Sensor cover

Abstract

Provided is a sensor cover including a base material and a silver particle layer provided on the base material, the silver particles in the silver particle layer having a radio wave-transmitting layer on the surface.

Description

Technical Field

[0001] The present disclosure relates to a sensor cover. Background Art

[0002] In recent years, attention to millimeter wave sensors has continued to increase.

[0003] For example, cars have made significant progress in safety features in recent years; for example, automatic collision avoidance systems have become commonplace.

[0004] The automatic collision avoidance system uses image data from the vehicle's camera and information about the relative distance to an object obtained by the millimeter-wave radar to automatically apply the brakes.

[0005] In addition, as the focus on energy saving, resource conservation, safety, and health increases, the use of millimeter wave sensors in buildings such as homes is also gaining attention. In addition to the conventional functions of infrared human body sensors that detect people, hands, etc. and automatically switch on and off, millimeter wave sensors can also sense the movements of objects such as people, so they can also detect falls and monitor health conditions such as pulse and respiratory rate.

[0006] Until now, the sensor cover of human detection sensors has been mainly made of flat or curved plastic, lacking design and artistry. However, if a metal coating is placed on the sensor cover to give it a clean and high-end metallic look, the sensor placed behind it will not function because neither millimeter waves nor infrared rays can pass through the metal coating.

[0007] As a material replacing the metal plating layer, that is, as a material that forms a metallic surface and transmits millimeter waves, an indium vapor-deposited film, a metallic film, and the like are known (for example, Japanese Patent Application Laid-Open No. 2022-082052). Summary of the invention

[0008] Problems to be solved by the invention

[0009] However, indium vapor-deposited films are insufficient in terms of metallic feel, and metallic-style films are difficult to decorate into complex artistic shapes.

[0010] Infrared sensors, which are widely used as human body detection sensors, are also required to have a metal-like sensor cover that gives a clean and high-quality feel.

[0011] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a sensor cover having excellent metallic gloss and excellent radio wave transmittance.

[0012] Methods for solving problems

[0013] The specific method for achieving the above-mentioned subject is as follows.

[0014] <1> A sensor cover comprising a substrate and a silver particle layer provided on the substrate and comprising silver particles,

[0015] The silver particles have a radio wave transmission layer on the surface.

[0016] <2> In the sensor cover according to <1>, the radio wave transmission layer is an organic layer.

[0017] <3> The sensor cover according to <1> or <2>, wherein the silver particles include secondary particles, and the radio wave transmission layer is provided on the surface of the silver particles which are primary particles.

[0018] <4> The sensor cover according to any one of <1> to <3>, wherein the radio wave transmission layer is a millimeter wave transmission layer.

[0019] <5> The sensor cover according to any one of <1> to <4>, wherein the radio wave transmission layer is a layer that transmits at least a portion of wavelengths in a wavelength range from infrared light to visible light.

[0020] <6> The sensor cover according to any one of <1> to <5>, which is a cover for a millimeter wave sensor or an infrared sensor.

[0021] Effects of the Invention

[0022] According to the present disclosure, a sensor cover having excellent metallic gloss and excellent radio wave transmittance can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] [ Figure 1 ] is a scanning transmission electron microscope (STEM) photograph of the silver particle layer obtained in the example.

[0024] [ Figure 2 ] is a transmission electron microscope-energy dispersive X-ray spectroscopy (TEM-EDX) image of the silver particle layer obtained in the example.

[0025] [ Figure 3 ] is the spectral transmittance spectrum in the infrared to ultraviolet region of the laminate A and the single polycarbonate substrate B prepared in the example.

[0026] [ Figure 4 ] is the spectral reflectance spectrum in the infrared to ultraviolet region of the laminate A and the single polycarbonate substrate B prepared in the example. DETAILED DESCRIPTION

[0027] Hereinafter, the method for implementing the present disclosure is described in detail. However, the present disclosure is not limited to the following embodiments. In the following embodiments, except for the cases explicitly stated otherwise, its constituent elements (including element steps, etc.) are not necessary. Numerical values ​​and their ranges are also the same and do not limit the present disclosure.

[0028] In the present disclosure, a numerical range expressed using "to" includes the numerical values ​​described before and after "to" as a minimum value and a maximum value, respectively.

