JP2006188049A - Biaxially oriented polyester film and packaging bag - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film which, while maintaining low moisture absorption property, dimensional stability, flatness and transparency which are the characteristics of a polyester film, combines resistance to pinhole formation by flexing and impact resistance required as a film for a packaging material. <P>SOLUTION: The biaxially oriented polyester film is a polyester film in which layers A and layers B are alternately laminated in five or more layers, the layers A consist of a polyester resin (A), the layers B consist of 99-60 mass% of a polyester resin (B) and 1-40 mass% of an elastomer (C), and the relation of d<SB>C</SB>≤t<SB>B</SB>≤2d<SB>C</SB>is satisfied when the average layer thickness per one layer of the layers B is indicated by t<SB>B</SB>and the average dispersion diameter of the elastomer (C) to the film thickness direction is indicated by d<SB>C</SB>. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a biaxially oriented polyester film, a vapor deposition film using the same, a packaging film, and a packaging bag.

  Polyethylene terephthalate biaxially stretched film, which is a typical example of polyester film, has excellent 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 materials, and packaging materials. It is used in a wide range of fields.

  However, in packaging materials where bending pinhole resistance and impact resistance are particularly important, polyethylene terephthalate film has insufficient properties due to its hardness, which is the reverse of its toughness, excellent flexibility, and impact resistance Polyamide biaxially stretched films having bent pinhole resistance typified by gelbotest and excellent properties at low temperatures are often used.

  Aromatic polyamides have an aromatic ring that improves hygroscopicity, but it is difficult to form a melt film, and a special and high-risk solvent must be used even for solution film formation. There is a problem that productivity is inferior.

  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 the subject that it was inferior to impact property.

  Conventionally, for example, Patent Document 1 discloses a flexible polyester film having a specific Young's modulus as an attempt to improve the bending-resistant pinhole property of polyester with respect to these problems.

  Patent Documents 2 and 3 disclose polyester films in which polytetramethylene glycol having a specific molecular weight is mixed with polyester at a specific ratio. Note that Patent Document 2 also describes that a specific amount of specific particles is added.

  Furthermore, Patent Document 4 discloses a flexible polyester film obtained by adding polyethylene terephthalate to a modified polybutylene terephthalate containing a specific amount of polytetramethylene glycol. Patent Document 5 has a different melting point. A method of kneading two polyesters to obtain a polyester film having excellent bending resistance is disclosed.

  However, these conventional methods have problems such as deterioration of the mechanical properties and transparency of the film, poor transparency deposition using aluminum oxide, silicon oxide, etc., and the most important bending-resistant pinhole property There was a problem that the impact resistance after bag making was still insufficient.

Furthermore, Patent Document 6 discloses a polyester film in which a polymer having a specific glass transition point is dispersed in a film, and the dispersion diameter is within a specific range, so that the polyester film has excellent characteristics as a packaging material. However, in this film, since the dispersion position of the low glass transition polymer cannot be controlled, it is unavoidable that the dispersion state is biased. There was a problem that holes were generated or bags were broken.
JP-A-6-79976 JP-A-7-330926 JP-A-8-41184 JP 2001-11213 A JP 2003-113259 A JP 2004-18742 A

  An object of the present invention is to eliminate the above-described problems. That is, an object of the present invention is to provide a biaxially oriented polyester film that maintains the characteristics of a polyester film and is excellent in bending pinhole resistance and impact resistance.

The above problem is a polyester film in which five or more layers of A and B layers are alternately laminated, wherein the A layer is made of a polyester resin (A), the B layer is 99 to 60% by mass of the polyester resin (B), and an elastomer. (C) consists of 1 to 40 wt%, and, _{when t B} the average layer thickness per one layer of the B layer, the average dispersion diameter of the film thickness direction of the elastomer (C) was _{d C, d C} ≦ t _This can be achieved by a biaxially oriented polyester film characterized by satisfying the relationship of _B ≦ 2d _C.

  The biaxially oriented polyester film of the present invention has excellent properties such as bending pinhole resistance and impact resistance required as packaging materials, and is suitable as a gas barrier film or packaging film by taking advantage of these excellent properties. It can be preferably used for food packaging applications.

  In the biaxially oriented polyester film of the present invention, it is necessary that five or more layers of A layers and B layers are alternately laminated. The number of laminated layers is preferably 10 to 2000 layers, more preferably 30 to 1000 layers, and particularly preferably 50 to 500 layers. When the number of laminated layers is 4 or less, it is difficult to obtain a film excellent in bending pinhole resistance and puncture strength. In addition, the upper limit of the number of layers is not particularly limited. However, if the number exceeds 2000 layers, the layer thickness per layer becomes extremely thin, and the resin constituting the A layer and the resin constituting the B layer are simply In some cases, only properties equivalent to a blended monolayer film can be obtained.

  In the polyester film of the present invention, the A layer is composed of a polyester resin (A), and the B layer is composed of 99 to 60% by mass of the polyester resin (B) and 1 to 40% by mass of the elastomer (C). From the viewpoint of bending pinhole resistance, impact resistance, heat-resistant dimensional stability, and transparency, the amount of elastomer (C) added is more preferably 2 to 20% by mass, and particularly preferably 3 to 10% by mass. .

In the polyester film of the present invention, the relationship between the average layer thickness t _B per layer of the B layer and the average dispersion diameter d _C in the film thickness direction of the elastomer (C) is a relationship of d _C ≦ t _B ≦ 2d _C. It is necessary to satisfy more preferably if _{d C ≦ t B ≦ 1.8d C} , particularly preferred if _{d C ≦ t B ≦ 1.5d C} . This is because when the relationship between t _B and d _C is satisfied, the elastomer (C) is uniformly dispersed in the film, and the dispersion state is not biased. In addition, the distance between the closest dispersions of the elastomers (C) can be reduced, the stress generated by deformation such as bending and drop impact can be uniformly dispersed, and the resistance to bending pinholes and impact can be improved. improves. On the other hand, when the relationship of d _C > t _B is satisfied, the elastomer (C) after film formation may have residual stress, or thickness unevenness caused by the elastomer may occur, resulting in poor characteristics. On the other hand, if t _B > 2d _C , the dispersion state of the elastomer (C) is biased, and the significance of alternately laminating the A layer and the B layer becomes poor, and improvement in characteristics is not recognized.

Here, the relationship between the average layer thickness t _B per B layer and the average dispersion diameter d _C in the film thickness direction of the elastomer (C) satisfies the relationship d _C ≦ t _B ≦ 2d _C. The achieving method is not particularly limited, but after alternately laminating the A layer and the B layer in the molten state, a relationship of d _C ≦ t _B ≦ 2d _C is satisfied using a square mixer or a static mixer. Thus, a method of increasing the number of stacked layers can be preferably used. Furthermore, it is within more preferable range of _{t B} by changing the discharge amount ratio from extruder A layer and the B layer is a more preferable _{range, d C ≦ t B ≦ 1.8d} C, d C ≦ A relationship of t _B ≦ 1.5d _C can be achieved. The average dispersion diameter d _C of the film thickness of the elastomer (C) is determined by the compatibility between the elastomer (C) and the polyester resin (B) that is the matrix resin, and the difference in melt viscosity. made to create a single-layer film, to evaluate the d _C at that time, it is possible to determine the range of t _B.

  The polyester constituting the biaxially oriented polyester film of the present invention is a general term for polymer compounds having an ester bond as the main bond in the main chain, and is usually a dicarboxylic acid component and a glycol component or a dicarboxylic acid ester compound. It can be obtained by polycondensation reaction of a glycol component. Here, examples of the dicarboxylic acid compound include terephthalic acid, 2,6-naphthalenedicarboxylic acid, isophthalic acid, diphenyldicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid, 5-sodiumsulfonedicarboxylic acid, and phthalic acid. Aromatic dicarboxylic 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 Examples thereof include oxycarboxylic acids such as acids. Examples of the dicarboxylic acid ester compounds include esterified products of the above dicarboxylic acid compounds, such as dimethyl terephthalate, diethyl terephthalate, 2-hydroxyethyl methyl terephthalate, dimethyl 2,6-naphthalenedicarboxylate, dimethyl isophthalate, and dimethyl adipate. , Diethyl maleate, dimethyl dimer, and the like. On the other hand, as the dihydroxy compound, for example, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6 -Aliphatic dihydroxy compounds such as hexanediol and neopentyl glycol, polyoxyalkylene glycols such as diethylene glycol, polyethylene glycol, polypropylene glycol and polytetramethylene glycol, alicyclic dihydroxy compounds such as 1,4-cyclohexanedimethanol, and bisphenol A And aromatic dihydroxy compounds such as bisphenol S. Among these, terephthalic acid, 2,6-naphthalenedicarboxylic acid, isophthalic acid or their dimethyl ester compounds are used as dicarboxylic acid compounds, and ethylene glycol, 1,3-propanediol, 1,4-butane are used as dihydroxy compounds. Diol, polytetramethylene glycol and the like can be preferably used. In particular, it is preferable to use terephthalic acid or dimethyl terephthalate and polyethylene terephthalate composed of ethylene glycol and terephthalic acid or dimethyl terephthalate and polybutylene terephthalate composed of 1,4-butanediol.

  The polyester resin (A) constituting the A layer of the polyester film of the present invention and the polyester resin (B) constituting the B layer are aromatic polyesters mainly composed of ethylene terephthalate units having a melting point of 245 to 265 ° C. And an aromatic polyester mainly composed of a butylene terephthalate unit having a melting point of 190 to 240 ° C. Here, the aromatic polyester having an ethylene terephthalate unit as a main constituent is a polyester resin having 95 mol% or more of an ethylene terephthalate unit. If melting | fusing point is less than 245 degreeC, the heat resistance of a film may be inferior and dimensional stability etc. may deteriorate. On the other hand, when the melting point exceeds 265 ° C., the difference in thermal characteristics from the elastomer (C) added to the B layer is excessively widened, which may adversely affect melt extrudability and film forming stability. From the viewpoint of dimensional stability, it is more preferable that the aromatic polyester having ethylene terephthalate as a main constituent has a melting point of 250 to 265 ° C. On the other hand, the aromatic polyester having a butylene terephthalate unit as a main constituent is a polyester resin in which 70 mol% or more is composed of a butylene terephthalate unit. If the melting point is less than 190 ° C, the heat resistance may deteriorate. On the other hand, it is difficult to set the melting point to 240 ° C. or higher as long as the main component is a butylene terephthalate unit. A more preferable melting point is 200 to 235 ° C, and more preferably 210 to 235 ° C.

  Furthermore, a polyester resin (A) and a polyester resin are prepared by mixing 98 to 70% by mass of an aromatic polyester mainly composed of an ethylene terephthalate unit and 2 to 30% by mass of an aromatic polyester mainly composed of a butylene terephthalate unit. (B) is preferable. In addition, the aromatic polyester used for the polyester resin (A) and the polyester resin (B) may be the same or different. Moreover, the mixing ratio may be the same or different. The blending ratio is more preferably 10 to 30% by mass of the aromatic polyester having a polybutylene terephthalate unit as a main constituent in terms of bending pinhole resistance, and 15 to 25% by mass in consideration of heat resistance. Is particularly preferred.

  As a method of mixing an aromatic polyester mainly composed of ethylene terephthalate units and an aromatic polyester mainly composed of butylene terephthalate units, an esterification reaction with terephthalic acid in the presence of ethylene glycol and butylene glycol at the polymerization stage Or a method of polycondensation by transesterification with an ester derivative of terephthalic acid to form a copolymer polyester (in this case, a third copolymer component may coexist in the polymerization system), or Examples include a method in which ethylene terephthalate and polybutylene terephthalate are separately polymerized (copolyester may be used), pelletized, blended so as to have a predetermined mixing ratio during film formation, dried, and mixed by melt extrusion. The latter separately polymerized aromatic poly Method of mixing ester is, handling property of the polyester resin, from the viewpoint of heat resistance of the film.

  The elastomer (C) used in the present invention is a rubber component that is plasticized at a high temperature and can be molded in the same manner as plastics, exhibits properties of a rubber elastic body at room temperature (20 to 30 ° C.), and exhibits entropy elasticity. It is a polymer composed of constraining components (hard segments) necessary to make a mechanism for preventing plastic deformation at normal temperature (20-30 ° C.), although it flows at (soft segment) and high temperature (temperature range of 100 ° C. or higher). Examples of the elastomer include polystyrene elastomer (hard segment: polystyrene, soft segment: polybutadiene, polyisoprene, hydrogenated polybutadiene, ethylene-propylene copolymer rubber, etc.), polyolefin elastomer (hard segment: polyethylene or polypropylene, soft segment: ethylene- Propylene copolymer rubber, polybutadiene, polyisoprene, hydrogenated polybutadiene, etc., polyester elastomer (hard segment: polyester, soft segment: polyether or polyester), polyamide elastomer (hard segment: polyamide, soft segment: polyether or polyester) ), And other hard segments are syndio-1,2-polybutadiene And down, like those of the soft segment and atactic-1,2-polybutadiene. Furthermore, a functional group such as a hydroxyl group, a carboxyl group, an epoxy group, an amide group and a maleic anhydride component and a functional group forming component may be partially introduced into the elastomer. Among these, polystyrene elastomers and polyester elastomers are preferable for improving impact resistance. Specifically, polystyrene systems such as SBS (styrene-butadiene-styrene copolymer), SEBS (styrene-ethylene / butylene-styrene copolymer), SIS (styrene-isoprene-styrene copolymer), SEP (styrene-ethylene / propylene copolymer), etc. Elastomers, polyester elastomers such as HYTREL (manufactured by Toray Deyupon), ARNITEL (manufactured by Akzo Chemie), perprene (manufactured by Toyobo), and LOMOD (manufactured by General Electric) can be suitably used. It is particularly preferable to use a polyester-based elastomer in terms of transparency, heat resistance, and film formation stability.

  When the biaxially oriented polyester film of the present invention is re-pelletized and used as a self-collecting raw material, the A layer may contain an elastomer (C). However, even in this case, the weight ratio (A / B) between the amount of the elastomer (C) contained in the A layer and the amount of the elastomer (C) contained in the B layer is 0.001 to 0.5. It is preferable that it is 0.001-0.3, more preferably 0.001-0.2. If the weight ratio (A / B) of the elastomer (C) exceeds 0.5, heat resistance, secondary workability such as vapor deposition and printing, and lamination accuracy may be inferior.

The composition and amount of the polyester resin (A), polyester resin (B) and elastomer (C) contained in the A layer and B layer described above are determined by proton nuclear magnetic resonance spectroscopy ( ¹ H-NMR) or carbon 13 nuclear magnetic field. The molar ratio or the weight ratio can be quantified by resonance spectroscopy ( ¹³ C-NMR).

  The average dispersion diameter in the film in-plane direction of the elastomer (C) is preferably 1 to 10 μm. From the viewpoints of bending resistance and impact resistance, the average dispersion diameter in the in-plane direction is more preferably 2 to 10 μm, and particularly preferably 3 to 8 μm. If the average dispersion diameter in the in-plane direction of the elastomer (C) is within such a range, when the cross section of the film is observed, the number of elastomers per unit cross-sectional area increases, and at any place in the film thickness direction. When a straight line is drawn vertically, the number of times the elastomer and the straight line cross each other is increased, and the stress generated by deformation such as bending and drop impact can be efficiently dispersed, and the resistance to bending pinholes and impact resistance is large. improves. When the average dispersion diameter is less than 1 μm, the number of elastomer applications per unit cross-sectional area decreases and the properties may be inferior. On the other hand, even when the average dispersion diameter exceeds 10 μm, if separation occurs between the matrix polyester (B) and the film is broken, the characteristics may be inferior.

Here, the average dispersion diameter in the in-plane direction and the thickness direction average dispersion diameter d _C of the elastomer (C) can be quantified as follows. The film is embedded in an epoxy resin, and an ultrathin section is prepared using a microtome so that the cross section of the film becomes the sample surface. The thin film section of the film cross section is stained with ruthenium tetroxide, and a film cross section photograph is taken at a magnification of 20,000 using a transmission electron microscope. For the elastomer (C) that is dyed and observed from the photograph obtained, the dispersion diameter in the in-plane direction and the dispersion diameter in the thickness direction are measured at 10 locations, and the average value is the average dispersion diameter in the in-plane direction or the thickness direction. and an average dispersion diameter _{d C.}

Here, the method for controlling the dispersion diameter of the elastomer (C) is not particularly limited, but the melt extrusion conditions such as compatibility with the polyester as the matrix resin, melt viscosity difference and shear rate, draft ratio, etc. Furthermore, a method in which the dispersion diameter in the in-plane direction is particularly controlled by the stretching conditions can be mentioned. In particular, when the same elastomer is used, it is possible to increase the dispersion diameter in the in-plane direction by making it more highly oriented according to the stretching conditions, and as a result, to satisfy the above-mentioned preferable average dispersion diameter range. In the laminated polyester film of the present invention, the A layer and the B layer in the laminated polyester film of the present invention can exhibit excellent properties. In order to improve the handleability and processability, particles having an average particle diameter of 0.01 to 5 μm It is preferable to contain. As the particles that can be added to the A layer and the B layer, for example, internal particles, inorganic particles, and organic particles can be preferably used. In the laminated polyester film according to a preferred embodiment of the present invention, particles are preferably contained in the A layer and the B layer in an amount of 0.01 to 3% by mass, more preferably 0.03 to 3% by mass, and further preferably 0.05 to 2%. It can be contained by mass%, particularly preferably 0.05 to 1 mass%.

  Examples of the method for precipitating the internal particles in the A layer and the B layer of the laminated polyester film of the present invention include, for example, JP-A-48-61556, JP-A-51-12860, and JP-A-53-41355. And techniques described in JP-A-54-90397 can be employed. Further, other particles described in Japanese Patent Publication No. 55-20496 and Japanese Patent Publication No. 59-204617 can be used in combination. When the average particle diameter is 0.01 to 5 μm, no defect occurs in the film.

  Examples of the inorganic particles that can be contained in the A layer and the B layer of the laminated polyester film of the present invention include wet and dry silica, colloidal silica, aluminum silicate, titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, and aluminum oxide. As organic particles such as mica, kaolin, and clay, particles containing styrene, silicone, acrylic acids, methacrylic acids, polyesters, divinyl compounds and the like as constituent components can be used. Among them, it is preferable to use inorganic particles such as wet and dry silica and alumina, and particles containing styrene, silicone, acrylic acid, methacrylic acid, polyester, divinylbenzene and the like as constituent components. Furthermore, these internal particles, inorganic particles, and organic particles may be used in combination of two or more.

  The laminated polyester film of the present invention is a laminated film of 5 layers or more, and the production method of this laminated polyester film is arranged by alternately arranging the polyester resin (A) for the A layer and the polyester resin (B) for the B layer. Therefore, using two or more melt extruders, supply the thermoplastic resin to each extruder, perform melt extrusion, and use a feed block, static mixer, multi-manifold, etc. installed on the top of the T-die The method of laminating can be preferably used.

  As a particularly preferred production method, the polyester resin (A) and the polyester resin (B) are laminated in three or more layers with a feed block, then the number of laminations is increased using a static mixer, and the sheet is discharged from a T-die. And the method of obtaining an unstretched sheet by quenching on a metal cooling roll can be mentioned. At this time, in order to reduce the thickness unevenness of each layer and obtain a film having a large adhesion between the layers, the melting point of the polyester resin (A), which is the main component of the A layer, and the main component of the B layer. The difference in melting point of the polyester resin (B) is preferably 10 ° C. or less. Further, it is preferable to laminate the A layer on both outermost layers of the film because the slipping property and the heat resistance of the surface are improved.

  The biaxially oriented polyester film of the present invention preferably has a haze of 0.01 to 5% in terms of a thickness of 12 μm. A film having a haze of less than 0.01% may be technically difficult to produce. Yes and not economical. In addition, when the haze exceeds 5%, the appearance and transparency of the film are inferior, so when used as a packaging material such as a transparent bag, the visibility of the contents may be inferior, or the commercial value may appear to decline. is there. The haze is more preferably 0.1 to 4%, and particularly preferably the internal haze is 0.1 to 3%. Although there is no particular limitation on the method of setting the preferred range for applying the haze, when the polyester resin and the elastomer (C) have poor compatibility, for example, when an olefin-based elastomer containing polypropylene is used as the elastomer In some cases, interfacial separation occurs in the polyester resin matrix, and voids are formed, resulting in increased haze. In addition, the cloudiness may be increased by adding inorganic particles added as a lubricant more than necessary. Further, when particles having a large average particle diameter are used, the surface haze becomes particularly large, and a matte surface may be formed. In order to adjust the haze to a preferable range, a polyester-based elastomer is used as the elastomer, and the lubricant particles are preferably added only to the outermost layer of the A and B layers.

  The laminated polyester film of the present invention preferably has a plane orientation coefficient of 0.164 to 0.180. The plane orientation coefficient is a value calculated by (Nx + Ny) / 2−Nz, where Nx, Ny, and Nz are the refractive indexes in the longitudinal, width, and thickness directions, respectively, and indicate the degree of orientation of the molecular chain in the plane direction. It is a parameter. Preferably, it is 0.164 to 0.180, more preferably 0.167 to 0.180, and particularly preferably 0.169 to 0.180. Thus, a film excellent in puncture strength and surface impact can be obtained. In addition, due to the in-plane orientation, the dispersion diameter of the elastomer becomes a disk shape, and it is possible to more efficiently absorb and disperse bending deformation and impact energy, and to obtain a film having excellent bending pinhole characteristics. Examples of the preferred range include a method of controlling the draw ratio and the temperature at the time of biaxial stretching, and the crystallization and amorphous orientation in the heat setting step.

  The absolute value of the birefringence of the laminated polyester film of the present invention is preferably 0.025 or less. When the refractive indexes in the longitudinal direction and the width direction measured with an Abbe refractometer are Nx and Ny, respectively, It is calculated from the absolute value | Nx−Ny |. A larger value means that the orientation of the molecular chain in the film plane is biased, and if it exceeds 0.025, sufficient puncture strength may not be exhibited. It is preferably 0.01 or less, more preferably 0.005 or less, and most preferably 0. However, it is not easy to make it 0 in the sequential biaxial stretching method. A method of controlling the orientation balance by the draw ratio in biaxial stretching and the temperature at that time is also preferably used to make the preferred range.

  Moreover, it is preferable that the refractive index of the thickness direction of the laminated polyester film of this invention is 1.515-1.47. More preferably, it is 1.51-1.48, More preferably, it is 1.505-1.48, Most preferably, it is 1.5-1.48. By setting the refractive index in the thickness direction within a preferable range, a film having excellent puncture strength, surface impact, and resistance to bending pinholes can be obtained. The preferred range for applying the refractive index in the thickness direction can also be achieved by controlling the draw ratio in biaxial stretching and the temperature at that time, but in addition, it was plane-oriented in the heat setting step after biaxial stretching. A method of controlling the refractive index in the thickness direction by growing a crystal is preferably used.

  The laminated polyester film of the present invention preferably has a thickness of 6 to 50 μm, more preferably 7 to 25 μm, and particularly preferably 8 to 20 μm. If the thickness exceeds 50 μm, the pinhole resistance may be inferior, and if it is less than 6 μm, the puncture strength may be inferior.

  The biaxially oriented polyester film of the present invention can be suitably used as a packaging material for packaging bags such as foods and beverages, or industrial materials, but can be more preferably used by further improving gas barrier properties. Therefore, it is preferable to provide a vapor deposition layer made of a metal compound such as metal aluminum, silicon oxide, aluminum oxide or a metal oxide on at least one surface of the film. These metal compounds or metal oxides deposited on the surface of the polyester film may be used alone, or two or more kinds of compounds may be mixed and used.

  Moreover, as a method for producing a vapor deposition film, a vacuum vapor deposition method, an EB vapor deposition method, a sputtering method, an ion plating method, or the like can be used, but the vacuum vapor deposition method is most preferable from the viewpoint of productivity and cost. Further, in order to improve the adhesion between the laminated polyester film and the vapor deposition layer, it is desirable to pretreat the surface of the film in advance by a method such as applying a corona discharge treatment or an anchor coating agent.

  The vapor-deposited polyester film provided with the vapor-deposited layer in this way has little decrease in gas barrier properties even when bent and deformed. In addition, since it has excellent heat resistance and a large elastic modulus, there is an advantage that the gas barrier property is not easily lowered due to the fracture of the deposited layer due to the film being stretched by the process tension in the processing step after the deposition.

  Moreover, in order to provide a barrier property, it is preferable to attach an aluminum foil to at least one surface of the film of the present invention. An adhesive such as urethane or epoxy can be used for laminating the aluminum foil.

  Furthermore, although the biaxially oriented polyester film of the present invention can be suitably used as a packaging material for packaging bags for foods, beverages, or industrial materials, a polyolefin film is preferably bonded to at least one side of the film. Here, as the polyolefin film, those having heat sealing properties are preferred, and unstretched films called sealants such as polyethylene, ethylene-vinyl acetate copolymer, polypropylene, and ionomer are particularly preferably used. As a method of laminating these sealants on the polyester film of the present invention, a dry lamination method using an adhesive such as urethane or an extrusion lamination method is preferably used.

  Below, the preferable manufacturing method of the biaxially-oriented polyester film of this invention is described concretely. First, as the polyester resin, a commercially available polyethylene terephthalate resin or polybutylene terephthalate resin can be used, but a method of polymerizing and obtaining as follows may be adopted. For example, in the case of polyethylene terephthalate resin, it can be produced by the following method.

  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 is gradually depressurized while being heated and heated, and a polycondensation reaction is performed at 290 ° C. under a reduced pressure of 1 hPa by a conventional method to obtain a polyethylene terephthalate resin having a desired intrinsic viscosity. In the case of adding particles, it is preferable to carry out polymerization by adding a slurry in which particles are dispersed in ethylene glycol to a polymerization reaction kettle so as to have a predetermined particle concentration.

  The production of polybutylene terephthalate can be performed, for example, as follows. A mixture of 100 parts by mass of terephthalic acid and 110 parts by mass of 1,4-butanediol was heated to 140 ° C. under a nitrogen atmosphere to obtain a homogeneous solution, and then 0.054 parts by mass of tetra-n-butyl orthotitanate. Then, 0.054 parts by mass of monohydroxybutyltin oxide is added, and an esterification reaction is performed by a conventional method. Next, 0.066 parts by mass of tetra-n-butyl orthotitanate is added, and a polycondensation reaction is performed under reduced pressure to obtain a polybutylene terephthalate resin having a desired intrinsic viscosity.

  The polyester resin constituting the polyester film of the present invention is preferably adjusted by mixing the polyethylene terephthalate and polybutylene terephthalate resin chips obtained as described above before melt extrusion in the film forming step. . In addition, in order to obtain a film with good dispersibility of the elastomer, a master batch obtained by kneading the elastomer in high concentration in advance in a polyethylene terephthalate resin or polybutylene terephthalate resin is used so that the film has a predetermined concentration during film production. It is a preferable method to mix with diluted resin and to use for a film forming process. When preparing the masterbatch, a masterbatch with excellent dispersibility of the elastomer can be obtained by a method such as strong kneading using a bent type twin screw extruder.

  A preferred method for producing the film of the present invention using the resin obtained as described above will be specifically described. First, a polyester resin, an elastomer, or a masterbatch containing an elastomer used for the A layer and the B layer is mixed at a predetermined ratio for each layer, and each is dried in a nitrogen atmosphere, a vacuum atmosphere, etc., for example, at 150 ° C. for 5 hours. Do. Thereafter, it is supplied to an individual extruder and melted. Next, the foreign matter is removed and the amount of extrusion is leveled through a filter and a gear pump in different paths, and the layers are laminated in three layers of A / B / A by a feed block. Lamination may be performed so that the final total number of layers is reached at the time of the feed block. However, it is necessary to feed several tens of layers at a time with the feed block because the equipment requires extremely high accuracy. In the block, the method of making the number of layers usually 20 or less is preferably used. Next, using a square mixer or a static mixer, the number of stacks is divided into two in the width direction and merged so that the number of stacks is (2n-1) layers with respect to the initial stack number n, and the desired number of layers is obtained. Thus, after providing a mixer and finally increasing the number of layers to a desired number, the sheet is discharged from the T die onto the cooling drum in a sheet form.

  In that case, for example, a method of applying static electricity using a wire-like electrode or a tape-like electrode, a casting method in which a water film is provided between a casting drum and an extruded polymer sheet, and the casting drum temperature from the glass transition point of polyester to (glass The sheet-like polymer is brought into close contact with the casting drum by a method of sticking the extruded polymer at a transition point of −20 ° C. or a combination of these methods, and solidified by cooling to obtain an unstretched film. Among these casting methods, when using polyester, a method of applying an electrostatic force is preferably used from the viewpoint of productivity and flatness.

  Subsequently, the unstretched film is stretched in the longitudinal direction and then stretched in the width direction, or the stretched film is stretched in the width direction and then stretched in the longitudinal direction, or the longitudinal direction and the width direction of the film. The film is stretched by a simultaneous biaxial stretching method that stretches the films almost simultaneously.

  As a draw ratio in such a drawing method, preferably 3 to 5.5 times, more preferably 3.3 to 5.3 times, and particularly preferably 3.5 to 5 times in each direction. The stretching speed is preferably 1,000 to 200,000% / min. The stretching temperature may be a glass transition point to (glass transition point + 50 ° C.), more preferably (glass transition point + 10 ° C.) to (glass transition point + 40 ° C.), particularly preferably longitudinal stretching. The temperature is preferably 90 to 125 ° C, and the stretching temperature in the width direction is preferably 80 to 130 ° C. Moreover, you may perform extending | stretching in multiple times with respect to each direction.

  Furthermore, the film is heat-treated after biaxial stretching. The heat treatment can be performed by any conventionally known method such as in an oven or on a heated roll. This heat treatment is performed at a temperature of 120 ° C. or higher and below the melting point of the polyester, but is preferably a heat treatment temperature of a stretching temperature to 230 ° C. From the viewpoint of bending pinholes and impact resistance, the heat treatment temperature is more preferably 170 to 210 ° C, and particularly preferably 180 to 205 ° C. The heat treatment time can be arbitrarily set within a range not deteriorating other characteristics, and is preferably performed for 1 to 60 seconds. Further, the heat treatment may be performed by relaxing the film in the longitudinal direction and / or the width direction. Furthermore, in order to improve the adhesive force with the ink print layer, the adhesive, and the vapor deposition layer, at least one surface can be subjected to corona treatment or a coating layer can be provided.

  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). When 5 mg of the sample is used as a sample and there are multiple endothermic peaks with the endothermic peak temperature at 25 ° C. up to 300 ° C. as the melting point, the peak temperature of the endothermic peak on the highest temperature side is the melting point It was.

(2) Refractive index, plane orientation coefficient, absolute value of birefringence Using sodium D line (wavelength 589 nm) as a light source, using methylene iodide as a mounting liquid, and using an Abbe refractometer at 25 ° C., the film longitudinal direction and width The refractive indexes in the direction and the thickness direction (Nx, Ny, Nz, respectively) were measured, and the plane orientation coefficient (fn) and the absolute value of birefringence (| Δn |) were determined by the following equations.
fn = (Nx + Ny) / 2−Nz.
| Δn | = | Nx−Ny |.

(3) Average dispersion diameter The film was embedded in an epoxy resin, and an ultrathin slice was prepared using a microtome so that the longitudinal direction-thickness direction cross section of the film was an observation surface. The thin film section of this film cross section was stained with ruthenium tetroxide, and a film cross section photograph was taken at a magnification of 20,000 using a transmission electron microscope. For the elastomer (C) dyed and observed from the photograph obtained, the dispersion diameter in the in-plane direction and the dispersion diameter in the thickness direction were measured at 10 locations, and the average value was averaged in the in-plane direction or the average in the thickness direction, respectively. It was dispersed diameter _{d C.}

(4) Haze Based on JIS K 7105 (1985), the haze was measured using a haze meter (HGM-2GP manufactured by Suga Test Instruments Co., Ltd.). Using tetralin as the mounting liquid, a proportional expression was calculated from the relationship between sample thickness and haze by the method of least squares, and haze (cloudiness) at a film thickness of 12 μm was calculated. Moreover, since the intercept of the proportional formula shows surface haze, the internal haze was calculated by subtraction.

(5) Bend-resistant pinhole property Adhesives diluted 4 times with ethyl acetate to polyester film (Mitsui Takeda Chemical Co., Ltd. Takerak A-616, Takenate A-65 were 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 (Tosero Co., Ltd.) having a thickness of 100 μm. FCD-MCS manufactured) was pasted together. Aging was carried out at 40 ° C. for 7 hours for evaluation. The evaluation is performed in accordance with ASTM F-392, and a laminate film cut out to a size of 300 × 210 mm is bent 500 times in a 10 ° C. temperature atmosphere using carbon dioxide gas using a gelbo flex tester. The test was conducted. In addition, when attaching to an apparatus, the polyester film was made to become an outer surface. The test was performed 5 times, and the average number of pinholes was calculated. When the number of pinholes was 2 or more, it was judged that there was a problem in performance as a packaging material.

(6) Impact resistance A
Two laminated films obtained in the same manner as above were overlapped so that the polyethylene films were in contact with each other, and four sides were sealed using a heat sealer under the conditions of 200 ° C., 0.2 seconds, pressure 0.1 MPa, A 200 mm × 135 mm bag containing 210 cm ³ of 5% saline was prepared. This was cooled to 0 ° C. and repeatedly dropped 20 times onto the concrete surface so that the seal portion was horizontal from a height of 2 m. When a bag breakage or water leakage occurred in the middle, the number of drops until the bag breakage was used as an index of impact resistance. Ten bags were tested and the average number of drops was examined.

(7) Impact resistance B
A bag containing 5% saline solution prepared in the same manner as described above was cooled to 0 ° C. and dropped repeatedly onto the concrete surface 20 times so that the long side portion of the bag sealed from a height of 1.5 m was vertical. When a bag breakage or water leakage occurred in the middle, the number of drops until the bag breakage was used as an index of impact resistance. Ten bags were tested and the average number of drops was examined.

(8) Pin puncture resistance The film is stretched on a ring with a diameter of 40 mm so as not to sag, 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 at a speed of 50 mm / min. The load when the needle penetrates was measured.

(Preparation of polyester)
The following polyesters were used in the examples.

Polyester (1)
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 (1).

Particle Master After the transesterification reaction during polymerization of the polyester (1), an ethylene glycol slurry of agglomerated silica particles having an average particle diameter of 2 μm is added and then a polycondensation reaction is performed to obtain a particle master having a particle concentration of 2% by mass in the polymer. Produced.

Polyester (2)
A mixture of 100 parts by mass of terephthalic acid and 110 parts by mass of 1,4-butanediol was heated to 140 ° C. under a nitrogen atmosphere to obtain a homogeneous solution, and then 0.054 parts by mass of tetra-n-butyl orthotitanate. Then, 0.054 parts by mass of monohydroxybutyltin oxide was added to carry out an esterification reaction. Next, 0.066 parts by mass of tetra-n-butyl orthotitanate was added and a polycondensation reaction was performed under reduced pressure to prepare a polybutylene terephthalate resin having an intrinsic viscosity of 0.88. Thereafter, crystallization was performed at 140 ° C. in a nitrogen atmosphere, followed by solid phase polymerization at 200 ° C. for 6 hours in a nitrogen atmosphere to obtain a polybutylene terephthalate resin having an intrinsic viscosity of 1.20. This is hereinafter referred to as polyester (2).

Polyester (3)
In the polymerization of polyester (1), instead of 100 parts by mass of dimethyl terephthalate, 96 parts by mass of dimethyl terephthalate and 4 parts by mass of dimethyl isophthalate are used for polymerization in the same manner as for polyester (1). A mol% copolymerized polyethylene terephthalate resin (melting point 247 ° C.) was prepared. This is hereinafter referred to as polyester (3).

Polyester (4)
In the polymerization of polyester (2), instead of 100 parts by mass of terephthalic acid, 90 parts by mass of terephthalic acid and 10 parts by mass of isophthalic acid were used for polymerization in the same manner as for polyester (2). A polymerized polybutylene terephthalate resin (melting point: 210 ° C.) was produced. This is hereinafter referred to as polyester (4).

Master batch Polyester (1) and polyester elastomer “Hytrel” 4777 (glass transition point: −35 ° C.) manufactured by Toray DuPont Co., Ltd. are mixed at a mass ratio of 8: 2, and vent type twin screw extrusion A master batch containing 20% by mass of an elastomer was prepared by supplying to a machine and performing melt kneading.

Example 1
As polyester A constituting the A layer, 76% by mass of polyester (1), 20% by mass of polyester (2) and 4% by mass of particle master were mixed and used. In addition, as the B layer, polyester B and elastomer C were used by mixing 60% by mass of polyester (1), 15% by mass of polyester (2), and 25% by mass of the masterbatch. A layer resin and B layer resin are each dried in a vacuum dryer at 170 ° C. for 3 hours, then supplied to a separate single-screw melt extruder and melt-kneaded. : B layer polymer = Extruded so that the ratio is 4: 1, and merged in a feed block so that 5 layers of A layer polymer and 4 layers of B layer polymer are alternately stacked (both outer layers become A layer) After being laminated into 129 layers by providing a square mixer, an unstretched sheet was obtained by applying electrostatic force onto a hard chrome plated cooling drum cooled to 25 ° C. from a T die. The obtained unstretched sheet was heated using a roll and stretched 3.7 times in the longitudinal direction at a stretching temperature of 95 ° C. Thereafter, the film was cooled with a cooling roll, and then both ends of the film were gripped and passed through a stenter-type transverse stretching heat treatment machine, and stretched 4.2 times in the film width direction at a preheating of 80 ° C. and a stretching temperature of 100 ° C. Further, while being relaxed by 6% in the width direction, heat setting was performed at 200 ° C. for 3 seconds, the film was cooled, and a biaxially oriented polyester film having a thickness of 12 μm was produced.

(Example 2)
With the same resin composition as in Example 1, the number of square mixers was changed, and the final number of layers was 65. Drying was performed in the same manner as in Example 1, and melt extrusion was performed so that the ratio of the discharge amount was A layer polymer: B layer polymer = 5: 1 to obtain an unstretched sheet. Hereinafter, the stretching conditions were changed to a longitudinal stretching ratio of 3.4 times and a width direction stretching ratio of 4 times (other conditions were the same as in Example 1) to produce a biaxially oriented polyester film having a thickness of 12 μm.

(Example 3)
As polyester A constituting the A layer, 66% by mass of polyester (3), 30% by mass of polyester (2) and 4% by mass of particle master were mixed and used. The B layer was polyester B and elastomer C mixed with 50% by mass of polyester (3), 25% by mass of polyester (2), and 25% by mass of the masterbatch. And the biaxially oriented polyester was changed in the same manner as in Example 1 except that the number of square mixers was changed, the final number of layers was changed to 257, and the discharge rate ratio of the A layer and B layer was changed to 1: 1. A film was produced.

Example 4
The polyester B and the elastomer C constituting the B layer were the same as in Example 1 except that the polyester (1) was used in a mixture of 72 mass%, the polyester (2) 18 mass%, and the masterbatch in a ratio of 10 mass%. Thus, a biaxially oriented polyester film having a total number of 129 layers and a thickness of 12 μm was produced.

(Example 5)
B layer is polyester B and elastomer C, 80% by weight of polyester (1), 10% by weight of polyester (2), 10% by weight of “Hytrel” 7277 (glass transition point: 12 ° C.) manufactured by Toray DuPont Co., Ltd. A biaxially oriented polyester film was produced in the same manner as in Example 1 except that the mixture was used.

(Example 6)
As polyester A constituting the A layer, 85% by mass of polyester (1), 10% by mass of polyester (4), and 5% by mass of particle master were mixed and used. The B layer was polyester B and elastomer C mixed with 70% by mass of polyester (1), 5% by mass of polyester (4), and 25% by mass of the masterbatch. The A layer resin and the B layer resin are each dried at 170 ° C. for 3 hours in a vacuum dryer, then supplied to a separate single-screw melt extruder, melt-kneaded, and the ratio of the discharge amount is the polymer for the A layer: B layer polymer = Extruded to be 3: 1 and merged in a feed block so that 4 layers of A layer polymer and 3 layers of B layer polymer are alternately stacked (so that both outer layers become A layer) The laminate was divided into 113 layers by providing a square mixer, and then extruded on a hard chrome-plated cooling drum cooled to 20 ° C. from a T-die to obtain an unstretched sheet. The obtained unstretched sheet was heated using a roll and stretched 3.5 times at a stretching temperature of 93 ° C. in the longitudinal direction. Thereafter, the film was cooled with a cooling roll, and then both ends of the film were gripped and passed through a stenter type transverse stretching heat treatment machine, and stretched 3.9 times in the film width direction at a preheating of 80 ° C. and a stretching temperature of 95 ° C. Further, while being relaxed by 4% in the width direction, the film was heat-fixed at 205 ° C. for 3 seconds, cooled, and the film was wound to produce a biaxially oriented polyester film having a thickness of 12 μm.

(Example 7)
The film longitudinal direction was stretched 4.0 times at a temperature of 90 ° C., the film width direction was stretched 4.1 times at a preheating of 80 ° C. and a stretching temperature of 95 ° C., and the relaxation in the width direction was 4.2%. Others were formed into the same film as in Example 4 to produce a 12 μm thick biaxially oriented polyester film.

(Comparative Example 1)
A polyester film was produced by carrying out film formation in the same manner as in Example 1 except that the square mixer was not used and only the feed block was used to make the total number of layers 9 layers.

(Comparative Example 2)
A polyester film was produced in the same manner as in Example 1 except that the polyester A of Example 1 was used for the polyester B constituting the B layer of Example 1 and the elastomer C was not added.

(Comparative Example 3)
A polyester film was produced in the same manner as in Example 1 except that the A layer was not provided, only the B layer composed of the polyester resin B and the elastomer C was used, and the layer configuration was a single layer. However, in order to improve the film handleability, the polymer composition of the B layer was 56% by mass of polyester (1), 4% by mass of particle master, 15% by mass of polyester (2), and 25% by mass of master batch.

(Comparative Example 4)
An unstretched sheet was obtained in the same manner as in Example 2 except that the ratio of the discharge amount was A layer polymer: B layer polymer = 7: 2. An axially oriented polyester film was produced.

(Comparative Example 5)
The unstretched sheet was obtained in the same manner as in Example 1 except that the number of square mixers installed was changed, the final number of layers was 17 layers, and the discharge rate ratio of the A layer and the B layer was 2: 1. A biaxially oriented polyester film having a thickness of 12 μm was produced in the same manner as in Example 1 except that the conditions were changed to a longitudinal stretching ratio of 3.5 times and a width direction stretching ratio of 3.7 times.

  The characteristics of the biaxially oriented polyester film thus obtained are shown in Tables 1 to 4. From the table, the laminated polyester film of the present invention had excellent flex pinhole resistance and impact resistance, and had excellent characteristics as a packaging film. On the other hand, the film obtained by the comparative example which is not this invention was inferior as a packaging film.

The abbreviations in the table are as follows.
PET: polyethylene terephthalate resin PET-I: isophthalic acid 4 mol% copolymerized polyethylene terephthalate resin PBT: polybutylene terephthalate resin PBT-I: isophthalic acid 10 mol% copolymerized polybutylene terephthalate resin Also, in Examples and Comparative Examples, particles Since the main component of the master is the same as that of the polyester (1), the mixing ratio of the raw materials was calculated by including it in the polyester (1).

  The laminated polyester film of the present invention is excellent in flex pinhole resistance and impact resistance required as a packaging material while maintaining the low hygroscopicity, dimensional stability, flatness and transparency that are the characteristics of the polyester film. Therefore, it can be preferably used for packaging applications, particularly food packaging applications.

Claims (9)

It is a polyester film in which 5 layers or more of A layers and B layers are alternately laminated, the A layer is made of a polyester resin (A), the B layer is 99 to 60% by mass of the polyester resin (B) and an elastomer (C ) 1-40 mass%, and when the average layer thickness per layer of layer _B is t _B and the average dispersion diameter in the film thickness direction of the elastomer (C) is d _C , d _C ≦ t _A biaxially oriented polyester film characterized by satisfying a relationship of _B ≦ 2d _C. The biaxially oriented polyester film according to claim 1, wherein the elastomer (C) is a polyester-based elastomer. The polyester resin (A) has 98 to 70% by mass of an aromatic polyester whose main component is an ethylene terephthalate unit having a melting point of 245 to 265 ° C. and a butylene terephthalate unit whose melting point is 190 to 240 ° C. as a main component. The biaxially oriented polyester film according to claim 1 or 2, comprising 2 to 30% by mass of an aromatic polyester. The polyester resin (B) has 98 to 70% by mass of an aromatic polyester whose main component is an ethylene terephthalate unit having a melting point of 245 to 265 ° C. and a butylene terephthalate unit whose melting point is 190 to 240 ° C. as a main component. The biaxially oriented polyester film according to any one of claims 1 to 3, comprising 2 to 30% by mass of an aromatic polyester. The biaxially oriented polyester film according to any one of claims 1 to 4, wherein the average dispersion diameter in the film in-plane direction of the elastomer (C) is 1 to 10 µm. The biaxially oriented polyester film according to claim 1, wherein the polyester film has a plane orientation coefficient (fn) of 0.164 to 0.180. A vapor-deposited film, wherein a metal or a metal oxide is vapor-deposited on at least one side of the polyester film according to claim 1. A packaging film comprising an aluminum foil and / or a polyolefin film laminated on at least one surface of the polyester film according to claim 1. The packaging bag which consists of a film in any one of Claims 1-7.