JPH0643449A - Liquid crystal optical device - Google Patents

Abstract

PURPOSE:To improve the contrast ratio at the time of transmission of light and at the time of shielding of light in the case of using a liquid crystal panel for which an electric field effect double refraction mode is used. CONSTITUTION:A nematic liquid crystal 7 having positive dielectric anisotropy in the main liquid crystal panel 10 is oriented in an arrow C direction and a nematic liquid crystal 7 having the positive dielectricanisotropy in the liquid crystal panel 11 for compensation is oriented in an arrow D direction orthogonal with the arrow C. The axes of polarization of first and second polarizing plates 21, 22 disposed in crossed nicols are aligned respectively to straight line A, B directions so that the straight line A forms 45 deg. angle with the arrow C and the arrow D. A voltage is kept impressed at all times to the liquid crystal panel 11 for compensation and the double refraction components generated by the liquid crystal 7 held in an oriented state within the main liquid crystal panel 10 when the voltage is impressed to the main liquid crystal panel 10 are offset by the double refraction components generated by the liquid crystal 7 held in the oriented state within the main liquid crystal panel 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal optical device utilizing a birefringence mode.

[0002]

2. Description of the Related Art Conventionally, a birefringence mode liquid crystal optical device using a nematic liquid crystal having a positive dielectric anisotropy has a liquid crystal interposed between electrodes aligned uniaxially horizontally on a panel surface by an alignment film. The polarizing plates are placed in a crossed Nicol position with each other, and the long axis direction of the aligned liquid crystal molecules has an angle of 45 degrees with the polarizing axis of the polarizing plate. The display and the like are performed by utilizing the light transmission state when no electric field is applied to the (see FIG. 7a) and the light blocking state when the electric field is applied (see FIG. 7b).

[0003]

In the above, FIG.
As shown in b, even when an electric field is applied to the electrodes, liquid crystal molecules near the interface on the inner surface of the panel are held in a horizontal state with respect to the panel surface by adsorption with the alignment film. Therefore, in the case of a liquid crystal optical device having a thin cell thickness of 2 μm or less, for example, the light leakage due to the liquid crystal molecules in the horizontally aligned state becomes relatively large in the light-shielded state, and the light blocking property is deteriorated. There is a problem that the contrast ratio between the time of transmission and the time of interruption is lowered.

Further, in general, the liquid crystal panel also has a problem that the threshold characteristic changes due to the change of the external temperature and the operation becomes unstable.

An object of the present invention is to improve the contrast ratio when light is transmitted and when light is blocked when a liquid crystal panel using a field effect birefringence mode is used.

[0006]

According to the present invention, a first electrode formed on one surface of a first substrate and one of a second substrate facing the one surface of the first substrate. A second electrode formed on the surface, a nematic liquid crystal having a positive dielectric anisotropy that is uniaxially oriented and intervenes in the gap between the first electrode and the second electrode, and the orientation direction. And an angle of 45 degrees or in the vicinity thereof, and the first and second surfaces provided on the other surface side of the first substrate and the other surface side of the second substrate, respectively, at positions of crossed Nicols. The main liquid crystal panel having a polarizing plate is provided with a compensating means for canceling the birefringence component of the liquid crystal molecules held in the alignment state when an electric field is applied between the first and second electrodes. Achieving the above objective by providing between the second polarizing plates There.

Then, the compensating means is provided on the fourth electrode formed on one surface of the third substrate and on the one surface of the fourth substrate opposite to the one surface of the third substrate. A nematic having a positive dielectric anisotropy, which is uniaxially oriented in a direction orthogonal to the orientation direction in the main liquid crystal panel and is present in the gap between the third electrode and the fourth electrode, with the formed fourth electrode being positive. A compensating liquid crystal panel comprising a liquid crystal, and the above-mentioned first and second
A driving circuit for applying an electric field to the compensating liquid crystal panel in order to obtain a birefringent component that cancels the birefringent component of the liquid crystal molecules held in the alignment state when an electric field is applied between the electrodes of By doing so, the above-mentioned object is achieved.

Further, the compensating means is a retardation film for canceling the birefringence component of the liquid crystal molecules held in the alignment state when an electric field is applied between the first and second electrodes, It has achieved the above objectives.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example in which the present invention is applied to a matrix type display device will be specifically described below based on an embodiment shown in the drawings.