[0029] In the numerical ranges recorded in stages in the present disclosure, the upper limit or lower limit recorded in one numerical range can be replaced by the upper limit or lower limit of the numerical range recorded in other stages. In addition, in the numerical ranges recorded in the present disclosure, the upper limit or lower limit of the numerical range can be replaced by the value shown in the embodiment.

[0030] In the present disclosure, each component may contain a plurality of substances corresponding to each component. When a plurality of substances corresponding to each component are present in the composition, the content rate or content of each component refers to the total content rate or content of the plurality of substances present in the composition unless otherwise specified.

[0031] In the present disclosure, particles corresponding to each component may include multiple types of particles. When multiple types of particles corresponding to each component exist in the composition, the particle size of each component refers to the value for the mixture of the multiple types of particles present in the composition unless otherwise specified.

[0032] In the present disclosure, the term “layer” or “film” includes a case where the layer or film is formed on the entire region when the region where the layer or film exists is observed, and also includes a case where the layer or film is formed on only a part of the region.

[0033] <Sensor cover>

[0034] The sensor cover disclosed in the present invention includes a substrate and a silver particle layer provided on the substrate and including silver particles, wherein the silver particles have a radio wave transmission layer on the surface.

[0035] The sensor cover of the present disclosure has excellent metallic gloss and excellent radio wave transmittance. The reason for this is presumably as follows.

[0036] The silver particles in the silver particle layer are easy to condense, in which case, radio waves (millimeter waves) do not penetrate or are difficult to penetrate the gaps between the silver particles. Therefore, in the present disclosure, a radio wave transmission layer is provided on the surface of the silver particles. It is believed that due to the presence of the radio wave transmission layer, gaps are provided between the silver particles, and radio waves can penetrate the gaps. If silver particles having a radio wave transmission layer on the surface are used, radio waves can penetrate even if the filling property of the silver particles is improved, so the filling property of the silver particles can be improved, and the metallic luster is excellent.

[0037] Hereinafter, each member used in the present disclosure will be described.

[0038] -Base Material-

[0039] The material of the substrate is not particularly limited, and inorganic materials such as glass, organic materials such as resins, etc. can be used. Examples of the resin include thermosetting resins and thermoplastic resins.

[0040] Examples of thermoplastic resins include polyethylene, polypropylene, polycarbonate, polystyrene, polyvinyl chloride, vinyl polymers, polyesters, polyamides, ABS resins (acrylonitrile-butadiene-styrene copolymer resins), polyesters, thermoplastic elastomers, acrylic resins, etc. These resins may be used alone or in combination of two or more. Examples of two or more combinations of two or more include polycarbonate / ABS resins, etc.

[0041] Examples of the thermosetting resin include silicone resins, polyurethane resins, polyester resins, melamine resins, epoxy resins, phenolic resins, urea resins, etc. These resins may be used alone or in combination of two or more.

[0042] When used for a sensor cover, as the material of the base material, for example, polypropylene, polycarbonate, ABS resin, polycarbonate / ABS, acrylic resin, etc. are preferably used. Polypropylene has a relatively light specific gravity among resins, is easy to process, has high tensile strength, impact strength and compression strength, and is also excellent in weather resistance and heat resistance. ABS resin is relatively easy to implement surface treatment among plastic materials, so it is a resin that is easy to implement coating after the base material is formed, has excellent chemical resistance and rigidity, and is also excellent in impact resistance, heat resistance and cold resistance. Polycarbonate has high impact resistance among plastic materials, is also excellent in weather resistance and heat resistance, and is also excellent in transparency. In addition, polycarbonate is also easy to process and is a relatively light and strong material among plastic materials.

[0043] The substrate may be provided with a primer layer in order to improve the adhesion between the substrate and the silver particle layer, smooth the surface of the substrate, and the like.

[0044] The material of the primer layer is not particularly limited and can be selected according to the purpose of the primer layer. For example, fluororesins, polyester resins, epoxy resins, melamine resins, silicone resins, acrylic silicone resins, acrylic urethane resins, etc. can be used. These resins can be in the form of coatings with solvents added.

[0045] The thickness of the primer layer is not particularly limited, but is preferably about 5 μm to 25 μm from the viewpoint of ensuring a smooth surface.

[0046] In order to improve the adhesion between the primer layer and the substrate, a primer layer may be provided between the primer layer and the substrate.

[0047] The thickness of the substrate can be appropriately designed according to the application of the sensor cover. The shape of the substrate is also not particularly limited.

