JPH08146373A - Production of liquid crystal display panel - Google Patents

Abstract

PURPOSE: To prevent sticking by rapidly eliminating the electrification of a liquid crystal display panel. CONSTITUTION: A pair of substrates provided with at least electrodes are formed by first executing a substrate forming stage. Next, the surfaces of the respective substrates are coated with oriented films and these oriented films are subjected to rubbing by executing an orientation treating stage. In succession, panel assembling stage is executed to join a pair of substrates via a prescribed spacing and to seal liquid crystals in the spacing to assemble the liquid crystal display panel. Finally, an electric discharge accelerating stage is executed to expose the liquid crystal display panel to a high-temp. atmosphere and to accelerate the discharge of the charges electrified on the substrates in the previous stage. The electric discharge accelerating stage accelerates the discharge more by resting the liquid crystal display panel in a highly moist atmosphere by case. The electric discharge accelerating stage is also commonly usable to execute, for example, a heat treatment to stabilize the orientation of the sealed liquid crystals. The stage may be otherwise executed as an additional treatment separately from the heat treatment to stabilize the orientation of the sealed liquid crystals.

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 display panel. More specifically, the present invention relates to a method of removing static electricity after injecting and sealing liquid crystal into a panel.

[0002]

2. Description of the Related Art A general method of manufacturing a conventional liquid crystal display panel will be briefly described with reference to the flowchart of FIG.
First, in step R1, a pair of substrates provided with at least electrodes and made of glass or the like is prepared. Next, in step R2, the surface of each substrate is coated with an alignment film such as polyimide. Then, in step R3, the surface of the alignment film is rubbed to perform a desired alignment treatment. As shown in the figure, in this rubbing, the surface of the alignment film applied to the glass substrate is rubbed with a rubbing roller. A buff material is attached around the rubbing roller, and the alignment film is rubbed along the rotation direction and the moving direction of the rubbing roller. At this time, charging and polarization occur in the alignment film due to friction between the buff material and the alignment film. Next, in step R4, a sealing material is printed on one of the glass substrates. Next, in step R5, the pair of glass substrates are superposed on each other and bonded to each other via a sealing material. When the upper and lower substrates are overlapped with each other, a flow of air is generated in the gap as shown in the figure, which charges or polarizes the alignment film. Then, in step R6, the large glass substrate is divided into individual panels. In the next step R7, liquid crystal is injected and sealed in the panel. Finally, the liquid crystal display panel thus assembled is heat-treated to stabilize the alignment state of the liquid crystal.

[0003]

As described above, in the conventional liquid crystal display panel manufacturing method, the rubbing in step R3 causes the alignment film to be charged or polarized due to the friction between the buff material and the alignment film. In addition, the alignment film is similarly charged or polarized by the flow of air generated in the gap between the two when the substrates are stacked in step R5. This state is shown in FIG. As shown in the figure, a transparent electrode 102 made of patterned ITO or the like is formed on the surface of the glass substrate 101. The surface is covered with an alignment film 103 made of polyimide or the like. The alignment film 103 is polarized by rubbing treatment or the like.

As described above, when the polarization of the alignment film occurs during the manufacturing process, as shown in FIG. 9, the DC component (0.1 to 0. 2V)
Is applied to further polarize the alignment film.
If the drive voltage AC is turned off or the amplitude of the drive voltage AC changes in this state, the previous display pattern does not completely disappear due to the influence of the residual DC component due to the polarization of the alignment film, which is a so-called burn-in phenomenon. Occurs.

The charging and polarization of the alignment film, which causes such a burn-in phenomenon, is not promptly removed in a state of being left unattended.
For example, a leaving time of about half a year is necessary. However, such long-term neglect is not practical in terms of shipping management.

[0006]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, it is an object of the present invention to provide a method for promptly removing charges remaining on a liquid crystal display panel after an assembling process. The following measures have been taken in order to achieve this object.
That is, the liquid crystal display panel is manufactured according to the present invention by the following steps. First, a substrate forming step of forming a pair of substrates provided with at least electrodes is performed. Next, an alignment treatment step of aligning the surface of each substrate is performed. Subsequently, a panel assembling step is performed in which the pair of substrates are bonded to each other through a predetermined gap and liquid crystal is sealed in the gap to assemble a liquid crystal display panel. Finally, the liquid crystal display panel is left in a high temperature atmosphere, and a discharge promoting step for promoting discharge of charges charged on the substrate in the previous step is performed.