In FIG. 1, reference numeral 1 denotes a first substrate, which is made of glass or the like, and a first electrode 2 made of ITO (tin oxide-doped indium oxide) or the like on one surface of the first substrate 1. Are formed in stripes. A first alignment film 3 is made of polyimide or the like and is formed on one surface of the first substrate 1. A second substrate 4 is made of glass or the like, and a second electrode 5 made of ITO or the like is formed on a surface (referred to as a first surface) of the first substrate 1 opposite to one surface thereof. It is formed in a stripe shape in a direction orthogonal to the electrode 2.
A second alignment film 6 is made of polyimide or the like and is formed on the first surface of the second substrate 4. The first alignment film 3 and the second alignment film 6 are uniaxially oriented with the nematic liquid crystal 7 having a positive dielectric anisotropy interposed in the gap between the first alignment film 3 and the second alignment film 6. An antiparallel alignment treatment is performed by a method such as rubbing so as to achieve homogeneous alignment. Reference numeral 8 denotes a spacer, which is made of acrylic resin or the like, is formed between the first substrate 1 and the second substrate 4, and the gap between the first electrode 2 and the second electrode 5 is set to a constant value (in this example). Then, 1.86 μm.)
Hold on. A sealing material 9 is made of an epoxy resin or the like and encloses the liquid crystal 7. Reference numeral 11 denotes a compensating liquid crystal panel, which includes a third substrate 12, a third electrode 13, a third alignment film 14, a fourth substrate 15, a fourth electrode 16, a fourth alignment film 17, a liquid crystal 18, and a spacer. 19 and the sealing material 20. The third substrate 12 is made of glass or the like, one surface of which is joined to the surface of the second substrate 4 facing the first surface, and the other surface of which is made of ITO or the like as shown in FIG. Electrode 13 is formed on the entire surface. The third alignment film 14 is
It is made of polyimide or the like and is formed on the other surface of the third substrate 12. The fourth substrate 15 is made of glass or the like,
A fourth electrode 16 made of ITO or the like is formed on the entire surface of the surface of the third substrate 12 that faces the other surface (referred to as the second surface). Note that the pixel formed by the intersection of the third electrode 13 and the fourth electrode 16 is formed wider than the display range including the matrix-shaped pixel formed by the first electrode 2 and the second electrode 5. is there. The fourth alignment film 17 is made of polyimide or the like and is formed on the second surface of the fourth substrate 15. It should be noted that the third alignment film 14 and the fourth alignment film 17 have liquid crystal molecules of nematic liquid crystal 18 having a positive dielectric anisotropy, which are present in the gap between the third alignment film 14 and the fourth alignment film 17. The antiparallel alignment treatment is performed by a method such as rubbing so that the liquid crystal 7 is homogeneously aligned in a uniaxial direction orthogonal to the long axis direction of the molecules. That is, the major axis direction of the liquid crystal molecules of the liquid crystal 7 and the major axis direction of the liquid crystal molecules of the liquid crystal 18 sealed in the compensating liquid crystal panel 11 are orthogonal to each other. The spacer 19 is made of acrylic resin or the like, is formed between the third substrate 12 and the fourth substrate 14, and the gap between the third electrode 13 and the fourth electrode 16 is a constant value (in this example, ,
1.84 μm. ) Hold. The sealing material 20 is made of epoxy resin or the like, and encloses the liquid crystal 18. Reference numeral 21 denotes a polarizing plate, which is arranged on the other surface of the first substrate 1. Reference numeral 22 denotes a polarizing plate, which is arranged on the surface of the fourth substrate 14 facing the second surface. The polarizing plate 21 and the polarizing plate 22 are located in a crossed Nicols position, and their polarization axes are arranged at an angle of 45 degrees with the long axis direction of the molecules of the liquid crystal 7 and the liquid crystal 18. In addition, the first substrate 1, the second electrode 2, the first alignment film 3, the second substrate 4, the second electrode 5, the second alignment film 6, the liquid crystal 7, the spacer 8, the sealing material 9 and The polarizing plates 21 and 22 form the main liquid crystal panel 10. Reference numeral 23 denotes a drive circuit, which applies a drive voltage to the first electrode 2 and the second electrode 5 to cause the main liquid crystal panel 10 to perform display, and also applies an electric field between the first and second electrodes. The voltage for obtaining the birefringence component that cancels the birefringence component of the liquid crystal molecules 7 held in the aligned state is applied to the third electrode 1.
It is applied to the third and fourth electrodes 16.

