JP2011170005A - Optical sheet and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet that can improve luminance and further prevent contamination of a roll during the manufacture of the optical sheet. <P>SOLUTION: The optical sheet 1 has a plurality of convex lenses 1c at least one side 1a of the optical sheet 1. The optical sheet 1 is formed from a resin composition containing a thermoplastic resin and a (meth)acrylic resin. The weight average molecular weight of the (meth)acrylic resin is 1,400,000 to 4,500,000. The content of the acrylic resin in the 100 wt.% of the resin composition is 0.1 to 0.3 wt.%. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical sheet that can be used to control light in, for example, a liquid crystal display device or a lighting fixture, and more specifically, an optical sheet in which a plurality of lenses are provided on at least one surface, The present invention also relates to a method for producing the optical sheet.

  Conventionally, in a liquid crystal display device or a lighting fixture, a transparent optical sheet is disposed on the light emission surface side of a light source such as a point light source or a linear light source for the purpose of light diffusion or light collection. As this type of optical sheet, a lens sheet in which a plurality of lenses are provided on the light emitting surface side of the optical sheet is widely used. After the light emitted from the light source enters the lens sheet, the exit direction of the incident light can be controlled by the shape of the lens. As a result, for example, the luminance unevenness of the liquid crystal display device is suppressed or the luminance is improved.

  As a method for producing the optical sheet, a method for forming a molding layer having a lens shape on a flexible support using an active energy ray curable resin such as an ultraviolet curable resin, and a thermoplastic resin And a method of forming a lens shape by a melt extrusion method.

  In recent years, in the above optical sheets such as a diffusion sheet and a brightness enhancement sheet, miniaturization of the lens shape has progressed in order to further improve the optical characteristics. With the miniaturization of the lens shape, it has become difficult to accurately shape the lens shape by the melt extrusion method.

  By the way, in order to improve the fluidity | liquidity of a thermoplastic resin, the method of adding an additive to a thermoplastic resin and reducing melt viscosity is known. For example, as a component for lowering the melt viscosity of polycarbonate, Patent Document 1 below has a polar group, a weight average molecular weight of 5,000 to 100,000, and a solubility parameter value of 9.3. And a fluidity modifier comprising an aromatic vinyl resin that is less than 11.5. Here, it is described that the fluidity and molding processability of polycarbonate can be improved by using the fluidity modifier.

Japanese Patent Laid-Open No. 11-181197

  When the fluidity modifier described in Patent Document 1 is used, the moldability when obtaining a molded product can be enhanced to some extent. However, when an optical sheet is obtained by the melt extrusion method using the fluidity modifier, rolls such as a shaping roll and a transport roll may be contaminated. Furthermore, the brightness of the obtained optical sheet may be lowered.

  An object of the present invention is to provide an optical sheet that can increase luminance and further suppress contamination of a roll during the production of the optical sheet, and a method for producing the optical sheet.

  According to a wide aspect of the present invention, an optical sheet having a plurality of convex lenses on at least one surface, which is formed of a resin composition containing a thermoplastic resin and a (meth) acrylic resin, The weight average molecular weight of the (meth) acrylic resin is 1.4 million to 4.5 million, and the content of the (meth) acrylic resin is 0.1 to 0.3% by weight in 100% by weight of the resin composition. An optical sheet is provided.

  On the specific situation with the optical sheet which concerns on this invention, the dynamic friction coefficient of the sheet | seat of the said resin composition and metal plate in 150 degreeC is less than 0.8.

  In another specific aspect of the optical sheet according to the present invention, the (meth) acrylic resin is an alkyl (meth) acrylate copolymer.

  In still another specific aspect of the optical sheet according to the present invention, the thermoplastic resin is polycarbonate.

  In another specific aspect of the optical sheet according to the present invention, the plurality of convex lenses are prism lenses, and the optical sheet is a prism sheet.

  Further, according to a wide aspect of the present invention, there is provided a method for producing the optical sheet by a melt extrusion method, comprising: a melt extrusion step of melt-extruding the resin composition from a mold; and the melt-extruded resin composition. There is provided a method for producing an optical sheet, comprising a shaping step of shaping so as to form the plurality of convex lenses.

