JP2012137646A - Optical filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce occurrence of ghost light and to realize thickness reduction and low cost.SOLUTION: A light absorbing structure 3 formed with a resin layer, into which a dye absorbing light having a predetermined wavelength is dispersed, and a near infrared light reflecting structure 4a being formed by laminating a plurality of inorganic thin films so as to reflect the light having the predetermined wavelength are deposited on one surface of a transparent substrate 2. A similar near infrared light reflecting structure 4b is deposited on an opposite surface thereof. Transmission of a light beam in any wavelength region is limited. At least a part of an absorbing wavelength region of the light absorbing structure 3 is overlapped with an inside of a transition wavelength region of near infrared light that transits from a transmitting wavelength region formed with near infrared light reflecting structures 4a and 4b to a non-transmitting wavelength region.

Description

  The present invention relates to an optical filter that restricts transmission of light in a predetermined wavelength region.

  A solid-state imaging device used in an imaging apparatus such as a video camera may be used in combination with a filter that adjusts optical characteristics such as spectral transmittance in order to correspond to the sensitivity characteristics of the human eye. Specifically, there are a near-infrared cut filter, an ultraviolet cut filter, or an ultraviolet / infrared cut filter in which these are realized by a single filter.

  In order to limit the transmission of light in a desired wavelength region, these optical filters are prepared by kneading or applying a material that absorbs light of a specific wavelength into the base material of the optical filter. Absorbs light of a specific wavelength. As such an absorption type optical filter, as shown in Patent Documents 1 to 4, a dye having a characteristic of kneading a metal ion, a dye, or the like into a substrate, or absorbing light of a specific wavelength in a resin binder, etc. There has been proposed a method of applying an organic thin film in which is dispersed on a substrate.

  Patent Document 5 discloses a technique in which two or more kinds of thin films having different refractive indexes are laminated on a base material, and light of a specific wavelength is reflected by using interference of the thin films. This reflection type infrared cut filter has the advantage that it has a high transmittance in the transmission wavelength region and can be made flat, so that color reproducibility is good, and it can be made thinner than an absorption type infrared cut filter. is doing.

  Reflective type optical filters are manufactured by laminating a multilayer film on a transparent substrate by vacuum deposition, IAD, ion plating, sputtering, etc. Recently, demands for weight reduction and processing to any shape are desired. Accordingly, synthetic resin transparent substrates have also been used.

  In Patent Documents 6 and 7, in order to reduce the thickness of an optical filter, an organic material in which a near-infrared light reflecting structure, which is a laminate of a plurality of thin films, and a dye having an absorption band in the infrared wavelength region are dispersed in a binder. A hybrid type combining a light absorbing structure using a thin film has been proposed. With this configuration, since the reflectance in the infrared wavelength region of the reflective structure can be designed to be small, the number of reflective structures stacked can be reduced, and a reduction in thickness can be achieved.

JP 2001-133623 A JP 2005-99820 A JP 2000-7870 A JP 2002-303720 A JP 2003-161831 A JP 2006-301894A JP 2008-51985 A JP 2005-62430 A JP 2005-148283 A Japanese Patent Laid-Open No. 5-134113

  The reflection-type optical filter as shown in Patent Document 5 is structurally configured to transmit a light transmission wavelength region, a non-transmission wavelength region that prevents transmission, and a transition wavelength region that transitions from a transmission wavelength region to a non-transmission wavelength region. And has a wavelength at which both transmittance and reflectance are about 50%. Of these, it is desirable that the band of the transition wavelength region is 0 nm in the wavelength region, that is, it does not exist. However, since it is actually difficult to realize, for example, the transmittance is ideally changed to 100 → between the wavelength region of about 50 nm. 0% or 0 → 100%.

  When the above-described reflection type filter is used in an imaging optical system such as a video camera, a part of the incident light incident on the transition wavelength region is reflected by the imaging element after passing through the filter. Part again enters the optical filter surface from the image sensor side. In the reflection type optical filter, a part of the re-incident light is reflected again by the optical filter, and the reflected light reaches the image sensor again, thereby generating ghost light and degrading the image. is there.

  When ghost light is a problem, it is preferable to use an absorption type optical filter using an absorbing material. An infrared cut filter using copper ions or a dye having an infrared absorption function has a low reflectance, and ghost light hardly poses a problem unlike the reflection type. However, an absorption type optical filter that shields light in the infrared wavelength region with only a dye has not been developed so far to obtain a spectrum that can be used in an imaging optical system such as a camera or a video camera.

  As described above, in the absorption type optical filters of Patent Documents 1 to 4, the transmittance in the non-transmission wavelength region over the near infrared light region is limited to only about 700 to 1100 nm or 1200 nm with only the absorption component. However, when approaching the ideal 0%, there is a problem that the transmittance in the visible wavelength region, which is the transmission wavelength region, is reduced or a large ripple is generated in the transmission wavelength region. Furthermore, when the absorbing layer needs to have a suitable thickness, especially when the absorbent is dispersed in the substrate, a substrate with a thickness of about 0.3 to 0.5 mm or more is required. It becomes difficult to achieve the demand for thinning and miniaturization.

  Even in the hybrid type optical filter as disclosed in Patent Documents 6 and 7, when the transmittance in the visible wavelength region is increased, the transition wavelength region that overlaps with a part of the visible wavelength region, particularly a near red formed by an inorganic thin film. Large absorption cannot be obtained at the outer half-value wavelength. For this reason, the reflection in this wavelength region cannot be greatly reduced, and it becomes difficult to reduce the intensity of the ghost light by the infrared rays.

  Further, infrared absorbing dyes such as those used in Patent Documents 6 and 7 may have a problem that spectral characteristics are likely to change due to the influence of ultraviolet rays. As a countermeasure against the ultraviolet rays of the dye, Patent Document 8 discloses an infrared cut filter that contains an ultraviolet absorber in a substrate and prevents the ultraviolet rays from entering the infrared absorbing layer containing the dye. However, in the configuration as in Patent Document 8, since only one side of the infrared absorption layer has an ultraviolet light absorption effect, the arrangement direction of the infrared cut filter is limited.

  Patent Document 9 discloses an infrared cut filter in which an ultraviolet absorption layer is provided on both sides of an infrared absorption layer containing a dye in order to solve the above problem when there is the above problem. However, the spectral characteristic of the infrared cut filter of Patent Document 9 is determined only by the dye, and as described above, an infrared cut filter as required for an imaging optical system of a camera or a video camera is produced only by the dye. It is difficult. Specifically, if the infrared rays are sufficiently shielded, the transmittance in the transmission wavelength region is lowered.

  Similarly, as disclosed in Patent Document 10, in the case where carbon nanotubes are used for the ultraviolet absorption layer, in consideration of absorption characteristics of the carbon nanotubes, absorption occurs in the visible wavelength region, and the visible wavelength region Therefore, there is a problem in terms of cost.

  A first object of the present invention is to provide an optical filter that eliminates the above-mentioned problems and reduces the generation of ghost light and has an infrared shielding function without hindering the reduction in thickness.

  A second object of the present invention is to provide an optical filter having an ultraviolet shielding function in addition to the first object.

  In order to achieve the above object, an optical filter according to the present invention includes a light absorption structure formed of a resin layer and having a predetermined absorption wavelength region on a transparent substrate and a plurality of inorganic thin films, and at least a near infrared wavelength. A transition wavelength region having at least one near-infrared light reflecting structure that reflects a part of the region, wherein the at least one near-infrared light reflecting structure transitions from a light transmission wavelength region to a non-transmission wavelength region And at least a part of the absorption wavelength region of the light absorption structure overlaps with the transition wavelength region.

  The optical filter according to the present invention includes a light absorption structure formed of a resin layer and having a predetermined absorption wavelength region on a transparent substrate and a plurality of inorganic thin films, and at least a part of the near infrared wavelength region. It has at least one near-infrared light reflecting structure that reflects and an ultraviolet light reflecting structure or an ultraviolet light absorbing structure, and the near-infrared light reflecting structure is not visible from the transmission wavelength region of near-infrared light. It has a transition wavelength region that transitions to a transmission wavelength region, and at least a part of the absorption wavelength region of the light absorption structure overlaps with the transition wavelength region.

  According to the optical filter of the present invention, in addition to the near-infrared reflecting function, the near-infrared shielding function is realized by light absorption by the resin layer containing the near-infrared absorbing dye, so that the thickness can be reduced, and the ghost light Can be reduced. In addition, since it is less necessary to combine a plurality of absorbing materials in order to obtain desired absorption characteristics, there is a low possibility of generating ripples in the transmission wavelength region, and costs can be reduced.

  Moreover, according to the optical filter which concerns on this invention, in addition to the above-mentioned effect, it has an ultraviolet-ray shielding function and can reduce the change of the optical characteristic of the infrared rays absorption layer by ultraviolet light.

2 is a configuration diagram of an optical filter according to Embodiment 1. FIG. It is a graph figure of the spectral transmittance by a near-infrared-light reflection structure. It is a graph of the spectral absorptance of a light absorption structure. It is a graph of the spectral characteristics of an infrared cut filter. It is a graph of the spectral transmittance of the filter by the organic thin film layer of a prior art example. It is a graph of the spectral transmittance of another near-infrared light reflecting structure. It is a graph of the spectral transmittance | permeability of the pigment | dye used for another light absorption structure. 6 is a configuration diagram of an optical filter of Example 2. FIG. 6 is a configuration diagram of an optical filter according to Embodiment 3. FIG. FIG. 6 is a configuration diagram of an optical filter of Example 4. FIG. 10 is a configuration diagram of an optical filter according to Modification 1. FIG. 10 is a configuration diagram of an optical filter according to Modification 2. FIG. 6 is an optical configuration diagram of an imaging apparatus according to Embodiment 5. It is a perspective view of the light quantity diaphragming device of Example 6.

  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 1 of Example 1 that functions as an infrared cut filter that restricts transmission of light in at least the near-infrared light region. In this optical filter 1, a light absorption structure 3 made of an organic thin film formed by dispersing a dye having absorption in a desired wavelength region in a resin binder is formed on a transparent substrate 2. On the light absorbing structure 3, a near infrared light reflecting structure 4a made of an inorganic thin film formed by laminating a plurality of vapor deposition films is formed. Further, on the opposite surface of the transparent substrate 2, a near-infrared light reflecting structure 4b made of an inorganic thin film is provided.

  The transparent substrate 2 is made of, for example, an Arton (product name) film made of synthetic resin, which is a norbornene-based material having a thickness of 0.1 mm. The Arton film has a glass transition temperature (Tg) of 100 ° C. or higher and a flexural modulus of about 3000 MPa, which is relatively high, and can reduce cracks and undulations of the transparent substrate 2. In Example 1, an Arton film was used, but in addition to this, a polyimide resin film or the like is also a suitable material. Furthermore, if it has transparency in the visible wavelength region, for example, use of PET, PEN, polyester, acrylic, aramid, PC (polycarbonate), acetate, polyvinyl chloride, PVA (polyvinyl alcohol), etc. Is possible.

  The light absorbing structure 3 is formed by applying a resin layer in which a pigment is dispersed, for example, by a spin coating method. An acrylic resin is used for the resin binder constituting the light absorbing structure 3, and this acrylic resin is an acrylic resin partially containing styrene from the viewpoint of adhesion between the transparent substrate 2 and the resin layer. Styrene copolymer resin is selected.

