NZ621873B2 - Biaxially stretched polyester film and method for producing same - Google Patents

Abstract

biaxially stretched polyester film which contains a modified polybutylene terephthalate (modified PBT) and a polyethylene terephthalate (PET). The biaxially stretched polyester film is characterized in that: the mass ratio of the modified PBT to the PET, namely (modified PBT/PET) is from 20/80 to 5/95; the modified PBT is a PBT that contains 5-20% by mass of a polytetramethylene glycol unit that has a molecular weight of 600-4,000; the amount of tetrahydrofuran (THF) generated by heating the biaxially stretched film at 180°C for 30 minutes in a helium gas atmosphere is 50 ?g/g or less; and the biaxially stretched polyester film has tear linearity in the longitudinal direction. 5/95; the modified PBT is a PBT that contains 5-20% by mass of a polytetramethylene glycol unit that has a molecular weight of 600-4,000; the amount of tetrahydrofuran (THF) generated by heating the biaxially stretched film at 180°C for 30 minutes in a helium gas atmosphere is 50 ?g/g or less; and the biaxially stretched polyester film has tear linearity in the longitudinal direction.

Description

Description Title of Invention: BIAXIALLY STRETCHED POLYESTER FILM AND METHOD FOR PRODUCING SAME Technical Field The present invention relates to a polyester film having tear linearity, suitable as a film used, for example, for packaging materials, electrical insulating materials and l industrial materials. ound Art For packaging food, medical and pharmaceutical products and miscellaneous goods, packaging bags using various plastic films are frequently used; packaging bags ed by laminating heat-sealable non-oriented plastic in two or three layers on biaxially stretched plastic films are widely used.

Among plastic films, biaxially hed polyester films are excellent in lity, moisture proofness, mechanical strength, heat resistance and oil resistance, are produced by the methods such as a tubular method, a ype simultaneous biaxial stretching method and a flat-type successive biaxial stretching method, and are widely used in the fields such as the field of food packaging.

However, packaging bags using biaxially hed polyester films are unfortunately poor in tear openability. There is a method for imparting a notch in order to e the openability; however,, tearing from a notch frequently results in a phenomenon such that no linear tearing occurs, and uently, the contents in 195002NZ AmndSpec 19Nov2014 EHB.doc the packaging bags are red to be wastes; additionally, soft confectionaries such as cookies are cracked at the time of opening packages, and when the contents are s, troubles such as staining of clothes may occur at the time of opening packages.

As easily openable materials excellent in the tear linearity such that when a film is torn, the film is torn linearly, there are materials prepared by laminating with a uniaxially stretched polyolefin film serving as an intermediate layer. Examples of such materials include a three-layer te film of biaxially stretched polyester film/uniaxially stretched polyolefin film/nonstretched polyolefin film; however, this three layer laminate film requires to be purposely ed with an intermediate layer, thus has a problem involving cost, and has been limited in the use thereof.

Accordingly, the present applicant has previously discovered, as a method for imparting the tear linearity to a biaxially stretched polyester film , a method in which a polybutylene thalate (modified PBT) including a polytetramethylene glycol (PTMG) having a molecular weight of 600 to 4000 in a proportion of 5 to 20% is mixed with polyethylene terephthalate (PET), in a ratio of modified PBT/PET = 30/70 to 5/95 (Patent Literature 1 to Patent Literature 6) .

Additionally, the present applicant has ed a biaxially stretched polyester film and a laminate having tear linearity while having a high level of barrier ty against oxygen or water vapor, on the basis of the vapor deposition of a metal compound such as aluminum oxide or silicon oxide at least on one side of a 195002NZ AmndSpec 19Nov2014 EHB.doc biaxially stretched polyester film having tear linearity (Patent Literature 7 and Patent Literature 8). r, the biaxially stretched ter film imparted with tear linearity is larger in the amounts of the outgases remaining in the film as compared to usual polyester films. Accordingly^ this film is not able to be used as the film constituting the containers or packages for housing electronic materials such as nductors, required to have high cleanliness. Additionally, this film unfortunately es a drawback such that the vapor deposition processing of this film in a vacuum atmosphere tends to cause the ility of the quality of the vapor deposited layer with the increase of the roll length.

