A polymerizable liquid crystal composition, a liquid crystal display grating and a liquid crystal display

Abstract

The application relates to the technical field of liquid crystal display, in particular to a polymerizable liquid crystal composition, a liquid crystal display grating and a liquid crystal display. The composition comprises an A component and a B component; the A component comprises 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin 0.5%-1% and a first solvent in the rest; the B component comprises high-bending liquid crystal 10%-15%, a second solvent 74.5%-83%, a chiral agent 2.0%-5.0%, a photoinitiator 3%-5% and a leveling agent 0.1%-0.5% in percentage by mass. The scheme provided by the application can solve the industry pain point that the ordinary photo-alignment system cannot effectively anchor the high-bending rigid liquid crystal by matching 7-[[[6-(methacryloyl)oxy]hexyl]oxy]-coumarin photo-alignment agent with high-bending rigid liquid crystal monomers, and can adapt to in-situ curing and micro-area patterning process, thereby providing a material basis with excellent adaptability for the preparation of AR optical waveguide, high-bending liquid crystal display and other high-end optoelectronic devices.

Description

Technical Field

[0001] This application relates to the field of liquid crystal display technology, and in particular to a polymerizable liquid crystal composition, a liquid crystal display grating, and a liquid crystal display. Background Technology

[0002] Traditional liquid crystal displays (LCDs) typically employ a polyimide (PI) triboelectric process to induce liquid crystal molecule alignment. This process suffers from inherent drawbacks, including susceptibility to static electricity generation, dust contamination, difficulty in adapting to flexible substrates, and inability to achieve complex micro-area patterning. Consequently, it fails to meet the fabrication requirements of next-generation high-end optoelectronic devices such as AR / VR displays and polarizing holographic gratings. Optical alignment technology, as a non-contact, high-precision, and patternable alignment technique, has become one of the key core technologies in the next-generation optoelectronic display field.

[0003] Currently, most commercially available photoalignment materials are polymers with azobenzene (such as the SD1 and BY series) or cinnamate groups in their side chains. Among them, azobenzene materials rely on photoinduced cis-trans isomerization to achieve orientation. They have a highly flexible molecular structure but limited orientation order. When applied to rigid high-refractive-index (high-refractive-index) liquid crystal systems, they cannot provide sufficient surface anchoring to overcome the rigid alignment resistance of high-refractive-index liquid crystals, making it difficult to induce high-refractive-index liquid crystal molecules to form a uniform torsional arrangement. Furthermore, the photoisomerization process of azobenzene is reversible, resulting in poor orientation thermal stability and easy failure after long-term use. Although cinnamate materials can achieve irreversible orientation through crosslinking, they generally have weak alignment forces and poor compatibility with high-refractive-index liquid crystals, making them unsuitable for the application requirements of high-refractive-index liquid crystal systems. Summary of the Invention

[0004] To overcome the problems existing in related technologies, this application provides a polymerizable liquid crystal composition, a liquid crystal display grating, and a liquid crystal display. By using 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin photoaligning agent in combination with high-refractive-index rigid liquid crystal monomers, it can not only solve the industry pain point that ordinary photoaligning systems cannot effectively anchor high-refractive-index rigid liquid crystals, but also adapt to in-situ curing and micro-patterning processes, providing a material basis with excellent adaptability for the preparation of high-end optoelectronic devices such as AR waveguides and high-refractive-index liquid crystal displays.

[0005] The first aspect of this application provides a polymerizable liquid crystal composition comprising component A and component B; Component A, by mass percentage, comprises 0.5%-1% 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin, with the balance being the first solvent; Component B, by mass percentage, comprises 10%-15% high-refractive liquid crystal, 74.5%-83% second solvent, 2.0%-5.0% chiral agent, 3%-5% photoinitiator, and 0.1%-0.5% leveling agent; The high-refractive-index liquid crystal is composed of a first liquid crystal and a second liquid crystal; the first liquid crystal is selected from at least one of 2-acrylate[1,1'-biphenyl]-4,4'-dimethylbis(oxy-2,1-ethylidene), 2-acrylic acid, 2-[(4'-cyano[1,1'-biphenyl]-4-yl)oxy]propyl ester and Compound 1; the second liquid crystal is selected from at least one of 1,4-bis[4-(3-acryloyloxypropoxy)benzoic acid]-2-toluene and (4-(((4-(acryloyloxy)butoxy)carbonyl)oxy)benzoic acid 2-methyl-1,4-diphenol ester). The mass ratio of the first liquid crystal to the second liquid crystal is 1:(4-6); Compound 1 has the structural formula shown in Formula 1: Formula 1.

[0006] In some embodiments, the first solvent is N,N-dimethylformamide; the second solvent is selected from at least one of propylene glycol methyl ether acetate, chloroform, and N-methylpyrrolidone.

