JP2005280217A - Optical film manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for obtaining an optical film excellent in thickness precision in manufacturing the optical film comprising an amorphous thermoplastic resin film by melt extrusion molding. <P>SOLUTION: In the method for manufacturing the optical film by the extrusion molding of the amorphous thermoplastic resin, the film extruded from the die attached to an extruder is closely brought into contact with a cooling roll by an elastically deformable touch roll so that the contact width of the touch roll with the cooling roll at the time of non-rotation becomes r/100 mm-5 r/100 mm when the radius of the touch roll is set to (r) in the contact width of the touch roll with the cooling roll at the time of non-rotation. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing an optical film used for optical applications, displays, and the like, and more specifically, a method for producing an optical film obtained by extrusion molding of a thermoplastic resin and having excellent thickness accuracy. About.

  In recent years, optical films excellent in thickness accuracy have been required for optical applications and displays. Therefore, conventionally, in order to obtain a high-quality optical film, a film forming method by a solution casting method has been frequently used. However, the solution casting method requires a solvent cost and the productivity is not sufficient. Therefore, instead of the solution casting method, a method for producing an optical film by melt extrusion molding has been attempted.

For example, the following Patent Document 1 discloses a production method using a die having a lip portion having a specific peel strength and a smoothing roll when a cyclic olefin resin is formed by melt extrusion. Here, it is said that an optical film having surface smoothness can be obtained.
JP 2000-280315 A

  However, when an optical film is produced by a melt extrusion molding method as described in Patent Document 1, the thickness accuracy of the film is still not sufficient.

  An object of the present invention is a method for producing an optical film using a melt extrusion molding method that eliminates the above-mentioned disadvantages of the prior art and is excellent in productivity, and can obtain a film that is further excellent in thickness accuracy. It is to provide a way to do.

  The inventors of the present application use an elastic touch roll whose surface has elasticity when manufacturing an optical film by a melt extrusion molding method of a thermoplastic resin, and by sticking the extruded film to a cooling roll, the thickness accuracy is improved. It has been found that an excellent film is obtained.

  For example, in the conventional manufacturing method as described in Patent Document 1, sufficient attention has not been paid to the hardness of the surface of the touch roll for bringing the film into close contact with the cooling roll and the pressure at the time of contact, and the thickness. A film with excellent accuracy could not be obtained. On the other hand, the inventors of the present application use an elastic touch roll, closely adhere the extruded film to the cooling metal roll, and further, an air gap that is the distance from the mold outlet to the contact point with the cooling metal roll; It was found that the thickness accuracy of the obtained film can be improved by controlling the temperature of the cooling roll.

  However, it is not sufficient to control the air gap and the roll temperature in order to further increase the thickness accuracy. Therefore, as a result of further investigation, the inventors of the present application have found that if the contact width between the rolls when the extruded film is brought into close contact with the cooling roll using a touch roll whose surface is elastically deformable, the thickness variation is further increased. The inventors have found that the size can be further reduced, and have reached the present invention.

That is, the present invention is a method for producing an optical film extruded using an amorphous thermoplastic resin, and the amorphous thermoplastic resin is extruded into a film form from a die attached to an extruder and extruded. When using a touch roll having an elastically deformable surface and closely contacting the cooling roll, when the radius of the touch roll is r (mm), the contact width between the touch roll and the cooling roll when not rotating is r. The film is brought into close contact with the cooling roll using a touch roll under the conditions of / 100 mm to 5r / 100 mm.

  In the method for producing an optical film according to the present invention, preferably, a norbornene resin is used as the amorphous thermoplastic resin.

  On the specific situation with the manufacturing method of the optical film which concerns on this invention, the surface of the touch roll which can be elastically deformed is further coat | covered with the metal tube.

  Details of the present invention will be described below.

  In the method for producing an optical film according to the present invention, as described above, the touch roll contact width during non-rotation when the film extruded from the extruder is brought into contact with the cooling roll using the touch roll is in the specific range. Then, the film is brought into contact with the cooling roll by the touch roll. In the present invention, the contact width of the touch roll is defined using the non-rotating contact width because it is difficult to determine the rotating contact width. That is, since it is difficult to obtain the contact width during rotation, the contact width during non-rotation is used instead of the contact width during rotation.

  When the radius of the touch roll is r (mm), if the contact width is less than r / 100 mm, the touch roll cannot sufficiently follow the fluctuation of the resin film or the rotation fluctuation of the cooling roll. There is a possibility that air may enter between the cooling roll and the thickness may vary. Conversely, when the contact width exceeds 5r / 100 mm, the thickness varies in the film flow direction. This is presumably because the distribution of pressure that the resin film receives from the roll and the viscosity at the time of cooling the resin are affected. If the contact width is large, the contact pressure immediately after the start of contact decreases, the resin solidifies in a state where the pressure is weak, and the influence of thickness variation increases.

  The pressure fluctuation or the film thickness fluctuation is greatly influenced by the rotation period fluctuation of the cooling roll or the touch roll, and is particularly easily influenced by the fluctuation of the rotation period of the touch roll. This is presumably because the influence of the eccentric runout of the roll is large. In general, an elastic touch roll is difficult to polish with high precision compared to a metal roll, and thus it is difficult to completely eliminate eccentric shake.

  On the other hand, in the manufacturing method of the present invention, since the contact width is in the specific range, the influence of the eccentric shake can be minimized. The upper limit of the contact width is 5 r / 100 mm, but more preferably 3 r / 100 mm or less.

  As a method of setting the contact width to r / 100 mm to 5r / 100 mm, a method of controlling the rubber hardness of the touch roll surface and / or a method of controlling a pinching force between the touch roll and the cooling roll are conceivable.

  The pinching pressure is usually represented by a linear pressure (N / mm) obtained by dividing the pressure applied to the roll by the width. If the linear pressure is too small, even if the contact width is in the range of r / 100 mm to 5 r / 100 mm, the resin film and the roll are not sufficiently adhered and air may be entrained. In addition, the roll may be affected by the eccentric runout. Therefore, specifically, the linear pressure is preferably 0.49 N / mm or more, and more preferably 0.98 N / mm or more.

  In addition, when the elastic touch roll is pressed not by the full width of the roll but only by an end portion such as a bearing, the elastic touch roll may bend when the roll pressure is increased. When bending occurs, the pressure in the center portion in the center direction of the touch roll becomes weak, and the contact width varies in the width direction. As a method for preventing such a state, a crown process for slightly narrowing the center portion of the touch roll is performed, a bending rigidity of the touch roll is increased, a contact roll pressure is not increased excessively, and an appropriate range is set. Etc.

  The material of the surface of the touch roll is not particularly limited, but a flexible material having a smooth surface may be used, and examples thereof include silicone resin and fluorine resin. Moreover, you may have the laminated structure which consists of a some material. Furthermore, when it has a laminated structure, it is sufficient that at least one layer has flexibility, and the outer surface may be covered with a metal tube.

  The hardness of the surface of the elastic touch roll is not particularly limited, but considering ease of processing and durability, for example, when made of silicone rubber, the Shore A hardness may be about 30 ° to 90 °.

  In addition, when the surface of the touch roll is covered with a metal tube, the film and the touch roll can be sufficiently adhered to each other by an internal flexible material, and the metal tube is disposed on the outer surface. Therefore, the outer surface of the roll is smoothed, and the surface smoothness of the resulting film can be enhanced. In addition, it is possible to suppress the eccentric roll of the touch roll.

  The material of the said metal tube is not specifically limited, The nickel etc. which were manufactured by the carbon steel, the stainless steel, or the electroforming method are mentioned. Further, the surface of the metal tube may be plated with another metal such as chromium, that is, the metal tube itself may have a laminated structure.

  Although the thickness of a metal tube is not specifically limited, What is necessary is just to have a softness | flexibility sufficient to make a metal roll and a resin film closely_contact | adhere when a predetermined pressure is applied. For example, when electroformed nickel is used, the thickness of the metal tube may be in the range of about 100 μm to 1 mm.

  When the molten resin is passed between the cooling roll and the touch roll and pinched, the cooling roll and the touch roll must have a robust structure made of a material that can withstand the pressure. Therefore, the shaft core part of the touch roll and the cooling roll is preferably made of a metal such as steel, stainless steel or aluminum.

  In general, the roll temperature greatly affects the solidification point of the resin, and therefore, it is desirable that the roll temperature is provided with a shaft portion having a structure capable of appropriately adjusting the roll temperature. Preferably used as the temperature adjusting means are a sheathed heater incorporated in the shaft core portion to heat the roll, and an electric heating type temperature adjusting means, and the roll is heated by electromagnetic induction heating by an induction heating coil. Examples thereof include induction heating type temperature adjustment means, and heat medium circulation heating type temperature adjustment means for indirectly heating the roll by circulating a temperature control heat medium through a flow path provided in the shaft core. Particularly preferably, a heat medium circulation heating method is used, and the heat medium may be a gas or a liquid such as water or oil, but a liquid such as water or oil is preferable. Preferable examples of the heat medium flow path include those having a structure such as a double spiral or a four spiral inside.

The outer diameters of the elastic touch roll and the cooling roll are not particularly limited, and either may be large or both may be the same size.

  The material of a cooling roll is not specifically limited, For example, metal rolls, such as a carbon rope and a stainless steel rope, are used suitably. If the temperature at the contact point between the cooling roll and the resin is too low, air is likely to be trapped during the pressure between the touch roll and the cooling roll. In addition, if the temperature becomes too high, the resin is difficult to cool and solidify, and thus appropriate temperature control is required. Specifically, the range of Tg + 50 ° C. to Tg + 150 ° C. is desirable when the glass transition temperature of the resin is Tg. As a method of controlling the resin temperature, a method of controlling the temperature of the die or shortening the air gap described above can be considered.

  If the temperature of the die fluctuates, the fluidity of the resin changes, so it is desirable that the die temperature be uniform. Preferably, the set temperature is ± 0.5 ° C. or less, more preferably 0.2 ° C. or less.

  It is desirable that the air gap, which is the distance from the die outlet to the contact point between the cooling roll and the resin sheet, is short. The air gap is a distance from the outlet of, for example, the T die 1 as a die to the contact point between the cooling roll 2 and the film A as shown in FIG. 3 represents a touch roll, and 4 represents a second cooling roll. If the air gap is too long, the air gap is likely to be affected by the disturbance, and the temperature of the resin may be lowered. Therefore, specifically, the air gap is preferably 90 mm or less, and more preferably 70 mm or less.

  In the method for producing an optical film according to the present invention, an amorphous thermoplastic resin is used. An amorphous thermoplastic resin is a polymer that maintains an amorphous state that can hardly take a crystal structure, and its glass transition point Tg varies depending on the resin and is not particularly limited. It is above ℃. Examples of the amorphous thermoplastic resin include polysulfone, polymethyl methacrylate, polystyrene, polycarbonate, polyvinyl chloride, and norbornene resin. As for the said amorphous thermoplastic resin, only 1 type may be used and 2 or more types may be used together.

  Among the above resins, norbornene resins are preferably used because of their low intrinsic birefringence and low photoelastic coefficient. In addition, since norbornene-based resin is a resin that solidifies rapidly due to a decrease in temperature, the thickness variation at the contact point between the metal roll and the resin is more likely to occur than other amorphous thermoplastic resins. Therefore, when a norbornene resin is used, the effect of the manufacturing method of the present invention, that is, the effect of reducing thickness variation is greater.

