JP3920842B2 - Method for producing optical film - Google Patents

Description

  The present invention relates to a method for producing an optical film, and more particularly to a method for producing an optical film having little thickness unevenness, excellent smoothness, and uniform optical characteristics over the entire surface.

  In recent years, optical films or sheets (hereinafter collectively referred to as films) are frequently used in liquid crystal display devices. The liquid crystal display device has an optical phase difference from a polarizing film for generating polarized light, a touch panel with a transparent electrode on the surface, a plastic substrate instead of a glass substrate with a transparent electrode, and retardation generated from liquid crystal molecules. A phase difference plate or the like for compensation is provided.

  In the polarizing film, in an example such as a stretched polyvinyl alcohol iodine adsorption film, a moisture-resistant protective film is bonded to protect it from moisture. As such a protective film, a cast film of triacetyl cellulose is usually used. The touch panel is used by providing a transparent conductive layer on a film substrate, and usually a biaxially stretched polyethylene terephthalate film is used. These films are required to be improved in transparency, moisture resistance and birefringence. Furthermore, a plastic substrate is desired instead of a glass substrate provided with a transparent electrode. For these, various polymer films have been proposed together with the retardation plate described below.

  A stretched optical film is used for the retardation plate. Such optical films have been exemplified by polymer films such as polycarbonate, polysulfone, polyarylate and polyphenylene sulfide. And a phase difference plate is obtained by extending | stretching and orienting these polymer films to a uniaxial or biaxial.

  In recent years, there has been a demand for rationalization and quality improvement of various optical films for liquid crystal display devices. In order to obtain an accurate liquid crystal display, these optical films have firstly low residual stress over the entire surface, low retardation and little variation, and secondly, the retardation is proportional to the thickness. Therefore, it is necessary that there is no uneven thickness or die line, and that the thickness is equal to the desired thickness. Third, of course, film scratches, foreign matter contamination, wrinkles, etc. must be avoided. And, since a film made of cyclic polyolefin hardly causes birefringence at the time of molecular orientation, it has attracted attention as an optical film.

Conventionally, the following methods have been proposed as a method for producing an optical film.
(1) The resin is dissolved in a solvent to form a solution, and the solution is cast on an endless metal belt or base film, and then the solvent is removed by drying to form a resin layer. A method of peeling and separating from a metal belt or a base film (see Patent Document 1).
(2) A method in which a resin is melt-extruded from a die into a film using an extruder and cooled by a cooling roll (see Patent Documents 2 to 4).

  However, in the method (1), it is difficult to completely dry and remove the solvent. If the residual solvent becomes uneven, stress becomes uneven during stretching and a uniform phase difference cannot be realized. In particular, in order to obtain uniform quality, it is necessary to start drying at a relatively low temperature and gradually increase the temperature. When the processing speed is increased, excessive drying equipment is required and a large amount of energy is required. As a result, the manufacturing equipment becomes high and the running cost becomes high. In addition, the working environment may be deteriorated by the solvent, and the maintenance is expensive.

  In the method (2), a plurality of cooling rolls are often used, and the adhesive strength with the metal roll is weak. Therefore, when the resin is cooled to about 50 ° C. or less between the rolls, the adhesive strength with the roll is reduced. Further, it peels off due to the volume change, and contraction stress is generated and tensile stress remains. In order to avoid this, precise control is required to control the temperature, the rotational speed of the roll and the bank amount, but it is difficult to make the residual stress constant. Furthermore, the residual stress at both ends of the film formation due to neck-in from the die is particularly large, requiring a large trimming. In addition, thickness unevenness, die lines, and gear marks are likely to occur in the obtained film, and it is difficult to obtain a raw material for optical use.

