JP2008023745A - Casting roll, apparatus for producing optical film, and method for producing optical film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a casting roll for producing an optical film which is excellent in retardation uniformity by preventing the contact between the casting roll and the end of a touch roll and pressing the thin film part of a film-shaped molten material extruded on the surface of the casting roll, an apparatus for producing the optical film, and a method for producing the optical film. <P>SOLUTION: With the use of the casting roll having a press part for pressing the thin film part of the film-shaped molten material and non-press parts which are positioned at both ends of the press part and do not press the film-shaped molten material, while the thick film part of the end part of the extruded film-shaped molten material is released, only the thin film part is pressed. The outside diameter of the press part is constant in the entire width, and the outside diameter of the non-press part is smaller than the outside diameter of the press part. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a cast roll for manufacturing an optical film containing a cellulose resin by a melt casting film forming method, an optical film manufacturing apparatus including the cast roll, and an optical film manufacturing method using the cast roll. About.

  A liquid crystal display device is widely used as a monitor because it saves space and energy compared to a conventional CRT display device. Furthermore, it is also spreading for TV. In such a liquid crystal display device, various optical films such as a protective film for a polarizing plate and a retardation film are used.

  The protective film for polarizing plates is a film for affixing to the polarizing film which consists of stretched polyvinyl alcohol etc., and protecting a polarizing film, and the film containing a cellulose resin is used. The retardation film is used for the purpose of, for example, increasing the viewing angle and improving the contrast, and is provided with retardation by stretching a film containing a cellulose resin. Sometimes called an optical compensation film.

  The manufacturing method of the optical film containing such a cellulose resin is roughly classified into a melt casting film forming method and a solution casting film forming method. The former is a method in which a polymer is heated and melted and cast onto a support, cooled and solidified, and further stretched as necessary to form a film. The latter is a solution in which the polymer is dissolved in a solvent. Is cast on a support, the solvent is evaporated, and if necessary, the film is stretched to form a film.

  Conventionally, production by a solution casting film forming method has been mainstream because the film thickness can be easily uniformed. However, the solution casting film forming method does not have these problems because it uses a large amount of solvent and has a large environmental load and requires a huge production facility to recover the solvent. The production of optical films by the melt casting method has attracted attention.

  On the other hand, these optical films are required to have uniform optical performance, particularly retardation. In particular, as monitors and TVs have become larger and lighter, retardation uniformity has become more and more demanding, and optical films have become increasingly demanding for wider and thinner optical films.

  The optical film is produced by the melt casting method by extruding a melt containing a cellulose resin from the casting die onto the surface of the cast roll, and the extruded film-like melt is formed by the cast roll and the touch roll. Generally, a film is obtained by clamping. At this time, the pressure applied to the film affects the orientation state of the resin, and the retardation of the resulting film changes. Therefore, in order to obtain an optical film with high uniformity of retardation, the sandwiching pressure should be sufficiently uniform. It becomes important to do.

As the touch roll, there is known a double cylinder roll in which a thin metal outer cylinder is covered on the outer side of the metal inner cylinder in order to make the roll elastic and to make the pressure uniform. In such a double-cylinder touch roll, in order to further increase the pressure uniformity, a roll device using a drum-shaped roll with a large diameter at the center and a thickness of a thin metal outer cylinder are rolled. Has been proposed (see, for example, Patent Document 1).
JP 11-235747 A

  However, when the melt containing the cellulose resin is actually extruded from the casting die onto the surface of the cast roll in the form of a film, the extruded film-like melt has the thin film portion at both ends of the thin film portion having a uniform thickness. It became clear that it has a thick film part with a larger film thickness. The film thickness of the thick film portion is 1.2 to 5 times the film thickness of the thin film portion.

  In Patent Document 1, the existence of such a thick film portion is not recognized at all, and even if the proposed roll apparatus is used, the film-like melt thin film portion is uniform due to the influence of the thick film portion. There was a problem that pressure could not be applied, and as a result, an optical film having high retardation uniformity could not be obtained. In particular, when the film thickness of the thin film portion is 15 μm to 60 μm, this influence is significant and has become a big problem.

  In addition, when a double-roller roll having elasticity is used as the touch roll, the touch roll bends and the touch roll comes into contact with the cast roll outside the film, and the pressure applied to the thin film portion varies greatly. There was a problem that.

  This problem can be suppressed to some extent by using a roll device in which the thickness of the thin metal outer cylinder proposed in Patent Document 1 is reduced in the vicinity of both ends of the roll. However, since the thickness of the thin metal outer cylinder is reduced, there is a problem that distortion tends to occur and the durability is inferior, and in particular, there remains a problem that it is not possible to cope with the production of a wide optical film having a width of 1500 mm to 4000 mm. It was.

  The present invention has been made in view of the technical problems as described above, and an object of the present invention is to prevent the contact between the cast roll and the end of the touch roll, and the film is extruded onto the surface of the cast roll. By providing a cast roll, an optical film manufacturing apparatus, and an optical film manufacturing method for manufacturing an optical film having excellent retardation uniformity by sandwiching a thin film portion of a molten material with uniform pressure is there.

  In order to solve the above problems, the present invention has the following features.

  1. A film-like melt containing cellulose resin extruded from a casting die and having a thick film portion thicker than the thin film portion at both ends of the thin film portion having a uniform film thickness is supported on the surface. In the cast roll for producing an optical film by sandwiching the melt with a touch roll, the cast roll comprises a sandwiching section for sandwiching the thin film portion of the melt, and the sandwiching section. A roll body including a non-clamping part that does not clamp the melt, and a rotating shaft for rotating the roll body, the clamping part being a width of the thin film part. The cast roll is characterized in that the outer diameter of the non-clamping portion is smaller than the outer diameter of the pinching portion.

  2. When the film thickness of the thin film portion is t1, the film thickness of the thick film portion is t2, the diameter of the pinching portion is φp, and the diameter of the outer end portion of the non-pressing portion is φq, 0.8φp ≦ φq ≦ φp−2 (t2−t1) is satisfied.

  3. 3. The cast roll according to 1 or 2 above, wherein the non-clamping part has a width of 20 mm to 1000 mm.

  4). 4. The cast roll according to any one of 1 to 3, wherein a width of the pinching portion of the cast roll is 1500 mm to 4000 mm.

  5. 5. The cast roll according to any one of 1 to 4, wherein the film thickness of the thin film portion is 15 μm to 60 μm.

  6). A casting die for extruding a melt containing a cellulose resin into a film, a cast roll for supporting the film-like melt extruded from the casting die on the surface, and being energized against the cast roll, the melting In the manufacturing apparatus of the optical film provided with the touch roll which pinches | interposes an object between the said cast rolls, the said cast roll is the cast roll of any one of said 1 thru | or 5 characterized by the above-mentioned. Optical film manufacturing equipment.

