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

Abstract

The present invention provides a photopolymer system based on a modified writing monomer, a grating device, and a preparation method thereof. Specifically, in the photopolymer system, the modified writing monomer interacts with the original writing monomer through the reaction of the writing monomer with a first film-forming resin, thereby improving the compatibility of the photopolymer system during holographic exposure. Secondly, two film-forming resins are introduced into the photopolymer system. After the first film-forming resin is preferentially reacted with the writing monomer to construct a basic framework for refractive index modulation of the photopolymer system, a second film-forming resin is introduced. By allowing the two film-forming resins to react and polymerize in steps, the synergistic effect between the two film-forming resins is achieved, leading to further directionally combining with the writing monomer and the modified writing monomer. This reduces the haze of the photopolymer system while improving the phase separation degree of the system, thereby improving the diffraction efficiency of the system.

Description

Technical Field

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

[0002] With the rapid development of the smart car and information security industries, the application of photopolymers is ushering in new development opportunities. With its mature process system and stable mass production, photopolymer materials have been widely used in scenarios such as in-vehicle head-up display systems (HUDs) and high-end anti-counterfeiting labels. In the application scenarios of in-vehicle 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 using a photopolymer system to prepare a holographic grating, the bright area triggers the monomer polymerization reaction due to illumination, while the dark area remains unpolymerized. The resulting monomer concentration gradient drives the formation of a periodic refractive index distribution within the material. Therefore, the quality of the phase separation structure ultimately formed by the photopolymer system directly determines the diffraction performance of the holographic grating.

[0003] Specifically, the refractive index modulation of the holographic grating directly determines key parameters such as the diffraction efficiency. Optimizing this modulation depends primarily on the coordinated regulation of two key parameters: the intrinsic refractive index difference (Δn) between the writing monomer and the film-forming matrix, and the degree of phase separation formed during the photopolymerization process. In theory, a monomer / matrix combination with a high refractive index difference, coupled with sufficient phase separation, can produce ideal refractive index modulation. However, in actual material systems, this theoretical model is often difficult to implement. The fundamental reason for this difficulty stems from the compatibility conflicts between the material components. Excessive refractive index differences are often accompanied by significant differences in molecular polarity, which inhibits the uniform dispersion of the monomer 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-sized aggregates. This not only reduces the effective refractive index modulation amplitude but also causes severe scattering losses, resulting in increased haze. At the same time, the selective adsorption of monomers by the film-forming matrix also has a significant effect. For example, an acrylate matrix with specific functional groups will preferentially adsorb monomer molecules containing benzene rings. This interaction at the molecular level will change the driving mechanism of phase separation. This strong interaction will significantly inhibit the long-range diffusion of monomers, 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 of the defects of the above-mentioned prior art and provides a photopolymer system based on modified writing monomers, 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, characterized in that it comprises, in percentage by mass:

[0006] Solvent: 1%-5%,

[0007] Photoinitiator: 0.01-1%,

[0008] Co-initiator: 0.1-1%,

[0009] Writing monomer: 40-80%,

[0010] First film-forming resin: 20-30%,

[0011] Second film-forming resin: 20-30%,

[0012] Surfactant: 0.1-1%,

[0013] Catalyst: 0.001-0.01%,

[0014] The writing monomer is an acrylic writing monomer;

[0015] The first film-forming resin and the second film-forming resin are respectively one or more of polyurethane, PVAC and epoxy resin;

[0016] The writing monomer preferentially reacts and combines with the first film-forming resin to form a modified writing monomer;

[0017] The writing monomer has functional chemical bonds and functional groups; the functional chemical bonds include amide bonds, ester groups, urea groups, and fatty ethers; the functional groups include hydroxyl groups, carboxyl groups, and thiol groups;

[0018] The first film-forming resin and the second film-forming resin both have reactive groups, and the reactive groups include mercapto groups, isocyanate groups, and hydrogen-containing silicon groups.

