Holographic polymer dispersed liquid crystal composition, holographic grating and preparation method

Abstract

The invention belongs to the technical field of optical materials, and discloses a holographic polymer dispersed liquid crystal composition, a holographic grating and a preparation method. The composition comprises the following components in parts by mass: 0.5-1.5 parts of a photoinitiator, 2-5 parts of a co-initiator, 15-20 parts of a first monomer, 15-20 parts of a second monomer, 10-15 parts of a third monomer, 10-15 parts of a solvent and 10-20 parts of mixed liquid crystal. Wherein the first monomer is a monofunctional acrylic monomer, the second monomer is a bifunctional acrylic monomer, the third monomer is a polyfunctional acrylic monomer, the mixed liquid crystal comprises 10-25 wt% of a monomer liquid crystal and 75-90 wt% of a nematic liquid crystal, and the monomer liquid crystal contains fluorine as a benzene ring substituent and contains cyano or isothiocyano as an end group. Through cooperation of the monomer liquid crystal and the nematic liquid crystal in the mixed liquid crystal and cooperation of fluorine atoms and cyano / isothiocyano groups in the monomer liquid crystal, the holographic grating prepared from the composition has the characteristics of low haze and high diffraction efficiency, and the grating can be thinner, so that the requirements of light weight and clearness of AR glasses can be met.

Description

Technical Field

[0001] This solution belongs to the field of optical materials technology, specifically involving a holographic polymer dispersed liquid crystal composition, a holographic grating, and a preparation method thereof. Background Technology

[0002] Holographic display technology is a technique 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 its color, texture, and dynamic changes. This technology has revolutionized our understanding of display technology, bringing a completely new visual experience. The core of holographic display technology lies in the creation of holograms. A hologram is created by shining a laser beam onto an object and using the principles of interference and diffraction to record the object's optical information. This information can then be reproduced as a three-dimensional image, allowing us to observe different sides of the object from different angles. This technology can be used to create various types of holograms, such as reflective, transmissive, and color holograms.

[0003] Holographic polymer-dispersed liquid crystal (H-PDLC) gratings are a product of combining holographic technology with polymer-dispersed liquid crystals. They are structurally ordered optoelectronic information materials and devices composed of periodically arranged polymer-rich and liquid-rich phases, exhibiting high efficiency, switchability, excellent processing performance, and superior optical properties. They are widely used in high-tech fields such as holographic storage, displays, tunable filters, modulated lasers, and augmented reality (AR). The fabrication principle involves uniformly mixing monomers, liquid crystals, and photoinitiators, then injecting the mixture into a liquid crystal cell of fixed thickness. Photopolymerization then occurs under laser coherence. In the bright regions of the laser coherence fringes, the photoinitiator absorbs photons, generating free radicals that initiate monomer polymerization. Changes in the system's chemical potential cause phase separation between the polymer and liquid crystal, promoting the diffusion of liquid crystal molecules from the bright to the dark regions of the coherence fringes. Simultaneously, monomers from the dark regions diffuse into the bright regions of the coherence fringes for further polymerization, thus forming a grating structure with a periodic distribution of composition and refractive index.

[0004] The holographic waveguide AR lenses fabricated using this technology have high requirements for haze and efficiency. However, existing photocurable polymer gratings, in order to improve diffraction efficiency, have increased material thickness and added a lot of liquid crystal, resulting in high grating haze. Therefore, we need a new liquid crystal composition to fabricate gratings with low haze and high diffraction efficiency for use in AR glasses waveguide lenses. Summary of the Invention

[0005] This solution aims to overcome at least one defect in the prior art and provide a holographic polymer-dispersed liquid crystal composition to solve the problem of the difficulty in achieving both high diffraction rate and low haze.

[0006] To solve the above-mentioned technical problems, the following technical solution is adopted: In a first aspect, a holographic polymer-dispersed liquid crystal composition is proposed. By mass parts, the composition comprises 0.5–1.5 parts photoinitiator, 2–5 parts co-initiator, 15–20 parts first monomer, 15–20 parts second monomer, 10–15 parts third monomer, 10–15 parts solvent, and 10–20 parts mixed liquid crystal. The first monomer is a monofunctional acrylic monomer, the second monomer is a difunctional acrylic monomer, and the third monomer is a polyfunctional acrylic monomer. The mixed liquid crystal comprises 10–25 wt% monomeric liquid crystal and 75–90 wt% nematic liquid crystal. The monomeric liquid crystal contains fluorine as a benzene ring substituent and cyano or isothiocyano as a terminal group.

