Photopolymer composition, holographic recording medium, method for producing the same, and optical element including the same

Abstract

The present application relates to a photopolymer composition, a holographic recording medium, a method for producing the same, and an optical element containing the same. The photopolymer composition can provide a holographic recording medium and an optical element containing the same that not only have excellent optical recording properties but also exhibit excellent reliability and transparency even in high-temperature environments.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0022505, filed February 16, 2024, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference.

[0002] The present application relates to a photopolymer composition, a holographic recording medium, a method for producing the same, and an optical element including the same. [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 produce 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 layer made from such a composition is irradiated with coherent laser light to induce local photopolymerization of the monomer.

[0006] This localized photopolymerization process results in a refractive index modulation, which in turn generates a diffraction grating. The refractive index modulation value (Δn) is affected by the thickness and diffraction efficiency (DE) of the photopolymer layer, and the angular selectivity becomes wider as the thickness decreases.

[0007] Recently, there has been an increasing demand for the development of materials that can achieve high diffraction efficiency and stable hologram maintenance, and various attempts are being made to manufacture holographic recording media that have high diffraction efficiency and refractive index modulation values ​​despite their thin thickness.

[0008] Meanwhile, when holographic recording media are used as optical elements in applications such as mobile devices and vehicle accessories (e.g., head-up displays), they are placed in high-temperature environments. In such cases, the diffraction gratings may deform, distorting the image or preventing the intended function from being achieved. Therefore, there is a need to develop a highly reliable photopolymer layer and a holographic recording medium including the same that exhibit minimal diffraction grating deformation despite the heat of the operating environment. Summary of the Invention [Problem to be solved by the invention]

[0009] According to one embodiment of the present invention, a photopolymer composition is provided.

[0010] According to another embodiment of the present invention, a holographic recording medium is provided.

[0011] According to yet another embodiment of the present invention, there is provided a method for manufacturing the holographic recording medium.

[0012] According to yet another embodiment of the present invention, there is provided an optical element including the holographic recording medium. [Means for solving the problem]

[0013] Hereinafter, a photopolymer composition, a holographic recording medium, a method for producing the same, and an optical element including the same according to specific embodiments of the present invention will be described.

[0014] Unless otherwise specified, the term "hologram recording medium" used herein refers to a medium capable of recording optical information in the entire visible and ultraviolet ranges (e.g., 300-1,200 nm) through an exposure process. For example, the term "hologram" used herein may include visual holograms such as in-line (Gabor) holograms, off-axis holograms, full-aperture transfer holograms, white-light transmission holograms ("rainbow holograms"), Denisyuk holograms, off-axis reflection holograms, edge-literature holograms, and holographic stereograms.

[0015] As used herein, in relation to the environmental conditions in which a holographic recording medium or an element including the same is placed, the term "high temperature" can refer to a temperature of 60°C or higher. For example, the high temperature can refer to a temperature of 65°C or higher, 70°C or higher, 75°C or higher, 80°C or higher, 85°C or higher, or 90°C or higher. The upper limit is not particularly limited, and may be, for example, 110°C or lower, 105°C or lower, 100°C or lower, 95°C or lower, 90°C or lower, 85°C or lower, or 80°C or lower. When temperature affects the characteristics of a substance, article, or each component, unless temperature is specifically mentioned, the temperature conditions under which the characteristics are measured or described can refer to room temperature (e.g., a temperature in the range of about 15 to 30°C, where no particular heating or cooling is performed).

[0016] In this specification, unless otherwise specified, the measured values ​​can be understood as the measured values ​​of the photopolymer layer contained in the holographic recording medium.

[0017] According to one embodiment of the present invention, there is provided a photopolymer composition comprising: a polymer matrix formed by crosslinking a siloxane-based polymer containing a silane functional group and an acrylic polyol, or a precursor thereof; a fluorine-based compound represented by the following Chemical Formula 1; a photoreactive monomer; and a photoinitiator system.

[0018] [ka]

[0019] In the above Chemical Formula 1, Z 1 is -O- or -NH-, Z 2 is a single bond, —O— or —NH—, L 1 represents a single bond or a divalent to hexavalent organic group obtained by removing a hydroxy group from a polyol having 2 to 6 alcohol groups, n and m each independently represent an integer of 1 to 5, and the sum of n and m is 2 to 6; R 1 , R 2 and R 3 are each independently a methyl group or an ethyl group, R 4 is a fluorine-containing substituent, which is an alkyl group having 1 to 20 carbon atoms and substituted with two or more fluorine atoms, a cycloalkyl group having 3 to 30 carbon atoms and substituted with two or more fluorine atoms, or an aryl group having 6 to 30 carbon atoms and substituted with two or more fluorine atoms.

[0020] The present inventors have confirmed that when a fluorine-based compound having a specific structure is used as a plasticizer for a photopolymer composition, a holographic recording medium can be provided that exhibits improved optical recording properties, as well as optical properties such as high reliability and high transparency even at high temperatures, and have completed the present invention.

[0021] Hereinafter, a photopolymer composition according to one embodiment of the present invention, a holographic recording medium formed from the photopolymer composition, a method for manufacturing the same, and an optical element including the holographic recording medium will be described in detail.

[0022] The photopolymer composition of one such embodiment includes a polymeric matrix or precursor thereof that acts as a support for the photopolymer layer formed therefrom.

[0023] The polymer matrix is ​​formed by crosslinking a siloxane-based polymer containing a silane functional group (Si-H) and an acrylic polyol. Specifically, the polymer matrix is ​​formed by crosslinking an acrylic polyol with a siloxane-based polymer containing a silane functional group. More specifically, the hydroxyl groups of the acrylic polyol can form crosslinks with the silane functional groups of the siloxane polymer through a hydrosilylation reaction. The hydrosilylation reaction can be rapidly carried out in the presence of a Pt catalyst even at room temperature (e.g., a temperature in the range of about 15 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.

[0024] The polymer matrix can enhance the mobility of components (e.g., photoreactive monomers or plasticizers) contained in the photopolymer layer through the flexible backbone of the siloxane-based polymer. In addition, the siloxane bond, which has excellent heat resistance and humidity resistance, can easily ensure the reliability of the photopolymer layer on which optical information is recorded and the holographic recording medium including the same.

[0025] The polymer matrix may have a relatively low refractive index, thereby enhancing the refractive index modulation of the layer formed from the photopolymer composition. 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, 1.40 or more, 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. In this specification, the "refractive index" may be a value measured using an Abbe refractometer at 25°C.

[0026] 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, an acrylic polyol, and a Pt-based catalyst.

[0027] The siloxane-based polymer may include, for example, a repeating unit represented by the following Chemical Formula 2 and a terminal group represented by the following Chemical Formula 3:

[0028] [ka]

[0029] In the above Chemical Formula 2, Multiple R 11 and R 12 are the same or different and each independently represents hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms, k is an integer from 1 to 10,000;

[0030] [ka]

[0031] In the above Chemical Formula 3, Multiple R 13 ~R15 are the same or different and each independently represents hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms, At least one repeating unit selected from the repeating units represented by the chemical formula 2 and any one of the terminal groups selected from the terminal groups represented by the chemical formula 3 11 ~R 15 At least one of is hydrogen.

[0032] In Chemical Formula 3, -(O)- means that when Si of the terminal group represented by Chemical Formula 3 is bonded to the repeating unit represented by Chemical Formula 2, it is bonded via oxygen (O) or directly without oxygen (O).

[0033] 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.), methyl ether ... pentyl, 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.), etc.

