Optical filter, its manufacturing method and optical module

Abstract

An optical filter (10) comprises a matrix (12) and fine particles (14) dispersed in the matrix (12), wherein the fine particles (14) have a parameter Ds of 8.0 to 30 inclusive, Ds being determined by a USAXS pattern and given by Ds=λ / (B･cosθ･Ra), where λ is the X-ray wavelength, θ is one half the scattering angle 2θ(rad) providing a scattering intensity peak, B is the half width (FWHM, rad) of the peak, and Ra is the average particle size of the fine particles (14).

Description

[Technical field]

[0001] The present invention relates to an optical filter, a manufacturing method thereof, and an optical module, and more particularly to an optical filter that is preferably used as an infrared filter having high rectilinear transmittance for infrared light and high diffuse reflectance for visible light, a manufacturing method thereof, and an optical module including such an optical filter on the front surface of an infrared receiving unit of a device, such as a sensing device or a communication device. [Background technology]

[0002] Sensor technology or communication technology using infrared rays has been developed and put to practical use. Since elements 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" includes at least light (electromagnetic waves) with wavelengths in the range of 760 nm to 2000 nm used for sensing or communication. In addition, "visible light" refers to light in the range of 400 nm to less than 760 nm.

[0003] Conventional infrared transmission filters are predominantly black in color because they absorb visible light, which has the problem of poor design.

[0004] For example, Patent Document 1 discloses an infrared receiving / emitting unit having a dielectric multilayer film that transmits infrared rays and reflects and transmits visible light, and a matte surface. Patent Document 2 discloses an optical article for infrared communication that scatters visible light by utilizing Rayleigh scattering due to fine unevenness formed by roughening the surface of a transparent substrate, thereby presenting a white color, and has an infrared transmittance of 12% or more. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2006-165493 A (Patent No. 4122010 A) [Patent Document 2] JP 2013-65052 A (Patent No. 5756962 A) [Patent Document 3] JP 2010-058091 A (Patent No. 5274164 A) [Non-patent literature]

[0006] [Non-Patent Document 1] M. Iwata et al. "Bio-Inspired Bright Structurally Colored Colloidal Amorphous Array Enhanced by Controlling Thickness and Black Background", Adv. Mater., 2017, 29, 1605050. Summary of the Invention [Problem to be solved by the invention]

[0007] The infrared ray receiving and emitting unit described in Patent Document 1 colors its appearance only with visible light reflected by a dielectric multilayer film, and the color changes depending on the viewing angle. Another problem is that the dielectric multilayer film is expensive.

[0008] According to the inventor's investigation, it was found that an infrared communication film using a dielectric multilayer film as described in Patent Document 1 is difficult to use for motion capture applications because the outline of the hand becomes blurred when hand movements are photographed through the film with an infrared camera. This is believed to be due to the low linear transmittance of infrared light.

[0009] On the other hand, for example, Patent Document 3 and Non-Patent Document 1 disclose that a microparticle dispersion or colloidal amorphous aggregate having an amorphous structure can exhibit a vivid structural color (e.g., blue) with little angle dependency. Patent Document 3 describes that a microparticle dispersion having an amorphous structure is particularly useful for applications that reflect light of a specific wavelength (e.g., coloring material, infrared reflective film, etc.).

[0010] The present invention has been made to solve the above-mentioned problems, and has an object to provide an optical filter having a novel structure that is white and can be suitably used as an infrared transmission filter with high in-line infrared transmittance, a manufacturing method thereof, and an optical module. [Means for solving the problem]

[0011] According to an embodiment of the present invention, the following solutions are provided: [Item 1] An optical filter including a matrix and particles dispersed in the matrix, The particle has a parameter Ds of 8.0 or more and 30 or less, which is obtained from a USAXS pattern and is given by Ds=λ / (B·cosθ·Ra), where λ is the wavelength of the X-ray, θ is half the scattering angle 2θ (rad) giving the peak of the scattering intensity, B is the half-width at half maximum (FWHM, rad), and Ra is the average particle size of the particle. [Item 2] Item 2. The optical filter according to item 1, which exhibits white color. [Item 3] 3. The optical filter according to item 1 or 2, wherein the x, y coordinates on the CIE 1931 chromaticity diagram of the color exhibited when a D65 light source is used as a standard light source are 0.25≦x≦0.40 and 0.25≦y≦0.40. [Item 4] L measured using a spectrophotometer with the SCE method * 4. The optical filter according to any one of items 1 to 3, wherein the value of is 20 or more. [Item 5] 5. The optical filter according to any one of items 1 to 4, having an in-line transmittance of 60% or more for light of at least a part of a wavelength within a wavelength range of 760 nm or more and 2000 nm or less. [Item 6] 6. The optical filter according to item 5, having an in-line transmittance of 60% or more for light having a wavelength of 950 nm. [Item 7] Item 7. The optical filter according to item 5 or 6, having an in-line transmittance of 60% or more for light having a wavelength of 1500 nm. [Item 8] 8. The optical filter according to any one of items 1 to 7, wherein the microparticles include monodisperse first microparticles having an average particle size in the range of 80 nm to 300 nm. [Item 9] 9. The optical filter according to item 8, wherein the first fine particles have an average particle size of 150 nm or more. [Item 10] 10. The optical filter according to any one of items 1 to 9, wherein the microparticles constitute at least a colloidal amorphous aggregate. [Item 11] 11. The optical filter according to any one of items 1 to 10, wherein the volume fraction of the fine particles is 6% or more and 60% or less. [Item 12] The refractive index of the matrix for light with a wavelength of 546 nm is n M The refractive index of the fine particles is n P Then, |n M -n P 12. The optical filter according to any one of items 1 to 11, wherein | is 0.03 or more and 0.6 or less. [Item 13] 13. The optical filter according to any one of items 1 to 12, having a three-dimensional shape. [Item 14] 14. The optical filter according to any one of items 1 to 13, wherein the matrix is ​​made of a resin, and the fine particles are made of an inorganic material. [Item 15] Item 15. A method for producing the optical filter according to item 14, comprising the steps of: preparing a curable resin composition by dispersing and mixing the fine particles in a curable resin; applying the curable resin composition to a surface of a substrate; curing the curable resin contained in the curable resin composition applied to the surface; The manufacturing method includes the steps of: [Item 16] Item 16. The method according to item 15, wherein the applying step is carried out by a coating method. [Item 17] Item 17. The method according to item 16, wherein the applying step is carried out by a dip coating method. [Item 18] A device having an infrared receiver; An optical filter according to any one of items 1 to 13, arranged in front of the infrared receiving unit of the device; An optical module having [Item 19] Item 19. The optical module of item 18, wherein the device is a sensing device, a communication device, a solar cell, a heater, or a power supply device. Effect of the Invention

