JP5280513B2 - Light guide plate - Google Patents

Description

  The present invention relates to a light guide plate, a surface light source device, and a transmissive image display device.

  A transmissive image display device such as a liquid crystal display device generally has a surface light source device as a backlight. As a method of the surface light source device, there are a direct type in which a light source is provided on the back side of the light guide plate and an edge light method in which a light source is provided along the side surface of the light guide plate. The edge light method is advantageous from the viewpoint of reducing the thickness of the image display device, and development of a high-luminance and large-sized surface light source device by the edge light method is strongly desired.

  In the case of an edge light type surface light source device, light incident from the side surface of the light guide plate is reflected by the action of a reflective portion such as a white dot provided on the back side of the light guide plate, and light having an angle component greater than the critical angle is reflected. The light exits from the exit surface of the light guide plate.

  As a translucent material for forming the base material of the light guide plate (light guide plate base material), in addition to the acrylic resin, a styrene resin that is a resin containing a styrene monomer unit is used. 1 [Japanese Unexamined Patent Application Publication No. 2007-204536] discloses that a styrene resin molded into a plate shape is used as a light guide plate.

  Polycarbonate resin is also used as a translucent material for forming the light guide plate substrate. Patent Document 2 [Japanese Patent Laid-Open No. 9-020860] and Patent Document 3 [Japanese Patent Laid-Open No. 11-158364] disclose that a polycarbonate resin molded into a plate shape is used as a light guide plate.

JP 2007-204536 A Japanese Patent Laid-Open No. 9-020860 JP-A-11-158364

  When styrene-based resin or polycarbonate resin is used for the light guide plate base material, the entire light guide plate base material is yellowish, which may affect the image display of the light guide plate. In order to cope with this, for example, as disclosed in Patent Document 1, it is conceivable to add a bluing agent to a styrenic resin and form it into a plate shape to form a light guide plate base material. However, when the bluing agent is uniformly contained in the light guide plate base material, the yellowness of the entire light guide plate base material is suppressed, but the light transmittance tends to decrease.

  The present invention has been made in view of the above circumstances, and includes a light guide plate that includes a styrene-based resin or a polycarbonate resin, suppresses yellowness and suppresses a decrease in light transmittance, and the light guide plate. An object of the present invention is to provide a planar light source device and a transmissive image display device.

  That is, the present invention is provided on the back side of the light guide plate base material portion having a light exit surface that emits light and a back surface opposite to the light exit surface, and reflects light to the light output surface side. The light guide plate base material part is a multilayer body in which at least one first layer and at least one second layer are laminated, and each of the first layer and the second layer is made of styrene. System resin or polycarbonate resin, the content of the blueing agent in the first layer is 0.1 ppm to 10 ppm, the content of the blueing agent in the second layer is less than 0.1 ppm, A light guide plate is provided.

  The light guide plate having such a configuration uses a styrene-based resin or a polycarbonate resin, and it is possible to suppress yellowness and suppress a decrease in light transmittance.

  In the styrene resin contained in the first layer and the second layer, the present invention has a styrene monomer unit content of 50% by mass to 100% by mass, and a (meth) acrylic acid ester unit content. Is preferably applied when it is 0 mass% to 50 mass%.

In the light guide plate according to the present invention, d ₁ / d preferably satisfies 0.01 to 0.05, where d is the thickness of the light guide plate base material portion and d ₁ is the thickness of the first layer.

  In the light guide plate according to the present invention, it is preferable that the outermost layer on the light exit surface side of the light guide plate base material portion is the first layer.

  In the light guide plate according to the present invention, it is also preferable that the outermost layer on the back side of the light guide plate base material portion is the first layer.

  Moreover, this invention provides the surface light source device provided with the said light-guide plate and the light source part which supplies light to the side surface of a light-guide plate base-material part.

  Furthermore, the present invention is provided on the light guide plate, the light source part for supplying light to the side surface of the light guide plate base material part, and the light exiting side of the light guide plate base material part, and is illuminated with light emitted from the light output surface. Provided is a transmissive image display device including a transmissive image display unit.

