JP2011232522A - Optical low-pass filter, and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical low-pass filter free from troubles, such as peeling and cracking upon a heating/cooling step, and to provide a method of manufacturing the optical low-pass filter.SOLUTION: The method of manufacturing the optical low-pass filter which includes an index modulation type diffraction grating layer 6 having a matrix layer 8 obtained by curing a photo-polymerizable composition, and a plurality of columnar structures 8 arranged inside the matrix layer and having an index different from that of the matrix layer, on a substrate having a linear expansion coefficient different from that of a diffraction grating layer. The method includes steps of: arranging the polymerizable composition for forming an adhesion layer 4 with a glass transition temperature in the range of -70°C to 10°C after cured, on the substrate in a thin-film state; curing the polymerizable composition so as to form the adhesion layer composed of the cured polymerizable composition on the substrate; arranging the photo-polymerizable composition for forming the diffraction grating layer on the adhesion layer in a thin-film state after the curing step; and curing the photo-polymerizable composition with photo-polymerization so as to form the diffraction grating layer on the adhesion layer.

Description

  The present invention relates to an optical low-pass filter and a manufacturing method thereof, and more particularly to an optical low-pass filter in which a plurality of columnar structures having a refractive index different from that of a matrix are arranged in a matrix and a manufacturing method thereof.

  An optical low-pass filter is used to suppress the occurrence of moire in the image sensor. As such an optical low-pass filter, there is one using a molded body as described in Patent Document 1.

  This molded body is a molded body that enables a high degree of light control by regularly arranging structures having a refractive index different from that of the matrix in a transparent matrix. Such a molded body is produced by irradiating the photopolymerizable composition held in a film (sheet) shape with parallel light having a full width at half maximum of 100 mm or less.

JP 2005-242340 A

Such a molded body is adhered to a glass substrate or the like and used as an optical low-pass filter in order to provide rigidity and facilitate assembly and reduce the number of parts.
However, such a molded body has a larger linear expansion coefficient than glass, which is a material of the glass substrate to be bonded. For this reason, at the time of heating / cooling, there is a problem that peeling or cracking occurs due to a difference in linear expansion coefficient between the molded body and the glass substrate.

  The present invention has been made to solve such problems, and provides an optical low-pass filter that does not cause problems such as peeling and cracking during heating / cooling, and a method for manufacturing such an optical low-pass filter. For the purpose.

According to the present invention,
A refractive index modulation type diffraction grating layer comprising: a matrix layer formed by curing a photopolymerizable composition; and a plurality of columnar structures disposed in the matrix layer and having a refractive index different from that of the matrix layer. A method of manufacturing an optical low-pass filter provided on a substrate having a linear expansion coefficient different from that of a diffraction grating layer,
Disposing a polymerizable composition constituting an adhesive layer having a glass transition temperature after curing of −70 ° C. or more and 10 ° C. or less in a thin film on a substrate;
Curing the polymerizable composition to form an adhesive layer made of a cured product of the polymerizable composition on the substrate;
Disposing a photopolymerizable composition constituting the refractive index modulation type diffraction grating layer after curing in a thin film form on the adhesive layer;
Curing the photopolymerizable composition by photopolymerization to form a refractive index modulation type diffraction grating layer on the adhesive layer.
An optical low-pass filter manufacturing method is provided.

  The optical low-pass filter manufactured by such a method has a flexibility that can absorb the thermal stress derived from the difference in linear expansion coefficient between the glass and the molded body during heating / cooling, and thus the adhesive layer has the flexibility. Further, it can be prevented from being peeled off from the molded body and causing cracks, and it can be manufactured from inexpensive raw materials that are easily available.

According to another preferred embodiment of the invention,
The polymerizable composition material contains hydroxyalkyl (meth) acrylate and poly (meth) acrylate.
According to another preferred embodiment of the invention,
The polymerizable composition material contains 50% by mass or more of an alkyl (meth) acrylate having an alkyl group having 2 or more carbon atoms.

According to another aspect of the invention,
An optical low-pass filter,
A substrate,
A photopolymerizable composition is cured, and has a matrix layer and a plurality of columnar structures that are disposed in the matrix layer and have a refractive index different from that of the matrix layer. A rate modulation type diffraction grating layer;
An adhesive layer disposed between the substrate and the refractive index modulation type diffraction grating layer, having a glass transition temperature of −70 ° C. or higher and 10 ° C. or lower and configured by a cured product of the polymerizable composition; Yes,
An optical low-pass filter is provided.

  According to the present invention, an optical low-pass filter that does not cause problems such as peeling and cracking during heating / cooling and a method for manufacturing such an optical low-pass filter are provided.

It is a perspective view which shows typically the structure of the optical low-pass filter 1 of preferable embodiment of this invention. It is drawing for demonstrating the step of the optical low-pass filter manufacturing method of preferable embodiment of this invention. It is drawing for demonstrating the step of the optical low-pass filter manufacturing method of preferable embodiment of this invention. It is drawing for demonstrating the step of the optical low-pass filter manufacturing method of preferable embodiment of this invention. It is drawing for demonstrating the step of the optical low-pass filter manufacturing method of preferable embodiment of this invention. 3 is a diagram for explaining a configuration of a photomask used in a method for manufacturing an optical low-pass filter according to a preferred embodiment of the present invention. It is drawing for demonstrating the other structure of the photomask used with the optical low-pass filter manufacturing method of preferable embodiment of this invention. It is drawing for demonstrating the step of the optical low-pass filter manufacturing method of preferable embodiment of this invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail. FIG. 1 is a perspective view schematically showing a configuration of an optical low-pass filter 1 according to a preferred embodiment of the present invention.

