JP2023116984A - Method for manufacturing optical element - Google Patents

Abstract

To manufacture an optical element in which holograms having uniform diffraction efficiency are multiple-recorded.SOLUTION: With a method for manufacturing an optical element, multiple recording of holograms is performed according to an exposure time schedule based on formula (1) with respect to media having a recording layer containing a polymerizable compound and a photopolymerization initiator. [In the formula (1), Tn represents an n-th recording exposure time (millisecond), n represents an integer of one or more and m or less, A represents first recording exposure time (millisecond), m is a total number of times of multiple recording exposure and being an integer of two or more, and x denotes a constant of 0.95 or more.]SELECTED DRAWING: None

Description

The present invention relates to a method for manufacturing a hologram recording medium.

A holographic recording medium that has been attracting attention in recent years is a recording medium that utilizes light interference and diffraction phenomena. A hologram is a recording technique that three-dimensionally records an interference pattern formed by interference fringes of two lights called reference light and information (or signal) light inside a recording medium. The hologram recording medium contains a photosensitive material in the recording layer, and the photosensitive material undergoes a chemical change in accordance with the interference pattern to locally change the optical properties to record the interference pattern.

Hologram recording media have been developed for memory applications, but AR is another application.
Application to optical elements such as glass light guide plates is being studied. For AR glass applications,
Hologram-recorded optical elements used in light guide plates are required to have a wide viewing angle, high diffraction efficiency for light in the visible region, and high transparency of the medium.
Hologram recording media are classified into several types according to the type of change in optical characteristics. Volume hologram media, which perform recording by creating a refractive index difference within a recording layer having a certain thickness or more, are the most popular. A because it can realize space, high diffraction efficiency, and wavelength selectivity
It is believed to be advantageous for R-glass light guide plate applications.

An example of a volume holographic recording medium is a write-once type that does not require wet processing or bleaching, and the general composition of the recording layer is a matrix resin in which a photoactive compound is dissolved. For example, it is known to use a photopolymer in which a photopolymerization initiator and a polymerizable reactive compound capable of radical polymerization or cationic polymerization are combined as a matrix resin and a photoactive compound as a recording layer (Patent document 1-4).

When recording a hologram, if there is a recording layer made of photopolymer in the area where the interference pattern is formed by the intersection of the reference beam and the object beam, the photopolymerization initiator chemically reacts in the area of the interference pattern where the light intensity is high. to form an active substance, which acts on the polymerizable compound to polymerize the polymerizable compound. At this time, if there is a difference in refractive index between the polymer produced from the matrix resin and the polymerizable compound, the interference pattern becomes a difference in refractive index and is fixed in the recording layer. Also,
When the polymerizable compound is polymerized, diffusion of the polymerizable compound occurs from the periphery, and concentration distribution of the polymerizable compound or its polymer is generated inside the recording layer. Based on this principle, an interference pattern is recorded as a refractive index difference on the hologram recording medium.
Hereinafter, the process of changing the optical characteristics of the recording layer by exposing the recording layer of the medium under predetermined conditions as described above will be referred to as "recording exposure". Recording and exposing different interference patterns at different positions is called "multiple recording exposure".
On the other hand, when reproducing data, only reproducing light is used, and the irradiated reproducing light is diffracted according to the interference pattern. At this time, even if the wavelength of the reproducing light does not match the wavelength of the recording light, diffraction occurs if the interference pattern and the Bragg condition are satisfied. Therefore, if the corresponding interference pattern is recorded according to the wavelength and incident angle of the reproduction light to be diffracted, it is possible to diffract the reproduction light over a wide wavelength range, thereby expanding the display color gamut of the AR glass. can be expanded. Also, the value obtained by dividing the intensity of the diffracted light by the intensity of the reproduced light is called "diffraction efficiency", and in AR glasses, it correlates with the brightness of the displayed AR increase. In other words, in order to widen the display color gamut and obtain a bright AR image, it is important to carry out multiple recording exposure so that the diffraction efficiency of the interference pattern corresponding to the display color gamut is as uniform as possible.

As a method of performing recording exposure so as to obtain a uniform diffraction efficiency during multiple recording exposure, it is known to gradually increase the exposure energy of the reference light and the object light each time multiple recording exposure is performed. Since this exposure energy is the product of the light intensity of the light source and the exposure time, the method for changing the exposure energy is to increase the light intensity of the light source as the multiplex recording progresses, or
A method of lengthening the light irradiation time is conceivable, but recording exposure while changing the light intensity arbitrarily is not suitable for production, because in addition to being inefficient in manufacturing, there is an upper limit to the light intensity. Therefore, usually, the time for light irradiation is determined before multiple recording exposure, and a method of controlling with an optical shutter or the like is adopted. This method is called "exposure time schedule" (Patent Document 5).
. However, it is difficult to implement this exposure time schedule so as to achieve uniform diffraction efficiency. is difficult to obtain uniform diffraction efficiency. Here, the accumulated exposure time means the total sum of exposure times until the end of multiplex recording when performing multiplex recording.

Japanese Patent Application Laid-Open No. 2021-12249 JP 2007-34334 A JP-A-8-160842 JP-A-2003-156992 JP 2012-141621 A

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical element in which a hologram having uniform diffraction efficiency is exposed for multiple recording.

As a result of intensive studies by the present inventors, by adopting a specific exposure time schedule,
We have found that multiple recording exposure with uniform diffraction efficiency can be performed on the holographic recording medium.

