JP2011064875A - Optical sheet and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet which has high light utilization efficiency and can emit light from a light source into a desired irradiation range. <P>SOLUTION: The optical sheet 1 includes: an optical sheet body 2 which has a light incidence surface 2a and a light exit surface 2b and further has two or more convex lenses 2c at a side of the light exit surface 2b; and a light-reflecting layer 3 which is arranged at a side of the light incidence surface 2a of the optical sheet body 2 and reflects light. The light-reflecting layer 3 has two or more openings 3a and each of two or more openings 3a is provided in an area facing vertexes 2e of two or more lenses 2c. In the light-reflecting layer 3, arithmetic average roughness Ra of a surface 3b of a side opposite to a side where the optical sheet body 2 is arranged is in a range of 0.1 to 5 μm. <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 the light exit surface side, 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 exit surface side of a light source such as a point light source or a linear light source for the purpose of diffusion or condensing. 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.

  An example of the lens sheet as described above is disclosed in Patent Document 1 below. In Patent Document 1, a plurality of cylindrical lenses are arranged on the light emitting surface side, and a light reflecting layer that reflects light is provided in a partial region on the light incident surface side that is the opposite surface. An optical sheet is disclosed. Here, the light reflection layer is provided in the region surrounding the opening so that the perpendicular passing from the apex of the convex portion of the cylindrical lens to the light incident surface side passes. In other words, the light reflecting layer is provided in a region on the light incident surface side facing the region between the cylindrical lenses.

  Patent Document 2 below discloses a lens sheet in which a plurality of cylindrical lenses are arranged on the light exit surface side, and a light-shielding pattern corresponding to the light collection characteristics of the lens is provided on the light incident surface side. ing. On the light incident surface side of the lens sheet, an opening that transmits light and a light shielding portion that shields light in a region on the light incident surface side facing the region between the lenses are formed by the light shielding pattern.

JP 2000-171617 A JP 2002-182309 A

  In the lens sheets described in Patent Documents 1 and 2, a light reflection layer or a light shielding portion is provided in a region on the light incident surface side facing the region between the lenses. Accordingly, since light is incident only from an opening provided in a specific region between a plurality of light reflecting layers or between a plurality of light shielding portions, light can be efficiently emitted from a lens surface to a predetermined region.

  However, the lens sheet described in Patent Document 1 has been manufactured by a complicated manufacturing process. Therefore, it is difficult to reduce the cost of the optical sheet. In addition, the lens sheet described in Patent Document 2 has a problem that the light-use efficiency is poor and the amount of light is insufficient because the light source side surface is a light shielding layer. Although it is possible to provide a reflective layer on the light source side surface of the lens sheet described in Patent Document 2, in this case, it is very difficult to open the reflective layer by laser ablation from the lens side in the opening process.

  An object of the present invention is to provide an optical sheet that has high light utilization efficiency and emits light from a light source in a desired irradiation range, and a method for manufacturing the optical sheet.

  A limited object of the present invention is to provide an optical sheet that can be obtained by a simple manufacturing process and can improve the yield, and a method for manufacturing the optical sheet.

  According to a wide aspect of the present invention, there is provided an optical sheet body having a light incident surface and a light emitting surface, and having a plurality of convex lenses on the light emitting surface side, and on the light incident surface side of the optical sheet body. And a light reflecting layer that reflects light, the light reflecting layer having a plurality of openings, each of the plurality of openings being provided in a region facing the vertices of the plurality of lenses. And an optical sheet in which the arithmetic mean roughness Ra of the surface of the light reflecting layer opposite to the side on which the optical sheet main body is disposed is in the range of 0.1 to 5 μm. The

  In a specific aspect of the optical sheet according to the present invention, the shape of the plurality of convex lenses is a part of a sphere or a part of a spheroid.

  In another specific aspect of the optical sheet according to the present invention, the optical sheet is further provided with a light absorbing layer that is disposed between the optical sheet main body and the light reflecting layer, and absorbs light. However, it has a plurality of openings, and each of the plurality of openings is provided in a region facing the vertices of the plurality of lenses.

