JPH10175260A - Composite resin sheet and face light source element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent dust or foreign matter from sticking to a resin sheet by using the resin sheet consisting of adjacent resin layers whose refractive index varies and (a) value is a specific value in formula expressing an uneven state in the X direction of an uneven shape formed on the border with at least, one of the resin layers in the X-Y cross section, given the thickness direction of a sheet as Y and the width direction as X. SOLUTION: The resin sheet consisting of a resin (c) formed between the counter- faced uneven faces of a resin (a) and a resin (b) is used as a light guide 1. In addition, the surface on which a light turning sheet 4 is laminated serves as the top face of the resin sheet with a face light source 3 set each in the X, Y and Z direction. The light source 3 is set on the Y-Z face as at least, one of the faces, in the X direction, of the light guide 1. As the interface of the resin layer is uneven, a light is transmitted through the interface or the surface according to the Snell's rule. Further, the light exceeding a critical angle is emitted, and the rate of emission is accepted, if the (a) value influencing the interfacial line between the resin layers is about 5-45 deg. by formula. In this case, f(X) is a formula in which the uneven shape of the interface of the X-Y cross section is expressed as function of X; and L is the length of the sheet in the width (X) direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite resin sheet suitable for a light guide sheet, a light diffusion sheet, a visibility control sheet, and the like, and a surface light source element using the same as a light guide.

[0002]

2. Description of the Related Art As a light diffusing sheet having an uneven shape on the surface, there is known a method in which a thermoplastic transparent resin sheet is superposed on a mold having an uneven shape and heated and pressed. Further, as a visibility control sheet, a sheet in which a light shielding layer is provided on the surface of a transparent resin sheet having an uneven shape is known. These sheets can be used as lighting covers or signboards, or diffusers for display devices that project light from behind,
Widely used for light guides, building materials and other applications. or,
Sheets requiring decorativeness are required to have a sense of depth, and sheets subjected to light and shade printing, shadow printing, and the like are used.

On the other hand, as a back light source device used for a liquid crystal display device, a signboard, a traffic guide plate, and the like, there is an edge light type in which a linear light source is arranged on an end face of a plate-shaped light guide. Such an edge light type back light source device
Usually, a plate-shaped transparent material such as an acrylic resin plate is used as the light guide,
This is a device in which light from a light source disposed at one end of the light guide is made incident on the light guide, and light is emitted from the surface (light emission surface) of the light guide in a planar manner. The light guide used here usually has a light scattering portion and / or a light diffusion portion formed on the front surface or the back surface. In such a surface light source element, it is necessary to ensure the uniformity of the luminance of the emitted light without being affected by the distance from the light source. This performance is particularly important for large surface light source elements.

Japanese Patent Application Laid-Open No. Hei 8-127159 discloses a surface light source element in which a light diffusing substance such as titanium white is printed in the form of dots on the surface of a light guide and a prism sheet is mounted on a light emitting surface. . Such a surface light source element can obtain uniformity of luminance by changing the dot coverage according to the distance from the light source.

Japanese Patent Application Laid-Open No. 2-84618 discloses a surface light source element in which a prism sheet is mounted on a light exit surface with a surface (light exit surface) of the light guide and at least one of the rear surfaces thereof having a matte surface. Has been disclosed. Such a surface light source element can obtain extremely high luminance.

[0006]

However, in the case of a light diffusing sheet having an uneven surface, dust and foreign matter easily adhere to the irregular surface of the surface, and it is difficult to secure the performance due to dropout or damage of the convex portion on the surface. And so on. In addition, the above-mentioned visibility control sheet has a similar problem.
In contrast, in the case of light and shade printing or shadow printing, the three-dimensional effect and the depth effect are insufficient, and the appearance is not always satisfactory.

Further, in a light guide having a dot pattern, the dots must be concealed by a sheet having a light diffusing property, which results in a decrease in luminance and a complicated structure of the surface light source element. Has become. Further, the conventional light guide having a matte surface does not satisfy the uniformity of the luminance of the emitted light.

SUMMARY OF THE INVENTION An object of the present invention is to provide a sheet to which dust and foreign matter are hardly adhered and to which optical functions such as light diffusion and visibility control are imparted, and a surface light source element having excellent uniformity of emitted light luminance. Is to provide.

[0009]

SUMMARY OF THE INVENTION The gist of the present invention is to provide a resin sheet having a laminated structure in which a transparent resin layer c is sandwiched between a transparent resin layer a and a transparent resin layer b and having a smooth outer surface. In addition, the refractive index of the resin of the adjacent resin layers is different, and when the thickness direction of the sheet is defined as y and the width direction is defined as x, at least one of the boundaries of the resin layer in the xy cross section has an uneven shape, In the following expression representing the unevenness state of the unevenness in the x direction, a
Resin sheet having a value of 5 to 45 degrees.