[0007] This composition formulation utilizes a mixed liquid crystal system containing monomeric liquid crystals and nematic liquid crystals to form a photopolymer system. The monomeric liquid crystals contain fluorine and either cyano or isothiocyano groups. The fluorine atoms, cyano groups, and isothiocyano groups can increase the dipole moment, thereby increasing the polarity of the liquid crystal molecules in the mixed liquid crystal (especially -CN and -NCS, increasing the Hammett constant σ). p The concentrations of fluorine atoms in the mixed liquid crystal are 0.66 and 0.9 respectively, which enhances the intermolecular interactions and thus improves the dielectric anisotropy (Δε) of the mixed liquid crystal material, thereby increasing the overall polarity of the mixed liquid crystal. Only when the end group is -CN or -NCS and the fluorine atom is located on the benzene ring can the effects of the fluorine atom and the cyano or isothiocyano groups be simultaneously utilized to achieve high Δε, narrowing the liquid crystal domain size distribution during photo-induced phase separation and thus improving grating performance. Furthermore, the fluorine atom can enhance the optical modulation effect of the mixed liquid crystal, thereby reducing the haze of the grating prepared based on this photopolymer system while improving diffraction efficiency. The combination of monomeric liquid crystals and nematic liquid crystals in the mixed liquid crystal, and the combination of fluorine atoms and cyano / isothiocyano groups in the monomeric liquid crystal, allows the grating prepared based on this photopolymer system to possess both low haze and high diffraction efficiency. Moreover, the grating thickness can be made thinner; even with a thickness reduced to 3 micrometers, the haze and diffraction efficiency can reach the level of commercially available 10-20 micrometer thick grating products, thus meeting the requirements of lightweight and high clarity for AR glasses.

[0008] Preferably, the monomer liquid crystal is selected from one of the following: biphenyl liquid crystals containing fluorine and cyano or isothiocyanate, difluoromethoxy liquid crystals containing fluorine and cyano or isothiocyanate, and acetylene liquid crystals containing fluorine and cyano or isothiocyanate.

[0009] More preferably, the monomeric liquid crystal is selected from , , , , or Among them, R1~R 16 M1 to M2 are -F or -H, and M1 to M2 are -CN, -NCS, -F, or alkyl groups with 2 to 4 carbon atoms. At least one of M1 to M2 is -CN or -NCS. R1 to R 16 Or at least one of M1~M2 is -F.

[0010] More preferably, the monomeric liquid crystal is selected from one of propylphenyl-2'-fluoro-4-cyanobiphenyl, p-ethyl-2,6-difluorobiphenyl-difluoromethoxy-4-cyano-3,5-difluorobenzene, and propylphenyl-2,3-difluoro-p-isothiocyanodiphenylacetylene.

[0011] Preferably, the Δε of the nematic liquid crystal is greater than 10, for example, E7 (Δε is 11.4). Nematic liquid crystals with Δε not less than 10 are better matched with the above-mentioned monomeric liquid crystals, improving the overall dielectric anisotropy of the mixed liquid crystal and enhancing the optical modulation effect of the mixed liquid crystal. This reduces the haze of the grating prepared based on this photopolymer system while improving the diffraction efficiency, achieving a balance and optimization between diffraction efficiency and haze performance.

[0012] Preferably, the first monomer is selected from one or more of cyclohexyl methacrylate, lauryl methacrylate, isodecyl methacrylate, isooctyl acrylate, butyl acrylate, methyl acrylate, benzyl methacrylate, 2-phenoxyethyl methacrylate, dicyclopentyl methacrylate, and isobornyl methacrylate.

[0013] Preferably, the second monomer is selected from one or more of 4-(ethoxy)bisphenol A dimethacrylate, triethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, and ethylene glycol dimethacrylate.

[0014] Preferably, the third monomer is selected from one or two of pentaerythritol triacrylate, pentaerythritol tetraacrylate, trimethylolpropane triacrylate, and hyperbranched acrylate.

[0015] Preferably, the photoinitiator is selected from one of the following: Bengal rose red, diiodofluorescein, methylene blue, TPO, rhodamine 6G, 3,3'-carbonylbis(7-diethylaminocoumarin), and 184.

[0016] Preferably, the co-initiator is selected from benzoyl peroxide and N-phenylglycine.

