JP3858953B2 - Surface light source device and light guide plate molding die - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface light source device and a light guide plate molding die. In particular, the present invention relates to a surface light source device used as a backlight of a liquid crystal display device and a structure of a mold for resin-molding the light guide plate.
[0002]
[Prior art]
A conventional surface light source device 1 is shown in an exploded perspective view of FIG. 1 and a cross-sectional view of FIG. The surface light source device 1 includes a light guide plate 2 for confining light, a light emitting unit 3, and a reflection plate 4. The light guide plate 2 is formed of a transparent resin having a large refractive index, such as polycarbonate resin or methacrylic resin, and a diffusion pattern 5 is formed on the lower surface of the light guide plate 2 by uneven processing. The light emitting unit 3 is a component in which a so-called point light source 7 such as a plurality of light emitting diodes (LEDs) is mounted on a circuit board 6, and faces the side surface (light incident surface 8) of the light guide plate 2. The reflection plate 4 is diffusive and is formed of, for example, a white resin sheet. Both sides of the reflection plate 4 are attached to the lower surface of the light guide plate 2 by a double-sided tape 9.
[0003]
Thus, the light f emitted from the light emitting unit 3 and guided into the light guide plate 2 from the light incident surface 8 is totally reflected inside the light guide plate 2 as shown in FIG. Confined inside. When the light f confined inside the light guide plate 2 is incident on the diffusion pattern 5, the light f is diffusely reflected by the diffusion pattern 5 and incident on the light emitting surface 10 on the upper surface at an incident angle smaller than the refractive index of total reflection. Is emitted from the light exit surface 10. Further, the light f that has passed through the region where the diffusion pattern 5 on the lower surface of the light guide plate 2 does not exist is reflected by the reflecting plate 4 and returns to the inside of the light guide plate 2 again, thereby preventing light loss from the lower surface of the light guide plate 2. Is done. However, the diffusion pattern 5 is not formed on the entire lower surface of the light guide plate 2, but is formed in a region excluding the outer peripheral portion (region smaller than the light emitting surface). This corresponds to the screen area of the liquid crystal display panel, for example, and is called an effective light emission area.
[0004]
Next, the manufacturing method of the light-guide plate 2 used for the said surface light source device 1 is demonstrated. The light guide plate 2 is manufactured by resin molding using a mold. However, since the diffusion pattern 5 is fine, the mold for forming the portion of the diffusion pattern 5 cannot be manufactured by ordinary machining. Therefore, a stamper obtained by replicating a master produced by photolithography with Ni or the like by electrocasting is used as a mold for forming the diffusion pattern 5. This stamper 11 is shown in FIG. Many protrusions 12 for forming the diffusion pattern 5 are provided on the upper surface of the stamper 11.
[0005]
FIG. 4 shows the structure of a mold 13 for forming the light guide plate 2. The mold 13 includes the stamper 11, the lower mold 14, and the upper mold 18. The stamper 11 is manufactured by photolithography and electroforming as described above, while the upper mold 18 and the lower mold 14 are manufactured by normal machining. The lower mold 14 is formed with a recess 15 for fitting the stamper 11 and a cavity 16 for molding the light guide plate 2. When the stamper 11 is fitted in the recess 15, a diffusion pattern is formed on the lower surface of the cavity 16. Projections 12 for molding 5 are arranged. Thus, the upper surface of the lower mold 14 to which the stamper 11 is attached is covered with the upper mold 18, and the light guide plate 2 is molded by injecting resin into the cavity 16.
[0006]
Here, the stamper 11 is one size smaller than the cavity 16, and a flat portion 17 that is flush with the upper surface of the stamper 11 is formed around the recess 15 of the lower mold 14. This is due to the following reason. The die (stamper 11) obtained by the electrocasting method has a larger surface roughness than the machined product. Therefore, unless a machined surface (planar portion 17) is placed around the stamper 11, the other parts and Combinations can be difficult. In addition, the outer peripheral portion of the light guide plate 2 is often complicated in shape to assemble with other parts, but the stamper 11 is made of a hard material such as Ni, and thus is processed into a desired shape. I can't. Therefore, the stamper 11 is made one size smaller than the cavity 16, and the flat portion 17 is formed around the stamper 11.
[0007]
[Problems to be solved by the invention]
However, when the light guide plate 2 is formed using the mold 13 having the above-described structure, the resin is inevitably sucked into the gap between the stamper 11 and the recess 15 of the lower mold 14 due to the capillary phenomenon. Convex streaks (burrs) 19 were generated on the lower surface of the light guide plate 2, resulting in uneven thickness of the light guide plate 2. Since this convex line 19 becomes a groove when viewed from the inside of the light guide plate 2, when the light f hits the convex line 19, the light f is emitted from the light emitting surface 10 as shown in FIG. 5. In particular, since the amount of light is large near the light emitting unit 3 (on the light incident side), if there are convex streaks 19 in the vicinity, a light streak 20 can be seen at the edge of the effective light emitting region as shown in FIG. The light streak 20 has a problem that the luminance uniformity in the vicinity of the light emitting portion 3 of the light guide plate 2 is greatly reduced.
