Fluorine-containing liquid crystal-based photopolymer system, grating device and preparation method thereof

Abstract

The present invention provides a photopolymer system based on fluorinated liquid crystal, a grating device and a preparation method thereof. In the photopolymer system provided by the present invention, a mixed liquid crystal containing both nematic liquid crystal and fluorinated liquid crystal is adopted, thereby improving the polarity and dielectric anisotropy of the mixed liquid crystal material, and improving the electro-optical performance, uniformity and stability of the overall photopolymer system, so that the grating device prepared based on this photopolymer system has good optical characteristics with low haze while having a high diffraction efficiency. Specifically, in the present invention, a fluorinated biphenyl liquid crystal, a fluorinated alkyne liquid crystal and a fluorinated difluoromethoxy liquid crystal with 2-5 carbon atoms in the flexible side chain are selected, and a nematic liquid crystal with Δε not less than 10 is selected to jointly form a mixed liquid crystal, realizing the balance and optimization between the diffraction efficiency and haze performance of the photopolymer system and the grating device prepared therefrom.

Description

Technical Field

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

[0002] Holographic display technology is a technology that uses the principles of interference and diffraction to record and reproduce the optical information of three-dimensional objects. It can not only present a three-dimensional image of an object, but also display the color, texture and dynamic changes of the object, thus bringing a brand-new visual experience to display technology. The core of holographic display technology lies in the production of holograms. Holograms are made by irradiating a laser onto an object and using the principles of interference and diffraction to record the optical information of the object. Subsequently, this optical information can be reproduced as a three-dimensional image, enabling users to observe different sides of the object from different angles. Based on different implementation methods, holographic display technology can be used to produce various types of holograms, such as reflective, transmissive and color holograms, etc.

[0003] Holographic Polymer Dispersed Liquid Crystal (H-PDLC) gratings are the product of the combination of holographic technology and polymer dispersed liquid crystals. They are optoelectronic information materials and devices with an orderly structure formed by the periodic arrangement of polymer-rich phases and liquid crystal-rich phases. They have the characteristics of high efficiency, switchability, excellent processing performance and excellent optical performance, and are widely used in high-tech fields such as holographic storage, display, tunable filters, laser modulation, and augmented reality (AR). Its preparation principle is to uniformly mix monomers, liquid crystals and photoinitiators and then pour them into a liquid crystal cell with a fixed cell thickness, and then carry out photopolymerization under the action of laser coherence. In the bright areas of the laser coherence fringes, free radicals generated by the photoinitiator absorbing photons initiate the polymerization of monomers. The change in the chemical potential of the system causes phase separation between the polymer and the liquid crystal, prompting the liquid crystal molecules to diffuse from the bright areas of the coherence fringes to the dark areas, while the monomers in the dark areas diffuse to the bright areas of the coherence fringes for further polymerization, thus forming a grating structure with a periodic distribution of components and refractive indices. The above-mentioned photopolymer system based on polymer dispersed liquid crystals has the characteristics that the polymerization reaction can be controlled by light irradiation and the arrangement state of liquid crystal molecules can be adjusted, and the dispersion degree of liquid crystal molecules can also be adjusted by controlling the degree of polymerization of the polymer matrix, thereby adjusting the optical properties of the system; at the same time, after the photopolymer system is cured, the polymer matrix provides good mechanical strength and chemical stability, and has high long-term stability, so it has wide application advantages in the fields of display, modulators, optical switches, etc.

[0004] However, there are still certain challenges in applying the holographic polymer dispersed liquid crystal-based photopolymer system to the field of holographic display. For example, when preparing holographic waveguide AR lenses, since the holographic waveguide AR lenses have relatively high requirements for haze and efficiency, in order to improve the diffraction efficiency of the gratings prepared by the existing holographic polymer dispersed liquid crystal-based photopolymer system, the common countermeasure is to increase the material thickness or the amount of liquid crystal used. Increasing the material thickness can increase the thickness of the grating to increase the path length of phase change, thereby enhancing the diffraction ability of the grating. However, it will also cause an increase in the volume of the material, further introducing more light scattering and resulting in an increase in haze. When adjusting the refractive index and diffraction efficiency of the grating by increasing the liquid crystal, due to the large refractive index difference of liquid crystal molecules, an uneven refractive index distribution may be caused in the polymer substrate, thereby increasing light scattering and causing an increase in haze. Therefore, it is necessary to provide a new holographic polymer dispersed liquid crystal-based photopolymer system and a grating device with low haze and high diffraction efficiency prepared therefrom for use in AR glasses waveguide lenses. Summary of the Invention

[0005] The present invention aims to overcome at least one defect of the above-mentioned prior art, and provides a photopolymer system based on fluorinated liquid crystal and its grating device, which improves the uniformity and thermal stability of the photopolymer system, and thus maintains low haze while maintaining the high diffraction efficiency of the grating device prepared by the photopolymer system, and has excellent optical properties.

