JPS625216A - Liquid crystal display element consisting of plastic substrate - Google Patents

Abstract

PURPOSE:To effectively prevent the generation of an orientation defect by using an adhesive agent which does not substantially contain low-molecular weight components having <=2,000mol.wt. and forming a sealing part in a manner as to have high joint strength and high non-transparency. CONSTITUTION:Plastic substrates 11, 13 having transparent electrodes 15, 17 are disposed to face each other. The substrates 11, 13 are formed with oriented films 19, 21 which are subjected to an orientation treatment. The substrates are further sealed by a sealing agent 23 on the outside circumference by which a cell construction is formed. A liquid crystal compsn. 25 is sealed into the space enclosed of the substrates 11, 13 and the sealing agent 23 to constitute the liquid crystal display element. A co-condensation polyester adhesive agent from which oligomer components having <=2,000mol.wt. are removed is used for the sealing agent. The high adhesive strength to the plastic substrates and the non-transparency are thus obtd. and the generation of the orientation defect is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in sealants for liquid crystal display elements using plastic film substrates.

A liquid crystal display element has a liquid crystal composition sealed between two substrates provided with an electrode pattern, and electro-optically modulates the liquid crystal material by applying a signal voltage to the electrodes to display characters, figures, etc. This is to display the following information. Traditionally, inorganic glass has been used as this substrate, but liquid crystal display elements using plastic film substrates are attracting attention due to demands for thinner, lighter, and curved displays, as well as lower strength and manufacturing costs. ing.

The liquid crystal composition is sealed between the substrates by sealing the substrates so that a cell structure is formed between the two substrates and the sealing portion. When glass is used as a substrate, a highly reliable liquid crystal display element is obtained by printing a seal portion on the substrate using an adhesive such as an epoxy resin, bonding the seal portion, and then thermally curing the substrate. However, when using a plastic film as a substrate, it is not possible to obtain the same adhesive strength as a glass substrate, and there is a large difference in elastic modulus between the adhesive and the substrate. There was also a problem in terms of reliability as it was easy to peel off when bending stress was applied.

On the other hand, when flexible adhesives such as silicone or acrylic adhesives are used, the adhesion may be insufficient or the adhesive itself may have poor gas permeability, water vapor permeability, or liquid crystal permeability. Due to its high temperature, impurities from outside and liquid crystal leakage are likely to occur.

In this way, in liquid crystal display elements using conventional plastic film substrates, the adhesive strength, air-tightness, and liquid-tightness of the sealant are insufficient, and as a result, deterioration over time, especially during high-temperature storage and high-temperature storage, is a problem. There were significant practical problems.

In order to solve these drawbacks and have sufficient adhesive strength, the applicant has previously developed a plastic substrate liquid crystal display element using a hot-melt adhesive mainly composed of co-condensed polyester as a sealant. proposed (Special application 1973-
xa7zss).

Co-condensed polyester-based hot-melt adhesives have high adhesion strength to plastics such as polyester, and are flexible and therefore resistant to bending stress.
Since gas permeability, water vapor permeability, and liquid crystal permeability are also low, impurity penetration and liquid crystal leakage do not occur, making it possible to manufacture highly reliable liquid crystal display elements. However, the co-condensed polyester adhesive has the drawback of causing alignment defects called twisted disc lineage in the liquid crystal layer near the bonded area.

Conventionally, liquid crystal display elements for watches and calculators use static drive or time-division drive with a duty of about 172 to 1/3, and in this case, the above-mentioned alignment defects are not a big problem. There wasn't. However, in recent years, 1/3
As high-duty (large-capacity) liquid crystal display elements with a duty of 2 to 1/64 have been developed, the above-mentioned defects have become a cause of a reversal phenomenon in the viewing angle direction and a significant deterioration of display quality.

The present invention has a sealing part that has great adhesive strength and is resistant to gas, moisture, and
It is an object of the present invention to provide a liquid crystal display element having high impurity and liquid crystal impermeability and effectively preventing the occurrence of alignment defects.

