Abstract:
This sheet manufacturing apparatus is provided with: a nozzle for extruding a heated resin sheet; a main roll with a surface on which microstructures are formed; a follower roll disposed at a distance from the main roll; and an electricity-supplying mechanism. The electricity-supplying mechanism heats an electrically conductive section of the main roll by supplying electricity to the electrically conductive section from both edges of the main roll.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a sheet manufacturing apparatus and method for manufacturing a sheet including microstructures in a surface thereof, and more specifically relates to a sheet manufacturing apparatus and method for manufacturing a prism sheet to be used for a back-lighting device in a liquid-crystal display apparatus. 
       BACKGROUND ART 
       [0002]    A back-lighting device in a general liquid-crystal display apparatus mainly includes a light source, a light-guiding plate (light-guiding film) that guides light from the light source; a reflective sheet that reflects light passing through the light-guiding plate, a diffusion sheet for homogenizing light emitted from a light-emission surface of the light-guiding plate, and a prism sheet that enhances a luminance of the light in a perpendicular direction of the light-emission surface. 
         [0003]    A method for manufacturing such prism sheet will be described. A conventional manufacturing apparatus  10 , which is illustrated in  FIG. 5 , includes a die  1  that receives and extrudes a heated resin, a rectangular extrusion outlet  2  formed in the die  1 , a main roll  3 , and a follower roll  4 . The main roll  3  and the follower roll  4  are disposed below the extrusion outlet  2  so as to sandwich a resin sheet  11  to be shaped therebetween, the resin sheet  11  being extruded from the extrusion outlet  2 . In a surface of the main roll  3 , microstructures for transferring prism shapes to the resin sheet  11  are formed. 
         [0004]    The manufacturing apparatus  10  lets the heated resin sheet  11  through between the main roll  3  and the follower roll  4  and thereby shapes the resin sheet  11  into a prism sheet  12 . In the shaping, as a result of the main roll  3  and the resin sheet being brought into contact with each other, a temperature of a surface of the resin sheet  11  decreases in area A of the main roll  3  illustrated in  FIG. 5 , and the resin sheet  11  thus becomes hard, which causes the problem of failure to accurately transfer the microstructures in the roll  3  to the resin sheet  11 . 
         [0005]    Therefore, in order to solve such problem, apparatuses including a mechanism that heats a vicinity of area A of the main roll  3  have been proposed. For example, Japanese Patent No. 5111800 describes a sheet molding apparatus in which a heating unit including a plurality of heat-transfer heaters is embedded in an outermost layer of a main roll  11  and the heat-transfer heaters are independently controlled, thereby preventing decrease in temperature of a resin sheet, as illustrated in  FIG. 5  thereof. Furthermore, Japanese Patent No. 5111800 also describes a sheet molding apparatus in which a radiation heating device such as a laser or a halogen lamp is provided outside a main roll to heat an outermost layer of the main roll  11 , as illustrated in  FIG. 6  thereof. 
       CITATION LIST 
     Patent Literature 
       [0006]    Patent Literature 1 
         [0007]    Japanese Patent No. 5111800 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0008]    However, in the sheet molding apparatus in Japanese Patent No. 5111800, the heating unit is embedded in the outermost layer of the main roll  11 , which results in the problem of complication of a structure of the outermost layer of the main roll, and with repeated heating of the outermost layer, the outermost layer deteriorates and is more likely to be broken. Also, the radiation heating device described in Japanese Patent No. 5111800 is unable to directly heat an area of the outermost layer of the main roll, the area being in contact with a resin sheet. Thus, the heating efficiency is poor and it is difficult to set proper heating conditions. 
         [0009]    Therefore, an object of the present invention is to provide a sheet manufacturing apparatus and method that enable a resin sheet to be heated to a proper temperature via a main roll, without complicating a structure of an outermost layer of the main roll. 
       Solution to Problem 
       [0010]    In order to solve the aforementioned problems, the present invention is intended to supply power to a conductor in an outermost layer of a main roll to make the conductor generate heat. In other words, aspects of the present invention are as follows. Aspect 1 provides a sheet manufacturing apparatus including a nozzle for extruding a heated resin sheet, a main roll including a surface portion with a microstructure formed therein, and a follower roll disposed at a distance from the main roll, the sheet being pressed between the main roll and the follower roll to transfer the microstructure to the sheet, the apparatus including: a conductive portion in the surface portion; and a power supply mechanism that supplies power to the conductive portion from opposite ends of the main roll in order to make the conductive portion generate heat. 
