Optical filters, detection devices, and optical laminates

Abstract

To provide an optical filter capable of reducing heat generated by absorbing visible light while reducing glare when detecting an object with infrared light.SOLUTION: In the optical filter, when visible light with a wavelength of 550 nm is incident at an angle of incidence of 0°, the BRDF (bidirectional reflectance distribution function) is 0.1 [1 / sr] or more at angles between -30° and -5° and between 5° and 30°, and in the BTDF (bidirectional transmittance distribution function) when infrared light with a wavelength of 850 nm is incident at an angle of incidence of 0°, (value at -1°) / (value at -10°) and (value at 1°) / (value at 10°) are 30 or less.SELECTED DRAWING: Figure 12D

Description

[Technical Field]

[0001] The present invention relates to an optical filter, a detection device utilizing the same, and an optical laminate. [Background technology]

[0002] In infrared-based object detection, an infrared light source that emits infrared light to illuminate an object and an infrared sensor that detects the infrared light reflected by the object are used (for example, Patent Document 1). Due to appearance and design concerns, it is sometimes necessary to conceal the infrared light source and infrared sensor so that they are not visible.

[0003] The objects to be concealed are not limited to infrared light sources and infrared sensors. In recent years, AR (Augmented Reality) markers such as barcodes, QR codes (registered trademarks), ArUco, and Chameleon Code have been used in various applications (see, for example, Patent Document 2). Due to appearance and design issues, it is sometimes necessary to conceal AR markers so that they cannot be seen. The AR markers are assumed to be readable by infrared light.

[0004] To achieve the above concealment, for example, an optical filter containing the black pigment described in Patent Document 3 could be used. The black pigment in Patent Document 3 absorbs visible light and transmits infrared light. By using this optical filter containing the black pigment, in object detection using infrared light, the infrared light source and infrared sensor can be concealed, the object can be irradiated with infrared light emitted from the infrared light source, and the infrared light reflected by the object can be detected by the infrared sensor. Furthermore, the AR marker can be concealed, and the AR marker can be read using infrared light.

[0005] In this specification, unless otherwise specified, "infrared light" shall include at least light with a wavelength in the range of 780 nm to 4000 nm. "Visible light" shall refer to light with a wavelength in the range of 380 nm to less than 780 nm. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Special Publication No. 2019-524602 [Patent Document 2] Japanese Patent Publication No. 2016-224485 [Patent Document 3] Japanese Patent Publication No. 2019-207303 [Overview of the project] [Problems that the invention aims to solve]

[0007] The black pigment described in Patent Document 3 absorbs visible light, which may generate heat in the optical filter. This heat generated in the optical filter may adversely affect the object being concealed. Furthermore, since the black pigment described in Patent Document 3 transmits infrared light with high linear transmittance, if an object is detected by infrared light through an optical filter containing this black pigment, glare may occur if the infrared light reflected by the object contains a large amount of linear reflection.

[0008] The present invention was made to solve the above problems, and aims to provide an optical filter that can reduce heat generation due to the absorption of visible light and reduce glare when detecting objects with infrared light, as well as a detection device and an optical laminate that utilize the same. [Means for solving the problem]

[0009] According to embodiments of the present invention, the following solutions are provided. [Item 1] Wavelength 550n m The BRDF (bidirectional reflectance distribution function) when visible light is incident at an incident angle of 0° is for angles between -30° and -5° and between 5° and 30°. below At this angle, it is 0.1[1 / sr] or greater, Wavelength 850n mIn the BTDF (Bidirectional Transmittance Distribution Function) when infrared rays enter at an incident angle of 0°, the values of (- value at -1°) / (- value at -10°) and (value at 1°) / (value at 10°) are 30 or less. An optical filter. [Item 2] The optical filter according to claim 1, wherein the values of (- value at -1°) / (- value at -10°) and (value at 1°) / (value at 10°) are 25 or less. [Item 3] The optical filter according to item 1 or 2, wherein the BTDF is 50 [1 / sr] or less at an angle of -5° or more and 5° or less. [Item 4] The optical filter according to any one of items 1 to 3, wherein the average value of the diffuse transmittance in the wavelength range of 800 nm or more and 2000 nm or less is 35% or more. [Item 5] The optical filter according to any one of items 1 to 4, comprising an optical layer that backscatters visible light and forward-scatters infrared rays, and the optical layer has a scattering surface that forward-scatters infrared rays. [Item 6] The optical filter according to item 5, wherein the arithmetic mean roughness Ra of the scattering surface is 1 μm or more, and the maximum height Rz is 15 μm or more. [Item 7] An optical layer that backscatters visible light and allows infrared rays to transmit linearly, A scattering layer that is disposed directly on the optical layer or via another layer and forward-scatters infrared rays, [[ID=2-eight]]And the optical filter according to any one of items 1 to 4. [[ID=2-nine]] [Item 8] The optical filter according to any one of items 1 to 7, wherein the average value of the haze value of the optical filter in the wavelength range of 800 nm or more and 2000 nm or less is 40% or more. [Item 9] The L of the optical layer measured by the SCE (specular component excluded) method using a spectrocolorimeter * The value of which is 20 or more. The optical filter according to any one of items 5 to 7. [Item 10] The optical filter according to any one of items 5 to 9, wherein the optical layer comprises a matrix and fine particles dispersed in the matrix that serve as light scatterers. [Item 11] The optical filter according to item 10, wherein the fine particles constitute at least a colloidal amorphous aggregate. [Item 12] The optical filter according to item 11, wherein the transmittance curve of the optical layer in the visible light wavelength region has a curve portion in which the linear transmittance decreases monotonically from the longer wavelength side to the shorter wavelength side, and the curve portion shifts to the longer wavelength side as the angle of incidence increases. [Item 13] A detection device for detecting objects, An infrared light source that emits infrared rays for irradiating the aforementioned object, An infrared sensor that detects infrared radiation reflected by the aforementioned object, An optical filter according to any one of items 1 to 12, comprising an optical filter arranged to cross the infrared light emitted from the infrared light source, A detection device equipped with the following features. [Item 14] An optical filter according to any one of items 1 to 12, comprising an optical filter having a first main surface and a second main surface opposite to the first main surface, A recording medium layer is disposed on the second main surface side of the optical filter and has a pattern that can be read by infrared light through the optical filter, An optical laminate comprising the above features. [Effects of the Invention]

[0010] According to embodiments of the present invention, an optical filter capable of reducing heat generation due to the absorption of visible light and reducing glare when detecting an object with infrared light is provided, as well as a detection device and an optical laminate utilizing the same. [Brief explanation of the drawing]

[0011] [Figure 1A] This is a schematic cross-sectional view of a detection device according to an exemplary embodiment of the present invention. [Figure 1B] This is another schematic cross-sectional view of a detection device according to an exemplary embodiment of the present invention. [Figure 2A] This is a schematic cross-sectional view of an optical laminate according to an exemplary embodiment of the present invention. [Figure 2B] This is another schematic cross-sectional view of an optical laminate according to an exemplary embodiment of the present invention. [Figure 3A] This is a schematic cross-sectional view of an optical filter according to an exemplary embodiment of the present invention. [Figure 3B] This is a schematic cross-sectional view of an optical filter according to another exemplary embodiment of the present invention. [Figure 3C] This is a schematic cross-sectional view of an optical filter according to yet another embodiment of the present invention. [Figure 3D] This is a schematic cross-sectional view of an optical filter according to yet another embodiment of the present invention. [Figure 4] This is a schematic cross-sectional view of the inside of the optical layer contained in an optical filter. [Figure 5] This is a cross-sectional TEM image of the visible light scattering layer. [Figure 6] This graph, normalized by maximum transmittance, shows the dependence of the linear transmittance spectrum of the visible light scattering layer on the incident angle. [Figure 7A] This is a schematic diagram illustrating an example of a design with a continuous pattern. [Figure 7B] This is a schematic diagram showing another example of a continuous pattern design. [Figure 7C] This is a schematic diagram illustrating an example of a tile-like design. [Figure 7D] This is a schematic diagram showing another example of a tile-like design. [Figure 8A] This is a schematic cross-sectional view illustrating the BRDF measurement method. [Figure 8B] This is a schematic cross-sectional view illustrating the method for measuring BTDF. [Figure 9A] This is a cross-sectional TEM image of the optical filter of Example 3. [Figure 9B] This is a cross-sectional TEM image of the optical filter of Example 6. [Figure 10A]These are the BRDFs of the optical filters in Comparative Examples 1 to 4 when visible light with a wavelength of 550 nm is incident at an incident angle of 0°. [Figure 10B] The BTDF of the optical filters in Comparative Examples 1 to 4 is calculated when visible light with a wavelength of 550 nm is incident at an incident angle of 0°. [Figure 10C] These are the BRDFs of the optical filters in Comparative Examples 1 to 4 when infrared light with a wavelength of 850 nm is incident at an incident angle of 0°. [Figure 10D] The BTDF of the optical filters in Comparative Examples 1 to 4 is calculated when infrared light with a wavelength of 850 nm is incident at an incident angle of 0°. [Figure 11A] These are the BRDFs of the optical filters in Examples 1 and 2 when visible light with a wavelength of 550 nm is incident at an incident angle of 0°. [Figure 11B] This is the BTDF of the optical filters in Examples 1 and 2 when visible light with a wavelength of 550 nm is incident at an incident angle of 0°. [Figure 11C] This is the BRDF of the optical filters in Examples 1 and 2 when infrared light with a wavelength of 850 nm is incident at an incident angle of 0°. [Figure 11D] This is the BTDF of the optical filters in Examples 1 and 2 when infrared light with a wavelength of 850 nm is incident at an incident angle of 0°. [Figure 12A] This is the BRDF of the optical filters of Examples 3 to 6 when visible light with a wavelength of 550 nm is incident at an incident angle of 0°. [Figure 12B] This is the BTDF of the optical filters of Examples 3 to 6 when visible light with a wavelength of 550 nm is incident at an incident angle of 0°. [Figure 12C] This is the BRDF of the optical filters of Examples 3 to 6 when infrared light with a wavelength of 850 nm is incident at an incident angle of 0°. [Figure 12D] This is the BTDF of the optical filters of Examples 3 to 6 when infrared light with a wavelength of 850 nm is incident at an incident angle of 0°. [Modes for carrying out the invention]