That is, the gist of the present invention is as follows.
[1] For a medium having a recording layer containing a polymerizable compound and a photopolymerization initiator, the following formula (1)
A method for manufacturing an optical element, wherein multiple recording exposure of holograms is performed with an exposure time schedule based on.

In formula (1), T _n is the n-th recording exposure time (milliseconds), n is an integer from 1 to m, A is the first recording exposure time (milliseconds), and m is the total number of multiple recording exposures. is an integer of 2 or more, and x is a constant of 0.95 or more.

[2] The method for producing an optical element according to [1], wherein m in formula (1) is 20 or more.
[3] The method for producing an optical element according to [1] or [2], wherein A in formula (1) is 3 milliseconds or longer.
[4] The method for manufacturing an optical element according to any one of [1] to [3], wherein the average diffraction efficiency of holograms multiple-recorded according to the exposure time schedule based on the formula (1) is 0.2 or more. .
[5] Manufacture of the optical element according to any one of [1] to [4], wherein the dispersion of the diffraction efficiency of each hologram multiple-recorded according to the exposure time schedule based on the formula (1) is 0.3 or less. Method.

According to the present invention, an optical element having uniform diffraction efficiency can be manufactured.

Fig. 4 is a flow chart for determining parameters of an exposure time schedule; 1 is a schematic diagram showing an example of a hologram recording device; FIG. It is an example of reproduction measurement of an optical element subjected to multiple recording exposure with a non-linear exposure time schedule (Example 3). It is an example of reproduction measurement of an optical element subjected to multiple recording exposure with a linear exposure time schedule (comparative example 1).

Embodiments of the method for manufacturing an optical element of the present invention will be described in detail below. Not specified in these contents.

(Manufacturing method of hologram recording medium of the present invention)
The present invention relates to a method of manufacturing an optical element by subjecting a recording layer of a medium to multiple recording exposure of an interference pattern of reference light and object light.
In this multiple recording exposure, a medium having a recording layer containing a polymerizable compound and a photopolymerization initiator is rotated based on preset conditions, for example, so that the incident angles of the reference light and the object light are changed, and each recording is performed at the same place. Although it can be performed by repeatedly recording and exposing the interference pattern based on the incident angle, in the present invention, multiple recording exposure is performed according to the exposure time schedule defined by equation (1).

In formula (1), T _n is the n-th recording exposure time (milliseconds), n is an integer from 1 to m, A is the first recording exposure time (milliseconds), and m is the total number of multiple recording exposures. is an integer of 2 or more, and x is a constant of 0.95 or more.

In the present invention, the reference light is light that serves as a reference when recording an interference pattern on a medium, and is light that irradiates the recording layer of the medium while overlapping with the object light when the recording layer of the medium is exposed. Further, in the present invention, the object light is used as an optical element used in AR glass or the like, in order to hologram-record a corresponding interference pattern in the medium by interference with the reference light according to the wavelength and diffraction of the reproduction light. This is the light that irradiates the recording layer of the medium.

The light source that can be used for recording exposure in the present invention can be arbitrarily selected within the absorption wavelength region of the photopolymerization initiator in the recording layer of the medium. Particularly suitable are, for example, ruby, glass, solid-state lasers such as Nd-YAG, Nd- _YVO4 ; GaAs, InGaAs
, GaN, etc.; gaseous lasers, such as helium-neon, argon, krypton, excimer, _CO2 ; dye lasers, etc., which are excellent in monochromaticity and directivity.

The wavelength of the light for recording exposure in the present invention may be in the absorption wavelength region of the photopolymerization initiator, and can be arbitrarily selected from the ultraviolet region to the visible region. is greater than or equal to 350 nm. Also, it is preferably 600 nm or less, more preferably 450 nm or less.

In the present invention, the exposure time schedule is the exposure time T _n (milliseconds) at the time of n-th multiplex hologram recording obtained by the above equation (1).
In this formula (1), A is the first (n=1) recording exposure time (milliseconds). This A can be selected as appropriate and is not particularly limited, but is preferably set to 3 milliseconds or more because there is a tendency for recording exposure to be performed with higher accuracy. It is more preferably 20 milliseconds or more, and still more preferably 100 milliseconds or more. On the other hand, if the recording exposure time is ^too long, hologram recording tends to be hindered due to deterioration of light coherence due to air fluctuations during exposure. preferable. More preferably, it is 10×10 ³ milliseconds or less.

In equation (1), m is the total number of multiple recording exposures (total multiple number). This m can be set to any integer as long as it is 2 or more, but if the total multiplex number is small, it tends to be difficult to obtain an AR image with a wide display color gamut from the resulting optical element. Therefore, m is preferably 20 or more, more preferably 40 or more, and even more preferably 60 or more. On the other hand, the greater the total number of multiplexes, the wider the display color gamut and the higher the color reproducibility of AR images, as described above, but the longer the time required for multiple recording exposure, the more the manufacturing efficiency of optical elements tends to decrease. be. Therefore, m is preferably 300 or less, more preferably 200 or less, and even more preferably 150 or less.

Furthermore, in formula (1), x is a dimensionless constant of 0.95 or more. Setting x to 0.95 or more tends to improve the uniformity of the diffraction efficiency in the optical element obtained by multiple recording exposure of the hologram. More preferably, it is 0.98 or more.
On the other hand, the larger the value of x, the longer the _Tn , which tends to reduce the manufacturing efficiency of the optical element. can.

