be a prepolymer selected from urethane acrylates, vinyl acrylates, epoxy acrylates, polyester acrylates, polyacrylates, polyether acrylates, polyolefin acrylates, and silicone acrylates. Urethane acrylate (UA) can be preferred, and urethane acrylate oligomers can be more preferred. Examples of urethane acrylate oligomers include difunctional or higher-functional acrylates of hydroxyl-terminated NCO-extended polyesters or polyethers, which can be aliphatic or aromatic.

[0093] The topcoat can contain a solvent and / or water, or it can be solvent- and / or water-free. In the present invention, the term "solvent" does not include water. In particular, the topcoat can be free of aromatic solvents such as benzene, toluene, and xylene.

[0094] Solvent-free topcoats usually contain reactive diluents to adjust viscosity and reaction rate. For example, the high viscosity of UA oligomers can be reduced by adding acrylate monomers as reactive diluents. The reactive diluent is reactive because it is polymerizable and becomes part of the molecules of the cured polymer structure, and it is a diluent because it reduces the viscosity of the composition. Preferably, the reactive diluent has at least one polymerizable double bond. The reactive diluent can be polymerized with the prepolymer to form a copolymerized elastomeric network of the cured polymer material in the finishing layer. The reactive diluent preferably has a weight average molecular weight Mw of less than 500 g / mol, and is therefore different from a prepolymer having a weight average molecular weight Mw of greater than 2000 g / mol. In any case, the reactive diluent is different from the prepolymer in its structure. The reactive diluent can be selected from aliphatic (meth) acrylates or polyether (meth) acrylates, in particular HDDA or TMP(EO)xTA. Multifunctional aliphatic or polyether (meth)acrylates, in particular comprising TMP(EO)9TA, TMP(EO)6TA, TMP(EO)3TA or TMPTA, can be used as reactive diluents to adjust the hardness of the polymer composition in addition to the viscosity of the finishing layer.

[0095] Reactive diluents may be toxic. If you want to avoid using them, you can use an aqueous dispersion as a topcoat. This topcoat is improved in that its viscosity can be easily adjusted without the use of reactive diluents. The use of aqueous dispersions makes it possible to easily adjust the viscosity by changing the water content of the aqueous dispersion. The viscosity of the aqueous dispersion can be adjusted by changing the content of water and / or reactive diluents. The dispersion preferably has a viscosity of 0.01 to 10 Pa s. The viscosity within this range leads to good fluidity of the aqueous dispersion and uniform coating of the surface to be molded. In the present invention, the viscosity is measured at 23 ° C according to DIN EN ISO 2555 (Brookfield method). The aqueous dispersion used in the present invention does not require a reactive diluent. The omission of reactive diluents makes the aqueous dispersion environmentally friendly and less toxic, and results in a less viscous embossing paint. In a preferred embodiment, the finishing layer is an aqueous dispersion that does not contain reactive diluents. However, reactive diluents may be contained, for example, for adjusting the viscosity. The dispersion may contain 0 to less than 2%, preferably less than 0.1%, more preferably 0% of reactive diluent. The aqueous dispersion may contain 10 to 90% of water and 90 to 10% of prepolymer. Preferably, the sum of the water content and the prepolymer content accounts for 80% to 100% of the aqueous dispersion.

[0096] The finishing layer may be an aqueous dispersion of a prepolymer having at least one polymerizable carbon-carbon double bond. In this case, the prepolymer is dispersible in an aqueous medium, preferably water. To achieve dispersibility, the prepolymer must have a certain degree of hydrophilicity and preferably contains hydrophilic residues selected from acidic or ionic residues, preferably hydrophilic residues other than acrylic acid residues. For example, the hydrophilic residues may be selected from carboxylic acid, sulfonic acid, carboxylate and sulfonate residues, which may be converted into anionic salt groups by adding an organic or inorganic neutralizing agent.

