JPH11258638A - Guest/host type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a guest/host type liquid crystal display device dissolving coloration at a dark display time and excellent in a contrast ratio and reflectance also by providing a phase plate on a pixel electrode through a transparent layer and forming the transparent layer in the thickness that the retardation of the phase plate formed on its becomes a 1/4 wavelength of a main transmission light wavelength of corresponding respective color filters. SOLUTION: The phase plate 17 is provided between a reflection electrode 21 and a liquid crystal layer 16. First, second transparent films 19, 18 are formed on the reflection electrode 73 corresponding to the color filter 63 of B. Further, only the first transparent film 19 is formed on the reflection electrode 72 corresponding to the color filter of G, and no reflection film is formed on the reflection electrode 71 corresponding to the color filter 61 of R. Further, the phase plate 17 whose layer thickness are different in respective reflection electrodes 71, 72, 73 of R, G, B is formed on it. A condition of a spin coat is adjusted properly, and the retardation of respective phase plates of R, G, B are formed so as to become 1/4 of the main transmission light wavelength of the answering color filter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display device, and more particularly to a guest-host type liquid crystal display device in which a dichroic dye is added to a liquid crystal layer.

[0002]

2. Description of the Related Art Liquid crystal display devices have been widely used as interfaces for notebook personal computers and the like. It is expected that the range of application of the liquid crystal display device will be further expanded with the advancement of functions and networks in all electronic devices.

With the spread of such liquid crystal display devices, it is important to further reduce the power consumption of the liquid crystal display device itself. In particular, a reflection type liquid crystal display device which does not require a backlight meets this demand.

Since the guest-host type liquid crystal display device does not use a polarizing plate, the light use efficiency is high. If this is applied to a reflection type liquid crystal display device, a display having a high reflectance may be obtained. There are several types of guest-host type liquid crystal display devices, and the phase plate type is one of them.

Before explaining the display principle of the guest-host type liquid crystal display device of the phase plate type, FIG. 2 shows a case of a guest-host type liquid crystal display device having no phase plate.

Light 51 incident on the liquid crystal layer is decomposed into two types of intrinsic polarized light (linearly polarized light) 31 and 32 and propagates through the liquid crystal layer. However, since the average orientation direction of the dichroic dye is equal to that of the liquid crystal layer 16, only the intrinsic polarization 31 of the absorption component whose vibration direction is parallel to the orientation direction among the two types of intrinsic polarization is sufficiently absorbed. The reflected light 21 is reflected by the reflection electrode 21 as it is without being substantially absorbed by the intrinsic polarized light 32 of the other transmitted component.
2 to pass through the liquid crystal layer 16. Therefore, the contrast ratio becomes low.

Next, FIG. 3 shows the structure and display principle of a guest-host type liquid crystal display device of the phase plate type. The phase plate 17 is provided between the liquid crystal layer 16 and the reflection electrode 21. The retardation of the phase plate is a quarter wavelength.

The inherent polarized light 32 of the transmission component whose vibration direction is perpendicular to the orientation direction is hardly absorbed by the liquid crystal layer 16 and is incident on the phase plate 17, but passes through the phase plate 17 and is reflected by the reflection electrode 21. Again, in the process of passing through the phase plate 17, the vibration direction is converted to linearly polarized light 31 parallel to the orientation direction.
As a result, the component (inherently polarized light 32) that is hardly absorbed at the time of incidence is also absorbed by the liquid crystal layer 16, and the reflectivity of dark display is sufficiently reduced.

However, the conventional phase plate method has a problem that the dark display is colored purple. The reason will be described with reference to FIG.

In FIG. 4, the ideal retardation wavelength dispersion of the phase plate is indicated by a broken line 41. If the retardation of the phase plate is a quarter wavelength in the entire visible wavelength range, the polarization conversion described in FIG. 3 is performed at the entire visible wavelength. However, since the retardation of the phase plate decreases as the wavelength increases, as indicated by the solid line 42 in FIG. 4, the broken line 41 and the solid line 42 intersect only at one point (550 nm) in the visible wavelength region.

FIG. 4 shows a case where the two are matched at 550 nm at which the visibility becomes maximum. In the visible wavelength region at both ends where the broken line 41 and the solid line 42 are far apart, the polarization conversion shown in FIG. 3 is not established, and the reflectivity of dark display does not decrease sufficiently. That is, the dark display is colored purple because mainly red and blue light leak. The phase plate method is disclosed in JP-A-9-90431.

[0012]

The liquid crystal display device has a color filter for color display, and has a red (R),
It is composed of three types of pixels corresponding to green (G) and (blue) B color filters. In JP-A-9-90431, the retardation of the phase plate is set to a different value for each pixel.

