JP2008233356A - Manufacturing method of optical filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent ghosts, flares, and cracks from developing at the cutting section and the vapor deposition film from peeling off when cutting out optical filters in the filter shapes. <P>SOLUTION: In step S1, a nonreflective asperity structure 12 is formed surrounding the area to form a thin film on the substrate 11 of a 100 μm thick PET sheet. In the following step S2, an ND film 13 is formed inside the nonreflective asperity structure 12 formed in step S1. In step S3, an ND filter is punched out using this nonreflective asperity structure 12 as the contour in a press machine. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method of manufacturing an optical filter suitable for use in adjusting the amount of light in a photographing system such as a video camera or a digital still camera.

  2. Description of the Related Art Conventionally, in a light amount adjusting device used for a video camera, a digital still camera, or the like, for example, an ND filter (Neutral Density Filter) is used as an optical filter for adjusting a light amount together with a diaphragm blade for adjusting a light amount. ing. The ND filter is inserted into the aperture opening together with the aperture blade in order to solve problems such as hunting when the aperture blade is a small aperture and a decrease in resolution due to an optical diffraction phenomenon.

  In the light amount adjusting device, with the recent improvement in sensitivity of the image sensor, the density of the ND filter is increased to reduce the light transmittance, and the aperture of the diaphragm is increased even if the brightness of the object field is the same. Ingenuity has been made. Usually, the ND filter is manufactured by forming a vapor-deposited film having optical filter characteristics and antireflection characteristics on the surface of the transparent resin sheet base material, and then cutting into a necessary filter shape by pressing or the like. .

  However, since this vapor-deposited film is a hard and brittle material, when the transparent resin sheet substrate on which the vapor-deposited film is formed is cut into a filter shape by a press device or the like, cracks may be generated from the cut surface. There is. This crack causes irregular reflection of light, causes flare in the lens optical system, and causes a decrease in optical resolution.

  Further, when the transparent resin sheet base material is pressed and cut with an upper die of a press mold at the time of cutting, the deposition film may be peeled off due to deformation in the thickness direction. If the vapor deposition film is peeled off, it becomes dust in the lens optical system, which not only causes an optical defect, but this dust may adversely affect movable parts such as the guide shaft of the movable lens.

  In order to prevent this problem, for example, Patent Document 1 discloses a method for preventing a vapor deposition film from being formed on a cutting portion that is an outer peripheral end portion of a filter. Patent Document 2 discloses a method for solving the above-described problem by cutting a part of the filter shape in advance, forming a vapor deposition film, and cutting the remaining part after the film formation.

JP 2003-202612 A JP 2003-202613 A

  However, there is a risk of cracking of the vapor deposition film and peeling of the vapor deposition film when performing cutting with a press device or the like as described above, and therefore, after the press processing, a peeling inspection process of the crack or vapor deposition film is indispensable. This inspection process and poor yield result in an expensive one. However, even if this inspection process is performed, it is insufficient to prevent small pieces from falling off the deposited film in the lens optical system.

  Moreover, in the method shown in Patent Document 1, since the transparent resin sheet base material itself is exposed at the outer peripheral end portion of the optical filter, the reflectance becomes high. Therefore, if the optical filter manufactured in this way is incorporated in an optical system and the outer peripheral end of the optical filter is inserted into the aperture opening, there is a high possibility that ghosts, flares, and the like will occur.

  Furthermore, in the method shown in Patent Document 2, the cutting process is performed twice, which complicates the process. In addition, since a part of the filter shape is cut in advance, there are few parts that support the filter, the base material is likely to be deformed due to heat during vapor deposition, etc. Absent.

  The object of the present invention is to eliminate the above-mentioned problems, prevent the occurrence of ghosts and flares, etc., and at the time of cutting into a filter shape, cracks are generated from the cut portion or the deposited film is peeled off. An object of the present invention is to provide a method of manufacturing an optical filter that can prevent the above-described problem.

  The technical feature of the method for producing an optical filter according to the present invention for achieving the above object is a process of forming a non-reflective uneven structure on a transparent resin substrate so as to surround a region where a thin film having a filter function is formed. And forming the thin film in a region surrounded by the non-reflective concavo-convex structure, and cutting the substrate in the region where the non-reflective concavo-convex structure is formed.

  According to the method for manufacturing an optical filter according to the present invention, by providing a non-reflective concavo-convex structure on the outer periphery of the optical filter, it is possible to prevent the occurrence of ghost, flare, etc. Peeling can be prevented.

  Furthermore, by forming a non-reflective concavo-convex structure around the thin film and reducing the reflectance of the substrate substrate, there is an effect of preventing ghost and flare when the filter is provided at the aperture opening of the light amount adjusting device. . In addition, the running cost can be reduced by reducing the number of times of deposition rather than forming an AR film (Anti-Reflection Coating).

