Liquid crystal alignment film forming liquid crystal orienting agent and liquid crystal display element

Abstract

This invention belongs to the field of liquid crystal displays and discloses a liquid crystal alignment agent for forming liquid crystal alignment films and a liquid crystal display element. The aim is to provide a liquid crystal alignment agent that, when using negative liquid crystals, can achieve photoalignment films with excellent light spots and image retention characteristics. Furthermore, the alignment agent exhibits excellent viscosity stability during storage, while simultaneously protecting the liquid crystal alignment film obtained from this alignment agent and the liquid crystal display element containing this film. This invention utilizes a modified benzidine reacted with a tetracarboxylic acid dianhydride containing a cyclobutane structure to prepare a polyamic acid coating solution. The resulting photoalignment agent exhibits good storage stability, high compatibility with negative liquid crystal materials, avoids bright spot defects, and possesses excellent image retention characteristics. It can be applied to FFS-driven liquid crystal display elements and other applications requiring high display quality.

Description

Technical Field

[0001] This invention relates to the field of liquid crystal display technology, specifically to a liquid crystal alignment agent used to form a liquid crystal alignment film, thereby manufacturing a liquid crystal display element with good image retention characteristics and excellent storage stability; it also relates to a liquid crystal alignment film obtained from the liquid crystal alignment agent, and a liquid crystal display element having the liquid crystal alignment film. Background Technology

[0002] Photoalignment, as a non-frictional alignment method, is a simple manufacturing process in industry. Especially in liquid crystal display (LCD) devices using IPS (In-Plane Switching) or FFS (Fringe Field Switching) driving methods, using liquid crystal alignment films obtained through photoalignment, compared to those obtained through friction methods, is expected to improve the contrast and viewing angle characteristics of the LCD device. This can enhance the performance of the LCD device, making this method a highly promising liquid crystal alignment technology that has attracted considerable attention.

[0003] However, liquid crystal alignment films obtained by photoalignment have the following problems: compared with alignment films obtained by rubbing, the polymer films have a lower degree of anisotropy in the alignment direction. If the anisotropy is insufficient, sufficient liquid crystal alignment cannot be obtained, leading to problems such as image retention after the liquid crystal display element is manufactured.

[0004] On the other hand, as a method to improve the anisotropy of liquid crystal alignment films obtained by photoalignment, there have been proposals to remove the low molecular weight components generated by the breakage of the polyimide backbone caused by light irradiation after light irradiation.

[0005] Traditionally, liquid crystal display elements driven by IPS or FFS use positive liquid crystals, but using negative liquid crystals can reduce transmission loss above the electrodes and improve contrast.

[0006] If the liquid crystal alignment film obtained by photoalignment is used in IPS / FFS driving liquid crystal display elements employing negative liquid crystals, higher display performance than conventional display elements is expected. However, according to patents, when display elements are fabricated using so-called photodecomposition-type liquid crystal alignment films that achieve liquid crystal alignment by decomposing polymers through light irradiation to generate anisotropy, and negative liquid crystals, the incidence of display defects (bright spots) caused by polymer decomposition products generated by polarized ultraviolet light irradiation is extremely high. Furthermore, patent JP6852771B2 proposes using a diamine with a specific structure as the alignment film polymer, which can achieve a photoalignment film with no bright spots and good image retention characteristics when using negative liquid crystals. However, even with this specific diamine alignment film, the above problems are not completely solved. Other diamines with similar structures have also been claimed to improve liquid crystal alignment, scratch resistance, vibration resistance, and sealing adhesion, but alignment films composed of such diamines still have shortcomings. More importantly, the viscosity of the alignment agent coating solution of the specific diamine described in existing patents is prone to fluctuation during storage, resulting in uneven film thickness.

[0007] The present invention aims to provide a liquid crystal alignment agent that can achieve a photoalignment film with excellent light spot and image retention characteristics when using negative liquid crystals, and the alignment agent has excellent viscosity stability during storage; at the same time, it protects the liquid crystal alignment film obtained by the alignment agent and the liquid crystal display element containing the film. Summary of the Invention

[0008] To address the problems mentioned in the background section, the present invention provides a liquid crystal alignment agent for forming a liquid crystal alignment film, a liquid crystal alignment film, and a liquid crystal display element.

[0009] This invention provides a liquid crystal alignment agent that, when using negative liquid crystals, can achieve a photoalignment film with excellent characteristics such as no bright spots and excellent image retention. Furthermore, the alignment agent exhibits excellent viscosity stability during storage and protects the liquid crystal alignment film obtained from this alignment agent and the liquid crystal display element containing this film. This invention utilizes a modified benzidine reacted with a tetracarboxylic acid dianhydride containing a cyclobutane structure to prepare a polyamic acid coating solution. The resulting photoalignment agent exhibits good storage stability, high compatibility with negative liquid crystal materials, avoids bright spot defects, and possesses excellent image retention characteristics. It can be applied to FFS-driven liquid crystal display elements and other applications requiring high display quality.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: A liquid crystal alignment agent for forming a liquid crystal alignment film comprises a polymer consisting of a polyamic acid obtained by the polycondensation reaction of a diamine and a tetracarboxylic acid dianhydride as shown in Formula 1 below, and a polyimide obtained by imidizing the polyamic acid. (Equation 1) In Formula 1, at least one of the R1 and R2 groups is a hydrogen atom, a methyl group, or a methoxy group.

[0011] Preferably, the polymer is synthesized from a diamine monomer in Formula 1, where R1 and R2 are both methyl groups.

[0012] Preferably, the polymer is synthesized from a diamine monomer in Formula 1, where R1 is a methyl group and R2 is a hydrogen atom.

[0013] Preferably, the tetracarboxylic dianhydride comprises any of the following structures (Formula 2). (Equation 2) R1 to R4 each independently represent a hydrogen atom, a halogen atom, an alkyl group with 1 to 6 carbon atoms, an alkenyl group with 2 to 6 carbon atoms, an alkynyl group with 2 to 6 carbon atoms, a monovalent organic group with 1 to 6 carbon atoms containing a fluorine atom, or a phenyl group; and at least one of R1 to R4 represents a group other than a hydrogen atom as defined above.

[0014] Preferably, in Formula 2, R1 and R4 are methyl groups, and R2 and R3 are hydrogen atoms.

[0015] A liquid crystal alignment agent is composed of the aforementioned polyamic acid and polyimide obtained by imidization.

[0016] A liquid crystal alignment film formed using the aforementioned liquid crystal alignment agent.

[0017] A liquid crystal display element having the aforementioned liquid crystal alignment film.

[0018] Compared with the prior art, the beneficial effects of the present invention are: By using a liquid crystal alignment agent containing the diamine synthetic polymer of this invention, the viscosity increase during the storage period of the alignment agent and the resulting increase in film thickness can be prevented, while bright spot defects caused by alignment film decomposition products during photoalignment processing are suppressed. This results in an alignment film with high exposure sensitivity and excellent liquid crystal alignment, thereby providing a liquid crystal display element with no display defects and high reliability.