FIG. 1 is an example of a flowchart for determining the values of A, x, and m in equation (1), which will be described in order below.
First, each numerical value for performing the first test multiple recording exposure is determined. The total multiplex number m is arbitrarily set within the above range, and as an initial setting, x = 1 and n =
Assume that the exposure time A at 1 is 100 milliseconds. A first test multiple recording exposure is performed under these setting conditions, and it is determined whether or not the dispersion of the diffraction efficiency of each multiple recorded hologram when reproduced is 0.3 or less.

If this dispersion is greater than 0.3, after adjusting each numerical value, a second test multiplex recording is performed using a new unexposed medium of the same specification, and the dispersion is found to be 0.3 or less. Make the judgment again.
For example, A is increased when the diffraction efficiency increases as the number of multiplexes goes to the latter half, and A is decreased when the diffraction efficiency decreases as the number of multiplexes goes to the latter half. If the diffraction efficiency is low in the first half of the multiplexing number, gradually increases as the multiplexing number increases, and then decreases again in the latter half of the multiplexing number, the value of x is decreased. If each diffraction efficiency change shows the opposite trend, then the value of x is increased.
When the dispersion of the second test multiplex recording is greater than 0.3, the test multiplex recording exposure with each value adjusted is repeated, and each value is adjusted until the dispersion value reaches the desired value of 0.3 or less. do.

By determining the values of A, x, and m in formula (1) in the above order, and subjecting the medium to multiple recording exposure according to the exposure time schedule based on formula (1), the polymerizable compound in the recording layer and An optical element having a uniform diffraction efficiency can be obtained while the photopolymerization initiator can be completely used up.

When a medium having a recording layer containing a polymerizable compound and a photopolymerization initiator is subjected to hologram recording exposure, a certain amount of the photopolymerization initiator is cleaved according to the exposure energy, and a certain amount of the polymerizable compound is formed. Polymerization forms an interference pattern in the medium. This recording exposure is repeated,
In the latter half of the multiple recording exposure, when the cumulative exposure time increases, the amount of the photopolymerization initiator and photoreactive compound in the recording layer is reduced. However, it is difficult to form an interference pattern in the medium with the same intensity as in the first half.
Therefore, in the present invention, in order to obtain an optical element having a uniform diffraction efficiency, the above formula (1
) is adopted, and the exposure energy is exponentially increased at each recording exposure.

When executing this exposure time schedule, the recording exposure time can be controlled by using a shutter that physically blocks light, a liquid crystal shutter that utilizes light-dark reversal of liquid crystal, or the like.

When manufacturing an optical element according to the present invention, in order to prevent exposure inhibition, pretreatment exposure is performed on the medium before multiple recording exposure to remove the polymerization inhibitor and oxygen contained in the recording layer of the medium. can be deactivated.
In the case of producing an optical element according to the present invention, post-exposure is performed on the medium after multiple recording exposure for the purpose of fixing the interference pattern to the optical element, and the unreacted polymerizable compound in the recording layer and the A photoinitiator can be stabilized.
Light sources used for this pretreatment exposure and post-exposure include LEDs, UV lamps, xenon lamps, mercury lamps, and the like. The same laser as for exposure can also be used.

The diffraction efficiency of the optical element manufactured according to the present invention can be obtained by irradiating the optical element with reference light as reproduction light.
The diffraction efficiency η _n from the hologram recorded and exposed for the nth time can be obtained from the relationship between the diffracted light intensity I _dn obtained from the recorded interference pattern and the transmitted light intensity I _tn of the reproduced light, and is given by the formula (
2).

For example, when the optical element of the present invention is applied to an AR glass light guide plate, a bright AR image tends to be obtained.
It is preferably 2 or more. More preferably 0.4 or more, still more preferably 0.6
That's it. The diffraction efficiencies of these holograms are preferably as high as possible, but should not exceed 1 in principle.

In the present invention, the dispersion σ ² of the diffraction efficiency expressed by Equation (3) is used as a value indicating the uniformity of the diffraction efficiency of each hologram subjected to multiple recording exposure.
The smaller the dispersion, the higher the uniformity of the diffraction efficiency of the hologram.
If it is below, the AR glass light guide plate tends to have a sufficiently uniform color display performance, which is preferable. It is more preferably 0.2 or less, still more preferably 0.1 or less.

(In the formula, _ηn is the diffraction efficiency of the hologram exposed for the n-th multiple recording exposure, and _ηavg is the average of the diffraction efficiencies.)

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

<Regarding composition for forming hologram recording layer>
The recording layer of the medium according to the present invention is formed from a composition for forming a recording layer, which will be described in detail below.
Here, with respect to the matrix resin, the composition for forming the recording layer is usually polymerized or crosslinked after being filled between the flat substrates so that it exists as a crosslinked network structure in the recording layer. It will be contained in the product in the form of a matrix resin composition for forming the matrix resin by polymerization or cross-linking.
That is, the composition for forming a recording layer according to the present invention can contain a polymerizable monomer, a composition for forming a matrix resin, a photopolymerization initiator and a polymerization inhibitor. The constituent components of the composition for forming a hologram recording layer are described in detail below.

<<About the polymerizable monomer>>
A polymerizable monomer according to the present invention refers to a compound that can be polymerized by a photopolymerization initiator, which will be described later. The type of polymerizable monomer is not particularly limited, and can be appropriately selected from known compounds. Examples of polymerizable monomers include cationically polymerizable monomers, anionically polymerizable monomers, and radically polymerizable monomers. Any of these may be used, or two or more thereof may be used in combination.

