JPH04340521A - Composition for liquid crystal oriented film, liquid crystal oriented film formed by using this composition, liquid crystal holding substrate and liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain the liquid crystal display element which exhibits a high voltage holding rate, has an adequately high pretilt angle and has high reliability even at the time of long-time use by using a compsn. for liquid crystal oriented films contg. a polymer Z having a specific unit structure. CONSTITUTION:This compsn. has the polymer Z having the unit structure expressed by formula I and/or formula II. In the formula, A denotes a residual tetracarboxylic group having a spiro ring; Y denotes a residual arom., aliphat. or alicyclic diamine group. The compsn. for liquid crystal orientation is formed by adding an org. solvent, additive, etc., at need to the org. solvent soln. of this polymer Z. This compsn. is applied on a prescribed electrode substrate surface by a spinner method, dipping method, etc., and is then calcined by heating, by which the liquid crystal holding substrate formed with the liquid crystal oriented film on the electrode substrate surface is formed. The liquid crystal display element in such a case is produced by using a pair of such liquid crystal holding substrates, holding and sealing a liquid crystal chiral agent, etc., between these substrates to constitute a liquid crystal cell and properly mounting attachments, such as polarizing plates, thereto.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a composition for liquid crystal alignment film,
The present invention relates to a liquid crystal alignment film, a liquid crystal holding substrate, and a liquid crystal display element using the same.

0002

[Prior Art] Conventionally, as a display element using liquid crystal, a pair of electrode substrates each having an alignment film formed on their surfaces are arranged facing each other so that their alignment directions intersect at a predetermined angle. Twisted nematic liquid crystal display elements, in which liquid crystal is twisted and oriented and sandwiched together, are widely used. Further, a device in which the twist angle of the liquid crystal is set to 90° or more is also known as a so-called super twisted nematic liquid crystal display device. Furthermore, so-called guest-host type liquid crystal display elements to which dyes are added are also known. These display modes will be hereinafter collectively referred to as a twisted nematic liquid crystal display element.

Among these, the above-mentioned twisted nematic liquid crystal display element for matrix display or TV display uses a large number of pixel electrodes (usually transparent electrodes) and this O
Devices using an electrode substrate incorporating a large number of MIM devices or TFT devices that perform N-OFF are known, and these devices are known as active twisted nematic liquid crystal display devices.

On the other hand, the alignment film formed on the electrode substrate surface of the liquid crystal display element has conventionally been made of various inorganic and organic materials, one of which is pyromellitic acid. Fully aromatic polyimide, which is formed from aromatic tetracarboxylic acid (or its anhydride) and aromatic diamine through polyamic acid, has excellent chemical stability and heat resistance. It has been used as a membrane material.

[0005]

[Problem to be Solved by the Invention] However, in order to obtain stable and good display in the above-mentioned active type liquid crystal display element, the voltage applied between each pixel electrode must be maintained without loss for a certain period of time. In other words, it is desired that the electrical resistance between the pixel electrodes be as high as possible. In order to evaluate such characteristics, for example, in a TFT-driven liquid crystal display element, the degree to which the drain voltage generated by applying a pulse to the TFT gate decreases after 1/60 seconds is expressed as voltage holding rate P = (1/60 second Effective value of drain voltage/
When expressed as source voltage), it is desirable that this voltage holding rate be as high as possible.

However, in the above-mentioned conventional liquid crystal display element using wholly aromatic polyimide as the alignment film material, this voltage holding ratio P is low even if other conditions are adapted, and active type liquid crystal display elements are not stable. Moreover, it was difficult to obtain good display characteristics. At the same time, because polymers derived from aromatic tetracarboxylic acid derivatives are highly electron-accepting compounds, they undergo various oxidation and reduction reactions under conditions where photoexcited electron transfer reactions can occur, such as when irradiated with a backlight. The major problem was that it deteriorated over time.