ILIL HigashiThe plastic substrate liquid crystal display element of the present invention includes plastic substrates placed spaced apart and facing each other and sealed with an adhesive to form a seal portion, and a liquid crystal material is applied to the gap formed inside the seal portion. The filled liquid crystal display device is characterized in that the adhesive is a co-condensed polyester adhesive that does not substantially age the low molecular weight component having a molecular weight of 2,000 or less.

The present invention will be explained in more detail below.

FIG. 1 shows an embodiment of the liquid crystal display element of the present invention, in which plastic substrates 11 and 13 having transparent electrodes 15 and 17 are disposed facing each other. Further, the substrates 11 and 13 have alignment films 19 and 21 formed thereon and are subjected to alignment treatment. Further, the outer peripheral portion of the substrate is sealed with a sealant 23 to form a cell structure, and a liquid crystal composition 25 is sealed in a space surrounded by the two substrates 11 and 13 and the sealant 23 to display a liquid crystal display. The element is configured.

As the sealant, a co-condensed polyester adhesive from which oligomer components having a molecular weight of 2,000 or less are removed is used. Co-condensed polyester adhesive is a resin synthesized by selecting co-condensed components to have a lower softening point than polyethylene terephthalate, which has high heat resistance for use as a hot-melt adhesive. .

For example, using terephthalic acid and adipic acid as dicarboxylic acid heptamers and ethylene glycol as the diol monomer, the copolymerization composition is 1 mol %: terephthalic acid: adivic acid: ethylene glycol = 35: 15
: By setting it as 50, a co-condensed polyester resin that can be bonded at a temperature lower than 180°C can be obtained. In addition, by increasing the amount of adipic acid, the pour point can be lowered, and the above ratio is reduced to 15-30:35-20.
: By setting it to 50, it becomes possible to bond at 150°C or lower.

Cocondensation components include, for example, terephthalic acid, isophthalic acid, 1.5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, dibenzoic acid, bis(p-carboxyphenyl)methane, and 4.4% dicarboxylic acid components.
Aromatic dicarboxylic acids such as '-sulfonyl dibenzoic acid; fatty acid dicarboxylic acids such as adipic acid, malonic acid, tartaric acid, and succinic acid. In addition, the diol component is ethylene glycol.

Propylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol,
Examples include cyclohexane glycol. Among the co-condensed polyesters, those whose heptamer component is terephthalic acid, adipic acid, or ethylene glycol are preferred.

In the adhesive of the present invention, the molecular weight in the co-condensed polyester is 2
,000 or less, and this can prevent twist disclination. Normally, in polymer synthesis, the molecular weight distribution is from several hundred to several hundred to several tens of edges. A resin with this is synthesized. Figure 2 shows that the copolymer composition (mol%) is terephthalic acid: adivic acid: ethylene glycol = 25.
It is a co-condensed polyester resin synthesized to have a number average molecular weight of: 25:50 and a number average molecular weight of zo, ooo.

It has a molecular weight distribution in the range of several hundred to several tens of blades.

In order to remove low-9 molecular weight substances from such resins, separation operations commonly used in the field of polymer chemistry, such as those listed below, may be performed.

■ Solvents that partially dissolve the resin, for example.

Thoroughly wash with toluene, benzene, chloroform, 1,2-dichloroethane, etc.

(2) Pour the resin solution into the above solvent and separate the precipitated polymer.

■ Extract low molecular weight substances by Soxhlet extraction using the above solvent.

■ Zone melt method.

FIG. 3 shows the molecular weight distribution of the resin treated by the method (2), in which components with a molecular weight of 2,000 or less were removed.

When such a resin is used as an adhesive to form the seal part of a plastic substrate liquid crystal display element, the properties of high adhesiveness and high sealing properties originally possessed by the co-condensed polyester resin are maintained, and the twisted disk It is possible to suppress the occurrence of lination.

