JP2723030B2 - 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 panel backlight for irradiating a transmissive or transflective panel 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 such as a laptop or book type word processor or computer. As such a backlight, an edge light system in which a linear light source such as a fluorescent tube is provided at one end of a light-transmitting light guide plate as shown in FIG. 1 is often used. In the case of this edge light type, as shown in FIG. 2, a light diffusing element is formed in a dot shape or a stripe shape on one surface of a light guide plate, and almost the entire surface is mirror-reflected or light-diffused. In many cases, the light guide plate is covered with a light diffusion sheet (2 in FIG. 2) so as to cover the opposite surface (light emitting surface) of the light guide plate.

In particular, recently, the backlight is driven by a battery, and further improvement in power consumption-luminance conversion efficiency has been desired. A prism or a convex top ridge is provided with a sheet made of a plurality of translucent materials in a state where the top ridges are substantially parallel to each other to provide directivity to light emitted from the backlight. It has been proposed to increase the luminance in the normal direction of the light exit surface. However, since the sheet itself has low light diffusing property, the performance of hiding the light diffusing element formed on the light guide plate is not sufficient, and there is a problem that the shape of the light diffusing element is seen through the sheet. Was. When the shape of the light diffusing element is seen through in this way, it is not preferable in that uniform planar light emission is obtained.

In order to solve this problem, it is conceivable to apply a light diffusing substance to the sheet itself, or to impart light diffusing properties by making the sheet surface random and rough. However, such a method has a problem that the property of imparting directivity to the light emitted from the backlight of the sheet is reduced, and the luminance of the light emitting surface is reduced.

Further, a method has been proposed in which a light diffusing sheet different from the above-mentioned sheet is used by lamination. However, in such a form, only the thickness of the light diffusing sheet itself is required. The thickness of the backlight increases, which does not satisfy the demand for a thinner backlight, and is not always preferable in terms of the luminance of the light emitting surface.

When the distance between the light diffusing elements formed on the light guide plate is reduced to, for example, 50 μm or less, it is possible to make the individual light diffusing elements as described above difficult to identify. However, it is technically difficult to form a light diffusing element in such a state.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thin backlight at a low cost, which has high power consumption-luminance conversion efficiency.

[0008]

As a result of various studies on the above points, the present inventors have introduced a sheet for improving the directivity of light on the light exit surface of the backlight so as to satisfy a certain condition. By arranging it on the light plate surface, the light diffusing element formed on the light guide plate surface is concealed and is not seen through, and the directivity of light is increased, and substantially in the vicinity of the normal direction lowered to the light output surface. As a result, the present inventors have found that a backlight having a high power consumption-luminance conversion efficiency and a relatively low thickness is obtained, and the present invention has been completed.

That is, according to the present invention, a light diffusing element is formed in a dot shape or a stripe shape on one wide surface of a light guide plate made of a light transmissive material. In a panel backlight having a linear light source close to the above, on the light emitting surface side of the light guide plate, a prism or a convex portion having linear top ridges at minute intervals is substantially parallel to the top ridge. A sheet made of a light- transmitting material having a large number on the same surface in a state where the straight top ridge is on the light guide plate surface
A state in which a formed virtual straight line connects centers of dot-shaped light diffusing elements adjacent to each other at the shortest distance, or a virtual straight line connecting center lines of the striped light diffusing elements at the shortest distance. And a backlight for a panel, which is disposed at least one of the panel backlights.

Next, the present invention will be described in more detail with reference to the drawings.

FIG. 3 is a perspective view of one embodiment of the present invention, and FIG. 4 is a sectional view showing an example of an edge light type backlight. In the drawing, reference numeral 1 denotes a light guide plate, which may be any substance that allows light to pass therethrough efficiently, and is made of quartz, glass, or a translucent natural or synthetic resin such as an acrylic resin.

