JP2011112834A - Sheet-like molded article and light guide for surface light source device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light guide in which the deterioration of optical performance is suppressed, mechanical characteristic is superior and the generation of a problem such as the break due to thinness is suppressed. <P>SOLUTION: The sheet-like molded article includes a core layer 1 composed of a (meth)acrylic resin composition and a skin layer 2 composed of a polycarbonate resin on one face or both faces of the core layer. In this case, the total thickness of the sheet-like molded article is 0.05 to 1.0 mm, and the total thickness a of the sheet-like molded article and the thickness b of the skin layer satisfy the relation 1/5≥b/a≥1/100. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a light guide for a surface light source device used for a key switch of a mobile phone, a video camera, a portable game machine, a liquid crystal television, a notebook computer, and the like, and a method for manufacturing the same.

  In recent years, electronic devices such as mobile phones, notebook computers, and portable game machines are operated by irradiating light from the back of a translucent key member in order to facilitate operation of the device in a dark environment. Lighting devices that illuminate keys are used. The surface light source device used for such an illuminating device is a direct type in which a plurality of linear light sources such as fluorescent lamps and point light sources such as light emitting diodes are arranged in a housing, and a line is formed on a side end surface of a plate-like light guide There are edge light systems in which a shape light source or a point light source is arranged. However, in devices that are strongly demanded to be compact and thin, an edge light system is often used.

  Edge light type surface light source devices usually use a plate-shaped transparent material as a light guide, and light from a light source arranged facing the side end face enters the light guide from the side end face (light incident face). Then, the incident light is scattered, reflected, refracted and emitted from the light emitting surface by forming a light emitting function on the front surface (light emitting surface) or the back surface of the light guide body corresponding to the region to be illuminated.

  As the sheet-like transparent material used for the edge light type surface light source device, a (meth) acrylic resin such as a methyl methacrylate (MMA) homopolymer or copolymer having high transparency and suitable for optical applications is used. Widely used.

  As a method of processing a (meth) acrylic resin into a sheet shape, cast molding and melt extrusion molding are widely known. However, (meth) acrylic resin has a low mechanical property, so it is thinned, particularly 1 mm or less. When trying to manufacture a thin sheet, problems such as cracks have become prominent. Moreover, even if it tried to manufacture a thin sheet | seat by cast shaping | molding etc., it was difficult to manufacture a thin sheet | seat of 1 mm or less.

  As a method for achieving thinning by melt extrusion molding while preventing problems such as cracking, a method using a resin material that is superior in mechanical strength to (meth) acrylic resins is used. ) A method using a resin composition in which rubber-like particles such as acrylic rubber are dispersed in an acrylic resin, and Patent Document 2 propose a method using a polycarbonate resin.

JP 2009-149038 A JP 2007-80824 A

  However, when rubber-like particles as described in Patent Document 1 are dispersed, the dispersed rubber-like particles cause light scattering in the light guide plate. When light scattering occurs, the emitted light turns yellow (yellowing), and light transmitted through the light guide plate is attenuated by light scattering, making it difficult to transmit light over long distances. It is.

  Also, when a polycarbonate resin as described in Patent Document 2 is used, the problem of yellowing is likely to occur due to the material absorption of the polycarbonate resin. Moreover, when the grade which added the bluing agent in order to avoid this is used, the fall of light guide performance will be caused by the light absorption of a bluing agent.

  In order to solve the above-mentioned problems, in a preferred embodiment of the present invention, a core layer mainly composed of (meth) acrylic resin and a polycarbonate resin as a main component on one surface or both surfaces of the core layer. A sheet-like light guide including a skin layer, wherein the light guide has a thickness of 0.05 to 1.0 mm, the light guide has a thickness a, and the skin layer has a thickness b of 1/5. A light guide for a surface light source device is provided that satisfies the relationship of ≧ b / a ≧ 1/100.

  In general, in a structure in which a skin layer mainly composed of polycarbonate is laminated on a core layer mainly composed of (meth) acrylic resin, the refractive index of the skin layer is larger than that of the core layer. Since total reflection of light does not occur at the interface, a waveguide structure cannot be taken. Therefore, it is not normally considered to use the structure as described above in the optical field such as a light guide. However, by using a sheet-like molded product in which a material having good optical properties is a core material and a material having excellent mechanical properties is a skin material, and the thickness of the core material and skin material is in a specific range, yellowing or In addition, it is possible to suppress the occurrence of problems such as cracking due to excellent mechanical properties while suppressing deterioration in optical performance due to bluing agents, rubber particles, and the like.