  According to the present invention, a light guide plate using a styrene-based resin or a polycarbonate resin, the light guide plate that suppresses yellowness and suppresses a decrease in light transmittance, and a surface light source including the light guide plate It is possible to provide a device and a transmissive image display device.

It is an end view which shows one Embodiment of a transmissive image display apparatus. It is sectional drawing which shows one Embodiment of the light-guide plate base-material part which concerns on this embodiment. It is a schematic diagram which shows 1 process of preparation of the light-guide plate which concerns on this embodiment. It is sectional drawing which shows other embodiment of the light-guide plate base-material part which concerns on this embodiment. It is the schematic diagram which showed the measuring method of the total light transmittance in an Example.

  Hereinafter, embodiments of a light guide plate, a surface light source device, and a transmissive image display device of the present invention will be described with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted. Further, the dimensional ratios in the drawings do not necessarily match those described.

  The transmissive image display device 10 of FIG. 1 includes a surface light source device 22 having a light guide plate 11 and a transmissive image display portion 18 provided on the light exit surface 12b side of the light guide plate base material portion 12 of the light guide plate 11. Have. In the following description, as shown in FIG. 1, the arrangement direction of the surface light source device 22 and the transmissive image display unit 18 is referred to as a z direction, which is two directions orthogonal to the z direction and two directions orthogonal to each other. They are called the x direction and the y direction.

  The transmissive image display device 10 displays an image by illuminating the transmissive image display unit 18 with light emitted from the surface light source device 22. An example of the transmissive image display unit 18 is a liquid crystal display panel. In this case, the transmissive image display device 10 is a liquid crystal display device (or a liquid crystal television).

  The transmissive image display device 10 may further include a plurality of optical films 20 disposed between the light guide plate 11 and the transmissive image display unit 18. Examples of the optical film 20 are a diffusion film, a prism film, and a brightness enhancement film.

  The surface light source device 22 includes an edge light type surface light source device including a light guide plate 11 having a plate-shaped light guide plate base material portion 12 and a light source portion 14 disposed in the vicinity of a side surface 12 a of the light guide plate base material portion 12. 22. The surface light source device 22 may further include a reflection sheet 16 disposed on the back surface 12 c side of the light guide plate base material portion 12. By providing the reflection sheet 16, the light emitted from the light guide plate 11 toward the reflection sheet 16 can be returned to the light guide plate 11. As a result, the light from the light source unit 14 can be used more effectively. Further, the surface light source device 22 may be configured to include the optical film 20.

  The light source unit 14 includes a light source 14 </ b> A provided along the y direction of the side surface 12 a of the light guide plate substrate unit 12 that is the incident surface. The light source 14A may be a point light source such as a light emitting diode, a halogen lamp, and a tungsten lamp, or may be a linear light source such as a fluorescent tube. An RGB type light emitting diode that emits red light, green light, and blue light is suitably used as the light source 14A.

  The distance between the light source 14A and the side surface (incident surface) 12a of the light guide plate base 12 is usually 1 mm to 15 mm, preferably 10 mm or less, more preferably 5 mm or less. When the light source 14A is a point light source, a plurality of point light sources are linearly arranged along the y direction of the side surface 12a. The distance between adjacent point light sources is usually 1 mm to 25 mm, and is preferably 10 mm or more so that the number of point light sources can be reduced from the viewpoint of power saving.

  The light source unit 14 may further include a reflector 14 </ b> B that is provided on the side opposite to the light guide plate 11 and reflects light. By having the reflector 14B, the light from the light source 14A can be efficiently incident on the side surface 12a of the light guide plate base 12. The reflector 14B is formed from, for example, a white resin plate or a white resin film.

  In the surface light source device 22 shown in FIG. 1, the light source unit 14 is provided on only one side surface among the four side surfaces of the light guide plate base member 12. However, the light source part 14 should just be provided in the side of the light-guide plate base-material part 12. FIG. For example, the light source unit 14 may be provided for each of the pair of opposing side surfaces of the light guide plate base member 12, or may be provided on all four side surfaces that intersect the emission surface 12 b and the back surface 12 c (orthogonal in FIG. 1). On the other hand, the light source unit 14 may be provided.

  The light guide plate 11 includes a light guide plate base material portion 12 and a reflection portion 24 provided on the back surface 12 c of the light guide plate base material portion 12.