  7). A casting process in which a melt containing a cellulose resin is extruded from the casting die onto the surface of the cast roll in a film form, and the film-like melt extruded in the casting process is sandwiched between the cast roll and the touch roll. The melt includes a thick film portion having a thickness greater than that of the thin film portion at both ends of the thin film portion having a uniform film thickness, and the cast roll includes the thin film portion of the melt. In the method of manufacturing an optical film having a roll body including a clamping part for clamping the roll and a rotating shaft for rotating the roll body, the casting step is performed such that the width of the thin film part is the cast roll. The melt is pushed out so as to be larger than the width of the clamping part, and the clamping process is a process of clamping only the thin film part of the melt. fill The method of production.

  8). 8. The method for producing an optical film according to 7, wherein the cast roll according to any one of 1 to 5 is used.

  According to the present invention, the contact between the cast roll and the end of the touch roll can be prevented, and the extruded film-like melt can be pinched in a state in which the thick film at the end is released. Cast roll, optical film manufacturing apparatus, and optical film manufacturing for manufacturing an optical film excellent in retardation uniformity by pressing a thin film portion of a film-like melt extruded on the surface with a uniform pressure Can provide a method.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings (FIGS. 1 to 4).

  The present invention relates to an apparatus for producing an optical film containing a cellulose resin by a melt casting film forming method. Here, the melt casting film-forming method means that an optical film is obtained by heating and melting a composition containing a cellulose resin to a temperature exhibiting fluidity, casting the fluid having the fluidity, and solidifying by cooling. Is the way to get.

  FIG. 1 is a view showing an example of an optical film manufacturing apparatus according to the present invention. The optical film manufacturing apparatus shown in FIG. 1 includes an extruder 1, a casting die 2, a cast roll 3, a touch roll 4, cooling rolls 5 and 6, a peeling roll 7, a stretching apparatus 8, and a winder 9. .

  In this embodiment, after mixing the film material containing a cellulose resin, the extruder 1 is used to melt and extrude the cast roll 3 from the casting die 2 to the surface of the cast roll 3, and the extruded film-like melt is cast. The roll 3 and the touch roll 4 are clamped at a predetermined pressure. Further, the two cooling rolls 5 and 6 are sequentially circumscribed and solidified by cooling, and are peeled off by the peeling roll 7. The peeled film 10 is gripped by the stretching device 8 and stretched in the width direction and then wound by the winding device 9.

(Preparation of materials)
In the present invention, it is preferable that the cellulose resin and other additives such as a stabilizer added as necessary are mixed before melting. Mixing may be performed by a mixer or the like, or may be performed in the cellulose resin preparation process. When a mixer is used, a general mixer such as a V-type mixer, a conical screw type mixer, a horizontal cylindrical type mixer, or the like can be used.

  In the present invention, after mixing the materials constituting the optical film as described above, the mixture may be directly melted using the extruder 1 to form a film. Then, the pellets may be melted by the extruder 1 to form a film. When the film constituent material includes a plurality of materials having different melting points, a so-called braided semi-melt is once produced at a temperature at which only the material having a low melting point is melted, and the semi-melt is supplied to the extruder 1. It is also possible to form a film by introducing it. If the film component contains a material that is easily pyrolyzed, in order to reduce the number of times of melting, a method of directly forming a film without producing pellets, or after making a paste-like semi-molten material as described above A method of forming a film is preferred.

  In addition, the detail of the material which comprises the optical film manufactured with the manufacturing apparatus of this invention is mentioned later.

(Extruder)
As the extruder 1, various extruders available on the market can be used, and among them, a melt-kneading extruder is preferable. A single screw extruder or a twin screw extruder may be used. When film formation is directly performed without producing pellets from film constituent materials, it is preferable to use a twin-screw extruder because an appropriate degree of kneading is necessary, but even with a single-screw extruder, the screw shape is a Maddock type. By using a kneading-type screw such as a unimelt type or a dull mage, an appropriate kneading can be obtained, which can be used. When a pellet or braided semi-melt is once used as a film constituent material, it can be used in either a single screw extruder or a twin screw extruder. These extruders are generally available as plastic molding machines.

  It is preferable to reduce the oxygen concentration by replacing the inside of the extruder 1 with an inert gas such as nitrogen gas or reducing the pressure.

  The melting temperature of the film constituent material in the extruder 1 varies depending on the viscosity and discharge amount of the film constituent material, the thickness of the film to be produced, etc., but generally, with respect to the glass transition temperature Tg of the film, Tg or more and Tg + 100 ° C. or less, preferably Tg + 10 ° C. or more and Tg + 90 ° C. or less. The melt viscosity at the time of extrusion is 10 to 100,000 poise, preferably 100 to 10,000 poise. Further, the residence time of the film constituting material in the extruder 1 is preferably short, and is within 5 minutes, preferably within 3 minutes, more preferably within 2 minutes. Although the residence time depends on the type of the extruder 1 and the extrusion conditions, it can be shortened by adjusting the material supply amount, L / D, screw rotation speed, screw groove depth, etc. It is.

  The shape, rotation speed, and the like of the screw of the extruder 1 are appropriately selected depending on the viscosity, the discharge amount, and the like of the film constituent material. In the present invention, the shear rate in the extruder 1 is 1 / second to 10000 / second, preferably 5 / second to 1000 / second, more preferably 10 / second to 100 / second.

(Casting die)
The melt discharged from the extruder 1 is supplied to the casting die 2 and is extruded from the casting die 2 into a film shape.

  The casting die 2 is not particularly limited as long as it is used for producing a sheet or a film. As the material of the casting die 2, for example, chromium, chromium carbide, chromium nitride, titanium carbide, titanium carbonitride, titanium nitride, super steel, ceramic (tungsten carbide, aluminum oxide, chromium oxide) or the like is sprayed or plated. Buffing as surface processing, lapping using # 1000 or higher grinding wheel, plane cutting using # 1000 or higher diamond grinding wheel (cutting direction is preferably perpendicular to the resin flow direction), electrolytic polishing, electrolytic composite polishing, etc. Examples include processed ones.

(Cast roll)
The cast roll 3 is a roll for producing an optical film by supporting a film-like melt containing a cellulose resin extruded from the casting die 2 on the surface and sandwiching the melt with the touch roll 4.

  FIG. 2 is a schematic view of the portion indicated by X in FIG. 1 as viewed from above. Originally, the cast roll 3, the film-like melt 20, and the touch roll 4 are in close contact with each other. However, in order to express the respective shapes in an easy-to-understand manner, in these drawings, between the cast roll 3 and the melt 20, the melt 20 And a gap between the touch rolls 4. In addition, the shape is exaggerated in order to explain the characteristics of the present invention.

  The cast roll 3 has a roll main body 33 including a pressing part for pressing the thin film part 21 of the melt 20, and a rotating shaft 34 for rotating the roll main body 33. Usually, it is a highly rigid metal roll, and also has the function of cooling the film-like melt supported on the surface. In order to cool the melt uniformly and efficiently, it is preferable to provide a structure in which a cooling medium such as water or oil flows inside the roll body 33. Carbon steel, stainless steel, aluminum, titanium, or the like can be used as the material for the surface of the roll body. Further, in order to increase the hardness of the surface or improve the releasability from the resin, it is preferable to perform a surface treatment such as hard chrome plating, nickel plating, amorphous chrome plating, or ceramic spraying.

