JPH05273531A - Liquid crystal display element - Google Patents

Abstract

(57) [Summary] [Structure] In a liquid crystal display device in which a liquid crystal layer containing a ferroelectric polymer liquid crystal is directly sandwiched between resin substrates with electrodes, one of the above substrates has Δn ₁ · d. Have a retardation of ₁ , or both substrates have a total of Δn ₁ ·
The liquid crystal layer has a retardation of d ₁ and the difference from the retardation Δn ₂ · d ₂ of the liquid crystal layer is within the range of 0.1 ≦ | Δn ₁ · d ₁ −Δn ₂ · d ₂ | ≦ 1.0 (μm). At the same time, the optical principal axis of at least one of the substrates is arranged so as to be inclined by 30 degrees or less from the normal line of the smectic layer of the liquid crystal. [Effect] It is possible to realize a large area and thin liquid crystal display element capable of displaying black and white with high visibility.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a liquid crystal containing a ferroelectric polymer liquid crystal to enable black and white display with high visibility.
The present invention relates to a large area and thin liquid crystal display element, and more particularly to a liquid crystal display element which can be used as various information display bodies such as OA equipment and street display devices.

[0002]

2. Description of the Related Art A liquid crystal display device comprising a liquid crystal containing a ferroelectric polymer liquid crystal sandwiched between resin substrates has a large area, a thin shape,
In addition to having excellent properties such as light weight and high memory property, the manufacturing process has been relatively simple, and thus has been extensively studied in recent years. However, the resin substrate does not always have sufficient surface smoothness as compared with the glass substrate. In order to realize a black and white display in an ordinary double-bending type liquid crystal display element, the thickness of the liquid crystal layer needs to be extremely thin, about 1 μm, but this is held by a resin substrate having insufficient surface smoothness. When it is manufactured, there arises a problem that a conduction defect is likely to occur. Therefore, considering the manufacturing yield,
At present, the thickness of the liquid crystal layer is generally about 2 μm or more. However, the thickness of the liquid crystal layer should be 2μ.
If it is about m or more, the display color is not black and white display but is slightly colored, and there is a problem that sufficient contrast cannot be obtained.

Therefore, a proposal has been made to improve the contrast. For example, in Japanese Unexamined Patent Publication No. 2-247616, a polarizer and an analyzer are provided so as to face each other, and a high substrate is provided between the substrates with electrodes. The contrast is improved by sandwiching the molecular liquid crystal, at least one of the substrates having birefringence, and tilting its optical principal axis from the polarization plane of the incident light by 30 to 60 degrees.

[0004]

However, in the technique described in JP-A-2-247616, the optical principal axis is tilted by 30 degrees or more from the plane of polarization of the incident light, so that in a substrate with a very large retardation, There is a problem that the color reduction due to the birefringence effect is remarkable, black and white display cannot be performed, and sufficient contrast cannot be obtained.

The present invention has been made in view of the above problems, and prevents coloring due to the birefringence effect to enable black and white display with high visibility, thereby increasing the contrast and providing a large area and thin type. The purpose of the present invention is to provide a liquid crystal display device.

[0006]

In order to achieve the above object, a liquid crystal display device having a liquid crystal layer containing a ferroelectric polymer liquid crystal of the present invention directly sandwiched between resin substrates with electrodes is provided. Either one of the substrates should have a retardation of Δn ₁ · d ₁ , or both substrates should have a retardation of Δn ₁ · d ₁ in total, and the difference from the retardation Δn ₂ · d ₂ of the liquid crystal layer should be 0.1 ≦. | Δn ₁ · d ₁ −Δn ₂ · d ₂ | ≦ 1.0 (μm) Δn ₁ is the birefringence of the substrate d ₁ is the gap of the substrate Δn ₂ is the birefringence of the liquid crystal layer d ₂ is the gap of the liquid crystal layer And the retardation Δn ₁ · d ₁ of the substrate is either the substrate itself or Δn ₁ · d ₁ if necessary.
Of the retardation film is laminated on the substrate, and at least one of the substrates has an optical principal axis inclined by 30 degrees or less from the normal line of the liquid crystal smectic layer. ..

The liquid crystal display device of the present invention will be described below with reference to the drawings. FIG. 1 shows one embodiment of the present invention, in which a liquid crystal layer 1 containing a ferroelectric polymer liquid crystal is sandwiched between resin substrates 2a and 2b having electrodes 3a and 3b. In this case, the resin substrates 2a and 2b
Is the liquid crystal layer 1 and the electrodes 3a without interposing an alignment control film.
The liquid crystal layer 1 is held so that the 3b is in direct contact. When the liquid crystal display element is used as a transmissive type or a reflective type, a polarizing plate, a reflective plate or a light emitting element may be arranged at an appropriate position like a normal liquid crystal display element.