  On the specific situation with the manufacturing method of the optical sheet which concerns on this invention, in the said shaping | molding process, the said melt-extruded resin composition is shape | molded, conveying with a roll.

  In another specific aspect of the optical sheet according to the present invention, in the shaping step, a shaping roll in which a plurality of concave portions corresponding to a shape obtained by inverting the shape of the plurality of convex lenses is provided on an outer peripheral side surface. The resin composition melt-extruded is shaped so as to form the plurality of convex lenses.

  The optical sheet according to the present invention is formed of a resin composition containing a thermoplastic resin and a (meth) acrylic resin, and the (meth) acrylic resin has a weight average molecular weight of 1,400,000 to 4,500,000. Since the content of the (meth) acrylic resin is 0.1 to 0.3% by weight in 100% by weight of the composition, the brightness of the optical sheet can be increased. Furthermore, contamination of the roll can be suppressed during the production of the optical sheet.

1A, 1B, and 1C are a schematic plan view, a perspective view, and a front sectional view of an optical sheet according to a first embodiment of the present invention. 2A and 2B are a schematic partial cutaway plan view and a partial cutaway front sectional view of an optical sheet according to the second embodiment of the present invention. FIG. 3 is a schematic diagram for explaining a method of manufacturing an optical sheet according to an embodiment of the present invention.

  Hereinafter, the present invention will be clarified by describing specific embodiments and examples of the present invention with reference to the drawings.

  1A to 1C are diagrams schematically showing an optical sheet according to the first embodiment of the present invention. FIG. 1A is a plan view, and FIG. 1B is a perspective view. FIG.1 (c) is front sectional drawing which follows the II line | wire in Fig.1 (a).

  The optical sheet 1 shown in FIG. 1 has a light emitting surface from which light is emitted to one surface 1a and a light incident surface from which light is incident to the other surface 1b. The light incident surface faces the light emitting surface.

  The optical sheet 1 has a plurality of lenses 1c formed in a convex shape on one surface 1a on the light emitting surface side. The optical sheet 1 does not have a lens on the other surface 1b. In the optical sheet 1, the lens 1c is a prism lens. The optical sheet 1 is a light collecting sheet and a prism sheet. The lens 1c has a substantially isosceles triangular prism shape and has a substantially isosceles triangular cross section. The lens 1c has a ridge line 1d extending in a direction orthogonal to the cross section, that is, in FIG. On one surface 1a of the optical sheet 1, the plurality of lenses 1c are arranged in parallel.

  As the prism structure in the optical sheet 1, it is preferable that the apex angle θ of the isosceles triangle of the lens 1c is in the range of 60 to 120 ° in order to exhibit a high light collecting ability. A more preferable lower limit of the apex angle θ is 70 °, and a more preferable upper limit is 110 °. When the apex angle θ satisfies the lower limit and the upper limit, the brightness of the optical sheet can be further increased.

  The distance between the apexes of the adjacent lenses 1c, 1c, that is, the groove pitch ΔW is preferably in the range of 30 to 300 μm. A more preferable lower limit of the groove pitch ΔW is 50 μm, and a more preferable upper limit is 200 μm. When the groove pitch ΔW satisfies the above lower limit, the optical sheet can be easily manufactured. When the groove pitch ΔW satisfies the above upper limit, the period and moire of the liquid crystal display cell or the color filter are hardly generated, and the appearance defect is hardly generated.

  The thickness of the optical sheet 1, that is, the thickness of the optical sheet 1 in the direction connecting the one surface 1a and the other surface 1b is not particularly limited, and is, for example, about 50 μm to 500 μm in average thickness. From the viewpoint of facilitating continuous production, the more preferable lower limit of the average thickness of the optical sheet 1 is 100 μm, and the more preferable upper limit is 400 μm.

  The other surface 1b of the optical sheet 1 is a flat surface. The flat surface is preferably a mirror surface. The structure of the other surface 1b having no lens is not particularly limited. The other surface that does not have a lens may be a flat surface, and a plurality of protrusions may be provided for the purpose of suppressing Newton's ring. Furthermore, the other surface that does not have the lens of the optical sheet may be subjected to a matting process, an embossing process, a printing process, or the like to make the other surface rough.

