JP2002328237A - Light transmission plate, and method of manufacturing light transmission plate as well as illuminator and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of easily manufacturing a light transmission plate which does not give rise to problems of interference fringes, etc., as well as the light transmission plate manufactured by this method and an illuminator and liquid crystal display device using the same. SOLUTION: This method of manufacturing the light transmission plate comprises injecting a molten synthetic resin from a gate bored at a casting mold into a cavity to mold a light transmission plate substrate 1 consisting of a light transmission plate body 3 and a gate section 4 succeeding to this light transmission plate body 3 and removing the gate section 4 from the light transmission plate body 1, in which the removal of the gate section 4 is performed by rough cutting by a sintered hard end mill 5 and finishing by a diamond cutter 6 in succession to this rough cutting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light guide plate, a method for manufacturing the light guide plate, a lighting device, and a liquid crystal display device.
More specifically, the present invention relates to a method of manufacturing a light guide plate used for a liquid crystal display, particularly a front light, and a light guide plate manufactured by the method.

[0002]

2. Description of the Related Art A non-light-emitting display device represented by a liquid crystal display device is indispensable as a display means of an electronic device because it has low power consumption and can be reduced in size and thickness. The liquid crystal display devices are roughly classified into a transmission type and a reflection type. The transmission type liquid crystal display device includes a backlight provided on the back side for illuminating a display screen from the back side, and is used in a reflection type liquid crystal display device. A so-called front light which is provided on the display surface side and illuminates the display screen from the front is incorporated.

[0003] In the above-mentioned front light type or backlight type illumination device, in order to guide light from a light source to a liquid crystal cell,
A light guide plate is used in which one side surface of the plate-like body is used as an incident surface and light incident from this incident surface is emitted from one of the upper and lower surfaces. Such a light guide plate is generally manufactured by injection molding. More specifically, a mold having a cavity having a concave portion substantially corresponding to the shape of the light guide plate and a gate portion communicating with the cavity is prepared, and molten synthetic resin is injected into the cavity through the gate. Thus, a light guide plate base including the light guide plate main body and the gate portion following the light guide plate main body is formed. Then, the light guide plate is obtained by removing the gate portion from the light guide plate base taken out from the mold.

Conventionally, a hot nipper has been used to remove the gate portion. That is, as shown in FIG. 5, in order to cut the light guide plate main body portion 51 and the gate portion 52 of the light guide plate base 50 at the cut surface 53, the heated hot nipper blades 54, 54 are driven from above and below, and cut. Push cutting was performed while the surface 53 was melted.

[0005]

However, when the gate portion is cut by the hot nipper as described above, the cut surface has a surface roughness Ra of 100 μm or more, causing a problem in display performance. Such a problem in display performance will be described with reference to FIG. 6 showing a front light according to the related art. That is, in FIG. 6, the light guide plate 60 has a gate portion cut by a hot nipper, and an incident surface 62 on which light from a light source 61 is incident and a prism surface 63 for reflecting this light.
And an emission surface 64 for emitting the reflected light toward an object to be illuminated (not shown) such as a liquid crystal cell, and a cut surface 65 formed by a hot nipper located on a side facing the incidence surface 62. . In the case of a front light using the light guide plate 60, most of the light incident from the light source 61 is emitted from the emission surface 64, but part of the light reaches the cut surface 65. Originally, light reaching the side surface facing the incident surface 62 is transmitted as it is. However, since the cut surface 65 is roughened by cutting with a hot nipper, irregular reflection occurs on the cut surface 65. I will. When the irregular reflection is increased due to the state of the rough surface of the cut surface 65, interference fringes due to irregularly reflected light may be generated near the cut surface 65 on the upper surface side of the prism surface 63. However, if the cut surface 65 is mirror-finished by polishing or the like after cutting for the purpose of preventing such irregular reflection, there is a problem that the manufacturing procedure becomes very complicated. The present invention has been made in view of the above circumstances, a light guide plate that does not cause problems such as interference fringes,
It is an object of the present invention to provide a simple manufacturing method, a light guide plate manufactured by the method, a lighting device and a liquid crystal display device using the same.

[0006]

In order to solve the above-mentioned problems, a method of manufacturing a light guide plate according to the present invention comprises the steps of: injecting a molten synthetic resin into a cavity from a gate opened in a mold; A method of manufacturing a light guide plate by forming a light guide plate base comprising a gate portion following a light guide plate main body portion and removing the gate portion from the light guide plate base, wherein the removal of the gate portion is performed by cutting with a carbide end mill. It is characterized by performing roughing and finishing by a diamond cutter following the rough cutting. According to the present invention, the surface roughness Ra of the cut surface from which the gate portion has been removed can be easily reduced to 1 μm or less. Further, the more desirable surface roughness R of the cut surface
a is 400 nm or less, more preferably 200 nm or less. In this case, the wavelength λ of the normally used light (380 to 380)
780 nm). Therefore, light can be transmitted without being reflected.

