JP2007206704A - Volume hologram recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a volume hologram recording method for a volume hologram recording medium, equipped with various functions that inorganic fine particles have and also ease of workability and formability of a polymer together. <P>SOLUTION: The recording medium comprises a composition for volume hologram recording, the composition containing (a) a compound (functional compound) having one or more polymerizable functional groups, (b) a photopolymerization initiator, and (c) inorganic fine particles, wherein the difference between the refractive indices of the inorganic fine particles and the refractive indices of a polymerized states of the functional compounds ranges from 0.03 to 1.3. The volume hologram recording method comprises forming interference fringes by interference of coherent light on the recording medium, generating a stripe distribution of the inorganic fine particles that correspond to a dark part in the polymer of the functional compound, and thereby forming a refractive index distribution that is recorded as a hologram. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a volume hologram recording method for recording interference fringes with a difference in refractive index inside a recording layer.

  The hologram records a pattern created by two interference fringes on a photosensitive material, and when this is irradiated with the same laser light from the same direction as the reference light, a three-dimensional image that looks exactly the same as the original object appears. That's it. This hologram technology is expected in the fields of three-dimensional image display devices, images, large-capacity memory of bit information, and diffractive optical elements.

Holograms are classified into several types according to the recording pattern of interference fringes. In recent years, so-called volume holograms that record interference fringes with a difference in refractive index inside a recording layer are being applied to applications such as three-dimensional displays and optical elements due to their high diffraction efficiency and excellent wavelength selectivity.
Conventionally, silver halide and dichromated gelatin have been used as photosensitive materials for recording such volume holograms, but these require the use of wet development and complicated development and fixing treatments, so that the holograms are industrially used. It is unsuitable for production, and has the problem that the image disappears after recording due to moisture absorption.

In order to overcome the above-mentioned problems of the prior art, it is possible to make a volume hologram by a simple dry process using a photopolymer, as described in US Pat. No. 3,658,526 and US Pat. No. 3,993. 485, etc. In addition, regarding the presumed formation mechanism of the hologram by the photopolymer, “Applied Optics”.
)] [B. L. Booth (B. L. Booth), Vol. 3, 593-601 (1975), and W.W. J. et al. Tomlinson, E.J. A. No. 15 of EA Chandross, No. 2, pp. 534-541 (1976)]. However, these initial techniques did not reach the conventional techniques in terms of refractive index modulation, which is a particularly important performance.

For example, U.S. Pat. No. 4,942,102 and U.S. Pat. No. 4,942,112 have been proposed as improved techniques, but these are used to improve the refractive index modulation capability. Since a non-reactive plasticizer or the like is used, there is a problem in the film strength of the formed hologram, and the refractive index modulation is not sufficient.
In JP-A-5-107999, therefore, a photopolymer composition, that is, (a) a cationic polymerizable compound, (b) a radical polymerizable compound, (c) the above ( (B) a photo-radical polymerization initiator system for polymerizing, and (d) a cationic polymerization initiator system for polymerizing the (a), and the average refractive index of the (a) is A composition having a refractive index lower than the average refractive index has been proposed, and the use of this composition is said to provide a hologram having excellent diffraction efficiency, wavelength selectivity, refractive index modulation, film strength, and the like.

However, the photopolymer-based composition is composed only of organic materials, and is still insufficient with respect to mechanical strength and environmental stability, and it is difficult to add new functions such as nonlinear optical characteristics. There was a problem.
US Pat. No. 3,658,526 US Pat. No. 3,993,485 US Pat. No. 4,942,102 U.S. Pat. No. 4,942,112 Japanese Patent Laid-Open No. 5-107999 Applied optics (APPLIED OPTICS), B.I. L. Booth (B. L. Booth), Vol. 3, 593-601 (1975) Applied Optics, W.W. J. et al. Tomlinson, E.J. A. No. 15 of EA Chandross, No. 2, pp. 534-541 (1976)

  An object of the present invention is to record a volume hologram in which a hologram having a high diffraction efficiency is permanently formed by employing a recording medium using a composition for volume hologram recording in which inorganic fine particles are dispersed in a functional compound. It is to provide a method.

