JP2003035901A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection type liquid crystal display device wherein contrast and luminance are enhanced. SOLUTION: In the reflection type liquid crystal display device 1, a transparent electrode 4, an insulating layer 5 and an alignment layer 6 are successively formed on a glass substrate 2, a light reflection layer 7, an insulating layer 8 and a diffraction grating 9 are successively layered and a color filter 10 and a black matrix 11 are further formed on a glass substrate 3 and both members are stuck to each other via a liquid crystal layer 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective or semi-transmissive liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have been used not only for small or medium-sized portable information terminals and notebook computers, but also for large and high-definition monitors. Furthermore, for the reflective liquid crystal display device that does not use a backlight,
Excellent in light weight and low power consumption. In addition, a semi-transmissive liquid crystal display device capable of selecting transmissive display or reflective display according to the surrounding environment is also used, and is used in various fields because it is excellent in low power consumption.

In the reflection type and semi-transmission type liquid crystal display devices as described above, when used as a reflection type, in order to obtain a bright display without using a backlight, incident light from all angles is obtained. It is necessary to emit light with a wide scattering angle.

Therefore, a technique has been proposed in which a liquid crystal display device is provided with a specular reflection plate and a scattering film is arranged on the front surface of the device (see Japanese Patent Laid-Open No. 8-201202).
Furthermore, the present applicant has proposed a technique in which a semi-transmissive film is provided on the inner surface of the liquid crystal display device and a scattering film is further provided on the front surface of the device (see Japanese Patent Application No. 10-244245).

[0005]

However, according to the liquid crystal technology proposed above, the provision of the scattering film enables the light to be emitted with a wide scattering angle.
The contrast was reduced due to backscattering of incident light.

Therefore, the present invention has been completed in view of the above circumstances, and an object thereof is to provide a liquid crystal display device having enhanced contrast and brightness.

[0007]

A liquid crystal display device according to the present invention comprises a member having a transparent electrode and an alignment layer sequentially laminated on a transparent substrate, a diffraction grating and a transparent electrode on a substrate having a light reflecting surface. And another layer in which an alignment layer and an alignment layer are sequentially laminated are bonded together via a nematic liquid crystal, and pixels are arranged in a matrix.

Another liquid crystal display device according to the present invention is one member formed by sequentially laminating a diffraction grating, a transparent electrode and an alignment layer on a transparent substrate, and a transparent electrode and the alignment layer on a substrate having a light reflecting surface. And the other member formed by sequentially stacking the two are laminated via a nematic liquid crystal to arrange pixels in a matrix.

In still another liquid crystal display device of the present invention, one member formed by sequentially laminating a transparent electrode and an alignment layer on a transparent substrate, and a diffraction grating and an alignment layer on a substrate having a light reflective electrode. It is characterized in that the other member, which is sequentially laminated, is bonded through a nematic liquid crystal to arrange pixels in a matrix.

Further, another liquid crystal display device of the present invention comprises one member formed by sequentially laminating a diffraction grating, a transparent electrode and an alignment layer on a transparent substrate, and an alignment layer on the substrate having a light reflective electrode. And the other member formed by sequentially stacking the two are laminated via a nematic liquid crystal to arrange pixels in a matrix.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION First, the present invention will be described with reference to a reflective liquid crystal display device. FIG. 1 is an enlarged cross-sectional view of an essential part of a reflective color liquid crystal display device of the present invention, and FIG. 2 is an enlarged sectional view of an essential part of another reflective color liquid crystal display device of the present invention. 3 and 4 are perspective views of the diffraction grating.

(Example 1) In the reflective liquid crystal display device 1,
2 is a glass substrate on the segment side which is the transparent substrate, 3
Is a glass substrate on the common side, and the one member is composed of a transparent electrode 4 made of ITO arranged in parallel on the glass substrate 2, an insulating layer 5 made of SiO2, and a polyimide resin rubbed in a certain direction. The alignment film 6 is formed sequentially.