Further, a light guide plate of the present invention is characterized by being manufactured by the above-described method of manufacturing a light guide plate of the present invention. In this case, since the surface roughness Ra of the cut surface formed by removing the gate portion can be set to 1 μm or less, even if this cut surface is used as a surface at any position of the light guide plate, for example, a light incident surface, Even when used as a surface located on the side opposite to this, irregular reflection does not occur due to this surface. Therefore, an excellent light guide plate capable of guiding light from a light source to an object to be illuminated without generating interference fringes or the like near a cut surface on the upper surface side of the light guide plate can be provided.

In this light guide plate, one side surface of the plate-like body is used as an incident surface, and a light guide plate that emits light incident from this incident surface from one of the upper and lower surfaces has a cut surface formed by removing a gate portion. Another side surface located on the side facing the incident surface may be used. In this case, since the surface roughness Ra of the cut surface facing the incident surface can be set to 1 μm or less, the light reaching the cut surface facing the incident surface can be transmitted as it is without irregular reflection. Therefore, interference fringes due to irregularly reflected light do not occur near the cut surface on the upper surface of the light guide plate.

Further, an illumination device according to the present invention includes the light guide plate according to the present invention, and a light source provided on an incident surface side of the light guide plate. ADVANTAGE OF THE INVENTION According to this invention, it can be set as the illuminating device which does not produce interference fringes etc. by irregular reflection light near the cut surface of a light-guide plate upper surface.

Further, the liquid crystal display device of the present invention is characterized in that the lighting device of the present invention is provided on one side of a liquid crystal cell. In this case, it is desirable to use a front light type in which a lighting device is arranged on the display surface side of the liquid crystal cell. According to the present invention, it is possible to provide a liquid crystal display device in which interference fringes and the like due to irregularly reflected light do not occur near the cut surface on the upper surface of the light guide plate.

[0011]

Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to the following embodiments. FIG. 1 shows a method of manufacturing a light guide plate according to an embodiment of the present invention.
FIG. 5 is a plan view showing a method of separating the light guide plate main body portion 3 and the gate portion 4 by cutting the light guide plate main body 3. The light guide plate substrate 1 is obtained by a known method of injection molding a synthetic resin using a mold. That is, a mold having a cavity having a recess substantially corresponding to the shape of the light guide plate and a gate portion communicating with the cavity is prepared, and the synthetic resin melted is injected into the cavity through the gate. As a result, the light guide plate base 1 including the light guide plate main body 3 and the gate portion 4 following the light guide plate main body is formed.

The cutting of the light guide plate substrate 1 is performed using a carbide end mill 5 and a diamond cutter 6, as shown in FIG. The carbide end mill 5 is disposed on an extension of the cut surface 2 and has, for example, 15000 to 20000 r. p. m. The diamond cutter 6 is disposed next to the carbide end mill 5 on the extension of the cut surface 2.
5000 to 20000 r.p. p. m. As shown in FIG. 2, the diamond cutter 6 has a disk-shaped rotating plate 8 that rotates in the direction of the arrow in FIG.
A diamond blade 9 is fixed to the light guide plate main body 3 side (the lower side in the drawing) on the front surface of the rotary plate 8. The diamond blade 9 is formed by solidifying diamond fine powder by a sintering method, and is formed in a rectangular chip shape. By moving the light guide plate base 1 in the direction of the arrow in the figure at a speed of 0.5 to 4 m / min,
The carbide end mill 5 and the diamond cutter 6 pass through the position of the cut surface 2 while rotating.

Here, the rotation of the carbide end mill 5 is set to 1
5000 to 20000 r.p. p. m is 1 m / m
This is because a peripheral speed of about 0.3πm / sec is required to be sent in. The feed speed and the peripheral speed are proportional, but as the speed decreases, the cut surface becomes rough. However, this required number of revolutions also varies depending on the material of the work. Further, the rotation of the diamond cutter 6 is set to 15,000 to 20,000 r.p. p. m
The number of rotations / feed rate is 10 to 15 r. p. This is because it is necessary to set m / mm. However, this required speed is
It also changes depending on the material of the work. In addition, the depth of cut greatly affects the roughness of the cut surface.

According to this embodiment, the light guide plate substrate 1 is first cut at the cut surface 2 by rough cutting with a carbide end mill 5. Next, in the finishing processing by the diamond cutter 6, the diamond blade 9 rotating at a high speed repeatedly passes at a high speed while being in contact with the light guide plate main body 3 side of the cut surface 2. Thus, the cut surface 2 on the light guide plate main body 3 side is polished and mirror-finished. Thus, the gate section 4
The remaining light guide plate main body 3 from which is removed becomes the light guide plate 10. In this case, the cut surface 2 of the obtained light guide plate 10 has a surface roughness Ra of 1 μm due to the mirror finish of the diamond cutter 6.
m or less.

Next, the light guide plate 10 thus obtained is
An embodiment of a front light and a liquid crystal display device, which are lighting devices using the present invention, will be described with reference to FIGS. FIG.
Is a sectional view of the front light according to the present embodiment, and FIG. 4 is a perspective view of a liquid crystal display device using the front light.

First, as shown in FIG. 3, the front light mainly includes a light guide plate 10 and a linear light source 20. The light guide plate 10 is a rectangular plate-shaped body made of a light-transmitting material such as an acrylic resin, and has an incident surface 11 that faces one of the light sources 20 and forms one side surface on which light from the light source 20 is incident.
A cut surface 12, which constitutes one side surface facing the incident surface 11, the other two side surfaces, a prism surface that reflects light from the light source 20 incident from the incident surface 11 and transmits external light ( A front surface 13 and a flat surface facing the prism surface 13 and having an emission surface (back surface) 14 for emitting light toward an object to be illuminated such as a liquid crystal cell.

Here, the cut surface 12 is the surface of the cut surface 2 on the light guide plate main body 3 side in FIG.
And the surface roughness is reduced to 1 μm or less. The prism surface 13 is formed by alternately forming a first inclined surface 13a inclined upward toward the cutting surface 12 and a two inclined surface 13b inclined downward toward the cutting surface 12, and the first inclined surface 13a A top line 15 and a valley line 16 are formed on the side where the surface of the second inclined surface 13b is in contact. Here, the top line 15 and the valley line 16 extend from the incident surface 11 to the cut surface 12.
, And are in parallel with the incident surface 11 and the cut surface 12, respectively. In addition, anti-reflection means such as attaching an anti-reflection film to improve the visibility is appropriately applied to the emission surface 14, but is not shown in this embodiment.
In the present embodiment, the light source 20 is an LED as shown in FIG.
The light-emitting elements 21 and 21 are composed of a bar light guide 22 and the light of the light-emitting elements 21 and 21 is changed in direction by the bar light guide 22 and can be incident on the light guide plate 10 from the incident surface 11. I have. It should be noted that the light source 20 may be a plurality of light emitting elements such as LEDs arranged in a pseudo linear shape, or a linear light source such as a cold cathode tube may be used.

Next, as shown in FIG. 4, the liquid crystal display device of the present embodiment mainly comprises a front light composed of a light guide plate 10 and a light source 20, and a liquid crystal cell 30. Here, the liquid crystal cell 30 is connected to the light exit surface 14 of the light guide plate 10.
, And can receive light emitted from the emission surface 14.

In the front light shown in FIGS. 3 and 4, a part of the light incident from the entrance surface 11 is reflected by the prism surface 13 and transmitted from various positions on the exit surface 14 so as to pass through the liquid crystal cell 3.
Illuminates 0. Among the inclined surfaces of the prism surface 13, the light reflected in the oblique direction by the first inclined surface 13 a is mainly sent in the direction from the incident surface 11 to the cut surface 12,
4, the light is reflected again by the second inclined surface 13a and the light exit surface 14 a plurality of times. Further, the light reflected by the second inclined surface 13b is mainly sent to the emission surface 14 near the lower position.
As described above, part of the light from the light source 20 is transmitted to the second inclined surface 1.
3b, the light is reflected toward any one of the emission surfaces 14 and is emitted toward the liquid crystal cell 30 as an object to be illuminated. here,
The cut surface 12 has a surface roughness Ra1μ by a diamond cutter 6.
m or less. Therefore, the cut surface 12
The light that has reached is transmitted as it is without irregular reflection.
Therefore, according to this front light, the prism surface 13
No interference fringes due to irregularly reflected light are generated in the vicinity of the cut surface 12 on the upper surface side of the liquid crystal display device, and in the liquid crystal display device of FIG. 4 using the same, excellent visibility of the liquid crystal cell 30 can be obtained.

[0020]

EXAMPLE A gate portion was removed from a light guide plate substrate formed by injection molding of a norbornene resin, and the length was 5 cm × 35 cm.
× A light guide plate 10 having a thickness of 0.8 mm was produced. Here, cutting and removal of the gate portion from the light guide plate base were performed as follows.

(Embodiment) As shown in FIG.
Rough cutting and finishing were performed by a carbide end mill 5 having a diameter of 8,000 rpm and a diamond cutter 6 having a rotation speed of 15,000 rpm. At this time, the light guide plate substrate 1
Was set at 1 m / min. As a result, the cut surface 1
The surface roughness Ra of No. 2 was 1 μm or less.

(Comparative Example) As shown in FIG. 5, a hot nipper heated to 150 ° C. was used to cut off by cutting. As a result,
The surface roughness Ra of the cut surface 12 was 100 μm.

The light guide plate 10 obtained by each of the above embodiments and comparative examples is mounted on a light source 20 comprising two light emitting elements (LEDs) 21 and a bar light guide 22 as shown in FIG. And assembled the front light. The state when the front light was turned on was observed from the prism surface (upper surface) 13 side of the light guide plate 10.

As a result, in the example, no interference fringes were observed near the cut surface 12. Further, in the comparative example, a large amount of interference fringes occurred near the cut surface 12. From the above examples, the usefulness of the present invention using the carbide end mill and the diamond cutter was confirmed. Also. It was confirmed that when the surface roughness Ra of the cut surface of the light guide plate was set to 1 μm or less, interference fringes could be suppressed to a practically acceptable level. further,
It was confirmed that when the surface roughness Ra of the cut surface of the light guide plate was 以下 or less of the wavelength λ of light, no interference fringes were generated, and the visibility of an object to be illuminated such as a liquid crystal cell could be significantly improved.

[0025]

As described above, according to the present invention, the removal of the gate portion is performed by cutting roughing with a carbide end mill,
Since the cutting is performed by a finishing process using a diamond cutter following the rough cutting, the surface roughness Ra of the cut surface from which the gate portion has been removed can be easily reduced to 1 μm or less. For this reason, according to the present invention, light reaching the side surface opposite to the incident surface can be transmitted as it is, and interference fringes due to irregularly reflected light do not occur near the cut surface of the light guide plate. Further, according to the present invention, a liquid crystal display device having excellent visibility of a liquid crystal cell can be obtained by the lighting device using the light guide plate.

[Brief description of the drawings]

FIG. 1 is a plan view showing a method of separating a light guide plate main body portion 3 and a gate portion 4 by cutting a light guide plate base 1 at a cutting surface 2 in a method of manufacturing a light guide plate according to an embodiment of the present invention. is there.

FIG. 2A shows a diamond cutter used in the present embodiment.
Is a plan view, and (b) is a front view.

FIG. 3 is a sectional view of the front light according to the embodiment.

FIG. 4 is a perspective view of the liquid crystal display device of the present embodiment.

FIG. 5 is an explanatory view of a method for manufacturing a light guide plate according to a conventional technique.

FIG. 6 is a sectional view of a front light according to the related art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Light guide plate base, 2 ... Cut surface, 3 ... Light guide plate main body part, 4 ...
Gate part, 5: Carbide end mill, 6: Diamond cutter

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G09F 9/00 336 G09F 9/00 336B // F21Y 103: 00 F21Y 103: 00 F term (reference) 2H038 AA55 BA06 2H091 FA23X FA23Z FA41X FA41Z FB02 FC16 FC17 LA03 LA16 LA21 5G435 AA17 BB12 BB16 EE22 FF08 GG24 KK07

Claims (6)

[Claims] 1. A light guide plate base comprising a light guide plate main body and a gate subsequent to the light guide plate main body is formed by injecting a molten synthetic resin into a cavity from a gate opened in a mold. A method for manufacturing a light guide plate by removing a gate portion from the above, wherein the removal of the gate portion is performed by rough cutting by a carbide end mill and finishing by a diamond cutter subsequent to the rough cutting. Manufacturing method of a light guide plate. 2. A light guide plate manufactured by the method for manufacturing a light guide plate according to claim 1. 3. A light guide plate manufactured by the method for manufacturing a light guide plate according to claim 1, wherein a surface roughness of a cut surface from which a gate portion is removed is 1 μm or less. 4. A light guide plate, wherein one side surface of a plate-like body is used as an incident surface and light incident from the incident surface is emitted from one of upper and lower surfaces, and a surface from which a gate portion is removed is opposed to the incident surface. The light guide plate according to claim 2, wherein the light guide plate is another side surface located on the side of the light guide plate. 5. An illumination device comprising: the light guide plate according to claim 2; and a light source provided on an incident surface side of the light guide plate. 6. A liquid crystal display device comprising the lighting device according to claim 5 on one side of a liquid crystal cell.