JP2003139940A - Color filter for liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the color temperature of a liquid crystal display panel by selectively heightening blue luminance. SOLUTION: In a liquid crystal display device having a pigment dispersion type color filter 14 and a selective reflection type color filter 32, the reflection wavelength region of the selective reflection type color filter 32 is set so as to reflect a blue color to the backlight side of the parts 14R, 14G of the pigment dispersion type color filter 14 transmitting a red color and the blue color and a part 32T not reflecting the blue color is disposed on the backlight side of the part 14B of the pigment dispersion type color filter 14 transmitting the bleu color.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a flat non-emissive display, and more particularly to a structure of a color filter of a transmissive liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, monochrome or color liquid crystal display devices (LCD) have been used as flat displays. Color liquid crystal display devices include an active matrix system and a simple matrix system for controlling the three primary colors, and a micro color filter is used in each system. In the liquid crystal display device, the constituent pixel portion is a sub-pixel of three primary colors (R, G, B), and the amount of transmitted light of each of the three primary colors is controlled by using the phase change of the liquid crystal due to electrical switching. Color display is performed.

As shown in FIG. 5, the color filter 10 includes, for example, a transparent substrate 12 and a colored layer 14 of R, G, and B color patterns, and a black matrix 16 located at the boundary of each pixel. A color filter layer including the protective film 18 and the transparent electrode layer 20 is provided. Currently, these color filters are mainly patterned into corresponding pixels using a photo-curable resin in which red, green and blue pigments are dispersed.

The color of the liquid crystal display device is obtained by arranging pixels of three primary colors of red, green and blue and adjusting the light intensity of each pixel. However, when a cold cathode tube is used for the backlight 24, it is originally The white light emission spectrum of the light source is fixed, and as the patterned color filter thereon, an absorption type color filter 10 using a pigment is used for each pixel to absorb excess light and Changing colors. Therefore, the intensity of the light that actually appears on the surface of the display is
The polarizing plate 26 halves the intensity, and the color filter 10 absorbs ⅔ of the energy thereof, so that the intensity of the backlight 24 is ⅙ or less.

[0005]

Particularly, for blue, it is difficult to increase the peak of blue light emission from the original backlight, and also for pigments used for color filters, there are no good colors, so red It was darker than green. In particular, when used in liquid crystal televisions, etc., it is necessary to increase the color purity after passing through the color filter, so the density is increased at the expense of the transmittance, which also reduces the blue light intensity. There is.

On the other hand, in television applications, on the contrary, it is desired that the color temperature of white displayed is high, and thus, it is a general CRT.
Etc., the temperature is about 10000C. Therefore, the demand for making blue brighter than other colors is becoming stronger.

[0007] On the other hand, the applicant has filed Japanese Patent Application Laid-Open 2000-3471.
At 79, as shown in FIG. 6, a cholesteric selective reflection type color filter 22 is installed under the pigment dispersion type color filter 14, and the light absorbed by the pigment dispersion type color filter 14 is a light source (backlight). It proposes a method to return to the direction and reuse. In this method, in the red pixel, on the light source side of the red pigment dispersion color filter portion 14R,
A cholesteric color filter unit 22C that reflects cyan complementary light is provided, and the pigment dispersion color filter units 14G and 14B of green and blue pixels also reflect the complementary color magenta and yellow cholesteric colors, respectively. By providing the filter portions 22M and 22Y and returning the reflected extra light to the backlight side once and reusing it,
The brightness is increased with the same power consumption.

However, in this case, there is a manufacturing difficulty in that two cholesteric layers need to be formed in a layered manner, and the brightness of RGB and white can be raised as a whole, but a particular color (especially It had a problem that only blue could not be brightened.

The present invention has been made in view of the above conventional problems, and a color for a liquid crystal display device capable of selectively increasing the brightness of blue color by newly designing the structure of a color filter. Intended to provide a filter.