  In addition to acrylic resins, polystyrene resin, polyester resin, polyurethane resin, fluororesin, PC resin, polyimide resin, polyolefin resin, etc. can be considered if they have high translucency in the visible wavelength region. It is done. These resins may be used alone or in admixture of two or more, or may be used as a copolymer. In other words, any material that absorbs less light in the visible wavelength region may be used, and an optimal resin is considered in consideration of various factors such as the material to be the transparent substrate 2, the preceding and following processes, the characteristics required for the filter, and compatibility with the dye. What is necessary is just to select a binder.

  More preferably, the resin binder has a small refractive index difference from the transparent substrate 2. When the transparent substrate 2 and the light-absorbing structure 3 are adjacent to each other, the refractive index difference is reduced to reduce the reflection at the interface between the transparent substrate 2 and the resin, and the influence of the interference effect even if the film thickness is reduced. Can be made smaller. For the same reason, even when a functional film layer such as an adhesive layer or a stress relaxation layer is inserted between the transparent substrate 2 and the light absorbing structure 3, the transparent substrate 2, the functional film layer, the light absorbing structure It is more preferable that the three members of the body 3 have similar refractive indexes.

  The coating of the light absorbing structure 3 is not limited to the spin coat method, and may be a dip coat method, a gravure coat method, a spray coat method, a kiss coat method, a die coat method, a knife coat method, a blade coat method, a bar coater method, Similar films can be formed. That is, an optimum film formation method may be selected in consideration of a film thickness, shape, productivity, and the like that satisfy a desired spectrum.

  The stress caused by curing shrinkage that occurs when the resin layer of the light absorption structure 3 is dried can be reduced by reducing the film thickness of the light absorption structure 3. At this time, in order to maintain the desired absorption characteristics, it is necessary to adjust the concentration of the dye and, for example, the coating process such as the rotation speed in the case of the spin coating method.

  In the case of the light-absorbing structure 3 composed of an organic thin film, the dye component is weak in moisture, so even if dispersed in a resin binder, the resin absorbs water notably from the surrounding environment such as temperature and humidity. In some cases, the optical properties of the pigment component may change due to the influence of the pigment component. For this reason, the near-infrared-light reflecting structure 4a is arranged on the surface layer side of the light absorbing structure 3.

  Each of the near-infrared light reflecting structures 4a and 4b is formed by laminating at least two kinds of inorganic thin films, and the reflecting structures 4a and 4b function as one thin film laminated structure and transmit in a certain wavelength region. Is limiting.

  When a synthetic resin material is used for the transparent substrate 2, a heat problem due to the film forming process of the near-infrared light reflecting structures 4a and 4b occurs. In the case of a resin transparent substrate having an extremely low glass transition temperature compared to a glass transparent substrate, the warp of the transparent substrate 2 due to the difference in the linear expansion coefficient between the transparent substrate 2 and the film, and the film accompanying this warp The occurrence of cracks on the surface can be considered. Therefore, measures for heat generated during film formation are necessary. Specifically, it is conceivable to select a material having a high glass transition temperature as the transparent substrate 2 or to employ a low-temperature process during film formation.

  In the film formation of the near-infrared light reflecting structures 4a and 4b, a method of providing a heat absorption mechanism in the film forming apparatus and removing heat generated in the transparent substrate 2 during film formation by a radiation cooling effect was selected. At that time, it is necessary to measure in advance the maximum temperature on the transparent substrate 2 reached in the film forming process and select a material that can withstand that temperature. In Example 1, considering the stability of the film forming process, a certain allowable value is added to the maximum temperature reached in the experiment, and the glass transition temperature is used as a parameter for determining the suitability. A transparent substrate 2 having a temperature is selected.

  Further, the temperature during the film formation of the near-infrared light reflecting structures 4a and 4b is added with some assistance compared to the case of the normal film formation temperature, or the film is formed with relatively high energy such as sputtering. It is more preferable to select a process that increases the density. Specifically, any film forming method capable of relatively accurately controlling the film thickness, such as a sputtering method, an IAD method, an ion plating method, an IBS method, and a cluster vapor deposition method, to obtain a highly reproducible film. Good. It may be formed by a physical or chemical film formation method other than vapor deposition, or may be formed by a wet process such as a sol-gel method. The required film properties and various materials including the transparent substrate 2 An optimal method may be selected based on the constraint conditions.

  FIG. 2 is a graph showing the spectral transmittance characteristics of the reflection type filter when only the near-infrared light reflecting structures 4a and 4b are formed on the transparent substrate 2 made of Arton film having a thickness of 0.1 mm. This filter has a high transmittance in the visible wavelength region, a first blocking wavelength region W1 that prevents transmission of wavelengths in the ultraviolet wavelength region to the visible wavelength region, and a wavelength region in the visible wavelength region to the near infrared wavelength region. A second blocking wavelength region W2 is provided. Further, the third blocking wavelength region W3 is provided in the wavelength region from the second blocking wavelength region W2 to the near-infrared wavelength, and is constituted by three blocking wavelength regions W1 to W3.

  Here, when the thin film laminated structure constituting one blocking wavelength region is considered as one block, it is formed by three blocks forming the first to third blocking wavelength regions W1 to W3. If each is the first to third stacks, the three stacks have different center wavelengths. When this central wavelength is λ, the basic structure is a structure in which high refractive index materials and low refractive index materials are alternately laminated by λ / 4, and in order to obtain desired optical characteristics, the film thickness of each layer is set. Laminate with a fine adjustment of about 0.7 to 1.3 times.

  The thin film laminated structure of the near-infrared light reflecting structures 4a and 4b is formed by sequentially laminating a plurality of dielectric films made of inorganic materials by the IAD method. Generally, in such a multilayer film, the film stress becomes very large, and if the thickness of the transparent substrate 2 is reduced from the viewpoint of reducing the thickness of the optical system, the transparent substrate 2 may be warped. As a countermeasure, when the reflective structures 4a and 4b are respectively formed on both surfaces of the transparent substrate 2 as shown in FIG. 1, ideally, the same material, film thickness, and film quality are laminated on both surfaces of the transparent substrate 2. Thus, the film stress can be reduced.