  In the case where protrusions are provided on the other surface of the optical sheet, a plurality of protrusions having substantially the same height may be provided regularly or irregularly (randomly). In the case where such a protrusion is provided, for example, when the optical sheet is bonded to the diffusion plate, not the entire other surface of the optical sheet but only the protrusion portion of the other surface is partially diffused. Can be adhered to. By such adhesion, the diffusion function of the diffusion plate is not hindered by the optical sheet, and as a result, the front luminance can be increased. If the protrusions are regularly arranged in a lattice shape or a straight line shape, it may interfere with a lens shape such as a prism structure on one surface to cause moire or the like. For this reason, it is preferable that the protrusions are provided irregularly. By providing projections irregularly, interference fringes are less likely to occur, so that the quality as a surface light source can be improved. The interval between the plurality of protrusions is preferably 10 μm or more. When the interval between the protrusions is 10 μm or more, it is difficult for the plurality of protrusions to be visually recognized as if they were one protrusion, and the plurality of protrusions are difficult to see with the naked eye.

  2A to 2B are views schematically showing an optical sheet according to the second embodiment of the present invention. FIG. 2A is a partially cutaway plan view. FIG. 2B is a partially cutaway front cross-sectional view taken along line II in FIG.

  The optical sheet 11 shown in FIG. 2 has a light emitting surface from which light is emitted to one surface 11a and a light incident surface from which light is incident to the other surface 11b.

  The optical sheet 11 has a plurality of convex lenses 11c on one surface 11a. In the optical sheet 11, the lens 11c is a microlens. In the optical sheet 11, a microlens array is constituted by a plurality of lenses 11c. The optical sheet 11 is a microlens array sheet. From the viewpoint of controlling the light emission direction on the entire surface of the optical sheet 11, it is desirable that the plurality of lenses 11c be arranged as densely as possible.

  The lens 11c has a convex shape protruding on one surface 11a on the light emitting surface side. In the optical sheet 11, the lens 11c has a convex shape protruding from the flat reference surface 11d of one surface 11a. The reference surface 11d is a flat surface portion located in a region other than the portion where the lens 11c is provided on the one surface 11a on the light emitting surface side.

  The shape of the plurality of convex lenses 11c is not particularly limited. From the viewpoint of controlling the light emission direction with high accuracy, the shape of the lens 11c is preferably a part of a sphere or a part of a spheroid. The shape of the lens 11c is more preferably a part of a spheroid.

  The preferable range of the thickness of the optical sheet 11 is the same as the preferable range of the thickness of the optical sheet 1.

  The distance D1 between the vertices 11e of the plurality of lenses 11c is not particularly limited. The distance D1 is preferably in the range of 30 to 1000 μm.

  The diameter D2 of the plurality of lenses 11c is not particularly limited. The diameter D2 is preferably 20 to 1000 μm. When used in a liquid crystal display device, the diameter D2 is particularly preferably 20 to 1000 μm. A preferable upper limit of the diameter D2 is 100 μm.

  The distance D3 between the adjacent lenses 11c and the gap between the lenses 11c is not particularly limited. The distance D3 is preferably 1 to 10 μm.

  The plurality of lenses 11c may be arranged periodically and in a matrix or randomly. “Matrix” means that the first direction and the first direction are periodically arranged in both the second direction forming an angle. The first direction and the second direction may not be perpendicular to each other and may be oblique. The optical sheet 11 may have a plurality of types of lenses 11c. For example, the optical sheet 11 may have a plurality of types of lenses 11c having different sizes.

  The optical sheets 1 and 11 are light transmissive. The optical sheets 1 and 11 are made of a light transmissive material. There is no particular limitation on the wavelength range of light through which the light of the optical sheets 1 and 11 passes. The wavelength region can be appropriately selected depending on the application. For example, when the optical sheets 1 and 11 are used as a light guide plate of a liquid crystal display device, generally, a visible light region of about 380 nm to 700 nm is set as a wavelength region of transmitted light.

