JP2000025159A - Laminated sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated sheet having light forescattering function taking in peripheral brightness to improve the brightness of liquid crystal display. SOLUTION: A light scattering layer 2a formed from a compsn. prepared by compounding filamentary particles 7b with a transparent resin base 7a mainly comprising a cellulose acetate resin so as to disperse them so that the number of the filamentary particles 7b become 1013-1016 per 1 m3 of the transparent resin base is laminated on at least one surface of a transparent base material sheet 2b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a laminated sheet having a forward light scattering function used for a reflection type liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal display device is a personal computer,
It has been used for display in word processors, LCD televisions, clocks, calculators and the like. In recent years, the development of information communication infrastructure such as the Internet and the networking of information by fusing computer and communication devices have been advanced, and access to information is no longer restricted by time and place due to this networking. Indispensable for using the network is the PDA (Person
It is a mobile information terminal typified by nal digital assistance, etc., and a thin and lightweight mobile personal computer more than a current notebook personal computer. Considering portability, these devices need to be driven for a long time by a battery and to be thin and compact. Therefore, the liquid crystal display devices required for these devices are thin, lightweight, and low power consumption. In order to meet these demands, a reflection type liquid crystal display device is regarded as the most promising.

Further, in order to cope with the diversification of information accompanying the advance of multimedia in the future, colorization and high definition are important, but in order to realize this, a single polarizing plate is required. The reflection type liquid crystal display device used is advantageous in that sufficient contrast can be realized. The reflection type liquid crystal display device using a single polarizing plate has high resolution, high speed response, low power consumption,
It has characteristics such as halftone display characteristics and easy production, but has a drawback in terms of brightness due to light loss in the polarizing plate.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a laminated sheet having a light forward scattering function which also takes in ambient brightness and improves the brightness of a liquid crystal display.

[0005]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventor, in the course of a series of researches, has a light scattering layer formed by dispersing filament-based particles in a transparent resin base. In the scattering sheet, by controlling the refractive index between the transparent resin base and the filament particles, and the number, material, shape, and size of the filament particles, it is possible to improve the use efficiency of ambient light. , Transparent resin base and number of filament particles, material
The inventors have further studied based on the idea that if the scattering characteristics depending on the light incident angle can be controlled by the combination of the shape and the size, the utilization efficiency of the ambient light can be improved, and the present invention has been reached.

That is, according to the present invention, filament-based particles are formed on at least one surface of a transparent base material sheet on a transparent resin base mainly composed of cellulose acetate resin.
It is a laminated sheet formed by laminating a light scattering layer mixed and dispersed such that the number of the filament-based particles is 10 ¹³ to 10 ¹⁶ with respect to 1 m ^{3 of the} transparent resin base.

In the present invention, the thickness of the "sheet" is not particularly limited, and even if "sheet" is replaced with "film" within the range of commonly used terms, Are the same, the term "sheet" in the specification of the present invention also encompasses "film".

[0008]

Next, the present invention will be described in detail. The material forming the transparent substrate sheet used in the present invention is not particularly limited, but the same material as the cellulose acetate resin used for the light scattering layer described below is suitable for laminating the transparent substrate sheet and the light scattering layer. Preferred from the point of view,
Preferably, it is triacetyl cellulose.

The method for forming the transparent substrate sheet is not particularly limited, and a commonly used forming method can be used. When formed on the transparent substrate sheet from the same cellulose acetate as the transparent resin base of the light scattering layer,
Preferably, it is formed by a solvent casting method or a melt casting method. In the solvent casting method, a solution (dope) in which cellulose acetate is dissolved in a solvent is cast on a support, the solvent is dried and removed, and then the sheet is formed by peeling off the support. In the melt casting method, a material obtained by melting cellulose acetate by heating is cast on a support, solidified by cooling, and then separated from the support to form a sheet. The solvent cast method is preferable because a film having higher flatness can be produced than the melt cast method.