[0019] In the present 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, fatty ethers, and hydroxyl groups, carboxyl groups, and mercapto groups. First, the writing monomer is reacted 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, fatty ethers, and hydroxyl groups, carboxyl groups, and mercapto groups in the writing monomer form dynamic covalent bonds with the mercapto groups, isocyanate groups, and hydrogen-containing silicon groups of the first film-forming resin, thereby reducing the solubility parameter difference between the writing monomer and the first film-forming resin and improving the compatibility of the writing monomer with the first film-forming resin. Furthermore, the modified writing monomer after the reaction, the remaining original writing monomer, the first film-forming resin, etc. are incorporated into a 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, the first film-forming resin is allowed to react preferentially with the writing monomer to construct a basic framework for refractive index modulation of the photopolymer system, and then the second film-forming resin is introduced, so that the thiol, isocyanate, hydrogenated silicon groups of the second film-forming resin react with the unreacted amide bonds, ester groups, urea groups, fatty ether groups and other functional chemical bonds on the modified writing monomer with the hydroxyl groups, carboxyl groups and thiol groups 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 allowing the two film-forming resins to react and polymerize in steps, the synergistic effect between the two film-forming resins and the modified writing monomer is further directionally combined, thereby reducing the haze of the photopolymer system while improving the phase separation degree of the system, thereby improving the diffraction efficiency of the system.

[0020] Furthermore, by precisely controlling the proportion of components and the catalytic system in the photopolymer system, a balance between exposure responsiveness, optical properties and stability is achieved; specifically, a certain amount of surfactants and catalysts are introduced into a system comprising a modified writing monomer and two film-forming resins, and the physical interface state is optimized by the surfactant, thereby ensuring the overall optical uniformity of the system; at the same time, the reaction kinetics are precisely controlled by the catalyst, thereby improving the conversion efficiency, and the refractive index modulation of the system is improved through the synergistic effect among the solvent, photoinitiator, co-initiator, modified writing monomer, two film-forming resins, surfactant and catalyst, so that the system has low haze characteristics while having high diffraction efficiency; at the same time, by adopting a writing monomer with a wide ratio window and a low ratio solvent system, the convenience of industrial production of holographic gratings in the photopolymer system is improved, making it suitable for large-scale production.

[0021] Furthermore, the writing monomer includes a first monomer, a second monomer, a third monomer and a fourth monomer; and in terms of mass percentage, includes:

[0022] First monomer: 10-20%,

[0023] Second monomer: 10-20%,

[0024] The third monomer: 10-20%,

[0025] The fourth monomer: 10-20%;

[0026] At least one type of writing monomer 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 writing monomer has a functionality of not less than 2.

[0027] In the present technical solution, an unsaturated monomer system is formed by selecting a first monomer, a second monomer, a third monomer, and a fourth monomer in combination, wherein at least one type of writing monomer 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 writing monomer has a functionality of not less than 2. Specifically, the writing monomer with a functionality of 1 has a faster migration speed and is prone to forming a concentration difference during the holographic exposure process of the photopolymer system. The multifunctional writing monomer with a functionality of not less than 2 has a short gelation time and is easy to polymerize in situ. Therefore, it can be used as the central core of the polymerization of the photopolymer system, so that the surrounding writing monomers move toward it. By utilizing the cross-linking synergistic effect between the two film-forming resins and the multiple unsaturated writing monomers, specifically, by adjusting the types and ratios of the added first film-forming resin, the second film-forming resin, and the added unsaturated monomers, the efficiency of the polymerization reaction between the monomers in the material can be adjusted, and at the same time, the diffraction efficiency and heat stability 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, and P, etc. The viscosity of the writing monomer can be adjusted by introducing writing monomers with different carbon chain lengths or carbon chain structures, and the refractive index of the writing monomer can be greatly increased by introducing writing monomers with different types of functional groups and different elements; therefore, the unsaturated monomers contained in the photopolymer system can be selected and combined from a wider range of writing monomer categories, and the choices are diverse, and the sources of raw materials are wide and easy to obtain. While ensuring the function of the holographic grating device, the production convenience is improved and the production cost is reduced.

[0028] Furthermore, the photoinitiator is selected from one or more of RB, SO, Acid Red 94, BTCP, BCIM, BDEA and DEAMC.

[0029] Furthermore, the co-initiator is selected from one or more of NPG, triethanolamine, HABI, EM and Cl-MBT.