In the recording medium, when a metal oxide is used as the inorganic fine particles, the high ultraviolet blocking function can be provided, and when the semiconductor fine particles are used, nonlinear optical characteristics can be provided.
That is, another object of the present invention is to disperse the inorganic fine particles in the functional monomer so that the volume hologram has various functions of the inorganic fine particles, the processability of the polymer, and the ease of moldability. An object of the present invention is to provide a method for recording a volume hologram on a recording medium using the recording composition.

  The gist of the present invention includes (a) a compound having one or more polymerizable functional groups (functional compound), (b) a photopolymerization initiator, and (c) inorganic fine particles, and the refractive index of the inorganic fine particles. And a difference between the refractive index of the polymerization state of the functional compound is 0.03 or more and 1.3 or less, the recording medium using the volume hologram recording composition is characterized in that coherent light Volume hologram recording in which interference fringes are formed by interference, and then a stripe distribution of inorganic fine particles corresponding to dark portions is formed in the polymer of the functional compound, and a hologram is recorded by the refractive index distribution formed thereby. Lies in the way.

  The present invention also includes (a) a compound having one or more polymerizable functional groups (functional compound), (b) a photopolymerization initiator, and (c) inorganic fine particles, and the refractive index of the inorganic fine particles The difference between the refractive index in the polymerization state of the functional compound is from 0.03 to 1.3, and two laser beams are applied to a recording medium using a volume hologram recording composition. Simultaneously irradiate to form interference fringes in which bright and dark portions are arranged in stripes on the medium, and then a stripe distribution of inorganic fine particles corresponding to the dark portions is formed in the polymer of the functional compound, thereby forming The present invention relates to a volume hologram recording method in which a hologram is recorded with a refractive index distribution.

The compound (functional compound) having one or more polymerizable functional groups (a) is preferably an acrylic ester or methacrylic ester monomer.
The inorganic fine particles preferably have a particle size of 1 nm or more and 400 nm or less.
The proportion of the inorganic fine particles in the total volume of the inorganic fine particles and the resin component in the polymerized state is preferably 3% by volume or more and 50% by volume or less.

According to the present invention, a volume hologram in which a hologram with high diffraction efficiency is permanently formed is obtained by employing a recording medium using a volume hologram recording composition in which inorganic fine particles are dispersed in a functional compound. I can do it.
In addition, according to the present invention, by dispersing inorganic fine particles in a functional compound, various functions (such as ultraviolet blocking function, nonlinear optical characteristics, mechanical strength and environmental stability) and polymers (functional It is possible to provide a method for recording a volume hologram on a recording medium using a volume hologram recording composition having both the processability and the moldability of the polymer of the functional compound.

  The composition for volume hologram recording used in the volume hologram recording method of the present invention comprises at least (a) a compound having one or more polymerizable functional groups (hereinafter referred to as component (a), a functional compound, or a functional monomer). (B) a photopolymerization initiator that initiates polymerization of the component (a) (hereinafter may be referred to as component (b)), (c) inorganic fine particles (hereinafter referred to as component (c)) There are some).

ADVANTAGE OF THE INVENTION According to this invention, the volume hologram in which a hologram with high diffraction efficiency is formed permanently can be provided by employ | adopting the composition for volume hologram recording which disperse | distributed the inorganic fine particle in the functional compound.
In order to obtain a hologram with high diffraction efficiency, it is necessary to increase the difference in refractive index between the area corresponding to the bright part and the area corresponding to the dark part of the interference fringes.

As the volume hologram recording composition used in the present invention, conventionally, a composition composed of a plurality of functional monomers having different refractive indexes and a composition composed of a liquid organic substance and a functional monomer are known. Since the refractive index is usually limited to about 1.3 to 1.6, there is a limit in increasing the refractive index difference in the combination of organic substances.
In contrast, inorganic fine particles made of dielectrics, semiconductors, metals, etc. have various refractive indexes, and many substances have a refractive index of 2 or more. For this reason, even in combination with an organic substance, a large difference in refractive index can be obtained, so that a hologram having a high diffracted light rate can be obtained.

