JP2014075310A - Light guide, illumination device provided with the same, and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light guide which is a single body and has shielding performance higher than that in the conventional manner.SOLUTION: A plurality of ridge-like second light deflection elements 19a with recesses and protrusions continuously provided in a ridge-like extension direction are formed on a second principal plane 7b of a light guide 7. Thus, incident light from a first principal plane 7a can be emitted in the extension direction of the second light deflection elements 19a in a scattered manner, a first light deflection element 18 formed on the first principal plane 7a is hardly visually recognized (improves shielding performance), and further, the luminance uniformity of a display device is also improved.

Description

  The present invention relates to a light guide mainly used for illumination optical path control, and an illumination device and a display device using the light guide.

  In recent large-sized liquid crystal televisions, flat display panels, and the like, direct type illumination devices or edge light illumination devices are mainly employed. The direct type illumination device has a structure in which a plurality of cold-cathode tubes and LEDs (Light Emitting Diodes) as light sources are regularly arranged on the back surface of an image display element such as a liquid crystal panel. Between the image display element and the light source, a diffuser plate having a strong light scattering property is used so that a cold cathode tube or LED as a light source is not visually recognized.

  On the other hand, an edge light type lighting device has a structure in which a plurality of cold cathode tubes and LEDs are arranged as light sources on the side surface of a translucent plate called a light guide (or a light guide plate). In general, incident light incident from the side surface of the light guide is efficiently guided to the exit surface on the surface (light deflection surface) opposite to the exit surface of the light guide (surface facing the image display element). A light deflection element is formed. At present, the light deflection element formed on the light deflection surface is generally one in which white ink is printed in the form of dots (see, for example, Patent Document 1). However, since the light incident on the white dots is diffusely reflected almost omnidirectionally, the light extraction efficiency to the exit surface side of the light guide is low. Also, light absorption by white ink cannot be ignored.

  Therefore, recently, a method of forming a light deflection element by a microlens on the light deflection surface of a light guide by an ink jet method, a method of forming a light deflection element on a light deflection surface of a light guide by a laser ablation method, There has been proposed a method of integrally forming a light deflection element composed of a groove having a shape, a U-shape, and various other shapes on a light deflection surface of a light guide (see, for example, Patent Document 2). Unlike the light deflection element formed by white ink printing, the light deflection element formed by these methods is a portion of the light deflection element on the light deflection surface of the light guide. Since reflection, refraction, and transmission due to a difference in refractive index are used, light absorption hardly occurs. Therefore, the above-described method of forming the light deflection element can obtain a light guide plate with higher light extraction efficiency than the method of forming the light deflection element by printing white ink in dots.

JP-A-1-241590 JP 2000-89033 A

  However, even if the light deflecting element is formed of a material other than the white ink described above, the light deflecting surface depends on the number, density, and shape of the light deflecting elements formed on the light deflecting surface, similarly to the light deflecting element formed of the white ink. There remains a problem that the light deflection elements formed in the above are visually recognized as bright spots from the exit surface. That is, the concealment performance of the light deflection element is poor. The term “poor concealment performance” means that when the light from the light source reaches the observer, the light and darkness of the light is seen through, and the light and darkness is perceived as unevenness.

  In order to improve this problem, for example, there is a method of stacking a plurality of optical sheets such as a diffusion sheet, but the number of parts increases, leading to an increase in cost. In addition, if the optical sheet of the optimum member is not stacked, it will return and cause a decrease in brightness, and light loss due to the lamination of the optical sheets is inevitable, and a complete solution has not been reached.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a light guide having high concealment performance even by itself, and an illumination device and a display device using the light guide.