[0048] -Silver particle layer-

[0049] The silver particle layer includes silver particles having an electric wave transmission layer on the surface. The silver particle layer may be a layer formed by a silver mirror reaction. In addition, the silver particles contained in the silver particle layer may include silver particles precipitated by the silver mirror reaction (precipitated silver particles). Furthermore, the silver particle layer may present a sea island structure in which silver particles are dispersed in an island shape.

[0050] The formation of the silver particle layer based on the silver mirror reaction can be carried out by bringing an aqueous ammoniacal silver nitrate solution into contact with an aqueous reducing agent solution, thereby causing a redox reaction to generate silver particles and form the silver particle layer.

[0051] In one embodiment of the present disclosure, the ammoniacal silver nitrate aqueous solution is obtained by dissolving silver nitrate, ammonia, and at least one amine compound selected from the group consisting of amino alcohol compounds, amino acids, and amino acid salts in water.

[0052] Specific examples of the amine compound include amino alcohol compounds such as monoethanolamine, diethanolamine, diisopropanolamine, triethanolamine, and triisopropanolamine; amino acids such as glycine, alanine, and sodium glycinate; and salts thereof.

[0053] The contents of silver nitrate, ammonia, and the amine compound contained in the aqueous ammoniacal silver nitrate solution are not particularly limited.

[0054] The concentration of silver nitrate contained in the aqueous ammoniacal silver nitrate solution is not particularly limited, but is preferably adjusted within a range of 0.1% by mass to 10% by mass from the viewpoint of controlling the reaction rate.

[0055] The pH of the ammoniacal silver nitrate aqueous solution is preferably adjusted to between 10 and 13, and more preferably between 11 and 12.

[0056] In one embodiment of the present disclosure, the reducing agent aqueous solution is obtained by dissolving a reducing agent including a phenolic compound and a strong base component in water.

[0057] Examples of the phenolic compound contained in the reducing agent include catechol compounds such as hydroquinone, catechol, and resorcinol, and among them, hydroquinone is preferred.

[0058] The reducing agent may be a phenolic compound alone or a combination of a phenolic compound and a compound other than a phenolic compound. Examples of the compound other than a phenolic compound include hydrazine compounds such as hydrazine sulfate, hydrazine carbonate, and hydrazine hydrate, sulfite compounds such as sodium sulfite, and thiosulfate compounds such as sodium thiosulfate.

[0059] When the reducing agent contains a phenolic compound and a compound other than the phenolic compound, the proportion of the phenolic compound is preferably 50% by mass or more, more preferably 70% by mass or more, and further preferably 90% by mass or more of the entire reducing agent.

[0060] Specific examples of the strong base component contained in the reducing agent aqueous solution include sodium hydroxide and potassium hydroxide.

[0061] The reducing agent aqueous solution may contain the above-mentioned amine compound as necessary.

[0062] The reducing agent aqueous solution may contain a compound containing a formyl group as necessary. Specific examples of the compound containing a formyl group include glucose and glyoxal.

[0063] The contents of the reducing agent, the strong base component, the amine compound contained as needed, and the compound containing a formyl group contained as needed in the reducing agent aqueous solution are not particularly limited.

[0064] The concentration of the reducing agent contained in the aqueous reducing agent solution is not particularly limited, but is preferably adjusted within a range of 0.1% by mass to 10% by mass from the viewpoint of controlling the reaction rate.

[0065] The pH of the reducing agent aqueous solution is preferably adjusted to between 10 and 13, and more preferably between 10.5 and 11.5.

[0066] The average primary particle size of the silver particles in the silver particle layer is preferably 1 nm to 30 nm, more preferably 5 nm to 25 nm, and further preferably 10 nm to 20 nm. If the average primary particle size of the silver particles in the silver particle layer is 15 nm or more, the homogeneity of the silver particle layer is further improved and the appearance is improved.

[0067] The silver particles in the silver particle layer may also aggregate to form secondary particles, and the average secondary particle size is preferably 350 nm or less, more preferably 300 nm or less, and further preferably 250 nm or less.

[0068] The average primary particle size and the average secondary particle size of the silver particles were determined by measuring the diameters of 50 silver particles using a scanning microscope (SEM) image or a transmission electron microscope (TEM) image and calculating the arithmetic average thereof.