  As shown in FIG. 1, the optical low-pass filter 1 of the present embodiment includes an adhesive layer 4 formed from a polymerizable composition (polymerizable composition for an adhesive layer) on one entire surface of a substrate 2. And a laminated structure in which a refractive index modulation type diffraction grating layer 6 formed of a photopolymerizable composition is provided on the adhesive layer 4.

  The refractive index modulation type diffraction grating layer 6 and the substrate 2 have different linear expansion coefficients. In a preferred embodiment of the present invention, a glass substrate is used as the substrate 2, and in the following description, the substrate 2 may be referred to as a glass substrate.

  The glass substrate 2 is a plate-like member having a smooth surface, and has a substantially uniform thickness of about 0.1 mm to 2.0 mm. The glass substrate 2 is formed of soda glass, quartz glass, borosilicate glass, Pyrex (registered trademark) glass, colored glass, or the like. Moreover, the glass substrate 2 may be formed from a glass material having an IR cut function. Furthermore, the structure which has the IR cut filter which reflects near infrared rays which consists of multilayer films, the IR cut filter using near infrared ray absorption glass, etc., and the antireflection function was given to the surface on the opposite side to the surface where the adhesive layer 4 was provided. It may be configured.

  The adhesive layer 4 is a polymer (polymerizable composition) obtained by curing an uncured polymerizable composition (polymerizable composition material) by photopolymerization, and has a substantially uniform thickness of about 2 μm to 200 μm. Have When the thickness of the adhesive layer 4 is less than 2 μm, the difference in linear expansion coefficient between the substrate and the refractive index modulation type diffraction grating layer 6 cannot be absorbed, and the substrate and the refractive index modulation type diffraction grating layer 6 are peeled off or cracked. There is a fear. When it exceeds 200 μm, it becomes difficult to apply the coating film so that the surface of the coating film becomes smooth with a uniform thickness. Moreover, it is preferable that the adhesive layer 4 is thin from the viewpoint of downsizing a device (such as a digital camera) using the optical low-pass filter 1. In this embodiment, the glass transition temperature of the adhesive layer 4 is set to −70 ° C. or higher and 10 ° C. or lower.

  The refractive index modulation type diffraction grating layer 6 is made of a photopolymerizable composition, and has a phase separation structure composed of a thin plate-like matrix 8 and a plurality of columnar structures 10 arranged in the matrix 8. .

The matrix 8 is a thin plate having a substantially uniform thickness in the range of about 10 μm to 500 μm.
Each columnar structure 10 has substantially the same shape, and its axis is oriented so as to extend in the thickness direction of the refractive index modulation type diffraction grating layer 6 having a thin plate (film) shape. Specifically, the columnar structure 10 has a cylindrical cross-sectional shape in the axial direction, and the columnar structures are oriented so that the axes are directed in the same direction, that is, substantially parallel to each other, on the surface of the matrix 8. Are arranged in a regular grid.

  The matrix 8 and the columnar structure 10 are both light transmissive, but the columnar structure 10 has a refractive index different from that of the matrix 8.

  The arrangement pattern of the columnar structures 10 in the matrix 8 is preferably the same as the arrangement pattern of the imaging elements of the image sensor. That is, when the imaging elements used together with the optical low-pass filter are arranged in a square lattice, the columnar structures 10 are also arranged in a square lattice, and when the imaging elements are arranged in a triangular lattice, the columnar structures 10 are arranged. Are also preferably arranged in a triangular lattice pattern (FIG. 1).

  The shape, cross-sectional shape, diameter, and pitch of the columnar structure 10 are not particularly limited, but when the columnar structure 10 is a cylinder, the cross-sectional diameter is preferably 80 nm to 20 μm, more preferably 1 μm to 10 μm, and the pitch is 120 nm. ˜30 μm is preferable, and more preferably 2 μm to 20 μm.

  In the optical low-pass filter 1 of the present embodiment, the refractive index modulation type diffraction grating layer 6 having such a configuration is bonded to the glass substrate 2 by the adhesive layer 4 having a glass transition temperature of −70 ° C. or higher and 10 ° C. or lower. Has been.

  As a result, during heating / cooling, the adhesive layer has sufficient flexibility to absorb the thermal stress resulting from the difference in linear expansion coefficient between the glass and the molded body, so that the molded body peels off and cracks occur. Can be prevented.

  When a cross-cut test (JIS-K5600) is performed from above the refractive index modulation type diffraction grating layer 6 with the adhesive layer 4 having a glass transition temperature of −70 ° C. or more and 10 ° C. or less, the substrate glass 2 and the adhesive layer The refractive index modulation type diffraction grating layer 6 can be bonded to the glass substrate 2 with such an intensity that peeling does not occur at both the interface 4 and the interface between the adhesive layer 4 and the refractive index modulation type diffraction grating layer 6. .

Next, a method for manufacturing an optical low-pass filter according to a preferred embodiment of the present invention will be described.
The polymerizable composition material 4 ′ (uncured polymerizable composition), which is a raw material of the adhesive layer 4, is coated on one surface of the glass substrate 2 with a uniform thickness and a smooth coating surface. The coating is performed by a known method such as a bar coater, a slit die coater, a spin coater, a circular coater, a gravure coater, or a CAP coater (FIG. 2).

  The polymerizable composition material 4 ′ is particularly limited as long as it is a polymerizable composition that maintains sufficient light transmittance after curing by polymerization and has a glass transition temperature of −70 ° C. or higher and 10 ° C. or lower. However, various active energy ray-curable polymerizable compositions (photopolymerizable compositions) or thermosetting polymerizable compositions (thermopolymerizable compositions) can be used.

Specifically, the following are used.
(monomer)
As the monomer that can be used as the polymerizable composition material, a (meth) acryl monomer containing a (meth) acryloyl group, a monomer containing a vinyl group, an allyl group, or the like is preferable, and a glass transition temperature of −70 ° C. or higher and 10 It is good to mix and use so that it may be below ℃. Hereinafter, specific examples will be described separately for monofunctional monomers and polyfunctional monomers.

  Specific examples of the monofunctional monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 3- (trimethoxysilyl) propyl (meth) acrylate, 3 -(Triethoxysilyl) propyl (meth) acrylate, methyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, ethyl carbitol (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, isobornyl (meth) acrylate, Phenyl carbitol (meth) acrylate, nonylphenoxyethyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, (meth) acryloyloxyethyl succinate, (meta Acryloyloxyethyl phthalate, phenyl (meth) acrylate, cyanoethyl (meth) acrylate, tribromophenyl (meth) acrylate, phenoxyethyl (meth) acrylate, tribromophenoxyethyl (meth) acrylate, benzyl (meth) acrylate, p-bromo (Meth) acrylate compounds such as benzyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, trifluoroethyl (meth) acrylate, 2,2,3,3-tetrafluoropropyl (meth) acrylate Vinyl compounds such as styrene, p-chlorostyrene, vinyl acetate, acrylonitrile, N-vinyl pyrrolidone, vinyl naphthalene; ethylene glycol bisallyl carbonate, dia Rufutareto, allyl compounds such as diallyl isophthalate and the like.

  Specific examples of the polyfunctional monomer include polyfunctional urethane (meth) acrylate, polyfunctional epoxy (meth) acrylate, triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, neopentyl glycol di (meth). ) Acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, hydrogenated dicyclopentadienyl di (meth) acrylate, ethylene oxide modified bisphenol A di (meth) acrylate , Trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, tetramethylolmethane tetra (meth) acrylate, pentaerythritol hexa (meth) acrylate, divinylbenzene, Triallyl cyanurate, triallyl isocyanurate, triallyl trimellitate, diallyl chlorendate, N, N'-m-phenylene bismaleimide, diallyl phthalate, and the like.

  Among the monomers or oligomers mentioned here, urethane is used to give the adhesive layer 4 adhesion to the glass substrate 2 and the refractive index modulation type diffraction grating layer 6 and to improve the physical properties of the adhesive layer 4. Monomers or oligomers such as a monomer having a bond, a monomer having a hydroxyl group, and a silane coupling agent having a (meth) acryloxy group may be selected singly or in combination so that the glass transition temperature is −70 ° C. or higher and 10 ° C. or lower. It is preferable to mix and use. In particular, 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate are preferable.

  Here, the use amount of the monomer or oligomer selected for improving adhesion and physical properties of the coating film is preferably in the range of 10 to 100% by mass and more preferably in the range of 65 to 95% by mass in the total amount.

(Polymer, low molecular weight compound)
Moreover, the homogeneous dissolution mixture containing the said polyfunctional monomer or oligomer and the compound which does not have a polymerizable carbon-carbon double bond can also be used for a polymeric composition.

  Examples of the compound having no polymerizable carbon-carbon double bond include polymers such as polymethyl methacrylate, polystyrene, polyethylene oxide, polyvinyl pyrrolidone, polyvinyl alcohol, and nylon, toluene, n-hexane, cyclohexane, acetone, methyl ethyl ketone, and methyl. Examples include alcohols, ethyl alcohol, ethyl acetate, acetonitrile, dimethylacetamide, dimethylformamide, low molecular compounds such as tetrahydrofuran, organic halogen compounds, organosilicon compounds, plasticizers, additives such as stabilizers, and the like.

  These compounds having no polymerizable carbon-carbon double bond are used to adjust the viscosity of the polymerizable composition to improve the handleability when forming the adhesive layer 4, or to increase the monomer component ratio in the polymerizable composition. The amount used is preferably in the range of 1 to 99% by mass of the total amount with the polyfunctional monomer or oligomer, and more preferably in the range of 1 to 50% by mass. preferable.

(Initiator)
When the polymerizable composition material 4 ′, which is a raw material of the adhesive layer 4, is cured by photopolymerization, a photopolymerization initiator is added. The photopolymerization initiator is not particularly limited as long as it is used in normal photopolymerization in which polymerization is performed by irradiating active energy rays such as ultraviolet rays.