[0034] As an example, R in Formulas 2 and 3 11 ~R 15 is methyl or hydrogen, and multiple R 11 ~R 15At least two of the R in the formula 2 may be hydrogen. 11 and R 12 are methyl and hydrogen, respectively, and R 13 ~R 15 are each independently methyl or hydrogen (e.g., polymethylhydrosiloxane having a terminal group of a trimethylsilyl group or a dimethylhydrosilyl group); 11 and R 12 are methyl and hydrogen, respectively, and the remaining R 11 and R 12 are all methyl, and R 13 ~R 15 are each independently methyl or hydrogen (e.g., poly(dimethylsiloxane-co-methylhydrosiloxane) having a terminal trimethylsilyl group or a dimethylhydrosilyl group); or R 11 and R 12 are all methyl, and R 13 ~R 15 and the remaining groups are each independently methyl or hydrogen (for example, polydimethylsiloxane in which one or all of the terminal groups are dimethylhydrosilyl groups).

[0035] 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 a decrease in the degree of matrix crosslinking due to volatilization of the siloxane-based polymer during crosslinking with an acrylic polyol at room temperature or higher, or poor compatibility of the siloxane-based polymer with other components of the photopolymer composition, resulting in phase separation with these components, can be prevented. As a result, holographic recording media formed from the photopolymer composition can exhibit excellent optical recording properties and excellent durability under high-temperature conditions.

[0036] The number average molecular weight refers to the number average molecular weight (unit: g / mol) measured in terms of polystyrene by GPC. The process of measuring the number average molecular weight in terms of polystyrene 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 25°C, tetrahydrofuran solvent, and a flow rate of 1 mL / min.

[0037] The 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 an acrylate polymer. In this specification, unless otherwise specified, "acrylic" refers to one or more selected from an acryloyl group, a methacryloyl group, and derivatives thereof, or a repeating unit formed by polymerization thereof, and unless otherwise specified, "acrylate" refers to one or more selected from an acrylate and a methacrylate, or a repeating unit formed by polymerization thereof.

[0038] The acrylic polyol may be a homopolymer of an acrylate monomer having a hydroxy group, a copolymer of two or more acrylate monomers having a hydroxy group, or a copolymer of an acrylate monomer having a hydroxy group and an acrylate monomer not having a hydroxy group. In this specification, the term "copolymer" encompasses random copolymers, block copolymers, and graft copolymers unless otherwise specified.

[0039] Examples of the 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 acrylate monomer not having a hydroxy group include alkyl(meth)acrylate and aryl(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. In this specification, "(meth)acrylate" is a term that refers to acrylate and / or methacrylate unless otherwise specified.

[0040] The acrylic polyol may have a weight-average molecular weight (Mw) in the range of 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 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 acrylic polyol satisfies the above range, the polymer matrix can fully function as a support, resulting in little decrease in optical information recording properties over time. Furthermore, the polymer matrix can be given sufficient flexibility, improving the mobility of components (e.g., photoreactive monomers or plasticizers) contained in the photopolymer composition, thereby minimizing the decrease in optical information recording properties.

[0041] In order to adjust the crosslink density of the acrylic polyol with the siloxane polymer to a level advantageous for ensuring the functionality of the holographic recording medium, the hydroxyl equivalent of the acrylic polyol can be adjusted to an appropriate level.

[0042] Specifically, the hydroxyl (—OH) equivalent of the acrylic polyol may be, for example, within a range of 500 to 3,000 g / equivalent. More specifically, the lower limit of the hydroxyl (—OH) equivalent of the 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 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 acrylic polyol is the equivalent weight (g / equivalent) per hydroxy functional group, and is calculated by dividing the weight-average molecular weight of the 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 hydroxyl group (—OH) equivalent of the acrylic polyol satisfies the above range, the polymer matrix has an appropriate crosslink density and fully functions 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 deterioration of recording characteristics for optical information.

[0043] The acrylic polyol may have a glass transition temperature (Tg) in the range of, for example, −60 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 range is satisfied, 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).

[0044] The refractive index of the 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 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 acrylic polyol has a refractive index within the above range, it can contribute to enhancing refractive index modulation. The refractive index of the acrylic polyol is a theoretical refractive index and can be calculated using the refractive index of the monomers used in producing the acrylic polyol (measured at 25°C using an Abbe refractometer) and the fraction (molar ratio) of each monomer.

[0045] The 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 acrylic polyol is 0.80 to 3.5. That is, when forming the polymer matrix, the type and content of the siloxane polymer and the acrylic polyol can be selected so as to satisfy this molar ratio. 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, or 0.95 or more, and the upper limit may be, for example, 3.4 or less, 3.3 or less, 3.2 or less, 3.1 or less, 3.05 or less, or 3.0 or less. When the molar ratio (SiH / OH) satisfies this range, the polymer matrix is ​​crosslinked at an appropriate crosslink density, improving reliability under high-temperature conditions and achieving sufficient refractive index modulation.

[0046] The Pt-based catalyst may be, for example, Karstedt's catalyst, etc. The polymer matrix precursor may further include, in addition to the Pt-based catalyst, a rhodium-based, iridium-based, rhenium-based, molybdenum-based, iron-based, nickel-based, alkali metal or alkaline earth metal-based, Lewis acid-based, or carbene-based non-metallic catalyst, if necessary.

[0047] Meanwhile, a hologram recording medium can be recorded by irradiating an object beam and a reference beam onto a photopolymer layer formed from the photopolymer composition of the embodiment. The interference field between the object beam and the reference beam prevents photopolymerization of the photoreactive monomer in the destructive interference region, but photopolymerization of the photoreactive monomer occurs in the constructive interference region. As the photoreactive monomer is continuously consumed in the constructive interference region, a concentration difference occurs between the photoreactive monomer in the destructive interference region and the constructive interference region, resulting in diffusion of the photoreactive monomer in the destructive interference region into the constructive interference region. The resulting refractive index modulation generates a diffraction grating.

[0048] Therefore, the photoreactive monomer may include a compound having a refractive index higher than that of the polymer matrix to achieve the above-described refractive index modulation. However, not all of the photoreactive monomers included in the photopolymer composition of the embodiment are limited to having a refractive index higher than that of the polymer matrix. At least some of the photoreactive monomers may have a refractive index higher than that of the polymer matrix to achieve a high refractive index modulation value. For example, the photoreactive monomer may include a monomer having a refractive index of 1.50 or more, 1.51 or more, 1.52 or more, 1.53 or more, 1.54 or more, 1.55 or more, 1.56 or more, 1.57 or more, 1.58 or more, 1.59 or more, or 1.60 or more and 1.70 or less.

[0049] The photoreactive monomer may include one or more monomers selected from the group consisting of monofunctional monomers having one photoreactive functional group and polyfunctional monomers having two or more photoreactive functional groups. In this case, the photoreactive functional group may be, for example, a (meth)acryloyl group, a vinyl group, or a thiol group. More specifically, the photoreactive functional group may be a (meth)acryloyl group.

[0050] The monofunctional monomer may include, for example, one or more selected from the group consisting of benzyl (meth)acrylate (Miwon Corporation, M1182, refractive index 1.5140), benzyl 2-phenylacrylate, phenoxybenzyl (meth)acrylate (Miwon Corporation, M1122, refractive index 1.565), phenol (ethylene oxide) (meth)acrylate (phenol (EO) (meth)acrylate; Miwon Corporation, M140, refractive index 1.516), phenol (ethylene oxide) 2 (meth)acrylate (Miwon Corporation, M142, refractive index 1.510), O-phenylphenol (ethylene oxide) (meth)acrylate (O-phenylphenol (EO) (meth)acrylate; Miwon Corporation, M1142, refractive index 1.577), phenylthioethyl (meth)acrylate (Miwon Corporation, M1162, refractive index 1.560), and biphenylmethyl (meth)acrylate.

