Conductive film, method for producing the same and use thereof

Abstract

The invention relates to a conductive film comprising a substrate, on the main surface of which a primer layer and subsequently a substantially conductive structure in the form of a close-meshed continuous network having a multiplicity of pores of different geometries are provided.

Description

Technical Field

[0001] The present invention relates to a conductive film (or conductive film), a method for manufacturing the conductive film and a use thereof. Background Art

[0002] Conductive films which are suitable, for example, as heating elements for windshields of vehicles are described in the prior art, see for example EP 2 764 996 B1, EP 2 284 134 B1 and WO 2016 / 192858 A1.

[0003] According to WO 2016 / 192858 A1, the production of the conductive film is carried out on the basis of a multi-stage method, wherein first a washable coating is applied to a carrier substrate, which coating forms a large number of cracks in the form of a continuous network with a fine mesh when drying. After the washable coating provided with cracks is removed in a cleaning step, the metal is then vapor-deposited. The product obtained has such properties that it has a conductive metallization in the form of a continuous network with a fine mesh above the carrier substrate.

[0004] In practice, it has been shown that, in particular when washable coatings are applied to carrier substrates based on polyethylene terephthalate (PET), a pronounced anisotropy in crack formation can be observed during drying. This leads to strong anisotropies in the resulting conductive film, for example in heating applications, with regard to the heat distribution. Furthermore, it is difficult to transfer the production method from carrier substrates based on polyethylene terephthalate (PET) to other carrier substrates, such as polycarbonate (PC), polymethyl methacrylate (PMMA), thermoplastic polyurethane (TPU) or glass, etc., so that the formulation of the washable coating must be developed individually for each surface, depending on the properties of the carrier substrate to be used. Summary of the invention

[0005] The object of the present invention is to improve the production of conductive films known from the prior art. In particular, a conductive film is to be provided which, despite the use of the same material composition to provide a washable crack-forming coating, independently of the material choice of the carrier substrate, has a reduced anisotropy compared to conductive films known from the prior art.

[0006] This object is achieved according to the invention by a conductive film, a method for producing the conductive film and a use thereof.

[0007] Summary of the Invention

[0008] 1. (First aspect of the invention) A conductive film comprising a substrate on a major surface of which a primer layer and subsequently a substantially conductive structure in the form of a close-meshed continuous network having a large number of pores of different geometric shapes are sequentially provided.

[0009] 2. (Preferred embodiment) The conductive film according to item 1, wherein the primer layer is based on a composition that essentially contains an adhesive and an organic solvent and / or water.

[0010] 3. (Preferred design scheme) A conductive film as described in item 2, wherein the adhesive is selected from methacrylates, styrene compounds, acrylate compounds, polyester compounds, especially ionic polyester compounds, polyurethanes and mixtures of two or more of the above elements.

[0011] 4. (Preferred design scheme) A conductive membrane as described in item 2 or 3, wherein the composition additionally contains auxiliary materials, and the auxiliary materials are selected from defoaming agents, cross-linking additives, process additives (Verlaufsadditive), agglomeration additives, additives for controlling surface energy and mixtures of two or more of the above elements.

[0012] 5. (Preferred configuration) The conductive film according to any one of items 1 to 4, wherein the layer thickness of the primer layer is in the range of 0.1 μm to 10 μm.

[0013] 6. (Preferred design) A conductive film as described in one of items 1 to 5, wherein the conductive structure is based on a conductive metallization part, and the metallization part is selected from copper, gold, aluminum, silver, alloys of two or more of the above elements and multilayer systems of two or more of the above elements.

[0014] 7. (Preferred design) A conductive film as described in one of items 1 to 6, wherein the conductive structure is based on a multilayer arrangement structure, which, in addition to the conductive metallization part, has an additional layer on one or both sides for adjusting the formation of a defined color or for reducing gloss.

[0015] 8. (Preferred design) A conductive film according to item 7, wherein the additional layer for adjusting the formation of a defined color or for reducing gloss is selected from: a metal, preferably chromium, titanium or nickel, a metal oxide layer, preferably a metal oxide layer based on substoichiometric black aluminum oxide, chromium oxide or copper oxide, a black PVD coating with a color tilt effect and a reflector / dielectric / absorber structure, chrome black, nickel black, a metal sulfide layer, an overprint based on a color paint or a pigment paint An antireflection layer formed by nanostructuring or moth-eye structure or a combination of two or more of the above elements.

[0016] 9. (Preferred embodiment) The conductive film according to any one of items 1 to 8, wherein the film additionally comprises a layer for leveling the conductive structure and an adhesive layer.