[0069] The radio wave transmission layer arranged on the surface of the silver particles is not limited as long as it transmits radio waves. As radio waves, millimeter waves, microwaves, etc. can be cited, and the radio wave transmission layer is preferably a millimeter wave transmission layer that transmits millimeter waves. In addition, the radio wave transmission layer is preferably a layer that transmits at least a portion of the wavelength in the wavelength region from infrared to visible light.

[0070] Examples of the radio wave transmitting layer include an organic layer.

[0071] The organic layer may be composed of a reducing agent used in the silver mirror reaction, a compound derived from the reducing agent, or a combination thereof. For example, when hydroquinone is used as the reducing agent, the organic layer may be composed of hydroquinone, benzoquinone obtained by oxidation of hydroquinone, or a combination of hydroquinone and benzoquinone.

[0072] The average thickness of the radio wave transmission layer is preferably 20 nm to 400 nm, more preferably 50 nm to 400 nm, further preferably 70 nm to 350 nm, and particularly preferably 100 nm to 250 nm. If the average thickness of the radio wave transmission layer is less than or equal to 400 nm, the radio wave transmittance is excellent, and if it is greater than or equal to 20 nm, the homogeneity of the silver particle layer is excellent and the appearance is improved.

[0073] The average thickness of the radio wave transmission layer is determined by measuring the thickness of 50 locations of the radio wave transmission layer using a scanning transmission electron microscope (STEM) image or a transmission electron microscope-energy dispersive X-ray spectroscopy (TEM-EDX) image and calculating the arithmetic average thereof.

[0074] When silver particles aggregate to form secondary particles, it is preferred that a radio wave transmission layer is provided on the surface of the silver particles of the primary particles. If a radio wave transmission layer is provided on the surface of the silver particles of the primary particles, even if the silver particles form secondary particles, gaps are provided in the primary particles due to the presence of the radio wave transmission layer, and since radio waves can pass through the gaps, the radio wave transmission property is excellent.

[0075] The radio wave transmission layer may be provided on the entire surface of the silver particles or may be provided partially. In addition, the radio wave transmission layer may be an aggregate of granular materials.

[0076] The thickness of the silver particle layer formed on the substrate is not particularly limited. From the perspective of obtaining sufficient metallic luster, the thickness of the silver particle layer is preferably greater than or equal to 50 nm, and from the perspective of obtaining sufficient millimeter wave transmittance, the thickness of the silver particle layer is preferably less than or equal to 300 nm.

[0077] When observing the cross section of the silver particle layer in the thickness direction, the proportion of silver particles in the silver particle layer is preferably less than or equal to 95%. If the proportion of silver particles in the silver particle layer is less than or equal to 95%, there is a tendency that the transmittance of millimeter waves is further improved. From the viewpoint of obtaining sufficient metallic luster, the proportion of silver particles in the silver particle layer is preferably greater than or equal to 80%.

[0078] The ratio of the silver particles in the silver particle layer refers to a value measured as follows.

[0079] A transmission electron microscope photograph is taken at a magnification of 300,000 times for a cross section of the silver particle layer in the sensor cover in the thickness direction. For the obtained electron microscope photograph, a center line passing through the center of the silver particle layer in the thickness direction is determined. Next, the length of the portion where the center line overlaps with the silver particles is calculated. The length of the portion where the center line overlaps with the silver particles is divided by the length of the entire center line, and the percentage of the value obtained is defined as the ratio of the silver particles in the silver particle layer.

[0080] The surface resistivity of the silver particle layer is preferably greater than or equal to 10 5 Ω / □, more preferably greater than or equal to 10 6 Ω / □. If the surface resistivity of the silver particle layer is within the above range, it can be determined that sufficient millimeter wave transmittance is achieved. The upper limit of the surface resistivity of the silver particle layer is not particularly limited.

[0081] The surface resistivity of the silver particle layer is a value measured in accordance with JIS K6911:2006.

[0082] -Top Coating-

[0083] The sensor cover may have layers other than the substrate and the silver particle layer as needed. For example, a top coating layer may be provided on the silver particle layer for the purpose of protecting the silver particle layer.

[0084] The top coat layer preferably has enough transparency not to obscure the metallic luster of the silver particle layer and enough transmittance not to block millimeter waves, and may be colorless and transparent (colorless transparent) or colored and transparent (colored transparent).

[0085] The material of the top coat layer is not particularly limited, and can be selected from, for example, the resins described above as the material of the base coat layer.