For example, as shown in FIG. 5, it is assumed that the retardation of the phase plate is set to a quarter wavelength of the main transmission wavelength of each color filter. The wavelength dispersion of the effective phase plate retardation at this time is collectively shown by a solid line 47 in FIG.

For example, since 600 to 700 nm corresponds to the maximum transmittance of the R color filter, the display characteristics in this wavelength range are substantially determined by the phase plate corresponding to the R color filter. Similarly, 400 to 500 nm is substantially determined by the phase plate corresponding to the B color filter, and 500 to 600 nm is substantially determined by the phase plate corresponding to the G color filter. As a result, the wavelength dispersion 47 of the effective phase plate retardation approaches the ideal wavelength dispersion 41. As a result, leakage of R and B light is suppressed, and coloring of dark display is eliminated.

In JP-A-9-90431, a photoreactive polymer is used as a raw material, and R, G,
A phase plate is formed for each pixel of B.

However, if the G phase plate is formed after the formation of the R phase plate, the R phase plate is damaged in the step of forming the G phase plate, and a reduction in the retardation value and the like are likely to occur.

In order to prevent this, for example, when forming the G phase plate, it is conceivable to form a protective layer on the R phase plate formed before that. However, such a protective layer causes a layer other than the liquid crystal layer to be interposed between the electrodes, so that the voltage value applied to the liquid crystal layer of interest is reduced, and as a result, the contrast ratio and the reflectance of bright display are reduced.

An object of the present invention is to provide a phase plate type guest-host type liquid crystal display device having an optimum structure in view of the above.

[0019]

The gist of the present invention to achieve the above object is as follows.

A liquid crystal layer containing a dichroic dye sandwiched between a first substrate and a second substrate, wherein the first substrate has a common electrode and a color filter on a side adjacent to the liquid crystal layer; The second substrate includes a reflective electrode for applying an electric field to the liquid crystal layer, a pixel electrode, and an active element connected thereto, and has a phase plate between the reflective electrode and the liquid crystal layer, and a slow axis of the phase plate. Is formed so as to form an angle of 45 degrees with respect to the orientation direction of the liquid crystal layer. In a guest-host type liquid crystal display device in which the first substrate and the second substrate are provided with an orientation film on a surface in contact with the liquid crystal layer,
[1] The phase plate is provided on the pixel electrode with a transparent layer interposed therebetween. The thickness of the transparent layer is determined by the retardation of the phase plate formed thereon and the main transmitted light of each corresponding color filter. The guest-host type liquid crystal display device is characterized in that the liquid crystal display device is formed so as to have a thickness that is a quarter wavelength.

[2] The phase plate is formed to have a thickness such that the retardation of each of the corresponding red, green and blue color filters is one quarter of the main transmitted light wavelength. The phase plate corresponding to each of the green and blue color filters is provided on the transparent layer, respectively, the layer thickness of the phase plate corresponding to each of the green and blue color filters and the transparent layer, The guest-host type liquid crystal display device is formed so as to have substantially the same thickness as a phase plate corresponding to the red color filter.

[3] The phase plate is provided in the lower layer so that the retardation of each of the corresponding red, green, and blue color filters is one quarter of the main transmitted light wavelength. The transparent layer is formed by controlling the thickness of the transparent layer, and the combined thickness of the phase plate and the transparent layer is formed to be substantially the same in each corresponding color filter. Guest-host type liquid crystal display device.

[4] The guest-host type liquid crystal display device described above, wherein the liquid crystal layer side surface of the phase plate provided for each pixel corresponding to each color filter is formed to be flat on all pixel surfaces. .

[5] The guest-host type liquid crystal display device described above, wherein each pixel corresponding to each color filter has one pixel composed of two or more minute regions having different alignment directions of the liquid crystal layer.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention provides a transparent layer between a phase plate and an electrode, and changes the thickness of the transparent layer so that the thickness of the adjacent phase plate is changed for each of R, G and B pixels. Is to change the retardation of the phase plate for each of R, G, and B pixels.

Specifically, the thickness of the transparent layer is made the thickest in the B pixel having the shortest wavelength, and then the thickness of the transparent layer is made thicker in the G pixel having the shortest wavelength than the B pixel. In the longest R pixel, the thickness of the transparent layer is minimized.

Such a transparent layer can be formed as follows. The transparent layer is composed of three transparent layers, that is, a first transparent layer, a second transparent layer, and a third transparent layer. The first transparent layer is formed so as to be distributed to all the R, G, and B pixels. The second transparent layer is formed so as to be distributed to G and B pixels. Then, the third transparent layer is formed so as to be distributed only to the B pixels. A phase plate is formed on such a transparent layer.

The R pixel may not be provided with a transparent layer. That is, the transparent layer is composed of a first transparent layer and a second transparent layer, the first transparent layer is formed so as to be distributed to the G and B pixels, and the second transparent layer is formed only for the B pixels. It is formed so as to be distributed.

