JPH10221684A - Liquid crystal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a liquid crystal device by which a design free degree is high, cost is inexpensive and a sufficient optical characteristic and durability are realized by permitting the polarization degree of a polarizing plate which is arranged at a light emitting side to be higher than that of the polarizing plate which is arranged at an incident side. SOLUTION: The polarizing plate 1 at the light emitting side, the polarizing plate 2 at the incident side, a liquid crystal cell 10 and a back light 3 such as a fluorescent tube, etc., are provided. The liquid crystal cell 10 is constituted by pinching liquid crystal between a pair of substrates 11a and 11b consisting of glass, etc., which is provided with a transparent electrode and an orienting film, etc. The polarizing plates 1 and 2 used for the liquid crystal device are obtained by adhering a protecting film to an polarizer. Then, the polarization degree of the polarizing plate 1 which is arranged at the light emitting side is higher than that of the polarizing plate 2 which is arranged at the incident side. When the liquid crystal cell which is provided with a characteristic for converting incident and straight polarized light into the oblong polarized light of straight polarized light or an almost straight line so as to execute emission is used as the liquid crystal cell, an optical characteristic which is synthetically superior concerning contrast and a transmissivity is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal device,
More specifically, the present invention relates to a low-cost liquid crystal device having excellent optical characteristics and durability.

[0002]

2. Description of the Related Art Liquid crystal devices are widely used as display devices for various OA devices such as liquid crystal televisions and notebook personal computers, and are required to have higher performance in terms of contrast, viewing angle characteristics, durability and the like during display. It has become.

By the way, a polarizing plate used in a liquid crystal device is:
It is an important optical member that determines the contrast and transmittance of the liquid crystal device. Parameters that determine this characteristic include the degree of polarization and transmittance of the polarizing plate, and durability such as heat resistance and moisture resistance.

[0004]

However, the conventional polarizing plate has a trade-off relationship between the degree of polarization and the transmittance because of the material limitation, and both of them have been expensive. Further, the optical characteristics and the durability also have a trade-off relationship, and it has been difficult to obtain an excellent polarizing plate. Furthermore, the characteristics of commercially available polarizing plates are limited, and it has been difficult to obtain desired optical characteristics.

An object of the present invention is to provide a liquid crystal device which solves the above problems, has a high degree of freedom in design, is inexpensive, and has sufficient optical characteristics and durability.

[0006]

The structure of the present invention to achieve the above object is as follows.

That is, a first aspect of the present invention is a liquid crystal device having at least a liquid crystal cell in which a liquid crystal is sandwiched between a pair of substrates, and two polarizing plates disposed on an incident side and an output side of the liquid crystal cell. Wherein the degree of polarization of the polarizing plate arranged on the emission side is higher than the degree of polarization of the polarizing plate arranged on the incident side.

In the first aspect of the invention, if a liquid crystal cell having a characteristic of converting incident linearly polarized light into linearly polarized light or substantially linear elliptically polarized light and emitting the same is used as the liquid crystal cell, the polarizing plates having different transmittances can be used. Overall better optical characteristics with respect to contrast and transmittance are realized than when each of them is used alone on both the incident side and the exit side.

This is because the use of the liquid crystal cell as described above efficiently converts the polarization state of the light incident from the incident side polarizing plate into linearly polarized light. This is because, since the contrast is determined, it is possible to increase the contrast by arranging a material having a higher degree of polarization on the emission side. Also, on the other hand,
As described above, the degree of polarization and the transmittance of a material generally used for a polarizing plate are in a trade-off relationship. Therefore, in the first invention, the transmittance of the polarizing plate on the exit side of the liquid crystal cell is usually Although the transmittance of the liquid crystal device is lower than the transmittance of the polarizing plate on the incident side, the transmittance of the liquid crystal device is not greatly influenced only by the transmittance of the polarizing plate on the emitting side unlike the above-described contrast. This is because a decrease in transmittance can be suppressed to be smaller than the transmittance when a high polarizing plate is used on both the incident side and the output side.

A second aspect of the present invention is a liquid crystal device having at least a liquid crystal cell in which liquid crystal is sandwiched between a pair of substrates, and two polarizing plates disposed on an incident side and an output side of the liquid crystal cell. Wherein the heat resistance and / or the moisture resistance of the polarizing plate arranged on the light exit side are superior to those of the polarizing plate arranged on the light incident side.

