Optical filters and near-infrared cutoff filters

Abstract

An optical filter includes: a pair of light-transmitting surfaces, which are symmetrically oriented opposite each other in the thickness direction of the plate; and an outer peripheral surface extending from the pair of light-transmitting surfaces in the thickness direction of the plate. The optical filter comprises a glass plate and a protective film covering the glass plate. The protective film forms the pair of light-transmitting surfaces and the outer peripheral surface. An edge portion that forms the boundary between the light-transmitting surfaces and the outer peripheral surface has a curved shape. The edge portion has a plurality of recesses. The characteristic feature is that the minimum radius of curvature of the bottom surface of the recesses existing on any line segment with a length of 200µm along the outer periphery of the light-transmitting surface in the edge portion is 5µm or more.

Description

[Technical Field]

[0001] This invention relates to an optical filter and a near-infrared cutoff filter for use in optical machines such as cameras. [Previous Technology]

[0002] In recent years, wearable devices, represented by smartphones, action cameras, and VR (Virtual Reality) / AR (Augmented Reality) devices, have become widespread. We assume that these devices will not only be used in normal environments, but also in harsh environments, such as underwater or in hot and humid environments. Therefore, the optical filters mounted on these devices require high durability.

[0003] Regarding optical filters, there are cover glass used to hermetically seal the imaging element, infrared cut-off filters used to adjust the camera's visual sensitivity, and cover glass for the camera window of the device, etc.

[0004] For example, infrared cutoff filters used to adjust the visual sensitivity of cameras mostly use copper-containing phosphate glass. However, phosphate glass is known to have low durability. Specifically, in high-temperature and high-humidity gas environments, the phosphate network structure in phosphate glass will break down due to moisture in the atmosphere, resulting in the leaching of liquid phosphate from the glass surface. Moreover, the leached phosphate may react with the glass, or the detached parts of the phosphate network may crystallize, causing deterioration of the glass surface.

[0005] To address the aforementioned issues, for example, Patent Document 1 discloses a filter that suppresses the degradation of phosphate glass by providing an alumina thin film on the surface of the glass. (Prior Art Documents, Patent Documents)

[0006] Patent Document 1: Japanese Patent Application Publication No. 4-139035 [Summary of the Invention]

[0007] Problem to be Solved by the Invention: In the filter described in Patent Document 1, although the light-transmitting surface (main surface) of the glass on which the alumina film is disposed is protected, the outer peripheral surface of the filter does not have the alumina film. Therefore, in a high-temperature and high-humidity gas environment, the deterioration of the glass will begin from the outer peripheral surface of the filter, and the deterioration will advance to the part where the glass and the alumina film are closely adhered, and there is a risk that the adhesion between the two will decrease and the alumina film will peel off.

[0008] One aspect of the present invention is to provide an optical filter that has high durability in high temperature and high humidity gas environments.

[0009] A means for solving the problem: One aspect of the optical filter of the present invention comprises: a pair of light-transmitting surfaces, which are opposite to each other in the thickness direction of the plate; and an outer peripheral surface, which extends from the pair of light-transmitting surfaces in the thickness direction of the plate. The optical filter comprises a glass plate and a protective film covering the glass plate. The protective film forms the pair of light-transmitting surfaces and the outer peripheral surface. The edge portion that forms the boundary between the light-transmitting surface and the outer peripheral surface has a curved shape. The edge portion has a plurality of pits. And characterized in that: in the edge portion, the minimum radius of curvature of the bottom surface of the pit existing on any line segment with a length of 200µm along the outer periphery of the light-transmitting surface is 5µm or more.

[0010] Effects of the Invention According to one aspect of the present invention, an optical filter can be obtained, which has high durability in a high temperature and high humidity gas environment.

Implementation Method

[0012] The following describes the embodiments of the present invention in detail. Furthermore, for ease of understanding, the same symbols are used for the same constituent elements in each drawing, and repeated descriptions are omitted. Also, the scale of each component in the drawings may sometimes differ from the actual scale. Unless otherwise specified, the "~" used in this specification to indicate a numerical range means that the values ​​recorded before and after it are included as the lower and upper limits.

[0013] An optical filter 1 according to an embodiment of the present invention will be described. FIG1 is a top view of the optical filter 1 of this embodiment, and FIG2 is a cross-sectional view of FIG1 (II). FIG3 is an enlarged view of the portion indicated by the dashed circle in FIG2. As shown in FIG1 to FIG3, the optical filter 1 of this embodiment includes: a pair of light-transmitting surfaces 3a and 3b, which are opposite to each other in the thickness direction; and an outer peripheral surface 4, which extends from the pair of light-transmitting surfaces 3a and 3b in the thickness direction. The optical filter 1 includes a glass plate 2 and a protective film 6 covering the glass plate 2. The protective film 6 forms the pair of light-transmitting surfaces 3a and 3b and the outer peripheral surface 4.

[0014] The shape of the optical filter 1 when viewed from above is not particularly limited, and may include straight sections, curved sections, etc. In addition to a rectangular shape, it may also be composed only of curved sections such as circles or ellipses. The shape of the optical filter 1 when viewed from above should preferably include curved sections. For example, the optical filter 1 is a roughly quadrilateral shape with rounded corners (curved sections) when viewed from above. The light-transmitting surface 3a becomes the surface (upper surface) of the optical filter 1, and the light-transmitting surface 3b opposite to the light-transmitting surface 3a becomes the back surface (lower surface) of the optical filter 1.

[0015] The ridge portion 5, which forms the boundary between each light-transmitting surface 3a, 3b and the outer peripheral surface 4, of the optical filter 1 is curved. Because the ridge portion 5 is curved, the protective film 6 can form a continuous coating covering the light-transmitting surfaces 3a, 3b, the ridge portion 5, and the outer peripheral surface 4, without any gaps allowing moisture to enter. Therefore, even in high-temperature and high-humidity gas environments, the adhesion between the glass plate 2 and the protective film 6 can be maintained. In particular, the ridge portion 5 should preferably be a curved shape where each light-transmitting surface 3a, 3b and the outer peripheral surface 4 are continuously connected without any height difference. This further enhances the adhesion between the glass plate 2 and the protective film 6. Furthermore, the optical filter 1 may sometimes be subjected to bending stress or impact during manufacturing, transportation, assembly of the device, and use. Because the ridge portion 5 is curved, even when bending stress is applied to the optical filter 1, breakage can be suppressed.

