JPH08146413A - Reflection sheet for surface light emitting device, surface light emitting device and liquid crystal display device formed by using the same - Google Patents

Abstract

PURPOSE: To provide a reflection sheet for a surface light emitting device capable of concentrating an exit light distribution to the front surface of a screen and a surface light emitting device and liquid crystal display device formed by using the same. CONSTITUTION: This reflection sheet 10 for the surface light emitting device consists of a transparent plastic sheet 11 having a structural surface alternately arranged with many peak parts 12 of a projecting shape or projecting arc shape in cross section and many valley parts having a recessed shape or recessed arc shape in cross section approximately in parallel on one surface and a smooth surface deposited by evaporation with a reflective metal 13 on the other surface. The surface light emitting device has a light diffusion sheet 7, a light transmission plate 2 which is disposed behind this light diffusion plate 7 and has dot patterns 4 on its rear surface and the linear light source 7 which is disposed at least on the one side surface of the light transmission plate 2 and the reflection sheet 10 which is disposed behind the light transmission plate 2. This liquid crystal display device has a liquid crystal panel on the front surface of the surface light emitting device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective sheet used in a planar light emitting device used in liquid crystal displays such as personal computers and word processors, and liquid crystal color televisions, a planar light emitting device using the same, and a liquid crystal display device.

[0002]

2. Description of the Related Art Word processors and personal computers have become smaller, lighter and thinner year after year, and so-called laptop or notebook size has become the mainstream. A laptop type or notebook type thin liquid crystal display device usually has no self-luminous property.
A backlight is provided on the back surface to improve visibility. This backlight needs to be thin and to illuminate the surface of the display device almost uniformly.

A planar light emitting device is usually used for this backlight. Currently, the most widely used planar light-emitting device is provided with a light source on the end surface of the light guide plate, and the light emitted from this light source is made substantially uniform from the surface of the light guide plate or the surface of the plate attached to the light guide plate. It is a type called an edge light system that emits light, and is widely used because of its thinness and lightness.

The edge light type planar light emitting device will be described in more detail. In general, an edge light type planar light emitting device has an end face 3 of a thin light guide plate 2 as shown in FIG.
Is provided with a linear light source 1, and the liquid crystal panel 6 arranged on the front side of the light guide plate 2 is illuminated in a plane shape by allowing light to enter the light guide plate 2 from the end surface 3 from the light source 1. However, in the case of only the light guide plate 2, the light is repeatedly totally reflected in the light guide plate 2 due to the difference in refractive index between the air and the light guide plate 2, and hardly exits from the light guide plate 2. Therefore, a diffused reflection layer, for example, a dot pattern 4 in which a paint containing small-diameter beads is dot-printed is provided on the back surface of the light guide plate 2, and a reflection sheet 5 is further attached to this back surface. The light incident on the back surface of the light guide plate 2 is diffusely reflected by the dot pattern 4, and the diffusely reflected light is directly emitted to the outside or is reflected by the reflection sheet 5 to be emitted to the outside.

[0005]

However, the light emitted from the light source 1 provided on the end face 3 of the light guide plate 2 is usually very small from the light guide plate 2 to the surface as shown in FIG. Emit at an angle. That is, the directivity is extremely strong (luminance distribution A).

Therefore, in order to improve this directionality, there has been proposed a method of providing a diffusion sheet 7 on the surface of the light guide plate 2 as shown in FIG. The diffusion sheet 7 is a transparent plastic sheet coated with a coating containing microspheres, or a transparent plastic sheet having fine irregularities (mats, embosses) on the surface (for example, Japanese Patent Laid-Open No. 3-78701). See the bulletin). When this diffusion sheet 7 is provided, as shown in FIG. 10, light in a direction perpendicular to the diffusion sheet 7 increases (luminance distribution B).

However, even when the diffusion sheet 7 is used,
A large amount of light is emitted in a direction that is not useful to the user, and the brightness as a planar light emitting device is insufficient. Moreover, in recent years, in order to cope with colorization and low power consumption, there is an increasing demand for improving the brightness of the planar light emitting device.