Although the thickness of the transparent substrate sheet is not particularly limited, a polarizing layer is provided on the laminated sheet of the present invention at least on a surface opposite to the polarizing layer side of the transparent substrate sheet as described later. Is formed so that there is a light scattering layer, when the protective layer of the polarizing layer is also used as the transparent substrate sheet in the laminated sheet of the present invention, it is preferably set to 1 to 80 μm, furthermore the light scattering layer thickness and 50-70μ from the correlation
It is preferable to set m.

In the present invention, the transparent resin base used for the light scattering layer is mainly composed of a cellulose acetate resin. The configuration of the cellulose acetate resin is not particularly limited, but a known method, for example, a resin produced by the following method can be used. That is, a cotton linter or a wood pulp is used as a raw material, and a methyl chlorination method using methylene chloride as a solvent, or a fibrous acetylation method in which a poor solvent of cellulose acetate (eg, benzene, toluene) is added and acetylated in a fibrous form. It is produced by acetylating (acetylating) cellulose with acetic acid-acetic anhydride-sulfuric acid. Cotton linter and wood pulp may be used as a mixture. Synthesizing from wood pulp is cheaper and more economical, but mixing with cotton linters can reduce the burden of stripping, and even if the film is formed in a short time, the surface of the film will not be very good. It is preferable because it does not deteriorate.

A preferred cellulose acetate resin has an average acetylation degree (acetylation degree) of 58.0 to 62.5% used as a photographic support or an optical film. However, the degree of acetylation means the amount of bound acetic acid per unit weight of cellulose, and the degree of acetylation is determined according to ASTM: D-81.
The measurement is performed based on the measurement and calculation of the degree of acetylation in 7-91 (test method for cellulose acetate and the like).

The transparent resin base used for the light scattering layer is preferably triacetyl cellulose. Further, it is preferable that both the transparent substrate sheet and the transparent resin base used for the light scattering layer are made of triacetyl cellulose.

The resin constituting the transparent substrate sheet or the cellulose acetate resin constituting the transparent resin base used for the light-scattering layer contains other components such as a plasticizer as long as the action of the present invention is not impaired. May be contained.

In the present invention, the filament-based particles used in the light scattering layer are transparent particles that scatter light.
The material is not particularly limited, but it is preferable to use particles mainly composed of non-alkali glass and / or acrylic resin. Since the cellulose acetate resin and the non-alkali glass or acrylic resin have similar refractive index values, interfacial reflection occurring at the interface between the transparent resin base and the filament-based particles is suppressed, and the utilization efficiency of ambient light is improved.

As the alkali-free glass, for example,
A material containing 0.1% or less of an alkali oxide used for a substrate of a liquid crystal display or an EL display,
As the filament-based particles, filament-based particles generally used as a spacer for a liquid crystal cell can be used. As such filament-based particles,
For example, a micro rod PF- manufactured by Nippon Electric Glass Co., Ltd.
30S or the like can be used.

Examples of the acrylic resin include methacrylate polymers such as methyl methacrylate, ethyl methacrylate, propyl methacrylate and butyl methacrylate, and acrylate polymers such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate and butyl acrylate. These may be copolymerized with an aromatic vinyl monomer such as styrene, vinyltoluene, α-methylstyrene, and halogenated styrene, and include a crosslinkable monomer such as acrylic methacrylate and triallyl cyanurate. Is also good.

The above-mentioned alkali-free glass or acrylic resin may contain other components as long as the action of the present invention is not impaired.

In the present invention, if the filament-based particles used in the light-scattering layer are transparent particles that scatter light,
Although the shape is not particularly limited, it is preferable that the shape is small and the rod shape is small. When the shape is the rod shape, the spread of the scattering angle varies depending on the incident angle with respect to the rod.

Preferably, the rods are dispersed in a state close to being parallel to the light scattering layer surface with respect to the light scattering layer surface. If the rods are dispersed parallel to the surface of the light scattering layer, the light incident perpendicular to the light scattering layer will be
It impinges on a relatively large particle and is scattered largely only forward. On the other hand, light in an oblique direction with respect to the vertical direction, for example, at an angle of 70 degrees, is incident on particles having a size close to the rod diameter, and is therefore scattered with a larger spread angle than the vertical direction. The scattered light includes light scattered in a direction perpendicular to the surface of the light scattering layer, and when applied to a liquid crystal display device, ambient light can be effectively used.