[0006] The technical solution adopted by the present invention is first to provide a photopolymer system based on fluorinated liquid crystal, which is characterized by comprising:

[0007] Solvent: 5 - 10 parts

[0008] Mixed liquid crystal: 5 - 25 parts

[0009] Photoinitiator: 0.5 - 2 parts

[0010] Co-initiator: 2 - 6 parts

[0011] First monomer: 5 - 15 parts

[0012] Second monomer: 5 - 15 parts

[0013] Third monomer: 10 - 20 parts;

[0014] The first monomer, the second monomer, and the third monomer are acrylate monomers with different functionalities;

[0015] The mixed liquid crystal includes 70% - 95% of nematic liquid crystal and 5% - 30% of fluorinated liquid crystal;

[0016] The Δε of the nematic liquid crystal is not less than 10;

[0017] Among them, the fluorinated liquid crystal has the following structural formula:

[0018] , , , , , , , , ;

[0019] Among them, Rn (n is an integer from 1 to 16) is -F or -H, Mi (i is an integer from 1 to 2) is -F or an alkyl group with 2 to 5 carbon atoms; and at least one of the groups in Rn or Mi is -F.

[0020] In this technical solution, a mixed liquid crystal is adopted in the provided photopolymer system. By adding a fluorinated liquid crystal monomer to the nematic liquid crystal, the balance and optimization of performance are achieved by adjusting the types and mixing ratios of the fluorinated liquid crystal monomer and the nematic liquid crystal monomer, improving the polarity and dielectric anisotropy of the mixed liquid crystal material, thereby improving the electro-optical performance, uniformity and stability of the overall photopolymer system, making the grating device prepared based on this photopolymer system have good optical characteristics with low haze while having a high diffraction efficiency. Specifically, the fluorinated liquid crystal used is such as fluorinated biphenyl liquid crystal, fluorinated alkyne liquid crystal and fluorinated difluoromethoxy liquid crystal. The fluorine atoms therein can increase the dipole moment, making the polarity of the liquid crystal molecules in the mixed liquid crystal increase, and then enhancing the interaction between molecules. Therefore, the dielectric anisotropy (i.e., Δε) of the mixed liquid crystal material can be improved, thereby increasing the overall polarity of the mixed liquid crystal. Further, since the fluorinated biphenyl liquid crystal molecule also has a polyaromatic ring structure and has strong conjugation, it is more conducive to improving the birefringence of the mixed liquid crystal and reducing the moment of inertia, thereby reducing the overall viscosity of the mixed liquid crystal, improving the fluidity of the mixed liquid crystal in the photopolymer system, thereby enhancing the uniformity of the liquid crystal distribution in the photopolymer system, and thus reducing the haze of the grating device prepared based on this photopolymer system; while the fluorinated difluoromethoxy liquid crystal has a difluoromethoxy group, making the mixed liquid crystal have a larger molecular polarity while maintaining a lower viscosity, thereby enhancing the dielectric anisotropy of the mixed liquid crystal in the photopolymer system and enhancing the optical modulation effect of the mixed liquid crystal, thereby improving the diffraction efficiency while reducing the haze of the grating device prepared based on this photopolymer system. Further, since the viscosity of the liquid crystal increases with the increase of the number of carbon atoms in the flexible side chain, in order to ensure the low-viscosity performance of the fluorinated liquid crystal while ensuring the length of the liquid crystal molecules and thus ensuring the normal use performance of the liquid crystal, the number of carbon atoms in the flexible side chain of the fluorinated liquid crystal molecule used is selected to be 2 to 5. Further, in order to match the fluorinated liquid crystal monomer used and achieve the balance and optimization between the diffraction efficiency and the haze performance, preferably, the Δε of the selected nematic liquid crystal is not less than 10, thereby improving the overall dielectric anisotropy of the mixed liquid crystal and enhancing the optical modulation effect of the mixed liquid crystal, thereby improving the diffraction efficiency while reducing the haze of the grating device prepared based on this photopolymer system.

[0021] Furthermore, since fluorine-containing liquid crystals with high polarity are added to the mixed liquid crystals, the compatibility of the entire mixed liquid crystal system becomes better, thereby reducing the haze of the system. Because the fluorine-containing liquid crystals will reduce the viscosity of the mixed crystals, the gel time will become longer during subsequent exposure, the grating regularity will be improved, and the diffraction efficiency will also be improved. If the dosage of the fluorine-containing liquid crystals is too low, the material compatibility may be insufficient. If the dosage is too high, it will instead change the properties of the mixed liquid crystals, which may lead to a change in the grating morphology formed subsequently. Therefore, it is controlled that the mixed liquid crystals include 70%-95% of nematic liquid crystals and 5%-30% of fluorine-containing liquid crystals, thereby improving the processing convenience while ensuring the optimization effect of the mixed liquid crystals. At the same time, by selecting a combination of three acrylate monomers with different functionalities to form an unsaturated monomer system, the degree of polymerization and crosslinking rigidity between the unsaturated monomers in the photopolymer system are improved through the crosslinking synergistic effect among the three unsaturated monomers. By adjusting the types and proportions of the added unsaturated monomers, the polymerization reaction efficiency between the monomers in the system can be adjusted in coordination with the mixed liquid crystals, and at the same time, the diffraction efficiency, haze, thermal stability and other functions of the prepared holographic volume grating device can be specifically adjusted and improved.

