JP2001042342A - Liquid crystal display element and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a liquid crystal display element having extremely small amount of contamination to its liquid crystal layer by incorporating particles having a property to adsorb materials into the liquid crystal layer. SOLUTION: One substrate having a liquid crystal controlling element and a picture element electrode and the other substrate are opposedly disposed at a prescribed interval. Liquid crystal is interposed between a pair of substrates opposed to each other and its peripheral part is sealed to form a liquid crystal display element. At this time, particles having a property to adsorb materials are incorporated into a liquid crystal layer. The material-adsorbing particles have properties such as: electrical resistivity equal to that of the liquid crystal or higher; porosity; particle size equal to a length of the interval between opposed display parts of the pair of opposed substrates or less and a generally spherical shape. Thereby, the liquid crystal display element having high display quality and reliability can be obtained, containing the particles which adsorb sealing agent-constituting materials to prevent elution of the materials into the liquid crystal material and besides perform a role of a spacer for highly accurately sticking the two substrates at a prescribed gap.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to liquid crystal sealing of a liquid crystal display device.

[0002]

2. Description of the Related Art Liquid crystal display elements are widely used as display screens of portable personal computers and the like, and in recent years, high definition, high contrast ratio, high viewing angle and other image quality are required. In particular, an active matrix type liquid crystal display element using a thin film transistor or the like as a switching element for selecting a pixel (a thin film transistor using a thin film transistor
-LCD) has performance comparable to that of a conventional cathode ray tube in terms of contrast performance and high-speed display performance.

In such an active matrix type liquid crystal display device, an electric field for changing the orientation of a liquid crystal layer is applied between an electrode formed on one substrate and an electrode formed on the other substrate. The vertical electric field method was generally used, but recently, an in-plane electric field method (In-Plane Sw) in which an electric field is applied to the liquid crystal in a direction substantially parallel to the substrate.
A switching mode (IPS mode) liquid crystal display device has been put to practical use.

First, a method of manufacturing a liquid crystal display element will be described.
Transmission type amorphous silicon (a-Si) type color TFT-
A conventional method of manufacturing an LCD will be briefly described as an example. TFT
The LCD manufacturing process includes a TFT process of forming thin film transistors and metal wiring on a glass substrate, a color filter process of forming a color filter on a glass substrate, and an LCD process of facing these two substrates and sandwiching a liquid crystal. .

In the TFT process, a series of processes of film formation, resist coating, exposure / development, etching, resist peeling, and cleaning are repeated several times for gate wiring, interlayer insulating film, a-Si, pixel electrode, protective film, and the like. It is. This gives T
The FT substrate is completed and sent to the LCD process.

In the color filter process, after a black matrix is formed, a series of processes of film formation, resist coating, exposure / development, etching, resist peeling and cleaning are repeated for three colors of red, green and blue. After patterning three colors of red, green and blue, to give the surface flatness,
Further, an overcoat layer is formed thereon. Finally, a transparent electrode film is formed and sent to the LCD process.

[0007] The TFT substrate and the color filter substrate formed as described above are sent to an LCD process, where the surfaces are cleaned. After that, as shown in the conventional manufacturing method of FIG. 1, the alignment film printing, the rubbing of the alignment film, the cleaning after rubbing, the application of the sealant, the drying of the sealant, the lamination of the TFT substrate and the color filter substrate, Gap setting to make the opposing distance between the substrate and the color filter substrate uniform in the plane, liquid crystal injection, liquid crystal sealing, and lighting inspection follow. The TFT-LCD panel that has undergone the lighting inspection is sent to a module process for mounting a driving integrated circuit and the like.

In the production of such a liquid crystal display device, it is important to control the display performance over the entire display section to be uniform, but it is very difficult. For example, in the case of a TFT-LCD, a high voltage holding ratio is required, and therefore, the resistivity of the liquid crystal layer is 1 × 10 ¹² to 1 × 10 ^13.
(Ω · cm), and sometimes as high as 1 × 10 ¹⁴ (Ω · cm). The liquid crystal display element requires uniformity of the display unit, and therefore, the resistivity of the liquid crystal must be uniform over the entire display unit (edited by Shunsuke Kobayashi, "Electronic Display", The Institute of Electronics, Information and Communication Engineers) Published). The high required value for the resistivity can be reduced by about one digit by devising a circuit, for example, by providing a storage capacitor for each pixel of the display unit.

