JPH09127338A - Light transmission body and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method suitable for the manufacture of light transmission bodies, especially larger-sized ones of >=12 inches. SOLUTION: A ultraviolet setting resin 4 is filled (b) in a fine clearance between a light transmission body substrate 3 having light transmissivity and a forming mold 5 (a) formed with a scattering reflection structure thereon, and is incidentally radiated (c) with ultraviolet rays 2 to cure a thin film of the ultraviolet setting resin 4. Thereafter, the scattering reflection structure consisting of the ultraviolet setting resin 4 is formed on at least one surface of the light transmission bodies by releasing (d) the light transmission body substrate 3 from the forming mold 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light guide used for a backlight of a liquid crystal display device and the like and a method for manufacturing the same.

[0002]

2. Description of the Related Art In general, a light guide used for a backlight of a surface light source device used for a liquid crystal display device, etc. is incident from an end surface by a surface facing the light emitting surface or a scattering reflection means provided on the light emitting surface. It scatters and reflects light, or scatters and reflects the light by means of scattering and reflecting means dispersed in the light guide, and by providing a density gradient by making the distribution of the scattering and reflecting means different, In many cases, the brightness is made uniform.

As the above scattering / reflecting means, a light-scattering / reflecting material is applied to the surface of the light guide body, an uneven shape for scattering / reflecting light is provided on the surface of the light guide body, and light is diffused in the light guide body. An example is one in which a material is dispersed and contained. In this case, it is common to apply a synthetic resin (paint or the like) containing a light diffusing material or a synthetic resin having a refractive index different from that of the light guide material. With regard to the above, there are those which roughen the surface of the light guide and those which provide a regular concavo-convex pattern. The shape of the concavo-convex pattern may be a line shape, a dot shape, or the like, and the cross-sectional shape may be a rectangular shape, a trapezoidal shape, a triangular shape, an arc shape, or the like. Regarding the above, in many cases, micro beads made of synthetic resin or glass having a different refractive index from the material forming the light guide body are dispersed in the light guide. In this specification, in the cases of to, in order to uniformize the luminance distribution on the light emitting surface of the light guide, the scattering reflecting means is distributed on the surface facing the light emitting surface of the light guide or on the light emitting surface. Things are called "scatter reflection patterns".

As a method for manufacturing these light guides, a screen printing method is used (Japanese Patent Laid-Open No. 60-2).
No. 05576, Japanese Patent Application Laid-Open No. 4-199001, etc.), molding is performed using a synthetic resin by using a mold having an uneven surface formed by a method such as an etching method, a sandblast method, or a machining method. Things (Japanese Patent Laid-Open No. 5-
60920, JP-A-6-118245, JP-A-6-250179, etc.), it is general that a light diffusing material (such as glass beads) is mixed in advance with a resin material. .

Among the above methods, a method of using a mold having a finely textured surface and using a synthetic resin is suitable for mass production and satisfies the required processing accuracy. It is effective because it can be done.

[0006]

When a light guide is manufactured by molding using a synthetic resin, in the injection molding method, which is one of the most preferable methods in terms of dimensional accuracy of a molded product and production efficiency, a metal mold is used. It requires a lot of cost and time to manufacture. Moreover, in the case of a large-sized light guide having a diagonal size of 12 inches or more, it is difficult to perform accurate molding by the injection molding method. The main reason for this is that there is a problem with the transferability of the fine irregularities that are the scattering reflection patterns on the mold surface. As the size of the light guide increases, the distance from the gate portion where the resin is introduced into the cavity to the end of the cavity of the mold increases, which causes a difference in surface transferability between the gate and the end. The decrease in surface transferability occurs at a portion far from or near the gate, which depends on molding conditions. This problem becomes more noticeable in the case of molding a light guide body having a tapered cross section, which is often adopted in recent years to reduce the weight of the light guide body. When the surface transferability is lowered, the fine uneven cross-sectional shape of the molded product becomes different from that of the mold, and the scattering / reflection performance of the unit scattering / reflecting means changes. As a result, a predetermined uniform brightness distribution of the light guide cannot be realized, and unevenness of brightness on the light emitting surface occurs when the light guide is incorporated into a backlight.

The present invention has been made in view of the above problems, and an object thereof is to provide a method suitable for manufacturing a large-sized light guide body having a size of 12 inches or more.