Examples of cationic polymerizable monomers include epoxy compounds, oxetane compounds, oxolane compounds, cyclic acetal compounds, cyclic lactone compounds, thiirane compounds, thietane compounds, vinyl ether compounds, spiroorthoester compounds, ethylenically unsaturated bond compounds, and cyclic ether compounds. , cyclic thioether compounds, vinyl compounds, and the like. One of the cationic polymerizable monomers may be used alone, or two or more of them may be used in any combination and ratio.

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

Examples of radically polymerizable monomers include (meth)acryloyl group-containing compounds, (meth)acrylamides, vinyl esters, vinyl compounds, styrenes, spiro ring-containing compounds, and the like. Any one of the radically polymerizable monomers may be used alone,
You may use two or more types together by arbitrary combinations and ratios. Among the above, a compound having a (meth)acryloyl group is more preferable from the viewpoint of steric hindrance during radical polymerization.
Among the above polymerizable monomers, a compound having a halogen atom (iodine, chlorine, bromine, etc.) or a heteroatom (nitrogen, sulfur, oxygen, etc.) in the molecule is preferable because of its high refractive index. Among the above, those having a heterocyclic structure are preferable because a higher refractive index can be obtained.

<<Regarding the matrix resin and the composition for forming the matrix resin>>
The matrix resin according to the present invention refers to a cured product having a crosslinked network structure formed by a polymerization reaction or a crosslinking reaction. Precursor.
Since the matrix resin has a crosslinked network structure, it moderately suppresses the mobility of the polymerizable monomer and the photopolymerization initiator, thereby spatially and uniformly dispersing the polymerizable monomer and the photopolymerization initiator in the recording layer. It has a role to keep stable state. In addition, the matrix resin prevents the recorded information from being erased by suppressing diffusion of the polymer by entanglement with the polymer generated in the recording layer. Furthermore, since it has a higher elastic modulus than the liquid state, it has a role of retaining the physical shape of the recording layer.

As the composition for forming the matrix resin, if it can maintain sufficient compatibility with the polymerizable monomer, its polymer, and the photopolymerization initiator even after bonding is formed by a polymerization reaction or a cross-linking reaction, There are no particular restrictions, and preferably a compound having at least two functional groups selected from the group consisting of isocyanate groups, hydroxyl groups, mercapto groups, epoxy groups, amino groups and carboxy groups in the molecule may be used alone. , may be used in combination.

Examples of realizing a certain chemical bond forming a crosslinked network structure by using these compounds alone or in combination include the following examples. That is, the reaction between compounds having an isocyanate group to form an isocyanurate bond, a compound having an isocyanate group and a compound having an active hydrogen in the molecule, such as a compound containing a hydroxyl group, a mercapto group, an amino group, or a carboxy group. to form a urethane bond, a thiourethane bond, a urea bond, an amide bond, etc., a compound having a hydroxyl group and a compound having a carboxy group to form an ester bond, a compound having an amino group and a carboxy group Forming an amide bond by combining compounds having an epoxy group, forming an ether bond by reacting compounds having an epoxy group, forming an ether bond by combining an epoxy group and a hydroxyl group, a compound having an epoxy group and an amino group It is conceivable to form an amine bond by a combination of compounds having and further to form a plurality of types of bonds including these.

Among them, a combination of a compound having an isocyanate group and a compound having two or more hydroxyl groups in the molecule as an isocyanate-reactive functional group is preferable in that the matrix resin structure can be selected with a high degree of freedom and that there is no odor.
Examples of compounds having an isocyanate group include isocyanic acid, butyl isocyanate, octyl isocyanate, butyl diisocyanate, hexyl diisocyanate (HMDI
), isophorodiisocyanate (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-cyclohexylene diisocyanate, isomeric cyclohexanedimethylene diisocyanate, 1,4-phenylene diisocyanate, 2,4- and/or 2,6-
toluene diisocyanate, 1,5-naphthylene diisocyanate, 2,4'- or 4
,4′-diphenylmethane diisocyanate and/or triphenylmethane 4,4′,4
''-triisocyanate and the like.

It is also possible to use isocyanate derivatives having urethane, urea, carbodiimide, acrylic urea, isocyanurate, allophanate, biuret, oxadiazinetrione, uretdione and/or iminooxadiazinedione structures. Any one of these may be used alone, or two or more thereof may be used in any combination and ratio.

Examples of compounds having two or more hydroxyl groups in the molecule as isocyanate-reactive functional groups include glycols such as ethylene glycol, triethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, and neopentyl glycol; butanediol , Pentanediol, hexanediol, heptanediol, diols such as tetramethylene glycol; bisphenols, or compounds obtained by modifying these polyfunctional alcohols with polyethyleneoxy or polypropyleneoxy chains; glycerin, trimethylolpropane, butanetriol, pentane Triol, hexanetriol, compounds obtained by modifying these polyfunctional alcohols such as triols such as decanetriol with a polyethyleneoxy chain or polypropyleneoxy chain; polyfunctional polyoxybutylene; polyfunctional polycaprolactone; polyfunctional polyester; polyfunctional polycarbonate;
polyfunctional polypropylene glycol and the like. Any one of these may be used alone, or two or more thereof may be used in any combination and ratio.