[0008]
The present invention has been made in view of the drawbacks of the conventional example described above, and an object of the present invention is to provide a surface light source device in which light streaks are not generated on the light exit surface due to convex streaks (burrs) during molding. It is another object of the present invention to provide a light guide plate molding die.
[0009]
DISCLOSURE OF THE INVENTION
The surface light source device according to claim 1, wherein light emitted from the light source is introduced into the light guide plate from the light incident surface, confined inside the light guide plate, diffused and reflected by a diffusion pattern, and emitted from the light exit surface. In the surface of the light guide plate on which the diffusion pattern is formed, a step is provided between the light incident surface of the light guide plate and the diffusion pattern forming region so that the light incident surface side is retracted more than the diffusion pattern forming region side. The width of the convex streak generated so as to protrude downward at the lower end of the stepped portion is w, the stepped portion between the recessed surface on the light incident surface side of the stepped portion and the diffusion pattern forming region When the step size is h, the step size of the step portion is
h ≧ w
It is characterized by satisfying .
[0010]
The light guide plate molding die according to claim 2 comprises a stamper for molding a diffusion pattern formation region of the light guide plate and a mold body for molding a surface other than the diffusion pattern formation region of the light guide plate. A light guide plate molding mold in which the stamper is fitted in a recess provided in a mold body, and a surface parallel to the stamper surface is formed around the recess of the mold body, and the depth of the recess in the mold body is Is characterized by being larger than the thickness of the stamper.
[0011]
A light guide plate constituting the surface light source device of claim 1 is manufactured by forming the light guide plate using the light guide plate forming mold according to claim 2. In this light guide plate, there is a step portion between the light incident surface and the diffusion pattern formation region, and the width of the convex streak generated to protrude downward at the lower end portion of the step portion is w, than the step portion. When the step size of the step portion between the recessed surface on the light incident surface side and the diffusion pattern formation region is h, the step size of the step portion is
h ≧ w
Since the region on the light incident surface side with respect to the stepped portion is recessed inward from the diffusion pattern forming region side so as to satisfy the condition, it is continuous with the diffusion pattern forming region side when viewed from the light of the light source incident on the light incident surface. The end of the step portion on the side is behind the end of the step portion on the side continuous with the light incident surface side. Therefore, even if a convex streak is generated at the end of the stepped portion on the diffusion pattern forming region side due to a gap between the mold body and the stamper, incident light does not hit the convex streak. Therefore, as in the conventional example, it is possible to solve the problem that the light exit surface partially shines with the light reflected by the convex streak and the luminance distribution becomes non-uniform.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
Hereinafter, an embodiment of the present invention will be described. The only difference between the surface light source device of the present invention and the conventional surface light source device described in FIG. 1 is the structure of the light guide plate. The structure and the molding die 21 will be described. First, a structure of a mold for forming the light guide plate 33 will be described with reference to FIG. Reference numeral 26 denotes a stamper for forming the lower surface of the light guide plate 33, and a protrusion 27 for forming the diffusion pattern 5 is formed on the lower surface of the light guide plate 33 on the upper surface. The stamper 26 is duplicated with Ni or the like by electrocasting based on a master produced by photolithography. Further, the upper mold 28 and the lower mold 22 constituting the mold body are manufactured by ordinary machining. The lower mold 22 is formed with a recess 23 for fitting the stamper 26 and a cavity 24 for molding the light guide plate 33. When the stamper 26 is fitted into the recess 23, a protrusion is formed on the lower surface of the cavity 24. 27 is arranged. The stamper 26 is one size smaller than the cavity 24, and a horizontal flat portion 25 is formed around the recess 23 of the lower mold 22. However, in the mold 21, the depth of the recess 23 is larger than the thickness of the stamper 26, and the flat portion 25 formed around the recess 23 is stamped into the recess 23. 26 is higher than the upper surface of 26.
[0013]
Then, the upper surface of the lower mold 22 to which the stamper 26 is attached is covered with the upper mold 28, and a molding resin such as polycarbonate resin or methacrylic resin is injected into the cavity 24 to form the light guide plate 33. The
[0014]
The shape of the light incident surface 8 side of the light guide plate 33 thus formed is shown in FIG. Since the flat portion 25 of the lower mold 22 is higher than the upper surface of the stamper 26, the diffusion pattern forming region 31 (the stamper 26) where the diffusion pattern 5 is formed in the light guide plate 33 formed by the mold 21. ) And a lower surface of the light incident portion 32 in the vicinity of the light incident surface 8, a step portion 29 is generated, and the diffusion pattern forming region 31 is lowered by one step.