  In order to improve the drawbacks of this melt extrusion method, a method has been proposed in which the molten resin discharged from the die of the extruder is clamped by a pair of rolls (see Patent Document 5). However, with this method, it is difficult to provide a film that can solve the die line, gear mark, and thickness unevenness that can be used for optical applications. In addition, the pressure between the pair of rolls has only a control gap between the crowns of the rolls. If the processing speed is increased, the operating conditions are restricted, which is insufficient to eliminate the above-described various irregularities. In order to improve this, a method has been proposed in which endless metal belts are installed one above the other and the molten resin is sandwiched therebetween (see Patent Document 6). However, even in this method, the pinching point is only the pinching force between the rolls that pinch the metal belt, and the adhesion between the metal belt and the resin is insufficient, or the temperature gradient cannot be removed, making it difficult to obtain a uniform film. .

  Many proposals have been made to improve the pinching pressure caused by endless metal belts. For example, in the case of polypropylene, there is a method in which one cast roll and one endless metal belt are combined and the metal belt is clamped along an arc of the cast roll (see Patent Documents 7 and 8). Further, based on this method, a method for setting the cooling temperature around the glass transition temperature of the extruded resin (see Patent Document 9) or a method for setting the cooling temperature higher than the glass transition temperature (see Patent Document 10), from a metal roll A method of adjusting the take-off speed after peeling (see Patent Document 11) and a method of providing a peeling roll in the immediate vicinity of the cast roll (see Patent Document 12) have been proposed. Furthermore, a method has been proposed in which the gap between the endless metal belt and the holding roll on the peeling side is adjusted to eliminate the peeling trace (see Patent Document 13). And the cost of equipment and operation becomes high.

  On the other hand, there is an attempt to increase the pinching effect of the molten resin by sandwiching the metal and the rubber substance between the metal and the metal. As an example, there is a proposal that combines a pressing means such as a spring or a hydraulic piston in order to keep a constant gap between rolls, although it is not necessarily a metal and a rubber substance (see Patent Document 14). Dissatisfaction remains with the characteristics.

Furthermore, in order to improve the surface property of the extruded polyolefin on the substrate, a method of laminating and transferring a film having a specular gloss and metal-depositing this surface (see Patent Document 15) is known. This is an improvement in the gloss of the laminated paper used as a material, and does not suggest the production of an optical film.
JP-A-4-301415 Japanese Patent Laid-Open No. 4-118213 JP-A-4-166319 JP-A-4-275129 JP 62-48523 A JP-A-3-75110 JP-A-6-170919 JP-A-6-166089 Japanese Patent Laid-Open No. 9-239812 JP 2000-280268 A JP-A-9-290427 JP-A-10-16034 Japanese Patent Laid-Open No. 10-10321 JP 2000-280315 A JP 59-5056 A

  The present invention solves the above-mentioned problems of the prior art, and is useful as a raw material for various optical films used in liquid crystal display devices, for example, optical films for retardation plates. The objective of the present invention is to produce an optical film having a uniform thickness and almost no residual retardation at a low cost with high productivity.

  In view of such circumstances, the present inventors have intensively studied to solve the above problems, and as a result, a thermoplastic resin melt-extruded in a film form from an extrusion die and a support roll and a cooling roll made of metal or ceramic and a rubber roll. When the optical film was produced by peeling and separating the support layer after the pinching, the optimum pinching method for the cooling roll and the rubber roll was found and the present invention was reached.

That is, the invention according to claim 1 of the present invention, a thermoplastic resin is melt-extruded, upon producing a nip pressure to the film with the support layer in the gap between the metal or ceramic chill roll and a rubber roll, as a support layer Using a synthetic resin film, the gap between the cooling roll and the rubber roll is set to any value between 10% and 90% of the sum of the thickness of the support layer and the thickness of the film, and the distance below this value should not be approached. Is provided with a stopper on either the cooling roll or the rubber roll, and a pressing force of 2.7 to 10.0 kgf / cm is applied to the roll on the side where the stopper is provided, and the support layer is peeled off after being picked up. Thus, a method for producing an optical film characterized in that a thermoplastic resin film is obtained.

The invention according to claim 2 of the present invention, rubber roll, and the contents a method for manufacturing an optical film according to claim 1 Symbol mounting surface hardness 60 or more rubber metal core is roll wound in thickness 5~15mm To do.

The invention according to claim 3 of the present invention includes the method for producing an optical film according to claim 1 or 2 , wherein the thermoplastic resin is a cyclic polyolefin.

