Photopolymer system based on modified writing monomer, grating device and preparation method of grating device

Abstract

The invention provides a photopolymer system based on a modified writing monomer, a grating device and a preparation method of the photopolymer system, and particularly, in the photopolymer system, the modified writing monomer is generated through the reaction of the writing monomer and first film-forming resin and interacts with an original writing monomer; the compatibility of the photopolymer system in the holographic exposure process is improved; secondly, two film-forming resins are introduced into the photopolymer system, on the basis that the first film-forming resin preferentially reacts with the writing monomer to construct a basic framework for modulating the refractive index of the photopolymer system, the second film-forming resin is introduced, and the refractive index of the photopolymer system is modulated through stepwise reaction and polymerization of the two film-forming resins; the two film-forming resins have a synergistic effect and are further directionally combined with the writing monomer and the modified writing monomer, so that the haze of a photopolymer system is reduced, the phase separation degree of the system is improved, and the diffraction efficiency of the system is improved.

Description

Technical Field

[0001] The present invention relates to the field of holographic projection display, and more specifically, to a photopolymer system based on modified writing monomers, a grating device and a preparation method thereof. Background Art

[0002] With the rapid development of smart cars and information security industries, the application of photopolymers is ushering in new development opportunities. With its mature process system and mass production stability, photopolymer materials have been widely used in scenarios such as vehicle-mounted head-up display systems (HUD) and high-end anti-counterfeiting labels. In the application scenarios of vehicle-mounted head-up display systems and high-end anti-counterfeiting labels, their optoelectronic functions are usually realized through photopolymer holographic gratings. The preparation of holographic gratings is essentially the precise construction of micro-nano structures through laser interference. When two coherent laser beams with specific polarization states meet, periodic light and dark interference fringes are formed in space. When a holographic grating is prepared using a photopolymer system, the light-induced polymerization reaction of the monomers in the bright area is triggered by light, while the dark area remains unpolymerized. The resulting monomer concentration gradient drives the formation of a periodic refractive index distribution inside the material. Therefore, the quality of the phase separation structure finally formed by the photopolymer system directly determines the diffraction performance of the holographic grating.

[0003] Specifically, the key parameters that directly determine the diffraction efficiency of the holographic grating are the refractive index modulation of the grating. The optimization of the refractive index modulation mainly depends on the coordinated regulation of two key parameters: one is the intrinsic refractive index difference (Δn) between the writing monomer and the film-forming matrix, and the other is the degree of phase separation formed during the photopolymerization process. In theory, a monomer / matrix combination with a high refractive index difference and sufficient phase separation can produce an ideal refractive index modulation effect. However, in actual material systems, this theoretical model is often difficult to achieve; the fundamental reason for this difficulty mainly stems from the compatibility contradiction between the material components. Excessive refractive index differences are often accompanied by significant differences in molecular polarity, which inhibits the uniform dispersion of monomers in the matrix and leads to kinetic hysteresis in the phase separation process. Within the limited time of the photopolymerization reaction, monomer molecules that fail to complete diffusion in time will form micron-scale aggregates, which not only reduces the effective refractive index modulation amplitude, but also causes severe scattering losses, thereby showing an increase in haze value. At the same time, the selective adsorption of the film-forming matrix on the monomer also has a significant effect. For example, an acrylate matrix with specific functional groups will preferentially adsorb monomer molecules containing benzene rings. This molecular-level interaction will change the driving mechanism of phase separation. This strong interaction will significantly inhibit the long-range diffusion of the monomer, resulting in a decrease in the spatial frequency of the periodic concentration distribution. Summary of the invention

[0004] The present invention aims to overcome at least one defect of the above-mentioned prior art, and provides a photopolymer system based on a modified writing monomer, a grating device and a preparation method thereof. By improving the compatibility of the photopolymer system, the comprehensive performance and service life of the photopolymer system and the grating device prepared therefrom are improved.