Citation List Patent Literature Patent Literature 1 JP10-168293A Patent Literature 2 JP11-227135A Patent Literature 3 JP11-300916A Patent Literature 4 JP11-302405A Patent Literature 5 JP2000-318035A Patent Literature 6 JP2002-20597A Patent Literature 7 JP2001-162752A Patent ture 8 JP2006-150617A Summary of Invention Technical Problem The technical problem of the present invention is to provide a biaxially stretched polyester film having tear linearity and being reduced in the amounts of the residual outgases in the film. 195002NZ AmndSpec 19Nov2014 EHB.doc on to Problem For the purpose of solving such a technical problem as described above, the present inventors made a diligent study, and have revealed that the outgases ted from a polyester film having tear linearity contain, in particular, tetrahydrofuran (THF) in a larger amount as compared to the outgases generated from a general PET film, and THF is generated from PBT (modified PBT) containing polytetramethylene glycol (PTMG). The present inventors d attention on the amount of THF remaining in the modified PBT, and have d the present invention by discovering that by mixing the modified PBT with PET resin after such THF is drastically removed in the stage of the modified PBT being in a form of chip, and by subsequently forming a film from the resulting mixture, a biaxially stretched polyester film is ed in which the polyester has a function of tear linearity and the amounts of the residual outgases are small.

Specifically, the gist of the present invention is as follows. (1) A biaxially stretched polyester film, being a biaxially hed film including a modified polybutylene terephthalate (modified PBT) and hylene terephthalate (PET), wherein the mass ratio (modified PBT/PET) between the modified PBT and PET is 20/80 to 5/95, the modified PBT is a PBT containing 5 to % by mass of a polytetramethylene glycol unit having a molecular weight of 600 to 4,000, the amount of tetrahydrofuran (THF) generated by heat treating the biaxially stretched film in a helium gas atmosphere at 180°C for 30 minutes is 50 pg/g or less, and the lly 195002NZ AmndSpec 19Nov2014 EHB.doc stretched film has tear linearity in the lengthwise direction thereof. (2) A biaxially stretched polyester film, wherein at least on one side of the biaxially stretched polyester film according to (1), at least one of aluminum, aluminum oxide and silicon oxide is vapor deposited, and the biaxially stretched polyester film has a gas r property and tear linearity. (3) A method for producing the biaxially hed polyester film according to (1), wherein a modified polybutylene terephthalate (modified PBT) including 5 to % by mass of a polytetramethylene glycol unit having a molecular weight of 600 to 4,000 and giving an amount of tetrahydrofuran (THF), generated by heat treating in a helium gas atmosphere at 180°C for 30 minutes, of 800 p.g/g or less and polyethylene terephthalate (PET) are mixed so as for the mass ratio (modified PBT/PET) between the ed PBT and PET to be 20/80 to 5/95, a film is formed from the resulting mixture and the formed film is stretched.

Advantageous Effects of Invention According to the present invention, a biaxially stretched polyester film is provided which has durability, moisture proofness, mechanical properties, heat resistance and oil resistance, and additionally has tear ity in the lengthwise direction and is small in the amounts of the al outgases. The film of the present invention is small in the amounts of the generated es, and accordingly suitable particularly for packaging bags in the fields requiring cleanliness, and allows a vapor-deposited layer to be stably formed even when the film is placed in a vacuum state. 195002NZ ec 014 EHB.doc Brief Description of Drawings [ is a m illustrating the shape of a specimen used for the tear linearity evaluation of a film, [ is diagrams illustrating the shapes of the specimens after g in a tear test; (a) illustrates an example of a specimen after tearing of a sample actory in tear linearity, and (b) illustrates an example of a specimen after tearing of a sample unsatisfactory in tear linearity.

