JP2018088347A - Light guide plate and lighting device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light guide plate capable of giving a transparent and open design when the light is turned off while having a high design property when the light is turned on, and a lighting device using the light guide plate. A light guide plate (10) is provided on at least one surface of a substrate (1) having transparency to visible light, and for a light absorber and visible light that absorb visible light of a specific wavelength. It includes a coating film 2 containing a transparent resin. The lighting device 100 includes the above-mentioned light guide plate 10 and a light source 20 that emits light incident on the light guide plate 10. [Selection diagram] Fig. 1

Description

  The present invention relates to a light guide plate and an illumination device using the same. More specifically, the present invention relates to a light guide plate that can obtain a light emitting surface that is transparent when turned off but has a color change when turned on, and an illumination device using the light guide plate.

  In general lighting devices using a light guide plate, light emitted from a light emitting element such as a light emitting diode is made incident from the side surface of the light guide plate, and the incident light is reflected inside the light guide plate. It has a structure for emitting light from the display area.

  As such an illuminating device, there exists a thing using the light-guide plate which arrange | positioned the decorated member (a sheet | seat, a film, etc.) on one surface, and the light-guide plate decorated with direct ink etc., for example. For example, Patent Document 1 discloses a decoration device that is excellent in design and decoration and is used for decoration such as a scuff plate portion of an automobile. The decoration device includes a first light guide plate, a metal dial disposed below the first light guide plate, and a dial having a character portion formed in a mesh shape by a through hole, and a dial The 2nd light guide plate arrange | positioned under and the light reflection layer arrange | positioned under the 2nd light guide plate are provided. Further, the decoration device includes a first light source that emits light introduced into the first light guide plate and a second light source that emits light introduced into the second light guide plate.

Japanese Patent Laid-Open No. 2005-221661

  In the decoration device of Patent Literature 1, light is reflected on the surface of the dial plate by irradiating the dial with light through the first light guide plate, thereby displaying in a metal color reflecting the material of the dial plate. It is described that. However, when the light source is turned off, the mesh-like character portion formed on the dial plate can be seen from the outside, so that the original transparent and open design of the light guide plate is impaired.

  The present invention has been made in view of such problems of the prior art. An object of the present invention is to provide a light guide plate that has a high designability when turned on, and that can be given a transparent and open design when turned off, and a lighting device using the light guide plate. There is.

  In order to solve the above problems, a light guide plate according to a first aspect of the present invention is provided on a substrate having transparency to visible light and at least one surface of the substrate, and further absorbs visible light having a specific wavelength. And a coating film containing a light absorber and a resin having transparency to visible light.

  An illumination device according to a second aspect of the present invention includes the light guide plate described above and a light source that emits light incident on the light guide plate.

  According to the present invention, it is possible to provide a light guide plate that has a high designability when turned on, and can provide a transparent and open design when turned off, and an illumination device using the light guide plate. It becomes possible.

It is a perspective view which shows schematically the light source which concerns on this embodiment, and the light source which discharge | releases the light which injects into a light guide plate. It is sectional drawing which shows schematically the pendant light to which the illuminating device which concerns on this embodiment is applied. It is the top view which looked at the pendant light of FIG. 2 from the lower surface side. It is an enlarged view of the part of the code | symbol A in FIG. It is the schematic which shows the vanity which applied the illuminating device which concerns on this embodiment. It is a graph which shows the relationship between the total light transmittance and a wavelength in the light-guide plate which concerns on Example 1, and the board | substrate used with the said light-guide plate. It is a graph which shows the relationship between the total light transmittance and a wavelength in the light-guide plate which concerns on Example 2, and the board | substrate used with the said light-guide plate. It is a graph which shows the relationship between the total light transmittance and a wavelength in the light-guide plate which concerns on a comparative example, and the board | substrate used with the said light-guide plate. It is a figure which shows the chromaticity distribution of the light guide plate which concerns on Example 1, and the board | substrate used with the said light guide plate.

