KR20080084690A - Optical sheet manufacture method and optical sheet - Google Patents

Abstract

An optical sheet manufacturing method and an optical sheet are provided to form a desired embossing pattern on a surface of a crystalline resin sheet by using a high transfer rate. An optical sheet manufacturing method includes a process for manufacturing an optical sheet by using a transparent thermoplastic resin sheet(10). A regular geometric design process is performed on a surface of the transparent thermoplastic resin sheet. In the optical sheet manufacturing method, a geometric design process is performed on the resin sheet at a temperature not lower than a glass transition temperature of the resin sheet by using a metal endless working belt having a geometric design formed on a surface thereof. The rapidly cooled resin sheet is separated from the metal endless working belt.

Description

Optical sheet manufacturing method and optical sheet {OPTICAL SHEET MANUFACTURE METHOD AND OPTICAL SHEET}

The present invention relates to an optical sheet manufacturing method made of a transparent crystalline resin sheet in an amorphous state embossed on its surface.

The so-called embossed sheet is made of a resin sheet or film having a regular three-dimensional geometric design (embossing pattern) formed on its surface. Typically, the thermoplastic resin melt is pushed out of the sheet-shaped T die, and the melt sandwiched and pressurized between the metal roll and convex / concave shape on its outer circumferential surface is cooled and solidified to form a convex / concave shape on the surface. The melt-extrusion method which continuously forms the sheet | seat with which the flat back surface is formed continuously is used widely (for example, refer Unexamined-Japanese-Patent No. 09-295346, patent document 1).

In the melt extrusion method, transfer and separation of the resin pushed out of the T die are simultaneously performed using the same solid roll having a geometric shape. It is necessary for the resin to have sufficient thermal energy to achieve complete transfer and to cool the resin below the glass transition temperature (Tg) of the resin in order to effect separation. Since the melt extrusion method performs transfer and cooling using the same solid roll, it is difficult to perform sufficient heating and cooling, and it is difficult to perform both transfer and separation completely.

According to another embossing sheet manufacturing method, an embossing pattern formed on the surface of the metal roll or the metal flat plate is transferred to the surface of the resin sheet. According to another known method, an embossing pattern is formed on the surface of a resin sheet by using a metal endless work belt wound around a plurality of rolls and an embossing pattern formed on the surface thereof (for example, Japanese Patent Laid-Open No. 2001-277354). See, Patent Document 2).

The embossed sheet produced by the above method can be used, for example, as an optical sheet for a liquid crystal display device. In particular, a prism sheet in which prism shapes having a triangular cross section are continuously arranged can be used as the embossing sheet. Prism sheets are well known as brightness improving sheets (films) for improving front brightness by covering the backlight. For example, WO 2006/071621 (Patent Document 3) discloses a prism sheet formed by stretching a resin sheet having a refractive index that is in-plane anisotropy and having a prism shape on its surface.

It is necessary to form an amorphous resin having an embossed pattern on the surface. In order to form the embossed sheet to have an in-plane anisotropic refractive index, the crystalline resin sheet is usually elongated along the uniaxial or biaxial direction. In this case, the crystalline resin sheet is preferably in an amorphous state so that the stretching treatment can be appropriately performed with high precision.

However, in the aforementioned embossing sheet manufacturing method, it is difficult to carry out the embossing treatment while keeping the resin sheet in an amorphous state. That is, in the embossing sheet manufacturing method of the prior art, after the embossing pattern is formed on the resin sheet by raising it to a temperature higher than the glass transition temperature or the crystal temperature range, the resin is crystallized during the cooling treatment of lowering the temperature of the resin sheet for separation. It is impossible to prevent that. As the crystallization of the resin sheet proceeds, the resin whitens and the transparency is lost, thus the resin sheet becomes unsuitable for use as an optical sheet. If the embossing pattern transfer temperature is low or the separation temperature is high, it is impossible to obtain high embossing pattern transfer accuracy.

The present invention has been made in view of these problems. According to one embodiment of the present invention, there is provided an optical sheet manufacturing method capable of preventing whitening due to crystallization of a resin sheet while ensuring high precision of an embossing pattern.

According to one embodiment of the invention, the method for producing an optical sheet is a method for producing an optical sheet made of a transparent thermoplastic resin sheet whose surface is subjected to regular geometric design processing. The optical sheet manufacturing method includes forming a geometric design on a resin sheet at a temperature above the glass transition temperature of the resin sheet by using a metal endless work belt having a geometric design formed on the surface thereof, and a resin having a geometric design formed at a temperature lower than the glass transition temperature. Rapidly cooling the sheet and separating the rapidly cooled resin sheet from the metal endless work belt.

In an embodiment of the present invention, the resin sheet is subjected to a geometric design (embossed shape) treatment at a temperature higher than the glass transition temperature of the resin sheet, and then to a temperature lower than the glass transition temperature or crystallization temperature to suppress crystallization of the resin sheet. Is rapidly cooled. Also in the embodiment of the present invention, the embossing treatment is performed on the resin sheet by using a metal endless work belt, and then the resin sheet combined with the metal endless work belt is cooled between the transfer treatment and the cooling treatment, and the resin sheet is It is separated from the metal endless work belt to a temperature lower than the glass transition temperature of the resin sheet. Thus, the embossed shape transfer performance and separation performance of the resin sheet are improved.

In order to prevent crystallization of the amorphous resin sheet, an important problem is the cooling rate of the resin sheet to a temperature below the glass transition temperature of the resin sheet after the embossed shape is transferred. Depending on the material used for the resin sheet, the cooling rate is set to, for example, 5 ° C / sec or more and 40 ° C / sec or less. If the cooling rate is lowered to less than 5 ° C / sec, it is impossible to prevent excessive crystallization of the resin sheet, causing whitening (loss of transparency). If the cooling rate is quickly set to exceed 40 ° C / sec, the embossing operation is lowered, making it difficult to obtain shape transfer.

Crystallization of the resin sheet when the resin sheet is separated from the metal endless work belt is set to 20% or less, preferably 5% or less. When the crystallization of a resin sheet exceeds 20%, transparency will fall largely by whitening, and a resin sheet becomes unsuitable for using as an optical sheet.

The geometric design (embossed shape) formed on the surface of the resin sheet is not particularly limited, but may be a shape having at least one corner portion (sharp edge portion) such as a prism shape, a rectangular wave and a trapezoid. An embossed shape having at least one corner portion can also be transferred at high transfer rates. The apex angle of the prism shape is set to, for example, 90 °, but it may be an acute angle of less than 90 ° or an obtuse angle exceeding 90 °. The embossed shape may be a lens shape.

The material of the resin sheet is not particularly limited as long as it is a transparent thermoplastic resin. Preferably PET, PEN, mixtures and copolymers thereof can be used. In order to maintain the cooling rate stably, the total thickness of the resin sheet may be set, for example, 500 µm or thinner. The ratio of the embossed shape height to the total thickness of the resin sheet is, for example, 90% or less. When height ratio exceeds 90%, a crack etc. generate | occur | produce in a resin sheet, and therefore handling performance falls. The resin sheet may be a sheet cut into a long bandage shape or a predetermined size.

The material of the metal endless work belt may be stainless steel, nickel steel, or the like. In the embodiment of the present invention, it is preferable that the resin sheet is adhered to the metal endless work belt so that the heating, pressurization and cooling treatments are respectively performed while the resin sheet moves with the metal endless work belt. As a method of adhering a resin sheet to a metal endless work belt, for example, there is a method of firmly attaching the resin sheet to the belt by heating the resin sheet on the metal endless belt to a softening temperature (temperature above the glass transition temperature) of the resin sheet. In this way, manufacturing facilities can be simplified and manufacturing costs can be reduced. Since the embossed sheet can be produced continuously, the manufacturing efficiency can be improved.

