KR101050238B1 - A liquid crystal display device having a polyimide-based varnish, an alignment film, and the alignment film for forming an alignment film for liquid crystal display devices - Google Patents

Abstract

The present invention provides a liquid crystal display device having good black display characteristics having a polyimide-based alignment agent varnish capable of forming an alignment film having particularly high uniaxial orientation, an alignment film formed by using the varnish, and the alignment film.

The polyimide varnish of the present invention can form an alignment film having an orientation index Δ of 1.3 or more after liquid crystal treatment represented by the following formula (1):

In the above formula, A ∥ is the absorbance by CN stretching vibration of the imide ring when the infrared light having the polarization component parallel to the alignment treatment direction is incident on the alignment film, A 'is the polarization component perpendicular to the alignment treatment direction The branch is the absorbance by CN stretching vibration of the imide ring when the infrared light is incident on the alignment film. d is the film thickness (unit is nm) of an oriented film.

Polyimide varnish, alignment film, liquid crystal display device, polarization component, stretching vibration, uniaxial orientation, orientation index

Description

POLYIMIDE TYPE VARNISH, LIQUID CRYSTAL ALIGNMENT FILM, AND LIQUID CRYSTAL DISPLAY ELEMENT for forming an alignment film for a liquid crystal display device

1 is a view showing a comb-tooth type electrode structure for IPS.

The present invention is a liquid crystal having a polyimide varnish for a liquid crystal display device capable of forming an alignment film having an orientation index Δ of 1.3 or more after liquid crystal treatment represented by a specific formula, an alignment film formed by using the varnish, and the alignment film. It relates to a display element. Particularly preferably, a transverse electric field system for displaying by forming a dominant parallel electric field with respect to the surface of the substrate, that is, a polyimide varnish for IPS (In Plane Switching) type liquid crystal display device, an alignment film formed by using the varnish; It relates to an IPS type liquid crystal display device having the alignment film.

Liquid crystal display devices are used in various liquid crystal display devices such as monitors of notebook computers and desktop personal computers, viewfinders of video cameras, projection displays, and the like, and have recently been used as televisions. It is also used as an optoelectronics related element, such as an optical printer head, an optical Fourier conversion element, a light valve. As a conventional liquid crystal display device, a display device using nematic liquid crystal is mainstream, a twisted nematic (TN) type liquid crystal display device twisted by 90 degrees, a super twisted nematic (STN) type liquid crystal display twisted by 180 degrees or more, A so-called thin-film-transistor (TFT) type liquid crystal display device using a thin film transistor has been put into practical use.

However, these liquid crystal display devices have a narrow viewing angle in which an image can be visually checked properly, and have a drawback of causing a decrease in luminance and contrast and inversion of luminance in an intermediate tone when viewed in an inclined direction. Have. In recent years, regarding the problem of the viewing angle, a TN type liquid crystal display device using an optical compensation film, a multi-domain vertical alignment (MVA) type liquid crystal display device using a combination of the vertical alignment and the projection structure technology, or an IPS of a transverse electric field method. It is improved by the technique, such as a type liquid crystal display element (for example, patent documents 1-3), and is utilized.

As one of the indicators of the performance of the liquid crystal display device, a contrast which is the ratio of the luminance of the white display to the luminance of the black display is used. In general, since the luminance of the white display does not change significantly, the contrast greatly depends on the luminance of the black display, which is the denominator. Therefore, in order to increase the contrast, it is important to lower the luminance of the black display. As a method of lowering the luminance of the black display, for example, in the TN type liquid crystal display device in the beneficiation mode, a method of optimizing the Δn (birefringence) and the cell gap of the liquid crystal under first minimum conditions (for example, Although non-patent literature 1) etc. are mentioned, black display characteristics may deteriorate by light leakage resulting from the distribution of the orientation direction of the liquid crystal represented by an order parameter, when the uniaxial orientation of an orientation film is not enough. .

In particular, an IPS type liquid crystal display device normally aligns a liquid crystal in the direction of one polarizing plate under cross nicol, and thus normally black display in which black display is performed when no voltage is applied. to be. In such a device configuration, light leakage due to the distribution of the alignment direction of the liquid crystal is remarkable, and there is a problem that black display characteristics tend to be deteriorated. Moreover, also in an IPS type liquid crystal display element, uniaxial orientation is provided to an oriented film by a rubbing process. However, since the area near the step of the electrode arranged in the shape of the comb is hardly rubbed, the uniaxial orientation of the alignment film is incomplete. Because this area is oriented in a disordered direction, light leakage occurs, resulting in deterioration of contrast.

As described above, in order to improve the contrast of the liquid crystal display device, it is important to control the uniaxial orientation of the alignment film.

Up to now, the following two are proposed as an orientation mechanism of the liquid crystal on a rubbed alignment film.

(1) the surface shape effect due to the microgroup generated by the rubbing treatment,

(2) Intermolecular interaction of the alignment film uniaxially oriented by the rubbing process and the liquid crystal.

In recent years, the contribution of the surface shape effect of (1) is relatively small, and it has been confirmed that the contribution of the intermolecular interaction of (2) is dominant. Therefore, improvement can be expected also regarding the orientation state of the liquid crystal contacting an oriented film, and also the performance as a liquid crystal display element by controlling the uniaxial orientation of an oriented film.

As a method of directly evaluating the molecular orientation of a film made of a high molecular compound such as an alignment film, infrared absorption spectroscopy using polarized infrared light is widely used. This method detects the infrared dichroism that the amount of infrared rays absorbed when two linearly polarized infrared light orthogonal to a sample differs depending on the molecular orientation orientation, and evaluates molecular orientation. The scope of this method, the silicon and calcium fluoride: is limited to (calcium fluoride CaF ₂₎ film formed on the substrate such that the infrared light transmission. Since infrared light does not transmit through a glass substrate, the molecular orientation of the alignment film formed on the glass substrate cannot be measured by this method.