[0017] Preferably, the solvent is selected from one or more of N-vinylpyrrolidone, chloroform, tetrahydrofuran, and toluene.

[0018] Secondly, a low-haze, high-diffraction-efficiency holographic grating is proposed. This grating is prepared using the aforementioned holographic polymer-dispersed liquid crystal composition, which improves diffraction efficiency and reduces haze, thereby achieving clarity. It can also be made thinner, thus achieving weight reduction.

[0019] Preferably, the thickness of the holographic grating is 3 μm.

[0020] Thirdly, a method for fabricating the aforementioned low-haze, high-diffraction-efficiency holographic grating is proposed. This method includes the following steps: S1. Add the monomeric liquid crystal to the nematic liquid crystal and mix them evenly to form a mixed liquid crystal; S2. After thoroughly mixing the mixed liquid crystal with other components, pour it into a liquid crystal cell; S3. Place the filled liquid crystal cell in a dark room and let it stand. S4. Expose the settled liquid crystal cell in the interference light field of a dual-beam light source.

[0021] Preferably, the monomeric liquid crystal and the nematic liquid crystal are mixed uniformly by ultrasonication at 100±20℃ for 30±10 minutes.

[0022] Optionally, the mixed liquid crystal is mixed evenly with other components using an ultrasonic dispersion device.

[0023] Preferably, the thickness of the liquid crystal cell is controlled at 3μm.

[0024] Preferably, the liquid crystal cell is left to stand in the dark room for 1 to 2 hours.

[0025] Preferably, the exposure time of the liquid crystal cell in the interference light field is 1 to 5 minutes.

[0026] Preferably, the included angle between the two beam light sources is 35~60°.

[0027] Preferably, the illumination power of the dual-beam light source is 5±1mW / cm². 2 .

[0028] Fourthly, a waveguide lens is proposed. This waveguide lens contains the aforementioned low-haze, high-diffraction-efficiency holographic grating, which can be used to manufacture AR glasses to achieve both clarity and lightweight design.

[0029] Compared with existing technologies, this solution has the following advantages: The liquid crystal component in this solution adopts a mixed liquid crystal containing monomeric liquid crystal and nematic liquid crystal. The combination of monomeric liquid crystal and nematic liquid crystal in the mixed liquid crystal, as well as the synergy between fluorine atoms and cyano / isothiocyano groups in the monomeric liquid crystal, reduces the haze of the grating prepared based on this photopolymer system and improves the diffraction efficiency. It has the characteristics of low haze and high diffraction efficiency. Moreover, the grating thickness can be made thinner. Even if the thickness is reduced to 3 micrometers, the haze and diffraction efficiency can reach the level of grating products with a thickness of 10 to 20 micrometers in the market. Therefore, it can meet the requirements of lightweight and clear AR glasses. Detailed Implementation

[0030] To enable those skilled in the art to better understand this solution, the following detailed description is provided in conjunction with specific embodiments. Unless otherwise specified, the process methods used in the embodiments are conventional methods; and unless otherwise specified, the materials used are commercially available.

[0031] Among them, TPO, 3,3'-carbonylbis(7-diethylaminocoumarin), 184, benzoyl peroxide, and N-phenylglycine were purchased from Shanghai Maclean's Co., Ltd.; benzyl methacrylate, 2-phenoxyethyl methacrylate, isobornyl methacrylate, 4(ethoxy)bisphenol A dimethacrylate, 1,3-butanediol dimethacrylate, ethylene glycol dimethacrylate, pentaerythritol tetraacrylate, and trimethylolpropane triacrylate were purchased from Changxing Chemical; N-vinylpyrrolidone, chloroform, tetrahydrofuran, and toluene were purchased from Sinopharm Chemical Reagent Co., Ltd.; propylphenyl-2'-fluoro-4-cyanobiphenyl, p-ethyl-2,6-difluorobiphenyl-difluoromethoxy-4-cyano-3,5-difluorobenzene, and propylphenyl-2,3-difluoro-p-isothiocyanodiphenylacetylene were purchased from Hubei Weishi Chemical Reagent Co., Ltd.; and E7 was purchased from Merck.