Here, the liquid crystal layer containing the ferroelectric polymer liquid crystal is, for example, one or two or more ferroelectric polymer liquid crystals, one or two or more ferroelectric low molecular liquid crystals, and one or two. Ferroelectric polymer liquid crystal composed of one or more ferroelectric polymer liquid crystals, ferroelectric polymer composed of one or two or more ferroelectric low-molecular liquid crystals and one or more other polymer liquid crystals, etc. A liquid crystal etc. can be mentioned. That is, as the ferroelectric polymer liquid crystal, ferroelectric polymer liquid crystal (homopolymer or copolymer or mixture thereof) in which polymer molecules themselves exhibit ferroelectric liquid crystal characteristics, ferroelectric polymer liquid crystal and other Mixture of high molecular liquid crystal and / or ordinary polymer, mixture of ferroelectric high molecular liquid crystal and ferroelectric low molecular liquid crystal, ferroelectric high molecular liquid crystal, ferroelectric low molecular liquid crystal and high molecular liquid crystal, and / or Polymeric liquid crystals exhibiting all ferroelectric properties can be used, such as mixtures with common polymers or mixtures of these with normal low-molecular liquid crystals. Among the ferroelectric polymer liquid crystals, for example, a side chain type ferroelectric polymer liquid crystal having a chiral smectic C phase is preferably used.

Examples of ferroelectric liquid crystal compounds include desiloxybenzylidene-P'-amino-2-methylbutylcinnamate (DOBAMBC), hexyloxybenzylidene-P'-amino-2-chloropropylcinnamate (HOBACPC). And 4-o- (2-methyl)-
Butyl resorcylidene-4'-octylaniline (MB
RA8) and the like. When a device is formed by using these materials, the liquid crystal compound is SmC * phase or SmH *
If necessary, the element can be supported by a copper block or the like in which a heater is embedded, which is maintained in a temperature state in which the phases are in phase with each other. Further, in the present invention, the aforementioned SmC *, Sm
In addition to H *, chiral smectic F phase, I phase, J phase, G
It is also possible to use a ferroelectric liquid crystal that appears in the phase or K phase. Further, the ferroelectric liquid crystal composition, if necessary,
Adhesives, viscosity reducers, non-liquid crystal chiral compounds, pigments, etc. are included. The thickness of the liquid crystal layer is not particularly limited, but is 2 to 4 μm.
Is preferred.

The resin substrates 2a and 2b are preferably made of a flexible, transparent or translucent material, such as polyethylene terephthalate (PET),
A plastic film such as polyether sulfone (PES) or polycarbonate (PC) can be used. The thickness of the substrate may be as thin as it has flexibility, but is usually 10 μm to several mm.

Electrodes 3a and 3b are provided on one surface of the substrates 2a and 2b on the liquid crystal layer 1 side. The electrodes 3a and 3b are not particularly limited as long as they are transparent materials. For example, a transparent electrode such as an ITO film made of indium oxide or a mixture of indium oxide and tin oxide is suitable, and these are usually deposited on the above flexible substrate.

Although not shown, as the polarizing plate, a generally used one, for example, an iodine type or a dye type of polyvinyl alcohol (PUA) is used. As the reflector, a commonly used metal foil such as aluminum, or a laminate of a metal foil and a plastic film is used. EL for backlight
As the element, for example, a dispersion-side EL element is used.

Here, the retardation in the liquid crystal layer 1 and the retardations in the substrates 2a and 2b are as follows. That is, the retardation in the substrates 2a and 2b is Δn ₁ · d ₁ , but this retardation Δn
_At least _one of the substrates 2a and 2b itself may have ₁ · d ₁ , or the two substrates 2a and 2b may have a total of ₁ · d ₁ . In addition, the retardation Δn in the substrates 2a and 2b
₁ · d ₁ has a structure in which the substrate itself is provided as shown in FIG. 1 or a structure in which a retardation film 4 having a retardation of Δn ₁ · d ₁ is laminated on _one of the substrates as shown in FIG. Good. Further, a retardation film may be laminated on each of the two substrates so that the total retardation of the two substrates 2a and 2b becomes Δn ₁ · d ₁ as described above.

Usually, the substrate itself or the film having these retardations is easily obtained by stretching a polymer film. For example, the following can be used as the retardation film. That is, low density polyethylene film, high density polyethylene film, polypropylene film, polyester film, polyvinyl alcohol film, polyamide film, polycarbonate film, polyimide film, polyvinyl chloride film, polyvinyl fluoride film, polyacrylic film, polystyrene film, polychlorinated film. Examples include vinylidene film, cellulose film, and other liquid crystal polymer film. Further, in order to impart retardation to these films, there are uniaxial stretching, biaxial stretching, inflation stretching, application of shearing, etc., and the degree of the difference from the retardation of the liquid crystal layer used is 0.1.
~ 1.0 μm. Further, the same retardation value can be obtained by aligning another liquid crystal.

On the other hand, the retardation in the liquid crystal layer 1 is Δn ₂ · d ₂ . In order to realize monochrome display (high contrast), the retardation Δn of the substrates 2a and 2b is
The difference between ₁ · d ₁ and the retardation Δn ₂ · d ₂ of the liquid crystal layer 1 is in the range of 0.1 ≦ | Δn ₁ · d ₁ −Δn ₂ · d ₂ | ≦ 1.0 μm. If the difference between the two is less than 0.1 μm, the display may be dark, and if it exceeds 1.0 μm, the contrast cannot be sufficiently enhanced.

