Phase difference film with liquid crystal layer and photo-alignment layer capable of being separated in lossless mode and preparation method of phase difference film

Abstract

The invention provides a phase difference film and a preparation method, the phase difference film comprises a light alignment layer and a liquid crystal layer, the light alignment layer is formed by polymerizing a first composition, and the liquid crystal layer is formed by polymerizing a second composition; the first composition comprises an aldehyde substance and polyvinyl alcohol resin; the second composition includes a reactive monomer liquid crystal. The liquid crystal layer of the phase difference film can be completely and losslessly stripped from the light alignment layer, so that the requirement of a high-quality liquid crystal film required by a display screen manufacturer is met.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid crystal films, and in particular to a phase difference film in which a liquid crystal layer can be losslessly separated from a light alignment layer and a preparation method thereof. Background Art

[0002] With the advancement of display technology, liquid crystal displays (LCDs) and organic light-emitting diodes (OLEDs) are widely used in various electronic display devices. To improve the optical performance of displays, panel manufacturers typically use optical films such as polarizers, optical compensation sheets, or retardation films. Among these, vertical alignment (VA) LCDs have become a research focus due to their advantages such as high contrast, fast response, and wide viewing angle.

[0003] Technologies for achieving vertical alignment of liquid crystal molecules include rubbing, tilted evaporation, self-assembled monolayer (SAM), and microstructure induction. However, rubbing generates static electricity during the friction process, which can cause breakdown in TFT-LCD transistors. Tilted evaporation has demanding process conditions and low yields, making it unsuitable for large-scale panel production. The SAM method struggles to ensure the stability of the liquid crystal layer's alignment. The microstructure induction method is complex and carries a high risk of light leakage. With technological advancements, Chinese patent CN 116790166 B proposes using polyvinyl alcohol resins to produce vertically aligned retardation films. This eliminates the need for rubbing for vertical alignment, avoids the generation of dust and static electricity, and thus mitigates the effects of these on liquid crystal performance.

[0004] During production and use, it was discovered that the photo-alignment layer of liquid crystal retardation films made with polyvinyl alcohol resins had insufficient adhesion to the substrate layer, but strong adhesion to the liquid crystal layer due to polarity. This prevented panel manufacturers from completely peeling the liquid crystal layer from the photo-alignment layer when removing it, or caused the photo-alignment layer to partially adhere to the liquid crystal layer, significantly affecting the display's display quality. Furthermore, because the photo-alignment layer contains polyvinyl alcohol resins, it is easily hygroscopic and has poor weather resistance. After being bonded to the liquid crystal layer and subjected to long-term operating conditions, the performance of the liquid crystal retardation film deteriorated, shortening its service life.

[0005] In summary, in actual production, there is an urgent need for a vertically aligned phase difference film and a preparation method in which the liquid crystal layer can be completely and intactly separated from the photo-alignment layer. Summary of the Invention

[0006] In response to the existing problems faced by panel manufacturers in separating and removing the liquid crystal layer, such as the inability to completely peel the liquid crystal layer from the photo-alignment layer, or the partial adhesion of the photo-alignment layer to the liquid crystal layer, the present application aims to provide a retardation film and preparation process that allows for lossless separation of the liquid crystal layer from the photo-alignment layer. By adjusting the process formulas for the liquid crystal layer and the photo-alignment layer in the liquid crystal retardation film, and in conjunction with subsequent preparation processes, the liquid crystal layer can be completely and intactly peeled from the photo-alignment layer, with no residue of the photo-alignment layer remaining on the liquid crystal layer after peeling.

[0007] According to the first aspect of the present application, a phase difference film is provided, which includes a photo-alignment layer and a liquid crystal layer, wherein the photo-alignment layer is formed by polymerizing a first composition, and the liquid crystal layer is formed by polymerizing a second composition; the first composition includes: an aldehyde substance and a polyvinyl alcohol resin; the second composition includes: a reactive monomer liquid crystal.

[0008] Optionally, the aldehyde substance accounts for 0.5%-18% of the total mass of the first composition by mass; the polyvinyl alcohol resin accounts for 1%-30% of the total mass of the first composition by mass; and the reactive monomer liquid crystal accounts for 3%-20% of the total mass of the second composition by mass. Optionally, the second composition further includes a photoinitiator and a leveling agent; the photoinitiator accounts for 0.1%-5% of the total mass of the second composition by mass; the leveling agent accounts for 0.1%-10% of the total mass of the second composition by mass.

[0009] Optionally, the aldehyde substance can be selected from one or more combinations of glyoxal, benzaldehyde, acetaldehyde, octanal, octanal, p-methoxybenzaldehyde, p-chlorobenzaldehyde, o-chlorobenzaldehyde, 3-nitro-4-pyridinealdehyde, isohexaldehyde, valeraldehyde, butyraldehyde, pyridinecarboxaldehyde, thiophenecarboxaldehyde, 2-furaldehyde, glyoxylic acid, 6-ethoxy-2-naphthaldehyde, 4-chloro-2-hydroxybenzaldehyde, propionaldehyde, malondialdehyde, succinaldehyde, glutaraldehyde, adipaldehyde, nonanal, undecanal, lauric aldehyde, tridecanal, and myristic aldehyde; the polyvinyl alcohol resin can be selected from PVA17-88, PVA17-92, PVA17-99, PVA05-88, PVA24-99, PVA24-88, PVA-103, PVA-105, A combination of one or more of PVA-117, PVA-124, PVA-613, PVA-203, PVA-205, PVA-217, PVA-220, PVA-235, PVA-403, PVA-420H, PVA-422H, PVA-424H, PVA-505, polyvinyl formal, polyvinyl butyral, polyvinyl acetal, and carboxyl-modified polyvinyl alcohol resin; the photoinitiator may be a combination of one or more of a cleavage-type free radical photoinitiator, a hydrogen-abstraction-type free radical photoinitiator, a cationic photoinitiator, and an oxime ester photoinitiator; the leveling agent may be a combination of one or more of acrylates, silicones, and fluorocarbons.

