JPH0895048A - Liquid crystal display element - Google Patents

Abstract

PURPOSE: To prevent the deterioration of a liquid crystal layer and to lower electric power consumption further by changing a physical shape of the surface of an oriented film formed on a substrate principal plane, with which the liquid crystal layer is brought into contact, varying the arrangement of liquid crystal molecules in the liquid crystal layer according to the physical shape change, and controlling a transmitting condition of light in the liquid crystal layer so as to carry out display. CONSTITUTION: A glass substrate 2, in which a horizontally oriented resin film serving as an orientated film 1 is applied to one side to be rubbed in one direction, and a rubber film 3, which is provided with a principal plane formed into a fine rugged shape on one side and is made of highly transparent material such as silicon rubber, are used. The principal plane, on which the oriented film 1 is formed, of the glass substrate 2 and the principal plane, on which the fine rugged shape is formed, of the rubber film 3 are opposedly arranged while setting a clearance between them. In this way, a shape, which induces the orientation of liquid crystal molecules, such as a groove or a roughness is formed 1 the surface, and the orientation of the liquid crystal molecules is controlled by controlling the impression of electricity, heat, external force, or the like, and then, display can be performed.

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 device.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices, which have the great advantages of thinness, light weight and low power consumption, have been widely used as display devices for personal OA equipment such as Japanese word processors and desktop personal computers. As an example of the most typical method, TN (Twisted Nematic)
There is a method.

In this TN type liquid crystal display element, two substrates, which are the main components of a liquid crystal panel, are arranged so as to face each other with a gap therebetween, and the liquid crystal layer is sandwiched by the periphery being sealed in the gap. Has been done. The liquid crystal layer is between the two substrates
Although the molecules are twisted by 90 °, the liquid crystal molecules have a slight pretilt on the substrate surface of the liquid crystal panel (liquid crystal cell), but they are oriented almost parallel to the substrate,
In the state (state in which no voltage is applied), all the molecules in the liquid crystal layer are aligned in the direction substantially parallel to the substrate according to this.

When a nematic liquid crystal having a positive dielectric anisotropy is used, in the ON (voltage applied) state, the molecules in the liquid crystal layer rise in the direction of the electric field perpendicular to the surface of the substrate and the twisted arrangement of the parallel arrangement described above. The structure collapses. The display is performed by utilizing the change in the optical rotatory power of the liquid crystal layer due to the change in the liquid crystal molecule arrangement in the OFF state and the ON state due to the change in the molecular arrangement. In this way, the TN method can perform monochrome display or color display in combination with a color filter.

In addition to such a TN system, STN (Su
per Twisted Nematic) method, ECB (Electrically C)
ontrolled Birefringence method, PC (Phase Chang)
There are various display methods such as e) method and FLC (Ferroelectric Liquid Crystal) method, but most of the display methods have electrodes formed on the substrates and the liquid crystal layer sandwiched between the substrates is directly applied from the electrodes of both the substrates. An electric field is applied to. Therefore, in such a conventional type liquid crystal display element, when a liquid crystal display element is continuously driven by applying an electric field for a long time, the liquid crystal composition of the liquid crystal layer gradually deteriorates due to an action such as electrolysis. There is a problem. To avoid this, conventionally, the polarity of the applied voltage is inverted every specific period, such as every frame, to drive the liquid crystal layer in an alternating current.

However, even in such an AC driving method, when viewed in a small time unit, a DC voltage is applied to the liquid crystal layer. For such a liquid crystal layer, if a relatively large electric field is directly applied to the liquid crystal layer for a long time, it is inevitable that the liquid crystal layer will gradually deteriorate even though it is an AC driving method. There is.

When applying an electric field to the liquid crystal layer, the electric field is actually applied to the liquid crystal layer via the alignment film. Therefore, of the voltage applied to the electrodes, the loss of the electric field in the alignment layer is inevitably present, and there is energy loss due to the loss of the applied voltage, and the drive voltage creates an electric field effective for actual display. There is also a problem that the voltage is higher than the voltage for power consumption or the power consumption is high.