[0012] (Embodiment) In the following, with reference to the drawings, a detection device and optical laminate utilizing an optical filter according to an embodiment of the present invention will be described first, followed by a detailed description of the structure of the optical filter according to an embodiment of the present invention. Finally, an example of the optical filter will be described. Optical filter according to an embodiment of the present invention, and detection device and optical laminate according to an embodiment of the present invention. body This is not limited to the examples given below.

[0013] According to the optical filter of the embodiment of the present invention, the wavelength is 550n m The BRDF (bidirectional reflectance distribution function) when visible light is incident at an incident angle of 0° is for angles between -30° and -5° and between 5° and 30°. below The angle is 0.1 [1 / sr] or greater, and the wavelength is 850n m When infrared radiation is incident at an incident angle of 0°, the BTDF (bidirectional transmittance distribution function) is such that (value at -1°) / (value at -10°) and (value at 1°) / (value at 10°) are 30 or less.

[0014] The optical filter according to the embodiment of the present invention makes it possible to reduce heat generation due to the absorption of visible light and to reduce glare when detecting objects with infrared light.

[0015] An object detection device according to an embodiment of the present invention comprises an infrared light source that emits infrared rays for illuminating the object, an infrared sensor that detects infrared rays reflected by the object, and the optical filter described above, which is arranged to cross the infrared rays emitted from the infrared light source.

[0016] In the light detection device according to the embodiment of the present invention, the optical filter can reduce the possibility of the infrared light source and infrared sensor being visible.

[0017] An optical laminate according to an embodiment of the present invention comprises an optical filter having a first main surface and a second main surface opposite to the first main surface, and a recording medium layer disposed on the second main surface side of the optical filter and having a pattern readable by infrared light through the optical filter.

[0018] In the optical laminate according to the embodiment of the present invention, the optical filter can reduce the possibility of the pattern of the recording medium layer being visible.

[0019] [Detection device] First, with reference to Figures 1A and 1B, an example of the configuration of a detection device utilizing an optical filter according to an embodiment of the present invention will be described.

[0020] Figure 1A shows a schematic cross-sectional view of a detection device according to an exemplary embodiment of the present invention. Figure 1A also shows the object 10 to be detected. The object 10 is any object, for example, a person or a product carried by a conveyor belt. The detection device 100 shown in Figure 1A comprises an infrared light source 110, an infrared sensor 120, an optical filter 130, and a housing 140 that houses the infrared light source 110 and the infrared sensor 120.

[0021] The infrared light source 110 may be, for example, an infrared lamp or infrared LED that emits infrared light. The infrared sensor 120 may be, for example, an image sensor that acquires an infrared image. The optical filter 130 has a first main surface 132 and a second main surface 134 on the opposite side. The optical filter 130 forward scatters infrared light incident on the first main surface 132 or the second main surface 134 and backscatters visible light incident on the first main surface 132 or the second main surface 134. The detailed structure of the optical filter 130 and the evaluation of its scattering characteristics by BRDF and BTDF will be described later. Object 10 is located on the first main surface 132 side of the optical filter 130, and the infrared light source 110 and infrared sensor 120 are located on the second main surface 134 side of the optical filter 130. The housing 140 has a box shape with one side open, and the open opening 142 is covered by the optical filter 130.

[0022] The housing 140 is not an essential component of the detection device 100. For example, if the detection device 100 is installed as part of the ceiling, wall, or floor, that is, if the infrared light source 110 and infrared sensor 120 are installed inside the ceiling, wall, or floor and the optical filter 130 covers them, the detection device 100 does not need to have a housing 140.

[0023] In the detection device 100 according to an embodiment of the present invention, the object 10 is detected as follows. The infrared light source 110 emits infrared IR1 for illuminating the object 10 via the optical filter 130. The wavelength of the infrared IR1 is, for example, 780 nm to 4000 nm, and preferably 780 nm to 2500 nm. The infrared sensor 120 detects the infrared IR2 reflected by the object 10 via the optical filter 130. The optical filter 130 is positioned to cross the infrared IR1 emitted from the infrared light source 110. The optical filter 130 forward scatters the infrared IR1 incident on the second main surface 134, and the forward-scattered infrared IR1 is incident on the object 10. The optical filter 130 further forward scatters the infrared IR2 reflected by the object 10 and incident on the first main surface 132, and the forward-scattered infrared IR2 is incident on the infrared sensor 120.

[0024] Unlike the detection device 100 according to the embodiment of the present invention, in a configuration using an optical filter that linearly transmits infrared light, the infrared light emitted from the infrared light source 110 and incident on the infrared sensor 120 via the object 10 contains a large component of linear reflection from the object 10. Therefore, when such infrared light is detected, glare may occur due to the linear reflection component from the object 10, making it impossible to clearly detect the object 10.

[0025] In contrast, in the detection device 100 according to an embodiment of the present invention, infrared light emitted from the infrared light source 110 and incident on the infrared sensor 120 via the object 10 is forward-scattered twice by the optical filter 130. Since the object 10 is irradiated with the forward-scattered infrared light IR1, the component of linear reflection from the object 10 can be reduced. In addition, since the infrared light IR2 that is reflected by the object 10 and forward-scattered is detected, the component of linear reflection from the object 10 can be further reduced. As a result, glare when detecting the object 10 with infrared light IR1 can be effectively reduced, and the object 10 can be detected more clearly. In the detection of the object 10 by the detection device 100, the distance from the detection device 100 to the object 10 may be measured using the time-of-flight method.

[0026] Figure 1B shows another schematic cross-sectional view of the detection device 100 according to an exemplary embodiment of the present invention. The optical filter 130 receives visible light incident on the first main surface 132. VL It is backscattered. Due to backscattering by the optical filter 130, visible light VL This reduces the amount of light reaching the infrared light source 110 and the infrared sensor 120. VL Even if some of the visible light enters the infrared light source 110 and infrared sensor 120, it is reflected by the infrared light source 110 and infrared sensor 120, and the visible light that enters the second main surface 134 is backscattered by the optical filter 130. Therefore, the possibility of the infrared light source 110 and infrared sensor 120 being visible from the first main surface 132 side of the optical filter 130 can be reduced. If the object 10 shown in Figure 1A is a person, the possibility that the person's behavior or actions may change due to psychological changes caused by the visibility of the infrared light source 110 and infrared sensor 120 can be effectively reduced.

[0027] Unlike the detection device 100 according to the embodiment of the present invention, a configuration using an optical filter that absorbs visible light may generate heat in the optical filter. The heat generated in the optical filter may adversely affect the infrared light source 110 and the infrared sensor 120. In contrast, in the detection device 100 according to the embodiment of the present invention, the optical filter 130 backscatters visible light VL, thus reducing the heat generated due to the absorption of visible light VL.

[0028] The optical filter 130, as will be explained in detail later, has a white optical layer, unlike dielectric multilayer films which have a mirror-like appearance. The L* value of the optical layer, measured using the SCE method in the CIE1976 color space, is 20 or higher.

[0029] A white optical layer reduces the possibility of the infrared light source 110 and infrared sensor 120 being visible from the outside, and improves the design freedom of the detection device 100. When a design is added to a mirror-like surface, the mirror-like background may stand out more than the design. In contrast, when a design is added to a white surface, the design can stand out more than the white background. In this specification, "design" means the pattern or color of an article. Patterns include pictures or designs. Colors may be monochromatic or may include combinations of colors with the same hue but different saturations. Colors, pictures, or designs may be tile-like.

[0030] As described above, in the detection device 100 according to this embodiment, the optical filter 130 reduces the possibility of the infrared light source 110 and infrared sensor 120 being visible. Furthermore, it reduces the heat generated by the optical filter 130 due to the absorption of visible light VL, and also reduces glare when detecting the object 10 with infrared IR1.

[0031] Alternatively, a configuration in which the infrared sensor 120 is removed from the detection device 100 may be used as a light source device. In this light source device, the object 10 is illuminated with forward-scattered infrared rays IR1, thus reducing the linear reflection component from the object 10. Alternatively, a configuration in which the infrared light source 110 is removed from the detection device 100 may be used as a sensor device. In this sensor device, the infrared rays IR2 reflected by the object 10 and forward-scattered are detected, thus reducing the linear reflection component from the object 10. Both the light source device and the sensor device are useful for clearly detecting the object 10 using infrared rays.