[0019] The diamine, used as a polymer raw material for the alignment agent, has a specific number of substituents at specific positions, which promotes the formation of an optimized ordered structure among the polymers after film formation, thereby improving bright spots and display defects caused by light exposure. In addition, this moderate orderliness can suppress excessive interaction between polymer chains or viscosity increase caused by excessive crystallization during storage, thereby improving the storage viscosity stability of the alignment agent and the uniformity of film thickness. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Unless otherwise specified, the raw materials used in this invention are all from commercially available conventional products.

[0022] <Specific Structure> The polymer constituting the liquid crystal alignment agent of the present invention is prepared from a diamine having a specific structure represented by the following (Formula 1).

[0023] (Equation 1) In Formula 1, at least one of the R1 and R2 groups is a hydrogen atom, a methyl group, or a methoxy group.

[0024] As specific examples of diamines having the above-mentioned specific structure, the following diamines can be listed, but are not limited to these.

[0025]

[0026] To provide an alignment agent that can suppress bright spots caused by alignment film decomposition products during photoalignment processing, obtain an alignment film with high photosensitivity and excellent liquid crystal alignment, and thus realize a high-reliability liquid crystal display element without display defects, while preventing viscosity fluctuations during storage and the resulting uneven film thickness, the diamine shown in (Formula 1) contains: Preferably, at least one of R1 and R2 is a hydrogen atom, a methyl group, or a methoxy group; More preferably, at least one of R1 and R2 is a hydrogen atom or a methyl group; The optimal choice is for R1 to be a methyl group and for R2 to be a hydrogen atom.

[0027] Synthesis of diamines: The main synthetic methods for the aforementioned diamines will be described in detail in the examples. It should be noted that the methods described below are merely examples and are not intended to limit the scope of the methods described.

[0028] The polyimide precursor used in this invention is a product obtained by reacting a diamine component with a tetracarboxylic acid derivative, namely polyamic acid.

[0029] <Polyimide precursor (polyamic acid)> Polyamic acid, the polyimide precursor used in this invention, can be prepared by the following method: Specifically, it is synthesized by reacting tetracarboxylic acid dianhydride with diamine at -20 to 150°C (preferably 0 to 50°C) for 30 minutes to 24 hours (preferably 1 to 12 hours) in the presence of an organic solvent.

[0030] The reaction between the diamine and tetracarboxylic acid components is typically carried out in an organic solvent. There are no particular restrictions on the organic solvent used, as long as it can dissolve the resulting polyimide precursor. Specific examples of organic solvents used in the reaction are listed below, but are not limited to these. Examples include: N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, γ-butyrolactone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, or 1,3-dimethylimidazolinone.

[0031] In addition, when the polyimide precursor has high solubility, methyl ethyl ketone, cyclohexanone, cyclopentanone, 4-hydroxy-4-methyl-2-pentanone or organic solvents shown in formulas [D-1] to [D-3] can be used.

[0032]

[0033] In formula [D-1], D1 represents an alkyl group having 1 to 3 carbon atoms; in formula [D-2], D2 represents an alkyl group having 1 to 3 carbon atoms; and in formula [D-3], D3 represents an alkyl group having 1 to 4 carbon atoms.

[0034] These solvents can be used alone or in combination. Furthermore, even solvents that do not dissolve the polyimide precursor can be mixed with the aforementioned solvents as long as they do not cause the precipitation of the generated polyimide precursor. Additionally, since water in the solvent inhibits the polymerization reaction and causes hydrolysis of the generated polyimide precursor, solvents that have undergone dehydration and drying are preferred. The concentration of the polyamic acid polymer in the reaction system is preferably 1–30 wt%, more preferably 5–20 wt%, from the perspective of avoiding polymer precipitation and easily obtaining high molecular weight products.

[0035] The polyamic acid obtained as described above can be precipitated and recovered by injecting the reaction solution into a poor solvent under thorough stirring. Alternatively, after several precipitation operations, washing with a poor solvent, and drying at room temperature or with heat, refined polyamic acid powder can be obtained. There are no particular limitations on the poor solvent; examples include water, methanol, ethanol, hexane, butyl cellosolve, acetone, and toluene.

[0036] The polyimide used in this invention can be manufactured by imidizing the above-mentioned polyamic acid.

[0037] In the production of polyimides from polyamic acid, chemical imidization is a simple method involving the addition of a catalyst to a polyamic acid solution obtained by reacting a diamine component with a tetracarboxylic dianhydride. The advantages of chemical imidization are that the imidization reaction can be carried out at relatively low temperatures, and the molecular weight of the polymer does not easily decrease during the imidization process.

[0038] Chemical imidization can be carried out by stirring the polyamic acid to be imidized in an organic solvent in the presence of a basic catalyst and an acid anhydride. The organic solvent can be the same as that used in the aforementioned polymerization reaction. Examples of basic catalysts include pyridine, triethylamine, trimethylamine, tributylamine, and trioctylamine. Pyridine is particularly desirable due to its suitable basicity, which promotes the reaction. Furthermore, examples of acid anhydrides include acetic anhydride, trimellitic anhydride, and pyromellitic dianhydride. Acetic anhydride is particularly desirable because it is easy to purify after the reaction.

[0039] The imidization reaction is carried out at a temperature of -20 to 140°C, preferably 0 to 100°C, and for a reaction time of 1 to 100 hours. The amount of alkaline catalyst is 0.5 to 30 molar times that of the amic acid groups, preferably 2 to 20 molar times; the amount of acid anhydride is 1 to 50 molar times that of the amic acid groups, preferably 3 to 30 molar times. The imidization rate of the resulting polymer can be controlled by adjusting the amount of catalyst, temperature, and reaction time.

[0040] The solution obtained after the imidization reaction of polyamic acid may contain residual substances such as the added catalyst. Therefore, it is preferable to recover the imidized polymer obtained by the following method, and then redissolve it in an organic solvent to prepare the liquid crystal alignment agent of the present invention. The polyimide solution obtained by the above method is injected into a poor solvent under thorough stirring to precipitate the polymer. After several precipitation operations, the polymer is washed with the poor solvent and dried at room temperature or by heating to obtain refined polyimide powder. The poor solvent is not particularly limited, and examples include methanol, acetone, hexane, butyl cellosolve, heptane, methyl ethyl ketone, methyl isobutyl ketone, ethanol, toluene, and benzene.

[0041] <Liquid Crystal Alignment Agent> The liquid crystal alignment agent of the present invention contains at least one polymer selected from a polyimide precursor having a specific structure and an imidized polymer of the polyimide precursor. The molecular weight of the polymer, in terms of weight-average molecular weight (Mw), is preferably 2,000 to 500,000, more preferably 5,000 to 300,000, and even more preferably 10,000 to 100,000. Furthermore, the number-average molecular weight (Mn) is preferably 1,000 to 250,000, more preferably 2,500 to 150,000, and even more preferably 5,000 to 50,000.

[0042] The concentration of the polymer in the liquid crystal alignment agent of the present invention can be appropriately changed according to the desired coating thickness. From the perspective of forming a uniform and defect-free coating, it is preferably 1 wt% or more; from the perspective of solution storage stability, it is preferably 10 wt% or less. The polymer concentration is preferably 2 to 7 wt%.