[0007] In some embodiments, the synthesis method of compound 1 is as follows: Under ice bath conditions, bis(1,4-bis(4-(2-phenoxy-1-propanol))-2-fluorobenzene) and triethylamine were dissolved in a certain amount of anhydrous dichloromethane, followed by the dropwise addition of acryloyl chloride. After the addition was complete, the mixture was naturally heated to room temperature and stirred. After the reaction was completed, the reaction solution was washed with cold water, dried over anhydrous magnesium sulfate, and concentrated under reduced pressure. The crude product was purified by recrystallization from isopropanol to obtain compound 1 as shown in Formula 1. The molar ratio of bis(1,4-bis(4-(2-phenoxy-1-propanol))-2-fluorobenzene), triethylamine and acryloyl chloride is 1:2.25:2.1.

[0008] A second aspect of this application provides a method for preparing a polymeric liquid crystal composition, comprising the following steps: S1. 7-[(6-hydroxyhexyl)oxy]coumarin was added to anhydrous dichloromethane and stirred until completely dissolved. After degassing the reaction system, an inert protective atmosphere was introduced, and the temperature was lowered to 0°C and maintained at a constant temperature. A mixed solution of triethylamine and methacryloyl chloride was added dropwise to the system at a uniform rate. After the addition was completed, the reaction was kept at the temperature for 2-4 hours. After the reaction was completed, the reaction solution was washed three times each with hydrochloric acid, sodium hydroxide solution, and saturated sodium chloride solution. After separating the organic phase, anhydrous magnesium sulfate was added for drying. After filtering to remove the drying agent, the solvent was removed by rotary evaporation under reduced pressure to obtain the crude product. The crude product was purified by silica gel column chromatography to obtain 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin. S2. Dissolve 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin in the first solvent in a certain proportion and stir until completely dissolved to obtain component A; S3. Mix the high-refractive liquid crystal, the second solvent, the chiral agent, the photoinitiator and the leveling agent evenly according to the proportion to obtain component B.

[0009] In some embodiments, the mass ratio of 7-[(6-hydroxyhexyl)oxy]coumarin, triethylamine and methacryloyl chloride is 1.31:0.5:0.5.

[0010] A third aspect of this application provides a liquid crystal display grating, wherein the liquid crystal display grating is disposed on the surface of a glass substrate pretreated with plasma, and is prepared from the above-mentioned polymerizable liquid crystal composition, or from the polymerizable liquid crystal composition prepared by the above-mentioned preparation method, through the following steps: (1) Component A is spin-coated onto the surface of the glass substrate that has been pretreated by plasma. After spin-coating, the substrate is left to stand at room temperature for 5 minutes to obtain an alignment layer film. (2) A linearly polarized ultraviolet laser was used to irradiate the alignment layer film at a 45° tilt angle for 20s to induce a [2+2] cycloaddition reaction of the C3=C4 double bond of 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin to form a permanent cross-linked alignment network; (3) Component B was spin-coated onto the surface of the alignment layer film to obtain a liquid crystal film with a thickness of 2 μm, and then a power of 30 mW / cm was used. 2 Unpolarized ultraviolet light is used to irradiate the liquid crystal film for 30 seconds to obtain a liquid crystal display grating with a periodic arrangement structure.

[0011] In some embodiments, in step (3), before in-situ curing is completed by irradiation with non-polarized ultraviolet light, a photolithography mask is used for partitioned exposure to realize the fabrication of micro-patterned liquid crystal display gratings.

[0012] In some embodiments, in step (1), the spin coating is first spin-coated at a speed of 800 r / min for 5 s, and then spin-coated at a speed of 3000 r / min for 30 s; in step (3), the spin coating is spin-coated at a speed of 1500 r / min for 20 s.

[0013] In some embodiments, in step (2), the linearly polarized ultraviolet laser has a wavelength of 365 nm and a power of 50 mW / cm². 2 .

[0014] A fourth aspect of this application provides a liquid crystal display, including the liquid crystal display grating described above.

[0015] Compared with the prior art, the polymerizable liquid crystal composition provided in this application has the following beneficial effects: (1) Using 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin as a photoaligning agent, combined with high-refractive liquid crystal, the photoaligning agent undergoes a [2+2] cycloaddition reaction under ultraviolet irradiation, which can overcome the rigid alignment resistance of the conjugated aromatic ring structure of high-refractive liquid crystal. At the same time, the high-refractive liquid crystal is compatible and has no risk of delamination or precipitation. The orientation order of the high-refractive liquid crystal system can reach 0.88, which is more than 35% higher than the existing SD1 type azobenzene alignment agent. It can achieve uniform and stable orientation of high-refractive rigid liquid crystal, solving the industry pain point that the existing alignment agent cannot be adapted to the high-refractive liquid crystal system.

