JP2003005166A - Reflective liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflective liquid crystal display device excellent in visibility and in display quality. SOLUTION: The reflective liquid crystal display device is provided with a liquid crystal layer 19 with selective reflection characteristics and a light scattering layer 20 formed closer to the observer's side than the liquid crystal layer 19 and displays using light reflected by the liquid crystal layer 19. Distribution of scattered light intensity I (θ) of the light scattering layer 20 is kept in such a way that the average value for >=I (0 deg.) and <=I (10 deg.) is <=1,000 times of the average value for >=I (20 deg.) and <=I (30 deg.) and preferably is >=10 times thereof.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective liquid crystal display device that reflects external light to perform display.

[0002]

2. Description of the Related Art A liquid crystal display device, which is a non-light emitting element that modulates external light, has low power consumption, and since it can be applied to a flat panel display, it has an excellent feature that it is thin and lightweight. It is widely used as an information display device for clocks, calculators, computer terminals, word processors, television receivers and the like.

On the other hand, in the present age, as typified by the keyword of advanced information society, the amount of information distribution is increasing, and the demand for collecting and selecting information in each individual is increasing. Against this background, the need for personal portable information terminals has been widely recognized, and its realization is expected.
Development is actively underway.

In the field of portable information terminals, an information display device as a man-machine interface plays an important role and is positioned as a key device of portable information terminals. The display device of a portable information terminal is required to display a large amount of information, be lightweight and thin, have excellent visibility, and have low power consumption. A liquid crystal display device is expected as a display device satisfying the above-mentioned required characteristics, and its development is being actively promoted. In particular, the reflective liquid crystal display device can efficiently use the external light, and thus can be said to be a display mode in which the characteristic of low power consumption inherent in the liquid crystal display device can be sufficiently exhibited.

The TN method and the STN method, which are currently the mainstream, use two polarizers, and thus have a problem that the display becomes dark. to solve this problem,
Many reflective liquid crystal display devices have been proposed so far. However, in any of the methods using a polarizer for display, light loss due to the polarizer is as large as about 60%, and it is difficult to realize a bright display.

Therefore, as a reflective liquid crystal display device that does not use a polarizer, a reflective liquid crystal display device provided with a liquid crystal layer such as a cholesteric layer that selectively reflects light in the visible light region has been proposed.

The phenomenon in which this cholesteric layer selectively reflects light having a wavelength corresponding to its spiral pitch is described in the literature (Ap
pl.Opt. Vol.7, No.9, pp. 1729-1737 (1968), Phys. R
ev.25, No. 9, pages 577-581 (1970)) and the like. Specifically, a right-handed cholesteric liquid crystal has a refractive index of no and n of the liquid crystal layer for normal light and extraordinary light.
e, spiral pitch is p, and reflection wavelength is λ, no · p <
Only the right-handed circularly polarized light of the incident light having the wavelength λ in the range of λ <ne · p is selectively reflected, and the right-handed circularly polarized light of all other wavelengths and all the left-handed circularly polarized light components are transmitted. The reflection center wavelength λm at this time is represented by λm = na · p. Here, na is the average refractive index of the liquid crystal layer. Further, with respect to the left-handed cholesteric liquid crystal, the operation opposite to that of the right-handed case described above is performed.

As a liquid crystal material having a selective reflection characteristic, cholesteric liquid crystal is first mentioned. When the selective reflection characteristic of cholesteric liquid crystal is used for display, generally, the cholesteric liquid crystal is aligned in a planar state to efficiently cause selective reflection. Therefore, when the planar-oriented cholesteric liquid crystal is applied to the reflective liquid crystal display device, a very bright display can be realized in the regular reflection direction of the light source (the direction in which the light from the light source is reflected at the same reflection angle as the incident angle).

However, the intensity of the reflected light decreases in the direction inclined from the regular reflection direction of the light source. Further, since the color of the reflected light changes to the shorter wavelength side as the incident angle or the reflected angle increases, so-called color misregistration occurs in which the color purity of the reflected light deteriorates as the viewing angle increases. Furthermore, if the reflected light intensity is too different depending on the viewing angle, in other words, the change in reflectance is abrupt, it will show a metallic luster-like reflection characteristic when viewed from the direction of the regular reflection of the light source or in the vicinity thereof. It is not preferable in terms of quality.

[0010]

A reflection type liquid crystal display for the purpose of reducing the viewing angle dependence of the peak wavelength of reflected light is disclosed in JP-A-10-96917. The reflective liquid crystal display disclosed in the publication is provided with a liquid crystal display layer containing a cholesteric liquid crystal and an anisotropic scattering layer provided on the observation surface side of the liquid crystal display layer and having a different light transmission state depending on the incident angle of incident light. And layers.

According to the reflection type liquid crystal display disclosed in the above publication, by disposing the anisotropic scattering layer on the observation surface side of the liquid crystal display layer, the light incident on the liquid crystal display layer is increased and the display The brightness increases. Further, since the oblique illumination light becomes scattered light and enters the liquid crystal display layer due to the presence of the anisotropic scattering layer, the incident angle of the incident light to the liquid crystal display layer becomes small as a whole, and the color shift occurs. Can be suppressed.

