JP2007030410A - Manufacturing method of optical film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an optical film by melt extrusion which is capable of eliminating rugged defects produced on the surface of the film and reduces phase-difference unevenness defects produced on drawing of the film. <P>SOLUTION: The manufacturing method of an optical film comprises bringing an amorphous thermoplastic resin film extruded from a T die into contact with a cooling roll and drawing the film to produce an optical film. When the temperature of the cooling roll which the amorphous thermoplastic resin film extruded from the T die is brought first into contact with is represented by T1(°C), the preheating temperature of the film before drawing is represented by T2(°C), the temperature on drawing of the film is represented by T3(°C) and the glass transition temperature of the amorphous thermoplastic resin film is represented by Tg(°C), T2 is at least by 10°C higher than T1, at least by 10°C higher than Tg and higher than T3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing an optical film used in optical applications, display fields, and the like, and more particularly, to a method for producing an optical film having few retardation unevenness defects produced by stretching a film obtained by extrusion molding.

  In recent years, optical films with little retardation unevenness defect have been demanded in the field of optical applications and displays.

  The retardation unevenness defect in this optical film is such that when the optical film is used for optical applications or in the display field, the portion of the dotted retardation unevenness is visually perceived as if light is lost or the hue is different. This is a defect that is visually recognized.

 This phase difference unevenness defect is a cross-linked body in the resin, so-called gel, foaming, foreign matter, foreign matter adhering to the cooling roll at the time of resin melt extrusion or pinholes existing on the cooling roll, etc. This defect occurs due to a concave or convex defect formed by being transferred to the film.

  By the way, a solution casting method has been conventionally used as a method for producing an optical film, but in recent years, a melt extrusion method has been actively studied from the viewpoint of cost and productivity.

  However, when an optical film is produced by this melt extrusion method, as described above, a concave or convex shape formed by transferring foreign matter adhering to the cooling roll or pinholes existing on the cooling roll. This causes a problem that a defect occurs.

  If foreign matter adheres on the cooling roll or pinholes are present in this way, if the film is formed by melt extrusion using foreign matter or pinholes of a size exceeding several tens of microns, the film This also causes unevenness in retardation of a retardation film produced by stretching the defect. For this reason, in order to reduce the retardation unevenness defect of the optical film, it is important to manage such that no foreign matter adheres to the cooling roll or no pinhole or the like exists on the cooling roll.

  However, since foreign matter is likely to adhere to the cooling roll due to foreign matter from the environment, bleed from molten resin, etc., it is extremely difficult to manage the foreign matter so that no foreign matter adheres to the cooling roll. It is also difficult to completely eliminate pinholes and the like on the surface of the cooling roll.

  Under the circumstances as described above, a method for eliminating the protrusions formed on the film by the unmelted resin has been proposed (see, for example, Patent Document 1).

In this method, the protrusion formed on the film by the unmelted resin is eliminated by sandwiching the resin between an elastic touch roll having excellent surface properties cooled by a backup roll and a metal roll.
JP-A-4-82725

  However, in the above conventional example, it is suitable for eliminating convex defects such as gel defects generated in the film, but it is generated by being transferred to the film surface by being pinched by a roll to which foreign matter has adhered. Concave defects and convex defects generated on the film surface due to transfer of pinholes on the roll surface cannot be eliminated.

  Thus, in the conventional example, it was difficult to eliminate all the uneven defects generated on the film surface.

  The present invention was devised in view of such circumstances, and in the case of producing a film by a melt extrusion method, it is possible to eliminate uneven defects generated on the film surface, and the film is obtained by stretching the film. The present invention provides a method for producing an optical film with little retardation unevenness defect.

  In order to achieve the above object, the present invention relates to a method for producing an optical film by drawing an amorphous thermoplastic resin film extruded from a T die, after contacting the cooling roll, and from the T die. The temperature of the cooling roll with which the extruded amorphous thermoplastic resin film first contacts is T1 (° C.), the preheating temperature before stretching of the amorphous thermoplastic resin film is T2 (° C.), and the amorphous thermoplastic resin. When the temperature during stretching of the film is T3 (° C.) and the glass transition temperature of the amorphous thermoplastic resin film is Tg (° C.), T2 is at least 10 ° C. higher than T1 and at least higher than Tg It is characterized by being set to a temperature higher than 10 ° C. and higher than T3.

