JPH0990369A - Production of liquid crystal display panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an excellent liquid crystal display panel without impairing display characteristics by controlling the amt. of finely particulate adhesive to a specified range for the distance between substrates and controlling the average particle size of the adhesive to a specified range for the substrate distance. SOLUTION: In this liquid crystal display panel, a finely particulate adhesive having a distribution of particle size is used. The optimum amt. of the adhesive inserted into the display panel is controlled to satisfy formula I: B×1.6×10<-4> <A<B×1.6×10<-2> , wherein A is the amt. of the finely particulate adhesive (mg/cm<2> ) and B is the distance (μm) between substrates. The optimum average particle size which does not decrease the effect of the adhesive is in the range to satisfy formula II: 1.2×B<C<10×(B)<1/3> , wherein B is the distance (μm) between substrates and C is the average particle size (μm). As for the finely particulate adhesive, it is preferably prepared by effecting the reaction of an epoxy resin or the like in a solvent by heating to obtain a half-hardened epoxy resin soln., then spraying and drying the soln. to obtain fine particles, classifying and separating particles having <=40% variation of particle size.

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 panel in which a liquid crystal material such as a ferroelectric liquid crystal or a nematic liquid crystal is enclosed in a gap between two substrates, and the gap between the two substrates is uniform on the order of μm. The present invention relates to a method for manufacturing a liquid crystal display panel using a fine particle adhesive suitable for spot adhesion for keeping the above.

[0002]

2. Description of the Prior Art A liquid crystal display panel in which a liquid crystal material such as a ferroelectric liquid crystal or a nematic liquid crystal is enclosed as described above
It is necessary to keep the distance between the two substrates uniform to about 2 to 5 μm. For that purpose, conventionally, hard spacers, that is, particles of silica or hard plastic formed into spherical particles of uniform size, or finely pulverized I've been using glass fiber.

However, the hard spacer is effective in maintaining a gap in the direction of compressing the liquid crystal, that is, against the compressive force from the outside of the two substrates, but does not have adhesiveness with the substrates. Therefore, the liquid crystal is weak in the direction in which the liquid crystal expands, that is, the force from the inside of the substrate, and the large-screen liquid crystal display panel has no reinforcing effect on the entire deflection and distortion.

As a measure against this problem, an idea of using a point adhesive spacer in addition to the silica spacer has been proposed (JP-A-57-29031 and JP-A-60).
-69632 and JP-A-62-174726). Epoxy resins, nylon resins and the like are disclosed as materials for the point adhesive spacers in these inventions.

[0005]

However, the liquid crystal display panel using the point-adhesive spacer has a problem in that it has a poor memory property and a low contrast, and a fine spot unfavorable for display may occur on the panel. there were. In order to solve this problem, many investigations have been conducted on the adhesive component in the past, but no satisfactory improvement has been made yet.

To solve this problem, the present inventors have studied from a completely different point of view, such as the amount of the particulate adhesive to be inserted. Since the adhesive is inserted in the gap between the substrates, the memory property and contrast performance of the liquid crystal display panel are deteriorated, and a large amount of fine-grained adhesives have a particle size considerably larger than the gap between the substrates. We have found that, when present, fine spots are likely to occur. Therefore, the present inventors further studied the optimum range of the amount of the fine particle adhesive that can solve the problems of the liquid crystal display panel.