[0016] (2) The orientation is achieved by using irreversible cycloaddition reaction of coumarin, and the resulting covalent cross-linked orientation network structure is stable. The high-refractive liquid crystal has good compatibility with the alignment layer and there is no risk of free ion impurities being released. After aging test at 85℃ / 85%RH for 72 hours, the orientation order retention rate reaches 92% and the device voltage retention rate at 25℃ reaches 93%. Compared with the existing technology, the long-term reliability is greatly improved, which can meet the use requirements of harsh scenarios such as AR display and automotive display. At the same time, the photo-alignment process can control the exposure area through photolithography mask, and the polymerizable system can be formed in situ without filling the liquid crystal cell. It is compatible with both rigid glass substrates and flexible plastic substrates such as PET, and can directly prepare micro-patterned polarizer holographic gratings. The grating diffraction efficiency can reach up to 65%, which is far higher than the grating performance of existing alignment systems of the same type. Attached Figure Description

[0017] The above and other objects, features and advantages of this application will become more apparent from the more detailed description of exemplary embodiments thereof in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments thereof.

[0018] Figure 1 It is the 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin shown in Example 1 of this application. 1 HNMR spectrum. Detailed Implementation

[0019] Preferred embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While preferred embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0020] All raw materials described in this application are obtained commercially or prepared through conventional synthetic routes. In specific embodiments, each component is described as a mass percentage or mass parts.

[0021] The polymerizable liquid crystal composition described in this application is stored independently of component A and component B, and is formed into a film sequentially during use.

[0022] In this embodiment, component A consists of 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin and a first solvent. The mass percentage of 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin is 0.5%-1%, with the remainder being the first solvent. The first solvent can be an organic solvent capable of dissolving 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin, such as N,N-dimethylformamide or chloroform, and the viscosity of the system can be adjusted to suit the spin-coating process. As a photoalignment functional component, the coumarin core in the 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin undergoes a [2+2] cycloaddition reaction under polarized ultraviolet irradiation to form a covalently cross-linked orientation network, providing surface anchoring energy for the subsequent liquid crystal layer. The methacryloyl groups on the side chains can improve the compatibility between the alignment agent and polymerizable monomers in the liquid crystal layer, reducing interfacial ion precipitation.

[0023] In this embodiment, component B consists of high-refractive-index liquid crystal, a second solvent, a chiral agent, a photoinitiator, and a leveling agent. The mass percentages of each component are as follows: high-refractive-index liquid crystal 10%-15%, second solvent 74.5%-83%, chiral agent 2.0%-5.0%, photoinitiator 3%-5%, and leveling agent 0.1%-0.5%. The high-refractive-index liquid crystal has a birefringence at 25°C. The polymerizable rigid liquid crystal monomer is 0.2-0.25%, and its molecular backbone contains a conjugated aromatic ring / heterocyclic structure. The high-refractive-index liquid crystal is composed of a first liquid crystal and a second liquid crystal. The first liquid crystal is selected from at least one of 2-acrylate [1,1'-biphenyl]-4,4'-dimethylbis(oxy-2,1-ethylidene), 2-acrylic acid, 2-[(4'-cyano[1,1'-biphenyl]-4-yl)oxy]propyl ester, and Compound 1. Its molecular backbone has a conjugated aromatic ring / heterocyclic structure, and its birefringence value is ≥0.2, which can meet the optical performance requirements of high-refractive-index display scenarios.

[0024] Specifically, the 2-propenoic acid,[1,1'-biphenyl]-4,4'-diylbis(oxy-2,1-ethanediyl)ester (9CI), with CAS number 90549-12-5 and birefringence Δn=0.2, has the following structural formula:

[0025] The 2-[(4'-cyano[1,1'-biphenyl]-4-yl)oxy]propyl ester, with CAS number 853993-13-2 and birefringence Δn = 0.22, has the following structural formula:

[0026] The structural formula of compound 1 is as follows:

[0027] The synthetic route for compound 1 is as follows:

[0028] Furthermore, compound 1 can be synthesized via the following steps: Under ice bath conditions of 0–5 °C, 2.12 mmol of bis(1,4-bis(4-(2-phenoxy-1-propanol))-2-fluorobenzene) and 4.77 mmol of triethylamine were dissolved in 20 mL of anhydrous dichloromethane. Then, 4.39 mmol of acryloyl chloride was slowly added dropwise over 1 hour. After the addition was complete, the ice bath was removed, and the mixture was stirred at room temperature for 4 h. After the reaction was complete, the triethylamine hydrochloride was removed by washing with cold water, the organic phase was dried over magnesium sulfate, the solvent was removed under reduced pressure, and the mixture was recrystallized from isopropanol to give compound 1 as shown in Formula 1, with a yield of 83%. The birefringence Δn of compound 1 was measured to be 0.24.

[0029] The 1H NMR spectrum of compound 1 is as follows: 1 H NMR: δ 1.19-1.32 6H, 4.95-5.09 2H, 5.96-6.09 2H, 6.26-6.40 2H, 6.79-7.02 4H, 7.21 2H, 7.38-7.74 6H, 7.87 1H The second liquid crystal is selected from at least one of 1,4-bis[4-(3-acryloyloxypropoxy)benzoic acid]-2-toluene (RM257) and (4-(((4-(acryloyloxy)butoxy)carbonyl)oxy)benzoic acid 2-methyl-1,4-diphenol ester (LC242), and has polymerizable double bonds, which can undergo cross-linking reaction under ultraviolet light irradiation to fix the orientation structure of the liquid crystal molecules.