In addition, conventional volume hologram recording compositions made of only organic substances generally have low mechanical strength and tend to be inferior in environmental stability, nonlinear optical characteristics, and the like.
According to the present invention, by incorporating inorganic fine particles, the features such as high mechanical strength, high environmental stability, and excellent nonlinear optical properties possessed by the inorganic fine particles are added to the photopolymer-based volume hologram composition. A hologram can be recorded on a recording medium using the volume hologram recording composition.

Next, the volume hologram recording method of the present invention will be described.
First, when two laser beams are simultaneously irradiated onto the medium, interference fringes are formed on the medium in which bright portions and dark portions are arranged in stripes.
Then, the functional monomer (functional compound) (a) starts to polymerize in the bright part of the medium, and the concentration of the functional monomer in the bright part decreases. Accordingly, a concentration gradient of the functional monomer is generated in the dark part and the bright part, and the functional monomer is moved and supplied from the dark part to the bright part, and further polymerization proceeds.

Instead, the inorganic fine particles move from the bright part to the dark part. In addition, the distribution of inorganic fine particles is biased between the bright and dark areas.
When a certain amount of time has passed, the polymerization of the functional monomer finally proceeds even in the dark part, and the entire recording layer of the medium becomes a polymer.
In this way, a striped distribution of inorganic fine particles is formed in the polymer of the functional monomer corresponding to the dark part. Since the refractive index of the inorganic fine particles is different from the refractive index in the polymerization state of the functional monomer, a refractive index distribution is formed in the recording layer, and a hologram is recorded. At the time of reproduction, when the region where the interference fringes are formed is irradiated with reproduction light, diffraction occurs and a hologram image is reproduced.

Hereinafter, the structure of the volume hologram recording composition used in the present invention will be described in detail.
Component (a) contains, for example, an ethylenically unsaturated compound. This ethylenically unsaturated compound is a compound having at least one radically polymerizable ethylenically unsaturated bond in the molecule that undergoes addition polymerization by the action of the photopolymerization initiator of component (b) and may be crosslinked or cured in some cases. is there. In addition, the meaning of the sensitive compound in the present invention is a concept corresponding to a so-called polymer substance, and therefore includes a dimer, a trimer, and an oligomer in addition to a monomer in a narrow sense. Is.

  Examples of the functional monomer having an ethylenically unsaturated bond include unsaturated carboxylic acid, ester of aliphatic polyhydroxy compound and unsaturated carboxylic acid; ester of aromatic polyhydroxy compound and unsaturated carboxylic acid; unsaturated carboxylic acid And esters obtained by an esterification reaction of a polyvalent carboxylic acid and a polyvalent hydroxy compound such as the above-mentioned aliphatic polyhydroxy compound and aromatic polyhydroxy compound.

  The ester of the aliphatic polyhydroxy compound and the unsaturated carboxylic acid is not limited, but specific examples include ethylene glycol diacrylate, triethylene glycol diacrylate, trimethylol propane triacrylate, trimethylol ethane triacrylate, pentaerythritol. Diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, acrylic acid esters such as glycerol acrylate, methacrylic acid in which these acrylates of these exemplified compounds are replaced with methacrylate Acid ester, itaconic acid ester instead of itaconate, crotonay There are maleic acid esters in which instead of the crotonic acid ester or maleate was replaced.

Examples of the ester of an aromatic polyhydroxy compound and an unsaturated carboxylic acid include hydroquinone diacrylate, hydroquinone dimethacrylate, resorcin diacrylate, resorcin dimethacrylate, pyrogallol triacrylate, and the like.
The ester obtained by the esterification reaction of an unsaturated carboxylic acid with a polyvalent carboxylic acid and a polyvalent hydroxy compound is not necessarily a single substance, but typical examples include acrylic acid, phthalic acid and ethylene glycol. There are condensates, condensates of acrylic acid, maleic acid and diethylene glycol, condensates of methacrylic acid, terephthalic acid and pentaerythritol, condensates of acrylic acid, adipic acid, butanediol and glycerin.

  In addition to the above ester (meth) acrylates, there are so-called urethane (meth) acrylates and epoxy (meth) acrylates. The former can be prepared by an addition reaction between a polyvalent isocyanate and a hydroxyacrylic ester, and the latter can be prepared by an addition reaction between a polyvalent epoxy compound and a hydroxyacrylic ester.

Other examples of the ethylenically unsaturated compound used in the present invention include acrylamides such as ethylene bisacrylamide; allyl esters such as diallyl phthalate; vinyl group-containing compounds such as divinyl phthalate.
In the present invention, among the ethylenically unsaturated compounds, acrylate or methacrylate monomers are particularly preferred.

  Each functional monomer may be used alone, or may be used by mixing as necessary.

Component (b) is a polymerization initiator for initiating polymerization of the functional monomer of component (a), and includes cationic polymerization initiators, but is particularly preferably a radical photopolymerization initiator. The photo radical polymerization initiator generates active radicals by light for first exposure for producing a hologram.

  The radical polymerization initiator is not particularly limited as long as it functions as the polymerization initiator of component (a). For example, azo compounds, azide compounds, organic peroxides, onium salts, bisimidazole derivatives, titanocene compounds , Iodonium salts, organic thiol compounds, halogenated hydrocarbon derivatives and the like are used. Of these, titanocene compounds are preferred.

  The titanocene compound is not particularly limited, and specifically, di-cyclopentadienyl-Ti-di-chloride, di-cyclopentadienyl-Ti-bis-phenyl, di-cyclopentadienyl-Ti. -Bis-2,3,4,5,6-pentafluorophen-1-yl, dicyclopentadienyl-Ti-bis-2,3,5,6-tetrafluorophen-1-yl, di-cyclo Pentadienyl-Ti-bis-2,4,6-trifluorophen-1-yl, di-cyclopentadienyl-Ti-bis-2,6-difluorophen-1-yl, di-cyclopenta Dienyl-Ti-bis-2,4-di-fluorophen-1-yl, di-methylcyclopentadienyl-Ti-bis-2,3,4,5,6-pentafluorophen-1-yl, Di-methyl Lopentadienyl-Ti-bis-2,3,5,6-tetrafluorophen-1-yl, di-methylcyclopentadienyl-Ti-bis-2,6-difluorophen-1-yl, di-cyclopentadi And enyl-Ti-bis-2,6-difluoro-3- (pyr-1-yl) -phen-1-yl.

The radical photopolymerization initiator used in the present invention may be used alone or in combination with a sensitizer which is a component that absorbs light.
Specific examples of preferred sensitizers include, for example, 2,6-diethyl-1,3,5,7,8-pentamethylpyromethene-BF ₂ complex, 1,3,5,7,8-pentamethylpyrrole. Meten
Pyrromethene complexes such as BF ₂ complex; xanthene dyes such as eosin, ethyl eosin, erythrosine, fluorescein, rose bengal; 1- (1-methylnaphtho [1,2-d] thiazole-2 (1H) -ylidene-4 -(2,3,6,7) tetrahydro-1H, 5H-benzo [ij] quinolizin-9-yl) -3-buten-2-one, 1- (3-methylbenzothiazole-2 (3H) -ylidene Ketothiazoline compounds such as -4- (p-dimethylaminophenyl) -3-buten-2-one; 2- (p-dimethylaminostyryl) -naphtho [1,2-d] thiazole, 2- [4- Styryl or phenylbutadienyl heterocyclic compounds such as (p-dimethylaminophenyl) -1,3-butadienyl] -naphtho [1,2-d] thiazole; 2 4-diphenyl-6- (p-dimethylaminostyryl) -1,3,5-triazine, 2,4-diphenyl-6-(([2,3,6,7] tetrahydro-1H, 5H-benzo [ij ] Nanthryl-(([2,3,6,7] tetrahydro-1H, 5H-benzo [ij]) such as quinolizin-9-yl) -1-ethen-2-yl) -1,3,5-triazone Aminophenyl unsaturated ketone compounds such as quinolizin-9-yl) -1-ethen-2-yl) ketone, 2,5-bis (p-dimethylaminocinnamylidene) cyclopentanone; 20 Polyphenylporphyrins such as tetraphenylporphyrin, hematoporphyrin, etc. Examples of suitable sensitizers have been given above, and among these, pyromethene complexes are particularly preferred.

  As described above, the sensitizer is often a colored compound such as a dye for absorbing visible laser light. However, when the final hologram requires colorless transparency (for example, in automobiles) As a sensitizer for use as a head-up display, use of a cyanine dye as described in JP-A-58-29803, JP-A-1-287105, and JP-A-3-5569 Is preferred.

Moreover, when a titanocene compound is used as a photoradical generator, a pyromethene compound is preferably used as a sensitizer.
The inorganic fine particles of component (c) preferably have a refractive index difference of 0.01 or more from the polymerization state of the functional monomer of component (a). This is because it is desirable that the difference in refractive index between the inorganic fine particles and the functional monomer polymerized state is large in order to increase the final refractive index modulation when the functional monomer is polymerized by hologram exposure. More preferably, it is 0.03 or more.

However, the refractive index difference is preferably 1.3 or less. This is because in consideration of light scattering, the larger the refractive index difference, the smaller the particle size. More preferably, it is 1.1 or less.
In the present invention, the “polymerization state of the functional monomer” means a state in which the functional monomer is completely polymerized.

The particle size of the inorganic fine particles of component (c) is 400 nm or less. This is because if it is too large, light scattering tends to occur. More preferably, it is 200 nm or less. The smaller the particle size, the better. However, the smaller the particle size, the more difficult it is to manufacture.
Further, since the refractive index in the volume hologram composition is determined by the volume ratio of the constituent components, the refractive index difference that can be achieved increases as the volume ratio of the inorganic fine particles to the volume of the resin component increases. Therefore, the proportion of the inorganic fine particles in the total volume of the inorganic fine particles and the resin component in the polymerized state is preferably 3% by volume or more, and more preferably 5% by volume or more.

However, there is a limit to the amount of inorganic fine particles that can be dispersed in the composition, and if it is too large, it is difficult to disperse, so 50 volume% or less is preferable, and more preferably 40 volume% or less.
Here, the resin component is, for example, the functional monomer (a), but when the volume hologram composition includes a binder resin, the functional monomer and the binder resin (a) are referred to.

  The component (c) is not particularly limited as long as it is an inorganic fine particle capable of achieving the object of the present invention. For example, titanium oxide, silicon oxide, zinc oxide, aluminum oxide, antimony oxide, chromium oxide, cerium oxide, yttrium oxide Metal oxides such as zirconium oxide, tin oxide, copper oxide, iron oxide, magnesium oxide, manganese oxide, holmium oxide, bismuth oxide, cobalt oxide, erbium oxide, gadolinium oxide, indium oxide, nickel oxide, strontium oxide, ytterbium oxide Materials: nitrides such as silicon nitride, titanium nitride, zirconium nitride, niobium nitride; dielectric fine particles such as carbides such as silicon carbide, titanium carbide, molybdenum carbide, tungsten carbide, group IV semiconductors such as Si, Ge, CdS, CdSe , ZnSe, CdTe, Z II-VI group semiconductor particles such as S, HgS, HgSe, III-V group semiconductor particles such as GaAs, InP, InSb, IV-VI group semiconductor particles such as PbS, PbSe, gold, silver, copper, nickel, aluminum, There are no particular limitations as long as they are fine metal particles such as iron, cobalt, tungsten, molybdenum, niobium, and the like and can be uniformly dispersed in the functional monomer.

  In order to achieve uniform dispersion, it is preferable that the surface is chemically modified at the time of preparing the fine particles, or a treatment such as addition of a dispersant is performed after the fine particles are formed. The fine particles can be used alone, in a mixture, or in a complex. In addition, a material having a photocatalytic reaction such as titanium oxide may be subjected to a treatment such as coating the surface with a silicon compound or the like as necessary in order to prevent the resin from being decomposed by the reaction.