In order to form a light diffusing element (6 in the figure) on one wide surface of the light guide plate, a substance having an action of diffusing light, for example, silica, barium sulfate, calcium carbonate,
A method of printing a light-diffusing substance such as titanium white, glass bead, resin bead, paint containing air bubbles, printing ink or the like on the light guide plate surface by a method such as screen printing or the like in the form of dots or stripes. Or a method of roughening the surface of the light guide plate into a dot shape or a stripe shape, a method of forming a small hole or forming a small projection on the surface of the light guide plate, a method of cutting out the light guide plate in a step shape, and the like. is there. The dot-shaped light diffusing element referred to here is, for example, when it is screen printed.
The light diffusing element has a shape such as a circle or a square, and the stripe-shaped light diffusing element is formed linearly.

In the present invention, the straight line imagined when forming the light diffusing element on the light guide plate means that, when the light diffusing element is in a dot shape, the center of the adjacent dot is located at the substantially shortest distance. This is a straight line (virtual straight line) imagined when connecting the centers of the dots to be formed. When the light-diffusing element is in the form of a stripe, the straight line is imagined when connecting the center line of the stripe at the shortest distance. Such an imaginary line usually serves as a reference for positioning the light diffusing element formed on the light guide plate surface when the light diffusing element is formed on the light guide plate.

FIGS. 5 to 9 show examples of forming a light diffusing element on a light guide plate. In the figure, reference numeral 6 denotes a light diffusing element composed of a light diffusing substance or the like, and 7 denotes the above-mentioned virtual straight line. These virtual straight lines are generally vertically and horizontally orthogonal as shown in FIG. 5 and FIG. 8, and are located at positions substantially parallel to each other, that is, virtual straight lines connecting the centers of the adjacent light diffusing elements at the shortest distance (in the drawings). 7) is generally formed at a position where a square is formed in terms of manufacturing easiness. However, the arrangement as shown in FIG. 6, that is, the center of the adjacent light diffusing elements is set to the shortest distance. It is possible for the same reason that a virtual straight line (7 in the figure) connected by is formed at a position forming an equilateral triangle.

A straight line that intersects a straight top ridge of a sheet made of a translucent material described later used in the present invention is such a line. When the imaginary line is orthogonal as shown in FIG. 5, the imaginary line and the straight top ridge of the sheet made of a translucent material described later intersect at an angle of 90 degrees or 0 degree. The effect of the present invention is not so much obtained.

In the case where the light diffusing element is formed in a stripe shape as shown in FIG. 7 by coating or notching on the surface of the light guide plate, in a normal state, the stripe is substantially parallel to a linear light source described later. Is often formed,
In the present invention, when connecting the center lines of such stripes at the shortest distance, an imaginary straight line (7 in the figure) intersects a straight top ridge of a sheet made of a light-transmitting material described later.

FIG. 9 shows an example in which square dots are arranged at equal intervals in the horizontal direction (along line 7 in the figure) in the drawing. In this case, the adjacent light diffusing elements The line connecting the centers at the shortest distance is a virtual straight line (7 in the figure).

In addition, the above-mentioned imaginary straight line form makes it difficult for the human eyes to recognize the shape of the light-diffusing element throughout the entire light-emitting surface through a sheet made of a light-transmitting material described later. It is particularly preferable to make the state substantially parallel to It is not necessary that all the imaginary straight lines be parallel to only one direction, and it may be the case that the parallel directions are two directions as shown in FIG. 5 or the three directions as shown in FIG.

The distance between substantially parallel lines imagined on the light guide plate is preferably in the range of 0.01 mm to 5 mm, but when it is 3 mm or more, the shape of the light diffusing element itself passes through the sheet. It becomes easy to see through,
If the thickness is less than 0.03 mm, the production yield is extremely deteriorated. Therefore, the thickness is preferably in the range of 0.03 mm to 2 mm.