On the other hand, the conventional point adhesive spacer usually has some interaction with the liquid crystal material and disperses a large amount of organic substances in the liquid crystal, so that the alignment property of the liquid crystal is not a little adversely affected. As a result, the display function, which is the most important function as a liquid crystal display panel, is deteriorated, and a solution to this point has also been demanded.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted tests and studies to solve the above-mentioned problems, and as a result, set the insertion amount of the particulate adhesive to a specific range according to the distance between the substrates, Furthermore, by setting the average particle diameter of the adhesive within a specific range according to the distance between the substrates, it becomes possible to produce a liquid crystal display panel that exhibits both the reinforcing effect of the panel and the display function, and further, it is possible to produce a fine particle adhesive. As a result, they have found that superior performance can be obtained by using a specific epoxy adhesive, and have completed the present invention. Hereinafter, the present invention will be described in detail.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In a liquid crystal display panel using the fine particle adhesive having a particle size distribution, the optimum insertion amount of the adhesive into the display panel is in the range represented by the following formula (1). . That is, the optimum insertion amount (A) of the adhesive is proportional to the substrate gap (B), and satisfies the following formula (1) obtained from a value obtained by multiplying the gap (B) by a coefficient obtained from an experiment. The liquid crystal display panel having the best adhesive effect and display function of the panel can be produced by inserting the fine particle adhesive within this range. If the insertion amount of the particulate adhesive is larger than this range, the glass substrate may be destroyed by the peeling force. As a result of examination, when this level of strength is reached, the display function of the liquid crystal display panel deteriorates. Was found to happen. On the other hand, if the amount is less than this range, the effect of the adhesive cannot be expected, and any of them is ineligible. B × 1.6 × 10 ⁻⁴ <A <B × 1.6 × 10 ⁻² (1) A: Insertion amount of fine particle adhesive (mg / cm ² ) B: Distance between substrates (μm)

Since the fine particle adhesive has a particle size distribution,
There are particles with a particle size that deviates from the average particle size. At this time,
Particles smaller than the distance between the two substrates do not function as an adhesive because they adhere only to one side of the substrates, and conversely deteriorate the display function of the panel. The particles, which are considerably larger than the distance between the substrates, have a size such that the cured product of the adhesive can be easily confirmed with the naked eye after heating and curing, and appear as fine spots on the liquid crystal display panel.

For these reasons, particles having a particle size deviating from the average particle size reduce the effect of using the adhesive agent. It has been found that there is a specific range of average particle size that does not reduce. That is, when the optimum average particle size is within the range that satisfies the following formula (2), most of the particles are larger than the thickness of the substrate, and most of the particles are so large that they can be easily confirmed by the naked eye. Then, by inserting a fine particle adhesive having an average particle diameter within this range, it becomes possible to manufacture a liquid crystal display panel having an excellent panel adhesion effect and an excellent display function. 1.2 × B <C <10 × (B) ^1/3 (2) B: substrate spacing (μm), C: average particle size (μm)

When the average particle size is smaller than this range, the display function such as contrast of the liquid crystal display panel is deteriorated, while when it is larger than this range, the liquid crystal display is caused by an adhesive cured product of a size which can be easily confirmed by the naked eye. Neither is preferable because a fine spot that is not preferable for display appears on the panel.

The fine particle adhesive used in the present invention includes:
Epoxy resin and dicyandiamide are heated and reacted in a solvent to form a solution of a semi-curable epoxy resin (hereinafter referred to as “semi-curable epoxy resin”), which is spray-dried and fine particles obtained by removing the solvent, Particle size fluctuation rate is 40
% Of fine particles is used, the above-mentioned point adhesive spacer (Japanese Patent Laid-Open No. 57-2903) is used.
1, JP-A-60-69632 and JP-A-62-174
726), the adhesive effect with the substrate is high, the adhesive force is increased, and a small amount of adhesive is required to be inserted into the liquid crystal display panel, which is preferable. It has the feature of hardly disturbing the orientation.

The epoxy resin is a compound having one or more epoxy groups in one molecule, and examples thereof include bisphenol A, bisphenol F, phenol novolac resin or bisphenol which is a polycondensate of cresol novolac resin and epichlorohydrin. A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin or cresol novolac type epoxy resin, polyhydric alcohol such as (poly) ethylene glycol or glycerin, or amine compound such as aniline or diaminodiphenylmethane and epichlorohydrin Examples thereof include condensates, and these may be used as a mixture of plural kinds.