[0097] The radiation curable compound may be a biomolecule or a derivative thereof. In particular, it may be an alcohol esterified with one or two or more, preferably two, (meth)acrylate groups. The alcohol may be selected from a hydroxyl-containing biomolecule, a hydroxylated derivative of a biomolecule, a hydroxyl-containing or hydroxylated degradation product of a biomolecule, and an ester or ether of a hydroxyl-containing or hydroxylated degradation product of a biomolecule. A specific example is an aliphatic hydroxyl-containing compound esterified with two or more (meth)acrylate groups, selected from C 6 -C 24 Alcohol, containing C 2 -C 6 Alkoxylated oligoethers or polyethers, hydroxylated C-containing 2 -C 6 Oligoesters or polyesters of monocarboxylic acids or dicarboxylic acids, containing C 2 -C 6 Alkoxy and C 2 -C 6 Oligoesters or polyesters of dicarboxylic acids, hydroxylated polyurethanes (especially non-isocyanate polyurethanes (NIPU)), glycerol oligomers or polymers, C 6 -C 24 Epoxidized triglycerides of fatty acids or epoxidized C 6 -C 24 Fatty acids. Each of these compounds contains at least one hydroxyl group and can therefore be called an alcohol.

[0098] Bio-based compounds can be cured by using bio-based photoinitiators. By using bio-based materials, fossil raw materials can be replaced with bio-based, sustainable and renewable raw materials, and the topcoat can be made entirely from renewable raw materials.

[0099] In addition to the photoinitiator, the topcoat may also contain other additives, such as UV stabilizers and antioxidants. In addition, the topcoat may contain a surfactant, which is a compound different from the radiation-curable compound and the optionally contained reactive diluent, and is selected from the following group: alkyl (meth) acrylates, polysiloxane (meth) acrylates, perfluoroalkyl (meth) acrylates, perfluoropolyether (meth) acrylates, alkyl vinyl ethers, polysiloxane vinyl ethers, perfluoroalkyl vinyl ethers and perfluoropolyether vinyl ethers. In other words, the surfactant is selected from the group, while the prepolymer and the optionally contained reactive diluent are not selected from the group. The finishing layer may contain 0.1% to 3% of the surfactant. In the case of an aqueous dispersion, the content is based on a dry mass basis. The surfactant changes the surface properties, such as hydrophobicity, water resistance and touch.

[0100] Radiation curing

[0101] The topcoat can be obtained by radiation curing. Examples of radiation curing include UV (ultraviolet) curing and excimer curing. Preferably, radiation curing is carried out by UV curing and / or excimer curing. UV curing means UV-induced curing, and excimer curing means excimer-induced curing.

[0102] Excimers (excited dimers) are short-lived molecules formed by inducing bonds between a pair of smaller electronically excited molecules. Excimer radiation differs from UV radiation in that it has a higher radiation power spectral density and higher emitted photon energy, and is a quasi-monochromatic radiation with a spectral half-width of 2 to 15 nm. Excimer lamps are UV light sources generated by spontaneous emission of excimers. Excimer lamps are quasi-monochromatic light sources operating over a wide wavelength range in the ultraviolet (UV: 100 to 400 nm) and vacuum ultraviolet (VUV: 10 to 200 nm) spectral regions. Excimer curing can be performed at short wavelengths (e.g., 172 nm).

[0103] The difference between UV curing and excimer curing is that the latter is usually performed with higher energies. UV curing can use 350 to 1000 mJ / cm 2 If excimer curing is performed before UV curing, the curing energy of the excimer may be higher than the curing energy of the subsequent UV curing.

[0104] In excimer curing, the penetration depth of high-energy photons is low, for example less than 500nm in the case of acrylates, and only the surface layer of the coating undergoes polymerization. The accompanying volume shrinkage leads to varying degrees of surface wrinkles. This deformed "skin" forms a structure that leads to diffuse reflection of light (i.e., matte effect). The depth of the depression of the surface wrinkles is generally less than 10μm, preferably less than 5μm, more preferably at most 1000nm, for example 10nm to 1000nm. Therefore, the surface wrinkles are preferably nanostructured. The nanostructured surface obtained by radiation curing can be used to change the physical properties of the surface. For example, optical properties such as refractive properties can be changed. Moreover, the surface energy can be changed. Therefore, properties such as water resistance can be adjusted.