[0022] Preferably, in order to achieve the balance and optimization between the overall diffraction efficiency and haze performance of the photopolymer system, while reducing the haze of the grating device prepared based on this photopolymer system, the diffraction efficiency is improved; preferably, in order to achieve the performance matching between the mixed liquid crystals, thereby improving the dielectric anisotropy of the overall mixed liquid crystals and enhancing the optical modulation effect of the mixed liquid crystals, the fluorinated liquid crystal is selected from one or more of ethyl p-fluorodiphenylacetylene, 4-ethyl-2,6-difluoro-4'-(4-propylphenyl)-diphenylacetylene, propyl-3,4-difluorodiphenylacetylene, pentyl p-fluorobiphenyl, propylphenyl-2',3,4,5-tetrafluorobiphenyl, p-propyl-2,6-difluorobiphenyl-difluoromethoxy-3,4,5-trifluorobenzene; the nematic liquid crystal is E7. Further preferably, in order to match the performance of the above-mentioned mixed liquid crystals and simultaneously targetedly adjust and improve the performance of the prepared holographic volume grating device such as diffraction efficiency, haze and thermal stability, the types of the three unsaturated monomers added are selected accordingly. Specifically, the first monomer is a monofunctional monomer, selected from one or more of isobornyl methacrylate, isodecyl methacrylate, 2-phenoxyethyl methacrylate, cyclohexyl methacrylate, lauryl methacrylate, dicyclopentanyl methacrylate, benzyl methacrylate; the second monomer is a difunctional monomer, selected from one or more of ethylene glycol dimethacrylate, 4(ethoxy)bisphenol A dimethacrylate, 1,3-butanediol dimethacrylate, triethylene glycol dimethacrylate; the third monomer is one or more of the trifunctional monomer trimethylolpropane triacrylate or the tetrafunctional monomer pentaerythritol tetraacrylate. In this technical solution, the combination use of the mixed liquid crystals and the unsaturated monomers improves the diffraction efficiency, uniformity and thermal stability of the photopolymer system, while reducing the haze of the system, so that the grating device prepared from this photopolymer system has better comprehensive performance and service life. At the same time, the unsaturated monomers contained in the photopolymer system can be selected and combined from polymer monomers with different functional degrees, and the selection is diverse, and the raw materials are widely sourced and easy to obtain, which improves the production convenience and reduces the production cost while ensuring the function of the holographic volume grating device.

[0023] Further, the photoinitiator is selected from one or more of photoinitiator 184, TPO, 3,3'-carbonylbis(7-diethylaminocoumarin), rose bengal, methylene blue, rhodamine 6G, diiodofluorescein.

[0024] Further, the co-initiator is selected from one or more of N-phenylglycine, benzoyl peroxide.

[0025] Further, the solvent is selected from one or more of N-vinylpyrrolidone, chloroform, tetrahydrofuran, toluene.

[0026] The present technical solution also provides a method for preparing a grating device. The grating device is prepared by using the photopolymer system described in the present technical solution. The method for preparing the grating device includes the following steps:

[0027] S1. Add the fluorinated liquid crystal to the nematic liquid crystal, and ultrasonically mix for 20 - 40 min at 80 - 120 °C to form the mixed liquid crystal.

[0028] S2. Mix the photopolymer system containing the mixed liquid crystal prepared in step S1 evenly and pour it into a liquid crystal cell. Let it stand still in a dark room, and then perform interference exposure under the interference light field of a double-beam light source.

[0029] Optionally, the time of the interference exposure is 1 - 5 min, the irradiation power is 4 - 6 mW / cm2; and the included angle between the two double-beam light sources is 35° - 60°.

[0030] Optionally, the thickness of the liquid crystal cell is 4 - 6 μm.

[0031] Further, in step S2, the mixing step is: Place the photopolymer system containing the mixed liquid crystal prepared in step S1 in an ultrasonic instrument and ultrasonically mix evenly for 20 - 40 min at 60 °C to obtain a photopolymer mixed liquid; Pour the photopolymer mixed liquid into a liquid crystal cell under a vacuum atmosphere and let it stand still in a dark room for 1 - 2 h.

[0032] The present technical solution also provides a grating device prepared by the preparation method described in the present technical solution.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] 1. By using a mixed liquid crystal containing both nematic liquid crystal and fluorinated liquid crystal in the provided photopolymer system, the balance and optimization of performance are achieved by adjusting the types and mixing ratios of the fluorinated liquid crystal monomer and the nematic liquid crystal monomer, improving the polarity and dielectric anisotropy of the mixed liquid crystal material, thereby improving the electro-optical performance, uniformity and stability of the overall photopolymer system, making the grating device prepared based on this photopolymer system have good optical characteristics with high diffraction efficiency and low haze.

