JPH07140451A - Plastic substrate liquid crystal display panel and its production - Google Patents

Abstract

PURPOSE:To provide a plastic substrate liquid crystal display panel having an arbitrarily curved shape and high reliability. CONSTITUTION:The plastic substrates 1, 3 of the liquid crystal display panel composed of a pair of the plastic substrates are composed of a partially crystallized polyurethane-based polymer. The plastic substrates 1, 3 have a shape memory function or shape restoration function with the glass transition temp. (Tg) of the polyurethane-based polymer as a boundary. Since the plastic substrates 1, 3 are composed of the polymer having the shape memory function or shape restoration function, the storage of the curved surface shape or the restoration of the curved surface shape is made possible by heating to over the Tg point of the polymer and cooling, by which the holding of the curved surface shape is made possible without applying external force thereon. There is thus an extremely high effect in improving the reliability of the plastic substrate liquid crystal display panel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic substrate liquid crystal display panel utilizing the electro-optical characteristics of liquid crystal, and more particularly to a plastic substrate liquid crystal display panel which enables curved display and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, along with the spread of portable information equipment, liquid crystal display panels are required to be lightweight, thin and non-destructive. In order to meet these requirements, liquid crystal display panels using plastic substrates instead of glass substrates have been actively developed and put to practical use. Compared to a glass substrate, the plastic substrate has a specific gravity of about 1/2 and a thickness of about 1/5, which is a feature that can be considerably reduced in weight and thickness. Another characteristic of the plastic substrate is that it has flexibility, so that it can be displayed without being broken or curved.

As described above, the plastic substrate has good characteristics that the glass substrate does not have, but on the other hand, it has a defect that the glass substrate does not have. Generally, plastic has a large coefficient of thermal expansion of one digit or more as compared with glass, and has a drawback that it is likely to change in dimension. Therefore, a low temperature material / low temperature process is required for manufacturing a liquid crystal display panel, and a plastic substrate is required to have a material having a glass transition temperature as high as possible and a change in characteristics being small. Polyether sulfone (PES), polyarylate (PA)
Generally, materials such as R) and polycarbonate (PC) having high heat resistance and little optical anisotropy are used. However, in general, plastic has high oxygen permeability and moisture permeability, and also has poor chemical resistance, so it is
Since it is easily attacked by an organic solvent, it cannot be used as a substrate of a liquid crystal display panel as it is. Therefore, it is necessary to provide a barrier layer on the plastic in order to prevent the entry of oxygen and water or improve the chemical resistance. For example, a multilayer substrate in which polyvinylidene chloride is formed as a gas barrier on PES (Japanese Patent Laid-Open No. 60-26001)
9), a large number of plastic substrates have been devised such as an ethylene / vinyl alcohol copolymer film laminated as a gas barrier layer on a PC and a phenoxy resin laminated as an undercoat material on the surface in contact with the liquid crystal (JP-A-59-198429). .

When performing curved surface display using such a plastic substrate liquid crystal display panel, it is necessary to bend the plastic substrate. Since the plastic substrate has resilience in the elastic deformation region against an external force, it is necessary to continue to apply the external force by some method in order to display a curved surface. For example, as a method of displaying a curved surface, a method of adhering and fixing a plastic substrate liquid crystal display panel to a support having a circular curved surface (JP-A-57-168285), two plastic substrates are sandwiched between curved molds, A method of laminating two substrates (JP-A-57-188015), a method of sandwiching a plastic substrate liquid crystal display panel between rollers having different peripheral speeds and forcibly bending one polarizing plate (JP-A-62-021124). ), A method of bending a plastic substrate liquid crystal panel on a curved table having a specific shape and attaching a polarizing plate (JP-A-02-101426).

[0005]

As described above, in the conventionally devised method, the elastic deformation stress is constantly applied to the liquid crystal display panel in order to bend the display surface. For this reason, in the configuration in which the curved surface is held by the peripheral support, the connection portion between the liquid crystal display panel and the drive circuit, which is thermocompression bonded by the anisotropic conductive resin, peels off with the passage of time, or by the polarizing plate. In the configuration that keeps the curved shape, there is a problem that the polarizing plate that is forcibly distorted is peeled off from the substrate surface of the liquid crystal display panel, or the seal part for bonding the two substrates is peeled off. There is a problem that the reliability of the display panel is significantly reduced.

In view of the problems of the conventional method for manufacturing a plastic substrate liquid crystal display panel, the present invention provides a plastic substrate liquid crystal display panel capable of retaining a curved shape without continuously applying an external force and a manufacturing method thereof. It is intended to be provided.