[0010]

(Equation 3)

Here, f (x) is an equation representing the uneven shape of the boundary surface of the xy section as a function of x. L is the length of the sheet in the width (x) direction.

The gist of the present invention is that a resin sheet having a laminated structure composed of a transparent resin layer a and a transparent resin layer b has a smooth outer surface, and the refractive index of the resin of the adjacent resin layer. When the thickness direction of the sheet is y and the width direction is x, an uneven shape is formed at the resin layer boundary in the xy cross section.
It is on a resin sheet at ~ 45 degrees.

Further, the gist of the present invention is that the above-mentioned resin sheet is used as a light guide, a reflecting material is provided on the back surface of the light guide, and at least one end face (yz plane) in the x direction of the light guide. A surface light source element is provided with a light source, and a light diverting sheet having a function of changing light emitted from the surface of the light guide in a direction normal to the light guide is provided on the surface of the light guide.

In the resin sheet having a two-layer structure or a three-layer structure according to the present invention, the x direction, the y direction, and the z direction are orthogonal triaxial directions, y is the thickness direction, x is the width direction, and The shape is formed in the xy section toward the x direction.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIGS. 1 to 11 show an uneven state in the xy cross section of the resin sheet. Various shapes such as the following parabolic shape can be taken. FIG.
A shape without regularity as shown in FIG. 11 can also be taken.
6 to 11 show a resin sheet composed of three resin layers. The resin sheets shown in FIGS. 9 and 10 have a planar boundary surface between the second layer and the third layer.

The resin used for each resin layer constituting the resin sheet includes polyethylene terephthalate, polyvinyl chloride, polystyrene, polycarbonate, acrylic resin, amorphous polyolefin, polyamide, copolymer resin thereof, and blend resin. And the like.

The difference between the refractive indices of the resins in the adjacent resin layers is 0.1.
It is preferably from 1 to 0.3. If the difference in refractive index is too small, the effect of diffusing light is weakened. On the other hand, if the refractive index difference is too large, it is necessary to use a special resin, which increases the cost. Preferred combinations of resins include polycarbonate, polyethylene terephthalate,
Examples include a combination of polystyrene or polyethylene with polymethyl methacrylate having good transparency and weather resistance. In addition, it is preferable to select a resin in consideration of the adhesiveness between adjacent resins.

In the case of a three-layer resin sheet, the resins a and b on both surfaces may be the same resin or different resins. However, in consideration of prevention of sheet warpage, it is preferable to use the same resin or a resin having a similar water absorption.

In the case where the resin sheet is given a design property or a sense of depth, or in the case where optical properties such as light diffusion properties are given, organic and inorganic dyes / pigments,
A light diffusing agent or the like can be added.

The resin sheet of the present invention can be produced by, for example, coextrusion using a melt extruder so that the resin a and the resin b or the resin c is laminated. Further, the resin sheet of the present invention is obtained by pouring a raw material (monomer or the like) of another resin b onto an uneven surface of a resin a sheet having an uneven shape formed on one surface and then polymerizing the same. It can be manufactured by doing. Further, the resin sheet of the present invention comprises a sheet of resin a and a sheet of resin b, each of which has an irregular shape formed on one surface thereof, opposing each other at a predetermined interval on each of the irregular surfaces, and the other resin c therebetween. Can be produced by pouring the raw material and polymerizing it.

Next, the surface light source device of the present invention will be described. Since the resin sheet of the present invention has excellent light diffusing properties, it can be used as a light guide of a surface light source element.

With respect to the surface light source element, the same directions as the x, y, and z directions of the resin sheet constituting the surface light source are defined as the x, y, and z directions, respectively. For the light guide (resin sheet), for convenience of explanation, the side on which the reflecting material 2 is attached is referred to as the back surface (or the lower surface), and the side on which the light diverting sheet 4 such as a prism is laminated is referred to as the front surface. (Or top). Therefore, these vertical relations do not always coincide with the vertical relation when the surface light source element is actually used.

In the surface light source device of the present invention, the light source 3 is provided on at least one end surface (yz surface) of the light guide in the x direction. In FIG. 12, only one end face is provided.
A reflecting material is appropriately applied to the other two or three end surfaces where the light source is not installed.

