JPH04188113A - Liquid crystal display panel - Google Patents

Abstract

PURPOSE:To display multi-color of high color purity by laminating a plurality of liquid crystal layers having ECB effect, and controlling optical phase difference of respective liquid crystal layers. CONSTITUTION:Between a reflecting plate 1c and a second polarizing plate 5 opposite to each other, a plurality of liquid crystal layers 4a, 4b having property of birefringence are laminated through a first polarizing plate 2 between. Consequently, reflecting light 6b can be colored by the use of white light, the liquid crystal layers 4a, 4b have ECB(Electrically Controlled Birefringence) effect, and because the birefringence factor is varied at applying electrical field, reflecting light 6b of various hues can be taken out. Hereby, a liquid crystal display panel capable of displaying multi-color of high and bright transmission factor and high color purity can be obtained.

Description

[Detailed Description of the Invention] [Summary] Regarding a reflective multi-color liquid crystal display panel, the purpose is to provide a bright display using ECB type liquid crystal, and a birefringent film is created between a reflective plate and a second polarizing plate that face each other. A plurality of liquid crystal layers having different characteristics are laminated with a first polarizing plate interposed between the layers.

[Industrial application field]

The present invention relates to a liquid crystal display panel, and particularly to an ECB type liquid crystal display panel that is bright and has high color purity even if it is a reflective type.

In recent years, advances in electronics have promoted the miniaturization of electronic devices, but displays, which are one of the elemental devices for the interface between machines and humans, are using so-called LCDs (Liquid C), which use liquid crystal display panels.
crystal display)
It is also attracting attention as a thin and lightweight display that can replace CRT displays.

With recent advances in the development of new liquid crystal materials and driving methods, as well as improvements in display element manufacturing technology, LCDs have the potential to become displays comparable to CRT displays.

Various studies are underway toward the realization of color liquid crystal display devices, but the emergence of a reflective multicolor liquid crystal display device that takes advantage of its thin and lightweight features and does not require a so-called backlight on the back. is desired.

[Conventional technology]

Liquid crystal display panels move large molecules in a viscous liquid and use optical effects such as polarization to obtain a display. Generally, the response is slow, so liquid crystal display panels are used. LCDs were said to be unsuitable for displaying fast-moving images such as moving images.

However, TN (Twist Nematic) and STN (Super TN)
While a new liquid crystal material called Super TN is being developed, TPT (Thin Film Transist
An active matrix method has been realized in which pixels are arranged and switched pixel by pixel, and liquid crystal display devices have become the type of display that is attracting the most attention.

On the other hand, for the colorization of liquid crystal display devices, R (red) and G (green) are
Technology has been developed that uses a fine B (blue) filter to switch light using liquid crystals to display multicolor images.For example, color TVs and color monitors, both portable and wall-mounted, are beginning to appear.

FIG. 6 is a cross-sectional view of an example of a conventional color liquid crystal display panel.

In the figure, 4 is a liquid crystal layer, 10 is a substrate, 11 is a color filter layer, 12 is an electrode, and 13 is a coating layer.

The liquid crystal layer 4 is sandwiched between two substrates 10.

The substrate 1O is a transparent and smooth glass plate, and on one side of the substrate 10, tod-shaped color filter layers 11 of three colors of cyan, yellow, and magenta are alternately arranged and adhered. The gaps between the color filter layers 11 are covered with, for example, a chrome film to prevent light from leaking.

Since the electrode 12 must be transparent, it is generally
O (Indium Tin Oxide) films are often used. However, since the ITO film is several nanometers thick,
A highly uneven substrate 1 provided with a color filter layer 11
It is difficult to provide it directly on the surface of 0.

Therefore, in order to fill in the unevenness of the color filter layer 11 and make the surface smooth, a covering layer 13 made of polyimide, for example, is used.
is provided. An ITO film is provided on this coating layer 13, and the ITO film is etched in stripes in the X direction or the Y direction to form the electrode 12. In this way, when the two substrates 10 are stacked facing each other, the intersection of the electrodes 12 overlaps the color filter layer 11, for example, 640 x 40
A so-called matrix electrode that becomes a 0-dot pixel is constructed.

There is also a driving method called an active matrix method in which a TPT (thin film transistor) is provided for each pixel to perform switching.

On the other hand, in the case of a liquid crystal display panel or a TN type, a liquid crystal material called a nematic type is used, and an alignment film (not shown) or, for example, polyimide or polyvinyl alcohol with a thickness of several tens of nanometers is provided on the electrode 12. is provided.