  However, in that case, the structural design of the film becomes difficult, and if the film design is performed so that the number of stacked layers is the same as that in the case of designing on one side of the transparent substrate 2, the optical characteristics may be greatly sacrificed. In addition, in order to satisfy both the optical characteristics and the relaxation of the film stress at the same time, the number of layers increases, which increases the number of steps for manufacturing the filter. When warping of the transparent substrate 2 due to film stress becomes a problem, it is preferable to divide and arrange the thin film laminated structure on both surfaces of the transparent substrate 2 as shown in FIG.

  Although the above description is a case where only the near-infrared light reflecting structures 4a and 4b are disposed on the transparent substrate 2, in addition, in Example 1, the light-absorbing structure 3 and the near-infrared light reflecting structures 4a and 4b are used. It is also necessary to take into account the stress balance. It is preferable to balance the stresses on both sides of the transparent substrate 2 by measuring each stress in advance and optimizing the arrangement on both sides of the transparent substrate 2.

Therefore, in Example 1, the light absorption structure 3 is first formed on the transparent substrate 2, and a 29-layer thin film of the near-infrared light reflection structure 4 a is formed thereon, and then the opposite of the transparent substrate 2. A 21-layer thin film made of the near-infrared light reflecting structure 4b is formed on the surface. The material for such a reflective structure 4a, a dielectric film made of 4b, TiO ₂ in the high refractive index material, the low refractive index material using SiO _2, were laminated TiO ₂ and SiO ₂ alternately .

In addition, although it depends on the film forming method, generally Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ or the like is used for the high refractive index material, and MgF ₂ is used for the low refractive index material. In some cases. For reasons of design and film formation, Al ₂ O ₃ or the like, which is an intermediate refractive index material, may be used in some layers, but an optimal combination of materials may be selected as appropriate.

  However, the layer at the interface with the transparent substrate 2 or air and the layer in which the stacks having different center wavelengths λ are adjacent to each other may exceed the fine adjustment range, for example, 0.5 times λ / 4 The film thickness may be about the same. Furthermore, in addition to the interface layer described above, there may be several layers, for example, about 1 to 3 layers if the total number of layers is 40, and there may be layers exceeding the fine adjustment range. Further, depending on the design, it may be composed of three or more kinds of materials including an intermediate refractive index material.

  As described above, since the infrared cut filter using the near-infrared light reflecting structures 4a and 4b formed only of the inorganic thin film has the maximum ghost light intensity at the half-wavelength of infrared light in the transition wavelength region, the light absorption structure It is preferable that the body 3 is used to absorb light having a half-wavelength of infrared light.

  In general, when an infrared cut filter is composed of only a near-infrared light reflecting structure, as shown in FIG. 2, this half-wavelength of infrared light is a part of the visible wavelength region and is 600 to 750 nm in the transition wavelength region. Often formed within a range. Further, when an infrared cut filter is configured including the light absorbing structure 3 as described above, the near infrared light reflecting structure as shown in FIG. 4 is also considered in consideration of the light absorption characteristics of the light absorbing structure 3. The transition wavelength region may be shifted to the infrared side. That is, you may make it form an infrared-light half-value wavelength in the transition wavelength area | region of 650-750 nm range.

  Thus, it is preferable that the light absorption structure 3 has an absorption wavelength region when the transition wavelength region where the half-wavelength of infrared light is formed is between 600 and 750 nm. Furthermore, in the wavelength region from the visible wavelength region to the near-infrared wavelength region of about 400 to 1200 nm, it is more preferable to have the maximum absorption characteristic in the wavelength region of about 650 to 800 nm including the above half-value wavelength. . This is because if the characteristic has an absorption peak at a wavelength shorter than 650 nm, light in the transmission wavelength region that is originally required is also largely absorbed. In addition, if the characteristic has an absorption peak at a wavelength longer than 800 nm, there is a possibility that sufficient absorption cannot be obtained in the transition wavelength region.

  Moreover, in the case of a hybrid type filter like the optical filter 1 of Example 1, the absorption by the organic thin film and the reflection by the inorganic thin film are taken into consideration so that the desired wavelength becomes the half-wavelength of infrared light in advance. It may be necessary to adjust.

  FIG. 3 shows spectral characteristics having a predetermined absorption wavelength region when the cyanine dye of the light absorption structure 3 is dispersed in an acrylic resin binder, and the concentration of the dye and the dye so as to obtain a desired absorption. It is formed by adjusting the film thickness and coating it into a film. The pigment dispersed in this manner is red in the spectral transmittance in the transition wavelength region where the near-infrared light formed by the near-infrared light reflecting structures 4a and 4b transitions from the transmission wavelength region that transmits the near-infrared light to the non-transmission wavelength region. It has an absorption band in the vicinity of the wavelength including the external light half-value wavelength.

  The light absorbing structure 3 uses a cyanine dye as an infrared light absorbing dye, but is not limited thereto. For example, azo dyes, phthalocyanine dyes, naphthalocyanine dyes, diimonium dyes, polymethine dyes, anthraquinone dyes, naphthoquinone dyes, triphenylmethane dyes, aminium dyes, pyrylium dyes, squarylium dyes may be used alone or in combination. it can. However, in consideration of the color reproducibility of the infrared cut filter, a dye having a small absorption in the transmission wavelength region and a flat or continuously changing transmittance in the transmission wavelength region is preferable.