[0105] Surface wrinkles caused by excimer curing are fixed by through-curing the underlying uncured topcoat layer using UV light (eg, with a conventional medium pressure mercury lamp) or electron beams.

[0106] Photoinitiator

[0107] The free radical polymerization induced by radiation curing can be initiated by photoinitiators optionally contained in the topcoat.

[0108] Radiation-curable compounds and photoinitiators differ from each other in structure. They are not chemically bound and are therefore present as separate substances in the finishing layer. Photoinitiators preferably do not fall within the definition of UV-curable compounds and in this case do not contain radiation-curable compounds such as polymerizable C=C double bonds.

[0109] The photoinitiator may be aromatic, which is typically a petrochemical photoinitiator, or aliphatic, which may be bio-based. Examples of photoinitiators are thioxanthones, ketosulfones, (alkyl)benzoylphenylphosphine oxides, 1-hydroxyalkylphenyl ketones or 2,2-dimethoxy-1,2-diphenylethane-1-one. The content of the photoinitiator may be from 0.1% to 10%, in particular from 0.5% to 5%.

[0110] The photoinitiator has a preferred molecular weight of less than 300 g / mol and is contained in the final finishing layer in modified form or preferably in unmodified form. The finishing layer may contain photoinitiator degradation products or photoinitiator that has not been chemically converted. Thus, the composite structure of the present invention can be distinguished from prior art structures prepared by thermal curing.

[0111] Touch sensor applications

[0112] The composite structure of the present invention can be used as the top layer of a composite structure containing a touch sensor. In this embodiment, the finishing layer contained in the composite structure of the present invention can be applied to the composite structure disclosed in EP 3 575 121 A1. In particular, the finishing layer corresponds to the paint layer (9), and the base layer contained in the composite structure of the present invention corresponds to the semi-transparent layer (1) in the drawings and description of EP 3 575 121 A1. The composite structure of EP 3 575 121 A1 meets the requirements of "seamless" and "matte hiding". The components of the touch sensor application will be discussed in detail below.

[0113] Under the base layer, the composite structure may contain an opaque region or an opaque layer having an opaque region and a semi-transparent region; a touch sensor region or a sensor layer having a touch sensor region; a light source; a support layer; and a soft layer.

[0114] In a preferred embodiment, the composite structure containing the touch sensor can show a matte hiding effect. In order to achieve this desired effect, the base layer preferably has a light transmittance of 1% to 50%. The composite structure containing the touch sensor can also be a seamless structure. To this end, the elements and / or layers below the semi-transparent layer of the composite structure can be applied by a printing step. In a more preferred embodiment, the composite structure containing the touch sensor is a seamless structure showing a matte hiding effect.

[0115] The opaque layer contains translucent areas and opaque parts. The opaque areas can be discontinuous and therefore do not have to be connected to each other. The opaque areas can be large opaque areas and / or relatively thin opaque graphics, such as letters, symbols or borders. The opaque layer can be a film, which is preferably made of a polymer, which is applied to another layer. The opaque layer can be made of a dense layer or a soft layer, such as a foam layer or any other soft material, such as a fabric layer. The translucent area can simply be a gap area surrounded by an opaque part, i.e., an area where no opaque part is arranged, such as a mask. Preferably, the opaque layer is a mask printed on the B side of the substrate layer. In one embodiment, the film can contain a touch sensor area and other electrical parts that are optionally present, such as those required for the touch sensor area to perform its function.

[0116] The touch sensor area is preferably a sensor that is sensitive to changes in pressure, or temperature, or both pressure and temperature. Preferably, the sensor signal can be affected by the touch of a finger of a human user. The function of the touch sensor area can be a switch or a button to actuate an electrical device such as a lamp or a motor. The touch sensor area can be a membrane touch switch known in the art. The sensor can be a capacitive layer sensor. The sensor can be functionally connected to other electrical or electronic components and can contain elements that connect it to other electrical parts. Therefore, the sensor is preferably contained in a sensor layer, which includes at least an electrical conductor or contact. The touch sensor area can be a capacitive layer sensor, which includes a first conductive layer, a ferroelectric polymer and a second conductive layer in this order. The touch sensor area includes a touch sensor or consists of a touch sensor. Because the touch sensor area can consist of a touch sensor, these two expressions can be used interchangeably in this specification. The arrangement of the touch sensor area is at least partially in or above or below the semi-transparent area of ​​the opaque layer. Preferably, the touch sensor area is in direct contact with the semi-transparent area of ​​the opaque layer, which means that there are no other layers or materials between them.