  The method for producing an optical sheet according to the present invention comprises a first composition layer for forming the optical sheet main body and a second composition layer for forming the light reflecting layer by a coextrusion method. The step of laminating directly or indirectly, and using a mold roll in which a plurality of concave portions corresponding to a shape obtained by inverting the shape of the convex lenses of the optical sheet body are provided on the outer peripheral side surface, A step of treating the surface of the first composition layer so as to form a plurality of lenses; a side on which the optical sheet body of the light reflecting layer obtained by the second composition layer is disposed; Treating the surface of the second composition layer so that the arithmetic mean roughness Ra of the opposite surface is 0.1 to 5 μm, and the plurality of openings in the second composition layer Forming a portion.

  In a specific aspect of the method for producing an optical sheet according to the present invention, in the step of laminating, a first composition layer for forming the optical sheet body and a third for forming the light absorption layer. And the second composition layer for forming the light reflecting layer are laminated in this order by a coextrusion method, and in the step of forming the opening, the second and third layers are formed. The plurality of openings are formed in each of the composition layers.

  In another specific aspect of the method for producing an optical sheet according to the present invention, an embossing roll is used in the step of treating the surface of the second composition layer.

  In another specific aspect of the method for producing an optical sheet according to the present invention, the step of treating the surface of the first composition layer and the step of treating the surface of the second composition layer are performed simultaneously. .

  The optical sheet according to the present invention includes the optical sheet main body and the light reflecting layer having an opening in the specific region, and the side of the light reflecting layer on which the optical sheet main body is disposed is Since the arithmetic mean roughness Ra of the surface on the opposite side is in the range of 0.1 to 5 μm, the diffuse reflection becomes strong and the light use efficiency becomes high. From another point of view, since the light use efficiency is increased, the reflective layer can be made thin, and the opening of the reflective layer can be easily formed.

  In the method for producing an optical sheet according to the present invention, a first composition layer for forming the optical sheet main body and a second composition layer for forming the light reflecting layer are formed by a coextrusion method. After directly or indirectly laminating, the surface of the first composition layer is treated to form a lens, and the second composition is used to control the arithmetic average roughness Ra of the surface of the resulting light reflecting layer. Since the surface of the physical layer is processed and the opening is formed in the second composition layer, an optical sheet can be obtained with a simple manufacturing process, and the yield can be increased.

FIGS. 1A, 1B, and 1C are a partially cutaway plan view, a partially cutaway bottom view, and a partially cutaway front sectional view of an optical sheet according to the first embodiment of the present invention. FIG. 2 is a schematic front sectional view for explaining a method of using the optical sheet according to the first embodiment of the present invention. FIG. 3 is a partially cutaway front sectional view of an optical sheet according to the second embodiment of the present invention. FIG. 4 is a schematic diagram for explaining a method of manufacturing an optical sheet according to an embodiment of the present invention. Fig.5 (a) is a schematic perspective view which shows the type | mold roll used for the manufacturing method of the optical sheet which concerns on one Embodiment of this invention, FIG.5 (b) demonstrates the recessed part of the type | mold roll surface. FIG. 5C is a partially cutaway cross-sectional view for explaining the concave portion of the mold roll. FIG. 6 is a partially cutaway front sectional view showing a laminated sheet fed from a mold roll.

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

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

  An optical sheet 1 shown in FIG. 1 includes an optical sheet body 2 and a light reflection layer 3 that is directly laminated on the optical sheet body 2. The optical sheet body 2 has a light incident surface 2a on which light is incident and a light emitting surface 2b from which light is emitted. The light reflecting layer 3 is disposed on the light incident surface 2 a side of the optical sheet body 2. The light reflecting layer 3 has a function of reflecting light.

