JP2000347041A - Light transmission plate for front light unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light transmission plate constituted by filling an outer rugged surface with an outer protective layer consisting of material which is smoothed on an outer surface and has high damage resistance. SOLUTION: The light transmission plate 1 is formed by successively laminating a first intermediate layer 20 which is made of TiO2 and has a refractive index M of about 2.2 to 2.4, a second intermediate layer 30 which is made of SiO2 and has a refractive index N of about 1.5 and the outer protective layer 40 which consists of a hard coating material, such as siloxane or acrylic resin, closely in tight contact with each other on the outer side of a light transmission plate body 10 which is made of acryl and has a refractive index L of about 1.5. The surface of the outer protective layer is formed smooth. Since the refractive index M of the first intermediate layer is greater than the refractive index L of the light transmission plate body and the refractive index N of the second intermediate layer, the incident light on the light transmission plate body from a light source 2 is reflected at the boundary surface of the first intermediate layer and the second intermediate layer shown by arrows, is emitted from the inner flank 12 of the light transmission plate body and directed toward a liquid crystal display section 4.

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 for a front light used in a front light for irradiating an illuminated object such as a liquid crystal display device with light from the front side.

[0002]

2. Description of the Related Art A front light unit for irradiating an illuminated object such as a liquid crystal display device with light from the front side is known. In this front light unit, a light guide plate is arranged on the front side of a liquid crystal display device or the like, and light incident from a light source arranged on the side of the light guide plate is reflected in the light guide plate and emitted toward the liquid crystal display device. . Therefore, the front surface of the light guide plate, so that light incident from the side of the light guide plate is reflected to the illuminated object side,
A prism surface is provided.

[0003]

By the way, the light guide plate is arranged on the front side of the object to be illuminated, and the prism surface is exposed to the outside, so that it is easily damaged. If the prism surface is scratched, light will not be reflected as intended, and the display quality of the illuminated object will deteriorate. Further, if the surface is not sealed due to the prism surface, dust tends to accumulate, and if the dust accumulates, the display quality also deteriorates. Therefore, it is conceivable to laminate an outer protective layer made of a material having high damage resistance, which is unlikely to be scratched on the surface of the prism, with a smooth outer surface.

In such a case, the refractive index of the light guide plate must be higher than the refractive index of the outer protective layer so that light incident from the light source can be reflected toward the illuminated object. By the way, as the light guide plate as described above, acrylic resin is the most excellent in terms of moldability, weight, cost, etc., and its refractive index is about 1.5. On the other hand, there is no substance whose refractive index is sufficiently lower than that of the above acrylic resin, has high damage resistance, and is excellent in moldability, weight, cost, etc., like the light guide plate. .

Therefore, a flat flat protective layer is disposed on the uneven surface of the light guide plate without laminating the outer protective layer outside the light guide plate so as to fill the uneven surface of the light guide plate. Have been. However, in this case, since there is a gap between the flat plate protective layer and the (valley) of the uneven surface, the flat plate protective layer needs to be attached so as to seal the uneven surface of the light guide plate, and a difficult operation is forced. I have. The present invention has been made in view of the above problems, and has as its object to provide a light guide plate in which an outer protective layer made of a material having high damage resistance and having a smooth outer surface is filled with an outer uneven surface.

[0006]

According to the first aspect of the present invention, there is provided a light guide plate for a front light unit for irradiating an object to be illuminated with light from the outside. Outside the light guide plate body having a side surface and an outer surface on which a prism surface capable of reflecting light incident from a light source disposed on the side of the light guide plate toward the object to be illuminated, a material having high damage resistance is used. The formed outer protective layer having a smooth outer surface is formed by laminating with no gap therebetween through the intermediate layer adjacent to the light guide plate body, and the refractive index of the intermediate layer is larger than the refractive index of the light guide plate body. And a light guide plate provided with a refractive index larger than that of the outer protective layer. In the light guide plate configured as described above, the refractive index of the intermediate layer is larger than the refractive index of the light guide plate body, and larger than the refractive index of the outer protective layer. The incident light is reflected at the boundary surface between the intermediate layer and the outer protective layer toward the object to be illuminated, and then can be emitted from the inner side surface of the light guide plate body toward the object to be illuminated.

According to a second aspect of the present invention, in the first aspect, the intermediate layer is formed of a plurality of layers, and the innermost first layer is formed.
The refractive index of the intermediate layer is larger than the refractive index of the light guide plate body,
Further, there is provided a light guide plate in which the refractive index of the second intermediate layer adjacent to the outside of the first layer is made larger than that of the second intermediate layer so that the refractive index of the outer protective layer can be arbitrarily selected. According to the light guide plate configured as described above, even if the refractive index of the outer protective layer is arbitrarily selected, the light incident from the side of the light guide plate is not transmitted to the first intermediate layer and the second intermediate layer.
At the boundary surface of the intermediate layer, the light is reflected toward the object to be illuminated, and then can be emitted from the inner side surface of the light guide plate body toward the object to be illuminated.

