DECORATIVE ELEMENT

Abstract

Decorative element (1), comprising: a base material (2) consisting of synthetic resin; and a film body (4) arranged on the base material (2) and consisting of an agglomeration of inorganic fine particles having a metal surface, wherein each of the inorganic fine particles has a gold coating layer or a silver coating layer on a surface of a non-metallic fine particle, an attenuation rate when a millimeter wave with a frequency in the range of 18 to 300 GHz is transmitted is in a range of 0.001 to 2 dB and an L* value (brightness) is in a range of 45 to 95.

Description

TECHNICAL FIELD

[0001] The present invention relates to a decorative element used for an emblem or the like indicating, for example, a vehicle manufacturer. Background technology

[0002] Recently, a technique for measuring the distance between, for example, a preceding vehicle or an obstacle and the host vehicle, and the relative speed for automated driving (automated driving mode) has been investigated. A sensor mounted on the front of a vehicle is used to control the distance between the vehicles while the host vehicle accelerates and decelerates. A radio wave transmitting and receiving device, such as a millimeter-wave radar, is typically used as the sensor.

[0003] The radio wave transmitting and receiving device such as millimeter-wave radar is preferably arranged at the center of the vehicle front portion to perform its function, and is often arranged behind an emblem or the like indicating, for example, a vehicle manufacturing company. In this case, after a millimeter wave emitted from the radio wave transmitting and receiving device is radiated forward by the emblem or the like, it is reflected by, for example, the preceding vehicle or the obstacle, and the radio wave transmitting and receiving device receives the reflected wave again by the emblem or the like. Therefore, the emblem is preferably made of a decorative member that has low transmission loss of the millimeter wave and, moreover, has an excellent fine appearance due to the metallic luster as its original purpose.

[0004] As a decorative element used for the emblem or the like, one in which nanoparticles of, for example, gold, silver, tin, indium, their alloys or the like are dispersed as a binder in a synthetic resin layer is known (see, for example, Patent Document 1).

[0005] While the decorative element described in Patent Document 1 can obtain a fine appearance due to the metallic luster of the metal nanoparticles, the millimeter wave can be transmitted through discontinuous portions of the metal nanoparticles, so its transmission loss is considered to be reduced.

[0006] Patent Document 1: JP-A-2013-185869 (paragraph 0007 and Fig. 5a)

[0007] WO 2018 / 079547 A1 discloses a laminated body comprising a plastic base material, an ITO layer, and a metal film body. The film body consists of metal nanoparticle agglomerates, in particular aluminum or silver. Disclosure of the invention Problems to be solved by the invention

[0008] However, in the decorative element where the metal nanoparticles are dispersed in the resin layer, the resin impairs the metallic luster of the nanoparticles, and it is unsuitable to easily achieve a sufficiently fine appearance.

[0009] It is an object of the present invention to provide a decorative member which eliminates such a lack of suitability to reduce the transmission loss of a millimeter wave and which further has an excellent metallic luster. SOLUTIONS TO THE PROBLEMS

[0010] To achieve this object, a decorative element comprises the features of claim 1.

[0011] The decorative element of the present invention comprises a film body comprising an agglomeration of inorganic fine particles having a metal surface on the synthetic resin base material. The film body is the agglomeration of the inorganic fine particles, and the inorganic fine particles do not form mutual couplings. Therefore, the millimeter wave can be transmitted through the gaps between the inorganic fine particles, reducing its transmission loss.

[0012] Since the film body essentially contains only the inorganic fine particles, does not contain any synthetic resin, and the inorganic fine particles have at least one metal surface, an excellent metallic luster can be achieved.

[0013] Accordingly, in the decorative member of the present invention, the attenuation rate as an index of the transmission loss of the millimeter wave is in the range of 0.001 to 2 dB, and the L* value (brightness) as an index of the metallic luster is in the range of 45 to 95, preferably in the range of 50 to 95, and more preferably in the range of 60 to 95.