  By using the present invention, it is possible to provide a light guide that is thin and has little color change while preventing problems such as cracking. In addition, since cracking hardly occurs, process passability is improved, and a thin light guide can be produced efficiently at low cost.

It is a figure which shows the sheet-like molded object (light guide) which concerns on this invention. It is a figure which shows the sheet-like molded object (light guide) which concerns on this invention. It is the figure shown about manufacture of the sheet-like molding based on this invention. It is a disassembled perspective view which shows the surface light source device for keyboard illumination which is one of the embodiments of this invention. It is the schematic of the light guide produced in the Example of this invention. It is the figure which showed the example of the measurement system of a light guide.

  The sheet-like molded product A (light guide) according to the present invention will be described with reference to FIGS. In addition, although processing, such as cut | disconnecting a sheet-like molded object in various shapes, is given and a light guide is manufactured, since there is no change in an essential sheet-like structure, in this invention, it is a sheet-like The molded product and the light guide are treated as equivalents.

  As shown in FIG. 1, the skin layer 2 covers at least one surface of the core layer 1 and is formed so that the thickness a of the entire sheet-like molded product and the thickness b of the skin layer 2 satisfy a predetermined range. However, it is more preferable that the core layer 1 is formed so as to cover both sides of the core layer 1 as shown in FIG. 2 because the difference in thermal shrinkage between materials is offset and deformation such as warpage can be reduced. . In addition, when providing the skin layer 2 on both surfaces of the core layer 1 (refer FIG. 2), let the thickness of a skin layer be the thickness of one side.

  The total thickness of the sheet-like molded product is preferably in the range of 0.05 to 1.0 mm in order to realize compactness and thinning of the device. A range of 1 to 0.5 mm is more preferable.

  The material for forming the core layer is not particularly limited as long as it has a (meth) acrylic resin as a main component. For example, a homopolymer of methyl methacrylate (PMMA) or a copolymer is used as a main component. be able to. In the case of using a methyl methacrylate copolymer, the content of methyl methacrylate units is preferably 50% by mass or more. Examples of the copolymerizable monomer include acrylic acid esters such as methyl acrylate, ethyl acrylate, and n-butyl acrylate, and methacrylates such as ethyl methacrylate, propyl methacrylate, and cyclohexyl methacrylate, Examples include maleimides, acrylic acid, methacrylic acid, maleic anhydride, and styrene. Among these, it is preferable to configure PMMA as a main component because it is excellent in translucency and durability and is inexpensive.

  The material for forming the skin layer is not particularly limited as long as it has a polycarbonate resin as a main component, but the polycarbonate resin tends to cause yellowing of light transmitted through the resin due to material characteristics. It is preferable to use a grade containing a bluing agent. In order to obtain good optical properties, it is preferable to make the layer ratio of the skin layer to the thickness of the core layer as small as possible. The change in chromaticity of the light emitted from the light guide is acceptable if both the x value and the y value are about 0.01 or outside, but if there is a change of 0.02 or more, the color change can be visually confirmed. This is unsuitable for a surface light source device.

  The homopolymer of methyl methacrylate (PMMA) or copolymer used for the core material has a small tensile fracture strain of 10% or less. For example, a thin sheet having a thickness of 1 mm or less is formed as a single layer by a melt extrusion molding machine. If it tries to manufacture, it will be easy to produce the crack by bending when passing a cooling roll, and a process passage defect will occur easily.

  Polycarbonate resin, on the other hand, is known as one of engineering plastics with excellent mechanical properties and heat resistance, and has a very large tensile fracture strain of 40% or more, so it is placed as a skin layer on one or both sides of the core layer. It functions as a reinforcing layer, mechanical properties are improved, and process passability is improved. The tensile fracture strain is measured by a method according to Japanese Industrial Standard JIS K 7162 (1A / 5).

  As for the thickness ratio between the core layer and the skin layer, the larger the core layer ratio, the better the optical characteristics, and the larger the skin layer ratio, the better the mechanical properties can be expected. In the present invention, when the thickness of the entire sheet-shaped molded product is a and the thickness of the skin layer is b, the entire sheet-shaped molded product is configured so that the ratio b / a of both satisfies the following formula (1). The When b / a exceeds 1/5, yellowing of the light to be guided tends to occur, and when it falls below 1/100, mechanical properties are lowered and defects tend to occur during the manufacturing process. The upper limit of b / a is more preferably 1/10 or less, and further preferably 1/15 or less.

