JP6701791B2 - Holographic recording medium recording method and recording apparatus - Google Patents

Description

  The present invention relates to a recording method and a recording device for a hologram type optical recording medium.

  Holographic recording media, which have been drawing attention in recent years, are recording media that utilize the interference and diffraction phenomena of light. The hologram is a recording method for stereoscopically recording 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 a recording layer, and the photosensitive material chemically changes according to an interference pattern to locally change optical characteristics, thereby recording information data. It can be classified into several types depending on what kind of optical characteristics are changed. However, the volume hologram medium for recording by making a difference in refractive index in the recording layer having a certain thickness or more has high diffraction efficiency and It is believed to be advantageous due to wavelength selectivity.

  An example of the volume hologram recording medium is a write-once type that does not require wet treatment or bleaching treatment, and the composition of the recording layer is generally a matrix resin in which a photoactive compound is compatible. For example, there is a photopolymer system in which a matrix resin is combined with a photopolymerization initiator as a photoactive compound and a polymerizable monomer capable of radical polymerization or cation polymerization.

The photopolymer here means a material including at least a matrix resin, a polymerizable reactive compound, and a photopolymerization initiator.
When recording a hologram, if there is a recording layer made of a photopolymer in the part where the reference light and the information light intersect to form an interference fringe, the photopolymerization initiator chemically reacts in the part of the interference fringe where the light intensity is high. To become an active substance, which acts on the polymerizable reactive compound to polymerize the reactive compound. At this time, if there is a difference in the refractive index between the matrix resin and the polymer formed from the polymerizable reactive compound, the interference fringes become the refractive index difference and are fixed in the recording layer. Further, when the polymerizable reactive compound is polymerized, the reactive compound is diffused from the periphery, and the concentration distribution of the reactive compound or the polymer of the reactive compound is generated inside the recording layer. According to this principle, the interference pattern is recorded on the hologram recording medium as a refractive index difference. Furthermore, by changing the crossing angle of the reference light and the information light, different data can be recorded at the same position in an overlapping manner.

On the other hand, only the reference light is used during data reproduction. When the reference light is incident at the same angle as when the information was recorded, the recorded hologram acts as a diffraction grating and guides the recorded information as a reproduction signal.
The photopolymer method is a practical and promising method that can achieve both high diffraction efficiency and dry processing, but it has high sensitivity, sufficient diffraction efficiency, and high S/N ratio for recording, and achieves high multiplicity. A composition is required, and a hologram recording medium having excellent stability and reliability is also desired.

It is known that a pre-exposure process of irradiating a recording area of the hologram recording medium with a predetermined pre-exposure light is necessary before recording on the hologram recording medium by the photopolymer method. In the pre-exposure treatment, as described in Patent Document 1, the polymerizable reactive compound in the photopolymer and the polymerization inhibitor added to maintain the storage stability of the photopolymerization initiator are treated with a pre-exposure light. It is performed to inactivate by irradiation. Therefore, if this pre-exposure treatment is insufficient, the polymerization of the polymerizable reactive compound during hologram recording is hindered, and the interference pattern is not sufficiently recorded. On the other hand, if the pre-exposure treatment is excessive, the polymerizable reactive compound in the photopolymer reacts before hologram recording, and in this case too, the interference pattern is not sufficiently recorded, resulting in high diffraction efficiency and high multiplicity. It becomes impossible to record the hologram. Therefore, it is necessary to perform an appropriate pre-exposure process.

  On the other hand, in order to obtain high diffraction efficiency and high multiplicity in the volume hologram medium, a method of thickening the recording layer of the hologram recording medium is generally used. However, when the recording layer becomes thick, especially when the light transmittance of the hologram recording medium is not sufficient, the pre-exposure process tends to be excessive near the surface of the recording layer on the irradiation side of the pre-exposure light, and the depth of penetration of light is increased. As the number increases, the pre-exposure process tends to become insufficient. Therefore, since a concentration difference between the polymerizable reactive compound and the photopolymerization initiator is formed in the thickness direction of the recording layer, uniform recording cannot be performed in the thickness direction of the recording layer, and high diffraction efficiency and high There was a problem that the severity could not be obtained.

  Patent Document 2 describes a technique of performing appropriate pre-exposure processing by irradiating pre-exposure light from both sides of the hologram recording medium of a photopolymer type. However, in this document, the reaction of the polymerization inhibitor is not taken into consideration, and it is difficult to carry out an appropriate pre-exposure treatment capable of obtaining high diffraction efficiency and high multiplicity by the method described.

JP-A-7-5796 JP, 2014-51060, A

  The present invention has been made in view of the above problems, and provides a recording method and a recording apparatus capable of achieving high diffraction efficiency and high multiplicity even when the recording layer of a hologram recording medium is thickened. With the goal.

As a result of intensive studies by the inventors, the hologram recording medium having a recording layer containing a polymerization inhibitor was exposed to pre-exposure light having a light transmittance of 20% or more with respect to the recording layer on both sides of the hologram recording medium. It was found that high diffraction efficiency and high multiplicity can be achieved by irradiating the same with pre-exposure treatment.
(1) For a hologram recording medium having a recording layer containing a polymerizable reactive compound, a photopolymerization initiator and a polymerization inhibitor, a pre-exposure light having a light transmittance of 20% or more with respect to the recording layer, A recording method for a hologram recording medium, which comprises performing hologram recording after irradiation from both sides of the hologram recording medium.
(2) The recording method for a hologram recording medium according to (1), wherein a dark reaction waiting time of 1 second or more is provided after the irradiation of the pre-exposure light.
(3) The recording method for a hologram recording medium according to (1) or (2), wherein the pre-exposure light is incoherent light.
(4) The hologram recording medium recording method according to any one of (1) to (3), wherein the hologram recording medium has antireflection films on both surfaces.
(5) The hologram recording medium recording method according to any one of (1) to (4), wherein the recording layer of the hologram recording medium has a thickness of 0.5 mm or more.
(6) A hologram recording medium recording apparatus including a pre-exposure unit capable of irradiating both surfaces of a hologram recording medium with pre-exposure light, wherein all light sources of the pre-exposure unit are LEDs.
Recording device for hologram recording medium.
( 7 ) A hologram including a pre-exposure unit capable of irradiating both sides of a hologram recording medium with pre-exposure light.
A recording device for a holographic recording medium , wherein the pre-exposure unit has one light source and one concave mirror, and the light source is an LED .