For example, in a liquid crystal device used for outdoor use such as a car navigation system and a portable TV, the environment outside the device becomes extremely severe compared to the inside due to the influence of sunlight, weather, and the like. Therefore, in the second invention, by using a polarizing plate having higher weather resistance (heat resistance and / or moisture resistance) than the polarizing plate on the incident side as the polarizing plate on the emitting side which is easily affected by the external environment, In particular, high durability of the liquid crystal device used outdoors is realized as described above. On the other hand, as described above, in the material generally used for the polarizing plate, there is a trade-off between the optical characteristics and the durability. Therefore, in the second invention, the optical plate of the polarizing plate on the exit side of the liquid crystal cell is usually used. The characteristics are inferior to the optical characteristics of the polarizing plate on the incident side, but this can be compensated for by using a polarizing plate with particularly excellent optical characteristics on the incident side.

A third aspect of the present invention is a liquid crystal device having at least a liquid crystal cell in which liquid crystal is sandwiched between a pair of substrates, and two polarizing plates disposed on an incident side and an output side of the liquid crystal cell. Wherein the polarizing plate disposed on the incident side is a polarizing plate formed of an iodine-based material, and the polarizing plate disposed on the output side is a polarizing plate formed of a dye-based material. In liquid crystal devices.

The third aspect of the present invention is to use an iodine-based polarizing plate having excellent optical properties but inferior durability on the incident side and a dye-based polarizing plate having high durability but poor optical properties on the emitting side. As in the second aspect, it is possible to suppress deterioration of optical characteristics while realizing high durability.

As described above, according to the present invention, by using polarizing plates having different characteristics on the incident side and the emitting side of the liquid crystal cell, overall superior characteristics can be obtained as compared with the case where the same type is used. Thus, the degree of freedom in designing optical designs such as transmittance and contrast, and durability design such as heat resistance and moisture resistance can be expanded, and costs can be reduced.

[0015]

FIG. 1 schematically shows the general structure of a liquid crystal device according to the present invention. In the drawing, reference numeral 1 denotes a polarizing plate on the output side, 2 denotes a polarizing plate on the incident side, 10 is a liquid crystal cell, 3
Denotes a backlight such as a fluorescent tube.

The liquid crystal cell 10 is constructed by sandwiching a liquid crystal 12 between a pair of substrates 11a and 11b made of glass or the like having a transparent electrode, an alignment film and the like. The liquid crystal 12 can be arbitrarily selected, for example, a twisted nematic type using a nematic liquid crystal, a super twisted nematic type,
In-plane switching type, SS using ferroelectric liquid crystal
FLC type is mentioned. In the present invention, in particular, a chiral smectic liquid crystal, which is a ferroelectric liquid crystal, can be preferably applied, thereby realizing an improvement in the speed and memory performance of the liquid crystal device.

The polarizing plates 1 and 2 used in the liquid crystal device of the present invention are obtained by bonding a protective film to a polarizer. FIG. 2 shows an example of the configuration. In the figure, 21 is a protective film, 22 is an adhesive layer, and 23 is a polarizer. The protective film 21 may be provided only on one side of the polarizer 23 (see FIG. 2).
(A)) If necessary, it can be provided on both surfaces of the polarizer 23 (FIG. 2 (b)).

As the protective film 21, for example, polycarbonate, triacetyl cellulose, polymethyl methacrylate, polyether sulfone, polyethylene terephthalate, polyarylate, polyimide, polyvinyl alcohol, polystyrene and the like can be used. Is not particularly limited.

As the polarizer 23, a film made of a hydrophilic polymer such as polyvinyl alcohol, partially formalized polyvinyl alcohol, ethylene / vinyl acetate copolymer partially saponified film is treated with iodine and / or a dichroic dye. And a film made of a plastic film such as polyvinyl chloride treated and oriented with a polyene. As the durable polarizer, a dye-based polarizer is particularly preferably used.

The type of the adhesive 22 for bonding the polarizer 23 and the protective film 21 is not particularly limited. However, in consideration of preventing the optical characteristics of the polarizer 23 and the protective film 21 from changing, a high temperature is required during curing and drying. Those which do not require a process are preferable, and those having a short curing treatment time and a short drying treatment time are desirable.

[0021]

Embodiments of the present invention will be described below in detail.

(Embodiment 1) The liquid crystal device of the present embodiment is shown in FIG.
Is the same as that shown in FIG.