[0008]

As described above, the conventional liquid crystal display element has problems of power consumption loss for applying an electric field to the liquid crystal layer during driving and deterioration of the liquid crystal layer. The present invention has been made to solve such a problem, and an object of the present invention is to provide a liquid crystal display device that eliminates deterioration of a liquid crystal layer and further reduces power consumption.

[0009]

A liquid crystal display device of the present invention has a liquid crystal layer sandwiched between two substrates arranged in parallel and facing each other, and a light transmission state of the liquid crystal layer. In the liquid crystal display element for controlling the image to display an image, the physical shape of the surface of the alignment film formed on the main surface of the substrate in contact with the liquid crystal layer is changed, and the physical shape of the surface of the alignment film is changed to change the physical shape of the liquid crystal layer. It is characterized in that the arrangement of liquid crystal molecules is changed to control the light transmission state of the liquid crystal layer to perform display.

Further, the above liquid crystal display device is characterized in that the physical shape of the surface of the alignment layer is changed by using a piezoelectric element whose surface physical shape is changed by applying a voltage.

[0011]

In the liquid crystal display device, the liquid crystal molecules are aligned on the surface of the liquid crystal alignment film formed on the substrate surface of the liquid crystal display device. It is considered to be due to the physical shape of the surface generated by the intermolecular interaction such as the Delwar force or the rubbing treatment. As an example showing that the liquid crystal molecules are aligned according to the physical shape of the surface of the alignment film, for example, when a substrate is coated with photosensitive polyimide and fine grooves with a pitch of about 5 μm or less are formed by photolithography, Molecules are arranged in this groove direction. This is well known, but in this case, since the anisotropy is not given to the arrangement of the polyimide film molecules on the surface, it is not the intermolecular interaction on the alignment film surface, but the physical shape (fine groove).
Is considered to be the cause of the orientation.

In the conventional liquid crystal display device, light transmission is controlled and display is performed by using the difference between the liquid crystal molecule arrangement provided by the liquid crystal alignment film and the liquid crystal molecule arrangement deformed by the electric field application. Changes the orientation of the liquid crystal molecules in contact with the surface of the alignment film by changing the physical shape of the surface of the alignment film in contact with the liquid crystal layer. As a result, the twisted nematic liquid crystal existing between both substrates is changed. It was found that the orientation of the whole molecule can be controlled.

As a method of changing the physical shape of the surface of the alignment film in contact with the liquid crystal layer as described above, specifically, for example, a piezoelectric element whose shape is changed by voltage application or a high degree of expansion / contraction by current flow. A molecular gel, a shape memory alloy or a bimetal whose shape is changed by applying heat, and a film made of rubber or an elastic material which is easily deformed by a mechanical external force can be preferably used.

An alignment film formed of a material that changes these physical shapes or an element made of such a material whose physical shape changes is formed for each pixel, and a deformable orientation that covers the pixel is formed. Forming a film, forming a shape that induces alignment of liquid crystal molecules such as grooves and irregularities on the surface, and controlling the alignment of liquid crystal molecules by controlling the application of electricity, heat, external force, etc. to perform display You can

The liquid crystal layer is not limited to TN type liquid crystal, STN type liquid crystal, GH (guest host) type liquid crystal obtained by adding a dye to nematic type liquid crystal, or nematic type liquid crystal. It is also possible to use a cholesteric liquid crystal or a smectic liquid crystal.

Further, as the piezoelectric element, for example, LiTaO ₃ or LiNb used in a SAW filter is used.
O ₃ , Bi ₁₂ GeO ₂₀ , LBO, ZnO, PTZ-based ceramics, crystal for oscillation, and the like can be preferably used. Using such a material, for example, by applying a voltage to each pixel and changing the physical state of the alignment film for each pixel, that is, the width, length or direction of the groove of the alignment film, An image can be displayed by changing the orientation of various liquid crystal molecules.

Alternatively, in addition to the above-described piezoelectric element, an element formed of, for example, bimetal may be used. Other,
It can be formed using a material whose state physically changes according to the image data.