However, the inventors of the present invention have found that the above-mentioned reflective liquid crystal display body still does not solve the problem of metallic luster and that the display image may be blurred or a double image may be deteriorated. Got

In view of the above situation, it is an object of the present invention to provide a reflective liquid crystal display device which is excellent in visibility and display quality.

[0014]

A reflective liquid crystal display device according to a first aspect of the present invention comprises a liquid crystal layer having selective reflection characteristics, and a scattering layer formed closer to the viewer than the liquid crystal layer. In the reflective liquid crystal display device for displaying by utilizing the reflected light from the liquid crystal layer, the distribution of the scattered light intensity I (θ) of the scattering layer is I (0 °) or more and I (10).
The reflection-type liquid crystal display device has an average value of ≦ °) of 1000 times or less of an average value of I (20 °) or more and I (30 °) or less. “Θ” in the scattered light intensity I (θ) is the light receiving angle with reference to the direction in which the parallel light from the light source travels straight, and the scattered light intensity I (θ) represents the scattered light intensity at the light receiving angle θ.

In the reflective liquid crystal display device according to the first aspect of the present invention, the distribution of the scattered light intensity I (θ) of the scattering layer has an average value of I (0 °) or more and I (10 °) or less. I (2
It is preferably 10 times or more the average value of 0 °) or more and I (30 °) or less.

The reflection type liquid crystal display device according to the second aspect of the present invention comprises a liquid crystal layer having selective reflection characteristics and a scattering layer formed on the viewer side of the liquid crystal layer, and is reflected by the liquid crystal layer. A reflective liquid crystal display device that performs display using light, wherein the scattering layer has a light scattering characteristic depending on an azimuth angle of incident light incident from a direction inclined with respect to a layer normal of the scattering layer. In the first azimuth direction in which the incident light enters the scattering layer, the distribution of the scattered light intensity I (θ) of the scattering layer is an average of I (0 °) or more and I (10 °) or less. The value is 1000 times or less of the average value of I (20 °) or more and I (30 °) or less, and the scattered light intensity I (0 °) or more and I (10 °) or less of the scattering layer at the first azimuth angle. The ratio of the average value to the average value of I (20 °) or more and I (30 °) or less is the first azimuth. Scattered light intensity of the light scattering layer is different from the second azimuthal direction I (0 °) or I (10
The reflective liquid crystal display device is smaller than the ratio of the average value of (°) or less to the average value of I (20 °) or more and I (30 °) or less.

In the reflective liquid crystal display device according to the second aspect of the present invention, the distribution of the scattered light intensity I (θ) of the scattering layer in the second azimuth direction is I (0 °) or more and I (0 °) or more.
The average value of (10 °) or less is I (20 °) or more and I (30
It is preferable to exceed 1000 times the average value of

In the reflective liquid crystal display device according to the first and second aspects of the present invention, the distribution of the scattered light intensity I (θ) of the scattering layer in the first azimuth direction is I (0
The average value of (°) or more and I (10 °) or less is 600 times or less of the average value of I (20 °) or more and I (30 °) or less, and further 10
It is preferably 0 times or less.

Further, in the reflective liquid crystal display device according to the first and second aspects of the present invention, the full width at half maximum of the wavelength of the reflected light is 150 nm or more, and 50% selective reflection wavelength of the reflected light is 0450 nm or more. It is preferable to include the range of 600 nm or less. The 50% selective reflection wavelength means that the reflectance is 50% when standardized with the maximum value of the reflectance being 100%.
It means the wavelength of the reflected light as described above.

[0020]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In the following embodiments, unless otherwise specified, the case of using a chiral nematic liquid crystal will be described. However, even if the chiral nematic liquid crystal is changed to a cholesteric liquid crystal or a chiral smectic liquid crystal, there is no particular difference from the following description. Also,
In the following embodiments, a simple matrix drive type liquid crystal display device will be described as an example. However, the reflection type liquid crystal display device of the present invention includes a thin film transistor (TFT) and a metal-insulator-metal (MIM). It can be applied to an active matrix drive type liquid crystal display device using a switching element.

(Embodiment 1) In Embodiment 1, a reflective liquid crystal display device according to the first aspect of the present invention will be described. FIG. 1 is a cross-sectional view schematically showing the reflective liquid crystal display device of this embodiment. In this embodiment, a case of a reflective liquid crystal display device for monochrome display will be described. The reflective liquid crystal display device of the present embodiment includes a pair of upper substrate 13 and lower substrate 18 which are arranged to face each other, and both substrates 13, 18
And a scattering layer 20 formed on the viewer side of the upper substrate 13. The liquid crystal layer 19 is formed by enclosing a liquid crystal composition adjusted to selectively reflect light in the visible light region in both substrates 13 and 18. Both boards 13,
18 is the liquid crystal layer 19 of the glass substrates 10 and 17, respectively.
On the side, transparent electrodes 11 and 15 and parallel alignment layers 12 and 14
Have a laminated structure. Also, the lower substrate 1
8 has the light absorption layer 16 on the liquid crystal layer 19 side of the glass substrate 17.