According to a third aspect of the present invention, in the first aspect of the invention, the thickness of the intermediate layer is much smaller than the depth of the valley of the prism surface of the light guide plate main body, and the outer surface of the intermediate layer has a smaller thickness. The uneven surface is similar to the prism surface of the light guide plate body, and the inner surface of the outer protective layer is an uneven surface complementary to the uneven surface similar to the prism surface of the light guide plate body outside the intermediate layer. A light guide plate is provided.

According to a fourth aspect of the present invention, there is provided the light guide plate according to the first aspect of the present invention, wherein a contamination prevention film for preventing contamination is laminated outside the outer protective layer.

According to a fifth aspect of the present invention, there is provided the light guide plate according to the first aspect of the present invention, wherein the anti-reflection material is laminated inside the light guide plate body.

According to a sixth aspect of the present invention, there is provided the light guide plate according to the first aspect of the present invention, wherein each element to be laminated is laminated via an adhesive.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In the drawings, constituent elements are appropriately exaggerated for easy understanding. FIG. 1 shows a front light unit having a light guide plate according to the present invention, which irradiates a liquid crystal display device with light. The upper side in the figure is the outside, and the light guide plate 1 is outside the liquid crystal display device 4. The light source 2 is disposed along with the reflection cover 3 on the side of the light guide plate 1. The light guide plate 1 is formed by sequentially stacking a first intermediate layer 20, a second intermediate layer 30, and an outer protective layer 40 on the light guide plate main body 10 on the outside. The elements are in close contact with each other without any gap.

The material of the light guide plate body 10 is made of acrylic resin and has a refractive index L of 1.5, which is the same as that of a conventional light guide plate which is arranged so as to come into direct contact with air. And
The outer surface is formed on a prism surface 11 as shown. Although only two prisms are shown in the drawing, actually, for example, about 400 prisms are formed in a width of 250 mm. The depth of the valley of the prism is about 5 μm, and the height from the inner surface 12 to the top of the prism is about 1 mm.

[0014] The first intermediate layer 20 made of Ti0 ₂ (Titanium dioxide), the refractive index M is an approximately 2.2 to 2.4 and a thickness of about 100 nm.

The second intermediate layer 30 is made of SiO ₂ (silicon dioxide)
And has a refractive index N of about 1.5 and a thickness of about 100 n.
m. Although the first intermediate layer 20 and the second intermediate layer 30 are both exaggerated in the drawing, they are actually several tenths of the depth of the valley of the prism. I can't make up for it. Therefore, the second intermediate layer 30
, Irregularities substantially equal to the prism surface 11 of the light guide plate main body 10 remain.

The outer protective layer 40 is made of a hard coat material such as siloxane or acrylic resin, and its outer surface 42 is made smooth, while its inner surface 41 is made of the second intermediate layer 30 as described above. Since irregularities substantially equal to the prism surface 11 of the light guide plate main body 10 remain on the outside, the irregularities are formed so as to be complementary to the irregularities. Therefore, the entire thickness of the outer protective layer 40 (from the outer surface 42 to the inner surface 4
1 to the downward ridge line of the mountain) is at least larger than the depth of the valley of the prism of the light guide plate body 10 of about 5 μm, and in this case, it is about 10 μm.

In the first embodiment, since the outer protective layer 40 is formed of a hard coat material and has a smooth surface as described above, the outer protective layer 40 is less likely to be scratched and less likely to accumulate dust. There is no dust in between. Then, since the refractive index M of the first intermediate layer 20 is larger than the refractive index L of the light guide plate main body 10 and the refractive index N of the second intermediate layer 20, light incident on the light guide plate main body 10 from the light source 2 is: FIG.
As shown with an arrow at, it is incident on the first intermediate layer 20, reflects at the interface between the first intermediate layer 20 and the second intermediate layer 30, and then exits the first intermediate layer 20. Light guide plate body 1
0 again, exits from the inner surface 12 of the light guide plate main body 10, enters the liquid crystal display unit 4, and can illuminate the liquid crystal display unit 4.

Here, the thickness of the first intermediate layer 20 is
When the wavelength of the light (about 550 nm) is divided by a value four times the refractive index, the reflectance becomes lowest, and the first intermediate layer 20
Light is most easily emitted from the light guide plate 10 to the light guide plate main body 10.