  The optical sheet body 2 is light transmissive. The optical sheet body 2 is made of a light transmissive material. The wavelength region of the light that the light of the optical sheet body 2 transmits is not particularly limited. The wavelength region can be appropriately selected depending on the application. For example, when the optical sheet 1 is 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.

  The material of the optical sheet main body 2 is not particularly limited as long as it has optical transparency. The optical sheet body 2 is formed of a material such as resin or glass, for example. Examples of the resin include curable resins and thermoplastic resins. Since the optical sheet 1 can be obtained by a co-extrusion method, the material of the optical sheet body 2 is preferably a thermoplastic resin. The optical sheet body 2 is preferably formed of a thermoplastic resin composition. As for the material of the optical sheet main body 2, only 1 type may be used and 2 or more types may be used together.

  Examples of the thermosetting resin include (meth) acrylic resins, epoxy resins, and urethane resins.

  Examples of the thermoplastic resin include thermoplastic saturated norbornene resin, polycarbonate resin, polyester resin, polysulfone resin, polyether sulfone resin, poly (meth) acrylate methyl resin, polyarylate resin, polystyrene resin, polyacetal resin, polyvinyl chloride. Examples thereof include resins, cellulose resins, acrylonitrile resins, polyolefin resins, and olefin-maleimide copolymers.

  As a material for the optical sheet main body 2, a weathering agent, a crosslinking aid, a reinforcing agent, or the like may be appropriately used as long as the translucency is not impaired.

  The thickness of the optical sheet body 2, that is, the thickness of the optical sheet body 2 in the direction connecting the light incident surface 2 a and the light emitting surface 2 b is not particularly limited, but is preferably a thickness that focuses on the incident surface depending on the lens shape. The thickness of the optical sheet body 2 is, for example, about 20 μm or more and 500 μm or less in average thickness.

  The surface of the optical sheet main body 2 on the light incident surface 2a side is a flat surface in the present embodiment. The flat surface is preferably a mirror surface. The surface may be roughened by forming a plurality of protrusions on the surface of the optical sheet main body 2 on the light incident surface 2a side, or performing matting, embossing, or printing.

  The optical sheet main body 2 includes a plurality of convex lenses 2c on the light exit surface 2b side. In the optical sheet 1, the lens 2c is a microlens. The lens 2c is preferably a microlens. It is preferable that a microlens array is constituted by the plurality of lenses 2c. From the viewpoint of efficiently controlling the light emission direction on the entire surface of the optical sheet 1, it is desirable that the plurality of lenses 2c be arranged as densely as possible. The lens 2c is integrally formed of the same material in the optical sheet body 2.

  The lens 2c has a convex shape protruding toward the light exit surface 2b. In the optical sheet 1, the lens 2c has a convex shape protruding from the flat reference surface 2d on the light emitting surface 2b side. The reference surface 2d is a flat surface portion located in a region other than the portion where the lens 2c is provided on the light emitting surface 2b side.

  The shape of the plurality of convex lenses 2c is not particularly limited. From the viewpoint of controlling the light emission direction with high accuracy, the shape of the lens 2c is preferably a part of a sphere or a part of a spheroid. The shape of the lens 2c is more preferably a part of a spheroid.

  The distance D1 between the vertices 2e of the plurality of lenses 2c 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 2c 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.

  The distance D3 between the adjacent lenses 2c and the gap between the lenses 2c is not particularly limited. The distance D3 is preferably 1 to 10 μm.

  The plurality of lenses 2c 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 body 2 may have a plurality of types of lenses 2c. For example, the optical sheet body 2 may have a plurality of types of lenses 2c having different sizes.

  The light reflecting layer 3 disposed on the light incident surface 2a side of the optical sheet main body 2 has a plurality of openings 3a. Each of the plurality of openings 3a is provided in a region facing the apexes 2e of the plurality of lenses 2c. That is, when the optical sheet 1 is disposed so that the light exit surface 2b is on the upper side and the light incident surface 2a is on the lower side (arrangement in FIG. 1C), the apexes 2e of the plurality of lenses 2c A plurality of openings 3a are provided in the region directly below. In other words, the opening 3a is formed so as to include a region through which the perpendicular passes when the perpendicular indicated by the broken line Y in FIG. 1C is drawn from the apex 2e of the plurality of lenses 2c to the light incident surface 2a. Has been.

