JPH0210327A - Liquid crystal oriented film and production thereof - Google Patents

Abstract

PURPOSE:To decrease the pretilt angle of a liquid crystal to a substrate to the smallest possible angle by using the liquid crystal oriented film which has a straight chain alkyl group on the surface in contact with the liquid crystal and specifying the chain length thereof to <=8 or >=16C. CONSTITUTION:The liquid crystal oriented film has the straight chain alkyl group on the surface in contact with the liquid crystal and the chain length thereof is <=8C or >=16C. This alkyl group is effectual for liquid crystal orientation of said group exists only in the surface. Various surface treatments can, therefore, be used. A high-polymer film contg. such alkyl group as a constituting unit may be used as well. A Langmuir-Blodgett's (LB) technique, vacuum vapor deposition method, coupling agent treatment method, etc., may be used for the surface treatment method. Of these methods, the method which treats the surface of the high-polymer film with the coupling agent is simplest. Such liquid crystal oriented film is capable of decreasing the pretilt angle.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an alignment film for a liquid crystal display element and a method for manufacturing the same. In particular, the present invention relates to an alignment film used in an element in which a liquid crystal has a small tilt angle with respect to a substrate, and a method for manufacturing the same.

A conventional liquid crystal display device generally includes two transparent substrates, a liquid crystal sandwiched between the transparent substrates, a transparent electrode or driving element formed on the transparent substrate, and a transparent electrode or driving element formed on the transparent electrode or driving element. The main component is an alignment film.

Conventional liquid crystal display elements mainly use nematic liquid crystal, and T
Image display is performed using the N (Twisted Nematic) method. In this case, the molecular long axis direction of the nematic liquid crystal is on average oriented parallel to the substrate and regulated by the alignment film when no electric field is applied. As the alignment film, a polyimide thin film that is unidirectionally rubbed has been used. One sheet of polyimide alignment film is
The angle between the liquid crystal and the substrate (bretilt angle) is 5 degrees or less. Alignment films for high tilt are also commercially available, but these are made by introducing long-chain alkyl groups having vertical alignment into polyimide resin. This method of introducing a long-chain alkyl group involves mixing a long-chain alkyl group with a polyimide resin, or using a diamine having a long-chain alkyl group as a diamine component as a precursor of the polyimide resin.

On the other hand, when the surface is treated with a treatment agent having an alkyl chain,
For example, it is known that when a glass substrate is treated with stearyltrimethoxysilane, liquid crystals are aligned perpendicular to the substrate.

Note that in a liquid crystal display element in which liquid crystals are aligned in parallel when no electric field is applied, a preferable pretilt angle is generally said to be 25 degrees or less.

Problems to be Solved by the Invention Therefore, by using an alignment film whose surface is treated with an alkyl group,
It is desirable that the pretilt angle of the liquid crystal with respect to the substrate be as small as possible.

An object of the present invention is to provide a liquid crystal alignment film that satisfies such demands and a method for manufacturing the same.

Means for Solving the Problems The present invention as claimed in claim 1 provides an α-crystal alignment film having a linear alkyl group on the surface in contact with the liquid crystal, the chain length of which is 8 or less or 16 or more carbon atoms. Claim 30 The present invention is characterized in that the above object is achieved by a liquid crystal alignment film, wherein the liquid crystal alignment film of Claim 1 is created by reacting an alkylsilyl compound on a thin film having a hydroxyl group on the surface. Achieve your purpose.

Function: The linear alkyl group on the surface of the alignment film of the present invention interacts with the liquid crystal substance. The inventors have newly discovered that the degree of this interaction varies greatly depending on the alkyl chain length. That is, when the alkyl chain length is short, such as 8 or less, the pretilt becomes small due to the rubbing effect of the underlying film.

Further, when the alkyl chain length is long, such as 16 or more, the pretilt becomes small due to the rubbing effect of the alkyl chain itself. When the alkyl chain length is between 8 and 16, the pretilt of the liquid crystal becomes large. That is, in order to reduce the pretilt angle of the liquid crystal, the alkyl chain length should be 8 or less or 16 or more. The present invention exhibits its effects based on such a mechanism.

Example The present invention will be explained in detail below.

The liquid crystal alignment film of the present invention has a linear alkyl group on the surface in contact with the liquid crystal, and the chain length thereof is 8 or less or 16 or more carbon atoms. If this alkyl group exists only on the surface, it has an effect on liquid crystal alignment. Therefore, various surface treatment methods can be used, and a polymer film containing such an alkyl group as a constituent unit may also be used. As the surface treatment method, known methods such as the Langmuir-Brogier (IB) method, vacuum evaporation method, and coupling agent treatment method can be used. Among these methods, the method of treating the surface of the polymer membrane with a coupling agent is the simplest. In this case, the coupling reaction is preferably carried out by reacting an alkyltrichlorosilane with a hydroxyl group on the surface of the polymer membrane because the reaction can be carried out at room temperature.