[0030] Furthermore, the solvent is selected from one or more of EM, EA, THF, DMF, DCM, NVP and NMP.

[0031] Furthermore, the surfactant is selected from silicone surfactants or epoxy surfactants.

[0032] Furthermore, the catalyst is an organic tin catalyst, an organic bismuth catalyst or a photothermal curing catalyst.

[0033] Another object of the present invention is to provide a method for preparing a photopolymer holographic grating device. Specifically, the photopolymer holographic grating device adopts the photopolymer system as described in the present technical solution. The writing monomer is mixed with the first film-forming component to form a modified writing monomer, which is then mixed with the remaining components and poured into a liquid crystal box, and exposed under a coherent light source to form a grating device.

[0034] Furthermore, the specific steps of mixing the writing monomer with the first film-forming component to form the modified writing monomer are: mixing the writing monomer and the first film-forming component uniformly and reacting them at 50-70° C. for 3-5 hours.

[0035] Another object of the present invention is to provide a photopolymer holographic grating device fabricated using the method provided in this technical solution. Preferably, the holographic grating device exhibits a diffraction efficiency exceeding 90%, an angular bandwidth within 10°, a refractive index modulation of 0.04, and a haze of less than 1%.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. Provided is a photopolymer system based on a modified writing monomer, wherein the writing monomer used in the system simultaneously introduces functional chemical bonds and functional groups, firstly reacts the writing monomer with a 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, thereby reducing the solubility parameter difference between the writing monomer and the first film-forming resin and improving the compatibility of the writing monomer with the first film-forming resin; further, the modified writing monomer after the reaction and the remaining writing monomer, the first film-forming resin, etc. are added into a photopolymer system including a solvent, a photoinitiator, a co-initiator, a second film-forming resin, a surfactant and a catalyst, and the like is reacted with the writing monomer to form a modified writing monomer. Two film-forming resins are introduced into the physical system. The first film-forming resin is allowed to react preferentially with the writing monomer to construct the basic framework of the refractive index modulation of the photopolymer system. Then, 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 solubility parameter difference of the photopolymer system and improving the overall compatibility of the photopolymer system. At the same time, by allowing the two film-forming resins to react and polymerize in steps, the synergistic effect between the two film-forming resins and the modified writing monomer is further directionally combined, thereby reducing the haze of the photopolymer system while improving the phase separation degree of the system, thereby improving the diffraction efficiency of the system.

[0038] 2. By precisely controlling the component ratios and catalytic system in the photopolymer system, a balance between exposure responsiveness, optical properties, and stability is achieved. Specifically, a certain amount of surfactants and catalysts are introduced into a system comprising a modified writing monomer and two film-forming resins. The surfactants optimize the physical interface state, thereby ensuring the overall optical uniformity of the system. At the same time, the catalysts precisely control the reaction kinetics, thereby improving the conversion efficiency. Through the synergistic effects of the solvent, photoinitiator, co-initiator, modified writing monomer, two film-forming resins, surfactants, and catalysts, the refractive index modulation of the system is improved, enabling the system to have both high diffraction efficiency and low haze characteristics. At the same time, by adopting a writing monomer with a wide ratio window and a low ratio solvent system, the industrial production convenience of holographic gratings in the photopolymer system is improved, making it suitable for large-scale production.

[0039] 3. In the photopolymer system, the writing monomers include a first monomer, a second monomer, a third monomer, and a fourth monomer. Specifically, the functionality of at least one type of writing monomer among the first monomer, the second monomer, the third monomer, and the fourth monomer is set to be 1, and at least one type of writing monomer has a functionality of not less than 2. Among them, the writing monomer with a functionality of 1 moves faster and is prone to forming 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 easy to polymerize in situ. Therefore, it can be used as the central core of the polymerization of the photopolymer system, so that the surrounding writing monomers move closer to it. By adjusting the types and proportions of the added first film-forming resin, the second film-forming resin, and the added unsaturated monomer, the efficiency of the polymerization reaction between the monomers in the material can be adjusted. At the same time, the diffraction efficiency and heat resistance stability of the prepared holographic 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, and P, etc. The viscosity of the writing monomer can be adjusted by introducing writing monomers with different carbon chain lengths or carbon chain structures, and the refractive index of the writing monomer can be greatly increased by introducing writing monomers with different types of functional groups and different elements; therefore, the unsaturated monomers contained in the photopolymer system can be selected and combined from a wider range of writing monomer categories, and the choices are diverse, and the sources of raw materials are wide and easy to obtain. While ensuring the function of the holographic grating device, the production convenience is improved and the production cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The figure is a schematic structural diagram of the exposure light path of the holographic film in the method for preparing the photopolymer holographic grating device of the present invention.