The present invention will be described in detail based on the embodiments shown in the drawings.
FIG. 1 is a configuration diagram of a photographing optical system of a camera, in which a solid-state imaging device 7 including a lens 1, a light amount diaphragm device 2, lenses 3, 4, and 5, a low-pass filter 6, a CCD, and the like are sequentially arranged. In the light quantity diaphragm device 2, a pair of diaphragm blades 9 a and 9 b are movably attached to the diaphragm blade support plate 8. The diaphragm blade 9a is formed with a substantially rhombic variable opening formed by the diaphragm blades 9a and 9b, and an ND filter 10 for attenuating the amount of light passing through the opening is bonded.

  The subject image is received by the solid-state imaging device 7 through the lens 1, the light amount diaphragm device 2 including the ND filter 10, the lenses 3, 4, 5, and the low-pass filter 6.

  FIG. 2 is a plan view of the ND filter 10 manufactured in this embodiment. In the ND filter 10, a non-reflective concavo-convex structure 12 is formed in a substantially triangular outline on a PET substrate 11 made of a transparent resin substrate, and an ND film 13 having a filter function is formed on the inside thereof. It punches out using a press along the dashed-dotted line on the non-reflective uneven structure 12 shown in FIG. As a result, the material of the substrate 11 is not exposed in the ND filter 10.

  FIG. 3 shows a process chart of the manufacturing process of the ND filter 10 manufactured in this embodiment. First, in step S1, a non-reflective concavo-convex structure 12 is formed on a substrate 11 made of sheet-like PET (polyethylene teflate) having a thickness of 100 μm so as to surround a region where a thin film having a filter function is formed. In the present embodiment, the contoured non-reflective concavo-convex structure 12 having a predetermined width is formed. In the next step S2, an ND film 13 is formed inside the non-reflective concavo-convex structure 12 formed in step S1. In step S3, the ND filter 10 is punched using a press with the region of the non-reflective uneven structure 12 as an outline.

  The base material used for the substrate 11 of the ND filter 10 is more preferably a synthetic resin film material made of an organic-inorganic composite material than a glass plate in terms of moldability, mass productivity and the like. The organic-inorganic composite material is obtained by mixing and compounding an organic component and an inorganic component at a molecular level or a nanoscale level. The organic component in the organic-inorganic composite material having an IPN structure is a polymer composed of a so-called organic skeleton mainly having a carbon-carbon bond in the main chain skeleton, and is a chain or a cross-linked one, depending on the purpose. It can be selected appropriately.

  For example, cellulose ester, polyamide, polycarbonate, polyester, polystyrene, polyolefin, polysulfone, polyethersulfone, polyarylate, polyetherimide, polymethyl methacrylate, polyether ketone and the like.

  Examples of the cellulose ester include triacetyl cellulose, diacetyl cellulose, propionyl cellulose, butyryl cellulose, acetyl propionyl cellulose, and nitrocellulose.

  Examples of the polyester include PET, polyethylene naphthalate, poly-1,4-cyclohexanedimethylene terephthalate, polyethylene-1,2-diphenoxyethane-4,4′-dicarboxylate, polybutylene terephthalate, and the like.

  Examples of polystyrene include syndiotactic polystyrene.

  Examples of the polyolefin include polypropylene, polyethylene, and polymethylpentene. Among these, triacetyl cellulose, polycarbonate, polyethylene terephthalate and polyethylene naphthalate are particularly preferable.

  FIG. 4 is an enlarged perspective view of the non-reflective concavo-convex structure 12, and a large number of ND filters 10 are obtained on the PET substrate 11, and the non-reflective concavo-convex structure is formed at the contour position of each ND filter 10. 12 is formed. As shown in FIG. 5A, the non-reflective concavo-convex structure 12 is composed of a large number of conical undulations 12a arranged periodically.

The principle of antireflection is that total reflection occurs due to the difference in refractive index when light is transmitted through the interface of media having different refractive indexes. The critical angle θc for total reflection is represented by θc = sin ⁻¹ (n1 / n2) (n1 and n2 are the refractive indexes of the respective media). The non-reflective concavo-convex structure 12 serving as the anti-reflective surface can obtain an anti-reflective effect equivalent to that of the layer whose refractive index continuously changes. n2, which is a very large critical angle.

  For this reason, it is known that a good antireflection effect can be obtained even when the incident angle of light increases. The uneven period (Λ) of the non-reflective uneven structure 12 on the surface is preferably 10 to 400 nm, and when the refractive index of the non-reflective uneven structure 12 is n, Λ <400 / n (nm) is more preferable, Under such conditions, visible light scattering hardly occurs. Moreover, 50-1000 nm is preferable, as for the height (depth) of the fine unevenness | corrugation 12a, 200-1000 nm is more preferable, Furthermore, 300-1000 nm is preferable.

