Optical filter, method of manufacturing the same, and optical module

Abstract

The optical filter has an L* of 20 or more as measured by the SCE method, a linear transmittance of 60% or more for at least some wavelengths within a wavelength range of 760 nm to 2000 nm, and the absolute value of the change in C* as measured by the SCE method using a spectrophotometer before and after a light tolerance test in which light from a xenon arc lamp (average integrated illuminance of light with a wavelength of 300 nm to 400 nm is 120 W / m²) is 6 or less.

Description

Technology Field

[0001] The present invention relates to an optical filter, a method for manufacturing the same, and an optical module. Specifically, it relates to an optical filter suitable for use as, for example, an infrared filter having high direct transmittance of infrared light and high diffuse reflectance of visible light, a method for manufacturing the same, and an optical module having such an optical filter on the front surface of an infrared receiving portion having a device. The device is, for example, a sensing device or a communication device. Background Technology

[0002] Sensor or communication technologies utilizing infrared rays have been developed and commercialized. Since devices that receive infrared rays are also sensitive to visible light, infrared transmission filters that selectively transmit only infrared rays are used. The definition of infrared rays varies depending on the technical field. In this specification, "infrared rays" shall include at least light (electromagnetic waves) with a wavelength in the range of 760 nm or more and 2000 nm or less, used for sensing or communication. Furthermore, "visible light" refers to light in the range of 400 nm or more and less than 760 nm.

[0003] Conventional infrared transmission filters are predominantly black to absorb visible light, which has resulted in a problem of low aesthetic appeal.

[0004] Thus, for example, Patent Document 1 discloses an infrared receiving and emitting part having a dielectric multilayer film that transmits infrared rays and also reflects and transmits visible light, and a surface processed with a satin finish. Additionally, Patent Document 2 discloses an optical article for infrared communication that scatters visible light and produces white light by utilizing Rayleigh scattering caused by fine irregular shapes formed by roughening the surface of a transparent substrate, and has an infrared transmittance of 12% or more. Prior art literature

[0005] Japanese Patent Publication No. 2006-165493 (Japanese Patent No. 4122010) Japanese Patent Publication No. 2013-65052 (Japanese Patent No. 5756962) Japanese Patent Publication No. 2010-058091 (Japanese Patent No. 5274164)

[0006] M. Iwata et al. “Bio-Inspired Bright Structurally Colored Colloidal Amorphous Array Enhanced by Controlling Thickness and Black Background”, Adv. Mater., 2017, 29, 1605050. The problem to be solved

[0007] The infrared light-emitting unit described in Patent Document 1 colors its exterior only with visible light reflected by a dielectric multilayer film, and the color changes depending on the viewing angle. In addition, there is a problem that dielectric multilayer films are expensive.

[0008] According to the inventor's review of the infrared communication film using a dielectric multilayer film as described in Patent Document 1, it was found that when the movement of a hand is captured with an infrared camera through this film, the outline of the hand becomes blurry, making it difficult to use for motion capture purposes. This is thought to be due to the low linear transmittance of infrared light.

[0009] Meanwhile, for example, Patent Document 3 and Non-Patent Document 1 disclose that a fine particle dispersion or a colloidal amorphous aggregate having an amorphous structure can exhibit a vivid structural color (e.g., blue) with low angle dependence. Patent Document 3 states that a fine particle dispersion having an amorphous structure is particularly useful for applications that reflect light of a specific wavelength (e.g., colorants or infrared reflective films).

[0010] The present invention is made to solve the above problem and aims to provide an optical filter that is capable of realizing an infrared transmission filter with high linear transmittance of infrared rays, generally exhibits white color, and has excellent light resistance. means of solving the problem

[0011] According to an embodiment of the present invention, a solution means as described in the following items is provided.

[0012] [Item 1]

[0013] L measured by the SCE method * As an optical filter in which α is 20 or greater,

[0014] The linear transmittance for light of at least some wavelengths within a wavelength range of 760 nm to 2000 nm is 60% or more, and

[0015] C measured by the SCE method using a spectrophotometer before and after a light tolerance test involving 300 hours of irradiation with light from a xenon arc lamp (average integrated illuminance of light with a wavelength of 300 nm to 400 nm is 120 W / m²). * An optical filter in which the absolute value of the change is 6 or less.

[0016] [Item 2]

[0017] L measured by the SCE method using a spectrophotometer * , a * , b * The color difference ΔE of white before and after the lightfastness test obtained from * ab is an optical filter listed in Item 1 that is 8 or less.

[0018] [Item 3]

[0019] An optical filter described in Item 1 or 2, wherein the change in linear transmittance for light with a wavelength of 950 nm before and after the lightfastness test is 15% or less.

[0020] [Item 4]

[0021] An optical filter described in any 1 of items 1 to 3, having a linear transmittance of 60% or more for light with a wavelength of 950 nm.

[0022] [Item 5]

[0023] An optical filter described in any 1 of items 1 to 4 having a linear transmittance of 60% or more for light with a wavelength of 1550 nm.

[0024] [Item 6]

[0025] An optical filter described in any 1 of items 1 to 5, wherein the x, y coordinates on the CIE1931 chromaticity diagram of the color when the standard light is a D65 light source are 0.25≤x≤0.40 and 0.25≤y≤0.40.

[0026] [Item 7]

[0027] An optical filter described in any 1 of items 1 to 6, wherein the transmittance curve of the above filter in the wavelength region of visible light has a curve portion in which linear transmittance decreases monotonically from the long wavelength side to the short wavelength side, and said curve portion shifts toward the long wavelength side as the angle of incidence increases.

[0028] [Item 8]

[0029] An optical filter described in any 1 of items 1 to 7, wherein the linear transmittance for light with a wavelength of 950 nm at an angle of incidence of 60° is 80% or more of the linear transmittance at an angle of incidence of 0°.

[0030] [Item 9]

[0031] An optical filter described in any 1 of items 1 to 8, further having a print layer formed of infrared-transmitting ink.

[0032] [Item 10]

[0033] An optical filter having a three-dimensional shape as described in any one of items 1 to 9.

[0034] [Item 11]

[0035] An optical filter described in any 1 of items 1 to 10, comprising a matrix and fine particles dispersed in the matrix.

[0036] [Item 12]

[0037] The above-mentioned fine particles are an optical filter described in Item 11, comprising monodisperse first fine particles having an average particle size within the range of 80 nm to 300 nm.

[0038] [Item 13]

[0039] An optical filter described in Item 12, wherein the average particle size of the first fine particles is 150 nm or more.

[0040] [Item 14]

[0041] An optical filter described in any 1 of items 11 to 13, wherein the average value of the distance between the centers of gravity of the fine particles in a cross-section perpendicular to the plane direction of the filter is 200 nm or more.

[0042] [Item 15]

[0043] An optical filter described in any 1 of items 11 to 14, wherein the coefficient of variation of the average value of the distance between the centers of gravity of the fine particles in a cross-section perpendicular to the plane direction of the filter is 10% or more.

[0044] [Item 16]

[0045] An optical filter described in any 1 of items 11 to 15, wherein the coefficient of variation of the average value of the distance between the centers of gravity of the fine particles in a cross-section perpendicular to the plane direction of the filter is 45% or less.

[0046] [Item 17]

[0047] The above matrix is ​​an optical filter described in any 1 of items 11 to 16, comprising a resin having a cross-linked structure.

[0048] [Item 18]

[0049] The above-mentioned fine particles are an optical filter described in any one of items 11 to 17, constituting at least a colloidal amorphous aggregate.

[0050] [Item 19]

[0051] An optical filter described in any 1 of items 11 to 18, wherein the volume fraction of the above-mentioned fine particles is 6% or more and 60% or less.

[0052] [Item 20]

[0053] The refractive index of the above matrix for light with a wavelength of 546 nm is n M , the refractive index of the above-mentioned fine particle is n P When saying, |n M -n P An optical filter described in any 1 of items 11 to 19, wherein | is 0.03 or greater and 0.6 or less.

[0054] [Item 21]

[0055] An optical filter described in any 1 of items 11 to 20, wherein the matrix is ​​formed of a resin and the microparticles are formed of an inorganic material.