  For example, benzophenone, benzyl, Michler's ketone, 2-chlorothioxanthone, benzoin ethyl ether, diethoxyacetophenone, pt-butyltrichloroacetophenone, benzyldimethyl ketal, 2-hydroxy-2-methylpropylphenone, 1-hydroxycyclohexyl phenyl ketone, Examples include 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1, dibenzosuberone and the like.

  The amount of the photopolymerization initiator used is preferably in the range of 0.001 to 20 parts by mass with respect to 100 parts by mass of the other polymerizable composition, and the transparency of the refractive index modulation type diffraction grating layer 6 is reduced. In order to avoid this, it is more preferable that the content be 0.01 to 5 parts by mass.

  In addition, as a thermal polymerization initiator that can be used when the polymerizable composition material, which is a raw material of the adhesive layer 4, is cured by thermal polymerization, normal thermal polymerization in which polymerization is performed by heating the polymerizable composition. If it is used, it will not specifically limit, For example, a benzoyl peroxide, an azobisisobutyronitrile, etc. are mentioned. The amount of these thermal polymerization initiators used is preferably in the range of 0.001 to 1.0 part by mass with respect to 100 parts by mass of the other polymerizable composition.

Next, the adhesive layer 4 is polymerized and cured. The curing method is appropriately selected according to the material of the adhesive layer 4. For example, when a photopolymerization initiator is added to the polymerizable composition, it is cured by irradiating light L1 from a light source corresponding to the absorption wavelength of each photopolymerization initiator (FIG. 3). In the case of thermal polymerization, the polymerizable composition is heated to a temperature suitable for polymerization.
In the photopolymerization curing of the adhesive layer 4 described above, it is not necessary to use a light source with high parallelism.
The polymerizable composition 4 ′ may not be completely cured, and may proceed to the next step in a semi-cured state.

Next, the refractive index modulation type diffraction grating layer 6 is formed on the cured or semi-cured adhesive layer 4.
First, a photopolymerizable composition material 6 ′ (uncured photopolymerizable composition), which is a raw material of the refractive index modulation type diffraction grating layer 6 made of a photopolymerizable composition, is coated with a uniform thickness and a coating film. It coat | covers by well-known methods, such as a bar coater, a slit die coater, a spin coater, a circle coater, a gravure coater, a CAP coater, so that the surface may become smooth (FIG. 4). Moreover, the structure which arrange | positions a frame shape on the contact bonding layer 4, and fills this shape with the 2nd polymeric composition may be sufficient.

A photopolymerizable composition material containing the following materials may be used.
(Polyfunctional monomer)
It is preferable that a polyfunctional monomer is contained in the photopolymerizable composition. As such a polyfunctional monomer, a (meth) acryl monomer containing a (meth) acryloyl group, a monomer containing a vinyl group, an allyl group, or the like is particularly preferable.

  Specific examples of the polyfunctional monomer include triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6 -Hexanediol di (meth) acrylate, hydrogenated dicyclopentadienyl di (meth) acrylate, ethylene oxide modified bisphenol A di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, Tetramethylolmethane tetra (meth) acrylate, pentaerythritol hexa (meth) acrylate, polyfunctional epoxy (meth) acrylate, polyfunctional urethane (meth) acrylate, divinylbenzene, toluene Examples include allyl cyanurate, triallyl isocyanurate, triallyl trimellitate, diallyl chlorendate, N, N′-m-phenylenebismaleimide, diallyl phthalate, and the like. These are used alone or as a mixture of two or more. can do.

  A polyfunctional monomer having three or more polymerizable carbon-carbon double bonds in the molecule is preferable because the density of the crosslink density due to the difference in the degree of polymerization is likely to increase and a columnar structure is easily formed.

  Particularly preferred polyfunctional monomers having three or more polymerizable carbon-carbon double bonds are trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, tetramethylolmethanetetra (meth) acrylate, penta There is erythritol hexa (meth) acrylate.

  When two or more kinds of polyfunctional monomers or oligomers thereof are used as the photopolymerizable composition, it is preferable to use those having different refractive indexes when the respective homopolymers are used. It is more preferable to combine large ones.

  In order for the refractive index modulation type diffraction grating layer 6 to obtain functions such as diffraction, deflection, and diffusion with high efficiency, it is necessary to increase the refractive index difference between the matrix 8 and the columnar structure 10. The refractive index difference is preferably 0.01 or more, and more preferably 0.05 or more. Further, since the difference in refractive index is increased by the diffusion of the monomer during the polymerization process, a combination having a large difference in diffusion constant is preferable.

  In addition, when using 3 or more types of polyfunctional monomers or oligomers, the refractive index difference between at least any two of the respective homopolymers may be within the above range. In addition, the two monomers or oligomers having the largest refractive index difference of the homopolymer should be used at a weight ratio of 10:90 to 90:10 in order to obtain highly efficient functions such as diffraction, deflection, and diffusion. Is preferred.

(Monofunctional monomer)
In the photopolymerizable composition, a monofunctional monomer or oligomer having one polymerizable carbon-carbon double bond in the molecule may be used together with the polyfunctional monomer or oligomer as described above. As such a monofunctional monomer or oligomer, those containing a (meth) acryl monomer containing a (meth) acryloyl group, a vinyl group, an allyl group or the like are particularly preferable.

