JP2664563B2 - Backlight - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmissive or transflective panel, for example, a panel backlight for illuminating a liquid crystal display of a word processor or a personal computer from the back.

[0002]

2. Description of the Related Art Recently, a liquid crystal display device having a thin and easy-to-see backlight mechanism has been used as a display device of a laptop or notebook type word processor or computer. As shown in FIG. 8, an edge light system in which a linear light source 104 such as a fluorescent tube is provided at one end of a light-transmitting light guide plate 101 is often used for such a backlight. In the case of this edge light method, as shown in FIG. 9, one surface (the lower surface in the figure) of the light guide plate 101 is partially covered with a light diffusing substance 106 having a higher refractive index than the material of the light guide plate. The light-reflecting layer 103 covers almost the entire surface, and a light-diffusing plate or sheet is disposed on the other surface (the upper surface in the drawing) of the light guide plate 101 to form the light-diffusing layer 102. There are many things. in this case,
The light diffusion material 106 that is partially covered is often formed by screen printing or the like in a dot shape such as a circle or an ellipse for technical reasons.

[0003] The structure and operation of a conventional backlight generally used will be described below with reference to the sectional view of FIG.

A linear light source 104 (hereinafter referred to as a "lamp")
Is usually used, and is covered with a lamp case 105 having a high reflection effect. When the lamp 104 is turned on, light from the lamp is guided into the light guide plate 101 from the light incident side end face 107 of the light guide plate 101 made of a transparent acrylic plate or the like facing the lamp. Light emitted in a direction not facing the light incident side end face 107 is reflected by the lamp case 105, collected at the light incident side end face 107, and guided into the light guide plate 101.

[0005] On one surface of the light guide plate 101, irregular reflection printing of a light diffusing substance 106 is performed with white ink or the like. This irregular reflection printing (hereinafter referred to as “printing surface”) is performed by the lamp 10.
In the vicinity of No. 4, the density is low and the density increases as the distance from the lamp increases. In practice, it is difficult to change the density of the ink step by step. Therefore, halftone dot printing such as a circle is reduced by reducing the area ratio of the halftone dots near the lamp 104, and increasing the distance from the lamp 104. Printing is performed to increase the area ratio. Light diffusely reflected on the printing surface 106 passes through the light guide plate 101 and is combined with light reflected on a light reflecting layer 103 (hereinafter, referred to as a “light reflecting sheet”) formed of a sheet material or the like.
Light is emitted to the outside via a light diffusion layer 102 (hereinafter, referred to as a “light diffusion sheet”) similarly formed of a sheet material or the like.

The light reflecting sheet 103 is provided to prevent light from going out from the printing surface 106 side and to emit light from the surface of the light diffusing sheet 102. Light diffusion sheet 10
In No. 2, the light reflected from the halftone dots on the printing surface 106 is not diffused without it, and it becomes a bright spot like a star in the night sky, so that a uniform light emitting surface cannot be obtained. It is provided in order to obtain a converted light emitting surface. Part of the light that has entered from the light guide plate light incident side end surface 107 reaches an end surface 108 (hereinafter, referred to as an “end surface”) on the opposite side of the light guide plate 101, and exits from this end surface 108 as it is. Originally, it is desirable that all the light incident on the light guide plate 101 be emitted from the surface of the light diffusion sheet 102, and if the light is emitted from the end surface of the light guide plate 101, the light emitted from the surface of the light diffusion sheet 102 is correspondingly increased. Light guide plate 1
A reflection sheet (or a reflection plate: hereinafter, collectively referred to as a “reflection tape”) is attached to the end surface of the light guide plate 01 or a reflection plate is disposed via an air layer, and the light reaching the end surface 108 is reflected to reflect the light guide plate 101. I try to put it back inside. In addition, this reflection tape is stuck on the side surface of the light guide plate 101 which does not directly face the lamp in addition to the end surface 108, or is arranged via an air layer.

[0007]

However, the following problems occur in the above-described conventional backlight configuration. (1) In recent years, the thickness of the device itself tends to be thin, and accordingly, a light guide plate having a small thickness is required. Accordingly, in order to maintain uniform surface light emission, the size of each halftone dot on the printing surface 106 must be reduced, and since the distance from the halftone dot to the light diffusion sheet 102 is short, printing is difficult. There is a problem that the shadow of the halftone dot on the surface 106 cannot be completely diffused and is visually recognized as a bright spot. For this reason, in practice, the reduction of the thickness of the light guide plate is limited to at most about 3 mm.

(2) Increasing the total thickness of the light diffusion sheet can solve the problem of luminance unevenness in which halftone dots are visually recognized as bright spots, but on the other hand, the increased thickness results in reduced light transmittance. Surface brightness decreases.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a backlight which eliminates the above-mentioned problems, has better characteristics, and can perform stable planar light emission without luminance unevenness even when the thickness is reduced. .