[0017] 10. (Preferred design) A conductive film according to any one of items 1 to 9, wherein the substrate is selected from polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), thermoplastic polyurethane (TPU) and glass and is preferably a transparent substrate.

[0018] 11. (Preferred design) The conductive film according to any one of items 1 to 10, wherein the conductive film is transparent.

[0019] 12. (Second aspect of the present invention) A method for producing a conductive film according to any one of items 1 to 11, comprising the following steps:

[0020] - providing a substrate;

[0021] - providing a main surface of the substrate with a primer layer;

[0022] - applying a crack-forming coating on the primer layer and drying the crack-forming coating, wherein the coating forms a large number of cracks in the form of a continuous network with a fine mesh when drying;

[0023] - structures that impart conductivity;

[0024] - The coating provided with cracks and the conductive structure located above said coating are removed together, so that the substrate obtained has such properties that a conductive structure in the form of a continuous network with a dense mesh is formed on its main surface provided with the primer layer, and the continuous network has a large number of pores of different geometric shapes.

[0025] 13. (Third aspect of the invention) Use of a conductive film as described in one of items 1 to 11, wherein the conductive film is used as a heating film, in particular a heating film in a windshield of a vehicle, in other windows or in the glazing of a building, and for introducing current without visible input lines, for example for use in LEB films, in solar cells, in smart glass applications, in OLEDs or in touch panels.

[0026] Detailed description of the invention

[0027] The present invention is based on the technology for fine structuring of metallizations known from WO 2016 / 192858 A1, based on which electrical devices, for example heating films for use in windshields of vehicles, can be provided. The technology also includes the application of a crack-forming coating, preferably a dispersion or solution of a polymer. The crack-forming coating is applied to a substrate, for example, by printing, thereby producing a film, which forms cracks in the form of a continuous network with a fine mesh during drying. Subsequently, the metal is vapor-plated, and the washable coating provided with cracks is then removed in a cleaning step. The obtained product has such properties that it has a conductive structure in the form of a continuous network with a fine mesh on a transparent substrate.

[0028] The invention is based on the knowledge that an isotropic metal network can be obtained by providing a carrier substrate with a primer layer, more precisely independently of the material composition for providing the washable crack-forming coating and independently of the material choice of the carrier substrate. The invention not only ensures the applicability of the production method known from WO 2016 / 192858 A1 on carrier substrates based on polyethylene terephthalate (PET), but also ensures applicability on any carrier substrate, such as polycarbonate (PC), polymethyl methacrylate (PMMA), thermoplastic polyurethane (TPU), glass, etc., without having to adapt or adjust the material formulation of the washable crack-forming coating to each surface individually depending on the carrier substrate to be used. In addition, the conductive film according to the invention has excellent direction-independent electrical and thermal conductivity due to its isotropic metal network.

[0029] Preferably, the primer layer is based on a composition which essentially comprises an adhesive and an organic solvent and / or water. The composition is in particular selected such that the adhesive is selected from the group consisting of methacrylates, styrene compounds, acrylate compounds, polyester compounds, in particular ionic polyester compounds, polyurethanes and mixtures of two or more of the above elements. In addition, in particular, the composition may additionally contain auxiliary materials selected from the group consisting of defoamers, crosslinking additives, process additives, coalescing additives, additives for controlling surface energy and mixtures of two or more of the above elements.

[0030] Alternatively, the primer layer can be based on a 100% UV lacquer system or a reactive system, for example a one-component system or a two-component system.

[0031] The layer thickness of the primer layer is preferably adjusted such that it is in the range of 0.1 μm to 10 μm. A particularly preferred layer thickness of the primer layer is approximately 1 μm.

[0032] In order to achieve advantageous conductivity, the conductive structure is based on a conductive metal, preferably by a copper, gold, aluminum or silver layer.

[0033] If necessary, the conductive film according to the invention can additionally have a preferably transparent layer and a preferably transparent adhesive layer for leveling the conductive structure. For example, a UV-hardening or heat-hardening primer is suitable for leveling the conductive metallization. The product obtained in this way can then be provided with an adhesive layer, which is arranged, for example, on the side of the substrate opposite the conductive metallization. Alternatively, the adhesive layer can be arranged above the coating that leveled the conductive metallization. For example, a heat-sealing lacquer is suitable as the adhesive layer. According to a special variant, the adhesive layer used, for example a heat-sealing lacquer, can be the same as the transparent coating used to level the conductive metallization.