  The light guide plate base member 12 is a plate-like body having a substantially rectangular shape in plan view when viewed from the z direction. The light guide plate base 12 has an exit surface 12b that emits light and a back surface 12c opposite to the exit surface 12b.

  The thickness of the light guide plate substrate portion 12 is preferably 1 mm to 30 mm, more preferably 1 mm to 10 mm. The side surface 12a of the light guide plate base 12 is preferably smoothed by a polishing process or the like. The light guide plate base material portion 12 can be obtained by a method usually employed as a method for forming a resin plate. For example, the light guide plate base material portion 12 can be manufactured by a hot press method, a melt extrusion method, an injection molding method, or the like.

  The reflection unit 24 is provided on the back surface 12c side of the light guide plate base material portion 12, and reflects the light that has reached the back surface 12c of the light guide plate base material portion 12 to the emission surface 12b side. Examples of the reflection part 24 include diffusion dots. The diffusion dots reflect the light propagating toward the back surface 12c while diffusing the light toward the exit surface 12b. The diffusion dots are typically white dots and are formed in a pattern designed so that the emitted light is uniform. The diffusion dots can be formed by, for example, screen printing or ink jet printing.

  The reflection part 24 is not limited to a diffusing dot. For example, an uneven shape having a predetermined pattern may be formed on the back surface 12c, and the back surface 12c having the uneven shape may be used as the reflecting portion 24. Alternatively, a lens-shaped transparent or translucent dot may be provided on the back surface 12 c as the reflecting portion 24. The light can be emitted from the emission surface 12b by changing the traveling direction of the light by the effect of the lens.

  Next, the structure of the light-guide plate base-material part 12 is demonstrated in detail using FIG. The light guide plate base 12 is a laminated body (multilayer body) in which the first layer 12d and the second layer 12e are laminated in the order of the first layer 12d, the second layer 12e, and the first layer 12d. That is, the light guide plate base material portion 12 has a two-type three-layer structure in which the second layer 12e that is an intermediate layer is sandwiched between the first layers 12d that are surface layers.

  The first layer 12d and the second layer 12e are layers made of a styrene resin. An example of the styrenic resin is polystyrene. The content of the bluing agent in the first layer 12d is 0.1 ppm to 10 ppm, preferably 0.1 ppm to 1 ppm, based on the mass of the first layer 12d. The content of the bluing agent in the second layer 12e is less than 0.1 ppm, preferably 0.07 ppm or less, more preferably 0 ppm, based on the mass of the second layer 12e.

  The bluing agent is not particularly limited as long as it is usually used. For example, Macrolex Blue RR (trade name, manufactured by Bayer), Macrolex Blue 3R (trade name, manufactured by Bayer), and polysynthrene. Blue RLS (manufactured by Clariant, trade name) can be mentioned.

The thickness of the first layer 12d is such that d ₁ / d satisfies 0.01 to 0.05, where d is the thickness of the light guide plate substrate portion 12 and d ₁ is the thickness of the first layer 12d. ₁ is preferable. The light guide plate substrate portion 12, if a plurality of the first layer 12d as the structure of the two-kind three-layer shown in FIG. 2, the thickness d ₁ is the sum of the thickness d ₁ of the plurality of first layer 12d when the _{d 2,} d ₂ / d is further preferably _{d 1} satisfying 0.02 to 0.1. If the thickness of the first layer 12d is smaller than the above range, the effect of suppressing the yellowness of the light guide plate base material portion 12 tends to be reduced. The rate tends to decrease. In the light guide plate substrate portion 12 having the two-layer / three-layer structure, a specific example of the thickness (d) is 3.6 mm, and a specific example of the thickness (d ₁ ) of each first layer 12 d is 50 μm. .

  The light guide plate base material 12 has various additions such as an ultraviolet absorber, a heat stabilizer, an antioxidant, a weathering agent, a light stabilizer, a fluorescent whitening agent, and a processing stabilizer within the scope of the present invention. An agent and light diffusing particles may be included.