[0030] In this embodiment, the mass ratio of the first liquid crystal to the second liquid crystal is 1:4 to 1:6. At this ratio, the high-refractive liquid crystal has the best compatibility with the coumarin alignment layer, with no risk of delamination or precipitation.

[0031] Chiral agents are used to induce liquid crystal molecules to form a helical arrangement to match the optical periodicity requirements of gratings. Chiral agents such as R811, S811, S1011, CB15, and R1011 can be selected. R811 is an enantiomer of S811, with the same helical twisting force as S811, and can induce liquid crystals to form a left-handed helical structure, suitable for the fabrication of left-handed gratings. S1011 has a helical twisting force approximately three times that of S811, achieving the target pitch at a lower addition amount and reducing the influence of the chiral agent on the birefringence of the liquid crystal system. CB15 exhibits excellent temperature stability, with a pitch change rate ≤0.1 nm / ℃, suitable for grating devices used over a wide temperature range. R1011 is a left-handed enantiomer of S1011, with high helical twisting force, suitable for the fabrication of small-pitch left-handed gratings.

[0032] Photoinitiators are used to absorb ultraviolet energy and initiate the crosslinking reaction of the second liquid crystal. Suitable photoinitiators include Irgacure 651, Irgacure 184, Irgacure 907, Darocur 1173, and Irgacure 369.

[0033] Leveling agents are used to reduce the surface tension of the system and improve the uniformity of spin-coated films. Optional leveling agents include BYK306, BYK307, BYK333, BYK341, EFKA 3777 and TEGO Glide 410. The leveling agent must meet the following requirements: First, the selected leveling agent must be soluble in propylene glycol methyl ether acetate, chloroform, and N-methylpyrrolidone solvents to ensure that precipitation or delamination does not occur at room temperature; Second, the selected leveling agent must not migrate to the interface between the coumarin alignment layer and the liquid crystal layer, must not reduce the surface anchoring energy of the alignment layer, and must not affect the orientation order of the liquid crystal molecules; Third, the selected leveling agent must be optically inert, must not generate ultraviolet absorption in the 365nm wavelength band, must not compete with the [2+2] cycloaddition reaction of coumarin or the decomposition reaction of the photoinitiator, and must not affect the alignment efficiency and curing rate; Fourth, the selected leveling agent must have good compatibility, be compatible with high-refractive liquid crystals, chiral agents, and photoinitiators, and must not cause phase separation in the system or lead to a decrease in grating diffraction efficiency. To facilitate the adjustment of the surface tension of component B to 22-28 mN / m by the leveling agent, its addition amount is 0.1%-0.5%.

[0034] Based on the above-mentioned polymerizable liquid crystal composition, this application also provides a method for preparing the polymerizable liquid crystal composition, as follows: S1. Synthesis of 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin: 7-[(6-hydroxyhexyl)oxy]coumarin was added to anhydrous dichloromethane and stirred until completely dissolved. After degassing the reaction system, argon gas was introduced as a protective atmosphere. The temperature was lowered to 0℃ and maintained at a constant temperature. A mixed solution of triethylamine and methacryloyl chloride was added dropwise to the system at a uniform rate. The mass ratio of 7-[(6-hydroxyhexyl)oxy]coumarin, triethylamine, and methacryloyl chloride was 1.31:0.5:0.5. After the addition was completed, the reaction was maintained at this temperature for 2 hours. -4h; after the reaction was completed, the reaction solution was washed three times each with 0.8-1mol / L hydrochloric acid, 10% sodium hydroxide solution, and saturated sodium chloride solution. After each washing, the organic phase was allowed to stand and separated. Finally, anhydrous magnesium sulfate was added to the organic phase and dried for 2h. After filtration to remove the desiccant, the solvent was removed by rotary evaporation under reduced pressure to obtain the crude product. The crude product was purified by silica gel column chromatography with a 1:15 volume ratio of ethyl acetate and dichloromethane as the eluent to obtain 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin.

[0035] The 1H NMR spectrum of 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin is as follows: 1 H-NMR(CDCl3)1.47-1.84(m,8H),1.94(s,3H),4.02(t,2H),4.16(t,2H),5.55 (s.1H),6.10(s,1H),6.24(d,1H),6.80-6.83(m,2H).7.36(d,1H),7.63(d,1H) S2. Preparation of component A: Dissolve the obtained 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin in N,N-dimethylformamide in a certain proportion, stir at 600 rpm for 30 min until completely dissolved to obtain component A, and store it in a light-proof and sealed container.

