JP3688036B2 - Surface light source device using non-light diffusing light guide plate and lens film - Google Patents

Description

【００２０】
【発明の効果】
本発明のレンズフィルムによれば、その三角柱プリズムを導光板側に向けて配置して使用することで、レンズフィルムの出光面に平行な面に対してｘ〔°〕の角度でレンズフィルムに入光した光を、法線方向に向けて出光することができる。
そして、このレンズフィルムを光拡散機能を持たない導光板とともに用い、且つ光拡散フィルムを用いずに組み立てた本発明の面光源装置は、出光面の法線方向に対して鋭い輝度分布を持った、光の利用効率に優れたものとなる。
【図面の簡単な説明】
【図１】本発明の非光拡散性導光板を用いた面光源装置の一実施例を示す断面図。
【図２】図１の面光源装置に用い得る、本発明のレンズフィルムの一実施例の要部断面図。
【図３】導光板の出光面から光の出光ピーク角度を説明する図。
【図４】レンズフィルムの三角柱プリズムの特定形状を説明する説明図。
【図５】導光板の輝度測定箇所を示す平面図。
【図６】導光板の輝度角度分布の測定方向を示す説明図。
【図７】本発明と従来の面光源装置と輝度角度分布の比較図。
【図８】従来のエッジ方式の面光源装置の構成例を示す断面図。
【符号の説明】
１ 導光板
２ 光源
３ 反射体、反射フィルム
４ 光拡散フィルム
５ レンズフィルム
６ 三角柱プリズム
７ 頂角先端
８ 光拡散反射部
ａ 頂角
ｂ 光源側頂角（頂角を法線で分割した時の光源側の成す角度）
ｃ 反光源側頂角（頂角を法線で分割した時の反光源側の成す角度）
ｐ１ レンズフィルムの出光面、面光源装置の出光面
ｐ２ 導光板の出光面
ｖ１ 法線
ｖ２ 法線
ｘ 導光板からの出光ピークのレンズフィルム出光面に対する角度（導光板出光面がレンズフィルム出光面に平行な時は、導光板出光面に対する角度）[0001]
BACKGROUND 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, and the like, and a lens film as a component thereof. In particular, the present invention relates to a surface light source device having a sharp light emission distribution, little light loss, and a small number of parts.
[0002]
[Prior art]
Conventionally, backlights used in transmissive display bodies such as liquid crystal display devices have an edge method and a direct method depending on the position of the light source, but the edge method is the mainstream in liquid crystal display devices because it can be made small and thin. It is. A conventional edge-type surface light source device has a structure as shown in the cross-sectional view of FIG. In the figure, 1 is a light guide plate, 2 is a line 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. For the light guide plate 1, a transparent resin base material such as an acrylic resin is cut out and the surface thereof is polished, or a predetermined shape is formed by injection molding. The line light source 2 is a cold cathode tube, the reflective film 3 is a metal-deposited resin film, the light diffusion film 4 is a milky white resin film, and the lens film 5 is provided with many triangular prisms. Resin film is used. And as the light-diffusion reflection part 8, many fine dots printed and formed with the white ink on the back surface of the light-guide plate are used. It should be noted that the density at which dots are scattered is increased as the distance from the light source increases (the right side of the drawing) so that a shortage of emitted light quantity does not occur on the far side. In addition, the light diffusing film 4 uses scattered light as light emitted from the light guide plate to prevent the light source and dots from being directly seen by the light and to broaden the light to improve the viewing angle of the display device.
[0003]
[Problems to be solved by the invention]
However, depending on the application of the display device, there is a device for viewing only from a specific narrow direction (for example, the normal direction). As a surface light source device used for such an application, the above-described conventional structure device is used. Since the emitted light spreads too much, there is much light that is wasted, and it was not appropriate.
Further, in the conventional surface light source device as described above, the light diffuse reflection part on the back surface of the light guide plate is composed of a large number of fine dots printed on the screen, so that the screen mesh of the printing plate is clogged during screen printing. As a result, a desired dot shape and dot area cannot be obtained, resulting in a poor yield. In addition, since it is necessary to incorporate such dot printing and light diffusion film, it is inevitable that the manufacturing process becomes complicated and expensive.
