JPH1020124A - Light transmission plate for back light and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To substantially prevent the occurrence of wear and chipping at the time of a rear surface treatment, etc., and to substantially prevent the chipping in shapes even during handling by forming peak parts and valley parts alternately continuously in parallel on a light exist surface, which peak parts are formed to an arc shape and which valley parts are V-shaped grooves and specifying the angle of the bottoms thereof to a specific angle. SOLUTION: The peak parts 2 and valley parts 3 of the light exit surface are alternately continuous and parallel. The peak parts 2 are formed to the circular arc shape and the valley parts 3 are the V-shaped grooves. The angle of the bottoms 4 is 80 deg.<=θ<=110 deg.. The light exist surface is constituted to have the circular arc-shaped peak parts 2 and, therefore, the partial wear of the peak part 2 does not arise even if the light exit surface is positioned downward at the time of subjecting the rear surface to a diffusion reflection treatment, such as dot printing. The chipping in the shapes hardly arises even during handling other than the cases described above. The recessed shapes of the inserts of the metal molds used for injection molding are formed to the circular arc shapes. The easy infiltration of the molten resin is made possible without forming spacings and mold parting is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a light guide plate for a backlight used in a surface light source device and a method for manufacturing the same.
In particular, the present invention relates to a light guide plate for a backlight suitably used for a liquid crystal display of an OA device such as a word processor or a personal computer, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, various types of backlights have been proposed for use in a surface light source device.
In particular, a thin liquid crystal display such as a laptop type word processor or a computer uses an edge light type backlight. For example, a linear lamp is provided on one or both end surfaces of a light guide plate, and a back surface of the light guide plate is provided. There is widely known a structure in which a diffuse reflector and a diffuser and a lens sheet are provided on the surface, and various types of light guide plates, diffuse reflectors, diffusers, lens sheets, and the like used for these are proposed. For example, Japanese Patent Application Laid-Open No. 5-127159 proposes a backlight in which a sheet having a large number of prisms having linear top ridges is arranged on the light exit surface side of a light guide plate.
Japanese Patent Application Laid-Open No. 3-2649982 proposes a diffuse reflection treatment to be performed on the back surface of a light guide plate.
Japanese Patent Application Publication No. 244490 discloses a proposal in which a large number of lens units are formed on a light exit surface of a light guide plate so as to be perpendicular to a light traveling direction. However, each has advantages and disadvantages, and a backlight that is totally satisfactory has not been obtained. Therefore, Japanese Patent Application Laid-Open No. 5-203947 discloses a method for further increasing the luminance.
In Japanese Patent Application Laid-Open Publication No. H11-157, a proposal has been made in which reflection processing is directly performed on the back surface of a light guide plate and a plurality of linear prism cuts (triangular prism-shaped protrusions) are formed on the light exit surface side of the light guide plate in parallel with the traveling direction of light. .

[0003]

However, the light guide plate in the backlight described in Japanese Patent Application Laid-Open No. 5-203947 cannot be mass-produced stably due to its surface shape. That is, when the light guide plate having such a surface shape is manufactured by injection molding, the cross-sectional shape of the mold insert piece used is the shape of the prism surface, and the concave portion and the convex portion are each at a right angle. Problems such as insufficient entry of the molten resin (hot water) into the corners occur. Further, even if the molten resin (hot water) can sufficiently enter the recess without forming a void (nest), the mold release is poor,
It was necessary to release the mold using external means such as a suction mechanism and an extrusion mechanism. For these reasons, the time required for molding per sheet is long. Furthermore, since the scale easily adheres to the corners of the concave portion, there is a problem that the life of the mold insert piece is short.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and has been proposed in order to meet the above-mentioned demands. A light guide plate for a backlight that emits light from a light source incident from a light exit surface, wherein the light exit surface has peaks and valleys alternately and continuously alternately parallel, and the peaks are arc-shaped. , The valley is a V-shaped groove, and the angle θ of the bottom is 8
The present invention relates to a light guide plate for a backlight, wherein 0 ° ≦ θ ≦ 110 °.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The light guide plate for a backlight of the present invention having the above-described structure is based on injection (compression) molding, is excellent in handleability, and can be mass-produced in a stable manner. Since the light emitting surface of the light guide plate of the present invention has a configuration having an arc-shaped peak, even when the light emitting surface is down when the back surface is subjected to diffuse reflection processing such as dot printing, the peak is partially worn. And it is difficult to lose the shape in other handling. In addition, the concave shape of the mold insert piece used for injection molding has an arc (concave surface) shape, and the molten resin (hot water) can easily (smoothly) enter without generating a void (nest), and furthermore, a suction mechanism and an extrusion mechanism. Good mold release can be achieved without using external means such as Therefore, the yield is good, the time required for molding per sheet is short, and the production of a light guide plate having a surface shape as designed can be continued with stable quality. Furthermore, since the scale is hardly attached to the concave portion of the mold insert piece,
The service life is long. In addition, the light emitting surface of the light guide plate of the present invention has a valley that is a V-shaped groove, and the angle θ of the bottom is 80 degrees ≦ θ ≦ 110 degrees, but the angle θ of the bottom is more than 80 degrees. When it is small (sharp angle), abrasion occurs, the life of the mold insert piece is shortened, and it is difficult to remove it at the time of mold release. If the angle θ of the bottom exceeds 110 degrees, or if the valley is not a V-shaped groove (that is, if the valley is not formed from two planes that are substantially orthogonal to each other), the amount of light finally reaching the light emitting surface is reduced. Lose.

