KR20130050862A - Liquid crystal display and method of fabricating the same - Google Patents

Abstract

The present invention is to provide a liquid crystal display device having a high contrast and preventing the light leakage during black display due to AC afterimage, and a manufacturing method thereof.
A liquid crystal display according to the present invention comprises: a thin film transistor substrate having an alignment layer formed on a pixel having a pixel electrode and a thin film transistor; An opposite substrate facing the thin film transistor substrate and having an alignment layer formed thereon; And a liquid crystal layer formed between the thin film transistor substrate and the counter substrate, wherein the alignment layer includes a first alignment layer in contact with the liquid crystal layer and a second alignment layer formed under the first alignment layer. The first alignment film is formed of a material imparted with anisotropy by photolysis reaction, and the second alignment film is formed of a material which does not cause photolysis reaction, and the film thickness ratio of the first alignment film to the second alignment film is 0.5 or less. It is characterized by.

Description

Liquid crystal display and its manufacturing method {LIQUID CRYSTAL DISPLAY AND METHOD OF FABRICATING THE SAME}

The present invention relates to a liquid crystal display device and a manufacturing method thereof. Specifically, the present invention relates to an IPS or FFS mode liquid crystal display device and a method for manufacturing the same, which are used for a display panel of a clock, a display of a mobile phone, a display of a computer or a television, and the like.

Since liquid crystal display devices have characteristics such as low driving voltage, low power consumption, and light weight, they are used for display panels of watches, displays of mobile phones, displays of computers and televisions, and the like. In this liquid crystal display device, a means for controlling the alignment of liquid crystal molecules is required, and a means for forming an alignment film formed of polyimide or the like is generally used.

However, when the alignment control of liquid crystal molecules is performed by the alignment film, there are generally various problems resulting from the formation of the alignment film.

For example, when forming an alignment film, there exists a problem that the ratio of the manufacture product of a printing falls by a foreign material or a pinhole, or the cost required for the formation process of an alignment film increases according to enlargement of a board | substrate.

Moreover, in liquid crystal display devices, such as an IPS mode, liquid crystal molecules are orientated by carrying out a rubbing process to this alignment film. In general, the rubbing treatment of the alignment film is performed by rotating a roller wound with a cloth such as rayon or cotton in a state in which the rotation speed and the distance between the roller and the substrate are kept constant and rubbing the surface of the alignment film in one direction.

However, there are various problems in the rubbing treatment of the alignment film as follows.

(1) Since the rubbing treatment causes large damage to the alignment film, the damage causes light leakage during black display of the liquid crystal display device, thereby reducing the contrast of the liquid crystal display device.

(2) By the rubbing treatment, the alignment film is torn off or the rubbing cloth wound around the roller is dropped, so that a uniform cell thickness is not obtained, resulting in uneven display of the liquid crystal display device.

(3) The step by which the TFT element etc. formed on the board | substrate generate | occur | produces the part which a rubbing does not occur, or an alignment film tears.

(4) The rubbing treatment is difficult to quantify rubbing and difficult to manage.

(5) The electrostatic charge generated by the friction between the substrate and the roller damages the TFT element formed on the substrate.

(6) As the substrate size increases, the influence of bending of the substrate and the roller increases, making it difficult to uniformly rub the product, lowering the product ratio and increasing the apparatus for the rubbing process, thereby increasing the investment cost.

In recent years, the use of TFT (Thin Film Transistor) type liquid crystal display devices is increasing in view of response speed, contrast, and viewing angle. This TFT type liquid crystal display device includes: a TFT substrate in which pixel electrodes, thin film transistors (TFTs), and the like are formed in a matrix form; An opposing substrate which opposes the TFT substrate and has a color filter or the like formed in a region corresponding to the pixel electrode of the TFT substrate; The liquid crystal layer is formed between the TFT substrate and the counter substrate. In a liquid crystal display device having such a structure, a fine stepped structure by pixel electrodes, TFTs, or the like is formed. Therefore, many problems caused by the above rubbing process can be seen by this step structure.

As an orientation technique that does not require a rubbing treatment, a method of performing photoalignment treatment using a photodegradable material (polymer) for an alignment film has been proposed (see Patent Document 1, for example). In this photo-alignment process, by irradiating polarization to the alignment film of a polymer, only the polymer which is in parallel with a polarization photodecomposes, the main chain is cut | disconnected, and uniaxiality is provided by this. Moreover, in patent document 2, in order to improve the orientation stability of the orientation film formed by photo-alignment process, it was proposed to make an orientation film into a two-layer structure.