As the transparent layer, for example, silicon nitride (Si
It may be formed of an inorganic material such as an Nx) film. Further, it may be formed of an organic polymer material such as an acrylic resin or an epoxy resin. Furthermore, any material that is sufficiently transparent with a thickness of about 1 μm and is optically isotropic can be used as a transparent layer.

In order not to apply mechanical stress to the phase plate, a photoreactive organic polymer film is used as an alignment film on the phase plate, and the alignment treatment is performed by irradiating the organic polymer film with polarized light.

At this time, the direction of polarization oscillation is changed to 1
A pixel is irradiated with polarized light a plurality of times, and a plurality of minute regions having different alignment directions with respect to the liquid crystal layer are formed in one pixel.

Since the thickness of the phase plate is determined by the thickness of the adjacent transparent layer, the phase plate can form R, G, and B pixels at once by a method such as spin coating or printing. In addition, various problems that occur when a phase plate is formed for each of R, G, and B pixels using a conventional photomask or the like can be avoided. For example, there is no fear that the retardation of the phase plate of a specific pixel among the R, G, and B pixels in the phase plate forming process is reduced.

Further, since a protective layer is not required when forming the phase plate, the total thickness of the phase plate and the transparent electrode can be reduced to 1 μm or less, and the contrast ratio and the reflectivity of bright display due to the decrease in applied voltage can be reduced. The decrease can be suppressed.

By providing a plurality of micro regions in which the orientation direction of the liquid crystal layer is different in one pixel, the azimuth angle dependency of the display characteristics originally possessed by the liquid crystal layer is offset, and almost the same display characteristics are obtained from any azimuth angle. can get.

[0035]

Next, the present invention will be described in detail with reference to examples.

[Embodiment 1] FIG. 1 is a schematic sectional view of a liquid crystal display device of the present invention. The figure shows three pixel portions, and corresponds to each of R, G, and B colors from the right. The first substrate 10 of the pair of substrates is made of borosilicate glass having a thickness of 0.7 mm, and has a color filter 15 and a common electrode 24 laminated thereon.

The common electrode 24 is made of ITO (Indium Tin Ox).
ide), and its thickness is 1000 mm. The color filter 15 was produced by a pigment dispersion method. FIG. 8 shows the transmission spectrum. The maximum of the transmittance is about 620 nm, 540 nm, and 480 nm for R, G, and B, respectively.

The second substrate 11 of the pair of substrates is made of the same material and has the same thickness as the first substrate 10.
It has an active element 20. The reflective electrode 21 is made of Al and has a thickness of 2000 mm. Active element 20
Is an inverted staggered thin film transistor.

The reflection electrode 21 is formed for each pixel, and has a substantially rectangular shape and a size of about 100 μm × 300 μm.
It is. The reflective electrode 21 and the active element 20 are connected by a through hole 22, and the reflective electrode 21 and the through hole 22 of each pixel are insulated by an insulating layer 25 made of SiNx.

The phase plate 1 is placed on the reflection electrode 21 on the second substrate side.
7 was formed. FIG. 7 shows the formation process. The first transparent film 19 was formed on the reflective electrodes 72 and 73 corresponding to the G and B color filters by photolithography [FIG.
(A)].

Next, a second transparent film 18 was formed on the reflective electrode 73 corresponding to the B color filter [FIG.
(B)]. The first transparent film 19 and the second transparent film 18 have S
Using iNx, the film thickness was 0.13 μm and 0.09 μm, respectively.
m.

Next, a first photo-alignment film 12 was formed by spin coating, and this was irradiated with light and subjected to an alignment treatment (FIG. 7C).

Photopolymerizable liquid crystal molecules were formed on the first photo-alignment film 12. Since the photopolymerizable liquid crystal molecular layer was sufficiently thin, the alignment regulating force of the photo-alignment film spread over the entire layer, and the layer formed a homogeneous alignment parallel to the direction defined by the photo-alignment film. Thereafter, this was irradiated with light to polymerize the photopolymerizable liquid crystal molecules, thereby forming a phase plate 17 (FIG. 7D).

Thereafter, a second photo-alignment film 13 was formed by a spin coating method, and this was irradiated with light to perform an alignment treatment (FIG. 7E). The orientation directions of the first photo-alignment film 12 and the second photo-alignment film 13 were set at 45 ° to each other.

The thicknesses of the first transparent film 19 and the second transparent film 18 were determined as follows. The maximum of the transmittance of the color filter is 620 nm, 540 nm for R, G, and B, respectively.
At a wavelength of 480 nm. The quarter wavelengths are 155 nm, 135 nm, and 120 nm, respectively. Assuming that the birefringence of the phase plate 17 is 0.16, as described later, the retardation of the phase plate 17 is 4 minutes at the maximum wavelength of the transmittance of each color filter. In order to obtain one wavelength, the thickness of the phase plate 17 should be 0.97 μm, 0.84 μm, and 0.75 μm, respectively.

