JPH0682181B2 - Liquid crystal display - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid crystal display device of a transmissive negative display utilizing a twisted nematic (TN) effect.

(Prior Art) A TN type liquid crystal display device has a liquid crystal layer 1 as shown in FIG.
However, in the case of a negative display, it is 2 It has a structure in which two polarizing plates 4 and 5 are combined to form a parallel Nicol. The liquid crystal cell is oriented so that the liquid crystal has a TN alignment.

This type of TN negative type liquid crystal display device has a display with a strong viewing angle dependency and originally has to block light, but there is a drawback that light of a specific wavelength leaks depending on the viewing angle and direction. There is. In addition, light of a specific wavelength may leak even when viewed from the front.

The wavelength of the leaking light depends on the product of the cell thickness d and the refractive index anisotropy Δn of the liquid crystal enclosed in the cell. Therefore, even if the cell thickness d and the refractive index anisotropy Δn of the liquid crystal are set to certain values so as to increase the contrast when viewed from the front, the wavelength of the wavelength corresponding to the product of these two values must be determined. There is light leakage (color loss).

(Object of the Invention) An object of the present invention is to provide a TN negative type liquid crystal display device in which color loss is extremely small and contrast can be improved.

(Summary of the Invention) The present invention is to laminate a plurality of TN-arranged liquid crystal cells, and to provide a polarizing plate so that the polarization directions are the same between the layers of the liquid crystal layer and the front and rear surfaces of the laminated cells, and the thickness of the liquid crystal cell This is characterized in that the value of the product Δn · d of d and the refractive index anisotropy Δn of the liquid crystal is selected so that the color of light passing through each liquid crystal cell has a complementary color relationship. When the negative is displayed in the form, the color loss is extremely small.

(Embodiment) FIG. 1 shows an embodiment of the present invention in which two layers of TN array liquid crystal cells are laminated and a polarizing plate having the same polarization direction is provided in the middle and front and rear surfaces thereof. That is, the TN array liquid crystal cell 1
0, 20 are laminated, and polarizing plates 31, 32, 33 are provided on the front surface (the upper surface in the drawing), the middle and the rear surface (the lower surface in the drawing) of the polarization directions (arrows a1, a2,
a3) are set to be the same.

In the liquid crystal cell 10, two glass substrates 11A and 11B are formed with transparent electrodes 12 and 13 on their inward faces and subjected to an alignment treatment so as to form a TN array, and then they are superposed with a sealing agent 14 interposed at the periphery. To form an empty cell, and the liquid crystal 15 is injected into the inside. Similarly, the other liquid crystal cell 20 has two glass substrates 21A,
After the transparent electrodes 22 and 23 are formed on the inward surface of 21B and subjected to an alignment treatment to form a TN array, the peripheral portion is overlapped with a sealant 24 to form an empty cell, and a liquid crystal 25 is injected therein. It is a thing. When the cells 10 and 20 are laminated, a polarizing plate 32 is interposed between them, that is, between the glass substrate 11B and the glass substrate 21A to be integrated, and a polarizing plate 31 is provided on the front surface (the surface of the glass substrate 11A).
And a polarizing plate 33 is attached to the rear surface (the surface of the glass substrate 21B).

Further, the cells 10 and 20 have different values of the product Δn · d of the cell thickness d and the refractive index anisotropy Δn of the liquid crystal material. In that case, the color of the light that passes through the liquid crystal cell 10 (the color of the light that is lost)
And the color of the light that passes through the liquid crystal cell 20 (the color of the light that is lost)
The value of Δn · d of both liquid crystal cells 10 and 20 is selected so as to have a complementary color relationship. For example, the value of Δn · d of the liquid crystal cell 10 is 0.
5. The value of Δn · d of the liquid crystal cell 20 is 0.8.

With such a structure, most of the incident light is blocked by the intermediate and front polarizing plates 32 and 31 when no electric field is applied.
At this time, light of a specific wavelength is transmitted, but both cells 10, 20
The transmitted light has a complementary color relationship, and the same effect as when two color filters having a complementary color relationship are overlapped is obtained, and the display surface becomes an ideal dark field. In addition, the color loss when the cells are viewed obliquely is also improved.

On the other hand, when an electric field is applied, the 90 ° illuminance is lost due to the TN effect, and light is transmitted through the three polarizing plates 31, 32 and 33 to form a bright field with high brightness.

Although the liquid crystal cell has two layers in the embodiment, it may have three or more layers. Further, the polarizing plate 32 in the middle part may be provided on the inward surface of the glass substrate 11B.

(Effect) (1). A TN array liquid crystal cell is made into a laminated cell of multiple layers, and a polarizing plate with the same polarization direction is provided between the layers and the front and back surfaces of the laminated cell, and Δn · d of each layer is decolorized. Since the color of the transmitted light has a complementary color relationship, in the case of a negative display by the transmission method, white light can be surely blocked in an electric field not applied state to obtain an ideal dark field. That is, color loss when viewed from the front can be extremely reduced, and the contrast can be improved. Moreover, it is possible to prevent color loss when viewed from an angle.

(2). Since light only passes through the three polarizing plates when an electric field is applied, a bright field with high brightness can be secured.

(3). Since it is an ideal dark field with no loss of light of a specific wavelength (color loss), there is no restriction on the color when arranging a color filter on the back to color display characters or pictures.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the liquid crystal display device according to the present invention, and FIG. 2 is a sectional view showing a conventional example. 10 and 20 …… TN array liquid crystal cell, 11A, 11B, 21A and 21B …… glass substrate, 12,13,22 and 23 …… transparent electrode, 14 and 24 …… sealant, 15 and 25 …… liquid crystal, 31 ~ 33 …… Polarizing plate.

Claims (1)

[Claims] 1. A plurality of TN-arranged liquid crystal cells are laminated, and a polarizing plate is provided so that the polarization directions are the same between the layers of the liquid crystal layer and the front and rear surfaces of the laminated cell, and the thickness d of the liquid crystal cell and the liquid crystal A liquid crystal display device characterized in that the value of the product Δn · d of the refractive index anisotropy Δn is selected so that the color of the light passing through each liquid crystal cell has a complementary color relationship.