[0007]

In view of the above problems, the liquid crystal display panel of the present invention provides two solutions. (Means 1) In a plastic liquid crystal display panel in which liquid crystal is sandwiched between a pair of plastic substrates, the plastic substrate is made of a polymer that is in a high rigidity state below the glass transition temperature and in a rubber elastic state above the glass transition temperature. , The deformation of the plastic substrate caused by an external force in the temperature range of the glass transition temperature or higher is retained in the temperature range of the glass transition temperature or lower, and is restored to the state before the deformation by reheating to the temperature range of the glass transition temperature or higher. It has a shape memory function. (Means 2) In a liquid crystal display panel in which a liquid crystal is sandwiched between a pair of substrates, the substrate is in a high rigidity state below the glass transition temperature, in a rubber elastic state above the glass transition temperature, and in an initial shape in the rubber elastic state. The substrate is made of a polymer having a function of restoring to the above, and the substrate exhibits a curved state in a temperature range equal to or higher than the glass transition temperature of the polymer when it is not subjected to an external force.

[0008]

[Action]

(Operation 1) According to the configuration of the above means 1, since the substrate is made of a polymer having a shape memory function, an external stress is applied to the liquid crystal display panel at a temperature not lower than the glass transition temperature of the polymer constituting the substrate so that the display surface is The curved shape of the liquid crystal display panel is maintained by bending it to a curved shape and cooling it to the glass transition temperature of the polymer or lower with external stress applied, allowing curved shape even without external stress. . (Operation 2) According to the configuration of the above means 2, since the substrate is formed of the polymer having the shape recovery function, if the initial shape of the substrate is curved, the substrate is heated above the glass transition temperature of the polymer. By the shape recovery function of the polymer forming the substrate, it returns to the initial curved shape, and by cooling in this state, it becomes possible to form a curved surface without external stress.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 is a schematic sectional view showing an embodiment of a liquid crystal display panel of the present invention. 1 is the upper plastic substrate,
2 is a segment electrode, 3 is a lower plastic substrate, 4 is a common electrode, 5 is a polyimide thin film, 6 is a liquid crystal layer, 7 is a spacer, 8 is a sealing material, and 9 is a polarizing plate. Each of the upper substrate 1 and the lower substrate 3 is a plastic film having a thickness of 0.2 mm to 0.5 mm formed of a polyurethane polymer having a shape memory function (for example, Diary: Mitsubishi Heavy Industries, Ltd.), and a gas barrier layer and an undercoat. It is a plastic substrate in which layers are laminated. This polyurethane polymer is partially crystallized in terms of molecular structure, and is in a plastic state below the glass transition temperature (hereinafter referred to as Tg), and in a rubber elastic state above Tg due to the micro Brownian motion of constituent molecules. When an external force is applied in this rubber elastic state, it is easily deformed. When cooled to a temperature below Tg in the deformed state, the Micro Brownian motion of the molecule freezes,
The deformed state will be retained and stored. T again
It has the function of starting the Micro Brownian motion by heating over g and restoring the original shape. The Tg of the polyurethane polymer used in this example is around 100 ° C.

Indium tin oxide (I) having a sheet resistance of 30 Ω / □ on two flat plastic substrates made of a polymer having such a shape memory function.
After forming (TO), patterning is performed by photolithography to obtain 64 stripe-shaped segment electrodes 2 on the upper plastic substrate 1. Using the same method, 64 common electrodes 4 are formed on the lower plastic substrate 3. The segment electrode 2 and the common electrode 4 are arranged so as to be orthogonal to each other. On such plastic substrates 1 and 3, a polyimide thin film 5 having a thickness of 800 Å is formed by a printing method. As a polyimide thin film, for example, RN-779 (manufactured by Nissan Chemical Industries, Ltd.)
A relatively low temperature curable material such as The polyimide thin film has a function of aligning liquid crystal molecules horizontally or with a pretilt angle of several degrees on the plastic substrate surface.
In order to give orientation to these polyimide thin films 5,
Rubbing treatment with rayon cloth is performed. The rubbing process is performed so as to be parallel to the longitudinal direction of the striped electrodes formed on each plastic substrate.