When the light guide is composed of two or more resin layers having different refractive indices, and the interface between the resin layers has an uneven shape, light is transmitted at the interface and the surface of the light guide according to Snell's law. The light propagates through the light guide while repeating reflection or refraction. Of the light that reaches the front or back surface of the light guide,
Light exceeding the critical angle exits the light guide.

The inventors of the present invention have found that in the surface light source element, the relationship between the light emission intensity (I) at a certain point and the light emission intensity (I ₀ ) at the end of the light incident surface is as follows: It was experimentally found that the distance (L ') from the light incident surface and the thickness (t) of the light guide were expressed by the following equation (1).

[0026]

(Equation 4)

If the length (L) and the thickness (t) of the light guide are determined from the equation (1), the uniformity of the luminance in the light emission surface is determined by the emission rate (ψ). I understand.

The emission rate (ψ) of the light guide is obtained by measuring the luminance at the center of the light guide in the z-direction at intervals of 20 mm from the light incident surface, and measuring the ratio of the distance from the light incident surface to the thickness. (L '/ t) is plotted on the horizontal axis, and the logarithm of luminance is plotted on the vertical axis, and its slope (K) is obtained, which is obtained by the following equation (2).

Ψ = (1−10K) × 100 (2) In the present invention, as a measure of the uniformity of the luminance distribution, the degree of variation (R%) represented by the following equation (3) is used. Then, the uniformity of the luminance distribution in the surface light source element was evaluated and examined. The degree of variation (R%) is approximately 15 mm away from the light-incident end face in the x-direction from the light-incident end face in the substantially central portion in the z-direction of the light guide. Is measured at intervals of 20 mm within the range, and the maximum value of the measured luminance (Imax), the minimum value of the measured luminance (Imin), and the average value of the measured luminance (Iav) are obtained, and are obtained by the following equation (3).

R% = {(Imax−Imin) / Iav} × 100 (3) As a result, the emission rate (ψ) and the degree of variation (R%) are determined by the length (L) of the light guide. And a specific relationship depending on the thickness (t). When the emission rate (ψ) increases, the degree of variation (R%) increases accordingly, and the emission rate (ψ) remains constant. If present, the ratio (L) of the length (L) to the thickness (t) of the light guide is
/ T) increases, the degree of variation (R%) also increases. That is, in a light guide of a certain size,
The uniformity (degree of variation) of the luminance distribution in the light exit surface of the light guide 1 depends on the exit rate (ψ) from the light guide, and the luminance is controlled by controlling the exit rate (ψ). Uniformity of distribution can be achieved.

On the other hand, it is necessary for the surface light source element to efficiently emit the light incident from the incident end face from the light emitting face. Therefore, the light emission rate (ψ) of the light guide must be a certain value or more. If the emission rate is too low, the amount of light that reciprocates in the light guide without being emitted from the emission surface increases. In other words, the emission rate (ψ) of the light guide should be set to an optimal value corresponding to the size of the light guide in consideration of both the uniformity of the brightness distribution and the high brightness in each region of the light emission surface. is required.

As a resin sheet suitable for such a light guide, a difference in refractive index between resins of adjacent resin layers is 0.03.
It is preferably from 0.3 to 0.3, more preferably from 0.05 to 0.25, and particularly preferably from 0.05 to 0.20. If the refractive index difference is too small, the change in the traveling direction of the light at the resin interface is too small, and the emission rate (率) of the light guide becomes small. Conversely, if the difference in the refractive index is too large, the change in the traveling direction of the light at the resin interface is too large, and the emission rate (ψ) of the light guide increases.

A preferred resin combination is polycarbonate.
-A combination of polyethylene, polyethylene tererate, polystyrene or polyethylene with polymethyl methacrylate.

When the resin sheet of the present invention is used as a light guide for a surface light source element, the emission ratio of the light guide is as shown in FIGS.
Is affected by the a value of the boundary line between the resin layers. a value is 5
Preferably, it is about 45 degrees. In addition, a value is shown in FIGS.
These values are calculated not only in the uneven state clearly shown in FIG. 11 but also in the fine uneven state not explicitly shown in these figures.

When the resin sheet of the present invention is used as a light guide in an edge light type surface light source element as shown in FIG. 12, the light emitted from the surface of the light guide is
The direction showing the maximum intensity is x
It is inclined more than 50 degrees in the direction. Therefore, it is necessary to change the direction of the emitted light to the normal direction where the observer is located. Therefore, in the surface light source element of the present invention, the light diverting sheet 4 is mounted on the light guide. The light diverting sheet means a sheet capable of changing the traveling direction of light.