  The film-like melt 20 extruded from the casting die 2 and supported on the surface of the cast roll 3 has thick film portions 22 thicker than the thin film portions 21 at both ends of the thin film portion 21 having a uniform film thickness. Have. The film thickness of the thick film portion 22 varies depending on various conditions, but is 1.2 to 5 times the film thickness of the thin film portion. Such a thick film portion 22 usually exists in a width of about 10 mm to 40 mm from the both ends in the width direction of the melt 20 inward. In addition, the film thickness of the thin film part 21 is uniform, and is normally set to fall within the range of 90% to 110% of the film thickness of the central part of the thin film part.

  When the film-like melt 20 is sandwiched between the cast roll and the touch roll, if the entire melt 20 including the thick film portion 22 is sandwiched, the thick film portion 22 may affect the thin film portion 21. Pressure cannot be applied evenly. As a result, the obtained optical film has poor retardation uniformity and cannot satisfy the required quality.

  In the present invention, the width of the pressing portion for pressing the thin film portion of the melt of the cast roll is made smaller than the width of the thin film portion of the melt, and only the thin film portion of the melt is pressed. Solves this problem. For this reason, the cast roll 3 of the present invention includes a clamping unit 31 for clamping the thin film part 21 of the melt 20 and a non-clamping part that is positioned at both ends of the clamping unit 31 and does not clamp the melt 20. 32 and a rotating shaft 34 for rotating the roll body 33.

  The pinching portion 31 needs to have a constant outer diameter across the entire width in order to apply a uniform pressure to the thin film portion 21 of the film-like melt 20 and to make the thickness of the film uniform. is there. However, it is difficult to actually manufacture a cast roll having the pinching portion 31 having a completely constant outer diameter, and variations such as processing errors that are unavoidable during the manufacture of the cast roll are allowed. In general, it is difficult to suppress the variation in outer diameter as such a processing error to 10 μm or less in diameter.

  The width of the clamping part 31 is made smaller than the width of the thin film part 21. As described above, the thick film portion 22 usually exists in a width of 10 mm to 40 mm from the both ends in the width direction of the film-like melt 20, so that the width of the pressing portion 31 is increased. The width of the melt 20 is preferably shorter by 20 mm or more. However, it is not preferable to reduce the width of the pinching portion 31 more than necessary because the width of the optical film to be manufactured is shortened. From such a viewpoint, it is preferable to make the width of the pressing portion 31 20 mm to 100 mm smaller than the width of the melt.

  On the other hand, the non-clamping part 32 needs to have an outer diameter smaller than that of the clamping part 31 so that the thick film part 22 of the melt 20 can escape during clamping. The difference between the outer diameters of the clamping part 31 and the non-clamping part 32 only needs to be different enough to allow the thick film part 22 of the melt 20 to escape. Therefore, when the film thickness of the thin film portion 21 is t1, the film thickness of the thick film portion 22 is t2, the diameter of the pinching portion 31 is φp, and the diameter of the outer end portion of the non-pressing portion is φq, φq ≦ φp−2 It is necessary to be (t2-t1). However, when the touch roll bends during pinching, not only the difference in film thickness between the thin film portion 21 and the thick film portion 22 of the melt 20 but also the amount of deflection of the touch roll during pinching is considered. And it is preferable to set the diameter of the non-clamping part 32 small.

  Moreover, since temperature control is difficult near the edge part of a roll main body, and it is difficult to cool the melt on the surface uniformly, the thin film part 21 of the melt 20 is pinched in the vicinity of the edge part of a roll main body. That is not preferable. From such a viewpoint, it is preferable that the widths of the non-clamping parts 32 at both ends of the clamping part 31 are 20 mm or more. Conversely, if the width of the non-clamping portion 32 is too large, the cast roll is unnecessarily large, which is not preferable. From this point of view, the width of the non-clamping part is preferably 20 mm to 1000 mm. Furthermore, if the difference in diameter between the clamping part 31 and the non-clamping part 32 is too large, it becomes difficult to control the temperature in the vicinity of the end part of the clamping part 31, and therefore it is preferable that φq ≧ 0.8φp. . In summary, it is preferable that 0.8φp ≦ φq ≦ φp−2 (t2−t1) is satisfied.

  The non-clamping part 32 may not be in contact with the film-like melt 20, or may be in contact with the melt 20 as long as the pressure does not affect the pressure applied to the thin film part 21.

  The smoother the surface of the pressing part 31, the better the surface of the film obtained. The surface roughness of the pinched portion 31 is preferably 0.1 μm or less in terms of arithmetic average roughness Ra, and more preferably 0.05 μm or less. When the non-clamping portion 32 does not come into contact with the film-like melt 20, the surface roughness is not limited. However, when the non-clamping portion 32 is in contact with the film-like melt 20, it is preferable that the non-clamping portion 32 has a smoothness that does not cause a problem of peelability from the melt 20.

  As the film thickness of the thin film portion 21 becomes thinner, the influence of the pressure during clamping on the retardation of the film becomes more prominent. In particular, the effect of the present invention is great when the thickness of the thin film portion 21 is 60 μm or less. On the other hand, a film that is too thin is weak in strength and not practical. From this viewpoint, the present invention is particularly suitable when the thickness of the thin film portion 21 is 15 μm to 60 μm, and further suitable when the film thickness is 20 μm to 50 μm.

  Since the non-clamping part 32 does not clamp the melt 20 unlike the clamping part 31, the outer diameter does not need to be constant, and the outer diameter may be different depending on the position.

  FIG. 3 is a schematic view of a portion indicated by X in FIG. 1 as viewed from above when a cast roll 3a having another shape according to the present invention is used. The outer diameter of the non-clamping portion 32a of the cast roll 3a is not constant, and the outer diameter is smaller at the end portion.

  Moreover, the schematic diagram which looked at the part shown by X of FIG. 1 from the upper direction at the time of using the elastic roll which is easy to bend as a touch roll is shown in FIG. The cast roll 3 is the same as that shown in FIG.

  When the conventional cast roll is used, the touch roll 4a is bent at the time of pinching and both ends of the touch roll 4a come into contact with the cast roll, and the pressure applied to the thin film portion 21 varies greatly. It was. Since the cast roll 3 of the present invention has the non-clamping portion 32 having a small outer diameter at both end portions, the problem that the cast roll 3 contacts the cast roll 3 even if the touch roll 4a is slightly bent does not occur. Such a problem was remarkable when the width of the optical film to be produced was wide. From this point of view, the cast roll of the present invention is particularly effective when the width of the pinching portion 31 is 1500 mm to 4000 mm.

(Touch roll)
In the present invention, the touch roll 4 is not particularly limited as long as it is generally used for production of a film by a melt casting film forming method, and can be appropriately selected and used. For example, a metal roll such as carbon steel, stainless steel, aluminum, or titanium, or a roll whose surface is covered with rubber, resin, or the like can be used.

  From the viewpoint of equalizing the pressure applied to the melt 20 when the film-like melt 20 is sandwiched between the cast rolls 3, the metal outer cylinder, the inner cylinder, the metal outer cylinder, and the inner cylinder It is preferable to use a double-structured elastic touch roll provided with a space for flowing fluid between them.

