Holographic recording medium, composition for forming photopolymer layer, and optical element

Abstract

The present invention relates to a hologram recording medium in which the adhesive strength between the photopolymer layer and the adhesive protective layer before light irradiation is 500 gf / 20 nm to 5,000 gf / 20 nm and the haze value of the photopolymer layer is 3% or less, and an optical element including the hologram recording medium.

Description

[Technical Field]

[0001] [Cross-Citation of Related Applications] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0134345 dated October 18, 2022 and Korean Patent Application No. 10-2023-0138056 dated October 16, 2023, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a holographic recording medium, a composition for forming a photopolymer layer, and an optical element including the holographic recording medium. [Background technology]

[0003] A hologram recording medium records information by changing the refractive index in a holographic recording layer through an exposure process, and reproduces the information by reading the difference in the refractive index recorded in this way.

[0004] In this regard, photopolymer compositions can be used to manufacture holograms. Photopolymers can easily store optical interference patterns as holograms through photopolymerization of photoreactive monomers. Therefore, photopolymers can be used in a variety of fields, including smart devices such as mobile devices, components of wearable displays, vehicle accessories (e.g., head-up displays), holographic fingerprint recognition systems, optical lenses, mirrors, deflection mirrors, filters, diffusion screens, diffractive elements, light guides, waveguides, holographic optical elements having the functions of projection screens and / or masks, optical memory system media and light diffusion plates, optical wavelength splitters, and reflective and transmissive color filters.

[0005] Specifically, the photopolymer composition for hologram production includes a polymer matrix, a photoreactive monomer, and a photoinitiator system, and a photopolymer film made from such a composition is irradiated with laser interference light to induce local photopolymerization of the monomer.

[0006] This local photopolymerization process results in refractive index modulation, which in turn creates a diffraction grating. The refractive index modulation value (Δn) is affected by the thickness and diffraction efficiency (DE) of the photopolymer film, and the thinner the thickness, the wider the angular selectivity.

[0007] In recent years, there has been an increasing demand for the development of materials that have high diffraction efficiency and can stably maintain holograms, and various attempts have been made to manufacture photopolymer films that have high diffraction efficiency and refractive index modulation values ​​despite their thin thickness.

[0008] On the other hand, when the holographic recording medium is used as an optical element in a mobile device or vehicle accessories (e.g., a head-up display), it is placed in a high-temperature / high-humidity environment.

[0009] Furthermore, a film in which a diffraction grating is formed using a holographic recording medium must have excellent reliability in terms of heat resistance, moisture resistance, etc. in order to be applicable to actual products. In this case, reliability mainly depends on the matrix characteristics.

[0010] However, the holographic recording media currently in use have the problem that they do not exhibit the desired level of adhesive strength in high temperature / high humidity environments, resulting in reduced reliability.

[0011] Therefore, there is a demand for the development of photopolymer films and holographic recording media containing the same that are excellent in both recording efficiency and reliability in a variety of surrounding usage environments. Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention provides a holographic recording medium having high recording efficiency and diffraction efficiency, and including a photopolymer layer having excellent adhesive strength and low haze characteristics.

[0013] The present invention also provides a composition for forming a photopolymer layer that can efficiently provide a photopolymer layer of the holographic recording medium, which can achieve a higher refractive index modulation value even in a thin thickness range by using an adhesive additive, and has improved adhesive properties and excellent reliability compared to conventional compositions.

[0014] The present invention also provides an optical element including a holographic recording medium. [Means for solving the problem]

[0015] The present specification provides a holographic recording medium comprising a substrate; an adhesive protective layer; and a photopolymer layer, wherein the adhesive strength between the photopolymer layer and the adhesive protective layer before light irradiation is 500 gf / 20 nm to 5,000 gf / 20 nm, and the haze value of the photopolymer layer measured in accordance with JIS K7136:2000 is 3% or less.

[0016] The present specification also provides an optical element including the holographic recording medium.

[0017] The present specification also provides a photopolymer composition for forming a hologram, comprising: a polymer matrix or a precursor thereof; photoreactive monomers including monofunctional monomers and polyfunctional monomers; an adhesion additive; and a photoinitiator; wherein the proportion of monofunctional monomers in the photoreactive monomers is greater than 40% by weight and not greater than 70% by weight.

[0018] Hereinafter, a holographic recording medium according to a specific embodiment of the present invention, a composition for forming a photopolymer layer contained in the holographic recording medium, a method for producing the same, and an optical element including the same will be described.

[0019] As used herein, (meth)acrylate means methacrylate or acrylate.

[0020] In this specification, the (co)polymer means a homopolymer or a copolymer (including a random copolymer, a block copolymer, and a graft copolymer).

[0021] In this specification, the term "hologram" refers to a recording medium on which optical information is recorded in the entire visible range and near-ultraviolet range (300-800 nm) through an exposure process, and includes all visual holograms, such as in-line (Gabor) holograms, off-axis holograms, full-aperture holograms, white-light transmission holograms ("rainbow holograms"), Denisyuk holograms, biaxial reflection holograms, edge-literature holograms, and holographic stereograms.

[0022] In this specification, the alkyl group may be linear or branched, and the number of carbon atoms is not particularly limited, but preferably ranges from 1 to 40. According to one embodiment, the alkyl group has 1 to 20 carbon atoms. According to another embodiment, the alkyl group has 1 to 10 carbon atoms. According to another embodiment, the alkyl group has 1 to 6 carbon atoms. Specific examples of alkyl groups include, but are not limited to, methyl, ethyl, propyl, n-propyl, isopropyl, butyl, n-butyl, isobutyl, tert-butyl, sec-butyl, 1-methylbutyl, 1-ethylbutyl, pentyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, hexyl, n-hexyl, 1-methylpentyl, 2-methylpentyl, 4-methyl-2-pentyl, 3,3-dimethylbutyl, 2-ethylbutyl, heptyl, n-heptyl, 1-methylhexyl, cyclopentylmethyl, cyclohexylmethyl, octyl, n-octyl, tert-octyl, 1-methylheptyl, 2-ethylhexyl, 2-propylpentyl, n-nonyl, 2,2-dimethylheptyl, 1-ethylpropyl, 1,1-dimethylpropyl, isohexyl, 2-methylpentyl, 4-methylhexyl, 5-methylhexyl, and the like.

[0023] In this specification, an alkylene group is a divalent functional group derived from an alkane, and is, for example, linear, branched, or cyclic, and includes a methylene group, an ethylene group, a propylene group, an isobutylene group, a sec-butylene group, a tert-butylene group, a pentylene group, and a hexylene group.

[0024] As used herein, the term "substituted or unsubstituted" refers to a group substituted or unsubstituted with one or more substituents selected from the group consisting of deuterium, halogen, cyano, nitro, hydroxy, carbonyl, ester, imide, amide, primary amino, carboxy, sulfonic acid, sulfonamide, phosphine oxide, alkoxy, aryloxy, alkylthioxy, arylthioxy, alkylsulfoxy, arylsulfoxy, silyl, boron, alkyl, haloalkyl, cycloalkyl, alkenyl, aryl, aralkyl, aralkenyl, alkylaryl, alkoxysilylalkyl, arylphosphine, or heterocyclic groups containing one or more N, O, and S atoms, or a group substituted or unsubstituted with two or more of the above-listed substituents linked together. For example, a "substituent linked to two or more substituents" may be a biphenyl group. That is, a biphenyl group may be an aryl group or may be interpreted as a substituent linked to two phenyl groups. Preferably, the substitution may be a halogen group, and an example of the halogen group is a fluoro group.

[0025] Unless otherwise specified, the term "hologram" as used herein refers to a recording medium in which optical information is recorded in the entire visible and ultraviolet ranges (e.g., 300 nm to 1,200 nm) through an exposure process. For example, the term "hologram" as used herein includes visual holograms such as in-line (Gabor) holograms, off-axis holograms, full-aperture transfer holograms, white-light transmission holograms ("rainbow holograms"), Denisyuk holograms, biaxial reflection holograms, edge-literature holograms, and holographic stereograms.

[0026] In the present invention, the holographic recording medium may include a photopolymer film.