[0012] The optical filter having the novel structure according to the embodiment of the present invention is white and can be suitably used as an infrared transmission filter having a high linear transmittance of infrared rays. According to the embodiment of the present invention, a manufacturing method of such an optical filter and an optical module including such an optical filter can be applied. [Brief description of the drawings]

[0013] [Figure 1] 1 is a schematic cross-sectional view of an optical filter 10 according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram for explaining the technical meaning of parameter Ds, which represents the dispersion state of particles in a particle aggregate. [Diagram 3] 1 is a graph showing particle size distribution of fine particles. [Figure 4]FIG. 2 is a diagram showing the USAXS patterns of the optical films of Examples 1 to 6. [Diagram 5] FIG. 1 shows USAXS patterns of the optical films of Examples 7 to 12. [Figure 6] FIG. 1 shows USAXS patterns of the optical films of Examples 13 to 17. [Figure 7] FIG. 2 is a diagram showing USAXS patterns of the optical films of Comparative Examples 1 to 4. [Figure 8] FIG. 2 is a diagram showing USAXS patterns (normalized) of the optical films of Examples 1 to 6. [Figure 9] FIG. 1 shows USAXS patterns (normalized) of the optical films of Examples 7 to 12. [Figure 10] FIG. 2 is a diagram showing USAXS patterns (normalized) of the optical films of Examples 13 to 17. [Figure 11] FIG. 1 is a diagram showing USAXS patterns (normalized) of Comparative Examples 1 to 4. [Figure 12] 1A and 1B are schematic diagrams illustrating optical characteristics of an optical filter 10 according to an embodiment of the present invention. [Figure 13] FIG. 2 is a schematic diagram showing a method for measuring the diffuse transmittance of an optical filter. [Figure 14] FIG. 2 is a schematic diagram showing a method for measuring the linear transmittance of an optical filter. [Figure 15] 2 shows linear transmittance spectra of the optical films of Examples 1 to 6. [Figure 16] 1 shows linear transmittance spectra of the optical films of Examples 7 to 12. [Figure 17] 1 shows linear transmittance spectra of the optical films of Examples 13 to 17. [Figure 18] 2 shows linear transmittance spectra of the optical films of Comparative Examples 1 to 3. [Figure 19] 1 is a bar graph showing the value of the parameter Ds for each sample. [Figure 20A] FIG. 13 is a diagram showing a two-dimensional X-ray scattering pattern of the optical film of Comparative Example 3. [Figure 20B]FIG. 13 shows the two-dimensional X-ray scattering pattern of the optical film of Example 12. [Figure 20C] FIG. 13 is a diagram showing a two-dimensional X-ray scattering pattern of the optical film of Comparative Example 4. [Figure 21] 2 is a diagram showing a cross-sectional TEM image of the optical filter 10A of the first embodiment. FIG. [Figure 22] 1 is a diagram showing a cross-sectional TEM image of an optical filter 20A of Comparative Example 1. FIG. [Diagram 23] 1 is an example of a camera image captured using a motion capture device. [Figure 24] 1 is an example of a camera image captured by a motion capture device via the optical filter 10A of the first embodiment. [Diagram 25] 13 is an example of a camera image acquired using a motion capture device via the optical filter 20A of Comparative Example 1. [Figure 26] 3 is a diagram showing an optical image of the optical filter 10A of the first embodiment. FIG. [Figure 27] 1 is a diagram showing an optical image of an optical filter 20A of Comparative Example 1. FIG. [Figure 28A] FIG. 2 is a diagram showing an optical image (visible light) illustrating an optical filter of an embodiment formed in a hemispherical shape. [Figure 28B] FIG. 28B shows an infrared image of the hemispherical embodiment optical filter shown in FIG. 28A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, optical filters according to embodiments of the present invention will be described with reference to the drawings. The optical filters according to the embodiments of the present invention are not limited to the following examples.

