JPH0216528A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To allow a uniform orientation treatment with decreased fluctuations of even the large-area element and to improve quality and production yield by consisting an oriented film which constitutes the liquid crystal display element of polyamide acid salt having a long-chain alkyl group and forming the element by a Langmuir- Blodgett's technique. CONSTITUTION:The oriented film which constitutes the liquid crystal display element consists of the polyamide acid salt which has the long chain alkyl group and is expressed by the formula I. The liquid crystal display element is constituted by forming said film by a Langmuir-Blodgett's (LB) technique. The LB method is a method of forming the thin film of several molecular layers by repeating the formation of the thin org. film having the thickness of the molecules and transferring the film to a substrate and is the method of obtaining the cumulated molecular film in which the directions of the atom configuration are unified by repeating the above-mentioned operation. The oriented film consisting of the several molecular layers is formed by using the LB method to orderly arranged hydrophilic groups and hydrophobic groups, by which the perpendicular orientation of the liquid crystal is surely and uniformly executed. The fluctuations in the characteristics of even the large-area liquid crystal display elements are decreased in this way.

Description

[Detailed Description of the Invention] [Summary] The purpose of this invention is to commercialize a liquid crystal display element with uniform display quality regarding a liquid crystal display element capable of displaying a large capacity. It is made of a polyamic acid salt having an alkyl group, and is formed by the Langmuir-Blodgett method to constitute a liquid crystal display element.

[Industrial application field]

The present invention relates to improvements in liquid crystal display elements.

The LCD display is TN (Tivisted Nemati).
c) type liquid crystal and S T N (Super Twist)
There are various types such as those using a d nematic type liquid crystal, those using a strong electric liquid crystal, and those using an active matrix type driving method.
The inventors have proposed a display method using a nematic-cholesteric phase transition liquid crystal. (Unexamined Japanese Patent Publication No. 61-607
82. Released on March 28, 1986, JP-A-60-254
195. (Published on December 14, 1985, etc.) Liquid crystal display elements using phase-change liquid crystals use TN liquid crystals and STN liquid crystals to perform display by utilizing the scattering and transmission of light in a bistable state. Unlike the case where a polarizing plate is used, a polarizing plate is not required, so a bright display can be achieved, for example, 1280 x 960 with a simple matrix panel configuration.
Large-capacity display larger than dots is possible.

In addition, various applications including projection type display are being attempted by taking advantage of this feature. (Japanese Unexamined Patent Publication No. 1982-198270, published on September 2, 1986, etc.) [Prior art] Figure 3 shows the display principle of a nematic-cholesteric phase transition type liquid crystal, and the horizontal axis shows the applied voltage, Furthermore, the vertical axis indicates the light transmittance of the projected light that passed through the liquid crystal layer without being scattered (non-scattered transmittance).

Here, when selecting the transparent state, 2 of the drive voltage Vd
By applying twice the voltage (2Vd), homeotropic B (
After setting it to the H state for short, the voltage is dropped to Vd and the transparent state of H' is maintained.

In addition, when you want to select a cloudy state, apply 2Vd to create an H state in the same way as when selecting a transparent state, then reduce the voltage to Ov to create a cloudy focal conic state (abbreviated as F0 state), and then Vd is applied to maintain the cloudy F state.

Therefore, in the phase change type liquid crystal, by controlling the voltage applied to the liquid crystal as described above, it is possible to select between transparent and cloudy with the same voltage Vd.

Next, the applied voltage value VD9° indicates a value of 90% light transmittance in the falling curve of the figure, and 2 indicates a value of light transmittance of 20% in the rising curve. The difference between (Vuz.

+VD,. ) is defined as the drive voltage margin or hysteresis width Δ.

As described above, a nematic-cholesteric phase transition type liquid crystal display is premised on exhibiting wide hysteresis.

That is, as shown in FIG. 3, if the hysteresis width Δ is sufficiently wide, uniform alignment can be obtained over the entire surface of the panel, but if Δ is not sufficiently large, bistable driving becomes impossible.

Here, Δ is determined by the correlation between the liquid crystal material and the alignment film. To explain the alignment film, FIG. 4 is a cross-sectional view showing the structure of a liquid crystal display element, which consists of two glass substrates,
On top of 1.1', transparent electrode patterns 2 and 2' made of a solid solution of tin oxide (SnO2) and indium oxide (Ing03) (abbreviated as ITO) are arranged facing each other in a matrix shape with a small gap between them. The transparent electrode pattern 2.2' is coated with an alignment film 3, 3'.
The gap between them is filled with liquid crystal 4.

Here, the alignment films 3 and 3' are vertical alignment films in the case of the phase change type liquid crystal display element according to the present invention, and the liquid crystal molecules are aligned perpendicularly to the plane of the alignment film. Membrane 3.3
If the thickness of ′ is uneven or if it is poorly compatible with the liquid crystal material, effective alignment treatment cannot be performed, and therefore phase change type liquid crystal display may become impossible, or even if it is possible, it will become extremely unstable. There is a problem that this happens.

This problem is noticeable in panels with a large display capacity and a large effective display area, and is a cause of deterioration in display quality and manufacturing yield.

[Problem to be solved by the invention]

In a phase change type liquid crystal display, in order to increase the hysteresis width Δ, stabilize it, and maintain a homeotropic state (transparent nematic phase state) as far as possible to the low electric field side, liquid crystal molecules must be placed on the substrate surface (transparent electrode pattern surface). ), but vertical alignment is more difficult to perform alignment treatment than horizontal alignment, and this tendency is noticeable when using a large-area substrate.

