JPS60185925A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To enhance bending strength of a plastic base and to prevent disconnection of the ITO film of a liquid crystal display element by forming an org. material coat film on the plastic base before forming the ITO film. CONSTITUTION:Since an electrode base used for a liquid crystal display element needs acid and alkali resistances, and further, resistance to liquid crystals, an epoxy type resin highest in resistance to chemicals is selected as an org. material coat film to be formed on a plastic base., especially, a bis-phenol A type epoxy resin small in contraction rate in thermosetting is selected as the principal material. This material coat film is formed on the plastic base film before forming a light transmitting electrode. As a result, since scratches formed on the surface of the base is buried, very favorable effects can be obtained, that is, the bending strength of the base can be enhanced and the disconnection of an ITO film can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a liquid crystal display element, and particularly to a liquid crystal display element using a plastic film substrate.

[Background of the invention]

Conventionally, liquid crystal display elements were constructed by sandwiching the liquid crystal between two glass substrates (upper and lower) with opposing electrodes formed on their inner surfaces, and sealing the periphery with a sealant, but in recent years, glass substrates have been replaced with A plastic liquid crystal display element using a plastic film substrate has been proposed.

In a liquid crystal display device using this type of plastic film substrate, evaporation using FB (electron beam) or sputtering is used as a method for forming electrodes on the plastic film substrate. Also,
As the electrodes of liquid crystal display elements, since translucency is usually important, a film made of indium and tin oxide (ITO
When using a film), a film thickness of about 100 to 500X is required.

Furthermore, unlike the case where a glass substrate is used, a liquid crystal display element using a plastic film substrate has the characteristic that the substrate itself can be bent freely, but the ITO film is an inorganic substance, and the plastic film substrate is Since it is an organic substance, its elastic modulus differs greatly, which ultimately causes cracks to occur in the ITO film, resulting in the ITO film being disconnected. In this case, the curvature or number of bends until the ITO film breaks depends on the material of the plastic film.

It also varies greatly depending on the composition, crystallinity, film thickness, etc. of the ITO film. This property deterioration due to bending of the ITO film is a phenomenon that inevitably occurs because materials with widely different Young's moduli are put together, but it also occurs on the surface of plastic films and their substrates. Characteristic deterioration also occurs due to scratches. In particular, the ITO film resistance value deteriorates rapidly due to scratches, and the resistance value becomes infinite.

Figure 1 shows a model for the occurrence of disconnection defects due to scratches on the electrode substrate, as described above. Figure (a) shows the state before bending, and Figure (b) shows the bent state. Same figure (
e) is a SEM photograph of the damaged area. In the figure, 1 is a glass film substrate, 2 is a scratch on the plastic film substrate 1, and 3 is an ITO film formed on the plastic film substrate 1.

As is clear from the figure, wire breakage due to scratches 2 on the plastic film substrate 1 may occur even without bending stress if the plastic film substrate 1 itself undergoes a dimensional change such as stretching. For example, ■To film 3
It also occurs due to the difference in thermal expansion coefficient α between the glass film substrate 1 and the glass film substrate 1.

[Purpose of the invention]

Therefore, the present invention has been made in view of the above-mentioned problems, and its purpose is to provide a liquid crystal display element in which the bending strength of a glass film substrate is improved and disconnection of the ITO film is prevented. There is a particular thing.

[Summary of the invention]

In order to achieve this object, the present invention is designed to fill in scratches by forming an organic material coating on a plastic film substrate before forming an ITO film.

[Embodiments of the invention]

Next, the present invention will be explained in detail using examples.

Example 1 Electrode substrates used in liquid crystal display elements are usually required to have liquid crystal resistance as well as acid resistance and alkali resistance, so epoxy-based organic material coatings, which have the best chemical resistance, are used as organic material coatings to be formed on plastic film substrates. The resin was selected, and in particular, bisphenol A epoxy resin (epoxy equivalent: about 185), such as Epicoat 8280 (trade name, manufactured by Tai Mitsubishi Yukagaku Co., Ltd.), which has a low shrinkage rate upon heat curing, was selected as the main resin. In addition, Epicoat 828 as this main agent
As shown in Table 1 below, five types of curing agents A, B, C, D, and E are used, which have different thermal deformation temperatures Tg of the film after completion of the film.

Table 1 First, the above-mentioned Epicoat 828 and each of the five types of curing agent A
, B, C, D, and E to prepare 5 types of mixed solutions, respectively. Then, each of these 5 types of mixed solutions was added to a 1:1 mixed solution of methyl ethyl ketone/toluene prepared in advance. Dissolves at a concentration of about 10 parts, heat distortion temperature T
Five types of coating liquids with different g: A/, Bl, c/
, DI, E/. Next, the substrate is polyethylene terephthalate (hereinafter abbreviated as PET).
A board made of a plastic film with a thickness of approximately 250 μm (2).

Five film substrates were selected and surface treated by immersing them in a highly concentrated NaOH solution to improve the adhesion of the coatings. Next, the surface is treated;
, E/ to apply a coating solution to both sides of the substrate and dry to form a resin film with a thickness of approximately 2000 to 3000×. Next, an ITO film was deposited to a thickness of 200 to 400× by vapor deposition or sputtering under the same conditions on each PET film substrate on which various resin films were formed, and its heat resistance was evaluated. In this case, the heat resistance test temperature is 80°C according to the test standard for liquid crystal display elements.