  Since the light reflecting layer 3 having the opening 3a is provided, light enters the optical sheet main body 2 only from the opening 3a. For this reason, it is difficult for light from an oblique direction to reach the vicinity of the apex 2e of the lens 2c with respect to the main surface of the optical sheet 1, and light incident in a direction orthogonal to the main surface is near the outer peripheral edge of the lens 2c. Hard to reach. That is, since light is reflected by the light reflecting layer 3, it is difficult for light to pass as indicated by arrows Z1 and Z2 in FIG.

  One of the main features of the present embodiment is that the arithmetic average roughness Ra of the surface 3b on the side opposite to the side where the optical sheet body 2 of the light reflecting layer 3 is disposed is in the range of 0.1 to 5 μm. It is to be. As a result, as described later, the light reaching the light reflecting layer 3 is irregularly reflected by the rough surface of the light reflecting layer 3. The irregularly reflected light is reflected by a reflector on the opposite side of the light source, enters the optical sheet again, passes through the opening, and is emitted. When the arithmetic average roughness Ra of the light reflecting layer 3 is in the range of 0.1 to 5 μm, the light reuse efficiency is increased. If the arithmetic average roughness Ra of the light reflecting layer 3 exceeds 5 μm, it is necessary to increase the thickness of the light reflecting layer 3, and it may be difficult to provide the opening 3a.

  The arithmetic average roughness Ra can be measured by a method defined in JIS B0601-2001.

  The aperture ratio of the light reflecting layer 3 is preferably in the range of 3 to 30%. The aperture ratio is 100% of the total area of the region where the light reflecting layer 3 on the light incident surface 2a side of the optical sheet body 2 is provided and the region where the light reflecting layer 3 is not provided (opening 3a). The area of the area | region where the light reflection layer 3 is not provided is shown.

  The light reflecting layer 3 reflects light from the light incident surface 2a side to the light incident surface 2a side. The light reflecting layer 3 can be formed of an appropriate light reflecting material. The light reflective material is not particularly limited. Examples of the light reflective material include a mixture of a resin and titanium oxide or magnesium oxide. Examples of the resin of the light reflecting material include the same resins as the resin as the material of the optical sheet body.

  When the optical sheet 1 is used in, for example, a liquid crystal display device, as shown in FIG. 2, a light diffusing plate 4 may be disposed before the light incident surface 2a, that is, on the light source side. When light from a light source (not shown) is irradiated in the directions of arrows A1 to A5 and B1 to B5, the light reaching the surface 3b of the light reflecting layer 3 is rough because the surface 3b of the light reflecting layer 3 is rough. As shown by arrows B <b> 1 to B <b> 5, it is irregularly reflected by the light reflecting layer 3. For example, even if light reaches the surface 3b of the light reflecting layer 3 at an angle of 30 °, the light is not necessarily reflected at an angle of 30 ° because the surface 3b of the light reflecting layer 3 is rough. . That is, the light reaching the surface 3b of the light reflecting layer 3 is irregularly reflected in various directions.

  The light that has reached the region where the light reflecting layer 3 is not provided, that is, the opening 3a of the light reflecting layer 3, passes through the opening 3a as indicated by arrows A1 to A5, and from the light incident surface 2a of the optical sheet body 2. Incident. The light incident on the optical sheet body 2 travels straight and exits from the light exit surface 2b which is the surface of the lens 2c. Further, when light is emitted from the light emitting surface 2b of the lens 2c, the traveling direction of the light changes depending on the surface shape of the lens 2c. As a result, as indicated by arrows X1 to X5, light can be emitted from the light emitting surface 2b of the lens 2c in the directions of arrows X1 to X5. For example, parallel light can be emitted in one direction.

