JPS6083012A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain a fine liq. crystal display by properly selecting the kinds, particle sizes and amounts of electrically conductive carbonaceous powders contained in an electrically conductive adhesive for a common transition body. CONSTITUTION:Transparent electrode patterns 2, 2' and films 3, 3' for controlling the orientation of a liq. crystal are successively formed on the insides of two glass substrates 1, 1'. The substrates are placed opposite to each other, a liq. crystal 4 is injected into the gap between the substrates, and the peripheries are sealed with a sealant 5 contg. a common transition body 7 made of electrically conductive carbon paste. The carbon paste is prepd. by kneading polyimide resin as a binder with 25-30wt% electrically conductive powders of purified acetylene black (A) of <=100mmu average particle size, a purified furnace black- channel black mixture (B) of <=100mmu average particle size, graphite (C) of 1mum average particle size and graphite (D) of 5mum average particle size.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a liquid crystal display device having an improved electrode transition material.

Conventional technology> Conventionally, a liquid crystal display element has a glass substrate 1, as shown in FIG.
Transparent electrode patterns 2, 2' made of indium oxide, tin oxide, etc. are arranged on 1', and liquid crystal alignment control films 3, 3/2' are formed on this.
In most cases, the liquid crystal 4 is fixed and held in the gap between two sheets facing each other, and the peripheral portion is sealed with a sealing material 5.

A liquid crystal display element having this structure requires a structure 6 for electrically connecting the electrode turns disposed on the two glass substrates. This structure 6 can be called a common transition,
Conventionally, a silver-based conductive adhesive (so-called conductive silver paste) has been used. However, silver thread conductive adhesives are expensive and tend to cause silver migration, so in recent years, cheaper silver/carbon based conductive adhesives (so-called conductive silver/carbon pastes) and even more Car-type conductive adhesive (so-called conductive car, I-line paste) is used, which is inexpensive and does not cause migration.・Carbon-based conductive adhesives are made by cross-dispersing carbon powder or silver powder and carbon powder as conductive powder in a binder resin such as epoxy resin, phenol resin, polyimide resin, polyester resin, silicone resin, or urethane resin. At this time, the initial resistance value can be changed by changing the amount of the conductive powder added.In addition, the silver/carbon-based conductive adhesive can change the mixing ratio of silver powder and carbon powder without changing the amount of conductive powder added to the binder. You can change the initial resistance value over a wide range just by changing it.Also, the specific resistance of the carbon-based conductive adhesive itself is higher than the specific resistance of the silver powder, so the silver thread conductive adhesive has a lower resistance value. However, by increasing the amount of conductive powder added, the initial resistance value can be lowered and K can be used as a common transfer.

However, if the amount added is too large, the paste state of the adhesive cannot be maintained, so there is a limit to the amount of conductive powder added.

The purpose of common transition in liquid crystal display elements (LCD) is to maintain electrical connection between electrode patterns arranged on two opposing substrates. In order to obtain the common transfer material,
■Low voltage drop, i.e., small initial resistance value, ■Low variation in initial resistance value, ■Low rate of change in resistance value after reliability test, ■Improvement of electrical connection failure after reliability test. ■Have high adhesive strength;
It is necessary to satisfy requirements such as ■ not causing migration, and ■ not reacting with other materials.

The constituent materials of the conductive adhesive described above are broadly classified into binder resin, conductive powder, and additives. Among these, conductive powder is particularly important for carbon-based conductive adhesives, and the types of carbon powder that are conductive powder, The particle size and amount added greatly affect the common transition characteristics and reliability of the liquid crystal display element. Therefore, when using a carbon-based conductive adhesive as a common transfer adhesive, it is important to select the type, particle size, and amount of carbon powder to be added.

By the way, graphite is often used as the carbon conductive powder used in conventional carbon-based conductive adhesives, and moreover, many of the particles have a particle size of 1 μm or more. When such graphite is kneaded into a binder resin, it has a large bulk specific gravity, so it is not possible to achieve the initial resistance value unless the amount added is increased, and if the amount added is too increased, the adhesion of the coating film may be affected. was significantly inferior. On the other hand, carbon black may be used instead of graphite, or the specific resistance of carbon black itself is higher than graphite and lower than pastes using graphite as conductive powder. I just couldn't get it. Also, in order to improve the dispersibility of carbon black in the binder resin, carbon black with a relatively large particle size is often used, and for this reason, it was necessary to increase the amount added in order to obtain a low resistance value. . At this time, if the amount added is too large, there is a problem in that adhesiveness deteriorates.

Furthermore, some binder resins gelled when kneaded due to the r-eye properties of carbon black and binder resin, while some binder resins could not be mixed when used as a single carbon blank.

When a conductive adhesive containing such carbon conductive powder is used as a common transfer, there is a large variation in resistance value.
In addition, in one moisture resistance test, the resistance in one cycle increased and the adhesiveness significantly decreased, resulting in poor moisture resistance. Therefore, as a liquid crystal display element, there have been problems such as uneven contrast of display patterns, non-lighting, and a significant increase in current consumption >X+.