Further, in the liquid crystal display element of the present embodiment, the direction of the optical principal axis of at least one of the substrates 2a and 2b having the retardation Δn ₁ · d ₁ alone or totally, the smectic of the liquid crystal layer 1 is set. Place it at an angle of ± 30 degrees from the layer normal (see Fig. 3). By doing this, the coloring effect due to birefringence can be suppressed,
A good black and white display is realized.

[0017]

EXAMPLES The present invention will be described below based on examples, but the present invention is not limited to these examples. Example 1

[0018]

[Chemical 1]

A PES substrate with ITO electrodes (polyether sulfone, thickness 100 μm, width 150 mm, length 10) was prepared by using the above ferroelectric polymer liquid crystal as a 25 wt% toluene solution.
The electrode surface of m) was continuously coated and film-formed using a gravure coater. Then, a similar substrate to which nothing was applied was laminated with the electrode surface facing inside. After that, a length of 300 mm was cut out, and the entire device was subjected to uniaxial horizontal orientation treatment by applying a uniform bending deformation several times with 30 V DC while heating the entire device to 40 ° C. The retardation of the PES substrate itself is Δn ₁ · d ₁ = 0.0 based on accurate transmission spectrum measurement.
It was 2. Further, the optical principal axis direction was tilted by 20 degrees from the smectic layer normal obtained by the above-mentioned alignment treatment. On the other hand, the retardation of the liquid crystal layer was similarly Δn ₂ · d ₂ = 1.2 from the spectrum measurement. Therefore, | Δn
₁ · d ₁ −Δn ₂ · d ₂ | = 1.8. When this device was placed between orthogonal polarizers and the contrast ratio was measured in a greenhouse, it was 25 with an applied voltage of ± 10 v. The display color was black / yellow. Then, a polyester film (thickness 4 μm) uniaxially stretched 1.2 times at 150 ° C. was laminated on the element between the polarizers, and its optical principal axis direction was matched with that of the PES substrate, and the contrast ratio was improved to 32. The yellow color became lighter and closer to black and white display. At this time, the retardation of the polyester film is Δn ₁ · d ₁ =
0.9, and | Δn ₁ · d ₁ −Δn ₂ · d ₂ | = 0.
It was 3.

Example 2 A device was prepared in the same manner as in Example 1 except that one plastic substrate was changed to a biaxially stretched PET film. Δn ₁ · d ₁ of this substrate is 0.5, and Δn ₂ · d of the liquid crystal layer is
₂ was 1.2. Therefore, | Δn ₁ · d ₁ −Δ
n ₂ · d ₂ | = 0.7. The optical principal axis direction of the PET film substrate was tilted about 5 degrees with respect to the smectic layer normal. When the contrast ratio was measured in the same manner as in Example 1, 39 was obtained by applying ± 10 v. The display color was black and light yellow, and the visibility was good.

[0021]

As described above, according to the present invention, it is possible to realize a thin liquid crystal display device having a large area and capable of displaying black and white with high visibility.

[Brief description of drawings]

FIG. 1 shows a partial cross-sectional view of an embodiment of the present invention.

FIG. 2 shows a partial cross-sectional view of another embodiment of the present invention.

FIG. 3 is a diagram for explaining a direction of an optical principal axis in the embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal layer 2a, 2b ... Substrate 3a, 3b ... Electrode 4 ... Retardation film

Claims (5)

[Claims] 1. A liquid crystal display device in which a liquid crystal layer containing a ferroelectric polymer liquid crystal is directly sandwiched between resin substrates with electrodes, wherein a retardation of Δn ₁ · d _{1 is applied} to one of the substrates. The liquid crystal layer retardation Δn ₂
・ The difference from d ₂ is 0.1 ≦ | Δn ₁ · d ₁ −Δn ₂ · d ₂ | ≦ 1.0 (μm) Δn ₁ is the birefringence of the substrate d ₁ is the gap of the substrate Δn ₂ is the liquid crystal layer The birefringence index d _{2 of} is within the range of the gap of the liquid crystal layer. 2. A liquid crystal display device in which a liquid crystal layer containing a ferroelectric polymer liquid crystal is directly sandwiched between resin substrates with electrodes, wherein the substrate has a retardation of Δn ₁ · d ₁ in total, and the liquid crystal layer Retardation Δn ₂ · d ₂ of 0.1 ≦ | Δn ₁ · d ₁ −Δn ₂ · d ₂ | ≦ 1.0 (μm) Δn ₁ is the birefringence of the substrate d ₁ is the gap of the substrate Δn ₂ is a birefringence index of the liquid crystal layer, and d ₂ is within the range of the gap of the liquid crystal layer. 3. The liquid crystal display device according to claim ₁ , wherein the substrate itself has a retardation of Δn ₁ · d ₁ . 4. The liquid crystal display element according to claim 1, wherein a resin film having a retardation of Δn ₁ · d ₁ is laminated on the substrate. 5. The liquid crystal display device according to claim 1, wherein the optical principal axis of at least one of the substrates is arranged at an angle of 30 degrees or less from a normal line of the smectic layer of the liquid crystal.