JPH05173134A - Dimming sheet - Google Patents

Abstract

PURPOSE:To provide the dimming sheet which has both a light diffusing function and the large quantity of output light by composing the dimming sheet of a light diffusing layer and a light converging layer laminated on its front surface and making the nonlamination surface of the light converging layer uneven. CONSTITUTION:The dimming sheet 7 is formed of the light diffusing layer 8 made of polycarbonate and the light converging layer 9 which is made of polycarbonate and laminated on its front surface. The light diffusing layer 8 is 50mum (>=10mum) thickness and molded out of a mixed body obtained by adding 20 pts.wt. titanium oxide as a light diffusing agent to 100 pts.wt. polycarbonate of 5.0 (290 deg.C, 1.9kg) in melt index. Further, the light converging layer 9 is 150mum (>=80mum) thickness, and the nonlamination surface of the light converging layer 9 is an uneven surface 10, which is laterally sectioned in a right- angled isosceles triangle shape (having a 90 vertical angle).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light control sheet used for a light source unit of a liquid crystal display screen such as a computer and a word processor.

[0002]

BACKGROUND OF THE INVENTION Liquid crystal display screens do not have self-luminous properties, and thus require illumination from other sources in order to improve visibility.
Therefore, a light source unit (hereinafter, referred to as a backlight unit) that applies light from the back surface of the liquid crystal display element has been devised.

At the beginning of its development, the backlight unit had a structure in which a light source such as a fluorescent lamp was arranged directly on the back surface of the liquid crystal display element, but recently, the thickness of the entire unit is reduced to make the device smaller. In order to achieve this, a structure called an edge light system in which a light source is arranged on at least one side surface of a liquid crystal display element is often adopted.

FIG. 6 is a sectional view showing the basic structure of a backlight system. In FIG. 6, a fluorescent lamp (1) as a light source is arranged directly on the back surface of the liquid crystal display element (2).
That is, the fluorescent lamp (1) is located in the center of the front surface of the reflection plate (3), and the liquid crystal display element (2) is provided on the front side of the reflection plate (3) via the light diffusion sheet (4).

FIG. 7 is a sectional view showing the basic structure of an edge light type light source unit. In FIG. 7, a fluorescent lamp (1) as a light source is arranged on the side surface of a light guide (6) having a dot pattern (5) on the back surface. A reflector (3) is arranged on the rear side of the light guide (6), and a liquid crystal display element (2) is provided on the front side of the light guide (6) via a light diffusion sheet (4).
The edge light type dot pattern (5) is a light formed on the back surface of the light guide (6) so that the light incident from the side fluorescent lamp (1) is evenly emitted from any position on the screen. It is a scattered print pattern and can be called a pseudo light source.

In these structures, the liquid crystal display element (2)
A unit including members other than the above is called a backlight unit.

The light diffusion sheet is a light source on the back side through the liquid crystal display element (2) when using the liquid crystal display screen, that is, a fluorescent lamp (1) in the backlight system or a pseudo light source in the edge light system. It functions so that the dot pattern (5) is not visually recognized and is regarded as a surface that uniformly emits light.

The light control sheet according to the present invention is used in place of the above light diffusion sheet.

[0009]

2. Description of the Related Art Conventional light diffusing sheets are roughly classified into two types: a plastic film or sheet having a surface coated with titanium oxide or glass short fibers, or a sheet containing the same, and a surface having irregularities. There are processed sheets.

As an example of the former, a transparent film or sheet of polyester, polycarbonate, polymethylmethacrylate or the like coated with a light diffusing agent such as titanium oxide or short glass fiber on one or both sides (Japanese Patent Laid-Open No. 63-63). 33703), and polyester,
A film or sheet molded from a material obtained by adding a light diffusing agent such as titanium oxide or short glass fiber to a resin such as polycarbonate or polymethylmethacrylate (JP-A-1
No. 209402 and JP-A No. 1-172801).

As an example of the latter, there is a film or sheet made of a resin such as polyester, polycarbonate, polymethylmethacrylate or the like, on one or both sides of which a desired concavo-convex process is applied (see JP-A-2-13925).