Purpose> The present invention has been made in view of these problems. That is, the object is to obtain a good liquid crystal display by appropriately selecting the type, particle size, and amount of carbon conductive powder of the carbon-based conductive adhesive for common transition.

<Example> Hereinafter, an example of the liquid crystal display element according to the present invention will be described.

Figure 2 shows the structure of an embodiment according to the present invention.
(a) is a partial plan view, and (b) is a partial side cross-sectional view taken along the line AA'. Note that the same parts as in FIG. , 1' are formed with transparent electrode patterns 2, 2', on which are formed liquid crystal alignment control films 3, 3', which are placed opposite to each other, and a liquid crystal 4 is fixedly held in the gap between them. A sealing material 5 is sealed around the periphery.

7 is a common transfer and is located inside the sealing material 5. A major feature of the present invention lies in the improvement of the material constituting this common transition 7. An experimental example of the composition of the common transition 7 will be explained below.

Experimental Example 1 ■Purified acetylene black with an average particle size of 100 cm or less (sample ■) in a polyimide resin, ■average particle size of 10
Mixed conductive powder of refined furnace black and channel black (sample ■) with a particle size of 0 or less, ■graphite with an average particle size of 1μ (sample ■beautiful)■graphite with an average particle size of 5/l (sample ■) as a binder. A conductive carb paste was obtained by kneading 25 to 30 Wt96 of resin.

Each sample of a cell in which these conductive carbon pastes were mounted as a material for the above-mentioned common transition 7 of a liquid crystal display element was
0 c, 95941t-H-calcium (C1000
After leaving it for a while, 2. A rectangular wave of Ov, I KHz was applied to investigate the electrical connection failure of this common transition. The results are shown in the table below. As a comparative example, Table 1 shows the results of a conductive silver paste prepared by kneading approximately 70 wt96 flaky silver powder with an average particle size of 5 l into a binder in a polyimide resin.

As shown in the table above, it can be seen that those using carbon black or graphite are superior to those using silver powder when left for long periods of time in high temperature, high humidity surroundings. As shown in the table above, when acetylene black was kneaded into polyimide resin, gelation occurred, and as a result, it could not be mounted on a liquid crystal display element.

Experimental Example 2 ■Purified furnace black with an average particle size of 1 μm (sample ■), ■Purified furnace black with an average particle size of 100 μm or less (sample ■), ■Purified furnace black with an average particle size of 100 μm or less in polyimide resin A mixture of furnace black and channel black (sample ■) was kneaded with binder resin in an amount of about 25 wt % to obtain a conductive carbon paste. The initial volume resistivity and adhesion of these conductive carbon pastes were investigated. The results are shown in the table below.

Table 2 It can be seen from the above table that the initial volume resistivity and adhesion can be improved by reducing the average particle diameter of carbon lj'F and starch powder. In addition, by mixing two types of carbon conductive powder '5' in an appropriate ratio, it can be seen that the initial volume resistance value and adhesion can be further improved. By appropriately combining particle sizes, a conductive carbon paste with low initial resistance and high adhesion can be obtained.

Experimental Example 3 Conductive powder (sample ■) made by mixing refined furnace black with an average particle size of 30 cm, acetylene black, and churnel black in a phenolic resin at an appropriate ratio
, ■ Conductive powder made by mixing refined furnace black and acetylene black in an appropriate ratio with an average particle size of 80 watts (sample ■), ■ Refined graphite with an average particle size of 5 μm (
Sample ■) ■ Conductive powder (sample ■), which is a mixture of refined furnace black and acetylene black with an average particle size of 80 mm, and graphite made in Sui with an average particle size of 5 mm in an appropriate ratio (sample ■), is kneaded to make conductive carbon. It was made into a paste.

A mounting cell was fabricated using these conductive carbon pastes as a common transition material for a liquid crystal display element. This is 80
・After being left in the c 9596R-H atmosphere for 1000 hours, 2. A rectangular wave of OV and 5 KHz was applied to check for electrical connection failure at the common transition portion. The results are shown in the table below.

As shown in the table above, carbon conductive powder with a small average particle size is
The kneaded conductive carbon paste is effective against poor electrical connections at the common transition area.

In fact, Experimental Example 4 A mixture of purified furnace black 7-channel black with an average particle size of 30 wu or less was added to polyimide resin.
50wt96 (sample ■), 040wt96 (sample ■), ■30wt94- (sample ■), ■2
0 wt, 915 (sample ■), ■15'wt94
(Sample ■) Knead and bind with conductive carbon paste. These conductive carbon pastes were printed on a 325mm/7mm metal screen to examine their printability. The results are shown in the table below.

