JP3537712B2 - Reflective liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent decrease in contrast due to backward scattering. SOLUTION: In a reflection type liquid crystal display device 17, a protruding array group is formed on a glass substrate 2, and a light-reflecting film 18, color filter 5, transparent electrode 7 and alignment film 8 are formed on the protruding array group. A transparent electrode 10 and alignment layer 11 are formed on a glass substrate 9, and both glass substrates 2, 9 are disposed facing each other through a liquid crystal 12. Further, a first phase difference film 14, second phase difference film 15 and polarizing plate 16 are successively formed on the outside of the glass substrate 9. The light-reflecting film 18 is produced by successively laminating a metal film, low refractive index layer and high refractive index layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, a technology of a reflection type liquid crystal display device which does not use a backlight has been developed and is excellent in thinness, light weight and low power consumption.

[0003] As a reflection type liquid crystal display device, there has been proposed a function separation type in which a light reflection layer having a mirror surface is provided on a surface of a substrate provided behind and a scattering plate is provided outside a substrate provided in front. (See JP-A-8-201802).

According to this function-separated type, ambient light is effectively used by not using a backlight. On the other hand, however, it is difficult to increase the viewing angle, and backscattering of incident light by a scattering plate is difficult. Had occurred.

In order to solve this problem, there has been proposed a scattering reflection type in which a light reflection layer having an uneven shape is formed on a substrate disposed behind (see Japanese Patent Application Laid-Open No. Hei 4-243226).

FIG. 13 shows a TN mode or STN mode scattering / reflection type liquid crystal display device. In the liquid crystal display device 1,
A plurality of substantially hemispherical convex portions 3 made of resin are randomly arranged on a glass substrate 2 by a photolithography process to form a convex array group, and light formed of a metal film such as Al by sputtering on the convex array group. A color filter 5 covering the reflection layer 4 and disposed on the light reflection layer 4 for each pixel is formed. Further, an overcoat layer 6 made of an acrylic resin and a plurality of transparent electrodes 7 made of ITO arranged in parallel are formed. On the transparent electrode 7, an alignment film 8 made of a polyimide resin rubbed in a certain direction is formed.

A large number of ITs arranged in parallel on a glass substrate 9
A transparent electrode 10 made of O and an alignment film 11 made of a polyimide resin rubbed in a certain direction are sequentially formed.

[0008] Then, the glass substrate 2 and the glass substrate 9 are bonded to each other by the seal member 13 via the liquid crystal 12.
Further, a first retardation film 14 and a second retardation film 15 made of polycarbonate or the like are provided outside the glass substrate 9.
And an iodine-based polarizing plate 16 are sequentially formed.

In the liquid crystal display device 1 having the above-described structure, incident light from external illumination such as sunlight, a fluorescent lamp, etc.
6, second retardation film 15, first retardation film 14
Then, the light passes through the liquid crystal 12, the color filter 5, and the like, reaches the light reflecting film 4, is reflected by the light reflecting film 4, and the reflected light is emitted.

[0010] Thus, in the liquid crystal display device 1, the problem of back scattering as in the prior art is eliminated by not using a light scattering plate. As a result, the luminance at the time of OFF is reduced,
Contrast improved.

[0011]

However, in the above-mentioned reflection-type liquid crystal display device of the scattering reflection type, when the light reflection layer 4 is coated on the convex array group, such a concave-convex surface causes the light to be particularly positive. The reflection intensity in the reflection direction tends to decrease.

Accordingly, an object of the present invention is to provide a reflection type liquid crystal display device in which the reflection intensity in the regular reflection direction is increased.

[0013]

Means for Solving the Problems A reflective liquid crystal display device according to the present invention forms a convex array group in which a large number of resin convex portions are randomly arranged on one main surface of a glass substrate, and the convex array group is formed. One member formed by sequentially laminating a transparent electrode and an alignment layer on the light reflection film, and the other member formed by sequentially laminating a transparent electrode and an alignment layer on a glass substrate. A reflective liquid crystal display device in which pixels are arranged in a matrix with a nematic liquid crystal interposed therebetween, wherein the resin convex portions constituting the convex array group are connected to the adjacent convex portions. The light-reflecting film formed on the glass substrate of one member so as to be adhered on the convex array group includes a metal film, and a low-refractive-index layer and a high-refractive-index layer on the metal film. No by alternately stacking the door, formed by further coating the outermost layer in the SiO ₂ layer And wherein the door.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to FIGS. FIG. 1 is a schematic cross-sectional view of a reflection type liquid crystal display device, FIG. 2 is a process diagram of forming a convex array group, FIG. 3 is a plan view of a photomask for forming the convex array group, and FIG. FIG.