  A translucent light guide according to an embodiment of the present invention connects a first main surface, a second main surface opposite to the first main surface, and the first main surface and the second main surface 4. A plurality of first light deflecting elements having two or more side surfaces, formed on the first main surface, for deflecting light in the light guide body toward the second main surface, and formed on the second main surface; A plurality of bowl-shaped second light deflection elements that emit light propagating through the light guide body from the second main surface, and the first light deflection element has a depth or height from the surface of the first main surface. 5 μm or more and 70 μm or less, and the second light deflection element is provided with unevenness having a maximum depth difference of 0.2 μm or more and 5 μm or less continuously in the eaves extending direction. To do. It is preferable that the unevenness provided in the second light deflection element has a center line average roughness in the extending direction of the bowl shape of 0.5 μm or more and 3 μm or less.

  The light guide of the present invention may be used in a lighting device, or a display device may be configured by mounting the lighting device. The lighting device can be configured by combining the light guide of the present invention and a prism sheet or an optical sheet having regularity.

  According to the present invention, the plurality of bowl-shaped second light deflecting elements provided with concavities and convexities in the bowl-shaped extending direction are formed on the second main surface of the light guide. Thereby, the incident light from the first main surface can be scattered and emitted also in the extending direction of the second light deflection element, and the first light deflection element formed on the first main surface becomes difficult to be visually recognized ( (Concealment performance is improved), and brightness uniformity of the display device is also improved.

The figure which shows the outline of the display apparatus provided with the light guide which concerns on one Embodiment of this invention. The transmission perspective view of the light guide concerning one embodiment of the present invention. The figure which shows the example of formation of the 1st light deflection | deviation element in the 1st main surface of the light guide of this invention. The figure which shows the example of formation of the 2nd light deflection | deviation element in the 2nd main surface of the light guide of this invention. The figure which shows the example of formation of the 2nd light deflection | deviation element in the 2nd main surface of the conventional light guide. The figure explaining the shape difference of the conventional 2nd light deflection element (a) and the 2nd light deflection element (b) of the present invention. Illustration explaining the mold The figure explaining an example of the processing method of the metal mold | die of FIG. Diagram showing schematic configuration of extruder Table showing results of performance evaluation by actual measurement using light guide

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram schematically illustrating a display device 1 including a light guide according to an embodiment of the present invention. A display device 1 shown in FIG. 1 includes a liquid crystal panel 2 and a lighting device 3. In this display device 1, an image is displayed on the polarizing plate 10 of the liquid crystal panel 2, and the image is provided to an observer who is in the direction F of FIG. 1.

The liquid crystal panel 2 has a configuration in which a plurality of pixels are arranged and a desired image can be displayed as a display image by switching each pixel, and the liquid crystal element 11 is sandwiched between polarizing plates 9 and 10.
The illuminating device 3 plays a role of deflecting light emitted from the two light sources 6 to emitted light K directed toward the liquid crystal panel 2. The light guide 7 of the present invention is housed in the housing 5 of the lighting device 3. A reflective sheet 4 is provided between the light guide 7 and the housing 5.

1. Structure of Light Guide 7 FIG. 2 is a transparent perspective view of the light guide 7 according to an embodiment of the present invention. The light guide 7 shown in FIG. 2 includes a first main surface 7a, a second main surface 7b facing the first main surface 7a, and two side surfaces 7L connecting the first main surface 7a and the second main surface 7b. A light-transmitting substantially rectangular parallelepiped plate having a (light incident surface) and two side surfaces 7S (light non-incident surface). The side surfaces 7L and 7S may be four or more. Formed on the first main surface 7a are first light deflection elements 18 arranged in a plurality of dots for deflecting the light in the light guide 7 toward the second main surface 7b. The second main surface 7b has a plurality of bowl-shaped second light deflection elements that emit light propagating through the light guide 7 from the second main surface 7b to the viewer side (F direction in FIG. 2). 19a is formed.

  The light emitted from the light source 6 enters the side surface 7L of the light guide 7. The incident light is deflected by the first light deflecting element 18 on the first main surface 7a and emitted from the second light deflecting element 19a on the second main surface 7b. The emitted light is then transmitted through the diffusive light collecting sheet 8, the prism sheet 20, and the polarization separation sheet 28, and is emitted as the emitted light K from the illumination device 3 toward the liquid crystal panel 2. The diffusive light collecting sheet 8 is formed with a prism lens or a lenticular lens.

