Photopolymer composition for holographic grating, holographic grating and holographic display system

Abstract

The invention provides a photopolymer composition for a holographic grating, the holographic grating and a holographic display system. The photopolymer composition is prepared from the following components in percentage by mass: 30 to 65 percent of polymeric monomer containing an epoxy group, 0.5 to 5 percent of epoxy modified dye, 0.5 to 5 percent of epoxy modified photoinitiator, 30 to 65 percent of film-forming agent and 0.1 to 5 percent of optional additive, the epoxy modified photoinitiator comprises the following raw materials: first epoxy resin containing at least one epoxy group and a micromolecular photoinitiator containing at least one hydroxyl group. According to the photopolymer composition, the first epoxy resin and the small molecular initiator are connected through the ring-opening reaction to form the modified photoinitiator with an epoxy polymer side chain with large molecular weight, and the modified photoinitiator is easily dispersed in a non-solvent organic system, so that the solubility and dispersity of the modified photoinitiator in a photopolymer material are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of optical materials, and in particular to a photopolymer composition for a holographic grating, a holographic grating and a holographic display system. Background Art

[0002] Photopolymer is a new type of holographic material with outstanding advantages such as low cost and good color performance. It has broad application prospects in the field of AR display. The composition of photopolymer mainly includes photoinitiator, photosensitive dye, photopolymer monomer and film-forming agent. In the process of photopolymer forming holographic grating structure, there are mainly two stages of polymerization reaction: in the first stage, the film-forming monomer forms a film-forming matrix with a cross-linked network structure through heating and curing reaction, providing mechanical support, and evenly distributing the photopolymer monomer in the cross-linked network for subsequent holographic exposure. In the second stage, under the interference exposure of the double-beam coherent laser, the dye absorbs photons in the corresponding wavelength range and transitions to an excited state, and transfers the energy of the excited state to the initiator through energy transfer or electron transfer. The initiator obtains electrons or energy to generate free radicals, which causes the photopolymer monomer to undergo a photopolymerization reaction in the coherent bright area, inducing the photopolymer monomer in the coherent dark area to diffuse to the coherent bright area and participate in the photopolymerization reaction, which ultimately causes the photopolymer generated in the coherent bright area to have a different polymer density and refractive index from the film-forming matrix generated by the first stage of the thermosetting reaction, thereby generating microphase separation. As the degree of microphase separation increases during the photopolymerization reaction, the diffraction efficiency increases, and the grating will have a certain degree of fogging, and the transmittance will decrease. In the above-mentioned second stage reaction, polymerization and diffusion usually occur simultaneously in the exposure area in a relatively uncontrolled manner. During the exposure process and after the termination of exposure, the polymer that is not bound to the matrix can freely diffuse out of the coherent bright area into the coherent dark area, which will also cause the resulting grating to fog and reduce the transmittance. In addition, most of the current photoinitiators are solid organic small molecules, and most of the photosensitive dyes are conjugated compounds with relatively small molecular weights and their ionized salts, which results in poor solubility of both in oligomers and monomers. This will also cause the grating to become foggy and reduce the transmittance to a certain extent.

[0003] In view of this, the present invention is proposed. Summary of the invention

[0004] The main purpose of the present invention is to provide a photopolymer composition for holographic grating, a holographic grating and a holographic system to solve the problems of fogging and low light transmittance of the current photopolymer holographic grating.

[0005] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, there is provided a photopolymer composition for holographic grating, which comprises, by mass percentage, 30-65% of a polymerizable monomer containing an epoxy group, 0.5-5% of an epoxy-modified dye, 0.5-5% of an epoxy-modified photoinitiator, 30-65% of a film-forming agent and 0.1-5% of an optional additive, wherein the raw materials of the epoxy-modified photoinitiator comprise a first epoxy resin and a small molecule photoinitiator, the first epoxy resin contains at least one epoxy group, and the small molecule photoinitiator contains at least one hydroxyl group.

[0006] Furthermore, the small molecule photoinitiator is an α-hydroxy aromatic ketone initiator containing a hydroxyl group.

[0007] Furthermore, the small molecule photoinitiator is selected from at least one of the compounds represented by formula (I) to formula (IV):

[0008]

[0009] Further, the first epoxy resin contains at least two epoxy groups.

[0010] Furthermore, the first epoxy resin is selected from at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, polyphenol glycidyl ether epoxy resin, aliphatic glycidyl ether epoxy resin, epoxidized olefin compound, and cyanuric acid epoxy resin.

[0011] Furthermore, the first epoxy resin is at least one of polypropylene glycol diol diglycidyl ester and polyethylene glycol diglycidyl ether, and the number average molecular weights of polypropylene glycol diol diglycidyl ether and polyethylene glycol diglycidyl ether are each independently 1000 to 5000.

[0012] Furthermore, the first epoxy resin is calculated based on the molar amount of epoxy groups, and the small molecule photoinitiator is calculated based on the molar amount of hydroxyl groups, and the molar ratio of the first epoxy resin to the small molecule photoinitiator is 1 to 4:1.

[0013] Furthermore, the raw materials of the epoxy-modified dye include a second epoxy resin and a small molecule dye, the second epoxy resin contains at least two epoxy groups, and the small molecule dye contains at least one group capable of undergoing a ring-opening reaction with the epoxy group.