[0018]

Embodiments of the liquid crystal display device of the present invention will be described below in detail with reference to the drawings.

(Example 1) A glass substrate 2 having a horizontally oriented resin film applied as an orientation film 1 on one side and subjected to a rubbing treatment in one direction, and a main surface on one side thereof are fine as shown in FIG. By using a rubber film 3 formed of a highly transparent material such as silicone rubber formed in an uneven shape, the main surface of the glass substrate 4 on the side where the alignment film is formed and the rubber as shown in FIG. The film 3 is placed opposite to the main surface of the side where the fine irregularities are formed so as to face each other with a gap, and a nematic liquid crystal material to which a small amount of dichroic dye is added is heated to an isotropic state. Then, the liquid crystal layer 5 was formed by cooling and returning to a liquid crystal state to prepare a liquid crystal display element cell.

In the initial state, the ratio of the transmittance of light polarized in the rubbing direction of the alignment film 1 formed on the glass substrate 2 to the transmittance of light polarized in the direction perpendicular thereto is:
When measured with the transmitted light from the back surface of the glass substrate 2, it is about 1:
It was 2 and it was found that the liquid crystal molecules of the liquid crystal layer 5 were aligned almost in the rubbing direction. However, when observed with a polarization microscope, many fine domains with different orientations were observed.

Next, when the rubber film 3 is stretched along the same direction as the rubbing direction by applying a mechanical tensile force,
The ratio of the transmittance of the light polarized in the rubbing direction of the alignment film 1 on the glass substrate 2 side to the transmittance of the light polarized in the direction perpendicular thereto increases gradually, and when stretched by about 10%. To about 1: 3. When observed with a polarization microscope, it was observed that fine domains with different orientations were reduced and the orientation was made more uniform.

When the rubber film 3 is stretched in the direction perpendicular to the rubbing direction, the alignment film 1 on the glass substrate 2 side is formed.
The ratio between the transmittance of light polarized in the rubbing direction and the transmittance of light polarized in the vertical direction gradually increases in the same manner as in the case of stretching in the rubbing direction, and is about 10% when stretched. It became 1: 3. However, when observed with a polarizing microscope, fine domains with different orientations are reduced, and it is observed that the orientation is more uniform and the 90 °
It was confirmed that the optical rotatory power similar to that of the twisted TN element occurred. This is because the fine concavo-convex shape 6 on the rubber film 3 is elongated in the stretching direction and the orientation of the liquid crystal molecules of the liquid crystal layer 5 is oriented in the stretching direction of the rubber film 3 due to the shape anisotropy. Conceivable.

By the way, a piezoelectric element is formed under each of the fine concavo-convex shapes 6 of the rubber film 3,
A shape change element (not shown) is formed whose surface is physically deformed when a voltage is applied. In this shape changing element, one scanning wiring and one signal wiring (both not shown in FIG. 1) orthogonal to each other in the conventional active matrix type liquid crystal display device are connected to each one of the shape changing elements. Matrix driving is performed by superimposing a voltage applied from the wiring and a voltage applied from the signal wiring.

In such a liquid crystal cell, a polarizing plate is placed on the back surface of a glass substrate in parallel with the rubbing direction, and a polarizing plate whose absorption axis is orthogonal to the polarizing plate is placed on the front surface of the rubber film 3.
Visual comparison was made between the case of stretching in the rubbing direction and the case of stretching in the direction perpendicular to the rubbing direction. As a result, it was observed that when stretched in the rubbing direction, transmitted light was blocked and a black display state was obtained, and when stretched in the direction perpendicular to the rubbing direction, a transmissive state was obtained and a white display state was exhibited. The transmittance ratio at this time was 1:30.
Further, when only the polarizing plate on the front surface of the rubber film was rotated by 90 °, the relationship between the stretching direction and the black and white display state was reversed.

The liquid crystal display element of the present example as described above was driven by using the shape changing element this time to obtain a white display state and a black display state, and the display was held for 1000 hours. As a result, no deterioration of the used liquid crystal material was found.