During the heat treatment, for example, heating starts from the inside of the metal endless work belt. By initiating heating from the inside of the belt, the sheet adhered to the heated endless work belt can be directly heated to improve heating efficiency. As a means for starting heating from the inside of a metal endless work belt, the method by which the roll by which a belt is wound is used as a heating roll is the most efficient. In addition to the above, there is a method in which the heating is performed by an electric heater provided on the roll or a method of circulating the heated oil in the roll. Depending on the cooling means, the coolant flows inside the metal roll. Supplementary heating by an external infrared heater or supplementary heating by air flow may also be possible.

In an embodiment of the present invention, the metal endless work belt is wound around a heating roll set to a temperature above the glass transition temperature of the resin sheet and a cooling roll set to a temperature below the glass transition temperature of the resin sheet, the belt being heated roll and It is conveyed in synchronization with the rotation of the cooling roll. According to the cooling rate required to prevent crystallization of the resin sheet, the temperature of the heating roll and the cooling roll, the roll mutual distance, and the linear speed (the conveying speed of the metal endless work belt) are set.

The in-plane temperature uniformity of the metal endless work belt greatly affects the working precision of the shape transferred to the surface of the resin sheet. In an embodiment of the present invention, the roll temperature at the center of the heating roll is set higher than the opposite end, and the roll temperature at the center of the cooling roll is set lower than the opposite end. It is therefore possible to produce in-plane temperature uniformity of metal endless work belts and to produce embossed sheets with good form precision.

The embossing treatment is performed on the resin sheet by supplying the resin sheet between the nip roll disposed on the heating roll and the metal endless work belt. In such a case, when the nip pressure between the metal endless work belt and the nip roll is low, the embossed shape transfer accuracy is lowered, while the high nip pressure adversely affects the durability of the nip roll and makes stable production difficult. Preferred nip pressures have a linear pressure of at least 5 kg / cm and at most 30 kg / cm.

If the conveyance speed of the metal endless work belt is increased to increase the cooling rate of the resin sheet, the running performance of the resin sheet becomes unstable or sufficient preheating cannot be obtained, and thus the conveying performance is lowered. The endless belt is wound around the nip roll and the opposing roll facing the cooling roll, and the resin sheet is conveyed by sandwiching between the endless belt and the metal endless work belt. Therefore, it is possible to improve the running stability and the feeding speed of the resin sheet.

As described above, according to the optical sheet manufacturing method of the present invention, it becomes possible to form a desired embossed shape on the surface of the crystalline resin sheet at a high transfer rate while preventing whitening of the sheet by crystallization.

Each embodiment of the present invention is described with reference to the accompanying drawings.

(First embodiment)

Fig. 1 is a diagram showing an external structure of a sheet manufacturing apparatus 1 for explaining the optical sheet manufacturing method according to the first embodiment of the present invention.

The sheet manufacturing apparatus 1 faces the heating roll 11, the cooling roll 12, and the embossed belt 13 and the heating roll 11 wound around the rolls 11 and 12 arrange | positioned at predetermined distances. It has the nip roll 15 arrange | positioned and the opposing roll (backup roll) 16 arrange | positioned facing the cooling roll 12. As shown in FIG.

The sheet manufacturing apparatus 1 transfers the transparent amorphous crystalline resin sheet 10 in synchronization with the embossing belt 13 between the embossing belt 13 and the nip roll 15, and the resin sheet is heated by the heating roll 11. The resin sheet is pressed against the embossing belt while being heated to a temperature above the glass transition temperature, so that the embossed shape of the embossing belt 13 is transferred to the surface of the resin sheet 10. In order to manufacture the transparent amorphous crystalline resin sheet 10 having the embossed shape (prism pattern) 10a having a predetermined shape on its surface, the resin sheet 10 is attached with the resin sheet attached to the embossing belt 13. It is moved, rapidly cooled by the cooling roll 12, and is separated from the embossing belt 13.

The heating roll 11 has built-in heating means, such as a heater, and the surface temperature is set to a temperature higher than the softening temperature of the resin sheet 10, for example, higher than the glass transition temperature of the resin sheet 10. Therefore, the portion located on the heating roll 11 of the embossing belt 13 is also heated to this temperature so that the heat treatment of the resin sheet 10 can be performed at this position.

In the present embodiment, 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 Tg (° C.) is the glass transition temperature of the resin sheet 10. If the set temperature is less than Tg + 60 ° C., high transfer accuracy of the embossing pattern for the resin sheet 10 cannot be achieved. If the set temperature exceeds Tg + 90 ° C. and the resin sheet 10 is made of a crystalline resin that is difficult to remain in an amorphous state, crystallization of the resin sheet 10 is excessively accelerated, resulting in a significant decrease in transparency due to whitening. .

The cooling roll 12 has built-in cooling means like a water cooling system, and the surface temperature is set 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. Thus, the portion located on the cooling roll 12 of the embossing belt 13 can also be cooled so that the cooling treatment for the resin sheet 10 can be performed at this position.

In this embodiment, as shown in Fig. 8A, the roll temperature of the central portion of the heating roll 11 is set higher than the opposite end. On the other hand, as shown in Fig. 8B, the roll temperature at the center of the cooling roll 12 is set lower than the opposite end. Therefore, it is possible to produce an embossed sheet having improved in-plane temperature uniformity of the endless belt and having excellent form accuracy. In the method for implementing such a temperature distribution, when the heating source for the heating roll 11 is constituted by an electric heater, the number of windings of the electric wire in the center of the roll is larger than the opposite roll end.

At least one of the heating roll 11 and the cooling roll 12 is configured to be rotatable by being coupled to a rotation drive means such as a motor.

The embossed belt 13 corresponds to the "metal endless work belt" of the present invention made of a metal embossed belt having excellent thermal conductivity. In this embodiment, the embossing belt 13 is made of nickel steel and has an embossing shape (geometric design) in which grooves having a triangular (prism shape) cross section are continuously arranged on the surface thereof. The prism right angle is not particularly limited, but it is contemplated that for example 120 ° or less and 90 ° are preferable. The embossing belt 13 is preferably seamless (no joints). The embossed belt is preferably formed by nickel steel growth by electroforming on a tubular resin master having an embossed shape on its inner surface side, or by winding around a roll and performing a precise cutting process directly. The present invention is not limited only to these methods.

Although the extension direction (ridge direction) of the embossed shape 13a is set in the width direction (lateral direction TD) of the resin sheet 10 of this embodiment, the direction is not limited to this, but the direction of the resin sheet 10 Travel direction (machining direction MD). In order to improve the separability with the resin sheet 1, a release agent may be coated on the surface in which the embossing shape 13a was formed with respect to the embossing belt 13. The release agent is preferably a fluorine-containing resin, a silicone-containing resin, or the like.

The embossing shape 13a is not limited to a triangle (prism shape) in cross section. The right angle of the prism shape is not limited to 90 ° as shown in FIG. 9A, and the right angle may be an acute angle of less than 90 ° as shown in FIG. 9B or exceeding 90 ° as shown in FIG. 9C. It can be obtuse. Embossing shape 13a may be sinusoidal as shown in FIG. 9D or trapezoidal as shown in FIG. 9E. The shape can also be formed for an embossed shape having at least one corner portion (sharp shape) described above at a high transfer rate.

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

The nip roll 15 is a roll which interacts with the embossed belt 13 sandwiches the resin sheet 10 to pressurize, and transfers the embossed shape 13a of the surface of the embossed belt 13 to the surface of the resin sheet 10. Is provided. In the present embodiment, similar to the heating roll 11, the nip roll 15 has a built-in heating source and has a function of heating the resin sheet 10 of the embossing belt 13 from the back side as an auxiliary roll. The outer circumferential surface of the nip roll 15 has a flat and smooth shape, but a predetermined embossed shape may be formed on the outer circumferential surface of the nip roll 15 so that the shape can be transferred to the back side of the resin sheet 10. The nip roll 15 may be a cooling roll having a cooling mechanism for assisting separation on the back side and preventing transfer of the shape of the back roll.

The nip pressure applied to 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 this embodiment, the nip pressure has a linear pressure of 5 kg / cm or more and 30 kg / cm or less. If the nip pressure is lower than 5 kg / cm, the transfer accuracy of the embossed shape 13a to the resin sheet 10 is lowered, while if the nip pressure is higher than 30 kg / cm, the nip roll 15 and the embossed belt 13 It adversely affects durability and makes it difficult to manufacture stably.

When the resin sheet 10 is separated from the embossing belt 13 of the cooling roll 12, the opposing roll 16 is mounted as a usable auxiliary roll. Similar to the cooling roll 12, the opposing roll 16 has a built-in cooling means for maintaining a surface temperature similar to that of the cooling roll 12, and has a function of cooling the resin sheet 10 from the back side. The outer circumferential surface of the opposing roll 16 has a flat and smooth shape. The nip pressure applied to the resin sheet 10 by the opposing roll 16 and the embossing belt 13 is not particularly limited, but the nip pressure is such that the outer circumferential surface of the opposing roll 16 is the back side of the resin sheet 10. It is enough if it can be in intimate contact.

The material of the resin sheet 10 is not particularly limited as long as it is a transparent thermoplastic crystalline resin. In this embodiment, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), mixtures or copolymers thereof are used, which are crystalline resins under harsh manufacturing conditions during cooling treatment to maintain an amorphous state. In this embodiment, a method of forming a long strip-shaped amorphous resin sheet 10 and continuously transferring it to the sheet manufacturing apparatus 1 is employed. Alternatively, the method may be adopted in which the resin sheet 10 cut to a predetermined size is sequentially transferred to the sheet manufacturing apparatus 1.

Here, the resin sheet 10 in an amorphous state means having a crystallization ratio of 3% or less, for example. The sheet manufacturing apparatus 1 of this embodiment performs an embossing process on the surface of the resin sheet 10 in an amorphous state by using the embossing belt 13, and has a crystallization ratio of 20% or less, preferably 10% or less. A process of rapidly cooling the resin sheet (embossed shape or prism shape) 10 in an amorphous state is performed. When the crystallization ratio exceeds 20%, the decrease in transparency caused by whitening becomes remarkable, and the resin sheet becomes unsuitable for use as an optical sheet.

If the crystallization ratio exceeds 20%, the Young's modulus of the material will typically be high. Therefore, when the resin sheet to be embossed is subjected to the stretching treatment next, the load required for stretching is increased and the heating temperature during stretching is set high. If the resin sheet is given birefringence in particular by stretching treatment, and the resin sheet before stretching has a crystallization ratio of more than 20%, preferable birefringence is difficult to be obtained.

In order to maintain the amorphous state of the resin sheet 10 before and after the embossing process of the resin sheet 10, the cooling rate (° C / sec) of the resin sheet 10 is a shape transfer to the resin sheet on the heating roll 11. Becomes an important problem during separation of the resin sheet 10 on the cooling roll 12 from the. According to the material of the resin sheet 10, a cooling rate becomes like this. Preferably it is set to 5 degrees C / sec or more and 40 degrees C / sec or less, More preferably, it is set to 10 degrees C / sec or more and 30 degrees C / sec or less. When the cooling rate is lowered to less than 5 ° C / sec, it is impossible to prevent excessive crystallization of the resin sheet, causing whitening (loss of transparency). If the cooling rate is quickly set to exceed 40 ° C / sec, the embossing operation is lowered, making it difficult to obtain shape transfer. By implementing the cooling rate of the above-mentioned range, it becomes possible to suppress the increase of the crystallization ratio of the resin sheet to 5% or less before and after performing the embossed shape transfer process by the sheet manufacturing apparatus 1. It is also possible to suppress the crystallization ratio of the resin sheet separated from the embossed belt to 20% or less.

In order to realize the cooling rate of the resin sheet 10, the sheet manufacturing apparatus 1 includes the roll mutual distance between the heating roll 11 and the cooling roll 12, the conveying speed of the endless belt 13, and the cooling roll 12. The contact angle of the resin sheet 10 with respect to), etc. are specified. A plurality of cooling rolls 12 may be provided.

If the distance between the rolls 11 and 12 becomes too long, it is necessary to increase the feed speed of the endless belt 13 to secure the cooling rate. However, as the feed speed of the endless belt 13 is increased, the running stability of the resin sheet 10 is lowered. Therefore, it is difficult to expect stable productivity or preheating is insufficient and transfer performance is lowered. If the distance between the rolls 11 and 12 becomes too short, heat exchange of the endless belt 13 becomes insufficient, thus making it difficult to perform the heating and cooling treatment for the resin sheet 10 at a desired temperature.

In a preferred example, when the temperature of the heating roll 11 is set to a temperature of at least Tg + 60 ° C and is at most Tg + 90 ° C, when the temperature of the cooling roll 12 is set to 30 ° C, and the endless belt 13 When the feed speed of the) is set to 3 m / min, the roll mutual distance between the heating roll 11 and the cooling roll 12 is set to 100 mm or more and 400 mm or less. This roll mutual distance changes with the material of the resin sheet 10. For example, roll mutual distance is 100 mm or more and 200 mm or less for PET, and 100 mm or more and 400 mm or less for PEN. The roll mutual distance of 100 mm corresponds to a cooling rate of 20 ° C./sec at 5 m / min, and the roll mutual distance of 400 mm corresponds to a cooling rate of 5 ° C./sec.

It is apparent that the required cooling rate can be obtained by changing the feed rate of the embossing belt 13 while keeping the distance between the rolls 11 and 12 constant. In this case, the preferred feed speed is at least 5 m / min and at most 10 m / min when the distance between the rolls 11, 12 is 800 mm.

In order to maintain cooling conditions stably, it is preferable to set the total thickness of the resin sheet 10 to 500 micrometers or less. The ratio of the height of the embossed shape to the total thickness of the resin sheet 10 is preferably 90% or less. When height ratio exceeds 90%, a crack etc. generate | occur | produce in the resin sheet 10, and handling performance falls.

Next, the optical sheet manufacturing method of this embodiment is explained using the sheet manufacturing apparatus 1 comprised as mentioned above.

The resin sheet 10 in an amorphous state preset for a supply roll (not shown) is supplied between the embossing belt 13 and the nip roll 15. Next, the resin sheet 10 is heated to a temperature corresponding to the glass transition temperature or higher in the heating roll 11, and transfers the embossed shape 13a of the embossing belt 13 to the surface of the resin sheet 10. Sandwiched between the embossed belt 13 and the nip roll 15 so as to be pressed.

The resin sheet 10 to which the embossed shape has been transferred is attached to the embossing belt 13 and conveyed to the cooling roll 12 together with the embossing belt 13. The resin sheet 10 is cooled to a temperature lower than the glass transition temperature of the cooling roll 12 together with the embossing belt 13. During this cooling treatment, the resin sheet 10 is rapidly cooled at a cooling rate at which an amorphous state is maintained after the embossed shape is transferred. The cooled resin sheet 10 is separated from the embossing belt 13 after passing through the nip point between the embossing belt 13 and the opposing roll 16 wound around the winding roll (not shown).

In this manner, the resin sheet 10 in the amorphous state in which the embossed shape 10a is formed on the surface is manufactured. By using the sheet manufacturing apparatus 1 configured as described above, the resin sheet 10 can be embossed, so that the manufacturing equipment can be simplified to reduce the cost. Since the embossed sheet can be produced continuously, the manufacturing efficiency can be improved.

In this embodiment, embossing is performed on the resin sheet 10 at a temperature corresponding to the glass transition temperature or higher, and the resin sheet is then rapidly cooled to a temperature lower than the glass transition temperature. Therefore, it is possible to hold | maintain in an amorphous state, suppressing the crystallization of the resin sheet 10. FIG. Further, the embossing treatment is performed on the resin sheet by using the embossing belt 13, the resin sheet 10 is cooled together with the embossing belt 13 during the period between the transfer treatment and the cooling treatment, and the resin sheet 10 is It is separated from the embossing belt 13 at a temperature lower than the glass transition temperature of the resin sheet. Thus, the embossed shape transfer performance and separation performance for the resin sheet 10 can be improved.

According to this embodiment, a desirable embossed shape can be formed on the surface of the sheet at a high transfer rate while suppressing whitening due to crystallization of the crystalline resin sheet 10 in the amorphous state. In particular, in this embodiment, the embossed shape can be transferred to the resin sheet 10 at a high transfer rate of 98% or more.

The transfer rate is defined herein as follows. That is, as shown in Figs. 2A and 2B, when H2 represents the embossed shape height formed in the resin sheet 10 and H1 represents the embossed shape height formed in the embossing belt 13, the transfer rate (%) is (H2 / H1) x 100.

The present inventors use an embossing method using a melt extrusion style and an embossing method using the lamination style of the present invention by using a master having an embossed shape in which a cross section having a right angle of 90 ° disposed at a pitch of 50 μm is an isosceles triangle. The actual embossed shape of the resin sheet was measured. The measurement results are shown in FIG. Compared with the melt extrusion style, it has been found that the lamination style can form an embossed shape with a high transfer rate.

In-plane temperature uniformity of the embossing belt 13 greatly influences the working precision of the shape formed on the surface of the resin sheet. In this embodiment, the roll temperature of the center part of the heating roll 11 is set higher than the opposite end, and the roll temperature of the center part of the cooling roll 12 is set lower than the opposite end. Therefore, it is possible to improve the in-plane temperature uniformity of the embossing belt 13 and to manufacture the embossing sheet which has very excellent shape precision.

The resin sheet 10 in which the embossed shape is formed in the above-described manner is cut into a predetermined size and used as an optical sheet having target optical properties. 4 schematically shows the structure of the resin sheet 10 used as the prism sheet of the liquid crystal display device. The prism pattern (embossed shape) 10a having a ridge direction along the X axis direction is continuously arranged along the Y axis direction at a predetermined pitch of the surface of the resin sheet 10. The resin sheet 10 can be used in this state as a prism sheet of the liquid crystal display device.

When the resin sheet 10 shown in Fig. 4 is elongated at a predetermined elongation along the prism ridge direction (X-axis direction), the sheet optical properties can be changed. That is, by performing the stretching process, the refractive index difference may be made between the in-plane refractive index nx along the X-axis direction and the in-plane refractive index ny along the Y-axis direction. Since the resin sheet 10 is in an amorphous state having a crystallization ratio of 20% or less, the stretching treatment can be appropriately performed with high precision.

In this embodiment, resin materials such as PET and PEN having a large refractive index along the stretching direction are used as the material of the resin sheet 10, and the resin sheet 10 is given refractive index anisotropy of nx > ny by the stretching treatment. . The resin sheet 10 constructed as described above has a prism whose polarized component along the prism ridge direction (X-axis direction) is larger than the polarized component along the prism array direction (Y-axis direction) with respect to the prism from the surface of the output light. Since the light amount is returned to the light incident side again by the repetition of total reflection of the critical angle reflection on the inclined plane, the output light amount of the component polarized along the prism array direction has an optical characteristic greater than the output light amount of the component polarized along the prism extension direction. .

Fig. 5 is a schematic diagram showing the structure of the liquid crystal display device 20 using the resin sheet 10 having such a structure as a prism sheet. The liquid crystal display device 20 includes a liquid crystal display panel 21, first and second polarizers 22A and 22B sandwiched on the liquid crystal display panel 21, a prism sheet 10, a diffusion sheet 23, and a backlight unit ( 24).

The prism sheet 10 corresponds to the resin sheet 10 in which the embossing shape was formed by the sheet manufacturing apparatus 1, and is used as a luminance improving film for improving the front luminance of the liquid crystal display device 20. The prism sheet 10 is disposed on the light output side of the diffusion sheet 23 to diffuse and output the illumination light (backlight) from the backlight unit 24, and has a function of converging the output light from the diffusion sheet 23 in the forward direction. Has

The pair of polarizers 22A and 22B sandwiched on the liquid crystal display panel 11 are arranged such that their transmission axes " a " and " b " In the illustrated example, the prism sheet 10 has a prism array direction (Y-axis direction) of the prism sheet 10 approximately parallel to the transmission axis "a" of the first polarizer 22A positioned on the backlight unit 24 side. Are arranged in such a way that This example is particularly effective when the prism sheet 10 extended along the prism ridge direction (X-axis direction) is used. Since the polarization component having a large output light amount can effectively enter the liquid crystal display panel 21, the front luminance can be improved.

The prism sheet 10 is not limited to a single prism sheet structure, and a plurality of prism sheets may be stacked. In this case, it is preferable that the prism sheets are laminated while the ridge directions of the respective prism sheets are made perpendicular to each other.

(2nd Example)

Next, a second embodiment of the present invention will be described. Fig. 6 is a schematic diagram showing the structure of the sheet manufacturing apparatus 2 of the second embodiment. In Fig. 6, parts corresponding to those in the first embodiment are indicated by using the same reference numerals, and detailed description thereof is omitted.

In the sheet manufacturing apparatus 2 of the second embodiment, the metal endless belt 14 is the nip roll 15 and the opposing roll 16 facing the back side of the resin sheet 10 (the side where the embossed shape is not formed). It is wound around. The resin sheet 10 is sandwiched and pressed between the embossing belt 13 and the endless belt 14 during the cooling / separation treatment period from the heat / transfer treatment of the resin sheet 10.

The endless belt 14 is made of a metal such as nickel steel, but the material is not limited to this metal and a heat resistant resin such as heat resistant PET can be used. The surface of the endless belt 14 is mirror surface. If necessary, a shape may be formed on the endless belt, such that the shape may be transferred to the back surface of the resin sheet 10.

Depending on the material, the endless belt 14 has a thickness of 30 µm or more and preferably 1000 µm or less. If the thickness exceeds 1000 m, it is impossible to wind the endless belt around the heating roll and the cooling roll. If the thickness is less than 30 µm, warpage is liable to occur during the transfer of the resin sheet 10, or cracks containing problems in terms of strength are generated.

In the sheet manufacturing apparatus 2 of the second embodiment configured as described above, the resin sheet 10 is formed by the sheet being embossed with the embossed belt 13 during the period from heating / transferring treatment to cooling / separation treatment of the resin sheet 10. It is conveyed in a state sandwiched and held between the endless belts 14. Therefore, it is possible to improve the running stability of the resin sheet 10, so that the flexibility of setting the cooling rate for preventing whitening caused by crystallization of the resin sheet 10 can be improved by increasing the conveying speed.

According to the second embodiment, by embossing the surface of the endless belt 14 and forming an embossed shape thereon, the embossed shape can be formed with high precision not only on the front face but also on the back face of the resin sheet 10. .

(Third Embodiment)

Fig. 7 shows the manufacture of the laminated sheet 10L in which two resin sheets 10s and 10t are thermally bonded by using the sheet manufacturing apparatus 2. In this example, the embossed belt 13 and the endless belt (so that the two resin sheets 10s, 10t are thermally bonded and coalesced with each other while the embossed shape is transferred to the surface of the resin sheet 10s by the embossed belt 13). 14) sandwiched and pressed between. Therefore, it becomes possible to easily manufacture the laminated sheet 10L having a predetermined embossed shape formed on the surface thereof.

Two resin sheets 10s and 10t are conveyed together to the sheet manufacturing apparatus 2. The resin sheets 10s and 10t may be made of the same kind of resin sheet or may include different types of resin sheets. Also, three or more resin sheets can be conveyed at the same time.

[Yes]

Examples of the present invention are described, but the present invention is not limited only to these examples.

(Example 1)

A 200 μm thick amorphous PET sheet (Tg: about 75 ° C.) is formed by the T die extrusion method. The amorphous PET sheet is transferred to the sheet manufacturing apparatus 1 or 2, and a prism sheet having a plurality of isosceles triangles of prisms having a 90 ° right angle arranged on the sheet surface is produced under the following conditions.

(Manufacturing conditions)

Seat Material: Amorphous PET

Thickness: 200 ㎛

Prism Pitch: 50 ㎛

Surface temperature of heating roll 11: 150 degreeC

Surface temperature of nip roll 15: 50 ° C

Surface temperature of cooling roll 12: 30 degreeC

Surface temperature of the opposing roll 16: 30 ° C

Cooling rate of resin sheet: 20 ° C./sec

(Sheet Feed Speed: 5 m / min)

Nip line pressure between heating roll 11 and nip roll 15: 15 kg / cm

(Example 2)

A 200 μm thick amorphous PEN sheet (Tg: about 120 ° C.) is formed by the T die extrusion method. The amorphous PEN sheet is transferred to the sheet manufacturing apparatus 1 or 2, and a prism sheet having a plurality of isosceles triangles of prisms having a 90 ° right angle arranged on the sheet surface is produced under the following conditions.

(Manufacturing conditions)

Sheet Material: Amorphous PEN

Thickness: 200 ㎛

Prism Pitch: 100 ㎛

Surface temperature of heating roll 11: 190 degreeC

Surface temperature of nip roll 15: 70 ° C

Surface temperature of cooling roll 12: 30 degreeC

Surface temperature of the opposing roll 16: 30 ° C

Cooling rate of the resin sheet: 10 ° C./sec

(Sheet Feed Speed: 3 m / min)

Nip line pressure between heating roll 11 and nip roll 15: 15 kg / cm

(Example 3)

A 200 μm thick amorphous PEN sheet (Tg: about 120 ° C.) is formed by the T die extrusion method. The amorphous PEN sheet is transferred to the sheet manufacturing apparatus 1 or 2, and a prism sheet having a plurality of isosceles triangles of prisms having a 90 ° right angle arranged on the sheet surface is produced under the following conditions.

(Manufacturing conditions)

Sheet Material: Amorphous PEN

Thickness: 200 ㎛

Prism Pitch: 300 ㎛

Surface temperature of heating roll 11: 190 degreeC

Surface temperature of nip roll 15: 70 ° C

Surface temperature of cooling roll 12: 30 degreeC

Surface temperature of the opposing roll 16: 30 ° C

Cooling rate of the resin sheet: 10 ° C./sec

(Sheet Feed Speed: 3 m / min)

Nip line pressure between heating roll 11 and nip roll 15: 15 kg / cm

(Example 4)

A 200 μm thick amorphous PEN sheet (Tg: about 120 ° C.) is formed by the T die extrusion method. The amorphous PEN sheet is transferred to the sheet manufacturing apparatus 1 or 2, and a prism sheet having a plurality of isosceles triangles of prisms having a 90 ° right angle arranged on the sheet surface is produced under the following conditions.

(Manufacturing conditions)

Sheet Material: Amorphous PEN

Thickness: 200 ㎛

Prism Pitch: 10 ㎛

Surface temperature of heating roll 11: 190 degreeC

Surface temperature of nip roll 15: 70 ° C

Surface temperature of cooling roll 12: 30 degreeC

Surface temperature of the opposing roll 16: 30 ° C

Cooling rate of the resin sheet: 10 ° C./sec

(Sheet Feed Speed: 3 m / min)

Nip line pressure between heating roll 11 and nip roll 15: 15 kg / cm

(Example 5)

A 500 μm thick amorphous PET sheet (Tg: about 75 ° C.) is formed by the T die extrusion method. The amorphous PET sheet is transferred to the sheet manufacturing apparatus 1 or 2, and a prism sheet having a plurality of isosceles triangles of prisms having a 90 ° right angle arranged on the sheet surface is produced under the following conditions.

(Manufacturing conditions)

Seat Material: Amorphous PET

Thickness: 500 ㎛

Prism Pitch: 100 ㎛

Surface temperature of heating roll 11: 150 degreeC

Surface temperature of nip roll 15: 50 ° C

Surface temperature of cooling roll 12: 30 degreeC

Surface temperature of the opposing roll 16: 30 ° C

Cooling rate of resin sheet: 15 ° C./sec

(Sheet Feed Speed: 5 m / min)

Nip line pressure between heating roll 11 and nip roll 15: 15 kg / cm

(Example 6)

A 20 μm thick amorphous PET sheet (Tg: about 75 ° C.) is formed by the T die extrusion method. The amorphous PET sheet is transferred to the sheet manufacturing apparatus 1 or 2, and a prism sheet having a plurality of isosceles triangles of prisms having a 90 ° right angle arranged on the sheet surface is produced under the following conditions.

(Manufacturing conditions)

Seat Material: Amorphous PET

Thickness: 20 ㎛

Prism Pitch: 20 ㎛

Surface temperature of heating roll 11: 150 degreeC

Surface temperature of nip roll 15: 50 ° C

Surface temperature of cooling roll 12: 30 degreeC

Surface temperature of the opposing roll 16: 30 ° C

Cooling rate of the resin sheet: 30 ° C./sec

(Sheet Feed Speed: 5 m / min)

Nip line pressure between heating roll 11 and nip roll 15: 30 kg / cm

(Example 7)

A 200 μm thick amorphous PEN sheet (Tg: about 120 ° C.) is formed by the T die extrusion method. The amorphous PEN sheet is transferred to the sheet manufacturing apparatus 1 or 2, and a prism sheet having a plurality of isosceles triangles of prisms having a 90 ° right angle arranged on the sheet surface is produced under the following conditions.

(Manufacturing conditions)

Sheet Material: Amorphous PEN

Thickness: 200 ㎛

Prism Pitch: 50 ㎛

Surface temperature of heating roll 11: 200 degreeC

Surface temperature of nip roll 15: 70 ° C

Surface temperature of cooling roll 12: 50 degreeC

Surface temperature of the opposing roll 16: 50 ° C

Cooling rate of resin sheet: 40 ° C./sec

(Sheet Feed Speed: 5 m / min)

Nip line pressure between heating roll 11 and nip roll 15: 30 kg / cm

(Example 8)

A 150 μm thick amorphous PEN sheet (Tg: about 120 ° C.) is formed by the T die extrusion method. The amorphous PEN sheet is transferred to the sheet manufacturing apparatus 1 or 2, and a prism sheet having a plurality of isosceles triangles of prisms having a 90 ° right angle arranged on the sheet surface is produced under the following conditions.

(Manufacturing conditions)

Sheet Material: Amorphous PEN

Thickness: 150 ㎛

Prism Pitch: 100 ㎛

Surface temperature of heating roll 11: 180 degreeC

Surface temperature of nip roll 15: 70 ° C

Surface temperature of cooling roll 12: 30 degreeC

Surface temperature of the opposing roll 16: 30 ° C

Cooling rate of the resin sheet: 30 ° C./sec

(Sheet Feed Speed: 5 m / min)

Nip line pressure between heating roll 11 and nip roll 15: 30 kg / cm

(Example 9)

A 200 μm thick amorphous PEN sheet (Tg: about 120 ° C.) is formed by the T die extrusion method. The amorphous PEN sheet is transferred to the sheet manufacturing apparatus 1 or 2, and a prism sheet having a plurality of isosceles triangles of prisms having a 90 ° right angle arranged on the sheet surface is produced under the following conditions.

(Manufacturing conditions)

Sheet Material: Amorphous PEN

Thickness: 200 ㎛

Prism Pitch: 350 ㎛

Surface temperature of heating roll 11: 190 degreeC

Surface temperature of nip roll 15: 70 ° C

Surface temperature of cooling roll 12: 30 degreeC

Surface temperature of the opposing roll 16: 30 ° C

Cooling rate of the resin sheet: 10 ° C./sec

(Sheet Feed Speed: 3 m / min)

Nip line pressure between heating roll 11 and nip roll 15: 15 kg / cm

(Example 10)

A 300 μm thick amorphous PEN sheet (Tg: about 120 ° C.) is formed by the T die extrusion method. The amorphous PEN sheet is transferred to the sheet manufacturing apparatus 1 or 2, and a prism sheet having a plurality of isosceles triangles of prisms having a 90 ° right angle arranged on the sheet surface is produced under the following conditions.

(Manufacturing conditions)

Sheet Material: Amorphous PEN

Thickness: 300 ㎛

Prism Pitch: 75 ㎛

Surface temperature of heating roll 11: 190 degreeC

Surface temperature of nip roll 15: 70 ° C

Surface temperature of cooling roll 12: 30 degreeC

Surface temperature of the opposing roll 16: 30 ° C

Cooling rate of the resin sheet: 10 ° C./sec

(Sheet Feed Speed: 4 m / min)

Nip line pressure between heating roll 11 and nip roll 15: 5 kg / cm

(Example 11)

A 100 μm thick amorphous PET sheet (Tg: about 75 ° C.) is formed by the T die extrusion method. The amorphous PET sheet is transferred to the sheet manufacturing apparatus 1 or 2, and a prism sheet having a plurality of isosceles triangles of prisms having a 90 ° right angle arranged on the sheet surface is produced under the following conditions.

(Manufacturing conditions)

Seat Material: Amorphous PET

Thickness: 100 ㎛

Prism Pitch: 100 ㎛

Surface temperature of heating roll 11: 150 degreeC

Surface temperature of nip roll 15: 50 ° C

Surface temperature of cooling roll 12: 30 degreeC

Surface temperature of the opposing roll 16: 30 ° C

Cooling rate of resin sheet: 25 ° C./sec

(Sheet Feed Speed: 5 m / min)

Nip line pressure between heating roll 11 and nip roll 15: 5 kg / cm

(Example 12)

A 100 μm thick amorphous PET sheet (Tg: about 75 ° C.) is formed by the T die extrusion method. The amorphous PET sheet is transferred to the sheet manufacturing apparatus 1 or 2, and a prism sheet having a plurality of isosceles triangles of prisms having a 90 ° right angle arranged on the sheet surface is produced under the following conditions.

(Manufacturing conditions)

Seat Material: Amorphous PET

Thickness: 100 ㎛

Prism Pitch: 100 ㎛

Surface temperature of heating roll 11: 150 degreeC

Surface temperature of nip roll 15: 50 ° C

Surface temperature of cooling roll 12: 30 degreeC

Surface temperature of the opposing roll 16: 30 ° C

Cooling rate of resin sheet: 6 ° C./sec

(Sheet Feed Speed: 2 m / min)

Nip line pressure between heating roll 11 and nip roll 15: 20 kg / cm

(Example 13)

A 300 μm thick amorphous PEN sheet (Tg: about 120 ° C.) is formed by the T die extrusion method. The amorphous PEN sheet is transferred to the sheet manufacturing apparatus 1 or 2, and a prism sheet having a plurality of isosceles triangles of prisms having a 90 ° right angle arranged on the sheet surface is produced under the following conditions.

(Manufacturing conditions)

Sheet Material: Amorphous PEN

Thickness: 300 ㎛

Prism Pitch: 50 ㎛

Surface temperature of heating roll 11: 190 degreeC

Surface temperature of nip roll 15: 80 ° C

Surface temperature of cooling roll 12: 60 degreeC

Surface temperature of the opposing roll 16: 60 ° C

Cooling rate of resin sheet: 5 ° C./sec

(Sheet Feed Speed: 3 m / min)

Nip line pressure between heating roll 11 and nip roll 15: 20 kg / cm

(Comparative Example 1)

A 200 μm thick amorphous PET sheet (Tg: about 75 ° C.) is formed by the T die extrusion method. The amorphous PET sheet is transferred to the sheet manufacturing apparatus 1 or 2, and a prism sheet having a plurality of isosceles triangles of prisms having a 90 ° right angle arranged on the sheet surface is produced under the following conditions.

(Manufacturing conditions)

Seat Material: Amorphous PET

Thickness: 200 ㎛

Prism Pitch: 100 ㎛

Surface temperature of heating roll 11: 170 degreeC

Surface temperature of nip roll 15: 40 ° C

Surface temperature of cooling roll 12: 30 degreeC

Surface temperature of the opposing roll 16: 30 ° C

Cooling rate of the resin sheet: 3 ° C./sec

(Sheet Feed Speed: 4 m / min)

Nip line pressure between heating roll 11 and nip roll 15: 15 kg / cm

(Comparative Example 2)

A 200 μm thick amorphous PEN sheet (Tg: about 120 ° C.) is formed by the T die extrusion method. The amorphous PEN sheet is transferred to the sheet manufacturing apparatus 1 or 2, and a prism sheet having a plurality of isosceles triangles of prisms having a 90 ° right angle arranged on the sheet surface is produced under the following conditions.

(Manufacturing conditions)

Sheet Material: Amorphous PEN

Thickness: 200 ㎛

Prism Pitch: 100 ㎛

Surface temperature of heating roll 11: 170 degreeC

Surface temperature of nip roll 15: 60 ° C

Surface temperature of cooling roll 12: 30 degreeC

Surface temperature of the opposing roll 16: 30 ° C

Cooling rate of resin sheet: 20 ° C./sec

(Sheet Feed Speed: 5 m / min)

Nip line pressure between heating roll 11 and nip roll 15: 15 kg / cm

(Comparative Example 3)

An 560 μm thick amorphous PEN sheet (Tg: about 120 ° C.) is formed by the T die extrusion method. The amorphous PEN sheet is transferred to the sheet manufacturing apparatus 1 or 2, and a prism sheet having a plurality of isosceles triangles of prisms having a 90 ° right angle arranged on the sheet surface is produced under the following conditions.

(Manufacturing conditions)

Sheet Material: Amorphous PEN

Thickness: 560 ㎛

Prism Pitch: 200 ㎛

Surface temperature of heating roll 11: 190 degreeC

Surface temperature of nip roll 15: 80 ° C

Surface temperature of cooling roll 12: 30 degreeC

Surface temperature of the opposing roll 16: 30 ° C

Cooling rate of the resin sheet: 3 ° C./sec

(Sheet Feed Speed: 2 m / min)

Nip line pressure between heating roll 11 and nip roll 15: 15 kg / cm

(Comparative Example 4)

A 200 μm thick amorphous PET sheet (Tg: about 75 ° C.) is formed by the T die extrusion method. The amorphous PET sheet is transferred to the sheet manufacturing apparatus 1 or 2, and a prism sheet having a plurality of isosceles triangles of prisms having a 90 ° right angle arranged on the sheet surface is produced under the following conditions.

(Manufacturing conditions)

Seat Material: Amorphous PET

Thickness: 200 ㎛

Prism Pitch: 50 ㎛

Surface temperature of heating roll 11: 150 degreeC

Surface temperature of nip roll 15: 40 ° C

Surface temperature of cooling roll 12: 30 degreeC

Surface temperature of the opposing roll 16: 30 ° C

Cooling rate of the resin sheet: 10 ° C./sec

(Sheet Feed Speed: 4 m / min)

Nip line pressure between heating roll 11 and nip roll 15: 3 kg / cm

(Comparative Example 5)

A 200 μm thick amorphous PET sheet (Tg: about 75 ° C.) is formed by the T die extrusion method. The amorphous PET sheet is transferred to the sheet manufacturing apparatus 1 or 2, and a prism sheet having a plurality of isosceles triangles of prisms having a 90 ° right angle arranged on the sheet surface is produced under the following conditions.

(Manufacturing conditions)

Seat Material: Amorphous PET

Thickness: 200 ㎛

Prism Pitch: 50 ㎛

Surface temperature of heating roll 11: 150 degreeC

Surface temperature of nip roll 15: 40 ° C

Surface temperature of cooling roll 12: 30 degreeC

Surface temperature of the opposing roll 16: 30 ° C

Cooling rate of the resin sheet: 10 ° C./sec

(Sheet Feed Speed: 4 m / min)

Nip line pressure between heating roll 11 and nip roll 15: 35 kg / cm

(Comparative Example 6)

A 200 μm thick amorphous PET sheet (Tg: about 75 ° C.) is formed by the T die extrusion method. The amorphous PET sheet is transferred to the sheet manufacturing apparatus 1 or 2, and a prism sheet having a plurality of isosceles triangles of prisms having a 90 ° right angle arranged on the sheet surface is produced under the following conditions.

(Manufacturing conditions)

Seat Material: Amorphous PET

Thickness: 200 ㎛

Prism Pitch: 50 ㎛

Surface temperature of heating roll 11: 150 degreeC

Surface temperature of nip roll 15: 40 ° C

Surface temperature of cooling roll 12: 80 degreeC

Surface temperature of the counter roll 16: 80 degreeC

Cooling rate of the resin sheet: 10 ° C./sec

(Sheet Feed Speed: 3 m / min)

Nip line pressure between heating roll 11 and nip roll 15: 15 kg / cm

(Comparative Example 7)

A 100 μm thick amorphous PET sheet (Tg: about 75 ° C.) is formed by the T die extrusion method. The amorphous PET sheet is transferred to the sheet manufacturing apparatus 1 or 2, and a prism sheet having a plurality of isosceles triangles of prisms having a 90 ° right angle arranged on the sheet surface is produced under the following conditions.

(Manufacturing conditions)

Seat Material: Amorphous PET

Thickness: 100 ㎛

Prism Pitch: 185 ㎛

Surface temperature of heating roll 11: 150 degreeC

Surface temperature of nip roll 15: 40 ° C

Surface temperature of cooling roll 12: 50 degreeC

Surface temperature of the opposing roll 16: 50 ° C

Cooling rate of the resin sheet: 10 ° C./sec

(Sheet Feed Speed: 3 m / min)

Nip line pressure between heating roll 11 and nip roll 15: 15 kg / cm

(Comparative Example 8)

A 200 μm thick amorphous PET sheet (Tg: about 75 ° C.) is formed by the T die extrusion method. Amorphous PET sheets are used such that a prism sheet having a plurality of prisms, which is an isosceles triangle with an angle of 90 ° arranged on the sheet surface by a melt extrusion method, is produced under the following conditions.

(Manufacturing conditions)

Seat Material: Amorphous PET

Thickness: 200 ㎛

Prism Pitch: 50 ㎛

Fig. 10 collectively shows sheet manufacturing conditions of Examples 1 to 13 and Comparative Examples 1 to 8;

Next, the prism shape transfer rate (%), the radius of curvature of the prism vertex (right angle R (μm)), and the total thickness of the sheet, respectively, in the samples prepared under the sheet manufacturing conditions of Examples 1 to 13 and Comparative Examples 1 to 8, respectively. The prism ratio (%), crystallization ratio (%) and forward luminance increase rate (%) of the prism height with respect to are measured.

The limitation of the transfer rate has already been explained. The crystallization rate is measured through density calculations with a differential scanning calorimeter (DSC). The front luminance increase rate is the rate of increase of the front luminance when the prism sheet samples and the diffusion sheet of the respective examples and the comparative examples are provided under the following conditions, and this condition is the configuration of the liquid crystal display device shown in FIG. The front luminance in the dark room of the sheet 10 or the diffusion sheet 23 is the standard (100%). The front luminance is measured by the instrument "CS-1000" manufactured by Konica Minolta Holdings, Inc.

The measurement results are shown in FIG. Three grades of judgment are used, and the evaluation criteria are "◎" indicating a substantially superior level compared to the current product, "○" indicating a level which is substantially trouble free, and a substantially unsatisfactory characteristic. And "X" to indicate the level of having.

As shown in Fig. 11, all the samples of Examples 1 to 13 have a transcription rate of 99% or more. The radius of curvature of the prism vertex is 5 or less of the prism pitch, thus providing the best transfer accuracy. In addition, the crystallization rate is suppressed to 10% or less in all the samples, and the fall of transparency by whitening is not observed. For all the samples, the front luminance of the liquid crystal display is improved by 180% or more.

Although the first comparative example has a high transfer rate, the rate of increase in front luminance is maintained at 175% because the crystallization rate exceeds 20% and the transparency decreases due to whitening. This is due to the factor that the surface temperature of the heating roll 11 is high (greater than Tg + 90 ° C.) and the cooling rate necessary to prevent crystallization cannot be obtained. Although the second comparative example can prevent the progress of crystallization, the transfer rate is low and the increase in luminance is also insufficient. This is due to the factor that the surface temperature of the heating roll 11 is low (less than Tg + 60 ° C.) and the shape transfer is insufficient. The resin sheet of Comparative Example 3 was too thick at 560 µm, the cooling rate was insufficient, the crystallization proceeded excessively, and the permeability was lowered by whitening.

In the fourth comparative example, since the nip linear pressure between the heating roll 11 and the nip roll 15 is too low at 3 kg / cm, the shape transfer is insufficient, and a high rate of increase in the front luminance cannot be obtained. On the other hand, in the fifth comparative example, the nip linear pressure is too high at 35 kg / cm, and stable sheet production is impossible. In addition, about the 6th comparative example, since the surface temperature of the cooling roll 12 is high (greater than Tg) and the separation performance is bad, stable sheet manufacture is impossible.

In the seventh comparative example, the ratio of the prism height to the total sheet thickness is high (greater than 90%), so that the sheet is cracked or cracked along the prism ridge direction, resulting in poor durability and handleability, and cannot be stably manufactured. Since the shape transfer of the eighth comparative example uses the melt extrusion method, the transfer rate is bad and excellent rise in luminance is not observed.

The surface temperature of the heating roll 11 is Tg + 60 degreeC or more, Tg + 90 degreeC or less, the thickness of a resin sheet is 500 micrometers or less, and the cooling rate is 5 degreeC / sec or more and 40 degrees C / sec or less, Examples 1-13. In, excessive crystallization of the sheet can be prevented, and the crystallization ratio can be suppressed to 20% or less. Since the nip line pressure is 5 kg / cm or more and 30 kg / cm or less is satisfied, the best shape transfer performance and separation performance can be obtained to realize stable manufacturability.

While embodiments and examples of the present invention have been described, it is clear that the present invention is not limited to these and various modifications are possible based on the technical concept of the present invention.

For example, the resin sheet 10 in the rolled state or the resin sheet cut into the sheet size is transferred to the sheet manufacturing apparatuses 1 and 2 in the embodiments. Instead, a melt extrusion apparatus for producing an resin sheet in an amorphous state can be provided on the front stage side of the sheet manufacturing apparatus to continuously perform resin sheet production and embossing.

An stretching device for stretching the embossed sheet manufactured in a predetermined direction can be installed on the rear stage side of the sheet manufacturing apparatus to continuously perform the embossing operation and the stretching process.

It is understood that various modifications, combinations, subcombinations, and substitutions may be made by those skilled in the art, depending on design requirements or other factors, so long as they are within the scope of the appended claims or equivalents.

This specification is Japanese Patent Application No. 2007-069639 filed with Japan Patent Office on March 16, 2007, the entire contents of which are incorporated herein by reference, and Japanese Patent Application Filed on Japan Patent Office on January 30, 2008. Includes topics related to 2008-021860.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a view showing the external structure of a sheet manufacturing apparatus used for the optical sheet manufacturing method according to the first embodiment of the present invention.

2A and 2B are enlarged cross-sectional views showing the embossed forming surface of the resin sheet and the main part of the embossed belt of the sheet manufacturing apparatus shown in FIG.

3 is a graph of experimental results illustrating the difference in pattern transfer performance between a pattern transferred by a lamination method and a pattern transferred by a melt extrusion method.

FIG. 4 is a perspective view showing the entire structure of a resin sheet (optical sheet) manufactured by the sheet manufacturing apparatus shown in FIG.

Fig. 5 is a diagram showing an external structure of a liquid crystal display device using the optical sheet shown in Fig. 4 as a prism sheet.

Fig. 6 is a diagram showing an external structure of a sheet manufacturing apparatus used for the optical sheet manufacturing method according to the second embodiment of the present invention.

7 illustrates an optical sheet manufacturing method according to a third embodiment of the present invention.

8A and 8B show temperature distributions of a heating roll and a cooling roll.

9A to 9E show examples of embossed shapes formed on the surface of the resin sheet.

10 is a table showing the results of examples of the present invention.

11 is a table showing the results of examples of the present invention.

<Description of the symbols for the main parts of the drawings>

10: resin sheet

11: heating roll

12: cooling roll

13: embossing belt

15: Nip Roll

16: facing roll

Claims (21)

An optical sheet manufacturing method made of a transparent thermoplastic sheet in which regular geometric design work is performed on a surface thereof, Performing a geometric design work on the resin sheet at a temperature above the glass transition temperature of the resin sheet by using a metal endless work belt having a geometric design formed on the surface thereof; Rapidly cooling the resin sheet on which the geometric design work is performed at a temperature lower than the glass transition temperature; Separating the rapidly cooled resin sheet from the metal endless work belt. The optical sheet manufacturing method according to claim 1, wherein the resin sheet is made of a transparent crystalline resin. The method of claim 2, wherein the resin sheet is made of PET, PEN, or a mixture or copolymer of PET and PEN. The optical sheet manufacturing method of Claim 1 which is more than Tg + 60 degreeC and below Tg + 90 degreeC based on the premise that Tg (degreeC) is the glass transition temperature of a resin sheet. The optical sheet manufacturing method according to claim 1, wherein the resin sheet is cooled at a rate of 5 ° C / sec or more and 40 ° C / sec or less in a rapid cooling step of the resin sheet. The optical sheet manufacturing method according to claim 1, wherein the resin sheet has a crystallization ratio of 20% or less when the resin sheet is separated from the metal endless work belt. The optical sheet manufacturing method according to claim 1, wherein the increase in the crystallization ratio of the resin sheet is 5% or less before and after performing the optical sheet manufacturing method. The optical sheet manufacturing method according to claim 1, wherein a plurality of resin sheets are inserted, and the plurality of resin sheets are thermally bonded and coalesced while the shape is transferred by the metal endless work belt. The optical sheet manufacturing method according to claim 1, wherein the total thickness of the resin sheet is 500 µm or less. The optical sheet manufacturing method according to claim 1, wherein the ratio of the height of the transfer portion to the total thickness of the resin sheet is 90% or less. The optical sheet manufacturing method according to claim 1, wherein the geometric design transferred to the resin sheet is an embossed shape. The optical sheet manufacturing method according to claim 11, wherein the embossed shape transferred to the resin sheet is a prism shape. The optical sheet manufacturing method according to claim 12, wherein the prism shape transferred to the resin sheet is an isosceles triangle having a right angle of 90 degrees. The optical sheet manufacturing method according to claim 13, wherein the transfer rate of the prism shape with respect to the resin sheet is 98% or more. The metal endless work belt is wound around a heating roll set at a temperature higher than the glass transition temperature of the resin sheet and a cooling roll set at a temperature lower than the glass transition temperature of the resin sheet. The optical sheet manufacturing method transferred in synchronization with rotation of the. The method of claim 15, wherein the resin sheet is processed between a nip roll and a metal endless work belt disposed in a manner facing the heating roll, A nip line pressure between the metal endless work belt and the nip roll is 5 kg / cm or more and 30 kg / cm or less. The belt according to claim 16, wherein an endless belt is wound around the nip roll and the opposing roll facing the cooling roll. And the resin sheet is sandwiched between the metal endless work belt and the endless belt and transferred in a retained state. The optical sheet manufacturing method according to claim 17, wherein, while the shape is transferred to the resin sheet by the metal endless work belt, 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. The optical sheet manufacturing method according to claim 1, wherein the geometric design worked on the surface of the resin sheet has at least one corner portion. The center temperature is set high in the roll temperature of the heating roll for transferring to the said resin sheet compared with the roll temperature of an opposite edge part, An optical sheet manufacturing method in which the roll temperature of the cooling roll for transferring to said resin sheet is set lower than the roll temperature of the opposite end part. It is an optical sheet manufactured by the optical sheet manufacturing method of Claim 1, And the optical sheet is used as a prism sheet disposed between a liquid crystal display panel and a light source for illuminating the liquid crystal display panel.

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