In this embodiment, a ferroelectric liquid crystal is used as the liquid crystal. The mode was proposed by Clark and Lagerwall (Japanese Patent Application Laid-Open No. Sho 56).
-107216, U.S. Pat. No. 4,368,924, etc.), and an SSFLC mode in which transmitted light is controlled in combination with a polarizing element utilizing the refractive index anisotropy of ferroelectric liquid crystal molecules.

As the liquid crystal cell 10, as shown in FIG. 3, a cell having a structure in which the surface properties of the opposing substrate are different is used. In the figure, 31 and 37 are glass substrates, 32 and 36 are transparent electrodes,
33 is a rubbed alignment film having a horizontal alignment function, 34 is a ferroelectric liquid crystal layer, 35 is a vertical alignment material,
8, 39, and 40 are front views of cones characterizing liquid crystal molecules in the chiral smectic layer.
Numeral 39 indicates two stable states in the uniform alignment, and numeral 40 indicates an example of the splay alignment state. The procedure for producing the liquid crystal cell will be described below.

First, a pair of glass substrates 31 and 37 on which an ITO film having a thickness of 70 nm is formed by sputtering as the transparent electrodes 32 and 36 are prepared, and a polyamic acid LP-, a polyimide precursor, is formed on one of the ITO films. NMP (N-methylpyrrolidone): n-BC (n-
(Butyl cellosolve) mixed solution was spin-coated. The coating solution is LP-6 in a mixed solvent of NMP: n-BC = 2: 1.
4 was adjusted to 1% by weight, and spinning was performed at 45 rpm for 20 seconds. After drying the substrate in an oven at 80 ° C. for 5 minutes, the substrate was heated and baked in an oven at 200 ° C. for 1 hour to imidize the substrate. The obtained polyimide film was about 10 nm thick, and this film was rubbed to form an alignment film. Rubbing was performed using a nylon film wound around a roller having a diameter of 10 cm, and the rotation was performed at 16.7 revolutions /
Rubbing was performed twice (one way) in the same direction at a pressure of 0.4 mm for pushing the cloth against the surface of the alignment film and a feed speed of the substrate of 10 mm / sec. Thereafter, an IPA (isopropyl alcohol) solution in which silica beads having an average particle diameter of 2.0 μm are dispersed at 0.008% by weight is spin-coated on the surface of the substrate for 10 seconds under a spin condition of 25 rotations / second to obtain a dispersion density. About 300 bead spacers / mm ² were sprayed.

The other substrate on the opposite side is the ITO of the substrate.
A 0.5% by weight solution of a silane coupling agent (ODS-E) in ethyl alcohol was spin-coated on the film at 45 rpm for 20 seconds to perform vertical alignment treatment. Thereafter, a thermosetting sealing agent was applied on the substrate by printing.

The two substrates thus obtained were adhered to each other and thermally cured in an oven at 150 ° C. for 90 minutes to form a cell.

The liquid crystal composition used in this example was obtained by mixing the following compounds A and B at a ratio of 95/5 (weight ratio).

[0029]

Embedded image

The above-mentioned liquid crystal composition has characteristics of a spontaneous polarization at 30 ° C. of 26 nC / cm ² and a tilt angle of 22 °,
The phase transition temperatures are as follows.

[0031]

Embedded image

The tilt angle and spontaneous polarization of the liquid crystal composition were measured as follows.

[Measurement of tilt angle] ± 30 to ± 50 V, 1
While applying an AC (alternating current) of １００100 Hz between the upper and lower substrates of the liquid crystal element via electrodes, the liquid crystal element disposed therebetween is rotated in parallel with the polarizer under orthogonal crossed Nicols, and at the same time, photomultiplier (Hamamatsu) The first extinction position (the position where the transmittance is lowest) and the second extinction position are determined while detecting the optical response with Photonics Co., Ltd.). At this time, 1/2 of the angle from the first extinction position to the second extinction position was defined as the tilt angle.

[Method of measuring spontaneous polarization]
Miyasato et al., "Direct Measurement Method of Spontaneous Polarization of Ferroelectric Liquid Crystal by Triangular Wave" (Journal of the Japan Society of Applied Physics 22, 10 (66)
1) 1983, "Direct Method wit
h Triangular Waves for Me
asuring Spontaneous Polar
Ization in Ferroelectric L
liquid Crystal ", as describ
ed by K. Miyasato et al. (J
ap. J. Appl. Phys. 22. No. 10, L
661 (1983)).

The polarizing plates 1 and 2 were prepared by bonding a 50 μm-thick triacetyl cellulose film to both surfaces of a 30 μm-thick iodine / polyvinyl alcohol-based polarizing film via a polyvinyl alcohol-based adhesive.

