JP5614707B2 - Surface light source device, light guide used therefor, and manufacturing method thereof - Google Patents

Description

  The present invention relates to an edge light type surface light source device and a light guide used for constituting the same, and particularly has a light emission function structure (light emission mechanism) formed on a main surface. The present invention relates to a light source for a surface light source device, a manufacturing method thereof, and a surface light source device using the light guide.

  The surface light source device configured using the light guide of the present invention is suitable for a backlight of a liquid crystal display device used as a display unit of a monitor such as a portable notebook personal computer or a liquid crystal television.

  A liquid crystal display device basically includes a backlight and a liquid crystal display element. As the backlight, an edge light type is often used from the viewpoint of making the liquid crystal display device compact. In an edge-light type backlight, at least one end surface of a rectangular plate-shaped light guide is used as a light incident end surface, and a linear or rod-shaped primary light source such as a straight tube fluorescent lamp along the light incident end surface Alternatively, a point-like primary light source such as a light emitting diode (LED) is disposed, and light emitted from the primary light source is incident on the light incident end face of the light guide to be introduced into the light guide. It is made to radiate | emit from the light-projection surface which is one of these two main surfaces. The light emitted from the light emitting surface of the light guide is diffused and deflected in a required direction by a light diffusing element such as a light diffusing film and a light deflecting element such as a prism sheet disposed on the light emitting surface. Light is also emitted from the back surface, which is the other of the two main surfaces of the light guide, and a light reflecting element such as a light reflecting sheet is disposed opposite the back surface to return this light to the light guide. The

  A light emission mechanism as an optical functional structure for appropriately emitting light guided through the light guide is formed on the light emission surface or the back surface of the light guide. As this light emitting mechanism, for example, a rough surface that is moderately roughened or a micro uneven structure such as a lens array forming surface in which a large number of lens arrays are arranged is used.

  In order to form such a fine concavo-convex structure, a translucent material such as a methacrylic resin is formed using a molding apparatus including a molding die member having a shape transfer surface formed by blasting or cutting. A transfer method is known (see Patent Document 1 and Patent Document 2).

  A method of using a light diffusing agent or a foam layer as a light emitting mechanism is also known. For example, Patent Document 3 discloses a light guide made of a foam foamed by application of radiation energy and thermal energy. .

  Further, in Patent Document 4, a surface of an acrylic resin plate having a weight average molecular weight of 100,000 or less is irradiated with laser light to form a large number of concave portions having a large number of fine irregularities, thereby diffusing (scattering) the surface. ) Surface light guide plate is disclosed.

International Publication No. 2005/073625 JP 2009-266830 A JP 2006-155937 A JP 2010-103068 A

  When the light emitting mechanism is formed by shape transfer from the molding die member as in the light guides of Patent Literature 1 and Patent Literature 2, it is necessary to prepare a die member for each product type. Furthermore, in order to manufacture a light guide for a surface light source device used for a large-sized liquid crystal display device such as a liquid crystal television, it is necessary to prepare a large mold member and shape the entire surface with high accuracy in the molding process. Since there is a problem that it is difficult to transfer, it is difficult to apply.

  In addition, blasting is widely used to form a micro uneven structure on a molding die, but blast processing changes the micro uneven structure formed by variations in blast particles and environmental conditions such as humidity. Therefore, there is a problem that reproducibility is difficult to obtain. In addition, when the light emitting mechanism is formed by cutting or the like, light diffusion is performed based only on the surface shape of the main surface, so the emitted light is concentrated in a specific direction, and the light diffusibility is low, that is, the half width. Becomes narrow and sharp light emission. When such a light guide for a surface light source device is used, when the surface light source device is configured in combination with an optical sheet such as a diffusion sheet and / or a prism sheet, the arrangement pattern of the micro uneven structure of the light guide is transparent. Since it is easy to see, it is difficult to obtain a high-quality surface light source device. In order to solve such a problem of seeing through the fine concavo-convex structure arrangement pattern and obtain a high-quality surface light source device, it is necessary to arrange the fine concavo-convex structure arrangement pattern of the light guide body to be smaller and denser. Design is required.

  Moreover, in the light guide plate of Patent Document 4, since the concave portion is formed by laser irradiation processing, it is possible to cope with a large number of varieties only by changing the processing data. In order to obtain a surface light source device with low diffusion efficiency and high quality because it is diffused, it is necessary to form light emitting mechanisms at a high density as in the light guides of Patent Document 1 and Patent Document 2. . As a result, the design is complicated, and it takes a long time to perform laser irradiation processing of a high-density pattern, resulting in low productivity.

  On the other hand, the light guide body of Patent Document 3 realizes light emission based on light diffusion by the foamed portion. However, in order to manufacture this light guide, both a radiation irradiation process and a heating process are required, the manufacturing process is complicated, and an additive that induces foaming is required, which causes an increase in cost. .

  One object of the present invention is to provide a light emitting mechanism having a high-efficiency light diffusing function by a simple method in view of the technical problems as described above, whereby a high-quality surface light source device can be easily obtained. An object of the present invention is to provide a light guide for a surface light source device that can be obtained and is easy to manufacture.

  Another object of the present invention is to provide a method that is advantageous for manufacturing a light guide for a surface light source device as described above, and a surface light source device that uses the light guide for a surface light source device as described above. is there.

According to the present invention, to achieve any of the above objects,
A method of manufacturing a light guide for a plate-shaped surface light source device,
Prepare a plate-shaped light guide material made of methacrylic resin with a weight average molecular weight exceeding 100,000,
A method for producing a light guide for a surface light source device, wherein a foamed surface layer is formed by laser irradiation processing on at least a part of a main surface of at least one of the light guide material;
Is provided.

  In one aspect of the present invention, the light guide material is produced by a cast plate method. In one aspect of the present invention, the methacrylic resin is a homopolymer of methyl methacrylate. In one aspect of the present invention, the methacrylic resin is a copolymer of 100 to 80 parts by weight of methyl methacrylate and 0 to 20 parts by weight of a (meth) acrylic acid ester. In one aspect of the present invention, the laser used for the laser irradiation processing is an infrared laser. In one aspect of the present invention, the infrared laser is a carbon dioxide laser. In one aspect of the present invention, the foamed surface layer has a thickness of 1 μm to 20 μm.

In addition, according to the present invention, to achieve any of the above objects,
A light guide for a plate-like surface light source device comprising a light incident end face, a light exit face, and a back face located on the opposite side of the light exit face,
At least one of the light exit surface and the back surface is formed with a foamed surface layer in at least a part of the region,
A portion of the light guide other than the foamed surface layer is made of a methacrylic resin having a weight average molecular weight exceeding 100,000,
Is provided.

  In one aspect of the present invention, the foamed surface layer has a thickness of 1 μm to 20 μm. In one aspect of the present invention, the foamed surface layer has a concave cross section including the direction of the normal to the light emitting surface or the back surface.

Furthermore, according to the present invention, to achieve any of the above objects,
A surface light source device comprising: a light guide for the surface light source device; and a primary light source disposed adjacent to a light incident end surface of the light guide.
Is provided.

  In one aspect of the present invention, the surface light source device further includes a light reflecting element disposed adjacent to the back surface of the light guide. In one aspect of the present invention, the surface light source device further includes a light deflection element disposed adjacent to the light emitting surface of the light guide. In one aspect of the present invention, the light deflection element includes a light incident surface close to the light guide and a light output surface opposite to the light input surface, and the light output surfaces are parallel to each other. It comprises a plurality of arranged prism rows.

  According to the present invention, the foamed surface layer of the light guide has an optical function of emitting the guided light from the light exit surface. In particular, the arrangement of the bubbles is substantially random and the inside of the bubbles is guided. Since the refractive index is significantly different from that of the light body material, a random and large light diffusion effect can be obtained, and thus a broad light emission with a wide half-value width can be obtained. It becomes possible to obtain a quality surface light source device. Moreover, since the light guide for surface light source devices of the present invention is obtained by subjecting a specific light guide material to laser irradiation processing, it is easy to manufacture.

It is a typical block diagram which shows one Embodiment of the surface light source device by this invention. It is a typical fragmentary sectional view which shows the light guide in the surface light source device of FIG. It is a SEM top view which shows the foaming surface layer formed in the back surface of the light guide of the surface light source device of FIG. It is a SEM cross-sectional perspective view which shows the foaming surface layer formed in the back surface of the light guide of the surface light source device of FIG. It is a typical block diagram which shows an example of the apparatus for manufacturing the plate-shaped light guide material used in the case of manufacture of the light guide for surface light source devices by this invention. FIG. 4 is a SEM plan view of a laser irradiation processing portion of a light guide material made of a methacrylic resin plate obtained by extrusion molding having a weight average molecular weight of 100,000 or less (86,000) for comparison with FIG. 3. is there. The SEM cross-sectional perspective view of the laser irradiation processing part of the light-guide body material which consists of a methacrylic resin board obtained by the extrusion molding whose weight average molecular weight is 100,000 or less (86,000) for the comparison with FIG. It is. It is the schematic of the light-guide body sample for surface light source devices produced in the Example. It is explanatory drawing of the evaluation method of the optical characteristic of a surface light source device. It is a SEM top view which shows the foaming surface layer or recessed part used as the light-projection mechanism of the light guide for surface light source devices obtained in Examples 2-4 and Comparative Examples 2-5. It is a SEM cross-sectional perspective view which shows the foaming surface layer of the light guide for surface light source devices obtained in Examples 2-4. It is a SEM top view which shows the foaming surface layer or recessed part used as the light-projection mechanism of the light guide for surface light source devices obtained in Examples 5-7 and Comparative Examples 6-9. It is a SEM top view which shows the foaming surface layer or recessed part used as the light-projection mechanism of the light guide for surface light source devices obtained in Examples 8-10 and Comparative Examples 10-13. It is a SEM top view which shows the foaming surface layer or recessed part used as the light emission mechanism of the light guide for surface light source devices obtained in Examples 11-13 and Comparative Examples 14-17. It is a SEM cross section perspective view which shows the foaming surface layer of the light guide for surface light source devices obtained in Examples 5-7. It is a SEM cross section perspective view which shows the foaming surface layer of the light guide for surface light source devices obtained in Examples 8-10. It is a SEM cross-sectional perspective view which shows the foaming surface layer of the light guide for surface light source devices obtained in Examples 11-13.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing an embodiment of a surface light source device according to the present invention, and FIG. 2 is a schematic partial sectional view showing a light guide in the surface light source device. As shown in FIG. 1, the surface light source device of the present embodiment includes an LED 22 as a point-like primary light source, a plate-shaped light guide 24 that guides light emitted from the LED, and light diffusion. An element 26, a first light deflection element 28, a second light deflection element 30, and a light reflection element 32 are provided.

  The light guide 24 has a thickness direction in the vertical direction in FIGS. 1 and 2, spreads in a direction perpendicular to the paper surface, and has a rectangular plate shape as a whole. The light guide 24 has four side end surfaces. One of the pair of side end surfaces is a light incident end surface 241, and the LEDs 22 are arranged adjacent to each other so as to face the light incident end surface. Yes. In the present embodiment, the light guide 24 has one light incident end face 241. However, the present invention is not limited to this, and if desired, both the pair of side end faces or two pairs of side end faces. All may be the light incident end face. In this case, the LEDs are arranged adjacent to each other so as to face all the light incident end faces.

  An upper surface which is one of two main surfaces substantially orthogonal to the light incident end surface 241 of the light guide 24 is a light emitting surface 242. In the present embodiment, the light emission surface 242 is a smooth surface (mirror surface), but is not limited to this, and a prism shape, a microlens shape, or the like can be imparted to the light emission surface.

  Note that a plurality of LEDs 22 may be provided. In this case, it is preferable that the plurality of LEDs 22 are arranged at an appropriate interval in a direction perpendicular to the paper surface of FIG. 1 and that the directions of the maximum intensity light of the light emitted therefrom are parallel to each other.

  A light emitting mechanism is formed on the main surface (back surface) 243 opposite to the light emitting surface 242 of the light guide 24. The light emitting mechanism includes a foam surface layer 244 formed in a partial region of the back surface 243. The foamed surface layer 244 has a concave cross section (longitudinal cross section) including the direction of the normal line of the light emitting surface 242 or the back surface 243.

  The region where the foamed surface layer 244 is formed is composed of a plurality of dot-like regions on the back surface 243. The dimensions of the dot-shaped region are, for example, a diameter of 30 μm to 1000 μm and a depth of 0.1 μm to 500 μm. The foam surface layer 244 preferably has a thickness of 1 μm to 20 μm.

  The shape of the region where the foam surface layer 244 is formed is not limited to the dot shape as described above, and may be a stripe region, that is, a linear or belt-like region. Also in this case, the description of the shape of the cross section (vertical cross section) in the case of the dot shape applies to the shape of the cross section (vertical cross section) orthogonal to the extending direction of the stripe.

  The foam surface layer 244 is formed by performing laser irradiation processing as described later using a plate-shaped light guide material made of a methacrylic resin having a weight average molecular weight exceeding 100,000 as described later. Can do.

  FIG. 3 is an SEM plan view showing an example of the foam surface layer 244, and FIG. 4 is an SEM sectional perspective view thereof. These are a SEM plan view and a SEM sectional perspective view of a laser irradiation processing portion of a light guide material made of a methacrylic resin plate obtained by cast molding having a weight average molecular weight of 61 million.

  The vertical cross-sectional shape (profile) of the foam surface layer 244 is changed by changing the laser output, the scanning speed, and the focal position (focus position) on the main surface of the light guide material in the manufacturing method as described below. Can be realized.

  The foam surface layer 244 includes a large number of bubbles, and a layer having a refractive index significantly different from that of the light guide material is included in the bubbles. Thus, the foam surface layer 244 functions as a non-uniform layer for light transmission and reflection, and functions as a light diffusion layer in its optical properties. As a result, the light that enters the light incident end surface 241 and is guided through the light guide is diffusely reflected by the foam surface layer 244, and a part of the light is emitted at an angle at which emission from the light exit surface 242 is allowed. The light exits from the light exit surface toward the exit surface 242.

  Since the foamed surface layer 244 as described above is formed in a partial region of the light guide rear surface 243, the normal direction of the light emitting surface 242 (the vertical direction in FIGS. 1 and 2) from the light emitting surface 242 ) And light having a somewhat broad directivity in the in-plane distribution including both directions orthogonal to the light incident end face 241.

  The function of the foamed surface layer 244 depends on the foamed state of the foamed surface layer 244. If the formed bubbles are too small or the number of bubbles per unit area is too small, it is difficult to obtain a good light diffusion function. The present inventors have found that as one of the factors affecting the foamed state, there is a molecular weight of a methacrylic resin constituting a plate-like light guide material subjected to laser irradiation processing. That is, by using a plate-like light guide material having a weight average molecular weight exceeding 100,000, foaming in laser irradiation processing can be easily made appropriate (that is, having a good light diffusion function). Can do. When a light guide material having a weight average molecular weight of 100,000 or less is used, bubbles formed in laser irradiation processing tend to be too small or the number of bubbles per unit area is too small.

  A plurality of regions of the foam surface layer 244 on the back surface 243 can be provided. When the area | region of the foaming surface layer 244 is dot shape, the distribution can be made into random shape, a grid shape, a zigzag shape, and a close-packed form, for example. When the area | region of the foaming surface layer 244 is stripe shape, the distribution can be made into parallel stripe shape, for example.

  The light emitting mechanism of the light guide 24 is formed by mixing and dispersing light diffusing fine particles inside the light guide 24 in combination with the foam surface layer 244 formed on the back surface 243 as described above. Things can be used. Further, the light exit surface 242 or the back surface 243 may be provided with shapes such as a prism array and a cylindrical lens array.

  The light guide 24 is a plate having a uniform thickness as shown in FIGS. 1 and 2 (thickness when the concave shape of the foam surface layer 244 on the back surface 243 is ignored). In addition, it is possible to use various cross-sectional shapes such as a wedge shape so that the thickness gradually decreases from the light incident end surface 241 toward the opposite end surface.

  The thickness of the light guide 24 is, for example, 0.3 to 15 mm.

  The light diffusing element 26 is disposed on the light emitting surface 242 of the light guide 24 and is made of, for example, a light diffusing film. When the directivity of light emitted from the light emitting surface 242 has a desired emission angle and viewing angle, the light diffusing element 26 may be omitted.

  The first light deflection element 28 is disposed on the light diffusion element 26, and the second light deflection element 30 is disposed on the first light deflection element 28. That is, the light diffusing element 26 is interposed between the first light deflecting element 28 and the light emitting surface 242 of the light guide.

  The first and second light deflecting elements 28 and 30 each include a light incident surface close to the light guide 24 and a light output surface opposite to the light incident surface, and the light output surfaces are arranged in parallel to each other. A plurality of prism rows. However, in the first light deflection element 28 and the second light deflection element 30, the extending directions of the plurality of prism rows on the light exit surface are orthogonal to each other.

  In the present embodiment, the extending direction of the plurality of prism rows on the light exit surface of the first light deflection element 28 is parallel to the light incident end surface 241, and the plurality of prism rows on the light exit surface of the second light deflection element 30 are arranged. The extending direction is perpendicular to the light incident end surface 241. However, it is not limited to this. Both the extending direction of the plurality of prism rows on the light exit surface of the first light deflection element 28 and the extending direction of the plurality of prism rows on the light exit surface of the second light deflection element 30 are both relative to the light incident end surface 241. They may be diagonal and orthogonal to each other.

  The thickness of the first and second light deflection elements 28 and 30 is, for example, 30 to 350 μm.

  In the case where the light emitted from the light exit surface 242 has a distribution peak in a required direction, the first or second light deflection elements 28 and 30 may be omitted. Further, when the angular distribution of the light emitted from the light emitting surface 242 or the light emitted from the light diffusing element 26 can be used in a required application (for example, a signboard) without requiring light deflection. May omit the first or second light deflection elements 28 and 30.