[0014] Furthermore, the raw materials of the film-forming agent include epoxy monomer and curing agent, and the mass ratio of the two is (29-60):(1-5); wherein the epoxy monomer is an epoxy compound containing an epoxy group, and the refractive index of the epoxy compound is preferably ≤1.45.

[0015] Furthermore, the curing agent includes at least one of polyamine, acid anhydride, tertiary amine, boron trifluoride, boron amine complex or imidazole curing agent.

[0016] Furthermore, the polymerizable monomer is an acrylate monomer, and preferably the acrylate monomer is a mixture of epoxy acrylate containing epoxy groups and acrylate not containing epoxy groups; and the mass ratio of the two is (10:90) to (40:60), and more preferably 30:70.

[0017] According to the third aspect of the present application, the present application further provides a holographic grating, which comprises a polymer film having a grating structure, and the material of the polymer film is the photopolymer composition provided in the second aspect above.

[0018] Furthermore, the preparation method of the polymer film includes the following steps: step S1, mixing a photopolymer composition including a polymerizable monomer containing an epoxy group, an epoxy-modified dye, an epoxy-modified photoinitiator, a film-forming agent and optional additives to obtain a mixture; step S2, forming the mixture into a film and forming a grating structure at least in part to obtain a polymer film having a grating structure.

[0019] Further, step S2 includes the step of performing exposure using coherent light.

[0020] According to a fourth aspect of the present application, a holographic system is also provided, which comprises the holographic grating provided in the third aspect.

[0021] By applying the technical solution of the present application, the photopolymer composition provided by the present application adopts a combination of an epoxy-modified photoinitiator, an epoxy-modified dye, a photopolymerizable monomer containing an epoxy group, and a film-forming agent formed by thermosetting the epoxy monomer. Since the same organic group - epoxy group - is introduced into the main components of the photopolymer composition, the compatibility of each component can be improved, and the grating fogging problem caused by phase separation of the polymer in the photopolymerization part and the film-forming agent can be reduced. At the same time, the grating fogging caused by the poor solubility of the photoinitiator and the dye can also be improved.

[0022] In addition, the photopolymer composition provided in the present application uses epoxy-modified photoinitiators and epoxy-modified dyes. Since the epoxy-modified photoinitiators and epoxy-modified dyes both have epoxy polymer side groups with relatively large molecular weights, they will be easier to disperse in organic epoxy systems, thereby improving the compatibility of the photosensitizing dye with the various components in the photopolymer composition, thereby improving the grating fogging problem caused by the poor solubility of the photoinitiator and the dye in the oligomer and monomer.

[0023] In addition, the photopolymer composition provided in the present application controls the molar ratio of the reactants and the unreacted epoxy groups on the epoxy-modified initiator. During the process of the epoxy monomer thermosetting reaction to form a film-forming matrix, the epoxy groups on the epoxy-modified photoinitiator are ring-opened and grafted to be fixed on the film-forming matrix, which can effectively inhibit the mobility of the initiator, thereby improving the grating fogging problem caused by the photopolymer that is not combined with the film-forming matrix freely diffusing out of the coherent bright area into the coherent dark area during the exposure process; in addition, since the photopolymer monomer contains an epoxy group, it can also be ring-opened and grafted on the film-forming matrix during the process of the epoxy monomer thermosetting reaction to form a film-forming matrix, thereby improving the grating fogging problem caused by the photopolymer that is not combined with the film-forming matrix freely diffusing out of the coherent bright area into the coherent dark area during the exposure process. DETAILED DESCRIPTION

[0024] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0025] As analyzed in the background of the present application, the existing gratings formed by photopolymers have the problems of fogging and reduced light transmittance. In order to solve this problem, the present application provides a photopolymer composition, a holographic grating and a holographic display system.

[0026] In a first typical embodiment of the present application, a photopolymer composition for a holographic grating is provided, which comprises, by mass percentage, 30-65% of a polymerizable monomer containing an epoxy group, 0.5-5% of an epoxy-modified dye, 0.5-5% of an epoxy-modified photoinitiator, 30-65% of a film-forming agent and 0.1-5% of optional additives, wherein the raw materials of the epoxy-modified photoinitiator comprise a first epoxy resin and a small molecule photoinitiator, the first epoxy resin contains at least one epoxy group, and the small molecule photoinitiator contains at least one hydroxyl group.

[0027] Typically but not restrictively, in the photopolymer composition provided in the present application, the mass content of the polymerizable monomer containing an epoxy group is 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% or a range consisting of any two numerical values; the mass content of the epoxy-modified dye is 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5% or a range consisting of any two numerical values; the mass content of the epoxy-modified photoinitiator is 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5% or a range consisting of any two numerical values; the mass content of the film-forming agent is 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%; the mass content of the additive is 0%, 0.1%, 0.2%, 0.8%, 1%, 2%, 5% or a range consisting of any two numerical values.