[0032] Example 1 The holographic polymer-dispersed liquid crystal composition of this embodiment comprises, by weight parts: 0.5 parts of 3,3'-carbonylbis(7-diethylaminocoumarin), 2 parts of N-phenylglycine, 15 parts of 2-phenoxyethyl methacrylate, 20 parts of 4-(ethoxy)bisphenol A dimethacrylate, 10 parts of trimethylolpropane triacrylate, 12 parts of N-vinylpyrrolidone, 3 parts of propylphenyl-2'-fluoro-4-cyanobiphenyl and 12 parts of E7 (Δε is 11.4).

[0033] Three parts of propylphenyl-2'-fluoro-4-cyanobiphenyl were added to 12 parts of E7 and mixed by ultrasonication at 100°C for 30 minutes to form a mixed liquid crystal. The dielectric constant of the mixed liquid crystal was then obtained by a dielectric constant tester, and the results are shown in Table 1. The mixed liquid crystal and the remaining components in the composition were placed in an ultrasonic instrument and ultrasonically mixed for 30 minutes. The viscosity at 25°C was measured according to GB / T22235-2008 DIN53229 "Determination of Viscosity of Liquids", and the results are shown in Table 1. Under vacuum conditions, the homogenized composition was poured into a liquid crystal cell with a thickness of 3 μm. After pouring, the liquid crystal cell and the mixture were moved to a dark room and left to stand for 1 hour. Then, the mixture was moved to an irradiation chamber with an angle of 60° and an irradiation power of 5 mW / cm². 2 The holographic grating was obtained by interferometry exposure for 5 minutes in the interference field of a dual-beam light source. The diffraction efficiency of the obtained holographic grating was tested using a grating diffraction efficiency tester, and the haze of the obtained holographic grating was tested using a haze meter at 23±2℃ according to GB2410-2008 "Test Methods for Transmittance and Haze of Transparent Plastics". The results are shown in Table 1.

[0034] Example 2 The holographic polymer-dispersed liquid crystal composition of this embodiment comprises, by weight parts: 1.5 parts photoinitiator 184, 5 parts benzoyl peroxide, 20 parts isobornyl methacrylate, 15 parts ethylene glycol dimethacrylate, 13 parts pentaerythritol tetraacrylate, 10 parts chloroform, 2 parts propylphenyl-2,3-difluoro-p-isothiocyanodiphenylacetylene and 18 parts E7 (Δε is 11.4).

[0035] Two parts of propylphenyl-2,3-difluoro-p-isothiocyanodiphenylacetylene were added to 18 parts of E7 and mixed by ultrasonication at 100°C for 30 minutes to form a mixed liquid crystal. The dielectric constant of the mixed liquid crystal was then obtained by a dielectric constant tester, and the results are shown in Table 1. The mixed liquid crystal and the remaining components in the composition were placed in an ultrasonic instrument and ultrasonically mixed for 30 minutes. The viscosity at 25°C was measured according to GB / T22235 2008 DIN53229 "Determination of Viscosity of Liquids", and the results are shown in Table 1. Under vacuum conditions, the homogenized composition was poured into a liquid crystal cell with a thickness of 3 μm. After pouring, the liquid crystal cell and the mixture were moved to a dark room and left to stand for 1 hour. Then, the mixture was moved to an irradiation chamber with an angle of 60° and an irradiation power of 5 mW / cm². 2 The holographic grating was obtained by interferometry exposure for 5 minutes in the interference field of a dual-beam light source. The diffraction efficiency of the obtained holographic grating was tested using a grating diffraction efficiency tester, and the haze of the obtained holographic grating was tested using a haze meter at 23±2℃ according to GB 2410-2008 "Test Methods for Transmittance and Haze of Transparent Plastics". The results are shown in Table 1.

[0036] Example 3 The holographic polymer-dispersed liquid crystal composition of this embodiment comprises, by weight parts: 1 part TPO, 4 parts N-phenylglycine, 17 parts benzyl methacrylate, 18 parts 1,3-butanediol dimethacrylate, 15 parts pentaerythritol tetraacrylate, 15 parts toluene, 1.5 parts p-ethyl-2,6-difluorobiphenyl-difluoromethoxy-4-cyano-3,5-difluorobenzene, and 8.5 parts E7 (Δε is 11.4).