FIG. 5 shows the relationship between the development time and the height difference of the convex and concave groups, and FIG. 6 shows the change in the shape of the photosensitive resin layer due to the difference in the development time. 7 is an enlarged view of the convex array group, FIG. 8 is a photograph of the convex array group, and FIG. 9 is an enlarged view of another convex array group.

FIG. 10 is a schematic sectional view of a light reflecting film according to the present invention. FIG. 11 is a schematic sectional view of a conventional light reflecting film.
Indicates a change in the reflection intensity with respect to the light receiving angle. FIG.
3 are assigned the same reference numerals as those of the conventional liquid crystal display device 1 shown in FIG.

[0017] illustrating the reflection type liquid crystal display device 17 for color display by reflection type liquid crystal display device Figure 1.

2 is a common side glass substrate (0.7 mm
3) Glass substrate on segment side (0.7mm thick)
As for the one member, the substantially hemispherical convex portion 3 (diameter:
5 to 15 μm), a random convex group is formed (however, the convex portion 3 is not limited to a transparent resin, and may be a colored resin), and light is reflected on the convex group. The membrane 18 is covered. The light reflection film 18 is formed by sequentially laminating a metal film, a low refractive index layer, and a high refractive index layer.

The color filters 5 arranged for each pixel are formed on the convex array group. The color filter 5 is a pigment dispersion method, that is, a pigment (red, green, blue)
Is coated on a substrate and formed by photolithography. Further, an overcoat layer 6 made of an acrylic resin and a plurality of transparent electrodes 7 made of ITO arranged in parallel are formed. On the transparent electrode 7, an alignment film 8 made of a polyimide resin rubbed in a certain direction is formed.

Although the alignment film 8 is formed directly on the transparent electrode 7, an insulating film made of resin or SiO ₂ may be interposed between the alignment film 8 and the transparent electrode 7. Moreover, the overcoat layer 6 need not be provided. Furthermore, a smooth film made of resin or SiO ₂ is formed on the convex array group,
Color filters 5 arranged for each pixel may be formed on the smooth film.

As for the other member, a transparent electrode 10 made of ITO arranged in parallel on a glass substrate 9 and an alignment film 11 made of polyimide resin rubbed in a certain direction.
Are sequentially formed. An insulating layer made of resin or SiO ₂ may be interposed between the transparent electrode 10 and the alignment film 11.

Then, the one member and the other member having the above structure are bonded together by a seal member 13 via a liquid crystal 12 made of a chiral nematic liquid crystal twisted at an angle of, for example, 200 to 260 °. A large number of spacers are arranged between the two members to keep the thickness of the liquid crystal 11 constant.

Further, on the outside of the glass substrate 9, a first retardation film 14, a second retardation film 15, and an iodine polarizing plate 16 made of polycarbonate or the like are sequentially formed. About these arrangement | positioning, it sticks by applying the adhesive material which consists of an acrylic material.

In the liquid crystal display device 17 having the above configuration,
Incident light from external lighting such as sunlight or fluorescent light is polarized
6, second retardation film 15, first retardation film 14
And the glass substrate 9, and reaches the light reflecting film 18 through the liquid crystal 12, the color filter 5, and the like.
And the reflected light is emitted.

Thus, in the liquid crystal display device 17 of the present invention, the problem of back scattering as in the prior art is eliminated by not using a light scattering plate. As a result, the luminance at the time of OFF is reduced and the contrast is improved. . In addition, since the light reflecting film 18 is formed by sequentially laminating a metal film, a low refractive index layer, and a high refractive index layer, the reflection enhancement effect increases the reflection intensity, and particularly the reflection intensity in the regular reflection direction is remarkable. Could be enhanced.

