JPH09145937A - Back light device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a bright line on a light emission surface from being generated owing to a liquid drooping, etc., by arranging an infinite number of unspecified-shape diffusing bodies at irregular intervals and constituting a diffusion pattern part, and diffusing the luminous flux of a light source which enters a light guide plate and projecting it from the top surface. SOLUTION: This device is equipped with the parallel flat light guide plate 1, light sources 2 and 2 which are arranged along the opposite end parts of the light guide plate 1, reflecting mirrors 3 and 3 which are formed covering the light sources 2 and 2 from the edge of the light guide plate 1, a reflecting sheet which is arranged on the reverse-surface side of the light guide plate 1, and a diffusion sheet 1 and a prism sheet which are laminated in order on the top surface side of the light guide plate 1. The diffusion pattern part 7 formed on the reflecting surface 1c of the light guide plate 1 has an infinite number of unspecified-shape diffusing bodies 8... arranged at irregular intervals by silk screen printing using white paint. Consequently, a bright line on the light emission line due to a liquid drooping and a defect in printing adhesion at the time of the formation of the diffusion part can be prevented from being generated even if the diffusion part is made thinner and smaller in interval accompanying making the back light device further thinner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight device that illuminates a liquid crystal display panel from the back side.

[0002]

2. Description of the Related Art In recent years, since a backlight device for illuminating a liquid crystal display panel from the back side can be easily thinned, a tubular light source such as a cold cathode tube is a transparent light guide having excellent light transmittance. The edge light method is mainly used, which is attached along a side end portion of a light guide plate made of polymethylmethacrylate, guides a light beam from a light source into the light guide plate, and causes the light beam to be emitted from an emission surface on the upper surface of the light guide plate.

As the edge light type backlight device, as shown in FIG. 14 (a), a single light type device in which a light source 32 is arranged along one end of a parallel plate-shaped light guide plate 31, or the same. As shown in FIG. 2B, a two-lamp type in which the light sources 32 are arranged along two opposite ends of the light guide plate 31, and as shown in FIG. The light sources 32 are arranged along the three ends of the light guide plate 31.

Here, the principle of forming a surface light source in the edge light type backlight device will be described with reference to FIG. FIG. 15 is a cross-sectional view showing a configuration example of a two-light type backlight device.

The light flux from the light source 32 enters the light guide plate 31 directly or after being reflected by the reflecting mirror 33 provided on the back side of the light source 32. The incident light beam is guided by the light guide plate 3
Although it propagates in 1, the light is totally reflected as long as it is incident on the boundary surface between the air and the light guide plate 31 at an angle equal to or larger than the total reflection angle (determined by the refractive indexes of the substances existing on both sides of the boundary surface). Therefore, when each surface of the light guide plate 31 is a mirror surface,
An upper surface (hereinafter referred to as an emission surface) 31b of the light guide plate 31 and a bottom surface (hereinafter referred to as a reflection surface) 31c of the light guide plate 31, which are in a vertical relationship with a side end surface 31a of the light guide plate 31 on which the light source 32 is arranged. No luminous flux is emitted from.

However, when the reflecting surface 31c is not a mirror surface, the light beam is reflected or transmitted, and depending on the form of the reflecting surface 31c, it is also emitted from the emitting surface 31b. Therefore, a surface light source can be realized by appropriately providing the reflecting surface 31c with a portion (hereinafter referred to as a diffusion portion) that diffuses (diffusely reflects) the light flux without totally reflecting it and a portion that totally reflects the light flux.

As a method of forming the diffusing portion, at present, a method of printing a white paint on the reflection surface of the light guide plate, which is called a printing method, and a reflection surface of the light guide plate, which is called a rough surface method, are used. The method of processing into irregularities is the mainstream. In the former case, FIG.
As shown in (a), a plurality of diffusers 38 made of white paint in a dot shape or in a wedge shape as shown in (b) of the drawing are arranged on the reflecting surface 31c of the light guide plate 31. In the backlight device of FIG. 15, the diffusion pattern portion 37 formed on the reflection surface 31c of the light guide plate 31 has dot-shaped diffusers 38 ... Formed by this method.
On the other hand, in the latter method, as shown in FIG. 17A, the reflecting surface 31c of the light guide plate 31 has a cone-shaped recess, or as shown in FIG. 17B, a V-shaped groove-shaped recess. A plurality of diffusion recesses 39 ... Are formed.

By the way, it is desirable that the backlight device has a uniform brightness, and a uniform light flux must be emitted from the emission surface of the light guide plate over the entire area thereof. The light flux emitted from this emission surface is determined by the area ratio of the diffusion part per unit area occupied in the reflection surface formed on the mirror surface (hereinafter referred to as the occupied area ratio), and the amount of light incident on these diffusion parts. .

