JPH08227005A - Light control sheet - Google Patents

Abstract

PURPOSE: To prevent optical adhesion and to eliminate interference patterns and the nonunifomity of light emission by providing the surface of a light diffusion sheet on the side in contact with a light transmission plate with a sticking preventive layer consisting of beads and binders. CONSTITUTION: This light control sheet 1 has a light diffusion surface 12 consisting of plural projecting parts 11 on one side surface of a base material sheet 10 and the sticking preventive layer 20 on the opposite side of this light diffusion surface 12. Namely, the rear surface of the base material sheet 10 having the light diffusion surface 12 on the front surface is provided with the sticking preventive layer 20 composed of the beads having transparency and the binders having transparency. In such a case, the beads and the binders have preferably nearly the same refractive indices. As a result, the refraction of light between the beads and the binders doe not arise any more and simultaneously, the reflection of the light between the beads and the binders is prevented at the time when the light transmits from the beads to the binders or from the binders to the beads. The loss by repetitive reflection of the light is lessened and the high-luminance light is supplied to the optical display screen.

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 for use with a light guide plate for guiding a light beam from a light source to a display element in an optical display device such as a liquid crystal display device and an illuminated signboard. More specifically, the present invention relates to a light control sheet for reducing the loss of light by diffusing more light from a light source transmitted to the upper surface of the light guide plate and uniformly diffusing it in the optical display screen direction on the upper surface of the light guide plate. .

[0002]

2. Description of the Related Art Conventionally, as a light source used inside an optical display screen such as a liquid crystal display, an optical display screen is used in order to reduce the size and weight of the optical display device. The edge light system has been adopted in which at least one light source is arranged on the lower side surface.

FIG. 5 shows the inside of an optical display device in which a light guide plate 2 for receiving light from a light source 5 is arranged on the same plane as the light source 5.

In order to supply more light from the light source 5 to the upper surface of the light guide plate 2, dots 3 are printed on the lower surface of the light guide plate 2. The dots 3 reflect and diffuse light, which is repeatedly reflected in the light guide plate 2, toward the upper surface of the light guide plate 2.

Further, a light reflection sheet 4 is disposed on the lower surface of the light guide plate 2 in order to reflect the light transmitted from the gap between the dots 3 to the upper surface of the light guide plate 2, and the optical reflection sheet 4 is provided on the upper surface of the light guide plate 2. A light diffusing sheet 6 for supplying light with uniform brightness is arranged on the display screen.

The light diffusion sheet 6 is disposed on the upper surface of the light guide plate 2 as described above. The surface of the light guide plate 2 forms an optically smooth surface, and the optically smooth surface is formed. When the surface of the light diffusion sheet 6 that is in contact with the surface is an optically smooth surface, there is a problem that optical contact called sticking occurs, which causes an interference pattern and uneven light emission.

Conventionally, in order to prevent sticking, an uneven surface such as matt processing or embossing processing is formed on the surface side of the light diffusion sheet 6 which is in contact with the light guide plate 2 to prevent optical adhesion.

However, in this case, although the optical adhesion can be prevented, a reflection phenomenon of light toward the lower surface of the light guide plate 2 occurs due to the uneven surface such as the mat processing and the emboss processing.
There is a problem that the amount of light emitted to the upper surface of the light diffusion sheet 6 is reduced, that is, the brightness on the upper surface of the optical display screen is reduced.

Therefore, the light diffusion sheet has the effect of preventing the sticking with the light guide plate 2 and also the effect of preventing the decrease in the brightness of the optical display screen, and can be easily manufactured industrially. Was desired.

[0010]

The present invention has been made in order to achieve the above object, and in order to prevent the above-mentioned optical contact, a certain fine gap is provided between the light guide plate and the light diffusion sheet. A light control sheet in which a sticking prevention layer is provided on the surface of the light diffusing sheet that is in contact with the light guide plate so as to maintain the space, and the following (1) to (5) are the gist of the invention.

(1) In a liquid crystal display device, an optical display device such as an illuminated signboard, a light control sheet used together with a light guide plate for guiding a light beam from a light source to a display element, and a light diffusing surface on the upper surface. An optical control sheet, wherein a sticking prevention layer composed of transparent beads and a transparent binder is provided on the lower surface of the base sheet having the above.

(2) The light control sheet according to the above item 1, wherein the beads and the binder have substantially the same refractive index.