[0086] The thickness of the top coating layer is not particularly limited, but is preferably about 20 μm to 40 μm. If the thickness of the top coating layer is greater than or equal to 20 μm, it tends to be able to fully protect the silver particle layer, while if it is less than or equal to 40 μm, it tends to be less likely to cause cracks, peeling, poor adhesion, etc. due to changes over time.

[0087] <Physical properties of sensor cover>

[0088] The transmission attenuation of the sensor cover at 77.0 GHz, which is a millimeter wave region, is preferably 3.0 dB or less, more preferably 2.0 dB or less, and further preferably 1.0 dB or less.

[0089] The transmission attenuation of the sensor cover can be measured based on JIS R1679:2007 (Method for measuring the radio wave absorption characteristics of radio wave absorbers in the millimeter wave band). The transmission wave (transmission coefficient) is obtained by placing the sample between the transmitting antenna and the receiving antenna and irradiating the electromagnetic wave perpendicularly to the sample using the free space method, and the transmission wave (transmission coefficient) is calculated from the transmission wave (transmission coefficient). The transmission attenuation can be calculated using the transmission coefficient (absolute value) using the following formula.

[0090] Transmission attenuation = 20log 10 |(Transmittance coefficient)|

[0091] The spectral transmittance at a wavelength of 800 nm in the infrared region is preferably 5% or more, and the spectral transmittance at a wavelength of 900 nm to 1600 nm is preferably 10% or more.

[0092] The spectral transmittance in the visible light region at a wavelength of 400 nm is preferably 1% or more, the spectral transmittance at a wavelength of 500 to 600 nm is preferably 0.05% or more, and the spectral transmittance at a wavelength of 700 nm is preferably 1% or more.

[0093] It was confirmed that the color can be sufficiently recognized visually even if the spectral transmittance at a wavelength of 580 nm in the measurement method described below is about 0.1%.

[0094] The spectral reflectivity at a wavelength of 400nm in the visible light region is preferably greater than or equal to 40%, the spectral reflectivity at a wavelength of 500nm is preferably greater than or equal to 60%, the spectral reflectivity at a wavelength of 600nm is preferably greater than or equal to 50%, and the spectral reflectivity at a wavelength of 700nm to 800nm ​​is preferably greater than or equal to 35%.

[0095] The spectral transmittance and spectral reflectance of the sensor cover in the infrared to visible light wavelength range were measured at 25° C. in the air using an ultraviolet-visible-near-infrared (UV-VIS-NIR) spectrophotometer.

[0096] <Method for manufacturing sensor cover>

[0097] The method for producing the sensor cover is not particularly limited. Hereinafter, a method for forming a silver particle layer by a silver mirror reaction will be described.

[0098] In forming the silver particle layer by the silver mirror reaction, the method of contacting the aqueous ammoniacal silver nitrate solution with the aqueous reducing agent solution is not particularly limited, and examples thereof include a method of applying these aqueous solutions to the surface of the substrate in a mixed or unmixed state.

[0099] There is no particular limitation on the method of applying the ammoniacal silver nitrate aqueous solution and the reducing agent aqueous solution to the reaction treated surface of the silver mirror. Among them, spraying that can form a uniform silver particle layer regardless of the shape of the substrate is suitable. Spraying can be carried out using known means such as an air brush and a spray gun.

[0100] When the radio wave transmission layer is composed of a reducing agent, a compound derived from a reducing agent, or a combination thereof, the spraying is preferably performed by the following method from the viewpoint of making the radio wave transmission layer more reliably present on the surface of the silver particles.

[0101] Different spray brushes are used for the ammoniacal silver nitrate aqueous solution and the reducing agent aqueous solution. Then, the position and spray direction of the spray brush are fixed, and the substrate is moved to spray the entire surface of the substrate. It is preferably adjusted so that the spraying position of the ammoniacal silver nitrate aqueous solution and the spraying position of the reducing agent aqueous solution sprayed from different spray brushes overlap.

[0102] Since the spraying conditions of each liquid are fixed by fixing the position and the spraying direction of the spray brush, the radio wave transmission layer can be homogeneous and reliably present on the surface of the silver particles. The moving method of the substrate is not particularly limited, and the substrate can be rotated or slid. In addition, in the method, the spraying performed by the spray brush and the movement of the substrate can be automated.

[0103] The discharge amount of each liquid discharged from the airbrush can be set to, for example, 1 g / 10 sec to 10 g / 10 sec, and preferably 4 g / 10 sec to 8 g / 10 sec.