As a method of evaluating the infrared dichroism of an alignment film, (1) the method of evaluating an infrared dichroic ratio (for example, refer patent document 4, nonpatent literature 2), (2) the method of evaluating a dichroism (for example, For example, nonpatent literature 3, nonpatent literature 4), etc. are proposed.

The infrared dichroism of the alignment film is obtained when the infrared light having the polarization component parallel to the alignment treatment direction is incident on the alignment film and the infrared light having the polarization component perpendicular to the alignment treatment direction is incident on the alignment film. Obtained from absorbance. Moreover, the non-patent document 2 describes the measuring method of an infrared dichroic ratio. That is, a polarizer is disposed between the light source of the infrared spectrophotometer (preferably FT-IR) and the sample holder holding the sample having the alignment film, so that the rubbing treatment direction of the alignment film is parallel to the polarization direction of the polarizer. The sample is fixed to the sample holder and the infrared absorbance is measured. Next, the sample holder is rotated 90 degrees while the alignment film is fixed to the sample holder so that polarized infrared light passing through the polarizer is incident on the alignment film perpendicular to the rubbing alignment treatment direction, and the infrared absorbance is measured. In the infrared absorbance obtained in this way, a dichroic ratio is computed from the value in wavelength which shows strong absorption (peak).

[Patent Document 1] JP 63-21907

[Patent Document 2] Japanese Unexamined Patent Publication No. 6-160878

[Patent Document 3] Japanese Unexamined Patent Publication No. 9-15650

[Patent Document 4] Japanese Unexamined Patent Publication No. 64-35419

[Non-Patent Document 1] Yoshino, Co., Ltd., Co., Ltd., The Foundation of Liquid Crystal and Display Applications, Corona Screw, P 107-109

[Non-Patent Document 2] S. Ishibashi et al., Liquid Crystals, 4, 669 (1989)

[Non-Patent Document 3] R. Hasegawa et al., Mol. Cryst. & Liq. Cryst., 262 (1995) 7

[Nonpatent Literature 4] Hon-Tegawa et al., Liquid Crystal Discussion Forum 21st, 1A07, P 14-157

An object of the present invention is to provide a liquid crystal display device having good black display characteristics having a polyimide varnish capable of forming an alignment film having a high uniaxial alignment property, an alignment film formed using the varnish, and the alignment film.

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining in order to solve the said subject, as an polyimide varnish for forming the orientation film for liquid crystal display elements, the orientation film after liquid-crystal processing represented by following formula (1) is 1.3 or more, By using the polyimide varnish that can be formed, it has been found that the black display characteristics of the liquid crystal display device can be remarkably improved, and according to this finding, the present invention has been completed.

In the above formula, A ∥ is the absorbance by CN stretching vibration of the imide ring when the infrared light having the polarization component parallel to the alignment treatment direction is incident on the alignment film, A 'is the polarization component perpendicular to the alignment treatment direction The branch is the absorbance by CN stretching vibration of the imide ring when the infrared light is incident on the alignment film. d is the film thickness (unit is nm) of an oriented film.

This invention consists of the following structures.

[1] A polyimide varnish for forming an alignment film for forming a liquid crystal display device, wherein the alignment film having an orientation index? After liquid crystal treatment represented by the following formula (1) is 1.3 or more:

In the above formula, A ∥ is the absorbance due to CN stretching vibration of the imide ring when the infrared light having a polarization component parallel to the alignment treatment direction is incident on the alignment film, and A ′ is perpendicular to the alignment treatment direction. Absorbance by CN stretching vibration of an imide ring when the infrared light which has a phosphorus polarizing component is made to enter an alignment film, d is a film thickness (unit is nm) of an alignment film.

[2] The polyimide varnish according to the above [1], wherein the liquid crystal display element is a transverse electric field type liquid crystal display element in which display is performed by forming an electric field dominantly parallel to the surface of the substrate.

[3] The polyimide varnish according to the above [1] or [2], wherein the orientation index Δ after the liquid crystal treatment represented by the formula (1) of the above 1 item is 1.5 to 10.0.

[4] The above-mentioned [1], wherein the polymer component of the polyimide varnish is a soluble polyimide obtained from at least one of the tetracarboxylic dianhydrides shown below and at least one of the diamines shown below or a precursor thereof. The polyimide varnish according to any one of-[3] (wherein n is an integer of 1 to 20, R is hydrogen or alkyl having 1 to 20 carbons, and optionally -CH ₂ -in this alkyl). May be substituted with —O—, —CH═CH— or —C≡C—, and any hydrogen of the cyclohexane ring and the benzene ring may be substituted with halogen or alkyl having 1 to 5 carbon atoms):

[5] tetracarboxylic dianhydride is formula 1-1, formula 1-2, formula 1-13, formula 1-17, formula 1-18, formula 1-19, formula 1-20, formula 1-27, The polyimide varnish as described in said [4] which is at least 1 sort (s) chosen from tetracarboxylic dianhydride represented by Formula 1-28 and Formula 1-29.

[6] The diamine is formula 2-5, formula 2-6, formula 2-9, formula 2-10, formula 2-11, formula 2-12, formula 2-13, formula 2-14, formula 2- 15, Expression 2-16, Expression 2-17, Expression 2-18, Expression 2-19, Expression 2-20, Expression 2-30, Expression 2-35, Expression 2-39, Expression 2-40, Expression 2- The polyimide varnish according to the above-mentioned [4], which is at least one selected from 41, formula 2-42, formula 2-43, and diamine represented by formula 2-56 (wherein n is an integer of 2 to 10). And any hydrogen of the benzene ring may be substituted with halogen or alkyl having 1 to 5 carbon atoms.

[7] The diamine is formula 2-12, formula 2-13, formula 2-14, formula 2-15, formula 2-16, formula 2-17, formula 2-18, formula 2-19, formula 2- Polyimide-based varnish of the above-mentioned [4] item which is at least 1 sort (s) chosen from 20 and the diamine represented by Formula 2-39 (In these formula, n is an integer of 2-10, and arbitrary hydrogen of a benzene ring is halogen or May be substituted with alkyl having 1 to 5 carbon atoms.