Description of Embodiments The lly stretched polyester film of the present invention includes a modified polybutylene terephthalate (modified PBT) and hylene terephthalate (PET).

In the present invention, PET includes terephthalic acid and ethylene glycol as the polymerization components thereof, and other components may also be copolymerized with these ents within a range not impairing the advantageous effects of the present invention.

Examples of other copolymerization components include: oxylic acids such as isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, succinic acid, adipic acid, sebacic acid, dodecanedioic acid, c acid, maleic anhydride, maleic acid, c acid, itaconic acid, citraconic. acid, mesaconic acid and cyclohexanedicarboxylic acid; oxycarboxylic acids such as 4-hydroxybenzoic acid, s-caprolactone and lactic acid; glycols such as 1,3-propanediol, 1,6-hexanediol and cyclohexanedimethanol; and multifunctional compounds such as trimellitic acid, trimesic acid, pyromellitic acid, trimethylolpropane, glycerin and pentaerythritol. 195002NZ AmndSpec 19Nov2014_EHB.doc PET can be obtained by heretofore known method as follows: after an oligomer is obtained by the transesterification reaction between dimethyl terephthalate and ethylene , or by a direct esterification method between thalic acid and ethylene glycol, PET is obtained by melt polymerization of the oligomer, or by further performing the solid phase rization of the product of the melt polymerization.

In the present invention, the modified polybutylene terephthalate (modified PBT) is a polybutylene terephthalate (PBT) including 5 to 20% by mass of a polytetramethylene glycol (PTMG) unit having a molecular weight of 600 to 4,000.

[0017] In the present invention, the molecular weight of PTMG constituting the modified PBT is required to be 600 to 4,000, and is preferably 1,000 to 3,000 and more preferably 1,000 to 2,000. When the molecular weight of PTMG is less than 600, the tear ity of the obtained film is not achieved, and when the molecular weight of PTMG exceeds 4,000, the performances such as mechanical strength, dimensional stability and haze of the obtained film are degraded, and additionally, no stable tear ity is developed.

The content of the PTMG unit in the modified PBT is ed to be 5 to 20% by mass, and is preferably 10 to % by mass and more preferably 10 to 15% by mass. When the content of PTMG is less than 5% by mass/ no tear linearity of the obtained film is developed, and when the content of PTMG exceeds 20% by mass, the performances such as ical strength, dimensional stability and haze of the obtained film are degraded, and additionally, it comes to be difficult to obtain a stable tear 195002NZ AmndSpec 014 EHB.doc linearity of the film. Also, in the case where the content of PTMG exceeds 20% by mass, in particular, when the film is produced on a mass production scale, a phenomenon of the pulsation (the so-called Barus phenomenon) of the film at the time of extrusion may occur, and unfortunately the unevenness of the film thickness may become large.

The modified PBT can be obtained by performing, in the polymerization process of PBT, a polycondensation reaction under the addition of PTMG. For example, the modified PBT can be obtained by the polycondensation between the sterification product of dimethyl terephthalate and tanediol and PTMG having a lar weight of 600 to 4,000.

In the biaxially stretched polyester film of the present invention, the mass ratio (modified PBT/PET) n the modified PBT and PET is required to be 20/80 to 5/95, and is preferably 15/85 to 10/90. When the mass proportion of the modified PBT is less than 5% by mass, it comes to be difficult to obtain the tear linearity of the film. When the mass proportion of the modified PBT s 20% by mass, there is an adverse possibility such that the variation of the film thickness comes to be large, the tear ity of the obtained film is degraded, and additionally, the amounts of the generated outgases exceed the values specified in the present invention. In other words, for the e of imparting tear linearity to a film and reducing the amounts of the ted outgases^ the mixing ratio between the modified PBT and PET is required to be within the above-described range. 0021' 195002NZ AmndSpec 19Nov2014 EHB.doc The biaxially stretched polyester film of the present invention can include other polymers such as polyethylene naphthalate and polycyclohexylene dimethylene terephthalate within a range not impairing the advantageous effects of the present invention.