The filament-based particles used in the present invention are rod-shaped, and preferably have a rod diameter of 1 to 5 μm and a rod length of 3 to 20 μm, more preferably 1 to 3 μm. The rod length is 3-10
It is good to be μm. When the size of the filament-based particles is within the above range, the incident light from the vertical direction is scattered appropriately forward, and the incident light from the oblique direction is scattered with a wider angle. It can be used effectively.

In the present invention, the blending ratio between the transparent resin base made of cellulose acetate resin and the filament-based particles is required to be 10 ¹³ to 10 ¹⁶ filament-based particles per 1 m ³ of the transparent resin base. It is. If the number of filament particles is less than 10 ^{13 with} respect to 1 m ^{3 of the} transparent resin base, an appropriate scattering property cannot be obtained,
Conversely, when the number exceeds 10 ¹⁶ , the light transmittance decreases,
The display characteristics when used as a member of a liquid crystal display device are impaired.

In the laminated sheet of the present invention, the method for forming the light-scattering layer is not particularly limited, and the light-scattering layer may be separately formed into a sheet shape and laminated with a transparent substrate sheet by adhesion or the like. As described below, it may be directly laminated on the transparent substrate sheet. As a method of directly laminating the light scattering layer on the transparent substrate sheet, for example, the cellulose acetate resin is dissolved in a solvent such as methylene chloride in a desired blending number, and the filament particles are mixed and dispersed in the solution. After dispersing the dispersion solution on the surface of the transparent substrate sheet of cellulose acetate resin by coating or the like, a method of drying and removing the solvent may be used.

As the above-mentioned solvent, methylene chloride is preferable, and methanol may be added as necessary and used as a mixed solvent with methylene chloride.

When the light-scattering layer is directly laminated on the transparent substrate sheet, the mixing ratio of the cellulose acetate resin and the solvent at the time of production is not particularly limited, and the application method, workability, type of the solvent, etc. Thus, the mixing ratio may be appropriately set, but the solvent is preferably set to 500 to 3000 parts by weight based on 100 parts by weight of the cellulose acetate resin,
More preferably, it is 1000 to 2000 parts by weight.

The method of mixing the cellulose acetate resin and the filament-based particles with the solvent is not particularly limited either. The mixing may be carried out simultaneously or sequentially and the mixture may be mixed and dispersed using a commonly used stirrer or the like. it can.

The method of applying the mixed dispersion solution to the surface of the transparent substrate sheet includes a comma direct method, a roll coating method, a dipping method, a knife coating method, a curtain flow method, a spray coating method, a spin coating method, and the like.
Various methods such as a laminating method and a bar code method may be mentioned, but are not particularly limited. The mixing ratio of the solvent and the filament particles, the viscosity of the mixed and dispersed solution, the desired thickness of the light scattering layer, the transparent substrate It is appropriately selected according to the surface condition of the material sheet.

The method of drying and removing the solvent in the mixed and dispersed solution spread on the surface of the transparent substrate sheet is not particularly limited, and various methods such as natural drying, hot air heating drying, and vacuum drying can be used. Can be

In the present invention, the thickness of the light scattering layer is not particularly limited, but is preferably from 10 to 80 μm, more preferably from 10 to 30 μm, from the viewpoint of the balance between the light scattering characteristics and the light transmittance. Is good.

Furthermore, in the present invention, the ratio of the thickness of the light-scattering layer to the thickness of the transparent substrate sheet is not particularly limited, and is appropriately set according to the desired properties of the laminated sheet.