[0004]
[Means for Solving the Problems]
Therefore, in the surface light source device using the non-light diffusable light guide plate of the present invention, the light guide plate omits dot printing on the back surface, and the light exit surface uses a non-light diffusable light guide plate with a smooth surface. By omitting the film, using the direction of the light that spreads in the oblique direction from the light guide plate exit surface caused by omitting these, using a triangular prism prism in a specific shape and arranged downward on the lens film, This is a surface light source device having a sharp luminance distribution in the normal direction by changing the direction of light in the normal direction which is a desirable direction with respect to the light output surface of the surface light source. Also, the lens film used in the above Symbol surface light source device is a lens film of the present invention, as a particular triangular prism shape for changing the light exiting from the light guide plate in the normal direction, the horizontal light emitting surface of the lens film The light output peak angle of the light from the light guide plate with respect to the direction (if the light output surface of the light guide plate is horizontal with the light output surface of the lens film is the same as the horizontal direction of the light output surface of the light guide plate) is x [° ], The apex angle of the triangular prism is (90−x) ÷ 2 + x [°], and the apex angle is divided by the normal to the light exit surface of the lens film (the light source side apex). The angle (angle) was x [°], and the angle on the opposite light source side (vertical angle on the opposite light source side) was (90−x) / 2 [°]. As a result, the light emitted from the light guide plate and incident on the triangular prism of the lens film is vertically incident on one side surface of the triangular prism, and the incident light is totally reflected on the other side surface. Light was emitted vertically from the light exit surface of the sheet in the normal direction.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, 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 that is optimal for the surface light source device will be described.
[0006]
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 the light guide plate, and a second feature is that a lens film having a lens having a specific shape is assembled in a specific arrangement. There are features.
First, the non-light diffusive light guide plate used in the present invention is a normally flat plate-like object made of a translucent material such as acrylic resin, and its light exit surface, back surface, and side end surface, and It is a light guide plate that is non-light diffusing by not including an element that scatters light inside the object or in the object itself. A light guide plate that is used more frequently than before is originally a light diffusible light guide plate because dot printing is formed as a light diffusive reflecting portion on the back surface (originally with respect to a non-light diffusable transparent base material). In addition, there is a light diffusing light guide plate that has a light output surface of the light guide plate as a rough surface such as a satin surface and scatters light on the light output surface.
Conventionally, the light diffusing function is provided in the light guide plate because, in dot printing, a pseudo secondary light source is formed and light is emitted in the normal direction perpendicular to the light exit surface of the light guide plate. The reason for roughening the light-emitting surface was 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, light scattered in a useless direction is reduced, and a luminance component in a desired normal direction is maximized. It can be set as the light-guide plate which emits the light ray which contributes.
The shape of the light guide plate base material that can emit such a light beam is a wedge shape whose thickness gradually decreases as the distance from the light source side increases. As the thickness of the light guide plate on the side opposite to the light source becomes thinner, the chance that incident light exceeds the critical angle increases and the amount of emitted light increases, but it is not necessary to limit 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.
[0007]
Next, the lens film will be described. FIG. 2 is a cross-sectional view of the main part 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 counter light source side. The light exit surface p1 of the lens film 5 is the light exit 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 can be divided into two by the normal V of the light exit surface p1 of the lens film, 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 apex angle b is 8 °, the counter light source side apex angle c is 41 °, and the convenient apex angle a is 49 °. The light source side apex angle b is the light output peak angle x from the light guide plate with respect to the horizontal direction of the light exit surface p1 of the lens film 5 (the light incident on the lens film based on the light exit surface p1 of the lens film). In the arrangement relationship in which the light exit surface p2 of the light guide plate is parallel to the light exit surface p1 of the lens film, the light exit surface p2 of the light guide plate is set as shown in FIG. It is equal to the light output peak angle y of light from the light guide plate as a reference. Normally, the light guide plate light exit surface p2 and the light exit surface p1 of the lens film are arranged in parallel with the light exit surface of the surface light source device, respectively. Unless otherwise indicated, the light emission peak angle y is also treated as the light emission peak angle x.
[0008]
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 drawing, the light L1 emitted from the light exit surface p2 of the light guide plate at the light exit peak angle x is emitted as L2 perpendicularly from the light exit surface p1 of the lens film. The apex angle a of the triangular prism is bisected into a light source side apex angle b and an anti-light source side apex angle c by the normal line v1. First, the light source side apex angle b = the light emission peak angle x. This is because when light is incident on the slope HD on the light source side of the triangular prism, light loss due to reflected light is reduced if light is incident perpendicular to the slope. The light L1 emitted from the point A enters vertically at the slope HD, is totally reflected at the point B on the slope FD on the side opposite to the light source, and emerges as light L2 perpendicular from the point E on the light exit surface p1. The anti-light source side apex angle c required to emit light L2 in the normal direction perpendicular to the light exit surface p1 of the lens film is obtained as follows. First, ∠ABD = ∠EBF from the relation of total reflection at 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, if the intersection points of the normal line v1 with the light exit surface p1 and the light exit surface p2 are G and D, respectively, and the intersection points of the normal line v2 with the light exit surface p1 and the light exit surface p2 are E and C, respectively, the line segment GD Since the line CE is parallel, ∠GDB which is the opposite light source side apex angle c is ∠DBC = ∠GDB. Therefore, ∠ABD = ∠DBC = ∠GDB. Here, since the triangle ABC is a right triangle with ∠ACB = 90 °, ∠ABC = 90 ° −∠BAC = 90 ° −x and ∠ABC = ∠DBC + ∠ABD, so that ∠GDB = (90−x) ÷ 2 [°]. Accordingly, since it is the apex angle a = source-side apex angle b + side opposite to the light source apex angle c of the triangular pillar prisms, and (90-x) ÷ 2 + x [°].
[0009]
In addition, in the above, although the light emission peak angle x can theoretically range from 0 to 90 °, it is practically in the range of 0 ° <x ≦ 30 °.
[0010]
In addition, although the shape which has the specific apex angle of the triangular prism which a lens film has is normally designed all the same over the whole surface light source device, it is not necessarily required to make all the same. Further, the present invention does not limit the apex shape to the same in the lens film. Here, if the definition of the apex angle shape according to the present invention is reconfirmed, when the light output peak angle of the light from the light guide plate with respect to the horizontal direction of the light output surface of the lens film is x [°], a triangular prism The angle on the light source side (light source side apex angle) when the apex angle is divided by the normal to the light exit surface of the lens film is x [°], where (90−x) ÷ 2 + x [°] The angle on the side opposite to the light source (vertical angle on the side opposite to the light source) was set to (90−x) ÷ 2 [°]. That is, only the relationship between the light emission peak angle x [°] and the apex angle shape is defined. If the light emission peak angle varies depending on the location of the light exit surface of the light guide plate, the apex angle shape can be changed accordingly. It is also an indication of what is better. However, even if there is a slight difference in the light output peak angle x at the location of the light output surface of the light guide plate, it may be represented by a certain light output peak angle x, and the surface light source device may be assembled as an apex angle shape for this representative value, Further, the gist of the present invention is not to hinder such specifications.
[0011]
【Example】
Next, the present invention will be described specifically by way of examples.
[0012]
Light guide plate The light guide plate has a light exit surface dimension of 220 mm wide x 168 mm long, with a cross-sectional dimension of 3 mm at the light incident part on the light source side, and the thickness decreases linearly with increasing distance from the light source side, and is farther from the light source. A wedge-shaped product having a diameter of 1 mm on the side opposite to the light source was prepared by ordinary injection molding using a transparent acrylic resin (Delpet 80NH manufactured by Asahi Kasei Kogyo Co., Ltd.).
[0013]
Lens film First, a 125 μm-thick adhesive polyethylene terephthalate film (A-4300 manufactured by Toyobo Co., Ltd.), a medium for chemical mats (produced by The Inktec Co., Ltd.) and an isocyanate curing agent (The Ink, Inc.). XEL curing agent manufactured by Tech Co., Ltd.) 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 base film, the manufacturing method disclosed by the present applicant in Japanese Patent Laid-Open No. Hei 5-169015 (filling a resin liquid into a concave part of a roll intaglio having a triangular prism and a concave part having a reverse concave-convex part, The resin film is cured by irradiating with ultraviolet rays in the state of contact with the material film, and then peeled off.), A triangular prism made of ultraviolet curable resin (Z-9002A manufactured by Nippon Synthetic Rubber Co., Ltd.) on the base film. A prism film was formed to produce the lens film of the present invention. The prism shape was such that the apex angle a = 49 °, the light source side apex angle b = 8 °, the non-light source side apex angle c = 41 ° as shown in FIG. 2, and the height was about 40 μm and the base was about 50 μm.
[0014]
Surface light source device A linear light source is disposed on one side end surface of the light guide plate obtained above, a white polyethylene terephthalate film is disposed on the back surface side as a reflective film as a reflector, and on the light exit surface side. One of the lens films is arranged so that the triangular prism is directed to the light guide plate side so that the light source side apex angle and the non-light source side apex angle are in the predetermined relationship as described above, and a book as shown in FIG. A surface light source device using the non-light diffusing light guide plate of the invention was obtained.