[0009] However, the resistivity varies when impurities enter the liquid crystal layer. When impurities are unevenly distributed in a certain portion of the display unit, even if a storage capacitor is provided in each pixel of the display unit, the display becomes non-uniform, that is, display unevenness occurs. It is difficult to control the display performance to be uniform. These are not limited to the above-mentioned transmission type a-Si type TFT-LCD, but also apply to other transmission type liquid crystal display elements, reflection type liquid crystal display elements, projection type liquid crystal display elements and the like.

[0010]

One of the factors that cause the resistivity of the liquid crystal to fluctuate is the influence of the sealant mentioned above. This sealant is for bonding two substrates with high precision at a predetermined gap. At present, a thermosetting epoxy resin is mainly used as such a sealant.

Immediately after the completion of the liquid crystal display element, it is completely inconspicuous to human eyes, but the display becomes gradually non-uniform as time passes. When the energization acceleration test is performed under a constant temperature condition, the display becomes non-uniform. In most cases, the appearance appears almost in conformity with the shape of the applied sealant. Actually, when the analysis was performed by gas chromatography, constituent substances (solvent, unreacted substances, etc.) of the sealant were detected from the liquid crystal material sampled from the non-uniform display area.

A comparison between a portion where the constituent material of the sealant is eluted and unevenly distributed in the liquid crystal material and a portion where the constituent material of the sealant does not exist is compared with the portion where the constituent material of the sealant is eluted and unevenly distributed. Because the resistivity of the liquid crystal layer fluctuates,
Even if a constant voltage is applied to the liquid crystal layer, the response of the liquid crystal layer to an electric field differs, and a difference occurs in transmitted light or reflected light intensity. This is because, for example, even if the entire display element surface of a normally white mode is displayed black in a transmission type liquid crystal display element, a part thereof looks whitish, that is, the transmitted light intensity of light which should be uniform over the entire display element. Means non-uniform. The appearance of this whitish part is
In most cases, it appears almost in conformity with the shape of the applied sealant.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned reliability problems relating to a liquid crystal display element. It is an object of the present invention to provide a liquid crystal display element having a high display quality and a high reliability, which also plays a role of a spacer for bonding a plurality of substrates at a predetermined gap with high precision.

[0014]

The means described below solves the above-mentioned problems.

(1) A liquid crystal in which one substrate having a liquid crystal control element and a pixel electrode and another substrate are opposed to each other at a predetermined interval, and a liquid crystal is sandwiched between the pair of opposed substrates and a peripheral portion is sealed. In the display element, the liquid crystal layer contains particles having a property of adsorbing a substance.

(2) The particles having the property of adsorbing the substance described in (1) above have an electric resistivity higher than the electric resistivity of the liquid crystal.

(3) The particles having the property of adsorbing the substance in the above (2) have the property of being porous.

(4) The particle diameter of the particles having the property of adsorbing the substance in (2) is set to be equal to or less than the distance between the pair of opposing substrates in the display section.

(5) The particles having the property of adsorbing the substance described in (4) are substantially spherical.

(6) The particles having the property of adsorbing the substance described in the above (1) are present only in the vicinity of the seal on the display portion side of the liquid crystal display element.

(7) In the liquid crystal display device according to (6), the distance between the particles having the property of adsorbing the substance is set so as not to exceed the size of two display pixels.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an outline of a conventional manufacturing process of a liquid crystal display element and an additional process according to the method of the present invention. However,
Only the LCD process after the formation of the alignment film is shown here.

A first embodiment will be described. First, the adsorbent was adjusted. In this case, materials of Al2O3 and SiO2 were mixed and used at a ratio (weight ratio) of 3: 8 as an adsorbent. Resistivity Al2O3 at ^{1 × 10 28 (Ω · cm} ), a SiO2 at ^{1 × 10 27 (Ω · cm} ), the resistivity of the conventional liquid crystal ~
It has a resistivity far exceeding 1 × 10 ¹³ (Ω · cm).
Also, microcrystals can be synthesized in a binary system of Al2O3-SiO2, pulverized and classified, and used as an adsorbent. As the adsorbent, in addition to the above-mentioned inorganic oxide materials of the Al2O3 and SiO2 series, those which are commercially available for chromatography, for example, a porous synthetic organic polymer such as diphenylphenylene oxide can be used. The particle size was measured by a laser method. The maximum diameter is 5.5
μm, and the average particle size was 5 μm. The distance between the opposing substrates in the display section of the liquid crystal display element is designed to be 5.5 μm.