Examples of the light diverting sheet include a diffusion sheet and a lens sheet in which a large number of columnar lens units are arranged on at least one surface so as to be parallel to the longitudinal direction of the column.

[0037]

The present invention will be described below with reference to examples. still,
The evaluation method of the surface light source element is as follows.

1) Measurement of Luminance in Normal Direction As shown in FIG. 13, a 20 mm wide portion at the center of the light emitting surface of the surface light source element in the z direction was used as a measurement region. Excluding the first 5 mm in the x direction from the light incident surface, the light incident surface is divided into squares of 20 mm square, and these are defined as regions 1, 2, 3, ..., n. A cold cathode tube (KC130T4E 4 mmφ × 130 m) installed on one end surface (yz surface) in the x direction of the light guide
m, manufactured by Matsushita Electric Industrial Co., Ltd.)
(CXA-M10L) and a DC1
Lighting is performed by applying 2V.

The surface light source element is mounted on a measuring table. Next, the optical axis of a luminance meter (nt-1 ° manufactured by Minolta Co., Ltd.) is made to coincide with the normal direction of the xz plane passing through the center of the measurement area 1. Further, the luminance meter is fixed at a distance from the surface light source element so that the measurement circle of the luminance meter is 8 to 9 mmφ. In this state, the normal luminance of the measurement area 1 is measured, and this value is defined as G1. The surface light source element is moved by 20 mm in the x direction, and the normal luminance value of the area 2 is measured, and this value is defined as G2. By repeating this operation, the normal luminance value is measured for all the regions G1 to Gn.

2) Emission Rate Using the values of G1 to Gn measured in 1), the horizontal axis represents the distance (L) between the distance between the center of each measurement area and the light incident end of the light guide and the light guide thickness. '/ t) and the vertical axis is the logarithm of the normal luminance (logG
1,..., LogGn). After obtaining the slope (K) of the straight line obtained by the plot, the emission rate (ψ) is obtained by the above equation (2).

3) Variation (R%) Among G1 to Gn measured in the above 1), the maximum value is I
Assuming that max is the minimum value, Imin is the average value, and Iav is the average value, R% is calculated from the above equation (3).

Example 1 Polycarbonate (Iupilon H-3000 manufactured by Mitsubishi Gas Chemical Co., Ltd.) was used as resin a and resin b, and polymethyl methacrylate (Acrypet VH manufactured by Mitsubishi Rayon Co., Ltd.) was used as resin c.

Resins a and b were sandwiched between a mold having an uneven surface and a mold having a smooth surface, respectively, and two sheets whose shapes were transferred by hot pressing were manufactured. Next, a resin sheet having a thickness of 3 mm was obtained by sandwiching the resin c between the uneven surfaces of the two sheets and hot pressing (FIG. 1).
1).

The a value of this resin sheet was 17 degrees. The outer surface was smooth, without warpage, and had good appearance and light transmittance.

Example 2 Polycarbonate (Iupilon H-3000 manufactured by Mitsubishi Gas Chemical Co., Ltd.) was used as resin a, and polymethyl methacrylate (Acrypet VH manufactured by Mitsubishi Rayon Co., Ltd.) was used as resin b.

A sheet having a resin b sandwiched between a metal mold having an uneven surface and a metal mold having a smooth surface was transferred by hot pressing to produce a sheet. Next, the resin a was sandwiched between the uneven surface of the sheet and a mold having a smooth surface, and a resin sheet having a thickness of 3 mm was obtained by hot pressing (FIG. 5).

The a value of this resin sheet was 20 degrees. The outer surface was smooth, without warpage, and had good appearance and light transmittance.

Embodiment 3 This is an embodiment of a small surface light source element. The resin sheet obtained in Example 1 was 100 mm long in the z direction and 30 mm long in the x direction.
It was cut into 0 mm to obtain a light guide (small surface light source element) for measuring the emission ratio.

A silver-deposited PET film is adhered to the two xy end faces in the length direction of the light guide with an adhesive, and the silver-deposited PET film is taped on the back surface of the light guide to form a reflection surface. did. Further, a cold-cathode tube was placed beside the other yz end face of the light guide such that the long side of the tube was in the z direction, and the cold-cathode tube and the light guide were covered with a silver-evaporated PET film.

On the other hand, a large number of columnar prism units having a vertical angle of 63 degrees and a pitch of 50 microns are formed on a PET film using an acrylic ultraviolet curable resin having a refractive index of 1.53 so that their longitudinal directions are parallel to each other. -Was manufactured.
This was placed on the surface of the light guide, with the prism surface facing downward and the longitudinal direction of the prism unit being in the z direction. When the emission efficiency of the small surface light source element manufactured as described above was evaluated, the emission efficiency was 1.91.