[0012]

However, in the former light diffusing sheet, when the amount of the light diffusing agent is increased in order to improve the light diffusing function, the light output amount decreases due to its concealing power,
Practical screen brightness tends to be insufficient.

The latter light diffusing sheet utilizes scattering due to the surface shape of the sheet, and is superior to the former sheet in terms of the amount of emitted light, but it is difficult to obtain a sheet having a very excellent diffusing function and it is thin. Since the dot pattern becomes easy to see when it is made, it is necessary to increase the thickness of the sheet or the light source unit as a whole in order to obtain sufficient diffusion. This drawback is a serious problem because the recent trend toward thinner devices makes thinner fluorescent lamps, that is, the amount of incident light is reduced.

In view of the above points, an object of the present invention is to provide a light control sheet having both a light diffusion function and a large amount of light output.

[0015]

According to the present invention, two layers having a high light diffusing property and a light converging property, which have different functions, are integrally laminated so that the light diffusing function and the light output amount are increased as described above. It was completed based on the finding that a light control sheet having both the above and the other aspects can be obtained.

That is, the light control sheet according to the present invention comprises a light diffusing layer and a light collecting layer provided on the front surface thereof, and the non-laminated surface of the light collecting layer is an uneven surface.

In a preferred mode of operation of the present invention, the light control sheet is formed of a composition in which the light diffusion layer is added with 5 to 100 parts by weight of a light diffusion agent to 100 parts by weight of the transparent resin. And has a thickness of 10 μm or more, while the light collecting layer is made of a transparent resin layer having a thickness of 80 μm or more.

The resin forming the light diffusion layer is not particularly limited as long as it is a transparent resin, and examples of the transparent resin include polycarbonate, polyester, polymethylmethacrylate and the like.

As the light diffusing agent, conventionally known ones can be applied, and examples thereof include titanium oxide, glass fiber, glass beads, silica-alumina and the like.

The thickness of the light diffusion layer is 10 μm or more, preferably 20 to 100 μm. If this thickness is less than 10 μm, sufficient diffusivity may not be obtained.

The light diffusing layer is molded from a mixture of 100 parts by weight of a transparent resin, preferably 5 to 100 parts by weight, more preferably 10 to 50 parts by weight of a light diffusing agent. .. If the amount of the light diffusing agent added is less than 5 parts by weight with respect to 100 parts by weight of the transparent resin, sufficient diffusivity may not be obtained. On the other hand, if the amount added exceeds 100 parts by weight, the amount of light emitted may decrease or the moldability may deteriorate.

As the method for molding the film or sheet for producing the light diffusion layer, a method of hot pressing a material, a method of extruding the material with a T-die, a flow casting method,
Other known methods can be applied, and if the haze value of the formed layer is 50 to 90%, preferably 70 to 85%,
The molding method is not particularly limited. When the haze value is less than 50%, the diffusion function is insufficient and the dot pattern on the back surface is seen through. Further, when the haze value exceeds 90%, the amount of light emitted becomes too small and the screen brightness becomes insufficient.

On the other hand, the light collecting layer is also made of a transparent resin, and examples of the transparent resin include polycarbonate, polyester, polymethylmethacrylate and the like. The light collecting layer is preferably made of the same resin as the base resin of the light diffusion layer.

The thickness of the light collecting layer is 80 μm or more, preferably 90 to 300 μm. If the thickness is less than 80 μm, the shaping required for light collection becomes difficult.

The light emitted through the light diffusing layer is diffused within the range of −90 ° <α <90 ° from the direction normal to the screen. The light condensing layer provided on the upper surface of the light diffusion layer, that is, on the liquid crystal display element side has a function of condensing the emitted light distributed at a large angle from the normal line closer to the normal line as described above.