  An example of a method for producing the light guide plate 11 according to the present embodiment will be described with reference to FIG. FIG. 3A is a diagram illustrating a schematic configuration of the manufacturing apparatus 40 for the light guide plate base material portion 12. FIG. 3B is an enlarged view of a region b surrounded by a broken line in FIG. The light guide plate 11 is produced by forming the light guide plate substrate portion 12 with the manufacturing apparatus 40 shown in FIG.

  The configuration of the manufacturing apparatus 40 will be described. 3A includes a first extruder 41 connected to the multi-manifold die 43 and a second extruder 42 also connected to the multi-manifold die 43. In addition, in order to mold a resin sheet extruded from the multi-manifold die 43, the manufacturing apparatus 40 includes a first pressing roll 44, a second pressing roll 45, and a third pressing roll 46. As for the 1st press roll 44, the 2nd press roll 45, and the 3rd press roll 46, the axis | shaft of each roll is arrange | positioned substantially parallel. The surface of the 1st press roll 44, the 2nd press roll 45, and the 3rd press roll 46 is a mirror surface.

  Next, the manufacturing process of the light guide plate 11 will be described. First, a styrene resin and a bluing agent are prepared. Next, the styrenic resin and the bluing agent are hand blended. And the mixture is melt-kneaded at 190 degreeC-230 degreeC, and the masterbatch pellet containing a bluing agent is produced.

  The styrene resin is melt-kneaded by the first extruder 41 having a temperature in the cylinder of 200 ° C. to 245 ° C. and supplied to the multi-manifold die 43. Similarly, a pellet obtained by hand blending styrene resin and masterbatch pellets so that the concentration of the bluing agent is in the range exemplified above is melt-kneaded in the second extruder 42 having a temperature in the cylinder of 200 ° C. to 245 ° C. Then, the multi-manifold die 43 is supplied.

  The multi-manifold die is formed so that the resin supplied from the first extruder 41 becomes an intermediate layer (second layer 12e) and the resin supplied from the second extruder 42 becomes a surface layer (first layer 12d). 43 is used for coextrusion molding at a die temperature of 245 ° C. The co-extruded resin is sandwiched and cooled by the first pressing roll 44, the second pressing roll 45, and the third pressing roll 46, so that both sides of the intermediate layer as shown in FIG. The light guide plate base material portion 12 which is a laminated plate having a structure of two types and three layers provided with a surface layer is obtained.

  In this manufacturing method, the thickness of the light-guide plate base-material part 12 can be adjusted by adjusting the space | interval between the 1st press roll 44 and the 2nd press roll 45 shown to Fig.3 (a). Moreover, the surface roughness of the surface of the light-guide plate base-material part 12 can be adjusted by adjusting the space | interval between the 2nd press roll 45 and the 3rd press roll 46. FIG.

  Diffusion dots (reflecting portions 24) are formed on the back surface 12c of the obtained light guide plate substrate portion 12 by screen printing or ink jet printing to obtain the light guide plate 11. In addition, the manufacturing method of the light-guide plate 11 is not limited to this. For example, the light guide plate 11 in which the reflection portion 24 is formed on the back surface 12c of the light guide plate base material portion 12 may be directly produced by injection molding or the like. For example, when the reflection part 24 is the uneven | corrugated shape formed in the back surface 12c, in the process of manufacturing the said light-guide plate base-material part 12, the press roll by which the uneven | corrugated shape which has a predetermined pattern on the surface was provided. The light guide plate 11 may be directly produced by using the second pressing roll 45 or the third pressing roll 46. When a transparent dot or a semi-transparent dot or the like is used as the reflecting portion 24 instead of the diffusion dot, the transparent dot or the semi-transparent dot can be formed in the same manner as in the case of the diffusion dot.

  Although the manufacturing method of the light guide plate 11 when using the manufacturing apparatus 40 has been described above, the manufacturing method of the light guide plate 11 is not limited to this. For example, the light guide plate substrate 12 can be manufactured by independently manufacturing sheets containing components (resin and bluing agent) constituting each layer, and superposing and hot pressing these sheets. .

