JP4450078B2 - Optical sheet manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing an optical sheet made of an amorphous transparent crystalline resin sheet having an embossed surface.

  Conventionally, so-called embossed sheets in which a three-dimensional geometric pattern (embossed pattern) is regularly formed on the surface of a resin sheet or film have been manufactured. As a commonly practiced technique, a thermoplastic resin melt is extruded into a sheet form from a T-die, and sandwiched between a metal roll having a concavo-convex shape on a peripheral surface and a rubber roll and solidified by cooling, thereby forming a concavo-convex shape on the surface. A melt extrusion method for continuously forming a sheet having a smooth surface with a back surface is widely adopted (see, for example, Patent Document 1).

  In the melt extrusion method, the resin extruded from the T die is simultaneously transferred and peeled by the same rigid roll having a geometric shape. In order to perform the transfer completely, it is necessary to give the resin sufficient thermal energy, and in order to perform the peeling, it is necessary to cool the resin below the glass transition temperature (Tg). In the melt extrusion method, since transfer and cooling are performed with the same rigid roll, sufficient heating and cooling cannot be performed, and it is difficult to achieve both transfer and separation completely.

  On the other hand, as another method for producing an embossed sheet, a method is known in which embossing is formed on the surface of a metal roll or a metal flat plate, and this is transferred to the surface of a resin sheet. Further, there is known a method of forming an emboss pattern on the surface of a resin sheet using a metal endless processing belt in which emboss is formed on the surface of an endless belt wound around a plurality of rolls (see, for example, Patent Document 2). ).

  The embossed sheet manufactured as described above can be used as an optical sheet for a liquid crystal display device, for example. Specifically, a prism sheet in which prism shapes having a triangular cross section are continuously arranged can be used as the embossed sheet. The prism sheet is widely known as a brightness enhancement sheet (film) that collects backlight light and improves the front brightness. For example, Patent Document 3 discloses a prism sheet in which a resin sheet having a prism shape formed on the surface thereof is stretched to have in-plane anisotropy of refractive index.

JP 9-295346 A JP 2001-277354 A WO 2006/071621

  By the way, there is a case where it is desired to produce an amorphous resin sheet having an embossed shape on the surface. For example, when the processed embossed sheet has an in-plane anisotropy of refractive index, the crystalline resin sheet is generally stretched in a uniaxial or biaxial direction. In this case, when the crystalline resin sheet is in an amorphous state, the stretching process can be performed appropriately and with high accuracy.

  However, in the conventional embossed sheet manufacturing method described above, it is very difficult to perform embossing while maintaining the amorphous state of the resin sheet. That is, in the conventional method for producing an embossed sheet, after the resin sheet is heated to a temperature above its glass transition temperature or near the crystallization temperature region to give an embossed shape, the resin is cooled during the cooling process to the resin sheet peeling temperature. Crystallization cannot be prevented. As the crystallization of the resin sheet progresses, the resin becomes white and the transparency is lost, making it unsuitable for use as an optical sheet. Further, when the transfer temperature of the emboss shape is low or when the peeling temperature is high, high transfer accuracy of the emboss shape cannot be obtained.

  This invention is made in view of the above-mentioned problem, and makes it a subject to provide the manufacturing method of the optical sheet which can prevent the whitening by crystallization of a resin sheet, obtaining the transfer precision with high emboss shape.

  In solving the above problems, the optical sheet manufacturing method of the present invention is a method for manufacturing an optical sheet comprising a transparent thermoplastic resin sheet having a regular geometric pattern processed on its surface, Using a metal endless processing belt having a geometric shape formed thereon, a geometric pattern is processed at a temperature equal to or higher than the glass transition temperature of the resin sheet, and the resin sheet processed with the geometric pattern is converted into a glass transition thereof. The resin sheet is rapidly cooled to a temperature lower than the temperature, and the quenched resin sheet is peeled off from the metal endless belt.

  In the present invention, the resin sheet is subjected to processing of a geometric pattern (emboss) at a temperature equal to or higher than the glass transition temperature, and then rapidly cooled to a temperature lower than the glass transition temperature or the crystallization temperature region, thereby the resin. The crystallization of the sheet is suppressed. And in the present invention, after embossing the resin sheet using a metal endless processing belt, the resin sheet is cooled in an integrated state with the metal endless processing belt between the transfer step and the cooling step, The resin sheet is peeled off from the metal endless belt at a temperature lower than its glass transition temperature, thereby improving the embossed shape transferability and peelability.

  In order to prevent crystallization of the amorphous resin sheet, the cooling rate of the resin sheet after the embossed transfer to a temperature not higher than the glass transition temperature becomes a problem. The cooling rate varies depending on the constituent material of the resin sheet to be used, but is, for example, 5 ° C./second or more and 40 ° C./second or less. When the cooling rate is less than 5 ° C./second, excessive crystallization of the resin sheet cannot be prevented, which causes whitening (devitrification). On the other hand, when the cooling rate is higher than 40 ° C./second, the embossability is impaired and good shape transferability cannot be obtained.

  The degree of crystallinity of the resin sheet when peeled from the metal endless belt is 20% or less, preferably 5% or less. When the crystallinity of the resin sheet exceeds 20%, the decrease in transmittance due to whitening becomes remarkable, and it becomes unsuitable for use as an optical sheet.

  The geometric pattern (embossed shape) processed on the surface of the resin sheet is not particularly limited, but in the present invention, it has a shape having at least one corner (sharp edge) such as a prism shape, a rectangular wave shape, or a trapezoidal shape. A shape can be imparted to a product at a high transfer rate. The apex angle of the prism shape is, for example, 90 degrees, but may be an acute angle of less than 90 degrees or an obtuse angle of more than 90 degrees. Note that the embossed shape may be a lens shape.

  The resin sheet is not particularly limited as long as it is a transparent thermoplastic resin. For example, PET, PEN, or a mixture or copolymer thereof is preferably used. The total thickness of the resin sheet is, for example, 500 μm or less in order to ensure the above-described cooling rate stably. Further, the ratio of the shape height of the emboss to the total thickness of the resin sheet is, for example, 90% or less. When the ratio of the heights exceeds 90%, the resin sheet is cracked and the handling property is deteriorated. The resin sheet may be in the form of a long band or a single sheet cut into a predetermined size.

  As a material of the metal endless belt, for example, stainless steel, nickel steel or the like can be employed. In the present invention, it is preferable to perform the heating, pressurizing and cooling steps while fixing the resin sheet to the metal endless processing belt and moving the resin sheet together with the metal endless processing belt. Here, as a method of fixing the resin sheet to the metal endless processing belt, for example, a method of heating the resin sheet on the metal endless processing belt to its softening temperature (a temperature equal to or higher than the glass transition temperature) to adhere to the belt Etc. By such a method, manufacturing equipment can be simplified and cost reduction can be achieved. Moreover, since it becomes possible to manufacture an emboss sheet | seat continuously, it becomes possible to aim at the improvement of manufacturing efficiency.

  Here, the heating in the heating step is performed, for example, from the inside of the metal endless processing belt. By heating from the inside of the belt, the sheet fixed to the heated endless processing belt can be directly heated, and the heating efficiency can be improved. Here, as the heating means from the inside of the metal endless belt, for example, a method in which a roll around which the belt is wound is a heating roll is most effective. In addition to this, there are a method of heating with an electric heater or the like installed inside the roll, and a method of circulating heated oil inside the roll. Moreover, as a cooling means, it can be set as the structure which distribute | circulates a cooling water inside a metal roll, for example. Further, as an auxiliary role, heating may be performed from the outside, for example, by an infrared heater, or cooling may be performed by airflow.

