JPH095762A - Liquid crystal panel manufacturing method - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent display unevenness on the panel surface due to the influence of various impurities existing in the liquid crystal panel manufacturing atmosphere. [Structure] Alignment-treated 2 on transparent electrode patterns 3 and 4
The bonding speed at the time of holding the liquid crystal 8 between the glass substrates 1 and 2 by the dropping method is made sufficiently slow, and the liquid crystal is held at a temperature equal to or higher than the clearing point of the liquid crystal. [Effect] By suppressing the influence of external energy which is exerted when the liquid crystal spreads on the substrate, impurities existing in the liquid crystal or on the substrate are not unevenly distributed macroscopically in the panel surface, and display unevenness does not occur uniformly. It is possible to manufacture various liquid crystal panels.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a liquid crystal panel, and more particularly to uniforming the display of the liquid crystal panel.

[0002]

2. Description of the Related Art A liquid crystal display device is a display device in which the initial alignment direction of a liquid crystal is changed to another alignment state by an action utilizing the anisotropy of the liquid crystal, and a change in optical characteristics accompanying the change is performed. Compared with conventional display devices, it can be driven at a lower voltage, is suitable for driving LSIs, is a low power consumption type, and can be thinner and lighter. Aiming to be installed in OA equipment, it is being developed and commercialized.

Currently, a simple matrix type Super Twisted Nematic (STN) type display device utilizing the change of the alignment state of liquid crystal by applying an electric field, that is, an electro-optical characteristic is mainly used, and an active matrix type thin film transistor (TFT) type display device. The device follows. The liquid crystal display device is a sandwich type in which a liquid crystal is sandwiched between two glass substrates having a transparent electrode film formed thereon, and a polymer thin film for aligning the liquid crystal is formed on the transparent electrode film. In the case of the STN type display device, the cell thickness between the two substrates is about 5 to 7 μm, and the alignment of the liquid crystal is controlled by rubbing on the polymer thin film.
The pretilt angle (the rising angle formed by the substrate and the liquid crystal molecules) is about 3 to 8 °. The STN type display device utilizes the birefringence of liquid crystal and the optical rotation of light.
Since it is possible to obtain a remarkably steep threshold characteristic by twisting the orientation direction of the liquid crystal between the substrates of 180 ° to 270 °, the cell thickness requires an accuracy of 0.05 to 0.1 μm.

The optical characteristics of the liquid crystal panel are obtained by the birefringence and dielectric anisotropy of the liquid crystal molecules. In addition, the optical characteristics of the liquid crystal panel are changed by adjusting the composition of the liquid crystal material used, including the viscosity and elastic constant, and the ratio of the components. At present, various liquid crystal materials have been developed, and it is possible to obtain desired characteristics by mixing the liquid crystal materials.

Usually, a desired liquid crystal in which several or more kinds of liquid crystal molecules are mixed is sandwiched between two substrates by a dropping method (JP-A-63-179328) or a vacuum injection method. The liquid crystal dropping method is a method in which a spacer is dispersed on one glass substrate and liquid crystals prepared in several syringes are dropped on the other glass substrate with a constant pulse.

[0006]

At present, when a liquid crystal panel is manufactured by a liquid crystal dropping method, the liquid crystal is dropped on one of two substrates that have been subjected to an alignment treatment in order to hold the liquid crystal, and a pair is formed. A liquid crystal panel is produced by leaking after bonding the other substrate in a vacuum atmosphere. However, the bonding speed of the two substrates depends on the natural falling speed of the substrates and the external pressure due to the leak from the vacuum state, and the bonding speed has not been particularly adjusted.

By the way, on the substrate and the liquid crystal before bonding, impurities exist according to the atmosphere at the time of manufacturing the panel. When this impurity is dissolved or dispersed in the liquid crystal, a concentration distribution of the impurity occurs on the substrate when the liquid crystal expands and spreads. At this time, the concentration distribution of the impurities becomes more remarkable by forcibly and rapidly spreading the liquid crystal dropped on the substrate.

Such a chromatographic phenomenon causes a pretilt change of the alignment film and formation of an electric double layer within the liquid crystal panel surface, and there is a problem that display unevenness occurs within the liquid crystal panel surface due to the change in threshold value. . This chromatographic phenomenon depends not only on the amount of impurities in the liquid crystal or on the substrate, the solubility in the liquid crystal, the adsorptivity of the substrate surface, but also the spreading speed of the liquid crystal and the flow direction.

In view of such a point, the present invention controls the external stress applied to the liquid crystal and the spreading speed of the liquid crystal on the substrate in the process of sandwiching the liquid crystal between the two substrates, thereby controlling the liquid crystal panel surface. It is an object of the present invention to provide a manufacturing method capable of preventing the occurrence of a biased impurity concentration distribution within a liquid crystal panel and obtaining a liquid crystal panel with a uniform display in the plane of the liquid crystal panel.

[0010]

In order to achieve the above object, the present invention is a substrate in a liquid crystal panel in which a liquid crystal is sandwiched by a liquid crystal dropping method between two substrates on which an electrode pattern is oriented. In the bonding step, the speed at which the liquid crystal expands and spreads between the two substrates is adjusted by adjusting the bonding speed, thereby reducing display unevenness associated with the liquid crystal dropping method.

[0011]

According to the present invention, by adjusting the spreading speed of the liquid crystal sufficiently slowly, the impurities dissolved and dispersed in the liquid crystal are abruptly exposed to external energy, that is, parallel to the surface of the substrate due to pressing in the direction perpendicular to the substrate. Macroscopically, it spreads on the substrate while remaining uniformly in the liquid crystal macroscopically.
In addition, since the spreading speed of the liquid crystal slows down, the energy received by the impurities on the substrate from the liquid crystal also decreases, and the concentration of impurities remaining at existing positions on the substrate is not affected by the flow of liquid crystals even at the physical adsorption level. Not involved in distribution.

Further, when the substrates are bonded at a temperature equal to or higher than the clearing point of the liquid crystal to hold the liquid crystal, the solubility of impurities in the liquid crystal is increased. That is, the influence on the instability of the molecular alignment caused by the presence of impurities in the liquid crystal is weakened, and the impurities in the liquid crystal are unlikely to be separated or unevenly distributed even if the liquid crystal is subjected to an excessive external stress.

Therefore, by spreading the liquid crystal sufficiently gently on the substrate, the bias of the impurity concentration distribution on the substrate is suppressed,
The display quality of the panel is prevented and the display quality is made uniform. By sandwiching the liquid crystal at a temperature equal to or higher than the clearing point of the liquid crystal, the effect of spreading the liquid crystal sufficiently slowly on the substrate is further enhanced.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a process drawing showing a liquid crystal panel manufacturing method in the first and second embodiments of the present invention.

(Example 1) First, as shown in FIG. 1 (1), an alignment film 6 (polyimide alignment film) was formed on each of the glass substrates 1 and 2 provided with transparent electrode patterns 3 and 4 by flexographic printing. After forming and thermosetting, the surface is rubbed to give orientation. At this time, an alignment treatment is performed between the opposing substrates in a direction in which the molecules of the liquid crystal 8 shown in FIG. 3 to be described later are twisted by 240 °, and the glass substrate 1 is uniformly dispersed with a spacer 7 of 7.0 μm shown in FIG. 3 to be described later. Let

Next, the other glass substrate 2 is placed on the dropping stage 10, and the liquid crystal 8 containing the chiral agent (nematic liquid crystal) sucked into the three glass syringes housed in the dropping syringe 9 on the glass substrate 2. Is dripped. UV curable resin is used for the sealing agent 5 shown in FIGS.
After the spacer 7 is contained at a ratio of 1.5 wt% in advance, it is printed on the substrate in which the spacer 7 is dispersed by screen printing.

Next, as shown in FIG. 1B, a vertically movable pin 12 is placed on the substrate bonding stage 11 at a position 10 mm above the glass substrate 2 so that the glass substrate 1 is parallel to the glass substrate 2.
Then, the inside of the vacuum chamber 14 is evacuated by the vacuum pump 15. After that, the vertically movable pin 12 is gently lowered at a speed of 5 mm / sec, and the glass substrates 1 and 2 are bonded together as shown in FIG. 1 (3).

By making it possible to adjust the bonding speed when the glass substrates 1 and 2 are bonded to each other sufficiently slowly, the spreading speed of the liquid crystal 8 on the substrate can be made sufficiently slow, and this process is performed to make the liquid crystal transparent. It is characterized in that it is performed at more points.

Next, as shown in FIG. 1C, the vertically movable pin 12
Is further lowered, the bonded glass substrates 1 and 2 are leaked, and the sealing agent 5 shown in FIGS. As a result, a liquid crystal panel as shown in the plan view of FIG. 2 and the sectional view of FIG. 3 can be manufactured.

2 and 3, 1 is a glass substrate provided with the segment electrode 3, 2 is a glass substrate provided with the common electrode 4, and in FIG. 1, the segment electrode 3 and the common electrode 4 are shown. Simply transparent electrode pattern 3, 4
I am calling. 5 is a sealant using a UV curable resin, and a liquid crystal 8 containing a spacer 7 as shown in FIG.
Seal around the. Reference numeral 6 is an alignment film provided on the segment electrodes 3 and the common electrode 4 on the glass substrates 1 and 2.

As a result of applying a static waveform to the liquid crystal panel shown in FIG. 2 and FIG. 3 and evaluating the lighting of the liquid crystal panel, there is almost no display unevenness depending on the liquid crystal dropping position, and the threshold voltage between the dropping position and its surroundings. (The voltage at which the maximum transmittance is 100% and the transmittance is 10%) The difference was 10 mV or less.

(Embodiment 2) A heater 13 is provided below the substrate bonding stage 11 of FIG. 1 (2) in the embodiment 1, and the surface temperature of the stage is set to a temperature not lower than the clearing point of the liquid crystal 8 to be dropped. The same work as in Example 1 was performed. as a result,
Display unevenness did not occur at all, and it was not detected as a threshold voltage difference between the dropping position and its periphery.

Comparative Example 1 The glass substrate 1 is replaced with the glass substrate 2
The sample was naturally dropped from a position 10 mm above and the same evaluation as in Example 1 was carried out. As a result, display unevenness depending on the dropping position occurred, and a threshold difference of about 30 mV was confirmed between the dropping position and its periphery. .

[0024]

As described above, in the method for manufacturing a liquid crystal panel of the present invention, the substrate bonding speed of the liquid crystal panel is sufficiently slowed down, and in some cases, the bonding is performed at a temperature above the clearing point of the liquid crystal. Thus, it is possible to manufacture a uniform liquid crystal panel without the display unevenness on the panel surface that occurs in the conventional dropping method.

[Brief description of drawings]

FIG. 1 is a process drawing showing a method for manufacturing a liquid crystal panel in first and second embodiments of the present invention.

FIG. 2 is a plan view of a liquid crystal panel manufactured by the method of the present invention.

3 is a cross-sectional view of the liquid crystal panel of FIG.

[Explanation of symbols]

1 ... Segment electrode side glass substrate, 2 ... Common electrode side glass substrate, 3 ... Segment electrode, 4 ... Common electrode, 5 ... Spacer-containing UV curable resin sealant,
6 ... Alignment film, 7 ... Spacer, 8 ... Liquid crystal, 9 ... Dropping syringe, 10 ... Dropping stage, 11 ... Substrate bonding stage, 12 ... Vertically movable pin, 13 ... Heater,
14 ... vacuum chamber, 15 ... vacuum pump.

Claims (2)

[Claims] 1. A substrate bonding step in a liquid crystal panel in which a liquid crystal is sandwiched by a liquid crystal dropping method between two substrates whose alignment is performed on an electrode pattern, by adjusting the bonding speed. A method for manufacturing a liquid crystal panel, characterized in that the display unevenness associated with the liquid crystal dropping method is reduced by controlling the speed at which the liquid crystal expands and spreads between the two substrates. 2. The method for producing a liquid crystal panel according to claim 1, wherein the liquid crystal is sandwiched between two substrates at a temperature equal to or higher than the clearing point of the liquid crystal.