[0027] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) refer to the molecular weight (unit: Da (Dalton)) measured in terms of polystyrene by gel permeation chromatography (GPC). The measurement of the polystyrene-equivalent weight average molecular weight by GPC can be performed using commonly known analytical equipment, detectors such as a refractive index detector, and analytical columns, and commonly used temperature conditions, solvents, and flow rates can be applied. Specific examples of the measurement conditions include a temperature of 30°C, a chloroform solvent, and a flow rate of 1 mL / min. Specific examples of the measurement conditions include using a Polymer Laboratories PLgel MIX-B 300 mm column and a Waters PL-GPC220 instrument, with an evaluation temperature of 160°C, 1,2,4-trichlorobenzene as the solvent, a flow rate of 1 mL / min, and a sample prepared at a concentration of 10 mg / 10 mL and supplied in a volume of 200 μL. Mw and Mn values ​​can be determined using a calibration curve formed using polystyrene standards. Nine molecular weights of polystyrene standards were used: 2,000 / 10,000 / 30,000 / 70,000 / 200,000 / 700,000 / 2,000,000 / 4,000,000 / 10,000,000.

[0028] According to one embodiment of the present invention, there is provided a holographic recording medium comprising: a substrate; an adhesive protective layer; and a photopolymer layer; wherein the adhesive strength between the photopolymer layer and the adhesive protective layer before light irradiation is 500 gf / 20 nm to 5,000 gf / 20 nm, and the haze value of the photopolymer layer measured in accordance with JIS K7136:2000 is 3% or less.

[0029] The inventors have confirmed through experiments that by using a specific adhesive additive in addition to the matrix of the hologram recording medium and the recording monomer in the photopolymer composition for forming the photopolymer layer contained in the hologram recording medium, the adhesive strength between the photopolymer layer of the hologram recording medium and the adhesive protective layer can be improved compared to conventional methods, resulting in excellent reliability, and that even with a thin thickness, diffraction efficiency and a high refractive index modulation value can be achieved, and that excellent reliability can be achieved even under high temperature / high humidity conditions, thereby completing the invention.

[0030] The adhesion additive improves the adhesion between the photopolymer layer and the adhesive protective layer formed on the substrate after forming the photopolymer layer using the photopolymer composition, and also enables the photopolymer layer to exhibit a specific water contact angle.

[0031] Furthermore, the adhesive additive not only allows the surface of the photopolymer layer to be uniform, but also provides low haze and prevents the surface from becoming sticky.

[0032] More specifically, the haze value of the photopolymer layer measured in accordance with JIS K7136: 2000 may be 3% or less, or 2.5% or less, or 2.0% or less, or 0.1% or more, or 0.5% or more. When the photopolymer layer has a haze value of 3% or less, it can have excellent optical properties and high transmittance, and can prevent a decrease in the refractive index modulation value and diffraction index of the holographic recording medium.

[0033] The haze value of the photopolymer layer may be a value measured before or after recording on the holographic recording medium.

[0034] In other words, the use of the additive improves the coating properties of the composition for forming a photopolymer layer, and provides a hologram medium with excellent reliability, which exhibits a difference in adhesive strength between the photopolymer layer and the adhesive protective layer compared to conventional methods.

[0035] Therefore, a holographic recording medium using a photopolymer composition containing the adhesive additive can maintain excellent optical properties and can be easily attached or detached when attaching or detaching the holographic recording medium (photopolymer film) to or from another medium.

[0036] In addition, the photopolymer composition uses a mixture of a monofunctional monomer and a polyfunctional monomer as a photoreactive monomer, and the ratio of the monofunctional monomer to the total content of the photoreactive monomers is adjusted to a specific ratio, thereby further improving the adhesion between the adhesive protective layer and the photopolymer layer.

[0037] The holographic recording medium of the embodiment can be provided by sequentially forming an adhesive protective layer and a photopolymer layer on a substrate.

[0038] In such a holographic recording medium, the adhesive strength between the photopolymer layer and the adhesive protective layer before light irradiation may be 500 gf / 20 nm to 5,000 gf / 20 nm.

[0039] Specifically, the photopolymer layer includes a crosslinked polymer matrix or its precursor, an adhesive additive, and a cured product of a photoreactive monomer including a monofunctional monomer and a polyfunctional monomer with an adjusted content of the monofunctional monomer, and can improve the adhesion between the adhesive protective layer and the photopolymer layer compared to conventional ones.

[0040] In the holographic recording medium, the photopolymer layer may have a water contact angle of 50° to 100° after light irradiation.

[0041] Furthermore, when the adhesive protective layer and the release film are peeled off, the photopolymer layer exhibits a water contact angle decrease rate of 5° / min to 15° / min after light irradiation.

[0042] By achieving the above adhesive strength and water contact angle, the rate of decrease in water contact angle after light irradiation can be adjusted to be low within the above range, thereby improving adhesive strength compared to conventional films. That is, films having a small water contact angle tend to have high adhesive strength, but when the photopolymer composition of the above embodiment is used, the adhesive strength between the photopolymer layer and the adhesive protective layer formed on the substrate after formation of the photopolymer layer is improved, making it possible to provide a holographic recording medium with a small water contact angle.

[0043] At this time, the adhesive strength can be evaluated by performing a 180° Peel Test using a Texture Analyzer and measuring the load applied to a width of 25 mm.

[0044] The water contact angle can be measured by dropping 2 μl of H2O onto a photopolymer layer exposed to a red light source of a certain wavelength, and then measuring the water contact angle (surface contact angle) of the photopolymer layer using a drop shape analyzer.

[0045] Each of the components of the holographic recording medium of the embodiment will be specifically described.

[0046] The type of the substrate is not particularly limited, and any substrate disclosed in the related technical field can be used. For example, cellulose ester-based substrate films, polyester-based substrate films, poly(meth)acrylate-based substrate films, polycarbonate-based substrate films, cycloolefin (COP)-based substrate films, glass, acrylic-based substrate films, etc. can be used. Specifically, substrates such as PET (polyethylene terephthalate), TAC (triacetyl cellulose), PC (polycarbonate), COP (cycloolefin polymer), and polymethyl methacrylate (PMMA) can be used.

[0047] The thickness of the substrate is not particularly limited, and may be, for example, 1 μm to 1,000 μm.

[0048] The adhesive protective layer can be used as a protective film for the photopolymer layer, and can include a barrier pressure sensitive adhesive (BPSA) for absorbing unevenness at a thickness level having unevenness absorption properties on one surface of the substrate.

[0049] The adhesive protective layer may contain a conventional photocurable pressure-sensitive adhesive, but the type is not limited thereto. For example, the pressure-sensitive adhesive may be one or more selected from the group consisting of acrylic pressure-sensitive adhesives, silicone pressure-sensitive adhesives, urethane pressure-sensitive adhesives, and rubber pressure-sensitive adhesives. Specifically, the pressure-sensitive adhesive layer may contain a polymer containing one or more selected from the group consisting of (meth)acrylate resins and polysiloxanes.

[0050] The thickness of the adhesive protective layer may be, but is not limited to, 10 μm to 100 μm.

[0051] The photopolymer layer can be formed by laminating one or more layers on the adhesive protective layer, and specifically, the photopolymer layer can be formed by laminating two or more layers on the adhesive protective layer.

[0052] The photopolymer layer includes a photopolymer composition including a polymer matrix or its precursor; photoreactive monomers including monofunctional monomers and polyfunctional monomers; an adhesion additive; and a photoinitiator; and the proportion of the monofunctional monomers in the photoreactive monomers may be more than 40 wt % and not more than 70 wt %, 42 to 68 wt %, or 45 to 65 wt %.

[0053] The adhesion additive includes a polydimethylsiloxane-based additive.

[0054] By including a polydimethylsiloxane-based additive, the adhesive strength between the photopolymer layer and the adhesive protective layer formed on the substrate after the photopolymer layer is formed can be improved, and the photopolymer layer can exhibit a specific water contact angle and be made hydrophilic.

[0055] The polydimethylsiloxane additive has a weight-average molecular weight of 100 to 10,000 and may include at least one selected from polyether-modified polydimethylsiloxane, polymethylalkylsiloxane silicon surfactant, and organically modified silicon. Specifically, the polydimethylsiloxane additive may be polyether-modified polydimethylsiloxane; or silicon and polyether macromer-modified polyacrylate.

[0056] The adhesive additive may be present in an amount of 0.001 to 0.1 parts by weight relative to 100 parts by weight of the polymer matrix or its precursor. If the content of the adhesive additive does not satisfy the above range, i.e., is too low or too high, the photopolymer film may not be easily attached or detached from another medium.

[0057] The photopolymer composition may further include a non-reactive fluorine-based compound, which may be used as a plasticizer.