  The operation and effect of the light guide plate base material portion 12 according to the present embodiment will be described by taking as an example a case where it is applied to the transmissive image display device 10 as a part of the surface light source device 22 as shown in FIG. When the light source 14A included in the light source unit 14 emits light, the light from the light source 14A enters the light guide plate substrate unit 12 from the side surface 12a of the light guide plate substrate unit 12 facing the light source 14A. The light incident on the light guide plate base material portion 12 propagates while totally reflecting inside the light guide plate base material portion 12. A part of the light propagating through the light guide plate base material portion 12 is reflected by the reflecting portion 24 under conditions other than the total reflection condition. Therefore, the light reflected by the reflecting portion 24 is emitted from the emission surface 12b. Thereby, the emission surface 12b can emit planar light.

  The light guide plate base portion 12 included in the light guide plate 11 is a laminate in which a first layer 12d and a second layer 12e are laminated, and the main component of the first layer 12d and the second layer 12e is a styrene resin. is there. Therefore, the light guide plate 11 can be manufactured at low cost. The first layer 12d constituting a part of the light guide plate base material portion 12 includes 0.1 ppm to 10 ppm (hereinafter referred to as a predetermined amount) of a bluing agent based on the mass of the first layer 12d. Therefore, even if the light-guide plate base material part 12 is comprised by making a styrene resin into a main component, the yellowishness resulting from a styrene resin can be suppressed. As a result, the transmissive image display device 10 including the light guide plate 11 can display an image with a color closer to nature. Furthermore, while the first layer 12d contains the predetermined amount of the bluing agent, the content of the bluing agent in the second layer 12e is less than 0.1 ppm, and 0.1 ppm or more based on the mass of the second layer 12e. Since the bluing agent is not contained, a decrease in light transmittance due to the bluing agent can be suppressed. Therefore, even when the bluing agent is included in the light guide plate base material portion 12, the luminance of the light emitted from the emission surface 12b can be ensured.

  As shown in FIG. 2, when the light guide plate substrate 12 has a configuration in which the first layer 12 d as the surface layer is provided on both sides of the second layer 12 e as the intermediate layer, the light guide plate from the light source unit 14. The light incident on the side surface 12a of the base material part 12 mainly propagates through the second layer 12e. As a result, a reduction in light transmittance can be further suppressed. Further, the first layer 12d containing the bluing agent is disposed on the surface layer, which is the outermost layer in the laminated structure, so that yellowness due to the main component of the styrene resin is efficiently suppressed. As a result, the transmissive image display device 10 including the light guide plate 11 can display an image with a more natural hue.

When the light guide plate base material portion 12 is viewed from the stacking direction of the first layer 12d and the second layer 12e (z direction in FIG. 1), the amount of the bluing agent in the predetermined region is 0.1 ppm to 10 ppm. Even if the light guide plate substrate portion 12 has a plurality of first layers 12d or the content of the bluing agent in the second layer 12e is less than 0.1 ppm, the light guide plate substrate portion 12 has a yellowish color. While suppressing, the fall of the transmittance | permeability of light can be suppressed more reliably. The predetermined region is a columnar region extending in the stacking direction of the light guide plate base material portion 12 and an area of a cross section perpendicular to the stacking direction is a unit area. The unit area is, for example, 1 mm ² .

  Moreover, since the surface light source device 22 includes the light guide plate 11 having the light guide plate base material portion 12, the surface light source device 22 can emit planar light having a hue close to natural and having secured luminance. Since the transmissive image display device 10 includes the light guide plate 11, it is possible to display an image having a hue close to natural and with a sufficient luminance.

  The present invention is not limited to the embodiment described above, and can be appropriately modified without departing from the spirit of the present invention. For example, the styrene resin that is the main component of the first layer 12d and the second layer 12e is not limited to the exemplified polystyrene, and may be a resin including a styrene monomer unit. For example, the first layer 12d and the second layer 12e may be resins obtained by copolymerizing a styrene monomer and a (meth) acrylic acid ester, respectively. In the present invention, methacrylic acid ester and acrylic acid ester are collectively referred to as (meth) acrylic acid ester.