[0034] It is further preferred that the conductive structure is based on a multilayer arrangement which, in addition to the conductive metallization, has on one or both sides an additional layer for adjusting a defined color or for reducing gloss. The additional layer for adjusting a defined color or for reducing gloss is selected in particular from: a metal oxide layer, preferably a metal oxide layer based on substoichiometric black aluminum oxide or copper oxide, a black PVD coating with a color-tilting effect and a reflector / dielectric / absorber structure, chrome black, nickel black, a metal sulfide layer, an overprint based on a color lacquer or a pigmented lacquer, an antireflection layer formed by a nanostructuring or a moth-eye structure or a combination of two or more of the aforementioned elements.

[0035] The present invention also relates to an aspect of manufacturing a conductive film, which comprises the following steps:

[0036] - providing a substrate;

[0037] - providing a main surface of the substrate with a primer layer;

[0038] - applying a crack-forming coating on the primer layer and drying the crack-forming coating, wherein the coating forms a large number of cracks in the form of a continuous network with a fine mesh when drying;

[0039] - structures that impart conductivity;

[0040] - The coating provided with cracks and the conductive structure located above said coating are removed together, so that the substrate obtained has such properties that a conductive structure in the form of a continuous network with a dense mesh is formed on its main surface provided with the primer layer, and the continuous network has a large number of pores of different geometric shapes.

[0041] The production method according to the invention is based on the production described in WO 2016 / 192858 A1.

[0042] According to the invention, preferably a dispersion, more preferably a colloidal dispersion, is used as the crack-forming coating. Other alternatives are, for example, found in WO 2014 / 136039 A1. In addition, the crack-forming coating can be based on a polymer present in solution. The polymer solution is applied to the substrate, for example, by printing, thereby producing a polymer film. The polymer film forms cracks during drying.

[0043] Due to the use of a primer layer, the formation of the cracks extends independently of the material choice of the substrate and independently of the material formulation of the coating that forms the cracks. In this case, the line width that can be achieved at the end of the production method, for example when using silver, is in the range of 0.1 μm to 50 μm, preferably in the range of 1 μm to 30 μm, wherein the lines are generally so thin that they can only be recognized as lines using a magnifying glass. In the surface, the human eye cannot distinguish the individual lines, but the difference with respect to the untreated or bare film can be recognized both in reflected light (or reflection) and in transmitted light (or transmission). Since the fine lines form an irregular continuous network, undesired diffraction effects can be minimized. By varying the island size (Insel- ) and crack width, the reflectivity or light transmittance can be adjusted in an appropriate manner.

[0044] The method for removing the coating provided with cracks is advantageously realized by dissolving through a suitable solvent. The choice of solvent is suitably carried out in coordination with the coating. The following solvents can usually be used: methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methoxypropyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, methylene chloride, chloroform, toluene, xylene, methanol, ethanol, 2-propanol. In addition, acetal or a mixture of the above-mentioned solvents can be used. Alternatively, the detachment of the coating forming cracks can also be achieved by penetration (Unterwanderung). In this case, in addition to the mentioned dissolution, an aqueous solution, a mixture of a solvent and water, a surfactant, a defoamer and other additives can also be used. The detachment and dissolution of the coating provided with cracks can also be assisted by a nozzle or mechanically by a brush, a roller or by a felt.

[0045] Conductive structures, especially metallizations, in the form of dense mesh-like continuous networks show electrical conductivity and optical transmission comparable to that of full-surface ITO layers. Here, thin metal lines can be used in combination with conventional embossing lacquers, conventional primer compositions and conventional heat-sealing lacquers.

[0046] The conductive film according to the invention is particularly suitable for use in electrical devices, for example as a heating film in windshields of vehicles, in other windows or in glazing of buildings, and for introducing current without visible input lines, for example for use in LEB films, in solar cells, in smart glass applications, in OLEDs or in touch panels. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Further exemplary embodiments and advantages of the invention are explained below with reference to the drawings, which are not shown to scale or to proportion in the figures in order to improve the clarity.

[0048] In the attached picture:

[0049] Figures 1 to 4 shows the individual manufacturing steps for obtaining a conductive film according to a first embodiment; and

[0050] Figure 5 The conductive film according to the first exemplary embodiment is shown when viewed from above. DETAILED DESCRIPTION

[0051] Figures 1 to 4 The individual production steps for obtaining a conductive film according to a first exemplary embodiment are shown.

[0052] according to Figure 1 and Figure 2 , firstly a substrate 1 is provided, in this case a polycarbonate (PC) film, a primer layer 2 is provided for the substrate 1 and then a crack-forming coating 3 is applied. The primer layer 2 has a layer thickness of about 1 μm in this example. The crack-forming coating 3 is, for example, based on an inorganic dispersion or made of an acrylic resin dispersion. The crack-forming coating 3 is preferably applied by printing technology, for example by means of gravure printing, flexographic printing, slot coating, screen printing or by means of an inkjet method. The crack-forming coating 3 forms a large number of cracks in the form of a densely meshed continuous network when drying. The continuous network is formed isotropically, i.e., independently of direction.

[0053] In the next step, a conductive layer 4, in this case a Cu layer (see Figure 2 ). The Cu layer 4 is deposited both above the coating 3 provided with cracks and inside the cracks of the coating 3 .

[0054] according to Figure 3 , the coating 3 provided with cracks and the layer 4 present above the coating 3 are subsequently removed in a cleaning step. Cleaning is achieved by dissolution with a suitable solvent, for example methyl acetate. On the transparent primer layer 2, a transparent, conductive metallization in the form of a continuous network in the form of a dense mesh remains.

[0055] according to Figure 4 A transparent leveling lacquer 5 can optionally be applied. The adhesive layer 6, for example a heat-sealing lacquer layer, which is optionally present, serves to apply the conductive film 7, for example, to a windshield of a vehicle.

[0056] Figure 5 The conductive metallization in the form of a continuous mesh-like network is shown schematically in a top view in an enlarged view ( Figure 4 Here a cross-sectional view along the dashed line AA' is shown).

Claims

1. A method for producing a conductive film, the conductive film comprising a substrate (1) on the main surface of which a primer layer (2) and subsequently a conductive structure (4) in the form of a close-meshed continuous network with a large number of pores of different geometric shapes are sequentially provided, the method comprising the following steps: - providing a substrate (1); - providing a main surface of the substrate (1) with a primer layer (2); - applying a crack-forming coating (3) onto the primer layer (2) and drying the crack-forming coating (3), wherein the coating forms a large number of cracks in the form of a continuous network with fine mesh when drying; - a structure for imparting conductivity (4); - The coating (3) provided with cracks and the conductive structure (4) located above the coating are removed together, so that the substrate (1) obtained has such properties that a conductive structure (4) in the form of a continuous network with a dense mesh is formed on its main surface provided with the primer layer (2), and the continuous network has a large number of pores with different geometric shapes.

2. The method according to claim 1, wherein: The primer layer is based on a composition which essentially comprises an adhesive and an organic solvent and / or water.

3. The method according to claim 2, wherein: The adhesive is selected from methacrylate, styrene compounds, acrylate compounds, polyester compounds, polyurethane, and a mixture of two or more of the above elements.

4. The method according to claim 2, wherein: The composition additionally comprises auxiliary materials selected from defoamers, crosslinking additives, process additives, coalescing additives, additives for controlling surface energy, and mixtures of two or more of the above elements.

5. The method according to claim 1, wherein: The layer thickness of the primer layer is in the range from 0.1 μm to 10 μm.

6. The method according to claim 1, wherein: The conductive structure is based on a conductive metallization selected from copper, gold, aluminum, silver, alloys of two or more of these elements, multilayer systems of two or more of these elements.

7. The method according to claim 1, wherein: The conductive structure is based on a multilayer arrangement which, in addition to the conductive metallization, has additional layers on one or both sides for the purpose of adjusting a defined color or for reducing gloss.

8. The method according to claim 7, wherein: The additional layer used to adjust the formation of a defined color or to reduce gloss is selected from: metal, metal oxide layer, black PVD coating with a color tilt effect and a reflector / dielectric / absorber structure, chrome black, nickel black, metal sulfide layer, overprinting based on color paint or pigment paint, anti-reflection layer formed by nanostructured part or moth-eye structure, or a combination of two or more of the above elements.

9. The method according to claim 8, wherein: The metal is chromium, titanium or nickel.

10. The method according to claim 8, wherein: The metal oxide layer is a substoichiometric black metal oxide layer based on aluminum oxide, chromium oxide or copper oxide.

11. The method according to claim 1, wherein: The film additionally has a layer which flattens the conductive structure and an adhesive layer.

12. The method according to claim 1, wherein: The substrate is selected from polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), thermoplastic polyurethane (TPU), and glass.

13. The method according to claim 12, wherein: The substrate is a transparent substrate.

14. The method according to claim 1, wherein: The conductive film is transparent.

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