JP2013058318A - Sheet-shaped light guide body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet-shaped light guide body excellent in light volume uniformity and capable of obtaining an illumination device without the need of sophisticated optical design.SOLUTION: The sheet-shaped light guide body 1 including at least one light-incident face 4 and at least one light emission face 5 is provided with a light guide body 10 in which a plurality of high-refractive-index layers 2 each composed of transparent resin with a refractive index η1 satisfying 1.45≤η1<1.6 and a plurality of low-refractive-index layers 3 each composed of transparent resin with a refractive index η2 satisfying 1.35≤η2<1.45 are alternately laminated in a perpendicular direction to the light-incident face 4. On the light guide body 10, a plurality of recesses 6a to 6c which become deeper along a lamination direction of the high-refractive-index layers 2 and the low-refractive-index layers 3 are formed, and they are arranged along an extended direction of the high-refractive-index layers 2 and the low-refractive-index layers 3 so that depths H1 to H3 become gradually deeper as they are apart from the light-incident face 4.

Description

  The present invention relates to a sheet-like light guide used in a side light leakage type illumination device.

2. Description of the Related Art Conventionally, a side surface that is schematically configured from a sheet-like light guide and a light source device optically connected to at least one end of the light guide, and causes light incident from the light source device to leak from the side of the sheet-like light guide A light leakage type illumination device is known.
When a sheet-like light guide is used as this type of side light leakage type illumination device, a side portion of the sheet-like light guide is formed in order to leak light from a desired side portion of the sheet-like light guide to the outside. It is necessary to remove the low refractive index layer or to form a recess from the low refractive index layer to the high refractive index layer that is the light guide.

In order to remove the low refractive index layer or to form a recess from the low refractive index layer to the high refractive index layer that is the light guide portion, for example, a laser processing or a processing method using an end mill may be mentioned. it can. In the case of these processing methods, for example, laser processing, the low refractive index layer can be easily and dimensionally cut by adjusting the focal position and output of the laser light source according to the material of the sheet-like optical transmission body and the thickness of the sheet. There is an advantage that you can.
The side leakage type illumination device including the sheet-shaped light guide configured as described above is excellent in small space and can be designed with a light weight. It is suitable for backlight applications of screens, liquid crystal panels, and touch-type control panels (see, for example, Patent Document 1, Patent Document 2, and Patent Document 3).

JP 2007-80824 A JP 2005-32703 A Special table 2008-508556 gazette

However, in the above-described conventional technology, when the high refractive index layer that is the light guide portion is a single layer, a large amount of light leaks in the light emitting portion close to the light source. There is a problem that it tends to be low.
Further, for example, a light guide plate having a two-kind / three-layer structure using a methacrylate resin for the high refractive index layer and using, for example, PVDF (PolyVinylline DiFluoride) resin as the low refractive index resin for the low refractive index layers on both sides of the high refractive index layer. When the surface is roughened or grooved on the side surface and used in a side-light leakage type illumination device, since there is only one light guide path, the optimum rough surface roughness and groove depth are required to uniformly emit the entire side surface. There is a problem that it is necessary to derive the sheath size by advanced calculation and to perform processing by advanced processing technology.

  Accordingly, the present invention has been made in view of the above-described circumstances, and provides a sheet-like light guide that can realize an illumination device that is excellent in light quantity uniformity and does not require an advanced optical design. It is.

  In order to solve the above problems, a sheet-like light guide according to the present invention is a sheet-like light guide having at least one light incident surface and at least one light exit surface, and has a refractive index η1. 1. High refractive index layer made of transparent resin set to satisfy 1.45 ≦ η1 <1.6, and transparent resin set to satisfy refractive index η2 of 1.35 ≦ η2 <1.45 A light guide body having a plurality of low refractive index layers alternately stacked in a direction perpendicular to the light incident surface, and the light guide body includes the high refractive index layer and the low refractive index layer. A plurality of recesses whose depth increases along the stacking direction is formed, and the plurality of recesses are separated from the light incident surface along the extending direction of the high refractive index layer and the low refractive index layer. According to the above, the depth is gradually increased.