  Hereinafter, the light guide plate according to the present embodiment and a lighting device using the light guide plate will be described in detail. In addition, the dimension ratio of drawing is exaggerated on account of description, and may differ from an actual ratio.

[Light guide plate]
As shown in FIG. 1, the light guide plate 10 according to the present embodiment includes a substrate 1 having transparency to visible light. The light guide plate 10 further includes a coating film 2 provided on at least one surface of the substrate 1 and including a light absorber that absorbs visible light having a specific wavelength and a resin that is transparent to visible light. is there.

  The substrate 1 is transparent to visible light of 380 nm to 780 nm. By using such a highly translucent substrate 1 for the light guide plate 10, the light guide plate 10 becomes transparent when the light source 20 described later is turned off, and the design can be made open.

  The substrate 1 is not particularly limited as long as it has transparency to visible light. As the substrate 1, for example, a substrate formed of at least one selected from the group consisting of acrylic resin (acrylic ester or methacrylic ester polymer), polycarbonate resin, styrene resin, epoxy resin, and glass is used. it can. Among them, acrylic resin and polycarbonate resin have high light transmittance. Therefore, it is preferable that the board | substrate 1 is formed in at least any one of an acrylic resin and a polycarbonate resin. In addition, it is preferable that the total light transmittance of the visible light in the board | substrate 1 is 90 to 100%, and a total light transmittance can be measured using a spectral haze meter.

  Although the thickness of the board | substrate 1 is not specifically limited, For example, it is preferable that it is 0.1 mm-10 mm. In consideration of strength and translucency, the thickness of the substrate 1 is more preferably 1 mm to 5 mm. In addition, the board | substrate 1 can use what was obtained by sheet molding methods, such as a glass cast manufacturing method, a continuous cast manufacturing method, and an extrusion manufacturing method.

  The light guide plate 10 of this embodiment includes a coating film 2 on at least one surface of the substrate 1. The coating film 2 contains a resin having transparency to visible light as a main component. Furthermore, in the coating film 2, the light absorber is dispersed inside the translucent resin. With such a configuration, when the light source 20 is turned off, the coating film 2 becomes transparent, but when the light source 20 is turned on, a part of the light incident on the substrate 1 from the light source 20 is absorbed. Thus, it is possible to cause a change in chromaticity.

  The resin as the main component of the coating film 2 is not particularly limited as long as it has transparency to visible light and can stably disperse the light absorber. The translucent resin is preferably at least one selected from the group consisting of acrylic resin, polyester and epoxy resin. Since these resins have high transparency to visible light and high durability, the transparency of the coating film 2 can be maintained over a long period of time. Further, as translucent resins, alkyd resins, polycarbonate resins, polyurethane resins, melamine resins, diethylene glycol bisallyl carbonate resins, acrylonitrile-styrene copolymers, methyl methacrylate-styrene copolymers, and alloy materials containing these as main components At least one translucent binder selected from the group consisting of can also be used.

  The acrylic resin is a resin obtained by polymerizing a (meth) acrylate monomer. The acrylic resin may be a copolymer of a (meth) acrylate monomer and a monomer having a carbon-carbon double bond. Examples of the monomer having a carbon-carbon double bond include at least one selected from the group consisting of a styrene monomer, an olefin monomer, and a vinyl monomer. “(Meth) acrylate” means acrylate or methacrylate.

  Examples of (meth) acrylate monomers include methyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isobornyl (meth) acrylate, glycidyl (meth) acrylate, benzyl (meth) acrylate, stearyl (meth) acrylate, and lauryl. There may be mentioned at least one selected from the group consisting of (meth) acrylate and 2-hydroxy-3-phenoxypropyl (meth) acrylate. Examples of the styrenic monomer include styrene. Examples of the olefin monomer include ethylene and propylene. Examples of the vinyl monomer include vinyl chloride and vinylidene chloride. One of these monomer components may be used alone, or two or more thereof may be mixed and used.

