JP2007118476A - Biaxially oriented polyester film for packaging - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film, which not only excels in resistance to pinhole by flexure, an important characteristic as a packaging material, but also excels in resistance to pinhole by thrust because the balance of the physical properties of the film longitudinal direction and the width direction is excellent and excels in the gas barrier property when a metallic compound is vapor-deposited. <P>SOLUTION: The biaxially oriented polyester film for packaging is a biaxially oriented film composed mainly of a polyethylene terephthalate, has a plane orientation coefficient of 0.168-0.172, an absolute value of birefringence of <5, a thermal shrinkage factor of 0.5-2% at 150°C in the film width direction, and a film thickness of 7-20 μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a biaxially oriented polyester film for packaging. In particular, biaxial orientation suitable for use as a packaging material that is excellent in heat resistance, pin puncture resistance, and bending pin hole resistance, and also exhibits excellent gas barrier properties when a metal or metal oxide is deposited. It relates to a polyester film.

  Polyethylene terephthalate biaxially stretched film, which is a representative example of polyester film, has good mechanical strength, thermal characteristics, humidity characteristics, and many other excellent characteristics, so it can be used for industrial materials, magnetic recording materials, optical materials, information communication materials, and packaging. It is used in a wide range of fields such as materials. However, in packaging material applications where bending pinhole resistance and pin puncture resistance are particularly important, polyethylene terephthalate has insufficient properties due to its hardness, which is the reverse of its toughness, and has excellent flexibility. Many polyamide biaxially stretched films are used.

  However, aliphatic polyamides have high water absorption due to their high chemical structure, resulting in high water absorption, poor humidity dimensional stability, poor flatness, and changes in film properties over time due to moisture absorption. However, there is a problem that vapor deposition of a metal compound for improving the gas barrier property is difficult, and printing or adhesion with the laminate layer is reduced due to moisture absorption. On the other hand, although aromatic polyamide has an aromatic ring, hygroscopicity is improved, but melt film formation is difficult, and a special and high-risk solvent must be used even for solution film formation. There is a problem that it is difficult to use for packaging materials in terms of productivity and economy.

  On the other hand, polyester can be melt-formed and has poor hygroscopicity, so it does not have the same problems as polyamide. However, as mentioned above, it is resistant to bending pinholes and resistance to packaging materials. There was a problem that it was inferior to the pinhole property.

  In order to solve these problems, the following proposals have been made so far for improving the polyester film. For example, Patent Documents 1 and 2 (JP-A-11-10725 and JP-A-2001-232739) disclose highly oriented vapor deposition films, but the difference in the refractive index between the longitudinal direction and the width direction (birefringence). ) Is negative or the thermal shrinkage rate at 150 ° C. is preferably extended in the film width direction, etc., and films with orientations biased in the width direction have been proposed. As a result, these films have been proposed. However, since the orientation balance in the film longitudinal direction and the width direction is poor, the pinhole resistance is insufficient.

  Further, for example, Patent Documents 3 and 4 (Japanese Patent Laid-Open Nos. 11-320672 and 11-320789) disclose vapor deposition gas barrier films having a plane orientation coefficient larger than 0.166. However, these proposals actually only disclose the plane orientation coefficient up to 0.168. Furthermore, since the balance and uniformity between the longitudinal direction and the width direction of the film are insufficient, the resistance to bending pinholes and the resistance to pin puncture were insufficient.

  Further, for example, Patent Document 5 (Japanese Patent Laid-Open No. 2001-342267) is characterized in that the plane orientation coefficient is 0.160 to 0.180 and the refractive index in the thickness direction is 1.495 to 1.505. A transparent vapor deposition polyester film is disclosed. In this proposal, specifically, a film having a plane orientation coefficient of 0.1605 to 0.1650 and a film having a plane orientation coefficient of 0.1723 are disclosed in Examples. However, when the plane orientation coefficient is the former, high orientation is insufficient, and pin puncture resistance and bending pin hole resistance are insufficient. In addition, the latter film of 0.1723 is too highly oriented, so that it is poor in practicality such as cleaving when used as an actual packaging material.

  Further, for example, Patent Document 6 (Japanese Patent Laid-Open No. 2002-370277) also discloses a vapor deposition polyester film having a plane orientation coefficient of 0.160 to 0.180. In this proposal, a film having a plane orientation coefficient of 0.1593 to 0.1672 is specifically disclosed in the examples. However, in the range of this plane orientation coefficient, as described above, high orientation is insufficient. Yes, puncture pinhole resistance and bending pinhole resistance are insufficient.

  For example, Patent Documents 7 and 8 (Japanese Patent Laid-Open Nos. 2004-114476 and 2004-115782) disclose films whose upper limit of the plane orientation coefficient is 0.17. In these proposals, only a film having a plane orientation coefficient of at most 0.165 is disclosed in the examples, and the pinhole resistance is inferior as described above. Furthermore, these proposals disclose that the film contains a tetramethylene terephthalate unit or a polyether component, but if these components are included, thermal bonding in a bonding process with other materials when used as a packaging material. In some cases, deterioration of physical properties becomes severe in the process, which causes a problem in practical use.