[0010]

As a result of various studies on the above points, the present inventors have found that in an edge light type backlight, a plurality of light diffusion layers provided on the light exit surface side of a light guide plate are provided. along with forming a laminate of the light diffusion sheet and the like are laminated, at least one light diffusion sheet and the like for forming the light diffusion layer, to the other light diffusion sheet or the like, and combinations material is that Do different, and Brightness song when emitting light
Light diffusion system with relatively strong directivity to the normal direction
If the sheet is arranged on the outer surface side of the laminate, the brightness unevenness of the light emitted from the light diffusion layer is small, that is, the printed halftone pattern is hardly visually recognized (hereinafter, this is referred to as “sheet concealment”). Not only effect) but also the brightness curve of the backlight changes, the directivity of light in the direction of the normal dropped on the light exit surface becomes stronger, and in the normal direction dropped on the light exit surface, The present inventors have found that a backlight having higher luminance can be obtained as compared with a case where this is not used, and completed the present invention.

In the above structure, a light diffusion sheet or the like forming a laminate constituting a light diffusion layer is generally called a plate (light diffusion plate) when it is made of a hard material, and is made of a soft material. In the case where it is composed of a sheet (light diffusion sheet), the present invention may be any of these plates and sheets. The light diffusion sheet and the like are made of a light-transmissive material, and are made of polyester, polyvinyl chloride (PVC), high-density polyethylene (HDPE), acrylic, polycarbonate (PC), triacetate (T
AC), a transparent material such as glass is not particularly limited. These can be used alone, but it is a particularly preferred embodiment to use them in combination with HDPE or TAC and PC.

These light diffusion sheets and the like can be obtained by subjecting the above-mentioned light-transmitting material to, for example, biaxial stretching extrusion molding, calender forming, inflation forming, embossing, sand blasting, die molding by hot pressing, chemical treatment, or the like. It can be formed by a method that results in imparting light diffusing properties. The thickness of the light diffusion sheet used here is generally 5 to 400 μm, preferably 20 to 300 μm. Outside of this range, the effect of improving the luminance and the effect of hiding the sheet tend to decrease.

In the present invention, a light diffusion layer is formed by laminating a plurality of light diffusion sheets and the like described above. At least one of the laminated light diffusion sheets and the other light diffusion sheets It is important to use a sheet having a different material and a different light diffusing property. Here, "different light diffusivity" means the following. That is, when each of the light diffusing sheet is arranged to face the light emitting the light exit surface of the backlight, varies with the angle relative to the plane of the light intensity of the measuring points with the top thereof faces the light exit, shows a change in its curve refers different depending etc. the material and thickness of the light diffusion sheet.

By the way, in the liquid crystal display to which the present invention is applied, since the contrast becomes lower as the viewing angle from the normal direction dropped on the display surface becomes larger, the liquid crystal display is practically used.
The luminance near the normal direction is emphasized. Therefore, sheets having different light diffusing properties are selected based on the difference in the directivity of the light diffusing sheet with respect to the normal direction.

[0015] Incidentally, stronger light diffusing sheet above the directivity, the upper surface, i.e. of the light-diffusing sheet odor in which a plurality of sheets stacked
It is arranged at a portion farther from the light guide plate.

When light from a light guide plate of a backlight driven at a constant power enters the light diffusion sheet, the light repeats diffuse transmission or reflection and refraction, and exits from the light diffusion sheet. The surface luminance at this time was measured by a luminance meter 10 as shown in FIG.
Changes the angle 11 with respect to the normal direction dropped to an arbitrary measurement point 12 on the light emitting surface from 0 degree to 60 degrees at a viewing angle of 1 degree, and measures at a distance of 50 cm from the measurement point to the luminance meter. FIG. 4 shows the luminance curve obtained when the above-mentioned operation was performed. From this figure, when the light diffusion sheet of Material used are different, also different brightness curve,
It can be seen that the directivity varies in the normal direction. In the present invention, a light diffusion sheet having a larger luminance value in the normal direction than a luminance value in a direction other than the normal direction is referred to as a light diffusion sheet having higher directivity. In the present invention, the light diffusion sheet is 2 to
6 sheets, preferably 2 to 4 sheets are used.

In the present invention, as described above, by laminating the light diffusing sheet on the light emitting surface side of the light guide plate, the luminance with respect to the normal direction substantially lowered on the light emitting surface side of the light diffusing sheet becomes normal. from increased compared to the luminance of 60 degrees location of the light diffusing heterogeneous material different and configuring an optical diffusing sheet laminating a plurality of light diffusing material which is formed on one surface of the light guide plate In addition to making the halftone dot pattern less visible due to the concealing effect of the light diffusion sheet in which a plurality of halftone dot patterns are stacked, the luminance of light emitted from the light guide plate is amplified, and the directivity of light is further enhanced.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in further detail with reference to the embodiments shown in the drawings.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in further detail with reference to the embodiments shown in the drawings. FIG. 1 is a perspective view of an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing an example of an edge light type backlight. The configuration of the present invention is basically the same as the configuration of the above-described conventional backlight except that a specific light diffusion sheet is used. In the figure, reference numeral 1 denotes a light guide plate, which may be any substance that can efficiently transmit light, such as quartz, glass, or a translucent natural or synthetic resin such as an acrylic resin. Reference numeral 2 denotes a light diffusion sheet that can have a higher luminance in a normal direction that is substantially lowered to the light emission surface side of the light diffusion sheet by stacking the light diffusion plate on the light emission surface side of the light guide plate. one is a light diffusion sheet what a light diffusing property was set to be different laminating a plurality by the material to constitute it with other light diffusing sheet is different. Further, if necessary, the periphery of the laminated light diffusion sheet may be welded or bonded to the light guide plate.

As shown in FIG. 2, the light diffusing substance 6 applied to the light guide plate has a high refractive index as compared with the material of the light guide plate and a pigment having a large diffuse reflectance, for example, a paint containing titanium white, printing, or the like. And ink. These are printed in dot form on the light guide plate surface by a method such as screen printing. The light reflecting sheet 3 is disposed so as to cover almost the entire surface of the light guide plate coated with the light diffusing substance. Reference numeral 4 denotes a linear light source. In a preferred embodiment, a light reflector 5 having a gap (slit) for allowing light to enter the end of the light guide plate has a gap of a certain width from the light source surface of the linear light source. The light guide plate is installed so that its central axis is substantially parallel to the end surface of the light guide plate.

The linear light source includes a fluorescent tube, a tungsten incandescent tube, an optical rod, an LED arrayed LED, and the like. The fluorescent tube is preferable. It is preferable that the length of the end portion of the adjacent light guide plate is substantially equal to that of the light guide plate.

A light reflecting tape is provided on all or part of the end of the light guide plate 1 where the linear light source 4 is not brought close to the light guide plate in order to effectively use the light leaking therefrom and increase the luminous efficiency of the backlight. It is preferable to provide them in close contact with each other (or close to the reflector).

The main part of the present invention has such a structure and is used as a backlight of a panel, especially a liquid crystal panel. In the present invention, it is preferable to adopt the following configuration.

That is, the light diffusing substance applied to the light guide plate of the present invention is formed in a dot shape, that is, a halftone dot shape, but the shape of the dot is not particularly limited, and may be circular, elliptical, square, Any may be formed by the intersection line. These are applied on intersections (grids) of orthogonal lines having a certain interval imaginary on the light guide plate, and the interval between the orthogonal lines is 0.5
To 3 mm, more preferably 0.8 to 2 mm, depending on the thickness of the light guide plate.

Further, the covering state of the light diffusing substance is preferably 1% to 50% in the vicinity of the linear light source on the light guide plate surface, and 20% to 100% in the farthest part from the light source. ,
As the distance from the light source increases, it is preferable to cover the linear light source from the light source such that the coverage gradually increases starting from the coating point on one side end where the linear light source is brought closer. Further, in the vicinity of the end of the light guide plate opposite to the linear light source, the coverage may be equal to or smaller than the previous coverage. The coverage here refers to the ratio of the area covered by the light diffusing substance applied per unit area of the light guide plate surface.

Example In this example, an acrylic plate having a thickness of 2.5 mm was used as a light guide plate. The light diffusion sheet is a polyester sheet having a thickness of 100 μm. With this single sheet, a halftone dot (shape: circular, size: 360 to 1150 μm) is printed on the light guide plate surface.
m, density: 1.2 mm pitch) The pattern was visible. Also, the luminance in the present embodiment refers to the luminance in the normal direction to the light emitting surface, as in the case of normal use. As shown in FIG. 3, the luminance was measured by a luminance meter 10 at a viewing angle of 1.
The angle 11 with respect to the normal direction dropped to an arbitrary measurement point 12 on the light emitting surface was changed from 0 degree to 60 degrees, and the measurement was performed at a distance of 50 cm from the measurement point to the luminance meter. Although the determination of the state of the halftone dot pattern was made by the observer,
Generally, the resolution limit of human eyes is about 50 to 75 μm.

A backlight having the structure shown in FIG. 2 was formed using the above light guide plate and various light diffusion sheets, and the above test was conducted. In addition, among the plurality of light diffusion sheets 2,
On the upper surface, a light diffusion sheet having stronger directivity was used. As a result of this measurement test, when laminating in the above order,
The highest number of laminated sheets before and after the halftone dot pattern disappeared (2 to 4 sheets in this example) showed the highest luminance.

FIGS. 5 and 6 show the effect of improving the brightness when a light diffusion sheet having higher directivity is laminated on the brightness when one polyester light diffusion sheet is used. FIG. The directivity was determined by arranging each light diffusion sheet on the light emitting surface of the backlight to emit light, and determining the luminance at a certain measurement point on the surface. As a result, the one obtained by laminating three TAC 38 μm films was the best, and the luminance was improved by about 14%. However, when the number was larger than that, the luminance was reduced due to the effect of the decrease in light transmittance. Further, the halftone dot pattern was concealed before and after the number of sheets showing the highest luminance value. Practically, it is preferable that halftone dot printing can be concealed with as few sheets as possible without showing too many light diffusion sheets and the highest luminance is exhibited. FIG. 7 is a graph showing the brightness of each of the light diffusion sheets 1 to 5 when the brightness of one polyester light diffusion sheet is used.
This is a study of how much one light diffusion sheet (specifically, PC) having stronger directivity is stacked on five sheets to have a luminance improving effect. As a result, the one obtained by laminating two or three TAC 38 μm films was the best, and the luminance was improved by about 16%. However, when the number was larger than that, the luminance was reduced due to the effect of the decrease in light transmittance. Further, the halftone dot pattern was concealed before and after the number of sheets showing the highest luminance value. Practically, it is preferable that halftone dot printing can be concealed with as few sheets as possible without showing too many light diffusion sheets and the highest luminance is exhibited.

[0029]

According to the present invention, at least one sheet is laminated with a plurality of light diffusing sheets having different light diffusing properties to emit light.
Brightness curve is relatively strong in directivity to the normal direction
By adopting a structure in which a light diffusion sheet is disposed on the outer surface side of the laminate, the effect of improving the brightness without impairing the inherent characteristics of the backlight can be obtained. Further, for example, the effect of shielding a light-scattering substance printed with halftone dots is also improved, and an effect of reducing the thickness of a surface light-emitting body using the same to, for example, 2.5 mm can be expected.

[Brief description of the drawings]

FIG. 1 is a perspective view of a backlight according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the backlight.

FIG. 3 is a diagram illustrating an outline of a measurement method used in the present invention.

FIG. 4 is a view showing a measurement result of directivity of a light diffusion sheet used in an example of the present invention.

FIG. 5 is a diagram showing combinations of light diffusion sheets used in Example 1 and changes in luminance.

FIG. 6 is a diagram showing a combination of light diffusion sheets used in Example 2 and a change in luminance.

FIG. 7 is a diagram showing a combination of light diffusion sheets used in Example 3 and a change in luminance.

FIG. 8 is a perspective view of a conventional backlight.

FIG. 9 is a cross-sectional view of the conventional backlight.

DESCRIPTION OF SYMBOLS 1 ... light guide plate 2 ... light diffusion sheet 3 ... light reflection sheet 4 ... linear light source 5 ... light reflector 6 ... light diffusion material 7 ... light incident side end face 8 ... end face 9 ... one embodiment of the present invention Backlight of the embodiment 10: Arbitrary light-emitting surface of the luminance meter light-diffusing sheet 11: Angle with respect to the normal direction dropped on the light-emitting surface 12: Measurement point

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Harumi Tsuchiya 2-84 Sakabegaoka, Yokkaichi-shi, Mie (56) References Japanese Utility Model 1-105974 (JP, U) Japanese Utility Model 62-158427 (JP) , U) Hikaru 4-15109 (JP, U)

Claims (3)

(57) [Claims] 1. A panel backlight comprising a light reflection layer, a light guide plate, and a light diffusion layer laminated in this order in a thickness direction, wherein the light diffusion layer forming a light exit surface of light from the light guide plate is formed by a light diffusion sheet. thereby forming a plurality as a laminate formed by laminating, at least one of the light diffusion sheet to form the laminate, and the remaining other light diffusion sheet, that different material is <br/> The brightness curve when emitting light is a normal
A light diffusion sheet having a relatively strong directivity to the
A backlight for a panel having a structure arranged on an outer surface side of a laminate . 2. The panel backlight according to claim 1, wherein the light diffusion sheet is a hard plate or a soft sheet. 3. The method of claim 1 or 2, the material of the light diffusion sheet, panel, wherein the polyester, polyvinyl chloride, high density polyethylene, acrylic, polycarbonate, triacetate, that is at least one selected from glass Backlight.