Rubber composition

Abstract

This rubber composition contains (A) a polymer, (B) a crosslinking agent, and (C) a coloring agent. The coloring agent (C) does not contain an inorganic black pigment. As a rubber sheet, the rubber composition demonstrates: a minimum transmittance at a wavelength of 800-1600 nm of 50% or greater; a minimum transmittance at a wavelength of 900-1100 nm of 80% or greater; a maximum transmittance at a wavelength of 300-700 nm of 40% or less; and a maximum transmittance at a wavelength of 300-650 nm of 1% or less.

Description

rubber composition

[0001] The present invention relates to a rubber composition.

[0002] Near-infrared rays are widely used in in-vehicle sensors, biometric sensors, and bio-biological applications, and further expansion of their use is expected in the future. In the various sensors using near-infrared rays as described above, resins that selectively absorb light of specific wavelengths are widely used (see, for example, Patent Documents 1 to 9).

[0003] For example, Patent Document 1 discloses a selective wavelength absorbing resin composition for LiDAR that detects the distance and direction to an object. Here, "LiDAR" is an abbreviation for Light Detection and Ranging, and is a technology that measures the distance and angle to an object by irradiating the object with a scanning laser beam and observing the reflected light.

[0004] The selective wavelength absorbing resin composition for LiDAR disclosed in Patent Document 1 is primarily composed of epoxy resin, and when molded to a thickness of 1 mm, the cured product has an average light transmittance of 40% or less in the wavelength range of 380 nm or more and 700 nm or less, and is specified to have a transmittance of 80% or more for the wavelengths of laser light used in LiDAR (850 nm to 950 nm, 1500 nm to 1600 nm).

[0005] Patent Documents 2 and 3 disclose polycarbonate-containing resins as wavelength-selective transparent resins for LiDAR. For example, Patent Document 2 discloses a polycarbonate resin composition having wavelength-selective transparent properties, and Patent Document 3 discloses a thermoplastic resin containing a polycarbonate resin. Patent Documents 2 and 3 also propose a technique for specifying the type of wavelength-absorbing dye for the above-mentioned polycarbonate-containing resin.

[0006] Patent Document 4 discloses a thermoplastic resin composition containing a thermoplastic resin and a colorant. The thermoplastic resin composition disclosed in Patent Document 4 has a maximum wavelength transmittance of 1% or less in the 380 to 630 nm range and an average transmittance of 80% or more in the 840 to 940 nm range when the thickness is 1 mm. Patent Document 4 also discloses a technique for specifying pigments and the like used as colorants, and states that the thermoplastic resin composition can be used in optical lenses, infrared camera lenses, biometric camera lenses, etc.

[0007] Patent Document 5 discloses an optical film capable of absorbing specific wavelengths using multiple filters. The optical film disclosed in Patent Document 5 includes a near-infrared blocking layer having an absorption maximum in the wavelength range of 600 to 800 nm, and is said to be used in biometric authentication devices and imaging devices.

[0008] Patent Document 6 discloses an optical filter containing a green pigment and a black pigment. The optical filter disclosed in Patent Document 6 has a structure having a continuous 50 nm wavelength range in which the average transmittance is 2% or less between 400 and 730 nm and 80% or more between 800 and 1000 nm. In the optical filter disclosed in Patent Document 6, the green pigment and the black pigment are present in a dispersed or dissolved state in a transparent resin. The optical filter disclosed in Patent Document 6 is said to be used in imaging devices, infrared sensors, biometric authentication devices, and three-dimensional distance imaging cameras.

[0009] Furthermore, Patent Documents 7 to 9 propose visible light-shielding silicone rubber compositions and infrared-transmitting compositions using silicone rubber.

[0010] Japanese Patent No. 6899061, Japanese Patent Application Laid-Open No. 2021-147470, International Publication No. 2021 / 025097, International Publication No. 2020 / 138050, Japanese Patent Application Laid-Open No. 2020-177147, Japanese Patent No. 6662299, Japanese Patent No. 5170463, Japanese Patent Application Laid-Open No. 2021-70772, Japanese Patent Application Laid-Open No. 2019-131806

[0011] The resin compositions disclosed in Patent Documents 1 to 6 that selectively absorb light of a specific wavelength use a resin as a main component, and therefore the cured product (resin) is hard and lacks flexibility. For this reason, the resin compositions disclosed in Patent Documents 1 to 6 have problems such as the cured product being prone to cracking and having low ability to follow deformation.

[0012] Furthermore, the rubber compositions disclosed in Patent Documents 7 to 9 have the problem of poor selectivity for light of the required wavelength. In other words, rubber, which is a cured product of a rubber composition, generally has low transparency, so that the rubber composition contains additives such as carbon black. In rubbers made from such rubber compositions, colorants such as carbon black absorb a wide range of light from visible light to infrared, making it difficult to achieve infrared light transmittance. On the other hand, transparent rubbers are also commonly available, but these transparent rubbers transmit a wide range of light from ultraviolet to visible light to infrared, making it difficult to selectively transmit light of the required wavelength.

[0013] Currently, sensors that utilize light of a specific wavelength, for example, use silicone semiconductor lasers with a wavelength of 905 nm. Such silicone semiconductor lasers have the advantages of being inexpensive and consuming low power. However, because the laser light is close to visible light and has an effect on the retina, the laser output cannot be increased, and they are also susceptible to sunlight. In recent years, the use of indium gallium arsenide phosphide (InGaAsP) semiconductor lasers with a wavelength of 1550 nm has also been considered as a second-generation, mechanism-less technology. Although InGaAsP semiconductor lasers are expensive in terms of cost and power consumption, they have the advantages of having little effect on the retina, allowing for increased output, and being less susceptible to sunlight.

[0014] The rubber compositions disclosed in the above-mentioned Patent Documents 7 to 9 have a specified infrared transmittance range of 800 nm or 800 to 900 nm, and there is an increasing demand for a wider range of infrared transmittance in order to provide versatility for the above-mentioned various lasers.

[0015] In particular, among the above rubber compositions, silicone rubber (vinyl methyl silicone rubber (VMQ)) is known to have low mechanical strength and is also known to have slightly inferior resistance (chemical resistance) to strong acid solutions, strong alkaline solutions, silicone oil, chlorine water, etc. On the other hand, fluororubber (FKM) and ethylene propylene diene rubber (EPDM) are known to exhibit superior mechanical strength and chemical resistance properties to silicone rubber.

[0016] In order to improve the mechanical strength, chemical resistance, and other properties of these rubber compositions, for example, a rubber composition has been prepared by combining multiple organic colorants without incorporating the well-known carbon black, which has traditionally been used to reinforce rubber. As a result, rubber compositions have been proposed that have the excellent properties of absorbing visible light, which can be a hindrance when used in sensors, over a wide wavelength range, and selectively transmitting infrared light. However, there is a growing demand for the development of more highly functional rubber compositions that further improve the minimum transmittance, particularly in the near-infrared wavelength range.

[0017] The present invention has been made in consideration of the problems associated with the conventional technology, and provides a rubber composition that can absorb a wide range of visible light, which is a hindrance to sensors and the like, and selectively transmit infrared light, and that can produce a rubber material with improved transmittance, particularly in the wavelength region of near-infrared light.

[0018] According to the present invention, there is provided the following rubber composition.

[0019] [1] A rubber composition comprising (A) a polymer, (B) a crosslinking agent, and (C) a colorant, wherein the colorant (C) does not contain an inorganic black pigment, and wherein the rubber sheet has a minimum transmittance of 50% or more at wavelengths of 800 to 1600 nm and a minimum transmittance of 80% or more at wavelengths of 900 to 1100 nm, a maximum transmittance of 40% or less at wavelengths of 300 to 700 nm, and a maximum transmittance of 1% or less at wavelengths of 300 to 650 nm.

[0020] [2] The rubber composition according to [1], wherein (C) the colorant contains two or more kinds of organic colorants for blocking visible light.

[0021] [3] The rubber composition according to [2], wherein the organic colorant is an oil-soluble dye.

[0022] [4] The rubber composition according to [3], wherein at least one of the oil-soluble dyes is an anthraquinone dye.

[0023] [5] The rubber composition according to [4], further comprising an organic peroxide as the crosslinking agent (B).

[0024] [6] The rubber composition according to any one of [1] to [5], which is used in a product that uses infrared light having a wavelength in the range of 800 to 1600 nm.

[0025] [7] The rubber composition according to any one of [1] to [5], which is used for selective wavelength absorption for LiDAR and its cover.

[0026] [8] The rubber composition according to any one of [1] to [5], which is used for an optical lens, an infrared camera lens, a lens for a biometric authentication camera, and a cover thereof.

[0027] [9] The rubber composition according to any one of [1] to [5] above, which is used for a biometric authentication device and a cover thereof.

[0028]

[10] The rubber composition according to any one of [1] to [5] above, which is used for an imaging device and a cover thereof.

[0029]

[11] The rubber composition according to any one of [1] to [5] above, which is used for a three-dimensional distance imaging camera and a cover thereof.

[0030]

[12] The rubber composition according to any one of [1] to [5] above, which is used for infrared communication.

[0031]

[13] The rubber composition according to any one of [1] to [5], which is used in a near-infrared spectrometer.

[0032]

[14] The rubber composition according to any one of [1] to [5] above, which is integrally formed as a visible light filter having sealing properties.

