JP2012137649A - Optical filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical filter comprising a transparent substrate, a near infrared light reflecting structure, a light absorbing structure and a hard protective film layer and having excellent scratch resistance and abrasion resistance with respect to the light absorbing structure.SOLUTION: A near infrared light reflecting structure 3a deposited by alternately laminating a low refractive material and a high refractive material, a light absorbing structure 4 deposited by applying a coating liquid made by dissolving a dye having absorption in a near infrared wavelength region and resin into an organic solvent and a hard protective film layer 5, being hard, made of epoxy resin are sequentially laminated on a transparent substrate 2, and a near infrared light reflecting structure 3b is deposited on an opposite surface of the transparent substrate 2.

Description

  The present invention relates to an optical filter mounted on a video camera, a digital still camera, or the like using a solid-state image sensor.

  2. Description of the Related Art Conventionally, an imaging element such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) sensor is used in an imaging optical system such as a video camera or a digital still camera. These image sensors have sensitivity in a relatively wide wavelength, and also have sensitivity in light in the near infrared wavelength region in addition to light in the visible wavelength region. However, in an ordinary camera application, an image in the infrared wavelength region that is invisible to the human eye is unnecessary. For this reason, in an imaging optical system such as a camera, an infrared cut filter that shields light in the infrared wavelength region is disposed on the incident light side of the imaging element to prevent infrared light from entering the imaging element.

  Infrared cut filters include a reflective type in which a plurality of thin films having different refractive indexes are stacked to reflect unnecessary near infrared rays by interference. This reflection type infrared cut filter is manufactured by forming a multilayer film on a transparent substrate made of glass or resin by vacuum deposition, IAD, ion plating, sputtering, or the like.

  Further, there are absorption type infrared cut filters that absorb an infrared ray in an absorption element such as a metal ion, and an absorption type infrared cut filter that disperses and absorbs a dye such as a dye that absorbs infrared rays or a pigment in a resin binder. This absorption type infrared cut filter is manufactured by kneading or applying a pigment such as a metal ion or a pigment to glass or resin as a substrate.

JP 2003-161831 A JP 2000-7870 A JP 2002-303720 A JP 2006-301894A JP 2008-51985 A

  Patent Document 1 discloses a reflection-type infrared cut filter in which a plurality of low-refractive materials and high-refractive materials are stacked to form a near-infrared light reflecting structure to obtain desired spectral characteristics. . This reflection type infrared cut filter has the advantage that it can be made thinner than the absorption type, has high transmittance in the transmission wavelength region, and has good color reproducibility.

  However, the reflection type infrared cut filter has an infrared half-value wavelength with a transmittance of 50% in the near-infrared wavelength region or in the wavelength from the visible wavelength region to the near-infrared wavelength region. The reflectance at the half wavelength of light is approximately 50%.

  The intensity of the ghost light for the image sensor is affected by the spectral characteristics of the infrared cut filter, the arrangement position, the incident angle of the incident light, the sensitivity of the image sensor, etc., but simply (spectral transmittance of the infrared cut filter) The product of (the spectral reflectance of the infrared cut filter) is a guide. This ghost light may cause deterioration of the image obtained by the image sensor.

  Patent Document 2 discloses an absorption type infrared cut filter containing copper ions or the like in a resin, which uses an infrared absorption action of copper ions or the like, and has a low reflectance at a half-wavelength of infrared light, Ghost light is rarely a problem. However, in order to sufficiently absorb light in the near-infrared wavelength region, the thickness of the filter is required to be at least 0.35 mm or more, which is in conflict with the recent demand for smaller optical systems. is there.

  Patent Document 3 discloses an absorption type infrared cut filter produced by applying a coating liquid in which a dye having absorption in the near infrared wavelength region is dispersed in a resin or an organic solvent on a substrate. Yes. As described above, the infrared cut filter hardly causes deterioration of image quality due to ghost light, as in Patent Document 2, but the dye absorbs light in the visible wavelength region slightly, so that the transmittance in the visible wavelength region decreases. It will end up.