In addition to the components (a) to (c) described above, the recording layer in the volume hologram recording medium on which the hologram is recorded according to the present invention, if necessary, a sensitizer, a chain transfer agent, a plasticizer, a colorant, etc. These additives may be added.
In addition, a binder resin may be added as a binder in order to make the film thickness uniform and allow the interference film formed by polymerization by light irradiation to exist stably.

As described above, according to the volume hologram recording method of the present invention, interference fringes are formed on the volume hologram recording medium by interference of coherent light, and then bright portions and dark portions are arranged in stripes. In the coalescence, a striped distribution of inorganic fine particles is formed corresponding to the dark portion, and a hologram is recorded by the refractive index distribution formed thereby. Therefore, the volume hologram recording medium used in the method of the present invention does not necessarily need to use a binder resin blended in a conventional recording medium material. However, as long as the effects of the present invention are not impaired, the binder resin exemplified below may be included in the volume hologram recording medium.
Binder resins preferably have good compatibility with functional monomers. Specific examples thereof include chlorinated polyethylene, polymethyl methacrylate, copolymers of methyl methacrylate and other (meth) acrylic acid alkyl esters, vinyl chloride and acrylonitrile. Examples include copolymers, polyvinyl acetate, polyvinyl alcohol, polyvinyl formal, polyvinyl butyral, polyvinyl pyrrolidone, ethyl cellulose, and acetyl cellulose.

  In order to make a volume hologram recording medium using the volume hologram recording composition, the component (a), the component (b), and the component (c) are mixed with a sensitizer and a binder resin as necessary, and left as it is. It may be coated on a transparent support without using a solvent, or a solvent or an additive may be added to and mixed with these mixtures, and this is coated on a support and dried to form a recording layer. Subsequently, a transparent support or a protective layer for blocking oxygen can be provided on the recording layer.

  The solvent is not particularly limited as long as it has sufficient solubility with respect to the components used and gives good coating properties. For example, methyl cellosolve, ethyl cellosolve, methyl cellosolve acetate, ethyl cellosolve acetate, etc. Cellosolve solvents, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monobutyl ether acetate, dipropylene glycol dimethyl ether and other propylene glycol solvents, Butyl acetate, amyl acetate, ethyl acetate, butyl acetate, diethyl oxalate, ethyl pyruvate, ethyl-2- Ester solvents such as loxybutyrate ethyl acetoacetate, methyl lactate, ethyl lactate, methyl 3-methoxypropionate, alcohol solvents such as butanol, heptanol, hexanol, diacetone alcohol, furfuryl alcohol, methyl isobutyl ketone, cyclohexanone, Examples thereof include ketone solvents such as methyl amyl ketone, highly polar solvents such as dimethylformamide and dimethylacetamide N-methylpyrrolidone, mixed solvents thereof, and those obtained by adding aromatic hydrocarbons thereto. The proportion of the solvent used is usually in the range of about 1 to 20 times by weight with respect to the total amount of the volume hologram composition.

As the transparent support, a transparent glass plate, an acrylic plate, a polyethylene terephthalate film, a polyethylene film, or the like is used.
As the coating method, conventionally known methods such as spin coating, wire bar coating, dip coating, air knife coating, roll coating, blade coating, and curtain coating can be used.

As the protective layer, a known technique for preventing adverse effects such as a decrease in sensitivity due to oxygen and deterioration in storage stability, for example, application of a water-soluble polymer or the like can be used.
The volume hologram recording medium can be used for three-dimensional image display, large-capacity memory for images, bit information, diffractive optical elements, and the like.

Next, the present invention will be described more specifically with reference to examples.
Example 1
Functional monomer (the following compound (I)) 5 g
Silica (SiO ₂ ) fine particles 5g
0.1 g of photopolymerization initiator (the following titanocene compound (II))
45g of solvent (toluene)

シリカ微粒子の屈折率は１．４６、官能性モノマー（Ｉ）の重合状態における屈折率は１．６０であり、両者の屈折率差は０．１４であった。
シリカ微粒子の密度は２．１ｇ／ｃｍ³であるから、その体積は５／２．１＝２．３８
ｃｍ³である。官能性モノマー（Ｉ）の重合状態における密度は１．２５ｇ／ｃｍ³であるから、その体積は５／１．２５＝４ｃｍ³である。従ってシリカ微粒子と官能性モノマー
（Ｉ）の重合状態の体積に占めるシリカ微粒子の割合は、２．３８／（２．３８＋４）＝０．３７．３、即ち３７．３体積％であった。

The refractive index of the silica fine particles was 1.46, the refractive index in the polymerization state of the functional monomer (I) was 1.60, and the refractive index difference between them was 0.14.
Since the density of the silica fine particles is 2.1 g / cm ^3, the volume is 5 / 2.1 = 2.38
cm ³ . Since the density of the functional monomer (I) in the polymerization state is 1.25 g / cm ³ , the volume is 5 / 1.25 = 4 cm ³ . Therefore, the ratio of the silica fine particles to the volume of the polymerization state of the silica fine particles and the functional monomer (I) was 2.38 / (2.38 + 4) = 0.37.3, that is, 37.3 vol%.

The above mixture was stirred at room temperature, and further ultrasonically applied to sufficiently disperse.
The particle size of the silica fine particles in the dispersion was 97.1 nm as a median value as measured by a Microtrac UPA particle size distribution meter (manufactured by LEED & NORTHRUP) by the Doppler scattering method.
Next, a polyethylene terephthalate film having a thickness of 50 μm is attached as a spacer to both ends of the slide glass, the mixture is dropped onto the center of the slide glass (region sandwiched between the spacers), and dried under reduced pressure at 80 ° C. for 10 minutes in a vacuum oven. A recording layer was formed. Thereafter, a slide glass was placed on the volume hologram recording medium.

The recording medium was subjected to two-beam interference exposure using the apparatus shown in FIG. The medium 1 was subjected to two-beam interference exposure at an exposure power density of 5 mW / cm ² using an argon ion laser 2 having a wavelength of 514.5 nm. The light emitted from the argon ion laser 2 is split into two by a half mirror 4 through a beam expander 3 and irradiated onto the medium 1 through mirrors 5 and 6, respectively, and interference fringes of both lights are recorded to form a hologram. The

At the same time, the hologram formation process was monitored by evaluating the diffraction efficiency by irradiating the medium 1 with a helium neon laser 7 having a wavelength of 632.8 nm, which is not exposed to the medium 1, and detecting the diffracted light with the photodetector 10.
A graph showing the change of the diffraction efficiency of this sample with time is shown in FIG. The diffraction efficiency increased rapidly and reached 30% in about 50 seconds, and thereafter high diffraction efficiency was maintained. That is, it was confirmed that a hologram having a diffraction efficiency of about 30% was permanently formed.

(Example 2)
Functional monomer (the following compound (III)) 8g
Titania (TiO ₂ ) fine particles 17g
Photopolymerization initiator (the titanocene compound (II)) 0.08 g
Solvent (Mixed solvent of methyl isobutyl ketone and butanol (4: 1)) 75g

チタニア微粒子の屈折率は２．５５、官能性モノマー（ＩＩＩ）の重合状態における屈折率は１．５３であり、両者の屈折率差は１．０２であった。
チタニア微粒子の密度は３．９５ｇ／ｃｍ³であるから、その体積は１７／３．９５＝
４．３０ｃｍ³である。官能性モノマー（ＩＩＩ）の重合状態における密度は１．１６ｇ
／ｃｍ³であるから、その体積は８／１．１６＝６．９０ｃｍ³である。従ってチタニア微粒子と官能性モノマー（ＩＩＩ）の重合状態の体積に占めるチタニア微粒子の割合は、４．３０／（４．３０＋６．９０）＝０．３８４、即ち３８．４体積％であった。

The refractive index of the titania fine particles was 2.55, the refractive index in the polymerization state of the functional monomer (III) was 1.53, and the refractive index difference between the two was 1.02.
Since the density of the titania fine particles is 3.95 g / cm ³ , the volume is 17 / 3.95 =
4.30 cm ³ . The density of the functional monomer (III) in the polymerized state is 1.16 g.
Since a / cm ^3, its volume is 8 / 1.16 = 6.90cm ^3. Therefore, the ratio of the titania fine particles in the polymerization volume of the titania fine particles and the functional monomer (III) was 4.30 / (4.30 + 6.90) = 0.384, that is, 38.4% by volume.