[0037] 1.5 parts of p-ethyl-2,6-difluorobiphenyl-difluoromethoxy-4-cyano-3,5-difluorobenzene were added to 8.5 parts of E7 and mixed by ultrasonication at 100°C for 30 minutes to form a mixed liquid crystal. The dielectric constant of the mixed liquid crystal was then obtained by a dielectric constant tester, and the results are shown in Table 1. The mixed liquid crystal and the remaining components in the composition were placed in an ultrasonic instrument and ultrasonically mixed for 30 minutes. The viscosity at 25°C was measured according to GB / T22235 2008 DIN53229 "Determination of viscosity of liquids", and the results are shown in Table 1. Under vacuum conditions, the homogenized composition was poured into a liquid crystal cell with a thickness of 3 μm. After pouring, the liquid crystal cell and the mixture were moved to a dark room and left to stand for 1 hour. Then, the mixture was moved to an irradiation chamber with an angle of 60° and an irradiation power of 5 mW / cm². 2 The holographic grating was obtained by interferometry exposure for 5 minutes in the interference field of a dual-beam light source. The diffraction efficiency of the obtained holographic grating was tested using a grating diffraction efficiency tester, and the haze of the obtained holographic grating was tested using a haze meter at 23±2℃ according to GB 2410-2008 "Test Methods for Transmittance and Haze of Transparent Plastics". The results are shown in Table 1.

[0038] Example 4 The holographic polymer-dispersed liquid crystal composition of this embodiment comprises, by weight parts: 0.5 parts of 3,3'-carbonylbis(7-diethylaminocoumarin), 2 parts of N-phenylglycine, 15 parts of 2-phenoxyethyl methacrylate, 20 parts of 4-(ethoxy)bisphenol A dimethacrylate, 10 parts of trimethylolpropane triacrylate, 12 parts of N-vinylpyrrolidone, 3 parts of propylphenyl-2'-fluoro-4-cyanobiphenyl and 12 parts of E7 (Δε is 11.4).

[0039] Three parts of propylphenyl-2'-fluoro-4-cyanobiphenyl were added to 12 parts of E7 and mixed by ultrasonication at 100°C for 30 minutes to form a mixed liquid crystal. The dielectric constant of the mixed liquid crystal was then obtained by a dielectric constant tester, and the results are shown in Table 1. The mixed liquid crystal and the remaining components in the composition were placed in an ultrasonic instrument and ultrasonically mixed for 30 minutes. The viscosity at 25°C was measured according to GB / T22235-2008 DIN53229 "Determination of Viscosity of Liquids", and the results are shown in Table 1. Under vacuum conditions, the homogenized composition was poured into a liquid crystal cell with a thickness of 10 μm. After pouring, the liquid crystal cell and the mixture were moved to a dark room and left to stand for 1 hour. Then, the mixture was moved to an irradiation chamber with an angle of 60° and an irradiation power of 5 mW / cm². 2 The holographic grating was obtained by interferometry exposure for 5 minutes in the interference field of a dual-beam light source. The diffraction efficiency of the obtained holographic grating was tested using a grating diffraction efficiency tester, and the haze of the obtained holographic grating was tested using a haze meter at 23±2℃ according to GB2410-2008 "Test Methods for Transmittance and Haze of Transparent Plastics". The results are shown in Table 1.

[0040] Comparative Example 1 The holographic polymer-dispersed liquid crystal composition of this comparative example comprises, by weight parts: 0.5 parts of 3,3'-carbonylbis(7-diethylaminocoumarin), 2 parts of N-phenylglycine, 15 parts of 2-phenoxyethyl methacrylate, 20 parts of 4-(ethoxy)bisphenol A dimethacrylate, 10 parts of trimethylolpropane triacrylate, 12 parts of N-vinylpyrrolidone, and 15 parts of E7 (Δε = 11.4).

[0041] All components of the above composition were ultrasonically mixed for 30 minutes. The viscosity at 25°C was measured according to GB / T22235-2008 and DIN53229 "Determination of Viscosity of Liquids". The results are shown in Table 1. The homogenized composition was then poured into a 3μm thick liquid crystal cell under vacuum. After pouring, the cell and liquid crystal cell were moved to a dark room and allowed to stand for 1 hour. Then, the mixture was moved to an irradiation chamber at a 60° angle with an irradiation power of 5mW / cm². 2 The holographic grating was obtained by interferometry exposure for 5 minutes in the interference field of a dual-beam light source. The diffraction efficiency of the obtained holographic grating was tested using a grating diffraction efficiency tester, and the haze of the obtained holographic grating was tested using a haze meter at 23±2℃ according to GB2410-2008 "Test Methods for Transmittance and Haze of Transparent Plastics". The results are shown in Table 1.