[0016] Figure 4 is a schematic diagram showing the state of a protective film disposed on glass in a conventional optical filter; Figure 5 is a schematic diagram showing the state of a protective film disposed on glass in an optical filter according to an embodiment of the present invention; Figure 6 is a diagram illustrating the definition of the physical film thickness of the protective film and the cross-sectional direction of the pits. The ridge portion 5 of the optical filter 1 has a plurality of pits 7 as shown in Figure 5. The pits include the following shapes: the shape of a ball or ellipsoid accurately cut in half, and the shape of a roughly sphere or roughly ellipsoid cut in a manner that does not pass through the center. In cross-section, the pit 7 may contain straight lines in addition to the bottom surface. Moreover, in the ridge portion 5, the minimum radius of curvature of the bottom surface of the pit 7 existing on any line segment with a length of 200µm along the outer periphery of the light-transmitting surfaces 3a and 3b is 5µm or more. Here, the minimum radius of curvature is measured in cross-section. The cross-section is not orthogonal to the outer periphery of the light-transmitting surfaces 3a and 3b, but rather a cross-section along the outer periphery of the light-transmitting surfaces 3a and 3b. It is either a cross-section containing the line segment connecting point X3a and point Z3a as shown in Figure 6, or a cross-section containing the line segment connecting point X3b and point Z3b as shown in Figure 6. In other words, the cross-section is either a surface containing point X3a and forming a 45° angle with the light-transmitting surface 3a, or a surface containing point X3b and forming a 45° angle with the light-transmitting surface 3b. Furthermore, let point X3a be the point where the imaginary line M3a containing the light-transmitting surface 3a intersects with the imaginary line N containing the outer periphery surface 4, and let point X3b be the point where the imaginary line M3b containing the light-transmitting surface 3b intersects with the imaginary line N containing the outer periphery surface 4. Then, when moving from point X3a along the imaginary line M3a towards the light-transmitting surface 3a, the point where the imaginary line M3a intersects with the light-transmitting surface 3a is designated as point Y3a. Similarly, when moving from point X3b along the imaginary line M3b towards the light-transmitting surface 3b, the point where the imaginary line M3b intersects with the light-transmitting surface 3b is designated as point Y3b. Then, the intersection of the line segment that rotates the imaginary line M3a 45° towards the light-transmitting surface 3b with point X3a as the center of rotation, and the line segment connecting points Y3a and Y3b, is designated as point Z3a. Similarly, the intersection of the line segment that rotates the imaginary line M3b 45° towards the light-transmitting surface 3a with point X3b as the center of rotation, and the line segment connecting points Y3a and Y3b, is designated as point Z3b.

[0017] The ridge portion 5 of the optical filter 1 has a plurality of pits 7, and the minimum radius of curvature of the bottom surface of the pits 7 existing on any line segment with a length of 200µm along the outer periphery of the light-transmitting surfaces 3a and 3b is 5µm or more. This allows for a high degree of adhesion between the glass plate 2 and the protective film 6, which is particularly evident under high temperature and high humidity conditions. Therefore, the optical filter of this embodiment can suppress the deterioration of optical properties under high temperature and high humidity conditions, and thus achieve high durability. We hypothesize the mechanism as follows.

[0018] The glass plates used in optical filters are usually optically polished with very fine surface roughness on the light-transmitting surface. In contrast, the outer peripheral surface or edge portion is generally rougher and has scratches. For example, after the edge portion of the glass plate is processed with a grinding stone, there will be many tiny and deeper scratches on the edge portion.

[0019] When a protective film covers the edge of a glass plate with a deep scratch, as shown in Figure 4, the protective film does not reach the front end of the deep scratch 8, and therefore cannot effectively protect the entire surface of the scratch. If the optical filter is exposed to a high-temperature and high-humidity gas environment, atmospheric moisture will easily condense at the front end of the deep scratch 8. Then, the condensed moisture will degrade the glass plate, starting from the front end of the deep scratch without a protective film. Moreover, this degradation will extend to the glass plate, reducing the adhesion between the glass plate and the protective film, and further degrading the optical characteristics of the optical filter.

[0020] That is, even if a protective film such as an aluminum oxide film is provided on the outer peripheral surface of the glass plate, a tiny gap will still be generated in the protective film depending on the surface condition of the glass plate in contact with the protective film, and there is a risk that the durability of the filter will be degraded due to the gap.

[0021] As shown in FIG5, the optical filter 1 of this embodiment has a protective film 6 that reaches the bottom surface of the recess 7, thus ensuring that the protective film 6 completely covers the entire surface of the recess 7, i.e., the edge portion 5. In this way, even if the optical filter is exposed to a high temperature and high humidity gas environment, the moisture, which is the main cause of glass plate deterioration, will not directly contact the glass plate, thereby suppressing the deterioration of the optical characteristics of the optical filter.

[0022] Furthermore, in the optical filter 1 of this embodiment, the protective film 6 can easily adhere to the bottom surface of the recess 7, thereby suppressing the degradation of the optical filter 1. If the minimum radius of curvature of the bottom surface of the recess 7 is 5µm or more, the protective film 6 can be fully adhered to the bottom surface of the recess 7, thereby suppressing the degradation of the glass plate. The minimum radius of curvature of the bottom surface of the recess 7 is preferably 5µm to 200µm. If the minimum radius of curvature of the bottom surface of the recess 7 is greater than 200µm, the manufacturing time for forming the recess 7 will be longer, which may increase the manufacturing cost of the optical filter 1. The minimum radius of curvature of the bottom surface of the recess 7 is preferably in the range of 6µm to 175µm, more preferably 7µm to 150µm, even more preferably 9µm to 100µm, and most preferably 10µm to 90µm. The minimum radius of curvature of the bottom surface of the pit 7 refers to the smallest radius of curvature among a plurality of pits 7 existing on any line segment with a length of 200µm, including the pit 7, within the edge portion 5. Furthermore, the radius of curvature of the bottom surface of the pit 7 or the total number of its apexes in this embodiment refers to the value measured when the glass plate 2 is covered by the protective film 6.