[0005] The technical solution adopted by the present invention is first to provide a photopolymer system based on a modified writing monomer, which is characterized in that, by mass percentage, it includes: Solvent: 1% - 5%, Photoinitiator: 0.01 - 1%, Co-initiator: 0.1 - 1%, Writing monomer: 40 - 80%, First film-forming resin: 20 - 30%, Second film-forming resin: 20 - 30%, Surfactant: 0.1 - 1%, Catalyst: 0.001 - 0.01%, The writing monomer adopts an acrylate writing monomer; The first film-forming resin and the second film-forming resin respectively adopt one or more of polyurethane, PVAC and epoxy resin; The writing monomer preferentially reacts with the first film-forming resin to form a modified writing monomer; The writing monomer has functional chemical bonds and functional groups; the functional chemical bonds include amide bonds, ester groups, ureido groups, aliphatic ethers; the functional groups include hydroxyl groups, carboxyl groups, mercapto groups; Both the first film-forming resin and the second film-forming resin have reactive groups, and the reactive groups include mercapto groups, isocyanate groups, hydrosilyl groups.

[0006] In this technical solution, a photopolymer system based on a modified writing monomer is provided. The writing monomer used in the system simultaneously introduces functional chemical bonds such as amide bonds, ester groups, urea groups, and aliphatic ethers, as well as hydroxyl groups, carboxyl groups, and mercapto groups. First, the writing monomer reacts with the first film-forming resin to form a modified writing monomer, so that the functional chemical bonds such as amide bonds, ester groups, urea groups, and aliphatic ethers in the writing monomer, as well as hydroxyl groups, carboxyl groups, and mercapto groups, form dynamic covalent bonds with the mercapto groups, isocyanate groups, and hydrosilyl groups of the first film-forming resin, reducing the solubility parameter difference between the writing monomer and the first film-forming resin and improving the compatibility between the writing monomer and the first film-forming resin. Further, the modified writing monomer after the reaction, the remaining original writing monomer, the first film-forming resin, etc. are incorporated into the photopolymer system including a solvent, a photoinitiator, a co-initiator, a second film-forming resin, a surfactant, and a catalyst. By introducing two film-forming resins into the photopolymer system, on the basis of constructing the basic framework of the refractive index modulation of the photopolymer system by making the first film-forming resin react with the writing monomer preferentially, the second film-forming resin is introduced, so that the mercapto groups, isocyanate groups, and hydrosilyl groups of the second film-forming resin react with the unreacted functional chemical bonds such as amide bonds, ester groups, urea groups, and aliphatic ethers, as well as hydroxyl groups, carboxyl groups, and mercapto groups on the modified writing monomer to form dynamic covalent bonds, thereby reducing the overall solubility parameter difference of the photopolymer system and improving the overall compatibility of the photopolymer system; at the same time, by making the two film-forming resins react and polymerize step by step, the synergistic effect between the two film-forming resins and the modified writing monomer is further combined directionally, reducing the haze of the photopolymer system while increasing the phase separation degree of the system, thereby improving the diffraction efficiency of the system.

[0007] Further, through the precise regulation of the component ratio and the catalytic system in the photopolymer system, the balance of exposure responsiveness, optical properties, and stability is achieved; specifically, a certain amount of surfactant and catalyst are introduced into the system containing the modified writing monomer and two film-forming resins. The physical interface state is optimized by the surfactant to ensure the overall optical uniformity of the system; at the same time, the reaction kinetics is precisely controlled by the catalyst, thereby improving the conversion efficiency. Through the synergistic effect among the solvent, the photoinitiator, the co-initiator, the modified writing monomer, the two film-forming resins, the surfactant, and the catalyst, the refractive index modulation degree of the system is improved, so that the system has both high diffraction efficiency and low haze characteristics; at the same time, by using a writing monomer with a wide ratio window and a low-ratio solvent system, the industrial production convenience of the holographic grating of the photopolymer system is improved, which is suitable for large-scale production.

[0008] Further, the writing monomer includes a first monomer, a second monomer, a third monomer, and a fourth monomer; and by mass percentage, it includes: First monomer: 10 - 20%, Second monomer: 10 - 20%, The third monomer: 10 - 20%, The fourth monomer: 10 - 20%; Among the first monomer, the second monomer, the third monomer and the fourth monomer, at least one type of the writing monomers has a functionality of 1, and at the same time, at least one type of the writing monomers has a functionality of not less than 2.