Considering the propagation of a light beam in a light guide plate whose entire surface is a mirror surface, naturally, the light beam first reaches a portion near the light source, and is totally reflected and propagates to a portion away from the light source. Therefore, in order to reach the part far from the light source, the part of the light beam may be diffused in the part close to the light source, and the rest of the light beam may be totally reflected. In other words, by manipulating the occupation area ratio of the diffusing portion between the portion close to the light source and the portion distant from the light source, the amount of light from the emission surface can be changed, and the occupation area ratio can be improved when forming the diffusion pattern portion. By designing, a uniform light flux can be emitted over the entire emission surface of the light guide plate. Basically, as the distance from the light source increases, the occupation area ratio of the diffusion portion may be increased, and the occupation area ratio of the diffusion portion in the two-light type backlight device is as shown in FIG.

However, in reality, as shown in FIG. 15, a diffusion sheet 35 is arranged on the emission surface 31b of the light guide plate 31 to form a surface light source. This is because, unless the shape and pitch of each diffuser 38 of the diffusion pattern portion 37 is so small that the diffusion pattern portion 37 cannot be recognized by human eyes, density unevenness due to the pattern occurs and it is not practical as a surface light source. Because there is no. In addition to the diffusion sheet 35, the reflection surface 31 of the light guide plate 31 is provided below the reflection surface 31c.
Reflective sheet 3 for effectively utilizing the light flux leaking from c
4. The exit surface 31b of the light guide plate 31 is provided on the diffusion sheet 35.
Directivity conversion sheets 36 for increasing the luminance in the normal direction are arranged respectively.

[0011]

By the way, in recent years, as the liquid crystal display device has become thinner, more compact, and cheaper, further thinning of the backlight device has been required. Therefore, it is necessary to reduce the diameter of the tubular light source and the thickness of the light guide plate accordingly. However, the above-mentioned conventional diffusion pattern portion cannot meet the needs for further thinning of the backlight device for the following reasons.

That is, in the case where the diffusion pattern portion is formed even in the light guide plate which is further thinned, as shown in FIG.
The shapes and pitches of the diffuser 38 shown in (a) and (b) and the diffused recess 39 shown in FIGS. 17 (a) and (b) are at least fine enough to be unrecognizable by the diffuser sheet arranged thereon. Must be one. Therefore, as the light guide plate becomes thinner, the diffuser 38 and the diffusion recess 39 become thinner,
Fine pitching is required.

However, the diffuser 38 and the diffused recess 39 in the conventional diffusion pattern portion are formed in various shapes and pitches that are optimally designed, and in any case, the shapes are similar. It is a shape and is the same in pitch, or regular based on a certain relationship.

Therefore, the dot-shaped or wedge-shaped diffuser 3
In the case of printing No. 8, if the pitch is made fine and the pitch is small, for example, as shown in FIG. 19A exemplifying a dot shape, individual diffusive substances 38 are likely to be bonded at the portion between them due to liquid sagging. In the figure, the portion where the paint adheres due to the liquid sag is shown by the diagonal lines. When such liquid sagging occurs, the area of the diffuser 38 increases at that portion, and the luminous flux emitted from the emission surface of the light guide plate at that portion also increases, resulting in the brightness desired in advance on the light emitting surface of the backlight device. Distribution cannot be obtained.

Further, in the case of the dot-shaped diffuser 38, even if the design shape is circular, if the adhesiveness at the time of printing is poor, print adhesion failure occurs, and the shape when actually printed is perfect. Strictly speaking, it is not a perfect circle, but FIG.
A defective print portion such as a shaded portion shown in (b) is formed. Such defective printing adhesion is caused by the size of the diffuser 38 itself.
It is not a problem if it is much larger than the defective print portion, but it cannot be ignored if the diffuser 38 itself becomes smaller due to the slimming down, and as in the case of the liquid sag described above, the brightness of the light emitting surface which is desired in advance is obtained. Distribution cannot be obtained.

In the structure of the conventional diffusion pattern portion in which the diffusers 38 are regularly arranged, the influence of the liquid drip is concentrated on the portion of the diffuser 38 having a large shape away from the light source side, while the print adhesion is performed. The bad influence caused by defects is concentrated on the light source side where the shape of the diffuser 38 is small, resulting in uneven density, which is recognized as a bright line on the light emitting surface, resulting in a low-quality backlight device.

As a measure against this, the shape of the diffuser 38 is increased to such an extent that liquid dripping does not occur, or to the extent that it is not affected by print adhesion defects. Make the light guide plate or the diffusion sheet disposed on it thicker so that it cannot be recognized on the light emitting surface, or make the light guide plate or the light guide plate so that density unevenness due to liquid sagging or defective printing adhesion cannot be recognized as bright lines on the light emitting surface. Either the thickness of the diffusion sheet is made thicker, which is a countermeasure against the thinning. Also, due to liquid dripping and poor print adhesion,
It is also clear that the yield will decrease in the manufacturing process,
Incurs high costs.