[0032] [Optical laminate] The objects to be concealed are not limited to the infrared light source 110 and the infrared sensor 120. Next, with reference to Figures 2A and 2B, an example of the configuration of an optical laminate utilizing an optical filter according to an embodiment of the present invention will be described.

[0033] Figure 2A shows a schematic cross-sectional view of an optical laminate according to an exemplary embodiment of the present invention. The optical laminate 200 shown in Figure 2A comprises the optical filter 130 described above and a recording medium layer 150 having a pattern that can be read by infrared light through the optical filter 130. Figure 2A also shows an infrared light source 110 and an infrared sensor 120 used to read the pattern of the recording medium layer 150. The infrared light source 110 and infrared sensor 120 are located on the first main surface 132 side of the optical filter 130, and the recording medium layer 150 is located on the second main surface 134 side of the optical filter 130. In the example shown in Figure 2A, the pattern of the recording medium layer 150 is a QR code, which is a type of AR marker. The pattern of the recording medium layer 150 may be a pattern containing information, such as an AR marker, or it may be a general design. The optical laminate 200 may be installed, for example, as part of a ceiling, wall, or floor.

[0034] In the optical laminate 200 according to an embodiment of the present invention, the pattern of the recording medium layer 150 is read as follows. The infrared light source 110 emits infrared IR1 via the optical filter 130 to illuminate the pattern of the recording medium layer 150. The infrared sensor 120 detects the infrared IR2 reflected by the recording medium layer 150 via the optical filter 130. The optical filter 130 forward scatters the infrared IR1 incident on the first main surface 132. The forward-scattered infrared IR1 is incident on the recording medium layer 150. The optical filter 130 further forward scatters the infrared IR2 that is reflected by the recording medium layer 150 and incident on the second main surface 134. The forward-scattered infrared IR2 is incident on the infrared sensor 120.

[0035] Unlike the optical laminate 200 according to the embodiment of the present invention, in a configuration using an optical filter that linearly transmits infrared light, the infrared light emitted from the infrared light source 110 and incident on the infrared sensor 120 via the recording medium layer 150 contains a large component of linear reflection from the recording medium layer 150. Therefore, when such infrared light is detected, glare may occur due to the linear reflection component from the recording medium layer 150, making it difficult to clearly detect the pattern of the recording medium layer 150.

[0036] In contrast, in the optical laminate 200 according to the embodiment of the present invention, the infrared light emitted from the infrared light source 110 and incident on the infrared sensor 120 via the recording medium layer 150 is scattered forward twice by the optical filter 130, so that the linear reflection component from the recording medium layer 150 can be effectively reduced. As a result, glare when detecting the pattern of the recording medium layer 150 with infrared IR1 can be reduced, and the pattern of the recording medium layer 150 can be detected more clearly.

[0037] Figure 2B shows another schematic cross-sectional view of an optical laminate according to an exemplary embodiment of the present invention. The optical filter 130 receives visible light incident on the first main surface 132. VL It is backscattered. Due to backscattering by the optical filter 130, visible light VL This reduces the amount of light reaching the recording medium layer 150. VL Even if some of the light enters the recording medium layer 150, the visible light reflected by the recording medium layer 150 is backscattered by the optical filter 130. Therefore, the possibility of the recording medium layer 150 being visible from the first main surface 132 side of the optical filter 130 can be reduced.

[0038] Unlike the optical laminate 200 according to the embodiment of the present invention, in a configuration using an optical filter that absorbs visible light, heat may be generated by the optical filter. The heat generated by the optical filter may adversely affect the pattern of the recording medium layer 150. In contrast, in the optical laminate 200 according to the embodiment of the present invention, the optical filter 130 backscatters visible light VL, so the heat generated due to the absorption of visible light VL can be reduced.

[0039] As described above, the optical filter 130 has a white optical layer. The white optical layer reduces the possibility of the pattern of the recording medium layer 150 being visible from the outside and improves the design freedom of the optical laminate 200.

[0040] As described above, in the optical laminate 200 according to this embodiment, the optical filter 130 can reduce the possibility of the pattern of the recording medium layer 150 being visible. Furthermore, it is possible to reduce the heat generated by the optical filter 130 due to the absorption of visible light VL, and to reduce glare when detecting the pattern of the recording medium layer 150 with infrared IR1.

[0041] Furthermore, the objects that the optical filter 130 can conceal are not limited to the patterns of the infrared light source 110 and infrared sensor 120 included in the detection device 100, or the recording medium layer 150 included in the optical laminate 200, but can be any object.

[0042] [Structure of optical filters] Next, the structure of an optical filter according to an embodiment of the present invention will be described in detail with reference to Figures 3A to 3D.

[0043] Figure 3 A Figure 3 shows a schematic cross-sectional view of an optical filter according to an exemplary embodiment of the present invention. A The optical filter 130 shown in Figure 3 comprises an optical layer 130A that backscatters visible light and linearly transmits infrared light, a scattering layer 130B disposed on the optical layer 130A and forward-scattering infrared light, and a substrate layer 130C that supports the optical layer 130A. The scattering layer 130B does not need to forward-scatter or backscatter visible light. The scattering layer 130B may be disposed directly on the optical layer 130A or on the optical layer 130A via another layer. The scattering layer 130B may be, for example, an anti-glare layer or a layer formed from an adhesive containing a scattering component. AThe haze value of the optical filter 130 shown is, for example, 40% or more, and more preferably 60% or more. Here, the haze value for infrared radiation is the average value of the haze value at wavelengths between 800 nm and 2000 nm.

[0044] In the optical filter 130 shown in Figure 3A, the first main surface 132 shown in Figures 1A to 2B is the surface of the scattering layer 130B opposite to the optical layer 130A, and the second main surface 134 is the surface of the substrate layer 130C opposite to the optical layer 130A. The first main surface 132 and the second main surface 134 may be reversed.

[0045] In the optical filter 130 shown in Figure 3A, infrared light incident from the scattering layer 130B side is forward-scattered by the scattering layer 130B and transmitted through the optical layer 130A and the substrate layer 130C in that order. Infrared light incident from the substrate layer 130C side is transmitted through the substrate layer 130C and the optical layer 130A in that order and is forward-scattered by the scattering layer 130B. Visible light incident from the scattering layer 130B side is transmitted through the scattering layer 130B, back-scattered by the optical layer 130A, and transmitted through the scattering layer 130B again. Visible light incident from the substrate layer 130C side is transmitted through the substrate layer 130C, back-scattered by the optical layer 130A, and transmitted through the substrate layer 130C again. In this way, the optical filter 130 shown in Figure 3A back-scatters visible light and forward-scatters infrared light.

[0046] Figure 3B shows a schematic cross-sectional view of an optical filter according to another exemplary embodiment of the present invention. The optical filter 130 shown in Figure 3B comprises an optical layer 130D that backscatters visible light and forward scatters infrared light, and a substrate layer 130C that supports the optical layer 130D. The optical layer 130D has a scattering surface 132D that forward scatters infrared light. The scattering surface 132D does not need to forward or backscatter visible light. Unlike the optical layer 130D, an optical layer having a flat surface instead of a scattering surface 132D corresponds to the optical layer 130A shown in Figure 3A, which backscatters visible light and linearly transmits infrared light. The scattering surface 132D can be formed, for example, by transferring the uneven shape of an uneven member to the flat surface of the optical layer 130A, or by sandblasting. The arithmetic mean roughness Ra of the scattering surface 132D is, for example, 1 It is greater than or equal to μm, and the maximum height Rz is, for example, 15 The haze value may be greater than or equal to μm. The haze value of the optical filter 130 shown in Figure 3B for infrared radiation is, for example, 40% or more, more preferably 60% or more, and even more preferably 80% or more. Here, the haze value for infrared radiation is the average value of the haze value at wavelengths of 800 nm to 2000 nm.

[0047] In the optical filter 130 shown in Figure 3B, the first main surface 132 shown in Figures 1A to 2B is the scattering surface 132D of the optical layer 130D, and the second main surface 134 is the surface of the substrate layer 130C opposite to the optical layer 130D. The first main surface 132 and the second main surface 134 may be reversed.

[0048] In the optical filter 130 shown in Figure 3B, infrared light incident from the optical layer 130D side is forward-scattered by the scattering surface 132D and transmitted through the optical layer 130D and the substrate layer 130C in that order. Infrared light incident from the substrate layer 130C side is transmitted through the substrate layer 130C and the optical layer 130D in that order and is forward-scattered by the scattering surface 132D. Visible light incident from the optical layer 130D side is back-scattered by the optical layer 130D. Visible light incident from the substrate layer 130C side is transmitted through the substrate layer 130C, back-scattered by the optical layer 130D, and transmitted through the substrate layer 130C again. In this way, the optical filter 130 shown in Figure 3B back-scatters visible light and forward-scatters infrared light.

[0049] Typically, a scattering layer or scattering surface scatters visible light forward or backward to reduce glare when viewed. In contrast, the scattering layer 130B or scattering surface 132D included in the optical filter 130 according to the embodiment of the present invention scatters infrared light forward. The optical filter 130 according to the embodiment of the present invention is superior to an optical filter that linearly transmits infrared light in that the scattering layer 130B or scattering surface 132D can reduce glare when detecting the pattern of the object 10 or the recording medium layer 150 with infrared light IR1.

[0050] The optical filter 130 according to an embodiment of the present invention may further comprise other layers. Figures 3C and 3D show schematic cross-sectional views of optical filters according to yet another embodiment of the present invention. The optical filter 130 shown in Figure 3C comprises, in addition to the optical layer 130A, scattering layer 130B, and substrate layer 130C shown in Figure 3A, a design layer 130E disposed on the scattering layer 130B. The optical filter 130 shown in Figure 3D comprises, in addition to the optical layer 130D and substrate layer 130C shown in Figure 3B, a design layer 130E disposed on the optical layer 130D.

[0051] The design layer 130E preferably has a high infrared transmittance. The design layer 130E may be in the form of a film, such as a decorative film, or it may not be in the form of a film. The thickness of the design layer 130E is, for example, 1 μm or more and 150 μm or less. In this specification, if the surface of the layer is not flat, the maximum thickness of the layer is treated as the thickness of the layer.

[0052] The optical filter 130 according to an embodiment of the present invention may further comprise other functional layers that perform specific functions. In this case, a single functional layer may perform two or more functions, and at least one of the layers described above may be given other functions. The functions that can be provided to the optical filter 130 are not particularly limited, but the optical filter 130 according to an embodiment of the present invention further comprises a surface protection layer 130F disposed on the design layer 130E, as shown in Figures 3C and 3D. The surface protection layer 130F is configured to perform, for example, a hard coating (HC) function that provides scratch resistance, an anti-fouling function, an anti-glare (AG) function, or an anti-reflection (AR) function.

[0053] In the optical filter 130 shown in Figures 3C and 3D, the first main surface 132 shown in Figures 1A to 2B is the surface of the surface protective layer 130F opposite to the design layer 130E, and the second main surface 134 is the surface of the base layer 130C opposite to the optical layers 130A and 130D.

[0054] The optical filter 130 according to an embodiment of the present invention also functions as a cover for the detection device 100 and the optical laminate 200. The substrate layer 130C included in the optical filter 130 has mechanical strength as a cover and high infrared transmittance. The substrate layer 130C may be formed of a transparent plastic such as acrylic resin. The substrate layer 130C may also include a dielectric multilayer film having a mirror-like appearance to improve visibility suppression in visible light. The thickness of the substrate layer 130C is, for example, about 2 μm or more and about 10 mm or less.

[0055] The optical layers 130A and 130D included in the optical filter 130 according to the embodiment of the present invention exhibit a white color. Here, white refers to a color where the x and y coordinates on the CIE1931 chromaticity diagram, when the standard light source is a D65 light source, are within the ranges of 0.25≦x≦0.40 and 0.25≦y≦0.40, respectively. Of course, the closer 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. Furthermore, the L* measured using the SCE method in the CIE1976 color space is preferably 20 or higher, more preferably 40 or higher, even more preferably 50 or higher, and particularly preferably 60 or higher. If L* is 20 or higher, it can generally be said to be white. The upper limit of L* is, for example, 100. For example, measurements using the SCE method can be performed using a spectrophotometer CM-2600-D (manufactured by Konica Minolta Japan, Inc.).

[0056] The L* value of optical layers 130A and 130D can be adjusted by changing the thickness of optical layers 130A and 130D. The greater the thickness of optical layers 130A and 130D, the greater the L* value of optical layers 130A and 130D.

[0057] Figure 4 shows a schematic cross-sectional view of the interior of the optical layers 130A and 130D contained in the optical filter 130. The optical layers 130A and 130D have a matrix 12 and fine particles 14 that act as light scatterers dispersed in the matrix 12. The fine particles 14 behave as light scatterers. The fine particles 14 may, for example, constitute at least a colloidal amorphous aggregate. In this case, other fine particles that do not disturb the colloidal amorphous aggregate composed of the fine particles 14 may also be included.

[0058] Optical layers 130A and 130D do not contain cholesteric liquid crystals (a broad category including polymer liquid crystals, low molecular weight liquid crystals, mixtures thereof, and materials obtained by mixing and crosslinking these liquid crystal materials with a crosslinking agent and solidifying them, thereby exhibiting a cholesteric phase). Optical layers 130A and 130D are, for example, generally in the form of films, but are not limited to this.

[0059] 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 process can be used. Alternatively, inorganic fine particles other than silica fine particles may be used as the fine particles, and resin fine particles may also be used. As resin fine particles, for example, fine particles consisting of at least one of polystyrene and polymethyl methacrylate are preferred, and fine particles consisting of crosslinked polystyrene, crosslinked polymethyl methacrylate, or crosslinked styrene-methyl methacrylate copolymer are more preferred. As such fine particles, for example, polystyrene fine particles or polymethyl methacrylate fine particles synthesized by emulsion polymerization can be used as appropriate. In addition, hollow silica fine particles and hollow resin fine particles containing air can also be used. Fine particles formed from inorganic materials have the advantage of excellent heat resistance and light resistance. The volume fraction of the fine particles to the total (including the matrix and fine particles) is preferably 6% to 60%, more preferably 20% to 50%, and even more preferably 20% to 40%. The transparent fine particles 14 may have optical isotropy.

[0060] The matrix 12 can be, but is 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 from the viewpoint of mass production, it is preferable to form it using a photocurable resin. Various (meth)acrylates can be used as the photocurable resin. The (meth)acrylate preferably contains bifunctional or trifunctional or more (meth)acrylates. Furthermore, it is preferable that the matrix 12 has optical isotropy. If a curable resin containing polyfunctional monomers is used, a matrix 12 having a crosslinked structure can be obtained, thereby improving heat resistance and light resistance.

[0061] The optical layers 130A and 130D, formed from a resin material in the matrix 12, may be flexible films. The thickness of the optical layers 130A and 130D is, for example, 10 μm to 10 mm. If the thickness of the optical layers 130A and 130D is, for example, 10 μm to 1 mm, or even 10 μm to 500 μm, significant flexibility can be achieved.

[0062] When using silica fine particles with a hydrophilic surface, it is preferable to form them, for example, 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, or 2-hydroxypropyl(meth)acrylate, acrylamide, methylenebisacrylamide, and ethoxylated bisphenol A di(meth)acrylate. These monomers may be used individually or in combination of two or more. Of course, the two or more monomers may include monofunctional monomers and polyfunctional monomers, or may include two or more polyfunctional monomers.

[0063] These monomers can be cured using a photopolymerization initiator as appropriate. Examples of photopolymerization initiators include carbonyl compounds such as benzoin ether, benzophenone, anthraquinone, thioxane, ketal, and acetophenone; sulfur compounds such as disulfide and dithiocarbamate; organic peroxides such as benzoyl peroxide; azo compounds; transition metal complexes; polysilane compounds; and dye sensitizers. The amount added is preferably 0.05 parts by mass to 3 parts by mass, and more preferably 0.05 parts by mass to 1 part by mass, per 100 parts by mass of the mixture of fine particles and monomer.

[0064] The refractive index of the matrix for visible light is nM , the refractive index of the fine particles is n P When |n M -n P The refractive index difference (hereinafter simply referred to as the refractive index difference) is preferably 0.01 or greater, preferably 0.6 or less, more preferably 0.03 or greater, and more preferably 0.11 or less. If the refractive index difference is less than 0.03, the scattering intensity becomes weak, making it difficult to obtain the desired optical properties. Also, if the refractive index difference exceeds 0.11, the linear transmittance of infrared light may decrease. Furthermore, for example, by using zirconia nanoparticles (refractive index 2.13) and acrylic resin, if the refractive index difference is 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 of the visible light scattering layer and the refractive index difference. Furthermore, depending on the application, it can also be used in combination with an infrared-absorbing filter. Note 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.

[0065] Figure 5 shows cross-sectional TEM images of optical layers 130A and 130D. In the TEM images in the figure, white circles represent silica nanoparticles, and black circles represent the traces left by the missing silica nanoparticles. As shown in the cross-sectional TEM images of optical layers 130A and 130D, the silica nanoparticles are dispersed almost uniformly.

[0066] Figure 6 shows, MostThis graph, normalized to high transmittance, shows the incident angle dependence of the linear transmittance spectra of optical layers 130A and 130D. Looking at the transmittance curves of optical layers 130A and 130D shown in Figure 6, the portion of the curve where linear transmittance monotonically increases from visible light to infrared light shifts to longer wavelengths (approximately 50 nm) as the incident angle increases. In other words, the portion of the curve where linear transmittance monotonically decreases from infrared light to visible light shifts to longer wavelengths as the incident angle increases. This characteristic incident angle dependence is thought to be due to the silica nanoparticles contained in the optical film constituting a colloidal amorphous aggregate. Details of the structure, optical properties, and manufacturing method of optical layers 130A and 130D are described in the international application PCT / JP2021 / 010413 by the present applicant. All disclosures of international application PCT / JP2021 / 010413 are incorporated herein by reference.

[0067] The optical layers 130A and 130D are not limited to layers in which fine particles 14 that act as light scatterers are dispersed in the matrix 12. The optical layers 130A and 130D may be, for example, fluororesin films. The fluororesin may be, for example, PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxyalkane), FEP (perfluoroethylene propene copolymer), ETFE (ethylene tetrafluoroethylene copolymer), PVDF (polyvinylidene fluoride), PCTFE (polychlorotrifluoroethylene), ECTFE (ethylene chlorotrifluoroethylene copolymer), or Cytop (manufactured by AGC Inc.). The fluororesin may also form a foam. Furthermore, to improve mechanical strength, the resin may be impregnated into the glass cloth. The thickness of the optical layers 130A and 130D is, for example, 10 μm or more and 10 mm or less.

[0068] (Example of a design added to the optical filter 130) This section describes an example of a design added to an optical filter 130 in a configuration where the detection device 100 or optical laminate 200 is arranged as part of the ceiling, wall, or floor. The design of the surface surrounding the location where the detection device 100 or optical laminate 200 is arranged is called the peripheral design, and the design of the surface of the optical filter 130 is called the filter design. The filter design is identical or similar to the peripheral design. The filter design and the peripheral design may have the same pattern or color. For example, a decorative film can be used to add a pattern or color design to the surface of the optical filter 130 and the surrounding surface. The surface protection layer described above may be provided on the surrounding surface.

[0069] Referring to Figures 7A to 7D, examples of designs that can be added to the surface of the optical filter 130 and the surrounding surface where the detection device 100 or optical laminate 200 is located will be described. Figure 7A shows an example in which a continuous pattern design is added to the surface of the optical filter 130 and the surface of the periphery 100P. In this example, a single pattern (design) is added to the surface of the periphery 100P and the surface of the optical filter 130. This design can be realized using a single decorative film. Therefore, there is no physical film boundary. The optical filter 130 is positioned at any point in the single pattern, and the patterns of the infrared light source 110 and infrared sensor 120 included in the detection device 100 or the recording medium layer 150 included in the optical laminate 200 are hidden on the back side of the optical filter 130.

[0070] Figure 7B shows an example in which a tile-like pattern is added to the surface of the optical filter 130 and the surrounding surface 100P. The design in this example is a tile-like pattern including a design, and can be realized by arranging multiple decorative films side by side on a planar or curved surface including the surface of the optical filter 130 and the surrounding surface 100P. Therefore, physical film boundaries exist as the seams between each film. The tile-like design includes not only patterns composed of regularly arranged identical shapes as shown in Figure 7B, but also patterns composed of irregularly arranged different shapes with non-uniform boundary widths. The optical filter 130 may be placed at the boundary or may be placed straddling the boundary. The pattern of the infrared light source 110 and infrared sensor 120 included in the detection device 100 or the recording medium layer 150 included in the optical laminate 200 is hidden on the back side of the optical filter 130. In the example shown in Figure 7B, the optical filter 130 is placed straddling the boundary within a pattern composed of regularly arranged star shapes.

[0071] Figure 7C shows another example in which a tile-like pattern is added to the surface of the optical filter 130 and its periphery 100P. The pattern in this example is a tile-like color scheme that includes combinations of colors with the same hue but different saturations, and can be realized by arranging multiple decorative films side by side on a planar or curved surface that includes the surface of the optical filter 130 and its periphery 100P. Thus, physical film boundaries exist as seams between each film. This pattern includes multiple regions 100R divided by visible boundaries 100B. The optical filter 130 is positioned in one of the multiple regions 100R. The patterns of the infrared light source 110 and infrared sensor 120 included in the detection device 100 or the recording medium layer 150 included in the optical laminate 200 are concealed on the back side of the optical filter 130. If there are multiple detection devices 100 or optical laminates 200, the multiple optical filters 130 are each positioned in different regions of the multiple regions 100R. Each of the multiple regions 100R may have any color or pattern.

[0072] FIG. 7D shows still another example in which a tile-like pattern design is added to the surface of the optical filter 130 and the surface of the periphery 100P. This design includes a plurality of regions 100R divided by a visible boundary 100B, and each of the plurality of regions 100R has an arbitrary pattern. The optical filter 130 is disposed in one of the plurality of regions 100R. The patterns of the infrared light source 110 and the infrared sensor 120 included in the detection device 100 or the recording medium layer 150 included in the optical laminate 200 are hidden on the back side of the optical filter 130.

[0073] As described above, it is possible to harmonize the color of the peripheral portion where the detection device 100 or the optical laminate 200 is disposed and the color of the surface of the optical filter 130 included in the detection device 100 or the optical laminate 200 so that they cannot be distinguished. When the color of the peripheral surface where the detection device 100 or the optical laminate 200 is disposed is referred to as the peripheral color and the color of the surface of the optical filter 130 is referred to as the filter color, neither the peripheral color nor the filter color is black, and the color difference between the peripheral color and the filter color when measured by the SCE method is 3 or less. Here, the color difference being 3 or less means that L * a * b * the a * value and b [[ID=~13]] * value of the peripheral surface in the color system are a1 * and b1<~ * respectively, and L * [[ID=~20]]a * b * the a * value and b * value of the surface of the optical filter 130 in the color system are a2 * and b2 * respectively, which means the case where the condition of Equation 1 is satisfied. [Equation 1] |a1 * - a2 * | ≤ 3 and |b1 * - b2 * | ≤ 3 L * a * b * An example of the color system is CIE1976L * a *b * This is a color system. From the viewpoint of enhancing the harmony between the surrounding color and the filter color, the color difference is preferably 1.5 or less, and more preferably 0.4 or less. If the color difference is 3 or less, the surrounding color and the filter color can be harmonized to the point where they are indistinguishable, resulting in excellent design quality.

[0074] (Examples) The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Here, the optical filters of the comparative examples and examples are evaluated by BRDF (bidirectional reflectance distribution function) and BTDF (bidirectional transmittance distribution function). First, the methods for measuring BRDF and BTDF will be described. Next, the results of measuring BRDF and BTDF for visible light and infrared light for the optical filters of the comparative examples and examples will be described.

[0075] [Methods for measuring BRDF and BTDF] The measurement methods for BRDF and BTDF will be explained with reference to Figures 8A and 8B, respectively. BRDF is a function of the reflection angle of the intensity of reflected scattered light produced when an object is illuminated with light. BTDF is a function of the transmission angle of the intensity of transmitted scattered light produced when an object is illuminated with light. B A goniotograph (Nikka Densoku Co., Ltd., model number: GP-4) was used to measure RDF and BTDF.

[0076] Figure 8A shows a schematic cross-sectional view illustrating the BRDF measurement method. In the example shown in Figure 8A, the light source 80 and sensor 90 are positioned on the first main surface 132 side of the optical filter 130. The first main surface 132 of the optical filter 130 is illuminated perpendicularly by light emitted from the light source 80, and the reflected scattered light generated by the illumination is detected by the sensor 90. The detection of reflected scattered light is performed by moving the sensor 90 in 1° increments within an angle range of -30° to 30°. This angle is the angle between the normal to the first main surface 132 and the optical axis of the lens included in the sensor 90. When the sensor 90 overlaps with the light source 80, reflected scattered light is not detected. In the following examples and comparative examples, BRDF at angles between -5° and 5° is not measured.

[0077] Figure 8B shows a schematic cross-sectional view illustrating the BTDF measurement method. In the example shown in Figure 8B, the light source 80 is positioned on the second main surface 134 side of the optical filter 130, and the sensor 90 is positioned on the first main surface 132 side of the optical filter 130. The second main surface 134 of the optical filter 130 is illuminated perpendicularly by light emitted from the light source 80, and the transmitted scattered light generated by the illumination is detected by the sensor 90. The detection of transmitted scattered light is performed by moving the sensor 90 in 1° increments within an angle range of -30° to 30°.

[0078] [Structure of optical filters in comparative examples and examples] First, the structures of Comparative Examples 1-4 will be described.

[0079] The optical filter of Comparative Example 1 comprises a substrate layer with a thickness of 3 mm formed from glass, and an optical layer with a thickness of 1 mm or less disposed on the substrate layer. This optical layer corresponds to the optical filter of Example 6 of the above-mentioned international application (average silica particle size 221 μm, silica content: 40% by mass).

[0080] The optical filter in Comparative Example 2 is a 0.2 mm thick film made of Nafuron (manufactured by AS ONE, model number: Nafuron Tape).

[0081] The optical filter in Comparative Example 3 is a fluororesin film with a thickness of 0.2 mm (manufactured by Nitto Denko, model number: Nitoflon).

[0082] The optical filter in Comparative Example 4 is a black film with a thickness of 0.5 mm (manufactured by Nitto Resin, model number: CLAREX).

[0083] Next, the structures of the optical filters in Examples 1 to 6 will be described. The optical filters in Examples 1 and 2 correspond to the optical filter 130 shown in Figure 3A. The optical filters in Examples 3 to 6 correspond to the optical filter 130 shown in Figure 3B.

[0084] The optical filter of Example 1 includes, in addition to the substrate layer and optical layer included in the optical filter of Comparative Example 1, an anti-glare layer with a thickness of 60 μm (manufactured by Daicel Corporation, model number: PEN60) placed on the optical layer.

[0085] The optical filter of Example 2 comprises the substrate layer and optical layer included in the optical filter of Comparative Example 1, plus the following layer disposed on the optical layer. This layer has a haze value 80 This is a 30 μm thick layer formed from an adhesive (manufactured by Nitto Denko) adjusted to a specific percentage.

[0086] Unlike the optical filter of Comparative Example 1, the optical filters of Examples 3 to 6 have a scattering surface in the optical layer. The scattering surfaces of the optical filters of Examples 3 to 6 are, respectively, on the surface of the optical layer contained in the optical filter of Comparative Example 1, as shown in the table below. 1 This is achieved by forming an uneven surface with the surface roughness shown.

[0087] Figures 9A and 9B show cross-sectional TEM images of the optical filters of Examples 3 and 6, respectively. As shown in Figures 9A and 9B, the scattering surface becomes coarser as the diffusion angle of the lens diffuser increases.

[0088] Table 1 shows the arithmetic mean roughness Ra and maximum height Rz of the scattering surface in the optical filters of Comparative Example 1 and Examples 3 and 6. A laser microscope VK-X1000 (manufactured by Keyence Corporation) was used to measure the arithmetic mean roughness Ra and maximum height Rz. The arithmetic mean roughness Ra and maximum height Rz were calculated based on measurements of 1000 × 1000 points in a 2800 μm square area at 5x magnification.

[0089] [Table 1]

[0090] The arithmetic mean roughness Ra of the surface of the optical filter in Comparative Example 1 is 0.3 μm or less, and the maximum height Rz is 14 μm or less. In contrast, the arithmetic mean roughness Ra of the scattering surface of the optical filters in Examples 3 and 6 is 1 μm or more, and the maximum height Rz is 15 μm or more. Thus, the scattering surfaces of the optical filters in Examples 3 and 6 are rougher than the surface of the optical filter in Comparative Example 1.

[0091] The haze values ​​for infrared radiation of the optical filters in Comparative Examples 1-4 and the optical filters in Examples 1-6 are shown in Table 2. Here, the haze value for infrared radiation is the average value of the haze value in the wavelength range of 800 nm to 2000 nm.

[0092] [Table 2]

[0093] The haze values ​​of the optical filters in Comparative Examples 1-4 are 45% or less. In contrast, the haze values ​​of the optical filters in Examples 1-6 are 40% or more. The haze values ​​of the optical filters in Examples 1 and 3-6 are 60% or more. The haze values ​​of the optical filters in Examples 3-6 are 80% or more. The haze values ​​of the optical filters in Examples 1 and 2, which have a scattering layer, are smaller than the haze values ​​of the optical filters in Examples 3-6, which have a scattering surface, but are still significantly larger than the haze value of the optical filter in Comparative Example 1, which does not have a scattering layer.

[0094] [BRDF and BTDF of optical filters in comparative examples and examples] The following describes the BRDF and BTDF of optical filters in comparative examples and examples for visible light and infrared light. We will use light with a wavelength of 550 nm as visible light and light with a wavelength of 850 nm as infrared light. However, the wavelengths of visible light and infrared light incident on the optical filter are not limited to these wavelengths. The BTDF is expressed logarithmically. When visible light and infrared light are incident at an incident angle of 0°, the BRDF and BTDF are symmetrical with respect to 0°. Note that due to measurement errors, the measured BRDF and BTDF may not be symmetrical with respect to 0°.

[0095] First, the BRDF and BTDF of the optical filters in Comparative Examples 1 to 4 will be explained with reference to Figures 10A to 10D.

[0096] Figures 10A and 10B show the wavelength 550n, respectively. m Figure 10A shows the BRDF and BTDF of the optical filters of Comparative Examples 1 to 4 when visible light is incident at an incident angle of 0°. As shown in Figure 10A, the BRDF of the optical filters of Comparative Examples 1 to 3 is 0.1 [1 / sr] or more at angles between -30° and -5° and between 5° and 30°. The BRDF of the optical filter of Comparative Example 4 is almost zero at angles between -30° and -5° and between 5° and 30°. This is because the optical filter of Comparative Example 4 is a black film and absorbs visible light. As shown in Figure 10B, the BTDF of the optical filter of Comparative Example 1 is 150 [1 / sr] or more around an angle of 0°. In other words, the optical filter of Comparative Example 1 shows high linear transmittance for visible light. In contrast, the BTDF of the optical filters in Comparative Examples 2 and 3 is 3[1 / sr] or less at angles between -30° and 30°, and the BTDF of the optical filter in Comparative Example 4 is 0.2[1 / sr] or less at angles between -30° and 30°. Therefore, the optical filters in Comparative Examples 1 to 3 effectively backscatter visible light, the optical filters in Comparative Examples 2 and 3 effectively reduce the transmission of visible light, and the optical filter in Comparative Example 4 effectively absorbs visible light.

[0097] Wavelength 550n m The more detailed behavior of the BRDF of the optical filters in Comparative Examples 1 to 3 for visible light is as follows: The BRDF of the optical filters in Comparative Examples 1 and 3 is nearly constant at angles between -30° and -5° and between 5° and 30°, and is greater than or equal to 0.1 [1 / sr]. The BRDF of the optical filter in Comparative Example 2 decreases monotonically as the angle approaches -5° to -30° and as it approaches 5° to 30°, but is greater than or equal to 0.1 [1 / sr].

[0098] Figures 10C and 10D show the wavelength 850n, respectively. m Figure 10C shows the BRDF and BTDF of the optical filters of Comparative Examples 1 to 4 when infrared light is incident at an incident angle of 0°. As shown in Figure 10C, the BRDF of the optical filters of Comparative Examples 1 to 4 is 0.1 [1 / sr] or less at angles between -30° and -5° and between 5° and 30°. As shown in Figure 10D, the BTDF of the optical filters of Comparative Examples 1 to 4 shows a high value of 100 [1 / sr] or more near an angle of 0°. In other words, the optical filters of Comparative Examples 1 to 4 show high linear transmission for infrared light. The logarithmic representation of the BTDF of the optical filters of Comparative Examples 1 to 4 decreases monotonically as the angle approaches ±30° from 0°. The logarithmic representation of the BTDF of the optical filters of Comparative Examples 1 to 4 changes to a downward convex shape at angles between -30° and less than 0°, and at angles greater than 0° and less than or equal to 30°. Thus, the logarithmic representation of the BTDF of Comparative Examples 1 to 4 shows a Lambertsian distribution. Therefore, the optical filters of Comparative Examples 1 to 4 effectively reduce infrared reflection and effectively transmit infrared light in a straight line.

[0099] Wavelength 850n m The following describes the more detailed behavior of the BTDF of the optical filters in Comparative Examples 1-4 for infrared radiation. The BTDF of the optical filters in Comparative Examples 1 and 4 are almost the same. inYes. The logarithmic representation of the BTDF of the optical filters in Comparative Examples 1 and 4 decreases monotonically in a convex downward direction as the angle approaches ±30° from 0°, and the BTDF approaches 0.01 [1 / sr]. In contrast, the logarithmic representation of the BTDF of the optical filters in Comparative Examples 2 and 3 decreases monotonically in a convex downward direction as the angle approaches ±30° from 0°, but the BTDF is greater than or equal to 0.1 [1 / sr].

[0100] The BTDF of the optical filters in Comparative Examples 1 to 4 can be defined by (value at -1°) / (value at -10°) and (value at 1°) / (value at 10°). The larger the values ​​of (value at -1°) / (value at -10°) and (value at 1°) / (value at 10°), the higher the linear transmittance of infrared radiation. If the BTDF value at -1° is denoted as value A, the BTDF value at -10° as value B, the BTDF value at 1° as value C, and the BTDF value at 10° as value D, then the A, B, C, D, A / B, and C / D values ​​for the BTDF of the optical filters in Comparative Examples 1 to 4 are as shown in Table 3. The A / B value corresponds to (value at -1°) / (value at -10°), and the C / D value corresponds to (value at 1°) / (value at 10°).

[0101] [Table 3]

[0102] In the BTDF of the optical filters of Comparative Examples 1 to 4, (value of -1°) / (value of -10°) and (value of 1°) / (value of 10°) are greater than 30. The optical filters of each comparative example are as follows: In the BTDF of the optical filter of Comparative Example 3, (value of -1°) / (value of -10°) and (value of 1°) / (value of 10°) are greater than 30. In the BTDF of the optical filter of Comparative Example 2, (value of -1°) / (value of -10°) and (value of 1°) / (value of 10°) are greater than 40. In the BTDF of the optical filters of Comparative Examples 1 and 4, (value of -1°) / (value of -10°) and (value of 1°) / (value of 10°) are greater than 500.

[0103] From the above, the optical filters of Comparative Examples 1-3 effectively backscatter visible light and effectively transmit infrared light in a straight line. The optical filter of Comparative Example 4 effectively absorbs visible light and effectively transmits infrared light in a straight line.

[0104] Next, the BRDF and BTDF of the optical filters in Examples 1 and 2 will be described with reference to Figures 11A to 11D.

[0105] Figures 11A and 11B show the wavelength 550n, respectively. m The BRDF and BTDF of the optical filters of Examples 1 and 2 when visible light is incident at an incident angle of 0° are shown. As shown in Figure 11A, the BRDF of the optical filters of Examples 1 and 2 is 0.1 [1 / sr] or more at angles between -30° and -5° and between 5° and 30°. As shown in Figure 11B, the BTDF of the optical filters of Examples 1 and 2 is 12 [1 / sr] or less at angles between -30° and 30°. Therefore, the optical filters of Examples 1 and 2 effectively backscatter visible light and effectively reduce the transmission of visible light.

[0106] Wavelength 550n m The more detailed behavior of the BRDF of the optical filters in Examples 1 and 2 with respect to visible light is as follows: The BRDF of the optical filters in Examples 1 and 2, which have a scattering layer, is larger than that of the optical filter in Comparative Example 1, which does not have a scattering layer, at angles between -10° and -5° and between 5° and 10°. From this, it can be seen that the scattering layer included in the optical filters in Examples 1 and 2 increases the backscattering of visible light.

[0107] Figures 11C and 11D show the wavelength 850n, respectively. m The BRDF and BTDF of the optical filters of Examples 1 and 2 are shown when infrared light is incident at an incident angle of 0°. As shown in Figure 11C, the BRDF of the optical filters of Examples 1 and 2 is at angles of -30° to -5° and 5° to 30°. 0.35[1 / sr] or less, more specifically at angles between -30° and -15° and between 15° and 30°. 0.1 It is less than [1 / sr]. As shown in Figure 11D, the BTDF of the optical filter in Example 2 shows a high value of 100[1 / sr] or more near an angle of 0°, while the BTDF of the optical filter in Example 1 is less than 50[1 / sr] at angles between -5° and 5° near 0°, and more specifically less than 30[1 / sr]. The logarithmic representation of the BTDF of the optical filters in Examples 1 and 2 decreases monotonically as the angle approaches ±30° from 0°. The logarithmic representation of the BTDF of the optical filters in Examples 1 and 2 is for angles between -30° and -2°, and 2° That's all. It has a portion that becomes convex upwards at angles of 30° or less. The optical filters for each embodiment are as follows. The logarithmic representation of the BTDF of the optical filter in Embodiment 1 is for angles of -10° to -2° and 2°. That's all. It has a portion that becomes convex upwards at angles of 10° or less. The logarithmic representation of the BTDF of the optical filter of Example 2 is for angles between -15° and -5°, and 5° That's all. It has a portion that becomes convex upwards at angles of 15° or less. Thus, the logarithmic representation of the BTDF of Examples 1 and 2 shows a non-Lambertian distribution. The portion that becomes convex upwards means that forward scattering increases. Therefore, the optical filters of Examples 1 and 2 effectively reduce infrared reflection and effectively forward scatter infrared light.

[0108] Wavelength 850n m The more detailed behavior of the BTDF of the optical filters in Examples 1 and 2 with respect to infrared radiation is as follows: The BTDF of the optical filters in Examples 1 and 2 with a scattering layer is -30° to -2° lower than that of the optical filter in Comparative Example 1 without a scattering layer. twist The scattering effect is increased at small angles and at angles greater than 2° and less than or equal to 30°. This indicates that the scattering layer included in the optical filters of Examples 1 and 2 increases forward scattering of infrared light.

[0109] The BTDF of the optical filters in Examples 1 and 2, which forward scatter infrared light, can be defined by (value of -1°) / (value of -10°) and (value of 1°) / (value of 10°). The smaller the values ​​of (value of -1°) / (value of -10°) and (value of 1°) / (value of 10°), the greater the forward scattering of infrared light. The A, B, C, D, A / B, and C / D values ​​in the BTDF of the optical filters in Examples 1 and 2 are shown in Table 4.

[0110] [Table 4]

[0111] In the BTDF of the optical filters of Examples 1 and 2, (value of -1°) / (value of -10°) and (value of 1°) / (value of 10°) are 20 or less. The optical filters of each example are as follows: In the BTDF of the optical filter of Example 1, (value of -1°) / (value of -10°) and (value of 1°) / (value of 10°) are 20 or less, more specifically 16 or less. In the BTDF of the optical filter of Example 2, (value of -1°) / (value of -10°) and (value of 1°) / (value of 10°) are 10 or less, more specifically 8 or less. The (value of -1°) / (value of -10°) and (value of 1°) / (value of 10°) in the BTDF of the optical filters of Examples 1 and 2 are smaller than the (value of -1°) / (value of -10°) and (value of 1°) / (value of 10°) in the BTDF of the optical filters of Comparative Examples 1 to 4.

[0112] From the above, the optical filters of Examples 1 and 2 effectively backscatter visible light and effectively forward scatter infrared light.

[0113] Next, the BRDF and BTDF of the optical filters in Examples 3 to 6 will be described with reference to Figures 12A to 12D.

[0114] Figures 12A and 12B show the wavelength 550n, respectively. mThe BRDF and BTDF of the optical filters of Examples 3 to 6 when visible light is incident at an incident angle of 0° are shown. As shown in Figure 12A, the BRDF of the optical filters of Examples 3 to 6 are almost the same, and are 0.1 [1 / sr] or more at angles between -30° and -5° and between 5° and 30°. As shown in Figure 12B, the BTDF of the optical filters of Examples 3 to 6 is 2 [1 / sr] or less at angles between -30° and 30°. Therefore, the optical filters of Examples 3 to 6 effectively backscatter visible light and effectively reduce the transmission of visible light.

[0115] Wavelength 550n m The more detailed behavior of the BRDF of the optical filters of Examples 3 to 6 with respect to visible light is as follows: The BRDF of the optical filters of Examples 3 to 6, which have a scattering surface in the optical layer, is almost the same as that of the optical filter of Comparative Example 1, which does not have a scattering surface in the optical layer. From this, it can be seen that the scattering surface in the optical layer included in the optical filters of Examples 3 to 6 has almost no effect on the backscattering of visible light.

[0116] Figures 12C and 12D show the wavelength 850n, respectively. m The BRDF and BTDF of the optical filters of Examples 3 to 6 when infrared light is incident at an incident angle of 0° are shown. As shown in Figure 12C, the BRDF of the optical filters of Examples 3 to 6 is 0.1 [1 / sr] or less at angles between -30° and -5° and between 5° and 30°. As shown in Figure 12D, the BTDF of the optical filters of Examples 3 to 6 is near an angle of 0°. - For angles between 5° and 5°, the value is 10[1 / sr] or less. The logarithmic representation of the BTDF of the optical filters in Examples 3 to 6 decreases monotonically as the angle approaches ±30° from 0°. The logarithmic representation of the BTDF of the optical filters in Examples 3 to 6 is for angles between -30° and -2°, and 2° That's all.It has a portion that becomes convex upward at angles of 30° or less. Thus, the logarithmic representation of the BTDFs of Examples 3 to 6 shows a non-Lambertian distribution. As mentioned above, the portion that becomes convex upward means that forward scattering increases. Therefore, the optical filters of Examples 3 to 6 effectively reduce infrared reflection and effectively forward scatter infrared light.

[0117] Wavelength 850n m The following describes the more detailed behavior of the BTDF of the optical filters of Examples 3-6 against infrared radiation. The BTDF of the optical filters of Examples 3-6, which have a scattering surface in the optical layer, is -30° to -2° lower than that of the optical filter of Comparative Example 1, which does not have a scattering surface in the optical layer. twist The BTDF increases at small angles and at angles greater than 2° but less than or equal to 30°. Near an angle of 0°, the BTDF decreases as the diffusion angle of the lens diffuser increases. From this, it can be seen that the scattering surface of the optical layer included in the optical filters of Examples 3 to 6 increases the forward scattering of infrared rays.

[0118] The BTDF of the optical filters in Examples 3 to 6, which forward scatter infrared light, can be defined by (value of -1°) / (value of -10°) and (value of 1°) / (value of 10°), similar to the BTDF of the optical filters in Examples 1 and 2. The A, B, C, D, A / B, and C / D values ​​in the BTDF of the optical filters in Examples 3 to 6 are shown in Table 5.

[0119] [Table 5]

[0120] In the BTDF of the optical filters of Examples 3 to 6, the ratios (-1° value) / (-10° value) and (1° value) / (10° value) are 5 or less, and more specifically, 2 or less. The ratios (-1° value) / (-10° value) and (1° value) / (10° value) in the BTDF of the optical filters of Examples 3 to 6 are sufficiently smaller than the ratios (-1° value) / (-10° value) and (1° value) / (10° value) in the BTDF of the optical filters of Comparative Examples 1 to 4.

[0121] From the above, the optical filters of Examples 3 to 6 effectively backscatter visible light and effectively forward scatter infrared light.

[0122] The results obtained from the BRDF and BTDF of the optical filters in Examples 1-6 for visible light and infrared light can be summarized as follows.

[0123] Regarding the optical filters of Examples 1 to 6, the wavelength is 550n m The BRDF (bidirectional reflectance distribution function) when visible light is incident at an incident angle of 0° is for angles between -30° and -5° and between 5° and 30°. below The angle is 0.1 [1 / sr] or greater. Therefore, the optical filters of Examples 1 to 6 can effectively backscatter visible light. As a result, it becomes possible to reduce the heat generated due to the absorption of visible light.

[0124] Regarding the optical filters of Examples 1 to 6, the wavelength is 850n m The logarithmic representation of the BTDF when infrared radiation is incident at an incident angle of 0° is for the ranges of -30° to -2° and 2° to 30°. below It has a portion that changes to an upward convex shape at a certain angle. Therefore, the optical filters of Examples 1 to 6 can effectively scatter infrared light forward. As a result, it becomes possible to reduce glare when detecting objects with infrared light.

[0125] Wavelength 850n mIn the BTDF of the optical filters of Examples 1 to 6 when infrared light is incident at an incident angle of 0°, the values ​​of (-1° value) / (-10° value) and (1° value) / (10° value) are 20 or less. The optical filters of each example are as follows: In the BTDF of the optical filter of Example 1, the values ​​of (-1° value) / (-10° value) and (1° value) / (10° value) are 20 or less. In the BTDF of the optical filter of Example 2, the values ​​of (-1° value) / (-10° value) and (1° value) / (10° value) are 10 or less. In the BTDF of the optical filters of Examples 3 to 6, the values ​​of (-1° value) / (-10° value) and (1° value) / (10° value) are 5 or less.

[0126] Wavelength 850n m In the BTDF of the optical filters in Comparative Examples 1 to 4 when infrared light is incident at an incident angle of 0°, (value at -1°) / (value at -10°) and (value at 1°) / (value at 10°) are greater than 30. Therefore, for a wavelength of 850n m When infrared radiation is incident at an incident angle of 0°, if the BTDF of the optical filter is 30 or less for (-1° value) / (-10° value) and (1° value) / (10° value), the optical filter can scatter infrared radiation more effectively forward than the optical filters of Comparative Examples 1 to 4. If the BTDF of the optical filter is 25 or less for (-1° value) / (-10° value) and (1° value) / (10° value), the optical filter can scatter infrared radiation more effectively forward. If the BTDF of the optical filter is 20 or less for (-1° value) / (-10° value) and (1° value) / (10° value), the optical filter can scatter infrared radiation even more effectively forward.

[0127] For the optical filters of Examples 1 and 3-6, the wavelength is 850n m When infrared light is incident at an incident angle of 0°, the BTDF is 50 [1 / sr] or less at angles between -5° and 5°. In particular, for the optical filters of Examples 3 to 6, the wavelength is 850n mThe BTDF when infrared light is incident at an incident angle of 0° is 10[1 / sr] or less at angles between -5° and 5°. Therefore, the optical filters of Examples 1 and 3-6 can more effectively reduce linear transmission of infrared light, and as a result, glare when detecting objects with infrared light can be reduced more effectively. In particular, the optical filters of Examples 3-6 can more effectively reduce linear transmission of infrared light, and as a result, glare when detecting objects with infrared light can be reduced more effectively.

[0128] [Linear and diffuse transmittance of optical filters for visible light in comparative examples and examples] Optical filters and examples of Comparative Examples 1-4 1 ~ 6 The linear transmittance, diffuse transmittance, and total transmittance of the optical filter for visible light are shown in Table 6 below. Here, the linear transmittance, diffuse transmittance, and total transmittance for visible light are the average values ​​of the linear transmittance, diffuse transmittance, and total transmittance for wavelengths between 380 nm and 780 nm, respectively.

[0129] [Table 6]

[0130] Linear transmittance was evaluated as follows. Linear transmittance is the transmittance measured with the optical laminate placed at a certain distance (e.g., 20 cm) from the aperture of the integrating sphere. A UV-Vis-Near-Infrared Spectrophotometer UH4150 (manufactured by Hitachi High-Tech Science Corporation) was used as the spectrometer. Diffuse transmittance was evaluated as follows. Diffuse transmittance was obtained by the difference between total transmittance and linear transmittance. Total transmittance is the transmittance measured with the optical laminate placed at the aperture of the integrating sphere.

[0131] As shown in Table 6, the linear transmittance of the optical filter in Comparative Example 1 is 15% or more. In contrast, the linear transmittance of the optical filters in Comparative Examples 2-4 and Examples 1-4 is 10% or less. The diffuse transmittance of the optical filters in Comparative Examples 1-4 and Examples 1-4 is 51% or less. The total transmittance of the optical filters in Comparative Examples 1-4 and Examples 1-4 is 54% or less.

[0132] From this, it can be seen that the optical filters of Comparative Examples 2-4 and Examples 1-4 have a linear transmittance of 10% or less, thus effectively reducing the linear transmission of visible light. The optical filters of Comparative Examples 1-3 and Examples 1-4 have a total transmittance of 54% or less, so they do not transmit visible light very effectively.

[0133] [Linear and diffuse transmittance of optical filters for infrared radiation in comparative examples and examples] Optical filters and examples of Comparative Examples 1-4 1 ~ 6 The linear transmittance, diffuse transmittance, and total transmittance of the optical filter for infrared radiation are shown in Table 7 below. Here, the linear transmittance, diffuse transmittance, and total transmittance for infrared radiation are the average values ​​of the linear transmittance, diffuse transmittance, and total transmittance in the wavelength range of 800 nm to 2000 nm, respectively.

[0134] [Table 7]

[0135] As shown in Table 7, the linear transmittance of the optical filters in Comparative Examples 1-4 is 40% or more. In contrast, the optical filters in Examples 1 and 3-6 have a linear transmittance of 35% or less. The optical filters in Examples 3-6 have a linear transmittance of 15% or less, more specifically 11% or less. From this, it can be seen that the optical filters in Examples 1 and 3-6 can effectively reduce the linear transmission of infrared rays compared to the optical filters in Comparative Examples 1-4. In particular, it can be seen that the optical filters in Examples 3-6 can reduce the linear transmission of infrared rays more effectively.

[0136] As shown in Table 7, the diffuse transmittance of the optical filters in Comparative Examples 1 to 4 is less than 35%. In particular, the diffuse transmittance of the optical filters in Comparative Examples 1 and 4 is 5% or less. In contrast, the optical filters in Examples 1 to 6 have a diffuse transmittance of 35% or more. The optical filters in Examples 1 and 3 to 6 have a diffuse transmittance of 53% or more. In particular, the optical filters in Examples 3 to 6 have a diffuse transmittance of 70% or more. Although the optical filters in Examples 1 and 2, which have a scattering layer, have a lower diffuse transmittance compared to the optical filters in Examples 3 to 6, which have a scattering surface, they have a higher diffuse transmittance compared to the optical filter in Comparative Example 1, which does not have a scattering layer. From this, it can be seen that the optical filters in Examples 1 to 6 can effectively increase the forward scattering of infrared rays compared to the optical filters in Comparative Examples 1 to 4. In particular, it can be seen that the optical filters in Examples 3 to 6 can more effectively increase the forward scattering of infrared rays.

[0137] As shown in Table 7, the total transmittance of the optical filters in Comparative Examples 1-4 and Examples 1-6 is 75% or higher. Therefore, including linear and diffuse transmittance, it can be seen that the optical filters in Comparative Examples 1-4 and Examples 1-6 effectively transmit infrared light. [Explanation of Symbols]

[0138] 10: Object 12: Matrix 14: Microparticle 100: Detection device 100B: Boundary 100P: Periphery 100R: Region 110: Infrared light source 120: Infrared sensor 130: Optical filter 130A: Optical layer 130B: Scattering layer 130C: Substrate layer 130D: Optical layer 130E: Design layer 130F: Surface protection layer 132: First main surface 132D: Scattering surface 134: Second main surface 140: Housing 142: Aperture 150: Recording medium layer 200: Optical laminate

Claims

1. When visible light with a wavelength of 550 nm is incident at an incident angle of 0°, the BRDF (bidirectional reflectance distribution function) is 0.1 [1 / sr] or greater at angles between -30° and -5° and between 5° and 30°. An optical filter in which, when infrared light with a wavelength of 850 nm is incident at an incident angle of 0°, the BTDF (bidirectional transmittance distribution function) is such that (value at -1°) / (value at -10°) and (value at 1°) / (value at 10°) are 30 or less, An optical layer that backscatters the visible light and linearly transmits the infrared light, A scattering layer disposed directly on the optical layer or via another layer, which forward scatters the infrared light, An optical filter equipped with [the necessary components].

2. The optical filter according to claim 1, wherein the ratio of (value of -1°) / (value of -10°) and (value of 1°) / (value of 10°) is 25 or less.

3. The optical filter according to claim 1, wherein the BTDF is 50 [1 / sr] or less at angles of -5° to 5°.

4. The optical filter according to claim 1, wherein the average value of the diffuse transmittance in the wavelength range of 800 nm to 2000 nm is 35% or more.

5. The optical filter according to claim 1, wherein the average value of the haze value of the optical filter in the wavelength range of 800 nm to 2000 nm is 40% or more.

6. The L of the optical layer was measured using a spectrophotometer with the SCE (Specular Reflectance Removal) method. ＊ The optical filter according to claim 1, wherein the value of is 20 or more.

7. The optical filter according to claim 1, wherein the optical layer comprises a matrix and fine particles dispersed in the matrix that serve as light scatterers.

8. The optical filter according to claim 7, wherein the fine particles constitute at least a colloidal amorphous aggregate.

9. The optical filter according to claim 8, wherein the transmittance curve of the optical layer in the visible light wavelength region has a curve portion in which the linear transmittance monotonically decreases from the longer wavelength side to the shorter wavelength side, and the curve portion shifts to the longer wavelength side as the angle of incidence increases.

10. A detection device for detecting objects, An infrared light source that emits infrared rays for irradiating the aforementioned object, An infrared sensor that detects infrared radiation reflected by the aforementioned object, An optical filter according to any one of claims 1 to 9, comprising an optical filter arranged to cross the infrared light emitted from the infrared light source, A detection device equipped with the following features.

11. An optical filter according to any one of claims 1 to 9, comprising an optical filter having a first main surface and a second main surface opposite to the first main surface, A recording medium layer is disposed on the second main surface side of the optical filter and has a pattern that can be read by infrared light through the optical filter, An optical laminate comprising the above features.

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