JPH023017A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To improve liquid crystal orienting power and stability by forming a perpendicularly oriented film consisting of a long chain silane compd. and short chain silane compd. on at least one surface in contact with a liquid crystal of a pair of liquid crystal crimping substrates. CONSTITUTION:The perpendicularly oriented film 6 consisting of the long chain silane compd. and the short chain silane compd. is formed on at least one surface in contact with the liquid crystal 3 of a pair of the liquid crystal crimping substrates 1. The short chain silane compd. which itself has no perpendicular orientation power is used mixedly with the long chain silane compd. in such a manner. The stereoscopic fault occurring in the long chain alkyl group or long chain fluoroalkyl group is relieved in this way and the rate of a dehydration condensation reaction is increased; in addition, the stability of the perpendicularly oriented film obtd. in such a manner and the reproducibility of the liquid crystal orientation power are improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention utilizes alignment deformation of liquid crystal molecules that is caused by vertically aligning liquid crystal molecules in advance and changing the intensity of an electric field, magnetic field, heat, etc. Regarding liquid crystal display elements, a liquid crystal display element having a vertical alignment film that exhibits particularly good liquid crystal alignment ability and stability [Prior art] A liquid crystal display element generally consists of two pieces of glass arranged in parallel at a certain distance. Alternatively, liquid crystal is filled between substrates made of plastic or the like.

Transparent electrodes are selected on the opposing surfaces of the substrate, respectively.
An alignment film is provided on at least one surface facing the liquid crystal of the substrate on which these transparent electrodes are formed for the purpose of aligning the liquid crystal molecules in a certain direction depending on the display method. There is. The orientation direction of the liquid crystal molecules is a homogeneous orientation in which the long sleeves of the liquid crystal molecules are parallel to the substrate surface;
It is roughly divided into three types: 2) vertical home-first-ropink orientation, and 3) (intertilted first-round oblique orientation), and various orientations that overlap these are also known.

For example, the DAP method that applies the electric field birefringence effect is a display method that uses homeotropic alignment as the initial alignment of liquid crystal molecules. A vertical alignment film is used in a liquid crystal display element based on such a display method, and a material having a low surface energy, that is, a high IB aqueous property is generally used as the material for the vertical alignment film. Various materials have been proposed as this type of material. Long-chain silane compounds are one of them, for example, as disclosed in JP-A-58-72923.
The publication discloses a mixture of alkyl alkoxysilane having a long-chain alkyl group and polysylmethylene, and JP-A No. 5
No. 8-88723 discloses a mixture of a long-chain alkylsilane-silanol oligomer composition and a polymer solution.

A typical example of the long-chain silane compound is a trialkoxylorganosilane compound represented by the following formula.

R1Z Si (ORz)z Rz=Cg)fz*, +(g≦2) Z = -CH, -, -CF, -, or N'(ChHz
It is expressed as ゎ=)z(Cr H2,)(h≦2. i≦5). However, f, g, h, and i in the above formula are all natural numbers.

In the conventional technology, a trialkoxylorganosilane compound as described above is hydrolyzed to produce a silanol derivative, and the silanol derivative is further dehydrated and condensed to form a vertically aligned film. It is known that the liquid crystal alignment ability of the vertical alignment film increases as the chain length of the long-chain alkyl group or long-chain fluoroalkyl group represented by R1 in the above formula increases.

Here, in the above formula, R+, Rz and Z are each R+ ”
'CtHzt,l, or CtF□. .

(r≧8) [Problems to be Solved by the Invention] However, if the chain length of the long-chain alkyl group or long-chain fluoroalkyl group described above becomes too long, steric hindrance increases and the dehydration condensation reaction is suppressed. Problems such as a decrease in the liquid crystal alignment ability, or a lack of crosslinking due to the tendency to generate linear polymers, resulting in a decrease in the stability of the vertical alignment film, and a loss of reproducibility in the liquid crystal alignment ability. was there.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a liquid crystal display element having a vertical alignment film that does not require a long time for the alignment process and has excellent stability.

It is characterized by:

Here, the short chain silane compound has the following general formula % Formula % Here, R1 and R4 in the above formula are each the following formula [Means for Solving the Problem] The present inventors have achieved the above object. As a result of repeated studies, we found that by adding a short-chain silane compound, which itself does not have vertical alignment ability, to the above-mentioned long-chain silane compound, we were able to create a vertical alignment film that has excellent liquid crystal alignment ability and stability even in a short alignment treatment time. The inventors have discovered that the following can be obtained, and have arrived at the present invention.

That is, the liquid crystal display element according to the present invention is a liquid crystal display element in which a liquid crystal is sandwiched between a pair of liquid crystal sandwiching substrates, and a long-chain silane compound is provided on the surface facing the liquid crystal of at least one of the liquid crystal sandwiching substrates. The fact that a vertical alignment film made of a short-chain silane compound was formed is expressed as nz""C1Hzi,+R4""Cm Hzk. (j≦6) (k≦2). However, both j and k in the above formula are natural numbers.