[0009] In this technical solution, an unsaturated monomer system is formed by selecting the first monomer, the second monomer, the third monomer and the fourth monomer. Among them, at least one type of the writing monomers has a functionality of 1, and at the same time, at least one type of the writing monomers has a functionality of not less than 2; specifically, the writing monomers with a functionality of 1 have a relatively fast moving speed and are likely to form a concentration difference during the holographic exposure of the photopolymer system; the multi-functional writing monomers with a functionality of not less than 2 have a short gelation time and are easily polymerized in place. Therefore, they can be used as the central core for the polymerization of the photopolymer system, causing the surrounding writing monomers to approach it. By utilizing the crosslinking synergy between two kinds of film-forming resins and various unsaturated writing monomers respectively, specifically, by adjusting the types and proportions of the first film-forming resin, the second film-forming resin and the unsaturated monomers added, the polymerization reaction efficiency between the monomers in the material can be adjusted, and at the same time, the diffraction efficiency and heat resistance stability and other functions of the prepared holographic volume grating device can be targeted adjusted and improved to obtain the expected polymer grating structure. Preferably, the differences between the first monomer, the second monomer, the third monomer and the fourth monomer include but are not limited to functionality, and also include the types of functional groups included, the number of spacer groups in the carbon chain, viscosity, the presence of elements such as N, S, P, etc. By introducing writing monomers with different carbon chain lengths or carbon chain structures, the viscosity of the writing monomers can be adjusted, and by introducing writing monomers with different types of functional groups and different elements, the refractive index of the writing monomers can be greatly increased; therefore, the unsaturated monomers contained in the photopolymer system can be selected and combined from a wider range of writing monomer categories, with diverse selections and wide sources of raw materials, which are easy to obtain. While ensuring the functions of the holographic volume grating device, the production convenience is improved and the production cost is reduced.

[0010] Further, the photoinitiator is selected from one or more of RB, SO, Acid Red 94, BTCP, BCIM, BDEA and DEAMC.

[0011] Further, the co-initiator is selected from one or more of NPG, triethanolamine, HABI, EM and Cl-MBT.

[0012] Further, the solvent is selected from one or more of EM, EA, THF, DMF, DCM, NVP and NMP.

[0013] Further, the surfactant is selected from silicone surfactants or epoxy surfactants.

[0014] Further, the catalyst is an organotin catalyst, an organobismuth catalyst or a photo-thermal curing catalyst.

[0015] Another object of the present invention is to provide a method for preparing a photopolymer holographic grating device. Specifically, the photopolymer holographic grating device uses the photopolymer system described in the present technical solution. After the writing monomer and the first film-forming component are mixed and reacted to form a modified writing monomer, they are mixed with the remaining components and poured into a liquid crystal cell, and exposed under a coherent light source to form a grating device.

[0016] Further, the specific steps for the writing monomer and the first film-forming component to be mixed and reacted to form a modified writing monomer are: mixing the writing monomer and the first film-forming component evenly, and reacting at 50-70 °C for 3-5 h.

[0017] Another object of the present invention is to provide a photopolymer holographic grating device prepared by the preparation method provided by the present technical solution. Preferably, the diffraction efficiency of the holographic grating device is above 90%, the angular bandwidth is within 10°, the refractive index modulation is 0.04, and the haze is less than 1%.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1. A photopolymer system based on a modified writing monomer is provided. The writing monomer used in the system simultaneously introduces functional chemical bonds and functional groups. First, the writing monomer reacts with the first film-forming resin to form a modified writing monomer, so that the functional chemical bonds and functional groups in the writing monomer form dynamic covalent bonds with the reactive groups of the first film-forming resin, reducing the difference in solubility parameters between the writing monomer and the first film-forming resin and improving the compatibility between the writing monomer and the first film-forming resin. Further, the modified writing monomer after the reaction, the remaining writing monomer, the first film-forming resin, etc. are incorporated into the photopolymer system including a solvent, a photoinitiator, a co-initiator, a second film-forming resin, a surfactant and a catalyst. By introducing two film-forming resins into the photopolymer system, on the basis of constructing the basic framework of refractive index modulation of the photopolymer system by making the first film-forming resin react with the writing monomer preferentially, the second film-forming resin is introduced, so that the reactive groups of the second film-forming resin react with the unreacted functional chemical bonds and functional groups on the modified writing monomer to form dynamic covalent bonds, thereby reducing the overall difference in solubility parameters of the photopolymer system and improving the overall compatibility of the photopolymer system. At the same time, by making the two film-forming resins react and polymerize step by step, the synergistic effect between the two film-forming resins and the modified writing monomer is further combined directionally, reducing the haze of the photopolymer system while increasing the phase separation degree of the system, thus improving the diffraction efficiency of the system.