As for the other member, a light reflecting layer 7 made of aluminum metal is formed on the glass substrate 3 by sputtering, and an insulating layer 8 made of SiO2 and a diffraction grating 9 are sequentially laminated on the light reflecting layer 7. Then, a color filter 10 arranged for each pixel is formed on the diffraction grating 9, and a black matrix 11 of chromium metal or a photosensitive resist arranged between the color filters 10 is formed. Resin or SiO 2 is provided between the diffraction grating 9 and the color filter 10.
You may provide the smooth layer which consists of. As the light reflection layer 7,
Other than aluminum metal, aluminum alloy, silver alloy, etc. may be used.

The diffraction grating 9 has a shape as shown in FIG. 3 or FIG. 4, and may be formed in a stripe shape as shown in FIG. 3, but if it is formed in a dot shape as shown in FIG. It is desirable in that light is scattered in all directions.

The diffraction grating 9 is formed by applying an ultraviolet curable resin on a substrate with a roll coater, a spinner or the like, pressing it with a mold having a concave portion, and irradiating it with ultraviolet rays to cure it.

In addition, an ultraviolet curable resin is coated on a substrate with a roll coater or a spinner, and is pressed with a mold having a recess and heated to cure and form, or exposed and developed with a pattern mask to form an uneven portion, It may be formed by heat curing.

By forming such a diffraction grating 9,
The direction of the light passing through the diffraction grating can be changed by utilizing the light diffraction phenomenon. That is, when light is incident on the diffraction grating, in addition to the light reflected as it is, light emitted at a certain angle is generated.

The color filter 10 is formed by a pigment dispersion method, that is, a photosensitive resist prepared in advance with a pigment is applied on a substrate and photolithography is performed. The R, G, and B displays in the figure are red,
The color filter 10 is colored green and blue.

An insulating layer 1 made of an acrylic resin is formed thereon.
2 and a transparent electrode 13 made of ITO arranged in parallel with each other
And form. The transparent electrode 13 is the transparent electrode 4 described above.
Is orthogonal to. Further, an alignment film 14 made of a polyimide resin rubbed in a certain direction is formed on the transparent electrode 13.

Then, one of these members (glass substrate 2)
And the other member (glass substrate 3), for example, 200 to 26
The seal member 16 is used for bonding via the liquid crystal layer 15 made of chiral nematic liquid crystal twisted at an angle of 0 °. Further, a large number of spacers 17 are arranged between the glass substrates 2 and 3 in order to keep the thickness of the liquid crystal layer 15 constant.

Further, on the outside of the glass substrate 2, a retardation plate 18 made of polycarbonate or the like and an iodine type polarizing plate 19 are provided.
And are sequentially stacked. When arranging these,
It is attached by applying an adhesive material made of an acrylic material. The retardation plate 18 and the polarizing plate 19 are arranged outside the glass substrate facing the glass substrate on which the light reflection layer is formed.

The insulating layers 5, 8, 12 and the black matrix 11 may not be provided.

Thus, in the liquid crystal display device 1 having the above-described structure, the irradiation light from external illumination such as sunlight or a fluorescent lamp sequentially passes through the polarizing plate 19, the phase difference plate 18 and the glass substrate 2, and the incident light is the liquid crystal. Through the layer 15 and further through the diffraction grating 9
Through the diffraction grating 9 and the liquid crystal layer 15, the backscattering of the incident light is reduced, and as a result, the brightness and the brightness are reduced. The contrast is improved. Moreover, in that the incident light does not pass through the glass substrate 3,
The parallax due to the thickness was reduced.

Further, the liquid crystal display device 1 has a structure in which the diffraction grating 9 is formed on the common side glass substrate 3, but instead of this, a diffraction grating is formed on the segment substrate 2, and then resin or SiO 2 is used. A liquid crystal display device may be used in which a smooth film made of is formed, and a transparent electrode and an alignment film are formed thereon. Further, in the liquid crystal display device 1, instead of the structure in which the light reflection layer 7 is formed on the common side glass substrate 3, the reflection layer 7 is formed on the segment side glass substrate 2, and a resin or Si is used.
It may be a liquid crystal display device having a structure in which an insulating layer made of O2 and a transparent electrode and an alignment film are formed thereon, or a liquid crystal display device in which the light reflection layer 7 and the diffraction grating 9 are formed on a segment side glass substrate. . (Example 2) Next, the liquid crystal display device 20 shown in FIG. 2 will be described. The same parts as those of the liquid crystal display device 1 of FIG. 1 are designated by the same reference numerals.