[0010] Optionally, the first composition further includes a first solvent; the second composition further includes a second solvent; the first solvent may be a combination of one or more of glycerol, phenol, propylene glycol, dimethyl sulfoxide, acetone, ethyl acetate, butyl acetate, methanol, ethanol, isopropanol, n-butanol, isobutanol, and water; the second solvent may be a combination of one or more of acetone, butanone, methyl ethyl ketone, cyclohexanone, cyclopentanone, methyl isobutyl ketone, isophorone, N-methylpyrrolidone, dioxane, tetrahydrofuran, ether, anisole, diethyl ether, propylene glycol methyl ether, n-hexane, heptane, cyclohexane, cyclopentane, toluene, xylene, dichloromethane, dichloroethane, dichlorobenzene, chlorotoluene, ethyl acetate, butyl acetate, propylene glycol methyl ether acetate, water, ethanol, n-butanol, sec-butanol, isopropanol, cyclohexanol, dimethyl sulfoxide, diethyl sulfoxide, benzylphenyl sulfoxide, dimethylformamide, dimethylacetamide, etc.

[0011] According to the second aspect of the present application, a method for preparing a phase difference film is also provided, which is characterized in that it includes: providing a substrate; applying the first composition described in the first aspect of the present application on the substrate to form a photo-alignment layer; and applying the second composition described in the first aspect of the present application on the photo-alignment layer to form a liquid crystal layer.

[0012] Optionally, the average roughness of the surface of the substrate is ≤15 nm, the maximum height roughness Sz of the surface of the substrate is ≤150 nm, the total light transmittance of the substrate is above 80%, and the substrate has good hydrophilicity (water drop angle of the coated surface is <90°).

[0013] Optionally, the step of coating the first composition on the substrate to form a photo-alignment layer further comprises: heating and drying the film after coating the first composition on the substrate, the heating and drying treatment temperature is 30-180° C. and the heating time is 0.5-20 min.

[0014] Optionally, the step of coating the second composition on the photo-alignment layer to form a liquid crystal layer further comprises: b1) heating and drying the film after coating the second composition on the photo-alignment layer, wherein the temperature of the heating and drying treatment is 30-100° C.; b2) curing the dried film with ultraviolet light in an N2 atmosphere to obtain the liquid crystal layer, wherein the concentration of N2 is 30%-99.999% and the irradiation energy of the ultraviolet light is 10 mJ / cm 2 -3000mJ / cm 2 .

[0015] Optionally, the liquid crystal molecules in the liquid crystal layer are vertically aligned.

[0016] The technical solution adopted by the present invention can achieve the following beneficial effects: According to the formula and preparation process of the photo-alignment layer and the liquid crystal layer in the phase difference film provided by the present invention, on the one hand, the adhesion between the photo-alignment layer and the substrate is enhanced, and on the other hand, the peeling force between the liquid crystal layer and the photo-alignment layer is effectively reduced, so that the liquid crystal layer of the prepared phase difference film can be peeled off from the photo-alignment layer intact, thereby meeting the requirements of display manufacturers for high-quality liquid crystal films. DETAILED DESCRIPTION

[0017] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0018] According to one embodiment of the present application, a phase difference film is provided, which includes a photo-alignment layer and a liquid crystal layer, wherein the photo-alignment layer is formed by polymerizing a first composition, and the liquid crystal layer is formed by polymerizing a second composition; the first composition includes: an aldehyde substance and a polyvinyl alcohol resin; the second composition includes: a reactive monomer liquid crystal.

[0019] The aldehydes can be selected from one or more compositions of glyoxal, benzaldehyde, acetaldehyde, octanal, octanal, p-anisaldehyde, p-chlorobenzaldehyde, o-chlorobenzaldehyde, 3-nitro-4-pyridinealdehyde, isohexaldehyde, valeraldehyde, butyraldehyde, pyridinealdehyde, thiophenealdehyde, 2-furaldehyde, glyoxylic acid, 6-ethoxy-2-naphthaldehyde, 4-chloro-2-hydroxybenzaldehyde, propanal, malondialdehyde, succinaldehyde, glutaraldehyde, adipaldehyde, nonanal, undecanal, lauric aldehyde, tridecanal and myristic aldehyde. In other words, the aldehydes can be selected from one or more of the above-mentioned aldehydes for use in combination. Preferably, in one embodiment, when the aldehyde substance includes multiple aldehyde substances, the aldehyde substance having a main chain alkyl group number less than 5 accounts for 50-100% of the total mass of the multiple aldehyde substances in terms of mass percentage. In actual processes, the proportion can be adjusted according to different production requirements. For example, the aldehyde substance having a main chain alkyl group number less than 5 accounts for 50%, 60%, 70%, 80%, 90%, 100% of the total mass of the multiple aldehyde substances, or any value between these values. Preferably, in another embodiment, when the aldehyde substance includes multiple aldehyde substances, the aldehyde substance of the polyaldehyde accounts for 50-100% of the total mass of the multiple aldehyde substances in terms of mass percentage. In actual processes, the proportion can be adjusted according to different production requirements. For example, the aldehyde substance of the polyaldehyde accounts for 50%, 60%, 70%, 80%, 90%, 100% of the total mass of the multiple aldehyde substances, or any value between these values. In one embodiment, the aldehyde substance accounts for 0.5%-20% of the total mass of the first composition in terms of mass fraction. In actual processes, the proportion of the aldehyde substance in the first composition can be adjusted according to different production requirements. For example, the aldehyde substance accounts for 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.25%, 1.5%, 1.75%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5% of the total mass of the first composition. , 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, 20% or any value therebetween; preferably, the aldehyde substance accounts for 2%-10% of the total mass of the first composition.