[0043] The organic solvent (hereinafter also referred to as a good solvent) contained in the liquid crystal alignment agent used in this invention for dissolving the polymer is not particularly limited as long as it can make the polymer dissolve uniformly.

[0044] Examples include N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, dimethyl sulfoxide, γ-butyrolactone, 1,3-dimethyl-imidazolinone, methyl ethyl ketone, cyclohexanone, cyclopentanone, or 4-hydroxy-4-methyl-2-pentanone. N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, or γ-butyrolactone are preferred.

[0045] Furthermore, when the polymer of the present invention has high solubility in a solvent, it is preferable to use the solvents shown in the above formulas [D-1] to [D-3].

[0046] The content of good solvent in the liquid crystal alignment agent of the present invention is preferably 20 to 99 wt%, based on the total amount of solvent contained in the liquid crystal alignment agent. More preferably, it is 20 to 90 wt%, and even more preferably, it is 30 to 80 wt%.

[0047] The liquid crystal alignment agent of the present invention can be made using solvents (also known as undesirable solvents) that improve the coating performance and surface smoothness of the liquid crystal alignment agent, without compromising the effectiveness of the present invention. Specific examples of undesirable solvents are listed below, but the invention is not limited to these examples.

[0048] For example, ethanol, isopropanol, 1-butanol, 2-butanol, isobutanol, tert-butanol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, isopentanol, tert-pentanol, 3-methyl-2-butanol, neopentanol, 1-hexanol, 2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-ethyl-1-butanol, 1-heptanol, 2-heptanol, 3-heptanol, 1-octanol, 2-octanol, 2-ethyl-1-hexanol, cyclohexanol, 1-methylcyclohexanol, 2-methylcyclohexanol, 3-methylcyclohexanol, 1,2-ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 2-methyl- 2,4-Pentanediol, 2-Ethyl-1,3-Hexanediol, Dipropyl ether, Dibutyl ether, Dihexyl ether, Dioxane, Ethylene glycol dimethyl ether, Ethylene glycol diethyl ether, Ethylene glycol dibutyl ether, 1,2-Butoxyethane, Diethylene glycol dimethyl ether, Diethylene glycol diethyl ether, Diethylene glycol methyl ethyl ether, Diethylene glycol dibutyl ether, 2-Pentanone, 3-Pentanone, 2-Hexanone, 2-Heptanone, 4-Heptanone, 3-Ethoxybutyl acetate, 1-Methylpentyl acetate, 2-Ethylbutyl acetate, 2-Ethylhexyl acetate, Ethylene glycol monoacetate, Ethylene glycol diacetate, Propylene carbonate, Ethylene carbonate, 2-(Methoxymethoxy)ethanol, Ethylene glycol monobutyl ether, Ethylene glycol monoisopentyl ether, Ethylene glycol monohexyl ether, 2 -(hexyloxy)ethanol, furfuryl alcohol, diethylene glycol, propylene glycol, propylene glycol monobutyl ether, 1-(butoxyethoxy)propanol, propylene glycol monomethyl ether acetate, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol dimethyl ether, tripropylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, ethylene glycol monoacetate, ethylene glycol diacetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, 2-(2-ethoxyethoxy)ethyl acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ... Diol acetate, triethylene glycol, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, methyl lactate, ethyl lactate, methyl acetate, ethyl acetate, n-butyl acetate, propylene glycol monoethyl ether acetate, methyl pyruvate, ethyl pyruvate, methyl 3-methoxypropionate, methyl 3-ethoxypropionate, ethyl 3-methoxypropionate, 3-ethoxypropionic acid, 3-methoxypropionic acid, propyl 3-methoxypropionate, butyl 3-methoxypropionate, methyl lactate, ethyl lactate, n-propyl lactate, n-butyl lactate, isoamyl lactate, and solvents shown in formulas [D-1] to [D-3] above.

[0049] Preferably, 1-hexanol, cyclohexanol, 1,2-ethylene glycol, 1,2-propanediol, propylene glycol monobutyl ether, ethylene glycol monobutyl ether, or dipropylene glycol dimethyl ether are used.

[0050] The content of these undesirable solvents, based on the total amount of solvents contained in the liquid crystal alignment agent, is preferably 1 to 80 wt%. More preferably, it is 10 to 80 wt%, and even more preferably, it is 20 to 70 wt%.

[0051] In addition to the above-mentioned components, the liquid crystal alignment agent of the present invention may also include, without impairing the effect of the present invention, other polymers besides those described in the present invention, dielectrics or conductive substances added to change the dielectric constant and conductivity of the liquid crystal alignment film, silane coupling agents added to improve the adhesion between the liquid crystal alignment film and the substrate, crosslinking compounds added to improve the film hardness and density after the liquid crystal alignment film is formed, and imidization accelerators used during baking coating to enable the polyimide precursor to undergo an efficient imidization reaction by heating.

[0052] <Liquid crystal alignment film> The liquid crystal alignment film of the present invention is obtained by coating the aforementioned liquid crystal alignment agent onto a substrate, followed by drying and firing. As for the substrate coated with the liquid crystal alignment agent of the present invention, there are no particular limitations as long as it is a highly transparent substrate; glass substrates, silicon nitride substrates, acrylic substrates, polycarbonate substrates, and other plastic substrates can be used. From the perspective of simplifying the process, a substrate with ITO electrodes for driving the liquid crystal is preferred. Furthermore, in reflective liquid crystal display elements, if only a single-sided substrate is used, an opaque material such as a silicon wafer can be used, and the electrodes can be made of light-reflective materials such as aluminum.

[0053] The coating method for the liquid crystal alignment agent of the present invention includes spin coating, printing, inkjet printing, etc. The drying and firing processes after coating the liquid crystal alignment agent can be performed at any temperature and for any time. Generally, to fully remove the contained organic solvents, the drying temperature is preferably 50–120°C, and the drying time is preferably 1–10 minutes. Furthermore, the firing temperature is preferably 150–300°C, and the firing time is preferably 5–120 minutes. The film thickness after firing is not particularly limited, but if it is too thin, it may damage the reliability of the liquid crystal display element; therefore, it is preferably 5–300 nm, more preferably 10–120 nm.

[0054] As a method for photo-aligning liquid crystal alignment films, one method includes irradiating the coating surface with polarized light in a specific direction, and sometimes further heating it at a temperature of 150–250°C to impart liquid crystal alignment capability. The light source can be ultraviolet light or visible light with wavelengths of 100–800 nm. Ultraviolet light with wavelengths of 100–400 nm is preferred, and ultraviolet light with wavelengths of 200–400 nm is particularly preferred. Furthermore, to improve liquid crystal alignment, illumination can be performed while heating the coating substrate to 50–250°C. The irradiation dose of the light source is preferably 1–10,000 mJ / cm², and particularly preferably 100–5,000 mJ / cm². Liquid crystal alignment films prepared by the above method enable stable alignment of liquid crystal molecules along a specific direction.

[0055] Since it can impart higher anisotropy, the higher the extinction ratio of polarized ultraviolet light, the better. Specifically, the extinction ratio of linearly polarized ultraviolet light is preferably 10:1 or higher, and more preferably 20:1 or higher.