2 g of this adsorbent was put into a tube made of Pyrex glass, lightly plugged with glass fiber after washing and drying with acetone, and then aged at 350 ° C. for 12 hours while passing 150 cm of nitrogen in an oven. FIG. 2 schematically shows the state of the adsorbent placed in the Pyrex glass tube.

After aging, 1 g of the adsorbent was taken out, and it was confirmed by thermal desorption gas chromatography that the total amount of adsorbed substances was below the detection limit (10 pg) of the present method. The adsorbent was continuously aged at 350 ° C. while passing nitrogen at 150 ccm until immediately before use.

Next, a sealant was prepared. The sealing agent was composed of (a) an epoxy resin, (b) a curing agent composed of a novolak resin, (c) a filler, (d) a curing accelerator, (e) a coupling agent, and (f) a solvent.

As the epoxy resin (a), a liquid bisphenol A type epoxy resin (Nippon Kayaku RE
-310S) and a solid bisphenol A type epoxy resin (Epicoat 1001 manufactured by Yuka Shell) were used in a ratio of 78:22. However, the epoxy resin used for the sealant is not limited to bisphenol A type epoxy resin, but may be bisphenol F type epoxy resin, N, N-diglycidyl-o-toluidine, N, N-
Diglycidyl aniline, phenyl glycidyl ether,
(3,4-3 ′, 4 ′ epoxycyclo) hexylmethylhexanecarboxylate, hexahydrophthalic anhydride diglycidyl ester and the like. These epoxy resins can be used as a mixture of two or more.

The total chlorine content of the epoxy resin used in the present invention is 1500 ppm or less, preferably 1000 pp.
m or less. This is because when the total chlorine content is 1500 ppm or more, the corrosion of the ITO transparent electrode of the liquid crystal element becomes significant.
This time, the total chlorine content was measured by the hydrolysis method, and 600pp
m.

A curing agent (b) comprising the novolak resin
This time, two kinds of phenol novolak resins were used, Nippon Kayaku's PN-152: binucleate content of 40% and Nippon Kayaku's PN-80: binucleate content of 12% in a ratio of 28:13. Was. However, the curing agent used for the sealing agent is not limited to the phenol novolak resin using the above-mentioned phenols as a raw material, and it is also possible to use various novolak resins such as a cresol novolak resin using a cresol as a raw material. good. These novolak resins can be used as a mixture of two or more.

As the filler (c), fused silica and alumina were used in this case. However, the filler used for the sealant is not limited to the above two types, and may include crystalline silica, silicon carbide, silicon nitride, boron nitride, calcium carbonate, mica, pyrophyllite, talc, aluminum silicate and the like. May be used. These fillers can be used as a mixture of two or more kinds.

The maximum particle size of the filler used in the present invention is 6 μm.
m or less, the average particle size is preferably 2 μm or less, but the filler used this time is a fused silica as measured by a laser method,
The maximum particle size was 4.5 μm, the average particle size was 1 μm, and in the case of alumina, the maximum particle size was 1 μm and the average particle size was 0.5 μm. This time, this was used at a weight ratio of 31:85.

The curing accelerator (d) has an average particle size of 3 so that the coating shape with a dispenser this time becomes uniform.
amine adduct (μm or less) (Ajinomoto AMICURE MY-
H) was used. However, the curing accelerator used for the sealing agent is not limited to this, and other than that, 2,4-diamino-
6- (2'-methylimidazolyl (1) ') ethyl-s
-Triazine / isocyanuric acid adduct, 2: 3 adduct of 2-methylimidazole isocyanuric acid, 2-phenylimidazole isocyanuric acid adduct, imidazoles and phthalic acid, isophthalic acid, terephthalic acid and the like.

In this case, N-phenyl-γ-aminopropyltrimethoxysilane (KBM-573, manufactured by Shin-Etsu Chemical Co., Ltd.) was used as the coupling agent (e). But,
The coupling agent used for the sealant is not limited to the aminosilane-based coupling agent, and may include a silicon-based coupling agent, a zirconium or aluminum-based coupling agent, and the like.