[0015] The optical filter according to the embodiment of the present invention is an optical filter including a matrix and fine particles dispersed in the matrix, and has a novel structure that is white in color and can be suitably used as an infrared transmission filter with high linear transmittance of infrared light.

[0016] In the previous applications (Japanese Patent Application No. 2020-045671 and Japanese Patent Application No. 2020-163409), the applicant disclosed that the fine particles dispersed in the matrix preferably constitute at least a colloidal amorphous aggregate. Here, the colloidal amorphous aggregate refers to an aggregate of colloidal particles (particle size 1 nm to 1 μm) that does not have long-range order and does not cause Bragg reflection. In contrast, when colloidal particles are distributed so as to have a long-range order, a so-called colloidal crystal (a type of photonic crystal) is formed, and Bragg reflection occurs. The fine particles (colloidal particles) constituting the colloidal amorphous aggregate do not form a diffraction grating. The entire disclosure of Japanese Patent Application No. 2020-045671 and Japanese Patent Application No. 2020-163409 is incorporated herein by reference.

[0017] The applicant further investigated the matter and found that, as will be described in detail later with reference to examples and comparative examples, it is possible to obtain an optical filter that exhibits white color and has high infrared linear transmittance even if it has Bragg reflection in the visible light region. The degree of white color and the magnitude of infrared linear transmittance vary depending on the application, and can be adjusted by changing the thickness of the filter, but in order to obtain an optical filter that exhibits white color and has high infrared linear transmittance, it is important to control the dispersion state of the fine particles.

[0018] The present inventors have found that an optical filter having a parameter Ds of 8.0 or more and 30 or less, given by Ds=λ / (B·cosθ·Ra) obtained from an ultra-small angle X-ray scattering (USAXS) pattern, where λ is the wavelength of the X-ray, θ is half the scattering angle 2θ (rad) at which the scattering intensity peaks, B is the half-width at half maximum (FWHM, rad) of the peak, and Ra is the average particle size of the particles, can be suitably used as an infrared transmission filter in which the particles are in a moderately dispersed state, exhibits white color, and has high infrared linear transmittance. The dispersed state of the particles characterized by the parameter Ds is considered to have an order (periodicity) suitable for exhibiting white color and high infrared linear transmittance. The dispersed state of the particles characterized by the parameter Ds can include those that can be classified as colloidal crystals having Bragg reflection in the visible light region and colloidal amorphous aggregates that do not have Bragg reflection. Since Bragg reflection causes a colored appearance when viewed from a specific direction, it is preferable for the particles to form a colloidal amorphous aggregate in order to appear white from any angle. The technical meaning of the parameter Ds will be explained in detail later with reference to Figure 2.

[0019] The optical filter according to the embodiment of the present invention can exhibit white color. The optical filter exhibiting white color can be designed in various colors. White color can be defined in various ways depending on the application. For example, the color exhibited when the standard light is a D65 light source can be said to be white when the x and y coordinates on the CIE1931 chromaticity diagram are 0.25≦x≦0.40 and 0.25≦y≦0.40. Of course, the closer to x=0.333 and y=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, the L measured by the SCE method on the CIE1976 color space can be expressed as * is preferably 20 or more, more preferably 40 or more, even more preferably 50 or more, and particularly preferably 60 or more. * If the value is 20 or more, it can be said to be roughly white. * The upper limit is, for example, 100.

[0020] The optical filter according to the embodiment of the present invention may have a linear transmittance of 60% or more for light of at least a part of wavelengths in the wavelength range of 760 nm to 2000 nm. For example, an optical filter can be obtained with a linear transmittance of 60% or more for light of wavelengths of 950 nm and 1500 nm. The wavelength range of light (near infrared rays) in 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 preferably used for, for example, 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").

[0021] The infrared linear transmittance of the optical filter can be appropriately set depending on the application. The optical filter according to the embodiment of the present invention can be disposed in front of an infrared receiving unit of various devices to form an optical module. Examples of devices having an infrared receiving unit include sensing devices, communication devices, solar cells, heaters, and power supply devices.

[0022] The fine particles contained in the optical filter according to the embodiment of the present invention include monodisperse fine particles having an average particle size of at least one tenth of the wavelength of the infrared ray. That is, for infrared rays having a wavelength in the range of 760 nm to 2000 nm, the average particle size of the fine particles is preferably at least 80 nm, preferably 150 nm or more, and more preferably 200 nm or more. The upper limit of the average particle size of the fine particles is, for example, 300 nm. The optical filter according to the embodiment of the present invention may contain two or more monodisperse fine particles having different average particle sizes. Each fine particle is preferably approximately spherical. In this specification, fine particles (plural) are also used to mean an aggregate of fine particles, and monodisperse fine particles refer to those having a coefficient of variation (a value representing the standard deviation / average particle size as a percentage) of 20% or less, preferably 10% or less, and more preferably 1 to 5%. The optical filter according to the embodiment of the present invention uses particles having a particle size (particle diameter, volume sphere equivalent diameter) of at least one tenth of the wavelength, thereby increasing the linear transmittance of infrared rays. The principle is different from that of the optical article described in Patent Document 2, which uses Rayleigh scattering. The average particle size of the fine particles is measured, for example, by a disk centrifugal particle size distribution analyzer.