By the way, N,N-dimethyl-N-octadecyl-3-aminopropyltrimethoxysilyl chloride (N,N-di
methyl-N-octadecyl-3-amine
opropy ltrimethoxysilylch
A method using LORIDE (abbreviated as DMOAP) is known and commonly used.

(Frederick J, Kahn, Appl, Phy
s, Lett,, Vol, 22+No.

8, 15 April 1973) In this method, a substrate to be processed is immersed in a 0.15% by weight aqueous solution of DMOAP and then dried at about 110'C for 30 minutes to form a thin alignment film.

However, even with this method, there is a problem that the characteristics of large-area liquid crystal display elements vary widely.
This solution was necessary.

[Means to solve the problem]

The above problem was solved by constructing the liquid crystal display element by using the Langmuir-Blodgett method to form the alignment film that constitutes the liquid crystal display element, which is made of a polyamide acid salt having a long-chain alkyl group and represented by the structural formula below. can do.

R: C)+3 (CHz)n NCCH3)z n
: t2-22 [Function] The present invention relates to a proposal by Frederick J. A vertical alignment treatment agent is used, and this is formed into a thin layer by the Langmuir-Prodgett method (abbreviated as LB method) to form an alignment film.

As a result of study, the inventors found that dimethylofdecylamine (CHl(CH2)
qN (CH3) z ) was selected, and polyamic acid was selected as the main compound having hydrophilic properties.

By combining the two to form a polyamic acid salt, the LB method can be applied.

The LB method is a method of creating a thin film of several molecular layers by repeatedly creating an organic thin film with a thickness of the size of a molecule and transferring it to a substrate. A monomolecular film with uniform orientation is created by arranging molecules with groups on both ends densely on the water surface, and the substrate to be treated is immersed in this and pulled up to form a monomolecular film with the hydrophobic groups facing outward. This is a method in which the material is transferred onto the substrate to be processed.

By repeating this process, a cumulative molecular film in which the directions of atomic arrangement are aligned is obtained.

The present invention reliably and uniformly aligns liquid crystal vertically by forming an alignment film consisting of several molecular layers using the LB method in which hydrophilic groups and hydrophobic groups are arranged in an orderly manner.

〔Example〕

Figure 1 shows the structural formula and second diagram of the polyamide acid salt according to the present invention.
The figure is an explanatory diagram of the reaction for obtaining this polyamic acid salt.

That is, 0.05 mol of diaminodiphenyl ether was dissolved in 160 g of dehydrated dimethylacetamide, and an equal amount of pyromellitic anhydride was added with vigorous stirring in a nitrogen (N2) stream, followed by stirring at room temperature for about 1 hour. Thereafter, this solution was dropped into stirring water to obtain a polyamic acid precipitate.

This was centrifuged to remove water, acetone was added to pulverize the precipitate, centrifugation was repeated three times, and the same operation was repeated using ether, followed by drying under reduced pressure to obtain polyamic acid powder.

Next, 2.87 x 10-3 mol of this polyamic acid was added to a mixed solvent of benzene and dimethylacetamide (1:1).
), and dimethyloctadecylamine (5,74X10-3 mol) similarly dissolved therein was added and reacted to obtain a polyamic acid salt as shown in FIG.

Next, this polyamic acid solution was dropped onto pure water kept at 20°C to form a film, on which a transparent electrode pattern was formed, 25 x 25 ml, thickness l, l m * (7)
The operation of dipping and pulling up the glass substrate was repeated five times under the condition of a surface pressure of 25 dynes/cm.

The LB film thus transferred onto the substrate was used as an alignment film, and a liquid crystal panel was fabricated using 6 μm glass fibers as spacers while leaving the long chain alkyl groups.

Note that the directions in which the LB films were pulled up on the upper and lower glass substrates were opposite to each other.

Five panels thus formed were filled with a nematic cholesteric phase transition liquid crystal whose main components were an ethane liquid crystal and a phenylcyclohexane liquid crystal, and the hysteresis width Δ was measured.

In addition, the same liquid crystal was sealed in five panels that were similarly aligned using DMOAP, a conventional vertical alignment agent.
Δ with respect to a driving voltage Vd of 5V was measured.

Table 1 Table 1 shows the difference between the actual measured value of Δ obtained in this manner and the value of Δ of 2.5■.

As a result, it was revealed that the panel of this example had extremely small variations in Δ and that a high-quality liquid crystal display element could be formed.

〔Effect of the invention〕

By implementing the present invention, it becomes possible to perform uniform alignment treatment with little variation even for large-area devices, thereby making it possible to improve quality and manufacturing yield.

[Brief explanation of the drawing]

Figure 1 shows the structural formula of the polyamide salt, Figure 2 shows an explanatory diagram of the reaction to obtain the polyamide salt, Figure 3 shows the relationship between applied voltage and light transmittance, and Figure 4 shows the structure of the liquid crystal display element. It is a sectional view. In the figure, 1 is a glass substrate, 2.2' is a transparent electrode pattern, 3.3' is an alignment film, and 4 is a liquid crystal.

Claims (1)

[Claims] Utilizing the hysteresis loop of applied voltage and light transmittance drawn by a nematic-cholesteric phase transition type liquid crystal, by changing the driving voltage application conditions, a transparent state and a cloudy state can be selected at the same voltage. In a liquid crystal display element for displaying images, a liquid crystal alignment film constituting the display element has a long-chain alkyl group and is made of a polyamide salt represented by the following structural formula,
A liquid crystal display element characterized by being formed by the Langmuir-Blodgett method. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ R: CH_3(CH_2)_nN(CH_3)_2 n
=12-22 However, m is the degree of polymerization