[0056] The film irradiated with polarized light can then be contacted with a solvent containing at least one selected from water and organic solvents. The solvent used for contacting the film is not particularly limited, as long as it can dissolve the decomposition products generated by light irradiation. Specific examples include water, methanol, ethanol, 2-propanol, acetone, methyl ethyl ketone, 1-methoxy-2-propanol, 1-methoxy-2-propanol acetate, butyl cellosolve, ethyl lactate, methyl lactate, diacetone alcohol, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, propyl propionate, butyl acetate, cyclohexyl acetate, etc. Two or more of these solvents can be mixed. From the perspective of versatility and safety, at least one selected from the group consisting of water, 2-propanol, 1-methoxy-2-propanol, and ethyl lactate is more preferred. Water, 2-propanol, or a mixture of water and 2-propanol are particularly preferred.

[0057] In this invention, the contact treatment of the membrane after polarized light irradiation with a solution containing an organic solvent can include immersion treatment, spray treatment, etc., with treatments that allow the membrane to fully contact the liquid being preferred. Preferably, the membrane is immersed in a solution containing an organic solvent for a treatment time of 10 seconds to 1 hour, more preferably 1 to 30 minutes. The contact treatment can be performed at room temperature or with heating, but is preferably carried out at 10 to 80°C, more preferably at 20 to 50°C. Furthermore, if necessary, methods that enhance the contact effect, such as ultrasound, can be used. After the contact treatment, to remove the organic solvent from the solution used, rinsing can be performed with low-boiling-point solvents such as water, methanol, ethanol, 2-propanol, acetone, or methyl ethyl ketone, or drying can be performed, or both rinsing and drying can be performed simultaneously.

[0058] Furthermore, for membranes treated with solvent contact, heating at 150°C or higher can be performed to achieve solvent drying and molecular chain reorientation within the membrane. The preferred heating temperature is 150–300°C. Higher temperatures promote molecular chain reorientation, but excessively high temperatures may lead to molecular chain decomposition. Therefore, a heating temperature of 180–250°C is more preferred, and particularly 200–230°C is more suitable. Regarding heating time, too short a time may not achieve the desired molecular chain reorientation, while too long a time may lead to molecular chain decomposition. Therefore, a heating time of 10 seconds to 30 minutes is preferred, and more preferably 1 to 10 minutes.

[0059] Liquid crystal display element The liquid crystal display element of the present invention is a device made by first obtaining a substrate having a liquid crystal alignment film formed by the liquid crystal alignment agent of the present invention, then fabricating liquid crystal cells using a known method, and using the element. As an example of the method for fabricating liquid crystal cells, a passive matrix structure liquid crystal display element will be described below. Alternatively, an active matrix structure liquid crystal display element may also be used, in which switching elements such as thin-film transistors (TFTs) are provided in each pixel portion constituting the image display.

[0060] First, transparent glass substrates are prepared. A common electrode is disposed on one substrate, and segmented electrodes are disposed on the other substrate. These electrodes can be, for example, ITO electrodes, and are patterned in a manner that enables the desired image display. Next, an insulating film is disposed on each substrate to cover the common electrode and the segmented electrodes. The insulating film can be, for example, a SiO2-TiO2 film formed by a sol-gel method. Next, the liquid crystal alignment film of the present invention is formed on each substrate. Then, one substrate is stacked with the alignment film surfaces facing each other, and the periphery is bonded using a sealing material. To control the gap between the substrates, it is generally preferable to incorporate spacers into the sealing material. Furthermore, spacers for controlling the substrate gap are preferably pre-distributed in the in-plane portions where no sealing material is disposed. Additionally, an opening for injecting liquid crystal from the outside is typically provided in a portion of the sealing material.

[0061] Next, liquid crystal material is injected into the space enclosed by the two substrates and the sealing material through an opening in the sealing material. The opening is then sealed with adhesive. Injection can be performed using a vacuum injection method or by utilizing capillary action in the atmosphere. Next, polarizers are applied. Specifically, a pair of polarizers are attached to the surfaces of the two substrates opposite to the liquid crystal layer. After these steps, the liquid crystal display element of the present invention is obtained. In the present invention, as the sealing material, a resin having reactive groups such as epoxy, acryloyl, methacryloyl, hydroxyl, allyl, and acetyl groups, and capable of curing by ultraviolet irradiation or heating, can be used. In particular, a curing resin system having both epoxy and (meth)acryloyl groups is preferred.

[0062] To improve properties such as adsorption and moisture resistance, inorganic fillers can be incorporated into the above-mentioned sealants. There are no particular limitations on the inorganic fillers that can be used; specifically, they include spherical silica, fused silica, crystalline silica, titanium dioxide, titanium black, silicon carbide, silicon nitride, boron nitride, calcium carbonate, magnesium carbonate, barium sulfate, calcium sulfate, mica, talc, clay, alumina, magnesium oxide, zirconium oxide, aluminum hydroxide, calcium silicate, aluminum silicate, lithium aluminum silicate, zirconium silicate, barium titanate, glass fiber, carbon fiber, molybdenum disulfide, asbestos, etc. Preferred fillers include spherical silica, fused silica, crystalline silica, titanium dioxide, titanium black, silicon nitride, boron nitride, calcium carbonate, barium sulfate, calcium sulfate, mica, talc, clay, alumina, aluminum hydroxide, calcium silicate, aluminum silicate, etc. Two or more of the above-mentioned inorganic fillers can be mixed. Example

[0063] The present invention will be described in more detail below through examples, but the present invention is not limited to these examples. The abbreviations of the compounds used are as follows.

[0064] NMP: N-methyl-2-pyrrolidone; BC: ethylene glycol butyl ether

[0065] <Diamine Synthesis> [Synthesis example]

[0066] Synthesis of intermediate M1 In a three-necked flask equipped with a nitrogen inlet tube, 2.0 g (9.29 mmol) of 4-hydroxy-4'-nitrobiphenyl, 3.32 g (23.2 mmol) of bis(2-chloroethyl) ether, 23.2 mmol of potassium carbonate, and 41 g of N,N-dimethylformamide were added, and the mixture was stirred at 80 °C for 48 hours. After the reaction was complete, ethyl acetate was added, and the mixture was washed with water. The organic phase was concentrated under reduced pressure to obtain the crude product. The crude product was subjected to column chromatography using ethyl acetate and hexane to give intermediate (M1) (yield: 67%). The ¹H-NMR results of intermediate (M1) are as follows.

[0067] 1 H NMR (DMSO-d6): δ8.27(d, 2H), 7.68(d, 2H), 7.57(d, 2H), 7.01(d, 2H),4.22(br, 2H), 3.92(br, 2H), 3.86(br, 2H), 3.67(br, 2H) Synthesis of intermediate M2

[0068] In a three-necked flask equipped with a nitrogen inlet tube, 1.95 g (6.06 mmol) of intermediate (M1), 1.02 g (6.66 mmol) of 2-methyl-4-nitrophenol, 12.1 mmol of potassium carbonate, and 27 g of dimethylformamide were added, and the mixture was stirred at 100 °C for 20 hours. After cooling to room temperature, the salt was removed by filtration, and the filtrate was concentrated under reduced pressure. Isopropanol was added to the filtrate to precipitate crystals. The crystals were collected by filtration, washed with water and isopropanol, and dried to obtain intermediate (M2) (yield: 78%). The ¹H-NMR results of intermediate (M2) are as follows.

[0069] 1 H NMR (DMSO-d6): δ8.29 (d, 2H), 8.20(d,1H), 8.10(s, 1H), 7.95(d, 2H),7.63(d, 2H), 7.19(d, 1H), 6.99(d, 2H), 4.31(br, 4H), 3.77(br, 4H), 2.15(s,3H) Synthesis of diamines

[0070] The synthesis of diamine (DA-1) was carried out in a three-necked flask equipped with a nitrogen inlet tube. 2.18 g (4.97 mmol) of intermediate (M2), 0.26 g of 10% palladium on carbon, 30.0 mmol of hydrazine monohydrate, 7 g of tetrahydrofuran, and 6 g of isopropanol were added, and the mixture was stirred at 60 °C for 2 hours. After the reaction was complete, the reaction solution was filtered through diatomaceous earth, concentrated under reduced pressure, and crystals were precipitated by adding isopropanol. The crystals were collected by filtration, washed with isopropanol, and dried to obtain diamine (DA-1) (yield: 91%). The ¹H-NMR results of diamine (DA-1) are as follows.

[0071] 1 H NMR (DMSO-d6): δ 7.63(d 2H), 7.44(d, 2H), 6.99(d,2H), 6.87(s, 1H), 6.67(d, 1H), 6.58(br, 3H), 5.28(s, 2H), 5.24(s,2H), 4.31(br, 4H), 3.77(br,4H), 2.15(s, 3H) Synthesis of intermediate (M3)

[0072] In a three-necked flask equipped with a nitrogen inlet tube, 1.95 g (6.06 mmol) of intermediate (M1), 1.11 g (6.66 mmol) of 2,6-dimethyl-4-nitrophenol, 12.1 mmol of potassium carbonate, and 27 g of dimethylformamide were added, and the mixture was stirred at 100 °C for 20 hours. After cooling to room temperature, the salt was removed by filtration, and the filtrate was concentrated under reduced pressure. Isopropanol was added to the filtrate to precipitate crystals. The crystals were collected by filtration, washed with water and isopropanol, and dried to obtain intermediate (M3) (yield: 80%). The ¹H-NMR results of intermediate (M3) are as follows.

[0073] 1 H NMR (DMSO-d6): δ 8.29(d, 2H), 8.00(s, 2H), 7.95(d, 2H), 7.63(d, 2H), 6.99(d, 2H), 4.31(br, 4H), 3.77(br, 4H), 2.15(s, 6H) Synthesis of diamines

[0074] Synthesis of diamine (DA-2): In a three-necked flask equipped with a nitrogen inlet tube, 2.25 g (4.97 mmol) of intermediate (M3), 0.26 g (10% palladium on carbon), 30.0 mmol (hydrazine monohydrate), 7 g (tetrahydrofuran), and 6 g (isopropanol) were added, and the mixture was stirred at 60 °C for 2 hours. After the reaction was complete, the reaction solution was filtered through diatomaceous earth, concentrated under reduced pressure, and crystals were precipitated by adding isopropanol. The crystals were collected by filtration, washed with isopropanol, and dried to obtain diamine (DA-2) (yield: 89%). The ¹H-NMR results of diamine (DA-2) are as follows.

[0075] 1 H NMR (DMSO-d6): δ7.62(d, 2H), 7.44(d, 2H), 7.00(d, 2H), 6.77(s, 2H), 6.58(d, 2H), 5.29(s, 2H), 5.24(s, 2H), 4.32(br, 4H), 3.77(br, 4H), 2.14(s,6H) Synthesis of diamines

[0076] The synthesis of diamine (DA-3) was carried out according to the method described in patent JP6852771B2. The ¹H-NMR determination results of diamine (DA-3) are as follows.

[0077] 1 H NMR (DMSO-d6): δ7.62(d, 2H), 7.44(d, 2H), 6.99(d, 2H), 6.77(d, 2H), 6.67(d,2H), 6.58(d, 2H), 5.50(s, 2H), 5.24(s, 2H), 4.24 (br, 2H), 4.16 (br, 2H). Synthesis of diamines

[0078] The synthesis of diamine (DA-4) was carried out according to the method described in patent JP2024132878A. The ¹H-NMR determination results of diamine (DA-4) are as follows.

[0079] 1H NMR (DMSO-d6): δ7.42(d, 2H), 7.27(d, 2H), 6.93(d, 2H), 6.65(d, 2H), 6.63(d,2H), 6.48(d, 2H), 5.20(s, 2H), 4.60(s, 2H), 4.10(br, 2H), 3.96(br,2H), 3.79(br, 2H), 3.76(br,2H) Furthermore, the hydrogen nuclear magnetic resonance (¹H NMR, 500 MHz) in the synthetic examples was measured in deuterated dimethyl sulfoxide (DMSO-d6) solvent, and the chemical shift was expressed as δ value (ppm) with tetramethylsilane as an internal standard.

[0080] [Viscosity] The viscosity of each solution was measured using a cone-plate viscometer (DVNXLVCJG, manufactured by BROOKFIELD) under the following conditions: sample volume 0.5 mL, cone rotor CPA-40Z, temperature 25 °C.

[0081] [Molecular weight] GPC testing conditions: KD803 and KD805 tandem columns were used. Column temperature: 50℃. Eluent: N,N-dimethylformamide (as an additive, lithium bromide hydrate (LiBr·H2O) 30 mmol / L, phosphoric acid·anhydrous crystals (o-phosphoric acid) 30 mmol / L, tetrahydrofuran (THF) 10 ml / L), flow rate: 1.0 ml / min. Standard samples used for calibration curve preparation: Tosoh TSK standard polyethylene oxide (weight average molecular weight (Mw); approximately 900,000, 150,000, 100,000 and 30,000), and polyethylene glycol (Mp peak molecular weight approximately 12,000, 4,000 and 1,000). To avoid peak overlap, two types of samples were measured separately: one was a mixed sample of four values ​​(900,000, 100,000, 12,000 and 1,000), and the other was a mixed sample of three values ​​(150,000, 30,000 and 4,000).

[0082] <Determination of Imine Rate> 20 mg of polyimide powder was placed in an NMR sample tube (standard NMR sampling tube), and 0.53 mL of deuterated dimethyl sulfoxide (DMSO-d6, a mixture containing 0.05% TMS (tetramethylsilane)) was added. The solution was then sonicated to dissolve completely. The solution was subjected to proton NMR at 500 MHz using an NMR analyzer. The imidization rate was determined using a proton whose structure remained unchanged before and after imidization as a reference proton. The peak area integral of this proton was compared with the peak area integral of the proton corresponding to the NH group of the amic acid appearing near 9.5 ppm to 10.0 ppm, and calculated using the following formula: Imidization rate (%) = (1 - α·x / y) × 100 Where x is the peak area integral of the proton corresponding to the NH group of the amic acid, y is the peak area integral of the reference proton, and α is the proportion of the reference proton relative to one NH proton in the polyamic acid (imidization rate 0%).

[0083] [LCD cell manufacturing] A liquid crystal cell with a fringe field switching (FFS) mode liquid crystal display element structure was fabricated. A glass substrate with dimensions of 30mm × 50mm and a thickness of 0.7mm and equipped with electrodes was prepared. ITO electrodes with a solid pattern were formed on the substrate as the first layer, constituting the opposing electrode. Above the first opposing electrode, a SiN (silicon nitride) film formed by CVD was formed as the second layer. The thickness of the second SiN film was 500nm, serving as an interlayer insulating film. Above the second SiN film, a comb-shaped pixel electrode formed by patterning the ITO film was disposed as the third layer, forming the first pixel and the second pixel. Each pixel has a vertical dimension of 10mm and a horizontal dimension of approximately 5mm. At this point, the opposing electrode of the first layer and the pixel electrode of the third layer are electrically insulated by the second SiN film.

[0084] The third layer of pixel electrodes is comb-shaped, composed of multiple "く"-shaped electrode units with a curved central portion. Each electrode unit has a short-side width of 3μm, and the spacing between electrode units is 6μm. Because each pixel's electrode is composed of multiple "く"-shaped electrode units with a curved central portion, each pixel is not rectangular in shape, but rather, similar to the electrode units, curved in the center, resembling a bold "く" shape. Furthermore, each pixel is divided into a first region above the curved central portion and a second region below it.

[0085] Comparing the first and second regions of each pixel, the electrode units of the pixel electrodes that constitute them are formed in different directions. That is, with the friction direction of the liquid crystal alignment film described later as a reference, in the first region of the pixel, the electrode units of the pixel electrode are formed at an angle of +10° (clockwise), and in the second region of the pixel, the electrode units of the pixel electrode are formed at an angle of -10° (clockwise). In other words, in the first and second regions of each pixel, the direction of the rotational movement (in-plane switching) of the liquid crystal induced by applying a voltage between the pixel electrode and the opposing electrode within the substrate surface is configured to be opposite to each other.

[0086] Next, the liquid crystal alignment agent was filtered through a 0.1 μm filter and then spin-coated onto the prepared electrode substrate and a glass substrate with an ITO film formed on the back and columnar spacers with a height of 4 μm. After coating, it was first dried on a hot plate at 80°C for 5 minutes, and then baked in a hot air circulating oven at 230°C for 20 minutes to form a coating with a thickness of 100 nm. The surface of the coating was irradiated with linearly polarized ultraviolet light with an extinction ratio of 10:1 or higher through a polarizer at a wavelength of 254 nm. The substrate was then immersed in at least one solvent selected from water and organic solvents for 3 minutes, followed by immersion in pure water for 1 minute, and then heated on a hot plate at 150–300°C for 5 minutes to obtain a substrate with a liquid crystal alignment film.

[0087] Two substrates were grouped together. A sealant was printed on one substrate, and the other substrate was bonded together with the liquid crystal alignment film surfaces facing each other and the alignment direction at 0°. The sealant was then cured to create an empty cell. Liquid crystal was injected into the empty cell using a depressurized injection method, and the injection port was sealed to obtain an FFS-driven liquid crystal cell. Subsequently, the obtained liquid crystal cell was heated at 110°C for 1 hour and left overnight before being used for various evaluations.

[0088] [Evaluation of Afterimages Driven by Long-Term Communication] Prepare a liquid crystal cell with the same structure as described above. In a constant temperature environment of 60°C, apply an AC voltage of ±5V at a frequency of 60Hz for 240 hours. Afterward, short-circuit the pixel electrode and the opposing electrode of the liquid crystal cell and place it directly at room temperature for one day. After this period, place the liquid crystal cell between two polarizers with orthogonal polarization axes. With no voltage applied, turn on the backlight and adjust the placement angle of the liquid crystal cell to minimize the brightness of the transmitted light. Then, rotate the liquid crystal cell from the angle at which the second region of the first pixel is darkest to the angle at which the first region is darkest, and calculate this rotation angle as angle Δ. For the second pixel, calculate the same angle Δ by comparing the second region and the first region in the same way as for the first pixel.

[0089] [Highlights and Reviews of the LCD Case] The bright spots of the aforementioned liquid crystal cells were evaluated. The evaluation of bright spots was conducted by observing the liquid crystal cells using a polarizing microscope. Specifically, the day before this evaluation, the liquid crystal cells were heated at 110°C for 1 hour, left at room temperature overnight, and then placed under orthogonally polarized light. The liquid crystal cells were observed using a polarizing microscope with 5x magnification, and the number of confirmed bright spots was counted. Cells with fewer than 5 bright spots were rated "good," while those with 5 or more were rated "poor."

[0090] [Orientation agent storage stability evaluation] The storage stability of the alignment agent was evaluated by the following method. The liquid crystal alignment agents (1) to (6) were filtered through a 0.1 μm filter, and the initial viscosity of the resulting liquid was measured. The same liquid was placed in a storage container and sealed. The viscosity was measured after 30 days of storage at 25°C. If the change in viscosity relative to the initial viscosity was within ±30%, the stability was considered good; if the change was ±30% or more, the stability was considered poor. The viscosity was measured after 60 days of storage at 5°C. If the change in viscosity relative to the initial viscosity was within ±10%, the stability was considered good; if the change was ±10% or more, the stability was considered poor.

[0091] The change value was calculated using the following formula: Viscosity change rate (%) = (viscosity after storage) / (initial viscosity value) × 100, and the results are shown in Table 2.

[0092] [Example of polyamic acid polymer synthesis] <Synthesis example 1> In a 50 mL four-necked flask equipped with a stirrer and a nitrogen inlet tube, 1.50 g (4.50 mmol) of DA-1 and 0.49 g (4.53 mmol) of p-phenylenediamine were weighed out, and 25.81 g of NMP (N-methylpyrrolidone) was added. The mixture was stirred while purging with nitrogen to dissolve the DA-1. During stirring of the diamine solution, 1.92 g (8.56 mmol) of 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic acid dianhydride was added, followed by 2.87 g of NMP to adjust the polymer concentration to 12 wt%. The mixture was stirred at room temperature for 24 hours to obtain a polyamic acid solution (A). The viscosity of this polyamic acid solution at 25 °C was 287 mPa·s. Furthermore, the molecular weight of this polyamic acid was: number average molecular weight (Mn) = 25300, weight average molecular weight (Mw) = 58300.

[0093] <Synthesis example 2> In a 50 mL four-necked flask equipped with a stirrer and a nitrogen inlet tube, 1.57 g (4.50 mmol) of DA-2 and 0.49 g (4.53 mmol) of p-phenylenediamine were weighed, and 26.27 g of NMP (N-methylpyrrolidone) was added. The mixture was stirred while purging with nitrogen to dissolve the diamine solution. While stirring the diamine solution, 1.92 g (8.56 mmol) of 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic acid dianhydride was added, followed by 2.92 g of NMP to adjust the polymer concentration to 12 wt%. The mixture was stirred at room temperature for 24 hours to obtain a polyamic acid solution (B). The viscosity of this polyamic acid solution at 25 °C was 271 mPa·s. Furthermore, the molecular weight of this polyamic acid was: number average molecular weight (Mn) = 24800, weight average molecular weight (Mw) = 57400.

[0094] <Synthesis example 3> In a 50 mL four-necked flask equipped with a stirrer and a nitrogen inlet tube, 1.44 g (4.50 mmol) of DA-3 and 0.49 g (4.53 mmol) of p-phenylenediamine were weighed out, and 25.41 g of NMP (N-methylpyrrolidone) was added. The mixture was stirred while purging with nitrogen to dissolve the DA-3. During stirring of the diamine solution, 1.92 g (8.56 mmol) of 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic acid dianhydride was added, followed by 2.82 g of NMP to adjust the polymer concentration to 12 wt%. The mixture was stirred at room temperature for 24 hours to obtain a polyamic acid solution (C). The viscosity of this polyamic acid solution at 25 °C was 271 mPa·s. Furthermore, the molecular weight of this polyamic acid was: number average molecular weight (Mn) = 25000, weight average molecular weight (Mw) = 57900.

[0095] <Synthesis example 4> In a 50 mL four-necked flask equipped with a stirrer and a nitrogen inlet tube, 1.64 g (4.50 mmol) of DA-4 and 0.49 g (4.53 mmol) of p-phenylenediamine were weighed, and 26.73 g of NMP was added. The mixture was stirred while nitrogen was introduced to dissolve the diamine solution. During stirring, 1.92 g (8.56 mmol) of 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride was added, followed by 2.97 g of NMP to adjust the polymer concentration to 12 wt%. The mixture was stirred at room temperature for 24 hours to obtain a polyamic acid solution (D). The viscosity of this polyamic acid solution at 25 °C was 279 mPa·s. Furthermore, the molecular weight of this polyamic acid was: number average molecular weight (Mn) = 24900, weight average molecular weight (Mw) = 57600.

[0096] [Example of acylation reaction of polyamic acid] <Synthesis example 5> NMP was added to the polyamic acid solution obtained in Synthesis Example 1 to bring the solution concentration to 10 wt%. Acetic anhydride and pyridine, in the same molar amounts as polyamic acid in polyamic acid solution (A), were added. The mixture was heated at 55°C for 3 hours to carry out a chemical imidization reaction. The resulting reaction solution was concentrated to 15 wt% using a rotary evaporator, and NMP was added to the concentrate to bring the concentration to 10%. The mixture was then concentrated again to 15 wt% using a rotary evaporator, and NMP was added to the concentrate to bring the concentration to 10%, yielding a polyimide solution PI-A. The imidization rate of this polyimide was 55%, and its molecular weight was: number average molecular weight (Mn) = 23100, weight average molecular weight (Mw) = 51400.

[0097] <Synthesis example 6> Except for the polyamic acid used, which was a polyamic acid solution (B), all other imidization reactions were carried out according to the same formulation as in Synthesis Example 5 to obtain a polyimide solution PI-B. The imidization rate of this polyimide was 53%, and the molecular weight was: number average molecular weight (Mn) = 21500, weight average molecular weight (Mw) = 52200.

[0098] <Synthesis example 7> Except for the polyamic acid used, which was a polyamic acid solution (C), all other polyimides were subjected to imidization reactions according to the same formulation as in Synthesis Example 5 to obtain a polyimide solution PI-C. The imidization rate of this polyimide was 54%, and its molecular weight was: number average molecular weight (Mn) = 20100, weight average molecular weight (Mw) = 50100.

[0099] <Synthesis example 8> Except for the polyamic acid used, which was a polyamic acid solution (D), all other polyimides were subjected to imidization reactions according to the same formulation as in Synthesis Example 5 to obtain a polyimide solution PI-D. The imidization rate of this polyimide was 54%, and its molecular weight was: number average molecular weight (Mn) = 22500, weight average molecular weight (Mw) = 52300.

[0100] <Example 1> 15.00 g of a 12 wt% polyamic acid solution (A) was weighed into a 100 ml Erlenmeyer flask, and 25.6 g of NMP and 19.4 g of BC were added. The mixture was stirred at 25 °C for 8 hours to obtain a 3 wt% liquid crystal alignment agent (1). It was confirmed that the liquid crystal alignment agent showed no abnormalities such as turbidity or precipitation, and was a homogeneous solution. The results of the storage stability evaluation of this alignment agent are shown in Table 1.

[0101] <Example 2> Except for using polyamic acid solution (B) instead of polyamic acid solution (A), all other operations were the same as in Example 1, yielding a 3 wt% liquid crystal alignment agent (2). It was confirmed that the liquid crystal alignment agent exhibited no abnormalities such as turbidity or precipitation, and was a homogeneous solution. The results of the storage stability evaluation of this alignment agent are shown in Table 1.

[0102] <Comparative Example 1> Except for using polyamic acid solution (C) instead of polyamic acid solution (A), all other operations were the same as in Example 1, yielding a 3 wt% liquid crystal alignment agent (3). It was confirmed that the liquid crystal alignment agent showed no abnormalities such as turbidity or precipitation, and was a homogeneous solution. The results of the storage stability evaluation of this alignment agent are shown in Table 1.

[0103] <Comparative Example 2> Except for using polyamic acid solution (D) instead of polyamic acid solution (A), all other operations were the same as in Example 1, yielding a 3wt% liquid crystal alignment agent (4). It was confirmed that the liquid crystal alignment agent showed no abnormalities such as turbidity or precipitation, and was a homogeneous solution. The results of the storage stability evaluation of this alignment agent are shown in Table 1.

[0104] <Example 3> Weigh 15.00 g of 10 wt% polyimide solution PI-A into a 100 ml Erlenmeyer flask, add 25.3 g of NMP and 9.7 g of BC, and mix at 25 °C for 2 hours to obtain a liquid crystal alignment agent with a polymer concentration of 3% (5). It was confirmed that the liquid crystal alignment agent showed no abnormalities such as turbidity or precipitation, and was a homogeneous solution. The results of the storage stability evaluation of this alignment agent are shown in Table 1.

[0105] <Example 4> Except for using polyimide solution PI-B instead of polyimide solution PI-A, all other operations were the same as in Example 3, yielding a 3wt% liquid crystal alignment agent (6). It was confirmed that the liquid crystal alignment agent showed no abnormalities such as turbidity or precipitation, and was a homogeneous solution. The results of the storage stability evaluation of this alignment agent are shown in Table 1.

[0106] <Comparative Example 3> Except for using polyimide solution PI-C instead of polyimide solution PI-A, all other operations were the same as in Example 3, yielding a 3wt% liquid crystal alignment agent (7). It was confirmed that the liquid crystal alignment agent showed no abnormalities such as turbidity or precipitation, and was a homogeneous solution. The results of the storage stability evaluation of this alignment agent are shown in Table 1.