Therefore, in order to efficiently emit light to the front, a method has been proposed in which a lens sheet 8 is further provided on the diffusion sheet 7 as shown in FIG. The lens sheet 8 is a sheet having on its surface a structural surface in which a large number of peak portions having a convex or convex arc-shaped cross section and valley portions having a concave or concave arc-shaped cross section are arranged alternately and substantially in parallel. See, for example, JP-A-63-318003). By using the lens sheet 8, as shown in FIG. 11, light can be efficiently collected in the front direction (luminance distribution C). However, there is a drawback that moire fringes are likely to occur due to interference between the ridgelines of the lens sheet 8 and the grid-like division lines on the display surface of the liquid crystal display device.

An object of the present invention is to provide a reflection sheet for a planar light emitting device, which can concentrate the light emission distribution on the front surface of the screen. Another object of the present invention is to provide a planar light emitting device in which the brightness in the front direction is improved and moire fringes are not generated. Another object of the present invention is to provide a liquid crystal display device whose screen is bright and easy to see.

[0010]

A reflection sheet for a planar light emitting device according to claim 1 of the present invention has a large number of peaks having a convex or convex arc-shaped cross section and a concave or concave arc-shaped cross section on one side. Of a transparent plastic sheet having a structured surface in which a large number of valleys are alternately and substantially parallelly arranged, and a smooth surface on which a reflective metal is vapor-deposited on the other surface. .

According to a second aspect of the present invention, there is provided a planar light emitting device, a light diffusing sheet, a light guide plate provided behind the light diffusing sheet and having a dot pattern on its back surface, and at least one side surface of the light guide plate. A linear light source provided on the light guide plate, and the reflection sheet according to claim 1 provided on the rear side of the light guide plate.

A liquid crystal display device according to a third aspect of the present invention is characterized in that a liquid crystal panel is provided in front of the planar light emitting device according to the second aspect.

According to a fourth aspect of the present invention, there is provided a reflection sheet for a planar light emitting device, wherein one side is provided with valleys having a concave or concave arc-shaped cross section and arranged substantially parallel to each other, and a reflective metal is provided on the surface thereof. It is characterized by comprising a transparent plastic sheet having a vapor-deposited structural surface.

According to a fifth aspect of the present invention, in the planar light emitting device, a light diffusing sheet, a light guide plate provided behind the light diffusing sheet and having a dot pattern on the back surface, and at least one side surface of the light guide plate. A linear light source provided on the light guide plate, and the reflection sheet according to claim 4 provided behind the light guide plate.

A liquid crystal display device according to a sixth aspect of the present invention is characterized in that a liquid crystal panel is provided in front of the planar light emitting device according to the fifth aspect.

The present invention will be described in more detail below.

The "sheet" in the sheet for a planar light emitting device of the present invention includes not only a sheet in a strict sense limited by the thickness but also a thin sheet usually called a film. The average thickness is preferably 50 μm or more, more preferably 90 to 300 μm. In addition, the convex arcs or the like formed on the structural surface being “substantially parallel” means that they are arranged substantially in parallel.

The reflection sheet for a planar light emitting device of the present invention is made of a transparent plastic sheet. Examples of transparent plastics include polycarbonate, polymethylmethacrylate, polyester, polystyrene, polyvinyl chloride and the like. The manufacturing method is as follows: melt extrusion of transparent plastic, then molding uneven surface through embossing roll, press using a template with uneven surface, uneven surface. There is a method in which a monomer is poured into a template in which a strip is punched and then photocured or heat-cured. A metal such as aluminum or silver is vacuum-deposited on the surface of the plastic sheet molded in this manner.

