JP2765066B2 - Liquid crystal display - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high-quality liquid crystal display device using a retardation plate.

<Prior Art> A retardation plate formed of a polymer film having uniaxial orientation has been used as an optical compensator for an STN liquid crystal display device or the like in order to improve display quality of a liquid crystal display device. As a result, the display quality is improved as compared with a liquid crystal display device that does not use a retardation plate.

<Problem to be Solved by the Invention> FIG. 1 shows an example of a liquid crystal display device using a retardation plate.
In FIG. 1, 1 is a retardation plate, 2 and 3 are a pair of polarizing plates,
4 is a liquid crystal cell. The liquid crystal cell is exemplified by an STN liquid crystal cell and the like. The conventional STN crystal display device using a retardation plate produces a display close to black and white due to the difference in wavelength dependence of retardation of the retardation plate (hereinafter referred to as dispersion) and that of the liquid crystal cell, but lacks contrast. There is a problem that display quality is inferior.

<Means for Solving the Problems> In the liquid crystal display device of the present invention, the α ₁ value of the polymer film having uniaxial orientation defined by the formula (1) and the α ₁ value of the liquid crystal cell defined by the formula (2) are used. A liquid crystal display device characterized in that _two values satisfy the condition of Expression (3).

Here, R _1F is a retardation value of a polymer film having uniaxial orientation measured by F line of hydrogen (486.1 nm). R _1D is a polymer having uniaxial orientation measured by D line of sodium (589.3 nm). Retardation value of film R _2F : Retardation value of liquid crystal cell measured by F line of hydrogen (486.1 nm) R _2D : Retardation value of liquid crystal cell measured by D line of sodium (589.3 nm), α ₁ and alpha ₂ values can be determined routinely using Abbe refractometer or a spectrophotometer.

Examples of the liquid crystal display device include an STN liquid crystal display device in which the twist angle of liquid crystal molecules is 180 degrees or more, and an improvement in contrast and the like as compared with a conventional liquid crystal display device using a uniaxially oriented polymer film. The display quality is greatly improved.

Retardation plate used in the present invention, ₂ alpha of the liquid crystal cell as defined in formula (1) Part alpha ₁ values and expressions as defined in (2)
A uniaxial value whose value satisfies the condition of Expression (3), preferably Expression (4), and more preferably Expression (5). Any polymer film may be used as long as it is a polymer film having an orientation property, has an appropriate retardation value, and has little optical unevenness in color. A retardation value in the range of 80 to 1200 nm is used,
What is necessary is just to select a more appropriate retardation value according to a specific use.

The thermoplastic resin for a retardation plate used in the present invention, when formed into a film or sheet, satisfies the above characteristics, and has an average transmittance of 50% or more in a visible light wavelength region of 400 to 700 nm. Preferably, it is 80% or more, and more preferably, 85% or more.

For example, poly (meth) acrylate resin such as methyl methacrylate copolymer obtained by copolymerizing other ethylene comonomer with polymethyl methacrylate and methyl methacrylate as main components, polystyrene and styrene as main components. Polystyrene resins such as styrene copolymers obtained by copolymerizing other ethylene comonomers and acrylonitrile resins such as polyacrylonitrile and acrylonitrile copolymers, polyesters such as polyethylene terephthalate, polyester copolymers and polyarylates Resins, polyamide resins such as nylon 6 and nylon 66, polyvinyl chloride resins such as polyvinyl chloride and vinyl chloride copolymer, polyethylene, polypropylene,
Polyolefin-based resins such as ethylene copolymer and propylene copolymer, polysulfone, polyethersulfone, fluorine-based resin, polycarbonate-based resin and the like, and modified products thereof, and high-molecular liquid crystal or low-molecular liquid crystal At least one resin material selected from a blend of a transparent low-molecular compound or a transparent inorganic compound is exemplified.

The retardation plate used in the present invention is obtained by forming the thermoplastic polymer into a raw film or sheet by a known film-forming method, that is, a solvent casting method, a calendering method, or an extrusion method, and then moderately uniaxially. It is manufactured by stretching.

As the method of stretching in the uniaxial direction, a known method such as an inter-roll tension stretching method, an inter-roll compression stretching method, and a tenter transverse uniaxial stretching method can be applied.