[0019] 2. Through the precise regulation of the component ratios and the catalytic system in the photopolymer system, the balance of exposure responsiveness, optical properties and stability is achieved. Specifically, a certain amount of surfactant and catalyst are introduced into the system containing the modified writing monomer and two film-forming resins. The physical interface state is optimized by the surfactant to ensure the overall optical uniformity of the system. At the same time, the reaction kinetics is precisely controlled by the catalyst, thereby improving the conversion efficiency. Through the synergistic effect among the solvent, the photoinitiator, the co-initiator, the modified writing monomer, the two film-forming resins, the surfactant and the catalyst, the refractive index modulation degree of the system is improved, enabling the system to have low haze characteristics while having high diffraction efficiency. At the same time, by using a writing monomer with a wide ratio window and a low-ratio solvent system, the industrial production convenience of the holographic grating of the photopolymer system is improved, making it suitable for large-scale production.

[0020] 3. In the photopolymer system, the writing monomers include a first monomer, a second monomer, a third monomer, and a fourth monomer. Specifically, at least one type of the writing monomers among the first monomer, the second monomer, the third monomer, and the fourth monomer is set to have a functionality of 1, and at least one type of the writing monomers has a functionality of not less than 2. Among them, the writing monomer with a functionality of 1 has a relatively fast moving speed and is likely to form a concentration difference during the holographic exposure process of the photopolymer system. The multi-functional writing monomer with a functionality of not less than 2 has a short gelation time and is easily polymerized in place. Therefore, it can be used as the central core for the polymerization of the photopolymer system, causing the surrounding writing monomers to approach it. By adjusting the types and proportions of the first film-forming resin, the second film-forming resin, and the unsaturated monomers added, the polymerization reaction efficiency between the monomers in the material can be adjusted, and at the same time, the diffraction efficiency and heat resistance stability and other functions of the prepared holographic volume grating device can be specifically adjusted and improved to obtain the expected polymer grating structure. Preferably, the differences among the first monomer, the second monomer, the third monomer, and the fourth monomer include, but are not limited to, functionality, and also include the types of functional groups included, the number of spacer groups in the carbon chain, viscosity, the presence or absence of elements such as N, S, P, etc. By introducing writing monomers with different carbon chain lengths or carbon chain structures, the viscosity of the writing monomers can be adjusted. By introducing writing monomers with different types of functional groups and different elements, the refractive index of the writing monomers can be greatly increased. Therefore, the unsaturated monomers contained in the photopolymer system can be selected and combined from a wider range of writing monomer categories. The selection is diverse, and the raw materials are widely sourced and easily obtained, improving the production convenience and reducing the production cost while ensuring the functions of the holographic volume grating device. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 FIG. is a schematic structural diagram of the holographic film exposure optical path in the preparation method of a photopolymer holographic grating device according to the present invention.

[0022] Figure 2 FIG. is a schematic diagram of the process in which the writing monomer in the photopolymer system provided in Example 3 of the present invention reacts with the first film-forming resin to form a modified writing monomer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0024] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they specify the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0025] The present invention will be further described in conjunction with specific examples below. The following examples are only for explaining the present invention and do not constitute a limitation to the present invention. The test samples and test procedures used in the following examples include the following content (if the specific experimental conditions are not specified in the examples, they are usually in accordance with conventional conditions or the conditions recommended by the reagent company; the reagents, consumables, etc. used in the following examples can be obtained from commercial sources without special instructions). Example 1 This example provides a photopolymer system based on a modified writing monomer. By mass percentage, it includes: Solvent: 1% - 5%, Photoinitiator: 0.01% - 1%, Co-initiator: 0.1% - 1%, Writing monomer: 40% - 80%, First film-forming resin: 20% - 30%, Second film-forming resin: 20% - 30%, Surfactant: 0.1% - 1%, Catalyst: 0.001% - 0.01%, The writing monomer uses an acrylate writing monomer; The first film-forming resin and the second film-forming resin respectively use one or more of polyurethane, PVAC, and epoxy resin; The writing monomer preferentially reacts with the first film-forming resin to form a modified writing monomer; The writing monomer has functional chemical bonds and functional groups; the functional chemical bonds include amide bonds, ester groups, ureido groups, and aliphatic ethers; the functional groups include hydroxyl groups, carboxyl groups, and mercapto groups; Both the first film-forming resin and the second film-forming resin have reactive groups, and the reactive groups include mercapto groups, isocyanate groups, and hydrosilyl groups.