[0035] 2. The fluorine-containing liquid crystals used are fluorine-containing biphenyl liquid crystals, fluorine-containing alkyne liquid crystals, or fluorine-containing difluoromethoxy liquid crystals. The fluorine atoms can increase the dipole moment, making the polarity of the liquid crystal molecules in the mixed liquid crystal increase, and further enhancing the interaction between molecules. Therefore, the dielectric anisotropy of the mixed liquid crystal material can be improved, thereby increasing the overall polarity of the mixed liquid crystal and improving the diffraction efficiency of the photopolymer system. At the same time, since the fluorine-containing biphenyl liquid crystal molecules also have a polyaromatic ring structure, due to strong conjugation, it is more conducive to improving the birefringence of the mixed liquid crystal and reducing the moment of inertia, thereby reducing the overall viscosity of the mixed liquid crystal and improving the fluidity of the mixed liquid crystal in the photopolymer system, thus enhancing the uniformity of the liquid crystal distribution in the photopolymer system and reducing the haze of the photopolymer system based on this. And the fluorine-containing difluoromethoxy liquid crystal has a difluoromethoxy group, making the molecular polarity of the mixed liquid crystal increase while maintaining a low viscosity, thereby enhancing the dielectric anisotropy of the mixed liquid crystal in the photopolymer system and enhancing the optical modulation effect of the mixed liquid crystal, thus improving the diffraction efficiency while reducing the haze of the grating device prepared based on this photopolymer system.

[0036] 3. By selecting a nematic liquid crystal with Δε not less than 10, the nematic liquid crystal in the mixed liquid crystal used is matched with the fluorine-containing liquid crystal used, thereby improving the dielectric anisotropy of the mixed liquid crystal as a whole and enhancing the optical modulation effect of the mixed liquid crystal, achieving the balance and optimization between the diffraction efficiency and haze performance of the photopolymer system. At the same time, since a highly polar fluorine-containing liquid crystal is added to the mixed liquid crystal, the compatibility of the entire mixed liquid crystal system becomes better, thereby reducing the haze of the system. Because the fluorine-containing liquid crystal will reduce the viscosity of the mixed crystal and increase the gel time during subsequent exposure, the grating regularity is improved and the diffraction efficiency will also increase. By controlling the mixed liquid crystal to include 70%-95% of the nematic liquid crystal and 5%-30% of the fluorine-containing liquid crystal, the processing convenience is improved while ensuring the optimization effect of the mixed liquid crystal.

[0037] 4. In the provided photopolymer system, by selecting three acrylate monomers with different functionalities to form an unsaturated monomer system, by adjusting the types and proportions of the added unsaturated monomers and through the crosslinking synergistic effect among the three unsaturated monomers, the degree of polymerization and crosslinking rigidity among the unsaturated monomers in the photopolymer system are improved, thereby coordinating with the mixed liquid crystal to adjust the efficiency of the polymerization reaction among the monomers in the system, and specifically adjusting and optimizing the diffraction efficiency, haze, thermal stability and other properties of the prepared holographic volume grating device. Detailed implementation mode

[0038] 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 this application belongs.

[0039] 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 indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0040] The present invention will be further described in conjunction with specific examples. The following embodiments 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 embodiments include the following content (if the specific experimental conditions are not specified in the embodiments, they are usually in accordance with conventional conditions or the conditions recommended by the reagent company; the reagents, consumables, etc. used in the following embodiments, unless otherwise specified, can be obtained from commercial channels).

[0041] In the present invention, a mixed liquid crystal system formed by mixing fluorinated liquid crystal and nematic liquid crystal is adopted. Since the fluorinated liquid crystal molecules have a strong dipole moment and a unique electronic structure, they can enhance the response of liquid crystal molecules in an electric field through their polarity, and enhance the polarization effect of liquid crystal molecules under the action of an electric field through the electron-attracting effect of fluorine atoms, thereby increasing the Δε of the mixed liquid crystal; at the same time, due to the strong electronegativity of fluorine atoms, the intermolecular force of liquid crystal molecules is weak, and fluorinated liquid crystal molecules usually have a low viscosity. Incorporating a certain amount of fluorinated liquid crystal into nematic liquid crystal helps to improve the fluidity of the liquid crystal, thereby enhancing the electro-optical response performance of the photopolymer system in various device applications. Further, the strong bonding effect between fluorine atoms and carbon atoms (such as C-F bonds) makes fluorinated liquid crystal molecules more heat-resistant than ordinary liquid crystal molecules, so that fluorinated liquid crystal molecules have good thermal stability. At the same time, the low polarity and strong electronegativity of fluorine elements will result in a low thermal expansion coefficient of fluorinated liquid crystal, thereby reducing the size change of the liquid crystal material under thermal load. Introducing fluorinated liquid crystal monomers into nematic liquid crystal can improve the stability of the mixed liquid crystal material at higher temperatures, thereby broadening the working temperature range of the mixed liquid crystal material, and thus enhancing the service performance of the photopolymer system in various device applications.

[0042] Example 1

[0043] This embodiment provides a photopolymer system based on fluorinated liquid crystal, a grating device and a preparation method thereof. Specifically, it includes the following steps:

[0044] (1) Preparation of a photopolymer system:

[0045] S1. Add 4.5 parts of ethyl p-fluorodiphenylacetylene to 10.5 parts of E7, and ultrasonically mix for 20 - 40 min at 80 - 120 °C to form a mixed liquid crystal. Then, measure the dielectric constant of the mixed liquid crystal; among them, the Δε of E7 is 11.4 or 13.8.

[0046] S2. Weigh the raw materials from a brown sample bottle according to the following amounts: 0.5 part of 3,3'-carbonylbis(7-diethylaminocoumarin), 2 parts of N-phenylglycine, 10 parts of 2-phenoxyethyl methacrylate, 15 parts of 4-(ethoxy)bisphenol A dimethacrylate, 10 parts of trimethylolpropane triacrylate, and 7 parts of N-vinylpyrrolidone.