  In the present invention, the metal endless processing belt is wound around a heating roll set to a temperature higher than the glass transition temperature of the resin sheet and a cooling roll set to a temperature lower than the glass transition temperature of the resin sheet. These are conveyed in synchronization with the rotation of the heating roll and the cooling roll. At this time, the set temperature of the heating roll and the cooling roll, the distance between the rolls, and the line speed (conveying speed of the metal endless processing belt) are set according to the cooling speed necessary for preventing the crystallization of the resin sheet. .

  The in-plane temperature uniformity of the metal endless processing belt greatly affects the processing accuracy of the shape imparted to the surface of the resin sheet. Therefore, in the present invention, for the heating roll, the roll temperature is set higher at the center than at both ends, and for the cooling roll, the roll temperature is set lower at the center than at both ends. Thereby, it is possible to manufacture an embossed sheet with high shape accuracy by improving the in-plane temperature uniformity of the metal endless belt.

  Embossing of the resin sheet is performed by supplying the resin sheet between a nip roll disposed opposite to the heating roll and a metal endless processing belt. In this case, if the nip pressure between the metal endless belt and the nip roll is low, the transfer accuracy of the emboss shape is lowered, and if the nip pressure is high, the durability of the nip roll is affected and stable production cannot be performed. A preferable nip pressure is 5 kg / cm or more and 30 kg / cm or less in terms of linear pressure.

  Further, if the conveyance speed of the metal endless processing belt is increased in order to increase the cooling rate of the resin sheet, the runnability of the resin sheet becomes unstable, or sufficient heat cannot be applied and transferability is lowered. Therefore, the nip roll is wound with an endless belt together with an opposing roll facing the cooling roll, and the resin sheet is sandwiched and conveyed between the endless belt and the metal endless processing belt, thereby stabilizing the running of the resin sheet. It becomes possible to improve the property and increase the transport speed.

  As described above, according to the method for producing an optical sheet of the present invention, a desired embossed shape can be formed on the sheet surface at a high transfer rate while preventing whitening due to crystallization of the crystalline resin sheet. it can.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic configuration diagram of a sheet manufacturing apparatus 1 for explaining an optical sheet manufacturing method according to a first embodiment of the present invention.

  The sheet manufacturing apparatus 1 includes a heating roll 11 and a cooling roll 12 arranged at a predetermined interval, an emboss belt 13 wound around each of the rolls 11 and 12, and a nip roll arranged to face the heating roll 11. 15 and an opposing roll (backup roll) 16 disposed to face the cooling roll 12.

  The sheet manufacturing apparatus 1 supplies a transparent amorphous crystalline resin sheet 10 between an embossing belt 13 and a nip roll 15 while conveying the crystalline resin sheet 10 in synchronization with the embossing belt 13. The embossed shape of the embossed belt 13 is transferred to the surface of the resin sheet 10 by applying pressure while heating to a temperature equal to or higher than the transition temperature. Then, the resin sheet 10 is moved in a state of being fixed to the embossing belt 13, rapidly cooled on the cooling roll 12, and then peeled off from the embossing belt 13, whereby an embossed shape (prism pattern) 10 a having a predetermined shape is formed on the surface. The formed transparent amorphous crystalline resin sheet 10 is manufactured.

  The heating roll 11 incorporates a heating means such as a heater, and its surface temperature is set to a temperature higher than the softening temperature of the resin sheet 10, that is, the glass transition temperature of the resin sheet 10. Thereby, the part located on the heating roll 11 of the emboss belt 13 is also heated to the said temperature, and it becomes possible to perform the heat processing with respect to the resin sheet 10 in this position.

  In the present embodiment, when the glass transition temperature of the resin sheet 10 is Tg (° C.), the surface temperature of the heating roll 11 is set to a temperature range of Tg + 60 ° C. or more and Tg + 90 ° C. or less. When the set temperature is less than Tg + 60 ° C., good transfer accuracy of the embossed shape with respect to the resin sheet 10 cannot be obtained. Further, when the set temperature exceeds Tg + 90 ° C., when the resin sheet 10 is composed of a crystalline resin that is difficult to maintain an amorphous state, the crystallization of the resin sheet 10 is excessively promoted, and the transparency decreases due to whitening. Becomes prominent.

  The cooling roll 12 includes, for example, a water-cooling type cooling means, and the surface temperature thereof is set to a temperature lower than the glass transition temperature of the resin sheet 10. In the present embodiment, the surface temperature of the cooling roll 12 is set to 30 ° C. Thereby, the part located on the cooling roll 12 of the emboss belt 13 is also cooled, and it becomes possible to perform the cooling process with respect to the resin sheet 10 at this position.

  In the present embodiment, as shown in FIG. 8A, the heating roll 11 is set so that the roll temperature is higher in the center than at both ends. On the other hand, as shown in FIG. 8B, the cooling roll 12 is set so that the roll temperature is lower in the center than at both ends. Thereby, the in-plane temperature uniformity of the emboss belt can be increased, and an emboss sheet having excellent shape accuracy can be manufactured. As a method for realizing the temperature distribution as described above, for example, regarding the heating roll 11, when the heating source is configured by an electric heater, the number of turns of the heating wire is set to be larger at the roll center than at both ends of the roll.

  Note that at least one of the heating roll 11 and the cooling roll 12 can be rotated by being connected to a rotation driving means such as a motor.

  The embossed belt 13 corresponds to the “metal endless processed belt” of the present invention, and is constituted by a metal endless belt having excellent thermal conductivity. In the present embodiment, the embossed belt 13 is made of nickel steel, and the surface thereof is provided with an embossed shape (geometric pattern) 13a in which grooves having a triangular cross section (prism shape) are continuously arranged. . The prism apex angle is not particularly limited, and is, for example, 120 ° or less, preferably 90 °. The embossed belt 13 is desirably seamless (seamless), and a method of producing nickel steel by electroforming on a cylindrical resin master having an embossed shape on the inner surface side, or a cylindrical roll Although it is desirable to wind and perform precision cutting directly, it is not restricted to this.

  In addition, although the extending direction (ridgeline direction) of the embossed shape 13a is the width direction (TD (Transverse Direction) direction) of the resin sheet 10 in this embodiment, the present invention is not limited thereto, and the traveling direction of the resin sheet 10 is not limited thereto. (MD (Machine Direction) direction) may be used. Further, a release agent may be applied to the embossed belt 13 on the surface where the embossed shape 13a is formed in order to improve the peelability from the resin sheet 10. As the release agent, fluorine resin, silicone resin, and the like are preferable.

  The embossed shape 13a is not limited to a triangular cross section (prism shape). The apex angle of the prism shape is not limited to 90 degrees as shown in FIG. 9A, but may be an acute angle of less than 90 degrees as shown in FIG. 9B or an obtuse angle of more than 90 degrees as shown in FIG. 9C. The embossed shape 13a may be a rectangular wave (pulse wave) shape shown in FIG. 9D or a trapezoidal shape shown in FIG. 9E. As described above, it is possible to give a shape with a high transfer rate even to a shape having at least one corner (sharp edge).

  Further, the embossed shape may be various lens shapes. The lens shape may be a cylindrical shape or an array shape. The lens surface is not limited to a curved surface shape such as a spherical surface or an aspherical surface, but is not limited to a continuous curved surface shape, and may be a composite shape of a plurality of curved surface shapes.