The invention according to claim 4 of the present invention includes the method for producing an optical film according to any one of claims 1 to 3 , wherein the support layer is a film made of biaxially stretched polyethylene terephthalate.

  According to the production method of the present invention, there is provided an optical film having little thickness unevenness, excellent smoothness, and uniform optical characteristics over the entire surface.

  When trying to manufacture an optical film by melt extrusion, even if various ideas and improvements are made, the die line generated from the extrusion die and the resin flow due to the shearing of the melt extrusion resin, the resin shrinkage by cooling and the film due to take-off Such stress causes a residual phase difference. In order to improve this, usually, a metal roll and a metal roll or a smooth metal belt are clamped to copy the smooth surface, and the resin flow in the extrusion direction and the thickness unevenness of the resin in the extrusion direction such as a die line. Attempts have been made to eliminate this by causing the resin to flow in the other direction due to pressure.

  The present inventors previously used a support layer made of a synthetic resin film or the like using a hard roll, i.e., a cooling roll made of metal or ceramics, and a roll made of a soft material, i.e., a rubber roll. By sandwiching the melt-extruded resin layer through the metal, the adhesion and adhesion between the support layer and the extruded resin is strengthened compared to the case of metal-to-metal sandwich pressure, causing pressure distribution by the rubber roll, and melting from the die. Even if the thickness of the resin is uneven, the flow of the resin is easily generated in the other direction and the surface is smoothed, and the smooth surface is well copied. The residual stress due to die line disappearance and flow in the die is greatly increased. It has been found that it has decreased, and a patent application has already been filed (Japanese Patent Application No. 2003-106433).

The reason why the above effects can be obtained is that the synthetic resin film of the support layer has heat insulation properties, becomes flexible as the temperature rises and easily blends with the molten resin, and the bank resin bites more smoothly than the metal. Conceivable. Furthermore, when a synthetic resin film is used, the temperature gradient is reduced in the thickness direction of the molten resin, and distortion of the front and back of the product film is unlikely to occur.
In addition, since the melt-extruded resin layer is transported to the appropriate temperature together with the support layer, it is possible to avoid the shrinkage due to cooling and the stress of the take-off to the target optical film, thereby causing uneven thickness of the die line and the like. This is because the residual phase difference generated by the manufacturing process can be eliminated at the same time.
As a result of continuing researches, the inventors of the present invention have found that, in order to further enhance the effect of the pinching force in the above-described technique, the gap between the cooling roll and the rubber roll is appropriately maintained as described later, and the appropriate pressing force is maintained. By backing up by means of rubber elasticity and back-up pressing force with a certain gap, it is possible to level out variations such as accuracy error of machine equipment including rubber roll and thickness unevenness of molten film with synthetic resin film of support layer As a result, it has been found that an optical film that is further improved in terms of thickness unevenness, smoothness and uniform optical properties can be obtained.

  As the thermoplastic resin used in the present invention, a resin suitable for the production of an optical film is selected. For this purpose, it must be a transparent resin and, for example, provided with sufficient heat resistance and humidity resistance so as to increase reliability in use of an incorporated liquid crystal display device. Is required. As such a thermoplastic resin, polycarbonate, polysulfone, polyarylate, aromatic polyester, cyclic polyolefin and the like are suitable. In particular, cyclic polyolefins have low hygroscopicity and high heat resistance compared to other thermoplastic resins, and have excellent optical properties. Especially, when molecules are oriented, birefringence due to molecular orientation is less likely to occur. Suitable for production of film stock.

  A cyclic polyolefin has an alicyclic structure in the main chain and / or side chain. Examples of the alicyclic structure include cycloalkane and cycloalkene structures, but the cycloalkane structure is suitable for optical use. The unit of these alicyclic structures preferably has 5 to 15 carbon atoms. And the polymer in which the unit which has these alicyclic structures is contained 50weight% or more is preferable. Examples of such polymers include norbornene polymers, monocyclic olefin polymers, cyclic conjugated diene polymers, hydrocarbon polymers having a side chain alicyclic structure, and hydrogenated products thereof. It is done. Among these, norbornene polymers and hydrogenated products thereof, cyclic conjugated diene polymers and hydrogenated products thereof are preferable. As these representative resins, Arton (trade name, manufactured by JSR Corporation), Zeonex (trade name, manufactured by ZEON Corporation), Zeonoa (trade name, manufactured by ZEON Corporation), Apel (trade name, manufactured by Mitsui Chemicals, Inc.) Etc.