  At this time, it is common to add a solvent such as methyl ethyl ketone (MEK), toluene, methyl isobutyl ketone (MIBK), and volatilize it through a drying process after coating. What is necessary is just to select the optimal solvent suitably from a relationship. For example, the solvent is not limited to ketones, but hydrocarbons such as cyclohexane and toluene, esters such as methyl acetate and ethyl acetate, ethers such as diethyl ether and tetrahydrofuran, alcohols such as methanol and ethanol, dimethylformamide, etc. The amine solvent or water may be selected so as to be an optimum combination as a single substance or a mixture of two or more kinds in consideration of the solubility and volatility of the pigment / resin binder.

  In addition, by adding an antioxidant to the light absorption structure 3, deterioration of the pigment may be reduced in some cases. Examples of the antioxidant include phenol-based, binderd phenol-based, amine-based, binderd amine-based, sulfur-based, phosphoric acid-based, phosphorous acid-based and the like.

  FIG. 4 is a graph showing the spectral transmittance characteristics of the optical filter 1 manufactured by the above-described method. The spectral characteristics of the near-infrared light reflecting structures 4a and 4b shown in FIG. 2 and the light absorbing structure 3 shown in FIG. It is a composite of characteristics. The intensity of the ghost light by the infrared cut filter is simply a value calculated by (spectral transmittance of the infrared cut filter) / (spectral reflectance of the infrared cut filter). When the optical filter is composed of only an inorganic thin film, the intensity of the ghost light is maximum at the half-wavelength of infrared light, and assuming that the transmittance is 50% and the reflectance is 50%, the value is about 25%.

  Practically, it is necessary to reduce the intensity of ghost light to at least about 15 to 16%. Therefore, for example, in order to reduce the strength to 16% or less, when the light absorption structure 3 is combined, the light absorption structure 3 is at least 40% transmittance and 40% reflectance. The absorptance at the half-wavelength of infrared light needs to be about 20% or more.

  In a simple calculation, the maximum intensity of the ghost light with only the near-infrared light reflecting structures 4a and 4b is about 25% as described above, but in the transition wavelength region of the optical filter 1 manufactured in Example 1. The maximum intensity of the ghost light is 8% or less. The effect of ghost light also varies depending on the sensitivity characteristics of the image sensor, the total value of unnecessary light generated from the transition wavelength region to the non-transmission wavelength region, and the like. However, the optical filter 1 manufactured in Example 1 reduces the maximum intensity in the transition wavelength region by 30% or more, and can reduce the generation of ghost light in many optical systems.

  After the light absorption structure 3 and the near infrared light reflection structures 4a and 4b described above are formed on the entire surface of the transparent substrate 2, it is processed into a 10 mm square shape by punching into a desired shape. It is to be noted that a similar filter can be produced by a method in which a mask is formed on the transparent substrate 2 at the time of film formation, and a desired range is partially formed and then cut out after film formation.

  FIG. 5 is a graph showing the spectral transmittance of an optical filter of a comparative example produced based on Patent Document 7 for comparison. FIG. 5A is a graph of an organic thin film layer, FIG. 5B is a graph of two inorganic thin film layers arranged on both sides of the substrate, and FIG. 5C is an organic thin film layer and an inorganic thin film. Fig. 2 shows a graph produced by layers.

  It can be seen from FIG. 5B that the half-wavelength of infrared light formed by the inorganic thin film layer is a wavelength around 650 nm. Moreover, even if it is a case where an organic thin film layer and an inorganic thin film layer are comprised from FIG.5 (c), an infrared-light half value wavelength is 650 nm vicinity, and has become the wavelength similar to FIG.5 (b). I understand. Further, from the characteristics of the organic thin film layer shown in FIG. 5 (a), the absorption rate in the transition wavelength region of the organic thin film layer presented in Patent Document 7, in particular, the absorption rate at the half-value wavelength of infrared light is maximum. However, it is expected to be an extremely small value of about 10%.

  In the transmission wavelength region and the non-transmission wavelength region, either the transmittance or the reflectance approaches 0. Therefore, as described above, the intensity of the ghost light simply represents the transmittance and the reflectance in the transition wavelength region. The multiplied value becomes dominant. Therefore, when sufficient absorption cannot be obtained in this transition wavelength region, if the transmittance is low, the reflectance is high, and if the reflectance is low, the transmittance is high, thereby reducing the intensity of the ghost light. Is extremely difficult.

  The influence of the ghost light is slightly different depending on the configuration of the entire optical system, such as the sensitivity characteristics of the image sensor and the arrangement position of the filter. However, in the optical characteristics as shown in FIG. It is difficult to reduce sufficiently.

  In Example 1, the thermosetting method is used as the curing method after the light absorbing structure 3 is formed, but other active energy rays such as visible light, electron beam, plasma, infrared rays, ultraviolet rays, etc. may be used. . The irradiation amount of active energy rays should just be an energy amount which the hardening of a resin composition advances, and what is necessary is just to add a photoinitiator and antioxidant as needed.

  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, but are not limited to, methylpropiophenone, 1-hydroxycyclohexyl phenyl ketone, tetramethylthiuram monosulfide, tetramethylthiuram disulfide, hydrazone, α-acyloxime ester. It may be used.

  Examples of electron beam curing initiators 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 plurality.

  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, not limited to these, may be used singly or a plurality.

  FIG. 6 shows the spectral characteristics of other near-infrared light reflecting structures 4a and 4b. Both near-infrared light reflecting structures 4a and 4b have a first blocking wavelength region W4 for ultraviolet rays, and reflect near-infrared light. The structure 4a is designed to shield at least the second blocking wavelength region W5, and the other near-infrared light reflecting structure 4b is designed to shield at least the third blocking wavelength region W6.