         [0011]    Aspect 2 provides the sheet manufacturing apparatus according to aspect 1, wherein the power supply mechanism includes a pair of terminal portions that are in contact with the conductive portion at the opposite ends of the main roll, respectively, and a power source that supplies power to the conductive portion via the pair of terminal portions. Aspect 3 provides the sheet manufacturing apparatus according to aspect 2, wherein the terminal portions each include a looped conductive belt that is in contact with the conductive portion, a roll-side pulley that presses the conductive belt against the conductive portion, and a tension pulley that maintains tension of the conductive belt. Aspect 4 provides the sheet manufacturing apparatus according to aspect 3, wherein the conductive belt is a stainless steel belt. Aspect 5 provides the sheet manufacturing apparatus according to aspect 2, wherein the terminal portions include a pair of conductive brushes or conductive pulleys that are in contact with the conductive portion at the opposite ends of the main roll, respectively, and a power source that supplies power to the conductive portion via the pair of conductive brushes or conductive pulleys. 
         [0012]    Aspect 6 provides the sheet manufacturing apparatus according to any one of aspects 1 to 5, wherein the conductive portion is a conductive sleeve. Aspect 7 provides the sheet manufacturing apparatus according to any one of aspects 1 to 5, wherein the conductive portion is a plating layer. Aspect 8 provides the sheet manufacturing apparatus according to any one of aspects 1 to 7, wherein a part of the conductive portion, the part being parallel to a rotation axis direction of the main roll, is made to generate heat using the power supply mechanism. Aspect 9 provides the sheet manufacturing apparatus according to any one of aspects 1 to 8, wherein the conductive portion of the main roll is made to generate heat on a side on which the sheet is guided between the main roll and the follower roll. 
         [0013]    Aspect 10 provides a sheet manufacturing method for shaping a resin sheet using a main roll including a surface portion with a microstructure formed therein, and a follower roll disposed at a distance from the main roll, the method including the steps of: extruding the heated sheet from a nozzle; supplying power to a conductive portion of the surface portion from opposite ends of the main roll via a power supply mechanism; making the conductive portion generate heat using the power supplied by the power supply mechanism; and pressing the resin sheet between the main roll and the follower roll in a state in which the conductive portion generates heat, thereby transferring the microstructure to the resin sheet. 
         [0014]    Aspect 11 provides the sheet manufacturing method according to claim  10 , wherein the power supply mechanism includes a pair of terminal portions that are in contact with the conductive portion at the opposite ends of the main roll, respectively, and a power source that supplies power to the conductive portion via the pair of terminal portions. Aspect 12 provides the sheet manufacturing method according to aspect 11, wherein the terminal portions each include a looped conductive belt that is in contact with the conductive portion, a roll-side pulley that presses the conductive belt against the conductive portion, and a tension pulley that maintains tension of the conductive belt. Aspect 13 provides the sheet manufacturing method according to aspect 12, wherein the conductive belt is a stainless steel belt. Aspect 14 provides the sheet manufacturing apparatus according to aspect 11, wherein the terminal portions include a pair of conductive brushes or conductive pulleys that are in contact with the conductive portion at the opposite ends of the main roll, respectively, and a power source that supplies power to the conductive portion via the pair of conductive brushes or conductive pulleys. 
         [0015]    Aspect 15 provides the sheet manufacturing method according to any one of aspects 10 to 14, wherein the conductive portion is a conductive sleeve. Aspect 16 provides the sheet manufacturing method according to any one of claims  10  to  14 , wherein the conductive portion is a plating layer. Aspect 17 provides the sheet manufacturing method according to any one of aspects 10 to 16, wherein the step of making the conductive portion generate heat includes making a part of the conductive portion, the part being parallel to a rotational axis direction of the main roll, generate heat. Aspect 18 provides the sheet manufacturing method according to any one of aspects 10 to 17, wherein the step of making the conductive portion generate heat includes making the conductive portion of the main roll generate heat on a side on which the sheet is guided between the main roll and the follower roll. 
       Advantageous Effects of Invention 
       [0016]    The present invention enables a surface part of a main roll to be maintained at a proper temperature in order to transfer microstructures in the main roll to a sheet, without complicating an outermost layer structure of the main roll and thus enables efficient manufacturing of a sheet including microstructures. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0017]      FIG. 1  is a schematic configuration diagram of a sheet manufacturing apparatus according to a first embodiment of the present invention. 
           [0018]      FIG. 2  is a perspective diagram illustrating a main roll and a power supply mechanism in the sheet manufacturing apparatus in  FIG. 1 . 
           [0019]      FIG. 3  is an enlarged view of a major part of a power supply mechanism according to a second embodiment of the present invention. 
           [0020]      FIG. 4  is an enlarged view of a major part of a power supply mechanism according to a third embodiment of the present invention. 
           [0021]      FIG. 5  is a schematic configuration diagram of a conventional sheet manufacturing apparatus. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0022]    Embodiments of a sheet manufacturing apparatus and a sheet manufacturing method according to the present invention will be described with reference to the drawings. In the drawings of the embodiments, parts that are identical to each other are provided with a same reference numeral and description thereof will not be repeated. 
       First Embodiment 
       [0023]    A sheet manufacturing apparatus according to a first embodiment will be described with reference to  FIGS. 1 and 2 . As illustrated in  FIG. 1 , a sheet manufacturing apparatus  100  includes a die  101  that receives and extrudes a heated resin such as polycarbonate, a rectangular extrusion outlet  102  formed in the die  101 , a main roll  130  with microstructures, such as prisms, for transfer in a surface thereof, a follower roll  140 , and a power supply mechanism  150  that supplies power to the main roll  130 . The main roll  130  and the follower roll  140  are disposed below the extrusion outlet  102  so as to sandwich a resin sheet  110  to be shaped therebetween, the resin sheet  110  being extruded from the extrusion outlet  102 . In an entire circumference of a surface portion  131  of the main roll  130 , microstructures for transferring prism shapes to the resin sheet  110  and a later-described conductive portion  131   a  formed by, e.g., plating or a sleeve are formed. 
         [0024]    As illustrated in  FIG. 2 , the power supply mechanism  150  includes a first terminal portion  153  that is in contact with the conductive portion  131   a  on the left end side of the main roll  130 , a second terminal portion  154  that is in contact with the conductive portion  131   a  on the right end side of the main roll  130 , and a power source  155  electrically connected to the first terminal portion  153  and the second terminal portion  154  via wirings  156 . The first terminal portion  153  includes a conductive belt  153   c  that is in contact with the conductive portion  131   a  that is exposed to a curved surface on the left end side of the main roll  130 , roll-side pulleys  153   a  and  153   b  that press the conductive belt  153   c  against the conductive portion  131   a , and a tension pulley  153   d  provided at a position distant from the main roll  130 . Proper tension of the conductive belt  153   c  is maintained by the tension pulley  153   d , whereby an outer surface of a part of the conductive belt  153   c  between the roll-side pulleys  153   a  and  153   b  is brought into surface contact with the conductive portion  131   a  on the left end side of the main roll  130 . 
         [0025]    The second terminal portion  154  includes a conductive belt  154   c  that is in contact with the conductive portion  131   a  that is exposed to the curved surface on the right end side of the main roll  130 , roll-side pulleys  154   a  and  154   b  that press the conductive belt  154   c  against the conductive portion  131   a , and a tension pulley  154   d  provided at a position distant from the main roll  130 . Proper tension of the conductive belt  154   c  is maintained by the tension pulley  154   d , whereby a surface of a part of the conductive belt  154   c  positioned between the roll-side pulleys  154   a  and  154   b  is brought into surface contact with the conductive portion  131   a  on the left end side of the main roll  130 . Upon power supply from the first terminal portion  153  and the second terminal portion  154  to the conductive portion  131   a , a heat generation area  131   b  positioned between the first terminal portion  153  and the second terminal portion  154  generates heat. Here, in order to electrically interconnect the conductive belts  153   c  and  154   c , which rotate, and the respective wirings  156 , conductive brushes can be provided at respective terminal portion-side ends of the wirings  156 . Although the follower roll  140  is not illustrated in  FIG. 2 , the follower roll  140  has a length in a rotation axis direction that is smaller than that of the main roll  130  so as not to become an obstacle to the first terminal portion  153  and the second terminal portion  154 . 
         [0026]    The pulleys are rotatably held by, e.g., non-illustrated holding members such as frames. The conductive belt  153   c  is preferably formed from stainless steel (SUS), but may be formed from another conductive material such as conductive rubber. The power source  155  can provide power of, for example, around 10 V and 200 A. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Conventional main roll 
                 Main roll in embodiment 
               