[0117] The touch sensor area and the electrical conductors or contacts may be included in the sensor layer. The sensor layer may additionally be connected to or include elements necessary for the touch sensor area to function, such as resistors, capacitors, control elements, etc. These additional elements may be arranged outside the sensor layer or at least partially within the sensor layer. The touch sensor layer may be applied to the B side of the translucent layer by inkjet printing of screen printing, preferably after applying the opaque layer to the B side of the translucent layer. The touch sensor layer may additionally include a light source.

[0118] The light source can be used to illuminate the translucent area of ​​the composite structure for the purpose of indicating the position of the sensor. Thus, when the light source is activated, the light source simplifies the user's orientation or draws the user's attention to the illuminated area. The light source mentioned in the present invention can be a light source arranged on the B side of the composite structure. The light source can be contained in the composite structure or adhered to the B side of the support layer, and can therefore be part of the composite structure of the present invention. Alternatively, the light source can be positioned at a distance from the B side of the composite structure. In this case, the light source is not part of the composite structure of the present invention. It is necessary to align the translucent area and the element to allow vertical light to be transmitted through the composite structure. An example of a light source is an LED or an electroluminescent element.

[0119] The support layer may be translucent or may not be translucent, and it may be flexible and / or soft or rigid and / or hard material. In one embodiment, the support layer is transparent, flexible and soft. It may be made of fabric, textile, spacer fabric or foam. In particular, it may be made of polyolefin foam, woven spacer fabric, translucent molded fabric or translucent knitted fabric. The material and the thickness of the material must be selected according to the desired properties (e.g., translucency) of the layer.

[0120] The soft layer can contribute to the desired softness and tactile feel of the composite structure. The soft layer can be foam or textile. Preferably, the foam layer has a thickness of 0.05 to 0.5 g / cm 3 or 0.1 to 0.3 g / cm 3 The thickness of the foam layer is preferably 30 to 3000 μm or 500 to 2000 μm. The foam layer can be made of polyolefins, in particular polypropylene. In one embodiment, the soft layer is arranged between the substrate layer and the opaque layer. In another preferred embodiment, the soft layer is arranged on the A side of the support layer, that is, between the opaque layer or (if present) the sensor layer and the support layer. Depending on the position of the light source, the soft layer can be opaque or translucent.

[0121] Manufacturing method

[0122] The present invention relates to a method for producing a composite structure comprising a finishing layer arranged on a substrate layer, preferably a composite structure according to the invention.

[0123] The method comprises the following steps:

[0124] (i) providing a substrate comprising a substrate layer as a top layer or consisting of a substrate layer;

[0125] (ii) providing a liquid topcoat comprising a radiation curable compound;

[0126] (iii) applying a liquid topcoat on the base layer to obtain a topcoat layer;

[0127] (iv) radiation curing of the radiation curable compounds of the topcoat layer to prepare the polymer and obtain a composite structure.

[0128] Step (i)

[0129] The substrate may be a film that forms a substrate layer in the composite structure to be produced. Alternatively, the substrate may contain a substrate layer as a top layer. The bottom layer or structure below the translucent layer is not limited and may be an opaque and / or sensor structure and layer disclosed above for touch sensor applications. Suitable substrate materials may be PVC, PUR or TPU. In the case of TPO as the substrate material, a corona treatment (e.g., at 41-44 Nm / m2 Down).

[0130] Step (ii)

[0131] The topcoat contains the components necessary to form a finishing layer when polymerized and irradiated with UV and / or excimer radiation. For example, the topcoat contains diisocyanates and polyols to result in polyurethane being included in the finishing layer. In addition, the topcoat preferably contains a photoinitiator capable of initiating crosslinking of photopolymerizable groups such as carbon-carbon double bonds. The topcoat to be applied to the substrate is adjusted according to its physical properties such as viscosity.