  The light-absorbing structure 3 is a 1: 9 mixture of a cyanine dye having a spectral transmittance as shown in FIG. 7, a resin binder made of acrylic-styrene copolymer resin, methyl ethyl ketone (MEK) and methyl isobutyl ketone (MIBK). A coating solution comprising a solvent mixed at a ratio of (weight ratio) is used. This coating solution is formed into a thickness that provides a desired spectrum by spin coating, and is dried and cured in a drying furnace.

  On this light absorption structure 3, the near-infrared-light reflection structure 4a which shields the 1st stop wavelength region W4 and the 2nd stop wavelength region W5 is formed into a film by the vacuum evaporation method. Next, a near infrared light reflecting structure 4b that shields the first blocking wavelength region W4 and the third blocking wavelength region W6 is formed on the opposite surface of the transparent substrate 2 by vacuum evaporation.

  The optical filter 1 according to the first embodiment reduces ghost light, and the near-infrared light reflecting structures 4a and 4b having an ultraviolet shielding function arranged on both surfaces of the transparent substrate 2 allow any ultraviolet light to be applied to the light absorption structure 3. The incident from the surface is also prevented.

  FIG. 8 shows a configuration diagram of the optical filter 11 of Example 2 that functions as an ultraviolet-infrared cut filter or an infrared cut filter. A light absorbing structure 13 and a near-infrared light reflecting structure 14 are laminated on one side of the transparent substrate 12, and on the opposite side, for example, reflection from the back side is prevented and the transmittance in the visible wavelength region is increased. An antireflection structure 15 in which a plurality of inorganic thin films are stacked is formed. The antireflection structure 15 has a function of balancing the stress between the light absorption structure 13 and the opposite surface on which the near infrared light reflection structure 14 is disposed.

  In addition, when the light absorption structure 13 which is a resin layer is exposed to the surface layer, the reflectance on the surface layer may become a problem. Therefore, when the light absorption structure 13 is arranged on the surface layer, such reflection is performed. This can be improved by forming the prevention structure 15 on the light absorption structure 13.

  The near-infrared light reflecting structure 14 has a transition wavelength region that transitions from the transmission wavelength region to the non-transmission wavelength region as in the first embodiment, and a part of the wavelength absorbed by the light absorption structure 13 and the transition wavelength region are It is necessary to overlap.

  If the near-infrared light reflecting structure 14 has a function of shielding ultraviolet rays, the optical filter 11 according to the second embodiment has a light absorbing structure for ultraviolet light incident from the near-infrared light reflecting structure 14 side. The ultraviolet ray shielding function for reducing the ultraviolet ray incident on the body 13 is performed.

  FIG. 9 shows a configuration diagram of the optical filter 21 of Example 3 functioning as an ultraviolet and infrared cut filter, and an ultraviolet light reflecting structure is used. For example, an Arton film having a thickness of 0.1 mm is used for the transparent substrate 22.

  In the optical filter 21 a of FIG. 9A, a light absorbing structure 23 and a near infrared light reflecting structure 24 are formed on one side of the transparent substrate 22 from the transparent substrate 22 side, and ultraviolet light is formed on the opposite surface of the transparent substrate 22. A light reflecting structure 25 is formed. The light absorption structure 23 and the reflection structure 24 are formed in the same manner as the light absorption structure 3 and the near infrared light reflection structures 4a and 4b of the first embodiment, and the near infrared light reflection structure 24 has an ultraviolet shielding function. have.

  The transparent substrate 22 has a refractive index of about 1.52 at a wavelength of 589 nm, the refractive index of the acrylic-styrene copolymer resin of the light absorption structure 23 is about 1.49, and a material having a relatively small refractive index difference. The composition is combined.

  This optical filter 21a is designed to have the spectral transmittance characteristic as shown in FIG. 4 described in the first embodiment, and further, the ultraviolet light is incident from the surface on which the ultraviolet light reflecting structure 25 is provided. Limiting and preventing the incidence of ultraviolet rays from both sides.

  As described above, when the light absorbing structure 23 is arranged on the surface layer, the ultraviolet light reflecting structure 26 can be further arranged on the surface layer side as shown in the optical filter 21b of FIG. 9B.

  In the optical filters 21c and 21d shown in FIGS. 9C and 9D, the light absorbing structure 23 and the near infrared light reflecting structure 24 are formed on one surface of the transparent substrate 22, and the ultraviolet shielding function is provided on the opposite surface. The near-infrared light reflecting structure 27 and the ultraviolet light reflecting structure 25 that are not provided are formed. In the optical filter 21c, the ultraviolet light reflecting structure 25 is disposed on the outermost layer, and in the optical filter 21d, the near-infrared light reflecting structure 27 is disposed on the outermost layer.

  In the optical filters 21e and 21f of FIGS. 9E and 9F, a near-infrared light reflecting structure 24 is formed on one surface of the transparent substrate 22, and a light absorbing structure 23 and a near-red light are formed on the opposite surface. An external light reflecting structure 27 and an ultraviolet light reflecting structure 25 are formed. In the optical filters 21e and 21f, the near-infrared light reflecting structure 27 and the ultraviolet light reflecting structure 25 are interchanged.

  In this manner, in any of the optical filters 21a to 21f, ghost light is reduced and ultraviolet light is prevented from entering the light absorbing structure 23 from both sides.

  FIG. 10 shows a configuration diagram of the optical filter 31 of Example 4 functioning as an ultraviolet and infrared cut filter, and an ultraviolet light absorbing structure is used. A light absorbing structure 33 and a near-infrared light reflecting structure 34 having an ultraviolet shielding function are formed on one surface of the transparent substrate 32 from the transparent substrate 32 side. An ultraviolet light absorbing structure 35 and a near infrared light reflecting structure 36 having no ultraviolet shielding function are formed on the opposite surface of the transparent substrate 32 from the transparent substrate 32 side.

