JPH09160507A - Surface light source device using non-light-diffusive light guide plate, and lens film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface light source device having a good light utilization efficiency and a luminance distribution sharp in the normal direction of its light-emitting surface and to provide a lens film therefor. SOLUTION: This surface light source device has a light source 2 placed on the side end face of a non-light-diffusive light guide plate 1, a light reflector 3 on the back of the plate, and on the light-emitting surface side of the plate a lens film 5 having a number of triangular prisms, with the prism side directed to the light guide plate 1. The shape of the triangular prism is such that when the emission peak angle of light from the light guide plate with respect to the horizontal direction of the light-emitting surface of the lens film 5 is (x) [ deg.], the apex angle (a) of the triangular prism is (90-x)÷2+(x) [ deg.], and that the angle (b) on the light source side when the apex angle is divided by the normal is (x) [ deg.] while the angle (c) opposite to the light source side is (90-x)÷2[ deg.].

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an edge type surface light source device used as a backlight of a transmissive liquid crystal display device, an advertising board, etc., and a lens film as a component thereof. In particular, the light distribution is sharp and the loss of light quantity is small,
The present invention relates to a surface light source device having a small number of parts.

[0002]

2. Description of the Related Art Conventionally, a backlight used for a transmissive display such as a liquid crystal display device has an edge type and a direct type depending on the light source position, but the liquid crystal display device can have a small space and a thin shape. The edge method is the mainstream.
A conventional edge-type surface light source device has a structure as shown in a sectional view of FIG. 8, for example. In the figure, 1 is a light guide plate, 2 is a linear light source, 3 is a reflection film, 4 is a light diffusion film, 5 is a lens film, and 8 is a light diffusion reflection part. In the light guide plate 1,
A transparent resin base material such as an acrylic resin is cut out and the surface is polished, or a predetermined shape is formed by injection molding. A cold cathode tube is used for the line light source 2, a metal-deposited resin film is used for the reflection film 3, a milky white resin film is used for the light diffusion film 4, and a large number of triangular prisms are provided for the lens film 5. Resin film is used. As the light diffusing and reflecting portion 8, a large number of fine dots printed and formed with white ink on the back surface of the light guide plate are used. It should be noted that the density of the dots scattered is made higher as the distance from the light source is increased (on the right side of the drawing) so that insufficient light emission amount at the far side does not occur. In addition, the light diffusing film 4 makes the light emitted from the light guide plate scattered light to prevent the light source and the dots from being directly visible and to spread the light to improve the viewing angle of the display device.

[0003]

However, depending on the use of the display device, there is a device which is viewed only from a certain narrow direction (for example, a normal direction), and as a surface light source device used for such a use, However, in the above-described device having the conventional structure, the emitted light spreads too much and is wasted, so that it cannot be said to be appropriate. Further, in the conventional surface light source device as described above, since the light diffusing and reflecting portion on the back surface of the light guide plate is composed of a large number of fine dots that are screen-printed, clogging of the screen mesh of the printing plate during screen printing occurs. There is also a problem that the desired dot shape and dot area cannot be obtained and the yield is poor. In addition, it is inevitable that the manufacturing process is complicated and expensive because the dot printing and the incorporation of the light diffusion film are required.

[0004]

Therefore, in the surface light source device using the non-light-diffusing light guide plate of the present invention, the light guide plate does not need to be dot-printed on the back surface, and the light-exiting surface is a smooth surface that does not diffuse light. The light guide plate is used and the light diffusing film is also omitted, and the direction of the light with little spread that is emitted obliquely from the light exit surface of the light guide plate caused by omitting these is made a triangular prism on the lens film in a specific shape and directed downward. The surface light source device has a sharp luminance distribution in the normal direction by changing the direction of light to the normal direction which is a desirable direction with respect to the light emitting surface of the surface light source. . Further, the lens film that can be used in the above surface light source device is the lens film of the present invention, but as a specific triangular prism shape for changing the light emitted from the light guide plate to the normal direction, the horizontal light exit surface of the lens film is used. The light emission peak angle of light from the light guide plate based on the direction (if the light exit face of the light guide plate is in a horizontal relationship with the light exit face of the lens film is the same as the horizontal direction of the light exit face of the light guide plate), x [° ],
The angle on the light source side (vertical angle on the light source side) when the vertical angle of the triangular prism is (90−x) ÷ 2 + x [°] and this vertical angle is divided by the normal to the light exit surface of the lens film is x.
[°], the angle on the side opposite to the light source (vertical angle on the side opposite to the light source) is (90-
x) / 2 [°]. By this, the light emitted from the light guide plate and entering the triangular prism of the lens film is vertically incident on one side surface of the triangular prism, and the light after the incident light is totally reflected on the other side surface. The light was emitted vertically from the light emitting surface of the sheet toward the normal direction.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION A surface light source device using a non-light-diffusing light guide plate of the present invention, and an embodiment of a lens film of the present invention, which is most suitable for this, will be described below.

