JP2010167768A - Biaxially stretched polyethylene terephthala-based resin film and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially stretched polyethylene terephthalate-based resin film which is excellent in dimensional stability and is extremely less in thickness unevenness, and in which scratches causing optical defects hardly exist on its surface. <P>SOLUTION: The biaxially stretched polyethylene terephthalate-based resin film is manufactured through a biaxial stretching step and a thermal fixing step, and is obtained by narrowing the heating width in a vertical stretching step in the longitudinal direction, wherein, the thickness unevenness is ≥0.5% to ≤4%, the number of the scratches is ≤10 m<SP>2</SP>, and an average HS150 is ≥-0.25% to <0.40%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a biaxially stretched polyethylene terephthalate resin film, and more specifically, a biaxially stretched polyethylene terephthalate system suitable for various processing applications having a small thickness variation rate, less scratches, and less dimensional change due to heat. The present invention relates to a resin film.

  Biaxially oriented films made of polyethylene terephthalate resin are widely used as various processing base films because of their excellent transparency, dimensional stability, and chemical resistance. Widely used as a base material for precision printing such as mold release for green sheet manufacturing for ceramic capacitors, which is required for excellent strength and dimensional stability, base film such as transfer foil, and offset printing It's being used. Moreover, it is used also as a base material of various optical films used in the state which permeate | transmitted and reflected light. A relatively thin film is used in the former, and a relatively thick film is used in the latter because strength and dimensional stability are required.

  The biaxially stretched polyethylene terephthalate resin film for precision applications as described above has better flatness (flatness when placed on a flat table) than films for normal packaging applications. Required. In particular, a relatively thin film used for a substrate film such as a mold release for producing a green sheet for a ceramic capacitor or a transfer foil is easily affected by a thickness variation rate. On the other hand, with the recent high precision printing and high performance of optical products, the demand for flatness has become higher. The applicants consider that it is essential to improve the thickness unevenness of the film (particularly, the thickness unevenness in the longitudinal direction) in order to develop such good flatness (for example, a patent application). 2007-308374, Japanese Patent Application No. 2007-308375). As a method for reducing the uneven thickness of the biaxially stretched polyethylene terephthalate resin film, as disclosed in Patent Document 1, a stretching method in which stretching at a relatively low magnification is repeated in multiple stages, or as disclosed in Patent Document 2, A stretching method is known in which stretching at a high magnification is performed at a temperature and then stretching at a low magnification is performed.

  In addition, as in Patent Document 3, in the stretching step of stretching a thermoplastic resin film having an average thickness in the range of 10 μm to 800 μm between the low speed roll and the high speed roll, at least in a non-contact manner. In addition, a method of heating a film using a heat source of 30 kW / m or more and 200 kW / m or less, or a heating means provided 5 mm to 100 mm before the contact point between the film and the stretching roll as in Patent Document 4, longitudinally A method of heating over a width of 3 to 30 mm and stretching in the film flow direction with a stretching roll, and further, as in Patent Document 5, in addition to the method of Patent Document 4, in a plurality of stages in the film flow direction with a stretching roll. Methods of stretching are known (note that these stretching methods will be described in detail later).

  Furthermore, as in Patent Document 6, a film is known in which an easy-sliding layer containing spherical particles is provided on at least one surface of a polyester film, and fine particles resulting from a catalyst are present in the polyester film.

  On the other hand, for precision printing applications and optical applications, it is desired to have excellent transparency and to have as few optical defects as possible. As the performance of products increases, so does the demand for reducing optical defects. Such optical defects are caused by scratches on the surface of the base film. If there are minute scratches on the surface of the base film, for example, there may be an optical defect in a display portion of a liquid crystal display (LCD). As a method of suppressing the occurrence of such scratches, as in Patent Document 7, the surface roughness of the roll, the prevention of deposit accumulation on the roll surface, the regulation of cleanness, a method of cleaning the roll using an abrasive, Regulating static electricity on film, reducing roll surface roughness, reducing roll diameter, improving film adhesion to roll, regulating temperature between rolls, regulating roll speed, regulating running tension, surface modification Methods such as drying conditions in the resin coating process, regulation of cooling conditions, regulation of the friction coefficient between the film and roll, regulation of the rotational resistance of the free roll, regulation of heat shrinkage stress after longitudinal stretching, and the like are disclosed.

  In addition, when a biaxially stretched polyethylene terephthalate resin film is used as the base film, heat treatment may be performed in a subsequent process. Although the dimensions of the film are changed by such heat treatment, it is desired that the heat shrinkage due to the heat treatment step is small in precision processing. In applications that particularly dislike dimensional changes, an annealing process is performed again before processing, before use.

  As a method of reducing the thermal shrinkage rate of the biaxially stretched polyethylene terephthalate resin film, a method in which the relaxation treatment in the longitudinal direction is performed in an off-line heat treatment process (Patent Document 8), and a razor is cut at the end of the tenter. A method of performing relaxation processing in the longitudinal direction while avoiding the influence of clips (Patent Document 9) and a method of performing relaxation processing in the longitudinal direction by gradually narrowing the clip interval of the tenter (Patent Document 10) have been proposed. .

JP-A 48-43772 Japanese Patent Laid-Open No. 54-56774 Japanese Patent Laid-Open No. 11-170357 JP 2000-181015 A JP 2000-181016 A International Publication No. 03/093008 Pamphlet JP 2002-254565 A JP 2001-138466 A Japanese Examined Patent Publication No.57-054290 Japanese Patent Publication No. 4-0221818

  The film processing is expected to be further refined in the future. Thereby, even if it was a film used conventionally without a problem, it was thought that a problem arose in the point of flatness. For example, in a release sheet for a ceramic capacitor, there is a concern that the flatness of the base film may cause a problem of yield reduction when the capacitor is thinned. Also. In optical applications, fine planarity of the substrate film may cause optical problems due to the refinement of the optical design. Furthermore, as processing becomes more precise, it is predicted that yield reduction due to surface flaws will become more problematic than before.

  However, in each of the stretching methods of Patent Document 1, Patent Document 2, Patent Document 4, and Patent Document 5, each stretching at the time of multi-stage stretching is a simple stretching using a difference in peripheral speed between heated rolls. Therefore, the film is rubbed on the low-speed roll due to the film being stretched from the heated low-speed roll, and many scratches that may cause optical defects are generated on the film surface.

On the other hand, although the generation of scratches is reduced by the methods of Patent Document 3 and Patent Document 7, thickness unevenness cannot be reduced to a high degree, and a biaxially stretched polyethylene terephthalate system that satisfies a high level requirement for recent planarity A resin film cannot be obtained at all. The particle size of the fine particles due to the catalyst in Patent Document 6 are described a method of 1~10μm fine particles with 200 to 20,000 pieces / mm ^2, the stretching is 200 / mm ² or less Uniformity tends to be poor, and unevenness in thickness and orientation is likely to occur. However, in the case of particles based on a catalyst, variation in particle formation occurs due to slight fluctuations in temperature and pressure during polymerization, and it is difficult to control the particle amount and particle size (see, for example, JP-A-5-154969). That is, conventionally, the biaxially stretched polyethylene terephthalate resin film suitable for precision printing applications and optical applications that have a highly reduced thickness unevenness and good flatness and have few scratches that can cause optical defects on the film surface It did not exist.

  On the other hand, also in the case of reducing the heat shrinkage rate, it is not economical to perform off-line processing with the method of Patent Document 8. Further, the method of Patent Document 9 is not affected by the gripping of the clip, but has a problem that the film is loosened by its own weight during the relaxation treatment, and the film comes into contact with the plenum duct in the tenter and is damaged. To avoid this, finely adjusting the upper and lower air balance to prevent scratches, the air balance collapses the temperature uniformity in the oven, and the flatness of the film deteriorates or the uniformity is impaired. There was a problem. Furthermore, in the method of Patent Document 10, the ease of movement of the film at the end portion and the central portion at the time of clipping is different, and a difference in physical properties between the vicinity of the grip portion in the longitudinal direction and the central portion is unavoidable, and the thermal shrinkage rate is reduced. Therefore, when relaxation is increased, the flatness of the film is deteriorated.

  The present invention has been made in view of the above circumstances, and its main purpose is that the thickness unevenness is extremely small and the flatness is good, and there is almost no scratch on the film surface that can be an optical defect. An object of the present invention is to provide a biaxially stretched polyethylene terephthalate resin film suitable for precision printing applications and optical applications having a low thermal shrinkage rate.

Among the present inventions, the first invention is a film-forming process for forming an unstretched film by melt-extruding a raw material resin from an extruder, and an unstretched film obtained in the film-forming process in a longitudinal direction and a transverse direction. A biaxially stretched polyethylene terephthalate resin film manufactured through a biaxial stretching step for biaxial stretching and a heat setting step for heat fixing the film after biaxial stretching, wherein the width of heating is increased in the longitudinal stretching step. It is a biaxially stretched polyethylene terephthalate resin film characterized by satisfying the following requirements (1) to (3) obtained by narrowing in the longitudinal direction.
(1) A film sample having a length of 30 m and a width of 3 cm is taken along the longitudinal direction of a biaxially stretched polyethylene terephthalate-based resin film from a film cutting portion provided by the following cutting method A, and the thickness variation in the longitudinal direction of the film sample The thickness variation rate in the longitudinal direction is 0.5% or more and 4% or less (cutting-out method A)
At both end portions in the film width direction (portions within 50 mm from the edge), film cutout portions are provided at the beginning, middle and end of the film in the longitudinal direction. Here, the “starting portion” and “end portion” refer to a region including the length of the film in the longitudinal direction within 2 m from the end portion. Further, the “intermediate portion” refers to a region including 50% position in the film longitudinal direction. (2) A length along the longitudinal direction of the biaxially stretched polyethylene terephthalate resin film from the film cutting portion provided by the following cutting method B An average HS150, which is an average value of the heat shrinkage rate in the longitudinal direction of the film when a film sample of 250 mm × width 20 mm is taken and heated at 150 ° C. for 30 minutes, is −0.25% or more and 0.40. % (Cutout method B)
A biaxially stretched polyethylene terephthalate-based resin film is divided into four portions in the width direction and a portion 50 mm from the end in the width direction, and five cutout portions are provided. The cut-out portions in the width direction are provided at the start, middle and end of the roll (15 in total). Here, “winding start” and “winding end” of the roll are regions of 50 mm or more and 2 m or less from the end of the winding start and the end of winding of the entire film roll, and “intermediate” is the film longitudinal direction It is an area including the 50% position.
(3) About 16 film samples having a length of 250 mm and a width of 250 mm collected from the film cutting portion provided by the following cutting method C, the following measurement method was used to measure scratches having a depth of 1 μm or more and a length of 3 mm or more on the surface. When the number is measured, the number of scratches is not more than 10 / m ² (cutout method C)
From the biaxially stretched polyethylene terephthalate resin film, the beginning (5% of the total length in the longitudinal direction) and two intermediate portions (35% of the total length in the longitudinal direction, 65%) with respect to the length in the longitudinal direction of the film Position) and the end part (position of 95% of the total length in the longitudinal direction), the position of the center line of the part sampled from both ends in the width direction is divided into three equal parts in the width direction as the center line Provide a part.
(A) Scratch detection method By the following optical defect detection method, an optical defect recognized as a size of 50 μm or more is detected for 16 film samples of 250 mm × 250 mm.
[Optical defect detection method]
A fluorescent lamp of 20 W × 2 lamps is arranged as a projector at 400 mm below the XY table, and a film sample to be measured is placed on a mask having a slit width of 10 mm provided on the XY table. Light is incident so that the angle between the line connecting the projector and the receiver and the vertical direction of the film sample surface is 12 °, and the reflected light amount is converted into an electrical signal by a CCD image sensor camera placed 500 mm above the XY table. The electric signal is converted, amplified, differentiated, and compared with a threshold (threshold) level by a comparator to output an optical defect detection signal. This threshold value is preliminarily formed by drilling a hole of about 50 μm on a 2 mm thick aluminum plate, polishing burrs formed on the aluminum plate, and finishing the surface with a No. 200 buff. It adjusted so that a hole of 50 micrometers might be detected using this. Also, using a CCD image sensor camera, a scratch image is input, the video signal of the input image is analyzed by a predetermined procedure, the size of the optical defect is measured, and the position of the defect of 50 μm or more is displayed. To do. Optical defects are detected on both sides of the film sample.
(B) Measurement of Scratch Size A defect due to a scratch is selected from the optical defect portion detected in (a) above. The film sample is cut into an appropriate size, and observed using a three-dimensional shape measuring device TYPE550 manufactured by Micromap Co., Ltd. from the direction perpendicular to the surface of the film sample, and the size of the scratch is measured. When observed from the direction perpendicular to the surface of the film sample, that is, the film surface, the unevenness of the scratches close to each other within 50 μm is regarded as the same scratch, and the length and width of the rectangle with the smallest area covering the outermost part of those scratches are set. The length and width of the scratch. From this result, the number of scratches (pieces / m ² ) having a depth of 1 μm or more and a length of 3 mm or more is obtained.
Among the present inventions, the second invention is the biaxially stretched polyethylene terephthalate resin film, wherein the biaxially stretched polyethylene terephthalate resin film has a thickness of 20 μm or more and 400 μm or less.
Of the present invention, a third invention is a biaxially stretched polyethylene terephthalate resin film roll comprising the biaxially stretched polyethylene terephthalate resin film.
Among the present inventions, the fourth invention is a production method for producing the biaxially stretched polyethylene terephthalate resin film, wherein the raw resin is melt-extruded from an extruder to form an unstretched film. A biaxial stretching process in which the unstretched film obtained in the film forming process is biaxially stretched in the machine direction and the transverse direction, a heat setting process in which the film after biaxial stretching is heat-set, and a relaxation treatment in the longitudinal direction The longitudinal stretching step is performed by heating to 105 ± 20 ° C. using a heating device while narrowing the heating width between rolls having a difference in peripheral speed, and 2 in the longitudinal direction. After stretching to a magnification of 0.0 times or more and 3.2 times or less, the film after the longitudinal stretching is passed between cooled nip rolls, and the heating width is narrowed between the rolls provided with a peripheral speed difference. Biaxially stretched polyethylene terephthalate, which is heated to 100 ± 20 ° C. using a heating device while being stretched and stretched in the longitudinal direction so as to have a magnification of 1.05 times to 1.5 times This is a method for producing a resin film.
Among the present inventions, the fifth invention is characterized in that when the film is heated using a heating device in the longitudinal stretching step, the heating width in the longitudinal direction between the rolls is 2 mm or more and 25 mm or less. This is a method for producing an axially stretched polyethylene terephthalate resin film.
Among the present inventions, the sixth invention is such that after the maximum temperature portion in the transverse stretching step and then the transverse relaxation treatment is performed, the film edge portion is cut and separated, and then the edge portion is cut. In the method for producing a biaxially stretched polyethylene terephthalate resin film, the longitudinal relaxation treatment is performed by reducing the take-up speed of the separated film.
Of the present invention, the seventh invention is the biaxially stretched polyethylene terephthalate-based resin film, wherein the film is cooled while retaining the film edge after the longitudinal relaxation treatment. It is a manufacturing method.

  The biaxially stretched polyethylene terephthalate-based resin film of the present invention has good dimensional stability, extremely small thickness unevenness (particularly, thickness unevenness in the longitudinal direction) and good flatness, and scratches that may cause optical defects. Almost no surface. Therefore, the biaxially stretched polyethylene terephthalate-based resin film of the present invention is a basis for use in precision printing such as mold release for manufacturing green sheets for ceramic capacitors, substrate films such as transfer foil, and offset printing. Prism sheets used for liquid crystal displays for optical applications as materials for optical printing, and for various optical films used in the state of transmitting and reflecting light, and base films such as anti-reflection films and hard coat films, light diffusion plates, Optical applications such as base films for near-infrared absorbing films and electromagnetic wave absorbing films used for the front plates of plasma displays, transparent conductive films for touch panels and electroluminescence, and anti-crushing films for cathode ray tubes, back sheets for solar cells Can be suitably used for film . In addition, according to the method for producing a polyethylene terephthalate resin film of the present invention, it is possible to efficiently produce a biaxially stretched polyethylene terephthalate resin film suitable for optical applications and processing applications as described above at low cost.

It is explanatory drawing which shows the stress distortion curve (SS curve) of the polyethylene terephthalate-type resin film in a deformation rate of 30,000% / min. It is explanatory drawing of the cutting-out method A. FIG. It is explanatory drawing of the cutting-out method B. FIG. It is explanatory drawing of the clipping method C. FIG. It is explanatory drawing of the cutting-out method C in case the length of the width direction is less than 1000 mm and 500 mm or more. It is explanatory drawing of the cutting-out method C in case the length of the width direction is less than 500 mm. It is explanatory drawing of the cutting-out method D. FIG. It is a top view which shows a relaxation process zone and a cooling zone from the heat setting zone which implements relaxation of the longitudinal direction in this invention. It is a side view which shows a relaxation process zone and a cooling zone from the heat setting zone made when implementing relaxation | loosening of the longitudinal direction in this invention. It is an enlarged view which shows the cutting condition of the film edge part of the film edge part made when implementing relaxation of the longitudinal direction in this invention. It is a top view which shows the enlarged part of the clip chain which implements relaxation of the longitudinal direction in a comparative example. (A) It is a longitudinal cross-sectional view which shows the enlarged part of the clip chain which implements relaxation of the longitudinal direction in a comparative example. (B) shows a state in which the guide rail is displaced by about half. It is explanatory drawing which shows the whole horizontal stretching machine in a comparative example.

  The film constituting the biaxially stretched polyethylene terephthalate resin film 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 from PET, the intrinsic viscosity (IV) of the raw material PET is preferably in the range of 0.45 to 0.70 dl / g, and in the range of 0.50 to 0.65 dl / g. Is more preferable. When the intrinsic viscosity of the PET raw material is 0.45 or less, for example, when it passes through the extruder again by recovery, the degree of polymerization of the PET 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.

  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 which is a 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 the case of producing a film for optical use, when melt-extruding, high-precision filtration is performed using a filter medium having a filtration particle size (initial filtration efficiency of 90%) of 15 μm or less, and the film 1 m after film formation ^It is preferable to adjust so that the number of foreign matters having a diameter of 20 μm or more per ² is 10 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.

  The thickness of the film constituting the biaxially stretched polyethylene terephthalate resin film of the present invention is not particularly limited. However, when used for various processing applications, the thickness is preferably 20 μm or more and 400 μm or less. In particular, as a base material for precision sheet printing such as mold release for green sheet production for ceramic capacitors and transfer film, etc., which require excellent strength and dimensional stability, offset printing, etc. 20 μm or more and less than 70 μm is preferable, and the substrate is preferably 70 μm or more and 400 μm or less for various optical films that require strength and dimensional stability.

  In order to efficiently perform post-processing, a roll body is also a preferred embodiment of the present invention. The width of the biaxially stretched polyethylene terephthalate resin film roll of the present invention is not particularly limited, but from the viewpoint of ease of handling, the lower limit of the width of the film roll is preferably 700 mm or more, and 1000 mm or more. More preferably. On the other hand, the upper limit of the width of the film roll is determined by the size of the post-processing apparatus, but at present, 2.2 m is considered the maximum width, more preferably 2.0 m or less, and 1.5 m or less. More preferably. In addition, the winding length of the film roll is not particularly limited, but from the viewpoint of ease of winding and handling, when the film has a thickness of about 20 μm, it is preferably 25,000 m or less, and 4,000 m or more. Is more preferable. When the film has a thickness of about 70 μm, it is preferably 7,000 m or less, and more preferably 1,100 m or more. In addition, when the film has a thickness of about 400 μm, it is preferably 1,300 m or less, and more preferably 200 m or more. As the take-up core, usually, paper of 3 inches, 6 inches, 8 inches, etc., a plastic core or a metal core can be used.

[Thickness fluctuation rate]
The film of the present invention was obtained by taking a strip-like film sample having a length of 30 m and a width of 3 cm along the longitudinal direction and measuring the thickness variation rate (thickness variation) in the longitudinal direction of the film sample. The thickness unevenness in the direction must be in the range of 0.5% or more and 4% or less. In the conventional patent document, when the thickness accuracy is evaluated, a material having a short thickness measurement length (10 m or less) has been used. On the other hand, since the present invention has high thickness unevenness reduced, the long film sample is the target of thickness unevenness evaluation as described above. According to the method of the present invention, unevenness in thickness and orientation does not occur even when evaluated with a long film.

  Furthermore, as an aspect of the present invention, even in the case of a biaxially stretched polyethylene terephthalate resin film roll, a strip-shaped film sample having a length of 30 m × width of 3 cm is taken along the longitudinal direction, and the longitudinal direction of the film sample is taken. When the thickness variation is measured, it is necessary that the thickness variation in the longitudinal direction of the film sample is in the range of 0.5% or more and 4% or less. Furthermore, in the biaxially stretched polyethylene terephthalate resin film roll, it is preferable that the variation (the difference between the maximum value and the minimum value) of the thickness variation (thickness variation rate) measured above is 0.5% or less. If the variation in thickness unevenness is within the above range, it is preferable to stably perform continuous precision processing in post-processing. In addition, although the lower one of the fluctuation | variation of thickness variation is preferable, 0.05% becomes a lower limit on production.

  Here, the film sample used for the measurement of thickness spots is collected from the film cut-out part provided by the following cut-out method A.

(Cutout method A)
At both end portions in the film width direction (portions within 50 mm from the edge), film cutout portions are provided at the beginning, middle and end of the film in the longitudinal direction. Here, the “starting portion” and “end portion” refer to a region including the length of the film in the longitudinal direction within 2 m from the end portion. The “intermediate portion” refers to a region including a 50% position in the film longitudinal direction.

[Heat shrinkage]
The film of the present invention is characterized by high dimensional stability by heat treatment. That is, when the average HS150, which is the average value of the heat shrinkage rate in the longitudinal direction of the film production when a film sample taken from the following cutout portion is heated at 150 ° C. for 30 minutes, the HS150 is obtained. However, it is -0.25% or more and less than 0.40%.

When the average HS150 is less than 0.40%, the dimensional stability is good even in the heat treatment in the post-processing, which is preferable. For example, when the film is dried by heating in a tenter, the passability is good, which is preferable. The average HS150 is more preferably 0.30% or less, and further preferably 0.20% or less. In addition, although the said average HS150 is so preferable that it is low, in this invention, -0.25% is considered to be a minimum in a design.
The film sample used for the measurement of the heat shrinkage rate is collected from the cutout portion from the cutout portion provided by the following cutting method B.

(Cutout method B)
A biaxially stretched polyethylene terephthalate-based resin film is divided into four portions in the width direction and a portion 50 mm from the end in the width direction, and five cutout portions are provided. The cut-out portions in the width direction are provided at the start, middle and end of the roll (15 in total). Here, “winding start” and “winding end” of the roll are regions of 50 mm or more and 2 m or less from the end of the winding start and the end of winding of the entire film roll, and “intermediate” is the film longitudinal direction It is an area including the 50% position.

[Scratches]
In addition, the biaxially stretched polyethylene terephthalate resin film of the present invention is characterized in that there are few minute scratches that are disadvantageous. That is, for 16 film samples having a length of 250 mm and a width of 250 mm collected from the film cutting portion provided by the cutting method C described below, the scratches having a depth of 1 μm or more and a length of 3 mm or more existing on the surface were measured by the measurement method described later. When the number is measured, the number of scratches is 10 / m ² or less. When the number of scratches on the film exceeds 10 / m ² , optical defects are recognized when used as an optical member, which is not preferable. The number of scratches on the film is preferably 5 / m ² or less, more preferably 3 / m ² or less, and particularly preferably 0 / m ² .

(Cutout method C)
From the biaxially stretched polyethylene terephthalate resin film, the beginning (5% of the total length in the longitudinal direction) and two intermediate portions (35% of the total length in the longitudinal direction, 65%) with respect to the length in the longitudinal direction of the film Position) and the end part (position of 95% of the total length in the longitudinal direction), the position of the center line of the part sampled from both ends in the width direction is divided into three equal parts in the width direction as the center line Provide a part. Film samples are collected from a total of 16 cut portions provided in this manner, 4 in the longitudinal direction and 4 in each width direction. In this cutting method, when the length of the film in the width direction is less than 1000 mm, it is preferable that the film is sampled by shifting by 300 mm in the longitudinal direction when collecting the two films at the center in the width direction. Furthermore, when the width of the film is less than 500 mm, four film samples are collected at one place provided in the longitudinal direction by shifting by 250 mm in the longitudinal direction including both ends of the film.

[Flatness]
As described above, the biaxially stretched polyethylene terephthalate resin film of the present invention has a small thickness variation rate and high flatness. The term “planarity” as used herein means that there is no wrinkle or warp. For example, the planarity can be evaluated by the following method. A sample of 300 mm in the longitudinal direction of the film and 210 mm in the width direction perpendicular thereto was taken, and the heights of the four corners of the sample (height in the vertical direction from the horizontal plane) were measured with a JIS metal scale (0.5 mm scale). In this case, it is preferable that the maximum value of the height of the four corners is equal to or less than the thickness of the film, and the average value of the height of the four corners is equal to or less than 20% of the thickness of the film. When the maximum value of the warp is less than the film thickness or the average value is 20% or less, since the flatness distortion is small at the time of film processing and the processing accuracy is good, it is preferable from the viewpoint of yield. In addition, since it is desirable that the flatness of the film is good in a wide range, when evaluating the flatness, 50 film samples (300 mm × 210 mm) collected from the film cutting portion provided by the following cutting method D ( It is desirable to measure a total area of about 3 m × 1 m).

(Cutout method D)
With respect to the length in the longitudinal direction of the biaxially stretched polyethylene terephthalate resin film, the beginning (5% position of the total length in the longitudinal direction) and eight intermediate portions (15% position, 25% position of the total length in the longitudinal direction), 35 % Position, 45% position, 55% position, 65% position, 75% position, 85% position) and the end portion (95% position of the total length in the longitudinal direction) and samples from both ends in the film width direction. A cutout portion is provided with each position obtained by dividing the position of the center line of the part into four equal parts in the width direction. Film samples are collected from a total of 50 cut portions, which are 10 places in the longitudinal direction and 5 places in each width direction. In this cutting method, when the length in the width direction of the film is less than 1050 mm, it is preferable that the film is sampled by shifting by 300 mm in the longitudinal direction when collecting the three films at the central portion in the width direction.

  The film of the present invention can be obtained by melting and extruding the above polyethylene terephthalate resin raw material with an extruder to form an unstretched film, and biaxially stretching the unstretched film by a predetermined method shown below.

  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.

  Furthermore, the obtained unstretched film is stretched in the longitudinal direction (longitudinal direction) by a predetermined method, and the film of the present invention can be obtained by stretching the film after longitudinal stretching in the width direction and heat-treating it. It becomes. 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.

[Production Method of Film of the Present Invention]
<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 order to stretch the film so as not to amplify the uneven thickness of the unstretched film, it is considered necessary to accurately grasp the tensile characteristics of the film and to stretch the film in consideration of the tensile characteristics. In general, when a tensile test of a film made of polyethylene terephthalate resin is performed, the stress is substantially reduced until a predetermined strain amount is reached as shown in a stress-strain curve (so-called SS curve) as shown in FIG. When it increases at a certain rate and reaches a predetermined strain amount, a plateau region where the stress does not increase appears even if the strain amount increases (the point at which the stress at the initial stage of tension is saturated is called the yield point). After such a plateau region appears, a region where the stress increases as the amount of strain increases again (the point where the stress begins to rise again after the yield point is called a rising point) It shows a tendency to break after a secondary increase.

  From the tensile properties of such a film, conventionally, it is more likely that stretching is performed in a region excluding the plateau region in the above-described SS curve, that is, in a region where stress increases as the amount of strain increases. Was thought to be smaller. And based on such an idea, the extending | stretching method of the above patent documents 1 and the extending | stretching method of patent document 2 as mentioned above are proposed.

  The stretching method of Patent Document 1 is a stretching method intended to repeat stretching at a magnification equal to or lower than the yield point in the SS curve in multiple stages. However, in the stretching method of Patent Document 1, each stretching is simply performed by using a difference in peripheral speed between heated rolls, so that the film is stretched from the heated low-speed roll. The film is rubbed on the low-speed roll due to the difference between the rotation speed of the low-speed roll and the film speed, and many scratches that may cause optical defects are generated on the film surface.

  On the other hand, the stretching method of Patent Document 2 is a stretching method intended to perform stretching at a magnification equal to or lower than the yield point after performing stretching at a magnification equal to or higher than the rising point in the SS curve at a high temperature. However, the stretching method of Patent Document 2 is similar to the method of Patent Document 1, because each stretching is simply a stretch using the peripheral speed difference between heated rolls. The film is stretched from the time of separation, and the film is rubbed on the low-speed roll, so that many scratches are generated on the film surface. In addition, the film sticks to the roll due to stretching at a high temperature first, and many scratches are caused by the stick.

  The stretching method of Patent Document 3 is a stretching method that stretches between a low-speed roll and a high-speed roll, and is a non-contact type and uses a heat source of 30 kW / m to 200 kW / m to heat the film. Although generation | occurrence | production is suppressed, a thickness spot cannot be reduced highly and cannot satisfy the high level request | requirement with respect to recent planarity.

  The method of Patent Document 4 is a method in which an unstretched film is heated over a length of 3 mm to 30 mm by a heating means provided 5 mm to 100 mm before the contact point between the film and the stretching roll, and stretched in the film flow direction with a stretching roll. Although there is a high-speed nip roll behind the drawing roll that holds the heated film on the high-speed side by the heating means, it means that there is no deviation between the drawing roll and the film to prevent scratches. Is required. However, it is difficult to match these speeds, and if there is a slight variation in stretching, there is a disadvantage that the speed is shifted and the film is scratched.

  Although the method of patent document 5 is a method of extending | stretching in the multistage of an extending | stretching roll, extending | stretching at the time of separation | separation of a roll occurred, and there also existed a fault that a crack entered.

  With the method of Patent Document 6, it is difficult to control spherical particles, and thickness spots cannot be stably reduced.

  Thick spots may look good at short distances (less than 10 m). However, when the length is long (10 m or more), the thickness unevenness deteriorates, and in practice, a long thickness of about 100 m or more is required. Therefore, even if the particle size of the fine particles according to Patent Document 6 can be controlled, considering the post-processability of the film, a thickness of about 1,000 m is necessary at a thickness of 20 μm to 70 μm. With a thickness of about 100 m, stability of a thickness of about 100 m is necessary, and it is difficult to obtain a long biaxially stretched film with extremely high thickness accuracy unless there is a device in the stretching process.

<Characteristics of the film production method of the present invention>
In order to eliminate the problems of the conventional stretching methods described above, the present inventors are able to improve the thickness spots without forming scratches that can cause optical defects on the film surface. We studied diligently. As a result, by adopting a special stretching method that narrows the width of heating in the longitudinal stretching process as described below, it is completely different from the conventional stretching method without forming scratches on the film surface. The inventors have found that a small film can be obtained, and have come up with the present invention.

(1) Narrowing of the width of heating with a heating device In order to obtain the film of the present invention, it is preferable to perform longitudinal stretching in two or more stages as a method of biaxial stretching. The transverse stretching can be performed before longitudinal stretching, after longitudinal stretching, or in the middle of two or more stages of longitudinal stretching. However, a method of transverse stretching after performing longitudinal stretching in two or more stages (hereinafter, longitudinal-longitudinal- ( Longitudinal) -lateral stretching method) is preferred. Moreover, in order to obtain the film of the present invention, when performing the above-described two or more stages of longitudinal stretching, the length of the heating width in the longitudinal direction can be increased by using a heating device described later in each longitudinal stretching. The temperature is narrowed to 2 mm or more and 25 mm or less, and the temperature difference before and after the stretching point is abrupt. The upper limit of the length of the heating width in the longitudinal direction by the heating device is more preferably 25 mm or less, and most preferably 10 mm or less. The same applies to the second and subsequent stages. The lower limit of the heating width is more preferably 3 mm or more. Here, the width of heating specifically refers to the full width at half maximum which is an interval of half the intensity of the energy peak when the energy distribution irradiated to the film by the heating device is measured in the flow direction of the film. . Thereby, it is preferable to control the temperature difference of the film before and after the stretching point as described later. In addition, when the width of the heating for stretching is narrowed, it becomes difficult to be affected by fluctuations in the external environment, so that fluctuations in thickness spots in the film roll can be suppressed.

  The reason why the thickness unevenness is eliminated by performing longitudinal stretching with a narrow stretching point and a very large temperature difference as described above is not clear, but the inventors consider as follows. That is, when a film is stretched between rolls (usually nip rolls) provided with a circumferential speed difference, an equal tension acts in the width direction of the film between the rolls. The difference in stress due to the property is smaller, and the portion with the smaller thickness is stretched before the portion with the larger thickness. Therefore, if the tensile strength of the portion with a small thickness is increased quickly and the stretched portion is not shifted from the portion with a small thickness to a portion with a large thickness, the thickness unevenness of the unstretched film is increased and the film with good thickness unevenness is obtained. Can't get. Here, when longitudinal stretching with a very large temperature difference is performed in the narrowed portion as described above, as soon as stretching starts, the substantial stretching temperature of the small thickness portion decreases (so-called temperature-time law). The tensile strength of the small thickness portion increases, the thin thickness portion becomes difficult to stretch and the large thickness portion becomes easy to be stretched. It is thought that. Moreover, since the tensile strength is high at low temperatures, it is difficult to be affected by the tension during stretching from the stretched part, so the difference in stretching between the thin part and the thick part is difficult to occur, and stretching without causing deterioration in thickness unevenness. Is considered possible.

  In other words, the film to be stretched is subjected to the same tension between the front and rear nip rolls, so if the actual temperature of the film is constant, the thin part will stretch first and the thick part will be difficult to stretch, Is performed in a narrow range, the thin portion is stretched abruptly, the substantial stretching temperature is lowered, the tension is increased, and the temperature of the thick portion is higher than that of the thin portion, so the tension is lowered and the overall tension is reduced. A thick part is stretched by balancing. When stretching occurs, the substantial temperature of the thick portion again decreases, and the tension is balanced as a whole, so that the thickness is uniformed.

  The heating device used in the film longitudinal stretching process of the present invention is not particularly limited as long as it can be heated with a narrow heating width as described above, but is not limited to a laser heating device, a plasma beam heating device, a high-temperature air jet heating. A device, an infrared heating device (particularly, an infrared heating device having a wavelength of 2.5 μm or less) and the like can be suitably used.

Examples of the laser that can be used as the heating device include a CO ₂ laser and a YAG laser. In particular, these lasers are preferable because they can impart a high energy density to the film, and are suitable for heating the film in a narrow width.

  When the laser light source is used by scanning in the film width direction, strictly speaking, it is slanted with respect to the film width direction from the relationship between the scanning speed of the laser light source in the film width direction and the traveling speed in the longitudinal direction of the film. In this case, the laser beam travels. If the travel line of the laser beam is excessively inclined with respect to the film width direction axis, the stretched region may not be fixed, and thickness spots may easily occur. Therefore, it is desirable to control the laser spot diameter (irradiation diameter on the film surface), the laser scanning speed in the film width direction, and the traveling speed in the longitudinal direction of the film. Specifically, the laser scanning speed is set to 1/3 or less of the laser spot diameter, and the moving distance in the longitudinal direction of the film is 0.2 mm or less until the laser light source reciprocates once in the film width direction. It is preferable to control the scanning speed of the laser and so on. For example, when the laser beam having a spot diameter of 0.3 mm reciprocates and the progression in the longitudinal direction of the film is 0.2 mm or less, about 1/3 of the spot diameter is exposed twice by one reciprocal scanning of the laser. Will be. Although it depends on the film width, the laser spot diameter is more preferably about 3 mm, which is larger than 0.3 mm, from the viewpoint of productivity. If the spot diameter becomes too large, the difference in film strength around the spot diameter becomes small, the difference in film temperature before and after the stretching point is difficult to be attached, and it is easy to cause unevenness in thickness. preferable.

(2) Optimization of stretching conditions In order to obtain the film of the present invention, when the above-described longitudinal-longitudinal- (longitudinal) -stretching is performed, the first-stage longitudinal stretching ratio is 2.0 times or more and 3.2 times. The first stage longitudinal stretching temperature is adjusted to 105 ± 20 ° C., and the second stage and subsequent longitudinal stretching ratios are adjusted to 1.05 to 1.5 times, and the second and subsequent longitudinal stretches are adjusted. The stretching temperature is preferably adjusted to 100 ± 20 ° C. Furthermore, the temperature difference between the film before and after the stretching point in the first stage is preferably 15 ° C. or higher, and more preferably 20 ° C. or higher. Although it is considered that the thickness is improved when the temperature difference is provided, the temperature difference is considered to be 50 ° C. or less. Further, the temperature difference before and after the stretching point in the second and subsequent stages is preferably 2 ° C. or more, more preferably 5 ° C. or more. The upper limit of the temperature difference before and after the stretching point after the second stage is preferably 20 ° C. or less. In addition, when the temperature distribution is localized in the film before and after the stretching point (for example, when there is a difference in temperature between the film surface, inside, and back surface), the average is taken as the film temperature. The film temperature before the stretching point is specifically measured by the temperature of the film immediately before heating by the heating device, and the film temperature after the stretching point is specifically measured by the temperature of the film after being heated by the heating device. To do. In the examples described later, for example, when using a laser, the temperature of the film where the laser irradiation light is not applied in the longitudinal direction is measured with a non-contact infrared thermometer, and the film is passed when passing through the laser. The temperature was measured and the difference was taken as the film temperature difference before and after the stretching point. Moreover, it can measure similarly to this also in another heating apparatus.

  If the stretch ratio of the first stage exceeds 3.2 times, the stretching tension becomes too high, so that the stretching point spreads without being fixed, and as a result, the thickness unevenness of the film tends to deteriorate. On the other hand, if the first stage draw ratio is less than 2.0 times, the draw tension will be extremely reduced, so there will be no tension between the thin part and the thick part. In addition, the thickness unevenness of the film tends to deteriorate. In addition, if the stretching ratio of the second stage exceeds 1.5 times, the stretching tension becomes too high, and the stretching point spreads without fixing, resulting in poor film thickness spots. easy.

  In addition, when the average temperature difference between the film before and after the stretching point in the first stage is less than 15 ° C., the stretching stress is high and the deformation of the film before the stretching point becomes large, the deformation on the low-speed roll, and the low-speed roll and the film The difference in speed is large and it is easy to get scratched. Conversely, if the temperature at the stretching point becomes too high, even if the temperature difference is 15 ° C. or higher, there will be no difference in stretching stress, and the stretching will be deformed and scratched on the low speed roll, or the low speed roll. A small stick is generated on the surface, which is a drawback. Therefore, it is desirable to control the preheating temperature so that the temperature difference between the stretching temperature and the film before and after the stretching point is in the above range.

  The first-stage longitudinal stretching condition (that is, stretching at a relatively high magnification around 105 ° C.) in the film production method of the present invention has been conventionally considered to have an adverse effect on thickness spots. This is considered to correspond to “stretching that gives a strain amount corresponding to a plateau region”. Nevertheless, as described above, the first stage of longitudinal stretching is performed at a high magnification (2.0 to 3.2 times) at around 105 ° C., and a low magnification (1.05 to 1.5 times) at around 100 ° C. The reason why thickness unevenness is eliminated by applying the second stage of longitudinal stretching is not clear, but as described above, heating with a laser fixes (narrows) the stretching point and makes the temperature change extreme. By increasing it, it is thought that the effect of strain and stress reduces the influence on thickness spots due to the balance of force in the minimum due to the effect of temperature time law.

(3) Stretching at the center position between rolls In order to obtain the film of the present invention, in addition to the laser in each of the first and second longitudinal stretching steps as described above, a plasma beam, a high-temperature air jet, an infrared ray ( In particular, it is possible to make the temperature difference before and after the stretching point satisfying the concept of the present invention abrupt. At that time, when the gap between rolls is increased, the thickness unevenness tends to be deteriorated due to disturbance such as flapping of the film. Therefore, in order to obtain the film of the present invention, it is necessary to make the gap between rolls as small as possible. Also, when the front roll is separated and the rear roll is in contact, the traveling speed of the film is made substantially equal to the surface speed of the roll so that there is no speed difference, and the deformed portion accompanying stretching is in the air. Therefore, it is necessary to make the gap between rolls as small as possible. Therefore, it is preferable to provide a heating position by a heating device at a central position where it can be as close as possible to the roll.

(4) Lowering the temperature of the roll In order to obtain the film of the present invention, as described above, in each of the first and second longitudinal stretching steps, a heating site is provided at the center position between the rolls having a circumferential speed difference. In this case, it is preferable to adjust the temperature of the rear roll after the first stage of longitudinal stretching (the front roll in the second stage of longitudinal stretching) to a lower temperature than during normal roll stretching. Thus, by lowering the surface temperature of the rear roll after the first stage of longitudinal stretching (front roll in the second stage of longitudinal stretching) from the usual level, the temperature of only the film surface is lowered, and the surface of the film is hardened. , The unevenness of the roll on the rear side (scratches on the roll surface that cannot be seen or adhesion of dust etc. to the roll surface) can be prevented from being transferred to the film, and a film with less scratches can be obtained. It becomes.

  The rear roll after the first stage of longitudinal stretching is preferably nipped, and the temperature of the nip roll is not intended to cause flaws or unevenness on the surface to be set at 5 ° C. or more lower than the surface temperature of the film subjected to longitudinal stretching. It is effective in preventing minute irregularities. A more preferable temperature is a glass transition point or lower, and a still more preferable temperature is a temperature lower by 5 ° C. or more than the glass transition point. If the lower limit is 20 ° C. or more lower than the glass transition point in consideration of the next stretching, the thickness tends to deteriorate.

  In addition, in the longitudinal stretching process of the film, by using the means (1) to (4) described above, the thickness of the film (especially the thickness in the longitudinal direction) can be obtained without scratching the surface of the film, which may cause an optical defect. ) Can be reduced. It should be noted that only one of the above-mentioned means (1) to (4) does not effectively contribute to the reduction in thickness unevenness and scratches on the film roll, and (1) to (4) By combining the means, it is considered that the thickness unevenness of the film and the scratch can be reduced very efficiently.

  Further, in order to obtain the film of the present invention, it is necessary to subject the film subjected to specific longitudinal stretching as described above to transverse stretching and heat setting treatment. In the case of stretching in the width direction, the stretching temperature needs to be 80 to 210 ° C, and preferably 130 to 200 ° C. If the stretching temperature in the width direction is less than 80 ° C., the film tends to break, which is not preferable. Moreover, when it exceeds 210 degreeC, since the planarity of the obtained film worsens, it is not preferable. The draw ratio in the width direction is 3.0 to 5.0 times, preferably 3.6 to 4.8 times. If the draw ratio in the width direction is less than 3.0 times, the thickness unevenness of the obtained film is deteriorated, which is not preferable. If the draw ratio in the width direction exceeds 5.0 times, the frequency of breaking increases in the drawing, which is not preferable.

  Subsequently, heat setting is performed. The temperature in the heat setting treatment step is preferably 180 ° C. or higher and 240 ° C. or lower. If the temperature of the heat setting treatment is less than 180 ° C., the absolute value of the heat shrinkage rate is increased, which is not preferable. On the other hand, if the temperature of the heat setting treatment exceeds 240 ° C., the film tends to become opaque and the frequency of breakage increases, which is not preferable. A suitable heat setting method will be described later.

  It is effective to control the heat shrinkage rate, particularly the heat shrinkage rate in the width direction, by narrowing the guide rail of the gripping tool by the heat setting process. The temperature for the relaxation treatment can be selected in the range from the heat setting treatment temperature to the glass transition temperature Tg of the polyethylene terephthalate resin film, and is preferably (heat setting treatment temperature) −10 ° C. to Tg + 10 ° C. The width relaxation rate is preferably 1 to 6%. If it is less than 1%, the effect is small, and if it exceeds 6%, the flatness of the film is deteriorated.

  However, in the above heat fixing method, the movement of the film in the vicinity of the clip is restricted by the clip, so the longitudinal direction is not sufficiently relaxed, and the heat shrinkage rate is sufficient for the film edge. It may not be improved. Even when trying to reduce the heat shrinkage in the longitudinal direction, simply increasing the temperature at heat setting may cause problems such as coloration of the film or crystallization progressing to whiten the film, resulting in deterioration of transparency. It was difficult to reduce the rate.

<Longitudinal relaxation treatment>
Therefore, in the present invention, in addition to the above-described heat setting treatment method, the thermal contraction rate of the film can be suppressed by further taking the following means (1) to (3). That is, (1) cutting and removing the film edge held by the clip, (2) reducing the film take-off speed, and relaxing the entire film width removed from the clip in the longitudinal direction, (3) The film having the full width subjected to the relaxation treatment is again gripped with a clip, and the film is cooled to room temperature while maintaining the flatness. Hereinafter, each of the above-described means will be described sequentially (see FIGS. 8, 9, and 10).

  (1) First, the film edge held by the clip is cut and removed. Since the film portion held by the clip is not uniformly stretched in the transverse stretching, the thickness is usually thicker than other regions of the film. When there are regions having different thicknesses as described above, the entire film width cannot be relaxed uniformly in the step (2). Therefore, prior to the longitudinal relaxation treatment, the film edge portions having different thicknesses (the vicinity being held by the clip for lateral stretching) are cut and removed. The film edge is cut by setting a cutting blade in the vicinity where the edge is released from the clip so that the influence of gripping the clip does not reach the center. The phenomenon that the film plane undulates due to the cutting of the film, but in order to suppress such undesired fluttering, it is desirable to provide the cutting blade in a place where the wind from the air duct installed in the tenter does not hit. The edge portion of the film that has been cut and removed is recovered, but it is preferable to cut the film just before the film leaves the clip so that the change in tension accompanying the cutting and recovery does not reach the film body. Also, for collecting the film edge, it is preferable to use a grooved metal roll and insert a blade between the grooves to nip the film where there is no groove. Further, in order to perform uniform relaxation in the longitudinal direction, the thickness of the film cut surface is preferably the thickness of the central portion in the width direction, that is, ± 10% or less of the average value of the product thickness. Preferably it is ± 8% or less, particularly preferably ± 4% or less.

  (2) Next, by reducing the take-up speed of the film, the entire width of the film removed from the clip is relaxed in the longitudinal direction. After removing the film edge, the film is again held by the clip by the clip chain installed in the next step (cooling zone). Here, by setting the progress speed of the clip chain (second clip chain) in the cooling zone to be slower than the progress speed of the clip chain (first clip chain) until the heat setting process, the film take-up speed is attenuated. Until the film edge is gripped again in the next step, the longitudinal relaxation is performed over the entire width of the film. The relaxation rate is adjusted by the take-up speed. The relaxation rate in the present invention is preferably 1% or more and 6% or less. If it is less than 1%, the effect is small, and if it exceeds 6%, the flatness of the film is deteriorated. Furthermore, it is preferable that the temperature of the relaxation zone is controlled by hot air whose temperature is adjusted. In the system according to the present invention, the system disclosed in Japanese Patent Publication No. 4-0221818 (Patent Document 10), that is, by providing a bendable structure between adjacent clips, the vertical clip interval is adjusted, and the vertical direction As compared with the method of achieving the relaxation, a larger relaxation rate can be obtained. In the method described in Patent Document 10, it is difficult to suppress the fluctuation of the relaxation rate due to mechanical operation, and the same degree as the slit relaxation method of the present invention unless the relaxation rate is 2.0% or less. The effect cannot be obtained. Therefore, in the method according to the present invention, effective relaxation processing can be performed even with a higher relaxation rate.

  (3) Finally, the film having the full width subjected to the relaxation treatment is again gripped with a clip and cooled to room temperature while maintaining the flatness. Since the film relaxed in the longitudinal direction is still at a high temperature of 170 to 120 ° C., the film is easily deformed due to disturbance in the state as it is, and when the temperature is lowered in the deformed state, the deformation is fixed and flatness is improved. Collapse. Therefore, in order to maintain flatness, cooling is performed with the film edge held by a clip. The film is cooled to room temperature such that it is below the glass transition temperature (Tg). After the film has cooled, the film edge is released from the clip and led to a conventional winding process.

  When the film is biaxially stretched as described above, there are places where the traveling film and the rotating roll come into contact. In order to prevent the occurrence of scratches on the film, (a) the film surface itself or the roll surface, in particular, the roll surface in contact with the film should not generate “defects” that cause scratches. It is desirable to prevent the film from shifting vertically and laterally.

  The above-mentioned “defects” refer to all factors that cause fine scratches on the film by coming into contact with the film such as scratches, deposits, deposits, and foreign matters formed on the roll surface. Therefore, by eliminating these defects, it is possible to further reduce the occurrence of scratches on the film surface. In order to prevent the occurrence of the above-mentioned defects, for example, a method of setting the surface roughness of the roll used in film production to Ra of 0.1 μm or less, or a roll surface that causes scratches such as deposits, deposits, and foreign matters. In order to prevent the accumulation of slag, a method of installing a roll cleaner at the preheating inlet and the cooling roll in the longitudinal stretching process can be suitably employed.

  Factors that cause vertical scratches or horizontal scratches include deformations such as expansion and contraction in the vertical or horizontal direction of the film, respectively. These film deformations are mainly caused by temperature changes in the film. Therefore, by suppressing the temperature change of the film on the roll surface, the amount of film deformation due to such temperature can be reduced, and the occurrence of longitudinal scratches and lateral scratches can be prevented. Specifically, the temperature change of the film per roll is 40 ° C. or less, preferably 30 ° C. or less, more preferably 20 ° C. or less, still more preferably 10 ° C. or less, and particularly preferably 5 ° C. or less. Is recommended.

  Further, by setting the relationship between the relative speeds of the plurality of rolls to a speed profile that is closest to the amount of deformation due to the temperature and tension of the film, it is possible to reduce the vertical shift of the film.

  In addition, the various methods for preventing generation | occurrence | production of the crack mentioned above can be used combining several types of methods according to the required quality level of the member in which the film of this invention is used.

  The biaxially stretched polyethylene terephthalate resin film of the present invention may be a single layer or a film having a laminated structure of two or more layers, or one side of a biaxially stretched polyethylene terephthalate resin film that does not contain fine particles with emphasis on transparency. Alternatively, there may be no problem even if various coatings are applied to the both surfaces at the time of film formation for the purpose of improving the adhesiveness in the post-processing step and improving the slipperiness.

  Further, fine particles can be added to the biaxially stretched polyethylene terephthalate resin film constituting the film of the present invention as required. 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.

  As a method of blending the above-mentioned particles into a biaxially stretched polyethylene terephthalate resin film, for example, it can be added at any stage for producing a biaxially stretched polyethylene terephthalate resin, but preferably at the stage of esterification or ester After completion of the exchange reaction, it may be added as a slurry dispersed in ethylene glycol or the like at the stage before the start of the polycondensation reaction, and the polycondensation reaction may proceed. 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 biaxially stretched 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 above-described method is excellent in transparency, thickness unevenness (particularly thickness unevenness in the longitudinal direction), and optical performance, and is a prism lens sheet base used for LCD for precision printing and optical applications. Film, base film for hard coat 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 absorption used for front panel of plasma display It can be suitably used for a film, a back sheet of a solar cell, an electromagnetic wave absorbing film, and the like.

  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) Longitudinal thickness variation rate (thickness unevenness)
At both end portions in the film width direction (portions within 50 mm from the edge), film cutout portions are provided at the beginning, middle and end of the film in the longitudinal direction (cutout method A). Here, the “starting portion” and “end portion” are regions including the length of the film in the longitudinal direction within 2 m from the end portion, and cutout portions were provided at the positions shown in Table 2. The “intermediate portion” is a region including a 50% position in the film longitudinal direction, and a cutout portion was provided at the position shown in Table 2. For the sampled film sample, the thickness is continuously measured along the longitudinal direction of the film sample at a speed of 5 m / min using a continuous contact thickness gauge manufactured by Micron Measuring Instruments Co., Ltd. (measurement length is 30 m). . Then, the maximum thickness of each film sample at the time of measurement is Tmax., The minimum thickness is Tmin., The average thickness is Tave., And the thickness variation rate in the longitudinal direction of the film is calculated from the following formula. Thickness variation rate = {(Tmax.−Tmin.) / Tave.} × 100 (%)
Table 2 shows the maximum, minimum, and average values.

(2) Thermal contraction rate of the film In the width direction, the film is divided into four portions of 50 mm from the end and between them, and five cutout portions are provided. The cut-out portions in the width direction are provided at the beginning, middle and end of winding of the roll, and a long strip-like film sample having a length of 30 m and a width of 30 mm is sampled from each cut-out portion. Here, “winding start” and “winding end” of the roll are regions of 50 mm or more and 2 m or less from the end of winding start and end of winding of the entire film roll, and “intermediate” is the entire film roll It is an area including the center of the length. A sample film having a width of 20 mm and a length of 250 mm is cut out from each cutout portion along the longitudinal direction of film formation (15 pieces in total). A marked line is marked at an interval of 200 mm on the cut out sample having a width of 20 mm and a length of 250 mm, put in a heating oven adjusted to 150 ° C., and the thermal shrinkage rate is measured in accordance with JIS / C-2318. . The average value of the obtained heat shrinkage rate was calculated and used as the average value of the heat shrinkage rate.

(3) Scratch detection The beginning (5% of the total length in the longitudinal direction) and two intermediate portions (35% and 65% of the total length in the longitudinal direction) and the end of the film in the longitudinal direction In each part of the part (position of 95% of the total length in the longitudinal direction), a cutout part is provided with each position obtained by dividing the position of the center line of the part collected from both ends in the width direction into three equal parts in the width direction. (Cutout method B). A film sample of 250 mm × 250 mm was collected from each cut-out site (16 sheets in total). For 16 film samples of 250 mm × 250 mm, an optical defect that is optically recognized as having a size of 50 μm or more is detected by the following optical defect detection method.

(A) Scratch detection As a projector, a 20 W × 2 fluorescent lamp is placed 400 mm below the XY table, and a film sample to be measured is placed on a mask having a slit width of 10 mm provided on the XY table. Light is incident so that the angle between the line connecting the projector and the receiver and the vertical direction of the film sample surface is 12 °, and the reflected light amount is converted into an electrical signal by a CCD image sensor camera placed 500 mm above the XY table. The electric signal is converted, amplified, differentiated, and compared with a threshold (threshold) level by a comparator to output an optical defect detection signal. This threshold value is preliminarily formed by drilling a hole of about 50 μm on a 2 mm thick aluminum plate, polishing burrs formed on the aluminum plate, and finishing the surface with a No. 200 buff. It adjusted so that a hole of 50 micrometers might be detected using this. Also, using a CCD image sensor camera, a scratch image is input, the video signal of the input image is analyzed by a predetermined procedure, the size of the optical defect is measured, and the position of the defect of 50 μm or more is displayed. To do. Optical defects are detected on both sides of the film sample.

(B) Measurement of Scratch Size A defect due to a scratch is selected from the optical defect portion detected in (1) above. The film sample is cut into an appropriate size, and observed using a three-dimensional shape measuring device TYPE550 manufactured by Micromap Co., Ltd. from the direction perpendicular to the surface of the film sample, and the size of the scratch is measured. When observed from the direction perpendicular to the surface of the film sample, that is, the film surface, the unevenness of the scratches close to each other within 50 μm is regarded as the same scratch, and the length and width of the rectangle with the smallest area covering the outermost part of those scratches are set. The length and width of the scratch. From this result, the number of scratches (pieces / m ² ) having a depth of 1 μm or more and a length of 3 mm or more is obtained.

(4) Flatness of the film The flatness of the film was measured by the following method except for the film thickness of 25 μm. With respect to the length of the film in the longitudinal direction, the beginning (5% position of the entire length in the longitudinal direction) and 8 intermediate portions (15% position, 25% position, 35% position, 45% position of the entire length in the longitudinal direction) 55% position, 65% position, 75% position, 85% position) and the end line (95% position of the total length in the longitudinal direction) and the position of the center line of the part sampled from both ends in the film width direction. A cutout portion is provided with each position divided into four in the width direction as a center line (cutout method D). Film samples are collected from a total of 50 cutouts, which are 10 places in the longitudinal direction and 5 places in the respective width directions (total area is about 3 m × 1 m). This film sample was placed on a horizontal glass plate (thickness 5 mm) in a room controlled at a temperature of 23 ± 2 ° C. and a humidity of 65 ± 5% with the surface first in contact with the cooling roll in the film forming process facing up. The height of the warp at the four corners of the film sample (height in the vertical direction from the horizontal plane) is measured with a JIS metal ruler (0.5 mm scale). If the height of the four corners is “0” or the cross section appears to be M-shaped, measure the warp with the opposite side facing up. The average value of the heights of the four corners measured in all the samples and the maximum value of the heights of the four corners measured in all the samples are displayed.

(5) Temperature difference of the film before and after the stretching point at the time of longitudinal stretching When the temperature of the film not irradiated with laser light in the longitudinal direction is measured with a non-contact infrared thermometer, The temperature of the film is measured, and the difference is taken as the film temperature difference before and after the stretching point.
In addition, when extending | stretching by a heater, the film temperature difference before and behind the extending | stretching point by a heater was measured.

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

[Example 1]
Polyethylene terephthalate [A] was produced as follows. 1000 parts of dimethyl terephthalate, 700 parts of ethylene glycol, and 0.16 part of manganese acetate tetrahydrate were charged into a transesterification can, subjected to a transesterification reaction at 120 to 210 ° C., and produced methanol was distilled off. When the transesterification reaction was completed, 0.13 part of antimony triacid and 0.017 part of normal phosphoric acid were added, and the pressure in the system was gradually reduced to 133 Pa in 75 minutes. At the same time, the temperature was gradually raised to 280 ° C. Under these conditions, a polycondensation reaction was carried out for 70 minutes, and the molten polymer was extruded into water from a discharge nozzle, and a cylindrical chip having a diameter of about 3 mm and a length of about 5 mm was obtained by a cutter. The intrinsic viscosity [η] of the obtained polyethylene terephthalate [A] was 0.63 dl / g.

  Polyethylene terephthalate [A] ([η] = 0.63) containing 0.03% by mass of silica particles (manufactured by Fuji Silysia Chemical Co., Ltd., Silicia 310) as an additive so that the moisture content is 50 ppm or less. After drying, it was charged and melted at a temperature of 285 ° C. During melting with an extruder, it was filtered with a filter material of a sintered stainless steel (nominal filtration accuracy: particles having a size of 10 μm or more were cut by 90%). Next, a resin sheet is extruded from a T-shaped die, wound around a casting drum having a surface temperature of 30 ° C. by using an electrostatic application casting method, and cooled and solidified to form an unstretched film having a thickness of 1,680 μm and a width of 490 mm. Obtained.

The obtained unstretched film was heated with a group of heated rolls, and then the CO ₂ laser provided between the nip rolls between the first nip roll and the second nip roll arranged before and after. While being heated to 105 ° C. by (first laser), the film was stretched 2.77 times in the longitudinal direction (longitudinal direction) (first-stage longitudinal stretching).

The spot diameter of the CO ₂ laser was adjusted to 3 mm in diameter, and the scanning width in the width direction was adjusted to be the full sheet width. Further, the scanning speed was adjusted so that the unstretched film reciprocated once while proceeding 0.2 mm in the longitudinal direction. The first nip roll on the front side was adjusted to maintain the film temperature, and the second nip roll on the rear side was adjusted to the cooling side. The first CO ₂ laser was arranged so as to scan in the width direction at the center position between the first nip roll and the second nip roll. The temperature difference of the film before and after the stretching point of the first-stage longitudinal stretching described above was 33 ° C.

Thereafter, the film after the longitudinal stretching is set to 100 by a CO ₂ laser (second laser) provided between the second nip roll and the third nip roll disposed immediately after the second nip roll. While heating at 0 ° C., the film was stretched 1.17 times in the longitudinal direction (longitudinal direction) (second longitudinal stretching). The spot diameter of the second laser was set to 3 mm as in the case of the first laser, and the scanning width in the width direction was adjusted to be the full width of the sheet. The third nip roll was adjusted to the cooling side. Note that the scanning position of the second laser was arranged at the center position between the second nip roll and the third nip roll. Moreover, the temperature difference in the above-described second-stage longitudinal stretching was 11 ° C.

Further, the film after the longitudinal stretching was subjected to 100 ° C. by a CO ₂ laser (third laser) provided between the third nip roll and the fourth nip roll disposed immediately after the third nip roll. While being heated, the film was stretched 1.08 times in the longitudinal direction (longitudinal direction) (third longitudinal stretching). The spot diameter of the third laser was 3 mm as in the first case, and the scanning width in the width direction was adjusted to be the full width of the sheet. The fourth nip roll was adjusted to the cooling side. In addition, the scanning position of the third laser was arranged at the center position between the third nip roll and the fourth nip roll. Moreover, the temperature difference of the film before and behind the stretching point of the above-described third stage of longitudinal stretching was 10 ° C.

  As described above, after the unstretched film is stretched in two stages in the longitudinal direction, the longitudinally stretched film is guided to a tenter, stretched 4.0 times in the width direction in an atmosphere of 130 ° C., and heat-set at 235 ° C. gave. Next, a lateral relaxation treatment of 1.7% was performed at 225 ° C. by adjusting the tenter clip interval in the film width direction. Further, after passing through a heat setting zone at 170 ° C., when leaving the heat setting zone, a region of 140 mm from the film end was cut off from both ends of the film held by the clips of the first clip chain. The edge of the cut film edge was collected by inserting a blade into the groove of a grooved metal roll and niping the non-grooved part to minimize undulation of the film surface due to edge cutting. .

  The film with the edge cut away was passed through a heat relaxation zone at 170 ° C. without holding the edge with a clip and then led to the cooling zone with a second clip chain. The longitudinal relaxation treatment was performed in the thermal relaxation zone by reducing the speed of the second clip chain by 2.5% from the speed of the first clip chain. Thereafter, the film temperature is lowered to room temperature below the glass transition temperature through the cooling zone, and the edges of both ends are cut and removed, and the film is wound into a roll shape, thereby obtaining a biaxially stretched film having a thickness of 125 μm and a width of 800 mm to 500 m. A film roll (mill roll) wound up over the length of was obtained. Thereafter, the properties of the obtained film were evaluated by the respective measuring methods described above. The evaluation results are shown in Table 3.

[Example 2]
An unstretched film was obtained in the same manner as Example 1 except that the take-up speed of the unstretched film was adjusted to change the thickness of the unstretched film to 330 μm. Thereafter, the unstretched film obtained was changed into a first stage longitudinal stretch ratio of 3.00 times, a second stage longitudinal stretch ratio was changed to 1.17 times, and stretched in two stages. A lateral relaxation treatment of 5.0% was performed at 0 ° C., and an area of 140 mm from the film end was excised from both ends of the film held by the tenter clip. The edge of the cut film edge was collected by inserting a blade into the groove of a grooved metal roll and niping the non-grooved part to minimize the waviness of the film surface by cutting the edge. .

  The film with the edge cut away was passed through a 170 ° C. thermal relaxation zone without holding the edge with a clip and then led to the cooling zone with a second clip chain. The longitudinal relaxation treatment was performed in the thermal relaxation zone by reducing the speed of the second clip chain by 2.5% from the speed of the first clip chain. Thereafter, the film temperature was lowered to room temperature below the glass transition temperature through the cooling zone, and both edge portions were cut and removed, and a biaxially stretched film having a width of 25 μm and a width of 800 mm was wound over a length of about 2,000 m. A film roll was prepared. And the characteristic of the obtained film was evaluated by the same method as Example 1. The evaluation results are shown in Table 3.

[Example 3]
Polyethylene terephthalate [A] ([η] = 0.63) containing 0.03% by mass of silica particles (manufactured by Fuji Silysia Chemical Co., Ltd., Silicia 310) as an additive so that the moisture content is 50 ppm or less. After drying, it was charged and melted at a temperature of 285 ° C. During melting with an extruder, it was filtered with a filter material of a sintered stainless steel (nominal filtration accuracy: particles having a size of 10 μm or more were cut by 90%). Next, the resin sheet is extruded from a T-shaped die, wound around a casting drum having a surface temperature of 30 ° C. using an electrostatic application casting method, and then cooled and solidified to form an unstretched film having a thickness of 1,000 μm and a width of 475 mm. Obtained.

The obtained unstretched film was heated to 72 ° C. with a heated roll group, and then heated by a laser in the same manner as in Example 2 while being 3.00 times in the longitudinal direction (longitudinal direction). Stretched (first-stage longitudinal stretching). The laser spot diameter was 4 mm, and the scanning speed was adjusted so that the sheet traveled in the longitudinal direction by 0.2 mm during one reciprocation in the width direction. The first nip roll on the front side was adjusted to maintain the film temperature, and the second nip roll on the rear side was adjusted to the cooling side. The first CO ₂ laser was arranged so as to be at the center position between the first nip roll and the second nip roll. Further, the temperature difference of the film before and after the stretching point of the first-stage longitudinal stretching described above was 28 ° C.

Thereafter, the film after the longitudinal stretching is subjected to a CO ₂ laser similar to the first laser provided between the nip rolls between the second nip roll and the third nip roll disposed immediately after the second nip roll ( While being heated to 100 ° C. by the second laser), the film was stretched 1.17 times in the longitudinal direction (longitudinal direction) (second-stage longitudinal stretching). The spot diameter of the second CO ₂ laser was also adjusted to 4 mm. The third nip roll was adjusted to 30 ° C.

As described above, after the unstretched film is stretched in two stages in the longitudinal direction, the longitudinally stretched film is guided to a tenter, stretched 4.0 times in the width direction in an atmosphere of 130 ° C., and heat-set at 235 ° C. Then, a lateral relaxation treatment of 3.0% was performed at 225 ° C., and the guide rail position of the tenter clip was further displaced to adjust the tenter clip interval in the longitudinal direction of the film, and a longitudinal relaxation treatment of 2.5% was performed. The film roll (mill roll) which wound the biaxially stretched film of thickness 75 micrometers and 800 mm width over the length of about 900 m was obtained by cutting and removing both edge parts. And the characteristic of the obtained film was evaluated by each measuring method mentioned above. The evaluation results are shown in Table 3.

[Example 4]
An unstretched film was obtained in the same manner as in Example 1. Thereafter, the obtained unstretched film was heated to 72 ° C. with a heated roll group, and then stretched 2.8 times in the longitudinal direction (longitudinal direction) while being heated by a laser (first stage) Longitudinal stretching). The laser spot diameter was 4 mm, and the scanning speed was adjusted so that the sheet advanced in the longitudinal direction by 0.2 mm during one reciprocation in the width direction. The first nip roll on the front side was adjusted to maintain the film temperature, and the second nip roll on the rear side was adjusted to the cooling side. The first CO ₂ laser (first laser) was arranged so as to be at the center position between the first nip roll and the second nip roll.

Thereafter, the film after the longitudinal stretching is subjected to a CO ₂ laser similar to the first laser provided between the nip rolls between the second nip roll and the third nip roll disposed immediately after the second nip roll ( The second laser was stretched 1.25 times in the longitudinal direction (longitudinal direction) (second longitudinal stretching). The spot diameter of the second CO ₂ laser was also adjusted to 4 mm. The third nip roll was adjusted to 30 ° C.

  As described above, after the unstretched film was stretched in two stages in the longitudinal direction, the longitudinally stretched film was led to a tenter and subjected to transverse stretching, heat setting, transverse and longitudinal relaxation treatment in the same manner as in Example 1, A film roll obtained by winding a biaxially stretched film having a thickness of 125 μm and a width of 1,060 mm over a length of about 500 m was obtained. The characteristics of the film were evaluated by the same method as in Example 1. In addition, the temperature difference of the film before and behind the extending | stretching point of the 1st step | paragraph and the 2nd step | paragraph longitudinal stretch in Example 4 was 28 degreeC and 10 degreeC, respectively. The evaluation results are shown in Table 3.

[Example 5]
By changing the width of the extrusion die and adjusting the take-up speed of the unstretched film to change the thickness of the unstretched film to 2,230 μm, and cooling it with cooling air using air when it is wound around the casting drum. The obtained unstretched film was stretched 2.58 times in the longitudinal direction, and then stretched 1.20 times on the rear side. Then, the biaxially stretched film having a thickness of 188 μm and a width of 1,040 mm is obtained by transverse stretching and heat setting in the same manner as in Example 2 to obtain a transverse relaxation treatment of 1.7% and a longitudinal relaxation treatment of 2.8%. The film roll which wound up about 500 m in length was obtained. And the characteristic of the obtained film was evaluated by the same method as Example 1. In addition, the temperature difference of the film before and behind the extending | stretching point of the 1st stage | paragraph and the 2nd stage | paragraph longitudinal stretch in Example 5 was 26 degreeC and 10 degreeC, respectively. The evaluation results are shown in Table 3.

[Example 6: Film formation according to Comparative Example 2 of WO 03/093008 pamphlet]
Dimolic acid component (based on the entire dicarboxylic acid component) 49 mol% dimethyl terephthalate, 49 mol% dimethylisophthalate, and 2 mol% 5-sulfonatoisophthalic acid, ethylene glycol as the glycol component (relative to the entire glycol component) Using 50 mol% and neopentyl glycol 50 mol%, a transesterification reaction and a polycondensation reaction were carried out by a conventional method to prepare a water-dispersible sulfonic acid metal base-containing copolymer polyester resin.

  Next, after mixing 51.4 parts by weight of water, 38 parts by weight of isopropyl alcohol, 5 parts by weight of n-butyl cellosolve, and 0.06 parts by weight of nonionic surfactant, the mixture was heated and stirred and reached 77 ° C. After adding 5 parts by mass of the above water-dispersible sulfonic acid metal base-containing copolymer polyester resin and continuing to stir until the resin is no longer agglomerated, the resin aqueous dispersion is cooled to room temperature, and the solid content concentration is 5.0% by mass. A uniform water-dispersible copolymerized polyester resin solution was obtained.

  Further, 3 parts by mass of aggregated silica particles (Fuji Silysia Co., Ltd., Silicia 310) was dispersed in 50 parts by mass of water with a homogenizer at 1000 rpm for 1 hour, and then the above-mentioned water-dispersible copolyester resin solution 99.46. 0.54 parts by mass of an aqueous dispersion of silicia 310 was added to parts by mass, and 20 parts by mass of water was added with stirring to obtain coating solution A.

  Polyethylene terephthalate [B] is produced by charging 1000 parts of dimethyl terephthalate, 650 parts of ethylene glycol, and 0.4 part of manganese acetate tetrahydrate into a transesterification can, and performing a transesterification reaction at 120 to 210 ° C. Methanol was distilled off. When the transesterification reaction was completed, 0.1 part of trimonic acid antimony and 0.6 part of normal phosphoric acid were added, and the pressure in the system was gradually reduced to 133 Pa in 75 minutes. At the same time, the temperature was gradually raised to 280 ° C. Under these conditions, a polycondensation reaction was carried out for 70 minutes, and the molten polymer was extruded into water from a discharge nozzle, and a cylindrical chip having a diameter of about 3 mm and a length of about 5 mm was obtained by a cutter. The intrinsic viscosity of the obtained polyethylene terephthalate [B] was 0.63 dl / g.

The polyethylene terephthalate [B] obtained in this way was dried so that the moisture content was 50 ppm or less, and charged and melted at 286 ° C. An unstretched film obtained in the same manner as in Example 1 was longitudinally stretched in the same manner as in Example 1, and the coating liquid A was applied to one side of this film so that the wet coating amount was 6.5 g / m ^2. Then, after drying at a temperature of 120 ° C., the film was guided to a tenter and stretched, heat-set, and longitudinally relaxed in the same manner as in Example 1 to form a biaxially stretched film having a thickness of 125 μm and a width of 1,060 mm of about 500 m. A film roll wound up over the length of was obtained. The film characteristics were evaluated in the same manner as in Example 1. Although it corresponds to a comparative example in the pamphlet of International Publication No. 03/093008, the thickness unevenness was improved by the method of the present invention.

[Example 7]
An unstretched sheet obtained in the same manner as in Example 1 above was heated with a group of heated rolls, and then a high-temperature heated jet stream was jetted between the first nip roll and the second nip roll arranged in front and back. Thus, the film was stretched 2.8 times in the longitudinal direction (longitudinal direction) (first-stage longitudinal stretching).

  The irradiation width of the high-temperature heating jet stream was adjusted to be 18 mm. The front first nip roll was adjusted to maintain the film temperature, and the rear second nip roll was adjusted to the cooling side. In addition, the 1st high temperature heating jitt air flow was arrange | positioned in the center position between the 1st nip roll and the 2nd nip roll. Further, the temperature difference of the first-stage sheet was 13 ° C.

  Thereafter, the film after the longitudinal stretching is subjected to the same process as the first high-temperature heating jet stream provided between the second nip roll and the third nip roll disposed immediately after the second nip roll. The film was stretched 1.25 times in the longitudinal direction (longitudinal direction) by two high-temperature heated jet streams (second-stage longitudinal stretching). Note that the irradiation width of the heated airflow was adjusted to be 18 mm. The third nip roll was adjusted to 30 ° C. In addition, the 2nd high temperature heating jet stream was arrange | positioned in the center position between the 2nd nip roll and the 3rd nip roll. Moreover, the temperature difference of the sheet | seat in the above-mentioned 2nd stage longitudinal stretch was 8 degreeC.

  As described above, after the unstretched film was stretched in two stages in the longitudinal direction, the longitudinally stretched film was guided to a tenter, and stretched, heat-set, and longitudinally relaxed in the same manner as in Example 1 to obtain a thickness of about 125 μm. The film roll (mill roll) which wound up the biaxially stretched film of width 1060mm over the length of about 500 m was obtained. The characteristics of the film were evaluated by the same method as in Example 1.

[Comparative Example 1: Film formation according to Example 1 in JP-A-48-43772]
The unstretched film obtained in the same manner as in Example 2 was heated to 85 ° C. with a heated roll group, and then stretched 1.43 times between the first nip roll and the second nip roll (first-stage longitudinal stretching), Then, after guiding to a cooling roll, it heated again at 90 degreeC and extended | stretched 1.53 times (2nd stage longitudinal extension). Furthermore, after guiding the film to a cooling roll, the film was heated to 95 ° C. and stretched 1.60 times (third-stage longitudinal stretching). Therefore, the total draw ratio is 3.30 times. In Comparative Example 1, stretching between rolls by roll heating was performed. Then, the above-described longitudinally stretched film was transversely stretched and heat-set in the same manner as in Example 2 to wind a biaxially stretched film having a thickness of 25 μm and a width of 1,000 mm over a length of about 2,000 m. A film roll was prepared. And the characteristic of the obtained film was evaluated by the same method as Example 1. The evaluation results are shown in Table 3.

[Comparative Example 2: Film formation according to Example 1 in JP-A-54-56774]
An unstretched film was obtained in the same manner as in Example 1 except that the take-up speed of the unstretched film was adjusted to change the thickness of the unstretched film to 400 μm. Thereafter, the unstretched film was heated to 85 ° C. with a heated roll group, heated to 100 ° C. with a far-infrared heater, stretched 1.30 times, cooled with a cooling roll, and further heated to 85 ° C. Heated and stretched 3.3 times. In addition, since the far-infrared heater was used in the said longitudinal stretch, the width | variety of the heating was very wide compared with Example 1 (about 200 mm width). Moreover, the temperature difference of the film before and after the stretching point of the first and second longitudinal stretches was 14 ° C. and 1 ° C., respectively. Then, the above-described longitudinally stretched film was transversely stretched and heat-set in the same manner as in Example 2 to wind a biaxially stretched film having a thickness of 25 μm and a width of 1,000 mm over a length of about 2,000 m. A film roll was prepared. And the characteristic of the obtained film was evaluated by the same method as Example 1. The evaluation results are shown in Table 3.

[Comparative Example 3]
An unstretched film obtained in the same manner as in Example 4 was heated to 80 ° C. with a heated roll group, then heated to 90 ° C. with a far-infrared heater, stretched 2.80 times, and cooled with a cooling roll. Further, the film was heated to 90 ° C. by a far infrared heater and stretched 1.25 times. In addition, since the far-infrared heater was used in the said longitudinal stretch, the width | variety of the heating was very wide compared with Example 4 (about 200 mm width). Moreover, the film temperature difference before and after the stretching point of the first-stage longitudinal stretching described above was 13 ° C., and the film temperature difference before and after the stretching point of the second-stage longitudinal stretching described above was 1 ° C. The characteristics of the film obtained in the same manner as in Example 4 were evaluated by the same method as in Example 1.

[Comparative Example 4: Film formation according to Example 2 of pamphlet of International Publication No. 03/093008]
Polyethylene terephthalate [C] is 1000 parts dimethyl terephthalate and 650 parts ethylene glycol. Then, 0.4 part of magnesium acetate tetrahydrate was charged into a transesterification can, subjected to a transesterification reaction at 120 to 210 ° C., and produced methanol was distilled off. When the transesterification reaction was completed, 0.2 part of trimonic acid antimony and 0.2 part of normal phosphoric acid were added, and the pressure in the system was gradually reduced to 133 Pa in 75 minutes. At the same time, the temperature was gradually raised to 280 ° C. Under these conditions, a polycondensation reaction was carried out for 70 minutes, and the molten polymer was extruded into water from a discharge nozzle, and a cylindrical chip having a diameter of about 3 mm and a length of about 5 mm was obtained by a cutter. The intrinsic viscosity of the obtained polyethylene terephthalate [C] was 0.63 dl / g.

  Polyethylene terephthalate [C] ([η] = 0.63) containing 0.03% by mass of silica particles (manufactured by Fuji Silysia Chemical Co., Ltd., Silicia 310) as an additive so that the moisture content is 50 ppm or less. After drying, it was charged and melted at a temperature of 285 ° C. During melting with an extruder, it was filtered with a filter material of a sintered stainless steel (nominal filtration accuracy: particles having a size of 10 μm or more were cut by 90%). Next, the resin sheet is extruded from a T-shaped die, wound around a casting drum having a surface temperature of 30 ° C. by using an electrostatic application casting method, and cooled and solidified to form an unstretched film having a thickness of 1,680 μm and a width of 490 mm. Obtained. And after heating the obtained unstretched film to 85 degreeC with the heated roll group, it heated at 100 degreeC with the far-infrared heater, and was extended 3.50 times. Thereafter, a tenter was passed in the same manner as in Example 1 to obtain a 125 μm film. The properties of the obtained film were evaluated by the same method as in Example 1. The evaluation results are shown in Table 3. In the republished WO2003 / 093008 pamphlet, 2 m is measured in the length direction, but the thickness unevenness is deteriorated in the evaluation of the present invention.

[Comparative Example 5]
The unstretched film obtained in the same manner as in Example 1 except that the thickness of the unstretched film was changed to 1,700 μm by adjusting the take-up speed of the unstretched film, and the three-stage longitudinal stretching was performed in the same manner as in Example 1. , Transverse stretching, heat setting, and transverse relaxation treatment were performed. Next, the guide rail position of the tenter clip is displaced to adjust the angle of the connecting portion between the clips that can be interlocked with it, and the tenter clip interval in the vertical direction of the film is narrowed to reduce the longitudinal relaxation by 1.5%. Went. If the longitudinal relaxation treatment is larger than 1.5%, wrinkles are generated from the clip, and if it is larger than this, the flatness deteriorates. A film was obtained in the same manner as in Example 1 except that the method of longitudinal relaxation was changed. And it evaluated by the method similar to Example 1. FIG. The evaluation results are shown in Table 3.

[Comparative Example 6]
The unstretched film obtained in the same manner as in Example 2 was subjected to two-stage longitudinal stretching, lateral stretching, heat setting, and lateral relaxation treatment in the same manner as in Example 2. Next, the guide rail position of the tenter clip is displaced to adjust the angle of the connecting portion between the clips that can be interlocked with it, and the tenter clip interval in the vertical direction of the film is narrowed to reduce the longitudinal relaxation by 1.5%. Went. A film was obtained in the same manner as in Example 2 except that the longitudinal relaxation treatment method was changed. And it evaluated by the method similar to Example 1. FIG. The evaluation results are shown in Table 3.

  The production conditions of each example and comparative example are shown in Table 1, the position of the cutout part of the film sample used for evaluation is shown in Table 2, and the evaluation results are shown in Table 3.

[Effects of Example Film]
From Table 3, all of the films of the examples have good dimensional stability, extremely small thickness fluctuation rate (thickness unevenness) in the longitudinal direction, good flatness, and very few scratches on the film surface. Optical defects were hardly detected. On the other hand, it can be seen that the film of the comparative example has a large thickness fluctuation rate (thickness unevenness) in the longitudinal direction, poor flatness, and many scratches on the film surface. In Table 3, Example 1-6 used a laser as a heating means in longitudinal stretching, and Example 7 used a high-temperature jet heating apparatus. Comparative Example 1 does not use a heating device. In Comparative Examples 2 to 4, a far infrared heater was used as a heating means in longitudinal stretching. Comparative Example 7 also used a laser. In Example 1-7, the longitudinal relaxation treatment was performed between the first clip chain and the second clip chain. In Comparative Example 1-4, the longitudinal relaxation process was performed in the same manner as in the example, and the longitudinal relaxation process in Comparative Example 5-6 was performed by a method of narrowing the clip interval.

  Since the biaxially stretched polyethylene terephthalate resin film of the present invention has excellent properties as described above, it can be suitably used as an optical film for various precision printing applications and displays. In particular, green sheet manufacturing for ceramic capacitors, applications such as transfer foil and other substrate films, substrates for precision printing such as offset printing, and precision printing applications and light transmission and reflection. Prism sheets used in liquid crystal displays for optical applications as various optical films used in a wet state, antireflection films and hard coat films, base films such as light diffusion plates, near-infrared absorbing films and electromagnetic waves used for the front plates of plasma displays It can be suitably used for an optical film such as a base film for an absorption film, a base film for a touch panel or a transparent conductive film for electroluminescence, a crush prevention film for a cathode ray tube, a back sheet for a solar cell, and the like.

A ... Yield point,
B ... Rising point,
F: film X: film winding direction N1, N2, N3: intermediate zone HS: heat setting zone R: relaxation zone C: cooling zone R1: grooved roll R2: nip roll CU: blade F1: trimmed film edge 1: Traveling rail of the first clip chain 2: Traveling rail of the second clip chain 3: Clip 4, 5: Bearing connected to the clip 6: Chain link 7: Joint part 8: Table to which the clip is attached 9: Clip 10: Bearing connected to the joint 11: Clip traveling rail 12: Guide rail

Claims (7)

A film-forming process for forming an unstretched film by melt-extruding the raw material resin from an extruder, a biaxial stretching process for biaxially stretching the unstretched film obtained in the film-forming process in the machine direction and the transverse direction, A biaxially stretched polyethylene terephthalate-based resin film produced by undergoing a heat setting step for heat fixing the film after axial stretching, obtained by narrowing the width of heating in the longitudinal direction in the longitudinal stretching step,
A biaxially stretched polyethylene terephthalate resin film characterized by satisfying the following requirements (1) to (3).
(1) A film sample having a length of 30 m and a width of 3 cm is taken along the longitudinal direction of a biaxially stretched polyethylene terephthalate-based resin film from a film cutting portion provided by the following cutting method A, and the thickness variation in the longitudinal direction of the film sample The thickness variation rate in the longitudinal direction is 0.5% or more and 4% or less (cutting-out method A)
At both end portions in the film width direction (portions within 50 mm from the edge), film cutout portions are provided at the beginning, middle and end of the film in the longitudinal direction. Here, the “starting portion” and “end portion” refer to a region including the length of the film in the longitudinal direction within 2 m from the end portion. Further, the “intermediate portion” refers to a region including 50% position in the film longitudinal direction. (2) A length along the longitudinal direction of the biaxially stretched polyethylene terephthalate resin film from the film cutting portion provided by the following cutting method B An average HS150, which is an average value of the heat shrinkage rate in the longitudinal direction of the film when a film sample of 250 mm × width 20 mm is taken and heated at 150 ° C. for 30 minutes, is −0.25% or more and 0.40. % (Cutout method B)
A biaxially stretched polyethylene terephthalate-based resin film is divided into four portions in the width direction and a portion 50 mm from the end in the width direction, and five cutout portions are provided. The cut-out portions in the width direction are provided at the start, middle and end of the roll (15 in total). Here, “winding start” and “winding end” of the roll are regions of 50 mm or more and 2 m or less from the end of the winding start and the end of winding of the entire film roll, and “intermediate” is the film longitudinal direction It is an area including the 50% position.
(3) About 16 film samples having a length of 250 mm and a width of 250 mm collected from the film cutting portion provided by the following cutting method C, the following measurement method was used to measure scratches having a depth of 1 μm or more and a length of 3 mm or more on the surface. When the number is measured, the number of scratches is not more than 10 / m ² (cutout method C)
From the biaxially stretched polyethylene terephthalate resin film, the beginning (5% of the total length in the longitudinal direction) and two intermediate portions (35% of the total length in the longitudinal direction, 65%) with respect to the length in the longitudinal direction of the film Position) and the end part (position of 95% of the total length in the longitudinal direction), the position of the center line of the part sampled from both ends in the width direction is divided into three equal parts in the width direction as the center line Provide a part.
(A) Scratch detection method By the following optical defect detection method, an optical defect recognized as a size of 50 μm or more is detected for 16 film samples of 250 mm × 250 mm.
[Optical defect detection method]
A fluorescent lamp of 20 W × 2 lamps is arranged as a projector at 400 mm below the XY table, and a film sample to be measured is placed on a mask having a slit width of 10 mm provided on the XY table. Light is incident so that the angle between the line connecting the projector and the receiver and the vertical direction of the film sample surface is 12 °, and the reflected light amount is converted into an electrical signal by a CCD image sensor camera placed 500 mm above the XY table. The electric signal is converted, amplified, differentiated, and compared with a threshold (threshold) level by a comparator to output an optical defect detection signal. This threshold value is preliminarily formed by drilling a hole of about 50 μm on a 2 mm thick aluminum plate, polishing burrs formed on the aluminum plate, and finishing the surface with a No. 200 buff. It adjusted so that a hole of 50 micrometers might be detected using this. Also, using a CCD image sensor camera, a scratch image is input, the video signal of the input image is analyzed by a predetermined procedure, the size of the optical defect is measured, and the position of the defect of 50 μm or more is displayed. To do. Optical defects are detected on both sides of the film sample.
(B) Measurement of Scratch Size A defect due to a scratch is selected from the optical defect portion detected in (a) above. The film sample is cut into an appropriate size, and observed using a three-dimensional shape measuring device TYPE550 manufactured by Micromap Co., Ltd. from the direction perpendicular to the surface of the film sample, and the size of the scratch is measured. When observed from the direction perpendicular to the surface of the film sample, that is, the film surface, the unevenness of the scratches close to each other within 50 μm is regarded as the same scratch, and the length and width of the rectangle with the smallest area covering the outermost part of those scratches are set. The length and width of the scratch. From this result, the number of scratches (pieces / m ² ) having a depth of 1 μm or more and a length of 3 mm or more is obtained.   The biaxially stretched polyethylene terephthalate resin film according to claim 1, wherein the thickness of the biaxially stretched polyethylene terephthalate resin film is 20 µm or more and 400 µm or less.   A biaxially stretched polyethylene terephthalate resin film roll comprising the biaxially stretched polyethylene terephthalate resin film according to claim 1.   A production method for producing a biaxially stretched polyethylene terephthalate-based resin film according to claim 1 or 2, wherein the film forming step forms an unstretched film by melting and extruding a raw material resin from an extruder, It includes a biaxial stretching step for biaxially stretching the unstretched film obtained in the film forming step in the machine direction and the transverse direction, and a heat setting step for heat-setting the film after biaxial stretching, and the longitudinal stretching step. However, it is heated to 105 ± 20 ° C. using a heating device while narrowing the width of heating between rolls having a difference in peripheral speed, and the magnification becomes 2.0 to 3.2 times in the longitudinal direction. Then, the film after the longitudinal stretching is passed between the cooled nip rolls, and the heating width is reduced between rolls having a difference in peripheral speed by using a heating device 100 ±. A method for producing a biaxially stretched polyethylene terephthalate resin film, which is heated to 20 ° C. and stretched so as to have a magnification of 1.05 times or more and 1.5 times or less in the longitudinal direction.   5. The biaxially stretched polyethylene terephthalate resin according to claim 4, wherein when the film is heated using a heating device in the longitudinal stretching step, the width of heating in the longitudinal direction between the rolls is 2 mm or more and 25 mm or less. A method for producing a film.   After passing through the maximum temperature part in the transverse stretching process and then performing the transverse relaxation treatment, the film edge is cut and separated, and then the edge is cut and separated by reducing the take-up speed of the film. 6. The method for producing a biaxially stretched polyethylene terephthalate resin film according to claim 4, wherein a direction relaxation treatment is performed.   The method for producing a biaxially stretched polyethylene terephthalate resin film according to claim 6, wherein after the longitudinal relaxation treatment, the film cooling treatment is performed while holding the edge portion of the film.