[8] An alignment film formed by using the polyimide varnish according to any one of [1] to [7].

[9] The alignment film according to the above [8], wherein the alignment treatment conditions for the alignment film are a rubbing treatment at a base group indentation amount of 0.2 to 0.8 mm, a stage movement speed of 5 to 250 mm / sec, and a roller rotation speed of 500 to 2,000 rpm.

[10] A liquid crystal display device having the alignment film as described in the above [8] or [9].

[11] A transverse electric field liquid crystal display device having an alignment film as described in the above [8] or [9].

This invention implement | achieves the liquid crystal display element which has the outstanding black display characteristic especially by using the high uniaxial orientation, ie, the alignment film whose orientation index (DELTA) after liquid crystal processing is 1.3 or more.

In this invention, the uniaxial orientation of an orientation film is evaluated by the orientation index (DELTA) of the orientation film after orientation processing and then liquid-crystal processing represented by following formula (1).

In the above formula, A ∥ is the absorbance by CN stretching vibration of the imide ring when the infrared light having the polarization component parallel to the alignment treatment direction is incident on the alignment film, A 'is the polarization component perpendicular to the alignment treatment direction The branch is the absorbance by CN stretching vibration of the imide ring when the infrared light is incident on the alignment film. d is the film thickness (unit is nm) of an oriented film.

When using the polyimide-based orientation film, of a strong infrared absorption spectrum of the polyimide peak near 1380cm ^-1 (imide ring CN stretching vibration), 1510cm ^-1 vicinity (CC stretching vibration of phenyl), and the vicinity of 1720cm ^-1 (imide group C = O stretching vibration). Originally, any infrared absorption spectrum peak can be used, but the direction of polarization caused by molecular vibration is along the polyimide backbone, and the change in the infrared absorption spectrum peak due to the polyimide composition is relatively close to 1380 cm ^-1 (already Decyclic CN stretching vibration) is particularly preferably used. In addition, since the infrared dichroic ratio may vary depending on the film thickness of the alignment film, it is preferable to remove the influence of the film thickness and to evaluate the uniaxial orientation using the infrared dichroism.

As mentioned above, in this invention, the uniaxial orientation of an oriented film shall be evaluated by the infrared two-color difference of CN stretching vibration of the imide ring of 1380 cm <^-1> vicinity. In addition, the absorbance near 1380cm <^-1> in this invention shows the peak height of the maximum value of the absorption spectrum in the range of 1330-1430cm <^-1> . In addition, in order to correct | amend the influence of a film thickness, it measured also about the film thickness (unit is nm).

Originally, the liquid crystal display device is driven in a state in which the alignment film and the liquid crystal are in contact with each other. However, since the uniaxial orientation of the alignment film may change when the alignment film and the liquid crystal come into contact with each other, 1 of the alignment film is determined by the orientation index? It is necessary to evaluate the axial orientation.

The liquid crystal treatment in the present invention, after dropping the liquid crystal onto the surface of the alignment film after the alignment treatment, preferably at 60 to 140 ℃, more preferably at 80 to 120 ℃, preferably 5 to 600 minutes, more preferably It means heat-processing for 10 to 180 minutes. In this invention, after the said liquid-crystal process, after removing a liquid crystal using a suitable solvent, and drying an oriented film at room temperature (22-24 degreeC), the orientation index (DELTA) is measured. The solvent for removing the liquid crystal can be applied without particular limitation as long as the object of the present invention is not impaired, but n-hexane can be particularly preferably used.

Although the liquid crystal used by the liquid crystal process of this invention does not have a restriction | limiting in particular, The thing used by the liquid crystal display element which concerns on this invention can use especially preferable.

As for the alignment film for liquid crystal display elements used by this invention, the orientation index (DELTA) after liquid crystal processing represented by said Formula (1) is 1.3 or more. Although the upper limit of orientation index (DELTA) after liquid crystal processing is not specifically limited, Considering film shaving of the alignment film by a rubbing process, etc., a practical upper limit is about 10.0. The orientation index (DELTA) after preferable liquid-crystal processing is 1.5-10.0, More preferably, it is 2.0-8.0. If the orientation index (DELTA) after liquid-crystal processing is 1.3 or more, uniaxial orientation is enough and the black display characteristic of the liquid crystal display element obtained will become favorable.

The film thickness of the alignment film for liquid crystal display elements of this invention is 10-500 nm normally, Preferably it is 30-200 nm.

The polyimide varnish which can form the orientation film which has the said orientation index (DELTA) after liquid-crystal processing concerning this invention is a varnish of the state which melt | dissolved high molecular components, such as a polyamic acid, a polyamic acid ester, soluble polyimide, and polyamidoimide, in a solvent. Composition. After apply | coating this varnish composition on a board | substrate, an alignment film is formed when a solvent is dried. Copolymers, such as a random copolymer and a block copolymer, may be sufficient as the said polymer component, and may use multiple types of polymer component together.

The polyimide varnish for forming the alignment film can be used as long as it is a high molecular compound having an imide bond. The high molecular compound which has especially preferable imide bond is a polyamic acid obtained by making diamine react with tetracarboxylic dianhydride etc., a soluble polyimide obtained by dehydration reaction of the said polyamic acid, etc.

The tetracarboxylic dianhydride which gives the polyamic acid and the soluble polyimide is an aromatic system having a dicarboxylic acid anhydride directly bonded to an aromatic ring (including a heteroaromatic ring system), and an aliphatic system having no dicarboxylic acid anhydride directly bonded to an aromatic ring ( Or a heterocyclic system). It is preferable that the soluble polyimide obtained by the said polyamic acid, the dehydration reaction of the said polyamic acid, etc. has a structure which does not contain oxygen and sulfur, such as ester and an ether bond which are a cause of the fall of the electrical property of a liquid crystal display element. However, even if it has such a structure, it will not be a problem at all if it is used within the range which does not affect these characteristics weakly.

Specific examples of the tetracarboxylic dianhydride that can be used in the present invention are 1-1 to 1-38.

