JPS61232419A - Optical modulator element - Google Patents

Abstract

PURPOSE:To obtain the titled element having a high contrast ratio by treating one of a pair of the orientation films with rubbing, and by un-treating another one of the pair of the orienta tion films with rubbing so as to be a direction of controlling the orientation which is given to the liquid crystal substance by the orientation film to a single one. CONSTITUTION:The pair of the transparent substrates 11, 12 made of the transparent plates of glass etc. are arranged to the liquid crystal cell 10 so as to be the pair of the electrodes face to face each other with a prescribed space. The transparent electrodes 13, 14 composed of ITO dopped with for example, tin are vapor-deposited on the counter surfaces respectively. And, the orientation films 15, 16 which coat the electrodes 13, 14, and give the orientation to the liquid crystal substance are formed on the counter surface respectively. The orientation film 15, 16 are made of a polyvinyl alcohol, and one of the orientation films is treated with rubbing, and another of the films is not treated with rubbing. The ferroelectricity chiral smectic liquid crystal 18 is enclosed in the space surrounded by the substrates 11, 12 and a sealing material 17. A pair of polarizing plates 19, 20 are overlapped on the outside surfaces of the substrates 11, 12 respectively so as to intersect polarizing directions of the plates at right angles each other, thereby preventing the lowering of the optical transmissivity due to slipping off the direction based on the force for controlling the orientation of the polarizing plates, and enabling to obtain a sufficiently large contrast ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal type light modulation element, and particularly to a light modulation element configured to obtain sufficient contrast.

[Prior Art] and [Problems to be Solved by the Present Invention] Various types of light modulation elements of this type have been developed in the past, depending on the orientation of the liquid crystal material, the method of controlling the arrangement of the liquid crystal material, etc.

The types of liquid crystal substances are roughly divided into three types, nematic type, cholesteric type, and smectic type, depending on the difference in their molecular arrangement. In addition, as a method for controlling the alignment of liquid crystal substances, in the case of a parallel alignment method in which liquid crystal substances are aligned in parallel, scratches are formed parallel to a certain direction on the alignment film (referred to as a rubbing process). The rubbing method that arranges liquid crystal materials in parallel is mainly used.

For example, a twisted nematic field effect type light modulation element uses a nematic liquid crystal material and orients the directions of scratches formed on a pair of alignment films at right angles to each other.
It is widely used in display devices such as electronic weight calculators and digital watches.

However, this type of device lacks high-speed response because changes in the arrangement of the liquid crystal material are accompanied by changes in the arrangement of the layer structure. It is inappropriate to use it for equipment that requires performance.

As a light modulation element suitable for such devices that require high-speed response, one using ferroelectric chiral smectic liquid crystal is known. This liquid crystal substance is shown in Figure 2 (
As schematically shown in a), each liquid crystal molecule 1 has a helical structure arranged at a tilt angle θ with respect to the helical axis direction 2, and each molecule exhibits spontaneous polarization in a direction perpendicular to this. have.

Then, when an electric field (1) is applied vertically to this, the liquid crystal molecules face in the same direction, exhibiting opacity, and the electric field (1) acts on them, as shown in Figure 2, etc. and the second
As shown in Figure (C), the liquid crystal molecules are reoriented in different directions and exhibit light transmission. In this way, the ferroelectric chiral smectic liquid crystal does not involve any change in the arrangement of the layer structure, but only changes in the orientation of the molecules within the layer, so high-speed response can be achieved. In addition, in this liquid crystal material, by making the thickness of the liquid crystal layer thinner than the helical pitch of the liquid crystal molecules, in a steady state where no electric field is applied,
It is known that bistability that maintains state C) can be obtained.

By the way, conventionally, in a light modulation element using this ferroelectric chiral smectic liquid crystal, the liquid crystal material is arranged on transparent substrates facing each other.
For example, it is common to perform a so-called homogeneous alignment process in which an alignment film made of polyimide or the like is rubbed in the same direction.

However, in reality, it is difficult to precisely match the rubbing directions of a pair of alignment films, and the liquid crystals are often not aligned accurately in parallel due to different alignment directions of the liquid crystals by each alignment film. do not have. As a result, the ratio of the optical output in the bright state showing translucency to the optical output in the dark state showing non-transparent property, that is, the contrast ratio is, for example, 6.8.
is relatively low.

[Means for solving problems]

The present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide a light modulation element that can obtain a high contrast ratio.

In order to achieve the above object, the present invention applies a rubbing treatment to only one of a pair of alignment films and does not apply rubbing treatment to the other, thereby controlling the alignment direction that the alignment film gives to the liquid crystal material. It is configured so that there is a single number.

〔Example〕

Hereinafter, the present invention will be specifically explained based on the drawings.

