CN117916673A - Method for manufacturing optical element - Google Patents

Abstract

A method for manufacturing an optical element, wherein a medium having a recording layer containing a polymerizable compound and a photopolymerization initiator is subjected to recording exposure, and further subjected to post-exposure in a state where the temperature of the medium is lower than that in the recording exposure. The recording exposure is holographic recording exposure.

Description

Method for manufacturing optical element

Technical Field

The present invention relates to a method for producing an optical element having a hologram or the like recorded thereon.

Background Art

Holographic recording media, which have attracted much attention in recent years, are recording media that utilize the interference and diffraction phenomena of light. Holography refers to a recording method that records the interference pattern formed by the interference fringes of two kinds of light, called reference light and object light (also called information light or signal light), three-dimensionally inside the recording medium. The holographic recording medium contains a photosensitive material in the recording layer, and the photosensitive material undergoes chemical changes in accordance with the interference pattern, and the interference fringes are recorded by locally changing the optical properties.

Holographic recording media are being developed for storage applications, and as other applications, research is being conducted on the use of optical elements for AR glasses light guide plates (waveguide plates). In the case of AR glasses (AR Glass), the holographically recorded optical element used for the light guide plate is required to have a wide viewing angle, high diffraction efficiency for light in the visible region, and high transparency of the medium.

Holographic recording media are classified into several types depending on which optical properties are changed. It is believed that volume holographic media that record by creating a refractive index difference in a recording layer with a certain thickness or more can save space and achieve high diffraction efficiency and wavelength selectivity, which is beneficial for use in AR glasses light guide plates.

As an example of a volume holographic recording medium, there is a write-once type that does not require a wet treatment or a bleaching treatment. The composition of its recording layer is generally a composition in which a photoactive compound and a matrix resin are compatible. For example, it is well known to use the following photopolymer as a recording layer, which is a combination of a photopolymerization initiator as a photoactive compound and a polymerizable reactive compound capable of free radical polymerization or cationic polymerization in a matrix resin (Patent Documents 1 to 4).

When recording a hologram, if there is a recording layer formed of a photopolymer in the portion where the reference light and the object light intersect to form interference fringes, the photopolymerization initiator in the portion with high light intensity in the interference fringes causes a chemical reaction and becomes an active substance, which acts on the polymerizable compound to polymerize the polymerizable compound. At this time, if there is a refractive index difference between the matrix resin and the polymer generated by the polymerizable compound, the interference fringes become a refractive index difference and are fixed in the recording layer. In addition, when the polymerizable compound is polymerized, the polymerizable compound diffuses from the periphery, and a concentration distribution of the polymerizable compound or its polymer is generated inside the recording layer. Based on this principle, the interference pattern is recorded in the form of a refractive index difference in the holographic recording medium.

Furthermore, by changing the intersection angle between the reference light and the object light, different data can be repeatedly recorded at the same position.

Hereinafter, as described above, a process of changing the optical characteristics of the recording layer by exposing the recording layer of the medium under prescribed conditions is referred to as "recording exposure".

On the other hand, when only regeneration light is used for data regeneration, the regeneration light irradiated generates diffraction corresponding to the above-mentioned interference fringes. At this time, even if the wavelength of the regeneration light is inconsistent with the wavelength of the recording light, diffraction will still occur as long as the above-mentioned interference fringes satisfy the Bragg condition. Therefore, if the corresponding interference fringes are recorded according to the wavelength and incident angle of the regeneration light that is desired to be diffracted, diffraction can be generated for the regeneration light in a wide wavelength region, which can widen the display color gamut of the AR glasses.

After recording exposure, post-exposure is usually performed to irradiate the entire recording layer with light. That is, in the case of recording a hologram on a medium by recording exposure, light is irradiated to the portion other than the hologram recording portion (hereinafter also referred to as the "non-recording portion"), and post-exposure is performed (Patent Documents 5 to 7). In this case, post-exposure is used to fix the concentration distribution of the polymer formed by recording exposure by promoting the polymerization of the photopolymer in the non-recording portion where the hologram is not recorded. Post-exposure is performed for the following purpose: by preventing the polymerization reaction of the photopolymer caused by light from occurring after this process, the concentration distribution of the polymer obtained by recording exposure is not destroyed, and a new concentration distribution is not formed.

As a problem of optical elements that have been holographically recorded like this, the optical element itself looks slightly turbid. The turbidity that is a problem here is mainly caused by light scattering from the material that constitutes the recording layer, which is called haze. Especially in the use of AR glasses light guide plates, the required optical performance is strict, and a small amount of haze in the recording layer part other than the holographic recording part, that is, the non-recording part, can also cause image quality degradation.

Prior art literature

Patent Literature

Patent Document 1: Japanese Patent Application Publication No. 2021-12249

Patent Document 2: Japanese Patent Application Publication No. 2007-34334

Patent Document 3: Japanese Patent Application Laid-Open No. 8-160842

Patent Document 4: Japanese Patent Application Publication No. 2003-156992

Patent Document 5: Japanese Patent Application Laid-Open No. 10-187013

Patent Document 6: Japanese Patent Application Publication No. 2014-209217

Patent Document 7: Japanese Patent Application Publication No. 2005-134762

Summary of the invention

Technical problem to be solved by the invention

An object of the present invention is to reduce the haze of a non-recording portion of an optical element on which a hologram or the like is recorded.

Means for solving technical problems

The present inventors have found that the haze of a non-recorded portion of an optical element having a hologram or the like recorded thereon can be reduced by performing post-exposure under specific conditions.

That is, the gist of the present invention is as follows.

(1) A method for producing an optical element, comprising subjecting a medium having a recording layer containing a polymerizable compound and a photopolymerization initiator to recording exposure, and further subjecting the medium to post-exposure in a state where the temperature of the medium is lower than that during the recording exposure.

(2) The method for manufacturing an optical element according to (1), wherein a difference between a temperature of the medium during the recording exposure and a temperature of the medium during the post-exposure is 5° C. or more.

(3) The method for producing an optical element according to (1) or (2), wherein the temperature of the medium during the post-exposure is 5° C. or higher.

(4) The method for producing an optical element according to any one of (1) to (3), wherein a temperature of the medium during the recording exposure is 10° C. or higher and 40° C. or lower.

(5) The method for producing an optical element according to any one of (1) to (4), wherein the post-exposure is performed at a light intensity that is 0.3 times or more of that during the recording exposure.

(6) The method for producing an optical element according to any one of (1) to (5), wherein the light source for post-exposure in the post-exposure is incoherent light.

(7) The method for producing an optical element according to any one of (1) to (6), wherein post-exposure is performed from both sides of the medium.

(8) The method for producing an optical element according to any one of (1) to (7), wherein the recording exposure is holographic recording exposure.

Effects of the Invention

According to the method for manufacturing an optical element of the present invention, the haze of a non-recorded portion of an optical element on which a hologram or the like is recorded can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an example of a holographic recording device for a medium.

FIG. 2 is a schematic diagram showing an example of a post-exposure device for a medium on which hologram recording is performed.

FIG. 3 is a schematic diagram showing another example of a post-exposure device for a holographically recorded medium.