The tetracarboxylic dianhydride that can be used in the present invention is not limited to these, and various forms exist in addition to those within the scope of the object of the present invention. Moreover, these tetracarboxylic dianhydrides can also be used individually or in combination of 2 or more types.

Among these, formula 1-1, formula 1-2, formula 1-13, formula 1-17, formula 1-18, formula 1-19, formula 1-20, formula 1-27, formula 1-28, and The tetracarboxylic dianhydride represented by Formula 1-29 is preferable. More preferably, they are tetracarboxylic dianhydride represented by Formula 1-1, Formula 1-13, Formula 1-17, Formula 1-19, Formula 1-20, and Formula 1-29, respectively.

Aliphatic tetracarboxylic dianhydride is excellent in electrical characteristics, such as voltage retention. However, the aliphatic tetracarboxylic dianhydride has some difficulties in the orientation characteristics such as the pretilt angle, and in particular, the orientation may be easily broken at low temperature firing at 180 ° C or lower. On the other hand, although aromatic tetracarboxylic dianhydride is excellent in orientation stability, it is rather preferable to use aliphatic tetracarboxylic dianhydride regarding electrical characteristics. Therefore, it is more preferable to use aromatic tetracarboxylic dianhydride and aliphatic tetracarboxylic dianhydride together.

Specific examples of the diamine to which the polyamic acid and the soluble polyimide which are the polymer components of the polyimide varnish of the present invention are given are 2-1 to 2-56.

In addition, cholesteryl, androsteryl, β-cholesteryl, epiandrosteryl, erygosteryl, estoryl, 11α-hydroxymethylsteryl, 11α-progesteryl, lanosteryl, methyltest And diamines having side chains of steroid skeletons such as rosteryl, noleciteryl, pregnnonyl, β-sitosteryl, stegmasteryl, testosteryl, and cholesterol esters.

Moreover, the siloxane type diamine which has a siloxane bond is mentioned as another diamine which can be used together with said diamine which can be used by this invention. Although the said siloxane diamine is not specifically limited, What is represented by following formula (2) can be used preferably in this invention.

Wherein R 2 and R 3 are independently alkyl or phenyl having 1 to 3 carbon atoms, and R 4 is methylene, phenylene or alkyl substituted phenylene. x is an integer of 1-6, y is an integer of 1-10.

The diamine which can be used by this invention is not limited to these, A various form exists besides the range within which the objective of this invention is achieved, of course. In addition, these diamine can be used individually or in combination of 2 or more types.

Among them, Expression 2-5, Expression 2-6, Expression 2-9, Expression 2-10, Expression 2-11, Expression 2-12, Expression 2-13, Expression 2-14, Expression 2-15, Expression 2- 16, Expression 2-17, Expression 2-18, Expression 2-19, Expression 2-20, Expression 2-30, Expression 2-35, Expression 2-39, Expression 2-40, Expression 2-41, Expression 2- Preference is given to diamines represented by 42, formula 2-43, and formula 2-56. More preferably, Formula 2-12, Formula 2-13, Formula 2-14, Formula 2-15, Formula 2-16, Formula 2-17, Formula 2-18, Formula 2- with linear alkylene In the aromatic diamine represented by 19, Formula 2-20, and Formula 2-39, diamine of n is 2-10, Formula 2-13, Formula 2-16, which has amino in the 3,3'-position of a benzene ring The diamine represented by Formula 2-20 and the diamine represented by Formula 2-14 which has an amino at 3,4'-position of a benzene ring. By using these diamines, high orientation index (DELTA) can be obtained easily.

On the other hand, the diamines that can be used in the present invention, like the tetracarboxylic dianhydrides described above, are also aromatic systems (including complex aromatic ring systems) in which amino groups are bonded directly to aromatic rings, and aliphatic systems in which no amino groups are directly bonded to aromatic rings. It may belong to any one group (including a heterocyclic system). Among them, aromatic diamines having a ring structure and aliphatic diamines having a ring structure are preferred because they maintain the alignment of the liquid crystal satisfactorily. Moreover, the thing of the structure which does not contain oxygen and sulfur, such as ester and ether bond which are a cause of the fall of the electrical property of a liquid crystal display element, is preferable. However, even if it has such a structure, it will not be a problem at all if it is used within the range which does not affect these characteristics weakly.                     

In addition to these tetracarboxylic dianhydrides and diamines, it is also possible to use together the monoamine compound which forms the reaction terminal of polyamic acid, soluble polyimide, and / or monocarboxylic acid anhydride. In order to improve the adhesiveness to a board | substrate, an amino silicone compound may be introduce | transduced.

Examples of the aminosilicon compound include paraaminophenyltrimethoxysilane, paraaminophenyltriethoxysilane, metaaminophenyltrimethoxysilane, metaaminophenyltriethoxysilane, aminopropyltrimethoxysilane, and aminopropyltrie. Oxysilane and the like.

The molecular weight of the polyamic acid or the soluble polyimide used in the present invention is, for example, a weight average molecular weight (Mw) in terms of polystyrene in gel permeation chromatography (GPC), preferably 10,000 to 500,000, more preferably 20,000 to 200,000.

Although the density | concentration of the polymer component in the polyimide varnish of this invention is not specifically limited, 0.1-40 weight% is preferable. When apply | coating the said varnish to a board | substrate, the operation | movement which dilutes the polymer component contained with the solvent in advance may be needed for film thickness adjustment. If the concentration of the polymer component is 40% by weight or less, the viscosity of the varnish is optimum, and when the varnish needs to be diluted for film thickness adjustment, the solvent can be easily mixed with the varnish. In the case of application | coating methods, such as a spinner method and the printing method, in order to maintain film thickness favorably, it is usually made into 10 weight% or less in many cases. In other coating methods, for example, the dipping method and the inkjet method, the concentration may be lower. On the other hand, when the density | concentration of a polymer component is 0.1 weight% or more, it is easy to optimize the film thickness of the orientation film obtained. Therefore, the density | concentration of a polymer component is 0.1 weight% or more, Preferably it is 0.5-10 weight% in application | coating methods, such as a spinner method and the printing method. However, depending on the method of applying the varnish, it may be used at a thinner concentration.