One of the substrates 10 thus formed and the other substrate 10 are placed facing each other with a gap of, for example, about 7 μm, and the periphery is sealed with a thermosetting sealant made of, for example, epoxy resin. Liquid crystal, for example, is injected in a vacuum into the gap between the substrates 10 and sealed liquid-tight, thereby forming the liquid crystal layer 4.

Furthermore, in the case of the TN system, polarizing plates are provided on both sides of each substrate 10 to complete a liquid crystal display panel.

By using this liquid crystal display panel and switching the light that passes through color filters provided corresponding to individual pixels, multicolor display can be performed.

[Problem to be solved by the invention]

In this way, the multi-color method that has been widely used in the past,
This method uses color filters.

However, the transmittance of such a liquid crystal display panel is theoretically reduced to 1/3 or less by the color filter, and in addition, light is absorbed by the polarizing plate.

Therefore, a backlight is required to obtain a bright display, and there is a problem in that it is difficult to obtain a reflective display panel.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a liquid crystal display panel in which a plurality of ECB-type liquid crystal layers are stacked to provide a bright reflective multicolor display with high transmittance.

[Means to solve the problem]

The problem mentioned above is that the liquid crystal layer is constructed such that multiple liquid crystal layers with birefringence are stacked between the opposing reflecting plate and the second polarizing plate with the first polarizing plate interposed between the layers. The solution is a liquid crystal display panel.

[For production]

The effect of changing the birefringence of the liquid crystal itself due to an electric field and thus changing the optical phase difference Δn-d (Δn: birefringence of the liquid crystal layer, d: layer thickness of the liquid crystal layer) is called ECB (Electri
Cally Controlled Birefrin
gence.

A liquid crystal display panel using a nematic liquid crystal exhibiting this property is called an ECB type liquid crystal display/i-channel. This effect depends on the wavelength of the incident light, and the output light is colored by interference phenomena, so it can be applied to multi-color liquid crystal display panels.

FIG. 5 is a diagram explaining the principle of the present invention.

In the figure, 1c is a reflecting plate, 2 is a first polarizing plate, 4a is a first liquid crystal layer, 4b is a second liquid crystal layer, 2c is an absorption axis, 5 is a second polarizing plate, 5a is an absorption axis, and 6a is incident light , 6b is reflected light.

In the figure, liquid crystal layers 4a and 4b are made of liquid crystal having an ECB effect, and the liquid crystal layers 4a and 4b are aligned in the same direction. And liquid crystal layer 4
The orientation direction of each of a and 4b is set at 45° with respect to the direction of each absorption axis 2C15a of the polarizing plate 2.5.

Now, the linearly polarized incident light 6a that has passed through the second polarizing plate 5 undergoes wavelength dispersion in the second liquid crystal layer 4b, and unnecessary wavelength components are absorbed by the second polarizing plate 5. Next, the incident light 6a that has passed through the first polarizing plate 2 and has become linearly polarized light is again directed to the first liquid crystal layer 4.
Reflected light 6b that undergoes wavelength dispersion at a and is reflected by the reflector IC
Unnecessary wavelength components are absorbed by the first polarizing plate 2. Next, this reflected light 6b causes wavelength dispersion in the second liquid crystal layer 4b,
Unnecessary wavelength components are absorbed by the second polarizing plate 5 and emitted.

In this way, the light that is converted into linearly polarized light by the polarizing plate 2.5 is wavelength-dispersed by the liquid crystal layers 4a and 4b, and then linearly polarized again by the polarizing plate 2.5, and unnecessary wavelength components are absorbed and colored. Therefore, if white light is used as the incident light 6a, the reflected light 6b can be colored. Moreover, EC
In the liquid crystal layers 4a and 4b having the B effect, the birefringence Δn changes when an electric field is applied, so if this effect is used to control the optical phase difference Δn・d, reflected light of various hues can be produced. 6b and take it out.

In this way, the first liquid crystal layer 4a and the second liquid crystal layer 4b are independently formed.
Moreover, if the wavelengths of the light transmitted through the respective liquid crystal layers 4a and 4b are controlled at the same time and interfered with each other, highly pure BGR (blue, green, and red) can be selectively extracted, allowing multicolor display. It becomes possible.

〔Example〕

Fig. 1 is a cross-sectional view of the configuration of one embodiment of the present invention, Fig. 2 is a spectrum of the color display process, Fig. 3 is a spectrum of color display characteristics, and Fig. 4 is a cross-sectional view of the configuration of another embodiment of the present invention. It is.