[0042] Comparative Example 2 The holographic polymer-dispersed liquid crystal composition of this comparative example comprises, by weight parts: 0.5 parts of 3,3'-carbonylbis(7-diethylaminocoumarin), 2 parts of N-phenylglycine, 15 parts of 2-phenoxyethyl methacrylate, 20 parts of 4-(ethoxy)bisphenol A dimethacrylate, 10 parts of trimethylolpropane triacrylate, 12 parts of N-vinylpyrrolidone, 3 parts of propylphenyl-4-cyanobiphenyl and 12 parts of E7 (Δε = 11.4).

[0043] Three parts of propylphenyl-4-cyanobiphenyl were added to 12 parts of E7 and ultrasonically mixed at 100°C for 30 minutes to form a mixed liquid crystal. The dielectric constant of the mixed liquid crystal was then obtained using a dielectric constant tester, and the results are shown in Table 1. The mixed liquid crystal and the remaining components in the composition were ultrasonically mixed for 30 minutes. The viscosity at 25°C was measured according to GB / T22235 2008 DIN53229 "Determination of Viscosity of Liquids", and the results are shown in Table 1. Under vacuum conditions, the homogeneous composition was poured into a liquid crystal cell with a thickness of 3 μm. After pouring, the liquid crystal cell and the mixture were moved to a dark room and left to stand for 1 hour. Then, the mixture was moved to an irradiation chamber at an angle of 60° and an irradiation power of 5 mW / cm². 2 The holographic grating was obtained by interferometry exposure for 5 minutes in the interference field of a dual-beam light source. The diffraction efficiency of the obtained holographic grating was tested using a grating diffraction efficiency tester, and the haze of the obtained holographic grating was tested using a haze meter at 23±2℃ according to GB 2410-2008 "Test Methods for Transmittance and Haze of Transparent Plastics". The results are shown in Table 1.

[0044] Comparative Example 3 The holographic polymer-dispersed liquid crystal composition of this comparative example comprises, by weight parts: 0.5 parts of 3,3'-carbonylbis(7-diethylaminocoumarin), 2 parts of N-phenylglycine, 15 parts of 2-phenoxyethyl methacrylate, 20 parts of 4-(ethoxy)bisphenol A dimethacrylate, 10 parts of trimethylolpropane triacrylate, 12 parts of N-vinylpyrrolidone, 3 parts of propylphenyl-2'-fluorobiphenyl and 12 parts of E7 (Δε = 11.4).

[0045] Three parts of propylphenyl-2'-fluorobiphenyl were added to 12 parts of E7 and ultrasonically mixed at 100°C for 30 minutes to form a mixed liquid crystal. The dielectric constant of the mixed liquid crystal was then obtained using a dielectric constant tester, and the results are shown in Table 1. The mixed liquid crystal and the remaining components in the composition were ultrasonically mixed for 30 minutes. The viscosity at 25°C was measured according to GB / T22235 2008 DIN53229 "Determination of Viscosity of Liquids", and the results are shown in Table 1. Under vacuum conditions, the homogenized composition was poured into a liquid crystal cell with a thickness of 3 μm. After pouring, the liquid crystal cell and the mixture were moved to a dark room and left to stand for 1 hour. Then, the mixture was moved to an irradiation chamber with an angle of 60° and an irradiation power of 5 mW / cm².2 The holographic grating was obtained by interferometry exposure for 5 minutes in the interference field of a dual-beam light source. The diffraction efficiency of the obtained holographic grating was tested using a grating diffraction efficiency tester, and the haze of the obtained holographic grating was tested using a haze meter at 23±2℃ according to GB 2410-2008 "Test Methods for Transmittance and Haze of Transparent Plastics". The results are shown in Table 1.

[0046] Comparative Example 4 The holographic polymer-dispersed liquid crystal composition of this comparative example comprises, by weight parts: 0.5 parts of 3,3'-carbonylbis(7-diethylaminocoumarin), 2 parts of N-phenylglycine, 15 parts of o-phenylphenoxyethyl acrylate, 20 parts of 4-(ethoxy)bisphenol A dimethacrylate, 10 parts of trimethylolpropane triacrylate, 12 parts of N-vinylpyrrolidone, 3 parts of propylphenyl-2'-fluoro-4-cyanobiphenyl and 12 parts of E7 (Δε = 11.4).