[0047] Place the weighed raw materials and the mixed liquid crystal prepared in step S1 in an ultrasonic instrument and ultrasonically mix for 30 min to obtain a uniformly mixed photopolymer system; subsequently, measure the viscosity of the photopolymer system at 25 °C according to GB / T22235-2008 DIN53229 "Determination of Liquid Viscosity".

[0048] (2) Preparation of a grating device:

[0049] Under vacuum conditions, fill the above photopolymer system into a liquid crystal cell with a thickness of 5 μm. After filling, move the liquid crystal cell together with the cell to a dark room and let it stand for 1 hour, then move it to an interference light field of a two-beam light source with an angle of 60° and an irradiation power of 5 mW / cm 2 and perform interference exposure for 5 min to finally obtain a grating device.

[0050] (3) Diffraction efficiency test:

[0051] The specific steps for the diffraction efficiency test are as follows: Use a grating diffraction efficiency tester to test the diffraction efficiency of the above holographic grating device.

[0052] (4) Haze test:

[0053] The specific steps for the haze test are as follows: Use a haze meter to test the haze of the obtained holographic grating device under the condition of 23 ± 2 °C according to GB 2410-2008 "Test Methods for Transmittance and Haze of Transparent Plastics".

[0054] Example 2

[0055] This example provides a photopolymer system, a grating device, and a preparation method thereof based on a fluorine-containing liquid crystal. Specifically, it includes the following steps:

[0056] (1) Preparation of a photopolymer system:

[0057] S1. Add 1.3 parts of pentyl-p-fluorobiphenyl to 23.8 parts of E7, and ultrasonically mix for 20 - 40 min at 80 - 120 °C to form a mixed liquid crystal, and then measure the dielectric constant of the mixed liquid crystal; among them, the Δε of E7 is 11.4 or 13.8;

[0058] S2. Weigh the raw materials from a brown sample bottle according to the following parts: 2 parts of photoinitiator 184, 6 parts of benzoyl peroxide, 15 parts of isobornyl methacrylate, 10 parts of ethylene glycol dimethacrylate, 15 parts of pentaerythritol tetraacrylate, and 5 parts of chloroform;

[0059] Place the weighed raw materials and the mixed liquid crystal prepared in step S1 into an ultrasonic instrument and ultrasonically mix for 30 min to obtain a uniformly mixed photopolymer system; subsequently, measure the viscosity of the photopolymer system at 25 °C according to GB / T22235 - 2008 DIN53229 "Determination of Liquid Viscosity".

[0060] (2)Preparation of a grating device:

[0061] Under vacuum conditions, fill the above photopolymer system into a liquid crystal cell with a thickness of 5 μm. After filling, move the liquid crystal cell together with the cell to a dark room and let it stand for 1 hour, and then move it to an interference light field of a double-beam light source with an included angle of 60° and an irradiation power of 5 mW / cm 2 for interference exposure for 5 min, and finally obtain a grating device.

[0062] (3)Diffraction efficiency test:

[0063] The specific steps for the diffraction efficiency test are as follows: Use a grating diffraction efficiency tester to test the diffraction efficiency of the above holographic grating device.

[0064] (4)Haze test:

[0065] The specific steps for the haze test are as follows: Use a haze meter to test the haze of the obtained holographic grating device under the condition of 23 ± 2 °C according to GB 2410 - 2008 "Test Methods for Transmittance and Haze of Transparent Plastics".

[0066] Example 3

[0067] This example provides a photopolymer system based on fluorinated liquid crystal, a grating device and a preparation method thereof. Specifically, it includes the following steps:

[0068] (1)Preparation of a photopolymer system:

[0069] S1. Add 4.5 parts of pentyl-p-fluorobiphenyl to 20.5 parts of E7, and ultrasonically mix for 20 - 40 min at 80 - 120 °C to form a mixed liquid crystal. Then, measure the dielectric constant of the mixed liquid crystal. Among them, the Δε of E7 is 11.4 or 13.8;

[0070] S2. Weigh the raw materials from a brown sample bottle according to the following parts: 1 part of TPO, 4 parts of N-phenylglycine, 12 parts of benzyl methacrylate, 13 parts of 1,3-butanediol dimethacrylate, 20 parts of pentaerythritol tetraacrylate, and 10 parts of toluene;

[0071] Place the weighed raw materials and the mixed liquid crystal prepared in step S1 into an ultrasonic instrument and ultrasonically mix for 30 min to obtain a uniformly mixed photopolymer system. Subsequently, measure the viscosity of the photopolymer system at 25 °C according to GB / T22235-2008 DIN53229 "Determination of Liquid Viscosity".

[0072] (2)Preparation of a grating device:

[0073] Under vacuum conditions, fill the above photopolymer system into a liquid crystal cell with a thickness of 5 μm. After filling, move the liquid crystal cell together with the cell to a dark room and let it stand for 1 hour. Then, move it to an interference light field of a double-beam light source with an angle of 60° and an irradiation power of 5 mW / cm 2 for interference exposure for 5 min to finally obtain a grating device.

[0074] (3)Diffraction efficiency test:

[0075] The specific steps for the diffraction efficiency test are as follows: Use a grating diffraction efficiency tester to test the diffraction efficiency of the above holographic grating device.