When forming the matrix resin, for example, a combination of a compound having an epoxy group and a compound having an amino group has a relatively high bond formation reaction rate of the composition for forming the matrix resin. Some matrix resins are formed as bond-forming reactions proceed over time.
On the other hand, for example, a combination of a compound having an isocyanate group and a compound having a hydroxyl group, which is a preferable combination as a composition for forming a matrix resin because of the high degree of freedom in selecting the matrix resin structure, has a reaction rate for bond formation. The temperature is not high, and there are cases where the bond formation is not completed and the matrix resin is not formed even after being left at room temperature for several days. When a matrix resin-forming composition having such a low bond-forming reaction rate is used, the bond-forming reaction of the matrix resin-forming composition can be promoted by heating, as in general chemical reactions. . Therefore, depending on the composition for forming the matrix resin, it is preferable to appropriately heat the mixture after filling the space between the substrates with the composition for forming the recording layer in order to form the matrix resin.

Furthermore, the bond-forming reaction of the matrix resin-forming composition can also be promoted by using a suitable catalyst. Examples of such catalysts include onium salts such as bis(4-t-butylphenyl)iodonium perfluoro-1-butanesulfonate, bis(4-t-butylphenyl)iodonium p-toluenesulfonate, zinc chloride, Lewis acid-based catalysts such as tin chloride, iron chloride, aluminum chloride, and BF3; protic acids such as hydrochloric acid and phosphoric acid; trimethylamine, triethylamine, triethylenediamine, dimethylbenzylamine, and diazabicycloundecene; Amines, imidazoles such as 2-methylimidazole, 2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazolium trimellitate, bases such as sodium hydroxide, potassium hydroxide and potassium carbonate , tin catalysts such as dibutyltin laurate, dioctyltin laurate, dibutyltin octoate, tris(2-ethylhexanate) bismuth, tribenzoyloxybismuth, bismuth triacetate, tris(dimethyldiocarbamate) bismuth, bismuth hydroxide, etc. of bismuth catalysts. Any one of the above catalysts may be used alone, or two or more thereof may be used in any combination and ratio.

<<About the photoinitiator>>
The photopolymerization initiator according to the present invention is one that generates cations, anions, and radicals upon irradiation with light, and contributes to the polymerization of the polymerizable monomers described above. The type of photopolymerization initiator is not particularly limited, and can be appropriately selected according to the type of polymerizable monomer and the like.
Any known cationic photopolymerization initiator can be used as the cationic photopolymerization initiator. Examples include aromatic onium salts and the like. As a specific example, SbF ₆ ^-
, BF ₄ ⁻ , AsF ₆ ⁻ , PF ₆ ⁻ , CF ₃ SO ₃ ⁻ , B(C ₆ F ₅ ) ₄ ⁻ and other anion components, and aromatic cation components containing atoms such as iodine, sulfur, nitrogen and phosphorus. A compound consisting of Among them, diaryliodonium salts, triarylsulfonium salts and the like are preferable. Any one of the cationic photopolymerization initiators exemplified above may be used alone,
You may use two or more types together by arbitrary combinations and ratios.

Any known anionic photopolymerization initiator can be used as the anionic photopolymerization initiator. Examples include amines and the like. Examples of amines include dimethylbenzylamine, dimethylaminomethylphenol, 1,8-diazabicyclo[5.4.0]
amino group-containing compounds such as undecene-7, and derivatives thereof; imidazole compounds such as imidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, and derivatives thereof; Any one of the anionic photopolymerization initiators exemplified above may be used alone, or two or more thereof may be used in combination in any desired ratio.

Any known radical photopolymerization initiator can be used as the radical photopolymerization initiator. Examples include phosphine oxide compounds, azo compounds, azide compounds, organic peroxides, organic borate salts, onium salts, bisimidazole derivatives, titanocene compounds,
Iodonium salts, organic thiol compounds, halogenated hydrocarbon derivatives, oxime ester compounds and the like are used. Any one of the radical photopolymerization initiators exemplified above may be used alone, or two or more thereof may be used in any combination and ratio.

Other examples include imidazole derivatives, oxadiazole derivatives, naphthalene, perylene, pyrene, anthracene, coumarin, chrysene, p-bis(2-phenylethenyl)benzene and their derivatives, quinacridone derivatives, coumarin derivatives, Al ( _{C9H6NO _}
) ₃ , rubrene, perimidone derivatives, benzopyran derivatives, rhodamine derivatives, benzothioxanthene derivatives, azabenzothioxanthenes, phenylpyridine complexes, porphyrin complexes, and polyphenylenevinylene-based materials.

<<About the polymerization inhibitor>>
The polymerization inhibitor according to the present invention refers to those that inhibit the polymerization reaction of the polymerizable monomer,
It can be used as needed. For example, in the recording layer before hologram recording, radicals generated by the polymerization initiator or polymerizable monomer due to slight light or heat in the storage environment may cause the polymerization reaction of the polymerizable monomer to start. It has the effect of inhibiting the progress of the polymerization reaction and improving the storage stability of the medium before hologram recording.