[0028] By applying the technical solution of the present application, the photopolymer composition provided by the present application adopts a combination of an epoxy-modified photoinitiator, an epoxy-modified dye, a photopolymerizable monomer containing an epoxy group, and a film-forming agent formed by thermosetting the epoxy monomer. Since the same organic group - epoxy group - is introduced into the main components of the photopolymer composition, the compatibility of each component can be improved, and the grating fogging problem caused by phase separation of the polymer in the photopolymerization part and the film-forming agent can be reduced. At the same time, the grating fogging caused by the poor solubility of the photoinitiator and the dye can also be improved.

[0029] In addition, the photopolymer composition provided in the present application uses epoxy-modified photoinitiators and epoxy-modified dyes. Since the epoxy-modified photoinitiators and epoxy-modified dyes both have epoxy polymer side groups with relatively large molecular weights, they will be easier to disperse in organic epoxy systems, thereby improving the compatibility of the photosensitizing dye with the various components in the photopolymer composition, thereby improving the grating fogging problem caused by the poor solubility of the photoinitiator and the dye in the oligomer and monomer.

[0030] In addition, the photopolymer composition provided in the present application controls the molar ratio of the reactants and the unreacted epoxy groups on the epoxy-modified initiator. During the process of the epoxy monomer thermosetting reaction to form a film-forming matrix, the epoxy groups on the epoxy-modified photoinitiator are ring-opened and grafted to be fixed on the film-forming matrix, which can effectively inhibit the mobility of the initiator, thereby improving the grating fogging problem caused by the photopolymer that is not combined with the film-forming matrix freely diffusing out of the coherent bright area into the coherent dark area during the exposure process; in addition, since the photopolymer monomer contains an epoxy group, it can also be ring-opened and grafted on the film-forming matrix during the process of the epoxy monomer thermosetting reaction to form a film-forming matrix, thereby improving the grating fogging problem caused by the photopolymer that is not combined with the film-forming matrix freely diffusing out of the coherent bright area into the coherent dark area during the exposure process.

[0031] [Epoxy modified photoinitiator]

[0032] In the present application, a first epoxy resin containing epoxy groups and a small molecule photoinitiator containing hydroxyl groups are used to carry out a ring-opening reaction, and an epoxy polymer is grafted onto the small molecule photoinitiator. The specific reaction principle is as follows:

[0033]

[0034] Among them, Photoinitiator-OH represents a small molecule photoinitiator containing hydroxyl groups. represents a first epoxy resin containing epoxy groups.

[0035] In order to improve the efficiency of photoinitiation, the small molecule photoinitiator is preferably an α-hydroxy aromatic ketone initiator containing a hydroxyl group, including but not limited to at least one of the compounds represented by the following formula (I) to formula (IV):

[0036]

[0037]

[0038] The first epoxy resin is preferably an epoxy resin containing two or more epoxy groups, so that it is more conducive to still containing unopened epoxy groups after reacting with the small molecule photoinitiator, so as to facilitate the reaction with the film-forming agent, etc., so that the modified photoinitiator can be fixed on the film-forming matrix, which can further improve the dispersibility of the initiator on the one hand; on the other hand, it has the effect of inhibiting the migration of the initiator. Since the mobility of the modified photoinitiator is reduced, the probability of free radical coupling in the initial exposure is reduced, the light curing rate of the system is accelerated, and the diffraction efficiency is increased. At the same time, it will inhibit the photopolymer that is not connected to the film-forming matrix from migrating to the dark area during the exposure process and after the exposure is terminated, further effectively reducing the grating haze and improving the transmittance.

[0039] In some embodiments of the present application, the first epoxy resin includes, but is not limited to, any one of bisphenol A epoxy resin, bisphenol F epoxy resin, polyphenol glycidyl ether epoxy resin, aliphatic glycidyl ether epoxy resin, epoxidized olefin compound, and cyanuric acid epoxy resin, or a mixture of two or more thereof. In particular, when the epoxy resin is an aliphatic glycidyl ether epoxy resin, since this type of epoxy resin is mostly a long-chain molecule, which is formed by two or more epoxy groups directly connected to an aliphatic chain, and there are no structures such as benzene rings, alicyclic rings, and heterocyclic rings in the molecular structure, the viscosity of the aliphatic glycidyl ether epoxy resin will be low, the molecular chain will be flexible, and the dispersibility with the organic system will be better. In addition, the number average molecular weight of the aliphatic glycidyl ether will also affect the dispersibility of the epoxy-modified photoinitiator formed therefrom in the organic system. The larger the molecular weight of aliphatic glycidyl alcohol, the longer the molecular chain, and the easier it is for the epoxy-modified photoinitiator to be miscible with the organic system. However, when the molecular weight is too large, the viscosity of the epoxy-modified photoinitiator is too high, which will weaken its solubility. When the molecular weight is too small, the lipophilicity of the epoxy-modified photoinitiator is not significantly improved, and it is still difficult to disperse. In particular, when the number average molecular weight of aliphatic glycidyl ether is 1000-5000, it is more conducive to the dispersion of the epoxy-modified photoinitiator in the organic system.

[0040] In some embodiments of the present application, the first epoxy resin is selected from any one of polypropylene glycol diglycidyl ether or polyethylene glycol diglycidyl ether, especially when the number average molecular weight of polypropylene glycol diglycidyl ether and polyethylene glycol diglycidyl ether is independently 500-8000, and further preferably 1000-5000, the modified photoinitiator formed by reacting with a small molecule photoinitiator containing a hydroxyl group has better dispersibility in the organic system.