According to the present invention, a plurality of high-refractive-index layers that are light guide portions are provided, and a portion where light emission is necessary on the side surface of the sheet-like light guide using a laser processing or machining using an end mill, and the depth are provided. A recess can be formed. For this reason, since only the light guide in the predetermined high refractive index layer can be used for illumination as light leakage, it is possible to realize an illumination device that is excellent in light quantity uniformity and does not require advanced optical design.
In addition, by increasing or decreasing the high refractive index layer, which is the light guide portion, according to the number of light leakage locations, and processing the recesses according to the thickness of each layer, it is possible to easily respond to the increase or decrease of the light leakage locations It becomes.

It is a side view of the sheet-like light guide in the embodiment of the present invention. It is a schematic diagram of the measurement system used for optical evaluation in the embodiment of the present invention.

(Sheet light guide)
Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a side view of a sheet-like light guide 1 used in an illumination device.
As shown in the figure, the sheet-like light guide 1 includes a liquid crystal display device which is an illumination device used in, for example, a mobile phone, a notebook computer, a liquid crystal television, a video camera, a back light key of a mobile phone, and a back of a personal computer. It is used for a display device which is an illumination device such as a light keyboard and a display switch of an electric device.
The sheet-shaped light guide 1 is configured such that three high-refractive index layers 2 and four low-refractive index layers 3 are alternately stacked, and the low-refractive index layers 3 are disposed on both surfaces in the stacking direction. The light guide body 10 is shaped.

  The light guide body 10 has at least one surface in a direction perpendicular to the stacking direction, that is, the side surface 1a of the sheet-like light guide 1 (for example, the left side surface in FIG. 4 is set. Light enters the sheet-like light guide 1 from the light incident surface 4 from an external light source (not shown).

Further, in the light guide body 10, one surface 1 b (upper surface in FIG. 1) of both surfaces in the stacking direction is set as a light emitting surface 5 that emits light. A plurality of recesses 6 a to 6 c are formed on the other surface 1 c facing the light emitting surface 5. The plurality of recesses 6a to 6c function as light emitting means 7 for emitting light incident from the light incident surface 4 from the light emitting surface 5 (details will be described later).
The shape of the light guide body 10 is not particularly limited as long as the light guide body 10 is formed in a plate shape, and may be a circular shape or the like in addition to a polygonal shape such as a short shape or a triangular shape. Moreover, the curved shape may be sufficient.

(High refractive index layer)
The high refractive index layer 2 has a refractive index η1 of 1.45 ≦ η1 <1.6 (1)
It is a transparent layer that is set to satisfy. As a material for forming each high refractive index layer, a known material can be used. For example, a homopolymer of methyl methacrylate (PMMA) or a copolymer can be used as a main component. Among them, it is preferable to use PMMA as a main component because it is excellent in transparency and durability and is inexpensive.

  In addition, when using the copolymer of methyl methacrylate, it is preferable that content of methyl methacrylate shall be 50 mass% or more. Examples of the copolymerizable monomer include acrylic acid esters such as methyl acrylate, ethyl acrylate, and n-butyl acrylate, and methacrylic acid esters such as ethyl methacrylate, propyl methacrylate, and cyclohexyl methacrylate, Maleimides, acrylic acid, methacrylic acid, maleic anhydride, styrene and the like can be mentioned.

Further, from the viewpoint of excellent heat resistance, polycarbonate resins, alicyclic polyolefin resins, and the like can be suitably used. In particular, since the polycarbonate-based resin has a higher bending rate than PMMA, the numerical aperture is increased. As a result, when the sheet-like light guide 1 is bent, light leakage can be suppressed low. Here, the numerical aperture means “light collecting performance”, and the larger the numerical aperture, the larger the amount of received light, and the light leakage can be suppressed when the sheet light guide 1 is bent. be able to.
The thickness T1 of each high refractive index layer 2 is not particularly limited, but is preferably determined in the range of 10 μm to 500 μm from the viewpoint of reducing the thickness of the liquid crystal display device and the light source device.