The type of polymerization inhibitor is not particularly limited as long as it can inhibit the polymerization reaction of the polymerizable monomer. Specifically, for example, phosphinates such as sodium phosphate and sodium hypophosphite, mercaptans such as mercaptoacetic acid, mercaptopropionic acid, 2-propanethiol, 2-mercaptoethanol and thiophenol, acetaldehyde and propionaldehyde. Aldehydes such as acetone, ketones such as methyl ethyl ketone, halogenated hydrocarbons such as trichlorethylene and perchlorethylene, terpinolene, α-terpinene, β-
terpenes such as terpinene and γ-terpinene, 1,4-cyclohexadiene, 1,4-cycloheptadiene, 1,4-cyclooctadiene, 1,4-heptadiene, 1,4-hexadiene, 2-methyl-1 ,4-pentadiene, 3,6-nonanedien-1-ol, 9
, 12-octadecadienol and other non-conjugated dienes, linolenic acid, γ-linolenic acid, methyl linolenate, ethyl linolenate, isopropyl linolenate, linolenic acids such as linolenic anhydride, linoleic acid, methyl linoleate, Linoleic acids such as ethyl linoleate, isopropyl linoleate and linoleic anhydride, eicosapentaenoic acid and eicosapentaenoic acids such as ethyl eicosapentaenoate, docosahexaenoic acid and docosahexaenoic acids such as ethyl docosahexaenoate, 2,6-di-t- butyl-p-cresol, p-methoxyphenol, diphenyl-p-benzoquinone, benzoquinone, hydroquinone, pyrogallol,
Resorcinol, phenanthraquinone, 2,5-toluquinone, phenol derivatives such as butylhydroxytoluene such as benzylaminophenol, p-dihydroxybenzene, 2,4,6-trimethylphenol, o-dinitrobenzene, p-dinitrobenzene , m
- nitrobenzene derivatives such as dinitrobenzene, N-phenyl-1-naphthylamine, N
- phenyl-2-naphthylamine, cupferron, phenothiazine, tannic acid, p-nitrosamine, chloranil, aniline, hindered aniline, iron(III) chloride, copper(I) chloride
I), triethylamine, hindered amines, nitroxy radicals including 2,2,6,6-tetramethylpiperidine 1-oxyl, triphenylmethyl radicals, and oxygen. As these components, conventionally known materials may be used singly, or two or more of them may be used in any combination and ratio.

<<About other additives>>
Other components contained in the recording layer-forming composition include solvents, plasticizers, dispersants, leveling agents, antifoaming agents, adhesion promoters, compatibilizers and sensitizers. As these components, conventionally known materials may be used singly, or two or more of them may be used in any combination and ratio.

<<Regarding the content of each material>>
The content of each component in the composition for forming a recording layer according to the present embodiment is arbitrary as long as it does not violate the gist of the present invention. Preferably.
The total amount of the matrix resin is usually 0.1% by mass or more, preferably 10% by mass or more,
More preferably, it is 35% by mass or more. Moreover, 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 equal to or higher than the above lower limit, it becomes easy to form the recording layer.

The content of the curing catalyst used to promote formation of the matrix resin is preferably determined in consideration of the bond formation rate of the matrix-forming components, and is usually 5% by mass or less, preferably 4% by mass or less, and more preferably 1% by mass. % or less. Moreover, it is preferable to use 0.005 mass % or more.
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. Also, it is usually 80% by mass or less, preferably 50% by mass or less, more preferably 30% by mass or less. Sufficient diffraction efficiency can be obtained when the content of the polymerizable monomer is more than the above lower limit, and the compatibility of the recording layer is maintained when it is less than the above upper limit.

The content of the photopolymerization initiator is usually 0.1% by mass or more, preferably 0.3% by mass or more,
It is usually 20% by mass or less, preferably 18% by mass or less, more preferably 16% by mass or less. Sufficient recording sensitivity can be obtained when the content of the photopolymerization initiator is higher than the above lower limit.
The content of the polymerization inhibitor is usually 0.001% by mass or more, preferably 0.005% by mass or more. Moreover, it is usually 30% by weight or less, preferably 10% by weight or less. When the content of the polymerization inhibitor is within the above range, it is possible to inhibit the progress of an unexpected polymerization reaction initiated by radicals generated by a slight amount of light or heat.
The total amount 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, more preferably 0.3 mm or more and 2 mm or less. Within this range, the selectivity of each hologram tends to be high during multiplex recording on the hologram recording medium, and the degree of multiplex recording can be increased. In addition, the light transmittance of the recording layer at the wavelength of the recording light can be maintained at a high level, enabling uniform recording over the entire recording layer in the thickness direction, and there is a tendency to realize multiplex recording with a high S/N ratio.

The medium in the present invention comprises a recording layer and, if necessary, a support and other layers.
A medium usually has a support, and a recording layer and other layers are laminated on this support to constitute the medium. However, if the recording layer or other layers have the strength and durability required for the medium, the medium need not have a support. Examples of other layers include protective layers, reflective layers,
An antireflection layer (antireflection film) and the like are included.

<Support>
There are no particular restrictions on the details of the support, 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 also not limited, but it is usually formed into a flat plate shape or a film shape.
There are no restrictions on the material that constitutes the support, and it may be transparent or opaque.

Examples of transparent support materials include acrylic, polyethylene terephthalate,
Organic materials such as polyethylene naphthoate, polycarbonate, polyethylene, polypropylene, amorphous polyolefin, polystyrene and cellulose acetate; and inorganic materials such as glass, silicon and quartz. Among these, polycarbonate, acryl, polyester, amorphous polyolefin, glass and the like are preferable, and polycarbonate, acryl, amorphous polyolefin and glass are particularly preferable.

On the other hand, examples of opaque support materials include metals such as aluminum; and transparent supports coated with metals such as gold, silver, and aluminum, or dielectrics such as magnesium fluoride and zirconium oxide. things, etc.

Although the thickness of the support is not particularly limited, it is usually preferably in the range of 0.05 mm or more and 1 mm or less. When the thickness of the support is at least the above lower limit value, the medium can have sufficient mechanical strength and the substrate can be prevented from warping. Further, when the thickness of the support is equal to or less than the above upper limit, the amount of light transmitted can be maintained, and an increase in cost can be suppressed.