[0023] 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 the embodiment of the present invention includes a matrix 12 that is transparent to visible light, and transparent fine particles 14 dispersed in the transparent matrix 12.

[0024] The optical filter 10 has a substantially flat surface as shown in FIG. 1. Here, a substantially flat surface refers to a surface that does not have an uneven structure of a size that scatters (diffracts) or diffusely reflects visible light or infrared light. The optical filter 10 does not include cholesteric liquid crystal (which broadly includes polymer liquid crystal, low molecular liquid crystal, a liquid crystal mixture thereof, and a liquid crystal material thereof that is mixed with a crosslinking agent and solidified by crosslinking or the like, and which exhibits a cholesteric phase). The optical filter 10 is, for example, in the form of a film, but is not limited thereto.

[0025] The transparent fine particles 14 are, for example, silica fine particles. As the silica fine particles, for example, silica fine particles synthesized by the Stöber method can be used. In addition, inorganic fine particles other than silica fine particles may be used as the fine particles, and resin fine particles may be used. As the resin fine particles, for example, fine particles made of at least one of polystyrene and polymethyl methacrylate are preferable, and fine particles made of cross-linked polystyrene, cross-linked polymethyl methacrylate, or cross-linked styrene-methyl methacrylate copolymer are more preferable. In addition, as such fine particles, for example, polystyrene fine particles or polymethyl methacrylate fine particles synthesized by emulsion polymerization can be appropriately used. In addition, hollow silica fine particles and hollow resin fine particles containing air can also be used. In addition, fine particles formed of inorganic materials have the advantage of being excellent in heat resistance and light resistance. The volume fraction of the fine particles with respect to the whole (including the matrix and the fine particles) is preferably 6% or more and 60% or less, more preferably 20% or more and 50% or less, and even more preferably 20% or more and 40% or less. The transparent fine particles 14 may have optical isotropy.

[0026] Examples of the matrix 12 include, but are not limited to, acrylic resins (e.g., polymethyl methacrylate, polymethyl acrylate), polycarbonate, polyester, poly(diethylene glycol bisallyl carbonate), polyurethane, epoxy resin, and polyimide. The matrix 12 is preferably formed using a curable resin (thermosetting or photocurable), and is preferably formed using a photocurable resin from the viewpoint of mass production. As the photocurable resin, various (meth)acrylates can be used. The (meth)acrylate preferably contains a bifunctional or trifunctional or higher functional (meth)acrylate. In addition, the matrix 12 preferably has optical isotropy. When a curable resin containing a polyfunctional monomer is used, a matrix 12 having a crosslinked structure can be obtained, and thus the heat resistance and light resistance can be improved.

[0027] The optical filter 10, in which the matrix 12 is made 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, or even 10 μm or more and 500 μm or less, the optical filter 10 can exhibit remarkable flexibility.

[0028] When silica fine particles having a hydrophilic surface are used as the fine particles, it is preferable to form the fine particles 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 (meth)acrylate, 2-hydroxypropyl (meth)acrylate, acrylamide, methylene bisacrylamide, and ethoxylated bisphenol A di(meth)acrylate. In addition, one type of these monomers may be used alone, or two or more types may be used in combination. Of course, the two or more types of monomers may include a monofunctional monomer and a polyfunctional monomer, or may include two or more types of polyfunctional monomers.

[0029] These monomers can be cured by appropriately using a photopolymerization initiator. Examples of photopolymerization initiators include carbonyl compounds such as benzoin ether, benzophenone, anthraquinone, thioxane, ketal, and acetophenone, sulfur compounds such as disulfides and dithiocarbamates, organic peroxides such as benzoyl peroxide, azo compounds, transition metal complexes, polysilane compounds, and dye sensitizers. The amount of addition 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, based on 100 parts by mass of the mixture of the fine particles and the monomer.

[0030] The refractive index of the matrix for visible light is n M, the refractive index of the microparticle is n P Then, |n M -n P | (hereinafter, sometimes simply referred to as the refractive index difference) is preferably 0.01 or more, preferably 0.6 or less, more preferably 0.03 or more, and more preferably 0.11 or less. If the refractive index difference is smaller than 0.03, the scattering intensity is weak, making it difficult to obtain the desired optical characteristics. If the refractive index difference exceeds 0.11, the linear transmittance of infrared rays may decrease. If the refractive index difference is set to 0.6 by using, for example, zirconia fine particles (refractive index 2.13) and acrylic resin, the linear transmittance of infrared rays can be adjusted by reducing the thickness. In this way, the linear transmittance of infrared rays can also be adjusted, for example, by controlling the thickness and refractive index difference of the optical filter. Also, depending on the application, it can be used by overlapping with a filter that absorbs infrared rays. The refractive index for visible light can be represented by, for example, the refractive index for light of 546 nm. Here, unless otherwise specified, the refractive index refers to the refractive index for light of 546 nm.

[0031] The optical filter according to the embodiment of the present invention can be manufactured by a manufacturing method including, for example, a step of preparing a curable resin composition in which fine particles are dispersed and 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 may be, for example, a glass substrate, or may be, for example, a resin film such as PET (polyethylene terephthalate), TAC (triacetyl cellulose), or PI (polyimide), but is not limited thereto. The step of dispersing and mixing fine particles in a curable resin can be performed using a known dispersion and mixing device such as a homomixer or a homogenizer (for example, an ultrasonic homogenizer, a high-pressure homogenizer). In addition, the application step can be performed by various known methods such as a coating method (for example, a dip coating method, a spray coating method, a die coating method) or a printing method.