  In the form in which the main component of the first layer 12d or the second layer 12e is a resin in which a styrene monomer and a (meth) acrylic acid ester are copolymerized, the amount of the styrene monomer unit is (meth) It is more than the amount of acrylate units. That is, the resin constituting the first layer 12d and the second layer 12e has a styrene monomer unit content of 50% by mass to 100% by mass and a (meth) acrylic acid ester unit content of 0% by mass. Resins that are% to 50% by weight are preferred. Since such a styrene-based resin is derived from a styrene-based monomer unit or is likely to have a yellowish color, the present invention is preferably applied. Examples of the resin in which such a styrene monomer and a (meth) acrylic acid ester monomer are copolymerized include MS resin in which styrene and methyl methacrylate are copolymerized.

  As the styrene monomer, substituted styrene or the like can be used in addition to styrene. Examples of the substituted styrene include halogenated styrene such as chlorostyrene and bromostyrene, and alkylstyrene such as vinyltoluene and α-methylstyrene. Examples of (meth) acrylic acid esters include, in addition to methyl methacrylate, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethylhexyl methacrylate, and 2-hydroxyethyl methacrylate. And methacrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, 2-ethylhexyl acrylate, and 2-hydroxyethyl acrylate. .

  As a main component of the first layer 12d and the second layer 12e, a polycarbonate resin can also be used. Polycarbonate resin is excellent in heat resistance. Therefore, heat resistance can be imparted to the first layer 12d or the second layer 12e. The molding temperature of the light guide plate base material portion 12 can be appropriately set according to the polycarbonate resin to be used, and is, for example, 260 to 320 ° C. Examples of the polycarbonate resin include Iupilon (model number: H-3000, H-4000, HL-4000, HL-7001, HL-8000) manufactured by Mitsubishi Engineering Plastics Co., Ltd., and Macrolon (model number: 2205, 2405) manufactured by Bayer. CD2605), Teflon (model number: # 1700, # 1900, # 2200) manufactured by Idemitsu Kosan Co., Ltd., Panlite (model number: L-1225L, L-1225-Y, LV-2225Y) manufactured by Teijin Chemicals Ltd., ST-3000 manufactured by Teijin Bayer Polytech Co., Ltd., Lexan manufactured by GE Plastics (model number: 101R, 103R, 153R) and Caliber manufactured by Sumitomo Dow Co., Ltd. (model numbers: 301-15, 301-22, 301-30) Is mentioned.

  The main components of the first layer 12d and the second layer 12e may be the same or different. For example, the main components of the first layer 12d and the second layer 12e may be both polystyrene-based resins or polycarbonate resins. The main component of the first layer 12d may be a polystyrene resin, the main component of the second layer 12e may be a polycarbonate resin, or the main component of the first layer 12d is a polycarbonate resin, The main component of the layer 12e may be a polystyrene resin. As shown in FIG. 2, when there are a plurality of first layers 12d, the main components of the plurality of first layers 12d may be the same or different. For example, in the case of the light guide plate substrate 12 shown in FIG. 2, the main component of one first layer 12d may be a polystyrene-based resin, and the main component of the other first layer 12d may be a polycarbonate resin.

  In addition, the light guide plate base member 12 has a first layer 12d and a second layer 12e as shown in FIG. 4, and the first layer 12d is on the light exit surface 12b side of the light guide plate base member 12. The structure which is the outermost layer may be taken. The first layer 12d may be an intermediate layer instead of the outermost layer of the light guide plate base material portion 12. Furthermore, a configuration may be adopted in which the concentration of the bluing agent changes stepwise at the interface between the first layer 12d and the second layer 12e.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

<Raw materials>
In the examples and comparative examples, the following resins (raw materials) were used to form a resin sheet.
Thermoplastic resin A: Styrenic resin (manufactured by Toyo Styrene Co., Ltd., HRM-40)
Coloring agent B: Blueing agent (trade name “Macrolex Blue RR” manufactured by Bayer)

  After hand blending 100.0 parts by mass of thermoplastic resin A and 0.001 parts by mass of colorant B, the mixture is melt-kneaded at 190 ° C. to 230 ° C. in a granulator with a screw diameter of 30 mmφ and contains a bluing agent. Master batch pellet C was prepared.

