Holographic recording medium based on a monomer containing a fluorene group and use thereof

Abstract

This invention relates to the field of organic optical functional materials, specifically to a holographic recording medium based on a fluorene-containing monomer and its application. The photopolymer-type holographic recording medium provided by this invention comprises a fluorene-containing acrylate monomer as its raw material, wherein the fluorene-containing acrylate monomer has the general structural formula G1, G2, G3, or G4. The photopolymer-type holographic recording medium of this invention uses a high-refractive-index fluorene-containing monomer / polymerizable monomer or oligomer as the recording component, and a low-refractive-index isocyanate-alcohol and epoxy resin-amine curing agent crosslinking system as the film-forming resin. This increases the refractive index difference between the polymerizable monomer and the film-forming resin. Furthermore, the fluorene-containing monomer has a high polymerization reaction and migration rate, and after polymerization, it exhibits good compatibility with the film-forming resin, enabling the preparation of a high-performance holographic recording medium.

Description

Technical Field

[0001] This invention relates to the field of organic optical functional materials, specifically to a holographic recording medium based on a fluorene-containing monomer and its application. Technical Background

[0002] With the rapid development of artificial intelligence, big data, and other technologies, and the continuous improvement of people's living standards, holographic technology has attracted much attention due to its ability to achieve multi-dimensional, full-color augmented reality (AR) displays and low-energy, high-density information storage, marking a new stage in its technological development. Holographic gratings are the core of holographic technology; their quality directly affects the clarity of AR display devices and the fidelity of stored data. High-precision gratings also place high demands on the recording medium. Photopolymers are currently the most promising holographic recording material. They typically contain components such as film-forming resins, recording monomers, and photoinitiation systems. Under interference exposure, the monomers polymerize and migrate, thereby forming a refractive index-modulated phase-type holographic grating with the film-forming resin.

[0003] However, existing holographic gratings fabricated with photopolymers often struggle to simultaneously achieve high refractive index modulation, high spatial frequency, low haze, and high stability. When the refractive index modulation and spatial frequency of the grating are too high, it means that the polymerization and migration of the photopolymer involved in grating formation during holographic exposure are greater, making it easier for micro-phase separation to form between components, leading to increased haze and reduced stability of the holographic grating. Covestro's Bayfol... ®HX series photopolymers (CN202380022996.3; Optical Materials, 2020, No. 109, p. 110362) can prepare holographic gratings with diffraction efficiency of nearly 99% and spatial frequency greater than 3000 lp / mm, but their transparency in the visible light band is poor after photobleaching. Bomwan et al. (Macromolecules, 2025, No. 58(2), pp. 919–930; ACS Appl. Mater. Interfaces, 2025, No. 17(20), pp. 30340–30347) designed a new monomer BPTPUA to replace the original monomer BPTPA based on the principle of similar compatibility, which improved its compatibility in polyurethane film-forming resin, greatly reduced the haze of the grating recorded by the photopolymer, and improved its temperature resistance, but the spatial frequency of the grating is only 1000 lp / mm. The polymethyl methacrylate (PMMA) photopolymer developed by Tan Xiaodi et al. (ZL202211337119.9; ACS Applied Materials & Interfaces, 2024, 16(38), pp. 51575–51583) has excellent optical quality and a recording grating angular selectivity of less than 0.1°, but its sensitivity and resolution are relatively low. The polymer-dispersed liquid crystal (PDLC) recording grating developed by Peng Haiyan et al. (CN202310368492.9; Macromolecules, 2024, 57(6), pp. 2557–2573) has a refractive index modulation of 0.04, but its haze is relatively high (≥1%) and its stability is generally poor. Therefore, it is essential to provide a high refractive index monomer with good compatibility in film-forming resins while ensuring the high refractive index modulation and spatial frequency of the grating, controlling its haze and improving its stability.

[0004] The fluorene group is a rigid, planar aromatic group with advantages such as high refractive index, low birefringence, excellent thermal stability, and high transparency. This invention provides a monomer containing a fluorene structure, which has a high refractive index and polymerization rate, exhibiting good compatibility with photopolymers using isocyanate-alcohol and epoxy-amine as film-forming resins. Furthermore, using this monomer as one of the recording monomers, a high-performance holographic recording medium formulation is provided. High diffraction efficiency, high spatial frequency, and low haze holographic gratings are prepared using interference exposure, which can be applied to holographic displays, high-density holographic data storage, and holographic anti-counterfeiting fields.

[0005] CN113316746A reports a holographic recording composition that uses a monofunctional monomer, such as

[0006] CN113527143A discloses a photopolymer composition using an acrylate monomer containing a fluorene group, with the following structural formula:

[0007]

[0008] However, because these monomers have added multiple aromatic rings to the fluorene parent ring, their molecular volume is relatively large and their solubility is generally poor. They are prone to micro-phase separation in film-forming resins, which increases the haze of the holographic recording medium. Summary of the Invention

[0009] One objective of this invention is to provide a polymerizable monomer containing a fluorene structure. This series of monomers contains at least a fluorene group and a polymerizable active group, has a high refractive index, exhibits good compatibility in film-forming resin systems, and can be used alone or mixed with commercially available acrylate, olefin, or acetylene monomers / oligomers.

[0010] A second objective of this invention is to provide a holographic recording medium using the aforementioned fluorene-containing monomer as the writing monomer. This medium exhibits high photosensitivity (≥30 cm⁻¹). 2 / J), after photobleaching, it has high transmittance (≥90%) in the visible light region.

[0011] A third objective of this invention is to provide applications for the aforementioned holographic recording medium. By utilizing interference exposure, holographic gratings with high diffraction efficiency (≥90%), high spatial frequency (≥3000 lp / mm), and low haze (≤0.3%) can be obtained, which can be applied to fields such as optical waveguide devices for AR displays, high-density holographic optical storage, and holographic anti-counterfeiting.