  In such a double-structure elastic touch roll, the metal outer cylinder is preferably made of a smooth, moderately elastic material and durable. Carbon steel, stainless steel, titanium, nickel produced by electroforming, etc. can be preferably used. Further, in order to increase the hardness of the surface or improve the releasability from the resin, it is preferable to carry out a surface treatment such as hard chrome plating, nickel plating, amorphous chrome plating, or ceramic spraying.

  The thickness of the metal outer cylinder is preferably set in a range satisfying 0.003 ≦ (thickness of the metal outer cylinder) / (touch roll radius) ≦ 0.03 in consideration of elasticity, strength, rotation unevenness, and the like. If the thickness of the metal outer cylinder is too thin, the strength is insufficient and there is a concern of breakage. Conversely, if it is too thick, it will be difficult to keep the pressure applied to the film uniform. On the other hand, if the radius of the touch roll is large, moderate elasticity can be ensured even if the metal outer cylinder is thick. The diameter of the touch roll is preferably 100 mm to 600 mm.

  The smoother the surface of the metal outer cylinder is, the more preferable it is because the surface of the obtained film can be smoothed. The surface roughness of the metal outer cylinder is preferably 0.1 μm or less in terms of arithmetic average roughness Ra, and more preferably 0.05 μm or less.

  The inner cylinder is preferably made of a lightweight and rigid metal such as carbon steel, stainless steel, aluminum, or titanium. By giving rigidity to the inner cylinder, it is possible to suppress the rotational shake of the roll. A sufficient rigidity can be obtained by setting the thickness of the inner cylinder to 2 to 10 times that of the outer cylinder. The inner cylinder may be further coated with a resin elastic material such as silicone or fluororubber.

  The reason for providing a space for fluid flow is to make the temperature of the roll surface uniform. For this reason, for example, the temperature distribution on the roll surface can be reduced by using a structure in which going and returning flow alternately in the width direction or a structure in which the flow flows spirally. The fluid for cooling is not particularly limited, and water or oil can be used according to the temperature range to be used.

  The surface temperature of the touch roll 4 is preferably lower than the glass transition temperature (Tg) of the film. If it is higher than Tg, the peelability between the film and the touch roll may be inferior. If it is too low, volatile components from the film may be deposited on the roll, so that the temperature is more preferably 10 ° C to Tg-10 ° C. Here, Tg is Tg of the film, and is a temperature obtained by DSC measurement (temperature increase rate: 10 ° C./min) at which the baseline starts to deviate.

  The touch roll 4 used in the manufacturing apparatus of the present invention preferably has a so-called drum shape in which the diameter of the central portion in the width direction is larger than the diameter of the end portion. In general, the touch roll is pressed against the film at both end portions by a pressurizing means. In this case, the touch roll is bent, so that the touch roll is more strongly pressed toward the end portion. By making the touch roll into a drum shape, it becomes possible to pinch with a more uniform pressure.

  In the manufacturing apparatus of the present invention, a device for cleaning dirt on the touch roll 4 may be provided. Examples of the cleaning device include a device that presses a member such as a nonwoven fabric infiltrated with a solvent on the surface of the touch roll 4 if necessary, a device that volatilizes dirt on the surface of the touch roll by plasma discharge such as corona discharge and glow discharge, and the like. Is mentioned.

  In order to make the surface temperature of the touch roll 4 more uniform, a temperature control roll may be brought into contact with the touch roll 4, temperature-controlled air may be sprayed, or a heat medium such as a liquid may be brought into contact.

(Cooling roll)
In the present embodiment, the extruded film-like melt is sandwiched between the cast roll 3 and the touch roll 4 at a predetermined pressure, and then is externally contacted with the two cooling rolls 5 and 6 in order to be cooled and solidified. Film 10 is obtained.

  The cooling rolls 5 and 6 are high-rigidity metal rolls, and, like the cast roll 3, a cooling medium such as water or oil flows inside in order to make the film supported on the surface uniform and to improve the cooling efficiency. It is preferable to have such a structure. The diameter of the cooling rolls 5 and 6 should just be large enough to cool the film supported on the surface, and is usually about 100 mm to 1 m. Carbon steel, stainless steel, aluminum, titanium, or the like can be used as the surface material. Further, in order to increase the hardness of the surface or improve the releasability from the resin, it is preferable to perform a surface treatment such as hard chrome plating, nickel plating, amorphous chrome plating, or ceramic spraying. The surface roughness is preferably 0.1 μm or less, more preferably 0.05 μm or less, in terms of arithmetic average roughness Ra.

  Although the manufacturing apparatus of the present embodiment includes two cooling rolls, the number of cooling rolls is not limited to this, and a manufacturing apparatus including a larger number of cooling rolls can also be used.

(Stretching device)
In the present embodiment, the film cooled and solidified by the cooling rolls 5 and 6 is peeled from the cooling roll 6 by the peeling roll 7 and then stretched by the stretching device 8 according to the use of the film.

  As the stretching device 8, a known film stretching machine can be used. In addition to the uniaxial stretching machine, a simultaneous biaxial stretching machine or the like can be used as necessary. For stretching, conditions such as temperature and magnification may be selected so that desired retardation characteristics can be obtained according to the use of the optical film to be produced.

  For example, in the case of producing a retardation film for a polarizing plate, it is preferable to make the stretching direction the width direction because lamination with a polarizing film can be performed in a roll form. By stretching the film containing the cellulose resin produced in the present embodiment in the width direction, a retardation film in which the width direction of the film is a slow axis is obtained. On the other hand, the transmission axis of the polarizing film bonded to the retardation film is also usually in the width direction. A good viewing angle can be obtained by incorporating a polarizing plate in which the transmission axis of the polarizing film and the slow axis of the retardation film are parallel to each other into the liquid crystal display device.

  When producing a retardation film for a polarizing plate, the stretching ratio is usually 1.1 to 3.0 times, preferably 1.2 to 1.5 times, and the stretching temperature is usually a resin constituting the film. In many cases, it is carried out in a temperature range of Tg to Tg + 50 ° C., preferably Tg to Tg + 40 ° C. If the draw ratio is too small, the desired retardation may not be obtained, and if it is too large, it may break. Further, if the stretching temperature is too low, it may break, and if it is too high, the desired retardation may not be obtained.

  In the case of a retardation film, the in-plane retardation (Ro) is preferably 20 to 200 nm, the thickness direction retardation (Rt) is 90 to 400 nm, the in-plane retardation (Ro) of the film is 20 to 100 nm, and the thickness direction retardation (Rt). Is more preferably 90 to 200 nm. Further, the ratio Rt / Ro of Rt and Ro is preferably 0.5 to 4, particularly preferably 1 to 3. In either case, the measurement wavelength is 590 nm.

In addition, when the refractive index Nx in the slow axis direction of the film, the refractive index Ny in the fast axis direction, the refractive index Nz in the thickness direction, and the film thickness of the film are d (nm),
Ro = (Nx−Ny) × d
Rt = {(Nx + Ny) / 2−Nz} × d
Represented as:

  The variation in retardation is preferably as small as possible, and is usually within ± 10 nm, preferably ± 5 nm or less, and more preferably ± 2 nm or less. By using the production apparatus of the present invention, an optical film with high uniformity of retardation can be produced.

  A stretching device (longitudinal stretching device) for stretching the optical film in the longitudinal direction may be provided before or after the stretching device (lateral stretching device) for stretching the optical film in the width direction. As such a longitudinal stretching apparatus, for example, an apparatus described in JP 2001-198976 A can be used.

(Winding machine, etc.)
The optical film to which a desired retardation characteristic is imparted by the stretching device 8 is wound up by a winder 9 after the end portion is cut into a predetermined width by a slitter (not shown).

  In addition, the manufacturing apparatus of this invention may be provided with another apparatus suitably according to a use. For example, a heat treatment machine for heat setting may be provided after the stretching apparatus. Further, before the winder, a knurling device (embossing device), a cooling device, a static eliminator, or the like may be provided to prevent sticking scratches at the end of the film.

(Materials that make up optical films)
The material constituting the optical film produced by the production apparatus of the present invention is a cellulose resin, if necessary, a stabilizer, a plasticizer, an ultraviolet absorber if necessary, a matting agent as a slipping agent, a retardation control agent, etc. included. These materials are appropriately selected depending on the required characteristics of the target optical film.

  The presence of a volatile component in the material constituting the optical film is not preferable because it may be a factor that hinders the flatness and transparency required for the optical film. This is because if the volatile component is mixed in the film formed, the transparency is lowered, and the surface of the film extruded from the casting die may be streaked and the flatness may be deteriorated. . From the viewpoint of avoiding the generation of volatile components at the time of heating and melting, it is not preferable that a component that volatilizes in a temperature region lower than the melting temperature for forming a film in the material constituting the optical film.

  Examples of the volatile component include moisture absorbed by any of the materials constituting the optical film, solvents mixed before the material is purchased or at the time of synthesis, and volatilization occurs due to evaporation, sublimation, or decomposition by heating. . Therefore, selection of the material constituting the optical film is important for avoiding the generation of volatile components.

(Cellulose resin)
The cellulose resin as a material constituting the optical film produced by the production apparatus of the present invention has a cellulose ester structure and is at least one of an aliphatic acyl group and a substituted or unsubstituted aromatic acyl group. It is the single or mixed acid ester of cellulose containing the structure of these.

  Hereinafter, although illustrated about the cellulose resin suitable as a material which comprises the optical film manufactured with the manufacturing apparatus of this invention, it is not limited to these.

When the cellulose resin contains an aromatic acyl group, when the aromatic ring is a benzene ring, examples of the substituent of the benzene ring include a halogen atom, cyano, alkyl group, alkoxy group, aryl group, aryloxy group, acyl group , Carbonamido group, sulfonamido group, ureido group, aralkyl group, nitro, alkoxycarbonyl group, aryloxycarbonyl group, aralkyloxycarbonyl group, carbamoyl group, sulfamoyl group, acyloxy group, alkenyl group, alkynyl group, alkylsulfonyl group, Arylsulfonyl group, alkyloxysulfonyl group, aryloxysulfonyl group, alkylsulfonyloxy group and aryloxysulfonyl group, -S-R, -NH-CO-OR, -PH-R, -P (-R) ₂ ,- PH-O-R, -P (-R) -O-R), - P ( -O-R) 2, -PH (= O) -R-P (= O) (- R) 2, -PH (= O) -O-R, -P ( = O) (-R) (-O-R), -P (= O) (-O-R) ₂ , -O-PH (= O) -R, -O-P (= O) (-R ) _2- O-PH (= O) -O-R, -O-P (= O) (-R) (-O-R), -O-P (= O) (-O-R) ₂ , —NH—PH (═O) —R, —NH—P (═O) (— R) (— O—R), —NH—P (═O) (— O—R) ₂ , —SiH ₂ — _{R, -SiH (-R) 2,} -Si (-R) 3, -O-SiH 2 -R, -O-SiH (-R) 2, -O-Si (-R) 3 , and the like. R is an aliphatic group, an aromatic group or a heterocyclic group.

  The number of substituents is 1 to 5, preferably 1 to 4, more preferably 1 to 3, and even more preferably 1 or 2. Further, when the number of substituents substituted on the aromatic ring is 2 or more, they may be the same as or different from each other. Further, they may be linked to each other to form a condensed polycyclic compound (for example, naphthalene, indene, indane, phenanthrene, quinoline, isoquinoline, chromene, chroman, phthalazine, acridine, indole, indoline, etc.).

  As the substituent, a halogen atom, cyano, alkyl group, alkoxy group, aryl group, aryloxy group, acyl group, carbonamido group, sulfonamido group or ureido group are preferable, halogen atom, cyano, alkyl group, alkoxy group, An aryloxy group, an acyl group or a carbonamido group is more preferred, a halogen atom, cyano, an alkyl group, an alkoxy group or an aryloxy group is further preferred, and a halogen atom, an alkyl group or an alkoxy group is most preferred.

  The halogen atom includes a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. The alkyl group may have a cyclic structure or a branch. The number of carbon atoms in the alkyl group is preferably 1-20, more preferably 1-12, still more preferably 1-6, and most preferably 1-4. Examples of the alkyl group include methyl, ethyl, propyl, isopropyl, butyl, t-butyl, hexyl, cyclohexyl, octyl and 2-ethylhexyl.

  The alkoxy group may have a cyclic structure or a branch. The number of carbon atoms in the alkoxy group is preferably 1-20, more preferably 1-12, still more preferably 1-6, and most preferably 1-4. The alkoxy group may be further substituted with another alkoxy group. Examples of alkoxy groups include methoxy, ethoxy, 2-methoxyethoxy, 2-methoxy-2-ethoxyethoxy, butyloxy, hexyloxy, octyloxy.

  The number of carbon atoms of the aryl group is preferably 6-20, and more preferably 6-12. Examples of aryl groups include phenyl and naphthyl. The aryloxy group preferably has 6 to 20 carbon atoms, more preferably 6 to 12 carbon atoms. Examples of the aryloxy group include phenoxy and naphthoxy.

  The number of carbon atoms in the acyl group is preferably 1-20, and more preferably 1-12. Examples of acyl groups include formyl, acetyl and benzoyl. The number of carbon atoms of the carbonamide group is preferably 1-20, and more preferably 1-12. Examples of the carbonamido group include acetamide and benzamide.

  The number of carbon atoms in the sulfonamide group is preferably 1-20, and more preferably 1-12. Examples of the sulfonamide group include methanesulfonamide, benzenesulfonamide, and p-toluenesulfonamide. The number of carbon atoms in the ureido group is preferably 1-20, and more preferably 1-12. An example of a ureido group is (unsubstituted) ureido.

  The number of carbon atoms in the aralkyl group is preferably 7-20, and more preferably 7-12. Examples of aralkyl groups include benzyl, phenethyl and naphthylmethyl. The number of carbon atoms in the alkoxycarbonyl group is preferably 1-20, and more preferably 2-12. An example of an alkoxycarbonyl group is methoxycarbonyl.