  According to this invention, by preheating and stretching in the above temperature range, it is possible to eliminate uneven defects generated on the surface of the amorphous thermoplastic resin film, and to relieve the retardation unevenness defect of the optical film. it can. This is because the uneven defects transferred to the surface of the amorphous thermoplastic resin film by the cooling roll in the melt extrusion method are determined by the temperature of the cooling roll and the temperature at the time of deformation is preheated and stretched in the above temperature range. This is based on the fact that residual stress is relieved.

  The temperature range of T2 is preferably set to a temperature 15 ° C. or more higher than T1 and 15 ° C. or more higher than Tg, and more preferably 20 ° C. or more higher than T1 and 20 times higher than Tg. It is a range higher than ℃.

  Even when the stretching temperature T3 is increased, the same effect can be obtained. However, if the temperature is increased too much at the stretched portion, the retardation of the optical film does not appear, and a sufficient retardation cannot be obtained. End up. However, in the present invention, by increasing the temperature in the preheating portion, the temperature in the stretched portion can be freely set in a range lower than the preheating temperature, and therefore a sufficient phase difference can be obtained.

 In addition, as the stretching method, “longitudinal uniaxial stretching” for stretching in the longitudinal direction of the roll, “lateral stretching” for stretching in the width direction of the roll using a tenter clip, etc., “sequential biaxial stretching” is a sequential combination of these stretching methods. "Simultaneous biaxial stretching" in which these stretching methods are performed simultaneously is known, but according to the production method of the present invention, the effects of the present invention can be achieved in any stretching method.

  In the method for producing an optical film having the above-described configuration, if the thickness of the amorphous thermoplastic resin film before stretching is set to 200 μm or less, the necessary thickness is ensured even if the thickness is reduced by stretching. be able to. It is also effective for downsizing the display.

  Here, examples of the amorphous thermoplastic resin include polysulfone, polymethyl methacrylate, polystyrene, polycarbonate, polyvinyl chloride, norbornene resin, and among these, norbornene resins are preferably used. These amorphous thermoplastic resins may be used alone or in combination of two or more.

  In the method for producing an optical film having the above structure, when the amorphous thermoplastic resin is made of a norbornene resin, it has excellent heat resistance and transparency, has a low intrinsic birefringence, and a low photoelastic coefficient. A film suitable as an optical film can be produced. In addition, since the norbornene-based resin has a property of solidifying rapidly due to a decrease in temperature, the above production method is particularly effective.

  Examples of the norbornene-based resin include a ring-opening polymer hydrogenated product of a norbornene-based monomer, an addition-type polymer of a norbornene-based monomer and an olefin, an addition polymer of norbornene-based monomers, and derivatives thereof. . These norbornene-based resins may be used alone or in combination of two or more.

  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 bonds are widely used. This may be a norbornene homopolymer or a copolymer of norbornene and another cyclic olefin monomer.

  Examples of the addition polymer of norbornene monomer and olefin include a copolymer of norbornene monomer and α-olefin. Examples of the α-olefin include α-olefins having 2 to 20 carbon atoms, preferably 2 to 10 carbon atoms, such as ethylene, propylene, 1-butene, 3-methyl-1-butene, 1-pentene, and 3-methyl-1. -Pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene and the like. Among these, ethylene is preferable because of its high copolymerizability, and even when other α-olefins are copolymerized with norbornene monomers, the presence of ethylene is preferable because the copolymerizability is enhanced.

 In the production method described above, the present invention was adjusted to the glass transition temperature Tg + 5 ° C. to Tg−40 ° C. of the amorphous thermoplastic resin when the amorphous thermoplastic resin film was adhered to the cooling roll. The surface roughness specified by JISB0601-1994 is sandwiched between an elastically deformable touch roll having a Ry of 0.5 μm or less and a cooling roll.

  According to the present invention, since the amorphous thermoplastic resin film is sandwiched between the touch roll and the cooling roll, the uneven defects of the amorphous thermoplastic resin film due to the gel generated in the molten state can be eliminated. . Therefore, by combining with the above manufacturing method, it is possible to more effectively eliminate uneven defects generated on the surface of the amorphous thermoplastic resin film.

  The temperature of the touch roll is desirably Tg + 5 ° C. to Tg−40 ° C., and the optimum temperature varies depending on the resin, but basically the higher the roll temperature, the uneven defects generated in the amorphous thermoplastic resin film are eliminated. Cheap.

