JPH04118624A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve the contrast and to make a black-to-yellow display or improve black-to-yellow visibility by using a green or yellow LED as a back light, giving an LCD a complementary color relation to this color, and providing a black mask. CONSTITUTION:An STN type LCD of DELTAnd=800 - 900 nm changes in the color tone of yellow and blue by the switching of a voltage, the LED of green - yellow which has a 5400 - 580 nm light emission peak is combined, and the black mask 8 is provided between electrodes of one of substrate which constitute the STN type LCD. Consequently, the transmission type liquid crystal display device which has the superior visibility of yellow or green on a black background and the superior contrast can easily be constituted. Further,the STN type liquid crystal display element is utilized as the LCD, so such effect that time-division operation is superior is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a transmissive STN liquid crystal display device, and particularly to improvement of contrast.

[Prior Art] Conventionally, as a backlight constituting an STN type liquid crystal display device, it has been common to use something close to white light, such as a cold cathode tube or an electroluminescent element. When these backlights are combined with an STN type LCD, in the case of positive mode, the spectrum will be as shown in Figure 4, so the lighting color will be blue on a yellow background, and in the case of negative mode, the spectrum will be as shown in Section 5. Because of this, the color of the light is yellow. In any case, since neither the non-lit parts nor the lit parts turn black, there is a problem of low contrast. Furthermore, there are methods to make the STN type LCD black and white by combining a second layer of the STN type LCD as an optical compensator or by pasting a retardation film, but this increases the cost.

[Problem to be solved by the invention 1 The present invention has been made in view of the above problems,
The purpose is to improve the contrast of a transmissive STN type liquid crystal display device and to provide a liquid crystal display device with high visibility such as black versus yellow display or black versus yellow display. Still another object of the present invention is to provide a liquid crystal display device having a long-life backlight.

[Means for Solving the Problems 1] The present invention uses a green or green LED having an emission peak of 540 nm to 580 nm as a backlight, and
A positive mode or negative mode STN type LCD with Δnd=800 nm to 900 nm is used as the CD, and a black mask is formed between the electrodes of at least one substrate constituting the STN type LCD.

[Example] FIG. 1 is a sectional view showing a model of the structure of a liquid crystal display device of the present invention. In the figure, 1 is the upper substrate, 2
is the lower substrate. These two substrates are sandwiched with a sealing material 3 in between, and a twisted nematic liquid crystal 4 is sealed between them. 5 indicates an upper polarizing plate, and 6 indicates a lower polarizing plate. 7 is an LED used as a backlight. Note that the upper substrate has a transparent electrode IA and an alignment film IB, and the lower substrate has a transparent electrode 2A.
An alignment film 2B is formed. Further, a black mask 8 is formed between the transparent electrodes on the lower substrate. Note that the black mask may be provided between the electrodes of at least one substrate, but may be provided between the electrodes of both substrates, and does not necessarily have to be pure black. On the contrary, the display quality is further improved by matching the background color of the STN LCD.

(Example 1) As a cell parameter of the STN type LCD, Δn=0.
130 liquid crystals are sandwiched with cell thickness (d) = 6.3LLm,
The torsion angle (TA) was set to 230°.

In this case, Δn×d=819 nm.

FIG. 2 shows the relationship between the upper and lower rubbing directions and the absorption axes of the upper and lower polarizing plates. As a black mask, a carbon-based black organic pigment was formed to a thickness of about 1 um using the ii interelectrode printing method on the lower substrate. By setting such cell parameters, the portion without the black mask, that is, the illuminated backlight portion, has a spectrum as shown in FIG. Next, a yellow LED having a peak at 565 nm as shown in FIG. 7 was used as a backlight. The spectrum of the STN type LCD in yellow positive mode in Figure 4 and the emission spectrum of the yellow LED in Figure 7 are different from each other. When the STN type LCD (7) is in the OFF state, the color tone of the LCD is yellow and LE.
The color tone of D is also yellow, so the amount of light from the backlight is efficient.
Can pass through CDs.

On the other hand, when the STN LCD is in the ON state, the color tone of the LCD is blue, which is a complementary color to the yellow color of the LED.
Most of the light from the backlight is cut off by the LCD, making it black. From the above, the LCD should be turned off in the areas that you would like to see as a display, and the LCD should be in the OFF state in the areas that you want to erase.
By turning on D, the color becomes black similar to that of a black mask, and a transparent liquid crystal display device with excellent yellow-on-black visibility and contrast is constructed.

(Example 2) As a cell parameter of the STN type LCD, Δn=0.
150, d=5.8LLm, and TA=220″′.

In this case, ΔnXd=870 nm.