<Example 1>
A resin sheet as the light guide plate base material portion 12 was manufactured by the manufacturing apparatus 40 shown in FIG. 100 parts by mass of thermoplastic resin A was melt-kneaded at 200 ° C. to 245 ° C. with a first extruder 41 (single screw extruder with a screw diameter of 40 mmφ). A pellet obtained by hand blending 10 parts by mass of the master batch pellet C and 90 parts by mass of the thermoplastic resin A was melt-kneaded at 200 ° C. to 245 ° C. in a second extruder 42 (single screw extruder having a screw diameter of 20 mmφ). Then, the melt-kneaded thermoplastic resin A and the pellets were continuously coextruded through a multi-manifold die 43 having a width of 250 mm at a die temperature of 245 ° C. and having a structure of two types and three layers. The extruded resin sheet was pressed with a first pressing roll 44 and a second pressing roll 45 which are mirror surface cooling rolls. Thereafter, the resin sheet was conveyed along with the rotation of the second pressing roll 45 in a state of being in close contact with the second pressing roll 45. Next, the resin sheet was pressed with the second pressing roll 45 and the third pressing roll 46. The temperature of each roll at this time was 94 ° C for the first pressing roll 44, 97 ° C for the second pressing roll 45, and 102 ° C for the third pressing roll 46. Thereby, the resin sheet as the light-guide plate base-material part 12 of Example 1 which has the surface layer (1st layer 12d) containing a bluing agent on both surfaces of a resin sheet was manufactured. Table 1 shows the form (layer structure) and thickness (d) of the resin sheet, the thickness (d ₁ ) of the surface layer, and the concentration of the bluing agent contained in the surface layer.

<Example 2>
A resin sheet was co-extruded from the multi-manifold die 43 in the same manner as in Example 1 except that a resin sheet having a structure of two types and two layers was continuously co-extruded from the multi-manifold die 43. This extruded resin sheet was molded with the first pressing roll 44, the second pressing roll 45 and the third pressing roll 46 in the same manner as in Example 1. The temperature of each roll at this time was the same as in Example 1. Thereby, the resin sheet as the light-guide plate base-material part 12 of Example 2 which has the surface layer (1st layer 12d) containing a bluing agent in the single side | surface of a resin sheet was manufactured. Table 1 shows the form and thickness (d) of the resin sheet, the thickness (d ₁ ) of the surface layer, and the concentration of the bluing agent contained in the surface layer.

<Comparative Example 1>
100 parts by mass of the thermoplastic resin A was melt-kneaded at 200 ° C. to 245 ° C. in the first extruder 41. The melt-kneaded thermoplastic resin A was continuously extruded through a multi-manifold die 43 having a width of 250 mm at a die temperature of 245 ° C. This extruded resin sheet was molded with the first pressing roll 44, the second pressing roll 45 and the third pressing roll 46 in the same manner as in Example 1. The temperature of each roll at this time was the same as in Example 1. Thereby, the resin sheet as a light-guide plate base-material part of the comparative example 1 was obtained. Table 1 shows the form and thickness (d) of the resin sheet and the concentration of the bluing agent contained in the resin sheet.

<Comparative example 2>
A pellet obtained by hand blending 90 parts by mass of the thermoplastic resin A and 10 parts by mass of the master batch pellet C was melt kneaded at 200 ° C. to 245 ° C. in the first extruder 41. Then, the melt-kneaded pellets were continuously extruded through a multi-manifold die 43 having a width of 250 mm at a die temperature of 245 ° C. This extruded resin sheet was molded with the first pressing roll 44, the second pressing roll 45 and the third pressing roll 46 in the same manner as in Example 1. The temperature of each roll at this time was the same as in Example 1. Thereby, the resin sheet as a light-guide plate base-material part of the comparative example 2 was obtained. Table 1 shows the form and thickness (d) of the resin sheet and the concentration of the bluing agent contained in the resin sheet.

<Method for Preparing Sample for Measuring Light Transmittance>
The resin sheets of Examples 1 and 2 and Comparative Examples 1 and 2 were cut out with a panel saw at a long side of 250 mm and a short side of 50 mm to obtain strip-shaped samples having a length of 250 mm × width of 50 mm × thickness of 3.6 mm.

  Next, the four side surfaces of the sample were polished by a polishing machine (manufactured by Megaro Technica, trade name, Plavity PB-500) so as not to hinder measurement of light transmittance.