The laminated sheet of the present invention can be suitably used as a forward scattering layer in a liquid crystal display device, in particular, a single polarizing plate type reflection type liquid crystal display device. The single-polarizer-type reflective liquid crystal display device usually has a protective layer provided on the outer side of the polarizer. However, the transparent base sheet in the laminated sheet of the present invention can also be used as the protective layer of the polarizer. That is, a polarizing layer (a polarizing layer in a polarizing plate) is added to the laminated sheet of the present invention.
By forming at least the light scattering layer on the surface opposite to the polarizing layer side of the transparent substrate sheet, the number of members in the liquid crystal display device can be reduced, and from the viewpoint of cost and quality retention. It will be advantageous. Usually, the protective layer is
Although a large amount of cellulose acetate resin is used, in that case, even if the transparent base sheet and the protective layer of the polarizing plate are also used,
There is no complicated refraction or loss at the interface, light can be transmitted effectively, and the suitability for lamination with the light scattering layer is improved.

FIGS. 1 and 2 show an embodiment in which the laminated sheet of the present invention is used as a forward scattering layer of a reflection type liquid crystal display device. FIG. 1 is a configuration of a reflective liquid crystal display device using the laminated sheet of the present invention as a forward scattering layer, and FIG.
2 shows a configuration of a laminated sheet used in the liquid crystal display device of FIG. 1.
The reflection type liquid crystal display device 1 includes the laminated sheet 2 (2a) of the present invention.
Is a light scattering layer, 2b is a transparent base sheet also serving as a protective layer of the polarizing layer, 2c is a polarizing layer, and 2d is the other protective layer of the polarizing layer. ), A birefringent layer 3, a reflection type liquid crystal cell 4, a specular reflection layer 5, and a back glass 6. As shown in FIG. 2, the laminated sheet 2 of the present invention includes a cellulose acetate resin (transparent resin base) 7 on one surface of a transparent base sheet 2b.
and a light-scattering layer 2a comprising a filament a and a filament-based particle 7b, a polarizing layer 2c on the other surface, and a protective layer 2 comprising a cellulose acetate resin inward of the display device.
d is formed. The light-scattering layer 2a has acrylic filament-based particles 7b dispersed in a transparent resin base 7a made of cellulose acetate resin.
Light passing through “a” is scattered forward to exhibit a forward scattering effect. Further, since the filament-based particles 7b are rod-shaped, they act as a kind of lens that partially scatters light incident from an oblique direction in the direction of the specular reflector, thereby exhibiting a more effective light scattering effect, and This has the effect of brightening the screen.

FIG. 3 shows a reflection state of incident light in the liquid crystal display device having the structure shown in FIG. Light 10 incident from a direction close to the vertical direction to the display screen 8 is scattered in the forward direction 10 ′ by the light scattering layer in the laminated sheet 2 of the present invention,
The light 11 "is reflected by the specular reflection layer 5 as light 10" in the viewing direction of the display device. On the other hand, the light 11 incident obliquely has a large spread because the particle cross section in the incident direction is significantly different from the particle cross section in the light 10 direction. And a part of the scattered light is scattered in the direction of the specular reflection layer 5 (11 '),
This is reflected by the specular reflection layer 5 as light 11 ″ in the viewing direction.
Since the light is more effectively utilized in the viewing direction by scattering and reflection, a brighter display is obtained.

The laminated sheet of the present invention is used not only as a forward scattering layer of a reflective liquid crystal display device as described above, but also for the purpose of controlling light of various devices such as lighting fixtures and illuminated signboards. Is also possible.

Hereinafter, the present invention will be described in more detail with reference to Test Examples and Examples. Test example Test object The solutions (dopes) used in Examples 1 and 2 and Comparative Examples 1 and 2 were cast on a support made of non-alkali glass by a solvent casting method, and were heated at 40 ° C for 3 minutes and at 100 ° C for 1 minute. The solvent was dried and removed to obtain a light-scattering layer having a thickness of 30 μm as a sheet, which was used as a test object (samples 1 to 4). 2. Test method (1) Measurement of total light transmittance The haze meter (Nippon Denshoku Industries Co., Ltd.) of the light-scattering layers (samples 1 to 4) of the laminated sheets of Examples 1 and 2 and Comparative Examples 1 and 2 was based on JIS K7105. ND
H-300A) was used to measure the total light transmittance.