<Patent Document 1> Japanese Patent Laid-Open No. 2004-206091

Patent Document 2: Japanese Patent Laid-Open No. 2010-72011

However, in the conventional photo-alignment treatment, not only the polymer on the surface of the alignment film but also the polymer inside the alignment film is subjected to photo-alignment, so that the entire alignment film is composed of a low molecular weight polymer. In general, a polymer having a small molecular weight tends to move by switching of liquid crystal molecules, and in an alignment film subjected to conventional photoalignment, the alignment film moves by switching of liquid crystal molecules. In a liquid crystal display device having such an alignment film, when an AC voltage is applied and driven, a phenomenon in which the liquid crystal molecules do not return to the initial alignment state when the voltage is turned off (hereinafter referred to as "AC afterimage") There is a problem that light leakage occurs during black display.

On the other hand, in Patent Document 2, the alignment stability of the alignment film is increased by making the alignment film have a two-layer structure. However, even when the polymer of the upper alignment film is photoaligned, even the polymer of the lower alignment film is photodegraded, and thus still remains in AC residual. Light leakage at the time of black display resulting from it cannot fully be prevented.

In order to solve the above problems, the present invention is to provide a liquid crystal display device with a high contrast and a manufacturing method thereof by preventing light leakage during black display due to AC afterimage.

In order to achieve the above technical problem, a liquid crystal display device according to the present invention includes a TFT substrate having an alignment film formed on a pixel having a pixel electrode and a TFT, an opposing substrate facing the TFT substrate, and having an alignment film formed thereon, and the TFT substrate and the A liquid crystal display device having a liquid crystal layer formed between an opposing substrate, wherein the alignment film is composed of a first alignment film in contact with the liquid crystal layer and a second alignment film formed under the first alignment film, and the first alignment film. Silver is formed of a material imparted with anisotropy by a photolysis reaction, and the second alignment film is made of a material which does not cause photolysis reaction, and the film thickness ratio of the first alignment film to the second alignment film is 0.5 or less. .

As described above, the present invention can provide a liquid crystal display device having high contrast by preventing light leakage during black display due to AC afterimage.

1 is a cross-sectional view of a liquid crystal display device according to the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings and embodiments.

1 is a cross-sectional view of a liquid crystal display of the present invention.

The liquid crystal display shown in FIG. 1 includes a TFT substrate 1, an opposing substrate 2 provided to oppose the TFT substrate 1, and a liquid crystal layer formed between the TFT substrate 1 and the opposing substrate 2. (4) is provided. Moreover, the alignment film 3 is formed in the surface which contacts the liquid crystal layer 4 of each of the TFT substrate 1 and the counter substrate 2.

Although not shown, the TFT substrate 1 includes a pixel electrode and a TFT (thin film transistor). The TFT substrate 1 is not particularly limited, and a known one can be used in the technical field. For example, an active matrix array substrate can be used as the TFT substrate 1. In this active matrix array substrate, in general, gate wirings and source wirings are arranged in a matrix form on a glass substrate, and active elements such as thin film transistors (TFTs) are formed at intersections thereof, and pixel electrodes are formed on the active elements. Are connected, and a lower alignment film is formed so as to cover them.

The counter substrate 2 is not particularly limited, and a known one can be used in the technical field. For example, a color filter substrate can be used as the counter substrate 2. This color filter substrate generally forms a black matrix on a glass substrate in order to prevent unnecessary light leakage, and then pattern-forms the colored layers of R (red), G (green), and B (blue), A planarization film is formed as needed, and an upper alignment film is formed so that these may be covered.

The alignment film 3 formed in each of the TFT substrate 1 and the counter substrate 2 is composed of a first alignment film in contact with the liquid crystal layer 4 and a second alignment film formed under the first alignment film. The first alignment film is formed of a material to which anisotropy is imparted by the photolysis reaction, and the second alignment film is formed of a material which does not cause photolysis reaction. By forming the second alignment film with a material that does not cause photolysis reaction, it is possible to prevent the second alignment film from photodegrading when the photoalignment treatment of the first alignment film is performed.

The first alignment film can be formed by photoalignment treatment with an alignment film formed by using a material causing a photolysis reaction.