[0047] Three parts of propylphenyl-2'-fluoro-4-cyanobiphenyl were added to 12 parts of E7 and mixed by ultrasonication at 100°C for 30 minutes to form a mixed liquid crystal. The dielectric constant of the mixed liquid crystal was then obtained by a dielectric constant tester, and the results are shown in Table 1. The mixed liquid crystal and the remaining components in the composition were placed in an ultrasonic instrument and ultrasonically mixed for 30 minutes. The viscosity at 25°C was measured according to GB / T22235-2008 DIN53229 "Determination of Viscosity of Liquids", and the results are shown in Table 1. Under vacuum conditions, the homogenized composition was poured into a liquid crystal cell with a thickness of 3 μm. After pouring, the liquid crystal cell and the mixture were moved to a dark room and left to stand for 1 hour. Then, the mixture was moved to an irradiation chamber with an angle of 60° and an irradiation power of 5 mW / cm². 2 The holographic grating was obtained by interferometry exposure for 5 minutes in the interference field of a dual-beam light source. The diffraction efficiency of the obtained holographic grating was tested using a grating diffraction efficiency tester, and the haze of the obtained holographic grating was tested using a haze meter at 23±2℃ according to GB2410-2008 "Test Methods for Transmittance and Haze of Transparent Plastics". The results are shown in Table 1.

[0048] Comparative Example 5 The holographic polymer-dispersed liquid crystal composition of this comparative example comprises, by weight parts: 0.5 parts of 3,3'-carbonylbis(7-diethylaminocoumarin), 2 parts of N-phenylglycine, 15 parts of 2-phenoxyethyl methacrylate, 20 parts of 4-(ethoxy)bisphenol A dimethacrylate, 10 parts of trimethylolpropane triacrylate, 12 parts of N-vinylpyrrolidone, 3 parts of propylphenyl-2'-fluoro-4-cyanobiphenyl and 12 parts of E7 (Δε = 11.4).

[0049] 1.5 parts of 4-hydroxy-4'-nitrobiphenyl and 1.5 parts of propylphenyl-4-cyanobiphenyl were added to 12 parts of E7 and mixed by ultrasonication at 100°C for 30 minutes to form a mixed liquid crystal. The dielectric constant of the mixed liquid crystal was then obtained by a dielectric constant tester, and the results are shown in Table 1. The mixed liquid crystal and the remaining components in the composition were placed in an ultrasonic instrument and ultrasonically mixed for 30 minutes. The viscosity at 25°C was measured according to GB / T22235 2008 DIN53229 "Determination of viscosity of liquids", and the results are shown in Table 1. Under vacuum conditions, the homogenized composition was poured into a liquid crystal cell with a thickness of 3 μm. After pouring, the liquid crystal cell was moved to a dark room and left to stand for 1 hour. Then, it was moved to an irradiation chamber with an angle of 60° and an irradiation power of 5 mW / cm². 2 The holographic grating was obtained by interferometry exposure for 5 minutes in the interference field of a dual-beam light source. The diffraction efficiency of the obtained holographic grating was tested using a grating diffraction efficiency tester, and the haze of the obtained holographic grating was tested using a haze meter at 23±2℃ according to GB 2410-2008 "Test Methods for Transmittance and Haze of Transparent Plastics". The results are shown in Table 1.

[0050] Table 1. Test results of Examples 1-4 and Comparative Examples 1-5

[0051] As shown in Example 4, the grating (10 μm thick) fabricated using this composition achieves a diffraction efficiency of 91% and a haze of only 3.8%. Both the haze and diffraction efficiency are superior to the corresponding specifications of commercially available 10 μm thick grating products (50% diffraction efficiency, 8% haze). As shown in Examples 1-3, even when the grating thickness is reduced to 3 μm, the diffraction efficiency can still basically reach the level of commercially available products, while the haze is significantly reduced.

[0052] Obviously, the above embodiments of this solution are merely examples for clearly illustrating this solution, and are not intended to limit the implementation of this solution. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this solution should be included within the scope of protection of the claims of this solution.

Claims

1. A holographic polymer-dispersed liquid crystal composition, characterized in that, The composition comprises, by weight parts, 0.5 to 1.5 parts of photoinitiator, 2 to 5 parts of co-initiator, 15 to 20 parts of first monomer, 15 to 20 parts of second monomer, 10 to 15 parts of third monomer, 10 to 15 parts of solvent, and 10 to 20 parts of mixed liquid crystal, wherein the first monomer is a monofunctional acrylic monomer, the second monomer is a difunctional acrylic monomer, the third monomer is a polyfunctional acrylic monomer, and the mixed liquid crystal comprises 10 to 25 wt% of monomeric liquid crystal and 75 to 90 wt% of nematic liquid crystal, wherein the monomeric liquid crystal contains fluorine as a benzene ring substituent and cyano or isothiocyano as a terminal group.