The polarizing plate 1 on the emission side used in the present embodiment is a high-polarization type polarizing plate having a polarization degree of 0.999 and a transmittance of 42.8%. The polarizing plate 2 on the incident side is a general-purpose polarizing plate having a polarization degree of 0.995 and a transmittance of 4%.
5.0%.

Table 1 shows the results of measuring the contrast and the transmittance of the liquid crystal device of this embodiment. The liquid crystal cell 1
The liquid crystal device in which the polarizing plate 1 is used on both surfaces of the liquid crystal cell 10 is Comparative Example 1, and the liquid crystal device in which the polarizing plate 2 is used on both surfaces of the liquid crystal cell 10 is Comparative Example 2. It is shown in FIG.

[0038]

[Table 1]

In the liquid crystal device of this embodiment, the transmittance is an intermediate value between the two comparative examples, but the contrast shows a high value close to that of the second comparative example. This is because the liquid crystal cell efficiently converts the polarization state of light incident from the incident side polarizing plate into linearly polarized light, and the exit side polarizing plate mainly determines the contrast.

As described above, when two polarizing plates having different characteristics are used, overall superior characteristics can be obtained as compared with the case where they are used alone, and the degree of freedom of design relating to the optical design of transmittance and contrast is obtained. Spreads. In addition, sufficient optical characteristics can be obtained with one expensive high polarization type polarizing plate, and the cost can be reduced as compared with the case where two high polarization type polarizing plates are used.

In the above embodiment, an example using a ferroelectric liquid crystal has been described. However, an example using a nematic liquid crystal having bistability will be briefly described. The principle of this liquid crystal element is described in JP-A-6-230751. The liquid crystal material was prepared by adding an optical activator (S811: manufactured by Merck) to a commercially available liquid crystal material KN-4000 (manufactured by Chisso) to adjust the helical pitch of the nematic liquid crystal to 3.6 μm. The cell was composed of a pair of substrates coated with 100 nm of polyimide and rubbed so as to be antiparallel to each other, and the cell thickness was 2.0 μm. As a result, the same effect as in the above embodiment was obtained.

(Embodiment 2) The liquid crystal cell used in this embodiment is the same as that in Embodiment 1 and will not be described. Polarizing plate 1
The polarizing plate 2 was prepared by bonding a 50 μm-thick triacetyl cellulose film to both sides of a 30 μm-thick iodine / polyvinyl alcohol-based polarizing film via a polyvinyl alcohol-based adhesive.

The polarization degree of the exit-side polarizing plate 1 used in this embodiment is 0.9995, and the transmittance is 43.0%. The degree of polarization of the polarizing plate 2 on the incident side is 0.992, and the transmittance is 45.5%.

Table 2 shows the results of measuring the contrast and the transmittance of the liquid crystal device of this embodiment. A liquid crystal device using the polarizing plate 1 on both sides of a liquid crystal cell is shown in Comparative Example 3,
Table 2 also shows the measurement results of the liquid crystal device in which the polarizing plate 2 was used on both sides of the liquid crystal cell as Comparative Example 4.

[0045]

[Table 2]

(Embodiment 3) The liquid crystal cell used in this embodiment is the same as that in Embodiment 1 and will not be described. The polarizing plate 1 on the emission side is a dye-based polarizing plate, and a 50 μm-thick triacetyl cellulose film is bonded to both surfaces of a 30 μm-thick two-color dye / polyvinyl alcohol-based polarizing film via a polyvinyl alcohol-based adhesive. Created. The polarizing plate 2 on the incident side is an iodine-based polarizing plate, and a 50 μm-thick triacetyl cellulose film is bonded to both surfaces of a 30 μm-thick iodine / polyvinyl alcohol-based polarizing film via a polyvinyl alcohol-based adhesive. Created.

The optical characteristics of each polarizing plate used in this example,
The durability characteristics were as follows.

[0048]

[Table 3]

Table 4 shows the results of measuring the contrast and the transmittance of the liquid crystal device of this embodiment. In addition, a liquid crystal device using the polarizing plate 1 on both sides of a liquid crystal cell is shown in Comparative Example 5,
Table 4 also shows the measurement results of the liquid crystal device in which the polarizing plate 2 was used on both sides of the liquid crystal cell as Comparative Example 6.