  The light reflected by the light reflecting layer 3 is guided to the light diffusion plate 4 side. Then, the light reflected by the light reflecting layer 3 is reflected again by the light diffusing plate 4 as shown by the broken line arrow C, or is reflected again by the light reflector passing through the light diffusing plate 4 and opposite to the light source. Or The reflected light re-reflected by the light diffuser 4 and the light reflector on the opposite side of the light source is guided to the optical sheet 1. Therefore, the reflected light can be used, and the intensity of the light emitted from the lens 2a can be increased. Therefore, in the liquid crystal display device, the light from the light source can be used efficiently and the luminance can be increased.

  The thickness of the light reflecting layer 3 is not particularly limited as long as the function as a reflecting means is exhibited. The thickness of the light reflecting layer 3 is preferably 3 to 20 μm.

  Next, an optical sheet according to the second embodiment of the present invention will be described.

  FIG. 3 is a front sectional view showing an optical sheet according to the second embodiment. The optical sheet 11 shown in FIG. 3 includes an optical sheet main body 2, a light absorption layer 12 laminated on the optical sheet main body 2, and a side opposite to the side on which the optical sheet main body 2 of the light absorption layer 12 is laminated. And a light reflection layer 3 laminated on the substrate. The light absorbing layer 12 is disposed between the optical sheet main body 2 and the light reflecting layer 3. The light absorption layer 12 has a function of absorbing light. In the optical sheet 11, the light reflecting layer 3 is indirectly laminated on the optical sheet body 2 via the light absorbing layer 12.

  The optical sheet body 2 and the light reflection layer 3 in the optical sheet 11 are configured in the same manner as the optical sheet body 2 and the light reflection layer 3 in the optical sheet 1.

  The light absorbing layer 12 can be formed of an appropriate light absorbing material. The light absorbing material is not particularly limited. Examples of the light absorbing material include a mixture of a resin and carbon black or a dye. Examples of the resin of the light absorbing material include the same resins as the resin as the material of the optical sheet main body.

  The light reflecting layer 3 reflects light. However, for example, depending on the wavelength region, some wavelengths of light may pass through the light reflecting layer 3. In such a case, light having a wavelength transmitted through the light reflection layer 3 is absorbed by the light absorption layer 12. Therefore, since such a light absorption layer 12 is provided, light from an oblique direction with respect to the main surface of the optical sheet 11 becomes more difficult to reach near the apex of the lens, and further, a direction orthogonal to the main surface. Becomes more difficult to reach near the outer periphery of the lens. Moreover, the opening process mentioned later can be easily performed by providing the light absorption layer 12.

  The light absorbing layer 12 disposed on the light incident surface 2a side of the optical sheet body 2 has a plurality of openings 12a. Each of the plurality of openings 12a is provided in a region facing the vertices 2e of the plurality of lenses 2c, similarly to the openings 3a of the light reflecting layer 3. When the optical sheet 11 is arranged so that the light emitting surface 2b is on the upper side and the light incident surface 2a is on the lower side, a plurality of openings 12a are formed in regions immediately below the vertices 2e of the plurality of lenses 2c. Is provided. In other words, the opening 12a is formed so as to include a region through which the perpendicular passes when the perpendicular shown by the broken line Y in FIG. 3 is drawn on the light incident surface 2a from the apexes 2e of the plurality of lenses 2c. .

  The aperture ratio of the light absorption layer 12 is preferably in the range of 3 to 30%, like the light reflection layer 3. The aperture ratio is 100% of the total area of the region where the light absorption layer 12 on the light incident surface 2a side of the optical sheet body 2 is provided and the region where the light absorption layer 12 is not provided (opening portion 12a). The area of the area | region where the light absorption layer 12 is not provided is shown.

  The thickness of the light absorption layer 12 is not particularly limited as long as the function as an absorbing means is exhibited. The thickness of the light absorption layer 12 is preferably 3 to 30 μm.