  Specific examples of the monofunctional monomer include methyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, ethyl carbitol (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, isobornyl (meth) acrylate, and phenyl carbitol. (Meth) acrylate, nonylphenoxyethyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, (meth) acryloyloxyethyl succinate, (meth) acryloyloxyethyl phthalate, phenyl (meth) acrylate, cyanoethyl (Meth) acrylate, tribromophenyl (meth) acrylate, phenoxyethyl (meth) acrylate, tribromophenoxyethyl (meth) acrylate, benzyl (meth ) Acrylate, p-bromobenzyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, trifluoroethyl (meth) acrylate, 2,2,3,3-tetrafluoropropyl (meth) acrylate, etc. (Meth) acrylate compounds; vinyl compounds such as styrene, p-chlorostyrene, vinyl acetate, acrylonitrile, N-vinyl pyrrolidone and vinyl naphthalene; and allyl compounds such as ethylene glycol bisallyl carbonate, diallyl phthalate and diallyl isophthalate It is done.

  These monofunctional monomers or oligomers are used for imparting flexibility to the refractive index modulation type diffraction grating layer 6, and the amount used is preferably in the range of 10 to 99% by mass in the total amount with the polyfunctional monomers or oligomers. The range of 10-50 mass% is more preferable.

(Polymer, low molecular weight compound)
The photopolymerizable composition may also be a homogeneous solution mixture containing the polyfunctional monomer or oligomer and a compound having no polymerizable carbon-carbon double bond.
Examples of the compound having no polymerizable carbon-carbon double bond include polymers such as polystyrene, polymethyl methacrylate, polyethylene oxide, polyvinyl pyrrolidone, polyvinyl alcohol, and nylon, toluene, n-hexane, cyclohexane, acetone, methyl ethyl ketone, and methyl. Examples include alcohols, ethyl alcohol, ethyl acetate, acetonitrile, dimethylacetamide, dimethylformamide, low molecular compounds such as tetrahydrofuran, organic halogen compounds, organosilicon compounds, plasticizers, additives such as stabilizers, and the like.

These compounds having no polymerizable carbon-carbon double bond are used for adjusting the viscosity of the photopolymerizable composition material to improve the handleability when the refractive index modulation type diffraction grating layer 6 is manufactured, or for photopolymerizability. It is used to improve the curability by reducing the monomer component ratio in the composition material.
The amount used is preferably in the range of 1 to 99% by mass of the total amount with the polyfunctional monomer or oligomer, and in order to form a columnar structure having a regular arrangement while improving the handleability. The range of 1-50 mass% is more preferable.

(Initiator)
The photopolymerization initiator used in the photopolymerizable composition is not particularly limited as long as it is used in normal photopolymerization in which polymerization is performed by irradiating active energy rays such as ultraviolet rays. For example, benzophenone , Benzyl, Michler's ketone, 2-chlorothioxanthone, benzoin ethyl ether, diethoxyacetophenone, pt-butyltrichloroacetophenone, benzyldimethyl ketal, 2-hydroxy-2-methylpropylphenone, 1-hydroxycyclohexyl phenyl ketone, 2-benzyl -2-dimethylamino-1- (4-morpholinophenyl) -butanone-1, dibenzosuberone and the like.
The amount of these photopolymerization initiators used is preferably in the range of 0.001 to 10% by mass relative to the weight of the other photopolymerizable composition, and the transparency of the refractive index modulation type diffraction grating layer 6 is reduced. In order to avoid this, it is more preferable that the content be 0.01 to 5% by mass.

Next, the photopolymerizable composition material 6 ′ is cured by photopolymerization in the following procedure, and the refractive index modulation type diffraction grating layer 6 is formed on the adhesive layer 4.
Specifically, the step of curing the photopolymerizable composition of the present embodiment by photopolymerization is performed by dividing it into first and second light irradiation steps.

(First light irradiation step)
The first light irradiation step is performed as texturing using a photomask. In the present embodiment, the arrangement pattern of the columnar structures 10 is determined by texturing using the photomask 12. The texturing described here is a method of giving a highly regular structure to a structure to be formed by inputting positional information in advance.

  First, the photomask 12 is disposed between the applied photopolymerizable composition and the irradiation light source (FIG. 5). At this time, the photomask 12 is disposed substantially parallel to the upper surface of the photopolymerizable composition material applied on the adhesive layer 4 formed on the glass substrate 2.

  In order to control the circular diameter and pitch of the columnar structure 10 more precisely, it is preferable that the gap between the upper surface of the applied photopolymerizable composition material and the photomask 12 is 50 μm to 300 μm.

  In the method of the present embodiment in which the formation position of the columnar structure 10 is determined using the photomask 12, it is necessary to pay attention to the fact that ultraviolet light is diffracted at the mask opening. Due to diffraction, the formation position may be determined in a pattern different from the photomask, or the formation position cannot be determined because the pattern deteriorates too much, so the distance between the photomask and the photopolymerizable composition can be accurately determined. Must be determined.

  As the photomask 12, those used in the photolithography method can be used. The mask hole pattern, hole size, pitch, and shape are not particularly limited. The shape may be, for example, a circle, a triangle, a rectangle, a hexagon, a polygon such as an octagon, or the like. When the mask hole is circular, the hole diameter is preferably 80 nm to 20 μm, more preferably 1 μm to 10 μm, and the pitch is preferably 120 nm to 30 μm, more preferably 2 μm to 20 μm.

