JPH01272003A - Light conducting panel - Google Patents

Abstract

PURPOSE:To obtain a thin type light conducting panel with little light transmission loss and little dispersion of brightness by laminating multiple plastic sheets with an excellent light transmission property and rough face sections so that the rough face sections are staggered respectively in the lengthy direction. CONSTITUTION:A light conducting panel 31 is formed in a thin type by laminating a required number of plastic sheets 32 with an excellent light transmission property and arranged on the back face of a liquid crystal display panel 30, for example, and reflects and transmits the light of light emitting diodes 35 and 36 to the panel 30. The plastic sheet 32 has rough face sections 32a and 32b to scatter and reflect the light, the rough face sections of each sheet are staggered in the lengthy direction of the sheet when the sheets are laminated, the rough face sections illuminate the partial region of the display panel 30. The size of the rough face sections in the lengthy direction can be reduced, the dispersion of light is reduced. The light transmission loss to the rough face sections of the sheet 32 is nearly zero, the light leakage quantity from the rough face sections is made nearly constant.

Description

[Detailed Description of the Invention] (Summary) Regarding a light guide panel for backlighting a display panel, the present invention relates to a light guide panel that is thin, has little light transmission loss, and is capable of backlighting with little variation in brightness. The aim of this technology is to stack multiple light guide sheets made of plastic with excellent light transmission properties in a multilayered state, and direct light incident on each layer of light guide sheets from the edges toward the back of the display panel. A rough surface portion is formed for scattering and reflecting the light guide sheet in each layer, and the positions of the rough surface portions of the light guide sheet in each layer are shifted in the longitudinal direction of the light guide sheet from the lower layer to the upper layer.

[Industrial application field]

The present invention relates to a light guide panel for back illuminating a liquid crystal display panel (LCD) or a keyboard switch, etc., and particularly to realize uniform back illumination for an LCD or keyboard switch of a portable device that is required to be light, thin, short, and compact. The present invention relates to a thin surface-emitting type light guide panel that can be used.

[Prior Art and Problems to be Solved by the Invention] FIGS. 5 to 7 show the conventional structure of a display operation section of a mobile phone terminal. As shown in FIG. 5, the display and operation section of the mobile phone terminal includes a display 1 that displays the transmission/reception status of dial numbers, memory dials, etc., a keyboard switch 2, a large-scale integrated circuit (LSI) 3 for control, and other components. and a wiring board 4 to which desired circuits are connected.

Since such a mobile phone terminal needs to be operable even in a dark environment due to its functionality, the display 1 is equipped with a back lighting structure 6 for illuminating the LCD 5 from the back side, as shown in detail in FIG. The back lighting structure 6 includes an LED 8 as a point light source provided in a light shielding plate 7, and a plastic light guide plate 9 for diffusing the light from the LED 8 and guiding it to the back surface of the LCD 5. There is. Light guide plate 9
On the back surface of the display panel 1, irregularities 9a are formed to enhance the light scattering effect, and a white paint 10 is applied.

Thereby, the display on the LCD 5 can be recognized even in a dark environment.

On the other hand, as shown in detail in the perspective view of the back lighting structure of the keyboard switch shown in FIG. 5 and the sectional view of the main part in FIG. and chip-type light emitting diodes (LEDs) 13 mounted in holes 12a provided at multiple locations in the light guide plate +&12. It is composed of In addition, in Fig. 7, 15
1 is a casing of a mobile phone terminal, and 16 is a rubber key provided with a conductor 18 that can be contacted with a key contact 17 on a wiring board 4.

The conventional light guide plate 9 in the above-mentioned display back lighting structure 6 merely uses the back surface opposite to the LCD 5 as a light reflecting surface with unevenness 9a, etc., so if the light guide plate 9 is made thinner, the area away from the LEI) 8 is reduced. There has been a problem in that the area near the LED 8 is bright and the central area of the LCD 5 is dark.

On the other hand, in the keyboard switch 2, the positions of each key for illumination are functionally dispersed, so compared to the conventional light guide plate 12.
In order to backlight the entire key top 14 using the LED, a large number of LEDs 13 are required. In addition, the light guide plate 12 generally has a wide light guide area, and the conventional light guide plate 12 diffuses light to unnecessary locations, resulting in uneven distribution of back illumination and poor illumination efficiency. Problems such as increased power consumption occurred.