  For this reason, the reflection type infrared cut filter that increases the intensity of ghost light in the transition wavelength region that transitions from the transmission wavelength region to the non-transmission wavelength region is likely to cause ghost light as described above. Absorption type is often used. However, the absorption type infrared cut filter requires a sufficient thickness of the absorption layer to sufficiently absorb infrared light, and tends to be heavy.

  Patent Documents 4 and 5 disclose a hybrid type infrared cut filter having a near infrared light reflection structure and a light absorption structure for the purpose of reducing the thickness of the filter. However, in order to prevent the near-infrared absorbing structure from causing a spectral change due to heat due to the film formation of the near-infrared reflecting structure, the light-absorbing structure is formed after forming the near-infrared light reflecting structure. There is a case. At this time, in the infrared cut filters of Patent Documents 4 and 5, since the light absorption structure is the outermost layer, the light absorption structure is easily damaged, and the transparency of the infrared cut line filter is lowered. There is.

  An object of the present invention is to solve the above-mentioned problems and to provide an optical filter having a near-infrared light reflecting structure, a light absorbing structure, and a hard protective film layer, which has excellent scratch resistance and hardly generates ghost light. It is to provide.

  In order to achieve the above object, an optical filter according to the present invention is formed by laminating a plurality of thin films having different refractive indexes on a transparent substrate, and forms a transition wavelength region from a transmission wavelength region that transmits light to a non-transmission wavelength region. A near-infrared light reflecting structure that reflects at least a part of the near-infrared wavelength region, a film formed by dispersing a dye in a resin, and the transition wavelength region of the near-infrared light reflecting structure A light absorption structure having a predetermined absorption wavelength region that overlaps at least a part thereof and a hard protective film layer are provided, and the hard protective film layer is formed on the light absorption structure.

  The optical filter according to the present invention reduces image degradation due to ghost light and is thin and has good scratch resistance and wear resistance by providing a hard protective film layer on the light absorbing structure.

2 is a configuration diagram of an optical filter according to Embodiment 1. FIG. It is a graph of the spectral characteristic of a near-infrared-light reflection structure. It is a graph of the spectral characteristics of the pigment | dye used for a light absorption structure. It is a graph of the spectral characteristics of other pigments. FIG. 6 is a configuration diagram of an imaging optical system of Example 2. It is a graph of the sensitivity characteristic of the image sensor used for the monitoring camera.

  The present invention will be described in detail based on the embodiments shown in the drawings.

  FIG. 1 shows a configuration diagram of an optical filter including an infrared cut filter 1 according to the first embodiment. On the transparent substrate 2, a near-infrared light reflecting structure 3 a, a light-absorbing structure 4, and a hard protective film layer 5 made of an epoxy resin are sequentially laminated, and the opposite surface of the transparent substrate 2 reflects near-infrared light. A structure 3b is formed.

  In this embodiment, a plastic film substrate, specifically, F1 (trade name, manufactured by Gunze Co., Ltd.) having a thickness of about 0.1 mm is used for the transparent substrate 2. If the transparency in the visible wavelength region is high, not only F1, but also a film made of other norbornene-based resins such as Arton (made by JSR, trade name), Zeonex, Zeonor (made by Nippon Zeon, trade name) is used. May be. In addition to norbornene-based resins, various plastic film substrates such as PMMA, PET, PEN, PC, and polyimide-based resins can be used, and a glass substrate or the like can be used as necessary.

  However, considering the thermal stress and film stress due to the film formation of the near-infrared light reflecting structures 3a and 3b, and changes in the spectrum due to moisture, the transparent substrate 2 has high heat resistance (glass transition temperature Tg), and bending Those having high elasticity and low water absorption are more preferred. Considering these conditions, norbornene-based resin and polyimide-based resin are one of the most suitable materials for the transparent substrate 2.