Accordingly, the phase plate 17 corresponding to R is the thickest, the difference between the thicknesses of G and R is 0.13 μm, and the difference between the thicknesses of B and G is 0.09 μm. Thus, the first transparent film 19
And the second transparent film 18 have a film thickness of 0.13 μm and 0.13 μm, respectively.
09 μm.

The first photo-alignment film 12 and the second photo-alignment film 13
Used a polyvinyl ester having paramethoxycinnamic acid in the side chain. Its molecular structure is shown in Formula 1.

[0048]

Embedded image

N in the formula is usually about 20 to 10
000. In this organic alignment film, the side chain paramethoxycinnamic acid causes a photodimerization reaction by light irradiation.
If linearly polarized light is used as the irradiation light, a combination of two paramethoxycinnamic acids that produce a photoreaction can be selected according to the vibration direction of the electric vector, and thus the direction of the chemical bond produced by the photoreaction can be controlled. Since it is empirically known that the liquid crystal molecules are aligned in the direction perpendicular to the vibration direction of the linearly polarized light, the orientation direction of the liquid crystal can be controlled by the vibration direction of the irradiation light (linearly polarized light).

A high-pressure mercury lamp having a bright line at a wavelength of 320 nm was used as a light source, and natural light was converted into linearly polarized light through a Glan-Thompson prism. The irradiation light amount was 5 J / cm ² and the irradiation time was 2 minutes. Under this irradiation condition, all photoreactions are completed, for example, the first photo-alignment film 1
Even if the second photo-alignment film 13 is subjected to the alignment process after the second photo-alignment process, the alignment state of the first photo-alignment film 12 is not substantially disturbed.

Regarding the photo-alignment film and the photo-alignment technique, see, for example, Japanese Patent No. 2608661, Martin S.
Chadt, Hubert Seiberle, Andreas Schuster et al. (NATURE Vol. 381, 16 May 199).
5) is described in detail. In addition to the photo-alignment film shown in Chemical Formula 1, for example, chalcone-based organic polymers can be used in the same manner.

Photo-polymerizable liquid crystal molecules include Dirk J. Broer,
Rifat AM Hikment, Ger Challenger et al.
omol. Chem. Vol. 190, 3201 to 215 (1
989)]. [Formula 2] shows the molecular structure.

[0053]

Embedded image

The photopolymerizable liquid crystal molecules have an acrylic group at both ends, and can be polymerized into a polymer. Further, a liquid crystal state can be obtained by the mesogen portion at the center and the rod-like structure. The birefringence after the polymerization is about 0.15 to 0.16, depending on the polymerization conditions.

Next, a method for forming the phase plate 17 using photopolymerizable liquid crystal molecules will be described. The second substrate 11 was heated to 160 ° C., and photopolymerizable liquid crystal molecules dissolved in a solvent were applied thereon. Thereafter, the solvent was removed, and the photopolymerizable liquid crystal molecules were heated to 160 ° C. to form an isotropic layer. The temperature was lowered to 140 ° C., and the photopolymerizable liquid crystal molecules were used as a liquid crystal layer, and were aligned in the alignment direction of the first photoalignment film 12. Subsequently, the film was irradiated with light and polymerized, and the phase plate 17 was formed in a state where the orientation direction of the first photo-alignment film 12 was maintained.

As a light source, a high-pressure mercury lamp having a bright line at a wavelength of 320 nm was used as in the case of the photo-alignment film. The irradiation light amount was 5 J / cm ² and the irradiation time was 5 minutes.

The photopolymerizable liquid crystal molecules were formed into a film by a spin coating method.
A large number of second substrates 11 were manufactured by finely changing the speed in the range of 00 rpm. Among these, those having the most appropriate value of the retardation of the phase plate 17 were selected as follows.

The transmission axis is 4 with respect to the orientation direction of the phase plate 17.
A polarizing plate was arranged on the second substrate 11 so as to be 5 °. If the phase plate 17 is an ideal quarter-wave plate, the reflectance should be 0% in this state. In this state, the light reflection of the second substrate 11 was measured, and the one having the lowest reflectance was selected.

As the alignment film 14 of the first substrate 10, a polyimide organic polymer manufactured by Nissan Chemical was used. The alignment film 14 is subjected to an alignment process by a rubbing method, and the second substrate 1 is assembled at the time of assembly.
The orientation direction of the second photo-alignment film 13 was the same as that of the second photo-alignment film 13.

Next, the two substrates 10 and 11 were assembled so that the alignment films 13 and 14 faced each other. In order to make the distance between the two substrates and the thickness of the liquid crystal layer 16 uniform over the entire display portion, a spacer and a seal portion (not shown) were formed between them.