Similarly, the resin sheet obtained in Example 1 was cut into a length of 100 mm in the z direction and a length of 105 mm in the x direction. For this light guide, two xy end faces and one y
A PET film with silver deposited on the z end face was adhered with an adhesive, and a cold cathode tube was placed beside another yz end face of the light guide.
The other conditions were the same as described above to produce and evaluate a small surface light source element for evaluating the degree of variation.
%Met.

Example 4 A surface light source was manufactured in the same manner as in Example 3 using the sheet of Example 2. The emission rate is 2.23, and the variation is 23%.
Met.

Comparative Example 1 3 mm × 100 mm (z direction) × 105 mm (x direction)
A spot pattern was formed by screen printing using a white paint containing titanium oxide particles on the back surface of the acrylic resin plate. At this time, the density of the spots was low near the light incident side end face, and increased as the distance from the light incident face in the x direction increased. Using this as a light guide, a small surface light source element was manufactured in the same manner as in Example 3. In this surface light source element, the degree of variation was as small as 12%, but spot patterns were observed through the prism.

[0054]

According to the present invention, a sheet to which dust and foreign matter are hardly adhered and which is provided with an optical function such as light diffusing property and visibility control property, and a design sheet having a deep feeling and a three-dimensional feeling. Etc. are provided. Further, the surface light source element using this sheet as a light guide is excellent in uniformity of luminance of emitted light.

[Brief description of the drawings]

FIG. 1 is a diagram showing an uneven state in an xy cross section of a resin sheet.

FIG. 2 is a diagram showing an uneven state in an xy cross section of a resin sheet.

FIG. 3 is a diagram showing an uneven state in an xy cross section of the resin sheet.

FIG. 4 is a diagram showing an uneven state in an xy cross section of the resin sheet.

FIG. 5 is a diagram showing an uneven state in the xy cross section of the resin sheet.

FIG. 6 is a diagram showing an uneven state in the xy cross section of the resin sheet.

FIG. 7 is a diagram showing an uneven state in the xy cross section of the resin sheet.

FIG. 8 is a diagram showing an uneven state in the xy cross section of the resin sheet.

FIG. 9 is a diagram showing an uneven state in the xy section of the resin sheet.

FIG. 10 is a diagram showing an uneven state in an xy cross section of the resin sheet.

FIG. 11 is a diagram showing an uneven state in the xy cross section of the resin sheet.

FIG. 12 is a perspective view of a surface light source element.

FIG. 13 is a diagram showing a method for evaluating a surface light source element.

[Brief description of reference numerals]

 DESCRIPTION OF SYMBOLS 1 Light guide 2 Reflector 3 Fluorescent lamp 4 Light deflection sheet 5 Surface light source element 6 Luminance meter

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masaharu Oda 3816 Noborito, Tama-ku, Kawasaki City, Kanagawa Prefecture Mitsubishi Rayon Co., Ltd. Tokyo Technology and Information Center

Claims (3)

[Claims] An outer surface of a laminated resin sheet having a transparent resin layer c sandwiched between a transparent resin layer a and a transparent resin layer b is a smooth resin sheet. When the refractive index is different and the thickness direction of the sheet is y and the width direction is x, an uneven shape is formed on at least one of the resin layer boundaries in the xy cross section, which represents the unevenness of the unevenness in the x direction. A resin sheet having an a value of 5 to 45 degrees in the following formula. (Equation 1) Here, f (x) is a formula expressing the uneven shape of the boundary surface of the xy section as a function of x. L is the length of the sheet in the width (x) direction. 2. A resin sheet having a laminated structure composed of a transparent resin layer a and a transparent resin layer b and having a smooth outer surface, wherein the adjacent resin layers have different refractive indices. When the thickness direction is y and the width direction is x, an uneven shape is formed at the resin layer boundary in the xy cross section, and the a value is 5 to 45 degrees in the following equation representing the unevenness state of the unevenness in the x direction. Resin sheet. (Equation 2) Here, f (x) is a formula expressing the uneven shape of the boundary surface of the xy section as a function of x. L is the length of the sheet in the width (x) direction. 3. The resin sheet according to claim 1 or 2 as a light guide, a reflective material provided on the back surface of the light guide, and at least one end face (yz) of the light guide in the x direction. A surface light source element in which a light source is installed on a surface of a light guide, and a light diverting sheet having a function of changing light emitted from the surface of the light guide in a normal direction of the light guide is installed on the surface of the light guide.