The sheath comprising the light-transmitting material described above in the present invention.
The intersection angle between the straight top ridge and the virtual straight line is preferably 10 to 70 degrees in order to cover the light diffusing element of the light guide plate. Further, the preferred range differs depending on the pattern of the light diffusing element. That is, in the case where the virtual straight line forms a square (FIGS. 5 and 8), the light diffusing element has a stripe shape (FIG. 7), and the light diffusing element has a square shape (FIG. 9), the intersection angle is 20 to 70 degrees. Further, around 45 degrees is preferable. When the virtual straight line forms an equilateral triangle (FIG. 6), the intersection angle is preferably 10 to 50 degrees, and more preferably around 30 degrees.

Reference numeral 4 denotes a linear light source.
BaSO ₄ , TiO 2 on a mirror reflection sheet such as Ag or Al or polyethylene terephthalate (PET) having a gap (slit) for light to enter the end of the light guide plate
_2. A light reflector 5 formed of a light diffusion reflection sheet provided with a light diffusion property by air bubbles or the like is covered with a gap of a certain width from the light source surface of the linear light source. Light type (one side , two adjacent end faces ), two light type (both sides , two adjacent end faces ),
Alternatively, the light guide plate is installed so as to be close to at least one end surface of the light guide plate on the three or four sides and the center axis thereof is substantially parallel to the end surface of the light guide plate. Examples of the linear light source include a fluorescent tube, a tungsten incandescent tube, an optical rod, an LED array, and the like, but a fluorescent tube is preferable. It is preferable that the length of the light guide plate is substantially equal to the length of the end portion.

A mirror-reflective sheet such as Ag or Al or a light-diffuse reflection sheet (3 in the figure) obtained by imparting light-diffusing properties to PET with BaSO ₄ , TiO ₂ , bubbles or the like forms a light-diffusing element. The light guide plate is disposed so as to cover almost the entire surface of the light guide plate.

In the drawings, reference numerals 10 and 12 denote sheets made of a light-transmitting material, which are parallel to each other at a fine interval on the same surface, for example,
A prism having a straight top ridge as shown in FIG. 10 or a plurality of similarly convex portions as shown in FIG. 11 so that the top ridges are substantially parallel to each other. Are arranged such that the top ridge is on the outside (the side opposite to the surface facing the light guide plate). The shape of the prism described above is not limited to the shape shown in FIG. 10, but may be a shape having different oblique sides.

According to the present invention, when arranging one or more such sheets on the light emitting surface of the light guide plate, one or more sheets are arranged so that the top ridge intersects a straight line imagined on the light guide plate. Is the feature. By arranging the sheet in this manner, the directivity of light emitted from the light emitting surface of the backlight can be changed, and the directivity in the vicinity of the normal direction dropped on the light emitting surface can be further increased, and power consumption can be increased. Not only a backlight with high luminance conversion efficiency is obtained, but also a backlight in which the shape of the light-diffusing element in the form of dots or stripes is not seen through is obtained.

If necessary, a conventional light diffusion sheet may be further provided. In this case, the light diffusion property of the light diffusion sheet is considerably higher than that of the conventional light diffusion sheet due to the effect of the present invention. It may be low. Therefore, the light transmittance of the light diffusion sheet is improved, and even if the light diffusion sheet is arranged between the light guide plate and the sheet, the luminance is hardly reduced, and the light diffusion sheet is not scattered. If the light exit surface is rougher than the light entrance surface, the luminance is further improved. Further, even if the light diffusion sheet is disposed outside the sheet, the directivity of light obtained by the sheet does not change much.

The sheet made of a translucent material used in the present invention will be described in more detail. The material of the sheet is not particularly limited as long as it is made of a light-transmitting material, but, for example, methacrylic acid ester, polycarbonate, polyvinyl chloride, polystyrene, polyamide, polyester, polyethylene, polypropylene, cellulose resin, It is glass or the like.

As an example of the shape of the straight top ridges formed on the light emitting surface side of the sheet and parallel to each other, as shown in FIG. 10, a so-called prism shape having two or more optical planes is used. The top ridge (8 in the figure) where the two optical planes intersect is linear, and there are a number of linear prisms parallel to each other at minute intervals (P in the figure) within the same plane. is there. The apex angles of the apexes formed on the sheet have substantially the same shape, which means that the apex angles at the apex are substantially the same when cut under the same conditions. Means having

The apex angle (9 in the figure) of the top ridge of the sheet is preferably 70 to 150 degrees. The more preferable angle range of the top ridge depends on the refractive index of the material of the sheet to be used and the light distribution characteristics of the planar light emitter to be used. For example, a material having a large refractive index (polycarbonate, refractive index n = 1.5)
In the case where 9) is used, when the apex angle is 90 degrees or less, the light emitted from the planar light emitter emits light other than in the vicinity of the normal direction dropped on the light emitting surface, and when the apex angle is 110 degrees or more, the normal line Since the directivity of light near the direction decreases, 90 to 110
Is particularly preferred.

As another example of the translucent sheet used in the present invention, there is a convex shape (11 in FIG. 11) in which the top ridge has an arc shape. The convex shape of these sheets is not particularly limited as long as the convex top ridges are substantially parallel, but the cross section perpendicular to the top ridge has a part of a circle or a part of an ellipse. Or a corrugated shape (for example, a shape having a sine curve in cross section) , and a so-called Kamaboko shape. When the shape of such a top ridge is convex, the convex shape itself has a lens function, so that the shape of the light diffusing element described above is distorted, making it more difficult to see through the shape. preferable.

The distance between the many ridges formed on the sheet is adjacent to each other so that the light emitted from the surface makes it difficult for the distance between these ridges to be visually recognized by human eyes. The distance between the top ridge and the top ridge is preferably 1 to 1000,
More preferably, it is 10 to 1000 μm. In particular, when the backlight of the present invention is used in a liquid crystal display, the distance between the top ridges formed on the sheet is narrower than the pixel pitch of the liquid crystal, and is particularly one third or less (for example, when the pixel pitch of the liquid crystal is smaller). When the distance is 0.3 mm, the distance between the top ridges formed on the sheet is preferably 0.3 mm or less, particularly preferably 0.1 mm or less. This is preferable for suppressing the spatial moire phenomenon between a large number of ridges formed on the sheet.

The thickness of the top ridge (t _{2 in} FIG. 10)
Is determined by the apex angle of the apex or the size of the convex portion and the distance between the apex and the apex, the thickness for maintaining a large number of linear apexes in a finely spaced parallel relationship to each other. (T _{1 in} FIG. 10) is required, and it is preferable that t ₁ is thin in order to reduce the light transmittance and the thickness of the backlight. Total thickness of sheet (Fig. 10
Medium T) is 10 to 3000 μm, preferably 50 to 100 μm.
0 μm is good. In addition, the top ridges formed on the same surface preferably have the same shape more effectively.

The method of forming the sheet used in the present invention is not particularly limited. For example, die forming by hot pressing, embossing, casting, and a method of using an ultraviolet curable resin on a base film. Any method can be used as long as it can be formed so as to have a plurality of substantially the same top ridges in parallel with each other at minute intervals by a method such as chemical treatment. In addition, a slight droop occurs on the top ridge for manufacturing reasons, but it may be within a range where the effects of the present invention can be recognized.

Since it is preferable that the sheet and the light guide plate do not optically contact each other (for example, through an air layer), the surface of the sheet facing the light guide plate may be slightly roughened, It is preferable to provide a spacer element to reduce optical adhesion.

In a liquid crystal display, the contrast becomes lower as the angle of viewing from the vicinity of the normal line dropped on the display surface becomes larger, so that the luminance near the normal direction is regarded as important in practical use. Furthermore, since the viewfinder is viewed only from the normal direction dropped on the display surface,
In practice, the luminance near the normal direction is regarded as important.

In the present invention, as described above, when a sheet having a large number of linear prisms whose light emitting surfaces are parallel to each other at fine intervals is arranged on the light emitting surface of the backlight, light directivity appears. . That is, when the luminance of light emitted from the surface is measured in a normal direction dropped onto the light exit surface, the luminance is increased as compared with the case where the sheet is not provided. The luminance measured in the same direction from a certain angle with respect to the normal dropped on the surface, for example, from a direction of 40 degrees becomes substantially smaller than the luminance measured in the normal direction (for example, the normal The brightness decreases to approximately 50% of the luminance when measured in the direction), which indicates that the above-described directivity of light appears.

A feature of the present invention is that the top ridge of the sheet made of a light-transmitting material having a substantially parallel shape crosses a straight line imagined on the light guide plate. It is characterized in that a plurality of sheets are arranged. When the crossing state is described in more detail, as shown in FIG. 12, a top ridge (8 in the figure) of the sheet and a straight line imaginary on the light guide plate ( 7) in the figure are arranged so as to intersect each other.

By arranging the top ridge of the sheet and the imaginary straight line on the light guide plate intersecting each other as described above, the concealing power against the shape of the light diffusing element is increased. I do. That is, the light-diffusing element, such as a dot or a stripe, is spatially formed by the above-mentioned sheet even in a portion where the light-diffusing element is not formed on the light guide plate. It looks as if you are. Such an action is obtained by the optical action of the sheet by arranging the top ridge of the sheet and the straight line imagined on the light guide plate so as to intersect each other. Things.

When two or more sheets are stacked, the brightness is further increased as compared with the case where only one sheet is used. In order to increase the hiding power for the shape more,
It is preferable that the top ridges of the sheet cross each other.

The state of intersection between the top ridges of the sheet described above will be described in detail. It is preferable that the top ridge substantially intersects at 75 to 115 degrees. Although there is a hiding power to the shape of the dot-shaped or striped light-diffusing element which is a light-diffusing element even if the angle is deviated from 75 to 115 degrees, a larger hiding power is obtained at 75 to 115 degrees, particularly preferably. Is around 90 degrees. Further, under this condition, the luminance is also improved at the same time.

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.

1) The light diffusing element to be applied to the light guide plate of the present invention is formed, for example, in a dot shape or a stripe shape. The shape of the dot shape is not particularly limited. Any of a square and an intersection line may be used. These are applied on intersections (grids) of straight lines having a certain interval imagined on the light guide plate, and the interval between the intersections is preferably 0.01 to 5 mm, more preferably 0.03 to 2 mm. Is appropriately selected according to the thickness of the substrate.

Further, when the light diffusing substance is applied, the coating state is such that the coating rate is 1% near the linear light source on the light guide plate surface.
５０50%, preferably 20% １００100% at the farthest part from the light source, and as the distance from the light source increases, the coating starts from the coating point at one side end where the linear light source is brought closer to the light source. It is preferable that the coating is performed so that the ratio becomes larger sequentially. The coverage here refers to the ratio of the light diffusing element covering area applied per unit area of the light guide plate surface.

Further, according to the present invention, the coverage of the light diffusing substance coated on the grid in a state parallel to the axis of the linear light source on the light emitting surface is adjusted to the center on the parallel line (that is, the linear light source). (Center in the longitudinal direction of the light guide plate) from the line on the light guide plate perpendicular to the linear light source to the light diffusing substance in the direction toward both ends. The present invention is used by installing an optical display panel such as a liquid crystal panel on the upper surface of the light emitting surface.

[0044]

According to the present invention, a light guide plate having a high power consumption-luminance conversion efficiency and a light diffusing element formed on the light guide plate is sufficiently concealed. Even in this case, a sufficient concealing effect can be obtained and a thin backlight can be obtained.