[0023] In the optical filter 1 of this embodiment, the total number of sharp points in the ridge portion 5 existing on any line segment with a length of 200µm along the outer periphery of the light-transmitting surfaces 3a and 3b is preferably 50 or less. This ensures that the thickness of the protective film 6 in the ridge portion 5 is not uneven, and suppresses the formation of film defects such as pinholes. The total number of sharp points is preferably 2 to 50. If the total number of sharp points is greater than 50, film defects in the protective film 6 may occur, which is undesirable. Furthermore, if the total number of sharp points is less than 2, the manufacturing time for forming the ridge portion 5 will be long, potentially increasing the manufacturing cost of the optical filter 1. The preferred range for the total number of sharp points in the ridge portion 5 existing on any line segment with a length of 200µm along the outer periphery of the light-transmitting surfaces 3a and 3b is 2 to 45, more preferably 2 to 40, even more preferably 2 to 30, and most preferably 2 to 25. Furthermore, in this embodiment, the tip is defined as the vertex of the foliate curve in the cross-sectional profile of the surface after measuring the surface irregularity of the region containing the pit 7.

[0024] The protective film 6, by covering the surface of the glass plate 2, has the function of preventing the glass plate 2 from directly contacting moisture in a high-temperature and high-humidity gas environment. Therefore, the protective film 6 can suppress the degradation of the optical characteristics of the optical filter 1.

[0025] The protective film 6 is preferably a dielectric film with one or more layers. The dielectric film is, for example, a thin film composed of metal oxides, metal fluorides, etc. Such films have high moisture-blocking properties (especially against moisture penetrating from the vertical direction) in high-temperature and high-humidity gas environments, and the protective film 6 itself is not easily degraded. Furthermore, because the dielectric film has high light transmittance, it will at least not degrade the optical characteristics of the optical filter. The number of layers in the protective film 6 is preferably 1 to 100 layers, and more preferably 1 to 50 layers.

[0026] The protective film 6 should preferably contain Al₂O₃. The dissociation energy of Al and O atoms in Al₂O₃ is very high, meaning they have the characteristic of forming strong bonds. We believe that after Al₂O₃ is formed on the glass plate 2, it will become amorphous, and because the atoms will be strongly pulled together while forming a random stacking structure, a very strong and dense structure will be formed. Based on this, we speculate that the protective film 6 can prevent water molecules from penetrating the glass plate 2.

[0027] In the optical filter 1 of this embodiment, the protective film 6 preferably contains Al₂O₃ and the glass plate 2 contains Al (aluminum) components. In the glass plate, the Al component is a constituent component of the glass network structure. If an Al₂O₃-containing protective film 6 is formed on the glass plate 2, covalent chemical bonds will be generated between the Al component of the glass network structure of the glass plate 2 and the Al₂O₃ of the protective film 6, thereby strengthening the adhesion of the protective film 6 to the glass plate 2. Therefore, the degradation of the optical properties of the optical filter 1 in a high-temperature and high-humidity gas environment can be further suppressed.

[0028] When the physical film thickness of the protective film 6 on the light-transmitting surfaces 3a and 3b is A, and the physical film thickness of the protective film 6 on the edge portion 5 is B, the optical filter 1 of this embodiment should satisfy the following relationship (1). 1.0<A / B<2000・・・(1)

[0029] By ensuring that A / B is within the aforementioned range, the moisture-blocking effect of the protective film 6 in the ridge portion 5 can be improved. If A / B is less than 2000, the difference between the physical film thickness A of the protective film 6 on the light-transmitting surfaces 3a and 3b and the physical film thickness B of the protective film 6 on the ridge portion 5 is smaller, thus adequately protecting the ridge portion 5 and further suppressing the degradation of the optical characteristics of the optical filter 1. Furthermore, if A / B is greater than 1.0, the productivity of forming the protective film 6 on the ridge portion 5 can be improved, thereby reducing the manufacturing cost of the optical filter 1.

[0030] The upper limit of A / B should preferably be below 1500, more preferably below 1000, and even more preferably below 500. The lower limit of A / B should preferably be above 2, more preferably above 5, and even more preferably above 10.

[0031] Furthermore, in this embodiment, the physical film thickness of the protective film 6 at the ridge portion 5 is defined as follows. As shown in FIG6, in the cross-sectional view of the optical filter, the point where the imaginary line M3a containing the light-transmitting surface 3a intersects with the imaginary line N containing the outer peripheral surface 4 is designated as point X3a, and the point where the imaginary line M3b containing the light-transmitting surface 3b intersects with the imaginary line N containing the outer peripheral surface 4 is designated as point X3b. Then, when moving from point X3a along the imaginary line M3a toward the light-transmitting surface 3a, the point where the imaginary line M3a connects with the light-transmitting surface 3a is designated as point Y3a. Similarly, when moving from point X3b along the imaginary line M3b toward the light-transmitting surface 3b, the point where the imaginary line M3b connects with the light-transmitting surface 3b is designated as point Y3b. Then, the intersection of the line segment of imaginary line M3a rotated 45° towards the light-transmitting surface 3b with point X3a as the center of rotation, and the line segment connecting points Y3a and Y3b, is designated as point Z3a. Similarly, the intersection of the line segment of imaginary line M3b rotated 45° towards the light-transmitting surface 3a with point X3b as the center of rotation, and the line segment connecting points Y3a and Y3b, is designated as point Z3b. In the straight line connecting points X3a and Z3a, or the straight line connecting points X3b and Z3b, the width of the protective film 6 existing in the direction of the straight line is defined as the physical film thickness of the protective film 6 at the edge portion 5. Furthermore, when there is no plane on the outer peripheral surface 4 (a straight line portion in the cross-sectional view), the line orthogonal to the imaginary line M and passing through the outermost part of the outer peripheral surface 4 is designated as the imaginary line N encompassing the outer peripheral surface 4.

[0032] The physical film thickness of the protective film 6 at the ridge portion 5 should preferably be 10 nm or more. This can reliably protect the ridge portion 5 of the optical filter 1. The physical film thickness of the protective film 6 at the ridge portion 5 should preferably be 15 nm to 15 µm, more preferably 20 nm to 10 µm, and most preferably 25 nm to 7 µm.

[0033] The protective film 6 should have any of the following functions: resistance to visible light reflection, infrared reflection, ultraviolet reflection, or both infrared and ultraviolet reflection. Therefore, since the protective film 6 also has optical functions, there is no need to separately install a functional film on the optical filter 1, thereby reducing the manufacturing cost of the optical filter 1.