FIG. 2 is a plan view of FIG. 1, showing the liquid crystal 7 described above.
And the orientation direction of the molecules of the liquid crystal 18 and the directions of the polarization axes of the polarizing plates 21 and 22. The straight line A indicates the polarizing plate 21.
Of the polarization axis of the liquid crystal 7, the straight line B indicates the direction of the polarization axis of the polarizing plate 22, the arrow C indicates the alignment direction of the liquid crystal 7, and the arrow D indicates
Indicates the alignment direction of the liquid crystal 18.

Next, the operation will be described. The drive circuit 23 is
A birefringence component that cancels out a light leakage component, that is, a birefringence component generated when a predetermined drive voltage is applied to the first electrode 2 and the second electrode 5 of the main liquid crystal panel 10 to put it in a light shielding state is for compensation. A voltage is constantly applied so that it is generated in the liquid crystal panel 11.

For example, in the above example, when the driving voltage of the main liquid crystal panel 10 is a rectangular wave of ± 0 to ± 10 v of 10 kHz, the voltage applied to the compensating liquid crystal panel 11 is 10 kHz.
z, ± 7v rectangular wave voltage.

By applying a voltage to the compensating liquid crystal panel 11, when a voltage is applied to the main liquid crystal panel 10 to make it in a light-shielded state, adsorption to the first alignment film 3 and the second alignment film 6 etc. 2 causes the birefringence component (the length of the liquid crystal molecule 7) of the liquid crystal molecule 7 which is not induced by the electric field in the vicinity of the interface between the first substrate 1 and the second substrate 4 and is kept in the aligned state in the direction of arrow C in FIG. The phase difference between the phase of the light oscillated in the axial direction and the phase of the light oscillated in the direction orthogonal to the long axis direction) is the third due to adsorption between the third alignment film 14 and the fourth alignment film 17, or the like. A birefringence component due to the liquid crystal molecules 18 which is not induced by an electric field in the vicinity of the interface between the substrate 12 and the fourth substrate 15 and is kept in the alignment state in the direction of arrow D in FIG. Vibration in the direction orthogonal to the phase of the generated light and the major axis direction Offset by the phase difference) between the phase of the light, the light-shielding property when a voltage is applied is increased in the main liquid crystal panel 10.

FIG. 3 is a diagram showing voltage-contrast ratio characteristics of a conventional liquid crystal optical device utilizing a field effect birefringence mode, that is, only the main liquid crystal panel 10 and the liquid crystal optical device of the above embodiment. The curve a shows the characteristics of the conventional liquid crystal optical device, and the curve b shows the characteristics of the liquid crystal optical device of this embodiment. The conventional liquid crystal optical device has a cell thickness of 1.86 μm. In the present embodiment, the main liquid crystal panel has a cell thickness of 1.86 μm and the compensating liquid crystal panel has a cell thickness of 1.84 μm. The voltage applied to the conventional liquid crystal optical device and the main liquid crystal panel of this embodiment is a square wave of ± 0 to ± 10 v at 10 kHz. A rectangular wave voltage of 10 kHz and ± 7 v is constantly applied to the compensating liquid crystal panel. From the figure, it can be seen that the present invention can achieve the improvement of the contrast ratio.

Further, since the birefringence component of the compensating liquid crystal panel 11 can be changed by changing the voltage applied to the compensating liquid crystal panel 11, the main liquid crystal panel 10 can be changed.
Even if Vsat (voltage value indicating a light-shielded state: 10 V in FIG. 3) fluctuates due to ambient temperature change, the compensating liquid crystal panel 1
Vsat of the main liquid crystal panel 10 can be maintained at a constant value by appropriately changing the voltage value applied to the first liquid crystal panel 1. For example, the temperature becomes low and Vsat of the main liquid crystal panel 10
When becomes larger, the voltage applied to the compensating liquid crystal panel 11 can be made smaller and Vsat as the liquid crystal optical device can be maintained at a constant value.

Although the present invention is applied to the matrix type display device in the above-mentioned embodiments, it may be applied to a segment type display device and further applied to an optical shutter element of a liquid crystal printer or the like. The effect of is obtained.