[0058] Specifically, the non-reactive fluorine-based compound may contain one or more functional groups selected from the group consisting of an ether group, an ester group, and an amide group, and two or more difluoromethylene groups.

[0059] More specifically, the non-reactive fluorine-based compound may include a compound represented by the following Chemical Formula 3 (Chemical Formula 1).

[0060] [ka] In the above Chemical Formula 3, R 11 and R 12 are each independently a difluoromethylene group, R 13 and R 16 are each independently a methylene group, R 14 and R 15are each independently a difluoromethylene group, k is an integer from 1 to 10, R 17 and R 18 are each independently a linear or branched alkyl group having 1 to 10 carbon atoms or a functional group represented by the following chemical formula 4 (Chemical Formula 2), [ka] In the above Chemical Formula 4, R 21 , R 22 and R 23 are each independently a linear or branched alkylene group having 1 to 10 carbon atoms, R 24 is a linear or branched alkyl group having 1 to 10 carbon atoms, I is an integer from 1 to 30.

[0061] More specifically, R in Formula 3 11 and R 12 are each independently a difluoromethylene group, and R 13 and R 16 are each independently a methylene group, and R 14 and R 15 are each independently a difluoromethylene group, and R 17 and R 18 are each independently a 2-methoxyethoxymethoxy group, and k is an integer of 2.

[0062] The fluorine-based compound may have a lower refractive index than the photoreactive monomer, which can reduce the refractive index of the polymer matrix and increase the refractive index modulation.

[0063] The refractive index of the fluorine-based compound may be as low as 1.45 or less. Specifically, the upper limit of the refractive index of the fluorine-based compound may be, for example, 1.44 or less, 1.43 or less, 1.42 or less, 1.41 or less, 1.40 or less, 1.40 or less, 1.39 or less, 1.38 or less, or 1.37 or less, and the lower limit of the refractive index may be, for example, 1.30 or more, 1.31 or more, 1.32 or more, 1.33 or more, 1.34 or more, or 1.35 or more. By using a fluorine-based compound having a refractive index lower than that of the photoreactive monomer, the refractive index of the polymer matrix can be lowered, and the refractive index modulation with the photoreactive monomer can be increased.

[0064] The fluorine-based compound may be included in an amount ranging from 20 to 75 parts by weight based on 100 parts by weight of the polymer matrix or its precursor. Specifically, the lower limit of the content of the fluorine-based compound may be, for example, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 40 parts by weight or more, 45 parts by weight or more, 50 parts by weight or more, or 55 parts by weight or more, and the upper limit may be, for example, 70 parts by weight or less, 65 parts by weight or less, 60 parts by weight or less, 55 parts by weight or less, or 50 parts by weight or less. Satisfying this range is advantageous for ensuring excellent optical recording properties. If the content of the fluorine-based compound is less than this range, the refractive index modulation value after recording may be low due to a lack of low-refractive-index components. If the content of the fluorine-based compound exceeds this range, compatibility issues between components contained in the photopolymer film may increase haze or cause some of the fluorine-based compound to leach onto the surface of the coating layer.

[0065] The fluorine-based compound may have a weight-average molecular weight of 300 or more. Specifically, the lower limit of the weight-average molecular weight of the fluorine-based compound may be, for example, 350 or more, 400 or more, 450 or more, 500 or more, 550 or more, or 600 or more, and the upper limit may be, for example, 1000 or less, 900 or less, 800 or less, 700 or less, 600 or less, or 500 or less. In consideration of refractive index modulation, compatibility with other components, and elution problems of the fluorine-based compound, it is preferable that the weight-average molecular weight be within the above-mentioned range. Here, the weight-average molecular weight refers to the weight-average molecular weight in terms of polystyrene measured by the above-mentioned GPC method.

[0066] The photopolymer layer may be irradiated with light from a red light source. The photopolymer layer may be laminated in a mixed state by exposing a red hologram. When the photopolymer layer is irradiated with light from the red light source, the light may be within the known red wavelength range of 600 nm to 700 nm, for example, at a wavelength of 630 nm to 680 nm and with a light intensity of 0.3 mW to 3.0 mW.

[0067] The photopolymer layer also includes a crosslinked matrix. For example, the photopolymer layer may include or be formed from a composition including at least a crosslinked matrix or a precursor thereof. In a specific example related to the present application, the photopolymer layer may include or be formed from a composition including a crosslinked matrix or a precursor thereof, a photoreactive monomer, and a photoinitiator.

[0068] In such a holographic recording medium, the photopolymer layer can have a thickness in the range of 5 μm to 50 μm as a holographic recording layer. Specifically, the thickness of the photopolymer film may be, for example, 5 μm or more, 10 μm or more, 15 μm or more, or 30 μm or more. The upper limit of the thickness may be, for example, 30 μm or less, or 20 μm or less, specifically 15 μm or less, 12 μm or less, or 8 μm or less. Even when the holographic recording medium of the present application has a small thickness within the above-mentioned range, it exhibits excellent refractive index modulation, diffraction efficiency, and driving reliability.

[0069] The holographic recording medium of the another embodiment can achieve a refractive index modulation value (Δn) of 0.020 or more, 0.021 or more, 0.022 or more, 0.023 or more, 0.024 or more, 0.025 or more, 0.026 or more, 0.027 or more, 0.028 or more, 0.029 or more, or 0.030 or more, even when the photopolymer layer has a thickness as thin as 5 μm to 30 μm. The upper limit of the refractive index modulation value is not particularly limited, but may be, for example, 0.035 or less.

[0070] According to another embodiment of the present invention, the holographic recording medium may further include a release film between the photopolymer layer and the adhesive protective layer.

[0071] Therefore, the holographic recording medium may have a structure in which a substrate, an adhesive protective layer, a release film, and a photopolymer layer are sequentially laminated from the bottom.

[0072] FIG. 1 is a simplified diagram showing the structure of a holographic recording medium according to an embodiment, which further includes a release film.

[0073] As shown in FIG. 1, the holographic recording medium may include a structure in which two photopolymer layers 1 and 2, a release film 3, an adhesive protective layer 4, and a substrate 5 are stacked.

[0074] The release film may be formed via the adhesive protective layer, and may be formed to intersect at some ends of the adhesive protective layer at a predetermined interval.

[0075] Specifically, the release film is a layer positioned between the adhesive protective layer and the photopolymer layer to act as an indicator when they are peeled off, and refers to a transparent layer attached to a portion of the edge of one side of the adhesive protective layer.

[0076] According to one embodiment of the present invention, the release film may be laminated at a predetermined interval to cross the edge of the adhesive protective layer within a range of 0.5 cm to 1 cm.

[0077] The release film may be a commercially available fluorine-treated release film or silicone-treated release film, but the type is not limited thereto. The thickness of the release film is not limited thereto, and may be within a range known in the art.

[0078] The holographic recording medium may have a total thickness of 40 μm to 100 μm.

[0079] The holographic recording medium can exhibit a diffraction efficiency of 80% or more and a haze characteristic of 3.0% or less even with a small thickness.

[0080] Meanwhile, according to another embodiment of the present invention, there is provided a photopolymer composition for forming a hologram, comprising: a polymer matrix or a precursor thereof; photoreactive monomers including a monofunctional monomer and a polyfunctional monomer; an adhesion additive; and a photoinitiator; wherein the proportion of the monofunctional monomer in the photoreactive monomer is more than 40 wt % and not more than 70 wt %, 42 wt % to 68 wt %, or 45 wt % to 65 wt %.

[0081] The photopolymer composition of one embodiment includes a polymeric matrix, or a precursor thereof, that acts as a support for the photopolymer layer to be formed therefrom.

[0082] The polymer matrix is ​​formed by crosslinking a siloxane-based polymer containing one or more silane functional groups (Si—H) with a (meth)acrylic polyol. Specifically, the polymer matrix is ​​formed by crosslinking a (meth)acrylic polyol with a siloxane-based polymer containing a silane functional group. More specifically, the hydroxyl groups of the (meth)acrylic polyol can form crosslinks with the silane functional groups of the siloxane-based polymer through a hydrosilylation reaction. The hydrosilylation reaction can proceed rapidly in the presence of a Pt catalyst even at room temperature (e.g., a temperature in the range of about 15°C to 30°C without heating or cooling). Therefore, by employing a polymer matrix that can be rapidly crosslinked even at room temperature as a support, the photopolymer composition of one embodiment can improve the manufacturing efficiency and productivity of holographic recording media.

