JPH03190004A - Plane light source device - Google Patents

Abstract

PURPOSE:To thin a device by providing diffusing patterns, where the diffusion/ scattering becomes larger as a distance from a light source becomes larger, on at least either of the reflecting layer side of a transparent photoconductive layer and the transparent photoconductive layer side of the reflecting layer. CONSTITUTION:A light diffusing layer 1 is disposed all over the surface between tubular light sources 5, 5. Under the light diffusing layer 1, a transparent photoconductive layer 2 and a reflecting layer 4 are superposed in order. Acryl resin or polyester resin is used as the light diffusing layer 1 for the purpose of uniformly diffusing light emitted from the transparent photoconductive layer 2 over the whole surface. Grid-like diffusing/scattering patterns are screen-printed on one surface of the reflecting layer side of the acryl resin plate in such a manner that the area of a grid-like square becomes larger at every pitch proceding from the light receiving surface toward the center of the photoconductive layer, to be used for the transparent photoconductive layer 2. Therefore, the disposition of the diffusing/scattering patterns can be varied density, or a quantity of the light permeating in the direction of a visual field can be controlled. Consequently, the transparent photoconductive layer thinner than a conventional one can provide a plane luminance equal to or more than that of the conventional one as well as uniformity of the plane luminance, and additionally, a device can be formed thinly.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a planar light source device used for illumination, etc., and in particular, to uniformly illuminating a relatively wide area by receiving light from a point light source or a linear light source. The present invention relates to a lighting device that is used as a planar light source to perform a display, for example, a planar light source device that is used as a display lighting panel for advertisements or the backside illumination of a transmissive liquid crystal display device.

[Conventional technology]

Conventionally, when fluorescent lamps are used for indoor lighting, advertising billboards outdoors at night, etc., a linear light source is created by placing a light-diffusing plate-like object such as a breast plate in parallel with several fluorescent lamps and above them. It is common practice to convert the light emitted from a fluorescent lamp into a pseudo surface light source, but in this conventional method, the light source flux that is uniform all around the fluorescent lamp is forcibly converted into a flat light source at a certain position. As a result, the brightness distribution on the flat area where the light diffusion plate is placed sometimes becomes unsightly and uneven, which visually becomes the outline of the fluorescent lamp, which is one reason why it spoils the aesthetic appearance of the lighting device. Therefore, the light diffusing plate and the fluorescent light transducer must be placed at a considerable distance, which poses a problem from the viewpoint of space saving.

In addition, recently there has been an increasing demand for a relatively small planar light source having a uniform luminance distribution for use in back lighting of liquid crystal cameras, portable personal computers, or liquid crystal displays.

To deal with this, there are currently EL (electroluminescence) and direct type backlights in which a fluorescent lamp is placed directly below and the brightness distribution is adjusted using a light-shielding filter, etc., but they are not durable and are used as diffused lighting. Since it is not possible to obtain a transparent light that fully satisfies the above, there have been proposals to use two transparent light guide plates to guide light from their side edges, thereby providing diffused illumination of the surface. This has already been done and put into practical use in some areas.

[Problem to be solved by the invention]

However, when using a single transparent light guide plate in the past, it has a low light diffusion rate and low brightness, so it is possible to improve efficiency by providing a hairline-like rough surface on the back side or stacking a large number of light guide plates. (It is necessary to increase the brightness by scattering or guiding light, or it is necessary to provide a light control member to make the brightness distribution within the light emitting surface as uniform as possible.

However, these improvement methods have limitations and are not satisfactory considering the complicated processing involved, and it is necessary to increase the thickness of the transparent light guiding layer considerably in order to achieve the surface brightness required for a planar light source device. This has caused problems as it has not been possible to meet the demand for smaller and lighter equipment.

The present invention aims to solve these conventional problems, and is a planar light source device that can obtain brightness equal to or higher than conventional ones with an extremely thin transparent light guiding layer, and can reduce the size and weight of the device. The purpose is to provide a simple structure, easy to manufacture, and inexpensive form.

[Means to solve the problem]

In the present invention, a light-diffusing layer, a transparent light-guiding layer having at least one edge serving as a light incident surface, and a reflective layer are sequentially laminated from the viewing direction, and at least one edge of the transparent light-guiding layer is laminated. A light source and a reflective layer for the light source are installed on at least one of the reflective layer side of the transparent light guide layer or the transparent light guide layer side of the reflective layer,
Alternatively, the planar light source device is characterized in that a diffusion pattern is provided between the reflective layer and the transparent light guide layer, in which diffusion and scattering increase as the distance from the light source increases.