Further, Patent Documents 9 to 14 (Japanese Patent Laid-Open Nos. 2003-17360, 2001-219521, 2001-57315, 2001-301603, 2000-30973, 9-1754) discloses highly oriented polyester films, but these proposals relate to film for capacitors, and it is necessary to reduce the film thickness in order to improve the characteristics as a capacitor. Therefore, the film thickness is preferably 6 μm or less. Therefore, when trying to use these proposed films for packaging applications, the strength is insufficient and the pinhole resistance is inferior. This is also the case with proposals relating to films for magnetic materials that are desired to be thinned in order to increase the recording volume, which is insufficient as a packaging material. Examples of the magnetic material film include, for example, Patent Document 15 (Japanese Patent Laid-Open No. 7-249219).
Japanese Patent Laid-Open No. 11-10725 Japanese Patent Laid-Open No. 2001-232739 JP-A-11-320672 JP-A-11-320789 JP 2001-342267 A JP 2002-370277 A JP 2004-114476 A JP 2004-115782 A JP 2003-17360 A JP 2001-219521 A JP 2001-57315 A JP 2001-301603 A JP 2000-30973 A Japanese Patent Laid-Open No. 9-1754 JP 7-249219 A

  An object of the present invention is to eliminate the above-described problems of the prior art. In other words, it is not only excellent in bending pinhole property, which is an important property for use as a packaging material, but also has excellent physical property balance in the film longitudinal direction and width direction, so Another object of the present invention is to provide a biaxially oriented polyester film having excellent gas barrier properties when a metal compound is deposited.

  The above-mentioned problem is a biaxially oriented film mainly composed of polyethylene terephthalate, having a plane orientation coefficient of 0.168 to 0.172, an absolute value of birefringence of less than 5, and a thermal contraction rate in the film width direction at 150 ° C. It can be achieved by a biaxially oriented polyester film for packaging, characterized in that it is 0.5-2% and the film thickness is 7-20 μm.

  The biaxially oriented polyester film for packaging of the present invention is excellent in pinhole resistance in various deformation modes required as a packaging material, and exhibits excellent gas barrier properties by vapor deposition with a metal compound. It can be suitably used as a material for use.

  The polyester film of the present invention needs to be made of a polyester resin mainly composed of polyethylene terephthalate. Here, the polyester resin mainly composed of polyethylene terephthalate is a polyester resin in which 95 mol% or more of the dicarboxylic acid component constituting the polyester is a terephthalic acid component and 95 mol% or more of the glycol component is an ethylene glycol component. Means. Residue components other than terephthalic acid and ethylene glycol may be contained as a dicarboxylic acid component and a glycol component in a range of 5 mol% or less, and as a manner of inclusion, copolymerized polyethylene terephthalate may be used. A polyester resin may be blended and used. From the viewpoint of heat resistance and dimensional stability, it is preferable to use a polyethylene terephthalate resin itself which is not copolymerized or blended.

  Examples of dicarboxylic acid components other than terephthalic acid include aromatic dicarboxylic acids such as 2,6-naphthalenedicarboxylic acid, isophthalic acid, diphenyldicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid, 5-sodiumsulfonedicarboxylic acid, and phthalic acid. Acids, oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, fumaric acid and other aliphatic dicarboxylic acids, 1,4-cyclohexanedicarboxylic acid and other alicyclic dicarboxylic acids, paraoxybenzoic acid and other oxy A carboxylic acid etc. can be mentioned.

  Examples of glycol components other than ethylene glycol include 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexane. Examples include aliphatic dihydroxy compounds such as diol and neopentyl glycol, polyoxyalkylene glycols such as diethylene glycol, polyethylene glycol, polypropylene glycol and polytetramethylene glycol, and alicyclic dihydroxy compounds such as 1,4-cyclohexanedimethanol. it can.

  If these dicarboxylic acid components and glycol components are used, in the case of copolymerization, 2,6-naphthalenedicarboxylic acid, isophthalic acid, 1,4-butanediol, neopentyl glycol, 1,4-cyclohexanedimethanol is used. It is preferable. When blended with a polyethylene terephthalate resin, polytrimethylene terephthalate, polybutylene terephthalate, or polyethylene-2,6-naphthalenedicarboxylate is preferably used.

The packaging polyester film of the present invention needs to be a biaxially oriented film, and has a plane orientation coefficient of 0.168 to 0.172 from the viewpoint of pinhole resistance, dimensional stability, and gas barrier properties after vapor deposition. It is necessary. Furthermore, it is more preferable if it is 0.169 to 0.171 from the viewpoint of the pinhole resistance and the sealing strength when it is used as a package. When the plane orientation coefficient is less than 0.168, the pinhole resistance of piercing and bending is inferior, and the gas barrier property after vapor deposition of the metal compound may be inferior. In addition, when the plane orientation coefficient exceeds 0.172, in the packaging material used by combining the polyester film and other materials, cleavage and peeling occur within the polyester film, and the film tends to tear, resulting in high orientation. Pinhole resistance may be inferior due to excessive conversion. As a method for setting the plane orientation coefficient in the range of 0.168 to 0.172, when a polyester film is produced, particularly when a sequential biaxial stretching method is adopted, first, a uniaxially stretched film stretched in the film longitudinal direction is used. A method in which the refraction (difference between the film longitudinal direction and the refractive index in the width direction × 10 ³ ) is set to 70 to 130 and then stretched in the film width direction is preferable. Here, when the birefringence of the uniaxially stretched film is less than 70, the orientation in the longitudinal direction of the film after stretching in the width direction is insufficient, and the plane orientation coefficient may not be 0.168 or more. On the other hand, if the birefringence of the uniaxially stretched film exceeds 130, film tearing tends to occur during stretching in the width direction, and the film-forming stability is greatly deteriorated. In addition, when stretching in the longitudinal direction, the unstretched film is usually heated by using a heating roll, but if stretched at a temperature higher than the temperature of the heating roll due to heat generation of the resin itself due to stretching, the orientation in the longitudinal direction of the film is increased. It is preferable because it is easy to optimize. In addition, heat treatment is performed after stretching in the width direction. However, if heat treatment is performed at a high temperature of 230 ° C. or higher, orientation relaxation of the polyester molecular chains in the film is likely to occur, and the plane orientation coefficient may decrease. As long as the dimensional stability is not deteriorated, the heat treatment temperature is preferably low, more preferably 190 to 235 ° C, and particularly preferably 200 to 230 ° C.

  The polyester film of the present invention needs to have an absolute value of birefringence of less than 5 in order to have particularly excellent characteristics of pin puncture resistance. Here, birefringence is obtained by multiplying the difference between the refractive index in the longitudinal direction and the refractive index in the width direction by 1000. If the absolute value of the birefringence exceeds 5, the high orientation direction and the low orientation direction exist in the plane of the film. Therefore, the strength in the low orientation direction becomes low, and the pin puncture resistance is inferior. . From the viewpoint of pin puncture resistance, it is more preferable that the absolute value of birefringence is less than 4. Further, if the difference between the maximum value and the minimum value of the refractive index in the film plane is less than 5, it is particularly preferable because the orientation balance is extremely excellent, and the film has a very excellent pin puncture resistance. . As a method of setting the absolute value of birefringence to less than 5, it can be adjusted by appropriately controlling the stretching temperature and the stretching ratio in the film width direction. However, when the stretching temperature exceeds 120 ° C., thermal crystallization is performed rather than stretching. May advance, so-called necking stretching, resulting in a film whose orientation is biased in the width direction. On the other hand, when the temperature is lower than 80 ° C., the film may be a film in which the heating is insufficient and the orientation is biased in the width direction. The draw ratio is preferably 3.5 to 5.5 times. However, since film tearing is likely to occur when the film is used by stretching 4.5 times or more, it may be 3.6 to 4.4 times. preferable. Further, in the heat treatment step after biaxial stretching, if the heat treatment temperature is less than 190 ° C., the orientation may be biased in the film width direction, so the heat treatment temperature is preferably 190 to 235 ° C., 230 ° C. is particularly preferable.

  The biaxially oriented polyester film of the present invention preferably has a refractive index in the thickness direction of 1.480 to 1.495. If the refractive index in the thickness direction is less than 1.480, the plane orientation may progress too much and cleavage may occur easily. Conversely, if it exceeds 1.495, the pinhole resistance may be inferior. From the viewpoint of pinhole resistance and cleavage suppression, 1.480 to 1.490 is more preferable. As a method for setting the refractive index in the thickness direction of the film to 1.480 to 1.495, a method of further increasing the plane orientation by heat-treating a film having a higher plane orientation by biaxial stretching is desirable. It is especially preferable to set it to -230 degreeC.

  The biaxially oriented polyester film of the present invention needs to have a heat shrinkage ratio in the film width direction at 150 ° C. of 0.5 to 2% from the viewpoint of pinhole resistance and gas barrier properties after vapor deposition. When the heat shrinkage rate at 150 ° C. is less than 0.5%, the vapor deposition film and the film are in balance with the mechanism that shrinks when the metal compound, particularly the metal oxide, which is a high temperature during vapor deposition is cooled and solidified on the film surface. It is considered that a high gas barrier property cannot be achieved because of the rough interface structure. On the other hand, if the shrinkage rate exceeds 2%, the shrinkage is excessively large in the printing process as a packaging material and the bonding process with other materials, which causes pitch deviation and width fluctuation. In addition, since the structure changes due to heat shrinkage and pinhole resistance may deteriorate, the heat shrinkage rate at 150 ° C. in both the film longitudinal direction and the width direction is 0.5 to 1.5%. preferable. As a method of setting the heat shrinkage rate in the film width direction at 150 ° C. to 0.5 to 2%, it is preferable to perform heat treatment while relaxing during the heat treatment after sufficiently stretching in the film width direction. The content is preferably 2 to 10%, more preferably 3 to 7%. Further, it is particularly preferable to use a so-called low temperature relaxation method in which heat treatment is performed under tension when relaxing, and then relaxation heat treatment is performed at a temperature 5 to 30 ° C. lower than the heat treatment temperature under tension. Moreover, as a method of setting the heat shrinkage rate in the longitudinal direction to a preferable range, a method in which the heat treatment temperature under tension is 200 to 230 ° C. is preferable.

  The biaxially oriented polyester film for packaging of the present invention is required to have a film thickness of 7 to 20 μm from the viewpoint of puncture resistance and bending pinhole resistance. When the film thickness is less than 7 μm, the pin puncture strength is low, so that pinholes are likely to occur when filling the contents as a package. On the other hand, if the thickness exceeds 20 μm, it becomes difficult to handle such as curling due to pasting with other materials, and the strength becomes overspec, and the container recycling law increases the burden and waste weight. Is not preferable from the viewpoint of the environment in that it increases. If it is 8-18 micrometers from a viewpoint of intensity | strength, a handleability, and economical efficiency, it is more preferable, and if it is 8-16 micrometers, it is especially preferable.

  The biaxially oriented polyester film for packaging of the present invention preferably has a breaking strength of 260 to 400 MPa in the film longitudinal direction and the width direction from the viewpoint of expressing characteristics excellent in both pinhole resistance and gas barrier properties. Here, the breaking strength is the breaking strength in a tensile test at 25 ° C. When the breaking strength is less than 260 MPa, a direction with low strength exists, and in the puncture strength that simultaneously deforms the in-plane direction of the plane, the presence of the low strength direction may easily cause pinholes. On the other hand, if the breaking strength exceeds 400 MPa, the cutability for taking out the contents in the case of a package may be deteriorated. In terms of achieving both pinhole resistance and cutting property, the breaking strength in the longitudinal direction and the width direction is more preferably 265 to 350 MPa, and particularly preferably 270 to 330 MPa. As a method for setting the preferred range to take the tensile breaking strength of the film, it satisfies the above-described requirements for the plane orientation coefficient and birefringence, and the intrinsic viscosity of the film is 0.60 to 0.70. preferable. If the film intrinsic viscosity is less than 0.60, the molecular weight of the polyester resin is small, so that the film becomes brittle. Conversely, if the intrinsic viscosity exceeds 0.70, it is difficult to adjust the in-plane orientation balance.