[0083] The polymer matrix can enhance the mobility of components (e.g., photoreactive monomers or plasticizers) contained in the photopolymer layer due to the flexible main chain of the siloxane-based polymer. In addition, the siloxane bond, which has excellent heat resistance and humidity and heat resistance, can easily ensure the reliability of the photopolymer layer on which optical information is recorded and the holographic recording medium including the same.

[0084] The polymer matrix may also have a relatively low refractive index, thereby enhancing the refractive index modulation of the photopolymer film. For example, the upper limit of the refractive index of the polymer matrix may be 1.53 or less, 1.52 or less, 1.51 or less, 1.50 or less, or 1.49 or less. The lower limit of the refractive index of the polymer matrix may be, for example, 1.41 or more, 1.42 or more, 1.43 to 1.44 or more, 1.45 or more, or 1.46 or more. In this specification, the "refractive index" may be a value measured using an Abbe refractometer at 25°C.

[0085] The photopolymer composition of the present invention may include the crosslinked polymer matrix or a precursor thereof. When the photopolymer composition includes a precursor of the polymer matrix, the precursor may include a siloxane-based polymer, a (meth)acrylic polyol, and a Pt-based catalyst.

[0086] As a specific example, the siloxane-based polymer may include a repeating unit represented by the following Chemical Formula 1 (Chemical Formula 3) and a terminal group represented by the following Chemical Formula 2 (Chemical Formula 4).

[0087] [ka] In the above Chemical Formula 1, Multiple R 1 and R 2 are the same or different and each independently represent hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms, n is an integer from 1 to 10,000, [ka] In the above Chemical Formula 2, Multiple R 11 ~R 13 are the same or different and each independently represent hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms, R of at least one repeating unit of the repeating unit represented by the chemical formula 1 and any one of the terminal groups of the terminal groups represented by the chemical formula 2 1 , R 2 and R 11 ~R 13 At least one of these is hydrogen.

[0088] In Chemical Formula 2, -(O)- means that when Si of the terminal group represented by Chemical Formula 2 is bonded to the repeating unit represented by Chemical Formula 1, it is bonded via oxygen (O) or directly without oxygen (O).

[0089] As used herein, the term "alkyl group" may be a straight-chain, branched-chain, or cyclic alkyl group. Non-limiting examples of the term "alkyl group" include methyl, ethyl, propyl (e.g., n-propyl, isopropyl, etc.), butyl (e.g., n-butyl, isobutyl, tert-butyl, sec-butyl, cyclobutyl, etc.), pentyl (e.g., n-pentyl, isopentyl, neopentyl, tert-pentyl, 1,1-dimethylpropyl, 1-ethylpropyl, 1-methylbutyl, cyclopentyl, etc.), hexyl (e.g., n-hexyl, 1-methylpentyl, 2-methylpentyl, etc.), and the like. butyl, 4-methylpentyl, 3,3-dimethylbutyl, 1-ethylbutyl, 2-ethylbutyl, cyclopentylmethyl, cyclohexyl, etc.), heptyl (e.g., n-heptyl, 1-methylhexyl, 4-methylhexyl, 5-methylhexyl, cyclohexylmethyl, etc.), octyl (e.g., n-octyl, tert-octyl, 1-methylheptyl, 2-ethylhexyl, 2-propylpentyl, etc.), nonyl (e.g., n-nonyl, 2,2-dimethylheptyl, etc.), and the like.

[0090] For example, R in Formulas 1 and 2 1 , R 2 and R 11 ~R 13 is methyl or hydrogen, and multiple R 1 , R 2 and R 11 ~R 13 At least two of R in Formula 1 may be hydrogen. 1 and R 2 are methyl and hydrogen, respectively, and R 11 ~R 13 are each independently methyl or hydrogen (e.g., polymethylhydrosiloxane having a terminal trimethylsilyl group or dimethylhydrosilyl group); 1 and R 2 are methyl and hydrogen, respectively, and the remaining R 1 and R 2are all methyl, and R in the above Chemical Formula 2 11 ~R 13 are each independently methyl or hydrogen (e.g., poly(dimethylsiloxane-co-methylhydrosiloxane) having a terminal trimethylsilyl group or a dimethylhydrosilyl group); or R 1 and R 2 are all methyl, and R in the above Chemical Formula 2 11 ~R 13 and the remaining groups are each independently methyl or hydrogen (for example, polydimethylsiloxane in which any or all of the terminal groups are dimethylhydrosilyl groups).

[0091] The siloxane-based compound may have a number-average molecular weight (Mn) ranging from 200 to 4,000. Specifically, the lower limit of the number-average molecular weight of the siloxane-based polymer may be, for example, 200 or more, 250 or more, 300 or more, or 350 or more, and the upper limit may be, for example, 3,500 or less, 3,000 or less, 2,500 or less, 2,000 or less, 1,500 or less, or 1,000 or less. When the number-average molecular weight of the siloxane-based polymer satisfies the above range, problems such as volatilization of the siloxane-based polymer during crosslinking with a (meth)acrylic polyol at room temperature or higher, resulting in a low degree of matrix crosslinking, or poor compatibility of the siloxane-based polymer with other components of the photopolymer composition, resulting in phase separation from these components, can be prevented, thereby enabling holographic recording media formed from the photopolymer composition to exhibit excellent optical recording properties and excellent durability under high-temperature / high-humidity conditions.

[0092] The number average molecular weight refers to the water average molecular weight (unit: g / mol) in terms of polystyrene measured by GPC. The process of measuring the number average molecular weight in terms of polystyrene measured by GPC can use commonly known analytical equipment, detectors such as a refractive index detector, and analytical columns, and commonly used temperature conditions, solvents, and flow rates can be applied. Specific examples of the measurement conditions include a temperature of 30°C, tetrahydrofuran solvent, and a flow rate of 1 mL / min.

[0093] The (meth)acrylic polyol may refer to a polymer in which one or more, specifically two or more, hydroxy groups are bonded to the main chain or side chain of a (meth)acrylate polymer. In this specification, unless otherwise specified, "(meth)acrylic (based)" refers to acrylic (based) and / or methacrylic (based), and is a term that includes all of acrylic (based), methacrylic (based), and a mixture of acrylic (based) and methacrylic (based).

[0094] The (meth)acrylic polyol may be a homopolymer of a (meth)acrylate monomer having a hydroxy group, a copolymer of two or more types of (meth)acrylate monomers having a hydroxy group, or a copolymer of a (meth)acrylate monomer having a hydroxy group and a (meth)acrylate monomer not having a hydroxy group. In this specification, the term "copolymer" includes all of random copolymers, block copolymers, and graft copolymers, unless otherwise specified.

[0095] Examples of the (meth)acrylate monomer having a hydroxy group include hydroxyalkyl(meth)acrylate and hydroxyaryl(meth)acrylate, where the alkyl may be an alkyl having 1 to 30 carbon atoms and the aryl may be an aryl having 6 to 30 carbon atoms. Examples of the (meth)acrylate monomer not having a hydroxy group include alkyl(meth)acrylate monomer and aryl(meth)acrylate monomer, where the alkyl may be an alkyl having 1 to 30 carbon atoms and the aryl may be an aryl having 6 to 30 carbon atoms.

[0096] The (meth)acrylic polyol may have a weight-average molecular weight (Mw) in the range of, for example, 150,000 to 1,000,000. The weight-average molecular weight refers to a weight-average molecular weight in terms of polystyrene measured by the GPC method described above. For example, the lower limit of the weight-average molecular weight may be 150,000 or more, 200,000 or more, or 250,000 or more, and the upper limit may be, for example, 900,000 or less, 850,000 or less, 800,000 or less, 750,000 or less, 700,000 or less, 650,000 or less, 600,000 or less, 550,000 or less, 500,000 or less, or 450,000 or less. When the weight-average molecular weight of the (meth)acrylic polyol satisfies the above range, the polymer matrix can fully exhibit its support function, resulting in little deterioration in the recording properties for optical information even over time, and the polymer matrix can be given sufficient flexibility to improve the mobility of components (e.g., photoreactive monomers or plasticizers) contained in the photopolymer composition, thereby minimizing deterioration in the recording properties for optical information.

[0097] In order to adjust the crosslinking density of the (meth)acrylic polyol with the siloxane polymer to a level advantageous for ensuring the functionality of the holographic recording medium, the hydroxyl group equivalent of the (meth)acrylic polyol can be adjusted to an appropriate level.

[0098] Specifically, the hydroxyl group (—OH) equivalent weight of the (meth)acrylic polyol can be, for example, in the range of 500 to 3,000 g / equivalent. More specifically, the lower limit of the hydroxyl group (—OH) equivalent weight of the (meth)acrylic polyol may be 600 g / equivalent or more, 700 g / equivalent or more, 800 g / equivalent or more, 900 g / equivalent or more, 1000 g / equivalent or more, 1100 g / equivalent or more, 1200 g / equivalent or more, 1300 g / equivalent or more, 1400 g / equivalent or more, 1500 g / equivalent or more, 1600 g / equivalent or more, 1700 g / equivalent or more, or 1750 g / equivalent or more. The upper limit of the hydroxyl (-OH) equivalent weight of the (meth)acrylic polyol may be 2900 g / equivalent or less, 2800 g / equivalent or less, 2700 g / equivalent or less, 2600 g / equivalent or less, 2500 g / equivalent or less, 2400 g / equivalent or less, 2300 g / equivalent or less, 2200 g / equivalent or less, 2100 g / equivalent or less, 2000 g / equivalent or less, or 1900 g / equivalent or less. The hydroxyl (-OH) equivalent weight of the (meth)acrylic polyol is the equivalent weight (g / equivalent) per hydroxy functional group, and is calculated by dividing the weight-average molecular weight of the (meth)acrylic polyol by the number of hydroxy functional groups per molecule. The smaller the equivalent weight value, the higher the functional group density, and the larger the equivalent weight value, the lower the functional group density. When the equivalent weight of the hydroxyl group (—OH) of the (meth)acrylic polyol satisfies the above range, the polymer matrix has an appropriate crosslink density and can fully function as a support, and the fluidity of the components contained in the layer formed from the photopolymer composition is improved, so that the boundary surface of the diffraction grating formed after recording does not collapse, and the initial refractive index modulation value can be maintained at an excellent level even over time, minimizing the decrease in recording characteristics for optical information.

[0099] The (meth)acrylic polyol may have a glass transition temperature (Tg) in the range of, for example, −60°C to −10°C. Specifically, the lower limit of the glass transition temperature may be, for example, −55°C or higher, −50°C or higher, −45°C or higher, −40°C or higher, −35°C or higher, −30°C or higher, or −25°C or higher, and the upper limit may be, for example, −15°C or lower, −20°C or lower, −25°C or lower, −30°C or lower, or −35°C or lower. When the glass transition temperature falls within the above range, the glass transition temperature can be lowered without significantly reducing the modulus of the polymer matrix, thereby increasing the mobility (fluidity) of other components in the photopolymer composition and improving the moldability of the photopolymer composition. The glass transition temperature can be measured using known methods, such as DSC (Differential Scanning Calorimetry) or DMA (Dynamic Mechanical Analysis).

[0100] The refractive index of the (meth)acrylic polyol may be, for example, 1.40 or more and less than 1.50. Specifically, the lower limit of the refractive index of the (meth)acrylic polyol may be, for example, 1.41 or more, 1.42 or more, 1.43 or more, 1.44 or more, 1.45 or more, or 1.46 or more, and the upper limit may be, for example, 1.49 or less, 1.48 or less, 1.47 or less, 1.46 or less, or 1.45 or less. When the (meth)acrylic polyol has a refractive index within the above range, it can contribute to enhancing refractive index modulation. The refractive index of the (meth)acrylic polyol is a theoretical refractive index and can be calculated using the refractive index of the monomers used in producing the (meth)acrylic polyol (measured at 25°C using an Abbe refractive index system) and the fraction (molar ratio) of each monomer.

[0101] The (meth)acrylic polyol and siloxane polymer can be used so that the molar ratio (SiH / OH) of the silane functional groups (Si-H) of the siloxane polymer to the hydroxy groups (-OH) of the (meth)acrylic polyol is 0.80 to 1.20. That is, the types and contents of the siloxane polymer and the (meth)acrylic polyol can be selected so that this molar ratio is satisfied when forming the polymer matrix. The lower limit of the molar ratio (SiH / OH) may be, for example, 0.81 or more, 0.85 or more, 0.90 or more, 0.95 or more, 1.00 or more, or 1.05 or more, and the upper limit may be, for example, 1.19 or less, 1.15 or less, 1.10 or less, 1.05 or less, 1.00 or less, or 0.95 or less. When the molar ratio (SiH / OH) satisfies the above range, the polymer matrix is ​​crosslinked at an appropriate crosslink density, improving reliability under high-temperature / high-humidity conditions and achieving a sufficient refractive index modulation value.

[0102] The Pt-based catalyst may be, for example, Karstedt's catalyst, etc. The polymer matrix precursor may further contain, if necessary, a non-metallic catalyst such as a rhodium-based, iridium-based, rhenium-based, molybdenum-based, iron-based, nickel-based, alkali metal or alkaline earth metal-based, Lewis acids-based, or Carbene-based catalyst in addition to the Pt-based catalyst.

[0103] The photoreactive monomer includes a monofunctional monomer and a polyfunctional monomer.

[0104] Specifically, the photoreactive monomer may include a polyfunctional (meth)acrylate monomer and a monofunctional (meth)acrylate monomer.

[0105] In addition, in the photopolymer composition, the proportion of the monofunctional monomer among the photoreactive monomers may be more than 40 wt% to 70 wt% or less, 42 wt% to 68 wt%, or 45 wt% to 65 wt%, and therefore, the remaining content based on the total of 100 of the photoreactive monomers may include the polyfunctional monomer.

[0106] As described above, during the photopolymerization process of the photopolymer composition, the photoreactive monomer is polymerized, and the refractive index becomes higher in areas where the polymer is present in a relatively large amount, and becomes lower in areas where the polymer binder is present in a relatively large amount, resulting in refractive index modulation, and this refractive index modulation generates a diffraction grating.

[0107] Specifically, examples of the polyfunctional monomer include (meth)acrylate-based α,β-unsaturated carboxylic acid derivatives, such as (meth)acrylate, (meth)acrylamide, (meth)acrylonitrile, or (meth)acrylic acid, or compounds containing a vinyl group or a thiol group.

[0108] An example of the polyfunctional monomer among the photoreactive monomers is a polyfunctional (meth)acrylate monomer having a refractive index of 1.5 or more, or 1.53 or more, or 1.5 to 1.7. Such a polyfunctional (meth)acrylate monomer having a refractive index of 1.5 or more, or 1.53 or more, or 1.5 to 1.7 may contain a halogen atom (bromine, iodine, etc.), sulfur (S), phosphorus (P), or an aromatic ring.

[0109] More specific examples of the polyfunctional (meth)acrylate monomer having a refractive index of 1.5 or more include bisphenol A modified diacrylates, fluorene acrylates (HR6022, etc., Miwon), bisphenol fluorene epoxy acrylates (HR6100, HR6060, HR6042, etc., Miwon), and halogenated epoxy acrylates (HR1139, HR3362, etc., Miwon).

[0110] An example of the monofunctional monomer is a monofunctional (meth)acrylate monomer. The monofunctional (meth)acrylate monomer may contain an ether bond and a fluorene functional group inside the molecule, and specific examples of such a monofunctional (meth)acrylate monomer include 2-phenylphenoxyethyl acrylate, phenoxybenzyl (meth)acrylate, o-phenylphenol ethylene oxide (meth)acrylate, benzyl (meth)acrylate, 2-(phenylthio)ethyl (meth)acrylate, and biphenylmethyl (meth)acrylate.

[0111] In this case, the polyfunctional monomer may include a monofunctional monomer. For example, HR6042 is a product containing 40% monofunctional acrylate, and the polyfunctional:monofunctional ratio may be 6:4.

[0112] Meanwhile, the photoreactive monomer may have a weight average molecular weight of 50 g / mol to 1000 g / mol, or 200 g / mol to 600 g / mol. The weight average molecular weight means a weight average molecular weight in terms of polystyrene measured by a GPC method.

[0113] In one embodiment, the photopolymer composition may include 20 to 300 parts by weight of the photoreactive monomer relative to 100 parts by weight of the polymer matrix or its precursor. For example, the lower limit of the content of the photoreactive monomer may be 20 parts by weight or more, 40 parts by weight or more, 50 parts by weight or more, or 70 parts by weight or more, and the upper limit may be 300 parts by weight or less, 200 parts by weight or less, 150 parts by weight or less, or 100 parts by weight or less. In this case, the reference content of the polymer matrix refers to the combined content (by weight) of the (meth)acrylic polyol and siloxane polymer that form the matrix. Meeting this range is advantageous for ensuring excellent optical recording properties and durability in high-temperature / high-humidity environments.