The material causing the photolysis reaction is not particularly limited, and materials known in the art can be used. Especially, it is preferable that the material which causes a photolysis reaction is a polyimide which has a structural unit represented by following General formula (1) from a viewpoint of orientation stability.

In said Formula (1), R1-R4 represents an independent hydrogen atom, a fluorine atom, or a C1-C6 alkyl group or an alkoxy group, respectively.

The polyimide which has a structural unit as mentioned above can be formed by the polymerization reaction using the diacid anhydride and diamine represented by following formula (2).

Specific examples of the diacid anhydride include 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA); 1,2-dimethyl-l, 2,3,4-cyclobutanetetracarboxylic acid dianhydride; 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride; 1,2,3,4-tetra methyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride etc. are mentioned. These can be used individually or in combination of 2 or more types.

Specific examples of the diamine include p-phenylene diamine; 4,4'-oxydianiline (4,4'-Oxydianiline); 4,4'-diaminodiphenylamine; 2,4-diaminodiphenylamine; 1,4-diaminocyclohexane, 1,3- diocyclohexane; 4,4'-diaminodicyclohexylmethane; 4,4'-diamino 3,3'-dimethyl dicyclo hexylamine; Isophorone diamine; o-phenylene diamine; m-phenylene diamine; 2,4-diamino toluene; 1,4-diamino-2-methoxy benzene; 1,3-diamino 4-chlorobenzene; 1,4-diamino2,5-dichloro benzene; 1,3-diamino 4-isopropyl benzene; 4,4'-diaminodiphenyl2,2'-propane; 4,4'-diaminodiphenylmethane; 2,2'-diaminostilbene; 4,4'-diaminostilbene; 4,4'-diamino diphenyl ether; 4,4'-diphenyl thioether; 4,4'-diamino diphenyl sulfone; 3,3'-diaminodiphenylsulfone; 4,4'-diamino benzoic acid phenyl ester; 2,2'-diamino benzophenone; 4,4'-diamino benzyl; Bis (4-aminophenyl) phosphine oxide (bis (4-aminophenyl) phosphine oxide); Bis (3-amino phenyl) methyl phosphine oxide; Bis (4-amino phenyl) phenyl phosphine oxide; Bis (4-amino phenyl) cyclohexyl phosphine oxide, N, N'-bis (4-amino phenyl) -N-phenyl amine; N, N-thread (4-amine phenyl)-N-methyl amine; 4,4'-diaminodiphenyl urea; 1,8-diaminonaphthalene; 1,5-diaminonaphthalene; 1,5-diaminoanthraquinone; Diaminofluorene; Bis (4-aminophenyl) diethyl silane (bis (4-aminophenyl) diethyl silane); Bis (4-amino phenyl) dimethyl silane; Bis (4-amino phenyl) tetramethyldisiloxane; 3,4'-diaminodiphenyl ether; Benzidine; 2,2'-dimethylbenzidine; 2,2-bis [4- (4-amino phenoxy) phenyl] propane, bis [4- (4-amino phenoxy) phenyl] sulfone; 4,4'-bis (4-amino phenoxy) biphenyl; 2,2- ㅂ bis [4- (4-amino phenoxy) phenyl] hexafluoro propane; 1,4-screw (4-amino phenoxy) benzene, 1,3-screw (4-amino phenoxy) benzene; 2,6-diaminopyridine; 2,4-diaminopyridine; 2,4-diamino-s-triazine; 2,7-diamino dibenzofuran; 2,7-diamino carbazole; 3,7-diamino phenothiazine; 2,5-diamino-1,3,4-thiadiazole; 2,4-diamino6-phenyl-s-triazine; Diaminomethane; 1,2-diaminoethane; 1,3-diaminopropane; 1,4-diaminobutane; 1,6-diaminohexane; 1,7-diaminoheptane; 1,8-diaminooctane; 1,9-diamino nonane; 1,10-diamino decane; 1,3-diamino2,2-dimethyl propane; 1,4-diamino2,2-dimethyl butane; 1,6-diamino2,5-dimethyl hexane; 1,7-diamino2,5-dimethylheptane; 1,7-diamino4,4-dimethylheptane; 1,7-diamino3-methylheptane; 1,9-diamino5-methylnonane; 2,11-diaminodedecane; 1,12-diaminooctadecane; 1,2-bis (3-aminopropoxy) ethane and the like. These can be used individually or in combination of 2 or more types.