[0104] If necessary, the surface of the substrate may be subjected to a surface activation treatment before forming the silver particle layer.

[0105] In one embodiment of the present disclosure, as a surface activation treatment, a surface activation treatment liquid containing an inorganic tin compound is applied to the surface of the substrate. Thus, tin is present on the surface of the substrate. The presence of tin between the silver particle layer and the substrate tends to improve the adhesion between the substrate and the silver particles.

[0106] Examples of the inorganic tin compound contained in the surface activation treatment liquid include inorganic tin compounds such as tin (II) chloride, tin (II) oxide, and tin (II) sulfate.

[0107] The surface activation treatment liquid may contain hydrogen chloride, hydrogen peroxide, polyol, etc., in addition to the inorganic tin compound, as necessary.

[0108] The content of these components contained in the surface activation treatment liquid is not particularly limited.

[0109] The pH of the surface activation treatment liquid is preferably adjusted to between 0.5 and 3.0, and more preferably between 0.5 and 1.5.

[0110] As a method of applying the surface activation treatment liquid to the surface of the substrate, there are: a method of immersing the substrate in the surface activation treatment liquid; a method of applying the surface activation treatment liquid to the surface of the substrate, etc. Among them, spraying is suitable because it can be applied uniformly regardless of the shape of the substrate.

[0111] After the surface activation treatment, it is preferred to remove excess surface activation treatment liquid adhering to the surface of the substrate. For example, it is preferred to wash the surface of the substrate with deionized water or purified distilled water.

[0112] If necessary, the surface of the substrate may be pretreated before forming the silver particle layer.

[0113] In one embodiment of the present disclosure, as a pretreatment, after the above-mentioned surface activation treatment, a pretreatment liquid such as a silver nitrate aqueous solution is applied to the surface of the substrate. Thus, silver is present on the surface of the substrate. Since silver exists between the silver particle layer and the substrate, there is a tendency to easily precipitate silver particles of uniform size.

[0114] The pH of the pretreatment liquid is preferably adjusted to between 4.0 and 8.0, and more preferably between 6.0 and 7.0.

[0115] As a method of applying the pretreatment liquid to the surface of the substrate, there can be cited a method of immersing the substrate in the pretreatment liquid; a method of applying the pretreatment liquid to the surface of the substrate, etc. Among them, spraying is suitable because it can be applied uniformly regardless of the shape of the substrate.

[0116] If necessary, a deactivation treatment may be performed after the silver particle layer is formed on the surface of the substrate.

[0117] In one embodiment of the present disclosure, as a deactivation treatment, an aqueous solution containing a strong alkali component such as potassium hydroxide and a sulfite such as sodium sulfite, i.e., a deactivation treatment solution, is brought into contact with the silver particle layer. This can reduce the reactivity of silver in the silver particle layer with residual ions such as chloride ions and sulfur ions.

[0118] The content of the components contained in the deactivation treatment liquid is not particularly limited.

[0119] The pH of the deactivation treatment solution is preferably adjusted to between 4.0 and 8.0, and more preferably between 7.0 and 8.0.

[0120] As a method for bringing the deactivation treatment liquid into contact with the silver particle layer, there are: a method of immersing the substrate formed with the silver particle layer in the deactivation treatment liquid; a method of applying the deactivation treatment liquid to the silver particle layer, etc. Among them, spraying is suitable because it can be applied uniformly regardless of the shape of the substrate.

[0121] Before and after the deactivation treatment, the silver particle layer is preferably washed with deionized water or purified distilled water.

[0122] <Purpose of sensor cover>

[0123] The sensor cover of the present disclosure has excellent metallic luster and excellent millimeter wave transmittance, and can therefore be particularly suitably used as an artistic cover for various sensors.

[0124] Examples of sensors include millimeter wave sensors and infrared sensors, which can be used as sensors for detecting human activities, monitoring health status, etc. They can be used as life sensors, crime prevention human body sensing sensors, automatic faucet sensors, toilet seat and vacancy sensors, toilet automatic switch sensors, automatic cleaning sensors, automatic lighting sensors, elderly care sensors, automatic door sensors, induction escalator sensors, remote controller sensors, contactless body temperature sensors, induction traffic light sensors, traffic volume measurement sensors, and other sensor covers installed indoors and outdoors.