The surface light source device of the present invention has a first feature in that a non-light-diffusing light guide plate is used as a light guide plate, and a lens film having a lens of a specific shape is assembled in a specific arrangement. Has a second feature. First, the non-light-diffusing light guide plate used in the present invention is a normally dense inner plate-like object made of a light-transmitting material such as acrylic resin, and its light-exiting surface, back surface, and side end surface, and It is a light guide plate that is non-light diffusive by not including an element that scatters light inside or on the object itself. A light guide plate that is more often used than before is a light diffuser light guide plate because dot printing is formed as a light diffuse reflector on the back surface (originally for a non-light diffuse transparent substrate). In addition, there is a light guide plate having a light exit surface having a rough surface such as satin to scatter light on the light exit surface. This is also a light diffusing light guide plate. Conventionally, the light guide plate is provided with a light diffusing function because, in terms of dot printing, a pseudo secondary light source is formed and light is emitted in a direction normal to the light emitting surface of the light guide plate. The reason why the light emitting surface is roughened is to make dot printing invisible. However, in the present invention, by using a non-light-diffusing light guide plate that does not have such a light-diffusing function, the light scattered in unnecessary directions is reduced and the luminance component in the desired normal direction is maximized. The light guide plate can emit light rays that contribute. The shape of the light guide plate base material capable of emitting such light rays is a wedge shape in which the thickness gradually decreases as the distance from the light source side increases. The thinner the thickness of the light guide plate on the side opposite to the light source, the more chances that the incident light will exceed the critical angle and the amount of light emitted will increase, but the invention is not limited to this. With this shape, a desired light beam can be emitted without performing dot printing or the like on the light guide plate, and the light guide plate can be easily obtained by injection molding or the like.

Next, the lens film will be described.
FIG. 2 is a cross-sectional view of essential parts showing the cross-sectional shape of the triangular prism 6 of the lens film 5. In the figure, the left side of the drawing is the light source side, and the right side is the non-light source side. The light emitting surface p1 of the lens film 5 serves as a light emitting surface when the surface light source device is used. The apex angle tip 7 of the triangular prism 6 faces the lower side of the drawing (the direction of the light guide plate not shown). The apex angle 7 is the light emitting surface p of the lens film.
It can be divided into two parts with a normal line V of 1 and can be divided into a light source side apex angle b and an anti-light source side apex angle c. In the figure, the light source side vertical angle b is 8 °, the anti-light source side vertical angle c is 41 °, and the convenient vertical angle a is 4 °.
It is 9 °. The light source side apex angle a is the light emission peak angle x of the light from the light guide plate based on the horizontal direction of the light exit surface p1 of the lens film 5 (light entering the lens film based on the light exit surface p1 of the lens film). Is also the light incident peak angle of light), but the light exit surface p1 of the lens film
When the light output surface p2 of the light guide plate is parallel, the light output peak angle y of the light from the light guide plate is equal to the light output surface p2 of the light guide plate as a reference, as shown in FIG. Normally, the light guide plate light emitting surface p2 and the light emitting surface p1 of the lens film are respectively arranged in parallel to the light emitting surface of the surface light source device. Therefore, hereinafter, in order to simplify the description, it is assumed that there is this parallel relationship.
Unless otherwise specified, the light emission peak angle y is also treated as the light emission peak angle x.

Next, it will be described with reference to FIG. 4 that the shape of the apex angle of the lens film may be a specific shape in relation to the light emission peak angle x. In the figure, the light L1 emitted from the light emitting surface p2 of the light guide plate at the light emitting peak angle x is vertically emitted from the light emitting surface p1 of the lens film as L2. The vertical angle a of the triangular prism is divided into a vertical angle v1 into a vertical angle b on the light source side and a vertical angle c on the anti-light source side. First, the light source side apex angle b = light emission peak angle x. This is because, when light enters the inclined surface HD on the light source side of the triangular prism, if light enters perpendicularly to the inclined surface, light loss due to reflected light is reduced. The light L1 emitted from the point A is vertically incident on the slope HD, is totally reflected at the point B of the slope FD on the side opposite to the light source, and is emitted from the surface p1.
A vertical light L2 is emitted from the point E. The value of the apex angle c on the side opposite to the light source, which is necessary for emitting the light L2 from the light emitting surface p1 of the lens film in the normal direction perpendicular to the light emitting surface p1, is obtained as follows. First, ∠ABD = ∠EBF from the relationship of total reflection at the point B of the slope FD on the side opposite to the light source of the triangular prism.
Next, from the diagonal relationship between the slope FD and the normal line v2 passing through the point B of the slope FD, ∠EBF = ∠DBC. here,
Let G and D be the intersections of the normal v1 and the light emitting surface p1 and the light emitting surface p2, respectively, and let the light emitting surface p1 and the light emitting surface p2 of the normal v2 be respectively.
If the intersections with and are E and C, respectively, the line segment GD and the line segment CE are parallel, and therefore the vertical angle c on the side opposite to the light source is ∠GDB
Is ∠DBC = ∠GDB. Therefore, ∠ABD =
∠DBC = ∠GDB. Where triangle ABC is
∠ACB = 90 ° Right triangle, so ∠ABC =
90 ° −∠BAC = 90 ° −x, and ∠ABC =
Since it is also ∠DBC + ∠ABD, ∠GDB =
(90−x) ÷ 2 [°]. Therefore, since the apex angle a of the triangular prism is equal to the apex angle b on the light source side + the apex angle on the anti-light source side c, (90−x) / 2 + x [°].