[0041] In order to further improve the yield of the modified photoinitiator, it is preferred that the molar ratio of the first epoxy resin and the small molecule photoinitiator in the raw materials of the modified photoinitiator is 1 to 4:1 (such as 1:1, 2:1, 3:1, 4:1), wherein the first epoxy resin is measured by the molar amount of epoxy groups and the small molecule photoinitiator is measured by the molar amount of hydroxyl groups.

[0042] [Epoxy modified dyes]

[0043] In order to further improve the dispersibility and solubility of the dye in the organic system formed by the photopolymer composition, it is preferred that the raw materials of the epoxy-modified dye include a second epoxy resin and a small molecule dye, the second epoxy dye contains at least one epoxy group, and the small molecule dye contains at least one group capable of undergoing a ring-opening reaction with the epoxy group.

[0044] The above-mentioned epoxy-modified dye is formed by connecting a second epoxy resin and a small molecule dye through a ring-opening reaction. According to the similar solubility of the molecular structure, the epoxy-modified dye will be easier to disperse in a non-solvent organic system, specifically an organic epoxy system, due to its epoxy polymer side chain with a larger molecular weight, thereby improving the solubility and dispersibility of the epoxy-modified dye in the photopolymer material, promoting the increase of the photopolymerization rate of the polymerization monomer, and then improving the diffraction efficiency, refractive index modulation, uniformity and stability of the holographic material, while reducing the grating haze and improving the grating transmittance.

[0045] The groups in the above-mentioned small molecule dyes that can undergo a ring-opening reaction with epoxy groups include, but are not limited to, at least one of amino groups, imino groups, hydroxyl groups, and carboxyl groups.

[0046] The epoxy-modified dye is produced by epoxy reaction of a second epoxy resin and a small molecule dye. The specific reaction is as follows:

[0047]

[0048] Wherein Dye-R represents a small molecule dye, and R represents a group capable of undergoing a ring-opening reaction with an epoxy group, including but not limited to an amino group, an imino group, a hydroxyl group, and a carboxyl group; represents a second epoxy resin containing epoxy groups.

[0049] The above-mentioned small molecule dye is selected from one or more of cationic dyes, anionic dyes and non-ionic dyes. In some specific embodiments of the present application, the small molecule dye is selected from one or more of the compounds represented by the following formula (V) to formula (VII):

[0050]

[0051] The second epoxy resin has the same meaning as the first epoxy resin, which will not be described in detail herein.

[0052] [Epoxy-containing polymerizable monomers]

[0053] The above-mentioned polymerizable monomer containing epoxy groups is an acrylate monomer, and the acrylate monomer is a mixture of epoxy acrylate containing epoxy groups and acrylate not containing epoxy groups; for the acrylate monomer not containing epoxy groups, it is preferred to use one or a mixture of two or more of aromatic acrylate monomers and polyurethane acrylate monomers; for the epoxy acrylate monomer containing epoxy groups, it is preferred to use a mixture of one or more of bisphenol A epoxy acrylate and novolac epoxy acrylate monomers having aromatic groups.

[0054] In the present application, since the epoxy acrylate monomer and the film-forming agent in the photopolymer monomer both have epoxy groups, the fogging problem caused by the phase separation of the photopolymer part and the film-forming agent part can be improved, and since the epoxy groups in the epoxy acrylate monomer will participate in the reaction of the film-forming matrix and be fixed on the film-forming matrix, the grating fogging problem caused by the free diffusion of the photopolymer that is not combined with the film-forming matrix out of the coherent bright area into the coherent dark area during the exposure process can be improved. At the same time, it will also be unfavorable for the movement and reaction of the photopolymer monomer to the coherent bright area during the exposure process, thereby limiting the increase in the diffraction efficiency. In order not to limit the diffraction efficiency, in some embodiments of the present invention, the polymerized monomer containing epoxy groups is epoxy acrylate containing epoxy groups and acrylate not containing epoxy groups. The mass ratio is preferably (10:90) to (40:60), and further preferably 30:70.

[0055] [Film-forming agent]

[0056] In order to further improve the uniformity of the dispersion of the modified photoinitiator in the photopolymer material, the raw materials of the film-forming agent preferably include epoxy monomers and curing agents, and then the film-forming agent is formed by the reaction of the epoxy monomers and curing agents under heating conditions. In the reaction process, the unreacted epoxy groups in the epoxy acrylate, the modified photoinitiator, and the modified dye can also participate in the reaction process of the film-forming agent, thereby making the polymerized monomers, the modified photoinitiator, and the modified dye fixed on the film-forming matrix in the form of chemical bonds, thereby improving the grating fogging problem caused by the free diffusion of the photopolymer that is not bound to the film-forming matrix from the coherent bright area to the coherent dark area during the exposure process.