The near-infrared light reflecting structures 3a and 3b are formed by alternately stacking a plurality of thin films made of a low refractive material and a high refractive material having different refractive indexes on the transparent substrate 2 by a vacuum deposition method. Specifically, SiO ₂ is used as the low refractive material, and TiO ₂ is used as the high refractive material. The spectral characteristics of the reflective structures 3a and 3b are determined by the optical film thicknesses n · d (n: refractive index, d: physical film thickness) of the low refractive material and the high refractive material, but at least one reflective structure. 3a and 3b have transition wavelength regions that transition from a transmission wavelength region to a non-transmission wavelength region.

  The spectral characteristics of FIG. 2 are an example when the near-infrared light reflecting structures 3 a and 3 b are formed on the transparent substrate 2. It is designed to have an infrared light half-value wavelength in which the transmittance and the reflectance are both approximately 50% between wavelengths of 650 to 700 nm, and has the above-described transition wavelength region. Since this has a shielding function in the near infrared region, it functions as an infrared cut filter.

  The transition wavelength region of the near-infrared light reflecting structure may be set between wavelengths of 650 to 750 nm in consideration of a combination with a light absorbing structure described later formed on the same transparent substrate. In consideration of the light transmittance in the visible light region and the shielding property of near infrared light, the transition wavelength region may be set in the range of 600 to 650 nm. That is, the transition wavelength region of the near-infrared light reflecting structure can be arbitrarily selected between wavelengths of about 600 to 750 nm depending on the optical system into which the infrared cut filter is inserted and the purpose of use. In the embodiment, considering such conditions, the transition wavelength region is set in the range of 650 to 700 nm.

In the near-infrared light reflecting structures 3a and 3b, SiO ₂ and TiO ₂ are used for the low refractive material and the high refractive material, but the invention is not particularly limited thereto. For example, MgF ₂ , Al ₂ O ₃ , MgO, ZrO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ or the like may be used, and a material suitable for desired spectral characteristics may be selected. In addition, although the vacuum deposition method was used for the film formation of SiO ₂ and TiO ₂ , film formation methods such as an ion plating method, an ion assisted vapor deposition method, and a sputtering method are possible, and film formation that is optimal for the purpose and conditions You just have to choose a method.

  On the other hand, the light absorbing structure 4 is formed by applying a coating solution in which a dye having absorption in the near infrared wavelength region and a resin are dissolved and dispersed in an organic solvent. For example, FIG. 3 shows spectral characteristics of a cyanine dye, and an acrylic resin containing a styrene structure is used. By adjusting and coating the concentration and film thickness of these pigments, it is possible to take measures against ghost light of a reflection type infrared cut filter composed of a reflective structure. By using such a pigment, an infrared cut filter in which the number of layers of the reflecting structures 3a and 3b is reduced can be produced.

  Specifically, a coating solution in which the above-described dye and resin are dissolved in a mixed solution of methyl ethyl ketone and toluene is applied onto the near-infrared light reflecting structure 3a by a spin coating method, dried in a heating furnace, and the solvent is removed. A film is formed by volatilization. In addition to the spin coating method, the film may be formed using a dipping method, a spray method, a gravure method, a bar coater method, or the like.

  FIG. 4 shows the spectral characteristics of a diimonium dye, and this dye may be used for the light absorbing structure 4. This dye has a predetermined absorption wavelength region, and at least a part thereof overlaps the non-transmission wavelength region of the near-infrared light reflecting structures 3a and 3b. Thereby, since the non-transmission characteristics of the reflecting structures 3a and 3b can be compensated, an infrared cut filter with a reduced number of layers of the reflecting structures 3a and 3b can be produced.

  As described above, the intensity of the ghost light of the infrared cut filter is simply a product of (spectral transmittance of the infrared cut filter) · (spectral transmittance of the infrared cut filter). In the infrared cut filter including only the near-infrared light reflecting structures 3a and 3b, the intensity of the ghost light is maximum in the transition wavelength region at the boundary between the transmission wavelength region and the non-transmission wavelength region, and is approximately 25%. Practically, the intensity of the ghost light needs to be about 15 to 16% or less although it depends on the sensitivity of the imaging optical system and the imaging device.