[0132] Step (iii)

[0133] A topcoat is applied to the semi-transparent layer of the substrate to obtain a topcoat layer on the semi-transparent layer. The application of a liquid topcoat can be performed by using a roller coater or a curtain coater. The topcoat layer obtained is liquid and its viscosity can be increased by removing at least part of the solvent and / or water. To this end, the topcoat layer can be gelled by heating the topcoat or by using, for example, a gallium / ozone-free LED system. The topcoat can be applied two or more times.

[0134] Step (iv)

[0135] Step (iv) includes a curing step performed by radiation curing. In addition, step (iv) may include a polymerization step of polymerizing monomers or chain extension prepolymers or oligomers, wherein the polymerization step may be performed by radiation curing or other means. Preferably, the polymerization step involves polymerizable groups that cannot be polymerized by radiation curing and therefore cannot be free radical polymerized. For example, they can be polymerized by addition polymerization or condensation polymerization. In this case, step (iv) may include a step (iv-1) of polymerizing the polymerizable groups and a step (iv-2) of irradiating the topcoat layer to crosslink the radiation curable compound. Steps (iv-1) and (iv-2) may be performed simultaneously or sequentially, i.e., in the order of (iv-1) and (iv-2) or (iv-2) and (iv-1).

[0136] An example of step (iv-1) is the polymerization of diisocyanates and polyols to obtain polyurethane. The polymerization can be carried out by known methods. For example, the topcoat layer may contain a catalyst activated at an elevated temperature, and the polymerization can be initiated by increasing the temperature.

[0137] The step (iv-2) of irradiating to crosslink the photopolymerizable groups uses a photoinitiator to initiate polymerization. This step results in intermolecular crosslinking of the polyurethane or its raw material and can be performed by UV curing and / or excimer curing. In a preferred embodiment, step (iv-2) includes the step of excimer curing the surface of the composition layer and then UV curing the entire composition layer.

[0138] The groups capable of reacting in steps (iv-1) and (iv-2) may be contained in the same compound of the topcoat or in different compounds. For example, the diisocyanate and / or the polyol may contain radiation curable groups, such as acrylates.

[0139] In one embodiment, the preparation of the composite structure may include applying a primer coating (e.g., 8 to 16 g / m 2 ), dried with UV lamp, topcoat 1 is applied, topcoat 2 (last layer) is applied (wherein the total thickness of the topcoat applied can be 8 to 24 g / m 2 ), using 1000mJ / cm 2 The total curing energy is used for excimer curing and drying with a UV lamp. These steps can be applied in the case of PVC, PUR or TPU as the substrate material. In the case of TPO as the substrate material, the substrate can be corona treated (41-44Nm / m 2 ).

[0140] Example

[0141] The wear tests were carried out using the apparatus and application test procedure according to DIN EN 60068-2-70.

[0142] The following evaluation scheme was applied:

[0143]

[0144] Samples evaluated with a rating of 7, 8, 9, or 10 were acceptable, and were referred to as samples "showing only slight dulling and having an unchanged overall structure."

[0145] About 10g / m 2 A primer of about 15 g / m is applied to the substrate film and dried. 2 The following topcoats:

[0146] (A) Topcoat for UV / excimer curing

[0147] Two-component polyurethane paint containing:

[0148] - Isocyanate: undiluted isocyanate-containing urethane acrylate - Polyol: OH-functional acrylic acrylate, solvent-based.

[0149] -Flow modifier: Acrylic based, silicone free.

[0150] -Polyurethane catalyst: a mixture of bismuth neodecanoate and zinc neodecanoate.

[0151] - Matting agent: Silicone based.

[0152] - Photoinitiators: based on alpha cleavage of ketones.

[0153] -Solvent: Butyl acetate.

