JPH1039308A - Production of liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the unequal display, after images and burn which arise in a liquid crystal display device. SOLUTION: A first oriented film 3 consisting essentially of polyamic acid is applied on the electrodes 2 of a thin-film transistor substrate 1a or color filter substrate 1b and is subjected to temporally baking at about a temp. at which polyimidization does not arise after drying. Further, a second oriented film 4 consisting essentially of soluble polyimide is applied thereon and is dried. The oriented film is then subjected to normal baking at about the temp. at which the first oriented film 3 induces the polyimidization. As a result, the residual potential of the oriented film 5 is lowered and the generation of boundaries is obviated. Then, the occurrence of the unequal display, after images and burn is averted when the liquid crystal display device is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a liquid crystal display, and more particularly to a method for manufacturing an active matrix type color liquid crystal display.

[0002]

2. Description of the Related Art Hitherto, as an alignment film of a display device using a twisted nematic (TN) liquid crystal, a polyimide film having excellent alignment properties has been used. Polyimide film is a polyimide precursor polyamic acid-based alignment agent on the substrate and applied to the substrate and baked to polyimide, or pre-polyimide soluble polyimide-based alignment agent on the substrate It was formed by coating and drying the solvent.

[0003] However, a polyimide agent containing a polyamic acid as a main component has good coatability, but has a problem that unreacted polyamic acid remains even after sintering and stain-like display unevenness occurs on a liquid crystal display device. On the other hand, a polyimide agent containing a soluble polyimide as a main component has a problem that it has poor applicability and is easily peeled off.

[0004] In any of the alignment films using any of the above-mentioned polyimide agents, there is a problem that a residual potential is high and afterimages or printing occur when the liquid crystal display is used continuously for a long time.

[0005] From the viewpoint of seeking a more excellent liquid crystal display device, many proposals have been made to form an alignment film in multiple layers. For example, in the technique disclosed in JP-A-3-55523, a lower layer uses a two-layer polyimide film having a higher imidation ratio than the upper layer, and in the technique disclosed in JP-A-2-59723, 10 ¹⁴ [Omega] cm or more dielectric thin film, using a surface耐向polymer thin film having a weak adsorbing force to the TN liquid crystal as an upper layer.

[0006]

In a conventional liquid crystal display device using an alignment film, even if it is multi-layered, it is effective in a short time use, but if it is used continuously for a long time, an afterimage or burning occurs. There was a problem of doing.

[0007] The reason is that the residual potential of the liquid crystal display device gradually accumulates over a long period of use.

Further, when the orientation film is multi-layered as in the conventional example, there is a problem that the unevenness of the panel is apt to occur unlike the case of a single layer.

The reason is that a new charge trap is easily formed at the interface between the multilayer alignment films.

An object of the present invention is to provide a method of manufacturing a liquid crystal display device which prevents display unevenness of the liquid crystal display device and an afterimage or a burn-in which occurs when used for a long time.

[0011]

In order to achieve the above object, a method of manufacturing a liquid crystal display device according to the present invention includes a preliminary firing step and a main firing step, and forms an alignment film for aligning liquid crystal molecules. In the method of manufacturing a liquid crystal display device, the calcination step is a process of applying a first alignment film containing polyamic acid as a main component and calcination at a temperature at which no polyimide is formed after drying. The main baking process is a process of applying a second alignment film containing soluble polyimide as a main component on the first alignment film, drying the second alignment film, and performing main firing at a temperature at which the first alignment film causes polyimide. It is.

Further, the first alignment film containing polyamic acid as a main component contains 10% by weight or less, preferably 5% by weight or less of a soluble polyimide.

The ratio of the film thickness of the first alignment film is 0.2 with respect to the total of the film thicknesses of the second alignment film being 1.
-0.9, preferably 0.5-0.8.

[0014]

A first alignment film containing a polyamic acid as a main component is applied (FIG. 1 (a)), dried, and calcined at a temperature at which no polyimide is formed. Is applied and dried (FIG. 1B), and the main firing is performed at a temperature at which the first alignment film undergoes polyimide (FIG. 1C).

Since the first alignment film made of polyamic acid in the lower layer and the second alignment film made of soluble polyimide in the upper layer are simultaneously baked to form a polyimide, the lower layer is often made of polyamic acid and the upper layer is often made of polyimide. As a result, a structural alignment film containing a large amount of polyimide formed from a soluble polyimide is obtained.

[0016] Therefore, compared with the case where a single-layer alignment film is simply formed into a multi-layer, electric charges flow more easily from the liquid crystal layer side to the electrode side, and the residual potential of the liquid crystal display device can be reduced.
Almost no afterimages or prints occur.

In addition, compared with the case of simply forming a multilayer, there is no generation of an interface, and it is possible to prevent unevenness of the liquid crystal display device.

[0018]

Next, an embodiment of the present invention will be described in detail with reference to the drawings.

(Embodiment 1) FIG. 1 is a sectional view for explaining a method of manufacturing a liquid crystal display device according to Embodiment 1 of the present invention in the order of steps.

As shown in FIG. 1A, SE7311 manufactured by Nissan Chemical Industries, Ltd. is applied as a first alignment agent made of polyamic acid onto the electrode 2 formed on the thin film transistor substrate 1a or the color filter substrate 1b. After drying,
1 at a temperature of 120 ° C at which almost no polyimide occurs
Temporary calcination is performed for a time to form a first alignment film 3 of 300 °.

Thereafter, as shown in FIG. 1B, as a second alignment agent composed of a soluble polyimide, SE5291 manufactured by Nissan Chemical Co., Ltd. is applied on the first alignment film 3, dried, and dried. An alignment film 4 is formed on the first alignment film 3.