In the present invention, first, a short chain silane compound as described above is dissolved in a suitable solvent together with a long chain silane compound to prepare a vertical alignment film coating, and the coating is applied to a liquid crystal sandwiching substrate. At this time, the concentration of the short chain silane compound in the solvent is 2 to 20% by weight,
The concentration of the long-chain silane compound in the solvent is selected to be 0.5 to 2%. Therefore, the ratio of the amount of short-chain silane compound to long-chain silane compound added is from 1:1 to 40:l. If the short-chain silane compound is less than 11, the addition effect will not be sufficient, and if the short-chain silane compound is more than 40:1, the liquid crystal alignment ability of the vertical alignment film obtained will be insufficient.

Further, the above-mentioned solvent is not particularly limited as long as it can dissolve the short-chain silane compound and the long-chain silane compound at the same time, but examples of solvents having excellent solubility and coating properties include ethanol, isopropyl alcohol, n Examples include alcohols such as -decyl alcohol and tridecyl alcohol, polyhydric alcohol derivatives such as ethyl cellosolve, butyl cellosolve, diethylene glycol butyl ether, butyl cellosolve acetate and diethylene glycol diethyl ether, and ketones such as methyl isobutyl ketone.

The vertical alignment film coating prepared using the above-mentioned solvent can be applied to the liquid crystal sandwiching substrate by a method such as a brush coating method, a dipping method, a spin code method, a spray method, or a printing method. At this time, the vertical alignment film does not necessarily have to be formed on both of the pair of liquid crystal sandwiching substrates. For example, when creating a so-called high-print type liquid crystal display element in which liquid crystal molecules are aligned vertically on one substrate and liquid crystal molecules are aligned in parallel on the other substrate, only one substrate is used. A vertical alignment film coating as described above may be applied, and a horizontal alignment film may be formed on the other substrate by a conventionally known method such as a vapor deposition method or a rubbing method.

After applying the vertical alignment film paint, it is usually 100 to 250
The heat treatment is carried out at a temperature of °C. At this time, 100
At temperatures lower than 250°C, the stability of the resulting vertical alignment film decreases because the condensation reaction does not occur sufficiently, and at temperatures higher than 250°C, long-chain alkyl groups or long-chain fluoroalkyl groups undergo thermal decomposition, resulting in liquid crystal display. There is a risk that the orientation ability will be reduced.

The thickness of the vertical alignment film is selected to be in the range of 0.005 to 1 μm.

Moreover, the liquid crystal that can be used in combination with the vertical alignment film according to the present invention is not particularly limited.

For example, nematic liquid crystals or smectinque liquid crystals include thick base (azomethine) liquid crystals, azo liquid crystals, azoxy liquid crystals, biphenyl liquid crystals, ester liquid crystals, terphenyl liquid crystals, phenylcyclohexane liquid crystals, phenylcyclohexane ester liquid crystals, and phenylcyclohexane liquid crystals. Examples include pyrimidine liquid crystals, which can be used alone or in combination.

Furthermore, cholesteric liquid crystals, or mixtures of the above-mentioned nematic liquid crystals or smectinque liquid crystals with cholesterol derivatives or chiral nematic liquid crystals can also be used.

Furthermore, the display method of the liquid crystal display element to which the present invention is applied is as follows:
Any method may be used as long as it requires vertical alignment of liquid crystal molecules in the initial state.

[Effect]

The silane compound-based vertical alignment film is bonded to the liquid crystal sandwiching substrate via oxygen atoms, and has hydrophobic long-chain alkyl groups or long-chain fluoroalkyl groups protruding from the surface. In this way, the surface tension of the vertical alignment film is smaller than the surface tension of the liquid crystal, so if the liquid crystal to be sandwiched is a nematic liquid crystal, the alignment is homeotropic, and if the liquid crystal is cholesteric or chiral nematic, the alignment is focal conic. It is thought that it takes an orientation or a fingerprint orientation.

In the present invention, steric hindrance caused by long-chain alkyl groups or long-chain fluoroalkyl groups is alleviated by mixing a short-chain silane compound that does not have vertical alignment ability by itself with a long-chain silane compound. It becomes possible to improve the speed of the dehydration condensation reaction, and also to improve the stability of the obtained vertical alignment film and the reproducibility of the liquid crystal alignment ability.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described.

First, prior to explaining the embodiments, the basic structure of a liquid crystal display element will be explained with reference to FIG.

This liquid crystal display element consists of two transparent glass substrates (1) arranged in parallel with a spacer (4) of a predetermined thickness interposed therebetween.
A liquid crystal is sealed in the internal space formed between the two, and the periphery is sealed with a sealing material (2) made of, for example, an Ebony adhesive.On the liquid crystal facing surface of the glass substrate (1) A transparent electrode (5) is selectively formed in advance, and the entire liquid crystal facing surface including the transparent electrode (5) is covered with a vertical alignment film (6).In this figure, each liquid crystal molecule A so-called homeotropic orientation is shown in which the long axis of the glass substrate (1) is oriented perpendicularly to the glass substrate (1).

