JP4849511B2 - Backlight unit - Google Patents

Description

  The present invention relates to a backlight unit for illuminating a light-receiving display device such as a liquid crystal display device, and more particularly to a backlight unit for a liquid crystal display device used for small information equipment such as a mobile phone.

  Conventionally, in a light receiving display device such as a display device using liquid crystal, a light source called a backlight unit has been required because the display device is not a self-luminous body.

Since the light receiving display device has an important advantage of low power consumption, it is important to increase the light utilization efficiency in the backlight unit as well, especially in small information devices such as mobile phones. Was outstanding.
Therefore, in the backlight unit, the sheet on which the prism is formed is placed between the light guide plate and the display device, and the light that illuminates the display device is condensed in a direction perpendicular to the display surface of the display device to collect most of the light. There has been proposed a technique of increasing light use efficiency by converting light that is effective for recognition of a display device (see, for example, Patent Document 1).

However, since then, various sheets for improving the display characteristics have been developed, and the improvement of the display characteristics has been accompanied by a significant increase in cost.
FIG. 9 is a diagram showing a configuration of a recent typical backlight unit. For example, a light emitting diode (hereinafter abbreviated as LED) 90 is used as a light source, and a prism 91 is formed in the lower portion of the emitted light of the LED light source 90. The light emitted from the light guide plate 92 is emitted as illumination light via the diffusion sheet 94 and the two brightness enhancement films 96 and 98 arranged so that the ridge lines of the prisms are orthogonal to each other. The device 100 was illuminated. Here, the light source 90, the light guide plate 92, the diffusion sheet 94, and the two brightness enhancement films 96 and 98 constitute the backlight unit 99.
Here, as the brightness enhancement film, for example, Thin BEF series manufactured by Sumitomo 3M Co. was used.
In the following drawings, the same members are denoted by the same numbers.
Thus, it is common to use at least three sheets 94, 96, and 98, and the display quality of the display device is improved, but the cost is greatly increased. As a backlight unit for small information equipment, it has been a big problem.

Therefore, a proposal has been made to reduce the cost of the backlight unit by removing the diffusion sheet 94 from the sheets shown in FIG. 9 (see, for example, Patent Document 2).
However, the most expensive sheet is a brightness enhancement film, and the reduction of the brightness enhancement film is the most important issue.

Therefore, there is a method of reducing the cost by deleting one brightness enhancement film from the configuration of FIG. However, by removing one brightness enhancement film, the brightness has been reduced by nearly 50%.
When one brightness enhancement film is used, the optimum incident angle of incident light with respect to the brightness enhancement film is higher than that of the two brightness enhancement film. The angle is defined as an angle with respect to the normal line of the light guide plate exit surface. When two brightness enhancement films are used, the optimum angle is around 48 °, and when only one brightness enhancement film is used, it is around 30 °. Has been.
In general, the angle of light emitted from the light guide plate with a reflecting prism as shown by 92 in FIG. 9 is approximately 60 °, and the light is emitted through the diffusion sheet by being bent in a direction in which the light emission angle is reduced by the diffusion sheet 94 on the light guide plate. The angle is around 40-50 °. This angle is the optimum incident angle when using two brightness enhancement films, but when only one brightness enhancement film is used, the angle is far from the optimum incidence angle, resulting in a problem that the rate of decrease in brightness increases.

Japanese Patent No. 2739730 JP 2004-117606 A

The problem to be solved is to suppress the deterioration of the function while reducing the cost of the backlight unit for the light receiving display device.

A backlight unit for illuminating a light-receiving display device such as a liquid crystal display device of the present invention has one prism type light guide plate and a brightness enhancement film having a convex prism on one sheet, and the light guide plate An exit angle adjustment diffusion sheet for raising the exit angle of the output light from the light guide plate is provided between the brightness enhancement films, the exit angle diffusion adjustment sheet is a lenticular lens sheet, and the reflection prism of the light guide plate The ridgeline, the ridgeline of the prism of the brightness enhancement film, and the ridgeline of the lenticular lens of the emission angle adjusting diffusion sheet are parallel and set perpendicular to the light traveling direction .