  Therefore, for example, in order to reduce the intensity to 16% or less, when the light absorption structure 4 is combined, the light absorption structure 4 is in the near infrared so that the transmittance is 40% and the reflectance is 40%. The absorption rate may be 20% or more in the transition wavelength region of the light reflecting structures 3a and 3b. In addition, when providing the some light absorption structure 4, the combined light absorption structure 4 should just have an absorptivity of 20% or more in a transition wavelength area | region.

  Moreover, the pigment | dye used by the light absorption structure 4 is not restricted to the above-mentioned diimonium type or cyanine type, but has an absorption function in the vicinity of the near infrared wavelength region or the infrared half-value wavelength of the light absorption structure 4. What is necessary is just to have. Preferably, the near infrared light reflecting structures 3a and 3b have a high transmittance in the transmission wavelength region. Examples of such dyes include phthalocyanine-based, polymethine-based, azo compound-based, anthraquinone-based, naphthoquinone-based, triphenylmethane-based, aminium-based, etc., and these may be used alone or in combination. .

  Moreover, as long as the resin used for the light absorption structure 4 has a high transmittance in the visible wavelength region, not only acrylic but also polyester, styrene, polyimide, PC, and polyolefin resins are used. Alternatively, a plurality of resins can be mixed and used.

  The organic solvent is not limited to ketones such as methyl ethyl ketone and methyl isobutyl ketone, but hydrocarbons such as cyclohexane, esters such as ethyl acetate, ethers such as methyl cellosolve, alcohols such as methanol, amines such as dimethylformamide, etc. A single organic solvent or a mixture of a plurality of organic solvents may be used. These dyes, resins, and organic solvents can be selected in an optimal combination depending on the purpose and conditions.

  As in the first embodiment, the near-infrared light reflecting structures 3a and 3b in the case of constituting the infrared cut filter 1 require at least about 20 to 40 layers in order to satisfy the spectral characteristics. The thickness is about 2 to 3 μm. Even when the reflective structures 3a and 3b are divided and formed on both surfaces of the transparent substrate 2 in consideration of film stress, the number of layers is about 10 or more on one side, and the film thickness is 1 μm or more.

  As described above, the near-infrared light reflecting structures 3a and 3b are formed by a vacuum vapor deposition method or the like. At the time of film formation, the temperature of the film forming portion is increased by radiant heat due to heating of the vapor deposition material or the like. Although the radiant heat depends on the TS distance (distance between the vapor deposition source and the transparent substrate 2), the vapor deposition material, and the number of layers, the temperature of the transparent substrate 2 becomes about 150 ° C. or more when the laminated film thickness is about 1 μm or more.

  When the resin reaches a temperature equal to or higher than the glass transition temperature Tg, a micro-Brownian motion is generated, and pores are generated between the polymers forming the resin by this motion, and the gas permeability is increased. Moreover, the pigment | dye which is disperse | distributed to the light absorption structure 4 is generally weak to a water | moisture content etc., and is easy to raise | generate a spectral change.

  The film formation of the near-infrared light reflecting structures 3a and 3b is performed in a certain degree of vacuum. However, when the reflecting structures 3a and 3b are formed after the light absorbing structure 4 is formed, the dye is in the film forming atmosphere. There is a concern that it may be easily affected by a small amount of water vapor or the like present in the water and the spectral characteristics will change. Since a general resin has a glass transition temperature Tg lower than 150 ° C., if the light absorption structure 4 is configured before the reflection structures 3a and 3b, the resin usable for the resin binder of the light absorption structure 4 is a reflection structure. The resin is limited to a resin having good heat resistance that can withstand the heat generated when the bodies 3a and 3b are formed. For this reason, the light absorption structure 4 is formed after forming the reflection structures 3a and 3b.