(2) Measurement of diffused light transmittance The diffused light transmittance of the light-scattering layers (samples 1 to 4) of the laminated sheets of Examples 1 and 2 and Comparative Examples 1 and 2 was the same as in the test (1). Was measured.

(3) Parallel Line Transmittance The parallel line transmittance of the light-scattering layers (samples 1 to 4) of the laminated sheets of Examples 1 and 2 and Comparative Examples 1 and 2 was measured in the same manner as in the test (1). It was measured.

(4) Haze Measurement Haze was measured for the light-scattering layers (samples 1 to 4) of the laminated sheets of Examples 1 and 2 and Comparative Examples 1 and 2 in the same manner as in Test (1).

(5) Measurement of Filament-Based Particle Density The filament-based particle densities of the laminated sheets of Examples 1 and 2 and Comparative Examples 1 and 2 were calculated as follows. The total weight of the filament-based particles blended per 1 m ^{3 of the} transparent resin base was weighed, and the filament-based particles were formed into a rod shape and assumed to have the same diameter and length.
Following formula to calculate the number of filaments based particles to be incorporated in the transparent resin base 1m per ³ than 1. Formula 1: A = M / (πr ² × l × ρ) A: Number of filament-based particles per 1 m ^{3 of} transparent resin base (pieces) M: Total weight of total filament-based particles per 1 m ^{3 of} transparent resin base (g) ) R: rod diameter of filament-based particles (cm) l: rod length of filament-based particles (cm) ρ: specific gravity of filament-based particles (g / cm ³ )

(6) Measurement of scattering characteristics when light is incident on the light scattering layer in a vertical direction. The light scattering layers (samples 1 to 4) of the laminated sheets of Examples 1 and 2 and Comparative Examples 1 and 2 The relationship between the light scattering intensity and the scattering angle when light was incident on the light scattering layer from a perpendicular direction was measured using a laser light scattering automatic measuring device (manufactured by Nippon Kagaku Engineering Co., Ltd.).

(7) Measurement of scattering characteristics when light is incident on the light scattering layer from a direction of 60 degrees Light scattering layers (samples 1 to 4) of the laminated sheets of Examples 1 and 2 and Comparative Examples 1 and 2 The relationship between the light scattering intensity and the scattering angle when light enters the light scattering layer from the direction of 60 degrees was measured in the same manner as in the test (7).

3. Test Results The results of the tests (1) to (5) are shown in Table 1, the results of the test (6) are shown in FIG. 4, and the results of the test (7) are shown in FIG.

[0043]

[Table 1]

From the results shown in Table 1, Examples 1 and 2 have high total light transmittance and high haze. Also, it can be seen that the scattering intensity is higher than the comparative example. Further, the spread of the scattering angle at the time of light incidence from the direction of 60 degrees is larger than that of the comparative example, and it can be seen that light can be used effectively. Comparative Example 1 is inferior in scattering intensity because of low particle density, and Comparative Example 2 in which spherical particles are dispersed and blended, rather than rod-shaped, has a scattering characteristic when incident at 60 degrees because of spherical shape. The spread is smaller than that of the first embodiment, and is inferior in effective light utilization.

[0045]

EXAMPLES Laminated sheets of Examples and Comparative Examples were prepared using the following materials. [Transparent substrate sheet] Cellulose triacetate resin (LT-55, manufactured by Daicel Chemical Industries, Ltd., specific gravity 1:
3, average acetylation degree 61%)-Solvent mixed solvent (methylene chloride / methanol = 9/1) [Light scattering layer]-Transparent resin base Cellulose triacetate resin (TAC) (LT-55, manufactured by Daicel Chemical Industries, specific gravity 1) : 3, average acetylation degree 61%) Filament-based particles Non-alkali glass rod (Micro rod PF-30S; NEC Glass Co., Ltd.)
Average rod diameter 2.99 μm, average rod length 16.
7 μm, density 2.57 g / cm ³ ) Alkali-free glass rod (Micro Rod PF-50S; NEC Corporation)
Made, average rod diameter 5.0 μm, average rod length 14.5
μm, density 2.57 g / cm ³ ) Polymethyl methacrylate spherical particles (Techpolymer MBX-20; manufactured by Sekisui Plastics Co., Ltd., average spherical shape 2.5 μm, specific gravity 1.2) ・ Plasticizer TPP ・ Solvent Mixed solvent ( (Methylene chloride / methanol = 9/1)