The backlight unit of the present invention is characterized in that the ridge line of the lenticular lens of the emission angle adjusting diffusion sheet is 130 or less per inch.

  According to the present invention, when only one brightness enhancement film is used, light can be incident on the brightness enhancement film at a matching angle. Therefore, a backlight unit that can reduce the brightness and can be greatly reduced in cost is provided. It can be realized.

  A backlight unit for illuminating a light receiving display device such as a liquid crystal display device of the present invention has one prism type light guide plate and one piece of brightness enhancement film, and the light guide plate and the brightness enhancement film. An exit angle adjusting diffusion sheet for raising the exit angle of the emitted light from the light guide plate is provided therebetween. The exit angle adjusting diffusion sheet was a lenticular lens sheet. Furthermore, the ridge line of the reflection prism of the light guide plate and the ridge line of the brightness enhancement film prism were made parallel, and the ridge line of the lenticular lens of the emission angle adjusting diffusion sheet and the ridge line of the brightness enhancement film prism were also made parallel.

FIG. 1 is a perspective view of an embodiment of a backlight unit according to the present invention.
The backlight unit of FIG. 1 uses an LED 90 as a light source, and the light emitted from the LED light source 90 is incident on a light guide plate 92 having a reflection prism 91 formed below, and the light emitted from the light guide plate 92 is an emission angle adjusting diffusion sheet. 10. It is emitted as illumination light through a brightness enhancement film 96 on which a prism surface is formed, and illuminates the liquid crystal display device 100 which is a light receiving display device. The ridge line 14 of the reflecting prism 91 of the light guide plate 92, the ridge line 16 of the prism of the brightness enhancement film 96, and the ridge line 18 of the lenticular lens of the emission angle adjusting diffusion sheet 10 to be described later are set in parallel. It is orthogonal to the direction 15. Here, the light source 90, the light guide plate 92, the emission angle adjusting diffusion sheet 10, and the brightness enhancement film 96 constitute the backlight unit 12.
Here, as the brightness enhancement film, for example, Thin BEF series manufactured by Sumitomo 3M Limited can be used.
The configuration of the backlight unit 12 of FIG. 1 is different from the configuration of FIG. 9 in that one brightness enhancement film is omitted and only one sheet is used, and the emission angle adjusting diffusion sheet 10 is replaced with a general diffusion sheet. It is a point to use.

Next, the shape of the emission angle adjusting diffusion sheet 10 will be described with reference to FIG.
FIG. 2 is an enlarged view of the exit angle adjusting diffusion sheet 10 used in the present invention, and the upper part has a kamaboko shape to form a lenticular lens 12.
As the material of the exit angle adjusting diffusion sheet 10, highly transparent PET, acrylic resin or the like can be used, and as a manufacturing method, a method of pouring the above material into a mold having the shape of a lenticular lens, a film of the above material is used. There can be various methods such as hot pressing with a similar mold.
In addition, since such lenticular lens sheets are widely used in consumer devices and there are standard products, they can be manufactured at a very low cost for a brightness enhancement film. Therefore, the backlight unit having the configuration shown in FIG. 1 can be greatly reduced in price as compared with the conventional configuration shown in FIG.

Next, the optical operation of the backlight unit according to the present invention will be described with reference to FIG. 8, but before that, the coordinate axes used in this specification are defined in FIG.
As shown in FIG. 4, the vertical axis of the plane of the light guide plate 92 is the Y axis, the horizontal axis is the X axis, and the normal direction that is the display device direction above the plane of the light guide plate 92 is the Z axis. The Z ′ direction in which the illumination light is actually emitted is inclined with respect to the normal axis Z, and this inclination angle is defined as the light emission angle.

FIG. 8 is a diagram in which the state of illumination light is added to the backlight unit having the configuration of the present embodiment shown in FIG.
In FIG. 8, the emitted light 30 of the LED light source 90 is emitted in the X-axis direction and propagates in the X-axis direction while being reflected by the upper surface of the light guide plate 92 and the reflecting prism surface 91 in the light guide plate 92. Is emitted at an angle α with respect to the normal direction 38 as indicated by light 32. In general, the emission angle α of the prism type light guide plate 92 is about 60 °.
The outgoing light 32 of the light guide plate 92 is incident on the outgoing angle adjusting diffusion sheet 10, but the outgoing light of the outgoing angle adjusting diffusion sheet 10 is diffused as indicated by 34. The outgoing light 34 is anisotropically diffused by the action of the lenticular lens. That is, it is diffused in the XZ plane but not in the YZ plane. This point is different from the conventionally used diffusion sheet 94, and conventionally, light is diffused in all directions by the diffusion sheet 94.

