Optical filter, detection device, and optical stack

Abstract

In the optical filter, the BRDF (Bidirectional Reflectance Distribution Function) at the time of incidence of visible light of wavelength 550 nm at an incidence angle of 0° is 0.1 [1 / sr] or more at angles of -30° or more and -5° or less and 5° or more and 30° or less, and in the BTDF (Bidirectional Transmittance Distribution Function) at the time of incidence of infrared light of wavelength 850 nm at an incidence angle of 0°, (value at -1°) / (value at -10°) and (value at 1°) / (value at 10°) are 30 or less.

Description

Technical Field

[0001] The present invention relates to optical filters, detection devices utilizing such optical filters, and optical laminates. Background Technology

[0002] In infrared object detection, an infrared light source that emits infrared light to illuminate the object and an infrared sensor that detects infrared light reflected by the object are used (e.g., Patent Document 1). For aesthetic and design reasons, it is sometimes necessary to conceal the infrared light source and infrared sensor so that they are not visible.

[0003] Hiding objects is not limited to infrared light sources and infrared sensors. In recent years, AR (Augmented Reality) tags such as barcodes, QR codes (registered trademarks), ArUco, and Chameleon codes have been used for various purposes (e.g., patent document 2). For aesthetic and design reasons, there is sometimes a requirement to hide AR tags so they are not visible. AR tags can be read using infrared light.

[0004] To achieve the aforementioned concealment, for example, the optical filter containing black pigment described in Patent Document 3 could be considered. The black pigment in Patent Document 3 absorbs visible light while allowing infrared light to pass through. If an optical filter containing this black pigment is used, in object detection utilizing infrared light, by illuminating the object with infrared light emitted from the infrared light source while concealing the infrared light source and infrared sensor, the infrared light reflected by the object can be detected by the infrared sensor. Furthermore, AR tags can be read using infrared light while concealing them.

[0005] In this specification, unless otherwise specified, "infrared light" includes light with wavelengths of 780 nm or more and 4000 nm or less. "Visible light" refers to light with wavelengths of 380 nm or more and less than 780 nm.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Publication No. 2019-524602

[0009] Patent Document 2: Japanese Patent Application Publication No. 2016-224485

[0010] Patent Document 3: Japanese Patent Application Publication No. 2019-207303 Summary of the Invention

[0011] The technical problem that the invention aims to solve

[0012] The black pigment in Patent Document 3 absorbs visible light, which could potentially generate heat in the optical filter. This heat generated by the optical filter could adversely affect the concealed object. Furthermore, the black pigment in Patent Document 3 allows infrared light to pass through with high linear transmittance; therefore, when an object is detected by infrared light through an optical filter containing this black pigment, glare could potentially occur if the infrared light reflected by the object contains a large amount of linearly reflected components.

[0013] The present invention was made to solve the above-mentioned problems, and its object is to provide an optical filter that can reduce heat generation caused by absorption of visible light and reduce glare when detecting objects by infrared light, as well as a detection device and an optical laminate utilizing the optical filter.

[0014] Technical solutions for solving technical problems

[0015] According to embodiments of the present invention, solutions are provided as shown in the following items.

[0016] [Project 1] An optical filter wherein, when visible light with a wavelength of 550 nm is incident at an angle of 0°, the BRDF (bidirectional reflectivity distribution function) is greater than or equal to 0.1[1 / sr] at angles greater than or equal to -30° and less than -5° and greater than or equal to 5° and less than 30°, and the BTDF (bidirectional transmittance distribution function) when infrared light with a wavelength of 850 nm is incident at an angle of 0° is less than or equal to 30 for (value of -1°) / (value of -10°) and (value of 1°) / (value of 10°).

[0017] [Project 2] The optical filter according to Project 1, wherein (value of -1°) / (value of -10°) and (value of 1°) / (value of 10°) are 25 or less.

[0018] [Item 3] The optical filter according to Item 1 or 2, wherein the BTDF is less than 50[1 / sr] at angles above -5° and below 5°.

[0019] [Item 4] An optical filter according to any one of Items 1 to 3, wherein the average value of the diffusion transmittance in the range of wavelength above 800 nm and below 2000 nm is 35% or more.

[0020] [Item 5] An optical filter according to any one of Items 1 to 4, wherein it comprises an optical layer that backscatters the visible light and forward scatters the infrared light, the optical layer having a scattering surface that forward scatters the infrared light.

[0021] [Project 6] According to the optical filter described in Project 5, the arithmetic mean roughness Ra of the scattering surface is greater than 1 μm, and the maximum height Rz is greater than 15 μm.

[0022] [Item 7] An optical filter according to any one of Items 1 to 4, comprising: an optical layer that backscatters the visible light and transmits the infrared light in a straight line; and a scattering layer disposed on the optical layer directly or via other layers to forward scatter the infrared light.

[0023] [Item 8] 8. An optical filter according to any one of Items 1 to 7, wherein the average haze value of the optical filter in the range of wavelength above 800 nm and below 2000 nm is above 40%.

[0024] [Item 9] An optical filter according to any one of Items 5 to 7, wherein the L of the optical layer is measured using a spectrophotometer in the SCE (positive reflection removal) manner. * The value is 20 or higher.

[0025] [Item 10] An optical filter according to any one of items 5 to 9, wherein the optical layer has a matrix and particles dispersed in the matrix as light scatterers.

[0026] [Item 11] The optical filter according to Item 10, wherein the microparticles at least constitute a colloidal amorphous aggregate.

[0027] [Item 12] According to the optical filter of Item 11, the transmittance curve of the visible light wavelength region of the optical layer has a linear portion where the transmittance decreases monotonically from the long wavelength side to the short wavelength side, and the portion of the curve shifts towards the long wavelength side as the incident angle increases.

[0028] [Item 13] A detection apparatus for detecting an object, comprising: an infrared light source that emits infrared rays for illuminating the object; an infrared sensor that detects infrared rays reflected by the object; and an optical filter as described in any one of items 1 to 12, configured to cut across the infrared rays emitted from the infrared light source.

[0029] [Item 14] An optical laminate comprising: an optical filter as described in any one of items 1 to 12, 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, having a pattern that can be read by infrared light via the optical filter.

[0030] Invention Effects

[0031] According to embodiments of the present invention, an optical filter capable of reducing heat generation caused by absorption of visible light and reducing glare when detecting objects by infrared light is provided, as well as a detection device and an optical laminate utilizing the optical filter. Attached Figure Description

[0032] Figure 1A This is a schematic cross-sectional view of a detection device according to an exemplary embodiment of the present invention.

[0033] Figure 1B This is another schematic cross-sectional view of the detection device according to an exemplary embodiment of the present invention.

[0034] Figure 2A This is a schematic cross-sectional view of an optical laminate according to an exemplary embodiment of the present invention.

[0035] Figure 2B This is another schematic cross-sectional view of an optical laminate according to an exemplary embodiment of the present invention.

[0036] Figure 3A This is a schematic cross-sectional view of an optical filter according to an exemplary embodiment of the present invention.

[0037] Figure 3B This is a schematic cross-sectional view of an optical filter according to another embodiment of the present invention.

[0038] Figure 3C This is a schematic cross-sectional view of an optical filter according to another embodiment of the present invention.

[0039] Figure 3D This is a schematic cross-sectional view of an optical filter according to another embodiment of the present invention.

[0040] Figure 4 This is a schematic cross-sectional view of the interior of the optical layers contained in an optical filter.

[0041] Figure 5 This is a cross-sectional TEM image of the visible light scattering layer.

[0042] Figure 6 It is a curve normalized to maximum transmittance, and it is a graph showing the incident angle dependence of the linear transmittance spectrum of the visible light scattering layer.

[0043] Figure 7A This is a schematic diagram illustrating an example of a continuous texture design.

[0044] Figure 7B This is a schematic diagram illustrating another example of a continuous texture design.

[0045] Figure 7C This is a schematic diagram illustrating an example of a tile style design.

[0046] Figure 7D This is an illustration of another example of a tile style design.

[0047] Figure 8A This is a schematic cross-sectional diagram used to illustrate the method for determining BRDF.

[0048] Figure 8B This is a schematic cross-sectional diagram used to illustrate the method for determining BTDF.

[0049] Figure 9A This is a cross-sectional TEM image of the optical filter in Example 3.

[0050] Figure 9B This is a cross-sectional TEM image of the optical filter in Example 6.

[0051] Figure 10A The BRDFs are optical filters of Comparative Examples 1 to 4 when visible light with a wavelength of 550 nm is incident at an incident angle of 0°.

[0052] Figure 10B The BTDFs are optical filters of Comparative Examples 1 to 4 when visible light with a wavelength of 550 nm is incident at an incident angle of 0°.

[0053] Figure 10C The BRDFs are optical filters of Comparative Examples 1 to 4 when infrared light with a wavelength of 850 nm is incident at an incident angle of 0°.

[0054] Figure 10D The BTDFs are optical filters of Comparative Examples 1 to 4 when infrared light with a wavelength of 850 nm is incident at an incident angle of 0°.

[0055] Figure 11A It is the BRDF of the optical filters of Examples 1 and 2 when visible light with a wavelength of 550nm is incident at an incident angle of 0°.

[0056] Figure 11B It is the BTDF of the optical filters of Examples 1 and 2 when visible light with a wavelength of 550nm is incident at an incident angle of 0°.

[0057] Figure 11C It is the BRDF of the optical filters of Examples 1 and 2 when infrared light with a wavelength of 850nm is incident at an incident angle of 0°.

[0058] Figure 11D It is the BTDF of the optical filters of Examples 1 and 2 when infrared light with a wavelength of 850nm is incident at an incident angle of 0°.

[0059] Figure 12AIt is the BRDF of the optical filters of Examples 3 to 6 when visible light with a wavelength of 550nm is incident at an incident angle of 0°.

[0060] Figure 12B It is the BTDF of the optical filters of Examples 3 to 6 when visible light with a wavelength of 550nm is incident at an incident angle of 0°.

[0061] Figure 12C It is the BRDF of the optical filter of Examples 3 to 6 when infrared light with a wavelength of 850nm is incident at an incident angle of 0°.

[0062] Figure 12D It is the BTDF of the optical filters in Examples 3 to 6 when infrared light with a wavelength of 850nm is incident at an incident angle of 0°. Detailed Implementation

[0063] (Implementation Method)

[0064] Hereinafter, with reference to the accompanying drawings, the detection device and optical laminate of the optical filter according to an embodiment of the present invention will first be described, followed by a detailed description of the structure of the optical filter according to an embodiment of the present invention. Finally, embodiments of the optical filter will be described. The optical filter, detection device, and optical laminate of the present invention are not limited to the examples described below.

[0065] According to the optical filter of the present invention, the BRDF (bidirectional reflectance distribution function) of visible light with a wavelength of 550 nm incident at an incident angle of 0° is 0.1 [1 / sr] or more at angles of -30° to -5° and 5° to 30°, and the BTDF (bidirectional transmittance distribution function) of infrared light with a wavelength of 850 nm incident at an incident angle of 0° is 30 or less for (value of -1°) / (value of -10°) and (value of 1°) / (value of 10°).

[0066] In the optical filter of the present invention, heat generation caused by absorption of visible light can be reduced, and glare when detecting objects by infrared light can be reduced.

[0067] The object detection apparatus according to an embodiment of the present invention includes: an infrared light source that emits infrared rays for illuminating the object; an infrared sensor that detects infrared rays reflected by the object; and an optical filter configured to cut across the infrared rays emitted from the infrared light source.

[0068] In the optical detection device of the present invention, the possibility of the infrared light source and the infrared sensor being seen can be reduced by using an optical filter.

[0069] An optical laminate according to an embodiment of the present invention comprises: the optical filter described above, 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, having a pattern that can be read by infrared light via the optical filter.

[0070] In the optical stack of the present invention, the possibility of the pattern of the recording medium layer being seen can be reduced by using an optical filter.

[0071] [Detection device]

[0072] First, refer to Figure 1A and Figure 1B An example of the structure of a detection device using the optical filter according to an embodiment of the present invention will be described.

[0073] Figure 1A A schematic cross-sectional view of a detection device illustrating an exemplary embodiment of the present invention. Figure 1A The object 10 being detected is also referred to in the text. Object 10 can be any object, such as a person or a product transported by a belt conveyor. Figure 1A The detection device 100 shown includes an infrared light source 110, an infrared sensor 120, an optical filter 130, and a housing 140 for housing the infrared light source 110 and the infrared sensor 120.

[0074] Infrared light source 110 may be, for example, an infrared lamp or infrared LED that emits infrared light. Infrared sensor 120 may be, for example, an image sensor that acquires infrared images. Optical filter 130 has a first main surface 132 and a second main surface 134 on its opposite side. Optical filter 130 causes infrared light incident on the first main surface 132 or the second main surface 134 to scatter forward and causes visible light incident on the first main surface 132 or the second main surface 134 to scatter back. The detailed structure of optical filter 130 and the evaluation of scattering characteristics based on BRDF and BTDF will be described later. Object 10 is located on the first main surface 132 side of optical filter 130, and infrared light source 110 and infrared sensor 120 are configured on the second main surface 134 side of optical filter 130. Housing 140 has a box shape with one open side, and the open opening 142 is blocked by optical filter 130.

[0075] It should be noted that the housing 140 is not a necessary component of the detection device 100. For example, when the detection device 100 is configured as part of a ceiling, wall, or floor, that is, when the infrared light source 110 and the infrared sensor 120 are disposed 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.

[0076] In the detection apparatus 100 of this embodiment, an object 10 is detected as follows: An infrared light source 110 emits infrared rays IR1 to illuminate the object 10 via an optical filter 130. The wavelength of the infrared rays IR1 can be, for example, 780 nm or more and 4000 nm or less, preferably 780 nm or more and 2500 nm or less. An infrared sensor 120 detects infrared rays IR2 reflected by the object 10 via the optical filter 130. The optical filter 130 is configured to cut across the infrared rays IR1 emitted from the infrared light source 110. The optical filter 130 forward-scatters the infrared rays IR1 incident on the second main surface 134, and the forward-scattered infrared rays IR1 are incident on the object 10. The optical filter 130 also forward-scatters the infrared rays IR2 reflected by the object 10 and incident on the first main surface 132, and the forward-scattered infrared rays IR2 are incident on the infrared sensor 120.

[0077] Unlike the detection device 100 of this embodiment, in the structure using an optical filter that allows infrared light to be transmitted in a straight line, the infrared light emitted from the infrared light source 110 and passing through the object 10 into the infrared sensor 120 contains a large amount of linearly reflected components from the object 10. Therefore, when such infrared light is detected, glare is generated due to the linearly reflected components from the object 10, which may prevent the object 10 from being detected clearly.

[0078] In this regard, in the detection device 100 of this embodiment, infrared light emitted from the infrared light source 110 and passing through the object 10 into the infrared sensor 120 is forward-scattered twice by the optical filter 130. Since the object 10 is illuminated by the forward-scattered infrared light IR1, the linear reflection component from the object 10 can be reduced. Furthermore, since the forward-scattered infrared light IR2 reflected by the object 10 is detected, the linear reflection component from the object 10 can be further reduced. As a result, glare when detecting the object 10 through 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 time-of-flight method can also be used to determine the distance from the detection device 100 to the object 10.

[0079] Figure 1BAnother schematic cross-sectional view of the detection device 100, illustrating an exemplary embodiment of the present invention, is shown. An optical filter 130 backscatters visible light VL incident on the first principal surface 132. This backscattering by the optical filter 130 reduces the amount of visible light VL reaching the infrared light source 110 and the infrared sensor 120. Even if a portion of the visible light VL enters the infrared light source 110 and the infrared sensor 120, the visible light reflected by the infrared light source 110 and the infrared sensor 120 and incident on the second principal surface 134 is also backscattered by the optical filter 130. Therefore, the likelihood of seeing the infrared light source 110 and the infrared sensor 120 from the first principal surface 132 side of the optical filter 130 is reduced. Figure 1A When the object 10 shown is a person, it can effectively reduce the possibility that the person's original actions or movements may change due to psychological changes caused by being able to see the infrared light source 110 and the infrared sensor 120.

[0080] Unlike the detection device 100 of this embodiment, in structures using optical filters that absorb visible light, heat may be generated in the optical filters. The heat generated by the optical filters may adversely affect the infrared light source 110 and the infrared sensor 120. In contrast, in the detection device 100 of this embodiment, the optical filter 130 backscatters visible light VL, thus reducing the heat generated by the absorption of visible light VL.

[0081] Unlike dielectric multilayer films with a mirror-like appearance, optical filter 130 has a white optical layer, which will be described in detail later. The L* value of the optical layer, measured by SCE method in the CIE 1976 color space, is 20 or higher.

[0082] A white optical layer reduces the likelihood of the infrared light source 110 and infrared sensor 120 being visible from the outside, and increases the design freedom of the detection device 100. When a design is applied to a mirror-like surface, the mirror background may be more noticeable than the design itself. In contrast, when a design is applied to a white surface, the design is more noticeable than the white background. In this specification, "design" refers to the texture and color of an object. Texture includes graphics or patterns. Color can also be monochromatic, and can include combinations of colors with the same hue but different chroma. Colors, graphics, or patterns can also employ tile-style textures.

[0083] As described above, in the detection device 100 of this embodiment, the possibility of seeing the infrared light source 110 and the infrared sensor 120 can be reduced by the optical filter 130. In addition, the heat generated by the optical filter 130 due to the absorption of visible light VL can be reduced, and glare when detecting the object 10 by infrared IR1 can be reduced.

[0084] Alternatively, the structure of the detection device 100 without the infrared sensor 120 can be used as a light source device. In this light source device, the object 10 is illuminated by forward-scattered infrared light IR1, thus reducing the linear reflection component from the object 10. Alternatively, the structure of the detection device 100 without the infrared light source 110 can be used as a sensor device. In this sensor device, infrared light IR2 reflected and forward-scattered by the object 10 is detected, thus reducing the linear reflection component from the object 10. Both the light source device and the sensor device facilitate clear detection of the object 10 using infrared light.

[0085] [Optical laminate]

[0086] The hidden object is not limited to the infrared light source 110 and the infrared sensor 120. Next, refer to... Figure 2A and Figure 2B An example of the structure of the optical laminate of the optical filter using an embodiment of the present invention will be described.

[0087] Figure 2A The figure shows a schematic cross-sectional view of an optical laminate according to an example embodiment of the present invention. Figure 2A The optical laminate 200 shown includes the aforementioned optical filter 130 and a recording medium layer 150 having a pattern that can be read by infrared light via the optical filter 130. Figure 2A The diagram also shows an infrared light source 110 and an infrared sensor 120 for reading 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 disposed on the second main surface 134 side of the optical filter 130. Figure 2A In the example shown, the pattern on the recording medium layer 150 is a QR code, a type of AR tag. The pattern on the recording medium layer 150 can be an information-containing pattern like an AR tag, or it can be a general design. The optical laminate 200 can be configured, for example, as part of a ceiling, wall, or floor.

[0088] In the optical laminate 200 of this embodiment, the pattern of the recording medium layer 150 is read as follows: An infrared light source 110 emits infrared light IR1 to illuminate the pattern of the recording medium layer 150 via an optical filter 130. An infrared sensor 120 detects infrared light IR2 reflected by the recording medium layer 150 via the optical filter 130. The optical filter 130 causes the infrared light IR1 incident on the first main surface 132 to be forward scattered. The forward-scattered infrared light IR1 is incident on the recording medium layer 150. The optical filter 130 also causes the infrared light IR2 reflected by the recording medium layer 150 and incident on the second main surface 134 to be forward-scattered. The forward-scattered infrared light IR2 is incident on the infrared sensor 120.

[0089] Unlike the optical laminate 200 of this embodiment, in the structure using an optical filter that allows infrared light to be transmitted in a straight line, the infrared light emitted from the infrared light source 110 and passing through the recording medium layer 150 to enter the infrared sensor 120 contains a large amount of linearly reflected components from the recording medium layer 150. Therefore, when such infrared light is detected, glare is generated due to the linearly reflected components from the recording medium layer 150, which may prevent the pattern on the recording medium layer 150 from being clearly detected.

[0090] In this regard, in the optical laminate 200 of this embodiment, the infrared light emitted from the infrared light source 110 and passing through the recording medium layer 150 to enter the infrared sensor 120 is forward-scattered twice by the optical filter 130, thus effectively reducing the linear reflection component from the recording medium layer 150. As a result, glare when detecting the pattern of the recording medium layer 150 using infrared IR1 can be reduced, and the pattern of the recording medium layer 150 can be detected more clearly.

[0091] Figure 2B The image shows another schematic cross-sectional view of an optical laminate according to an exemplary embodiment of the present invention. The optical filter 130 backscatters visible light VL incident on the first principal surface 132. Due to the backscattering by the optical filter 130, the amount of visible light VL reaching the recording medium layer 150 can be reduced. Even if a portion of the visible light VL enters the recording medium layer 150, the visible light reflected by the recording medium layer 150 is also backscattered by the optical filter 130. Therefore, the likelihood of seeing the recording medium layer 150 from the first principal surface 132 side of the optical filter 130 can be reduced.

[0092] Unlike the optical laminate 200 of this embodiment, in structures using optical filters that absorb visible light, heat may be generated in 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 of this embodiment, the optical filter 130 backscatters visible light VL, thus reducing the heat generated by the absorption of visible light VL.

[0093] 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 increases the design freedom of the optical stack 200.

[0094] As described above, in the optical laminate 200 of this embodiment, the optical filter 130 can reduce the likelihood of the pattern of the recording medium layer 150 being seen. Furthermore, it can reduce the heat generated by the optical filter 130 due to absorption of visible light (VL), and reduce glare when detecting the pattern of the recording medium layer 150 using infrared light (IR1).

[0095] It should be noted that the object hidden by the optical filter 130 is not limited to the pattern of the infrared light source 110 and infrared sensor 120 included in the detection device 100 and the recording medium layer 150 included in the optical laminate 200, but can be any object.

[0096] [Structure of an optical filter]

[0097] Next, refer to Figures 3A to 3D The structure of the optical filter according to the embodiments of the present invention will be described in detail.

[0098] Figure 3A A schematic cross-sectional view of an optical filter illustrating an exemplary embodiment of the present invention. Figure 3A The illustrated optical filter 130 includes: an optical layer 130A that backscatters visible light and transmits infrared light in a straight line; a scattering layer 130B disposed on the optical layer 130A that forward-scatters infrared light; and a substrate layer 130C that supports the optical layer 130A. The scattering layer 130B does not need to forward or backscatter visible light. The scattering layer 130B can be disposed directly on the optical layer 130A or disposed on the optical layer 130A via other layers. The scattering layer 130B can be, for example, an anti-glare layer or a layer formed of an adhesive containing scattering components. Figure 3A The haze value of the optical filter 130 for infrared light shown can be, for example, 40% or more, more preferably 60% or more. Here, the haze value for infrared light is the average of the haze values ​​with wavelengths of 800 nm or more and 2000 nm or less.

[0099] exist Figure 3A In the optical filter 130 shown, Figures 1A to 2B The first main surface 132 shown 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 can also be opposite.

[0100] exist Figure 3AIn the optical filter 130 shown, infrared light incident from the scattering layer 130B side is forward-scattered by the scattering layer 130B and passes sequentially through the optical layer 130A and the substrate layer 130C. Infrared light incident from the substrate layer 130C side passes sequentially through the substrate layer 130C and the optical layer 130A, and is forward-scattered by the scattering layer 130B. Visible light incident from the scattering layer 130B side passes through the scattering layer 130B, is backscattered by the optical layer 130A, and passes through the scattering layer 130B again. Visible light incident from the substrate layer 130C side passes through the substrate layer 130C, is backscattered by the optical layer 130A, and passes through the substrate layer 130C again. Thus, Figure 3A The optical filter 130 shown causes visible light to backscatter and infrared light to forward scatter.

[0101] Figure 3B A schematic cross-sectional view illustrating another embodiment of the optical filter of the present invention. Figure 3B The illustrated optical filter 130 includes: 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 is equivalent to backscattering visible light and forward transmitting infrared light. Figure 3A The optical layer 130A is shown. The scattering surface 132D can be formed, for example, by transferring the uneven shape of the uneven part onto the flat surface of the optical layer 130A or by performing sandblasting. The arithmetic mean roughness Ra of the scattering surface 132D can be, for example, 1 μm or more, and the maximum height Rz can be, for example, 15 μm or more. Figure 3B The haze value of the optical filter 130 relative to infrared light can be, for example, 40% or more, more preferably 60% or more, and even more preferably 80% or more. Here, the haze value relative to infrared light is the average of haze values ​​with wavelengths of 800 nm or more and 2000 nm or less.

[0102] exist Figure 3B In the optical filter 130 shown, Figures 1A to 2B The first main surface 132 shown 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 can also be opposite.

[0103] exist Figure 3BIn the optical filter 130 shown, infrared light incident from the optical layer 130D side is forward-scattered by the scattering surface 132D and passes through the optical layer 130D and the substrate layer 130C in sequence. Infrared light incident from the substrate layer 130C side passes through the substrate layer 130C and the optical layer 130D in sequence and is forward-scattered by the scattering surface 132D. Visible light incident from the optical layer 130D side is backscattered by the optical layer 130D. Visible light incident from the substrate layer 130C side passes through the substrate layer 130C, is backscattered by the optical layer 130D, and passes through the substrate layer 130C again. Thus, Figure 3B The optical filter 130 shown causes visible light to backscatter and infrared light to forward scatter.

[0104] Typically, scattering layers or scattering surfaces cause visible light to scatter forward or backward in order to reduce glare when viewed. In contrast, the scattering layer 130B or scattering surface 132D included in the optical filter 130 of this embodiment causes infrared light to scatter forward. The optical filter 130 of this embodiment is superior to optical filters that cause infrared light to transmit in a straight line because it can reduce glare when detecting the pattern of the object 10 or the recording medium layer 150 using infrared IR1.

[0105] The optical filter 130 of the present invention may also include other layers. Figure 3C and Figure 3D The figure shows a schematic cross-sectional view of an optical filter according to another embodiment of the present invention. Figure 3C The optical filter 130 shown, in addition to Figure 3A In addition to the optical layer 130A, scattering layer 130B and substrate layer 130C shown, there is also a design layer 130E disposed on the scattering layer 130B. Figure 3D The optical filter 130 shown, in addition to Figure 3B In addition to the optical layer 130D and the substrate layer 130C shown, the optical layer 130D also includes a design layer 130E disposed on the optical layer 130D.

[0106] Design layer 130E preferably has high infrared transmittance. Design layer 130E can be a film, such as a decorative film, or it can be non-film. The thickness of design layer 130E is, for example, 1 μm or more and 150 μm or less. In this specification, when the surface of the layer is not flat, the maximum thickness of the layer is treated as the thickness of the layer.

[0107] The optical filter 130 of this embodiment may also have other functional layers that perform specific functions. In this case, a single functional layer may perform two or more functions, or at least one of the aforementioned layers may be assigned other functions. The functions that can be assigned to the optical filter 130 are not particularly limited; the optical filter 130 of this embodiment is as follows: Figure 3C and Figure 3D As shown, it also includes a surface protective layer 130F disposed on the design layer 130E. The surface protective layer 130F may be configured to perform functions such as hard coating (HC) to provide scratch resistance, anti-fouling, anti-glare (AG) or anti-reflection (AR).

[0108] exist Figure 3C and Figure 3D In the optical filter 130 shown, Figures 1A to 2B The first main surface 132 shown 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 substrate layer 130C opposite to the optical layers 130A and 130D.

[0109] The optical filter 130 of this embodiment 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 can be formed, for example, from a transparent plastic such as acrylic resin. To improve visibility suppression in visible light, the substrate layer 130C can include a dielectric multilayer film with a mirror-like appearance. The thickness of the substrate layer 130C is, for example, about 2 μm or more and about 10 mm or less.

[0110] The optical layers 130A and 130D included in the optical filter 130 of this embodiment are white. Here, white means that the x and y coordinates on the CIE 1931 chromaticity diagram, when using standard light as the D65 light source, are in the range of 0.25 ≤ x ≤ 0.40 and 0.25 ≤ y ≤ 0.40, respectively. Of course, the closer to x = 0.333 and y = 0.333, the higher the whiteness; preferably, it is 0.28 ≤ x ≤ 0.37 and 0.28 ≤ y ≤ 0.37, more preferably 0.30 ≤ x ≤ 0.35 and 0.30 ≤ y ≤ 0.35. Furthermore, the L* measured by SCE method in the CIE 1976 color space is preferably 20 or higher, more preferably 40 or higher, more preferably 50 or higher, and particularly preferably 60 or higher. If L* is 20 or higher, it can be said to be approximately white. The upper limit of L* is, for example, 100. For example, measurements based on the SCE method can be performed using a spectrophotometer CM-2600-D (manufactured by Konica Minolta Japan Co., Ltd.).

[0111] 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.

[0112] Figure 4 This is a schematic cross-sectional view of the interior of optical layers 130A and 130D included in optical filter 130. Optical layers 130A and 130D have a matrix 12 and particles 14 dispersed in the matrix 12 as light scatterers. Particles 14 function as light scatterers. Particles 14 may, for example, at least constitute a colloidal amorphous aggregate. In this case, other particles that do not disturb the colloidal amorphous aggregate constituted by particles 14 may also be included.

[0113] Optical layers 130A and 130D do not contain cholesterol-type liquid crystals (high molecular weight liquid crystals, low molecular weight liquid crystals, liquid crystal mixtures thereof, and liquid crystals cured by mixing crosslinking agents in these liquid crystal materials and crosslinking, etc., broadly including liquid crystals exhibiting a cholesterol-type phase). Furthermore, optical layers 130A and 130D are, for example, generally film-like, but not limited to this.

[0114] The transparent microparticles 14 are, for example, silica microparticles. As silica microparticles, silica microparticles synthesized via the Sterb process can be used, for example. Alternatively, inorganic microparticles other than silica microparticles, or resin microparticles, can be used as microparticles. As resin microparticles, microparticles composed of at least one of polystyrene and polymethyl methacrylate are preferred, and microparticles composed of cross-linked polystyrene, cross-linked polymethyl methacrylate, or cross-linked styrene-methyl methacrylate copolymers are more preferred. It should be noted that, for example, polystyrene microparticles or polymethyl methacrylate microparticles synthesized by emulsion polymerization can be appropriately used as such microparticles. Additionally, hollow silica microparticles containing air and hollow resin microparticles can also be used. Furthermore, microparticles formed from inorganic materials have the advantages of excellent heat resistance and light resistance. The volume fraction of microparticles relative to the total (including the matrix and microparticles) 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 microparticles 14 can also be optically isotropic.

[0115] Matrix 12 may include, for example, acrylic resins (e.g., polymethyl methacrylate, polymethyl acrylate), polycarbonate, polyester, poly(diethylene glycol dielyl carbonate), polyurethane, epoxy resin, polyimide, but is not limited to these. Matrix 2 is preferably formed using a curable resin (thermosetting or photocurable), and from the viewpoint of mass production, it is preferred to use a photocurable resin. Various (meth)acrylates can be used as photocurable resins. The (meth)acrylate is a difunctional or trifunctional (or higher) meth)acrylate. It is preferred to include acrylates. Furthermore, matrix 12 is preferably optically isotropic. If a curable resin containing multifunctional monomers is used, a matrix 12 with a cross-linked structure can be obtained, thus improving heat resistance and lightfastness.

[0116] The optical layers 130A and 130D formed from the resin material in the matrix 12 can be flexible films. The thickness of the optical layers 130A and 130D is, for example, 10 μm or more and 10 mm or less. If the thickness of the optical layers 130A and 130D is, for example, 10 μm or more and 1 mm or less, and further 10 μm or more and 500 μm or less, then significant flexibility can be achieved.

[0117] When using silica microparticles with a hydrophilic surface, the microparticles are preferably formed, 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 methacrylate, or 2-hydroxypropyl methacrylate, acrylamide, methylenebisacrylamide, and ethoxylated bisphenol A di(meth)acrylate. Furthermore, these monomers can be used alone or in combination. Of course, the two or more monomers can include monofunctional and polyfunctional monomers, or can include two or more polyfunctional monomers.

[0118] These monomers can be cured using a photopolymerization initiator. Examples of photopolymerization initiators include carbonyl compounds such as benzoin ethers, benzophenone, anthraquinones, thioalkanes, ketals, and acetophenone; sulfur compounds such as disulfides and dithiocarbamates; organic peroxides such as benzoyl peroxide; azo compounds; transition metal complexes; polysilane compounds; and pigment sensitizers. The additional amount is preferably 0.05 parts by mass or more and 3 parts by mass or less, more preferably 0.05 parts by mass or more and 1 part by mass or less, relative to 100 parts by mass of the mixture of fine particles and monomers.

[0119] When the refractive index of the matrix relative to visible light is set to n... M Let the refractive index of the particles be n. P When, |n M -n PThe refractive index difference (hereinafter sometimes simply referred to as the refractive index difference) is preferably 0.01 or more and preferably 0.6 or less, more preferably 0.03 or more and more preferably 0.11 or less. If the refractive index difference is less than 0.03, the scattering intensity weakens, making it difficult to obtain the desired optical properties. Furthermore, when the refractive index difference exceeds 0.11, the linear transmittance of infrared light sometimes decreases. Alternatively, for example, by using zirconium oxide microparticles (refractive index 2.13) and acrylic resin, when the refractive index difference is set to 0.6, the linear transmittance of infrared light can be adjusted by reducing the thickness. Thus, the linear transmittance of infrared light can also be adjusted, for example, by controlling the thickness and refractive index difference of the visible light scattering layer. Additionally, depending on the application, it can be used in conjunction with a filter that absorbs infrared light. It should be noted that the refractive index for visible light can be represented, for example, by the refractive index for light at 546 nm. Here, unless otherwise specified, the refractive index refers to the refractive index relative to light at 546 nm.

[0120] Figure 5 The images show cross-sectional TEM images of optical layers 130A and 130D. In the TEM images, white circles represent silica particles, and black circles represent traces of silica particle detachment. As shown in the cross-sectional TEM images of optical layers 130A and 130D, the silica particles are generally uniformly dispersed.

[0121] Figure 6 This is a curve normalized to maximum transmittance, representing the incident angle dependence of the linear transmittance spectra of optical layers 130A and 130D. (Observation) Figure 6 The transmittance curves of optical layers 130A and 130D, as shown, exhibit a linear transmittance curve that monotonically increases from visible light to infrared light, but this portion shifts towards longer wavelengths (approximately 50 nm) with increasing incident angle. In other words, the linear transmittance curve that monotonically decreases from infrared to visible light also shifts towards longer wavelengths with increasing incident angle. This characteristic incident angle dependence is attributed to the presence of colloidal amorphous aggregates of silica microparticles within the optical films. It should be noted that detailed information regarding the structure, optical properties, and manufacturing methods of optical layers 130A and 130D is described in the applicant's international application PCT / JP2021 / 010413. The entire disclosure of international application PCT / JP2021 / 010413 is incorporated herein by reference.

[0122] Optical layers 130A and 130D are not limited to layers in which particles 14, which serve as light scatterers, are dispersed in the matrix 12. Optical layers 130A and 130D can, for example, be fluoropolymer films. Fluoropolymers can be, for example, PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxyalkylene), FEP (perfluoroethylene-propylene copolymer), ETFE (ethylene tetrafluoroethylene copolymer), PVDF (polyvinylidene fluoride), PCTFE (polychlorotrifluoroethylene), ECTFE (ethylene trifluorochloroethylene copolymer), or CYTOP (manufactured by AGC). Additionally, fluoropolymers can also form foams. Furthermore, to improve mechanical strength, the resin can be impregnated with glass cloth. The thickness of optical layers 130A and 130D is, for example, 10 μm or more and 10 mm or less.

[0123] (Example of a design attached to optical filter 130)

[0124] Here, an example of the design added to the optical filter 130 is described in a structure where the detection device 100 or optical laminate 200 is configured as part of a ceiling, front wall, or floor. When the design of the surface surrounding the location where the detection device 100 or optical laminate 200 is configured is referred to as the peripheral design, and the design of the surface of the optical filter 130 is referred to as the filtering design, the filtering design is the same as or similar to the peripheral design. The filtering design and the peripheral design can have the same texture and color. For example, a decorative film can be used to add texture and color design to the surface of the optical filter 130 and the peripheral surface. The aforementioned surface protective layer can also be provided on the peripheral surface.

[0125] Reference Figures 7A to 7D This illustrates an example of the design of the surface that can be attached to the optical filter 130 and the surface surrounding the portion where the detection device 100 or the optical laminate 200 is configured. Figure 7A This illustrates an example where a continuous texture design is applied to the surface of the optical filter 130 and the surface of its periphery 100P. In this example, a single texture (design) is applied to the surface of the periphery 100P and the surface of the optical filter 130. This design can be achieved using a single decorative film. Therefore, there is no boundary of the physical film. The optical filter 130 is located at any position on the single texture, and 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.

[0126] Figure 7BThis example illustrates the application of a tile-style texture design to the surface of the optical filter 130 and the surrounding surface 100P. This design incorporates a patterned tile-style texture, achievable by arranging multiple decorative films on a planar or curved surface containing the optical filter 130 and the surrounding surface 100P. Therefore, physical film boundaries exist as seams between the films. The tile-style design includes not only... Figure 7B The texture shown includes textures formed by regularly arranging the same shape, as well as textures formed by irregularly arranging different shapes with varying boundary widths. The optical filter 130 can be configured at the boundary or across 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. Figure 7B In the example shown, the optical filter 130 is configured to span the boundary of a texture formed by regularly arranged star-shaped patterns.

[0127] Figure 7C This is another example of adding a tile-style texture design to the surface of the optical filter 130 and its surrounding surface 100P. This example design uses a tile-style color scheme, incorporating a combination of colors with the same hue but different chroma, which can be achieved by arranging multiple decorative films on a plane or curved surface containing the optical filter 130 and its surrounding surface 100P. Therefore, physical film boundaries exist as seams between the films. The design includes multiple regions 100R divided by the visible boundary 100B. The optical filter 130 is disposed in one of the multiple regions 100R. 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 presence of multiple detection devices 100 or optical laminates 200, the multiple optical filters 130 are respectively disposed in different regions of the multiple regions 100R. The multiple regions 100R can each have arbitrary colors or textures.

[0128] Figure 7D This is another example of a tile-style textured design applied to the surface of the optical filter 130 and the surface of its surrounding area 100P. The design comprises multiple regions 100R divided by a visible boundary 100B, each region 100R having an arbitrary texture. The optical filter 130 is positioned within one of these regions 100R. The patterns of the infrared light source 110 included in the detection device 100 and the infrared sensor 120, or the recording medium layer 150 included in the optical laminate 200, are hidden on the back side of the optical filter 130.

[0129] As described above, the color of the peripheral portion where the detection device 100 or optical stack 200 is disposed can be blended with the color of the surface of the optical filter 130 included in the detection device 100 or optical stack 200 to an indistinguishable degree. When the color of the surface surrounding the portion where the detection device 100 or optical stack 200 is disposed is called the peripheral color, and the color of the surface of the optical filter 130 is called 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, measured by the SCE method, is 3 or less. Here, a color difference of 3 or less means that if the a* and b* values ​​of the peripheral surface in the L*a*b* color system are set to a1* and b1* respectively, and the a* and b* values ​​of the surface of the optical filter 130 in the L*a*b* color system are set to a2* and b2* respectively, then the condition of the mathematical expression in mathematical formula 1 is satisfied.

[0130] [Mathematical Expression 1]

[0131] |a1*-a2*|≤3, and |b1*-b2*|≤3

[0132] An example of the L*a*b* color system is the CIE 1976 L*a*b* color system. From the viewpoint of improving the harmony between peripheral colors and filter colors, the color difference is preferably 1.5 or less, more preferably 0.4 or less. If the color difference is 3 or less, it can be harmonized to the point that peripheral colors and filter colors are indistinguishable, thus achieving excellent design flexibility.

[0133] (Example)

[0134] The present invention will now be specifically described through examples, but the present invention is not limited to these examples. Here, the optical filters of the comparative examples and embodiments will be evaluated using BRDF (bidirectional reflectance distribution function) and BTDF (bidirectional transmittance distribution function). First, the measurement methods for BRDF and BTDF will be explained. Next, the results of measuring BRDF and BTDF relative to visible light and infrared light will be explained for the optical filters of the comparative examples and embodiments.

[0135] [Methods for determining BRDF and BTDF]

[0136] Reference Figure 8A and Figure 8B The methods for measuring BRDF and BTDF are explained separately. BRDF is the intensity of reflected and scattered light produced by an object illuminated by light, as a function of the reflection angle. BTDF is the intensity of transmitted and scattered light produced by an object illuminated by light, as a function of the transmission angle. A goniometer (Nikka Electric Measurement, model: GP-4) is used for measuring BRDF and BTDF.

[0137] Figure 8AThis is a schematic cross-sectional view illustrating the method used to determine BRDF. Figure 8A In the example shown, the light source 80 and the sensor 90 are disposed on the first main surface 132 side of the optical filter 130. The first main surface 132 of the optical filter 130 is perpendicularly illuminated by light emitted from the light source 80, and the reflected and scattered light generated by the illumination is detected by the sensor 90. The reflected and scattered light is detected while the sensor 90 is moved in 1° increments within an angle range of -30° to 30°. This angle is the angle between the normal of 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, no reflected and scattered light is detected. In the following embodiments and comparative examples, the BRDF at angles of -5° to 5° was not measured.

[0138] Figure 8B This is a schematic cross-sectional view illustrating the method used to determine BTDF. Figure 8B In the example shown, the light source 80 is positioned on the second principal surface 134 side of the optical filter 130, and the sensor 90 is positioned on the first principal surface 132 side of the optical filter 130. The second principal surface 134 of the optical filter 130 is perpendicularly illuminated by light emitted from the light source 80, and the transmitted and scattered light generated by the illumination is detected by the sensor 90. The transmitted and scattered light is detected while the sensor 90 is moved in 1° increments within an angle range of -30° to 30°.

[0139] [Construction of optical filters in comparative examples and embodiments]

[0140] First, the construction of comparative examples 1 to 4 will be explained.

[0141] The optical filter of Comparative Example 1 comprises a substrate layer of glass with a thickness of 3 mm and an optical layer disposed on the substrate layer with a thickness of 1 mm or less. This optical layer is equivalent to the optical filter of Example 6 of the aforementioned international application (average particle size of silicon dioxide 221 μm, silicon dioxide content: 40% by mass).

[0142] The optical filter of Comparative Example 2 is a polyimide film (Aswan material, model: polyimide tape) with a thickness of 0.2 mm.

[0143] The optical filter of Comparative Example 3 is a fluoropolymer film with a thickness of 0.2 mm (manufactured by Nitto Denko, model: NITOFLON).

[0144] The optical filter of Comparative Example 4 is a black film (made by Nitto Resin, model: CLAREX) with a thickness of 0.5 mm.

[0145] Next, the construction of the optical filters in Examples 1 to 6 will be described. The optical filters in Examples 1 and 2 correspond to... Figure 3A The optical filter 130 shown. The optical filters of Examples 3-6 are equivalent to Figure 3B The optical filter 130 shown.

[0146] In addition to the substrate layer and optical layer included in the optical filter of Comparative Example 1, the optical filter of Example 1 also has an anti-glare layer (manufactured by Daicel Co., Ltd., model: PEN60) with a thickness of 60 μm disposed on the optical layer.

[0147] In addition to the substrate layer and optical layer included in the optical filter of Comparative Example 1, the optical filter of Example 2 also includes the following layer disposed on the optical layer. This layer is a 30 μm thick layer formed by an adhesive (manufactured by Nitto Denko) with a haze value adjusted to 80%.

[0148] The optical filters of Examples 3-6 differ from the optical filter of Comparative Example 1 in that they have a scattering surface in the optical layer. The scattering surface of the optical filters of Examples 3-6 is achieved by forming an uneven shape with the surface roughness shown in Table 1 on the surface of the optical layer included in the optical filter of Comparative Example 1.

[0149] Figure 9A and Figure 9B The images show cross-sectional TEM images of the optical filters from Examples 3 and 6, respectively. Figure 9A and Figure 9B As shown, the larger the diffusion angle of the lens diffuser, the rougher the scattering surface.

[0150] The arithmetic mean roughness Ra and maximum height Rz of the scattering surfaces in the optical filters of Comparative Example 1, Example 3, and Example 6 are shown in Table 1. The arithmetic mean roughness Ra and maximum height Rz were measured using a VK-X 1000 laser microscope (manufactured by KEYENCE). The arithmetic mean roughness Ra and maximum height Rz were calculated based on measurements of 1000 × 1000 points on a 2800 μm square at 5x magnification.

[0151] Table 1

[0152]

[0153] 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 in the optical filters of Examples 3 and 6 is 1 μm or more, and the maximum height Rz is 15 μm or more. Thus, the scattering surface in the optical filters of Examples 3 and 6 is rougher than the surface of the optical filter in Comparative Example 1.

[0154] Table 2 shows the haze values ​​relative to infrared light for the optical filters of Comparative Examples 1-4 and the optical filters of Examples 1-6. Here, the haze value relative to infrared light is the average value of the haze value in the range of wavelengths above 800 nm and below 2000 nm.

[0155] Table 2

[0156]

[0157] 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. Although the haze values ​​of the optical filters in Examples 1 and 2, which have scattering layers, are less than those of the optical filters in Examples 3-6, which have scattering surfaces, they are significantly greater than the haze value of the optical filter in Comparative Example 1, which does not have a scattering layer.

[0158] [BRDF and BTDF of optical filters in comparative and exemplary embodiments]

[0159] The BRDF and BTDF of the optical filters in the comparative examples and embodiments for visible light and infrared light will be described below. Visible light with a processing wavelength of 550 nm is used, and infrared light with a processing wavelength of 850 nm is used. However, the wavelengths of visible light and infrared light incident on the optical filter are not limited to these wavelengths. BTDF is expressed logarithmically. The BRDF and BTDF of visible light and infrared light incident at an angle of 0° are symmetrical about 0°. It should be noted that due to measurement errors, the measured BRDF and BTDF may not always be symmetrical about 0°.

[0160] First, refer to Figures 10A to 10D The BRDF and BTDF of the optical filters in Comparative Examples 1 to 4 will be explained.

[0161] Figure 10A and Figure 10B The BRDF and BTDF of the optical filters in Comparative Examples 1-4 represent the optical filters when visible light with a wavelength of 550 nm is incident at an angle of 0°. Figure 10A As shown, the BRDF of the optical filters in Comparative Examples 1-3 is 0.1 [1 / sr] or higher at angles above -30° and below -5° and below, and at angles above 5° and below 30°. The BRDF of the optical filter in Comparative Example 4 is approximately zero at angles above -30° and below -5° and below, and at angles above 5° and below 30°. This is because the optical filter in Comparative Example 4 is a black thin film that absorbs visible light. Figure 10BAs shown, the BTDF of the optical filter of Comparative Example 1 is 150 [1 / sr] or more near an angle of 0°. In other words, the optical filter of Comparative Example 1 exhibits high linear transmittance for visible light. In contrast, the BTDF of the optical filters of Comparative Examples 2 and 3 is 3 [1 / sr] or less at angles between -30° and 30°, and the BTDF of the optical filter of Comparative Example 4 is 0.2 [1 / sr] or less at angles between -30° and 30°. Therefore, the optical filters of Comparative Examples 1 to 3 effectively backscatter visible light, and the optical filters of Comparative Examples 2 and 3 effectively reduce the transmission of visible light. The optical filter of Comparative Example 4 effectively absorbs visible light.

[0162] The BRDF of the optical filters in Comparative Examples 1-3 for visible light with a wavelength of 550 nm is described in more detail below. The BRDF of the optical filters in Comparative Examples 1 and 3 is approximately constant at angles between -30° and -5° and between 5° and 30°, and is 0.1 [1 / sr] or more. The BRDF of the optical filter in Comparative Example 2 decreases monotonically as the angle approaches -5° to -30° or from 5° to 30°, but remains 0.1 [1 / sr] or more.

[0163] Figure 10C and Figure 10D The BRDF and BTDF of the optical filters in Comparative Examples 1-4 are represented respectively when infrared light with a wavelength of 850 nm is incident at an angle of 0°. Figure 10C As shown, the BRDF of the optical filters in Comparative Examples 1 to 4 is 0.1 [1 / sr] or less at angles of -30° to 5° and 5° to 30°. Figure 10D As shown, the BTDF of the optical filters in Comparative Examples 1-4 exhibits a high value of over 100 [1 / sr] near the angle of 0°. In other words, the optical filters in Comparative Examples 1-4 exhibit high linear transmission relative to infrared light. The logarithmic representation of the BTDF of the optical filters in Comparative Examples 1-4 monotonically decreases as the angle approaches ±30°. The logarithmic representation of the BTDF of the optical filters in Comparative Examples 1-4 bulges downward at angles above -30° and below 0°, and at angles above 0° and below 30°. Thus, the logarithmic representation of the BTDF of Comparative Examples 1-4 represents a Lambertian distribution. Therefore, the optical filters in Comparative Examples 1-4 effectively reduce infrared reflection, enabling efficient linear transmission of infrared light.

[0164] The more detailed behavior of the BTDF of the optical filters in Comparative Examples 1-4 for infrared light with a wavelength of 850 nm is described below. The BTDF of the optical filters in Comparative Examples 1 and 4 is approximately the same. The logarithmic representation of the BTDF of the optical filters in Comparative Examples 1 and 4 decreases monotonically downwards with an angle approaching ±30°, and the BTDF is close to 0.01 [1 / sr]. In contrast, the logarithmic representation of the BTDF of the optical filters in Comparative Examples 2 and 3 decreases monotonically downwards with an angle approaching ±30°, but the BTDF is greater than 0.1 [1 / sr].

[0165] The BTDF of the optical filters in Comparative Examples 1-4 can be specified 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 light. With the BTDF value at -1° set as value A, the BTDF value at -10° set as value B, the BTDF value at 1° set as value C, and the BTDF value at 10° set as value D, the values ​​A, B, C, D, A / B, and C / D of the BTDF of the optical filters in Comparative Examples 1-4 are 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°).

[0166] Table 3

[0167]

[0168] In the BTDF of the optical filters in Comparative Examples 1 to 4, the ratio of (-1° value) to (-10° value) and the ratio of (1° value) to (10° value) are greater than 30. The optical filters of each comparative example are described below. In the BTDF of the optical filter in Comparative Example 3, the ratio of (-1° value) to (-10° value) and the ratio of (1° value) to (10° value) are greater than 30. In the BTDF of the optical filter in Comparative Example 2, the ratio of (-1° value) to (-10° value) and the ratio of (1° value) to (10° value) are greater than 40. In the BTDF of the optical filters in Comparative Examples 1 and 4, the ratio of (-1° value) to (-10° value) and the ratio of (1° value) to (10° value) are greater than 500.

[0169] As described 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.

[0170] Next, we will refer to Figures 11A to 11DThe BRDF and BTDF of the optical filters in Examples 1 and 2 will be described.

[0171] Figure 11A and Figure 11B The BRDF and BTDF of the optical filters in Examples 1 and 2 represent the optical filters when visible light with a wavelength of 550 nm is incident at an angle of 0°. Figure 11A As shown, the BRDF of the optical filters in Embodiments 1 and 2 is 0.1 [1 / sr] or higher at angles above -30° and below -5° and above 5° and below 30°. Figure 11B As shown, the BTDF of the optical filters of Embodiments 1 and 2 is less than 12 [1 / sr] at angles above -30° and below 30°. Therefore, the optical filters of Embodiments 1 and 2 effectively backscatter visible light and effectively reduce the transmission of visible light.

[0172] The BRDF of the optical filters of Examples 1 and 2 for visible light with a wavelength of 550 nm is described in more detail below. Compared to the BRDF of the optical filter of Comparative Example 1 without a scattering layer, the BRDF of the optical filters of Examples 1 and 2 with the scattering layer increases at angles of 10° to 5° and 5° to 10°. Therefore, it can be seen that the scattering layer included in the optical filters of Examples 1 and 2 increases the backscattering of visible light.

[0173] Figure 11C and Figure 11D The BRDF and BTDF of the optical filters in Examples 1 and 2 are respectively represented when infrared light with a wavelength of 850 nm is incident at an incident angle of 0°. Figure 11C As shown, the BRDF of the optical filters in Embodiments 1 and 2 is 0.35 [1 / sr] or less at angles above -30° and below -5° and above 5° and below 30°, and more specifically, it is 0.1 [1 / sr] or less at angles above -30° and below -15° and above 15° and below 30°. Figure 11DAs shown, the BTDF of the optical filter of Embodiment 2 exhibits a high value of over 100 [1 / sr] near an angle of 0°, but the BTDF of the optical filter of Embodiment 1 is less than 50 [1 / sr] at angles between -5° and 5° near 0°, more specifically less than 30 [1 / sr]. The logarithmic representation of the BTDF of the optical filters of Embodiments 1 and 2 monotonically decreases as the angle approaches ±30° from 0°. The logarithmic representation of the BTDF of the optical filters of Embodiments 1 and 2 has a portion that bulges upward at angles between -30° and -2° and at angles between 2° and 30°. The optical filters of each embodiment are as follows. The logarithmic representation of the BTDF of the optical filter of Embodiment 1 has a portion that bulges upward at angles between -10° and -2° and at angles between 2° and 10°. The logarithmic representation of the BTDF of the optical filter in Example 2 has a portion that bulges upward at angles greater than -15° and less than -5°, and at angles greater than 5° and less than 15°. As described above, the logarithmic representation of the BTDF in Examples 1 and 2 represents a non-Lambertian distribution. The bulging upward variation indicates increased forward scattering. Therefore, the optical filters of Examples 1 and 2 effectively reduce infrared reflection and effectively forward scatter infrared light.

[0174] The BTDF of the optical filters of Examples 1 and 2 for infrared light with a wavelength of 850 nm is described in more detail below. Compared to the BTDF of the optical filter of Comparative Example 1 without a scattering layer, the BTDF of the optical filters of Examples 1 and 2 with the scattering layer is larger at angles greater than -30° and less than -2° and at angles greater than 2° and less than 30°. Therefore, it can be seen that the scattering layer included in the optical filters of Examples 1 and 2 increases the forward scattering of infrared light.

[0175] The BTDF of the optical filters in Examples 1 and 2, which cause infrared forward scattering, can be specified 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.

[0176] Table 4

[0177]

[0178] In the BTDF of the optical filters of Embodiments 1 and 2, the ratio of (-1° value) / (-10° value) and the ratio of (1° value) / (10° value) are 20 or less. The optical filters of each embodiment are as follows. In the BTDF of the optical filter of Embodiment 1, the ratio of (-1° value) / (-10° value) and the ratio of (1° value) / (10° value) are 20 or less, more specifically 16 or less. In the BTDF of the optical filter of Embodiment 2, the ratio of (-1° value) / (-10° value) and the ratio of (1° value) / (10° value) are 10 or less, more specifically 8 or less. The ratios of (-1° value) / (-10° value) and (1° value) / (10° value) in the BTDF of the optical filters of Embodiments 1 and 2 are less than those in the BTDF of the optical filters of Comparative Examples 1 to 4.

[0179] As described above, the optical filters of Embodiments 1 and 2 effectively backscatter visible light and effectively forward scatter infrared light.

[0180] Next, we will refer to Figures 12A to 12D The BRDF and BTDF of the optical filters in Examples 3 to 6 will be described.

[0181] Figure 12A and Figure 12B The BRDF and BTDF of the optical filters in Examples 3-6 represent the optical filters when visible light with a wavelength of 550 nm is incident at an angle of 0°. Figure 12A As shown, the BRDF of the optical filters in Examples 3-6 is approximately the same, and is 0.1 [1 / sr] or higher at angles above -30° and below -5° and above 5° and below 30°. Figure 12B As shown, the BTDF of the optical filters in Examples 3-6 is less than 2[1 / sr] at angles above -30° and below 30°. Therefore, the optical filters in Examples 3-6 effectively backscatter visible light and effectively reduce the transmission of visible light.

[0182] The BRDF of the optical filters of Examples 3-6 for visible light at a wavelength of 550 nm is described in more detail below. The BRDF of the optical filters of Examples 3-6, which have a scattering surface in the optical layer, is substantially the same as that of the optical filter of Comparative Example 1, which does not have a scattering surface in the optical layer. Therefore, it can be seen that the scattering surface of the optical layer included in the optical filters of Examples 3-6 has almost no effect on the backscattering of visible light.

[0183] Figure 12C and Figure 12DThe BRDF and BTDF of the optical filters in Examples 3-6 represent the optical filters when infrared light with a wavelength of 850 nm is incident at an angle of 0°. Figure 12C As shown, the BRDF of the optical filters in Examples 3-6 is 0.1 [1 / sr] or less at angles between -30° and 5° and between 5° and 30°. Figure 12D As shown, the BTDF of the optical filters in Examples 3-6 is less than 10[1 / sr] at angles between -5° and 5° near 0°. The logarithmic representation of the BTDF of the optical filters in Examples 3-6 monotonically decreases as the angle approaches ±30° from 0°. The logarithmic representation of the BTDF of the optical filters in Examples 3-6 exhibits an upwardly convex variation at angles between -30° and -2° and angles between 2° and 30°. Thus, the logarithmic representation of the BTDF of Examples 3-6 represents a non-Lambertian distribution. As described above, the upwardly convex variation indicates increased forward scattering. Therefore, the optical filters in Examples 3-6 effectively reduce infrared reflection and effectively forward scatter infrared light.

[0184] The BTDF of the optical filters of Examples 3-6 for infrared light with a wavelength of 850 nm is described in more detail below. Compared to the optical filter of Comparative Example 1, which does not have a scattering surface, the BTDF of the optical filters of Examples 3-6, whose optical layers have a scattering surface, increases at angles greater than -30° and less than -2°, and at angles greater than 2° and less than 30°. The larger the diffusion angle of the lens diffuser, the smaller the BTDF near the 0° angle. Therefore, it can be seen that the scattering surface of the optical layer included in the optical filters of Examples 3-6 increases the forward scattering of infrared light.

[0185] The BTDF of the optical filters of Examples 3-6 that cause infrared forward scattering can be defined by (value of -1°) / (value of -10°) and (value of 1°) / (value of 10°) in the same way as the BTDF of the optical filters of Examples 1 and 2. The A value, B value, C value, D value, A value / B value, and C value / D value in the BTDF of the optical filters of Examples 3-6 are shown in Table 5.

[0186] Table 5

[0187]

[0188] In the optical filters of Examples 3-6, the ratio of (-1° value) / (-10° value) and the ratio of (1° value) / (10° value) are 5 or less, more specifically, 2 or less. The ratios of (-1° value) / (-10° value) and (1° value) / (10° value) of the BTDF of the optical filters of Examples 3-6 are significantly smaller than those of the optical filters of Comparative Examples 1-4.

[0189] As can be seen from the above, the optical filters of Examples 3 to 6 effectively backscatter visible light and effectively forward scatter infrared light.

[0190] The results obtained from the optical filters of Examples 1-6 relative to the BRDF and BTDF of visible light and infrared light are summarized as follows.

[0191] Regarding the optical filters of Examples 1-6, the BRDF (bidirectional reflectance distribution function) of visible light with a wavelength of 550 nm incident at an angle of 0° is 0.1 [1 / sr] or higher at angles of -30° to 5° and 5° to 30°. Therefore, the optical filters of Examples 1-6 can effectively backscatter visible light. As a result, heat generation caused by the absorption of visible light can be reduced.

[0192] Regarding the optical filters of Examples 1-6, infrared light with a wavelength of 850 nm, expressed as the logarithm of the BTDF at an incident angle of 0°, exhibits a portion that bulges upward at angles greater than -30° and less than -2°, and greater than 2° and less than 30°. Therefore, the optical filters of Examples 1-6 can effectively scatter infrared light forward. As a result, glare when detecting objects using infrared light can be reduced.

[0193] In the optical filters of Examples 1 to 6, when infrared light with a wavelength of 850 nm is incident at an angle of 0°, the BTDF (value of -1°) / (value of -10°) and (value of 1°) / (value of 10°) are 20 or less. The optical filters of each embodiment are as follows: In the optical filter of Example 1, the BTDF (value of -1°) / (value of -10°) and (value of 1°) / (value of 10°) are 20 or less. In the optical filter of Example 2, the BTDF (value of -1°) / (value of -10°) and (value of 1°) / (value of 10°) are 10 or less. In the optical filters of Examples 3 to 6, the BTDF (value of -1°) / (value of -10°) and (value of 1°) / (value of 10°) are 5 or less.

[0194] In the BTDF of the optical filters of Comparative Examples 1-4 when infrared light of wavelength 850 nm is incident at an angle of 0°, the ratios (-1°) / (-10°) and (1°) / (10°) are greater than 30. Therefore, in the BTDF of the optical filters when infrared light of wavelength 850 nm is incident at an angle of 0°, when the ratios (-1°) / (-10°) and (1°) / (10°) are 30 or less, this optical filter can effectively forward scatter infrared light compared to the optical filters of Comparative Examples 1-4. When the ratios (-1°) / (-10°) and (1°) / (10°) are 25 or less, this optical filter can more effectively forward scatter infrared light. When the ratios (-1°) / (-10°) and (1°) / (10°) are 20 or less, this optical filter can more effectively forward scatter infrared light.

[0195] Regarding the optical filters of Examples 1 and 3-6, the BTDF (transmission resistance factor) of infrared light with a wavelength of 850 nm incident at an angle of 0° is 50 [1 / sr] or less at angles between -5° and 5°. Specifically, regarding the optical filters of Examples 3-6, the BTDF of infrared light with a wavelength of 850 nm incident at an 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 the linear transmission of infrared light, and as a result, can more effectively reduce glare when detecting objects using infrared light. In particular, the optical filters of Examples 3-6 can more effectively reduce the linear transmission of infrared light, and as a result, can more effectively reduce glare when detecting objects using infrared light.

[0196] [Linear transmittance and diffuse transmittance of visible light for optical filters in comparative examples and embodiments]

[0197] The linear transmittance, diffuse transmittance, and total transmittance of the optical filters of Comparative Examples 1-4 and Examples 1-6 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 linear transmittance, diffuse transmittance, and total transmittance for wavelengths of 380 nm and above and 780 nm and below.

[0198] Table 6

[0199]

[0200] Linear transmittance was evaluated as follows. Linear transmittance was measured with the optical stack positioned at a certain distance (e.g., 20 cm) from the opening of the integrating sphere. A UH4150 UV-Vis-NIR spectrophotometer (manufactured by Hitachi High Technology Scientific Co., Ltd.) was used as the spectrometer. Diffusion transmittance was evaluated as follows. Diffusion transmittance was obtained as the difference between total transmittance and linear transmittance. Total transmittance was measured with the optical stack positioned at the opening of the integrating sphere.

[0201] 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 diffusion 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.

[0202] Therefore, it can be seen that the optical filters of Comparative Examples 2-4 and Examples 1-4 have a linear transmittance of less than 10%, 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 less than 54%, thus they are not as effective at transmitting visible light.

[0203] [Comparative Examples and Embodiments: Linear Transmittance and Diffusion Transmittance of Optical Filters for Infrared Rays]

[0204] The linear transmittance, diffuse transmittance, and total transmittance of infrared light for the optical filters of Comparative Examples 1-4 and Examples 1-6 are shown in Table 7 below. Here, the linear transmittance, diffuse transmittance, and total transmittance for infrared light are the average values ​​of linear transmittance, diffuse transmittance, and total transmittance in the range of wavelengths above 800 nm and below 2000 nm.

[0205] Table 7

[0206]

[0207] As shown in Table 7, the optical filters of Comparative Examples 1-4 have a linear transmittance of 40% or more. In contrast, the optical filters of Examples 1 and 3-6 have a linear transmittance of 35% or less. The optical filters of Examples 3-6 have a linear transmittance of 15% or less, more specifically 11% or less. Therefore, it can be seen that the optical filters of Examples 1 and 3-6 can effectively reduce the linear transmittance of infrared radiation compared to the optical filters of Comparative Examples 1-4. In particular, it can be seen that the optical filters of Examples 3-6 can reduce the linear transmittance of infrared radiation even more effectively.

[0208] As shown in Table 7, the diffusion transmittance of the optical filters in Comparative Examples 1-4 is less than 35%. In particular, the diffusion transmittance of the optical filters in Comparative Examples 1 and 4 is less than 5%. In contrast, the optical filters in Examples 1-6 have a diffusion transmittance of 35% or more. The optical filters in Examples 1 and 3-6 have a diffusion transmittance of 53% or more. In particular, the optical filters in Examples 3-6 have a diffusion transmittance of 70% or more. The optical filters in Examples 1 and 2, which have a scattering layer, have a lower diffusion transmittance than the optical filters in Examples 3-6, which have a scattering surface, but a higher diffusion transmittance than the optical filter in Comparative Example 1, which does not have a scattering layer. Therefore, it can be seen that the optical filters in Examples 1-6 can effectively increase the forward scattering of infrared light 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 more effectively increase the forward scattering of infrared light.

[0209] Furthermore, 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, it can be seen that, including linear transmittance and diffuse transmittance, the optical filters in Comparative Examples 1-4 and Examples 1-6 effectively transmit infrared radiation.

[0210] Explanation of reference numerals in the attached figures

[0211] 10: Objects

[0212] 12: Matrix

[0213] 14: Particles

[0214] 100: Detection device

[0215] 100B: Boundary

[0216] 100P: Merchandise

[0217] 100R: Area

[0218] 110: Infrared light source

[0219] 120: Infrared sensor

[0220] 130: Optical Filter

[0221] 130A: Optical layer

[0222] 130B: Scattering layer

[0223] 130C: Substrate layer

[0224] 130D: Optical layer

[0225] 130E: Design Layer

[0226] 130F: Surface protective layer

[0227] 132: First Main Page

[0228] 132D: Scattering surface

[0229] 134: Second Main Page

[0230] 140: Casing

[0231] 142: Opening

[0232] 150: Recording medium layer

[0233] 200: Optical laminate

Claims

1. An optical filter, characterized in that, The BRDF (bidirectional reflectance distribution function) of visible light with a wavelength of 550 nm incident at an angle of 0° is greater than 0.1 [1 / sr] at angles above -30° and below -5° and above 5° and below 30°. In the BTDF (bidirectional transmittance distribution function) of infrared radiation with a wavelength of 850 nm incident at an incident angle of 0°, the ratios of (value at -1°) / (value at -10°) and (value at 1°) / (value at 10°) are both below 30. The optical filter has the following features: An optical layer that backscatters the visible light and allows the infrared light to be transmitted in a straight line; A scattering layer, disposed directly or via other layers on the optical layer, forward scatters the infrared radiation.

2. The optical filter according to claim 1, characterized in that, The values ​​of (-1°) / (-10°) and (1°) / (10°) are below 25.

3. The optical filter according to claim 1, characterized in that, The BTDF is less than 50[1 / sr] at angles above -5° and below 5°.

4. The optical filter according to claim 1, characterized in that, The average diffusion transmittance in the wavelength range of 800 nm and above to 2000 nm is above 35%.

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

6. The optical filter according to claim 1, characterized in that, The L of the optical layer was measured using a spectrophotometer in the SCE (spot reflection removal) method. * The value is 20 or higher.

7. The optical filter according to claim 1, characterized in that, The optical layer has a matrix and particles dispersed in the matrix that act as light scatterers.

8. The optical filter according to claim 7, characterized in that, The particles at least constitute a colloidal amorphous aggregate.

9. The optical filter according to claim 8, characterized in that, The transmittance curve of the visible light wavelength region of the optical layer has a linear portion where the transmittance decreases monotonically from the long wavelength side to the short wavelength side, and this portion shifts towards the long wavelength side as the incident angle increases.

10. A detection device for detecting objects, characterized in that, have: An infrared light source that emits infrared rays to illuminate the object; An infrared sensor that detects infrared light reflected by the object; The optical filter according to any one of claims 1 to 9 is configured to cut across the infrared light emitted from the infrared light source.

11. An optical laminate, characterized in that, have: The optical filter according to any one of claims 1 to 9 has a first main surface and a second main surface opposite to the first main surface; A recording medium layer, disposed on the second main surface side of the optical filter, has a pattern that can be read by infrared light via the optical filter.

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