JP6874277B2 - Biaxially stretched polyester film and its manufacturing method - Google Patents

Description

INDUSTRIAL APPLICABILITY The present invention is particularly preferably used for packaging materials such as foods, pharmaceuticals, and cosmetics, particularly for applications where press molding is performed by a mold and applications where puncture resistance is required for packaging solid materials. The present invention relates to a sealable biaxially stretched polyester film.
Furthermore, the present invention relates to a heat-sealing biaxially stretched polyester film that is preferably used without lowering the sealing strength even in applications such as high-temperature sterilization treatment in which the film is exposed to a high temperature after heat-sealing.

As the heat-sealing film, a non-stretched film (CPP) mainly made of linear low density polyethylene (LLDPE) or polypropylene is generally used, and heat-sealing is used in various applications such as food packaging. It is used as a sex sealant. However, LLDPE and CPP have problems such as inferior chemical resistance and aroma retention of the contents.
Further, since these films have low heat resistance, in applications where they are exposed to high temperatures, a decrease in seal strength and a dimensional change due to deterioration of the seal portion have been problems.

Therefore, in recent years, for example, as disclosed in Patent Document 1, a heat-sealing film mainly composed of polyester having excellent solvent resistance has been developed.
According to the technique according to Patent Document 1, a stretched film composed of a base material layer and a heat seal layer, wherein the base material layer is a copolymerized polyester and a block copolymerized polyester elastomer having a specific structure is a stretched film having a sea-island structure. It has excellent mechanical strength, heat resistance, transparency, chemical resistance and fragrance retention of contents, and also has linear tearability, and also has strong interlayer adhesion between the base material layer and the heat seal layer, after bag making. A heat-sealable biaxially stretched laminated film having strong mechanical strength can be obtained.
However, since the puncture resistance is insufficient with such a technique, cracks and pinholes may occur at the time of molding in applications such as press molding by a mold.

Japanese Unexamined Patent Publication No. 2006-247870

The present invention has been made against the background of the problems of the prior art. That is, an object of the present invention is that it has the functions of both a base material layer and a seal layer, is excellent in puncture resistance, heat resistance, transparency, chemical resistance and tear straightness, and is exposed to high temperature. The purpose of the present invention is to obtain a heat-sealable biaxially stretched polyester film having excellent interlayer adhesion even afterwards.

The present inventor has completed the present invention as a result of diligent studies to achieve such an object.
In the present invention, polybutylene terephthalate is 65 % by weight or more, and polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), polypropylene terephthalate (PPT), and polyester resins other than PBT resin are used. dicarboxylic acid or diol 5 wt% or more copolymerized PBT resin made of a thermoplastic resin composition comprising a 35 wt% 0 a polyester resin selected from the gall not Re one or more, piercing of the film Resin strength is 0.75 N / μm or more, films are heat-sealed at 230 ° C, heat-sealed at 150 ° C for 1 hour, heat-seal strength is 10 N / 15 mm or more, and haze value per film thickness is 0.35%. A heat-sealable biaxially stretched polyester film having a temperature of / μm or less.

Further, in this case, it is preferable that the film satisfies the following (1) and (2) at the same time.
(1) The angle formed by the main axis of the molecular chain with respect to the width direction of the film is 30 ° or less.
(2) The heat shrinkage rate at 150 ° C. in both the longitudinal direction and the width direction of the film is 4.0% or less.

The present inventors have the functions of both a base material layer and a sealing layer by such a technique, and are excellent in puncture resistance, heat resistance, transparency, chemical resistance and tear straightness, and when heat-sealed. It has become possible to obtain a heat-sealable biaxially stretched polyester film having excellent interlayer adhesion.

Hereinafter, the present invention will be described in detail.
The polyester thermoplastic resin composition used in the present invention contains PBT resin as a main component, and the content of PBT resin is preferably 60% by mass or more, more preferably 70% by mass or more, and further 90% by mass. % Or more is preferable. If it is less than 60% by mass, the impact strength and pinhole resistance will be lowered, and the film characteristics will not be sufficient.
The PBT used as the main constituent component preferably contains terephthalic acid in an amount of 90 mol% or more, more preferably 95 mol% or more, still more preferably 98 mol% or more, and most preferably 100 mol% as a dicarboxylic acid component. %. The glycol component of 1,4-butanediol is preferably 90 mol% or more, more preferably 95 mol% or more, still more preferably 97 mol% or more, and most preferably 1,4-butanediol at the time of polymerization. It does not contain anything other than by-products produced by the ether bond of the diol.