100°C, 120°C, and 140°C were selected. the result,
The data shown in Table 2 below was obtained.

Table 2 In the same table, ○ marks indicate that there is no change in the ITO film, and The surface of the membrane has changed significantly. From the above explanation, it was found that there is a large relationship between the heat distortion temperature Tg of each coating liquid A' l B', + C' r D' + E' and the heat resistance of the ITO film. However, due to practical problems of liquid crystal display devices, the heat distortion temperature Tg is desirably 80° C. or higher. Further, in the examples, a resin film was deposited on the PET film substrate to a thickness of 2,000 to 30,000 mm, but the heat resistance also changes depending on the film thickness. Although heat resistance can be improved if the film thickness is small, a certain degree of film thickness is required to fill in surface scratches on the PET film substrate. Therefore, it may be determined as appropriate, taking into consideration the degree of surface scratches, the range of usage conditions of the liquid crystal display device, and the like.

Example 2 The coating liquid used in Example 1 was used to determine the coating film thickness and ITO
We investigated the relationship with membrane disconnection. That is, the film thickness was adjusted by the concentration of the coating liquid and the speed at which the PET film substrate was pulled up during dipping. As a result, it is difficult to fill in surface scratches on the PET film substrate with a coating film with a thickness of less than 500X, and it is difficult to fill in scratches on the surface of a PET film substrate with a coating film with a thickness of more than 10μm.
It was found that the bending strength was significantly affected by causing cracks in the O film. Therefore, the thickness of the coating film is preferably in the range of 500X to 10 μm.

Example 3 A scratch-resistant material with the highest hardness other than epoxy resin was evaluated as an organic paint to be applied on a PET film substrate. This material is, for example, HAR manufactured by Dainippon Ink Co., Ltd.
Product names in the DIC series are RC-5501 and RC-
5505, Re-5509. In addition, this material has different characteristics from those of Examples 1 and 2 described above; it is not thermosetting, but a type that is cured by UV light; RC-5501 has the best heat resistance, Re-5501, RC-
5505 and RC-5509. Next, an example of the procedure for forming these coating films will be shown below.

1. Clean the PET film.

2. Apply by dipping in primer solution (if applying to only one side, use a spinner, etc.).

3. Irradiation with UV light (irradiation conditions are 80-100m
Cured with W (365 nm) for 20-60 seconds).

4. Furthermore, apply RC-5509, a scratch-resistant paint, using the same method as in Mu2. 05. Irradiate with UV light (conditions are the same as A3).

As for the thickness of the primer and the scratch paint, a thickness of about 500× to 10 μm was found to be good according to experimental results.

The higher the hardness of the entire film, the higher the bending strength, which allowed the film to be thicker and provide sufficient properties for practical use.

〔Effect of the invention〕

As explained above, according to the present invention, by forming an organic material film on a plastic film substrate before forming a light-transmitting electrode, scratches formed on the surface of the film substrate can be embedded. , an extremely excellent effect can be obtained in that the bending strength of the film substrate can be improved and disconnection of the ITO film can be prevented.

[Brief explanation of drawings]

Figure 1 (a), ω) is a cross-sectional view showing a model for the occurrence of disconnection defects due to scratches on the electrode substrate, and Figure 1 (c) is an SEM of the scratch area.
The photographs, FIGS. 2(a) and 2(b) are enlarged photographs of the ITO film surface. 1...Plastic film substrate, 211.0. Wounds, 300.・ITO film. Figure 1 Procedural amendment (method) Indication of the case Patent application No. 40338 of 1982 Name of the invention Relationship with the 11 cases who amended the liquid crystal display element Name of the patent applicant (510) Manufactured by Hitachi Co., Ltd. Procurement fee
Subject of the administrator's amendment Detailed description of the invention column 1 of the description Brief description of the drawings and Contents of drawing amendment 1 Change the ``SEM photo'' in the 3rd page, line 15 of the description to ``
"Enlarged perspective view". 2. On page 7, lines 10 to 11 of the specification, "270x, 65x enlargement......changed" is replaced with "plan view and cross section." As shown in the figure (estimated diagram), the surface of the lT (J film has changed significantly. In the figure, it is now an organic material film placed between the substrate l and the lTu film 3.) 3. [1st
Figure (C) is an enlarged perspective view of the hot water part, Figure 2 (a) is an enlarged perspective view of the hot water part,
(b) is a plan view and a cross-sectional view of the surface of the 1'l'0 film. l...Plastic film substrate, 2...
・・Scratch,〕・・・・l'J”0%, 4・・・・・・
Organic material coating. ” he corrected. 4. The drawings in Figure 1 (C) and Figures 2 (a) and (b) will be amended in the attached circular. that's all

Claims (1)

[Claims] 1. A liquid crystal display element in which a liquid crystal is sandwiched between two upper and lower plastic substrates whose inner surfaces are coated with electrodes made of a transparent conductive film, and the periphery is sealed with a sealant. 2. A liquid crystal display device according to claim 1, characterized in that an organic material film is interposed between the substrate and the electrodes. 2. The liquid crystal display element according to claim 1, wherein the organic material film is a patented resin characterized by being made of an epoxy resin having a heat distortion temperature of 80° C. or higher.