In the figure, 1 is the first substrate, la is the first arranged inner film, 1b is the reflective data electrode, 1c is the reflective plate, 2 is the first polarizing plate, 2a is the second alignment film, 2b is the scanning electrode, 3 is the third 2 substrates, 3a is a transparent data electrode, 4a is a first liquid crystal layer, 4b is a second liquid crystal layer, 5 is a second polarizing plate, 6a is incident light, and 6b is reflected light.

Example=1 In FIG. 1, the first substrate! A transparent and smooth glass plate is used for the second substrate 3, or the first substrate 1 does not need to be transparent.

The reflective data electrode 1b provided on the first substrate 1 also serves as a reflector IC, and is designed to reflect light on the electrode surface.
A thin metal film of Cr or Cr is formed by photolithography. Further, the transparent data electrode 3a provided on the second substrate 3 needs to be transparent, and for example, a transparent conductive film made of a transparent ITO film is formed by photolithography.

Then, on the reflective data electrode 1b and the transparent data electrode 3a, a first alignment film 1a made of, for example, polyimide or polyvinyl alcohol and having a film thickness of several tens of nanometers is provided. As the first alignment film 1a, a parallel alignment film or a vertical alignment film provided with a pretilt by rubbing treatment can be used. In this case, a vertical alignment film with pretilt is used.

On the other hand, the first polarizing plate 2 should be as thin as possible in order to improve the light transmittance of the liquid crystal display panel and to increase the viewing angle of the display panel to make it easier to see. Therefore, the first polarizing plate 2 is made by dyeing a uniaxially stretched polymer film with a thickness of several tens of micrometers to several hundred micrometers with an iodine dye, or by dyeing the surface of a transparent thin glass plate called a microsheet, for example. It is constructed by subjecting it to rubbing treatment to orient the dye.

Scanning electrodes 2b made of, for example, a transparent ITO film are formed on both surfaces of the first polarizing plate 2 by photolithography. A second alignment film 2a made of, for example, a thin film of polyimide, a chromium complex, a silane coupling agent, etc. is provided on the scanning electrode 2b. Since these thin films may be extremely thin, they can also be constructed by, for example, the LB (Langmuir-Prodgett) method.

Like the first alignment film 1a, the second alignment film 2a may be a parallel alignment film or a vertical alignment film.In this case, since the first polarizing plate 2 is a film, there is no need to perform rubbing etc. A vertical alignment film is used as the second alignment film 2a.

The reflective data electrode 1b provided on the first substrate 1, the scanning electrode 2b provided on the back side of the first polarizing plate 2, and the scanning electrode 2b provided on the front side of the first polarizing plate 2 and the scanning electrode 2b provided on the second substrate 3. Transparent data electrodes 3a are configured to face each other to form pixels. Further, voltages are applied independently between the reflective data electrode 1b and the scanning electrode 2b, and between the scanning electrode 2b and the transparent data electrode 3a. Then, by applying a voltage, the first liquid crystal layer 4a
By changing the optical phase difference Δn-d between the first liquid crystal layer 4a and the first liquid crystal layer 4a, the wavelength of the transmitted light can be changed.

In this way, by sandwiching the first liquid crystal layer 4a and the second liquid crystal layer 4b with the first polarizing plate 2 interposed between the first substrate 1 and the second substrate 3, a liquid crystal display panel according to the present invention is completed. At the knee, the first polarizing plate 2 side is vertically aligned, and the first substrate 1 and second substrate 3 side are vertically aligned with pretilt.

By the way, the liquid crystal used for the first liquid crystal layer 4a and the second liquid crystal layer 4b is a nematic liquid crystal having an ECB effect. Depending on the initial molecular alignment of the liquid crystal molecules with respect to the substrate, liquid crystals with this ECB effect can be arranged in a vertical molecular alignment (DAP) type, a parallel molecular alignment (homogeneous) type, or one side perpendicular to the substrate and the other aligned parallel to the substrate. It is classified into types such as hybrid (HAN) type. Therefore, the liquid crystal display panel illustrated here is a DAP type panel.

In this liquid crystal display panel, in region A where no voltage is applied, the traveling direction of the incident light 6a linearly polarized by the second polarizing plate 5 is parallel to the molecular arrangement of the second liquid crystal layer 4b, so the incident light 6a is Not subject to refraction. Therefore, the incident light 6a can only pass through the first polarizing plate 2, and the reflected light 6b is not emitted.

On the other hand, the electrodes 1b, 2b, 3a facing each other
In region B, where a voltage is applied between them, as the applied voltage is increased, the alignment of the liquid crystal molecules in the liquid crystal layers 4a and 4b tilts, and the incident light 6a, which is linearly polarized light, becomes birefringent and becomes elliptically polarized light. becomes. A part of the incident light 6a is transmitted to the second liquid crystal layer 4b, the first polarizing plate 2ψ, the first liquid crystal layer 4a6 and the reflecting plate 1c.
Reflection φ first liquid crystal layer 4a φ first polarizing plate 2 φ second liquid crystal layer 4
b===) The light passes through the second polarizing plate 5 and is emitted as reflected light 6b.

White light is used as the incident light 6a, and between the electrodes 1a-2b, 2b-
By controlling the voltage applied to each liquid crystal layer 4a
, 4b shows the color display process of the reflected light 6b that occurs when the optical phase difference Δn-d of 4b is adjusted.

In Figure 2, the vertical axis is transmittance (%) and the horizontal axis is wavelength (%).
The spectrum of the color display process of the three primary colors of BGR is shown by a broken line for the first liquid crystal layer 4a, a broken line for the second liquid crystal layer 4b, and a solid line for the reflected light 6b. The numbers in parentheses are Δn-d
is the value of

First, regarding blue (B), the optical retardation Δn-d of the first liquid crystal layer 4a is set to 10 nm, and Δn of the second liquid crystal layer 4b.
When nd=630 nm, the first liquid crystal layer 4a transmits the incident light 6a as it is as shown in FIG. Light 6b is obtained.

Next, regarding green (G), △n− of the first liquid crystal layer 4a
When d=550 nm and Δn''d of the second liquid crystal layer 4b is 80 nm, the blue wavelength component transmitted through the first liquid crystal layer 4a interferes with the second liquid crystal layer 4b, as shown in FIG. The G reflected light 6b having a transmission peak in green is obtained.

Furthermore, for red (R), Δn of the first liquid crystal layer 4a
−d=660 nm, Δn·d= of the second liquid crystal layer 4b
When the wavelength is 370 nm, wavelength components from green to blue that are transmitted through the first liquid crystal layer 4a interfere with each other and are erased by the second liquid crystal layer 4b, as shown in FIG. 4(C).

As a result, R reflected light 6b having a transmission peak in red is obtained.

The color display characteristics from the color display process shown in FIG. 2 are summarized in FIG.

In Figure 3 (A), looking at the color display characteristics of the three primary colors of BGR, the color purity of each primary color is reduced and the wavelength components that cause turbidity are erased due to interference, and the hues with high color purity are erased. I know what I'm getting.

Next, white light is visible light in a wide wavelength range, and Δn-d of the first liquid crystal layer 4a is 10 nm, and Δn of the second liquid crystal layer 4b.
When -d = 250 nm, both the first liquid crystal layer 4a and the second liquid crystal layer 4b have good transmittance in a wide wavelength range, and a white color can be obtained, as shown in FIG. 4(B).

Next, in the case of black, only the reflected light 6b is not emitted, and both the first liquid crystal layer 4a and the second liquid crystal layer 4b have Δn.
When −d=10 nm, as shown in the same figure (C), the white light of the incident light 6a transmitted through the first liquid crystal layer 4a is interfered with and extinguished by the second liquid crystal layer 4b, and the reflected light 6b is emitted. It disappears and turns black.

Example: 2 In FIG. 4, the scanning electrode 2b provided on the first substrate 1 also serves as a reflection plate IC, and a first alignment film la is deposited thereon.

On the other hand, the first polarizing plate 2 is made of a transparent material with a high dielectric constant, such as a thin glass plate, and has second alignment films on both sides.
a is attached.

The second substrate 3 has the configuration described in the first embodiment.

Then, as in Example 1, by sandwiching the first liquid crystal layer 4a and the second liquid crystal layer 4b between the first substrate 1 and the second substrate 3 with the first polarizing plate 2 interposed therebetween, a liquid crystal display panel is completed.

A liquid crystal display panel having this configuration includes a scanning electrode 2b provided on the first substrate 1 and a transparent data electrode 3a provided on the second substrate 3.
When a voltage is applied between them, the intervening first polarizing plate 2 has a high dielectric constant, so they are inductively coupled, and an electric field is effectively applied to the first liquid crystal layer 4a and the second liquid crystal layer 4b, so that the liquid crystal layer 4a,
4b can be controlled simultaneously by one drive system. However, it is not possible to independently and finely control each liquid crystal layer 4a, 4b.

The orientation format of liquid crystal molecules in the liquid crystal layer also relates to the configuration of the first polarizing plate, and various modifications are possible.

Further, the value of the optical retardation Δn-d of the liquid crystal layer can take various values depending on the selection of the wavelengths of the three primary colors of BGR, and various modifications are possible.

〔Effect of the invention〕

Conventional liquid crystal display panels that display multicolor using color filters have low transmittance, making it difficult to display in a reflective manner.According to the present invention, multiple liquid crystal layers with ECB effect are stacked. By controlling the optical retardation Δn-d of each liquid crystal layer, multi-color display with high color purity can be achieved. Furthermore, by interposing an extremely thin polarizing plate between the liquid crystal layers without using a color filter, the decrease in transmittance can be suppressed to a low level.

Therefore, the present invention will greatly contribute to the realization of reflective ECB type liquid crystal display devices, which are expected to be put into practical use in the future.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of the configuration of an embodiment of the present invention, Fig. 2 is a spectrum of the color display process, Fig. 3 is a spectrum of color display characteristics, and Fig. 4 is a cross-sectional view of the configuration of another embodiment of the present invention. , FIG. 5 is a diagram explaining the principle of the present invention, and FIG. 6 is a sectional view of the configuration of an example of a conventional color liquid crystal display panel. In the figure, 1 is a first substrate, 1a is a first alignment film, 1b is a reflective data electrode, 1c is a reflection plate, 2 is a first polarizing plate,
2a is a second alignment film, 2b is a scanning electrode, 3 is a second substrate, 3a is a transparent data electrode, 4a is a first liquid crystal layer, 4b is a second liquid crystal layer, and 5 is a second polarizing plate. (A) Blue color (F3) cypress bark length (nnnn) (B) Green color (q) Display process display ,) Red g (R) Display process Figure 2 (1,000/) 2) Liquid length (〃da) (A, 33-Hara 11, 12!, 10a, 10a, 12!
/7λ to °2 Tor Fig. 5 (1 at) Return table (nm) (F3) White 〆n door display field 1 life 1 [shi' table (nnLn (black to G/) display'Pr work Figure 3 (92) Tree, Snow, Moon, 4th Fruit, Color, Structure, Thickness, 1st Side, 4th Gutsf, Sun, Moon Source, Lil] Moon, β Circle, 5th G]

Claims (1)

[Claims] 1) A plurality of liquid crystal layers (4) having birefringence are provided between the reflecting plate (1c) and the second polarizing plate (5) which face each other. ) A liquid crystal display panel characterized by being laminated through a 2) It has a first substrate (1), the first polarizing plate (2), a second substrate (3), and the liquid crystal layer (4), and the first substrate (1) has a first orientation. The first polarizing plate (2) has a reflective data electrode (1b) coated with a film (1a) and also serves as the reflective plate (1c), and the first polarizing plate (2) is coated with a second alignment film (2a) on both sides. The second substrate (3) is transparent and has a back surface covered with the first alignment film (1a) and has a transparent scanning electrode (2b) coated and transparent. The liquid crystal layer (4) has an electrode (3a) and the second polarizing plate (5) on its surface, and the liquid crystal layer (4) has a birefringence controlled by an electric field, and the liquid crystal layer (4) has a birefringence controlled by an electric field. ) and second board (3)
2. The liquid crystal display panel according to claim 1, wherein a plurality of layers are provided in a gap with the first polarizing plate (2) interposed therebetween. 3) The first substrate (1) is covered with a first alignment film (1a) and has a scanning electrode (2) which also serves as the reflection plate (1c).
3. The liquid crystal display panel according to claim 2, wherein the first polarizing plate (2) is made of a transparent dielectric material with a high dielectric constant and whose both surfaces are coated with a second alignment film (2a). . 4) The liquid crystal display panel according to claim 1, wherein the first polarizing plate (2) is a uniaxially stretched transparent polymer film dyed with a dye. 5) The liquid crystal display panel according to claim 1, wherein the first polarizing plate (2) is a transparent member whose surface is rubbed to orient the dye. 6) The reflective data electrode (1b) and the transparent data electrode (3)
4. The liquid crystal display panel according to claim 2, wherein the scanning electrode (2b) and the scanning electrode (2b) independently and simultaneously apply an electric field to the liquid crystal layer (4) between opposing electrodes.