[0045]

Next, the present invention will be described in more detail with reference to Comparative Examples and Examples. As shown in FIG. 3, a 3.8 mm diameter cold cathode fluorescent tube (Harrison) was attached to both ends of a 4 mm-thick rectangular light guide plate (AC-999, manufactured by Asahi Kasei Corporation, material: 210 mm × 155 mm). (Manufactured by Denki Co., Ltd.), and an Ag film having a 4 mm slit in a portion in contact with the light guide plate is arranged in an elliptical shape so that the reflection surface faces the light source. It was arranged so as to enter the light guide plate. On the other hand, the light diffusing element formed on the surface of the light guide plate is formed by applying a paint containing titanium white on the intersection (grid) of orthogonal lines having an interval of 1 mm imaginary on the light guide plate as shown in FIG. It was printed in a circular dot pattern and formed under the following conditions. Printing was performed so that the coverage of the light diffusing element was 26% at the minimum point, 90% at the maximum point, and these ratios were sequentially increased in the middle. Further, the coverage of the light diffusing substance coated on the grid in a state parallel to the axis of the linear light source is perpendicular to the linear light source from the center on the parallel line, that is, from the center in the longitudinal direction of the linear light source. With respect to the distance from the line on the surface of the light guide plate to the light diffusing material in the direction toward both ends, 26% at the minimum point, 40% at the maximum point, and the middle point between these points. The printing was performed so that the ratio was gradually increased.

The surface of the light guide plate on which the light spreading element was printed was covered with a 0.125 mm thick light diffuse reflection sheet (Melinex 329 manufactured by ICI). Furthermore, a light diffusion sheet having a rough surface on both sides with a thickness of 0.1 mm (Tsujimoto Electric Manufacturing Co., Ltd.)
D-204).

Inverter (CXAM-1 manufactured by TDK) is installed in the cold cathode tube.
0L) and applying a 30 KHz alternating voltage to drive at a constant current (5 mA for one cold-cathode tube, 10 mA in total for two tubes), view the surface luminance with a luminance meter (Topcon BM-8). It was 1300 cd / m ² when measured with respect to the normal direction dropped on the light emitting surface at an angle of 2 degrees. At this time, the dots could not be seen through the light diffusion sheet. Further, there was almost no directivity of light (Comparative Example 1).

In place of the light diffusion sheet, there are many parallel linear convex portions made of polycarbonate, and the distance between adjacent top ridges of the linear convex portions is 140 μm.
The translucent sheet having a thickness of 250 μm processed so as to have an interval of is set so that the straight top ridge is parallel to a substantially parallel line imagined on the light guide plate, and the top ridge side is The same operation as in Comparative Example 1 was carried out under the same apparatus and conditions except that one sheet was disposed on the light exit surface side so as to be on the outside, and the measured luminance was 1800 cd / m.
^{Was 2} . At this time, the dots were seen through the translucent sheet. The state in which the dots were visible was a state in which dots adjacent to each other in a direction orthogonal to the linear top ridges parallel to each other continued in a line (more specifically, a skewered dumpling). In addition, the directivity of light was observed with respect to the normal direction dropped on the light exit surface (Comparative Example 2).

The same apparatus as that of Comparative Example 2 except that the sheet having a large number of convex portions is arranged so that the straight top ridge thereof intersects with the substantially parallel straight line imagined on the light guide plate. The operation was performed under the following conditions and the measured brightness was 1800 cd / m ² . At this time, the dots were not seen through the translucent sheet. Then, when the sheet was rotated to check the concealing power with respect to the dot shape, the concealing power was further increased if the sheet intersected at 20 to 70 degrees. In particular, the hiding power was maximized in the vicinity of 45 degrees (observed visually, the same applies hereinafter), and the directivity of light was observed with respect to the normal direction dropped on the light emitting surface (Example 1).

The operation and measurement were carried out using the same apparatus and conditions as in Comparative Example 2 except that two translucent sheets having the above-mentioned convex portions were used, and the linear top ridges were arranged so as to be parallel to each other. The obtained brightness was 1850 cd / m ² . At this time, the dots were seen through the translucent sheet. The state in which the dots were visible was a state in which dots adjacent to each other in a direction orthogonal to the linear top ridges parallel to each other continued in a line (more specifically, a skewered dumpling). In addition, the two sheets optically interfered with each other, and a moire phenomenon was observed. In addition, the directivity of light was observed with respect to the direction of the normal dropped onto the light emitting surface (Comparative Example 3).