[0154] (B) For heat-curing topcoats

[0155] - Polyurethanes: solvent-based aliphatic, polycarbonate-based - Crosslinkers: aliphatic polyisocyanates for solvent-based systems

[0156] -Solvent: Methoxypropyl acetate

[0157] - Silicones: Silicones (C) containing alcohol (10% to 14%) and octamethylcyclotetrasiloxane (0.2% to 1.0%) for heat-cured topcoats

[0158] Same as (B), but without silicone

[0159] The results of the examples and comparative examples are shown in Tables 1 and 2.

[0160] Table 1

[0161]

[0162] Table 2

[0163]

[0164] In automotive interiors, gloss is measured at 60° and, depending on the texture, values ​​less than 2.0 are acceptable. The sample of Example 2 meets this requirement.

[0165] Additional experiments were performed using the above samples and additional samples with TPU as substrate film. These experiments showed that the type of substrate film had no influence on the results obtained.

[0166] Additional experiments also showed that all examples using UV curing outperformed thermal curing in terms of the physical properties of "cracks on bending" and "whiteness." The samples of the examples using UV / excimer curing showed the best results.

[0167] Reference numerals

[0168] (1) Basal layer

[0169] (2) Topcoat

[0170] (3) Curing part of topcoat

[0171] (4) Fully cured topcoat (corresponding to the final finish)

Claims

1. A composite structure comprising a finishing layer arranged on a substrate layer and a touch sensor under the substrate layer, wherein the finishing layer is based on a cured polymer and is obtainable by a process comprising radiation curing a topcoat to obtain the cured polymer, the topcoat being applied on the substrate layer and comprising a radiation curable compound.

2. The composite structure of claim 1, wherein the composite structure is a flexible film.

3. A composite structure according to claim 1 or 2, wherein the radiation curing comprises excimer curing.

4. A composite structure according to any one of the preceding claims, wherein the first step of radiation curing is a step of excimer curing the surface of the topcoat composition, and the second step of radiation curing is a step of UV curing the entire topcoat composition.

5. The composite structure according to any one of the preceding claims, wherein the finishing layer contains depressions and protrusions on its surface, wherein the depth of the depressions is from 10 nm to 1000 nm. 6 . The composite structure according to claim 1 , wherein a sample of the composite structure shows only slight matting after 40,000 cycles at 5 N in an abrasion test according to DIN EN 60068-2-70 and has an unchanged overall structure.

7. A composite structure according to any one of the preceding claims, wherein the touch sensor is a printed structure.

8. A composite structure according to any one of the preceding claims, wherein the substrate layer is a translucent layer having a light transmittance of 1 to 50%.

9. A method for preparing a composite structure comprising a finishing layer disposed on a substrate layer, the method comprising the following steps: (i) providing a substrate comprising a substrate layer as a top layer or a substrate consisting of a substrate layer; (ii) providing a liquid topcoat comprising a radiation curable compound; (iii) applying the liquid topcoat onto the base layer to obtain a topcoat layer; (iv) radiation curing the radiation curable compound of the topcoat layer to prepare a polymer and obtain the composite structure, wherein the radiation curing comprises a first step of excimer curing and a second step of UV curing.

10. A method according to claim 9, wherein the radiation-curable compound of the topcoat contains polymerizable groups that are not polymerizable by radiation curing, and step (iv) comprises a step (iv-1) of subjecting the topcoat layer to polymerization of the polymerizable groups and a step (iv-2) of irradiating to crosslink the radiation-curable compound.

11. The method according to claim 9 or 10, wherein the topcoat contains an isocyanate, a polyol and a photoinitiator, wherein the diisocyanate is a radiation-curable compound and / or the polyol is a radiation-curable compound.

12. The method according to any one of claims 9 to 11, wherein the first step of radiation curing is a step of excimer curing the surface of the topcoat composition, and the second step of radiation curing is a step of UV curing the entire topcoat composition.

13. The method according to any one of claims 9 to 12, wherein the step of excimer curing forms nanostructures on the surface of the finishing layer.

14. A composite structure obtainable by a method according to any one of claims 9 to 13.

15. Use of a composite structure according to any one of claims 1 to 8 or 14 as a material for vehicle interiors.

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