JPH11153789A - Liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display element having an improved surface brightness, an excellent display characteristic without increasing a power consumption. SOLUTION: A color filter 203 applied to a liquid crystal display element is formed of cholesteric liquid crystal layer. A direction of a spiral axis of the cholesteric liquid crystal contained in this color filter 203 is set so as to incline at an arbitrary angle from the normal Z to the substrate within a predetermined range. Moreover, a spiral pitch of the cholesteric liquid crystal is set so as to be arbitrarily distributed within a predetermined range to an average spiral pitch length.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having improved viewing angle characteristics, transmittance characteristics, and color purity unevenness in gradation display.

[0002]

2. Description of the Related Art In recent years, a liquid crystal display device having a great advantage of thinness, light weight and low power consumption, that is, an LCD, has been actively used as a display device for OA equipment such as a personal computer and a television. Most of the LCDs used in these devices use a twisted nematic liquid crystal, and can be roughly classified into two types of display systems: a TN type and an STN type.

[0003] Since all LCDs including the TN type and the STN type are non-light emitting types, they are provided with a light source that illuminates from the back of the LCD, ie, a backlight. Also,
TN-type and STN-type LCDs include a pair of polarizing plates to control display on / off. Further, the TN type or STN type LCD has a color filter for each pixel below a transparent electrode on one substrate in order to realize color display.

[0004]

LCDs are generally characterized by low power consumption, but the power consumption of the backlight is large, and in the case of an LCD with a backlight,
Power consumption does not always decrease. In addition, if the power consumption of the backlight is reduced to reduce power consumption, LC
Since the surface brightness of D decreases, it is necessary to increase the transmittance of the LCD to avoid this.

However, the TN type and the S
Since the TN type LCD includes a polarizing plate, the transmittance of the polarizing plate with respect to natural light is 50% at the maximum.
It is impossible to make the transmittance itself 50% or more.

Further, the above-mentioned LCD is applied with a color filter mainly using pigments and dyes. Such a color filter has a characteristic of transmitting light of a wavelength containing a color component to be displayed and absorbing light of other wavelengths. For example, a red filter that displays red transmits only light of the wavelength of the red component and absorbs light of other wavelengths.
Therefore, light utilization efficiency is very poor, and the amount of light transmitted through the color filter is only tens of percent of the amount of light illuminated from the light source.

[0007] Therefore, the light finally passing through the color filter and the polarizing plate is only a few% of the light source, and in order to obtain sufficient surface luminance, the power consumption of the backlight is increased to increase the amount of light. Problems that must be done.

As described above, in the conventional LCD, it is difficult to obtain a sufficiently bright display with low surface power while reducing the power consumption of the backlight. Therefore, an object of the present invention is to
It is an object of the present invention to provide a liquid crystal display device having improved display characteristics without increasing power consumption and having good display characteristics.

[0009]

According to the present invention, in order to solve the above problems, according to the present invention, at least one of the main surfaces has an electrode and the main surfaces are opposed to each other. A first substrate and a second substrate disposed on the substrate, a liquid crystal layer sandwiched between the first and second substrates,
A cholesteric liquid crystal composition formed on at least one of the first and second substrates;
A liquid crystal display device comprising: a color filter layer containing a cholesteric liquid crystal composition having a helical axis inclined with respect to a normal line of the first or second substrate.

According to a third aspect of the present invention, the first substrate and the second substrate each having an electrode formed on at least one main surface thereof and arranged so that the main surfaces face each other; And a liquid crystal layer sandwiched between the second substrate and
A cholesteric liquid crystal composition formed on at least one of the first and second substrates;
A liquid crystal display device comprising: a color filter layer containing the cholesteric liquid crystal composition having a plurality of helical pitch lengths for selectively reflecting a predetermined wavelength region.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the liquid crystal display device of the present invention will be described with reference to the drawings. FIG.
FIG. 2 is a plan view schematically showing a structure of a display area of an array substrate applied to the liquid crystal display element of the present invention.

FIG. 2 shows the liquid crystal display device shown in FIG.
It is sectional drawing which shows roughly the cross section fractured | ruptured along the A 'line. As shown in FIG. 2, this liquid crystal display element is a light transmission type active matrix type liquid crystal display panel 10 having a thin film transistor, ie, a TFT as a switching element.
And a surface light source unit, that is, a backlight 20 as illumination means for illuminating the liquid crystal display panel 10 from behind.