  A schematic diagram for explaining the melt extrusion molding method of the present invention is shown in FIG. In the figure, the film-like molten resin 8 extruded from the extrusion die 1 is shown. The extruder may be a single screw, a twin screw or a melt kneader. The shape of each screw is appropriately selected and is not particularly limited. Usually, the diameter of the screw is 40 to 150 mm, the L / D is 20 to 38, preferably 25 to 34, and the compression ratio is 2.5 to 4.

  There are no restrictions on the method of charging the resin into the extruder, but it should be dried and transported so that the generation of resin powder in the hopper is minimized, and charged to the extruder at a resin temperature of ± 2 ° C close to the drying temperature. In the case of a resin type having a high Tg, if the temperature is increased to 60 to 80% of the Tg, the residence time in the screw is shortened and a good quality film is easily obtained. Further, it is a preferred embodiment to reduce the oxygen concentration by purging the inside of the hopper and the melting zone of the cylinder with nitrogen.

  The molten resin preferably passes through a mesh or porous filter material to remove foreign matters, and then ensures a certain discharge amount per time through a gear pump. Then, it is extruded as a film-like molten resin 8 from the extrusion die 1. The extrusion die 1 may have a normal shape used for forming a sheet or a film. For example, a coat hanger type, a straight manifold type, or a fishtail type die can be used. The gap of the opening portion of the extrusion die 1 is selected according to the thickness of the target sheet or film, but is usually about 0.1 to 3 mm.

  In FIG. 1, a film-like molten resin 8 extruded from an extrusion die 1 is sandwiched between a support layer 9 sandwiched between a cooling roll 2 and a rubber roll 3 made of metal or ceramic. The rubber roll 3 is pressed against the cooling roll 2 side by the metal backup roll 4 in order to apply a uniform pressure to the entire width of the molten resin 8, and a gap with the cooling roll is set.

  As shown in FIG. 3, the method for setting the gap between the cooling roll 2 and the rubber roll 3 uses two stoppers 13 called cotters having the same gradient. That is, one stopper 13b is provided on the rotating shaft of the cooling roll 2 or the rubber roll 3 (rubber roll 3 in the figure), and the other stopper 13a is provided on the rail 14, and slides on the rail 14 to a desired position. It is fixed to. The stoppers 13a and 13b are configured such that the gap W between the cooling roll 2 and the rubber roll 3 can be finely adjusted by sliding the inclined surfaces facing each other in the vertical direction. Further, the stoppers 13a and 13b can prevent the gap W between the cooling roll 2 and the rubber roll 3 from approaching a certain level. And it is pressed down with the pressing force set through the backup roll 4 so that the set gap W is maintained. The set pressing force is transmitted to the backup roll 4 by an air cylinder through air pressure.

  The temperature of the cooling roll 2 is precisely controlled, and usually a range from + 30 ° C. to −70 ° C. is appropriate starting from the glass transition temperature of the molten resin 8. The molten resin 8 is conveyed to the second cooling roll 5 while being pseudo-adhered to the support layer 9 while being sandwiched between the cooling roll 2 and the support layer 9 and pressed against the cooling roll 5 under a certain tension. And cooled to form a molded film.

  The molded film 11 and the support layer 9 are taken up by the take-up force adjusted by the third cooling roll 6 from the second cooling roll 5 in a pseudo adhesion state. The film product 12 is fed through a roll 7 to a take-up reel (not shown) and taken up. Each roll is operated so that the support layer 9 and the molten resin 8 or the molded film 11 are transported together in conjunction or independently.