In the light guide plate, the radius R of the arc-shaped peak and the pitch P are desirably in a relationship of R ≦ 0.4P. It is desirable that the radius R of the peak is 10 to 120 μm and the pitch P is 25 to 300 μm. If the radius R of the ridge is less than 10 μm or the pitch P is less than 25 μm, the number of grooves with respect to the area increases when creating a die insert piece, which requires advanced processing technology. It causes cost increase. When the radius R of the peak exceeds 120 μm or the pitch P exceeds 300 μm, the size of one dot including the R, G, B, and black stripes of the color filter is about 300 μm. In this case, there is a problem in appearance as a streak.
Therefore, as a more preferable range, the radius R of the peak is about 20 to 40 μm, and the pitch P is about 50 to 100 μm.

In the light guide plate of the present invention having such a configuration, the configuration other than the light exit surface is not particularly limited. For example, an appropriate diffuse reflection process may be performed on the back surface, or one side surface may be provided. You may make it shape | mold so that it may become thin gradually from an entrance surface to an end surface. Also, a backlight structure using this light guide plate can be appropriately combined with a linear light source, a reflection sheet, a diffusion sheet, a lens sheet, and the like.

[0008]

【Example】

Embodiment 1 FIG. 2 shows a cross-sectional shape of a light-emitting surface of a light guide plate (11.3 inch) 1 made of an acrylic resin according to one embodiment of the present invention. The radius R of the arc-shaped peak 2 of the light guide plate 1
Is 20 μm, and the pitch P is 50 μm. Also,
The bottom 4 of the valley 3 is formed so as to be located on a line connecting the centers O of the ridges 2. Further, the light guide plate 1
Is formed so as to become gradually thinner from the incident surface on one side to the terminal surface as shown in FIG.
Are formed parallel to the light traveling direction. The back surface of the light guide plate 1 is subjected to a diffuse reflection process by dot printing. Such a light guide plate 1 is made of polymethyl methacrylate ("PARAPET GH-10" manufactured by Kuraray Co., Ltd.).
00S ") and the injection molding machine has a mold clamping force of 350 tons.
The injection compression operation was performed with an injection compression amount of 120 μm. Molding temperature 230 to 240 ° C, injection pressure at peak pressure of 1,150 kg / cm ² , mold temperature 85 to 90
Injection molding was performed under the condition of ° C. FIG. 1 shows the die insert piece 5 used at that time. This mold nest piece 5 has a projection 6
Is a shape in which the valley 3 of the light guide plate 1 is turned upside down,
Is a shape in which the peak 2 of the light guide plate 1 is turned upside down.

[Comparative Example 1] As Comparative Example 1, the cross-sectional shape of the light-emitting surface is as shown in FIG.
The light guide plate 1 ′ was formed in which the apex angle of the peak 2 ′ and the corner of the valley 3 ′ were both perpendicular at μm. The material, other configuration conditions, and preparation method were all the same as those in the first embodiment.

[1. Injection molding time]
0000 light guide plates were continuously manufactured, and the injection molding time per sheet was calculated from the time required for the manufacture. [2. Mold release] Mold release was visually observed. [3. Mold life] Average luminance unevenness of 10 sheets at the initial stage of production and 10
The average luminance unevenness of five sheets at the end of the molding of 000 sheets was measured.
The diagonal 10.4 inch portion of the light output surface of the light guide plate is 5
Using the intersection point equally divided as a measurement point, the luminance was measured using a luminance meter (“Topcon BM-7” manufactured by Topcon Corporation), and from the maximum value (max) and the minimum value (min), the luminance unevenness = (min) / Max) × 100 (%). [4. Luminance] Five randomly selected light guide plates were assembled into a backlight having the structure shown in FIG. 3 and the luminance was measured with a luminance meter (“Topcon BM-7” manufactured by Topcon Corporation).
In the figure, A is a lamp, C is a light guide plate, D is a diffuse reflection treatment, and a mirror sheet 60B is used as a reflection sheet indicated by B.
(Toray PET white), ZN as a diffusion sheet indicated by E
BS (Towa Shoko Amorphous Polyolefin), P-150 (Diaart) and W as lens sheets indicated by F
-518 (wave sheet) was used. Table 1 shows the test results of the above four items.

[Table 1]

As shown in Table 1, Example 1 of the present invention
It was confirmed that, compared to Comparative Example 1, the injection molding time was shorter and the mold release was good. In Comparative Example 1, 100
There was a clear change in the luminance unevenness between the start and end of as many as 00 sheets, but there was almost no change in Example 1.