On the other hand, alignment films derived from 1,2,3,4-cyclobutanetetracarboxylic acid and 1,2,4-tricarboxycyclopentyl-3-acetic acid have appeared as a method to solve these problems. However, there was a new problem in that the pretilt angle, which is important for controlling the alignment of liquid crystals, was small.

The present invention was made in view of the above circumstances, and in particular, since the voltage holding rate is high and the electron acceptability is poor, the alignment film is stable without being involved in undesired reactions, and at the same time, the alignment film is stable. A twisted nematic liquid crystal alignment film composition suitable for active type liquid crystal displays that exhibits an appropriate pretilt angle for aligning liquid crystals, which is particularly important as a liquid crystal alignment film, a liquid crystal alignment film using the same, a liquid crystal holding substrate, and a liquid crystal display element. It provides:

[0009]

[Means for Solving the Problems] The present invention provides general formula (I)

[Image Omitted] Unit structure a represented by (A is a tetracarboxylic acid residue having a spiro ring, Y is an aromatic, aliphatic or alicyclic diamine residue) and/or general formula (II)

[C9
] (A is a tetracarboxylic acid residue having a spiro ring, Y is an aromatic, aliphatic or alicyclic diamine residue.) For liquid crystal alignment films containing a polymer Z having a unit structure b represented by The present invention relates to a composition, a liquid crystal alignment film using the same, a liquid crystal holding substrate, and a liquid crystal display element.

The present invention will be explained in detail below. Polymer Z in the present invention has, for example, general formula (VI)

embedded image (wherein A represents a tetracarboxylic acid residue having a spiro ring) or general formula (VII)

It can be synthesized by reacting a tetracarboxylic acid represented by the formula (wherein A has the same meaning as the formula (VI)) with a diamine as an amine component by a conventional method.

Examples of the tetracarboxylic acid anhydride represented by the general formula (VI) include the following.

embedded image These can be used alone or in combination of two or more.

Examples of the tetracarboxylic acid represented by the general formula (VII) include compounds prepared by ring-opening the compounds (A-1) to (A-6) above with water. These can be used alone or in combination of two or more.

Further, examples of the diamine include para-phenylene diamine, meta-phenylene diamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylethane, benzidine, 4,4'-diaminodiphenyl sulfide, and 4,4'-diaminodiphenyl methane. Diaminodiphenylsulfone, 4,
4'-diaminodiphenyl ether, 1,5-diaminonaphthalene, 3,3'-dimethyl-4,4'-diaminobiphenyl, 3,4'-diaminobenzanilide, 3,
4'-diaminodiphenyl ether, 3,3'-diaminobenzophenone, 3,4'-diaminobenzophenone, 4,4'-diaminobenzophenone, 2,2-bis[
4-(4-aminophenoxy)phenyl]propane, bis[4-(4-aminophenoxy)phenyl]sulfone, 1,4-bis(4-aminophenoxy)benzene, 1
, 3-bis(4-aminophenoxy)benzene, 1,3
-bis(3-aminophenoxy)benzene, 9,9-bis(4-aminophenyl)-10-hydroanthracene, 9,9-bis(4-aminophenyl)fluorene, 4
, 4'-methylenebis(2-chloroaniline), 2,2
',5,5'-tetrachloro-4,4'-diaminobiphenyl, 2,2'-dichloro-4,4'-diamino-5
, 5'-dimethoxybiphenyl, aromatic diamines such as 3,3'-dimethoxy-4,4'-diaminobiphenyl, 1,1'-methaxylylene diamine, 1,3-propanediamine, tetramethylene diamine, pentamethylene Diamine, hexamethylene diamine, heptamethylene diamine, octamethylene diamine, nonamethylene diamine, 4,4'-dimethylheptamethylene diamine, 1,
Aliphatic or Alicyclic diamines can be mentioned. These diamines can be used alone,
A combination of two or more types can also be used. The proportion of diamine used is based on tetracarboxylic acids (general formula (VI)
, (VII)) is generally 0.5 to 2 mol, preferably 0.8 to 1.3 mol.

The reaction between tetracarboxylic acids and diamines is usually carried out in an organic solvent. The organic solvent is not particularly limited as long as it can dissolve the obtained polymer product (polyamic acid, etc.), and examples include N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethyl Formamide, dimethyl sulfoxide, γ-butyrolactone, tetramethylurea, bis(methoxyethyl)ether, tetrahydrofuran, chloroform, 1,
4-dioxane, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methyl acetate,
Ethyl acetate, butyl acetate, diethyl oxalate, diethyl malonate, diethyl ether, ethylene glycol dimethyl ether, ethylene glycol ethyl ether acetate, diethylene glycol dimethyl ether, dichloromethane, 1,2-dichloroethane, 1,4-dichlorobutane, trichloroethane, chlorobenzene, o -dichlorobenzene, hexane, heptane, octane, cyclohexane, benzene, toluene, xylene, etc., and these can be used alone or in a mixed state.

As described above, by reacting the tetracarboxylic acids as the acid component and the diamine as the amine component, the structural unit a represented by the general formula (I) and/or the structure represented by the general formula (II) is obtained. An organic solvent solution of polymer Z having units b can be obtained. Polymer Z has a repeating number of structural units a as m, and a structural unit b as
When the number of repetitions of is n, m/(m+n) is preferably 0.50 or more, more preferably 0.70 or more, and 0.90 from the viewpoint of heat resistance, orientation characteristics, etc.
It is especially preferable that it is 0.95 or more, and it is extremely preferable that it is 0.95 or more. All structural units may be a. It is preferable that m+n is 5 to 4000, and 50
-3000 is more preferable, 100-200
It is especially preferable that it is 0, and it is extremely preferable that it is 500-1500. If (m+n) is too small, film formability, strength, heat resistance, adhesion, etc. tend to be too high, resulting in poor workability.

In the general formulas (I) and (II), the spiro ring-containing tetracarboxylic acid residue represented by A is represented by the formula (I).
II)

[Image Omitted] (In the formula, X represents C, Si, Ge or Sn, and a plurality of R
each independently represents a hydrogen atom or an alkyl group),
Formula (IV)

embedded image (wherein X and R have the same meanings as in formula (III)) or the formula (
V)

A group represented by the formula (wherein X and R have the same meanings as in formula (III)) is preferred from the viewpoint of synthesis and properties.

In the general formulas (I) and (II), the spiro ring-containing tetracarboxylic acid residue represented by A is represented by the formula (V
)

A group represented by the formula (wherein X and R have the same meanings as in formula (III)) is preferable from the viewpoint of synthesis and properties.

In the general formulas (I) and (II), the spiro ring-containing tetracarboxylic acid residue represented by A is represented by the formula (V
III)

A group represented by the formula (wherein X and R represent C or Si) is preferable from the viewpoint of synthesis and properties.

[0019] An organic solvent, additives, etc. may be added to the organic solvent solution of the polymer Z, if necessary, to prepare a composition for a liquid crystal aligning film.

[0020] The composition for a liquid crystal alignment film is applied to a predetermined electrode substrate surface by a spinner method, a dipping method, etc., and then heated and baked to produce a liquid crystal holding substrate in which a liquid crystal alignment film is formed on the electrode substrate surface. can do. The heating temperature is preferably about 100°C to 300°C, and 150°C to 25°C.
0°C is more preferred. Further, the thickness of the liquid crystal alignment film that is finally formed is usually suitably about 300 to 1500 Å, and this can be adjusted as appropriate by controlling the coating amount and solution concentration.

The liquid crystal alignment film can also be obtained by applying the Langmuir-Blodgett method (LB method) using a composition for a liquid crystal alignment film.

[0022] The liquid crystal display element of the present invention uses a pair of liquid crystal holding substrates, and a liquid crystal, a chiral agent, etc. are held and sealed therebetween in a conventional manner to constitute a liquid crystal cell, and accessories such as polarizing plates are added as appropriate. It can be manufactured by attaching it. In the case of an active type, it is suitable to use an electrode substrate with a large number of MIM elements or TFT elements attached, and in particular, it is suitable to use an electrode substrate with TFT elements made of amorphous silicon integrally formed on a glass substrate. is preferred.

The liquid crystal display element of the present invention is applicable not only to active type twisted nematic liquid crystal display devices but also to
The display device may have the structure of a liquid crystal display device or a super twisted nematic display device that performs normal segment display.

Since the polymer Z of the present invention is not derived from an aromatic tetracarboxylic acid that exhibits high electron acceptability, it not only exhibits an excellent voltage holding rate but also achieves stable reliability even during long-term use. . Furthermore, an excellent alignment film exhibiting a high tilt angle is provided.

[0025]

[Examples] The present invention will be explained below with reference to Examples. Example 1 (Measurement of voltage holding rate) The following compound was used as a tetracarboxylic acid anhydride having a spiro ring for forming an alignment film.

[Chemical formula 18]

On the other hand, the following compound was used as the diamine.

[Chemical formula 19]

Coating solutions were prepared by dissolving the polymers synthesized from the various tetracarboxylic anhydrides and diamines in a suitable solvent to a concentration of 8% by weight. ITO transparent electrodes with predetermined patterns were formed on two glass substrates (30 x 30 x 1.0 mm) by sputtering, respectively. This pattern is shown in FIGS. 1A and 1B. In the figure, 1 indicates a glass substrate, and 2 indicates an ITO transparent electrode.

The predetermined coating solution prepared above was spin-coated onto each of the substrates to a thickness of about 1000 ű100 Å.
After forming a coating film, it was heated and baked at 200° C. for 1 hour to convert it into a polyimide film. Next, the surface of this polyimide film was rubbed in one direction to obtain an alignment film. Note that the rubbing direction was performed so that both substrates crossed at 90 degrees.

Next, both substrates (pattern A substrate and pattern B substrate) were placed so that the alignment films faced each other, and bonded together using an epoxy thermosetting adhesive. At this time, short glass fibers having a diameter of 5.0 μm were interposed as spacers in order to maintain a constant gap between both substrates. A nematic liquid crystal (PCH-based liquid crystal mixture, manufactured by Merck & Co., Ltd.) was injected between the two substrates by a vacuum impregnation method, and the injection port was sealed with a UV curable resin to obtain the liquid crystal cell shown in FIG. 2. In the figure, 3 is a seal pattern, 4 is a polyimide alignment film, 5 is a liquid crystal, and 6 is a seal pattern.
1 and 2 indicate sealants, respectively.

Using such a liquid crystal cell, the voltage holding ratio was measured. The voltage holding ratio was measured using the I of both the above substrates.
A pulse voltage was applied using the model circuit shown in FIG. 3 while the voltage between the TO electrodes was monitored using a digital memory scope, and changes in the voltage between the ITO electrodes were measured. The measurement conditions were to input a gate signal with a pulse width of 30 μs and a voltage of 10 V and a gate signal with a frequency of 30 Hz and a voltage of 10 V between the gate G and source S in the model circuit, and measure the change in the drain (D) voltage VD. The effective value of the waveform on the scope was determined and calculated using the following formula.

[0031] Voltage holding rate = drain waveform effective value (V)/
5 (V) x 100 (%) Thus, the voltage holding rates of liquid crystal cells having various polyimide alignment films are shown in Tables 1 and 2. Note that the voltage holding rate varies by about ±3%, and each calculated value represents an average value. As shown in Tables 1 and 2, all of the polymers of the present invention exhibited very high voltage holding rates (%).

[0032]

[Table 1]

[0033]

[Table 2]

Comparative example 1 The following aromatic tetracarboxylic acid anhydride and

[Chemical formula 20] Using the diamines B-1 to B-4, the voltage holding ratio was measured in the same manner as in Example 1 (coating film was fired at 250°C for 1 hour). The results are shown in Table 3. It was shown to. As is clear from Table 3, those using aromatic tetracarboxylic acid anhydride did not show a very good voltage holding rate.

[0035]

[Table 3]

Example 2 Tetracarboxylic anhydrides A-1 to A-6 and diamine B
-1 to B-4, the pretilt angles were measured for the liquid crystal cells prepared in the same manner as in Example 1. As shown in Tables 4 and 5, in all cases the pretilt angles were found to be moderately high for practical use. It showed an effective pretilt angle.

[0037]

[Table 4]

[0038]

[Table 5]

Comparative example 2 Alicyclic tetracarboxylic acid anhydride (D-1 to D-4)

When the pretilt angle was measured for a liquid crystal cell prepared in the same manner as in Example 1 using [Chemical Formula 21] and diamines (B-1 to B-4), as shown in Tables 6 and 7, The cell also showed a low pretilt angle, indicating that it did not reach a practical level.

[0040]

[Table 6]

[0041]

[Table 7]

[0042]

Effects of the Invention: Since the liquid crystal alignment film obtained using the liquid crystal alignment film composition of the present invention has a high voltage holding rate, a liquid crystal display element using a liquid crystal holding substrate equipped with this liquid crystal alignment film can be stabilized. It can provide good display, achieve stable reliability even during long-term use, and exhibit a high pretilt angle.

[0043]

[Brief explanation of the drawing]

FIG. 1 is an explanatory plan view showing a pattern of a glass substrate during manufacturing of a liquid crystal display element.

FIG. 2 shows an embodiment of the liquid crystal display element of the present invention, in which (A) is an explanatory view of the configuration from a side, and (B) is an explanatory view of the configuration from a plane.

FIG. 3 is an equivalent circuit diagram when measuring voltage holding ratio. Explanation of symbols 1 Glass substrate
2 ITO transparent electrode 3 Seal pattern
4 Polyimide alignment film 5 Liquid crystal
6 Sealant

Claims (7)

[Claims] Claim 1: A unit represented by the general formula (I) [Formula 1] (A is a tetracarboxylic acid residue having a spiro ring, Y is an aromatic, aliphatic or alicyclic diamine residue) A unit represented by structure a and/or general formula (II) [Formula 2] (A is a tetracarboxylic acid residue having a spiro ring, Y is an aromatic, aliphatic or alicyclic diamine residue) A composition for a liquid crystal alignment film containing a polymer Z having structure b. 2. In the general formulas (I) and (II), the spiro ring-containing tetracarboxylic acid residue represented by A is represented by the formula (III) [Image Omitted] (wherein X is C, Si, Ge or Sn and multiple R
each independently represents a hydrogen atom or an alkyl group),
Formula (IV) [Chemical formula 4] (wherein X and R have the same meanings as in formula (III)) or formula (
V) The composition for a liquid crystal aligning film according to claim 1, which is a group represented by the following formula (wherein X and R have the same meanings as in formula (III)). 3. In general formulas (I) and (II), the spiro ring-containing tetracarboxylic acid residue represented by A is represented by formula (V) ) The composition for a liquid crystal aligning film according to claim 1, which is a group represented by the following. 4. In the general formulas (I) and (II), the spiro ring-containing tetracarboxylic acid residue represented by A is represented by the formula (V) (wherein X and R are C or Si The composition for a liquid crystal aligning film according to claim 1, which is a group represented by the following formula. 5. A liquid crystal alignment film formed from the composition for liquid crystal alignment film according to claim 1, 2, 3, or 4. 6. A liquid crystal holding substrate comprising the liquid crystal alignment film according to claim 5. 7. A liquid crystal display element having a liquid crystal alignment film obtained from the composition for a liquid crystal alignment film according to claim 1, 2, 3, or 4 on a liquid crystal holding substrate provided with electrodes facing the liquid crystal. .