JP3271660B2 - Light path control diffusion sheet and backlight unit using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light path control diffusion sheet used for a backlight unit for a liquid crystal display device, and a backlight unit using the light path control diffusion sheet.

[0002]

2. Description of the Related Art In a liquid crystal display device, a backlight system in which a liquid crystal layer is illuminated from the back surface to emit light has become widespread, and a backlight unit is provided on a lower surface side of the liquid crystal layer. As shown in FIG. 6, the backlight unit 20 generally includes a rod-shaped lamp 21 as a light source, a square plate-shaped light guide plate 22 arranged so that an end thereof is along the lamp 21,
A light diffusion sheet 23 disposed on the surface side of the light guide plate 22,
Prism sheet 2 disposed above light diffusion sheet 23
4 is provided.

The function of the backlight unit 20 will be described. First, a light beam incident on the light guide plate 22 from the lamp 21 is reflected by a reflection dot or a reflection sheet (not shown) on the back surface of the light guide plate 22, The light is emitted as a light beam having a distribution that shows a peak in a specific direction obliquely upward from the surface. The light beam having a peak in a specific direction obliquely upward enters the light diffusion sheet 23, is diffused by the light diffusion sheet 23, and is emitted from the surface of the light diffusion sheet 23. At this time,
The emitted light becomes a light having a distribution that shows a peak in an upward direction due to diffusion of the light diffusion sheet 23. afterwards,
The light beam emitted from the light diffusion sheet 23 enters the prism sheet 24 and is emitted by the prism portion 24a formed on the surface of the prism sheet 24 as a light beam having a distribution having a peak almost directly above. Thus, lamp 2
The light emitted from 1 is diffused by the light diffusion sheet 23, is refracted by the prism sheet 24 so as to show a peak almost directly above, and illuminates the entire liquid crystal layer (not shown) further above. .

[0004]

Since the light guide plate 22 receives a light beam from one end side, the light guide plate 22 cannot emit the light beam in the upward direction even if the reflection mechanism on the back surface is modified. The peak direction of the light beam emitted from the surface of the light plate 22 is inclined at a predetermined angle to the side opposite to the side where the lamp 21 is provided. This inclination direction is constant by the light guide plate 22. In the prism sheet 24 as well, the peak direction of the incident light beam suitable for refracting the peak of the outgoing light beam in the upward direction is determined by its shape.

[0005] Therefore, the light diffusion sheet 23 is
It is desired that the light beam having a predetermined peak direction emitted from the prism sheet 24 can be guided to the peak direction suitable for the light beam incident on the prism sheet 24.

On the other hand, as the conventional light diffusion sheet 23,
There are a type in which a light diffusion layer in which a light diffusion agent such as beads is dispersed is laminated on the surface, and a type in which fine irregularities are formed on the surface by embossing or the like. Each of these types of light diffusion sheets 23 has only a function of diffusing transmitted light, and the light diffusion function can also direct the peak direction of the emitted light more directly. The operation of only the diffusion function cannot make the peak direction of the emitted light beam coincide with the desired direction. Therefore, it is difficult to manufacture the light diffusing sheet 23 that can cope with the directional characteristics of the emitted light from the light guide plate 22 and the directional characteristics of the incident light suitable for the prism sheet 24. Therefore, in the conventional backlight unit 20, there is a possibility that the liquid crystal layer is not illuminated vertically and luminance unevenness occurs.

The present invention has been made in view of these inconveniences, and is provided with an optical path control means capable of controlling the peak direction of an outgoing light beam in an arbitrary direction in addition to the light diffusing means. An optical path control diffusion sheet and a light path control diffusion sheet capable of coping with the peak characteristic of a light ray and the peak characteristic of an incident light beam suitable for a prism sheet, and as a result, the peak direction of a light ray emitted from the prism sheet can be directed directly upward. It is an object of the present invention to provide a backlight unit using the same.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem. The invention is directed to a linear lamp and a rectangular lamp which is disposed laterally along the lamp and guides light emitted from the lamp upward. A backlight unit for a liquid crystal display device, comprising: a plate-shaped light guide plate; and a prism sheet that refracts a light beam incident from below so that its peak direction becomes more vertical and emits the light upward. An optical path control diffusion sheet disposed and used between the sheet and a light diffusion means for diffusing light rays incident from the lower surface side and emitting the light rays to the upper surface side, and refracting the peak direction of the light rays incident on the lower surface. A sheet having a refractive index of 1.59, and a large number of light diffusing means formed on the sheet surface as the light diffusing means. A prism portion having a pyramid shape is formed, and the prism portion is formed such that a pair of side surfaces thereof, which are perpendicular to the linear direction of the lamp, are inclined at an angle of 10 ° or more and 20 ° or less with respect to a sheet surface. The direction of the peak on a vertical plane parallel to the linear direction of the lamp, which is emitted from the light guide plate, is approximately 60 ° to the left and right with respect to the direction perpendicular to the sheet surface of the sheet. The light is refracted so as to be directed upward and emitted upward.

According to this means, while the light diffusing means diffuses the light beam incident from the lower surface of the sheet, the light path control means makes the peak direction of the light ray transmitted right above the peak direction of the light ray emitted from the light guide plate. Can be refracted in the peak direction of the incident light beam suitable for exiting the light beam.

Further, since the optical path control means includes a large number of quadrangular pyramid-shaped prism portions formed on the sheet surface, the prism portions are refracted on the four inclined side surfaces of the quadrangular pyramid-shaped prism portion. Of the luminance distribution of the light beam passing through the lamp, both the peak direction of the luminance distribution on the plane perpendicular to the linear lamp and the peak direction on the plane parallel to the lamp can be refracted upward (in the normal direction). Also, by changing the inclination angle of the side surface of the prism section, the peak direction of the emitted light beam can be adjusted arbitrarily. The light path control diffusion sheet is formed on the sheet surface such that one side surface of the plurality of prism portions is parallel to the sheet surface, and the light path control diffusion sheet is positioned such that the side surfaces are parallel to the linear lamp and on the opposite side to the lamp. By arranging in the unit, mainly the light beam passes through the side surface, and it is effective to adjust the inclination angle of the side surface.

As described above, a pair of opposing side surfaces of the side surfaces of the prism portion, in other words, a pair of side surfaces facing the longitudinal direction of the linear lamp and perpendicular to the linear direction, correspond to the sheet surface. From 10 ° to 20 °. In general, the light emitted from many light guide plates on the market has a peak direction in the luminance distribution on a plane parallel to the lamp in addition to the peak direction of the luminance distribution on a plane perpendicular to the longitudinal direction of the linear lamp. The inclination is about 60 ° left and right with respect to the direction perpendicular to the sheet surface. According to this means, a synthetic resin (for example, polycarbonate) having a refractive index of 1.59 is used as a sheet material, and a pair of opposing side surfaces of the prism portion in the backlight unit face the longitudinal direction of the linear lamp. By disposing the optical path control diffusion sheet, the pair of side surfaces perpendicular to the linear direction of the lamp having the above-mentioned inclination angle allows the peak direction of the light beam on the vertical surface parallel to the lamp to be perpendicular (true). (Upward).

[0012] One of the side surfaces of the prism portion other than the pair of opposing side surfaces is set at 20 degrees with respect to the sheet surface.
It is preferable to incline it from not less than {30}. According to this means, the light path control diffusion sheet is backlighted such that the one side surface inclined at an angle of 20 ° or more and 30 ° or less with respect to the sheet surface is positioned in parallel with the linear lamp and on the opposite side to the lamp. When the same sheet material (for example, polycarbonate having a refractive index of 1.59) used in the unit is used, the light emitted from the light guide plate on the market, that is, the normal direction is used as a reference. Outgoing light at an angle of about 75 ° can be refracted into a light beam inclined at about 30 °, which is suitable as an incident light of a commercially available prism sheet.

On the other hand, one of the side surfaces of the prism portion other than the pair of opposed side surfaces may be inclined by 45 ° or more and 55 ° or less with respect to the sheet surface. When the above two commercially available prism sheets are stacked, a suitable incident light beam has a peak direction of about 45 ° with respect to a vertical direction. According to this means, the same sheet material as described above is used. When the backlight unit is disposed such that the one side surface is positioned parallel to the linear lamp and on the opposite side to the lamp, the peak direction of the light beam inclined by about 75 ° with respect to the normal direction is determined. The light can be refracted to an inclination of about 45 °, and can be adapted to a backlight unit equipped with a commercially available light guide plate and two prism sheets.

The light diffusing means is selected from the group consisting of a number of fine irregularities formed on the sheet surface, a light diffusing agent dispersed inside the sheet, and a light diffusing layer dispersed inside the sheet. It is preferable to provide one or more types. According to this means, the light can be effectively diffused while refracting the peak direction of the light beam by the optical path control means.

[0015]

A) a linear lamp; b) a rectangular light guide plate disposed along the lamp and guiding light emitted from the lamp to the surface side; and c) a light guide plate on the surface side of the light guide plate. A liquid crystal display device comprising: the light path control diffusion sheet provided; and d) a prism sheet provided on the front surface side of the light path control diffusion sheet and refracting the light so that the peak direction of the light beam becomes more vertical. As described above, the backlight unit can refract the peak direction of the light beam emitted from the light guide plate by the light path control diffusion sheet in the peak direction of the incident light beam suitable for the prism sheet. Light can be dispersed over the entire surface of the light unit and emitted vertically.
Therefore, luminance unevenness of a liquid crystal display device using the backlight unit can be reduced.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings as appropriate. FIG. 1 is a perspective view showing the periphery of an optical path control diffusion sheet according to an embodiment of the present invention.
FIGS. 3A and 3B are schematic diagrams illustrating light beams passing through the optical path control diffusion sheet of FIG. 1, and FIGS.
FIGS. 4A and 4B are schematic diagrams illustrating light diffusion means of the light path control diffusion sheet of FIG. 4, and FIG. 5A is a graph showing a relative luminance distribution of light rays emitted from the light guide plate, and FIGS. FIG. 3 is a side view, a plan view, and a front view showing a prism unit according to an optical path control diffusion sheet having a different form from FIG.

As shown in FIG. 1, the light path control diffusion sheet 1 is disposed in parallel with the upper surface of the light guide plate 6 in the backlight unit 8 and the lower surface of a prism sheet (not shown). It is similar to the above-described conventional light diffusion sheet in that light emitted from the upper surface of the light guide plate 6 is diffused and made incident on the prism sheet, but is characterized in that an optical path control means is provided in addition to the light diffusion means. .

The light path control diffusion sheet 1 comprises a flat sheet part 2 and a prism part 3 formed on the upper surface thereof. The prism part 3 constitutes the light path control means.
This prism part 3 is formed in a triangular convex stripe in cross section.
It comprises a side surface 4 having an inclination angle α and a side surface 5 having an inclination angle β with respect to the seat portion 2. In addition, the prism unit 3 includes the sheet unit 2
Are arranged in parallel with each other, and the side surface 4 and the side surface 5 are oriented in the same direction. The light path control diffusion sheet 1 having the above configuration is disposed so that the prism portion 3 is parallel to the lamp 7.

Examples of the material forming the light path control diffusion sheet 1 include synthetic resins such as polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, and weather resistant vinyl chloride. And polycarbonate are preferred. Further, the light path control diffusion sheet 1 is transparent because it is necessary to transmit light.
Preferably, a colorless and transparent material is used.

The path of the light beam passing through the light path control diffusion sheet 1 will be described below. However, the angle indicating the peak direction of the light beam described below is an angle inclined to the side opposite to the side where the lamp 7 is provided, with reference to the direction perpendicular to the surface of the light guide plate 6. As shown in FIG. 2A, the light beam emitted from the lamp 7 enters the light guide plate 6 from its end and exits from the upper surface. The peak direction of the emitted light beam is inclined at an angle δ. This angle δ has a value determined by the light guide plate 6. The light beam emitted from the light guide plate 6 is refracted in the direction of the angle ε on the back surface of the light path control diffusion sheet 1. After that, the light beam is angled θ at the side surface 5 of the inclination angle β.
Refracted in the direction of.

On the other hand, as shown in FIG. 2B, the relative position between the light path control diffusion sheet 1 and the lamp 7 is reversed,
That is, when the lamp 7 is disposed on the side surface 5, the light beam emitted from the light guide plate 6 in the direction of the angle δ is refracted in the direction of the angle ε on the back surface of the light path control diffusion sheet 1, and the side surface 4 having the inclination angle α
At the angle κ.

Now, the light path control diffusion sheet 1 is formed from polycarbonate having a refractive index of 1.59, and the inclination angle α is 2
When the inclination angle β is 5 ° and the inclination angle β is 50 °, it is suitable for combination with a large number of light guide plates 6 and prism sheets generally available on the market. The reason will be described below. The peak direction of the light beam emitted from the large number of light guide plates 6 is 7
5 ° direction. On the other hand, the peak direction of the incident light necessary for many prism sheets to refract the peak direction of the outgoing light beam vertically is about 30 ° when one prism sheet is used and about 45 ° when two prism sheets are used. It is. When the light path control diffusion sheet 1 is disposed so that the side surface 4 of the prism portion 3 faces the lamp 7 as shown in FIG.
A light beam having a peak direction of 75 ° emitted from the light guide plate 6 is refracted at the bottom of the optical path control diffusion sheet 1 by about 37 degrees, and
In this case, the incident light can be directed perpendicularly to the peak direction of the emitted light in the case of one prism sheet. When the light path control diffusion sheet 1 is arranged so that the side surface 5 of the prism portion 3 faces the lamp 7 as shown in FIG. 2B, the peak direction emitted from the light guide plate 6 becomes 7.
The 5 ° ray is refracted at about 37 degrees at the bottom surface of the light path control diffusion sheet 1 and is refracted at about 45 ° at the side face 4, so that when two prism sheets are used, the peak direction of the emitted light can be directed vertically. Can be incident light.

The size of the prism section 3 is as follows.
For example, the projection length of the side surface 4 on the surface of the sheet portion 2 is 60 μm.
m, the projection length of the side surface 5 on the surface of the sheet portion 2 is 23.5 μm
m, the height of both sides 4 and 5 from the surface of the sheet portion 2 is 28μ.
Although it can be m, the present invention is not limited to this, and any similarity to this size is acceptable. The thickness of the sheet portion 2 is not particularly limited, but is, for example, 100 μm to 200 μm.
m or less. If the thickness of the sheet portion 2 is less than the above range, the required strength cannot be secured. Conversely, if the thickness of the sheet portion 2 exceeds the above range, the brightness of the liquid crystal display device may decrease, The thickness of the backlight unit 8 is increased, which is against the demand for thinning the liquid crystal display device.

As described above, by setting the inclination angle α and the inclination angle β of the prism portion 3 as described above, it is possible to cope with the case where one prism sheet is provided on the side surface 5 of the inclination angle β. It is possible to cope with the case where there are two prism sheets on the side surface 4 of α, that is, one light path control diffusion sheet 1 can cope with both types of backlight units. Table 1 below shows the inclination angle α and the inclination angle β when the peak directions of the light beams emitted from the light guide plate 6 are different.

[0026]

[Table 1]

Next, the light diffusion means of the light path control diffusion sheet 1 will be described. As shown in FIG. 3A, it is possible to form fine irregularities 10 on the surface by embossing, sandblasting, or the like, and to diffuse light rays by the irregularities 10. Further, as shown in FIG. 3 (b), it is also possible to knead and mold a fine granular light diffusing agent 11 formed of an acrylic resin or the like into the cloth and to diffuse the light beam by the dispersed light diffusing agent 11. It is. Further, as shown in FIG. 3 (c), it is possible to disperse the light diffusing agent 11 in the cloth and to form the irregularities 10 on the surface.

As shown in FIG. 3 (d), the sheet portion 2 is formed from the above-mentioned polyethylene terephthalate, polycarbonate or the like, and the prism portion 3 is formed on the surface of the sheet portion 2 from an ultraviolet curable resin in which a light diffusing agent 11 is dispersed. It is also possible. As shown in FIG. 3E, it is also possible to form the prism portion 3 on the surface of the sheet portion 2 in which the light diffusing agent 11 is dispersed by using an ultraviolet curable resin in which the light diffusing agent 11 is dispersed. Further, as shown in FIG. 3 (f), it is possible to form the prism portion 3 on the surface of the sheet portion 2 in which the light diffusing agent 11 is dispersed by using an ultraviolet curable resin. Although not shown, it is also possible to form irregularities 10 similar to those in FIG. 3A on the surface of each of the optical path control diffusion sheets 1 shown in FIGS. 3D to 3F.

The passing light beam can be diffused by the light diffusing means as described above, and the diffusion function has an effect of slightly shifting the peak direction of the passing light beam to the vertical direction. The effect of directing the peak direction in the vertical direction increases as the light diffusion function increases. It is necessary to reduce the inclination angles α and β in accordance with the action of raising light rays by such a light diffusion function.

As described above, the backlight unit 8 incorporating the light path control diffusion sheet 1 has a lamp 7 as a light source, a light guide plate 6 disposed on the side of the lamp 7, and a light guide plate. An optical path control diffusion sheet 1 disposed on the front side of the light plate 6 and a prism sheet (not shown) disposed on the surface side of the optical path control diffusion sheet 1 are provided (see FIG. 1). In FIG. 1, the light guide plate 6 and the light path control diffusion sheet 1 are shown separated from each other for convenience of explanation, but they are actually in contact with each other.

The backlight unit 8 can match the light guide plate 6 and the prism sheet with the peak characteristics of the emitted light by the light path control diffusion sheet 1, and make the light from the surface of the prism sheet more even and more perpendicular. Can be injected. Therefore, the liquid crystal display device using the backlight unit 8 can suppress luminance unevenness on the screen.

Incidentally, among the distributions of light rays emitted from the surface of the light guide plate 6, the distribution on the plane perpendicular to the lamp 7 has a peak direction at about 75 ° as described above.
The distribution on a plane parallel to the light guide plate 6 and perpendicular to the light guide plate 6 has a peak direction at about 60 ° left and right (see FIG. 4). The peak characteristics of such light rays in the direction parallel to the lamp 7 cannot be controlled by the above-described prism unit 3. The prism portion 13 shown in FIG. 5 is formed in a quadrangular pyramid.
With respect to the vertical direction (perpendicular to the lamp 7). This prism part 13
The inclination angles of the side surface 14 and the side surface 15 facing each other are the same as those of the side surface 4 and the side surface 5 of the prism portion 3, respectively.
And β. The inclination angle of the side surface 16 perpendicular to the side surfaces 14 and 15 is λ. By arranging the prism portion 13 such that the side surface 14 and the side surface 15 facing each other are parallel to the lamp 7, the peak direction in the plane parallel to the lamp 7 can be more refracted by the side surface 16,
The peak characteristic in the direction parallel to the lamp 7 can be controlled by adjusting the inclination angle λ. Therefore, the prism unit 1
According to 3, the peak characteristic in the direction perpendicular to the lamp 7 can be controlled by the side surface 14 or the side surface 15, and the peak characteristic in the direction parallel to the lamp 7 can be controlled by the side surface 16. Now, when the peak direction of the light emitted from the light guide plate 6 with respect to the direction parallel to the lamp 7 is 60 ° left and right, the side 1
Preferably, the inclination angle λ of the prism 6 is set to about 15 °, and the length of the prism section 13 in the left-right direction is set to about 220 μm.

[0033]

As described above, according to the optical path control diffusion sheet of the present invention, it is possible to match the peak characteristic of the light emitted from the light guide plate and the peak characteristic of the incident light suitable for the prism sheet. A backlight unit using a diffusion sheet can emit light more uniformly and more vertically.

[Brief description of the drawings]

FIG. 1 is a perspective view showing the periphery of an optical path control diffusion sheet according to an embodiment of the present invention.

FIGS. 2A and 2B are schematic diagrams illustrating light rays passing through the optical path control diffusion sheet of FIG.

FIGS. 3A to 3F are schematic diagrams illustrating a light diffusing unit of the light path control diffusion sheet of FIG.

FIG. 4 is a graph showing a relative luminance distribution of a light beam emitted from a light guide plate.

FIGS. 5 (a), (b) and (c) are a side view, a plan view and a front view, respectively, showing a prism portion relating to an optical path control diffusion sheet having a form different from that of FIG.

FIG. 6 is a perspective view illustrating a conventional backlight unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical path control diffusion sheet 2 Sheet part 3 Prism part 4 Side surface 5 Side surface 6 Light guide plate 7 Lamp 8 Backlight unit 10 Unevenness 11 Light diffusing agent 13 Prism part 14 Side surface 15 Side surface 16 Side surface

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ identification code FI G09F 9/00 332 G09F 9/00 336J 336 G02F 1/1335 530 (58) Investigated field (Int. Cl. ⁷ , DB name) G02B 5/02 G02B 5/04 G02B 6/00 331 G02F 1/13357 G09F 9/00 332

Claims (5)

(57) [Claims] 1. A linear lamp and a lamp extending along the lamp.
Light rays emitted from the lamps
A rectangular plate-shaped light guide plate and light rays incident from below
Beam refracted so that the work direction becomes more vertical and exit upward
And a prism sheet for a liquid crystal display
Of the light guide plate and the prism sheet of the light unit
An optical path control diffusion sheet disposed and used between the light diffusion means, which diffuses light rays incident from the lower surface side and emits the light rays to the upper surface side, and refracts the peak direction of light rays incident on the lower surface from the upper surface. I and a light path control means for emitting
The sheet is formed of a material having a refractive index of 1.59.
A plurality of square pyramid-shaped prism portions formed on the sheet surface as the light diffusing means , and the prism portions are
A pair of side surfaces that are perpendicular to the linear direction of the lamp
Sides incline between 10 ° and 20 ° with respect to the seat surface
It is formed as, parallel to the linear direction of the lamp to be emitted from the light guide plate
The direction of the peak in the vertical plane is
A ray that makes approximately 60 degrees to the left and right with respect to the direction perpendicular to the plane
Is refracted so that the peak direction is just above
An optical path control diffusion sheet, wherein the light is emitted to a light source. 2. The light guide plate , wherein one of the side surfaces of the prism portion other than the pair of side surfaces is formed to be inclined from 20 ° to 30 ° with respect to a sheet surface.
Perpendicular to the linear direction of the lamp emitted from
The direction of the peak in the plane is perpendicular to the surface of the light guide plate.
A light beam that is approximately 75 ° to the normal direction,
The light path control diffusion sheet according to claim 1, wherein the light is emitted so as to have an inclination of 30 ° . 3. The light guide plate , wherein one of the side surfaces of the prism portion other than the pair of side surfaces is formed to be inclined from 45 ° to 55 ° with respect to a sheet surface.
Perpendicular to the linear direction of the lamp emitted from
The direction of the peak in the plane is perpendicular to the surface of the light guide plate.
A light beam that is approximately 75 ° to the normal direction,
The light path control diffusion sheet according to claim 1, wherein the light is emitted so as to have an inclination of 45 ° . 4. The light diffusing means is selected from the group consisting of a large number of fine irregularities formed on a sheet surface, a light diffusing agent dispersed inside the sheet, and a light diffusing layer dispersed inside the sheet. The optical path control diffusion sheet according to any one of claims 1 to 3 , comprising one or more of the following. 5. A linear lamp, a rectangular light guide plate disposed laterally along the lamp and guiding light emitted from the lamp upward, and a light guide plate disposed on the front side of the light guide plate. Claim 1 to Claim 4
A backlight unit for a liquid crystal display device, comprising: the optical path control diffusion sheet according to any one of the above, and a prism sheet that refracts a light beam incident from below so that its peak direction becomes more vertical and emits the light beam upward.