  The near-infrared light reflecting structures 3a and 3b are relatively hard because they are formed by a physical film-forming method, but the light-absorbing structure 4 is formed by coating a resin and has low scratch resistance. In this embodiment, a hard protective film layer 5 having a hardness higher than that of the light absorption structure 4 is formed on the surface.

  The hard protective film layer 5 uses a protective film coating solution prepared by dissolving an epoxy resin, which is a thermosetting resin, in a mixed solution of methyl ethyl ketone and cyclohexanone and adding diethylenetriamine as a curing agent. A leveling agent, an ultraviolet absorber, an antioxidant, an antifoaming agent, etc. are added to this protective film coating solution to the extent that it does not affect the scratch resistance, abrasion resistance and transparency of the hard protective film layer 5. May be.

  The hard protective film layer 5 needs to have high transparency in the visible wavelength region. Resins that are cured by active energy rays such as polyfunctional acrylic resins having acryloyl groups, vinyl groups, mercapto groups, melamine resins, urethane resins, fluorine resins, silicon resins, etc. Can be used. And these resin may be used individually or in mixture of multiple, and may use a polymerization initiator as needed.

  The hard coating film 5 is formed by coating the protective film coating solution on the light absorbing structure 4 to a thickness of 2 μm by spin coating, and heating and curing at 100 ° C. for 30 minutes in a nitrogen atmosphere. It is filming. The film thickness of the hard protective film layer 5 may be any film thickness that provides desired scratch resistance and abrasion resistance and can maintain transparency in the visible wavelength region, and the optimal thickness is about 0.1 to 10 μm. It is. When the thickness is 10 μm or more, there is a risk of film cracking or warping due to stress.

  When reflection of the hard protective film layer 5 is a problem, a material having a small refractive index is selected, and a film thickness that minimizes the reflectance, generally λ / 4 (λ: design wavelength) is preferable. .

  When a thermosetting resin is provided as the hard protective film layer 5 as in this embodiment, the curing temperature is preferably lower than the glass transition temperature Tg of the resin binder of the light absorbing structure 4. Considering the glass transition temperature Tg, specifically, 150 ° C. or lower is preferable.

  In addition, for curing the resin of the hard protective film layer 5, active energy rays other than heat rays, for example, visible light, electron beam, plasma, ultraviolet rays, infrared rays, etc. may be used, but a dye weak to ultraviolet rays is used for the absorption layer. In consideration of production and production facilities, thermosetting resins are preferable. The irradiation amount of active energy rays should just be the energy amount which hardening of a resin composition advances.

  Examples of the photopolymerization initiator include benzophenone, benzyl, 4,4-dimethylaminobenzophenone, 2-chlorothioxanthone, 2,4-diethylthioxanthone, benzoin ethyl ether, diethoxyacetophenone, benzyldimethyl ketal, 2-hydroxy-2- Examples include methylpropiophenone, 1-hydroxycyclohexyl phenyl ketone, tetramethylthiuram monosulfide, tetramethylthiuram disulfide, hydrazone, α-acyloxime ester, and the like, but not limited to these. It may be used.

  Examples of the electron beam curing initiator include benzophenone, 2-ethylanthraquinone, 2,4-diethylthioxanthone, methyl orthobenzoylbenzoate, isopropylthioxanthone, diethoxyacetophenone, benzyldimethyl ketal, 1-hydroxycyclohexyl-phenyl ketone, benzoin methyl ether, Benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis-phenylphosphine oxide, methylbenzoylformate, 1,7-bisacridinylheptane, 9-phenylacridine, etc. However, it is not limited to these, You may use individually or in multiple.

  Thermal polymerization initiators include benzoyl peroxide, t-butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di (2-ethoxyethyl) peroxydicarbonate. , T-butyl peroxyneodecanoate, t-butyl peroxybivalate, (3,5,5-trimethylhexanoyl) peroxide, dipropionyl peroxide, diacetyl peroxide, 2,2-azobisisobutyro Nitrile, 2,2-azobis (2-methylbutyronitrile), 1,1-azobis (cyclohexane-1-carbonyl), 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2-azobis (2,4-dimethyl-4-methoxyvaleronitrile), dimethyl 2 2- azobis (2-methyl propionate), 4,4-azobis (4-cyanovaleric acid) and others as mentioned, is not limited thereto, may be used singly or a plurality.

  Further, by adding inorganic fine particles to the resin cured by the above-mentioned active energy, the crosslinking shrinkage rate can be improved and the hardness of the hard protective film layer 5 can be improved. As such inorganic fine particles, particles such as silicon dioxide, aluminum oxide, zirconium oxide, titanium dioxide, tin oxide, calcium carbonate, barium sulfate, talc, kaolin and calcium sulfate can be used. The particle diameter may be a size that does not cause aggregation of the particles, but is preferably 400 nm or less. When the size is 400 nm or more, light is scattered by the inorganic particles, which may reduce the transparency. The addition amount of the inorganic fine particles may be an amount suitable for the desired hardness or the like, but is preferably about 5 to 80% by weight.

  The spin coat method was used to apply the protective film coating solution, but it may be applied by the bar coater method, dipping method, gravure method, spray method, etc., and the optimum method should be used in consideration of the characteristics of the protective film coating solution. That's fine.

The hard protective film layer 5 is not limited to the wet method described above, and may be formed by a so-called dry method such as a vacuum evaporation method. In this case, as the hard protective film layer 5, it is sufficient if the transparency in the visible wavelength region is high. For example, SiO ₂ , SiO, DLC (diamond-like carbon), organosilane, or the like can be used.

  When the hard protective film layer 5 is formed by the dry method, scratch resistance and wear resistance can be obtained even with a relatively thin film thickness as compared with the wet method. Examples of the dry film forming method include an ion plating method, an ion assist vapor deposition method, a sputtering method, and the like other than the vacuum vapor deposition method, and an optimum method may be selected in consideration of material characteristics and the like.

  When reflection of the hard protective film layer 5 is a problem, a material having a small refractive index is selected, and the film thickness is generally λ / 4 (λ: design wavelength) so that the reflectance is minimized. Is preferred. Moreover, the hard protective film layer 5 may have a reflection preventing function and may be a laminate of hard vapor deposition films having different refractive indexes. In this case, considering the radiant heat at the time of film formation, the film thickness is preferably 1 μm or less.

  Table 1 shows the results of the scratch resistance test with and without the hard protective film layer 5. The resin constituting the light-absorbing structure 4 is an acrylic resin containing a styrene structure, and the scratch resistance test is performed by rubbing ethanol impregnated with Sylbon paper 10 times with a force of 500 g, and the presence or absence of scratches. Furthermore, the loss of transmittance in visible light was tested.

  As shown in Table 1, by providing the hard protective film layer 5, scratch resistance is improved and scratches are hardly generated, so that loss of transmittance can be reduced.

Table 1
Hard protective film layer Scratches Maximum transmittance loss (λ = 400-700nm)
None Many 7.8%
Yes No About 0%

  When the infrared cut filter 1 manufactured in this way is arranged in an optical system, the light absorption structure 4 is made of near-infrared light reflecting structures 3a and 3b having a transition region which is a main factor of ghost light, and the solid-state imaging device 16. The ghost light can be further reduced by arranging between the two.

  FIG. 5 shows an imaging optical system used in the surveillance camera or the like of the second embodiment, and the infrared cut filter 1 obtained in the first embodiment is used. On the optical path, the lens 11, the light quantity diaphragm 12, the lenses 13 to 15, the infrared cut filter 1, and the solid-state image sensor 16 are sequentially arranged.

