JP4228115B1 - Polyethylene terephthalate resin film and method for producing the same - Google Patents

Abstract

[PROBLEMS] To improve process passability during high-temperature processing at 80 to 180 ° C., and to suppress generation of whiskers at the cut edge during film cutting, and to be used for optical films, precision printing applications, and single wafers. A good film is provided as a base film.
A difference between a refractive index in a direction forming an angle of 45 degrees with a winding direction of a film and a refractive index in a direction forming an angle of 90 degrees with the film is polyethylene terephthalate having a difference Δn _ab of 0.015 or more and 0.060 or less. The ratio TS / TE between the breaking strength TS in four directions and the breaking elongation TE is 0.6 (MPa /%) or more and 2.6 (MPa /%) or less in the width direction. The difference in heat shrinkage ratio (HS150) is 0.1% or less.
[Selection figure] None

Description

  The present invention relates to a polyethylene terephthalate resin film, and more specifically, a film having excellent processing characteristics, specifically, in a film processed using various thermal processing steps, when the thermal processing step is passed. There is little difference in the heat shrinkage in the longitudinal direction in the width direction, the film does not meander, the occurrence of whiskers at the cut ends becomes a foreign object during film cutting, and the flatness of the film causes problems in terms of quality as the base film The present invention relates to a polyethylene terephthalate resin film suitable for use in optical films and precision printing applications.

  Biaxially oriented polyethylene terephthalate resin films are widely used as various processing base films because of their excellent transparency, dimensional stability, and chemical resistance. In particular, it is suitably used for applications such as optical films and offset printing films that require excellent strength and dimensional stability. Such a biaxially stretched polyethylene terephthalate resin film is stretched in the longitudinal direction between rolls having a difference in rotational speed, and then stretched in the width direction with the end of the film held in the tenter. It is manufactured by being heat-fixed at. However, there is a difference in the isotropic orientation and relaxation in the longitudinal direction of the central part and the edge part during transverse stretching and heat setting at the edge in the width direction of the film, and the orientation depends on the position of the slit roll in the width direction of the film. A different situation will occur. Therefore, among the slit rolls that have slit the mill roll once wound up in a wide width, in the slit roll corresponding to the edge of the mill roll, the physical properties related to the alignment characteristics at the edge of the width direction collapse from isotropic. There is a large difference in the physical properties in the vertical and horizontal intermediate directions (two directions of 45 degrees in the vertical direction). When such a distorted portion is used, anisotropy occurs at the cut edge when the film is cut into sheets, the fine cut beard of the film remains, and when the films are stacked, the beard causes the sheet. One side of the leaf film becomes higher or the whiskers are scraped to become foreign matter. When such a state occurs, the flatness of the single-wafer film may be lost, or a bearded foreign substance may cause a defect in a subsequent processing step, resulting in a great decrease in yield.

  However, in order to clean the cut end of this film, selection of a cutting method and a sharp blade are required. Even if a cutting method is selected and a blade with good sharpness is used, if it is used for a long time, the sharpness becomes worse, and it is necessary to replace the blade and adjust other conditions. The replacement and adjustment of the blade is not preferable because the time and cost loss are large and the apparatus becomes large, and a device that can cut the film as little as possible is desired.

  In addition, there is an increasing demand for wide slit rolls in order to reduce post-processing costs, but in order to collect such wide slit rolls with a high yield from the limited mill roll width, the narrow width is required as in the past. It is better to collect from a wider mill roll than from a mill roll. However, when the mill roll is widened, it becomes difficult to maintain temperature uniformity in the width direction of the heat setting device. That is, a temperature difference occurs between the left and right, or the temperature becomes unstable over time. As a result, it becomes difficult to control the heat shrinkage rate constant in the width direction and the longitudinal direction. Therefore, the difference in the heat shrinkage rate in the width direction affects the runnability of the film in the process where heat is applied in the post-processing. The passability is adjusted by adjusting. Therefore, there is a loss due to adjustment.

  In order to widen the mill roll, it is indispensable to finely adjust the amount of hot air blown out in the heat fixing device in order to maintain good temperature uniformity in the width direction of the heat fixing device. However, fine adjustment of the hot air blowing amount, etc. can improve the temperature uniformity in the width direction and reduce the difference in thermal shrinkage between the left and right to a certain extent. It is not possible to reduce the difference in thermal shrinkage between the left and right edges to a level sufficient to achieve the desired level.

  Therefore, regardless of the width of the mill roll, a method for reducing the difference in the heat shrinkage rate in the width direction of the film (the heat shrinkage rate in the longitudinal direction of the film) in order to improve the film passability in the post-processing step In the heat fixing process of the film, the applicant puts a continuous shielding plate on a plenum duct (hot air outlet) arranged at regular intervals with respect to the film traveling direction, and the width of the shielding plate By gradually expanding the film toward the film traveling direction side, the temperature in the width direction of the film is increased from the central part to the end part, and the relaxation amount at the end part approaches the relaxation amount at the central part. It has been proposed (Patent Document 1). Further, as a method for reducing the difference in the heat shrinkage rate in the width direction of the film, the applicant attached discontinuous shielding plates to the five plenum ducts in the film heat setting step, and from each plenum duct, per unit time Discloses a method of increasing the amount of hot air impinging on the end by increasing the speed of air blown from the plenum duct while keeping the amount of hot air blown to the outside (Patent Document 2).

JP 2001-138462 A JP 2002-79638 A

  In the future, it is predicted that the line speed of post-processing will be improved from the viewpoint of productivity improvement, and it is considered that a film that can be suitably used even in high-temperature post-processing is required. However, with regard to the technology for improving the film permeability in the post-processing step, in the method of simply covering the plenum duct (hot air blowing portion) with a continuous shielding plate in the heat setting process, The film cannot be relaxed sufficiently. Therefore, although the passability when heat treatment in post-processing (coating and drying) is performed at a low temperature of about 120 ° C. is improved to some extent, the drying efficiency of the coating film (hard coat film, etc.) is increased or the processing speed is increased. When the heat treatment in the post-processing is performed for a relatively long time (10 to 60 seconds) in the high temperature zone (about 180 ° C.) for the purpose of increasing the temperature, the passability is not improved so much. Therefore, when post-processing is performed at a high temperature for a long time, the conditions must be adjusted in the post-processing step, and there may be a situation where the conditions cannot be adjusted.

  In addition, in the method of simply covering the plenum duct with the heat-fixing process, the temperature hunting in the heat-fixing zone becomes large, so when manufacturing a long film (mill roll) of 1,000 m or more. In other words, a portion having poor permeability (that is, a portion having a large difference in thermal shrinkage in the width direction of the film) or a portion having poor planarity is formed.

  Further, when the wind speed was changed for each plenum duct, temperature hunting occurred, and this also failed to obtain a stable quality.

  Further, in order to obtain the film of the present invention, it is necessary to perform transverse stretching on the film subjected to longitudinal stretching. However, when stretching in the width direction, the transmission of force in the width direction differs between the end portion and the center portion in the transverse stretching machine. That is, the end portion is gripped by the grip portion in order to perform lateral stretching, and the movement is limited, but the central portion is in a state where it can move in the longitudinal direction. In this state, a catenary curve is drawn just like a single rope pulled to the left and right. In the case of lateral stretching, the shape of the catenary line in the longitudinal direction changes from the initial stage of stretching to the latter stage of stretching. This change can be visualized by, for example, drawing a line with a fast-drying ink on the surface of the film sheet perpendicular to the longitudinal direction (parallel to the width direction) on the film sheet before the lateral stretching starts. In the initial stage of transverse stretching, the line appears to be convex toward the rear side in the flow direction, and as the stretching proceeds, the line becomes straight at some point, and then appears to be concave in the flow direction.

Due to this lateral stretching behavior, there is a difference in physical properties in the width direction under conventional stretching conditions, and the film taken from the center of the machine base does not cause any problems when using the film, but the end of the machine base (the film winding direction) The difference between the refractive index in the direction forming an angle of 45 degrees and the refractive index in the direction forming an angle of 90 degrees Δn _ab is 0.015 or more and 0.060 or less). There is a difference in the mechanical characteristics between the direction forming an angle of 90 degrees and the direction forming an angle of 90 degrees. As a result, the cutting property of the film differs in the width direction, and the cutting force applied to the film in the width direction during cutting is substantially different, which causes generation of whiskers or the like at the cut end. In particular, when the thickness is 70 μm or more, it is necessary to improve the thickness of the processed film (70 μm or more) in which the generation of beard is drenched with a single sheet.

  In order to eliminate the problems of the conventional stretching methods described above, the present inventors have improved how the film can be cut and how to improve the workability in post-processing regardless of the width of the mill roll. I studied whether I could do it. As a result, when the film is cut, there is an influence not only in the direction but also in the oblique direction, and paying attention to the fact that it functions as a surface, and not only in the conventional vertical and horizontal characteristics but also in the vertical and horizontal directions. The characteristics in the direction of the direction have an effect on the cleanliness at the time of cutting the film, and it is possible to keep the breaking strength and breaking elongation within a specific range, and furthermore, using a shielding plate, the difference in heat shrinkage rate in the width direction Is found to be extremely important in efficiently solving the above problems (improvement of process passability during processing, improvement of whiskers during cutting), and the stretching conditions of the transverse stretching process are conventional The present invention is completed by finding that it is possible to improve the processability of the film processing process and improve the whisker when cutting by using a completely different stretching method and using a shielding plate in the heat setting process. It came to.