  According to the hologram recording medium recording method of the present invention, high diffraction efficiency and high multiplicity can be achieved.

7 is a graph showing a result of calculating a light intensity ratio in a recording layer when a single-sided pre-exposure treatment or a double-sided pre-exposure treatment is performed while changing the light transmittance of the pre-exposure light to the recording layer. It is a schematic diagram showing an example of a recording device of a hologram recording medium of the present invention. It is a schematic diagram showing another example of the recording device of the hologram recording medium of the present invention. It is a schematic diagram showing another example of the recording device of the hologram recording medium of the present invention. It is a block diagram which shows the outline of the recording/reproducing apparatus of the hologram recording medium used for the hologram recording of an Example and a comparative example. It is a graph which shows the angle distribution of the standardized diffraction efficiency of an example and a comparative example.

  Hereinafter, embodiments of a recording method and a recording apparatus for a hologram recording medium of the present invention will be described in detail, but the following description is an example (representative example) of the embodiments of the present invention, and the present invention includes the gist thereof. Unless specified, these contents are not specified.

(Recording method of hologram recording medium of the present invention)
The recording method of the hologram recording medium of the present invention is as follows. First, in the recording layer of the holographic recording medium, a predetermined pre-exposure process is performed on an area where an interference pattern is recorded (hereinafter, simply referred to as a recording area), and then a reference beam is applied to a recording area on which the pre-exposure process is performed. The information light is crossed to form interference fringes, and the interference pattern is recorded (hereinafter, referred to as hologram recording).

  In the present invention, the reference beam is a reference beam when recording an interference pattern on a hologram recording medium (hereinafter referred to as hologram recording), and is a hologram that overlaps with information light when performing hologram recording on the hologram recording medium. The light that is applied to the recording layer of the recording medium and that is applied to the recording layer of the hologram recording medium when reproducing the interference pattern recorded on the hologram recording medium.

Further, in the present invention, the information light is light containing information to be recorded on the hologram medium, and usually, the information is converted into digital data, the digital data is modulated into two-dimensional bar code data, and the two-dimensional bar code is modulated by the spatial modulator. It is a light containing coded data.
Further, in the present invention, the recording light refers to the light that irradiates the recording layer of the hologram recording medium when performing hologram recording on the hologram recording medium. That is, it corresponds to the reference light and the information light.

In the recording method of the present invention, in the pre-exposure process in the above-mentioned hologram recording medium recording method, the pre-exposure light having a light transmittance of 20% or more with respect to the recording layer of the target hologram recording medium is supplied to the hologram recording medium. Irradiate from both sides.
The pre-exposure process refers to a process of irradiating the hologram recording medium with predetermined light for pre-exposure before recording the hologram on the hologram recording medium.

The reason why high diffraction efficiency and high multiplicity can be achieved by performing the predetermined pre-exposure treatment defined in the present invention is as follows.
The pre-exposure treatment for the hologram recording medium is carried out by reacting the active substance generated by irradiating light in the wavelength region where the photopolymerization initiator has absorption with the polymerization inhibitor before hologram recording (hereinafter referred to as inactivation treatment). However, when the pre-exposure light is irradiated from only one side of the hologram recording medium (hereinafter referred to as one-side pre-exposure treatment), As the exposure light travels in the thickness direction in the recording layer, the light intensity exponentially decreases due to light absorption, and the light intensity decreases on the back surface side of the recording layer.

As a result, the inactivation treatment by the polymerization inhibitor becomes insufficient as it goes to the back side, and when hologram recording is performed, uniform recording cannot be performed in the film thickness direction of the recording layer, the diffraction efficiency decreases, and the diffraction angle decreases. Since the selectivity is lowered, it tends to be difficult to obtain high multiplicity.
Further, as a method of obtaining high diffraction efficiency and high multiplicity in a hologram recording medium having the same composition, it is known to thicken the recording layer, but if the thickness of the recording layer is increased, the light intensity reaching the back surface side Since it is further decreased, it is difficult to obtain the expected effect due to the increased thickness.

The pre-exposure light is irradiated from both sides of the hologram recording medium to perform the pre-exposure treatment (hereinafter, referred to as double-side pre-exposure treatment). It has been found that it is necessary to control the light transmittance of the layer within a predetermined range in order to enhance the effect of the double-sided pre-exposure treatment.
Incidentally, the light transmittance to the recording layer in the present invention considers only the loss of the transmitted light due to the light absorption of the recording layer, and the loss of the transmitted light due to the light absorption other than the recording layer and the light reflection due to the refractive index interface is Not included.

The wavelength of the pre-exposure light in the present invention may be in the absorption wavelength region of the photopolymerization initiator, preferably 300 nm or more, more preferably 350 nm or more. Further, it is preferably 600 nm or less, more preferably 450 nm or less. Within this range, effective inactivation treatment with a polymerization inhibitor is possible.
The light transmittance of the pre-exposure light in the present invention with respect to the recording layer is 20% or more, preferably 30% or more, and more preferably 40% or more. The higher the light transmittance of the recording layer, the easier the uniform pre-exposure treatment in the film thickness direction of the recording layer. Therefore, the upper limit of the light transmittance of the pre-exposure light to the recording layer is not particularly limited, but is usually 80%. It is below.