[0014] In the decorative element of the present invention, the transmission loss of the millimeter wave becomes large when the attenuation rate exceeds 2 dB, and the millimeter wave cannot be transmitted substantially. Furthermore, it is technically difficult to adjust the attenuation rate to less than 0.001 dB.

[0015] Furthermore, in the decorative element of the present invention, if the L* (brightness) value is below 40, the metallic luster cannot be achieved. Furthermore, it is technically difficult to adjust the L* (brightness) value to more than 95.

[0016] Further, in the decorative member of the present invention, the inorganic fine particle only needs to have at least the metal surface, for example, it may contain a metal coating layer on a surface of a non-metallic fine particle such as alumina.

[0017] When the inorganic fine particle contains the metal plating layer on the surface, for example, a gold plating layer or a silver plating layer is preferably used as the plating layer in order to impart a fine appearance to the decorative member of the present invention by the metallic luster.

[0018] Furthermore, the inorganic fine particles in the decorative element of the present invention preferably have an average particle diameter in a range of 1 to 100 nm, and more preferably, an average particle diameter of 10 to 70 nm. When the decorative element of the present invention has an average particle diameter of the inorganic fine particles exceeding 100 nm, the transmission loss of the millimeter wave becomes excessively large in some cases. Moreover, it is technically difficult to set the average particle diameter of the inorganic fine particles to less than 1 nm.

[0019] Furthermore, in the decorative element of the present invention, the film body preferably has a thickness in the range of 10 to 300 nm, and more preferably a thickness in the range of 10 to 100 nm. If the decorative element of the present invention has a film body thickness exceeding 300 nm, the transmission loss of the millimeter wave becomes excessively large in some cases. If it is less than 10 nm, sufficient metallic luster cannot be achieved in some cases.

[0020] Furthermore, the decorative element of the present invention preferably comprises a protective coating layer positioned on the film body. Since the film body essentially comprises only the inorganic fine particles and contains no synthetic resin, if the surface of the film body is exposed, the individual inorganic fine particles may be separated from the film body. However, the enclosed protective coating layer can prevent the inorganic fine particles from being separated.

[0021] Furthermore, the decorative element of the present invention preferably has a base layer disposed between the base material and the film body. The decorative element of the present invention has the base layer, whereby the adhesion of the film body to the base material can be improved. BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 is an explanatory cross-sectional view illustrating a configuration of a decorative member of the present invention. DESCRIPTION OF PREFERRED EMBODIMENTS

[0022] An embodiment of the present invention will now be described in more detail with reference to the accompanying drawings.

[0023] A decorative member 1 of this embodiment is used, for example, for an emblem or the like, which is arranged on a path of the millimeter wave to be transmitted and received, for example, by a radio wave transmitting and receiving device such as a millimeter-wave radar mounted on a vehicle or the like. The decorative member 1 includes, for example, a base material 2 made of a synthetic resin, a sub-layer 3 positioned on the base material 2 as a base layer, a film body 4 positioned on the sub-layer 3 and containing an agglomeration of inorganic fine particles having at least one metal surface, and a protective layer 5 positioned on the film body 4 as a protective coating layer.

[0024] The synthetic resin constituting the base material 2 can be listed, for example, as: a polycarbonate resin, an acrylic resin, an epoxy resin, a polystyrene resin, a polyethylene terephthalate resin, a polyurethane resin, a polyethylene resin, a polypropylene resin, and an ABS resin.

[0025] The undercoat layer 3 can be anything as long as the adhesion of the film body 4 to the base material 2 can be improved. For example, the undercoat layer 3 may comprise a coating material using a synthetic resin such as a two-component urethane coating material, an epoxy coating material, a UV-curable coating material, and an air-dry coating material as the main agent. An example of the coating material may be a mixture in a mass ratio of 100:25:120 of a main agent (product name: EC-MM82-1003X) manufactured by Musashi Paint Co., Ltd., a hardener (product name: Z-EC-H-400), and a thinner (product name: Z-EC-K785).