The non-laminated surface of the light-collecting layer is an uneven surface. The uneven shape may be such that the emitted light direction is gathered more in the direction normal to the screen, and it is composed of a large number of ridges having a triangular cross section or a semicircle provided in parallel with the fluorescent lamp. Examples thereof include Fresnel lens shapes and lenticular lens shapes. The apex angle of the ridge having a triangular cross section is preferably in the range of 50 to 100 °, more preferably about 70 to 90 °.

Examples of the method for forming the uneven shape include a profile extrusion method, a roll embossing method during extrusion molding, a hot pressing method on a flat plate, and a monomer casting method, but the uneven formation method is not limited thereto.

The light diffusing layer and the light collecting layer may be laminated and integrated, or an air layer may be interposed therebetween.

The total thickness of the light control sheet is 90 μm or more, but if it is too thick, the needs for thinning cannot be met, so it is preferable to keep it to 5 mm or less. The preferable range of the thickness of the entire light control sheet is 110 to 500 μm.

[0030]

EXAMPLES The present invention will be specifically described with reference to the following examples.

Embodiment 1 FIG. 1 showing a basic structure of an edge light type light source unit.
In, the fluorescent lamp (1) as a light source is arranged on the side surface of the light guide (6) having the dot pattern (5) on the back surface. The reflector (3) is arranged on the rear side of the light guide (6),
A liquid crystal display element (2) is provided on the front side of (6) through a light control sheet (7) according to the present invention.

As shown in FIG. 2, the light control sheet (7) according to the present invention comprises a light diffusion layer (8) made of polycarbonate and a light collecting layer (9) made of polycarbonate laminated on the front surface thereof. ..

The thickness of the light diffusion layer (8) is 50 μm. The light diffusion layer (8) has a melt index (290 ° C, 1.9 k
g) Molded from a composition prepared by adding 20 parts by weight of titanium oxide as a light diffusing agent to 100 parts by weight of 5.0 polycarbonate.

The non-laminated surface of the light collecting layer (9) is an uneven surface (10). This uneven shape forms an isosceles triangle having a right angle in cross section and provided in parallel with the fluorescent lamp (1).

The uneven shape is formed by the hot pressing method.

The thickness of the light collecting layer (9) is 150 μm, of which the height of the convex portion is 80 μm.

The light collecting layer (9) has a melt index (29
0 ° C., 1.9 kg) 4.0 polycarbonate.

The lamination of the light diffusion layer and the light collecting layer was carried out by coextrusion.

Example 2 In FIG. 3, the light control sheet (7) according to the present invention is a light diffusion layer (8) made of polymethylmethacrylate containing short glass fibers.
And a light collecting layer made of polycarbonate laminated on the front surface
(9) consists of.

The thickness of the light diffusion layer (8) is 100 μm.
The light diffusion layer (8) is made of methyl methacrylate monomer 100.
It is composed of polymethylmethacrylate obtained by molding a composition obtained by adding 30 parts by weight of glass short fibers to parts by weight by monomer casting.

The light collecting layer (9) has the same structure as that of the first embodiment. The light collecting layer (9) was molded by single extrusion. The uneven shape was formed by the hot pressing method.

The light diffusing layer and the light collecting layer are used in an overlapping manner.

Example 3 In FIG. 4, a light control sheet (7) according to the present invention comprises a light diffusion layer (8) made of polymethylmethacrylate and a light collection layer (9) made of polycarbonate laminated on the front surface thereof. Consists of.

The non-laminated surface of the light collecting layer (9) is an uneven surface (10). This concavo-convex shape is composed of a large number of ridges arranged in parallel with the fluorescent lamp (1) and having rounded corners and an approximately isosceles triangular cross section.

The light collecting layer (9) is composed of a polymethylmethacrylate film obtained by casting by polymethylmethacrylate monomer casting.

The uneven shape is formed by the hot pressing method.

The thickness of the light collecting layer (9) is 200 μm, and the height of the convex portion is 100 μm. The convex line of the isosceles triangle having a cross section of the light converging layer (9) has an apex angle of 70 °, and the top and the bottom have an arcuate cross section with a radius of curvature of 20 μm.