In order to arrange the columnar structures in a square lattice pattern, as shown in FIG. 6, a photomask 12 in which circular mask holes 14 are regularly arranged in a square lattice pattern is used.
In order to arrange the columnar structures in a triangular lattice pattern, as shown in FIG. 7, a photomask 16 in which mask holes 14 are regularly arranged in a triangular lattice pattern is used.

  In this embodiment, texturing using a photomask is used to form the columnar structure 10, but the present invention is not limited to this, and radiation such as laser light in the visible or ultraviolet wavelength band, X-rays, and γ-rays is used. The position information may be input by scanning irradiation.

(Irradiation light source)
In order to arrange the columnar structures 10 with high regularity, it is necessary to advance the polymerization reaction uniformly in a plane perpendicular to the film thickness direction of the optical film 1. For this reason, the irradiation light source uses a light intensity distribution that is substantially uniform in the irradiation range.
As the irradiation light source, one capable of irradiating parallel light such as ultraviolet rays to the photocurable polymer coated on the substrate is used. The parallelism of the irradiated light is preferably such that the spread angle is ± 0.03 rad or less, and more preferably ± 0.001 rad or less.

  In addition to being able to irradiate parallel light, an irradiation light source having a substantially constant light intensity distribution of the parallel light in a cross section perpendicular to the traveling direction of the parallel light to be irradiated is used. Specifically, light from a point light source or a rod-shaped light source is converted into parallel light having a substantially uniform light intensity distribution (hat distribution) by a mirror or lens, or a planar light source such as a VCSEL is used. Can do.

  Laser light is a preferred light source in terms of parallelism, but its light intensity distribution has a Gaussian distribution, so that it can be used with a substantially uniform light intensity distribution using an appropriate filter or the like. preferable.

The irradiation light source divides the irradiation area into a plurality of areas (9 areas in the present embodiment), measures the light intensity of each area, and the value of the illuminance distribution given by equation (1) is 2.0% The following are used. More preferably, 1.0% or less is used.
Illuminance distribution = (maximum value−minimum value) / (maximum value + minimum value) × 100 (1)

Furthermore, the first light irradiation step of the present embodiment is performed by placing the photopolymerizable composition material in an inert gas atmosphere.
The placement in the inert gas atmosphere may be performed before the photomask 12 is placed or after the photomask 12 is placed. However, under conditions where oxygen remains above a certain level, there is a high possibility that poor curing will occur on the surface of the refractive index modulation type diffraction grating layer 6. Examples of the inert gas include nitrogen, argon, helium and carbon dioxide. Since the purpose of using the inert gas is to expel oxygen, any gas may be used as long as it has a composition not containing oxygen.

  In the first light irradiation step, the irradiation light source irradiates parallel light L2 such as ultraviolet rays having a full wavelength half width of 100 nm or less and a substantially uniform light intensity distribution in the irradiation target range in an inert gas atmosphere (FIG. 5). Thereby, the parallel light L2 which passed the photomask 12 is irradiated to a photopolymerizable composition with a predetermined pattern.

  In this way, in the first light irradiation step, the refractive index modulation type diffraction grating layer is formed by irradiating light such as ultraviolet rays as parallel light until the parallel light irradiation portion of the photopolymerizable composition is cured in a gel form. 6, the formation position of the columnar structure 10 is determined.

  Specifically, in order to achieve both the regularity and the high diffraction efficiency of the columnar structure 10, until the degree of cure of the photopolymerizable composition is in the range of 10% to 80%, more preferably 20% to 60. Irradiate until the% range is reached. In the present embodiment, a state in which the photopolymerizable composition completely reacts and does not generate further heat even when irradiated with light is set to a curing rate of 100% by the optical DSC method.

(Second light irradiation step)
In the second light irradiation step subsequent to the first light irradiation step, the photomask 12 is removed, and the parallel light L3 having a full wavelength half width of 100 nm or less and a substantially constant light intensity distribution is used as the photopolymerizable composition material. 6 ′ is irradiated (FIG. 8). Thereby, a phase separation structure composed of the columnar structure 10 whose formation position is determined in the first light irradiation step and the matrix 8 which is the other part is formed in the film thickness direction, and the matrix 8 and the columnar structure are formed. Curing of the photopolymerizable composition material 6 ′ is completely completed while increasing the difference in refractive index with the body 10.

  Since parallel light is used as the irradiation light, the columnar structure 10 is formed as a clear columnar structure in the matrix 8 so as not to extend in the plane direction and to extend in parallel to the film thickness direction. Thereby, the refractive index modulation type diffraction grating layer 6 is formed so that the change of the refractive index clearly appears at the boundary between the matrix 8 and the columnar structure 10.

・・・（２） In general, the resolution when light emitted from a point light source such as a high-pressure mercury lamp is exposed to a photomask by adjusting the uniformity and parallelism of illuminance by a mirror or lens is as follows. If the slit width of the photomask is a and the gap is L, the light passing through the slit is approximated by Fresnel diffraction when the size of a cannot be ignored with respect to L (when the values of a and L are close), On the other hand, when the magnitude of a is negligible with respect to L (when a << L), it is approximated by Fraunhofer diffraction. When image degradation due to diffraction is expressed by the function F in the equation (2), a resolution limit appears when F is close to 2. λ is the wavelength of light.