The operation and measurement were carried out using the same apparatus and conditions as in Example 1 except that two translucent sheets having the above-mentioned convex portions were used and arranged so that their linear top edges crossed each other. The brightness was 1900 cd / m ² . At this time, the dots could not be seen through the translucent sheet, but their hiding power was examined. As a result, the linear top ridges of the two sheets were 75-1
When the vehicle crosses at 15 degrees, the hiding power is further increased.
In particular, the hiding power became maximum around 90 degrees. The brightness is 2
The brightness increased when the linear top ridges of the sheets intersected each other at 75 to 115 degrees, and the brightness reached a maximum (2200 cd / m ² ) particularly at around 90 degrees. In addition, the directivity of light was observed with respect to the normal direction dropped on the light exit surface (Example 2).

Adjacent top ridges of linear prisms having a large number of linear prisms each made of polycarbonate and having an apex angle of 90 degrees in parallel with each other in place of the translucent sheet having the convex portions. The operation was performed under the same apparatus and conditions as in Comparative Example 2 except that a sheet having a thickness of 360 μm was machined so as to have an interval of 350 μm.
It was 00 cd / m ² . At this time, the dots were seen through the translucent sheet. The state in which the dots were visible was a state in which dots adjacent to each other in a direction orthogonal to the linear top ridges parallel to each other were elliptical (they were not connected as in Comparative Example 2). In addition, the directivity of light was observed with respect to the direction of the normal dropped onto the light emitting surface (Comparative Example 4).

The luminance measured in the same manner as in Example 1 using a translucent sheet having a prism was 2000 cd / m ² . At this time, the dots were not seen through the translucent sheet. Then, when the translucent sheet was rotated to examine the concealing power for the dot shape, the concealing power was further increased when the opaque power crossed at 20 to 70 degrees. In particular, the hiding power was maximized at around 45 degrees. In addition, the directivity of light was observed in the direction of the normal dropped onto the light exit surface (Example 3).

Further, the second embodiment uses two light-transmitting sheets.
As a result of examining the concealing power for the dots in the same manner as in the above, the concealing power was further increased when the linear top ridges of the two sheets intersect each other at 75 to 115 degrees. In particular, the hiding power became maximum around 90 degrees. Also, the brightness of the two sheets
When the straight top ridges intersect each other at 75 to 115 degrees, the brightness increases, especially around 90 degrees.
0 cd / m ² ). Further, the directivity of light was observed with respect to the normal direction dropped on the light emitting surface (Example 4).

Next, a paint containing titanium white is applied onto a light guide plate as shown in FIG. 6 by forming a circular dot pattern on an intersection (grid) of straight lines intersecting each other at a minimum angle of 30 degrees with an interval of 1 mm. When the sheet was rotated using the same apparatus and conditions as in Example 1 except that the printing was performed in the same manner as in Example 1, and the concealing force against the dot shape was examined, the straight line ridge of the translucent sheet was formed with the virtual line. The hiding power further increased when the angle intersected at an angle of 13 to 47 degrees. In particular, the hiding power became maximum around 30 degrees. In addition, the directivity of light was observed with respect to the normal direction dropped on the light exit surface (Example 5).

Next, a paint containing titanium white was printed on the light guide plate as shown in FIG. 7 in a striped pattern on lines parallel to each other and spaced apart by 1 mm. When the translucent sheet was rotated by operating the same apparatus and conditions as in Example 1 and the concealing force against the dot shape was examined, the angle between the straight top edge of the sheet and the imaginary line was 20 to
When the vehicle crosses at 70 degrees, the hiding power is further increased.
In particular, the hiding power was maximized at around 45 degrees. In addition, the directivity of light was observed with respect to the direction of the normal dropped onto the light exit surface (Example 6).

