Holographic recording medium and preparation and application thereof

Abstract

The invention discloses a holographic recording medium and preparation and application thereof, the holographic recording medium is characterized by comprising a matrix with high glass transition temperature and high refractive index, a low refractive index monomer and a photo-initiation system, and a plasticizer and a leveling agent are added as required; the glass transition temperature of the substrate is 100 DEG C or higher. When the holographic recording medium is irradiated by coherent laser, the coherent bright area and the photo-initiation system rapidly generate active centers, the low-refractive-index monomers are attacked by the active centers to initiate polymerization, the monomers in the coherent bright area are consumed, and the monomers between the coherent bright area and the coherent dark area generate concentration difference to drive the monomers to diffuse from the coherent dark area to the coherent bright area, so that the holographic recording medium is formed. And the plasticizer and the matrix move to the coherent dark area due to the increase of potential energy in the coherent bright area, and finally the refractive index change of the low refractive index of the coherent bright area and the high refractive index of the coherent dark area is formed, so that the periodic refractive index difference is generated.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical materials, and more specifically, relates to a holographic recording medium and a preparation method and application thereof. Background Art

[0002] Holographic recording media are carriers for recording holograms. Through coherent laser exposure technology, they can simultaneously store all information such as light wave amplitude and phase, and generally have a periodic ordered structure. As the most promising holographic recording medium, holographic plastics not only have properties such as light weight and easy processing, but also have the characteristics of large information storage capacity and strong light modulation ability. They have shown broad application prospects in high-tech fields such as naked-eye 3D display, augmented reality (AR), high-end anti-counterfeiting, high-density holographic data storage and holographic sensors.

[0003] Holographic plastics are mainly composed of a matrix, photopolymer monomers, and a photoinitiator system, wherein the photoinitiator system includes a dye and a co-initiator. The dye absorbs visible light and reacts with the co-initiator to produce an active center. The active center reacts with the photopolymer monomer to initiate polymerization, thereby causing the monomer and the matrix to phase separate and form a holographic grating with a periodic refractive index distribution. The properties of holographic plastics include parameters such as refractive index modulation, transmittance, diffraction efficiency, and photosensitivity. Among them, increasing the refractive index modulation is conducive to improving the diffraction efficiency and reducing the thickness of the holographic recording material (Holographic Polymer Materials, Science Press, 2020). It is generally believed that the size of the refractive index modulation determines the performance of the grating and is the most important performance parameter of holographic plastics.

[0004] The refractive index modulation of holographic plastics is determined by the phase separation degree and refractive index difference between the matrix and the photopolymer monomer. The phase separation degree between the matrix and the photopolymer monomer is related to the viscosity of the system. Generally speaking, the smaller the viscosity of the system, the more conducive it is to the migration of the photopolymer monomer and the more conducive it is to improving the phase separation degree. In addition, since the period of the reflective grating is smaller, the migration distance of the photopolymer monomer is shorter than that of the transmission grating, so the refractive index modulation of the reflective grating is higher.

[0005] At present, the matrix of holographic plastics is mostly made of polymers with low glass transition temperature. The advantage of this is that the matrix has better solubility, which is convenient for subsequent film processing, and at room temperature, the matrix has a larger free volume and even the chain segments of the matrix polymer have a certain mobility, which facilitates the diffusion of photopolymer monomers and improves the degree of phase separation. However, holographic plastics prepared using this matrix often do not have good environmental weather resistance. Under high temperature conditions, it will cause problems such as drift of the diffraction peak of the grating and increased haze of the grating. Therefore, how to use a matrix with a high glass transition temperature to prepare a reverse-diffusion photopolymer holographic plastic system, and thus prepare a holographic plastic with a high refractive index modulation, is still a challenge. Summary of the invention