  When using polyester, a well-known thing can be used. Examples of the polyester that can be used include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polybutylene naphthalate. Polyester may be used individually by 1 type of these, and may be used in combination of 2 or more type.

  Also when using an epoxy resin, a well-known thing can be used. As the epoxy resin, for example, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, biphenyl type epoxy resin, naphthalene diol type epoxy resin, phenol novolac type epoxy resin can be used. Further, a cresol novolac type epoxy resin, a bisphenol A novolac type epoxy resin, a cyclic aliphatic epoxy resin, a heterocyclic epoxy resin (triglycidyl isocyanurate, diglycidyl hydantoin, etc.) can also be used. Furthermore, modified epoxy resins obtained by modifying these epoxy resins with various materials can be used. Moreover, halides such as bromides and chlorides of these epoxy resins can also be used. One of these epoxy resins may be used alone, or two or more of them may be used in combination.

  The light absorber contained in the coating film 2 will not be specifically limited if it is a compound which can absorb at least one part of visible light of 380 nm-780 nm. As the light absorber, antimony-doped tin oxide (ATO), tin-doped indium oxide (ITO), aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO), indium-doped zinc oxide (IZO), and polystyrene sulfonic acid were added. It is preferably at least one selected from the group consisting of polyethylene dioxythiophene (PEDOT: PSS). That is, as the light absorber, a material having both transparency and conductivity can be used. Such a material looks transparent by forming a thin film, but basically has a light absorption band in visible light, and therefore can be suitably used for the coating film 2.

  In order to increase the transparency of the coating film 2, the light absorber is preferably in the form of particles. The average secondary particle diameter of the light absorber is not particularly limited, but it is preferably 1 μm or less from the viewpoint of enhancing the translucency of the coating film 2 while efficiently absorbing visible light from the light source. The following is more preferable. Moreover, the lower limit of the average secondary particle diameter of the light absorber is not particularly limited, but can be, for example, 10 nm or more. In addition, the average secondary particle diameter of a light absorber can be measured by observing the coating film 2 with a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Further, the shape of the light absorber is not particularly limited, and may be any of a spherical shape, a needle shape, and a scale shape.

  The thickness t of the coating film 2 is not particularly limited as long as the light absorber can be highly dispersed while having translucency. However, the coating film 2 preferably has a thickness t of 0.1 μm to 100 μm, and particularly preferably 0.5 μm to 10 μm. When the thickness t of the coating film 2 is within this range, the coloring of the coating film 2 can be suppressed and the light guide plate 10 can be kept transparent.

  The light guide plate 10 of the present embodiment includes a coating film 2 formed by dispersing the above-described light absorber in a translucent resin on at least one surface (main surface) of the substrate 1. As shown in FIG. 1, a light source 20 is provided facing one end surface 1a of the light guide plate 10, and visible light emitted from the light source 20 enters the substrate 1 through the one end surface 1a. The incident visible light 3 is reflected by the main surface of the substrate 1, and propagates toward the other end surface 1b on the opposite side of the one end surface 1a by repeating this reflection. At this time, part of the propagating light is emitted from the main surface of the substrate 1 in the Y-axis direction.

  Here, the visible light 3 incident on the inside of the substrate 1 is reflected by the main surface of the substrate 1 and repeats this reflection. In the process, the light absorber contained in the coating film 2 has a specific wavelength in the visible light 3. Absorbs light. As the incident visible light 3 propagates from the one end surface 1a of the substrate 1 toward the other end surface 1b, the light having a specific wavelength is gradually absorbed by the light absorbent, so that the light having the specific wavelength is separated from the light source. Visible light with gradually decreasing is emitted from the surface 2a. Therefore, the visible light emitted from the surface 2a changes in chromaticity from the one end surface 1a to the other end surface 1b, so that a lighting device with high design can be obtained. Moreover, the light of the specific wavelength absorbed changes with the absorption wavelength range of the light absorber to be used. Therefore, it is possible to emit visible light having a desired chromaticity by using an appropriate light absorber.

  For example, when antimony-doped tin oxide (ATO) is used as a light absorber and a light emitting diode that emits white light is used as the light source 20, visible light 3 incident on the inside of the substrate 1 is only light having a specific wavelength by ATO. Is gradually absorbed. Therefore, white light is emitted from the light guide plate 10 in the vicinity of the light source 20, but yellowish light is emitted as the distance from the light source 20 increases. Therefore, the light absorber is preferably antimony-doped tin oxide.

  Thus, since visible light having a different wavelength is emitted from one light guide plate during lighting, it is possible to improve the design of the entire light guide plate.

  Moreover, since the board | substrate 1 and the coating film 2 have transparency with respect to visible light as mentioned above, when the light source 20 is extinguished, transparency is high. Therefore, when the light is extinguished, the original transparent and open design of the light guide plate can be obtained. Further, the light guide plate of the present embodiment is not decorated by providing irregularities on the substrate as in the prior art, and further, a metal dial plate as in Patent Document 1 is not used. Therefore, since the decorative pattern does not appear when the light is turned off, higher transparency can be obtained and the open feeling can be improved.

  Next, a method for manufacturing the light guide plate 10 of the present embodiment will be described. In the present embodiment, first, a coating composition is prepared by mixing a resin having transparency to visible light and a light absorber. At this time, the viscosity may be adjusted so that the coating composition is easy to apply by adding a solvent.

  For example, water or an organic solvent is preferably used as the solvent for adjusting the viscosity. The organic solvent is not particularly limited, but it is preferable to appropriately select an organic solvent that volatilizes easily at the time of coating film formation and does not cause curing inhibition at the time of coating film formation. Examples of the organic solvent include aromatic hydrocarbons (such as toluene and xylene), alcohols (such as methanol, ethanol, and isopropyl alcohol), and ketones (such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone). Furthermore, aliphatic hydrocarbons (such as hexane and heptane), ethers (such as tetrahydrofuran), and amide solvents (such as N, N-dimethylformamide (DMF) and dimethylacetamide (DMAc)) may be mentioned. Of these, aromatic hydrocarbons and alcohols are preferred. These organic solvents may be used individually by 1 type, and may be used in combination of 2 or more type.

  Next, the obtained coating composition is applied to the main surface of the substrate 1 and dried. Under the present circumstances, the coating method and drying conditions of a coating composition are not specifically limited. As a method for applying the coating composition to the main surface of the substrate 1, a coating method or a printing method can be used. In the coating method, the coating agent composition can be applied using an air spray, a brush, a bar coater, a Mayer bar, an air knife or the like. In the printing method, methods such as gravure printing, reverse gravure printing, offset printing, flexographic printing, and screen printing can be used. The drying conditions are not particularly limited as long as the solvent is removed, and heat treatment may be performed as necessary. In this way, the light guide plate 10 having the coating film 2 formed on the main surface of the substrate 1 can be obtained.

  As described above, the light guide plate 10 according to the present embodiment includes a substrate 1 that is transmissive to visible light, a light absorber that is provided on at least one surface of the substrate 1, and further absorbs visible light having a specific wavelength. And a coating film 2 including a resin having transparency to visible light. Therefore, it is possible to give a color pattern on the light source surface without changing the appearance by simply applying the paint composition and forming the coating film 2 without giving a pattern such as gradation directly to the light guide plate. It becomes.

  The light guide plate 10 shown in FIG. 1 has the coating film 2 formed only on one main surface (XZ surface) of the substrate 1. However, the light guide plate 10 of the present embodiment is not limited to the mode of FIG. 1, and the coating film 2 may be formed on both main surfaces of the substrate 1. When the coating film 2 is formed on both surfaces of the substrate 1, the visible light 3 is efficiently absorbed by the light absorber, so that the chromaticity is likely to change and the design can be improved.

[Lighting device]
Next, the illumination device according to the present embodiment will be described in detail with reference to the drawings. The illumination device 100 according to the present embodiment includes the light guide plate 10 described above and a light source 20 that emits light incident on the light guide plate 10.

  The light source 20 is not particularly limited as long as visible light can enter the inside of the substrate 1 through the one end surface 1a of the substrate 1. As the light source 20, for example, a point light source such as a light emitting diode (LED) or a linear light source such as a fluorescent lamp can be used.

  As shown in FIG. 1, the light source 20 faces one end face 1a of the light guide plate 10, and visible light emitted from the light source 20 enters the substrate 1 through the one end face 1a. Therefore, in the lighting device 100 of the present embodiment, the light source 20 is preferably located at the end of the light guide plate 10. As shown in FIG. 1, when the light guide plate 10 is flat, light is emitted from the main surface of the light guide plate 10 in the Y-axis direction by providing the light source 20 on one end face 1 a of the light guide plate 10. As a result, it is possible to efficiently irradiate light while saving space in the lighting device.

  2 to 4 show application examples of the lighting device 100, and show an example in which the lighting device 100 is applied to a pendant light that is used by being suspended from the ceiling. As illustrated in FIG. 2, the lighting device 100 </ b> A includes a device main body 30 and a power supply line 41 that is led out from the device main body 30 and supplies power to the device main body 30. Further, the lighting device 100A includes a connector 42 that is attached to an end portion of the power supply line 41 and engages with a hook ceiling C1 provided on the ceiling C. The apparatus main body 30 includes a light source 20, a light guide plate 10 that guides light emitted from the light source 20 and emits the light to the outside, and a housing 50 that holds the light source 20 and the light guide plate 10.

  As shown in FIGS. 2 and 4, the housing 50 includes a light source holding unit 51 that holds the light source 20 and a first light guide plate holding unit 52 that is disposed above the light source holding unit 51 and holds the light guide plate 10. And a second light guide plate holding portion 53 that is disposed below the light source holding portion 51 and holds the light guide plate 10. The light source holding part 51 is formed in a cylindrical shape, and is arranged so that its cylindrical axis coincides with the vertical direction. The first light guide plate holding part 52 and the second light guide plate holding part 53 are each formed in a disk shape, and are arranged so that their centers intersect the cylindrical axis of the light source holding part 51. The casing 50 is made of a light material having excellent heat dissipation and light reflectivity, for example, white polybutylene terephthalate resin.

  The light guide plate 10 is formed in a larger disk shape than the first light guide plate holding part 52 and the second light guide plate holding part 53. The light guide plate 10 is sandwiched between the first light guide plate holder 52 and the second light guide plate holder 53 with the center of the light guide plate 10 intersecting the cylindrical axis of the light source holder 51. Yes. The light guide plate 10 is disposed to face the ceiling C and is exposed to the outside. The light guide plate 10 has a circular opening 11 in the center, and a light source holding part 51 holding a light source 20 is disposed in the opening 11.

  As shown in FIG. 4, the light source 20 includes a wiring board 21 attached over the outer peripheral surface of the light source holding unit 51, a plurality of LEDs 22 mounted at predetermined intervals on the wiring board 21, and lighting of the LEDs 22. And a lighting circuit 23 to be controlled. The wiring board 21 is composed of a flexible circuit board, and is attached to the light source holding part 51 via an insulating sheet having excellent thermal conductivity and electrical insulation. The plurality of LEDs 22 are arranged so that their optical axes Ax are orthogonal to the wiring board 21, and face the inner end face 13 of the light guide plate 10. LED22 is comprised by white LED which radiate | emits white light, for example. The lighting circuit 23 is housed inside the light source holding part 51 and is electrically connected to each LED 22 via a distribution line and a wiring pattern provided on the wiring board 21.

  The light emitted from the LED 22 enters the light guide plate 10 from the inner end surface 13 and is guided in the direction of the outer end surface 12 through the inner end surface 13 as indicated by the broken line arrows in FIG. The light is emitted from the back surface 4 to the outside. The light emitted from the back surface 4 is irradiated in the direction of the ceiling C. The light emitted from the surface 2a is irradiated in the floor surface direction opposite to the ceiling C direction.

  And in the illuminating device 100A, when the light source 20 is lit, the chromaticity changes from the inner end surface 13 to the outer end surface 12 of the light guide plate 10, so that a pendant light excellent in design can be obtained. Become. Moreover, since the light-guide plate 10 becomes transparent when the light source 20 is not turned on, it can be set as a design with an open feeling. That is, as shown in FIG. 2, since there is a gap between the light guide plate 10 and the ceiling C, it is possible to perform a space effect with an open feeling.

  FIG. 5 shows another application example of the lighting device 100, and shows an example in which the lighting device 100 is applied to a bathroom vanity. In the vanity table of FIG. 5, the illuminating device 100 is arrange | positioned at the both right and left sides of the mirror 200 located in the front. And when the light source 20 of the illuminating device 100 is not lighting, since the light-guide plate 10 becomes transparent, the state of the back side of the light-guide plate 10 can be seen, and it can be set as a design with an open feeling. In addition, when the light source 20 of the lighting device 100 is turned on, light is emitted from both sides of the mirror 200, so that the face and upper body can be efficiently illuminated regardless of the height of the user. It becomes possible.

  In addition, when the illuminating device 100 is applied to a bathroom vanity, the position of the light source 20 is not particularly limited, but for example, as illustrated in FIG. Thereby, space saving of the illuminating device 100 can be achieved. In addition, when the light source 20 is turned on, the chromaticity changes from the upper part to the lower part of the light guide plate 10, so that it is possible to provide a vanity with excellent design.

  Hereinafter, the present embodiment will be described in more detail with reference to examples and comparative examples, but the present embodiment is not limited to these examples.

[Example 1]
First, Acrydic (registered trademark) WAL-578 (solid content: 50% by mass), which is an acrylic resin manufactured by DIC Corporation, was prepared as a translucent resin. In addition, FSS-10M (solid content 30% by mass) manufactured by Ishihara Sangyo Co., Ltd., which is a dispersion of antimony-doped tin oxide (ATO), was prepared as a light absorber.

  And ATO was added so that solid content might be 40 mass parts with respect to 100 mass parts of solid content of translucent resin. Next, the coating composition was obtained by diluting the mixture with cyclohexanone so that the solid content was 10% by mass. This coating composition was applied to a substrate by spraying and dried to obtain a light guide plate of this example having a coating film having a thickness of 1 μm. As the substrate, an acrylic plate made of acrylic resin and having a length of 50 mm, a width of 70 mm, and a thickness of 2 mm was used.

[Example 2]
First, tin-doped indium oxide (ITO) nanoparticles (particle diameter: 50 nm or less) manufactured by Sigma-Aldrich were prepared as a light absorber.

  And with respect to 100 mass parts of solid content of the translucent resin same as Example 1, ITO was added so that solid content might be 40 mass parts. Next, the coating composition was obtained by diluting the mixture with cyclohexanone so that the solid content was 10% by mass. This coating composition was applied to the same substrate as in Example 1 by spraying and dried to obtain a light guide plate of this example having a coating film having a thickness of 1 μm.

[Example 3]
First, as a light absorber, passet CK-K (BET diameter: 12 nm or less), which is aluminum-doped zinc oxide (AZO) nanoparticles manufactured by Hakusui Tech Co., Ltd., was prepared.

  And AZO was added with respect to 100 mass parts of solid content of the same translucent resin as Example 1 so that solid content might be 40 mass parts. Next, the coating composition was obtained by diluting the mixture with cyclohexanone so that the solid content was 10% by mass. This coating composition was applied to the same substrate as in Example 1 by spraying and dried to obtain a light guide plate of this example having a coating film having a thickness of 1 μm.

[Example 4]
First, Denatron (registered trademark) P-800SL, a PEDOT: PSS dispersion manufactured by Nagase ChemteX Corporation, was prepared as a light absorber.