[0026] Specifically, by first reacting the writing monomer with the first film-forming resin to form a modified writing monomer, functional chemical bonds such as amide bonds, ester groups, urea groups, and aliphatic ethers in the writing monomer form dynamic covalent bonds with the hydroxyl groups, carboxyl groups, mercapto groups, mercapto groups, isocyanate groups, and hydrosilyl groups of the first film-forming resin. The reaction between the writing monomer and the first film-forming resin generates an interaction between the modified writing monomer and the original writing monomer, reducing the difference in solubility parameters between the writing monomer and the first film-forming resin, thereby improving the compatibility of the photopolymer system during the holographic exposure process. Secondly, two film-forming resins are introduced into the photopolymer system. On the basis of constructing the basic framework of refractive index modulation of the photopolymer system by making the first film-forming resin react with the writing monomer preferentially, the second film-forming resin is introduced. By making the two film-forming resins react and polymerize step by step, the synergistic effect between the two film-forming resins is further directionally combined with the writing monomer and the modified writing monomer, reducing the haze of the photopolymer system while increasing the phase separation degree of the system, thereby enhancing the diffraction efficiency of the system.

[0027] Furthermore, a certain amount of surfactant and catalyst are introduced into the system containing the writing monomer, modified writing monomer, and two film-forming resins. The physical interface state is optimized by the surfactant, ensuring the overall optical uniformity of the system; at the same time, the reaction kinetics is precisely controlled by the catalyst, thereby enhancing the conversion efficiency. Through the synergistic effect among the solvent, photoinitiator, co-initiator, writing monomer, modified writing monomer, two film-forming resins, surfactant, and catalyst, the refractive index modulation degree of the system is improved, enabling the system to have low haze characteristics while having high diffraction efficiency; at the same time, by using a writing monomer with a wide ratio window and a low-ratio solvent system, the industrial production convenience of the holographic grating of the photopolymer system is improved, making it suitable for large-scale production. By precisely regulating the component ratios and catalytic system in the photopolymer system, a balance among exposure responsiveness, optical properties, and stability is achieved.

[0028] Furthermore, the writing monomer includes a first monomer, a second monomer, a third monomer, and a fourth monomer; and in terms of mass percentage, it includes: First monomer: 10 - 20%, Second monomer: 10 - 20%, Third monomer: 10 - 20%, Fourth monomer: 10 - 20%; Among the first monomer, second monomer, third monomer, and fourth monomer, at least one type of writing monomer has a functionality of 1, and at least one type of writing monomer has a functionality of not less than 2.

[0029] Preferably, the differences among the first monomer, the second monomer, the third monomer and the fourth monomer include but are not limited to functionality, and also include the types of functional groups included, the number of spacer groups in the carbon chain, viscosity, the presence of elements such as N, S, P, etc. By introducing writing monomers with different carbon chain lengths or carbon chain structures, the viscosity of the writing monomers can be adjusted. By introducing writing monomers with different types of functional groups and different elements, the refractive index of the writing monomers can be greatly increased. Therefore, the unsaturated monomers contained in the photopolymer system can be selected and combined from a wider range of writing monomer categories, with diverse choices, wide sources of raw materials, easy access, improving production convenience and reducing production costs while ensuring the functions of the holographic volume grating device.

[0030] Further, the photoinitiator is selected from one or more of RB, SO, Acid Red 94, BTCP, BCIM, BDEA and DEAMC.

[0031] Further, the co-initiator is selected from one or more of NPG, triethanolamine, HABI, EM and Cl-MBT.

[0032] Further, the solvent is selected from one or more of EM, EA, THF, DMF, DCM, NVP and NMP.

[0033] Further, the surfactant is selected from silicone surfactant or epoxy surfactant.