Among the present inventions, the first invention is such that the difference Δn _ab between the refractive index in the direction that forms an angle of 45 degrees with the winding direction of the film and the refractive index in the direction that forms an angle of 90 degrees is 0.015 or more. It is a polyethylene terephthalate-type resin film which is 0.060 or less, Comprising: The following requirements (1)-( 5 ) are satisfy | filled.
(1) Ratio TS / TE of breaking strength TS and breaking elongation TE in a direction forming an angle of 45 degrees with the winding direction of the film, and breaking strength TS in a direction forming an angle of 135 degrees with the winding direction of the film The ratio TS / TE of the breaking elongation TE, the ratio TS / TE of the breaking strength TS in the winding direction and the breaking elongation TE, and the breaking strength TS in the direction (width direction) forming an angle of 90 degrees with the winding direction The ratio TS / TE of the breaking elongation TE is 0.6 (MPa /%) or more and 2.6 (MPa /%) or less. (2) About the film whose length in the width direction of the film is 70 cm or more HS150, which is the heat shrinkage rate in the film winding direction when heated at 150 ° C. for 30 minutes for five samples that were equally divided into five in the film width direction and cut out from the center in the width direction of each of the five divided films. H The difference between the maximum and minimum values of 150 is 0.1% or less (3) The five samples HS150 be both 2.0% or less than 0.7%
(4) The thickness variation rate in the winding direction of the film is 6% or less.
(5) The thickness of the film is 70 μm or more and 400 μm or less, and the second invention is a manufacturing method for manufacturing the polyethylene terephthalate resin film by melting and extruding a raw material resin from an extruder. A film forming process for forming an unstretched sheet, a biaxial stretching process in which the unstretched sheet obtained in the film forming process is biaxially stretched in the shape of the longitudinal sheet and in the lateral direction, and the film after biaxial stretching is heat-set. The transverse stretching step satisfies the following requirements ( 6 ) to ( 10 ), and the thermal fixing step satisfies the following requirements ( 11 ) to ( 13 ): Is.
(6) In the transverse stretching step, the difference in the set temperature of the continuous temperature zone is 5 ° C. or higher and 30 ° C. or lower in the first half of the horizontal stretching (up to the temperature zone where the draw ratio includes 1.8 times). ( 7 ) The temperature range that passes 1.8 times in the stretching in the transverse stretching step is 100 ° C. or more and less than 160 ° C. ( 8 ) In the transverse stretching step, the difference in temperature setting in the continuous temperature zone is the transverse stretching. Between the first half (up to the temperature zone including the draw ratio of 1.8 times) and the first temperature zone of the next second half is 5 ° C. to 40 ° C. ( 9 ) The difference in the temperature setting of the temperature section to be performed is 5 ° C. or more and 30 ° C. or less in the latter half of the transverse stretching (from the temperature section area next to the temperature section area including the draw ratio of 1.8 times to the final draw ratio). stretching in it (10) transverse stretching Oite final drawing that temperature range to reach a magnification of 220 under ° C. 160 ° C. or higher (11) wider plurality of plenums ducts blowing hot air, is arranged to face up and down relative to the traveling direction of the film ( 12 ) A shielding plate for shielding hot air outlets is attached to the plurality of plenum ducts. ( 13 ) The dimension of each shielding plate in the traveling direction of the film is equal to each plenum in the traveling direction of the film. is adjusted to the size substantially the same outlet of the duct, the dimension in the width direction of the film of each shielding plate, it is adjusted to be gradually increased to the traveling direction of the film the third Invention, manufacturing method for producing the polyethylene terephthalate resin film, wherein the biaxial stretching step stretches the film in the longitudinal direction With those extending in the lateral direction after, between the zone and the heat setting apparatus for performing the transverse stretching, is characterized in that an intermediate zone that does not execute the blowing wind.
Moreover, 4th invention is a manufacturing method of the said polyethylene terephthalate type-resin film, Comprising: While the heat setting apparatus is divided | segmented into the several heat setting zone, the temperature difference and wind speed between adjacent heat setting zones are provided. The product of the difference is set to be 250 ° C. · m / s or less.
The fifth invention is a method for producing the polyethylene terephthalate film, wherein a filter medium having an initial filtration efficiency of 95% or more and a filtration particle size of 15 μm or less is used in an arbitrary melt line at the time of melt extrusion of polyester. Thus, microfiltration is performed.

  The polyethylene terephthalate-based resin film of the present invention has good process passability during high-temperature processing at 80 to 180 ° C., and suppresses the occurrence of whiskers at the cut edge when cutting the film. An object of the present invention is to provide a good film as a base film used in a sheet.

  The film constituting the polyethylene terephthalate resin film roll of the present invention contains ethylene glycol and terephthalic acid as main components. Other dicarboxylic acid components and glycol components may be copolymerized as long as the object of the present invention is not impaired. Examples of the other dicarboxylic acid components include isophthalic acid, p-β-oxyethoxybenzoic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-dicarboxybenzophenone, bis- (4-carboxyphenylethane), adipine Examples include acid, sebacic acid, 5-sodium sulfoisophthalic acid, cyclohexane-1,4-dicarboxylic acid, and the like. Examples of the other glycol component include propylene glycol, butanediol, neopentyl glycol, diethylene glycol, bisphenol A and other ethylene oxide adducts, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like. In addition, oxycarboxylic acid components such as p-oxybenzoic acid can also be used.

  As a polymerization method of such polyethylene terephthalate (hereinafter simply referred to as PET), a direct polymerization method in which terephthalic acid and ethylene glycol and, if necessary, other dicarboxylic acid component and diol component are directly reacted, and dimethyl terephthalate are used. Any production method such as a transesterification method in which an ester (including a methyl ester of another dicarboxylic acid as necessary) and ethylene glycol (including another diol component as necessary) are transesterified can be used. .

  When the film of the present invention is formed of PET, the intrinsic viscosity (IV) of the raw material PET is preferably in the range of 0.45 to 0.70 dl / g. When the intrinsic viscosity of the PET raw material is 0.45 or less, the degree of polymerization of the PET after being recovered and passed through the extruder again becomes too low, and the stretchability of the film deteriorates or the tear resistance decreases. Is not preferable. On the other hand, if the intrinsic viscosity exceeds 0.70 dl / g, the filtration pressure becomes excessively high and high-precision filtration becomes difficult, which is not preferable. In addition, IV of resin raw material is calculated | required with the following methods, for example.

[Intrinsic viscosity (IV)]
After the PET ground sample is dried, it is dissolved in a mixed solvent of phenol / tetrachloroethane = 60/40 (weight ratio), and a solution having a concentration of 0.4 (g / dl) is obtained at 30 ° C. using an Ostwald viscometer. The flow time and the flow time of the solvent alone are measured, and the calculation is performed from the time ratio on the assumption that the constant of Huggins is 0.38 using the Huggins formula. The intrinsic viscosity is also expressed as [η].

  Moreover, when forming the film of this invention by PET, the range of 3-30 eq / t is preferable and, as for the acid value (AV) of PET raw material, it is more preferable in it being 5-25 eq / t. An acid value of 3 eq / t or less is not preferable because the polymerization rate becomes slow and the production efficiency is lowered. On the other hand, an acid value of 30 eq / t or more is not preferable because hydrolysis tends to proceed and the degree of polymerization tends to decrease. The acid value of the resin raw material is determined by the following method, for example.

[Acid value]
After pulverizing the raw material, it is dissolved in benzyl alcohol, and after adding chloroform, neutralization titration with a sodium hydroxide solution is performed to calculate the equivalent of sodium hydroxide per 1 ton of PET.

Furthermore, when the film of the present invention is formed by PET, it is desirable that the raw material (including the recycled raw material) before being put into the extruder does not contain foreign matters. In particular, in order to reduce defects due to foreign matter, it is preferable to perform high-accuracy filtration during melt extrusion so that the number of foreign matters having a diameter of 20 μm or more present per 1 m ^{2 of} film after film formation is 10 or less. . When performing the above-described high-precision filtration, it is preferable to use a filter medium having an initial filtration efficiency of 90% or more, preferably 95% or more and a filtration particle size of 15 μm or less. Here, the initial filtration efficiency refers to a numerical value measured by ANSI / B93.36-1973. Note that the number of foreign substances in the raw material is obtained by the following method, for example.

[Number of foreign objects]
An enlarged image of the melted raw material chip is taken using a phase contrast microscope and a CCD camera, and the number of foreign matters is counted using an image processing apparatus.

[Δn _ab ]
During the production of a biaxially oriented polyethylene terephthalate resin film, it is known that a phenomenon occurs in which the uniformity of physical properties in the film width direction is disturbed when the film is stretched in the width direction in the tenter. In order for this phenomenon to occur, the obtained biaxially oriented film has a difference of Δn _ab (the refractive index and the winding in a direction that forms an angle of 45 degrees with the winding direction of the wound film) as the distance from the center in the film width direction increases. The difference (absolute value) between the film winding direction and the refractive index in the direction forming an angle of 135 degrees increases. Here, the polyethylene terephthalate resin film of the present invention is limited to those having Δn _ab of 0.015 or more and 0.060 or less in all regions. The lower limit of Δn _ab is 0.015, more preferably 0.020, and even more preferably 0.030. A film having Δn _ab less than 0.015 does not cause the above-mentioned problem of “strain (that is, physical property difference in the width direction)”. On the other hand, the upper limit of Δn _ab is 0.060, more preferably 0.055, and still more preferably 0.050. A film having Δn _ab exceeding 0.060 has significant distortion, and it is difficult to adjust TS / TE or the like so as to satisfy the requirements of the present invention. Note that the [Delta] n _ab of the present invention, respectively to measure the [Delta] n _ab from the position and the other edge within 50mm from parallel one end edge to the film take-up direction at a position within 50mm, larger of those two values Say better.