[0056] [Item 22]

[0057] A method for manufacturing an optical filter as described in Item 21,

[0058] A process for preparing a curable resin composition in which the above-mentioned fine particles are dispersed and mixed in a curable resin, and

[0059] A process of applying the above-mentioned curable resin composition to the surface of a substrate, and

[0060] A manufacturing method comprising a process of curing the curable resin included in the curable resin composition applied to the surface.

[0061] [Item 23]

[0062] The above imparting process is the manufacturing method described in Item 22, which is carried out by the coating method.

[0063] [Item 24]

[0064] The above imparting process is the manufacturing method described in Item 22, which is carried out by the dip coating method.

[0065] [Item 25]

[0066] A device equipped with an infrared receiver, and

[0067] An optical module having an optical filter described in any 1 of items 1 to 21 disposed on the front surface of the infrared receiving part of the above device.

[0068] [Item 26]

[0069] The above device is an optical module described in Item 25, which is a sensing device, a communication device, a solar cell, a heater, or a power supply device.

[0071] According to an embodiment of the present invention, it is possible to realize an infrared transmission filter having a high linear transmittance of infrared rays, and an optical filter that generally exhibits white color and excellent light resistance, a method for manufacturing the same, and an optical module are provided. Effects of the invention

[0070] (Effect of the invention) Brief explanation of the drawing

[0072] FIG. 1 is a schematic cross-sectional view of an optical filter (10) according to an embodiment of the present invention. FIG. 2 is a diagram showing a cross-sectional TEM image of the optical filter (10A) of Example 1. FIG. 3 is a diagram showing a cross-sectional TEM image of the optical filter (20A) of Comparative Example 1. FIG. 4 is a histogram of the distance between the centroids of particles obtained from a cross-sectional TEM image of the optical filter (10A) of Example 1. FIG. 5 is a histogram of the distance between the centroids of particles obtained from a cross-sectional TEM image of the optical filter (20A) of Comparative Example 1. Figure 6 is an example of a camera image acquired using a motion capture device. FIG. 7 is an example of a camera image acquired using a motion capture device through the optical filter (10A) of Example 1. FIG. 8 is an example of a camera image acquired using a motion capture device through the optical filter (20A) of Comparative Example 1. FIG. 9 is a drawing showing the optical image of the optical filter (10A) of Example 1. FIG. 10 is a drawing showing the optical image of the optical filter (20A) of Comparative Example 1. FIG. 11 is a schematic diagram illustrating the optical characteristics of an optical filter (10) according to an embodiment of the present invention. Figure 12 is a schematic diagram showing the method for measuring the diffuse transmittance of an optical filter. Figure 13 is a schematic diagram showing the method for measuring the linear transmittance of an optical filter. FIG. 14 is a linear transmittance spectrum of the optical filter (10A) of Example 1. FIG. 15 is a diagram showing the absorption spectrum obtained as the difference between the diffuse transmittance spectrum and the diffuse reflectance spectrum of the optical filter (10A) of Example 1. FIG. 16 is the linear transmittance spectrum of the optical filter (20A) of Comparative Example 1. Figure 17 is a diagram showing a cross-sectional TEM image of the optical filter of Example 2. Figure 18 is a histogram of the distance between the centroids of particles obtained from a cross-sectional TEM image of the optical filter of Example 2. Figure 19 is the linear transmittance spectrum of the optical filter of Example 2. Figure 20 is the linear transmittance spectrum of the optical filters of Examples 3 and 4. Figure 21 is the linear transmittance spectrum of the optical filter of Example 5. Figure 22 is the linear transmittance spectrum of the optical filter of Example 6. Figure 23 is the linear transmittance spectrum of the optical filter of Example 7. Figure 24 is the linear transmittance spectrum of the optical filter of Example 8. Figure 25 is the linear transmittance spectrum of the optical filter of Example 9. Figure 26 is the linear transmittance spectrum of the optical filter of Example 10. Figure 27 is a diagram showing a cross-sectional TEM image of the optical filter of Example 10. Figure 28 is a histogram of the distance between the centroids of particles obtained from a cross-sectional TEM image of the optical filter of Example 10. Figure 29 is the linear transmittance spectrum of the optical filter of Example 11. Figure 30 is the linear transmittance spectrum of the optical filter of Example 12. Figure 31 is the linear transmittance spectrum of the optical filter of Example 13. Figure 32 is a diagram showing a cross-sectional TEM image of the optical filter of Comparative Example 2. Figure 33 is a histogram of the distance between the centroids of particles obtained from the cross-sectional TEM image of the optical filter of Comparative Example 2. FIG. 34 is the linear transmittance spectrum of the optical filter of Comparative Example 2 (angle of incidence 0°, 60°). Figure 35 is a diagram showing a cross-sectional TEM image of the optical filter of Comparative Example 3. Figure 36 is a histogram of the distance between the centroids of particles obtained from the cross-sectional TEM image of the optical filter of Comparative Example 3. Figure 37 is the linear transmittance spectrum of the optical filter of Comparative Example 3. FIG. 38 is a diagram showing the angle of incidence dependence of the linear transmittance spectrum of the optical filter (10A) of Example 1 and the optical filter of Comparative Example A. FIG. 39 is a diagram showing the angle of incidence dependence of the linear transmittance spectrum of the optical filter (10A) of Example 1. Figure 40 is a diagram showing the angle of incidence dependence of the linear transmittance spectrum of the optical filter of Comparative Example A. Figure 41 is a diagram showing the angle of incidence dependence of the linear transmittance spectrum of the optical filter of Example 2. Figure 42 is a diagram showing the angle of incidence dependence of the linear transmittance spectrum of the optical filter of Example 6. Figure 43 is a diagram showing the angle of incidence dependence of the linear transmittance spectrum of the optical filter of Comparative Example 3. FIG. 44a is a drawing showing an optical image (visible light) representing an optical filter of an embodiment formed in a hemispherical shape. FIG. 44b is a drawing showing an infrared image of an optical filter of a hemispherical embodiment shown in FIG. 44a. FIG. 45 shows C of the optical filter of Example 6 and Comparative Example A. * This is a graph showing the change in the light resistance test. FIG. 46 shows the ΔE of the optical filters of Example 6 and Comparative Example A. * ab This is a graph showing the change in the light resistance test. FIG. 47 is a graph showing the change in linear transmittance of the optical filters of Example 6 and Comparative Example A for infrared (wavelength 950 nm) in a lightfastness test. Specific details for implementing the invention

[0073] Hereinafter, an optical filter according to an embodiment of the present invention will be described with reference to the drawings. The optical filter according to an embodiment of the present invention is not limited to those exemplified below.

[0074] An optical filter according to an embodiment of the present invention is an optical filter comprising a matrix and fine particles dispersed within the matrix, wherein the fine particles constitute at least a colloidal amorphous aggregate, and the linear transmittance for light of at least some wavelengths within a wavelength range of 760 nm to 2000 nm is 60% or more. For example, an optical filter having a linear transmittance of 60% or more for light with wavelengths of 950 nm and 1550 nm can be obtained. The wavelength range of light (near-infrared) for which the linear transmittance of the optical filter is 60% or more is preferably, for example, 810 nm to 1700 nm, and more preferably 840 nm to 1650 nm. Such an optical filter is suitably used, for example, in an InGaAs sensor, an InGaAs / GaAsSb sensor, a CMOS sensor, an NMOS sensor, or a CCD sensor. Here, it is preferable that both the matrix and the fine particles are transparent to visible light (hereinafter simply referred to as "transparent"). An optical filter according to an embodiment of the present invention can display white.

[0075] An optical filter according to an embodiment of the present invention comprises a colloidal amorphous aggregate. A colloidal amorphous aggregate refers to an aggregate of colloidal particles (particle size 1 nm to 1 μm) that does not possess long-range order and does not cause Bragg reflection. This is in contrast to the case where colloidal particles are distributed to possess long-range order, which results in a so-called colloidal crystal (a type of photonic crystal) and causes Bragg reflection. That is, the fine particles (colloidal particles) of the optical filter according to an embodiment of the present invention do not form a diffraction grating.