The polyester thermoplastic resin composition used in the present invention can contain a polyester resin other than the PBT resin for the purpose of adjusting the film-forming property at the time of biaxial stretching and the mechanical properties of the obtained film.
Examples of polyester resins other than PBT resin include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), and the like.
In addition to polyester resins such as polypropylene terephthalate (PPT), PBT resins in which dicarboxylic acids such as isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, cyclohexanedicarboxylic acid, adipic acid, azelaic acid, and sebacic acid are copolymerized. , Ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, cyclohexanediol, polyethylene glycol, polytetramethylene glycol, polycarbonate Examples thereof include a PBT resin in which a diol component such as a diol is copolymerized. The amount of the copolymerization component in the copolymerized PBT resin is 5 wt% or more with respect to the entire PBT resin. However, those containing polyalkylene oxides are not suitable.

The upper limit of the amount of the polyester resin other than the PBT resin added is preferably 40% by mass or less, more preferably 30% by mass or less, further preferably 10% by mass or less, and particularly preferably 5% by mass or less. If the amount of polyester resin other than PBT resin added exceeds 40% by mass, the mechanical properties of PBT resin are impaired, impact strength, bag breakage resistance, and pinhole resistance become insufficient, as well as transparency and barrier. Sexual deterioration may occur.

The lower limit of the melting temperature of the polyester-based thermoplastic resin composition is preferably 200 ° C., and if it is less than 200 ° C., the discharge may become unstable. The upper limit of the resin melting temperature is preferably 300 ° C., and if it exceeds 300 ° C., deterioration of the PBT resin may occur.

If necessary, the polyester-based thermoplastic resin composition may contain conventionally known additives such as lubricants, stabilizers, colorants, antioxidants, antistatic agents, and ultraviolet absorbers.

As the lubricant type, in addition to inorganic lubricants such as silica, calcium carbonate and alumina, organic lubricants are preferable, silica and calcium carbonate are more preferable, and silica is particularly preferable in that haze is reduced. These can be expressed as transparent and slippery.

The lower limit of the lubricant concentration in the polyester-based thermoplastic resin composition is preferably 100 ppm, and if it is less than 100 ppm, the slipperiness may decrease. The upper limit of the lubricant concentration is preferably 20000 ppm, and if it exceeds 20000 ppm, the transparency may decrease.

The lower limit of the puncture strength of the film of the present invention is preferably 0.75 N / μm, more preferably 0.85 N / μm, and even more preferably 0.9 N / μm. If it is less than the above, it may cause cracks and pinholes during press molding by the mold.

In the film of the present invention, the heat seal strength after heat-sealing the films at a temperature of 200 ° C. or higher and heat-treating at 150 ° C. for 1 hour is preferably 10 N / 15 mm or more, more preferably 15 N / 15 mm or more. More preferably, it is 17 N / mm or more. If the heat seal strength at this time is less than 15 N / mm, the seal strength after exposure to a high temperature is lowered, and the contents may leak.

The upper limit of the orientation axis angle of the film of the present invention is preferably 30 °, more preferably 28 °, and even more preferably 25 °. As a result, the linear tearability is improved, it is possible to reduce the tearing when the film is opened in the longitudinal direction when it is used as a packaging bag, and it becomes easy to tear the film in the intended direction.
If the orientation angle of the molecular chain main axis with respect to the main orientation direction of the polyester film is 30 ° or less, the reason why the linear tearability in the longitudinal direction is excellent is not clear, but the front and back polyesters that form the packaging bag when made into a packaging bag. Since the difference in the orientation direction of the main axis of the molecular chain of the film can be reduced, it is presumed that the tearing is small and the linear tearability is excellent.
Conventionally, the phenomenon that the orientation angle of the main axis of the molecular chain exceeds 20 ° is grasped by the clip when the film is formed by stretching in the width direction using a tenter after stretching in the longitudinal direction, especially in the sequential biaxial stretching method. It may be found in films that have been slit (cut) from a portion close to the edge in the width direction.
In order to reduce the orientation angle of the main axis of the molecular chain, the stretching temperature in the longitudinal stretching direction (hereinafter referred to as MD) in the film manufacturing process should be increased, the MD stretching ratio should be reduced, and the relaxation rate in the transverse stretching direction (hereinafter referred to as TD) should be reduced. Can be mentioned.

The lower limit of the refractive index of the film of the present invention in the longitudinal direction is preferably 1.610, more preferably 1.612, and even more preferably 1.613. If it is less than the above, the orientation is weak, so that sufficient strength as a film cannot be obtained, and the bag breaking resistance may be lowered.

The upper limit of the refractive index of the film of the present invention in the longitudinal direction is preferably 1.640, more preferably 1.635, and even more preferably 1.630. If it exceeds the above, the effect on film mechanical properties and straight-line tearability may be saturated.

The lower limit of the refractive index of the film of the present invention in the width direction is preferably 1.649, more preferably 1.650, and even more preferably 1.651. If it is less than the above, the orientation is weak, so that sufficient strength as a film cannot be obtained, and the bag breaking resistance may be lowered.