The diacid anhydride and the diamine react with each other by mixing in an organic solvent to form a polyamic acid, which can be formed into a polyimide by dehydrating and closing the polyamic acid. The method of mixing the diacid anhydride and the diamine in the organic solvent is not particularly limited, and the method of dispersing or dissolving the diamine anhydride in the organic solvent or dispersing or dissolving the diacid anhydride intact or in the organic solvent, On the contrary, the method of adding diamine to the solution which disperse | distributed or dissolved the diacid anhydride in the organic solvent, the method of adding diacid anhydride and diamine alternately, etc. can be used.

Although the temperature at the time of making diacid anhydride and diamine react in an organic solvent is not specifically limited, Generally 0-150 degreeC, Preferably it is 5-100 degreeC, More preferably, it is 10-80 degreeC. The reaction can be carried out at any concentration, but if the concentration is too low, the reaction takes a long time. If the concentration is too high, the viscosity of the reaction solution becomes too high, making uniform stirring difficult. For this reason, concentration is generally 1-50 mass%, Preferably it is 5-30 mass%.

The organic solvent used in the reaction is not particularly limited as long as the produced polyamic acid is dissolved. Specific examples of the organic solvent include N, N-dimethylformamide; N, N-dimethyl acetamide; N-methyl-2-pyrrolidone; N-methyl caprolactam; Dimethyl sulfoxide; Tetramethyl urea, pyridine, dimethyl sulfone, hexamethyl sulfoxide, γ-butyrolactone, and the like. These can be used individually or in mixture of 2 or more types.

Although the ratio of the diacid anhydride and diamine used for the polymerization reaction of a polyamic acid is not specifically limited, It is 1: 0 in molar ratio. 8--1: 1. 2

In the imidization reaction for dehydrating and ringing polyamic acid, thermal imidization for heating a solution of polyamic acid as it is, and chemical imidization for adding a catalyst to a solution of polyamic acid are common, but chemical imidization reaction proceeds at a relatively low temperature. Imidization is preferred.

Chemical imidation can be performed by stirring a polyamic acid in presence of an alkaline catalyst and an acid anhydride in an organic solvent. The reaction temperature at this time is generally -20 to 250 ° C, preferably 0 to 180 ° C, and the reaction time is generally 1 to 100 hours. The amount of the alkaline catalyst is 0.5 to 30 mol times, preferably 2 to 20 mol times, of the amic acid group, and the amount of the acid anhydride is 1 to 50 mol times, preferably 3 to 30 mol times of the amic acid group. If the amount of the alkaline catalyst or the acid anhydride is small, the reaction does not proceed sufficiently. If the amount is too high, it is difficult to completely remove the reaction after the reaction is completed. Examples of the alkaline catalyst used in this case include pyridine, triethylamine, trimethylamine, tributylamine, trioctylamine, and the like, among which pyridine reacts. It is preferable because it has moderate alkalinity to proceed. Moreover, acetic anhydride, trimellitic anhydride, a pyromellitic dianhydride etc. are mentioned as an acid anhydride. Especially, since acetic anhydride is used, since purification after completion | finish of reaction becomes easy, it is preferable. As the organic solvent, the solvent used in the synthesis of the polyamic acid described above can be used. The imidation ratio by chemical imidation can be controlled by adjusting catalyst amount, reaction temperature, and reaction time.

At the time of formation of the first alignment layer, a solution in which raw materials (diacid anhydride and diamine) are added to the organic solvent can be used as the liquid crystal aligning agent. Or you may use the reaction solution of the polyamic acid or polyimide obtained by the above as a liquid crystal aligning agent.

Although solid content concentration of a liquid crystal aligning agent is not specifically limited, Generally, it is 1-10 mass%. If solid content concentration is less than 1 mass%, it is difficult to form a uniform and defect-free alignment film, and when more than 10 mass%, the storage stability of a liquid crystal aligning agent will fall.

After apply | coating on a 2nd alignment film demonstrated below using the above-mentioned liquid crystal aligning agent, a 1st alignment film is formed into a coating film by baking at dry and high temperature, and photo-alignment process is given to this coating film.

It does not specifically limit as a coating method of a liquid crystal aligning agent, A spin coating method, the printing method, the inkjet method, etc. can be used.