In addition to these general epoxy resins, for example, diglycidyl ether of polyethylene glycol or polypropylene glycol, glycidyl ester of higher fatty acid, or special epoxy resin such as glycidylamine type epoxy is used, and heat resistance and flexibility after curing are improved. It may be added for the purpose of imparting properties.

Among these epoxy resins, the softening point by the ring and ball method (RB softening point based on JIS-K-7234 (hereinafter referred to as “R
"B softening point". )) Is preferably 60 to 120 ° C., more preferably an RB softening point of 75 to 100.
Epoxy resin at ℃. If the RB softening point is lower than 60 ° C., the particles of the dried semi-curable epoxy resin are likely to be fused, and it is difficult to obtain stable spherical particles in the spray drying described below. If the softening point is higher than 120 ° C., the liquid crystal display panel is used. It becomes difficult to melt the semi-cured epoxy resin and press-bond it to a predetermined substrate interval in the step of assembling.

As the epoxy resin having a softening point in this range, for example, a bisphenol A type epoxy resin or a bisphenol F type epoxy resin having an epoxy equivalent of 200 to 900 and a molecular weight (weight average molecular weight; hereinafter the same) of about 800 to 2000, or Epoxy equivalent 170 to 23
Examples thereof include a phenol novolac type or cresol novolac type epoxy resin having a molecular weight of 0 and a molecular weight of about 600 to 1800.

In the present invention, the epoxy resin and the curing agent are uniformly blended, and a semi-cured epoxy resin which is a reaction product of both is spray-dried from the solution, preferably 1.0 to
It is desirable to form fine particles of 20 μm, and in addition, in order to perform spray drying, it is necessary to form a solution having a low viscosity. Therefore, the curing agent for the epoxy resin used is required to have the condition that the semi-curable epoxy resin is stable in the solution.

In the present invention, dicyandiamide is preferable as a curing agent satisfying this condition. Dicyandiamide is
Higher adhesive strength than other latent curing agents such as amine-based or phenol-based curing agents, or two-pack type curing agents, and the spacers after final heat curing may disturb liquid crystal alignment. It has the feature that it is rare.

The present invention is characterized by using a solution of a reaction product (semi-cured epoxy resin) obtained by previously reacting an epoxy resin and dicyandiamide by heating for the following reason. Since epoxy values and solubility parameters of epoxy resin and dicyandiamide are originally different, it is difficult to select a solvent suitable for both. From the viewpoint of solubility, the solvent used is preferably an ester or ketone solvent for the epoxy resin, while the dicyandiamide is preferably a highly polar solvent such as dimethylformamide, dimethylacetamide or N-methylpyrrolidone.

When each of the epoxy resin and dicyandiamide is dissolved in a suitable solvent and then mixed to form one liquid, crystals of dicyandiamide are likely to precipitate, and the epoxy resin and dicyandiamide are likely to be non-uniform. Therefore, when a solution of an epoxy resin and dicyandiamide is mixed, a heat treatment is performed to cause a reaction in advance, and further 50% or more of tetrahydrofuran is added, the resulting semi-curable epoxy resin solution is stable. If a solution is used, fine particles having a uniform composition can be prepared.

Next, the method and conditions for the reaction between the epoxy resin and dicyandiamide in the present invention will be described. The epoxy resin is dissolved in a solvent in advance and the solid content concentration is 30 to 5
It is preferable to prepare a 0% solution. Methyl ethyl ketone is optimal as the solvent in terms of boiling point and solubility. On the other hand, dicyandiamide is difficult to dissolve unless it is a highly polar solvent such as dimethylformamide, dimethylacetamide or N-methylpyrrolidone as described above, and it is preferable to dissolve it in these solvents to obtain a solid content concentration of about 20 to 40%. Solution.

Further, in the present invention, in addition to the epoxy resin and the curing agent, it is preferable to use a curing accelerator for the purpose of lowering the temperature at the time of finally heating and curing the particulate adhesive obtained in the present invention. . Examples of the curing accelerator include tertiary amine-based compounds and phosphine-based compounds, but amine-based imidazole compounds are most preferred from the viewpoint of storage stability of the solution and curing-accelerating effect. Specific examples include 1-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 1-benzyl-2-methylimidazole and 1-phenylimidazole. These imidazole compounds are easily dissolved in methyl ethyl ketone to obtain a solution having a solid content concentration of about 30 to 50%.