[0006] In view of the above defects or improvement needs of the prior art, the purpose of the present invention is to provide a holographic recording medium and its preparation and application, so as to solve the problem that when a matrix with a high glass transition temperature exists in a holographic plastic, the monomer diffusion is difficult. The holographic recording medium is constructed by using a matrix with a high glass transition temperature and a high refractive index, a low refractive index monomer, and a photoinitiator system, and adding a leveling agent or a plasticizer as needed. The preparation method of the holographic recording medium is as follows: (1) mixing a matrix with a high glass transition temperature and a high refractive index, a low refractive index monomer, and a photoinitiator system under light-proof conditions to obtain a mixed liquid; during the mixing process, an appropriate amount of organic solvent, a plasticizer or a leveling agent can be selectively added; (2) under light-proof conditions, the mixed liquid obtained in step (1) is scraped on a substrate to form a film, so as to obtain a holographic recording medium. The holographic recording medium is exposed to a coherent laser to form a photopolymerized holographic plastic with a periodic refractive index distribution in which the coherent bright area is a low refractive index and the coherent dark area is a high refractive index. The grating structure generated based on the present invention can be either transmission type or reflection type.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] A holographic recording medium, characterized in that it comprises a matrix with a high glass transition temperature and a high refractive index, a low refractive index monomer and a photoinitiator system;

[0009] The glass transition temperature of the substrate is above 100°C.

[0010] According to an embodiment of the present invention, the holographic recording medium further comprises a plasticizer.

[0011] According to an embodiment of the present invention, the holographic recording medium further comprises a leveling agent.

[0012] According to an embodiment of the present invention, the matrix with high glass transition temperature and high refractive index is at least one of polyimide, polyurea, polythiourea and polyimide ketone, preferably polyimide; the polyimide may have the following chemical structure:

[0013]

[0014] Wherein, 2≤(n+m)≤50, m is an integer greater than or equal to 0 and less than 50, X1 is at least one of sulfur, selenium, and tellurium, and X2 is at least one of carbon, oxygen, and sulfur.

[0015] According to an embodiment of the present invention, the number average molecular weight of the polyimide is 2000-50000, preferably 8000-40000.

[0016] According to an embodiment of the present invention, the refractive index of the substrate is greater than 1.5, preferably, the refractive index of the substrate is greater than 1.55, more preferably greater than 1.6, for example, 1.6 to 1.8, and for example, 1.6 to 1.7. The substrate has good solution processing characteristics and a high glass transition temperature, and its film has a high light transmittance.

[0017] According to an embodiment of the present invention, the light transmittance of the base film at 400 nm is above 70%, preferably above 80%.

[0018] According to an embodiment of the present invention, the matrix can be dissolved in an organic solvent. Preferably, the organic solvent is selected from at least one of tetrahydrofuran, dichloromethane, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone.

[0019] According to an embodiment of the present invention, the glass transition temperature of the substrate is above 150°C, for example, 150-230°C, and for example, 150-190°C.

[0020] According to an embodiment of the present invention, the refractive index of the low-refractive-index monomer is less than 1.55; preferably, the refractive index of the low-refractive-index monomer is below 1.50; more preferably, it is below 1.46.

[0021] According to an embodiment of the present invention, the viscosity of the low refractive index monomer at 20° C. is less than 200 mPa·s, preferably, the viscosity at 20° C. is less than 100 mPa·s.

[0022] According to an embodiment of the present invention, the refractive index of the plasticizer is above 1.50, preferably, the refractive index of the plasticizer is above 1.55, more preferably, the refractive index of the plasticizer is above 1.60, for example, 1.55-1.80, and for example, 1.60-1.80.

[0023] According to an embodiment of the present invention, the difference in refractive index between the matrix and the low-refractive-index monomer is greater than 0.02, and preferably not less than 0.06.

[0024] According to an embodiment of the present invention, the holographic recording medium comprises, based on 100% by mass, 15 to 90% of a matrix having a high glass transition temperature and a high refractive index, 9 to 70% of a low refractive index monomer and 0 to 50% of a plasticizer;

[0025] The photoinitiator system accounts for 0.1-10% of the total mass of the matrix, the low-refractive index monomer and the plasticizer; the leveling agent accounts for 0-2% of the total mass of the matrix, the low-refractive index monomer and the plasticizer.

[0026] Preferably, the holographic recording medium comprises, based on 100% by mass, 30-60% of a matrix with a high glass transition temperature and a high refractive index, 30-60% of a low refractive index monomer and 0-20% of a plasticizer; the photoinitiator system accounts for 0.5-5% of the total mass of the matrix, the low refractive index monomer and the plasticizer.