  The nip roll 15 is provided to clamp the resin sheet 10 in cooperation with the embossing belt 13 and transfer the embossed shape 13 a on the surface of the embossing belt 13 to the surface of the resin sheet 10. In the present embodiment, the nip roll 15 has a built-in heating source, similar to the heating roll 11, and also has a function as an assist roll that heats the resin sheet 10 on the emboss belt 13 from the back side. Although the peripheral surface of the nip roll 15 is a smooth surface, by providing a predetermined embossed shape on the peripheral surface of the nip roll 15 as well, it is possible to simultaneously transfer the shape to the remote side of the resin sheet 10. Become. The nip roll 15 may be a cooling roll having a cooling mechanism in order to assist the peeling of the back surface and to prevent transfer of a slight shape of the back surface roll.

  The nip pressure of the resin sheet 10 by the nip roll 15 and the embossing belt 13 greatly affects the transfer accuracy of the embossed shape 13a to the resin sheet 10. In the present embodiment, the nip pressure is 5 kg / cm or more and 30 kg / cm or less in terms of linear pressure. If the nip pressure is less than 5 kg / cm, the transfer accuracy of the embossed shape 13a with respect to the resin sheet 10 decreases, and if the nip pressure exceeds 30 kg / cm, the durability of the nip roll 15 and the emboss belt 13 is affected and stable production can be performed. Disappear.

  The facing roll 16 is installed as an auxiliary roll when the resin sheet 10 is peeled from the emboss belt 13 on the cooling roll 12. The opposing roll 16 has a built-in cooling means like the cooling roll 12 and has a function of cooling the resin sheet 10 from the back side by being maintained at the same surface temperature as the cooling roll 12. The peripheral surface of the opposing roll 16 is a smooth surface. The nip pressure of the resin sheet 10 by the opposing roll 16 and the embossing belt 13 is not particularly limited, and a nip pressure enough to bring the peripheral surface of the opposing roll 16 into close contact with the back surface of the resin sheet 10 is sufficient.

  The resin sheet 10 is not particularly limited as long as it is a transparent thermoplastic crystalline resin. In the present embodiment, PET (polyethylene terephthalate), PEN (polyethylene naphthalate), or a mixture or copolymer thereof, which is a crystalline resin that requires more severe manufacturing conditions in the cooling process in order to maintain an amorphous state, Used. In the present embodiment, a method is used in which the amorphous resin sheet 10 is formed into a long belt shape and continuously supplied to the sheet manufacturing apparatus 1. In addition to this, it is possible to adopt a method in which the resin sheet 10 is formed as a single sheet cut into a predetermined size and is sequentially supplied to the sheet manufacturing apparatus 1.

  Here, the amorphous state of the resin sheet 10 means that the crystallinity is 3% or less, for example. The sheet manufacturing apparatus 1 according to the present embodiment performs an embossing process on the surface of the resin sheet 10 in an amorphous state by using an embossing belt 13 and then rapidly cools, whereby a crystallinity of 20% or less, preferably 10% or less. An amorphous resin sheet (embossed sheet or prism sheet) 10 is manufactured. This is because if the crystallinity exceeds 20%, a decrease in transmittance due to whitening becomes remarkable, and it becomes unsuitable for use as an optical sheet.

  Moreover, when the crystallinity exceeds 20%, the Young's modulus of the material generally increases. For this reason, when the embossed resin sheet is subsequently stretched, the load required for stretching increases, and the heating temperature during stretching must be set higher. In particular, when birefringence is developed in the resin sheet by the stretching treatment, if the crystallinity of the resin sheet before stretching exceeds 20%, it is difficult to obtain desired birefringence.

  On the other hand, in order to maintain the amorphous state of the resin sheet 10 before and after processing of the embossed shape with respect to the resin sheet 10, from the shape transfer of the resin sheet 10 on the heating roll 11 to the peeling of the resin sheet 10 on the cooling roll 12. The cooling rate [° C./second] of the resin sheet 10 is important. The cooling rate varies depending on the constituent material of the resin sheet 10, but is preferably 5 ° C./second or more and 40 ° C./second or less, more preferably 10 ° C./second or more and 30 ° C./second or less. When the cooling rate is less than 5 ° C./second, excessive crystallization of the resin sheet cannot be prevented, which causes whitening (devitrification). On the other hand, when the cooling rate is higher than 40 ° C./second, the embossability is impaired and good shape transferability cannot be obtained. By realizing the cooling rate, an increase in the crystallinity of the resin sheet before and after the shape transfer process by the sheet manufacturing apparatus 1 can be suppressed to 5% or less. Moreover, the crystallinity of the resin sheet peeled from the emboss belt 13 can be suppressed to 20% or less.

  In order to realize the cooling rate of the resin sheet 10 described above, in the sheet manufacturing apparatus 1, the distance between the heating roll 11 and the cooling roll 12, the conveyance speed of the endless belt 13, and the holding angle of the resin sheet 10 with respect to the cooling roll 12. Etc. are prescribed. A plurality of cooling rolls 12 may be installed.

  Here, if the distance between the rolls 11 and 12 is too large, it is necessary to increase the transport speed of the endless belt 13 in order to ensure the cooling speed. However, when the conveyance speed of the endless belt 13 is increased, the running stability of the resin sheet 10 is lowered, and stable productivity cannot be expected, or the heat transfer is insufficient and the transferability is lowered. If the distance between the rolls 11 and 12 is too short, heat exchange of the endless belt 13 becomes insufficient, so that the heat treatment and cooling treatment at a desired temperature cannot be performed on the resin sheet 10.

  As a preferable example, when the set temperature of the heating roll 11 is Tg + 60 ° C. or more and Tg + 90 ° C. or less, the setting temperature of the cooling roll 12 is 30 ° C., and the conveying speed of the emboss belt 13 is 5 m / min, the heating roll 11 and the cooling roll The distance between the rolls 12 is set to 100 mm or more and 400 mm or less. The distance between the rolls varies depending on the constituent material of the resin sheet 10 and is, for example, 100 mm to 200 mm in the case of PET, and 100 mm to 400 mm in the case of PEN. The cooling rate when the distance between rolls is 100 mm corresponds to 20 ° C./second at 5 m / min, and corresponds to 5 ° C./second when 400 mm.

  Of course, a necessary cooling rate can be obtained by changing the transport speed of the emboss belt 13 while keeping the distance between the rolls 11 and 12 constant. In this case, a preferable transport speed is 5 m / min or more and 10 m / min or less when the distance between the rolls 11 and 12 is 800 mm.

  Moreover, in order to ensure the said cooling rate conditions stably, it is preferable that the total thickness of the resin sheet 10 is 500 micrometers or less. The ratio of the emboss shape height to the total thickness of the resin sheet 10 is preferably 90% or less. This is because if the ratio of the heights exceeds 90%, the resin sheet 10 is cracked and the handling properties are deteriorated.

  Next, the optical sheet manufacturing method of this embodiment using the sheet manufacturing apparatus 1 configured as described above will be described.

  First, an amorphous resin sheet 10 set in advance on a supply roll (not shown) is supplied between the emboss belt 13 and the nip roll 15. Next, the resin sheet 10 is heated on the heating roll 11 to a temperature equal to or higher than the glass transition temperature, and the resin sheet 10 is sandwiched between the embossing belt 13 and the nip roll 15, so that the embossing belt 13 is placed on the surface of the resin sheet 10. The embossed shape 13a is transferred.

  The resin sheet 10 to which the embossed shape has been transferred is fixed to the embossed belt 13 and conveyed toward the cooling roll 12 together with the embossed belt 13. The resin sheet 10 is cooled to a temperature lower than the glass transition temperature together with the emboss belt 13 on the cooling roll 12. In this cooling step, after the embossed shape is transferred, the resin sheet 10 is rapidly cooled at the above-described cooling rate that maintains the amorphous state. The cooled resin sheet 10 passes through the nip point between the embossing belt 13 and the opposing roll 16, and is then peeled off from the embossing belt 13 and taken up by a take-up roll (not shown).