[0020] The polyvinyl alcohol resin may be selected from one or more of PVA17-88, PVA17-92, PVA17-99, PVA05-88, PVA24-99, PVA24-88, PVA-103, PVA-105, PVA-117, PVA-124, PVA-613, PVA-203, PVA-205, PVA-217, PVA-220, PVA-235, PVA-403, PVA-420H, PVA-422H, PVA-424H, PVA-505, polyvinyl formal, polyvinyl butyral, polyvinyl acetal, and a carboxyl-modified polyvinyl alcohol resin. The polyvinyl alcohol resin can provide hydroxyl groups, thereby imparting greater polarity to the surface of the photo-alignment layer obtained based on the first composition, thereby ensuring vertical alignment of the liquid crystal molecules. However, the strong polarity of the photo-alignment layer creates a significant peeling force between the liquid crystal layer and the photo-alignment layer, which can easily damage the liquid crystal layer or cause the photo-alignment layer to partially adhere to the liquid crystal layer during the peeling process. The technical challenge is how to reduce the polarity of the photo-alignment layer after the liquid crystal molecules have achieved vertical alignment while maintaining molecular alignment in the liquid crystal layer.

[0021] On the one hand, the hydroxyl groups provided by the polyvinyl alcohol resin in the first composition can undergo an aldol condensation reaction with the aldehyde groups provided by the aldehyde in the first composition, thereby reducing the number of polar groups in the photo-alignment layer formed by applying the first composition, thereby reducing the intermolecular polar forces with the liquid crystal molecules in the liquid crystal layer. The inventors have creatively discovered that the added amounts of the aldehyde and polyvinyl alcohol resin can be controlled. For example, the molar number of hydroxyl groups provided by the polyvinyl alcohol resin can be greater than the molar number of aldehyde groups provided by the aldehyde. This allows a certain amount of polar molecules to remain in the photo-alignment layer after the aldol condensation reaction. These polar molecules interact strongly with the polar groups in the liquid crystal molecules, thereby ensuring vertical alignment of the liquid crystal molecules. On the other hand, enhancing the polarity of the substrate by introducing abundant carboxyl and hydroxyl groups on the substrate surface can increase the polar forces between the substrate and the photo-alignment layer, thereby ensuring that the photo-alignment layer adheres completely to the substrate during the separation process from the liquid crystal layer, without causing the photo-alignment layer to adhere partially to the photo-alignment layer. In one embodiment, multiple polyvinyl alcohol resins with different degrees of alcoholysis can be used in combination. In one embodiment, the polyvinyl alcohol resin accounts for 1%-30% of the total mass of the first composition, and in actual processes, the proportion of the polyvinyl alcohol resin in the first composition can be adjusted according to different production requirements. For example, the polyvinyl alcohol resin accounts for 1%, 1.25%, 1.5%, 1.75%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, and 12.5% ​​of the total mass of the first composition. %, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, 20%, 20.5%, 21%, 21.5%, 22%, 22.5%, 23%, 23.5%, 24%, 24.5%, 25%, 25.5%, 26%, 26.5%, 27%, 27.5%, 28%, 28.5%, 29%, 29.5%, 30% or any value therebetween; preferably, the polyvinyl alcohol resin accounts for 10%-30% of the total mass of the first composition.

[0022] In one embodiment, in order to coat the first composition on a substrate to form a photo-alignment layer, the first composition for preparing the photo-alignment layer needs to contain a certain amount of a first solvent. The first solvent includes glycerol, phenol, propylene glycol, dimethyl sulfoxide, acetone, ethyl acetate, butyl acetate, methanol, ethanol, isopropyl alcohol, n-butanol, isobutyl alcohol, isopropyl alcohol, and water, and any one or more of these can be selected and mixed. If a mixed solvent is used, the selected mixed solvent needs to be mixed in a certain ratio. The amount of the solvent can be selected according to the process requirements.

[0023] In one embodiment, the second composition may include a reactive monomer liquid crystal. The reactive monomer liquid crystal can be synthesized by itself or purchased commercially. It only needs to satisfy the requirement that one end of the liquid crystal molecule in the reactive monomer liquid crystal carries a polar group. There is a strong polar repulsion between the liquid crystal molecule with the polar group and the photo-alignment layer, inducing the liquid crystal molecules to align vertically. The polar group includes but is not limited to hydroxyl, carboxyl, hydroxymethyl, cyano, amino, amide, nitro, aldehyde, ketone, ester, sulfonic acid and other groups, among which hydroxyl and carboxyl groups are preferred. Preferably, the liquid crystal molecules in the reactive monomer liquid crystal have reactive groups, and the reactive liquid crystal molecules cross-link under ultraviolet light to form a network structure, achieving a relatively stable vertical alignment. Its reactive groups can be selected from acrylate, methacrylate, epoxy, azobenzene, coumarin derivatives, unsaturated double bonds, unsaturated acetylenic bonds, succinimide groups, etc., among which acrylate and methacrylate are preferred. A single liquid crystal molecule can be selected or a mixture of multiple liquid crystal molecules can be selected. In one embodiment, the reactive monomer liquid crystal accounts for 3%-20% of the total mass of the second composition in terms of mass fraction; in actual processes, the proportion of the reactive monomer liquid crystal in the second composition can be adjusted according to different production requirements. For example, the reactive monomer liquid crystal accounts for 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, 20% or any value between these values ​​of the total mass of the second composition; preferably, the reactive monomer liquid crystal accounts for 5%-20% of the total mass of the second composition.