DETAILED DESCRIPTION

The following is an example (representative example) of the embodiment of the present invention, and the present invention is not limited to these contents unless it exceeds the gist thereof.

[Method for producing optical element of the present invention]

For example, in the case of producing an optical element that performs holographic recording in the present invention, first, for a medium having a recording layer containing a polymerizable compound and a photopolymerization initiator, reference light and object light (information light) are made to cross to form interference fringes, recording exposure of the interference pattern is performed on the recording layer, and further post-exposure is performed on the medium after the recording exposure.

In the present invention, reference light is light that serves as a reference when recording an interference pattern on a medium (hereinafter also referred to as “recording exposure”) and is irradiated onto the recording layer of the medium while overlapping with the object light when exposing the recording layer of the medium.

In the present invention, object light refers to light irradiated onto a recording layer of a medium in order to holographically record corresponding interference fringes in the medium by interfering with reference light according to the wavelength and diffraction of reproduction light required as an optical element used in AR glasses, etc.

The exposure amount in the present invention refers to the total exposure energy per unit area of light irradiated to the medium having the recording layer.

In addition, light intensity refers to the intensity (energy) per unit area of light irradiated onto a medium having a recording layer.

[Record the temperature during exposure and post-exposure]

The ambient temperature during the recording exposure is preferably 10°C or higher, more preferably 15°C or higher, and even more preferably 20°C or higher, from the perspective of preventing light scattering caused by water droplets generated by condensation on the medium. If the temperature is within this range, there is a tendency to prevent the increase in haze of the optical element caused by water droplets generated by condensation on the medium. On the other hand, the ambient temperature during the recording exposure is preferably 40°C or lower, more preferably 35°C or lower, and even more preferably 30°C or lower. If the temperature is within this range, it is easy to suppress the deactivation of the photopolymerization initiator in the holographic recording medium due to high temperature, and there is a tendency to maintain high diffraction efficiency.

The temperature of the medium during the recording exposure is preferably 10°C or higher, more preferably 15°C or higher, and even more preferably 20°C or higher. By setting the temperature of the medium to 10°C or higher, there is a tendency to prevent light scattering caused by water droplets generated by condensation of the medium during the recording exposure, and it is also possible to prevent haze of the optical element caused by it. In addition, the temperature of the medium during the recording exposure is preferably 40°C or lower, more preferably 35°C or lower, and even more preferably 30°C or lower. By setting the temperature of the medium to 40°C or lower, it is possible to suppress the deactivation of the photopolymerization initiator in the holographic recording medium due to high temperature, and thus there is a tendency to maintain high diffraction efficiency.

In addition, from the perspective of preventing the non-uniformity of interference fringes formed by recording exposure and maintaining high diffraction efficiency by keeping the density and refractive index of the medium constant, the temperature of the medium during the recording exposure is preferably kept constant. Here, keeping the temperature constant means suppressing the temperature change to less than 3°C.

In the present invention, the temperature of the medium during post-exposure is lower than the temperature of the medium during recording exposure. This can reduce the haze of the non-recording portion of the optical element on which the hologram or the like is recorded.

The reason is considered to be as follows.

Generally, post-exposure is performed immediately after recording exposure is completed in the same atmosphere, so the temperature of the medium during post-exposure is the same as that during recording exposure.

However, by performing post-exposure at a lower temperature of the medium, the unreacted polymerizable compound is photopolymerized in an environment where the movement of the polymer in the matrix resin constituting the recording layer of the medium is slowed down. As a result, the polymers are less likely to agglomerate with each other, thereby reducing the size of the scatterers from the polymers, thereby achieving low haze.

In the present invention, the difference between the temperature of the medium during recording exposure and the temperature of the medium during post-exposure is preferably 5°C or more, more preferably 10°C or more. By making the temperature difference 5°C or more, there is a tendency that the haze of the non-recording part of the optical element is significantly reduced. In addition, the difference between the temperature during recording exposure and the temperature during post-exposure is preferably 40°C or less, more preferably 35°C or less, and further preferably 25°C or less. By making the temperature difference 40°C or less, there is a tendency to prevent condensation on the medium due to temperature changes and prevent the haze from increasing.

The temperature of the medium during the above-mentioned post-exposure is preferably above 5°C. By setting the temperature of the medium to above 5°C, there is a tendency to prevent light scattering caused by water droplets generated due to condensation of the medium during post-exposure, and the increase in haze of the optical element caused by it can be prevented. In addition, the temperature of the medium during the above-mentioned post-exposure is preferably below 35°C, more preferably below 33°C, and further preferably below 30°C. By performing post-exposure within this range, the diffusion of polymers generated by photopolymerization during recording exposure can be suppressed, and the polymerization of photopolymers in the non-recording part where the hologram is not recorded can be promoted. Therefore, fixation can be performed while maintaining the concentration distribution during recording exposure, and there is a tendency to achieve high diffraction efficiency.

In addition, regarding the temperature of the medium during the recording exposure, it is preferable to keep the temperature constant from the perspective of preventing the unevenness of the interference fringes formed by the recording exposure and maintaining high diffraction efficiency by keeping the density and refractive index of the medium constant. Here, keeping the temperature constant means suppressing the temperature change to less than 3°C.

[Record light intensity and exposure during exposure and post-exposure]

The light intensity in the present invention refers to the energy per unit area of light irradiated onto a medium having a recording layer, and the light intensity in the above-mentioned recording exposure is the sum of the respective light intensities of the reference light and the object light.

The light intensity during the recording exposure is preferably 2 mW/cm ² or more, more preferably 5 mW/cm ² or more, and further preferably 10 mW/cm ² or more. When the light intensity is within this range, the recording exposure can be performed quickly, and by reducing the haze of the recorded part, there is a tendency to reduce the noise generated when the recorded information is reproduced.

On the other hand, the light intensity during the recording exposure is preferably 200 mW/cm ² or less, more preferably 100 mW/cm ² or less, and further preferably 40 mW/cm ² or less. When the light intensity is within this range, the polymerization reaction control based on the exposure time becomes easy, and there is a tendency that the desired interference fringes can be stably recorded.

The exposure amount during recording exposure in the present invention can be arbitrarily selected according to the type of photopolymerization initiator and the efficiency of the photopolymerization initiator, and is preferably 0.5 J/cm ² or more, and more preferably 1 J/cm ² or more. If the exposure amount is within this range, the photopolymerization initiator required during recording exposure reacts under the action of light to become an active substance.

On the other hand, the exposure amount during recording exposure is preferably 100 J/cm ² or less, more preferably 60 J/cm ² or less, and further preferably 24 J/cm ² or less. When the exposure amount is within this range, the time required for recording is shortened, and the manufacturing cycle can be shortened.

The exposure amount during post-exposure in the present invention is 10 J/cm ² or more, preferably 20 J/cm ² or more. By irradiating the recording layer with light having an energy in this range, the photopolymerization initiator is sufficiently deactivated, and the concentration distribution of the polymer in the optical element can be prevented from being destroyed by light from the outside.

On the other hand, since the manufacturing tact time can be shortened by setting an appropriate exposure amount, the exposure amount in the post-exposure is preferably 5000 J/cm ² or less, more preferably 1000 J/cm ² or less, and further preferably 500 J/cm ² .