The electrode structure of the main liquid crystal panel, the spacer material, the driving voltage of the main liquid crystal panel 10 and the applied voltage of the frequency compensating liquid crystal panel are not limited to the above, but can be changed as appropriate.

Further, in the above-mentioned example, the orientation directions of the liquid crystals 7 and 18 form an angle of 45 degrees with the respective polarization axes of the first polarizing plate 21 and the second polarizing plate 22, so that the best contrast is obtained. However, the angle is not limited to the above and may be an angle in the vicinity of 45 degrees, for example, an angle of 40 degrees to 50 degrees.

Next, an example in which the retardation film cancels the birefringence component of the liquid crystal molecules held in the aligned state when an electric field is applied between the electrodes of the liquid crystal optical device will be described.

In FIG. 4, reference numerals 24 and 25 denote retardation films, which are laminated between the second substrate 4 and the polarizing plate 22 in this example, and the stretching direction of the retardation film 24 is shown in FIG. The straight line E direction is set, and the stretching direction of the retardation film 25 is the straight line F direction orthogonal to the straight line E. By making the stretching directions of the two retardation films orthogonal to each other in this way,
A desired retardation can be obtained by the difference in retardation between the two retardation films. By setting the phase difference between the phase difference film 24 and the phase difference film 25 to be the phase difference of light to be canceled, the light shielding property is improved.

The same reference numerals as in FIG. 1 are the same, and the directions of the polarization axes of the polarizing plates 21 and 22 and the alignment treatment directions of the first alignment film 3 and the second alignment film 6 are as shown in FIG. A straight line G, a straight line H, and an arrow J shown in FIG. The straight line G, the straight line H, and the arrow J shown in FIG. 5 correspond to the straight line A, the straight line B, and the arrow C shown in FIG. 2, respectively, and the straight line E is orthogonal to the arrow J.

For example, when a voltage is applied to the first electrode 2 and the second electrode 5, the first substrate 1 and the second substrate 5
The phase difference of the light of the birefringence component due to the liquid crystal molecules 7 held in the orientation of the arrow J direction at the interface
In the case of m, the retardation film 24 has a retardation of 280
with a wavelength of 270 nm as a retardation film 25 having a retardation of 270
It is possible to cancel the phase difference of 10 nm due to the above birefringence component by using each of those having a wavelength of nm.
That is, by laminating the retardation films 24 and 25, it is possible to obtain 10 in the stretching direction (straight line E) of the retardation film 24.
A phase difference of nm is created, and this direction has a symmetrical relationship with the alignment direction (arrow J) of the liquid crystal molecule 7 with respect to the polarization axis G. Therefore, the birefringence component due to the alignment direction of the liquid crystal molecule 7 when an electric field is applied. Will be offset by the retardation film.

FIG. 6 shows a liquid crystal optical device using the conventional field effect birefringence mode and the liquid crystal optical device of the above embodiment.
It is a thing which shows the voltage-contrast ratio characteristic at the time of applying the drive voltage of the square wave of +/- 10v and 10kHz between electrodes. The curve c is the characteristic of the conventional liquid crystal optical device,
A curve d is the characteristic of the liquid crystal optical device of this embodiment. From the figure, it can be seen that the present invention can improve the contrast ratio.

In the above example, the retardation film is the second
However, it may be arranged between the first substrate 1 and the polarizing plate 21, and the respective retardation films may be arranged on the first substrate side. You may arrange | position separately from the 2nd board | substrate side.

The following can be said in the above-described embodiment in which the phase difference film is used to cancel the light leakage component.

The retardation of each retardation film is not limited to the above, and the same effect as above can be obtained by using, for example, a retardation film having a retardation of 300 nm and a retardation film having a retardation of 290 nm.

Further, the retardation due to the birefringence which is canceled by the retardation film is not limited to the above 10 nm, but can be appropriately changed according to the retardation to be canceled.

Further, a desired retardation was obtained by superposing two retardation films at right angles to each other, but it is technically possible to obtain a minute retardation with one retardation film. This is because it is difficult, and if the desired retardation can be obtained with only one retardation film, the same effect as above can be obtained by setting the stretching direction to be the direction orthogonal to the alignment direction of the liquid crystal molecules. Further, a desired retardation may be obtained by stacking two or more retardation films so that the stretching directions are orthogonal to each other.