As described above, in the first embodiment, the light guide plate main body 10 is made of the same material as in the prior art, and has a refractive index L of about 1.5. In the prior art, the light guide plate body 10 is in contact with air, and the refractive indices of the light guide plate body 10 and air are about 1.5 and about 1.0, respectively.
The ratio is about 1.5. On the other hand, in the first embodiment of the present invention, the refractive index M of the first intermediate layer 20 is about 2.2 to 2.2.
2.4, since the refractive index N of the second intermediate layer 30 is about 1.5, the ratio is about 1.5. That is, L: M ≒ M:
N, in other words, M ² ≒ L × N.

The illumination performance is such that the light incident on the light guide plate main body 10 from the light source 2 is bent toward the object to be illuminated (the liquid crystal display device 4 in this case) at the boundary surface between the light guide plate main body 10 and the substance outside thereof. It depends on the ability, and this ability
Determined by the ratio of the refractive indices of the two substances. Therefore, in the first embodiment of the present invention, it is possible to obtain illumination performance equivalent to that of the related art while using the light guide plate main body 10 made of the same material as that of the related art.

Since the light from the light source 2 is reflected at the interface between the first intermediate layer 20 and the second intermediate layer 30 as described above, the refractive index of the outer protective layer 40 outside the second intermediate layer is equal to the illumination. There is no influence on the performance and the range of choice of the material of the outer protective layer 40 is large. That is, the refractive index of the material of the outer protective layer 40 is the refractive index N of the material of the second intermediate layer (in this case, the material is SiO _2).
The refractive index may be larger or smaller than about 1.5).

FIG. 7 shows a combination of the inclination angle α of the prism (see FIG. 1), the refractive index M of the first intermediate layer 20, the refractive index L of the light guide plate main body 10, and the refractive index N of the second intermediate layer 20. Outgoing angle φ with respect to the range of incident angle θ (see FIG. 1)
(See FIG. 1) It is a table showing a range. From this table, M / N
Is larger, the emission angle φ approaches 0 (zero), the component vertically emitted from the light guide plate increases, and it is understood that the illumination efficiency is higher.

FIG. 2 is a view showing the structure of the second embodiment, in which only one intermediate layer is provided as compared with the first embodiment. As can be understood from this intermediate layer, which is indicated by the same reference numeral 20 as the first intermediate layer in the first embodiment, the intermediate layer in the second embodiment is the first intermediate layer.
Similarly to the first intermediate layer in the embodiment, the first intermediate layer is made of TiO ₂ , has a refractive index M of about 2.2 to 2.4, and has a thickness of about 1
00 nm. The outer protective layer also has the same specifications as the outer protective layer 40 in the first embodiment, and has a refractive index N of about 1.5.

In the second embodiment, the number of stacked layers is smaller than that of the first embodiment, and unlike the first embodiment, the second embodiment is unlikely to be damaged and hardly accumulates dust. Since the refractive index M of the intermediate layer 20 is larger than the refractive index L of the light guide plate main body 10 and the refractive index N of the outer protective layer 40, the light source 2
The light emitted from the liquid crystal display unit 4 travels in the same manner as in the first embodiment, and can illuminate the liquid crystal display unit 4 as in the case of only the conventional light guide plate. However, in the first embodiment, since the refractive index of the outer protective layer does not affect the illumination performance, the range of choice of the material of the outer protective layer is large. Since the refractive index directly affects the lighting performance, the range of choice of the material of the outer protective layer is small.

FIG. 3 is a view showing the structure of the third embodiment. Compared to the first embodiment, each layer is made of an adhesive 7.
0, and on the outside of the outer protective layer 40,
For example, a pollution prevention film 50 made of a fluororesin is laminated,
An anti-reflection material 60 is similarly laminated on the inside of the light guide plate main body 10 via an adhesive 70.

FIG. 5 shows the details of the anti-reflection material 60. The film 61 made of PET (polyethylene terephthalate) or TAC (triacetyl cellulose) and the function of the adhesive material are shown from the side closer to the upper light guide plate main body 10. It comprises a hard coat layer 62, an antireflection layer 63, and a contamination prevention film 64.

[0027] Figure 6 further provides a diagram showing details of the anti-reflection layer 63, a two laminate of Ti0 ₂ which outermost layer is either the Si0 ₂ in the vertical, manufactured by vacuum evaporation Is what is done. Si0 ₂ and Ti0 thickness of each one layer of ₂ is about 100 nm.

FIG. 4 is a view showing the structure of the fourth embodiment.
Is the lower light guide plate main body first portion 10A that does not include the prism surface 11, and the upper light guide plate main body second portion that includes the prism surface 11 is
The difference is that it is divided into a portion 10B. The light guide plate main body 10 forms an intermediate product in which the first intermediate layer 20, the second intermediate layer 30, and the outer protective layer 40 are stacked on the upper light guide plate main body second portion 10B including the prism surface 11, and thereafter, ,
The upper light guide plate main body first portion 10A is closely bonded to the first light guide plate main body 10 via the adhesive 70, thereby completing the process.

[0029]

According to the invention described in each claim, light incident from a light source disposed on the inner side surface which is flat and opposed to the object to be illuminated and on the side of the light guide plate can be reflected toward the object to be illuminated. Outside the light guide plate body having an outer surface on which a prism surface is formed,
An outer protective layer formed of a material having high damage resistance and having a smooth outer surface is formed by laminating through an intermediate layer adjacent to the main body of the light guide plate without any gap therebetween, and the refractive index of the intermediate layer is increased by Since it is larger than the refractive index of the main body and larger than the refractive index of the outer protective layer, the prism surface of the light guide plate body is buried and hardly scratched, and the light guide plate is prevented from collecting dust. The light incident from the side can be reflected toward the object to be illuminated at the boundary surface between the intermediate layer and the outer protective layer, and thereafter can be emitted from the inner side surface of the light guide plate body toward the object to be illuminated. In particular, according to the second aspect, the intermediate layer is composed of a plurality of layers, the illumination performance is determined by the refractive indexes of the first intermediate layer and the second intermediate layer, and the range of selection of the outer protective layer is large. . In particular, according to the sixth aspect, the anti-contamination film for preventing contamination is laminated outside the outer protective layer, so that it is less likely to be contaminated.

[Brief description of the drawings]

FIG. 1 is a diagram showing a front light unit having a light guide plate according to a first embodiment of the present invention disposed outside a liquid crystal display device.

FIG. 2 is a diagram illustrating a light guide plate according to a second embodiment of the present invention.

FIG. 3 is a diagram illustrating a light guide plate according to a third embodiment of the present invention.

FIG. 4 is a diagram showing a light guide plate according to a fourth embodiment of the present invention.

FIG. 5 is a diagram illustrating details of a configuration of an antireflection member 60 according to a third embodiment.

FIG. 6 is a diagram showing details of an antireflection layer 63 of FIG. 5;

FIG. 7 shows a combination of the inclination angle α of the prism, the refractive index M of the first intermediate layer 20, the refractive index L of the light guide plate main body 10, and the refractive index N of the second intermediate layer 20 in the first embodiment. In this case, the outgoing angle φ with respect to the incident angle θ is shown.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light guide plate 2 ... Light source 4 ... Liquid crystal display part 10 ... Light guide plate main body 11 ... Prism surface 20 ... 1st intermediate layer 30 ... 2nd intermediate layer 40 ... Outer protective layer 50 ... Contamination prevention film 60 ... Antireflection layer

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor, Isao Shiozawa, 654 Kawawa-cho, Tsuzuki-ku, Yokohama, Kanagawa Prefecture Inside Fujitsu Kasei Co., Ltd. (72) Masaya Hirano, 654 Kawawa-cho, Tsuzuki-ku, Yokohama, Kanagawa Prefecture Fujitsu Kasei Co., Ltd. (72) Inventor Shingo Furukawa 654 Kawawa-cho, Tsuzuki-ku, Yokohama-shi, Kanagawa Prefecture

Claims (6)

[Claims] 1. A light guide plate for a front light unit for irradiating an object to be illuminated with light from the outside, comprising: a light source disposed on a flat inner surface facing the object to be illuminated; An outer protective layer having a smooth outer surface formed of a highly damage-resistant material, outside the light guide plate body having an outer surface on which a prism surface capable of reflecting incident light toward an illuminated object is formed. The intermediate layer adjacent to the light guide plate main body is interposed and laminated without any gap therebetween. The refractive index of the intermediate layer is larger than the refractive index of the light guide plate main body.
And a light guide plate having a refractive index larger than a refractive index of the outer protective layer. 2. An intermediate layer comprising a plurality of layers, wherein a refractive index of an innermost first intermediate layer is larger than a refractive index of the light guide plate main body and a second intermediate layer adjacent to the outside of the first layer. The light guide plate according to claim 1, wherein the refractive index of the outer protective layer is made larger than the refractive index of the layer, and the refractive index of the outer protective layer can be arbitrarily selected. 3. The thickness of the intermediate layer is much smaller than the depth of the valley of the prism surface of the light guide plate main body, and the outer surface of the intermediate layer has an uneven surface similar to the prism surface of the light guide plate main body. The light guide plate according to claim 1, wherein an inner surface of the outer protective layer is a concave / convex surface complementary to a concave / convex surface similar to the prism surface of the light guide plate body outside the intermediate layer. . 4. The light guide plate according to claim 1, wherein a contamination prevention film for preventing contamination is laminated outside the outer protective layer. 5. The light guide plate according to claim 1, wherein an anti-reflection material is laminated inside the light guide plate main body. 6. The light guide plate according to claim 1, wherein each element to be laminated is laminated via an adhesive.