[0027] Preferably, the leveling agent accounts for 0-1% of the total mass of the matrix, the low refractive index monomer and the plasticizer.

[0028] Preferably, the holographic recording medium comprises, based on 100% by mass, 30-60% of a matrix with a high glass transition temperature and a high refractive index, 30-60% of a low refractive index monomer, and 5-20% of a plasticizer; the photoinitiator system accounts for 0.5-5% of the total mass of the matrix, the low refractive index monomer, and the plasticizer.

[0029] According to an embodiment of the present invention, the low refractive index monomer is at least one of acrylate, methacrylate, acrylamide and methacrylamide; preferably, it is one or two of acrylate and acrylamide; more preferably, it is acrylate.

[0030] Preferably, the acrylic ester includes but is not limited to at least one of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-octyl acrylate, decyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-ethoxyethyl acrylate, 2-cyanoethyl acrylate, cyclohexyl acrylate, isobornyl acrylate, tetrahydrofurfuryl acrylate, tricyclo[5.2.1.0 2,6]decanedioic acid diacrylate, diurethane dimethacrylate, 2-phenoxyethyl acrylate, (5-ethyl-13-dioxane-5-yl)methyl acrylate, tetrahydrofuran-2-yl methacrylate, cyclopentyl methacrylate, and the like.

[0031] Preferably, the acrylamide includes but is not limited to at least one of N,N-dimethylacrylamide, N,N-diethylacrylamide, N-methylacrylamide, N-ethylacrylamide, diacetoneacrylamide, methyl alcoholacrylamide, N-phenylacrylamide, m-xylene diacrylamide, N-hydroxyethylacrylamide, N-tert-octylacrylamide, N-tert-butylacrylamide, hexamethylenebisacrylamide, N-dodecylacrylamide, N-p-hydroxyphenylacrylamide, 4-(acrylamide)benzoic acid, etc.

[0032] According to an embodiment of the present invention, the photoinitiator system comprises a photoinitiator; the photoinitiator includes, but is not limited to, at least one of bisacylphosphine oxides, organic borates, organometallic compounds, light-absorbing amines, purine dyes, thiazine dyes, acridine dyes, phenazine dyes, phenoxazine dyes, fluorescent dyes, phenoxazole dyes, thiazole dyes, iodonium salts, ketone derivatives, bisaryl imidazole derivatives, coumarin and coumarin keto derivatives, pyridine and thiopyridinium salts, etc. For example, the photoinitiator is at least one of safranin O, tetrapropylammonium fluoroborate, erythrosine, benzylammonium tetrafluoroborate, tetra-n-butylammonium tetraphenylborate, bis(4-tert-butylphenyl)iodonium hexafluorophosphate, and tetrapropylammonium fluoroborate.

[0033] According to an embodiment of the present invention, the plasticizer is at least one of an oxygen heterocyclic compound, a nitrogen heterocyclic compound, a sulfur heterocyclic compound, a liquid crystal, bromonaphthalene, bromobenzene, and iodonaphthalene. Preferably, it is an oxygen heterocyclic compound, a nitrogen heterocyclic compound, and more preferably an oxygen heterocyclic compound. Preferably, the plasticizer is selected from the group consisting of, but not limited to, epichlorohydrin, biphenyl glycidyl ether, cyclohexene oxide, butyl oxirane, ethyl oxirane, glycidyl phenyl ether, meta-oxirane chlorobenzene, 1,2-epoxyoctane, glycidyl guaiacol ether, oxirane, 4-epoxypropaneoxycarbazole, glycidyl phenyl ether, 2-phenyl-3-methylcycloaziridine, 3-hydroxy-1-diphenylmethylcycloazolidine, 2-methyl oxirane, 2-methyloxirane, 2-(chloromethyl)oxirane, cyclohexyl-4-thiomorpholinyl-methyl mercaptan, and the like.

[0034] According to an embodiment of the present invention, the leveling agent is selected from at least one of the leveling agent 310, the leveling agent 313, the leveling agent 333, the leveling agent 354, the leveling agent 381, and the like.