On the other hand, when a conventional TN type normally black liquid crystal display element is set to a white display state in which a voltage is applied and the display state is held for 1000 hours, the liquid crystal is produced by electrolysis of the liquid crystal material. Due to the deterioration of Layer 5, display unevenness occurred on the screen.

(Embodiment 2) In the liquid crystal display element of the first embodiment, BaTiO ₃ (barium titanate) is used on the glass substrate 4 as shown in FIG. 3 instead of the substrate on which the rubber film 3 is formed. The piezoelectric element 302 which is formed by driving the scanning line 300 and the voltage applied to the signal line 301 is provided, and photosensitive polyimide is applied onto the piezoelectric element 302. A transparent physical state variable alignment film 303 having the same fine concavo-convex shape 6 and having a variable physical state on the surface was formed.

In this example, no dye was added to the liquid crystal material. A liquid crystal display device was produced under the same conditions as in Example 1 except for the above conditions. Note that, also in the second embodiment, the same parts as those in the first embodiment are designated by the same reference numerals.

In the initial state, the liquid crystal molecules of the liquid crystal layer 5 are aligned substantially in the rubbing direction, as in the first embodiment.
When an electric field of 5 kv / cm is applied to the piezoelectric element, the piezoelectric element 30
It was confirmed that No. 2 was stretched in the direction perpendicular to the rubbing direction, and the optical rotation similar to that of the 90 ° TN device was generated along with it. This is because the fine concavo-convex shape 6 on the piezoelectric element 302 is elongated and elongated in the stretching direction, and liquid crystal molecule alignment is aligned in the stretching direction due to the shape anisotropy.

A polarizing plate is arranged on the back surface of the liquid crystal cell and the glass substrate 2 side without the piezoelectric element 302 so that the rubbing direction is parallel to the absorption axis (polarization axis).
A polarizing plate having an absorption axis (polarization axis) orthogonal to that of the polarizing plate (matching the electric field application direction of the piezoelectric element) is arranged on the outward main surface of the glass substrate 4 side having the piezoelectric element. A comparison was made between the case where an electric field was applied to and the case where no electric field was applied.

As a result, it was observed that when no electric field was applied, transmitted light was blocked and a black display state was obtained, and when an electric field was applied, a transmission state was obtained and a white display state was exhibited. The transmittance ratio was 1:10.

The liquid crystal display device of this example was kept in a white display state and a black display state for 1000 hours, but no deterioration of the used liquid crystal material was observed.

On the other hand, when the normally black type liquid crystal display device of the TN system of the conventional structure was kept for 1000 hours in a white display state with an electric field applied, display unevenness occurred due to deterioration due to electrolysis of the liquid crystal material.

In each of the above examples, a nematic liquid crystal material was used, and liquid crystal molecules were aligned in parallel with the substrate to form a transmission type display element. But,
The effect of the present invention is not limited to the conditions of these examples, and a cholesteric liquid crystal or a smectic liquid crystal other than the nematic liquid crystal may be used as the liquid crystal material. As the liquid crystal molecule alignment, horizontal alignment with respect to the substrate, inclined horizontal alignment, vertical alignment, inclined vertical alignment, or a combination thereof may be used. Further, any type of transmission, semi-transmission and reflection may be used.

Further, in each of the above-mentioned embodiments, the fine concavo-convex shape 6 has a shape in which rectangular projections are arranged in an island shape in plan view. However, the physical state variable alignment film according to the present invention. The shape of the alignment groove (orientation protrusion) on the surface of 303 or the rubber film 3 is not limited to this. Besides the above,
For example, it is possible to form it in the shape of an elongated groove, or to form it in the shape of a curved ridge. Alternatively, a prismatic, pyramidal, conical, hemispherical, or periodic arrangement of ridges or grooves, or these ridges or grooves may be inclined.