[0034] The protective film 6 can be formed by methods such as sputtering, vacuum evaporation, ion beam deposition, ion plating, and CVD. According to these methods, the physical thickness of the protective film 6 applied to the surface of the glass plate 2 can be precisely controlled. Furthermore, since sputtering or ion plating involves a plasma gas environment, the adhesion of the protective film 6 to the glass plate 2 can be improved, which is advantageous. Also, since the protective film 6 itself can be made into a dense film, sputtering or ion plating is preferable from the viewpoint of shielding the glass plate 2 from moisture.

[0035] In order to obtain the desired optical characteristics, the optical filter 1 of this embodiment may also have, in addition to the above-mentioned protective film 6, a dielectric multilayer film that reflects light of a specific wavelength, or an absorption film containing metal oxides or pigments that reflect light of a specific wavelength.

[0036] The glass plate 2 of the optical filter 1 in this embodiment is preferably any one of phosphate glass, fluorophosphate glass, thiophosphate glass, and silica phosphate glass. These glasses can obtain excellent optical properties by containing appropriate transition metal components in order to meet the desired optical characteristics.

[0037] Specifically, for optical filters that are required to block near-infrared light, Cu or Fe ions with absorption bands in that region are often used. Phosphate glass, which uses these ions, is more likely to show significant near-infrared absorption.

[0038] For the above-mentioned phosphate glass, fluorophosphate glass containing fluorine, sulfur phosphate glass containing sulfur, and silicon phosphate glass containing silicon can be used appropriately.

[0039] Furthermore, the glass plate 2 can be made of, for example, borosilicate glass, soda-lime glass, or high silica glass. The size, thickness, and shape of the glass plate 2 are appropriately selected according to the application of the optical filter 1. When the optical filter 1 is used in a device, it helps to make the device thinner, so the thickness of the glass plate 2 is preferably 0.05mm to 0.5mm, and more preferably 0.05mm to 0.3mm.

[0040] The glass plate 2 of the optical filter 1 in this embodiment should preferably contain P₂O₅, Al₂O₃, R'O (where R'O represents any one or more selected from MgO, CaO, SrO, BaO, and ZnO) and Fe₂O₃ as essential components; and the content of Fe₂O₃, expressed in moles (%) based on oxides, is 0.1% to 35%. Therefore, the optical filter 1 can have near-infrared shielding function.

[0041] P₂O₅ is the main component of glass (the oxide that forms glass) and is an essential component for improving the cutoff performance in the near-infrared region.

[0042] Al₂O₃ is the main component of glass (the oxide that forms glass), and is an essential component for improving weather resistance and strength of glass.

[0043] R'O (where R'O means selected from any one or more of MgO, CaO, SrO, BaO and ZnO) is an essential component used to lower the melting temperature of glass, lower the liquidus temperature of glass, stabilize glass, and improve the strength of glass.

[0044] Fe₂O₃ is an essential component for blocking near-infrared radiation. The content of Fe₂O₃ should preferably be between 0.1% and 35%. If the content is less than 0.1%, its effect will not be fully achieved after reducing the thickness of the glass; if it is greater than 35%, the transmittance of light in the visible area will decrease, which is not ideal. The content of Fe₂O₃ should preferably be 0.5-35%, more preferably 1.0-35%, and even more preferably 2.0-35%.

[0045] Furthermore, in this embodiment, Fe2O3 refers to the total amount of all Fe (iron) components converted into Fe2O3.

[0046] The glass plate 2 of the optical filter 1 of this embodiment, expressed in moles based on oxides, preferably contains: P2O5: 25%~75%, Al2O3: 2.5%~22%, R''O: 0.1%~35% (where R''O represents the total of MgO, CaO, SrO, BaO and ZnO), Fe2O3: 0.1%~35% and R2O: 0%~20% (where R2O represents the total of Li2O, Na2O and K2O).

[0047] P₂O₅ is the main component of glass and an essential component for improving the cutoff of near-infrared light. However, when the P₂O₅ content is less than 25%, the effect of cutting off near-infrared light cannot be fully achieved, and the transmittance of visible light is reduced due to the increased proportion of Fe³⁺ in the iron composition of the glass, which is undesirable. If the content is greater than 75%, problems such as glass instability and reduced weather resistance will occur, which is also undesirable. The P₂O₅ content is preferably 30~73%, more preferably 35~70%, and even more preferably 40~65%.

[0048] Al₂O₃ is the main component of glass and is essential for improving its weather resistance and strength. However, when its content is less than 2.5%, its effects cannot be fully achieved; if it is greater than 22%, problems such as glass instability and reduced infrared cutoff will occur, which is undesirable. The preferred content of Al₂O₃ is 3-20%, and more preferably 4-18%.

[0049] R''O (where R''O represents the total of MgO, CaO, SrO, BaO, and ZnO) is an essential component used to lower the melting temperature of glass, lower the liquidus temperature of glass, stabilize glass, and improve glass strength. However, if the content is less than 0.1%, its effect cannot be fully obtained; if it is greater than 35%, problems such as glass instability, reduced infrared cutoff, and reduced glass strength will occur, which is not ideal. The R''O content is preferably 1~33%, more preferably 1.5~32%, even more preferably 2~30%, and most preferably 2.5~29%.

[0050] MgO is a component used to lower the melting temperature of glass, lower the liquidus temperature of glass, stabilize glass, and improve the strength of glass. When MgO is present, its content should preferably be 0.5% to 15%. If the content is less than 0.5%, its effect will not be fully achieved, and if it is greater than 15%, the glass will become unstable, which is not ideal. The MgO content is more preferably 1.0% to 13%, and even more preferably 1.5% to 10%.

[0051] CaO is a component used to lower the melting temperature of glass, lower the liquidus temperature of glass, stabilize glass, and improve the strength of glass. When CaO is present, its content should preferably be 0.1% to 10%. If the content is less than 0.1%, its effect will not be fully achieved, and if it is greater than 10%, the glass will become unstable, which is not ideal. The CaO content is preferably 0.3% to 8%, and more preferably 0.5% to 6%.

[0052] SrO is a component used to lower the melting temperature of glass, lower the liquidus temperature of glass, and stabilize glass. When SrO is present, its content should preferably be 0.1% to 10%. If the content is less than 0.1%, its effect will not be fully obtained, and if it is greater than 10%, the glass will become unstable, which is not ideal. The SrO content is preferably 0.3% to 8%, and more preferably 0.5% to 8%.