In the above description, the value that the light emission peak angle x can take is theoretically 0 to 90 °, but practically it is in the range of 0 ° <x ≦ 30 °.

The shape of the triangular prism of the lens film having a specific apex angle is normally designed to be the same over the entire surface of the surface light source device, but it is not always necessary to make them all the same. Further, the present invention does not limit the apex shape to the same in the lens film. Here, by reconfirming the definition of the apex shape according to the present invention, when the light emission peak angle of the light from the light guide plate with reference to the horizontal direction of the light emission surface of the lens film is x [°], the triangular prism The vertical angle of (90-x) / 2 + x
[°], and the angle on the light source side (vertical angle on the light source side) when this vertical angle is divided by the normal to the light exit surface of the lens film is x [°], the angle on the anti-light source side (vertical angle on the anti-light source side) ) Was (90-x) / 2 [°]. That is, only the relationship between the light output peak angle x [°] and the apex angle shape is defined. If the light output peak angle differs depending on the position of the light emitting surface of the light guide plate, the apex angle shape can be changed accordingly. It also indicates what is better. However, even if there is a slight difference in the light emission peak angle x at the light emitting surface of the light guide plate, the surface light source device may be assembled as a vertex angle shape represented by a certain light emission peak angle x, Further, the gist of the present invention does not hinder such specifications.

[0011]

EXAMPLES Next, the present invention will be described in detail with reference to examples.

Light guide plate The light guide plate has a light emitting surface of 220 mm in width and 168 mm in length.
Then, as a cross-sectional dimension, a wedge-shaped one having a thickness of 3 mm at the light entrance side on the light source side and a thickness that linearly decreases as it goes away from the light source side and becomes 1 mm on the side opposite to the light source farther from the light source is Asahi Kasei Co., Ltd. Delpet 80N
H) was used for normal injection molding.

Lens film First, a 125 μm thick easily-adhesive polyethylene terephthalate film (A-4300 manufactured by Toyobo Co., Ltd.) and a medium for chemical mat (manufactured by The Inktech Co., Ltd.)
And isocyanate curing agent (manufactured by The Inktech Co., Ltd.)
XEL curing agent) was applied at a weight ratio of 100: 10 to form a 2 μm undercoat layer to obtain a transparent base film. Then, using this substrate film,
The manufacturing method disclosed in Japanese Patent Application Laid-Open No. 169015/1993 by the present applicant (a resin liquid is filled in the concave portion of a roll intaglio having concave and convex portions opposite to those of a triangular prism, and ultraviolet rays are applied in a state where the base film is brought into contact therewith. Of the present invention to cure the resin liquid, and then peel it off.) To form a triangular prism made of an ultraviolet curable resin (Z-9002A manufactured by Japan Synthetic Rubber Co., Ltd.) on the base film to form a prism of the present invention. A lens film was produced. The prism shape has an apex angle a = 4 as shown in FIG.
9 °, light source side vertical angle b = 8 °, anti-light source side vertical angle c = 41 °
The height was about 40 μm and the bottom was about 50 μm.

Surface light source device A linear light source is arranged on one end surface of the light guide plate obtained above, a white polyethylene terephthalate film is arranged on the back surface side as a reflective film which is a reflector, and a light emitting surface side is formed on the above side. One lens film is arranged so that the triangular prism is directed toward the light guide plate and the apex angle on the light source side and the apex angle on the anti-light source side have the above-described predetermined relationship with the light source, and the present invention as shown in FIG. The surface light source device using the non-light-diffusing light guide plate.