  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 the optical sheet 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 coextrusion method is demonstrated.

  First, a first composition for forming the optical sheet body 2 and a second composition for forming the light reflecting layer 3 are prepared.

  Next, as shown in FIG. 4, the first and second compositions in the molten state are coextruded from the mold 22 of the melt extrusion apparatus 21, and the first composition layer and the second composition layer are obtained. A laminated sheet 23 is obtained. The laminated sheet 23 is guided between the mold roll 24 and the embossing roll 25. The laminated sheet 23 is led so that the first composition layer is in contact with the mold roll 24 and the second composition layer is in contact with the embossing roll 25. In FIG. 4, the laminated sheet 23 is schematically shown.

  As shown in FIGS. 5A to 5C, the mold roll 24 has a substantially cylindrical shape. A plurality of recesses 24 a are formed on the outer peripheral side surface of the mold roll 24. The recess 24a has a shape obtained by inverting the lens 2c described above.

  Therefore, as shown in FIG. 5C, the remaining region other than the portion provided with the plurality of recesses 24a is a cylindrical curved surface 24b.

  As shown in FIG. 4, the mold roll 24 is rotated in the direction of arrow F, and the embossing roll 25 is driven to rotate in the direction indicated by arrow G.

  Although the outer peripheral side surface of the embossing roll 25 is not illustrated, it has an appropriate embossed shape. When the second composition layer of the laminated sheet 23 comes into contact, the arithmetic average roughness Ra of the surface of the second composition layer is set to a predetermined range, and the arithmetic average roughness of the surface 3b of the obtained light reflecting layer 3 is set. In order to make the thickness Ra within a range of 0.1 to 0.5 μm, the outer peripheral side surface of the embossing roll 25 has an appropriate embossed shape.

  Therefore, when the laminated sheet 23 passes between the mold roll 24 and the embossing roll 25, the laminated sheet 23 is shaped, and the surface of the first composition layer is formed so as to form a plurality of convex lenses 2c. The surface of the second composition layer is treated so that the arithmetic average roughness Ra of the surface 3b of the light reflecting layer 3 to be treated is 0.1 to 0.5 μm. In this way, as shown in FIG. 6, the first composition layer 2A on which the lens 2c is formed and the second composition layer 3A in which the arithmetic average roughness Ra of the surface 3b is controlled within a predetermined range. Can be obtained.

  From the viewpoint of increasing the manufacturing efficiency of the optical sheet 1, it is preferable to use the embossing roll 25. Further, from the viewpoint of increasing the manufacturing efficiency of the optical sheet 1, the step of treating the surface of the first composition layer for forming the lens 2c and the arithmetic average roughness Ra of the surface 3b of the obtained light reflecting layer 3 The step of treating the surface of the second composition layer for controlling the thickness is preferably performed inline, and more preferably performed simultaneously.

  Instead of the embossing roll 25, a roll having no embossed shape may be used. In the melt extrusion process using the melt extrusion apparatus 21 shown in FIG. 4, the surface roughness of the surface of the second composition layer may not be controlled. That is, in the step different from the melt extrusion step, for example, the arithmetic average roughness Ra of the surface 3b of the light reflecting layer 3 is 0.1 to 0.5 μm, so that the second composition layer or the light reflecting layer 3 is formed. The surface may be treated.

  As shown in FIG. 6, the laminated sheet 23A fed out from the mold roll 24 includes a first composition layer 2A having a lens 2c and a second composition layer 3A having no opening 3a.

  Next, the opening 3a is formed in the second composition layer 3A that does not have the opening 3a. The method for forming the opening 3a is not particularly limited. As a method for forming the opening 3a, the second composition layer 3A at a desired position is irradiated with parallel light from the lens surface side, condensed at a desired position of the second composition 3A by the lens effect. For example, by sublimation, explosion or melting.