Reference numeral 22 is a glass substrate on the segment side, and 21 is a glass substrate on the common side, and the color filters 10 arranged for each pixel on one main surface of the glass substrate 21 and the black arranged between the color filters 10. And the matrix 11. Further, an insulating layer 12 made of acrylic resin and a plurality of transparent electrodes 1 made of ITO arranged in parallel with each other.
3 and 3 are formed. An alignment film 14 made of a polyimide resin rubbed in a certain direction is formed on the transparent electrode 13 to form one member.

Regarding the other member, a plurality of light-reflective electrodes 24 made of chromium metal or aluminum metal arranged in parallel on the glass substrate 22, an insulating layer 25 made of resin or SiO 2, and the diffraction grating 9 in a certain direction. An alignment film 26 made of a rubbed polyimide resin is sequentially formed.
A smooth film made of resin or SiO 2 may be provided between the diffraction grating 9 and the alignment film 26.

Similar to the liquid crystal display device 1, a liquid crystal layer 1 made of a chiral nematic liquid crystal containing a large number of spacers 17.
The seal member 16 is used to attach the two. Further, on the outside of the glass substrate 21, a retardation plate 27 made of polycarbonate or the like and an iodine polarizing plate 28 are sequentially stacked. Similarly, the insulating layers 12 and 25 and the black matrix 11 may not be provided.

In the liquid crystal display device 20 having the above structure,
Illumination light from external lighting such as sunlight or fluorescent light is polarized by the polarizing plate 2.
8, the phase difference plate 27, and the glass substrate 21 are sequentially passed, and the incident light is reflected by the electrode 24 through the light scattering resin layer 9 and the liquid crystal layer 15, and the reflected light is transmitted through the liquid crystal layer 15 by the diffraction grating 9. The light is scattered and emitted.

Even in such a structure, the backscattering is reduced by the diffraction grating 9, whereby the brightness and the contrast are improved.

Further, the liquid crystal display device 20 has a structure in which the diffraction grating 9 is formed on the segment side glass substrate 22, but instead of this, a diffraction grating is formed on the common substrate 21, and resin or SiO 2 is used. Forming a smooth film consisting of
A liquid crystal display device having a structure in which a color filter, a transparent electrode, and an alignment film are formed thereon may be used.

(Example 3) Although the liquid crystal display device of the present invention is described as a reflection type as described above, it may be a semi-transmission type liquid crystal display device.

In the case of a semi-transmissive liquid crystal display device, the light reflection layer 7 provided in the liquid crystal display device 1 is replaced with a semi-transmissive film having both light transmissive and light reflective properties, and the liquid crystal display device 20 is obtained. Similarly, the light-reflective electrode 24 provided in the above is replaced with a semi-transmissive film.

For one of the transmissive display modes, a retardation film made of polycarbonate or the like and an iodine type polarizing plate are sequentially formed on the outside of the glass substrate 3 or the glass substrate 22, and a backlight is further provided. Good. Note that the backlight may be arranged outside the glass substrate 2 or the glass substrate 21 depending on the arrangement position of the semi-transmissive film.

The semi-transmissive film does not cause a phase difference when sandwiched between two polarizing plates. Then, a thin film made of a metal such as chromium, aluminum, silver, an aluminum alloy, or a silver alloy is used, but as the film thickness increases, the light transmittance decreases and the light reflectivity increases. The thickness of such a metal thin film has a different light absorption coefficient depending on the type of metal, and is also defined by which of the reflective and transmissive applications is required to have improved performance. However, it is usually 50 to 500Å, preferably 10
It should be 0 to 400 Å. This gives a reflectance of 30
The characteristics of a semi-transmissive liquid crystal display device of ˜75% and transmittance of 5 to 50% can be obtained.

