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

Abstract

A filter with backscattering characteristics, wherein the filter has a linear transmittance of 60% or more for at least a portion of wavelengths in the wavelength range of 760 nm to 2000 nm. The bidirectional reflectance distribution function (BRDF) is defined as follows: BRDF(0°; 20°, -60°) is defined for the direction where the polar angle of the incident light's incident direction is 0° and the azimuth angle formed with the incident surface is 20° and the polar angle is -60°. Similarly, BRDF(30°; 20°, -60°) is defined for the direction where the polar angle of the incident light's incident direction is 30° and the azimuth angle formed with the incident surface is 20° and the polar angle is -60°. The value of the bidirectional reflectivity distribution function in the direction where the polar angle of the incident direction is 60°, the azimuth angle formed with the incident surface is 20°, and the polar angle is -60° is BRDF(60°; 20°, -60°), and when the incident light is light with at least a portion of the wavelengths within the visible light wavelength range, |BRDF(0°; 20°, -60°)-BRDF(30°; 20°, -60°)| / BRDF(0°; 20°, -60°) is 1.0 or less, and |BRDF(0°; 20°, -60°)-BRDF(60°; 20°, -60°)| / BRDF(0°; 20°, -60°) is 1.0 or less.

Description

Technical Field

[0001] This invention relates to filters, methods of manufacturing the same, and optical modules. For example, it relates to infrared filters suitable for use as infrared filters with high linear transmittance for infrared light and high diffuse reflectance for visible light, methods of manufacturing the same, and optical modules in which such filters are provided in front of an infrared light-receiving portion of a device. Such devices are, for example, sensing devices or communication devices. Background Technology

[0002] Infrared sensor and communication technologies are being developed and put into practical use. Elements that receive infrared light are sensitive to visible light; therefore, infrared filters are used to selectively transmit infrared light. The definition of infrared light varies depending on the technical field. In this specification, "infrared light" includes light (electromagnetic waves) in the range of wavelengths from 760 nm to 2000 nm used in sensing or communication. Additionally, "visible light" refers to light in the range of wavelengths from 400 nm to 760 nm.

[0003] Existing infrared filters are mostly black because they absorb visible light, which results in poor design flexibility.

[0004] Therefore, for example, Patent Document 1 discloses an infrared light-receiving part having a dielectric multilayer film that transmits infrared light and reflects and transmits visible light, and a surface processed into a pear-skin shape. Furthermore, Patent Document 2 discloses an optical article for infrared communication that utilizes Rayleigh scattering caused by the fine unevenness formed by roughening the surface of a transparent substrate to scatter visible light, thereby appearing white, and achieving an infrared transmittance of 12% or more.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2006-165493 (Japanese Patent No. 4122010)

[0008] Patent Document 2: Japanese Patent Application Publication No. 2013-65052 (Japanese Patent No. 5756962)

[0009] Patent Document 3: Japanese Patent Application Publication No. 2010-058091 (Japanese Patent No. 5274164)

[0010] Non-patent literature

[0011] Non-patent document 1: M.Iwata et al. "Bio-Inspired Bright Structurally ColoredColloidal Amorphous Array Enhanced by Controlling Thickness and BlackBackground", Adv.Mater., 2017, 29, 1605050. Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] The infrared light-emitting part described in Patent Document 1 only utilizes visible light reflected through a dielectric multilayer film to achieve a colored appearance, with the color changing depending on the viewing angle. Furthermore, the dielectric multilayer film is also expensive.

[0014] According to the inventors' research, for infrared communication films utilizing dielectric multilayer films as described in Patent Document 1, when a hand's movement is captured through the film by an infrared camera, the hand's outline is blurred, making it difficult to use for motion capture. This is believed to be due to the low linear transmittance of infrared light.

[0015] On the other hand, for example, Patent Document 3 and Non-Patent Document 1 disclose that particulate dispersions or colloidal amorphous aggregates with amorphous structures can exhibit bright structural colors (e.g., blue) with low angle dependence. Patent Document 3 describes that particulate dispersions with amorphous structures are particularly useful for applications that reflect light of specific wavelengths (e.g., color materials, infrared reflective films, etc.).

[0016] The present invention is made to solve the above-mentioned problems, and its purpose is to provide a filter with isotropic backscattering characteristics, its manufacturing method and optical module, wherein the filter can achieve an infrared filter with high linear transmittance of infrared light.

[0017] Problem Solving Methods

[0018] According to embodiments of the present invention, solutions illustrated in the following items are provided.

[0019] [Project 1]

[0020] A filter that has backscattering properties.

[0021] The aforementioned filter has a linear transmittance of 60% or more for at least a portion of the wavelengths in the wavelength range of 760nm and below 2000nm.

[0022] The bidirectional reflectance distribution function (BRDF) for the direction where the polar angle of the incident light is 0° and the azimuth angle formed with the incident surface is 20° and the polar angle is -60° is defined as BRDF(0°; 20°, -60°). The BRDF(30°; 20°, -60°) for the direction where the polar angle of the incident light is 30° and the azimuth angle formed with the incident surface is 20° and the polar angle is -60° is defined as BRDF(60°; 20°, -60°) for the direction where the polar angle of the incident light is 60° and the azimuth angle formed with the incident surface is 20° and the polar angle is -60° is defined as BRDF(60°; 20°, -60°). This applies when the incident light is light with at least a portion of its wavelengths within the visible light wavelength range.

[0023] |BRDF(0°; 20°, -60°)-BRDF(30°; 20°, -60°)| / BRDF(0°; 20°, -60°) is less than or equal to 1.0, and |BRDF(0°; 20°, -60°)-BRDF(60°; 20°, -60°)| / BRDF(0°; 20°, -60°) is less than or equal to 1.0.

[0024] [Project 2]

[0025] According to the filter described in Project 1, wherein,

[0026] The value of |BRDF(0°; 20°, -60°)-BRDF(30°; 20°, -60°)| / BRDF(0°; 20°, -60°) is less than 0.50, and the value of |BRDF(0°; 20°, -60°)-BRDF(60°; 20°, -60°)| / BRDF(0°; 20°, -60°) is less than 0.50.

[0027] [Project 3]

[0028] According to the filter described in Project 1, wherein,

[0029] The value of |BRDF(0°; 20°, -60°)-BRDF(30°; 20°, -60°)| / BRDF(0°; 20°, -60°) is less than 0.25, and the value of |BRDF(0°; 20°, -60°)-BRDF(60°; 20°, -60°)| / BRDF(0°; 20°, -60°) is less than 0.25.

[0030] [Project 4]

[0031] The filter according to any one of items 1 to 3, wherein...

[0032] The L* value measured by SCE method is above 20.

[0033] [Project 5]

[0034] The filter according to any one of items 1 to 4 has a three-dimensional shape. The aforementioned three-dimensional shape includes, for example, a three-dimensional curved surface.

[0035] [Project 6]

[0036] The filter according to any one of items 1 to 5, wherein...

[0037] The aforementioned three-dimensional shape includes at least a portion of a solid shape.

[0038] [Project 7]

[0039] According to the filter described in Project 6, wherein...

[0040] The aforementioned solid shapes include any shape among spheres, ellipsoids, polyhedra, cones, and cylinders.

[0041] [Project 8]

[0042] The filter according to any one of items 1 to 7 has a substrate and a film formed on the substrate.

[0043] The aforementioned film exhibits a linear transmittance of 60% or more for at least a portion of wavelengths within the wavelength range of 760 nm to 2000 nm.

[0044] The bidirectional reflectance distribution function (BRDF) for the direction where the polar angle of the incident light is 0° and the azimuth angle formed with the incident surface is 20° and the polar angle is -60° is defined as BRDF(0°; 20°, -60°). The BRDF(30°; 20°, -60°) for the direction where the polar angle of the incident light is 30° and the azimuth angle formed with the incident surface is 20° and the polar angle is -60° is defined as BRDF(60°; 20°, -60°) for the direction where the polar angle of the incident light is 60° and the azimuth angle formed with the incident surface is 20° and the polar angle is -60° is defined as BRDF(60°; 20°, -60°). This applies when the incident light is light with at least a portion of its wavelengths within the visible light wavelength range.

[0045] |BRDF(0°; 20°, -60°)-BRDF(30°; 20°, -60°)| / BRDF(0°; 20°, -60°) is less than or equal to 1.0, and |BRDF(0°; 20°, -60°)-BRDF(60°; 20°, -60°)| / BRDF(0°; 20°, -60°) is less than or equal to 1.0.

[0046] [Project 9]

[0047] According to the filter described in Project 8, wherein,

[0048] The aforementioned substrate is formed of plastic or glass.

[0049] [Project 10]

[0050] According to the filter described in item 8 or 9, wherein,

[0051] The surface of the aforementioned substrate has undergone any of the following treatments: corona treatment, plasma treatment, UV ozone treatment, and primer treatment.

[0052] [Project 11]

[0053] The filter according to any one of items 1 to 10 has a linear transmittance of more than 60% for light with a wavelength of 950 nm.

[0054] [Project 12]

[0055] The filter according to any one of items 1 to 11 has a linear transmittance of more than 60% for light with a wavelength of 1550nm.

[0056] [Project 13]

[0057] According to any one of items 1 to 12, the color of the filter presented when the standard light is set to a D65 light source has x,y coordinates of 0.25≤x≤0.40 and 0.25≤y≤0.40 on the CIE1931 chromaticity diagram.

[0058] [Project 14]

[0059] The filter according to any one of items 1 to 13, wherein,

[0060] The transmittance curve of the above-mentioned filter in the visible light wavelength region has a linear portion in which the transmittance decreases monotonically from the long wavelength side to the short wavelength side, and the above-mentioned portion of the curve shifts towards the long wavelength side as the incident angle increases.

