rubber composition

Abstract

Provided is a rubber composition capable of providing a rubber material capable of absorbing a wide range of visible light which may obstruct sensors and the like and of selectively passing infrared light.　This rubber composition comprises: (A) a polymer; (B) a crosslinking agent; and (C) a coloring agent, the coloring agent (C) not containing an inorganic black pigment, and the rubber composition having, as a rubber sheet with a thickness of 2 mm, a minimum transmission of light with a wavelength of 800-1,600 nm of 50% or more and a maximum transmission of light with a wavelength of 350-700 nm of 40% or less.

Description

[Technical Field]

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

[0002] Near-infrared rays are widely used in in-vehicle sensors, biometric authentication 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 8).

[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 to 700 nm, 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 techniques for specifying the type of wavelength-absorbing dye for the above-mentioned polycarbonate-containing resins.

[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 composition has a thickness of 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 that can absorb specific wavelengths using multiple filters. The optical film disclosed in Patent Document 5 includes a near-infrared blocking layer that has 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 from 400 to 730 nm and 80% or more from 800 to 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 and 8 propose a visible light-shielding silicone rubber composition and an infrared-transmitting composition using silicone rubber. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent No. 6899061 [Patent Document 2] Patent Publication No. 2021-147470 [Patent Document 3] International Publication No. 2021 / 025097 [Patent Document 4] International Publication No. 2020 / 138050 [Patent Document 5] Japanese Patent Publication No. 2020-177147 [Patent Document 6] Patent No. 6662299 [Patent Document 7] Patent No. 5170463 [Patent Document 8] Patent Publication No. 2021-70772 Summary of the Invention [Problem to be solved by the invention]

[0011] The resin compositions disclosed in Patent Documents 1 to 6 that selectively absorb light of a specific wavelength use a resin as the main component, and therefore the cured product (resin) is hard and lacks flexibility. Therefore, 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 and 8 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 a rubber composition is added with, for example, carbon black. In rubber made from such a rubber composition, colorants such as carbon black absorb a wide range of light from visible light to infrared, making it generally difficult to achieve infrared light transmittance. On the other hand, transparent rubbers are also commonly available, but such 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 specific wavelengths, such as silicone semiconductor lasers with a wavelength of 905 nm, are used. These silicon semiconductor lasers have the advantages of being inexpensive and 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, mechanical-less technology. While 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 and 8 have a specified infrared transmittance range of 800 nm or 800 to 900 nm, and there is a growing demand for a wider range of infrared transmittance in order to provide versatility for the various lasers described above.

[0015] The present invention has been made in view of the problems of the prior art. The present invention provides a rubber composition that can obtain a rubber material that absorbs a wide range of visible light that interferes with sensors and the like, and selectively transmits infrared light. [Means for solving the problem]

[0016] According to the present invention, there is provided the following rubber composition.

[0017] [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 a rubber sheet having a thickness of 2 mm has a minimum transmittance of 50% or more at wavelengths of 800 to 1600 nm and a maximum transmittance of 40% or less at wavelengths of 350 to 700 nm.

[0018] [2] The rubber composition according to [1], wherein the colorant (C) is two or more organic colorants for blocking visible light.

[0019] [3] The rubber composition according to [1] or [2], wherein the amount of the colorant (C) is 1 part by mass or less per 100 parts by mass of the polymer (A).

[0020] [4] The rubber composition according to any one of [1] to [3] above, which contains an organic peroxide as the crosslinking agent (B).

[0021] [5] The rubber composition according to any one of the above [1] to [4], wherein the polymer (A) contains at least one of a fluororubber and an ethylene propylene diene rubber.

[0022] [6] The rubber composition according to any one of [1] to [5] above, wherein a minimum transmittance of a 2 mm thick rubber sheet at wavelengths of 800 to 1600 nm is 60% or more.

[0023] [7] The rubber composition according to any one of the above [1] to [6], wherein a minimum transmittance of a 2 mm thick rubber sheet at wavelengths of 900 to 1600 nm is 50% or more.

[0024] [8] The rubber composition according to any one of [1] to [7] above, which is used in a product that uses infrared light having a wavelength in the range of 800 to 1600 nm.

[0025] [9] The rubber composition according to any one of [1] to [7] above, which is used for selective wavelength absorption for LiDAR and as a cover therefor.

[0026]

[10] The rubber composition according to any one of [1] to [7] above, which is used for an optical lens, an infrared camera lens, a lens for a biometric authentication camera, and a cover thereof.

[0027]

[11] The rubber composition according to any one of [1] to [7] above, which is used for a biometric authentication device and a cover thereof.

[0028]

[12] The rubber composition according to any one of [1] to [7] above, which is used for an imaging device and a cover thereof.

[0029]

[13] The rubber composition according to any one of [1] to [7] above, which is used for a three-dimensional distance imaging camera and a cover thereof. [Effects of the Invention]

[0030] The rubber composition of the present invention can provide a rubber material that absorbs a wide range of visible light, which can interfere 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 material 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 material has improved impact absorption and can extremely effectively suppress the occurrence of damage such as cracking. DETAILED DESCRIPTION OF THE INVENTION

[0031] 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.

[0032] [Rubber composition] One embodiment of the rubber composition includes (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 a maximum transmittance of 40% or less in wavelengths of 350 to 700 nm when measured through a 2 mm thick rubber sheet. The rubber composition of this embodiment can provide a rubber material that absorbs a wide range of visible light, which can interfere with sensors, and selectively transmits infrared light. In particular, the rubber composition of this embodiment does not contain an inorganic black pigment, resulting in excellent transmittance to infrared light. Furthermore, compared to resin materials, the rubber composition has superior flexibility, enabling application to products that undergo deformation and contributing to improved design flexibility for the entire device using the rubber material. Furthermore, compared to resin materials, the rubber composition has improved impact absorption and can effectively suppress the occurrence of breakage, such as cracking.

[0033] Here, the 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" means that components other than the (C) colorant are also 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 of unavoidable impurities varies depending on various conditions, but it is preferably an amount that does not substantially affect, for example, the minimum transmittance at wavelengths of 800 to 1600 nm and the maximum transmittance at wavelengths of 350 to 700 nm through a 2 mm thick rubber sheet. For example, the inorganic black pigment as an unavoidable impurity is preferably 0.001 parts by mass or less (i.e., 10 ppm or less) per 100 parts by mass of the (A) polymer.

[0034] As described above, the rubber composition of this embodiment has a minimum transmittance of 50% or more in the wavelength range of 800 to 1600 nm and a maximum transmittance of 40% or less in the wavelength range of 350 to 700 nm when measured on a 2 mm thick rubber sheet. The transmittance in each wavelength range can be measured using, for example, an ultraviolet-visible-near-infrared spectrophotometer. An example of such a spectrophotometer is an ultraviolet-visible-near-infrared spectrophotometer (UH4150 (product name)) manufactured by Hitachi High-Tech Science Corporation. The transmittance in the wavelength range of 800 to 1600 nm is measured at 1 nm intervals within that range using the spectrophotometer, and the minimum (lowest) value of the measured transmittance is defined as the "minimum transmittance." Furthermore, the transmittance in the wavelength range of 350 to 700 nm is measured at 1 nm intervals within that range using the spectrophotometer, and the maximum (highest) value of the measured transmittance is defined as the "maximum transmittance."

[0035] If a 2mm thick rubber sheet has a minimum transmittance of 50% or more for wavelengths of 800 to 1600nm, it will have excellent transmittance for infrared light. Also, if a 2mm thick rubber sheet has a maximum transmittance of 40% or less for wavelengths of 350 to 700nm, it will be able to effectively suppress the transmission of visible light that interferes with sensors, etc.

[0036] The rubber composition of this embodiment preferably has a minimum transmittance of 60% or more at wavelengths of 800 to 1600 nm when used on a 2 mm thick rubber sheet. This configuration provides excellent transmittance to infrared light. Another preferred aspect of the rubber composition of this embodiment is that the minimum transmittance of 50% or more at wavelengths of 900 to 1600 nm when used on a 2 mm thick rubber sheet. This configuration provides excellent transmittance to infrared light of a specific wavelength.

[0037] There is no particular upper limit to the minimum transmittance of a 2 mm thick rubber sheet at wavelengths of 800 to 1600 nm. For example, the upper limit to the minimum transmittance may be 100%, 90%, or 80%. There is also no particular lower limit to the maximum transmittance of a 2 mm thick rubber sheet at wavelengths of 350 to 700 nm. For example, the lower limit to the maximum transmittance may be 0%.

[0038] There are no particular limitations on the method for producing a 2 mm thick rubber sheet, but for example, a rubber sheet can be produced by the following method. First, a rubber composition for producing the rubber sheet, such as the rubber composition of the present embodiment described above, is prepared. The rubber composition used to produce the rubber sheet is preferably kneaded, for example, with an open roll until the components are uniformly mixed, 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 a 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 and 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, measured using a rheometer to measure the vulcanization behavior of an unvulcanized rubber composition. When performing press vulcanization, the vulcanization should be promptly terminated once t90 is exceeded. A 2-mm-thick rubber sheet is prepared in this manner. 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.

[0039] 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, when used on a 2 mm thick rubber sheet, the minimum transmittance at wavelengths of 800 to 1600 nm is 50% or more and the maximum transmittance at wavelengths of 350 to 700 nm is 40% or less. 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.

[0040] The polymer used as component (A) can be any of various known rubber polymers. 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 overcomes the problems of conventional resins, such as hardness and poor flexibility, making them suitable for use in products that require deformation.

[0041] For the polymer used as component (A), fluororubber (FKM) or ethylene propylene diene rubber (EPDM) is more suitable because the transparency of the rubber can be increased by using, for example, a peroxide crosslinking agent. Furthermore, fluororubber (FKM) and ethylene propylene diene rubber (EPDM) have higher mechanical strength than, for example, silicone rubber (VMQ), and are also highly resistant to strong acids, strong alkalis, silicone oil, chlorine water, and the like.

[0042] 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 used as a suitable crosslinking agent in the rubber composition of this embodiment.

[0043] 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).

[0044] The colorant serving as component (C) may be any known colorant other than inorganic black pigments. In the rubber composition of this embodiment, an organic colorant composed 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 of the rubber sheet, it is preferable to appropriately adjust the type and amount of the colorant, taking into account the transmittance of the rubber sheet made of the rubber composition at wavelengths of 800 to 1600 nm and 350 to 700 nm. For example, although not particularly limited, it is preferable that the colorant serving as component (C) be 1 part by mass or less per 100 parts by mass of the polymer serving as component (A).

[0045] The rubber composition of this embodiment preferably contains two or more organic colorants for blocking visible light as colorants. This configuration effectively provides a rubber material made from the rubber composition that absorbs a wide range of visible light that interferes with sensors 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).

[0046] 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.

[0047] The rubber composition of this embodiment may contain other additives, but it is necessary to blend various additives so that the minimum transmittance at wavelengths of 800 to 1600 nm and the maximum transmittance at wavelengths of 350 to 700 nm through a 2 mm thick rubber sheet 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.

[0048] 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 further subjected to 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 with a wavelength range of 800 to 1600 nm. For example, although not particularly limited, the rubber composition of this embodiment can be suitably used in selective wavelength absorption for LiDAR and covers thereof, optical lenses, infrared camera lenses, biometric authentication camera lenses and covers thereof, biometric authentication devices and covers thereof, imaging devices and covers thereof, and three-dimensional distance imaging cameras and covers thereof. [Example]

[0049] 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.

[0050] (Examples 1 to 5, Comparative Examples 1 to 7) [Sample preparation] The rubber compositions of Examples 1 to 5 and Comparative Examples 1 to 7 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 materials, which were then placed in a mold with a depth of 2 mm. The rubber compositions (rubber materials) placed in the mold were then press-vulcanized at 170°C for 12 minutes. In this manner, rubber sheets each having a thickness of 2 mm were prepared from the rubber compositions of Examples 1 to 5 and Comparative Examples 1 to 7. When preparing the rubber sheets, care was taken not to touch the surfaces of the rubber sheets to prevent foreign matter or other components from adhering to the surfaces.

[0051] [Component (A): Polymer] (A-1) Fluorine rubber, "TECNOFLON P757 (product name)" manufactured by Solvey. (A-2) Ethylene propylene diene rubber, "EPT 3045H (product name)" manufactured by Mitsui Chemicals, Inc. (A-3) Fluorine rubber, "Viton A500 (product name)" manufactured by Chemours. (A-4) Acrylonitrile butadiene rubber, manufactured by Nippon Zeon Co., Ltd., "Nipol 3350 (trade name)".

[0052] [Component (B): Crosslinking agent (vulcanizing agent / vulcanization aid)] (B-1) "Perhexa 25B (product name)" manufactured by Nippon Oil & Fats Co., Ltd. (B-2) "TAIC WH60 (product name)" manufactured by Mitsubishi Chemical Corporation. (B-3) "Perkmill D (product name)" manufactured by Nippon Oil & Fats Co., Ltd. (B-4) "Curative 30 (product name)" manufactured by Chemours. (B-5) "Curative 20 (product name)" manufactured by Chemours. (B-6) "CALDIC2000 (product name)" manufactured by Omi Chemical Industry Co., Ltd. (B-7) "Colloidal sulfur A" manufactured by Tsurumi Chemical Industry Co., Ltd. (B-8) "Suncera TT (product name)" manufactured by Sanshin Chemical Industry Co., Ltd. (B-9) "Suncera CZ (product name)" manufactured by Sanshin Chemical Industry Co., Ltd. (B-10) "Zinc oxide (ZnO)" manufactured by Seido Chemical Industry Co., Ltd. (B-11) "DTST (product name) (stearic acid)" manufactured by Miyoshi Oil & Fats Co., Ltd.

[0053] [Component (C): Colorant (organic colorant / non-organic colorant)] (C-1) "Phthalocyanine Blue" manufactured by Resinocolor. (C-2) "Pigment Orange 34" manufactured by Resinocolor. (C-3) Pigment Yellow 55 manufactured by Resinocolor. (C-4) "THERMAX N990 LSR (product name) (carbon (MT grade))" manufactured by Cancarb. (C-5) "Brown 601 (product name) (ferric oxide)" manufactured by Resino Color Industries Co., Ltd.

[0054] [Table 1]

[0055] In Examples 1 and 2, rubber compositions were prepared by compounding two types of organic colorants (phthalocyanine blue and pigment orange 34) with peroxide-crosslinked fluororubber (FKM). In Example 3, a rubber composition was prepared by compounding two types of organic colorants (phthalocyanine blue and pigment yellow 55) with peroxide-crosslinked fluororubber (FKM). In Example 4, a rubber composition was prepared by compounding three types of organic colorants (phthalocyanine blue, pigment orange 34, and pigment yellow 55) with peroxide-crosslinked fluororubber (FKM). In Example 5, a rubber composition was prepared by compounding two types of organic colorants (phthalocyanine blue and pigment yellow 55) with peroxide-crosslinked ethylene propylene diene rubber (EPDM).

[0056] In Comparative Example 1, a rubber composition was prepared from peroxide-crosslinked fluororubber (FKM) without blending a colorant. In Comparative Examples 2 and 6, rubber compositions were prepared by compounding one type of organic colorant (phthalocyanine blue) with peroxide-crosslinked fluororubber (FKM). In Comparative Example 3, a rubber composition was prepared by compounding peroxide-crosslinked fluororubber (FKM) with carbon black (carbon (MT grade)) as a non-organic colorant. In Comparative Example 4, a rubber composition was prepared by compounding ferric oxide as a non-organic colorant into peroxide-crosslinked fluororubber (FKM). In Comparative Example 5, a rubber composition was prepared using a fluororubber (FKM) different from that used in Comparative Example 1, without compounding a colorant. In Comparative Example 7, a rubber composition was prepared by compounding acrylonitrile butadiene rubber (NBR) with no colorant.

[0057] The "maximum transmittance (%) at wavelengths of 350 to 700 nm" and "minimum transmittance (%) at wavelengths of 800 to 1600 nm" were measured by the following method for the 2 mm thick rubber sheets produced from the rubber compositions of Examples 1 to 5 and Comparative Examples 1 to 7. The results are shown in Table 1.

[0058] [Maximum transmittance (%) for wavelengths from 350 to 700 nm] Using a Hitachi High-Tech Science ultraviolet-visible-near-infrared spectrophotometer (UH4150 (trade name)), the transmittance (%) of the rubber sheet to be measured was measured in the wavelength range of 350 to 1600 nm. The highest transmittance (%) in the wavelength range of 350 to 700 nm and the wavelength (nm) at that value were then determined. The highest transmittance (%) in the wavelength range of 350 to 700 nm was designated the "maximum transmittance (%) in the wavelength range of 350 to 700 nm," and the transmittance (%) and its wavelength (nm) were recorded in the "maximum transmittance (%) in the wavelength range of 350 to 700 nm" column in Table 1. The maximum transmittance (%) in the wavelength range of 350 to 700 nm was also evaluated based on the following evaluation criteria. The evaluation results are shown in Table 1. <Evaluation criteria> Evaluation "Good": Passed when the maximum transmittance at wavelengths of 350 to 700 nm is 40% or less. Evaluation "x": A case where the maximum transmittance at wavelengths of 350 to 700 nm exceeds 40% is regarded as unacceptable.