[0041] Figure 2 This is a schematic diagram of the process of chemically reacting the writing monomer with the first film-forming resin in the photopolymer system provided in Example 3 of the present invention to form a modified writing monomer. DETAILED DESCRIPTION

[0042] It should be noted that the following detailed descriptions are illustrative and 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 skilled in the art to which the present application belongs.

[0043] 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 form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0044] The present invention will now be further described with reference to specific examples. The following examples are intended only to illustrate the present invention and are not intended to limit the present invention. The experimental samples and experimental procedures used in the following examples include the following (if the specific experimental conditions are not specified in the examples, they are generally based on conventional conditions or the conditions recommended by the reagent company; the reagents and consumables used in the following examples are all commercially available unless otherwise specified).

[0045] Example 1

[0046] This embodiment provides a photopolymer system based on a modified writing monomer, which comprises, by mass percentage:

[0047] Solvent: 1%-5%,

[0048] Photoinitiator: 0.01-1%,

[0049] Co-initiator: 0.1-1%,

[0050] Writing monomer: 40-80%,

[0051] First film-forming resin: 20-30%,

[0052] Second film-forming resin: 20-30%,

[0053] Surfactant: 0.1-1%,

[0054] Catalyst: 0.001-0.01%,

[0055] The writing monomer is an acrylic writing monomer;

[0056] The first film-forming resin and the second film-forming resin are respectively one or more of polyurethane, PVAC and epoxy resin;

[0057] The writing monomer preferentially reacts and combines with the first film-forming resin to form a modified writing monomer;

[0058] The writing monomer has functional chemical bonds and functional groups; the functional chemical bonds include amide bonds, ester groups, urea groups, and fatty ethers; the functional groups include hydroxyl groups, carboxyl groups, and thiol groups;

[0059] The first film-forming resin and the second film-forming resin both have reactive groups, and the reactive groups include mercapto groups, isocyanate groups, and hydrogen-containing silicon groups.

[0060] Specifically, by first reacting a writing monomer with a first film-forming resin to form a modified writing monomer, functional chemical bonds such as amide, ester, urea, and fatty ether in the writing monomer form dynamic covalent bonds with hydroxyl, carboxyl, and thiol groups in the first film-forming resin, forming dynamic covalent bonds with the thiol, isocyanate, and hydrogenated silicon groups in the first film-forming resin. The reaction between the writing monomer and the first film-forming resin results in interaction between the modified writing monomer and the original writing monomer, reducing the solubility parameter difference between the writing monomer and the first film-forming resin, thereby improving the compatibility of the photopolymer system during holographic exposure. Secondly, two film-forming resins are introduced into the photopolymer system. After the first film-forming resin is preferentially reacted with the writing monomer to construct the basic framework for refractive index modulation of the photopolymer system, a second film-forming resin is introduced. By allowing the two film-forming resins to react and polymerize in separate steps, the synergistic effect between the two film-forming resins is further directed toward bonding with the writing monomer and the modified writing monomer, thereby reducing the haze of the photopolymer system while improving the degree of phase separation, thereby enhancing the diffraction efficiency of the system.

[0061] Furthermore, a certain amount of surfactant and catalyst was introduced into the system containing a writing monomer, a modified writing monomer, and two film-forming resins. The surfactant optimized the physical interface state and ensured the overall optical uniformity of the system. Simultaneously, the catalyst precisely controlled the reaction kinetics, thereby improving the conversion efficiency. The synergistic effect between the solvent, photoinitiator, co-initiator, writing monomer, modified writing monomer, two film-forming resins, surfactant, and catalyst increased the refractive index modulation of the system, resulting in a system with both high diffraction efficiency and low haze. Furthermore, by using a writing monomer with a wide ratio window and a low solvent ratio, the industrial fabrication of holographic gratings in the photopolymer system was improved, making it suitable for large-scale production. By precisely controlling the component ratios and the catalytic system in the photopolymer system, a balance between exposure responsiveness, optical properties, and stability was achieved.