On the other hand, in the method of processing the light guide plate 31 into unevenness like the diffusion recess 39 shown in FIGS. 17 (a) and 17 (b),
The problems of dripping and defective printing adhesion as described above do not occur.
However, with the conventional structure of the diffusion pattern portion in which the diffusion recesses 39 are regularly arranged, it is obvious that the manufacture becomes extremely difficult by making the diffusion recesses 39 finer in shape and finer in pitch, and thus it is inevitable that high-level processing is required. It requires technology and leads to high costs.

As described above, in the conventional structure of the diffusion pattern portion, as the light guide plate becomes thinner, it becomes difficult to form the diffusion pattern portion, and bright lines are likely to occur on the light emitting surface of the backlight device. Moreover, even if good formation is possible, there is a problem in terms of manufacturing cost due to poor mass productivity, such as a low yield and the need for expensive manufacturing equipment.

[0020]

In order to solve the above-mentioned problems, the backlight device of the present invention according to claim 1 is
A tubular light source is arranged along at least one end of a light-transmissive flat light guide plate, and a bottom surface of the light guide plate diffuses a light flux from the light source incident on the light guide plate and emits the light from the upper surface. In the backlight device provided with a diffusion pattern portion for, the diffusion pattern portion is characterized in that an infinite number of irregular diffusion portions are arranged at an irregular pitch.

According to a second aspect of the present invention, in the backlight device of the first aspect, the diffusing portion is formed by applying a diffusing material to the bottom surface of the light guide plate. .

According to a third aspect of the present invention, in the backlight device of the first aspect, the diffusing portion is formed by processing the bottom surface of the light guide plate into an uneven shape.

According to the structure of claim 1, in the diffusion pattern portion, an infinite number of irregular diffusion portions are arranged at an irregular pitch, and the diffusion portions are the conductors as described in claim 2. Some are formed by applying a diffuser to the bottom surface of the light plate, and some are formed by processing the reflecting surface of the light guide plate as described in claim 3 into an uneven shape.

For example, in the case of the former diffuser formed by applying the diffuser, the shape of the diffuser is similar to that of the conventional diffuser pattern, and the pitch is the same or regular based on a certain relationship. And with the reduction in shape and pitch,
A change in the occupied area ratio of the diffusion portion due to liquid sagging or defective printing adhesion occurred concentratedly in a specific region, and a bright line was recognized on the light emitting surface of the backlight device. On the other hand, in the diffusion pattern portion of the present invention, the shape of the diffusion portion is indefinite and the pitch thereof is also indefinite. It does not occur in a concentrated manner, but at random positions on the reflective surface.

Therefore, the influence of the liquid dripping and the defective printing adhesion on the brightness of the light guide plate is remarkably smaller than that of the conventional one, and as the backlight device is further thinned, the diffusion part is thinned and the pitch is reduced. Even if it is achieved, it is possible to prevent the generation of bright lines on the light emitting surface due to liquid dripping or defective printing adhesion.

Further, in this case, even if a large amount of liquid dripping or defective printing adhesion occurs, the diffusion pattern portion of the present invention has an irregular shape of the diffusion portion and its pitch is also indefinite. By designing the pattern in advance in consideration of the occupied area ratio, the problem can be dealt with without any problem.

Further, in the case of the latter diffusing portion formed by processing the reflecting surface of the light guide plate into unevenness, the conventional diffusing pattern portion is extremely difficult to manufacture due to the thinning and fine pitch of the diffusing portion. However, in the diffusion pattern portion of the present invention, since the shape of the diffusion portion is indefinite and the pitch thereof is also indefinite, it is possible to achieve a fine shape and a fine pitch without difficulty.

In the diffusion pattern portion of the present invention, innumerable irregular diffusion portions are arranged at an irregular pitch.
When viewed at the micro level of each diffuser, the amount of diffusion of the light flux is different everywhere on the reflecting surface, but when viewed at the macro level targeting the area where many diffusers are incorporated,
If the occupying area ratio of the diffusing part is the same, the diffusing amount of the light flux can be made the same everywhere on the reflecting surface. Therefore, the indefinite shape and pitch of the diffusing part does not affect the luminance distribution. Not at all.

According to a fourth aspect of the present invention, in the backlight device of the first aspect, the diffusion pattern portion has a unit area as the distance from the light source side end portion side where the light source is disposed increases. It is characterized in that it is formed so that the occupancy rate of the diffusion portion with respect to the bottom surface of the light guide plate per hit is high.

The luminous flux emitted from the upper surface of the light guide plate is determined by the occupation area ratio (occupancy rate) of the diffusing portion per unit area occupying the bottom surface and the amount of light incident on these portions. Therefore, according to the configuration of the fourth aspect, as the diffusion pattern portion is separated from the light source side end portion side where the light source is arranged, the occupancy ratio of the diffusion portion to the bottom surface of the light guide plate per unit area becomes higher. Since it is formed, the amount of the emitted light flux emitted from the upper surface of the light guide plate becomes uniform regardless of the distance from the light source, and the backlight device has a uniform light emitting surface.