  FIG. 2 is a schematic diagram in the case where support layers 9 and 10 are arranged on both sides of the film-like molten resin 8, that is, both the side in contact with the rubber roll 3 and the side in contact with the cooling roll 2. The operation is performed in substantially the same manner as in the case of the support layer on one side in FIG. The formed film 11 is wound up as a film product 12 after the support layers 9 and 10 are separated and separated by the cooling roll 6 and the roll 7.

As the support layer is clamped, films such poor conductor der Ru synthetic resin heat is used than metal. Since the smoothness of the surface of the support layer may be transferred to the surface of the target film product, a support layer having a surface with as few asperities as possible is preferred, and the center line average roughness defined in JIS B0601 is preferred. A support layer having a surface roughness characteristic of 0.01 μm or less is preferable. Furthermore, in the case of synthetic resin films as the support layer, the film must be resistant to the molten resin extruded into a film. Therefore, mention is made of films such as polycarbonate, polysulfone, polyethersulfone, polyphenyl sulfide, polyimide, biaxially stretched films such as biaxially stretched polyethylene terephthalate and biaxially stretched polyethylene naphthalate, etc., which have relatively high heat resistance. Can do. In particular, from the viewpoint of good smoothness, films made of the above-mentioned resin obtained by casting with a solvent, casting films of triacetyl cellulose, and biaxially stretched polyester films are preferable. Then, the molten resin extruded into a film and the support layer are sandwiched and conveyed together. The extruded (melted) resin and the support layer may be the same or different as long as they can be pseudo-bonded or separated after cooling.

  The rubber roll used for pinching has a structure in which various rubber-like substances are concentrically wound around the outer periphery of the metal core, and the thickness of the rubber-like substance is appropriately selected, but 5 to 15 mm is appropriate. The hardness of the rubber substance has an influence on the effect of pinching pressure, and if the Shore hardness is not more than 60, the effect is small. If the Shore hardness is less than 60, the effect of flattening the uneven thickness of the molten resin from the die is small, and the residual phase difference is also large. Further, there are few rubber rolls having a Shore hardness of 100 or more. The rubber-like substance can be selected from SBR, NBR, chloroprene, chlorinated polyethylene, chlorosulfonated polyethylene, polyester elastomer, urethane dam, silicone rubber, and the like, and combinations thereof. Silicon rubber is preferred.

  Optical unevenness of optical films includes die lines along the direction of film production, vertical stripes such as thick and thin unevenness, horizontal stripes due to gear marks orthogonal thereto, and adhesion due to insufficient adhesion between film cooling rolls and support layers. There are three types of unevenness.

  If the pressing force of the rubber roll or the cooling roll to the clamping partner is excessive, vertical stripes are easily eliminated, but horizontal stripes are likely to occur. When the pressing force is too low, horizontal stripes do not occur, but vertical stripes cannot be eliminated, causing uneven adhesion due to air entrainment. Accordingly, the pressing force is suitably in the range of 2.7 to 10.0 kgf / cm, preferably in the range of 3.0 to 7.0 kgf / cm, expressed as linear pressure. This appropriate range of linear pressure has characteristics that are extremely lower than the linear pressure used for laminated products of synthetic resins produced by ordinary clamping and lamination of resin to paper.

The set value of the gap must be set within 10 to 90% of the sum of the thickness of the support layer sandwiched at the same time and the thickness of the obtained thermoplastic film. If this gap ratio is less than 10%, a melted resin bank is formed in the gap between the cooling roll and the rubber roll, and a gear mark is formed. On the other hand, if it exceeds 90%, not only vertical stripes cannot be eliminated, but also birefringence increases. Preferably it is 40 to 60%.
The thickness of the support layer is not limited, but if it is too thin, it is less effective, and if it is too thick, it tends to hinder driving. Therefore, 50 μm to 200 μm are usually suitable.
The support layer can be supplied by preheating before being sandwiched with the molten resin. The temperature is equal to or higher than the cooling temperature of the operation and the support layer does not cause thermal shrinkage.

  As described above, the support layer and the molten resin layer are transported together until they are cooled and separated. If the two are different, it may be difficult to transport due to insufficient adhesion. In such a case, in order to increase the adhesive strength on the support layer side, the surface on the lamination side is treated with corona discharge treatment, ozone treatment. It is preferable to perform surface treatment such as flame treatment, glow discharge, plasma discharge treatment, etc. to increase the adhesion.

As an extruded film used as a raw material for various optical films, a film having a uniform film thickness without a die line is required. The difference between the maximum and minimum film thickness is preferably 5% or less, more preferably 2% or less of the average film thickness. The surface roughness of the film is preferably 0.01 μm or less in terms of the center line average roughness Ra based on JISB0601. The elimination of the die line is achieved by reducing the amount of foreign matter through the molten resin through an appropriate filter material, and by setting the extrusion conditions with less generation of burnt resin, reducing the die line from the die and smoothing the inner surface of the die that is extruded into a film. Needless to say, this is achieved by precisely adjusting the die gap and optimizing the operating conditions for clamping with the support layer as described above.
As an extruded film used as a raw material for various optical films, it is important that there is no optical unevenness. As described above, the optical unevenness is roughly classified into three types of vertical stripes, horizontal stripes, and uneven contact. Even if these optical non-uniformities are not observed with normal transmitted light, it can be confirmed very well when light is incident in an oblique direction and the transmitted light is projected on a vertical surface and observed. Although it is easier to observe as the oblique direction is increased, it is not practically hindered unless it is normally visible at an incident angle of 45 degrees.

  Furthermore, an extruded film used as a raw material for various optical films needs to be a low birefringence film with little variation. This variation is preferably 5 nm or less when the retardation is expressed in nm, and in order to realize this, it is advantageous that the retardation of the film is small. Therefore, when the film thickness is 100 μm, it is 20 nm or less, preferably 10 nm or less. good. For this purpose, it is necessary to select an appropriate resin, further select an appropriate support layer, adjust conditions for clamping, and set other operating conditions appropriately. Such a film having a small variation can be sufficiently achieved by using a cyclic polyolefin having a small photoelastic coefficient that hardly causes birefringence at the time of molecular orientation and nipping with a support layer.

  The optical film obtained as described above can be used as a moisture-resistant protective film for an iodine adsorption-stretched polyvinyl alcohol polarizing film by being bonded with various pressure-sensitive adhesives or adhesives. Furthermore, in a touch panel with a transparent conductive layer provided on the surface or a plastic substrate instead of a glass substrate for liquid crystal display, a metal oxide film such as an ITO (indium-tin oxide) film or an AZO (aluminum doped zinc oxide) film is sputtered. It can be formed by metal deposition.

Further, the retardation film is preheated with the above optical film as a raw fabric, and then stretched in the same direction as the film winding direction between two rolls having different peripheral speeds at a constant temperature. Thus, a longitudinally stretched retardation film is obtained. On the other hand, a retardation film in the lateral direction can be obtained by grasping both sides of the optical film with a clamp or a pin and stretching it in a direction perpendicular to the traveling direction while traveling. Similarly, when the film is stretched in both the traveling direction and the direction orthogonal to the traveling direction while traveling the clamp or pin, a simultaneous biaxially stretched film is obtained, and a retardation film in the thickness direction is obtained. Moreover, after extending | stretching to the vertical or horizontal direction, it can also extend | stretch in two steps from which direction. The draw ratio is usually 1.5 to 4 times. Instead of stretching, a stretching effect can be obtained by rolling between rolls that does not shrink in the film width direction.
The obtained stretched optical film is useful as various optical films.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited only to these Examples.

Example 1
(Method of resin melt extrusion)
Cyclic polyolefin resin (Arton D4531, Tg132 ° C, manufactured by JSR Corporation) is passed through a porous filter with an L / D32 single screw with an inner diameter of 65 mm, following the schematic diagram in Fig. 1, and then discharged with a gear pump. The film was extruded from the extrusion die 1 having a width of 884 mm. As the extrusion die 1, a chalkless coat hanger die was used. The film was discharged from the extrusion die 1 to a film thickness of 100 μm, and the temperature of the molten resin 11 was 267 ° C.

(Support layer and pinching method)
The support layer 9 has a film thickness of 125 μm, and the surface roughness characteristics defined in JIS B0601 are 0.005 μm for the center line average roughness, 0.07 μm for the maximum roughness, and 0.07 μm for the 10-point average roughness. A biaxially stretched polyethylene terephthalate film (O3LF8, manufactured by Teijin DuPont Films Ltd.) is placed on the rubber roll 3 side, and a metal cooling roll 2 maintained at 90 ° C. and an NBR wound around a metal core with a thickness of 6.5 mm Between the rubber roll 3 having a length of 850 mm. Since the position of the stopper was set so that the gap between the cooling roll and the rubber roll was 110 μm, the ratio of the gap between the cooling roll and the rubber roll with respect to the total thickness of the support and the product film was 48.9% [110 μm / (125 μm + 100 μm) × 100]. Also, the pressure on the rubber roll 3 through the backup roll 4 was 5 kgf / cm ² , and the air pressure of 5 kgf / cm ² was used to press both ends of the roll against the cooling roll by two air cylinders with a radius of 3.15 cm. 67kgf / cm.

(Cooling winding method)
Both the support layer 9 and the molten resin layer 8 are transported to the second cooling roll 5 maintained at 47 ° C., and then transported to the third cooling roll 6 maintained at 35 ° C., where the support layer No. 9 polyethylene terephthalate film was peeled and separated, and the molded film 11 was wound up as a film product 12 through the next roll 7. The operation line speed was 6 m / min.

(Method for observing and measuring film properties)
The surface roughness characteristics of the obtained molded film showed characteristics almost similar to those of the support layer, and other characteristics were observed and measured by the following methods, and the results are shown in Table 1.

Film thickness:
The film thickness at 35 locations was measured with a film thickness meter at intervals of 20 mm in the sample film width direction to obtain an average value, and the maximum and minimum tolerances were obtained.

Retardation:
Automatic birefringence meter KOBRA-21ADH puts both Nicol polarizer and Nicol analyzer in parallel, irradiates a sample film (sample size 35mm x 35mm) with a single wavelength light beam, and transmits light when rotated around the beam axis A phase difference is calculated from the angle dependency of intensity (measurement wavelength: 590 nm).
Five sample films were taken in the width direction, and the average value of the five locations and the highest and lowest tolerances were determined.

Optical unevenness:
As shown in FIG. 4, in the case of vertical stripe observation, the light direction from the point light source of a 150 W xenon lamp as the light source 15 is set so that the flow direction of the film product 12 is set and light is incident from the 45 degree direction of the product to transmit the transmitted light behind. It is projected on the screen 16 and observed. In the case of horizontal stripe observation, the film product is observed sideways, and uneven adhesion is observed from both sides. Evaluation of the observation results is based on the following criteria.
Striped pattern, uneven state clearly exists 0 points Striped pattern, uneven state exists 1 point Striped pattern, uneven state exists slightly 2 points Striped pattern, uneven state cannot be confirmed 3 points

Example 2
A film was prepared in the same manner as in Example 1 except that the gap ratio between the cooling roll and the rubber roll was set to 13.3%. The characteristic values and the like are shown in Table 1.

Example 3
A film was prepared in the same manner as in Example 1 except that the gap ratio between the cooling roll and the rubber roll was set to 88.9%.

Comparative Examples 1 and 2
The method was the same as in Example 1 (Comparative Example 1) except that the gap ratio between the cooling roll and the rubber roll was 0% (the state where the cooling roll and the rubber roll were in contact), and the gap ratio was 100% (support layer) Each film was prepared in the same manner as in Example 1 (Comparative Example 2) except that the total thickness of 125 μm and the product film thickness of 100 μm was 225 μm). Table 1 shows the characteristic values and the like of the obtained films. It was.

  As can be seen from Table 1, when the gap between the cooling roll and the rubber roll is clogged too much, the horizontal stripe gear mark becomes conspicuous. On the contrary, when the gap is too wide, the vertical stripe appears. That is, it can be seen that the gap between the cooling roll and the rubber roll has an appropriate range for minimizing optical unevenness. Within an appropriate range of this gap, there is little variation in film thickness and retardation.

Example 4
Except that the 5.87kgf / cm ² the linear pressure of the rubber roller increases the air pressure to 8 kgf / cm ² is a film in the same manner as in Example 1, the characteristic value or the like of the resulting film are shown in Table 2 .

Example 5
A film was prepared in the same manner as in Example 1 except that the air pressure was increased to 12 kgf / cm ² and the linear pressure of the rubber roll was set to 8.8 kgf / cm ^2. The characteristic values and the like of the obtained film are shown in Table 2. .

Comparative Examples 3 and 4
Except for air pressure of 3 kgf / cm ² and rubber roll linear pressure of 2.2 kgf / cm (Comparative Example 3), and air pressure of 20 kgf / cm ² and rubber roll linear pressure of 14.67 kgf / cm (Comparative Example 4), Films were prepared in the same manner as in Example 1, and the characteristic values and the like of the obtained films are shown in Table 2.

  From Table 2 and Table 1, it can be seen that if the linear pressure applied to the rubber roll is excessive, horizontal stripes mainly consisting of gear marks are conspicuous, and if it is too low, the vertical stripes cannot be eliminated and optical unevenness caused by poor adhesion occurs. On the other hand, it can be seen that a film free from variations in film thickness and retardation and optical unevenness can be obtained under an appropriate pressing force.

As described above, when the resin melt-extruded into a film is pressed between the hard and soft rolls, that is, between the metal or ceramic roll and the rubber roll, together with the support layer made of a synthetic resin film which is a poor heat conductor , The gap between the rolls is set to 10 to 90% of the sum of the thickness of the support layer and the film, and a stopper is provided on one of the rolls so as not to approach this distance, and this stopper is provided. By applying a pressing force of 2.7 to 10.0 kgf / cm to the roll on the other side, die lines, gear marks, etc. are eliminated, retardation is small, variation is small, and there is no optical unevenness. A suitable film can be produced.

It is a schematic diagram in the case of producing the optical film of the present invention by arranging a single-sided support layer and sandwiching it. It is a schematic diagram in the case of producing the optical film of the present invention by disposing a double-sided support layer and sandwiching it. It is a schematic diagram which shows the structure of the stopper (cotter) for setting the clearance gap between the cooling roll and rubber roll of this invention. (A) is a top view, (b) is a side view, and (c) is a schematic diagram showing a state when a gap is set. It is a schematic diagram for observing the optical nonuniformity of a product film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Extrusion die 2 Cooling roll consisting of metal or ceramic 3 Rubber roll 4 Backup roll 5 Second cooling roll 6 Third cooling roll 7 Roll 8 Thermoplastic resin layer, film-like molten resin (layer)
9 Rubber roll side support layer 10 Cooling roll side support layer 11 Molded film 12 Film product 13, 13a, 13b Stopper (cotter)
14 rail 15 xenon lamp ignition source 16 screen

Claims (4)

When a thermoplastic resin is melt-extruded and a film is produced by pressing together with a support layer in a gap between a metal or ceramic cooling roll and a rubber roll, a synthetic resin film is used as the support layer, and the gap between the cooling roll and the rubber roll is increased. Set to any value between 10% and 90% of the sum of the thickness of the support layer and the film, and provide a stopper on either the cooling roll or the rubber roll so as not to approach the distance below this value, An optical device characterized in that a pressing force of 2.7 to 10.0 kgf / cm is applied to the roll on the side provided with the stopper to pinch and take off, and then the support layer is peeled off to obtain a thermoplastic resin film. Film manufacturing method. Rubber roll method for producing an optical film according to claim 1 Symbol mounting a roll surface hardness of 60 or more rubber is wound on the thickness 5~15mm the metal core. The method for producing an optical film according to claim 1 or 2 , wherein the thermoplastic resin is a cyclic polyolefin. Method for producing an optical film of any one of claims 1 to 3 the support layer is a film comprising a biaxially stretched polyethylene terephthalate.

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