[0026] The film body 4 comprises the agglomeration of inorganic fine particles having at least the metal surface. An example of the inorganic fine particle may include one having a gold coating layer or a silver coating layer on the surfaces of non-metallic fine particles such as alumina. Furthermore, the inorganic fine particles may use those having an average particle diameter in a range of 1 to 100 nm, preferably in a range of 10 to 50 nm.

[0027] The film body 4 can be formed by applying a dispersion liquid of inorganic fine particles, which is prepared by dispersing the inorganic fine particles in a volatile solvent, over the underlayer 3 and evaporating the volatile solvent. The dispersion liquid of inorganic fine particles can be diluted with the volatile solvent as a diluent (thinner).

[0028] The volatile solvents can be listed as, for example, isopropanol, methanol, ethanol, toluene, xylene, ethyl acetate, butyl acetate, methyl ethyl ketone, and cyclohexanone. Each of the volatile solvents can be used alone, and two or more of them can be mixed for use. The volatile solvent in which the inorganic fine particles are dispersed and the volatile solvent used as the diluent can be the same or different.

[0029] An example of the inorganic fine particle dispersion liquid may be a liquid comprising propylene glycol monomethyl ether as a dispersion medium.

[0030] The film body 4 is formed as described above and can thus have a thickness in a range of 10 to 300 nm, for example.

[0031] The protective layer 5 may be anything as long as it can prevent individual inorganic fine particles from detaching from the film body and falling off the film body 4. For example, the protective layer 5 may comprise a coating material using a synthetic resin such as a two-component urethane coating material, an epoxy coating material, a UV-curable coating material, and an air-dry coating material as the main agent. An example of the coating material may be a mixture in a mass ratio of 100:15:80 of a main agent (product name: EC-MM62-1003X) manufactured by Musashi Paint Co., Ltd., a hardener (product name: Z-EC-H-760), and a thinner (product name: Z-EC-K785).

[0032] In the decorative member 1 of this embodiment having the above-described configuration, an attenuation rate as an index of transmission loss when transmitting a millimeter wave having a frequency in the range of 18 to 300 GHz is in a range of 0.001 to 2 dB, and an L* value (brightness) as an index of metallic luster is in a range of 50 to 95, preferably in a range of 60 to 95.

[0033] Note that the decorative element 1 of this embodiment is configured to include the undercoat layer 3 positioned between the base material 2 and the film body 4 as a base layer, and the protective layer 5 positioned on the film body 4 as a protective coating layer. However, the decorative element 1 of this embodiment may be configured to include neither of the undercoat layer 3 and the protective layer 5, or in some cases, both of them.

Claims

[1] Decorative element (1), comprising: a base material (2) consisting of synthetic resin; and a film body (4) arranged on the base material (2) and consisting of an agglomeration of inorganic fine particles having a metal surface, wherein each of the inorganic fine particles has a gold coating layer or a silver coating layer on a surface of a non-metallic fine particle, an attenuation rate when a millimeter wave with a frequency in the range of 18 to 300 GHz is transmitted is in a range of 0.001 to 2 dB and an L* value (brightness) is in a range of 45 to 95. [2] The decorative member (1) according to claim 1, wherein the attenuation rate is an attenuation rate when a millimeter wave having a frequency in a range of 18 to 100 GHz is transmitted. [3] Decorative element (1) according to claim 1, wherein the L* value (brightness) is in a range of 50 to 95. [4] Decorative element (1) according to claim 1, wherein the L* value (brightness) is in a range of 60 to 95. [5] Decorative element (1) according to claim 1, wherein the inorganic fine particles have an average particle diameter in a range of 1 to 100 nm. [6] Decorative element (1) according to claim 5, wherein the inorganic fine particles have an average particle diameter in a range of 10 to 70 nm. [7] Decorative element (1) according to claim 1, wherein the film body (4) has a thickness in a range of 10 to 300 nm. [8] Decorative element (1) according to claim 1, comprising a protective coating layer (5) positioned on the film body (4). [9] Decorative element (1) according to claim 1, comprising a base layer (3) arranged between the base material (2) and the film body (4).

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