Moreover, the surface of the support may be subjected to a surface treatment. This surface treatment is usually carried out to improve the adhesion between the support and the recording layer. Examples of the surface treatment include subjecting the support to corona discharge treatment and previously forming an undercoat layer on the support. here,
Compositions for the undercoat layer include halogenated phenols, or partially hydrolyzed vinyl chloride-vinyl acetate copolymers, polyurethane resins, and the like.

Furthermore, the surface treatment may be performed for purposes other than improving adhesion. Examples thereof include reflective coating processing for forming a reflective coating layer made of metal such as gold, silver and aluminum; dielectric coating processing for forming a dielectric layer such as magnesium fluoride and zirconium oxide. be done. Moreover, these layers may be formed as a single layer, or may be formed as two or more layers.
Moreover, these surface treatments may be provided for the purpose of controlling the gas or moisture permeability of the substrate. For example, the reliability of the medium can be further improved by giving the support sandwiching the recording layer a function of suppressing gas and moisture permeability.

Further, the support may be provided either on the upper side or the lower side of the recording layer of the medium in the present invention, or may be provided on both sides. However, when supports are provided on both upper and lower sides of the recording layer, at least one of the supports should be transparent so as to transmit active energy rays (excitation light, reference light, reproduction light, etc.).
Also, in the case of media having a support on one or both sides of the recording layer, transmission or reflection holograms can be recorded. In addition, when a support having reflective properties is used on one side of the recording layer, a reflective hologram can be recorded.
Furthermore, the support may be provided with patterning for data addressing. In this case, the patterning method is not limited, but for example, unevenness may be formed on the support itself, a pattern may be formed on the reflective layer described later, or a combination of these methods may be used.

<Protective layer>
The protective layer is a layer for preventing influences such as deterioration of sensitivity and storage stability due to oxygen and moisture in the recording layer. There is no restriction on the specific configuration of the protective layer, and any known configuration can be applied. For example, a layer made of a water-soluble polymer, an organic/inorganic material, or the like can be formed as a protective layer.
The formation position of the protective layer is not particularly limited. For example, it may be formed on the surface of the recording layer, between the recording layer and the support, or formed on the outer surface side of the support. It may also be formed between the support and another layer.

<Reflective layer>
The reflective layer is formed when the medium is configured as a reflective hologram medium. In the case of a reflective hologram recording medium, the reflective layer may be formed between the support and the recording layer, or may be formed on the outer surface of the support. preferably between
As the reflective layer, a known layer can be arbitrarily applied, and for example, a metal thin film or the like can be used.

<Anti-reflection film>
When the medium of the present invention is constructed as a hologram recording medium of either transmission type or reflection type, an antireflection film is provided on the side on which the object light and the reading light are incident and emitted, or between the recording layer and the support. may be provided. The antireflection film works to improve the efficiency of light utilization and to suppress the generation of ghost images.
Any known antireflection film can be used.

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention.

[raw materials used]
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)
・ Plaxel PCL-205U: polycaprolactone diol (molecular weight 530, manufactured by Daicel)
・ Plaxel PCL-305: polycaprolactone triol (molecular weight 550, manufactured by Daicel)
(Polymerizable monomer)
・ HLM201: 2-[[2,2-bis(4-dibenzothiophenylthiomethyl)-3
-(4-dibenzothiophenylthio)propoxy]carbonylamino]ethyl acrylate (photoinitiator)
· HLI02: 1-(9-ethyl-6-cyclohexanoyl-9H-carbazole-3
-yl)-1-(O-acetyloxime) methyl glutarate (curing catalyst)
・ Tris(2-ethylhexanoate) bismuth octylic acid solution (56% by weight of active ingredient, polymerization inhibitor)
・ 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl free radical (TEMPOL, manufactured by Tokyo Chemical Industry Co., Ltd.)

<<Preparation of TEMPOL masterbatch>>
TEMPOL: 0.03 g was dissolved in Duranate ^TM TSS-100: 2.97 g. Then here tris(2-ethylhexanoate)bismuth in octylic acid: 0
. After dissolving 0003 g, the mixture was stirred at 45° C. under reduced pressure and reacted for 2 hours.

<<Preparation of composition for recording layer and production of hologram recording medium>>
<Hologram recording medium>
Duranate ^TM TSS-100: 5.8207 g, polymerizable monomer HLM201:
2.0811 g, photopolymerization initiator HLI02: 0.0749 g, and TEMPOL masterbatch: 2.8095 g were dissolved to obtain liquid A.
Separately, Praxel PCL-205U: 3.949 g and Praxel PCL-305 (polycaprolactone triol (molecular weight 550)): 3.949 g were mixed (Plaxel PC
L-205U: Plaxel PCL-305 = 50:50 (weight ratio)) and tris(2-ethylhexanoate)bismuth in octyl acid solution: 0.00025 g were dissolved to prepare solution 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.
1955 g and 3.8045 g of liquid B were stirred and mixed.
Subsequently, the mixed solution was poured onto a slide glass with a spacer sheet of 0.5 mm thickness placed on two opposite edges, and the slide glass was placed on top of it. was heated for 24 hours to prepare a sample for evaluating the composition for a hologram recording medium. In this evaluation sample, a recording layer with a thickness of 0.5 mm was formed between slide glasses as a cover.

