JP5017140B2 - Light guide for surface light source device and surface light source device - Google Patents

Description

  The present invention is used for a display device such as a liquid crystal display device used in a mobile phone, a notebook computer, a liquid crystal television, a video camera, a backlight numeric keypad of a mobile phone, a backlight keyboard of a personal computer, a display switch of an electric device, More particularly, the present invention relates to a surface light source device and a light source for a surface light source device capable of controlling the occurrence of color spots in a light emitting surface.

Conventionally, as a back light source device used in a liquid crystal display device, a display device, etc., there are a direct light system in which a plurality of linear light sources such as fluorescent lamps and point light sources such as light emitting diodes are arranged in a housing, and a plate-shaped light guide device. There is an edge light system in which a linear light source or a point light source is arranged on the side end face of the light body.
However, since it is difficult to reduce the weight and thickness of a light source unit in a direct-type rear light source device, an edge light type is widely used as a light source and a thin back light source device that can be thinned.

  Such an edge-light type rear light source device usually uses a plate-shaped transparent material such as an acrylic resin plate as a light guide, and light from a light source arranged facing one side end surface of the light guide. Is incident on the light guide from the side end surface (light incident surface), and the incident light is provided with a light scattering portion on the front surface (light emitting surface) or back surface of the light guide, or is guided. It is a surface light source device that emits light from the light emitting surface by providing a light emitting function such as containing light diffusing fine particles in the body.

Here, as the light guide used in the edge light type rear light source device, a plate-like transparent material is used as a core layer, and a transparent material having a refractive index lower than the refractive index of the core layer is provided around the core layer as a cladding layer. Patent Document 1 proposes a clad light guide formed as follows.
Japanese Patent Laid-Open No. 5-273414

However, the edge light type surface light source device using such a clad light guide changes in the order of blue, green, dark red, and white from the vicinity of the light incident surface to the center of the light guide on the light exit surface. The problem is that the color shift phenomenon that appears is visually recognized.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a surface light source device having a small color spot and a light guide used therefor, by reducing the color shift phenomenon occurring on the light exit surface by a simple method.

  The present invention is a light guide in which a cladding layer having a refractive index lower than the refractive index of the core layer is formed on at least one surface of the core layer, and the light guide has at least one side end face as a light guide. A light exit surface that is substantially orthogonal to the light entrance surface, and a surface treatment for erasing the cladding mode is applied to at least one surface of the light exit surface and the back surface of the light exit surface. The present invention relates to a light guide for a surface light source device, and relates to a surface light source device using the light guide.

  ADVANTAGE OF THE INVENTION According to this invention, the color shift which generate | occur | produces on the light-projection surface of the light guide with a clad can be reduced with a simple method, and a surface light source device with small color spots and a light guide used therefor can be provided.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 is a perspective view illustrating a configuration example of a light guide body 10 for a surface light source device according to a first embodiment. That is, the surface light source device light guide 10 according to the embodiment of the present invention is a waveguide in which a clad layer 12 having a refractive index lower than the refractive index of the core layer 11 is formed on at least one surface of the core layer 11. Further, the surface light source device light guide 10 includes at least one side end surface 14 that serves as a light incident surface and a light emitting surface 15 that is substantially orthogonal to the light emitting surface 15. In the vicinity of the light incident surface 14 on at least one surface of the back surface 16, a surface treatment layer 17 subjected to a surface treatment for erasing the clad mode is applied.

  Here, the clad layer 12 of the light guide 10 for the surface light source device may be formed on at least one of the upper and lower surfaces of the core layer 11, for example, on the upper surface of the core layer 11 as shown in FIG. 1. When the clad layer 12 is formed, or as a modification, the clad layer 12 may be formed on the lower surface of the core layer 11 as shown in FIG. In addition, as shown in FIG. 2 (2), the cladding layer 12 may be formed on both upper and lower surfaces of the core layer 11. Further, as shown in FIG. 2 (3), the cladding layer 12 may be formed on the upper surface, the lower surface and the side surface so as to cover the entire core layer 11.

  The core layer 11 is generally made of an acrylic resin or polycarbonate resin, which is an optical material with high transparency, and has a thickness t of about 0.1 to 6 mm depending on the size of the light source.

  The clad layer 12 is made of a material having a refractive index lower than that of the core layer 11 in order to confine light in the core layer 11. For example, when the core layer 11 is an acrylic resin, the clad layer 12 is a fluorine resin such as a vinylidene fluoride polymer, a tetrafluoroethylene polymer, a hexafluoropropylene polymer, a fluorinated acrylate, or a copolymer thereof. Is used. Among these, vinylidene fluoride-tetrafluoroethylene copolymer and the like are preferably used because of good adhesion to acrylic resin and transparency. When the core layer 11 is a polycarbonate resin, an acrylic resin having a lower refractive index than that of the polycarbonate resin is used as the cladding layer 12.

  The thickness of the clad layer 12 is required to be several times the wavelength of visible light or less, even if it is thin in order to confine light in the core layer 11. However, if the thickness is too thick, the light guide becomes thick and the cost is high, so about 3 to 500 μm is preferable.

  The method of manufacturing the light guide 10 for the surface light source device is not particularly limited, but includes a method of integrally forming the core layer and the clad layer by multilayer melt extrusion, a resin sheet (or film) corresponding to the core layer, and a resin corresponding to the clad layer. There is a method of manufacturing by coating the material.

  The light source 10 for a surface light source device has at least one side end surface as a light incident surface 14 and a light exit surface 15 substantially orthogonal thereto, as shown in FIG. One side end face is used as a light incident face 14 and light from a light source such as a light emitting diode 31 is made incident thereon, and two side end faces of the core layer 11 are used as a light incident face 14 as shown in FIG. There is a method in which light from a light source such as the light emitting diode 31 is incident from both sides. Here, a fluorescent lamp such as a cold cathode tube may be used as the light source.

  Here, as described in the above problem, a color shift phenomenon occurs in which the color appears to change in the order of blue, green, dark red, and white from the vicinity of the light incident surface to the center of the light guide on the light exit surface 15. The reason is that the inventors consider Rayleigh scattering in the clad mode as described below.

ここに，ｎ_coreはコア層１１の屈折率，ｎ_claddはクラッド層１２の屈折率を示す。 As shown in FIG. 4 which is a cross-sectional view of a light guide for a surface light source device with a clad, a clad mode 42 is generated. The clad mode is a component of light that is reflected at the interface between the clad layer 12 and the air 44 and is confined inside the light guide 10 for the surface light source device. The longitudinal direction of the light guide 10 for the surface light source device is z, When the direction perpendicular to the light emitting surface 15 of the light guide for the surface light source device 10 is x and the angle extending from z to the x direction is θ, the light beam falls within the range of (Expression 2).

Here, n _core represents the refractive index of the core layer 11, and n _cladd represents the refractive index of the cladding layer 12.

  The clad mode 42 is scattered by the refractive index fluctuation of the resin constituting the clad layer, and a part of the scattered light is converted into the radiation mode 43 and emitted from the light emitting surface 15 of the light guide 10 for the surface light source device. Since this scattering is Rayleigh scattering based on refractive index fluctuation in a range smaller than the wavelength, such as the crystallinity of the cladding layer, the scattering intensity is inversely proportional to the fourth power of the wavelength. Therefore, in the vicinity of the light incident surface, the blue component having a short wavelength is strongly scattered, and at the same time, the blue component of the cladding mode is attenuated. Further, as the distance from the vicinity of the light incident surface increases, the green and red components are scattered and the green and red components of the cladding mode are attenuated. Finally, the cladding mode is erased and the transmission mode 41 remains.

  The transmission mode 41 is the same as the light emission mechanism of a normal (without clad) light guide for a surface light source device, and is a light scattering portion formed on the front surface (light emission surface) or the back surface of the light guide. And light exiting function such as containing light diffusing fine particles in the light guide and using Mie scattering or geometrical optical scattering, which has no wavelength dependence on the light scattering intensity, and emits white light from the light exit surface .

  For the above reasons, it is considered that a color shift phenomenon appears in which the color changes in the order of blue, green, dark red, and white from the vicinity of the light incident surface to the center of the light guide on the light exit surface 15.

  According to the study of the present inventors, the surface treatment layer 17 for erasing the clad mode is applied to the light source 10 for the surface light source device, and the light incident surface 14 on at least one of the light emitting surface 15 and the back surface 16 thereof. By applying it to the vicinity, the color shift can be prevented.

In order to form the surface treatment layer 17 for erasing the clad mode, there are a method of applying a color that absorbs visible light, and a method of performing a roughening process for scattering visible light.
The color of the paint that absorbs visible light is not particularly limited, but black is preferable. For black coating, carbon black-containing printing ink is easily available and effective. The thickness of the coating is not particularly limited as long as it has a thickness that does not allow cladding mode light to pass through the coating and leak into the air.
The surface roughening method is not particularly limited, and examples thereof include polishing paper, polishing with polishing powder, sand blasting, pressing of a minute uneven surface with a mold, and laser etching. is there.
The degree of roughening is not particularly limited as long as the cladding mode light leaks into the air, and the depth is preferably less than the thickness of the cladding layer.

  Although it is more effective to make the surface treatment range as wide as possible, there is a problem that the area of the effective light exit surface is reduced. Therefore, it is desirable to perform a surface treatment on the side near the light emitting surface in the most effective range for erasing at least the cladding mode. That is, it is preferable to perform surface treatment in a range where the light emitted from the light source unit repeats reflection several times from the portion where the light source 10 for the surface light source device first reaches the upper surface and the lower surface.

Specifically, when the refractive index of the core layer of the light guide is n _core , the thickness of the core layer is t, and the distance from the light incident surface side end on the light exit surface and its back surface is a, the light guide It is effective to apply a surface treatment for erasing the cladding mode in the vicinity of the light incident surface on at least one of the light exit surface and the back surface of the light source over the range a shown in (Equation 1). is there. The range of surface treatment should just be over the range of the range a shown by (Formula 1), and surface treatment may be performed exceeding this range.

(Second Embodiment)
FIG. 5 is a perspective view showing a configuration example of the light guide 50 for the surface light source device according to the second embodiment. The structure of the light source for surface light source device 50 according to the second embodiment is arranged on at least one surface of the light emitting surface and the back surface of the light source for surface light source device 10 according to the first embodiment. A light emitting mechanism 51 for converting the transmission mode 41 to the radiation mode 43 is formed.

ここに，ｎ_core はコア層１１の屈折率，ｎ_claddはクラッド層１２の屈折率を示す。 The transmission mode 41 is a component of light reflected at the interface between the core layer 11 and the clad layer 12 and confined inside the core layer 11 of the light source 10 for the surface light source device. When the direction is z, the direction perpendicular to the light emitting surface 15 of the light guide for the surface light source device 10 is x, and the angle extending from z to the x direction is θ, the light beam falls within the range of (Expression 3).

Here, n _core represents the refractive index of the core layer 11, and n _cladd represents the refractive index of the cladding layer 12.

伝送モード４１を放射モード４３に変換する光出射機構５１とは，伝送モードの光に対して，散乱強度に波長依存性のないミー散乱または幾何光学的な散乱を与える機構である。例えば，可視光の波長範囲３８０〜７８０ｎｍよりも大きい傷または凹面形状をコア層まで到達する程度にクラッド層に形成することで，伝送モードの光に対して，散乱強度に波長依存性のないミー散乱または幾何光学的な散乱を与える機構を実現できる。（図４，図５）。一般に，光出射面での均斉度を高めるために，光入射面近傍では傷（凹面）の密度を低く，光入射面近傍から離れるに従い傷の密度を高く加工することを行う。 The radiation mode 43 is a component of light that is not confined inside the light guide 10 for the surface light source device, and similarly refers to a light beam that satisfies (Equation 4).

The light emitting mechanism 51 that converts the transmission mode 41 to the radiation mode 43 is a mechanism that gives Mie scattering or geometric optical scattering whose wavelength is not dependent on the scattering intensity for light in the transmission mode. For example, by forming scratches or concave shapes larger than the visible light wavelength range of 380 to 780 nm on the cladding layer to the extent that they reach the core layer, the scattering intensity of the transmission mode light has no wavelength dependence. A mechanism for providing scattering or geometric optical scattering can be realized. (FIGS. 4 and 5). In general, in order to increase the uniformity on the light exit surface, the density of the scratches (concave surface) is low near the light incident surface, and the scratch density is increased as the distance from the light incident surface increases.

(Measurement method of color shift)
FIG. 6 shows an outline of a color shift measurement system. A light source 61 (using three NSSW020BT manufactured by Nichia Corporation) driven by a constant current power source 65 at 20 mA is disposed on the side end face of the light guide 60 for a surface light source device to be measured. The light emitted from the light emitting surface 64 of the light source for the surface light source device 60 is measured with a chromaticity measuring system 63 (ProMetric 8 manufactured by Radiant Imaging). A reflective sheet 62 (Eiwa made Leila) is installed on the lower surface of the light guide 60 for the surface light source device. Differences Δx and Δy between the maximum and minimum chromaticities x and y of the entire photometric surface are calculated. A light guide having a small Δx and Δy is a small color shift.

Example 1
A light guide sheet having a three-layer structure of clad layer / core layer / cladding layer was molded using a coextrusion sheet manufacturing machine having a T-die having a width of 600 mm. Acrylic resin (manufactured by Mitsubishi Rayon, Acrypet MF001, refractive index 1.49) for core layer, tetrafluoroethylene-vinylidene fluoride copolymer (made by Daikin Industries, VP-50, refractive index 1.40) for cladding layer A light guide sheet having a width of about 650 mm and a thickness of 0.3 mm was manufactured. When the thickness of the clad layer of the light guide sheet was measured with a film thickness meter, it was about 15 μm on both the upper surface side and the lower surface side. Four rectangular sheets having a width of 170 mm and a length of 200 mm were cut out from the light guide sheet to obtain a light guide.

  For one of the four sheets, the light exit surface and the back surface of the light guide are covered with carbon black ink (Magic Ink (registered trademark) No. .500 black) and was subjected to surface treatment. The light-emitting diode light was incident and measured from the side end face of the light guide on the surface-treated side as described above. As shown in Table 1, Δx and Δy were both small, and almost no color shift was detected visually, and good results were obtained.

(Example 2)
For one of the four sheets produced in Example 1, the light exit surface and back surface of this light guide were roughened using # 2000 sandpaper over a range of 5 mm from the end surface on the incident side, Surface treatment was applied. The light-emitting diode light was incident and measured from the side end face of the light guide on the surface-treated side as described above. As shown in Table 1, Δx and Δy were both small, and almost no color shift was detected visually, and good results were obtained.

(Example 3)
For one of the sheets produced in Example 1, the light emitting surface and the back surface of this light guide were formed using a CO2 laser marker (Keyence Corporation ML-Z9520T output 20 W, wavelength 9.3 μm). Surface treatment was performed in which a total of 20 scratches were made in a range from the end face to 5 mm in parallel with the end face on the incident side at intervals of 0.25 mm. The output of the CO2 laser marker was 50% and the scanning speed was 500 mm / sec. The light-emitting diode light was incident and measured from the side end face of the light guide on the surface-treated side as described above. As shown in Table 1, Δx and Δy were both small, and almost no color shift was detected visually, and good results were obtained.
(Comparative example)
One of the four sheets produced in Example 1 was used as it is as a light guide without any surface treatment, and light-emitting diode light was incident and measured as described above. As shown in Table 1, both Δx and Δy were large, and a clear color shift was confirmed visually.

It is a figure which shows the structural example of the surface light source device required light guide which concerns on 1st Embodiment. It is a figure which shows the modification of the surface light source device required light guide which concerns on 1st Embodiment. It is a figure which shows a light incident position. It is a figure explaining the mode in a light guide. It is a figure which shows the structural example of the surface light source device light guide required based on 2nd Embodiment. It is a figure which shows the measurement system of a color shift.

Explanation of symbols

10, 50, 60 Light guide for surface light source device 11 Core layer 12 Cladding layer 14 Side end surfaces 15, 54, 64 Light exit surface 16 Back surface of light exit surface 17 Surface treatment 31, 61 for erasing clad mode Light emitting diode 41 Transmission Mode 42 Clad Mode 43 Radiation Mode 44 Air 51 Light Output Mechanism 62 Reflective Sheet 63 Chromaticity Measurement System 65 Constant Current Power Supply

Claims (6)

  A light guide body in which a clad layer having a refractive index lower than the refractive index of the core layer is formed on at least one surface of the core layer, wherein the light guide body has at least one side end surface as a light incident surface, A light exit surface substantially orthogonal to the light exit surface, and a surface treatment for erasing the clad mode is performed on the light exit surface near the light incident surface of at least one of the light exit surface and the back surface thereof. A light guide for a surface light source device.   2. The light guide for a surface light source device according to claim 1, wherein the surface treatment for erasing the cladding mode is painting with a color that absorbs visible light.   2. The light guide for a surface light source device according to claim 1, wherein the surface treatment for erasing the cladding mode is a roughening process for scattering visible light. When the refractive index of the core layer of the light guide is n _core , the thickness of the core layer is t, and the distance from the light exit surface side end on the light exit surface and its back surface is a, the light exit surface of the light guide Further, a surface treatment for erasing the cladding mode is performed in the vicinity of the light incident surface on at least one surface of the rear surface over the range a shown in (Expression 1). Item 4. A light guide for a surface light source device according to any one of Items 1 to 3.

  The light emission mechanism which converts a transmission mode into a radiation mode is formed in at least one surface of the light-projection surface of the said light guide, and its back surface, The Claim 1 characterized by the above-mentioned. A light guide for a surface light source device.   The surface light source device using the light guide for surface light source devices in any one of Claims 1-5.

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