The solvent used together with the polymer component in the polyimide varnish of the present invention can be applied without particular limitation as long as it is a solvent having the ability to dissolve the polymer component. Such a solvent can be suitably selected according to the purpose of use, including the solvent normally used in the manufacturing process of a polymeric component, such as a polyamic acid and a soluble polyimide, and a use aspect. When these solvents are illustrated, it is as follows. Examples of aprotic polar organic solvents that are aprotic to polyamic acid or soluble polyimide include N-methyl-2-pyrrolidone, dimethylimidazolidinone, N-methylcaprolactam, N-methylpropionamide, And lactones such as N, N-dimethylacetamide, dimethyl sulfoxide, N, N dimethylformamide, N, N-diethylformamide, diethylacetamide and γ-butyrolactone. Examples of other solvents for the purpose of improving coating properties include ethylene glycol monoalkyl ethers such as alkyl lactate, 3-methyl-3-methoxybutanol, tetralin, isophorone, and ethylene glycol monobutyl ether, and diethylene glycol mono Diethylene glycol monoalkyl ethers such as ethyl ether, ethylene glycol monoalkyl or phenyl acetate, propylene glycol monoalkyl ethers such as triethylene glycol monoalkyl ether, propylene glycol monobutyl ether, and dialkyl malonic acid such as diethyl malonate and dipropylene Dipropylene glycol monoalkyl ethers, such as glycol monomethyl ether, and ester compounds, such as these acetates, are mentioned. Among them, N-methyl-2-pyrrolidone, dimethylimidazolidinone, γ-butyrolactone, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl Ether and the like can be particularly preferably used.

The polyimide varnish of this invention can contain various additives as needed. For example, a surfactant according to this purpose is desired when the applicability is improved, an antistatic agent is required when the antistatic property is required, and a silane coupling agent or a titanium-based coupling agent when the adhesiveness with the substrate is desired. It can also mix | blend.

The liquid crystal display element which concerns on this invention contains the liquid crystal normally inserted between the board | substrates with which two transparent electrodes were formed. The liquid crystal is twisted at 90 degrees in the TN type liquid crystal display device, and is twisted at least 180 degrees in the STN type liquid crystal display device. In particular, in the TFT type liquid crystal device of a color display using a thin film transistor, a thin film transistor, an insulating film, a protective film, a pixel electrode, and the like are formed on the first transparent substrate, and light is blocked on the second transparent substrate. Black matrix, color filter, planarization film, and pixel electrode.

Further, the IPS type liquid crystal display device according to the present invention comprises a first transparent substrate on which a thin film transistor is formed, an opposing second transparent substrate, and a liquid crystal inserted between the substrates. The first transparent substrate has a pixel electrode and a common electrode formed so that the comb teeth alternately extend. Like the conventional liquid crystal display device, the second transparent substrate has a black matrix, a color filter, a planarization film, or the like, which blocks light other than the pixel region. A comb-tooth shaped electrode is formed by depositing metals, such as Cr, on transparent substrates, such as glass, using a sputtering method etc., and then etching using a resist pattern of a predetermined shape as a mask.                     

Next, the process of apply | coating varnish on the obtained two transparent substrates, the following drying process, and the process of heat processing required for dehydration and ring-closure reaction are performed.

As a coating method in a varnish coating process, the spinner method, the printing method, the dipping method, the dropping method, the inkjet method, etc. are generally known. These methods can be equally applied to the present invention. Moreover, as a method of the heat processing required for a drying process and a dehydration and ring-closure reaction, the method of heat-processing in oven or infrared furnace, the method of heat-processing on a hotplate, etc. are generally known. These methods can be equally applied in the present invention.

It is preferable to perform a drying process at comparatively low temperature within the range which can evaporate a solvent. It is preferable to perform a heat processing process at the temperature of about 150-300 degreeC generally.

Next, a liquid crystal display element is manufactured through the process of orientation-processing the obtained orientation film, the process of opposing the said board | substrate through a spacer, the process of encapsulating a liquid crystal material, and the process of adhering a polarizing film. As the orientation treatment method in the alignment treatment step, a rubbing method, a photo alignment method, a transfer method, and the like are generally known. As long as the object of the present invention is achieved, these methods can be equally applied to the present invention.

The orientation treatment method which can be used especially preferably in this invention is a rubbing method. Any rubbing treatment condition is possible as long as the object of the present invention is achieved. Particularly preferable conditions are 0.2-0.8 mm of group foot indentations, 5-250 mm / sec of stage movement speeds, and 500-2,000 rpm of roller rotation speeds. More preferable stage moving speed is 31 to 250 mm / sec. The larger the amount of hair press, the smaller the stage moving speed, or the larger the roller rotational speed, the stronger the conditions of the rubbing treatment are, so that a high orientation index Δ is obtained after the liquid crystal treatment. However, when the rubbing treatment conditions become excessively strong, film shaping of the alignment film may occur. The alignment film of the present invention can have a stage moving speed of 31 mm / sec or more, and also has an advantage of increasing production speed.

The liquid crystal display element of this invention can also perform the washing process with a washing | cleaning liquid before and after an alignment process. Examples of the cleaning method include brushing, jet spray, steam cleaning or ultrasonic cleaning. These methods may be used alone or in combination. Pure water or various alcohols such as methyl alcohol, ethanol and isopropyl alcohol, aromatic hydrocarbons such as benzene, toluene and xylene, halogen solvents such as methylene chloride, ketones such as acetone and methyl ethyl ketone can be used as the washing liquid. However, it is not limited to these. Of course, these washing | cleaning liquids are refine | purified sufficiently and the thing with few impurities is used.

The value of the pretilt angle preferable in the liquid crystal display element which can be used by this invention changes with the form of a liquid crystal display element. When the pretilt angle is small, it is preferable for an IPS type liquid crystal display element, and when the pretilt angle is about 3 to 8 degrees, it is suitable for a TN type liquid crystal display element. In the case of the STN type liquid crystal display element and the VA type liquid crystal display element, a larger pretilt angle may be required in some cases.

Especially the preferable pretilt angle in the IPS type liquid crystal display element of this invention is 0.1-5.0 degree | times, More preferably, it is 0.2-3.0 degree | times. In the IPS type liquid crystal display element, the driving principle does not require a large pretilt angle of the liquid crystal. The viewing angle characteristic of the IPS type liquid crystal display element obtained as a pretilt angle is the range of 0.1-5.0 degree is favorable.

There is no restriction | limiting in particular in the liquid crystal composition used by the liquid crystal display element of this invention, Various liquid crystal compositions with a positive dielectric anisotropy can be used. Examples of preferred liquid crystal compositions include Japanese Patent Nos. 3086228, 2,435,435, JP-A 5-501735, JP-A-8-157828, JP-A-8-231960 and JP-A. Japanese Patent Application Laid-Open No. 9-241644 (EP 885272 A1), Japanese Patent Application Laid-Open No. 9-302346 (EP 806466 A1), Japanese Patent Application Laid-Open No. 8-199168 (EP 722998 A1), Japanese Patent Application Laid-Open No. 9-235552, and Japanese Patent Application Laid-Open No. 9-255956 Japanese Patent Application Laid-Open No. 9-241643 (EP 885271 A1), Japanese Patent Application Laid-Open No. 10-204016, Japanese Patent Application Laid-Open No. 10-204436, Japanese Patent Application Laid-Open No. 10-231482, Japanese Patent Application Laid-Open No. 2000-087040 And Japanese Patent Laid-Open No. 2001-48822.

Various liquid crystal compositions having negative dielectric anisotropy can be used. Examples of preferred liquid crystal compositions are JP-A-57-114532, JP-A-2-4725, JP-A-4-224885, JP-A-8-40953 and JP-A-8-104869. Japanese Patent Laid-Open No. 10-168076, Japanese Patent Laid-Open No. 10-168453, Japanese Patent Laid-Open No. 10-236989, Japanese Patent Laid-Open No. 10-236990, Japanese Patent Laid-Open No. 10-236992, Japanese Patent Laid-Open No. 10-236993, Japanese Patent Laid-Open No. 10-236994, Japanese Patent Laid-Open No. 10-237000, Japanese Patent Laid-Open No. 10-237004, Japanese Patent Laid-Open No. 10-237024, Japanese Patent Laid-Open No. 10-237035, Japanese Patent Laid-Open No. 10-237075 10-237076, JP 10-237448, EP 967261 A1, JP 10-287874, JP 10-287875, JP 10-291945, JP 11-029581 Japanese Patent Laid-Open No. 11-080049, Japanese Patent Laid-Open No. 2000-256307, Japanese Patent Laid-Open No. 2001-019965, Japanese Patent Laid-Open No. 2001-072626, Japanese Patent Laid-Open No. 2001-192657, and the like.

Even if the said dielectric anisotropy adds 1 or more types of optically active compound to the liquid crystal composition which is positive or negative, it does not interfere at all.

[Example]

Hereinafter, although an Example and a comparative example demonstrate this invention, this invention is not limited to these Examples. In addition, the names of the tetracarboxylic dianhydride, the diamine, and the solvent used by the Example and the comparative example are shown by symbol. Subsequent descriptions may use this abbreviation.

● tetracarboxylic dianhydride

Pyromellitic dianhydride: PMDA

1,2,3,4-cyclobutanetetracarboxylic dianhydride: CBDA

1,3,3a, 4,5,9b-hexahydro-5- (tetrahydro-2,5-dioxo-3-furanyl) -naphtho

[1,2-c] furan-1,3-dione: TDA

● diamine

1,3-bis (4- (4-aminobenzyl) phenyl) propane: BZ3

4,4'-diaminodiphenylethane: DDE

● solvent component

N-methyl-2-pyrrolidone: NMP                     

γ-butyrolactone: GBL

Butyl Cellosolve: BC

Example  One

1) Preparation of polyimide varnish A1

In a 200 ml four-necked flask equipped with a thermometer, a stirrer, a raw material inlet, and a nitrogen gas inlet, 2.7760 g of BZ3, 0.3624 g of DDE, and 30.00 g of dehydrated NMP were added and stirred and dissolved under a dry nitrogen stream. 1.8616g of PMDA was added and reaction was carried out for 30 hours, keeping the temperature of the reaction system at 5 degreeC, and 35.00g of BC and 30.00g of GBL were added, and the varnish of the polyamic acid of 5 weight% of polymer components was prepared. When the temperature rose by the reaction temperature during the reaction of the raw materials, the reaction temperature was limited to about 70 ° C. or lower and allowed to react. Moreover, in the Example of this invention, reaction is performed, checking the viscosity during reaction, and reaction is complete | finished when the viscosity of the varnish after BC addition became 30-35 mPa * s (using an E-type viscosity meter, 25 degreeC), Preserved under low temperature. The weight average molecular weight of the obtained polyamic acid was 70,000. In addition, the weight average molecular weight was measured at the column temperature of 50 degreeC using the GPC measuring apparatus (Chromatopack C-R7A) made from Shimadzu Corporation.

Varnish A1 obtained by the above-mentioned method was diluted with the one-to-one mixed solvent of NMP and BC, and it adjusted so that the density | concentration of all the polymer components may be 3 weight%, and it was set as the varnish for application | coating.

2) Absorbance of Infrared Light, Film Thickness Measurement of Alignment Film, and Calculation of Orientation Index Δ

The varnish for application | coating obtained was apply | coated with the spinner on the silicon substrate. Coating conditions were 2300 rpm and 15 second. After coating, it dried for about 5 minutes at 80 degreeC, and then heated at 210 degreeC for 30 minutes, and formed the orientation film of about 80 nm in film thickness. The obtained polyimide membrane was used under the conditions of 0.40 mm of the base group indentation amount of a rubbing cloth (a head length of 1.9 mm: rayon), stage movement speed of 60 mm / sec, and roller rotation speed of 1000 rpm using a rubbing treatment device manufactured by Inuma Gauge Seisakusho Co., Ltd. Rubbing treatment.

The obtained alignment film (approximately 13 mm in width and length) was placed in the center of a watch plate having a diameter of 30 mm, and the liquid crystal (4-cyano-4'-pentylbiphenyl) was loaded so as to cover the surface of the polyimide film. After heating this for 30 minutes in 110 degreeC oven, it took out and cooled to room temperature (22-24 degreeC). Subsequently, the polyimide membrane was carefully put into the beaker which contained about 20 ml of n-hexane, and it immersed for 15 minutes, stirring occasionally. n-hexane was poured out, and about 20 ml of n-hexane was newly added, and it was immersed for 15 minutes. Subsequently, the polyimide membrane was taken out from n-hexane, and the surface n-hexane was dried at room temperature, and left to stand in a desiccator for 12 hours or more. Moreover, as to whether the liquid crystal (4-cyano-4'-pentylbiphenyl) was removed from the polyimide film, it was confirmed from the measurement of the infrared absorption spectrum of the following alignment film that the peak of a cyano group was not detected.

The infrared absorption spectrum of the obtained alignment film was measured under conditions of 4 cm ^-1 resolution and 144 times of integration using a FT-IR device (Paragon 1000) manufactured by Perkin Elmer. Moreover, in order to remove the noise of water vapor, each chamber was purged with 10 liters / minute of sample chamber and 5 liters / minute of spectral chamber using dry nitrogen or air (dew point -60 degrees C or less).

The infrared light transmitted through the polarizer was incident on the alignment film side perpendicularly to the alignment film. The absorbance when the rubbing direction (orientation treatment direction) of the sample and the polarization direction were measured in parallel was set to A, and the absorbance when measured vertically was set to A '. The difference spectrum of the infrared light spectrum measured in parallel and perpendicularly was calculated by absorbance, and the peak height corresponding to C-N stretching vibration was set to (A∥-A⊥). In addition, the sum of peak heights corresponding to the C-N stretching vibrations of the parallel and vertical spectrums indicated by the absorbance (A∥ + A⊥) was calculated. Moreover, it was 82.2 nm when the film thickness d of the oriented film was measured using the Ellipsometer (DVA-FL3G) by the Corporation.

Subsequently, when it calculates from the values of obtained (A, A-A ', A | + A') and film thickness d according to following formula (1), the orientation index (DELTA) of the alignment film after liquid crystal processing was 2.62.

3) Fabrication of cell for measuring black display characteristics and voltage retention

The alignment film was formed by the method according to the method using a silicon substrate, except using two glass substrates which are the glass substrate with an IPS comb-shaped electrode shown in FIG. 1, and the glass substrate without an electrode.

The alignment film obtained as described above was ultrasonically cleaned in ethanol for 5 minutes, and then washed with pure water for 30 minutes at 120 ° C in an oven. 4 micrometers gap material was spread | dispersed on the glass substrate with an IPS comb-shaped electrode, and the glass substrate without an electrode was made to face the surface which formed the orientation film inward, and it sealed with an epoxy hardening | curing agent, I made a parallel cell. Liquid crystal composition A was injected into the said cell, and the injection hole was sealed with the photocuring agent. Subsequently, heat processing were performed for 30 minutes at 110 degreeC, and it was set as the cell for black display characteristics and voltage retention measurement. Moreover, the rubbing direction of the glass substrate with a comb-tooth shaped electrode for IPS and the glass substrate without an electrode made it the same direction mutually. The composition of the liquid crystal composition A used as the liquid crystal material is shown below. The NI point of this composition was 100.0 degreeC, and birefringence was 0.093.                     

LCD  Composition A

Subsequently, the light transmittance was measured according to the polarizer direction under the cross nicol by using the liquid crystal characteristic evaluation apparatus (OMS-CA3) made by Jusei Seiki Co., Ltd., and it is 0.0022%, and this is shown as a black display characteristic. Evaluated. Moreover, the light transmittance was computed by making into 100% the light quantity when the polarizer and the analyzer were arrange | positioned in parallel in the state without the cell for black display characteristic measurement.

In addition, no orientation unevenness or orientation defect such as a rubbing line was observed at all, and a very uniform display was obtained.

In addition, the voltage retention rate of this cell was 98.3% by a conventional method (see et al., P. 14, Liquid Crystal Debate Preview, p. 78). The measurement conditions of voltage retention are 69 microseconds of gate widths, a frequency of 60 Hz, wave height of + 4.5V, and a measurement temperature is 60 degreeC.

4) Fabrication of pretilt angle measuring cell

A glass substrate with a pair of ITO transparent electrodes, made of a gap material for 20 µm, and made free by the same method as the cell for measuring black display characteristics and voltage retention, except that the rubbing direction was antiparallel. Tilt angle measurement cells were produced. Moreover, the liquid crystal material in the pretilt angle measurement also used the same thing as the black display characteristic measurement. It was 1.7 degree | time when the pretilt angle of the liquid crystal was measured by the crystal rotation method using this cell.

Example  2 To 6, Comparative example  One To 3

Instead of varnish A1 in Example 1, varnishes A2 to A6 and varnishes B1 to B3 were respectively prepared according to the raw material compositions shown in Table 1 below, and the orientation index Δ, the black display characteristics, the voltage retention, and the pretilt angle were used using this. It evaluated like 1st.

Preparation of various varnishes

About preparation of varnish A2-A6 and varnish B1-B3, it prepared by the method similar to varnish A1. When the temperature rose by the heat of reaction during the reaction, the reaction temperature was limited to about 70 ° C or lower and allowed to react. The synthesis of the polyamic acid is carried out while checking the viscosity of the reaction mixture, and the reaction is performed when the viscosity of the polyamic acid after adding BC and GBL becomes 30 to 35 mPa · s (using an E-type viscometer, 25 ° C.). It terminated and stored the polyamic acid at low temperature.

That is, the original polyamic acid was synthesized only with NMP, then BC and GBL were added to finally adjust the polyamic acid concentration to 5% by weight.

Table 1 shows the molar ratios of the raw materials and the weight average molecular weights of the examples and the comparative examples.

TABLE 1

niece Tetracarboxylic dianhydride Diamine Weight average
Molecular Weight PMDA CBDA TDA BZ3 DDE  Example 1 A1 50 - - 40 10 70,000  Example 2 A2 40 10 - 40 10 68,000  Example 3 A3 30 20 - 40 10 65,000  Example 4 A4 20 30 - 40 10 63,000  Example 5 A5 40 - 10 40 10 60,000  Example 6 A6 30 - 20 40 10 55,000  Comparative Example 1 B1 10 40 - 40 10 58,000  Comparative Example 2 B2 20 - 30 40 10 53,000  Comparative Example 3 B3 10 - 40 40 10 50,000

Table 2 shows the evaluation results of the film thickness of the alignment film formed by using the varnish A1 to A6 and the varnish B1 to B3, the orientation index Δ after the liquid crystal treatment, the black display characteristic, the voltage retention and the pretilt angle.

In addition, in the test method of the Example of this invention, the outstanding black display characteristic means the value below 0.005%, The preferable pretilt angle in an IPS liquid crystal display element means the range of 0.1-5.0 degree, and a preferable voltage retention is A value of 97.0% or more.

TABLE 2

niece Film thickness
/ nm After liquid crystal treatment
Orientation Index Δ Black display characteristic
/% Voltage retention rate
/% Pretilt angle
/Degree  Example 1 A1 82.2 2.62 0.0022 98.3 1.7  Example 2 A2 79.4 2.12 0.0025 98.3 1.6  Example 3 A3 78.5 1.73 0.0028 98.4 1.5  Example 4 A4 83.7 1.35 0.0040 98.6 1.5  Example 5 A5 75.6 2.00 0.0026 98.4 1.5  Example 6 A6 80.8 1.52 0.0031 98.5 1.5  Comparative Example 1 B1 86.6 1.03 0.0067 98.6 1.4  Comparative Example 2 B2 75.9 1.22 0.0055 98.7 1.4  Comparative Example 3 B3 83.6 0.98 0.0069 98.7 1.4

From the result of Examples 1-6 and Comparative Examples 1-3, it turns out that the IPS type liquid crystal display element which shows the outstanding black display characteristic of 0.005% or less is obtained by using the orientation film whose orientation index (DELTA) after liquid crystal processing is 1.3 or more. Moreover, it turns out that the orientation film of Examples 1-6 shows the voltage retention and pretilt angle which are preferable as an IPS type liquid crystal display element.

According to the present invention, an alignment film for realizing a liquid crystal display device having particularly excellent black display characteristics and a polyimide varnish capable of forming the alignment film can be provided.

Claims (14)

A polyimide varnish for forming an oriented film for liquid crystal display elements of a transverse electric field system which displays by forming an electric field parallel to the surface of a substrate, the orientation index after liquid crystal processing represented by the following formula (1): A polyimide varnish capable of forming an alignment film having a Δ of 1.3 or more, wherein the polymer component of the polyimide varnish is a soluble poly obtained from at least one of tetracarboxylic dianhydrides shown below and at least one of diamines shown below. 30 mol% or more of at least 1 sort (s) of tetracarboxylic dianhydride selected from the tetracarboxylic dianhydride represented by following formula 1-1-formula 1-12 among the said tetracarboxylic dianhydride, respectively, as a mid or its precursor. Polyimide Varnishes:

In the above formula, A ∥ is the absorbance due to CN stretching vibration of the imide ring when an infrared light having a polarization component parallel to the alignment treatment direction is incident on the alignment film, and A ′ is perpendicular to the alignment treatment direction. Absorbance by CN stretching vibration of an imide ring when the infrared ray which has a polarizing component is made to enter an alignment film, d is a film thickness (unit is nm) of an alignment film, Here, n is an integer of 2-10 in the formula of following formula 2-12, formula 2-15, formula 2-17, formula 2-18, formula 2-19, and formula 2-39, and following formula 2-13 And n is an integer of 1 to 10 in the formulas 2-14, 2-16, and 2-20, and any hydrogen of the cyclohexane ring and the benzene ring may be substituted with halogen or alkyl having 1 to 5 carbon atoms. have:

. delete The method of claim 1, The orientation index (DELTA) after liquid crystal processing represented by said Formula (1) is 1.5-10.0, The polyimide varnish characterized by the above-mentioned. delete delete delete delete The method according to claim 1 or 3, The diamine is formula 2-12, formula 2-13, formula 2-14, formula 2-15, formula 2-16, formula 2-17, formula 2-18, formula 2-19, formula 2-20, And at least one kind selected from diamines represented by Formula 2-39 (wherein n is an integer of 2 to 10, and any hydrogen of the benzene ring is halogen or alkyl having 1 to 5 carbons). May be substituted). The alignment film formed using the polyimide varnish of Claim 1 or 3 and whose orientation index (DELTA) after liquid crystal processing represented by Formula (1) of Claim 1 is 1.3 or more. 10. The method of claim 9, The alignment process conditions of the said alignment film are a rubbing process in which the base group indentation amount is 0.2-0.8 mm, stage movement speed 5-250 mm / sec, and roller rotation speed 500-2,000 rpm. It is formed using the polyimide varnish of claim 8, the following formula (1):

Alignment film whose orientation index (DELTA) after liquid crystal processing represented by is 1.3 or more (In the formula (1), A ′ is absorbance due to CN stretching vibration of the imide ring when an infrared light having a polarization component parallel to the alignment treatment direction is incident on the alignment film, and A ′ is the orientation. The absorbance by CN stretching vibration of an imide ring when the infrared light which has the polarizing component perpendicular | vertical to a process direction is made to enter an alignment film, and d is the film thickness (unit is nm) of an alignment film. delete A transverse electric field liquid crystal display device having the alignment film of claim 9. A transverse electric field liquid crystal display device having the alignment film of claim 10.

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