[0114] The photopolymer composition of the embodiment includes a photoinitiator, which is a compound that is activated by light or actinic radiation to initiate polymerization of compounds that contain photoreactive functional groups, such as the photoreactive monomers.

[0115] As the photoinitiator, any commonly known photoinitiator can be used without any particular limitation, and specific examples thereof include a photoradical polymerization initiator, a photocationic polymerization initiator, and a photoanionic polymerization initiator.

[0116] Specific examples of the photoradical polymerization initiator include imidazole derivatives, bisimidazole derivatives, N-arylglycine derivatives, organic azide compounds, titanocene, aluminate complexes, organic peroxides, N-alkoxypyridinium salts, thioxanthone derivatives, and amine derivatives. More specific examples of the photoradical polymerization initiator include 1,3-di(t-butyldioxycarbonyl)benzophenone, 3,3',4,4''-tetrakis(t-butyldioxycarbonyl)benzophenone, 3-phenyl-5-isoxazolone, 2-mercaptobenzimidazole, bis(2,4,5-triphenyl)imidazole, 2,2-dimethoxy-1,2-diphenylethane-1-one (product name: Irgacure 651 / manufacturer: BASF), 1-hy Examples include hydroxy-cyclohexyl-phenyl-ketone (product name: Irgacure 184 / manufacturer: BASF), 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 (product name: Irgacure 369 / manufacturer: BASF), bis(η5-2,4-cyclopentadiene-1-yl)-bis(2,6-difluoro-3-(1H-pyrrole-1-yl)-phenyl)titanium (product name: Irgacure 784 / manufacturer: BASF), and Ebecryl P-115 (manufacturer: SK entis).

[0117] Examples of the photocationic polymerization initiator include diazonium salts, sulfonium salts, and iodonium salts, such as sulfonic acid esters, imidosulfonates, dialkyl-4-hydroxysulfonium salts, arylsulfonic acid-p-nitrobenzyl esters, silanol-aluminum complexes, (η-benzene)(η-cyclopentadienyl)iron(II), etc. Further examples include benzoin tosylate, 2,5-dinitrobenzyl tosylate, and N-tosylphthalimide. More specific examples of the photocationic polymerization initiator include commercially available products such as Cyracure UVI-6970, Cyracure UVI-6974, and Cyracure UVI-6990 (manufacturer: Dow Chemical Co. in USA), Irgacure 264 and Irgacure 250 (manufacturer: BASF), and CIT-1682 (manufacturer: Nippon Soda).

[0118] Examples of the photoanionic polymerization initiator include borate salts, such as butylyl chlorine butyltriphenylborate. More specific examples of the photoanionic polymerization initiator include commercially available products such as Borate V (manufacturer: Spectra Group).

[0119] The photopolymer compositions of the present invention can also use unimolecular (Type I) or bimolecular (Type II) initiators. The (Type I) systems for free radical photopolymerization include, for example, aromatic ketone compounds combined with tertiary amines, such as benzophenone, alkylbenzophenones, 4,4'-bis(dimethylamino)benzophenone (Michler's ketone), anthrone, and halogenated benzophenones, or mixtures of the above types. The bimolecular (Type II) initiators include benzoin and its derivatives, benzil ketals, acylphosphine oxides, such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bisacylphosphine oxides, phenylglyoxyl esters, camphorquinone, alpha-aminoalkylphenones, alpha-, alpha-dialkoxyacetophenones, 1-[4-(phenylthio)phenyl]octane-1,2-dione 2-(O-benzoyloxime), and alpha-hydroxyalkylphenones.

[0120] The photopolymer composition may contain the initiator in a range of 0.1 to 10.0 parts by weight based on 100 parts by weight of the polymer matrix component. Specifically, the lower limit of the initiator content may be, for example, 0.2 parts by weight or more, 0.3 parts by weight or more, 0.4 parts by weight or more, 0.5 parts by weight or more, 0.6 parts by weight or more, 0.7 parts by weight or more, 0.8 parts by weight or more, or 0.9 parts by weight or more, and the upper limit may be, for example, 5.0 parts by weight or less. Satisfying this range is advantageous for ensuring optical recording properties and high-temperature / high-humidity durability.

[0121] Meanwhile, the photopolymer composition for forming a hologram may further include a non-reactive fluorine-based compound, the specific details of which are as described above.

[0122] Meanwhile, the adhesive additive may include a polydimethylsiloxane-based additive, and the polydimethylsiloxane-based additive may include all of the above.

[0123] As described above, the ratio of the monofunctional monomer among the photoreactive monomers may be more than 40 wt% to 70 wt% or less, 42 wt% to 68 wt%, or 45 wt% to 65 wt%, and in this case, in addition to a product containing both a monofunctional monomer and a polyfunctional monomer, a monofunctional acrylate monomer may be additionally used to achieve the above weight ratio.

[0124] The additionally used monofunctional acrylate monomer can also function as an adhesive additive to improve adhesive strength, and when used together with a polydimethylsiloxane additive, can further improve the adhesion enhancing effect and optical performance.

[0125] The additional adhesive additive may be the same as the monofunctional monomer, and examples of the acrylate monomer include 2-phenylphenoxyethyl acrylate, phenoxybenzyl (meth)acrylate, o-phenylphenol ethylene oxide (meth)acrylate, benzyl (meth)acrylate, 2-(phenylthio)ethyl (meth)acrylate, and biphenylmethyl (meth)acrylate.

[0126] The photopolymer composition may further include one or more selected from the group consisting of a dye, a catalyst, an antifoaming agent, and a plasticizer.

[0127] Specifically, the photopolymer composition may further include a photosensitive dye. The photosensitive dye acts as a photoinitiator, and more specifically, the photosensitive dye may also function as an initiator that initiates polymerization of the monomer and crosslinking monomer when stimulated by light irradiated onto the photopolymer composition. The photopolymer composition may include 0.01 wt % to 30 wt %, or 0.05 wt % to 20 wt % of the photosensitive dye.

[0128] The photosensitive dye is not particularly limited, and various commonly known compounds can be used. Specific examples of the photosensitive dye include sulfonium derivatives of ceramidonin, new methylene blue, thioerythrosine triethylammonium, 6-acetylamino-2-methylceramidonin, eosin, erythrosine, rose bengal, thionine, basic yellow, pinacyanol chloride, rhodamine 6G, gallocyanine, ethyl violet, Victoria blue R, Celestine blue, Quinaldine Red, crystal violet, brilliant green, and Astrazon orange G. G), Darrow Red, Pyronin Y, Basic Red 29, Pyrylium Iodide, Safranin O, Cyanine, Methylene Blue, Azure A, or a combination of two or more thereof.

[0129] The photopolymer composition may contain a commonly known catalyst to promote polymerization of the polymer matrix and photoreactive monomer. Examples of such catalysts include platinum-based catalysts such as Karstedt catalysts, rhodium-based catalysts, iridium-based catalysts, rhenium-based catalysts, molybdenum-based catalysts, iron-based catalysts, and nickel-based catalysts, as well as alkali metal and alkaline earth metal catalysts. Examples of non-metal catalysts include Lewis acids-based catalysts and Carbene-based catalysts.

[0130] The photopolymer composition may further include other additives.

[0131] Examples of the other additives include antifoaming agents and phosphate-based plasticizers. Examples of the antifoaming agent include silicon-based reactive additives, such as Tego Rad 2500. Examples of the plasticizer include phosphate compounds such as tributyl phosphate. The plasticizer can be added together with the fluorine-based compound in a weight ratio of 1:5 to 5:1. The plasticizer may have a refractive index of less than 1.5 and a molecular weight of 700 or less.

[0132] The photopolymer composition may further include an organic solvent, non-limiting examples of which include ketones, alcohols, acetates, and ethers, or a mixture of two or more thereof.

[0133] Specific examples of such organic solvents include ketones such as methyl ethyl ketone, methyl isobutyl ketone, acetylacetone, or isobutyl ketone; alcohols such as methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, or t-butanol; acetates such as ethyl acetate, i-propyl acetate, or polyethylene glycol monomethyl ether acetate; ethers such as tetrahydrofuran or propylene glycol monomethyl ether; or mixtures of two or more of these.

[0134] The organic solvent is added when mixing the components of the photopolymer composition, or when the components are dispersed or mixed in the organic solvent and added to the photopolymer composition. If the organic solvent content in the photopolymer composition is too low, the fluidity of the photopolymer composition may decrease, resulting in defects such as stripes in the final film. Furthermore, if the organic solvent is added in excess, the solids content may decrease, preventing sufficient coating and film formation, resulting in poor film properties and surface characteristics, and defects during drying and curing. Therefore, the photopolymer composition may contain an organic solvent such that the total solids concentration of the components contained therein is 1 wt% to 70 wt%, or 2 wt% to 50 wt%.

[0135] Specifically, the photopolymer composition may contain a solvent such that the total solids concentration of the composition is 1% to 70% by weight. Specifically, the solvent may be contained such that the total solids concentration of the composition is 2% by weight or more, 5% by weight or more, 10% by weight or more, or 20% by weight or more, and 65% by weight or less, 60% by weight or less, 55% by weight or less, or 50% by weight or less. If the solvent content in the composition is too low, the flowability of the composition may decrease, resulting in defects such as streaks in the final film. Furthermore, if excessive solvent is added, the solids content may decrease, resulting in insufficient coating and film formation, which may degrade the physical properties and surface characteristics of the photopolymer film and cause defects during the drying and curing processes.

[0136] The photopolymer composition can be used in holographic recording applications.

[0137] Furthermore, according to one embodiment of the present invention, a holographic recording medium including a photopolymer layer in which no visual hologram is recorded can be manufactured through the process of mixing and curing the photopolymer composition, and a visual hologram can be recorded on the medium through a predetermined exposure process.

[0138] A visual hologram can be recorded in the medium provided by the process of mixing and curing the photopolymer composition using known equipment and methods under commonly known conditions.

[0139] For example, the method for manufacturing the holographic recording medium may include the steps of: applying a photopolymer composition to a substrate to form a photopolymer film; and irradiating a predetermined region of the photopolymer film with a coherent laser to polymerize photoreactive monomers, including monofunctional monomers and polyfunctional monomers, contained in the photopolymer film, thereby recording optical information.

[0140] The photopolymer composition may be the photopolymer composition of the embodiment described above, and as the photopolymer composition has been described in detail above, a detailed description thereof will be omitted here.

[0141] In the step of forming the photopolymer film, a photopolymer composition having the above-described structure can be first prepared. When preparing the photopolymer composition, a commonly known mixer, stirrer, or mixer can be used to mix the components without any particular limitation. This mixing process can be carried out at a temperature ranging from 0°C to 100°C, from 10°C to 80°C, or from 20°C to 60°C.

[0142] In the step of forming the photopolymer film, the prepared photopolymer composition may be applied to a substrate to form a coating film formed from the photopolymer composition. The coating film may be dried naturally at room temperature or at a temperature ranging from 30°C to 80°C. This process may induce a hydrosilylation reaction between the remaining unreacted hydroxyl groups of the (meth)acrylic polyol and the silane functional groups of the siloxane polymer.

[0143] Meanwhile, according to still another embodiment of the present invention, an optical element including a holographic recording medium can be provided.

[0144] Specific examples of the optical element include an optical lens, a mirror, a deflection mirror, a filter, a diffusion screen, a diffraction element, a light guide, a wave guide, a holographic optical element having the function of a projection screen and / or a mask, a medium and a light diffusion plate of an optical memory system, an optical wavelength splitter, a reflective or transmissive color filter, etc.

[0145] An example of an optical element including the holographic recording medium is a holographic display device.

[0146] The hologram display device includes a light source unit, an input unit, an optical system, and a display unit. The light source unit emits a laser beam used to provide, record, and reproduce 3D image information of an object in the input unit and display unit. The input unit pre-inputs 3D image information of the object to be recorded in the display unit. For example, the input unit can input 3D information of the object, such as spatial light intensity and phase, into an electrically addressed liquid crystal SLM (SLM), using an input beam. The optical system includes mirrors, polarizers, beam splitters, beam shutters, lenses, etc., and can split the laser beam emitted from the light source unit into an input beam sent to the input unit, and a recording beam, reference beam, erase beam, read beam, etc. sent to the display unit.

[0147] The display unit receives 3D image information of an object from the input unit, records it on a hologram plate consisting of an optically addressed SLM (SLM), and reproduces the 3D image of the object. The 3D image information of the object can be recorded by interference between an input beam and a reference beam. The 3D image information of the object recorded on the hologram plate can be reproduced as a 3D image by a diffraction pattern generated by a read beam, and an erase beam can be used to quickly remove the formed diffraction pattern. Meanwhile, the hologram plate can be moved between a position where the 3D image is input and a position where it is reproduced. [Effects of the Invention]

[0148] In this specification, it is possible to provide a holographic recording medium having a photopolymer layer that not only has excellent recording efficiency but also achieves a higher refractive index modulation value even in a thin thickness range, has improved adhesive strength between adhesive protective layers, has low haze characteristics, and is more reliable than conventional holographic recording media.

[0149] Furthermore, in this specification, it is possible to provide a holographic recording medium and an optical element that realize a higher refractive index modulation value even in a thin thickness range, and that have low haze characteristics and excellent adhesive properties. [Brief explanation of the drawings]

[0150] [Figure 1] 1 is a simplified diagram illustrating a structure of a holographic recording medium according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0151] The functions and effects of the present invention will be described in more detail below through specific examples of the present invention, but these are presented as examples of the present invention and do not limit the scope of the invention in any way.

[0152] [Manufacturing example] (Production Example 1: Production of (meth)acrylic polyol) A 2L jacketed reactor was charged with 132g of butyl acrylate, 420g of ethyl acrylate, and 48g of hydroxybutyl acrylate, and diluted with 1200g of ethyl acetate. The reaction temperature was set to 60-70°C, and the mixture was stirred for 30 minutes to 1 hour. 0.42g of n-dodecyl mercaptan (n-DDM) was then added, and the mixture was stirred for another 30 minutes. 0.24g of the polymerization initiator AIBN was then added, and the mixture was polymerized at the reaction temperature for at least 4 hours until the residual acrylate content was less than 1%. This produced a (meth)acrylate copolymer with hydroxyl groups located in branched chains (weight average molecular weight approximately 300,000, OH equivalent approximately 1802g / equivalent).

[0153] (Production Example 2: Production of Fluorine-Based Compounds) 20.51 g of 2,2'-{oxybis[(1,1,2,2-tetrafluoroethane-2,1-diyl)oxy]}bis(2,2-difluoroethan-1-ol) was placed in a 1000 mL flask and dissolved in 500 g of tetrahydrofuran. While stirring at 0°C, 4.40 g of sodium hydride (60% dispersion in mineral oil) was carefully added in several portions. After stirring at 0°C for 20 minutes, 12.50 mL of 2-methoxyethoxymethyl chloride was slowly added dropwise. After confirming complete consumption of the reactants by 1H NMR, 29 g of a liquid product with a purity of over 95% was obtained in 98% yield by workup using dichloromethane. The weight-average molecular weight of the produced fluorine-based compound was 586, and the refractive index measured by Abbe refractometer was 1.361.

[0154] [Examples and Comparative Examples: Production of Photopolymer Compositions and Holographic Media] Example 1: Production of photopolymer composition and holographic recording medium (1) Preparation of photopolymer composition (prepared under darkroom conditions) A mixture was prepared by first mixing 0.48 g of trimethyl silyl terminated poly(methylhydrosiloxane) (manufactured by Sigma-Aldrich, number average molecular weight: approximately 390) as a siloxane polymer and 28.0 g (30 wt%) of the (meth)acrylic polyol prepared in Preparation Example 1 (SiH / OH molar ratio = 1.0).

[0155] As shown in Table 1 below, a photopolymer composition was prepared so that the ratio of monofunctional monomers to photoreactive monomers was approximately 46% by weight. That is, 14.5 g of a polyfunctional monomer (HR6042 (polyfunctional:monofunctional = 6:4); Miwon, refractive index 1.6) as the photoreactive monomer, 1.6 g of a monofunctional monomer (2-phenylphenoxyethyl acrylate), and 0.11 g of an adhesive additive BYK 331 (Byk Gardner, Vessel Materials, Germany) were mixed together intimately.

[0156] Next, 0.21 g of a photoinitiator, Borate V, 0.05 g of H-Nu 254, 0.08 g of a photosensitive dye, H-Nu 640, 9.1 g of the fluorine-based compound of Preparation Example 2, and a solvent of methyl ethyl ketone, methanol, EA, and methyl isobutyl ketone (MIBK) in a ratio of 3:2:4:4 were added to the mixture, and the mixture was thoroughly mixed again for about 10 minutes in the dark using a Paste mixer.