[0062] Furthermore, the writing monomer includes a first monomer, a second monomer, a third monomer and a fourth monomer; and in terms of mass percentage, includes:

[0063] First monomer: 10-20%,

[0064] Second monomer: 10-20%,

[0065] The third monomer: 10-20%,

[0066] The fourth monomer: 10-20%;

[0067] At least one type of writing monomer 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 writing monomer has a functionality of not less than 2.

[0068] 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, and P, etc. The viscosity of the writing monomer can be adjusted by introducing writing monomers with different carbon chain lengths or carbon chain structures, and the refractive index of the writing monomer can be greatly increased by introducing writing monomers with different types of functional groups and different elements; therefore, the unsaturated monomers contained in the photopolymer system can be selected and combined from a wider range of writing monomer categories, and the choices are diverse, and the sources of raw materials are wide and easy to obtain. While ensuring the function of the holographic grating device, the production convenience is improved and the production cost is reduced.

[0069] Furthermore, the photoinitiator is selected from one or more of RB, SO, Acid Red 94, BTCP, BCIM, BDEA and DEAMC.

[0070] Furthermore, the co-initiator is selected from one or more of NPG, triethanolamine, HABI, EM and Cl-MBT.

[0071] Furthermore, the solvent is selected from one or more of EM, EA, THF, DMF, DCM, NVP and NMP.

[0072] Furthermore, the surfactant is selected from silicone surfactants or epoxy surfactants.

[0073] Furthermore, the catalyst is an organic tin catalyst, an organic bismuth catalyst or a photothermal curing catalyst.

[0074] Example 2

[0075] This embodiment adopts the photopolymer system described in Example 1 to prepare a method for preparing a photopolymer holographic grating device, specifically comprising the following steps:

[0076] (1) Weigh all the materials contained in the photopolymer system as needed;

[0077] (2) The writing monomer and the first film-forming component are preferentially mixed and reacted at 50-70° C. for 3-5 hours to partially or completely react to form a modified writing monomer to obtain a prepolymer material;

[0078] (3) The prepolymer material in step (2) and the remaining components of the photopolymer system weighed in step (1) are mixed and poured into a liquid crystal box, and the mixture is then heated under a coherent light source. Figure 1 The holographic film exposure light path shown is used to expose and form a photopolymer holographic grating device; specifically, the adjustment of θ1 and θ2 in the light path is adapted to the requirements of the photopolymer system.

[0079] (4) Diffraction efficiency, haze and transmittance test

[0080] The specific steps of the diffraction efficiency test are: testing the diffraction efficiency of the photopolymer holographic grating device by using a grating diffraction efficiency tester.

[0081] The specific steps of the haze and transmittance test are: wipe the grating area of ​​the above-mentioned photopolymer holographic grating device with alcohol, and then test it through a haze transmittance test machine. Specifically, each photopolymer holographic grating device is tested in parallel at multiple points and the average value is taken.

[0082] In the preparation method provided in this embodiment, the modified writing monomer generated by the reaction of the writing monomer with the first film-forming resin interacts with the original writing monomer, thereby improving the compatibility of the photopolymer system during the holographic exposure process. 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 high diffraction efficiency and low haze.

[0083] Example 3

[0084] This embodiment provides a photopolymer holographic grating device, which uses the photopolymer system described in Example 1 and the preparation method described in Example 2. Figure 2 As shown, in the photopolymer system, the functional group R2 of the writing monomer used is hydroxyl, amino or carboxyl, and the photopolymer system contains writing monomers with various functionalities, which can be monofunctional, difunctional, trifunctional or above; the first film-forming resin adopts a polyurethane system, and its reactive group R4 is an NCO group. Before the overall reaction and polymerization of the photopolymer system, the writing monomer preferentially reacts and combines with the first film-forming resin to form a modified writing monomer. The reaction process is as follows: Figure 1 As shown, the writing monomer reacts chemically with the first film-forming resin to form modified writing monomers M1, M2 and M3; when the writing monomer partially reacts with the first film-forming resin, the prepolymer material contains exposed NCO groups to be reacted, retaining its polymerization motive force in the photopolymer system. During the entire reaction, there are no exposed NCO groups in the prepolymer material, which can become the reaction core of the polymerization in the photopolymer system, thereby 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 improving the diffraction efficiency of the photopolymer holographic grating device.