In the reflection sheet for a planar light emitting device according to the first aspect of the present invention, the structural surface forms, for example, a curved surface in which peaks and valleys arranged alternately are continuous. Further, the mountain portion of the structure surface is, for example, an isosceles triangle or a convex arc shape having an apex angle of 90 °. Furthermore, the peaks are arranged substantially in parallel, and the pitch between the peaks is, for example, 50 to 500 μm. For example, aluminum or silver is vapor-deposited on the smooth surface opposite to the structure surface.

In the reflection sheet for a planar light emitting device according to claim 4 of the present invention, the structural surface has, for example, a cross section of diameter 50.
~ 1000μm arc-shaped troughs are arranged substantially parallel,
The pitch between the valleys is 50 to 500 μm. Also,
Aluminum or silver is vapor-deposited on the surface of the structure surface.

Next, in the planar light emitting device according to claim 2 or 4, as the light diffusion sheet, a transparent plastic sheet such as PET or polycarbonate is coated with a coating material containing microspheres as a diffusion material. Sheet, 50 on the surface
A sheet of polycarbonate or the like embossed with a depth of ˜100 μm, a sheet of polycarbonate or the like containing microspheres having different refractive indexes as a diffusing material, or a sheet of polymethylmethacrylate or the like is used. In addition, the light guide plate,
Made of highly transparent plastic such as polycarbonate, polyester, polymethylmethacrylate, etc., and has a printed dot pattern on the back surface that causes diffuse reflection so that light from the light source is evenly emitted from any position on the light emitting surface. Is used.

FIG. 1 shows an example of a reflection sheet for a planar light emitting device according to claim 1 of the present invention. This reflective sheet 10
Is a transparent plastic sheet 11 made of polycarbonate, for example, and has a structure surface in which a plurality of mountain portions 12 having an isosceles right triangle having a vertical cross section of 90 ° are formed in parallel on one surface. It has a reflective layer 13 on which aluminum or the like is deposited.

FIG. 2 shows another example of the reflection sheet for a planar light emitting device according to claim 1 of the present invention. This reflective sheet 20
Is, for example, on one surface of a transparent plastic sheet 21 made of polycarbonate, peaks 22 having a convex arc shape in transverse cross section and valleys 24 having a concave arc shape in cross section which form a continuous curved surface are alternately arranged at a pitch of 200 μm. It has a plurality of structured surfaces and has a reflective layer 23 on the smooth back surface of which aluminum or the like is deposited.

FIG. 3 shows an example of a reflection sheet for a planar light emitting device according to claim 4 of the present invention. This reflective sheet 30
Has a structure surface in which a plurality of arc-shaped valleys 32 having a width of 35 μm and a depth of 10 μm are in contact with one surface of a transparent plastic sheet 31 made of, for example, polycarbonate. Has a reflective layer 33 on which aluminum or the like is deposited.

FIG. 4 shows another example of the reflection sheet for a planar light emitting device according to claim 4 of the present invention. This reflective sheet 40
Has a structure surface in which a plurality of arc-shaped troughs 42 each having a width of 100 μm and a depth of 50 μm are formed at intervals of 20 μm on one surface of a transparent plastic sheet 41 made of, for example, a surface of the structure surface. Has a reflective layer 43 on which aluminum or the like is deposited.

FIG. 5 shows an example of an edge light type planar light emitting device using the reflection sheet 10 of the present invention. This planar light emitting device is similar to a conventional device in that the end face 3 of the light guide plate 2 is
A linear light source 1 such as a fluorescent tube is arranged on the light guide plate 2, and a light diffusion sheet 7 is arranged on the surface side of the light guide plate 2. Further, a dot pattern 4 is formed on the back surface of the light guide plate 2, and the reflection sheet 10 of the present invention is provided outside the dot pattern 4 instead of the conventional reflection sheet.
Is arranged. The liquid crystal panel 6 is arranged on the front surface of the planar light emitting device to form a liquid crystal display device.

In the planar light emitting device of the present invention, as shown in FIG. 6, light is efficiently condensed in the direction of the line (luminance distribution D).