The liquid crystal display panel 10 includes an array substrate 100 as a first substrate including a display area for displaying an image and a peripheral area on which a wiring pattern is formed, and a second substrate opposed to the array substrate 100. Substrate 200 and a liquid crystal material disposed between the array substrate 100 and the counter substrate 200, for example, a TN-type liquid crystal composition 300
And

The display area of the array substrate 100 is, as shown in FIGS. 1 and 2, an insulating substrate, for example, having a thickness of 0.7.
It comprises 1024 × 3 signal lines 103 and 768 scanning lines 111 arranged orthogonally to each other on a glass substrate 101 mm. The scanning line 111 is formed of a low-resistance material such as aluminum or molybdenum-tungsten, and is provided directly on the glass substrate 101. On the other hand, the signal line 103 is formed of a low-resistance material such as aluminum, and is disposed on an insulating film 113 formed on the glass substrate 101 and formed of a multilayer film of silicon oxide and silicon nitride.

The array substrate 100 is provided with each signal line 10
3 and a TFT 121 disposed in the vicinity of each intersection between each scanning line 111 and each scanning line 111;
And a pixel electrode 151 connected thereto via the first electrode 121. The pixel electrode 151 is formed of a transparent conductive member, for example, I
It is formed by TO.

As shown in FIG. 2, a portion of the TFT 121 protruding from the scanning line 111 is used as a gate electrode 112, on which a gate insulating film 113 is laminated. And
A semiconductor film 115 formed of an a-Si: H film is stacked on the gate insulating film 113. Further, a channel protective film 117 made of silicon nitride is laminated on the semiconductor film 115.

The semiconductor film 115 is electrically connected to the pixel electrode 151 via the low-resistance semiconductor film 119 formed of an n + type a-Si: H film and the source electrode 131. Further, the semiconductor film 115 is formed of the low-resistance semiconductor film 11.
9, and the drain electrode 13 extended from the signal line 103
2 and is electrically connected to the signal line 103 via the signal line 2. T
Channel protection film 117 of FT121, source electrode 13
1 and the drain electrode 132 are covered with a protective film 171 made of an insulating film such as a silicon nitride film.

The surface of the array substrate 100 is covered with an alignment film 141 for aligning the liquid crystal composition 300 interposed between the array substrate 100 and the counter substrate 200. The display area 102 of the counter substrate 200 is formed on a transparent insulating substrate, for example, a glass substrate 201 having a thickness of 0.7 mm, on a wiring pattern of the array substrate 100, that is, a gap between the TFT 121 and the signal line 103 of the array substrate 100, A light-shielding film 202 is provided so as to shield a position facing a gap between the pixel electrode 151 and the signal line 103 and a position facing the gap between the pixel electrode 151 and the scanning line 111. The light shielding film 202 is formed of a black photosensitive resin, for example, a chromium film. The opposing substrate 200 includes a color filter 203 for realizing color display, which is disposed at a position facing the pixel electrode 151 of the glass substrate 201 and between the light shielding films 202. This light shielding film 20
A counter electrode 204 formed of a transparent conductive member, for example, ITO is provided on the second and color filters 203. Further, the surface of the counter electrode 204 is covered with an alignment film 205 for aligning the liquid crystal composition 300 interposed between the counter electrode 204 and the array substrate 100.

On the front and back surfaces of the liquid crystal display panel 10, that is, on the outer surfaces of the glass substrate 101 and the glass substrate 201,
Polarizing plates 190 and 290 whose polarization directions are orthogonal to each other are provided.

The backlight 20 arranged on the back side of the liquid crystal display panel 10 is of an edge light type and has a slightly larger outer dimension than the display area 102 of the liquid crystal display panel 10. The backlight 20 has a light guide plate on which a milky white scattering pattern is printed and formed on the back side, or a light guide plate integrally formed with a scattering groove, and a tubular light source having a diameter of 2.6 mm disposed close to the light guide plate. And a reflection film that wraps the tubular light source around the light guide plate 5 so as to efficiently guide the light from the tubular light source into the light guide plate.

Thus, the light source light from the tubular light source enters from one end face of the light guide plate and propagates through the light guide plate, and a flat light beam L from one main surface of the light guide plate to the liquid crystal display panel 10 side.
Is emitted.