[0033] The rubber composition of the present invention can provide a rubber material that absorbs a wide range of visible light, which interferes with sensors, and selectively transmits infrared light. In particular, the rubber composition does not contain inorganic black pigments such as carbon black, which are widely used for rubber reinforcement, and therefore has excellent transmittance to infrared light. Furthermore, compared to resin materials, the rubber composition has excellent flexibility, making it possible to apply it to products that undergo deformation and contributing to improved design freedom for the entire device that uses the rubber material. Furthermore, compared to resin materials, the rubber composition has improved impact absorption and can effectively suppress the occurrence of damage such as cracking. In particular, a high-performance rubber material can be obtained that exhibits high transmittance in the near-infrared wavelength region, with a transmittance of 1% or less for wavelengths of 650 nm or less and a transmittance of 80% or more for wavelengths of 800 nm or more.

[0034] While the present invention will be described below with reference to exemplary embodiments, it should be understood that the present invention is not limited to the following exemplary embodiments. Therefore, it should be understood that modifications and improvements to the following exemplary embodiments, based on the ordinary knowledge of those skilled in the art, are also within the scope of the present invention, provided that they do not deviate from the spirit of the present invention.

[0035] [Rubber Composition] One embodiment of the rubber composition comprises (A) a polymer, (B) a crosslinking agent, and (C) a colorant, wherein the colorant (C) does not contain an inorganic black pigment. The rubber composition of this embodiment has a minimum transmittance of 50% or more in wavelengths of 800 to 1600 nm and 80% or more in wavelengths of 900 to 1100 nm, and a maximum transmittance of 40% or less in wavelengths of 300 to 700 nm and 1% or less in wavelengths of 300 to 650 nm. The rubber composition of this embodiment can provide a rubber material that absorbs a wide range of visible light that interferes with sensors and selectively transmits infrared light. In particular, since the rubber composition of this embodiment does not contain an inorganic black pigment, it has excellent transmittance to infrared light. Furthermore, compared to resin materials, it has excellent flexibility, allowing it to be applied to products that undergo deformation and contributing to improved design freedom for the entire device using the rubber material. Furthermore, compared to resin materials, it has improved impact absorption and can effectively suppress the occurrence of damage such as cracking.

[0036] Here, the term "inorganic black pigment" refers to a pigment made of an inorganic compound that, when used as a colorant to form a rubber material, exhibits a black to brownish color. Examples of inorganic black pigments include inorganic oxides such as titanium black and iron oxide (iron black), and known inorganic pigments such as carbon black. The rubber composition of this embodiment is substantially free of such inorganic black pigments. In this context, the phrase "the (C) colorant does not contain an inorganic black pigment" in the rubber composition of this embodiment means that each component constituting the rubber composition is substantially free of an inorganic black pigment. In other words, the phrase "the (C) colorant does not contain an inorganic black pigment" also means that components other than the (C) colorant are substantially free of an inorganic black pigment. Furthermore, the phrase "substantially free of" an inorganic black pigment means that an inorganic black pigment is not actively (in other words, intentionally) blended in, except in cases where an inorganic black pigment is inevitably mixed in. Therefore, the rubber composition of this embodiment may contain a trace amount of a black inorganic compound as an unavoidable impurity. The upper limit of the concentration allowable as an unavoidable impurity varies depending on various conditions, but is preferably an amount that does not substantially affect, for example, the minimum transmittance of the rubber sheet at wavelengths of 800 to 1600 nm and 900 to 1100 nm, and the maximum transmittance at wavelengths of 300 to 700 nm and 300 to 650 nm. For example, the inorganic black pigment as an unavoidable impurity is preferably 0.001 part by mass or less (i.e., 10 ppm or less) per 100 parts by mass of the (A) polymer.

[0037] The rubber composition of this embodiment can be formed, for example, into a rubber sheet of a predetermined thickness. The thickness of the rubber sheet is not particularly limited, but a thickness in the range of 0.5 mm to 2 mm can be suitably used. That is, when the thickness of the rubber sheet is in the range of 0.5 mm to 2 mm, the rubber sheet can have a minimum transmittance of 50% or more in the wavelength range of 800 to 1600 nm and a minimum transmittance of 80% or more in the wavelength range of 900 to 1100 nm, a maximum transmittance of 40% or less in the wavelength range of 300 to 700 nm, and a maximum transmittance of 1% or less in the wavelength range of 300 to 650 nm. The transmittance in each wavelength range can be measured, for example, using an ultraviolet-visible-near-infrared spectrophotometer. An example of such a spectrophotometer is the V-770 (product name) spectrophotometer manufactured by JASCO Corporation. The transmittance in the wavelength ranges of 800 to 1600 nm and 900 to 1100 nm is measured in 1 nm increments within that range using a spectrophotometer, and the minimum (lowest) value of the measured transmittance is defined as the "minimum transmittance." The transmittance in the wavelength ranges of 300 to 700 nm and 300 to 650 nm is measured in 1 nm increments within that range using a spectrophotometer, and the maximum (highest) value of the measured transmittance is defined as the "maximum transmittance."

[0038] The rubber composition of this embodiment has excellent infrared light transmittance if it has a minimum transmittance of 50% or more in the wavelength range of 800 to 1600 nm and a minimum transmittance of 80% or more in the wavelength range of 900 to 1100 nm. Furthermore, if it has a maximum transmittance of 40% or less in the wavelength range of 300 to 700 nm and a maximum transmittance of 1% or less in the wavelength range of 300 to 650 nm, it can effectively suppress the transmission of visible light that interferes with sensors, etc.

[0039] The rubber composition of this embodiment preferably has a minimum transmittance of 60% or more in the wavelength range of 800 to 1600 nm. This configuration results in extremely excellent transmittance to infrared light. Another preferred aspect of the rubber composition of this embodiment is that it has a minimum transmittance of 80% or more in the wavelength range of 900 to 1100 nm. This configuration results in excellent transmittance to infrared light of a specific wavelength.

[0040] There is no particular restriction on the upper limit of the minimum transmittance for wavelengths of 800 to 1600 nm and 900 to 1100 nm. For example, the upper limit of the minimum transmittance may be 100% or 90%. There is also no particular restriction on the lower limit of the maximum transmittance for wavelengths of 300 to 700 nm and 300 to 650 nm. For example, the lower limit of the maximum transmittance may be 0%.

[0041] There are no particular limitations on the method for producing a rubber sheet of a predetermined thickness from the rubber composition of this embodiment, but for example, the rubber sheet can be produced by the following method. First, the rubber composition of this embodiment, which serves as the raw material for producing the rubber sheet, is prepared. The rubber composition used to produce the rubber sheet is preferably kneaded, for example, with an open roll until the contained components are uniform, and then the rubber composition is cut into a sheet to produce a rubber dough. Next, the prepared rubber composition is placed in a mold with a depth of 1.9 to 2.0 mm. When placing the rubber composition in the mold, the amount added is adjusted so that the thickness of the rubber sheet obtained by vulcanization is 2 mm. For example, the method for producing the rubber sheet can refer to JIS K6299:2012, "Rubber - Method for preparing test samples." Next, the rubber composition placed in the mold is press-vulcanized. Regarding the vulcanization conditions (temperature, time), the vulcanization rate (t90) of the rubber composition to be vulcanized is separately measured, and vulcanization is carried out for a time (minutes) equal to or exceeding t90. The vulcanization rate (t90) is the time (minutes) from the start of measurement until the torque reaches 90% of (MH-ML), where MH is the maximum torque and ML is the minimum torque, in a test to measure the vulcanization behavior of an unvulcanized rubber composition using a rheometer. When press vulcanization is performed, the vulcanization is promptly terminated once t90 is exceeded. In this manner, a 2 mm thick rubber sheet is prepared. When preparing the rubber sheet, care is taken to avoid touching the surface of the sample rubber sheet as much as possible to prevent foreign matter or other components from adhering to the surface. When preparing rubber sheets of other thicknesses (e.g., 0.5 mm thick rubber sheets), a mold with a depth varied according to the desired thickness (e.g., a mold with a depth of 0.4 to 0.5 mm) can be used to prepare rubber sheets of any thickness.

[0042] The rubber composition of this embodiment contains (A) a polymer, (B) a crosslinking agent, and (C) a colorant. For example, the components contained in the rubber composition are not limited to the above-mentioned components, and may be any rubber composition that does not contain an inorganic black pigment and is prepared so that the rubber sheet has a minimum transmittance of 50% or more in the wavelength range of 800 to 1600 nm, a minimum transmittance of 80% or more in the wavelength range of 900 to 1100 nm, a maximum transmittance of 40% or less in the wavelength range of 300 to 700 nm, and a maximum transmittance of 1% or less in the wavelength range of 300 to 650 nm. Hereinafter, the (A) polymer may be referred to as the (A) component, the (B) crosslinking agent may be referred to as the (B) component, and the (C) colorant may be referred to as the (C) component.