An outline of a method of manufacturing the reflective liquid crystal display device of this embodiment will be described. A transparent electrode 11, for example, an ITO film is formed on the glass substrate 10 by a sputtering method so as to have a film thickness of 100 nm, and then a parallel alignment layer 12 is formed.
To a thickness of 50 nm by spin coating or the like.
The parallel alignment layer 12 is rubbed by a rubbing method to form the upper substrate 13. Next, on the glass substrate 17, a black resin is applied to a film thickness of 3 μm by a spin coating method or the like to form the light absorption layer 16. In the same manner as the upper substrate 13, the transparent electrode 15 (ITO film) having a film thickness of 100 nm and the parallel alignment layer 14 having a film thickness of 50 nm are formed, and the lower substrate 18 is formed.

The cell gap between both substrates 13 and 18 is 5 μm.
After bonding so that the liquid crystal composition is injected,
The liquid crystal layer 19 is formed. Although the light absorption layer 16 is formed on the liquid crystal layer 19 side of the glass substrate 17 in this embodiment, it may be formed outside the glass substrate 17.

The liquid crystal composition is adjusted so as to selectively reflect light in the visible light region. For example, nematic liquid crystal material E
7 (made by Merck) CB15 (made by Merck)
40 wt% is mixed to prepare a chiral nematic liquid crystal composition. At this time, the central value of the selective reflection wavelength is about 55.
It is 0 nm, and this chiral nematic liquid crystal composition exhibits a green color. FIG. 2 shows the spectral characteristics of the green display color in the chiral nematic liquid crystal display panel according to the present embodiment.

As a result of observing the chiral nematic liquid crystal display panel produced as described above, the liquid crystal layer 19 has a uniform planar orientation, the reflecting surface has a metallic luster, and a very bright display is obtained within a limited viewing angle range. It was realized.

However, when observed from the direction tilted from the regular reflection direction, the reflected light intensity was remarkably lowered, and the color of the reflected light was changed to the short wavelength side, resulting in different hues. FIG. 3 shows the angle dependence of the reflectance at this time.

Therefore, the scattering layer 20 is formed on the glass substrate 10 on the observer side. Since it is not necessary to form a polarizer in the present invention, many methods can be adopted for forming the scattering layer 20. For example, there is a method in which titanium oxide particles are dispersed in a transparent resin and the resin is applied onto the glass substrate 10 to form the scattering layer 20, and the particle density, the particle diameter, the thickness of the scattering layer, and the refraction of the resin. The scattering characteristics can be changed by changing the rate or the like. In this embodiment, as the scattering layer 20, a plurality of easily available scattering films and scattering liquid crystal layers were used, and the visibility and the display quality were evaluated.
In this case, the reflected light from the selective reflection layer (liquid crystal layer 19) is scattered by the scattering layer 20 and reaches a direction other than the regular reflection direction, so that it is preferable to observe it from a direction other than the regular reflection direction. I could confirm the image. FIG. 4 shows an example of the angle dependence of the reflectance at this time.

When observed from a direction other than the direction of specular reflection,
The scattering characteristics of the scattering layer 20 have an important influence on the visibility.
That is, if the reflectance is too different depending on the viewing angle, a metallic luster-like texture is obtained. Further, when the scattering is too strong, that is, when the reflectance hardly changes depending on the viewing angle, such as paper, it is good from the viewpoint of visibility, but the display blur becomes large and the display quality becomes poor. The present inventors have found that optimizing the scattering characteristics of the scattering layer 20 is important for achieving good visibility and display quality of the reflective liquid crystal display device. From this knowledge, the visibility was evaluated using four kinds of films (IDS film manufactured by Dai Nippon Printing Co., Ltd.) having various scattering characteristics and a scattering type liquid crystal cell.

The scattering type liquid crystal cell was prepared as follows. 1 wt% of a chiral agent S811 (manufactured by Merck) was mixed in a nematic liquid crystal material E7 (manufactured by Merck), and this chiral nematic liquid crystal composition was injected into a cell adjusted to have a cell thickness of 10 μm. The state in which an AC voltage of 2 V was applied to this liquid crystal cell was LC (ON), and the state in which no voltage was applied was LC (OFF).

(Evaluation of Visibility) When evaluating the visibility, the influence of the viewing angle and the viewing distance on the visibility was examined. The reflective liquid crystal display device is mainly used for portable information display because of its features. Therefore, as shown in FIG. 5, when the observer 101 views a predetermined visual distance 103 from the one end of the screen in the normal direction, the viewing angle 102 at which the other end of the screen in the vertical direction can be seen is set to the screen vertical length. Table 1 shows the results calculated for each length 104. The viewing distance was 40 cm and 50 cm. As is clear from Table 1, even in a liquid crystal display device having a diagonal size of 15 inches,
It was found that the visual angle 102 was within 30 °. When the screen size is smaller than the diagonal size of 15 inches, or when the viewing distance exceeds 50 cm, the viewing angle 102 becomes smaller. From this result, it is understood that it is practically sufficient if good visibility is secured within about 30 degrees from the regular reflection direction.

[0031]

[Table 1]

The evaluation test was carried out by using the above-mentioned chiral nematic liquid crystal display panel and disposing a scattering film or a scattering type liquid crystal cell on the observer side of the liquid crystal display panel. The IDS 30 having the strongest scattering has a good reflection-scattering property, and is a stable display when viewed from any angle. In addition, since the change in reflectance due to the change in the observed angle was gradual, no metallic luster-like texture was observed. LC (OFF), which has the weakest scattering, was bright in the normal direction of the screen (the lower part of the screen in FIG. 5), but darkened at the opposite end (the upper part of the screen). In addition, since the change in reflectance was rapid, the bright portion near the bottom of the screen had a metallic luster-like texture. IDS showing intermediate scattering properties
21 and IDS16 were good displays although there were some changes in reflectance within the screen. The LC (ON) using the IDS10 and the scattering type liquid crystal cell had a scattering characteristic within an allowable range, although it had a metallic luster-like texture.