  As a material for the light guide 7, a transparent resin such as acrylic, polycarbonate, polystyrene, AS resin, or MS resin can be used. Further, as a means for forming the light guide 7, it is possible to adopt means such as injection molding, extrusion molding, or casting to form a square resin plate.

[First optical deflection element 18]
The first light deflection element 18 formed on the first main surface 7a of the light guide 7 may be a plurality of three-dimensional dot shapes, and can be formed in various convex and concave dot shapes. That is, the shape of the first light deflection element 18 can be formed in the shape of a hemispherical dot, a pyramidal dot, a cube, or the like, and the shape of the first light deflection element 18 is not particularly limited. In addition, the first light deflection element 18 is different in dot size, shape, and arrangement interval depending on the distance from the light source 6, and the first light deflection element 18 is continuously arranged in the two-dimensional direction. The incident light incident from the side surface 7L can be efficiently guided to the exit surface. FIG. 3 is a diagram illustrating an example of forming the first light deflection element 18 on the first main surface 7 a of the light guide 7.

  It is preferable that the depth or height from the 1st main surface 7a of the 1st light polarizing element 18 is 5 micrometers or more and 70 micrometers or less. This is because if it is less than 5 μm, it is difficult to control the processing accuracy when forming the first light deflection element 18, and there is a possibility that the variation in depth or height becomes large, which is assumed in the optical design. Since it becomes a big factor which shifts from a characteristic, it is not preferred. On the other hand, in the case of 70 μm or more, the size of the first light deflection element 18 becomes too large, and the rise of light by the first light deflection element 18 is visually recognized as a bright spot from the second main surface 7b side of the light guide 7. This is not preferable because the concealability of the light deflection element is reduced.

[Second optical deflection element 19]
FIG. 4A is a diagram showing a formation example of the second light deflection element 19a on the second main surface 7b of the light guide 7 of the present invention. Various materials and shapes can be adopted for the second light deflection element 19a formed on the second main surface 7b. For example, the second light deflection element 19a may be a lens formed of a UV curable resin, a convex lens formed by machining, or a concave formed on the second main surface 7b by a mold. A shape or convex lens may be used. The lens may be formed by being put in a mold when forming the light guide 7 or may be formed by a heated mold after the light guide 7 is formed. As the lens shape, a prism lens, a lenticular lens, a trapezoidal lens, or the like well known in the art can be employed.

  In general, when forming a lenticular lens, as shown in FIG. 4B, the second light deflection element 19 in which cylindrical structures are continuously arranged in a one-dimensional direction is formed. In this case, the second light deflection element 19 is preferably bowl-shaped. Here, the saddle shape means that a certain state of elevation is continued horizontally. With this bowl-shaped second light deflection element 19, light can be diffused and emitted in a direction perpendicular to the extending direction D (see FIG. 5A). Furthermore, by reflecting the light incident on the bowl-shaped second light deflection element 19 and guiding it in the extending direction D, it is possible to suppress the occurrence of a dark portion at a location away from the light source 6, The emitted light can be diffused and luminance unevenness can be reduced, and the emitted light with high luminance can be obtained.

  However, when the plurality of bowl-shaped second light deflection elements 19 are simply formed horizontally on the second main surface 7b of the light guide body 7, the first main surface 7a formed on the first main surface 7a. There is a problem that the light polarizing element 18 is visually recognized as a bright spot.

  Therefore, in the light guide 7 of the present invention, a plurality of bowl-shaped second light deflection elements 19 provided with irregularities continuous in the bowl-shaped extending direction D are formed on the second main surface 7b. The second light deflection element 19a provided with the continuous unevenness scatters the incident light from the first main surface 7a also in the extending direction D (see FIG. 5B) of the second light deflection element 19a. Let it emit. Thereby, the first light polarization element 18 formed on the first main surface 7a is hardly visually recognized as a bright spot, and the luminance uniformity of the display device 1 can be improved.