[0007] In some cases, the discharge accelerating step further accelerates the discharge by leaving the liquid crystal display panel in a high temperature and high humidity atmosphere. The discharge promoting step can also serve as a heat treatment for stabilizing the orientation of the enclosed liquid crystal, for example. Alternatively, the discharge accelerating step can be performed as an additional treatment in addition to the heat treatment for stabilizing the orientation of the enclosed liquid crystal. The substrate forming step is a step of forming one substrate provided with a pixel electrode and a switching element for driving the pixel electrode and the other substrate provided with a counter electrode.

[0008]

According to the present invention, in the process of manufacturing a liquid crystal display panel, for example, when a heat treatment for the purpose of stabilizing the alignment of the liquid crystal is performed after the panel is assembled, it is humidified at the same time. That is, the liquid crystal display panel is left in a high temperature and high humidity atmosphere. Further, high temperature application or high temperature and high humidity application is performed even after the heat treatment for stabilizing the alignment or after the polarizing plate is attached to reduce the electric charge charged inside the liquid crystal display panel. By humidifying the panel during the heat treatment, the electric charge on the panel can be quickly discharged into the air. Even after the heat treatment of the panel, it is possible to remove the charge of the panel by applying high temperature or high temperature humidification. As described above, by discharging the charge in the panel, it is possible to significantly reduce image deterioration such as burn-in, which has been a problem in the past.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a process diagram showing a liquid crystal display panel manufacturing method according to the present invention. First, in step S1, a pair of substrates provided with at least electrodes are prepared. Next, in step S2, the surface of each substrate is oriented. For example, an alignment film such as polyimide is applied to the surface of each substrate and rubbing is performed. In this alignment treatment step, the alignment film is charged and polarized. Subsequently, in step S3, the pair of substrates are bonded to each other with a sealing material or the like. Even when the two substrates are superposed on each other, a flow of air occurs along the alignment film, so that charging and polarization may occur. Further, in step S4, liquid crystal is injected and sealed in the gap between the pair of substrates. The above steps S3 and S4 are the panel assembly process.

Next, in step S5, heat treatment is performed to stabilize the alignment of the liquid crystal. For example, the liquid crystal is left at a high temperature for about 0.5 to 2.0 hours at a temperature around the nematic phase / isotropic phase transition point (NI point, usually about 90 ° C.) + 10 ° C. of the liquid crystal. At this time, 90 to 40 at the same time in step S6.
By performing the humidification at a relative humidity of about%, it is possible to discharge the charge and polarization remaining in the alignment film inside the liquid crystal display panel and the package charge of the panel. That is,
The liquid crystal display panel is left in a high temperature and high humidity atmosphere to accelerate the discharge of the charges charged on the substrate in the previous step. As a result, it is possible to significantly reduce image sticking due to electrification, which has been a problem in display quality. The humidity applied at this time may be set to an optimum value depending on the difference in the charge amount due to the difference in the alignment film, the liquid crystal material, and the manufacturing process.

Thereafter, in step S7, a polarizing plate is attached to the outer surface of the liquid crystal display panel. In addition, FPC for external connection (Fl
An exposed printed circuit is pressure-bonded to the exposed electrode surface of one substrate. After this, in step S8, an additional discharge promoting step can be performed. In this case, in consideration of the heat resistance and humidity resistance of the previously attached polarizing plate, leave it at a high temperature of 70 ° C (dry) or at 40 ° C, 90% R
By relaxing the application conditions such as H (relative humidity) and extending the time, it is possible to obtain the desired discharge effect. The application time may also be appropriately set according to the difference in the charge amount depending on the alignment film, the liquid crystal material, the process conditions, and the like. Of course, this additional discharge promoting step may be performed between step S5 and step S7.

An example of the liquid crystal display panel manufactured according to the present invention will be described with reference to FIG. This example is an example of manufacturing an active matrix type liquid crystal display panel. The liquid crystal display panel has a structure in which a lower glass substrate 1 and an upper glass substrate 2 are bonded together with a predetermined gap. The liquid crystal 3 is injected and sealed in this gap. Pixel electrodes 4 arranged in a matrix and switching elements 5 for individually driving the pixel electrodes 4 are integrally formed on the inner surface of the lower glass substrate 1. In this example, the switching element is a thin film transistor. The surface of the pixel electrode 4 is covered with an alignment film 6 such as a rubbing-treated polyimide. Therefore, there is a high possibility that a considerable amount of electric charge will remain when the panel is assembled. On the other hand, a counter electrode 7 is entirely formed on the inner surface of the upper glass substrate 2. Further, the surface thereof is covered with the alignment film 8 similarly subjected to the rubbing treatment. In the active matrix type liquid crystal display panel having such a configuration,
The pixel electrode 4 is electrically separated from the outside by the switching element 5 and is in a substantially floating state. Therefore, it is difficult to remove the charge of the alignment film 6 by allowing it to stand. In view of this point, in the present invention, heating and / or humidification treatment is performed to forcibly remove the charge. It is needless to say that the discharge promoting method according to the present invention can be applied not only to the active matrix type liquid crystal display panel but also to the simple matrix type liquid crystal display panel.

As described above, in the present invention, static electricity remaining on or in the alignment film caused by friction such as rubbing or air blow in the previous step is removed by heating after panel assembly. . When heated, the specific resistance of the liquid crystal decreases as shown in the graph of FIG. 3, and the charge can escape to the outside of the panel through the liquid crystal. As shown in the graph of FIG. 3, the specific resistance of the liquid crystal is 2.0 × 10 ¹³ Ω at 20 ° C.
While it is about cm, it is 2.0 × 10 ¹² Ω at 100 ° C.
・ It drops to about cm. Furthermore, humidification can accelerate the air discharge. As a result, it is possible to suppress the burn-in phenomenon which is a problem particularly in the active matrix type liquid crystal display panel.

In addition to discharging the charge on the alignment film, heat treatment is performed as shown in FIG. 4 to promote a reaction of adsorbing impurity ions (metal ions, etc.) contained in the liquid crystal to the alignment film. Things are possible. By this action,
It is possible to obtain the effect of reducing the content of impurity ions that cause charging in the liquid crystal.

FIG. 5 shows a graph used for setting the applied temperature and the standing time in the discharge promoting step. As shown in the figure, the higher the applied temperature is, the shorter the standing time is, and the desired discharge promoting effect is obtained. For example, when left at 70 ° C. for a high temperature, there is a discharge effect in about 150 hours, and discharge can be greatly promoted as compared with natural standing. If the temperature is set lower than 70 ° C, the leaving time is extended accordingly.

FIG. 6 shows the relationship between the applied temperature and the standing time in the case of standing in a high temperature and high humidity atmosphere.
The humidity is 90% RH or higher. Discharge is further promoted in high-temperature and high-humidity storage as compared with simple high-temperature storage, so the storage time can be shortened.

[0017]

As described above, according to the present invention, after assembly, the liquid crystal display panel is left in a high temperature atmosphere or a high temperature and high humidity atmosphere for a predetermined period of time to promote discharge of electric charges charged on the substrate in the previous step. . As a result, the image sticking phenomenon caused by charging can be significantly reduced, and the image quality can be improved.

[Brief description of drawings]

FIG. 1 is a process drawing showing a liquid crystal display panel manufacturing method according to the present invention.

FIG. 2 is a schematic cross-sectional view showing an example of a liquid crystal display panel manufactured according to the present invention.

FIG. 3 is a graph showing temperature characteristics of specific resistance of liquid crystal.

FIG. 4 is an explanatory diagram showing an adsorption phenomenon of impurity ions due to heat treatment.

FIG. 5 is a graph showing the relationship between applied temperature and standing time.

FIG. 6 is a graph showing a relationship between an applied temperature and a standing time under high humidity.

FIG. 7 is a process chart showing an example of a conventional liquid crystal display panel manufacturing method.

FIG. 8 is a schematic diagram showing a charged state of a substrate of a liquid crystal display panel.

FIG. 9 is an equivalent circuit diagram for explaining a burn-in phenomenon of a liquid crystal display panel.

[Explanation of symbols]

 1 Glass Substrate 2 Glass Substrate 3 Liquid Crystal 4 Pixel Electrode 5 Switching Element 6 Alignment Film 7 Counter Electrode 8 Alignment Film

Claims (5)

[Claims] 1. A substrate forming step of forming a pair of substrates provided with at least electrodes, an alignment treatment step of aligning the surface of each substrate, and a step of joining the pair of substrates with each other through a predetermined gap. A method for manufacturing a liquid crystal display panel, which includes a panel assembling step of enclosing a liquid crystal and assembling a liquid crystal display panel, and a discharge accelerating step of leaving the liquid crystal display panel in a high temperature atmosphere and accelerating the discharge of charges charged on the substrate in the previous step . 2. The method for manufacturing a liquid crystal display panel according to claim 1, wherein in the discharge promoting step, the discharge is further promoted by leaving the liquid crystal display panel in a high temperature and high humidity atmosphere. 3. The method of manufacturing a liquid crystal display panel according to claim 2, wherein the discharge promoting step also serves as a heat treatment for stabilizing the alignment of the enclosed liquid crystal. 4. The method of manufacturing a liquid crystal display panel according to claim 1, wherein the discharge promoting step is performed as an additional treatment in addition to the heat treatment for stabilizing the orientation of the enclosed liquid crystal. 5. The liquid crystal display panel manufacturing method according to claim 1, wherein the substrate forming step forms one substrate provided with a pixel electrode and a switching element for driving the pixel electrode and the other substrate provided with a counter electrode. Method.