Table 2 shows the results of these evaluations. In the table,
“⊚” indicates that the visibility is excellent and the display characteristics are stable when viewed from any angle. "○" indicates that the display characteristics are excellent in visibility and can withstand practical use. “△” indicates that the display content is within the permissible limit. "X"
Indicates that the displayed contents cannot be visually recognized in directions other than the direction of specular reflection, which is not practical.

(Measurement of Scattered Light Intensity) The scattered light intensity within a predetermined angle of the scattering film and scattering type liquid crystal cell to be evaluated was measured as shown in FIG. Specifically, the average scattered light intensity [I (0 °) or more and I (1
The average value of 0 °) or less] and the average scattered light intensity at 20 ° or more and 30 ° or less [average value of I (20 °) or more and I (30 °) or less] were measured. The average scattered light intensity is a value obtained by integrating the scattered light intensity within each angle and calculating the average scattered light intensity per unit angle. The scattered light intensity is a relative value with 100 as the light intensity when the straight light from the light source is received with air as a control.

The scattered light intensity is measured by the light intensity measuring device 15
5 was used. That is, as shown in FIG. 6, parallel light is incident from the light source 151 in the normal direction of the scattering film or the scattering type liquid crystal cell 152, and the light receiver (optical sensor) 15
The angle 153 of No. 4 was changed, and the change of the light intensity due to the change of the angle 153 was measured. Here, the average scattered light intensity is 10
The reason for averaging ° is that the 10 ° field color system of CIE1964 is taken into consideration. CIE1964 is a standard created in consideration of the structure of a human eyeball because data varies in a 2 ° visual field. In the central portion of the retina, nerves that selectively sense single-wavelength light are distributed in a diameter of about 10 °, and appear different between a wide viewing angle and a narrow viewing angle. Table 2 shows the measurement results
Shown in.

[0036]

[Table 2]

From the above results, it is understood that the smaller the average scattered light intensity ratio, the better the visibility. Specifically, the average value of I (0 °) or more and I (10 °) or less is I (2
It is preferably 1000 times or less of the average value of 0 °) or more and I (30 °) or less, and further 600 times or less, 400 times or less, 200 times or less, 100 times or less, 50 times or less, 30 times or less, 20 times. The visibility is further improved as the ratio becomes 10 times or less and 5 times or less. The average value of the scattered light intensity I (0 °) or more and I (10 °) or less, and I
The ratio with the average value of (20 °) or more and I (30 °) or less is also referred to as “average scattered light intensity ratio” below.

When the scattering is strong, the change in luminance accompanying the change in viewing angle becomes small, and good display can be realized, but on the other hand, some blurring was observed in the boundary region between the voltage applying section and the non-applying section. This corresponds to the blurring of the display image and causes a deterioration in display quality. Therefore, we evaluated the image blur and display quality by using a scattering material with a strong scattered light intensity.

Polymer dispersion type liquid crystal was used as the scattering medium. The polymer liquid crystal was prepared as follows. BL002 (80 wt%) manufactured by Merck Ltd. is used as the liquid crystal material, and 2-Hydroxy-3-phenoxypropyl acrylat is used as the polymer material.
e (5 wt%) and 4-Hydroxybutyl acrylate (13 wt
%) And Bisphenol A glycerolate diacrylate (2w
t%) was used. To 100 parts by weight of the above material, 1 part by weight of Irgacure Irg369 manufactured by Ciba-Geigy Co., Ltd. was further added as a photopolymerization initiator to prepare a starting material. The above materials are well mixed by stirring to obtain a cell thickness of 10 μm and 20 μm.
After injecting into each cell prepared to m, ultraviolet rays (20
PDLC (polymer dispersed liquid crystal) was prepared by irradiating mW / cm ² ).

In order to evaluate the scattering characteristics of the PDLC cell prepared in this way, as in the above, 0 ° or more and 10 ° or more.
The following average scattered light intensity, average scattered light intensity of 20 ° or more and 30 ° or less, and the ratio of the average scattered light intensity were measured. Table 3 shows the measurement results and the evaluation results of white display and image blur when these PDLC cells are arranged on the observer side of the above-mentioned chiral nematic liquid crystal display panel. In the “Visibility evaluation” column of the table, “⊚” indicates that the visibility is excellent and the display characteristics are stable when viewed from any angle. In the column of “Display quality” in the table, “◯” indicates that the image is clear without blurring. “Δ” indicates that the image is slightly blurred, but is within the allowable range. "X" indicates that the image is significantly blurred and exceeds the allowable limit.

[0041]

[Table 3]

From the above evaluation results, it can be seen that the stronger the scattering, the smaller the change in luminance due to the change in the viewing angle, and that a good display can be obtained, but on the other hand, the image is blurred and the display quality is not preferable. The effect of image blur on the display quality depends on the unit pixel size, but as a result of evaluating the image blur point in a commonly used pixel of about 300 μm, the average scattered light intensity ratio is shown. It has been found that the value of 10 or more, preferably 50 or more is a display that can be used practically.