The light transmittance in the present invention is measured from the ratio of the intensity of incident light to the hologram recording medium and the intensity of transmitted light passing through the hologram recording medium. The same light source as the pre-exposure light is used for the incident light. The power density of incident light adjusted to be parallel to the traveling direction of light is 15 mW/cm ² . The hologram recording medium is arranged so as to be perpendicular to the optical axis of incident light. The light intensity of the incident light and the transmitted light is measured by a power meter (optical power meter 8250A made by ADC and optical sensor 82321B made by ADC). The measurement of the light transmittance for the recording layer excluding the influence of the substrate is performed as follows. First, the light transmittance of only the substrate is measured. Next, the light transmittance of the hologram recording medium having the recording layer was measured, and the light transmittance of only the recording layer was calculated by subtracting the influence of the substrate from the ratio of the light transmittance of the hologram recording medium to the light transmittance of the substrate only. obtain.

Exposure energy density before exposure light in the present invention is usually in the range of ^{1mJ / cm 2 ~1000mJ / cm 2} , the composition of the recording layer, since the optimum exposure energy density changes, following exposure energy It is preferable to use the value determined by the density optimization method.
First, the recording layer of the hologram recording medium is irradiated with the pre-exposure light having an arbitrary exposure energy density within the above range of the exposure energy density. Next, after passing a dark reaction time of 1 second or more (details will be described later), recording light having an exposure energy density adjusted so that the diffraction efficiency is 3% or less is irradiated, and after 60 seconds, a post-exposure treatment (details). Will be described later). When this hologram recording is reproduced while rotating the hologram recording medium so that the incident angle of the reference light is changed, an incident angle distribution of diffraction efficiency is obtained, and the hologram recorded in the pre-exposure process at an arbitrary exposure energy density, The full width at half maximum of the incident angle distribution of the reference light during reproduction can be obtained. These pre-exposure processing and hologram recording/reproduction are repeated by changing the exposure energy density of the pre-exposure light to another position not irradiated with the pre-exposure light and repeating the same process to expose the pre-exposure light. It is possible to understand the relationship between the energy density and the full width at half maximum of the incident angle distribution of the reproduction light. From this data, the minimum exposure energy density when the full width at half maximum becomes the narrowest is regarded as the optimum exposure energy density of the pre-exposure light in the hologram recording medium.

The exposure power density of the pre-exposure light in the present invention is preferably 1 mW/cm ² or more, more preferably 10 mW/cm ² or more. Also, preferably 1000 mW/cm
² or less, and more preferably 500 mW/cm ² or less. Further, the ratio of the exposure power density of the pre-exposure light composed of both surfaces is preferably 1:0.5 or more, more preferably 1:0.8 or more. Within this range, the pre-exposure processing time can be shortened and the pre-exposure processing can be effectively performed. The pre-exposure time may be appropriately set within a range where the optimum exposure energy density and the preferable exposure power density are compatible with each other.

  Either one of the pre-exposure light from each surface in the present invention is preferably incoherent light, and more preferably both are incoherent light. By using such incoherent light, it is possible to perform uniform pre-exposure processing in the film thickness direction of the recording layer. LEDs and lamps are used as the light source of incoherent pre-exposure light, but the fact that the pre-exposure light is incoherent light means that even if the light source is coherent light such as a laser, some kind of light is emitted before irradiation. The case in which the light becomes incoherent light at the time of irradiation is also included. The optical treatment includes, for example, a method using a multiple reflection element or a diffraction element.

  FIG. 1 shows the maximum light intensity and the minimum light intensity in the film thickness direction in the recording layer when the one-side pre-exposure treatment or the both-side pre-exposure treatment is performed by changing the light transmittance of the pre-exposure light to the recording layer. This is the result of calculating the intensity ratio (hereinafter, simply referred to as the light intensity ratio). It can be seen that the higher the light transmittance of the pre-exposure light with respect to the recording layer, the closer the light intensity ratio is to 1, and the more uniform the pre-exposure process in the recording layer.

  Methods for controlling the light transmittance of the recording layer include changing the wavelength of the light source for pre-exposure light and changing the type and concentration of the photopolymerization initiator, which can be easily realized by devising a recording device. Therefore, a method of changing the wavelength of the light source is preferable. As a method of controlling the wavelength of the light source, for example, in the case of an LED light source, there is a method of preparing a plurality of LEDs having different central wavelengths of oscillation. In the case of an incoherent light source having a wide emission spectrum such as a lamp, wavelength selection is performed. As possible, there is a method of simultaneously using an optical filter such as a light absorption filter or a dielectric multilayer film filter.

Thus, by performing the double-sided pre-exposure process with the pre-exposure light having a light transmittance of 20% or more with respect to the recording layer, the pre-exposure process is made more uniform in the film thickness direction of the recording layer. It becomes possible to perform uniform hologram recording, and it is possible to achieve high diffraction efficiency and high multiplicity in a hologram recording medium having a thick recording layer.
Pre-exposure treatment is a photopolymerization initiator by pre-exposure light irradiation, a reaction involving the diffusion of a polymerizable reactive compound and a polymerization inhibitor, because the reaction proceeds even after the irradiation of pre-exposure light, In consideration of the time of the entire reaction including diffusion, a certain waiting time may be set for the reaction from the end of the irradiation of the pre-exposure light to the start of the irradiation of the recording light for hologram recording. The waiting time for this reaction is called the dark reaction waiting time. Providing an appropriate dark reaction waiting time after the double-sided pre-exposure process allows the reaction in the pre-exposure process to proceed sufficiently, enabling higher diffraction efficiency and higher multiplicity recording even on a holographic recording medium with a thick recording layer. Becomes The appropriate dark reaction waiting time depends on the material used for the recording layer, but is usually 1 second or longer, preferably 5 seconds or longer, more preferably 30 seconds or longer, further preferably 60 seconds or longer, and 120 seconds or longer. Particularly preferred. This is because the reaction in the pre-exposure process proceeds sufficiently. The dark reaction waiting time is usually 90 minutes or less, preferably 60 minutes or less, more preferably 30 minutes or less, and particularly preferably 15 minutes or less. Within this range, it is possible to suppress the diffusion of the polymerization inhibitor to the area not irradiated with the pre-exposure light and maintain the characteristics when performing hologram recording in the area not subsequently irradiated with the pre-exposure light. Is.

In the double-sided pre-exposure process, the pre-exposure light may be sequentially irradiated on each side, but by simultaneously irradiating the pre-exposure light from both sides, the pre-exposure process time is shortened and the pre-exposure process is effectively performed. You can do it.
It is also preferable to perform post-exposure processing on the recording area after hologram recording. The post-exposure process in the present invention refers to irradiating the recording area with predetermined incoherent light after irradiating the hologram recording medium with the recording light. The post-exposure treatment causes the unreacted polymerizable monomer to react with the polymer, which has the effect of increasing storage stability.

(Holographic Recording Medium Used in Recording Method of the Present Invention)
The hologram recording medium used in the recording method of the present invention has a recording layer containing at least a polymerizable reactive compound, a photopolymerization initiator and a polymerization inhibitor. As a composition for forming such a recording layer (hereinafter, referred to as a hologram recording layer forming composition), a polymerizable resin capable of radical polymerization or cationic polymerization as a polymerizable reactive compound is used in a suitable matrix resin. A photopolymer in which a monomer, a photopolymerization initiator that accelerates the polymerization of the polymerizable monomer, and a polymerization inhibitor that is a substance that inhibits the polymerization of the polymerizable monomer are combined is preferably used.

<Regarding the composition for forming the hologram recording layer>
The recording layer of the hologram recording medium according to the present invention is formed by the hologram recording layer forming composition described in detail below. Here, the matrix resin usually exists as a crosslinked network structure in the recording layer by polymerizing or crosslinking after filling the composition for forming the hologram recording layer between the flat substrates, thus forming the hologram recording layer. The composition for use will be contained in the form of a matrix resin composition for forming a matrix resin by polymerization or crosslinking.
That is, the hologram recording layer forming composition according to the present invention contains at least a polymerizable monomer, a matrix resin forming composition, a photopolymerization initiator and a polymerization inhibitor. The constituent components of the composition for forming the hologram recording layer will be described in detail below.

<<About Polymerizable Monomer>>
The polymerizable monomer according to the present invention refers to a compound that can be polymerized with a photopolymerization initiator described below. The type of the polymerizable monomer is not particularly limited and can be appropriately selected from known compounds. Examples of the polymerizable monomer include a cation polymerizable monomer, an anion polymerizable monomer, a radical polymerizable monomer and the like. Any of these may be used, or two or more thereof may be used in combination.

  Examples of cationically polymerizable monomers include epoxy compounds, oxetane compounds, oxolane compounds, cyclic acetal compounds, cyclic lactone compounds, thiirane compounds, thietane compounds, vinyl ether compounds, spiro orthoester compounds, ethylenically unsaturated bond compounds, cyclic ether compounds. , Cyclic thioether compounds, vinyl compounds and the like. As the cationically polymerizable monomer, any one kind may be used alone, and two or more kinds may be used in optional combination and ratio.

  Examples of anionically polymerizable monomers include hydrocarbon monomers and polar monomers. Examples of the hydrocarbon monomer include styrene, α-methylstyrene, butadiene, isoprene, vinylpyridine, vinylanthracene, and derivatives thereof. Examples of polar monomers include methacrylic acid esters, acrylic acid esters, vinyl ketones, isopropenyl ketones, and other polar monomers. As the anion-polymerizable monomer, any one kind may be used alone, and two kinds or more may be used in optional combination and ratio.

Examples of the radically polymerizable monomer include compounds having a (meth)acryloyl group, (meth)acrylamides, vinyl esters, vinyl compounds, styrenes, spiro ring-containing compounds and the like. Any one of the radical-polymerizable monomers may be used alone, or two or more thereof may be used in any combination and ratio. Among the above, a compound having a (meth)acryloyl group is more preferable from the viewpoint of steric hindrance during radical polymerization.
Of the above polymerizable monomers, a compound having a halogen atom (iodine, chlorine, bromine, etc.) or a compound having a hetero atom (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.

<<About matrix resin and composition for forming 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, and the matrix resin forming composition is a matrix resin before the bond formation by the polymerization reaction and the crosslinking reaction. Refers to the precursor.
Since the matrix resin has a crosslinked network structure, the mobility of the polymerizable monomer and the photopolymerization initiator is appropriately suppressed, so that the polymerizable monomer and the photopolymerization initiator in the recording layer are dispersed spatially and uniformly. It has a role to keep the stable condition. Further, the matrix resin prevents the recorded information from being erased by suppressing the diffusion of the polymer due to the entanglement with the polymer generated in the recording layer. Furthermore, since it has a higher elastic modulus than that of a liquid state, it has a role of maintaining the physical shape of the recording layer, and is one of the constituent components necessary for the recording layer.

  The composition for forming a matrix resin, as long as it can maintain sufficient compatibility with a polymerizable monomer or a polymer thereof, and a photopolymerization initiator even after a bond is formed by a polymerization reaction or a crosslinking reaction, It is not particularly limited, and preferably, a compound having at least two functional groups selected from the group consisting of an isocyanate group, a hydroxyl group, a mercapto group, an epoxy group, an amino group and a carboxy group in a molecule may be used alone. Alternatively, a plurality of combinations may be used.

  The following examples can be given as examples of realizing a certain kind of chemical bond forming a crosslinked network structure by using these compounds alone or in combination. That is, by forming an isocyanurate bond by the reaction between compounds having an isocyanate group, a compound having an isocyanate group, a compound having active hydrogen in the molecule, for example, a hydroxyl group or a mercapto group, an amino group, a compound containing 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 Combining compounds having an amide bond, forming an ether bond by a reaction between 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 a, and further to form a plurality of kinds of bonds containing them.

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 degree of freedom in selecting a matrix resin structure is high and there is no odor.
Examples of the compound having an isocyanate group include isocyanic acid, butyl isocyanate, octyl isocyanate, butyl diisocyanate, hexyl diisocyanate (HMDI), isophorodiisocyanate (IPDI), 1,8-diisocyanato-4-(isocyanato). Methyl)octane, 2,2,4- and/or 2,4,4-trimethylhexamethylene diisocyanate, the isomer bis(4,4'-isocyanatocyclohexyl)methane and mixtures thereof with any isomer content, isocyanato Natomethyl-1,8-octane diisocyanate, 1,4-cyclohexylene diisocyanate, isomer cyclohexane dimethylene diisocyanate, 1,4-phenylene diisocyanate, 2,4- and/or 2,6-toluene diisocyanate, 1,5- Examples include naphthalene diisocyanate, 2,4′- or 4,4′-diphenylmethane diisocyanate and/or triphenylmethane 4,4′,4″-triisocyanate.

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

  Examples of the compound having two or more hydroxyl groups in the molecule as an isocyanate-reactive functional group include glycols such as ethylene glycol, triethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol and neopentyl glycol; butanediol. , Pentanediol, hexanediol, heptanediol, tetramethylene glycol, and other diols; bisphenols or compounds obtained by modifying these polyfunctional alcohols with polyethyleneoxy or polypropyleneoxy chains; glycerin, trimethylolpropane, butanetriol, pentane Compounds obtained by modifying these polyfunctional alcohols such as triols such as triol, hexanetriol, and decantriol with polyethyleneoxy chains or polypropyleneoxy chains; polyfunctional polyoxybutylenes; polyfunctional polycaprolactones; polyfunctional polyesters; polyfunctional polycarbonates; Examples include polyfunctional polypropylene glycol. Any of these may be used alone, or two or more of them may be used in any combination and ratio.

In the case of forming a matrix resin, for example, a combination of a compound having an epoxy group and a compound having an amino group has a relatively high reaction rate of bond formation in the composition for forming a matrix resin, and therefore, it may be left at room temperature for a short time. In some cases, the matrix resin is formed by the progress of the bond forming reaction 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 has a high degree of freedom in selection of a matrix resin structure and is a preferable combination as a composition for forming a matrix resin, has a reaction rate of bond formation. It is not so high that the bond formation may not be completed and the matrix resin may not be formed even if left at room temperature for several days. When such a composition for forming a matrix resin having a low bond formation reaction rate is used, the bond forming reaction of the composition for forming a matrix resin can be promoted by heating, as in a general chemical reaction. .. Therefore, depending on the composition for forming the matrix resin, it is preferable to heat the composition for forming the matrix resin after filling the composition for forming the hologram recording layer between both substrates.

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

<<About Photopolymerization Initiator>>
The photopolymerization initiator according to the present invention refers to an agent that generates a cation, anion or radical upon irradiation with light, and contributes to the polymerization of the above-mentioned polymerizable monomer. The type of photopolymerization initiator is not particularly limited and can be appropriately selected depending on 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. Specific examples thereof include anion components such as SbF ₆ ⁻ , BF ₄ ⁻ , AsF ₆ ⁻ , PF ₆ ⁻ , CF ₃ SO ₃ ⁻ , B(C ₆ F ₅ ) ₄ ⁻ , iodine, sulfur, nitrogen, phosphorus and the like. And a compound comprising an aromatic cation component containing the atom of. Of these, diaryl iodonium salts and triaryl sulfonium salts are preferable. Any of the above-exemplified cationic photopolymerization initiators may be used alone, or two or more thereof may be used in any combination and ratio.

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

  As the radical photopolymerization initiator, any known radical photopolymerization initiator can be used. 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. Etc. are used. Any one of the above-exemplified radical photopolymerization initiators 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( Aluminum complexes such as C ₉ H ₆ NO) ₃ , rubrene, perimidone derivatives, benzopyran derivatives, rhodamine derivatives, benzothioxanthene derivatives, azabenzothioxanthene, phenylpyridine complexes, porphyrin complexes, polyphenylene vinylene materials and the like can be mentioned.

<<About polymerization inhibitors>>
The polymerization inhibitor according to the present invention refers to an agent that inhibits the polymerization reaction of the polymerizable monomer. In the recording layer before hologram recording, an unexpected polymerization reaction such as the polymerization reaction of the polymerizable monomer being initiated by radicals generated by the polymerization initiator or the polymerizable monomer due to slight light and heat in the storage environment. Of the hologram recording medium and the storage stability of the hologram recording medium before hologram recording are improved.

  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, sodium phosphate, phosphinates such as sodium hypophosphite, mercaptoacetic acid, mercaptopropionic acid, 2-propanethiol, 2-mercaptoethanol, mercaptans such as thiophenol, acetaldehyde and propionaldehyde. Aldehydes such as acetone, ketones such as acetone and methyl ethyl ketone, halogenated hydrocarbons such as trichloroethylene and perchloroethylene, terpenes such as terpinolene, α-terpinene, β-terpinene and γ-terpinene, 1,4-cyclohexadiene , 1,4-cycloheptadiene, 1,4-cyclooctadiene, 1,4-heptadiene, 1,4-hexadiene, 2-methyl-1,4-pentadiene, 3,6-nonanedien-1-ol, 9 , Non-conjugated dienes such as 12-octadecadienol, linolenic acid, γ-linolenic acid, methyl linolenate, ethyl linolenate, isopropyl linolenate, linolenic acid such as linolenic anhydride, linoleic acid, methyl linoleate, Linoleic acids such as ethyl linoleate, isopropyl linoleate, linoleic anhydride, eicosapentaenoic acid, eicosapentaenoic acids such as ethyl eicosapentaenoate, docosahexaenoic acid, 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, benzylaminophenol, p-dihydroxybenzene, 2,4,6 -Phenol derivative such as butylhydroxytoluene such as trimethylphenol, nitrobenzene derivative such as o-dinitrobenzene, p-dinitrobenzene, m-dinitrobenzene, N-phenyl-1-naphthylamine, N-phenyl-2-naphthylamine, cuperone , Phenothiazine, tannic acid, p-nitrosamine, chloranil, aniline, hindered aniline, iron (III) chloride, copper (II) chloride, triethylamine, hindered amine, 2,2,6,6-tetramethylpiperidine 1-oxyl Examples thereof include nitroxy radical, triphenylmethyl radical, oxygen and the like. As these components, any one of conventionally known materials may be used alone, or two or more of them may be used in any combination and ratio.

<< About other additives >>
Other components contained in the composition for forming a hologram recording layer include a solvent, a plasticizer, a dispersant, a leveling agent, a defoaming agent, an adhesion promoter, a compatibilizer and a sensitizer. As these components, any one of the conventionally known materials may be used alone, or two or more thereof may be used in any combination and ratio.

<<About the content rate of each material>>
The content of each component in the composition for forming a hologram recording layer according to the present embodiment is arbitrary as long as it is not against the gist of the present invention, the ratio of each component is in the following range based on the total mass of the composition. Is preferred.
The total amount of the matrix resin is usually 0.1% by mass or more, preferably 10% by mass or more, and more preferably 35% by mass or more. Further, it is usually 99.9 mass% or less, preferably 99 mass% or less. By setting the content of the matrix resin to be the above lower limit value or more, the recording layer can be easily formed.

The content of the curing catalyst used to accelerate the formation of the matrix resin is preferably determined in consideration of the bond formation rate of the matrix-forming component, and is usually 5% by mass or less, preferably 4% by mass or less, and more preferably 1% by mass. % Or less. Further, 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. It is usually 80% by mass or less, preferably 50% by mass or less, and more preferably 30% by mass or less. When the content of the polymerizable monomer is more than the above lower limit, sufficient diffraction efficiency is obtained, and when the content is less than the above upper limit, the compatibility of the recording layer is maintained.

The content of the photopolymerization initiator is usually 0.001% by mass or more, preferably 0.01% by mass or more, and usually 5% by mass or less, preferably 3% by mass or less. When the content of the photopolymerization initiator is higher than the above lower limit value, sufficient recording sensitivity can be obtained.
The content of the polymerization inhibitor is usually 0.001 mass% or more, preferably 0.005 mass% or more. Further, 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 prevent the progress of an unexpected polymerization reaction initiated by radicals generated by slight light or heat.
The total amount of other components is usually 30% by mass or less, preferably 15% by mass or less, and more preferably 5% by mass or less.

<About film thickness of recording layer>
The thickness of the recording layer of the present invention is preferably 0.5 mm or more, more preferably 1.0 mm or more. Within this range, the selectivity of each hologram is increased during multiple recording on the hologram recording medium, and the degree of multiple recording tends to be increased. Further, it is preferably 10 mm or less, more preferably 2 mm or less. Within this range, the light transmittance of the recording layer at the wavelength of the recording light can be kept high, uniform recording can be performed over the entire recording layer in the thickness direction, and multiple recording with a high S/N ratio tends to be realized. It is in.

<Structure of hologram recording medium>
The hologram recording medium according to the present invention may have any shape as long as it has the above-mentioned recording layer, but generally has a disk-like shape in which the recording layer is sandwiched by two disk-shaped substrates facing each other. Target.
As a method for manufacturing the hologram recording medium, a conventionally known method may be used as appropriate, but an example is shown below.

First, the disc-shaped substrate with the central hole and the disc-shaped substrate without the central hole are vertically opposed so that the distance between the substrates is equal to the thickness of the desired recording layer, and positioned so that the upper and lower substrate centers are aligned. After that, the composition for forming a hologram recording layer is filled from the center hole of the substrate between both the substrates while keeping the arrangement.
Next, the composition for forming a matrix resin is cured by heating as necessary to form a recording layer. Then, the side surface portion is sealed with metal foil or the like.

<< About board >>
The substrate of the hologram recording medium according to the present invention sufficiently irradiates the recording layer with the pre-exposure light, the reference light and the information light, so that the light transmittance for these lights is preferably 50% or more, more preferably 80%. That is all.
Examples of the material of the substrate include organic materials such as acrylic, polyethylene terephthalate, polyethylene naphthoate, polycarbonate, polyethylene, polypropylene, amorphous polyolefin, polystyrene, and cellulose acetate; inorganic materials such as glass, silicon, and quartz. Among these, polycarbonate, acrylic, amorphous polyolefin, glass and the like are preferable, and glass is particularly preferable. This is because it has a high light transmittance, an excellent mechanical strength, a good barrier property against moisture and the like, and can be manufactured at low cost.

<<About antireflection film>>
An antireflection film is preferably provided on the surface of the substrate sandwiching the recording layer. This is because it is possible to suppress the generation of noise light due to the reflected light generated from the substrate surface and prevent the loss of the light intensity of the pre-exposure light and the recording light. In particular, in the present invention, it is preferable to provide an antireflection film on both surfaces of the hologram recording medium on which the pre-exposure light is incident, that is, both surfaces of the substrate for performing the pre-exposure processing on both surfaces. A conventionally known technique may be appropriately used for the configuration of the antireflection film.
When the antireflection film is provided on the substrate, the reflectance on the surface of the substrate is preferably 3% or less, more preferably 1.5% or less in terms of the wavelength of light used for hologram recording and the incident angle. Within this range, the generation of noise light due to the reflected light generated from the substrate surface can be effectively suppressed.