  A pair of diaphragm blades 18 a and 18 b is movably attached to the diaphragm blade support plate 17 in the light quantity diaphragm device 12. An ND (Neutral Density) filter 19 is attached to the diaphragm blade 18a for the purpose of reducing the amount of light passing through the opening formed by the diaphragm blades 18a and 18b. In addition, the infrared cut filter 1 can be moved back and forth with respect to the optical path by the filter drive unit 20, and the amount of infrared light can be limited and an appropriate image can be obtained in accordance with the characteristics of the solid-state imaging device 16. .

  The light quantity diaphragm device 12 also uses the ND filter 19 to control the quantity of incident light, so that the apertures of the diaphragm blades 18a and 18b can be made larger even if the brightness of the object field is the same, and hunting is performed. Degradation of resolution due to a phenomenon or a light diffraction phenomenon can be reduced.

  The solid-state imaging device 16 used for such a monitoring camera has a relatively high sensitivity to red as shown in FIG. 6 so that it can be photographed even under conditions of a small amount of light such as at night. FIG. 6 shows the sensitivity of each color sensor of the solid-state imaging device 16, and the red sensitivity is increased in the combined sensitivity.

  By using the infrared cut filter 1 having the light absorbing structure 4 that absorbs at the infrared half-value wavelength of the near-infrared light reflecting structures 3a and 3b as in the first embodiment, it is small and reduces ghost light by infrared rays. Is possible. Further, due to the presence of the hard protective film layer 5, scratch resistance and abrasion resistance against driving by the filter driving unit 20 can be obtained.

  When the amount of incident light that has passed through the light amount diaphragm 12 is sufficiently bright as in the daytime, the infrared cut filter 1 is inserted into the optical path by the filter driving unit 20 and the amount of light is insufficient and dark at night. When it is used, it is retracted from the optical path.

  By applying such an infrared cut filter 1 to, for example, a surveillance camera, a stable light quantity stop device having high scratch resistance and wear resistance and little change in spectral characteristics due to scratches or the like can be obtained.

DESCRIPTION OF SYMBOLS 1 Infrared cut filter 2 Transparent substrate 3a, 3b Near-infrared light reflection structure 4 Light absorption structure 5 Hard protective film layer 12 Light quantity stop device 16 Solid-state image sensor 18a, 18b Aperture blade 19 ND filter 20 Filter drive part

Claims (8)

  Multiple thin films with different refractive indexes are laminated on a transparent substrate, and has a transition wavelength region that changes from a transmission wavelength region that transmits light to a non-transmission wavelength region, and reflects at least a part of the near-infrared wavelength region. A near-infrared light reflecting structure and a light-absorbing structure having a predetermined absorption wavelength region that is formed by dispersing a dye in a resin and at least partially overlaps the transition wavelength region of the near-infrared light reflecting structure An optical filter comprising: a body; and a hard protective film layer, wherein the hard protective film layer is formed on the light absorbing structure.   The optical filter according to claim 1, wherein the near-infrared light reflecting structure has the transition wavelength region between wavelengths of 600 to 750 nm.   The said light absorption structure has the absorptivity of 20% or more in the wavelength from which the transmittance | permeability becomes 50% in the transition wavelength area | region of the said near-infrared-light reflection structure. Optical filter.   The optical filter according to any one of claims 1 to 3, wherein the hard protective film layer is formed by curing a thermosetting resin having a curing temperature of 150 ° C or higher.   The optical filter according to claim 4, wherein the hard protective film layer is obtained by mixing inorganic fine particles in the thermosetting resin.   The optical filter according to claim 1, wherein the hard protective film layer is formed by a physical method having a thickness of 1 μm or less.   An optical filter according to any one of claims 1 to 6 is provided between the light quantity diaphragm device having an opening and the image sensor, and the optical filter can be moved forward and backward by the drive unit in the opening. An imaging optical system characterized by being driven.   The imaging optical system according to claim 7, wherein the hard protective film layer of the optical filter is directed to the imaging element side.

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