[0085] Specifically, by adjusting the ratio of writing monomers with different functionalities, different functional groups, and different reactive elements, and combining it with the selection of the types and ratios of the two film-forming resins, a film-forming formula that conveniently and directionally increases the compatibility of the system can be formed. The film-forming formula can be modified by calculating the residual NCO content in the system and then determining the addition ratio of the monomer alcohol, thereby determining the R value of the entire system. Among them, the R value largely determines the mechanical properties of the polyurethane. By modifying the chemical structure and type of the alcohol, 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:

[0086] .

[0087] Preferably, the photopolymer holographic grating device has a diffraction efficiency of over 90%, an angular bandwidth within 10°, a refractive index modulation of 0.04, and a haze of less than 1%. It has excellent optical properties and is suitable for more sophisticated use cases.

[0088] Example 4

[0089] This embodiment provides a photopolymer system based on a modified writing monomer, a grating device, and a preparation method thereof. The photopolymer system is prepared by preferentially reacting the writing monomer with a first film-forming resin to modify the chemical properties of the writing monomer, thereby changing the compatibility of the writing monomer with the film-forming resin, and modifying the diol. Specifically, the process includes the following steps:

[0090] (1) Weigh all the materials of the photopolymer system as needed:

[0091] RB 1%, NPG 2%, TPO 1%, OPPEA 14%, PETA 2%, α-hydroxypropyl acrylamide 16%, N-vinyl carbazole 4%, ethoxylated bisphenol A diacrylate 10%, PPG-400 20%, N3390 25%; dibutyltin laurate 0.001%, EA, 2%, DMF 3%.

[0092] (2) The α-hydroxypropyl acrylamide writing monomer and N3390 are preferentially mixed and reacted at 50-70°C for 3-5 hours to partially or completely react to form a modified writing monomer to obtain a prepolymer material;

[0093] (3) The prepolymer material in step (2) and the remaining components of the photopolymer system weighed in step (1) were stirred for 30 minutes and poured into a liquid crystal box. The prepared raw materials were filled into a 10 μm liquid crystal box under a darkroom vacuum environment. After filling, the liquid crystal box was sealed and transferred to a 60°C oven for post-treatment for 30 minutes; then, the reflective grating was exposed using a coherent beam with a double beam angle of 90° and an exposure dose of 6 mW / cm 2 , time is 20s.

[0094] (4) Diffraction efficiency, haze and transmittance test

[0095] The specific steps of the diffraction efficiency test are as follows: the diffraction efficiency of the above-mentioned photopolymer holographic grating device at 532nm is tested by using a grating diffraction efficiency tester UV-VIs spectrophotometer; and the diffraction efficiency of the photopolymer holographic grating device is obtained to be 92%.

[0096] The specific steps of the haze and transmittance test are as follows: wipe the grating area of ​​the above-mentioned photopolymer holographic grating device with alcohol, and then test it through a haze transmittance test machine. Specifically, each photopolymer holographic grating device is tested at 5 parallel points and the average value is taken. The haze of the photopolymer holographic grating device is 0.78%.

[0097] Comparative Example 1

[0098] This embodiment provides a photopolymer system, a grating device and a preparation method thereof, which specifically includes the following steps:

[0099] (1) Weigh all the materials of the photopolymer system as needed:

[0100] RB 1%, NPG 2%, TPO 1%, OPPEA 14%, PETA 2%, N-vinyl carbazole 20%, ethoxylated bisphenol A diacrylate 10%, PPG-400 20%, N3900 25%; dibutyltin laurate 0.001%, EA, 2%, DMF 3%.