According to a fifth aspect of the present invention, in the backlight device of the first aspect, there is a side end face that reflects light from the light source, and the light source is arranged in the diffusion pattern section. Further, it is characterized in that the occupancy rate of the diffusing portion with respect to the bottom surface of the light guide plate per unit area increases as the distance from the light source side end portion side and the light reflecting side end surface side increases.

When there is a side end surface that reflects the light from the light source, the side end surface can be a secondary light source. Therefore,
According to the configuration of claim 5, as the diffusion pattern portion is separated from the light source side end portion side where the light source is arranged and the light reflecting side end face side, the diffusion portion of the diffusion portion relative to the bottom surface of the light guide plate per unit area is increased. Since it is formed to have a high occupancy rate,
Even the luminous flux by the secondary light source configured by the side end surface that reflects the light from the light source is considered, and the amount of the outgoing luminous flux emitted from the upper surface of the light guide plate is further irrespective of the reflection on the side end surface. The backlight device becomes uniform and has a more uniform light emitting surface.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to FIGS. still,
A 12-inch class two-light type backlight device is exemplified here. Needless to say, the specific dimensions, materials, etc. of each part can be changed in various ways.

The backlight device according to the present invention is shown in FIG.
As shown in (a) and (b), a light guide plate 1 in the form of a parallel plate and a light source 2 arranged along two opposite ends of the light guide plate 1.
2 and the reflecting mirrors 3 and 3 formed so as to cover the light sources 2.2 from the edge of the light guide plate 1, the reflection sheet 4 arranged on the lower surface side of the light guide plate 1, and the upper surface side of the light guide plate 1. A diffusion sheet 5 and a prism sheet 6 which are sequentially stacked are provided.

The light guide plate 1 is a flat plate of polymethylmethacrylate, which is a transparent light guide having excellent light transmittance, and has a mirror finish of 252 mm in width and 198 mm in length.
mm, thickness 5 mm. Further, in the light guide plate 1, the side end faces 1a, 1a on which the light sources 2 are arranged are incident surfaces for making the light fluxes from the light sources 2, 2 incident inside, and the upper surface 1b emits the guided light fluxes. The emission surface and the lower surface 1c of the light guide plate 1 are reflection surfaces that reflect the light flux guided inside. Hereinafter, they will be referred to as an entrance surface 1a, an exit surface 1b, and a reflection surface 1c. Then, on the reflection surface 1c of the light guide plate 1, a diffusion pattern portion 7 for diffusing the light flux and emitting it from the emission surface 1b.
Although the details of the diffusion pattern portion 7 will be described later, the diffusion pattern portion 7 has a pattern different from the conventional one.

The light source 2 is a tubular light source composed of a cold cathode three-wavelength tube fluorescent lamp, and its dimensions are a tube diameter of 3 mm and a tube length of 265.
mm. The reflecting mirror 3 is made of a white polyethylene terephthalate film, and is for reflecting the luminous flux emitted to the back side of the light source 2 (the side opposite to the light guide plate 1) and efficiently entering the light guide plate 1. The reflection sheet 4
Is also made of a white polyethylene terephthalate film, and is for returning the light flux leaking from the reflecting surface 1c of the light guide plate 1 to the inside of the light guide plate 1 again to achieve effective use of light.

The diffusion sheet 5 is made of a polycarbonate resin sheet having beads and having a uniform uneven surface. The light flux emitted from the emission surface 1b of the light guide plate 1 is
It will spread further. The prism sheet 6 is made of a polycarbonate resin sheet having a saw-like cross section and having a groove extending parallel to the tube axis direction of the light source 2, and is for increasing the luminance in the normal direction of the emission surface 1b.

Next, the diffusion pattern portion 7 formed on the reflecting surface 1c of the light guide plate 1 will be described with reference to FIGS. As shown in FIG. 1, the diffusion pattern section 7 has
Innumerable irregular shaped diffusers (diffusion parts) 8 are arranged at irregular pitches. And diffuser 8 ...
Are distributed from the side where the light sources 2 are arranged toward the central part of the light guide plate so as to become sparse to dense.

The diffusers 8 ... Are formed by silk printing using a white paint, and such an irregular shape and irregular pitch pattern are easily formed as follows. That is, as in the conventional case, desired gradation data such as the occupied area ratio of the diffuser 8, the printing range, and the fineness of the pattern are input to the computer, and the pattern output editing machine (for example, Dreb series 250 manufactured by Cytex) is input. ) Is converted into data that can be imported. Then, the pattern output editing machine is operated by dedicated software (for example, Fm screen manufactured by Cytex Co., Ltd.) that converts gradation data into an irregular shape. As a result, the printing plate of the diffusion pattern portion 7 having a configuration in which the irregular shaped diffusers 8 are arranged innumerably at an irregular pitch is output. After that, silk printing is performed using this printing plate in the same manner as in the conventional method, and the diffusion pattern portion 7 is formed on the surface that becomes the reflection surface 1c of the light guide plate 1.