The outgoing light 34 is diffused as shown in the figure by the action of the lenticular lens of the outgoing angle adjusting diffusion sheet 10, and the central angle β of the diffused light is lifted with respect to the normal direction 38 and becomes approximately 30 °. 30 ° is a recommended angle when one brightness enhancement film is used. As a result, when the light 34 is incident on the brightness enhancement film 96, the light is condensed by the brightness enhancement film 96 and substantially perpendicular to the display device 100. Therefore, the liquid crystal display device 100 is provided with substantially vertical illumination light.
As shown in FIG. 8, the outgoing light is diffused with respect to the incident light in the outgoing angle adjusting diffusion sheet 10, and the outgoing light is condensed with respect to the incident light in the brightness enhancement film 96.

Next, the light diffusion state of the emission angle adjusting diffusion sheet 10 provided with the lenticular lens surface will be described.
FIG. 3 is a diagram showing the light diffusion state of the emission angle adjusting diffusion sheet 10 depending on the density of the lenticular lens.
3A shows a case where the density per inch of the ridge line of the lenticular lens (hereinafter abbreviated as LPI) is infinite, that is, the sheet is a mirror surface, FIG. 3B shows 160 LPI, and FIG. 3C shows 100 LPI. In this case, FIG. 3D shows a case of 70 LPI.
When the sheet 30 has a mirror surface as shown in FIG. 3A, the incident light 20 passes through the sheet 30 as light 22 that is not diffused.
When the lenticular lens ridge density of the sheet 32 is 160 LPI as shown in FIG. 3B, the incident light 20 becomes light 24 diffused by approximately + -30 °.
When the lenticular lens ridge line density of the sheet 34 is 100 LPI as shown in FIG. 3C, the incident light 20 becomes light 26 diffused by about + -45 °.
When the lenticular lens ridge line density of the sheet 36 is 70 LPI as shown in FIG. 3D, the incident light 20 becomes light 28 diffused by approximately + -60 °.
Thus, the lenticular lens has the function of refracting the light angle as shown by α and β in FIG.

FIG. 5A is a graph in which the light intensity when the emission angle adjusting diffusion sheet 10 is placed on the light guide plate 92 is measured along the XZ plane as shown in FIG. , + 90 °, and −90 ° respectively indicate angles with respect to the normal direction Z-axis of the irradiation light exit surface on which the light intensity measuring device is installed. In FIG. 5B, the LED light source 90 is placed on the left side of the light guide plate 92, and the emitted light travels to the right while repeating reflection in the light guide plate 92.
The vertical axis of the graph shown in FIG. 5A indicates the light intensity of the outgoing light, the horizontal axis indicates the outgoing angle of the outgoing light in the Z-axis direction, and the alternate long and short dash line uses a 160 LPI sheet as the outgoing angle adjusting diffusion sheet 10. The dotted line indicates the characteristics when a 100 LPI sheet is used as the exit angle adjusting diffusion sheet 10, and the solid line indicates the characteristics when a 70 LPI sheet is used as the exit angle adjusting diffusion sheet 10.

As shown in the graph of FIG. 5A, the peak position of the light intensity is about 60 ° when the LPI is 160, which is substantially the same as the emission angle of a general prism-type light guide plate. The smaller the value is from 100 to 70, the closer to the optimum incident angle of 30 ° in the case of a single brightness enhancement film.
That is, it was found that the smaller the LPI value, the greater the effect of raising the emitted light in the Z-axis direction.
The peak value of the light intensity decreases as the LPI is decreased from 160 → 100 → 70. That is, it is shown that the diffusivity of the emitted light increases as the LPI value decreases, which is consistent with the description of FIG.
From FIG. 5A, it was found that the LPI value can be set closer to the recommended incident light angle of 30 ° when one brightness enhancement film is used.