(Recording apparatus for hologram recording medium of the present invention)
FIG. 2 is a schematic diagram showing an example of a recording device for a hologram recording medium of the present invention. The pre-exposure light emitted from the pre-exposure light sources L1 and L2 composed of LED units is emitted from both sides of the hologram recording medium S. After that, the region subjected to the pre-exposure processing is irradiated with recording light by two light fluxes of the information light B1 and the reference light B2, and hologram recording is performed. As a procedure for performing the double-sided pre-exposure process, it is preferable to start and end the irradiation of L1 and L2 at the same time, but it is not necessary to do so at the same time. In that case, in a recording apparatus having only L1 as a light source for pre-exposure light, after irradiating the pre-exposure light from either one side of the hologram recording medium with L1, the hologram recording medium or L1 is rotated and the remaining one The surface may be irradiated with the pre-exposure light.

Further, another example of the recording device of the hologram recording medium of the present invention is shown in FIG. The light source for pre-exposure light of the present invention has only L1, and the light from L1 that has been irradiated as the pre-exposure light and transmitted through the hologram recording medium is reflected again in the same region of the recording layer. By having the mirror M1, double-sided exposure processing can be enabled.
Further, as shown in FIG. 4, when the light emitted from L1 is not parallel light but is focused on the recording area, the mirror M2 installed on one side is a concave mirror to efficiently reflect the reflected light. Can be irradiated.

  Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples without departing from the gist thereof.

<Preparation of composition for forming hologram recording layer>
27.199 g of hexamethylene diisocyanate (isocyanate), 4.175 g of acrylic acid-2,4,6-tribromophenyl ester (polymerizable monomer), diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (photopolymerization initiation) 0.418 g of the agent) and 0.01253 g of 2,2,6,6-tetramethylpiperidine 1-oxyl (radical scavenger) were dissolved to prepare a solution A.

Next, 0.0270 g of an octylic acid solution of tris(2-ethylhexanoate)bismuth (urethane polymerization catalyst) was dissolved in 107.80 g of polyoxypropylene glycol (polyol) having a molecular weight of about 1000 to prepare a liquid B.
The solutions A and B obtained above were degassed under reduced pressure at 45° C. for 2 hours, then the solutions A and B were mixed by stirring, and further degassed in vacuum for several minutes to prepare a hologram recording layer forming composition. Item 1 was prepared.

<Production of hologram recording medium 1>
Subsequently, a spacer sheet having a thickness of 0.5 mm and a width of 10 mm is placed on the ends of two sides of 75 mm which are opposed to each other on a rectangular slide glass of 25 mm×75 mm, and the hologram recording layer forming layer is formed between the spacer sheets on the slide glass. The composition 1 was poured, another slide glass was placed on the composition 1, the periphery was fixed with a clip, and heating was performed at 80° C. for 24 hours to prepare a hologram recording medium 1. In this hologram recording medium 1, a recording layer made of a photopolymer having a thickness of 1.5 mm is formed between two slide glasses as substrates. An antireflection film is formed on the slide glasses on both sides, and the reflectance at the interface between air and glass is suppressed to 1% or less.

<Evaluation of recording/reproducing characteristics of hologram recording medium>
Using the hologram recording medium 1, the recording/reproducing characteristics of the hologram recording medium were evaluated by the procedure described below. 120 multiplex-recorded on the hologram recording medium 1 pre-exposed with the LED and reproduced thereafter, the sum of square roots of diffraction efficiency was defined as M/# (em number). Hereinafter, the measuring method will be described in detail with reference to FIG.

<<Pre-exposure processing>>
FIG. 5 is a configuration diagram showing an outline of a recording/reproducing apparatus for a hologram recording medium used for hologram recording. In FIG. 5, S represents a hologram recording medium, M1 and M2 represent mirrors, PBS represents a polarization beam splitter, LD represents a laser light source (single mode laser manufactured by TOPTICA Photonics) that emits light having a wavelength of 405 nm, and PD1 And PD
Reference numeral 2 represents a photo detector (S2281, C9329 manufactured by Hamamatsu Photonics KK). Further, L1 and L2 represent LEDs which are light sources for the pre-exposure light and the post-exposure light.

The pre-exposure treatment was performed using LEDs (L1 and L2 in the figure) having a wavelength of 405 nm at which the light transmittance of the recording layer of the hologram recording medium 1 was 43%. The exposure power density of a single LED was 100 mW/cm ² , and the exposure power density ratio of L1 and L2 was 1:1. In the case of the double-sided pre-exposure treatment, the pre-exposure light was irradiated simultaneously from L1 and L2, and in the case of the pre-exposure treatment from one side, the pre-exposure light was irradiated only from L1.

As the exposure energy density during the pre-exposure process, a value optimized by the above-described optimization method was used. The specific optimization method was performed as follows.
First, a double-sided pre-exposure treatment was performed with an exposure energy density of 20 mJ/cm ² on both sides. After a dark reaction time of 5 seconds, recording light having an exposure energy density of 1.5 mJ/cm ² was irradiated to perform hologram recording. After the post-exposure treatment was performed 60 seconds later, the full width at half maximum was measured from the incident angle distribution of the reference light of the diffraction efficiency obtained by reproducing the hologram recording medium while rotating it. The recording position is newly changed to an unirradiated portion of the hologram recording medium, and the same double-sided pre-exposure treatment and recording/reproduction are performed by changing the exposure energy density of the double-sided pre-exposure light by 20 mJ/cm ² to 300 mJ/cm ^2. The full width at half maximum was obtained under each double-sided pre-exposure treatment condition. Among the double-sided pre-exposure processing conditions where the full width at half maximum is the narrowest, the minimum exposure energy density was set as the optimum double-sided pre-exposure processing condition. The optimum exposure energy density in the double-sided pre-exposure treatment for the hologram recording medium 1 was 120 mJ/cm ² .
In the case of the one-side pre-exposure treatment, the one-side pre-exposure treatment condition was optimized in the same manner. The optimum exposure energy density in the single-sided pre-exposure treatment for the hologram recording medium 1 was 160 mJ/cm ² .