[0010]

The present invention is made by using a cholesteric liquid crystal or a chiral nematic liquid crystal or a multilayer interference film which is patterned and transmits light of different specific wavelengths. A selective reflection type color filter and a pigment dispersion type color filter transmitting the light transmitted by the selective reflection type color filter on the viewer side with respect to the selective reflection type color filter. The reflection wavelength range of the filter is set so that blue is reflected on the backlight side of the pigment dispersion type color filter that transmits red and green, and the blue side of the pigment dispersion type color filter is transmitted on the backlight side. A color filter for a liquid crystal display device is provided with a portion that does not reflect blue color to achieve the above object. Than it is.

Here, the selective reflection type color filter that reflects blue may be configured such that the low wavelength end of the reflection wavelength range is on the lower wavelength side than 435 nm and the reflection wavelength range includes 435 nm.

Further, an interference filter can be used as the selective reflection type color filter.

A UV-curable cholesteric liquid crystal can be used for the interference filter.

The present invention also provides a liquid crystal display device including the color filter.

The structure of the color filter in the present invention is shown in FIG. Pigment dispersion type RGB color filter (CF
The selective reflection type CF 32 according to the present invention is installed on the side of the backlight 24 of 14). However, blue is reflected on the backlight side of the red and green pigment-dispersed CF parts 14R and 14G so as to be a complementary color. Selective reflection type CF part 32 that transmits yellow
Y is installed, and on the backlight side of the blue pigment dispersion type CF portion 10B, a transparent CF portion 32T that is transparent in all wavelength regions,
Alternatively, a selective reflection type CF section that reflects colors other than blue is installed. In this way, in the ordinary pigment dispersion type CF14,
By adding a single layer, the selective reflection type CF 32, it is theoretically possible to increase blue light to a brightness three times higher than usual.

An interference filter including a cholesteric color filter having a reflection wavelength range other than blue, a transparent resin, or the like can be used for the backlight side portion 32T of the blue pigment dispersion CF portion 14B.

Further, since the intensity of blue can be controlled by controlling the reflectance of the blue reflecting CF portion 32Y, the color temperature can be changed.

The interference color filter reflects light of a specific wavelength with respect to light perpendicular to the plane on which it is formed, but with respect to light incident at an angle, it has a reflection wavelength range. It has the property of being misaligned. Therefore, as shown in FIG. 2, it is desirable that the reflection wavelength range of the interference filter of the blue reflection CF portion 32Y includes 435 nm, and the low wavelength side end of the reflection wavelength range is as close to 430 nm as possible. This makes it possible to maintain the reflection efficiency in a wide angle range even if the reflection wavelength band is shifted to the low wavelength side due to the influence of oblique light.

As the interference filter, a cholesteric liquid crystal having a pitch adjusted to reflect blue, a resin or metal oxide having a different refractive index, an optical multilayer film in which metals are laminated in multiple layers, and the like can be used.

It should be noted that the pigment-dispersed CF 14 and the selective reflection CF 32 may be overlapped or separated from each other between the observer and the backlight, between the observer and the pigment-dispersed CF 1.
4, the selective reflection CF 32, and the backlight 24 may be installed in this order.

In this way, the blue light of the backlight of the liquid crystal display device can be effectively used.

[0022]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

As shown in FIG. 3, a transmissive liquid crystal display device 30 of left-handed circularly polarized light absorption and right-handed circularly polarized light transmission type according to the first embodiment of the present invention includes red, green and blue wavelength light beams. A back light 24 that emits a back light including light, and a selective transmission / reflection type color filter (CF) 10 that is patterned for each pixel and that transmits only the corresponding wavelength light of red, green, and blue and reflects the other. , A quarter-wave plate 34 and a linear polarizing plate 36 arranged so as to face the light emitting surface of the backlight 24.
And a liquid crystal cell 38 of, for example, a TFT.

The color filter 10 and the liquid crystal cell 38
Are sandwiched between a pair of glass substrates 12 and 40.

As the backlight 24, for example, a uniform planar light-emitting body including a diffusion plate 24B having a cold cathode tube 24A as a light source is used, and a metal thin film is formed on the back side (lower side in FIG. 3). The reflective layer 24C made of is disposed.

The quarter-wave plate 34 and the linear polarizing plate 36
Constitutes a dichroic circularly polarizing plate 37 that absorbs left-handed circularly polarized light and transmits right-handed circularly polarized light.

The liquid crystal cell 38 controls the birefringence of the liquid crystal layer by applying an electric field.
B) type, which includes a VAN system, a PAN system, a HAN system, and the like, and the phase shift amount of transmitted light becomes 0 or π by turning on / off an applied voltage.

As shown in the enlarged view of FIG. 1, the color filter 10 includes a selective reflection type CF 32, a pigment dispersion type CF 14 formed on the light emitting surface side thereof, and a black matrix 16.

The selective reflection type CF 32 is composed of a cholesteric liquid crystal layer or a chiral nematic liquid crystal layer laminated on the glass substrate 12.

Similar to the selective reflection type CF 32, the pigment dispersion type CF 14 is patterned for each pixel and is formed by dispersing a pigment or dye of a required color in a photocurable transparent resin.

In the present liquid crystal display device 30, the selective reflection type CF 32 has portions 14R, 1R that transmit the reflection wavelength range of right-handed circularly polarized light through the red and green colors of the pigment dispersion type CF 14.
On the backlight side 32Y of 4G, a transparent portion 32T that is set to reflect blue, and that does not reflect blue is provided on the backlight side of the portion 14B of the pigment dispersion type CF 14 that transmits blue.

Of the white light from the backlight 24, the left-handed circularly polarized light is absorbed by the two-faced circularly polarizing plate 37, so that only the white right-handed polarized light reaches the color filter 10. Of the white right-handed circularly polarized light, the blue right-handed circularly polarized light is reflected at the portions 14R and 14G that transmit red and green, passes through the dichroic circularly polarizing plate 37, and returns to the backlight 24 side. The blue light returned at this time is converted into linearly polarized light, reflected by the reflection layer 24A on the back surface of the backlight 24, and transmitted through the dichroic circularly polarizing plate 37, again converted to right-handed circularly polarized light, and transmits blue light. It is incident on the portion 14B to be turned.

Therefore, in the portion 14B which transmits blue color,
Since blue right-handed circularly polarized light is incident in addition to white right-handed circularly polarized light, for blue, the amount of light emitted through the liquid crystal cell 38 is approximately twice that for red and green.

In this way, the blue light of the backlight of the liquid crystal display device can be effectively used.

The selective reflection CF 32 is disclosed in, for example, Japanese Patent Laid-Open No.
-318807 may be composed of a cholesteric film or a chiral nematic film.

Next, a right-handed circularly polarized light transmission type and a left-handed circularly polarized light reflection type transmissive liquid crystal display device according to the second embodiment of the present invention will be described in detail with reference to FIG.

In this embodiment, in a liquid crystal display device similar to that of the first embodiment, between the backlight 24 and the color filter 10, as in JP-A-2000-347179,
By providing the circularly polarized light separating film 42, the left-handed circularly polarized light is reused.

The circularly polarized light separating film 42 reflects left-handed circularly polarized light and transmits right-handed circularly polarized light.

On the back side (lower side in FIG. 4) of the diffuser plate 24B of the backlight 24, a reflection layer 24C made of a metal thin film is arranged similarly to the above.

The reflection layer 24C reflects the left-handed circularly polarized light component emitted from the diffuser plate 24B and reflected by the circularly polarized light separating film 42 toward the circularly polarized light separating film 42 again, and at this time, the phase of the polarized light component is inverted. Alternatively, or in a non-polarized state, the light utilization efficiency is improved by making all or part of the right-handed circularly polarized light component that can be transmitted through the circularly polarized light separating film 42.

In the present embodiment, the circularly polarized light separating film 42 transmits right-handed circularly polarized light and reflects left-handed circularly polarized light. The birefringent film is laminated in three or more layers. The 1/4 wavelength layer is laminated on this so that the fast axis or the slow axis has an angle of 45 degrees. The film having birefringence as described above can be obtained by stretching a substance such as polycarbonate resin, polyester resin, polyvinyl alcohol resin, or the like, which exhibits in-plane birefringence.

As the circularly polarized light separating film 42, a cholesteric liquid crystal is used, and the cholesteric liquid crystal has a pitch dispersion so that right-handed circularly polarized light is reflected in all visible light regions. be able to.

According to this embodiment, the intensity improvement by the selective reflection type CF 32 according to the present invention is tripled, and the intensity improvement by reusing the left-handed circularly polarized light is doubled.
2 = 6 times.

[0044]

EXAMPLES Examples of the color filter will be described in detail.

In this embodiment, in order to first prepare a cholesteric interference filter, a photocurable cholesteric liquid crystal is applied to 5 μm, the temperature is adjusted so that the low wavelength end of cholesteric reflection is 430 nm, and a photomask is used. A portion corresponding to two pixel portions of red and green of RGB was exposed and cured. Thereby, the reflection wavelength 430-5
A cholesteric layer having a thickness of 00 nm could be formed. After that, the temperature was changed to cure the remaining portion in the isotropic layer where the reflection of cholesteric reflection disappeared.

Further, a blue pigment-dispersed photocurable resin was applied thereon to a thickness of 1 μm, and a blue mask was formed only on the transparent portion of the cholesteric color filter using a photomask. For other blue reflection cholesteric parts, repeat green and red in the same process,
Finally, the composite color filter 10 having the cross section shown in FIG. 1 could be formed.

By using this color filter, circularly polarized light in the direction in which the cholesteric color filter reflects is passed through the ordinary cold cathode fluorescent lamp backlight 24, and circularly polarized light separation that reflects different circularly polarized light as in the second embodiment. When the film 42 was installed and the brightness was measured, as shown in FIG. 5, it was found that blue had a brightness 2.4 times higher than that of a color filter prepared only by dispersing a pigment without forming a cholesteric layer. The color temperature was 4680 ° C. when it was formed with only a normal pigment-dispersed color filter.
It was possible to raise the temperature to 50 ° C. Also, the blue reflectance is 50
%, The color temperature could be 5430 ° C.

[0048]

Since the present invention is constructed as described above,
It has an excellent effect that the blue brightness can be selectively increased and the color temperature of the liquid crystal display panel can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a composite color filter showing a main configuration of the present invention.

FIG. 2 is a spectrum diagram showing an example of the relationship between the reflection wavelengths of the backlight and the selective reflection color filter in the preferred embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view showing a transmissive liquid crystal display device according to a first embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view showing a second embodiment of the same.

FIG. 5 is a sectional view of an example of a conventional color filter.

FIG. 6 is a sectional view of a color filter proposed by the applicant in JP 2000-347179 A.

[Explanation of symbols]

10 ... Color filter 14 ... Pigment dispersion type color filter (CF) 24 ... Backlight 32 ... Selective reflection type color filter (CF) 38 ... Liquid crystal cell 34 ... Quarter-wave (inclusion) plate 36 ... Linear polarizing plate 42 ... Circularly polarized light separating film

Claims (5)

[Claims] 1. A selective reflection type color filter formed by using a cholesteric liquid crystal, a chiral nematic liquid crystal, or a multilayer interference film that is patterned and transmits light of different specific wavelengths, and transmits the light transmitted by them. In a color filter for a liquid crystal display device having a pigment dispersion type color filter on the viewer side with respect to the selective reflection type color filter, the reflection wavelength range of the selective reflection type color filter is set to the red color of the pigment dispersion type color filter. It is characterized in that the blue side is set to reflect blue on the backlight side of the green transmitting part, and the blue side is not reflected on the blue side of the pigment dispersion type color filter. Color filters for liquid crystal display devices. 2. The low wavelength side end of the reflection wavelength range of the selective reflection type color filter for reflecting blue color according to claim 1,
A color filter for a liquid crystal display device, which is on the lower wavelength side than nm and includes 435 nm in the reflection wavelength range. 3. A color filter for a liquid crystal display device, characterized in that an interference filter is used in the selective reflection type color filter according to claim 1. 4. A color filter for a liquid crystal display device, wherein a UV-curable cholesteric liquid crystal is used in the interference filter according to claim 3. 5. A liquid crystal display device comprising the color filter according to any one of claims 1 to 4.