The spacers are spherical polymer beads having a diameter of 6 μm, and are dispersed throughout the display section. The dispersion density was about 100 per 1 cm ² . The seal portion was formed by applying a mixture of spherical polymer beads to an epoxy resin around the display portion.

As the liquid crystal layer 16, LA1 manufactured by Mitsubishi Kasei is used.
Using 21-4, vacuum sealing was performed from the sealing port. LA121
-4 has a positive dielectric anisotropy and contains a dichroic dye, and exhibits almost an achromatic color. A liquid crystal layer 16 having a homogeneous alignment was obtained according to the alignment directions of the first and second substrates.

The light diffusing film 23 was attached to the surface of the liquid crystal panel manufactured as described above to reduce the reflection of the user and the surrounding scene. Further, a driving device was connected to obtain a liquid crystal display device.

As described above, the reflection electrode 21 and the liquid crystal layer 16
A guest-host type liquid crystal display device having a phase plate 17 between them was produced. Reflective electrode 7 corresponding to B color filter
3 and a first transparent film is formed on the reflective electrode 72 corresponding to the G color filter, and only the first transparent film is formed on the reflective electrode 72 corresponding to the R color filter. Did not form a transparent film.

Further, the photopolymerizable liquid crystal molecules are made into an isotropic layer,
This was made into a film having a flat surface by spin coating in a state of low viscosity. Thus, the phase plate 17 having different thicknesses of the R, G, and B reflection electrodes 71, 72, and 73 was formed. That is, R was made thickest, then G was made thicker, and B was made thinnest. By appropriately adjusting the conditions of the spin coating, the retardation of each of the R, G, and B phase plates 17 was formed so as to be ４ of the main transmitted light wavelength of the corresponding color filter.

The display characteristics of the phase plate type guest-host type liquid crystal display device obtained as described above were measured by the following method.

A metal halide lamp was used as a light source. Irradiation was performed from a direction of about 20 ° with respect to the liquid crystal panel normal, and reflected light reflected in a direction of about 25 ° with respect to the liquid crystal panel normal was measured with a luminance meter. . Since the measurement is performed from an angle that does not satisfy the specular reflection condition, the measurement is not affected by light reflected on the liquid crystal panel surface or the like. The luminance of the STN-LCD reflector measured under the same conditions was defined as a reflectance of 100%.

FIG. 10 shows the dependence of the reflectance on the applied voltage.
Numeral 93 in FIG. 10 denotes light incident on the liquid crystal panel in a plane including the liquid crystal alignment direction and reflected, and numeral 94 denotes light incident on the liquid crystal panel in a plane orthogonal to 93 and reflected. In each case, a normally closed type applied voltage dependency was obtained. Focusing on 94, the reflectance at an applied voltage of 8 V is 3
2.6% and a contrast ratio of 4.1: 1. Also,
FIG. 9 shows the measurement results of the hue in dark display (applied voltage 0 V).
Shown in The hue is (u, v) = (0.21 in the CIS color system).
1,0.413), which was almost achromatic.

As described above, in the pixel portions corresponding to the G and B color filters, the transparent layers are respectively formed to have the predetermined thicknesses, and the retardation corresponds to four quarters of the main transmitted light wavelength of the corresponding color filters. The phase plate 17 which is one of the
The liquid crystal display device having a high reflectivity and an almost achromatic dark display was obtained by forming the liquid crystal layer between the second liquid crystal layer 73 and the guest host liquid crystal layer 16.

[Embodiment 2] In the liquid crystal display device of Embodiment 1, the first transparent film 19 and the reflection electrodes (71, 72, 7) were used.
A third transparent film was newly disposed between 3). The third transparent film is a reflective electrode (71, 7) corresponding to R, G, B.
2, 73), and the film thickness was 0.09 μm as in the case of the second transparent film.

In this case, almost the same display characteristics as in Example 1 were obtained.

Example 3 In the liquid crystal display device of Example 1, a sensitizer was added to the first photo-alignment film 12 and the photopolymerizable liquid crystal molecules to carry out photopolymerization. As a sensitizer, 1,2-benzanthraquinone was used. The sensitizer may be 5-nitroacenaphthene.

Even if the light irradiation time was shortened to one third by incorporating a sensitizer, the photo-alignment film could obtain substantially the same orientation as in Example 1. Also, by selecting the phase plate 17 from those manufactured under the above-described series of spin coating conditions, optical characteristics almost similar to those of Example 1 were obtained.

By adding the sensitizer, the production time could be shortened and the productivity could be improved.

[Embodiment 4] In the liquid crystal display device of Embodiment 1, a plurality of minute regions having different alignment directions of the liquid crystal layer 16 are provided in one pixel.