(Examples 1 and 2 and Comparative Examples 1 and 2)
In the above pre-exposure treatment, the case where the dark reaction wait time after performing the both-side pre-exposure treatment was 30 seconds was set as Example 1, and the dark reaction wait time after performing the both-side pre-exposure treatment was set to 0 second. Was set as Example 2. Further, in the above pre-exposure treatment, a case where the dark reaction waiting time after performing the pre-exposure treatment from only one side using only L1 was set to 30 seconds was set as Comparative Example 1, and pre-exposure from only one side using only L1. The case where the dark reaction waiting time after the treatment was set to 0 seconds was set as Comparative Example 2.

<<Hologram recording/reproduction>>
After the above-mentioned pre-exposure treatment and the dark reaction waiting time, the following hologram recording/reproduction was performed in all Examples and Comparative Examples to evaluate M/#.
The light having a wavelength of 405 nm generated from the LD is split by the PBS, and they are regarded as the reference light and the information light so that they intersect each other on the recording surface so that the angle formed by the two beams becomes 37.3°. Irradiated. At this time, the bisector of the angle formed by the two beams (hereinafter, referred to as an optical axis) is made perpendicular to the recording surface of the recording layer of the hologram recording medium, and further obtained by division. Irradiation was performed so that the plane of vibration of the electric field vector of the two beams was perpendicular to the plane containing the two intersecting beams. When the above case is 0°, the direction of the hologram recording medium is changed and the angle with respect to the optical axis of the recording surface is changed from −14.64° to 14.87° while the incident directions of the two beams are fixed. , While changing from 0.23° to 0.27° in increments of 120, hologram recording of 120 multiplex was performed. At this time, the exposure power density per beam was 7.5 mW/cm ² , and the exposure energy density of the recording light per multiplex recording was 12 mJ/cm ² . After 120 multiple recordings, 60 seconds have elapsed, post-exposure was performed by irradiating L1 and L2 with light at 6 J/cm ² to completely polymerize the remaining polymerizable monomer without being polymerized.

Subsequently, only the light (wavelength 405 nm) from the mirror M1 in FIG. 5 is irradiated as the reference light, the reproduction light is detected by PD1 and PD2, and the diffraction efficiency from the angle -15.5° to 15.5° is measured. did. The sum of the square roots of the obtained diffraction efficiency over all multiplex recordings was defined as M/#. Further, the angle dependence of the reproduced signal during reproduction was evaluated by the following method.
The hologram recorded at the first multiplex, that is, when the angle with respect to the optical axis was −14.64° was reproduced by changing the angle with respect to the optical axis from −14.68° to −14.58°. FIG. 6 shows the angular distribution of the standardized diffracted light rate normalized by the maximum value of the diffraction efficiency of the reproduced signal. As shown in FIG. 6, a diffraction pattern centered on an angle (hereinafter, referred to as a central angle) at which the normalized diffracted light ratio has the maximum value is obtained. The sharper the angular distribution is, the more the multiple recording is performed. It is possible to reduce the influence of crosstalk with the hologram recording of adjacent angles of, and it is possible to perform hologram recording with high multiplicity. As an index showing the sharpness of the angular distribution, the average value of the normalized diffractive light rates in the case of ±0.05° from the central angle was calculated from the angular distribution data of the standardized diffractive light rates of each Example and Comparative Example. .. It can be said that the smaller this value, the smaller the crosstalk and the more suitable for high multiplicity recording.

<Evaluation result>
Table 1 shows the evaluation results of Examples 1 and 2 and Comparative Examples 1 and 2.

From the results of Table 1, by using the recording method of the present invention, higher M/# can be obtained and high diffraction efficiency can be realized, and the average value of the standardized diffractive light rates of ±0.05° can be lowered and the high value. It has been found that multiplicity recording can be realized.
It was also found that hologram recording suitable for higher diffraction efficiency and higher multiplicity recording can be performed by setting a constant dark reaction waiting time.

  The recording method of the hologram recording medium of the present invention is useful as a means for achieving high diffraction efficiency and high multiplicity even when the medium is made thick.

B1 Information light B2 Reference lights L1 and L2 Pre-exposure light source LD Laser light sources M1 and M2 Mirrors PD1 and PD2 Photodetector PBS Polarizing beam splitter
S hologram recording medium

Claims (7)

For a hologram recording medium having a recording layer containing a polymerizable reactive compound, a photopolymerization initiator and a polymerization inhibitor, pre-exposure light having a light transmittance to the recording layer of 20% or more is recorded on the hologram recording medium. A method for recording a hologram recording medium, characterized by performing hologram recording after irradiation from both sides of the medium. The hologram recording medium recording method according to claim 1, wherein a dark reaction waiting time of 1 second or more is provided after the irradiation of the pre-exposure light. The hologram recording medium recording method according to claim 1, wherein the pre-exposure light is incoherent light. 4. The hologram recording medium according to claim 1, wherein the hologram recording medium has antireflection films on both sides.
A method for recording on a hologram recording medium according to item. The hologram recording medium recording method according to any one of claims 1 to 4, wherein the recording layer of the hologram recording medium has a thickness of 0.5 mm or more. A hologram recording medium recording device including a pre-exposure unit capable of irradiating both surfaces of a hologram recording medium with pre-exposure light, wherein all light sources of the pre-exposure unit are LEDs. Hologram including pre-exposure unit capable of irradiating pre-exposure light on both sides of hologram recording medium
A recording device for a recording medium, wherein the pre-exposure unit has one light source and one concave mirror, and the light source is an LED .

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