[0034] Further, the catalyst uses an organotin catalyst, an organobismuth catalyst or a photo-thermal curing catalyst.

[0035] Example 2 This example uses the photopolymer system described in Example 1 to prepare a method for preparing a photopolymer holographic grating device. Specifically, it includes the following steps: (1) Weigh all the materials contained in the photopolymer system as required; (2) First, uniformly mix the writing monomer and the first film-forming component, and react at 50-70 °C for 3-5 h, partially or fully react to form a modified writing monomer, and obtain a prepolymerized material; (3) Mix the prepolymerized material in step (2) with the remaining components in the photopolymer system weighed in step (1), pour them into a liquid crystal cell together, and use the holographic film exposure optical path as shown in Figure 1 to expose and form a photopolymer holographic grating device; specifically, the adjustment of θ1 and θ2 in the optical path is adapted to the requirements of the photopolymer system.

[0036] (4) Diffraction efficiency, haze and transmittance testing The specific steps for diffraction efficiency testing are as follows: Use a grating diffraction efficiency tester to test the diffraction efficiency of the above-mentioned photopolymer holographic grating device.

[0037] The specific steps for haze and transmittance testing are as follows: Wipe the grating area of the above-mentioned photopolymer holographic grating device with alcohol, and then conduct the test through a haze and transmittance testing machine. Specifically, multiple parallel tests are performed on each photopolymer holographic grating device and the average value is taken.

[0038] In the preparation method provided in this embodiment, the reaction between the writing monomer and the first film-forming resin generates modified writing monomers that interact with the original writing monomers, thereby improving the compatibility of the photopolymer system during holographic exposure. At the same time, the refractive index modulation degree can be formed by adjusting the types and proportions of other film-forming components, thereby preparing a photopolymer holographic grating device with a relatively high diffraction efficiency and a relatively low haze.

[0039] Example 3 This embodiment provides a photopolymer holographic grating device, using the photopolymer system described in Example 1 and the preparation method described in Example 2. As Figure 2 shown, in the photopolymer system, the functional group R2 of the writing monomer used is a hydroxyl group, an amino group or a carboxyl group, and in the photopolymer system, writing monomers with multiple functionalities are included. The writing monomers can be mono-functional, bi-functional, tri-functional and above; the first film-forming resin uses a polyurethane system, and its reactive group R4 is an NCO group. Before the overall reaction polymerization of the photopolymer system, the writing monomer and the first film-forming resin react preferentially to form a modified writing monomer, and its reaction process is as Figure 1 shown. The writing monomer and the first film-forming resin undergo a chemical reaction to form modified writing monomers M1, M2 and M3; when the writing monomer and the first film-forming resin react partially, the prepolymer material contains exposed NCO groups to be reacted, retaining its polymerization driving force in the photopolymer system. When the reaction is complete, there are no exposed NCO groups in the prepolymer material, which can become the reaction core for polymerization in the photopolymer system, thus providing a good polymerization basis for the subsequent introduction of the second film-forming resin in the photopolymer system, ensuring the phase separation degree of the photopolymer system, and reducing the haze while increasing the diffraction efficiency of the photopolymer holographic grating device.

[0040] Specifically, by adjusting the ratios of writing monomers with different functionalities, different functional groups, different reactive elements, etc., and simultaneously combining the selection of the types and ratios of two film-forming resins, a film-forming formulation can be formed that can conveniently and directionally increase the compatibility of the system. The modification of the film-forming formulation can be achieved by calculating the residual amount of NCO in the system and then determining the addition ratio of monomer alcohols, thereby determining the R value in the entire system. Among them, the magnitude of the R value mostly determines the mechanical properties of the polyurethane. By modifying the chemical structure and type of alcohols, the refractive index of the film-forming resin can be reduced, and a better refractive index modulation can be obtained. Specifically, the R value of the system is determined by the following formula: .

[0041] Preferably, the diffraction efficiency of the photopolymer holographic grating device is above 90%, the angular bandwidth is within 10°, the refractive index modulation is 0.04, and the haze is less than 1%. It has excellent optical properties and is suitable for more precise usage scenarios.