  The difference in the maximum depth of the unevenness provided in the bowl-shaped extending direction D of the second light deflection element 19a is preferably 0.2 μm or more and 5 μm or less. The reason is that if the difference in maximum depth of the unevenness is 0.2 μm or less, the problem that the first light polarization element 18 formed on the first main surface 7a is visually recognized as a bright spot cannot be solved, and the unevenness is reduced. This is not preferable because it is difficult to control the processing accuracy to be formed, resulting in deviation from the desired optical design. On the other hand, if the difference in the maximum depth of the unevenness is 5 μm or more, the loss of light due to scattered light increases, resulting in a decrease in luminance, and furthermore, the luminance of the entire display device screen cannot be made uniform, which is not preferable. That is, the desired optical design is disturbed.

  Further, the surface roughness (Ra) in the extending direction D of the second light deflection element 19a is desirably 0.5 μm or more and 3 μm or less. The reason is that, as described above, when the surface roughness (Ra) is 0.5 μm or less, the problem that the first light polarization element 18 formed on the first main surface 7a is visually recognized as a bright spot cannot be solved. is there. On the other hand, when the surface roughness (Ra) is 3 μm or more, the loss of light due to scattered light increases, resulting in a decrease in luminance, and furthermore, the luminance of the entire display device screen cannot be made uniform. That is, the desired optical design is disturbed.

2. Method for Manufacturing Second Main Surface 7b Hereinafter, a method for manufacturing the second main surface 7b using the mold 30 will be described.
For manufacturing, a substantially cylindrical mold 30 as shown in FIG. 6 is used. And the optical structure formation part 31 corresponding to the 2nd light deflection | deviation element 19a is formed in the surface of the metal mold | die 30 with the following processing method.

Processing in the circumferential direction: As shown in FIG. 7A, a cutting tool 40 having a desired shape and a die 30 are attached to a die processing machine. Then, the desired intaglio of the second light deflection element 19a is processed in the circumferential direction of the surface of the mold 30 by pressing the cutting tool 40 while amplifying the mold 30 while rotating the mold 30.
Processing in the longitudinal direction: As shown in FIG. 7B, a cutting tool 40 having a desired shape and a die 30 are attached to a die processing machine. Then, the intaglio of the desired second light deflection element 19a is processed in the longitudinal direction of the surface of the mold 30 by pressing the mold 30 while rotating the cutting tool 40 without rotating.

  As shown in FIG. 4A, the second light deflection element 19a is formed on the second main surface 7b of the light guide 7 by transferring it to the light guide sheet as shown in FIG. Such a light guide sheet can be produced.

As a material of the light guide 7 when the light guide 7 is formed by molding with the mold 30, a material having optical transparency with respect to the wavelength of light emitted from the light source unit 6 is used. For example, plastic materials that can be used for optical members can be used. Polyester resin, acrylic resin, polycarbonate resin, polystyrene resin, MS (acrylic and styrene copolymer) resin, polymethylpentene resin, cycloolefin polymer And a transparent resin such as a radiation curable resin made of an oligomer such as polyester acrylate, urethane acrylate, epoxy acrylate, or acrylate.
The light guide 7 may have a single layer structure or a multilayer structure, and the multilayer structure may include a transparent layer. And the light guide 7 is shape | molded and manufactured by pouring the above materials into a metal mold | die and solidifying it.

  On the other hand, the light guide 7 may be manufactured by being molded by a UV curing method. When the light guide 7 is molded by the UV curing method, a UV curable resin is applied on a sheet-like base material, and UV irradiation is performed while pressing a mold 30 having a desired shape. A light guide 7 composed of an optical protrusion and a light deflection element is obtained. As the sheet-like substrate, PET (polyethylene terephthalate), polycarbonate, acrylic, polypropylene films and the like well known in the art can be used.