(Low refractive index layer)
The low refractive index layer 3 has a refractive index η2 of 1.35 ≦ η2 <1.45 (2)
It is a transparent layer that is set to satisfy. That is, each low refractive index layer 3 is set lower than the refractive index of each high refractive index layer 2. The material for forming each low refractive index layer 3 can be determined in consideration of the refractive index of each high refractive index layer 2.

  For example, the material of each low refractive index layer 3 includes a resin composition containing a fluorine-containing olefin resin as a main component. Examples of the fluorinated olefin-based resin include a vinylidene fluoride homopolymer, a binary copolymer of vinylidene fluoride and tetrafluoroethylene, a binary copolymer of vinylidene fluoride and hexafluoropropylene, and fluoride. Examples thereof include vinylidene fluoride copolymers such as a binary copolymer of vinylidene and trifluoroethylene, and a terpolymer of vinylidene fluoride, tetrafluoroethylene, and hexafluoropropylene.

The refractive index difference Δη between the refractive index of each high refractive index layer and the refractive index of each low refractive index layer is
Δη = η1-η2 (3)
More preferably,
Δη ≧ 0.1 (4)
It is desirable to satisfy.
This is because when the refractive index difference Δη exceeds 0, and more preferably satisfies the formula (4), the incident light propagates far without loss while being totally reflected in the sheet-like light guide 1, This is because light leakage does not occur even when a light reflection layer (not shown) is optically adhered to the surface of the light body 1 and light emission with high luminance is easily obtained.

The thickness T2 of each low refractive index layer 3 is not particularly limited, but is preferably determined in the range of 3 to 50 μm from the viewpoint of the handleability of the sheet light guide 1. If it is this range, the sheet-like light guide 1 will have flexibility and handleability will become favorable.
The ratio between the thickness T1 of each high refractive index layer 2 and the thickness T2 of each low refractive index layer 3 can be determined in consideration of the material of each high refractive index layer 2 and each low refractive index layer 3.

(Light emitting means)
The light emitting means 7 may have any structure that can emit light that is incident from the light incident surface 4 and propagates through each high refractive index layer 2 from the light emitting surface 5. That is, for example, for easy control of the light emission position, as shown in FIG. 1, the light emission means 7 has recesses 6 a to 6 c that penetrate the low refractive index layer 3 and reach the high refractive index layer 2. Preferably there is.

More specifically, the recesses 6 a to 6 c are formed in a so-called “scratch” shape such as a groove-like crack that penetrates each low refractive index layer 3 and reaches each high refractive index layer 2. And the recessed parts 6a-6c are formed so that these depth H1-H3 may become deep gradually as it leaves | separates from the light-incidence surface 4. As shown in FIG.
That is, the recess 6a formed at a position closest to the light incident surface 4 is formed between the other surface 1c of the light guide body 10 and the first high refractive index layer 2, and is provided on one surface. As it goes to 1b, it is formed to be tapered.

The concave portion 6b formed at the second position from the light incident surface 4 is formed between the other surface 1c of the light guide body 10 and the second high refractive index layer 2, and one of the concave portions 6b is formed. It forms so that it may taper off as it goes to the surface 1b.
Further, the recess 6c formed at the closest position away from the light incident surface 4 is formed between the other surface 1c of the light guide body 10 and the third high refractive index layer 2; It is formed to taper as it goes to the surface 1b.
As described above, each of the recesses 6a to 6c gradually increases in depth H1 to H3 along the extending direction of the high refractive index layer 2 and the low refractive index layer 3 and as the distance from the light incident surface 4 increases. Has been placed.

By providing the recesses 6a to 6c formed in this way, the light that has entered the high refractive index layers 2 from the light incident surface 4 is reflected by the recesses 6a to 6c and emitted from the light exit surface 5, thereby forming a sheet shape. The light guide 1 emits light.
The shape of the recesses 6a to 6c provided in each low refractive index layer 3 is not particularly limited. The light amount of an external light source (not shown), the distance from the light incident surface 4 to the opposite side, the light source device light guide The shape can be determined in consideration of the form of light emission required in