The upper limit of the refractive index of the film of the present invention in the width direction is preferably 1.670, more preferably 1.669, and even more preferably 1.668. If it exceeds the above, the effect on the mechanical properties of the film and the straight-line tearability may be saturated.

In the film of the present invention, the value of the difference (Nx-Ny) between the refractive index Nx in the longitudinal direction of the film and the refractive index Nx in the width direction of the film is preferably −0.022 or less, more preferably −0.022 or less. It is 0.025 or less, more preferably −0.03 or less. If it exceeds the above, the tearing straightness of the film in the longitudinal direction may decrease.

The lower limit of the intrinsic viscosity of the film of the present invention is preferably 0.8, more preferably 0.85, still more preferably 0.9, particularly preferably, and most preferably. If it is less than the above, the piercing strength, impact strength, rupture resistance, etc. may decrease. The upper limit of the intrinsic viscosity of the film is preferably 1.2. If it exceeds the above, the stress at the time of stretching becomes too high, and the film forming property may deteriorate.

The biaxially stretched polyester film of the present invention preferably has a resin having the same composition over the entire film. Further, a layer of another material may be laminated on the biaxially stretched polyester film of the present invention, and as a method thereof, the biaxially stretched polyester film of the present invention can be bonded after being produced or during film formation.

The lower limit of the impact strength of the film of the present invention, J / μm, is preferably 0.055, more preferably 0.060, and even more preferably 0.065. If it is less than the above, the strength may be insufficient when used as a bag.

The upper limit of impact strength and J / μm is preferably 0.2. If it exceeds the above, the effect of improvement may be saturated.

The upper limit of the haze (% / μm) per thickness of the film of the present invention is preferably 0.35%, more preferably 0.33%, and even more preferably 0.31%.
If it exceeds the above, the quality of the printed characters and images may be impaired when the film is printed.

The lower limit of the heat shrinkage rate (%) in the longitudinal direction and the width direction of the film of the present invention is preferably 0. If it is less than the above, the effect of improvement is saturated and it may become mechanically brittle.

The upper limit of the heat shrinkage rate (%) in the longitudinal direction and the width direction of the film of the present invention is preferably 4.0, more preferably 3.5, and even more preferably 3.0. If it exceeds the above, pitch deviation may occur due to dimensional changes during processing such as printing.

In the biaxially stretched film of the present invention, the lower limit of the film thickness is preferably 3 μm, more preferably 5 μm, and further preferably 8 μm. If it is less than 3 μm, the strength of the film may be insufficient.
The upper limit of the film thickness is preferably 100 μm, more preferably 75 μm, and even more preferably 50 μm. If it exceeds 100 μm, it may become too thick and it may be difficult to process it for the purpose of the present invention.

(Manufacturing method of biaxially stretched polyester film)
A suitable method for obtaining the film according to the present invention is to cast a raw material having the same composition in multiple layers at the time of casting.
Since the PBT resin has a high crystallization rate, crystallization proceeds even during casting. At this time, when cast in a single layer without multi-layering, these crystals grow into spherulites having a large size because there is no barrier that can suppress the growth of the crystals. As a result, the yield stress of the obtained unstretched sheet becomes high, and not only is it easy to break during biaxial stretching, but also the flexibility of the obtained biaxially stretched film is impaired, resulting in pinhole resistance and rupture resistance. The film will have insufficient properties.
On the other hand, the present inventors have found that by laminating the same resin in multiple layers, the stretching stress of the unstretched sheet can be reduced and stable biaxial stretching becomes possible.

Specifically, the method for producing a biaxially stretched polyester film of the present invention is a molten fluid formed in the step (1) of melting a thermoplastic resin composition containing 90% by weight or more of a polybutylene terephthalate resin to form a molten fluid. The step (3) of forming a laminated body by discharging the laminated fluid formed in the step (2) of forming a laminated fluid having a number of laminated layers of 60 or more and bringing the laminated fluid into contact with a cooling roll to solidify the laminated body. It has at least the step (4) of biaxial stretching.
Other steps may be inserted between the steps (1) and the steps (2), and between the steps (2) and the steps (3). For example, a filtration step, a temperature changing step, or the like may be inserted between the steps (1) and (2). Further, a temperature changing step, a charge adding step, and the like may be inserted between the steps (2) and the steps (3). However, there must be no step between the step (2) and the step (3) to break the laminated structure formed in the step (2).

In the step (1), the method of melting the thermoplastic resin in the present invention to form a molten fluid is not particularly limited, but as a preferable method, a method of heating and melting using a single-screw extruder or a twin-screw extruder is used. Can be mentioned.