  As described above, the amorphous resin sheet 10 having the embossed shape 10a formed on the surface is manufactured. By embossing the resin sheet 10 using the sheet manufacturing apparatus 1 configured as described above, the manufacturing equipment can be simplified and the cost can be reduced. Moreover, since it becomes possible to manufacture an emboss sheet | seat continuously, it becomes possible to aim at the improvement of manufacturing efficiency.

  Moreover, in this embodiment, after embossing the resin sheet 10 at a temperature equal to or higher than its glass transition temperature, the resin sheet 10 is rapidly cooled to a temperature lower than the glass transition temperature. The amorphous state can be maintained by suppressing the formation. Moreover, the embossing with respect to the resin sheet 10 is performed using the embossing belt 13, and the resin sheet 10 is cooled in an integrated state with the embossing belt 13 between the transfer process and the cooling process. Since it peels from the embossing belt 13 at a low temperature, the transferability and peelability of the embossed shape with respect to the resin sheet 10 can be enhanced.

  Therefore, according to the present embodiment, a desired embossed shape can be formed on the sheet surface at a high transfer rate while preventing whitening due to crystallization of the amorphous crystalline resin sheet 10. In particular, according to the present embodiment, the embossed shape can be transferred to the resin sheet 10 with a high transfer rate of 98% or more.

  Here, in this specification, the transfer rate is defined as follows. That is, as shown in FIGS. 2A and 2B, when the shape height of the emboss formed on the resin sheet 10 is H2, and the shape height of the emboss formed on the emboss belt 13 is H1, the transfer rate (%). Is represented by (H2 / H1) × 100.

  The inventors of the present invention, using a master having an isosceles triangle embossed shape with a vertical angle of 90 degrees formed at a pitch of 50 μm, in an embossing method by a melt extrusion method and an embossing method by a laminate method of the present invention, The actual embossed shape of the resin sheet was measured. The measurement results are shown in FIG. It can be seen that the laminate method can form an embossed shape with a higher transfer rate than the melt extrusion method.

  On the other hand, the in-plane temperature uniformity of the embossed belt 13 greatly affects the processing accuracy of the shape imparted to the surface of the resin sheet. In the present embodiment, the heating roll 11 is set so that the roll temperature is higher at the center than at both ends, and the cooling roll 12 is set so that the roll temperature is lower at the center than both ends. Is set. Thereby, the in-plane temperature uniformity of the embossed belt 13 can be improved, and an embossed sheet with excellent shape accuracy can be manufactured.

  The resin sheet 10 having the embossed shape formed as described above is used as an optical sheet having the desired optical characteristics by being cut into a predetermined size. FIG. 4 schematically shows the configuration of a resin sheet 10 used as a prism sheet for a liquid crystal display device. On the surface of the resin sheet 10, prism patterns (embossed shapes) 10 a having a ridge line direction in the X-axis direction are continuously arranged in the Y-axis direction at a predetermined pitch. This resin sheet 10 can be used as it is as a prism sheet for a liquid crystal display device.

  On the other hand, by stretching the resin sheet 10 shown in FIG. 4 in the prism ridgeline direction (X-axis direction) at a predetermined stretching ratio, the optical characteristics of the sheet can be changed. That is, the above-described stretching treatment can provide a refractive index difference between the in-plane refractive index (nx) in the X-axis direction and the in-plane refractive index (ny) in the Y-axis direction. Since the resin sheet 10 is in an amorphous state with a crystallinity of 20% or less, the stretching process can be performed appropriately and with high accuracy.

  In the present embodiment, since a resin material having a refractive index large in the stretching direction, such as PET or PEN, is used as a constituent material of the resin sheet 10, nx> ny is applied to the resin sheet 10 by the stretching process. Refractive index anisotropy is provided. In the resin sheet 10 having such a configuration, with respect to the light emitted from the prism forming surface, the polarization component in the prism ridge line direction (X-axis direction) is more critical than the polarization component in the prism array direction (Y-axis direction). Since the amount of total reflection due to reflection is repeatedly returned to the light incident side, the polarization component in the prism arrangement direction has an optical characteristic that the amount of emitted light is larger than the polarization component in the prism extending direction.

  FIG. 5 is a schematic configuration diagram of a liquid crystal display device 20 using the resin sheet 10 having the above-described configuration as a prism sheet. The liquid crystal display device 20 includes a liquid crystal display panel 21, a first polarizer 22A and a second polarizer 22B that sandwich the liquid crystal display panel 21, a prism sheet 10, a diffusion sheet 23, and a backlight unit 24. ing.

  The prism sheet 10 corresponds to the resin sheet 10 embossed by the sheet manufacturing apparatus 1 described above, and is used as a brightness enhancement film for improving the front brightness of the liquid crystal display device 20. The prism sheet 10 is disposed on the light emission side of the diffusion sheet 23 that diffuses and emits the illumination light (backlight light) from the backlight unit 24, and has a function of collecting the light emitted from the diffusion sheet 23 in the front direction. is doing.

  Further, the pair of polarizers 22A and 22B sandwiching the liquid crystal display panel 11 are arranged so that the transmission axes a and b are orthogonal to each other. In the illustrated example, the prism sheet 10 is arranged so that the prism arrangement direction (Y-axis direction) of the prism sheet 10 is substantially parallel to the transmission axis a of the first polarizer 22A located on the backlight unit 24 side. Is arranged. This example is particularly effective when the prism sheet 10 stretched in the prism ridge line direction (X-axis direction) is used, and allows the polarized component with the larger amount of emitted light to be efficiently incident on the liquid crystal display panel 21. As a result, the front luminance can be improved.

  The prism sheet 10 is not limited to a single configuration, and a plurality of prism sheets can be used in a stacked manner. In this case, it is preferable that the ridge line directions of the prism sheets are arranged so as to be orthogonal to each other.

(Second Embodiment)
Subsequently, a second embodiment of the present invention will be described. FIG. 6 shows a schematic configuration of the sheet manufacturing apparatus 2 according to the present embodiment. In the figure, portions corresponding to those of the first embodiment described above are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the sheet manufacturing apparatus 2 of the present embodiment, a metal endless belt 14 is wound around a nip roll 15 and a counter roll 16 that face the back side (non-embossed surface) of the resin sheet 10, and the resin sheet 10 is heated and transferred. The resin sheet 10 is sandwiched between the embossed belt 13 and the endless belt 14 from the process to the cooling / peeling process.

  The endless belt 14 is formed of a metal such as nickel steel, but is not limited to a metal and may be formed of a heat resistant resin such as heat resistant PET. Although the surface of the endless belt 14 is mirror-finished, a shape may be given as necessary, and thereby a shape corresponding to the back side of the resin sheet 10 can be transferred and formed.

  The thickness of the endless belt 14 is preferably 30 μm or more and 1000 μm, although it depends on the material. When the thickness exceeds 1000 μm, winding around the heating roll and the cooling roll becomes impossible. On the other hand, if the thickness is less than 30 μm, there may be a problem in terms of strength such that undulation is likely to occur when the resin sheet 10 is conveyed and cracks are likely to occur.

  In the sheet manufacturing apparatus 2 of the present embodiment configured as described above, the resin sheet 10 includes the embossed belt 13 and the endless belt 14 from the heating / transfer process to the cooling / peeling process of the resin sheet 10. It is conveyed in a state of being sandwiched between them. Therefore, it becomes possible to improve the running stability of the resin sheet 10, thereby increasing the degree of freedom in setting the cooling speed for increasing the transport speed and preventing whitening due to crystallization of the resin sheet 10. Become.

  Further, according to the present embodiment, the surface of the endless belt 14 is embossed to form an emboss shape, so that the emboss shape can be formed with high transfer accuracy not only on the surface of the resin sheet 10 but also on the back surface side. Is possible.

(Third embodiment)
FIG. 7 shows an example in which a laminate sheet 10L is manufactured by thermally bonding two resin sheets 10s and 10t to each other using the sheet manufacturing apparatus 2 described above. In this example, the embossed belt 13 is used to transfer the embossed shape to the surface of one resin sheet 10s, and at the same time, the two resin sheets 10s and 10t are heat-bonded by being sandwiched between the embossed belt 13 and the endless belt 14 and integrated. To do. This makes it possible to easily manufacture a laminate sheet 10L having a predetermined embossed shape on the surface.

  In the sheet manufacturing apparatus 2, two resin sheets 10s and 10t are loaded simultaneously. The resin sheets of the same type may be used for these resin sheets 10s and 10t, or other types of resin sheets may be used. Also, three or more resin sheets may be charged simultaneously.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

Example 1
An amorphous PET sheet (Tg: about 75 ° C.) having a thickness of 200 μm was produced by a T-die extrusion method. This amorphous PET sheet was supplied to the sheet manufacturing apparatus 1 or the sheet manufacturing apparatus 2 described above, and a prism sheet in which a large number of isosceles triangular prisms having an apex angle of 90 degrees was arranged on the sheet surface under the following conditions.
[Production conditions]
Sheet material: Amorphous PET
Thickness: 200 μm
Prism pitch: 50 μm
Surface temperature of heating roll 11: 150 ° C.
Surface temperature of the nip roll 15: 50 ° C.
Surface temperature of cooling roll 12: 30 ° C
Opposite roll 16 surface temperature: 30 ° C.
Resin sheet cooling rate: 20 ° C./second (sheet conveyance speed: 5 m / min)
Nip linear pressure between the heating roll 11 and the nip roll 15: 15 kg / cm

(Example 2)
An amorphous PEN sheet (Tg: about 120 ° C.) having a thickness of 200 μm was produced by a T-die extrusion method. This amorphous PEN sheet was supplied to the sheet manufacturing apparatus 1 or the sheet manufacturing apparatus 2 described above, and a prism sheet having a large number of isosceles triangular prisms having an apex angle of 90 degrees was manufactured on the sheet surface under the following conditions.
[Production conditions]
Sheet material: Amorphous PEN
Thickness: 200 μm
Prism pitch: 100 μm
Surface temperature of heating roll 11: 190 ° C
Surface temperature of nip roll 15: 70 ° C.
Surface temperature of cooling roll 12: 30 ° C
Opposite roll 16 surface temperature: 30 ° C.
Resin sheet cooling rate: 10 ° C./second (sheet conveyance speed: 3 m / min)
Nip linear pressure between the heating roll 11 and the nip roll 15: 15 kg / cm

(Example 3)
An amorphous PEN sheet (Tg: about 120 ° C.) having a thickness of 200 μm was produced by a T-die extrusion method. This amorphous PEN sheet was supplied to the sheet manufacturing apparatus 1 or the sheet manufacturing apparatus 2 described above, and a prism sheet having a large number of isosceles triangular prisms having an apex angle of 90 degrees was manufactured on the sheet surface under the following conditions.
[Production conditions]
Sheet material: Amorphous PEN
Thickness: 200 μm
Prism pitch: 300 μm
Surface temperature of heating roll 11: 190 ° C
Surface temperature of nip roll 15: 70 ° C.
Surface temperature of cooling roll 12: 30 ° C
Opposite roll 16 surface temperature: 30 ° C.
Resin sheet cooling rate: 10 ° C./second (sheet conveyance speed: 3 m / min)
Nip linear pressure between the heating roll 11 and the nip roll 15: 15 kg / cm

Example 4
An amorphous PEN sheet (Tg: about 120 ° C.) having a thickness of 200 μm was produced by a T-die extrusion method. This amorphous PEN sheet was supplied to the sheet manufacturing apparatus 1 or the sheet manufacturing apparatus 2 described above, and a prism sheet having a large number of isosceles triangular prisms having an apex angle of 90 degrees was manufactured on the sheet surface under the following conditions.
[Production conditions]
Sheet material: Amorphous PEN
Thickness: 200 μm
Prism pitch: 10 μm
Surface temperature of heating roll 11: 190 ° C
Surface temperature of nip roll 15: 70 ° C.
Surface temperature of cooling roll 12: 30 ° C
Opposite roll 16 surface temperature: 30 ° C.
Resin sheet cooling rate: 10 ° C./second (sheet conveyance speed: 3 m / min)
Nip linear pressure between the heating roll 11 and the nip roll 15: 15 kg / cm

(Example 5)
An amorphous PET sheet (Tg: about 75 ° C.) having a thickness of 500 μm was produced by a T-die extrusion method. This amorphous PET sheet was supplied to the sheet manufacturing apparatus 1 or the sheet manufacturing apparatus 2 described above, and a prism sheet in which a large number of isosceles triangular prisms having an apex angle of 90 degrees was arranged on the sheet surface under the following conditions.
[Production conditions]
Sheet material: Amorphous PET
Thickness: 500μm
Prism pitch: 100 μm
Surface temperature of heating roll 11: 150 ° C.
Surface temperature of the nip roll 15: 50 ° C.
Surface temperature of cooling roll 12: 30 ° C
Opposite roll 16 surface temperature: 30 ° C.
Resin sheet cooling rate: 15 ° C./second (sheet conveyance speed: 5 m / min)
Nip linear pressure between the heating roll 11 and the nip roll 15: 15 kg / cm

(Example 6)
An amorphous PET sheet (Tg: about 75 ° C.) having a thickness of 20 μm was produced by a T-die extrusion method. This amorphous PET sheet was supplied to the sheet manufacturing apparatus 1 or the sheet manufacturing apparatus 2 described above, and a prism sheet in which a large number of isosceles triangular prisms having an apex angle of 90 degrees was arranged on the sheet surface under the following conditions.
[Production conditions]
Sheet material: Amorphous PET
Thickness: 20μm
Prism pitch: 20 μm
Surface temperature of heating roll 11: 150 ° C.
Surface temperature of the nip roll 15: 50 ° C.
Surface temperature of cooling roll 12: 30 ° C
Opposite roll 16 surface temperature: 30 ° C.
Resin sheet cooling rate: 30 ° C./second (sheet conveyance speed: 5 m / min)
Nip linear pressure between the heating roll 11 and the nip roll 15: 30 kg / cm

(Example 7)
An amorphous PEN sheet (Tg: about 120 ° C.) having a thickness of 200 μm was produced by a T-die extrusion method. This amorphous PEN sheet was supplied to the sheet manufacturing apparatus 1 or the sheet manufacturing apparatus 2 described above, and a prism sheet having a large number of isosceles triangular prisms having an apex angle of 90 degrees was manufactured on the sheet surface under the following conditions.
[Production conditions]
Sheet material: Amorphous PEN
Thickness: 200 μm
Prism pitch: 50 μm
Surface temperature of heating roll 11: 200 ° C
Surface temperature of nip roll 15: 70 ° C.
Surface temperature of cooling roll 12: 50 ° C.
Opposite roll 16 surface temperature: 50 ° C.
Resin sheet cooling rate: 40 ° C./second (sheet conveyance speed: 5 m / min)
Nip linear pressure between the heating roll 11 and the nip roll 15: 30 kg / cm