[0008]

In order to solve the above problems, the present invention uses a metal mold or resin mold having a mother pattern of a scattering reflection pattern formed on the surface thereof, and a flat plate, a plate having a tapered cross section, and the like. A molding method of forming a scattering reflection pattern made of an ultraviolet curable resin on the surface of an optically transparent light guide substrate having an arbitrary shape is adopted.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, 2P (Photo-
The mold for polymerization may be made of metal (mold) or synthetic resin (resin mold). The molding die is processed into a desired shape by a machining method such as a lathe, a sandblast method, a photolithography method, or the like. Whichever method is used, in order to obtain a light guide having a uniform luminance distribution, it is necessary to take means capable of accurately processing the fine uneven shape with a distribution as designed.

At the time of applying the ultraviolet curable resin, a molding die having a surface on which a scattering reflection pattern is processed is fixed to a flat base. When the molding die is a thin metal plate or is made of synthetic resin with insufficient rigidity, it is effective to take measures such as vacuum suction or adding a reinforcing material as a fixing method to the flat base. An ultraviolet curable resin (hereinafter referred to as "2P resin") is applied to the surface of the fixed mold. A transparent synthetic resin plate serving as a substrate of the light guide is gently placed thereon, and pressure is evenly applied to push out an extra 2P resin between the synthetic resin plate and the mold or the resin mold to bring them into close contact with each other. At this time, it is important to work carefully so that air bubbles do not remain in the 2P resin and remain. Next, while maintaining the above state, the entire surface is uniformly irradiated with ultraviolet rays emitted from the high-pressure mercury lamp through the substrate to cure the 2P resin. After the 2P resin is completely cured, the molded product in which the 2P resin and the substrate are integrated is removed from the molding die. The resin that has been extruded to the periphery and hardened is removed, and the outer shape is processed into the required shape.

During the 2P molding, the concave portion of the uneven pattern is 2
This is the portion where the film thickness of the P resin is the thinnest, and it is necessary to make it uniform and minimum within the plane. Ideally, the film thickness should be zero if the surface connecting the convex portions (which become the concave portions in the molded product) of the concave-convex pattern of the molding die and the molding surface of the substrate are parallel, but practically Does not pose a problem if the light guide is designed by predicting the 2P resin film thickness in advance.

It is desirable to select the combination so that the refractive index of the 2P resin is substantially the same as the refractive index of the light transmissive substrate, but in practice, a difference of about ± 0.05 does not pose a problem. The light guide obtained by the 2P molding method by matching the refractive indexes of the synthetic resin serving as the substrate and the 2P resin is an injection molding method which is another molding method using resin.
The optical performance is comparable to that of the light guide obtained by the press molding method, the extrusion molding method, the cast molding method, or the like.

An advantage of the method of manufacturing a light guide body by the 2P molding method is that it can be manufactured by a relatively small-scale facility without requiring a temperature and pressure adjusting device as compared with other resin molding methods. In the injection molding method, it is necessary to process a cavity (space) having the same dimensions as the molded product in the mold. Further, the elements necessary for designing the mold, such as the position of the gate and the position of the cooling water channel, are complicated, and a great amount of labor and cost are required for the optimum mold design. Even if the mold for the scattering / reflection pattern surface has a replaceable nested structure, if the outer shape of the light guide changes, the mold must be modified or newly manufactured. On the other hand, in the 2P molding method, the above problems are not recognized when manufacturing a large-sized light guide plate.

The feature of the 2P molding method that various scatter reflection patterns can be easily formed is that it is effective in trial production at the development stage of scatter reflection patterns. It can be quickly reflected in the shape design of the body section.

[0015]