Further, in the above example, the alignment direction of the liquid crystal 7 is set at an angle of 45 degrees with the respective polarization axes of the first polarizing plate 21 and the second polarizing plate 22, so that the best contrast is obtained. However, the angle is not limited to the above, and may be an angle in the vicinity of 45 degrees, for example, an angle of 40 degrees to 50 degrees.

The present invention can be applied to various liquid crystal display devices and liquid crystal shutters of optical printers.

[0032]

According to the present invention, the compensating means for canceling the birefringence component of the liquid crystal molecules held in the aligned state when the electric field is applied between the first and second electrodes has first and second polarizing plates. By providing the space between them, it is possible to improve the light shielding property at the time of blocking light and improve the contrast ratio.

When a compensating liquid crystal panel is used as the compensating means, the birefringence component of the compensating liquid crystal panel can be changed by changing the voltage applied to the compensating liquid crystal panel. Even if the (voltage value indicating the light-shielded state) fluctuates due to a change in ambient temperature, the Vsat of the main liquid crystal panel can be maintained at a constant value by appropriately changing the voltage value applied to the compensating liquid crystal panel.

Further, when the retardation film is used as the compensating means, the light shielding property at the time of blocking the light can be increased and the contrast ratio can be improved by a simple structure of laminating the retardation film.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a plan view of FIG.

FIG. 3 is an explanatory diagram showing a voltage-contrast ratio between the present invention and a conventional liquid crystal optical device.

FIG. 4 is a sectional view showing another embodiment of the present invention.

5 is a plan view of FIG.

FIG. 6 is an explanatory diagram showing a voltage-contrast ratio between the present invention and a conventional liquid crystal optical device.

FIG. 7 is an explanatory diagram showing states of liquid crystal molecules when an electric field is not applied and when an electric field is applied.

[Explanation of symbols]

 1 First Substrate 2 First Electrode 4 Second Substrate 5 Second Electrode 7 Nematic Liquid Crystal with Positive Dielectric Anisotropy 10 Main Liquid Crystal Panel 11 Compensation Liquid Crystal Panel 12 Third Substrate 13 Third Electrode 15 Fourth substrate 16 Fourth electrode 18 Nematic liquid crystal with positive dielectric anisotropy 21 First polarizing plate 22 Second polarizing plate 23 Drive circuit 24 Phase difference film 25 Phase difference film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideki Shoji 4-1-1 Taihei, Sumida-ku, Tokyo Inside Seikosha Co., Ltd. (72) Masanori Fujita 4-1-1 Taihei, Sumida-ku, Tokyo Shares Inside the company Seikosha

Claims (3)

[Claims] 1. A first substrate formed on one surface of a first substrate.
In the gap between the first electrode and the second electrode, the second electrode formed on the one surface of the second substrate facing the one surface of the first substrate, and the gap between the first electrode and the second electrode. The nematic liquid crystal that is homogeneously oriented in the axial direction and has a positive dielectric anisotropy and forms an angle of 45 degrees with or near the orientation direction, respectively, and at the positions of crossed Nicols with respect to each other on the other side of the first substrate. When an electric field is applied between the first and second electrodes to the main liquid crystal panel including the first and second polarizing plates provided on the other side of the second substrate and on the other side of the second substrate. A liquid crystal optical device, characterized in that a compensating means for canceling a birefringent component of the liquid crystal molecules held in an aligned state is provided between the first and second polarizing plates. 2. The compensating means according to claim 1, wherein the compensating means includes a third electrode formed on one surface of the third substrate and a fourth substrate facing the one surface of the third substrate. A fourth electrode formed on one surface and a dielectric anisotropy that is uniaxially aligned in a direction orthogonal to the alignment direction in the main liquid crystal panel and is present in the gap between the third electrode and the fourth electrode. Compensating liquid crystal panel comprising a nematic liquid crystal having a positive property, and birefringence for canceling a birefringent component of the liquid crystal molecules held in an alignment state when an electric field is applied between the first and second electrodes. A liquid crystal optical device comprising a driving circuit for applying an electric field to the compensating liquid crystal panel to obtain a component. 3. The retardation film according to claim 1, wherein the compensating means cancels a birefringence component of the liquid crystal molecules held in an aligned state when an electric field is applied between the first and second electrodes. And a liquid crystal optical device.