In the biaxially stretched polyester film of the present ion, the amount of ydrofuran (THF) generated by heat treating the biaxially stretched polyester film in a helium gas atmosphere at 180°C for 30 minutes is required to be 50 |J,g/g or less, and is preferably 30 pg/g or less and more preferably 20 ^g/g or less. In the present invention, the reason for particularly specifying the amount of generated THF among the generated components s in the fact that THF is a volatile (low g point) component.

When the amount of generated THF exceeds 50 |n,g/g, the packaged contents may be possibly contaminated by the generated THF. Even when the vapor deposition processing is applied to the lly stretched polyester film for the purpose of improving the gas barrier property or water vapor gas barrier property, there is an adverse possibility such that THF is generated from the film during the vapor deposition treatment, the generated THF adversely affects the formation of the vapor deposited layer, and the gas barrier property or water vapor gas barrier property of the film is not stably improved.

For the purpose of regulating the amount of THF ted from the biaxially hed polyester film of the present invention to be equal to or less than 50 p-g/g specified in the present invention, the amount of THF generated from the modified PBT chip used at the time of tion of the film is preferably set at 800 p.g/g or less, more preferably set at 500 |ng/g or less and most 195002NZ AmndSpec 014 EHB.doc - ably set at 300 jng/g or less. When the amount of THF generated from the modified PBT is larger than 800 p.g/g, depending on the mixing ratio n the modified PBT and PET, the amount of THF generated from the film may become larger than the value ied in the present invention.

Examples of the method for regulating the amount of THF generated from the modified PBT chip to be 800 ^ig/g or less include a method in which the polymerized modified PBT chip is dried in a reduced pressure environment, a method in which the rized modified PBT chip is dried in a nitrogen atmosphere, and a method in which the polymerized modified PBT chip is dried in a hot air dryer: among these, the drying in a reduced pressure environment is most efficient, and preferable also from the viewpoint of workability/economic efficiency.

When the polymerized modified PBT chip is dried by these s, the drying temperature is preferably 80 to 180°C and the drying time is preferably 12 hours or more and more preferably 24 hours or more. When the polymerized modified PBT chip is dried in a reduced pressure environment, in addition to the above-described temperature and time, the pressure reduction degree is preferably 10 Pa or less.

In the production of the biaxially stretched polyester film of the present invention, for example, first, a mixture composed of the modified PBT and PET is placed in an er, heated and melted, and then extruded from the die orifice of a T-die in a sheet shape to produce an unstretched sheet. The sheet extruded from the die orifice of the T-die is cooled as y wound around a cooling drum, for example, by an electrostatic 195002NZ AmndSpec 19Nov2014 EHB.doc 11 - casting method, then at a temperature of 90 to 140°C, stretched udinally and transversely with a magnification of 3.0 to 5.0, and further heat treated at a temperature of 210 to 245°C to yield a lly stretched film.

When the stretching temperature is lower than 90°C, a uniform stretched film cannot sometimes be obtained, and when the stretching temperature exceeds 140 C, the crystallization of PET is promoted to sometimes e the transparency of the film. When the stretching magnification is less than 3.0, the strength of the obtained stretched film is low, and a bag prepared with such a stretched film tends to undergo the occurrence of pin holes; when the stretching magnification exceeds 5.0, the stretching mes becomes difficult. When the heat treatment temperature is lower than 210°C, the thermal shrinkage coefficient of the ed stretched film becomes large, the bag made of such a film is sometimes deformed; when the heat treatment ature is higher than 245°C, the fusion of the film sometimes occurs.

As the biaxially stretching method,. either of the tenter simultaneous biaxial stretching method and the successive biaxial stretching method using a roll and a tenter may be used. Alternatively, a biaxially stretched film may also be produced by a tubular method.