As for the dimensions of the fine unevenness 6 and the orientation groove (orientation protrusion) on the surface of the physical state variable orientation film 303 or the rubber film 3, the pixel size of one pixel in the above embodiment is 300 .mu.m. 300 μm, where one dimension of the fine concavo-convex shape 6 is 1 μm (vertical) × 1 μm (horizontal)
× 0.3 μm (height), and the interval between adjacent fine concavo-convex shapes 6 was 1 μm. The dimensions of such alignment grooves are
When a general TN type liquid crystal is used as the liquid crystal layer, it is preferable that the gap between the adjacent alignment grooves is 2 μm or less and the size of the fine unevenness 6 is 2 μm or less. Or T
When using a liquid crystal other than the N-type liquid crystal, in the case of the STN-type liquid crystal, it is preferable that the gap between the adjacent alignment grooves is 1.5 μm or less and the size of the fine concavo-convex shape 6 is 1.5 μm or less μm.

Further, in the above embodiment, the voltage applied to the piezoelectric element is a DC voltage, but it goes without saying that the present invention is not limited to the DC voltage application. In addition to this, while considering the matching with the response characteristics of the liquid crystal used, for example, it is possible to apply multiple pulses of an AC waveform voltage with a cycle shorter than the response time of the liquid crystal layer during one scanning selection period. It is possible.

[0038]

As clearly stated in the detailed description above, according to the present invention, the deterioration of the liquid crystal layer is eliminated, the durability is further improved, and the power consumption is further reduced. A liquid crystal display device can be provided.

[Brief description of drawings]

FIG. 1 is a diagram showing a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a diagram partially showing a fine concavo-convex shape 6 of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a liquid crystal display device according to a second embodiment of the present invention.

FIG. 4 is a diagram partially showing a fine concavo-convex shape 6 of the liquid crystal display device according to the second embodiment of the present invention.

[Explanation of symbols]

 1 ... Alignment film 2 ... Glass substrate 3 ... Rubber film 4 ... Glass substrate 5 ... Liquid crystal layer 6 ... Fine concavo-convex shape 302 ... Piezoelectric element 303 ... Physical state variable alignment film

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[Procedure amendment]

[Submission date] February 28, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 1

[Correction method] Change

[Correction content]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction content]

[0019] (Example 1) and the glass substrate 2 was subjected to rubbing treatment in one direction by applying a horizontal orientation of the resin film as an alignment film 1 on one side, one side of the main surface is fine as shown in FIG. 2 By using a rubber film 3 formed of a highly transparent material such as silicone rubber formed in an uneven shape, the main surface of the glass substrate 2 on the side where the alignment film is formed and the rubber as shown in FIG. 1 are used. The film 3 is arranged so as to face the main surface on the side where the fine concavo-convex shape is formed so as to face each other with a gap, and a nematic liquid crystal material in which a small amount of a dichroic dye is added to the gap is isotropic while heating. Then, the liquid crystal layer 5 was formed by cooling and returning to a liquid crystal state to prepare a liquid crystal display element cell.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0023

[Correction method] Change

[Correction content]

By the way , under the fine unevenness 6 of the rubber film 3,
Is a shape change element (not shown) formed by using a piezoelectric element, the surface of which deforms physically when a voltage is applied.
Are formed. In this shape changing element, one scanning wiring and one signal wiring (both not shown in FIG. 1) orthogonal to each other in the conventional active matrix type liquid crystal display device are connected to each one of the shape changing elements. Matrix driving is performed by superimposing a voltage applied from the wiring and a voltage applied from the signal wiring.

[Procedure amendment 4]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

FIG.

Claims (2)

[Claims] 1. Between two substrates arranged in parallel and facing each other,
A liquid crystal display element for enclosing and surrounding a liquid crystal layer and controlling a light transmission state of the liquid crystal layer to display an image, comprising an alignment film formed on a main surface of a substrate in contact with the liquid crystal layer. The physical shape of the surface of the film is changed, and the alignment of the liquid crystal molecules of the liquid crystal layer is changed by the change of the physical shape of the surface of the alignment film to control the light transmission state of the liquid crystal layer to perform display. A liquid crystal display device comprising a dynamic state variable alignment film. 2. The liquid crystal display element according to claim 1, wherein the physical shape of the surface of the physical state variable alignment film is changed by using a piezoelectric element whose surface physical shape is changed by applying a voltage. Liquid crystal display device.