[0024] In one embodiment, the second composition for preparing the liquid crystal layer may contain a photoinitiator, and the photoinitiator may be a cleavage-type free radical photoinitiator (including but not limited to 2,4,6-trimethylbenzylphosphine oxide, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 1-hydroxycyclohexylphenyl ketone, 2-methyl-1-(4-methylthiophenyl)-2-morpholinyl-1-propanone, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl) butanone, phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide, 4-phenylbenzophenone, 2,4,6-trimethylbenzoylphosphonic acid ethyl ester, 2,4,6-trimethylbenzoylphenylphosphonic acid ethyl ester, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, etc.); a hydrogen abstraction-type free radical photoinitiator (including but not limited to benzophenone, 2-isopropylthioxanthone, 2,4-diethyl Thioxanthone, 2-chlorothioxanthone, 4,4-bis(diethylamino)benzophenone, ethyl 4-dimethylaminobenzoate, 2-ethylhexyl 4-dimethylaminobenzoate, 4-phenylacyl-4-methyldiphenyl sulfide, 4-benzoyl-4-methyldiphenyl sulfide, 4-benzoyl-4-methyldiphenyl sulfide, etc.); cationic photoinitiators (including but not limited to iodonium salts (hexafluorophosphates), sulfonium salts, diphenyliodonium hexafluoroantimonate , triarylsulfonium salts, diphenyliodonium tetrafluoroborate, iodonium salts, etc.); oxime ester photoinitiators (including but not limited to 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]ethanone 1-(O-acetyl oxime) (OXE-02), 1-[4-(phenylthio)phenyl]-1,2-octanedione 2-(O-benzoyl oxime) (OXE-05), etc.), one or more of which can be used in combination. In which, the photoinitiator accounts for 0.1%-5% of the total mass of the second composition in terms of mass fraction; in actual processes, the proportion of the photoinitiator in the second composition can be adjusted according to different production requirements. For example, the photoinitiator accounts for 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.75%, 1%, 1.25%, 1.5%, 1.6%, 1.8%, 2%, 2.25%, 2.5%, 2.75%, 3%, 3.25%, 3.5%, 3.75%, 4%, 4.5%, 5% of the total mass of the second composition, or any value between these values; preferably, the photoinitiator accounts for 0.2%-2% of the total mass of the second composition.

[0025] In order to coat the second composition on the photo-alignment layer to form a liquid crystal layer, the second composition may contain a certain amount of a second solvent. For example, the second solvent may be selected from one or more of acetone, butanone, methyl ethyl ketone, cyclohexanone, cyclopentanone, methyl isobutyl ketone, isophorone, N-methylpyrrolidone, dioxane, tetrahydrofuran, ethyl ether, anisole, diethyl ether, propylene glycol methyl ether, n-hexane, heptane, cyclohexane, cyclopentane, toluene, xylene, dichloromethane, dichloroethane, dichlorobenzene, chlorotoluene, ethyl acetate, butyl acetate, propylene glycol methyl ether acetate, water, ethanol, n-butanol, sec-butanol, isopropyl alcohol, cyclohexanol, dimethyl sulfoxide, diethyl sulfoxide, benzylphenyl sulfoxide, dimethylformamide, dimethylacetamide, etc. The amount of the second solvent can be selected according to process requirements.

[0026] The second composition used to prepare the liquid crystal layer may also contain a leveling agent, which can help the second composition coating form a smooth, uniform coating film during the drying process, adjust the surface tension of the second composition solution, and improve the leveling properties of the second composition solution. The leveling agent may include silicone leveling agents (including but not limited to BYK-306, BYK-360, TegoGlide 420, Dow Corning DC-57, YP-323, etc.); acrylate leveling agents (including but not limited to EFKA-3777, BYK-358N, Tego Flow 370, Drewplus L-475, Modaflow 9200, BYK-354, etc.); or fluorocarbon leveling agents (including but not limited to Capstone FS-61, Fluorad FC-4430, DIC S393, Unidyne TG-656, ZonylFSO, etc.). One or more of these may be used in combination. In one embodiment, the leveling agent accounts for 0.1%-10% of the total mass of the second composition by mass. In actual processes, the proportion of the leveling agent in the second composition can be adjusted according to different production requirements. For example, the leveling agent accounts for 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10% of the total mass of the second composition, or any value therebetween. Preferably, the leveling agent accounts for 0.1%-5% of the total mass of the second composition.

[0027] In one embodiment, a low molecular weight resin, such as pentaerythritol triacrylate, may be added to the second composition according to actual production needs. However, those skilled in the art will appreciate that this material is not essential.

[0028] In one embodiment, the present application provides a method for preparing a phase difference film, comprising: providing a substrate; coating the above-mentioned first composition on the substrate to form a photo-alignment layer; and coating the above-mentioned second composition on the photo-alignment layer to form a liquid crystal layer.