[Thickness fluctuation rate in the winding direction (thickness unevenness)]
In addition, the film of the present invention was obtained by collecting a strip-shaped film sample having a length of 30 m and a width of 3 cm along the winding direction of the film and measuring the thickness variation in the winding direction of the film sample. The thickness variation rate in the winding direction, that is, the thickness unevenness, needs to be in the range of 4% or more and 6% or less. Thickness variation rate is more preferably 5.5% or less, more preferably more than 5.0% or less, and particularly preferably 4.5%. The thickness variation rate is preferably as small as possible, but 3% is considered the lower limit due to manufacturing restrictions. In addition, the preferable film forming method for obtaining the film whose thickness fluctuation rate of the film winding direction is in the above range will be described later.

[TS / TE]
In the present invention, the breaking strength (TS) is a stress necessary for the film to break, specifically, gradually adding a tensile force to the film to determine the force when the film breaks, This is expressed as a value (unit: MPa) converted to stress per unit area. The elongation at break (TE) is the ratio (elongation) of the film that stretched until it broke, and specifically, the length that stretched until the film broke when a tensile force was applied to the film. Is expressed by a value (unit:%) divided by the original length. In the present invention, the breaking strength (TS) and the breaking elongation (TE) are measured according to JIS K 7127, and specifically, the following methods are used. That is, a film test piece having a width of 12.7 mm and a length of 200 mm was sampled, and the film test piece was set in a tensile tester (for example, Tensilon RTC-125A manufactured by ORIENTEC Co., Ltd.) at a temperature of 23 ° C. and a humidity of 65% RH. Under the environment, the film was stretched at a distance between chucks of 100 mm and a take-off speed of 200 mm / min, and the breaking strength (TS) and elongation at break (TE) were determined from the measured values of the elongation at break of the film specimen and the load required for breaking. Is calculated.

  The ratio of the breaking strength (TS) to the breaking elongation (TE) (TS / TE) and the film cutting workability have the following relationship. That is, a film having a large TS / TE means a film having a high breaking strength and a low elongation. A film having such characteristics becomes a fragile and low-strength film, and the cut surface becomes fluffy during cutting, and beards and chips are likely to be generated. On the other hand, a film having a small TS / TE means a film having a low breaking strength and a high elongation. A film having such characteristics is a sticky and firm film, has little roughness on the cut surface even during cutting, and has good cutting properties (cutting properties). Further, when the TS / TE ratio varies depending on the part of the film, there is a difference in the cutting workability depending on the part even for the same shearing force, and the difference in the cut surface and the whisker easily occur due to the difference. Therefore, it is most desirable that the TS / TE ratio is isotropic. From the above, a film having a small TS / TE ratio and a small variation in the TE / TE ratio depending on the part is preferable in the cutting processability.

  The film of the present invention has a ratio TS / TE of a breaking strength TS and a breaking elongation TE in a direction (A direction) forming an angle of 45 degrees with the winding direction of the film, and an angle of 135 degrees with the winding direction of the film. The ratio TS / TE of the breaking strength TS and breaking elongation TE in the forming direction (B direction), the ratio TS / TE of the breaking strength TS and breaking elongation TE in the winding direction (MD direction), and the winding direction 90 The ratio TS / TE between the breaking strength TS and the breaking elongation TE in the direction forming the angle (TD direction) is 0.6 (MPa /%) or more and 2.6 (MPa /%) or less. Features. The upper limit of the TS / TE ratio is preferably 2.6 (MPa /%), more preferably 2.4 (MPa /%), and even more preferably 2.2 (MPa /%). If the TS / TE ratio is 2.6 (MPa /%) or less in the MD direction, the TD direction, the A direction, and the B direction, the film has good cutting properties and is suitable for cutting. The lower limit of the TS / TE ratio is preferably 0.6 (MPa /%), more preferably 0.9 (MPa /%). When the TS / TE ratio is 0.6 (MPa /%) or more, it is preferable that the film is hardly mechanically deformed. Further, when the TS / TE ratio is within the above ranges in the MD direction, the TD direction, the A direction, and the B direction, shear deviation due to the TS / TE ratio is unlikely to occur. A preferred film forming method for obtaining a film having a TE / TE ratio in the above range will be described later.

[Heat shrinkage]
The polyethylene terephthalate-based resin film of the present invention has a film winding direction when heated at 150 ° C. for 30 minutes with respect to five film samples cut out from each cut-out portion when the sample cut-out portion is set by a method described later. HS150, which is the heat shrinkage ratio, is obtained, and the difference between the maximum value and the minimum value needs to be 0.1% or less.

When the difference between the maximum value and the minimum value of HS150 is 0.1% or less, the film can be easily passed in post-processing, which is preferable. Further, the difference in heat shrinkage rate between the cutout portions is more preferably 0.08% or less, and particularly preferably 0.06% or less. In addition, although the difference between the maximum value and the minimum value of HS 150 in each cutout portion is preferably as low as possible, 0.05% is considered to be the lower limit in design.

The film sample used for the measurement of the heat shrinkage rate is cut out from five cut-out portions provided by the following procedure.
(1) A film having a length in the width direction of 70 cm or more and Δn _ab of 0.015 or more and 0.060 or less is equally divided into five.
(2) A cutout portion is provided at the center in the width direction for each of the five divided films.
(3) A sample film having a width of 20 mm and a length of 250 mm is cut out from each cutout portion along the film winding direction, and five film samples are cut out.

  Furthermore, the polyethylene terephthalate resin film of the present invention has a film winding direction when heated at 150 ° C. for 30 minutes with respect to five film samples cut out from each cutout portion when the sample cutout portion is set by the above-described method. When HS150, which is the heat shrinkage ratio, is determined, it is necessary that the HS150 of the samples at both ends at all the cutout portions is 0.7% or more and 2.0% or less.

It is preferable that the HS150 value of the film sample cut out from each cut-out portion is 2.0% or less because the film can be easily passed in post-processing. Moreover, the value of HS150 of the film sample cut out from each cut-out part is more preferably 1.5% or less, and particularly preferably 1.2% or less. In addition, although the value of HS150 of the film sample cut out from each cutting part is so preferable that it is low, from the point of productivity, 0.7% thinks that it is a minimum.

[Production Method of Film of the Present Invention]
When the raw resin is melt-extruded, the polyethylene terephthalate resin raw material is preferably dried using a dryer such as a hopper dryer or a paddle dryer, or a vacuum dryer. After the polyethylene terephthalate-based resin material is dried in such a manner, it is melted at a temperature of 200 to 300 ° C. and extruded into a film using an extruder. For this extrusion, any existing method such as a T-die method or a tubular method can be employed.

  And an unstretched film can be obtained by rapidly cooling the sheet-like molten resin after extrusion. In addition, as a method of rapidly cooling the molten resin, a method of obtaining a substantially unoriented resin sheet by casting the molten resin on a rotating drum from a die and rapidly solidifying it can be suitably employed.

  Further, the obtained unstretched film is stretched in the longitudinal direction (longitudinal direction) by the method shown below, and the film after the longitudinal stretching is transversely stretched by the method shown below in the width direction, and heated by the method shown below. The film of the present invention can be obtained by fixing treatment. Hereinafter, a preferable film forming method for obtaining the film of the present invention will be described in detail in consideration of a difference from a conventional film forming method.

<Problems of conventional stretching methods>
The unstretched film is formed by winding a sheet-like molten resin around a metal cooling roll as described above. At that time, due to factors such as non-uniformity of the shape of the metal cooling roll and fluctuations in the discharge amount of the molten resin, thickness unevenness is formed in the unstretched film. Various attempts have been made in the past to reduce such thickness unevenness, but it is currently impossible to completely eliminate the thickness unevenness of the unstretched film. Therefore, in order to finally obtain a film with good thickness unevenness, how to amplify the thickness unevenness in the unstretched film in the stretching process is a big point.

  In the longitudinal stretching step, longitudinal stretching may be performed by a known method, and the longitudinal stretching can be performed by one stage, two stages, or multistage stretching. The magnification may be performed when the overall draw ratio is between 2.5 and 4.2. If the overall draw ratio is less than 2.5 times, the variation in the longitudinal thickness becomes large, and preferably 3 times or more. Further, when the overall draw ratio exceeds 4.2 times, breakage is likely to occur in the transverse drawing step. 3.9 times or less is preferable.

  Further, in order to obtain the film of the present invention, it is necessary to perform transverse stretching on the film subjected to longitudinal stretching. However, when stretching in the width direction, the transmission of force in the width direction differs between the end portion and the center portion in the transverse stretching machine. That is, the end portion is gripped by the grip portion in order to perform lateral stretching, and the movement is limited, but the central portion is in a state where it can move in the longitudinal direction. In this state, a catenary curve is drawn just like a single rope pulled to the left and right. In the case of lateral stretching, the shape of the catenary line in the longitudinal direction changes from the initial stage of stretching to the latter stage of stretching. This change can be visualized by, for example, drawing a line with a fast-drying ink on the surface of the film sheet perpendicular to the longitudinal direction (parallel to the width direction) on the film sheet before the lateral stretching starts. In the initial stage of transverse stretching, the line appears to be convex toward the rear side in the flow direction, and as the stretching proceeds, the line becomes straight at some point, and then appears to be concave in the flow direction.