[0101] (2) Weigh the above raw materials and stir them with a magnetic stirrer for 6 hours at a speed of not less than 800 r / min and at room temperature. The preparation environment is preferably in a glove box to isolate the interference of oxygen and water. Fill the prepared raw materials into a 10um liquid crystal box under a darkroom vacuum environment. After filling, seal the liquid crystal box and transfer it to a 60℃ oven for post-processing for 30 minutes; then use a coherent beam with a double beam angle of 90° to expose the reflective grating, and the exposure dose is 6mw / cm 2 , time is 20s.

[0102] (3) Diffraction efficiency, haze and transmittance test

[0103] The specific steps of the diffraction efficiency test are as follows: the diffraction efficiency of the above-mentioned photopolymer holographic grating device at 532nm is tested by using a grating diffraction efficiency tester UV-VIs spectrophotometer; and the diffraction efficiency of the photopolymer holographic grating device is obtained to be 72%.

[0104] The specific steps of the haze and transmittance test are as follows: wipe the grating area of ​​the above-mentioned photopolymer holographic grating device with alcohol, and then test it through a haze transmittance test machine. Specifically, each photopolymer holographic grating device is tested at 5 parallel points and the average value is taken. The haze of the photopolymer holographic grating device is 2.5%.

[0105] Comparison of the diffraction efficiency and haze performance of the grating device prepared by the photopolymer system provided in Example 4 and Comparative Example 1 shows 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 act synergistically, and the overall compatibility of the photopolymer system is poor, thereby limiting the diffraction efficiency and haze of the prepared grating device; and Example 4 is a preferred embodiment, by introducing two film-forming resins into the photopolymer system, and allowing the first film-forming resin to preferentially react with the writing monomer to construct the basic framework of the photopolymer system refractive index modulation, and then introducing the second film-forming resin. The film resin allows the mercapto group, isocyanate group, hydrogenated silicon group of the second film-forming resin to react with the unreacted functional chemical bonds such as amide bond, ester group, urea group, fatty ether group on the modified writing monomer and hydroxyl group, carboxyl group, and mercapto group 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 allowing the two film-forming resins to react and polymerize in steps, the synergistic effect between the two film-forming resins and the modified writing monomer is further directionally combined, thereby reducing the haze of the photopolymer system while improving the phase separation degree of the system, thereby improving the diffraction efficiency of the system.

[0106] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the technical solutions of the present invention, and are not intended to limit the specific implementation methods of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the claims of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A photopolymer system based on a modified writing monomer, characterized in that: In percentage by mass, including: 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 is an acrylic writing monomer; The first film-forming resin and the second film-forming resin are respectively one or more of polyurethane, PVAC and epoxy resin; On the basis of allowing the writing monomer to preferentially react with the first film-forming resin to form a modified writing monomer, a second film-forming resin is introduced, and the two film-forming resins are allowed to react and polymerize in steps; The writing monomer has functional chemical bonds and functional groups; the functional chemical bonds include amide bonds, ester groups, urea groups, and fatty ethers; the functional groups include hydroxyl groups, carboxyl groups, and thiol groups; The first film-forming resin and the second film-forming resin both have reactive groups, and the reactive groups include mercapto groups, isocyanate groups, and hydrogen-containing silicon 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 the monomers are expressed in percentage by mass, including: First monomer: 10-20%, Second monomer: 10-20%, The third monomer: 10-20%, The fourth monomer: 10-20%; At least one type of writing monomer 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 writing monomer has a functionality of not less than 2.

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

6. The photopolymer system according to claim 1, wherein The surfactant is selected from silicone surfactants or epoxy surfactants.

7. The photopolymer system according to claim 1, wherein The catalyst is an organic tin catalyst, an organic bismuth catalyst or a photothermal curing catalyst.

8. A method for preparing a photopolymer holographic grating device, characterized in that: The photopolymer holographic grating device adopts the photopolymer system as described in any one of claims 1 to 7. After the writing monomer is mixed and reacted with the first film-forming component to form a modified writing monomer, it is mixed together with the remaining components and poured into a liquid crystal box, and 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 of mixing the writing monomer with the first film-forming component to form the modified writing monomer are: uniformly mixing the writing monomer with the first film-forming component and reacting them at 50-70° C. for 3-5 hours.

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

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