[0032] The configuration and optical characteristics of the optical filters according to the embodiments of the present invention will be described below with specific experimental examples (Examples and Comparative Examples). The configurations 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 combining different types of silica microparticles and resins, adding aggregating agents or dispersants, and using different dispersion and mixing methods.

[0033] The optical filters of Examples 1 to 17 and Comparative Examples 1 to 3 were formed as films using the acrylic resin and silica particles listed in Table 1. As the silica particles, monodisperse silica particles synthesized by the Stöber method were used. Five types of particles 1 to 5 with different average particle sizes shown in Table 2 were used. The average particle size, standard deviation, and CV value were measured using a disk centrifugal particle size distribution meter (DC24000UHR) manufactured by CPS Instruments. The particle size distribution of particles 1 to 5 is shown in FIG. 3. Note that Comparative Example 4 is a photonic rubber commercially available from Soft Photonics LLC, in which nanoparticles constitute a photonic crystal, and light of a specific color is strongly reflected by Bragg reflection. When deformed, the interval between the nanoparticles constituting the photonic crystal changes, and the color of the reflected light changes. Note that the particle size (*) of Comparative Example 4 listed in Table 1 is a value obtained from the scattering pattern by USAXS described later.

[0034] Silica particles were mixed and dispersed in acrylic monomers A to E in a specified ratio to prepare a curable resin composition, which was then applied to the surface of the substrate using an applicator to obtain a film of a specified thickness, followed by curing. Darocure 1173 was mixed as a photopolymerization initiator at 0.2 parts by mass per 100 parts by mass of acrylic monomer, and cured by photopolymerization under irradiation with a UV lamp. Resins (polymers) with different refractive indices were formed depending on the type of monomer.

[0035] The 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 a monofunctional acrylate.

[0036] A: Pentaerythritol triacrylate B: Ethoxylated bisphenol A diacrylate (m+n=10) C: Ethoxylated bisphenol A diacrylate (m+n=3) D: Methoxypolyethylene glycol #400 methacrylate E: Trimethylolpropane EO modified triacrylate F: Ethoxylated bisphenol A diacrylate (m+n=4) G: Ethoxylated bisphenol A diacrylate (m+n=6) The acrylic monomers B, C, F and G are represented by the following chemical formula (Chemical Formula 1). [ka]

[0037] In order to examine the change in the dispersion state of the fine particles, in Comparative Example 1, 0.1 mass% of polyethylene glycol was added as a flocculant to acrylic monomer A. In Example 8, 0.5 mass% of DISPERBYK-111 manufactured by BYK was added as a dispersant to acrylic monomer B, and in Example 11, 0.1 mass% of DISPERBYK-180 manufactured by BYK was added as a dispersant to acrylic monomer B.

[0038] The dispersion state of the particles in the optical filter according to the embodiment of the present invention is such that the parameter Ds given by Ds=λ / (B·cosθ·Ra), which is determined from the USAXS pattern, is 8.0 or more and 30 or less, where λ is the wavelength of the X-ray, θ is half the scattering angle 2θ (rad) that gives the peak of the scattering intensity, B is the half-width at half maximum (FWHM, rad) of the peak, and Ra is the average particle size of the particles.

[0039] The technical meaning of the parameter Ds will be explained with reference to Figure 2. Figure 2 is a schematic diagram for explaining the relationship between the dispersion state (degree of periodicity) of fine particles in a fine particle aggregate and the half-width of the peak of scattering intensity of USAXS. Figure 2 compares the well-known Scherrer formula used to estimate the relationship between the half-width of the X-ray diffraction peak and the size of the crystal grains (crystallites) of a polycrystalline body. The circles in the schematic diagram of the polycrystalline body in Figure 2 represent atoms, while the circles in the schematic diagram of the fine particle aggregate represent fine particles. To obtain information on the dispersion state of fine particles with a particle size of about 100 nm, it is necessary to analyze the X-ray scattering pattern in the ultra-small angle region.

[0040] The grain size of a polycrystal (an aggregate of microcrystals) can be estimated using the well-known Scherrer equation: D=K λ / (B cosθ)

[0041] Here, B is the broadening of the diffraction line width (half-width) due to the finite crystal grains, and the following equation (1) holds between the actually measured diffraction line width Bo bs and the line width broadening b due to the instrument. Bobs=B+b (1)

[0042] Additionally, D is the size of the crystal grain, λ is the wavelength of the X-rays, and θ is the Bragg angle (half the diffraction angle 2θ). The constant K is called the Scherrer constant, and its value varies depending on how the intensity is approximated and what measured quantity defines the spread B. The intensity of the diffraction peak increases and the linewidth narrows the more the structure with the period that gives the diffraction is repeated, that is, the larger the crystal grains are.

[0043] On the other hand, the intensity of the scattering peak (halo) of an aggregate of fine particles increases and the line width decreases as the spread of the fine particles distributed at a distance close to the average distance that gives the scattering angle increases. Focusing on a particular fine particle, the closer the distance to the average distance between that fine particle and its neighboring fine particles, and the more such fine particles there are, the greater the intensity of the scattering peak and the narrower the line width. Therefore, the parameter Ds, which represents the "spread of fine particles distributed at the average distance" in an aggregate of fine particles, is expressed as the relative size to the average particle diameter Ra of the fine particles, by the following formula (2). Ds = λ / (B cosθ Ra) (2)

[0044] Here, USAXS used the BL08B2 small-angle X-ray scattering station at Spring 8, so the parallelism of the X-rays was high, b in the above formula (1) could be ignored, and Bobs = B was used. The distance between the sample and the two-dimensional X-ray detector was 16 m (meters). CuKα rays (wavelength λ = 0.1542 nm) were used for the X-rays.

[0045] Figures 4, 5, 6 and 7 show the baseline-corrected measurement results of the USAXS patterns, while Figures 8, 9, 10 and 11 show the scattering intensities normalized by the maximum value. The parameter Ds calculated from the peaks of these scattering patterns using the above formula (2) is shown in Table 1. The horizontal axis in Figures 4 to 11 is the scattering vector q, and θ=sin -1 (qλ / 4π). Also, the half-width B (FWHM, rad) = sin -1 (B q λ / 4π). B q is the full width at half maximum (FWHM, nm -1 ).

[0046] The optical characteristics of the optical filter can be evaluated as follows.

[0047] As shown in FIG. 12, when incident light I0 is incident on the optical filter 10, a portion of the incident light I0 is transmitted through the optical filter 10 (transmitted light I i ), some of it is reflected at the interface (interface reflected light Ri ), and the other part is scattered. The scattered light includes forward scattered light S emitted in front of the optical filter 10. f and the backscattered light S emitted backwards b Backscattered light S b This gives the optical filter 10 a white color. A portion of the incident light I0 is absorbed by the optical filter 10, but the resin and silica particles used here have a low absorptivity for light in the range of 400 nm to 2000 nm.

[0048] Fig. 13 is a schematic diagram showing a method for measuring the diffuse transmittance of an optical filter, and Fig. 14 is a schematic diagram showing a method for measuring the linear transmittance of an optical filter. As shown in Fig. 13, the diffuse transmittance is measured by placing a sample (optical filter 10) at the opening of an integrating sphere 32 and measuring the transmitted light I i and forward scattered light S f The total intensity of the incident light I0 was calculated as a percentage of the intensity of the incident light I0. The 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 i The intensity of the incident light I0 was calculated as a percentage of the intensity of the incident light I0. The diameter of the aperture was 1.8 cm, which corresponds to a solid angle of 0.025 sr. The spectrometer used was an ultraviolet-visible-near infrared spectrophotometer UH4150 (manufactured by Hitachi High-Tech Science Corporation). Table 1 shows the linear transmittance values ​​for infrared rays of 760 nm, 950 nm, and 1500 nm. The linear transmittance spectra of each sample are shown in Figures 15, 16, 17, and 18. The presence or absence of Bragg reflection can be determined by the presence or absence of dimples (localized reduction in transmittance) in the linear transmittance spectrum.

[0049] Backscattered light S b The whiteness of the sample was measured using a spectrophotometer CM-2600-D (Konica Minolta Japan, Inc.). * The values ​​of x and y on the CIE 1931 chromaticity diagram were also calculated. * The larger 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.

[0050] [Table 1]

[0051] [Table 2]

[0052] As shown in Table 1, all of Examples 1 to 17 exhibit white color, and the x, y coordinates on the CIE 1931 chromaticity diagram of the color exhibited when the standard light is a D65 light source satisfy 0.25≦x≦0.40 and 0.25≦y≦0.40. * is 20 or greater.

[0053] In addition, all of Examples 1 to 17 have linear transmittance of 60% or more for light of at least a part of wavelengths in the wavelength range of 760 nm to 2000 nm. In particular, linear transmittance of 60% or more for light of wavelengths of 950 nm and 1500 nm. The linear transmittance spectrum shown above shows only up to 1500 nm, but the linear transmittance in the region of more than 1500 nm to 2000 nm or less is almost the same as the linear transmittance for light of 1500 nm, although there may be a slight local decrease.

[0054] FIG. 19 shows the value of the parameter Ds of each sample in a bar graph. The Ds values ​​of all Examples 1 to 17 are larger than the Ds value of Comparative Example 1, 7.7, and smaller than the Ds value of Comparative Example 2, 31.7. Comparative Example 1 with a Ds value of 7.7 and Comparative Example 2 with a Ds value of 7.4 have sufficient whiteness, but none of them have infrared linear transmittance reaching 60% in the range from 760 nm to 1500 nm, and do not have a sufficiently high infrared linear transmittance. On the other hand, Comparative Example 2 with a large Ds value of 31.7 has a sufficiently high infrared linear transmittance, but the whiteness is low. From these points of view, the Ds value is preferably 8.0 or more and 30 or less, and more preferably 8.2 or more and 22 or less. Since the infrared transmittance of Example 2 and Example 6, which have a Ds value of less than 10, is relatively low, from the viewpoint of infrared transmittance, the Ds value is preferably 10 or more, and more preferably 14 or more.