[0029] The substrate on which the photo-alignment layer is applied needs to be sufficiently flat and smooth, and have good hydrophilicity. The substrates available can be inorganic or organic. The point defect size of the selected substrate should be ≥1mm. 2 The point defect density needs to be ≤5ea / m 2 The substrate must be free of visible scratches, marks, or streaks, with an end surface flatness of ≤3mm and low surface roughness (average roughness Sa ≤15nm, maximum height roughness Sz ≤150nm). The total light transmittance must not be less than 80%, and the substrate's long-term stable operating temperature must not be lower than 80°C. The substrate must have good hydrophilicity (containing abundant hydrophilic groups such as hydroxyl, carboxyl, amino, and sulfonic acid groups). The coated surface of the substrate can be further hydrophilized through surface pretreatment to reduce the substrate's water drop angle. Surface pretreatment can include one or more methods such as plasma treatment, corona treatment, alkaline cleaning, acid cleaning, and ultraviolet treatment to increase the substrate's hydrophilicity and reduce the water drop angle. The water drop angle of the coated surface of the substrate should be <90°, and preferably the water contact angle of the coated surface should be ≤50° (i.e., the coated surface should have a high number of hydrophilic groups, such as carboxyl, hydroxyl, and other active groups).

[0030] In the above embodiment, the photo-alignment layer is formed by uniformly coating a first composition (hereinafter referred to as the photo-alignment layer solution) on a substrate and drying it in a hot air oven; and the liquid crystal layer is formed by uniformly coating a second composition (hereinafter referred to as the liquid crystal layer solution) on the photo-alignment layer, drying it in a hot air oven, and then VU curing it. Specifically, the method for preparing the retardation film includes the following steps: Step 1: Evenly coat the prepared photo-alignment layer solution on the substrate as described above and place in a hot air oven for a predetermined period of time to dry to obtain the photo-alignment layer. The hot air oven temperature is 30-180°C, preferably 50-120°C. The drying time can be 0.5-20 minutes, preferably 1-10 minutes. Step 2: Evenly coat the prepared liquid crystal layer solution on the photo-alignment layer prepared in step 1, and place in a hot air oven for a certain period of time for drying. The hot air oven temperature can be selected from 30-100°C, preferably 50-90°C. Step 3: Place the film dried in step 2 in an N2 atmosphere and irradiate the liquid crystal layer with ultraviolet light of a certain energy to obtain a liquid crystal retardation film after complete curing. The N2 concentration is 30%-99.999%, preferably 70%-99.999%, and the ultraviolet light energy can be 10mJ / cm 2 -3000mJ / cm2 , preferably 500mJ / cm 2 -2500mJ / cm 2 .

[0031] The photo-alignment layer coated on the flat and smooth substrate can make the liquid crystal molecules align vertically and realize lossless separation of the photo-alignment layer and the liquid crystal layer in the subsequent transfer process.

[0032] In one embodiment, a phase difference film prepared by the above-mentioned preparation method is provided, wherein the vertical alignment (VA) of the liquid crystal molecules in the phase difference film is characterized in that the long axis direction (optical axis) of the liquid crystal molecules is arranged perpendicular to the surface of the substrate, so that the liquid crystal molecules form an angle of nearly 90° with the substrate in a static state, forming a special orientation arrangement. This orientation arrangement can be used to determine the vertical orientation of the liquid crystal by detecting the pretilt angle of the liquid crystal film. The pretilt angle of the qualified liquid crystal alignment film in the present invention is ±90.00±0.5 (°).

[0033] The liquid crystal retardation film provided by the present invention forms a vertical alignment of liquid crystal molecules on the photo-alignment layer, which is the core of achieving high contrast and wide viewing angle designs in liquid crystal display technology. The photo-alignment layer provides physical confinement for the liquid crystal molecules, with their long axes constrained by the grooves, achieving vertical or mixed alignment. The photo-alignment layer contains a large number of polar molecules, which interact strongly with the polar groups in the liquid crystal molecules, thereby inducing vertical alignment of the liquid crystal molecules. However, the strong polar interaction between the liquid crystal layer and the photo-alignment layer affects the subsequent use of the liquid crystal retardation film. Based on this defect, the inventors creatively discovered that after the liquid crystal molecules are induced to vertically align by the photo-alignment layer, the liquid crystal retardation film of the present invention adds an aldehyde substance to the first composition used to prepare the photo-alignment layer, so that the aldehyde substance and the polyvinyl alcohol resin substance undergo an aldol condensation reaction, thereby reducing the number of polar groups in the photo-alignment layer and further reducing the polar interaction force between the photo-alignment layer and the liquid crystal layer. At the same time, the present invention adopts a hydrophilic substrate, the surface of which contains abundant hydrophilic groups such as hydroxyl groups and carboxyl groups. On the one hand, since the aldehyde substance having an aldehyde group is added to the photo-alignment layer, the aldehyde group can enhance the adhesion between the photo-alignment layer and the substrate through chemical bonding force with the hydroxyl groups on the substrate surface. On the other hand, the polar groups in the polyvinyl alcohol resin substance in the photo-alignment layer can also enhance the adhesion between the photo-alignment layer and the substrate through intermolecular polar forces with the polar groups on the substrate surface. Ultimately, the liquid crystal layer is completely peeled off from the photo-alignment layer without any residue of the photo-alignment layer after peeling. In addition, the present invention uses reactive liquid crystal molecules for cross-linking and curing, thereby maintaining the vertical alignment of the liquid crystal layer after being peeled off from the photo-alignment film.

[0034] The retardation film provided by the present invention is further described below with reference to specific examples. Unless otherwise specified, all raw materials used are commercially available. Percentages are by weight, and temperatures are in degrees Celsius. The reactive monomeric liquid crystals used in the following examples were purchased from Merck.