  Examples of the norbornene resin include hydrogenated ring-opening polymers of norbornene monomers, addition polymers of norbornene monomers and olefins, addition polymers of norbornene monomers, and derivatives thereof.

  Moreover, only 1 type may be used for norbornene-type resin, and 2 or more types may be used together.

  Examples of the norbornene-based monomer include bicyclo [2,2,1] hept-2-ene (norbornene), 6-methylbicyclo [2,2,1] hept-2-ene, and 5,6-dimethylbicyclo. [2,2,1] hept-2-ene, 1-methylbicyclo [2,2,1] hept-2-ene, 6-ethylbicyclo [2,2,1] hept-2-ene, 6-n -Butylbicyclo [2,2,1] hept-2-ene, 6-isobutylbicyclo [2,2,1] hept-2-ene, 7-methylbicyclo [2,2,1] hept-2-ene, etc. And norbornene derivatives thereof.

  As the ring-opening polymer hydrogenated product of the norbornene monomer, those obtained by subjecting the norbornene monomer to ring-opening polymerization by a known method and then hydrogenating the remaining double bond can be widely used. The ring-opening polymer hydrogenated product may be a norbornene monomer homopolymer or a copolymer of a norbornene monomer and another cyclic olefin monomer.

  Examples of the addition polymer of the norbornene monomer and the olefin include a copolymer of a norbornene monomer and an α-olefin. The α-olefin is not particularly limited, but is an α-olefin having 2 to 20 carbon atoms, preferably 2 to 10 carbon atoms, such as ethylene, propylene, 1-butene, 3-methyl-1-butene, 1-pentene, 3 -Methyl-1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene and the like. Especially, since it is excellent in copolymerizability, ethylene is used suitably. Also, when other α-olefin is copolymerized with a norbornene-based monomer, it is preferable that ethylene is present because the copolymerizability can be improved.

  The norbornene resin is known and commercially available. Examples of known norbornene resins include those described in JP-A-1-240517, and examples of commercially available norbornene resins include, for example, products manufactured by JSR Corporation. Name "Arton" series, manufactured by Nippon Zeon Co., Ltd., trade name "Zeonoa" series, etc. are listed.

  In the present invention, various additives may be added to the thermoplastic resin as necessary, as long as the object of the present invention is not impaired. Examples of such additives include various additives that prevent deterioration of the thermoplastic resin and improve the heat resistance, ultraviolet resistance, or smoothness of the molded optical film. Antioxidants, lactone-based thermal deterioration inhibitors, benzophenone-based, benzotriazole-based, acrylonitrile-based ultraviolet absorbers; aliphatic alcohol ester-based, polyhydric alcohol partial ester-based and partial ether-based lubricants; Examples thereof include an antistatic agent such as an amine. These additives may be added alone or in combination of two or more.

  Since the optical film obtained by the production method of the present invention is excellent in thickness accuracy, it can be widely used in the optical field such as an optical disk and a liquid crystal display. For example, it is suitably used for a protective film for optical disks, a protective film for polarizers, and the like. Furthermore, since the thickness accuracy is high, it can be suitably used as a raw material before stretching between retardations, whereby a retardation plate with small retardation unevenness can be obtained.

  As described above, the thickness accuracy of the obtained film may not be sufficiently increased only by controlling the temperature of the touch roll and the cooling roll. More specifically, for example, if the pressure of the touch roll contacting the cooling roll is increased too much, thickness fluctuation in the flow direction is likely to occur, and particularly when the rubber hardness of the surface of the touch roll is low, the thickness fluctuation occurs. It tends to appear remarkably. On the contrary, when the contact pressure becomes too low or the rubber hardness becomes too high, the film does not come into contact with the cooling roll over the entire surface, and air may be entrained, resulting in variation in thickness.

  On the other hand, in the manufacturing method according to the present invention, since the contact width of the film with respect to the metal roll of the touch roll is in the range of r / 100 mm to 5r / 100 mm, the thickness variation of the obtained optical film is reduced. Is possible.

  In other words, in the manufacturing method according to the present invention, the contact width is in the range of r / 100 mm to 5r / 100 mm by controlling the rubber hardness of the surface of the touch roll and the cooling pressure of the touch roll, and thus the contact pressure against the film. Thus, it is possible to manufacture an optical film whose thickness accuracy is remarkably improved.

  In the production method according to the present invention, when a norbornene-based resin is used as the amorphous thermoplastic resin, the norbornene-based resin has a low intrinsic birefringence and a small photoelastic coefficient. A film can be provided. In addition, since norbornene-based resin is a resin that is rapidly solidified due to a decrease in temperature, the thickness variation at the contact point between the metal roll and the film is likely to occur as compared with other amorphous resins. Even when a norbornene resin is used, an optical film with little thickness variation can be obtained.

  When the surface of the touch roll that can be elastically modified is covered with a metal tube, the film and the cooling roll are securely adhered to each other by the flexible material inside, and the outer surface of the touch roll is smoothed. The surface smoothness of the optical film can also be enhanced.

  Hereinafter, the present invention will be clarified by describing specific examples of the present invention. In addition, this invention is not limited to a following example.

  (1) Resin used: A thermoplastic norbornene-based resin (manufactured by ZEON Corporation, trade name: ZEONOR1420, Tg = 135 ° C) preliminarily dried under conditions of 110 ° C and 3 hours.

(2) Manufacturing apparatus L / D = 32, an extrusion apparatus having a shaft core diameter of 100 mm, the extrusion temperature was adjusted in the range of 220 to 280 ° C., and the extrusion rate was 120 kg / hour. Also, a coat hanger type T die having a width of 1800 mm and a lip clearance of 800 μm was used as the T die, and the temperature of the T die was set to 280 ° C. The temperature error is ± 0.1 ° C. or less. The resin film extruded from the T-die has an air gap of 60 mm, a diameter of 200 mm × width of 1700 mm, a silicone rubber layer, and an outer surface covered with a 200 μm metal tube made of Ni—Cr. Using an elastic touch roll, an optical film was manufactured by sandwiching a roll eccentric temperature controlled with oil having a diameter of 300 mm and a width of 1900 mm with a cooling metal roll having a thickness of 5 μm. The temperature adjustment of the elastic touch roll is configured to be performed with water, and the roll eccentricity is 30 μm.

  Using the above apparatus and manufacturing apparatus, a film having a width of 1400 mm excluding the side end portion is obtained by the following examples and comparative examples, and about a total of three points of the touch roll that is 600 mm away from the center in the width direction and from the center in the width direction The thickness of 3 m in length was measured at a pitch of 5 mm. For the measurement of thickness, a contact type thickness measuring device Millitron 1240 manufactured by Seiko EM was used. In addition, the thickness difference shown below is obtained by subtracting the minimum value from the maximum thickness value at all points measured as described above.

  In addition, after a prescale film manufactured by Fuji Photo Film Co., Ltd. was sandwiched between the touch roll and the cooling roll for 1 minute and pressed for 1 minute, the discoloration was observed at a total of 3 points including the center in the width direction of the roll and the point 600 mm away from the center. The contact width was determined by measuring the width of the portion in the roll circumferential direction.

(Example 1)
The film was manufactured by setting the metal roll temperature for cooling, the surface temperature of the elastic touch roll, the structure of the elastic touch roll, and the pressure of the elastic touch roll to the following magnitudes. The contact width is 2.8 mm at the center in the width direction of the film, and is 4 mm at two points 600 mm away from the center in the width direction.

Metal roll temperature: 120 ° C
Elastic touch roll surface temperature: 110 ° C
Elastic touch roll structure: Silicone rubber 70 °, 5 mm thickness Elastic touch roll pressure: 39.2 N / cm
As a result, an optical film having an average thickness of 60 μm was obtained, and the thickness difference was 0.81 μm at the center in the width direction, and 0.98 μm and 1.12 μm at two points 600 mm away from the center in the width direction.

(Example 2)
The film was manufactured by setting the metal roll temperature for cooling, the surface temperature of the elastic touch roll, the structure of the elastic touch roll, and the pressure of the elastic touch roll to the following magnitudes.

  The contact width is 2 mm at the center in the width direction of the film, and is 3 mm at two points that are 600 mm away from the center in the width direction.

Metal roll temperature: 120 ° C
Elastic touch roll surface temperature: 110 ° C
Elastic touch roll structure: Silicone rubber 70 °, 5 mm thickness Elastic touch roll pressure: 2 kg / cm
As a result, an optical film having an average thickness of 60 μm was obtained, and the difference in thickness was 0.46 μm at the center in the width direction, and 0.8 μm and 0.66 μm at two points 600 mm away from the center in the width direction.

(Comparative Example 1)
The film was manufactured by setting the metal roll temperature for cooling, the surface temperature of the elastic touch roll, the structure of the elastic touch roll, and the pressure of the elastic touch roll to the following magnitudes. The contact width is 4.8 mm at the center in the width direction of the film, and 6 mm at each of two points 600 mm away from the center in the width direction.

Metal roll temperature: 120 ° C
Elastic touch roll surface temperature: 110 ° C
Elastic touch roll structure: Silicone rubber 30 ° C., 5 mm thickness Elastic touch roll pressure: 7 kg / cm
As a result, an optical film having an average thickness of 60 μm was obtained, and the difference in thickness was 1.42 μm at the center in the width direction, and 1.75 μm and 1.89 μm at two points 600 mm away from the center in the width direction.

(Comparative Example 2)
The film was manufactured by setting the metal roll temperature for cooling, the surface temperature of the elastic touch roll, the structure of the elastic touch roll, and the pressure of the elastic touch roll to the following magnitudes. The contact width is 1.0 mm at the center in the width direction of the film, and is 0.8 mm at two points that are 600 mm away from the center in the width direction.

Metal roll temperature: 120 ° C
Elastic touch roll surface temperature: 110 ° C
Elastic touch roll structure: Silicone rubber 90 ° C., 5 mm thickness Elastic touch roll pressure: 0.5 kg / cm
As a result, an optical film having an average thickness of 60 μm was obtained, and the thickness difference was 1.12 μm at the center in the width direction, and 2.15 μm and 2.09 μm at two points 600 mm away from the center in the width direction.

(Comparative Example 3)
The film was manufactured by setting the metal roll temperature for cooling, the surface temperature of the elastic touch roll, the structure of the elastic touch roll, and the pressure of the elastic touch roll to the following magnitudes. The contact width is 1.0 mm at the center in the width direction of the film, and is 1.0 mm at two points 600 mm away from the center in the width direction.

  As a result, an optical film having an average thickness of 60 μm was obtained, and the thickness difference was 3.92 μm at the center in the width direction, and 2.29 μm and 2.34 μm at two points 600 mm away from the center in the width direction.

The schematic block diagram for demonstrating the manufacturing method of the optical film which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... T die 2 ... Cooling roll 3 ... Touch roll 4 ... 2nd cooling roll 5 ... Resin

Claims (3)

A method for producing an optical film extruded using an amorphous thermoplastic resin,
When a non-crystalline thermoplastic resin is extruded into a film form from a die attached to an extruder and the extruded film is brought into close contact with a cooling roll using an elastically deformable surface, the radius of the touch roll is set to r. (Mm), when the non-rotating touch roll and the cooling roll have a contact width of r / 100 mm to 5r / 100 mm, the film is brought into close contact with the cooling roll using the touch roll. Manufacturing method of optical film.   The method for producing an optical film according to claim 1, wherein a norbornene-based resin is used as the amorphous thermoplastic resin. The manufacturing method of the optical film of Claim 1 or 2 with which the touch roll surface which has the surface which can be elastically deformed is coat | covered with the metal tube.

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