First, the reason why such a plurality of minute regions are provided will be described. As shown in FIG.
The liquid crystal display device has an azimuth angle dependency in display characteristics. 9
In 3 and 94, the voltage values (threshold voltages) at which the reflectance starts to change are different from 2.6 V and 1.2 V, respectively. Focusing on a specific applied voltage, 93 and 94 have different reflectances. Therefore, in the liquid crystal display device according to the first embodiment, the appearance of the display changes depending on the incident azimuth angle of the light, and the display may be difficult to see depending on the light incident condition. Therefore, in the present embodiment, the above-described problem seen in the liquid crystal display device of the first embodiment is solved.

A specific method of providing a plurality of minute regions having different alignment directions of liquid crystal molecules in one pixel in this embodiment will be described below.

After the second photo-alignment film 13 was applied to the second substrate 11, the light irradiation for the alignment process was performed twice. The substantially rectangular pixel shown in FIG. 12 is divided into halves,
One was a first region 81 and the other was a second region 82.
In the first light irradiation, the second region was shielded from light using a photomask, and only the first region was irradiated with light. In the second light irradiation, the first region was shielded from light using a photomask, and only the second region was irradiated with light.

In the first light irradiation and the second light irradiation, the vibration directions of the irradiation light (linearly polarized light) were made different by 90 degrees. The liquid crystal alignment direction 83 in the first region 81 and the second region 8
2 so that the liquid crystal alignment directions 84 are orthogonal to each other, and
The orientation direction 83 and the orientation direction 84 were set at 45 degrees with the slow axis direction 85 of the phase plate.

The same optical alignment film as the second optical alignment film 13 of the second substrate 11 was used as the alignment film 14 of the first substrate 10. First area 81 and second area 82 of second substrate 11
Are subjected to an orientation treatment so as to be parallel to the orientation direction of the first substrate 10.

FIG. 11 shows the applied voltage dependence of the reflectance of the liquid crystal display device manufactured as described above. In the drawing, reference numeral 91 denotes the reflectivity of light incident on and reflected from the liquid crystal panel in a plane including the liquid crystal alignment direction in the first region 81, and reference numeral 92 denotes an in-plane including the liquid crystal alignment direction in the second region 82. Is the reflectivity of the light incident on the liquid crystal panel and reflected. Note that 91
And 92, the measurement directions differ by 90 degrees. Both have substantially the same threshold voltage characteristics and substantially the same reflectance.

The display state of the liquid crystal display device was observed while changing the azimuth angle at which the light from the light source was incident in various ways, but the display did not become difficult to see.

As described above, the azimuth dependence of the display characteristics of each liquid crystal layer is offset by providing two minute regions in which the orientation direction of the liquid crystal layer is different in one pixel. Also obtained almost the same display characteristics.

Comparative Example 1 In the liquid crystal display device of Example 1, the transparent layer on the reflective electrode 21 was removed. The phase plate was separately manufactured for each of the R, G, and B pixels using a photolithography. The method is described below.

A photopolymerizable liquid crystal molecule dissolved in the same solvent as in Example 1 was applied by spin coating. Thereafter, light was selectively irradiated only to the R pixels using a photomask, thereby causing a polymerization reaction only to the photopolymerizable liquid crystal molecules on the R pixels. A phase plate having a thickness of 0.97 μm was formed only on the R pixel. Thereafter, unreacted photopolymerizable liquid crystal molecules on the G and B pixels were removed using a solvent.

In the photomask used at this time, the openings are distributed in a stripe pattern, the width of the openings is the length of the short side of one pixel, and the width between the openings is the length of the short side of one pixel. Twice as long. This is because one pixel is almost rectangular and R, G, B
The pixels corresponding to the respective color filters correspond to the pixels distributed in a stripe shape.

Next, a solution of the photopolymerizable liquid crystal molecules is applied again by the spin coating method, and thereafter, only the pixels of G are selectively irradiated with light using a photomask, and the photopolymerization on the pixels of G is performed. Only the reactive liquid crystal molecules caused a polymerization reaction. A phase plate having a thickness of 0.84 μm was formed only on the G pixel. Thereafter, unreacted photopolymerizable liquid crystal molecules on the R and B pixels were removed using a solvent.

In the same manner, a solution of the photopolymerizable liquid crystal molecules is applied, and then only the pixels of B are selectively irradiated with light using a photomask, so that only the photopolymerizable liquid crystal molecules on the pixels of B are applied. A polymerization reaction occurred. 0.75 thickness only on B pixels
A μm phase plate was formed. Then, R, G using a solvent
Unreacted photopolymerizable liquid crystal molecules on the pixels were removed. Using this, a liquid crystal display device was obtained in the same manner as in the example.

The display characteristics are normally closed type.
The reflectance at an applied voltage of 8 V was 33.2%, and the contrast ratio was 2.1: 1. The contrast ratio was reduced to less than half as compared with Example 1.

To clarify the cause of the decrease in the contrast ratio, the liquid crystal display was disassembled, the second substrate 11 was taken out, and the retardation of the phase plate 17 was measured in the same manner as in Example 1. A polarizing plate was arranged on the second substrate 11 so that the transmission axis of the liquid crystal panel was at 45 ° with respect to the orientation direction of the phase plate, and the reflectance was measured. As a result, R and G
It was found that the reflectance of the phase plate did not decrease sufficiently, and the retardation of the R and G phase plates was considerably deviated from a quarter wavelength.

The reason why only the retardation of the R and G phase plates among R, G, and B is reduced is that after forming the R phase plate,
A solution of photopolymerizable liquid crystal molecules was applied to form a G phase plate. At this time, the solution of the photopolymerizable liquid crystal molecules is also applied on the R phase plate. At this time, it is considered that the R phase plate was partially dissolved. Similarly, it is considered that the retardation of the phase plate of G also decreased due to melting during the formation of the phase plate of B.

As described above, the retardation of the R and G phase plates is reduced by producing the phase plates separately for each of the R, G, and B pixels by using photolithography. It is considered that the contrast ratio has been reduced to less than half.

[Comparative Example 2] In this comparative example, the manufacturing method of the phase plate of the liquid crystal display device of Comparative Example 1 was changed. After forming a phase plate on the R pixel, a protective film was applied to the entire surface of the panel. An epoxy resin was used for the protective film, and its thickness was about 1.5 μm. Next, a phase plate is formed on the G pixel,
In addition, a protective film was applied on the entire surface of the panel. Using this, a liquid crystal display device was similarly formed.

The display characteristics are normally closed type, the reflectance at an applied voltage of 8 V is 19%, and the contrast ratio is 2.
8: 1. The contrast ratio is 8 compared to the first embodiment.
The reflectance at V decreased. In particular, the reflectivity at 8 V dropped to almost half.

Since the reflectance at a voltage of 0 V is almost the same as that of the first embodiment, the retardation of the phase plate is almost as designed. It can be seen that the protective film prevented the dissolution of the phase plate, which caused the deterioration of the display characteristics in Comparative Example 1.

When the dependence of the reflectance on the applied voltage is compared with that of the liquid crystal display device of Example 1, the voltage at which the reflectance starts to change in the liquid crystal display device of this comparative example is shifted to the higher voltage side. The cause is considered to be a decrease in the voltage value applied to the liquid crystal layer.

In this comparative example, two protective films were formed.
The sum of these thicknesses is about 3 μm. Phase plate thickness is 1μm
Since it is weak, a layer of about 4 μm in total is interposed between the electrodes separately from the liquid crystal layer. Since the thickness of the liquid crystal layer is 6 μm, only about half of the voltage applied between the upper and lower electrodes is applied to the liquid crystal layer. As a result, the reflectance of the bright display was reduced to nearly half as compared with Example 1.

[0098]

According to the present invention, the substantial wavelength dispersion of the retardation of the phase plate approaches a quarter wavelength in the entire visible wavelength range, and coloring during dark display is eliminated. Further, a guest-host type liquid crystal display device excellent in both the contrast ratio and the reflectance can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a liquid crystal display device of the present invention.

FIG. 2 is a diagram illustrating a display principle of a guest-host type liquid crystal display device.

FIG. 3 is a diagram illustrating a display principle of a phase plate type guest-host type liquid crystal display device.

FIG. 4 is a diagram illustrating an ideal value of retardation of a phase plate and an actual wavelength dispersion characteristic.

FIG. 5 is a diagram illustrating a wavelength dispersion characteristic of retardation of a phase plate in the present invention.

FIG. 6 is a diagram showing substantial wavelength dispersion characteristics of retardation of a phase plate in the present invention.

FIG. 7 is a schematic cross-sectional view illustrating a step of forming a phase plate in the present invention.

FIG. 8 is a diagram showing a transmission spectrum of a color filter.

FIG. 9 is a diagram illustrating chromaticity of dark display.

FIG. 10 is a diagram showing the dependence of the reflectance of the liquid crystal display device of Example 1 on the applied voltage and the azimuth angle.

FIG. 11 is a diagram showing the dependency of the reflectance of the liquid crystal display device of Example 4 on the applied voltage and the azimuth angle.