  From the viewpoint of increasing the transparency of the optical sheets 1 and 11, the material of the optical sheets 1 and 11 is preferably transparent. It is preferable that 80% by weight or more of the material of 100% by weight of the optical sheets 1 and 11 is transparent.

  A feature of the first and second embodiments is that the optical sheets 1 and 11 are formed of a resin composition containing a thermoplastic resin and a (meth) acrylic resin (hereinafter also referred to as (meth) acrylic resin A). The weight average molecular weight of the (meth) acrylic resin A is 1.4 million to 4.5 million, and the content of the (meth) acrylic resin A is 0.1 to 0.3 weight in 100% by weight of the resin composition. It is to be%. When the optical sheet is formed of such a resin composition, the brightness of the optical sheet is increased. Furthermore, the use of the resin composition can suppress contamination of the roll during the production of the optical sheet.

  The (meth) acryl indicates acryl and methacryl.

  The thermoplastic resin contained in the resin composition is a resin other than the (meth) acrylic resin A. As for the said thermoplastic resin, only 1 type may be used and 2 or more types may be used together.

  The thermoplastic resin is not particularly limited. Examples of the thermoplastic resin include (meth) acrylic resins other than the (meth) acrylic resin A, polyolefins such as polycarbonate, polystyrene, polyvinyl chloride, polypropylene, and polymethylpentene, cyclic polyolefin, polyethylene terephthalate, polybutylene terephthalate, and polyethylene. Examples thereof include polyester resins such as naphthalate, polyamide resins, polyarylate, and polyimide. Of these, polycarbonate is preferable. By using polycarbonate, the transparency of the optical sheet can be increased, and the heat resistance and weather resistance can also be increased.

  From the viewpoint of further enhancing the transparency and brightness of the optical sheet, the content of the thermoplastic resin in the resin composition of 100% by weight is preferably in the range of 80 to 99.9% by weight. In 100% by weight of the resin composition, a more preferable lower limit of the content of the thermoplastic resin is 90% by weight, a further preferable lower limit is 95% by weight, a further preferable lower limit is 99% by weight, and a most preferable lower limit is 99.7% by weight. It is.

  As the materials 1 and 11 of the optical sheet, a weathering agent, a crosslinking aid, a reinforcing agent, or the like may be appropriately used as long as the translucency is not inhibited.

  The (meth) acrylic resin A contained in the resin composition is, for example, (meth) acrylic acid, acrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, etc. It can be obtained by polymerizing these acrylic monomers or monomers containing these as main components.

  The (meth) acrylic resin A is preferably an alkyl (meth) acrylate copolymer. The (meth) acrylic resin A is preferably an alkyl (meth) acrylate copolymer using two or more kinds of alkyl (meth) acrylates. The (meth) acrylic resin A is more preferably a methyl methacrylate-alkyl acrylate copolymer. By using such (meth) acrylic resin A, the brightness of the optical sheet can be further increased.

  The weight average molecular weight of the (meth) acrylic resin A is in the range of 1.4 million to 4.5 million. When the weight average molecular weight is less than 1,400,000, the (meth) acrylic resin may bleed out on the surface of the optical sheet and adhere to a roll or the like during the production of the optical sheet. When the weight average molecular weight exceeds 4.5 million, the fluidity of the resin composition is greatly reduced, so that film formation becomes difficult and the optical sheet itself is difficult to obtain. In particular, with the weight average molecular weight of 1.4 million of the (meth) acrylic resin A as a boundary, the contamination of the roll is significantly different during the production of the optical sheet. The more preferable lower limit of the weight average molecular weight of the (meth) acrylic resin A is 1.5 million, the more preferable upper limit is 4 million, the still more preferable upper limit is 3.5 million, and the particularly preferable upper limit is 3 million.

  In 100% by weight of the resin composition, the content of the (meth) acrylic resin A is 0.1 to 0.3% by weight. When the content of the (meth) acrylic resin A is less than 0.1% by weight, the slipperiness between the metal plate and the resin composition is lowered. For this reason, rolls, such as a metal mold | die and a shaping roll, become easy to be contaminated at the time of manufacture of an optical sheet. When content of the said (meth) acrylic resin A exceeds 0.3 weight%, the said resin composition will become cloudy easily and the brightness | luminance of an optical sheet will fall. When the content of the (meth) acrylic resin A is within the above range, the lens can be formed with high accuracy without decreasing the luminance of the optical sheet even if the lens shape is fine.

  The dynamic friction coefficient between the sheet of the resin composition and the metal plate at 150 ° C. is preferably less than 0.8. When the dynamic friction coefficient is less than 0.8, contamination of the mold and the roll can be remarkably suppressed during the production of the optical sheet. From the viewpoint of further suppressing contamination of rolls and the like, the dynamic friction coefficient between the sheet of the resin composition and the metal plate at 150 ° C. is more preferably less than 0.7, and is preferably 0.68 or less. Further preferred. In addition, the sheet | seat for measuring a dynamic friction coefficient is formed with the said resin composition. The surface on which the dynamic friction coefficient of the sheet is measured is a flat surface. The reason why the dynamic friction coefficient between the sheet and the metal plate is measured is that the roll surface at the time of obtaining the optical sheet is generally formed of metal.

  The manufacturing method of the optical sheets 1 and 11 is not particularly limited. In order to manufacture the optical sheets 1 and 11, conventionally used optical sheet manufacturing methods can be applied. Examples of the method for producing an optical sheet include a method of injection molding into a mold or a method of compression molding a sheet-like material with a mold.

  Specific examples of the method for producing the optical sheets 1 and 11 include a solution casting method and a melt molding method. Examples of the melt molding method include a melt extrusion molding method, a press molding method, and an injection molding method. In particular, the optical sheets 1 and 11 can be efficiently manufactured by adopting the melt molding method, particularly by adopting the melt extrusion molding method. Examples of the melt extrusion molding method include a T-die method and an inflation method.

  Next, the manufacturing method of the optical sheet which concerns on one Embodiment of this invention for obtaining the optical sheet 1 using a melt extrusion method is demonstrated.

  First, the resin composition for forming the optical sheet 1 is prepared.

  Next, as shown in FIG. 3, the molten resin composition is melt-extruded from the mold 22 of the melt-extrusion apparatus 21 to form a film.

  The shaping roll 24 is rotated in the direction of arrow F, and the touch roll 25 is driven to rotate in the direction indicated by arrow G. The sheet 23, which is a melt-extruded and film-formed resin composition, is guided between the shaping roll 24 and the touch roll 25. The sheet 23 is conveyed by the shaping roll 24 and the touch roll 25. The sheet 23 is guided so that one surface 23 a of the sheet 23 contacts the shaping roll 24 and the other surface 23 b of the sheet 23 contacts the touch roll 25. Instead of the touch roll 25, an air knife or electrostatic pinning may be used.

  The shaping roll 24 has a substantially cylindrical shape. A plurality of recesses are formed on the outer peripheral side surface of the shaping roll 24. The concave portion has a shape corresponding to a shape obtained by inverting the plurality of convex lenses 1c described above. The remaining region other than the portion where the plurality of concave portions of the shaping roll 24 is provided is a cylindrical curved surface.

  Therefore, when the sheet 23 passes between the shaping roll 24 and the touch roll 25, the sheet 23, which is a resin composition melt-extruded and formed into a film, forms a plurality of convex lenses 1c. So shaped. When the sheet 23 passes between the shaping roll 24 and the touch roll 25, one surface 23a of the sheet 23 is shaped. From the viewpoint of increasing the production efficiency of the optical sheet, it is preferable to mold the sheet 23 which is the resin composition that has been melt-extruded and formed into a film while being conveyed by a roll.

  The sheet 23 on which the one surface 23a is shaped is cooled by, for example, a cooling roll 26, conveyed, and wound up.

  In this manner, as shown in FIG. 1, an optical sheet 1 having a plurality of lenses 1c on one surface 1a can be obtained. According to the manufacturing method of the present embodiment, the lens 1c can be easily formed by pressing the melt-extruded sheet 23 against the shaping roll 24 and the touch roll 25.

  From the viewpoint of improving the production efficiency of the optical sheet 1, a plurality of convex lenses 1c are formed by a melt extrusion step of melt-extruding the resin composition and a sheet 23 that is the resin composition melt-extruded. It is preferable to perform in-line with the shaping | molding process shape | molded in this way.