[0055] The reason why the whiteness of Comparative Example 2, which has a large Ds value of 31.7, is low is due to Bragg reflection. In the linear transmittance spectrum of Comparative Example 2 shown in FIG. 18, a steep dimple (reduction in transmittance) is seen near 650 nm. This indicates that light of this wavelength is reflected (Bragg reflection). Note that the linear transmittance spectra of Example 7 (FIG. 16), Example 16, and Example 17 (FIG. 17) also have dimples in the visible light region, but unlike the spectrum of Comparative Example 2, the spectra of Example 7 (FIG. 16), Example 16, and Example 17 have relatively low linear transmittance in the visible light region, and backscatter visible light of a wavelength shorter than the wavelength where the dimples exist. As a result, it is considered that the effect of Bragg reflection on the whiteness of the backscattered light is relatively suppressed. However, since Bragg reflection makes it appear colored when viewed from a specific direction, it is preferable that the fine particles form a colloidal amorphous aggregate in order to appear white from any angle.

[0056] Here, the relationship between the two-dimensional pattern of small-angle X-ray scattering and the value of Ds will be described with reference to Figs. 20A, 20B, and 20C. Fig. 20A shows the scattering pattern of Comparative Example 3 (Ds value of 7.4), Fig. 20B shows the scattering pattern of Example 12 (Ds value of 11.0), and Fig. 20C shows the scattering pattern of Comparative Example 4 (Ds value of 37.7). It can be seen that the scattering pattern of Comparative Example 3 in Fig. 20A is a very broad isotropic halo (see Figs. 7 and 11). On the other hand, the scattering pattern of Comparative Example 4 (photonic rubber) in Fig. 20C shows diffraction points at point-symmetric positions, and shows high periodicity. No diffraction points are seen in the scattering pattern of Example 12 in Fig. 20B, and the line width of the halo is narrower than that of the scattering pattern of Comparative Example 3 in Fig. 20A (see Figs. 5 and 9). It can be seen that a large Ds value indicates high periodicity, and a small Ds value indicates low periodicity.

[0057] Fig. 21 shows a cross-sectional TEM image of the optical filter 10A of Example 1, and Fig. 22 shows a cross-sectional TEM image of the optical filter 20A of Comparative Example 1. When the thickness of each film is d, the samples for TEM observation were obtained by cutting with a microtome at a position of d / 2 in the cross-sectional direction to obtain sample pieces of the same thickness as the average particle size of the silica microparticles. The white circles in the TEM images in the figures are silica microparticles, and the black circles are traces of silica microparticles that have fallen out.

[0058] In the cross section of the optical filter 10A shown in Fig. 21, the silica fine particles are almost uniformly dispersed, whereas in the cross section of the optical filter 20A shown in Fig. 22, the silica fine particles are partially aggregated. This is because, in addition to the acrylic monomer A, 0.1 mass % of polyethylene glycol was added as an aggregating agent relative to the acrylic monomer A when the optical filter 20A of Comparative Example 1 was produced. As a result, it is considered that the Ds value of Example 1 was 10.3, whereas the Ds value of Comparative Example 1 was 7.7, which is smaller.

[0059] In addition, no significant difference was observed between Example 8 in which a dispersion aid was added and Example 7 in which no dispersion aid was added, and it is considered that a sufficiently uniform dispersion state can be obtained without adding a dispersion aid at least up to a fine particle fraction of 50 mass% (38 volume%). On the other hand, when Example 11 in which a dispersion aid was added is compared with Example 10 in which no dispersion aid was added, the Ds value of Example 11 in which a dispersion aid was added is smaller. Therefore, it is suggested that it is not necessarily easy to obtain a uniform dispersion state. In addition, from these facts, it is considered that the Ds value can be an excellent index that sensitively reflects the difference in the dispersion state of fine particles.

[0060] Next, 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 described with reference to Figs. 23, 24, and 25. Fig. 23 is an example of a camera image acquired using a motion capture device, and is a camera image acquired without using a filter. Fig. 24 is an example of a camera image acquired using a motion capture device via the optical filter 10A of Example 1, and Fig. 25 is an example of a camera image acquired using a motion capture device via the optical filter 20A of Comparative Example 1.

[0061] Here, a Leap Motion Controller (registered trademark) was used as the motion capture device to capture a camera image of a hand located about 20 cm away. This device uses infrared rays with a wavelength of 850 nm. As is clear from a comparison of Figs. 23, 24, and 25, when the optical filter 10A of the embodiment was used (Fig. 24), an image as clear as that obtained when no filter was used (Fig. 23) was obtained, whereas when the optical filter 20A of the comparative example was used (Fig. 25), a clear image could not be obtained and the hand could not be recognized.

[0062] FIG. 26 shows an optical image of the optical filter 10A of Example 1, and FIG. 27 shows an 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 were arranged as films of about 5 cm x about 10 cm so as to cover the front of the device. As can be seen from FIG. 26 and FIG. 27, both films are white. Therefore, the optical filter 10A of Example 1 is suitably used as an infrared transmission filter, and has high designability because it is white. Of course, a color or pattern can be imparted to the surface of the optical filter 10A of Example 1 by printing or the like.

[0063] Since the optical filter according to the embodiment of the present invention can exhibit white color as described above, it is possible to obtain an optical filter with rich colors and rich design by printing, for example, characters, pictures, and photos on the surface of the optical filter using infrared transmitting ink. That is, the optical filter according to the embodiment of the present invention may have an optical filter layer containing a matrix and fine particles, and a print layer formed of infrared transmitting ink and 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 the infrared transmitting ink, a known infrared transmitting ink may be selected according to the application or the wavelength of the infrared light to be transmitted.