[0076] (4)Haze test:

[0077] The specific steps for the haze test are as follows: Use a haze meter to test the haze of the obtained holographic grating device under the condition of 23 ± 2 °C according to GB 2410-2008 "Test Methods for Transmittance and Haze of Transparent Plastics".

[0078] Comparative Example 1

[0079] This comparative example provides a photopolymer system, a grating device, and a preparation method thereof. Specifically, it includes the following steps:

[0080] (1)Preparation of a photopolymer system:

[0081] Weigh the raw materials from a brown sample bottle according to the following parts:

[0082] 0.5 parts of 3,3'-carbonylbis(7-diethylaminocoumarin), 2 parts of N-phenylglycine, 10 parts of 2-phenoxyethyl methacrylate, 15 parts of 4(ethoxy)bisphenol A dimethacrylate, 10 parts of trimethylolpropane triacrylate, 7 parts of N-vinylpyrrolidone, 15 parts of E7; among them, the Δε of E7 is 11.4;

[0083] Place the weighed raw materials above in an ultrasonic instrument and ultrasonically mix them for 30 min to obtain a uniformly mixed photopolymer system; then, measure the viscosity of the photopolymer system at 25 °C according to GB / T 22235-2008 DIN53229 "Determination of Liquid Viscosity".

[0084] (2) Preparation of a grating device:

[0085] Under vacuum conditions, fill the above photopolymer system into a liquid crystal cell with a thickness of 5 μm. After filling, move it together with the liquid crystal cell to a dark room and let it stand for 1 hour, and then move it to an interference light field of a two-beam light source with an included angle of 60° and an irradiation power of 5 mW / cm 2 for interference exposure for 5 min, and finally obtain a grating device.

[0086] (3) Diffraction efficiency test:

[0087] The specific steps of the diffraction efficiency test are as follows: Use a grating diffraction efficiency tester to test the diffraction efficiency of the above holographic grating device.

[0088] (4) Haze test:

[0089] The specific steps of the haze test are as follows: Use a haze meter to test the haze of the obtained holographic grating device under the condition of 23 ± 2 °C according to GB 2410-2008 "Test Methods for Transmittance and Haze of Transparent Plastics".

[0090] Comparative Example 2

[0091] This example provides a photopolymer system based on fluorinated liquid crystal, a grating device and a preparation method thereof. Specifically, it includes the following steps:

[0092] (1) Preparation of a photopolymer system:

[0093] S1. Add 4.5 parts of 4,7-dibromo-5,6-difluoro-benzothiadiazole to 10.5 parts of E7, and ultrasonically mix at 80-120 °C for 20-40 min to form a mixed liquid crystal, and then test the dielectric constant of the mixed liquid crystal; among them, the Δε of E7 is 11.4 or 13.8;

[0094] S2. Weigh the raw materials from the brown sample bottle in the following amounts: 0.5 part of 3,3'-carbonylbis(7-diethylaminocoumarin), 2 parts of N-phenylglycine, 10 parts of 2-phenoxyethyl methacrylate, 15 parts of 4(ethoxy)bisphenol A dimethacrylate, 10 parts of trimethylolpropane triacrylate, and 7 parts of N-vinylpyrrolidone;

[0095] Place the weighed raw materials and the mixed liquid crystal prepared in step S1 into an ultrasonic instrument and ultrasonically mix for 30 min to obtain a uniformly mixed photopolymer system; subsequently, measure the viscosity of the photopolymer system at 25 °C in accordance with GB / T22235-2008 DIN53229 Determination of the Viscosity of Liquids.

[0096] (2) Preparation of a grating device:

[0097] Under vacuum conditions, fill the above photopolymer system into a liquid crystal cell with a thickness of 5 μm. After filling, move the cell together with the liquid crystal cell to a dark room and let it stand for 1 hour, and then move it to an interference light field of a two-beam light source with an angle of 60° and an irradiation power of 5 mW / cm 2 for interference exposure for 5 min to finally obtain a grating device.

[0098] (3) Diffraction efficiency test:

[0099] The specific steps of the diffraction efficiency test are as follows: Use a grating diffraction efficiency tester to test the diffraction efficiency of the above holographic grating device.

[0100] (4) Haze test:

[0101] The specific steps of the haze test are as follows: Use a haze meter to test the haze of the obtained holographic grating device under the condition of 23 ± 2 °C in accordance with GB 2410-2008 Test Methods for Transmittance and Haze of Transparent Plastics.

[0102] Comparative Example 3

[0103] This example provides a photopolymer system based on fluorinated liquid crystal, a grating device, and a preparation method thereof. Specifically, it includes the following steps:

[0104] (1) Preparation of a photopolymer system:

[0105] S1. Add 4.5 parts of ethyl p-fluorodiphenylacetylene to 10.5 parts of E7, ultrasonically mix at 80-120 °C for 20-40 min to form a mixed liquid crystal, and then test the dielectric constant of the mixed liquid crystal; wherein, the Δε of E7 is 11.4 or 13.8;

[0106] S2. Weigh the raw materials from the brown sample bottle according to the following amounts: 0.5 parts of 3,3'-carbonylbis(7-diethylaminocoumarin), 2 parts of N-phenylglycine, 10 parts of o-phenylphenoxyethyl acrylate, 15 parts of 4-(ethoxy)bisphenol A dimethacrylate, 10 parts of trimethylolpropane triacrylate, and 7 parts of N-vinylpyrrolidone;

[0107] Place the weighed raw materials above and the mixed liquid crystal prepared in step S1 into an ultrasonic instrument and ultrasonically mix for 30 min to obtain a uniformly mixed photopolymer system; subsequently, measure the viscosity of the photopolymer system at 25 °C in accordance with GB / T 22235-2008 DIN53229 Determination of the Viscosity of Liquids.