  According to the manufacturing method of the present embodiment, the arithmetic average roughness of the surface 3b of the reflective layer 3 is formed simultaneously with the formation of the lens 2c by pressing the melt-extruded laminated sheet 23 to the mold roll 24 and the embossing roll 25. Ra can be controlled within a predetermined range. Therefore, the optical sheet 1 can be provided efficiently and inexpensively by the manufacturing method of the present embodiment.

  In addition, when manufacturing the optical sheet 11 instead of the optical sheet 1, the first composition for forming the optical sheet body 2 and the second composition for forming the light reflecting layer 3 are provided. In addition to the above, a third composition for forming the light absorption layer 12 is prepared.

  The first composition, the third composition, and the second composition are coextruded from the mold 22 of the melt extrusion apparatus 21, and the first composition layer, the third composition layer, A laminated sheet in which the two composition layers are laminated in this order is obtained. The third composition layer for forming the light absorption layer immediately after being extruded does not have the opening 12a. When the opening 3a is formed in the second composition layer, the opening 12a is formed in the light absorption layer. In this way, the optical sheet 11 can be obtained.

  In addition, the optical sheet used for a liquid crystal display device was demonstrated. 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, a microlens array sheet provided with a plurality of hemispherical lenses 2c has 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. From the viewpoint of controlling the light emission direction with higher accuracy, the optical sheet is preferably a microlens array sheet.

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

Example 1
The optical sheet 1 shown in FIG. 1 was produced by the coextrusion method using the melt extrusion apparatus 21 shown in FIG. The opening 3a of the light reflection layer 3 was formed by irradiating parallel laser light from the lens surface side.

  The optical sheet body 2 of the obtained optical sheet 1 was formed of a polycarbonate resin. The average thickness of the optical sheet body 2 is 110 μm, the distance D1 between the apexes 2e of the plurality of lenses 2c is 105 μm, the diameter D2 of the plurality of lenses 2c is 100 μm, and the distance D3 between the adjacent lenses 2c and 2c is 5 μm. did. The light reflecting layer 3 was formed of a mixture containing a polycarbonate resin and magnesium oxide. The light reflection layer 3 had an average thickness of 10 μm and an aperture ratio of 10%. The arithmetic average roughness Ra of the surface 3b on the side opposite to the side where the optical sheet body 2 of the light reflecting layer 3 is disposed was 0.5 μm.

(Example 2)
The optical sheet 1 was obtained in the same manner as in Example 1 except that the embossing shape of the embossing roll was changed so that the arithmetic average roughness Ra of the surface 3b of the light reflecting layer 3 was 0.1 μm.

(Example 3)
The optical sheet 1 was obtained in the same manner as in Example 1 except that the embossing shape of the embossing roll was changed so that the arithmetic average roughness Ra of the surface 3b of the light reflecting layer 3 was 1 μm.

Example 4
The optical sheet 1 was obtained in the same manner as in Example 1 except that the embossing shape of the embossing roll was changed so that the arithmetic average roughness Ra of the surface 3b of the light reflecting layer 3 was 5 μm.

(Example 5)
The optical sheet 11 shown in FIG. 3 was produced by the coextrusion method using the melt extrusion apparatus 21 shown in FIG.

  An optical sheet 11 was obtained in the same manner as in Example 1 except that the light absorbing layer 12 was disposed between the optical sheet main body 2 and the light reflecting layer 3. The opening 3a of the light reflection layer 3 and the opening 12a of the light absorption layer 12 were each formed by irradiating parallel laser light from the lens surface side.

  The light absorption layer 12 of the obtained optical sheet 11 was formed by a mixture of polycarbonate resin and carbon black. The average thickness of the light absorption layer 12 was 12 μm, and the aperture ratio was 10%.

(Comparative Example 1)
In the same manner as in Example 1, except that the embossing roll was replaced with a roll having no embossed shape and the arithmetic average roughness Ra of the surface 3b of the light reflecting layer 3 was set to 0.01 μm. Sheet 1 was obtained.