  In the case where a plurality of protrusions are provided on the other surface of the optical sheet 1, a shaping roll in which a concave portion having a shape corresponding to a shape obtained by inverting the protrusion is provided on the outer peripheral side surface is used instead of the touch roll 25. Can do.

  Alternatively, both surfaces of the sheet 23 may be simultaneously molded by using a shaping sheet on one side and a shaping roll on the other side. Furthermore, when manufacturing the optical sheet 11 instead of the optical sheet 1, the shape of the concave portion on the outer peripheral side surface of the shaping roll may be changed to a shape corresponding to the shape obtained by inverting the lens 11c.

  Like the lenses 1c and 11c, the lens in the optical sheet is preferably a prism lens or a microlens, and more preferably a prism lens. Like the optical sheets 1 and 11, the optical sheet is preferably a prism sheet or a microlens array sheet, and is preferably a prism sheet. The optical sheet is preferably a light collecting sheet.

  The optical sheets 1 and 11 are suitably used for a liquid crystal display device. The optical sheet can be appropriately used for increasing the utilization efficiency of light from a light source in various optical devices such as a transflective display device or a television receiver. Furthermore, the optical sheet can also be used for lighting equipment.

  In the above embodiment, the prism sheet and the microlens array sheet have been described. The optical sheet according to the present invention can also be applied to an optical sheet composed of a lenticular sheet provided with a plurality of cylindrical lenses.

  Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to these examples.

  In order to manufacture a prism sheet, the following materials were prepared.

(Thermoplastic resin)
Polycarbonate: Transparent resin, model number “Panlite L-1225LL”, manufactured by Teijin Chemicals

((Meth) acrylic resin)
Four types of (meth) acrylic resins having different weight average molecular weights were prepared.

Methyl methacrylate-alkyl acrylate copolymer: weight average molecular weight 1,500,000, model number “methabrene P551A”, manufactured by Mitsubishi Rayon Co., Ltd. Methyl methacrylate-alkyl acrylate copolymer: weight average molecular weight 3,000,000, model number “methabrene P530A”, Methyl methacrylate-alkyl acrylate copolymer manufactured by Mitsubishi Rayon Co., Ltd .: weight average molecular weight 250,000, model number “methabrene P570A”, methyl methacrylate-alkyl acrylate copolymer manufactured by Mitsubishi Rayon Co., Ltd .: weight average molecular weight 800,000 model number METABLEN P501A ", manufactured by Mitsubishi Rayon Co., Ltd.

Example 1
The optical sheet 1 shown in FIG. 1 was produced by the melt extrusion method using the melt extrusion apparatus 21 shown in FIG.

  99.9 parts by weight of a transparent resin (“Panlite L-1225LL”, manufactured by Teijin Chemicals Ltd.) which is a polycarbonate, and a methyl methacrylate-alkyl acrylate copolymer having a weight average molecular weight of 1,500,000 (meth) acrylic resin ( A resin composition mixed with 0.1 part by weight of “Metabrene P551A” (manufactured by Mitsubishi Rayon Co., Ltd.) was melt-extruded from a die into a sheet to form a film. A sheet of the resin composition that has been melt-extruded and formed into a film is sandwiched between a shaping roll 24 in which concave portions having a shape corresponding to a prism shape are provided on the outer peripheral side surface and a touch roll 25 having a flat surface. The prism sheet was manufactured by pressing and conveying.

  The prism shape of the obtained prism sheet was an isosceles triangle having a vertical cross section of 90 °, and the groove pitch ΔW was 100 μm. The average thickness of the obtained prism sheet was 200 μm.

(Examples 2 to 4 and Comparative Examples 1 to 7)
Example 1 except that the blending ratio of the used polycarbonate and the (meth) acrylic resin, the presence or absence of the blending of the (meth) acrylic resin, and the type of the (meth) acrylic resin used were changed as shown in Table 1 below. In the same manner, a prism sheet was obtained.

(Evaluation)
(1) Coefficient of Dynamic Friction Using a resin composition in which the materials for obtaining the prism sheets in Examples and Comparative Examples were mixed, a sheet having a length of 50 mm, a width of 125 mm, and a thickness of 200 μm was prepared.