In the present invention, it is preferred that the light intensity during post-exposure is 0.3 times or more the light intensity during recording exposure.

By making the light intensity during post-exposure 0.3 times or more than that during recording exposure, the haze of the non-recording portion of the optical element can be reduced. The light intensity during post-exposure is more preferably 0.5 times or more than that during recording exposure. Since there is a tendency that the reduction of haze becomes more significant, it is more preferable to make the light intensity during post-exposure higher than that during recording exposure, that is, to set the light intensity during post-exposure to be more than 1 times the light intensity during recording exposure. The light intensity ratio is particularly preferably 1.2 times or more, particularly preferably 2 times or more, and most preferably 4 times or more.

In addition, in order to suppress the coloring caused by photodegradation of the base resin of the recording layer due to post-exposure and to have a tendency to reduce the haze of the non-recording part of the optical element, the light intensity during post-exposure is preferably 100 times or less, more preferably 20 times or less, further preferably 15 times or less, and particularly preferably 10 times or less of that of the photopolymerization initiator during recording exposure.

Generally, the purpose of post-exposure is to fix the concentration distribution of the polymer formed by recording exposure by promoting the polymerization of the photopolymer in the non-recording part, and to prevent the concentration distribution of the polymer formed by recording exposure from being destroyed by light irradiation after this process, etc. Therefore, the light intensity of post-exposure is not particularly considered.

However, by further increasing the light intensity during post-exposure, more photopolymerization initiators can be decomposed in a short time, and the polymerization starting points in the matrix resin constituting the recording layer of the medium can be increased, so that the post-exposure can be completed quickly. As a result, the chain polymerization of the polymerizable compound in the non-recording part is suppressed, and the size of the polymer constituting the scatterer (which is the cause of the haze of the non-recording part) can be reduced, and low haze can be achieved.

Furthermore, since the irradiation time until the light energy required to achieve the above-mentioned constant concentration distribution can be shortened, the tact time in manufacturing can also be shortened.

On the other hand, by appropriately setting the upper limit of the light intensity during post-exposure, excessive temperature rise of the matrix resin constituting the recording layer of the medium can be prevented, thereby making it less likely to cause the above-mentioned chain polymerization, and thus having a tendency to reduce the haze of the non-recording portion of the optical element.

[Temperature rise during exposure]

In the present invention, even if the temperature of the matrix resin may excessively rise during post-exposure, the excessive temperature rise of the matrix resin can be prevented by dissipating heat from the medium during post-exposure.

The heat dissipation means is not particularly limited, and for example, the following methods may be adopted: using an air supply fan to supply air to the medium; removing heat from the medium by installing a heat sink or a temperature regulator; and the like.

In the manufacture of optical elements, when recording exposure is performed on a medium having a recording layer containing a polymerizable compound and a photopolymerization initiator, exposure is usually performed in an atmosphere near room temperature from the perspective of ease of management of manufacturing equipment. However, in the present invention, as described above, the temperature of the matrix resin of the recording layer of the medium may rise during post-exposure. By suppressing the temperature rise of the medium, coloration caused by light degradation of the matrix resin can be suppressed, and the haze of the non-recording part of the optical element can be reduced, which has a tendency to suppress degradation of the recording (blurring of interference fringes, etc.) after recording exposure.

The post-exposure in the present invention can be implemented by single-sided exposure from any one side of the medium, but preferably exposure is performed from both sides of the medium. This allows the post-exposure to be completed in a short time and also allows the temperature rise of the medium to be suppressed.

As a method for exposing a medium from both sides, the following methods can be cited: a method of configuring a light source on each side of the medium for exposure; when the light source is configured on a single side of the medium, a reflector or lens is configured on the incident back side to reflect light that has passed through the medium once, thereby exposing from both sides.

[Exposure light source]

The light source that can be used for recording exposure in the present invention can be arbitrarily selected in the absorption wavelength region of the photopolymerization initiator. Particularly suitable light sources include: solid lasers such as ruby, glass, Nd-YAG, and Nd- _YVO4 ; diode lasers such as GaAs, InGaAs, and GaN; gas lasers such as helium-neon, argon, krypton, excimer, and _CO2 ; lasers with excellent monochromaticity and directivity such as dye lasers having pigments; and the like.

The light source that can be used for the post-exposure in the present invention is not particularly limited as long as it can irradiate light in the absorption wavelength region of the photopolymerization initiator, and any light source can be selected from LEDs, UV lamps, xenon lamps, mercury lamps, and the like.

As the light source used in the post-exposure in the present invention, it is preferred that at least one light source is incoherent light. By using incoherent light, even in the case of using two or more light sources such as in the above-mentioned double-sided exposure, it is possible to suppress the formation of unnecessary interference fringes in the non-recording portion. As the light source of incoherent light, there are LEDs, UV lamps, xenon lamps, mercury lamps, etc., and any light source can be selected as long as it can irradiate light in the absorption wavelength region of the photopolymerization initiator.

The wavelength of the light used for recording exposure in the present invention may be within the absorption wavelength region of the photopolymerization initiator, and may be arbitrarily selected from wavelengths ranging from the ultraviolet region to the visible region, preferably 300 nm or more, more preferably 350 nm or more. In addition, preferably 600 nm or less, more preferably 450 nm or less. If the wavelength is within this range, the photopolymerization initiator required for recording exposure reacts under the action of light and becomes an active substance.

The wavelength of the light used for post-exposure in the present invention may be within the absorption wavelength region of the photopolymerization initiator, preferably 300 nm or more, more preferably 350 nm or more. Also, preferably 600 nm or less, more preferably 450 nm or less. By setting the wavelength within this range, the polymerization inhibitor can be effectively deactivated.

[Total light transmittance of optical components]

The total light transmittance of the optical element obtained by the present invention under standard light source D65 is preferably 80% or more, more preferably 85% or more. When the transmittance is within the above range, for example, when the holographically recorded optical element is used as an AR light guide plate, the optical element has sufficient light transmittance.

[Components of the medium in the present invention]

The medium used in the present invention is useful as a holographic recording medium, and has a recording layer containing at least a polymerizable compound and a photopolymerization initiator. As a composition for forming such a recording layer (hereinafter also referred to as a "recording layer forming composition"), for example, a photopolymer obtained by combining a polymerizable monomer capable of free radical polymerization or cationic polymerization as a polymerizable compound in an appropriate matrix resin, a photopolymerization initiator that promotes the polymerization of the polymerizable monomer, and a polymerization inhibitor that is a substance that inhibits the polymerization of the polymerizable monomer is preferably used.

[Record layer]

<About the composition for forming a hologram recording layer>

The recording layer of the medium of the present invention is formed by a recording layer forming composition described in detail below. Here, the matrix resin is generally present in the recording layer in the form of a crosslinked network structure by filling the recording layer forming composition between the planar substrates and then polymerizing or crosslinking, and is therefore contained in the recording layer forming composition in the form of a matrix resin composition for forming the matrix resin by polymerization or crosslinking.