The color filter 203 applied to the above-described liquid crystal display element is formed of cholesteric liquid crystal composed of liquid crystal molecules which are arranged in a spirally spontaneous arrangement independently of the regulating force of the alignment interface. I have.

The cholesteric liquid crystal has a characteristic of causing a phenomenon of selectively reflecting only light of a specific wavelength, that is, a phenomenon called selective reflection or selective light scattering. The liquid crystal appears to be colored by the light reflected or transmitted by the selective reflection phenomenon. The color filter applied to the liquid crystal display device of the present invention displays a specific color by utilizing such a selective reflection phenomenon to realize a color display.

The wavelength at which the maximum intensity of the reflected light reflected by the selective reflection phenomenon is obtained is the product of the helical pitch length p of the twisted cholesteric liquid crystal and the average refractive index n in a plane perpendicular to the helical axis of the cholesteric liquid crystal. , That is, p ×
n (JL Fergason; Molec
ullar Crystals. 1. pp. 293-
307 (1966)). Due to the relationship described above, in general,
It is known that the wavelength at which the reflected light due to the selective reflection phenomenon has the maximum intensity shifts to the shorter wavelength side as the helical pitch length p decreases.

The reflected light that is selectively reflected by this selective reflection phenomenon depends on the direction of the twist arrangement of the cholesteric liquid crystal. That is, circularly polarized light having an optical rotation direction that is the same as the twist direction of the cholesteric liquid crystal is selectively scattered and reflected. For example, left-circularly polarized light incident on a cholesteric liquid crystal having a left-twisted arrangement parallel to the helical axis is reflected, and right-circularly polarized light having an optical rotation direction opposite to the twisting direction of the cholesteric liquid crystal is transmitted. For this reason,
The light reflectance or transmittance of the cholesteric liquid crystal is at most about 50%.

As described above, the cholesteric liquid crystal is
It has the property of selectively reflecting circularly polarized light having the same optical rotation direction as the liquid crystal twist direction, out of the light of a specific wavelength determined by the helical pitch length p with respect to the incident light. Therefore, the light is seen to be colored in a specific color by the light reflected or transmitted by the cholesteric liquid crystal. By utilizing such a phenomenon and setting the spiral pitch length so as to correspond to each color, it is possible to realize a color filter using cholesteric liquid crystal.

Now, suppose that light in the wavelength range of 400 to 500 nm is blue light (B), light in the wavelength range of 500 to 600 nm is green light (G), and light in the wavelength range of 600 to 700 nm is red light (R). And

At this time, as shown in FIG. 3, a cholesteric liquid crystal color filter 20 having a helical pitch length set so as to selectively reflect the wavelength of red light (R).
When white light W, that is, natural light, is incident on the light 3, red light is reflected and scattered, blue light and green light are transmitted, and light of a color similar to cyan (C) as a complementary color of red. Is transmitted.

When white light W enters a cholesteric liquid crystal whose helical pitch length is set so as to selectively reflect the wavelength of green light (G), the green light is reflected and reflected.
While being scattered, red light and blue light are transmitted, and light of a color similar to magenta (M) as a complementary color of green is transmitted.

Further, when white light W enters the cholesteric liquid crystal whose helical pitch length is set so as to selectively reflect the wavelength of the blue light (B), the blue light is reflected and scattered, and , Red light and green light are transmitted,
Light of a color similar to yellow (Y) as a complementary color of blue is transmitted.

In this embodiment, since the above-described color filter using cholesteric liquid crystal is applied to a transmission type liquid crystal display element, a color reduction method using cyan, magenta, and yellow as transmitted light is used. Thus, a color display is realized. When a color filter using the cholesteric liquid crystal is applied to a reflective liquid crystal display device, color display can be realized by using an additive method in which red, green, and blue are reflected light. .

However, when a color filter is constructed using such a cholesteric liquid crystal, there are the following problems. First, if the helical axes of the cholesteric liquid crystal are all set in a certain direction, for example, a direction parallel to the normal direction of the substrate, if the helical axis of the cholesteric liquid crystal in some regions faces a different direction, In some cases, the area may appear as display unevenness. In addition, cholesteric liquid crystals mainly have a viewing angle dependency such as reflecting or transmitting light parallel to the helical axis. Therefore, when the helical axes of all the cholesteric liquid crystals are oriented in a certain direction, the normal of the substrate becomes normal. When the viewing angle is tilted from the direction, the viewing is performed from a direction oblique to all the helical axes, and the change in the apparent average refractive index n increases. For this reason, a change occurs in the color purity of a color that is colored by the cholesteric liquid crystal, thereby deteriorating the quality of a displayed image.