  Moreover, the metal plate by which the chromium plating process was given to the surface was prepared.

  Place the sheet on the chrome-plated surface of the metal plate so that the entire surface is in contact, and set the weight so that a vertical load of 200 gf is applied to the entire surface in contact with the sheet and the metal plate. The mixture was allowed to stand for 5 minutes in a state where the temperature was maintained. Thereafter, the sheet was moved at a speed of 100 m / s in a direction parallel to the contact surface between the sheet and the metal plate. The resistance at this time was evaluated using a surface property measuring instrument “HEIDON 14DR” (manufactured by Shinto Kagaku Co., Ltd.), and a dynamic friction coefficient was calculated.

(2) Front luminance increase rate The obtained prism sheet was cut into a length of 300 mm and a width of 400 mm.

  A cut prism sheet was incorporated into an edge light type backlight provided in a commercially available 19-inch liquid crystal monitor so that the ridge line direction of the lens was in the horizontal direction (horizontal direction) of the screen. Using EzContrast EI80 (manufactured by ELDIM), the front luminance of the liquid crystal monitor incorporating the prism sheet was measured. Further, the front luminance when the prism sheet was incorporated was evaluated as the front luminance increase rate with reference to the value when the prism sheet was not incorporated into the edge light type backlight.

(3) Contamination property of roll The shaping roll 24 and the touch roll 25 after manufacturing a prism sheet were observed visually, and the presence or absence of the deposit | attachment was evaluated.

  The results are shown in Table 1 below. In addition, as a comprehensive evaluation, the case where the coefficient of dynamic friction was less than 0.8, the front luminance increase rate was 142% or more, and there was no contamination of the roll was set as “◯”, and other cases were set as “X”.

  As shown in Table 1 above, it can be seen that all the prism sheets of Examples 1 to 4 have a front luminance increase rate of 142% or more and no contamination of the roll. Even if the difference in the front luminance increase rate is 1%, the influence is great.

DESCRIPTION OF SYMBOLS 1 ... Optical sheet 1a ... One surface 1b ... The other surface 1c ... Lens 1d ... Edge line 11 ... Optical sheet 11a ... One surface 11b ... The other surface 11c ... Lens 11d ... Reference surface 11e ... Vertex 21 ... Melt extrusion apparatus 22 ... Mold 23 ... Sheet 23a ... One side 23b ... The other side 24 ... Molding roll 25 ... Touch roll 26 ... Cooling roll

Claims (8)

An optical sheet having a plurality of convex lenses on at least one surface,
It is formed by a resin composition containing a thermoplastic resin and a (meth) acrylic resin,
The weight average molecular weight of the (meth) acrylic resin is 1.4 million to 4.5 million,
The optical sheet in which the content of the (meth) acrylic resin is 0.1 to 0.3% by weight in 100% by weight of the resin composition.   The optical sheet according to claim 1, wherein a coefficient of dynamic friction between the sheet of the resin composition and the metal plate at 150 ° C. is less than 0.8.   The optical sheet according to claim 1 or 2, wherein the (meth) acrylic resin is an alkyl (meth) acrylate copolymer.   The optical sheet according to claim 1, wherein the thermoplastic resin is polycarbonate. The plurality of convex lenses are prism lenses;
The optical sheet according to any one of claims 1 to 4, which is a prism sheet. It is a manufacturing method of the optical sheet according to any one of claims 1 to 5 by a melt extrusion method,
A melt extrusion step of melt extruding the resin composition from a mold;
An optical sheet manufacturing method comprising: a molding step of molding the melt-extruded resin composition so as to form the plurality of convex lenses.   The method for producing an optical sheet according to claim 6, wherein in the shaping step, the melt-extruded resin composition is shaped while being conveyed by a roll.   In the molding step, the resin composition melt-extruded using a molding roll in which a plurality of concave portions corresponding to a shape obtained by inverting the shape of the plurality of convex lenses is provided on the outer peripheral side surface, The manufacturing method of the optical sheet of Claim 6 or 7 shape | molded so that the said convex-shaped several lens may be formed.

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