Although the process of drying after apply | coating a liquid crystal aligning agent is not necessarily required, when the time until baking after application | coating is not fixed for every board | substrate, or is not immediately baked after application | coating, it is preferable to include a drying process. This drying should just evaporate a solvent to the extent that the shape of a coating film does not deform | transform, and it does not specifically limit about the drying means. Generally, it is good to dry for 0.5 to 30 minutes, Preferably it is 1 to 5 minutes on 50-150 degreeC, Preferably it is 80-120 degreeC on the hotplate.

Although the baking temperature of a liquid crystal aligning agent is not specifically limited, Generally 100 degreeC-350 degreeC, Preferably it is 150 degreeC-300 degreeC, More preferably, it is 200 degreeC-250 degreeC.

It does not specifically limit as a photo-alignment process, A well-known method can be used in the said technical field. Specifically, it is good to irradiate the ultraviolet-ray which polarized with respect to the board | substrate using the polarizing plate of a fixed direction. Although it does not specifically limit as wavelength of the ultraviolet-ray used, Generally, it is 100 nm-400 nm, Preferably it is 230-280 nm. Moreover, the irradiation time of an ultraviolet-ray is not specifically limited, either, Generally, it is 0.5-100 J / cm <^2> . Moreover, although the irradiation time of an ultraviolet-ray is not specifically limited, It is generally the range of several seconds to several hours.

When the ultraviolet-ray which polarized on the polyimide which has a structural unit represented by said Formula (1) is irradiated, the following photolysis reaction will arise for the polyimide which is parallel to the said ultraviolet-ray. On the other hand, the polyimide which is perpendicular to the said ultraviolet-ray does not generate | occur | produce the following photolysis reaction, and remains in a state as it is.

By photodegrading only the polyimide in parallel with ultraviolet rays, uniaxiality (anisotropy) can be imparted to the first alignment film, so that alignment control of liquid crystal molecules can be performed.

Although the thickness of the 1st orientation film formed in this way is not specifically limited, Generally, it is 5-100 nm, Preferably it is 10-50 nm. If the thickness of the first alignment layer is less than 5 nm, the alignment control of the liquid crystal molecules may not be sufficiently performed. If the thickness of the first alignment layer exceeds 100 nm, the thickness of the entire alignment layer may be too thick, resulting in high driving voltage of the liquid crystal display device.

The second alignment film can be formed using a material that does not cause photolysis reaction.

The material that does not cause photolysis reaction is not particularly limited, and materials known in the art can be used. Especially, it is preferable that the material which does not produce a photolysis reaction is a polyimide which has a structural unit represented by following formula (4).

The polyimide which has a structural unit as mentioned above can be formed by the polymerization reaction using the diacid anhydride and diamine represented by following formula (5).

Since the kind of diamine and the polymerization reaction of diacid anhydride and diamine are the same as the case of a 1st orientation film, the description is abbreviate | omitted.

Since the second alignment film does not cause photolysis reaction even when exposed to ultraviolet rays by the photoalignment treatment of the first alignment film, the molecular weight of the material (polyimide) constituting the second alignment film does not decrease. Therefore, the molecular weight of a 2nd alignment film is large compared with the molecular weight of a 1st alignment film. Thereby, even if a liquid crystal molecule switches, it becomes difficult to move a 2nd alignment film, and the movement of a 1st alignment film can be suppressed. As a result, light leakage at the time of black display resulting from AC afterimage can be suppressed.

Although the thickness of the 2nd alignment film formed in this way is not specifically limited, Generally, it is 20-200 nm, Preferably it is 50-90 nm. If the thickness of the second alignment layer is less than 20 nm, it is difficult to sufficiently cover the fine stepped structure by the pixel electrode, the TFT, etc., and it is difficult to form the second alignment layer. If the thickness of the second alignment layer exceeds 200 nm, the thickness of the entire alignment layer is too thick. As a result, the driving voltage of the liquid crystal display becomes high.

The film thickness ratio of the 1st alignment film with respect to a 2nd alignment film is 0.5 or less, Preferably it is 0.1-0.5. When the film thickness ratio exceeds 0.5, the effect of suppressing the movement of the first alignment film by the switching of the liquid crystal molecules by the second alignment film is small, and AC afterimage cannot be prevented sufficiently. In addition, the total film thickness of the first alignment film and the second alignment film becomes too thick, and the driving voltage of the liquid crystal display device increases. On the other hand, when the film thickness ratio is less than 0.1, the first alignment film becomes too thin, and the orientation controllability of the liquid crystal molecules is lowered.