Polymer membranes with hydroxyl groups on the surface include not only substances that inherently have hydroxyl groups in their molecules, such as polyvinyl alcohol, polyacrylic acid, starch, cellulose, water-soluble nylon, or copolymers of these with polyethylene. , polyethylene, polystyrene, and the like may be subjected to plasma treatment to introduce hydroxyl groups onto the surface. There is no particular limit to the thickness of these polymer films, but if they are too thin, the liquid crystal alignment may be disturbed due to the unevenness of the surface of the substrate on which the polymer film is made.
The above is desirable.

In particular, polyvinyl alcohol is practically preferable because a film can be easily formed using a spin cord.

In addition, the types of display elements using this liquid crystal alignment film include TN liquid crystal display elements using nematic liquid crystal, G liquid crystal display elements using nematic liquid crystal or cholesteric liquid crystal, and dye.
)L liquid crystal display elements, SBE liquid crystal display elements that use nematic liquid crystals containing chiral components, ferroelectric liquid crystal display elements that use chiral smectic C liquid crystals, and other elements that align liquid crystals parallel to the substrate as an initial alignment. Any type of liquid crystal display element can be used.

When forming a liquid crystal alignment film on a substrate using this alkyltrichlorosilane, spin code method, dip method,
Although various known coating methods such as printing and vapor deposition methods can be used, the dip method is the easiest. Further, it is preferable to remove excess alkyltrichlorosilane remaining on the substrate during formation of the alignment film by cleaning the substrate with chloroform or the like.

Next, the present invention will be explained based on specific examples.

Although a nematic liquid crystal display element was created in the following examples, the present invention is not limited thereto, and can be applied to any liquid crystal display element that is initially aligned parallel to the substrate.

Examples 1 to 12 Circular electrodes of ITO having a diameter of 50 ml11 were obtained by sputtering onto a Corning $7059 type glass substrate having a thickness of 1.1 mm. A polyvinyl alcohol (PVA117 manufactured by Rare Co., Ltd.) film or a polycarbonate (PC) film was formed on this substrate using a spin code. For the polycarbonate membrane only, a plasma asher was used to introduce oxygen into the system at a flow rate of 101005e while 0.6t was applied.
Set the substrate temperature to 50℃ with a vacuum level of orr and output 50
It was processed at 0W for 5 minutes. As a result of measuring the infrared spectrum of this film, the presence of hydroxyl groups, which were not present before plasma treatment, was confirmed.

Next, this substrate was immersed in a carbon tetrachloride solution of alkyltrichlorosilane shown in Table 1, and then washed with chloroform for surface treatment to obtain liquid crystal alignment films of Examples 1 to 12.

(The following is a margin) Table 1 Comparative Examples 1 to 8 Using the same substrates as in Examples 1 to 12, liquid crystal alignment films were created.

Table 2 (blank below) Pretilt angle measurement In order to measure the pretilt angle, a liquid crystal cell was prepared as shown below.

The alignment film surface of the substrate having the alignment film prepared in the example or comparative example was rubbed in one direction, and the rubbed pair of substrates were stacked with a 16I1m spacer in between so that the upper and lower rubbing directions were in reverse W row. After aligning and sealing the parts other than the injection port,
LIXON) 9150 nematic liquid crystal was injected. Thereafter, the injection port was sealed to create a liquid crystal cell.

The pretilt angle of the liquid crystal was measured using the anisotropy of the capacitance or the anisotropy of the refractive index of the liquid crystal for these α-quality cells. The results are shown in Table 3.

(The following is a blank space) As described in detail of the invention, the liquid crystal alignment film of the present invention has a linear alkyl group on the surface in contact with the liquid crystal and the chain length is 8 or less or 16 or more carbon atoms. , the pretilt angle can be made smaller.

Name of agent: Rishi I, Toshio Nakao, 1 person Table 3

Claims (1)

[Scope of Claims] (1) A liquid crystal alignment film characterized in that it has a linear alkyl group on the surface in contact with the liquid crystal, and the chain length thereof is 8 or less or 16 or more carbon atoms. (2) The liquid crystal alignment film according to claim 1, wherein the liquid crystal alignment film contains an alkylsilyl group. (3) A method for producing a liquid crystal alignment film according to claim 1, wherein the liquid crystal alignment film is created by reacting an alkylsilyl compound on a thin film having a hydroxyl group on the surface. (4) The method for producing a liquid crystal aligning film according to claim 3, wherein the thin film having a hydroxyl group on its surface is made of polyvinyl alcohol. (5) The method for producing a liquid crystal aligning film according to claim 3 or 4, wherein the alkylsilyl compound is an alkyltrichlorosilane or an alkyltriethoxysilane.