FIG. 3 shows the relationship between the upper and lower rubbing directions and the absorption axes of the upper and lower polarizing plates. A dark blue organic pigment with a thickness of about 1 um was formed as a black mask between the electrodes of the upper substrate by photolithography. By setting these cell parameters, the part without the black mask, that is, the lighting pattern part, has a spectrum as shown in Figure 57.
Next, as a back light, 560 nm as shown in Section 8
A green LED having a peak at . As can be seen from the spectrum of the blue negative mode STN LCD in Figure 5 and the emission spectrum of the green LED in Figure 8, the ST
When the N-type LCD is in the OFF state, the LED backlight hardly passes through the LCD and becomes dark blue, whereas when the LCD is ON, the LED backlight can sufficiently pass through the LCD. From the above, the LCD is turned off.
In the state, it is the same color as the dark blue of the black mask, and in the ON state, it is green. In other words, a transmissive liquid crystal display device with excellent green visibility and contrast on a dark blue background is constructed.

(Example 3) As a cell parameter of the STN type LCD, Δn=0.
153, d = 6.8 um, TA = 230''. In this case, △nXd = 1 O40 nm. The relationship between the upper and lower rubbing directions and the absorption axes of the upper and lower polarizing plates is shown in Figure 2.
As a black mask, a carbon-based black organic pigment was formed with a thickness of about 1 μm between the electrodes of the lower substrate by a printing method. With such cell parameters, the portion without the black mask, that is, the lighting pattern portion, has a spectrum as shown in FIG. Next, as a backlight, a red L with a peak at 650 nm as shown in Figure 9 is used.
ED was used. As can be seen from the optical spectrum of the positive mode STN LCD in Figure 6 and the emission spectrum of the red LED in Figure 9, when the STN LCD is in the OFF state, the color tone of the LCD is almost red and the color tone of the LED is also red. The amount of light transmitted through the LCD is determined by its efficiency. On the other hand, when the STN LCD is in the ON state, the color tone of the LCD is blue, which is almost a complementary color to the red color of the LED.
Most of the light from the backlight is cut off by the LCD, making it black.

From the above, the LCD should be turned off in the areas that you originally want to see as a display.
By setting the F state and setting the LCD'+ON state in the portion to be erased, the color becomes black similar to a black mask, and a transmissive liquid crystal display device with excellent visibility and contrast of red on a black background is constructed.

[Effect of the invention] As described above, according to the present invention, Δnd=800 nm
A ~900nm STN type LCD that changes the color tone between yellow and blue by voltage switching, and a green to yellow LED having an emission peak of 540nm to 580nm as a backlight are combined, and at least By providing a black mask between the electrodes of one of the substrates, a transmissive liquid crystal display device with excellent visibility and contrast, such as yellow or green on a black background, can be easily constructed. Moreover, the present invention is an LCD
Since an STN type liquid crystal display element is used as the display element, it also has the advantage of being excellent in time sharing. Furthermore, another effect of the present invention is that since a long-life light emitting element called an LED is used for the backlight, the life of the liquid crystal display device can be extended.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the structure of the liquid crystal display device of the present invention, and FIGS. 2 and 3 are diagrams showing the relationship between the rubbing direction and the angle of the polarizing plate of an STN type LCD. FIGS. 4, 5, and 6 are diagrams showing the spectra of the STN type LCD. Figure 7, Figure 8,
FIG. 9 is a diagram showing the emission spectrum of the LED. l A, 2 A, l B, 2 B 8. ・ . .・Transparent electrode ・Alignment film ・Black mask ・Upper rubbing direction ・Lower rubbing direction ・Absorption axis direction of upper polarizing plate ・Absorption axis direction of lower polarizing plate Fig. 6 Fig. 8

Claims (3)

[Claims] (1) A light emitting diode (LED) having an emission peak at a specific wavelength is used as a backlight, and a liquid crystal display element (L
CD) in a liquid crystal display device configured using an STN type LCD, in which the color tone of the STN type LCD in either a non-lit state or a lit state has a substantially complementary color relationship with the color tone of the LED; A liquid crystal display device characterized in that a black mask is formed between electrodes of at least one substrate constituting the liquid crystal display device. (2) Use an LED with an emission peak of 540 nm to 580 nm as a backlight, and use Δn×d as an LCD.
(Δn represents the anisotropy of the refractive index of the nematic liquid crystal constituting the STN type LCD, and d represents the thickness of the nematic liquid crystal layer) = 800 nm to 900 nm STN type LCD is used. The liquid crystal display device described. (3) Use an LED with an emission peak of 630 nm to 670 nm as a backlight, and use Δn×d as an LCD.
2. The liquid crystal display device according to claim 1, wherein an STN type LCD having a wavelength of 950 nm to 1300 nm is used.