The method for forming the laminated fluid in the step (2) is not particularly limited, but a static mixer and / or a multilayer feed block is more preferable from the viewpoint of equipment simplicity and maintainability. Further, from the viewpoint of uniformity in the sheet width direction, those having a rectangular melt line are more preferable. It is further preferred to use a static mixer or multi-layer feed block with rectangular melt lines. The resin composition composed of a plurality of layers formed by merging the plurality of resin compositions may be passed through any one or more of the static mixer, the multilayer feed block, and the multilayer manifold.

The number of theoretical stacks in step (2) needs to be 60 or more. The lower limit of the theoretical stacking number is preferably 200, more preferably 500. If the number of theoretical layers is too small, the effect of accelerating crystallization is insufficient, or the distance between the layer interfaces becomes long and the crystal size becomes too large, so that the effect of the present invention tends not to be obtained. In addition, the transparency after molding may decrease near both ends of the sheet. The upper limit of the number of theoretical stacks in the step (2) is not particularly limited, but is preferably 100,000, more preferably 10,000, and even more preferably 7,000. Even if the number of theoretical stacks is made extremely large, the effect is saturated and problems may occur in terms of production efficiency.

When the lamination in the step (2) is performed by a static mixer, the theoretical number of laminations can be adjusted by selecting the number of elements of the static mixer. The static mixer is generally known as a static mixer (line mixer) without a drive unit, and the fluid entering the mixer is sequentially stirred and mixed by an element. However, when the high-viscosity fluid is passed through the static mixer, the high-viscosity fluid is divided and laminated, and the laminated fluid is formed. Each time it passes through one element of the static mixer, the high viscosity fluid is split into two and then merged and stacked. Therefore, when a high-viscosity fluid is passed through a static mixer having n elements, a laminated fluid ^{having a theoretical stacking number of N = 2n is formed.} It is also possible to use a laminated fluid as the high viscosity fluid to be supplied to the static mixer.

A typical static mixer element has a structure in which a rectangular plate is twisted 180 degrees, and there are right element and left element depending on the direction of twist, and the dimension of each element is 1.5 times as long as the diameter. Is the basis. The static mixer that can be used in the present invention is not limited to such a mixer.

When the lamination in the step (2) is performed by the multilayer feed block, the theoretical number of laminations can be adjusted by selecting the number of divisions / laminations of the multilayer feed block. Multiple multilayer feed blocks can be installed in series. Further, the high-viscosity fluid itself supplied to the multilayer feed block can be used as the multilayer fluid. For example, when the number of laminated high-viscosity fluids supplied to the multilayer feed block is p, the number of divided / stacked multilayer feed blocks is q, and the number of installed multilayer feed blocks is r, the number of stacked fluids N is N = p. It becomes × qr.

In step (3), the laminated fluid is discharged from the die and brought into contact with the cooling roll to solidify.

The lower limit of the die temperature is preferably 200 ° C., and if it is less than the above, the discharge may not be stable and the thickness may become non-uniform. The upper limit of the die temperature is preferably 320 ° C., and if it exceeds the above, the thickness becomes non-uniform, the resin deteriorates, and the appearance may be poor due to stains on the die lip.

The lower limit of the cooling roll temperature is preferably 0 ° C., and if it is lower than the above, the effect of suppressing crystallization may be saturated. The upper limit of the cooling roll temperature is preferably 25 ° C., and if it exceeds the above, the crystallinity may become too high and stretching may become difficult. When the temperature of the cooling roll is within the above range, it is preferable to lower the humidity of the environment near the cooling roll in order to prevent dew condensation.

In casting, the temperature of the surface of the cooling roll rises because the high-temperature resin comes into contact with the surface. Normally, the chill roll is cooled by flowing cooling water through a pipe inside, but the surface of the chill roll is cooled by ensuring a sufficient amount of cooling water, devising the arrangement of the pipe, and performing maintenance to prevent sludge from adhering to the pipe. It is necessary to reduce the temperature difference in the width direction. In particular, care must be taken when cooling at a low temperature without using a method such as multi-layering.
At this time, the thickness of the unstretched sheet is preferably in the range of 15 to 2500 μm.

Casting in the multi-layer structure described above is performed with at least 60 layers or more, preferably 250 layers or more, and more preferably 1000 layers or more. When the number of layers is small, the spherulite size of the unstretched sheet becomes large, and not only the effect of improving the stretchability is small, but also the effect of lowering the yield stress of the obtained biaxially stretched film is lost.

Next, the stretching method will be described. The stretching method can be either simultaneous biaxial stretching or sequential biaxial stretching, but in order to increase the piercing strength, it is necessary to increase the plane orientation coefficient, and in that respect, sequential biaxial stretching is preferable.

The lower limit of the stretching temperature in the longitudinal stretching direction (hereinafter referred to as MD) is preferably 55 ° C, more preferably 60 ° C. If the temperature is lower than 55 ° C., not only the fracture may easily occur, but also the vertical orientation becomes stronger due to the stretching at a low temperature. The strain may increase, resulting in reduced straight-line tearability in the longitudinal direction. The upper limit of the MD stretching temperature is preferably 100 ° C., more preferably 95 ° C. If the temperature exceeds 100 ° C., the mechanical properties may deteriorate because the orientation is not applied.

The lower limit of the MD draw ratio is preferably 2.6 times, particularly preferably 2.8 times. If it is less than the above, the orientation is not applied, and the mechanical properties and thickness unevenness may deteriorate. The upper limit of the MD draw ratio is preferably 4.3 times, more preferably 4.0 times, and particularly preferably 3.8 times. If it exceeds the above, not only the effect of improving the mechanical strength and thickness unevenness may be saturated, but also the orientation in the vertical direction becomes stronger. The strain may increase, resulting in reduced straight-line tearability in the longitudinal direction.

The lower limit of the stretching temperature in the transverse stretching direction (hereinafter referred to as TD) is preferably 60 ° C., and if it is lower than the above, fracture may easily occur. The upper limit of the TD stretching temperature is preferably 100 ° C., and if it exceeds the above, orientation may not be applied and the mechanical properties may deteriorate.

The lower limit of the TD stretching ratio is preferably 3.5 times, more preferably 3.6 times, and particularly preferably 3.7 times. If it is less than the above, the orientation is not applied, and the mechanical properties and thickness unevenness may deteriorate. The upper limit of the TD stretching ratio is preferably 5 times, more preferably 4.5 times, and particularly preferably 4.0 times. If it exceeds the above, the effect of improving the mechanical strength and thickness unevenness may be saturated.

The lower limit of the TD heat fixing temperature is preferably 200 ° C., more preferably 205 ° C. If it is less than the above, the heat shrinkage rate becomes large, and deviation or shrinkage during processing may occur. The upper limit of the TD heat fixing temperature is preferably 250 ° C., and if it exceeds the above, the film may melt, and even if it does not melt, it may become brittle.

The lower limit of the TD relaxation rate is preferably 0.5%, and if it is less than the above, fracture may easily occur during heat fixing. The upper limit of the TD relaxation rate is preferably 5%, and if it exceeds the above, not only slack may occur and thickness unevenness may occur, but also the contraction in the longitudinal direction at the time of heat fixing becomes large, and as a result, the end portion The distortion of molecular orientation may increase and the straight-line tearability may decrease.

The biaxially stretched polybutylene terephthalate film of the present invention can be provided with excellent gas barrier properties by forming a laminated film in which a gas barrier layer is provided on at least one side of the film.
As the gas barrier layer laminated on the biaxially stretched polybutylene terephthalate film of the present invention, a thin film made of a metal or an inorganic oxide or a coating layer made of a barrier resin such as polyvinylidene chloride is preferably used as the inorganic thin film layer.
Among the gas barrier layers, the inorganic thin film layer is preferably a thin film made of a metal or an inorganic oxide. The material for forming the inorganic thin film layer is not particularly limited as long as it can be formed into a thin film, but from the viewpoint of gas barrier properties, inorganic oxidation such as silicon oxide (silica), aluminum oxide (alumina), and a mixture of silicon oxide and aluminum oxide. Things are preferred. In particular, a composite oxide of silicon oxide and aluminum oxide is preferable from the viewpoint of achieving both flexibility and denseness of the thin film layer. In this composite oxide, the mixing ratio of silicon oxide and aluminum oxide is preferably in the range of 20 to 70% of Al in terms of mass ratio of metal content.
If the Al concentration is less than 20%, the water vapor barrier property may be lowered. On the other hand, if it exceeds 70%, the inorganic thin film layer tends to be hard, and the film may be broken during secondary processing such as printing or laminating, and the barrier property may be lowered. The silicon oxide referred to here is various silicon oxides such as SiO and SiO2 or a mixture thereof, and aluminum oxide is various aluminum oxides such as AlO and Al2O3 or a mixture thereof.

The film thickness of the inorganic thin film layer is usually 1 to 800 nm, preferably 5 to 500 nm. If the film thickness of the inorganic thin film layer is less than 1 nm, it may be difficult to obtain a satisfactory gas barrier property. On the other hand, even if the thickness exceeds 800 nm, the corresponding improvement effect of the gas barrier property can be obtained. This is not possible, and it is rather disadvantageous in terms of bending resistance and manufacturing cost.

The method for forming the inorganic thin film layer is not particularly limited, and is known, for example, a physical vapor deposition method (PVD method) such as a vacuum vapor deposition method, a sputtering method, or an ion plating method, or a chemical vapor deposition method (CVD method). The method may be adopted as appropriate. Hereinafter, a typical method for forming the inorganic thin film layer will be described by taking a silicon oxide / aluminum oxide thin film as an example. For example, when the vacuum vapor deposition method is adopted, a mixture of SiO2 and Al2O3, a mixture of SiO2 and Al, or the like is preferably used as the vapor deposition raw material.
Particles are usually used as these vapor deposition raw materials, but at that time, it is desirable that the size of each particle is such that the pressure at the time of vapor deposition does not change, and the particle size is preferably 1 mm to 5 mm.
For heating, methods such as resistance heating, high frequency induction heating, electron beam heating, and laser heating can be adopted. Further, it is also possible to introduce oxygen, nitrogen, hydrogen, argon, carbon dioxide gas, water vapor or the like as the reaction gas, or to adopt reactive vapor deposition using means such as ozone addition and ion assist.
Further, the film forming conditions can be arbitrarily changed, such as applying a bias to the film to be vapor-deposited (laminated film to be subjected to vapor deposition) or heating or cooling the film to be vapor-deposited. Such vapor deposition material, reaction gas, bias of the vapor-deposited body, heating / cooling, and the like can be similarly changed when the sputtering method or the CVD method is adopted.

Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples. The film was evaluated by the following measurement method.

[Thickness]
The measurement was performed by a method conforming to JIS-Z-1702.

[Intrinsic viscosity of film]
The sample is vacuum dried at 130 ° C. for 24 hours, then crushed or cut, 80 mg thereof is precisely weighed, dissolved in a mixed solution of phenol / tetrachloroethane = 60/40 (volume ratio) by heating at 80 ° C. for 30 minutes, and filtered. After filtering with, the mixture was made into 20 ml with the same mixed solution, and then measured at 30 ° C.

[Orientation axis angle]
A 100 mm square film sample was cut out from the end and the center of the obtained film having a total width of 4200 mm at a position 300 mm from the end of the mill roll. Using a 6004 type molecular orientation meter, the orientation angle of the main axis of the molecular chain with respect to the film width direction was measured.

[Distance without edges]
As an index of linear tearability, the distance was measured by the following method.
(Sample preparation)
A polyester film piece having a width of 210 mm in the tearing direction (longitudinal direction) and a width of 50 mm in the orthogonal direction is cut out at a position 300 mm from the end of the mill roll of the obtained film having a total width of 4200 mm. A double-sided adhesive tape having a width of 10 mm is attached to one short side of the film piece, folded in half along the center line, and both short sides are overlapped and attached to obtain a test piece. Next, a 30 mm notch is made in the tearing direction in the central portion (25 mm from both ends) on the short side on which the test pieces are overlapped.
(Measurement)
The distance between the chucks of the tensile tester (Tencilon RTC-1225A manufactured by Orientec Co., Ltd.) is set to 50 mm, and the two short sides separated by the notches of the sample are attached to the upper and lower chucks, respectively. The chuck is then displaced by 130 mm and torn at a speed of 1000 mm / min. The amount of deviation at a position of 50 mm from the tearing start point of the tearing line of the film on the front side of the paper surface and the tearing line of the film on the back side of the paper surface of the torn test piece is defined as the distance.
Each sample was measured 5 times to obtain the average value.

[Haze value per film thickness]
Using a method similar to JIS-K-7105, the sample was measured at three different locations using a haze meter (Nippon Denshoku Co., Ltd., NDH2000), and the average value divided by the film thickness was the haze value per thickness. And said.

[Impact strength]
Using an impact tester manufactured by Toyo Seiki Seisakusho Co., Ltd., the strength of the film against impact punching in an atmosphere of 23 ° C. was measured. The impact spherical surface used was one with a diameter of 1/2 inch. Unit J / μm.

[Puncture strength]
Puncture at 23 ° C in accordance with "2. Strength test method" of "Standards for foods, additives, etc. 3: Equipment and containers and packaging" (Ministry of Health and Welfare Notification No. 20 of 1982) in the Food Sanitation Law. The intensity was measured. A needle having a tip diameter of 0.7 mm was pierced into the film at a piercing speed of 50 mm / min, and the strength of the needle penetrating the film was measured. The obtained measured value was divided by the thickness of the film to calculate the piercing strength [N / mm] per 1 μm of the film.

[Heat seal strength]
The two obtained films were laminated and pressure-bonded at 230 ° C. and 0.15 MPa for 3 seconds to prepare a laminated sample.
The laminated sample obtained above was cut into strips having a width of 15 mm, and then heat-treated in a heating oven set at 150 ° C. for 1 hour.
Set the laminated sample after heat treatment on the cross head of a tensile tester (Tencilon RTC-1225A manufactured by Orientec Co., Ltd.), pull at a speed of 100 mm / min, peel off the heat seal part, and measure the load at the time of peeling. So, the heat seal strength was used.

[Heat shrinkage rate]
Five films each having a width of 10 mm and a length of 150 mm were cut out from the vertical direction and the horizontal direction to prepare test pieces.
Each test piece was marked with a spacing of 100 mm ± 2 mm centered on the center of the test piece.
The distance between the marked lines of the test piece before heating was measured with an accuracy of 0.1 mm.
The test piece was hung in a hot air dryer (PHH-202 manufactured by ESPEC) under no load, and heat-treated at 150 ° C. for 15 minutes.
After taking out the test piece from the constant temperature bath and cooling it to room temperature, the length and width of the same part as the first measurement were measured.
The dimensional change rate of each test piece was calculated as a percentage of the initial value of the dimensional change in the vertical and horizontal directions. The dimensional change rate in each direction was taken as the average of the measured values in that direction.

[Continuous film forming property]
The film-forming property of the biaxially stretched film was evaluated according to the following criteria. If it is ○ and △, it is judged that the productivity is good.
◯: Film formation was possible without breakage, and continuous production was possible. Δ: Film formation property was somewhat unstable, and breakage occurred rarely, but continuous production was possible.
X: Breakage occurred frequently, making continuous production difficult.

[Raw material resin]
(PBT resin; Examples 1 to 11, Comparative Examples 1, 3 to 5)
In the production of the films of Examples 1 to 11 and Comparative Examples 1 and 3 to 5, which will be described later, 1100-211XG (CHANGE CHUN PLASTICS CO., LTD., Intrinsic viscosity 1.28 dl / g) is used as the main raw material PBT resin. There was.

(Polyester A; Comparative Example 2)
Using dimethyl terephthalate, ethylene glycol and mol% isophthalate as raw materials, tetrabutoxytitanium is used as a transesterification catalyst, germanium dioxide is used as a polymerization catalyst, orthophosphoric acid is used as a stabilizer, and aggregated silica having an average particle size of 3.2 μm is used as a lubricant. Copolymerized polyester (polyester A) was produced by a conventional method by adding particles so as to be 0.05% by weight based on the polymer.

(Polyester B; Comparative Example 2)
Further, polyester B was obtained by using terephthalic acid as an acid component, 50 wt% of tetramethylene glycol and 50 wt% of polyethylene glycol as raw materials, tetrabutoxytitanium as a transesterification catalyst, and germanium dioxide as a polymerization catalyst.

(Polyester C; Comparative Example 2)
Polyester C was produced by a conventional method using dimethyl terephthalate, ethylene glycol and 20 wt% isophthalic acid as copolymerization components, using tetrabutoxytitanium as a transesterification catalyst, germanium dioxide as a polymerization catalyst, and positive phosphoric acid as a stabilizer. ..

(PET resin; Examples 8 to 10, Comparative Example 4)
In the production of the films of Examples 8 to 10 and Comparative Example 5 described later, a polyethylene terephthalate resin having an intrinsic viscosity of 0.62 dl / g composed of terephthalic acid // ethylene glycol = 100 // 100 (mol%) was used.

[Example 1]
Using a uniaxial extruder, a masterbatch containing PBT resin and silica particles having an average particle size of 2.4 μm as inert particles was added, and the mixture was blended so as to have a lubricant concentration of 1600 ppm, and then melted at 295 ° C. The melt line was introduced into a 12-element static mixer. As a result, the PBT melt was divided and laminated to obtain a multilayer melt made of the same raw material. It was cast from a T-die at 265 ° C. and adhered to a cooling roll at 15 ° C. by an electrostatic adhesion method to obtain an unstretched sheet. Then, it was rolled 2.8 times in the longitudinal direction at 65 ° C., then passed through a tenter and stretched 4.0 times in the lateral direction at 90 ° C., and tension heat treatment at 210 ° C. for 3 seconds and relaxation of 1% for 1 second. After the treatment, the grips at both ends were cut and removed by 10% to obtain a mill roll of a PBT film having a thickness of 12 μm. Table 1 shows the film forming conditions, physical properties, and evaluation results of the obtained film.

[Examples 2 to 8]
In Example 1, the same procedure as in Example 1 was carried out except that the raw material composition and the film forming conditions were changed to the biaxially stretched film shown in Table 1.

[Examples 9 to 11]
In Example 1, the same procedure as in Example 1 was carried out except that the raw material composition and the film forming conditions were changed to the biaxially stretched film shown in Table 2.

[Comparative Example 1]
Biaxial stretching was performed using a uniaxial extruder under the conditions shown in Table 3, but with this method, fractures occurred frequently during transverse stretching, making continuous film formation difficult.