[0028]

When the reflective sheet according to the present invention is used, light can be more efficiently collected in front of the white PET sheet which is generally used at present. It is considered that this is because the light leaked from the back surface of the light guide plate is reflected by the vapor deposition surface of the reflective metal on the front surface or the back surface of the reflection sheet and is collected in the front direction by the structural surface. Therefore, when the reflection sheet is used for an edge light type planar light emitting device or a planar light emitting device in which a light source is provided on the back side of a diffusion plate, and the planar light emitting device is attached to a liquid crystal display device, it is bright and extremely easy to see. The screen is obtained. The planar light emitting device of the present invention is
It can be used not only as a display device using liquid crystal but also as a facility lighting used in stores, houses, offices, etc., which has a small thickness.

[0029]

Example 1 The present invention will be specifically described by the following examples. The edge-light type planar light emitting devices of Examples 1 to 6 and Comparative Examples 1 to 3 were prepared under the following conditions, and JIS-C76 was used.
Luminance was measured according to No. 14, and a liquid crystal panel was combined on the planar light emitting device to observe the appearance quality of light emission. In addition, as shown in FIG. 7, the measurement of the emission light brightness of the planar light emitting device is performed by setting the direction of the light emitting surface of the planar light emitting device to 0 ° and measuring the brightness of a point P on the planar light emitting device. -90 ° to + 90 ° about a straight line passing through P and parallel to the axis of the light source 1
Was measured by the luminance meter 13 from several positions within the range.

[Example 1] Light diffusing sheet: a stack of two sheets of polycarbonate having a depth of 150 µm and a thickness of 250 µm with an irregular surface having an irregular density of 120 / inch. Cathode tube: diameter 3 mm, length 130mm cold cathode tube Light guide plate: thickness 3.0mm, length 130mm, width 260m
m, material acrylic resin, dot-printed for irregular reflection on the lower surface Reflective sheet: a polycarbonate sheet having a structural surface and a smooth surface and having a thickness of 300 mm. Aluminum is vapor-deposited on the smooth surface. On the structural surface, ridges of an isosceles right triangle having a transverse cross section are arranged substantially in parallel at a pitch of 200 μm (FIG. 1).

Example 2 Light diffusion sheet: 30 μm coating layer of methyl methacrylate containing 50% of methyl methacrylate and 50% of trimethylolpropane triacrylate and having a refractive index of 1.51 and particle size of 110 μm and 30%. 20-μm 0-PET film with a cathode tube: same as in Example 1 light guide plate: same as in Example 1 reflection sheet: same as in Example 1 polycarbonate sheet with silver evaporated on the back side

[Example 3] Light diffusion sheet: same as in Example 1 Cathode tube: same as in Example 1 Light guide plate: same as in Example 1 Reflective sheet: Polycarbonate having corrugated structure surface as shown in FIG. Aluminum with vapor deposited on the back of the sheet

[Example 4] Light diffusing sheet: same as in Example 1 Cathode tube: Same as in Example 1 Light guide plate: Same as in Example 1 Reflective sheet: Polycarbonate sheet with a thickness of 300 mm, concave cross section (width 35 μm) , The depth of 10 μm, the arc of a circle with a diameter of 40 μm) are arranged in parallel at a pitch of 35 μm, and aluminum is vapor-deposited on the surface (FIG. 3).

[Example 5] Light diffusion sheet: same as in Example 2 Cathode tube: same as in Example 1 Light guide plate: same as in Example 1 Reflective sheet: same as in Example 1 Silver was vapor-deposited on the surface of a polycarbonate sheet. thing

[Example 6] Light diffusing sheet: same as in Example 1 Cathode tube: same as in Example 1 Light guide plate: same as in Example 1 Reflecting sheet: 250 μm thick polycarbonate sheet, semicircular cross section (diameter) A row of valleys of a semicircle of a circle of 100 μm) arranged substantially parallel with a pitch of 120 μm, and aluminum is vapor-deposited on the surface (FIG. 4)