2. The holographic polymer-dispersed liquid crystal composition according to claim 1, characterized in that, The monomer liquid crystal is selected from one of the following: biphenyl liquid crystals containing fluorine and cyano or isothiocyanate, difluoromethoxy liquid crystals containing fluorine and cyano or isothiocyanate, and acetylene liquid crystals containing fluorine and cyano or isothiocyanate.

3. The holographic polymer-dispersed liquid crystal composition according to claim 2, characterized in that, The monomeric liquid crystal is selected from , , , , or Where R1~R 16 M1 to M2 are -F or -H, and M1 to M2 are -CN, -NCS, -F, or alkyl groups with 2 to 4 carbon atoms. At least one of M1 to M2 is -CN or -NCS. R1 to R 16 Or at least one of M1~M2 is -F.

4. The holographic polymer-dispersed liquid crystal composition according to claim 2, characterized in that, The monomeric liquid crystal is selected from one of ethylphenyl-2,3-difluoro-p-cyanodiphenylacetylene, propylphenyl-2'-fluoro-4-cyanobiphenyl, propylphenyl-3'-fluoro-4-cyanobiphenyl, p-ethyl-2,6-difluorobiphenyl-difluoromethoxy-4-cyano-3,5-difluorobenzene, and propylphenyl-2,3-difluoro-p-isothiocyanodiphenylacetylene.

5. The holographic polymer-dispersed liquid crystal composition according to any one of claims 1 to 4, characterized in that, The Δε of the nematic liquid crystal is greater than or equal to 10.

6. The holographic polymer-dispersed liquid crystal composition according to any one of claims 1 to 4, characterized in that, The first monomer is selected from one or more of cyclohexyl methacrylate, lauryl methacrylate, isodecyl methacrylate, isooctyl acrylate, butyl acrylate, methyl acrylate, benzyl methacrylate, 2-phenoxyethyl methacrylate, dicyclopentyl methacrylate, and isobornyl methacrylate; and / or The second monomer is selected from one or more of 4-(ethoxy)bisphenol A dimethacrylate, triethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, and ethylene glycol dimethacrylate; and / or The third monomer is selected from one or two of pentaerythritol triacrylate, pentaerythritol tetraacrylate, trimethylolpropane triacrylate, and hyperbranched acrylate.

7. The holographic polymer-dispersed liquid crystal composition according to any one of claims 1 to 4, characterized in that, The photoinitiator is selected from one of the following: Bengal rose red, diiodofluorescein, methylene blue, TPO, rhodamine 6G, 3,3'-carbonylbis(7-diethylaminocoumarin), and 184; and / or The co-initiator is selected from benzoyl peroxide, N-phenylglycine; and / or The solvent is selected from one or more of N-vinylpyrrolidone, chloroform, tetrahydrofuran, and toluene.

8. A holographic grating, characterized in that, The holographic grating is prepared from the holographic polymer dispersed liquid crystal composition according to any one of claims 1 to 7.

9. A method for preparing the holographic grating of claim 8, characterized in that, The method includes the following steps: S1. Add the monomeric liquid crystal to the nematic liquid crystal and mix them evenly to form a mixed liquid crystal; S2. After thoroughly mixing the mixed liquid crystal with other components, pour it into a liquid crystal cell; S3. Place the filled liquid crystal cell in a dark room and let it stand. S4. Expose the settled liquid crystal cell in the interference light field of a dual-beam light source.

10. The method for fabricating a holographic grating according to claim 9, characterized in that, The monomeric liquid crystal and the nematic liquid crystal are mixed uniformly by ultrasonication at 100±20℃ for 30±10 minutes; and / or The mixed liquid crystal is mixed evenly with other components using an ultrasonic dispersion device; and / or The thickness of the liquid crystal cell is controlled at 3μm; and / or The liquid crystal cell is left to stand in the dark room for 1-2 hours; and / or The exposure time of the liquid crystal cell in the interference light field is 1-5 minutes; and / or The included angle of the dual-beam light source is 35~60°; and / or The illumination power of the dual-beam light source is 5±1mW / cm². 2 .

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