  As the light reflecting element 8, for example, a plastic sheet (light reflecting sheet) having a metal vapor deposition reflecting layer on the surface can be used. In addition, it is preferable to attach a reflective member also to end surfaces other than the end surface utilized as the light-incidence end surface of the light guide 24. FIG. When the amount of light emitted from the back surface 243 is small enough to be ignored, the light reflecting element 8 may be omitted.

  The light emitting surface of the surface light source device (the second light deflecting element 30 of the second light deflecting element 30) comprising the LED 22, the light guide 24, the light diffusing element 26, the first and second light deflecting elements 28 and 30, and the light reflecting element 32 as described above. A liquid crystal display device is configured by disposing a liquid crystal display element on the light exit surface. The liquid crystal display device is observed by an observer through the liquid crystal display element from above in FIG.

  Note that the second light diffusing element is disposed adjacent to the light exit surface of the second light deflecting element 30 to suppress glare, brightness spots, and the like that cause degradation in the quality of image display, thereby improving image display quality. Can be improved.

  Next, an embodiment of a manufacturing method according to the present invention for manufacturing the light guide for a surface light source device as described above will be described.

  First, a light guide material in which a foam surface layer is not formed on the main surface is manufactured. This light guide material is a plate-like material made of a methacrylic resin plate and has a thickness equivalent to that of the light guide 24.

  The light guide material is made of, for example, methacrylic acid on a mold that is sealed with two endless metal rotating belts disposed so as to face each other and gaskets sandwiched between the belts on both sides. It is produced by a plate making method (cast plate making method) in which methyl syrup is continuously injected and polymerized to obtain a plate.

Specifically, this method is a continuous cast plate making method as described in, for example, JP-A-8-151403,
One or more polymerization initiators are added to methyl methacrylate-based syrup having a viscosity at 20 ° C. of 100 poise or more and a polymer content of 25 to 60% by weight. Polymerization is performed using a polymerization exotherm that is spontaneously generated at a temperature substantially equal to or higher than the syrup temperature during polymerization after the polymer content reaches at least 70 wt% by heating to a temperature of A method for producing a methacrylic plate polymer,
It is.

  Here, Preferably, the temperature which is substantially the same as or higher than the syrup temperature during polymerization is 60 to 150 ° C. Preferably, the peak temperature of syrup that is polymerized by utilizing the self-generated polymerization exotherm is 105 to 140 ° C. Preferably, the mold is composed of two endless belts arranged so that the molds face each other at the same speed in the same direction, and a continuous gasket that runs between the endless belts on both sides. It is a mold to be made.

  The monomer used as a raw material for the syrup used in the present invention is methyl methacrylate alone or a monomer mixture mainly composed of methyl methacrylate. In the case of the monomer mixture, methyl methacrylate is 80% by weight or more. It is desirable to be.

  Monomers used with methyl methacrylate include ethyl methacrylate, propyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, benzyl methacrylate and other methacrylate esters, methyl acrylate, acrylic Examples include ethyl acrylate, butyl acrylate, cyclohexyl acrylate, acrylate-2-ethylhexyl, acrylate esters such as benzyl acrylate, styrene, α-methylstyrene, and the like.

  Examples of the polymerization initiator used for polymerizing the above monomers to obtain syrup include di-isopropyl peroxydicarbonate, t-butyl neodecanoate, t-butyl peroxypivalate, t Organic peroxides such as hexyl peroxypivalate, lauroyl peroxide, benzoyl peroxide, t-butyl peroxyisopropyl carbonate, t-butyl peroxybenzoate, dicumyl peroxide, di-t-butyl peroxide; 2 , 2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobisisobutyronitrile, 1,1′-azobis (1-cyclohexanecarbonitrile), 2,2′-azobis (2, Azo compounds such as 4,4-trimethylpentane). The addition amount of the polymerization initiator is usually 0.01 to 0.5% by weight based on the monomer, but is appropriately determined depending on the polymerization temperature and the target polymer conversion rate.

  In obtaining syrup, a molecular weight modifier can be used as necessary. Specifically, a primary, secondary or tertiary mercaptan having an alkyl group or a substituted alkyl group, for example, n-butyl mercaptan, i-butyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, s- Examples include butyl mercaptan, s-dodecyl mercaptan, and t-butyl mercaptan. Although the usage-amount of a molecular weight modifier is not specifically limited, It is the range of 0.01 to 0.1 weight% with respect to syrup.

  The syrup produced from the above monomers needs to have a viscosity at 20 ° C. of 100 poise or more and a polymer content of 25 to 60% by weight. When the viscosity of the syrup is less than 100 poise or the polymer content is less than 25% by weight, the polymerization time becomes long. On the other hand, when the polymer content exceeds 60% by weight, the polymerization initiator is mixed and the syrup is supplied to the mold. It becomes difficult.

  The syrup having the above-mentioned viscosity and polymer content should be produced by a known method, for example, a method described in JP-B-40-3701, JP-B-47-35307, JP-B-53-39918, etc. Can do.

  Next, as a polymerization initiator added to said syrup, the thing similar to the polymerization initiator used when obtaining the above-mentioned syrup is used. The addition amount of the polymerization initiator is usually preferably 0.03 to 0.5% by weight based on syrup.

  In addition, you may add various additives, for example, an oxidation stabilizer, a plasticizer, a dye, a pigment, a mold release agent, etc. further to the syrup used by this invention as needed.

  As a mold used to obtain the methacrylic plate-like polymer of the present invention, it is disposed so as to face up and down as described in JP-B-46-41602, JP-A-47-33495, etc. A method of continuously producing a plate-like polymer composed of two endless belts traveling at the same speed in the same direction and continuous gaskets that are sandwiched between endless belts on both sides of the belt. preferable.

  FIG. 5 is a schematic explanatory view showing an example of a polymerization apparatus used for continuously producing the methacrylic plate polymer (light guide material) of the present invention.