[0076] The microparticles included in the optical filter according to an embodiment of the present invention comprise monodisperse microparticles having an average particle size of at least one-tenth of the wavelength of infrared radiation. That is, for infrared radiation with a wavelength in the range of 760 nm to 2000 nm, the average particle size of the microparticles is preferably at least 80 nm, preferably 150 nm, and more preferably 200 nm. The upper limit of the average particle size of the microparticles is, for example, 300 nm. Two or more monodisperse microparticles with different average particle sizes may be included. Each microparticle is preferably nearly spherical. Furthermore, in this specification, microparticles (plural) are also used to mean an aggregate of microparticles, and monodisperse microparticles refer to those having a coefficient of variation (standard deviation / average particle size expressed as a percentage) of 20% or less, preferably 10% or less, and more preferably 1 to 5%. The optical filter according to an embodiment of the present invention increases the linear transmittance of infrared rays by using particles with a particle diameter (particle diameter, volume sphere equivalent diameter) of at least one-tenth of the wavelength. The principle is different from that of the optical article described in Patent Document 2, which utilizes Rayleigh scattering.

[0077] The average particle size was determined here based on the 3D SEM image. Specifically, a continuous cross-sectional SEM image was acquired using a focused ion beam scanning electron microscope (hereinafter referred to as "FIB-SEM"), specifically the Helios G4 UX model manufactured by FEI, and the 3D image was reconstructed after correcting the continuous image positions. More specifically, the acquisition of cross-sectional reflected electron images by the SEM and FIB (acceleration voltage: 30 kV) processing were repeated 100 times at 50 nm intervals to reconstruct the 3D image. Binarization was performed on the obtained 3D image using the Segmentation function of analysis software (AVIZO by Thermo Fisher Scientific) to extract the image of the fine particles. Subsequently, the volume of each fine particle was calculated after performing a separate object operation to identify each fine particle. Assuming each particle was a sphere, the diameter equivalent to the volume sphere was calculated, and the average value of the fine particle sizes was defined as the average particle size.

[0078] An optical filter according to an embodiment of the present invention has a linear transmittance of at least some wavelengths within a wavelength range of 760 nm to 2000 nm or more of 60% or more by adjusting any one of the refractive index of the fine particles and matrix, the average particle size of the fine particles, the volume fraction, the distribution (degree of non-periodicity), and the thickness.

[0079] An optical filter according to an embodiment of the present invention can exhibit white. Here, white refers to a state where the x and y coordinates on the CIE 1931 chromaticity diagram, when the standard light is a D65 light source, fall within the ranges of 0.25 ≤ x ≤ 0.40 and 0.25 ≤ y ≤ 0.40, respectively. Of course, the closer x is to 0.333 and y is to 0.333, the higher the whiteness; preferably, 0.28 ≤ x ≤ 0.37 and 0.28 ≤ y ≤ 0.37, and more preferably, 0.30 ≤ x ≤ 0.35 and 0.30 ≤ y ≤ 0.35. In addition, L measured by the SCE method in the CIE 1976 color space *It is preferable that it be 20 or more, more preferable that it be 40 or more, more preferable that it be 50 or more, and particularly preferable that it be 60 or more. L * If α is 20 or higher, it can generally be considered white. L * The upper limit of is, for example, 100. The method for measuring linear transmittance will be described later in experimental examples (including examples and comparative examples).

[0080] FIG. 1 shows a schematic cross-sectional view of an optical filter (10) according to an embodiment of the present invention. The optical filter (10) according to an embodiment of the present invention comprises a matrix (12) that is transparent to visible light and transparent microparticles (14) dispersed within the transparent matrix (12). The microparticles (14) constitute at least a colloidal amorphous aggregate. Other microparticles that do not disturb the colloidal amorphous aggregate formed by the microparticles (14) may also be included.

[0081] The optical filter (10) has a substantially flat surface as schematically shown in FIG. 1. Here, a substantially flat surface refers to a surface that does not have an irregular structure of a size that scatters (diffracts) or diffusely reflects visible light or infrared light. In addition, the optical filter (10) does not contain cholesteric liquid crystals (which broadly include high-molecular-weight liquid crystals, low-molecular-weight liquid crystals, mixtures of these liquid crystals, and liquid crystal materials that are solidified by mixing a crosslinking agent with these liquid crystal materials and crosslinking, and which exhibit a cholesteric phase). In addition, the optical filter (10) is, for example, in the form of a film, but is not limited thereto.

[0082] The transparent microparticles (14) are, for example, silica microparticles. As silica microparticles, for example, silica microparticles synthesized by the Stöber method may be used. In addition, inorganic microparticles other than silica microparticles may be used as microparticles, or resin microparticles may be used. As resin microparticles, microparticles composed of at least one of polystyrene and polymethyl methacrylate are preferred, for example, and microparticles composed of cross-linked polystyrene, cross-linked polymethyl methacrylate, or cross-linked styrene-methyl methacrylate copolymer are more preferred. In addition, as such microparticles, polystyrene microparticles or polymethyl methacrylate microparticles synthesized by emulsion polymerization may be appropriately used. In addition, hollow silica microparticles containing air and hollow resin microparticles may also be used. Furthermore, microparticles formed from inorganic materials have the advantage of excellent heat resistance and light resistance. The volume fraction of the total of the microparticles (including the matrix and microparticles) is preferably 6% or more and 60% or less, more preferably 20% or more and 50% or less, and more preferably 20% or more and 40% or less. The transparent microparticles (14) may have optical isotropy.

[0083] The matrix (12) may be, for example, an acrylic resin (e.g., polymethyl methacrylate, polymethyl acrylate), a polycarbonate, a polyester, a poly(diethylene glycol bisallyl carbonate), a polyurethane, an epoxy resin, or a polyimide, but is not limited thereto. It is preferable to form the matrix (12) using a curable resin (thermosetting or photocurable), and from the perspective of mass production, it is preferable to form it using a photocurable resin. Various (meth)acrylates may be used as photocurable resins. It is preferable that the (meth)acrylates include difunctional or trifunctional (meth)acrylates. In addition, it is preferable that the matrix (12) has optical isotropy. If a curable resin containing a polyfunctional monomer is used, a matrix (12) having a cross-linked structure is obtained, which can improve heat resistance and light resistance.

[0084] An optical filter (10) in which the matrix (12) is formed of a resin material may be in the form of a flexible film. The thickness of the optical filter (10) is, for example, 10 μm or more and 10 mm or less. If the thickness of the optical filter (10) is, for example, 10 μm or more and 1 mm or less, and also 10 μm or more and 500 μm or less, it can exhibit significant flexibility.

[0085] When using silica microparticles with a hydrophilic surface as microparticles, it is preferable to form them, for example, by photocuring a hydrophilic monomer. Examples of hydrophilic monomers include polyethylene glycol (meth)acrylate, polyethylene glycol di(meth)acrylate, polyethylene glycol tri(meth)acrylate, polypropylene glycol (meth)acrylate, polypropylene glycol di(meth)acrylate, polypropylene glycol tri(meth)acrylate, 2-hydroxyethyl (meth)acrylate, or 2-hydroxypropyl (meth)acrylate, acrylamide, methylenebisacrylamide, and ethoxylated bisphenol A di(meth)acrylate, but are not limited to these. Additionally, one type of these monomer may be used alone, or two or more types may be used in combination. Of course, two or more types of monomers may include monofunctional monomers and polyfunctional monomers, or two or more types of polyfunctional monomers.

[0086] These monomers can be cured by using a photopolymerization initiator in a suitable manner. Examples of photopolymerization initiators include carbonyl compounds such as benzoin ether, benzophenone, anthraquinone, thioxane, ketal, and acetophenone; sulfur compounds such as disulfide and dithiocarbamate; organic peroxides such as benzoyl peroxide; azo compounds; transition metal complexes; polysilane compounds; and color sensitizers. The amount added is preferably 0.05 parts by weight or more and 3 parts by weight or less per 100 parts by weight of the mixture of fine particles and monomers, and more preferably 0.05 parts by weight or more and 1 part by weight or less.

[0087] The refractive index of the matrix for visible light is n M , the refractive index of the particle is n P When saying, |n M -n PIt is preferable that the difference in refractive index (hereinafter simply referred to as the difference in refractive index) be 0.01 or greater, 0.6 or less, 0.03 or greater, and 0.11 or less. If the difference in refractive index is less than 0.03, the scattering intensity weakens, and it becomes difficult to obtain the desired optical properties. Furthermore, if the difference in refractive index exceeds 0.11, the linear transmittance of infrared radiation may decrease. In addition, for example, if the difference in refractive index is 0.6 by using zirconia fine particles (refractive index 2.13) and acrylic resin, the linear transmittance of infrared radiation can be adjusted by reducing the thickness. Thus, the linear transmittance of infrared radiation can also be adjusted by controlling, for example, the thickness of the optical filter and the difference in refractive index. Additionally, depending on the application, it may be used in combination with a filter that absorbs infrared radiation. Furthermore, the refractive index for visible light can be represented, for example, by the refractive index for light at 546 nm. Unless otherwise specified, the refractive index here refers to the refractive index for light of 546 nm.

[0088] An optical filter according to an embodiment of the present invention may be manufactured by a manufacturing method comprising, for example, a process of preparing a curable resin composition in which fine particles are dispersed and mixed in a curable resin, a process of applying the curable resin composition to the surface of a substrate, and a process of curing the curable resin included in the curable resin composition applied to the surface. The substrate may be, for example, a glass substrate, or a resin film such as PET (polyethylene terephthalate), TAC (triacetylcellulose), or PI (polyimide), but is not limited thereto. The process of dispersing and mixing fine particles in a curable resin may be performed using a known dispersion and mixing device such as a homomixer or a homogenizer (e.g., an ultrasonic homogenizer, a high-pressure homogenizer). In addition, the application process may be performed by various known methods, such as a coating method (e.g., a dip coating method, a spray coating method, a die coating method) or a printing method.

[0089] Specific experimental examples (examples and comparative examples) are described below, and the composition and optical characteristics of the optical filters according to the embodiments of the present invention are explained. The composition and optical characteristics of the optical filters of the examples and comparative examples are shown in Table 1. Various optical filters shown in Table 1 were produced by varying the combination of silica microparticles and resin types, the addition of a coagulant, and the dispersion and mixing methods.

[0090] The optical filters of Examples 1 to 13 and Comparative Examples 1 to 3 were formed as films using the acrylic resin and silica microparticles listed in Table 1. As silica microparticles, monodisperse silica microparticles synthesized by the Stöber method were used (average particle size 110 nm, CV value of particle size 4.5%), (average particle size 181 nm, CV value of particle size 4.7%), (average particle size 221 nm, CV value of particle size 4.9%), and (average particle size 296 nm, CV value of particle size 6.1%). Here, Houtoform Sibol 220 manufactured by Fuji Chemical Co., Ltd. was used as the silica microparticles. The particle size distribution of the silica microparticles was measured using a scanning electron microscope SU3800 manufactured by Hitachi High-Tech Co., Ltd.

[0091] A curable resin composition was prepared by mixing and dispersing silica fine particles in a predetermined proportion with acrylic monomers A to E, applying it to the surface of a substrate using an applicator to obtain a film of a predetermined thickness, and curing it. Darocure 1173 was added as a photopolymerization initiator in an amount of 0.2 parts by mass per 100 parts by mass of acrylic monomer, and cured by photopolymerization by irradiating with a UV lamp. A resin (polymer) with a different refractive index was formed depending on the type of monomer.

[0092] Acrylic monomers A to E are shown below. Monomers A and E are trifunctional acrylates, monomers B and C are difunctional acrylates, and monomer D is monofunctional acrylate.

[0093] A: Pentaerythritol triacrylate

[0094] B: Ethoxylated bisphenol A diacrylate (m+n=10)

[0095] C: Ethoxylated bisphenol A diacrylate (m+n=3)

[0096] D: Methoxypolyethylene glycol #400 methacrylate

[0097] E: Trimethylolpropane EO-modified triacrylate

[0098] In addition, acrylic monomers B and C are represented by the following chemical formula (Phenomenon 1).

[0099] [Painting 1]

[0100]

[0101] When the thickness of the obtained film was denoted as d, a sample section with a thickness equal to the average particle size of the silica particles was cut by cutting at a position d / 2 with respect to the cross-sectional direction using a microtome, and a sample for TEM observation was obtained. Using a TEM (HT7820 manufactured by Hitachi High-Tech Co., Ltd.), the average value (La) and standard deviation (Ld) of the distance between adjacent particles were calculated by performing Delaunay plot analysis using image processing software Image J on cross-sectional TEM images containing images of more than 200 particles. In addition, the coefficient of variation (CV value of the distance) was calculated from the average value of the distance between the centers of gravity (also referred to as the "average distance between centers of gravity") and the standard deviation. Here, in calculating the distance between the centers of gravity, only particles with a particle size of 150 nm or more were considered, and particles with a particle size of less than 150 nm were not considered. As described below, these values ​​serve as indicators of whether silica microparticles constitute a colloidal amorphous aggregate and the distribution state of silica microparticles within the colloidal amorphous aggregate. The lower limit of La is preferably 100 nm or more, more preferably 150 nm or more, even more preferably 175 nm or more, and particularly preferably 200 nm or more. The upper limit of La is preferably 600 nm or less, and more preferably 500 nm or less.

[0102] The colloidal amorphous aggregate of the optical filter according to the embodiment of the present invention can be characterized by the coefficient of variation of the distance between the average centers of gravity of the microparticles (14). When the coefficient of variation is small, it indicates that long-range order is large, and an angle-dependent reflection color due to Bragg reflection is exhibited. On the other hand, when the coefficient of variation is large, the influence of Mie scattering increases, and the wavelength dependence of light scattering tends to decrease. Accordingly, in the optical filter according to the embodiment of the present invention, the coefficient of variation of the distance between the average centers of gravity of the microparticles (14) is preferably 10% or more, preferably 45% or less, more preferably 15% or more, more preferably 40% or less, more preferably 20% or more, more preferably 40% or less, even more preferably 25% or more, and even more preferably 35% or less.

[0103]

[0104] FIG. 2 shows a cross-sectional TEM image of the optical filter (10A) of Example 1, and FIG. 3 shows a cross-sectional TEM image of the optical filter (20A) of Comparative Example 1. In the TEM images in the drawings, white circles are silica microparticles, and black circles are traces where silica microparticles have been removed. In image processing, black circles were also treated as silica microparticles.

[0105] In the cross-section of the optical filter (10A) shown in FIG. 2, silica microparticles are almost uniformly dispersed, whereas in the cross-section of the optical filter (20A) shown in FIG. 3, silica microparticles are partially aggregated. This is because when manufacturing the optical filter (20A) of Comparative Example 1, 0.1 mass% of polyethylene glycol was added as an aggregator to acrylic monomer A in addition to acrylic monomer A.

[0106] Next, FIG. 4 shows a histogram of the distance between the centers of gravity of particles obtained from a cross-sectional TEM image of the optical filter (10A) of Example 1, and FIG. 5 shows a histogram of the distance between the centers of gravity of particles obtained from a cross-sectional TEM image of the optical filter (20A) of Comparative Example 1. The average distance between the centers of gravity La (nm), standard deviation Ld (nm), and coefficient of variation (CV value of the distance) obtained from these are shown in Table 1. Hereinafter, the CV value of the distance may be simply referred to as the CV value.

[0107] It can be seen that the distribution of silica microparticles in the optical filter (10A) of Example 1 has higher uniformity compared to the distribution of silica microparticles in the optical filter (20A) of Comparative Example 1. While the Ld of the optical filter (10A) of Example 1 is 84 nm and the CV value is 27.8%, the Ld of the optical filter (20A) of Comparative Example 1 is 168 nm and the CV value is 49.3%, showing larger values.

[0108] Next, with reference to FIGS. 6 to 8, the results of comparing the performance of the optical filter (10A) of Example 1 and the optical filter (20A) of Comparative Example 1 as infrared filters will be explained. FIG. 6 is an example of a camera image acquired using a motion capture device, and is a camera image acquired without using a filter. FIG. 7 is an example of a camera image acquired using a motion capture device through the optical filter (10A) of Example 1, and FIG. 8 is an example of a camera image acquired using a motion capture device through the optical filter (20A) of Comparative Example 1.

[0109] Here, a Leap Motion Controller (registered trademark) was used as a motion capture device, and a camera image of a hand located about 20 cm away was acquired. Additionally, this device uses infrared light with a wavelength of 850 nm. As is evident when comparing FIGS. 6, 7, and 8, when the optical filter (10A) of the embodiment was used (Fig. 7), a clear image was obtained to the same degree as when no filter was used (Fig. 6), whereas when the optical filter (20A) of the comparative example was used (Fig. 9), a clear image could not be obtained and the hand could not be recognized.