[0043] Various known rubber polymers can be used as the polymer for component (A). Examples of general-purpose rubbers include, but are not limited to, natural rubber (NR), butadiene rubber (BR), isoprene rubber (IR), and styrene-butadiene rubber (SBR). Examples of specialty rubbers include acrylic rubber (ACM), ethylene acrylate rubber (AEM), ethylene propylene rubber (EPM), ethylene propylene diene rubber (EPDM), fluororubber (FKM), epichlorohydrin rubber (ECO), hydrogenated nitrile rubber (HNBR), butyl rubber (IIR), isoprene rubber (IR), acrylonitrile butadiene rubber (NBR), silicone rubber (vinyl methyl silicone rubber (VMQ)), and urethane rubber (U). The use of such polymers can solve the problems of conventional resins, such as hardness and poor flexibility, and allows for suitable application to products that undergo deformation.

[0044] For the polymer of component (A), for example, fluororubber (FKM) or ethylene propylene diene rubber (EPDM) can be more preferably used because the transparency of the rubber can be further increased by using a peroxide crosslinking agent. Furthermore, fluororubber (FKM) and ethylene propylene diene rubber (EPDM) have higher mechanical strength than, for example, silicone rubber (VMQ), and also have high resistance to strong acids, strong alkalis, silicone oil, chlorine water, etc.

[0045] The crosslinking agent as component (B) may be a crosslinking agent used in known rubber compositions, such as a vulcanizing agent, a vulcanization aid, or a vulcanization accelerator. For example, the crosslinking agent may be selected from peroxide-based crosslinking agents, polyol-based crosslinking agents, or the like depending on the purpose. Although not particularly limited, an organic peroxide may be mentioned as a suitable example of the crosslinking agent in the rubber composition of this embodiment.

[0046] There are no particular restrictions on the amount of crosslinking agent used, and it can be determined appropriately depending on the type and amount of polymer used as component (A).

[0047] The colorant for component (C) can be any known colorant other than inorganic black pigments. In the rubber composition of this embodiment, an organic colorant made of an organic substance can be suitably used as the colorant. There are no particular limitations on the colorant color, and it can be appropriately determined depending on the intended use of the rubber composition. However, since the colorant affects the transmittance, it is preferable to appropriately adjust the type and amount of the colorant, taking into account the transmittance at wavelengths of 800 to 1600 nm, 900 to 1100 nm, 300 to 700 nm, and 300 to 650 nm. For example, although not particularly limited, it is preferable that the colorant for component (C) be 1 part by mass or less per 100 parts by mass of the polymer for component (A).

[0048] The rubber composition of this embodiment preferably contains, as a colorant, two or more organic colorants for blocking visible light. By configuring in this manner, a rubber material made from the rubber composition can be effectively obtained that absorbs a wide range of visible light that interferes with sensors, etc., and selectively transmits infrared light. Even when two or more organic colorants are contained, it is preferable that the colorant of component (C) be 1 part by mass or less per 100 parts by mass of the polymer of component (A).

[0049] Examples of organic colorants as colorants include organic pigments. Examples of red pigments include diketopyrrolopyrrole-based, anthraquinone-based, and perylene-based red pigments. Examples of yellow pigments include isoindoline-based and anthraquinone-based yellow pigments. Examples of blue pigments include copper phthalocyanine-based and anthraquinone-based blue pigments. Examples of green pigments include phthalocyanine-based and isoindoline-based green pigments.

[0050] More preferably, the organic colorant is a dye. Known dyes are classified according to their chemical structure, and include, for example, azo dyes, stilbene dyes, triarylmethane dyes, acridine dyes, quinoline dyes, polymethine dyes, anthraquinone dyes, indigo dyes, and phthalocyanine dyes. There are no particular restrictions on the use of these dyes as long as they can be mixed with component (A), but from the viewpoint of compatibility, oil-soluble dyes are particularly preferred.

[0051] Here, the oil-soluble dye is a dye that is insoluble or slightly soluble in water and easily soluble in organic solvents. An example of the oil-soluble dye is shown below, but many other oil-soluble dyes are also available, and these oil-soluble dyes may be used in the rubber composition of the present invention.

[0052] Examples of oil-soluble dyes include rhodamine B acetate, tetrachlorotetrabromofluorescein, tetrabromofluorescein, Sudan III, Sudan IV, Sudan II, quinizarin green SS, pyranine concentrate, Sudan blue, dibromofluorescein, diiodofluorescein, orange SS, quinoline yellow SS, yellow AB, yellow OB, quinizarin blue, Sudan black, phenylazoresorcinol, solvent red 197, oil biored, quinizarin, 4-phenylazo-1-naphthylamine, 4-(diethylamino)azobenzene, methyl yellow, Nile red, Sudan I, Sudan R, p-phenylazophenol, and solvent black 5 (some of which include trade names, etc.).

[0053] The rubber composition of this embodiment may contain other additives, but various additives must be blended so that the minimum transmittance of the rubber sheet at wavelengths of 800 to 1600 nm and 900 to 1100 nm, and the maximum transmittance at wavelengths of 350 to 700 nm and 300 to 650 nm, fall within the numerical ranges described above. Examples of other additives include processing aids, waxes, plasticizers, etc. Furthermore, fillers such as nanofillers may be included within a range that does not impair the permeability of the resulting rubber material. The rubber composition of this embodiment may, for example, be free of other additives, taking into account the effect on the permeability of the resulting rubber material.

[0054] The rubber composition of this embodiment can be used as a product obtained by vulcanizing and molding the rubber composition. For example, the rubber composition can be used as a rubber product obtained by primary vulcanization, or as a rubber product obtained by further secondary vulcanization depending on the properties of the product. For example, the rubber composition of this embodiment can be suitably used in products that use infrared light in the wavelength range of 800 to 1600 nm (near-infrared spectroscopic devices and parts of infrared communication equipment).

[0055] Furthermore, although not particularly limited, the rubber composition of the present embodiment can be suitably used for selective wavelength absorption for LiDAR and its cover, optical lens, infrared camera lens, biometric authentication camera lens and its cover, biometric authentication device and its cover, imaging device and its cover, three-dimensional distance imaging camera and its cover, etc.

[0056] Furthermore, the rubber composition of this embodiment can be used for wavelength filters (visible light filters) that can be attached to the above-mentioned lenses, etc. Such visible light filters can be configured to have sealing properties. That is, a rubber material formed from the rubber composition of this embodiment has specific transmittance in the infrared or near-infrared wavelength range and also has rubber elasticity that allows elastic deformation under stress. Therefore, a visible light filter having sealing properties that utilizes both properties can be integrally formed. As a result, a visible light filter can be formed that aims to reduce the number of parts, reduce costs, etc.

[0057] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0058] (Examples 1 to 5, Comparative Examples 1 to 4) [Sample Preparation] The rubber compositions of Examples 1 to 5 and Comparative Examples 1 to 4 were prepared by weighing and blending the components to the blending ratios (parts by mass) shown in Table 1 below, followed by kneading with an open roll until the components were uniform. The resulting rubber compositions were then cut into sheets to prepare rubber dough, which were then placed in a 2 mm deep mold. The rubber compositions (rubber dough) placed in the mold were then press-vulcanized at 170°C for 12 minutes. In this manner, 2 mm thick rubber sheets were prepared from the rubber compositions of Examples 1 to 5 and Comparative Examples 1 to 4. When preparing the rubber sheets, care was taken not to touch the surface of the rubber sheet to prevent foreign matter or other components from adhering to the surface. For Example 5, a 0.5 mm deep mold was used to prepare a 0.5 mm thick rubber sheet.

[0059] [Component (A): Polymer] (A-1): Ethylene propylene diene rubber ("EPT 3045H (product name)"), manufactured by Mitsui Chemicals, Inc.

[0060] [Component (B): Crosslinking agent (vulcanizing agent / vulcanization aid)] (B-1): "Perkmyl D (product name)", manufactured by NOF Corporation

[0061] [Component (C): Colorants (organic colorants and non-organic colorants)] (C-1): "Quinizarin Blue", manufactured by Tokyo Chemical Industry Co., Ltd. (C-2): "Quinizarin Green SS", manufactured by Tokyo Chemical Industry Co., Ltd. (C-3): "Sudan II (trade name)", manufactured by Tokyo Chemical Industry Co., Ltd. (C-4): "Rhodamine B Base (trade name)", manufactured by Kanto Chemical Co., Ltd. (C-5): 1-(methylamino)anthraquinone, manufactured by Tokyo Chemical Industry Co., Ltd. (C-6): Carbon black (black colorant) ("THERMAX N990 (trade name)"), Cancarb Limited (C-7): Iron oxide (red colorant) ("Brown 601" (trade name)), manufactured by Resino Color Kogyo Co., Ltd. (C-8): Organic pigment ("Phthalocyanine Blue"), manufactured by Resino Color Kogyo Co., Ltd. (C-9): Organic pigment ("Pigment Yellow"), manufactured by Resino Color Kogyo Co., Ltd.

[0062] In Examples 1 to 5 and Comparative Examples 1 to 4, (A-1) ethylene propylene diene rubber was used as the component (A), and "Percumyl D (trade name)" was used as the component (B). The component (B) was further added in a blending ratio of 2 parts by mass per 100 parts by mass of the component (A). To the mixture of components (A) and (B) thus prepared, a colorant of the type and amount specified for each of Examples 1 to 5 and Comparative Examples 1 to 4 was further added as component (C). The details are shown in Table 1 below.

[0063]

[0064] In Example 1, a rubber composition was prepared by adding 2 parts by mass of component (B) to 100 parts by mass of component (A), and then adding 0.1 parts by mass (=0.1 phr) of each of (C-1) and (C-2) as component (C). Here, "phr" is a unit used in rubber compounding and indicates the weight of compounding chemicals and compounds required to be added per 100 parts by weight of rubber (here, corresponding to component (A)). Therefore, Example 1 contains 2 phr of component (B) and 0.1 phr each of two types of component (C) per 100 parts by weight of component (A). Similarly, in Example 2, the same amounts of component (A) and component (B) as in Example 1 were compounded, and 0.1 parts by mass each of (C-2), (C-3), and (C-4) were added as component (C) to prepare a rubber composition. In Example 3, the same amounts of component (A) and component (B) as in Example 1 were blended, and 0.1 parts by mass each of (C-2) and (C-5) were added as the (C) component to prepare a rubber composition. In Example 4, the same amounts of component (A) and component (B) as in Example 1 were blended, and 0.2 parts by mass each of (C-2) and (C-5) were added as the (C) component to prepare a rubber composition. In Example 5, the same amounts of component (A) and component (B) as in Example 1 were blended, and 0.5 parts by mass each of (C-2) and (C-5) were added as the (C) component to prepare a rubber composition.

[0065] In Comparative Example 1, a rubber composition was prepared by adding 2 parts by mass of component (B) to 100 parts by mass of component (A). That is, it was prepared without adding component (C). In Comparative Example 2, the same amounts of components (A) and (B) as in Comparative Example 1 were blended, and 0.1 parts by mass of carbon black (C-6), a black colorant, was added as component (C). In Comparative Example 3, the same amounts of components (A) and (B) as in Comparative Example 1 were blended, and 0.1 parts by mass of iron oxide (C-7), a red colorant, was added as component (C). In Comparative Example 4, the same amounts of components (A) and (B) as in Comparative Example 1 were blended, and 0.05 parts by mass each of components (C-8) and (C-9) was added as component (C).

[0066] For the rubber sheets having a thickness of 2 mm (0.5 mm for Example 5) made from the prepared rubber compositions of Examples 1 to 5 and Comparative Examples 1 to 4, the "maximum transmittance (%) at wavelengths of 300 to 700 nm," "maximum transmittance (%) at wavelengths of 300 to 650 nm," "minimum transmittance (%) at wavelengths of 800 to 1600 nm," and "minimum transmittance (%) at wavelengths of 900 to 1100 nm" were measured by the following methods. The respective measurement results are shown in Table 1.

[0067] - Maximum transmittance (%) for "wavelengths of 300 to 700 nm" and "wavelengths of 300 to 650 nm" Using a spectrophotometer (V-770 (trade name)) manufactured by JASCO Corporation, the transmittance (%) for the rubber sheet to be measured in the wavelength range of 300 to 1600 nm was measured. Then, the highest transmittance value (%) between wavelengths of 300 to 700 nm and between wavelengths of 300 to 650 nm and the wavelength (nm) at that value were determined. The highest transmittance value (%) between wavelengths of 300 to 700 nm was defined as the "maximum transmittance (%) for wavelengths of 300 to 700 nm," and the highest transmittance value (%) between wavelengths of 300 to 650 nm was defined as the "maximum transmittance (%) for wavelengths of 300 to 650 nm," and the transmittance (%) and wavelength (nm) are listed in the respective columns of Table 1. Furthermore, evaluation was performed on the maximum transmittance (%) for wavelengths of 300 to 700 nm and 300 to 650 nm based on the following evaluation criteria. The evaluation results are shown in Table 1. <Evaluation Criteria> (1) Evaluation Criteria for Wavelengths of 300 to 700 nm Evaluation "Good": Pass if the maximum transmittance for wavelengths of 300 to 700 nm is 40% or less. Evaluation "Poor": Fail if the maximum transmittance for wavelengths of 300 to 700 nm exceeds 40%. (2) Evaluation Criteria for Wavelengths of 300 to 650 nm Evaluation "Good": Pass if the maximum transmittance for wavelengths of 300 to 650 nm is 1% or less. Evaluation "Poor": Fail if the maximum transmittance for wavelengths of 300 to 650 nm exceeds 1%.

[0068] - Minimum transmittance (%) for "wavelengths of 800 to 1600 nm" and "wavelengths of 900 to 1100 nm" Using a spectrophotometer (V-770 (trade name)) manufactured by JASCO Corporation, the transmittance (%) for the rubber sheet to be measured in the wavelength range of 300 to 1600 nm was measured. Then, the lowest transmittance value (%) between wavelengths of 800 to 1600 nm and wavelengths of 900 to 1100 nm and the wavelength (nm) at that value were determined. The lowest transmittance value (%) between wavelengths of 800 to 1600 nm was defined as the "minimum transmittance (%) for wavelengths of 800 to 1600 nm," and the lowest transmittance value (%) between wavelengths of 900 to 1100 nm was defined as the "minimum transmittance (%) for wavelengths of 900 to 1100 nm," and the transmittance (%) and wavelength (nm) were listed in the respective columns of Table 1. Furthermore, the minimum transmittance (%) for wavelengths of 800 to 1600 nm and 900 to 1100 nm was evaluated based on the following evaluation criteria. The evaluation results are shown in Table 1. <Evaluation Criteria> (3) Evaluation Criteria for Wavelengths of 800 to 1600 nm Evaluation "Good": Pass if the minimum transmittance for wavelengths of 800 to 1600 nm is 50% or more. Evaluation "Poor": Fail if the minimum transmittance for wavelengths of 800 to 1600 nm is less than 50%. (4) Evaluation Criteria for Wavelengths of 900 to 1100 nm Evaluation "Good": Pass if the minimum transmittance for wavelengths of 900 to 1100 nm is 80% or more. Evaluation "Poor": Fail if the minimum transmittance for wavelengths of 900 to 1100 nm is less than 80%.

[0069] [Results] As shown in Table 1, the rubber sheets made from the rubber compositions of Examples 1 to 5 had a maximum transmittance of 40% or less in the wavelength range of 300 to 700 nm and a maximum transmittance of 1% or less in the wavelength range of 300 to 650 nm, and a minimum transmittance of 50% or more in the wavelength range of 800 to 1600 nm and a minimum transmittance of 80% or more in the wavelength range of 900 to 1100 nm. Therefore, the rubber compositions of Examples 1 to 5 were capable of obtaining rubber materials that absorb a wide range of visible light that interferes with sensors, etc., and selectively transmit infrared light. On the other hand, the rubber sheet made from the rubber composition of Comparative Example 1 had a maximum transmittance of more than 40% in the wavelength range of 300 to 700 nm, and the rubber sheets made from the rubber compositions of Comparative Examples 1 and 4 had a maximum transmittance of more than 1% in the wavelength range of 300 to 650 nm, indicating that they had significantly low visible light blocking properties. Furthermore, the rubber sheets made of the rubber compositions of Comparative Examples 2, 3, and 4 had a minimum transmittance of less than 50% at wavelengths of 800 to 1600 nm, and the rubber sheets made of the rubber compositions of Comparative Examples 2, 3, and 4 had a minimum transmittance of less than 80% at wavelengths of 900 to 1100 nm, indicating low transmittance to infrared light.

[0070] The rubber composition of the present invention can be used as a rubber material that absorbs a wide range of visible light that interferes with sensors and the like, and selectively transmits infrared light, and can be used in various products such as lenses and covers thereof.

Claims

1. A rubber composition comprising (A) a polymer, (B) a crosslinking agent, and (C) a colorant, wherein the colorant (C) does not contain an inorganic black pigment, and wherein the rubber sheet has a minimum transmittance of 50% or more at wavelengths of 800 to 1600 nm and a minimum transmittance of 80% or more at wavelengths of 900 to 1100 nm, a maximum transmittance of 40% or less at wavelengths of 300 to 700 nm, and a maximum transmittance of 1% or less at wavelengths of 300 to 650 nm.

2. The rubber composition according to claim 1, comprising as the colorant (C) two or more types of organic colorant for blocking visible light.

3. The rubber composition according to claim 2, wherein the organic colorant is an oil-soluble dye.

4. The rubber composition according to claim 3, wherein at least one of said oil-soluble dyes is an anthraquinone dye.

5. The rubber composition according to claim 4, further comprising an organic peroxide as the crosslinking agent (B).

6. The rubber composition according to any one of claims 1 to 5, which is used in a product that uses infrared light having a wavelength in the range of 800 to 1600 nm.

7. The rubber composition according to any one of claims 1 to 5, which is used for selective wavelength absorption for LiDAR and for a cover thereof.

8. The rubber composition according to any one of claims 1 to 5, which is used for optical lenses, infrared camera lenses, biometric camera lenses, and covers thereof.

9. The rubber composition according to any one of claims 1 to 5, which is used for a biometric authentication device and a cover thereof.

10. The rubber composition according to any one of claims 1 to 5, which is used for an imaging device and its cover.

11. The rubber composition according to any one of claims 1 to 5, which is used for a three-dimensional distance imaging camera and its cover.

12. The rubber composition according to any one of claims 1 to 5, which is used for infrared communication.

13. The rubber composition according to any one of claims 1 to 5, which is used in a near-infrared spectroscopic device.

14. The rubber composition according to any one of claims 1 to 5, which is integrally formed as a visible light filter having sealing properties.

Images