  An ultraviolet polymerizable viscous liquid (syrup) 2 is supplied from the supply die 1 to produce an acrylic cast sheet (light guide material) 2 '. The first film 13 is caused to travel using the feeding device 14 and the winding device 15, and the second film 16 is caused to travel using the feeding device 17 and the winding device 18. The supplied UV-polymerizable viscous liquid 2 is sandwiched between the first and second films 13 and 16, and is nipped by the upper surface pressing roll 8 and the lower surface pressing roll 8 'to form a layer having a required thickness and travel. Meanwhile, ultraviolet rays are irradiated by the ultraviolet irradiation device 4 through the first and second films 13 and 16, and further heated by the hot air heating device 10, whereby the ultraviolet polymerizable viscous liquid 2 is polymerized, and the acrylic cast sheet 2 ' It becomes.

  Next, the main surface of the light guide material obtained as described above is processed by laser light irradiation (laser irradiation processing) to form a foam surface layer 244 on the surface layer of the light guide material main surface. To do. The light guide material as described above may be a commercially available product (for example, Acrylite L000 manufactured by Mitsubishi Rayon Co., Ltd.).

As the laser used for the laser irradiation processing, it is preferable to use a laser having a good etching efficiency for the light guide material. For example, an infrared laser such as a carbon dioxide gas laser (CO ₂ laser) is used. By using an infrared laser, the laser beam irradiated by the acrylic sheet is efficiently absorbed, and the absorbed portion is heated, so that an efficient etching process is possible. The carbon dioxide laser, manufactured by Keyence Corporation CO ₂ laser marker ML-Z9520T (wavelength: 9.3 .mu.m, average output: 20W) and the like.

  As described above, the longitudinal cross-sectional shape (profile) of the foam surface layer 244 can be easily changed by changing the laser output, scanning speed, and focal position (focus position) with respect to the main surface of the light guide material. Can do.

  6 and 7 are shown for comparison with FIGS. 3 and 4 according to the present invention, respectively, and are made of a methacrylic resin plate obtained by extrusion molding having a weight average molecular weight of 86,000. It is the SEM top view and SEM cross section perspective view of the laser irradiation processing part of a light guide material. In this case, the foam surface layer was not formed. When a methacrylic resin plate produced by an extrusion molding method is used as a light guide material, the molecular weight of the polymer is lower than in the case of the present invention, so that the processing mechanism similar to that of the present invention is not obtained in laser irradiation processing. Presumed to be.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.

  In the following examples and comparative examples, the weight average molecular weight was measured as follows.

<Measurement of weight average molecular weight>
The weight average molecular weight of the acrylic sheet (methacrylic resin sheet), which is the light guide material for the surface light source device, is obtained by adding tetrahydrofuran (THF) to the sample and allowing it to stand still overnight, and then liquid chromatography (manufactured by Tosoh Corporation) Measurement was performed using a liquid chromatography model HLC-8120). The guard column is TSK guard column Super H-H manufactured by Tosoh Corporation, the separation column is two TSK-Gel Super HM-Hs manufactured by Tosoh Corporation, the solvent is THF, the flow rate is 0.6 ml / min, the detector is a differential refractometer, and the measurement temperature Was 40 ° C. and the injection volume was 10 μL. Polystyrene was used as the standard polymer.

Example 1
Acrylic cast sheet (manufactured by Mitsubishi Rayon Co., Ltd. ACRYLITE L000 thickness 4mm weight average molecular weight 610,000) surface, manufactured by Keyence Corporation CO ₂ laser marker ML-Z9520T (wavelength: 9.3 .mu.m, average output: 20W) laser irradiation using a Processing was performed to form dot-shaped recesses. The laser irradiation conditions were an output of 80%, a scanning speed of 500 mm / sec, and a focal position as a processed surface. The surface shape and cross-sectional shape of the obtained recess were observed with a scanning electron microscope (S-4300SE / N scanning electron microscope, hereinafter referred to as SEM, manufactured by Hitachi High-Technologies Corporation).

(Comparative Example 1)
The same method as in Example 1 except that acrylic resin pellets (Acrypet VH000 manufactured by Mitsubishi Rayon Co., Ltd., weight average molecular weight 86,000) were used as raw materials and an acrylic extruded sheet having a thickness of 4 mm obtained by a known extrusion process was used. The dot-shaped concave portions were formed by observing the surface shape and the cross-sectional shape of the concave portions.

  FIG. 3 is a plan view of an SEM image showing the foamed surface layer of the dot-shaped recess (laser irradiation processed portion) formed in Example 1, and FIG. 4 is the dot-shaped recess (laser irradiation processed portion) formed in Example 1. It is a SEM image section perspective view showing a foaming surface layer. 6 is a plan view of an SEM image showing the dot-shaped recess (laser irradiation processed portion) formed in Comparative Example 1, and FIG. 7 is an SEM showing the dot-shaped recess (laser irradiation processed portion) formed in Comparative Example 1. It is an image section perspective view.

  As shown in FIGS. 6 and 7, almost no foaming is observed on the surface of the concave portion obtained by subjecting the acrylic extruded sheet having a weight average molecular weight of 100,000 or less to laser irradiation processing, and a processing surface close to a mirror surface is obtained. On the other hand, as shown in FIG. 3 and FIG. 4, the surface of the concave portion obtained by laser irradiation processing on an acrylic cast sheet having a weight average molecular weight exceeding 100,000 has many fine foams over the entire area. Is formed. The thickness of the foam surface layer obtained in Example 1 was 6.9 μm.

(Example 2)
<Production of light guide material>
In order to evaluate in detail the relationship between the weight average molecular weight of the methacrylic resin, the surface state of the laser-irradiated surface, and the optical characteristics, a light guide for a surface light source device was produced by the following method.

  UV decomposition polymerization initiator 1-hydroxy-cyclohexyl-phenyl ketone (Irgacure 184 manufactured by Ciba Specialty Chemicals) is 0.05% by weight with respect to 60% by weight of methyl methacrylate monomer, and sodium dioctylsulfosuccinate (Igacure 184 as a release agent) 0.05 wt% of Mitsui Cyanamid Co., Ltd. Aerosol OT-100) was added and dissolved at room temperature, and then 40 wt% of methyl methacrylate polymer beads (BR-80 weight average molecular weight 100,000 manufactured by Mitsubishi Rayon Co., Ltd.) was added at 80 ° C. Was dissolved by heating for 30 minutes to prepare an ultraviolet polymerizable viscous liquid 2. The mixture was allowed to stand at 50 ° C. for 2 hours in order to remove bubbles during preparation, and then naturally cooled to room temperature.

  Next, an acrylic cast sheet 2 ′ was manufactured using the ultraviolet polymerizable viscous liquid with the apparatus shown in FIG. 5. A polyethylene terephthalate film (Cosmo Shine A4100 manufactured by Toyobo Co., Ltd.) having a width of 500 mm and a thickness of 188 μm was used as the first and second films 13 and 16, and a FL30S-BL lamp manufactured by Toshiba was used as the ultraviolet irradiation device 4.

After feeding the film 13, 16 at a conveyance speed of 0.13 m / min and supplying the ultraviolet polymerizable viscous liquid 2 previously adjusted from the supply die 1 onto the film 16 in a sheet form having a width of 400 mm and a thickness of 0.46 mm, The film 13 was covered. Thereafter, ultraviolet rays are irradiated for 20 minutes by the ultraviolet irradiation device 4 at an irradiation intensity of ² mW / cm ² , heat-treated at 143 ° C. for 3 minutes by the hot air heating device 10, then air-cooled to 90 ° C. and peeled off from the films 13 and 16. As a result, an acrylic cast sheet 2 ′ having a thickness of 0.4 mm was obtained. The obtained acrylic cast sheet 2 ′ was cut into a rectangle having a width of 30 mm and a length of 100 mm to produce a light guide material A1 for a surface light source device. The obtained light guide material A1 for surface light source device had a weight average molecular weight of 796,000.

<Production of light guide for surface light source device>
A schematic diagram of a sample produced in this example is shown in FIG.

Ahead of facing the light exit surface 310 of the obtained surface light source device for the light guide body material A1 in the process surface (the opposite surface of the light emitting surface 310), manufactured by Keyence Corporation CO ₂ laser marker ML-Z9520T (Wavelength : 9.3 μm, average output: 20 W), output 80%, scanning speed 500 mm / sec, laser irradiation processing is performed with the laser focus position matched to the processing surface, and the concave foamed surface layer is used as a unit dot A light emitting mechanism 301 formed by arranging a plurality of the dots was provided to obtain a light guide B1 for a surface light source device. The pattern of laser irradiation processing is a dot shape as shown in the enlarged view of FIG. 8, and is parallel to the light incident end face 320 in an area of 10 mm × 10 mm centering on a position 50 mm from the light incident end face 320 and 15 mm from the side end face. Five patterns arranged in a 2.5 mm pitch in a random direction were arranged in five rows at a 2.5 mm pitch in the light guide direction.

<Observation of foam surface layer>
The magnitude | size of the concave foaming surface layer of the obtained light-projection mechanism 301 was evaluated using the laser confocal microscope (The Olympus scanning confocal laser microscope LEXT OLS-3000). Moreover, the surface shape and cross-sectional shape of the formed concave foaming surface layer were observed with a scanning electron microscope (S-4300SE / N scanning electron microscope manufactured by Hitachi High-Technologies Corporation).

<Optical evaluation>
FIG. 9 is a schematic diagram of a measurement system used for optical evaluation. The optical characteristics of the surface light source device were evaluated by the following methods.

  An LED light source 440 (one LED NSSW020BT manufactured by Nichia Corporation) that emits light at 20 mA from a constant current power supply 450 is applied to the light incident end face 402 of the light guide for measurement, and a reflection sheet 410 (UX manufactured by Teijin DuPont Films Ltd.). An area with a viewing angle of 2 degrees centered on the portion where the light emitting mechanism 401 is provided using a luminance meter 460 (luminance meter BM-7 manufactured by TOPCON) with a thickness of 225 μm) disposed on the surface opposite to the light emitting surface The luminance distribution of the light emitted from the light exit surface was measured at a light output angle from −90 degrees to 90 degrees on a plane parallel to the light guide direction and perpendicular to the light guide surface. As for the emission direction, the normal direction is 0 degree, the direction of the light incident end face as viewed from the light emission mechanism is-(minus), and the opposite direction is + (plus).

Example 3
A light guide material A2 for a surface light source device having a weight average molecular weight of 196,000 was prepared in the same manner as in Example 2 except that 0.05 wt% of octyl mercaptan was added to prepare an ultraviolet polymerizable viscous liquid. did. A2 was processed by the same method as in Example 2 to produce a light guide B2 for a surface light source device, and observation of the concave foamed surface layer and optical evaluation were performed.

Example 4
A light guide material A3 for a surface light source device having a weight average molecular weight of 116,000 is produced in the same manner as in Example 2 except that 0.10% by weight of octyl mercaptan is added to prepare an ultraviolet polymerizable viscous liquid. did. A3 was processed by the same method as in Example 2 to produce a light guide B3 for a surface light source device, and the concave foamed surface layer was observed and optically evaluated.

(Comparative Example 2)
A light guide material A4 for a surface light source device having a weight average molecular weight of 97,000 was prepared in the same manner as in Example 2 except that 0.15% by weight of octyl mercaptan was added to prepare an ultraviolet polymerizable viscous liquid. did. A4 was processed by the same method as in Example 2 to produce a surface light source device light guide B4, and observation of the recesses and optical evaluation were performed.

(Comparative Example 3)
A light guide material A5 for a surface light source device having a weight average molecular weight of 78,000 was produced in the same manner as in Example 2 except that 0.20% by weight of octyl mercaptan was added to prepare an ultraviolet polymerizable viscous liquid. did. A5 was processed in the same manner as in Example 2 to produce a surface light source device light guide B5, and observation of the recesses and optical evaluation were performed.

(Comparative Example 4)
A light guide material A6 for a surface light source device having a weight average molecular weight of 74,000 is prepared in the same manner as in Example 2 except that 0.25% by weight of octyl mercaptan is added to prepare an ultraviolet polymerizable viscous liquid. did. A6 was processed in the same manner as in Example 2 to produce a surface light source device light guide B6, and observation of the recesses and optical evaluation were performed.

(Comparative Example 5)
A light guide material A7 for a surface light source device having a weight average molecular weight of 68,000 was produced in the same manner as in Example 2 except that 0.30% by weight of octyl mercaptan was added to prepare an ultraviolet polymerizable viscous liquid. did. A7 was processed by the same method as in Example 2 to produce a light guide B7 for a surface light source device, and observation of concave portions and optical evaluation were performed.

(Example 5)
A light source B8 for a surface light source device was produced in the same manner as in Example 2 except that the laser irradiation processing conditions were set to output 80%, scanning speed 100 mm / sec, and the laser focus position matched to the processing surface. The surface shape of the concave foam surface layer was observed.

(Example 6)
A surface light source device light guide B9 was produced in the same manner as in Example 5 except that A2 having a weight average molecular weight of 196,000 was used as the light source material for the surface light source device. The surface shape of the foamed surface layer was observed.

(Example 7)
A surface light source device light guide B10 was produced in the same manner as in Example 5 except that A3 having a weight average molecular weight of 116,000 was used as the light source material for the surface light source device. The surface shape of the foamed surface layer was observed.

(Comparative Example 6)
A surface light source device light guide B11 was produced in the same manner as in Example 5 except that A4 having a weight average molecular weight of 97,000 was used as the light source material for the surface light source device. The surface shape was observed.

(Comparative Example 7)
A surface light source device light guide B12 was produced in the same manner as in Example 5 except that A5 having a weight average molecular weight of 78,000 was used as the light source material for the surface light source device. The surface shape was observed.

(Comparative Example 8)
A surface light source device light guide B13 was produced in the same manner as in Example 5 except that A6 having a weight average molecular weight of 74,000 was used as the light source material for the surface light source device. The surface shape was observed.

(Comparative Example 9)
A surface light source device light guide B14 was prepared in the same manner as in Example 5 except that A7 having a weight average molecular weight of 68,000 was used as the light source material for the surface light source device. The surface shape was observed.

(Example 8)
A light guide B15 for a surface light source device was produced in the same manner as in Example 2 except that the laser irradiation processing conditions were set to conditions in which the output was 20%, the scanning speed was 100 mm / sec, and the laser focal position was adjusted to the processing surface. The surface shape of the concave foam surface layer was observed.

Example 9
A surface light source device light guide B15 was produced in the same manner as in Example 8 except that A2 having a weight average molecular weight of 196,000 was used as the light source material for the surface light source device. The surface shape of the foamed surface layer was observed.

(Example 10)
A surface light source device light guide B16 was produced in the same manner as in Example 8 except that A3 having a weight average molecular weight of 116,000 was used as the light source material for the surface light source device. The surface shape of the foamed surface layer was observed.

(Comparative Example 10)
A surface light source device light guide B18 was produced in the same manner as in Example 8 except that A4 having a weight average molecular weight of 97,000 was used as the light source material for the surface light source device. The surface shape was observed.

(Comparative Example 11)
A surface light source device light guide B19 was prepared in the same manner as in Example 8 except that A5 having a weight average molecular weight of 78,000 was used as the light source material for the surface light source device. The surface shape was observed.

(Comparative Example 12)
A surface light source device light guide B20 was produced in the same manner as in Example 8 except that A6 having a weight average molecular weight of 74,000 was used as the light source material for the surface light source device. The surface shape was observed.

(Comparative Example 13)
A surface light source device light guide B21 was produced in the same manner as in Example 8 except that A7 having a weight average molecular weight of 68,000 was used as the light source material for the surface light source device. The surface shape was observed.

(Example 11)
The light source for the surface light source device B22 is the same as in Example 2 except that the laser irradiation processing conditions are the same as the output 80%, the scanning speed 500 mm / sec, and the laser focus position adjusted to 10 mm above the processing surface. The surface shape of the concave foam surface layer was observed.

(Example 12)
A surface light source device light guide B23 was produced in the same manner as in Example 11 except that A2 having a weight average molecular weight of 196,000 was used as the light source material for the surface light source device. The surface shape of the foamed surface layer was observed.

(Example 13)
A surface light source device light guide B24 was produced in the same manner as in Example 11 except that A3 having a weight average molecular weight of 116,000 was used as the light source material for the surface light source device. The surface shape of the foamed surface layer was observed.

(Comparative Example 14)
A surface light source device light guide B25 was produced in the same manner as in Example 11 except that A4 having a weight average molecular weight of 97,000 was used as the light source material for the surface light source device. The surface shape was observed.

(Comparative Example 15)
A surface light source device light guide B26 was produced in the same manner as in Example 11 except that A5 having a weight average molecular weight of 78,000 was used as the light source material for the surface light source device. The surface shape was observed.

(Comparative Example 16)
A surface light source device light guide B27 was produced in the same manner as in Example 11 except that A6 having a weight average molecular weight of 74,000 was used as the light source material for the surface light source device. The surface shape was observed.

(Comparative Example 17)
A surface light source device light guide B28 was prepared in the same manner as in Example 11 except that A7 having a weight average molecular weight of 68,000 was used as the light source material for the surface light source device. The surface shape was observed.

  The test evaluation results of the light guides for surface light source devices obtained in Examples 2 to 4 and Comparative Examples 2 to 5 are shown below.

<Test evaluation results>
Regarding the surface light source device light guides B1 to B7 produced in Examples 2 to 4 and Comparative Examples 2 to 5, Table 1 shows the evaluation results of the size of the recesses, and FIG. 10 shows the observation results of the surface shapes. . Moreover, the observation result of the cross-sectional shape of the foaming surface layer of the light guides B1-B3 for surface light source devices produced in Examples 2-4 is shown in FIG.

As shown in FIGS. 10 and 11, many fine foams are formed over the entire surface of the concave portions of B1 to B3 having a weight average molecular weight exceeding 100,000, whereas the weight average molecular weight is 100,000 or less. In B4 to B7, almost no foaming is observed on the surface, and a processed surface close to a mirror surface is obtained. From this, it can be seen that when the weight average molecular weight exceeds 100,000, good foaming can be formed over the entire area of the foam surface layer.

  Table 2 summarizes the results of optical evaluation of B1 to B7. The normal luminance (luminance at an emission angle of 0 °) and the half-value width (50% or more of the emission peak value) of the light guide for each surface light source device. Angle width).

As shown in Table 2, in B4 to B7, in which foaming is hardly seen on the surface of the recess, only luminance of 30 cd / m ² or less is obtained, whereas many fine foams are formed over the entire foam surface layer. In B1-B3, luminance of 45 cd / m ² or more is obtained. From this, it can be seen that a light guide for a surface light source device having a high normal luminance can be obtained by using the manufacturing method of the present invention.

  Moreover, when the half value width of each sample is seen, it turns out that a remarkably wide half value width is obtained in B1-B3 compared with B4-B7. This is considered to be because light is emitted while being diffused by fine foaming that is well formed over the entire area of the foamed surface layer. In general, when a light guide for a surface light source device having a narrow half-value width, that is, a sharp emission pattern is used, when the surface light source device is combined with an optical sheet such as a diffusion sheet or an upward prism sheet, it is guided. Since the emission pattern of the light body is easily seen through, it is difficult to obtain a high-quality surface light source device. On the other hand, since the light guide for a surface light source device manufactured by the manufacturing method of the present invention has a wide half-value width, that is, a broad emission pattern, a high-quality surface light source device can be easily obtained.

  FIG. 12 is a diagram showing the observation results of the surface shape of the concave foamed surface layer or the concave portions of the light source bodies B8 to B14 for the surface light source devices produced in Examples 5 to 7 and Comparative Examples 6 to 9.

  FIG. 13 is a diagram showing the observation results of the surface shape of the foamed surface layer or the recesses of the light source bodies B15 to B21 for surface light source devices produced in Examples 8 to 10 and Comparative Examples 10 to 13.

  FIG. 14 is a diagram showing the observation results of the surface shape of the foamed surface layer or the recesses of the light guides B22 to B28 for the surface light source devices produced in Examples 11 to 13 and Comparative Examples 14 to 17.

  FIG. 15 is a diagram illustrating observation results of the cross-sectional shapes of the foamed surface layers of the light guides B8 to B10 for the surface light source devices manufactured in Examples 5 to 7.

  FIG. 16 is a diagram showing the observation results of the cross-sectional shapes of the foamed surface layers of the light guides B15 to B17 for the surface light source devices produced in Examples 8 to 10.

  FIG. 17 is a diagram showing the observation results of the cross-sectional shapes of the foamed surface layers of the light source bodies B22 to B24 for the surface light source devices produced in Examples 11 to 13.

  12 to 17, even if the laser irradiation processing conditions (output, scanning speed, focal position) are changed, the sample having a weight average molecular weight of 100,000 as a boundary and exceeding that is fine over the entire foam surface layer. It can be seen that foaming is well formed, and below that, foaming is hardly seen and a processed surface close to a mirror surface is obtained. From this, it can be seen that the surface property of the recess formed by laser irradiation processing depends on the molecular weight of the methacrylic resin sheet which is the light guide material for the surface light source device.

1 Supply die 2 UV-polymerizable viscous liquid (syrup)
2 'Acrylic cast sheet (light guide material)
4 Ultraviolet irradiation device 8 Upper surface pressing roll 8 'Lower surface pressing roll 10 Hot air heating device 13 First film 14 Feeding device 15 Winding device 16 Second film 17 Feeding device 18 Winding device 22 LED
24 Light guide 241 Light incident end surface 242 Light exit surface 243 Back surface 244 Foam surface layer 26 Light diffusion element 28 First light deflection element 30 Second light deflection element 32 Light reflection element A1 Light guide material 301 for surface light source device Light emitting mechanism 310 Light emitting surface 320 Light incident end face B1 Light guide for surface light source device 401 Light emitting mechanism 402 Light incident end face 410 Reflective sheet 440 LED light source 450 Constant current power supply 460 Luminance meter

Claims (14)

A method of manufacturing a light guide for a plate-shaped surface light source device,
Prepare a plate-shaped light guide material made of methacrylic resin with a weight average molecular weight exceeding 100,000,
A method for producing a light guide for a surface light source device, wherein a foamed surface layer is formed by laser irradiation processing in at least a partial region of at least one main surface of the light guide material.   2. The method of manufacturing a light guide for a surface light source device according to claim 1, wherein the light guide material is produced by a cast plate method.   The method for producing a light guide for a surface light source device according to claim 1, wherein the methacrylic resin is a homopolymer of methyl methacrylate.   3. The surface light source device guide according to claim 1, wherein the methacrylic resin is a copolymer of 100 to 80 parts by weight of methyl methacrylate and 0 to 20 parts by weight of (meth) acrylic acid ester. Manufacturing method of light body.   The method for manufacturing a light guide for a surface light source device according to any one of claims 1 to 4, wherein a laser used for the laser irradiation processing is an infrared laser.   The method for manufacturing a light guide for a surface light source device according to claim 5, wherein the infrared laser is a carbon dioxide gas laser.   The method of manufacturing a light guide for a surface light source device according to claim 1, wherein the foamed surface layer has a thickness of 1 μm to 20 μm. A light guide for a plate-like surface light source device comprising a light incident end face, a light exit face, and a back face located on the opposite side of the light exit face,
At least one of the light exit surface and the back surface is formed with a foamed surface layer in at least a part of the region,
A portion of the light guide other than the foamed surface layer is made of a methacrylic resin having a weight average molecular weight exceeding 100,000.   The light guide for a surface light source device according to claim 8, wherein the foamed surface layer has a thickness of 1 μm to 20 μm.   The light guide for a surface light source device according to claim 8 or 9, wherein the foamed surface layer has a concave shape in a cross section including a direction of a normal line of the light emitting surface or the back surface.   A light guide for a surface light source device according to any one of claims 8 to 10, and a primary light source disposed adjacent to a light incident end face of the light guide. Surface light source device.   The surface light source device according to claim 11, further comprising a light reflecting element disposed adjacent to a back surface of the light guide.   The surface light source device according to claim 11 or 12, further comprising a light deflection element disposed adjacent to a light emitting surface of the light guide.   The light deflection element includes a light incident surface close to the light guide and a light output surface opposite to the light incident surface, and the light output surface includes a plurality of prism rows arranged in parallel to each other. The surface light source device according to claim 13, comprising: