Laminate for housing

Abstract

Provided is a housing laminate which, if used for a housing for a smartphone or the like, has satisfactory steel wool resistance and low dielectric loss in a frequency band of 5 GHz or higher.　This housing laminate has a coating layer on a base material, which is a composite plate comprising a polycarbonate base material or polymethyl acrylate and polycarbonate, is a laminate used in a housing, and is characterized by satisfying condition 1 and condition 2 below.　Condition 1: In a frequency band of 5 GHz or higher, the relationship between relative permittivity Dk and dielectric loss tangent Df when measured using the split-post dielectric resonator technique satisfies the following formula.　Df×(√Dk)<0.02 Condition 2: No flaws can be visually confirmed after subjecting the coating layer to #0000 steel wool at a load of 1.5 kg / cm2 300 times back and forth.

Description

[Technical field]

[0001] The present invention relates to a laminate for a housing having excellent properties suitable for use in the housings of mobile communication devices such as smartphones. [Background technology]

[0002] In recent years, highly portable terminal devices such as smartphones, mobile phones, and tablet devices with communication functions have become widespread. In communications equipment, communication means using high frequency bands such as millimeter waves are becoming a reality in response to increases in communication speeds and the amount of data transmitted and received. As a result, reducing communication errors caused by noise and dielectric loss during data transmission and reception has become an urgent task.

[0003] Metals and glass have been used suitably for such communication devices up until now, but it has been reported that metals have poor radio wave permeability, and glass also has poor transmission of high frequency radio waves. As a countermeasure, it is expected that plastic housings with excellent dielectric loss will be used for the housings of the above terminal devices.

[0004] On the other hand, plastic housings have the disadvantage that their surfaces are easily scratched and that they have a less luxurious appearance than glass or metal housings. For this reason, a method of applying a coating to the surface of a plastic housing is used. Acrylic resins are often used for such coatings, and they exhibit excellent surface hardness (steel wool resistance) when photocured by exposure to actinic rays.

[0005] As a coating layer for plastic housings, the following Patent Document 1 proposes a method of transferring a functional hard coat layer to satisfy scratch resistance. Patent Documents 2 to 4 use silicon compounds to obtain slipperiness, releasability, flexibility (softness), and steel wool resistance through stress relaxation. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-25739 A [Patent Document 2] JP 2015-196748 A [Patent Document 3] International Publication No. WO 2015 / 152288 [Patent Document 4] International Publication No. WO 2015 / 152289 Summary of the Invention [Problem to be solved by the invention]

[0007] In the above-mentioned laminate, it is always required to improve the steel wool resistance of the coating layer. On the other hand, the housing of a communication device needs to have low dielectric loss in order to be applied to communication in a high frequency band. Therefore, an object of the present invention is to provide a housing laminate that is resistant to steel wool and has low dielectric loss in a frequency band of 5 GHz or more when used for the housing of a smartphone or the like.

[0008] That is, the present invention relates to a laminate for use in a housing, which has a coating layer on a substrate that is a polycarbonate substrate or a composite plate made of polymethyl methacrylate and polycarbonate, and which is characterized in that the laminate satisfies the following conditions 1 and 2: Condition 1: The relationship between the dielectric constant Dk and the dielectric loss tangent Df measured by the split post dielectric resonator method in the frequency band of 5 GHz or higher must satisfy the following formula. Df×(√Dk)<0.02 Condition 2: 1.5 kg / cm of #0000 steel wool applied to the coating layer 2 No visible scratches are found after 300 reciprocations under load. Effect of the Invention

[0009] According to the present invention, it is possible to provide a laminate for a housing that is both scratch-resistant and has low dielectric loss characteristics in a frequency band of 5 GHz or more. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Each element constituting the present invention will be described in detail below, but the following description is an example of an embodiment of the present invention, and the present invention is not limited to the following description as long as it does not deviate from the gist of the invention. In this specification, when the expression "~" is used, it is used as an expression including the numerical value or physical property value before and after it. In addition, when the expression "(meth)acrylic" is used in the present invention, it means one or both of "acrylic" and "methacrylic". The same applies to "(meth)acrylate" and "(meth)acryloyl".

[0011] The laminate for a housing of the present invention comprises a substrate having a coating layer, and the substrate is a polycarbonate substrate or a composite plate made of polymethyl methacrylate and polycarbonate.

[0012] The dielectric loss of a laminate can be calculated from the relative dielectric constant Dk, the dielectric loss tangent Df, and the signal frequency f using the following formula. Dielectric loss = k × f × Df × (√Dk) (k: constant, f: signal frequency, Df: dielectric tangent, Dk: relative dielectric constant) Therefore, in order to use it in the high frequency range, it is necessary to keep Df×(√Dk) low. In the present invention, for Dk and Df measured by the split post dielectric resonator method in the frequency band of 5 GHz or more, Df×(√Dk) is <0.02, preferably <0.015, and more preferably <0.012. If Df×(√Dk) is within this range, it can be used as a housing laminate in high frequency band communications without any problems.

[0013] The split post dielectric resonator method is one of the methods that can measure the relative dielectric constant Dk and the dielectric loss tangent Df with high accuracy in the frequency band from 1GHz to 20GHz. This measurement is a type of resonance method, and there is a space in the center of the resonator to insert the board to be measured. The relative dielectric constant Dk and the dielectric loss tangent Df can be measured by determining the resonance frequency before and after inserting the board to be measured into this space. The resonator used is one that conforms to IEC-61189.

[0014] The thickness of the polycarbonate substrate as the substrate of the present invention, or the substrate as a composite plate made of polymethyl methacrylate and polycarbonate, is preferably 0.4 mm to 2.0 mm. This is because if the thickness of the supporting substrate is less than 0.4 mm, there may be a problem with the durability of the laminate, and if it exceeds 2.0 mm, there may be a problem with the processability and transparency of the substrate. The thickness of the substrate also affects the dielectric properties, but within this thickness range, Df × (√Dk), which affects the dielectric loss of the housing laminate, does not exceed 0.02. Since the polycarbonate substrate has a relatively low surface hardness, it is preferable to make the coating layer thick in order to provide the desired steel wool resistance, but by using a composite plate substrate made of polymethyl methacrylate and polycarbonate with a higher surface hardness, a laminate with excellent steel wool resistance and impact resistance can be obtained even if the coating layer is relatively thin.

[0015] The housings of mobile communication devices such as smartphones are in frequent contact with the outside world and therefore require resistance to scratches. To evaluate this, the resistance to steel wool is required. Specifically, the resistance to scratches is measured by applying 1.5 kg / cm of #0000 steel wool. 2 It is required that no scratches are visible after 300 reciprocations under a load.

[0016] The coating layer is a cured product of the following photocurable resin composition. The photocurable resin composition for forming the coating layer is preferably composed of (a) a photocurable compound, (b) a photopolymerization initiator, and (c) a solvent.

[0017] Furthermore, the photocurable compound of component (a) preferably contains a photocurable polyfunctional monomer represented by the following formula (1) or (2) as an essential component. [ka] [ka]

[0018] By including (1) and (2), the crosslink density during curing is increased, and as a result, the steel wool resistance can be satisfied. If the above (1) or (2) is not included, the crosslink density during curing is insufficient, making it difficult to satisfy the steel wool resistance, which is not preferred.

[0019] The photocurable compound (a) should have an acrylic mole number per 100 g in the range of 0.8 to 1.1, preferably 0.9 to 1.1, and more preferably 0.95 to 1.05. If the acrylic mole number is less than 0.8, the crosslink density may be low and the scratch resistance may be reduced. On the other hand, if it is more than 1.1, cracks may occur due to excessive stress caused by shrinkage during curing, which may cause poor appearance.

[0020] The number of acrylic moles per 100 g is the number of acrylic moles of each component per 100 g of photocurable compound (number of acrylic functional groups / molecular weight g mol -1 ) is shown.

[0021] It is preferable that 75% by weight or more of the photocurable compound (a) has three or more (meth)acrylic groups in the molecule. If it is less than 75% by weight, the crosslink density decreases and it becomes difficult to satisfy the steel wool resistance.

[0022] Examples of compounds having three or more (meth)acrylic groups in the molecule include pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, trimethylolpropane triacrylate, dimethylolpropane tetraacrylate, trimethylolpropane ethylene oxide-modified triacrylate, trimethylolpropane propylene oxide-modified triacrylate, pentaerythritol ethylene oxide-modified tetraacrylate, dipentaerythritol ethylene oxide-modified pentaacrylate, dipentaerythritol ethylene oxide-modified hexaacrylate, and tris(2-acryloyloxyethyl)isocyanurate.

[0023] The photocurable compound (a) should have a hydroxyl group mole number per 100 g in the range of 0.06 to 0.20, preferably 0.07 to 0.15, and more preferably 0.08 to 0.12. If the mole number is less than this range, the elastic modulus may decrease and the desired steel wool resistance may not be obtained. Conversely, if the mole number exceeds this range, no further improvement can be expected.

[0024] The number of moles of hydroxyl groups per 100 g is the number of hydroxyl groups of each component per 100 g of the photocurable compound (number of hydroxyl groups / molecular weight g mol -1 ) is shown.

[0025] Examples of hydroxyl group-containing (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxyethyl-phthalic acid, glycerin di(meth)acrylate, 2-hydroxy-3-(meth)acryloyloxypropyl (meth)acrylate, pentaerythritol triacrylate, dipentaerythritol pentaacrylate, etc. Among these, those having three or more functional groups are preferred.

[0026] The photocurable compound of component (a) may contain up to two acrylate groups in the molecule in order to adjust the number of acrylic moles and the number of hydroxyl group moles per 100 g.

[0027] Specific examples of the compound containing two or less acrylates in the molecule include 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, tetraethylene glycol dimethacrylate, and dicyclopentanyldimethylol di(meth)acrylate.

[0028] The photocurable compound (a) may contain urethane-modified (meth)acrylates or ethylene oxide-modified (meth)acrylates, which are effective in preventing cracks caused by shrinkage during curing.

[0029] Examples of the (b) photopolymerization initiator of the photocurable resin composition include benzoins such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, and benzoin isobutyl ether; acetophenones such as acetophenone, 2,2-diethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 1,1-dichloroacetophenone, 2-hydroxy-2-methyl-phenylpropan-1-one, diethoxyacetophenone, 1-hydroxycyclohexyl phenyl ketone, and 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one; 2-ethylanthraquinone, 2-phenylpropan-1-one, and the like. Examples of the thioxanthones include anthraquinones such as 2,4-diethylthioxanthone, 2-isopropylthioxanthone, and 2-chlorothioxanthone; ketals such as acetophenone dimethyl ketal and benzyl dimethyl ketal; benzophenones such as benzophenone, 4-benzoyl-4'-methyldiphenyl sulfide and 4,4'-bismethylaminobenzophenone; and phosphine oxides such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide.

[0030] These components (b) can be used alone or as a mixture of two or more kinds, and can further be used in combination with accelerators such as tertiary amines such as triethanolamine and methyldiethanolamine, and benzoic acid derivatives such as N,N-dimethylaminobenzoic acid ethyl ester and N,N-dimethylaminobenzoic acid isoamyl ester.

[0031] The amount of the photopolymerization initiator (b) used is preferably 0.1 to 20 wt% relative to the total of 100 wt% of the (a) components, and more preferably 1 to 10 wt%. If the amount is less than this range, crosslinking may be insufficient, resulting in a decrease in elastic modulus and a failure to obtain the desired steel wool resistance. On the other hand, if the amount exceeds this range, further improvement in the reaction rate may not be expected.

[0032] Examples of the solvent for component (c) that can be used include known organic solvents such as aromatic organic solvents such as toluene and xylene, ketone organic solvents such as methyl ethyl ketone and methyl isobutyl ketone, ester organic solvents such as ethyl acetate, n-propyl acetate, isopropyl acetate and isobutyl acetate, alcohol organic solvents such as methanol, ethanol, n-propanol, isopropanol and n-butanol, and glycol ether organic solvents such as propylene glycol monomethyl ether. In particular, it is preferable to use a glycol organic solvent.

[0033] Examples of the glycol ether organic solvent include ethylene glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol n-propyl ether, ethylene glycol monoisopropyl ether, ethylene glycol dipropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, ethylene glycol dibutyl ether, ethylene glycol isoamyl ether, ethylene glycol monohexyl ether, ethylene glycol mono-2-ethylhexyl ether, methoxyethoxyethanol, and ethylene glycol monoallyl ether; and propylene glycols such as propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, and butoxypropanol, with propylene glycol monomethyl ether being preferred.

[0034] The thickness of the coating layer is preferably 1 to 30 μm. More preferably, it is 5 μm to 20 μm. If it is less than 1 μm, it is easily affected by the supporting substrate, and the desired steel wool resistance may not be obtained. On the other hand, if it exceeds this range, cracks may occur due to excessive stress caused by shrinkage during curing, which may cause poor appearance. Also, within this range, Df × (√Dk), which affects the dielectric loss of the housing laminate, does not exceed 0.02.

[0035] Various additives can be added to the photocurable resin composition within the scope of the present invention. Examples of the various additives include organic / inorganic fillers, slip agents, plasticizers, flame retardants, heat stabilizers, antioxidants, light stabilizers, UV absorbers, lubricants, antistatic agents, release agents, foaming agents, nucleating agents, colorants, crosslinking agents, dispersing agents, resin components, etc.

[0036] The photocurable resin composition can be cured by irradiation with ultraviolet light having a wavelength of 10 to 400 nm or visible light having a wavelength of 400 to 700 nm. The wavelength of the light used is not particularly limited, but near ultraviolet light having a wavelength of 200 to 400 nm is preferably used. Examples of lamps used as ultraviolet light sources include low-pressure mercury lamps (output: 0.4 to 4 W / cm), high-pressure mercury lamps (40 to 160 W / cm), ultra-high-pressure mercury lamps (173 to 435 W / cm), and metal halide lamps (80 to 160 W / cm).

[0037] The method of obtaining a coating film by light irradiation may be either in an oxygen-blocking atmosphere or in an air atmosphere, but the composition of the present invention can provide a good coating even when polymerized and cured in an air atmosphere. Examples of the method include the dripping method, roller coating method, bar coating method, spray coating method, air knife coating method, spin coating method, flow coating method, curtain coating method, and dipping method. The coating film thickness is adjusted by the solid content concentration, taking into account the molded film thickness after drying and curing. EXAMPLES

[0038] The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0039] (Reference Example 1) <Preparation of photocurable resin composition A1 for coating film> Dipentaerythritol hexaacrylate: Mw = 578.57, number of acrylic groups = 6, number of hydroxyl groups = 0 (including dipentaerythritol pentaacrylate: Mw = 524.52, number of acrylic groups = 5, number of hydroxyl groups = 1 35%) (manufactured by Kyoeisha Chemical Co., Ltd., product name DPHA) 60 parts by weight, pentaerythritol triacrylate: Mw = 298.29, number of acrylic groups = 3, number of hydroxyl groups = 1 (including pentaerythritol tetraacrylate: Mw = 352.34, number of acrylic groups = 4, number of hydroxyl groups = 0 40%) (manufactured by Kyoeisha Chemical Co., Ltd., Light Acrylate PE-3A) 20 parts by weight, trimethylolpropane triacrylate: Mw = 296.32, number of acrylic groups = 3, number of hydroxyl groups = 0 (manufactured by Kyoeisha Chemical Co., Ltd. A photocurable resin composition A1 for coating films was obtained by mixing 20 parts by weight of a light acrylate (TMP-A), and further mixing with 8 parts by weight of 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one (Omnirad 907 manufactured by IGM Resins BV) as a photopolymerization initiator and propylene glycol monomethyl ether as an organic solvent so that the solid content was 40%. In this composition A1, the number of moles of acrylic per 100 g of photocurable compound was {[(6 / 578.57×0.65)+(5 / 524.52×0.35)]×0.6+[(4 / 352.34×0.4)+(3 / 298.29×0.6)]×0.2+(3 / 296.32)×0.2}×100=1.02, and the number of moles of hydroxyl groups per 100 g of photocurable compound was [(1 / 524.52×0.35)×0.6+(1 / 298.29×0.6)×0.2]×100=0.08. The ratio of (meth)acrylic groups with three or more functional groups among the components of the photocurable compound was 100%.

[0040] (Reference Examples 2 to 4 and Comparative Reference Examples 1 to 4) Photocurable resin compositions A2 to A4 and B1 to B4 for coating films were obtained in the same manner as in Reference Example 1, except that the raw materials and compositional ratios shown in Table 1 were used. Other abbreviations in the table are as follows: PE-4A: Pentaerythritol tetraacrylate, Mw=352.34, number of acrylic groups=4 (manufactured by Kyoeisha Chemical Co., Ltd.) DCPA: Dimethylol-tricyclodecane diacrylate, Mw = 304.39, number of acrylic groups = 2 (Kyoeisha Chemical Co., Ltd.) G201P: 2-hydroxy-3-acryloyloxypropyl methacrylate, Mw=214.22, (meth)acrylic group number=2, hydroxyl group number=1 (Kyoeisha Chemical Co., Ltd.) TMP-6EO-3A: 6EO modified trimethylolpropane triacrylate, Mw = 560.64, number of acrylic groups = 3 (manufactured by Kyoeisha Chemical Co., Ltd.) EBECRYL210: Aromatic urethane acrylate, Mw=1,500, acrylic group number=2 (manufactured by Daicel-Allnex Corporation) Number of moles of acrylic per 100 g of photocurable compound = Number of moles of acrylic of each component per 100 g of photocurable compound (number of acrylic functional groups / molecular weight g mol -1 ) Number of moles of hydroxyl groups per 100 g of photocurable compound = Number of hydroxyl groups of each component per 100 g of photocurable compound (number of hydroxyl groups / molecular weight g mol -1 )

[0041] (Examples 1 and 2) <Preparation of housing laminates S1 and S2> The above-mentioned photocurable resin composition A1 was applied by spin coating onto a polycarbonate substrate (thickness 0.54 mm, length 10 cm, width 10 cm, manufactured by S-Carbo Sheet Co., Ltd.) so that the film thickness after drying would be 10 μm (S1) or 20 μm (S2), and the coating was dried at 80° C. for 5 minutes and then cooled at room temperature for 5 minutes. Then, the coating was heated at 2 kW / cm in an oxygen atmosphere. 2 A high-pressure mercury lamp is used, with a light output of 2,800 mJ / cm 2 The films were formed with an integrated exposure dose (calculated at 365 nm) to obtain laminates for housings S1 and S2, respectively.

[0042] (Examples 9 and 10) <Preparation of Laminates for Housings T1 and T2> The above-mentioned photocurable resin composition A1 was applied to the polymethyl methacrylate side of a composite plate made of polymethyl methacrylate / polycarbonate (thickness 650 μm, length 10 cm, width 10 cm, manufactured by S-Carbo Sheet Co., Ltd.) by spin coating so that the film thickness after drying would be 10 μm (T1) and 20 μm (T2), and the plate was dried at 80° C. for 5 minutes and then cooled at room temperature for 5 minutes. Thereafter, the plate was heated at 2 kW / cm in an oxygen atmosphere. 2 A high-pressure mercury lamp is used, with a light output of 2,800 mJ / cm 2 The films were formed with an integrated exposure dose (calculated at 365 nm) to obtain laminates for housings T1 and T2, respectively.

[0043] (Examples 3 to 8) <Preparation of laminates S3 to S8> Housing laminates S3 to S8 were produced in the same manner as in Examples 1 and 2, except that photocurable resin compositions A2 to A4 mixed in the composition ratios shown in Table 1 were used.

[0044] (Examples 11 to 12) <Preparation of Laminates T3 to T4> Housing laminates T3 to T4 were produced in the same manner as in Examples 9 and 10, except that the photocurable resin composition A2 having the composition ratio in Table 1 was used.

[0045] (Comparative Examples 1, 2, and 3) Gorilla Glass (reinforced, Corning) without a coating layer, polycarbonate without a coating layer, and a polymethyl methacrylate / polycarbonate composite plate without a coating layer were used as Comparative Examples 1, 2, and 3, respectively.

[0046] (Comparative Examples 4 to 11) Housing laminates U1 to U8 were produced in the same manner as in Examples 9 and 10, except that photocurable resin compositions B1 to B4 having the composition ratios shown in Table 1 were used.

[0047] <Evaluation> The following evaluations were carried out using the laminates for housings S1 to S8 (Examples), T1 to T4 (Examples), Gorilla Glass without a coating layer, polycarbonate without a coating layer, and polymethyl methacrylate / polycarbonate composite plate without a coating layer (Comparative Example), as well as the laminates for housings U1 to U8 (Comparative Example). The evaluation results are shown in Tables 2 and 3. <Steel wool resistance> Using #0000 steel wool, a reciprocating abrasion tester (Type: 30S, manufactured by HEIDON) was used with a load of 1.5 kg / cm 2 The surface of the coating layer was abraded 300 times with a swipe of a cloth. Scratches of 1 mm or more in length were considered to be scratches, and the presence or absence of scratches was visually observed under fluorescent lights, and the number of scratches was evaluated according to the following criteria. 〇: No scratches △: Less than 10 scratches ×: 10 or more scratches

[0048] <Dielectric constant Df, dielectric loss tangent Dk, Df×(√Dk)> The sample was left to stand for 24 hours or more in an atmosphere of 23°C and 50% RH, and the dielectric constant Df and dielectric loss tangent Dk were measured at frequencies of 5 GHz and 10 GHz by the split post dielectric resonator method using a Network Analyzer E8363C (product name) manufactured by Agilent Technologies in an atmosphere of 23°C. In addition, Df × (√Dk) was calculated from the obtained values.

[0049] [Table 1]

[0050] [Table 2]

[0051] [Table 3]

Claims

1. A laminate for use in a housing, comprising a coating layer on a substrate that is a polycarbonate substrate or a composite plate made of polymethyl methacrylate and polycarbonate, wherein the coating layer is a cured product of a photocurable resin composition, the composition containing (a) a photocurable compound, (b) a photopolymerization initiator, and (c) a solvent, the photocurable compound contains a photocurable polyfunctional monomer represented by the following formula (1) or (2) as an essential component, the number of acrylic moles per 100 g of the photocurable compound is 0.8 or more and 1.1 or less, and the laminate for a housing is characterized in that it satisfies the following conditions 1 and 2: 【Chemistry 1】 【Chemistry 2】 Condition 1: The relationship between the relative dielectric constant Dk and the dielectric loss tangent Df measured by the split post dielectric resonator method in a frequency band of 5 GHz or more satisfies the following formula: Df × (√Dk) < 0.02 Condition 2: 1.5 kg / cm of #0000 steel wool applied to the coating layer ２ No visible scratches should be observed after 300 reciprocations under a load.

2. 2. The laminate for a casing according to claim 1, wherein the substrate which is a polycarbonate substrate or a composite plate made of polymethyl methacrylate and polycarbonate has a thickness of 0.4 to 2.0 mm.

3. (delete)

4. (delete)

5. 3. The laminate for a casing according to claim 1, wherein 75% by mass or more of the photocurable compound has three or more (meth)acrylic groups in the molecule.

6. 6. The laminate for a casing according to claim 1, wherein the number of moles of hydroxyl groups per 100 g of the photocurable compound is 0.06 or more and 0.2 or less.

7. 7. The laminate for a casing according to claim 1, 2, 5 or 6, wherein the coating layer has a thickness of 1 to 30 μm.

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