[0035] The present invention also provides a method for preparing the above holographic recording medium, characterized in that the method is prepared by the following steps:

[0036] (1) mixing a high glass transition temperature and high refractive index matrix, a low refractive index monomer, and a photoinitiator system under light-proof conditions to obtain a mixed solution;

[0037] (2) Under light-proof conditions, the mixed solution obtained in step (1) is coated on a substrate to form a film to obtain a holographic recording medium.

[0038] According to an embodiment of the present invention, at least one of a plasticizer, an organic solvent or a leveling agent may be added in step (1).

[0039] For example, when at least one of the matrix and the low refractive index monomer is a liquid, the mixed liquid can be directly mixed uniformly by the liquid substance. Alternatively, when at least one of the high refractive index resin and the low refractive index monomer is a liquid, the mixed liquid can also use an additional organic solvent.

[0040] For example, when both the matrix and the low-refractive-index monomer are not liquid, the uniform reaction mixture is formed by using an organic solvent.

[0041] Preferably, the organic solvent is at least one of tetrahydrofuran, dichloromethane, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone.

[0042] According to an embodiment of the present invention, in step (2), the film thickness of the holographic recording medium is 8 μm or less.

[0043] The present invention also provides a photopolymerizable holographic plastic, characterized in that the photopolymerizable holographic plastic is a grating structure with a periodic distribution of refractive index formed by irradiating the above-mentioned holographic recording medium with coherent laser light.

[0044] According to an embodiment of the present invention, the refractive index modulation degree of the holographic plastic is not less than 0.02, preferably not less than 0.03, preferably not less than 0.04, and further preferably not less than 0.045.

[0045] According to an embodiment of the present invention, the haze of the holographic plastic is not higher than 4%, preferably not higher than 3%, and further preferably not higher than 2%.

[0046] The present invention also provides a method for preparing the above-mentioned photopolymerizable holographic plastic, the method comprising:

[0047] The holographic recording medium is subjected to holographic exposure to obtain the photopolymerizable holographic plastic.

[0048] According to an embodiment of the present invention, the wavelength of light applied to the holographic recording medium is 400-800 nm.

[0049] The present invention also provides the use of the above-mentioned holographic recording medium or photopolymerized holographic plastic in anti-counterfeiting, virtual reality, augmented reality or data storage.

[0050] It should be noted that: in the present invention, if there is no special description, all the embodiments and preferred implementation methods mentioned in the present invention can be combined with each other to form a new technical solution. In the present application, if there is no special description, all the technical features and preferred features mentioned in the present invention can be combined with each other to form a new technical solution. In the present invention, if there is no special description, the percentage (%) or part refers to the weight percentage or weight part relative to the composition. In the present invention, if there is no special description, the various components or their preferred components involved can be combined with each other to form a new technical solution. In the present application, unless otherwise specified, the numerical range "a~b" represents an abbreviation of any real number combination between a and b, and includes a and b, where a and b are both real numbers. For example, the numerical range "1~5" means that all real numbers between "1~5" have been listed in the present invention, and "1~5" is just an abbreviation of these numerical combinations. The "range" disclosed in the present invention can be in the form of a lower limit and an upper limit, which can be one or more lower limits, and one or more upper limits respectively. Beneficial effects of the present invention:

[0051] The photopolymerizable holographic plastic of the present invention not only has a higher refractive index modulation degree and a lower haze, but is also the first to use a substrate with a high glass transition temperature and a high refractive index (such as polyimide) to prepare the holographic plastic, and the holographic plastic has good environmental weather resistance.