[0036] S3. Preparation of component B: Weigh the high-refractive liquid crystal and the second solvent according to the proportion and add them to the stirring container. Stir at 600 rpm for 60 min until completely dissolved. Then add the chiral agent, photoinitiator and leveling agent in sequence, and continue stirring for 30 min until the system is homogeneous to obtain component B. Store in a light-proof and sealed container.

[0037] This application also proposes a method for fabricating a liquid crystal display grating. The liquid crystal display grating is fabricated using a glass substrate pretreated with plasma as the substrate, and the process is carried out according to the following steps: (1) Preparation of alignment layer film: Component A is spin-coated onto the surface of a glass substrate that has been cleaned with 300W plasma for 5 min. The spin-coating process is to first spin-coat at 800 r / min for 5 s, and then spin-coat at 3000 r / min for 30 s. After spin-coating is completed, the substrate is left to stand at room temperature for 5 min to allow the first solvent to evaporate naturally, and an alignment layer film with a thickness of 20-30 nm is obtained.

[0038] (2) Polarization orientation treatment: using a wavelength of 365nm and a power of 50mW / cm 2 Linearly polarized ultraviolet lasers were used to irradiate the alignment layer film at a 45° tilt angle for 20 seconds, inducing a [2+2] cycloaddition reaction of the C3=C4 double bond of 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin in the alignment layer. This reaction formed a permanent cross-linked alignment network through cyclobutane four-membered ring bridging, providing orientation anchoring energy for the subsequent liquid crystal layer.

[0039] (3) Preparation of liquid crystal layer: Component B was spin-coated onto the surface of the alignment layer film at 1500 r / min for 20 s to obtain a liquid crystal film with a thickness of 2 μm. Then, a power of 30 mW / cm was used. 2 Unpolarized ultraviolet light is irradiated onto the liquid crystal film for 30 seconds, initiating a cross-linking reaction in the second liquid crystal, which fixes the orientation structure of the liquid crystal molecules, resulting in a liquid crystal display grating with a periodic arrangement structure.

[0040] In addition, if it is necessary to prepare micro-patterned liquid crystal display gratings, before in-situ curing is completed by irradiation with unpolarized ultraviolet light, a photomask with the corresponding pattern is set above the liquid crystal film, and the liquid crystal components in the unexposed areas are exposed in sections according to a preset path. The liquid crystal components in the unexposed areas can be eluted by organic solvents to obtain the grating structure with the corresponding pattern.

[0041] This application also proposes a liquid crystal display including the above-mentioned liquid crystal display grating, in which the liquid crystal display grating is used as an optical waveguide coupling input / output structure and assembled with a backlight module, a liquid crystal panel and a driving circuit, thereby achieving higher light efficiency and display resolution.

[0042] To facilitate a further understanding of this application, the solutions described below are further described in conjunction with embodiments. Those skilled in the art will understand that the examples described in this application are only a portion of the examples, and any other suitable specific examples are within the scope of this application.

[0043] Example 1 1. Raw material formula: The raw materials for the preparation of Example 1 are shown in Table 1: Table 1: Raw Material Formulation

[0044] 2. Preparation of polymerizable liquid crystal compositions: Component A: Add 0.8 parts by weight of 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin to N,N-dimethylformamide, stir at 600 rpm for 60 min, remove and store in a dry storage room.

[0045] Component B: Add 2 parts by weight of compound 1 and 10 parts by weight of RM257 to propylene glycol methyl ether acetate, stir at 600 rpm for 60 min, then add S811, Irgacure 651 and BYK-307, continue stirring for 30 min, remove and store in a dry storage room.

[0046] 3. Fabrication of liquid crystal display gratings Substrate pretreatment: A 2cm×2cm glass substrate was cleaned with 300W plasma for 5 minutes; Preparation of orientation layer: Component A was spin-coated onto the substrate surface at 800 r / min for 5 s, followed by spin-coating at 3000 r / min for 30 s, and then allowed to stand at room temperature for 5 min. Polarization orientation: The alignment layer was irradiated with a 365nm, 50mW / cm² linearly polarized ultraviolet laser at a 45° angle for 20s. Liquid crystal layer preparation: Component B was spin-coated onto the surface of the alignment layer at 1500 r / min for 20 s, and then cured with 30 mW / cm² unpolarized ultraviolet light for 30 s to obtain a 2 μm thick polarizing holographic grating sample.

[0047] Example 2 The only difference from Example 1 is that the high-refractive liquid crystal is a compound of 2-acrylate [1,1'-biphenyl]-4,4'-dimethylbis(oxy-2,1-ethylene) ester (9CI) and LC242, and the ratio of the two is 1:4. The other components and process parameters are the same as in Example 1.

[0048] Example 3 The only difference from Example 1 is that the high-refractive liquid crystal is a complex of 2-acrylate [1,1'-biphenyl]-4,4'-dimethylbis(oxy-2,1-ethylene) ester (9CI), 2-[(4'-cyano[1,1'-biphenyl]-4-yl)oxy]propyl ester and LC242, and the ratio of the three is 1:1:10. The remaining components and process parameters are the same as in Example 1.

[0049] Example 4 The only difference from Example 1 is that the high-refractive liquid crystal is a complex of 2-acrylate [1,1'-biphenyl]-4,4'-dimethylbis(oxy-2,1-ethylene) ester (9CI), 2-[(4'-cyano[1,1'-biphenyl]-4-yl)oxy]propyl ester, compound 1, LC242 and RM257, and the ratio of the five components is 1:1:1:6:6. The remaining components and process parameters are the same as in Example 1.

[0050] Example 5 The only difference from Example 1 is that the content of 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin in component A is 0.5% and the content of DMF is 99.5%, while the other components and process parameters are the same as in Example 1.

[0051] Example 6 The only difference from Example 1 is that the content of 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin in component A is 1%, and the content of DMF is 99%. The remaining components and process parameters are the same as in Example 1.

[0052] Comparative Example 1 The only difference from Example 1 is that 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin in component A is replaced with SD1 azobenzene photoaligning agent, while the other components and process parameters are the same as in Example 1.

[0053] Comparative Example 2 The only difference from Example 1 is that 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin in component A is prepared as a coumarin photosensitive group organic polymer substitution polymer, while the other components and process parameters are the same as in Example 1.

[0054] The preparation method of the organic polymer substituted with coumarin photosensitive group is as follows: (1) 10 mmol of 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin and 10 mmol of recrystallized polymerization initiator azobisisobutyronitrile were dissolved in 50 ml of anhydrous N,N-dimethylformamide and repeatedly frozen to remove gas; (2) Place the system at 20-100℃ for 1-24 hours to react; (3) Then, the solution after the reaction is repeatedly added dropwise to methanol to precipitate the precipitate, and then filtered. (4) Vacuum drying yields a coumarin photosensitive group organic polymer substituted with a polymer.

[0055] Comparative Example 3 The only difference from Example 1 is that the ratio of high-refractive liquid crystal compound 1 to RM257 is 1:3, while the other components and process parameters are the same as in Example 1.

[0056] Comparative Example 4 The only difference from Example 1 is that 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin in component A is replaced with a cinnamic acid ester photoaligning agent; the remaining components and process parameters are the same as in Example 1.

[0057] Comparative Example 5 The only difference from Example 1 is that 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin in component A is replaced with coumarin without methacryloyl side chain; the other components and process parameters are the same as in Example 1.

[0058] For all the aforementioned embodiments and comparative examples, six types of performance characterization were conducted: photoorientation efficiency test, orientation order and high temperature and humidity stability test, long-term storage stability test, surface mechanical stability test, voltage retention rate test, and temperature dependence test. The specific test methods are as follows: 1. Photoalignment efficiency test The orientation state of liquid crystal molecules was observed using an orthogonal polarization microscope (POM). The time from the end of polarization ultraviolet irradiation to the complete orientation of the liquid crystal molecules and the stable extinction angle without deviation was recorded and defined as the orientation completion time T of the sample. The test results are shown in Table 2.

[0059] 2. High temperature and high humidity stability test The actual birefringence value (Δn) of the liquid crystal layer was measured using the phase difference measurement module of the polarizing microscope, and the orientation order (S) was calculated according to formula (1):

[0060] in, To correspond to the maximum birefringence value when the liquid crystal system is perfectly aligned, the high-refractive-index liquid crystal... It is calculated by weighting the components according to their proportions.

[0061] Initial orientation order The test environment was 25℃ room temperature and 50%RH relative humidity. Five different areas of each sample were randomly selected for testing, and the average value was taken as the final result. The test results are shown in Table 2.

[0062] Order retention rate at 85℃ / 85%RH for 72 hours: Samples were placed in a constant temperature and humidity chamber at 85℃ and 85%RH, sealed for 24 hours, 48 ​​hours, and 72 hours. After removal, the samples were cooled to room temperature and allowed to stand for 30 minutes. The orientation order was then tested using the same method described above. The retention rate S1 was calculated according to formula (2), and the test results are shown in Table 2.

[0063] 4. Mechanical stability test Uses polyester cleanroom wipes with a cleanliness level of 99.9% and a density of 50g / cm². 2 The sample surface was wiped 10 times with uniform pressure in the same direction. The liquid crystal orientation state of the wiped area was observed by polarized light microscope. The change rate S2 of the orientation order relative to before wiping was tested. The test results are shown in Table 2.

[0064] Table 2: Summary of Performance Parameters for Each Embodiment and Comparative Example

[0065] 4. Long-term stability test Samples were placed in a closed environment at room temperature of 25℃, relative humidity of 50%RH, and without direct ultraviolet radiation for 30, 60, and 90 days. The orientation order was tested and the retention rate S3 relative to the initial value was calculated using the same method as above. The test results are shown in Table 3.