In the liquid crystal display device 17, a large number of convex portions 3 are arranged on the glass substrate 2 to form a random convex arrangement group, and the light reflection film 18 is coated on the convex arrangement group. Instead of this, a convex array group in which a large number of convex portions are arranged on the glass substrate 9 is formed, the light reflecting film 18 is coated on the convex array group, and a resin, SiO _2, or the like is formed. A transparent film 10 made of ITO arranged in parallel in a large number, and an alignment film 11 made of a polyimide resin rubbed in a certain direction are sequentially formed thereon.
Then, the first retardation film 14 is provided on the outer surface of the glass substrate 2.
And the second retardation film 15 and the polarizing plate 16 may be provided to form a reflective liquid crystal display device in which light is incident from the glass substrate 2 side.

[Method of forming convex array group] The convex array group on the glass substrate 2 is formed through the steps (a) to (g) as shown in FIG.

Step (a) A photosensitive resin (product: PC405G, manufactured by JSR Corporation) using an acrylic resin as a main component and diethylene glycol methyl ethyl ether as a solvent is spin-coated. The thickness of this resin can be controlled by the spinner rotation speed. In this example, the spinner rotation speed was set to 750 rpm, and a positive photosensitive resin having a thickness of about 3 μm was applied.

(B) Step The substrate coated as described above was pre-baked on a hot plate at a temperature of, for example, 90 ° C. for 2 minutes.

(C) Step Next, exposure is performed using a photolithographic mask. This exposure is performed by using UV in the normal direction of the substrate.

FIG. 3 or FIG.
Shown in The photomask 19 is formed by arranging a large number of circular spots 21 (for example, 15 μm in diameter) made of Cr metal, iron oxide, or the like on a glass substrate 20 in a random state, and has a 5.7-inch image display surface. Approximately 50 million spots are arranged on the glass substrate 20 corresponding to one display surface.

The spot is not limited to a circle, but may be, for example, a square, a pentagon, or a photomask 22 as shown in FIG.
It may be a hexagonal or even a polygonal spot 23 or more, but it is better to make it circular so that there is no difference in the scattering characteristics depending on the viewing direction. Then, a convex portion 3 having substantially the same shape as the spot shape is formed.

(D) Step After the step (c), development is performed. As the developer, for example, PD523AD (concentration: 0.05%) manufactured by JSR Corporation is used. By changing the development time, the progress of the development can be controlled. However, by appropriately stopping the development, both ends are connected between the adjacent convex portions and are continuously connected.

FIGS. 5 and 6 show the states of the convex portions depending on the degree of development. In FIG. 5, the height difference between the concavities and convexities according to the development time is shown, the horizontal axis is the development time (seconds), the vertical axis is the difference in height between the concavities and convexities (μm), and the black points are the measurement data.

As the time increases up to the development time of about 25 seconds, the unevenness height difference increases. However, if the development time exceeds about 25 seconds, the glass substrate 2 is exposed and the depth of development becomes constant. , The fluctuation of the height difference is very small.

FIG. 6 shows the cross-sectional shapes of the convex array groups on the respective glass substrates 2 for (a), (b) and (c) among the black points which are the measurement data.

For example, the development time may be set to 20 seconds, and this development time may be appropriately changed depending on the resist coating amount, the developer concentration, the pre-bake conditions, and the like.

In the exposure in the step (c), UV
Is passed through the photomasks 19 and 22, causing interference, and the resin immediately below these masks also undergoes a slight photodecomposition reaction. Becomes round.

Step (e) By this heat treatment, for example, a low temperature (130 ° C., 2
In (1), heat melting is performed to such an extent that the surface shape does not significantly change.

Step (f) The next post bake is performed, for example, at a high temperature (200
(C, 30 minutes). Thus (e)
The surface shape is smoothed by slightly dissolving in the step, fine adjustment is performed on the uneven shape, and then curing is performed in the step (f).

(G) Step Finally, the light reflecting film 18 is coated on the convex array group by sputtering or vapor deposition. The light reflecting film 18 is formed by sequentially laminating a metal film, a low refractive index layer, and a high refractive index layer, and these layers are planarly sputtered.

With respect to the convex array group coated with the light reflecting film 18 obtained through each of the above steps (a) to (g), the surface properties were scanned or photographed.
However, instead of covering the entire light reflection film 18 for measurement, an aluminum metal film (thickness: 1000 °) was covered.