For example, when the semi-transmissive film is formed of an aluminum metal thin film with a film thickness of 250 Å, the reflectance is 65% and the transmittance is 15%.

The semi-transmissive film may be formed of a dielectric half mirror instead of the metal thin film. That is, a laminated structure in which low refractive index layers and high refractive index layers are alternately laminated in sequence may be used, whereby a part of the light incident through the liquid crystal 11 is reflected by the high refractive index layer and the other high refractive index layers. The light transmitted through the refractive index layer is reflected by the low refractive index layer, and these reflected lights are interfered with each other, the reflection performance is remarkably enhanced, and so-called increased reflection occurs.

If there is a difference in refractive index between the high refractive index layer and the low refractive index layer as described above, any material may be used. The range is preferably 2.0 to 2.8, TiO2, ZrO2, SnO.
It is good to configure with 2, etc. On the other hand, the range of the refractive index of the low refractive index layer is preferably 1.3 to 1.6.
, AlF3, CaF2, MgF2 or the like. By setting the thickness range of the high refractive index layer to 25 to 2000Å and the thickness range of the low refractive index layer to 25 to 2000Å, the above-mentioned increased reflection becomes most remarkable. Further, by increasing the thickness range of the semi-transmissive film to 50 to 12000Å, this increased reflection becomes remarkable.

Further, the semi-transmissive film has a laminated structure in which low-refractive index layers and high-refractive index layers are alternately laminated so that the total number of layers is 2, 4, 6, 8, and 10. Alternatively, the number of layers is more than that. The total number of layers may be an odd number.

Furthermore, in the case of such a laminated structure, the reflectance and the transmittance can be set as required by changing the number of laminated layers, which facilitates the design.

For example, a low refractive index layer made of SiO 2 (film thickness: 940 Å) and a high refractive index layer made of TiO 2 (film thickness: 630 Å) are alternately laminated in sequence, and the total number is 8 layers. In this case, the reflectance is 75% and the transmittance is 25%.

Preferred Design Example In the reflective liquid crystal display device of the liquid crystal display device 1 and the liquid crystal display device 20, the polarizing plate 19 and the polarizing plate 28 (hereinafter referred to as polarizing plate), the retardation plate 18 and the retardation plate 27 are optimal. Describe the sticking direction. However, the phase difference plate 18 and the phase difference plate 2
7 is a laminated structure of two retardation films,
It is called a first retardation film and a second retardation film.

FIG. 5 shows the sticking angle with respect to the reference direction with the average value of the double-sided rubbing direction in the liquid crystal display device 1 or the liquid crystal display device 20 as a reference, and when viewed from the display surface, it is counterclockwise (counterclockwise) from the reference direction. Angle)

The twist angle of the liquid crystal layer 15 is 250 ± 10 °.
And when the optical path difference Δnd is 850 ± 50 nm,
Regarding the polarizing plate, its absorption axis is 137 with respect to the reference direction.
It is good to set it to ± 5 °.

Further, the optical path difference Δnd of the first retardation film
Is 425 ± 50 nm, the stretching axis is 25 ± 5 ° with respect to the reference direction, the optical path difference Δnd of the second retardation film is 425 ± 50 nm, and the stretching axis is 55 ± 5 ° with respect to the reference direction. Good to do. With such a design, the brightness and contrast could be maximized.

[0045]

EXAMPLE A liquid crystal display device 1 and a liquid crystal display device 20 of the present invention.
The respective contrasts of the reflective liquid crystal display device of No. 1 were measured. As shown in FIG. 3, the diffraction grating 9 used for both is made of acrylic resin and has a pitch of 4.5 μm and a width of 2.
It is a diffraction grating in which a concavo-convex pattern having a size of 5 μm and a height of 0.5 μm is formed in a stripe shape.

Further, according to the liquid crystal display device of the comparative example, in the liquid crystal display device 1 shown in FIG. 1, the diffraction grating 9 is not formed, and instead of the diffraction grating 9, the glass substrate 2 and the phase difference plate 18 are provided. A film having a scattering function is interposed between and.