Further, in this case, propylene glycol monoethyl ether acetate was used as the solvent (f). However, the solvent used for the sealant is not limited to an acetate-based solvent, and may include an alcohol-based solvent, an ether-based solvent, and the like. These can be used alone or in combination of two or more at an arbitrary ratio.

The sealant prepared by mixing the above materials is applied to one of the opposing substrates by a dispenser. This time, it was applied to the TFT substrate side. At this time, an uncoated portion of the sealant is formed in a part of the peripheral edge, and is left as a liquid crystal injection port. The sealant is discharged from the tip of the syringe needle using high purity nitrogen gas evaporated from liquid nitrogen. The syringe barrel used this time has an inner diameter of 1.7 mm and the inner diameter of the needle is φ
0.57 mm, and the pressure of nitrogen was about 4 kgf / cm2. The adsorbent was also applied on the same substrate on which the sealant was applied using a dispenser. The syringe used had an inner diameter of 9.1 mm and the inner diameter of the needle was 0.21 m
The pressure of m and nitrogen was about 1.5 kgf / cm2. The syringe barrel for the adsorbent was made of Pyrex glass which had been heated in a nitrogen atmosphere at 300 ° C. for 2 hours in advance.
The tip of the adsorbent needle was placed 0.9 mm away from the end of the sealant on the display section side to the display section side, and the adsorbent was applied almost continuously (FIG. 3).

It was previously confirmed by a simple experiment that when the adsorbent was applied to this position, the sealant spread during the gap setting step and almost came into contact with the adsorbent.

Next, in the sealant drying step, 100
After performing the solvent volatilization of the sealant by heating at 15 ° C for 15 minutes,
The TFT substrate was superposed by aligning the color filter substrate and the pixel of the TFT substrate so as to correspond to each other. Note that spacer beads were semi-dry-dispersed on the color filter substrate so as to obtain a predetermined space (cell gap) between the color filter substrate and the TFT substrate. The dispersion method of the spacer beads may be a method such as dry dispersion. In this case, the facing distance between the facing substrates is set to 5.5 μm.

Thereafter, a liquid crystal composition was injected from the above-mentioned liquid crystal injection port to fill the space between the opposing substrates, and this time the injection port was sealed using an ultraviolet curable resin (3026B) made by Three Bond. In addition, as the sealing resin, an ultraviolet curable resin such as Sekisui Fine Chemical Photolec (A-718-120) may be used. When applying the sealing resin, the liquid crystal display element was pressurized so that the substrate spacing of the liquid crystal display element was adjusted to be uniform in the plane. In addition,
As the liquid crystal composition used in the present invention, known liquid crystal compositions can be used. For example, cyano diameter, fluorine type, biphenyl type, ester type, cyclohexane type, phenylcyclohexane type, Schiff base type, ferroelectric liquid crystal, Ferroelectric liquid crystals and the like can be given.

In the second embodiment, as shown in FIG. 1, contrary to the first embodiment, the step of applying the adsorbent is performed after the step of volatilizing the solvent of the sealant. Regarding the details of the implementation, the parts other than the reversal of the two steps were exactly the same.

FIG. 4 is a cross-sectional view of an essential part for explaining the structure of an example of a liquid crystal display device manufactured according to the present invention.

At the stage where the LCD process has been completed and the module process has been completed as described above, there is almost no difference between the display characteristics of the liquid crystal display device manufactured by the conventional manufacturing method and the liquid crystal display device manufactured by the manufacturing method of the present invention. Was not observed. Next, 20 liquid crystal display elements manufactured by the conventional manufacturing method, 20 liquid crystal display elements manufactured by the manufacturing method of the first embodiment of the present invention, and 20 liquid crystal display elements manufactured by the manufacturing method of the second embodiment.
A total of 60 units were driven in a constant temperature bath at 70 ° C. to perform a continuous energization acceleration test of the liquid crystal display device. In all of the devices manufactured by the conventional manufacturing method, display unevenness occurred almost in 600 hours within the shape of the applied sealant. on the other hand,
Regarding those produced by the production method of the present invention,
No display unevenness occurred at the end of the 600 hour test. FIG. 5 shows the relationship between the continuous energization acceleration test time and the cumulative occurrence rate of display unevenness.