(Manufacturing method of sheet light guide)
Next, the manufacturing method of the sheet-like light guide 1 is demonstrated.
As shown in FIG. 1, the light guide body 10 constituting the sheet light guide 1 can be manufactured by alternately stacking a plurality of high refractive index layers 2 and low refractive index layers 3.
Here, as a method of alternately laminating the high refractive index layer 2 and the low refractive index layer 3, for example, the following methods may be mentioned.
(1) Method of integrally forming a high refractive index layer 2 and a low refractive index layer 3 by multilayer fusion extrusion (2) Forming a resin sheet or resin film to be the high refractive index layer 2 and the low refractive index layer 3 Method of manufacturing by alternately laminating resin sheets and resin films (3) Method of manufacturing by laminating sheets of low refractive index layer / high refractive index layer / low refractive index layer structure (4) Heat press method and adhesive The method of alternately laminating the high refractive index layer 2 and the low refractive index layer 3 using the above method The method of laminating the high refractive index layer 2 and the low refractive index layer 3 alternately is the method of (1) to (4) The method is not limited to the above, and any method can be used as long as the high refractive index layer 2 and the low refractive index layer 3 can be laminated.

  Then, after obtaining the multilayer laminated body by which the high refractive index layer 2 and the low refractive index layer 3 were laminated | stacked alternately, the obtained multilayer laminated body is cut | disconnected to the dimension according to a use. Next, of both surfaces in the stacking direction, one surface 1b is set as the light emitting surface 5, and the recesses 6a to 6c are formed in the other surface 1b. Examples of the method for forming these recesses 6a to 6c include laser processing, processing by an end mill, and hot pressing. However, the present invention is not limited to this, and various processing methods can be employed.

Under such a configuration, light incident from the light incident surface 4 of the sheet light guide 1 is caused by total reflection that occurs at the interface between the high refractive index layers 2 and the low refractive index layers 3 having different refractive indexes. The light is propagated far in the high refractive index layer 2 without leaking light.
At this time, the recesses 6a to 6c formed in the light guide body 10 are formed so that the depths H1 to H3 gradually become deeper as the distance from the light incident surface 4 increases. The number of high refractive index layers 2 through which light propagates varies.

  That is, light propagated from one high refractive index layer 2 is emitted through the light exit surface 5 from the recess 6 a formed at a position closest to the light incident surface 4. Further, the light propagated from the two high refractive index layers 2 is emitted from the concave portion 6 b formed at the second position from the light incident surface 4 through the light emitting surface 5. Further, the light propagated from the three high refractive index layers 2 is emitted from the recesses 6 c formed at the closest position away from the light incident surface 4 through the light emitting surfaces 5.

  Here, for example, when the high refractive index layer 2 is a single layer, the light incident from the light incident surface 4 is closer to the light incident surface 4 than the concave portion 6 c formed at a position away from the light incident surface 4. It is easy to radiate | emit toward the light-projection surface 5 from the recessed part 6a formed in the position. For this reason, a luminance difference is generated between the recess 6 a formed at a position close to the light incident surface 4 and the recess 6 c formed at a position away from the light incident surface 4.

Conventionally, in order to reduce this luminance difference, advanced optical design technology and precise processing technology have been required.
However, the sheet-like light guide 1 of the present embodiment has three high refractive index layers 2, and the number of high refractive index layers 2 in which the concave portions 6a to 6c are formed is different. . For this reason, it becomes possible to extract the amount of light from many high refractive index layers 2 as the recesses 6 a to 6 c are separated from the light incident surface 4. Therefore, it is possible to reduce the luminance difference between the recess 6a closest to the light incident surface 4 and the recess 6c farthest away.

Therefore, according to the above-described embodiment, the plurality of recesses 6a to 6c are formed in the light guide body 10 constituting the sheet-like light guide 1, and the depths H1 to H3 of these recesses 6a to 6c are changed. By simple processing, only the light guide of the predetermined high refractive index layer 2 can be used for illumination as light leakage at a predetermined portion of the light emitting surface 5 of the sheet-like light guide 1. For this reason, the illumination device which is excellent in the uniformity of the light quantity of the light emission surface 5 of the sheet-like light guide 1 and does not require an advanced optical design can be realized.
In addition, by increasing or decreasing the high refractive index layer 2 that is a light guide portion corresponding to the number of light leakage locations and changing the shape of the recesses 6a to 6c according to the thickness of each layer, it is easy to increase or decrease the light leakage locations. It becomes possible to respond.

  Furthermore, if the single-layer resin is a sheet-like light guide, the part where dust or dirt adheres may have a refractive index that is equal to or higher than the refractive index of the single-layer resin, and light propagated through the single-layer resin leaks. However, since the sheet-like light guide 1 of the present embodiment causes total reflection at the interface between each high refractive index layer 2 and each low refractive index layer 3, dust is deposited on the surface of the low refractive index layer 3. Or the like does not leak light propagating through the high refractive index layer 2. For this reason, it becomes possible to provide the high quality sheet-like light guide 1.

Next, the embodiment of the present invention and a comparative example will be shown specifically to explain the yarn splicing method. In addition, the Example of this invention is not limited by the matter described below.
(Optical evaluation)
FIG. 2 is a schematic diagram of a measurement system used for optical evaluation of the sheet light guide 1.
As shown in the figure, the optical properties of the sheet-shaped light guide 1 are as follows: a light-emitting diode (using one NSSW020BT manufactured by Nichia Corporation) 11 emitted from a constant current power source at 20 mA is used. Is emitted from the light emitting surface 5 in an area with a viewing angle of 2 ° centered on the portion where the light emitting means is provided, using a luminance meter (luminance meter BM-7 manufactured by TOPCON) 12. The brightness in the normal direction (0 ° direction) of the emitted light C was measured by moving the measurement distances from the incident position to 50 mm, 100 mm, 150 mm, and 200 mm, respectively (see arrow Y in FIG. 1).

(Example)
Here, in manufacturing the light guide body 10 constituting the sheet-like light guide 1, the high refractive index layer 2 of the light guide body 10 has a methacrylic resin (ACRYPET VH000, refractive index 1.49, On the other hand, a vinylidene fluoride copolymer (KYNAR720, refractive index n = 1.42, manufactured by Arkema Co., Ltd.) was used for the low refractive index layer 3.
Then, a laminate having a three-layer structure of a low refractive index layer / high refractive index layer / low refractive index layer structure having a thickness of 100 μm and molded using a coextrusion manufacturing apparatus having a T die was molded to a width of 980 mm and a thickness of 100 μm. When the thickness of the low refractive index layer of the molded laminate was measured, it was 5 μm on both the upper side and the lower side.

  5 layers of this laminate cut out into a rectangle with a length of 400 mm and a width of 300 mm are stacked, and then sandwiched between a mirror plate (brass, nickel plating) and a copper plate (copper), and a high-pressure press (Shoji Iron Works Co., Ltd.) Manufactured, pressure 100 t, ram diameter 350 mm), preheated for 3 minutes (set 160 ° C.), then pressurized for 5 minutes (set 160 ° C., pressurized 15 MPa), cooled for 3 minutes (about 15 ° C., pressurized 10 MPa) Low refractive index layer / high refractive index layer / low refractive index layer / high refractive index layer / low refractive index layer / high refractive index layer / low refractive index layer / high refractive index layer / low refractive index layer / high refractive index A laminate having a refractive index layer / low refractive index layer structure was prepared.

The laminated body manufactured through these steps was cut into a short shape having a length of 200 mm and a width of 10 mm to obtain a light guide. Then, a light emitting means 7 (recessed) in the form of a notch is formed on one surface of the light guide in the stacking direction at a distance of 50 mm, 100 mm, 150 mm, 200 mm from the light incident surface using a laser marker (ML-Z9520T, Keyence) Was provided.
Here, the laser etching pattern has five line shapes parallel to the light incident direction at intervals of 1 mm. When the obtained concave shape was measured with a laser confocal microscope (Laser Confocal Microscope OLS-3000), groove-shaped concave portions having depths of about 90 μm, about 140 μm, about 220 μm, and 290 μm were formed, respectively.