[0110] FIG. 9 shows the optical image of the optical filter (10A) of Example 1, and FIG. 10 shows the optical image of the optical filter (20A) of Comparative Example 1. The optical filter (10A) of Example 1 and the optical filter (20A) of Comparative Example 1 are arranged as films of approximately 5 cm × approximately 10 cm to cover the front surface of the device. As can be seen from FIG. 9 and FIG. 10, both films are white. Therefore, the optical filter (10A) of Example 1 is suitable for use as an infrared transmission filter and has high design value because it is white. Of course, color or shape may be imparted to the surface of the optical filter (10A) of Example 1 by printing, etc. The advantages of the optical filter according to the embodiment of the present invention will be explained in detail below.

[0111] The optical characteristics of an optical filter can be evaluated as follows.

[0112] As shown in FIG. 11, when incident light (I0) is incident on an optical filter (10), a portion of the incident light (I0) passes through the optical filter (10) (transmitted light (I i )), some reflects at the interface (interface reflected light (R i )), and some of the other parts are scattered. The scattered light includes forward scattered light (S) emitted in front of the optical filter (10). f ) and backscattered light emitted from the rear (Sb There is ). Backscattered light (S b The optical filter (10) is white. Although some of the incident light (I0) is absorbed by the optical filter (10), the resin and silica microparticles used here have a low absorption rate for light in the range of 400 nm to 2000 nm.

[0113] FIG. 12 is a schematic diagram showing a method for measuring the diffuse transmittance of an optical filter, and FIG. 13 is a schematic diagram showing a method for measuring the linear transmittance of an optical filter. As shown in FIG. 12, the diffuse transmittance is measured by placing a sample (optical filter (10)) in the opening of an integrating sphere (32), and the transmitted light (I i ) and forward scattered light (S f The intensity of the sum of the ) was calculated as a percentage of the intensity of the incident light (I0). In addition, linear transmittance was measured by placing the sample (optical filter (10)) at a position 20 cm away from the opening of the integrating sphere (32). The transmitted light (I) obtained at this time i It was calculated as a percentage of the intensity of the incident light (I0) relative to the intensity of the incident light (I0). The diameter of the aperture is 1.8 cm, which corresponds to a solid angle of 0.025 sr. An ultraviolet-visible-near-infrared spectrophotometer UH4150 (manufactured by Hitachi High-Tech Science Corp.) was used as the spectrometer. Table 1 shows the linear transmittance values ​​for infrared light at 760 nm, 950 nm, and 1550 nm. In addition, the linear transmittance spectra of each sample are shown in Figure 14, etc. The presence or absence of Bragg reflection can be determined by whether or not dimples (local reduction in transmittance) are present in the linear transmittance spectrum. The presence or absence of Bragg reflection is also shown in Table 1.

[0114] Backscattered light (S b The whiteness of ) was measured using a spectrophotometer CM-2600-D (manufactured by Konica Minolta Japan Co., Ltd.). L of the SCE (Specular Rejection) method * The x, y coordinate values ​​on the CIE1931 chromaticity diagram were calculated along with the value of . L *The higher the value of , and the closer the values ​​of x and y are to 0.33, the higher the whiteness. These values ​​are also shown in Table 1.

[0115] FIG. 14 shows the linear transmittance spectrum of the optical filter (10A) of Example 1, and FIG. 15 shows the absorption spectrum obtained as the difference between the diffuse transmittance spectrum and the diffuse reflectance spectrum of the optical filter (10A) of Example 1. As can be seen from FIG. 14, the optical filter (10A) of Example 1 has a high infrared transmittance. In particular, the transmittance for infrared rays with a wavelength of 900 nm or more is high. In addition, the absorption for infrared rays with a wavelength of 1200 nm or more, as shown in the absorption spectrum of FIG. 15, is due to the characteristic absorption of the resin (organic compound) and is minimal.

[0116] FIG. 16 shows the linear transmittance spectrum of the optical filter (20A) of Comparative Example 1. As is evident when comparing FIG. 16 with FIG. 15, the transmittance of the optical filter (20A) of Comparative Example 1 is low. When comparing Example 1 and Comparative Example 1 with reference to Table 1, L representing whiteness * Although there is no significant difference in the x and y coordinate values ​​on the CIE chromaticity diagram between Example 1 and Comparative Example 1, the linear transmittance of infrared radiation differs significantly. This is because the CV value in Comparative Example 1 is 49.3%, which is higher than the 27.8% in Example 1, and it is thought that the aggregation of silica microparticles has an influence. In other words, it can be seen that the CV value can serve as an indicator for improving the linear transmittance of infrared radiation.

[0117] Next, the optical filter of Example 2 will be described with reference to FIGS. 17 to 19. FIG. 17 is a diagram showing a cross-sectional TEM image of the optical filter of Example 2, and FIG. 18 is a histogram of the distance between the centroids of the particles obtained from the cross-sectional TEM image of the optical filter of Example 2. FIG. 19 is the linear transmittance spectrum of the optical filter of Example 2. While silica microparticles with an average particle size of 221 nm were used in Example 1, silica microparticles with an average particle size of 296 nm are used in Example 2. The CV value of Example 2 is almost identical to that of Example 1, but the infrared linear transmittance is lower in Example 2. That is, it can be seen that the infrared linear transmittance can be controlled by controlling the average particle size of the silica microparticles.

[0118] Here, the optical filter of Comparative Example 3 is described with reference to FIGS. 35 to 37 for comparison. FIG. 35 is a diagram showing a cross-sectional TEM image of the optical filter of Comparative Example 3, and FIG. 36 is a histogram of the distance between the centroids of the particles obtained from the cross-sectional TEM image of the optical filter of Comparative Example 3. FIG. 37 is the linear transmittance spectrum of the optical filter of Comparative Example 3. Comparative Example 3 differs from Examples 1 and 2 in that it uses silica microparticles with an average particle size of 110 nm. As is evident from the results in FIG. 37 and Table 1, the CV value of Comparative Example 3 is almost identical to that of Examples 1 and 2, but Comparative Example 3 has a high infrared linear transmittance of 87% at 760 nm, and also a high linear transmittance of visible light. Furthermore, the whiteness of Comparative Example 3 is inferior to that of Examples 1 and 2. In this regard, it can be seen that infrared linear transmittance and whiteness can be controlled by controlling the average particle size of the silica microparticles. From the comparison of Example 1, Example 2, and Comparative Example 3, it is considered desirable to include silica microparticles with an average particle size of 221 nm or more.

[0119] Next, the optical filters of Examples 3 and 4 will be described with reference to FIG. 20. FIG. 20 is the linear transmittance spectrum of the optical filters of Examples 3 and 4. The volume fractions of silica microparticles in the optical filters of Examples 3 and 4 are 34% and 38%, respectively, which are greater than the 29% of Example 1. Compared to the results of Example 1, there is no significant difference in the infrared linear transmittance and x, y coordinates on the CIE chromaticity diagram at 950 nm and 1550 nm, and the infrared linear transmittance and L at 760 nm * The value of is slightly improved. Comparing the linear transmittance spectra of Example 3 and Example 4, as the volume fraction of silica microparticles increases, the scattering wavelength shifts toward the shorter wavelength side, and L * The value of has improved slightly.

[0120] Here, for comparison, we refer to the linear transmittance spectrum of the optical filter of Example 9 shown in FIG. 25. The optical filter of Example 9 has a low volume fraction of silica microparticles at 6%. Compared to the results of Example 1, the infrared linear transmittance at 950 nm is slightly lower, and L * The value of is significantly reduced. This is thought to be due to a decrease in the intensity of scattered light caused by a decrease in the volume fraction of silica fine particles.

[0121] By controlling the volume fraction of silica microparticles in this way, the infrared linear transmittance and L * You can control the value of.

[0122] Next, the optical filter of Example 5 will be described with reference to FIG. 21. FIG. 21 is the linear transmittance spectrum of the optical filter of Example 5. While the thickness of the optical filter of Example 1 is 100 μm, the thickness of the optical filter of Example 5 is 500 μm. When Example 5 is compared to Example 1, the transmittance of infrared linear transmittance is reduced, but the whiteness is improved. By increasing the thickness of the optical filter, the transmittance of visible light can also be reduced.