The biaxially hed polyester film, obtained as described above, of the present ion can be enhanced in the oxygen gas barrier property or the water vapor barrier property thereof, by applying a vapor deposition treatment to at least one side of the film, with aluminum, n oxide or aluminum oxide, or a combination of two or more of these components such as a combination of silicon oxide and aluminum oxide. As the method for 195002NZ AmndSpec 19Nov2014 EHB.doc 12 - producing a vapor deposited layer, for example, a vacuum vapor deposition method, an EB vapor tion method, a sputtering method and an ion plating method can be used; from the viewpoint of the productivity and the cost, the vacuum vapor deposition method is most preferable.

The vacuum vapor tion method is a method for forming a deposited layer as s: after the film is placed in a vacuum state in a chamber, the component to be deposited is melted and then vaporized to be deposited on the film to form the deposited layer. In this method, when the outgases are present in the film in large amounts, unfortunately the degree of vacuum in the chamber is not stabilized due to the diffusion of the outgases, the formation of the vapor ted layer becomes unstable, and it is sometimes difficult to obtain the intended oxygen barrier property or the intended water vapor barrier property. In particular, when a vacuum tion is performed on a roll film, the roll surface is continuously renewed, and hence even if a stable vapor deposited layer can be formed at the start of the vapor deposition, in the case where the es remain in the film, the formation of the vapor deposited layer sometimes comes to be unstable as the vapor deposition treatment proceeds. However, the biaxially stretched polyester film of the present invention is small in the residual amounts of the outgases,. and hence even on a roll film, a vapor deposited layer can be stably formed.

[0029] For the purpose of improving the adhesiveness to the vapor deposited layer such as an aluminum vapor deposited layer, the surface of the biaxially stretched polyester film of the present invention is preferably pretreated by 195002NZ AmndSpec 014 EHB.doc 13 - a method such as corona discharge ent or an application of an anchor coating agent.

The lly stretched polyester film of the present invention can be subjected to a surface treatment by utilizing,, according to the intended ations thereof, corona discharge treatment, surface hardening treatment, g treatment, coloring treatment, or various coating treatments.

Next, the present invention is specifically described by way of Examples. The evaluation methods of Examples and ative Examples are as s. (1) Evaluation of Tear Linearity From a biaxially stretched polyester film, stripshaped pieces of the film each piece being 205 mm in the lengthwise direction (MD) and 20 mm in the widthwise direction (TD) were sampled; in each of the pieces of the film, a cut (notch) of 5 mm in length was made into the center of one TD side to e a sample; thus ten samples were prepared in total; then, each sample was torn by hand from the notch in the MD direction; then, the number of the samples in each of which the tear propagation edges reached the TD side opposite to the TD side with the notch was evaluated.

The evaluation standards are shown below.

Evaluation E (Excellent): The number of the samples with the tear reaching the opposite TD side is 9 to 10.

Evaluation G(Good): The number of the samples with the tear reaching the opposite TD side is 7 to 8.

Evaluation A(Average): The number of the samples with the tear reaching the opposite TD side is 5 to 6. 195002NZ AmndSpec 19Nov2014 EHB.doc 14 - Evaluation P(Poor): The number of the samples with the tear reaching the opposite TD side is 4 or less.

In the present invention, the evaluation grades equal to or higher than G(Good) were determined as passing.

[0033] (2) Identification of Outgas Components and Measurement of s of Generated Outgas Components For the identification of the outgas components, about 15 mg of the biaxially stretched ter film or about 15 mg of the modified PBT chip was accurately weighed and packed in a sample cup, heated in a pyrolyzer (PY-20201D), in a helium gas here at 180°C for 30 minutes, and the generated volatile components were subjected to a GC/MS (GC: Agilent 6890N, MS: Agilent 5975C) measurement. In this case, the generated outgases were tetrahydrofuran (THF), 1,4-butanediol (BD) and water, and ethylene glycol (EG) was also generated from the biaxially hed polyester film.