  In addition, although the typical preparation example about the light guide 7 was demonstrated, if the optical characteristic of this embodiment can be achieved, it can manufacture using materials, structures, processes other than the above. Moreover, cutting, laser drawing, printing, etching, etc. are known as a manufacturing method of the 1st main surface 7a of the light guide 7. FIG.

3. Examples Hereinafter, specific examples will be described.
First, the manufacturing method of the metal mold | die 30 used as the base material for producing the light guide 7 is demonstrated.

  First, the second light deflection element 19a was processed into the mold 30 as follows. As shown in FIG. 7A, a cutting tool 40 and a mold 30 having a desired shape are attached to a mold processing machine. And the intaglio in the circumferential direction corresponding to the desired 2nd light deflection | deviation element 19a was processed on the surface of the metal mold | die 30 by pressing the cutting tool 40 to the metal mold | die 30 rotated, making it amplitude. Moreover, as shown in FIG.7 (b), the cutting tool 40 which has a desired shape is attached to a metal mold | die machine, and the metal mold | die 30 is pressed while making the cutting tool 40 oscillate without rotating, and a metal mold | die is carried out. The intaglio in the longitudinal direction corresponding to the desired second light deflection element 19a was processed on the surface of 30.

  As shown in FIG. 4A, the second light deflection element 19a is formed on the second main surface 7b of the light guide 7 by transferring the mold 30 thus processed to the light guide sheet as shown in FIG. A light guide sheet was formed.

(Measurement method of surface roughness)
For surface roughness measurement, the second light deflection formed on the mold 30 based on JIS-B0601 using Surf Test SJ-210 (Mitutoyo Co., Ltd.), which is a stylus type roughness measuring instrument. The Ra value (centerline average roughness) of the element 19a was measured. Specifically, after the mold 30 was produced, the surface roughness meter was fixed to a mold processing machine, and the extending direction D of the second light polarizing element 19a of the mold 30 was measured. In this embodiment, the unevenness is verified by providing a constant centerline average roughness (Ra) over the entire area of the mold 30, but the present invention has a constant value as long as it is 0.5 μm or more and 3 μm or less. Need not be.

<Examples 1-4>
As the set values, the difference in the maximum depth of unevenness in the extending direction D provided on the second light deflection element 19a of the second main surface 7b / the average roughness of the center line (Ra) is 0.2 μm / 0.5 μm, respectively. Example 1] A mold 30 was prepared so as to be 1 μm / 1 μm [Example 2], 3 μm / 2 μm [Example 3], and 5 μm / 3 μm [Example 4].

<Comparative Examples 1-3>
Next, as a comparative example, the difference in maximum unevenness depth in the extending direction D provided on the second light deflection element 19a of the second main surface 7b / centerline average roughness (Ra) is 0.1 .mu.m / 0. The mold 30 was prepared so as to be 3 μm [Comparative Example 1], 5 μm / 4 μm [Comparative Example 2], and 6 μm / 3 μm [Comparative Example 3].

Next, a method for producing the light guide 7 will be described.
In this experiment, a light guide sheet was prepared by an extrusion method. FIG. 8 shows a schematic view of the extruder 37. The mold 30 and the forming roll 38 produced in Examples 1 to 4 and Comparative Examples 1 to 3 were installed in an extruder 37. The acrylic resin melted from the T-die 36 was extruded between the mold 30 and the forming roll 38 and molded by the forming roll 39 before the extruded acrylic resin light guide sheet was cooled and cured. Thereby, the light guide 7 having a desired shape was obtained. The thickness of the light guide 7 was 320 μm.

  All the light guides 7 are produced by an extrusion method using an acrylic resin. The acrylic resin used in the present invention has an elastic modulus E = 2400 MPa and a specific gravity = 1.19 g / cm 3. The light guide 7 has a very good transfer rate from the mold 30 and a shaping rate of 99% or more.

  Performance evaluation was performed using seven types of light guides 7 produced based on the above-described conditions (Examples 1 to 4 and Comparative Examples 1 to 3). The evaluation results are shown in the list of FIG. Each evaluation was performed as follows.

(Concealment evaluation)
Each light guide 7 includes an LED edge light type liquid crystal television in which a light source is arranged on the two long sides of the light guide, and an LED edge light type liquid crystal in which a light source is arranged on the two short sides of the light guide. The concealability evaluation of the first light deflection element 18 on the first main surface 7a, which is mounted on a television, is a problem. In the concealment evaluation method, if the first light deflection element 18 was not visually recognized by visual inspection, it was determined to be acceptable (◯ mark), and if it was visually recognized, it was determined to be unacceptable (x mark). In addition, since external visual evaluation produced individual difference, it implemented by three persons, and even if one person had a disqualification (x mark) evaluation, it evaluated as a disqualification. In other words, the pass (circle) evaluation is a unanimous evaluation.

(Brightness uniformity evaluation)
Each light guide 7 includes an LED edge light type liquid crystal television in which a light source is arranged on the two long sides of the light guide, and an LED edge light type liquid crystal in which a light source is arranged on the two short sides of the light guide. It was mounted on a TV and evaluated with a brightness meter. The luminance measurement points are nine points that are the intersections of 3 vertical rows and 3 horizontal columns. If the luminance uniformity is better or the same as that of the conventional light guide, it is acceptable (circle), and if it is worse, it is not acceptable. It was set as a pass (x mark).

  In the evaluation result of FIG. 9, only when both the concealment evaluation and the luminance uniformity evaluation are acceptable, the overall evaluation is determined to be acceptable (circle mark). Since the condition that this comprehensive evaluation is acceptable is the effective value of the present invention, the difference in the maximum depth of the unevenness provided in the extending direction D of the second light deflection element 19a of the second main surface 7b according to the present invention is determined. It was confirmed that it is desirable to set the center line average roughness (Ra) to 0.5 μm or more and 3 μm or less to 0.2 μm or more and 5 μm or less.

  The light guide plate of the present invention can be widely used for applications in which incident light from a light source is diffused in the surface direction. For example, it is suitable for applications such as image display devices typified by flat panel displays, 3D liquid crystal display devices, color notebook PCs (personal computers), lighting fixtures, and building materials.

DESCRIPTION OF SYMBOLS 1 Display apparatus 2 Liquid crystal panel 3 Illuminating device 4 Reflective sheet 5 Case 6 Light source 7 Light guide 7a 1st main surface 7b 2nd main surface 7L Side surface (light incident surface)
7S side surface (light non-incident surface)
8 Diffusive condensing sheet 9, 10 Polarizing plate 11 Liquid crystal element 18 First light deflection element 19, 19a Second light deflection element 20 Prism sheet 28 Polarization separation sheet 30 Mold 31 Optical structure forming part 36 T die 37 Extrusion Machine 38, 39 Forming roll 40 Cutting tool

Claims (5)

A translucent light guide,
A first main surface, a second main surface opposite to the first main surface, and four or more side surfaces connecting the first main surface and the second main surface;
A plurality of first light deflection elements formed on the first main surface for deflecting light in the light guide body toward the second main surface;
A plurality of bowl-shaped second light deflection elements that are formed on the second main surface and emit light from the second main surface that propagates through the light guide;
The first light deflection element has a depth or height from the surface of the first main surface of 5 μm to 70 μm,
The light guide according to claim 1, wherein the second light deflection element is continuously provided with irregularities having a maximum depth difference of 0.2 μm or more and 5 μm or less in a bowl-shaped extending direction.   2. The light guide according to claim 1, wherein the unevenness provided in the second light deflection element has a center line average roughness of 0.5 μm to 3 μm in a bowl-shaped extending direction. .   A lighting device comprising the light guide according to claim 1. An illumination device comprising the light guide according to claim 1 and a prism sheet or an optical sheet having regularity.   A display device comprising the illumination device according to claim 3.