JP3405607B2 - Coating liquid for forming alignment film and liquid crystal display cell - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a coating solution for forming an alignment film on a transparent electrode of a substrate with a transparent electrode used in a liquid crystal display cell, and a transparent electrode and an alignment film formed on the substrate in this order. And a liquid crystal display cell having a substrate with a transparent electrode.

[0002]

2. Description of the Related Art Conventionally, there has been known a liquid crystal display cell provided with a pair of substrates with transparent electrodes in which a transparent electrode and an alignment film are formed in this order on a glass substrate. In this liquid crystal display cell, ITO (Indium Tin Oxid) is used as a transparent electrode.
A transparent conductive film such as e) is formed. A polymer such as polyimide is used as the alignment film.

Further, a liquid crystal display cell in which a thin film transistor (TFT) is formed together with the transparent electrode in the transparent electrode portion described above is also known. In these liquid crystal display cells, a spacer is interposed between the alignment films of the pair of transparent electrode-attached substrates so that the distance between the transparent electrodes is adjusted to be constant. Further, these liquid crystal display cells are manufactured by enclosing a liquid crystal between the transparent electrodes adjusted to have a predetermined interval in this way.

When manufacturing these liquid crystal display cells, a rubbing process is performed on each of the alignment films of the pair of substrates with transparent electrodes so that the liquid crystal in contact with the alignment films is aligned in a predetermined direction. ing.

At this time, in the conventional liquid crystal display cell, static electricity is generated on the alignment film, and a large amount of static electricity is instantaneously discharged through the transparent electrode. In some cases, the liquid crystal display cell provided with the above may cause deterioration in performance of the TFT element, or display unevenness due to charging of the alignment film may occur in the liquid crystal display cell.

On the other hand, the applicant of the present invention can prevent the alignment film from being destroyed by the static electricity by forming a conductive transparent protective film between the transparent electrodes and the alignment film of the pair of substrates with transparent electrodes. In view of this, a liquid crystal display cell provided with a pair of substrates with transparent electrodes having such a conductive transparent protective film has been proposed (JP-A-5-232459).

Further, the conductive transparent protective film causes image sticking which occurs after a still image is displayed on the liquid crystal display cell for a long time, that is, the image does not change even when the liquid crystal display cell is driven to change the image. It has been confirmed by the present inventors that it is effective in preventing such a phenomenon. It is presumed that this image sticking occurs because the ionic impurities contained in the liquid crystal are adsorbed to the alignment film when a voltage is applied between the transparent electrodes of the liquid crystal display cell.

When forming this conductive transparent protective film,
Usually, the substrate on which the transparent electrode is formed is heated at a temperature of 300 to 500 ° C. Due to this heating, the resistance value of the transparent electrode rises to increase the power consumption required for driving the liquid crystal display cell, or in the case of a liquid crystal display cell equipped with a TFT or a color filter, the performance of the TFT or the color filter Performance may decrease.

From this point of view, even if the conductive transparent protective film is not formed between the transparent electrode of the substrate with the transparent electrode and the alignment film, the alignment film is broken due to static electricity or an image generated in the liquid crystal display cell. It has been desired to develop a liquid crystal display cell capable of preventing image sticking.

By the way, Japanese Patent Laid-Open No. 3-92824 discloses a liquid crystal display device having an alignment film containing conductive fine particles dispersed therein for the purpose of improving the bistability of the ferroelectric liquid crystal display device. Further, as the conductive fine particles, S
Electron-conductive inorganic oxide fine particles such as tin oxide doped with b, or fine-particle conductive organic polymers (cationic or anionic polymer beads) are disclosed.

However, when the alignment film in which the electron conductive inorganic oxide fine particles are dispersed is formed on the transparent electrode of the liquid crystal display cell, most of the foreign substances mixed in the liquid crystal of the liquid crystal display cell are electrons. Because of the conductivity, when the foreign matter and the electron conductive inorganic oxide fine particles come into contact with each other, conduction is likely to occur at the contact portion, and this conduction may cause a display defect in the liquid crystal display cell.