On the other hand, recently, a surface-emitting type back lighting structure has been proposed in which a light guide sheet made of a plurality of plastic fibers is used to back-light a display panel by surface emission. Referring to FIGS. 8 and 9, this back lighting structure includes a light guide sheet 20 formed into a band shape by arranging a plurality of plastic fibers 21 in a row and bonding the back sides to each other with an adhesive 22. A surface emitting portion 20a having unevenness is formed at a desired location on the front surface of the light guide sheet 20 by roughening the surface. 23
24 is a display panel that displays characters, etc.; 24 is a light reflective sheet;
25 is a light emitting device equipped with a point light source such as an LED 26.

In such a back lighting structure, each light guide sheet 2 is emitted from a point light source such as an LED 26 through an end of the light guide sheet 20.
The light incident on the inside of the display panel 20 is scattered by the unevenness of the surface emitting section 20a, leaks to the outside of the light guide sheet 20, and emits light from the surface, thereby backlighting the back surface of the display panel 23. The light guide sheet 20 using such fibers 21 has the advantage of having less light transmission loss and being thinner.

However, even in such a structure of the light guide panel 20,
There is a drawback that the amount of light leakage varies between a region close to a point light source such as the LED 26 and a region far away.

In order to make the amount of light leakage uniform, it is conceivable to change the roughness of the surface roughening in the surface emitting part 20a according to the distance from the LED 26, but there is a limit.

Therefore, an object of the present invention is to provide a light guide panel that is thin, has little light transmission loss, and can perform back illumination with little variation in brightness.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a light guide panel for backlighting a display panel, which includes a plurality of light guide panels made of plastic with excellent light transmittance. The light guide sheet of each layer is stacked in a multi-layered state, and the light guide sheet of each layer has a rough surface part for scattering and reflecting the light incident from the edge toward the back surface of the display panel. The positions of the light guide sheets are shifted in the longitudinal direction of the light guide sheet from the lower layer toward the upper layer.

[For production]

In the surface-emitting light guide panel having the above configuration, the light incident on the light guide sheet of each layer is scattered and reflected by the rough surface portion and guided to the back surface of the display panel, but the position of the rough surface portion of the light guide sheet of each layer is shifted in the longitudinal direction of the light guide sheet from the lower layer to the upper layer, so the back surface of the display panel is back-illuminated by light leakage from the corresponding rough surface in each area facing the rough surface of the light guide sheet in each layer. That will happen. Since each rough surface portion formed on the light guide sheet of each layer is only responsible for illuminating a part of the display panel, the width of each rough surface portion in the longitudinal direction of the fiber can be reduced. Therefore, there is almost no variation in the amount of light scattering and reflection within the rough surface portion of the light guide sheet of each layer. Furthermore, since there is almost no light transmission loss up to the rough surface in any of the layers of the light guide sheet, the amount of light leaked from the rough surface of the light guide sheet in each layer is approximately constant. Therefore, the backside of the display panel can be efficiently and uniformly backlit. Further, since it has a laminated structure of thin plastic fiber sheets, it can be made into a thin surface-emitting type light guide panel.

Illumination efficiency decreases when light leaking from the rough surface of the lower light guide sheet passes through the upper light guide sheet toward the back surface of the display panel and interferes with light traveling from the edge of the upper light guide sheet toward the rough surface. Therefore, it is preferable that the position of the rough surface portion be closer to the end portion of the light guide sheet that becomes the light incident surface as it goes from the lower layer light guide sheet to the upper layer light guide sheet.

When both ends of the light guide sheet of each layer serve as light incident surfaces, it is preferable to form two rough surface parts on the light guide sheet of each layer that respectively scatter and reflect the light incident from both ends. It is preferable that the positions of the two rough surface portions be brought closer to the corresponding ends of the light guide sheet as the direction increases.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIGS. 1 and 2 show an embodiment in which the present invention is applied to a display of a mobile phone terminal. In these figures, a light guide panel 31 according to the present invention is provided on the back side of a liquid crystal display panel (LCD) 30 of a light transmission type or semi-transmission type. The light guide panel 31 includes a plurality of light guide sheets 32 (here, four sheets) made of plastic with excellent light transmission properties.
are superimposed in multiple layers. It is desirable to use an adhesive with excellent light transmittance.