The above mixture was stirred at room temperature, and further dispersed by applying ultrasonic waves.
The particle size of the titania fine particles in the dispersion was measured with a Microtrac UPA particle size distribution meter (manufactured by LEED & NORTHHRUP) by the Doppler scattering method, and the median value was 66.8 nm.
Next, a polyethylene terephthalate film having a thickness of 50 μm is attached as a spacer to both ends of the slide glass, the mixture is dropped onto the center of the slide glass (region sandwiched between the spacers), and dried under reduced pressure at 40 ° C. for 10 minutes in a vacuum oven. A recording layer was formed. Thereafter, a slide glass was placed on the volume hologram recording medium.

The recording medium was subjected to two-beam interference exposure in the same manner as in Example 1 using the apparatus shown in FIG.
At the same time, the hologram formation process was monitored by evaluating the diffraction efficiency by irradiating the medium 1 with a helium neon laser 7 having a wavelength of 632.8 nm, which is not exposed to the medium 1, and detecting the diffracted light with the photodetector 10. As a result, it was confirmed that a hologram having a diffraction efficiency of about 30% was permanently formed.

(Comparative example)
A volume hologram recording medium was produced in the same manner as in Example 1 except that it did not contain silica (SiO ₂ ) fine particles.
The medium shown in FIG. 1 was subjected to two-beam interference exposure in the same manner as in Example 1 to attempt to record a volume hologram. A graph showing the change of the diffraction efficiency of this sample with time is shown in FIG. Diffraction efficiency once improves, but decreases with time and eventually disappears. Since this is a single component of a functional monomer, it corresponds to the loss of refractive index modulation when polymerized as a whole.

It is a conceptual diagram of the two-beam interference exposure for the volume hologram recording medium. It is a graph showing the change by the time of the diffraction efficiency (Diffraction Efficiency) of the volume hologram recording medium in Example 1 and a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hologram recording medium 2 Ar + laser 3 Beam expander 4 Half mirror 5, 6, 8, 9 Mirror 7 He-Ne laser 10 Photodetector

Claims (5)

  (A) a compound (functional compound) having one or more polymerizable functional groups, (b) a photopolymerization initiator, and (c) a refractive index of the inorganic fine particles, and the functional compound. Interference fringes are formed by interference of coherent light on a recording medium using a volume hologram recording composition, wherein the difference between the refractive index of the polymerized state is 0.03 or more and 1.3 or less Next, a volume hologram recording method in which a stripe distribution of inorganic fine particles corresponding to dark portions is formed in the polymer of the functional compound, and a hologram is recorded by a refractive index distribution formed thereby.   (A) a compound (functional compound) having one or more polymerizable functional groups, (b) a photopolymerization initiator, and (c) a refractive index of the inorganic fine particles, and the functional compound. The difference between the refractive index of the polymerized state of the recording medium is 0.03 or more and 1.3 or less, and the recording medium using the volume hologram recording composition is irradiated with two laser beams simultaneously. An interference fringe in which bright and dark portions are arranged in stripes is formed on the top, and then a stripe distribution of inorganic fine particles corresponding to the dark portions is formed in the polymer of the functional compound, and a refractive index distribution formed thereby. A volume hologram recording method in which a hologram is recorded by the method.   The volume hologram recording method according to claim 1 or 2, wherein the compound (functional compound) having at least one polymerizable functional group (a) is a monomer of an acrylate ester or a methacrylate ester.   The volume hologram recording method according to claim 1, wherein the inorganic fine particles have a particle size of 1 nm or more and 400 nm or less. 5. The volume hologram recording method according to claim 1, wherein a ratio of the inorganic fine particles to a total volume of the inorganic fine particles and the resin component in a polymerization state is 3% by volume or more and 50% by volume or less.

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