The wavelength at which the intensity of the reflected light selectively reflected by the cholesteric liquid crystal is maximized depends on the helical pitch length. Therefore, if the helical pitch of the cholesteric liquid crystal is set to be constant,
Light of the same color is reflected in all areas,
If the helical pitch length of the cholesteric liquid crystal in a part of the region is different, light of a different wavelength is reflected in the region, which may cause a noticeable display unevenness.

Therefore, the cholesteric liquid crystal used for the color filter in this embodiment is arranged such that the helical axis is oriented in a non-uniform direction within a predetermined angle range with respect to the normal to the substrate. And the helical pitch length is formed to be non-uniform within a predetermined range.

Hereinafter, an embodiment of a liquid crystal display device in which a cholesteric liquid crystal having these structures is applied to a color filter will be described. First, a first embodiment will be described.

In the first embodiment, in the display area,
A cholesteric liquid crystal whose helical axis is oriented in a random direction within a predetermined angle range with respect to the normal of the substrate regardless of the pixel area is used as a color filter.

FIG. 4 is a diagram schematically showing a helical axis distribution of a cholesteric liquid crystal color filter applied to the liquid crystal display device of the first embodiment. As shown in FIG. 4, the color filter 203 includes, for each pixel, a red region 203R formed by a cholesteric liquid crystal for red reflection, a green region 203G formed by a cholesteric liquid crystal for green reflection, and a cholesteric liquid crystal for blue reflection. It includes the formed blue region 203B. Further, a black matrix 202 as a light shielding layer is provided between the color filters 203R, 203G, and 203B of each color.

The helical axes of the cholesteric liquid crystal constituting the color filter 203 are randomly distributed within a range of 0 ° to 45 ° with respect to the normal Z of the substrate. FIG. 5A shows a partial cross section of the color filter 203 when cut along the line AA in FIG. 4, and FIG.
4 shows a cross section of the color filter 203 when cut along the line BB in FIG.

As shown in FIGS. 5A and 5B, a part of the cholesteric liquid crystal included in each pixel of the color filter has a helical axis having a random inclination angle with respect to the normal Z of the substrate. have. The inclination angle of the spiral axis is randomly distributed for each pixel, and also randomly distributed within the same pixel region.

The color filter having such a structure is manufactured as follows. That is, the glass substrate is dipped in an aqueous solution of a silane coupling agent without being subjected to a rubbing treatment, and baked at 120 ° C. for 20 minutes. This makes it possible to randomly distribute the inclination angle of the helical axis of the cholesteric liquid crystal compound when a color filter of the cholesteric liquid crystal compound is formed later on the glass substrate.

Subsequently, a cholesteric liquid crystal compound having a cholesteric ring on the glass substrate was added with a photoinitiator (I
rgacure 907: Ciba Geigy)
In addition, 2.4 wt% of a chiral material for a blue color filter (CB15: manufactured by E. Merck) is mixed, and spin-coated to a thickness of 1 μm. At this time, the temperature of the substrate is maintained at about 60 ° C. in order to adjust the viscosity of the cholesteric liquid crystal compound. At this time, the prepared cholesteric liquid crystal compound had an average refractive index of 1.
5

Subsequently, ultraviolet light is irradiated at 15 mW / cm ² for 10 minutes through a blue color filter mask for curing, and then unnecessary cholesteric liquid crystal compounds are removed to form a blue color filter 203B. .

Similarly, a green color filter 203G is formed by spin coating and patterning a cholesteric liquid crystal compound containing 1.9 wt% of a chiral material for a green color filter.

Similarly, a red color filter 203R is formed by spin-coating and patterning a cholesteric liquid crystal compound mixed with 1.7% by weight of a chiral material for a red color filter.

The cholesteric liquid crystal color filter 203 thus obtained is a blue color filter 203.
The spiral pitch length of B was 0.29 μm, the spiral pitch length of the green color filter 203G was 0.37 μm, and the spiral pitch length of the red color filter 203R was 0.41 μm. The inclination angle of the helical axis of each cholesteric liquid crystal compound with respect to the substrate normal was randomly distributed between 0 ° and 45 °.

An opposing electrode 204 is formed on a glass substrate having a color filter 203 having such a structure to form an opposing substrate 200, which is bonded to an array substrate 100 having a pixel electrode 151 and a TFT 121.
A liquid crystal composition was injected between the substrate and the counter substrate 200, and polarizing plates 190 and 290 were attached to both substrates to produce a liquid crystal display element.

When the transmittance of the liquid crystal display device having this configuration was measured, a high value of 20% was obtained. In addition, although the color purity of each pixel is lower than that of the case where the spiral axis has no inclination, the color unevenness as a whole is reduced,
A uniform display could be obtained.

As described above, fluctuation occurs in the direction of the helical axis of the cholesteric liquid crystal, that is, a certain range is set in the direction of the helical axis which has been almost parallel to the normal direction of the substrate in order to display a certain color. By intentionally giving a variation in the inside, even if a part with a different helical axis direction is created for some reason, it becomes difficult to be recognized as unevenness due to variations in the helical axis direction around it, further improving the yield It becomes possible.

Further, when the viewing angle is inclined, the helical axes are distributed with variation, so that the helical axes are viewed from the front, that is, from the substrate normal side, and from a slightly oblique direction inclined with respect to the substrate normal. The change amount of the average refractive index at the time is small, the change amount of the color purity due to the viewing angle is suppressed to be small, and the image quality of the displayed image can be improved.

Next, a second embodiment will be described. In the second embodiment, a cholesteric liquid crystal in which a helical pitch length of a helical axis is randomly distributed within a predetermined range in a display area regardless of a pixel area is used as a color filter.

FIG. 6 is a diagram schematically showing a cross section of a cholesteric liquid crystal color filter having a constant helical pitch length, and FIG. 7 shows a helical pitch length randomly applied to the liquid crystal display element of the second embodiment. FIG. 2 is a diagram schematically showing a cross section of a cholesteric liquid crystal color filter obtained.

As shown in FIG. 6, in the case of a color filter using a cholesteric liquid crystal having a constant helical pitch length P in the whole area, if the helical pitch length of the cholesteric liquid crystal in a part of the area is different, the area is not changed. Reflection of light of different wavelengths may appear as noticeable display unevenness.

On the other hand, in the color filter shown in FIG. 7, a cholesteric liquid crystal having a helical pitch length within a predetermined range around a predetermined helical pitch length is applied, and the cholesteric liquid crystal having such a helical pitch length is used. The liquid crystal is randomly distributed so that the average helical pitch length is set to P. That is, as shown in FIG. 7, a cholesteric liquid crystal having a helical pitch length of P1, P2, or P3 is randomly distributed to selectively reflect a wavelength region of a predetermined color, and a color filter for a predetermined color is formed. Has formed. The spiral pitch lengths P1, P2, and P3 at this time are within the above-described predetermined range of the spiral pitch length, and the average spiral pitch length based on these spiral pitch lengths is set to P.

The average helical pitch length is set differently depending on the wavelength region of the color to be selectively reflected, based on the characteristics of the cholesteric liquid crystal as described above. For example, the cholesteric liquid crystal for blue reflection has an average helical pitch length of 0.29 μm, the cholesteric liquid crystal for green reflection has an average helical pitch length of 0.37 μm, and the cholesteric liquid crystal for red reflection has an average helical pitch length. 0.
It is 41 μm.

The spiral pitch length of these liquid crystals is
It is randomly distributed within a range of ± 0.02 μm with respect to the average helical pitch length. The spiral pitch length is randomly distributed for each pixel, and also randomly distributed within the same pixel region.

The color filter having such a structure is manufactured as follows. That is, after rubbing on a glass substrate in a certain direction, a cholesteric liquid crystal compound for blue reflection prepared under the same conditions as in Example 1 is spin-coated on the glass substrate.

Then, while setting the substrate temperature to repeat rising and falling at a rate of ± 4 ° C./min, the crystal was irradiated with ultraviolet rays at 15 mW / cm ² for 10 minutes through a mask for a blue color filter. Then, the unnecessary cholesteric liquid crystal compound is removed to form a blue color filter 203B.

As described above, by crystallizing the cholesteric liquid crystal compound, the helical pitch length of the cholesteric liquid crystal compound can be randomly distributed within a predetermined range.

The blue color filter formed by crystallizing the cholesteric liquid crystal compound under the conditions described above has an average spiral pitch length of 0.29 μm, and the average spiral pitch length is ± 0.02 μm. Cholesteric liquid crystal compounds of any helical pitch length within the range were randomly distributed.

Similarly, a cholesteric liquid crystal compound containing 1.9 wt% of a chiral material for a green color filter is spin-coated and patterned to form a green color filter 203G.

Similarly, a cholesteric liquid crystal compound mixed with 1.7 wt% of a chiral material for a red color filter is spin-coated and patterned to form a red color filter 203R.

An opposing electrode 204 is formed on a glass substrate having a color filter 203 having such a structure to form an opposing substrate 200, which is attached to an array substrate 100 having pixel electrodes 151 and TFTs 121.
A liquid crystal composition was injected between the substrate and the counter substrate 200, and polarizing plates 190 and 290 were attached to both substrates to produce a liquid crystal display element.

When the transmittance of the liquid crystal display device having this configuration was measured, a high value of 20% was obtained. Further, in each pixel, color unevenness as a whole was reduced, and a uniform display was obtained.

As described above, the helical pitch length of the cholesteric liquid crystal fluctuates, that is, the helical pitch length, which has been set to be constant for displaying a certain color, intentionally varies within a certain range. Accordingly, even if a portion having a different helical pitch length is formed for some reason, it becomes difficult to be recognized as unevenness due to a variation in the helical pitch length around the portion. The size of each of the portions having different helical pitch lengths may be about 1/4 of the pixel, but it is better to divide the region into as small a region as possible to make the unevenness less visible and to obtain a uniform display. .

Next, a third embodiment will be described. In the third embodiment, as in the second embodiment, in the display area,
A cholesteric liquid crystal set so that the helical pitch length of the helical axis is randomly distributed within a predetermined range regardless of the pixel region is used as a color filter.

The color filter according to the third embodiment is manufactured as follows. That is, after rubbing on a glass substrate in a certain direction, a cholesteric liquid crystal compound for blue reflection prepared under the same conditions as in Example 1 is spin-coated on the glass substrate.

At this time, the glass substrate is placed on a heater having irregularities formed on the surface with which the glass substrate comes into contact, and a temperature difference of up to 60 ± 5 ° C. is applied in the plane while passing through a mask for a blue color filter. By irradiating ultraviolet light at 15 mW / cm ² for 10 minutes to crystallize and remove unnecessary cholesteric liquid crystal compounds, the blue color filter 2
Form 03B.

As described above, by crystallizing the cholesteric liquid crystal compound, the helical pitch length of the cholesteric liquid crystal compound can be randomly distributed within a predetermined range.

The blue color filter formed by crystallizing the cholesteric liquid crystal compound under the above-mentioned conditions has an average spiral pitch length of 0.29 μm, and ± 0 with respect to the average spiral pitch length in one pixel. .02μ
Cholesteric liquid crystal compounds having an arbitrary helical pitch length in the range of m were arbitrarily distributed.

Similarly, a green color filter 203G is formed by spin-coating and patterning a cholesteric liquid crystal compound containing 1.9 wt% of a chiral material for a green color filter.

Similarly, a red color filter 203R is formed by spin coating and patterning a cholesteric liquid crystal compound in which 1.7% by weight of a chiral material for a red color filter is mixed.

A counter electrode 204 is formed on a glass substrate having a color filter 203 having such a structure to form a counter substrate 200, which is bonded to an array substrate 100 having a pixel electrode 151 and a TFT 121.
A liquid crystal composition was injected between the substrate and the counter substrate 200, and polarizing plates 190 and 290 were attached to both substrates to produce a liquid crystal display element.

When the transmittance of the liquid crystal display device having this configuration was measured, a high value of 20% was obtained. Further, in each pixel, color unevenness as a whole was reduced, and a uniform display was obtained.

As described above, the helical pitch length of the cholesteric liquid crystal fluctuates, that is, the helical pitch length that has been set to be constant to display a certain color has intentionally varied within a certain range. Accordingly, even if a portion having a different helical pitch length is formed for some reason, it becomes difficult to be recognized as unevenness due to a variation in the helical pitch length around the portion. The size of each of the portions having different helical pitch lengths may be about 1/4 of the pixel, but it is better to divide the region into as small a region as possible so that unevenness is less visible and uniform display can be obtained. .

Hereinafter, comparative examples of the liquid crystal display device of the present invention will be described. [Comparative Example 1] In Example 1, after a rubbing treatment was performed on a glass substrate, a color filter layer was formed in the same manner as in Example 1. As a result, the helical axis of the cholesteric liquid crystal layer was substantially horizontal to the substrate normal direction. It became. The liquid crystal display device manufactured using this substrate had a high transmittance of about 20%, but color unevenness occurred and uniform display was not obtained. [Comparative Example 2] In Example 2, crystallization was performed while the substrate temperature was kept constant during irradiation with ultraviolet light. As a result, the helical pitch of the cholesteric liquid crystal layer was substantially uniform without variation among red, green, and blue. The liquid crystal display device manufactured using this substrate had a high transmittance of about 20%, but color unevenness occurred and uniform display was not obtained.

As described above, according to the liquid crystal display device of the present invention, by improving the light use efficiency, the surface luminance can be improved without increasing the power consumption.
By improving transmittance characteristics and improving viewing angle dependence as compared with a liquid crystal display device using a conventional twisted nematic display method, it is possible to suppress unevenness in color purity and obtain good display characteristics.

As shown in the first embodiment, the direction of the helical axis of the cholesteric liquid crystal is distributed in an arbitrary direction within a predetermined range, and as shown in the second and third embodiments, It is needless to say that by arbitrarily distributing the spiral pitch length within a predetermined range with respect to the average spiral pitch length, it is possible to simultaneously improve the viewing angle and the color unevenness.

[0078]

As described above, according to the present invention, the surface luminance can be improved without increasing power consumption,
A liquid crystal display element having good display characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a plan view schematically showing a structure of a display area of an array substrate applied to a liquid crystal display device of the present invention.

FIG. 2 is a sectional view of the liquid crystal display device shown in FIG.
It is sectional drawing which shows roughly the cross section fractured | ruptured by the line.

FIG. 3 is a diagram for explaining the principle of the selective reflection characteristic of the cholesteric liquid crystal.

FIG. 4 is a diagram schematically illustrating a distribution of a helical axis of a cholesteric liquid crystal color filter applied to the liquid crystal display element according to the first embodiment.

5A is a diagram showing a partial cross section of the color filter when cut along the line AA in FIG. 4, and FIG.
(B) of FIG. 4 is a diagram illustrating a cross section of the color filter when cut along the line BB in FIG. 4.

FIG. 6 is a diagram schematically showing a cross section of a cholesteric liquid crystal color filter having a constant helical pitch length.

FIG. 7 is a diagram schematically showing a cross section of a cholesteric liquid crystal color filter applied to the liquid crystal display element of Example 2 and having a helical pitch length randomly distributed.

[Explanation of symbols]

 10: liquid crystal display panel 100: array substrate 200: counter substrate 203: cholesteric liquid crystal color filter

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuzo Kutake 8-8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Inside the Toshiba Yokohama Works Co., Ltd. (72) Inventor Jin Hato 1-9-2 Harara-cho, Fukaya-shi, Saitama No. Toshiba Fukaya Electronics Factory

Claims (4)

[Claims] A first substrate and a second substrate having electrodes formed on at least one main surface thereof and arranged such that the main surfaces face each other; and between the first and second substrates. A liquid crystal layer sandwiched between the cholesteric liquid crystal composition and at least one of the first and second substrates;
And a color filter layer containing a cholesteric liquid crystal composition having a helical axis inclined with respect to a normal to the first or second substrate. 2. The color filter layer is formed of a plurality of cholesteric liquid crystal compositions having a helical axis randomly distributed within a range of 0 ° to 45 ° with respect to a normal line of the first or second substrate. The liquid crystal display element according to claim 1, wherein the liquid crystal display element is formed. 3. A first substrate and a second substrate having electrodes formed on at least one main surface thereof and arranged such that the main surfaces face each other, and between the first and second substrates. A liquid crystal layer sandwiched between the cholesteric liquid crystal composition and at least one of the first and second substrates;
And a color filter layer containing the cholesteric liquid crystal composition having a plurality of helical pitch lengths for selectively reflecting a predetermined wavelength region. 4. A color filter layer comprising a plurality of cholesteric liquid crystal compositions having a helical pitch length randomly distributed within a range of ± 0.02 μm with respect to an average value of the helical pitch length. The liquid crystal display device according to claim 1, wherein