[Measurement of Luminance in Various Backlight Configurations] In the backlight having the structure shown in FIG. 3, the luminance of the backlight having the following configuration in which the lens sheet indicated by F was changed was measured. 1, F; One BEF II (manufactured by 3M) was provided. 2, F; Two BEF IIs were arranged so as to be orthogonal to each other. 3, F; P-150 and W-518 were combined and disposed. 4, F; P-150 (one sheet) was provided. The results are shown in Table 2. The light guide plate having a smooth light exit surface (referred to as Comparative Example 2) and the light guide plate of Comparative Example 1 were also configured under the same conditions to form a backlight having the above-described configuration, and the results of measuring the luminance are shown in Table 2. Shown.

[Table 2]

As shown in Table 2, Example 1 of the present invention
And the brightness | luminance of the form 3 of the comparative example 1 and the form 2 of the comparative example 2 were almost the same. Therefore, two BEF IIs
It can be changed to 150 and W-518 each, and cost reduction can be achieved.

[0014]

As described above, the light guide plate for a backlight according to the present invention has an arc-shaped peak and a V-shaped groove as a valley, so that abrasion and chipping are unlikely to occur during back surface treatment or the like. In addition, it becomes difficult to lose the shape in any other handling. In addition, a backlight having high luminance without loss of light amount can be formed.

When the radius R and the pitch P of the arc-shaped ridge of the light guide plate satisfy the relationship of R ≦ 0.4P, it is easy to remove the injection-molded product at the time of mold release (take-out). The radius R of the portion is 10 to 120 μm, and the pitch P is 25 to 300.
When it is set to μm, it is suitable for a backlight used for a liquid crystal display.

Further, when the peaks and valleys are formed in parallel to the traveling direction of light, light loss is small, and there is an effect of improving luminance. Also, when forming a groove in the mold insert piece,
The processing distance is short and correct processing can be performed.

Further, the light guide plate formed so that the bottom of the valley is located on or near the line connecting the centers of the arc-shaped ridges does not decrease in luminance, and the intensity of the ridge on the light emitting surface side is not reduced. This can be achieved with the aim of increasing.

If the light guide plate is formed so as to become gradually thinner from the incident surface on one side to the terminal surface, the luminance can be reduced and the weight can be reduced.

When such a light guide plate of the present invention is formed by injection molding of a synthetic resin, the concave shape of the mold nest piece used for the injection molding is an arc (concave surface), and the molten resin (hot water) is used.
Can easily (smoothly) penetrate without generating voids (nests), and the mold release can be improved without using external means such as a suction mechanism and an extrusion mechanism. Therefore, the yield is good, the time required for molding per sheet is short, and the production of a light guide plate having a surface shape as designed can be continued with stable quality. Furthermore, since the scale is hardly attached to the concave portion of the mold insert piece, the life is extended.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a part of a mold insert piece used when manufacturing a light guide plate of the present invention.

FIG. 2 is a sectional view showing a part of a light exit surface of a light guide plate according to one embodiment of the present invention.

FIG. 3 is an exploded perspective view showing an example of a backlight structure using a light guide plate according to one embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a part of a light exit surface of a light guide plate of a comparative example.

[Explanation of symbols]

 Reference Signs List 1 light guide plate 2 peak 3 valley 4 bottom

Claims (8)

[Claims] 1. A light guide plate for a backlight having at least one side surface having an incident surface of a light source, wherein light from a light source incident from the incident surface is emitted from a light emitting surface. Alternately and in parallel, the peaks are arc-shaped, the valleys are V-shaped grooves, and the angle θ at the bottom is 8
A light guide plate for a backlight, wherein 0 ° ≦ θ ≦ 110 °. 2. The radius R and pitch P of the arc-shaped peak are:
The light guide plate for a backlight according to claim 1, wherein R ≦ 0.4P. 3. The radius R of the arc-shaped peak is 10 to 120 μm.
The light guide plate for a backlight according to claim 2, wherein m and the pitch P are 25 to 300 m. 4. The light guide plate for a backlight according to claim 1, wherein the peaks and the valleys are formed in parallel to a traveling direction of light. 5. The ridge and the valley are formed such that the bottom of the valley is located on or near a line connecting the centers of the arc-shaped ridges. A light guide plate for a backlight according to item 9. 6. The light guide plate for a backlight according to claim 1, wherein the light guide plate is formed so as to become gradually thinner from an incident surface on one side surface to a terminal surface. 7. The backlight light guide plate according to claim 1, wherein the light guide plate is formed by injection molding of a synthetic resin. 8. A light guide plate for a backlight having at least one side surface having an incident surface of a light source, wherein light from the light source incident from the incident surface is emitted from the light emitting surface. The peaks are arc-shaped, the valleys are V-shaped grooves, and the angle θ of the bottom is 80 degrees ≦ θ ≦ 1.
A method for manufacturing a light guide plate for a backlight, wherein injection molding is performed using a synthetic resin so that the angle is 10 degrees.