  The shape of the fine irregularities 12a is not particularly limited, but can be appropriately selected according to the purpose. For example, in the present embodiment, the cone-shaped fine irregularities 12a having a small incident angle dependency shown in FIG. 5A are used, but the triangular pyramid-shaped fine irregularities 12b shown in FIG. It is possible to use the fine unevenness 12c made of a quadrangular pyramid shown in c). A structure in which the average refractive index from the air interface (refractive index of about 1) to the support continuously changes depending on the shape of a bell shape or a uniaxially undulating die that is sunk on the air interface side. Among these, those having no directivity such as a cone shape, a triangular pyramid shape, and a bell shape are more preferable. Like the cone shape, the triangular pyramid shape, and the quadrangular pyramid shape shown in FIGS. It is particularly preferable that the continuous change in the refractive index in the thickness direction is linear and a linear function.

  The array of the non-reflective uneven structure 12 includes a square array, a hexagonal close-packed array, and the like. In this embodiment, the exposed surface of the substrate 11 is small as shown in FIG. The configuration was as follows. Regarding the control of the reflectance, it can be changed by the relationship of the aspect ratio of the non-reflective concavo-convex structure 12 (depth of fine concavo-convex 12a / concave / convex cycle).

  In the present embodiment, in order to set the reflectance in the visible light range of wavelength 400 to 700 nm to 0.5% or less, the uneven period of the non-reflective uneven structure 12 is 250 nm, and the depth of the fine unevenness 12a is 250 nm or more. The aspect ratio was 1 or more. On the contrary, the same effect is acquired by fixing the depth of the fine unevenness | corrugation 12a, shortening the uneven | corrugated period of the non-reflective uneven structure 12 and making the aspect ratio 1 or more.

  As a method for producing the non-reflective concavo-convex structure 12, a method of transferring the fine concavo-convex 12a to the substrate 11 by pressing a stamper having a complementary fine concavo-convex structure is used from the viewpoint of inexpensive and stable manufacturing for large area processing. be able to. The transfer rate when transferring the fine irregularities 12a to the substrate 11 is usually about 80% because the tip may be rounded. Further, the concave / convex shape of the fine concave / convex portion 12a is higher in characteristic accuracy than the convex shape.

  In this embodiment, the non-reflective concavo-convex structure 12 is formed only on the contour shape of the filter 10 on one side of the substrate 11, but it may be formed on the entire surface of the substrate 11 excluding the region where the ND film 13 is formed. .

  FIG. 6 shows a configuration diagram of a chamber of a vacuum deposition machine for depositing an ND film. A vapor deposition source 22 and a rotatable vapor deposition umbrella 23 are provided in the chamber 21, and a substrate jig 24 is disposed on the vapor deposition umbrella 23. FIG. 7 is an enlarged cross-sectional view of the substrate jig 24. A PET substrate 11 which is a substrate of the ND filter 10 is attached to the substrate jig 24, and the film is formed with the vapor deposition umbrella 23 around the Z axis. Is called.

The film formation conditions were a substrate set temperature of 130 ° C., a film formation pressure of 8.40 × 10 ⁻⁴ Pa, and the film formation was performed at a distance of 950 mm from the vapor deposition source 22 to the substrate 11.

  In this embodiment, a thin film, which is a vapor deposition film, is formed on the substrate 11 by a vacuum vapor deposition method, but a sputtering method, an ink jet printing method, or the like can also be used.

FIG. 8 shows a configuration diagram of the ND film 13 of the ND filter 10 in this embodiment. The ND film 13 is formed on a PET substrate 11 by a thin film composed of a plurality of alternating layers of a metal film and a dielectric film that attenuate the amount of light. An oxide material obtained by oxidizing Ti, Tb, Nb, Ta, Y, Zn, Zr or the like is used as the light attenuating film, and Al ₂ O ₃ , SiO ₂ , MgF ₂ or the like is used as the dielectric film. . In this embodiment, Al ₂ O ₃ films 31 are alternately laminated on the first, _third , fifth, seventh and ninth layers of dielectric films, and TixOy films 32 are alternately laminated on the _second , fourth, sixth, eighth and tenth layers, and air The uppermost layer in contact with the MgF ₂ film 33 is an 11-layer film configuration. By adopting such a film configuration, it is possible to realize optical characteristics with excellent flatness of transmittance flatness of 6% or less and low reflectivity.