(Example 8)
An amorphous PEN sheet (Tg: about 120 ° C.) having a thickness of 150 μm was produced by a T-die extrusion method. This amorphous PEN sheet was supplied to the sheet manufacturing apparatus 1 or the sheet manufacturing apparatus 2 described above, and a prism sheet having a large number of isosceles triangular prisms having an apex angle of 90 degrees was manufactured on the sheet surface under the following conditions.
[Production conditions]
Sheet material: Amorphous PEN
Thickness: 150 μm
Prism pitch: 100 μm
Surface temperature of heating roll 11: 180 ° C
Surface temperature of nip roll 15: 70 ° C.
Surface temperature of cooling roll 12: 30 ° C
Opposite roll 16 surface temperature: 30 ° C.
Resin sheet cooling rate: 30 ° C./second (sheet conveyance speed: 5 m / min)
Nip linear pressure between the heating roll 11 and the nip roll 15: 30 kg / cm

Example 9
An amorphous PEN sheet (Tg: about 120 ° C.) having a thickness of 200 μm was produced by a T-die extrusion method. This amorphous PEN sheet was supplied to the sheet manufacturing apparatus 1 or the sheet manufacturing apparatus 2 described above, and a prism sheet having a large number of isosceles triangular prisms having an apex angle of 90 degrees was manufactured on the sheet surface under the following conditions.
[Production conditions]
Sheet material: Amorphous PEN
Thickness: 200 μm
Prism pitch: 350 μm
Surface temperature of heating roll 11: 190 ° C
Surface temperature of nip roll 15: 70 ° C.
Surface temperature of cooling roll 12: 30 ° C
Opposite roll 16 surface temperature: 30 ° C.
Resin sheet cooling rate: 10 ° C./second (sheet conveyance speed: 3 m / min)
Nip linear pressure between the heating roll 11 and the nip roll 15: 15 kg / cm

(Example 10)
An amorphous PEN sheet (Tg: about 120 ° C.) having a thickness of 300 μm was produced by a T-die extrusion method. This amorphous PEN sheet was supplied to the sheet manufacturing apparatus 1 or the sheet manufacturing apparatus 2 described above, and a prism sheet having a large number of isosceles triangular prisms having an apex angle of 90 degrees was manufactured on the sheet surface under the following conditions.
[Production conditions]
Sheet material: Amorphous PEN
Thickness: 300 μm
Prism pitch: 75 μm
Surface temperature of heating roll 11: 190 ° C
Surface temperature of nip roll 15: 70 ° C.
Surface temperature of cooling roll 12: 30 ° C
Opposite roll 16 surface temperature: 30 ° C.
Resin sheet cooling rate: 10 ° C./second (sheet conveyance speed: 4 m / min)
Nip linear pressure between the heating roll 11 and the nip roll 15: 5 kg / cm

(Example 11)
An amorphous PET sheet (Tg: about 75 ° C.) having a thickness of 300 μm was produced by a T-die extrusion method. This amorphous PET sheet was supplied to the sheet manufacturing apparatus 1 or the sheet manufacturing apparatus 2 described above, and a prism sheet in which a large number of isosceles triangular prisms having an apex angle of 90 degrees was arranged on the sheet surface under the following conditions.
[Production conditions]
Sheet material: Amorphous PET
Thickness: 100 μm
Prism pitch: 100 μm
Surface temperature of heating roll 11: 150 ° C.
Surface temperature of the nip roll 15: 50 ° C.
Surface temperature of cooling roll 12: 30 ° C
Opposite roll 16 surface temperature: 30 ° C.
Resin sheet cooling rate: 25 ° C./second (sheet conveyance speed: 5 m / min)
Nip linear pressure between the heating roll 11 and the nip roll 15: 5 kg / cm

(Example 12)
An amorphous PET sheet (Tg: about 75 ° C.) having a thickness of 100 μm was prepared by a T-die extrusion method. This amorphous PET sheet was supplied to the sheet manufacturing apparatus 1 or the sheet manufacturing apparatus 2 described above, and a prism sheet in which a large number of isosceles triangular prisms having an apex angle of 90 degrees was arranged on the sheet surface under the following conditions.
[Production conditions]
Sheet material: Amorphous PET
Thickness: 100 μm
Prism pitch: 100 μm
Surface temperature of heating roll 11: 150 ° C.
Surface temperature of the nip roll 15: 50 ° C.
Surface temperature of cooling roll 12: 30 ° C
Opposite roll 16 surface temperature: 30 ° C.
Resin sheet cooling rate: 6 ° C./second (sheet conveyance speed: 2 m / min)
Nip linear pressure between the heating roll 11 and the nip roll 15: 20 kg / cm

(Example 13)
An amorphous PEN sheet (Tg: about 120 ° C.) having a thickness of 300 μm was produced by a T-die extrusion method. This amorphous PEN sheet was supplied to the sheet manufacturing apparatus 1 or the sheet manufacturing apparatus 2 described above, and a prism sheet having a large number of isosceles triangular prisms having an apex angle of 90 degrees was manufactured on the sheet surface under the following conditions.
[Production conditions]
Sheet material: Amorphous PEN
Thickness: 300 μm
Prism pitch: 50 μm
Surface temperature of heating roll 11: 190 ° C
Surface temperature of the nip roll 15: 80 ° C.
Surface temperature of cooling roll 12: 60 ° C
Opposite roll 16 surface temperature: 60 ° C.
Resin sheet cooling rate: 5 ° C./second (sheet conveyance speed: 3 m / min)
Nip linear pressure between the heating roll 11 and the nip roll 15: 20 kg / cm

(Comparative Example 1)
An amorphous PET sheet (Tg: about 75 ° C.) having a thickness of 200 μm was produced by a T-die extrusion method. This amorphous PET sheet was supplied to the sheet manufacturing apparatus 1 or the sheet manufacturing apparatus 2 described above, and a prism sheet in which a large number of isosceles triangular prisms having an apex angle of 90 degrees was arranged on the sheet surface under the following conditions.
[Production conditions]
Sheet material: Amorphous PET
Thickness: 200 μm
Prism pitch: 100 μm
Surface temperature of heating roll 11: 170 ° C.
Surface temperature of nip roll 15: 40 ° C.
Surface temperature of cooling roll 12: 30 ° C
Opposite roll 16 surface temperature: 30 ° C.
Resin sheet cooling rate: 3 ° C./second (sheet conveyance speed: 4 m / min)
Nip linear pressure between the heating roll 11 and the nip roll 15: 15 kg / cm

(Comparative Example 2)
An amorphous PEN sheet (Tg: about 120 ° C.) having a thickness of 200 μm was produced by a T-die extrusion method. This amorphous PEN sheet was supplied to the sheet manufacturing apparatus 1 or the sheet manufacturing apparatus 2 described above, and a prism sheet having a large number of isosceles triangular prisms having an apex angle of 90 degrees was manufactured on the sheet surface under the following conditions.
[Production conditions]
Sheet material: Amorphous PEN
Thickness: 200 μm
Prism pitch: 100 μm
Surface temperature of heating roll 11: 170 ° C.
Surface temperature of the nip roll 15: 60 ° C.
Surface temperature of cooling roll 12: 30 ° C
Opposite roll 16 surface temperature: 30 ° C.
Resin sheet cooling rate: 20 ° C./second (sheet conveyance speed: 5 m / min)
Nip linear pressure between the heating roll 11 and the nip roll 15: 15 kg / cm

(Comparative Example 3)
An amorphous PEN sheet (Tg: about 120 ° C.) having a thickness of 700 μm was produced by a T-die extrusion method. This amorphous PEN sheet was supplied to the sheet manufacturing apparatus 1 or the sheet manufacturing apparatus 2 described above, and a prism sheet having a large number of isosceles triangular prisms having an apex angle of 90 degrees was manufactured on the sheet surface under the following conditions.
[Production conditions]
Sheet material: Amorphous PEN
Thickness: 560 μm
Prism pitch: 200 μm
Surface temperature of heating roll 11: 190 ° C
Surface temperature of the nip roll 15: 80 ° C.
Surface temperature of cooling roll 12: 30 ° C
Opposite roll 16 surface temperature: 30 ° C.
Resin sheet cooling rate: 3 ° C./second (sheet conveyance speed: 2 m / min)
Nip linear pressure between the heating roll 11 and the nip roll 15: 15 kg / cm

(Comparative Example 4)
An amorphous PET sheet (Tg: about 75 ° C.) having a thickness of 200 μm was produced by a T-die extrusion method. This amorphous PET sheet was supplied to the sheet manufacturing apparatus 1 or the sheet manufacturing apparatus 2 described above, and a prism sheet in which a large number of isosceles triangular prisms having an apex angle of 90 degrees was arranged on the sheet surface under the following conditions.
[Production conditions]
Sheet material: Amorphous PET
Thickness: 200 μm
Prism pitch: 50 μm
Surface temperature of heating roll 11: 150 ° C.
Surface temperature of nip roll 15: 40 ° C.
Surface temperature of cooling roll 12: 30 ° C
Opposite roll 16 surface temperature: 30 ° C.
Resin sheet cooling rate: 10 ° C./second (sheet conveyance speed: 4 m / min)
Nip linear pressure between the heating roll 11 and the nip roll 15: 3 kg / cm

(Comparative Example 5)
An amorphous PET sheet (Tg: about 75 ° C.) having a thickness of 200 μm was produced by a T-die extrusion method. This amorphous PET sheet was supplied to the sheet manufacturing apparatus 1 or the sheet manufacturing apparatus 2 described above, and a prism sheet in which a large number of isosceles triangular prisms having an apex angle of 90 degrees was arranged on the sheet surface under the following conditions.
[Production conditions]
Sheet material: Amorphous PET
Thickness: 200 μm
Prism pitch: 50 μm
Surface temperature of heating roll 11: 150 ° C.
Surface temperature of nip roll 15: 40 ° C.
Surface temperature of cooling roll 12: 30 ° C
Opposite roll 16 surface temperature: 30 ° C.
Resin sheet cooling rate: 10 ° C./second (sheet conveyance speed: 4 m / min)
Nip linear pressure between the heating roll 11 and the nip roll 15: 35 kg / cm

(Comparative Example 6)
An amorphous PET sheet (Tg: about 75 ° C.) having a thickness of 200 μm was produced by a T-die extrusion method. This amorphous PET sheet was supplied to the sheet manufacturing apparatus 1 or the sheet manufacturing apparatus 2 described above, and a prism sheet in which a large number of isosceles triangular prisms having an apex angle of 90 degrees was arranged on the sheet surface under the following conditions.
[Production conditions]
Sheet material: Amorphous PET
Thickness: 200 μm
Prism pitch: 50 μm
Surface temperature of heating roll 11: 150 ° C.
Surface temperature of nip roll 15: 40 ° C.
Surface temperature of cooling roll 12: 80 ° C.
Opposite roll 16 surface temperature: 80 ° C.
Resin sheet cooling rate: 10 ° C./second (sheet conveyance speed: 3 m / min)
Nip linear pressure between the heating roll 11 and the nip roll 15: 15 kg / cm

(Comparative Example 7)
An amorphous PET sheet (Tg: about 75 ° C.) having a thickness of 100 μm was prepared by a T-die extrusion method. This amorphous PET sheet was supplied to the sheet manufacturing apparatus 1 or the sheet manufacturing apparatus 2 described above, and a prism sheet in which a large number of isosceles triangular prisms having an apex angle of 90 degrees was arranged on the sheet surface under the following conditions.
[Production conditions]
Sheet material: Amorphous PET
Thickness: 100 μm
Prism pitch: 185 μm
Surface temperature of heating roll 11: 150 ° C.
Surface temperature of nip roll 15: 40 ° C.
Surface temperature of cooling roll 12: 50 ° C.
Opposite roll 16 surface temperature: 50 ° C.
Resin sheet cooling rate: 10 ° C./second (sheet conveyance speed: 3 m / min)
Nip linear pressure between the heating roll 11 and the nip roll 15: 15 kg / cm

(Comparative Example 8)
An amorphous PET sheet (Tg: about 75 ° C.) having a thickness of 200 μm was produced by a T-die extrusion method. A prism sheet in which a large number of isosceles prisms having an apex angle of 90 degrees are arranged on the surface of the amorphous PET sheet by melt extrusion molding was produced.
[Production conditions]
Sheet material: Amorphous PET
Thickness: 200 μm
Prism pitch: 50 μm

  The sheet manufacturing conditions of Examples 1 to 13 and Comparative Examples 1 to 8 are collectively shown in FIG.

  Subsequently, with respect to the samples manufactured under the manufacturing conditions of Examples 1 to 13 and Comparative Examples 1 to 8, the prism-shaped transfer rate [%], the radius of curvature of the prism top (vertical angle R) [μm], and the total sheet thickness The prism height ratio (prism ratio) [%], crystallinity [%], and front luminance increase rate [%] were measured.

  The transfer rate is as defined above. The crystallinity was measured by density calculation using DSC (differential scanning calorimeter). The front luminance increase rate is based on the configuration of the liquid crystal display device shown in FIG. 5, and the above-mentioned each embodiment is based on the front luminance when the prism sheet 10 and the diffusion sheet 23 are not present in the dark room as a reference (100%). The increase rate of the front luminance when the prism sheet sample and the diffusion sheet according to the example and the comparative example were installed. In addition, “CS-1000” manufactured by Konica Minolta Co., Ltd. was used as the front luminance measuring instrument.

  The measurement results are shown in FIG. Judgment is made in three stages, and the evaluation criteria are “◎” is a level that shows superiority in practical use compared to the current product, “○” is a level that does not cause practical problems, and “×” is a level that does not satisfy practical characteristics. .

  As shown in FIG. 11, in each of Examples 1 to 13, a result that the transfer rate was 99% or more was obtained. Also, it can be seen that the radius of curvature of the prism top is 5% or less of the prism pitch, and good transfer accuracy is obtained. In addition, the crystallinity of each sample was suppressed to 10% or less, and no decrease in transparency due to whitening was observed. From these results, it was possible to improve the front luminance of the liquid crystal display device by 180% or more for any sample.

  On the other hand, in Comparative Example 1, although the transfer rate was high, the degree of crystallinity exceeded 20%. Therefore, the rate of increase in front luminance was only 175% due to the decrease in transparency due to whitening. This is presumably because the surface temperature of the heating roll 11 was high (Tg + 90 ° C.) and the cooling rate required to prevent crystallization was not obtained. In Comparative Example 2, although the promotion of crystallization could be prevented, the transfer rate was low and the luminance was not sufficiently increased. This is presumably because the surface temperature of the heating roll 11 was low (less than Tg + 60 ° C.) and shape transfer was insufficient. In Comparative Example 3, since the resin sheet was too thick at 560 μm, the cooling rate was not sufficient, crystallization was excessively accelerated, and a decrease in transmittance due to whitening was observed.