(Embodiment 2) In Embodiment 1, a chiral nematic liquid crystal was used as the selective reflection layer (liquid crystal layer 19), but in this embodiment, a holographic PDLC was used as the selective reflection layer (liquid crystal layer 19). In this embodiment, the steps other than the liquid crystal layer 19 are formed by the same procedure as in the first embodiment. The liquid crystal layer 19 was produced by the following procedure.
A nematic liquid crystal material E7 (manufactured by Merck) was mixed with 30 wt% of a monoacrylate monomer and 2 wt% of a diacrylate monomer, and further added with 2 wt% of a photopolymerization initiator. By subjecting this liquid crystal composition to phase separation polymerization by a method of interference exposure with a laser beam, a reflective holographic PDLC layer 19 having a diffractive reflection function was obtained. The formation of the holographic PDLC layer in this embodiment is described in, for example, Jpn. J. Appl. Phys. Vol. 38 (1999) pp. 14
66-1469 or Jpn. J. Appl. Phys. Vol. 38 (1999) p.
It is possible by the known method described in p.805-808.

As a result of observing the above reflection type holographic PDLC display device, the reflection surface has metallic luster, and a very bright display can be realized within a limited viewing angle range.

However, when observed from a direction tilted from the regular reflection direction, the reflected light intensity was remarkably reduced, and a display with good visibility was not obtained. Therefore, as in the case of the first embodiment, as a result of disposing the scattering film or the scattering liquid crystal cell on the viewer side of the reflective holographic PDLC display device, good display was realized in a wide viewing angle range.

(Embodiment 3) In Embodiment 3, a reflective liquid crystal display device according to the second aspect of the present invention will be described. In the first and second embodiments, the polar angle from the surface normal direction of the scattering film or the scattering type liquid crystal cell is measured only for a certain fixed azimuth angle. These scattering films and scattering type liquid crystal cells are isotropic with respect to the azimuth angle, and exhibit similar scattering characteristics at any azimuth angle.

In this embodiment, an anisotropic scattering layer is used.
The anisotropic scattering layer has a characteristic that the light scattering characteristics differ depending on the azimuth angle of incident light that is incident from a direction inclined with respect to the layer normal of the scattering layer.

The selective reflection layer (liquid crystal layer 19) is the same as in the first embodiment.
It was manufactured by the same method as in. For the anisotropic scattering layer, a scattering film (Lumisty) manufactured by Sumitomo Chemical Co., Ltd. was used. As shown in FIG. 7, the film scatters light incident at an angle within a predetermined range with respect to the surface normal of the film (see FIG.
(A)), even if the angle is within the same range as this incident light,
The film is characterized in that light incident from directions with different azimuth angles of 180 ° is not scattered (FIG. 7 (b)).
That is, even if the polar angle α of the incident light from the normal direction to the film surface is the same, the anisotropic scattering film has different scattering characteristics when the azimuth angles are different by 180 °, for example.

FIG. 8 shows the angle (polar angle) dependence of the scattered light intensity of the Lumisty used in this embodiment. In addition, FIG.
Shows the method of measuring the scattered light intensity. As shown in FIG. 9, the light source 6 with respect to the scattering film (lumis tea) 62.
An optical sensor 63 was installed on the side opposite to 1, and the scattered light intensity was measured using a light intensity measuring device 64. The incident light angle (polar angle) 65 that the incident light makes with the surface normal of the film is 30 °
Then, the direction in which the parallel light from the light source 61 travels straight is set to a light receiving angle of 0 °. Therefore, the light receiving angle shown in FIGS. 8A and 8B is an angle obtained by subtracting 30 ° from the outgoing light angle 66 shown in FIG.

As shown in FIG. 8 (a), the transmitted light is detected only in a very narrow angle range in the direction in which no scattering occurs. On the other hand, as shown in FIG. 8B, in the scattering direction, the transmitted light is detected over a wide angle range. That is, it can be seen that the incident light is scattered.

By using this film, even in the case of a high-definition display device, the reflected light from different pixels does not mix, and there is an effect that display deterioration such as image blurring and double images does not occur. This principle will be described below with reference to FIGS. 10 and 11. 10 and 11
In the figure, 84 and 94 are glass substrates, 85 and 95 are display electrodes (transparent electrodes), and 86 and 96 are lower substrates.

As shown in FIG. 10, using the anisotropic scattering film 83, the light source 81 was placed in the direction of the azimuth angle at which the incident light 87 was scattered, and observation was performed from the direction of the azimuth angle at which the specularly reflected light 89 was not scattered. In this case, the scattering film 83 behaves as if it were a light source, and the observer 82 sees the light 89 in the specular direction.
You will only see the statue by. In other words, the incident light 87 incident from the direction of the scattered azimuth angle is scattered by the anisotropic scattering film 83 and functions as a planar light source in which a plurality of light sources are gathered. The scattered incident light 87 is reflected by the liquid crystal layer, and the anisotropic scattering film 83, respectively.
Incident on. The regular reflection light 89 reflected in the direction of the azimuth angle that does not cause the scattering goes straight through the anisotropic scattering film 83.
In FIG. 10, the observer 82 cannot see the images of the two specular reflection lights 89 at the same time, and can see only the image of one specular reflection light 89, so that the image is not blurred. That is, the observer 82 can see the image of the specularly reflected light 89 such as the light reflected by the mirror-like reflector, and the display characteristics close to ideal are realized.