FIG. 7 shows a result obtained by scanning the shape using a surface shape measuring microscope manufactured by KEYENCE. The horizontal axis (X) indicates the scanning direction, the vertical axis (Z) indicates the height, and each unit. Is μm. FIG. 8 is a photograph taken at a magnification of 500 times using an optical microscope (BH3MJL manufactured by Olympus).

As is apparent from these figures, the convex portions have a smooth shape due to the heat melting, and the adjacent convex portions are further connected.

In the reflection type liquid crystal display device 17, it is preferable to connect the adjacent convex portions 3 of the convex array group, so that there is no flat portion between the convex portions 3 The flatness of the array was reduced, the light scattering property was improved, and as a result, the viewing angle was widened. In addition, as far as confirmed by the photograph, each adjacent convex portion 3 in the convex array group
Are connected almost entirely, but even if there is a part that is slightly disconnected, there is no effect on light scattering.

In forming the convex array group,
Except for the heat treatment in the step (e) (a heat melting step in which the surface shape does not significantly change), each of the other steps (a) to
(D), (f), and (g).

As shown in FIG. 9, a convex array group covered with an aluminum metal film (thickness: 1000 °) was provided by the forming method excluding the step (e), and the surface properties were scanned. Such a result was obtained. When not melted, the convex shape has a slightly flat portion on the upper surface, but the flatness of the convex array group is reduced similarly to the above, the light scattering property is similarly improved, and the viewing angle is widened. Was.

[About the Light Reflecting Film 18] Next, the structure of the light reflecting film 18 will be described in detail. The light reflection film 18 is formed by sequentially laminating a metal film made of aluminum metal or the like, a low refractive index layer made of SiO ₂ or the like, and a high refractive index layer made of TiO ₂ or the like, as shown in FIG. On (Al), a low refractive index layer (SiO ₂ ), a high refractive index layer (TiO ₂ ), a low refractive index layer (SiO ₂ ), and a high refractive index layer (TiO ₂ ) are alternately laminated in this order. Is good. Numerical values in parentheses of each layer in FIG.

With the light reflecting film 18 having such a laminated structure, a part of the incident light is reflected by the high refractive index layer, and the light passing through the layer is reflected by the low refractive index layer. While repeating such reflection and transmission, finally the metal film (Al)
Is reflected at These reflected lights interfere with each other, whereby the reflection performance is remarkably enhanced, and a so-called enhanced reflection effect is produced.

The above-described high refractive index layer and low refractive index layer may be made of any material as long as there is a refractive index difference between them. range 2.0 to 2.8 selfishness, TiO _2, ZrO _2, SnO
_It is good to consist of ₂ etc. The range of the refractive index of the low refractive index layer is preferably 1.3 to 1.6.
_{O 2, AlF 3, CaF 2} , may be configured MgF ₂ or the like.

The thickness range of the high refractive index layer is from 25 to 2000.
{When the thickness range of the low refractive index layer is 25 to 2000}, the above-described enhanced reflection is most remarkable. Further, the thickness range of the light reflecting film 18 (excluding the metal film) is set to 50 to
By setting the angle to 12000 °, the enhanced reflection becomes remarkable.

The light reflecting film 18 has a laminated structure in which low refractive index layers and high refractive index layers are alternately laminated in order, so that the total number of each layer is 2, 4, 6, 8, 10 It is composed of layers or more layers.

Then, it is preferable to coat the outermost layer with a layer of SiO ₂ or the like with a thickness of 300 ° as shown in FIG.
With the O ₂ layer, the adhesiveness with the layer coated thereon can be enhanced.

Thus, by coating the light reflecting film 18 on the convex array group, the conventional light scattering plate is not used, so that back scattering does not occur.
The brightness at the time of F was reduced, and the contrast was improved. In addition, the reflection intensity was increased by the light reflection film 18, and the reflection intensity in the regular reflection direction could be significantly increased.

[0055]

FIG. 12 shows the reflection intensity characteristics of the enhanced reflection film structure shown in FIG. 10 and the conventional structure. In each case, a sample for measuring the reflection intensity was prepared.
As shown in FIG. 1, an Al film was coated at a thickness of 1000 °, and an SiO ₂ film was coated thereon at a thickness of 300 °.

In FIG. 12, the horizontal axis indicates the light receiving angle from the regular reflection direction, and the vertical axis indicates the reflection intensity.