In the above, the method of separately forming the first alignment film and the second alignment film has been described, but the first alignment film and the second alignment film are formed by using a liquid crystal aligning agent containing a material for forming the first alignment film and a material for forming the second alignment film. You may form simultaneously. For example, if the second alignment film is molecularly designed to be hydrophilic and high polarity, a second alignment film is formed on the side of the substrate (TFT substrate 1 and the counter substrate 2), and a first alignment film is formed on the liquid crystal layer 4 side. can do. It does not specifically limit as a method of making a 2nd alignment film hydrophilic and high polarity, A well-known method can be used in the said technical field. For example, functional groups, such as -OH group and -COOH group, may be introduce | transduced into the material which forms a 2nd orientation film.

In the case where the first and second alignment films are formed at the same time, a liquid crystal aligning agent including a material for forming the first alignment film and a material for forming the second alignment film is applied to the substrate, and then dried and baked at a high temperature to form a coating film. It is good to perform a photo-alignment process on this coating film. The conditions at this time are the same as in the case of the method of separately forming the first alignment film and the second alignment film, and the description thereof will be omitted.

Although it does not specifically limit as a liquid crystal component used for the liquid crystal layer 4, It is preferable that it is a mixed liquid crystal containing 2 or more types of liquid crystal components. This mixed liquid crystal is defined uniquely by mixing several liquid crystal components so as to satisfy desired physical properties (for example, refractive index anisotropy, dielectric anisotropy, viscosity, phase potential temperature, etc.) according to the intended use. Although it is difficult, it may be a mixed liquid crystal generally called a fluorine-based mixed liquid crystal, a cyano-based mixed liquid crystal, or the like. Among these, it is preferable to use the fluorine-type mixed liquid crystal currently generally used for a liquid crystal display device. Here, in this specification, a "fluorine-type mixed liquid crystal" means the mixed liquid crystal containing 1 or more types of fluorine-type liquid crystal, and a "cyano type liquid crystal" means the mixed liquid crystal containing 1 or more types of cyano type liquid crystals.

The above-mentioned mixed liquid crystals are generally known and commercially available. For example, fluorine-based mixed liquid crystals are sold by Merck Co., Ltd. under the trade names ZLI-4792 (p-type) and MLC-6608 (n-type). It is becoming. Cyano-based mixed liquid crystals are sold by Chisso Petrochemical Co., Ltd. under a trade name of JC-5066XX (p-type).

The method of forming the liquid crystal layer between the TFT substrate 1 and the counter substrate 2 is not particularly limited and can be carried out by a known method in the technical field. For example, an ODF (liquid drop injection method) or a vacuum injection method using capillary action may be used.

Such a liquid crystal display device of the present invention forms the alignment layer in a two-layer structure, and forms a second alignment layer located in the lower layer using a material that does not cause photolysis reaction, and at the same time, a film of the first alignment layer located in the upper layer. Since the ratio between the thickness and the film thickness of the second alignment layer in the lower layer is defined in an appropriate range, light leakage during black display due to AC afterimage can be prevented and the contrast can be increased.

Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by these.

(Example 1)

1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) and 4,4'-oxy dianiline are added to the organic solvent in a molar ratio of 1: 1, mixed, and the liquid crystal aligning agent for a 1st alignment film Got. Solid content concentration of this liquid crystal aligning agent is 5 mass%.

On the other hand, a pyromellitic dianhydride and p-phenylene diamine were added to the organic solvent in the molar ratio of 1: 1, and it mixed, and the liquid crystal aligning agent for 2nd alignment films was obtained. Solid content concentration of this liquid crystal aligning agent is 5 mass%.

Thereafter, the liquid crystal aligning agent for the second alignment film was applied to one surface of each of the TFT substrate and the counter substrate using the spin coating method, and then dried on an 80 ° C. hot plate for 3 minutes, followed by an oven at 230 ° C. for 1 hour. The 2nd alignment film was formed by baking at high temperature. The thickness of the formed second alignment film was 50 nm.

Thereafter, the liquid crystal aligning agent for the first alignment film was coated on the surface of the second alignment film by using a spin coating method, then dried on an 80 ° C hot plate for 3 minutes, and then heated at 230 ° C for 1 hour using an oven. The 1st alignment film was formed by baking. The thickness of the formed first alignment film was 10 nm.

Subsequently, the first alignment film is irradiated with ultraviolet radiation (wavelength: 254 nm) polarized using a polarizing plate in a constant direction to a TFT substrate and a counter substrate on which the first alignment film and the second alignment film are formed, respectively, at an irradiation amount of 1 J / cm ² . This photoalignment process is performed.

Next, a liquid crystal cell was produced by injecting the fluorine-based mixed liquid crystal ZLI-4792 (P type, Merck Co., Ltd.) by the liquid crystal drop injection method between the TFT substrate and the counter substrate.

(Example 2)

By controlling the coating amount of the liquid crystal aligning agent, the liquid crystal cell was produced like Example 1 except having made the thickness of a 1st alignment film into 30 nm, and the thickness of a 2nd alignment film into 60 nm.

(Comparative Example 1)

A liquid crystal cell was produced in the same manner as in Example 1 except that only the first alignment film was formed on one surface of the TFT substrate and the opposing substrate to perform the photo alignment process. Here, the thickness of the first alignment film was 50 nm.

About the liquid crystal cell obtained by said Example and the comparative example, the brightness | luminance of the initial state (state before applying and driving an alternating voltage) was measured using the luminance meter (BM-5, Topcon Corporation make). Next, after driving by applying an alternating current (AC) voltage, the voltage was turned off and the luminance after driving was measured using a luminance meter.

As a result, in the liquid crystal cells of Examples 1 and 2, the luminance after driving was almost the same as the luminance in the initial state, and generation of AC afterimage could be suppressed. On the other hand, in the liquid crystal cell of the comparative example 1, the brightness after drive changed significantly compared with the brightness | luminance of an initial state, and AC afterimage generate | occur | produced. Therefore, the liquid crystal cell of Example 1 and 2 can suppress light leakage at the time of black display.

As can be seen from the above results, the present invention can provide a liquid crystal display device with high contrast by preventing light leakage during black display due to AC afterimage.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Will be clear to those who have knowledge of.

1: TFT substrate 2: Opposing substrate
3: alignment film 4: liquid crystal layer

Claims (6)

A thin film transistor substrate having a lower alignment layer formed on a pixel having a pixel electrode and a thin film transistor;
An opposite substrate facing the thin film transistor substrate and having an upper alignment layer formed thereon;
A liquid crystal layer formed between the thin film transistor substrate and the opposing substrate;
Each of the upper alignment layer and the lower alignment layer,
A first alignment layer in contact with the liquid crystal layer,
A second alignment layer formed under the first alignment layer,
The first alignment layer is formed of a material to which anisotropy is imparted by the photolysis reaction, and the second alignment layer is formed of a material which does not cause photolysis reaction.
And the film thickness ratio of the first alignment layer to the second alignment layer is 0.5 or less. The method of claim 1,
The first alignment layer includes a polyimide having the following general formula (1) as a structural unit.
&Lt; Formula 1 >

In said Formula (1), R1-R4 represents an independent hydrogen atom, a fluorine atom, or a C1-C6 alkyl group or an alkoxy group, respectively. 3. The method according to claim 1 or 2,
The second alignment layer comprises a polyimide having the formula (2) as a structural unit.
(2)

Providing a thin film transistor substrate on which a pixel having a pixel electrode and a thin film transistor is formed;
Providing an opposing substrate facing the thin film transistor substrate;
A first alignment layer formed of a material to which anisotropy is imparted by photolysis reaction on each of the thin film transistor substrate and the opposing substrate, and a second alignment layer formed of a material which does not cause photolysis reaction and formed under the first alignment layer. Forming an alignment film formed;
Forming a liquid crystal layer between the thin film transistor substrate and the opposing substrate to contact the first alignment layer formed on each of the thin film transistor substrate and the opposing substrate,
A film thickness ratio of the first alignment layer to the second alignment layer is 0.5 or less. The method of claim 4, wherein
The first alignment layer includes a polyimide having the following formula (3) as a structural unit, the method of manufacturing a liquid crystal display device.
(3)

In said Formula (3), R1-R4 represents an independent hydrogen atom, a fluorine atom, or a C1-C6 alkyl group or an alkoxy group, respectively. The method according to claim 4 or 5,
The second alignment layer includes a polyimide having the following formula (4) as a structural unit, the manufacturing method of the liquid crystal display device.
&Lt; Formula 4 >

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