[0061] [Project 15]

[0062] The filter according to any one of items 1 to 14, wherein,

[0063] The linear transmittance of light with a wavelength of 950 nm at an incident angle of 60° is more than 80% of the linear transmittance at an incident angle of 0°.

[0064] [Project 16]

[0065] The filter according to any one of items 1 to 15 further comprises a printed layer formed of infrared-transmitting ink.

[0066] [Project 17]

[0067] The filter according to any one of items 1 to 16 comprises a matrix and particles dispersed in the matrix.

[0068] [Project 18]

[0069] According to the filter described in item 17, wherein,

[0070] The aforementioned particles include monodisperse first particles with an average particle size in the range of 80 nm or more and 300 nm or less.

[0071] [Project 19]

[0072] According to the filter described in Project 18, wherein,

[0073] The average particle size of the first particle mentioned above is greater than 150 nm.

[0074] [Project 20]

[0075] The filter according to any one of items 17 to 19, wherein,

[0076] In a cross-section perpendicular to the surface direction of the filter, the average distance between the centroids of the particles is 200 nm or more.

[0077] [Project 21]

[0078] The filter according to any one of items 17 to 20, wherein,

[0079] In a cross section perpendicular to the surface direction of the filter, the average value of the distance between the centroids of the particles varies by a factor of 10% or more.

[0080] [Project 22]

[0081] The filter according to any one of items 17 to 21, wherein,

[0082] In a cross section perpendicular to the surface direction of the filter, the average value of the distance between the centroids of the particles is less than 45%.

[0083] [Project 23]

[0084] The filter according to any one of items 17 to 22, wherein,

[0085] The matrix described above contains a resin having a cross-linked structure.

[0086] [Project 24]

[0087] The filter according to any one of items 17 to 23, wherein...

[0088] The aforementioned particles at least constitute colloidal amorphous aggregates.

[0089] [Project 25]

[0090] The filter according to any one of items 17 to 24, wherein,

[0091] The volume fraction of the aforementioned particles is between 6% and 60%.

[0092] [Project 26]

[0093] The filter according to any one of items 17 to 25, wherein,

[0094] Let the refractive index of the above matrix for light with a wavelength of 546 nm be n. M And let the refractive index of the above-mentioned particles be n. P When, |n M -n P | is above 0.03 and below 0.6.

[0095] [Project 27]

[0096] The filter according to any one of items 17 to 26, wherein,

[0097] The matrix is ​​formed of resin, and the microparticles are formed of inorganic materials.

[0098] [Project 28]

[0099] A manufacturing method for manufacturing the filter described in item 27, the method comprising:

[0100] A process for preparing a curable resin composition in which the above-mentioned particles are dispersed / mixed in a curable resin;

[0101] The process of applying the above-described curable resin composition to the surface of a substrate; and

[0102] A process of curing the curing resin contained in the curing resin composition applied to the surface.

[0103] [Project 29]

[0104] According to the manufacturing method described in item 28, wherein,

[0105] The above-mentioned coating process is carried out by coating method.

[0106] [Project 30]

[0107] According to the manufacturing method described in item 29, wherein,

[0108] The above-mentioned coating process is carried out by dip coating.

[0109] [Project 31]

[0110] An optical module having:

[0111] Equipment with infrared light-receiving parts, and

[0112] The filter described in any one of items 1 to 27 is disposed in front of the infrared light-receiving part of the above-described device.

[0113] [Project 32]

[0114] According to the optical module described in item 31, wherein...

[0115] The aforementioned equipment includes sensing devices, communication devices, solar cells, heaters, or power supply equipment.

[0116] The effects of the invention

[0117] According to embodiments of the present invention, a filter having isotropic backscattering characteristics, a method for manufacturing the filter, and an optical module thereof can be provided, wherein the filter is an infrared filter with high linear transmittance of infrared light. Attached Figure Description

[0118] Figure 1 This is a cross-sectional schematic diagram of the filter 10 according to an embodiment of the present invention.

[0119] Figure 2 This is a TEM image showing a cross-sectional view of the filter 10A of Embodiment 1.

[0120] Figure 3 This is a TEM image showing a cross-sectional view of filter 20A of Comparative Example 1.

[0121] Figure 4 It is a histogram of the distance between the centroids of the particles, obtained from the cross-sectional TEM image of the filter 10A of Example 1.

[0122] Figure 5 It is a histogram of the distance between the centroids of the particles, obtained from the cross-sectional TEM image of filter 20A of Comparative Example 1.

[0123] Figure 6 This is an example of a camera image obtained using motion capture equipment.

[0124] Figure 7 This is an example of a camera image obtained via filter 10A of Embodiment 1 and using a motion capture device.

[0125] Figure 8Examples of camera images obtained via the filter 20A of Comparative Example 1 and using a motion capture device.

[0126] Figure 9 This is a diagram showing an optical image of the filter 10A of Embodiment 1.

[0127] Figure 10 This is a diagram showing an optical image of filter 20A of Comparative Example 1.

[0128] Figure 11 This is a schematic diagram used to illustrate the optical characteristics of the filter 10 according to an embodiment of the present invention.

[0129] Figure 12 This is a schematic diagram illustrating the method for measuring the diffuse transmittance of a filter.

[0130] Figure 13 This is a schematic diagram illustrating the method for measuring the linear transmittance of a filter.

[0131] Figure 14 This is the linear transmittance spectrum of filter 10A in Example 1.

[0132] Figure 15 This is a graph showing the absorptivity spectrum obtained by the difference between the diffuse transmittance spectrum and the diffuse reflectance spectrum of the filter 10A of Example 1.

[0133] Figure 16 The linear transmittance spectrum is that of filter 20A in Comparative Example 1.

[0134] Figure 17 This is a TEM image showing a cross-section of the filter in Example 2.

[0135] Figure 18 It is a histogram of the distance between the centroids of the particles, obtained from the cross-sectional TEM image of the filter in Example 2.

[0136] Figure 19 This is the linear transmittance spectrum of the filter in Example 2.

[0137] Figure 20 These are the linear transmittance spectra of the filters in Examples 3 and 4.

[0138] Figure 21 This is the linear transmittance spectrum of the filter in Example 5.

[0139] Figure 22 This is the linear transmittance spectrum of the filter in Example 6.

[0140] Figure 23 This is the linear transmittance spectrum of the filter in Example 7.

[0141] Figure 24 This is the linear transmittance spectrum of the filter in Example 8.

[0142] Figure 25 This is the linear transmittance spectrum of the filter in Example 9.

[0143] Figure 26 This is the linear transmittance spectrum of the filter in Example 10.

[0144] Figure 27 This is a TEM image showing a cross-section of the filter of Example 10.

[0145] Figure 28 It is a histogram of the distance between the centroids of the particles, obtained from the cross-sectional TEM image of the filter in Example 10.

[0146] Figure 29 This is the linear transmittance spectrum of the filter in Example 11.

[0147] Figure 30 This is the linear transmittance spectrum of the filter in Example 12.

[0148] Figure 31 This is the linear transmittance spectrum of the filter in Example 13.

[0149] Figure 32 This is a TEM image showing a cross-section of the filter in Comparative Example 2.

[0150] Figure 33 It is a histogram of the distance between the centroids of the particles, obtained from the cross-sectional TEM image of the filter in Comparative Example 2.

[0151] Figure 34 The linear transmittance spectrum of the filter in Comparative Example 2 (incident angles of 0° and 60°) is shown.

[0152] Figure 35 This is a TEM image showing a cross-section of the filter in Comparative Example 3.

[0153] Figure 36 It is a histogram of the distance between the centroids of the particles, obtained from the cross-sectional TEM image of the filter in Comparative Example 3.

[0154] Figure 37 The linear transmittance spectrum is that of the filter in Comparative Example 3.

[0155] Figure 38 This is a graph showing the incident angle dependence of the linear transmittance spectra of filter 10A of Example 1 and filter of Comparative Example A.

[0156] Figure 39 This is a graph showing the incident angle dependence of the linear transmittance spectrum of filter 10A of Example 1.

[0157] Figure 40 This is a graph showing the incident angle dependence of the linear transmittance spectrum of the filter in Comparative Example A.

[0158] Figure 41 This is a graph showing the incident angle dependence of the linear transmittance spectrum of the filter in Example 2.

[0159] Figure 42 This is a graph showing the incident angle dependence of the linear transmittance spectrum of the filter of Example 6.

[0160] Figure 43 This is a graph showing the incident angle dependence of the linear transmittance spectrum of the filter in Comparative Example 3.

[0161] Figure 44A This is a diagram showing an optical image (visible light) of a filter formed in a hemispherical shape.

[0162] Figure 44B It is shown Figure 44A An infrared image of the filter in the hemispherical embodiment shown.

[0163] Figure 45 This is a schematic diagram illustrating the optical system for measuring BRDF.

[0164] Figure 46 This is a graph showing the BRDF of the sample of the filter of Example 6.

[0165] Figure 47 This is a graph showing the BRDF of the sample of the filter in Comparative Example A.

[0166] Figure 48 This is a graph showing the difference between the sample of the filter in Example 6 and BRDF (0°).

[0167] Figure 49 This is a graph showing the difference between the sample of Comparative Example A filter and BRDF (0°).

[0168] Symbol Explanation

[0169] 10, 10A, 20A: Filters

[0170] 12: Matrix

[0171] 14: Particles Detailed Implementation

[0172] Hereinafter, filters according to embodiments of the present invention will be described with reference to the accompanying drawings. The filters according to embodiments of the present invention are not limited to the filters exemplified below.