[0059] [Minimum transmittance (%) for wavelengths between 800 and 1600 nm] Using a Hitachi High-Tech Science ultraviolet-visible-near-infrared spectrophotometer (UH4150 (trade name)), the transmittance (%) of the rubber sheet to be measured was measured in the wavelength range of 350 to 1600 nm. The lowest transmittance (%) in the wavelength range of 800 to 1600 nm and the wavelength (nm) at that value were then determined. The lowest transmittance (%) in the wavelength range of 800 to 1600 nm was designated the "minimum transmittance (%) in the wavelength range of 800 to 1600 nm," and the transmittance (%) and wavelength (nm) were listed in the "minimum transmittance (%) in the wavelength range of 800 to 1600 nm" column in Table 1. The minimum transmittance (%) in the wavelength range of 800 to 1600 nm was also evaluated based on the following evaluation criteria. The evaluation results are shown in Table 1. <Evaluation criteria> Evaluation "Good": Passed when the minimum transmittance in the wavelength range of 800 to 1600 nm is 50% or more. Evaluation "x": A case where the minimum transmittance at wavelengths of 800 to 1600 nm is less than 50% is regarded as unacceptable.

[0060] 〔result〕 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 350 to 700 nm and a minimum transmittance of 50% or more in the wavelength range of 800 to 1600 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 and selectively transmit infrared light. On the other hand, the rubber sheets made from the rubber compositions of Comparative Examples 1, 2, and 4 had a maximum transmittance of more than 40% in the wavelength range of 350 to 700 nm, indicating extremely low visible light blocking properties. Furthermore, the rubber sheets made from the rubber compositions of Comparative Examples 3 and 5 to 7 had a minimum transmittance of less than 50% in the wavelength range of 800 to 1600 nm, indicating low infrared light transmittance. In particular, the rubber sheets made from the rubber compositions of Comparative Examples 5 to 7 had transmittances of less than 1% in both the wavelength ranges of 350 to 700 nm and 800 to 1600 nm, indicating that they absorbed a wide range of light from visible light to infrared. [Industrial Applicability]

[0061] 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.

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 a rubber sheet having a thickness of 2 mm has a minimum transmittance of 50% or more at wavelengths of 800 to 1600 nm and a maximum transmittance of 40% or less at wavelengths of 350 to 700 nm.

2. The rubber composition according to claim 1, wherein the colorant (C) comprises two or more organic colorants for blocking visible light.

3. The rubber composition according to claim 1 or 2, wherein the colorant (C) is contained in an amount of 1 part by mass or less per 100 parts by mass of the polymer (A).

4. The rubber composition according to claim 1 or 2, further comprising an organic peroxide as the crosslinking agent (B).

5. The rubber composition according to claim 1 or 2, wherein the polymer (A) comprises at least one of a fluororubber and an ethylene propylene diene rubber.

6. The rubber composition according to claim 1 or 2, wherein a minimum transmittance of a 2 mm thick rubber sheet at wavelengths of 800 to 1600 nm is 60% or more.

7. The rubber composition according to claim 1 or 2, wherein a minimum transmittance of a 2 mm thick rubber sheet at wavelengths of 900 to 1600 nm is 50% or more.

8. The rubber composition according to claim 1 or 2, which is used in a product that uses infrared light having a wavelength in the range of 800 to 1600 nm.

9. The rubber composition according to claim 1 or 2, which is used for a selective wavelength absorbing product for LiDAR and a cover thereof.

10. The rubber composition according to claim 1 or 2, which is used for an optical lens, an infrared camera lens, a lens for a biometric authentication camera, and a cover thereof.

11. The rubber composition according to claim 1 or 2, which is used for a biometric authentication device and a cover thereof.

12. The rubber composition according to claim 1 or 2, which is used for an imaging device and a cover thereof.

13. The rubber composition according to claim 1 or 2, which is used for a three-dimensional distance imaging camera and a cover thereof.

Images