[For production]

In the planar light source device of the present invention, the reflection and diffusion efficiency of light is increased,
In order to improve surface brightness, a distance from the light source is provided on at least one of the reflective layer side of the transparent light guide layer, the transparent light guide layer side of the reflective layer, or between the reflective layer and the transparent light guide layer. Since it has a diffusion pattern in which the diffusion and scattering increases as the size increases, the light incident on the transparent light guide plate from the light incident surface is transmitted between the transparent light guide layer and the reflective layer or the light diffusion layer. Due to air, an adhesive layer, or other transparent material having a refractive index lower than that of the existing light guide layer, the light propagates through the light guide layer while repeating transmission or total reflection depending on the incident angle, and creates the above-mentioned diffusion/scattering pattern. It is scattered at the provided part, the direction of travel can be changed, and it is transmitted in the viewing direction, and the diffused/scattering pattern changes its arrangement densely as the distance from the light source increases, or the diffused/scattering pattern changes densely as the distance from the light source increases. Because the pattern itself changes the diffusion and scattering rate, the diffusion and scattering becomes large and the amount of transmitted light in the viewing direction is controlled, resulting in high brightness (and uniform brightness) with a relatively thin light guiding layer. A planar light source with a distribution can be obtained.

〔Example〕

Embodiments of the present invention will be described with reference to FIGS. 1 to 3. A light diffusing layer 1 is provided over the entire surface between the tubular light sources 5.5,
A transparent light guiding rgj 2 and a reflective layer 4 are sequentially laminated under the layer.

The light diffusion layer 1 is generally made of acrylic resin, because it further uniformly diffuses the light emitted from the transparent light guide layer 2 over the entire surface, and because a white surface light source is required for backside illumination of liquid crystals, etc. A milky white sheet or plate made of polyester resin or polycarbonate resin containing an appropriate light diffusing agent is used. In this case, depending on the type and amount of the light diffusing agent contained, the diffusion effect may decrease or
Furthermore, since the transmittance is low and the surface brightness is reduced as a result, it is desirable to select a material suitable for the required characteristics of the device.

The transparent light guide layer 2 has a size of, for example, 260×17. Ox
On one side of the reflective layer side of a 3m5 (thickness) or 4mm acrylic resin plate (Acrylite (product name), manufactured by Mitsubishi Rayon ■), a lattice-like diffusion/scattering pattern as shown in Figure 3 is placed on the light-receiving surface. A screen printing method was used to form a grid-like square in which the area of the grid-like squares increased with each pinch as the light guide layer progressed from the center to the center of the light guide layer.

In this case, the area for each pitch of the diffusion/scattering pattern is calculated using a logarithmic formula, since the amount of light transmitted is inversely proportional to the distance.
From various test results, by using the formula (a + b l nχ)2, where the distance from the light receiving surface is χ and the vertical and horizontal pinch of the diffused/scattering pattern is 0.5 yen, It was found that uniform and high brightness could be obtained overall. Note that the area changes only in the direction perpendicular to the light source,
It is constant in the parallel direction.

The pitch may be larger or smaller than 0.51, but when the pinch is P, it is necessary to have a diffused/scattering pattern. Also, pitches a and b may be changed vertically and horizontally, but when the pitch is 0.5IIIm, (a + b
The area should be adjusted to fit the formula of 1 nχ)2.0 In this example, pinch -1+u+a -0,18
4.b” 0.077, and two light sources were used on both sides as shown in Figure 1, so the length of the acrylic board was 170m+
The diffusion/scattering pattern 3 was formed so that the area was maximized at the center in the direction a, that is, at a position 85 mm from the end (light receiving surface).

In addition, in the formula “(a+b1nx)”, the a value is 0.05I
If the value is smaller than III11, the diffusion/scattering pattern becomes smaller over the entire area, so as shown in Table 1, sufficient brightness could not be obtained. Also, if it is larger than 0.5 mm, the diffusion/scattering pattern near the light receiving part will become too large.
A larger amount of light than necessary passed in the viewing direction near the light receiving section, and as a result, a uniform brightness distribution could not be obtained.

Furthermore, when the b value of (a+blnZ)'' was larger than 0.1, the area near the light receiving part changed rapidly, making it impossible to control the light amount and achieving a uniform brightness distribution.Thus, the a and b values are 0.05≦a≦0.5.0≦b≦, respectively.
A range of 0.1 is good. Also, if the pitch is smaller than 0.1 an, the transparent part existing between the diffusion/scattering pattern 3.3 will become too small, so the pitch between the reflective layer and the transparent light guiding layer will Light guiding efficiency decreases due to total internal reflection and reflection, resulting in a decrease in overall brightness. Moreover, when the pitch was made larger than 2 mm, the number of diffusion/scattering patterns decreased, so that the dimming effect for obtaining a uniform brightness distribution became insufficient, resulting in the problem of uneven brightness. Therefore, the pitch is 0.1 to 2.01
Good range.