[0108] (2) Preparation of the grating device:

[0109] Under vacuum conditions, fill the above photopolymer system into a liquid crystal cell with a thickness of 5 μm. After filling, move the liquid crystal cell together with the cell to a dark room and let it stand for 1 hour, and then move it to an interference light field of a double-beam light source with an included angle of 60° and an irradiation power of 5 mW / cm 2 for interference exposure for 5 min to finally obtain a grating device.

[0110] (3) Diffraction efficiency test:

[0111] The specific steps for the diffraction efficiency test are as follows: Use a grating diffraction efficiency tester to test the diffraction efficiency of the above holographic grating device.

[0112] (4) Haze test:

[0113] The specific steps for the haze test are as follows: Use a haze meter to test the haze of the obtained holographic grating device under the condition of 23 ± 2 °C in accordance with GB 2410-2008 Test Methods for Transmittance and Haze of Transparent Plastics.

[0114] In Examples 1 to 3, the photopolymerizable system is set to be selected and combined from the components and formulations provided in the present technical solution. While using the mixed liquid crystal material containing both fluorinated liquid crystal and nematic liquid crystal as provided by the present invention, a combination of the first monomer, the second monomer, and the third monomer with different functionalities provided by the present invention is selected to form an unsaturated monomer system. Specifically, the fluorinated liquid crystal is selected from one or more of ethyl p-fluorodiphenylacetylene, 4-ethyl-2,6-difluoro-4'-(4-propylphenyl)-diphenylacetylene, propyl-3,4-difluorodiphenylacetylene, pentyl p-fluorobiphenyl, propylphenyl-2',3,4,5-tetrafluorobiphenyl, p-propyl-2,6-difluorobiphenyl-difluoromethoxy-3,4,5-trifluorobenzene; the nematic liquid crystal is E7; the first monomer is a monofunctional monomer selected from one or more of isobornyl methacrylate, isodecyl methacrylate, 2-phenoxyethyl methacrylate, cyclohexyl methacrylate, lauryl methacrylate, dicyclopentanyl methacrylate; the second monomer is a difunctional monomer selected from ethylene glycol dimethacrylate, 4(ethoxy)bisphenol A dimethacrylate, 1,3-butanediol dimethacrylate, triethylene glycol dimethacrylate; the third monomer is one or more of the trifunctional monomer trimethylolpropane triacrylate or the tetrafunctional monomer pentaerythritol tetraacrylate. By using a mixed liquid crystal containing both nematic liquid crystal and fluorinated liquid crystal in the formed photopolymerizable system, the balance and optimization of properties are achieved by adjusting the types and mixing ratios of the fluorinated liquid crystal monomer and the nematic liquid crystal monomer, improving the polarity and dielectric anisotropy of the mixed liquid crystal material, thereby improving the electro-optical properties, uniformity, and stability of the overall photopolymerizable system, making the grating device prepared based on this photopolymerizable system have good optical characteristics with low haze while having a high diffraction efficiency; at the same time, by selecting a combination of three acrylate monomers with different functionalities to form an unsaturated monomer system, the degree of polymerization and crosslinking rigidity between the unsaturated monomers in the photopolymerizable system are increased by adjusting the types and ratios of the added unsaturated monomers and through the crosslinking synergistic effect between the three unsaturated monomers, thereby coordinating with the mixed liquid crystal to adjust the efficiency of the polymerization reaction between the monomers in the system, and specifically adjusting and optimizing the properties such as the diffraction efficiency, haze, and thermal stability of the prepared holographic volume grating device.

[0115] In the photopolymer system provided in Comparative Example 1, a fluorine-containing liquid crystal is not included, and at least one type of polymer monomer selected from the first monomer, the second monomer, or the third monomer is selected from other monomers that are not within the selection range of the first monomer, the second monomer, and the third monomer provided in this technical solution; in the photopolymer system provided in Comparative Example 2, the type of fluorine-containing liquid crystal provided in the present invention is not used, and at least one type of polymer monomer selected from the first monomer, the second monomer, or the third monomer is selected from other monomers that are not within the selection range of the first monomer, the second monomer, and the third monomer provided in this technical solution; in the photopolymer system provided in Comparative Example 3, the type of fluorine-containing liquid crystal provided in the present invention is used, and at least one type of polymer monomer selected from the first monomer, the second monomer, or the third monomer is selected from other monomers that are not within the selection range of the first monomer, the second monomer, and the third monomer provided in this technical solution.