[0173] The filter according to embodiments of the present invention comprises a substrate and microparticles dispersed in the substrate, the microparticles forming at least a colloidal amorphous aggregate, and the filter exhibits a linear transmittance of 60% or more for at least a portion of wavelengths in the wavelength range of 760 nm to 2000 nm. For example, a filter with 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 filter has a linear transmittance of 60% or more is preferably 810 nm to 1700 nm, and more preferably 840 nm to 1650 nm. Such a filter is suitable for applications such as InGaAs sensors, InGaAs / GaAsSb sensors, CMOS sensors, NMOS sensors, and CCD sensors. Here, both the substrate and the microparticles are preferably transparent to visible light (hereinafter referred to as "transparent"). The filter according to embodiments of the present invention can be white.

[0174] The filter of the embodiments of the present invention comprises colloidal amorphous aggregates. Colloidal amorphous aggregates refer to aggregates of colloidal particles (particle size 1 nm to 1 μm) that do not possess long-range order and do not cause Bragg reflection. If the colloidal particles are distributed in a manner possessing long-range order, they become so-called colloidal crystals (a type of photonic crystal), which cause Bragg reflection and serve as a contrast. That is, the microparticles (colloidal particles) in the filter of the embodiments of the present invention do not form a diffraction grating.

[0175] The filter of the present invention contains monodisperse particles with an average particle size of more than one-tenth of the wavelength of infrared light. That is, relative to infrared light with a wavelength range of 760 nm to 2000 nm, the average particle size is preferably at least 80 nm, more preferably 150 nm, and even more preferably 200 nm. The upper limit of the average particle size is, for example, 300 nm. Two or more monodisperse particles with different average particle sizes may be included. Each particle is preferably substantially spherical. It should be noted that in this specification, "particles (multiple)" is used in the sense of an aggregate of particles, and monodisperse particles refer to particles with a coefficient of variation (the value of standard deviation / average particle size expressed as a percentage) of 20% or less, preferably 10% or less, and more preferably 1 to 5%. The filter of the present invention improves the linear transmittance of infrared light by utilizing particles with a particle size (particle diameter, equivalent diameter of a sphere) of more than one-tenth of the wavelength. This differs from the optical article described in Patent Document 2 which utilizes the principle of Rayleigh scattering.

[0176] Here, the average particle size is determined based on 3D SEM images. Specifically, a Helios G4 UX (FEI) focused ion beam scanning electron microscope (FIB-SEM) was used to obtain continuous cross-sectional SEM images. After correcting the positions of the continuous images, the 3D images were reconstructed. In detail, the 3D images were reconstructed by repeatedly obtaining cross-sectional reflection electron images from the SEM and processing them with FIB (accelerating voltage: 30kV) at 50nm intervals 11 times. The obtained 3D images were binarized using the Segmentation function of analytical software (AVIZO, Thermo Fisher Scientific) to extract the images of the particles. Next, a Separate object operation was performed to identify each particle, and then the volume of each particle was calculated. Assuming each particle is a sphere, the equivalent diameter of the volume sphere was calculated, and the average particle size was obtained by averaging the particle sizes as the average particle size.

[0177] The filter of the present invention achieves a linear transmittance of 60% or more for at least a portion of the wavelengths in the wavelength range of 760 nm or more and 2000 nm or less by adjusting any parameter among the refractive index of the microparticles and the matrix, the average particle size, the volume fraction, the distribution (degree of non-periodicity), and the thickness.

[0178] The filter according to embodiments of the present invention can produce white light. Here, white light refers to the x and y coordinates on the CIE 1931 chromaticity diagram, where the standard light source is set to D65, being within the range of 0.25 ≤ x ≤ 0.40 and 0.25 ≤ y ≤ 0.40, respectively. Of course, the closer to x = 0.333 and y = 0.333, the higher the whiteness; preferably, it is 0.28 ≤ x ≤ 0.37 and 0.28 ≤ y ≤ 0.37, more preferably 0.30 ≤ x ≤ 0.35 and 0.30 ≤ y ≤ 0.35. Furthermore, the L* measured in the CIE 1976 color space using the SCE method is preferably 20 or higher, more preferably 40 or higher, more preferably 50 or higher, and particularly preferably 60 or higher. ＊ When the value is 20 or higher, it can be considered roughly white. L ＊ The upper limit is, for example, 100. The method for determining linear transmittance is described in the following experimental examples (including examples and comparative examples).

[0179] exist Figure 1The diagram shows a cross-sectional view of a filter 10 according to an embodiment of the present invention. The filter 10 of the present invention includes a substrate 12 transparent to visible light and transparent microparticles 14 dispersed in the transparent substrate 12. The microparticles 14 at least constitute colloidal amorphous aggregates. The microparticles 14 may include other microparticles that do not disturb the formed colloidal amorphous aggregates.

[0180] Filter 10 Figure 1 As schematically shown, it has a substantially flat surface. Here, a substantially flat surface means a surface without any unevenness or concavity that would cause visible light or infrared light to scatter (diffract) or diffusely reflect. Furthermore, the filter 10 does not contain cholesteric liquid crystal (broadly including cholesteric liquid crystals exhibiting a cholesteric phase, which are high-molecular-weight liquid crystals, low-molecular-weight liquid crystals, liquid crystal mixtures thereof, and liquid crystals obtained by crosslinking and curing these liquid crystal materials with a crosslinking agent). It should be noted that the filter 10 is, for example, a film, but is not limited to this.

[0181] The transparent microparticles 14 are, for example, silica microparticles. Silica microparticles, for example, can be silica microparticles synthesized by the Stober process. Alternatively, inorganic microparticles other than silica microparticles, or resin microparticles, can be used. As resin microparticles, microparticles preferably include at least one selected from polystyrene and polymethyl methacrylate, and more preferably microparticles including cross-linked polystyrene, cross-linked polymethyl methacrylate, or cross-linked styrene-methyl methacrylate copolymers. It should be noted that, for example, polystyrene microparticles or polymethyl methacrylate microparticles synthesized by emulsion polymerization can be appropriately used. Additionally, hollow silica microparticles containing air and hollow resin microparticles can also be used. It should be noted that microparticles formed from inorganic materials have the advantage of excellent heat resistance and light resistance. The volume fraction relative to the total 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 can be optically isotropic.

[0182] Examples of the matrix 12 include, but are not limited to, acrylic resins (e.g., polymethyl methacrylate, polymethyl acrylate), polycarbonate, polyester, poly(diethylene glycol diallyl carbonate), polyurethane, epoxy resin, and polyimide. The matrix 12 is preferably formed using a curable resin (thermosetting or photocurable), and from a mass production perspective, a photocurable resin is preferred. Various (meth)acrylates can be used as photocurable resins. The (meth)acrylate preferably contains two or more functional groups. Furthermore, the matrix 12 preferably has optical isotropy. If a curable resin containing multifunctional monomers is used, a matrix 12 with a cross-linked structure is obtained, thus improving heat resistance and lightfastness.

[0183] The filter 10, formed from a resin material, can be a flexible film. The thickness of the filter 10 is, for example, 10 μm or more and 10 mm or less. When the thickness of the filter 10 is, for example, 10 μm or more and 1 mm or less, and further 10 μm or more and 500 μm or less, it can exhibit significant flexibility.

[0184] When using silica microparticles with a hydrophilic surface as microparticles, it is preferable to form them by photocuring a hydrophilic monomer. Examples of hydrophilic monomers include, but are not limited to: 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 methacrylate, or 2-hydroxypropyl methacrylate, acrylamide, methylenebisacrylamide, ethoxylated bisphenol A di(meth)acrylate. Furthermore, these monomers can be used alone or in combination of two or more. Of course, the two or more monomers can include monofunctional monomers and polyfunctional monomers, or can include two or more polyfunctional monomers.

[0185] These monomers can be cured by using appropriate photopolymerization initiators. Examples of photopolymerization initiators include: benzoin ethers, benzophenone, anthraquinones, and thiazolinone. Carbonyl compounds such as alkanes, ketals, and acetophenones; sulfur compounds such as disulfides and dithiocarbamates; organic peroxides such as benzoyl peroxide; azo compounds; transition metal complexes; polysilane compounds; and pigment sensitizers are included. The amount of photopolymerization initiator added is preferably 0.05 parts by mass or more and 3 parts by mass or less, and more preferably 0.05 parts by mass or more and 1 part by mass or less, relative to 100 parts by mass of the mixture of microparticles and monomers.

[0186] Let the refractive index of the matrix for visible light be n. M And set the refractive index of the particles to n.P When, |n M -n P The refractive index difference (hereinafter sometimes simply referred to as the refractive index difference) is preferably 0.01 or more, more preferably 0.6 or less, further preferably 0.03 or more, and even more preferably 0.11 or less. When the refractive index difference is less than 0.03, the scattering intensity weakens, making it difficult to obtain the desired optical properties. Furthermore, when the refractive index difference exceeds 0.11, the linear transmittance of infrared light decreases. Alternatively, for example, by using zirconium oxide particles (refractive index 2.13) and acrylic resin to achieve a refractive index difference of 0.6, the linear transmittance of infrared light can be adjusted by reducing the thickness. In this way, the linear transmittance of infrared light can also be adjusted, for example, by controlling the thickness and refractive index difference of the filter. Additionally, depending on the application, it can be used in conjunction with an infrared-absorbing filter. It should be noted that the refractive index for visible light can be represented, for example, by the refractive index for light at 546 nm. Here, unless otherwise specified, the refractive index refers to the refractive index for light at 546 nm.

[0187] The filter according to embodiments of the present invention can be manufactured, for example, by a manufacturing method including the following steps: a step of preparing a curable resin composition in which particulate matter is dispersed / mixed in a curable resin; a step of applying the curable resin composition to the surface of a substrate; and a step of curing the curable resin contained in the curable resin composition applied to the surface. The substrate can be, for example, a glass substrate, or a resin film such as PET (polyethylene terephthalate), TAC (cellulose triacetate), or PI (polyimide), but is not limited thereto. The step of dispersing / mixing the particulate matter in the curable resin can be performed using known dispersion / mixing apparatus such as a homogenizer or a homogenizer (e.g., an ultrasonic homogenizer or a high-pressure homogenizer). Furthermore, the application step can be performed by various known methods such as coating (e.g., dip coating, spray coating, mold coating), printing, etc.