A solution of each of the above-mentioned epoxy resin, curing agent and curing accelerator added as necessary is mixed,
As described above, the stability of the solution is poor as it is, and particularly dicyandiamide is likely to precipitate in a solvent mainly containing methyl ethyl ketone. Therefore, in the present invention, the mixed solution is heated to add dicyandiamide to the epoxy group of the epoxy resin. , A semi-curable epoxy resin (so-called B stage). The reaction conditions are 70 to 90 under normal pressure.
A reaction time of 2 to 10 with a condenser installed at reflux at ℃
Time is appropriate. When methyl ethyl ketone is used as a solvent, its boiling point is about 79 ° C., but the solution can be heated to about 90 ° C. even under normal pressure due to the increase in boiling point.

The amount of dicyandiamide blended is preferably smaller than the amount calculated from the epoxy equivalent, which is usually used, in order to obtain a high adhesive strength with the substrate. When expressed in terms of solid content, epoxy is used. 2 to 5 parts by weight of dicyandiamide is preferable with respect to 100 parts by weight of the resin. 5
If the amount is more than parts by weight, the cured product becomes too hard and the adhesive strength becomes weak, and gelation tends to occur when the reaction is performed in a solvent. On the other hand, if the amount is less than 2 parts by weight, curing will be insufficient and it will be difficult to obtain sufficient adhesive strength.

The amount of the curing accelerator added is such that the fine particle adhesive obtained in the present invention has a curing temperature of 120 to 130 ° C.
It is preferable to prepare such that curing is completed within 30 minutes, and the amount thereof is, for example, 2-ethyl-4- as a curing accelerator.
When using methylimidazole, a curing accelerator of 0.1 to 0.5 is added to 100 parts by weight of the epoxy resin.
The range is parts by weight. If it exceeds 0.5 parts by weight, the storage stability of the solution will be poor, and if it is less than 0.1 part by weight, the accelerating effect will be insufficient, and the curing temperature will be high or it will take a long time to cure. Become.

One of the features of the present invention is that the semi-curable epoxy resin solution is spray-dried to form fine particles. By obtaining fine particles having a substantially spherical shape by spray drying, the accuracy of classification described later is increased, and a sharp particle size distribution with a small particle size variation rate is possible. The semi-cured epoxy resin solution used for spray drying needs to have a sufficiently low viscosity for spraying from a nozzle and atomization, and the viscosity measured by a B-type viscometer at room temperature is 50 cps.
It is preferably (centipoise) or less. In order to achieve this viscosity range, the solution of the semi-cured epoxy resin after the reaction is preferably diluted with methyl ethyl ketone and tetrahydrofuran to adjust the solid content concentration to 15 to 30% by weight. In order to control the particle size of the fine particles to be molded to 2 to 10 μm, which is suitable for the fine particle adhesive for liquid crystal elements, the more preferable solid content concentration is 15 to 25% by weight.

The temperature conditions for spray drying are hot air temperature 50 to 8
0 ° C. is preferable, and when the temperature is lower than 50 ° C., the drying is insufficient and the solvent remains. When the temperature exceeds 80 ° C., fine particles of the dried semi-curable epoxy resin are fused to each other, and uniform spherical particles are difficult to obtain.