FIG. 1 is a cell structure diagram schematically showing an embodiment of the present invention. The liquid crystal cell 10 includes a pair of transparent substrates 11 and 12 made of transparent plates such as glass.

These transparent substrates 11 and 12 are opposed to each other at a predetermined interval, and their opposing surfaces each have a
For example, transparent electrodes 13 and 14 made of soot-doped indium (ITO) are formed by vapor deposition, sputtering, or other methods. Further, on these opposing surfaces, alignment films 15.16 are formed which cover the electrodes 18.14 and provide alignment to a liquid crystal material to be described later. .

The space between the peripheral edges of these substrates 11 and 12 is sealed with a sealing material 17, and a ferroelectric chiral smectic liquid crystal 18 is sealed in the space surrounded by these substrates 11 and 12 and the sealing material 17. . Sub board 11
．． A pair of polarizers 19 and 20 whose polarization directions are orthogonal to each other are superimposed on the outer surface of the lens 12 . The polarization direction 8 of one of these polarizers 19° 20 is as shown in FIG. 2(b),
As shown in (c), the electric field (-
E) is directed in the long direction of the liquid crystal molecules 1 when applied, and the other deflection direction 4 is perpendicular to this.

The alignment films 15 and 16 are made of polyvinyl alcohol, and only one of them is subjected to a rubbing treatment, and the other is not subjected to a rubbing treatment.

The cell thickness is 2μ, and the liquid crystal 18 is bistable, with its internal molecular arrangement being switched between the dark state shown in FIG. 2(b) and the bright state shown in FIG. 2(C). It has a sexual nature. Also, the tilt angle θ of the liquid crystal molecule 1 is π/8, and the transmitted light intensity in the bright state is the wavelength λ = 450.55.
As shown in FIG. 8 for 0.650 nanometers.

According to the liquid crystal cell 10 configured in this way, the temperature is 25
The contrast ratio obtained at °C is 40.0,
While the contrast ratio of the conventional example subjected to homogeneous alignment treatment was 6.8, a contrast ratio of about 7 times was obtained.

Of course, the present invention is not limited to the above embodiment. For example, the transparent electrode IL 14 may be formed of a known material such as cadmium stannate (0'l'0) or tin oxide doped with antimony. Bye.

Further, as the material of the alignment films 15 and 16, polyimide resin other than polyvinyl alcohol may be used, and silicon oxide (
It may be composed of a known inorganic alignment film such as Si02).

Note that the ferroelectric chiral smectic liquid crystal 18 is D
OBAMDC, OOBAMBCO, DOBAMBOO,
'I'DOEAMBOO,)IOBACPO,OOEA
MBMO, PAOME.

All known products such as DDOBAMBO, COBAMBO, and HOBAMBO are publicly known.

〔Effect of the invention〕

As explained above, in the light modulation element according to the present invention, only one of the pair of alignment films is subjected to rubbing treatment, and the other is not subjected to rubbing treatment, so that one of the alignment films is applied to the liquid crystal material. The sequence-regulating force is given only by the sequence-regulating force, and the direction of the sequence-regulating force is single. Therefore, in the conventional product in which both alignment films are rubbed, the direction of the alignment regulating force exerted on the liquid crystal material by one of the alignment films deviates from the correct direction.
While the alignment of liquid crystal substances may be disturbed, in the case of the present invention, there is no risk of such deviation in the direction of the alignment regulating force. As a result, the present invention can prevent a decrease in light transmittance due to a deviation in the direction of the alignment regulating force,
A sufficiently large contrast ratio can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a cell structure diagram schematically showing an embodiment of the present invention;
Figure 2 (roll) is a schematic diagram showing the molecular arrangement of a ferroelectric chiral smectic liquid crystal in a steady state with no applied electric field, and Figure 2 (b) is a schematic diagram showing the molecular arrangement of a ferroelectric chiral smectic liquid crystal in a steady state with no applied electric field. Schematic diagram showing molecular arrangement,
Figure 2(c) is a schematic diagram showing the molecular arrangement of a ferroelectric chiral smectic liquid crystal when an electric field (-B) is applied, and Figure 8 shows the refractive index anisotropy ΔO of the ferroelectric chiral smectic liquid crystal. It is a diagram showing the transmitted light intensity versus the product ζ of the layer thickness d. 11.12...Transparent substrate, 13.14...Transparent ゛4
Pole, 15.16... Alignment film, 18... Ferroelectric liquid crystal material.

Claims (1)

[Claims] (1) 1 facing each other at a predetermined interval
In a light modulation element comprising a pair of transparent substrates, an electrode and an alignment film covering the electrodes are formed on opposing surfaces of each transparent substrate, and a ferroelectric liquid crystal substance is sealed between both alignment films, one of the alignment films is A light modulation element characterized by having been subjected to a rubbing process only.