(3) The light control sheet as described in 1 or 2 above, wherein the light diffusion surface of the base sheet has a saw-toothed cross section.

(4) The light control sheet as described in 1 or 2 above, wherein the light diffusing surface with the base material sheet has a substantially corrugated cross section.

(5) The light control sheet as described in any one of 1 to 4 above, wherein the surface of the base sheet that contacts the sticking prevention layer is an optically non-smooth surface.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a first embodiment of the present application, which has a light diffusing surface 12 composed of a plurality of protrusions 11 on one surface of a base sheet 10 and a light diffusing surface 12 opposite to the light diffusing surface 12. The surface is the light control sheet 1 having the sticking prevention layer 20.

Here, the projecting portion 11 has a saw-toothed cross section, and each slope of the projecting portion 11 having the sawtooth cross section has
It is formed as the light diffusion surface 12.

In use, as shown in FIG. 5, the lower sticking prevention layer 20 is in contact with the light guide plate 2, and the light diffusion surface 12 on the upper surface of the base sheet 10 is used so as to face the optical display screen. It is something. The above configuration will be described in detail below.

First, as the above-mentioned substrate sheet, polycarbonate (PC) or the like, which is a substance having excellent heat resistance with a heat distortion temperature of about 135 ° C. and further high transparency, can be used. The thickness of the substrate sheet 10 is preferably 20 to 1000 μm, particularly preferably 50 to 250 μm in consideration of light transmittance, refractive index, processing difficulty, handling property, and the like.

The projection portion 11 forming the light diffusing surface 12 is 1 in consideration of light diffusing property, handling property and the like.
It is preferably from 0 to 200 μm, particularly preferably from 20 to 100 μm.

Next, the sticking prevention layer 20 preferably has a thickness of 0.1 to 50 μm, particularly 1 to 15 μm in consideration of the sticking prevention effect and the refractive index.

The anti-sticking layer 20 is composed of beads and a binder. As the beads, beads made of polymethylmethacrylate (PMMA), which is a transparent material, are used.
Considering the refractive index and light diffusivity, etc., the particle size is 0.1 to 50 μm
Further, it is preferable to use the one having a size of 1 to 15 μm.

At this time, it is essential to use the binder together with the beads, and it is preferable to use the binder made of polymethylmethacrylate (PMMA) in consideration of the light transmittance and the refractive index, and the binder (solid content) is used. It is preferable to mix 0.5 to 5% by weight, and further 1 to 2% by weight of the beads.

It is preferable that the beads and the binder have substantially the same refractive index, so that when the light is transmitted from the bead to the binder or from the binder to the bead, the phenomenon of refraction of light between the bead and the binder is prevented. It is possible to prevent light from being reflected between the beads and the binder at the same time, reduce loss due to repeated reflection of light, and supply light with high brightness to the optical display screen.

The beads and the binder of the sticking prevention layer are preferably in the states shown in FIGS. 4a and 4b below.

FIG. 4a shows a binder 22 to beads 21.
Is what stands out. The particle size of the beads 21 is 0.1
It is preferably in the range of ˜50 μm from the viewpoint of coating difficulty, handleability, and effect of preventing sticking. At this time, as a method for dispersing the beads 21 in the binder 22, it is preferable to use a so-called dissolver method or a sand mill method.

FIG. 4 is an enlarged view of a part of FIG. 4a.
b. As shown in this enlarged view, the beads 2 in which only a part of the entire beads 21 in the binder 22 are projected
1a and beads 21b which are entirely embedded may be mixed. This further improves the light diffusivity.

FIG. 2 shows a second embodiment of the present invention, which is the first embodiment.
As in the above embodiment, since it is composed of the base sheet 10 having a plurality of protruding portions 11 on the upper surface and the sticking prevention layer 20 formed on the lower surface of the base sheet, the same constituent member is The same reference numerals as in the examples are added.

However, it differs from the first embodiment in that the lower surface of the base sheet 10 is an optically non-smooth surface 15.

Here, the optically non-smooth surface 15 of the base sheet 10 is one in which irregularities of 1 to 15 μm are formed, and by having the non-smooth surface 15, the sticking prevention layer is provided. The sticking prevention effect can be obtained without the provision of. However, incident light is reflected by the uneven slope of the non-smooth surface 15,
Repeated refraction causes loss of light supplied to the optical display screen.

However, according to the present invention, by filling the non-smooth surface 15 with a binder, light reflection and diffusion by the non-smooth surface can be prevented and the amount of light transmitted to the base sheet 10 can be increased. Sheet 1.

Further, the projecting portion 11 has a saw-toothed cross section as in the first embodiment of the present invention, and each slope of the projecting portion 11 is formed as a light diffusing surface 12.

In use, as shown in FIG. 5, the lower sticking prevention layer 20 is in contact with the light guide plate 2, and the light diffusion surface 12 on the upper surface of the base sheet 10 is used so as to face the optical display screen. It is something.

The configurations of the base sheet 10 and the sticking prevention layer 20 are the same as in the first embodiment of the present application.

FIG. 3 shows a third embodiment of the present invention, which is the first embodiment.
As in the above embodiment, since it is composed of the base sheet 10 having a plurality of protrusions 13 on the upper surface and the sticking prevention layer 20 formed on the lower surface of the base sheet, the same constituent member may include the first The same reference numerals as in the examples are added.

However, unlike the first embodiment in that the shape of the protrusions 13 on the upper surface of the base sheet 10 is substantially corrugated in cross section, the protrusions 13 having the substantially corrugated cross section are provided. The light control sheet has an effect of preventing damage to the apexes of the protrusions.

Here, the projecting portion 13 having a substantially wave-shaped cross section.
The contour line of the cross section corresponds to a sine wave or a cosine wave curve, and a plurality of protrusion portions 13 having a substantially wave cross section are formed on the base sheet 10.
It has a shape protruding on the surface. Then, an inclined curved surface of the sine wave curve is formed as the light reflecting surface 14.

In use, as shown in FIG. 5, the lower sticking prevention layer 20 is in contact with the light guide plate 2, and the light diffusion surface 14 on the upper surface of the base sheet 10 is used so as to face the optical display screen. It is something.

The configurations of the base sheet 10 and the sticking prevention layer 20 are the same as those of the first embodiment of the present application.

Example 1 One side of which was embossed with a saw-toothed cross section and had a thickness of 13
As a sticking prevention layer, beads made of polymethylmethacrylate (PMMA) were mixed in a PMMA binder at a ratio of 80: 1 on the lower surface of a 0 μm polycarbonate (PC) base sheet, and a well-known MB roll was prepared. The present invention was obtained by applying a coating method with a coating thickness of 3 μm and forming a sticking prevention layer under a drying condition of 110 ° C. for 60 seconds.

Example 2 Polycarbonate having a thickness of 130 μm, which is embossed with a saw-toothed cross section on one side and has an optically non-smooth surface (fine matte surface) on the surface opposite to the embossed surface. As a sticking prevention layer, polymethylmethacrylate (PMMA) beads were mixed in a PMMA binder at a ratio of 80: 1 on the lower surface of a (PC) base material sheet, and a well-known MB roll coating method was used. This was applied to a coat thickness of 3 μm and a sticking prevention layer was formed under drying conditions of 110 ° C. for 60 seconds to obtain Invention B.

Example 3 Thickness 1 with one side being embossed with a substantially wave-shaped cross section
As a sticking prevention layer, beads made of polymethylmethacrylate (PMMA) were mixed in a PMMA binder at a ratio of 80: 1 on the lower surface of a 30 μm polycarbonate (PC) base sheet, and a well-known MB roll was prepared. The present invention C was obtained by applying a coating having a coating thickness of 3 μm using a coating method and forming a sticking prevention layer under a drying condition of 110 ° C. for 60 seconds.

Referring to FIG. 5, each of the above sheets A to C is provided with a light source 5, a 4 mm thick acrylic light guide plate 2 having dots 3 on the lower surface, and a light reflection layer laid on the lower surface of the light guide plate 2. The sticking prevention effect and the front brightness were measured using the backlight unit composed of the sheet 4.

To confirm the sticking prevention effect, the sheets A to C are stacked on the acrylic light guide plate 2 whose upper surface is mirror-finished, and light is emitted from the light source 5 of the backlight unit. , A to C sheets are pressed against the surface of the light guide plate 2 with fingers, and the change in transmitted light is observed, and the central vertical portion of the upper surface of each sheet of A to C is set to 0.
The presence / absence of interference fringes was observed from a position at an angle of +90 to −90 degrees, which is defined as degrees.