That is, the recording layer forming composition of the present invention may contain a polymerizable monomer, a matrix resin forming composition, a photopolymerization initiator and a polymerization inhibitor, and may further contain a radical scavenger as required. Components of the holographic recording layer forming composition are described in detail below.

<<About polymerizable monomers>>

The polymerizable monomer of the present invention refers to a compound that can be polymerized by a photopolymerization initiator described later. The type of the polymerizable monomer is not particularly limited and can be appropriately selected from known compounds. Examples of polymerizable monomers include cationic polymerizable monomers, anionic polymerizable monomers, free radical polymerizable monomers, etc. Any one of them can be used, and two or more can also be used in combination.

Examples of cationic polymerizable monomers include epoxy compounds, oxetane compounds, tetrahydrofuran compounds, cyclic acetal compounds, cyclic lactone compounds, thiirane compounds, thietane compounds, vinyl ether compounds, spirocyclic orthoester compounds, ethylenically unsaturated bond compounds, cyclic ether compounds, cyclic thioether compounds, vinyl compounds, etc. Any one of the cationic polymerizable monomers may be used alone, or two or more thereof may be used in any combination and ratio.

Examples of anionic polymerizable monomers include hydrocarbon monomers and polar monomers. Examples of hydrocarbon monomers include styrene, α-methylstyrene, butadiene, isoprene, vinylpyridine, vinylanthracene and derivatives thereof. Examples of polar monomers include methacrylates, acrylates, vinyl ketones, isopropenyl ketones and other polar monomers. Any one of the anionic polymerizable monomers may be used alone, or two or more may be used in any combination and ratio.

Examples of free radical polymerizable monomers include compounds having a (meth)acryloyl group, (meth)acrylamides; vinyl esters; vinyl compounds, styrenes; spiro compounds, etc. The free radical polymerizable monomers may be used alone or in any combination and ratio. Among the above monomers, compounds having a (meth)acryloyl group are preferred from the perspective of steric hindrance during free radical polymerization.

Among the above polymerizable monomers, compounds having halogen atoms (iodine, chlorine, bromine, etc.) or heteroatoms (nitrogen, sulfur, oxygen, etc.) in the molecule have high refractive index and are preferred. Among the above monomers, compounds having a heterocyclic structure can obtain a higher refractive index and are therefore preferred.

<<About Matrix Resin and Matrix Resin Forming Composition>>

The matrix resin of the present invention refers to a cured product having a cross-linked network structure in which bonds are formed by polymerization reaction or cross-linking reaction. The matrix resin forming composition refers to a matrix resin precursor before bonds are formed by polymerization reaction and cross-linking reaction.

The matrix resin has a cross-linked network structure, and thus has the following functions: by appropriately suppressing the mobility of the polymerizable monomer and the photopolymerization initiator, the polymerizable monomer or the photopolymerization initiator in the recording layer can be stably maintained in a spatially uniformly dispersed state. In addition, the matrix resin suppresses the diffusion of the polymer by entanglement with the polymer generated in the recording layer, thereby preventing the recorded information from being erased. The matrix resin further has a higher elastic modulus than that in a liquid state, and thus has the function of maintaining the physical shape of the recording layer.

There is no particular limitation on the composition for forming the matrix resin as long as it can maintain sufficient compatibility with the polymerizable monomer or its polymer and the photopolymerization initiator after forming a bond by polymerization reaction or crosslinking reaction. The composition for forming the matrix resin can preferably use a compound having at least two or more functional groups selected from the group consisting of isocyanate group, hydroxyl group, mercapto group, epoxy group, amino group and carboxyl group in the molecule alone or in combination of two or more.

Examples of chemical bonding that forms a cross-linked network structure using these compounds alone or in combination of two or more thereof include the following examples (1) to (8).

(1) An isocyanurate bond is formed by reaction between compounds having an isocyanate group.

(2) A compound having an isocyanate group is combined with a compound having active hydrogen in the molecule, such as a compound containing a hydroxyl group, a mercapto group, an amino group, or a carboxyl group, to form a urethane bond, a thiourethane bond, a urea bond, an amide bond, or the like.

(3) A compound having a hydroxyl group and a compound having a carboxyl group are combined to form an ester bond.

(4) A compound having an amino group and a compound having a carboxyl group are combined to form an amide bond.

(5) An ether bond is formed by reaction between compounds having epoxy groups.

(6) An ether bond is formed by combining an epoxy group and a hydroxyl group.

(7) An amine bond is formed by combining a compound having an epoxy group and a compound having an amino group.

(8) Forming two or more bonds including the above (1) to (7).

Among them, a combination of a compound having an isocyanate group and a compound having two or more hydroxyl groups as isocyanate-reactive functional groups in the molecule is preferred from the viewpoint of high freedom of selection of the matrix resin structure and lack of odor.

Examples of the compound having an isocyanate group include isocyanic acid, butyl isocyanate, octyl isocyanate, butyl diisocyanate, hexyl diisocyanate (HMDI), isophorone diisocyanate (IPDI), 1,8-diisocyanato-4-(isocyanatomethyl)octane, 2,2,4- and/or 2,4,4-trimethylhexamethylene diisocyanate, isomeric bis(4,4′-isocyanatocyclohexyl)methane, and mixtures thereof with any isomeric content, isocyanatomethyl-1,8-octane diisocyanate, 1,4-cyclohexyl diisocyanate, isomeric cyclohexane dimethylene diisocyanate, 1,4-phenylene diisocyanate, 2,4- and/or 2,6-toluene diisocyanate, 1,5-naphthalene diisocyanate, 2,4′- or 4,4′-diphenylmethane diisocyanate and/or triphenylmethane 4,4′,4″-triisocyanate, etc.

Furthermore, isocyanate derivatives having a urethane, urea, carbodiimide, acrylated urea, isocyanurate, allophanate, biuret, oxadiazinetriane, uretdione and/or iminooxadiazinetriane structure can also be used.

These components may be used alone or in any combination and ratio.

Examples of compounds having two or more hydroxyl groups as isocyanate-reactive functional groups in the molecule include: diols such as ethylene glycol, triethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, and neopentyl glycol; diols such as butanediol, pentanediol, hexanediol, heptanediol, and tetramethylene glycol; bisphenols; or compounds obtained by modifying these polyfunctional alcohols with polyethylene oxide chains or polypropylene oxide chains; compounds obtained by modifying these polyfunctional alcohols such as triols such as glycerol, trimethylolpropane, butanetriol, pentanetriol, hexanetriol, and decantriol with polyethylene oxide chains or polypropylene oxide chains; polyfunctional polyoxybutylenes; polyfunctional polycaprolactones; polyfunctional polyesters; polyfunctional polycarbonates; polyfunctional polypropylene glycols; and the like.

These components may be used alone or in any combination and ratio.

When forming a matrix resin, for example, a combination of a compound having an epoxy group and a compound having an amino group, since the reaction rate of forming bonds of the matrix resin forming composition is relatively high, the bond forming reaction sometimes proceeds in a short time by leaving it at room temperature, thereby forming a matrix resin.

On the other hand, for example, the combination of a compound having an isocyanate group and a compound having a hydroxyl group, which is preferably used as a matrix resin forming composition, has a low reaction rate for forming bonds, and sometimes the bonding formation is not completed and the matrix resin is not formed even if it is left at room temperature for several days. In the case of using a matrix resin forming composition with a low bonding formation reaction rate, the bonding formation reaction of the matrix resin forming composition can be promoted by heating in the same manner as a common chemical reaction. Therefore, it is preferred to use a matrix resin forming composition to fill the recording layer forming composition between the two substrates, and then appropriately heat to form the matrix resin.

Furthermore, by using an appropriate catalyst, the bond-forming reaction of the matrix resin-forming composition can also be accelerated. Examples of such catalysts include onium salts such as bis(4-tert-butylphenyl)iodonium perfluoro-1-butanesulfonic acid and bis(4-tert-butylphenyl)iodonium p-toluenesulfonic acid; catalysts having Lewis acids as main components such as zinc chloride, tin chloride, ferric chloride, aluminum chloride, and _BF3 ; protonic acids such as hydrochloric acid and phosphoric acid; amines such as trimethylamine, triethylamine, triethylenediamine, dimethylbenzylamine, and diazabicycloundecene; imidazoles such as 2-methylimidazole, 2-ethyl-4-methylimidazole, and 1-cyanoethyl-2-undecylimidazolium trimellitate; bases such as sodium hydroxide, potassium hydroxide, and potassium carbonate; tin catalysts such as dibutyltin laurate, dioctyltin laurate, and dibutyltin octoate; and bismuth catalysts such as tri(2-ethylhexanoate)bismuth, tribenzoyloxybismuth, bismuth triacetate, tri(dimethyldithiocarbamate)bismuth, and bismuth hydroxide.

The catalyst may be used alone or in any combination and ratio.

<<About Photopolymerization Initiator>>

The photopolymerization initiator of the present invention is a component that generates cations, anions, and radicals by irradiation with light, and contributes to the polymerization of the above-mentioned polymerizable monomers. The type of the photopolymerization initiator is not particularly limited, and can be appropriately selected according to the type of the polymerizable monomers.

As for the cationic photopolymerization initiator, any known cationic photopolymerization initiator may be used. As examples, aromatic onium salts and the like may be cited. As specific examples, compounds composed of anionic components such as SbF ₆ ^- , BF ₄ ^- , AsF ₆ ^- , PF ₆ ^- , CF ₃ SO ₃ ^- , B(C ₆ F ₅ ) ₄ ^- and aromatic cationic components containing atoms such as iodine, sulfur, nitrogen, and phosphorus may be cited. Among them, diaryliodonium salts, triarylsulfonium salts and the like are preferred.

The cationic photopolymerization initiators exemplified above may be used alone or in any combination and ratio.

Any anionic photopolymerization initiator may be used as long as it is a known anionic photopolymerization initiator. Examples thereof include amines. Examples of amines include amino compounds such as dimethylbenzylamine, dimethylaminomethylphenol, and 1,8-diazabicyclo[5.4.0]undecene-7 and their derivatives; imidazole compounds such as imidazole, 2-methylimidazole, and 2-ethyl-4-methylimidazole and their derivatives; and the like.

The anionic photopolymerization initiators exemplified above may be used alone or in any combination and ratio.

Any known free radical photopolymerization initiator may be used as the free radical photopolymerization initiator. Examples thereof include phosphine oxide compounds, azo compounds, azide compounds, organic peroxides, organic borates, onium salts; biimidazole derivatives, cyclopentadienyl titanium compounds, iodonium salts; organic thiol compounds, halogenated hydrocarbon derivatives, oxime ester compounds; and the like.

The above-exemplified radical photopolymerization initiators may be used alone or in any combination and ratio.

Other examples of the photopolymerization initiator include imidazole derivatives, oxadiazole derivatives, naphthalene, perylene, pyrene, anthracene, coumarin, p-Bis(2-phenylvinyl)benzene and its derivatives, quinacridone derivatives, coumarin derivatives, aluminum complexes such as Al(C ₉ H ₆ NO) ₃ , rubrene, naphthyrimidine derivatives, benzopyran derivatives, rhodamine derivatives, benzothioxanthene derivatives, azabenzothioxanthene, phenylpyridine complexes, porphyrin complexes, polyphenylene vinylene materials, etc.

<<About polymerization inhibitors>>

The polymerization inhibitor of the present invention refers to a component that inhibits the polymerization reaction of the above-mentioned polymerizable monomers, and is a component that can be used as needed. The polymerization inhibitor has the effect of inhibiting the occurrence of unintended polymerization reactions, such as the polymerization reaction of the polymerizable monomers initiated by the generation of free radicals from the polymerization initiator and the polymerizable monomers due to a small amount of light or heat in the storage environment in the recording layer before holographic recording, and improving the storage stability of the medium before holographic recording.

There are no particular restrictions on the type of polymerization inhibitor as long as it can inhibit the polymerization reaction of the above-mentioned polymerizable monomers. Specifically, for example, phosphinates such as sodium phosphate and sodium hypophosphite; thiols such as thioglycolic acid, mercaptopropionic acid, 2-propanethiol, 2-mercaptoethanol, and thiophenol; aldehydes such as acetaldehyde and propionaldehyde; ketones such as acetone and methyl ethyl ketone; halogenated hydrocarbons such as trichloroethylene and perchloroethylene; terpenes such as terpinolene, α-terpinene, β-terpinene, and γ-terpinene; 1,4-cyclohexadiene, 1,4-cycloheptadiene, 1,4-cyclohex ... ,4-cyclooctadiene, 1,4-heptadiene, 1,4-hexadiene, 2-methyl-1,4-pentadiene, 3,6-nonadien-1-ol, 9,12-octadecadienol and other non-conjugated dienes; linolenic acid, γ-linolenic acid, methyl linolenate, ethyl linolenate, isopropyl linolenate, linolenic anhydride and other linoleic acids; linoleic acid, methyl linoleate, ethyl linoleate, isopropyl linoleate, linoleic anhydride and other linoleic acids; Eicosapentaenoic acid, eicosapentaenoic acid ethyl ester and other eicosapentaenoic acid derivatives; docosahexaenoic acid, docosahexaenoic acid ethyl ester and other docosahexaenoic acid derivatives; 2,6-di-tert-butyl-p-cresol, p-methoxyphenol, diphenyl-p-benzoquinone, benzoquinone, hydroquinone, pyrogallol, resorcinol, phenanthrenequinone, 2,5-methylquinone, benzylaminophenol, p-dihydroxybenzene, 2,4,6-trimethylphenol, butylated hydroxytoluene and other phenol derivatives nitrobenzene derivatives such as o-dinitrobenzene, p-dinitrobenzene, and m-dinitrobenzene; N-phenyl-1-naphthylamine, N-phenyl-2-naphthylamine, cuproferric reagent, phenothiazine, tannic acid, p-nitrosoamine, chloranil, aniline, hindered aniline, iron (III) chloride, copper (II) chloride, triethylamine, hindered amines, nitroxide free radicals including 2,2,6,6-tetramethylpiperidinyl 1-oxyl, triphenylmethyl free radicals, and oxygen, etc.

Any of conventionally known materials may be used alone or two or more thereof may be used in any combination and ratio.