As described above, the light that reaches the observer 82 is uniquely determined, and it is difficult for image blur caused by image formation by a plurality of light sources (scattered light 88) and display deterioration such as a double image to occur. Even if the azimuth direction of the observer 82 is changed, the light reaches the observer 82 as long as the scattered light 88 is generated, so that the display image is recognized. On the contrary, as shown in FIG. 11, when the film 93 having no scattering anisotropy is used, the light source 91 is placed in the direction in which the incident light 97 is scattered, and the light is observed from the direction in which the specularly reflected light 99 is scattered, Light 98-b reflected by different pixels
Is transmitted to the observer 92 together with the specularly reflected light 99, so that blurring of an image caused by image formation by a plurality of light sources (scattered light 98-a) and deterioration of display such as a double image occur.

FIG. 12 shows the angle dependence of the reflected light intensity in the liquid crystal display device when Lumisty is used as the anisotropic scattering film. In FIG. 12, the regular reflection direction is 0 °. As shown in FIG. 12, according to the present embodiment, it is possible to realize a liquid crystal display device which is extremely bright in a wide viewing angle range and has no deterioration in display such as image blur and double images.

Further, the film of 0 ° in this embodiment is 0 °.
Table 4 shows the average scattered light intensity of 10 ° or more, the average scattered light intensity of 20 ° or more and 30 ° or less, and the ratio thereof in each of the directions in which scattering does not occur and the directions in which scattering occurs.

[0056]

[Table 4]

As shown in Table 4, the ratio of the average scattered light intensity in the first azimuth direction (direction in which scattering occurs) is 10
Smaller than. In the first embodiment, if the ratio of the average scattered light intensities is less than 10, image blurring may occur and display quality may be degraded (see Table 3). However, in the present embodiment, since the anisotropic scattering layer (lumisty) is used, even when the ratio of the average scattered light intensity in the scattering direction is smaller than 10, the observation is performed from the azimuth direction in which scattering does not occur. As long as you do, blurring of the image is unlikely to occur. Therefore, if the ratio of the average scattered light intensities in the first azimuth angle direction (direction in which scattering occurs) is 1000 or less, there is no particular numerical limitation. However, the average scattered light intensity ratio in the first azimuth direction (direction in which scattering occurs) is 600 or less,
400 or less, 200 or less, 100 or less, 50 or less, 30
Hereafter, as it becomes smaller than 20 or less, 10 or less, or 5 or less,
Visibility is improved.

In this embodiment, the average scattered light intensity ratio in the second azimuth angle direction (direction in which scattering does not occur) different from the first azimuth angle direction is about 2000, but the first azimuth angle direction Greater than the ratio of the average scattered light intensity at
There is no particular numerical limitation. However, in order to avoid display deterioration such as image blurring and double images, the ratio of the average scattered light intensity in the second azimuth direction (direction in which scattering does not occur) is 1
It is preferably more than 000, more preferably 2,000 or more.

The incident light angle (polar angle) formed with the layer normal of the anisotropic scattering layer when the incident light is scattered can be appropriately selected according to the application and purpose of the reflective liquid crystal display device. . For example, an anisotropic scattering film that scatters incident light with a polar angle of 15 ° or more and 45 ° or less can be used.

In this embodiment, Lumisty manufactured by Sumitomo Chemical Co., Ltd. was used as the anisotropic scattering film, but the anisotropic scattering film is not particularly limited to this, and as shown in FIG. The same effect can be achieved if the scatterer has anisotropy in which the scattering characteristics are different when the azimuth angle of light is different.

(Embodiment 4) In the above Embodiments 1 to 3, a chiral nematic liquid crystal composition having the spectral characteristics shown in FIG. 2 was used as the liquid crystal composition. In this embodiment, the following chiral nematic liquid crystal composition was used, and a reflective liquid crystal display device was produced in the same manner as in Embodiments 1 to 3 except for the liquid crystal layer 19.

The liquid crystal composition used in this embodiment is (1)
A low molecular weight liquid crystal material, (2) low molecular weight chiral agent, (3) chiral monoacrylate monomer, (4) diacrylate monomer, (5) initiator, and (6) UV absorbing dye were mixed and prepared. FIG. 13 shows the structural formulas (1) to (6). The mixing ratio of each compound is 39.5% by weight of the low molecular weight liquid crystal material 5CB represented by the structural formula (1), 19% by weight of the chiral agent CB15 represented by the structural formula (2), and the structural formula (3). 40% by weight of the indicated chiral monomer,
The diacrylate monomer represented by the structural formula (4) was added to
5 wt% and 1 wt% of the UV absorbing dye Tinuvin P represented by the structural formula (5) were mixed. To 100 parts by weight of this mixture, 2 parts by weight of Irgacure 369 represented by the structural formula (6) was added as an initiator. The above mixture was sufficiently uniformly diffused and mixed, and then filled in a liquid crystal cell having a thickness of 20 μm. Then, using a UV exposure device, exposure was performed for 60 minutes at an exposure intensity of 0.1 mW, and the liquid crystal layer 19 in the present embodiment was produced.