Further, when an alignment film in which the above-mentioned fine particulate conductive organic polymer is dispersed is formed on the transparent electrode of the liquid crystal display cell, the conductive organic polymer has a high conductivity due to humidity. Therefore, depending on the conditions when forming the alignment film, there is a difference in the performance of the obtained liquid crystal display cell, or the conductive organic polymer exposed on the surface of the alignment film and the liquid crystal The interaction may cause unevenness in color in the liquid crystal display cell or uneven alignment in the liquid crystal in the liquid crystal display cell, and in particular, there is a problem in long-term reliability regarding the performance of the liquid crystal display cell.

[0013]

It is an object of the present invention to solve the problems associated with the prior art as described above, in which the alignment film has an electron conductive inorganic oxide fine particle or the above-mentioned fine particle-shaped conductive organic polymer. A coating solution for forming an alignment film capable of avoiding the problems caused by containing, and excellent in antistatic ability, and capable of forming an alignment film capable of preventing image sticking that occurs in a liquid crystal display cell, and It is an object of the present invention to provide a liquid crystal display cell having such an excellent alignment film.

[0014]

SUMMARY OF THE INVENTION The coating solution for forming an alignment film according to the present invention comprises conductive fine particles, an alignment film forming material and an organic solvent.
It is characterized in that the conductive fine particles are ion conductive inorganic compound fine particles.

The liquid crystal display cell according to the present invention comprises a substrate with a transparent electrode in which a transparent electrode and an alignment film are formed in this order on a substrate, and the alignment film contains ion-conductive inorganic compound fine particles. Is characterized by.

[0016]

DETAILED DESCRIPTION OF THE INVENTION Alignment Film Forming Coating Liquid First, the alignment film forming coating liquid according to the present invention will be specifically described.

The coating liquid for forming an alignment film according to the present invention comprises conductive fine particles, a material for forming an alignment film and an organic solvent. As the organic solvent, an organic solvent used in a conventional coating liquid for forming an alignment film is adopted, and specific examples thereof include N-methylpyrrolidone, γ-butyl lactone, butyl cellosolve, higher alcohols and glycols. To be

As the material for forming the alignment film, the material for forming the alignment film which is used in the conventional coating liquid for forming the alignment film is adopted, and specifically, polyamic acid, soluble polyimide,
Examples thereof include polyvinyl alcohol.

In the coating liquid for forming an alignment film according to the present invention, ion conductive inorganic compound fine particles are used as the conductive fine particles. Examples of the ion conductive inorganic compound include metal oxides having a pyrochlore type crystal structure.
Examples of the metal oxide having such a pyrochlore type crystal structure include metal oxides such as antimony, lead, bismuth, ruthenium, cadmium, yttrium, thallium, indium, copper and gadolinium, or two or more of these metals. Examples thereof include composite metal oxides in which oxides are composited. Among these metal oxides, P, B, Si
And at least one element selected from Ti may be doped. Further, heteropolyacids such as molybdophosphoric acid and tungstophosphoric acid also show ionic conductivity, and are therefore used as the ion conductive inorganic compound in the present invention.

The average particle size of the ion-conductive inorganic compound fine particles is preferably about 100 nm or less, and particularly preferably 10 to 80 nm. By using a coating liquid for forming an alignment film containing ion-conductive inorganic compound fine particles having an average particle size in such a range, an alignment film in which the ion-conductive inorganic compound fine particles are monodispersed can be used as a transparent substrate for transparent electrodes. It can be formed on the electrode.

From the viewpoint of forming an alignment film in which fine particles of ion-conductive inorganic compound are monodispersed on a transparent electrode of a substrate with a transparent electrode, the coating liquid for forming an alignment film according to the present invention contains fine particles of ion-conductive inorganic compound. Are preferably monodispersed.