(Comparative Example 2)
The optical sheet 1 was obtained in the same manner as in Example 1 except that the embossing shape of the embossing roll was changed so that the arithmetic average roughness Ra of the surface 3b of the light reflecting layer 3 was 6 μm.

(Evaluation)
The optical sheets obtained in Examples and Comparative Examples were placed on a light box, and the luminance was measured with a luminance measuring device EZ-Contrast (manufactured by ELDIM). The luminance referred to here is 0 ° luminance, that is, luminance in the normal direction with respect to the light box exit surface. The luminance of the light box was 640 cd / m ² .
The brightness | luminance of the optical sheet obtained by the Example and the comparative example was as follows, respectively.

Example 1: 1245 cd / m ² , Example 2: 1186 cd / m ² , Example 3: 1251 cd / m ² , Example 4: 1154 cd / m ² , Example 5: 1237 cd / m ² , Comparative Example 1: 1042 cd / M ² , Comparative Example 2: 968 cd / m ²

DESCRIPTION OF SYMBOLS 1 ... Optical sheet 2 ... Optical sheet main body 2A ... 1st composition layer 2a ... Light incident surface 2b ... Light emission surface 2c ... Lens 2d ... Reference | standard surface 2e ... Vertex 3 ... Light reflection layer 3A ... 2nd composition layer 3a ... opening 3b ... surface 4 ... light diffusion plate 11 ... optical sheet 12 ... light absorbing layer 12a ... opening 21 ... melt extrusion device 22 ... mold 23, 23A ... laminated sheet 24 ... mold roll 24a ... recessed 24b ... cylinder Curved surface 25 ... Embossed roll

Claims (7)

An optical sheet body having a light incident surface and a light exit surface, and having a plurality of convex lenses on the light exit surface side;
Disposed on the light incident surface side of the optical sheet body, and includes a light reflecting layer that reflects light,
The light reflecting layer has a plurality of openings, each of the openings is provided in a region facing the vertices of the plurality of lenses; and
An optical sheet in which the arithmetic average roughness Ra of the surface of the light reflecting layer opposite to the side on which the optical sheet main body is disposed is in the range of 0.1 to 5 μm.   The optical sheet according to claim 1, wherein a shape of the plurality of convex lenses is a part of a sphere or a part of a spheroid. Disposed between the optical sheet body and the light reflecting layer, further comprising a light absorbing layer for absorbing light,
The optical sheet according to claim 1, wherein the light absorption layer has a plurality of openings, and each of the plurality of openings is provided in a region facing the apexes of the plurality of lenses. It is a manufacturing method of the optical sheet according to any one of claims 1 to 3,
Laminating the first composition layer for forming the optical sheet main body and the second composition layer for forming the light reflecting layer directly or indirectly by a co-extrusion method;
In order to form the plurality of convex lenses using a mold roll in which a plurality of concave portions corresponding to a shape obtained by inverting the shape of the convex lenses of the optical sheet body is provided on the outer peripheral side surface. Treating the surface of the first composition layer;
The arithmetic mean roughness Ra of the surface opposite to the side on which the optical sheet main body of the light reflecting layer obtained by the second composition layer is disposed is 0.1 to 5 μm. Treating the surface of the composition layer of 2;
Forming the plurality of openings in the second composition layer. In the step of laminating, a first composition layer for forming the optical sheet body, a third composition layer for forming the light absorption layer, and a first composition layer for forming the light reflection layer. The two composition layers are laminated in this order by a coextrusion method,
5. The method of manufacturing an optical sheet according to claim 4, wherein, in the step of forming the openings, the plurality of openings are formed in the second and third composition layers, respectively.   The method for producing an optical sheet according to claim 4 or 5, wherein an embossing roll is used in the step of treating the surface of the second composition layer.   The optical sheet according to any one of claims 4 to 6, wherein the step of treating the surface of the first composition layer and the step of treating the surface of the second composition layer are performed simultaneously. Production method.

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