[0053] BaO is a component used to lower the melting temperature of glass, lower the liquidus temperature of glass, and stabilize glass. When containing BaO, its content should preferably be 0.1% to 10%. If the content is less than 0.1%, its effect cannot be fully obtained, and if it is greater than 10%, the glass will become unstable, which is not ideal. The BaO content is preferably 0.5% to 8%, and more preferably 1% to 6%.

[0054] ZnO has the effect of lowering the melting temperature and liquidus temperature of glass. When ZnO is present, its content should preferably be 0.5% to 20%. If the content is less than 0.5%, its effect cannot be fully obtained, and if it is greater than 20%, the solubility of the glass will deteriorate, which is not ideal. The ZnO content is preferably 1% to 18%, and more preferably 1.5% to 17%.

[0055] Fe₂O₃ is an essential component for blocking near-infrared radiation. The content of Fe₂O₃ should preferably be 0.1% to 35%. If the content is less than 0.1%, its effect will not be fully achieved after reducing the thickness of the glass; if it is above 35%, the transmittance of light in the visible area will decrease, which is not ideal. The content of Fe₂O₃ should preferably be 1% to 35%, more preferably 3% to 35%, and even more preferably 5% to 35%.

[0056] R₂O (where R₂O represents the sum of Li₂O, Na₂O, and K₂O) is a component used to increase the coefficient of thermal expansion of glass, to lower the melting temperature of glass, to lower the liquidus temperature of glass, and to stabilize glass. The content of R₂O should preferably be 0% to 20%. If the content is greater than 20%, the glass will become unstable, which is not ideal. The content of R₂O is preferably 0.5% to 18%, more preferably 1.0% to 16%, and even more preferably 1.5% to 15%.

[0057] Li₂O is a component used to lower the melting temperature of glass, lower the liquidus temperature of glass, and stabilize glass. The content of Li₂O should preferably be 0-10%. If the content is greater than 10%, the glass will become unstable, which is not ideal. The content of Li₂O is preferably 0.5-8%, and more preferably 1-7%.

[0058] Na₂O is a component used to lower the melting temperature of glass, lower the liquidus temperature of glass, and stabilize glass. The Na₂O content should preferably be 0-20%. If the content is greater than 20%, the glass will become unstable, which is not ideal. The Na₂O content is preferably 0.7-18%, and more preferably 1-16%.

[0059] K₂O is a component that has the effect of lowering the melting temperature and liquidus temperature of glass. The K₂O content should preferably be 0-15%. If the content is greater than 15%, the glass will become unstable, which is not ideal. The K₂O content is more preferably 0.5-13%, and even more preferably 0.7-10%.

[0060] To stabilize the glass, B₂O₃ can be contained in amounts below 10%. If this content exceeds 10%, the weather resistance may deteriorate, or the melting temperature may become too high, which is undesirable. The B₂O₃ content should preferably be 0-9%, more preferably 0-8.5%, even more preferably 0-8%, and most preferably 0-7.5%.

[0061] The glass plate 2 of the optical filter 1 in this embodiment may also contain CuO to replace Fe₂O₃. CuO is a component used to block near-infrared radiation. The content of CuO should preferably be 0.1% or more and 35% or less. If the content is less than 0.1%, its effect cannot be fully obtained after reducing the thickness of the glass; if it is greater than 35%, the transmittance of light in the visible area will decrease, which is not ideal. The content of CuO should preferably be 0.5-35%, more preferably 1.0-35%, and even more preferably 2.0-35%.

[0062] Furthermore, CuO in this embodiment refers to the total amount of all Cu (copper) components converted into CuO.

[0063] The glass plate 2 of the optical filter 1 in this embodiment preferably contains 5 mol% to 50 mol% or less of F- (fluoride ions) in terms of anion ratio. That is, the ratio of F- to all anions is preferably 5 mol% to 50 mol%.

[0064] F - can stabilize glass, so it is used to improve weather resistance; if it is less than 5%, its effect cannot be fully obtained; if it is greater than 50%, there is a risk of reduced mechanical properties such as strength, hardness or elastic modulus, increased volatility and increased streaks, so it is not ideal. The content of F - should be 7~50%, and more preferably 9~50%.

[0065] The glass plate 2 may contain other components such as Cl, Br, and I as arbitrary anionic components without compromising the effects of the present invention. The total content of these components should preferably be less than 5%.

[0066] The glass plate 2 preferably contains one or more of Li₂O, Na₂O, and K₂O as alkali metal components. These components are glass network modifiers. By containing these components, the glass network bonds are broken and become fragile, so it is easy to create pits 7 at the edge portion 5, for example, during the etching step.

[0067] On the line segment connecting point X3a and point Z3a, or on the line segment connecting point X3b and point Z3b in Figure 6, within a depth of 10-100 nm measured from the surface of the ridge portion 5 of the glass plate 2, the concentrations of Li₂O, Na₂O, and K₂O should preferably be less than 90% of the concentrations of these components in point Z3a or point Z3b shown in Figure 6. This increases the proportion of the ends of the glass network structure on the surface of the ridge portion 5 that are in a non-bonded state without glass network modifier components, making it easier to form new covalent chemical bonds with the components of the protective film 6 during film formation. Therefore, the adhesion of the protective film 6 to the glass plate 2 becomes stronger. Thus, the degradation of the optical properties of the optical filter 1 in a high-temperature and high-humidity gas environment can be further suppressed.

[0068] The optical filter 1 of this embodiment can be manufactured, for example, in the following manner. First, the raw materials are weighed and mixed to make the resulting glass within a predetermined composition range (mixing step). The raw material mixture is placed in a crucible and heated and melted in an electric furnace at a temperature of 700~1400°C (melting step). After thoroughly stirring and clarifying the molten glass, it is cast into a mold and cut and ground to form a flat plate of a predetermined thickness (forming step of plate glass). The boundaries between the light-transmitting surfaces 3a, 3b and the outer peripheral surface 4 of the formed glass, i.e., the edge portion 5, are cut using a grinding stone (beveling step). After optically grinding the light-transmitting surfaces 3a, 3b of the glass, the beveled glass is immersed in an etching solution and processed to make the edge portion 5 into a curved shape (etching step). The etched glass is washed to obtain a glass plate (washing step). In addition, if the desired glass plate can be obtained, the manufacturing steps are not limited to the above steps. For example, as a method to obtain sheet glass, the following well-known manufacturing methods can also be used: float glass method, flow hole down-drawing method (e.g., overflow down-drawing method), re-drawing method, pressing forming method, lifting method, etc.