For measuring the front luminance, a luminance measuring device "B
M-7 "(manufactured by Topcon Co., Ltd.) was used at a position where the central vertical portion of the upper surface of each of the sheets A to C was 0 ° and the height was 30 cm.

As a comparative example, a substrate sheet made of polycarbonate (PC) having a thickness of 130 μm and having a saw-tooth cross-section embossed on one side is designated as A ′, and one side has a saw-tooth cross-section emboss. B'that has been processed and has an optically non-smooth surface on the surface opposite to the embossed surface
Then, the test in which the sticking prevention effect and the front luminance were measured under the same conditions was performed with C'having one side of which embossed with a substantially wave-shaped cross section.

Table 1 shows the above measurement results.

[0049]

[Table 1]

As is clear from the above results, A of the present invention
Compared with A'and C'of Comparative Examples, C and C have a sticking prevention effect, and the front brightness is reduced by about 0.06 to.
It was found that the amount decreased only in a small range of 0.25% and had no effect on actual use.

Further, B of the present invention is provided with a sticking prevention layer, so that the front luminance of B'of the comparative example is about 0.
I was able to improve by 09%.

Accordingly, in order to prevent sticking, in B'having the uneven surface on the side of the light diffusion sheet which is in contact with the light guide plate, the brightness due to the phenomenon of reflection of light toward the lower surface of the light guide plate by the uneven surface is obtained. It was found that the decrease in

Therefore, it was found that the sticking prevention layer in the light control sheet of the present invention can completely prevent optical adhesion, that is, sticking, without lowering the front brightness of the conventional light diffusion sheet.

[0054]

The light control sheet according to the present invention is
As described above, the light control in which the sticking prevention layer including the beads and the binder is provided on the surface of the light diffusing sheet that is in contact with the light guide plate so as to maintain a constant fine distance between the light guiding plate and the light diffusing sheet. The sheet prevents optical contact called sticking when the sheet is arranged on the upper surface of the light guide plate, and simultaneously prevents interference patterns and uneven light emission.

Conventionally, as a means for preventing sticking, an uneven surface is formed on one surface of the light diffusing sheet which is in contact with the light guide plate. However, due to the reflection of light in the light guide plate direction by the uneven surface, an optical display screen is formed. Although there is a problem that the brightness is lowered on the upper surface, such a light diffusion sheet can also be used in the present invention.

That is, according to the present invention, by forming a sticking prevention layer on the uneven surface of the light diffusion sheet on the light guide plate side, a new sticking prevention layer is provided and beads forming the sticking prevention layer are provided. Also, since the binders have the same refractive index, it is possible to prevent a decrease in brightness.

Therefore, the present invention has the effect of preventing sticking with the above-mentioned light guide plate, and also has the effect of preventing a decrease in the brightness of the optical display screen, and can be easily manufactured industrially. It is a light control sheet.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of a first embodiment of a light control sheet of the present invention.

FIG. 2 is a partial cross-sectional view of a second embodiment of the light control sheet of the present invention.

FIG. 3 is a partial cross-sectional view of a third embodiment of the light control sheet of the present invention.

FIG. 4 is a partially enlarged view of a sticking prevention layer of the light control sheet of the present invention.

FIG. 5 is a partial cross-sectional view of the inside of the optical display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light control sheet 2 ... Light guide plate 3 ... Dot 4 ... Light reflection sheet 5 ... Light source 6 ... Light diffusion sheet 10 ... Base material sheet 11, 13 ... Projection part 12, 14 ... Light diffusion surface 15 ... Non-smooth surface 20 ... Sticking prevention layer 21, 21a, 21b ... Bead 22 ... Binder

Claims (5)

[Claims] 1. A light control sheet for use with a light guide plate for guiding a light beam from a light source to a display element in an optical display device such as a liquid crystal display device and an illuminated signboard, which has a light diffusing surface on its upper surface. An optical control sheet, wherein a sticking prevention layer composed of transparent beads and a transparent binder is provided on the lower surface of the substrate sheet. 2. The light control sheet according to claim 1, wherein the beads and the binder have substantially the same refractive index. 3. The light control sheet according to claim 1, wherein the light diffusion surface of the base sheet has a saw-toothed cross section. 4. The light control sheet according to claim 1, wherein the light diffusion surface of the base sheet has a substantially wavy cross section. 5. The light control sheet according to claim 1, wherein a surface of the base sheet which is in contact with the sticking prevention layer is an optically non-smooth surface.