The adhesive of the present invention can be used as a hot-melt adhesive, for example: 1) cutting a film-like hot-melt adhesive into a predetermined shape using a press or the like and placing it on a substrate; 2) powder-like adhesive; 3) Dissolve the hot melt adhesive in a solvent, place the solution on the substrate by coating, printing, etc., and then distill off the remaining solvent. A sealing layer is formed by forming a seal-shaped hot melt adhesive layer on a substrate by the method described above, and then stacking an opposing substrate on top of each other, applying a load, and heating at a temperature equal to or higher than the melting temperature.

Examples of the plastic film substrate include light-transmitting plastics such as polyesters such as polyethylene terephthalate and polyethylene terephthalate, polysulfones, polyethersulfones, polycarbonates, acetyl cellulose, and polymethacrylic esters. Among these, heat resistance, solvent resistance, liquid crystal resistance,
Polyethylene terephthalate is preferred from the viewpoint of physical properties such as gas permeability and water vapor permeability that affect the reliability of plastic substrate liquid crystal display elements, and one adhesive of the present invention is:
Has excellent adhesive properties to polyethylene terephthalate. Polyethylene terephthalate undergoes thermal deformation at 170 to 180°C when stress is applied, so it is preferable for hot melt adhesives to have a pour point of 130 to 150°C.Normally, polyester substrates are difficult to adhere to, and There are few adhesives with such adhesive strength, for example,
Epoxy adhesives that do not adversely affect the liquid crystal and alignment film required for substrates for liquid crystal display elements and have high airtightness have a T of about 10 to 30 g/am.
In contrast, the polyester hot melt adhesive used in the present invention has an adhesive strength of 400 to 800 g/CII+ to a polyester substrate.

According to the present invention, in a liquid crystal display device using a plastic film substrate, the sealing portion is formed using a co-condensed polyester that does not substantially deteriorate the low molecular weight component as an adhesive. It is particularly suitable as a sealing structure for a high-duty liquid crystal display element because it can provide high adhesive strength and high non-transparent properties, and prevent deterioration in display quality due to twist disclination.

Example 1 After forming a predetermined electrode on a polyester film with a transparent conductive film by photolithography, an alignment film made of polyamide was formed and rubbing was performed. 4 of co-condensed polyester 7p resin (terephthalic acid: 25 mol%, adipic acid = 25 mol%, ethylene glycol: 50 mol%) having the molecular weight distribution shown in No. 3@ on the outer periphery of this substrate.
150℃ after printing 0% by weight dimethylformamide solution
The solvent was distilled off by heating to . A substrate that had been subjected to a similar alignment treatment and the above substrate were bonded to each other with a 10 μ-spacer interposed therebetween so that the alignment axes were perpendicular to each other, and an empty cell was prepared by heating at 150° C. for 30 minutes. Me
Liquid crystal ZLI-1557 manufactured by RCK Corporation was sealed and the filling opening was sealed to produce a twisted nematic type liquid crystal display element. This liquid crystal display element shows almost no twist disclination even in a high temperature storage test at 80°C for 1000 hours, and its electro-optical properties also exhibit initial value fluctuations of ±20%.
It showed extremely high reliability within

In addition, good display quality was achieved even with time-division driving at 1/64 duty.

Comparative Example 1 A liquid crystal cell was prepared in the same manner as in Example 1, except that a co-condensed polyester resin having the molecular weight distribution shown in FIG. 2 before removal of low molecular weight components was used.

Although this liquid crystal cell showed good alignment initially, in a high temperature storage test at 80°C for 100 hours,
Twisted disclination occurred near the seal.

Furthermore, in the time division drive with a duty of 1164, a reversal phenomenon of the viewing angle occurred at the outer periphery of the display section.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing an embodiment of the present invention. FIG. 2 is a graph showing the molecular weight distribution of co-condensed polyester resin. FIG. 3 is a graph showing the molecular weight distribution of the co-condensed polyester resin from which low molecular weight substances have been removed.

Claims (1)

[Claims] 1. In a liquid crystal display element in which plastic substrates placed apart and facing each other are sealed with an adhesive to form a sealing part, and a gap formed inside the sealing part is filled with a liquid crystal substance, the adhesive is a co-condensed polyester adhesive substantially free of low molecular weight components having a molecular weight of 2,000 or less.