[0069] The etching step uses an etching solution. If the etching solution is acidic, HCl, HNO3, and HF can be used. If it is alkaline, KOH, NaOH, etc. can be used. The etching solution can be appropriate according to the glass composition or the desired shape of the edge portion 5, and is not limited to the etching solution mentioned above.

[0070] A protective film 6 is formed on the edge portion 5 of the glass plate 2 using the aforementioned film-forming method (sputtering, vacuum evaporation, ion beam method, ion plating, CVD method, etc.) (film-forming step). Furthermore, when forming the protective film 6, in order to form the protective film 6 not only on the edge portion 5 of the glass plate 2 but also on the outer peripheral surface 4, the method of holding the glass plate 2 within the film-forming apparatus should be considered.

[0071] The optical filter 1 of this embodiment can be used, for example, as an optical filter for image projection display devices, solid-state camera devices, optical recording and playback devices, optical communication devices, and light sensing devices. In particular, it is suitable for use as a near-infrared cutoff filter in solid-state camera devices. Furthermore, the optical filter 1 of this embodiment is not limited to the above-mentioned applications.

[0072] Examples are shown below to illustrate the embodiments in more detail, but the embodiments are not limited to these examples. Examples 1 and 3 are embodiments, and Example 2 is a comparative example.

[0073] <Example 1> [Fabrication of Optical Filter] The glass plate is manufactured by the following method. A glass substrate is prepared, wherein the glass composition after molten forming is a predetermined composition (P₂O 563mol%, Al₂O 317mol%, K₂O 1mol%, BaO+ZnO 11mol%, Fe₂O 38mol%). Next, the surface and back are optically ground to obtain a glass plate with a thickness of 0.2mm. Next, the glass is cut into 20×20mm pieces using a cutting wheel. Next, the glass end faces exposed by cutting are chamfered using a diamond wheel. Next, the plate-shaped glass is etched according to the following conditions (processing solution: etching solution containing 3wt% KOH, processing solution temperature: 30°C, etching time: 80 minutes) to obtain the glass plate.

[0074] Next, an Al2O3 film is deposited on the surface of a glass plate by vacuum evaporation to obtain an optical filter. Furthermore, the film deposition system is configured such that the physical thickness of the Al2O3 film on the light-transmitting surface of the optical filter is 150 nm, and the physical thickness of the Al2O3 film on the edge portion is 10 nm or more.

[0075] <Example 2> [Fabrication of Optical Filter] Except that no glass etching process was performed in Example 1, an optical filter was obtained in the same manner as in Example 1.

[0076] <Example 3> [Fabrication of Optical Filter] The glass plate is manufactured by the following method. A glass substrate is prepared, wherein the glass composition after molten forming is a predetermined composition (P₂O 558mol%, Al₂O 313mol%, Na₂O 6mol%, K₂O 11mol%, CuO 12mol%). Next, the surface and back are optically ground to obtain a glass with a thickness of 0.28mm. Next, the glass is cut into 20×20mm pieces using a cutting wheel. Next, the exposed glass end faces after cutting are chamfered using a diamond wheel. Next, the plate-shaped glass is etched according to the following conditions (processing solution: etching solution containing 10wt% KOH, processing solution temperature: 40°C, etching time: 3 hours) to obtain the glass plate.

[0077] Next, an Al₂O₃ film is deposited on the surface of a glass plate by vacuum evaporation to obtain an optical filter. Furthermore, the film deposition system is configured such that the physical thickness of the Al₂O₃ film on the light-transmitting surface of the optical filter is 150 nm, and the physical thickness of the Al₂O₃ film on the edge portion is 10 nm or more.

[0078] The ridge portion of the optical filters in Examples 1, 2, and 3 was evaluated using the following method. The surface shape of the ridge portion of the optical filters was measured using a laser microscope (VKX-1000 shape measurement laser microscope, manufactured by Keyence). Laser microscope photographs and cross-sectional profiles of the ridge portion of Example 1 are shown in Figures 7 and 8. Laser microscope photographs and cross-sectional profiles of the ridge portion of Example 2 are shown in Figures 9 and 10. Laser microscope photographs and cross-sectional profiles of the ridge portion of Example 3 are shown in Figures 11 and 12. In the laser microscope photographs of Figures 7 and 11, the pit-shaped recess is shown from above.

[0079] <Radius of curvature of the bottom surface of the pit> The radius of curvature of the bottom surface of the approximately hemispherical pit is determined as follows. The surface shape of the ridge portion of the optical filter is measured using the aforementioned laser microscope. Specifically, an arbitrary line segment with a length of 200µm along the outer periphery of the light-transmitting surface in the ridge portion is specified, and its cross-sectional profile is measured. Using this cross-sectional profile, any three points containing the bottom surface in the concave curve are specified, and the radius of the circle passing through these three points is taken as the radius of curvature of the pit. The radius of curvature is measured for each of the plurality of concave curves existing in the cross-sectional profile, and the minimum value is determined.

[0080] <Total Number of Tips> Using the above cross-sectional profile, the apex of the vine-like curve on the line segment with a distance of 200µm between two locations containing the pit is taken as the tip, and the total number is calculated. In addition, in the cross-sectional profile of Figure 8, the points indicated by the downward arrows are identified as tips.

[0081] <Durability of Optical Filters under High Temperature and High Humidity> The optical filters of Examples 1 and 2 were placed in an ESPEC-manufactured high-accelerated life testing apparatus at 121°C and 2 atm for 36 hours, and the degradation state of the optical filters after removal was observed using a laser microscope. In the ridge area of ​​the optical filters, those with peeling of the glass plate and protective film were rated as B, and those without peeling were rated as A.

[0082] The evaluation results of Examples 1 and 2 are shown in Table 1. The optical filter of Example 2 is shown in the cross-sectional profile of Figure 10. Since there is no approximately hemispherical pit, the radius of curvature cannot be measured, and the total number of tips cannot be calculated (recorded as "-" in Table 1).