Note that the transparent light guide layer 2 may be made of glass, epoxy resin,
Thermosetting resins such as silicone resins, acrylic resins, polycarbonate resins, thermoplastic resins such as polypropylene, polystyrene, polyethylene, etc. are acceptable, but from the viewpoint of transmittance, processability, and heat resistance, acrylic resins, polycarbonate resins, polystyrene resins, silicone rubber or
These polymer alloys are desirable.

Margin below 21 Furthermore, any method may be used to impart a diffusion/scattering pattern to the transparent light guide 112 or the reflective N4, and in addition to printing methods such as screen printing, gravure printing, pad printing, and offset printing, masking may be used. The diffusion/scattering portion may be cut by blasting or etching machining.

In addition, the ink used for printing may be any type of ink as long as it has a diffused/scattering reflection effect, and (trade name) was used in this example, but acrylic medium and Aerosil (Si(
h) may be mixed in a certain amount to give a diffusion effect, or TiO□ may be added thereto to give a reflection effect. Furthermore, the coating thickness of the ink is not particularly limited as long as the selected ink provides sufficient diffuse and scattering reflection effects, and in this example, it is 10
μm or more is better.

Furthermore, the reflective layer 4 may be made of, for example, an aluminum vapor-deposited sheet, PET containing a diffusing agent, acrylic, or ABS.
Although a synthetic resin plate such as ``Tetrite'' (trade name, manufactured by Tokyo Oike Sangyo ■), which is a PET base material on which silver is vapor-deposited and then top-coated, was used in this example.

5 in the figure is a light source, which has a tube diameter of φ5.8 mm and an effective light emission length of 2.
40+uw, tube current 13 mA % tube brightness 12.00
Two 0 cd/m 2 three-wavelength white cold cathode tubes (manufactured by Harrison Electric) were placed opposite each other in the long side direction of the transparent light guiding layer. 6 is a reflective layer for the light source, which is provided to reduce the loss of light emitted from the light source 5 and to provide directionality so that the light is efficiently guided to the incident end surface of the transparent light guide layer 3; Said reflection 11! The same parts as i4 were used.

Each layer is laminated and the outer periphery of the illumination surface is made of adhesive such as double-sided adhesive tape, adhesive, welding, or fitting into a formwork or other frame, and the light source 5 is attached to reduce light loss. It is preferable to affix a reflective sheet (not shown) similar to the reflective layer 4 to the uninstalled edge portions, and in any case, it is preferable to use a configuration in which each part is fixed together or assembled together.

In the planar light source device according to this embodiment, the power supply voltage is 12
When the light source was turned on via an inverter at V, as shown in Example 1.2 of Table 1, 4 m of Aku9114
150cd/+i” for m, 700cd for 3+m+m thickness
/m'', a planar light source with an effective luminance unevenness of 10% or less was obtained.

In addition, as Comparative Example 1, when the transparent light guide layer 2 was replaced with a flat plate (without printing) with a thickness of 4 m + w, the brightness was 150 cd/+
In addition, as Comparative Example 9, when a 51 Im thick acrylic plate with a hairline pattern with a pinch of 0.5 mm and a slope angle of 456 was used as a transparent light guiding layer, the luminance was 400 cd/m. ”, the effective light emitting part luminance unevenness is 15%, and the lattice-like diffusion/scattering pattern 3 of the present invention
By changing the area according to the distance from the light-receiving part, the surface brightness is higher than that of the conventional hairline pattern, and the brightness distribution is also more uniform.In addition, the thinner light guiding layer allows for higher brightness than before. I was able to obtain

Further, as shown in Comparative Examples 2, 3.4, and 5.6, the a value was set to 0.
If set to 05 If set to 0.5, the b value will be set to 0.
When set to 1, when the pitch is set to 0.1 mm, and when set to 2.0go+, the brightness is 450, 550, 550, 450° 600cd, respectively.
/m”, the brightness unevenness is 10, 40, 47°32.28%
Therefore, the effect of high brightness and uniformity due to the diffusion/scattering pattern was insufficient.

Incidentally, the diffusion/scattering pattern 3 is not limited to a square shape, but may be a round shape, a hexagonal shape, a rectangular shape, a halftone dot shape, etc. as shown in Example 7.8 shown in Table 1, and is not particularly limited. . However, based on (a + b J nχ)2, the area should be increased as the distance from the light source increases. 4th to 9th
The illustrated examples each show a specific example of the diffusion/scattering pattern 3.

In addition, the pinch does not need to be constant, and should be done after considering that the diffusion and scattering patterns have the same area ratio based on the area calculated by (a + b 1 nχ) 8 at a constant pitch. may be changed.

Further, in addition to providing the diffusion/scattering pattern 3 directly on the light guide layer and the reflective layer, it is also possible to provide the diffusion/scattering pattern 3 on a transparent base material and place it between the reflective layer and the light guide layer. Since there is a loss in light efficiency due to an increase in the number of members and an increase in the number of interfaces through which the light passes, it is preferable to provide the light directly on the light guiding layer or reflective layer as much as possible.

Unlike the previous example in which the diffusion/scattering pattern 3 was printed in a circular and square shape as shown in the example in Figure 8, a reverse printing pattern was used, in which white areas such as circles and squares were printed while remaining. It will be done.

In addition, as shown in the example in Fig. 9, the area of the diffusion/scattering pattern 3 is kept constant and the pitch is changed, and the farther from the light source the more densely the diffusion/scattering pattern 3 is arranged to reduce the amount of transmitted light in the viewing direction. Even when these methods, which can also be considered as control methods, were used, the same level of brightness and uniformity as in Example 1.2 was obtained.

Furthermore, the ink used when forming a diffusion/scattering pattern by printing method etc. is Ti1 in order to obtain the diffusion/scattering function.
t, Glass Peas, Sing or A7! Metal powders such as Ag and Ag are mixed, and diffusion and
The scattering function changes. In addition, the function of the same ink changes depending on the coating thickness, so regardless of the area, pinch, or density of the diffusion/scattering pattern, or in combination with these, the diffusion/scattering function of the ink itself changes depending on the coating thickness. It is conceivable that uniform and high brightness can be obtained as a whole of the device by controlling by changing the components and increasing the diffusion and scattering as the distance from the light source increases.

Actually, acrylic ink (PAL 2500 series 800 medium) was used as ink on the acrylic board mentioned above.
35% to 5% of Ti0z (fluorescent pigment mortar (product name), ■Mino Group) to obtain a reflective effect, and Sin to obtain a diffusion effect.
g (Aerosil R972 (trade name), manufactured by Nippon Aerosil ■) at a ratio of 10% to 3%, with the part farthest from the light source having the highest blending ratio, and gradually decreasing the blending ratio to change the diffusion/scattering function and print. Example 1 also applies when a light guide plate is used.
．． A planar light source with the same level of uniformity and high brightness as in Example 2 was obtained.

〔Effect of the invention〕

The present invention provides a structure in which at least one of the reflective layer side of the transparent light guide layer, the transparent light guide layer side of the reflective layer, or between the reflective layer and the transparent light guide layer is located at a large distance from the light source. By having a diffusion pattern that increases diffusion and scattering as the color increases,
The light incident from the light incident surface passes between the transparent light guiding layer and the reflective layer or light diffusing layer through an air layer with a lower refractive index than the transparent light guiding layer, an adhesive layer or other transparent material. Therefore, as the light passes through the transparent light guide layer by repeating transmission or total reflection depending on the angle of incidence, its direction of travel is changed by a diffusion/scattering pattern, and the arrangement of the diffusion/scattering pattern changes densely. By changing the diffusivity and reflectance of the diffusion/scattering pattern itself, the amount of light transmitted in the viewing direction can be controlled. Uniformity of brightness can be obtained, and it is also possible to make the device thinner and lighter, and to significantly reduce costs.

[Brief explanation of drawings]

FIG. 1 is a perspective view for explaining assembly of a planar light source device according to an embodiment of the present invention, FIG. 2 is a longitudinal sectional view, and FIG. 3 is a partially cutaway bottom view.
4 to 9 are enlarged plan views of a portion of the other side of the transparent light guide plate. DESCRIPTION OF SYMBOLS 1... Light diffusion layer, 2... Transparent light guide layer, 3... Diffusion/scattering pattern, 4... Reflection layer, 5... Light source, 6...
・Reflection layer for light source. 1 patent applicant

Claims (1)

[Claims] (1) A light diffusing layer, a transparent light guide layer with at least one edge serving as a light incident surface, and a reflective layer are sequentially laminated from the viewing direction, and a light source is placed on at least one edge of the transparent light guide layer. and a light source reflective layer, and a reflective layer for the light source is provided on at least one of the reflective layer side of the transparent light guide layer, the transparent light guide layer side of the reflective layer, or between the reflective layer and the transparent light guide layer. A planar light source device characterized by having a diffusion pattern in which diffusion and scattering increase as the distance between the two increases.