[0012] The first objective of this invention is to provide a photopolymer-based holographic recording medium, the raw material of which includes a fluorene-containing acrylate monomer, wherein the fluorene-containing acrylate monomer has a general structural formula as shown in G1, G2, G3, or G4:

[0013]

[0014] Where X represents S or O, n is an integer from 1 to 3, and R1 and R2 each independently represent H, C1~C5 alkyl, C1~C5 alkoxy, C1~C5 alkylthio, Br, or , This indicates the linking bond between the substituent and the main structure; R3 represents a C1-C5 alkyl group. , , A1, A2, A3, A4, and A5 each independently represent hydrogen, C1-C5 alkyl, C1-C5 alkoxy, C1-C5 alkylthio, or Br; R4 represents C 1-3 Alkyl or H.

[0015] The above-mentioned C1~C5 alkyl groups include straight-chain alkyl groups and branched alkyl groups; C1~C5 alkylthio groups include straight-chain alkylthio groups and branched alkylthio groups; and C1~C5 alkoxy groups include straight-chain alkylthio groups and branched alkoxy groups.

[0016] Further, the C1-C5 alkyl group is selected from methyl, ethyl, propyl, butyl, or pentyl; the C1-C5 alkylthio group is selected from methylthio, ethylthio, propylthio, butylthio, or pentylthio; and the C1-C5 alkoxy group is selected from methoxy, ethoxy, propoxy, butoxy, or pentoxy.

[0017] Furthermore, n=1, and R3 is methyl, ethyl, propyl, butyl, phenyl, biphenyl, fluorenyl, or anthracene.

[0018] The fluorene-containing acrylate monomer accounts for 5-20 wt% of the raw material of the photopolymer-type holographic recording medium.

[0019] For example, the fluorene-containing acrylate monomer has the following structural formula:

[0020]

[0021] The refractive index of the fluorene-containing acrylate monomer is ≥1.57, preferably between 1.60 and 1.66.

[0022] The preparation method of the fluorene-containing acrylate monomer refers to CN 2025111832211, and the reaction raw materials are at least two of the following: fluorene alcohol, 2-mercaptoethanol or 1,2-ethylenedithiol, acryloyl chloride or isocyanate acrylate.

[0023] This invention provides a photopolymer-type holographic recording medium comprising the fluorene-containing monomers described above. Depending on the film-forming resin, this invention provides two formulation combinations for photopolymer-type holographic recording media using polyurethane (isocyanate-alcohol) or epoxy-amine as the film-forming resin, the raw materials of which comprise the following components a) to g), specifically as follows:

[0024] The first composition, a polyurethane-type photopolymer-type holographic recording medium, comprises the following raw materials:

[0025] Component a) Polyisocyanate compounds;

[0026] Component b) Polyol compounds;

[0027] Component c) contains fluorene monomers;

[0028] Component d) optionally polymerizable monomers / oligomers;

[0029] Component e) Photosensitive initiation system;

[0030] Component f) Catalyst;

[0031] Component g) optionally, additives;

[0032] Alternatively, the second composition, an epoxy-amine type photopolymer type holographic recording medium, comprises the following raw materials:

[0033] Component a) Epoxy resin;

[0034] Component b) Polyamine curing agent;

[0035] Component c) contains fluorene monomers;

[0036] Component d) optionally polymerizable monomers / oligomers;

[0037] Component e) Photosensitive initiation system;

[0038] Component f) Chain transfer agent;

[0039] Component g) optionally, additives;

[0040] The fluorene-containing monomer is at least one of the group consisting of acrylate monomers having the general structural formula G1, G2, G3, or G4, or a mixture thereof, accounting for 5 to 20 wt% of the photopolymer holographic recording medium; for example, it can be 5 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, or 20 wt%, etc.

[0041] Furthermore, the polyurethane-type photopolymer-type holographic recording medium comprises the following raw materials in parts by weight:

[0042] 20-40 parts of isocyanate, preferably 30-35 parts;

[0043] 20-40 parts of alcohol, preferably 25-30 parts;

[0044] Contains 5-20 parts of fluorenyl acrylate monomer, preferably 10-15 parts;

[0045] The polymerizable monomer can be 10-30 parts, preferably 20-28 parts;

[0046] The photosensitizer is used in amounts of 0.01 to 0.5 parts, preferably 0.05 to 0.1 parts;

[0047] The photoinitiator is used in an amount of 0.1 to 3.0 parts, preferably 0.2 to 0.5 parts;

[0048] Catalyst: 0.1-1.0 parts, preferably 0.2-0.5 parts;

[0049] Defoamer 0-2.0 parts, preferably 0.5-1 part;

[0050] Leveling agent: 0-2.0 parts, preferably 0.5-1 parts;

[0051] The dehydrating agent is 0-2.0 parts, preferably 0.5-1 parts;

[0052] Plasticizer 0-3.0 parts, preferably 1-1.5 parts;

[0053] Chain transfer agent: 0.1-2.0 parts, preferably 0.5-1 parts;

[0054] Antioxidant 0-1.0 parts, preferably 0.2-0.5 parts;

[0055] Alternatively, epoxy-amine type photopolymer type holographic recording media may include the following parts by weight of raw materials:

[0056] 20-50 parts of epoxy resin, preferably 30-45 parts;

[0057] 10-20 parts of amine, preferably 12-17 parts;

[0058] Contains 5-20 parts of fluorenyl acrylate monomer, preferably 13-17 parts;

[0059] The polymerizable monomer can be 10-30 parts, preferably 20-28 parts;

[0060] The photosensitizer is used in amounts of 0.01 to 0.5 parts, preferably 0.05 to 0.1 parts;

[0061] The photoinitiator is used in an amount of 0.1 to 3.0 parts, preferably 0.2 to 0.5 parts;

[0062] Chain transfer agent: 0.1-3.0 parts, preferably 1-2.5 parts;

[0063] Defoamer 0-2.0 parts, preferably 0.5-1 part;

[0064] Leveling agent: 0-2.0 parts, preferably 0.5-1 parts;

[0065] Plasticizer 0-3.0 parts, preferably 1-2 parts;

[0066] Antioxidant 0-1.0 parts, preferably 0.2-0.5 parts.

[0067] Furthermore, the isocyanate is selected from compounds with low refractive index and having two or more isocyanate groups; including but not limited to at least one or a mixture thereof from the group consisting of hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, (2,4,6-trioxotriazine-1,3,5(2H,4H,6H)-triyl)tri(hexamethylene)isocyanate, butane-1,4-diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, etc.

[0068] Furthermore, the alcohol is selected from compounds with low refractive index and two or more hydroxyl functional groups, including but not limited to at least one or a mixture of the group consisting of triethylene glycol, tetraethylene glycol, butanediol, hexanediol, trimethylolethane, glycerol, triethanolamine, pentaerythritol, polyester polyols with a molecular weight of 200 to 2000, polycarbonate polyols with a molecular weight of 200 to 2000, and polyether polyols with a molecular weight of 200 to 2000.

[0069] Furthermore, the epoxy resin is selected from various aliphatic epoxy resins containing epoxy groups, whether monofunctional or polyfunctional, and having a low refractive index. This includes, but is not limited to, at least one from the group consisting of n-butyl glycidyl ether, allyl glycidyl ether, 2-ethylhexyl glycidyl ether, diglycidyl ester, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, butylene glycol diglycidyl ether, pentylene glycol diglycidyl ether, glycerol triglycidyl ether, and 3,4-epoxycyclohexenemethyl-3,4-epoxycyclohexenoester. It can also be a self-made fluorinated epoxy resin, see ZL202110168535.X.

[0070] Furthermore, the amine curing agent is a medium-low temperature amine curing agent with a curing temperature ≤60℃, including but not limited to at least one selected from the group consisting of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, divinylpropylamine, 2-methylpentanediamine, 1,3-pentanediamine, 1,2-cyclohexanediamine, isophoronediamine, hexanediamine, 4,4'-diaminodicyclohexylmethane, and self-made fluorinated amine curing agents.

[0071] Furthermore, the polymerizable monomer is an aromatic monomer with a high refractive index, which contains a single or multiple functional group of C=C unsaturated double bond, including but not limited to common alkene, alkyne, or acrylate monomers, or at least one or a mixture thereof composed of self-made high refractive index monomers and their derivatives.Exemplarily, including but not limited to N-vinylpyrrole, N-vinylcarbazole, N-vinylimidazol, N-vinylindole, N-vinylpyrrolidone, trans-N-3-yntynebutenylcarbazole, styrene, 2-chlorostyrene, 2-bromostyrene, 3-chlorostyrene, 3-bromostyrene, 4-chlorostyrene, 4-bromostyrene, p-(chloromethyl)styrene, p-(bromomethyl)styrene, or 1-vinylnaphthalene, 2-vinylnaphthalene, 2-vinylanthracene, 9-vinylanthracene, 2-phenoxyethyl acrylate, 2-phenoxyethyl methacrylate, benzyl methacrylate, 9-anthracene methacrylate, benzyl acrylate, p-chlorophenyl acrylate, 2,4,6-trichlorophenyl acrylate, p-bromophenyl acrylate, p-bromophenyl methacrylate, methacrylate p-Chlorophenyl acrylate, 2,4,6-tribromophenyl acrylate, 2,4,6-tribromophenyl methacrylate, 2,4,6-trichlorophenyl methacrylate, pentabromophenyl acrylate, pentachlorophenyl acrylate, phenoxyethyl acrylate, pentabromophenyl methacrylate, pentachlorophenyl methacrylate, pentabromobenzyl acrylate, phenoxyethyl methacrylate, 2-naphthyl acrylate, 1,4-di(2-thionaphthyl)2-butyl acrylate, phenoxyethoxyethyl acrylate, phenoxyethoxyethyl methacrylate, 1,4-di(2-thionaphthyl)2-butyl methacrylate, pentabromobenzyl methacrylate, propane-2,2-diylbis[(2,6-dibromo-4,1-phenylene)oxy(2-{[3,3,3-tris(4-chlorophenyl)propionyl]oxy}propane- 3,1-Di(diyl)oxyethane-2,1-diyl]diacrylate, 2-naphthyl methacrylate, bisphenol A dimethacrylate, bisphenol A diacrylate, tetrabromobisphenol A dimethacrylate or tetrabromobisphenol A diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, 1,3-butanediol dimethacrylate, neopentyl glycol dimethacrylate, neopentyl glycol diacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, 1,4-butanediol dimethacrylate, bisphenol A dimethacrylate, bisphenol F diacrylate, ethoxybisphenol A. Diacrylate, commercially available polymerizable monomers such as SR348, SR349, SR540, SR541, SR542, SR601, and SR602 produced by Sartoma, or self-made high-refractive-index monomers and their derivatives, refer to patents CN202210077437.X, CN202210077188.4, CN202210972623.X, CN202210076846.8, CN202210077411.5, CN202310685655.6, and CN202511183221.1.

[0072] Preferably, the polymerizable monomer is a blend of methyl 9-anthracene methacrylate and a bisphenol type monomer containing two or more (meth)acrylate groups in a mass ratio of 8-10:1. The bisphenol type monomer containing two or more (meth)acrylate groups is selected from at least one of bisphenol A dimethacrylate, bisphenol F diacrylate, and ethoxylated bisphenol A diacrylate.

[0073] The inventors did not expect to discover that when the polymerizable monomers are in the above-mentioned compound, they have high diffraction efficiency and sensitivity, low haze, and excellent storage stability. After being stored at 0℃, 40℃, and 60℃ for 3 months, the diffraction efficiency did not decrease significantly.

[0074] Furthermore, the photoinitiating system is a mixed system capable of being activated by photochemical radiation and initiating the polymerization of corresponding polymerizable groups, generally comprising a photosensitizer, a photoinitiator, and / or a co-initiator. The photosensitizer includes, but is not limited to, cyanine dyes, fluorescein dyes, coumarin ketone dyes, benzylcyclopentanone dyes, and fluoroboron pyrrole dyes; exemplary examples include commercially available sodium fluorescein, eosin, rose red, methylene blue, or a mixture thereof, or a self-made photosensitizer, as described in CN200510135231.4, CN202211278279.0, CN202210490530.3, and CN202510259056.7. Photoinitiators include, but are not limited to, at least one or a mixture thereof from the group consisting of aromatic ketones, benzoin and its derivatives, benzoyl ketals, acylphosphine oxides, ammonium arylboronates, chromium salts, aryl diazonium salts, onium salts, and organometallic compounds; exemplary, they include benzophenone, alkylbenzophenone, 4,4'-bis(dimethylamino)benzophenone, serotonin and halogenated benzophenone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, diacylphosphine oxide, phenyl dihydroxyacetate, camphorquinone, α-aminoalkylphenyl ketone, α,α-dialkoxyacetophenone, α-hydroxyalkylphenyl ketone, tetrabutylammonium triphenylhexylborate, tri-(3-)-ethylhexyl boronic acid, etc. Tetra-(3-chloro-4-methylphenyl)hexylborate tetrabutylammonium, ferrocene-based compounds, iodide salts, thionium salts, hexaaryl diimidazole, commercially available IR651, IR784, IR1173, IR819, OXE-01, OXE-02, or a mixture thereof, can also be used as a self-made photoinitiator system, as per ZL202110196660.1, ZL202210490530.3, CN202410731829.2, CN202410655130.2, and CN202410186524.8.

[0075] Furthermore, the catalyst is a tertiary amine catalyst or an organometallic catalyst, including but not limited to triethylenediamine, bis(dimethylaminoethyl) ether, dimethylethanolamine, 2-(2-dimethylamino-ethoxy)ethanol, trimethylhydroxyethylpropanediamine, N,N-bis(dimethylaminopropyl)isopropanolamine, dibutyltin dilaurate, stannous octoate, potassium carboxylate catalysts, and bismuth carboxylate catalysts.

[0076] Furthermore, the chain transfer agent is a thiol compound, exemplarily at least one of the group consisting of dodecyl thiol, hexamethylene thiol, phenylethyl thiol, 4-methyl-4H-1,2,4-triazol-3-thiol, 5-(4-pyridyl)-1,3,4-oxadiazol-2-thiol, and a self-made thiol compound.

[0077] Furthermore, the additives include one or more of the following: defoamers, leveling agents, plasticizers, antioxidants, and dehydrating agents.

[0078] Furthermore, the defoamer is an organosilicone defoamer, exemplarily BYK-011, BYK-012, BYK-014, BYK-023, BYK-051N, BYK-085, BYK-1610, BYK-1707, BYK-1740, BYK-1760, BYK-065, BYK-066, BYK-088, BYK-141, BYK-W 969, BYK-LPD 24043 manufactured by BYK Corporation, DC65 and AFE-7820 manufactured by Dow Corning, or mixtures thereof.

[0079] Furthermore, the leveling agent is an organosilicon surface additive, exemplarily at least one of the following groups: BYK-302, BYK-306, BYK-307, BYK-327, BYK-329, BYK-333, BYK-356, BYK-358, BYK-378, BYK-3455, BYK-3566, BYK-306, BYK-310, BYK-344, BYK-358, BYK-1790, BYK-1794 manufactured by BYK AG, and Dechian 455 and 466 manufactured by Dechian GmbH.

[0080] Furthermore, the plasticizer is selected from at least one of the group consisting of low-volatility toluene, xylene, dimethylformamide, dimethylacetamide, phthalates, etc.

[0081] Furthermore, the dehydrating agent is a type of chemical substance that removes moisture from the system through a chemical reaction, including but not limited to at least one of p-toluenesulfonyl isocyanate, triethyl orthoformate, CUWR-WB20 and CUWR-WB50 dehydrating agents from Guangzhou Yourun Synthetic Materials Co., Ltd., ALT-201 dehydrating agent from Anxiang Elite Chemical Co., Ltd., PCCI dehydrating agent from Shanghai Luer Chemical Trading Co., Ltd., Incozol dehydrating agent from ICL Company of the United Kingdom, and OF dehydrating agent from Bayer of Germany.

[0082] Furthermore, the antioxidant is a class of chemical additives used to inhibit or delay the oxidative degradation of polymer materials caused by factors such as heat, oxygen, and light during processing, storage, or use. These include, but are not limited to, one or more of commercially available Irganox 1010, Irganox 1076, Irganox 1098, Irganox 1330, Irganox 3114, Irgafos 168, Irgafos 38, Irganox MD1024, Irganox E201, Irganox 1520, and Irganox 1425.

[0083] This invention provides the application of the above-mentioned photopolymer holographic recording medium in optical waveguide devices for AR displays, high-density holographic optical storage, holographic anti-counterfeiting, etc.

[0084] The photopolymer-type holographic recording medium of the present invention is a disc or photosensitive film with a certain thickness of the above-mentioned photopolymer-type holographic recording medium sandwiched in the middle of an optical substrate or optical protective film, see ZL202110168535.X.

[0085] The fabrication steps of a high-precision holographic grating are as follows:

[0086] A laser with a wavelength of 400–800 nm is selected as the light source. Two laser beams with the same polarization are obtained by passing them through a beam expander, beam splitter, polarizer, half-wave plate, and mirror. The beams intersect and are exposed within the aforementioned photopolymer holographic recording medium. The angle between the two beams is 60°–180°, the beam intensity ratio is 0.5:1–2:1, and the total light intensity is 0.5–10 mW / cm². 2 Holographic gratings with spatial frequencies ranging from 3000 lp / mm to 6500 lp / mm were recorded.

[0087] Furthermore, when two beams of light are exposed on the same side of the recording medium, the resulting holographic grating is a transmissive volume grating; when two beams of light are exposed on opposite sides of the recording medium, the resulting holographic grating is a reflective volume grating. High spatial frequency gratings can be used as coupling-in or coupling-out gratings in optical waveguide devices for AR displays.

[0088] Furthermore, by using a spatial light modulator (such as DMD or SLM) or a mask to load image information onto one of the laser beams as the object light, the image information can be recorded in the holographic recording medium during coherent exposure. The recorded image information can then be reproduced by diffraction light when the exposure area is illuminated by another reference light. This method can be used for applications such as high-density holographic optical storage and holographic anti-counterfeiting.

[0089] To address the issues of insufficient refractive index modulation and low resolution in existing photopolymer-based holographic recording media, this invention utilizes high-refractive-index fluorene-containing monomers / polymerizable monomers or oligomers as recording components and a low-refractive-index isocyanate-alcohol and epoxy resin-amine curing agent crosslinking system as the film-forming resin. This increases the refractive index difference between the polymerizable monomer and the film-forming resin. Furthermore, the fluorene-containing monomer exhibits high polymerization and migration rates, resulting in good compatibility with the film-forming resin after polymerization, enabling the preparation of high-performance holographic recording media. By selecting different photosensitive initiation systems, various wavelength-matched lasers can be chosen as information recording light sources within a wide wavelength range of 450–670 nm. Interference exposure yields holographic gratings with high diffraction efficiency, high spatial frequency, and low haze. Through angle or wavelength multiplexing, storage density or eye-tracking range can be improved, ultimately leading to applications in holographic displays, high-density holographic data storage, and holographic anti-counterfeiting. Attached Figure Description

[0090] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0091] Figure 1 The 532 nm holographic exposure characteristic curves of the photopolymer holographic recording medium in Examples 1-4 of this invention are shown.

[0092] Figure 2 The angular selectivity curves of the 5600 lp / mm reflective gratings prepared by 532 nm laser exposure of the photopolymer holographic recording medium in Examples 1-4 of this invention are shown.

[0093] Figure 3 The wavelength selectivity curves of the 5600 lp / mm reflective gratings prepared by 532 nm laser exposure of the photopolymer holographic recording medium in Examples 1-4 of the present invention are shown.

[0094] Figure 4 The angular selectivity curves of the 3200 lp / mm transmission gratings prepared by 532 nm laser exposure of the photopolymer holographic recording medium in Examples 5-7 of the present invention are shown.

[0095] Figure 5The wavelength selectivity curves of the 6300 lp / mm reflective gratings prepared by 457 nm laser exposure of the photopolymer holographic recording medium in Examples 8-9 of the present invention are shown.

[0096] Figure 6 The illustration shows a schematic diagram and actual scene of AR display using a holographic optical waveguide device (including coupling in and coupling out gratings) fabricated from a photopolymer holographic recording medium according to Embodiment 2 of the present invention.

[0097] Figure 7 The diffraction efficiency of the grating after exposure for different times is shown in Embodiment 3 of the present invention. Detailed Implementation

[0098] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further explains the invention. Similar components in the drawings are indicated by the same reference numerals. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0099] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; the reagents and chemical materials used in the following embodiments are commercially available unless otherwise specified. The experimental methods and optical equipment used in the following embodiments are conventionally used in this technical field.

[0100] Example 1

[0101] The steps for preparing photopolymer-based holographic recording media are as follows: In a darkroom, add the various material components listed in Table 1 sequentially to a 500 mL container equipped with a stirrer. Stir thoroughly at room temperature for 15 min to ensure uniform mixing. Filter out insoluble matter and impurities using a 0.22 μm pore size filter. Degas the filtrate, coat it evenly onto a glass medium, and then cover it with an optical protective film with a thickness of 15 μm. Curing is performed in a constant temperature and humidity chamber at 35℃ for 2 days. After curing, seal with aluminum foil and store away from light.

[0102] Table 1. Composition of photopolymer-based holographic recording media

[0103]

[0104] Example 2

[0105] The photopolymer-type holographic recording medium was prepared according to the method described in Example 1. The difference from Example 1 is that its material composition is shown in Table 2.

[0106] Table 2. Composition of photopolymer-based holographic recording media

[0107]

[0108] Example 3

[0109] The photopolymer-type holographic recording medium was prepared according to the method described in Example 1. The difference from Example 1 is that its material composition is shown in Table 3.

[0110] Table 3. Composition of photopolymer-based holographic recording media

[0111]

[0112] Example 4

[0113] The photopolymer-type holographic recording medium was prepared according to the method described in Example 1. The difference from Example 1 is that its material composition is shown in Table 4.

[0114] Table 4. Composition of photopolymer-based holographic recording media

[0115]

[0116] Example 5

[0117] The photopolymer holographic recording medium was prepared according to the method described in Example 1. The difference from Example 1 is that its material composition is shown in Table 5 and the coating thickness is 200 μm.

[0118] Table 5. Composition of photopolymer-based holographic recording media

[0119]

[0120] Example 6

[0121] The photopolymer holographic recording medium was prepared according to the method described in Example 1. The difference from Example 1 is that its material composition is shown in Table 6 and the coating thickness is 200 μm.

[0122] Table 6

[0123]

[0124] Example 7

[0125] The photopolymer holographic recording medium was prepared according to the method described in Example 1. The difference from Example 1 is that its material composition is shown in Table 7 and the coating thickness is 200 μm.

[0126] Table 7

[0127]

[0128] Example 8

[0129] The photopolymer holographic recording medium was prepared according to the method described in Example 1. The difference from Example 1 is that its material composition is shown in Table 8 and the coating thickness is 30 μm.

[0130] Table 8

[0131]

[0132] Example 9

[0133] The photopolymer holographic recording medium was prepared according to the method described in Example 1. The difference from Example 1 is that its material composition is shown in Table 9, and the coating thickness is 50 μm.

[0134] Table 9

[0135]

[0136] Comparative Example 1

[0137] The photopolymer holographic recording medium was prepared according to the method described in Example 1. The difference from Example 1 is that its material composition is shown in Table 10, which does not contain fluorene monomers and has a coating thickness of 200 μm.

[0138] Table 10

[0139]

[0140] Application Example 1

[0141] Holographic exposure performance testing of photopolymer-based holographic recording media:

[0142] A 532 nm wavelength single-longitudinal-mode laser was used as the light source. An 8 mm diameter laser spot was obtained using a beam expander. Two beams were then generated using a beam splitter, a half-wave plate, and an aperture. These beams were intersected within a photopolymer holographic recording medium for exposure. The optical path lengths of the two beams were adjusted to be equal. One beam was incident perpendicularly, while the other was incident from the opposite side of the recording medium at a 30° angle deviating from the normal. The included angle between the two beams was 150°, and the exposure intensity was 3.5 mW / cm². 2 Simultaneously, a photodetector is used to monitor the intensity of the diffracted light from the holographic grating in the exposure area in real time, monitoring once every 1 second, and measuring the direct transmitted light from the holographic exposure area. The diffraction efficiency (η) of a single grating is calculated by dividing the diffracted light by the direct transmitted light. The photosensitivity (S) of the recording medium is calculated using / E, where E is the exposure required to achieve maximum diffraction efficiency. The spatial frequency of the grating is obtained using the Bragg equation; under these exposure conditions, the photopolymers of Examples 1-4 can be used to fabricate reflective holographic gratings with a spatial frequency of 5600 lp / mm.

[0143] Figure 1The 532 nm holographic exposure characteristic curves (single grating diffraction efficiency versus exposure time) of the photopolymer holographic recording media in Examples 1-4 are shown. A higher maximum diffraction efficiency of the recording medium, and a shorter exposure time required to reach that efficiency, indicates higher sensitivity. Compared to Comparative Example 1, the diffraction efficiency of the gratings in Examples 1-9 exceeds 90%, and the sensitivity is higher than 30 cm⁻¹. 2 / J, with no significant change in haze, the experimental results indicate that the photopolymer holographic recording medium containing fluorene monomers has the characteristics of high sensitivity and high resolution.

[0144] Application Example 2

[0145] Fabrication of holographic gratings and their angular and wavelength selectivity:

[0146] Holographic exposure of a photopolymer holographic recording medium was performed using a similar optical path to Application Example 1, except that the angle between the two beams was 120°, the normal of the recording medium bisects the two beams, and the exposure intensity was 1 mW / cm². 2 Transmissive holographic gratings with a spatial frequency of 3200 lp / mm were prepared using photopolymers from Examples 5-7. A 520 nm wavelength laser was used as the detection light source. A rotating stage was used to adjust the beam so that it was normally incident on the grating region of the sample at the zero point of the angle. The sample was rotated to near the Bragg angle of the grating, and the incident angle of the probe light was changed by numerical control software (angular resolution of 0.01°). The changes in diffracted light were monitored in real time, and the curve of the grating's diffraction efficiency as a function of angle, i.e., the angle selectivity curve, was obtained. For the reflective gratings recorded in Examples 1-4, the angular bandwidth was high, with a scanning angle range from -15° to 45°. For the transmissive gratings recorded in Examples 5-7, the angle selectivity was high, with a scanning angle range from 55° to 65°.

[0147] Holographic exposure of a photopolymer-type holographic recording medium was performed using a similar optical path to Application Example 1. The difference was that the light source was a 457 nm wavelength single-longitudinal-mode laser, with one beam incident perpendicularly and the other beam incident at a 60° angle deviating from the normal from the other side. The angle between the two beams was 120°, and the exposure intensity was 3 mW / cm². 2 A reflective holographic grating with a spatial frequency of 6300 lp / mm was prepared using the photopolymers of Examples 8-9. Using a UV-Vis spectrophotometer with a blank glass or optical protective film as a background, the grating region of the sample was placed vertically in the instrument's test optical path. The wavelength was adjusted from 400 nm to 800 nm, and the transmitted light in the grating region was monitored in real time. Since a beam of light is incident perpendicularly during holographic exposure, the lower the measured transmitted light, the higher the diffraction efficiency, thus obtaining the wavelength selectivity curve of the grating.

[0148] Table 11 Holographic performance parameters of photopolymer holographic recording media.

[0149]

[0150] Figure 2 The angular selectivity curves (diffraction efficiency versus angle) of the 5600 lp / mm reflective gratings prepared by 532 nm laser exposure of the photopolymer holographic recording medium in Examples 1-4 are shown. Higher diffraction efficiency and angular bandwidth of the reflective grating result in a larger field of view and eye-tracking range, and better display effect, when used as an input / output grating for holographic displays. The gratings in Examples 1-4 have diffraction efficiencies exceeding 90% and angular bandwidths approaching 30°, significantly higher than Comparative Example 1. These experimental results demonstrate that the photopolymer holographic recording medium containing fluorene monomers can be used to prepare high-precision holographic gratings for holographic display waveguides, with the grating in Example 2 exhibiting the best holographic performance at a diffraction efficiency of 97%.

[0151] Figure 3 The wavelength selectivity curves (grating transmittance versus wavelength curves) of the 5600 lp / mm reflective gratings fabricated by 532 nm laser exposure of the photopolymer holographic recording medium in Examples 1-4 are shown. The smaller the wavelength bandwidth of the reflective grating, the stronger its selectivity for a specific wavelength of light. Compared with Comparative Example 1, the gratings in Examples 1-4 have extremely low transmittance in the 520-535 nm range and high diffraction efficiency for that wavelength. Simultaneously, the transmittance in the red light region is greater than 90%. The experimental results demonstrate that the high-precision gratings fabricated by the photopolymer holographic recording medium containing fluorene monomers exhibit good wavelength selectivity.

[0152] Figure 4 The angular selectivity curves of the 3200 lp / mm transmission gratings prepared by 532 nm laser exposure of the photopolymer holographic recording media in Examples 5-7 are shown. The smaller the selectivity angle of the transmission grating, the wider the range of angles that the recording medium can reuse at the same position, and the larger its dynamic storage range. The gratings in Examples 5-7 exhibit good angular selectivity, with Example 5 showing the highest diffraction efficiency and a selectivity angle half-width of less than 1°, indicating that the photopolymer holographic recording medium containing fluorene monomers has a large dynamic storage range.

[0153] Figure 5 The wavelength selectivity curves of the 4300 lp / mm reflective gratings prepared by 457 nm laser exposure of the photopolymer holographic recording medium in Examples 8-9 are shown. Compared with Comparative Example 1, the gratings of Examples 8-9 have extremely low transmittance at 445-460 nm and high diffraction efficiency at this wavelength, while the transmittance in the red light band is greater than 90%.

[0154] Application Example 3

[0155] Fabrication and AR display of holographic waveguide devices:

[0156] Using a narrow-linewidth 532 nm laser as the light source, two laser beams, each 20 mm × 20 mm in size, were obtained through a beam expander, beam splitter, half-wave plate, and aperture. Glycerin was used as the refractive index matching fluid, applied to a prism and attached to the left end of a photopolymer sample. One beam was incident perpendicularly through the prism, while the other beam was incident at the total internal reflection angle between the prism and the sample. According to... Figure 1 The holographic exposure characteristic curve of Example 2 shows an exposure time of 10 s and an exposure intensity of 3.5 mW / cm². 2 The coupling grating of the optical waveguide was fabricated. The sample was moved to the right end using a translation stage, and the prism bonding direction was changed. The displacement was 20 mm for each exposure, and the exposure was performed three times for 6 s, 8 s, and 10 s respectively to obtain the coupling grating of the optical waveguide. The sample was placed under a solar simulator for uniform light bleaching for 1 h, and finally the holographic optical waveguide device was fabricated.

[0157] Figure 6 This diagram illustrates an AR display using a holographic waveguide device (including coupling and coupling gratings) fabricated from a photopolymer-based holographic recording medium, as shown in Example 4, and a real-world scenario. The Institute of Physics and Chemistry's logo image is modulated onto a green light source, enters through the coupling grating, propagates via total internal reflection within the medium, and then exits through the coupling grating. The human eye can simultaneously observe the Institute of Physics and Chemistry's logo and the actual environment in the coupling region, achieving a combined virtual and real AR effect. Figure 6 It can be seen that the virtual and real integration of the optical waveguide is very clear, indicating that the photopolymer holographic recording medium containing fluorene monomers has the application potential of AR display.

[0158] Application Example 4

[0159] Storage stability of recording media:

[0160] The recording medium prepared in Example 3 was placed at room temperature, refrigerated at 0°C, 40°C, and 60°C for 1 month and 3 months, respectively. A grating was obtained by optical path holographic exposure in Application Example 2, and the diffraction efficiency of the grating was tested as a function of storage time.

[0161] Figure 7The diffraction efficiency of the photopolymer holographic recording medium in Example 3 after exposure for different periods is shown. In the experiment, the diffraction efficiency was greater than 95% after 3 months of storage under four different conditions, indicating that the recording medium of Example 3 has good storage stability. However, other examples did not consistently achieve a diffraction efficiency greater than 90% after 3 months under the same conditions. This may be due to a synergistic effect between the monomers methyl methacrylate-9-anthracene and bisphenol A diacrylate ethoxylate. This synergistic effect was not observed in other monomer combinations. For example, in Example 2, the polymerizable monomers were a mixture of 2,4,6-tribromophenyl acrylate and bisphenol A diacrylate ethoxylate in equal proportions, but after 3 months at 60°C, the diffraction efficiency decreased to 88.7%; in Example 4, 9-vinylanthracene and bisphenol A diacrylate ethoxylate were used, but after 3 months at 60°C, the diffraction efficiency was only 87.2%, and the stability was not as good as in Example 3.

Claims

1. A photopolymer-based holographic recording medium, characterized in that, Its raw materials include fluorene-containing acrylate monomers, wherein the general structural formula of the fluorene-containing acrylate monomers is shown as G1, G2, G3, or G4: Where X represents S or O, n is an integer from 1 to 3, and R1 and R2 each independently represent H, C1~C5 alkyl, C1~C5 alkoxy, C1~C5 alkylthio, Br, or , This indicates the linking bond between the substituent and the main structure; R3 represents a C1-C5 alkyl group. , , A1, A2, A3, A4, and A5 each independently represent hydrogen, C1-C5 alkyl, C1-C5 alkoxy, C1-C5 alkylthio, or Br; R4 represents C 1-3 Alkyl or H.

2. The photopolymer-type holographic recording medium according to claim 1, characterized in that, n=1, R3 is methyl, ethyl, propyl, butyl, phenyl, biphenyl, fluorenyl, anthracene.

3. The photopolymer-type holographic recording medium according to claim 1, characterized in that, The fluorene-containing acrylate monomer accounts for 5-20 wt% of the raw material of the photopolymer-type holographic recording medium.

4. The photopolymer-type holographic recording medium according to claim 1, characterized in that, The fluorene-containing acrylate monomer has the following structural formula: 。 5. The photopolymer-type holographic recording medium according to claim 1, characterized in that, It is a polyurethane-type photopolymer holographic recording medium or an epoxy-amine-type photopolymer holographic recording medium; The polyurethane-based photopolymer holographic recording medium comprises the following raw materials: Component a) Polyisocyanate compounds; Component b) Polyol compounds; Component c) contains fluorene monomers; Component d) optionally polymerizable monomers / oligomers; Component e) Photosensitive initiation system; Component f) Catalyst; Component g) optionally, additives; The epoxy-amine photopolymer holographic recording medium comprises the following raw materials: Component a) Epoxy resin; Component b) Polyamine curing agent; Component c) contains fluorene monomers; Component d) optionally polymerizable monomers / oligomers; Component e) Photosensitive initiation system; Component f) Chain transfer agent; Component g) optional additives.

6. The photopolymer-type holographic recording medium according to claim 1, characterized in that, The polyurethane-type photopolymer holographic recording medium comprises the following parts by weight of raw materials: 20-40 parts of isocyanate, preferably 30-35 parts; 20-40 parts of alcohol, preferably 25-30 parts; Contains 5-20 parts of fluorenyl acrylate monomer, preferably 10-15 parts; The polymerizable monomer can be 10-30 parts, preferably 20-28 parts; The photosensitizer is used in amounts of 0.01 to 0.5 parts, preferably 0.05 to 0.1 parts; The photoinitiator is used in an amount of 0.1 to 3.0 parts, preferably 0.2 to 0.5 parts; Catalyst: 0.1-1.0 parts, preferably 0.2-0.5 parts; Defoamer 0-2.0 parts, preferably 0.5-1 part; Leveling agent: 0-2.0 parts, preferably 0.5-1 parts; The dehydrating agent is 0-2.0 parts, preferably 0.5-1 parts; Plasticizer 0-3.0 parts, preferably 1-1.5 parts; Chain transfer agent: 0.1-2.0 parts, preferably 0.5-1 parts; Antioxidant 0-1.0 parts, preferably 0.2-0.5 parts; or The epoxy-amine photopolymer holographic recording medium comprises the following parts by weight of raw materials: 20-50 parts of epoxy resin, preferably 30-45 parts; 10-20 parts of amine, preferably 12-17 parts; Contains 5-20 parts of fluorenyl acrylate monomer, preferably 13-17 parts; The polymerizable monomer can be 10-30 parts, preferably 20-28 parts; The photosensitizer is used in amounts of 0.01 to 0.5 parts, preferably 0.05 to 0.1 parts; The photoinitiator is used in an amount of 0.1 to 3.0 parts, preferably 0.2 to 0.5 parts; Chain transfer agent: 0.1-3.0 parts, preferably 1-2.5 parts; Defoamer 0-2.0 parts, preferably 0.5-1 part; Leveling agent: 0-2.0 parts, preferably 0.5-1 parts; Plasticizer 0-3.0 parts, preferably 1-2 parts; Antioxidant 0-1.0 parts, preferably 0.2-0.5 parts.

7. The photopolymer-type holographic recording medium according to claim 5 or 6, characterized in that, The isocyanate comprises at least one from the group consisting of hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, (2,4,6-trioxotriazine-1,3,5(2H,4H,6H)-triyl)tri(hexamethylene)isocyanate, butane-1,4-diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, etc.; and / or The alcohol is selected from compounds with low refractive index and two or more hydroxyl functional groups, including but not limited to at least one group consisting of triethylene glycol, tetraethylene glycol, butanediol, hexanediol, trimethylolethane, glycerol, triethanolamine, pentaerythritol, polyester polyols with a molecular weight of 200-2000, polycarbonate polyols with a molecular weight of 200-2000, and polyether polyols with a molecular weight of 200-2000; and / or The epoxy resin is selected from various aliphatic epoxy resins containing epoxy groups, whether monofunctional or polyfunctional, and having a low refractive index, including but not limited to at least one of n-butyl glycidyl ether, allyl glycidyl ether, 2-ethylhexyl glycidyl ether, diglycidyl ester, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, butanediol diglycidyl ether, pentylene glycol diglycidyl ether, glycerol triglycidyl ether, and 3,4-epoxycyclohexenemethyl-3,4-epoxycyclohexenoester; and / or The amine curing agent is a low-to-medium temperature amine curing agent with a curing temperature ≤60℃, including but not limited to at least one selected from diethylenetriamine, triethylenetetramine, tetraethylenepentamine, divinylpropylamine, 2-methylpentanediamine, 1,3-pentanediamine, 1,2-cyclohexanediamine, isophoronediamine, hexanediamine, and 4,4'-diaminodicyclohexylmethane; and / or The photosensitizer is selected from at least one of cyanine dyes, fluorescein dyes, coumarin ketone dyes, benzylcyclopentanone dyes, and fluoroboron pyrrole dyes; the photoinitiator is selected from at least one of aromatic ketone compounds, benzoin and its derivatives, benzoyl ketal, acylphosphine oxides, ammonium arylboronate, chromium salts, aryl diazonium salts, onium salts, and organometallic compounds; the catalyst is a tertiary amine catalyst or an organometallic catalyst.

8. The photopolymer-type holographic recording medium according to claim 5 or 6, characterized in that, N-Vinylpyrrole, N-Vinylcarbazole, N-Vinylimidazol, N-Vinylindole, N-Vinylpyrrolidone, trans-N-3-yntynebutenylcarbazole, styrene, 2-chlorostyrene, 2-bromostyrene, 3-chlorostyrene, 3-bromostyrene, 4-chlorostyrene, 4-bromostyrene, p-(chloromethyl)styrene, p-(bromomethyl)styrene or 1-vinylnaphthalene, 2-vinylnaphthalene, 2-vinylanthracene, 9-vinylanthracene, 2-phenoxyethyl acrylate, 2-phenoxyethyl methacrylate, benzyl methacrylate, methyl 9-anthracene methacrylate, benzyl acrylate, p-chlorophenyl acrylate, 2,4,6-trichlorophenyl acrylate, p-bromophenyl acrylate, p-bromophenyl methacrylate, p-chlorophenyl methacrylate Ester, 2,4,6-tribromophenyl acrylate, 2,4,6-tribromophenyl methacrylate, 2,4,6-trichlorophenyl methacrylate, pentabromophenyl acrylate, pentachlorophenyl acrylate, phenoxyethyl acrylate, pentabromophenyl methacrylate, pentachlorophenyl methacrylate, pentabromobenzyl acrylate, phenoxyethyl methacrylate, 2-naphthyl acrylate, 1,4-di(2-thionaphthyl)2-butyl acrylate, phenoxyethoxyethyl acrylate, phenoxyethoxyethyl methacrylate, 1,4-di(2-thionaphthyl)2-butyl methacrylate, pentabromobenzyl methacrylate, propane-2,2-diylbis[(2,6-dibromo-4,1-phenylene)oxy(2-{[3,3,3-tris(4-chlorophenyl)propionyl]oxy}propane- [3,1-diyl)oxyethane-2,1-diyl]diacrylate, 2-naphthyl methacrylate, bisphenol A dimethacrylate, bisphenol A diacrylate, tetrabromobisphenol A dimethacrylate or tetrabromobisphenol A diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, 1,3-butanediol dimethacrylate, neopentyl glycol dimethacrylate, neopentyl glycol diacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, 1,4-butanediol dimethacrylate, bisphenol A dimethacrylate, bisphenol F diacrylate, ethoxybisphenol A diacrylate, and at least one of the commercially available polymerizable monomers SR348, SR349, SR540, SR541, SR542, SR601, and SR602 manufactured by Sartoma.

9. The photopolymer-type holographic recording medium according to claim 5 or 6, characterized in that, The polymerizable monomer is a mixture of methyl 9-anthracene methacrylate and a bisphenol type monomer containing two or more (meth)acrylate groups in a mass ratio of 8-10:1; the bisphenol type monomer containing two or more (meth)acrylate groups is selected from at least one of bisphenol A dimethacrylate, bisphenol F diacrylate, and ethoxylated bisphenol A diacrylate.

10. The application of the photopolymer-type holographic recording medium according to any one of claims 1-9 in optical waveguide devices for AR displays, high-density holographic optical storage, holographic anti-counterfeiting, etc.

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