[0083] [Table 1]

[0084] The optical filter of Example 3 was placed in a constant temperature and humidity chamber manufactured by ESPEC at a temperature of 85°C and a relative humidity of 85% for 500 hours, and the degradation state of the optical filter after removal was observed using a laser microscope. In the ridge area of ​​the optical filter, those with peeling of the glass plate and protective film were evaluated as B, and those without peeling were evaluated as A.

[0085] The evaluation results of Example 3 are shown in Table 2.

[0086] [Table 2]

[0087] <Physical Film Thickness> The cross-section of the optical filter was observed using a FE-SEM (Hitachi High-Technologies, field emission scanning electron microscope: Regulus 8100). In the optical filter of Example 1, the physical film thickness of the Al₂O₃ film on the light-transmitting surface is 150 nm, the physical film thickness of the Al₂O₃ film on the ridge portion 5 is 100 nm, and the physical film thickness of the Al₂O₃ film on the outer peripheral surface 4 is 50 nm. Furthermore, the physical film thicknesses of the Al₂O₃ film on each cross-section of the optical filter of Example 3 are the same as those in Example 1.

[0088] As shown in Tables 1 and 2, compared to the optical filter of Example 2, the optical filters of Examples 1 and 3 can suppress the peeling of the glass plate and the protective film even in a high-temperature and high-humidity gas environment. We believe this is because in the ridge portion of the optical filters of Examples 1 and 3, the minimum radius of curvature of the bottom surface of the pit is 5µm or more, and the total number of apexes is less than 50, thus ensuring that the glass plate and moisture are effectively shielded by the protective film even in a high-temperature and high-humidity gas environment.

[0089] In contrast, in the ridge portion of the optical filter in Example 2, the protective film did not completely cover the glass plate. Therefore, we believe that in a high-temperature and high-humidity gas environment, moisture will condense at the bottom of the scratch on the ridge portion of the glass plate, and the glass plate will deteriorate due to contact with moisture, causing the glass plate and the protective film to peel off.

[0090] (Examples of the Invention) The present invention includes the following examples. <Example 1> An optical filter comprising: a pair of light-transmitting surfaces, which are equally oriented opposite each other in the thickness direction; and an outer peripheral surface extending from the pair of light-transmitting surfaces in the thickness direction; the optical filter is characterized in that: it comprises a glass plate and a protective film covering the glass plate, and the protective film forms the pair of light-transmitting surfaces and the outer peripheral surface; the ridge portion forming the boundary between the light-transmitting surfaces and the outer peripheral surface has a curved shape; the ridge portion has a plurality of recesses; in the ridge portion, the recesses existing on any line segment with a length of 200µm along the outer periphery of the light-transmitting surface have a minimum radius of curvature of 5µm or more on their bottom surface. <Example 2> The optical filter of Example 1, wherein the total number of tips existing on the aforementioned arbitrary line segment is 50 or less. <Sample 3> An optical filter as described in Sample 1 or 2, wherein the light-transmitting surface and the outer peripheral surface of the aforementioned ridge portion are continuously connected without any height difference. <Sample 4> An optical filter as described in any one of Samples 1 to 3, wherein the aforementioned protective film is a dielectric film of one or more layers. <Sample 5> An optical filter as described in any one of Samples 1 to 4, wherein the aforementioned protective film contains Al 2O 3. <Sample 6> An optical filter as described in any one of Samples 1 to 5, wherein the aforementioned glass plate contains Al. <Sample 7> An optical filter as described in any one of Samples 1 to 6, wherein when the physical thickness of the aforementioned protective film on the aforementioned light-transmitting surface is A, and the physical thickness of the aforementioned protective film on the aforementioned ridge portion is B, the following relationship (1) is satisfied: 1.0 < A / B < 2000... (1). <Sample 8> An optical filter of any one of Samples 1 to 7, wherein the physical film thickness of the aforementioned protective film at the aforementioned ridge portion is 10 nm or more. <Sample 9> An optical filter of any one of Samples 1 to 8, wherein the aforementioned protective film possesses any of the following functions: resistance to visible light reflection, infrared reflection, ultraviolet reflection, or both infrared and ultraviolet reflection. <Sample 10> An optical filter of any one of Samples 1 to 9, wherein its shape, when viewed from above, includes a curved portion. <Sample 11> An optical filter of any one of Samples 1 to 10, wherein the aforementioned glass plate is any one of phosphate glass, fluorophosphate glass, thiophosphate glass, or silica phosphate glass. <Sample 12> The optical filter of Sample 11, wherein the aforementioned glass plate contains P2O5, Al2O3, R'O (where R'O represents any one or more of MgO, CaO, SrO, BaO and ZnO) and Fe2O3; and the content of Fe2O3 is expressed in moles % based on oxides, and is 0.1% to 35%.<Sample 13> The optical filter of Sample 12, wherein the aforementioned glass plate, expressed in moles (%) based on oxides, contains: P₂O₅: 25%~75%, Al₂O₃: 2.5%~22%, R''O: 0.1%~35% (where R''O represents the total of MgO, CaO, SrO, BaO and ZnO), Fe₂O₃: 0.1%~35% and R₂O: 0%~20% (where R₂O represents the total of Li₂O, Na₂O and K₂O). <Sample 14> An optical filter as described in Sample 11, wherein the aforementioned glass plate, expressed in moles (%) based on oxides, contains: P₂O₅: 25%~75%, Al₂O₃: 2.5%~22%, R''O: 0.1%~35% (where R''O represents the total of MgO, CaO, SrO, BaO, and ZnO), R₂O: 0%~20% (where R₂O represents the total of Li₂O, Na₂O, and K₂O), and CuO: 0.1%~35%. <Sample 15> An optical filter as described in any of Samples 12 to 14, wherein the aforementioned glass plate, expressed in moles (%), contains 5%~50% F⁻. <Sample 16> A near-infrared cutoff filter, comprising an optical filter as described in any of Samples 1 to 15.

[0091] This application claims priority based on Japanese Patent Application No. 2021-180650, filed on November 4, 2021, the entire contents of which are incorporated herein by reference.