1/5 ≧ b / a ≧ 1/100 (1)
Next, the production of the sheet-like molded product according to the present invention will be described with reference to FIG. The sheet-like molded product of the present invention can be obtained by melt extrusion molding using a die having a slit-like discharge port while covering at least one surface of a core layer made of a transparent organic polymer with a skin layer. In FIG. 3, the schematic of an example of the apparatus which manufactures the light guide for surface light source devices of this invention is shown.

  The core layer material mainly composed of (meth) acrylic resin and the skin layer material mainly composed of polycarbonate resin are extruded from the melt extruders 31 and 32 and led to the feed block 33, so that at least one surface of the core material After forming a layer structure that covers with a skin material, an extruded sheet-like molded product A is obtained from the die 34. The shape of the die 33 is not particularly limited. The die 33 has a widened portion in which the flow path cross-sectional shape gradually deforms toward the slit-like discharge port, and has a predetermined width and thickness while maintaining the layer structure. The shape that can be discharged with is suitable. By using such a slit die, it becomes possible to mold while uniformly controlling the thickness of the entire sheet and the thickness of each layer. Furthermore, it is preferable to provide two or more cooling rolls 35 that can sandwich and cool the molten resin discharged from the slit die because the sheet thickness and surface smoothness can be controlled more precisely.

  In addition, in order to obtain a sheet-like molded product in which the thickness and the smoothness of the surface are precisely controlled by multilayer melt extrusion, it is very important to align the flow rates between the core layer and the skin layer during extrusion. . Therefore, it is important to select the optimal combination of materials by appropriately adjusting the melt viscosity of the materials used for the core layer and skin layer. The combination of the melt viscosity of the core material and the skin material is not particularly limited as long as the thickness and the smoothness of the surface can be precisely controlled, but a material having a lower melt viscosity than the core material is used. It is preferable to select the skin material. In the present invention, the melt viscosity of the resin material is measured by a method according to Japanese Industrial Standard JIS K7210.

  Next, a method for processing the sheet-like molded product of the present invention into a light guide for a surface light source device will be described.

  FIG. 4 is an exploded perspective view showing a surface light source device for keyboard illumination which is one embodiment of the surface light source device according to the present invention. As shown in FIG. 4, the surface light source device of the present embodiment has a plurality of LEDs 41 as point-like primary light sources and light emitted from the LEDs 41 is incident from the light incident end face 42 to guide the light. A rectangular plate-shaped light guide 40 in the XY plane that is emitted from the light exit surface 43, and a light shielding sheet 45 and a reflection sheet 46 that are disposed adjacent to the light guide are provided. The light-shielding sheet has a shape that shields parts other than the keys of the keyboard to illuminate by providing a window-shaped opening on the light-shielding sheet that matches the part that you want to illuminate. It is possible to efficiently prevent light from entering other than the desired site. A light diffusion sheet may be inserted on the light shielding sheet or between the light guide and the light shielding sheet. Further, a light shielding pattern may be printed on the light diffusing sheet with a light shielding paint to combine the functions of the light shielding sheet.

  The LED 41 is adjacent to one of a pair of edges substantially parallel to each other of the light guide 40 (left edge in FIG. 4: light incident edge), and is appropriately connected to the center in the Y direction and both sides thereof. It is arranged at a distance. A plurality of point light sources such as LEDs, which are primary light sources, can be arranged at equal intervals or close to each other according to the size of the light guide 40 or the like.

  A light incident end face 42 corresponding to the position where the LED 41 is disposed is formed at the incident end edge of the light guide 40. The light incident end face 42 formed on the light guide 40 may be formed by cutting the incident end edge into a concave shape so as to have a concave cylindrical surface shape, or a part of the light guide 40 is cut out. , It may be formed inside. The light incident end face 42 may be roughened or may have a prism shape in order to increase the spread of light in the XY plane.

  A light emission mechanism is provided on a light emission surface 43 or a back surface facing the light emission surface at a portion corresponding to a key of the light guide 40 (a portion where illumination is desired). The light emitting mechanism can use an uneven structure such as a rough surface, a dot pattern, a lens array, and a groove shape. In addition to the concavo-convex structure, printing with light scattering ink can also be used. When the uneven structure is formed as the light emitting mechanism, the thickness a of the light guide and the thickness b of the skin layer may not partially satisfy the relationship of 1/5 ≧ b / a ≧ 1/100. . However, since the sheet-like molded product A satisfies the relationship of 1/5 ≧ b / a ≧ 1/100, even if the above relationship is partially not satisfied by forming irregularities, It shall be included in the range.