               
                   
                 (° C.) 
                 (° C.) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Temperature of heat 
                 130 
                 110-120 
               
               
                 medium 
               
               
                 Temperature of heat 
                 — 
                 150-160 
               
               
                 generation area 
               
               
                   
               
             
          
         
       
     
         [0027]    In the first embodiment, a temperature of a resin sheet can be increased to a temperature that is favorable for transfer of the microstructures, by heat generated by the heat generation area  131   b  itself, and thus, even if a roll rotation speed and a resin sheet feeding speed are increased, the microstructures can properly be transferred to the resin sheet, which provides an enhanced transfer efficiency. 
       Second Embodiment 
       [0028]    A sheet manufacturing apparatus and method according to a second embodiment will be described with reference to  FIG. 3 . The sheet manufacturing apparatus according to the second embodiment has a structure that is basically similar to that of the sheet manufacturing apparatus  100  illustrated in  FIGS. 1 and 2 . Therefore, only parts that are different from that of the sheet manufacturing apparatus  100  will be described. 
       Third Embodiment 
       [0029]    A sheet manufacturing apparatus according to a third embodiment will be described with reference to  FIG. 4 . The sheet manufacturing apparatus according to the third embodiment has a structure that is basically similar to that of the sheet manufacturing apparatus  100  illustrated in  FIGS. 1 and 2 , but is different from that of the sheet manufacturing apparatus  100  in terms of structures of first and second terminal portions of a power supply mechanism. 
         [0030]      FIG. 4  is an enlarged view of a major part as a main roll  130  is viewed in a rotation axis direction. As illustrated in  FIG. 4 , a first terminal portion  173  in the third embodiment includes a conductive brush  173   a  and a brush holder that holds the conductive brush  173   a . Although not illustrated, a second terminal portion in the third embodiment has a structure that is similar to that of the first terminal portion  173  and is provided on another end side of a main roll  130 . The conductive brushes provided at the opposite ends of the main roll are connected to a non-illustrated power source. It is also possible that conductive brushes are provided at the opposite ends of the main roll  130  and electrode portions fixed at respective positions that allow the electrode portions to face the respective conductive brushes are provided. Each of the electrode portions has an arc-like curved surface that is in contact with the corresponding conductive brush, and is connected to the power source. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           100  sheet manufacturing apparatus 
           101  die 
           102  extrusion outlet 
           110  resin sheet 
           120  prism sheet 
           130  main roll 
           131   a  conductive portion 
           131   b  heat generation area 
           140  follower roll 
           150  power supply mechanism 
           153  first terminal portion 
           153   a  roll-side pulley 
           153   b  roll-side pulley 
           153   c  conductive belt 
           154   d  tension pulley 
           154  second terminal portion 
           154   a  roll-side pulley 
           154   b  roll-side pulley 
           154   c  conductive belt 
           154   d  tension pulley 
           155  power source