In the liquid crystal display device manufactured in Example 1, 62
At the end of the 4-hour test, display unevenness almost conforming to the shape of the applied sealant occurred in the liquid crystal display device manufactured in Example 2 only at the end of the 936-hour test. When the liquid crystal display element in which display unevenness occurred was disassembled, the adsorbent was not continuously applied, and several liquid crystal display elements were spaced apart by two or more pixels at several places.

It can be seen that the occurrence rate of display unevenness is much lower in the liquid crystal display device manufactured by the manufacturing method of the present invention than in the liquid crystal display device manufactured by the conventional manufacturing method.

[0045]

As described above with reference to the embodiments,
According to the present invention, it is possible to prevent a sealant component applied for bonding a pair of opposed substrates and sandwiching liquid crystal between the opposed substrates from being eluted into the liquid crystal layer.
The present invention enables the production of a liquid crystal display element with extremely little contamination of the liquid crystal layer in the production process and, in turn, the use of the liquid crystal display element, and provides a liquid crystal display element with high display reliability.

[Brief description of the drawings]

FIG. 1 is a schematic view of a conventional liquid crystal display element and a manufacturing process (LCD process) of the present invention.

FIG. 2 is a side sectional view of an adsorbent aging method used in Examples 1 and 2 of the present invention.

FIG. 3 is a schematic diagram showing a positional relationship between a sealant and an adsorbent used in Examples 1 and 2 of the present invention.

FIG. 4 is a cross-sectional view of a principal part explaining a structure of an example of a liquid crystal display element manufactured according to the present invention.

FIG. 5 is a graph showing a relationship between a continuous energization acceleration test time and a display defect occurrence rate (cumulative occurrence rate) of a liquid crystal display element manufactured through a conventional manufacturing process and a manufacturing process of the present invention.

[Explanation of symbols]

1: Pyrex glass tube, 2: glass fiber, 3
... Adsorbent, 4 ... Sealant applied on TFT substrate,
5 ... Adsorbent applied on TFT substrate, 6 ... Sealant after substrate overlap, 7 ... Adsorbent after substrate overlap, 8
... spacer beads, 9 ... liquid crystal layer.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takashi Inoue 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture F-term in Hitachi, Ltd. Production Research Laboratory 2H089 HA15 KA11 KA15 LA07 LA19 LA46 MA16Y NA24 NA25 NA41 NA53 NA56 PA16 QA08 QA12 QA13 QA16 RA04 RA18 SA01 TA04 TA06 TA09 5C094 AA03 AA31 AA43 AA48 AA54 BA03 BA43 CA19 DA12 EB02 EC02 EC03 FB01 FB02 FB15 GB01

Claims (8)

[Claims] 1. A liquid crystal display element in which one substrate having a liquid crystal control element and a pixel electrode and another substrate are opposed to each other at a predetermined interval, and a liquid crystal is sandwiched between the pair of opposed substrates and a peripheral portion is sealed. 3. The liquid crystal display device according to claim 1, wherein the liquid crystal layer contains particles having a property of adsorbing a substance. 2. A liquid crystal display device according to claim 1, wherein the particles having the property of adsorbing said substance have an electric resistivity higher than that of said liquid crystal. 3. A liquid crystal display device according to claim 2, wherein said particles having a property of adsorbing said substance are porous. 4. A liquid crystal display device according to claim 2, wherein the particle diameter of the particles having the property of adsorbing said substance is less than or equal to the distance between said pair of opposing substrates in the display portion of said liquid crystal display device. . 5. A liquid crystal display device according to claim 4, wherein the particles having the property of adsorbing said substance are substantially spherical. 6. A liquid crystal display device according to claim 1, wherein the particles having the property of adsorbing said substance are present only in the vicinity of the display portion side of said seal. 7. A liquid crystal display device according to claim 6, wherein the distance between particles having a property of adsorbing said substance does not exceed the size of two display pixels. 8. A liquid crystal display device according to claim 1, wherein after the step of volatilizing the solvent of the sealant, the step of applying particles having a property of adsorbing the substance to the substrate. A method for manufacturing a liquid crystal display element.