<<Production of hologram recording medium>>
<Hologram recording device>
FIG. 2 is a configuration diagram showing an outline of an apparatus used for hologram recording on a medium.
In FIG. 2, S is a sample of the hologram recording medium, and both M1 and M2 are mirrors. CS is the exposure time control shutter and BS is the beam shutter. PBS is a polarizing beam splitter, LED is a light source for post-exposure (an LED with a center wavelength of 405 nm manufactured by THORLAB), and LD is a laser light source for recording light that emits light with a wavelength of 405 nm (light around 405 nm is obtained). A single-mode laser manufactured by TOPTICA Photonics) is shown, and PD1 and PD2 are photodetectors.

<Hologram recording exposure>
Light with a wavelength of 405 nm generated from the LD is split by a PBS, and these are regarded as object light (M1 side) and reference light (M2 side), and recorded so that the angle formed by the two beams is 59.3°. Irradiation was performed so as to intersect on the surface. At this time, the bisector of the angle formed by the two beams (hereinafter referred to as the optical axis) is set perpendicular to the recording surface of the recording layer of the hologram recording medium,
Furthermore, the vibration planes of the electric field vectors of the two beams obtained by splitting were made perpendicular to the plane containing the two intersecting beams. The above case is assumed to be 0°, the beam shutter is opened, the direction of incidence of the two beams is fixed, and the direction of the hologram recording medium is changed to an angle outside the multiple recording exposure angle. The control shutter was opened for 650 milliseconds, the object beam and the reference beam were illuminated, and the deactivation of oxygen acting as a radical quencher was waited in the dark for 10 seconds. Then, while gradually changing the angle of the recording surface with respect to the optical axis, the exposure time control shutter is opened based on the exposure time schedule of formula (1) having the values of m, A, and x in Table 1, and the total number of multiplexes is Hologram recordings of 72, 100 and 180 were made. At this time, the exposure power density per beam is 10.2 mW/cm ² . Also,
The exposure time schedules for each example and each comparative example are set so that the total exposure time is the same.

<Post-exposure>
After the multi-recording exposure, the rotation angle was returned to 0°, a signal growth time of 120 seconds was waited in a dark state, and the post-exposure light source LED was irradiated at 4 J/cm ² to fix the recording.

<Hologram recording and reproduction>
The beam shutter in FIG. 2 was closed, and the recorded hologram was reproduced using the light on the side of the mirror M2 as reference light. Assuming that the light intensity detected by PD1 is the diffracted light I _dn and the light intensity detected by PD2 is the transmitted light _Itn , the diffraction efficiency η _n of the light diffracted from each interference pattern was calculated. At this time, the diffraction caused by the interference pattern during the preprocessing exposure is also reproduced, but is not included in the number of multiplexes.

<Judgment Criteria>
Based on the relationship between the dispersion σ ² of the diffraction efficiency and the average η _avg of the diffraction efficiency, the following evaluation criteria were set.
◎: σ ² ≤ 0.1 and 0.6 ≤ η _avg
○: σ ² ≤ 0.2 and 0.4 ≤ η _avg < 0.6, or 0.1 < σ ² ≤ 0.2 and 0
. 6≦η _avg
Δ: σ ² ≤ 0.3 and η _avg < 0.4, or 0.2 < σ ² ≤ 0.3 and 0.4 ≤ η
_avg
×: 0.3< ^σ2

<Evaluation results>
Table 1 shows the diffraction efficiencies of the optical elements obtained with the exposure time schedule of Equation 1 based on m, A, and x in Table 1.
FIGS. 3 and 4 show the results of reconstruction of the optical element obtained by multiple recording exposure of the hologram in Example 3 and Comparative Example 1, respectively.

From the examples and comparative examples, when multiple recording exposure is performed using the exposure time schedule based on formula (1), the dispersion of the diffraction efficiency of the resulting optical element is significantly reduced, and the average diffraction efficiency is also increased. confirmed.

The method for manufacturing an optical element of the present invention is useful as a means for widening the display color gamut and recording uniform diffraction efficiency for obtaining a bright AR image, particularly in optical elements used in AR glass light guide plates and the like.

Figure 2
S Hologram recording medium M1, M2 Mirror LD Semiconductor laser light source for recording light PD1, PD2 Photodetector LED LED light source for post-exposure BS Beam shutter PBS Polarization beam splitter CS Exposure time control shutter

Claims (5)

A method for producing an optical element, wherein multiple recording of holograms is performed on a medium having a recording layer containing a polymerizable compound and a photopolymerization initiator according to an exposure time schedule based on the following formula (1).

[In formula (1), T _n is the n-th recording exposure time (milliseconds), n is an integer of 1 or more and m or less, A is the first recording exposure time (milliseconds), and m is the total number of multiple recording exposures. is the number of times and is an integer of 2 or more, and x is a constant of 0.95 or more. ] 2. The method for manufacturing an optical element according to claim 1, wherein m in formula (1) is 20 or more. 3. The method for manufacturing an optical element according to claim 1, wherein A in the formula (1) is 3 milliseconds or longer. The method for manufacturing an optical element according to any one of claims 1 to 3, wherein the average diffraction efficiency of holograms multiplexed and recorded according to the exposure time schedule based on the formula (1) is 0.2 or more. . The method for manufacturing an optical element according to any one of claims 1 to 4, wherein the dispersion of the diffraction efficiency of each hologram multiple-recorded according to the exposure time schedule based on the formula (1) is 0.3 or less. .

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