  When the temperature of at least one of the touch roll and cooling roll falls below Tg-40 ° C, the amorphous thermoplastic resin hardens instantaneously even if it is pinched, eliminating the convex defects on the film surface. Can hardly do. On the other hand, when the temperature of the touch roll and the cooling roll is Tg + 5 ° C. or higher, appearance defects may occur due to uneven peeling of the resin at the roll outlet due to insufficient cooling of the resin.

  In addition, when the surface roughness specified by JIS B0601-1994 of the touch roll and the cooling roll is set to 0.5 μm or less, preferably 0.3 μm or less in terms of Ry, the smoothness of the amorphous thermoplastic resin film Can be maintained, and transparency can be ensured. On the other hand, when the surface roughness of the roll is 0.5 μm or more in Ry, the surface of the amorphous thermoplastic resin film is damaged when sandwiched between the rolls. Convex streaks appear on the film, resulting in defects.

  The method for increasing the surface roughness of the touch roll is not particularly limited, and the touch roll may be polished, or the surface may be plated, or a metal or polished cured resin tube may be attached.

  The Ry used in the present invention is the maximum height defined in JIS B0601-1994, and refers to the difference between the maximum peak height and the maximum valley depth for each reference length.

  In addition, the amorphous thermoplastic resin used in the present invention is a polymer that maintains an amorphous state that hardly takes a crystal structure, and its glass transition temperature Tg varies depending on the resin, so that it is particularly limited. Although not, it is generally 100 ° C or higher.

  In the method of manufacturing an optical film having the above-described configuration, the surface of the elastically deformable touch roll is covered with a metal tube.

  According to this invention, since the surface of the touch roll is covered with the metal tube, the adhesiveness between the amorphous thermoplastic resin film and the roll can be improved by using a flexible material inside, and the surface of the roll Can be smoothed. Therefore, the amorphous thermoplastic resin film can be suitably sandwiched and the film surface can be smoothed to prevent occurrence of irregularities.

  The material of the touch roll is not particularly limited as long as the surface is smooth and flexible. For example, silicone resin, fluorine-based hydrocarbon resin, and the like can be given. Further, a plurality of materials may be multilayered. Furthermore, in the case of a multilayer, it is sufficient that at least one of them is flexible. For example, a metal tube or the like may be attached to the surface.

  The material of the metal tube is not particularly limited, and examples thereof include carbon steel, stainless steel, nickel manufactured by electroforming, and the like. Further, a multilayer structure such as plating on the surface with chromium or the like may be used.

  The thickness of the metal tube is not particularly limited as long as the cooling roll and the amorphous thermoplastic resin film are in close contact with each other when a predetermined pressure is applied. For example, when electroformed nickel is used, it may be about 100 μm to 1 mm.

  If the two rolls used for clamping are both rigid metal rolls, the fine thickness unevenness of the resin cannot be absorbed, and the adhesion between the roll and the amorphous thermoplastic resin film is not sufficient, and thickness accuracy is improved. It is not suitable for the production of an optical film at a required site.

  Usually, when the sheet is stamped and formed, the molten resin is passed between two pairs of rolls in the form of a film so as to be sandwiched between the rolls. Therefore, the rolls must have a robust structure made of a material that can withstand the pressure. Accordingly, a metal shaft such as steel, stainless steel, or aluminum is preferably used as the shaft core portion of the roll.

  In general, since the roll temperature greatly affects the transferability, an axial core part having a structure capable of adjusting the roll to an appropriate temperature is preferable. In this case, the temperature adjusting means preferably used includes an electric heating method in which a sheathed heater is incorporated in the shaft core portion to heat the roll, an induction heating method in which the roll is heated by electromagnetic induction by an induction heat generating coil, and the shaft core portion. And a heat medium circulation heating method in which a heat medium for temperature control is circulated through a flow path provided in the above to indirectly heat the roll. Among these, the heat medium circulation heating method is particularly preferable. The heat medium may be a gas, 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 shape of the touch roll is usually a cylindrical shape, but there is no problem even if the crown shape is slightly thick at the center. The width | variety of a touch roll is not specifically limited, What is necessary is just the required product width or more. Moreover, the outer diameter of a touch roll and a cooling roll is not specifically limited, Either one may be larger than the other and both may be the same magnitude | size. The pressure of the touch roll only needs to be equal to or higher than the pressure at which the cooling roll and the film are completely adhered, and the appropriate pressure is determined by the viscosity of the resin.

 The hardness of the touch roll is not particularly limited as long as the cooling roll and the film are in close contact with each other when a predetermined pressure is applied. For example, in the case of silicone rubber, it may be about 30 ° to 90 ° at Shore A.