[0125] The detection object can be an object other than a person, such as a bicycle, a car, a transport aircraft such as an airplane, an animal, a plant, a commodity (precious metals, etc.), etc.

[0126] Since it has a mirror-like appearance, it can be placed in a position where a mirror is already placed, or it can be placed as an interior or exterior decoration.

[0127] Example

[0128] Hereinafter, the present disclosure will be described based on examples, but the present disclosure is not limited to the following examples.

[0129] <Example>

[0130] (1) Preparation of substrate

[0131] The surface of a polycarbonate substrate having a thickness of 2 mm was wiped with a cloth containing isopropyl alcohol to remove oil film, dirt, and dust, and then the substrate was dried.

[0132] (2) Surface activation process

[0133] After the substrate with the primer layer formed thereon was spray-washed with pure water, a surface activation treatment liquid (MSPS-Sa1A manufactured by Mitsubishi Paper Industries, Ltd.) was spray-washed. Then, the substrate was spray-washed with pure water. The surface activation treatment liquid used was an aqueous solution of pH 1.0 containing tin (II) chloride, hydrogen chloride, hydrogen peroxide, and a polyol.

[0134] (3) Pre-treatment process

[0135] A pretreatment liquid (MSPS-Sa2A manufactured by Mitsubishi Paper Industries, Ltd.) was sprayed on the surface of the substrate after the surface activation treatment. Then, the substrate was spray-washed with pure water. The pretreatment liquid used was a silver nitrate aqueous solution with a pH of 6.8.

[0136] (4) Silver particle layer formation step

[0137] An ammoniacal silver nitrate aqueous solution and a reducing agent aqueous solution were prepared. The ammoniacal silver nitrate aqueous solution was an aqueous solution of pH 11.5 containing silver nitrate, ammonia and triethanolamine (silver nitrate concentration: 0.5 mass%). The reducing agent aqueous solution was an aqueous solution of pH 10.8 containing hydroquinone, triethanolamine, sodium hydroxide and amino alcohol (hydroquinone concentration: 4.5 mass%).

[0138] Each spray brush is arranged in such a way that an aqueous ammoniacal silver nitrate solution and an aqueous reducing agent solution are sprayed from different spray brushes at the same time. For each spray brush, the position and spray direction are fixed. The pre-treated substrate is mounted on a rotating support member, and each liquid is sprayed toward the substrate from the spray brush while rotating the substrate in a horizontal direction. The rotation speed of the substrate is set to 120 rpm. The spray amount of the spray brush is set to 1.0 g / 10 sec to 1.5 g / 10 sec, respectively. At this time, silver particles are precipitated on the surface of the substrate by a silver mirror reaction, forming a silver particle layer (thickness: 0.2 μm) with a silver luster. Then, it is sprayed with pure water.

[0139] (5) Inactivation treatment process

[0140] After the silver particle layer formation step, a deactivation treatment liquid (MSPS-R1A manufactured by Mitsubishi Paper Industries, Ltd.) was sprayed on the surface of the substrate, and then washed with pure water. The deactivation treatment liquid used was an aqueous solution of pH 7.5 containing potassium hydroxide and sulfite.

[0141] <Comparative Example>

[0142] A silver particle layer (thickness: 0.13 μm) was formed on the substrate in the same manner except that an aqueous solution (pH 10.1) containing hydrazine sulfate was used instead of hydroquinone as the reducing agent aqueous solution.

[0143] <Evaluation>

[0144] (1) Determination of surface resistivity

[0145] The surface resistivity of the silver particle layer of the laminated body prepared in the example and the comparative example was measured by a four-probe method using a low resistivity meter (trade name: LORESTA EP, DIA Instruments). The surface resistivity of the silver particle layer of the example was 5.08E05Ω / □, and the surface resistivity of the silver particle layer of the comparative example was 4.28E00Ω / □.

[0146] In the comparative example, it can be inferred from the value of the surface resistivity that no radio wave transmission layer is formed on the surface of the silver particles.

[0147] (2) Electron microscope observation

[0148] The silver particle layer of the example was observed with an electron microscope. Figure 1 This is a photo taken using a scanning transmission electron microscope (STEM) (manufactured by JEOL Ltd., JEM-2100F). Figure 2 This is an image obtained using transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX).

[0149] like Figure 1 and Figure 2 As shown, it was confirmed that the silver particles of the examples had an organic layer on the surface. The average thickness of the organic layer was 25 nm.

