JP3378690B2 - Light control sheet - Google Patents

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.

[0011] (1) and the base sheet having a light diffusing surface on surface, formed on the lower surface of the substrate sheet, and transparency sticking layer composed of a binder having a bead and transparency with And has the base sheet
The surface in contact with the anti-sticking layer is an optically non-smooth surface
Is a light control sheet.

[0012] (2) the beads and the light control sheet according to (1) a predicate on the refractive index of each of said binder Ru substantially identical der.

[0013] (3) Light control sheet described in (1) or (2) the predicate on the light diffusing surface of the substrate sheet Ru sectional serrated der.

[0014] (4) Light control sheet according to the light diffusing surface of the substrate sheet is a predicate on Ru cross section wave shape der (1) or (2).

(5) Liquid crystal display device
Light from a light source in an optical display device such as a display or an illuminated signboard
Light control sheet according to any of the above that are used in conjunction with the light guide plate for guiding (1) to the display element (4).

[0016]

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

FIG. 1 is a reference example of a light control sheet, in which a plurality of protrusions 1 are formed on one surface of a base sheet 10.
The light control sheet 1 has a light diffusing surface 12 of 1 and a sticking prevention layer 20 on the surface opposite to the light diffusing surface 12.

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 about 20 to 1000 μm ·, particularly preferably about 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 from 20 to 100 μm ·.

Next, the sticking prevention layer 20 preferably has a thickness of about 0.1 to 50 μm, particularly about 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
It is preferable to use one having a thickness of about 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 within 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.

[0029] Figure 2 is a real施例of the present application, the reference example <br/> Like the substrate sheet 10 having a plurality of protrusion 11 on the upper surface, sticking prevention formed on the base sheet lower surface Since it is composed of the layer 20, the same components are designated by the same reference numerals as in the reference example .

However, it differs from the reference example 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 an uneven shape of 1 to 15 μm is formed, and the presence of the non-smooth surface 15 prevents sticking. The sticking prevention effect can be obtained without providing a layer. 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 protruding portion 11 has a saw-toothed cross section as in the reference example, and each slope of the protruding portion 11 is
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 structures of the base sheet 10 and the sticking prevention layer 20 are the same as in the reference example .

FIG. 3 shows another reference example , which is similar to the above-mentioned reference example , in which a base sheet 10 having a plurality of protrusions 13 on the upper surface thereof and a sticking prevention formed on the lower surface of the base sheet. Since it is composed of the layer 20, the same components are designated by the same reference numerals as those in the above-mentioned reference example .

However, unlike the above-mentioned reference example in that the shape of the projection portion 13 on the upper surface of the base sheet 10 is substantially wavy in cross section, the projection portion 13 having the substantially wavy cross section has It is a light control sheet having an effect of preventing damage to the tops of parts.

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 in the above-mentioned reference example .

Reference Example 1 Embossing with a saw-tooth cross section on one side, thickness 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 coating method was applied to a coat thickness of 3 μm, and a sticking prevention layer was formed under a drying condition of 110 ° C. for 60 seconds to obtain a light control sheet A according to Reference Example 1 .

[0042] Example one surface section serrated embossing is performed, and, on the surface opposite to the embossing, optically with a non-smooth surface (fine matted surface), a thickness of 130μm Polycarbonate ( As a sticking prevention layer, beads made of polymethylmethacrylate (PMMA) are mixed in a binder made of PMMA at a ratio of 80: 1 on the lower surface of a base material sheet made of PC) and a well-known MB roll coating method is used. Te, was applied to coat thickness 3 [mu] m, drying conditions 110 ° C., to form a sticking prevention layer for 60 seconds, the light co according to example
A control sheet B was obtained.

Reference Example 2 One side of which is embossed with a substantially wave-shaped cross section and has a thickness of 1
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. Using the coating method, a coating thickness of 3 μm was applied, and a sticking prevention layer was formed under a drying condition of 110 ° C. for 60 seconds to obtain a light control sheet C according to Reference Example 2 .

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 a 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 embossed. 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.

[Table 1] As is clear from the above results, Reference Example 1 (A) and Reference
Consideration 2 (C) has an effect of preventing sticking and a reduction in front luminance of about 0, compared with A'and C'of Comparative Examples.
It was found that the amount decreased only in a small range of 06 to 0.25% and had no effect on actual use.

Further, in Example (B) of the present invention, by providing the sticking prevention layer, the front luminance of B'of Comparative Example could be improved by about 0.09%.

Accordingly, in order to prevent sticking, in B'having the uneven surface on the side of the light diffusing sheet 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 produced. 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 contact, that is, sticking, without lowering the front brightness of the conventional light diffusion sheet.

[0052]

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, an optical display screen is formed by light reflection toward the light guide plate by the uneven surface. 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 reference example of a light control sheet.

2 is a partial cross-sectional view of the solid施例light control sheet of the present invention.

FIG. 3 is a partial cross-sectional view of another reference example of the light control sheet.

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]

1 ... Optical control sheet 2 ... Light guide plate 3 dots 4 ... Light reflection sheet 5 ... Light source 6 ... Light diffusion sheet 10 ... Base sheet 11, 13 ... Projection 12, 14 ... Light diffusing surface 15 ... Non-smooth surface 20 ... Sticking prevention layer 21, 21a, 21b ... beads 22 ... Binder

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02B 5/02

Claims (5)

(57) [Claims] A base sheet having a 1. A light diffusing surface on surface, formed on the lower surface of the substrate sheet, and a transparent sticking layer composed of a binder having a bead and transparency with The surface of the base sheet that contacts the sticking prevention layer has a light
A light control sheet that has a non-smooth surface . Wherein said beads and light control sheet according to 請 Motomeko first refractive index Ru nearly identical Der of each of said binder. 3. The light control sheet of the light diffusing surface of the substrate sheet according to 請 Motomeko 1 or 2 Ru sectional sawtooth der. 4. The light control sheet according to 請 Motomeko 1 or 2 light diffusing surface Ru cross section wave shape der of the base sheet. 5. A liquid crystal display device and an electric lamp exclusively.
Displays the light from the light source in an optical display device such as a signboard.
Use with a light guide plate for guiding light to a child.
The optical control sheet according to any one of 1 to 4.