[0188] The following describes the structure and optical characteristics of the filters according to embodiments of the present invention through specific experimental examples (exemplary and comparative examples). The structure and optical characteristics of the filters of the examples and comparative examples are shown in Table 1. Various filters as shown in Table 1 were fabricated by combining different types of silica particles and resins, adding coagulants, and using different dispersion / mixing methods.

[0189] The filters of Examples 1-13 and Comparative Examples 1-3 were formed into films using acrylic resins and silica microparticles as described in Table 1. As silica microparticles, monodisperse silica microparticles synthesized by the Stober method were used (average particle size 110 nm, CV value 4.5%, average particle size 181 nm, CV value 4.7%, average particle size 221 nm, CV value 4.9%, and average particle size 296 nm, CV value 6.1%). Here, Hautform Sibol220 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 Science Corporation.

[0190] A curable resin composition is prepared by mixing / dispersing silica microparticles in acrylic monomers A to E in a given formulation. This composition is then applied to the surface of a substrate using a coating apparatus to obtain a film of a given thickness, and subsequently cured. Alternatively, 0.2 parts by weight of Darocure 1173 as a photopolymerization initiator are added to 100 parts by weight of the acrylic monomers, and the mixture is cured by photopolymerization under a UV lamp. Resins (polymers) with different refractive indices are formed depending on the type of monomer.

[0191] The following shows acrylic monomers A to E. Monomers A and E are trifunctional acrylates, monomers B and C are difunctional acrylates, and monomer D is a monofunctional acrylate.

[0192] A: Pentaerythritol triacrylate

[0193] B: Ethoxylated bisphenol A diacrylate (m+n=10)

[0194] C: Ethoxylated bisphenol A diacrylate (m+n=3)

[0195] D: Methoxylated polyethylene glycol #400 methacrylate

[0196] E: Trimethylolpropane (TMP) EO-modified triacrylate

[0197] It should be noted that acrylic monomers B and C are represented by the following chemical formula (Chemical Formula 1).

[0198] [Chemical Formula 1]

[0199]

[0200] When the thickness of the obtained film is set as d, the cross-section is cut at position d / 2 using a slicer, thereby cutting a sample piece with the same thickness as the average particle size of the silica particles, resulting in a sample for TEM observation. Using a TEM (Hitachi High-Tech Science Corporation HT7820), based on a cross-sectional TEM image containing more than 200 particles, and using image processing software ImageJ, the particles are automatically identified and analyzed using Delaunay diagrams, thereby determining the average (La) and standard deviation (Ld) of the distance between the centroids of adjacent particles. Furthermore, the coefficient of variation (CV value of the distance) is calculated based on the average distance between centroids (also called "average centroid distance") and the standard deviation. Here, when determining the distance between centroids, only particles with a diameter of 150 nm or larger are considered; particles with a diameter smaller than 150 nm are excluded. As described later, these values ​​serve as indicators of whether the silica particles constitute colloidal amorphous aggregates and the distribution state of the silica particles within the colloidal amorphous aggregates. The lower limit of La is preferably 100 nm or more, further 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 further preferably 500 nm or less.

[0201] The colloidal amorphous aggregates of the filter according to embodiments of the present invention can be characterized by the variation coefficient of the average intercentrifugal distance of the particles 14. When the variation coefficient is small, significant long-range order is exhibited, resulting in angle-dependent reflected colors due to Bragg reflection. On the other hand, when the variation coefficient is large, there is a tendency for the influence of Mie scattering to increase and the wavelength dependence of light scattering to decrease. Therefore, in the filter according to embodiments of the present invention, the variation coefficient of the average intercentrifugal distance of the particles 14 is preferably 10% or more and preferably 45% or less, more preferably 15% or more and more preferably 40% or less, further preferably 20% or more and further preferably 40% or less, and even more preferably 25% or more and even more preferably 35% or less.

[0202]

[0203] exist Figure 2 The image shown is a cross-sectional TEM image of filter 10A of Example 1. Figure 3 The figure shows a cross-sectional TEM image of filter 20A of Comparative Example 1. In the TEM image, the white circles represent silica particles, and the black circles represent traces of silica particle detachment. In image processing, the black circles are also treated as silica particles.

[0204] It can be known that in Figure 2 In the cross-section of the filter 10A shown, the silica particles are basically uniformly dispersed; in contrast, in... Figure 3 In the cross-section of the filter 20A shown, some silica particles agglomerated. This is because, in the manufacture of the filter 20A of Comparative Example 1, in addition to acrylic monomer A, 0.1% by mass of polyethylene glycol was added as a coagulant relative to acrylic monomer A.

[0205] Next, in Figure 4 The image shows a histogram of the distance between the centroids of the particles, calculated from a cross-sectional TEM image of the filter 10A according to Example 1. Figure 5 The table shows a histogram of the distance between the centroids of the particles, obtained from the cross-sectional TEM image of filter 20A of Comparative Example 1. The mean distance between centroids La (nm), standard deviation Ld (nm), and coefficient of variation (CV value of distance) obtained from these histograms are shown in Table 1. Hereinafter, the CV value of distance will sometimes be simply referred to as the CV value.

[0206] It can be seen that the distribution of silica particles in filter 10A of Example 1 is more uniform than that in filter 20A of Comparative Example 1. Filter 10A of Example 1 has an Ld of 84 nm and a CV value of 27.8%, while filter 20A of Comparative Example 1 has an Ld of 168 nm and a CV value of 49.3%, showing larger values.

[0207] Next, refer to Figures 6-8 The results show the performance of the filter 10A of Example 1 and the filter 20A of Comparative Example 1 as infrared filters. Figure 6 These are examples of camera images obtained using motion capture equipment, and they are camera images obtained without using filters. Figure 7 This is an example of a camera image obtained via filter 10A of Embodiment 1 and using a motion capture device. Figure 8 Examples of camera images obtained via the filter 20A of Comparative Example 1 and using a motion capture device.

[0208] Here, as a motion capture device, the Leap Motion Controller (registered trademark) was used to obtain a camera image of a hand located approximately 20cm away. It should be noted that this device uses infrared light with a wavelength of 850nm. Based on... Figure 6 , Figure 7 and Figure 8 A comparison clearly shows that in the case of using filter 10A of the embodiment ( Figure 7 Under these conditions, the results can be obtained compared to the case where no filter is used. Figure 6 Images with the same level of clarity, in contrast, when using the comparative example filter 20A ( Figure 9 Under these conditions, a clear image cannot be obtained, and the hand cannot be recognized.

[0209] exist Figure 9 An optical image of filter 10A of Embodiment 1 is shown in the figure. Figure 10 An optical image of filter 20A of Comparative Example 1 is shown. Filter 10A of Example 1 and filter 20A of Comparative Example 1 are made into a film of approximately 5 cm × approximately 10 cm, arranged to cover the front of the device. According to... Figure 9 and Figure 10 As can be seen, all films are white. Therefore, the filter 10A of Example 1 is suitable for use as an infrared filter and is white, thus having high aesthetic design flexibility. Of course, the surface of the filter 10A of Example 1 can also be colored or patterned by printing or the like. Hereinafter, the advantages of the filter according to the embodiment of the present invention will be described in detail.

[0210] The optical properties of a filter can be evaluated as follows.

[0211] like Figure 11 As shown, when incident light I0 is incident on filter 10, a portion of the incident light I0 is transmitted through filter 10 (transmitted light I). i A portion of the light undergoes interface reflection (interface reflected light R). i Another portion is scattered. The scattered light includes forward scattered light S emitted in front of filter 10. f and the backscattered light S emitted backward b Through backscattered light S b The filter 10 appears white. A portion of the incident light I0 is absorbed by the filter 10, but the resin and silica particles used here have a low absorption rate for light in the 400nm to 2000nm range.

[0212] Figure 12 This is a schematic diagram illustrating the method for measuring the diffuse transmittance of a filter. Figure 13 This is a schematic diagram illustrating the method for measuring the linear transmittance of a filter. Diffuse transmittance is as follows: Figure 12 As shown, a sample (filter 10) is placed at the opening of the integrating sphere 32, with the intensity of the incident light I0 relative to the transmitted light I. i and forward scattered light S f The total intensity is calculated as a percentage. Furthermore, the linear transmittance is measured by positioning the sample (filter 10) 20 cm from the opening of the integrating sphere 32. The intensity of the incident light I0 at this position is expressed as a percentage of the transmitted light I. iThe intensity was calculated as a percentage. The diameter of the opening was 1.8 cm, equivalent to 0.025 sr in solid angle. A UH4150 UV-Vis-NIR spectrophotometer (manufactured by Hitachi High-Tech Science Corporation) was used as the spectrometer. The linear transmittance values ​​for infrared light at 760 nm, 950 nm, and 1550 nm are shown in Table 1. Furthermore, the linear transmittance spectra of each sample are shown in... Figure 14 The presence or absence of Bragg reflection can be determined by the presence or absence of dimples (local decreases in transmittance) in the linear transmittance spectrum. The presence or absence of Bragg reflection is also shown in Table 1.

[0213] Backscattered light S b The whiteness was measured using a CM-2600-D spectrophotometer (manufactured by Konica Minolta, Japan). The L value was determined using the SCE (Specular Removal) method. ＊ The values ​​of L, and the x and y coordinates on the CIE 1931 chromaticity diagram. ＊ The larger the value, the closer the x and y values ​​are to 0.33, and the higher the whiteness. These values ​​are also shown in Table 1.

[0214] exist Figure 14 The linear transmittance spectrum of filter 10A of Example 1 is shown in the figure. Figure 15 The diagram shows the absorbance spectrum, calculated as the difference between the diffuse transmittance and diffuse reflectance spectra of the filter 10A of Example 1. According to... Figure 14 It can be seen that the filter 10A of Example 1 has high infrared transmittance, especially for infrared wavelengths above 900 nm. It should be noted that... Figure 15 The minimal absorption of infrared radiation above 1200 nm observed in the absorption spectrum is due to the characteristic absorption properties of the resin (organic compound).

[0215] exist Figure 16 The linear transmittance spectrum of filter 20A of Comparative Example 1 is shown in the figure. Based on the... Figure 16 and Figure 15 The comparison clearly shows that the transmittance of filter 20A in Comparative Example 1 is low. Referring to Table 1, comparing Example 1 and Comparative Example 1, although L represents whiteness... ＊ The x and y coordinate values ​​on the CIE chromaticity diagram showed no significant difference between Example 1 and Comparative Example 1, but the linear transmittance of infrared light differed considerably. The CV value in Comparative Example 1 was 49.3%, which was greater than the 27.8% in Example 1, and this was attributed to the agglomeration of silica particles. Therefore, the CV value can be considered an indicator of improved linear transmittance of infrared light.

[0216] Next, refer to Figures 17-19 The filter of Example 2 will be described. Figure 17 This is a TEM image showing the cross-section of the filter in Example 2. Figure 18 It is a histogram of the distance between the centroids of the particles, calculated from the cross-sectional TEM image of the filter in Example 2. Figure 19 This is the linear transmittance spectrum of the filter in Example 2. In Example 1, silica particles with an average particle size of 221 nm were used; in contrast, in Example 2, silica particles with an average particle size of 296 nm were used. The CV value of Example 2 is essentially the same as that of Example 1, but the infrared linear transmittance of Example 2 is lower. That is, it can be seen that the infrared linear transmittance can be controlled by controlling the average particle size of the silica particles.

[0217] Here, for comparison, refer to Figures 35-37 The filter of Comparative Example 3 will be described. Figure 35 This is a TEM image showing a cross-sectional view of the filter in Comparative Example 3. Figure 36 It is a histogram of the distance between the centroids of the particles, obtained from the cross-sectional TEM image of the filter in Comparative Example 3. Figure 37 This is the linear transmittance spectrum of the filter in Comparative Example 3. In Comparative Example 3, silica microparticles with an average particle size of 110 nm were used, which differs from Examples 1 and 2. Figure 37 As can be clearly seen from the results in Table 1, the CV value of Comparative Example 3 is basically the same as that of Examples 1 and 2. However, Comparative Example 3 has a higher infrared linear transmittance of 87% at 760 nm, and its visible light linear transmittance is also higher. In addition, the whiteness of Comparative Example 3 is worse than that of Examples 1 and 2. Therefore, it can be seen that the infrared linear transmittance and whiteness can be controlled by controlling the average particle size of the silica particles. Based on the comparison between Example 1, Example 2, and Comparative Example 3, it can be considered that silica particles with an average particle size of 221 nm or more are preferred.

[0218] Next, refer to Figure 20 The filters of Examples 3 and 4 will be described. Figure 20 These are the linear transmittance spectra of the filters from Examples 3 and 4. The volume fractions of silica particles in the filters of Examples 3 and 4 are 34% and 38%, respectively, which are greater than the 29% in Example 1. Comparison with the results of Example 1 shows that there are no significant differences in the infrared linear transmittance at 950 nm and 1550 nm, or in the x and y coordinates on the CIE chromaticity diagram. The infrared linear transmittance at 760 nm and the L... ＊ The value increased slightly. A comparison of the linear transmittance spectra of Examples 3 and 4 shows that as the volume fraction of silica particles increases, the scattering wavelength shifts towards shorter wavelengths. ＊The value has increased slightly.

[0219] Here, for comparison, refer to Figure 25 The linear transmittance spectrum of the filter of Example 9 is shown. The filter of Example 9 has a lower volume fraction of silica particles, at 6%. Comparison with the results of Example 1 shows a slight decrease in infrared linear transmittance at 950 nm. ＊ The value decreased significantly. This is believed to be due to a reduction in the intensity of scattered light caused by the decrease in the volume fraction of silica particles.

[0220] In this way, by controlling the volume fraction of silica particles, it is possible to control the infrared linear transmittance and L. ＊ The value of .

[0221] Next, refer to Figure 21 The filter of Example 5 will be described. Figure 21 This is the linear transmittance spectrum of the filter in Example 5. The filter in Example 1 has a thickness of 100 μm, while the filter in Example 5 has a thickness of 500 μm. Comparing Example 5 with Example 1 shows that the infrared linear transmittance is reduced, but the whiteness is increased. Increasing the filter thickness can also reduce the transmittance of visible light.

[0222] Next, refer to Figure 22 The filter of Example 6 will be described. Figure 22 This is the linear transmittance spectrum of the filter from Example 6. Example 6 uses a polymer with a refractive index of 1.52 as the matrix, a different monomer than that used in Examples 1-5. The refractive index of the matrix in Examples 1-5 is 1.49, which differs from the refractive index of the silica microparticles (1.43) by 0.06. In contrast, the refractive index difference in Example 6 is larger, at 0.09. A comparison with Example 1 shows that the linear transmittance of any infrared light at 760 nm, 950 nm, and 1550 nm, and the L... ＊ The values ​​all increased.

[0223] Next, refer to Figure 23 The filter of Example 7 will be described. Figure 23 This is the linear transmittance spectrum of the filter in Example 7. The filter in Example 6 was formed on a glass substrate, while the filter in Example 7 is formed on a PET film, which is a difference in this respect. Figure 23 and Figure 22 The comparison with the results in Table 1 suggests that the influence of the substrate is minimal.

[0224] Next, refer to Figure 24 The filter of Example 8 will be described. Figure 24This is the linear transmittance spectrum of the filter in Example 8. The filter in Example 7 has a thickness of 100 μm, while the filter in Example 8 has a thickness of 500 μm. Comparing Example 8 and Example 7, it can be seen that the infrared linear transmittance is reduced, but L... ＊ Increase the thickness of the filter to reduce the transmittance of visible light.

[0225] Next, refer to Figures 26-28 The filter of Example 10 will be described. Figure 26 This is the linear transmittance spectrum of the filter in Example 10. Figure 27 This is a TEM image showing a cross-section of the filter of Example 10. Figure 28 This is a histogram of the distance between the centroids of the particles, calculated from the cross-sectional TEM image of the filter in Example 10. Example 10 uses a polymer with a refractive index of 1.54 as the matrix, and the refractive index difference between it and the silica particles is 0.11, which is further greater than the refractive index difference in Example 6. Compared with Examples 1 and 6, the infrared linear transmittance is reduced, and L... ＊ The value increases.

[0226] Next, refer to Figure 29 The filter of Example 11 will be described. Figure 29 This is the linear transmittance spectrum of the filter from Example 11. Example 11 uses a polymer with a refractive index of 1.46 as the matrix. In Example 11, the refractive index difference is small, at 0.03. Compared with Example 1, the infrared linear transmittance at 1550 nm is reduced, the transmittance in the visible light region is increased, and the whiteness is reduced.

[0227] Next, refer to Figure 30 The filter of Example 12 will be described. Figure 30 This is the linear transmittance spectrum of the filter of Example 12. The filter of Example 12 contains silica particles with an average particle size of 110 nm and an average particle size of 221 nm, with a volume ratio (110 nm: 221 nm) of 1:1. Compared with Example 1, both the infrared linear transmittance and whiteness are reduced (see Table 1). This is considered to be the effect of mixing with silica particles with an average particle size of 110 nm (see Comparative Example 3). Figure 37 ).

[0228] Next, refer to Figure 31 The filter of Example 13 will be described. Figure 31 This is the linear transmittance spectrum of the filter from Example 13. The filter from Example 13 uses silica microparticles with an average particle size of 181 nm, which differs from the filter from Example 6. Figure 31and Figure 22 Comparison reveals that the wavelength at which the linear transmittance increases in Example 13 shifts towards shorter wavelengths compared to Example 6. That is, the linear transmittance in the visible light region of the filter in Example 13 is slightly improved compared to Example 6. As a result, L... ＊ The whiteness and lightness of the sample are slightly lower than those of Example 6, but the linear transmittance of infrared light is high. Therefore, silica microparticles with an average particle size of 181 nm are preferably used. It should be noted that, from the viewpoint of whiteness, it is preferable to include silica microparticles with an average particle size of 200 nm or more, and even more preferably, silica microparticles with an average particle size of 221 nm or more.

[0229] Next, refer to Figures 32-34 The filter of Comparative Example 2 will be described. Figure 32 This is a TEM image showing a cross-section of the filter in Comparative Example 2. Figure 33 It is a histogram of the distance between the centroids of the particles, obtained from the cross-sectional TEM image of the filter in Comparative Example 2. Figure 34 The linear transmittance spectrum of the filter in Comparative Example 2 shows the results at incident angles of 0° and 60°. An incident angle of 0° is the normal direction of the filter surface. Comparative Example 2 has a matrix with a refractive index of 1.48 formed using acrylic monomer E. The refractive index of the matrix changed by only 0.01 compared to Example 1. It should be noted that the incident angle dependence of the linear transmittance was determined by using the automatic angle adjustment system of the UH4150 UV-Vis-NIR spectrophotometer (manufactured by Hitachi High-TechScience Corporation) to adjust the angle of the sample surface relative to the incident light. Figure 11 The angle of the filter 10 in the filter is measured.

[0230] according to Figure 32 and Figure 33 It can be seen that the aggregates of silica particles in the filter of Comparative Example 2 exhibit long-range order. As a result, the CV value in Table 1 is relatively small, at 9.4%. Furthermore, in Figure 34 Steep valleys (localized reductions in transmittance) were observed in the visible light region of the linear transmittance spectrum shown. These steep valleys are caused by Bragg reflection. The aggregates of silica particles in the filter of Comparative Example 2 are not colloidal amorphous aggregates, but rather have a structure close to that of a colloidal crystal or colloidal crystal with long-range order. Furthermore, the steep valleys in the visible light region shift according to the incident angle; therefore, the color of the filter of Comparative Example 2 can be observed to change with the angle. Therefore, it is considered that a CV value of 10% or higher is preferable to suppress Bragg reflection in the visible light region. In addition, based on the results of Comparative Example 1 above, it is considered that a CV value of 49% or lower is preferable to suppress the aggregation of silica particles.

[0231] The filters of Examples 1-13 did not exhibit steep valleys in their linear transmittance spectra, indicating that the silica microparticles formed colloidal amorphous aggregates. Furthermore, the linear transmittance for at least a portion of the wavelengths in the range of 760 nm to 2000 nm showed a value of 60% or more. Additionally, when the standard light was set to a D65 illuminant, the x and y coordinates on the white CIE 1931 chromaticity diagram were within the range of 0.25 ≤ x ≤ 0.40. Moreover, color variations caused by the viewing angle were also suppressed.

[0232] As can be clearly seen from the above, the filter of the embodiments of the present invention can achieve desired optical properties (e.g., infrared linear transmittance and whiteness) by adjusting the refractive index of the particles and the substrate, the average particle size, volume fraction, distribution (degree of aperiodicity), and thickness, and color changes caused by the viewing angle are also suppressed. Furthermore, filters with different optical properties can be used in combination. Additionally, depending on the application, it can be used in combination with, for example, an infrared-absorbing filter. Figure 9 It is understood that, for example, even when used in conjunction with filters that are black or other colors, the filters of the embodiments of the present invention are white, thus improving design flexibility.

[0233] The filters of the embodiments of the present invention also have characteristics in terms of the incident angle dependence of the linear transmittance spectrum.

[0234] Reference Figures 38-40 The incident angle dependence (incident angles of 0°, 15°, 30°, 45°, and 60°) of the linear transmittance spectra of filter 10A of Example 1 and filter of Comparative Example A will be explained. The filter of Comparative Example A is a White IR window (https: / / www.tokaioptical.com / jp / product14 / ) manufactured by Tokai Optical Co., Ltd., which is commercially available as an infrared filter. The filter of Comparative Example A is equivalent to the optical article described in Patent Document 2, and is composed of a dielectric multilayer film and a PET film, having a pear-skin-like surface. The filter of Comparative Example A is white and has a thickness of 120 μm.

[0235] Figure 38 This is a graph showing the incident angle dependence of the linear transmittance spectra of filter 10A of Example 1 and filter of Comparative Example A. Figure 39 and Figure 40 This is a graph that has been standardized using the maximum transmittance for each curve icon. Figure 39 This is a graph showing the incident angle dependence of the linear transmittance spectrum of filter 10A of Example 1. Figure 40This is a graph showing the incident angle dependence of the linear transmittance spectrum of the filter in Comparative Example A.

[0236] like Figure 38 It can be seen that the linear transmittance of filter 10A in Example 1 is greater than that of filter in Comparative Example A. Furthermore, regarding the decrease in infrared linear transmittance due to the increase in the incident angle, filter 10A in Example 1 is smaller than that of filter in Comparative Example A. For example, the linear transmittance of 950nm infrared light is 88% at an incident angle of 0°, compared to 80% at an incident angle of 60°, meaning the transmittance at 0° is over 90%. In contrast, in Comparative Example A, the linear transmittance of 950nm infrared light is 30% at an incident angle of 0°, compared to 9% at an incident angle of 60°, decreasing to 30% of the linear transmittance at 0°. In this way, the infrared linear transmittance of the filter according to the embodiment of the present invention has a small dependence on the incident angle. For example, for 950nm infrared light, the linear transmittance at an incident angle of 60° can be 80% or more, and even 85% or more, and even 90% or more of the linear transmittance at an incident angle of 0°.

[0237] right Figure 39 When observing the transmittance curve of filter 10A in Example 1, the portion of the curve where the linear transmittance monotonically increases from visible light to infrared shifts towards longer wavelengths (approximately 50 nm) as the incident angle increases. Figure 41 , Figure 42 and Figure 43 This characteristic incident angle dependence was also observed in the incident angle dependence of the linear transmittance spectra of the filters shown in Examples 2, 6, and Comparative Example 3. That is, the characteristic incident angle dependence, where the portion of the linear transmittance curve monotonically increases from visible light to infrared shifts towards longer wavelengths with increasing incident angle, is attributed to the colloidal amorphous aggregates formed by the silica particles contained in the optical film. In contrast, in... Figure 40 In the transmittance curve of the filter in Comparative Example A, the portion of the curve where the linear transmittance increases monotonically from visible light to infrared light shifts towards the shorter wavelength side (approximately 100 nm) as the incident angle increases, i.e., it becomes the completely opposite trend.

[0238] In the filter of Comparative Example A, the portion of the linear transmittance curve that monotonically increases from visible light to infrared shifts towards the shorter wavelength side as the incident angle increases. Therefore, for obliquely incident light, there is a concern about light transmission (leakage) to the shorter wavelength side that is intended to be blocked. In contrast, in the filter where silica microparticles constitute colloidal amorphous aggregates, the transmittance for even shorter wavelengths decreases as the incident angle increases. Therefore, there is no concern about light leakage as seen in the filter of Comparative Example A.

[0239] The filters of the embodiments of the present invention, as described above, can be white. Therefore, by using infrared-transmitting ink to print text, drawings, or photographs onto the surface of the filter, filters with rich colors and diverse designs can be obtained. Specifically, the filters of the embodiments of the present invention can have a filter layer comprising a substrate and microparticles, and a printing layer formed of infrared-transmitting ink disposed on the filter layer. The printing layer can be formed directly on the surface of the filter layer, or a material on which the printing layer is formed on the surface of a transparent film can be disposed on the filter layer. As the infrared-transmitting ink, a known infrared-transmitting ink can be selected according to the application or the wavelength of the infrared light to be transmitted.

[0240] The filter in this embodiment can be a planar film as shown in the example, but is not limited thereto and can take various forms. The filter in this embodiment can have a three-dimensional shape. For example, it can be a film with a three-dimensional shape. Specifically, for example, the filter can be formed on the surface of an object with a three-dimensional shape using a coating method. The surface of the object can have any shape, such as part or all of a sphere, an arbitrary curved surface, part or all of a polyhedron surface, etc. However, it is preferable that the surface of the object does not scatter light.

[0241] For example, such as Figure 44A and Figure 44B As shown, a filter formed into a hemispherical shape can be obtained. Figure 44A This is a diagram showing an optical image (visible light) of a filter formed in a hemispherical shape, representing an embodiment. Figure 44B It is shown Figure 44A An infrared image of the filter in the hemispherical embodiment shown. Figure 44A and Figure 44B The image shown was taken using a full HD digital cinema camera, the DVSA10FHDIR, manufactured by KenkoTokina Corporation. Figure 44A The image was taken in visible light mode under white LED illumination. Figure 44B These are images taken in a dark room using only the light from the infrared LEDs of the aforementioned camera.

[0242] Figure 44A and Figure 44B The filter shown is a 300 μm thick filter formed by impregnating the surface of a hemisphere made of acrylic resin (PMMA) with a radius of 2 cm and a thickness of 1 mm with the same material as in Example 6. Figure 44A As shown, a white filter with a hemispherical shape was obtained. Additionally, as... Figure 44B As shown, this filter allows infrared light to pass through.

[0243] Next, a filter according to an embodiment of the present invention with high isotropic backscattering characteristics, suitable for use as a filter with a three-dimensional shape, will be described in more detail. A filter with a three-dimensional shape, such as... Figure 44A and Figure 44B The diagram shows a substrate and a film formed on the substrate, the film having desired optical properties; however, the three-dimensional filter of the embodiments of the present invention is not limited to this. The three-dimensional shape may also include a three-dimensional curved surface. Three-dimensional curved surfaces include, for example, spheres and ellipsoids. Furthermore, the three-dimensional shape may include at least a portion of a solid shape. Solid shapes include various shapes such as spheres, ellipsoids, polyhedra, cones, and cylinders. Examples of optical components that may include a filter as at least a portion include: a three-dimensional LiDAR, a car emblem with a built-in camera, a robot frame, a game controller equipped with a motion capture sensor, a switch, and a camera frame. Additionally, the filter may also serve as at least a portion of a cover for an optical component.

[0244] The filter of the present invention, as described above, appears white due to diffuse reflection of visible light. The filter of the present invention can be characterized by its backscattering properties. Hereinafter, the filter of the present invention will be described as having isotropic backscattering properties. The backscattering properties can be evaluated using the bidirectional reflectance distribution function (BRDF). BRDF is a function that quantifies the scattering properties of a material surface as a constant inherent to its surface; it is the ratio of (small) illuminance to luminance in a specific incident and reflection direction, possessing stereometric properties. -1 (sr -1 ) dimension.

[0245] For the samples (flat films) of Example 6 and Comparative Example A described above, BRDF was measured for various incident and reflection directions. Figure 45 The optical system for measuring BRDF is schematically shown in the figure.

[0246] The BRDF was measured using a GP-4L automatic goniometric photometer manufactured by NIKKA DENSOK LIMITED. The light source LS was a 150W xenon lamp L11033 manufactured by Hamamatsu Photonics KK, illuminating the sample with light transmitted through a 550nm bandpass filter (TS OD4 10nm Band Pass Filter 550nm 12.5mm) manufactured by Edmund Optics Inc. The diameter of the irradiated beam was set to 3mm. The detector DE was a photomultiplier tube (R13456) manufactured by Hamamatsu Photonics K.K., with a set voltage of 430V.

[0247] The BRDF was measured by setting the incident angle (polar angle of the incident light direction) θi of the light source LS to the sample surface as 0°, 30°, and 60°, and the reflection direction to an azimuth angle φr of 20° with the incident surface and a polar angle θr ranging from -70° to 70°. The BRDF (sr) was measured with an incident angle θi of 0°, an azimuth angle φr of 20°, and a polar angle θr of -70°. -1 This is represented as BRDF(0°; 20°, -70°).

[0248] The measurement results of Example 6 are shown in Tables 2 and 3, and the measurement results of Comparative Example A are shown in Tables 4 and 5. It should be noted that the incident angle θi is 0°, and the polar angle θr of the reflection direction is in the range of -10° to 10°, which cannot be accurately measured due to the influence of the calibration of the light source LS and the detector DE. Furthermore, the detection error is large in the range of polar angle θr of the reflection direction from 90° to 70°; therefore, the measured values ​​are not recorded. The measured values, maximum values, minimum values, average values, and standard deviations of BRDF are shown in Tables 2, 3, 4, and 5. The BRDF of the filter samples from Example 6 are shown in Tables 4 and 5. Figure 46 The BRDF of the filter sample of Comparative Example A is shown in the figure. Figure 47 .

[0249] Furthermore, as parameters representing the isotropic nature of backscattering characteristics, the differences between BRDF(0°) with an incident angle θi of 0°, BRDF(30°) with an incident angle θi of 30°, and BRDF(60°) with an incident angle θi of 60° were used. Specifically, |BRDF(0°; 20°, -60°)-BRDF(30°; 20°, -60°)| / BRDF(0°; 20°, -60°) and |BRDF(0°; 20°, -60°)-BRDF(60°; 20°, -60°)| / BRDF(0°; 20°, -60°) were used. Here, || represents the absolute value. In Tables 2, 3, 4, and 5, the difference of BRDF(0°) is set to D_30° and D_60°, respectively. The difference in BRDF(0°), D_30°, and D_60° of the filter samples from Example 6 are shown in the figure. Figure 48 The difference in BRDF(0°), D_30°, and D_60° of the sample of the filter of Comparative Example A are shown in the figure. Figure 49 .

[0250] First, refer to Figure 46 and Figure 48 Regarding the BRDF values ​​in Example 6, the dependence of the polar angle θr is small when the incident angle θi is 0°, 30°, and 60°. As shown in Tables 2 and 3, the maximum value of BRDF(30°) for an incident angle θi of 30° is 0.150, the minimum value is 0.123, the average value is 0.14, and the standard deviation is 0.005237. The maximum value of BRDF(60°) for an incident angle θi of 60° is 0.148, the minimum value is 0.120, the average value is 0.13, and the standard deviation is 0.009855. Furthermore, the difference between BRDF(30°) and BRDF(60°) is small for any polar angle θr. It is also known that... Figure 48 The difference between BRDF(0°) shown is small, with D_30° below 0.13 and D_60° below 0.25.

[0251] Next, refer to Figure 47 and Figure 49 Through comparison with Example 6 Figure 46 and Figure 48The comparison clearly shows that for the BRDF values ​​of Comparative Example A, the dependence of the polar angle θr is significant when the incident angle θi is 0°, 30°, and 60°. As shown in Tables 4 and 5, the maximum value of BRDF(30°) for an incident angle θi of 30° is 0.793, the minimum value is 0.054, the average value is 0.34, and the standard deviation is 0.252327. The maximum value of BRDF(60°) for an incident angle θi of 60° is 0.789, the minimum value is 0.042, the average value is 0.28, and the standard deviation is 0.269342. Furthermore, it can be seen that the difference between BRDF(30°) and BRDF(60°) is particularly large in the region where the polar angle θr is negative. It can also be seen that... Figure 48 The maximum value of the difference between BRDF(0°) D_30° is 1.91, and the maximum value of D_60° is 3.87, which are both large values.

[0252] Based on the above results, D_30° and D_60° can be used as parameters representing the high isotropy of the backscattering characteristics of the filter according to the embodiments of the present invention. For the filter of Example 6, D_30°(-30°) and D_60°(-30°) when the polar angle θr is -30° are 0.03 and 0.16, respectively. Furthermore, D_30°(-60°) and D_60°(-60°) when the polar angle θr is -60° are 0.01 and 0.09, respectively.

[0253] In contrast, for the filter of Comparative Example A, the values ​​of D_30°(-30°) and D_60°(-30°) when the polar angle θr is -30° are 1.17 and 0.14, respectively. Furthermore, the values ​​of D_30°(-60°) and D_60°(-60°) when the polar angle θr is -60° are 1.61 and 3.55, respectively. Thus, in the filter of Comparative Example A, |BRDF(0°; 20°, -60°)-BRDF(30°; 20°, -60°)| / BRDF(0°; 20°, -60°) is either greater than 1.0 or |BRDF(0°; 20°, -60°)-BRDF(60°; 20°, -60°)| / BRDF(0°; 20°, -60°) is greater than 1.0.

[0254] Therefore, it can be considered that, as an index of the isotropy of backscattering characteristics, |BRDF(0°; 20°, -60°)-BRDF(30°; 20°, -60°)| / BRDF(0°; 20°, -60°) is preferably 1.0 or less, and |BRDF(0°; 20°, -60°)-BRDF(60°; 20°, -60°)| / BRDF(0°; 20°, -60°) is 1.0 or less. Further preferably, |BRDF(0°; 20°, -60°)-BRDF(30°; 20°, -60°)| / BRDF(0°; 20°, -60°) is 0.50 or less, and |BRDF(0°; 20°, -60°)-BRDF(60°; 20°, -60°)| / BRDF(0°; 20°, -60°) is 0.50 or less. Even more preferably, |BRDF(0°; 20°, -60°)-BRDF(30°; 20°, -60°)| / BRDF(0°; 20°, -60°) is 0.25 or less, and |BRDF(0°; 20°, -60°)-BRDF(60°; 20°, -60°)| / BRDF(0°; 20°, -60°) is 0.25 or less. The optical film of Example 6 has high isotropy, with BRDF(0°; 20°, -60°)-BRDF(30°; 20°, -60°)| / BRDF(0°; 20°, -60°) being less than 0.2 and |BRDF(0°; 20°, -60°)-BRDF(60°; 20°, -60°)| / BRDF(0°; 20°, -60°) being less than 0.2.

[0255] Here, as an example of incident light within the visible light wavelength range, the backscattering characteristics of the optical film of Example 6 were explained for light with a wavelength of 550 nm. However, the optical film of the embodiments of the present invention can satisfy the above relationship not only for light with a wavelength of 550 nm, but also for light with at least a portion of wavelengths within the visible light wavelength range. That is, by adjusting any parameter among the refractive index of the particles and the substrate, the average particle size, volume fraction, distribution (degree of aperiodicity), and thickness, the linear transmittance for light with at least a portion of wavelengths within the wavelength range of 760 nm and 2000 nm can be made to be 60% or more, and isotropic with high backscattering characteristics for light with at least a portion of wavelengths within the visible light wavelength range.

[0256] [Table 2]

[0257]

[0258] [Table 3]

[0259] 2 - 0.144 0.127 - - 4 - 0.144 0.128 - - 6 - 0.143 0.128 - - 8 - 0.142 0.129 - - 10 0.156 0.142 0.131 0.09 0.16 12 0.155 0.142 0.132 0.09 0.15 14 0.156 0.141 0.132 0.10 0.15 16 0.156 0.141 0.134 0.10 0.15 18 0.158 0.140 0.135 0.11 0.14 20 0.158 0.140 0.136 0.11 0.14 22 0.159 0.141 0.138 0.12 0.14 24 0.160 0.141 0.139 0.12 0.13 26 0.161 0.141 0.139 0.12 0.13 28 0.162 0.141 0.141 0.13 0.13 30 0.163 0.142 0.142 0.13 0.13 32 0.164 0.143 0.143 0.13 0.13 34 0.164 0.144 0.144 0.12 0.12 36 0.164 0.145 0.145 0.12 0.12 38 0.164 0.146 0.148 0.11 0.11 40 0.163 0.147 0.146 0.10 0.10 42 0.163 0.148 0.147 0.09 0.09 44 0.161 0.148 0.148 0.08 0.08 46 0.159 0.150 0.148 0.06 0.07 48 0.158 0.150 0.148 0.05 0.07 50 0.156 0.149 0.148 0.05 0.05 52 0.154 0.149 0.148 0.03 0.04 54 0.153 0.149 0.148 0.03 0.04 56 0.152 0.148 0.148 0.03 0.03 58 0.149 0.147 0.147 0.02 0.02 60 0.148 0.147 0.146 0.01 0.01 62 0.146 0.144 0.145 0.01 0.01 64 0.144 0.143 0.144 0.00 0.00 66 0.140 0.141 0.142 0.01 0.01 68 0.138 0.138 0.140 0.00 0.02 70 0.135 0.135 0.137 0.00 0.02 MAX (0.164) 0.150 0.148 (0.13) (0.25) MIN (0.114) 0.123 0.120 (0.00) (0.00) AVG - 0.140 0.130 - - SD - 0.005237 0.009855 - -

[0260] [Table 4]

[0261]

[0262] [Table 5]

[0263] 2 - 0.276 0.136 - - 4 - 0.250 0.128 - - 6 - 0.227 0.121 - - 8 - 0.210 0.113 - - 10 0.666 0.191 0.107 0.71 0.84 12 0.606 0.175 0.101 0.71 0.83 14 0.565 0.164 0.095 0.71 0.83 16 0.531 0.153 0.089 0.71 0.83 1a 0.491 0.144 0.085 0.71 0.83 20 0.444 0.138 0.081 0.69 0.82 22 0.398 0.131 0.077 0.67 0.81 24 0.371 0.123 0.073 0.67 0.80 26 0.347 0.117 0.068 0.66 0.80 28 0.317 0.113 0.065 0.64 0.80 30 0.293 0.108 0.061 0.63 0.79 32 0.274 0.105 0.059 0.62 0.79 34 0.255 0.101 0.056 0.60 0.78 36 0.244 0.096 0.053 0.61 0.78 38 0.230 0.094 0.051 0.59 0.78 40 0.216 0.092 0.050 0.57 0.77 42 0.208 0.087 0.049 0.58 0.77 44 0.201 0.085 0.047 0.58 0.77 46 0.193 0.083 0.048 0.57 0.76 48 0.183 0.081 0.047 0.56 0.75 50 0.176 0.077 0.045 0.56 0.74 52 0.173 0.075 0.045 0.57 0.74 54 0.165 0.073 0.045 0.56 0.73 56 0.156 0.071 0.045 0.55 0.71 58 0.153 0.068 0.044 0.55 0.71 60 0.149 0.065 0.044 0.56 0.70 62 0.141 0.064 0.045 0.55 0.68 64 0.135 0.062 0.044 0.54 0.67 66 0.128 0.059 0.043 0.54 0.66 68 0.125 0.056 0.042 0.55 0.66 70 0.119 0.054 0.042 0.54 0.65 MAX (0.779) 0.793 0.789 (1.91) (3.87) MIN (0.119) 0.054 0.042 (0.06) (0.02) AVG - 0.34 0.28 - - SD - 0.252327 0.269342 - -

[0264] When the isotropy of backscattering is high, the color change caused by the viewing angle is small. In other words, the desired color is presented regardless of the shape of the filter. High isotropy of visible light backscattering characteristics means that the isotropy of infrared transmittance characteristics is also high. Therefore, the filter of the embodiments of the present invention can have the desired infrared transmittance characteristics even when processed into various three-dimensional shapes. Of course, the three-dimensional shape of the filter can be appropriately designed according to the shape and relative position relationship of the infrared light-receiving surface.

[0265] The filters of the embodiments of the present invention are not limited to the illustrated sensing devices (e.g., infrared cameras) and communication devices, and can be used for a variety of purposes. For example, they can be suitably used in solar cells, heaters that use infrared light, and light-powered devices that use infrared light.

[0266] Industrial applicability

[0267] The filters of the embodiments of the present invention can be used, for example, as infrared filters used in sensor technology or communication technology.

Claims

1. A filter comprising a matrix and microparticles dispersed in said matrix, The particles at least constitute colloidal amorphous aggregates that do not induce Bragg reflection. The filter has backscattering properties, wherein, The filter has a linear transmittance of 60% or more for at least a portion of the wavelengths in the wavelength range of 760 nm to 2000 nm. The bidirectional reflectance distribution function (BRDF) for the direction where the polar angle of the incident light's incident direction is 0° and the azimuth angle formed with the incident surface is 20° with a polar angle of -60° is defined as BRDF(0°; 20°, -60°). Similarly, the BRDF(30°; 20°, -60°) for the direction where the polar angle of the incident light's incident direction is 30° and the azimuth angle formed with the incident surface is 20° with a polar angle of -60° is defined as BRDF(60°; 20°, -60°) for the direction where the polar angle of the incident light's incident direction is 60° and the azimuth angle formed with the incident surface is 20° with a polar angle of -60° is defined as BRDF(60°; 20°, -60°). This applies when the incident light is light with at least a portion of its wavelengths within the visible light wavelength range. |BRDF(0°; 20°, -60°)-BRDF(30°; 20°, -60°)| / BRDF(0°; 20°, -60°) is 1.0 or less, and |BRDF(0°; 20°, -60°)-BRDF(60°; 20°, -60°)| / BRDF(0°; 20°, -60°) is 1.0 or less. The transmittance curve of the filter in the visible light wavelength region has a portion where the linear transmittance monotonically decreases from the long wavelength side to the short wavelength side, and this portion shifts towards the long wavelength side as the incident angle increases.

2. The filter according to claim 1, wherein, |BRDF(0°; 20°, -60°)-BRDF(30°; 20°, -60°)| / BRDF(0°; 20°, -60°) is less than 0.50, and |BRDF(0°; 20°, -60°)-BRDF(60°; 20°, -60°)| / BRDF(0°; 20°, -60°) is less than 0.

50.

3. The filter according to claim 1, wherein, |BRDF(0°; 20°, -60°)-BRDF(30°; 20°, -60°)| / BRDF(0°; 20°, -60°) is less than 0.25, and |BRDF(0°; 20°, -60°)-BRDF(60°; 20°, -60°)| / BRDF(0°; 20°, -60°) is less than 0.

25.

4. The optical filter according to any one of claims 1 to 3, having an L ＊ of 20 or more, measured by the SCE method.

5. The filter according to any one of claims 1 to 3, wherein the filter has a three-dimensional shape.

6. The filter according to claim 5, wherein, The three-dimensional shape comprises at least a portion of a solid shape.

7. The filter according to claim 6, wherein, The three-dimensional shape includes any shape among spheres, ellipsoids, polyhedra, cones, and cylinders.

8. The filter according to any one of claims 1 to 3, comprising a substrate and a film formed on said substrate, The film has a linear transmittance of 60% or more for at least a portion of the wavelengths in the wavelength range of 760 nm to 2000 nm. The bidirectional reflectance distribution function (BRDF) for the direction where the polar angle of the incident light's incident direction is 0° and the azimuth angle formed with the incident surface is 20° with a polar angle of -60° is defined as BRDF(0°; 20°, -60°). Similarly, the BRDF(30°; 20°, -60°) for the direction where the polar angle of the incident light's incident direction is 30° and the azimuth angle formed with the incident surface is 20° with a polar angle of -60° is defined as BRDF(60°; 20°, -60°) for the direction where the polar angle of the incident light's incident direction is 60° and the azimuth angle formed with the incident surface is 20° with a polar angle of -60° is defined as BRDF(60°; 20°, -60°). This applies when the incident light is light with at least a portion of its wavelengths within the visible light wavelength range. |BRDF(0°; 20°, -60°)-BRDF(30°; 20°, -60°)| / BRDF(0°; 20°, -60°) is less than or equal to 1.0, and |BRDF(0°; 20°, -60°)-BRDF(60°; 20°, -60°)| / BRDF(0°; 20°, -60°) is less than or equal to 1.

0.

9. The filter according to claim 8, wherein, The substrate is formed of plastic or glass.

10. The filter according to claim 8, wherein, The surface of the substrate has undergone any of the following treatments: corona treatment, plasma treatment, UV ozone treatment, and primer treatment.

11. The filter according to any one of claims 1 to 3, wherein the linear transmittance for light with a wavelength of 950 nm is 60% or more.

12. The filter according to any one of claims 1 to 3, wherein the linear transmittance for light with a wavelength of 1550 nm is 60% or more.

13. The filter according to any one of claims 1 to 3, wherein the color it presents when the standard light is set to a D65 light source has x,y coordinates of 0.25≤x≤0.40 and 0.25≤y≤0.40 on the CIE1931 chromaticity diagram.

14. The filter according to any one of claims 1 to 3, wherein, For light with a wavelength of 950 nm, the linear transmittance at an incident angle of 60° is more than 80% of the linear transmittance at an incident angle of 0°.

15. The filter according to any one of claims 1 to 3, further comprising a printed layer formed of infrared-transmitting ink.

16. The filter according to claim 1, wherein, The particles comprise a first, monodisperse particle with an average particle size in the range of 80 nm or more and 300 nm or less.

17. The filter according to claim 16, wherein, The average particle size of the first particle is greater than 150 nm.

18. The filter according to any one of claims 1 to 3, wherein, In a cross-section perpendicular to the surface direction of the filter, the average distance between the centroids of the particles is greater than 200 nm.

19. The filter according to any one of claims 1 to 3, wherein, In a cross section perpendicular to the surface direction of the filter, the average value of the distance between the centroids of the particles varies by a factor of 10% or more.

20. The filter according to any one of claims 1 to 3, wherein, In a cross section perpendicular to the surface direction of the filter, the average value of the distance between the centroids of the particles varies by a factor of 45% or less.

21. The filter according to any one of claims 1 to 3, wherein, The matrix comprises a resin having a cross-linked structure.

22. The filter according to any one of claims 1 to 3, wherein, The volume fraction of the particles is 6% or more and 60% or less.

23. The filter according to any one of claims 1 to 3, wherein, The refractive index of the base for light having a wavelength of 546 nm is set to n M , and the refractive index of the fine particles is set to n P When |n M -n P | is 0.03 or more and 0.6 or less.

24. The filter according to any one of claims 1 to 3, wherein, The matrix is ​​formed of resin, and the microparticles are formed of inorganic materials.

25. A method of manufacturing the filter of claim 24, the method comprising: A process for preparing a curable resin composition in which the microparticles are dispersed / mixed in a curable resin; The process of applying the curable resin composition to the surface of a substrate; as well as A process of curing the curing resin contained in the curing resin composition applied to the surface.

26. The manufacturing method according to claim 25, wherein, The coating process is performed using a coating method.

27. The manufacturing method according to claim 26, wherein, The coating process is performed by dip coating.

28. An optical module having: Equipment with infrared light-receiving parts, and The filter according to any one of claims 1 to 24 is disposed in front of the infrared light-receiving part of the device.

29. The optical module according to claim 28, wherein, The device may be a sensing device, a communication device, a solar cell, a heater, or a power supply device.

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