  The ultraviolet light absorbing structure 35 is a coating solution comprising a styrene resin, a resin binder made of 2,4-dihydroxybenzophenone, which is a 1.0 wt% benzophenone ultraviolet absorber, and a styrene resin, and MIBK. Then, a film is formed by a spin coating method, and dried and cured in a drying furnace.

Next, on the light absorption structure 33, the first blocking wavelength region W4 and the second blocking wavelength region W5 shown in FIG. 6 are made of SiO ₂ that is a low refractive index material and TiO ₂ that is a high refractive index material. The near-infrared light reflecting structure 34 to be shielded is formed by vacuum deposition. Further, a near-infrared light reflecting structure 36 that shields the third blocking wavelength region W6 is similarly formed on the ultraviolet light absorbing structure 35.

  Although 2,4-dihydroxybenzophenone was used as the ultraviolet absorber, other than this, benzophenone series such as 2-hydroxy-4-methoxy-benzophenone and 2-hydroxy-4-n-octoxy-benzophenone, 2- (2'-hydroxy-5'-t-butylphenyl) benzotriazole, 2- (2'-hydroxy-5'-methylphenyl) -enzotriazole, 2- (2'-hydroxy-5'-t-octylphenyl) ) Benzotriazoles such as benzotriazole and 2- (3 ′, 5′-di-t-amyl-2-hydroxyphenyl) benzotriazole, and 2,4-di-t-butylphenyl 3,5-di-t -Butyl-4-hydroxybenzoate, 4-t-butylphenyl-2-hydroxybenzoate, phenyl-2-hydroxybenzoate A benzoate system such as a salt can be used, but is not limited thereto. Moreover, you may use these ultraviolet absorbers individually or in mixture.

  If the near-infrared light reflecting structures 34 and 36 are both designed to shield ultraviolet rays, it is difficult to balance the film stress on both sides depending on the desired spectroscopy, and the warping of the optical filter 31 may not be reduced. .

  In the fourth embodiment, the near-infrared light reflecting structure 36 does not have an ultraviolet shielding function, but the ultraviolet light absorbing structure 35 is disposed between the reflecting structure 36 and the transparent substrate 32, and both surfaces of the optical filter 31 are disposed. In this case, it is possible to prevent ultraviolet rays from entering the light absorbing structure 33.

  Heat is generated during curing or film formation of the light absorption structure 33, near infrared light reflection structures 34 and 36, and ultraviolet light absorption structure 35, and deformation due to film stress / thermal stress, changes in spectrum due to moisture, and the like occur. easy. Therefore, it is preferable that the transparent substrate 32 has high heat resistance, that is, a glass transition point Tg, a large flexural modulus, and a low water absorption rate.

  FIG. 11 shows an optical filter 31 ′ according to the first modification of the fourth embodiment. Thus, the light absorption structure 33, the ultraviolet light absorption structure 35, and the near infrared light reflection structure 36 are sequentially formed on one surface of the transparent substrate 32, and the near infrared light reflection structure 34 is formed on the opposite surface. It is good also as a structure which provided.

  12 shows an optical filter 31 ″ of Modification 2. An ultraviolet light absorbing structure 35, a light absorbing structure 33, and a near infrared light reflecting structure 34 are sequentially provided on one surface of the transparent substrate 32. It can also be set as the structure which has arrange | positioned the near-infrared-light reflection structure 36 on the opposite surface.

  In this way, the ghost light is reduced, and the optical filters 31 and 31 ′ are configured such that the ultraviolet rays are not incident on the light absorption structure 33 and the spectral change of the light absorption structure 33 is small regardless of the arrangement direction of the optical filter 31. , 31 ″ are obtained.

  FIG. 13 shows an optical configuration diagram of an imaging apparatus such as a video camera of the fifth embodiment using the optical filter according to the first to fourth embodiments. An objective lens 41, a light amount diaphragm device 43 having diaphragm blades 42, lenses 44 to 46, an optical filter unit 47, and a solid-state imaging device 48 are arranged along the optical path. The optical filter unit 47 restricts the light rays from the object field transmitted through the imaging optical system 49 including the objective lens 41, the light amount diaphragm device 43, and the lenses 44 to 46 in accordance with the characteristics of the solid-state imaging device 48 including a CCD or CMOS sensor. And it is supposed to obtain a proper image.

  For example, the optical filter 1 manufactured in Example 1 is arranged in the optical filter unit 47 and is used by being incorporated in an imaging device, thereby shielding ultraviolet rays and infrared rays and reducing the generation of ghost light, thereby achieving high image accuracy. Can be realized. In addition, when the optical filter unit 47 is disposed, the position of the light absorption structure 3 with respect to the near-infrared light reflection structure 4a is set to the solid-state imaging device 48 so that ghost light due to reflection of the optical filter 1 can be further reduced. Try to be close.

  Specifically, the amount of light that has passed through the imaging optical system 49 and formed on the solid-state imaging device 48 is determined, and the optical filter unit 47 is driven by the driving member. When the amount of light in the object field is sufficient for normal shooting, the optical filter unit 47 is moved so as to cover the solid-state image sensor 48, and when the amount of light is insufficient, the optical element is not applied to the solid-state image sensor 48. The filter unit 47 is retracted out of the optical path.

  Depending on the presence or absence of the optical filter 1 in the optical filter unit 47, an optical path difference may occur in the light beam to be imaged, and the image may be deteriorated. In such a case, the same material as the transparent substrate 2 of the optical filter 1 is used. By inserting the transparent substrate 2 as a dummy, image deterioration can be reduced.

  Further, in the past, in order to reduce ghost light, the optical filter was sometimes inclined with respect to the optical path. However, in the present invention, the ghost light is reduced by the optical filter 1, so that the inclined arrangement is not necessary. It is possible to cope with downsizing of the photographing optical system.