In the case of the light guide plate 1 of the present backlight device, the occupation area ratio of the diffuser 8 is 16 to 80 at a position of ± 90 mm from the center position of the light guide plate 1 toward the light sources 2.2.
It is formed so that it changes linearly with%. FIG. 3 shows the pattern state of the diffusion pattern portion 7. In the figure, the diffusers 8 are shown in white, and the surface of the light guide plate 1 is shown in black. Also from this figure, it is understood that the shape and pitch of the diffuser 8 of the diffusion pattern portion 7 formed on the light guide plate 1 of the present backlight device are indefinite (random).

Then, such a diffusion pattern portion 7 is
When viewed at the micro level of each diffuser 8, the reflective surface 1c
The diffusion amount of the light flux is different everywhere, but at the macro level for the region including a large number of diffusers 8, ..., The diffusion amount of the light flux is equal everywhere in the tube surface direction of the reflecting surface 1c. . For example, in FIG. 3, the area S
Diffusion amount in the diffusion volume and area S ₂ of ₁ is equal, the area S
The diffusion amount of _{3 and} the diffusion amount of the area S ₄ are also equal.

In the backlight device having the above structure, the luminous flux emitted from the light sources 2 and 2 is directly or reflected by the reflecting mirror 3.
A light beam that is reflected by 3 and enters the inside of the light guide plate 1 through the incident surface 1a, and repeats total reflection to proceed to the inside of the light guide plate 1,
It is divided into a light beam emitted from the emission surface 1b and the light guide plate 1 is made into a surface light source. That is, of the light that has entered the light guide plate 1, the light that has entered the diffuser 8 of the diffusion pattern portion 7 formed on the reflection surface 1c is diffused and emitted from the emission surface 1c or the reflection surface 1c. Then, the light is reflected by the reflection sheet 4 and enters the light guide plate 1 again. On the other hand, what is incident on the mirror surface portion where the diffuser 8 is not formed is totally reflected, and then is totally reflected on the emitting surface 1b and reaches the reflecting surface 1c again, where it is also totally reflected and is further guided to the light guide plate. 1 is divided into a light flux that travels inside and a light flux that exits the light guide plate 1. The light flux emitted from the emission surface 1b of the light guide plate 1 is further diffused by the diffusion sheet 5 arranged on the upper surface thereof, and the directivity is converted by the prism sheet 6.

Next, the diffusion pattern portion 7 as described above is
The result of examining the influence on the luminance distribution is shown below. here,
Except for having a conventional diffusion pattern portion having a dot-like shape and a constant pitch on one surface (which will later become a reflection surface) of the light guide plate having the same configuration as the above light guide plate 1, a diffuser A comparative diffusion pattern portion made of a diffuser having the same structure as that of No. 8 was formed.

FIG. 4 shows the pattern state of the comparative diffusion pattern portion. In the figure, the diffuser is white and the surface of the light guide plate is black. As can be seen from the figure, the shapes of the diffusers are similar, only the diameter differs depending on the location, and the smaller the light source side is. And the pitch of the diffuser is the same. FIG. 5 shows an enlarged part of FIG. The pitch ad and the pitch ae in the dot-shaped diffuser 21 are 0.8.
In the case of 98 mm, the pitch ab and the pitch bc are 0.898
This is 0.635 mm, which is 2 ^1/2 of mm, and these pitches are equal among all diffusers 21.

Also in this comparative diffusion pattern portion, the occupation area ratio of the diffuser 21 is 16 to 80% at a position of ± 90 mm from the center of the light guide plate toward the light source.
It is formed to change linearly at.

First, the printing plate for forming the diffusion pattern portion 7 and the comparative diffusion pattern portion was measured with a densitometer. The results are as shown in FIG.
From this, it is understood that the diffusion pattern portion 7 and the comparison diffusion pattern portion have the same area ratio of the diffusers 8 and 21, although the shape and pitch of the diffusers 8 and 21 are different.

Next, using the light guide plate on which the comparative diffusion pattern portion is formed, a backlight device having the same structure as the present backlight device is manufactured, and the brightness of each light emitting surface of the present backlight device and the comparative backlight device. The distribution was measured. When no liquid dripping or print adhesion failure occurred during printing of the diffusers 8 ... 21 ..., the results were as shown in FIG. The measurement point indicates the luminance ratio when the center point of the light guide plate 1 is 0 mm, the point is measured in 10 mm steps in the vertical direction, and the basis of the center point is 100%.

From this, it can be seen that, in the case where liquid dripping or print adhesion failure does not occur, the luminance distribution of the light emitting surface is the same as long as the area ratio of the diffusers 8 and 21 is the same. Therefore, it can be seen that by optimally designing the diffusion pattern portion, a backlight device having a uniform luminance distribution can be obtained in both the diffusion pattern portion 7 and the comparison diffusion pattern portion of the present backlight device.

However, when liquid dripping or defective printing adhesion occurred during printing of the diffusers 8 ... 21 ..., a great difference was confirmed between the two. In the case of the comparative diffusion pattern portion, since the diffusers 21 of similar shape are scattered on the reflecting surface with only the diameter changed at the same pitch, a large shape whose occupied area ratio is likely to increase due to liquid sagging Are concentrated in the vicinity of the center of the light guide plate, and small shapes whose occupying area ratio is likely to be affected by defective printing adhesion are also concentrated in the end side where the light source is arranged. Also, the print adhesion failure was concentrated in those specific areas.

FIG. 8 (b) shows a solid line showing the occupied area ratio of the diffuser 21 in the case where liquid sagging occurs. Further, the diffuser 2 in the printing plate used for printing the comparative diffusion pattern portion 2
The occupied area ratio of 1 is shown by a broken line. This is a design value of the occupying area ratio, and is equal to the occupying area ratio when the diffusers 21 ... Are formed without liquid sagging and defective printing adhesion. From this figure, it can be seen that liquid sagging occurs near the center of the light guide plate where the diameter of the diffuser 21 is large, and the actual occupied area ratio at that portion suddenly becomes larger than the design value from a certain portion.

In FIG. 7C, the occupied area ratio of the diffuser 21 in the case where printing adhesion failure occurs is shown by a solid line, and the occupied area ratio of the diffuser 21 in the printing plate used at that time is shown by a broken line. Indicate. From this figure, the influence of the print adhesion defect becomes large on the light source side end portion side of the light guide plate where the diameter of the diffuser 21 becomes small, and the actual occupied area ratio at that portion suddenly becomes smaller than the design value from a certain portion. You can see that FIG. 7A shows a case where liquid sagging and print adhesion failure occur at the same time.

On the other hand, in the case of the diffusion pattern portion 7 of the present backlight device, since the irregular shaped diffusers 8 are arranged at an irregular pitch, there is a shape in which the occupied area ratio is likely to increase due to liquid sagging. Large ones and small ones whose occupying area ratio is likely to be affected by defective printing adhesion are scattered at random positions on the reflecting surface 1c, so that liquid sagging and defective printing adhesion also occur at random positions. . Therefore, unlike the comparative diffusion pattern portion, there is no sudden change from the portion having the occupied area ratio,
The occupied area ratio was linear, which was almost the designed value.

As described above, the diffusion pattern portion 7 formed on the reflecting surface 1c of the light guide plate 1 in the present backlight device.
Is composed of innumerable irregular diffusers 8 ... Arranged at irregular pitches. Therefore, if the shape of the diffuser is similar, and the pitch is the same or regular based on a certain relationship like the conventional diffusion pattern portion, liquid sag According to this, the change in the occupation area ratio of diffusers due to poor print adhesion occurred in a specific area. It does not occur in a concentrated manner, but at random positions on the reflective surface.

As a result, the influence of liquid dripping or defective printing adhesion on the brightness of the light guide plate is significantly reduced as compared with the conventional case, and further reduction in thickness can be achieved as in the backlight device of the present invention, and the diffuser 8 Even if the thin shape and the fine pitch are achieved, it is possible to prevent the generation of bright lines on the light emitting surface due to liquid dripping or defective printing adhesion, and it is possible to obtain a high-quality backlight device.

Further, in this case, even if a large amount of liquid dripping or defective printing adhesion occurs, the shape of the diffuser 8 in the diffusion pattern portion 7 is indefinite and its pitch is indefinite. By designing the pattern with the occupation area ratio that allows for it, it can be dealt with without any problems.

Further, the diffusion pattern portion 7 as described above has an effect that the reproducibility at the time of printing can be made higher than that of the structure of the conventional diffusion pattern portion, and the yield can be improved. Further, since the influence of liquid dripping and defective printing adhesion is small, the range of conditions such as adhesion of the paint used for forming the diffusion pattern portion 7 is widened, and the material cost can be reduced.

Further, in the present backlight device, as the diffusion pattern portion 7 is separated from the light source side end portion side where the light source 2 is arranged, the area ratio of the diffuser 8 to the reflecting surface 1c per unit area is higher. Since it is formed as described above, the amount of emitted light flux emitted from the emission surface 1b of the light guide plate 1 becomes uniform regardless of the distance from the light source 2, and the backlight device has a uniform light emitting surface. .

Here, only the formation of the printing type diffuser 8 for applying a printed matter has been described, but the structure of such a diffusion pattern portion 7 is diffused to the reflection surface 1c of the light guide plate 1 as a diffusion portion. Of course, it is also possible to apply to a rough surface method in which a concave portion is provided. As a result, it is possible to easily reduce the shape and pitch of the diffusion recesses at a low cost without requiring advanced technology, expensive manufacturing equipment, or the like.

Diffusion pattern portion 7 by the rough surface method described above.
Can be realized as follows, for example. That is, similar to the above-mentioned printing method, the diffusion pattern portion 7 having a configuration in which irregular shaped diffusers 8 are arranged innumerably at an irregular pitch
The printing plate may be formed, the pattern of the printing plate may be transferred to a mold for molding polymethylmethacrylate, which serves as a light guide, and the light guide plate may be formed in a conventional manner.

There are various conceivable means for transferring the pattern to the molding die. For example, there is a dry film etching method as shown in FIG. First, as shown in FIG. 3A, a dry film 21 which is a photosensitive resin and a printing plate 20 are laminated on a molding die 22 and irradiated with light. As a result, the pattern of the printing plate 20 is transferred to the dry film 21, and if it is washed (peeled), the resin 21a in which only the photosensitive portion of the dry film 21 is solidified is printed as shown in FIG. It is formed on the mold according to the pattern of the plate.

Next, when the etching solution is poured, the resin 2
If the metal part other than the part masked by 1a is eroded and is washed (peeled) so as to remove the resin 21a later, the pattern of the printing plate 20 is transferred to the molding die 22 as shown in FIG. To be done.

In addition to the two-lamp type described here, the present invention is of course applicable to the above-mentioned one-lamp type backlight device having a U-shaped light source. 10 (a) (b)
FIG. 12 shows a one-light type backlight device to which the above diffusion pattern portion 7 is applied, and FIGS. 12A and 12B show a U-shaped light source 2 ′ to which the above diffusion pattern portion 7 is applied. 1 shows a backlight device. The same effect as described above is achieved, except that the optimum occupation area ratio of the diffuser 8 on the light guide plate 1 is different. 10 (a) (b) and 12 (a) (b)
In each backlight device shown in, for convenience of explanation,
Members having the same functions as the members of the backlight device shown in FIGS. 2 (a) and 2 (b) are given the same reference numerals,
The description is omitted.

FIG. 11A shows the area ratio of the diffuser 8 in the one-light type backlight device. Further, FIG. 2B shows the side end surface 1 of the light guide plate 1 on which the light source 2 is not arranged.
The occupation area ratio of the diffuser 8 when d is considered as a secondary light source is shown. This is because the side end surface 1d reflects the light flux from the light source 2, and thus the light flux incident on the reflecting surface 1c on the side end surface 1d side increases as if the second light source was arranged on the side end surface 1d. is there. In this way, the diffusion pattern portion 7
However, by forming the diffuser 8 to have a higher occupied area ratio as the distance from the incident surface 1a side where the light source 2 is arranged and the side end surface 1d side that reflects the light flux is increased, as shown in FIG. It has a more uniform light emitting surface as compared with the backlight device of the diffusion pattern portion in which the diffuser 8 is formed in the occupied area ratio.

FIG. 13 shows the occupation area ratio of the diffuser 8 in the backlight device using the U-shaped light source 2'with contour lines. Also in this case, since the reflection from the side end surface of the light guide plate 1 where the light source 2'is not arranged is considered, the light guide plate 1 has a uniform light emitting surface.

[0065]

As described above, the backlight device of the present invention according to claim 1 is configured such that the diffusion pattern portion is composed of innumerable irregular diffusion portions arranged at an irregular pitch.

According to a second aspect of the present invention, there is provided the backlight device according to the first aspect, wherein the diffusing portion is formed by applying a diffusing material to the bottom surface of the light guide plate.

According to a third aspect of the present invention, there is provided the backlight device according to the first aspect, wherein the diffusing portion is formed by processing the bottom surface of the light guide plate to have irregularities.

As a result, in the structure in which the diffusion portion is formed by printing, as the backlight device becomes thinner,
Even if the diffusion part is made thinner and the pitch is made finer, it is possible to prevent the generation of bright lines on the light emitting surface due to liquid sagging when forming the diffusion part or defective printing adhesion.

Further, in the structure in which the light diffusing portion is formed by processing the light guide plate into unevenness, there is an effect that even if the diffusing portion is made finer in shape and finer in pitch, it can be processed without difficulty.

According to a fourth aspect of the present invention, in the backlight device according to the first aspect, the diffusion pattern portion has a unit area as it is farther from the light source side end portion side where the light source is arranged. It is configured such that the occupancy rate of the diffusion portion with respect to the bottom surface of the hitting light guide plate is high.

As a result, in addition to the effect of the first, second or third aspect, the amount of the light flux emitted from the upper surface of the light guide plate is made uniform regardless of the distance from the light source, and the light emitting surface is made uniform. It has the effect of being able to.

According to a fifth aspect of the present invention, in the backlight device according to the first, second or third aspect, there is a side end face that reflects the light from the light source, and the diffusion pattern portion is provided with the light source. Further, the occupancy of the diffusion part per unit area to the bottom surface of the light guide plate increases as the distance from the light source side end part side and the light reflecting side end face side increases.

As a result, the amount of the outgoing light flux emitted from the upper surface of the light guide plate becomes more uniform irrespective of the reflection on the side end face, and the light emitting surface can be made more uniform.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a diffusion pattern portion formed on a reflection surface which is a bottom surface of a light guide plate in a backlight device according to an embodiment of the present invention.

2A is a cross-sectional view of the backlight device, and FIG. 2B is a plan view.

FIG. 3 is an explanatory diagram showing a pattern state of a diffusion pattern portion formed on the light guide plate.

FIG. 4 is an explanatory diagram showing a pattern state of a comparative diffusion pattern portion.

5 is an explanatory diagram showing an enlarged main part of the comparative diffusion pattern part of FIG. 4. FIG.

FIG. 6 is an explanatory view common to both of the printing plates used for forming the diffusion pattern portion of FIG. 3 and the comparative diffusion pattern portion of FIG.

FIG. 7 shows a light emitting surface of each backlight device manufactured using each light guide plate on which the diffusion pattern portion of FIG. 3 and the comparison diffusion pattern portion of FIG. It is an explanatory view common to both showing a luminance ratio.

8A is an explanatory diagram showing an occupied area ratio of diffusers when both liquid sagging and print adhesion defects occur during formation of the comparative diffusion pattern portion of FIG. 4, and FIG. It is explanatory drawing which shows the occupation area ratio of the diffuser when only sagging occurs, and (c) is an explanatory view which shows the occupation area ratio of the diffuser when only printing adhesion failure occurs.

9A to 9C show the diffusion pattern portion of FIG.
It is explanatory drawing which shows the process at the time of forming by a rough surface system.

FIG. 10 shows a configuration of a backlight device according to another embodiment of the present invention, (a) is a cross-sectional view of the backlight device, and (b) is a plan view.

11 is an explanatory diagram showing an occupation area ratio of diffusers in a diffusion pattern portion formed on a light guide plate of the backlight device of FIG.

FIG. 12 shows a configuration of a backlight device according to another embodiment of the present invention, (a) is a cross-sectional view of the backlight device, and (b) is a plan view.

13 is an explanatory diagram showing an occupied area ratio of diffusers in a diffusion pattern portion formed on a light guide plate of the backlight device of FIG.

FIG. 14 is an explanatory diagram showing a configuration example of an edge light type backlight device.

FIG. 15 is a cross-sectional view showing a configuration of a conventional two-lamp type backlight device.

FIG. 16 is an explanatory diagram showing a conventional diffusion pattern portion in which a diffusion portion is formed by a printing method.

FIG. 17 is an explanatory diagram showing a conventional diffusion pattern portion in which a diffusion portion is formed by a rough surface method.

FIG. 18 is an explanatory diagram showing an occupation area ratio of a diffusion portion in a diffusion pattern portion formed on a light guide plate of a two-light type backlight device.

FIG. 19A is an explanatory diagram showing a liquid drip that is likely to occur when a diffusion portion is formed by a printing method in the configuration of the conventional diffusion pattern portion, and FIG. 19B is a configuration of the conventional diffusion pattern portion. FIG. 7 is an explanatory diagram showing a print adhesion defect that is likely to occur when a diffusion portion is formed by a printing method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light guide plate 1c Reflecting surface (bottom surface) 2 Light source 2'Light source 3 Reflecting mirror 4 Reflecting sheet 5 Diffusing sheet 7 Diffusion pattern part 8 Diffuser (diffusing part)

Claims (5)

[Claims] 1. A tubular light source is disposed along at least one end of a light-transmitting flat light guide plate, and a light flux from the light source incident on the light guide plate is diffused on the bottom surface of the light guide plate. In a backlight device having a diffusion pattern portion for emitting light from the upper surface, the diffusion pattern portion includes a myriad of irregular diffusion portions arranged at an irregular pitch. apparatus. 2. The diffusion part is formed by applying a diffusion material to the bottom surface of the light guide plate.
The backlight device as described in the above. 3. The backlight device according to claim 1, wherein the diffusing portion is formed by processing the bottom surface of the light guide plate into an uneven shape. 4. The diffusion pattern portion is formed so that the occupancy rate of the diffusion portion with respect to the bottom surface of the light guide plate per unit area increases as the distance from the light source side end portion side where the light source is disposed increases. The backlight device according to claim 1, 2, or 3. 5. A side end face for reflecting light from a light source is present,
The diffusion pattern portion is formed such that the occupancy ratio of the diffusion portion to the bottom surface of the light guide plate per unit area increases as the distance from the light source side end portion side where the light source is arranged and the light reflecting side end surface side increases. Claim 1 characterized in that
The backlight device according to 2 or 3.