Further, in the present invention, from the fine particles obtained by spray-drying the solution of the semi-curable epoxy resin, the fine particles having a particle size variation rate of 40% or less are fractionated as an object. The particle size variation rate is a value obtained by dividing the standard deviation of the particle size distribution by the average particle size in terms of weight (hereinafter simply referred to as “average particle size”). The most suitable classification method is a wind-powered classification using a cyclone or the like. According to the present invention, the particle size variation rate can be changed, and the particle size variation rate can be made smaller.
It is possible to make the cut points of the coarse powder and the fine powder closer to each other, or to repeat the classification operation. However, reducing the particle size variation rate lowers the yield of the classified powder accordingly, so the particle size variation rate is 20 to 40%.
It is appropriate to set to. According to the present invention, the standard deviation is 0.8 μm when the average particle size is 2 μm, the standard deviation is 2.0 μm when the average particle size is 5 μm, and the average particle size is 1
It is possible to obtain fine particles having a standard deviation of 4.0 μm in the case of 0 μm.

The powder obtained by spray drying is from 0.05 to
By surface-treating with about 0.5% by weight of ultrafine particulate anhydrous silica, aggregation is loosened, fluidity is improved, and classification is facilitated. The ultrafine particulate anhydrous silica used here constitutes the particulate adhesive of the present invention in a state of being attached to the fine particles of the semi-curable epoxy resin, and is integrated with the epoxy resin during the final curing. To be done.

The obtained fine particle adhesive and the hard spacer are inserted into the gap between the two substrates arranged to face each other, and the former fine particle adhesive is heat-cured to bond the two substrates. A liquid crystal display panel is obtained by enclosing a liquid crystal in the gap. The heat curing condition is 130 to 170 ° C.
It is preferably about 20 minutes to 2 hours. The heating method is preferably a method in which the substrate is hot pressed. In this step, after the semi-curable epoxy resin is slightly cured, it is crosslinked and cured, and at the same time, it firmly adheres to the two substrates. The hard spacer has a role of keeping the distance between both substrates constant against hot pressing.

[0032]

The present invention will be described in more detail with reference to the following examples. Example 1 (Preparation of semi-curable epoxy resin) 20 weight of cresol novolac type epoxy resin (EOCN-103S manufactured by Nippon Kayaku Co., Ltd. (RB softening point: 80 ° C., epoxy equivalent: 220 g / eq)) was used as an epoxy resin. Part, bisphenol A type epoxy resin (DER-made by Dow Chemical Japan Co., Ltd.)
661 (RB softening point: 80 ° C., epoxy equivalent: 530 g
/ Eq)) was dissolved in a total of 100 parts by weight of 80 parts by weight in 200 parts by weight of methyl ethyl ketone (solution A). Also,
As a curing agent, 4 parts by weight of dicyandiamide was dissolved in 12 parts by weight of dimethylformamide (solution B). Next, 0.3 part by weight of 2-ethyl-4-methylimidazole as a curing accelerator was dissolved in 0.6 part by weight of methyl ethyl ketone (solution C). Liquid A, liquid B and liquid C were all mixed, heated to 80 ° C. under reflux in a reaction vessel, reacted for 3 hours, cooled to room temperature, filtered with a 25 μm filter, and semi-cured epoxy resin. A solution of

(Spray drying) Methyl ethyl ketone was further added to the solution obtained above to dilute it to a solid content concentration of 20% by weight. This liquid was spray-dried with a spray dryer at a hot air temperature of 70 ° C. to obtain a powder. The powder thus obtained was
The powder was treated with 2% by weight of ultrafine particulate anhydrous silica (Aerosil RY-200 manufactured by Nippon Aerosil Co., Ltd.) using a Henschel mixer to improve the fluidity and dispersibility of the powder.

(Classification) Conditions were set based on the calculation formula when the fine powder cut line was 3 μm and the coarse powder cut line was 5.5 μm, and the above powder was subjected to each condition by a cyclone classifier. Then, a classification operation was performed once to obtain an epoxy resin fine particle adhesive for liquid crystal display panels, which was composed of spherical fine particles. The yield by classification with respect to the raw material powder was about 20%.

(Particle size distribution) The particle size distribution of the fine particle adhesive obtained by classification was measured by a laser light transmission type particle size distribution measuring device (LA-910 model, manufactured by Horiba Ltd.). The powder sample was dispersed in a 0.1% by weight aqueous surfactant solution. Regarding the particle size distribution, the average particle size was 4.5 μm and the standard deviation was 1.5 μm, and therefore the particle size variation rate was 33.3%.

(Evaluation of Adhesive Strength) Glass substrate for liquid crystal display panel (100 mm length × 100 mm width × 0.7 mm thickness)
In addition, 10 mg of silica fine particles (number average particle size 2.0 μm) as a hard spacer and 100 m of the fine particle adhesive
g total of 110 mg and isopropyl alcohol 100
and dispersed on the substrate by spin coating. At this time, the amount of silica fine particles dispersed on the substrate was 3.2.
× 10 ⁻⁴ mg / cm ² , the amount of the particulate adhesive is 4.0
It was × 10 ^-4 mg / cm ² . Wipe off the adhesive particles scattered from one piece of the substrate over a width of 5 cm, superimpose the substrate on which no adhesive has been dispersed on this substrate, and then cure by heat pressing for 30 minutes at 150 ° C. The substrates were bonded with an adhesive. A wedge was put between the two glass substrates, and how the glass plate was peeled off was observed. As a result, peeling was possible with an appropriate force. (Creation of liquid crystal display panel) A glass substrate on which the above-mentioned hard spacers and fine particle adhesives have been dispersed is overlaid with a substrate on which no adhesive has been dispersed, and then the substrate is cured by heat pressing at 150 ° C for 30 minutes to bond the substrate. After that, a liquid crystal material was enclosed to manufacture a liquid crystal display panel.

Examples 2 to 6 and Comparative Examples 1 and 2 The same as Example 1 except that the silica particle size (that is, the distance between the substrates), the amount of silica sprayed, the particle size of the adhesive and the amount of sprayed adhesive were changed as shown in Table 1. The adhesive strength was evaluated. The results are shown in Table 1. In addition, in each of the examples and comparative examples shown in Table 1, the amount of adhesive applied was adjusted by adjusting the amount of adhesive dispersed in isopropyl alcohol.

[0038]

[Table 1]

Examples 7 to 12, Comparative Examples 1 and 2 (Observation of cured product) The fine particle adhesive prepared in Example 1 was used, and the silica particle size (that is, the distance between the substrates), the amount of silica sprayed,
By changing the adhesive particle size and the adhesive spray amount as shown in Table 1,
From one side of the above-mentioned two glass plates adhered, the number of cured adhesives, which was easily confirmed by the naked eye, was observed. The results are shown in Table 2.

[0040]

[Table 2]

[0041]

According to the manufacturing method of the present invention, an excellent liquid crystal display panel can be obtained without impairing display characteristics.

Claims (3)

[Claims] 1. A hard spacer and a fine particle adhesive are inserted into a gap between two substrates which are arranged facing each other, and the two substrates are adhered by heat curing of the adhesive, and a liquid crystal is filled in the gap. In the manufacturing method of the liquid crystal display panel formed by encapsulation,
The insertion amount (A) of the adhesive with respect to the space (B) between the substrates
A method of manufacturing a liquid crystal display panel, characterized in that the range of the following expression (1) is satisfied. B × 1.6 × 10 ⁻⁴ <A <B × 1.6 × 10 ⁻² (1) A: Insertion amount of fine particle adhesive (mg / cm ² ), B: Distance between substrates (μm) 2. The liquid crystal display according to claim 1, wherein the fine particle adhesive has a number-converted average particle diameter (C) in a range satisfying the following formula (2) with respect to the substrate spacing (B). Panel manufacturing method. 1.2 × B <C <10 × (B) ^1/3 (2) B: substrate spacing (μm), C: average particle size (μm) 3. A fine particle obtained by subjecting an epoxy resin and dicyandiamide to a heat reaction in a solvent to form a semi-cured epoxy resin solution, spray-drying the solution, and removing the solvent to obtain a particle size variation rate of 40% or less. 3. The method for producing a liquid crystal display panel according to claim 1, wherein a fine particle adhesive obtained by separating the fine particles of 1. is used.