<Evaluation method of light transmittance>
FIG. 5 is a schematic diagram showing a method for measuring the total light transmittance (hereinafter sometimes simply referred to as transmittance). As shown in FIG. 5A, first, the slit plate 50 is parallel to the width direction of the sample (y direction in FIG. 1) on the side surface (incident surface side) of the sample (light guide plate base material portion 12). And it installed closely so that a slit might come to the center part of the side of a sample. As the slit plate 50, a plate provided with a slit having a width w of 0.5 mm as shown in FIG. Next, the sample with the slit plate 50 was installed in a spectrophotometer (Hitachi High-Technology Corporation U-4100 type spectrophotometer). Thereafter, the sample was irradiated with light L <b> 1 having a wavelength of 300 to 800 nm through the slit plate 50. The light L2 that passed through the sample was detected at a measurement interval of 1 nm by the light receiving unit 52 of the spectrophotometer, and the total light transmittance was obtained based on the light intensity of the light L1 and L2.

  Next, the transmittance | permeability in each resin sheet obtained as mentioned above and the result of visual observation from the side surface corresponding to the side surface 12a were evaluated. The evaluation results are shown in Table 1.

  As shown in Table 1, the transmittances of the resin sheets of Examples 1 and 2 according to the present invention are similar to those of Comparative Example 1 that does not contain a bluing agent. Therefore, it turned out that the fall of the transmittance | permeability is suppressed. Furthermore, since the resin sheet of Example 1 and 2 which concerns on this invention contains a bluing agent, the yellowishness of the resin sheet was not confirmed visually from the side surface of the resin sheet. In Comparative Example 2 containing the bluing agent, the yellowness of the resin sheet was not visually confirmed from the side of the resin sheet, but the transmittance was about 30% compared to the resin sheets of Examples 1 and 2. It was decreasing.

  Therefore, in the resin sheets of Examples 1 and 2 according to the present invention, it is clear that only the surface layer contains the bluing agent, thereby suppressing the yellowness of the resin and suppressing the decrease in light transmittance. It became.

DESCRIPTION OF SYMBOLS 10 ... Transmission type image display apparatus, 11 ... Light guide plate, 12 ... Light guide plate base material part, 12a ... Side surface, 12b ... Outgoing surface, 12c ... Back surface, 12d ... First layer, 12e ... Second layer, 14 ... Light source part , 16 ... reflective sheet, 18 ... transmissive image display unit, 20 ... optical film unit, 22 ... surface light source device, 24 ... reflective unit (diffusion dot).

Claims (7)

A light guide plate substrate portion having an exit surface for emitting light and a back surface opposite to the exit surface;
A reflection part that is provided on the back side of the light guide plate base part and reflects light on the emission surface side;
With
The light guide plate substrate is a multilayer body in which at least one first layer and at least one second layer are laminated,
Each of the first layer and the second layer includes a styrene resin or a polycarbonate resin,
The content of the bluing agent in the first layer is 0.1 ppm to 10 ppm,
The light guide plate, wherein the content of the bluing agent in the second layer is less than 0.1 ppm.   In the styrene resin contained in the first layer and the second layer, the content of the styrene monomer unit is 50% by mass to 100% by mass, and the content of the (meth) acrylate unit is 0% by mass. The light-guide plate of Claim 1 comprised including the resin which is% -50 mass%. The guide according to claim 1, wherein d ₁ / d satisfies 0.01 to 0.05, where d is a thickness of the light guide plate base portion and d ₁ is a thickness of the first layer. Light board.   The light guide plate as described in any one of Claims 1-3 whose outermost layer by the side of the said output surface of the said light-guide plate base material part is a said 1st layer.   The light guide plate according to any one of claims 1 to 4, wherein the outermost layer on the back side of the light guide plate base material portion is the first layer. The light guide plate according to any one of claims 1 to 5,
A light source unit for supplying light to a side surface of the light guide plate base material unit;
A surface light source device comprising: The light guide plate according to any one of claims 1 to 5,
A light source unit for supplying light to a side surface of the light guide plate base material unit;
A transmission-type image display unit that is provided on the emission surface side of the light guide plate substrate unit and illuminated with light emitted from the emission surface;
A transmissive image display device comprising:

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