[0015]
Comparative example A light source is arranged on one side end face of the light guide plate obtained above, and a white dot is screen-printed on the back side by a conventional method to form a large number of dots to form a light diffusing reflection part. Further, a white polyethylene terephthalate film was disposed as a reflective film as a reflector on the back side. A light-diffusing film made of milky white polyethylene terephthalate film is placed on the light exit surface side of the light guide plate, and two lens films with an isosceles triangle shape are placed on this side with the lens side facing up. An example surface light source device was obtained.
[0016]
Performance evaluation The surface light source devices of Examples and Comparative Examples were evaluated for the following items.
[0017]
(1) Surface uniformity of luminance:
The luminance in the normal direction at 9 points shown in FIG. 5 was measured with a luminance measuring device (BM-8 manufactured by Topcon Corporation). The measurement location 5 is the center, and the other 8 locations are on a line segment 15 mm inside from the periphery. The results are shown in Table 1. The unevenness in the table is (minimum luminance value / maximum luminance value) × 100 [%], and indicates surface uniformity of luminance.
[0018]
(2) Luminance angle distribution:
{Circle around (1)} The angular distribution with respect to the normal direction of the luminance was measured in the direction perpendicular to the side of the light guide plate on the light source side as shown in FIG. The results are shown in FIG.
[0019]
[Table 1]

[0020]
【The invention's effect】
According to the lens film of the present invention, when the triangular prism is disposed facing the light guide plate side, the lens film enters the lens film at an angle of x [°] with respect to a plane parallel to the light exit surface of the lens film. The emitted light can be emitted in the normal direction.
The surface light source device of the present invention assembled using this lens film with a light guide plate having no light diffusion function and without using the light diffusion film has a sharp luminance distribution with respect to the normal direction of the light exit surface. The light utilization efficiency is excellent.
[Brief description of the drawings]
FIG. 1 is a cross-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 an essential part of an embodiment of a lens film of the present invention that can be used in the surface light source device of FIG. 1;
FIG. 3 is a diagram for explaining a light output peak angle 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 luminance measurement points of the light guide plate.
FIG. 6 is an explanatory diagram showing the measurement direction of the luminance angle distribution of the light guide plate.
FIG. 7 is a comparison diagram of 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]
DESCRIPTION OF SYMBOLS 1 Light guide plate 2 Light source 3 Reflector, reflection film 4 Light diffusion film 5 Lens film 6 Triangular prism 7 Apex angle tip 8 Light diffuse reflection part a apex angle b Light source side apex angle (light source when apex angle is divided by normal line) Side angle)
c Anti-light source side apex angle (angle formed on the anti-light source side when the apex angle is divided by the normal)
p1 Light exit surface of lens film, light exit surface of surface light source device p2 Light exit surface of light guide plate v1 Normal line v2 Normal line x Angle of light output peak from light guide plate with respect to lens film light exit surface (light guide plate light exit surface on lens film light exit surface) When parallel, angle with respect to light exit surface of light guide plate)

Claims (3)

At least a non-light diffusing light guide plate having no light diffusion function, a light source arranged adjacent to the side end surface of the light guide plate, a light reflector arranged on the back surface side, and a light emitting surface side A surface light source device comprising a lens film,
The lens film has a lens in which a large number of triangular prisms each having a triangular cross section are arranged two-dimensionally, and is arranged with the apex tip of the triangular prism prism on the light guide plate side. When the light output peak angle from the light guide plate with respect to the horizontal direction of the surface is x [°], the apex angle of the triangular prism is (90−x) ÷ 2 + x [°], and this apex angle is A non-light diffusing light guide plate is used in which the angle on the light source side is x [°] and the angle on the non-light source side is (90−x) ÷ 2 [°] when divided by the normal to the light exit surface of the lens film. A surface light source device.   The surface light source device using a non-light diffusable light guide plate according to claim 1, wherein the light guide plate has a shape similar to a wedge whose thickness gradually decreases as the distance from the light source side increases. It has a lens in which a large number of triangular prisms with a triangular cross section are arranged two-dimensionally, and the apex angle 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 used as the light exit surface of the lens film In the lens film for the surface light source device using the non-light diffusing light guide plate to be used ,
The triangular prism has a shape in which the apex angle of the prism is (90−x) ÷ 2 + x [°], and when the apex angle is divided by the normal to the light exit surface of the lens film, the angle on the light source side is A lens film in which x [°] and the angle on the side opposite to the light source side are (90−x) ÷ 2 [°]. However, x [°] is a light output peak angle [°] of light from the light guide plate with respect to the horizontal direction of the light output surface of the lens film.

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