  Below, the manufacturing method of the polyester film for biaxial orientation for packaging of this invention is demonstrated concretely. The present invention is not limited to the following manufacturing method. First, for the polyester resin mainly composed of polyethylene terephthalate used in the film of the present invention, a commercially available polyethylene terephthalate resin can be used as it is, but it is produced through a polycondensation reaction as follows. Also good.

  To a mixture of 100 parts by weight of dimethyl terephthalate and 70 parts by weight of ethylene glycol, 0.09 parts by weight of magnesium acetate and 0.03 parts by weight of antimony trioxide are added and gradually heated. Transesterification is performed while distilling methanol to synthesize a polyethylene terephthalate precursor. Next, 0.02 part by mass of an 85% phosphoric acid aqueous solution is added to the precursor, and the mixture is transferred to a polycondensation reaction kettle. The reaction system is gradually depressurized while being heated and heated in a polycondensation reaction kettle, and a polycondensation reaction is performed at 290 ° C. under a reduced pressure of 1 hPa to obtain a polyethylene terephthalate resin having a desired molecular weight. In addition, when adding particles, it is preferable to add a slurry in which particles are dispersed in ethylene glycol to a polycondensation reaction kettle so as to have a predetermined particle concentration to perform a polycondensation reaction.

  Next, a preferred method for producing the film of the present invention using a polyester resin will be specifically described. First, the polyester resin to be used is heated under reduced pressure or in a nitrogen atmosphere and dried at, for example, 150 ° C. for 5 hours, and the moisture content in the resin is preferably 50 ppm or less. Then, it supplies to an extruder and performs melt extrusion. In addition, when using a vent type twin screw extruder, the drying step may be omitted. When a plurality of polyester resins are used in combination, they may be mixed in a drying process so as to have a predetermined mixing ratio, and when supplied to an extruder, the mixing ratio is measured while being supplied. Also good. In this way, the resin that has been melt-extruded is removed in a molten state with a filter, the amount of extrusion is measured by a gear pump, and discharged from a T-die onto a cooling roll. At that time, it is preferable that the molten polymer is brought into close contact with the cooling roll and solidified by applying static electricity using a wire electrode or the like to obtain an unstretched film sheet because the thickness unevenness and surface state of the final film are improved. .

  Next, with respect to the method of biaxially orienting the obtained unstretched film, the film is stretched in the longitudinal direction and then stretched in the width direction, or after being stretched in the width direction and then stretched in the longitudinal direction. Or by the simultaneous biaxial stretching method in which the longitudinal direction and the width direction of the film are stretched almost simultaneously.

  As a draw ratio in such a drawing method, it is preferred to draw in each direction, preferably 3 to 6 times, more preferably 3.5 to 5.5 times. The stretching speed is preferably 1,000 to 200,000% / min, but more preferably 10,000 to 200,000% / min from the viewpoint of realizing high orientation. As a preferable stretching temperature, a glass transition point to a temperature of (glass transition point + 50 ° C.) is adopted, but more preferably in the case of sequential biaxial stretching, the stretching in the longitudinal direction is preferably 80 to 120 ° C., In the preheating stage before stretching, the polyester is heated to 80 to 100 ° C., and the polyester spontaneously generates heat at the time of stretching, and stretching at 95 to 120 ° C. is more preferable because it becomes a uniaxially stretched film highly oriented in the longitudinal direction. Next, the uniaxially stretched film is stretched in the width direction, and the stretching temperature is more preferably 80 to 120 ° C. In the case of simultaneous biaxial stretching, stretching at 80 to 120 ° C. is more preferable. The stretching may be performed a plurality of times in each direction.

  Next, the biaxially stretched film is heat treated. The heat treatment can be performed in an oven or on a heating roll, but is preferably performed in an oven in terms of planarity. The heat treatment temperature is preferably 170 to 240 ° C., but is preferably 190 to 235 ° C. and particularly preferably 200 to 230 ° C. from the viewpoint of achieving both pinhole resistance and dimensional stability. The time for performing the heat treatment is usually 1 to 60 seconds, more preferably 1 to 30 seconds. The heat treatment may be performed by relaxing the film in the longitudinal direction and / or the width direction. Further, as described above, it is preferable to perform relaxation heat treatment at a low temperature of 10 to 30 ° C. after the heat treatment under tension. Furthermore, a coating layer can also be provided on the film surface in order to improve the adhesive force with the ink print layer, the adhesive, and the vapor deposition layer.

  As a method of providing the coating layer in-line in the film manufacturing process, at least uniaxially stretched film is obtained by uniformly applying a coating layer composition dispersed in water using a metalling ring bar, etc. A method of drying the coating while applying the coating is preferred, and in this case, the coating layer thickness is preferably 0.01 to 0.5 μm.

  The biaxially oriented polyester film of the present invention is a surface-free film on at least one side of the film from the viewpoint of easily applying it to other materials as a packaging material, coating with an adhesive, printing or vapor deposition of a metal compound, etc. The energy is preferably 45 to 60 mN / m. From the viewpoint of adhesion, 48 to 58 mN / m is more preferable. Examples of a preferable method for applying the surface free energy include a method of performing a surface treatment by corona discharge or the like on the film surface in air or a nitrogen gas atmosphere, a method of performing a surface treatment by a flame, and the like.

  The biaxially oriented polyester film of the present invention is preferably used as a gas barrier film by depositing a metal or metal oxide on at least one surface of the film to form a deposited film. Examples of the metal or metal oxide used to form the deposited film include magnesium, calcium, barium, group 2B, titanium, zirconium, group 3B, aluminum, indium, group 4B, silicon, germanium. And tin and their oxides. Among these, aluminum, silicon and oxides thereof are particularly preferable. These metals and their oxides may be combined to form a deposited film.

  As a method for forming the deposited film, a vacuum deposition method, an EB deposition method, a sputtering method, an ion plating method, or the like can be used. In addition, in order to improve the adhesion between the polyester film and the vapor deposition layer, it is desirable that the surface of the film is pretreated not only by a surface treatment such as corona treatment but also by applying an anchor coating agent. It is. The thickness of the deposited film is preferably 1 to 500 nm, more preferably 3 to 300 nm. From the viewpoint of productivity, the thickness is preferably 3 to 200 nm.

  The biaxially oriented polyester of the present invention is preferably laminated with a sealant as a structure suitable for use as a package. Here, the sealant is a non-stretched film having heat sealing properties such as a non-stretched polypropylene film, a non-stretched linear low density polyethylene film, and an ethylene-vinyl acetate copolymer unstretched film. As a method for laminating the sealant and the biaxially oriented polyester film, a method such as a dry laminating method using an ester or urethane adhesive or a polyethylene dry laminating method can be employed. Since the biaxially oriented polyester film of the present invention has excellent heat resistance, it has excellent characteristics in which pinhole resistance does not change even after lamination with a sealant by an extrusion lamination method.

  Hereinafter, the present invention will be described in detail by way of examples. The characteristics were measured and evaluated by the following methods.

(1) Melting point The melting point was measured using a differential scanning calorimeter (Seiko Denshi Kogyo RDC220). Using 5 mg of the sample as a sample, the endothermic peak temperature when the temperature was raised from 25 ° C. to 300 ° C. at 20 ° C./min was defined as the melting point.

(2) Refractive index Using a sodium D line (wavelength 589 nm) as a light source, using methylene iodide as a mounting solution, and using an Abbe refractometer at 25 ° C., the refractive indices in the film longitudinal direction, width direction, and thickness direction (respectively, _nMD , _nTD , _nZD ). The plane orientation coefficient (fn) and birefringence (Δn) were calculated from the determined refractive index according to the following formula. In addition, the measurement was performed on the surface side in close contact with the cooling drum after discharging from the T-die at the time of film formation, and the average of measured values at arbitrary three locations was evaluated.

fn = (n _MD + n _TD ) / 2-n _ZD
Δn = (n _MD −n _TD ) × 1000.

(3) Film thickness The mass of 10 films cut to a size of 300 × 200 mm is measured, and the specific gravity of the film is set to 1.4 × 10 ⁻³ (g / mm ³ ), and the following formula is used as the mass average thickness. The film thickness was determined.

T = W / (1.4 × 10 ⁻³ × 300 × 200 × 10)
However, T: Film thickness (mm), W: Mass of 10 films (g).

(4) Thermal contraction rate The film was cut into a rectangular shape with a length of 150 mm and a width of 10 mm in the longitudinal direction and the width direction to obtain a sample. Marks were drawn on the sample at intervals of 100 mm, and a heat treatment was performed by placing in a hot air oven heated to 150 ° C. with a 3 g weight suspended for 30 minutes. The distance between the marked lines after the heat treatment was measured, and the thermal shrinkage rate was calculated from the change in the distance between the marked lines before and after heating, and used as an index of dimensional stability. For each film, five samples were carried out in the longitudinal direction and the width direction for each film, and the average value was evaluated.

(5) Breaking strength The film was cut into a rectangle having a length of 150 mm and a width of 10 mm in the longitudinal direction and the width direction to obtain a sample. Using a tensile tester (Orientec Tensilon UCT-100), the initial chuck distance was 50 mm, the tensile speed was 300 mm / min, and tensile tests were performed in the longitudinal direction and the width direction of the film, respectively. The load applied to the film immediately before the sample broke was read, and the value obtained by dividing the load by the cross-sectional area (film thickness x 10 mm) of the sample before the test was taken as the breaking strength. In addition, the measurement was performed 5 times for each sample and each direction, and the average value was evaluated.

(6) Intrinsic viscosity The intrinsic viscosity of the polyester resin and the film was measured at 25 ° C using an Ostwald viscosity system by dissolving the polyester in orthochlorophenol.

(7) Bend-resistant pinhole property Adhesive diluted 4 times with ethyl acetate on polyester film (Takelac A-616, Takenate A-65 manufactured by Mitsui Takeda Chemical Co., Ltd.) is mixed at a mass ratio of 16: 1. Was applied with a metalling bar so that the adhesive coating thickness was 3 g / m ² , dried at 60 ° C. for 1 minute, and then an unstretched linear low-density polyethylene film having a thickness of 50 μm (manufactured by Tosero Co., Ltd.) FCD-MCS) was bonded together. Aging was carried out at 40 ° C. for 7 hours for evaluation. The evaluation was performed in accordance with ASTM F-392 using a gel film flex tester with a laminate film cut out to a size of 300 × 210 mm, and subjected to repeated bending tests 500 times in an atmosphere at 23 ° C. In addition, when attaching to an apparatus, the polyester film was made to become an inner surface. The test was performed 5 times, and the average number of pinholes was calculated.

(8) Pin puncture resistance (dry lamination)
Adhesive thickness of 3 g of an adhesive (taken by Mitsui Takeda Chemical Co., Ltd. Takelac A-616, Takenate A-65 mixed at a mass ratio of 16: 1) diluted to 4 times with ethyl acetate on a polyester film / M ² was applied with a metering bar, dried at 60 ° C. for 1 minute, and then bonded to a 20 μm-thick unstretched polypropylene film (Torphan NO 9141 manufactured by Toray Film Processing Co., Ltd.). The laminate film is stretched on a ring with a diameter of 40 mm so that the film does not slack, and a sapphire needle with a tip angle of 60 degrees and a tip R of 0.5 mm is used, and the center of the circle is pierced from the polypropylene film side at a speed of 50 mm / min. The load (N) when the needle penetrates was defined as the puncture strength.

(9) Pin puncture resistance (extrusion lamination)
A biaxially oriented polyester film and an unstretched polypropylene film having a thickness of 20 μm (Treffan NO 9160 manufactured by Toray Film Processing Co., Ltd.) are extruded and laminated on a polyester film at a resin temperature of 330 ° C., and this is used as an adhesive. Lamination was performed. The laminate film is stretched on a ring with a diameter of 40 mm so that the film does not slack, and a sapphire needle with a tip angle of 60 degrees and a tip R of 0.5 mm is used, and the center of the circle is pierced from the polypropylene film side at a speed of 50 mm / min. The load (N) when the needle penetrates was defined as the puncture strength.

(10) Vapor deposition barrier property Aluminum was vapor-deposited on the polyester film to a thickness of 25 nm by a continuous vacuum vapor deposition machine. Using this aluminum vapor-deposited film, the oxygen transmission rate is measured under the conditions of 20 ° C. and 0% RH using an oxygen transmission rate measuring device OX-TRAN100 manufactured by Modern Control Co., Ltd. according to ASTM D-3985. did. On the other hand, the water vapor transmission rate was measured under the conditions of 40 ° C. and 90% RH using a vapor deposited film in the same manner and using a water vapor transmission rate meter PERMATRAN-W1A manufactured by Modern Control Co., Ltd.

(Preparation of polyester resin)
In the examples, polyester resins produced by the method described below were used.

Polyester A
To a mixture of 100 parts by weight of dimethyl terephthalate and 70 parts by weight of ethylene glycol, 0.09 parts by weight of magnesium acetate and 0.03 parts by weight of antimony trioxide are added, the temperature is gradually raised, and finally Performs transesterification while distilling methanol at 220 ° C. Next, 0.020 parts by mass of an 85% aqueous solution of phosphoric acid is added to the transesterification reaction product, and then the mixture is transferred to a polycondensation reaction kettle. Further, the reaction system was gradually depressurized while being heated and heated, and a polycondensation reaction was performed by a conventional method at 290 ° C. under a reduced pressure of 1 hPa to produce a polyethylene terephthalate resin having an intrinsic viscosity of 0.65. This is hereinafter referred to as polyester A.

Polyester B
In the polymerization of polyester A, instead of 100 parts by mass of dimethyl terephthalate, 96 parts by mass of dimethyl terephthalate and 4 parts by mass of dimethyl isophthalate were used for polymerization in the same manner as for polyester A, An acid 4 mol% copolymerized polyethylene terephthalate resin (melting point 247 ° C.) was prepared. This is hereinafter referred to as polyester B.

Polyester C
In the polymerization of polyester A, instead of 100 parts by mass of dimethyl terephthalate, 88 parts by mass of dimethyl terephthalate and 12 parts by mass of dimethyl isophthalate are used for polymerization in the same manner as for polyester A. An acid 12 mol% copolymer polyethylene terephthalate resin (melting point 227 ° C.) was prepared. This is hereinafter referred to as polyester C.

Particle Master At the time of polymerization of each polyester described above, an ethylene glycol slurry of agglomerated silica particles having an average particle diameter of 2 μm is added after the transesterification reaction, and then a polycondensation reaction is performed to obtain a particle master A having a particle concentration of 2% by mass in the polymer. ~ C was made.

Example 1
Polyester A and particle master A were mixed and used at a mass ratio of 97: 3. First, it was dried at 180 ° C. for 3 hours in a rotary vacuum dryer, then supplied to a single screw melt extruder and extruded at a cylinder temperature of 280 ° C. Foreign matter was removed from the molten polymer using a 20 μm cut sintered filter, and the flow rate was measured and leveled using a gear pump, and then discharged from a T-die onto a cooling roll whose temperature was controlled at 20 ° C. At that time, the molten polymer was brought into close contact with the roll by electrostatic application, and cooled and solidified. The unstretched film thus obtained was heated to 95 ° C. with a heating roll, and stretched 3.8 times in the longitudinal direction of the film between a roll heated to 100 ° C. and a cooling roll temperature-controlled at 40 ° C. When the roll temperature was measured in the stretching section, it was 105 ° C. The film uniaxially stretched in the longitudinal direction was once cooled and then introduced into a tenter type transverse stretcher. The film was stretched 3.7 times in the width direction at a preheating temperature of 90 ° C. and a stretching zone temperature of 110 ° C., then heat-treated at 220 ° C. for 1.5 seconds, and then relaxed by 5% in the width direction for 1.5 seconds at 200 ° C. A heat treatment was performed to finally obtain a biaxially oriented film having a thickness of 8 μm.

(Example 2)
The polyester resin was weighed, mixed and dried in the same manner as in Example 1, and then supplied to the extruder in the same manner and extruded onto a cooling drum from a T-die in a sheet form to obtain an unstretched film. The unstretched film was heated to 95 ° C. with a heating roll, and stretched 3.8 times in the longitudinal direction of the film between a roll heated to 100 ° C. and a cooling roll temperature-controlled at 40 ° C. When the roll temperature was measured in the stretching section, it was 105 ° C. The film uniaxially stretched in the longitudinal direction was once cooled and then introduced into a tenter type transverse stretcher. After stretching 3.8 times in the width direction at a preheating temperature of 90 ° C. and a stretching zone temperature of 110 ° C., heat treatment was performed at 215 ° C. for 2 seconds as it was, and then heat treatment was performed at 215 ° C. for 2 seconds while relaxing 3% in the width direction. Finally, a biaxially oriented film having a thickness of 12 μm was obtained.

(Example 3)
Polyester A and particle master A were mixed and used at a mass ratio of 96: 4. First, drying was carried out at 180 ° C. for 4 hours in a rotary vacuum dryer, then supplied to a single screw melt extruder and extruded at a cylinder temperature of 280 ° C. Foreign matter was removed from the molten polymer using a 20 μm cut sintered filter, the flow rate was measured and leveled using a gear pump, and then discharged from a T-die onto a cooling roll whose temperature was controlled at 25 ° C. At that time, the molten polymer was brought into close contact with the roll by electrostatic application, and cooled and solidified. The unstretched film thus obtained was heated to 97 ° C. with a heating roll, and stretched 3.7 times in the longitudinal direction of the film between a roll heated to 103 ° C. and a cooling roll temperature-controlled at 45 ° C. The roll temperature measured in the stretching section was 107 ° C. The film uniaxially stretched in the longitudinal direction was once cooled and then introduced into a tenter type transverse stretcher. After stretching 3.7 times in the width direction at a preheating temperature of 95 ° C. and a stretching zone temperature of 110 ° C., heat treatment is performed at 210 ° C. for 3 seconds as it is, and then heat treatment is performed at 200 ° C. for 3 seconds while relaxing 3% in the width direction. Finally, a biaxially oriented film having a thickness of 16 μm was obtained.

Example 4
Polyester B and particle master B were mixed and used at a mass ratio of 97: 3. First, drying was carried out at 150 ° C. for 5 hours in a rotary vacuum dryer, then supplied to a single-screw melt extruder and extruded at a cylinder temperature of 275 ° C. Foreign matter was removed from the molten polymer using a 20 μm cut sintered filter, and the flow rate was measured and leveled using a gear pump, and then discharged from a T-die onto a cooling roll whose temperature was controlled at 20 ° C. At that time, the molten polymer was brought into close contact with the roll by electrostatic application, and cooled and solidified. The unstretched film thus obtained was heated to 90 ° C. with a heating roll, and stretched 3.7 times in the longitudinal direction of the film between a roll heated to 100 ° C. and a cooling roll temperature-controlled at 40 ° C. The film uniaxially stretched in the longitudinal direction was once cooled and then introduced into a tenter type transverse stretcher. The film was stretched 3.7 times in the width direction at a preheating temperature of 85 ° C. and a stretching zone temperature of 110 ° C., and then heat-treated at 200 ° C. for 6 seconds to finally obtain a biaxially oriented film having a thickness of 18 μm.

(Comparative Example 1)
Polyester A and polyester B were mixed at a mass ratio of 98: 2, and dried at 180 ° C. for 3 hours in a rotary vacuum dryer. Subsequently, it supplied to the single screw melt extruder, and extruded with the cylinder temperature of 280 degreeC. In the same manner as in Example 1, the film was discharged from a T-die and adhered and solidified on a cooling roll controlled at 25 ° C. while applying an electrostatic force to obtain an unstretched film. The unstretched film was heated to 105 ° C. and stretched 3.1 times in the longitudinal direction. Next, the film was introduced into a tenter type stretching apparatus, stretched 4.0 times in the width direction at a preheating of 100 ° C. and a stretching temperature of 110 ° C., and further heat-treated at 230 ° C. for 5 seconds to obtain a biaxially oriented film having a thickness of 12 μm. It was.

(Comparative Example 2)
Polyester A and polyester B were mixed at a mass ratio of 98: 2, and dried at 180 ° C. for 3 hours in a rotary vacuum dryer. Subsequently, it supplied to the single screw melt extruder, and extruded with the cylinder temperature of 300 degreeC. In the same manner as in Example 1, the film was discharged from a T-die and adhered and solidified on a cooling roll controlled at 30 ° C. while applying an electrostatic force to obtain an unstretched film. The unstretched film was gradually heated using rolls heated to 80, 90, 105, 110, and 117 ° C., and then stretched 4.3 times in the longitudinal direction. Next, the film was introduced into a tenter type stretching machine, stretched 4.0 times in the width direction at a preheating of 80 ° C. and a stretching temperature of 135 ° C., and further heat-treated at 230 ° C. for 3 seconds to obtain a biaxially oriented film having a thickness of 12 μm. It was.

(Comparative Example 3)
Polyester A and particle master A were mixed at a mass ratio of 94: 6, and dried at 180 ° C. for 3 hours in a rotary vacuum dryer. Next, it is supplied to an extruder and melt-extruded at 280 ° C., filtered through a 10 μm cut film ter, extruded into a sheet form from a T-die, and solidified by electrostatic application to a 25 ° C. cooling roll and unstretched film Got. The unstretched film was heated to 120 ° C. and stretched 2.2 times in the longitudinal direction, further 1.2 times at 120 ° C., and finally 2.4 times at 115 ° C., and 6.3 times in the total longitudinal direction. . Subsequently, it was 3.9 times in the width direction at a preheating temperature of 100 ° C. and a stretching temperature of 105 ° C. using a tenter type stretching machine. Tension heat treatment was performed for 3 seconds at 225 ° C., and relaxation heat treatment was further performed at 225 ° C. for 3 seconds at 5% relaxation to obtain a 12 μm biaxially oriented film.

(Comparative Example 4)
Polyester A and particle master A were mixed at a mass ratio of 97: 3, and dried at 180 ° C. for 3 hours in a rotary vacuum dryer. Next, it is supplied to an extruder and melt-extruded at 280 ° C., filtered through a 10 μm cut film ter, extruded into a sheet form from a T-die, and solidified by electrostatic application to a 25 ° C. cooling roll and unstretched film Got. The unstretched film was heated to 115 ° C. and stretched 1.2 times in the longitudinal direction, further 1.48 times at 125 ° C., finally 2.62 times at 113 ° C., and 4.65 times in the total longitudinal direction. . Subsequently, it was 3.9 times in the width direction at a preheating temperature of 100 ° C. and a stretching temperature of 105 ° C. using a tenter type stretching machine. Tension heat treatment was performed at 233 ° C. for 3 seconds as it was, and relaxation heat treatment was further performed at 233 ° C. for 3 seconds at 5% relaxation to obtain a 12 μm biaxially oriented film.