FIG. 14 shows the wavelength dependence of the reflected light by the liquid crystal display device of this embodiment. As shown in FIG. 14, the full width at half maximum of the wavelength of reflected light (hereinafter, also referred to as selective reflection wavelength) according to the present embodiment is about 200 nm, and the 50% selective reflection wavelength is about 430 nm to 650 nm. In the liquid crystal display device of the present embodiment, reflected light is present over a wide wavelength range of the entire visible light, and good black and white display is realized.

The full width at half maximum of the selective reflection wavelength is preferably over a wide wavelength range of visible light, specifically, 150.
It is desirable that the thickness is not less than nm. However, even if the half-value width of the selective reflection wavelength was 150 nm or more, when the lower limit of the 50% selective reflection wavelength was larger than 450 nm, the display was colored yellow, and good black and white display could not be realized. Further, even if the half-value width of the selective reflection wavelength was 150 nm or more, when the upper limit of the 50% selective reflection wavelength was less than 600 nm, the display was colored patina and good black and white display was not realized.

With respect to the tint of white display, the range of the color tone to be recognized as white is not strictly defined because it largely depends on individual differences and the color of illumination light, but the half-value width of the selective reflection wavelength is 150 nm in the visible light region. If the above is the case and the 50% selective reflection wavelength includes the range of 450 nm or more and 600 nm or less, the color tone can be said to be almost white display.

Since the selective reflection layer according to the present embodiment can display in black and white, color display can be performed as in a normal liquid crystal display by forming a color filter on the upper substrate 13 shown in FIG.

(Other Embodiments) Embodiments 1, 3 and 4
In the above, the chiral nematic liquid crystal was used for the selective reflection layer (liquid crystal layer 19), but a cholesteric liquid crystal or a chiral smectic liquid crystal having a selective reflection characteristic optically equivalent to that of the cholesteric liquid crystal can be used. However, cholesteric liquid crystals are generally unstable and unreliable in a chemical atmosphere or ultraviolet rays. On the other hand, the chiral nematic liquid crystal has excellent light resistance, is stable, is relatively easy to adjust the helical pitch, and is also easy to adjust the half-value width of the selective reflection wavelength. A chiral nematic liquid crystal is generally used.

Further, by controlling the spiral pitch of the chiral nematic liquid crystal, it is possible to obtain a reflection type liquid crystal display device which obtains red or blue selectively reflected light. The spiral pitch can be controlled by changing the mixing ratio of the chiral agent.

In the first to fourth embodiments, the case where the selective reflection layer (liquid crystal layer 19) is a single layer has been described, but it is a selective reflection layer in which three liquid crystal layers of red, green and blue are laminated. Is also good. In this case, each liquid crystal layer is sandwiched between the display electrodes and driven independently. The reflection type liquid crystal display device of the present invention is a reflection type liquid crystal display device of multi-color and full-color display in which layers of a spiral structure of both left and right rotations are laminated in order to selectively reflect either left or right polarized light. Can also be applied to. In addition to the above, the present invention can be applied to a reflective liquid crystal display device that utilizes selective reflection by all cholesteric structures such as broadband cholesteric having a different helical pitch in the surface normal direction of the substrate.

In the first to fourth embodiments, the scattering film and the scattering type liquid crystal cell are used as the scattering layer 20, but the present invention is not limited to this, and any scattering film having a light scattering function may be used as the scattering layer 20. be able to. Further, in the above embodiment, the scattering layer 20 is formed on the viewer side of the upper substrate 13, but the position where the scattering layer 20 is formed is not limited as long as it is on the viewer side of the liquid crystal layer 19. For example, the scattering layer 20 may be formed between the transparent electrode 11 of the upper substrate 13 and the parallel alignment layer 12.

Further, the scattering layer in the present invention includes a case where a part of the liquid crystal layer 19 has a light scattering function so that a part of the liquid crystal layer substantially functions as a scattering layer. For example, the alignment layer 12 may be subjected to vertical alignment treatment or not subjected to rubbing treatment.
A light scattering function can be imparted to the interface portion of the liquid crystal layer 19 which is in contact with.

In the first to fourth embodiments, the transparent electrodes 11 and 15 are used.
(Or display electrodes 85, 95) are glass substrates 10, 17
However, as long as the electric field is applied to the liquid crystal layer 19 to change the alignment state of the liquid crystal molecules, the transparent electrodes 11 and 15 are not provided.
Is not particularly limited. For example, a reflective liquid crystal display device is placed on an electrode plate, and an electric field is applied by touching the screen of the display device with a pen-type electrode to change the alignment state of liquid crystal molecules.

[0073]

According to the reflective liquid crystal display device of the first aspect of the present invention, the visibility is good not only in the regular reflection direction but also in a wide viewing angle region. Further, since the change in reflectance due to the change in the angle of observation is gradual, it is possible to suppress a metallic luster-like texture.

According to the reflection type liquid crystal display device of the second aspect of the present invention, the visibility is good in a wide viewing angle range, and the metallic luster-like texture can be suppressed, and
It is possible to suppress display deterioration such as blurring of a displayed image and double images.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing a reflective liquid crystal display device of Embodiment 1.