[0042] Example 4 This example provides a photopolymer system based on modified writing monomers, a grating device, and a preparation method thereof. By preferentially reacting the writing monomer with the first film-forming resin to modify the chemical properties of the writing monomer, the compatibility between the writing monomer and the film-forming resin is changed, and the diol is modified to prepare the photopolymer system. Specifically, it includes the following steps: (1) Weigh all the materials included in the photopolymer system as required as follows: RB 1%, NPG 2%, TPO 1%, OPPEA 14%, PETA 2%, α-hydroxypropyl acrylamide 16%, N-vinylcarbazole 4%, ethoxylated bisphenol A diacrylate 10%, PPG-400 20%, N3390 25%; dibutyltin dilaurate 0.001%, EA, 2%, DMF 3%.

[0043] (2) First, uniformly mix the α-hydroxypropyl acrylamide writing monomer and N3390, and react at 50 - 70 °C for 3 - 5 h. Partially or fully react to form a modified writing monomer to obtain a prepolymerized material; (3) Stir the prepolymerized material in step (2) together with the remaining components in the photopolymer system weighed in step (1) for 30 min, pour it into a liquid crystal cell, and fill the prepared raw material into a 10-μm liquid crystal cell in a darkroom vacuum environment. After filling, seal the liquid crystal cell and transfer it to an oven at 60 °C for post-treatment for 30 min; then, use a coherent beam with a double-beam angle of 90° for the exposure of the reflective grating, and the exposure dose is 6 mw / cm 2 , and the time is 20 s.

[0044] (4)Diffraction efficiency, haze, and transmittance tests The specific steps for the diffraction efficiency test are as follows: Use a grating diffraction efficiency tester UV-VIs spectrophotometer to test the diffraction efficiency of the above-mentioned photopolymer holographic grating device at 532 nm; the diffraction efficiency of the photopolymer holographic grating device is obtained as 92%.

[0045] The specific steps for the haze and transmittance tests are as follows: Wipe the grating area of the above-mentioned photopolymer holographic grating device with alcohol, and then test it with a haze and transmittance test machine. Specifically, each photopolymer holographic grating device is tested in parallel at 5 points and the average value is taken, and the haze of the photopolymer holographic grating device is obtained as 0.78%.

[0046] Comparative Example 1 This embodiment provides a photopolymer system, a grating device, and a preparation method thereof, specifically including the following steps: (1)Weigh all the materials included in the photopolymer system as required as follows: RB 1%, NPG 2%, TPO 1%, OPPEA 14%, PETA 2%, N-vinylcarbazole 20%, ethoxylated bisphenol A diacrylate 10%, PPG-400 20%, N3900 25%; dibutyltin laurate 0.001%, EA, 2%, DMF 3%.

[0047] (2)Stir the above raw materials with a magnetic stirrer for 6 h at a rotation speed of not less than 800 r / min, and set the temperature to room temperature. It is best to prepare in a glove box to isolate the interference of oxygen and water. Fill the prepared raw materials into a 10-μm liquid crystal cell in a darkroom vacuum environment. After filling, seal the liquid crystal cell and transfer it to an oven at 60 °C for post-treatment for 30 min; then use a coherent beam with a double-beam angle of 90° for exposure of the reflective grating, and the exposure dose is 6 mw / cm 2 , and the time is 20 s.

[0048] (3)Diffraction efficiency, haze, and transmittance tests The specific steps for the diffraction efficiency test are as follows: Use a grating diffraction efficiency tester UV-VIs spectrophotometer to test the diffraction efficiency of the above-mentioned photopolymer holographic grating device at 532 nm; the diffraction efficiency of the photopolymer holographic grating device is obtained as 72%.

[0049] The specific steps for haze and transmittance testing are as follows: wipe the grating area of the above-mentioned photopolymer holographic grating device with alcohol, and then conduct the test through a haze and transmittance testing machine. Specifically, 5 parallel tests are carried out for each photopolymer holographic grating device and the average value is taken, and the haze of the photopolymer holographic grating device is obtained as 2.5%.