FIG. 12 is a diagram showing a liquid crystal alignment direction and a phase plate slow axis direction in one pixel of the liquid crystal display device of Example 4.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal molecule, 2 ... Dichroic dye, 10 ... First substrate, 1
DESCRIPTION OF SYMBOLS 1 ... 2nd board | substrate, 12 ... 1st optical alignment film, 13 ... 2nd optical alignment film, 14 ... alignment film, 15 ... color filter, 16
... liquid crystal layer, 17 ... phase plate, 18 ... second transparent film, 19 ...
First transparent film, 20: active element, 21: reflective electrode, 22: through hole, 23: light diffusion film, 24
... common electrode, 25 ... insulating layer, 31 ... intrinsic polarization of absorption component, 32 ... intrinsic polarization of transmission component, 41 ... retardation wavelength dispersion of ideal phase plate, 42 ... retardation wavelength dispersion of actual phase plate, 44 ... The retardation wavelength dispersion of the phase plate corresponding to the R color filter, the retardation wavelength dispersion of the phase plate corresponding to the G color filter, the retardation wavelength dispersion of the phase plate corresponding to the B color filter, the present invention Corresponding to the substantial retardation wavelength dispersion of the phase plate, 51 ... incident light, 52 ... reflected light, 61 ... R color filter, 62 ... G color filter, 63 ... B color filter, 71 ... R color filter Reflective electrodes 72,... Reflective electrodes corresponding to the G color filters, 73... Reflective electrodes corresponding to the B color filters, 81. The liquid crystal alignment direction in the region 81, 82 ... second region, 83 ... first region 81,
84: orientation direction in the second region 82; 85: slow axis direction of the phase plate; 86: scanning wiring; 87: signal wiring;
... Reflectance of light incident on and reflected by the liquid crystal panel in a plane including the liquid crystal alignment direction in the first region 81, 92... Light reflectance 93, Reflection of light incident on and reflected from the liquid crystal panel in a plane including the liquid crystal alignment direction, 94 ...
The reflectance of light incident on and reflected from the liquid crystal panel in a plane orthogonal to 93.

Claims (5)

[Claims] A second substrate sandwiched between a first substrate and a second substrate;
A first substrate having a common electrode and a color filter on a side adjacent to the liquid crystal layer, and the second substrate having a reflective electrode and a pixel electrode for applying an electric field to the liquid crystal layer; And an active element connected thereto, having a phase plate between the reflective electrode and the liquid crystal layer, wherein the slow axis of the phase plate is formed so as to form 45 degrees with respect to the orientation direction of the liquid crystal layer. A guest-host type liquid crystal display device in which a first substrate and a second substrate are provided with an alignment film on a surface in contact with a liquid crystal layer, wherein the phase plate is provided on a pixel electrode with a transparent layer interposed therebetween; A guest host, wherein the thickness of the layer is such that the retardation of a phase plate formed thereon is a quarter of the main transmitted light wavelength of each corresponding color filter. Liquid crystal display device. A second substrate sandwiched between a first substrate and a second substrate;
A first substrate having a common electrode and a color filter on a side adjacent to the liquid crystal layer, and the second substrate having a reflective electrode and a pixel electrode for applying an electric field to the liquid crystal layer; And an active element connected thereto, having a phase plate between the reflective electrode and the liquid crystal layer, wherein the slow axis of the phase plate is formed so as to form 45 degrees with respect to the orientation direction of the liquid crystal layer. A first substrate and a second substrate each provided with an alignment film on a surface in contact with a liquid crystal layer, wherein the phase plate has a retardation corresponding to each color of red, green, and blue. Each filter is formed to a thickness that is a quarter of the main transmitted light wavelength, and phase plates corresponding to the green and blue color filters are provided on the transparent layers, respectively. Phase plate and transparent layer corresponding to each of the green and blue color filters Wherein the thickness of the phase plate is substantially equal to the thickness of the phase plate corresponding to the red color filter. 3. The two substrates sandwiched between a first substrate and a second substrate.
A first substrate having a common electrode and a color filter on a side adjacent to the liquid crystal layer, and the second substrate having a reflective electrode and a pixel electrode for applying an electric field to the liquid crystal layer; And an active element connected thereto, having a phase plate between the reflective electrode and the liquid crystal layer, wherein the slow axis of the phase plate is formed so as to form 45 degrees with respect to the orientation direction of the liquid crystal layer. A first substrate and a second substrate each provided with an alignment film on a surface in contact with a liquid crystal layer, wherein the phase plate has a retardation corresponding to each color of red, green, and blue. Each filter is formed by controlling the thickness of a transparent layer provided thereunder so as to have a quarter wavelength of the main transmitted light wavelength, and the phase plate and the transparent layer are combined. The layer thickness is substantially the same for each corresponding color filter. A guest-host type liquid crystal display device characterized by being formed in such a manner. 4. The guest according to claim 1, wherein a surface of a phase plate provided on each pixel corresponding to each of said color filters on a liquid crystal layer side is formed so as to be flat on all pixel surfaces. Host type liquid crystal display. 5. The guest-host type liquid crystal display device according to claim 4, wherein each pixel corresponding to each of said color filters is constituted by two or more minute regions having different alignment directions of a liquid crystal layer.