Next, spherical spacers 8 made of plastic (for example, Micropearl: Sekisui Fine Co., Ltd.) are uniformly dispersed on the lower plastic substrate 3 or the polyimide thin film 5. The spherical diameter of the spacer is 5 μm. UV-curable sealing material 9 around the upper plastic substrate 1
Is formed by printing with a liquid crystal injection port, the upper and lower plastic substrates 1 and 3 are attached so that the segment electrode 2 and the common electrode 4 are orthogonal to each other, and the sealing material 9 is completely cured by irradiating ultraviolet rays having a specific wavelength. Let

Next, a right-handed chiral substance (eg, R-1011: manufactured by Merck Japan Co., Ltd.) is added to a nematic liquid crystal having a refractive index anisotropy of 0.092 (eg, LIXON-6609: manufactured by Chisso Petrochemical Co., Ltd.). Add
The value of the spontaneous twist pitch p is d with respect to the cell gap d.
The density is adjusted so that /p=0.06. A liquid crystal display panel is manufactured by injecting between the plastic substrates 1 and 3 by a vacuum injection method and completely filling the chiral nematic liquid crystal 6 and then gradually cooling and sealing the liquid crystal injection port with a sealing resin.

FIG. 2 shows a method for displaying a curved surface on the liquid crystal display panel. Liquid crystal display panel 2 manufactured by the above method
0 is heated to a temperature not lower than Tg of the polyurethane polymer (for example, 120 ° C.), placed on the curved table 21 and external force is applied from both ends to bend the display surface into a curved surface. At this time, the molecules of the polyurethane polymer are in a rubber elastic state due to the micro Brownian motion, and are easily deformed by an external force. Then, in this state, by cooling to a temperature of Tg or lower, the micro Brownian motion of the molecule is frozen and becomes a plastic state, and the curved state is maintained. Even if the external force is removed in this state, the liquid crystal display panel maintains the curved state and the shape is fixed.

Thereafter, a polarizing plate is attached to the surfaces of the upper and lower plastic substrates so that their absorption axes are orthogonal to each other, whereby a curved surface twisted nematic (TN) type plastic substrate liquid crystal display panel can be manufactured. Further, by changing the shape of the curved surface table 21, it is possible to form a curved surface having an arbitrary curvature.

It has been confirmed that the liquid crystal display panel having a curved surface shape as described above does not need to be continuously subjected to an external stress, can solve the problem of peeling which occurs in the conventionally devised method, and greatly improves reliability. Was done.

Next, another embodiment of the present invention will be described. (Embodiment 2) FIG. 3 is a cross-sectional view of a configuration diagram of a laminated substrate in Embodiment 2 of the present invention. 22 is a base film made of partially crystallized polyurethane polymer, 23 is a gas barrier layer made of polyvinylidene chloride,
24 is an undercoat layer made of phenoxy resin, 25
Is an ITO layer. The Tg of the partially crystallized polyurethane polymer is about 120 ° C., and in the temperature range of Tg or higher, the molecular chain has a shape recovery function for recovering the molecular chain to the initial state due to the micro Brownian motion of the molecule and the partial crystallization.
The base film 22 is formed so that its initial shape is curved, and exhibits a curved shape even at a temperature of Tg or lower when no external force is applied.

Now, it is not easy to manufacture a liquid crystal display panel with a curved laminated substrate as it is. Therefore, an external force is applied to the curved laminated substrate so that the curved shape becomes a flat plate shape in a temperature region of Tg or higher. In the temperature region of Tg or higher, the base film 22 becomes a rubber elastic region due to the micro-Brownian motion of its molecules, and is easily deformed by an external force. When the temperature is lowered to Tg or lower while applying an external force, the deformed state is fixed, and the laminated substrate has a flat plate shape. A low-temperature curable alignment film (for example, HIMAL HL-1200: manufactured by Hitachi Chemical Co., Ltd.) is formed on a flat laminated substrate. The thickness of the alignment film is about 700Å, and it can be cured at 100 ° C in about 30 minutes. Next, two laminated substrates are bonded with a polyurethane-based sealing resin through a spacer having a particle size of 5 μm (for example, Eposter: manufactured by Catalysts & Chemicals Co., Ltd.) to fabricate a cell.

A nematic liquid crystal having a refractive index anisotropy of about 0.092 and a positive dielectric anisotropy (for example, LIX0).
N-6604: manufactured by Chisso Petrochemical Industrial Co., Ltd.) and a chiral nematic liquid crystal prepared by adding the same chiral agent as that of Example 1 so that d / p = 0.25 was obtained. The cell is filled at a temperature equal to or higher than the temperature (NI point), and the liquid crystal injection port is sealed with a sealing resin. The laminated substrate deformed into a flat plate is subjected to a thermal history by the above process, but since it does not receive a temperature higher than the Tg of the base film, its shape does not change during the panel fabrication, and it is similar to a conventional glass substrate. The panel can be easily manufactured.