The retardation plate used in the present invention can also be applied to a liquid crystal display device or the like by bonding it to one side of a polarizing plate to form an elliptically polarizing plate.

The method of applying the retardation plate to an STN-type liquid crystal display device or the like is not particularly limited, but a method of bonding a liquid crystal cell, a polarizing plate, or the like with an adhesive or the like and using the same is generally adopted. Further, the retardation plate may be disposed between the upper polarizing plate and the liquid crystal cell or between the lower polarizing plate and the liquid crystal cell. Further, any method may be used as long as the object and effects of the present invention are achieved.

A liquid crystal display device such as an STN liquid crystal display device using the retardation plate of the present invention provides good black and white display over the entire wavelength range of visible light, improves contrast, and significantly improves the display quality of the liquid crystal display device. I can do it.

<Effect of the Invention> The STN of the present invention in which the twist angle of liquid crystal molecules is 180 to 270 degrees
The liquid crystal display device is a liquid crystal display device having high-contrast, high-quality black and white display.

Further, by using a color filter, a liquid crystal display device of a color display is also possible.

<Examples> Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto.

In the following examples, the retardation value of the uniaxially stretched film was determined from its interference spectrum using a spectrophotometer. Further, the dispersion values (α ₁ , α ₂ ) of the uniaxially stretched film and the liquid crystal cell were determined by a conventional method using a spectrophotometer. The contrast ratio was obtained by measuring the transmittance (T _OFF ) of the background portion when the voltage was turned _off and the transmittance (T _ON ) of the display portion when the voltage was _{turned on} using a spectrophotometer, and was obtained as a T _OFF / T _ON ratio.

Polyether sulfone uniaxially stretched film Example 1 alpha ₁ value is the retardation value of about 560nm 1.10 a [Delta] n × d is 0.8μm at twist angle of 240 degrees of the liquid crystal molecules in alpha ₂ value 1.09 When an STN-type liquid crystal display device was disposed between an upper polarizing plate and a lower polarizing plate, a liquid crystal display device having a contrast ratio of 22 and having good display quality of monochrome display was obtained.

When Comparative Example 1 alpha ₁ value is applied to the same liquid crystal display device of Example 1 as a color compensation film for cellulose diacetate uniaxially stretched film retardation value of about 560nm at 0.96, the contrast ratio although almost monochrome display The result was 8.5, and only a liquid crystal display device having a lower display quality than that of Example 1 was obtained.

Comparative Example 2 When a uniaxially stretched polyvinyl chloride film having an α ₁ value of 1.02 and a retardation value of about 560 nm was used as a color compensation film in the same liquid crystal display device as in Example 1, the contrast was almost black and white. At a ratio of 10, only a liquid crystal display device having inferior display quality to Example 1 was obtained.

Comparative Example 3 The uniaxially stretched polyethersulfone film used in Example 1 was obtained by twisting liquid crystal molecules at a twist angle of 235 degrees and Δn · d of 0.8.
When placed between the upper polarizing plate and the lower polarizing plate of an STN type liquid crystal display device having a thickness of 5 μm and an α ₂ value of 1.18, the display became almost black and white, but the contrast ratio was 18 and the display was higher than that of Example 1. Only poor quality liquid crystal displays were obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of the STN liquid crystal display device of the present invention using the retardation plate of the present invention. 1... A retardation plate made of a polymer film having a uniaxial orientation that satisfies the relationship of the dispersion value α ₁ of the liquid crystal cell with the dispersion value α ₂ of the formula (3) ₂ , 3... A polarizing plate 4. ₂ is a liquid crystal cell that satisfies the relationship of the dispersion value α _{1 of the} retardation plate and the equation (3)

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/1335

Claims (1)

(57) [Claims] 1. The α ₁ value of a polymer film having uniaxial orientation defined by the formula (1) and the α ₂ value of a liquid crystal cell defined by the formula (2) satisfy the condition of the formula (3). A liquid crystal display device characterized by satisfying. Here, R _1F is a retardation value of a polymer film having uniaxial orientation measured by F line of hydrogen (486.1 nm). R _1D is a polymer having uniaxial orientation measured by D line of sodium (589.3 nm). Retardation value of film R _2F : Retardation value of liquid crystal cell measured at F line of hydrogen (486.1 nm) R _2D : Retardation value of liquid crystal cell measured at D line of sodium (589.3 nm)