[0052] Specific analysis:

[0053] (1) In the present invention, the principle of grating formation is that, when the holographic recording medium is irradiated by coherent laser, the coherent bright area and the photoinitiator system rapidly generate active centers, the low refractive index monomers are attacked by the active centers to initiate polymerization, the monomers in the coherent bright area are consumed, and the monomers between the coherent bright area and the coherent dark area generate a concentration difference, driving the monomers to diffuse from the coherent dark area to the coherent bright area and participate in the polymerization reaction in the coherent bright area. Due to the increase in potential energy in the coherent bright area, the plasticizer and the matrix move to the coherent dark area, and finally form a refractive index change of low refractive index in the coherent bright area and high refractive index in the coherent dark area, thereby generating a periodic refractive index difference. Among them, by adding a suitable plasticizer, the diffusion ability of the photopolymer monomer in the matrix is ​​given, the problem of difficult processing of holographic plastics with a high glass transition temperature matrix is ​​solved, and the phase separation degree and refractive index modulation degree of the holographic plastics are greatly improved.

[0054] (2) The substrate (eg, polyimide) used in the holographic recording medium of the present invention is synthesized by itself and has the characteristics of being solution processable and having a high refractive index, and its thin film has the characteristics of high light transmittance.

[0055] (3) Based on the present invention, the obtained grating structure can be either transmissive or reflective. Generally speaking, the refractive index modulation degree of the reflective grating will be higher because the period of the reflective grating is smaller and the migration distance of the photopolymer monomer is shorter than that of the transmissive grating.

[0056] (4) The holographic plastic obtained by the present invention has a high refractive index modulation and low haze, and for the first time uses a polymer with a high glass transition temperature as a matrix, and has a high glass transition temperature and good thermal stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 1 is a graph showing the relationship between the refractive index modulation (n) and the haze of the holographic plastics prepared in Examples 1-5.

[0058] Figure 2 It is a physical picture of the product of Example 1 and Example 2; wherein, Figure 2 (a) corresponds to the product of Example 1, Figure 2 (b) corresponds to the product of Example 2. DETAILED DESCRIPTION

[0059] The technical scheme of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only exemplary descriptions and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0060] The polyimide used in the following examples was synthesized by ourselves; the other chemicals, unless otherwise specified, were purchased from the market. The substrate can be glass or other substrates according to actual needs, and the protective film can be polyethylene terephthalate or other protective films.

[0061] Embodiment 1:

[0062] The holographic recording medium comprises, based on 100% by mass, 40% of polyimide, 55% of (5-ethyl-13-dioxane-5-yl) methyl acrylate and 5% of biphenyl glycidyl ether;

[0063] The photoinitiator system includes safranin O and tetrapropylammonium fluoroborate, which account for 0.1% and 0.7% of the total mass of the matrix, the low refractive index monomer and the plasticizer respectively.

[0064] The glass transition temperature of the polyimide is 163°C, and its film T 400 The light transmittance is 80.03%, the refractive index is 1.62, the number average molecular weight is 32000 (unit: g / mol, the same below), and the structure is:

[0065]

[0066] The refractive index of the low-refractive-index monomer is 1.46, and the viscosity at 20° C. is 10 mPa·s.

[0067] The refractive index of the plasticizer is 1.581.

[0068] The preparation method is as follows:

[0069] (1) mixing the above-mentioned polyimide, low refractive index monomer, photoinitiator system and plasticizer under light-proof conditions, adding an appropriate amount of tetrahydrofuran, and magnetically stirring to obtain a uniform reaction mixture;

[0070] (2) coating the mixed solution obtained in step (1) on a substrate using a coating machine to form a film under light-proof conditions, and after the solvent is volatilized, a holographic recording medium is obtained;

[0071] (3) Splitting a 532nm laser beam into two coherent beams of equal intensity, incident on the two sides of the holographic recording medium prepared in step (2) at an angle of 180°, and exposing the two beams to obtain a holographic plastic having a thickness of 4 μm, a refractive index modulation degree of 0.047, and a haze of 2.7%. The holographic plastic can be stably stored at 70°C for 24 hours.

[0072] Embodiment 2:

[0073] The holographic recording medium comprises, based on 100% by mass, 35% of polyimide, 55% of tetrahydrofuran-2-yl methacrylate and 10% of bromonaphthalene;

[0074] The photoinitiator system includes erythrosine and benzyl ammonium tetrafluoroborate, which account for 0.2% and 1.2% of the total mass of the matrix, the low refractive index monomer and the plasticizer respectively.