  And PEDOT: PSS dispersion was added with respect to 100 mass parts of solid content of the translucent resin same as Example 1 so that solid content might be 40 mass parts. Next, the coating composition was obtained by diluting the mixture with cyclohexanone so that the solid content was 10% by mass. This coating composition was applied to the same substrate as in Example 1 by spraying and dried to obtain a light guide plate of this example having a coating film having a thickness of 1 μm.

[Comparative example]
First, silica nanoparticles (particle diameter: 100 nm or less) manufactured by Sigma-Aldrich were prepared.

  And the nano silica fine particle was added so that solid content might be 40 mass parts with respect to 100 mass parts of solid content of the translucent resin same as Example 1. FIG. Next, the coating composition was obtained by diluting the mixture with cyclohexanone so that the solid content was 10% by mass. This coating composition was applied to the same substrate as in Example 1 by spraying and dried to obtain a light guide plate of this example having a coating film having a thickness of 1 μm.

  In addition, as a result of observing the light-guide plate of Examples 1-4 and a comparative example visually, it confirmed that all were substantially colorless and transparent.

[Evaluation]
(Total light transmittance measurement)
The total light transmittance of each wavelength in the wavelength range of 380 nm to 780 nm was measured using a spectrophotometer (Shimadzu Corporation UV-2600) for the light guide plates of Example 1, Example 2, and Comparative Example. The total light transmittance was measured at a wavelength interval of 5 nm. The measurement results are shown in FIGS.

  As shown in FIGS. 6 and 7, it can be seen that the light guide plates of Examples 1 and 2 have a reduced total light transmittance over the entire range of 380 nm to 780 nm. That is, it can be seen that visible light is absorbed by the action of the light absorber. 6 and 7 that the light guide plates of Examples 1 and 2 have wavelength dependency in the total light transmittance as compared with the substrate. And it turns out that especially the transmittance | permeability of 450 nm vicinity is low and light absorption is large. On the other hand, as shown in FIG. 8, the light guide plate of the comparative example shows that the total light transmittance hardly decreases in the entire range of 380 nm to 780 nm, and that no visible light absorption occurs.

(Chromaticity distribution measurement)
Using a two-dimensional color luminance meter (CA-2000 manufactured by Konica Minolta Co., Ltd.), the chromaticity distribution on the light guide plate of Example 1 and the light exit surface of the substrate used in Example 1 was measured. The measurement results are shown in FIG. In FIG. 9, the light source is on the lower side of the rectangular light guide plate, and is moved away from the light source as it goes from the lower side to the upper side of the light guide plate.

  As shown in FIG. 9, the chromaticity distribution of the substrate as a whole is substantially the same, and no color change is observed on the entire light exit surface. On the other hand, the light guide plate of Example 1 changes in color as it moves away from the light source. That is, it can be seen that as the light emitted from the light exit surface goes from the lower side to the upper side of the light guide plate, the x chromaticity changes continuously and the x chromaticity gradually increases. And as a result of visually observing the light guide plate of Example 1, it was confirmed that the color changed from white to yellow as it moved away from the light source.

  As described above, in the light guide plate of Example 1, light incident from the light source is repeatedly reflected inside, but only a specific wavelength is gradually absorbed by the light absorber in the process, and the chromaticity of the emitted light is continuous. You can see that it is changing.

  As described above, the contents of the present embodiment have been described according to the examples. However, the present embodiment is not limited to these descriptions, and it is obvious to those skilled in the art that various modifications and improvements are possible. is there.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Coating film 3 Visible light 10 Light guide plate 20 Light source 100 Illumination device

Claims (4)

A substrate that is transparent to visible light;
A coating film that is provided on at least one surface of the substrate and further includes a light absorber that absorbs visible light having a specific wavelength and a resin that is transparent to visible light;
A light guide plate comprising:   The light guide plate according to claim 1, wherein the light absorber is antimony-doped tin oxide.   The light guide plate according to claim 1, wherein the coating film has a thickness of 0.1 μm to 100 μm. The light guide plate according to any one of claims 1 to 3,
A light source that emits light incident on the light guide plate;
A lighting device.