... (2)

  In the case of F = 2 and λ = 0.4, a = 0.89 · √L is obtained from the equation (2). This a is the resolution limit line width. When L is 150 μm, the resolution is 10.9 μm. Therefore, since the hole diameter of the columnar structure is preferably 80 nm to 20 μm, even if the columnar structure is formed simply using a photomask, image degradation due to Fraunhofer diffraction (a << L) is severe. In such a system, it is not considered that a columnar structure having an aspect ratio of 10 or more is formed in the film.

  That is, when the columnar structure is completely formed only by the first light irradiation step as in the prior art, the light passing through the photomask is diffracted from the projection area of the mask hole (that is, the area of the columnar structure) to the matrix. It will spread to reach the area. For this reason, even if the second light irradiation step is performed after the first light irradiation step as in the prior art, a significant refractive index difference does not occur between the matrix and the columnar structure.

However, in this embodiment, the columnar structure 10 is not completely cured in the first light irradiation step, and only the formation position is determined. Then, in the second light irradiation step, the entire structure is completely cured by irradiating the entire surface with parallel light in an incompletely cured state where the matrix 8 and the columnar structure 10 have a certain degree of hardness difference.
At this time, due to the difference in cross-linking density with the matrix 8 due to the polymerization self-promoting effect of the columnar structure 10 and the composition distribution due to reaction diffusion between the columnar structure 10 and the matrix 8, a significant difference in refractive index between them is obtained. Moreover, the columnar structure 10 having a high aspect ratio that extends substantially parallel to the film thickness direction of the refractive index modulation type diffraction grating layer 6 can be formed.

(Diffraction efficiency calculation)
A laser beam having an intensity distribution of standard normal distribution is incident on the manufactured optical low-pass filter 1 to measure the intensities of the 0th, 1st and 2nd diffraction spots, and the measured intensity of the 1st diffraction spot is incident. A value divided by the intensity of the entire light is calculated as the diffraction efficiency of the optical low-pass filter 1. When a plurality of diffraction spots appear, the total intensity is divided by the intensity of the entire incident light.
The optical low-pass filter 1 of the present embodiment has a diffraction efficiency of 10% or more (10% ≦ diffraction efficiency ≦ 100%).

  The optical low-pass filter 1 can be used as an optical low-pass filter. In a photographing system such as a digital camera, moire (false color) is often a problem. This is because the sensors such as CCD and CMOS are regularly arranged and interfere with the regular pattern included in the object to be photographed. As one of means for solving this problem, an optical low-pass filter is used. The optical low-pass filter has an effect of suppressing moire by suppressing the influence of interference by separating input light into a plurality of points.

  The present invention is not limited to the above-described embodiment, and various changes and modifications can be made within the scope of the technical idea described in the claims.

Hereinafter, specific examples and comparative examples of the present invention will be described in detail.
Example 1
As a raw material for the adhesive layer, a mixture composed of 90 parts by mass of 4-hydroxybutyl acrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) and 10 parts by mass of polymethyl methacrylate (manufactured by Mitsubishi Rayon Co., Ltd., Mw = 120,000). 1.0 part by mass of 1-hydroxycyclohexyl phenyl ketone (trade name: IRGACURE184, manufactured by Ciba Japan Co., Ltd.) was dissolved to obtain a photopolymerizable composition.

  Next, 50 parts by mass of 1,10-decanediol diacrylate (trade name: A-DOD-N, manufactured by Shin-Nakamura Chemical Co., Ltd.) and NK-oligo U- are used as raw materials for the refractive index modulation type diffraction grating layer. 20 parts by mass of 2PPA (manufactured by Shin-Nakamura Chemical Co., Ltd.), 20 parts by mass of benzyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.), and 10 masses of polymethyl methacrylate (manufactured by Mitsubishi Rayon Co., Ltd., Mw = 120,000) 1 part of 1-hydroxycyclohexyl phenyl ketone (trade name: IRGACURE 184, manufactured by Ciba Japan Co., Ltd.) was dissolved in the mixture consisting of 1 part to obtain a photopolymerizable composition.

The obtained photopolymerizable composition for the adhesive layer was coated on a 100 mm square glass substrate having a thickness of 0.5 mm using a spin coater.
Next, ultraviolet light was irradiated from the upper part of the photopolymerizable composition for the adhesive layer at an integrated light amount of 1200 mJ / cm ² to be cured. When a glass transition temperature was measured with a differential scanning calorimeter DSC 6220 (manufactured by SII Nano Technology) using a part of the cured product, it was -36 ° C.

  Next, the material for the refractive index modulation type diffraction grating layer was applied and laminated on the upper surface of the cured adhesive layer using a spin coater.

Next, a photomask in which 4 μm square light passage areas were arranged in a square lattice pattern at a pitch of 8 μm was disposed on the photopolymerizable composition. From the upper direction of the photomask, ultraviolet parallel light having a substantially constant light intensity distribution was irradiated with an integrated light amount of 900 mJ / cm ² .
Thereafter, the photomask was removed, and the photopolymerizable composition was polymerized and cured by irradiating ultraviolet parallel light with an integrated light amount of 1200 mJ / cm ² to obtain an optical low-pass filter.

