JP2002122859A - Semitransmissive color liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the display chroma in a transmissive display of a semitransmissive color liquid crystal display device while maintaining the brightness and contrast in the reflective display. SOLUTION: A reflection region and a transmission region are clearly divided inside a pixel region forming a display unit. Heightening of chroma in the transmission region is attained by making the transmittance of a color filter formed in a position corresponding to the transmission region lower than the transmittance of a color filter formed in a position corresponding to the reflection region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transflective color liquid crystal display having a reflective function layer, and more particularly to a transmissive transflective color liquid crystal display emphasizing transmissive display.

[0002]

2. Description of the Related Art A transflective color liquid crystal display device is widely used as a display of a portable device or the like because of its features of low power consumption, transmissive display using a backlight, and use in any environment. I am trying to do.

In a conventional transflective color liquid crystal display device,
In order to perform color display, a color filter is stacked on a reflective film formed on the rear substrate, and has a light transmission opening in a part of a portion of the color filter facing a pixel as the reflective film. A transflective film is employed.

Here, the color filter and the reflection film are formed in a liquid crystal panel in order to prevent a decrease in display color saturation due to parallax due to the thickness of the substrate, and a color filter having a high transmittance is used in order to increase brightness during reflection. Have been.

[0005] Further, as other transflective films, a thin film of a metal such as aluminum or silver which is made into a half mirror,
Metal is patterned by etching, and the part where the metal remains is used for reflection, and the part where the metal is removed is used for transmission, or the one that uses dielectrics with different refractive indices laminated and uses interference .

The above liquid crystal display device is disclosed in, for example,
No. 052366. In this publication, a color filter is laminated on a reflective film formed on a rear substrate, and the transflective film has an opening for light transmission in a part of a portion of the color filter facing a pixel as the reflective film. A membrane is employed.

[0007]

However, in a color filter having a high transmittance for increasing brightness at the time of reflection,
In reflective display, the display color saturation is increased by passing through the color filter twice, but in transmissive display, the display color saturation is greatly reduced since it passes through the color filter only once. In addition, when a color filter having high chroma (low transmittance) is employed to increase the display color saturation during the transmissive display, there is a problem that the brightness at the time of reflection is greatly reduced, and the visibility is significantly reduced.

Accordingly, the present invention improves the display color saturation during transmissive display while maintaining the brightness contrast during reflective display in a transflective color liquid crystal display device, particularly a transflective color liquid crystal display device that emphasizes transmissive display. To make it happen.

[0009]

In order to solve the above-mentioned problems, a semi-transmissive color liquid crystal display device of the present invention has a liquid crystal interposed between a pair of substrates, and is provided in one pixel region serving as a display unit.
In a transflective color liquid crystal display device having a reflective area for reflecting light and a transmissive area for transmitting light, the transmissive area corresponds to the transmissivity of the color filter formed at the position corresponding to the reflective area. It is characterized in that the transmittance of the color filter formed at the position indicated by the arrow is small.

According to the above configuration, the transmissivity of the color filter corresponding to the transmissive area is reduced by using the transflective film in which the reflective area and the transmissive area are divided in one pixel area which is a unit of display. Thus, only the color filters in the transmission area can be made highly saturated. Therefore, it is possible to achieve high saturation of the display color at the time of transmission while maintaining the brightness at the time of reflection.

Further, according to the transflective color liquid crystal display device of the present invention, in the transflective color liquid crystal display device according to the first aspect, the transmissivity of the color filter corresponding to the reflection area is 50% or more and 70% or less. In this case, the transmittance of the color filter corresponding to the transmission area is less than 50%.

According to the above-described structure, by setting the transmittance of the reflection area portion and the transmittance of the transmission area portion separately, good display characteristics can be obtained for both the reflective display and the transmissive display. If the transmittance of the color filter corresponding to the reflection area portion is less than 50%, the brightness at the time of reflective display is insufficient, and if it exceeds 70%, the saturation at the time of reflective display becomes small. If the transmittance of the color filter corresponding to the transmission area is 50% or more, the saturation at the time of transmission display is reduced.

Further, according to the transflective color liquid crystal display device of the present invention, in the transflective color liquid crystal display device according to the second aspect, the transmissivity of the color filter corresponding to the reflective region is Tr, and the transmissive region is a transmissive color filter. When the transmittance of the corresponding color filter is Tt, 1.1 ≦ Tr / Tt ≦ 2.4.

According to the above arrangement, when the transmittance of the color filter corresponding to the reflection area is defined as Tr and the transmittance of the color filter corresponding to the transmission area is defined as Tt, 1.1.
If it satisfies that ≦ Tr / Tt ≦ 2.4, it is possible to achieve high saturation of the display color at the time of transmission while maintaining the brightness at the time of reflection.

Further, according to the transflective color liquid crystal display device of the present invention, in the transflective color liquid crystal display device according to any one of claims 1 to 3, a color filter formed at a position corresponding to the reflection region portion; The color filters formed at the positions corresponding to the portions have different transmittances.

According to the above configuration, for example, the transflective color liquid crystal display device of claims 1 to 3 can be easily obtained by changing the pigment concentration of the material constituting the color filter or changing the pigment itself.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS. The transflective color liquid crystal display device according to the present invention will be described with reference to FIG. From the observer side, upper polarizer 1, first retarder 2, second retarder 3, upper substrate 4, transparent display electrode 5, alignment film 7, STN liquid crystal 8, alignment film 7, transparent display electrode 5, overcoat layer 9, color filter 10, transflective plate 1
1, lower substrate 12, third retardation plate 13, lower polarizing plate 14
It consists of the following order.

The transflective plate used in the present invention is shown in FIG.
As shown in FIG.
Aluminum was patterned by photolithography to form a through hole for transmission by vapor deposition. The area of the through hole was set to 30% of the pixel. An RGB stripe color filter 10 is formed thereon. In this embodiment, the opening area is set to 30%.
If it is less than 25%, use of transmitted light is small and the screen becomes dark at the time of transmissive display. If it exceeds 80%, the reflective display screen is dark and there is a problem in visibility even in the case of the transmissive display emphasis type. Comes out.

Further, since the color filter surface becomes uneven due to the overlapping portion or the difference in the film thickness of each color, the orientation of the liquid crystal deteriorates. Therefore, an acrylic resin-based overcoat layer 9 was formed on the color filter 10. The transparent electrode 5 was formed by depositing and etching ITO (indium tin oxide) on the upper substrate 4 and the overcoat layer (planarization layer) 9 of the lower substrate 12 to form a matrix pixel electrode. . Further, a black matrix may be formed around the pixels by using a light-absorbing substance. By doing so, the black shielding power is improved, which can contribute to higher contrast. After the polyimide is applied thereon by printing and baked to form the alignment film 7, the twist angle of the liquid crystal molecules is 240
A rubbing treatment was performed so as to give a twist.

Further, after bonding the upper and lower substrates 4 with a sealing resin 6, a liquid crystal 8 having a controlled birefringence Δn and a pitch was injected to form an STN liquid crystal cell. The desired dΔn
The first retardation plate 2, the second retardation plate 3, the third retardation plate 13, the neutral polar upper polarizing plate 1 and the neutral gray lower polarizing plate 14 of the polycarbonate stretch having a predetermined axis with respect to the liquid crystal cell. Pasted like so.

Although not shown, after forming irregularities with an acrylic resin on the lower substrate 12, a semi-transmissive reflection film may be formed to provide a light diffusing function. May be mirror-finished, and a scattering layer may be separately formed.

FIG. 4 shows the axial angles of the respective optical elements in this embodiment. The angle at which the liquid crystal molecules are twisted from the orientation direction 15 on the lower substrate 12 side to the orientation direction 16 on the upper substrate 4 side of the STN liquid crystal 8 is 240 °, and the clockwise direction is positive and the slow axis 17 of the second retardation plate 3 is The angle between the liquid crystal molecule and the upper alignment direction 16 is 120 °, and the slow axis 18 of the first retardation plate 2 is
The angle between the slow axis 17 of the second retardation plate and the slow axis 17 of the second retardation plate is 40 °, and the angle between the absorption axis 19 of the upper polarizing plate 1 and the slow axis 18 of the first retardation plate 2 is 75 °. Further, the lower substrate 12 side alignment direction 1
5 and the slow axis 20 of the third retardation plate 13 make an angle of 50 °,
The angle between the slow axis 20 of the third retardation plate 13 and the absorption axis 21 of the lower polarizer 14 is 40 °.

Further, the setting of each retardation value is as follows:
STN liquid crystal layer 8 (800 nm), first retardation plate 2 (68
0 nm), the second retardation plate 3 (180 nm), and the third retardation plate 13 (140 nm) to constitute a liquid crystal display device that is in a normally black mode during reflection and transmission.

(Embodiment 1) Here, the color filter shown in FIG. 1 is used in the transflective color liquid crystal display device shown in FIG. 2, and a reflection film transmission region (here, a reflection plate through hole) and a reflection film The pigment concentration of the color filter is changed in the reflection area (here, a part other than the through-hole part of the reflection plate).

A resist direct electrodeposition method was used to produce a color filter having different pigment concentrations in the transmission region and the reflection region. The resist direct electrodeposition method is an electrodeposition ITO
Pattern the photosensitive resin applied on top, and
This is a method of exposing O and forming electrodeposited CF on the exposed portion. Using this method, color filters having different pigment concentrations for each color were formed in the transmission region and the reflection region. Although the electrodeposition ITO is not shown in FIG. 2, it is provided below the color filter on the transflective plate side.

Table 1 shows examples in which the pigment concentration of the color filter was changed in the reflective film transmitting region (here, the through-hole portion of the reflector) and the reflective film reflecting region (here, the portion other than the through-hole portion of the reflector). 2 shows the relationship between the transmittance of the color filter and the display color saturation.

Examples A to D in Table 1 employ the structure shown in FIG. 2 and form a color filter by the resist direct electrodeposition method. Example E has a configuration in which the color filter overcoat shown in FIG. 5 is formed on the upper substrate.

[0028]

[Table 1]

As can be seen from Table 1, although the reflectance of Example A was slightly lowered, higher chroma at the time of transmission could be achieved while maintaining the reflectance as compared with the conventional example. In particular, Examples A and B
Indicates that the performance at the time of transmission is substantially the same as that of the transmission type STN used for a notebook PC or the like. Further, as a result of the examination, it was found that a sufficient saturation can be obtained if the saturation at the time of transmission achieves "12" which is about twice the value "6" of the conventional example.

Embodiment E in which CF is formed on the upper substrate
In this case, the same effect is obtained (at this time, the transparent electrode 5 on the lower substrate 12 side may be replaced with a metal electrode having a reflection effect).

Further, 1/80 Duty, 1/9 Bia
s, when driven at a frame frequency of 80 Hz, the contrast at the time of reflection (reflectance ratio between white and black) is 10,
The contrast at the time of transmission satisfies 20, which is equal to or higher than the conventional value.

(Embodiment 2) Here, the color filter shown in FIG. 6 is used in the transflective color liquid crystal display device shown in FIG. 2, and a reflection film transmission region (here, a reflection plate through hole portion) and a reflection film The thickness of the color filter is changed in the reflection region (here, the portion other than the through-hole portion of the reflection plate).

In order to manufacture a color filter having different film thicknesses in the transmissive area and the reflective area, a color filter is formed in a thickness of 2 to 3 μm by an electrodeposition method, and then patterned by sandblasting so as to have a step of about 1 μm. Formed.
Although the ITO for electrodeposition is not shown in FIG. 2,
It is provided below the color filter on the transflective plate side.

Table 2 shows examples in which the film thickness of the color filter was changed between the reflective film transmitting region (here, the through hole portion of the reflector) and the reflective film reflecting region (here, the portion other than the through hole portion of the reflector). 2 shows the relationship between the transmittance of the color filter and the display color saturation.

Examples FG in Table 2 and Comparative Example H are shown in FIG.
In Example I, the color filter / overcoat shown in FIG. 5 is formed on the upper substrate.

[0036]

[Table 2]

As can be seen from Table 2, although the reflectance of Example F was slightly lowered, higher chroma at the time of transmission was achieved while maintaining the reflectance as compared with the conventional example. Comparative Example H could not satisfy the saturation at transmission of 12. From this, it is understood that the transmittance of the transmission portion color filter is preferably less than 50%.

Example I wherein CF was formed on the upper substrate
And the same effect is obtained. (At this time, the transparent electrode 5 on the lower substrate 12 side may be replaced with a metal electrode having a reflection effect.) Further, when driven at 1/80 Duty, 1/9 Bias, and a frame frequency of 80 Hz, the contrast at the time of reflection (white and white) (Reflectance ratio of black) was 10 when irradiated with diffused light, and the contrast when transmitted was 20, which was equal to or greater than the conventional value.

(Embodiment 3) Here, in the transflective color liquid crystal display device of FIG. 2, a concave portion is formed in a reflection film transmission region (here, a reflection plate through hole portion) as shown in FIG. A color filter in which a color filter is embedded in the concave portion is used, and a reflection film transmission region (here, a reflection plate through hole portion) and a reflection film reflection region (here, a portion other than the reflection plate through hole portion) are used. The thickness of the color filter is changed.

In the color filter as shown in FIG. 7, a substrate with a reflector before forming a through-hole is first etched in a concave shape (step difference: about 1 μm) by a sand blast method, and then the color filter is formed into a 3 to 5 μm color by a substrate pigment dispersion spin coating method. Obtained by forming. Further, according to this method, the process of forming the through hole in the reflector and the process of recessing the substrate for forming the CF reverse convex shape can be performed only once, so that the process can be simplified. Also,
The reason why the film thickness of the color filter is made thicker than that in Example 2 is that a certain degree of thickness is necessary in order to fill the steps and obtain a color filter having a flat surface by using the pigment dispersion spin method. .

Table 3 shows an example in which the thickness of the color filter is changed between the reflective film transmitting region (here, the through hole portion of the reflector) and the reflective film reflecting region (here, the portion other than the through hole portion of the reflector). 2 shows the relationship between the transmittance of the color filter and the display color saturation.

Example J and Comparative Example K in Table 3 employ the structure shown in FIG. 2, and Comparative Example L has a structure in which the color filter overcoat shown in FIG. 5 is formed on the upper substrate. .

[0043]

[Table 3]

As can be seen from Table 3, although the reflectivity of Example J was slightly lowered, higher chroma at the time of transmission was achieved while maintaining the reflectivity as compared with the conventional example. Comparative Examples KL could not satisfy the saturation at transmission of 12.

Further, 1/80 Duty, 1/9 Bia
s, when driven at a frame frequency of 80 Hz, the contrast at the time of reflection (reflectance ratio between white and black) is 10,
The contrast at the time of transmission satisfies 20, which is equal to or higher than the conventional value.

[0046]

According to the transflective color liquid crystal display device of the present invention, the liquid crystal is sandwiched between a pair of substrates to form a unit of display.
In a transflective color liquid crystal display device having a pixel region having a reflective region for reflecting light and a transmissive region for transmitting light, the transmissive color liquid crystal display device has a higher transmittance than a color filter formed at a position corresponding to the reflective region. The transmittance of the color filter formed at a position corresponding to the region is reduced. Therefore, the reflection area and the transmission area are clearly separated in one pixel area which is a unit of display, and the transmittance of the color filter corresponding to each area is determined, thereby maintaining the brightness at the time of reflection. It has made it possible to achieve higher saturation of display colors during transmission.

Further, according to the present invention, color filter materials having different transmittances are prepared for the color filter formed at the position corresponding to the reflection region and the color filter formed at the position corresponding to the transmission region. It has been shown that the transflective color liquid crystal display device of the present invention can be easily obtained by using the resist direct electrodeposition method.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an embodiment according to the present invention.

FIG. 2 is a cross-sectional view of a transflective color liquid crystal display device according to the present invention.

FIG. 3 is a detailed view of a reflection plate according to the present invention.

FIG. 4 is a view showing an axial angle of each member according to the present invention.

FIG. 5 is a sectional view of another transflective color liquid crystal display device according to the present invention.

FIG. 6 is a cross-sectional view showing another embodiment according to the present invention.

FIG. 7 is a cross-sectional view showing another embodiment according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Upper polarizing plate 2 1st phase difference plate 3 2nd phase difference plate 4 Upper substrate 5 Display electrode 6 Seal resin 7 Alignment film 8 STN liquid crystal 9 Overcoat 10 Color filter 11 Transflective reflection film 12 Lower substrate 13 Third Phase difference plate 14 Lower polarizing plate

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2H048 BA02 BA62 BB01 BB02 BB10 BB44 2H091 FA02Y FA08X FA08Z FA11X FA11Z FA14Z FA15Z FA41Z FC06 GA06 HA10 KA10 LA16 5C094 AA08 AA48 BA43 CA19 CA24 DA13 EA06 EB01 FB01

Claims (4)

[Claims] 1. A transflective color liquid crystal display device in which a liquid crystal is sandwiched between a pair of substrates, and one pixel region serving as a display unit has a reflection region reflecting light and a transmission region transmitting light. 3. The transflective color liquid crystal display according to claim 1, wherein the transmittance of the color filter formed at the position corresponding to the transmission region is smaller than the transmittance of the color filter formed at the position corresponding to the reflection region. apparatus. 2. The transflective color liquid crystal display device according to claim 1, wherein the color filter corresponding to the reflection area has a transmittance of 50%.
The transflective color liquid crystal display device, wherein the transmissivity of the color filter corresponding to the transmissive area is less than 50%. 3. The transflective color liquid crystal display device according to claim 2, wherein the transmissivity of the color filter corresponding to the reflective area is Tr, and the transmissivity of the color filter corresponding to the transmissive area is T.
A transflective color liquid crystal display device, wherein, when t, 1.1 ≦ Tr / Tt ≦ 2.4. 4. The transflective color liquid crystal display device according to claim 1, wherein the color filter formed at a position corresponding to the reflective region and the color filter formed at a position corresponding to the transmissive region. A transflective color liquid crystal display device having different transmittance.