[0066] 5. Voltage Hold-up Rate (VHR) Test The sample was fabricated as a parallel electrode liquid crystal cell with an electrode spacing of 5 μm. A square wave AC voltage with an amplitude of 5V and a frequency of 1kHz was applied using a voltage hold-up tester and applied continuously for 10ms. The power supply was then stopped, and the remaining voltage of the liquid crystal cell was recorded 1ms after the power was turned off. Calculate the voltage holding rate VHR according to formula (3):

[0067] in The initial voltage amplitude was applied. The test environment was room temperature (25℃). Each sample was tested 10 times, and the average value was taken. The test results are shown in Table 3.

[0068] 6. Grating diffraction efficiency A single-mode laser with a wavelength of 532 nm was used as the incident light source and incident perpendicularly onto the grating surface. A power meter was used to measure the 0th order transmitted light power and the +1st order diffracted light power, respectively, according to the formula η=(P +1 The diffraction efficiency is calculated as (P0) × 100%, where P +1 P0 represents the power of the +1st order diffracted light and the total incident light power.

[0069] The test results are shown in Table 3.

[0070] Table 3: Summary of Performance Parameters for Each Embodiment and Comparative Example

[0071] 7. Temperature dependence test At five temperature points—-20℃, 0℃, 25℃, 50℃, and 80℃—the samples were kept at the corresponding temperature for 1 hour to allow the performance to stabilize. The voltage retention rate was then tested using the same method described above to evaluate the effect of temperature on the electrical performance of the device. The test results are shown in Table 4.

[0072] Table 4: Summary of Temperature Dependence Parameters for Each Example and Comparative Example

[0073] As shown in Table 2-4, the orientation completion time of Example 1 in this application is only 25s, which is more than twice as efficient as Comparative Example 1 (80s) using SD1 azobenzene aligning agent. The orientation completion times of the other examples are all ≤35s, which is much lower than the orientation completion times of all comparative examples. This effect is due to the fact that the monomeric coumarin aligning agent used in this application does not require prepolymerization, has high molecular chain segment activity, and a fast [2+2] cycloaddition reaction rate, which can form a uniform cross-linked orientation network in a short time, meeting the cycle requirements of large-scale mass production. At the same time, the initial orientation order degree S0 of Example 1 can reach 0.88, which is more than 35% higher than that of Comparative Example 1 (0.65). The initial orientation order degree of the other examples is ≥0.83, which is much higher than the initial orientation order degree of all comparative examples. This effect verifies that the crosslinking network anchoring energy of the monomeric coumarin alignment agent in this application is 2-3 times higher than that of existing prepolymer coumarin, azobenzene, and cinnamic acid ester alignment agents. It can overcome the alignment resistance of high-refractive-index rigid liquid crystals. At the same time, the compounding ratio of high-refractive-index liquid crystals has been optimized for compatibility, with no risk of delamination or precipitation, and achieves uniform and stable orientation of the high-refractive-index liquid crystal system.

[0074] Regarding orientation retention rate, Example 1 achieved an order retention rate of 92% after aging at 85℃ / 85%RH for 72 hours, which is 24 percentage points higher than the 68% of Comparative Example 1. The high temperature and humidity retention rates of the other examples were all ≥90%, the order retention rates after long-term storage for 90 days were all ≥85%, and the order change rate after surface wiping was all ≤5%, which is far superior to the performance of the comparative example group.

[0075] In terms of electrical performance, the room temperature voltage retention rate of Example 1 can reach 93%, which is 11 percentage points higher than the 82% of Comparative Example 1; the room temperature voltage retention rate of the other examples is ≥90%, and the voltage retention rate fluctuation is ≤3% in a wide temperature range of -20℃ to 80℃, which fully meets the usage requirements of harsh scenarios such as AR display and automotive display.

[0076] The liquid crystal grating diffraction efficiency of Embodiment 1 of this application can reach 65%, while Comparative Example 1 cannot form an effectively ordered grating structure; the grating diffraction efficiency of the other embodiments is ≥59%, which is much higher than the conventional diffraction efficiency level of ≤40% of the existing similar alignment system, and can be directly applied to the fabrication of high-end optoelectronic devices such as AR waveguides and polarizing holographic gratings.

[0077] In summary, the technical solution of this application achieves multiple advantages, including high orientation efficiency, high orientation order, high reliability, and high photoelectric performance, through the synergistic effect of a specific coumarin photoaligning agent and a compatible high-refractive liquid crystal system.

[0078] The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A polymerizable liquid crystal composition, characterized in that, Includes component A and component B; Component A, by mass percentage, comprises 0.5%-1% 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin, with the balance being the first solvent; Component B, by mass percentage, comprises 10%-15% high-refractive liquid crystal, 74.5%-83% second solvent, 2.0%-5.0% chiral agent, 3%-5% photoinitiator, and 0.1%-0.5% leveling agent; The high-refractive-index liquid crystal is composed of a first liquid crystal and a second liquid crystal; the first liquid crystal is selected from at least one of 2-acrylate[1,1'-biphenyl]-4,4'-dimethylbis(oxy-2,1-ethylene) ester (9CI), 2-acrylic acid, 2-[(4'-cyano[1,1'-biphenyl]-4-yl)oxy]propyl ester and compound 1; the second liquid crystal is selected from at least one of 1,4-bis[4-(3-acryloyloxypropoxy)benzoic acid]-2-toluene and (4-(((4-(acryloyloxy)butoxy)carbonyl)oxy)benzoic acid 2-methyl-1,4-diphenol ester). The mass ratio of the first liquid crystal to the second liquid crystal is 1:(4-6); Compound 1 has the structural formula shown in Formula 1: Formula 1.

2. The polymerizable liquid crystal composition according to claim 1, characterized in that, The first solvent is N,N-dimethylformamide; the second solvent is selected from at least one of propylene glycol methyl ether acetate, chloroform, and N-methylpyrrolidone.

3. The polymerizable liquid crystal composition according to claim 1, characterized in that, The method for synthesizing compound 1 is as follows: Under ice bath conditions, bis(1,4-bis(4-(2-phenoxy-1-propanol))-2-fluorobenzene) and triethylamine were dissolved in a certain amount of anhydrous dichloromethane, followed by the dropwise addition of acryloyl chloride. After the addition was complete, the mixture was naturally heated to room temperature and stirred. After the reaction was completed, the reaction solution was washed with cold water, dried over anhydrous magnesium sulfate, and concentrated under reduced pressure. The crude product was purified by recrystallization from isopropanol to obtain compound 1 as shown in Formula 1. The molar ratio of bis(1,4-bis(4-(2-phenoxy-1-propanol))-2-fluorobenzene), triethylamine and acryloyl chloride is 1:2.25:2.

1.

4. A method for preparing a polymerizable liquid crystal composition, characterized in that, Includes the following steps: S1. 7-[(6-hydroxyhexyl)oxy]coumarin was added to anhydrous dichloromethane and stirred until completely dissolved. After degassing the reaction system, an inert protective atmosphere was introduced, and the temperature was lowered to 0°C and maintained at a constant temperature. A mixed solution of triethylamine and methacryloyl chloride was added dropwise to the system at a uniform rate. After the addition was completed, the reaction was kept at the temperature for 2-4 hours. After the reaction was completed, the reaction solution was washed three times each with hydrochloric acid, sodium hydroxide solution, and saturated sodium chloride solution. After separating the organic phase, anhydrous magnesium sulfate was added for drying. After filtering to remove the drying agent, the solvent was removed by rotary evaporation under reduced pressure to obtain the crude product. The crude product was purified by silica gel column chromatography to obtain 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin. S2. Dissolve 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin in the first solvent in a certain proportion and stir until completely dissolved to obtain component A; S3. Mix the high-refractive liquid crystal, the second solvent, the chiral agent, the photoinitiator and the leveling agent evenly according to the proportion to obtain component B.

5. The preparation method according to claim 4, characterized in that, The mass ratio of 7-[(6-hydroxyhexyl)oxy]coumarin, triethylamine and methacryloyl chloride is 1.31:0.5:0.

5.

6. A liquid crystal display grating, characterized in that, The liquid crystal display grating is disposed on the surface of a glass substrate pretreated with plasma, and is prepared by the following steps from the polymerizable liquid crystal composition according to any one of claims 1-3, or the polymerizable liquid crystal composition prepared by the preparation method according to claim 4 or 5: (1) Spin-coating component A onto the surface of the glass substrate that has been pretreated by plasma, and then allowing it to stand at room temperature for 5 minutes after spin-coating to obtain an alignment layer film; (2) A linearly polarized ultraviolet laser was used to irradiate the alignment layer film at a 45° tilt angle for 20s to induce a [2+2] cycloaddition reaction of the C3=C4 double bond of 7-[[[6-(methacryloyl)oxy]hexyl]oxy]coumarin to form a permanent cross-linked alignment network; (3) Component B was spin-coated onto the surface of the alignment layer film to obtain a liquid crystal film with a thickness of 2 μm, and then a power of 30 mW / cm was used. 2 Unpolarized ultraviolet light is used to irradiate the liquid crystal film for 30 seconds to obtain a liquid crystal display grating with a periodic arrangement structure.

7. The liquid crystal display grating according to claim 6, characterized in that, In step (3), before in-situ curing is completed by irradiation with unpolarized ultraviolet light, a photolithography mask is used to perform partitioned exposure to realize the fabrication of micro-patterned liquid crystal display gratings.

8. The liquid crystal display grating according to claim 6, characterized in that, In step (1), the spin coating is first spin coated at 800 r / min for 5 s, and then spin coated at 3000 r / min for 30 s; in step (3), the spin coating is spin coated at 1500 r / min for 20 s.

9. The liquid crystal display grating according to claim 6, characterized in that, In step (2), the wavelength of the linearly polarized ultraviolet laser is 365 nm and the power is 50 mW / cm². 2 .

10. A liquid crystal display, characterized in that, Includes the liquid crystal display grating as described in any one of claims 6-9.

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