[0157] Next, 0.25 g (2 wt %) of Karstedt (Pt-based) catalyst was added for matrix crosslinking, and the mixture was thoroughly mixed at room temperature for 30 minutes or more to produce a photopolymer composition (photopolymerizable composition) by liquid phase crosslinking.

[0158] (2) Manufacturing of holographic recording media The photopolymer composition was applied to a 40 μm thick TAC substrate using a Meyer bar at 1.2 m / min to form a 15 μm thick coating, resulting in a wet film thickness of 15 μm. The coating was then dried at 80°C for 10 minutes to form a non-tacky photopolymer layer approximately 15 μm thick. After drying, the photopolymer coating thickness was approximately 15 μm, and the refractive index (n) of the photopolymer was approximately 1.501. The sample was then left in a dark room under constant temperature and humidity conditions of approximately 25°C and 50% RH for at least 24 hours.

[0159] The photopolymer layer thus prepared was mixed by exposing a red hologram using a slanted recording method.

[0160] Next, a BPSA adhesive protective layer 4 of 25 μm thickness was laminated on a 0.70 mm thick and 10 × 10 cm sized slide glass 5 to produce a photopolymer film, and then a 60 μm mold release film (MRF) 3 was laminated at a predetermined distance from the edge of the adhesive protective layer so that it intersected with the edge at a distance of approximately 0.5 cm to 1 cm as a guide for peeling.

[0161] Next, the release film was first laminated at a thickness of 25 mm so that the photopolymer layer 2 was in contact with the adhesive protective layer formed by crossing the end of the adhesive protective layer, and then the photopolymer layer 1 was again laminated at a thickness of 25 mm so that it was in contact with the adhesive protective layer, thereby producing the final hologram recording medium (photopolymer film) with the structure shown in Figure 1 (width 25 mm, length 80 mm, thickness 55 μm).

[0162] [Examples 2 to 6 and Comparative Examples 1 to 3: Production of Photopolymer Compositions and Holographic Recording Media] Photopolymer compositions and holographic recording media were produced using the same methods as in Example 1, except that the additive components were changed as shown in Table 1 below.

[0163] [Table 1]

[0164] [Experimental example: Holographic recording (evaluation of physical properties and performance of holographic recording media)] The physical properties of the above-mentioned Examples and Comparative Examples were evaluated by the following methods, and the results are shown in Table 2.

[0165] (1) Adhesion evaluation For the holographic recording medium sample, the release film 3 and adhesive protective layer 4 were peeled off, and the adhesive strength between the photopolymer layer 2 and the adhesive protective layer 4 was measured using an adhesive strength tester, and the results are shown in Table 2. The adhesive strength tester used a Texture Analyzer device to perform a 180° Peel Test and measure the load applied over a width of 25 mm to evaluate the adhesiveness.

[0166] (2) Water contact angle measurement For the holographic recording medium sample, 2 μl of H2O was dropped onto the photopolymer layer exposed to a 660 nm red light source (light intensity 3.0 mJ), and the water contact angle (surface contact angle) of the photopolymer layer was measured using a drop shape analyzer.

[0167] (3) Diffractive Efficiency (DE) (unit: %) For a sample of a holographic recording medium using the photopolymer composition, the reflection spectrum of the recorded photopolymer was measured using a UV-VIS spectrophotometer (Shimadzu, Solid Spec-3700), and the diffraction efficiency was measured by confirming the reflection peak.

[0168] Specifically, the photopolymer coating surface prepared in each of the Examples and Comparative Examples was laminated onto a slide glass, and the glass surface was fixed so that the laser light passed through the glass surface first during recording.

[0169] Holographic recording is achieved by the interference of two interfering beams (reference beam and object beam). In transmission recording, the two beams are incident on the same surface of the sample. The diffraction efficiency varies depending on the angle of incidence of the two beams, and when the angles of incidence of the two beams are the same, it becomes non-slanted. In non-slanted recording, the angles of incidence of the two beams are the same relative to the normal, so a diffraction grating is generated perpendicular to the film.

[0170] Recording was performed in a transmission non-slanted mode using a laser with a wavelength of 532 nm (2θ=45°), and the diffraction efficiency (η) was calculated using the following equation 2.

[0171] [Formula 2] η(%)={P D / (P D +P T )}×100 In the above formula 2, η is the diffraction efficiency, and P D is the power (mW / cm) of the diffracted beam from the sample after recording. 2 ) and P T is the power (mW / cm) of the beam transmitted through the sample after recording. 2 )

[0172] (4) Refractive index modulation value (Δn) measurement The refractive index modulation value (Δn) of the lossless dielectric grating of a transmission hologram can be calculated from the following general formula 2 (mathematical formula 1).

[0173]

number

[0174] (5) Hayes The haze was measured at the recorded portion of the photopolymer using a HAZEMETER ("NDH-5000" manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7136: 2000. The measurement light was incident on the side surface of the substrate of the holographic recording medium.

[0175] [Table 2] Referring to Table 2, it was confirmed that the holographic recording medium manufactured from the photopolymer composition of the example according to one embodiment of the present invention has excellent adhesive strength and a refractive index modulation value (Δn) of 0.020 or more, as well as excellent diffraction efficiency and low haze, due to the inclusion of a specific adhesive additive in the photopolymer composition.

[0176] In contrast, the surface of the holographic recording medium provided as the composition of Comparative Example 1 was found to be excessively sticky and to have a relatively high haze value, which confirmed that the holographic recording medium provided in Comparative Example 1 not only had low transparency but also had the problem of surface components easily adhering to other substrates and other parts.

[0177] In addition, the holographic recording media provided by the compositions of Comparative Examples 2 and 3 contained different types of additives from those of the Examples, and it was confirmed that the results in terms of adhesive strength were all poor compared to those of the Examples.

[0178] Therefore, even if the comparative examples show similar refractive index modulation values ​​and diffraction rates to the examples, they have higher haze values ​​or poor adhesive strength, making it difficult to attach or detach the hologram recording medium from or to another medium, resulting in a decrease in the performance of the hologram recording medium.

Claims

1. a substrate, an adhesive protective layer, and a photopolymer layer; the adhesive strength between the photopolymer layer and the adhesive protective layer before light irradiation is 500 gf / 20 nm to 5,000 gf / 20 nm; the haze value of the photopolymer layer measured in accordance with JIS K7136:2000 is 3% or less; Holographic recording media.

2. 2. The holographic recording medium according to claim 1, wherein the photopolymer layer has a water contact angle of 50° to 100° after light irradiation.

3. The holographic recording medium according to claim 1 , further comprising a release film between the adhesive protective layer and the photopolymer layer.

4. The holographic recording medium according to claim 3 , wherein the release film is laminated so as to cross the adhesive protective layer and the photopolymer layer for peeling.

5. 4. The holographic recording medium according to claim 3, wherein the release films are laminated at predetermined intervals in the range of 0.5 cm to 1 cm at the edge of the adhesive protective layer so as to intersect.

6. 2. The holographic recording medium according to claim 1, wherein the adhesive protective layer includes one or more selected from the group consisting of an acrylic adhesive, a silicone adhesive, a urethane adhesive, and a rubber adhesive.

7. the photopolymer layer comprises a photopolymer composition including a polymer matrix or a precursor thereof, photoreactive monomers including monofunctional and polyfunctional monomers, an adhesion additive, and a photoinitiator; 2. The holographic recording medium according to claim 1, wherein the proportion of monofunctional monomers in the photoreactive monomers is more than 40% by weight and not more than 70% by weight.

8. The holographic recording medium according to claim 7 , wherein the adhesion additive comprises a polydimethylsiloxane-based additive.

9. The holographic recording medium according to claim 7 , wherein the photopolymer composition further comprises a non-reactive fluorine-based compound.

10. An optical element comprising the holographic recording medium according to claim 1 .

11. a polymer matrix or a precursor thereof; a photoreactive monomer including a monofunctional monomer and a polyfunctional monomer; an adhesion additive; and a photoinitiator; A photopolymer composition for forming a hologram, wherein the proportion of monofunctional monomers in the photoreactive monomers is more than 40% by weight and not more than 70% by weight.

12. 12. The hologram-forming photopolymer composition of claim 11, wherein the adhesion additive comprises a polydimethylsiloxane-based additive.

13. The hologram-forming photopolymer composition of claim 11 , further comprising a non-reactive fluorine-based compound.

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