Both ends in the longitudinal direction of the laminated light guide sheet 32 are fitted into open ends of light shielding plates 33 and 34 having a U-shaped cross section and provided at both ends of the back surface of the display panel 30. Light shielding plate 33
．． A plurality of light sources, for example, light emitting diodes (LEDs) 35 and 36 are provided inside each light guide sheet 34 as necessary, and the light emitted from the LEDs 35 and 36 is directed to the corresponding end of each light guide sheet 32. It is designed so that the light enters the inside of it. The lead bin 30a of the display panel 30 and the lead pins 35a, 36a of the LEDs 35, 36 are mechanically and electrically connected to a wiring board 37 (see FIG. 1), respectively.

The lower surface of the light guide sheet 32 of each layer, that is, the display panel 3
Rough surface portions 32a and 32b having mountain-shaped or Fresnel-shaped unevenness for scattering and reflecting light incident from the end toward the back surface of the display panel 30 are provided on the surface opposite to 0. Rough surface portions 32a, 3 of light guide sheet 32 of each layer
The position of 2b is shifted in the longitudinal direction of the light guide sheet 32 from the lower layer light guide sheet 32 toward the upper layer light guide sheet 32. More specifically, in this embodiment, there are two rough surface portions 32a from the lower layer to the upper layer.

32b are arranged so as to approach the ends of the respective light guide sheets 32.

In the light guide panel having the above configuration, LED35.3
The light emitted from the light guide sheet 32 of each layer enters the interior from the corresponding end of the light guide sheet 32, and the light emitted from the rough surface portions 32a, 32
The light guide sheet 3 of each layer leaks out from the light guide sheet 32 and is guided to the back surface of the display panel 30 by being scattered and reflected at
2 rough surface portion 32a.

32b is shifted in the longitudinal direction of the light guide sheet 32 from the lower layer to the upper layer, so that the back surface of the display panel 30 has roughness corresponding to each region facing the rough surface portions 32a and 32b of the light guide sheet 32 of each layer. Back illumination is caused by surface light emission due to light leakage from the surface portions 32a and 32b. That is, referring to FIG. 2, the areas 31a and 31b of the light guide panel 31 emit surface light due to the scattering and reflection of light by the rough surface portions 32a and 32b of the light guide sheet 32 in the lowermost layer. The rough surface portion 32a of the light guide sheet 32 of
, 32b, the sections 31c and 31d of the light guide panel 31 emit surface light, and the scattering and reflection of the light by the rough surface parts 32a and 32b of the third layer of light guide sheet 32 from the bottom causes the light guide panel 31 to emit light. The regions 31e and 31f of 31 emit surface light, and the rough surface portion 3 of the uppermost light guide sheet 32
2a.

The regions 31g and 31h of the light guide panel 31 emit surface light due to the scattering and reflection of light by the light guide panel 32b.

In this way, since each of the rough surface portions 32a and 32b formed on the light guide sheet 32 of each layer only serves to illuminate a part of the display panel 30, each of the rough surface portions 32a and 32b in the longitudinal direction of the fiber , 32b can be made smaller. Therefore, each rough surface portion 3 of the light guide sheet 32 of each layer
There is almost no variation in the amount of light scattering and reflection within 2a and 32b.

In addition, in any layer of the light guide sheet 32, the rough surface portion 3
Since there is almost no light transmission loss up to 2a and 32b, the amount of light leakage from the rough surface portions 32a and 32b of the light guide sheet 32 of each layer is almost constant. Therefore, the backside of the display panel 30 can be efficiently and uniformly backlit.

Moreover, since it has a laminated structure of thin plastic light guide sheets 32, a thin surface-emitting type light guide panel 31 can be obtained.

Note that, according to the arrangement of the rough surface portions 32a and 32b shown in FIG. 1, the rough surface portion 32a of the lower light guide sheet 32.

Since the light leaking from 32b passing through the upper light guide sheet 32 toward the back surface of the display panel 30 does not mutually interfere with the light traveling from the edge of the upper light guide sheet 32 toward the rough surface parts 32a and 32b, the illumination efficiency is improved. It is possible to prevent a decrease in

FIGS. 3 and 4 show an embodiment in which the present invention is applied to a membrane-type keyboard switch for a mobile phone terminal. In this figure, the same reference numerals are given to the same components as in the above embodiment.

In this embodiment, a light transmitting key top member 40 having a switch pattern 41a between a light transmitting key top member 40 which also functions as a display panel for displaying numbers, characters, etc. and a light guide panel 31 provided on the back side thereof is used. A recess provided on the back side of each key top portion 40a of the key top member 40 includes a key top portion 40'.
A conductor 40b is provided which contacts the switch pattern 41a and closes the switch circuit when the button a is pressed.