6A, as shown in FIG. 6B, the ridge line of the reflecting prism 91 of the light guide plate 92, the ridge line of the prism of the brightness enhancement film 96 on the light guide plate 92, the lenticular lens of the exit angle adjusting diffusion sheet 10 Is a graph obtained by measuring the light intensity along the XZ plane when the brightness enhancement film 96 and the emission angle adjusting diffusion sheet 10 are placed so that the ridge line of the image is substantially parallel to each other, and is 0 °, + 90 °, and −90 °. Indicates the angle with respect to the Z-axis in the normal direction of the irradiation light exit surface on which the light intensity measuring device is installed. FIG. 6A shows a graph in which the light intensity of the backlight unit according to the configuration of the present invention is measured.
In FIG. 6B, the LED light source 90 is placed on the left side of the light guide plate 92, and the emitted light travels to the right while repeating reflection in the light guide plate 92.
In the graph shown in FIG. 6A, as in FIG. 5A, the vertical axis indicates the light intensity of the outgoing light, the horizontal axis indicates the outgoing angle of the outgoing light in the Z-axis direction, and the alternate long and short dash line indicates the outgoing angle adjustment diffusion. Characteristics when a 160 LPI sheet is used as the sheet 10, dotted lines are characteristics when a 100 LPI sheet is used as the emission angle adjustment diffusion sheet 10, and solid lines are characteristics when a 70 LPI sheet is used as the emission angle adjustment diffusion sheet 10 Is shown.

As shown in the graph of FIG. 6A, each peak position of the light intensity moves in the 0 ° direction as the LPI is decreased from 160 → 100 → 70, and 0 which is the normal direction of the light guide plate 92. In the region where the display device is viewed by the human eye 38 at + 5 °, the light intensity is the highest when the LPI value is 70, and the light intensity decreases as the LPI value increases to 100 or 160.
That is, FIG. 6A shows that in the backlight unit using only one brightness enhancement film, the illumination light in the normal direction of the display device can be increased by setting the LPI value small.
Further, depending on the specifications of the device using the liquid crystal display device, the priority viewing angle may differ from the front, slightly above, or slightly below. Even in such a case, by setting the position of the light source 90 and the LPI value of the lenticular lens of the emission angle adjusting diffusion sheet, the emission angle of the illumination light is given priority to the liquid crystal display device even in a backlight unit using only one brightness enhancement film. Can be adjusted to the viewing angle.

FIG. 7 is a table showing the results of measuring the luminance of the backlight unit from the most important normal direction of the light guide plate 92, that is, the position of the eye 38 in FIG.
In the table, the plane of the backlight unit is divided into nine parts, and the brightness values of each part are measured. The light source is placed on the left side of the light guide plate. Table x-1 shows the measured luminance, and Table x-2 shows the result of calculating the ratio to the luminance of the conventional backlight unit. In the backlight unit in Table 1 showing the values of the prior art, the light guide plate, the diffusion sheet, and the two brightness enhancement films are arranged as shown in FIG. A diffusion sheet or an emission angle adjusting diffusion sheet and one brightness enhancement film are arranged as shown in FIG.

Table 1 shows luminance data of a conventional backlight unit using a normal diffusion sheet and two brightness enhancement films. An object of the present invention is to delete one expensive brightness enhancement film and obtain a brightness close to the conventional brightness shown in Table 1.
Table 2-1 shows the luminance data of a conventional backlight unit using one normal diffusion sheet and one brightness enhancement film, that is, a backlight unit in which one brightness enhancement film is simply reduced. As shown by AVG 48% of 2, the luminance is almost halved and cannot be used.
Table 3-1 shows the luminance data of a backlight unit using a 160 LPI exit angle adjusting diffusion sheet and one brightness enhancement film. As shown in AVG 40% in Table 3-2, a conventional normal diffusion sheet is used. The brightness is lower than that used, and it is still unusable.
Table 4-1 shows the luminance data of the backlight unit using one 100 LPI emission angle adjusting diffusion sheet and one luminance increasing film. As shown by AVG85% in Table 4-2, the luminance increase is remarkable. .
Table 5-1 shows the luminance data of the backlight unit using one 70 LPI emission angle adjusting diffusion sheet and one luminance increasing film. As shown by AVG 95% in Table 5-2, the luminance increase is more remarkable. A characteristic close to that of a conventional backlight unit using the two brightness enhancement films shown in Table 1 can be obtained.

  Thus, in the backlight unit according to the present invention shown in FIG. 1, the ridge line density of the lenticular lens of the emission angle adjusting diffusion sheet is important. According to the experiment, the ridge line of the lenticular lens is optimally about 70 per inch, but the characteristics are drastically improved at 130 or less per inch, which is between 160 LPI and 100 LPI. Furthermore, it was found that by setting this value to 85 or less per inch, which is intermediate between 100 LPI and 70 LPI, a characteristic approximate to that of a conventional expensive backlight unit can be obtained.

As described above, the backlight unit according to the present invention reduces the cost of the backlight by reducing one expensive brightness enhancement film and making the diffusion sheet an inexpensive sheet that can control diffusion such as a lenticular lens sheet. It was possible to suppress the decrease in function while achieving the above, that is, the decrease in luminance.
This was achieved by placing a diffusion-controllable sheet, such as a lenticular lens, on the light guide plate as a diffusion sheet. This is because it is close to the incident angle.
Further, since the diffusion by the lenticular sheet is anisotropic diffusion, light is diffused in the XZ plane, but light is not diffused in the YZ plane. In the backlight unit according to the present invention, there is one brightness enhancement film, and the light on the XZ plane can be collected but the light on the YZ plane cannot be collected. Therefore, anisotropic diffusion by the lenticular sheet is large. It is effective.

In this embodiment, an example in which a lenticular lens sheet is used as the exit angle adjusting diffusion sheet is shown, but other types of sheets can of course be used as the exit angle adjusting diffusion sheet as long as the optically similar effect is obtained. .
In the embodiment shown in FIG. 1, the lenticular lens surface of the exit angle adjusting diffusion sheet 10 is on the upper surface, and the prism surface of the brightness enhancement film 96 is on the upper surface. Of course, a configuration in which at least one of the surfaces is the lower surface can be established.

1 is a perspective view of an embodiment of a backlight unit according to the present invention. It is an enlarged view of the emission angle adjusting diffusion sheet used in the present invention. It is the figure which showed the diffusion state of the light of the output angle adjustment diffusion sheet by a difference in the density of a lenticular lens. It is a figure which defines the coordinate axis used by this specification. It is the figure which showed the structure of the to-be-measured object and the graph which measured the light intensity at the time of placing the output angle adjustment diffusion sheet used by this invention on a light-guide plate. It is the figure which measured the light intensity of the backlight unit by the structure of this invention, and the figure which showed the structure of to-be-measured object. The result of having measured the brightness | luminance of various backlight units from the normal line direction of the light-guide plate is made into a table | surface. It is the figure which added the state of the illumination light to the backlight unit structure of a present Example. It is the figure which showed the structure of the recent typical backlight unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Light reception type display apparatus 12, such as a liquid crystal display device Backlight unit 92 Prism-type light guide plate 96 Brightness increase film 10 Output angle adjustment diffusion sheet 14 Ridge line 16 of reflection prism of light guide plate Brightness increase film prism edge 18 Output angle adjustment diffusion sheet The edge of the lenticular lens

Claims (2)

In a backlight unit that illuminates a light receiving display device such as a liquid crystal display device,
In order to increase the emission angle of the light emitted from the light guide plate between the light guide plate and the brightness enhancement film, having a prism type light guide plate and a brightness enhancement film having a convex prism on the sheet. The exit angle adjustment diffusion sheet is a lenticular lens sheet, the ridge line of the reflection prism of the light guide plate, the ridge line of the prism of the brightness enhancement film, and the lenticular lens of the exit angle adjustment diffusion sheet The backlight unit is characterized in that the ridge lines are set parallel to each other and perpendicular to the light traveling direction . 2. The backlight unit according to claim 1, wherein the number of ridge lines of the lenticular lens of the emission angle adjusting diffusion sheet is 130 or less per inch.

Images