[0035] Example 1 A phase difference film with a liquid crystal layer and an optical alignment layer that can be separated without loss is prepared by the following steps: S1: PVA-403 (45 parts by mass), glyoxal (40 parts by mass), water (260 parts by mass), and ethanol (50 parts by mass) were stirred in a 70°C waterbath for 1.5 hours to obtain a photo-alignment layer solution. This solution was evenly coated onto a substrate using a 30-micron wire rod (with a 40° drop angle). The solution was then heated in a 100°C forced air oven for 2 minutes to obtain a photo-alignment layer.

[0036] S2: Reactive monomer liquid crystal 2435 (commercially available from Merck, 80 parts by mass), photoinitiator OXE-02 (2 parts by mass), leveling agent BYK-360 (2 parts by mass), leveling agent BYK-354 (0.5 parts by mass), pentaerythritol triacrylate (5 parts by mass), cyclohexanone (180 parts by mass), propylene glycol methyl ether acetate (180 parts by mass), and toluene (90 parts by mass). Stir in a 50°C water bath for 1.5 hours to obtain a liquid crystal layer solution. This photo-alignment layer solution was evenly coated on the photo-alignment layer using a wire rod (#15 micron) and heated in a 70°C forced air oven for 1 minute.

[0037] S3: Place the dried film in S2 in an atmosphere with a N2 concentration of not less than 90%, and use 1000mJ / cm 2 The photo-alignment film is cured by irradiation with ultraviolet rays.

[0038] Example 2 A phase difference film of a liquid crystal layer and a light alignment layer that can be separated without loss of separation is provided, wherein the phase difference film is different from that of Example 1 in that an equal amount of PVA-403 in step S1 is replaced by PVA-205.

[0039] Example 3 A phase difference film of a liquid crystal layer and a light alignment layer that can be separated without loss of separation is provided. The phase difference film is different from that of Example 1 in that an amount of PVA-205 equal to that of PVA-403 is added in step S1.

[0040] Example 4 A phase difference film with a liquid crystal layer and an optical alignment layer that can be separated without loss of separation, wherein the preparation steps are as follows: S1: PVA-403 (45 parts by mass), PVA-205 (45 parts by mass), water (260 parts by mass), and ethanol (50 parts by mass) were stirred in a 70°C waterbath for 1.5 hours. Then, glyoxal (40 parts by mass) was added and stirred for another 0.5 hours to obtain a photo-alignment layer solution. This photo-alignment layer solution was evenly coated onto the substrate using a #30 micron wire rod (the water contact angle on the coated substrate was 70°). The solution was then heated in a 100°C forced air oven for 2 minutes to obtain the photo-alignment layer.

[0041] S2: Reactive liquid crystal 2435 (commercially available from Merck, 80 parts by mass), photoinitiator OXE-02 (2 parts by mass), leveling agent BYK-360 (2 parts by mass), leveling agent BYK-354 (2 parts by mass), pentaerythritol triacrylate (5 parts by mass), cyclohexanone (180 parts by mass), propylene glycol methyl ether acetate (180 parts by mass), and toluene (90 parts by mass). Stir in a 50°C water bath for 1.5 hours to obtain a liquid crystal layer solution. This photoalignment layer solution was evenly coated on the photoalignment layer using a wire rod (#15 micron) and heated in a 70°C forced air oven for 1 minute.

[0042] S3: Place the dried film in S2 in an atmosphere with a N2 concentration of not less than 90%, and use 1000mJ / cm 2 The photo-alignment film is cured by irradiation with ultraviolet rays.

[0043] Example 5 A phase difference film of a liquid crystal layer and a light alignment layer that can be separated without loss of separation is provided, which differs from Example 4 in that the substrate in step S1 is replaced with a substrate with a substrate water drop angle of 40°.

[0044] Example 6 A phase difference film of a liquid crystal layer and a photo-alignment layer that can be separated without loss of separation is provided, which is different from Example 5 in that the pentaerythritol triacrylate in step S2 is removed.

[0045] Example 7 A retardation film of a liquid crystal layer and a photo-alignment layer that can be separated without loss of separation is provided, wherein the difference between the retardation film and the embodiment 6 is that ethyl acetate (30 parts by mass) is added in step S1.

[0046] Example 8 A phase difference film of a liquid crystal layer and a light alignment layer that can be separated without loss of separation is provided, which differs from Example 7 in that glutaraldehyde in an amount equal to that of glyoxal is added in step S1.

[0047] Example 9 A phase difference film of a liquid crystal layer and a photo-alignment layer that can be separated without loss, which is different from Example 8 in that the contents of glyoxal and glutaraldehyde are both halved.

[0048] Example 10 A phase difference film of a liquid crystal layer and a light alignment layer that can be separated without loss, which is different from Example 6 in that the content of glyoxal is doubled.

[0049] Example 11 A phase difference film of a liquid crystal layer and a light alignment layer that can be separated without loss of separation is provided, which is different from Example 9 in that the heating temperature in step S2 is increased to 80°C.

[0050] Example 12 A phase difference film with a liquid crystal layer and a light alignment layer that can be separated without loss, which is different from Example 11 in that the light curing energy in step S3 is increased to 2100 mJ / cm 2 .

[0051] Example 13 A phase difference film of a liquid crystal layer and an optical alignment layer that can be separated without loss of separation, which differs from Example 7 in that the thermal drying temperature in step S1 is increased to 110°C, the drying time is shortened to 1.5 minutes, and the curing energy in step S3 is increased to 1800mJ / m 2 .

[0052] Comparative Example 1 A phase difference film of a liquid crystal layer and a light alignment layer that cannot be separated without loss is prepared by the following steps: S1: PVA-403 (45 parts by mass), water (260 parts by mass), and ethanol (50 parts by mass) were stirred in a 70°C water bath for 1.5 hours to obtain a photo-alignment layer solution. This photo-alignment layer solution was evenly coated onto a substrate using a 30-micron wire rod (with a water drop angle of 110°). The solution was then heated in a 110°C forced air oven for 1.5 minutes to obtain a photo-alignment layer.