The thickness of the light diffusion layer (8) is 30 μm. The light diffusion layer (8) was prepared by adding 50 parts by weight of silica / alumina particles to 100 parts by weight of a methyl methacrylate monomer and applying the resulting mixed liquid to the laminated surface of the light collecting layer (9). It is formed by UV curing.

Comparative Example 1 In FIG. 1, an edge light type light source unit without the light control sheet (7) of Example 1 was constructed.

Comparative Example 2 In the light control sheet (7) of Example 1 shown in FIG. 2, an edge light type light source unit was constructed using the light diffusion layer (8) containing no titanium oxide.

Comparative Example 3 In the light control sheet (7) of Example 2 shown in FIG.
An edge light type light source unit having no (9) (the light diffusion layer (8) alone) was constructed.

Comparative Example 4 A polycarbonate sheet having a melt index of 3.0 and a thickness of 250 μm was formed on the light-exiting surface at a depth of 150 μm and the uneven density was 1
An irregular uneven surface of 20 lines / inch was formed. An edge light type light source unit was configured using the light diffusion sheet thus obtained.

Performance Evaluation Test In FIG. 5, a light source having a thickness of 35 mm and a length of 135 m is used.
m cold cathode fluorescent lamps (1) are arranged on the side surface of a light guide (6) having a dot pattern (5) on the back surface. The light guide (6) is made of a polymethylmethacrylate plate having a width of 196 mm, a length of 135 mm and a thickness of 2.5 mm. A reflective plate (3) is disposed on the rear side of the light guide (6), and a liquid crystal display element (7) is disposed on the front side of the light guide (6) through the light control sheets (7) of the examples and comparative examples. 2) is provided. The reflector (3) is made of an opaque film made of opaque polyethylene terephthalate.

The edge light type backlight thus constructed is driven by a DC 12V inverter,
It was used for evaluation of the light control sheet.

(1) Brightness of screen Brightness at a viewing angle of 2 ° was measured from positions 30 cm apart in the normal direction at fixed points (9 locations) on the screen, and the brightness data was obtained. If the measured data is 550 cd / m ² or more,
There is no problem in practical use.

(2) Visibility of dot pattern It was evaluated whether or not the dot pattern is visible when the display screen is viewed through the light control sheet from a position 50 cm away from the screen in the normal direction.

[0057]

[Table 1] ◯: Dot pattern is not visible ×: Dot pattern is visible, causing a problem in practical use

[0058]

The light control sheet according to the present invention comprises a light diffusing layer and a light collecting layer laminated on the front surface of the light diffusing layer, and the non-laminated surface of the light collecting layer is an uneven surface. It is possible to provide a light control sheet having both a light diffusion function and a large amount of light output.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a light control sheet of Example 1 and an edge light type light source unit incorporating the light control sheet.

FIG. 2 is a cross-sectional view showing a light control sheet of Example 1.

FIG. 3 is a cross-sectional view showing a light control sheet of Example 2.

FIG. 4 is a cross-sectional view showing a light control sheet of Example 3.

FIG. 5 is a cross-sectional view showing an edge light type light source unit used in a performance evaluation test of a light control sheet.

FIG. 6 is a cross-sectional view showing a basic structure of a backlight system.

FIG. 7 is a cross-sectional view showing the basic structure of an edge light type light source unit.

[Explanation of symbols]

 (1) Light source (2) Liquid crystal display element (3) Reflector (4) Light diffusion sheet (5) Dot pattern (6) Light guide (7) Light control sheet (8) Light diffusion layer (9) Light collection layer (10) Uneven surface

Claims (2)

[Claims] 1. A light control sheet comprising a light diffusing layer and a light collecting layer provided on the front surface of the light diffusing layer, wherein a non-laminated surface of the light collecting layer is an uneven surface. 2. A light diffusing layer is formed from a compounding composition in which 5 to 100 parts by weight of a light diffusing agent is added to 100 parts by weight of a transparent resin, and has a thickness of 10 μm or more. The light control sheet according to claim 1, wherein the light layer is a transparent resin layer having a thickness of 80 μm or more.