[0075] The glass transition temperature of the polyimide is 186°C, and its film T 400 The light transmittance is 86.5%, the refractive index is 1.62, the number average molecular weight is 28000 (unit: g / mol, the same below), and the structure is:

[0076]

[0077] The refractive index of the low-refractive-index monomer is 1.45, and the viscosity at 20° C. is 5 mPa·s.

[0078] The refractive index of the plasticizer is 1.656.

[0079] The preparation method is as follows:

[0080] (1) mixing the above-mentioned polyimide, low refractive index monomer, photoinitiator system and plasticizer under light-proof conditions, adding an appropriate amount of dichloromethane, and magnetically stirring to obtain a uniform reaction mixture;

[0081] (2) coating the mixed solution obtained in step (1) on a substrate using a coating machine to form a film under light-proof conditions, and after the solvent is volatilized, a holographic recording medium is obtained;

[0082] (3) Split a 532nm laser beam into two coherent beams of equal intensity, and expose them from both sides of the holographic recording medium prepared in step (2) at an angle of 180° to obtain a holographic grating with a thickness of 4 μm, a refractive index modulation of 0.041, and a haze of 2.4%. The holographic plastic can be stably stored at 70°C for 24 hours.

[0083] Embodiment 3:

[0084] The holographic recording medium comprises, based on 100% by mass, 50% of polyimide, 40% of tetrahydrofurfuryl acrylate and 10% of bromobenzene;

[0085] The photoinitiator system includes safranin O and tetra-n-butylammonium tetraphenylborate, which account for 0.4% and 2% of the total mass of the matrix, the low refractive index monomer and the plasticizer respectively.

[0086] The glass transition temperature of the polyimide is 179°C, and its film T 400 The transmittance is 83.41%, the refractive index is 1.62, the molecular weight is 36000 (unit: g / mol, the same below), and the structure is:

[0087]

[0088] The refractive index of the low-refractive-index monomer is 1.48, and the viscosity at 20° C. is 15 mPa·s.

[0089] The refractive index of the plasticizer is 1.556.

[0090] The preparation method is as follows:

[0091] (1) mixing the above-mentioned polyimide, low refractive index monomer, photoinitiator system and plasticizer under light-proof conditions, adding an appropriate amount of tetrahydrofuran, and magnetically stirring to obtain a uniform reaction mixture;

[0092] (2) coating the mixed solution obtained in step (1) on a substrate using a coating machine to form a film under light-proof conditions, and after the solvent is volatilized, a holographic recording medium is obtained;

[0093] (3) Split a 532nm laser beam into two coherent beams of equal intensity, and expose them from two sides of the holographic recording medium prepared in step (2) at an angle of 180° to obtain a holographic grating with a thickness of 4 μm, a refractive index modulation of 0.031, and a haze of 0.9%. The holographic plastic can be stably stored at 70°C for 24 hours.

[0094] Embodiment 4:

[0095] The holographic recording medium comprises, based on 100% by mass, 45% of polyimide, 45% of cyclopentyl methacrylate and 10% of iodonaphthalene;

[0096] The photoinitiator system is safranin O and bis(4-tert-butylphenyl)iodonium hexafluorophosphate, which account for 0.5% and 3% of the total mass of the matrix, the low-refractive index monomer and the plasticizer respectively.

[0097] The glass transition temperature is 188°C, and the film T 400 The light transmittance is 88.76%, the refractive index of the polyimide is 1.62, the molecular weight is 38000 (unit: g / mol, the same below), and the structure is:

[0098]

[0099] The refractive index of the low-refractive-index monomer is 1.46, and the viscosity at 20° C. is 25 mPa·s.

[0100] The refractive index of the plasticizer is 1.712.

[0101] The preparation method is as follows:

[0102] (1) mixing the above-mentioned polyimide, low refractive index monomer, photoinitiator system and plasticizer under light-proof conditions, adding an appropriate amount of tetrahydrofuran, and magnetically stirring to obtain a uniform reaction mixture;

[0103] (2) coating the mixed solution obtained in step (1) on a substrate using a coating machine to form a film under light-proof conditions, and after the solvent is volatilized, a holographic recording medium is obtained;

[0104] (3) Split a 532nm laser beam into two coherent beams of equal intensity, and expose them from two sides of the holographic recording medium prepared in step (2) at an angle of 180° to obtain a holographic grating with a thickness of 4 μm, a refractive index modulation of 0.035, and a haze of 1.1%. The holographic plastic can be stably stored at 70°C for 24 hours.

[0105] Embodiment 5:

[0106] A holographic recording medium comprises, by weight, 40 wt.% of polyimide, 50 wt.% of 5-ethyl-13-dioxane-5-yl methyl acrylate, 5 wt.% of diurethane dimethacrylate, and 5 wt.% of biphenyl glycidyl ether, wherein the photoinitiator system accounts for 1.6 wt.% of the total weight of the polyimide, the low refractive index monomer, and the plasticizer.

[0107] The holographic recording medium comprises, based on 100% by mass, 40% of polyimide, 50% of 5-ethyl-13-dioxane-5-yl methyl acrylate, 5wt.% of diurethane dimethacrylate and 5% of biphenyl glycidyl ether;

[0108] The photoinitiator system includes safranin O and tetrapropylammonium fluoroborate, which account for 0.1% and 0.7% of the total mass of the matrix, the low refractive index monomer and the plasticizer respectively.

[0109] The glass transition temperature of the polyimide is 163°C, and its film T 400 The light transmittance is 80.03%, the refractive index is 1.62, the number average molecular weight is 32000 (unit: g / mol, the same below), and the structure is:

[0110]

[0111] The refractive indexes of the low-refractive-index monomers are 1.46 ((5-ethyl-13-dioxane-5-yl)methyl acrylate) and 1.47 (diurethane dimethacrylate), and the viscosities at 20° C. are 10 mPa·s and 50 mPa·s, respectively.

[0112] The refractive index of the plasticizer is 1.581.

[0113] The preparation method is as follows:

[0114] (1) mixing the above-mentioned polyimide, low refractive index monomer, photoinitiator system and plasticizer under light-proof conditions, adding an appropriate amount of tetrahydrofuran, and magnetically stirring to obtain a uniform reaction mixture;

[0115] (2) coating the mixed solution obtained in step (1) on a substrate using a coating machine to form a film under light-proof conditions, and after the solvent is volatilized, a holographic recording medium is obtained;

[0116] (3) Splitting a 532nm laser beam into two coherent beams of equal intensity, incident on the two sides of the holographic recording medium prepared in step (2) at an angle of 180°, and exposing the two beams to obtain a holographic plastic having a thickness of 4 μm, a refractive index modulation degree of 0.045, and a haze of 2.4%. The holographic plastic can be stably stored at 85°C for 96 hours.

[0117] Embodiment 6:

[0118] The holographic recording medium comprises, based on 100% by mass, 45% of polyimide and 55% of (5-ethyl-13-dioxane-5-yl)methyl acrylate, without adding a plasticizer;

[0119] The photoinitiator system includes safranin O and tetrapropylammonium fluoroborate, which account for 0.1% and 0.7% of the total mass of the matrix and the low-refractive-index monomer, respectively.

[0120] The glass transition temperature of the polyimide is 163°C, and its film T 400 The light transmittance is 80.03%, the refractive index is 1.62, the number average molecular weight is 32000 (unit: g / mol, the same below), and the structure is:

[0121]

[0122] The refractive index of the low-refractive-index monomer is 1.46, and the viscosity at 20° C. is 10 mPa·s.

[0123] The preparation method is as follows:

[0124] (1) mixing the above-mentioned polyimide, low refractive index monomer and photoinitiator system under light-proof conditions, adding an appropriate amount of tetrahydrofuran, and magnetically stirring to obtain a uniform reaction mixture;

[0125] (2) coating the mixed solution obtained in step (1) on a substrate using a coating machine to form a film under light-proof conditions, and after the solvent is volatilized, a holographic recording medium is obtained;

[0126] (3) Splitting a 532nm laser beam into two coherent beams of equal intensity, incident on the two sides of the holographic recording medium prepared in step (2) at an angle of 180°, and exposing the two beams to obtain a holographic plastic having a thickness of 4 μm, a refractive index modulation degree of 0.011, and a haze of 2.3%. The holographic plastic can be stably stored at 70°C for 24 hours.

[0127] The above is an exemplary description of the embodiments of the present invention. However, the protection scope of the present invention is not limited to the above embodiments. Any modification, equivalent substitution, improvement, etc. made by those skilled in the art within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A holographic recording medium, characterized in that: It comprises a matrix with a high glass transition temperature and a high refractive index, a low refractive index monomer and a photoinitiator system; The glass transition temperature of the substrate is above 100°C.

2. The holographic recording medium according to claim 1, wherein The holographic recording medium further includes a plasticizer. Preferably, the holographic recording medium further comprises a leveling agent.

3. The holographic recording medium according to claim 1, wherein The matrix with high glass transition temperature and high refractive index is at least one of polyimide, polyurea, polythiourea and polyimide ketone, preferably polyimide; the polyimide has the following chemical structure: Wherein, 2≤(n+m)≤50, m is an integer greater than or equal to 0 and less than 50, X1 is at least one of sulfur, selenium or tellurium, and X2 is at least one of carbon, oxygen or sulfur. Preferably, the number average molecular weight of the polyimide is 2000-50000. Preferably, the refractive index of the matrix is ​​greater than 1.

5.

4. The holographic recording medium according to claim 1, wherein: The refractive index of the low-refractive-index monomer is less than 1.

55. Preferably, the refractive index of the plasticizer is above 1.

50.

5. The holographic recording medium according to claim 1, wherein The holographic recording medium comprises, based on 100% by mass, 15 to 90% of a matrix having a high glass transition temperature and a high refractive index, 9 to 70% of a monomer having a low refractive index and 0 to 50% of a plasticizer; The photoinitiator system accounts for 0.1-10% of the total mass of the matrix, the low-refractive index monomer and the plasticizer; the leveling agent accounts for 0-2% of the total mass of the matrix, the low-refractive index monomer and the plasticizer.

6. The holographic recording medium according to claim 5, characterized in that The low refractive index monomer is at least one of acrylate, methacrylate, acrylamide or methacrylamide. Preferably, the photoinitiator system comprises a photoinitiator; the photoinitiator is selected from at least one of bisacylphosphine oxides, organic borates, organometallic compounds, light-absorbing amines, purine dyes, thiazine dyes, acridine dyes, phenazine dyes, phenoxazine dyes, fluorescent dyes, phenoxazole dyes, thiazole dyes, iodonium salts, ketone derivatives, diarylimidazole derivatives, coumarins and coumarin keto derivatives, pyridine and thiopyridinium salts. Preferably, the plasticizer is at least one of oxygen heterocyclic compounds, nitrogen heterocyclic compounds, sulfur heterocyclic compounds, liquid crystals, bromonaphthalene, bromobenzene and iodonaphthalene. Preferably, the leveling agent is selected from at least one of the leveling agent 310 , the leveling agent 313 , the leveling agent 333 , the leveling agent 354 and the leveling agent 381 .

7. The method for preparing a holographic recording medium according to any one of claims 1 to 6, characterized in that: The method is prepared by the following steps: (1) mixing a high glass transition temperature and high refractive index matrix, a low refractive index monomer, and a photoinitiator system under light-proof conditions to obtain a mixed solution; (2) Under light-proof conditions, the mixed solution obtained in step (1) is coated on a substrate to form a film to obtain a holographic recording medium. Preferably, at least one of a plasticizer, an organic solvent or a leveling agent may be added in step (1).

8. A photopolymerizable holographic plastic, characterized in that: The photopolymerizable holographic plastic is a grating structure with a periodic refractive index distribution formed by irradiating the holographic recording medium according to any one of claims 1 to 6 with coherent laser light.

9. The method for preparing the photopolymerizable holographic plastic according to claim 8, characterized in that: The method comprises: The holographic recording medium is subjected to holographic exposure to obtain the photopolymerizable holographic plastic.

10. Use of the holographic recording medium according to any one of claims 1 to 6 or the photopolymerizable holographic plastic according to claim 8 in anti-counterfeiting, virtual reality, augmented reality or data storage.

Images