JP2010167771A - Biaxially stretched polyethylene terephthalate-based resin film and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a film base material which is excellent in dimensional stability, does not occur wrinkle or the like in a thermal processing and is suitably used for a green sheet for a ceramic capacitor excellent in flatness, a transfer film, a protective film for optical use or the like. <P>SOLUTION: In the biaxially stretched polyethylene terephthalate-based resin film, the difference of thermal shrinkage stress of two directions of a direction making an angle of 45° with the longitudinal direction of the film and a direction making an angle of 90°with the longitudinal direction of the film is ≤0.5 MPa at 160°C, and a thickness variation in the longitudinal direction is ≥0.5% to ≤4.0%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a biaxially stretched polyethylene terephthalate resin film, and more specifically, it has excellent processing characteristics and is required to have excellent flatness even under heat treatment, for use in production of green sheets for ceramic capacitors and transfer foil. Further, the present invention relates to a base film used by carrying out other coating.

  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. In particular, it is suitably used for a mold release for producing a green sheet for a ceramic capacitor that requires excellent strength and dimensional stability, and for a substrate film such as a transfer foil. In particular, with the increase in capacity and size of capacitors in recent years, the thickness of ceramic green sheets is becoming as thin as 2 to 5 μm, and the film substrate used in this application requires more precision and flatness than ever before. Has been. Furthermore, when used as a mold release application or transfer foil application for the production of green sheets for ceramic capacitors, the substrate film is subjected to various purposes in a state where tension is applied in the longitudinal direction at a high temperature (80 to 180 ° C.). Processing is performed. Also in this processing step, it is important to maintain the flatness of the film.

  The biaxially stretched polyethylene terephthalate resin film is first stretched in the longitudinal direction between rolls having a difference in rotational speed, and further stretched in the width direction with the end of the film held in a tenter. Manufactured by heat fixing in a tenter. In the stretching process in the width direction, both side edges of the film are gripped by the gripping means in the tenter, so that the longitudinal shrinkage stress accompanying the lateral stretching is restricted by the gripping means. In contrast, the central portion of the film is in a state where the restraining force by the gripping means is relatively weak. Therefore, there is a difference in the orientation and relaxation isotropy in the longitudinal direction, particularly in the central portion and the end portion, and the orientation is different depending on the position in the width direction of the film. Thus, when there is a remarkable distortion of the physical properties of the film, wrinkles in the vertical direction, the horizontal direction, or partial spots may occur. When using a base film in which the flatness of the post-processing step is disturbed, image distortion occurs in a ceramic capacitor molding defect or transfer foil application, which causes a significant decrease in yield.

  Furthermore, the flatness at the time of high-temperature processing such as mold release processing or transfer foil causes distortion of the film due to the tension applied in the longitudinal direction. Therefore, the thickness should be as small as possible. Further, if the thickness variation rate exceeds 5%, tarmi is generated due to the thinness of the thickness over a long period of time in a state of being wound by a roll, and thus workability in post-processing may be deteriorated.

  Regarding the flatness of the film, Patent Documents 1 to 4 have been disclosed so far. In addition to Patent Documents 1 to 4, as a method for reducing the uneven thickness of the biaxially stretched polyethylene terephthalate resin film, as in Patent Document 5, stretching at a relatively low magnification ratio is repeated in multiple stages. A method and a stretching method in which a low-magnification stretching is performed after performing a high-magnification stretching at a high temperature as in Patent Document 6 are known.

  Further, as in Patent Document 7, 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, an unstretched film is longitudinally stretched by a method of heating the film using a heat source of 30 kW / m or more and 200 kW / m or less, or by heating means provided 5 mm to 100 mm before the contact point between the film and the stretching roll as in Patent Document 8. A method of heating over a width of 3 mm to 30 mm and stretching in the film flow direction with a stretching roll, and further, as in Patent Document 9, in addition to the method of Patent Document 8, in multiple 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).

  Further, as in Patent Document 10, 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.

JP-A-6-254959 JP 2001-93771 A JP 2002-331575 A JP 2005-186555 A 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

  Further refinement is expected in the future in the film processing, particularly in the processing of the release sheet for ceramic capacitors. Thereby, even if it is a film conventionally used without a problem, there is a concern that the flatness of the base film may cause a problem of yield reduction when the capacitor is thinned.

  In addition, in order to obtain a biaxially stretched film, when performing transverse stretching on a film that has been longitudinally stretched, a difference in physical properties in the width direction occurs due to the behavior of transverse stretching under conventional stretching conditions, and the length of the film is formed. There is a difference in thermal characteristics between a direction that forms an angle of 45 degrees with the direction and a direction that forms an angle of 90 degrees with the direction. For this reason, since the thermal shrinkage rate in the vertical direction differs in the width direction, and the substantial tension applied to the film during thermal processing under tension differs in the width direction, the film is distorted. Furthermore, it will affect the generation of wrinkles due to the heat shrinkage stress difference in the oblique direction. For this reason, it is necessary to improve this situation in order to improve the productivity of processed films that require flatness even in a severely thermal environment during post-processing, especially films with a thickness of less than 60 μm called thin materials. It was.

  On the other hand, Patent Document 1 describes that a biaxially stretched polyester film having a difference in heat shrinkage stress between both ends of the film of 0 to 100 MPa is good for sagging. For wrinkles, a crystal size of 56 to 70 angstroms is considered good, but this is not a general indicator.

  Patent Document 2 discloses a flat carrier sheet for manufacturing a ceramic capacitor. Although these methods define the flatness of the carrier film and the thickness unevenness of the polyester film, they do not propose an index that optimizes the properties of the processed film especially on the premise of thinning.

  In Patent Document 3, regarding a biaxially stretched polyester film for mold release which improves the moldability of the mold while reducing the film thickness, the optimum birefringence Δn of the film is specified, and the tarmi at the time of mold release processing, etc. Although suppression is proposed, there is no description about heat resistance during processing, and it is difficult to maintain good flatness during processing only by optimizing the birefringence.

  Patent Document 4 discloses a film having a small difference in heat shrinkage stress. Although a great effect has been recognized as a result of this, the size of ceramic capacitors has become increasingly smaller recently, and it has become unsatisfactory at the conventional flatness level.

In addition, in each of the stretching methods of Patent Document 5, Patent Document 6, Patent Document 8, and Patent Document 9, each stretching at the time of multi-stage stretching is a simple stretching using a peripheral speed difference between heated rolls. For this reason, the thickness unevenness can be reduced, but the difference in physical properties in the width direction has not been improved. On the other hand, according to the methods of Patent Document 7 and Patent Document 11, the thickness unevenness cannot be reduced to a high degree, and a biaxially stretched polyethylene terephthalate resin film that satisfies a high level requirement for flatness in recent years cannot be obtained at all. . The particle size of the fine particles due to the catalyst in Patent Document 10 describes 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, it has excellent dimensional stability due to heat, thickness unevenness is highly reduced, flatness is good, and there is little difference in physical properties in the width direction, which is suitable for post-processing such as a release sheet. There was no axially stretched polyethylene terephthalate resin film.

  In order to solve the problems of the conventional stretching methods described above, the present inventors make a film with few thickness spots and very little wrinkling due to a difference in thermal shrinkage stress in the oblique direction (ab direction) of the film. We studied earnestly whether it was possible. As a result, as will be described later, by performing the stretching conditions in the longitudinal stretching process and the lateral stretching process under completely different conditions, there are few film thickness unevenness, extremely little wrinkling during thermal processing, and in the next process The present inventors have found that an extremely excellent film suitable for processing can be obtained, and have completed the present invention.

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 (2) obtained by narrowing.
(1) The difference in heat shrinkage stress value between two directions, ie, a direction that forms an angle of 45 degrees with a longitudinal direction of the biaxially stretched polyethylene terephthalate resin film and a direction that forms an angle of 90 degrees is 0 at 160 ° C. (2) A film sample having a length of 30 m and a width of 3 cm is taken along the longitudinal direction of the biaxially stretched polyethylene terephthalate resin film from the film cut-out portion provided by the cut-out method A described below, and the film sample When the thickness variation in the longitudinal direction is measured, the thickness variation rate in the longitudinal direction is 0.5% or more and 4.0% or less (cutting 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. In addition, the “intermediate portion” refers to a region including a 50% position in the film longitudinal direction. Among the present inventions, the second invention is characterized in that the film has a thickness of 10 μm or more and less than 60 μm. It is a terephthalate resin film.
Of the present application, 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 step for biaxially stretching the unstretched film obtained in the film forming step in the longitudinal direction and the transverse direction, and a heat setting step for heat-setting the film after biaxial stretching. The stretching process satisfies the following requirement (3), and the transverse stretching process satisfies the following requirements (4) to (8): A method for producing a biaxially stretched polyethylene terephthalate resin film.
(3) Heating to 105 ± 20 ° C. using a heating device while narrowing the width of heating between rolls provided with a peripheral speed difference, and a magnification of 2.0 to 3.2 times in the longitudinal direction; The film after longitudinal stretching is passed between cooled nip rolls and heated to 100 ± 20 ° C. using a heating device while narrowing the heating width between rolls provided with a difference in peripheral speed. (4) In the transverse stretching step, the difference in the set temperature in the continuous temperature zone is the transverse stretching. 5 ° C. or more and 30 ° C. or less in the first half portion (up to the temperature division region including the draw ratio of 1.8 times) (5) The temperature range that passes 1.8 times in the stretching in the transverse drawing step is 100 ° C. or more. (6) Transverse stretching step The difference in temperature setting between successive temperature zones is 5 ° C. between the first half of the horizontal stretching (up to the temperature zone including the draw ratio of 1.8 times) and the first temperature zone of the next second half. (7) In the transverse stretching step, the difference in temperature setting between successive temperature zones is the second half of the transverse stretching (the temperature zone next to the temperature zone including the draw ratio of 1.8 times). (From the region to the final draw ratio) is 5 ° C. or higher and 30 ° C. or lower. (8) The temperature range that reaches the final draw ratio in the stretching in the transverse drawing step is 160 ° C. or higher and lower than 220 ° C.

  The biaxially stretched polyethylene terephthalate-based resin film of the present invention has extremely small thickness unevenness (particularly thickness unevenness in the longitudinal direction) and good flatness, and is free from wrinkles due to tension adjustment during high-temperature processing at 80 to 180 ° C. Very little occurrence. Therefore, the biaxially stretched polyethylene terephthalate resin film of the present invention can be suitably used for films such as green sheets for ceramic capacitors, transfer films, and protective films for optical applications.

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.

  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. The intrinsic viscosity is also expressed as [η].

  Moreover, when forming the film of this invention by PET, the range of 3-30 eq / t is preferable and, as for the acid value (AV) of PET 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 order to reduce defects due to foreign matter, it is preferable to perform high-precision filtration during melt extrusion so that the number of foreign matters having a diameter of 20 μm or more present per 1 m ^{2 of the} film after film formation is 10 or less. . When performing the above-described high-precision filtration, it is preferable to use a filter medium having an initial filtration efficiency of 90% or more, preferably 95% or more and a filtration particle size of 15 μm or less. Here, the initial filtration efficiency refers to a numerical value measured by ANSI / B93.36-1973. Note that the number of foreign substances in the raw material is obtained by the following method, for example.

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

  The thickness of the film constituting the biaxially stretched polyethylene terephthalate resin film of the present invention is not particularly limited. However, it is preferable that the base material is 10 μm or more and less than 60 μm as a base material for precision printing such as a mold release for producing a green sheet for ceramic capacitors, a base film such as a transfer foil, or offset printing.

  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 10 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 60 μm, it is preferably 7,000 m or less, and more preferably 1,100 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.

[Heat shrinkage stress]
The film undergoes dimensional changes due to heating. When the film is processed at a high temperature (80 to 180 ° C.) in the post-processing flow operation, heat shrinkage stress is generated in the film in a state where tension is applied in the longitudinal direction. If there is anisotropy in the magnitude of this heat shrinkage stress, it will be a factor that causes wrinkles and tarmi on the film. The film of the present invention has a difference in heat shrinkage stress value between two directions, ie, a direction forming an angle of 45 degrees with the longitudinal direction of the film and a direction forming an angle of 90 degrees with the film in the longitudinal direction of the film. It is characterized by being 4 MPa or less. When the heat shrinkage stress difference is 0.5 MPa or less, the flatness of the film is maintained even during the temperature raising process in post-processing, and it is difficult to cause wrinkles and tarmi and good workability is obtained.

Here, the measurement of the heat shrinkage stress value is performed as follows.
(1) A film sample (for example, a sample width of 4 mm and a sample length of 15 mm) is cut out from the film along two directions, a direction that forms an angle of 45 degrees with the longitudinal direction of film formation and a direction that forms an angle of 90 degrees.
(2) Using a thermomechanical analyzer (for example, TMA / SS100, manufactured by Seiko Denshi Kogyo Co., Ltd.), it is set under the condition of an initial load initial load of 19.6 mN. The initial load is corrected to zero, the temperature is raised from 5 to 30 ° C / min in the range from 30 ° C to 230 ° C, and it occurs with film shrinkage in a state where the distance between chucks is kept constant in a series of temperature raising processes. Measure the stress.
(3) The heat shrinkage stress value at the 160 ° C. point in the temperature raising process is measured, the heat shrinkage stress value in the longitudinal direction and 45 ° direction of the film formation, and the longitudinal direction and 130 ° direction of the film formation. The absolute value of the difference from the heat shrinkage stress value was calculated.

[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 needs to be in the range of 0.5% to 4.0%. The upper limit of the thickness variation rate is more preferably 3.5% or less, still more preferably 3.0% or less, still more preferably 2.5% or less, and particularly preferably 2.0% 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 unevenness is measured, it is necessary that the thickness unevenness in the longitudinal direction of the film sample is within the range of 0.5% or more and 4.0% 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.

  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), and the film after the longitudinal stretching is laterally stretched in the width direction (transverse direction) by the method described below, and heat-fixed by the method described below. It becomes possible to obtain the film of this invention by processing. 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 5 and the extending method of patent document 6 are proposed.

  The stretching method of Patent Document 5 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 5, each stretching is simply performed by utilizing the difference in the peripheral speed between heated rolls, so that the film sticks to the roll when the heated low-speed roll leaves. As a result, so-called stick-like minute spots occur, the film is stretched slightly on a low-speed roll, and flatness deteriorates due to thermal spots in the thermal processing process without affecting the thickness spots. To do.

  On the other hand, the stretching method of Patent Document 6 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 6 is similar to the method of Patent Document 5, because each stretching is simply performed by using the difference in peripheral speed between heated rolls. The film sticks to the roll at the time of leaving, so that the so-called stick phenomenon minute spots occur, the film is stretched slightly on the low-speed roll, even if it does not affect the thickness spots in the thermal processing step Deterioration of flatness due to heat spots occurs.

  The stretching method of Patent Document 7 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 or more and 200 kW / m or less to heat the film. Although the occurrence of minute spots due to adhesion can be suppressed, the thickness spots cannot be reduced to a high degree, and a high level requirement for flatness in recent years cannot be satisfied.

  The method of Patent Document 8 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 stretch roll, and stretched in the film flow direction with a stretch roll. However, since the high-speed grip part of the heated film is located in the high-speed nip roll behind the stretching roll by the heating means, the stretching roll and the film are kept at the same speed to prevent minute spots. Is required. However, it is difficult to match this speed, and if there is a slight variation in stretching, the speed is shifted and there is a drawback that minute spots are formed on the film.

  Although the method of patent document 9 is a method of extending | stretching in several steps of an extending | stretching roll, there existed a fault that extending | stretching at the time of separation | separation of a roll occurred and a fine spot would enter again.

  With the method of Patent Document 10, 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 have intensively studied how to make the thickness unevenness good. As a result, it has been found that by adopting a special stretching method that narrows the width of heating in the longitudinal stretching process as described below, a film with small thickness unevenness can be obtained by a completely different stretching method from the conventional one. The present invention has been devised.

(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 increases and minute spots tend to occur. Conversely, if the temperature at the stretching point becomes too high, even if the temperature difference is 15 ° C. or more, there will be no difference in stretching stress, and the stretching will be deformed on the low-speed roll, or it will be minute on the low-speed roll. Sticks are generated, resulting in minute spots. 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. In addition, it is possible to prevent a situation in which unevenness of the rear side roll (scratches on the roll surface that cannot be visually observed, adhesion of dust etc. to the roll surface) is transferred to the film, and to obtain a film with less thickness unevenness It becomes possible.

  The back roll after the first stage of longitudinal stretching is preferably nipped, and the temperature of the nip roll is set to be 5 ° C. or more lower than the surface temperature of the film subjected to longitudinal stretching to prevent minute unevenness on the surface. It is effective. 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 the longitudinal stretching step of the film, by using the means (1) to (4) described above, it is possible to reduce film thickness unevenness (particularly, thickness unevenness in the longitudinal direction). Note that only one of the above-described means (1) to (4) does not effectively contribute to the reduction in thickness unevenness and minute unevenness of the film roll, and (1) to (4 ) Is used in combination, it is considered that the thickness unevenness of the film 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.

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

  Due to the behavior of the transverse stretching, a difference in physical properties in the width direction occurs under the conventional stretching conditions, and a difference occurs in the thermal characteristics between a direction that forms an angle of 45 degrees with the longitudinal direction of the film and a direction that forms an angle of 90 degrees. For this reason, since the thermal shrinkage rate in the vertical direction differs in the width direction, and the substantial tension applied to the film during thermal processing under tension differs in the width direction, the film is distorted. Furthermore, it will affect the generation of wrinkles due to the heat shrinkage stress difference in the oblique direction. For this reason, it is necessary to improve this situation in order to improve the productivity of processed films that require flatness even in a severely thermal environment during post-processing, especially films with a thickness of less than 60 μm called thin materials. It was.

  In order to eliminate the problems of the above-described conventional stretching methods, the present inventors do not cause strain due to tension in the thermal processing step due to the difference in thermal shrinkage in the width direction on the film. It was intensively studied whether a film with very little wrinkling due to a difference in thermal shrinkage stress in the oblique direction (ab direction) of the film could be produced. As a result, in addition to the above-described longitudinal stretching method, the stretching conditions of the transverse stretching process are performed under conditions completely different from the conventional ones as described below, so that the film has no heat spots, wrinkles during heat processing are extremely small, The inventors have found that a film excellent in processing suitability in the next step can be obtained without causing distortion due to processing tension due to a difference in shrinkage rate, and the present invention has been completed.

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

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

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

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

  As a result of the action of this force, the physical properties of the film end portion are different between the characteristics in the longitudinal direction and 45 degree direction of film formation and the characteristics in the direction perpendicular thereto. Among these characteristics, it is considered that the anisotropy of heat shrinkage stress affects the generation of wrinkles in thermal processing. In order to reduce the difference in heat shrinkage stress, when the stretching temperature in the transverse direction is simply set at a high temperature, the stretching corresponds to “stretching that gives a strain corresponding to a plateau region in the SS curve”, and the film There was a risk of uneven thickness. Further, when the stretching temperature in the transverse direction is increased, the temperature difference from the preheating region becomes large, and there is a possibility that thickness unevenness is caused due to the disorder in the temperature state in the tenter. If such a thickness unevenness occurs in a film, it cannot be used in a post-processing process that has been increasingly refined in recent years. However, surprisingly, it has been found that by optimizing the relationship between the transverse draw ratio and temperature as described below, it is possible to obtain a product with good thickness spots and good thermal properties.

(1) Control of temperature in temperature division region of transverse stretching step In the transverse stretching step, the tenter is usually provided with a plurality of temperature division regions. Set the temperature difference in the zone to 5 ° C to 30 ° C until the first half of the stretch (up to the temperature zone where the draw ratio includes 1.8 times) and the second half (the temperature zone including the draw ratio of 1.8 times) It is necessary to set the temperature range from the next temperature section region to the final draw ratio) to 5 ° C. or higher and 30 ° C. or lower. On the other hand, the temperature difference between the temperature zone including 1.8 times and the next temperature zone is preferably 5 ° C. or more and 40 ° C. or less.

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

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

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

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

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

(3) Temperature control at the final reaching part of the transverse stretching step In order to obtain the film of the present invention, the temperature range of the final reaching part of the transverse stretching step is set to 160 ° C or more and less than 220 ° C and set to a relatively high temperature. It is preferable to do. By setting to high temperature, the difference of the above-mentioned heat shrinkage stress value becomes small, and generation | occurrence | production of the wrinkle in high temperature processing can be suppressed.

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

  The film of the present invention can be obtained by carrying out highly controlled transverse stretching as described above. It is considered that the difference in the heat shrinkage stress value between the longitudinal direction of the film formation, the direction of 45 degrees and the direction of 90 degrees is reduced by the transverse stretching process due to the following mechanism. In the transverse stretching process, as described above, the force action is in a balanced state in the entire film in the transverse direction and the longitudinal direction. In the longitudinal direction, the film acts in the initial stage of stretching so as to advance toward the film traveling direction. It acts to be delayed with respect to the direction of travel. Here, when the stretching temperature of the final reaching portion of the transverse stretching is set to a high temperature, the final stretching tension in the transverse stretching step is lowered. Thereby, it is thought that the influence of the action of the force propagating from the heat fixing portion along the longitudinal direction of the film was alleviated, and the distortion of the force acting in the longitudinal direction was alleviated.

  On the other hand, the lateral force action can be considered as follows. Since only the force in the traveling direction acts at the center of the film, the force acting on the film is symmetrical with respect to the longitudinal direction. On the other hand, the film moves in an oblique direction while being held by the clip at the end of the film, and a force in the oblique direction as well as the traveling direction is applied. Therefore, the force action of the film end is not symmetrical with respect to the traveling direction. In order to reduce the difference between the heat shrinkage stress values, it is necessary to make this force action symmetrical. For this purpose, it is effective to reduce the stretching tension applied to the film by performing a transverse stretching step at a high temperature. However, if the stretching process is simply performed at a high temperature, there is a risk of unevenness in thickness. Therefore, in the first half of the transverse stretching process, stretching is performed in a “region where the stretching stress of the SS curve increases” where the thickness unevenness hardly occurs by relatively lowering the stretching temperature, and the thickness has been made uniform. In this case, the stretching temperature is increased, the stretching stress in the transverse direction is decreased, and stretching is performed in accordance with the balance of the action of the entire force. Thus, it is considered that it is possible to reduce the difference in thermal characteristics between 45 degrees in the longitudinal direction of film formation and 90 degrees in the longitudinal direction without increasing the unevenness of thickness.

  In the transverse stretching step of the film, by using the means (1) to (3) described above, the film thickness unevenness (especially in the width direction) is generated without generating fine spots that may become a heat wrinkle defect. It is thought that it was possible to achieve both reduction of the difference in thermal characteristics between 45 degrees in the longitudinal direction of film formation and 90 degrees in the longitudinal direction without excessively degrading the thickness unevenness of the film. In addition, only one of the above-described means (1) to (3) does not contribute to the reduction of thermal spots and the difference in thermal characteristics without deteriorating the thickness spots of the film. In addition, by using a combination of the means (1) to (3), it is possible to reduce the thermal spots and reduce the difference in thermal characteristics without deteriorating the thickness spots of the film very efficiently. Conceivable.

[Heat setting process]
In the film manufacturing method of the present invention, the heat setting treatment is performed following the stretching step. 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.

  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.

  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 biaxially stretched polyethylene terephthalate resin in the present invention to improve the workability (slidability) of the biaxially stretched polyethylene terephthalate resin film. Any fine particles can be selected. Examples of inorganic fine particles include silica, alumina, titanium dioxide, calcium carbonate, kaolin, and barium sulfate. Examples of the organic fine particles include acrylic resin particles, melamine resin particles, silicone resin particles, and crosslinked polystyrene particles. The average particle diameter of the fine particles can be appropriately selected as necessary within a range of 0.05 to 2.0 μm.

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

  Furthermore, the 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 has good dimensional stability, transparency, thickness unevenness (particularly thickness unevenness in the longitudinal direction), flatness during processing, and high temperature at 80 to 180 ° C. There is very little wrinkling during processing. Therefore, the biaxially stretched polyethylene terephthalate resin film of the present invention can be suitably used for films such as green sheets for ceramic capacitors, transfer films, and protective films for optical applications.

  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) Heat shrinkage stress value of film First, as a measurement sample, a cut-out portion of the sample is provided every 100 mm from a place entering the inside 50 mm from the end in the width direction of the film toward the center. At this time, setting is made so that the same number of cutout parts from the center to both ends are seen. The distance between the central cutouts should not exceed 200 mm. At each cut-out portion, a film sample having a sample width of 4 mm and a sample length of 15 mm was prepared along two directions perpendicular to each other at 45 degrees and 90 degrees with respect to the longitudinal direction of the film formation. Next, a film specimen having a sample width of 4 mm and a sample length of 15 mm was set in TMA (manufactured by Seiko Denshi Kogyo, TMA / SS100) under conditions of an initial load of 19.6 mN. The initial load is corrected to zero, the temperature from 30 ° C. to 230 ° C. is raised at 5 ° C./min, the stress generated as the film shrinks is measured with the chuck distance kept constant, and 160 The heat shrinkage stress value (MPa) in the heat shrinkage stress at ° C was measured. The heat shrinkage stress in the longitudinal direction and 45 ° direction of the film formation was σa, the heat shrinkage stress in the 90 ° direction was σb, and the absolute value of the difference between the heat shrinkage stresses in the two directions was Δσ. The table shows the maximum value of Δσ measured.

(2) 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 4 shows the maximum, minimum, and average values.

(3) Flatness of processed film Using a roll-shaped film and passing through a coater for 13 seconds at a transport tension of 4000 kPa and a temperature of 170 ° C. using an air-floating transport-type drying device with a space between the lower and upper airflow outlets of 38 cm Thus, a model film for post-processing was obtained. After the post-processing, the film was cooled at a rate of 20 ° C./second using a 50 ° C. cooling roll, and then wound into a roll. The flatness of the model film was evaluated by observing the number of corrugated wrinkles continuous in the running direction by the following method. That is, a processed model film having a width of 100 cm was hung in a room at a temperature of 25 ° C. and a humidity of 65% so that the longitudinal direction of the film film formation was vertical, and a load of 10 N / m was applied, and left for 30 minutes. During the post-processing process, the light source (fluorescent lamp, manufactured by Matsushita Electric Works Co., Ltd.) is 1 m away from the surface for counting the number of corrugated wrinkles that continue in the longitudinal direction of the film formation, and the film surface from above 45 degrees. And the number of wrinkles was visually counted from 45 degrees below the surface for counting wrinkles by 0.5 m and evaluated. The wrinkle was a wrinkle that was convex with respect to the surface to be observed, and the number of wrinkles in the film width direction was counted.
(Judgment)
○: The number of wrinkles is 10 / m or less with no wrinkles, and the wrinkles are evaluated with wrinkles of 11 / m or more or with wrinkles.

(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 the longitudinal stretching conditions of the films in Examples and Comparative Examples, Table 2 shows the transverse stretching conditions, Table 3 shows the positions of the cut-out portions of the film samples used for the evaluation of thickness unevenness, and Table 3 The evaluation results are shown in Table 4.

[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 was dried to a moisture content of 50 ppm or less. Thereafter, the resin was charged in a hopper immediately above the extruder, and the resin was melted at a temperature of 285 ° C. in the extruder, and the melted resin was filtered with a filter material of stainless sintered body (nominal filtration accuracy: 90% of particles having a size of 10 μm or more). . Subsequently, the resin sheet was extruded from a T-shaped die, and was wound around a casting drum having a surface temperature of 30 ° C. by using an electrostatic application casting method, and was cooled and solidified to obtain an unstretched film having a thickness of 425 μm.

Then, the unstretched film obtained, after raising the temperature in a heated roll group, between the first nip roll and a second nip roll arranged before and after, CO ₂ laser which is provided between these nip rolls (the The film was stretched 2.77 times in the longitudinal direction (longitudinal direction) while being heated to 105 ° C. by one laser) (first 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 of longitudinal stretching was 31 ° 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 3 mm as in the first, 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 of the film before and behind the extending | stretching point of the above-mentioned 2nd stage longitudinal stretch was 11 degreeC.

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 extending | stretching point of the above-mentioned 3rd stage longitudinal stretch was 10 degreeC.

  As described above, after stretching the unstretched film in the longitudinal direction in three stages, the longitudinally stretched film is guided to a tenter, and the first zone is stretched 2.0 times in the width direction in an atmosphere of 125 ° C. Is stretched up to 3.0 times in an atmosphere of 140 ° C., and the third zone is stretched up to 4.0 times at 170 ° C., followed by heat setting at 233 ° C., and 2.2% transverse at 225 ° C. A film roll obtained by winding a biaxially stretched film having a thickness of 31 μm and a width of 1,000 mm over a length of about 3,000 m by performing relaxation treatment and cutting and removing both edges. Manufactured. And the characteristic of the obtained film was evaluated by each measuring method mentioned above. The evaluation results are shown in Table 4.

[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 in the first stage longitudinal stretching ratio to 3.00 times, the second stage longitudinal stretching ratio was changed to 1.17 times, and stretched in two stages, and The biaxially stretched film was obtained by performing transverse stretching in the same manner as in Example 1 except that the preheating / stretching temperature of transverse stretching was changed as shown in Table 2. The evaluation results are shown in Table 4.

[Example 3]
Longitudinal stretching was carried out in the same manner as in Example 2 except that the winding speed around the casting drum was changed, the thickness of the unstretched film was changed to 165 μm, and the second stage magnification ratio was changed to 1.217 times. Then, the preheating / stretching temperature of the transverse stretching was changed as shown in Table 2, and a 12 μm biaxially stretched film was obtained. The evaluation results are shown in Table 4.

[Example 4]
Longitudinal stretching was performed in the same manner as in Example 2 except that the winding speed around the casting drum was changed, the thickness of the unstretched film was 680 μm, and the spot diameter of the CO ₂ laser was changed to 4 mm in diameter. Then, the transverse stretching was performed in the same manner as in Example 2 except that the preheating / stretching temperature of the transverse stretching was changed as shown in Table 2 to obtain a 50 μm biaxially stretched film. The evaluation results are shown in Table 4.

[Example 5: 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] was produced as follows. 1000 parts of dimethyl terephthalate, 650 parts of ethylene glycol, and 0.4 parts of manganese acetate tetrahydrate were charged into a transesterification reaction can and subjected to a transesterification reaction at 120 to 210 ° C. to distill off the produced methanol. . 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 [η] 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 roll was obtained by winding a biaxially stretched film having a thickness of 31 μm and a width of 1,000 mm over a length of about 500 m by guiding to a tenter, stretching and heat setting. Got. The film characteristics were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 4. 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 6]
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 31 μm. The film roll (mill roll) which wound up the biaxially stretched film of 1000 mm width over the length of 3,000 m was obtained. The characteristics of the film were evaluated by the same method as in Example 1. The evaluation results are shown in Table 4.

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

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

[Comparative Example 3]
A biaxially stretched film was obtained in the same manner as in Example 2, except that the longitudinally stretched film obtained in the same manner as in Example 2 was changed in the preheating / stretching temperature of the transverse stretch as shown in Table 2. The evaluation results are shown in Table 4.

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

[Comparative Example 5]
A biaxially stretched film was obtained in the same manner as in Example 1, except that the longitudinally stretched film obtained in the same manner as in Example 1 was changed in the prestretching / stretching temperature of the transverse stretch as shown in Table 2. The evaluation results are shown in Table 4.

[Comparative Example 6]
A biaxially stretched film was obtained in the same manner as in Example 2, except that the longitudinally stretched film obtained in the same manner as in Example 2 was changed in the preheating / stretching temperature of the transverse stretch as shown in Table 2. The evaluation results are shown in Table 4.

[Comparative Example 7]
A biaxially stretched film was obtained in the same manner as in Example 1, except that the longitudinally stretched film obtained in the same manner as in Example 1 was changed in the prestretching / stretching temperature of the transverse stretch as shown in Table 2. The evaluation results are shown in Table 4.

[Comparative Example 8]
A biaxially stretched film was obtained in the same manner as in Example 2, except that the longitudinally stretched film obtained in the same manner as in Example 2 was changed in the preheating / stretching temperature of the transverse stretch as shown in Table 2. Table 4 shows the evaluation results of the film.

[Comparative Example 9]
A biaxially stretched film was obtained in the same manner as in Example 2, except that the longitudinally stretched film obtained in the same manner as in Example 2 was changed in the preheating / stretching temperature of the transverse stretch as shown in Table 2. The evaluation results are shown in Table 4.

[Comparative Example 10: 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 520 μm. After that, the unstretched film was heated to 80 ° C. with a heated roll group, then heated to 90 ° C. with a far infrared heater, stretched 1.3 times, cooled with a cooling roll, and then further treated with a far infrared heater. Was heated to 90 ° C. 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. A biaxially stretched film was obtained in the same manner as in Example 1 except that the longitudinal stretching conditions were changed as described above. The evaluation results are shown in Table 4.

[Comparative Example 11]
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 310 μm. Thereafter, the unstretched film was heated to 80 ° C. with a heated roll group, then heated to 90 ° C. with a far-infrared heater, stretched 2.6 times, cooled with a cooling roll, and further treated with a far-infrared heater. To 90 ° C. and stretched 1.27 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. A biaxially stretched film was obtained in the same manner as in Example 1 except that the longitudinal stretching conditions were changed as described above. The evaluation results are shown in Table 4.

[Comparative Example 12]
An unstretched film obtained in the same manner as in Comparative Example 11 was heated to 72 ° C. with a heated roll group, then heated to 107 ° C. with the same laser as in Example 1 and stretched 3.3 times, and a cooling roll It was cooled with. In the longitudinal stretching, the stretching point was fixed in the same manner as in Example 1. However, the stretching tension increased, the film shrunk in the width direction, and the ears were wrinkled. Moreover, the temperature difference of the film before and after the stretching point of the first-stage longitudinal stretching described above was 30 ° C. A biaxially stretched film was obtained in the same manner as in Example 1 except that the longitudinal stretching conditions were changed as described above. The evaluation results are shown in Table 4.

[Comparative Example 13: Film formation according to Example 2 of WO 03/093008 pamphlet]
Polyethylene terephthalate [C] was produced as follows. 1000 parts of dimethyl terephthalate, 650 parts of ethylene glycol, and 0.4 part of magnesium acetate tetrahydrate were charged into a transesterification can and subjected to a transesterification reaction at 120 to 210 ° C., and methanol produced 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 [η] 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 was 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 cooled and solidified to obtain an unstretched film having a thickness of 425 μm. 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 31 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 4. 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.

  Tables 1 and 2 show the production conditions of each Example and Comparative Example, Table 3 shows the positions of the cutout portions of the film samples used for evaluation, and Table 4 shows the evaluation results.

[Effects of Example Film]
From Table 4, the films of the examples all have a very small thickness fluctuation rate (thickness unevenness) in the longitudinal direction, and the processed film has good flatness. On the other hand, the film of the comparative example has a large thickness variation rate (thickness unevenness) in the longitudinal direction, has poor flatness, and wrinkles and talmi after aging occur. In Table 4, Example 1-5 used a laser as a heating means in longitudinal stretching, and Example 6 used a high-temperature jet heating apparatus. In Comparative Examples 1 to 9, a laser was used for the heating device, but the transverse stretching condition was outside the present application. In Comparative Examples 10 and 11, a far infrared heater was used as a heating means in the longitudinal stretching. Although the comparative example 12 used the laser for the heating apparatus, longitudinal stretching is one step. Moreover, although the comparative example 13 is corresponded to the Example of patent document 10, it is bad in the thickness evaluation of this application.

  Since the biaxially stretched polyethylene terephthalate resin film of the present invention has excellent processing characteristics as described above, various processed film substrates, particularly green sheets for ceramic capacitors that require good flatness, It can be suitably used for a film substrate such as a transfer film and a protective film for optical use.

A ... Yield point,
B ... Rising point,

Claims (4)

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 resin film produced by undergoing a heat setting step for heat fixing the film after axial stretching, and obtained by narrowing the width of heating in the longitudinal stretching step,
A biaxially stretched polyethylene terephthalate resin film characterized by satisfying the following requirements (1) to (2).
(1) The difference in heat shrinkage stress value between two directions, ie, a direction that forms an angle of 45 degrees with a longitudinal direction of the biaxially stretched polyethylene terephthalate resin film and a direction that forms an angle of 90 degrees is 0 at 160 ° C. (2) A film sample having a length of 30 m and a width of 3 cm is taken along the longitudinal direction of the biaxially stretched polyethylene terephthalate resin film from the film cut-out portion provided by the cut-out method A described below, and the film sample When the thickness variation in the longitudinal direction is measured, the thickness variation rate in the longitudinal direction is 0.5% or more and 4.0% or less (cutting 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.   The biaxially stretched polyethylene terephthalate resin film according to claim 1, wherein the film has a thickness of 10 μm or more and less than 60 μm.   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 and 2, wherein a film-forming step of forming an unstretched film by melt-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, the following requirement (3) is satisfied, and the transverse stretching process satisfies the following requirements (4) to (8): A method for producing a biaxially stretched polyethylene terephthalate resin film.
(3) Heating to 105 ± 20 ° C. using a heating device while narrowing the width of heating between rolls provided with a peripheral speed difference, and a magnification of 2.0 to 3.2 times in the longitudinal direction; The film after longitudinal stretching is passed between cooled nip rolls and heated to 100 ± 20 ° C. using a heating device while narrowing the heating width between rolls provided with a difference in peripheral speed. (4) In the transverse stretching step, the difference in the set temperature in the continuous temperature zone is the transverse stretching. 5 ° C. or more and 30 ° C. or less in the first half portion (up to the temperature division region including the draw ratio of 1.8 times) (5) The temperature range that passes 1.8 times in the stretching in the transverse drawing step is 100 ° C. or more. (6) Transverse stretching step The difference in temperature setting between successive temperature zones is 5 ° C. between the first half of the horizontal stretching (up to the temperature zone including the draw ratio of 1.8 times) and the first temperature zone of the next second half. (7) In the transverse stretching step, the difference in temperature setting between successive temperature zones is the second half of the transverse stretching (the temperature zone next to the temperature zone including the draw ratio of 1.8 times). (From the region to the final draw ratio) is 5 ° C. or higher and 30 ° C. or lower. (8) The temperature range that reaches the final draw ratio in the stretching in the transverse drawing step is 160 ° C. or higher and lower than 220 ° C.