  In order to process the sheet-like molded product of the present invention into a light guide for a surface light source device, it is first necessary to cut it to a size suitable for the surface light source device. As a cutting method, a method such as guillotine, heat cutting, rotary saw, cutting tool, laser cutting, milling, etc. may be applied.

  As the light incident end face, the cut cross section may be used as it is, but in order to control the spread of light more precisely, the light incident end face may be prepared by post-processing. Specifically, methods such as a shaving machine, a refiner, and vibration cutting can be used.

  As a method of forming the light emitting mechanism on the light emitting surface and the back surface of the light guide 40, a desired transfer pattern may be provided on a cooling roll at the time of melt extrusion molding, and pattern transfer may be performed simultaneously with extrusion molding. You may form by heat-pressing later using the metal mold | die etc. which have a desired surface structure. Further, the surface may be scratched using a laser processing machine or machining. Furthermore, the light emitting mechanism can be formed by using screen printing, heat or photo-curing resin.

  Examples of the present invention will be described below.

Example 1
FIG. 5 shows a schematic view of the light guide produced in this example. Using a coextrusion sheet manufacturing machine having a slit die having a width of 1200 mm and a lip opening of 0.6 mm, a light guide having a three-layer structure of skin / core / skin was formed. The core material is methacrylic resin (manufactured by Mitsubishi Rayon Co., Ltd., Acrypet VH000, tensile fracture strain 6%), and the skin material is polycarbonate resin (manufactured by Idemitsu Kosan Co., Ltd., Toughlon IR2500, tensile fracture strain 90%). Was used. The extruder temperature is set to 250 ° C. for the core layer extruder, 265 ° C. for the skin layer extruder, the slit die temperature is set to 270 ° C., and the discharge amount of the skin material / core material / skin material is 1/13/1 by volume. The molten resin discharged from the slit die is sandwiched between cooling rolls set at a roll temperature of 110 ° C. and a roll gap of 0.08 mm, and trimming a portion where the thickness of the sheet end is irregular, A sheet-like molded product A1 having a width of 980 mm and a thickness of 0.3 mm was produced. In producing the sheet-like molded product A1, there was no particular process failure such as cracking. When the cross section of the obtained sheet was observed, it was a two-kind three-layer structure in the form of (skin / core / skin) in the thickness direction, and the thickness of each layer was 20 μm / 260 μm / 20 μm.

  This sheet-like molded product A1 was cut into a rectangular shape having a width of 15 mm and a length of 300 mm, and laser etching was performed using a CO2 laser marker ML-Z9520T manufactured by Keyence Co., Ltd. at a site of 50 mm and 250 mm from the light incident end face. The laser etching pattern was a line shape parallel to the longitudinal direction of the light guide, and three patterns each having a length of 5 mm were provided in parallel at intervals of 2.5 mm. Further, the etching strength was adjusted so that the depth of the etching groove 51 far from the light incident end face was deeper than the depth of the etching groove 50 near the light incident end face. The shapes of the obtained etching grooves 50 and 51 were evaluated with a laser confocal microscope (OLS-3000 manufactured by Olympus Corporation). The light incident end face 42 was finished to a mirror surface by a milling machine using a diamond blade to obtain a light guide C1.

  FIG. 6 shows an outline of the measurement system. In the measurement, the surface subjected to the etching process of C1 was directed downward, and the non-processed surface was used as the exit surface. An LED 41 driven by a constant current power supply 60 at 20 mA (using one LED NSSW020BT manufactured by Nichia Corporation) is placed in the center of the light incident end face 42 of the light guide C1 to be measured, and a luminance meter 61 ((stock) ) Using a luminance meter BM-7) manufactured by Topcon Techno House, the luminance and chromaticity of light emitted from the emission surface in an area with a viewing angle of 2 ° centered on the site where the etching grooves 50 and 51 were provided were measured. The results are shown in Table 1.

(Comparative Example 1)
Using the coextrusion sheet manufacturing machine used in Example 1, a single-layer sheet-like molded product of methacrylic resin (manufactured by Mitsubishi Rayon Co., Ltd., Acrypet VH000, tensile fracture strain 6%) was manufactured. The extruder temperature is 250 ° C., the slit die temperature is 250 ° C., and the molten resin discharged from the slit die is sandwiched between cooling rolls set at a roll temperature of 110 ° C. and a roll gap of 0.08 mm. By trimming this portion, a sheet-like molded product A2 having a width of 980 mm and a thickness of 0.3 mm was obtained. At this time, breakage of the sheet frequently occurred at the portion where the sheet-like molded product A2 was in contact with the roll and bent, and the process passability was very poor. The light guide body C2 was obtained by processing about the part which the crack etc. have not produced among obtained sheet-like molded object A2 similarly to Example 1. FIG. The intensity of laser etching was appropriately adjusted so that the same shape as in Example 1 was obtained. The luminance and chromaticity of light emitted from the emission surface were measured in the same manner as in Example 1 using C2. The results are shown in Table 1.

(Comparative Example 2)
Using the coextrusion sheet manufacturing machine used in Example 1, a single-layer sheet-like molded product of polycarbonate resin (manufactured by Idemitsu Kosan Co., Ltd., Taflon IR 2500, tensile fracture strain 90%) was manufactured. The extruder temperature is 270 ° C., the slit die temperature is 270 ° C., and the molten resin discharged from the slit die is sandwiched between cooling rolls set at a roll temperature of 110 ° C. and a roll gap of 0.08 mm. By trimming this portion, a sheet-like molded product A3 having a width of 980 mm and a thickness of 0.3 mm was obtained. At this time, there was no particular process failure such as breakage of the sheet. By using the obtained sheet-like molded product A3 and processing in the same manner as in Example 1, a light guide C3 was obtained. The intensity of laser etching was appropriately adjusted so that the same shape as in Example 1 was obtained. The luminance and chromaticity of light emitted from the emission surface were measured in the same manner as in Example 1 using C3. The results are shown in Table 1.

(Comparative Example 3)
Using the coextrusion sheet manufacturing machine used in Example 1, a single-layer sheet-like molded product of acrylic rubber-containing methacrylic resin (manufactured by Mitsubishi Rayon Co., Ltd., Acrypet IRS404, tensile fracture strain 40%) was manufactured. The extruder temperature is 250 ° C., the slit die temperature is 250 ° C., and the molten resin discharged from the slit die is sandwiched between cooling rolls set at a roll temperature of 110 ° C. and a roll gap of 0.08 mm. By trimming this portion, a sheet-like molded product A4 having a width of 980 mm and a thickness of 0.3 mm was obtained. At this time, there was no particular process failure such as breakage of the sheet. The obtained sheet-like molded product A4 was processed in the same manner as in Example 1 to obtain a light guide C4. The intensity of laser etching was appropriately adjusted so that the same shape as in Example 1 was obtained. The luminance and chromaticity of light emitted from the emission surface were measured in the same manner as in Example 1 using C4. The results are shown in Table 1.

  Table 1 shows the evaluation results of the sheet configuration, process passability, etching groove shape, and optical characteristics of Example 1 and Comparative Examples 1 to 3. The criteria for determining process passability were “X” when troubles such as sheet breakage occurred during production, and “◯” when troubles did not occur. The criteria for determining the optical characteristics are “X” when the numerical value of the chromaticity variation (Δx and Δy) is 0.02 or more, and “◯” when the numerical value is 0.02 or less.

  As shown from these results, by using the sheet-like molded product according to the present invention, there is no problem such as cracking during sheet processing, the processability is good, and the light guide has little color change. Was shown to be obtained.

Core layer 1
Skin layer 2
Sheet-shaped molded product A
Melt extruder 31, 32
Feed block 33
Die (slit die) 34
Cooling roll 35
Light guide 40
LED 41
Light incident end face 42
Light exit surface 43
Shading sheet 45
Reflective sheet 46
Light output mechanism 47
Etching groove 50, 51
Power supply 60
Luminance meter 61

Claims (3)

A sheet-shaped light guide comprising a core layer mainly composed of (meth) acrylic resin, and a skin layer mainly composed of polycarbonate resin on one or both surfaces of the core layer,
The surface light source device, wherein the light guide has a thickness of 0.05 to 1.0 mm, and the thickness a of the light guide and the thickness b of the skin layer satisfy the following formula (1): Light guide.
1/5 ≧ b / a ≧ 1/100 (1) Having a light exit surface and a back surface on the opposite side,
A light emission mechanism is formed on at least one of the light emission surface and the back surface,
The light guide for a surface light source device according to claim 1, wherein light is selectively emitted from a portion of the light emitting surface corresponding to the light emitting mechanism.   The manufacturing method of the light guide for surface light source devices of Claim 1 thru | or 2 by multilayer melt extrusion molding.

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