The same apparatus and conditions as in Example 1 were used except that a light guide plate having a thickness of 1 mm and a dot pattern formed so that imaginary lines connecting centers as shown in FIG. 8 formed a square was used. As a result, the same results as in Example 1 were obtained with respect to the dot hiding power (Example 7).

[Brief description of the drawings]

FIG. 1 is a perspective view of a backlight according to a conventional embodiment.

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

FIG. 3 is a perspective view of a backlight according to an embodiment of the present invention.

FIG. 4 is a cross-sectional view of a backlight according to an embodiment of the present invention.

FIG. 5 is a diagram illustrating a virtual line for a light diffusing element of the light guide plate used in the present invention.

FIG. 6 is a diagram illustrating a virtual line for a light diffusing element of the light guide plate used in the present invention.

FIG. 7 is a diagram illustrating a virtual line for a light diffusing element of the light guide plate used in the present invention.

FIG. 8 is a diagram illustrating an imaginary line for the light diffusing element of the light guide plate used in the present invention.

FIG. 9 is a diagram illustrating an imaginary line for the light diffusing element of the light guide plate used in the present invention.

FIG. 10 is a diagram showing an example of a surface structure of a light-transmitting sheet used in the present invention.

FIG. 11 is a diagram showing another example of the surface structure of the light-transmitting sheet used in the present invention.

FIG. 12 is a diagram showing an example of positions of virtual lines of a light-transmitting sheet and a light guide plate in the present invention.

[Explanation of symbols]

 1: light guide plate 2: light diffusing sheet 3: light reflecting plate 4: light source 5: light reflecting plate covering the light source 6: light diffusing element 7: virtual straight line on the light guiding plate 8: prism top apex 9: apex angle 10: Translucent sheet having a prism shape 11: Top ridge of a convex portion 12: Translucent sheet having a shape of a convex portion

Claims (9)

(57) [Claims] 1. A light-diffusing element is formed in a dot-like or stripe-like shape on one wide surface of a light-guiding plate made of a light-transmitting material. In a panel backlight having a linear light source close to this, on the light emitting surface side of the light guide plate, a prism or a convex portion having linear top ridges at minute intervals, and the top ridges are substantially parallel. The center of a dot-shaped light diffusing element in which the straight top ridges are formed on the surface of the light guide plate and whose centers are adjacent to each other at the shortest distance is formed. A panel backlight in which at least one panel is disposed so as to intersect a virtual straight line connecting the two or a virtual straight line connecting the center lines of the stripe-shaped light diffusing elements at the shortest distance. 2. A sheet made of a light-transmitting material whose cross section perpendicular to the top ridge of the convex portion has a circular or elliptical shape or a wavy shape. Backlight. 3. The straight top edge of the sheet and the imaginary straight line are between 10 and 10.
3. The backlight according to claim 1, wherein a sheet made of a light-transmissive material is arranged so as to intersect at 70 degrees. 4. The backlight according to claim 1, wherein the backlight is a light guide plate in which a dot-shaped light diffusing element in which a virtual straight line connecting the centers forms a square is formed on one wide surface. 5. The sheet according to claim 1, wherein the straight top edge and the imaginary straight line are 20 to 20.
5. The backlight according to claim 4, wherein a sheet made of a translucent material is arranged in a state of crossing at 70 degrees. 6. The backlight according to claim 1, wherein the light guide plate is formed by forming, on one wide surface, a dot-shaped light diffusing element in which a virtual straight line connecting the centers forms an equilateral triangle. 7. The sheet according to claim 1, wherein the straight top ridge and the virtual straight line are 10 to 10 inches.
7. The backlight according to claim 6, wherein a sheet made of a translucent material is arranged at a crossing angle of 50 degrees. 8. A plurality of sheets made of a translucent material are used,
The backlight according to any one of claims 1 to 7, wherein the straight ridges intersect each other substantially at 75 to 115 degrees. 9. The backlight according to claim 1, wherein a sheet having a distance between adjacent top ridges of the linear top ridge of the sheet made of a translucent material is 10 to 1000 μm. .