Such a liquid crystal display element was produced according to the procedure described below, and its liquid crystal alignment ability and stability were examined.

The long chain silane compound used in this example was n-octadecyltriethoxysilane, and the short chain silane compound used was methyltriethoxysilane.

First, in 4% aqueous ethanol, n-octadecyltriethoxysilane (manufactured by Chisso Corporation) was added at a concentration of 1%, and methyltriethoxysilane (manufactured by Toray Silicone Inc.) was added at a concentration of lθ%.
A vertical alignment film paint was prepared by dissolving the mixture to a certain concentration.

Next, two glass substrates (
1) The above-mentioned vertical alignment film coating material was applied onto the film using a spin cord (coating speed: 3000 rpm/15 seconds) while heating to 50 to 60°C. These glass substrates (1) were heat-treated at 130"C for 60 minutes to condense the silane compound and form vertical alignment M (6). Thereafter, the glass substrates (1) were heated with isopropyl alcohol. The unreacted silane compound was removed by washing, followed by Freon drying according to a conventional method.It has been previously confirmed that isopropyl alcohol does not dissolve and remove the condensation product.

These two glass substrates (1) are connected to the vertical alignment film (6) via a film-like spacer (4) with a thickness of 108 m.
A liquid crystal display element was fabricated by bonding the substrates so that their formed surfaces faced each other and injecting smectinok liquid crystal or nematic liquid crystal.

For comparison, a liquid crystal display element in which a vertical alignment film was formed without using methyltriethoxysilane, which is a short-chain silane compound, was also created in the same manner.

First, the liquid crystal alignment ability of these liquid crystal display elements was investigated. That is, the above liquid crystal element was placed between two polarizing plates whose polarization directions were orthogonal to each other, and the alignment state of liquid crystal molecules in the glass portion or the transparent electrode portion was visually evaluated. Here, if the liquid crystal display element appears transparent, it is "good".
If it looks transparent, it is "good", if it looks slightly opaque, it is "slightly poor", and if it looks opaque, it is "poor".
The results are shown in Table 1.

In the Examples in Table 1, good vertical alignment was observed in each part of the liquid crystal display element, regardless of whether smectine liquid crystal or nematic liquid crystal was used. On the other hand, in the comparative example,
When a smectic liquid crystal is used, a focal conic structure in which the refractive index is spatially disordered appears, and when a nematic liquid crystal is used, a schlieren structure due to point defects appears in the transparent electrode part. Ta. These structures are typically seen when a horizontal alignment process is performed on a liquid crystal sandwiching substrate.

Therefore, it is clear that the ability to align liquid crystals is improved by adding a short chain silane compound during the formation of a vertical alignment film.

Next, the stability of these liquid crystal display elements against heating and light irradiation was investigated. That is, one cycle consisted of first irradiating these liquid crystal display elements with ultraviolet rays for 50 hours to change the liquid crystal to an isotonic phase, holding this state for 1 hour, and then slowly cooling it, and this cycle was repeated four times. In addition, a black light (Toshiba FL2) is used as the ultraviolet light source.
0SBLB) and was irradiated from a distance of the liquid crystal display element hlocm.

The alignment state of liquid crystal molecules in these liquid crystal display elements is
Table 2 shows the results of 11 evaluations using the method described above.

Table 2 It can be said.

Therefore, it is clear that the stability of the vertical alignment film is improved by adding a short chain silane compound during the formation of the vertical alignment film.

Note that the present invention is not limited to the above-described embodiments, and for example, a so-called hybrid type liquid crystal display may be created by forming a vertical alignment film on one of a pair of liquid crystal sandwiching substrates and performing horizontal alignment treatment on the other. It can also be applied to elements.

In the example, smectinok liquid crystal or fumati,・
Regardless of whether liquid crystal was used, the vertical alignment state was stably maintained in each part of the liquid crystal display element.

On the other hand, in the comparative examples, when smectinok liquid crystal was used, significant deterioration occurred12, and when non-matink liquid crystal was used, too, some deterioration was observed. This is due to deterioration of the vertical alignment film due to ultraviolet irradiation and elution into the liquid crystal due to heating (effects of the invention). By adding a short chain silane compound to the long chain -7 run compound,
The liquid crystal alignment ability and stability of the obtained vertical alignment film are improved. Therefore, by applying the present invention, it is possible to provide a liquid crystal display element with excellent reliability and durability.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing the structure of a liquid crystal display element to which the present invention is applied. 1... Glass substrate 2... Sole material 3... Liquid crystal 4... Spacer 5... Transparent electrode 6... Vertical alignment film

Claims (1)

[Scope of Claims] A liquid crystal display element in which a liquid crystal is sandwiched between a pair of liquid crystal holding substrates, wherein at least one of the liquid crystal holding substrates has a long-chain silane compound and a short-chain silane compound on the surface facing the liquid crystal. A liquid crystal display element characterized by forming a vertical alignment film.