An embodiment of the present invention will be described with reference to the drawings. A scatter reflection pattern (FIG. 1: 6) having a concave trapezoidal unit with a width of 30 μm and a height of 10 μm and a length of 200 μm gives a density distribution designed to make the luminance distribution uniform. A nickel electroformed mold (Fig. 1: 5) applied to the surface was fixed on a flat base (Fig. 1 (a)). The range in which the scattered reflection pattern is distributed is 198.0 mm ×
It is 150.0 mm. A liquid 2P resin having a refractive index of 1.53 (FIG. 1: 4) was uniformly applied onto the mold without leaving bubbles (FIG. 1 (b)). Next, a taper-shaped cross-section (thickness: 1.1 mm to 3.0 mm), which is the substrate of the light guide, is used.
It has a size of 05mm x 157mm and a refractive index of 1.4.
The transparent acrylic resin plate 9 (Fig. 1: 3) is gently placed on the 2P resin, and pressure is applied from one side of the long side toward the other long side to obtain an extra 2P between the acrylic resin plate and the mold. The resin was extruded. Then, ultraviolet rays (Fig. 2: 2) generated from a high pressure mercury lamp (Fig. 2: 1) were irradiated from above through the acrylic resin plate (Fig. 1 (c)). During irradiation for about 12 seconds, a flat stand on which a set of a mold and an acrylic resin plate was placed was horizontally fed at a constant speed so that the entire 2P resin was uniformly irradiated with ultraviolet rays. After the irradiation was completed, the acrylic resin plate was peeled from the mold, but the 2P resin was not caught on the mold side, and the peeling was easy (FIG. 1 (d)). After removing the protruding 2P resin, the surface of the 2P resin layer (FIG. 1: 4a) on which the pattern as the light guide plate was formed was observed.
No defects such as bubbles or molding were found, and a good light guide was obtained.

As shown in FIG. 3, the light guide is provided with a cold cathode tube 7,
A reflection sheet 11, a diffusion sheet 10, a prism sheet 9,
It was attached to a backlight assembly incorporating the reflector 8 and the like, and the luminance distribution in the direction perpendicular to the light source was measured. Next, the mold used for the 2P molding this time was attached to an injection molding machine and molded, to obtain an acrylic resin light guide whose outer dimensions were equivalent to those of the 2P molded light guide, and the luminance distribution was measured in the same manner. As a result of comparing the luminance distributions of the above-mentioned two kinds of light guides obtained from the same mold, it was found that the distribution and the average value are almost the same as shown in FIG.

[0017]

According to the present invention, a large-sized light guide body of 12 inches or more can be easily manufactured, and if a stamper having a scattering reflection pattern formed on its surface is used, a light guide substrate of any shape can be obtained. A scattering reflection pattern can be formed on the surface, making it suitable for high-mix low-volume production. Further, not only a metal mold (mold) but also a resin mold (resin mold) can be molded. The present invention is advantageous in comparison with the extrusion molding method or the press molding method, which is limited to the rectangular cross section (flat plate), due to the feature that the cross-sectional shape of the light guide serving as the substrate does not matter, and the trapezoid cross section (flat plate with taper) Although it is possible to mold an arbitrary cross-sectional shape including the above, the present invention has merit even when compared with an injection molding method that requires a great deal of cost in manufacturing a mold.

[Brief description of the drawings]

FIG. 1 is a process explanatory view of a 2P molding method according to the present invention.

FIG. 2 is a diagram showing an example of a configuration during ultraviolet irradiation according to the present invention.

FIG. 3 is a configuration diagram of an example of a backlight unit incorporating the light guide body obtained by the present invention.

FIG. 4 is a diagram showing a comparison of luminance distributions of a light guide obtained by the present invention and a light guide obtained by an injection molding method.

[Explanation of symbols] 1 ... High pressure mercury lamp (ultraviolet irradiator) 2 ... Ultraviolet ray 3 ... Light guide substrate 4 ... 2P resin (liquid) 4a ... 2P resin (solid) 5 ... Molding mold 6 ...... Asperity-shaped scattered reflection pattern 7 ...... Cold-cathode tube (linear light source) 8 ...... Reflector 9 ...... Prism sheet 10 ...... Diffusion sheet 11 ...... Reflection sheet

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kozo Yasuda 36 Towada, Kamisu-cho, Kashima-gun, Ibaraki Prefecture Kuraray Co., Ltd.

Claims (2)

[Claims] 1. An edge light type light guide for guiding light from at least one side end surface, wherein a thin film having a scattering reflection structure made of an ultraviolet curable resin is provided on at least one surface of a light transmissive light guide substrate. Light guide. 2. A thin film of the ultraviolet curable resin is prepared by filling a minute gap between a light-transmitting light guide substrate and a mold having a scattering / reflecting structure formed on the surface thereof with an ultraviolet curable resin and then irradiating the ultraviolet ray. A method for manufacturing a light guide body, comprising: curing the resin and then releasing the light guide substrate from the mold to form a scattering / reflecting structure made of an ultraviolet curable resin on at least one surface of the light guide body.