(Comparative example)
As in the examples, methacrylic resin (Acrypet VH000, refractive index 1.49, Mitsubishi Rayon Co., Ltd.) is used for the high refractive index layer constituting the sheet-shaped light guide, while the low refractive index layer is used. A vinylidene fluoride copolymer (KYNAR720, refractive index n = 1.42, manufactured by Arkema Co., Ltd.) was used.
Then, a laminate having a three-layer structure of a low refractive index layer / high refractive index layer / low refractive index layer structure having a thickness of 450 μm and molded using a coextrusion manufacturing apparatus having a T die was molded to a width of 980 mm and a thickness of 100 μm.

When the thickness of the low refractive index layer of the molded laminate was measured, it was 5 μm on both the upper side and the lower side. This was cut out into a short shape having a length of 200 mm and a width of 10 mm in the same manner as in the example, and then a concave portion (light emitting means) was formed with a laser marker.
In this comparative example, it was confirmed that the luminance value from the concave portion close to the light incident surface side was high, and the luminance value was greatly decreased as the distance from the light incident surface side was increased. In comparison with this, in the embodiment, the decrease in luminance at the light emitting means 7 (recessed portion) away from the light emitting surface 5 side is very small compared to the recessed portion (not shown) closer to the light incident surface 4 side. It was confirmed that the emitted light C was made uniform. These results are shown in Table 1.

The present invention is not limited to the above-described embodiment, and includes various modifications made to the above-described embodiment without departing from the spirit of the present invention.
For example, in the above-described embodiment, one surface 1 b (upper surface in FIG. 1) of the light guide body 10 constituting the sheet light guide 1 is set as the light emission surface 5 and faces the light emission surface 5. The case where several recessed part 6a-6c was formed in the other surface 1b was demonstrated. However, it is not restricted to this, You may form the recessed parts 6a-6c in one surface 1b, ie, the light-projection surface 5 side.

In the above-described embodiment, the low refractive index layers 3 are disposed on both surfaces of the high refractive index layer 2, and the outermost surface in the stacking direction of the light guide body 10 constituting the sheet light guide 1 is the low refractive index layer 3. The case where it becomes becomes explained. However, the present invention is not limited to this, and the outermost surface in the stacking direction of the sheet light guide may be configured to be the high refractive index layer 2.
Furthermore, in the above-described embodiment, the light guide body 10 constituting the sheet-like light guide 1 is a plate-like structure in which three high refractive index layers 2 and four low refractive index layers 3 are alternately stacked. However, the case where three high refractive index layers 2 are provided has been described. However, the present invention is not limited to this, and the light guide body 10 only needs to have two or more high refractive index layers 2.

  In the above-described embodiment, in the sheet light guide 1, at least one of the side surfaces 1 a of the light guide body 10 is set as the light incident surface 4, and one surface 1 b of the both sides in the stacking direction is light. The case where the light emitting surface 5 is set to emit light has been described. However, the present invention is not limited to this, and a plurality of side surfaces 1 a of the light guide body 10 may be set as the light incident surface 4. Further, the light-emitting surface 5 may be set on both surfaces 1 b and 1 c in the stacking direction of the light guide body 10.

Postpartum availability

Since the sheet-like light guide 1 of the present invention can make the emitted light brightness uniform and simplify the optical design and the surface processing technique, it can provide an inexpensive uniform light source with high productivity.

DESCRIPTION OF SYMBOLS 1 Sheet-like light guide 1a One surface 1b The other surface 2 High-refractive-index layer 3 Low-refractive-index layer 4 Light-incidence surface 5 Light-projection surfaces 6a-6c Recessed part 7 Light-projection means 10 Light-guide body H1-H3 Depth

Claims (1)

A sheet-like light guide having at least one light incident surface and at least one light emitting surface,
The refractive index η1 is 1.45 ≦ η1 <1.6.
A high refractive index layer made of a transparent resin set to satisfy
Refractive index η2 is 1.35 ≦ η2 <1.45
A low refractive index layer made of a transparent resin set so as to satisfy a light guide body that is alternately stacked in a direction perpendicular to the light incident surface,
In the light guide body, a plurality of recesses whose depth is increased along the stacking direction of the high refractive index layer and the low refractive index layer,
The plurality of recesses are arranged such that the depth gradually increases along the extending direction of the high-refractive index layer and the low-refractive index layer and away from the light incident surface. A sheet-like light guide.

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