  The aryloxycarbonyl group preferably has 7 to 20 carbon atoms, and more preferably 7 to 12 carbon atoms. An example of an aryloxycarbonyl group is phenoxycarbonyl. The number of carbon atoms in the aralkyloxycarbonyl group is preferably 8-20, and more preferably 8-12. An example of an aralkyloxycarbonyl group is benzyloxycarbonyl.

  The number of carbon atoms of the carbamoyl group is preferably 1-20, and more preferably 1-12. Examples of the carbamoyl group include (unsubstituted) carbamoyl and N-methylcarbamoyl. The number of carbon atoms in the sulfamoyl group is preferably 20 or less, and more preferably 12 or less. Examples of sulfamoyl groups include (unsubstituted) sulfamoyl and N-methylsulfamoyl.

  The number of carbon atoms in the acyloxy group is preferably 1-20, and more preferably 2-12. Examples of the acyloxy group include acetoxy and benzoyloxy. The alkenyl group has preferably 2 to 20 carbon atoms, and more preferably 2 to 12 carbon atoms. Examples of alkenyl groups include vinyl, allyl and isopropenyl.

  The number of carbon atoms in the alkynyl group is preferably 2-20, and more preferably 2-12. An example of an alkynyl group is thienyl. The number of carbon atoms in the alkylsulfonyl group is preferably 1-20, and more preferably 1-12.

  The number of carbon atoms of the arylsulfonyl group is preferably 6-20, and more preferably 6-12. The alkyloxysulfonyl group preferably has 1 to 20 carbon atoms, more preferably 1 to 12 carbon atoms. The number of carbon atoms of the aryloxysulfonyl group is preferably 6-20, and more preferably 6-12. The number of carbon atoms in the alkylsulfonyloxy group is preferably 1-20, and more preferably 1-12. The number of carbon atoms of the aryloxysulfonyl group is preferably 6-20, and more preferably 6-12.

  When the hydrogen atom of the hydroxyl group of cellulose is a fatty acid ester with an aliphatic acyl group, the aliphatic acyl group has 2 to 20 carbon atoms, specifically, acetyl, propionyl, butyryl, isobutyryl, valeryl, pivaloyl , Hexanoyl, octanoyl, lauroyl, stearoyl and the like.

  Here, the aliphatic acyl group is meant to include those having a substituent. Examples of the substituent in this case include those exemplified as the substituent of the benzene ring when the aromatic ring is a benzene ring in the above-described aromatic acyl group.

  When producing an optical film used as a retardation film, the cellulose resin is selected from cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate, and cellulose phthalate. It is preferable to use at least one kind.

  Among these, particularly preferable cellulose resins include cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, and cellulose acetate butyrate.

  The raw material cellulose of the cellulose resin used in the present invention may be wood pulp or cotton linter, and the wood pulp may be softwood or hardwood, but softwood is more preferable. A cotton linter is preferably used from the viewpoint of peelability during film formation. Cellulose resins made from these can be used in appropriate mixture or independently.

  Polymeric materials and oligomers other than the cellulose resin may be appropriately selected and mixed with the cellulose resin. Such a polymer material or oligomer is preferably compatible with the cellulose resin and can obtain a high transmittance over the entire visible region (400 nm to 800 nm) when formed into a film.

(Stabilizer)
It is preferable to add a stabilizer before or during the heat melting of the cellulose resin. The stabilizer is required to function without being decomposed even at the melting temperature for film formation.

  Stabilizers include hindered phenol antioxidants, acid scavengers, hindered amine light stabilizers, peroxide decomposers, radical scavengers, metal deactivators, amines, and the like. These are described in JP-A-3-199201, JP-A-5-97073, JP-A-5-194789, JP-A-5-271471, JP-A-6-107854, and the like.

  Coloration and molecular weight reduction including decomposition reactions that have not been elucidated, such as oxidation prevention of materials constituting optical films, capture of acids generated by decomposition, suppression or prevention of decomposition reactions caused by radical species caused by light or heat, etc. Stabilizers are used to suppress the generation of volatile components due to alterations such as degradation and material decomposition. That is, the addition of the stabilizer to the material constituting the optical film is excellent from the viewpoint of suppressing or preventing the generation of volatile components due to alteration or decomposition of materials other than the stabilizer among the materials constituting the optical film. . Further, the stabilizer itself is required not to generate a volatile component in the melting temperature region of the film constituting material.

  Also when manufacturing the optical film used as a phase difference film, it is preferable to contain a stabilizer. By containing a stabilizer, it is possible to suppress the deterioration of the strength of the film constituting material or maintain the strength inherent to the material in the step of imparting retardation as a retardation film. In addition, the presence of the stabilizer suppresses the formation of a colored substance in the visible light region at the time of heating and melting, or prevents the volatile component from being mixed into the film, so that characteristics such as transmittance and haze value can be obtained. It is excellent in that it can be maintained at a preferable value as a retardation film. The haze value is preferably less than 1%, more preferably less than 0.5%.

  At least one or more stabilizers can be selected. The amount to be added is preferably 0.001 parts by mass or more and 5 parts by mass or less, more preferably 0.005 parts by mass or more and 3 parts by mass or less, further preferably 0.01 parts by mass or more with respect to 100 parts by mass of the cellulose resin. 0.8 parts by mass or less.

  If the added amount of the stabilizer is too small, the stabilizing effect is low and the effect of the stabilizer cannot be obtained, and if the added amount is too large, the transparency of the film as a film from the viewpoint of compatibility with the resin. This is not preferable because it causes a decrease and the film may become brittle.

  The stabilizer is preferably mixed before the resin is melted. Mixing can be performed by a known mixer or the like. You may mix in a cellulose resin preparation process. By mixing at a temperature not higher than the melting point of the resin and not lower than the melting point of the stabilizer, only the stabilizer may be melted to adsorb the stabilizer on the surface of the resin.

(Plasticizer)
From the viewpoints of improving the mechanical properties of the optical film, imparting flexibility, imparting water absorption resistance, reducing moisture permeability, and the like, it is preferable that a plasticizer is included. Further, it may contain a plasticizer from the viewpoint that the melting temperature can be lowered as compared with the case of the cellulose resin alone, or the melt viscosity can be reduced as compared with the case of the cellulose resin alone at the same heating temperature. preferable. In order to lower the melting temperature, the plasticizer to be added preferably has a melting point or glass transition temperature lower than the glass transition temperature of the cellulose resin.

  As the plasticizer, for example, phosphate ester derivatives and carboxylic acid ester derivatives are preferably used. Further, a polymer obtained by polymerizing an ethylenically unsaturated monomer having a mass average molecular weight of 500 or more and 10,000 or less as described in JP-A No. 2003-12859, an acrylic polymer, an acrylic polymer having an aromatic ring in the side chain, or cyclohexyl An acrylic polymer having a group in the side chain is also preferably used.

  Examples of phosphate ester derivatives include triphenyl phosphate, tricresyl phosphate, phenyl diphenyl phosphate, and the like.