[Production of Transparent Substrate Sheet] Cellulose triacetate resin was blended and dissolved in a solvent at a weight ratio of 1: 9, and the resulting solution (dope) was subjected to a solvent casting method to prepare a support (non-coated). After casting and drying the solvent at 40 ° C. for 3 minutes and at 100 ° C. for 1 minute, it was peeled off from the support to obtain a sheet having a thickness of 60 μm.

Examples 1 and 2 and Comparative Examples 1 and 2 The above materials as a transparent resin base, filament type particles, a plasticizer and a solvent were blended according to the blending in Table 2 below, and dissolved and dispersed and mixed using a three-one motor. After that, the obtained solution (dope) was cast on a transparent substrate sheet by a bar code method, and the solvent was dried and removed at 40 ° C. for 3 minutes and at 100 ° C. for 1 minute to form a light-scattering layer having a thickness of 30 μm. The obtained laminated sheet was used as an example and a comparative example.

[0048]

[Table 2]

[0049]

As described above, the laminated sheet of the present invention
Since it has both forward scattering properties and light collecting properties, good light forward scattering properties can be obtained, and when used as a forward scattering layer of a single-polarizer-type reflective liquid crystal display device, the effective use of incoming and outgoing light is effectively utilized. As a result, the display brightness of the display screen is improved, image blur is reduced, and good image quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a reflective liquid crystal display device using a laminated sheet of the present invention as a forward scattering layer.

FIG. 2 is a diagram showing a configuration of a laminated sheet used in the liquid crystal display device of FIG.

FIG. 3 is a diagram illustrating a reflection state of incident light in the liquid crystal display device of FIG.

FIG. 4 is a diagram showing a scattering characteristic when light is incident on the light scattering layer from a perpendicular direction in the liquid crystal display device of FIG. 1;

FIG. 5 is a diagram showing a scattering characteristic when light enters the light scattering layer from a direction of 60 degrees in the liquid crystal display device of FIG. 1;

[Explanation of symbols]

 Reference Signs List 1 reflective liquid crystal display device 2 laminated sheet of the present invention 2a light scattering layer 2b transparent base sheet 2c polarizing layer 2d protective layer 3 birefringent layer 4 reflective liquid crystal cell 4 'hybrid-aligned liquid crystal 5 mirror-reflective layer 6 back glass 7a Transparent resin base 7b Filament particles 8 Display screen

Claims (7)

[Claims] 1. Filament particles are provided on at least one surface of a transparent base material sheet on a transparent resin base mainly composed of cellulose acetate resin, and the number of the filament particles is 10 ¹³ per 1 m ^{3 of the} transparent resin base. ~
10. A laminated sheet comprising a stack of 10 ¹⁶ light scattering layers which are mixed and dispersed. 2. The laminated sheet according to claim 1, wherein the filament-based particles have a rod shape. 3. The filament type particles have an average rod diameter of 1 μm to 5 μm and an average rod length of 3 μm to 3 μm.
The laminated sheet according to claim 2, wherein the thickness is 20 µm. 4. The laminated sheet according to claim 1, wherein the filament-based particles mainly comprise alkali-free glass and / or an acrylic resin. 5. A transparent substrate sheet mainly comprising a cellulose acetate resin.
The laminated sheet according to any one of the above. 6. The laminated sheet according to claim 5, wherein the transparent base sheet mainly comprises triacetyl cellulose. 7. The laminated sheet according to any one of claims 1 to 6, wherein the polarizing layer is formed such that a light scattering layer is provided on at least a surface of the transparent substrate sheet opposite to the polarizing layer. A laminated sheet, comprising: