JP2017149987A - Polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film using a PET bottle recycled polyester resin large in laminate strength, small in thickness unevenness and hardly generating problems due to static electricity.SOLUTION: There is provided a polyester film containing a polyester resin recycled from a PET bottle of 50-95 wt.% and having percentage content of an isophthalic acid component based on total dicarboxylic acid component in total polyester resin constituting the polyester resin of 0.5-5.0 mol%, a specific intrinsic viscosity, thermal shrinkage, laminate strength, surface specific resistance and thickness unevenness.SELECTED DRAWING: None

Description

  The present invention relates to a polyester film using a polyester resin recycled from a PET bottle. More specifically, the present invention relates to a polyester film that uses a polyester resin recycled from a PET bottle, has low heat shrinkage and high laminate strength, has small thickness unevenness, and hardly causes trouble due to static electricity.

  Conventionally, by using polyester resin recycled from PET bottles, the technology to make polyester film for roll-wrap label from polyester with low oligomer content and less trouble due to static electricity without losing productivity and quality is known. (See, for example, Patent Document 1). However, this conventional technique uses a raw material resin (IV = 0.70) with a high intrinsic viscosity and extrudes at a low extrusion temperature (280 ° C.) to produce a film with a low intrinsic viscosity (IV = 0.62). There is variation in composition, resulting in unevenness in the laminate surface and uneven thickness. In addition, in order to obtain high laminate strength, the biaxially stretched film is heat-treated at a high temperature, but since the cooling to room temperature is rapid, there is unevenness in the relaxation of the film, and the thickness unevenness is poor. There was a problem of becoming.

  Moreover, the technique of setting it as the polyester film for transparent vapor deposition suitable for the adhesiveness of a vapor deposition film and a polyester film, boiling, and a retort process by controlling the orientation of a film was known (for example, refer patent document 2). However, this conventional technology is an example of polyethylene terephthalate that does not use polyester resin recycled from PET bottles. However, when a film is made using a resin having an intrinsic viscosity of 0.63 made of the recycled resin, Because of the variation in the composition, the variation of the laminate surface and the thickness unevenness are caused. In addition, in order to obtain high laminate strength, the biaxially stretched film is heat-treated at a high temperature, but since the cooling to room temperature is rapid, there is unevenness in the relaxation of the film, and the thickness unevenness is poor. There was a problem of becoming.

  Furthermore, there has been known a technique for improving the slit property and the scraping property in the calendar process for a magnetic recording medium by controlling the particles in the film and the film forming conditions (see, for example, Patent Document 3). However, this conventional technology is an example of polyethylene terephthalate that does not use polyester resin recycled from PET bottles, but when a film is made using a resin having an intrinsic viscosity of 0.62 made of the recycled resin, Due to variations in the internal composition, there will be variations in the laminate surface and uneven thickness. In addition, in order to obtain high laminate strength, the biaxially stretched film is heat-treated at a high temperature, but since the cooling to room temperature is rapid, there is unevenness in the relaxation of the film, and the thickness unevenness is poor. There was a problem of becoming.

In addition, there has been known a technique for improving the heat dimensional stability at the time of producing a ceramic sheet for a release sheet that optimizes the heat shrinkage characteristics by optimizing the film longitudinal and lateral stretching conditions and heat treatment conditions ( For example, see Patent Document 4). However, this prior art is an example of polyethylene terephthalate that does not use polyester resin recycled from PET bottles. However, when a film is made using a resin having an intrinsic viscosity of 0.62 made of the recycled resin, Because of the variation in the composition, the variation of the laminate surface and the thickness unevenness are caused. Further, in order to obtain a high laminate strength, the biaxially stretched film is heat-treated at a high temperature, and optionally a technical idea of cooling after the heat treatment is disclosed. However, even if the present technology is used as it is for a film containing 0.5 to 5 mol% of isophthalic acid, the film has unevenness in the surface and uneven thickness is inferior. In addition, it is disclosed that the planarity of the film is maintained by controlling the refractive index (Nz) in the thickness direction. However, this document describes that when polyethylene terephthalate is 100% as a raw material and Nz is 1.493.
The following cases are assumed: Films containing 0.5 to 5 mol% of isophthalic acid have the advantage that the laminate strength tends to be higher than that of the 0 mol% polyethylene terephthalate film, but Nz is required to improve both the laminate strength and thickness unevenness. There is a problem that this technique cannot be used as it is because it is too expensive.

Further, since the conventional polyester film is an insulator, there is a problem that static electricity is easily generated and accumulated. Static electricity causes troubles during processing, for example, in the manufacturing process, printing, bonding, and other secondary processing processes, the film wraps around the roll of manufacturing equipment, shocks the human body that touches the film, and handling is difficult It becomes a factor which decreases work efficiency. In addition, the product value is reduced, for example, the generation of so-called printing whiskers and the cause of dirt on the film surface.

JP 2012-91862 A JP 2001-342267 A JP-A-7-114721 JP 2010-260315 A

The present invention has been made against the background of the problems of the prior art. That is, the object of the present invention is to provide a polyester film as follows.
1. Uses recycled resin obtained by recycling PET bottles that contain 0.5 to 5.0 mol% isophthalic acid, have high melt viscosity, undergo solid phase polymerization, and frequently add high crystallization nucleating agents, etc. However, by optimizing the extrusion temperature, the extrusion of the resin can be stabilized, and the resin, additives, and particles in the film can be made uniform, thereby reducing unevenness in the thickness of the film and eliminating variations in the laminate. To improve the laminate strength.
2. Even if the melt viscosity of the resin after extrusion is high, the film can be stretched at a high magnification and reduced in thickness unevenness.
3. Even if the melt viscosity of the resin after extrusion is high, the film can be stretched at a high magnification and the thickness unevenness of the film can be reduced.
4). Reduce the vertical and horizontal thermal shrinkage of the film by performing high-temperature heat treatment.
5. To achieve a high laminate strength by adjusting the refractive index in the thickness direction of the film through high-temperature, high-magnification stretching and high-temperature heat treatment.
6). By gradually cooling after the heat treatment, the thickness unevenness of a film containing 0.5 mol% or more and 5.0 mol% or less of isophthalic acid as an acid component is reduced.
7). To prevent troubles caused by static electricity by applying an antistatic agent before the final heat treatment in the film manufacturing process.
Another object of the present invention is to provide an excellent polyester film using a polyester resin recycled from a PET bottle whose laminate strength does not vary inside the film.

As a result of intensive studies to achieve the above object, the present inventors have completed the present invention. That is, this invention consists of the following structures.
1. A polyester film containing 50% by weight to 95% by weight of a polyester resin recycled from a PET bottle and biaxially stretched, wherein the polyester film satisfies the following requirements.
(1) The content of the isophthalic acid component with respect to all the dicarboxylic acid components in all the polyester resins constituting the polyester film is 0.5 mol% or more and 5.0 mol% or less. (2) The intrinsic viscosity of the resin constituting the polyester film is 0.64 dl. / G or more and 0.80 dl / g or less (3) 150 ° C. heat shrinkage in the longitudinal and transverse directions is 0.1% or more and 1.5% or less (4) The laminate strength between the polyester film and the sealant layer is 4.0 N / 15 mm or more and 20.0 N / 15 mm or less (5) Surface resistivity of at least 65% relative humidity on one side is 13 log Ω or less (6) Each thickness Tn (n = 1 to 200) measured for each 1 mm length of the film in the vertical and horizontal directions every 5 mm ) (Unit: μm) When measuring 200 points, the thickness unevenness obtained by the following formula when the maximum thickness is Tmax, the minimum thickness is Tmin, and the average thickness is Tave is the vertical and horizontal directions. 16% or less thickness unevenness = {(Tmax−Tmin) / Tave} × 100 (%)
2. 1. The polyester film contains inorganic particles in an amount of 0.01% by weight to 1% by weight. The polyester film as described in.
3. Above 1. Or 2. A laminate obtained by laminating the polyester film described in 1 and a sealant layer.

The polyester film using the polyester resin recycled from the PET bottle according to the present invention has the following effects.
1. Using recycled resin obtained by recycling PET bottles that contain 0.5 to 5.0 mol% isophthalic acid, have high melt viscosity, undergo solid phase polymerization, and often add high crystallization nucleating agents However, by optimizing the extrusion temperature, the extrusion of the resin is stabilized, and the resin, additives, and particles in the film are made uniform, so the film thickness unevenness is reduced and there is no variation in the laminate. Strength is improved.
2. By performing high-strength longitudinal stretching at a high temperature, even when the melt viscosity of the resin after extrusion is high, high-strength lateral stretching can be achieved, and thickness unevenness of the film is reduced.
3. By making the transverse stretching at a high temperature, even when the melt viscosity of the resin after extrusion is high, the transverse stretching can be performed at a high magnification, and the thickness unevenness of the film is reduced.
4). By performing the heat treatment at a high temperature, the heat shrinkage in the vertical and horizontal directions of the film can be lowered.
5. High-strength stretching and high-temperature heat treatment make the refractive index in the thickness direction of the film appropriate, and high laminate strength is realized.
6). By gradually cooling after the heat treatment, the thickness unevenness of the film containing 0.5 mol% or more and 5.0 mol% or less of isophthalic acid as the acid component is reduced.
7). By applying the antistatic agent before the final heat treatment in the film manufacturing process, troubles due to static electricity can be prevented.
Further, the laminate strength does not vary within the film.

It is a schematic diagram which shows the one aspect | mode inside the extruder of the film forming equipment in this invention.

  The biaxial stretching method is not particularly limited, and a tubular method, a simultaneous biaxial stretching method, or the like can be employed. A sequential biaxial stretching method is preferred.

  The lower limit of the intrinsic viscosity of the resin constituting the film obtained by measuring the film is preferably 0.64 dl / g, more preferably 0.65 dl / g. If it is less than 0.64 dl / g, many recycled resins made of PET bottles have an intrinsic viscosity exceeding 0.70, and if the viscosity is lowered when a film is produced using the recycled resin, thickness unevenness may be caused. It is not preferable. Moreover, since a film may color, it is not preferable. The upper limit is preferably 0.80 dl / g, more preferably 0.70 dl / g. Exceeding 0.80 dl / g is not preferable because the resin from the extruder is difficult to be discharged and the productivity may be lowered.

  The lower limit of the thickness is preferably 8 μm, more preferably 10 μm, and even more preferably 12 μm. If it is less than 8 μm, the film strength may be insufficient, which is not preferable. The upper limit is preferably 200 μm, more preferably 50 μm, and even more preferably 30 μm. If it exceeds 200 μm, it may be too thick and difficult to process.

  The lower limit of the heat shrinkage rate in the longitudinal direction (may be described as MD) and in the lateral direction (may be described as TD) is preferably 0.1%, and more preferably 0.3%. If it is less than 0.1%, the improvement effect is saturated, and it may become mechanically brittle, which is not preferable. The upper limit is preferably 1.5%, more preferably 1.2%. If it exceeds 1.5%, it is not preferable because pitch deviation may occur due to dimensional changes during processing such as printing. On the other hand, if it exceeds 1.5%, shrinkage or the like in the width direction may occur due to dimensional changes during processing such as printing.

  The lower limit of the refractive index in the thickness direction is preferably 1.493, more preferably 1.494. If it is less than 1.493, the orientation is too high, so the laminate strength may not be obtained. The upper limit is preferably 1.4995, more preferably 1.498. If it exceeds 1.4995, the molecular orientation of the film is not sufficient, and the mechanical properties may be insufficient.

Measure 200 points up to each thickness Tn (n = 1 to 200) (unit: μm) of 1m length of film in the vertical and horizontal directions every 5mm, the maximum thickness at this time is Tmax, the minimum thickness is Tmin, the average thickness The thickness unevenness determined by the following formula when T is Tave is preferably 16% or less, more preferably 12% or less, and still more preferably 10% or less in each of the vertical and horizontal directions. If it exceeds 16%, winding misalignment occurs when it is used as a film roll, and when the laminated part is peeled off, the appearance of the peeling surface may be deteriorated and the commercial value may be lowered.
Unevenness of thickness = {(Tmax−Tmin) / Tave} × 100 (%)

  The lower limit of the laminate strength is preferably 4.0 N / 15 mm, more preferably 4.5 N / 15 mm, and even more preferably 5 N / 15 mm. If it is less than 4.0 N / 15 mm, it is not preferable since the laminate part may be easily peeled off when used as a bag. The upper limit is preferably 20 N / 15 mm, more preferably 15 N / 15 mm, and still more preferably 10 N / 15 mm. If it exceeds 20 N / 15 mm, the film may be substantially destroyed at the time of peeling, which is not preferable.

  Appearance evaluation after lamination is performed by visually observing a sample after peeling off the laminate. The evaluation is as follows. ○ Level means that there is no minute removal of the adhesive on the surface after peeling, △ level means that minute removal is 10% or less of the total peeled area, and × level means that there is no minute removal. It exceeds 10% of the peeled area. Preferably it is (triangle | delta), More preferably, it is (circle). In x, it is not preferable because the appearance of the laminated part after peeling is poor and the commercial value is lowered. When the laminate strength is less than 4 N / 15 mm, the basic characteristics in the present invention are not satisfied.

  As a raw material, it is preferable to use a recycled polyester resin comprising a PET bottle containing an isophthalic acid component as an acid component. Polyester used in PET bottles is controlled for crystallinity in order to improve the appearance of the bottle. As a result, polyester containing 10 mol% or less of isophthalic acid component may be used. . In order to utilize the recycled resin, a material containing an isophthalic acid component may be used.

  The lower limit of the amount of the terephthalic acid component in the total dicarboxylic acid component constituting the polyester resin contained in the film is preferably 95 mol%, more preferably 96 mol%, still more preferably 96.5 mol%. Particularly preferably 97 mol%. If it is less than 95 mol%, the crystallinity is lowered, and the thermal shrinkage rate may be increased, which is not preferable. Further, the upper limit of the amount of the terephthalic acid component of the polyester resin contained in the film is preferably 99.5 mol%, more preferably 99 mol%. Recycled polyester resins made of PET bottles often have dicarboxylic acid components other than terephthalic acid typified by isophthalic acid. Therefore, the content of terephthalic acid components constituting the polyester resin in the film exceeds 99.5 mol%. As a result, it is difficult to produce a polyester film having a high resin ratio, which is not preferable.

  The lower limit of the amount of the isophthalic acid component in the total dicarboxylic acid component constituting the polyester resin contained in the film is preferably 0.5 mol%, more preferably 0.7 mol%, still more preferably 0.9 mol%, Especially preferably, it is 1 mol%. Recycled polyester resins made of PET bottles contain many isophthalic acid components. Therefore, the content of the isophthalic acid component constituting the polyester resin in the film is less than 0.5 mol%. Manufacturing becomes difficult as a result, which is less preferred. The upper limit of the amount of the isophthalic acid component in the total dicarboxylic acid component constituting the polyester resin contained in the film is preferably 5 mol%, more preferably 4 mol%, still more preferably 3.5 mol%. And particularly preferably 3 mol%. If it exceeds 5 mol%, the crystallinity is lowered, so that the heat shrinkage rate may be increased, which is not preferable. In addition, it is preferable that the content of the isophthalic acid component is within the above range because a film excellent in laminate strength, shrinkage rate, and thickness unevenness can be easily produced.

  The upper limit of the intrinsic viscosity of the recycled resin made of PET bottles is preferably 0.9 dl / g, more preferably 0.8 dl / g, still more preferably 0.77 dl / g, and particularly preferably 0.75 dl / g. It is. The If it exceeds 0.9 dl / g, the resin from the extruder is difficult to be discharged and the productivity may be lowered, which is not preferable.

  The lower limit of the content of the polyester resin recycled from the PET bottle to the film is preferably 50% by weight, more preferably 65% by weight, and further preferably 75% by weight. When the content is less than 50% by weight, the content of recycled resin is poor, which is not preferable in terms of contribution to environmental protection. The upper limit of the content of the polyester resin recycled from the PET bottle is preferably 95% by weight, more preferably 90% by weight, and still more preferably 85% by weight. If it exceeds 95% by weight, a lubricant and additives such as inorganic particles may not be sufficiently added to improve the function of the film, which is not preferable. In addition, the polyester resin recycled from the PET bottle can also be used as a masterbatch (high concentration containing resin) used when adding lubricants and additives such as inorganic particles for the purpose of improving the function of the film.

  As the lubricant type, in addition to inorganic lubricants such as silica, calcium carbonate and alumina, organic lubricants are preferable, and silica and calcium carbonate are more preferable. By these, transparency and slipperiness can be expressed.

  The lower limit of the lubricant content in the film is preferably 0.01% by weight, more preferably 0.015% by weight, and still more preferably 0.02% by weight. If it is less than 0.01% by weight, the slipperiness may be lowered. The upper limit is preferably 1% by weight, more preferably 0.2% by weight, and still more preferably 0.1% by weight. If it exceeds 1% by weight, the transparency may be lowered, which is not preferable.

  In the polyester film of the present invention, an antistatic agent, particularly an anionic antistatic agent having an alkyl group having 10 to 20 carbon atoms, is preferably present on at least one side (preferably both sides). With such a configuration, generation and accumulation of static electricity can be suppressed during secondary processing of the film, and various troubles caused by this static electricity can be prevented. It is an index of antistatic property to have a surface specific resistance of 13 logΩ or less under a relative humidity of 65% RH on at least one side of the film. When the surface specific resistance exceeds 13 logΩ, the antistatic property is insufficient, which is not preferable. More preferably, it is 11 logΩ or less. However, it may be 2 logΩ or more practically.

  The anionic antistatic agent is preferably one having 10 to 20 carbon atoms. In the case of an antistatic agent having such a molecular structure, for example, when the film is subjected to heat during film processing (during film production and secondary processing), the antistatic agent is scattered from the film surface. -Since the disappearance can be suppressed, the antistatic effect can be ensured more reliably.

  That is, with an anionic antistatic agent having a carbon number below the above range, the rate of scattering / disappearing from the film becomes very large due to heat received during film processing, and the effect of using the antistatic agent cannot be fully exhibited. Since it may be, it is not so preferable. On the other hand, some anionic antistatic agents having a carbon number exceeding the above range are not preferable because some antistatic effects are insufficient, and the effect of using the antistatic agent may not be sufficiently secured. The carbon number of the anionic antistatic agent is more preferably 12 or more and 18 or less.

  Examples of the anionic antistatic agent include higher alcohol sulfuric acid ester salts, sulfuric acid ester salts of alkylphenol ethylene oxide adducts, sulfuric acid and sulfonic acid derivatives such as alkyl sulfonates and alkyl allyl sulfonates, and the like. Those having ~ 20 alkyl groups. More specifically, alkyl sulfonate, alkyl benzene sulfonate, alkyl sulfate ester salt, alkyl ethoxy sulfate ester salt, alkyl phosphate ester salt and the like having an alkyl group having 10 to 20 carbon atoms can be mentioned. Among them, preferred are dodecyl sulfonate, dodecyl benzene sulfonate, and the like.

  In the polyester film of the present invention, as a method for allowing the anionic antistatic agent to be present on the film surface, it is preferable to employ a method (coating method) in which a coating liquid containing an antistatic agent is applied to the film surface.

  As an antistatic measure for the film, in addition to the coating method, there is a method (kneading method) in which an antistatic agent is kneaded into the raw material resin of the film and a film is formed using this. In a film employing the kneading method, the antistatic effect is exhibited by the antistatic agent oozing out from the inside of the film. However, in the case of a polyester film, since the glass transition temperature of polyester is generally high, the antistatic agent hardly oozes out on the film surface at a temperature near room temperature, and the antistatic effect tends to be insufficient. In addition, polyester film has a relatively high film-forming temperature, and the reactivity of polar groups of polyester is also high. If an antistatic agent is blended, deterioration of the polyester is promoted during film formation. Deterioration of physical properties may be caused or coloring may occur, which is not preferable.

  On the other hand, in the case of the coating method, since the antistatic agent is directly present on the film surface, the antistatic effect is effectively exhibited regardless of the high glass transition temperature of the polyester, and the introduction of the antistatic agent is effective. It is preferable because film deterioration and coloring can be prevented.

  The timing for applying the coating solution containing the antistatic agent to the film surface is not particularly limited, and may be applied to an unstretched film after melt extrusion and before stretching, or after stretching (after uniaxial stretching or after biaxial stretching) ) May be applied (details will be described later).

  In the coating solution applied to the film, a mixed solvent of a lower alcohol having 1 to 3 carbon atoms and water is preferably used as a solvent. As the lower alcohol having 1 to 3 carbon atoms, those that can be mixed with water at an arbitrary ratio, such as methanol, ethanol, n-propanol, and isopropanol, are preferable. Alcohols having a large number of carbon atoms are not preferable because they are phase-separated from water when a coating solution is prepared, and application of such coating solutions tends to cause coating spots. However, as long as it does not cause phase separation, it may be used in combination with a lower alcohol having 1 to 3 carbon atoms.

  The lower alcohol is preferably 10% by mass or more in the coating solution. When the amount of the lower alcohol is less than 10% by mass, the surface tension of the coating solution is increased, the wettability to the film is decreased, and coating spots are easily generated. In a biaxially oriented film obtained by drying after coating, when a sudden temperature and humidity change occurs, the transparency of the film is lowered and the practicality may be impaired, which is not preferable.

  Moreover, it is preferable that the amount of lower alcohol in a coating liquid is 60 mass% or less. If the amount of lower alcohol exceeds 60% by mass, the amount of organic solvent in the coating solution will increase. It is preferable to take In addition, when using alcohol with many carbon atoms simultaneously with lower alcohol, it is recommended that the total amount of alcohol in a coating liquid shall be 60 mass% or less.

The amount of the anionic antistatic agent present on the film surface by application of the coating solution is preferably 0.001 to 0.5 g / m ² . If the amount of the anionic antistatic agent is less than the above range, the antistatic effect may not be sufficiently secured. On the other hand, when the amount of the anionic antistatic agent exceeds the above range, the transparency and blocking resistance of the film may be lowered.

  Although the manufacturing method of the film of this invention is not specifically limited, For example, the following manufacturing methods are recommended. The temperature setting for melting and extruding the resin in the extruder is important. The basic idea is that (1) polyester resin used in PET bottles contains an isophthalic acid component, so (2) limiting viscosity and fine high crystals while suppressing deterioration by extruding at the lowest possible temperature. In order to sufficiently and uniformly melt the sex part, it has a part that melts at a high temperature or high pressure. Inclusion of the isophthalic acid component reduces the stereoregularity of the polyester, leading to a decrease in the melting point. Therefore, in extrusion at a high temperature, the melt viscosity is greatly reduced or deteriorated due to heat, and the mechanical strength is reduced or deteriorated foreign matters are increased. Further, if the extrusion temperature is simply lowered, sufficient melt-kneading cannot be performed, and foreign matter such as an increase in thickness unevenness and fish eyes may become a problem. From the above, as a recommended manufacturing method, for example, there are a method of using two extruders in tandem, a method of increasing the pressure in the filter section, a method of using a screw having a strong shearing force as a part of the screw configuration, and the like. Can be mentioned. The following is an example of temperature control using a single extruder.

  FIG. 1 shows an embodiment of the inside of an extruder of a film forming facility in the present invention. In the screw 1 having the flight 2 between the barrels 3, there are a supply unit 4, a compression unit 5, and a measurement unit 6 from the screw base to the tip. The compression unit 5 is a region where the space between the screw 1 and the barrel 3 becomes narrower. In the present invention, the set temperature of the supply unit 4 and the measuring unit 6 is made as low as possible and the set temperature of the compression unit 5 is made high. It is preferable that the compression unit 5 having high shear is sufficiently melt-kneaded, and the supply unit 4 and the metering unit 6 are devised to prevent thermal deterioration.

  The lower limit of the set temperature of the resin melting part in the extruder (excluding the highest set temperature of the compression part of the screw in the extruder) is preferably 270 ° C, and the upper limit is preferably 290 ° C. Extrusion is difficult at temperatures below 270 ° C, and resin degradation may occur at temperatures above 290 ° C, which is not preferred.

  The lower limit of the maximum set temperature of the compression part of the screw in the extruder is preferably 295 ° C. Polyester resins used for PET bottles often have crystals with a high melting point (260 ° C. to 290 ° C.) from the viewpoint of transparency. In addition, additives, crystallization nucleating agents, and the like are added, and the fine melting behavior in the resin material varies. If it is less than 295 ° C., it is difficult to sufficiently melt them, which is not preferable. The upper limit of the maximum set temperature of the compression part of the screw in the extruder is preferably 310 ° C. If it exceeds 310 ° C, the resin may deteriorate, which is not preferable.

  The lower limit of the time for the resin to pass through the region of the maximum set temperature of the compression part of the screw in the extruder is preferably 10 seconds, more preferably 15 seconds. If it is less than 10 seconds, the polyester resin used in the PET bottle cannot be sufficiently melted, which is not preferable. The upper limit is preferably 60 seconds, more preferably 50 seconds. If it exceeds 60 seconds, the resin tends to deteriorate, which is not preferable. By setting the extruder to such a range, it is possible to obtain a film with less foreign matter such as uneven thickness and fish eyes and less coloring while using a large amount of polyester resin recycled from a PET bottle.

  The resin thus melted is extruded into a sheet shape on a cooling roll and then biaxially stretched. The stretching method may be a simultaneous biaxial stretching method, but a sequential biaxial stretching method is particularly preferable. These make it easy to meet productivity and quality required for the present invention.

  In the present invention, the method for stretching the film is not particularly limited, but the following points are important. In order to stretch a resin having an intrinsic viscosity of 0.64 dl / g or more and containing an isophthalic acid component, the ratio and temperature of machine direction (MD) stretching and transverse direction (TD) stretching are important. If the MD stretch ratio and temperature are not appropriate, the stretching force is not applied uniformly, the molecular orientation is insufficient, and the thickness unevenness and mechanical properties may be insufficient. Further, the film may be broken in the next TD stretching step, or an extreme increase in thickness unevenness may occur. If the TD draw ratio and temperature are not appropriate, the film may not be drawn uniformly, resulting in poor vertical / horizontal orientation balance and insufficient mechanical properties. In addition, if the process proceeds to the next heat setting step with large thickness unevenness or insufficient molecular chain orientation, it cannot be uniformly relaxed, resulting in insufficient thickness unevenness and insufficient mechanical properties. The problem that happens. Therefore, basically, in MD stretching, it is recommended that stretching is performed in stages by adjusting the temperature described below, and in TD stretching, stretching is performed at an appropriate temperature so that the orientation balance is not extremely deteriorated. Although it is not limited to the following aspects, an example is given and demonstrated.

  As the machine direction (MD) stretching method, a roll stretching method and an IR heating method are preferable.

  The lower limit of the MD stretching temperature is preferably 100 ° C, more preferably 110 ° C, and further preferably 120 ° C. When the temperature is less than 100 ° C., even if a polyester resin having an intrinsic viscosity of 0.64 dl / g or more is stretched and molecularly oriented in the longitudinal direction, the film may break in the next transverse stretching process or an extreme thickness defect may occur. It is not preferable. The upper limit is preferably 140 ° C, more preferably 135 ° C, and even more preferably 130 ° C. If it exceeds 140 ° C, the orientation of the molecular chain becomes insufficient, and the mechanical properties may be insufficient.

  The lower limit of the MD draw ratio is preferably 2.5 times, more preferably 3.5 times, and even more preferably 4 times. If it is less than 2.5 times, even if a polyester resin having an intrinsic viscosity of 0.64 dl / g or more is stretched and molecularly oriented in the longitudinal direction, the film will break in the next transverse stretching process or an extreme thickness defect will occur. This is not preferable. The upper limit is preferably 5 times, more preferably 4.8 times, and even more preferably 4.5 times. If it exceeds 5 times, the effect of improving mechanical strength and thickness unevenness may be saturated, which is not so meaningful.

  The MD stretching method may be the above-described one-stage stretching, but it is more preferable to divide the stretching into two or more stages. By dividing into two or more stages, it is possible to satisfactorily stretch a polyester resin having a high intrinsic viscosity and made of a recycled resin containing isophthalic acid, and the thickness unevenness, laminate strength, mechanical properties, etc. are improved.

  The lower limit of the preferred first stage MD stretching temperature is 110 ° C, more preferably 115 ° C. If it is less than 110 ° C., heat is insufficient, and sufficient longitudinal stretching cannot be achieved, resulting in poor flatness. The upper limit of the preferred first stage MD stretching temperature is 125 ° C, more preferably 120 ° C. If the temperature exceeds 125 ° C., the orientation of the molecular chain becomes insufficient, and the mechanical properties may be deteriorated.

  The lower limit of the preferred first stage MD draw ratio is 1.1 times, more preferably 1.3 times. By making it the first stage of weak stretching when it is 1.1 times or more, the polyester resin having an intrinsic viscosity of 0.64 dl / g or more can be sufficiently longitudinally stretched to increase productivity. The upper limit of the preferred first stage MD stretch ratio is 2 times, more preferably 1.6 times. If it exceeds 2 times, the orientation of the molecular chains in the longitudinal direction becomes too high, which makes it difficult to stretch in the second and subsequent stages and results in a film with poor thickness unevenness.

  The lower limit of the preferred second stage (or final stage) MD stretching temperature is preferably 110 ° C, more preferably 115 ° C. When the temperature is 110 ° C. or more, a polyester resin having an intrinsic viscosity of 0.64 or more can be sufficiently longitudinally stretched to be laterally stretched in the next step, and thickness unevenness in the longitudinal and lateral directions is improved. It may become. The upper limit is preferably 130 ° C, more preferably 125 ° C. If the temperature exceeds 130 ° C., crystallization is promoted and transverse stretching becomes difficult and thickness unevenness may increase, which is not preferable.

  The lower limit of the MD stretch ratio of the second stage (or final stage) is preferably 2.1 times, more preferably 2.5 times. If it is less than 2.1 times, a polyester resin having an intrinsic viscosity of 0.64 or more is stretched, and even if it is molecularly oriented in the longitudinal direction, the film may break in the next transverse stretching process, or extreme thickness defects may occur. Yes, not very desirable. The upper limit is preferably 3.5 times, more preferably 3.1 times. If it exceeds 3.5 times, the longitudinal orientation becomes too high, so that the second and subsequent stretches may not be possible, and the film may have a large thickness unevenness, which is not preferable.

  The lower limit of the TD stretching temperature is preferably 110 ° C, more preferably 120 ° C, and further preferably 125 ° C. If it is less than 110 ° C., the stretching stress in the transverse direction becomes high, and the film may be broken or the thickness unevenness may become extremely large. The upper limit is preferably 150 ° C, more preferably 145 ° C, and even more preferably 140 ° C. If the temperature exceeds 150 ° C., the orientation of the molecular chain does not increase, and the mechanical properties may be deteriorated.

  The lower limit of the transverse direction (TD) stretch ratio is preferably 3.5 times, more preferably 3.9 times. If it is less than 3.5 times, the molecular orientation is weak and the mechanical strength may be insufficient, which is not preferable. In addition, since the orientation of molecular chains in the vertical direction is large and the vertical and horizontal balance is deteriorated, thickness unevenness is increased, which is not preferable. The upper limit is preferably 5.5 times, more preferably 4.5 times. If it exceeds 5.5 times, it may break, which is not preferable.

  In order to obtain the film of the present invention, it is desirable to appropriately set the conditions for heat setting performed in the tenter after completion of TD stretching, and then lowering the film to room temperature. Polyester film containing recycled resin made from PET bottles containing isophthalic acid has lower crystallinity than ordinary polyethylene terephthalate film not containing isophthalic acid, and is easy to melt extremely finely, and also has mechanical strength. Low. Therefore, if the film is exposed to high temperature under tension suddenly after the end of stretching, or if it is cooled rapidly under tension after the completion of high-temperature heat setting, the tension balance in the width direction is disturbed due to the inevitable temperature difference in the width direction of the film. , Thickness unevenness and mechanical properties are poor. On the other hand, if an attempt is made to cope with this phenomenon by lowering the heat setting temperature, a sufficient laminate strength may not be obtained. In the present invention, it is recommended that after stretching, a slightly low temperature heat setting 1 and a sufficiently high temperature heat setting 2 (heat setting 3 if necessary) and then a slow cooling step to lower the temperature to room temperature. However, it is not limited to this method, for example, a method of controlling the film tension according to the speed of hot air in the tenter or the temperature of each zone, a heat treatment at a relatively low temperature with a sufficient furnace length after stretching. And a method of relaxing with a heating roll after completion of heat setting.

  As an example, a method by temperature control of a tenter is shown below.

  The lower limit of the temperature of heat setting 1 is preferably 160 ° C, more preferably 170 ° C. When the temperature is lower than 160 ° C., the thermal shrinkage rate is finally increased, and a shift or shrinkage at the time of processing may occur. The upper limit is preferably 215 ° C, more preferably 210 ° C. If the temperature exceeds 215 ° C., a high temperature is suddenly applied to the film, and thickness unevenness may be increased or the film may be broken.

  The lower limit of the time for heat setting 1 is preferably 0.5 seconds, and more preferably 2 seconds. If it is less than 0.5 seconds, the film temperature may be insufficiently increased. The upper limit is preferably 10 seconds, and more preferably 8 seconds. If it exceeds 10 seconds, the productivity may decrease, which is not preferable.

  The lower limit of the temperature of the heat setting 2 is preferably 220 ° C, more preferably 227 ° C. When the temperature is less than 220 ° C., the thermal shrinkage rate is increased, which may cause displacement or shrinkage during processing, which is not preferable. The upper limit is preferably 240 ° C, more preferably 237 ° C. If it exceeds 240 ° C., the film may melt, and if it does not melt, it may become brittle, which is not preferable.

  The lower limit of the time for heat setting 2 is preferably 0.5 seconds, and more preferably 3 seconds. If it is less than 0.5 seconds, breakage tends to occur during heat setting, which is not preferable. The upper limit is preferably 10 seconds, and more preferably 8 seconds. If it exceeds 10 seconds, sagging may occur and thickness unevenness may occur, which is not preferable.

  If necessary, the lower limit of the temperature when the heat fixing 3 is provided is preferably 205 ° C, more preferably 220 ° C. When the temperature is lower than 205 ° C., the thermal shrinkage rate is increased, which may cause a shift or shrinkage during processing, which is not preferable. The upper limit is preferably 240 ° C, more preferably 237 ° C. If it exceeds 240 ° C, the film will melt, and even if it does not melt, it may become brittle, which is not preferable.

  If necessary, the lower limit of the time when the heat fixing 3 is provided is preferably 0.5 seconds, and more preferably 3 seconds. If it is less than 0.5 seconds, breakage tends to occur during heat setting, which is not preferable. The upper limit is preferably 10 seconds, and more preferably 8 seconds. If it exceeds 10 seconds, sagging may occur and thickness unevenness may occur, which is not preferable.

  TD relaxation can be performed at any point of heat setting. The lower limit is preferably 0.5%, more preferably 3%. If it is less than 0.5%, the thermal shrinkage rate in the lateral direction is particularly large, which may cause a shift or shrinkage during processing, which is not preferable. The upper limit is preferably 10%, more preferably 8%. If it exceeds 10%, sagging may occur and thickness unevenness may occur, which is not preferable.

  The lower limit of the annealing temperature after TD heat setting is preferably 90 ° C, more preferably 100 ° C. If it is less than 90 ° C., it is a film containing isophthalic acid, so that thickness unevenness may increase due to shrinkage due to a rapid temperature change or breakage may occur. The upper limit of the annealing temperature is preferably 150 ° C, more preferably 140 ° C. If it exceeds 150 ° C., a sufficient cooling effect may not be obtained, which is not preferable.

  The lower limit of the slow cooling time after heat setting is preferably 2 seconds, more preferably 4 seconds. If it is less than 2 seconds, a sufficient slow cooling effect may not be obtained, which is not preferable. The upper limit is preferably 20 seconds, and more preferably 15 seconds. If it exceeds 20 seconds, it tends to be disadvantageous in terms of productivity, which is not preferable.

  EXAMPLES Next, although this invention is demonstrated in detail using an Example and a comparative example, naturally this invention is not limited to a following example. The evaluation method used in the present invention is as follows.

(1) Content ratio of terephthalic acid and isophthalic acid component contained in raw material polyester and polyester constituting film Chloroform D (manufactured by Yurisopp) and trifluoroacetic acid D1 (manufactured by Yurisop) at 10: 1 (volume ratio) Prepare sample solution by dissolving in mixed solvent, and measure NMR of proton of sample solution using NMR (“GEMINI-200”; manufactured by Varian) at a temperature of 23 ° C. and 64 times of measurement. did. In NMR measurement, the peak intensity of a predetermined proton was calculated, and the content (mol%) of the terephthalic acid component and isophthalic acid component in 100 mol% of the acid component was calculated.

(2) Intrinsic viscosity (IV) of the resin constituting the raw resin and film
The sample was vacuum-dried at 130 ° C. for a whole day and night, then crushed or cut, 80 mg of the sample was precisely weighed, and dissolved in a mixed solution of phenol / tetrachloroethane = 60/40 (volume ratio) at 80 ° C. for 30 minutes. After making it 20 ml with the same mixed solution, it measured at 30 degreeC (unit: dl / g).

(3) Thickness
Measured with a PEACOCK dial gauge (manufactured by Ozaki Seisakusho).

(4) Sampling to a width of 10 mm in the vertical and horizontal directions, marking the marked lines at intervals of 200 mm, measuring the distance between the marked lines (L 0), and then sandwiching the film between paper The sample was placed in a hot air oven controlled at a temperature of 150 ° C., treated for 30 minutes, and then taken out. Then, the interval between the marked lines was measured (L), and the thermal contraction rate was obtained from the following equation. Samples are taken in both the vertical and horizontal directions. carry out. Others were performed according to JIS-C-2318.

Thermal contraction rate (%) = {(L 0 −L) / L 0} × 100

(5) Refractive index in the thickness direction
Based on JIS K7105, the refractive index (Nz) in the thickness direction was determined using an Abbe refractometer NAR-1T (manufactured by Atago Co., Ltd.). The light source was sodium D line, a test piece having a refractive index of 1.74 was used, and methylene iodide was used as an intermediate solution.

(6) Surface resistivity Measured using a surface resistivity meter (main body: R8340, sample box: R12704) manufactured by Advantest Corporation under an applied voltage of 100 V, 23 ° C. and 65% RH, and the reading of the meter Was the surface resistivity.

(7) Laminated strength formed biaxially stretched film and 40μm thick polyethylene film (“L4102” manufactured by Toyobo Co., Ltd.) urethane adhesive (Toyo Morton, TM569, CAT10L, ethyl acetate 33.6: 4.0: 62.4 (weight ratio)) was applied at a coating amount of 3 g / m ² by a dry laminating method and aged at 40 ° C. for 4 days to obtain a laminate for evaluating laminate strength. The laminate was cut to a width of 15 mm and a length of 200 mm to form a test piece. Using “Tensilon UMT-II-500 type” manufactured by Toyo Baldwin, polyester under the conditions of a temperature of 23 ° C. and a relative humidity of 65% Create a laminate for laminate strength evaluation on both the surface of the film where the antistatic agent is applied and the polyethylene film, and the surface of the polyester film where the antistatic agent is not applied, and the surface where the polyethylene film is bonded. The strength (N / 15 mm) was measured. The tensile speed was 20 cm / min and the peeling angle was 180 degrees.

(8) Appearance evaluation after delamination The sample after the evaluation in (7) is visually observed. ○ Level means that there is no minute removal of the adhesive on the surface after peeling, △ level means that minute removal is 10% or less of the total peeling area, × level exceeds 10%, × The level is that a minute drop exceeds 10% of the total peeled area.

(9) Thickness unevenness
Using a PEACOCK dial gauge (manufactured by Ozaki Mfg. Co., Ltd.), measure the thickness Tn (n = 1 to 200) (μm) measured in 5 mm increments of 1 m length in the vertical and horizontal directions every 200 mm. Tmax, the minimum thickness was Tmin, and the average thickness was Tave, and were calculated from the following formula (1).
Unevenness of thickness = {(Tmax−Tmin) / Tave} × 100 (%) (1)

Example 1
(Adjustment of polyester resin recycled from plastic bottles)
After washing away the foreign matter such as the remaining beverage from the plastic bottle for beverage, the flakes obtained by crushing are melted with an extruder, and the filter is changed to a finer one with a mesh size, and the finer foreign matter is filtered twice. Separately, it was filtered with a filter having the smallest opening size of 50 μm the third time to obtain a recycled polyester material. The composition of the obtained resin was terephthalic acid / isophthalic acid // ethylene glycol = 97.0 / 3.0 // 100 (mol%), and the intrinsic viscosity of the resin was 0.70 dl / g. This is designated as polyester A.

(Preparation of anionic antistatic coating solution)
Coating liquid 1
Water was added to the dodecyl sulfonate to dilute it, and isopropanol was further added to obtain a coating solution having a solid content concentration of 2 mass% (dodecyl sulfonate: 2 mass%, water: 63 mass%, isopropanol: 35 mass%).

(Production of film)
Polyester B is a polyethylene terephthalate resin having an intrinsic viscosity of 0.62 dl / g made of terephthalic acid // ethylene glycol = 100 // 100 (mol%). Polyester C is an amorphous silica having an average particle diameter of 1.5 μm. Was prepared as a masterbatch containing 0.3%. Each raw material was dried at 125 ° C. for 8 hours under a reduced pressure of 33 Pa. What mixed them so that it might become A / B / C = 70/20/10 (weight ratio) was thrown into the single screw extruder. The temperature from the extruder to the melt line, filter and T-die was set so that the temperature of the resin would be 280 ° C. However, the temperature of the resin was set to be 305 ° C. for 30 seconds from the start point of the compression portion of the screw of the extruder, and then again 280 ° C.

The melt extruded from the T-die is brought into close contact with a cooling roll to form an unstretched sheet, which is then stretched 1.41 times in the longitudinal direction with a roll having a peripheral speed difference heated to 118 ° C. (MD1), Further, the film was stretched 2.92 times (MD2) in the machine direction with a roll heated at 128 ° C. and having a peripheral speed difference. Next, the coating solution 1 was applied to one side of a uniaxially stretched film by an air knife method so that the coating amount after drying was 0.008 g / m ^2, and then the uniaxially stretched film was guided to a tenter and preheated at 121 ° C. Later, the film was stretched 4.3 times transversely at 131 ° C. Subsequently, heat fixation was performed at 180 ° C. without relaxation (0%) for 2.5 seconds (TS1), followed by 231 ° C., relaxation at 5% for 3.0 seconds (TS2), then 222 ° C. without relaxation. Performed for 2.5 seconds (TS3). Subsequently, in the same tenter, cooling was performed at 120 ° C. for 6 seconds, and finally the film was wound with a winder to obtain a biaxially stretched polyester film having a thickness of 18 μm.

(Example 2)
A biaxially stretched polyester film having a thickness of 18 μm was obtained in the same manner as in Example 1 except that the polyester raw material was mixed so that A / B / C = 80/10/10 (weight ratio). .

(Example 3)
In the same manner as in Example 2, except that the resin temperature was set to 305 ° C. for 45 seconds from the start point of the compression part of the screw of the extruder, and finally the film was 12 μm thick. A stretched polyester film was obtained.

(Examples 4 and 5)
(Adjustment of polyester resin recycled from plastic bottles)
After washing away remaining foreign matters such as beverages from beverage bottles different from those in Example 1, the flakes obtained by pulverization were melted with an extruder, and the filter was changed to fine ones with an opening size of 2 times. Further, fine foreign matters were filtered off and filtered with a filter having the smallest opening size of 50 μm for the third time to obtain a recycled polyester material. The composition of the obtained resin was terephthalic acid / isophthalic acid // ethylene glycol = 95.0 / 5.0 // 100 (mol%), and the intrinsic viscosity of the resin was 0.70 dl / g. This is designated as polyester D.

(Create film)
The thickness was finally obtained in the same manner as in Example 1 except that the polyester raw material was D / B / C = 60/30/10 (Example 4) and = 80/10/10 (Example 5). An 18 μm biaxially stretched polyester film was obtained.

(Comparative Example 1)
The film after the transverse stretching was continuously heat-fixed, followed by 231 ° C., relaxation 5%, 3.0 seconds (TS2), then 222 ° C., 2.5 seconds without relaxation (TS3). A biaxially stretched polyester film having a thickness of 18 μm was obtained in the same manner as in Example 2 except that it was not provided.

(Comparative Example 2)
Biaxially stretched polyester having a thickness of 18 μm in the same manner as in Example 2 except that the temperature of the resin was set to 280 ° C. in all regions of the melt line, filter, and T-die from the extruder. A film was obtained.

(Comparative Example 3)
By an ordinary polymerization method, terephthalic acid / isophthalic acid // ethylene glycol = 90.0 / 10.0 // 100 (mol%), and the intrinsic viscosity of the resin was 0.70 dl / g. This is designated as polyester E. A biaxially stretched polyester film having a thickness of 18 μm was obtained in the same manner as in Example 2 except that E / B / C = 55/35/10 (weight ratio) was used as the polyester raw material.

(Comparative Example 4)
The temperature from the extruder to the melt line, filter and T-die was set so that the temperature of the resin would be 280 ° C. However, the temperature of the resin was set to be 305 ° C. for 90 seconds from the start point of the compression portion of the screw of the extruder, and then again 280 ° C. As film forming conditions, the film was heated to 100 ° C. with a roll group and an infrared heater, and then longitudinally stretched 4.1 times with a roll group having a difference in peripheral speed, and then the coating liquid 1 was dried on one side by an air knife method. After coating so that the coating amount was 0.008 g / m ² , the film was stretched 4.2 times at 130 ° C. Thereafter, heat treatment was carried out as heat setting at 229 ° C., relaxed 6.0% for 2.6 seconds (TS2) and 200 ° C., relaxed for 2.5 seconds, and TS 2 and cooling step were not provided. Example 2 In the same manner as above, a biaxially stretched polyester film having a thickness of 18 μm was obtained.

(Comparative Example 5)
The temperature from the extruder to the melt line, filter and T-die was set so that the temperature of the resin would be 280 ° C. However, the temperature of the resin was set to be 305 ° C. for 90 seconds from the start point of the compression portion of the screw of the extruder, and then again 280 ° C. The melt extruded from the T-die is brought into close contact with a cooling roll to form an unstretched sheet, which is then stretched 1.2 times in the machine direction by a roll having a peripheral speed difference heated to 110 ° C. (MD1), Further, the film was stretched 2.8 times in the longitudinal direction (MD2) with a roll heated at 120 ° C. and having a peripheral speed difference. Next, the coating liquid 1 was applied to one side of a uniaxially stretched film by an air knife method so that the coating amount after drying was 0.008 g / m ^2, and then the uniaxially stretched film was guided to a tenter and preheated at 100 ° C. Later, the film was stretched 3.9 times at 105 ° C. Thereafter, heat treatment was carried out as heat setting at 228 ° C. for 3.0 seconds without relaxation (TS2) and at 228 ° C. at 5.0% relaxation for 2.5 seconds, except that TS1 and the cooling step were not provided. In the same manner as above, a biaxially stretched polyester film having a thickness of 18 μm was obtained.

(Comparative Example 6)
By an ordinary polymerization method, terephthalic acid / isophthalic acid // ethylene glycol = 97.0 / 3.0 // 100 (mol%), and the intrinsic viscosity of the resin was 0.65 dl / g. This is polyester F. F / B / C = 80/10/10 (weight ratio) as a polyester raw material, and the temperature is set so that the temperature of the resin is 310 ° C. in all regions of the melt line, filter and T-die from the extruder. did. The melt extruded from the T-die was brought into close contact with a cooling roll to form an unstretched sheet, which was subsequently stretched 1.6 times in the longitudinal direction with a roll having a peripheral speed difference heated to 126 ° C. (MD1), Further, it was stretched 1.3 times in the machine direction with a roll having a circumferential speed difference heated to 126 ° C. (MD2), and further stretched 2.3 times in the machine direction in a roll with a circumferential speed difference heated to 118 ° C. MD3). Next, the coating solution 1 was applied to one side of a uniaxially stretched film by an air knife method so that the coating amount after drying was 0.008 g / m ^2, and then the uniaxially stretched film was guided to a tenter and preheated at 110 ° C. Later, it was transversely stretched 4.6 times at 120 ° C. Thereafter, heat-fixing was performed at 205 ° C. for 5.0 seconds without relaxation (TS2), except that TS1 and the cooling step were not provided. A film was obtained.

(Comparative Example 7)
The temperature from the extruder to the melt line, filter and T-die was set so that the temperature of the resin would be 280 ° C. However, the temperature of the resin was set to be 300 ° C. for 70 seconds from the starting point of the compression part of the screw of the extruder, and thereafter, the temperature was again 280 ° C. The melt extruded from the T-die was brought into close contact with a cooling roll to obtain an unstretched sheet, which was subsequently stretched 3.9 times in the machine direction (MD1) with a roll having a peripheral speed difference heated to 107 ° C. . Next, the coating solution 1 was applied to one side of a uniaxially stretched film by an air knife method so that the coating amount after drying was 0.008 g / m ^2, and the uniaxially stretched film was guided to a tenter, and 105 ° C. and 115 ° C. Then, each film was preheated for 2 seconds, and finally stretched 4.1 times in 4 stretching zones of 120 ° C, 130 ° C, 145 ° C, and 155 ° C for 2 seconds each. Subsequently, heat fixation was performed at 220 ° C. without relaxation (0%) for 2.0 seconds (TS1), followed by 235 ° C. without relaxation, after 2.0 seconds (TS2), followed by 195 ° C. and relaxation 2.0. %, 2.5 seconds (TS3). A biaxially stretched polyester film having a thickness of 18 μm was obtained in the same manner as in Example 2 except that a cooling step was not provided and the sample was finally wound up by a winder.

(Comparative Example 8)
The polyester raw material was set to B / C = 90/10 (weight ratio), and the temperature of the resin was set to 280 ° C. from the extruder to the melt line, filter, and T-die. However, the temperature of the resin was set to be 300 ° C. for 30 seconds from the starting point of the compression portion of the screw of the extruder, and thereafter, the temperature was again 280 ° C. A biaxially stretched PET film was obtained in the same manner as in Comparative Example 7, except that the final thickness was 31 μm.

(Comparative Example 9)
A biaxially stretched polyester film having a thickness of 18 μm was obtained in the same manner as in Example 2 except that the coating solution 1 was not applied after stretching in the longitudinal direction.

  The biaxially stretched PET films obtained in Examples 1 to 5 had good thickness unevenness, small surface specific resistance of the antistatic agent-coated surface, excellent laminate strength, and good appearance after lamination.

  On the other hand, since Comparative Example 1 did not have TS1 and a cooling process, the thickness unevenness was large due to shrinkage due to a rapid temperature change. In Comparative Example 2, since the temperature of the compression portion of the screw was low, sufficient melting could not be performed, and the thickness unevenness was large. In Comparative Example 3, since the content of the isophthalic acid component was high and the crystallinity was low, the resin was soft, sufficient force was not applied during stretching, and the thickness unevenness was large. Comparative Example 4 was an experiment in which the content of Patent Document 1 was re-examined, and because the TS3 temperature was low, the refractive index in the thickness direction was low, and the laminate strength was insufficient. Comparative Example 5 was an experiment in which the content of Patent Document 2 was re-examined. The TD stretching temperature was low, and there was no cooling step after heat setting, so the thickness unevenness was large due to rapid cooling. Comparative Example 6 is an experiment in which the content of Patent Document 3 was re-examined, and MD stretching was performed in three stages, but the extrusion temperature was as high as 310 ° C, the intrinsic viscosity of the film was low, and relaxation during heat fixation was reduced. Insufficient heat shrinkage rate. Comparative Example 7 was an experiment in which the content of Patent Document 4 was re-examined, and since there was no cooling step after heat setting, thickness unevenness was poor due to rapid cooling. Since Comparative Example 8 does not use recycled raw materials consisting of PET bottles, it was gradually cooled by lowering the TS3 temperature, and the thickness unevenness was small, but the refractive index in the thickness direction was low due to insufficient temperature of TS3, and the laminate strength was low. It was insufficient. Further, as in Comparative Example 9, when an antistatic agent was not applied, blocking and wrinkles were likely to occur, and it was difficult to obtain a film having a good appearance.

  According to the present invention, it is possible to provide a polyester film containing a polyester resin recycled from a high-quality PET bottle. More specifically, the polyester film contains a polyester resin recycled from a PET bottle and has low heat shrinkage and high laminate strength. It is possible to provide a polyester film that has less thickness unevenness and is less likely to cause trouble due to static electricity.

DESCRIPTION OF SYMBOLS 1 ... Screw 2 ... Flight 3 ... Barrel 4 ... Supply part 5 ... Compression part 6 ... Measurement part

Claims (3)

A polyester film containing 50% by weight to 95% by weight of a polyester resin recycled from a PET bottle and biaxially stretched, wherein the polyester film satisfies the following requirements.
(1) The content of the isophthalic acid component with respect to all the dicarboxylic acid components in all the polyester resins constituting the polyester film is 0.5 mol% or more and 5.0 mol% or less. (2) The intrinsic viscosity of the resin constituting the polyester film is 0.64 dl. / G or more and 0.80 dl / g or less (3) 150 ° C. heat shrinkage in the longitudinal and transverse directions is 0.1% or more and 1.5% or less (4) The laminate strength between the polyester film and the sealant layer is 4.0 N / 15 mm or more and 20.0 N / 15 mm or less (5) Surface resistivity of at least 65% relative humidity on one side is 13 log Ω or less (6) Each thickness Tn (n = 1 to 200) measured for each 1 mm length of the film in the vertical and horizontal directions every 5 mm ) (Unit: μm) When measuring 200 points, the thickness unevenness obtained by the following formula when the maximum thickness is Tmax, the minimum thickness is Tmin, and the average thickness is Tave is the vertical and horizontal directions. 16% or less thickness unevenness = {(Tmax−Tmin) / Tave} × 100 (%) The polyester film according to claim 1, wherein the polyester film contains inorganic particles in an amount of 0.01% by weight to 1% by weight. A laminate obtained by laminating the polyester film according to claim 1 or 2 and a sealant layer.