<<About Free Radical Scavengers>>

In holographic recording, in order to fix the interference light intensity pattern in the form of polymer distribution in the holographic recording medium with high precision, a free radical scavenger can be added. The free radical scavenger preferably has both a functional group for capturing free radicals and a reactive group fixed to the matrix resin by covalent bonding. As the functional group for capturing free radicals, a stable nitroxide free radical can be cited.

Examples of the reactive group fixed to the matrix resin by covalent bonding include hydroxyl, amino, isocyanate, and mercapto groups. Examples of such radical scavengers include 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl radical (TEMPOL), 3-hydroxy-9-azabicyclo[3.3.1]nonane N-oxyl, 3-hydroxy-8-azabicyclo[3.2.1]octane N-oxyl, and 5-HO-AZADO:5-hydroxy-2-azatricyclo[3.3.1.1 ^3,7 ]decane N-oxyl.

The above-mentioned various radical scavengers may be used alone or in combination of two or more in any ratio.

<<About other additives>>

Other components included in the recording layer forming composition include solvents, plasticizers, dispersants, leveling agents, defoamers, adhesion promoters, compatibilizers, sensitizers, etc. These components may be used alone or in any combination and ratio.

<<About the content of each material>>

The content of each component in the recording layer forming composition of the present embodiment is arbitrary unless it violates the gist of the present invention. However, the ratio of each component is preferably in the following range based on the total mass of the composition.

The total amount of the matrix resin is usually 0.1% by mass or more, preferably 10% by mass or more, and more preferably 35% by mass or more. In addition, it is usually 99.9% by mass or less, preferably 99% by mass or less, and more preferably 98% by mass or less. By making the content of the matrix resin above the lower limit, it is easy to form a recording layer.

The content of the catalyst for promoting the formation of the matrix resin is preferably determined in consideration of the bonding rate of the matrix forming component, and is usually 5% by mass or less, preferably 4% by mass or less, and more preferably 1% by mass or less. 0.005% by mass or more is usually used.

The content of the polymerizable monomer is usually 0.1% by mass or more, preferably 1% by mass or more, more preferably 2% by mass or more. In addition, it is usually 80% by mass or less, preferably 50% by mass or less, more preferably 30% by mass or less. By making the content of the polymerizable monomer above the above lower limit, sufficient diffraction efficiency can be obtained. By making the content of the polymerizable monomer below the above upper limit, the compatibility of the recording layer can be ensured.

The content of the photopolymerization initiator is usually 0.1% by mass or more, preferably 0.3% by mass or more, usually 20% by mass or less, preferably 18% by mass or less, more preferably 16% by mass or less. By making the content of the photopolymerization initiator above the above lower limit, sufficient recording sensitivity can be obtained. If the content of the photopolymerization initiator is below the above upper limit, coloration immediately after recording can be suppressed.

The content of the polymerization inhibitor is usually 0.001% by mass or more, preferably 0.005% by mass or more. In addition, it is usually 30% by mass or less, preferably 10% by mass or less. By making the content of the polymerization inhibitor within the above range, it is possible to suppress the unintended polymerization reaction caused by free radicals generated by a small amount of light or heat.

The content of the radical scavenger is preferably 0.5 μmol/g or more, more preferably 1 μmol/g or more, and preferably 100 μmol/g or less, more preferably 50 μmol/g or less in terms of molar amount per unit weight of the matrix-forming component.

If the content of the radical scavenger is above the lower limit, the radical scavenging efficiency is excellent, the polymer with a low degree of polymerization does not diffuse, and the components that do not contribute to the signal tend to decrease. On the other hand, if the content of the radical scavenger is below the upper limit, the polymerization efficiency of the polymer is excellent.

The total content of other components is usually 30% by mass or less, preferably 15% by mass or less, more preferably 5% by mass or less.

<Regarding the Film Thickness of the Recording Layer>

The thickness of the recording layer in the present invention is preferably 0.1 mm or more and 3.0 mm or less, and more preferably 0.3 mm or more and 2 mm or less. If the thickness is within this range, when multiple recording is performed in the holographic recording medium, there is a tendency that the selectivity of each hologram becomes higher and the degree of multiple recording can be improved. In addition, the light transmittance of the recording layer at the wavelength of the recording light can be maintained at a high level, and uniform recording can be performed on the entire recording layer in the entire thickness direction, and there is a tendency that multiple recording with a high S/N ratio can be achieved.

[Other layers]

The medium in the present invention has a recording layer, and a support and other layers as required. Usually, the medium has a support, and the recording layer and other layers are stacked on the support to form the medium. Wherein, in the case where the recording layer or other layers have the strength and durability required by the medium, the medium may not have a support. As examples of other layers, a protective layer, a reflective layer, an anti-reflective layer (anti-reflection film), etc. can be cited.

<Support>

The support is not particularly limited in detail as long as it has the strength and durability required for the medium, and any support can be used.

The shape of the support is not limited, but is usually formed in a flat plate or film shape.

The material constituting the support is also not limited, and may be transparent or opaque.

As the material of the transparent support, there can be mentioned organic materials such as acrylic resin, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyethylene, polypropylene, amorphous polyolefin, polystyrene, cellulose acetate, and inorganic materials such as glass, silicon, and quartz. Among them, polycarbonate, acrylic resin, polyester, amorphous polyolefin, glass, etc. are preferred, and polycarbonate, acrylic resin, amorphous polyolefin, and glass are particularly preferred.

Examples of the material of the opaque support include metals such as aluminum; materials obtained by coating the above-mentioned transparent support with metals such as gold, silver, and aluminum; or dielectrics such as magnesium fluoride and zirconium oxide; and the like.

The thickness of the support is not particularly limited, and is generally in the range of 0.05 mm to 1 mm. If the thickness of the support is above the lower limit, the mechanical strength of the medium can be obtained, and the warping of the substrate can be prevented. If the thickness of the support is below the upper limit, the transmittance of light can be ensured, and the rise in cost can be suppressed.

The surface of the support may be subjected to a surface treatment. The surface treatment is usually performed to improve the adhesion between the support and the recording layer. Examples of surface treatment include subjecting the support to a corona discharge treatment, or pre-forming an undercoat layer on the support. Here, as the composition of the undercoat layer, halogenated phenol or partially hydrolyzed vinyl chloride-vinyl acetate copolymer, polyurethane resin, etc. may be cited.

Furthermore, surface treatment may be performed for purposes other than improving adhesion. Examples thereof include: reflective coating treatment for forming a reflective coating using metals such as gold, silver, and aluminum as raw materials; dielectric coating treatment for forming a dielectric layer such as magnesium fluoride and zirconium oxide; and the like. In addition, these layers may be formed of a single layer or may be formed of two or more layers.

These surface treatments may be provided for the purpose of controlling the gas and water permeability of the substrate. For example, by making the support sandwiching the recording layer also have the function of suppressing the gas and water permeability, the reliability of the medium can be further improved.

The support may be disposed only on either the upper side or the lower side of the recording layer of the medium of the present invention, or may be disposed on both sides. In the case where the support is disposed on both the upper and lower sides of the recording layer, at least one of the supports is configured to be transparent so as to allow the active energy line (excitation light, reference light, regeneration light, etc.) to pass therethrough.

In the case of a medium having a support on one or both sides of the recording layer, a transmissive or reflective hologram can be recorded. In the case of a medium having a reflective property on one side of the recording layer, a reflective hologram can be recorded.

The support may be provided with patterning for data addresses. The patterning method in this case is not limited. For example, the patterning may be formed by forming a concave-convex shape on the support itself, by forming a pattern on the reflective layer described later, or by combining them.

<Protective layer>

The protective layer is a layer used to prevent the recording layer from being affected by oxygen or moisture, such as a decrease in sensitivity and degradation of storage stability. There is no limitation on the specific composition of the protective layer, and any known composition can be applied. For example, a layer composed of a water-soluble polymer, an organic/inorganic material, etc. can be formed as the protective layer.

The position where the protective layer is formed is not particularly limited, and it may be formed, for example, on the surface of the recording layer, between the recording layer and the support, or on the outer surface of the support. The protective layer may be formed between the support and other layers.

<Reflection layer>

The reflective layer is formed when the medium is configured as a reflective holographic medium. In the case of a reflective holographic recording medium, the reflective layer can be formed between the support and the recording layer, or can be formed on the outer side of the support. It is usually preferred that the reflective layer is located between the support and the recording layer.

As the reflective layer, any known material can be used, and for example, a metal thin film or the like can be used.

<Anti-reflective film>

When the medium in the present invention is configured as a holographic recording medium of any type, such as a transmission type or a reflection type, an anti-reflection film may be provided on the incident side and the emitting side of the object light and the reading light, or between the recording layer and the support. The anti-reflection film plays a role in improving the utilization efficiency of light and suppressing the generation of ghost images.

As the antireflection film, any known antireflection film can be used.

Example

The present invention is described in more detail below by way of examples. The present invention is not limited to the following examples unless it deviates from the gist thereof.

[Raw materials used]

The composition raw materials used in Examples and Comparative Examples are as follows.

(Compound having an isocyanate group)

DURANATE ^TM TSS-100: Hexamethylene diisocyanate-based polyisocyanate (NCO 17.6%) (manufactured by Asahi Kasei Corporation)

(Compound having an isocyanate-reactive functional group)

PLACCEL PCL-205U: Polycaprolactone diol (molecular weight 530, manufactured by Daicel)

PLACCEL PCL-305: Polycaprolactone triol (molecular weight 550, manufactured by Daicel)

(Polymerizable Monomer)

HLM101: 2,2-bis(4-dibenzothiophenylthiomethyl)-3-(4-dibenzothiophenylthio)propyl acrylate

HLM201: 2-[[2,2-bis(4-dibenzothiophenylthiomethyl)-3-(4-dibenzothiophenylthio)propoxy]carbonylamino]ethyl acrylate

(Photopolymerization Initiator)

HLI02: 1-(9-ethyl-6-hexanoyl-9H-carbazol-3-yl)-1-(O-acetyloxime)glutaric acid methyl ester

(Curing Catalyst)

Bismuth tris(2-ethylhexanoate)octanoate solution (active ingredient content 56% by mass)

(Free Radical Scavenger)

·4-Hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl radical (TEMPOL, manufactured by Tokyo Chemical Industry Co., Ltd.)

[Preparation of TEMPOL masterbatch]

0.03 g of TEMPOL was dissolved in 2.97 g of DURANATE ^™ TSS-100, and 0.0003 g of an octanoic acid solution of bismuth tri(2-ethylhexanoate) was dissolved therein, followed by stirring at 45° C. under reduced pressure and reacting for 2 hours.

[Preparation of recording layer composition and production of holographic recording medium]

<Hologram Recording Medium 1>

Liquid A was prepared by dissolving 0.7599 g of polymerizable monomer HLM101, 0.0304 g of photopolymerization initiator HLI02, and 1.0411 g of TEMPOL masterbatch in 2.8794 g of DURANATE ^™ TSS-100.

Separately, 1.795 g of PLACCEL PCL-205U and 1.795 g of PLACCEL PCL-305 were mixed (PLACCEL PCL-205U:PLACCEL PCL-305=50:50 (weight ratio)), and dissolved in 0.00023 g of bismuth tri(2-ethylhexanoate) octanoate solution to prepare liquid B.

Liquid A was degassed for 2 hours under reduced pressure, and liquid B was degassed for 2 hours at 45°C under reduced pressure, and then 2.5537 g of liquid A and 1.9463 g of liquid B were stirred and mixed. The mixed solution was then poured onto a glass slide with a 0.5 mm thick spacer on the two opposing ends, and a glass slide was placed thereon, the periphery was fixed with a clip, and heated at 80°C for 24 hours to prepare a sample for evaluating a composition for a holographic recording medium. The sample for evaluation was formed by forming a recording layer with a thickness of 0.5 mm between the glass slides as covers.

<Hologram Recording Medium 2>

Liquid A was prepared by dissolving 2.0811 g of polymerizable monomer HLM201, 0.0749 g of photopolymerization initiator HLI02, and 2.8095 g of TEMPOL masterbatch in 5.8207 g of DURANATE ^™ TSS-100.

Separately, 3.949 g of PLACCEL PCL-205U and 3.949 g of PLACCEL PCL-305 were mixed (PLACCEL PCL-205U:PLACCEL PCL-305=50:50 (weight ratio)), and dissolved in 0.00025 g of bismuth tri(2-ethylhexanoate) octanoate solution to prepare liquid B.

Liquid A was degassed under reduced pressure for 2 hours, and liquid B was degassed under reduced pressure at 45° C. for 2 hours, and then 5.1955 g of liquid A and 3.8045 g of liquid B were stirred and mixed.

Next, the mixed solution was poured onto a glass slide having spacers of 0.5 mm thickness placed on two opposing end edges, a glass slide was placed thereon, the periphery was fixed with a clip, and heated at 80° C. for 24 hours to prepare a sample for evaluating the composition for holographic recording media. The sample for evaluation had a recording layer of 0.5 mm thickness formed between the glass slides as covers.

[Manufacturing of optical components]

<Holographic Recording Device>

Fig. 1 is a schematic diagram showing the structure of an apparatus used for holographic recording on a medium. In Fig. 1, S is a sample of a holographic recording medium, M1 and M2 both represent mirrors. PBS represents a polarization beam splitter, LD represents a laser source for recording light that emits light of a wavelength of 405 nm (a single-mode laser manufactured by TOPTICA Photonics that can obtain light of a wavelength near 405 nm), and PD1 and PD2 represent photodetectors.

<Holographic Recording Exposure>

The light of wavelength 405nm generated by LD was split by PBS, and these were regarded as reference light and object light, and irradiated in the following manner: the two beams were made to intersect on the recording surface so that the angle formed was the following angle. At this time, the bisector of the angle formed by the two beams (hereinafter referred to as the optical axis) was made perpendicular to the recording surface of the recording layer of the holographic recording medium, and the vibration plane of the electric field vector of the two beams obtained by the split was made perpendicular to the plane containing the two intersecting beams. The above situation was set to 0°, and the direction of the holographic recording medium was changed in the state where the incident direction of the two beams was fixed, and 151 multiplex holographic recording was performed while changing the angle of the recording surface with respect to the optical axis in the range of -23.5° to 23.5° at intervals of 0.3°. At this time, the light intensity of each light beam was set to 10.2mW/ ^cm2 , and the exposure energy density of the recording light per multiplex recording was set to 20.4mJ/ ^cm2 . In addition, the recording exposure temperature was set to 25°C. At this time, the temperature of the recording medium was also 25°C.