(Comparative Example 5)
Polyester A and particle master A were mixed at a mass ratio of 94: 6, and dried at 180 ° C. for 3 hours in a rotary vacuum dryer. Next, it is supplied to an extruder and melt-extruded at 280 ° C., filtered through a 10 μm cut film ter, extruded into a sheet form from a T-die, and solidified by electrostatic application to a 25 ° C. cooling roll and unstretched film Got. The unstretched film was heated to 100 ° C. and stretched 1.15 times in the longitudinal direction, then 3.0 times at 105 ° C., and 3.45 times in the total longitudinal direction. Subsequently, it was 3.9 times in the width direction at a preheating temperature of 100 ° C. and a stretching temperature of 105 ° C. using a tenter type stretching machine. Tension heat treatment was performed at 200 ° C. for 3 seconds as it was, and relaxation heat treatment at 200 ° C. for 3 seconds at 4% relaxation was performed to obtain a 12 μm biaxially oriented film.

(Comparative Example 6)
Polyester A and particle master B were mixed with Toray polybutylene terephthalate resin ("Torcon 1200S") at a mass ratio of 90: 3: 7. First, drying was carried out at 150 ° C. for 5 hours in a rotary vacuum dryer, then supplied to a single-screw melt extruder and extruded at a cylinder temperature of 275 ° C. Foreign matter was removed from the molten polymer using a 20 μm cut sintered filter, and the flow rate was measured and leveled using a gear pump, and then discharged from a T-die onto a cooling roll whose temperature was controlled at 20 ° C. At that time, the molten polymer was brought into close contact with the roll by electrostatic application, and cooled and solidified. The unstretched film thus obtained was stretched 3.4 times in the longitudinal direction of the film between a roll heated to 95 ° C. with a heating roll and a cooling roll whose temperature was controlled at 40 ° C. The uniaxially stretched film is once cooled and then introduced into a tenter-type stretcher, stretched 3.7 times in the width direction at a preheating temperature of 85 ° C. and a stretching temperature of 105 ° C., and then heat treated at 210 ° C. for 5 seconds and further relaxed by 3%. Then, heat treatment was performed at 210 ° C. for 3 seconds to finally obtain a biaxially oriented film having a thickness of 12 μm.

(Comparative Example 7)
Polyester A and particle master A were mixed at a mass ratio of 98: 2, and dried at 180 ° C. for 3 hours in a rotary vacuum dryer. Subsequently, it was supplied to an extruder, melted at 290 ° C., extruded into a sheet shape, and adhered and solidified on a cooling roll while applying an electrostatic force to obtain an unstretched film. The unstretched film was 2.9 times at 84 ° C., 1.7 times at 70 ° C., then stretched 4.1 times at 110 ° C. by a tenter type stretching machine, and heat-treated at 245 ° C. An axially oriented film was obtained.

(Comparative Example 8)
Polyester C and particle master C were mixed at a mass ratio of 96: 4 and vacuum dried at 150 ° C. for 4 hours. It was supplied to a single screw extruder, melted at 270 ° C., and extruded from a T die into a sheet. It was made to adhere and solidify on a 35 degreeC cooling roll, applying an electrostatic, and the unstretched film was obtained. The unstretched film was heated to 85 ° C. and stretched 3.8 times, and then stretched 4.0 times with a tenter type stretching machine at a preheating temperature of 85 ° C. and a stretching temperature of 105 ° C. And it heat-processed for 5 seconds at 215 degreeC as it was, and obtained the 12-micrometer-thick biaxially oriented film.

ただし、表中の略号は以下の通り。ＰＥＴ：ポリエチレンテレフタレート。ＰＢＴ：ポリブチレンテレフタレート。ＰＥＴ−Ｉ：イソフタル酸共重合ポリエチレンテレフタレート。Δｎ：複屈折（フィルム長手方向と幅方向の屈折率の差を１０００倍した数値）。ｎＺＤ：フィルム厚み方向の屈折率。ＭＤ：フィルム長手方向。ＴＤ：フィルム幅方向。

However, the abbreviations in the table are as follows. PET: Polyethylene terephthalate. PBT: polybutylene terephthalate. PET-I: Isophthalic acid copolymerized polyethylene terephthalate. Δn: birefringence (a value obtained by multiplying the difference in refractive index between the film longitudinal direction and the width direction by 1000). nZD: refractive index in the film thickness direction. MD: Film longitudinal direction. TD: Film width direction.

  From the table, each film of the examples was excellent in bending pinhole resistance, pin puncture resistance, and gas barrier properties after vapor deposition. On the other hand, each film of the comparative example is inferior in pin puncture resistance due to poor orientation balance in the film longitudinal direction and width direction, or the occurrence of pinholes due to cleavage cleavage because the orientation is too high, etc. It was an insufficient property as a packaging material.

  The film of the present invention not only has excellent resistance to bending pinholes, but also has excellent balance of physical properties in the film longitudinal direction and width direction, so that it can also be used for pin puncture resistance and gas barrier properties when a metal compound is deposited. Since it is excellent, it can be suitably used as a constituent of food packaging and the like.

Claims (5)

A biaxially oriented film mainly composed of polyethylene terephthalate,
The plane orientation coefficient is 0.168 to 0.172,
The absolute value of birefringence is less than 5,
The thermal shrinkage in the film width direction at 150 ° C. is 0.5-2%,
A biaxially oriented polyester film for packaging, wherein the film thickness is 7 to 20 μm. The biaxially oriented polyester film for packaging according to claim 1, wherein the refractive index in the thickness direction of the film is from 1.480 to 1.495. The biaxially oriented polyester film for packaging according to claim 1 or 2, wherein the tensile breaking strength in the longitudinal direction and the width direction of the film is 260 to 400 MPa. A gas barrier film for packaging, comprising a metal or metal oxide deposited on the biaxially oriented polyester film for packaging according to any one of claims 1 to 3. A package comprising the polyester film according to any one of claims 1 to 4 and a sealant.