[0092] Industrial Applicability According to the present invention, an optical filter is obtained in which the protective film still functions even in a high temperature and high humidity gas environment, and has suppressed the deterioration of optical properties and has high durability, and is therefore particularly effective in optical device applications intended for use in harsh environments. [Simplified Explanation of the Diagram]

[0011] Figure 1 is a top view of an optical filter according to an embodiment of the present invention. Figure 2 is a cross-sectional view of II in Figure 1. Figure 3 is an enlarged view of the portion indicated by the dashed circle in Figure 2. Figure 4 is a schematic diagram showing the state of a protective film disposed on glass in a conventional optical filter. Figure 5 is a schematic diagram showing the state of a protective film disposed on glass in an optical filter according to an embodiment of the present invention. Figure 6 is a diagram illustrating the definition of the physical film thickness of the protective film and the cross-sectional direction of the pit. Figure 7 is a laser microscope photograph of the ridge portion of the optical filter of Example 1. Figure 8 is a cross-sectional outline of the ridge portion of the optical filter of Example 1. Figure 9 is a laser microscope photograph of the ridge portion of the optical filter of Example 2. Figure 10 is a cross-sectional outline of the ridge portion of the optical filter of Example 2. Figure 11 is a laser microscope photograph of the ridge portion of the optical filter of Example 3. Figure 12 is a cross-sectional outline of the ridge portion of the optical filter of Example 3.

Claims

1. An optical filter comprising: a pair of light-transmitting surfaces, which are equidistant from each other in the thickness direction; and an outer peripheral surface extending from the pair of light-transmitting surfaces in the thickness direction; the optical filter is characterized in that: it comprises a glass plate and a protective film covering the glass plate, and the protective film forms the pair of light-transmitting surfaces and the outer peripheral surface; the ridge portion that forms the boundary between the light-transmitting surfaces and the outer peripheral surface has a curved shape; the ridge portion has a plurality of pits; in the ridge portion, the minimum radius of curvature of the bottom surface of the pit existing on any line segment with a length of 200µm along the outer periphery of the light-transmitting surface is 5µm or more; when the physical film thickness of the protective film on the light-transmitting surface is A and the physical film thickness of the protective film on the ridge portion is B, the following relationship (1) is satisfied: 1.0<A / B<2000・・・(1).

2. An optical filter comprising: a pair of light-transmitting surfaces facing each other in the thickness direction; and an outer peripheral surface extending from the pair of light-transmitting surfaces in the thickness direction; characterized in that: it comprises a glass plate and a protective film covering the glass plate, the protective film forming the pair of light-transmitting surfaces and the outer peripheral surface; an edge portion forming the boundary between the light-transmitting surfaces and the outer peripheral surface has a curved shape; the edge portion has a plurality of pits; in the edge portion, the pits existing on any line segment with a length of 200µm along the outer periphery of the light-transmitting surface have a minimum radius of curvature of 5µm or more on their bottom surface; the glass plate contains one or more components selected from Li2O, Na2O, and K2O; As shown in Figure 6, on the line segment connecting point X3a and point Z3a or on the line segment connecting point X3b and point Z3b, at a depth of 10~100nm from the surface of the edge portion 5 of glass plate 2, the concentration of Li2O, Na2O and K2O is less than 90% of the concentration of these components in point Z3a or point Z3b.

3. The optical filter of claim 2, wherein when the physical thickness of the protective film on the aforementioned light-transmitting surface is A and the physical thickness of the protective film on the aforementioned ridge portion is B, satisfies the following relationship (1): 1.0 < A / B < 2000・・・ (1).

4. For the optical filter of claim 1 or 3, wherein the physical film thickness of the protective film on the aforementioned light-transmitting surface is A and the physical film thickness of the protective film on the aforementioned ridge portion is B, the following relationship (2) is satisfied: 2.0≦A / B<2000・・・(2) 5. An optical filter as claimed in any of claims 1 to 3, wherein the total number of tips present on any of the aforementioned line segments is 50 or less.

6. An optical filter as claimed in any of claims 1 to 3, wherein the aforementioned light-transmitting surface and the aforementioned outer peripheral surface in the aforementioned ridge portion are continuously connected without any height difference.

7. An optical filter as claimed in any of claims 1 to 3, wherein the aforementioned protective film is a dielectric film of one or more layers.

8. An optical filter as claimed in any of claims 1 to 3, wherein the aforementioned protective film comprises Al2O3.

9. An optical filter as claimed in any of claims 1 to 3, wherein the aforementioned glass plate contains an Al component.

10. An optical filter as claimed in any of claims 1 to 3, wherein the physical film thickness of the aforementioned protective film at the aforementioned ridge portion is 10 nm or more.

11. An optical filter as claimed in any of claims 1 to 3, wherein the aforementioned protective film has any of the following functions: resistance to visible light reflection, infrared reflection, ultraviolet reflection, or both infrared and ultraviolet reflection.

12. The optical filter of any of claims 1 to 3 has a curved portion in its shape when viewed from above.

13. An optical filter as claimed in any of claims 1 to 3, wherein the aforementioned glass plate is any one of phosphate glass, fluorophosphate glass, thiophosphate glass, or silica phosphate glass.

14. An optical filter as claimed in any of claims 1 to 3, wherein the aforementioned glass plate contains P2O5, Al2O3, R'O (where R'O represents any one or more selected from MgO, CaO, SrO, BaO and ZnO) and Fe2O3; and the content of Fe2O3, expressed in moles % based on oxides, is 0.1% to 35%.

15. An optical filter as claimed in any of claims 1 to 3, wherein the aforementioned glass plate, expressed in moles (%) based on oxides, contains: P2O5: 25% to 75%, Al2O3: 2.5% to 22%, R''O: 0.1% to 35% (where R''O represents the total of MgO, CaO, SrO, BaO and ZnO), Fe2O3: 0.1% to 35% and R2O: 0% to 20% (where R2O represents the total of Li2O, Na2O and K2O).

16. An optical filter as claimed in any of claims 1 to 3, wherein the aforementioned glass plate, expressed in moles (%) based on oxides, contains: P2O5: 25%~75%, Al2O3: 2.5%~22%, R''O: 0.1%~35% (where R''O represents the total of MgO, CaO, SrO, BaO and ZnO), R2O: 0%~20% (where R2O represents the total of Li2O, Na2O and K2O) and CuO: 0.1%~35%.

17. An optical filter as claimed in any of claims 1 to 3, wherein the aforementioned glass plate contains 5 mol% to 50 mol% F- by anion ratio.

18. A near-infrared cutoff filter, comprising an optical filter as claimed in any one of claims 1 to 17.

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