As is apparent from the figure, the reflection intensity in the regular reflection direction was approximately doubled.

Further, the liquid crystal display device 17 having the enhanced reflection film structure shown in FIG. 10 and the liquid crystal display device having the conventional structure shown in FIG. 13 were used as comparative examples (conventional examples) to evaluate the reflectance and contrast, respectively. However, the results shown in Table 1 were obtained.

[0059]

[Table 1]

The reflectance is -25 in the direction of light incidence on the device.
° (the normal direction is set to 0 °), and the luminance (reflectance) is measured by receiving the reflected light. The light receiving direction is defined as the normal direction.

The luminance (reflectance) was quantified using a standard white plate standard. That is, in the JIS standard, MgO
And the relative value to the reflected light of a standard white plate (MgO) assuming that the reflectance is 100%. And
The contrast was measured by measuring the reflectance of the liquid crystal panel when displaying white and the reflectance when displaying black.

As is clear from the table, it was possible to increase the reflectance by about 1.5 times.

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

For example, in the above embodiment, S
The description is made with reference to a TN type simple matrix type color liquid crystal display device. However, a monochrome STN type simple matrix type liquid crystal display device, a TN type simple matrix type liquid crystal display device, or a TN type simple matrix type liquid crystal display device may be used.
A similar effect can be obtained with a twisted nematic liquid crystal display device such as an N-type active matrix type liquid crystal display device and a bistable liquid crystal display device.

[0065]

As described above, in the reflection type liquid crystal display device of the present invention, a convex array group in which a large number of resin convex portions are randomly arranged is formed on a substrate, and a metal array is formed on the convex array group. The light-scattering plate can be removed by coating the light-reflecting film, which is formed by sequentially laminating a film, a low-refractive-index layer, and a high-refractive-index layer.
As a result, a high-performance reflective liquid crystal display device with reduced contrast at the time of FF and improved contrast was provided.

Further, according to the present invention, it was possible to provide a reflection type liquid crystal display device in which the reflection intensity was increased by the above-described reflection increasing effect of the light reflection film, and particularly the reflection intensity in the regular reflection direction was increased.

[Brief description of the drawings]

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

FIG. 2 is a process diagram of forming a convex array group according to the reflective liquid crystal display device of the present invention.

FIG. 3 is a plan view of a photomask for forming a convex array group.

FIG. 4 is a plan view of another photomask for forming a convex array group.

FIG. 5 is a diagram showing a relationship between a developing time when forming a convex array group and a difference in height of unevenness of the convex array group.

FIG. 6 is a diagram illustrating a change in shape of a photosensitive resin layer due to a difference in development time when a convex array group is formed.

FIG. 7 is an enlarged view of a convex array group.

FIG. 8 is a photograph of a convex array group.

FIG. 9 is an enlarged view of another convex array group.

FIG. 10 is a schematic sectional view of a light reflection film according to the present invention.

FIG. 11 is a schematic sectional view of a conventional light reflecting film.

FIG. 12 is a diagram showing a change in reflection intensity with respect to a light receiving angle.

FIG. 13 is a schematic sectional view of a conventional reflective liquid crystal display device.

[Explanation of symbols]

1,17 liquid crystal display 2,9 glass substrate 3 convex part 4,18 Light reflection layer 5 Color filters 6 Overcoat layer 7, 10 transparent electrode 8,11 alignment film 12 LCD 13 Seal member

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/1333-1/1343

Claims (1)

(57) [Claims] 1. A convex arrangement group in which a large number of resin projections are randomly arranged on one main surface of a glass substrate, and a light reflection film is coated on the convex arrangement group. A nematic liquid crystal is interposed between one member formed by sequentially laminating a transparent electrode and an alignment layer on the other, and the other member formed by sequentially laminating a transparent electrode and an alignment layer on a glass substrate in a matrix. A reflective liquid crystal display device in which pixels are arranged, wherein the resin convex portions forming the convex array group include the adjacent convex portions.
On the glass substrate of one member so that
While being formed, the light reflection film deposited on the convex array group , a metal film, a low refractive index layer and a high refractive index layer are alternately laminated on the metal film, and further, The outermost layer is Si
Reflection type liquid crystal display device characterized by comprising coated by O ₂ layer. A liquid crystal display device characterized by setting: