JPH0980429A - Back light and optical sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a back light and an optical sheet free from a black line and also having high front luminance by installing an optically worked face for emitting light emitted from a linear light source to the outside through a transmission face on a light transmission plate, and installing a lenticular lens made of an assembly of curved surface columnar lenses on one side of the optical sheet. SOLUTION: The device is constituted of the linear light source 11, the light transmission plate 10 for emitting the light emitted from the light source 11 through the transmission face 12 and the optical sheet 14 arranged on the transmission face of the transmission plate 10, and the light transmission plate 10 is provided with the optically worked face for emitting the light from the linear light source 11 through the transmission face 12, and the 1st lenticular lens 19 constituted of the assembly of the curved surface columnar lenses is formed on one side of the optical sheet 14. It is preferable that the optically worked face of the light transmission plate 10 is provided with a prism projection 13 whose projection area per unit area is made roughly larger as it goes away from the light source 11, and also, it is preferable that a 2nd lenticular lens 18 extending nearly parallel to the longitudinal direction of the light source 11 and for turning the light to a liquid crystal display element direction is formed on the other side of the optical sheet 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an edge light type backlight for illuminating a liquid crystal display device or the like from the rear, and more particularly to a backlight using a light guide plate having an optically processed surface.

[0002]

2. Description of the Related Art A reflective surface of a light guide plate (of the two surfaces of the light guide plate substantially parallel to the liquid crystal display element, which is far from the liquid crystal display element) provided with printing dots has been used. When the light that travels inside the light guide plate hits the printing dots, it diffuses,
Some light goes out of the light guide plate. However, when such a print dot is used, a part of the light is absorbed in the print dot portion and a loss occurs.

[0003]

As a substitute for a light guide plate using printed dots, the applicant of the present invention, as shown in FIG.
A backlight in which a prism projection 2b is formed on the transmission surface of a light guide plate 2 which emits light from a cold cathode tube 1 as a linear light source in one direction was examined.

The light guide plate 2 is provided with an optical processing surface, and as a method of emitting light from the light guide plate 2, the reflection / refraction action of light is controlled by design, so It was possible to obtain the effect that less light loss was required.

In the present invention, the optically processed surface means a surface whose reflection / refraction of light is controlled by design. This does not apply to the surface with printed dots or the roughened surface. However, as the emission characteristics from the light guide plate 2 provided with the protrusions 2b, almost all the light is emitted in an oblique direction with respect to the transmission surface 2a, and the light emitted to the front is slight. In order to direct this light to the front direction, which is the observer direction of the liquid crystal display element, two optical sheets 3 and 4 having prism-shaped lenticular lenses formed on the surface are arranged.

In the present invention, the lenticular lens means that the unit lenses have the same shape and cross section perpendicular to the ridgeline in the ridgeline direction, and are arranged in a plurality of planes so that the ridgeline directions are parallel to each other. Say something. At this time, the sectional shape of the unit lens portion does not matter. Further, lenses having different shapes may be mixed and the interval between the ridge lines may be a random pitch.

By the way, the cold cathode fluorescent lamp 1 used as a linear light source has a darker end portion than the other portions. This is because the tube wall at the end of the cold cathode tube becomes black due to sputtering, or the electrode of the non-light emitting portion is present at the end.

On the other hand, in order to make the backlight compact, the tube length of the cold cathode tube is limited, and it is common to use one in which the tube length of the cold cathode tube and the incident width of the light guide plate are almost equal. Therefore, in the backlight having the above-described structure, the brightness in the front direction is increased, but in the effective screen area, as shown in FIG. , Black line) occurs. In this figure, the cold cathode fluorescent lamp is arranged at the upper part.

This is because the backlight having the structure shown in FIG. 17 does not have a light diffusing effect, and the light emitted from the backlight is preserved even when the non-emission part of the cold cathode tube advances inside the backlight. This is because there is a discontinuity in the intensity of and appears as a black line.

On the other hand, in the light guide plate provided with the print dots, the print dots serve as a pseudo point light source, and therefore have the effect of weakening the influence of the non-light emitting portion of the cold cathode tube. Therefore, the black line phenomenon does not appear. In the light guide plate 2 having an optically processed surface as shown in FIG. 17, a black line portion is generated, and the brightness of the black line portion is almost 0.
Therefore, even if the formation density of the prism protrusions 2b of the light guide plate 2 is increased, it is difficult to increase the brightness of the black line portion.

Therefore, in order to erase the black line, a diffusion sheet is arranged between the light guide plate 2 and the optical sheet 3 or between the optical sheet 4 and the liquid crystal display element. It was found that the black line would not disappear unless a diffusion sheet with a high degree of diffusion was used.

Further, since a diffusion sheet having a high degree of diffusion necessarily has a low transmittance, there is a problem that the front luminance is lowered even if the black line disappears. The present invention has been made in view of the above problems, and its purpose is to:
An object of the present invention is to provide a backlight and an optical sheet that do not generate a black line and have high front brightness.

[0013]

A backlight of the present invention for solving the above-mentioned problems is arranged on a linear light source, a light guide plate for emitting the light of the light source from a transmission surface, and a transmission surface of the light guide plate. In an edge light type backlight configured to illuminate a liquid crystal display element, the light guide plate has an optical processed surface for emitting light from a linear light source to the outside from a transmission surface, On one surface of the optical sheet,
A first lenticular lens formed of an assembly of curved columnar lenses is formed.

Here, the curved surface is a shape for refracting parallel light in multiple directions, and includes a circular arc, an elliptic arc, a sine wave, a plurality of straight lines connected in a polygonal shape, a parabola, and the like. However,
Considering the ease of manufacturing, arcs, elliptical arcs, and sine waves are desirable.

The light emitted from the linear light source is the transmission surface of the light guide plate having the optically processed surface (of the two surfaces of the light guide plate substantially parallel to the liquid crystal display element, the surface near the liquid crystal display element). )
Emitted from

The light emitted from the transmitting surface of the light guide plate enters the optical sheet, and is refracted in multiple directions in the direction perpendicular to the ridgeline by the first lenticular lens composed of an assembly of curved columnar lenses. Then, the light emitted from the optical sheet illuminates the liquid crystal display element.

In the backlight of the present invention, since each optical element (light guide plate, optical sheet) controls the reflection / refraction action by design, the light loss in each optical element is very large. It is less and the brightness can be increased. Also,
By the first lenticular lens of the optical sheet, light is refracted in multiple directions, mainly in a cross section perpendicular to the lens ridge, so that a black line is prevented from occurring while preventing a decrease in front luminance.

Here, it is preferable that the optically processed surface of the light guide plate is a surface having prism protrusions whose projected area per unit area increases substantially with distance from the light source.

With this structure, the light emitted from the transmitting surface of the light guide plate can be directed in an oblique direction, and the amount of light can be substantially constant regardless of the distance from the light source. Further, it is desirable to form a second lenticular lens on the other surface of the optical sheet, the second lenticular lens extending substantially parallel to the longitudinal direction of the light source and directing light toward the liquid crystal display element.

With such a structure, the light in the oblique direction emitted from the transmitting surface of the light guide plate becomes the front direction of the liquid crystal display element. Here, the second lenticular lens effectively prevents a black line by arranging the first lenticular lens on a surface facing the light guide plate of the optical sheet, that is, arranging the first lenticular lens at an optical distance from the linear light source. it can.

The optical sheet may have a shape in which two sheets are superposed. As an example of the second lenticular lens of the optical sheet, there is one having a prism-shaped cross section and a prism apex angle of 60 degrees or more and 75 degrees or less.

It is preferable that the first lenticular lens of the optical sheet has a shape in which, when light is vertically incident, the traveling direction of light after refraction at the boundary surface is largely different depending on the incident position. An example of the sectional shape of the lenticular lens is an ellipse.

Further, it is desirable that the first lenticular lens of the optical sheet extends in a direction not parallel to the light source. In order to make the device compact, it is desirable that the incident width of the light guide plate is larger than the emission width of the linear light source.

The optical sheet of the second invention has, on one surface,
A first lenticular lens that refracts light in multiple directions is formed, and a second lenticular lens that extends in a direction intersecting with the first lenticular lens on the other surface and directs light in a predetermined direction is formed.
It is a lenticular lens formed by.

As an example of a specific configuration of the optical sheet, the first lenticular lens has an elliptical shape, the second lenticular lens is a prism, and the prism apex angle of the prism is 60 degrees or more and 75 degrees or more. There are the following:

[0026]

1 is a block diagram of an embodiment of the present invention, FIG. 2 is a sectional view taken along line YY 'in FIG. 1, and FIG. 3 is FIG.
4 is a cross-sectional view taken along line XX ′ in FIG. 4, and FIG. 4 is a top view excluding the liquid crystal display element in FIG.

In these figures, 11 is a cold cathode tube as a linear light source, and 10 is a light guide plate which emits light from the cold cathode tube 11 in one direction. As shown in FIG. 4, the emission width of the cold cathode tube 11 (the portion other than the hatched portion in FIG. 4) in this embodiment is set to be slightly smaller than the incident width of the light guide plate 10.

On the transmissive surface 12 of the light guide plate 10, there are formed minute protrusions 13 in the form of prisms that extend substantially parallel to the cold cathode tubes 11. Reference numeral 14 is an optical sheet that refracts light emitted from the light guide plate 10 in the front direction of the liquid crystal display element 17. The optical sheet 14 is formed by stacking two optical sheets 15 and 16.

On the surface of the optical sheet 15 facing the light guide plate 10, there is formed an assembly of prism-shaped columnar lenses that extend substantially parallel to the longitudinal direction of the cold cathode tubes 11 and direct light toward the liquid crystal display element 17. The second lenticular lens 18 is formed.

On the surface of the optical sheet 16 facing the liquid crystal display element 17, a group of curved columnar lenses extending in a direction substantially orthogonal to the longitudinal direction of the cold cathode tube 11 and refracting light in multiple directions is formed. The first lenticular lens 19 is formed.

Here, the light guide plate 10 is preferably made of a material having a high internal transmittance. Further, in order to form the minute protrusions 13, the light guide plate 10 is preferably made by a molding method, and the material is plastic. Considering dispersion, acrylic is more preferable.

Unit area of the projection 13 on the transparent surface 12 (1 mm ² )
The projected area of is substantially increasing with the distance from the cold cathode tube 11. Here, as shown in FIG. 5, the projected area is the sum of the areas of the protrusions (hatched portions in FIG. 5) observed as protrusions within a 1 mm ² rectangle when the transmission surface 12 is observed from the vertical direction. is there.

Further, in the present embodiment, the projected area of the projection 13 is increased as the projection 13 is separated from the cold cathode fluorescent lamp 11, as shown in FIG. As a method of increasing the projected area, the pitch is generally narrowed or the width of the protrusion 13 is generally widened. Actually, 1500 protrusions 13 were formed per 160 [mm].

The sectional shape of the protrusion 13 in the YY 'direction is
As shown in FIG. 7, it comprises a light source side projection slope 21 and an anti-light source side projection slope 22. Light source side projection slope 21 and transmission surface 12
The angle formed by and is 153 degrees, and the light source side projection slope 22 and the transmission surface 1
The angle formed with 2 was 92 degrees, and the apex angle of the protrusion was 65 degrees.

The pitch (Pi) of the protrusions 13 is a random pitch, and the width (Di) of the protrusions 13 is also randomly formed. Further, the height of the projection 13 changes in the length direction of the cold cathode tube 11, and the end of the light guide plate 10 is formed higher than the central portion.

The light guide plate 10 is obtained by cutting a groove of a die, which is flat-processed with a diamond bite having an apex angle of 65 degrees, with an NC lathe. The diamond bite moves in a straight line with respect to the fixed flat die, and controls the cut amount T (X) at a certain position. Using this mold, the light guide plate 10 provided with the projections is formed by injection molding. In this way, the light guide plate 10
By performing the die machining with the NC lathe, the pitch and width of the protrusions 13 can be machined to the design values in the micron order.

The sectional shape of the 15th second lenticular lens 18 of the optical sheet is an isosceles triangle as shown in FIGS. Moreover, the cross-sectional shape of the first lenticular lens 19 of the optical sheet 16 was elliptical as shown in FIGS.

Next, the operation principle of the above configuration will be described. The light emitted from the cold cathode tube 11 is incident on the incident surface 11 a of the light guide plate 11.
From inside the light guide plate 11. Since there is a difference between the refractive index of the light guide plate 11 and the refractive index of air, the light guide plate 11 proceeds while totally reflecting inside the light guide plate except for the protrusion 13. Here, the light hitting the protrusion 13 goes out from the light guide plate 10.

That is, the light that hits the anti-light source side projection slope 22 is directly reflected, and the light that hits the light source side projection slope 21 is totally reflected by this slope and hits the anti light source side projection slope 22 to the outside. Emit. At this time, the direction of the emitted light is oblique to the liquid crystal display element 17.

The light emitted from the transmission surface 12 of the light guide plate 10 is
The optical sheet 14 is oriented substantially in the front direction with respect to the liquid crystal display element 17 by the second lenticular lens 18,
The light is refracted in multiple directions by the lenticular lens 19 and is emitted to illuminate the liquid crystal display element 17.

In the center of the effective screen area of the light guide plate 11,
8 shows the luminance alignment characteristics in the YY 'direction, and FIG. 9 shows the luminance alignment characteristics in the XX' direction in the central portion of the effective screen area of the light guide plate 11.

According to the above structure, the following effects can be obtained. (1) The amount of light traveling inside the light guide plate 10 decreases as the distance from the cold cathode tube 11 increases, but the projected area of the protrusion 13 increases as the distance from the cold cathode tube 11 increases. The amount of light is approximately constant.

(2) Optical element (light guide plate 10, optical sheet 1)
In 4), since the reflection / refraction action is controlled by design, the loss of light in each optical element is very small, and the brightness can be increased.

(3) Since the first lenticular lens 19 of the optical sheet 16 refracts light in multiple directions in the direction perpendicular to the lens ridge, it is possible to prevent the front brightness from decreasing and the black line from occurring. You can

(4) The device can be made compact by setting the emission width of the cold cathode tubes 11 to be smaller than the incident width of the light guide plate 10. Next, a second embodiment of the present invention will be described with reference to FIG. The same parts as those of the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

The difference between this embodiment and the first embodiment is the optical sheet 26 on which the first lenticular lens 29 is formed. That is, the first lenticular lens 19 of the first embodiment example extends in a direction substantially orthogonal to the longitudinal direction of the cold cathode tube 11, but the first lenticular lens 29 of the present embodiment example does not cool. It extends in a direction not orthogonal to the cathode tube 11.

Even with such a configuration, the same effect as that of the first embodiment can be obtained. Note that the present invention is not limited to the above embodiment.

(1) The cross-sectional shape of the first lenticular lens 19 is not limited to an ellipse, and FIGS.
Various shapes are possible as shown in FIG. (2) Even with a backlight in which a prism protrusion is provided on the reflection surface of the light guide plate and a reflection sheet is installed under the light guide plate, the first curved surface
By using the lenticular lens of, it is possible to prevent the generation of black lines.

[0049]

EXAMPLES The inventor of the present application conducted the following experiment in order to confirm the effect of the backlight of the present invention.

The configuration is as shown in FIG. still,
The same parts as those of the first and second embodiments are designated by the same reference numerals and the description thereof will be omitted. In the figure, 40 is a diffusion sheet
A and 43 are diffusion sheets B, 41 is an optical sheet A, and 42 is an optical sheet B.

(1) Light guide plate 10 The external dimensions are as shown in FIG. 2 and FIG.
217 [mm], the length parallel to the length direction of the beam (incident width), the vertical length is 170 [mm], the height of the incident surface 10a is 3 [mm], the anti-incident surface 1
It is a substantially rectangular parallelepiped whose height of 0b is 1.2 [mm]. The size of the effective screen area is 210 × 160 [mm]. In addition, the light guide plate 10
The width of the protrusion 13 was set as shown in FIG.

(2) Optical sheet A41, optical sheet B42 As the optical sheets 41 and 42, those having the following specifications were used. 1. An optical sheet with an isosceles prism formed with a second lenticular lens with an apex angle of 63 ° and an apex angle of 68 ° 2. An optical sheet with a first lenticular lens having an elliptical cross section (Sumitomo "Lumithru" manufactured by Chemical Industry Co., Ltd.
R ”) 3. An optical sheet with an isosceles triangular prism and a lenticular lens with a vertical angle of 90 degrees (Sumitomo 3M
(BEF90) of (Inc.) (3) Diffusion sheet A40, diffusion sheet B43 PCD, D117, D116 Tsujimoto Electric Co., Ltd. (4) Cold cathode tube 11 Harrison Electric Co., Ltd. HMBS26BWE225C (5) Inverter Harrison Electric Co., Ltd. ) HIU-714 (tube current 4.0 [mA]) (6) Measurement luminance meter Topcon BM-7 (measurement distance: 50 [cm], measurement angle: 0.2
[Degree]) Then, in a combination as shown in FIG. 14, the average luminance of the effective screen area on the optical sheet and the presence or absence of the black line were examined. As can be seen from this figure, as in Comparative Example 6, as the optical sheet A, a prism-shaped lenticular lens with an apex angle of 63 degrees was used, and as the optical sheet B, a prismatic shape with an apex angle of 90 degrees was used. The average brightness is high when the lenticular lens formed is used. However, black lines occur.

When the diffusion sheets A and B are appropriately selected in such a combination, the black line may disappear (Comparative Example 2).
The average brightness drops considerably. On the other hand, as in the example, as the optical sheet A, a prism-shaped lenticular lens having an apex angle of 68 degrees is used, and as the optical sheet B, a lenticular lens having an elliptical cross-section is used. It was confirmed that the brightness was high and that no black line was generated without using a diffusion sheet.

Further, as shown in Comparative Example 7, it was confirmed that when the ridge lines of the lenticular lenses of the optical sheet A and the optical sheet B were substantially aligned with each other, the average brightness was low and a black line was generated.

Further, in the embodiment, when the optical sheet A is fixed and only the optical sheet B is rotated and the angle at which the black line is generated becomes Δ, it is confirmed that when it is rotated ± 74 degrees or more, it becomes Δ. did. Here, the rotation angle in the clockwise direction is + and the rotation angle in the counterclockwise direction is − with the upper left part of the incident width of the light guide plate in FIG. 4 as the rotation center.

Furthermore, in the embodiment, the optical sheet B is fixed and only the optical sheet A is rotated, and the black line is generated.
It was confirmed that when it was rotated -45 degrees or more or +30 degrees or more, it became △.

Further, it was confirmed that, when the optical sheet A and the optical sheet B were rotated twice at the same time while keeping the ridgelines vertical, when they were rotated by -70 degrees or more or +75 degrees or more, they became Δ. In addition, FIG. 15 shows the luminance distribution in the front direction on the optical sheet in the example.

In the embodiment shown in FIG. 16, when the optical sheet A is fixed and only the optical sheet B is rotated by -30 degrees (second
(Corresponding to the embodiment) of FIG. From these two figures, it can be seen that the brightness is highest when the ridgeline of the first lenticular lens and the ridgeline of the second lenticular lens are substantially orthogonal to each other.

[0059]

As described above, according to the backlight and the optical sheet of the present invention, since each optical element (light guide plate, optical sheet) controls the reflection / refraction action by design, The loss of light in each optical element is very small, and the brightness can be increased.

Further, since the first lenticular lens of the optical sheet refracts light in multiple directions in the vertical cross section of the lens ridge, it is possible to prevent the generation of the black line while preventing the deterioration of the luminance.

Here, since the optically processed surface of the light guide plate is a surface having prism protrusions whose projected area per unit area increases substantially with distance from the light source, the light emitted from the transmissive surface of the light guide plate is It is possible to face in an oblique direction and to make the light quantity substantially constant regardless of the distance from the light source.

On the other surface of the optical sheet, there is formed a second lenticular lens which extends substantially parallel to the longitudinal direction of the light source and directs the light toward the liquid crystal display element. The light in the oblique direction emitted from is in the front direction of the liquid crystal display element.

Here, by forming the first lenticular lens on the surface of the optical sheet that faces the transmission surface of the light guide plate, that is, since the first lenticular lens is arranged optically far from the light source, It is possible to effectively prevent the occurrence of black lines.

By making the incident width of the light guide plate larger than the emission width of the linear light source, the device can be made compact. Only one optical sheet can be used, and the number of backlight components can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line YY ′ in FIG.

FIG. 3 is a sectional view taken along line XX ′ in FIG.

4 is a top view excluding the liquid crystal display element in FIG. 1. FIG.

5 is an explanatory diagram of a projected area of a protrusion in FIG.

FIG. 6 is a diagram illustrating the relationship between the projected area of the protrusion in FIG. 1 and the distance from the incident surface.

FIG. 7 is an enlarged view of a protrusion in FIG.

8 is an alignment characteristic diagram of luminance in the YY 'direction of the light guide plate in FIG.

9 is an alignment characteristic diagram of luminance in the XX 'direction of the light guide plate in FIG.

FIG. 10 is a configuration diagram of a second embodiment example.

FIG. 11 is a diagram showing another example of the cross-sectional shape of the first lenticular lens.

FIG. 12 is a configuration diagram of an example.

FIG. 13 is a diagram illustrating a change in the width of the protrusion of the light guide plate in FIG.

FIG. 14 is a diagram showing an experimental result of an example.

FIG. 15 is a diagram illustrating a luminance distribution of an example.

FIG. 16 is a diagram illustrating a luminance distribution of another experiment.

FIG. 17 is a configuration diagram of a conventional backlight.

FIG. 18 is a diagram illustrating the luminance distribution of FIG.

[Explanation of symbols]

 10 Light Guide Plate 11 Cold Cathode Fluorescent Tube 12 Transmission Surface 13 Protrusions 14, 15, 16 Optical Sheet 19 First Lenticular Lens

Claims (12)

[Claims] 1. An edge light comprising a linear light source, a light guide plate for emitting the light of the light source from a transmissive surface, and an optical sheet arranged on the transmissive surface of the light guide plate to illuminate a liquid crystal display element. In the backlight of the method, the light guide plate has an optical processing surface for emitting light from a linear light source to the outside from a transmission surface, and one surface of the optical sheet is formed of a curved columnar lens. A backlight having a first lenticular lens formed of an aggregate. 2. The backlight according to claim 1, wherein the optically processed surface of the light guide plate is a surface having prism protrusions whose projected area per unit area increases substantially with distance from the light source. 3. The backlight according to claim 1, wherein a second lenticular lens that directs light toward a liquid crystal display element is formed on the other surface of the optical sheet. 4. The backlight according to claim 1, wherein the second lenticular lens is formed on a surface of the optical sheet that faces a transmission surface of the light guide plate. 5. The backlight according to claim 1, wherein the optical sheet is a stack of two sheets. 6. The cross-sectional shape of the second lenticular lens of the optical sheet is prismatic, and the prism apex angle is
6. The backlight according to claim 1, wherein the backlight is 60 degrees or more and 75 degrees or less. 7. The first lenticular lens has a shape in which, when light is vertically incident, the traveling direction of the light after refraction at the boundary surface is largely different depending on the incident location. The backlight according to any one of 1 to 6. 8. The cross-sectional shape of the first lenticular lens is elliptical.
Backlight according to any one. 9. The backlight according to claim 1, wherein the first lenticular lens of the optical sheet extends in a direction not parallel to the light source. 10. The incident width of the light guide plate is larger than the emission width of the linear light source.
Backlight according to any one. 11. A first lenticular lens for refracting light in multiple directions is formed on one surface, and is extended in a direction intersecting with the first lenticular lens on the other surface to direct light in a predetermined direction. An optical sheet having a second lenticular lens facing toward. 12. The optical sheet according to claim 1, wherein the first lenticular lens has an elliptical shape, the second lenticular lens is a prism, and the prism apex angle of the prism is 60 degrees or more and 75 degrees or less. Claim 1
1. The optical sheet according to 1.