Comparative Example A line light source is arranged on one end face of the light guide plate obtained above, and white ink is screen-printed on the back face side by a conventional method to form a large number of dots to form a light diffusion reflection portion. Further, a white polyethylene terephthalate film was arranged on the back side thereof as a reflective film which was a reflector. A diffusion film made of a milky white polyethylene terephthalate film is arranged on the light emitting surface side of the light guide plate, and two lens films each having an isosceles triangular lens shape are arranged on the diffusion film with the lens side facing upward. The surface light source device is used as an example.

Performance Evaluation The surface light source devices of Examples and Comparative Examples were evaluated for the following items.

Surface uniformity of brightness: brightness in the direction of the normal line at 9 points shown in FIG.
M-8). The measurement point 5 is the center, and the other eight points are on a line segment 15 mm inside from the periphery. Table 1 shows the results
Shown in The unevenness in the table is (minimum luminance value / maximum luminance value) x
A surface uniformity of brightness is shown at 100%.

Luminance angle distribution: As shown in FIG. 6, the angular distribution with respect to the normal direction of the luminance was measured in the direction perpendicular to the light source side of the light guide plate at the 5th measurement point in the center shown in FIG. The results are shown in Fig. 7.

[0019]

[Table 1]

[0020]

According to the lens film of the present invention, by arranging the triangular prism to face the light guide plate and using the prism film, it is possible to achieve x with respect to a surface parallel to the light exit surface of the lens film.
Light incident on the lens film at an angle of [°] can be emitted in the normal direction. And using this lens film with a light guide plate that does not have a light diffusion function,
Moreover, the surface light source device of the present invention assembled without using the light diffusion film has a sharp luminance distribution in the normal direction of the light output surface and is excellent in light utilization efficiency.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a surface light source device using a non-light-diffusing light guide plate of the present invention.

2 is a cross-sectional view of a main part of an embodiment of a lens film of the present invention that can be used in the surface light source device of FIG.

FIG. 3 is a diagram illustrating a light output peak angle of light from a light output surface of a light guide plate.

FIG. 4 is an explanatory diagram illustrating a specific shape of a triangular prism of a lens film.

FIG. 5 is a plan view showing the luminance measurement points of the light guide plate.

FIG. 6 is an explanatory view showing a measurement direction of a brightness angle distribution of a light guide plate.

FIG. 7 is a comparison diagram of a luminance angle distribution between the present invention and a conventional surface light source device.

FIG. 8 is a cross-sectional view showing a configuration example of a conventional edge-type surface light source device.

[Explanation of symbols]

1 light guide plate 2 light source 3 reflector, reflection film 4 light diffusing film 5 lens film 6 triangular prism 7 apex angle tip 8 light diffusing reflection part a apex angle b light source side apex angle (light source when the apex angle is divided by a normal line Side angle) c Anti-light source side apex angle (angle formed by the anti-light source side when the apex angle is divided by the normal line) p1 Light emitting surface of lens film, light emitting surface of surface light source device p2 Light emitting surface of light guide plate v1 method Line v2 Normal x Angle of light emission peak from light guide plate with respect to lens film light exit surface (when light guide plate light exit surface is parallel to lens film light exit surface, angle with respect to light guide plate light exit surface)

Claims (3)

[Claims] 1. A non-light diffusing light guide plate having no light diffusing function, a light source arranged adjacent to a side end surface of the light guide plate, a light reflector arranged on the back surface side, and a light emitting surface. A surface light source device including a lens film disposed on the side, wherein the lens film has a lens in which a plurality of triangular prisms each having a triangular cross section are two-dimensionally arranged, and the apex tip of the triangular prism is guided. When the triangular prism is arranged on the light plate side, and the peak angle of light emitted from the light guide plate with reference to the horizontal direction of the light exit surface of the lens film is x [°], the apex angle of the triangular prism (90-x) / 2
+ X [°], and the angle on the light source side when this apex angle is divided by the normal to the light exit surface of the lens film is x
A surface light source device using a non-light-diffusing light guide plate in which [°] and the angle on the side opposite to the light source are (90−x) / 2 [°]. 2. The surface light source device using the non-light-diffusing light guide plate according to claim 1, wherein the light guide plate has a shape similar to a wedge whose thickness gradually decreases with distance from the light source side. 3. A triangular prism having a triangular cross section and having a lens in which two or more triangular prisms are two-dimensionally arrayed, the apex tip of the triangular prism is arranged toward the light guide plate side, and the lens film surface on the bottom side of the prism is a lens. In the lens film for the surface light source device used as the light emitting surface of the film, the shape of the triangular prism is defined as (90-
x) ÷ 2 + x [°], and when this apex angle is divided by the normal to the light exit surface of the lens film, the angle on the light source side is x [°] and the angle on the anti-light source side is ( 90
-X) ÷ 2 [°], the lens film. Where x
[°] is the light emission peak angle [°] of the light from the light guide plate with reference to the horizontal direction of the light emitting surface of the lens film.