Due to this transverse stretching behavior, there is a difference in physical properties in the width direction under the conventional stretching conditions, and there is no problem with the film taken from the center of the machine base when using the film, but the end of the machine base (the film winding direction) The difference between the refractive index in the direction forming an angle of 45 degrees and the refractive index in the direction forming an angle of 90 degrees Δn _ab is 0.015 or more and 0.060 or less). There is a difference in the orientation characteristics between the direction forming an angle of 90 degrees and the direction forming an angle of 90 degrees. This influences the cutting property by the mechanical behavior in the oblique direction when the film is cut. For this reason, it has been necessary to improve a thick film (70 μm or more) of a processed film to be processed on a single sheet, which is strictly demanded.

  In order to eliminate the problems of the conventional stretching methods described above, the present inventors have found that the film does not generate strain due to tension in the thermal processing step due to the difference in thermal shrinkage in the width direction, and the film. Whether or not a film having extremely little influence on the cutting property of the film due to the orientation characteristics in the oblique direction (ab direction) can be made. As a result, by performing the stretching conditions in the transverse stretching process as described below under completely different conditions, and further by using a shielding plate in the heat setting zone to reduce the difference in thermal shrinkage in the width direction, the film In the present invention, it is found that a film having excellent cutting ability can be obtained without causing heat distortion and without causing distortion due to processing tension due to a difference in thermal shrinkage rate during heat processing. It came to complete.

<Characteristics of the film production method of the present invention in the transverse stretching step and heat setting treatment step>
The film that has undergone the longitudinal stretching step is then subjected to a transverse stretching process in a tenter. In the tenter, (a) a preheated portion for heating the film to a temperature suitable for stretching in order to stretch the film subjected to longitudinal stretching in the transverse direction, and (b) stretching the heated film in the transverse direction. A stretched part, (c) a heat-fixed part that is subsequently subjected to heat treatment to reduce strain caused by longitudinal and transverse stretching, (d) a relaxation-treated part that further reduces strain in the transverse direction, and (e) a heated film at the end. It can be divided into a cooling part that cools below the glass transition point (Tg). A rail for running a clip connected to a chain is installed on the side of the tenter, and the film runs in the tenter while being held by the clip.

In the preheating portion (a), the film temperature is raised by hot air blown from the pronum duct installed at the upper part and / or the lower part of the film. Although the film expands when the temperature rises, the running rail of the clip that holds the film end is slightly expanded in the width direction so that the slack due to the expansion is not generated. Thus, the fluttering of the film is suppressed by the wind pressure of the air blown from the plenum duct so that the hot air is uniformly applied to the film surface.
In order to stretch the film in the transverse direction at the stretched portion (b), the clip chain is installed so as to expand in the film width direction in an oblique direction with respect to the progress of the entire film in the longitudinal direction. The film whose end is held by a clip is pulled in the width direction and stretched in the transverse direction as it progresses. The stretch ratio of the film is determined according to the extent (angle and distance) of the travel rail of the clip chain.
In the heat setting part of (c), in order to reduce the distortion generated when the film is stretched in the vertical and horizontal directions, the film is subjected to high temperature heat to remove the distortion. The size of the heat shrinkage rate in the longitudinal direction is mainly determined by the temperature of this portion.
In order to further reduce distortion in the lateral direction, the relaxation treatment part (d) removes the distortion in the width direction by a process such as reducing the width of the traveling rail of the clip chain in the width direction. Depending on the extent of this treatment (temperature and relaxation rate), the thermal contraction rate in the lateral direction is mainly determined.
In the cooling part (e), the film is cooled to Tg or less, and the film is cooled so as to be taken out in the vicinity of room temperature with the distortions (c) and (d) reduced.

Each part plays a role as described above. In the present invention, the stretched part (b) achieves both uniform physical properties in all directions in the width direction of the biaxially stretched film and reduction of thickness spots. It is intended that the heat shrinkage rate in the vertical direction is uniform in the heat setting process part of (c).

In the stretched portion of (b), the film is stretched in the lateral direction according to the running rail of the clip chain installed in the oblique direction with respect to the traveling direction. In the stretching process, both ends of the film are held and fixed by clips. However, the area away from the clip, particularly in the central area of the film, has a higher degree of freedom than both ends. While there is a local difference in the degree of mechanical freedom, the film as a whole is stretched in a state where the action of force is balanced. Moreover, the film is in a state where the balance of force in the longitudinal direction is balanced in addition to the width direction, and is also affected by the heat fixing portion. The relationship between these force actions is balanced in a catenary-like state in which the ends are fixed in the width direction. When the action of this force is observed at the central part of the film, it acts so as to advance toward the film traveling direction at the initial stage of stretching, and acts so that the central part is delayed from the traveling direction at the latter stage of stretching. A so-called bowing phenomenon is observed by the action of such a force.

  As a result of the action of this force, the physical properties of the film end portion are different between the characteristics in the winding direction and the direction of 45 degrees and the characteristics in the direction perpendicular thereto. Among these characteristics, the difference in the ratio TS / TE between the breaking strength (TS) and the breaking elongation (TE) due to the state of the orientation characteristics is considered to affect the cutting characteristics.

  Generally, when a tensile test of a film made of polyethylene terephthalate resin is performed, the stress increases at a substantially constant rate until a predetermined strain amount is reached, and when the predetermined strain amount is reached, the strain amount increases. A plateau region where the stress does not increase appears (a point where the stress at the initial stage of saturation is saturated is called a yield point). Then, after such a plateau region appears, a region where the stress increases as the amount of strain increases again (a point where the stress starts to rise again after the yield point is referred to as a rising point), and the stress increases. It shows a tendency to break after increasing. Such a curve of stress and strain is called an SS curve.

In order to reduce the physical property difference, if the stretching temperature in the transverse direction is simply set to a high temperature, the stretching corresponds to “stretching that gives a strain corresponding to a plateau region in the SS curve”, and the film There was a risk of thick spots. Furthermore, when the stretching temperature in the transverse direction is increased, the temperature difference from the preheating region is increased, and there is a possibility that unevenness in the temperature state in the tenter may occur (the thickness Δn _{ab of} the film is 0). When the ratio is less than .015, the difference in the ratio TS / TE does not increase so much as to affect the cutting workability). If such a thickness unevenness occurs in a film, it cannot be used in a post-processing process that has been increasingly refined in recent years. However, surprisingly, it has been found that, by optimizing the relationship between the transverse draw ratio and the temperature as described below, it is possible to obtain a product having good thickness unevenness and good cutting workability.

-Controlling the temperature of the temperature zone in the transverse stretching step In the transverse stretching step, the tenter is usually provided with a plurality of temperature zone zones. Set the temperature difference between 5 ° C and 30 ° C up to the first half of the stretch (up to the temperature zone including the draw ratio of 1.8 times), and the latter half of the temperature zone including the draw rate of 1.8 times The range from the next temperature section region to the final draw ratio) needs to be 5 ° C. or higher and 30 ° C. or lower. On the other hand, the temperature difference between the temperature zone including 1.8 times and the next temperature zone is preferably 5 ° C. or more and 40 ° C. or less.

  The reason why it is preferable to control within the above temperature range is considered as follows. That is, in the first half of the transverse stretching step, stretching is performed in the stretch stress increasing region of the SS curve of the tensile properties of the film, so that the influence of temperature spots tends to occur. Therefore, as described above, it is desirable to keep the temperature difference between adjacent temperature sections in the first half of the drawing low. In the latter half of the transverse stretching step, the stretching temperature is set to a relatively high temperature, so that the stretching stress of the film decreases. Therefore, the temperature difference between adjacent temperature zones in the second half of stretching can be made larger than that in the first half. Furthermore, since it corresponds to the plateau region of the SS curve in the middle of the transverse stretching process, it is less affected by temperature changes than other temperature zones and has a larger temperature difference than other temperature zones. Permissible. Thus, in the present invention, the temperature difference between the temperature division zones is controlled as described above according to the SS curve.

Moreover, it is preferable that these temperature settings raise a set temperature in steps toward the advancing direction of a film. In the tenter, an accompanying flow is generated as the film progresses, so that an air flow from upstream to downstream occurs along the film traveling direction. For this reason, when there is a difference in the set temperature between two consecutive temperature zones, temperature disturbance occurs at the boundary between the temperature zones. If the set temperature difference is large, the temperature distribution in the tenter becomes more turbulent and the stretched state of the film is distorted, which causes thickness spots. Therefore, the set temperature of each continuous temperature section is set to a certain range, and the film temperature in the width direction and the longitudinal direction is stabilized. Thereby, the thickness unevenness of the film resulting from the disorder of the temperature of the lateral stretch part in a tenter can be reduced. The lower limit of the set temperature difference for obtaining the film of the present invention is 5 ° C. or higher, preferably 10 ° C. or higher. When the set temperature difference is less than 5 ° C., it becomes difficult to set the set temperature in the final temperature zone to the set temperature described later. In addition, the upper limit of the set temperature difference needs to be 30 ° C. or less up to a temperature division region including 1.8 times. On the other hand, a temperature of 30 ° C. or less is required from the temperature segmented region next to the temperature segmented region including the draw ratio of 1.8 times to the final draw ratio. On the other hand, it is desirable that the temperature section region including 1.8 times and the next temperature section region be 40 ° C. or less, preferably 30 ° C. or less. When the set temperature difference is more than 40 ° C., the film thickness is disturbed, and the above effect cannot be obtained.

  It is preferable that the set temperature difference is set to 5 ° C. or more and 40 ° C. or less also in two continuous temperature section areas from the preheating section (A) to the first temperature section of the stretched section (B). In the preheated part, it is necessary to warm the film so that the temperature is about the temperature at which stretching is possible. Therefore, when the temperature of the stretched portion is set to a high temperature, the film temperature is preferably about the stretching temperature of the longitudinal stretching to the stretching temperature of the longitudinal stretching + 15 ° C. In addition, it is desirable to control the set temperature of the preheating portion according to the length in the longitudinal direction of the preheating portion, the speed at which the film travels, and the thickness of the film.

(2) Temperature control in the first half of the transverse stretching step After the temperature of the film is raised in the preheating portion in the initial part of the transverse stretching step, in the first half of the stretching in the transverse stretching step, S- Stretching is performed in the stretch stress increasing region of the S curve. In order to obtain the film of the present invention, it is preferable to set the temperature range of the first half of the transverse stretching step to 100 ° C. or more and less than 160 ° C. and perform transverse stretching at a relatively low temperature. If the set temperature is less than 100 ° C., the film tends to break, which is not preferable. When the set temperature is 160 ° C. or higher, the stretching condition not only corresponds to “stretching that gives a strain amount corresponding to a plateau region in the SS curve”, but the temperature difference from the preheated portion is large. Therefore, the temperature balance in the tenter becomes unstable, and thickness spots are likely to occur, which is not preferable. As will be described later, it is desirable to set the temperature so as to increase from the first half to the second half of the drawing. However, if it is difficult to provide stepwise temperature settings in the first half of the stretching, it is necessary to adjust the temperature difference between the first half of the stretching and the second half of the stretching described below to obtain the desired effect. May be.

Here, the meaning of the first half of the stretching is stretching performed in the first half region of the transverse stretching step, and stretching performed in the stretching stress increasing region of the SS curve. Specifically, it refers to a segmented region including a transverse stretch ratio of 1.8 times. The draw ratio in the first half of the drawing depends on the total number of divided regions. For example, when the final transverse stretch ratio is 4 times, when the total number of segmented areas is 3, the ratio is 2.0 times, and when the total number of segmented areas is 4, the ratio is 2.5 times. In the present invention, stretching is performed at a relatively low temperature by setting the set temperature in the section region including 1.8 times to 100 ° C. or more and less than 160 ° C.

(3) Temperature control at the final reaching part of the transverse stretching step In order to obtain the film of the present invention, the temperature range of the final reaching part of the transverse stretching step is set to 160 ° C or more and less than 220 ° C and set to a relatively high temperature. It is preferable to do. By setting to high temperature, the difference of the above-mentioned TS / TE ratio becomes small and cutting property can be made favorable.

  Here, the meaning of the latter half of the stretching is stretching performed in the latter half region of the transverse stretching step, and specifically, from the next segmented region to the final reaching magnification of the segmented region including the lateral stretching ratio of 1.8 times. is there. The draw ratio in the latter half of the drawing depends on the total number of sections. For example, when the final transverse stretch ratio is 4 times, when the total number of segmented areas is 3, the number is 2.0 times, and when the total number of segmented areas is 4, the number is 2.5 times. The final magnification including the magnification of the first half can be set to 3 times or more and less than 5 times, preferably less than 4.8 times, more preferably 4.4 times. For example, the process conditions when the final transverse draw ratio is 4 and the transverse draw zone is three stages are as follows. First stage magnification is 1.0 to 2.0 times, second stage magnification is 2.0 to 3.0 times, third stage magnification is 3.0 times to 4.0 times, and first stage This zone is the first half of stretching. As for the temperature setting, when the final temperature in the preheating zone is 105 ° C. and the temperature in the final magnification reaching section is 165 ° C., the first zone is preferably 110 to 145 ° C. and the second zone is preferably 145 to 160 ° C. However, depending on settings such as the film forming speed, it is possible to set the temperature in two zones.

  The film of the present invention can be obtained by carrying out highly controlled transverse stretching as described above. It is thought that the difference in TS / TE ratio between the winding direction, the 45 ° direction, and the 90 ° direction is reduced by the transverse stretching process due to the following mechanism. In the transverse stretching process, as described above, the force action is in a balanced state in the entire film in the transverse direction and the longitudinal direction. In the longitudinal direction, the film acts in the initial stage of stretching so as to advance toward the film traveling direction. It acts to be delayed with respect to the direction of travel. Here, when the stretching temperature of the final reaching portion of the transverse stretching is set to a high temperature, the final stretching tension in the transverse stretching step is lowered. Thereby, it is thought that the influence of the action of the force propagating from the heat fixing portion along the longitudinal direction of the film was alleviated, and the distortion of the force acting in the longitudinal direction was alleviated. Furthermore, the orientation characteristics in the winding direction (MD direction) and the direction (TD direction) at 90 degrees can be obtained by appropriately adopting the ratio of longitudinal stretching and lateral stretching. That is, in the present invention, the overall magnification in the longitudinal direction is 2.1 to 4.8 times, but this preferable range is 2.7 to 3.8 times, but the transverse draw ratio is 0 from the longitudinal magnification. A magnification higher by 3 to 0.5 times can be preferably applied from the uniformity of the lateral thickness, but if the lateral stretching ratio is increased too much, the lateral orientation characteristics may become too large compared to the vertical.

  On the other hand, the lateral force action can be considered as follows. Since only the force in the traveling direction acts at the center of the film, the force acting on the film is symmetrical with respect to the longitudinal direction. On the other hand, at the film end, it proceeds in an oblique direction while being held by a clip, and not only the traveling direction but also an oblique force is applied. Therefore, the force action of the film end is not symmetrical with respect to the traveling direction. In order to reduce the difference in the TS / TE ratio, it is necessary to make this force action symmetrical. For this purpose, it is effective to reduce the stretching tension applied to the film by performing a transverse stretching step at a high temperature. However, if the stretching process is simply performed at a high temperature, there is a risk of unevenness in thickness. Therefore, in the first half of the transverse stretching process, stretching is performed in a “region where the stretching stress of the SS curve increases” where the thickness unevenness hardly occurs by relatively lowering the stretching temperature, and the thickness has been made uniform. In this case, the stretching temperature is increased, the stretching stress in the transverse direction is decreased, and stretching is performed in accordance with the balance of the action of the entire force. Thus, without increasing the unevenness of thickness, the winding direction (MD direction) and the winding direction are 45 degrees (A direction), the winding direction is 90 degrees (TD direction), and the winding direction is 135 degrees (B It is considered possible to reduce the difference in the ratio TS / TE between the breaking strength (TS) and the breaking elongation (TE) in the direction of 90 degrees in the direction A).

  In the longitudinal stretching step of the film, by using the means (1) to (3) described above, a reduction factor for the thickness of the film and a magnification taking into account the orientation characteristics of the longitudinal stretching and the lateral stretching are adopted for the film. Thus, the winding direction (MD direction) and the winding direction are 45 degrees (A direction), the winding direction is 90 degrees (TD direction), and the winding direction is 135 degrees (B direction: 90 degrees in the A direction). It is thought that it was possible to achieve both reduction in the difference in the ratio TS / TE between the breaking strength (TS) in the forming direction and the breaking elongation (TE). It should be noted that only one of the above-mentioned means (1) to (3) does not effectively contribute to the reduction in film thickness spots, the reduction in thermal spots and the difference in TS / TE ratio. , (1) to (3) are used in combination, it is considered that the thickness unevenness of the film and the difference in TS / TE ratio can be reduced very efficiently.

  In the present invention, heat setting treatment is performed following the transverse stretching step. The temperature in the heat setting treatment step is preferably 180 ° C. or higher and 240 ° C. or lower. When the temperature of the heat setting treatment is 180 ° C. or more, the absolute value of the heat shrinkage rate is preferably small, and conversely, when the temperature of the heat setting treatment is 240 ° C. or less, the film hardly becomes opaque, and the frequency of breakage Is preferable. A suitable heat setting process will be described below.

<Ingenuity of plenum duct in heat setting process>
Usually, the heat setting process of the stretched film is carried out in a heat setting device in which a plurality of plenum ducts having long hot air outlets are arranged perpendicular to the longitudinal direction. In such a heat fixing device, “circulation of hot air” is performed in order to improve the heating efficiency. Air in the heat fixing device is sucked by a circulation fan installed in the heat fixing device, the temperature of the sucked air is adjusted, and the air is again discharged from the hot air outlet of the plenum duct. In this manner, “hot air circulation” of “hot air blowing → suction by circulation fan → temperature adjustment of sucked air → hot air blowing” is performed.

  Further, as described above, the difference in thermal shrinkage in the width direction of the film roll (difference between HS 150 at the edge of one end and HS 150 at the edge of the other end) is that relaxation of the edge of the film does not occur when heat fixing is performed. It occurs because it is enough. As shown in FIG. 1, in the heat setting process, a continuous large shielding plate S is placed on the central portion of the hot air outlets 2, 2,... Of each plenum duct 3, 3,. See) improves the passage when short films are processed at relatively low temperatures (eg 120 ° C.) in post-processing. However, when excessive tension is applied to a long film, the passability is improved, but the flatness is lost, wrinkles occur, and heat treatment in post-processing is performed at a high temperature (for example, 160 ° C.). The flatness (such as wrinkles) of the film being processed is not improved. Further, as shown in FIG. 2, it has been found that the method (see Japanese Patent Application Laid-Open No. 2002-79638) in which the plenum duct is covered with a discontinuous shielding plate and the wind speed is changed (see Japanese Patent Application Laid-Open No. 2002-79638) lacks stability.

  The inventors show why the method shown in FIG. 1 does not improve “flatness in a long film” or “flatness when heat treatment in post-processing is performed at a high temperature”. Then, in order to understand why it lacks stability, we analyzed the phenomenon in the heat fixing device in detail. As a result, when a continuous large shielding plate that spans multiple plenum ducts is placed over the hot air outlet of the plenum duct, the flow of hot air is restricted by the shielding plate, and the above-mentioned "hot air circulation" is performed smoothly. As a result, it was found that temperature turbulence (temperature hunting phenomenon) occurred in the heat fixing device. In the case of FIG. 2 as well, it was found that the wind speed is different for each plenum duct and the balance of the wind is easily lost, temperature turbulence occurs, and stability is lacking.

Since the above-described “temperature hunting phenomenon” makes the thermal relaxation at the edge of the film insufficient, the “flatness in a long film” and “heat treatment in post-processing are performed at a high temperature. It was speculated that the “flatness in the case of going” would be worse. Therefore, the present inventors can improve “flatness in a long film” and “flatness when heat treatment in post-processing is performed at a high temperature” by smoothing “circulation of hot air”. I thought that. And, as a result of trial and error to grasp the relationship between the temperature air volume condition of the heat setting device, the covering mode of the shielding plate, and the film permeability in the post-processing, the following (1) By adopting the above means, there was a tendency that “flatness in a long film” and “flatness in the case where heat treatment in post-processing was performed at a high temperature” were improved. And based on the knowledge, as a result of further trial and error, the present inventors have taken the following means (1) and then taken the following means (2) and (3). The inventors have found that it is possible to obtain a film roll having good permeability, and have come up with the present invention.
(1) Adjustment of temperature and air volume of plenum duct in heat fixing device (2) Adjustment of shut-off condition of hot air outlet of plenum duct in heat fixing device (3) Heat cutoff between stretching zone and heat fixing device Each of the above-described means will be described sequentially.

(1) Adjusting the temperature and air volume of the plenum duct in the heat setting device In order to heat and cool the heat setting process step by step, the heat setting device is generally divided into several sections (heat setting zones) with different temperatures. I know. In the production of the film roll of the present invention, each plenum duct is designed such that the product of the temperature difference and the wind speed difference between adjacent heat setting zones of the heat setting device is 250 ° C. · m / s or less. It is indispensable to adjust the temperature and air volume of the hot air blown out from. For example, when the heat setting device is divided into first to third heat setting zones, the product of the temperature difference and the wind speed difference between the first zone and the second zone, and between the second zone and the third zone. Both products of the temperature difference and the wind speed difference are adjusted to be 250 ° C. · m / s or less. Thus, by adjusting the temperature and air volume of hot air, “circulation of hot air” becomes smooth. When combined with a method of attaching a discontinuous shielding plate, which will be described later, to the hot air outlet, the “temperature hunting phenomenon” is effectively suppressed. This makes it possible for the first time to obtain a long film with good flatness when the heat setting treatment in post-processing is performed at a high temperature.

  If the product of the temperature difference and the wind speed difference between adjacent heat setting zones is 250 ° C. · m / s or less (for example, the temperature difference between adjacent heat setting zones is set to 20 ° C. The temperature difference between adjacent heat setting zones is set to 10 m / s), “circulation of hot air” in the heat setting device is smoothly performed, and “temperature hunting phenomenon” is effectively suppressed. This is preferable. In addition, if the product of the temperature difference and the wind speed difference between adjacent heat setting zones is 250 ° C. · m / s or less, the heat setting zone downstream from the heat setting zone upstream as an accompanying flow caused by the passage of the film The temperature difference of the air flowing into Therefore, it is preferable because the temperature in the width direction of the downstream heat setting zone is stabilized. The product of the temperature difference and the wind speed difference is preferably 200 ° C. · m / s or less, and more preferably 150 ° C. · m / s or less.

(2) Adjustment of Plenum Duct Cut-off Conditions in Heat Fixing Device In the production of the film roll of the present invention, individual plenum ducts are not attached as shown in FIG. It is necessary to attach the rod-shaped shielding plates S, S,... So as to shield the hot air outlets (nozzles) 2, 3,. By using such a discontinuous shielding plate, “circulation of hot air” is performed smoothly. Moreover, it is preferable not to attach the same length of the shielding plate to each plenum duct, but to gradually increase the length of the shielding plate from the inlet to the outlet (film passing direction) of the heat fixing device (see FIG. 5). . Thus, by adjusting the length, the temperature of the hot air exposed to the film edge is adjusted, and the elimination of distortion at the film edge is promoted. The material of the shielding plate may be any material as long as it can withstand the temperature of the heat fixing device and does not stain the film or adhere the film, but it is the same material as the plenum duct from the viewpoint of thermal expansion. Is preferably used.

(3) Blocking of heating between the stretching zone and the heat setting device (installation of an intermediate zone)
The biaxially stretched polyethylene terephthalate resin film roll is usually heat-set after being longitudinally and laterally stretched. In the production of the film roll of the present invention, it is desirable to install an intermediate zone in which active hot air is not blown between the zone that is longitudinally and transversely stretched and the heat setting device that is heat set. As a result, the heat is completely shut off between the stretching zone and the heat setting device. More specifically, when a strip-shaped paper piece is hung between the stretching zone and the heat setting device in the state where the drawing zone and the heat setting device are in the same condition as in film production, the paper piece is almost completely removed. It is preferable to block the hot air from the stretching zone and the heat fixing device so as to hang down in the vertical direction. Note that such an intermediate zone may be surrounded by a housing, or may be provided so that a continuously manufactured film is exposed. When the hot air is sufficiently blocked in the intermediate zone, the shielding effect of the shielding plate in the heat fixing device is exhibited, and good film flatness during post-processing can be obtained. There may be no intermediate zone at the transverse stretching temperature in the present invention.

  As described above, by adopting the above methods (1) to (3), the “hot air circulation” in the heat fixing device can be smoothly executed, and the “temperature hunting phenomenon” can be suppressed. As a result, relaxation in the longitudinal direction can be sufficiently promoted at the edge of the width direction, and "flatness in a long film" and "flatness when heat treatment in post-processing is performed at a high temperature" It becomes possible to improve. In the above description, the method of suppressing the “temperature hunting phenomenon” by smoothly executing “circulation of hot air” in the heat fixing device in which the plenum duct is installed. The above description discloses the technical idea of how the film roll of the present invention can be obtained by applying thermal energy to the film at the production level. It can be easily carried out by a method different from the above-described method, and the film of the present invention can be obtained by a different method. For example, instead of providing a shielding plate, an infrared heater may be used to increase the temperature in the film width direction from the center to the end. In other words, even with another type of heat fixing device, the "circulation of hot air" is smoothly executed to suppress the "temperature hunting phenomenon" and then sufficiently relaxed in the longitudinal direction at the edge of the width direction. By imparting sufficient heat energy to the film, the film having improved “flatness in a long film” and “flatness when heat treatment in processing is performed at a high temperature” like the film of the present invention. It is possible to obtain

<Characteristics of polyethylene terephthalate resin film>
The film of the present invention produced by the above-described method is excellent in transparency, thickness unevenness (particularly longitudinal thickness unevenness), and optical performance, and is used for prism lens sheet base films and hard coat films used in LCDs. Base film, base film for AR film, base film for diffusion plate, anti-crushing film for CRT, transparent conductive film used for touch panel and electroluminescence, near infrared absorbing film and electromagnetic wave absorbing film used for front plate of plasma display, etc. Can be suitably used.

The thickness of the film constituting the polyethylene terephthalate-based resin film of the present invention is 70 μm or more and 400 μm or less when the film is used for a sheet as an optical application or a printing application . If the thickness of the film is 70 μm or more, it is preferable because the film can be handled easily. Further, the thickness of the film is preferably 400 μm or less, more preferably 300 μm or less, and further preferably 250 μm or less. If the thickness of the film is 400 μm or less, it is preferable because cutting processing becomes easy.

  The polyethylene terephthalate resin film of the present invention may be a single layer or a laminate structure of two or more layers. In addition, with an emphasis on transparency, various coatings for the purpose of improving the adhesion during post-processing and improving the slipperiness on one or both sides of a biaxially stretched polyethylene terephthalate resin film that does not contain fine particles No matter what is given at the time of film formation.

  Moreover, in the polyethylene terephthalate-type resin film which comprises the film of this invention, microparticles | fine-particles can be added as needed. Examples of the fine particles added at that time include known inorganic fine particles and organic fine particles. Furthermore, in the resin forming the film, various additives as necessary, for example, waxes, antioxidants, antistatic agents, crystal nucleating agents, viscosity reducing agents, heat stabilizers, coloring pigments, An anti-coloring agent, an ultraviolet absorber and the like can be added. It is preferable to add fine particles to the polyethylene terephthalate resin in the present invention to improve the workability (slidability) of the polyethylene terephthalate resin film. Any fine particles can be selected. Examples of inorganic fine particles include silica, alumina, titanium dioxide, calcium carbonate, kaolin, and barium sulfate. Examples of the organic fine particles include acrylic resin particles, melamine resin particles, silicone resin particles, and crosslinked polystyrene particles. The average particle diameter of the fine particles can be appropriately selected as necessary within a range of 0.05 to 2.0 μm.

  Examples of the method of blending the above-mentioned particles into the polyethylene terephthalate resin film include a method of adding at any stage of producing the polyethylene terephthalate resin, but preferably the esterification stage or the end of the transesterification reaction. Thereafter, a method of adding the slurry dispersed in ethylene glycol or the like at the stage before the start of the polycondensation reaction and advancing the polycondensation reaction may be employed. Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyethylene terephthalate resin raw material, or a dried particle and a polyethylene terephthalate system using a kneading extruder It can be performed by a method of blending with a resin raw material.

  Furthermore, the polyethylene terephthalate resin film constituting the film of the present invention can be subjected to corona treatment, coating treatment, flame treatment, etc. in order to improve the adhesion of the film surface.

  The film of the present invention produced by the method described above has excellent transparency, thickness unevenness (particularly, thickness unevenness in the longitudinal direction), flatness during processing, and high-temperature processing at 80 to 180 ° C. In addition to having good passability, generation of whiskers and the like at the cut edge can be suppressed at the time of cutting the film, and it can be suitably used as an optical film, precision printing applications, and a base film used on a sheet.

  Hereinafter, the present invention will be described in detail by way of examples. However, the present invention is not limited to the embodiments of the examples, and can be appropriately changed without departing from the spirit of the present invention. . In addition, the evaluation method of a film characteristic is as follows.

(1) Measurement of Δn _ab Film specimens were sampled from positions within 50 mm and the center of the obtained film from both ends parallel to the film winding direction. After leaving the film test piece in an atmosphere of 23 ° C. and 65% RH for 2 hours or more, using an “Abbe refractometer 4T type” manufactured by Atago Co., Ltd., in a direction forming an angle of 45 degrees with the film winding direction. refractive index (n _a), and the refractive index in the direction (i.e., the direction forming an angle of direction and 90 degrees 45 degrees as described above) at an angle of winding direction and 135 degrees in the wound film (n _b ) Were measured respectively. The calculated absolute value of the difference between the two refractive index thereof as [Delta] n _ab. The absolute value of the difference between these two refractive indexes is Δn _ab, and Δn _ab = | n _a −n _b | It was confirmed that Δn _ab at both ends and the center of the film roll was 0.015 or more and 0.060 or less, and the largest value was designated as Δn _ab in the table. In the present invention, the winding direction of the film is also referred to as the longitudinal direction or the longitudinal direction of the film.

(2) Longitudinal thickness variation rate (thickness unevenness)
The film sample was sampled in a long roll shape with a film length of 30 m and a width of 30 mm along the winding direction of the film. The thickness is continuously measured along the longitudinal direction (measurement length is 30 m). Then, assuming that the maximum thickness at the time of measurement is Tmax, the minimum thickness is Tmin, and the average thickness is Tave, the thickness variation rate in the winding direction of the film is calculated from Equation 1 below.
Thickness variation rate = {(Tmax−Tmin) / Tave} × 100 (%). Formula 1

(3) Breaking strength [TS], elongation at break [TE]
The film winding direction (MD direction), the direction forming an angle of 45 degrees (A direction), the direction forming an angle of 90 degrees (TD direction), and the direction forming an angle of 135 degrees (B direction) Samples of film specimens having a width of 12.7 mm and a length of 200 mm were sampled from four locations. The film test piece was set in a tensile tester (manufactured by ORIENTEC, Tensilon RTC-125A), and stretched at a distance between chucks of 100 mm and a take-off speed of 200 mm / min in an environment of a temperature of 23 ° C. and a humidity of 65% RH, and fractured. Stress and film elongation were measured. The breaking strength (MPa) and the breaking elongation (%) were determined from the average values of the two measurements.

(4) Cutting property of film A film is cut with a guillotine cutter, and the cutting property is evaluated. The cutting property means, for example, the ease of cutting with scissors or a cutter, and means that the cut surface is smooth. Although the cutting property varies depending on the cutting method, it was cut over a length of 200 mm using a cutting machine (DN-1N, manufactured by KOKUYO), and the state of the cut surface was visually observed. The cutting test was performed 30 times, and was evaluated as follows according to the state.
Judgment ○: Chips are not generated and cut hairs are not generated.
Δ: Chips or cut mustaches occur 1 to 10 times.
X: Chips or cut mustaches occur 11 times or more.

(5) Thermal contraction rate of film (HS150)
A film having a length in the width direction of Δn _ab of 0.015 or more and 0.060 or less and a length of 70 cm or more is equally divided into five. A cutout portion is provided at the center in the width direction for each of the divided five films. A sample film having a width of 20 mm and a length of 250 mm is cut out from each cutout portion along the film winding direction, and five film samples are cut out. Marks are marked at intervals of 200 mm on the sample having a width of 20 mm and a length of 250 mm cut out in the above, put in a heating oven adjusted to 150 ° C., and heat shrinkable for each film in accordance with JIS / C-2318. Measure the rate. Further, the difference between the maximum value and the minimum value is defined as a heat shrinkage rate difference.

(6) Using a flat roll-like film of processed film, using an air-floating and conveying type drying device with a coater having a distance of 38 cm between the lower and upper air flow outlets, at a conveying tension of 2000 kPa and a temperature of 160 ° C. for 16 seconds. A processed model film was obtained. For cooling, the film was cooled at a rate of 20 ° C./second using a 50 ° C. cooling roll, and then wound on the roll. After 7 days of winding on the roll, the film was drawn from the roll and the flatness of the film was observed. . That is, a processed model film having a width of 100 cm is set to a length of about 3 m in a room at a temperature of 25 ° C. and a humidity of 65%, and a reflected image reflected on the film is held while the two are lightly pulled in the longitudinal direction and the width direction by two people. Look to see if there is any tarmi.
Judgment O: No tarmi x: Talm.

(7) Film permeability The flatness of the film after heat treatment was evaluated by the following method. As a heat treatment step, a coater having a distance between two rolls of 1,900 mm was used, the temperature was set to 100 ° C. or 160 ° C., and the furnace tension was set to 100N. Next, two rolls are horizontally arranged so that the roll interval is 2,000 mm, and further, the iron bar is positioned at the center position of the two rolls at a position 30 mm below the common tangent of the roll upper surface. Arranged. The film passed through the heat treatment step was passed between two rolls under a tension of 98N. When the film was allowed to pass through, it was marked as ◯ when the film was not in contact with the iron bar, and x when it was in contact with the iron bar. These steps were performed continuously, and it was visually confirmed whether or not the film contacted the iron bar.

  In addition, Table 1 shows film forming conditions of the films in Examples and Comparative Examples.

[Example 1]
Polyethylene terephthalate ([η] = 0.60) containing 0.03% by mass of silica particles as an additive was dried so that the moisture content was 50 ppm or less, and then charged into a hopper immediately above the extruder and placed in 285 in the extruder. The resin was melted at a temperature of 0 ° C., and the melted resin was filtered through a filter material of stainless sintered body (nominal filtration accuracy: particles having a size of 10 μm or more were cut by 90%). Next, the resin sheet was extruded from a T-shaped die, and was wound around a casting drum having a surface temperature of 30 ° C. by using an electrostatic application casting method, and then cooled and solidified to obtain an unstretched sheet having a thickness of about 1710 μm.

  And after heating up the obtained unstretched sheet with the heated roll group, and extending | stretching 3.5 time, the longitudinally stretched film is led to a tenter and the 1st zone is width | variety in 140 degreeC atmosphere. Stretch 2.0 times in the direction, stretch the second zone to 3.0 times in an atmosphere of 155 ° C, stretch the third zone to 4.0 times at 180 ° C, and then heat set at 233 ° C Then, a transverse relaxation treatment of 2.2% was performed at 215 ° C., both edges were cut and removed, and wound into a roll to obtain a biaxially stretched film having a thickness of about 125 μm. And the characteristic of the obtained film was evaluated by each measuring method mentioned above. Table 4 shows the evaluation results.

[Heat setting]
The heat setting process was performed by a heat setting apparatus having a structure as shown in FIG. The heat setting device is divided into four heat setting zones called first to fourth zones, and eight plenum ducts a to x are provided in the first to third zones, respectively. In addition, eight plenum ducts are provided. Each plenum duct is vertically installed at 400 mm intervals with respect to the film traveling direction so as to be perpendicular to the film traveling direction. And hot air is sprayed on the film extended | stretched from the hot air blowing outlet (nozzle) of those plenum ducts.

  In Example 1, discontinuous rod-shaped shielding plates S, S,... Were attached to the hot air outlets of 15 plenum ducts a to o in the manner shown in FIG. FIG. 5 shows a state where the heat fixing device having the shielding plates S, S,... Attached to the hot air outlets of the plenum ducts a to o is viewed from above, and each of the attached shielding plates S, S,. The center in the longitudinal direction is set so as to substantially coincide with the center of the width of the film passing through the heat fixing device. Further, the length of each shielding plate S, S... (The dimension in the width direction of the film to be manufactured) is adjusted so that it gradually becomes wider (that is, widens toward the end) from the inlet to the outlet of the heat fixing device. Has been. Table 2 shows the shielding ratio of the hot air outlets of each of the plenum ducts a to o (the shielded area of the hot air outlet by the shielding plate / the area of the hot air outlet). In addition, let the shielding aspect by the shielding board in Example 1 be "A aspect."

  In Example 1, the temperatures and wind speeds in the first to fourth zones of the heat setting device were adjusted as shown in Table 3. In addition, in the temperature conditions of the 1st-4th zone of the heat setting apparatus of Example 1, and the wind speed conditions, the product of the temperature difference between the adjacent heat setting zones and the wind speed difference is 250 ° C. · m / s or less. The temperature and wind speed conditions in the first to fourth zones in Example 1 are defined as “I condition”.

[Example 2]
The unstretched sheet was obtained in the same manner as in Example 1 except that the speed of winding on the casting drum was changed to make the thickness of the unstretched sheet about 2290 μm, and cooling was performed using cooling air by air when it was wound on the casting drum. The obtained unstretched sheet was stretched in the same manner as in Example 1 except that the longitudinal stretching ratio was changed to 3.1 times. A biaxially stretched film of about 188 μm was obtained in the same manner as in Example 1 except that the preheating / stretching temperature for transverse stretching was changed as shown in Table 1 and the heat setting conditions were changed as shown in Tables 2 and 3. The evaluation results are shown in Table 4.

[Example 3]
Biaxial stretching of about 250 μm as in Example 2 except that the speed of winding around the casting drum was changed, the thickness of the unstretched sheet was about 3050 μm, and cooling was performed using cooling air by air when wound around the casting drum. A film was obtained. The evaluation results are shown in Table 4.

[Comparative Example 1]
A biaxially stretched film was obtained in the same manner as in Example 1 except that the longitudinally stretched film obtained in the same manner as in Example 1 was changed as shown in Table 1 in the preheating and stretching temperature of the transverse stretch. The evaluation results are shown in Table 4.

[Comparative Example 2]
A biaxially stretched film was obtained in the same manner as in Example 2, except that the longitudinally stretched film obtained in the same manner as in Example 2 was changed in the preheating / stretching temperature in the lateral stretch as shown in Table 1. The evaluation results are shown in Table 4.

[Comparative Example 3]
A biaxially stretched film was obtained in the same manner as in Example 1 except that the longitudinally stretched film obtained in the same manner as in Example 1 was changed as shown in Table 1 in the preheating and stretching temperature of the transverse stretch. The evaluation results are shown in Table 4.

[Comparative Example 4]
A biaxially stretched film was obtained in the same manner as in Example 1 except that the heat setting conditions of the longitudinally stretched film obtained in the same manner as in Example 1 were changed as shown in Table 1. The evaluation results are shown in Table 4.

[Comparative Example 5]
A biaxially stretched film was obtained in the same manner as in Example 2 except that the heat setting conditions of the longitudinally stretched film obtained in the same manner as in Example 2 were changed as shown in Table 1. The evaluation results are shown in Table 3.

[Comparative Example 6]
A biaxially stretched film was obtained in the same manner as in Example 3 except that the longitudinally stretched film obtained in the same manner as in Example 3 was changed in the prestretching / stretching temperature of the transverse stretch as shown in Table 1. The evaluation results are shown in Table 4.

  Since the polyethylene terephthalate resin film of the present invention has excellent characteristics as described above, during high-temperature processing at 80 to 180 ° C., the difference in heat shrinkage in the longitudinal direction is small in the width direction and the film meanders. It is easy to pass through the process, and also suppresses the occurrence of whiskers at the cut when cutting the film, and passes through the optical film and the process to be processed. In addition, since there is no collapse of flatness, it can be suitably used as an optical film used on a sheet or a processing film having excellent transparency and flatness when used in precision printing applications. it can.

Explanatory drawing (a) which shows the shielding aspect by the conventional shielding board shows the vertical cross section of a part of heat setting apparatus, (b) is the state which attached the shielding board to the hot-air blowing outlet of the plenum duct Is a view from above.) The figure of Unexamined-Japanese-Patent No. 2002-79638 shows that the wind speed which is shielded by the shielding plate of the plenum duct and blows out from the plenum duct is different for each plenum duct. It is explanatory drawing which shows the shielding aspect by the shielding board in this invention. (A) shows a vertical section of a part of the heat fixing device, and (b) shows a state in which a shield plate is attached to the hot air outlet of the plenum duct as viewed from above. is there. It is explanatory drawing which shows the state which saw through the heat fixing apparatus used by the Example and the comparative example from the top. It is explanatory drawing which shows the shielding aspect by a shielding board.

Explanation of symbols

F: Film S: Shielding plate A: Film winding direction Z1: First zone Z2: Second zone Z3: Third zone Z4: Fourth zone N1, N2, N3: Intermediate zone HS: Heat fixing zone 1: Heat Fixing device 2: Hot air outlet 3, ax: Plenum duct

Claims (5)

A polyethylene terephthalate resin film having a difference Δn _ab of 0.015 or more and 0.060 or less between a refractive index in a direction forming an angle of 45 degrees with a winding direction of the film and a refractive index in a direction forming an angle of 90 degrees with the film winding direction. A polyethylene terephthalate resin film characterized by satisfying the following requirements (1) to ( 5 ).
(1) Ratio TS / TE of breaking strength TS and breaking elongation TE in a direction forming an angle of 45 degrees with the winding direction of the film, and breaking strength TS in a direction forming an angle of 135 degrees with the winding direction of the film The ratio TS / TE of the breaking elongation TE, the ratio TS / TE of the breaking strength TS in the winding direction and the breaking elongation TE, and the breaking strength TS in the direction (width direction) forming an angle of 90 degrees with the winding direction The ratio TS / TE of the breaking elongation TE is 0.6 (MPa /%) or more and 2.6 (MPa /%) or less. (2) About the film whose length in the width direction of the film is 70 cm or more HS150, which is the heat shrinkage rate in the film winding direction when heated at 150 ° C. for 30 minutes for five samples that were equally divided into five in the film width direction and cut out from the center in the width direction of each of the five divided films. H The difference between the maximum and minimum values of 150 is 0.1% or less (3) The five samples HS150 be both 2.0% or less than 0.7%
(4) The thickness variation rate in the winding direction of the film is 6% or less.
(5) The thickness of the film is 70 μm or more and 400 μm or less. A manufacturing method for producing polyethylene terephthalate resin film of claim 1, and a film forming an unstretched sheet by melt extruding the material resin from the extruder, in the film of step A biaxial stretching step for biaxially stretching the resulting unstretched sheet in the machine direction and the transverse direction, and a heat setting step for heat-setting the film after biaxial stretching. 6 )-( 10 ) is satisfied, and the heat setting step satisfies the following requirements ( 11 )-( 13 ): A method for producing a polyethylene terephthalate-based resin film.
(6) In the transverse stretching step, the difference in the set temperature of the continuous temperature zone is 5 ° C. or higher and 30 ° C. or lower in the first half of the horizontal stretching (up to the temperature zone where the draw ratio includes 1.8 times). ( 7 ) The temperature range that passes 1.8 times in the stretching in the transverse stretching step is 100 ° C. or more and less than 160 ° C. ( 8 ) In the transverse stretching step, the difference in temperature setting in the continuous temperature zone is the transverse stretching. Between the first half (up to the temperature zone including the draw ratio of 1.8 times) and the first temperature zone of the next second half is 5 ° C. to 40 ° C. ( 9 ) The difference in the temperature setting of the temperature section to be performed is 5 ° C. or more and 30 ° C. or less in the latter half of the transverse stretching (from the temperature section area next to the temperature section area including the draw ratio of 1.8 times to the final draw ratio). stretching in it (10) transverse stretching Oite final drawing that temperature range to reach a magnification of 220 under ° C. 160 ° C. or higher (11) wider plurality of plenums ducts blowing hot air, is arranged to face up and down relative to the traveling direction of the film ( 12 ) A shielding plate for shielding hot air outlets is attached to the plurality of plenum ducts. ( 13 ) The dimension of each shielding plate in the traveling direction of the film is equal to each plenum in the traveling direction of the film. It is adjusted to be substantially the same as the size of the duct outlet, and the size of each shielding plate in the width direction of the film is adjusted to become gradually longer with respect to the film traveling direction. In the biaxial stretching process, the film is stretched in the transverse direction after stretching the film in the longitudinal direction, and an intermediate zone that does not perform wind blowing is provided between the zone that performs the transverse stretching and the heat setting device. The method for producing a polyethylene terephthalate resin film according to claim 2 . The heat setting device is divided into a plurality of heat setting zones, and the product of the temperature difference and the wind speed difference between adjacent heat setting zones is set to be 250 ° C. · m / s or less. The method for producing a polyethylene terephthalate-based resin film according to claim 2 or 3 , wherein: When melt extrusion of the polyester, in any melt line, the initial filtration efficiency using the media filter particle size is less 15μm 95% or more, in any one of claims 2 to 4, characterized in that the microfiltration Of manufacturing polyethylene terephthalate resin film

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