The transmittance flatness is expressed by the following formula (1) obtained by dividing the difference obtained by subtracting the minimum transmittance Tmin from the maximum transmittance Tmax in the wavelength range of 400 to 700 nm by the transmittance T550 at a wavelength of 550 nm.
(Tmax−Tmin) / T550 (1)

  FIG. 9 is an explanatory diagram in which the substrate 11 provided with the non-reflective concavo-convex structure 12 and the ND film 13 is processed by cutting out a portion of the ND filter 10 that has a substantially triangular outer shape by a press device or the like. The ND filter 10 on the substrate 11 has a region where the ND film 13 is formed and a region where the non-reflective uneven structure 12 is formed without forming the ND film 13 on the outer peripheral edge thereof.

  The ND filter 10 is desirably cut at a position away from the ND film 13 on the non-reflective concavo-convex structure 12, and the generation of cracks from the cut surface to the ND film 13 can be prevented. Further, the ND filter 10 forms the contoured non-reflective concavo-convex structure 12 so that there is no region where the substrate 11 is exposed, and ghosts and flares can be reduced. Furthermore, by increasing the distance from the ND film 13 at the time of cutting, stress is not applied to the formed ND film 13, and the ND film 13 can be prevented from peeling off from the substrate 11.

  In order to investigate the environmental stability of the ND filter 10 manufactured by the above-described method, a standing test for 240 hours was performed at a temperature of 60 ° C. and a humidity of 90%, and the transmittance before and after the test was measured. There was almost no difference from below%.

Moreover, when the same environmental test was done for the thing which does not heat-process and the transmittance | permeability before and behind a test was measured, it was increasing about 2%. A cause of such a phenomenon is that the substrate temperature during vacuum deposition is low. The sealing density of the deposited film greatly affects the substrate temperature at the time of film formation. When the deposition temperature is low, the sealing density is lowered and water, oxygen, and the like are easily transmitted. Therefore, the oxidation of the TixOy film 32 that is a light attenuation film is performed. Is promoted. Further, it is considered that the transmittance increases due to both the effects of the protective effect of the dielectric film of the Al ₂ O ₃ film 31 protecting it being small. It is thought that the environmental stability is improved by the heat treatment due to the aging effect.

  FIG. 10 is a graph comparing the reflectance of the conventional example in which the PET substrate 11 is exposed and the non-reflective concavo-convex structure 12 is formed on the outer peripheral edge of the ND film 13. When the substrate 11 is exposed, the reflectance is about 9%, and when the non-reflective concavo-convex structure 12 is formed, the reflectance is 1% or less.

  Thus, when the substrate 11 is exposed, it can be seen that the reflectance is overwhelmingly higher than the reflectance of 3% or less when the non-reflective concavo-convex structure 12 is formed or when the ND film 13 is formed.

It is a block diagram of an imaging optical system. It is a top view of an ND filter. It is process drawing of a manufacturing process. It is an expansion perspective view of a non-reflective uneven structure. It is a perspective view of a fine unevenness | corrugation. It is a block diagram of a chamber. It is an expanded sectional view of a substrate jig. It is a block diagram of ND film | membrane. It is explanatory drawing of the cutting process of ND filter. It is a graph of the reflectance by the presence or absence of a non-reflective uneven structure body.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 3, 4, 5 Lens 2 Light quantity diaphragm 6 Low pass filter 7 Solid-state image sensor 8 Diaphragm blade support plate 9 Diaphragm blade 10 ND filter 11 PET substrate 12 Non-reflective uneven structure 12a, 12b, 12c Fine uneven 13 ND film 21 Chamber 22 Deposition source 23 Deposition umbrella 24 Substrate jig 31 Al ₂ O ₃ film 32 TixOy film 33 MgF ₂ film

Claims (5)

Forming a non-reflective uneven structure on a transparent resin substrate so as to surround a region where a thin film having a filter function is formed, and forming the thin film in a region surrounded by the non-reflective uneven structure And a step of cutting out the substrate in the region where the non-reflective concavo-convex structure is formed.   The method of manufacturing an optical filter according to claim 1, wherein the region of the non-reflective uneven structure has a substantially triangular outline.   3. The optical filter according to claim 1, wherein the non-reflective concavo-convex structure has a plurality of concave or convex cones having a height of 50 to 1000 nm arranged at a period of 10 to 400 nm. Method.   In a light quantity diaphragm device comprising a plurality of movable diaphragm blades that vary the size of the diaphragm opening, and an ND filter for light quantity adjustment disposed in at least a part of the opening formed by the diaphragm blades, The said ND filter was manufactured with the manufacturing method of the optical filter as described in any one of Claims 1-3, The light quantity aperture device characterized by the above-mentioned.   A camera, comprising: an optical system; a light amount diaphragm device according to claim 4 that limits an amount of light that passes through the optical system; and a solid-state imaging device that receives an image formed by the optical system.