FIG. 2 is a diagram showing wavelength dependence of reflectance in the liquid crystal display panel of Embodiment 1.

FIG. 3 is a diagram showing the angular dependence of reflectance in a planar chiral nematic liquid crystal display panel.

FIG. 4 is a diagram showing the angular dependence of reflectance in the reflective liquid crystal display device of Embodiment 1.

FIG. 5 is a diagram showing a relationship between a viewing angle and a viewing distance.

FIG. 6 is a diagram showing a method for measuring scattering characteristics of a scattering film and a scattering type liquid crystal cell.

FIG. 7 is a diagram showing scattering characteristics of an anisotropic scattering film.

FIG. 8 is a diagram showing angle (polar angle) dependence of scattered light intensity of Lumisty used in the third embodiment.

FIG. 9 is a diagram showing a method of measuring scattered light intensity.

FIG. 10 is a diagram illustrating display when an anisotropic scattering film is used.

FIG. 11 is a diagram illustrating a display when a scattering film having no anisotropy is used.

FIG. 12 is a diagram showing angle dependence of reflected light intensity in the liquid crystal display device of the third embodiment.

13 is a structural formula of a material of the liquid crystal composition used in Embodiment 4. FIG.

FIG. 14 is a diagram showing wavelength dependence of reflected light in the liquid crystal display device of the fourth embodiment.

[Explanation of symbols]

10, 17 Glass substrates 11, 15 Transparent electrodes 12, 14 Parallel alignment films 13, 84, 94 Upper substrate 16 Light absorption layers 18, 86, 96 Lower substrate 19 Liquid crystal layer 20 Scattering layers 61, 81, 91, 151 Light source 62 , 83 Anisotropic scattering film 63, 154 Light sensor 64, 155 Light intensity measuring device 65 Incident light angle 66, 153 Emission light angle 82, 92, 101 Observer 85, 95 Display electrode (transparent electrode) 87, 97 Incident light 88, 98-a, 98-b Scattered light 89, 99 Specular reflected light 93, 152 Scattering film or scattering liquid crystal cell 102 Viewing angle 103 Viewing distance 104 Screen length

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kiyoshi Minoura             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company (72) Inventor Shun Ueki             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company F-term (reference) 2H042 BA02 BA14 BA20                 2H091 FA14Y FA16Z FA41Z GA01                       GA13 HA07 HA10 HA11 LA16

Claims (7)

[Claims] 1. A reflection type liquid crystal display device comprising a liquid crystal layer having a selective reflection characteristic and a scattering layer formed closer to the viewer than the liquid crystal layer, and performing display by utilizing light reflected by the liquid crystal layer. And the distribution of the scattered light intensity I (θ) of the scattering layer is I
The average value of (0 °) or more and I (10 °) or less is I (20 °)
A reflection type liquid crystal display device, which is 1000 times or less of an average value of I (30 °) or less. 2. The scattered light intensity I (θ) of the scattering layer
The reflection type according to claim 1, wherein an average value of I (0 °) or more and I (10 °) or less is 10 times or more of an average value of I (20 °) or more and I (30 °) or less. Liquid crystal display device. 3. A reflective liquid crystal display device comprising a liquid crystal layer having a selective reflection characteristic and a scattering layer formed closer to the viewer than the liquid crystal layer, and performing display by utilizing light reflected by the liquid crystal layer. The scattering layer has different light scattering characteristics depending on the azimuth angle of incident light incident from a direction inclined with respect to the layer normal of the scattering layer, and the incident light enters the scattering layer. In the first azimuth direction, the distribution of the scattered light intensity I (θ) of the scattering layer has an average value of I (0 °) or more and I (10 °) or less, I (2).
It is 1000 times or less of the average value of 0 ° or more and I (30 °) or less, and the scattered light intensity I (0) of the scattering layer at the first azimuth angle.
°) or more and I (10 °) or less and the ratio of the average value of I (20 °) or more and I (30 °) or less of the scattering layer in the second azimuth direction different from the first azimuth angle. Scattered light intensity I (0 °) or more and I (10 °) or less average value and I (20
A reflective liquid crystal display device having a ratio smaller than the average value of (°) or more and I (30 °) or less. 4. The distribution of scattered light intensity I (θ) of the scattering layer in the second azimuth direction has an average value of I (0 °) or more and I (10 °) or less, I (20 °). Above I (3
The reflective liquid crystal display device according to claim 3, wherein the reflection type liquid crystal display device is more than 1000 times an average value of 0 ° or less. 5. The distribution of the scattered light intensity I (θ) of the scattering layer in the first azimuth direction has an average value of I (0 °) or more and I (10 °) or less, I (20 °). Above I (3
The reflective liquid crystal display device according to claim 1, which is 600 times or less of an average value of 0 ° or less. 6. The distribution of scattered light intensity I (θ) of the scattering layer in the first azimuth direction has an average value of I (0 °) or more and I (10 °) or less, I (20 °). Above I (3
The reflective liquid crystal display device according to claim 1, which is 100 times or less of an average value of 0 ° or less. 7. The half width of the wavelength of the reflected light is 150 nm.
It is above, and the 50% selective reflection wavelength of the reflected light includes the range of 450 nm or more and 600 nm or less.
7. The reflective liquid crystal display device according to any one of items 1 to 6.