The amounts of the respective generated outgases were measured by using the following standard sample and internal standard. Specifically, as the rd sample, a on was prepared in which hexadecane, THF, BD and EG were dissolved in hexane each in a content of 100 ppm, the resulting on was subjected to the GC/MS measurement under the same conditions as for the sample, and the peak area ratios of the individual components to the peak area of hexadecane were derived. Next, as the internal standard, a hexane solution having a hexadecane concentration of 100 ppm was prepared, 5 |J,1 of the prepared al rd was added to a sample prepared by accurately weighing about 15 mg of the biaxially stretched polyester film or the modified PBT chip, and the resulting sample solution was ted to the GC/MS measurement to quantitatively determine the amounts of the individual generated outgas components. 195002NZ AmndSpec 19Nov2014 EHB.doc - (3) Evaluation of mances of Vapor-Deposited Film A polyester resin (Eritel UE-3200, ctured by Unitika Ltd., Tg: 65°C) and an isocyanate-based curing agent (CAT-10, manufactured by Toyo-Morton, Ltd.) were mixed with each other in a mixing ratio of 10/1 (mass ratio) to prepare a coating material. The ed coating material was applied as an anchor coating agent to the biaxially stretched polyester film having a winding length 8000 m so as for the thickness to be 0.1 p,m, and then by using a uous vacuum deposition apparatus, an aluminum oxide layer was vapor deposited so as for the vapor deposition thickness to be 40 to 50 nm. ng was performed in the portions of 100 m, 2000 m, 4000 m and 7500 m from the surface layer of the vapordeposited film (the winding core side of the placed biaxially stretched ter film), and the measurements of the oxygen permeability and the water vapor permeability were med. (3-a) Oxygen Permeability (ml/m2-day-MPa) According to JIS K-7129, by using the Model OX- TRAN100 manufactured by Modern Control Co., Ltd., a measurement was performed under the conditions of a temperature of 20°C and a humidity of 100%RH.

The evaluation standards are shown below.

Evaluation E (Excellent): The oxygen permeability is less than 20 ml/ (m2-day-MPa) .

Evaluation G(Good): The oxygen permeability is 20 or more and less than 30 ml/ (m2-day'MPa) .

Evaluation A(Average): The oxygen permeability is 30 or more and less than 50 ml/ (m -day-MPa) .

Evaluation P (Poor): The oxygen bility is 50 ml/(m-day-MPa) or more. 195002NZ AmndSpec 19Nov2014 EHB.doc 16 - In the present invention, the evaluation grades equal to or higher than G(Good) were determined as passing. (3-b) Water Vapor Permeability day) According to JIS , by using the PARMATRAN W3/31 manufactured by Modern Control Co., Ltd., a measurement was performed under the ions of a temperature of 40°C and a humidity of 90%RH.

The evaluation rds are shown below.

Evaluation E(Excellent): The water vapor permeability is less than 2 g/ (m -day) .

Evaluation G(Good): The water vapor permeability is 2 or more and less than 5 g/ (m -day) .

Evaluation A(Average): The water vapor permeability is 5 or more and less than 10 g/ (m -day) .

Evaluation P (Poor): The water vapor permeability is ay) or more.

In the present ion, the evaluation grades equal to or higher than G(Good) were determined as passing.

[0037] Example 1 <Production of Modified PBT> A transesterification reaction was performed for 2.5 hours while 194 parts by mass of dimethyl terephthalate, 108 parts by mass of 1,4-butanediol and 80 ppm (a numerical value in terms of the mass of titanium metal in relation to the polymer) of tetrabutyl titanate were heated to increase the temperature from 150°C to 210°C.

To a polymerization can, 85 parts by mass of the obtained transesterification reaction product was transferred, 40 ppm of tetrabutyl titanate was added to the can, then 15 parts by mass of PTMG having a molecular weight of 1,100 was added to the can; then, a pressure reduction was started, and finally, under a reduced pressure of 1 hPa, the temperature was increased from 210°C; finally, at a 195002NZ_AmndSpec 19Nov2014 EHB.doc 17 - temperature of 245°C, a melt polymerization was performed for 2 hours, to produce the modified PBT having a relative viscosity of 1.62.