[0116] Based on the six photopolymer systems in Examples 1 - 3 and Comparative Examples 1 - 3 and the grating devices prepared therefrom, the dielectric constant of the liquid crystal used in the photopolymer system, the overall viscosity of the photopolymer system, the diffraction efficiency and haze of the grating device are shown in the following table:

[0117]

[0118] By comparing Examples 1 - 3 with Comparative Example 1, it can be found that the results of the liquid crystal dielectric constant and viscosity of the obtained photopolymer system, as well as the diffraction efficiency and haze of the grating device prepared therefrom, show that: in the photopolymer system, adding a mixed liquid crystal containing a certain proportion of fluorine-containing liquid crystal can increase the liquid crystal dielectric constant of the mixed liquid crystal and at the same time reduce the overall viscosity of the photopolymer system, thereby improving the overall electro-optical performance, uniformity and stability of the photopolymer system, making the grating device prepared based on this photopolymer system have better optical characteristics with higher diffraction efficiency and lower haze.

[0119] By comparing Examples 1 - 3 with Comparative Examples 1 - 3, it can be found that there is a certain crosslinking synergistic effect between the mixed liquid crystal and the polymer monomer used in the photopolymer system. By selecting the types and proportions of the fluorine-containing liquid crystal and the nematic liquid crystal as in the present invention, combined with the selection of the types and proportions of the three unsaturated monomers as in the present invention, the crosslinking between the mixed liquid crystal system and the unsaturated monomers can be synergistic and cooperate with each other, so that the grating device prepared therefrom has higher diffraction efficiency and lower haze, and has better optical effects.

[0120] Obviously, the above 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, improvements, etc. 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 fluorinated liquid crystals, characterized in that: include: Solvent: 5-10 parts, Mixed liquid crystal: 5-25 parts, Photoinitiator: 0.5-2 parts, Co-initiator: 2-6 parts, First monomer: 5-15 parts, Second monomer: 5-15 parts, The third monomer: 10-20 parts; The first monomer, the second monomer, and the third monomer are acrylate monomers having different functionalities; The mixed liquid crystal includes 70%-95% nematic liquid crystal and 5%-30% fluorine-containing liquid crystal; The Δε of the nematic liquid crystal is not less than 10; The fluorine-containing liquid crystal has the following structural formula: , , , , , , , , , where R1~R 16 is -F or -H, M1-M2 is -F or an alkyl group having 2-5 carbon atoms; and at least one of R1-R4 or M1-M2 is -F; The first monomer is selected from one or more of isobornyl methacrylate, 2-phenoxyethyl methacrylate or benzyl methacrylate; The second monomer is selected from ethylene glycol dimethacrylate, 4 (ethoxy) bisphenol A dimethacrylate, 1,3-butanediol dimethacrylate, triethylene glycol dimethacrylate; The third monomer is selected from one or more of trimethylolpropane triacrylate and pentaerythritol tetraacrylate.

2. The photopolymer system according to claim 1, characterized in that The fluorine-containing liquid crystal is selected from one or more of ethyl p-fluorotolane, 4-ethyl-2,6-difluoro-4'-(4-propylphenyl)-tolane, propyl-3,4-difluorotolane, pentyl p-fluorobiphenyl, propylphenyl-2',3,4,5-tetrafluorobiphenyl, p-propyl-2,6-difluorobiphenyl-difluoromethoxy-3,4,5-trifluorobenzene; The nematic liquid crystal is E7.

3. The photopolymer system according to claim 1, characterized in that The photoinitiator is selected from one or more of photoinitiator 184, TPO, 3,3'-carbonylbis(7-diethylaminocoumarin), rose Bengal, methylene blue, rhodamine 6G, and diiodofluorescein.

4. The photopolymer system according to claim 1, characterized in that The co-initiator is selected from one or more of N-phenylglycine and benzoyl peroxide.

5. The photopolymer system according to claim 1, characterized in that The solvent is selected from one or more of N-vinyl pyrrolidone, chloroform, tetrahydrofuran and toluene.

6. A method for preparing a grating device, characterized in that: The grating device is prepared by using the photopolymer system according to any one of claims 1 to 5, and the preparation method of the grating device comprises the following steps: S1. adding the fluorine-containing liquid crystal to the nematic liquid crystal, and mixing by ultrasonication at 80-120° C. for 20-40 min to form the mixed liquid crystal; S2. The photopolymer system containing the mixed liquid crystal prepared in step S1 is mixed and poured into a liquid crystal box, which is placed still in a dark room, and then interference exposed under the interference light field of a double-beam light source.

7. The preparation method according to claim 6, characterized in that: The interference exposure time is 1-5 minutes, and the irradiation power is 4-6 mW / cm 2 ; and the angle between the dual-beam light sources is 35°-60°.

8. The preparation method according to claim 6, characterized in that: The thickness of the liquid crystal cell is 4-6 μm.

9. The preparation method according to claim 6, characterized in that: In the step S2, the mixing step is: placing the photopolymer system containing the mixed liquid crystal prepared in step S1 in an ultrasonic instrument and mixing it evenly at 60° C. for 20-40 minutes to obtain a photopolymer mixed liquid; filling the photopolymer mixed liquid into a liquid crystal box under a vacuum atmosphere, and leaving it to stand in a dark room for 1-2 hours.

10. A grating device, characterized in that: Prepared by the preparation method according to any one of claims 6 to 9.

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