[0053] S2: Reactive liquid crystal 2435 (commercially available from Merck, 80 parts by mass), photoinitiator OXE-02 (2 parts by mass), leveling agent BYK-360 (2 parts by mass), leveling agent BYK-354 (0.5 parts by mass), pentaerythritol triacrylate (5 parts by mass), cyclohexanone (180 parts by mass), propylene glycol methyl ether acetate (180 parts by mass), and toluene (90 parts by mass). Stir in a 50°C water bath for 1.5 hours to obtain a liquid crystal layer solution. This photo-alignment layer solution was evenly coated on the photo-alignment layer using a wire rod (#15 micron) and heated in a 70°C forced air oven for 1 minute.

[0054] S3: Place the dried film in S2 in an atmosphere with a N2 concentration of not less than 90%, and use 1800mJ / cm 2 The photo-alignment film is cured by irradiation with ultraviolet rays.

[0055] Comparative Example 2 A liquid crystal retardation film is provided, which is different from Comparative Example 1 in that PVA-205 (45 parts by mass) is added in step S1, and the substrate is replaced with a hydrophilic substrate with a water drop angle of 45°.

[0056] Comparative Example 3 A liquid crystal retardation film is provided, which is different from Comparative Example 2 in that pentaerythritol triacrylate (5 parts by mass) in step S2 is removed.

[0057] Performance Testing ① Optical performance test: Use AxoScan (produced by Axometrics, USA) to test the pre-tilt angle (Pre Tilt), optical film thickness (d), and optical delay in the vertical direction of the film (i.e., the phase difference value in the Z-axis direction, Rth). Specifically, by inputting the average refractive index ((N x +N y +N z ) / 3) and film thickness (d (μm)), calculate Rth=(N z -(N x +N y ) / 2)×d.

[0058] ② Peel Force Testing: A tensile testing machine (Model: KJ-1065A) was used to test the peel force between the retardation film layers. The test modes were 90° peeling (perpendicular to the sample) and 180° peeling (parallel to the sample). 3M transparent tape was applied to the liquid crystal layer and the system was programmed to automatically record the peel force during the peeling process. This system primarily tests the peel force at a 90° peeling angle, as required by the customer.

[0059] ③Interlayer peeling detection: Stick 3M tape or adhesive Tac evenly on the liquid crystal layer. Quickly tear off the 3M tape or adhesive Tac and check the peeling between the liquid crystal layer and the photo-alignment layer.

[0060] The optical performance test results of each embodiment and comparative example are shown in Table 1 below: Table 1: Optical properties of retardation films

[0061] As can be seen from Table 1, the liquid crystal molecules of the liquid crystal retardation films of Examples 1-13 and Comparative Examples 1-3 can all achieve vertical alignment (the pre-tilt angles are all close to 90 degrees), and the optical properties are qualified.

[0062] 3M tape was used to detect the peeling between the liquid crystal layer and the photo-alignment layer, and the results are shown in Table 2 below. In Tables 2 and 3 below, "liquid crystal layer peeling" means peeling the liquid crystal layer from the photo-alignment layer; "photo-alignment layer peeling" means peeling the photo-alignment layer from the substrate, and "whether the peeling is complete" means whether the peeling of the liquid crystal layer is complete and intact. Peelable means: the adhesion between the liquid crystal layer-photo-alignment layer or the photo-alignment layer-substrate layer is less than the adhesion provided by 3M tape or adhesive Tac, that is, the two layers can be separated using 3M tape or adhesive Tac. Unpeelable means: the adhesion between the liquid crystal layer-photo-alignment layer or the photo-alignment layer-substrate layer is greater than the adhesion provided by 3M tape or adhesive Tac, that is, the two layers cannot be separated using 3M tape or adhesive Tac.

[0063] Table 2 Separation between liquid crystal layer and photo-alignment layer

[0064] As can be seen from Table 2, Examples 1-13 all achieved complete peeling of the liquid crystal layer from the photo-alignment layer. When the water contact angle of the substrate decreases, the interaction between the photo-alignment layer and the substrate increases, making it impossible to peel the photo-alignment layer from the substrate. The peeling forces for different Examples and Comparative Examples vary, as shown in Table 3 below: Table 3 Peel force of different phase difference films

[0065] Combining Tables 2 and 3, it can be seen that even if different embodiments show the same peeling results, there are still obvious differences in their peeling forces. This shows that by adjusting the formulation ratio and process parameters, the reaction completion degree in the photo-alignment layer can be different, resulting in different peeling forces and peeling results.

[0066] The different peeling forces and peeling results of the above embodiments and comparative examples indicate that the present invention can achieve lossless peeling of the liquid crystal layer of the phase difference film, and provide high-quality liquid crystal films available for panel manufacturers to manufacture high-performance display screens.

[0067] In summary, the liquid crystal layer of the liquid crystal retardation film of the present invention can be completely and intactly peeled off from the photo-alignment layer, thereby avoiding the poor display effect of the display screen caused by incomplete peeling of the liquid crystal layer or partial adhesion of the photo-alignment layer to the liquid crystal layer during the use of the retardation film; the photo-alignment layer coated on the flat and smooth substrate can make the liquid crystal molecules vertically oriented while achieving lossless separation of the photo-alignment layer and the liquid crystal layer in the subsequent transfer process, thereby avoiding the degradation of the composite optical film layer performance caused by problems such as water absorption, aging and yellowing of the photo-alignment layer under long-term working conditions and poor weather resistance.

[0068] The above describes the embodiments of the present application, but the present application is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of this application, ordinary technicians in this field can also make many forms without departing from the purpose of this application and the scope of protection of the claims, all of which are within the protection of this application.

Claims

1. A phase difference film, characterized in that: The method comprises a photo-alignment layer and a liquid crystal layer, wherein the photo-alignment layer is formed by polymerizing a first composition, and the liquid crystal layer is formed by polymerizing a second composition; The first composition includes: an aldehyde substance and a polyvinyl alcohol resin; The second composition includes reactive monomeric liquid crystal.

2. The phase difference film according to claim 1, wherein In terms of mass fraction, the aldehyde substance accounts for 0.5%-20% of the total mass of the first composition; Calculated by mass fraction, the polyvinyl alcohol resin accounts for 1%-30% of the total mass of the first composition; Calculated by mass fraction, the reactive monomer liquid crystal accounts for 3%-20% of the total mass of the second composition.

3. The phase difference film according to claim 1, wherein The second composition further includes a photoinitiator and a leveling agent; In terms of mass fraction, the photoinitiator accounts for 0.1%-5% of the total mass of the second composition; Calculated by mass fraction, the leveling agent accounts for 0.1%-10% of the total mass of the second composition.

4. The phase difference film according to claim 3, characterized in that The aldehyde substance is selected from one or more combinations of glyoxal, benzaldehyde, acetaldehyde, octanal, octanal, p-methoxybenzaldehyde, p-chlorobenzaldehyde, o-chlorobenzaldehyde, 3-nitro-4-pyridinealdehyde, isohexaldehyde, valeraldehyde, butyraldehyde, pyridinealdehyde, thiophenealdehyde, 2-furaldehyde, glyoxylic acid, 6-ethoxy-2-naphthaldehyde, 4-chloro-2-hydroxybenzaldehyde, propionaldehyde, malondialdehyde, succinaldehyde, glutaraldehyde, adipaldehyde, nonanal, undecanal, lauric aldehyde, tridecanal, and myristic aldehyde; The polyvinyl alcohol resin is selected from one or more of PVA17-88, PVA17-92, PVA17-99, PVA05-88, PVA24-99, PVA24-88, PVA-103, PVA-105, PVA-117, PVA-124, PVA-613, PVA-203, PVA-205, PVA-217, PVA-220, PVA-235, PVA-403, PVA-420H, PVA-422H, PVA-424H, PVA-505, polyvinyl formal, polyvinyl butyral, polyvinyl acetal, and a carboxyl-modified polyvinyl alcohol resin; The photoinitiator is selected from a combination of one or more of a cleavage-type free radical photoinitiator, a hydrogen abstraction-type free radical photoinitiator, a cationic photoinitiator, and an oxime ester photoinitiator; The leveling agent is selected from one or more combinations of acrylates, silicones and fluorocarbons.

5. The phase difference film according to claim 1, wherein The first composition further includes a first solvent; The second composition further includes a second solvent; The first solvent is selected from one or more combinations of glycerol, phenol, propylene glycol, dimethyl sulfoxide, acetone, ethyl acetate, butyl acetate, methanol, ethanol, isopropanol, n-butanol, isobutanol, and water; The second solvent is selected from one or more combinations of acetone, butanone, methyl ethyl ketone, cyclohexanone, cyclopentanone, methyl isobutyl ketone, isophorone, N-methylpyrrolidone, dioxane, tetrahydrofuran, ethyl ether, anisole, diethyl ether, propylene glycol methyl ether, n-hexane, heptane, cyclohexane, cyclopentane, toluene, xylene, dichloromethane, dichloroethane, dichlorobenzene, chlorotoluene, ethyl acetate, butyl acetate, propylene glycol methyl ether acetate, water, ethanol, n-butanol, sec-butanol, isopropyl alcohol, cyclohexanol, dimethyl sulfoxide, diethyl sulfoxide, benzylphenyl sulfoxide, dimethylformamide, dimethylacetamide, etc.

6. A method for preparing a phase difference film, characterized in that: include: providing a substrate; applying the first composition according to any one of claims 1 to 5 on the substrate to form a photo-alignment layer; The second composition according to any one of claims 1 to 5 is coated on the photo-alignment layer to form a liquid crystal layer.

7. The method for preparing a phase difference film according to claim 6, wherein: The average roughness of the surface of the substrate is ≤15 nm, the maximum height roughness of the surface of the substrate is ≤150 nm, the total light transmittance of the substrate is above 80%, and the water drop angle of the coated surface of the substrate is <90°.

8. The method for preparing a phase difference film according to claim 6, wherein: The step of coating the first composition on the substrate to form a photo-alignment layer further comprises: After coating the first composition on the substrate, the film is heated and dried. The temperature of the heating and drying treatment is 30-180° C. and the heating time is 0.5-20 minutes.

9. The method for preparing a phase difference film according to claim 6, wherein: The step of coating the second composition on the photo-alignment layer to form a liquid crystal layer further comprises: b1) after coating the second composition on the photo-alignment layer, heating and drying the film, wherein the temperature of the heating and drying treatment is 30-100° C.; b2) curing the dried film with ultraviolet light in an N2 atmosphere to obtain the liquid crystal layer, wherein the concentration of N2 is 30%-99.999% and the irradiation energy of the ultraviolet light is 10 mJ / cm 2 -3000mJ / cm 2 .

10. The method for preparing a phase difference film according to claim 6, wherein: The liquid crystal molecules in the liquid crystal layer are vertically aligned.

Images