[0123] Next, the optical filter of Example 6 is described with reference to FIG. 22. FIG. 22 is the linear transmittance spectrum of the optical filter of Example 6. Example 6 uses monomers different from Examples 1 to 5 and has a polymer with a refractive index of 1.52 as the matrix. While the refractive index of the matrix in Examples 1 to 5 was 1.49 and the difference with the refractive index of the silica microparticles (1.43) was 0.06, the refractive index difference in Example 6 is 0.09, which is larger. Compared to Example 1, the infrared linear transmittance and L at any of 760 nm, 950 nm, and 1550 nm * The value of has also improved.

[0124] Next, the optical filter of Example 7 will be described with reference to FIG. 23. FIG. 23 is the linear transmittance spectrum of the optical filter of Example 7. It differs from the optical filter of Example 6 in that it is formed on a glass substrate, whereas the optical filter of Example 7 is formed on a PET film. When comparing FIG. 23 with FIG. 22 and the results in Table 1, it is thought that the influence of the substrate is minimal.

[0125] Next, the optical filter of Example 8 will be described with reference to FIG. 24. FIG. 24 is the linear transmittance spectrum of the optical filter of Example 8. While the thickness of the optical filter of Example 7 is 100 μm, the thickness of the optical filter of Example 8 is 500 μm. When Example 8 is compared to Example 7, the infrared linear transmittance is reduced, but L * It has been improved. By increasing the thickness of the optical filter, the transmittance of visible light can also be reduced.

[0126] Next, the optical filter of Example 10 will be described with reference to FIGS. 26–28. FIG. 26 is the linear transmittance spectrum of the optical filter of Example 10, and FIG. 27 is a diagram showing the cross-sectional TEM image of the optical filter of Example 10. FIG. 28 is a histogram of the distance between the centroids of the particles obtained from the cross-sectional TEM image of the optical filter of Example 10. Example 10 has a polymer with a refractive index of 1.54 as a matrix, and the difference in refractive index with the silica microparticles is 0.11, which is greater than the difference in refractive index in Example 6. Compared to Examples 1 and 6, the infrared linear transmittance is reduced, and L * The value of improves.

[0127] Next, the optical filter of Example 11 will be described with reference to FIG. 29. FIG. 29 is the linear transmittance spectrum of the optical filter of Example 11. Example 11 has a polymer with a refractive index of 1.46 as the matrix. In Example 11, the difference in refractive index is small at 0.03. Compared to Example 1, it can be seen that the infrared linear transmittance at 1550 nm is reduced, the transmittance in the visible light region is increased, and the whiteness is reduced.

[0128] Next, the optical filter of Example 12 will be described with reference to FIG. 30. FIG. 30 is the linear transmittance spectrum of the optical filter of Example 12. The optical filter of Example 12 comprises silica microparticles with an average particle size of 110 nm and microparticles with an average particle size of 221 nm. The volume ratio (110 nm:221 nm) is 1:1. Compared to Example 1, both the infrared linear transmittance and whiteness have decreased (see Table 1). This is thought to be due to the effect of mixing silica microparticles with an average particle size of 110 nm (see Comparative Example 3, FIG. 37).

[0129] Next, the optical filter of Example 13 will be described with reference to FIG. 31. FIG. 31 is the linear transmittance spectrum of the optical filter of Example 13. The optical filter of Example 13 differs from the optical filter of Example 6 in that it uses silica microparticles with an average particle size of 181 nm. Comparing FIG. 31 with FIG. 22, the wavelength at which linear transmittance increases in Example 13 is shifted toward the shorter wavelength side compared to Example 6. That is, the linear transmittance of the optical filter of Example 13 in the visible light region is slightly higher than that of Example 6, and as a result, L * It can be seen that silica microparticles with an average particle size of 181 nm are suitably used, as the value and whiteness are slightly lower than in Example 6, but the linear transmittance of infrared rays has a high value. In addition, from the perspective of whiteness, it is preferable to include silica microparticles with an average particle size of 200 nm or more, and it is more preferable to include silica microparticles with an average particle size of 221 nm or more.

[0130] Next, the optical filter of Comparative Example 2 will be described with reference to FIGS. 32 to 34. FIG. 32 is a diagram showing a cross-sectional TEM image of the optical filter of Comparative Example 2. FIG. 33 is a histogram of the distance between the centroids of particles obtained from the cross-sectional TEM image of the optical filter of Comparative Example 2. FIG. 34 is a linear transmittance spectrum of the optical filter of Comparative Example 2, showing results at an angle of incidence of 0° and 60°. An angle of incidence of 0° is the normal direction of the surface of the optical filter. Comparative Example 2 has a matrix with a refractive index of 1.48 formed using acrylic monomer E. The refractive index of the matrix changes by only 0.01 compared to Example 1. In addition, the dependence of linear transmittance on the angle of incidence was measured by changing the angle of the surface of the sample relative to the incident light (the angle of the optical filter (10) in FIG. 11) using an automatic angle variable system attached to the ultraviolet-visible-near-infrared spectrophotometer UH4150 (manufactured by Hitachi High-Tech Science Co., Ltd.).

[0131] As can be seen from FIGS. 32 and 33, the aggregate of silica microparticles in the optical filter of Comparative Example 2 has long-range order. As a result, the CV value in Table 1 is 9.4%, which is a small value. In addition, steep dimples (local decrease in transmittance) are visible in the visible light region of the linear transmittance spectrum shown in FIG. 34. These steep dimples are caused by Bragg reflection, and the aggregate of silica microparticles in the optical filter of Comparative Example 2 is not a colloidal amorphous aggregate, but rather has a structure similar to a colloidal crystal or a colloidal crystal with long-range order. Furthermore, since the steep dimples in the visible light region shift with the angle of incidence, the optical filter of Comparative Example 2 appears to change color depending on the viewing angle. Therefore, it is considered desirable that the CV value be 10% or higher to suppress Bragg reflection in the visible light region. In addition, from the results of Comparative Example 1 described above, it is considered that a CV value of 49% or less is desirable to suppress the aggregation of silica fine particles.

[0132] The optical filters of Examples 1 to 13 do not show steep dimples in the linear transmittance spectrum, and silica microparticles form a colloidal amorphous aggregate. In addition, the linear transmittance for light of at least some wavelengths within the wavelength range of 760 nm to 2000 nm is 60% or higher. Furthermore, when the standard light is a D65 light source, the x and y coordinates on the white CIE1931 chromaticity diagram are within the range of 0.25 ≤ x ≤ 0.40 and 0.25 ≤ y ≤ 0.40. In addition, color change depending on the viewing angle is suppressed.

[0133] As is evident from the above, the optical filter according to the embodiment of the present invention can obtain desired optical properties (e.g., infrared linear transmittance and whiteness) by adjusting the refractive index of the fine particles and matrix, the average particle size of the fine particles, the volume fraction, the distribution (degree of non-periodicity), and the thickness, and also suppresses color changes depending on the viewing angle. In addition, optical filters having different optical properties can be stacked and used. Furthermore, depending on the application, it can be stacked with, for example, a filter that absorbs infrared rays. As can be understood from FIG. 9, even when stacked with, for example, a filter that displays black or other colors, the optical filter according to the embodiment of the present invention displays white, thereby enhancing aesthetic appeal.

[0134] The optical filter according to an embodiment of the present invention is also characterized by the angle of incidence dependence of the linear transmittance spectrum.

[0135] With reference to FIGS. 38 to 40, the angle of incidence dependence of the linear transmittance spectra of the optical filter (10A) of Example 1 and the optical filter of Comparative Example A (angles of incidence 0°, 15°, 30°, 45°, 60°) is explained. The optical filter of Comparative Example A is a white IR window manufactured by Tokai Optical Co., Ltd. (https: / / www.tokaioptical.com / jp / product14 / ) which is commercially available as an infrared transmission filter. The optical filter of Comparative Example A corresponds to the optical article described in Patent Document 2, is composed of a dielectric multilayer film and a PET film, and has a satin finish surface. The optical filter of Comparative Example A exhibits white color and has a thickness of 120 μm.

[0136] FIG. 38 is a diagram showing the angle of incidence dependence of the linear transmittance spectrum of the optical filter (10A) of Example 1 and a conventional optical filter. FIG. 39 and FIG. 40 are graphs in which each graph is normalized to the maximum transmittance, FIG. 39 is a diagram showing the angle of incidence dependence of the linear transmittance spectrum of the optical filter (10A) of Example 1, and FIG. 40 is a diagram showing the angle of incidence dependence of the linear transmittance spectrum of a conventional optical filter.

[0137] As can be seen from FIG. 38, the linear transmittance of the optical filter (10A) of Example 1 is greater than that of the optical filter of Comparative Example A. In addition, the decrease in infrared linear transmittance due to an increase in the angle of incidence is smaller in the optical filter (10A) of Example 1 than in the optical filter of Comparative Example A. For example, the linear transmittance of 950 nm infrared is 88% when the angle of incidence is 0°, and is 80% when the angle of incidence is 60°, which is 90% or more of the transmittance when the angle of incidence is 0°. In contrast, in Comparative Example A, the linear transmittance for 950 nm infrared is 30% when the angle of incidence is 0°, and is 9% when the angle of incidence is 60°, which is reduced to 30% of the linear transmittance when the angle of incidence is 0°. Thus, the infrared linear transmittance of the optical filter according to the embodiment of the present invention has a small dependence on the angle of incidence, and for example, for infrared rays of 950 nm, the linear transmittance when the angle of incidence is 60° can be obtained at least 80%, at least 85%, and at least 90% of the linear transmittance when the angle of incidence is 0°.

[0138] Looking at the transmittance curve of the optical filter (10A) of Example 1 shown in FIG. 39, the portion of the curve where the linear transmittance increases monotonically from visible light to infrared light shifts toward the longer wavelength side (about 50 nm) as the angle of incidence increases. This characteristic angle of incidence dependence is also visible in the angle of incidence dependence of the linear transmittance spectra of the optical filters of Example 2, Example 6, and Comparative Example 3 shown in FIG. 41, FIG. 42, and FIG. 43. That is, the characteristic angle of incidence dependence, in which the portion of the curve where the linear transmittance increases monotonically from visible light to infrared light shifts toward the longer wavelength side as the angle of incidence increases, is thought to be due to the silica microparticles included in the optical film forming a colloidal amorphous aggregate. In contrast, in the transmittance curve of the optical filter of Comparative Example A shown in FIG. 40, the portion of the curve where the linear transmittance increases monotonically from visible light to infrared light shifts toward the shorter wavelength side (about 100 nm) as the angle of incidence increases. In other words, it is in a completely opposite trend.

[0139] In the optical filter of Comparative Example A, the curve portion in which linear transmittance increases monotonically from visible light to infrared light shifts toward the short wavelength side as the angle of incidence increases, so there is a concern that light of the short wavelength side, which is originally intended to be blocked, will be transmitted (light leakage) for obliquely incident light. In contrast, in the optical filter in which silica microparticles form a colloidal amorphous aggregate, the transmittance for light of the short wavelength side decreases as the angle of incidence increases, so there is no concern that light leakage will occur as in the optical filter of Comparative Example A.

[0140] In addition, in an optical filter in which colloidal amorphous silica microparticles constitute a colloidal amorphous aggregate, the decrease in transmittance for shorter wavelength light as the angle of incidence increases is due to the increase in the intensity of scattered light of visible light (especially on the long wavelength side). Therefore, when the optical filter of the embodiment according to the present invention is viewed at an angle, the intensity of diffuse reflected light (backscattered light) increases, so the white brightness can be increased.

[0141] As described above, since the optical filter according to the embodiment of the present invention can exhibit whiteness, an optical filter with rich design and rich colors can be obtained by using infrared-transmitting ink to print, for example, characters, pictures, or photographs on the surface of the optical filter. That is, the optical filter according to the embodiment of the present invention may have an optical filter layer comprising a matrix and fine particles, and a print layer formed of infrared-transmitting ink disposed on the optical filter layer. The print layer may be formed directly on the surface of the optical filter layer, or a print layer formed on the surface of a transparent film may be disposed on the optical filter layer. As for the infrared-transmitting ink, a known infrared-transmitting ink may be selected depending on the application or the wavelength of infrared light to be transmitted.

[0142] In addition, the optical filter according to the embodiment of the present invention increases the intensity of diffuse reflected light when viewed at an angle, thereby increasing white brightness and improving the appearance of the design (visibility of the design).

[0143] The optical filter according to the embodiment may be a planar film as exemplified, but is not limited thereto and may take various forms. The optical filter according to the embodiment may have a three-dimensional shape. For example, it may be a film shape having a three-dimensional shape. Specifically, for example, the optical filter may be formed by using a coating method on the surface of an object having a three-dimensional shape. The surface of the object may have any shape, such as part or all of a sphere, a curved surface of any shape, or part or all of a polyhedron. However, it is preferable that the surface of the object does not cause light scattering.

[0144] For example, an optical filter formed in a hemispherical shape can be obtained as shown in FIGS. 44a and 44b. FIG. 44a is a drawing showing an optical image (visible light) of an embodiment of an optical filter formed in a hemispherical shape, and FIG. 44b is a drawing showing an infrared image of the optical filter of the hemispherical embodiment shown in FIG. 44a. The images shown in FIG. 44a and 44b were captured using the DVSA10FHDIR full high-definition digital movie camera manufactured by Kenko Tokina Co., Ltd. FIG. 44a is an image captured in visible light mode under white LED lighting, and FIG. 44b is an image captured in a dark room using only the light from the infrared LED of the camera.

[0145] The optical filter shown in FIGS. 44a and 44b is an optical filter with a thickness of 300 μm formed by applying the same material as in Example 6 to the surface of a hemisphere made of acrylic resin (PMMA) with a radius of 2 cm and a thickness of 1 mm by dip coating. As shown in FIG. 44a, a white filter with a hemispherical shape was obtained. In addition, as shown in FIG. 44b, this filter transmits infrared rays.

[0146] The optical filter according to the embodiment of the present invention is not limited to the exemplified sensing device (e.g., infrared camera) or communication device, but is used for various applications. For example, it is suitably used in solar cells, heaters using infrared rays, and optical power supply devices using infrared rays.

[0147] Depending on the application of the optical filter, lightfastness is required. Therefore, the results of the lightfastness evaluation are explained below. The lightfastness test was conducted according to the method in accordance with JIS B 7754. The change in appearance before and after the lightfastness test is the chroma C measured using the SCE method in the CIE 1976 color space. * It was evaluated based on the change. As can be seen from the results below, the saturation C before and after the lightfastness test (300 hours) described later. * The change in is preferably 6 or less, more preferably 5 or less, and more preferably 3 or less. The conditions for the light resistance test, etc. are as follows.

[0148] Device: Super Xenon Weather Meter SX75 (Manufactured by Suga Testing Machine Co., Ltd.)

[0149] Sample: Width 20 mm × Length 10 mm

[0150] Ultraviolet irradiance: Average accumulated illuminance of light with wavelengths between 300 nm and 400 nm is 120 W / m²

[0151] Black Panel Temperature (BPT): 55℃

[0152] Tank temperature: 30℃

[0153] Humidity inside the tank: 55%

[0154] Test time: Up to approximately 500 hours (provided, C based on lightfastness test) * The change in used the value at 300 hours).

[0155] Lightfastness was evaluated based on changes in whiteness and linear infrared transmittance. Both whiteness and linear transmittance were measured using the methods described above. Additionally, chroma C was used as an evaluation index for whiteness.* and color difference ΔE * ab used.

[0156] The sample of Example 6 was obtained by peeling off a film formed of acrylic resin and silica microparticles of the optical filter of Example 6, prepared as described above, from a glass substrate. The sample of Example 6 was white and had a thickness of 120 μm.

[0157] C of the optical filter of Example 6 and Comparative Example A in FIG. 45 * A graph showing the change in the lightfastness test is shown, and in FIG. 46, the ΔE of the optical filters of Example 6 and Comparative Example A is shown. * ab A graph showing the change in the light resistance test is shown.

[0158] As can be seen from FIG. 45, the chroma C by the lightfastness test of the optical filter of Example 6 * The change in is very small compared to Comparative Example A. C of the optical filter in Comparative Example A * The lightfastness test is 300 hours, increasing from approximately 3 to approximately 9, and continues to increase thereafter, reaching approximately 11 at 500 hours. That is, C of the optical filter of Comparative Example A * It increases by about 6 in 300 hours of light resistance testing.

[0159] In this regard, C of the optical filter of Example 6 * decreases from approximately 5 to approximately 3 after 300 hours of lightfastness testing, then changes to an increase, and returns to approximately 5 after 500 hours. C of the optical filter of Example 6. * The maximum change is a decrease to about 2 after 300 hours of light resistance testing.

[0160] Referring to FIG. 46, the ΔE of the optical filter of Comparative Example A * abincreases to approximately 9 after 300 hours of lightfastness testing, and continues to increase thereafter, reaching approximately 12 after 500 hours. In contrast to this, the ΔE of the optical filter of Example 6 * ab The light resistance test increases to about 3 after 300 hours and to about 6 after 500 hours.

[0161] Thus, the optical filter of Example 6 shows a smaller change in whiteness due to the lightfastness test compared to the optical filter of Comparative Example A. The reason for this is thought to be as follows. Since the optical filter of Comparative Example A utilizes a dielectric multilayer film, the optical properties change significantly when the interlayer distance of the dielectric multilayer film changes due to the lightfastness test. In contrast, the optical filter of Example 6 has a structure in which fine particles are dispersed within a matrix, and since the optical properties are provided by fine particles (colloidal amorphous particles) that lack regularity, the change in optical properties is relatively small even if the structure (e.g., inter-particle distance) changes due to the lightfastness test. Furthermore, since the matrix is ​​composed of a resin having a cross-linked structure, it is thought that the structural change due to the lightfastness test is relatively small. Additionally, the fact that the fine particles are formed from inorganic materials also contributes to the improvement in lightfastness.

[0162] Although the lightfastness required for optical filters varies depending on the application, according to an embodiment of the present invention, C before and after a lightfastness test in which light from a xenon arc lamp (average integrated illuminance of light with a wavelength of 300 nm or more and 400 nm or less is 120 W / m²) is irradiated for 300 hours * An optical filter can be obtained in which the absolute value of the change is 6 or less, also 5 or less, and also 3 or less. Alternatively, the color difference ΔE before and after the lightfastness test above * ab An optical filter can be obtained in which α is 8 or less and α is also 5 or less.

[0163] Figure 47 shows a graph illustrating the change in linear transmittance of the optical filters of Example 6 and Comparative Example A during a lightfastness test for infrared (wavelength 950 nm). As can be seen from Figure 47, the change in linear transmittance of the optical filter of Example 6 during the lightfastness test is very small compared to Comparative Example A. The linear transmittance of the optical filter of Comparative Example A decreases from approximately 82% to approximately 73% after 100 hours of the lightfastness test, and continues to decrease thereafter, reaching approximately 66% after 300 hours and approximately 64% after 500 hours. Thus, the linear transmittance of the optical filter of Comparative Example A decreases in a relatively short period of time, and decreases by approximately 20% after 300 hours of the lightfastness test.

[0164] In this regard, the linear transmittance of the optical filter of Example 6 shows little change due to the lightfastness test, increasing from about 89% to about 91% after 100 hours, and also increasing slightly to about 91% after 300 hours and about 93% after 500 hours. The change in the linear transmittance of the optical filter of Example 6 due to the lightfastness test of 300 hours is only about 1%.

[0165] Thus, the optical filter of Example 6 shows a smaller change in linear transmittance during the lightfastness test compared to the optical filter of Comparative Example A. As described above, this reason is thought to be due to the fact that the optical filter of Example 6 has a structure in which fine particles are dispersed in a matrix, that fine particles without regularity (colloidal amorphous particles) are responsible for the optical properties, and that the matrix is ​​composed of a resin having a cross-linked structure.

[0166] Although the light resistance required for an optical filter varies depending on the application, according to an embodiment of the present invention, an optical filter can be obtained in which the change before and after a light resistance test in which light from a xenon arc lamp (average integrated illuminance of light with a wavelength of 300 nm or more and 400 nm or less is 120 W / m²) is irradiated for 300 hours is 15% or less and 5% or less.

[0167] (Industrial Applicability)

[0168] An optical filter according to an embodiment of the present invention can be used as an infrared transmission filter used, for example, in sensor technology or communication technology. Explanation of the symbols

[0169] 10, 10A, 20A: Optical filter 12: Matrix 14: Microparticles

Claims

Claim 1 L measured by the SCE method * An optical filter having a value of 20 or higher, with a linear transmittance of 60% or higher for light of at least some wavelengths within a wavelength range of 760 nm to 2000 nm, and C measured by the SCE method using a spectrophotometer before and after a lightfastness test in which light from a xenon arc lamp (average integrated illuminance of light with a wavelength of 300 nm to 400 nm is 120 W / m²) is irradiated for 300 hours. * An optical filter in which the absolute value of the change is 6 or less, and the transmittance curve of the visible light wavelength region of the filter has a curve portion in which linear transmittance decreases monotonically from the long wavelength side to the short wavelength side, and said curve portion shifts toward the long wavelength side as the angle of incidence increases. Claim 2 In claim 1, L measured by the SCE method using a spectrophotometer * , a * , b * The color difference ΔE of white before and after the lightfastness test obtained from * ab is an optical filter with 8 or less. Claim 3 An optical filter according to claim 1 or 2, wherein the change in linear transmittance for light with a wavelength of 950 nm before and after the light resistance test is 15% or less. Claim 4 An optical filter according to claim 1 or 2, having a linear transmittance of 60% or more for light with a wavelength of 950 nm. Claim 5 An optical filter according to claim 1 or 2, having a linear transmittance of 60% or more for light with a wavelength of 1550 nm. Claim 6 An optical filter according to claim 1 or 2, wherein the x, y coordinates on the CIE1931 chromaticity diagram of the color represented when the standard light is a D65 light source are 0.25≤x≤0.40 and 0.25≤y≤0.

40. Claim 7 delete Claim 8 An optical filter according to claim 1 or 2, wherein the linear transmittance for light with a wavelength of 950 nm at an angle of incidence of 60° is 80% or more of the linear transmittance at an angle of incidence of 0°. Claim 9 An optical filter according to claim 1 or 2, further having a print layer formed of infrared-transmitting ink. Claim 10 An optical filter having a three-dimensional shape according to claim 1 or 2. Claim 11 An optical filter comprising a matrix and fine particles dispersed in the matrix, in accordance with claim 1 or 2. Claim 12 In claim 11, the optical filter comprises monodisperse first particles having an average particle size within the range of 80 nm or more and 300 nm or less. Claim 13 An optical filter according to claim 12, wherein the average particle size of the first fine particle is 150 nm or more. Claim 14 An optical filter according to claim 11, wherein the average value of the distance between the centers of gravity of the fine particles in a cross-section perpendicular to the plane direction of the filter is 200 nm or more. Claim 15 An optical filter according to claim 11, wherein the coefficient of variation of the average value of the distance between the centers of gravity of the fine particles in a cross-section perpendicular to the plane direction of the filter is 10% or more. Claim 16 An optical filter according to claim 11, wherein the coefficient of variation of the average value of the distance between the centers of gravity of the fine particles in a cross-section perpendicular to the plane direction of the filter is 45% or less. Claim 17 In claim 11, the matrix is ​​an optical filter comprising a resin having a cross-linked structure. Claim 18 In claim 11, the above-mentioned fine particles constitute at least a colloidal amorphous aggregate, an optical filter. Claim 19 An optical filter according to claim 11, wherein the volume fraction of the fine particles is 6% or more and 60% or less. Claim 20 In claim 11, the refractive index of the matrix for light with a wavelength of 546 nm is n M , the refractive index of the above-mentioned fine particle is n P When saying, |n M -n P Optical filter with | 0.03 or greater and 0.6 or less. Claim 21 An optical filter according to claim 11, wherein the matrix is ​​formed of a resin and the microparticles are formed of an inorganic material. Claim 22 A method for manufacturing an optical filter as described in claim 21, comprising the steps of: preparing a curable resin composition in which the fine particles are dispersed and mixed in a curable resin; applying the curable resin composition to the surface of a substrate; and curing the curable resin included in the curable resin composition applied to the surface. Claim 23 In claim 22, the above-mentioned imparting process is a manufacturing method performed by a coating method. Claim 24 In claim 22, the above-mentioned imparting process is a manufacturing method performed by a dip coating method. Claim 25 A device having an infrared light receiving portion, and an optical module having an optical filter described in claim 1 or 2 disposed on the front surface of the infrared light receiving portion of the device. Claim 26 In claim 25, the device is an optical module that is a sensing device, a communication device, a solar cell, a heater, or a power supply device.

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