[0051] The polyfunctional monomer is, for example, bisphenol A (ethylene oxide). 2~10 Di(meth)acrylate (bisphenol A (EO) 2~10(meth)acrylate; Miwon's M240 refractive index 1.537, M241 refractive index 1.529, M244 refractive index 1.545, M245 refractive index 1.537, M249 refractive index 1.542, M2100 refractive index 1.516, M2101 refractive index 1.512), bisphenol A epoxy di(meth)acrylate (Miwon's PE210 refractive index 1.557, PE2120A refractive index 1.533, PE2120B refractive index 1.534, PE2020C refractive index 1.539, PE2120S refractive index 1.556), bisfluorene di(meth)acrylate (Miwon's HR6022 refractive index 1.600, HR6040 refractive index 1.600, HR604 The epoxy resin may include one or more selected from the group consisting of modified bisphenol A fluorene di(meth)acrylate (Miwon's HR6060 refractive index 1.584, HR6100 refractive index 1.562, HR6200 refractive index 1.530), tris(2-hydroxyethyl) isocyanurate tri(meth)acrylate (Miwon's M370 refractive index 1.508), phenol novolac epoxy (meth)acrylate (Miwon's SC6300 refractive index 1.525), and cresol novolac epoxy (meth)acrylate (Miwon's SC6400 refractive index 1.522, SC6400C refractive index 1.522).

[0052] In one embodiment, the photopolymer composition may include 50 to 300 parts by weight of the photoreactive monomer relative to 100 parts by weight of the polymer matrix. For example, the lower limit of the photoreactive monomer content may be 50 parts by weight or more, 60 parts by weight or more, 70 parts by weight or more, 80 parts by weight or more, or 90 parts by weight or more, and the upper limit may be 300 parts by weight or less, 280 parts by weight or less, 250 parts by weight or less, 220 parts by weight or less, 200 parts by weight or less, 190 parts by weight or less, or 180 parts by weight or less. In this case, the reference polymer matrix content refers to the combined content (by weight) of the acrylic polyol and siloxane polymer that form the matrix. Satisfying this range is advantageous for ensuring excellent optical recording properties and durability in high-temperature environments.

[0053] In this specification, the content of the polymer matrix refers to the combined content (by weight) of the acrylic polyol and siloxane polymer that form the matrix, i.e., the content of the polymer matrix includes both the polymer matrix formed by crosslinking the acrylic polyol and the siloxane polymer and the partially uncrosslinked polymer matrix precursor.

[0054] In one embodiment, the photopolymer composition includes a photoinitiator system, which may refer to a photoinitiator or a combination of a photosensitizer and a coinitiator that allows polymerization to be initiated by light.

[0055] The photopolymer composition of the embodiment can include a photosensitizer and a coinitiator as a photoinitiator system.

[0056] As the photosensitizer, for example, a photosensitive dye can be used. Specifically, examples of the photosensitive dye include silicon rhodamine compounds, 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, and crystal violet. One or more dyes selected from the group consisting of fluorescein violet, brilliant green, Astrazon orange G, darrow red, pyronin Y, basic red 29, pyrrylium iodide, safranin O, cyanine, methylene blue, Azure A, and BODIPY may be used.

[0057] For example, the photosensitive dye may be a cyanine dye such as Cy3 or Cy5 (H-Nu640, Spectra) or Safranin O.

[0058] The photopolymer composition of one embodiment may contain the photosensitive dye in a range of 0.01 to 10 parts by weight per 100 parts by weight of the polymer matrix. Specifically, the lower limit of the content of the photosensitive dye may be, for example, 0.05 parts by weight or more, 0.07 parts by weight or more, or 0.10 parts by weight or more, and the upper limit may be, for example, 5 parts by weight or less. When the content falls within this range, an appropriate polymerization reaction rate is exhibited, which is advantageous for ensuring the desired optical recording properties.

[0059] The coinitiator may be an electron donor, an electron acceptor, or a mixture thereof.

[0060] For example, the photopolymer composition of the embodiment may include an electron donor as a coinitiator, such as a borate anion represented by the following Chemical Formula 4:

[0061] [Chemical formula 4] BX 1 X 2 X 3 X 4

[0062] In the above chemical formula 4, X 1 ~X 4 are each independently a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an aryl group having 6 to 30 carbon atoms, an arylalkyl group having 7 to 30 carbon atoms, an alkylaryl group having 7 to 30 carbon atoms, or an allyl group, and X 1 ~X 4 At least one of is not an aryl group.

[0063] When the alkyl group having 1 to 20 carbon atoms, the alkenyl group having 2 to 20 carbon atoms, the aryl group having 6 to 30 carbon atoms, the arylalkyl group having 7 to 30 carbon atoms, the alkylaryl group having 7 to 30 carbon atoms or the allyl group is substituted, it may be substituted with one or more selected from the group consisting of halogen and an alkoxy group having 1 to 5 carbon atoms.

[0064] Specifically, X 1 ~X 3 are each independently methyl, ethyl, propyl, n-butyl, n-pentyl, n-hexyl, cyclobutyl, cyclopentyl, cyclohexyl, ethenyl, propenyl, phenyl, methylphenyl, methoxyphenyl, naphthyl, methylnaphthyl, or methoxynaphthyl, substituted or unsubstituted with halogen; 4 may be n-butyl, n-pentyl, or n-hexyl. More specifically, the borate anion represented by Chemical Formula 4 may be, for example, a triphenylbutylborate anion.

[0065] The cation bonded to the borate anion does not absorb light and may be an alkali metal cation or a quaternary ammonium cation. The quaternary ammonium cation refers to an ammonium cation in which nitrogen (N) is substituted with four substituents, and the four substituents may each independently be an alkyl group having 1 to 40 carbon atoms, an aryl group having 6 to 30 carbon atoms, an arylalkyl group having 6 to 40 carbon atoms, or an alkyl group having 2 to 40 carbon atoms linked via an ester bond (e.g., -CH2CH2-O-CO-CH2CH2CH3).

[0066] As the electron donor, for example, commercially available butyryl choline triphenylbutylborate (Borate V, manufactured by Spectra Group) can be used.

[0067] For example, the photopolymer composition of the embodiment can include an electron acceptor as a coinitiator, which can include, for example, an onium salt, such as a sulfonium salt, an iodonium salt, or a mixture thereof.

[0068] For example, the electron acceptor may include an iodonium salt, such as commercially available H-Nu254 (Spectra).

[0069] The photopolymer composition of one embodiment may contain the co-initiator in a range of 0.05 to 10 parts by weight per 100 parts by weight of the polymer matrix. Specifically, the lower limit of the co-initiator content may be, for example, 0.1 parts by weight or more, 0.2 parts by weight or more, 0.3 parts by weight or more, 0.4 parts by weight or more, or 0.5 parts by weight or more, and the upper limit may be, for example, 5 parts by weight or less. When the co-initiator content falls within this range, an appropriate polymerization reaction rate is exhibited, which is advantageous for ensuring the desired optical recording properties.

[0070] The photoinitiator system may contain an additional photoinitiator to remove the color of the photosensitive dye and to react all of the unreacted photoreactive monomers after irradiation with light for recording. Examples of the photoinitiator include acetophenone-based compounds, oxime-based compounds, phosphine oxide-based compounds, thioxanthone-based compounds, benzoate ester-based compounds, imidazole-based compounds, N-arylglycine derivatives, organic azide compounds, titanocene, aluminate complexes, organic peroxides, N-alkoxypyridinium salts, amine derivatives, diazonium salts, sulfonium salts, iodonium salts, sulfonate esters, imidosulfonates, dialkyl-4-hydroxysulfonium salts, arylsulfonic acid-p-nitrobenzyl esters, silanol-aluminum complexes, (η6-benzene)(η5-cyclopentadienyl)iron(II), benzoin tosylate, 2,5-dinitrobenzyl tosylate, N-tosylphthalimide, and mixtures thereof.

[0071] More specifically, examples of the photoinitiator include 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one (Irgacure 369), 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]ethanone-1-(O-acetyloxime) (Irgacure OXE02, BASF), [(Z)-(1-oxo-1-phenylpropan-2-ylidene)amino]benzoate (e.g., TPI-057 or TPI-059 manufactured by TREEEL), and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (Irgacure TPO), bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide (Irgacure 1700), phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (Irgacure 819), 2,4-diethylthioxanthone, 2-chlorothioxanthone, isopropylthioxanthone, diisopropylthioxanthone, ethyl 4-(dimethylamino)benzoate, 1,3-di(t-butyldioxycarbonyl)benzophenone, 3 ,3',4,4''-Tetrakis(t-butyldioxycarbonyl)benzophenone, 3-phenyl-5-isoxazoline, 2-mercaptobenzimidazole, bis(2,4,5-triphenyl)imidazole, 2,2-dimethoxy-1,2-diphenylethan-1-one (Irgacure 651), 1-hydroxy-cyclohexyl-phenyl ketone (Irgacure 184), bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl)titanium (Irgacure 784), Ebecryl P-115 (SK entis), Cyracure UVI-6970, Cyracure UVI-6974, Cyracure UVI-6990 (Dow Chemical Co.Examples include, but are not limited to, Irgacure 264, Irgacure 250 (BASF), CIT-1682 (Nippon Soda), or mixtures thereof.

[0072] The photopolymer composition of the embodiment includes a fluorine-based compound as a plasticizer.

[0073] The plasticizer facilitates refractive index modulation during the manufacture of a holographic recording medium. More specifically, the plasticizer lowers the glass transition temperature of the polymer matrix, improving the fluidity of the photoreactive monomer. Having a low refractive index and non-reactive properties, the plasticizer is uniformly distributed within the polymer matrix, and migrates in the opposite direction to the movement of the non-photopolymerized photoreactive monomer, thereby contributing to refractive index modulation. The plasticizer also contributes to improving the moldability of the photopolymer composition.

[0074] The fluorine-based compound may have a low refractive index of 1.45 or less to perform the function of the plasticizer. Specifically, the upper limit of the refractive index may be, for example, 1.44 or less, 1.43 or less, 1.42 or less, 1.41 or less, 1.40 or less, 1.39 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.

[0075] The non-reactive plasticizer is dispersed within the polymer matrix, which is the support for the photopolymer layer, without being chemically bonded to the polymer matrix. This allows the non-reactive plasticizer to migrate to the surface of the photopolymer layer depending on the environment in which the holographic recording medium is used, particularly at high temperatures. The plasticizer that migrates to the surface forms a modified refractive index layer with a different refractive index at the surface of the photopolymer layer, which is a major cause of reduced reliability of the holographic recording medium.

[0076] The photopolymer composition according to one embodiment of the present invention may contain a fluorine-based compound that exhibits little or negligible migration to the surface of the photopolymer layer even in high-temperature environments. As a result, a modified refractive index layer formed by migration of the plasticizer to the surface is not formed or is formed only to a very small extent, thereby providing a holographic recording medium that can clearly reproduce the intended image even at high temperatures and exhibits high transparency.

[0077] The photopolymer composition of the embodiment includes a fluorine-based compound represented by the following Chemical Formula 1:

[0078] [ka]

[0079] In the above Chemical Formula 1, Z 1 is -O- or -NH-, Z 2 is a single bond, —O— or —NH—, L 1 represents a single bond or a divalent to hexavalent organic group obtained by removing a hydroxy group from a polyol having 2 to 6 alcohol groups, n and m each independently represent an integer of 1 to 5, and the sum of n and m is 2 to 6; R 1 , R 2 and R3 are each independently a methyl group or an ethyl group, R 4 is a fluorine-containing substituent, which is an alkyl group having 1 to 20 carbon atoms and substituted with two or more fluorine atoms, a cycloalkyl group having 3 to 30 carbon atoms and substituted with two or more fluorine atoms, or an aryl group having 6 to 30 carbon atoms and substituted with two or more fluorine atoms.

[0080] In the above chemical formula 1, L 1 is a moiety containing a carbonyl group and R 4 Therefore, the sum of n and m is 2 to 6, and L 1 is the same as the number of bonds in

[0081] As an example, in the above-mentioned Chemical Formula 1, L 1 In the above Chemical Formula 1, L may be a single bond. 1 is a single bond, n and m are each 1, and Z 2 In this case, the fluorine-based compound represented by Chemical Formula 1 may be represented by the following Chemical Formula 1-1.

[0082] [ka]

[0083] In the above chemical formula 1-1, Z 1’ , R 1’ , R 2’ , R 3’ and R 4’ are Z in the above chemical formula 1. 1 , R 1 , R 2 , R 3 and R 4 It is the same as the above Z 1’ , R 1’ , R 2’ , R 3’ and R 4’ is herein defined as Z in Chemical Formula 1. 1 , R 1 , R 2 , R 3 and R4 The substituents may be those described as specific examples of the substituents.

[0084] As another example, in the above-mentioned Chemical Formula 1, L 1 is a polyol having 2 to 6 alcohol groups, the hydroxy group of which is Z 1 and Z 2 The polyol may be a divalent to hexavalent organic group in which the hydroxy group is removed from the polyol by substitution with one of the following:

[0085] [ka]

[0086] The trivalent organic group obtained by removing the hydroxy group from

[0087] [ka]

[0088] It is expressed as follows.

[0089] In the above Chemical Formula 1, the L 1 may be, for example, a divalent organic group obtained by removing a hydroxy group from a diol such as ethanediol, propanediol, or butanediol; a trivalent organic group obtained by removing a hydroxy group from a triol such as glycerol or trimethylolpropane; a tetravalent organic group obtained by removing a hydroxy group from a tetraol such as pentaerythritol or ditrimethylolpropane; a pentavalent organic group obtained by removing a hydroxy group from a pentaol such as 6-methylheptanepentaol; or a hexavalent organic group obtained by removing a hydroxy group from a hexaol such as dipentaerythritol.

[0090] In the above chemical formula 1, L 1 is a single bond or a divalent organic group, n and m are each 1. 1When is a trivalent to hexavalent organic group, n may be greater than m. For example, n may be an integer of 1 to 3, and m may be an integer of 1.

[0091] As an example, the above L 1 may be a trivalent organic group in the form in which a hydroxy group is removed from glycerol, which is a triol. Furthermore, n may be 2 and m may be 1. In this case, the fluorine-based compound represented by Chemical Formula 1 may be represented by the following Chemical Formula 1-2.

[0092] [ka]

[0093] In the above chemical formula 1-2, Z 1” , Z 2” , R 1” , R 2” , R 3” and R 4” are Z in the above chemical formula 1. 1 , Z 2 , R 1 , R 2 , R 3 and R 4 It is the same as the above Z 1” , Z 2” , R 1” , R 2” , R 3” and R 4” is herein defined as Z in Chemical Formula 1. 1 , Z 2 , R 1 , R 2 , R 3 and R 4 The substituents may be those described as specific examples of the substituents.

[0094] In Chemical Formula 1, the fluorine-containing substituent may be an alkyl group having 1 to 20 carbon atoms and substituted with two or more fluorines, a cycloalkyl group having 3 to 30 carbon atoms and substituted with two or more fluorines, or an aryl group having 6 to 30 carbon atoms and substituted with two or more fluorines. Specifically, the fluorine-containing substituent may be a linear alkyl group having 1 to 20 carbon atoms and substituted with two or more fluorines. More specifically, the fluorine-containing substituent may be -(CH2) a (CF2) b CHF2 or -(CH2) a (CF2) b CF3, where a is an integer of 0 to 3, an integer of 0 to 2, or an integer of 1, and b is an integer of 0 to 19, an integer of 0 to 15, an integer of 0 to 12, an integer of 0 to 11, an integer of 0 to 10, or an integer of 0 to 9.

[0095] The photopolymer composition of one embodiment may contain 20 to 200 parts by weight of the fluorine-based compound per 100 parts by weight of the polymer matrix. Specifically, the lower limit of the content of the fluorine-based compound may be, for example, 20 parts by weight or more, 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, 200 parts by weight or less, 180 parts by weight or less, 150 parts by weight or less, 120 parts by weight or less, or 100 parts by weight or less. When the content falls within this range, problems such as poor compatibility with components contained in the photopolymer composition, elution of some of the fluorine-based compound onto the surface of the photopolymer layer, or poor haze can be avoided. By using a fluorine-based compound with a sufficiently low refractive index, a large refractive index modulation value can be exhibited after recording, which is advantageous for ensuring excellent optical recording properties.

[0096] The photopolymer composition of the embodiment includes a predetermined polymer matrix, a photoreactive monomer, and a fluorine-based compound, and can ensure superior high-temperature reliability.

[0097] For example, the photopolymer composition of the embodiment may contain 25 to 40 wt % of the polymer matrix, 25 to 45 wt % of the photoreactive monomer, and 25 to 50 wt % of the fluorine-based compound, based on the total weight of the polymer matrix, the photoreactive monomer, and the fluorine-based compound.

[0098] More specifically, the polymer matrix may be included in an amount of, for example, 25% by weight or more and 40% by weight or less, 35% by weight or less, or 33% by weight or less. The photoreactive monomer may be included in an amount of, for example, 25% by weight or more, 30% by weight or more, or 33% by weight or more and 45% by weight or less, 43% by weight or less, or 41% by weight or less. The fluorine-based compound may be included in an amount of, for example, 25% by weight or more, 30% by weight or more, or 33% by weight or more and 50% by weight or less, 45% by weight or less, 40% by weight or less, or 38% by weight or less. Within these ranges, migration of the fluorine-based compound to the surface at high temperatures can be effectively prevented, making it easier to ensure high-temperature reliability and high-temperature transparency.

[0099] The photopolymer composition of the embodiment may further include additives such as antifoaming agents.

[0100] The photopolymer composition of the embodiment may include a silicone-based reactive additive as an antifoaming agent, such as Tego Rad 2500, which is a commercially available silicone-based reactive additive.

[0101] The content of the additive, for example, the antifoaming agent, can be appropriately adjusted to a level that does not impair the function of the holographic recording medium.

[0102] The photopolymer composition of the embodiment may additionally include a solvent.

[0103] The solvent may be an organic solvent, and may be, for example, one or more organic solvents selected from the group consisting of ketones, alcohols, acetates, and ethers, but is not limited thereto. Specific examples of such organic solvents include one or more selected from the group consisting of ketones such as methyl ethyl ketone, methyl isobutyl ketone, acetylacetone, and isobutyl ketone; alcohols such as methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, and t-butanol; acetates such as ethyl acetate, i-propyl acetate, and polyethylene glycol monomethyl ether acetate; and ethers such as tetrahydrofuran and propylene glycol monomethyl ether.

[0104] The organic solvent may be added when the components of the photopolymer composition are mixed together, or the components may be added in a dispersed or mixed state in the organic solvent and then added to the photopolymer composition.

[0105] The photopolymer composition of one embodiment may contain a solvent to provide a solids concentration of 1 to 90 wt %. Specifically, the photopolymer composition may contain a solvent to provide a solids concentration of 20 wt % or more, 30 wt % or more, 50 wt % or more, or 60 wt % or more, and 85 wt % or less, 80 wt % or less, 75 wt % or less, or 70 wt % or less. Within these ranges, the photopolymer composition exhibits suitable flowability, allowing it to form a coating film without defects such as streaks, and it is possible to form a photopolymer layer with desired physical properties and surface characteristics without defects occurring during the drying and curing process.

[0106] Meanwhile, according to another embodiment of the present invention, there is provided a holographic recording medium including a photopolymer layer formed from the photopolymer composition.

[0107] The holographic recording medium according to the other embodiment includes a fluorine-based compound represented by Chemical Formula 1, so that a modified refractive index layer formed by the plasticizer in the photopolymer layer migrating to the surface is not formed or is formed only to a very small extent, thereby enabling the intended image to be clearly reproduced even at high temperatures and exhibiting high transparency.

[0108] The holographic recording medium of the other embodiment may have a sufficiently low value of Pn calculated by the following equation 1. As an example, the holographic recording medium of the other embodiment may have a P80 (thickness ratio of the modified refractive index layer formed at 80°C) calculated by the following equation 1 of 0.10% or less.

[0109] [Formula 1] Pn(%) = {A1 / (A1+A2)} × 100

[0110] In the above formula 1, Pn is the thickness ratio of the modified refractive index layer formed at n° C., A1 is the thickness of the modified refractive index layer formed at n°C, and the modified refractive index layer refers to a surface portion of the photopolymer layer that exhibits a refractive index difference of 0.0010% or more from the central refractive index of the photopolymer layer measured at an incident angle of 70° and a wavelength of 320 to 1680 nm; A2 is the thickness of the remaining part of the photopolymer layer excluding the modified refractive index layer.

[0111] The modified refractive index layer refers to a surface portion of a photopolymer layer that exhibits a refractive index different from the central refractive index of the photopolymer layer, and refers to a portion that exhibits a refractive index difference of 0.0010% or more from the central refractive index. For example, if the central refractive index of the photopolymer layer is 1.5, the modified refractive index layer can be defined based on the boundary where the refractive index is higher or lower than 1.5 by 0.000015 (=1.5×0.00001).

[0112] The thickness (A1) of the modified refractive index layer is determined by measuring the refractive index from the surface to the center of the photopolymer layer within a wavelength range of 320 to 1680 nm and using the above formula 1. The thickness (A1) of the modified refractive index layer is determined as the thickness at the wavelength within the wavelength range of 320 to 1680 nm at which the thickness (A1) of the modified refractive index layer is observed to be the thickest.

[0113] A P80 of 0.10% or less means that even when the holographic recording medium is exposed to a high temperature of 80° C., migration of fluorine-based compounds to the surface is suppressed, and the degree of formation of a modified refractive index layer due to migration of fluorine-based compounds is minimal. Therefore, when Pn calculated by Equation 1 above is a sufficiently low value, the holographic recording medium can clearly reproduce the originally intended image without a decrease in image reproduction ability even at high temperatures.

[0114] The upper limit of the P80 may be, for example, 0.10% or less, 0.09% or less, 0.08% or less, 0.07% or less, 0.06% or less, or 0.05% or less, and the lower limit may be, for example, 0% or more.

[0115] For the method and detailed conditions for measuring the refractive index and the like for calculating Pn in the above formula 1, please refer to the contents described in the below-mentioned Test Example 1. Pn in the above formula 1 may be the thickness ratio of the modified refractive index layer formed at n° C. to the holographic recording medium before recording.

[0116] The holographic recording medium of the other embodiment may have a small difference in refractive index between the center and the surface. For example, the difference in refractive index between the center and the surface within 0.05% of the thickness of the photopolymer layer at 80°C may be 0.080 or less.

[0117] The difference in refractive index between the center of the photopolymer layer and the surface within 0.05% of the thickness at 80°C may be, for example, 0.080 or less, 0.070 or less, 0.060 or less, 0.050 or less, 0.040 or less, 0.030 or less, 0.028 or less, or 0.026 or less. The lower limit of the refractive index difference is not particularly limited and may be 0 or more or 0.001 or more. The method and detailed conditions for measuring the refractive index can be found in Test Example 1 described below.

[0118] Holographic recording media tend to be opaque due to the miscibility of a low-refractive-index component and a high-refractive-index component used to record optical properties. Furthermore, the decomposition and migration of the plasticizer, a component with a low refractive index, to the surface at high temperatures can easily make the holographic recording media even more opaque.

[0119] However, the holographic recording medium of the other embodiment can maintain excellent transparency even when exposed to high temperatures by using a fluorine-based compound represented by Chemical Formula 1 as a plasticizer, which minimizes decomposition and migration at high temperatures and exhibits excellent compatibility with components having a high refractive index.

[0120] Specifically, the holographic recording medium of the other embodiment may have a sufficiently low ΔHn calculated by the following equation 2. As an example, the holographic recording medium of the other embodiment may have a ΔH80 (increase in haze at 80°C) calculated by the following equation 2 of 10%p or less.

[0121] [Formula 2] △Hn(%p)=B2-B1

[0122] In the above formula 2, ΔHn is the increase in haze of the holographic recording medium at n° C. B1 is the initial haze of the holographic recording medium before being left at n°C, B2 is the haze of the hologram recording medium after it has been left at n° C. for 100 hours.

[0123] The ΔH80 of 10%p or less means that migration of fluorine-based compounds to the surface is suppressed and the increase in haze is small even when the holographic recording medium is exposed to a high temperature of 80° C. Therefore, when ΔHn calculated by the above formula 2 is a sufficiently low value, the holographic recording medium can exhibit transparent optical properties even at high temperatures.

[0124] The upper limit of ΔH80 may be, for example, 9%p or less, 8%p or less, 7%p or less, 6%p or less, 5%p or less, 4%p or less, 3%p or less, 2.5%p or less, 2%p or less, 1.5%p or less, or 1.0%p or less. The lower limit of the haze increase is not particularly limited and may be 0%p or more. The haze increase can be measured by the method described in Test Example 2 below. ΔHn in Equation 2 above may mean the haze increase at n°C for the holographic recording medium after recording.

[0125] The holographic recording medium according to another embodiment may further include a substrate on at least one surface of the photopolymer layer. The type of substrate is not particularly limited, and any substrate known in the related art may be used. For example, substrates such as glass, polyethylene terephthalate (PET), triacetyl cellulose (TAC), polycarbonate (PC), and cycloolefin polymer (COP) may be used.

[0126] The photopolymer layer is formed from the photopolymer composition of the embodiment, and thus exhibits a large refractive index modulation value and high diffraction efficiency despite its thin thickness, ensuring excellent optical recording properties and excellent reliability even in high temperature environments.

[0127] The thickness of the photopolymer layer may be, for example, in the range of 5.0 to 40.0 μm. Specifically, the lower limit of the thickness of the photopolymer layer may be, for example, 6 μm or more, 7 μm or more, 8 μm or more, or 9 μm or more. The upper limit of the thickness may be, for example, 35 μm or less, 30 μm or less, 29 μm or less, 28 μm or less, 27 μm or less, 26 μm or less, 25 μm or less, 24 μm or less, 23 μm or less, 22 μm or less, 21 μm or less, 20 μm or less, 19 μm or less, or 18 μm or less.

[0128] The holographic recording medium of the other embodiment is not limited to this, but may be one in which a reflection hologram or a transmission hologram is recorded.

[0129] The holographic recording medium may have a notch filter structure related to the diffraction grating structure. The notch filter structure of the holographic recording medium of the other embodiment may mean, for example, that the diffraction grating is non-slanted (substantially 0°) relative to the substrate surface, i.e., parallel to the substrate surface. Such a holographic recording medium may have a structure in which two layers with different refractive indices (e.g., a high refractive index layer and a low refractive index layer) are alternately repeated. The two repeated layers may have the same or different thicknesses. Such a non-slanted diffraction grating recording may be fabricated by making the angles of incidence of the incident object beam and reference beam equal relative to the normal. The non-slanted structure exhibits a clearer degree of deformation (e.g., contraction or expansion) under high temperature and high humidity conditions than the slanted structure, and is less susceptible to the contraction and expansion of the substrate.

[0130] The holographic recording medium of this embodiment may have high diffraction efficiency. For example, when a notch filter hologram is recorded in the holographic recording medium, the holographic recording medium may have a diffraction efficiency of 70% or more. In this case, the thickness of the photopolymer layer may be, for example, 5 to 30 μm. Specifically, when a notch filter hologram is recorded, the diffraction efficiency may be 71% or more, 72% or more, 73% or more, 74% or more, 75% or more, 80% or more, 81% or more, 82% or more, 83% or more, 84% or more, 85% or more, 86% or more, or 87% or more. Thus, the holographic recording medium of this embodiment may achieve excellent diffraction efficiency even when including a thin photopolymer layer. The diffraction efficiency can be measured using the method described in Test Example 2 below.

[0131] The holographic recording medium of the other embodiment can achieve a refractive index modulation value (Δn) of 0.020 or more, 0.025 or more, 0.026 or more, 0.027 or more, 0.028 or more, 0.029 or more, 0.030 or more, 0.031 or more, 0.032 or more, 0.033 or more, 0.034 or more, or 0.035 or more, even when the photopolymer layer is as thin as 5 to 30 μm. The upper limit of the refractive index modulation value is not particularly limited, but may be, for example, 0.060 or less. The refractive index modulation value can be measured by the method described in Test Example 2 below.

[0132] The holographic recording medium of the other embodiment is expected to provide a variety of optical elements that can be used in environments where a lot of heat is generated, by exhibiting not only excellent optical recording characteristics and excellent durability in high-temperature environments, but also highly transparent optical characteristics.

[0133] The application of the holographic recording medium according to the other embodiment is not particularly limited. As a non-limiting example, the holographic recording medium may be used in applications that are likely to be exposed to high-temperature environments, specifically, smart devices such as mobile devices, components for wearable displays, or automotive components (e.g., head-up displays). The holographic recording medium according to the other embodiment has excellent high-temperature reliability and can exhibit its intended optical recording characteristics even at high temperatures.

[0134] Meanwhile, according to yet another embodiment of the present invention, there is provided a method for manufacturing a holographic recording medium, comprising the step of applying the photopolymer composition to form a photopolymer layer.

[0135] 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.

[0136] In the step of forming the photopolymer layer, a photopolymer composition having the above-described structure can be first prepared. When preparing the photopolymer composition, a commonly known mixer, agitator, or mixer can be used without any limitation to mix the components. 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.

[0137] In the step of forming the photopolymer layer, a prepared photopolymer composition may be applied 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 to 80°C. This process may induce a hydrosilylation reaction between the remaining unreacted hydroxyl groups of the acrylic polyol and the silane functional groups of the siloxane polymer.

[0138] The photopolymer layer manufactured by the step of forming the photopolymer layer may have a fluorine-based compound, a photoreactive monomer, a photoinitiator system, and optional additives uniformly dispersed in a crosslinked polymer matrix.

[0139] According to yet another embodiment, the method for manufacturing a holographic recording medium may include, after forming a photopolymer layer, irradiating a predetermined region of the photopolymer layer with a coherent laser to selectively polymerize photoreactive monomers contained in the photopolymer layer, thereby recording optical information.

[0140] When a coherent laser is irradiated onto the photopolymer layer during the optical information recording step, polymerization of the photoreactive monomer occurs in regions where constructive interference occurs, forming a photopolymer, while polymerization of the photoreactive monomer does not occur or is suppressed in regions where destructive interference occurs, leaving the photoreactive monomer. The unreacted photoreactive monomer then diffuses into the photopolymer where the concentration of the photoreactive monomer is low, causing refractive index modulation, which in turn produces a diffraction grating. As a result, a hologram, i.e., optical information, is recorded in the photopolymer layer having the diffraction grating.

[0141] In yet another embodiment, the method for manufacturing a holographic recording medium may further include, after the step of recording optical information, a step of photobleaching by irradiating light entirely onto the photopolymer layer on which the optical information is recorded.

[0142] In the photo-bleaching step, ultraviolet light is irradiated onto the photopolymer layer on which optical information is recorded, thereby terminating the reaction of the photoreactive monomer remaining in the photopolymer layer and removing the color of the photosensitive dye. For example, in the photo-bleaching step, ultraviolet light (UVA) in the range of 320 to 400 nm is irradiated to terminate the reaction of the photoreactive monomer, thereby removing the color of the photosensitive dye.

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

[0144] Specific examples of the optical element include 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, diffraction members, light guides, waveguides, holographic optical elements having the functions of projection screens and / or masks, media and light diffusion plates in optical memory systems, optical wavelength splitters, reflective and transmissive color filters, etc.

[0145] An example of an optical element including the hologram recording medium is a hologram display device, which includes a light source unit, an input unit, an optical system, and a display unit.

[0146] Specifically, the light source unit is a part that emits a laser beam used to provide, record and reproduce three-dimensional image information of an object in the input unit and display unit.

[0147] The input unit is a part that inputs 3D image information of an object to be recorded on the display unit in advance. Specifically, it is a part that can input 3D information of an object, such as spatial light intensity and phase, into an electrically addressed liquid crystal SLM, and can use an input beam at this time.

[0148] The optical system may be composed of mirrors, polarizers, beam splitters, beam shutters, lenses, etc. The optical system can split the laser beam emitted from the light source unit into an input beam sent to the input unit, a recording beam sent to the display unit, a reference beam, an erase beam, a read beam, etc.

[0149] 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]

[0150] The photopolymer composition according to one embodiment of the present invention can provide a holographic recording medium and an optical element including the same that not only have excellent optical recording properties but also exhibit excellent reliability and transparency even in high temperature environments. [Brief explanation of the drawings]

[0151] [Figure 1] 1 is a schematic diagram showing the setup of a recording device for hologram recording. Specifically, Fig. 1 shows the process in which a laser beam of a predetermined wavelength is emitted from a light source 10, and then passes through mirrors 20, 20', an iris 30, a spatial filter 40, an iris 30', a collimation lens 50, and a polarized beam splitter (PBS) 60 before being irradiated onto a hologram recording medium (PP) 80 positioned on one side of a mirror 70. DETAILED DESCRIPTION OF THE INVENTION

[0152] 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.

[0153] In the following Production Examples, Examples, Comparative Examples, etc., the contents of raw materials and the like refer to the contents on a solid basis unless otherwise specified.

[0154] Production Example 1: Production of 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 stirring was continued for 30 minutes to 1 hour. 0.42g of n-dodecyl mercaptan (n-DDM) was added and stirring was continued for another 30 minutes. 0.24g of polymerization initiator AIBN was then added and polymerization was continued for at least 4 hours at the reaction temperature until the residual acrylate content was less than 1%. This produced an acrylate copolymer with hydroxyl groups located in the branched chain (weight average molecular weight approximately 300,000, OH equivalent approximately 1802g / equivalent).

[0155] Example 1: Preparation of photopolymer composition and holographic recording medium (1) Preparation of photopolymer composition 0.57 g of a siloxane polymer, poly(methylhydrosiloxane) (Sigma-Aldrich, number average molecular weight: approximately 590, Si-H equivalent: approximately 103 g / equivalent), and 33.4 g of the acrylic polyol with a solid content of 30 wt% (solid content: 10.02 g) prepared in Preparation Example 1 were mixed together (SiH / OH molar ratio = 1.0).

[0156] Next, 11.5g of HR6042 (Miwon, refractive index 1.60) as a photoreactive monomer, 0.08g of H-Nu640 (Spectra), 0.3g of Borate V as a coinitiator, 11.5g of a fluorine-based compound represented by the following formula a as a plasticizer, and 26g of methyl isobutyl ketone (MIBK) as a solvent were added and stirred in a paste mixer for about 30 minutes while shielded from light. A Karstedt (Pt-based) catalyst was then added for matrix crosslinking to produce a photopolymer composition.

[0157] [ka]

[0158] (2) Manufacturing of holographic recording media The photopolymer composition was coated to a predetermined thickness on a 60 μm thick TAC substrate using a Mayer bar and dried for 10 minutes at 80° C. After drying, the photopolymer layer had a thickness of approximately 10 μm.

[0159] Examples 2 and 3, Comparative Examples 1 and 2: 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 types of plasticizers were changed as shown in Table 1 below.

[0160] [Table 1]

[0161] Test Example 1: Evaluation of migration of holographic recording media The temperature-dependent transition of the holographic recording medium before recording was evaluated. Specifically, to evaluate the temperature-dependent transition of the photopolymer layer, the refractive index from the surface to the center of the photopolymer layer was measured as a function of temperature. The refractive index was measured at an incident angle of 70° and in the wavelength range of 320 to 1680 nm using a spectroscopic ellipsometry system from Ellipso Technology.

[0162] The thickness (A1) of the modified refractive index layer showing a refractive index difference of 0.0010% or more from the central refractive index of the photopolymer layer and the thickness (A2) of the remaining part of the photopolymer layer were measured at different temperatures and are listed in Table 2 below.

[0163] Furthermore, the percentage (Pn) of the thickness (A1) of the modified refractive index layer relative to the total thickness (A1+A2) of the photopolymer layer according to the temperature was calculated using the following formula 1, and is shown in Table 2 below.

[0164] [Formula 1] Pn(%) = {A1 / (A1+A2)} × 100

[0165] In the above formula 1, Pn is the thickness ratio of the modified refractive index layer formed at n° C., A1 is the thickness of the modified refractive index layer formed at n°C, and the modified refractive index layer refers to a surface portion of the photopolymer layer that exhibits a refractive index difference of 0.0010% or more from the central refractive index of the photopolymer layer measured at an incident angle of 70° and a wavelength of 320 to 1680 nm; A2 is the thickness of the remaining part of the photopolymer layer excluding the modified refractive index layer.

[0166] [Table 2]

[0167] The degree of temperature-dependent transition of the holographic recording medium before recording was evaluated. Specifically, the refractive index at the center and surface of the photopolymer layer was measured for each temperature and wavelength, and the results are listed in Table 3 below. The refractive index was measured using the device described above.

[0168] [Table 3]

[0169] Referring to Tables 2 and 3, it can be seen that the photopolymer layer of Example 1 is a modified refractive index layer with a negligible thickness that does not affect the function of the holographic recording medium, and that the difference in absolute refractive index between the center and the surface is also very small.

[0170] In contrast, the photopolymer layer of Comparative Example 1 has a very thick modified refractive index layer that interferes with the function of the holographic recording medium, and it is confirmed that the difference in absolute refractive index between the center and the surface is also very large.

[0171] Test Example 2: Performance evaluation of holographic recording media (1) P80 (thickness ratio of the modified refractive index layer at 80°C, %) The migration of the holographic recording medium before recording was evaluated at high temperatures. Specifically, to evaluate the migration of the photopolymer layer at 80°C, the refractive index from the surface to the center of the photopolymer layer was measured at 80°C. The refractive index was measured at an incident angle of 70° and wavelengths of 320 to 1680 nm using a spectroscopic ellipsometry system from Ellipso Technology.

[0172] Then, P80 (thickness ratio of the modified refractive index layer at 80° C.) was calculated using the following formula 1, and is shown in Table 4 below.

[0173] [Formula 1] Pn(%) = {A1 / (A1+A2)} × 100

[0174] In the above formula 1, Pn is the thickness ratio of the modified refractive index layer formed at n° C., A1 is the thickness of the modified refractive index layer formed at n°C, and the modified refractive index layer refers to a surface portion of the photopolymer layer that exhibits a refractive index difference of 0.0010% or more from the central refractive index of the photopolymer layer measured at an incident angle of 70° and a wavelength of 320 to 1680 nm; A2 is the thickness of the remaining part of the photopolymer layer excluding the modified refractive index layer.

[0175] (2) △H80 (Haze increase at 80℃, %p) A diffraction grating was recorded using the setup shown in Figure 1. Specifically, the manufactured photopolymer layer was laminated on a mirror and then irradiated with a laser. This allowed the recording of a notch filter hologram with periodic refractive index modulation in the thickness direction due to interference between the incident light (L) and the light (L') reflected by the mirror. In this example, the notch filter hologram was recorded with an incident angle of 0°. Notch filters and Bragg reflectors are optical elements that reflect only light of a specific wavelength, and have a structure in which two layers with different refractive indices are repeatedly stacked periodically at a constant thickness.

[0176] The difference in haze of a holographic recording medium with a recorded diffraction grating was evaluated before and after exposure to high temperatures. Haze was measured using a haze meter (Murakami Color Research Laboratory, HM-150) in accordance with JIS K 7136. The measurement light was incident on the side of the substrate of the holographic recording medium.

[0177] Specifically, the holographic recording medium was left at 80°C for 100 hours, and the difference in haze before and after leaving was calculated using the following formula 2. The increase in haze at 80°C (△H80) is shown in Table 4 below.

[0178] [Formula 2] △Hn(%p)=B2-B1

[0179] In the above formula 2, ΔHn is the increase in haze of the holographic recording medium at n° C. B1 is the initial haze of the holographic recording medium before being left at n°C, B2 is the haze of the hologram recording medium after it has been left at n° C. for 100 hours.

[0180] (3) Diffraction efficiency For the holographic recording medium in which the diffraction grating was recorded, the diffraction efficiency (η) was calculated using the following formula 3.

[0181] [Formula 3] η(%)={P D / (P D +P T )}×100

[0182] In the above formula 3, 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 )

[0183] (4) Refractive index modulation value (△n) For the holographic recording medium in which a diffraction grating is recorded, the refractive index modulation value (Δn) was calculated using the following formula 4 and Bragg's equation.

[0184]

number

[0185] In the above formula, η is the reflectivity diffraction efficiency (DE), d is the thickness of the photopolymer layer, λ is the wavelength of the incident light for recording (660 nm or 532 nm), θ is the incident angle of the incident light for recording, φ is the slant angle of the grating, Δn is the refractive index modulation value, n is the refractive index of the photopolymer, and Λ is the period of the diffraction grating. In the above examples and comparative examples, holograms were recorded using a notch filter method, so θ (incident angle) and φ (slant angle of the grating) were both 0°.

[0186] [Table 4]

[0187] Referring to Table 4, it can be seen that the holographic recording media manufactured in Examples 1 to 3 exhibit high diffraction efficiency and refractive index modulation values, and are excellent in high-temperature stability, resulting in only a small amount of modified refractive index layer formation and a very small increase in haze. In contrast, the holographic recording media manufactured in Comparative Examples 1 and 2 have poor optical recording properties, and are found to form thick modified refractive index layers, particularly at high temperatures, and to experience a significant increase in haze.

[0188] This confirms that the photopolymer composition according to one embodiment of the invention, by containing a fluorine-based compound with a specific structure, can provide a holographic recording medium that exhibits excellent optical recording properties, high-temperature stability, and high transparency.

Claims

1. a polymer matrix or a precursor thereof formed by crosslinking a siloxane-based polymer containing a silane functional group and an acrylic polyol; A fluorine-based compound represented by the following chemical formula 1: A photopolymer composition comprising: a photoreactive monomer; and a photoinitiator system: 【Chemistry 1】 In the above Chemical Formula 1, Z １ is —O— or —NH—, Z ２ is a single bond, —O— or —NH—, L １ represents a single bond or a divalent to hexavalent organic group obtained by removing a hydroxy group from a polyol having 2 to 6 alcohol groups, n and m are each independently an integer of 1 to 5, and the sum of n and m is 2 to 6; R １ , R ２ and R ３ are each independently a methyl group or an ethyl group, R ４ is a fluorine-containing substituent, which is an alkyl group having 1 to 20 carbon atoms and substituted with two or more fluorine atoms, a cycloalkyl group having 3 to 30 carbon atoms and substituted with two or more fluorine atoms, or an aryl group having 6 to 30 carbon atoms and substituted with two or more fluorine atoms.

2. 2. The photopolymer composition of claim 1, wherein the siloxane-based polymer comprises a repeating unit represented by the following Chemical Formula 2 and a terminal group represented by the following Chemical Formula 3: 【Chemistry 2】 In the above Chemical Formula 2, Multiple R １１ and R １２ are the same or different and each independently represent hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms, k is an integer from 1 to 10,000; 【Transformation 3】 In the above Chemical Formula 3, Multiple R １３ ~R １５ are the same or different and each independently represent hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms, At least one repeating unit selected from the repeating units represented by the chemical formula 2 and any one of the terminal groups selected from the terminal groups represented by the chemical formula 3, １１ ~R １５ At least one of is hydrogen.

3. 2. The photopolymer composition according to claim 1, wherein the acrylic polyol is a polymer having a structure in which a hydroxy group is bonded to a main chain or a side chain of an acrylate polymer.

4. The photoreactive monomers include benzyl (meth)acrylate, benzyl 2-phenylacrylate, phenoxybenzyl (meth)acrylate, phenol (ethylene oxide) (meth)acrylate, and phenol (ethylene oxide) ２ one or more monofunctional monomers selected from the group consisting of (meth)acrylate, O-phenylphenol(ethylene oxide)(meth)acrylate, phenylthioethyl(meth)acrylate, and biphenylmethyl(meth)acrylate; bisphenol A(ethylene oxide) ２～１０ 10. The photopolymer composition of claim 1, comprising one or more polyfunctional monomers selected from the group consisting of di(meth)acrylate, bisphenol A epoxy di(meth)acrylate, bisfluorene di(meth)acrylate, modified bisphenol fluorene di(meth)acrylate, tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate, phenol novolac epoxy (meth)acrylate, and cresol novolac epoxy (meth)acrylate; or a mixture of two or more thereof.

5. 2. The photopolymer composition according to claim 1, wherein the photoreactive monomer is contained in an amount of 50 to 300 parts by weight based on 100 parts by weight of the polymer matrix.

6. The photopolymer composition of claim 1 , wherein the photoinitiator system comprises a photosensitive dye and a coinitiator.

7. 7. The photopolymer composition of claim 6, wherein the coinitiator comprises a borate anion represented by Formula 4: [Chemical formula 4] BX １ X ２ X ３ X ４ In the above chemical formula 4, X １ ~X ４ are each independently a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an aryl group having 6 to 30 carbon atoms, an arylalkyl group having 7 to 30 carbon atoms, an alkylaryl group having 7 to 30 carbon atoms, or an allyl group, and X １ ~X ４ At least one of is not an aryl group.

8. L of Formula 1 １ The photopolymer composition of claim 1 , wherein is a single bond; or a trivalent organic group in the form of glycerol triol from which a hydroxy group has been removed.

9. 2. The photopolymer composition of claim 1, wherein the fluorine-containing substituent is a linear alkyl group having 1 to 20 carbon atoms and substituted with two or more fluorine atoms.

10. The fluorine-containing substituent is —(CH ２ ) ａ (CF ２ ) ｂ CHF ２ or -(CH ２ ) ａ (CF ２ ) ｂ CF ３ 2. The photopolymer composition of claim 1, wherein a is an integer from 0 to 3 and b is an integer from 0 to 19.

11. The photopolymer composition of claim 1, wherein the fluorine-based compound represented by Chemical Formula 1 includes one or more fluorine-based compounds selected from the group consisting of fluorine-based compounds represented by the following Chemical Formula 1-1 and the following Chemical Formula 1-2: 【Chemistry 4】 In the above chemical formula 1-1, Z １’ , R １’ , R ２’ , R ３’ and R ４’ are Z in the above formula 1. １ , R １ , R ２ , R ３ and R ４ is identical to 【Transformation 5】 In the above chemical formula 1-2, Z １” , Z ２” , R １” , R ２” , R ３” and R ４” are Z in the above formula 1. １ , Z ２ , R １ , R ２ , R ３ and R ４ is the same as

12. 2. The photopolymer composition of claim 1, wherein the fluorine-based compound represented by Chemical Formula 1 is contained in an amount of 20 to 200 parts by weight based on 100 parts by weight of the polymer matrix.

13. A holographic recording medium comprising a photopolymer layer formed from the photopolymer composition of claim 1.

14. A method for producing a holographic recording medium, comprising the step of applying the photopolymer composition of claim 1 to form a photopolymer layer.

15. 15. The method of claim 14, further comprising the step of irradiating a predetermined region of the photopolymer layer with a coherent laser to selectively polymerize a photoreactive monomer contained in the photopolymer layer, thereby recording optical information.

16. An optical element comprising the holographic recording medium according to claim 13.

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