Further, main firing is performed at 250 ° C. for 2 hours at a temperature at which the first alignment film 3 causes polyimide, and a 500 ° alignment film 5 composed of the first alignment film 3 and the second alignment film 4 is formed. Form.

The thin film transistor substrate 1a having the alignment film 5 formed as described above, the color filter substrate 1
FIG. 2 shows a cross-sectional structure of the liquid crystal display device assembled by sandwiching the liquid crystal 6 with b.

FIG. 4 shows the result of measuring the residual potential when the liquid crystal display device shown in FIG. 2 was used at a temperature of 50 ° C. for 240 hours.

As shown in FIG. 4, when the thickness ratio of the first alignment film 3 made of polyamic acid to the second alignment film 4 made of soluble polyimide is around 4: 6, the residual voltage becomes almost zero. I have. Therefore, the ratio of the thickness of the first alignment film 3 is set to 0.2 to 0.9, preferably 0.5 to 0.8, with the total thickness of the second alignment film 4 being 1. It is desirable to do.

In the case of a single layer of polyamic acid, the voltage is about 0.6 V, in the case of a single layer of soluble polyimide, about 1.0 V, and when only two layers are used, the voltage is about 0.75 V. It turns out that there is an effect peculiar to the manufacturing method of a liquid crystal display device.

Therefore, even after continuous use at a temperature of 50 ° C. for 240 hours, no afterimage or image sticking was observed in the liquid crystal display device using the present invention.

The alignment film made of polyamic acid is
There is a disadvantage that display-like unevenness is liable to occur in the display due to the action of the ionic substance in the liquid crystal, and there is a disadvantage that the alignment film made of soluble polyimide is difficult to be applied and peels off easily. In addition, there is a disadvantage that charge traps are generated at the interface and display unevenness easily occurs.
However, in the liquid crystal display device using the manufacturing method of the present invention,
No film peeling occurred, and no uneven display occurred.

Embodiment 2 FIG. 3 is a sectional view showing a method of manufacturing a liquid crystal display device according to Embodiment 2 of the present invention in the order of manufacturing steps.

As shown in FIG. 3A, the first alignment agent made of polyamic acid (SE7311 manufactured by Nissan Chemical Industries, Ltd.) is soluble on the electrode 2 formed on the thin film transistor substrate 1a or the color filter substrate 1b. 5% by weight of polyimide (SE5291 manufactured by Nissan Chemical Industries, Ltd.) is uniformly mixed and applied, dried, and calcined at 120 ° C. for 1 hour at a temperature at which imidization hardly occurs.
The first alignment film 3a of Å is formed.

Thereafter, a second alignment film 4 of 200 ° is formed by applying and drying a second alignment agent made of soluble polyimide (SE5291 manufactured by Nissan Chemical Industries, Ltd.).

Further, main firing is performed at 200 ° C. for 2 hours at a temperature at which the first alignment film 3a causes imidization, and
The alignment film 5 of Å is formed.

Using the alignment film 5 formed as described above,
When the liquid crystal display device shown in FIG.
The same effect as described above was obtained. In the second embodiment, the temperature of the main firing could be lower than that of the first embodiment.

This is considered to be effective when used for a color filter substrate or a thin film transistor substrate having low heat resistance. In the second embodiment, the first alignment film 3a containing polyamic acid as a main component is 10% by weight or less,
It is desirable to contain 5% by weight or less of soluble polyimide.

[0035]

As described above, according to the present invention, afterimages and image sticking can be prevented even after continuous use for a long time. The reason is that the residual potential of the liquid crystal display device can be made almost zero.

Further, since no interface is generated in the alignment film and no charge trap is formed, display unevenness can be prevented.

[Brief description of the drawings]

FIG. 1 is a sectional view illustrating a method for manufacturing a liquid crystal display device according to Embodiment 1 of the present invention in the order of steps.

FIG. 2 is a cross-sectional view illustrating a liquid crystal display device using an alignment film according to the present invention.

FIG. 3 is a sectional view illustrating a method for manufacturing a liquid crystal display device according to Embodiment 2 of the present invention in the order of steps.

FIG. 4 is a diagram illustrating a residual potential of the liquid crystal display device.

FIG. 5 is a cross-sectional view showing a conventional two-layer alignment film.

[Description of Signs] 1a Thin film transistor substrate 1b Color filter substrate 2 Electrode 3,3a First alignment film 4 Second alignment film 5 Alignment film 6 Liquid crystal 7,8 Alignment film

Claims (3)

[Claims] 1. A method of manufacturing a liquid crystal display device, comprising a pre-baking step and a main baking step, wherein an alignment film for aligning liquid crystal molecules is formed, wherein the pre-baking step comprises a polyamic acid as a main component. This is a treatment in which a first alignment film is applied and preliminarily baked at a temperature at which polyimide formation does not occur after drying. In the calcination step, the second alignment film containing soluble polyimide as a main component is subjected to the first alignment. A method for manufacturing a liquid crystal display device, comprising applying a film on a film, drying the film, and firing the film at a temperature at which the first alignment film causes polyimide. 2. A method according to claim 1, wherein said first component comprises said polyamic acid as a main component.
2. The method according to claim 1, wherein said alignment film contains 10% by weight or less, preferably 5% by weight or less of soluble polyimide. 3. The ratio of the film thickness of the first alignment film is 0.2 to 0.2 with the total of the film thicknesses of the second alignment film being 1.
3. The method for manufacturing a liquid crystal display device according to claim 1, wherein the ratio is 0.9, preferably 0.5 to 0.8.