Table 4 As shown in the table above, is it necessary to knead the carbon black conductive powder with the binder oil to a concentration of 40wt96 or less? These conductive carbon pastes were used as the common transition 4J of a liquid crystal display element to form a common transition by screen printing, and it was found that a conductive carbon paste with a 1-containing ratio of 4.0 wt% or less could obtain a normal common transition. was completed.

Experimental Example 5 Conductive carbon paste-'C Nippon Graphite Kogyo (medium film conductive paint ■"Everyohm 25P-IJ4 sample"), ■"Epriohm 800PTJ (sample ■), 6
A] Asahi Chemical (uF Shisho Carbon Paste, ■r
To-20SJ (sample ■), ■rTU-41-AJ
(Samplen 6-width electrostatic screen printing ink, ■rED-4,
2 3 8 S J (sample ■) is used as a common transition (O) of the liquid crystal display element, and it is placed at the sealing position of the opposite substrate (fc) on the other substrate υ (Screen printing C'C is used to print two sheets. The substrates were laminated together so that the common transition overlapped with the glue material. 3, 1 and 32 Hz square waves were applied to the liquid crystal display element thus produced, and 41 and 80 Hz of lighting were applied. 'C, 95 96R, I
After being left in an atmosphere for 300 hours, the presence or absence of electrical connection failure at the common transition area was examined when a 5 KHz square wave was applied. Sara 1c. The rate of increase in current consumption was also investigated. The results are shown in the table below. In addition, as an example of Himaki] "Tatekasei-[
The results are shown for "Conductive Silver Paste rEN-4200 Modified by A5".

Table 5 As can be understood from the above experimental examples, as a carbon-based conductive adhesive (conductive carbon paste) for common transfer applications, ■ Purified acetylene black with a volatile content of 396 or less;
Furnace plaque, channel plaque, and conductive carbon paste using conductive powder made of graphite alone or a mixture of two or more types in an appropriate ratio are used as the common transfer material.

-〇 40wt% of the above conductive powder based on the binder resin
The kneaded conductive carbon paste is used as a tracommon transition material below.

(2) A conductive carbon paste prepared by kneading conductive powder with an average particle size of 100 yen or less into a binder resin is used as the common transfer material.

As a result, ■Low initial resistance value, @small variation in initial resistance value, θ excellent moisture resistance, ○strong adhesive strength,
■Common transition without electrical connection defects can be obtained. Further, the carbon paste containing the conductive powder can be provided as a common transfer on the common substrate facing the seal position on the segment substrate, so-called common transfer within the seal.

FIG. 3(a) shows a common transition material according to the present invention. 7 is a common transition material located inside the sealing material (C position). 7a and 7b are mutually different conductive powders, each consisting of extremely fine particles. Figure 3(b) shows a conventional conductive powder with a large particle size. A common transition material 6 including the following is shown.

≦, Effects> According to the present invention described above, by using conductive carbon paste as a common transfer material, not only so-called common transfer within a seal is possible, but also the rate of increase in current consumption is reduced compared to silver paste. It is small and can improve reliability as a liquid crystal display element.In addition, by using the conductive carbon paste according to the present invention as a common transfer material, there is no contrast unevenness in the display pattern, no non-lighting, and low current consumption. It is possible to obtain a liquid crystal display element with less addition.

[Brief explanation of the drawing]

@ Figure 1 is a 13+g plane 1t'Ji plane view of a conventional liquid crystal display element, Figure 2 (a) is a partial plan view of an embodiment of a liquid crystal display element according to the present invention, and Figure 2 (b) is a partial plan view thereof. 3(a) is a more detailed partial side sectional view, and FIG. 3(b) is a partial side sectional view of a conventional liquid crystal display element. In the figure, 1. 1' Ni glass substrate, 2.2': Transparent electrode pattern, 3, 3': Liquid crystal alignment control film, 4 knee liquid crystal, 5: Seal material, 6, 7: Common transition. 1. Indication of the case Patent application No. 58-192079 2. Name of the invention Liquid crystal display element 3. Person making the amendment Relationship to the case Patent applicant 4. Agent Address 8545 Nagaike-cho, Abeno-ku, Osaka-shi 22 number 22 number 9
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Claims (1)

[Claims] 1. In a liquid crystal display device using carbon paste as an electrode transition material, refined acetylene black, furnace black, channel black carbon black, or granite may be used alone or as appropriate in two or more types. 1. A liquid crystal display device characterized in that a carbon paste containing conductive powder mixed in a suitable ratio is used as an electrode transfer material. 2. Add the above conductive powder to a binder resin (40wt% based on
Patent 3, characterized in that a carbon paste formed by mixing in the following ratio *l: is used as the transfer material of the above-mentioned electrode, carbon obtained by kneading conductive powder with an average particle size of 1.00rnμ or less into a binder resin. Pace 14 - Claim 1, which describes what device is used as the transfer material of the above-mentioned electrode
The liquid crystal display element described in Section 1. 2. The liquid crystal display element according to claim 1, wherein the carbon paste is provided as an electrode transfer material on a common substrate facing the sealing position on the segment 1 substrate.