As a method of obtaining a coating liquid for forming an alignment film in which fine particles of an ion-conductive inorganic compound are monodispersed, a liquid of the alignment film forming material containing the alignment film forming material dissolved in an organic solvent is used. A method of directly dispersing the ion-conductive inorganic compound fine particles, the organic solvent used in the solution of the material for forming an alignment film, or the ion-conductive inorganic compound fine particles dispersed in an organic solvent compatible with the organic solvent. Examples thereof include a method of mixing the sol and a solution of the alignment film forming material.

The amount of the alignment film forming material and the ion conductive inorganic compound fine particles in the alignment film forming coating liquid according to the present invention is determined by the resin component of the alignment film formed by using the alignment film forming coating liquid. It is adjusted so that 0.01 parts by weight or more and 0.8 parts by weight or less, preferably 0.05 to 0.4 parts by weight of the ion conductive inorganic compound fine particles are contained in the coating liquid for forming an alignment film per 1 part by weight. It is desirable to do.

If the amount is less than 0.01 parts by weight, an alignment film exhibiting sufficient antistatic ability to achieve the object of the present invention may not be obtained, and conversely 0.8 If it exceeds the weight part, an alignment film having sufficient hardness and mechanical strength may not be obtained.

The solid content concentration of the coating liquid for forming an alignment film according to the present invention is 1 to 50% by weight, preferably from the viewpoint of fluidity of the coating liquid and formation of an alignment film having a thickness as described later. It is preferably 5 to 30% by weight.

From the coating liquid for forming an alignment film according to the present invention, an alignment film is formed on a transparent electrode of a substrate with a transparent electrode as follows, for example. First, the coating liquid for forming an alignment film according to the present invention is applied onto the transparent electrode of the substrate with a transparent electrode by a method such as a spinner method or a flexographic printing method.

The substrate with a transparent electrode having a coating film formed on the transparent electrode in this manner is heated at a temperature of 120 to 250 ° C. to form an alignment film on the transparent electrode of the substrate with a transparent electrode. Then, the surface of the alignment film thus obtained is subjected to rubbing treatment so that the liquid crystal in contact with the alignment film is aligned in a predetermined direction.

Liquid Crystal Display Cell Next, the liquid crystal display cell according to the present invention will be described.
The liquid crystal display cell according to the present invention includes a substrate with a transparent electrode in which at least a transparent electrode and an alignment film are formed in this order on the substrate.

As the substrate, a substrate used in a known liquid crystal display cell can be adopted, and a transparent substrate such as glass or plastic is usually used. On this board,
A known transparent electrode such as an ITO thin film is formed. In addition, a thin film transistor (TFT), a color filter or the like may be formed together with the transparent electrode at this transparent electrode portion. Furthermore, a transparent protective film may be formed between the transparent electrode and the alignment film.

In the present invention, an alignment film containing the above-mentioned ion conductive inorganic compound fine particles is formed on this transparent electrode. The thickness of this alignment film is usually 10 to 100.
nm, preferably 30 to 70 nm.

In the liquid crystal display cell according to the present invention, the ion conductive inorganic compound fine particles contained in the alignment film are different from the electron conductive particles which show conductivity due to the movement of electrons in the particles, and are different from cations or The anion moves inside the particles to show conductivity. Therefore, even if the ion-conductive inorganic compound fine particles come into contact with an electron-conductive foreign substance mixed in the liquid crystal in the liquid crystal display cell, conduction is unlikely to occur at this contact portion, and the ion-conductive inorganic compound fine particles are mixed in the liquid crystal display cell. There is no possibility that a display defect of the liquid crystal display cell will occur due to conduction occurring at a contact portion with a foreign substance.

A typical example of the electron conductive material is tin oxide doped with Sb. In this tin oxide doped with Sb, pentavalent Sb is doped in the crystal lattice of tetravalent tin oxide, and free electrons generated at this Sb site participate in electric conduction.

On the other hand, a typical example of the ion conductive inorganic compound is antimony oxide. This antimony oxide is a hydrous oxide represented by Sb ₂ O ₅ .nH ₂ O, and is said to have a crystal structure containing H ⁺ (proton) as shown in FIG. In antimony oxide, this H ⁺ participates in electric conduction.