(Angle formed by 2 beams)

Examples 1 to 8 and Comparative Examples 1 to 6: 37.3°

Reference Examples 1 to 10 and Comparative Reference Example 1: 59.3°

[Examples and Comparative Examples showing the effect of the difference between the temperature during recording exposure and the temperature during post-exposure]

<Post-exposure>

Fig. 2 is a schematic diagram showing the structure of the apparatus used in post-exposure. The temperature of the medium subjected to recording exposure of the hologram was adjusted by the temperature control plate 2, and light was irradiated by the LED 1 so that the post-exposure amount was 25 J/ ^cm2 to manufacture an optical element.

In Examples 1 to 8, holographic recording medium 1 or 2 was used, and the temperature of the medium was adjusted so that the difference between the temperature during recording exposure and the temperature during post-exposure (temperature during recording exposure - temperature during post-exposure) was 5°C to 20°C, and then post-exposure was performed.

In Comparative Examples 1 to 6, hologram recording medium 1 or 2 was used, and the temperature of the medium was adjusted so that the difference between the temperature during recording exposure and the temperature during post-exposure was 0° C. to −15° C., and then post-exposure was performed.

<Evaluation of Haze of Non-recording Part>

The haze of the non-recording portion of the obtained optical element was evaluated using NDH700SPII (manufactured by Nippon Denshoku Co., Ltd.) (reference: air). The measurement was performed three times using the above-mentioned device, and the average value was taken as the haze value.

The calculation method of the haze (Haze) based on the device is as follows.

Haze [%] = (diffuse light component/total light transmittance) × 100

<Evaluation Results>

Table 1 shows the haze (%) of the non-recording portion of Examples 1 to 8 and Comparative Examples 1 to 6.

In Table 1, "hologram recording medium" is described as "medium".

[Table 1]

<Table 1>

※The temperature in brackets is the temperature during post-exposure

According to Examples 1 to 8 and Comparative Examples 1 to 6, it can be seen that when the recording exposure temperature - post-exposure temperature is a positive value, that is, when the temperature during post-exposure is lower than the temperature during recording exposure, the haze (Haze) of the non-recording part of the obtained optical element is significantly reduced in both cases of holographic recording media 1 and 2 compared with the case where the recording exposure temperature - post-exposure temperature is below 0°C.

[Reference example and comparative reference example showing the effect of the ratio of light intensity during recording exposure to light intensity during post-exposure]

<Post-exposure>

Fig. 3 is a schematic diagram showing the structure of the device used in the post-exposure. L1, L2, L3, and L4 are 405 nm LEDs manufactured by THORLAB, and F is a blower fan. The LEDs are adjusted so that the light intensity is an arbitrary value, the exposure time is changed, and the light irradiation is performed so that the post-exposure amount is 38 J/ ^cm2 to manufacture the optical element.

In Reference Examples 1 to 10, post-exposure was performed using hologram recording medium 1 with light intensity adjusted to 10 to 320 mW/cm ² (light intensity ratio 0.49 to 15.70). When the light intensity was 100 to 320 mW/cm ² , post-exposure was performed while heat was dissipated from the sample surface by a blower fan F.

In Comparative Reference Example 1, hologram recording medium 1 was used and post-exposure was performed while adjusting the light intensity to 5 mW/cm ² .

In Table 2 below, the ratio of the light intensity during post-exposure to the light intensity during recording exposure is described as "light intensity ratio (post-exposure/recording exposure)".

<Evaluation of Haze of Non-recording Part>

The haze of the non-recording portion of the obtained optical element was evaluated using NDH700SPII (manufactured by Nippon Denshoku Co., Ltd.) (reference: air). The measurement was performed three times using the above-mentioned device, and the average value was taken as the haze value.

The calculation method of the haze based on the device is as follows.

Haze [%] = (diffuse light component/total light transmittance) × 100

<Evaluation Results>

Table 2 shows the haze (%) of the non-recording portion of Reference Examples 1 to 10 and Comparative Reference Example 1.

[Table 2]

<Table 2>

※The temperature in brackets is the temperature during post-exposure

According to Reference Examples 1 to 10 and Comparative Reference Example 1, it can be seen that the haze of the non-recording portion of the obtained optical element is reduced by making the ratio of the light intensity of the post-exposure to the light intensity of the recording exposure 0.3 or more. In addition, it can be seen that the haze is further significantly reduced by suppressing the temperature rise during the post-exposure relative to the temperature during the recording exposure by using a heat dissipation fan to suppress the temperature rise.

Although the present invention has been described in detail using specific embodiments, it will be apparent to one skilled in the art that various modifications can be made without departing from the spirit and scope of the present invention.

This application is based on Japanese Patent Application No. 2021-176018 filed on October 28, 2021 and Japanese Patent Application No. 2021-215449 filed on December 29, 2021, the entire contents of which are incorporated by reference.

Industrial Applicability

The method for producing an optical element of the present invention is particularly useful as a means for reducing the haze of a non-recording portion of an optical element having a hologram recorded thereon and used in a light guide plate of AR glasses or the like.

Explanation of symbols

Figure 1

S Holographic recording medium

M1,M2 reflector

LD Semiconductor laser source for recording light

PD1,PD2 Photodetector

PBS Polarizing Beam Splitter

Figure 2

S The medium on which the hologram is recorded and exposed

1 LED unit

2 Temperature control panel

Figure 3

S The medium on which the hologram is recorded and exposed

L1, L2, L3, L4 LED units

F Air supply fan

Claims (8)

1. A method for manufacturing an optical element, wherein a medium having a recording layer containing a polymerizable compound and a photopolymerization initiator is subjected to recording exposure, and further, post-exposure is performed in a state where the temperature of the medium is lower than that at the time of the recording exposure.

2. The method for manufacturing an optical element according to claim 1, wherein a difference between a temperature of the medium at the time of the recording exposure and a temperature of the medium at the time of the post exposure is 5 ℃ or more.

3. The method for producing an optical element according to claim 1 or claim 2, wherein the temperature of the medium at the time of post-exposure is 5 ℃ or higher.

4. The method for producing an optical element according to any one of claims 1 to 3, wherein the temperature of the medium at the time of recording exposure is 10 ℃ to 40 ℃.

5. The method for manufacturing an optical element according to any one of claims 1 to 4, wherein the post-exposure is performed at a light intensity of 0.3 times or more as high as that at the time of the recording exposure.

6. The method for manufacturing an optical element according to any one of claims 1 to 5, wherein a light source for post exposure at the time of the post exposure is incoherent light.

7. The method for manufacturing an optical element according to any one of claims 1 to 6, wherein post-exposure is performed from both sides of the medium.

8. The method for manufacturing an optical element according to any one of claims 1 to 7, wherein the recording exposure is a hologram recording exposure.