Comparative Example 1 Reflective Sheet: White PET Sheet Conventionally Used Others are the same as in Example 1

Comparative Example 2 Reflective Sheet: Same as Comparative Example 1 Others are the same as Example 2

Comparative Example 3 Light Diffusing Sheet: A Polycarbonate Sheet with a Thickness of 250 μm Forming an Irregular Surface with an Asperity Density of 120 Pieces / inch at a Depth of 150 μm and a Ridge of an Isosceles Right Triangle at a Pitch of 200 μm A polycarbonate sheet having a thickness of 300 μm, which has a structure surface and a smooth surface arranged in parallel,
Stacked so that the latter is on top Reflective sheet: PET reflective sheet that has been conventionally used Others are the same as in Example 1

Table 1 shows the evaluation results of the above examples and comparative examples.
Shown in

[0040]

[Table 1]

[0041]

As described above, the reflection sheet for a planar light emitting device of the present invention can concentrate the light emission distribution on the front surface of the screen. It has a high emission appearance quality that is high and does not generate moire fringes.

[Detailed Description of Drawings]

FIG. 1 is a partial perspective view showing an example of a reflection sheet for a planar light emitting device of the present invention.

FIG. 2 is a partial perspective view showing another example of the reflection sheet for a planar light emitting device of the present invention.

FIG. 3 is a partial perspective view showing another example of the reflection sheet for a planar light emitting device of the present invention.

FIG. 4 is a partial perspective view showing another example of the reflection sheet for a planar light emitting device of the present invention.

FIG. 5 is a cross-sectional view showing an example of the planar light emitting device of the present invention.

FIG. 6 is an explanatory diagram showing a light distribution characteristic of the planar light emitting device of the present invention.

FIG. 7 is a schematic diagram showing a method for measuring the luminance distribution of the planar light emitting device.

FIG. 8 is a cross-sectional view showing a conventional planar light emitting device.

FIG. 9 is an explanatory diagram showing light distribution characteristics of a conventional planar light emitting device that does not use a light diffusion sheet.

FIG. 10 is an explanatory diagram showing a light distribution characteristic of a conventional planar light emitting device using a light diffusion sheet.

FIG. 11 is an explanatory diagram showing a light distribution characteristic of a conventional planar light emitting device using a lens sheet.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light source 2 light guide plate 3 end surface of light guide plate 4 dot pattern 6 liquid crystal panel 7 light diffusion sheet 10, 20, 30, 40 reflection sheet 11, 21, 31, 41 transparent plastic sheet 12, 22 mountain portion 24, 32 valley portion 13, 23, 33, 43 Reflective layer

Claims (6)

[Claims] 1. A structure surface having a plurality of crests having a convex or convex arc-shaped cross section and a plurality of troughs having a concave or concave arc-shaped cross section, which are alternately and substantially parallel to each other. A reflective sheet for a planar light emitting device, comprising a transparent plastic sheet having a smooth surface on which a reflective metal is vapor-deposited on the other surface. 2. A light diffusing sheet, and a light guide plate provided behind the light diffusing sheet and having a dot pattern on the back surface thereof.
A planar light emitting device comprising: a linear light source provided on at least one side surface of the light guide plate; and the reflection sheet according to claim 1 provided behind the light guide plate. 3. A liquid crystal display device comprising a liquid crystal panel on the front surface of the planar light emitting device according to claim 2. 4. A transparent plastic sheet having, on one surface thereof, valley portions having a concave or concave arc-shaped cross section arranged substantially in parallel and having a structural surface on which a reflective metal is vapor-deposited. A reflection sheet for a planar light emitting device. 5. A light diffusing sheet, and a light guide plate provided behind the light diffusing sheet and having a dot pattern on the back surface thereof.
A planar light emitting device comprising: a linear light source provided on at least one side surface of the light guide plate; and the reflection sheet according to claim 4 provided behind the light guide plate. 6. A liquid crystal display device comprising a liquid crystal panel on the front surface of the planar light emitting device according to claim 5.