[0064] Furthermore, in the optical filter according to the embodiment of the present invention, the intensity of diffusely reflected light increases when viewed obliquely, so that the white luminance increases and the appearance of the design (visibility of the design) improves.

[0065] The optical filter according to the embodiment may be a planar film as exemplified, but may have various forms without being limited thereto. The optical filter according to the embodiment may have a three-dimensional shape. For example, it may be a film having a three-dimensional shape. Specifically, for example, the optical filter may be formed on the surface of an object having a three-dimensional shape by using a coating method. The surface of the object may have any shape, such as a part or all of a sphere, a curved surface of any shape, or a part or all of a surface of a polyhedron. However, it is preferable that the surface of the object does not cause light scattering.

[0066] For example, an optical filter formed in a hemispherical shape can be obtained as shown in Fig. 28A and Fig. 28B. Fig. 28A is a diagram showing an optical image (visible light) showing an optical filter formed in a hemispherical shape according to an embodiment, and Fig. 28B is a diagram showing an infrared image of the hemispherical optical filter shown in Fig. 28A according to an embodiment. The images shown in Fig. 28A and Fig. 28B were taken using a full high-vision digital movie camera DVSA10FHDIR manufactured by Kenko Tokina Co., Ltd. Fig. 28A is an image taken in visible light mode under white LED illumination, and Fig. 28B is an image taken in a darkroom using only the light of the infrared LED of the camera.

[0067] The optical filter shown in Figures 28A and 28B is an optical filter with a thickness of 300 μm, formed by applying the same material as in Example 5 by dip coating to the surface of a hemisphere made of acrylic resin (PMMA) with a radius of 2 cm and a thickness of 1 mm. As shown in Figure 28A, a hemispherical white filter was obtained. In addition, as shown in Figure 28B, this filter transmits infrared light.

[0068] The optical filter according to the embodiment of the present invention is not limited to the exemplified sensing devices (e.g., infrared cameras) and communication devices, but can be used for various purposes. For example, the optical filter can be suitably used for solar cells, heaters using infrared rays, and optically powered devices using infrared rays. [Industrial Applicability]

[0069] Optical filters according to embodiments of the present invention can be used, for example, as infrared transmission filters for use in sensor technology or communication technology. [Explanation of symbols]

[0070] 10, 10A, 20A: Optical filters 12: Matrix 14: Fine particles

Claims

1. An optical filter including a matrix and particles dispersed in the matrix, The optical filter has a parameter Ds of 8.0 or more and 30 or less, which is determined from a USAXS pattern and is given by Ds = λ / (B cos θ Ra), where λ is the wavelength of X-rays, θ is half the scattering angle 2θ (rad) giving the peak of the scattering intensity, B is the half-width of the peak (FWHM, rad), and Ra is the average particle size of the fine particles, and exhibits a white color.

2. 2. The optical filter according to claim 1, wherein the x, y coordinates of the color exhibited on the CIE 1931 chromaticity diagram when a D65 light source is used as standard light are 0.25≦x≦0.40 and 0.25≦y≦0.

40.

3. 3. The optical filter according to claim 1, wherein the L* value measured by the SCE method using a spectrophotometer is 20 or more.

4. 4. The optical filter according to claim 1, which has an in-line transmittance of 60% or more for light having at least a part of a wavelength within a wavelength range of 760 nm or more and 2000 nm or less.

5. 5. The optical filter according to claim 4, which has an in-line transmittance of 60% or more for light having a wavelength of 950 nm.

6. 6. The optical filter according to claim 4, which has an in-line transmittance of 60% or more for light having a wavelength of 1500 nm.

7. 7. The optical filter according to claim 1, wherein the fine particles include monodisperse first fine particles having an average particle size within a range of 80 nm to 300 nm.

8. The optical filter according to claim 7 , wherein the first fine particles have an average particle size of 150 nm or more.

9. 9. The optical filter according to claim 1, wherein the fine particles form at least a colloidal amorphous aggregate.

10. 10. The optical filter according to claim 1, wherein a volume fraction of the fine particles is 6% or more and 60% or less.

11. The refractive index of the matrix for light having a wavelength of 546 nm is n Ｍ The refractive index of the fine particles is n Ｐ Then, |n Ｍ -n Ｐ The optical filter according to claim 1 , wherein | is 0.03 or more and 0.6 or less.

12. The optical filter of claim 1 having a three-dimensional shape.

13. The optical filter according to claim 1 , wherein the matrix is ​​made of a resin, and the fine particles are made of an inorganic material.

14. A method for producing an optical filter according to claim 13, comprising the steps of: preparing a curable resin composition by dispersing and mixing the fine particles in a curable resin; applying the curable resin composition to a surface of a substrate; curing the curable resin contained in the curable resin composition applied to the surface; The manufacturing method includes the steps of:

15. The method according to claim 14 , wherein the applying step is carried out by a coating method.

16. The method according to claim 15 , wherein the applying step is carried out by a dip coating method.

17. A device having an infrared receiver; The optical filter according to claim 1 , which is disposed in front of the infrared receiving unit of the device; An optical module having

18. The optical module of claim 17 , wherein the device is a sensing device, a communication device, a solar cell, a heater, or a power supply device.

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