  Examples of the carboxylic acid ester derivatives include phthalic acid esters and citric acid esters. Examples of the phthalic acid esters include dimethyl phthalate, diethyl phthalate, dicyclohexyl phthalate, dioctyl phthalate, and diethyl hexyl phthalate. Mention may be made of acetyltriethyl citrate and acetyltributyl citrate.

  Other examples of plasticizers that can be used include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, triacetin, trimethylolpropane tribenzoate, trimethylolpropane tris (3,4,5-trimethoxybenzoate), and the like. . Alkylphthalylalkyl glycolates are also preferably used for this purpose. The alkyl in the alkylphthalylalkyl glycolate is an alkyl group having 1 to 8 carbon atoms. Examples of alkyl phthalyl alkyl glycolates include methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, octyl phthalyl octyl glycolate, methyl phthalyl ethyl glycolate, Ethyl phthalyl methyl glycolate, ethyl phthalyl propyl glycolate, propyl phthalyl ethyl glycolate, methyl phthalyl propyl glycolate, methyl phthalyl butyl glycolate, ethyl phthalyl butyl glycolate, butyl phthalyl methyl glycolate, butyl Phthalyl ethyl glycolate, propyl phthalyl butyl glycolate, butyl phthalyl propyl glycolate, methyl phthalyl octyl glycolate, ethyl phthalyl octyl Collate, octyl phthalyl methyl glycolate, octyl phthalyl ethyl glycolate and the like can be mentioned, such as methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, Octyl phthalyl octyl glycolate is preferable, and ethyl phthalyl ethyl glycolate is particularly preferably used. Moreover, you may use these alkylphthalyl alkyl glycolates etc. in mixture of 2 or more types.

  The addition amount of the plasticizer is preferably 0.5 parts by mass or more and less than 20 parts by mass, more preferably 1 part by mass or more and less than 11 parts by mass with respect to 100 parts by mass of the cellulose resin.

(UV absorber)
Depending on the use of the optical film to be produced, it is preferable that an ultraviolet absorber is further contained. The ultraviolet absorber is excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less from the viewpoint of preventing deterioration of the polarizer and the display device with respect to ultraviolet rays, and has little absorption of visible light having a wavelength of 400 nm or more from the viewpoint of liquid crystal display properties. Those are preferred.

  Examples of ultraviolet absorbers include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like. Less benzotriazole compounds are preferred. Moreover, you may use the ultraviolet absorber of Unexamined-Japanese-Patent No. 10-182621, Unexamined-Japanese-Patent No. 8-337574, and the polymeric ultraviolet absorber of Unexamined-Japanese-Patent No. 6-148430.

(Matting agent)
A matting agent may be added to the optical film in order to facilitate slipping, transportability and winding. The matting agent is preferably as fine as possible. Examples of the fine particles include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, kaolin, talc, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, Examples thereof include inorganic fine particles such as magnesium silicate and calcium phosphate, and crosslinked polymer fine particles.

  Among these, silicon dioxide is preferable because it can reduce the haze of the film. In many cases, fine particles such as silicon dioxide are surface-treated with an organic material, but such a material is preferable because it can reduce the haze of the film. Preferred organic substances for the surface treatment include halosilanes, alkoxysilanes, silazane, siloxane and the like.

  The larger the average particle size of the fine particles, the greater the sliding effect, and the smaller the average particle size, the better the transparency. The average particle size of the fine particles is preferably in the range of 0.005 to 1.0 μm. The fine particles may be aggregated to form secondary particles. The average particle size of particularly preferable fine particles is 5 to 50 nm, more preferably 7 to 14 nm. The content of the fine particles is preferably 0.005 to 0.3 parts by mass with respect to 100 parts by mass of the cellulose resin.

  Examples of the fine particles of silicon dioxide include Aerosil 200, 200V, 300, R972, R972V, R974, R202, R812, OX50, TT600 manufactured by Nippon Aerosil Co., Ltd., preferably Aerosil 200V, R972, R972V, R974, R202, and R812. Two or more kinds of these fine particles may be used in combination. When using 2 or more types together, it can mix and use in arbitrary ratios.

  These fine particles can be added by kneading with a resin, and can also be kneaded with a stabilizer, a plasticizer, an ultraviolet absorber and the like. Alternatively, fine particles dispersed in advance in a solvent such as methanol or ethanol may be sprayed onto the cellulose resin, mixed and dried, and the fine particles dispersed in the solvent are mainly composed of methylene chloride or methyl acetate. What was added and mixed with the cellulose resin solution, dried and solidified into pellets may be used as a raw material for melt casting. In this case, it is more preferable that the cellulose resin solution containing fine particles further contains a part or all of a stabilizer, a plasticizer, an ultraviolet absorber and the like.

  Alternatively, a dispersion in which 0.1 to 20 parts by mass of fine particles are dispersed in 10 to 100 parts by mass of a solvent such as methanol, ethanol, isopropanol, or butanol per 100 parts by mass of the cellulose resin is added and kneaded while removing the solvent. The thermoplastic resin composition thus obtained may be used as a raw material (preferably in the form of pellets) for melt casting containing fine particles.

(Retardation control agent)
In the case of producing an optical film or the like used as a retardation film, a retardation control agent for adjusting retardation may be added. As the retardation control agent, an aromatic compound having two or more aromatic rings as described in European Patent No. 911,656A2 can be used. Two or more aromatic compounds may be used in combination. The aromatic ring of the aromatic compound includes an aromatic heterocyclic ring in addition to the aromatic hydrocarbon ring. Particularly preferred is an aromatic heterocycle, and the aromatic heterocycle is generally an unsaturated heterocycle. Of these, a 1,3,5-triazine ring is particularly preferred.

(Example 1)
A retardation film containing a cellulose resin was produced using the optical film production apparatus shown in FIG. This apparatus includes a cast roll 3 shown in FIG. 2 as a cast roll.

  First, the following materials were mixed for 30 minutes in a V-type mixer filled with nitrogen gas, and then melted at 240 ° C. using a twin-screw extruder (PCM30, manufactured by Ikegai Co., Ltd.) attached with a strand die. A cylindrical pellet having a thickness of 4 mm and a diameter of 3 mm was produced.

Cellulose acetate propionate (cellulose resin) 100 parts by mass (acetyl group substitution degree 1.4, propionyl group substitution degree 1.35,
Total acyl group substitution degree 2.75, number average molecular weight 60000,
(Glass transition point: Tg = 174 ° C.)
Trimethylolpropane tribenzoate (plasticizer) 10 parts by mass IRGANOX XP 420 / FD (manufactured by Ciba Specialty Chemicals)
(Stabilizer) 1 part by mass Seahorster KEP-30 (manufactured by Nippon Shokubai Co., Ltd.)
(Average particle size 0.3 μm silica fine particles) (matting agent) 0.1 part by mass Ti928 (manufactured by Ciba Specialty Chemicals) (ultraviolet absorber) 1.5 parts by mass The above acetyl group substitution degree, propionyl substitution degree, total The degree of acyl group substitution was measured by a method according to ASTM-D817-96.

  The obtained pellets were dried at 100 ° C. for 5 hours to a moisture content of 100 ppm, and a single screw extruder (GT-50; manufactured by Plastic Engineering Laboratory Co., Ltd.) equipped with a casting die (T die) having a width of 1900 mm. The film was formed by setting the extruder and the casting die to 250 ° C. The surface of the casting die was subjected to hard chrome plating and a mirror finish with a surface roughness of 0.1S. The extruded film-like melt was dropped into a gap for sandwiching the melt between the cast roll 3 and the touch roll 4. The extruded film-like melt had a width of about 1800 mm and a thickness of the thin film portion of about 100 μm, and a thick film portion having a width of 20 mm and a thickness of 250 μm was present at both ends.

  The cast roll 3 includes a pressing unit 31 for pressing the thin film portion 21 of the melt 20 and a non-pressing portion 32 that is positioned at both ends of the pressing unit 31 and does not clamp the melt 20. 33 and a rotating shaft 34 for rotating the roll body 33. The pinching portion 31 has a diameter of 300 mm and a width of 1740 mm, the non-pinching portion 32 has a diameter of 298 mm, and the roll body 33 has a width of 2200 mm. The surface of the clamping part is chrome-plated and further has a mirror finish with a surface roughness of 0.1S.

  The dropped melt was pressed by the cast roll 3 and the touch roll 4. The load at this time was 8700 N, and the linear pressure obtained by dividing the load by the width of the pinching portion 31 was 50 N / cm. The pressed film was further conveyed while being in contact with the two cooling rolls 5 and 6, cooled and solidified, and then peeled off from the cooling roll by the peeling roll 7. Next, the film was stretched 1.3 times in the width direction of the film by the stretching device 8, and the end of the film was cut by a slitter, and then wound by the winder 9.

  The retardation of the obtained optical film was measured. The measurement locations were three locations, a central portion in the width direction of the film, and a location 100 mm inside (two locations on the left and right) from the width of the pinching portion of the cast roll 3. In-plane retardation (Ro) and thickness direction retardation (Rt) were measured at each position to determine the amount of variation.

  The retardation was measured using Kobra-WX150K (manufactured by Oji Scientific Instruments). The measurement wavelength was 590 nm.

(Examples 2-9)
Similarly to Example 1, an optical film was produced using the cast roll 3 of the present invention. By changing the casting die and changing the amount of extrusion, the width and thickness of the film-like melt 20 extruded on the surface of the cast roll 3 are changed, and the width of the clamping part of the cast roll 3 is changed to the melt. It is changed according to the width of 20. The other conditions are basically the same as those in the first embodiment. However, the load by the touch roll was changed according to the width of the pinching portion of the cast roll 3 so that the linear pressure was equal. Under either condition, the cast roll and the end of the touch roll were not in contact with each other. Thereafter, the retardation of the produced optical film was measured under the same conditions as in Example 1.

(Comparative Examples 1-9)
As a cast roll, an optical film was produced in the same manner as in Examples 1 to 9, using a cast roll having a non-clamping portion and a uniform diameter over the entire width of the roll body. The diameter of the roll body of the used cast roll was 300 mm. In Comparative Examples 1-9, the value obtained by dividing the load by the width of the film was taken as the linear pressure. In the same manner as in the examples, the retardation of the produced optical film was measured. The measurement location was the same as in Examples 1-9.

  Table 1 shows the manufacturing conditions and retardation measurement results of Examples 1 to 9 and Comparative Examples 1 to 9.

  As shown in Table 1, in Examples 1 to 9 manufactured using the cast roll according to the present invention, the retardation variation amount is 5 nm or less, and a very good value is obtained. This is because the cast roll has a non-clamping part, so that when the film-like melt 20 is clamped with the touch roll, the influence of the thick film part can be eliminated and a uniform pressure can be applied. It is thought to be because.

  On the other hand, Comparative Examples 1 to 9 had a large retardation variation as compared with Examples under the same conditions, and a good optical film could not be obtained. In particular, the wider the film and the smaller the thickness, the greater the difference from the examples. Furthermore, when the width of the cast roll is wide, the cast roll and the end portion of the touch roll are in contact with each other, so that the variation amount of the retardation becomes very large.

The figure which shows an example of the manufacturing apparatus of the optical film in this invention Schematic view of the part indicated by X in FIG. The schematic diagram which looked at the part shown by X of Drawing 1 from the upper part at the time of using cast roll 3a of other shapes concerning the present invention. 1 is a schematic view of the portion indicated by X in FIG. 1 as viewed from above when an elastic roll that is easily bent is used as a touch roll.

Explanation of symbols

2 Casting die 3, 3a Cast roll 4, 4a Touch roll 20 Film-like melt 21 Thin film part 22 Thick film part 31, 31a Clamping part 32, 32a Non-clamping part 33, 33a Roll body 34 Rotating shaft

Claims (8)

A film-like melt containing cellulose resin extruded from a casting die and having a thick film portion thicker than the thin film portion at both ends of the thin film portion having a uniform film thickness is supported on the surface. In the cast roll for producing the optical film by sandwiching the melt with the touch roll,
The cast roll includes a roll body including a clamping unit for clamping the thin film part of the melt, and a non-clamping part that is positioned at both ends of the clamping part and does not clamp the melt; A rotating shaft for rotating the roll body,
The pinching portion is smaller than the width of the thin film portion, and the outer diameter is constant over the entire width.
The non-clamping part has a smaller outer diameter than the outer diameter of the clamping part. When the film thickness of the thin film portion is t1, the film thickness of the thick film portion is t2, the diameter of the pinching portion is φp, and the diameter of the outer end portion of the non-pressing portion is φq,
The cast roll according to claim 1, wherein 0.8φp ≦ φq ≦ φp−2 (t2−t1) is satisfied. The width of the said non-clamping part is 20 mm-1000 mm, respectively, The cast roll of Claim 1 or 2 characterized by the above-mentioned. The cast roll according to any one of claims 1 to 3, wherein a width of the pinching portion of the cast roll is 1500 mm to 4000 mm. The cast roll according to any one of claims 1 to 4, wherein the thin film portion has a thickness of 15 µm to 60 µm. A casting die for extruding a melt containing a cellulose resin into a film,
A cast roll supporting the film-like melt extruded from the casting die on the surface;
In an optical film manufacturing apparatus comprising a touch roll that is biased against the cast roll and sandwiches the melt with the cast roll.
The said cast roll is a cast roll of any one of Claims 1 thru | or 5, The manufacturing apparatus of the optical film characterized by the above-mentioned. A casting step of extruding a melt containing cellulose resin from the casting die onto the surface of the cast roll,
The film-like melt extruded in the casting step includes a pinching step of pinching with the cast roll and the touch roll,
The melt has thick film portions thicker than the thin film portion at both ends of the thin film portion having a uniform film thickness,
In the method for producing an optical film, the cast roll includes a roll main body including a pinching portion for pinching the thin film portion of the melt, and a rotating shaft for rotating the roll main body.
The casting step is a step of extruding the melt so that the width of the thin film portion is larger than the width of the pinching portion of the cast roll,
The said pinching process is a process of pinching only the said thin film part among the said melts, The manufacturing method of the optical film characterized by the above-mentioned. The method for producing an optical film according to claim 7, wherein the cast roll according to claim 1 is used.

Images