[0057] The epoxy monomer is a low molecular weight epoxy compound containing an epoxy group, and its specific type is not particularly limited. From the perspective of increasing the refractive index modulation degree of the photopolymer, in some embodiments of the application, an epoxy compound with a relatively low refractive index is preferred, including but not limited to any one of propylene oxide, ethylene oxide, 1,2-propylene oxide, n-butyl glycidyl ether, allyl glycidyl ether, 2-ethylhexyl glycidyl ether, cresol glycidyl ether, tertiary carboxylic acid glycidyl ester, diglycidyl ester, polyethanol diglycidyl ether, butanediol diglycidyl ether, and glycerol triglycidyl ether, or a mixture of at least two or more thereof.

[0058] In other embodiments of the present application, the epoxy monomer is a fluorinated epoxy compound to increase the refractive index difference between the polymerized monomer and the film-forming agent, thereby improving the refractive index modulation and the diffraction efficiency of the grating product. In some specific embodiments, the fluorinated epoxy monomer includes but is not limited to any one of bisphenol hexafluoropropane diglycidyl ether, 4,4-bis(2,2-epoxypropylene) octafluorobiphenyl, 1,3-bis[1-(2,3-epoxypropylene)-1-trifluoromethyl-2,2,2-trifluoroethyl]benzene, and 1,4-bis(hydroxyhexafluoroisopropanol)benzene diglycidyl ether, or a mixture of two or more thereof.

[0059] The specific type of the above-mentioned curing agent is not limited, and it can be applicable to epoxy monomers, including but not limited to addition curing agents (polyamines, acid anhydrides, etc.), catalytic curing agents (tertiary amines, boron trifluoride and boron amine complexes, etc.) or curing agents with both polymerization and catalytic effects (imidazole curing agents, etc.).

[0060] In some specific embodiments of the present application, the curing agent is selected from any one of C1-C10 straight-chain tertiary amines, tetramethylamine, tertiary alkyl monoamines, triethanolamine, piperidine, N,N-dimethylpiperazine, triethylenediamine, benzyldimethylamine, pyridine, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 1-benzyl-2-methylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-undecylimidazole, 1-undecyl-2-methyl-3-benzylimidazole chloride, boron trifluoride-monoethylamine, boron trifluoride-n-butylammonium, boron trifluoride-benzylamine, boron trifluoride-triethylamine, boron trifluoride-aniline, and boron trifluoride-piperidine, or a mixture of two or more thereof.

[0061] In some embodiments of the present application, from the perspective of improving the performance of the film-forming agent, the mass ratio of the epoxy monomer to the curing agent is preferably (29-60): (1-5). Based on the total mass of the photopolymer composition, the mass content of the epoxy monomer is 29-60% (such as 29%, 35%, 40%, 45%, 50%, 55%, 60%), and the mass content of the curing agent is 1-5% (such as 1%, 2%, 3%, 4%, 5%).

[0062] [additive]

[0063] In the present application, as long as the technical effect of the present application is not affected, additives commonly used in the art may be used according to actual production needs. These additives include, but are not limited to, polar solvents, plasticizers, inhibitors, light stabilizers, chain transfer agents, leveling agents, wetting agents, defoamers, tackifiers, oligomers, compounds with hydrophilic groups (such as salts and / or polyethylene oxide), oxygen-containing compounds (such as acetals, epoxides, oxetanes, oxazolines, dioxolanes) and any one or a mixture of two or more thereof.

[0064] In a third typical embodiment of the present application, a holographic grating is further provided. The holographic grating includes a polymer film having a grating structure. The material of the polymer film having the grating structure is the photopolymer composition provided in the second typical embodiment.

[0065] In the holographic grating provided in the present application, the polymer film with the grating structure is obtained by curing the above-mentioned photopolymer composition, and is matched with an epoxy-modified photoinitiator, an epoxy-modified dye, a photopolymerizable monomer containing an epoxy group, and a film-forming agent formed by thermosetting the epoxy monomer. Since the same organic group - epoxy group is introduced into the main components of the photopolymer composition, the compatibility of each component can be improved, and the grating fogging problem caused by the phase separation of the polymer in the photopolymerized part and the film-forming agent can be reduced. At the same time, the grating fogging caused by the poor solubility of the photoinitiator and the dye can also be improved.

[0066] In some embodiments of the present application, the above-mentioned polymer film with a grating structure is prepared according to the following steps: step S1, mixing a polymer monomer containing an epoxy group, an epoxy-modified dye, an epoxy-modified photoinitiator, a film-forming agent and optional additives to obtain a mixture; step S2, forming the mixture into a film and forming a grating structure at least in part to obtain a polymer film with a grating structure.

[0067] In some preferred embodiments of the present application, in the above step S1, the mixing temperature is 10-80°C to improve the mixing efficiency, and more preferably the mixing temperature is 30-80°C to further improve the mixing efficiency.

[0068] In order to improve the efficiency of forming the grating structure, it is preferred that step S2 includes a step of using coherent light for exposure to facilitate the formation of the grating structure. In some specific embodiments, two beams of coherent light can be used to simultaneously perform an exposure operation from one side of the film (transmission grating). In other specific embodiments, two beams of coherent light are used to perform an exposure operation from both sides of the film (reflection grating).

[0069] In some specific embodiments of the present application, the specific steps of forming a polymer film having a grating structure are as follows:

[0070] (1) In a dark room or a protected environment, a mixed solution formed by the photopolymer composition is coated on a glass or a high-transmittance plastic film substrate with a light transmittance greater than 90% to obtain a wet film; the coating method is not specifically limited, and a device known to those skilled in the art such as a doctor blade device or a slit nozzle can be used;

[0071] (2) placing the wet film in an oven at a preset temperature for heating and curing, wherein the curing temperature is 50 to 100° C., preferably 70 to 90° C.;

[0072] (3) After the wet film is cured, another layer of glass substrate or high-transmittance plastic protective film is covered on the surface of the film to obtain a photopolymer dry plate;

[0073] (4) exposing the photopolymer dry plate by laser interference in a dual-beam optical path, wherein a high laser intensity and short exposure time mode is preferably used;

[0074] (5) The exposed dry plate is irradiated with an LED lamp, a fluorescent lamp or an ultraviolet lamp until it is completely fixed and bleached to obtain a polymer film with a grating structure.

[0075] In a fourth typical embodiment of the present application, a holographic display system is further provided. The holographic display system includes the holographic grating provided in the third typical embodiment.

[0076] The holographic display system provided by the present application includes a holographic grating, which can be used alone or in combination with other optical elements. It is particularly suitable for augmented reality (AR) head-mounted display devices (such as AR display glasses, etc.) that have strict requirements on diffraction efficiency and light transmittance, as well as head-up displays (HUDs) of cars or aircraft.

[0077] The holographic display system provided in the present application adopts the above-mentioned holographic grating, thereby having more excellent imaging quality and having broader application prospects.

[0078] The beneficial effects of the present application will be further illustrated below with reference to examples and comparative examples.

[0079] (I) Modified photoinitiator

[0080] Four modified photoinitiators with different structures were prepared respectively, and their raw material compositions are shown in Table 1 below.

[0081] Table 1

[0082]

[0083]

[0084] Note: The above molar ratio refers to the molar ratio of the small molecule photoinitiator to the first epoxy resin.

[0085] The preparation method of the modified photoinitiator comprises the following steps:

[0086] (1) dissolving a small molecule photoinitiator in ethanol at a solubility of 1 wt %;

[0087] (2) adding a certain amount of epoxy resin to the ethanol solution of the above-mentioned small molecule photoinitiator, and stirring thoroughly at room temperature for 1 to 2 hours to obtain a modified photoinitiator suspension;

[0088] (3) Drying the modified photoinitiator suspension under reduced pressure at 50° C. to obtain a dried modified photoinitiator.

[0089] (ii) Epoxy modified dyes

[0090] Two epoxy modified dyes with different structures were prepared respectively, and their raw material compositions are shown in Table 2 below.

[0091] Table 2

[0092]

[0093] Note: The above molar ratio refers to the molar ratio of the small molecule photoinitiator to the second epoxy resin.

[0094] The preparation method of the modified dye comprises the following steps:

[0095] (1) dissolving a small molecule dye in ethanol at a solubility of 1 wt %;

[0096] (2) adding epoxy resin to the ethanol solution of the small molecule dye, and stirring the mixture at room temperature for 1 to 2 hours to obtain an epoxy-modified dye suspension;

[0097] (3) Finally, the dye suspension is dried under reduced pressure at 50° C. to obtain a dry epoxy-modified dye (powder or waxy solid or highly viscous liquid with substantially no fluidity at room temperature).

[0098] (III) Photopolymer composition

[0099] Example 1

[0100] This embodiment provides a photopolymer composition, the composition of which is shown in Table 3 below.

[0101] Table 3

[0102] composition Quality content Benzyl acrylate 6.3％ 9,9-Di(methylacrylate-9)fluorene 35.7％ Modified Photoinitiator C 1.5％ Epoxy modified dye A 1.5％ 4,4-Bis(2,2-propylene oxide)octafluorobiphenyl 50％ 2-Undecyl imidazole 4％ Dibutyl phthalate 1％

[0103] Example 2

[0104] The difference between this embodiment and embodiment 1 is that bisphenol A epoxy acrylate B-153 is used to replace benzyl acrylate, wherein bisphenol A epoxy acrylate B-153 comes from Guangdong Boxing Material Technology Co., Ltd.

[0105] Example 3

[0106] The difference between this embodiment and embodiment 1 is that benzyl acrylate is replaced by novolac epoxy acrylate B-191A, wherein novolac epoxy acrylate B-191A is from Guangdong Boxing Material Technology Co., Ltd.

[0107] Example 4

[0108] The difference between this embodiment and embodiment 1 is that modified photoinitiator A is used to replace modified photoinitiator C.

[0109] Example 5

[0110] The difference between this embodiment and embodiment 1 is that modified photoinitiator B is used to replace modified photoinitiator C.

[0111] Example 6

[0112] The difference between this embodiment and embodiment 1 is that modified photoinitiator D is used to replace modified photoinitiator C.

[0113] Example 7

[0114] The difference between this embodiment and embodiment 1 is that epoxy-modified dye B is used to replace epoxy-modified dye A.

[0115] Example 8

[0116] The difference between this embodiment and embodiment 1 is that the composition of the photopolymerizable composition of the holographic grating is as shown in Table 4 below.

[0117] Table 4

[0118] composition Quality content Bisphenol A epoxy acrylate B-153 12.6％ 9,9-Di(methylacrylate-9)fluorene 29.4％ Modified Photoinitiator C 2％ Epoxy modified dye A 2％ 4,4-Bis(2,2-propylene oxide)octafluorobiphenyl 49％ 2-Undecyl imidazole 4％ Dibutyl phthalate 1％

[0119] Example 9

[0120] The difference between this embodiment and embodiment 1 is that the composition of the photopolymerizable composition of the holographic grating is as shown in Table 5 below.

[0121] Table 5

[0122] composition Quality content Bisphenol A epoxy acrylate B-153 13.5％ 9,9-Di(methylacrylate-9)fluorene 31.5％ Modified Photoinitiator C 0.5％ Epoxy modified dye A 0.5％ 4,4-Bis(2,2-propylene oxide)octafluorobiphenyl 49％ 2-Undecyl imidazole 4％ Dibutyl phthalate 1％

[0123] Example 10

[0124] The difference between this embodiment and embodiment 1 is that the composition of the photopolymerizable composition of the holographic grating is shown in Table 6 below.

[0125] Table 6

[0126] composition Quality content Bisphenol epoxy acrylate B-153 10.8％ 9,9-Di(methylacrylate-9)fluorene 25.2％ Modified Photoinitiator C 5％ Epoxy modified dye A 5％ 4,4-Bis(2,2-propylene oxide)octafluorobiphenyl 49％ 2-Undecyl imidazole 4％ Dibutyl phthalate 1％

[0127] Embodiment 11

[0128] The difference between this embodiment and embodiment 1 is that the composition of the photopolymerizable composition of the holographic grating is shown in Table 7 below.

[0129] Table 7

[0130] composition Quality content Bisphenol A epoxy acrylate B-153 9％ 9,9-Di(methylacrylate-9)fluorene 21％ Modified Photoinitiator C 2％ Epoxy modified dye A 2％ 4,4-Bis(2,2-propylene oxide)octafluorobiphenyl 60％ 2-Undecyl imidazole 5％ Dibutyl phthalate 1％

[0131] Example 12

[0132] The difference between this embodiment and embodiment 1 is that the composition of the photopolymerizable composition of the holographic grating is as shown in Table 8 below.

[0133] Table 8

[0134]

[0135]

[0136] Embodiment 13

[0137] The difference between this embodiment and embodiment 2 is that the composition of the photopolymer of the holographic grating is as shown in Table 9 below.

[0138] Table 9

[0139] composition Quality content Bisphenol A epoxy acrylate B-153 25.2％ 9,9-Di(methylacrylate-9)fluorene 16.8％ Modified Photoinitiator C 1.5％ Epoxy modified dye A 1.5％ 4,4-Bis(2,2-propylene oxide)octafluorobiphenyl 50％ 2-Undecyl imidazole 4％ Dibutyl phthalate 1％

[0140] Comparative Example 1

[0141] The difference between Comparative Example 1 and Example 1 is that the modified initiator C is replaced by the compound of formula (III).

[0142] Comparative Example 2

[0143] The difference between Comparative Example 2 and Example 1 is that the modified dye A is replaced by the compound of formula (V).

[0144] Comparative Example 3

[0145] The difference between Comparative Example 3 and Example 1 is that the modified initiator C is replaced by the compound of formula (III), and the modified dye A is replaced by the compound of formula (V).

[0146] Test example

[0147] The photopolymers provided in the above examples and comparative examples were respectively prepared into holographic gratings, and the diffraction efficiency, haze, and transmittance of the holographic gratings were respectively measured. The results are shown in Table 10 below.

[0148] Wherein, (1) the holographic grating is prepared according to the following steps:

[0149] (1.1) Add benzyl acrylate (or bisphenol A epoxy acrylate, or novolac epoxy acrylate), 9,9-di(methyl acrylate-9)fluorene, 4,4-bis(2,2-propylene oxide)octafluorobiphenyl, 2-undecyl imidazole, and dibutyl phthalate to a sample bottle, heat and stir at 60°C until completely clear, then add modified photoinitiator and epoxy modified dye in a dark environment and stir for 30 minutes to obtain a uniform and clear photopolymer solution;

[0150] (1.2) The photopolymer solution prepared from the photopolymer composition provided in Implementations 1 to 6, Examples 8 to 13, and Comparative Examples 1 to 3 is coated on a glass or high-transmittance plastic film substrate in a dark place or under a green light. The photopolymer solution prepared from the photopolymer composition provided in Example 7 is coated on a glass or high-transmittance plastic film substrate in a dark place or under a red light. The above-coated wet films are respectively placed in an oven at 90° C. and heated for 40 minutes to completely cure the film-forming agent. Then, another layer of glass substrate or high-transmittance plastic protective film is covered on the surface of the dry film to obtain a photopolymer dry plate.

[0151] (1.3) The photopolymer dry plate prepared from the photopolymer compositions provided in Examples 1 to 6, Examples 8 to 13, and Comparative Examples 1 to 3 was subjected to a double beam optical path with an energy density of 15 mJ / cm 2 The photopolymer dry plate prepared from the photopolymer composition provided in Example 7 was exposed to 639 nm laser interference in a double beam optical path with an energy density of 15 mJ / cm 2 The 532nm laser interference exposure was carried out, and each was irradiated with UV light for about 30 minutes for fixing and bleaching to form a holographic grating.

[0152] (2) The test method of diffraction efficiency is: test the diffraction efficiency at different positions of the holographic grating (select 9 evenly distributed test points on the holographic grating) and take the average value.

[0153] (3) The test methods for haze and light transmittance are as follows: haze and light transmittance are measured using a light transmittance tester and a haze tester, respectively, in accordance with the American Society for Testing and Materials standard "ASTM DI003-61 (2007) Standard Test Method for Haze and Luminous Transmittance of Transparent Plastice".

[0154] Table 10

[0155]

[0156]

[0157] From the above description, it can be seen that the above-mentioned embodiments of the present invention achieve the following technical effects: the photopolymer composition provided in the present application is coordinated with an epoxy-modified photoinitiator, an epoxy-modified dye, a photopolymerizable monomer containing an epoxy group, and a film-forming agent formed by thermosetting the epoxy monomer. Since the same organic group-epoxy group is introduced into the main components of the photopolymer composition, the compatibility of each component can be improved, and the grating fogging problem caused by phase separation of the polymer in the photopolymerized part and the film-forming agent can be reduced. At the same time, the grating fogging caused by the poor solubility of the photoinitiator and the dye can also be improved.

[0158] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A photopolymer composition for holographic grating, characterized in that: The photopolymer composition comprises, by mass percentage, 30-65% of a polymerizable monomer containing an epoxy group, 0.5-5% of an epoxy-modified dye, 0.5-5% of an epoxy-modified photoinitiator, 30-65% of a film-forming agent and 0.1-5% of an optional additive, wherein the raw materials of the epoxy-modified photoinitiator comprise a first epoxy resin and a small molecule photoinitiator, wherein the first epoxy resin contains at least one epoxy group, and the small molecule photoinitiator contains at least one hydroxyl group.

2. The photopolymer composition according to claim 1, characterized in that The small molecule photoinitiator is an α-hydroxy aromatic ketone initiator containing a hydroxyl group; Preferably, the small molecule photoinitiator is selected from at least one of the compounds represented by the following formula (I) to formula (IV):

3. The photopolymer composition according to claim 1, characterized in that The first epoxy resin contains at least two epoxy groups; Preferably, the first epoxy resin is selected from at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, polyphenol glycidyl ether epoxy resin, aliphatic glycidyl ether epoxy resin, epoxidized olefin compound, and cyanuric acid epoxy resin; More preferably, the first epoxy resin is at least one of polypropylene glycol diol diglycidyl ether and polyethylene glycol diglycidyl ether, and the number average molecular weights of the polypropylene glycol diol diglycidyl alcohol and the polyethylene glycol diglycidyl ether are each independently 1000 to 5000.

4. The photopolymer composition according to claim 1, characterized in that The first epoxy resin is calculated based on the molar amount of epoxy groups, the small molecule photoinitiator is calculated based on the molar amount of hydroxyl groups, and the molar ratio of the first epoxy resin to the small molecule photoinitiator is 1 to 4:

1.

5. The photopolymer composition according to any one of claims 1 to 4, characterized in that The raw materials of the epoxy-modified dye include a second epoxy resin and a small molecule dye, wherein the second epoxy resin contains at least one epoxy group, and the small molecule dye contains at least one group capable of undergoing a ring-opening reaction with the epoxy group.

6. The photopolymer composition according to any one of claims 1 to 5, characterized in that The raw materials of the film-forming agent include epoxy monomer and curing agent, and the mass ratio of the two is (29-60):(1-5); wherein the epoxy monomer is an epoxy compound containing an epoxy group, and preferably the refractive index of the epoxy compound is ≤1.45; Preferably, the curing agent includes at least one of polyamine, acid anhydride, tertiary amine, boron trifluoride, boron amine complex or imidazole curing agent.

7. The photopolymer composition according to any one of claims 1 to 6, characterized in that The polymerizable monomer containing epoxy groups is an acrylate monomer; preferably, the acrylate monomer is a mixture of epoxy acrylate containing epoxy groups and acrylate not containing epoxy groups, and the mass ratio of the two is (10:90) to (40:60), preferably 30:

70.

8. The photopolymer composition according to any one of claims 1 to 7, characterized in that The additives include at least one of polar solvents, plasticizers, extenders, inhibitors, light stabilizers, chain transfer agents, leveling agents, wetting agents, defoamers, tackifiers, oligomers, compounds with hydrophilic groups, and oxygen-containing compounds.

9. A holographic grating, characterized in that: The holographic grating comprises a polymer film having a grating structure, and the material of the polymer film is the photopolymer composition according to any one of claims 1 to 8; Preferably, the method for preparing the polymer film comprises the following steps: Step S1, mixing a photopolymer composition including the polymerizable monomer containing epoxy groups, the epoxy-modified dye, the epoxy-modified photoinitiator, the film-forming agent and the optional additives to obtain a mixture; Step S2, forming the mixture into a film and forming a grating structure at least partially to obtain the polymer film having the grating structure; Preferably, step S2 includes the step of performing exposure using coherent light.

10. A holographic display system, characterized in that: The holographic display system comprises the holographic grating according to claim 9.

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