By reheating the liquid crystal display panel thus manufactured to a temperature of Tg or higher of the base film (for example, 130 ° C.), it is restored to the initial curved shape by its shape recovery effect, and as a result, the liquid crystal display panel is The display surface has a curved shape. Then, polarizing plates are attached to the front and back of the liquid crystal display panel so that their absorption axes are orthogonal to each other. By the above method, it was confirmed that it is not necessary to continuously apply external stress to the liquid crystal display panel as in Example 1, and the reliability is greatly improved.

In this embodiment, since the chiral nematic liquid crystal is injected without rubbing the alignment film, regions (domains) having different director directions of liquid crystal molecules are generated, and the viewing angle is expanded by this domain. Also has an effect.

[0021]

As is apparent from the above description,
According to the present invention, since the substrate is composed of a polymer having a shape memory function or a shape recovery function, the Tg of the polymer is
By heating and cooling above a point, the curved surface shape can be memorized or restored to the curved surface shape, which makes it possible to maintain the curved surface shape without continuously applying external force, which is extremely useful for improving the reliability of the plastic substrate liquid crystal display panel. Has a great effect on.

[Brief description of drawings]

FIG. 1 is a sectional view of a plastic substrate liquid crystal display panel according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing an example of a method of manufacturing a plastic substrate liquid crystal display panel in Example 1 of the present invention.

FIG. 3 is a sectional view of a laminated substrate of a plastic substrate liquid crystal display panel according to a second embodiment of the present invention.

[Explanation of symbols]

 1 Upper Plastic Substrate 2 Segment Electrode 3 Lower Plastic Substrate 4 Common Electrode 5 Polyimide Thin Film 6 Chiral Nematic Liquid Crystal Layer 7 Spacer 8 Sealant 9 Polarizing Plate

Claims (6)

[Claims] 1. A plastic substrate liquid crystal display panel comprising a pair of substrates and a liquid crystal sandwiched between the substrates, wherein the substrate is made of a polymer having a high rigidity state at a glass transition temperature or lower and a rubber elastic state at a glass transition temperature or higher. Is
The substrate is deformed by an external force in the temperature range of the glass transition temperature of the polymer or higher, is retained in the temperature range of the glass transition temperature or lower, and is in a state before the deformation by reheating to the temperature range of the glass transition temperature or higher. A plastic substrate liquid crystal display panel characterized by having a shape memory function that restores to. 2. A plastic substrate liquid crystal display panel in which liquid crystal is sandwiched between a pair of substrates, wherein the substrate is in a high rigidity state at a glass transition temperature or lower, and in a rubber elastic state at a glass transition temperature or higher, and a rubber elastic state. Is composed of a polymer that has the function of restoring the initial shape,
A plastic substrate liquid crystal display panel, wherein the substrate exhibits a curved state in a temperature range equal to or higher than a glass transition temperature of the polymer when not subjected to an external force. 3. The plastic substrate liquid crystal display panel according to claim 1, wherein the polymer has a urethane group. 4. A method of manufacturing a plastic substrate liquid crystal display panel, comprising a pair of substrates and a liquid crystal sandwiched between the substrates, wherein the substrate exhibits a high rigidity state at a glass transition temperature or lower and a rubber elastic state at a glass transition temperature or higher. And in a temperature range above the glass transition temperature of the polymer,
A method of manufacturing a plastic substrate liquid crystal display panel, which comprises curvedly fixing the liquid crystal display panel and then cooling the liquid crystal display panel to a temperature range of a glass transition temperature or lower to realize a curved display. 5. A method of manufacturing a plastic substrate liquid crystal display panel comprising a pair of substrates sandwiching a liquid crystal, wherein the substrate exhibits a high rigidity state at a glass transition temperature or lower, and a rubber elastic state at a glass transition temperature or higher, It is formed of a polymer having a function of restoring the initial shape in a rubber elastic state, the initial shape of the substrate is curved, and an external force is applied to the substrate in a temperature range of the glass transition temperature of the polymer or more to form a flat plate shape. A method for manufacturing a plastic substrate liquid crystal display panel, characterized in that a curved display is realized by producing a liquid crystal display panel with the flat plate shape fixed by cooling and then reheating the glass transition temperature of the polymer or higher. Law. 6. The method for producing a plastic substrate liquid crystal display panel according to claim 4 or 5, wherein the polymer has a urethane group.