The ion conductive inorganic compound fine particles are
Unlike the above-mentioned fine particle-shaped conductive organic polymer, the conductivity does not greatly change due to humidity, and it interacts with the liquid crystal to cause color unevenness in the liquid crystal display cell, or in the liquid crystal display cell. There is no possibility of causing uneven alignment in the liquid crystal.

The liquid crystal display cell according to the present invention comprises a pair of substrates with transparent electrodes having the above-mentioned alignment film. A liquid crystal display cell provided with this pair of substrates with transparent electrodes, for example, after subjecting each alignment film to a predetermined rubbing treatment, a spacer is provided between the alignment films of the pair of substrates with transparent electrodes, and then It is manufactured by a known method such as enclosing a liquid crystal between the transparent electrodes adjusted to have a constant interval in this way.

[0036]

EFFECTS OF THE INVENTION According to the coating liquid for forming an alignment film of the present invention, an alignment film containing ion conductive inorganic compound fine particles and having excellent antistatic properties can be formed on a transparent electrode of a substrate with a transparent electrode. it can.

Therefore, in the liquid crystal display cell according to the present invention in which the alignment film containing such ion-conductive inorganic compound fine particles is formed on the transparent electrode, the static electricity generated in the alignment film when the alignment film is rubbed is rubbed. Of the alignment film and the deterioration of the performance of the TFT element due to the discharge of the liquid crystal, or the display unevenness of the liquid crystal display cell due to the charging of the alignment film is prevented, and the still image is continuously displayed on the liquid crystal display cell for a long time. However, the image sticking of the display image does not occur, and thus the display unevenness of the liquid crystal display cell due to the image sticking of the display image does not occur.

Further, the liquid crystal display cell according to the present invention is different from the liquid crystal display cell in which the alignment film containing the electron conductive inorganic compound fine particles is formed on the transparent electrode, and the electrons mixed in the liquid crystal in the liquid crystal display cell. Even if a conductive foreign substance is contacted, conduction is unlikely to occur at this contact portion, and there is no risk of display failure in the liquid crystal display cell due to conduction at this contact portion. Further, in the liquid crystal display cell according to the present invention, problems caused by the conductive organic polymer material, for example, changes in conductivity due to humidity, uneven color of the liquid crystal display cell, uneven alignment of liquid crystal, etc. do not occur.

Further, according to the present invention, an alignment film having a function as a hard coat film is formed on a transparent electrode of a substrate with a transparent electrode according to the compounding amount of the ion conductive inorganic compound fine particles and the like. Therefore, it is possible to prevent defective display of the liquid crystal display cell caused by damage to the alignment film due to foreign matters or spacers in the liquid crystal display cell, and also to prevent damage to the alignment film due to rubbing.

Further, according to the present invention, the heat resistant temperature is about 150, since the high temperature heat treatment as described above does not have to be performed.
It is possible to provide a liquid crystal display cell with a color filter having a color filter of up to 200 ° C.

[0041]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0042]

Example 1 Material for forming an alignment film (Nissan Chemical Co., Ltd.)
Manufactured by San-Ever SE-4110, solid content concentration: 8% by weight), and antimony oxide sol (solid content concentration: 10% by weight) obtained by dispersing antimony oxide fine particles having an average particle size shown in Table 1 in a dispersion medium shown in Table 1. %) 16 g to prepare a coating liquid for forming an alignment film of Example 1.

A substrate with a transparent electrode in which ITO transparent electrodes are formed in a pattern on a glass substrate (manufactured by Asahi Glass Co., Ltd., 30
The coating liquid for forming an alignment film of Example 1 was applied onto a transparent electrode of (Ω type) by a flexographic printing method, dried at 90 ° C. for 5 minutes, and then baked at 200 ° C. for 30 minutes to form a glass substrate. A substrate with a transparent electrode in which a transparent electrode and an alignment film were formed in this order was prepared.

The following evaluation was performed on the alignment film of the substrate with the transparent electrode. (1) Film thickness The film thickness of the alignment film is measured by a contact-type film thickness meter (Taylor Hobson).
It was measured at. (2) Surface resistance The surface resistance of the alignment film was measured with an analog insulation resistance tester (2406A24 manufactured by Yokogawa Instruments). (3) Pencil hardness A pencil having a predetermined hardness is drawn on the alignment film with a load of 1 kg while observing the presence or absence of scratches formed on the alignment film to form scratches on the alignment film. The hardness of the alignment film was evaluated with the lowest pencil hardness. (4) Bencotton was slid 50 times under a load of 500 g on the scratch-resistant alignment film, and when the scratches did not reach the transparent electrode surface of the substrate with transparent electrodes, it was evaluated as good (○), and the substrate with transparent electrodes was evaluated. The case where the scratch reached the transparent electrode surface was evaluated as defective (x). (5) Appearance The presence or absence of turbidity and whitening of the alignment film was observed, and when neither turbidity nor whitening was evaluated as good (○), when at least one of turbidity and whitening was poor (×) ) Was evaluated. (6) Charge decay time The charge decay time after charging the alignment film was measured with a Honest meter (produced by Kasuga Electric Co., Ltd.), and the shorter the charge decay time was, the better the antistatic performance of the alignment film was evaluated. .

Table 2 shows the evaluation results of the above (1) to (6).

[0046]

Example 2, Reference Example 1 An example was carried out in the same manner as in Example 1 except that the ion conductive inorganic compound sol consisting of the ion conductive inorganic compound fine particles and the dispersion medium shown in Table 1 was used in place of the antimony oxide sol. 2 and the coating liquid for forming an alignment film of Reference Example 1 were prepared.

Thus obtained Example 2 and Reference
Using the coating liquid for forming an alignment film of Consideration 1, a substrate with a transparent electrode in which a transparent electrode and an alignment film were formed in this order on a glass substrate was prepared in the same manner as in Example 1, and the respective transparent substrates were formed. The same evaluation as in Example 1 was performed on the alignment film of the electrode-attached substrate.

The results are shown in Table 2.

[0049]

Example 4 Material for forming an alignment film (Nippon Synthetic Rubber Co., Ltd.)
Manufactured by Optomer AL-1524, solid content concentration: 24% by weight), antimony oxide sol having an average particle size shown in Table 1 dispersed in a dispersion medium shown in Table 1 (solid content concentration 10% by weight). %) 48 g to prepare a coating liquid for forming an alignment film of Example 4.

Using the coating liquid for forming an alignment film of Example 4 thus obtained, a transparent electrode and an alignment film are formed in this order on a glass substrate in the same manner as in Example 1. An attached substrate was prepared, and the same evaluation as in Example 1 was performed on the alignment film of the substrate with the transparent electrode.

The results are shown in Table 2.

[0052]

Example 5, Reference Example 2 An example was carried out in the same manner as in Example 4 except that the ion conductive inorganic compound sol comprising the ion conductive inorganic compound fine particles and the dispersion medium shown in Table 1 was used in place of the antimony oxide sol. 5 and the coating liquid for forming an alignment film of Reference Example 2 were prepared.

Thus obtained Example 5 and Reference
Using the coating liquid for forming an alignment film of Consideration 2 , a transparent electrode-attached substrate in which a transparent electrode and an alignment film were formed in this order on a glass substrate was prepared in the same manner as in Example 1, and the respective transparent substrates were formed. The same evaluation as in Example 1 was performed on the alignment film of the electrode-attached substrate.

The results are shown in Table 2.

[0055]

Comparative Example 1 Instead of the coating liquid for forming an alignment film of Example 1, a material for forming an alignment film (manufactured by Nissan Chemical Industries, Ltd., Sun Ever)
SE-4110, solid content concentration: 8% by weight) was used to prepare a substrate with a transparent electrode in which a transparent electrode and an alignment film were formed in this order on a glass substrate in the same manner as in Example 1, The same evaluation as in Example 1 was performed on the alignment films of the respective substrates with transparent electrodes.