[Comparative Example 2]
Polyester A and polyester B were mixed at a ratio of 80/20 (wt%) and extruded from one side of the two-layer stand at the temperatures shown in Table 3.
On the other hand, the polyester C was put into an extruder different from the mixture of the polyesters A and B, and extruded at 250 ° C. from the opposite side of the two-layer die.
An unstretched film having a thickness ratio of each layer (polyester A, B mixture / polyester C) of 200 μm / 22 μm was obtained.
The unstretched film thus obtained was biaxially stretched under the stretching conditions shown in Table 3 to obtain a film having a thickness of 15 μm.

[Comparative Example 3]
The unstretched sheet obtained under the conditions shown in Table 3 was used as a sample. The film was formed by adjusting the winding speed so that the thickness was 20 μm. The orientation axis angle at the edge of the film was 5 degrees or less, and no distortion of the sample was observed after the heat shrinkage measurement.

[Comparative Example 4]
Using a uniaxial extruder, a masterbatch containing PBT resin and calcium carbonate as a lubricant was added, and the mixture was blended so that the lubricant concentration was 2000 ppm, and then melted at 270 ° C., and then the melt line was statically composed of 12 elements. Introduced to the mixer. As a result, the PBT melt was divided and laminated to obtain a multilayer melt made of the same raw material. Then, it was introduced into a T-die at 270 ° C. and cast, and adhered to a cooling roll at 15 ° C. by an electrostatic adhesion method to obtain an unstretched sheet.
Then, it was rolled 3.8 times in the longitudinal direction at 60 ° C., then passed through a tenter and stretched 3 times in the horizontal direction at 65 ° C., and subjected to tension heat treatment at 200 ° C. for 3 seconds and relaxation treatment for 1 second. After that, both ends were cut off to obtain a PBT film having a thickness of 12 μm. Table 3 shows the film forming conditions, physical characteristics and evaluation results of the obtained film.

[Comparative Example 5]
In Example 1, the same procedure as in Example 1 was carried out except that the raw material composition and the film forming conditions were changed to the biaxially stretched film shown in Table 3.

[Reference example 1]
Toyobo ester film E5100-12 μm was used.

[Reference example 2]
Toyobo nylon film N1100-15 μm was used.

As shown in Tables 1 and 2, the biaxially stretched polybutylene terephthalate film obtained by the present invention (Examples 1 to 11) is excellent in puncture resistance, transparency, and tear straightness, and is heat-treated. Even after this, the high heat seal strength was maintained.

On the other hand, as shown in Table 3, the film obtained in Comparative Example 2 had a low piercing strength and a low heat seal strength after the heat treatment.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to obtain a heat-sealable biaxially stretched polyester film which is excellent in piercing resistance, heat resistance, transparency, chemical resistance and tear straightness, and also has excellent interlayer adhesion even after being exposed to high temperature. I was able to do it.
These films are particularly preferably used for packaging materials such as foods, pharmaceuticals and cosmetics, especially for press molding by dies and applications where puncture resistance is required for packaging solids. Can be done. Furthermore, even in applications where heat sealing is performed and then exposed to high temperatures, the sealing strength does not decrease, so it can be applied to applications where high temperature sterilization treatment is applied, which greatly contributes to the industrial world. Expected to do.

Claims (3)

Polyethylene terephthalate is 65 % by weight or more, and polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), polypropylene terephthalate (PPT), and dicarboxylic acid or diol are used as polyester resins other than PBT resin. There consists thermoplastic resin composition comprising a 0-35 wt% of a polyester resin selected from 5 Re not have a percent by weight or more copolymerized PBT resin one or more, piercing strength of the film is 0. The heat seal strength after heat-sealing 75 N / μm or more and heat-sealing the films at 230 ° C. for 1 hour at 150 ° C. is 10 N / 15 mm or more, and the haze value per film thickness is 0.35% / μm or less. A heat-sealable biaxially stretched polyester film. A PBT resin in which 5% by weight or more of dicarboxylic acid or diol was copolymerized was selected from any of isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, cyclohexanedicarboxylic acid, adipic acid, azelaic acid, and sebacic acid. PBT resin in which 5% by weight or more of one or more dicarboxylic acids are copolymerized, or ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, neopentyl glycol, 1,5-pentanediol, 1,6 -A claim characterized in that it is a PBT resin in which at least 5% by weight of one or more diols selected from any one of hexanediol, diethylene glycol, cyclohexanediol, polyethylene glycol, polytetramethylene glycol and polycarbonate diol is copolymerized. Item 2. The heat-sealable biaxially stretched polyester film according to Item 1. The heat-sealable biaxially stretched polyester film according to claim 1 or 2, wherein the film simultaneously satisfies the following (1) and (2).
(1) The angle formed by the main axis of the molecular chain with respect to the width direction of the film is 30 ° or less.
(2) The heat shrinkage rate at 150 ° C. in both the longitudinal direction and the width direction of the film is 4.0% or less.