[0150] (3) Appearance observation

[0151] The appearance of the samples obtained in the examples was observed and the metallic gloss was evaluated. The metallic gloss of the examples and comparative examples was excellent.

[0152] (4) Measurement of millimeter wave transmission attenuation

[0153] Topcoat Clear M for MSPS manufactured by Ohashi Chemical Industry Co., Ltd., topcoat thinner P-7 for MSPS, and topcoat curing agent W for MSPS were blended at 20:20:5 (parts by mass) to prepare a topcoat composition.

[0154] This composition was spray-coated on the silver particle layer of the samples of Examples and Comparative Examples to form a top coat layer having a thickness of 25 μm.

[0155] The attenuation (transmission attenuation) of the laminate having the top coating layer formed thereon when a millimeter wave (77.0125 GHz) was transmitted therethrough was measured by the following method.

[0156] The transmission attenuation is calculated from the transmitted wave (transmission coefficient) obtained by the free space method specified in JIS R1679:2007 (method for measuring radio wave absorption characteristics of radio wave absorbers in the millimeter wave band). In the free space method, the sample is placed between the transmitting antenna and the receiving antenna, and the electromagnetic wave is irradiated vertically to the sample.

[0157] Here, the transmission attenuation amount can be calculated by the following formula using the transmission coefficient (absolute value).

[0158] Transmission attenuation = 20log 10 |(Transmittance coefficient)|

[0159] The transmission attenuation of the laminated body of the example was 0.67 dB, and the transmission attenuation of the laminated body of the comparative example was 48.32 dB.

[0160] (5) Measurement of spectral transmittance and spectral reflectance in the infrared to ultraviolet range

[0161] The spectral transmittance and spectral reflectance of the sample for measuring the millimeter wave transmission attenuation in the infrared to ultraviolet range were measured using a UV-VIS-NIR spectrophotometer (Lambda 950, manufactured by PerkinElmer).

[0162] In addition, as a reference, the spectral transmittance and spectral reflectance in the infrared to ultraviolet range were also measured for a single polycarbonate (PC) substrate used as a substrate of the laminate.

[0163] The measurement conditions are as follows.

[0164] ·use Integrating sphere

[0165] · Standard sample (for 100% reflection): Spectralon manufactured by Labsphere

[0166] Wavelength range: 190-2500nm

[0167] Wavelength interval: 5nm step

[0168] ·Measurement environment: room temperature (25°C), air

[0169] Figure 3 shows the spectral transmittance spectrum, Figure 4 Spectral reflectance spectra are shown.

[0170] The spectral transmittance at a wavelength of 1000 nm in the infrared region is 13.7%, and the spectral transmittance at a wavelength of 600 nm in the visible region is 0.1%.

[0171] The spectral reflectance at a wavelength of 1000 nm in the infrared region is 39.3%, and the spectral reflectance at a wavelength of 600 nm in the visible region is 52.2%.

[0172] It should be noted that if the laminated body of the embodiment is irradiated with red, blue, and green light from the back side, the red, blue, and green colors can be fully recognized by visual observation from the front side. Since the laminated body of the embodiment has excellent metallic gloss, when these colors are irradiated from the back side, it has a metallic style and presents red, blue, and green colors.

[0173] The entire disclosure of International Application PCT / JP2022 / 023687 is incorporated into this specification by reference.

[0174] All documents, patent applications, and technical standards described in this specification are incorporated into this specification by reference to the same extent as if each document, patent application, or technical standard was specifically and individually described as being incorporated by reference.

Claims

1. A sensor cover comprising a substrate and a silver particle layer disposed on the substrate and comprising silver particles, The silver particles have a radio wave transmission layer on the surface. 2 . The sensor cover according to claim 1 , wherein the radio wave transmission layer is an organic layer. 3 . The sensor cover according to claim 1 , wherein the silver particles include secondary particles, and the radio wave transmission layer is provided on the surface of the silver particles which are primary particles. 4 . The sensor cover according to claim 1 , wherein the radio wave transmission layer is a millimeter wave transmission layer. 5 . The sensor cover according to claim 1 , wherein the radio wave transmission layer is a layer that transmits at least a portion of wavelengths in a wavelength range from infrared rays to visible light. 6 . The sensor cover according to claim 1 , which is a cover for a millimeter wave sensor or an infrared sensor.

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