  Further, by arranging the optical filters 11, 21, and 31 produced in Examples 2, 3, and 4 as the optical filter portion 47 and using them, the change in optical characteristics due to ultraviolet rays and infrared rays was significantly reduced. An imaging device can be obtained. In addition, even if light is incident from any surface of the optical filter, if the configuration is such that ultraviolet rays are shielded before reaching the absorption structure 3, when the optical filter is disposed in the imaging optical system, Any surface may be directed to the incident light side, and workability is improved.

  FIG. 14 is a perspective view of a light quantity stop device suitable for use in a photographing optical system of an image pickup apparatus such as a video camera or a digital still camera according to the fifth embodiment. The light quantity diaphragm 51 is provided to control the amount of light incident on the solid-state image sensor 48 shown in FIG. 13, and has a structure in which the diaphragm blades 42 are narrowed down as the quantity of light in the object field increases. Yes.

  At this time, an ND (Neutral Density) filter 52 is disposed in the vicinity of the diaphragm blade 42 as a countermeasure against image performance deterioration due to interference or the like generated when the diaphragm blade 42 is in a small diaphragm state. This prevents the aperture of the aperture blade 42 from becoming extremely small even if the brightness of the object scene is large.

  Incident light from the object field passes through the light amount diaphragm 51 and reaches the solid-state image sensor 48 through the imaging optical system 49, thereby being converted into an electrical signal and generating an image.

  Any one of the optical filters 1, 11, 21, and 31 produced in Examples 1 to 4 is disposed in the light quantity diaphragm device 51. In addition, the optical filters 1, 11, 21, and 31 can be disposed at the position of the ND filter 52 instead of the ND filter 52, and are fixed to the diaphragm blade support plate 53 that supports the diaphragm blade 42. It can also be arranged.

  In this case, although depending on the position of the optical filter and the mechanical mechanism of the light quantity diaphragm 51, the optical filter may be cut into an optimal shape, and by placing the optical filter in the imaging optical system 49, This can contribute to higher accuracy of the image. The light quantity restricting device 51 thus manufactured can significantly reduce the generation of ghost light.

1, 11, 21a to 21f, 31, 31 ', 31 "Optical filter 2, 12, 22, 32 Transparent substrate 3, 13, 23, 33 Light absorbing structure 4a, 4b, 14, 24, 27, 34, 36 Near-infrared light reflection structure 15 Antireflection structure 25 Ultraviolet light reflection structure 35 Ultraviolet light absorption structure 42 Diaphragm blade 43, 51 Light quantity diaphragm device 47 Optical filter section 48 Solid-state imaging device 49 Imaging optical system 52 ND filter

Claims (16)

  A light-absorbing structure formed of a resin layer on a transparent substrate and having a predetermined absorption wavelength region, and a plurality of inorganic thin films are laminated, and at least one near-infrared light reflection that reflects at least part of the near-infrared wavelength region The at least one near-infrared light reflecting structure has a transition wavelength region transitioning from a light transmission wavelength region to a non-transmission wavelength region, and the light absorption structure has an absorption wavelength region. At least a part of the optical filter overlaps the transition wavelength region.   2. The optical filter according to claim 1, wherein a peak of a wavelength absorbed by the light absorbing structure in a wavelength region between a visible wavelength region and a near infrared wavelength region is in the transition wavelength region.   The optical filter according to claim 2, wherein a peak of a wavelength absorbed by the light absorbing structure is in a wavelength region of 650 to 800 nm.   The at least one of the near-infrared light reflecting structures has an infrared light half-value wavelength having a transmittance of 50% between wavelengths of 600 to 750 nm. The optical filter according to claim.   5. The light absorption structure according to claim 4, wherein the light absorption structure has an absorptance of 20% or more at a wavelength at which the transmittance of the near infrared light reflection structure is 50% in the transition wavelength region. Optical filter.   The said light absorption structure was formed of the resin layer which disperse | distributed the pigment | dye which has the said absorption wavelength area to a part of wavelength of a near-infrared wavelength range, The claim in any one of Claims 1-5 characterized by the above-mentioned. The optical filter described.   The optical filter according to any one of claims 1 to 6, wherein the near-infrared light reflecting structures are laminated on both surfaces of the transparent substrate.   A light-absorbing structure formed of a resin layer on a transparent substrate and having a predetermined absorption wavelength region, and a plurality of inorganic thin films are laminated, and at least one near-infrared light reflection that reflects at least part of the near-infrared wavelength region A structure, and an ultraviolet light reflecting structure or an ultraviolet light absorbing structure, the near infrared light reflecting structure has a transition wavelength region that transitions from a light transmission wavelength region to a non-transmission wavelength region, An optical filter, wherein at least part of the absorption wavelength region of the light absorption structure overlaps with the transition wavelength region.   9. The optical filter according to claim 8, wherein the ultraviolet light reflecting structure is disposed with the light absorbing structure sandwiched between the near infrared light reflecting structure.   The optical filter according to claim 1, wherein at least one of the near-infrared light reflecting structures has an ultraviolet shielding function.   The optical filter according to claim 8 or 9, wherein the ultraviolet light reflecting structure is formed by laminating a plurality of inorganic thin films.   9. The optical filter according to claim 8, wherein the ultraviolet light absorbing structure is formed of a resin layer in which an ultraviolet absorber that absorbs ultraviolet rays is dispersed.   The optical filter according to any one of claims 1 to 12, wherein ultraviolet light incident on the light absorbing structure is shielded from any surface with respect to the transparent substrate.   An imaging apparatus comprising: an imaging optical system; the optical filter according to claim 1; and an imaging element that converts light that has entered the imaging optical system and has passed through the optical filter into an electrical signal. .   The imaging device according to claim 14, wherein the light absorption structure of the optical filter is disposed closer to the imaging element than the near-infrared light reflection structure having the transition wavelength region.   The imaging apparatus according to claim 14, further comprising a driving member that drives the optical filter in the imaging optical system.

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