The results are shown in Table 2.

[0057]

[Table 1]

[0058]

[Table 2]

[0059]

Example 7, Reference Example 2 Alignment films of two substrates with transparent electrodes, in which transparent electrodes and alignment films are formed in this order on the glass substrates obtained in Examples 1 and 2 and Reference Example 1 , respectively. After subjecting the surface to a predetermined rubbing treatment, using these two substrates with transparent electrodes, S with a cell gap of 6.5 μm was obtained.
Ten sets of TN liquid crystal display cells were prepared. When a liquid crystal display device was assembled using the respective liquid crystal display cells and the operating state thereof was observed, no display unevenness occurred in the liquid crystal display cells of the liquid crystal display device. In addition, the liquid crystal display cell after being energized at DC 3V for 100 hours was not burned.

[0060]

Comparative Example 2 An STN liquid crystal display cell was prepared in the same manner as in Example 7 except that the transparent electrode-provided substrate in which the transparent electrode and the alignment film were formed in this order on the glass substrate obtained in Comparative Example 1 was used. Ten sets of the provided liquid crystal display devices were assembled and the same evaluation as in Example 7 was performed.

As a result, display unevenness occurred in 4 of the 10 liquid crystal display cells, and burn-in occurred in the 6 liquid crystal display cells.

[0062]

[Embodiment 8] A transparent electrode substrate on which a transparent electrode, a TFT and an alignment film formed by using the coating liquid for forming an alignment film of Example 4 are laminated in this order on a glass substrate, and on a glass substrate A TFT type liquid crystal color having a cell gap of 5.0 μm using a color filter, a transparent electrode and a substrate with a transparent electrode in which an alignment film formed using the alignment film forming coating liquid of Example 4 is laminated in this order. Ten sets of display cells were created.

When a liquid crystal display device was assembled using this liquid crystal display cell and the operating state thereof was observed, no display unevenness occurred in the display cell of the liquid crystal display device. No burn-in occurred in any of the display cells after energization at DC 3V for 100 hours.

[0064]

Comparative Example 3 An alignment film forming material (manufactured by Nissan Kagaku Kogyo Co., Ltd., Sun Ever) was used in place of the alignment film forming coating liquid of Example 4.
SE-4110, solid content concentration: 8% by weight) T was prepared in the same manner as in Example 8 except that the alignment film was formed.
When a liquid crystal display device equipped with an FT type liquid crystal color display cell was assembled and the operating state thereof was observed, display unevenness occurred in two of the ten liquid crystal display cells, and burning occurred in four of the liquid crystal display cells.

[Brief description of drawings]

FIG. 1 is a drawing for explaining an electric conduction mechanism of ion-conductive inorganic compound fine particles.

Front Page Continuation (72) Inventor Hideaki Tokaji 13-2 Kitaminato-cho, Wakamatsu-ku, Kitakyushu, Fukuoka Prefecture Inside the Wakamatsu Plant of Catalysts & Chemicals Industries Co., Ltd. (56) Kaihei 8-54629 (JP, A) JP-A-8-54631 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02F 1/1337

Claims (2)

(57) [Claims] 1. A conductive fine particle, an alignment film forming material, and an organic solvent, wherein the conductive fine particle is an ion conductive inorganic compound fine particle, and the ion conductive inorganic compound is P, B, Si and T.
A coating liquid for forming an alignment film, which is Sb ₂ O ₅ .nH ₂ O which may be doped with at least one element selected from i. 2. A substrate with a transparent electrode having a transparent electrode and an alignment film formed in this order on a substrate, wherein the alignment film contains fine particles of an ion-conductive inorganic compound, and the ion-conductive inorganic compound. Is Sb ₂ O ₅ .nH ₂ O which may be doped with at least one element selected from P, B, Si and Ti.