[0107] <Comparative Example 4> Except for using polyimide solution PI-D instead of polyimide solution PI-A, all other operations were the same as in Example 3, yielding a 3wt% liquid crystal alignment agent (8). It was confirmed that the liquid crystal alignment agent showed no abnormalities such as turbidity or precipitation, and was a homogeneous solution. The results of the storage stability evaluation of this alignment agent are shown in Table 1.

[0108] <Example 5> The liquid crystal alignment agent (1) was filtered through a 0.1 μm filter and then spin-coated onto the electrode substrate and a glass substrate with an ITO film formed on the back and columnar spacers with a height of 4 μm. Next, it was dried on a hot plate at 80°C for 5 minutes and then baked in a hot air circulating oven at 230°C for 20 minutes to form a coating with a thickness of 100 nm. The coating surface was then irradiated with linearly polarized 254 nm ultraviolet light with an extinction ratio of 26:1 at a dose of 0.1 J / cm². Afterward, it was heated on a hot plate at 230°C for 10 minutes to obtain a substrate with a liquid crystal alignment film.

[0109] Two substrates were grouped together. A sealant was printed on one substrate, and the other substrate was bonded together with the liquid crystal alignment film surfaces facing each other and the alignment direction at 0°. The sealant was then cured to create a blank cell. Liquid crystal was injected into the blank cell using a reduced-pressure injection method, and the injection port was subsequently sealed to obtain an FFS-driven liquid crystal cell. The resulting liquid crystal cell was then heated at 110°C for 1 hour and left overnight for long-term AC drive image retention evaluation. The results are shown in Table 2.

[0110] <Example 6> Except for the use of the liquid crystal alignment agent (2) described above, all other steps were performed according to the same method as in Example 5: forming a coating, irradiating with ultraviolet light, and heating to obtain a substrate with a liquid crystal alignment film. Except for using this substrate with the liquid crystal alignment film, all other steps were performed according to the same method as in Example 5 to fabricate an FFS-driven liquid crystal cell, and the resulting liquid crystal cell was evaluated in the same way as in Example 5. The results are shown in Table 2.

[0111] <Comparative Example 5> Except for the use of the liquid crystal alignment agent (3) mentioned above, all other processes were carried out in the same manner as in Example 5, including forming a coating, irradiating with ultraviolet light, and heating, to obtain a substrate with a liquid crystal alignment film. Except for using this substrate with the liquid crystal alignment film, all other processes were carried out in the same manner as in Example 5 to fabricate an FFS-driven liquid crystal cell, and the resulting liquid crystal cell was evaluated in the same way as in Example 5. The results are shown in Table 2.

[0112] <Comparative Example 6> Except for the use of the liquid crystal alignment agent (4) mentioned above, all other processes were carried out in the same manner as in Example 5, including forming a coating, irradiating with ultraviolet light, and heating, to obtain a substrate with a liquid crystal alignment film. Except for using this substrate with the liquid crystal alignment film, all other processes were carried out in the same manner as in Example 5 to fabricate an FFS-driven liquid crystal cell, and the resulting liquid crystal cell was evaluated in the same way as in Example 5. The results are shown in Table 2.

[0113] <Example 7> Except for the use of the liquid crystal alignment agent (5) described above, all other steps were performed according to the same method as in Example 5: forming a coating, irradiating with ultraviolet light, and heating to obtain a substrate with a liquid crystal alignment film. Except for using this substrate with the liquid crystal alignment film, all other steps were performed according to the same method as in Example 5 to fabricate an FFS-driven liquid crystal cell, and the resulting liquid crystal cell was evaluated in the same way as in Example 5. The results are shown in Table 2.

[0114] <Example 8> Except for the use of the liquid crystal alignment agent (6) mentioned above, all other steps were performed according to the same method as in Example 5: forming a coating, irradiating with ultraviolet light, and heating to obtain a substrate with a liquid crystal alignment film. Except for using this substrate with the liquid crystal alignment film, all other steps were performed according to the same method as in Example 5 to fabricate an FFS-driven liquid crystal cell, and the resulting liquid crystal cell was evaluated in the same way as in Example 5. The results are shown in Table 2.

[0115] <Comparative Example 7> Except for the use of the liquid crystal alignment agent (7) mentioned above, all other steps were performed according to the same method as in Example 5: forming a coating, irradiating with ultraviolet light, and heating to obtain a substrate with a liquid crystal alignment film. Except for using this substrate with the liquid crystal alignment film, all other steps were performed according to the same method as in Example 5 to fabricate an FFS-driven liquid crystal cell, and the resulting liquid crystal cell was evaluated in the same way as in Example 5. The results are shown in Table 2.

[0116] <Comparative Example 8> Except for the use of the liquid crystal alignment agent (8) mentioned above, all other processes were carried out in the same manner as in Example 5, including forming a coating, irradiating with ultraviolet light, and heating, to obtain a substrate with a liquid crystal alignment film. Except for using this substrate with the liquid crystal alignment film, all other processes were carried out in the same manner as in Example 5 to fabricate an FFS-driven liquid crystal cell, and the resulting liquid crystal cell was evaluated in the same way as in Example 5. The results are shown in Table 2.

[0117] Table 1

[0118] Table 2

[0119] [Industry Availability] The liquid crystal alignment agent of the present invention has good storage stability and does not produce bright spots even when using negative liquid crystal. It can form a liquid crystal alignment film for photo-alignment method with good image retention characteristics and can be used in liquid crystal display elements with high display quality and FFS driving method.

[0120] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A liquid crystal alignment film forming liquid crystal alignment agent characterized by: A polymer comprising a polyamic acid obtained by polycondensation of a diamine and a tetracarboxylic acid dianhydride as shown in Formula 1 below, and a polyimide obtained by imidizing the polyamic acid; (Formula 1) In Formula 1, at least one of the R1 and R2 groups is a hydrogen atom, a methyl group, or a methoxy group.

2. The liquid crystal alignment film-forming liquid crystal orienting agent according to claim 1, characterized by: The polymer is synthesized from a diamine monomer in Formula 1, where R1 and R2 are both methyl groups.

3. The liquid crystal alignment film forming liquid crystal alignment agent according to claim 1, characterized by: The polymer is synthesized from a diamine monomer in Formula 1, where R1 is a methyl group and R2 is a hydrogen atom.

4. The liquid crystal alignment film forming liquid crystal orienting agent according to claim 1, characterized by: The tetracarboxylic acid dianhydride comprises any of the structures in Formula 2. (Formula 2) R1 to R4 each independently represent a hydrogen atom, a halogen atom, an alkyl group with 1 to 6 carbon atoms, an alkenyl group with 2 to 6 carbon atoms, an alkynyl group with 2 to 6 carbon atoms, a monovalent organic group with 1 to 6 carbon atoms containing a fluorine atom, or a phenyl group; and at least one of R1 to R4 represents a group other than a hydrogen atom as defined above.

5. The liquid crystal alignment film forming liquid crystal orienting agent according to claim 4, characterized by: In Formula 2, R1 and R4 are methyl groups, and R2 and R3 are hydrogen atoms.

6. A liquid crystal alignment film formed using the liquid crystal alignment agent according to any one of claims 1-5.

7. A liquid crystal display element comprising the liquid crystal alignment film of claim 6.

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