  In the obtained optical low-pass filter, a plurality of columnar structures with a diameter of 10 μm having a refractive index different from that of the matrix are formed in a plane perpendicular to the thickness direction, and the plurality of columnar structures have a square lattice with a period of 20 μm. Arranged in a shape.

  In the obtained optical low-pass filter, the thickness of the adhesive layer was 120 μm, and the thickness of the refractive index modulation type diffraction grating layer was 60 μm. The aspect ratio was about 3 and the diffraction efficiency was about 67%, which confirmed that the device had sufficient performance for use as an optical low-pass filter.

  In order to verify the effect of the present invention, a thermal shock of (85 ° C. × 1 hour / −40 ° C. × 1 hour) × 100 cycles was applied to the optical low-pass filter, and a crack resistance test of the optical low-pass filter was conducted. . As a result, it was found that the optical low-pass filter was peeled off and there was no crack, and good adhesiveness and crack resistance were exhibited.

(Example 2)
Instead of 4-hydroxybutyl acrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) as the raw material of the adhesive layer, 2-hydroxyethyl acrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) is used, and other conditions are as in Example 1. Accordingly, an optical low-pass filter was obtained. Moreover, it was -1 degreeC when the glass transition temperature of the contact bonding layer was measured by the method similar to Example 1. FIG.

  In the obtained optical low-pass filter, the thickness of the adhesive layer was 120 μm, and the thickness of the refractive index modulation type diffraction grating layer was 60 μm. The aspect ratio was about 3 and the diffraction efficiency was about 67%, which confirmed that the device had sufficient performance for use as an optical low-pass filter.

  In order to verify the effect of the present invention, a thermal shock of (85 ° C. × 1 hour / −40 ° C. × 1 hour) × 100 cycles was applied to the optical low-pass filter, and a crack resistance test of the optical low-pass filter was conducted. . As a result, it was found that the optical low-pass filter was peeled off and there was no crack, and good adhesiveness and crack resistance were exhibited.

(Comparative Example 1)
Next, in order to clarify the effect of the present invention, a detailed description will be given of a comparative example for comparison with the above embodiment.
Instead of 4-hydroxybutyl acrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) as the raw material for the adhesive layer, 2-hydroxyethyl methacrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) is used, and other conditions are as in Example 1. Accordingly, an optical low-pass filter was obtained. Moreover, it was 93 degreeC when the glass transition temperature of the contact bonding layer was measured by the method similar to Example 1. FIG.

  In the obtained optical low-pass filter, the thickness of the adhesive layer was 120 μm, and the thickness of the refractive index modulation type diffraction grating layer was 60 μm. The aspect ratio was about 3 and the diffraction efficiency was about 67%, which confirmed that the device had sufficient performance for use as an optical low-pass filter.

  In order to verify the effect of the present invention, a thermal shock of (85 ° C. × 1 hour / −40 ° C. × 1 hour) × 100 cycles was applied to the optical low-pass filter, and a crack resistance test of the optical low-pass filter was conducted. . As a result, it has been found that the optical low-pass filter has innumerable peeling and cracks, and exhibits poor adhesion and crack resistance.

1: Optical low-pass filter 2: Glass substrate 4: Adhesive layer 6: Refractive index modulation type diffraction grating layer 8: Matrix 10: Columnar structure

Claims (4)

A refractive index modulation type diffraction grating layer comprising: a matrix layer formed by curing a photopolymerizable composition; and a plurality of columnar structures disposed in the matrix layer and having a refractive index different from that of the matrix layer. A method of manufacturing an optical low-pass filter provided on a substrate having a linear expansion coefficient different from that of a diffraction grating layer,
Disposing a polymerizable composition constituting an adhesive layer having a glass transition temperature after curing of −70 ° C. or more and 10 ° C. or less in a thin film on a substrate;
Curing the polymerizable composition to form an adhesive layer made of a cured product of the polymerizable composition on the substrate;
Disposing a photopolymerizable composition constituting the refractive index modulation type diffraction grating layer after curing in a thin film form on the adhesive layer;
Curing the photopolymerizable composition by photopolymerization to form a refractive index modulation type diffraction grating layer on the adhesive layer.
An optical low-pass filter manufacturing method characterized by the above. The polymerizable composition comprises hydroxyalkyl (meth) acrylate and poly (meth) acrylate methyl;
The manufacturing method of the optical low-pass filter of Claim 1. The polymerizable composition contains 50% by mass or more of an alkyl (meth) acrylate having an alkyl group having 2 or more carbon atoms,
The manufacturing method of the optical low-pass filter of Claim 1 or 2. An optical low-pass filter,
A substrate,
A photopolymerizable composition is cured, and has a matrix layer and a plurality of columnar structures that are disposed in the matrix layer and have a refractive index different from that of the matrix layer. A rate modulation type diffraction grating layer;
An adhesive layer disposed between the substrate and the refractive index modulation type diffraction grating layer, having a glass transition temperature of −70 ° C. or higher and 10 ° C. or lower and configured by a cured product of the polymerizable composition; Yes,
An optical low-pass filter characterized by that.

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