As shown in FIG. 4, the light guide panel 31 has a multi-layered structure of a plurality of light guide sheets 32 made of an excellent light transmitting plastic.
That is, the surface opposite to the key top member 40 is provided with a rough surface portion 32a having mountain-shaped or Fresnel-shaped unevenness for scattering and reflecting light incident from the end toward the back surface of the key top member 40. The position of the rough surface portion 32a of the light guide sheet 32 in each layer changes from the light guide sheet 32 in the lower layer to the light guide sheet 32 in the upper layer.
is shifted in the longitudinal direction. More specifically, in this embodiment, the two rough surface portions 32a are arranged so as to approach the ends of the corresponding light guide sheets 32, which are light incident surfaces, from the lower layer to the upper layer.

Further, in this embodiment, as shown in FIG. 3, the key top portion 40a of the key top member 40 has three
Because they are arranged in rows and have a wide display surface,
On the back side of the key top member 40 is the light guide sheet 32 described above.
Light guide panels 31 having a laminated structure are arranged in three rows, and light from a point light source such as an LED 42 (FIG. 4) is directed into the interior of each light guide panel 31 from one end of each light guide panel 31. It is configured so that it can be made incident.

In addition, when light is made to enter from both ends of each light guide panel 31, the rough surface portions 32a may be arranged and formed in the same manner as in the embodiment described above.

In this embodiment, light scattered and reflected by the rough surface portions 32a of the light guide sheet 32 of each layer of the light guide panel 31 is guided to each key top portion 40a of the key top member 40 to perform back illumination. By appropriately setting the length of the section of each rough surface portion 32a, back lighting of the entire surface of the key top member 40 or back lighting of only each key top portion 40a can be performed. Since the amount of light leaking from each light guide sheet 32 is approximately the same, unevenness in brightness does not occur in the key top member 40.

Although the illustrated embodiments have been described above, the present invention is not limited to the embodiments described above, and changes may be made to the shapes, numbers, etc. of the constituent elements within the scope of the invention described in the claims. can be added. For example, as a modification of the embodiment shown in FIG. 4, if the light guide panel 31 made of a laminated structure of light guide sheets 32 can be made thin in the form of a sheet, a switch pattern may be provided between the light guide panel 31 and the wiring board 37. It is possible to provide a membrane switch structure in which a conductor provided on the back surface of the light guide panel 31 is brought into contact with the switch pattern of the film by the pressing force of the key top member 40.

[Effects of the Invention] As is clear from the above description, according to the configuration of the present invention, light from a light source is efficiently absorbed by the light that is scattered and reflected by the rough surface portion of the light guide sheet of each layer and leaks from the light guide sheet. This makes it possible to provide a thin light guide panel that can be guided to a display panel and provide uniform back illumination.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a light guide panel showing an embodiment in which the present invention is applied to the back lighting structure of a display panel of a mobile phone terminal, and FIG. 2 is a longitudinal sectional view of the back lighting structure shown in FIG. 1. 3 is a perspective view of a keyboard switch and a light guide panel showing an embodiment in which the present invention is applied to the back lighting structure of a keyboard switch of a mobile phone terminal; FIG. 4 is a perspective view of a light guide panel shown in FIG. FIG. 5 is an exploded perspective view of the display operation section of a conventional mobile phone terminal; FIG. 6 is a longitudinal cross-sectional view of the back lighting structure of the display panel shown in FIG. 5; 7 is a vertical sectional view showing the back lighting structure of the keyboard switch shown in FIG. 5; FIG. 8 is a partially cutaway perspective view of the back lighting structure of a conventional display panel using a light guide sheet; FIG. 9 is a sectional view of a main part of the back illumination structure shown in FIG. 8. In the figure, 30 is a liquid crystal display panel, 31 is a light guide panel, 32 is a light guide sheet, 32a is a rough surface portion, and 40 is a key top member that also serves as a display panel.

Claims (1)

[Claims] 1. A light guide panel (31) for backlighting a display panel (30, 40), comprising a plurality of light guide sheets (32) made of plastic with excellent light transmission properties. are stacked in a multi-layered state, and the light guide sheet (32) of each layer has rough surface portions (32a, 32b) for scattering and reflecting the light incident from the end toward the back surface of the display panel (30, 40).
), and the rough surface portions (32a, 32b) of the light guide sheet (32) of each layer are formed.
The light guide sheet (3
2) A surface-emitting type light guide panel characterized by being shifted in the longitudinal direction.