[0050]

[Table 4]

When used outdoors such as for car navigation and portable television, the environment outside the device is much harsher than the inside due to the effects of sunlight, weather, etc. Is required to have higher weather resistance (heat resistance and / or moisture resistance) than the polarizing plate on the incident side. Therefore, as in this example, by using an iodine-based polarizing plate having excellent optical characteristics but inferior in durability characteristics on the incident side, and using a dye-based polarizing plate having high durability but inferior in optical characteristics on the outgoing side, Desired durability can be obtained while improving optical characteristics.

Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments. Also,
The liquid crystal device of the present invention includes not only the liquid crystal display device described in the above embodiment but also other liquid crystal devices such as a liquid crystal shutter.

[0053]

As described above, according to the liquid crystal device of the present invention, the use of polarizing plates having different characteristics on the incident side and the output side of the liquid crystal cell makes it more comprehensive than when they are used alone. In addition to obtaining excellent characteristics, the degree of freedom in designing optical designs such as transmittance and contrast and durability design such as heat resistance and moisture resistance is expanded. In addition, two expensive polarizing plates
Sufficient optical characteristics and durability characteristics can be obtained without using
Cost reduction becomes possible.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing one example of a liquid crystal device of the present invention.

FIG. 2 is a sectional view schematically showing a polarizing plate according to the present invention.

FIG. 3 is a cross-sectional view schematically illustrating an arrangement of directors at respective positions between both substrates of a liquid crystal cell according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Emission-side polarizing plate 2 Incident-side polarizing plate 3 Backlight 10 Liquid crystal cell 11a, 11b Substrate 12 Liquid crystal 21 Protective film 22 Adhesive layer 23 Polarizer

Claims (14)

[Claims] 1. A liquid crystal device comprising at least a liquid crystal cell in which liquid crystal is sandwiched between a pair of substrates, and two polarizing plates disposed on an incident side and an output side of the liquid crystal cell, wherein the output side is Wherein the degree of polarization of the polarizing plate disposed on the incident side is higher than the degree of polarization of the polarizing plate disposed on the incident side. 2. The liquid crystal device according to claim 1, wherein the transmittance of the polarizing plate disposed on the incident side is higher than the transmittance of the polarizing plate disposed on the exit side. 3. The liquid crystal device according to claim 1, wherein the liquid crystal cell has a characteristic of converting incident linearly polarized light into linearly polarized light or substantially linear elliptically polarized light and emitting the light. 4. The liquid crystal device according to claim 1, further comprising a light source on a light incident side of the liquid crystal cell for causing light to enter the liquid crystal cell. 5. The liquid crystal according to claim 1, wherein said liquid crystal is a ferroelectric liquid crystal.
5. The liquid crystal device according to any one of items 1 to 4. 6. A liquid crystal device having at least a liquid crystal cell in which liquid crystal is sandwiched between a pair of substrates, and two polarizing plates disposed on an incident side and an emission side of the liquid crystal cell, wherein the emission side is provided. The heat resistance and / or moisture resistance of the polarizing plate arranged in
A liquid crystal device characterized by being superior to the polarizing plate disposed on the incident side. 7. The liquid crystal device according to claim 6, wherein the liquid crystal cell has a characteristic of converting incident linearly polarized light into linearly polarized light or substantially linear elliptically polarized light and emitting the light. 8. The liquid crystal device according to claim 6, further comprising a light source for making light incident on the liquid crystal cell, on a light incident side of the liquid crystal cell. 9. The liquid crystal according to claim 6, wherein said liquid crystal is a ferroelectric liquid crystal.
9. The liquid crystal device according to any one of items 1 to 8. 10. A liquid crystal device comprising at least a liquid crystal cell having a liquid crystal sandwiched between a pair of substrates, and two polarizing plates disposed on an incident side and an output side of the liquid crystal cell, wherein the incident side is A polarizing plate made of an iodine-based material, and a polarizing plate made of a dye-based material is arranged on the emission side. 11. The liquid crystal according to claim 10, wherein the polarizing plate disposed on the emission side has better heat resistance and / or moisture resistance than the polarizing plate disposed on the incident side. apparatus. 12. The liquid crystal device according to claim 10, wherein the liquid crystal cell has a characteristic of converting incident linearly polarized light into linearly polarized light or substantially linear elliptically polarized light and emitting the light. 13. The liquid crystal device according to claim 10, further comprising a light source for making light incident on the liquid crystal cell, on a light incident side of the liquid crystal cell. 14. The liquid crystal device according to claim 10, wherein the liquid crystal is a ferroelectric liquid crystal.