  The material of a cooling roll is not specifically limited, For example, carbon steel, stainless steel, etc. are mentioned.

  According to the present invention, in the case of producing a film by the melt extrusion method, it is possible to eliminate uneven defects generated on the film surface, and the production of an optical film having few retardation unevenness defects obtained by stretching the film. It becomes possible to provide a method.

  About the example which manufactures an optical film with the manufacturing method concerning the present invention, Examples 1, 2, and 3 which applied the specific matter of the present invention, and Comparative examples 1 and 2 which excluded from the specific matter of the present invention were manufactured. Therefore, it will be described with reference to Table 1.

まず、実施例１，２、３および比較例１、２の光学フィルムの原材料とする非晶性熱可塑性樹脂には、熱可塑性ノルボルネン系樹脂（日本ゼオン社製、商品名「ＺＥＯＮＯＲ１６００」、Ｔｇ=１６８℃）を用い、１１０℃の温度で３時間予備乾燥した。

First, an amorphous thermoplastic resin used as a raw material for the optical films of Examples 1, 2, 3 and Comparative Examples 1, 2 includes a thermoplastic norbornene resin (manufactured by Nippon Zeon Co., Ltd., trade name “ZEONOR1600”, Tg = 168 ° C.) and pre-dried at a temperature of 110 ° C. for 3 hours.

  As the extruder, a single screw extruder having a diameter of 100 mm, a lip clearance of 800 μm, and L / D = 32 was used, and the extrusion temperature was adjusted at 270 ° C. to 320 ° C.

  As a polymer filter, a leaf disk filter having a filtration accuracy of 10 μm manufactured by Nippon Seisen Co., Ltd. was used.

 The T die was a coat hanger type with a width of 1800 mm, and the surface of the resin flow path was H-Cr plated.

 The cooling roll is provided with a temperature control mechanism (oil is used as a heat medium) having an outer diameter of 350 mm, a width of 2000 mm, and a surface roughness of Ry of 0.3 μm.

 The touch roll has an outer diameter of 350 mm, a width of 1600 mm, a silicone rubber layer thickness of 5 mm, and a rubber hardness of 90 °, which is covered with a metal tube made of nickel and having a thickness of 200 μm. 0.4 μm.

In the following Examples and Comparative Examples, using a production apparatus having such specifications, a film having a width of 1600 mm was produced and evaluated at 1 m ² having a width of 1 m excluding the end and 1 m in the MD direction (film flow direction).

 Here, the defect of the film (amorphous thermoplastic resin film) before stretching was determined by using a KEYENCE laser microscope to illuminate light from 10 ° obliquely using a KEYENCE microscope. The average value of the length in the TD direction (width direction) and the length in the MD direction of the formed portion was taken as the size of the transferable irregularity defect, and evaluation was performed by counting those having a size of 50 μm or more. Of the concave defects and convex defects, the defects that appear to have occurred in the chill roll portion are transferable uneven defects before stretching, and the convex defects that appear to have occurred before contacting the cooling roll are gel defects before stretching. .

Furthermore, each pre-stretched film is stretched by the stretching methods of Examples 1 to 3 and Comparative Examples 1 and 2, the preheating temperature (T2), and the stretching temperature (T3), and the stretched film (optical film) is terminated. Evaluation was made at 1 m ² of 1 m in width and 1 m in the MD direction excluding the part.

  Then, the film defects after stretching are discriminated with a KEYENCE laser microscope, and the length of the portion in the TD direction, MD, which is a bright spot by applying light from an oblique angle of 10 ° using a KEYENCE microscope. The average value of the lengths in the direction was defined as the size of the transferable irregularity defect, and evaluation was performed by counting those having a size of 50 μm or more. After extending the concave defect and convex defect, the defect that seems to have occurred in the cooling roll part at the time of melt extrusion, after stretching the transferable uneven defect, and the convex defect that seems to have occurred before contacting the cooling roll A gel defect is assumed.

  The production conditions and evaluations of Examples 1 to 3 and Comparative Examples 1 and 2 are shown in Table 1, but will be briefly described below.

Example 1
The touch roll was not used, and the optical film was manufactured using the cooling roll which was 150 degreeC (T1). The thickness of the film before stretching was 70 μm, and the unevenness defects before stretching were evaluated as follows.

Pre-stretching gel defects: 7 Pre-stretching transfer irregularity defects: 3 Further, when the preheating temperature (T2) is 190 ° C. and the stretching temperature (T3) is 172 ° C. Met.

Post-stretching gel defects: 6 Post-stretching transferable irregularities: 0

(Example 2)
The optical film was manufactured using the cooling roll which was 150 degreeC (T1), and the touch roll which was 150 degreeC (T1). The thickness of the film before stretching was 70 μm, and the unevenness defects before stretching were evaluated as follows.

Gel defects before stretching: 1 Transferable uneven defects before stretching: 15 Further, when the preheating temperature (T2) is set to 195 ° C. and the stretching temperature (T3) is set to 172 ° C., the uneven defects after stretching are evaluated. Met.

Gel defects after stretching: 2 pieces Transferable unevenness defects after stretching: 0 pieces

(Example 3)
The optical film was manufactured using the cooling roll set to 165 degreeC (T1), and the touch roll set to 165 degreeC (T1). The thickness of the film before stretching was 70 μm, and the unevenness defects before stretching were evaluated as follows.

Pre-stretching gel defects: 0 Pre-stretching transferable irregularities: 22 In addition, when the preheating temperature (T2) is set to 195 ° C. and the stretching temperature (T3) is set to 172 ° C., the irregularities after stretching are evaluated. Met.

Gel defect after stretching: 0 pieces Transferable unevenness defect after stretching: 0 pieces

(Comparative Example 1)
The touch roll was not used, and the optical film was manufactured using the cooling roll which was 150 degreeC (T1). The thickness of the film before stretching was 70 μm, and the unevenness defects before stretching were evaluated as follows.

Pre-stretching gel defects: 6 Pre-stretching transferable unevenness defects: 5 Further, when the preheating temperature (T2) is set to 172 ° C. and the stretching temperature (T3) is set to 172 ° C., and the unevenness defects after stretching are evaluated, it is as follows. Met.

Gel defects after stretching: 8 Transferable irregularities after stretching: 4

(Comparative Example 2)
The optical film was manufactured using the cooling roll which was 150 degreeC (T1), and the touch roll which was 150 degreeC (T1). The thickness of the film before stretching was 70 μm, and the unevenness defects before stretching were evaluated as follows.

Pre-stretching gel defects: 2 Pre-stretching transferable irregularities: 18 In addition, when the preheating temperature (T2) is 172 ° C. and the stretching temperature (T3) is 172 ° C., the irregularities after stretching are evaluated. Met.

Gel defect after stretching: 1 transferable unevenness defect after stretching: 16 Based on such evaluation, Examples 1 to 3 satisfy the product standards, but Comparative Examples 1 and 2 do not satisfy the product standards. Think.

  As mentioned above, although the Example as an example of manufacturing conditions was described about embodiment of this invention, it is not restricted to the Example mentioned above.

  The present invention is a method for producing an optical film having few retardation unevenness defects obtained by stretching this film, which can eliminate irregularities generated on the film surface in the case of producing a film by melt-melt extrusion. Applicable to.

Claims (5)

In the method for producing an optical film by stretching after contacting an amorphous thermoplastic resin film extruded from a T die with a cooling roll,
The temperature of the cooling roll first brought into contact with the amorphous thermoplastic resin film extruded from the T die is T1 (° C.), the preheating temperature before stretching of the amorphous thermoplastic resin film is T2 (° C.), amorphous When the temperature during stretching of the thermoplastic resin film is T3 (° C.) and the glass transition temperature of the amorphous thermoplastic resin film is Tg (° C.), T2 is at least 10 ° C. higher than T1, and A method for producing an optical film, wherein the temperature is set at least 10 ° C. higher than Tg and higher than T3.   The method for producing an optical film according to claim 1, wherein the amorphous thermoplastic resin film has a thickness of 200 μm or less.   The method for producing an optical film according to claim 1, wherein the amorphous thermoplastic resin is a norbornene resin.   When the amorphous thermoplastic resin film is brought into close contact with the cooling roll, the surface roughness regulated by JIS B0601-1994, which is adjusted to the glass transition temperature Tg + 5 ° C. to Tg-40 ° C. of the amorphous thermoplastic resin. The method for producing an optical film according to any one of claims 1 to 3, wherein the elastic film is sandwiched between an elastically deformable touch roll having a thickness of Ry of 0.5 µm or less and a cooling roll.   5. The method for producing an optical film according to claim 1, wherein a surface of the elastically deformable touch roll is covered with a metal tube.