  In Comparative Example 4, since the nip linear pressure between the heating roll 11 and the nip roll 15 was too low, 3 kg / cm, the shape transfer was not sufficient, and a high front luminance increase rate was not obtained. On the other hand, in Comparative Example 5, since the nip linear pressure was too high at 35 kg / cm, stable sheet production could not be performed due to equipment. Moreover, about the comparative example 6, the surface temperature of the cooling roll 12 was high (above Tg), the peelability was bad, and the sheet could not be manufactured stably.

  In Comparative Example 7, since the ratio of the prism height to the total thickness of the sheet is high (over 90%), the sheet is torn along the prism ridge direction, and cracks are generated, resulting in durability and handling properties. The production was not stable. And since the comparative example 8 was shape transfer by the melt extrusion method, the transfer rate was poor, and a good luminance increase was not recognized.

  As described above, in Examples 1 to 13 where the cooling rate is 5 ° C./second or more and 40 ° C./second or less, the surface temperature of the heating roll 11 is Tg + 60 ° C. or more and Tg + 90 ° C. or less, and the thickness of the resin sheet is 500 μm or less. Excessive crystallization of the sheet was prevented, and the crystallinity could be suppressed to 20% or less. Further, since the nip pressure satisfies the condition of 5 kg / cm or more and 30 kg / cm or less in terms of linear pressure, good shape transferability and releasability were obtained, and stable productivity could be secured.

  As mentioned above, although embodiment and the Example of this invention were described, of course, this invention is not limited to these, A various deformation | transformation is possible based on the technical idea of this invention.

  For example, in the embodiment described above, the roll-shaped resin sheet or the single-wafer-sized resin sheet 10 is supplied to the sheet manufacturing apparatuses 1 and 2, but the amorphous resin is provided on the front side of the sheet manufacturing apparatus. A melt extrusion molding apparatus for producing a sheet may be installed so that the process from the production of the resin sheet to the formation of the emboss may be continuously performed.

  Moreover, it becomes possible to perform an embossing process and a extending | stretching process continuously by installing the extending | stretching apparatus which extends | stretches the manufactured embossed sheet to a predetermined direction in the back | latter stage side of a sheet manufacturing apparatus.

It is a schematic block diagram of the sheet manufacturing apparatus used for the manufacturing method of the optical sheet by the 1st Embodiment of this invention. It is a principal part expanded sectional view which respectively shows the embossing formation surface of the embossing belt and resin sheet in the sheet manufacturing apparatus of FIG. It is a figure which shows one experimental result explaining the difference in the shape transfer property of the shape transfer by a lamination system, and the shape transfer by a melt extrusion system. It is a schematic perspective view which shows the whole structure of the resin sheet (optical sheet) manufactured with the sheet manufacturing apparatus of FIG. It is a schematic block diagram of the liquid crystal display device which used the optical sheet shown in FIG. 4 as a prism sheet. It is a schematic block diagram of the sheet manufacturing apparatus used for the manufacturing method of the optical sheet by the 2nd Embodiment of this invention. It is a figure explaining the manufacturing method of the optical sheet by the 3rd Embodiment of this invention. It is a figure which shows the temperature distribution of a heating roll and a cooling roll. It is a figure which shows the example of the embossing shape formed in the surface of a resin sheet. It is a table | surface which shows the result of the Example of this invention. It is a table | surface which shows the result of the Example of this invention.

Explanation of symbols

1, 2 ... Sheet manufacturing apparatus 10 ... Resin sheet Prism sheet (optical sheet)
DESCRIPTION OF SYMBOLS 11 ... Heating roll 12 ... Cooling roll 13 ... Embossed belt 14 ... Endless belt 15 ... Nip roll 16 ... Opposite roll 20 ... Liquid crystal display device

Claims (14)

A method for producing an optical sheet comprising a transparent thermoplastic resin sheet whose surface is regularly processed with a geometric pattern,
When the glass transition temperature of an amorphous crystalline resin sheet made of PET (polyethylene terephthalate), PEN (polyethylene naphthalate), or a mixture or copolymer thereof is Tg (° C.), the temperature is higher than Tg. A set heating roll, a cooling roll set to a temperature lower than Tg, a metal endless processing belt wound around the heating roll and the cooling roll and having a geometric shape formed on the surface, and the heating Using a nip roll that is disposed opposite to the roll and sandwiches the resin sheet with the metal endless belt ,
In a state where the resin sheet is sandwiched between the metal endless processing belt and the nip roll with a nip line pressure of 5 kg / cm or more and 30 kg / cm or less, the surface of the resin sheet is Tg + 60 ° C. or more and Tg + 90 ° C. or less. Process geometric patterns with temperature,
The resin sheet having the geometric pattern processed by the cooling roll is cooled to a temperature lower than its glass transition temperature at a cooling rate of 5 ° C./second or more and 40 ° C./second or less, whereby crystals of the resin sheet are obtained. The degree of conversion is suppressed to 20% or less,
A method for producing an optical sheet, wherein the cooled resin sheet is peeled from the metal endless belt. It is a manufacturing method of the optical sheet according to claim 1,
The method for producing an optical sheet, wherein the increase in crystallinity of the resin sheet before and after the method for producing the optical sheet is 5% or less. It is a manufacturing method of the optical sheet according to claim 1,
Put a plurality of the resin sheets,
The method for producing an optical sheet, wherein the plurality of resin sheets are integrated with each other by heat bonding simultaneously with the transfer of the shape by the metal endless processing belt. It is a manufacturing method of the optical sheet according to claim 1,
The method for producing an optical sheet, wherein a height ratio of the transfer portion to the total thickness of the resin sheet is 90% or less. It is a manufacturing method of the optical sheet according to claim 1,
The geometric pattern transferred to the resin sheet has an embossed shape. It is a manufacturing method of the optical sheet according to claim 5 ,
The embossed shape transferred to the resin sheet is a prism shape. It is a manufacturing method of the optical sheet according to claim 6 ,
The prism shape transferred to the resin sheet is an isosceles triangle having an apex angle of 90 degrees. It is a manufacturing method of the optical sheet according to claim 7 ,
The method for producing an optical sheet, wherein the transfer rate of the prism shape to the resin sheet is 98% or more. It is a manufacturing method of the optical sheet according to claim 1,
The metal endless working belts, manufacturing method of optical sheets to be conveyed in synchronism with the pre-Symbol heating roll with rotation of the cooling roll. It is a manufacturing method of the optical sheet according to claim 1 ,
An endless belt is wound around the nip roll and an opposing roll facing the cooling roll,
The method for producing an optical sheet, wherein the resin sheet is nipped and conveyed between the metal endless belt and the endless belt. It is a manufacturing method of the optical sheet according to claim 10 ,
The shape of the resin sheet is transferred by the metal endless belt, and at the same time, the shape is also transferred to the opposite side of the resin sheet by the geometric shape formed on the surface of the endless belt. Method. It is a manufacturing method of the optical sheet according to claim 1,
The geometric pattern processed on the surface of the resin sheet has at least one corner portion. It is a manufacturing method of the optical sheet according to claim 1,
For the heating roll that conveys the resin sheet, set the roll temperature higher in the center than at both ends,
About the cooling roll which conveys the said resin sheet, the manufacturing method of an optical sheet which sets roll temperature lower than the center part rather than both ends. The method for producing an optical sheet according to claim 1, further comprising:
A method for producing an optical sheet, wherein the resin sheet subjected to the processing of the geometric pattern is stretched in a uniaxial direction to impart refractive index anisotropy to the resin sheet.

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