For the measurement of contrast, Minolta CS-
The measurement was performed by irradiating the liquid crystal panel with the same light source at a constant angle using 100. The contrast was expressed as a relative value with Comparative Example set to 1.00. Liquid crystal display device 1 (example 1). ． ． ． Contrast: 1.
15. Liquid crystal display device 20 (example 2). ． ． Contrast: 1.
25 As is apparent from these results, the liquid crystal display device of the present invention has improved brightness and thus improved contrast. In particular, the liquid crystal display device 20 of (Example 2) is superior to the liquid crystal display device 1 of (Example 1) by using the electrodes as reflecting surfaces.

The present invention is not limited to the above embodiment, and various modifications and improvements can be made without departing from the scope of the present invention.

For example, in the above embodiment, S
Although the description has been made using the TN type simple matrix type color liquid crystal display device, in addition to this, a monochrome STN type simple matrix type liquid crystal display device, or a TN type simple matrix type liquid crystal display device or a TN type active liquid crystal display device can be used. Similar effects can be obtained even in a twisted nematic liquid crystal display device such as a matrix type.

[0050]

As described above, according to the reflective or transflective color liquid crystal display device of the present invention, the backscattering of incident light is reduced by providing the diffraction grating instead of using the scattering film. As a result, a high-performance color liquid crystal display device with improved brightness and contrast can be provided.

Further, according to the present invention, by forming one of the electrodes as the light reflecting surface, it is possible to further increase the contrast and the brightness as compared with the combined structure of the transparent electrode and the light reflecting layer.

[Brief description of drawings]

FIG. 1 is an enlarged sectional view of an essential part of a reflective color liquid crystal display device of the present invention.

FIG. 2 is an enlarged sectional view of an essential part of another reflective color liquid crystal display device of the present invention.

FIG. 3 is a perspective view of a diffraction grating.

FIG. 4 is a perspective view of another diffraction grating.

FIG. 5 is an explanatory diagram showing an arrangement configuration of a retardation film and a polarizing plate.

[Explanation of symbols]

1, 20 ... Reflective liquid crystal display device 2, 3, 21, 22 ... Glass substrate 4, 13 ... Transparent electrodes 5, 8, 12, 25 ... Insulating layer 6, 14, 26 ... Alignment film 7 ... Light reflection layer 9 ... Diffraction grating 10 ... Color filter 11 ... Black Matrix 15 ... Liquid crystal layer 16 ... Seal member 18, 27 ... Retardation plate 19, 28 ... Polarizing plate 24 ... Electrode

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H042 BA04 BA15 BA20                 2H049 AA03 AA13 AA37 AA40 AA43                       AA48 AA55 AA61                 2H091 FA14Y FA19Y FA35Y FB08                       FD06 GA03 GA06 LA17

Claims (4)

[Claims] 1. A member comprising a transparent substrate and an alignment layer sequentially laminated on a transparent substrate, and a member comprising a diffraction grating, a transparent electrode and an alignment layer sequentially laminated on a substrate having a light reflecting surface. And a liquid crystal display device in which pixels are arranged in a matrix by laminating and a nematic liquid crystal. 2. A one-piece member in which a diffraction grating, a transparent electrode and an alignment layer are sequentially laminated on a transparent substrate, and another member in which a transparent electrode and an alignment layer are sequentially laminated on a substrate having a light reflecting surface. And a liquid crystal display device in which pixels are arranged in a matrix by laminating and a nematic liquid crystal. 3. One member formed by sequentially stacking a transparent electrode and an alignment layer on a transparent substrate, and the other member formed by sequentially stacking a diffraction grating and an alignment layer on a substrate having a light reflective electrode. A liquid crystal display device in which pixels are arranged in a matrix by laminating them through a nematic liquid crystal. 4. A one member formed by sequentially laminating a diffraction grating, a transparent electrode and an alignment layer on a transparent substrate, and another member formed by sequentially laminating an alignment layer on a substrate having a light reflective electrode. A liquid crystal display device in which pixels are arranged in a matrix by laminating them through a nematic liquid crystal.