[0015]
Further, although convex bars (burrs) 30 are also generated in the light guide plate 33 formed using such a mold 21, the convex bars 30 have a stepped portion 29 because of a gap between the lower mold 22 and the stamper 26. At the lower end of For this reason, as shown in FIG. 8, when viewed from the direction of the light incident surface 8, the convex streak 30 is behind the stepped portion 29 and the light f does not hit the convex streak 30. Therefore, as in the conventional example, it is possible to prevent the light striking the convex streak 30 from being reflected and causing light streaks on the light emitting surface 10.
[0016]
The size h of the stepped portion 29 is as follows when the width of the convex muscle 30 is w.
h ≧ w
You should decide to satisfy the relationship. Specifically, since the width of the convex stripe 30 is about 0.04 mm, the size h of the stepped portion 29 may be about 0.05 mm. If the size h of the stepped portion 29 is made approximately the same as the width W of the convex line 30, light f having an angle of light θ of 45 degrees or more hits the convex line 30, but light having θ> 45 ° or more. Is not totally reflected in the light guide plate 33 and cannot be confined in the light guide plate 33 in the first place. Therefore, the size h of the stepped portion 29 may be set so that the width of the convex line 30 is substantially equal to w.
[0017]
(Second Embodiment)
FIG. 9 is a partially broken sectional view showing the structure of a surface light source device 39 according to another embodiment of the present invention. The light emitting section 35 used in this embodiment is a case in which a point light source 37 such as a light emitting diode is housed in a case 36 made of white resin and sealed with a transparent resin 38. In the light guide plate 34, the lower surface of the diffusion pattern forming region 31 is shifted upward by inclining the lower surface of the light incident portion 32, thereby reducing the thickness of the light guide plate 34. In particular, the lower surface of the diffusion pattern forming region 31 is prevented from coming out below the lower surface of the light emitting unit 35. Further, the upper surface of the light incident portion 32 is also inclined at the same inclination so that the light reflected by the inclined lower surface of the light incident portion 32 does not leak from the upper surface of the light incident portion 32, and the plate thickness of the light incident portion 32 is a pattern. It is thinner than the plate thickness of the formation region 31.
[0018]
In the mold 21 of FIG. 7, the flat portion 25 around the recess 23 is made higher than the upper surface of the stamper 26 over the entire circumference, but is flat only on the side parallel to the light incident end surface 8 on the light incident side. The height of the portion 25 may be made higher than the height of the stamper 26, and the flat portion 25 and the stamper 26 may be flush with each other on the other sides.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view showing a conventional surface light source device.
FIG. 2 is a diagram for explaining the behavior of light in the surface light source device.
FIG. 3 is a side view of a stamper for forming a diffusion pattern.
FIG. 4 is a cross-sectional view showing a structure of a mold for forming a light guide plate.
FIG. 5 is a partially cutaway enlarged cross-sectional view of a light guide plate formed with the same mold as above.
FIG. 6 is a diagram showing light streaks generated in a surface light source device using the light guide plate.
FIG. 7 is a cross-sectional view showing a light guide plate molding die according to an embodiment of the present invention.
FIG. 8 is a partially broken cross-sectional view of a light guide plate formed by the above-described mold.
FIG. 9 is a partially broken cross-sectional view showing a surface light source device according to another embodiment of the present invention.
[Explanation of symbols]
5 Diffusion pattern 8 Light incident surface 22 Lower mold 23 Recess 24 Cavity 25 Plane portion 26 Stamper 29 Stepped portion 30 Convex streaks 31 Diffusion pattern formation region 33 Light guide plate

Claims (2)

A surface light source device that introduces light emitted from a light source into a light guide plate from a light incident surface, confines the light inside the light guide plate, diffuses and reflects the diffuse pattern, and emits the light from the light output surface,
In the surface where the diffusion pattern of the light guide plate is formed, a step portion is provided in the middle of the light incident surface of the light guide plate and the diffusion pattern forming region so that the light incident surface side is retracted from the diffusion pattern forming region side ,
The width of the convex streak generated so as to protrude downward at the lower end of the stepped portion is w, and the step size of the stepped portion between the recessed surface on the light incident surface side of the stepped portion and the diffusion pattern forming region is h. When the step size of the step portion is
h ≧ w
Surface light source device is characterized in that so as to meet. It consists of a stamper for forming the diffusion pattern formation region of the light guide plate and a mold body for forming a surface other than the diffusion pattern formation region of the light guide plate, and the stamper is fitted in a recess provided in the mold body. A mold for forming a light guide plate in which a surface parallel to the stamper surface is formed around the recess of the mold body,
A mold for light guide plate molding, wherein a recess depth of the mold body is larger than a thickness of the stamper.

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