[0050] Comparing the diffraction efficiency and haze performance of the grating devices prepared from the photopolymer systems provided in Example 4 and Comparative Example 1, it can be seen that: when the first film-forming resin is not used to preferentially modify the writing monomer as in Comparative Example 1, the two film-forming resins cannot react step by step and cooperate, and the overall compatibility of the photopolymer system is poor, thus limiting the diffraction efficiency and haze of the prepared grating device; while Example 4, as a preferred example, by introducing two film-forming resins into the photopolymer system, on the basis of constructing the basic framework of refractive index modulation of the photopolymer system by making the first film-forming resin react with the writing monomer preferentially, and then introducing the second film-forming resin, the thiol group, isocyanate group, and hydrosilyl group of the second film-forming resin react with the functional chemical bonds such as amide bond, ester group, urea group, and aliphatic ether on the modified writing monomer that have not fully reacted, as well as hydroxyl group, carboxyl group, and thiol group to form dynamic covalent bonds, thereby reducing the difference in solubility parameters of the overall photopolymer system and improving the overall compatibility of the photopolymer system; at the same time, by making the two film-forming resins react and polymerize step by step, the synergistic effect between the two film-forming resins and the modified writing monomer are further directionally combined, reducing the haze of the photopolymer system while increasing the phase separation degree of the system, thus improving the diffraction efficiency of the system.

[0051] Obviously, the above-mentioned embodiments of the present invention are merely examples for clearly illustrating the technical solutions of the present invention, rather than limitations on the specific implementation manners of the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the claims of the present invention shall be included within the protection scope of the claims of the present invention.

Claims

1. A photopolymer system based on a modified writing monomer, characterized in that, By mass percentage, it includes: Solvent: 1% - 5%, Photoinitiator: 0.01 - 1%, Co - initiator: 0.1 - 1%, Writing monomer: 40 - 80%, First film - forming resin: 20 - 30%, Second film - forming resin: 20 - 30%, Surfactant: 0.1 - 1%, Catalyst: 0.001 - 0.01%, The writing monomer uses acrylate writing monomer; The first film - forming resin and the second film - forming resin respectively use one or more of polyurethane, PVAC and epoxy resin; The writing monomer preferentially reacts with the first film - forming resin to form a modified writing monomer; The writing monomer has functional chemical bonds and functional groups; the functional chemical bonds include amide bonds, ester groups, urea groups, aliphatic ethers; the functional groups include hydroxyl groups, carboxyl groups, mercapto groups; Both the first film - forming resin and the second film - forming resin have reactive groups, and the reactive groups include mercapto groups, isocyanate groups, hydrosilyl groups.

2. The photopolymer system according to claim 1, characterized in that, The writing monomer includes a first monomer, a second monomer, a third monomer and a fourth monomer; and by mass percentage, it includes: First monomer: 10 - 20%, Second monomer: 10 - 20%, Third monomer: 10 - 20%, Fourth monomer: 10 - 20%; At least one type of the writing monomers among the first monomer, the second monomer, the third monomer and the fourth monomer has a functionality of 1, and at least one type of the writing monomers has a functionality of not less than 2.

3. The photopolymer system according to claim 1, wherein The photoinitiator is selected from one or more of RB, SO, Acid Red 94, BTCP, BCIM, BDEA and DEAMC.

4. The photopolymer system according to claim 1, characterized in that, The co - initiator is selected from one or more of NPG, triethanolamine, HABI, EM and Cl - MBT.

5. The photopolymer system according to claim 1, characterized in that, The solvent is selected from one or more of EM, EA, THF, DMF, DCM, NVP and NMP.

6. The photopolymerizable system according to claim 1, characterized in that, The surfactant is selected from silicone - based surfactants or epoxy - based surfactants.

7. The photopolymer system according to claim 1, characterized in that, The catalyst uses organotin - based catalysts, organobismuth - based catalysts or photo - thermal curing catalysts.

8. A method for preparing a photopolymer holographic grating device, characterized in that, The photopolymer holographic grating device uses the photopolymer system according to any one of claims 1 - 7. After the writing monomer reacts with the first film - forming component to form a modified writing monomer, it is mixed with the remaining components and poured into a liquid crystal cell, and then exposed under a coherent light source to form a grating device.

9. The preparation method according to claim 8, characterized in that, The specific steps for the writing monomer to react with the first film - forming component to form a modified writing monomer are: mixing the writing monomer and the first film - forming component evenly, and reacting at 50 - 70 °C for 3 - 5 h.

10. A photopolymer holographic grating device, characterized in that, Prepared by the preparation method according to any one of claims 8 - 9.

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