The amounts of the outgases generated from the produced modified PBT were THF: 3000 (-ig/g and 1,4- butanediol (BD) : 10 |^g/g.

The ed PBT ed by the above-described method was dried in a reduced pressure dryer, for 72 hours under the conditions of 120°C and 5 Pa. The amounts of the outgases generated from the dried ed PBT were THF: 280 |-ig/g and BD: 5 f^g/g. <Production of Biaxially Stretched Polyester Film> A mixture prepared by simple chip-mixing of the modified PBT with PET(relative viscosity: 1.38) in a mass ratio of 15/85 was melt extruded at a resin temperature of 280°C by using a 200-mm(() extruder provided with a coat hanger type T-die, and rapidly cooled, in a closely adhering manner, on a cast roll regulated at a temperature of 20°C by applying an electric voltage of 7 kV to a pinning wire, to yield an unstretched sheet having a thickness of about 190 j^m.

The obtained unstretched sheet was stretched by using a roll udinal stretching machine at 90°C with a ication of 3.5, and by using a tenter transverse stretching machine at 120°C with a magnification of 4.5, then heat treated at 235°C with a transverse relaxation rate set at 3%, and slowly cooled to room temperature to yield a biaxially stretched polyester film having a thickness of 12 ^m.

The amounts of the outgases ted from the produced biaxially stretched polyester film were THF: 8 ^ig/g, BD: 1 |-ig/g and ne glycol (EG): 70 |J,g/g.

Examples 2 to 3 and Comparative Example 1 195002NZ ec 19Nov2014 EHB.doc 18 - In each of Examples 2 to 3 and Comparative Example 1, a biaxially stretched polyester film was obtained in the same manner as in e 1 except that the drying time of the modified PBT chip was altered as shown in Table 1.

[0039] Example 4 The ed PBT chip was placed in a 5 m3 dryer, and dried in an atmosphere set at 120°C, for 24 hours while nitrogen was allowed to flow in the dryer at a flow rate of 5 m3/s. The amounts of the outgases generated from the modified PBT after drying were THF: 480 |^g/g and BD: 8 p,g/g. By using this modified PBT chip, a biaxially stretched polyester film was obtained in the same manner as in Example 1.

[0040] Example 5 and Comparative Example 2 In each of Example 5 and Comparative Example 2, a biaxially hed polyester film was obtained in the same manner as in Example 4 except that the drying time of the modified PBT chip was altered as shown in Table 1.

Example 6 The modified PBT chip was dried in a hot air dryer set at 120°C for 72 hours. The amounts of the outgases generated from the modified PBT after drying were THF: 1200 f^g/g and BD: 9 |-ig/g. By using this modified PBT chip, a biaxially stretched polyester film was obtained in the same manner as in Example 1.

Comparative e 3 A biaxially stretched ter film was obtained in the same manner as in Example 6 except that the drying time of the modified PBT chip was altered as shown in Table 1.

[0043] NZ AmndSpec 19Nov2014 EHB.doc 19 - Examples 7 to 9 and Comparative Examples 4 and 5 In each of Examples 7 to 9 and Comparative Examples 4 and 5, a biaxially hed polyester film was obtained in the same manner as in Example 1 except that the proportion of PTMG in the modified PBT chip was altered as shown in Table 1 .

Examples 10 to 12 and Comparative Examples 6 and 7 In each of Examples 10 to 12 and Comparative Examples 6 and 7, a biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the mixing ratio n the modified PBT and PET was altered as shown in Table 1.

Examples 13 to 15 and Comparative Examples 8 and 9 In each of Examples 13 to 15 and Comparative Examples 8 and 9, a biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the molecular weight of PTMG used in the modified PBT was altered as shown in Table 1.

Example 16 A biaxially stretched polyester film was obtained in the same manner as in Example 6 except that the mixing ratio n the modified PBT and PET was altered as shown in Table 1.

Comparative Example 10 A biaxially stretched polyester film was obtained in the same manner as in Comparative e 1 except that the mixing ratio between the ed PBT and PET was d as shown in Table 1.

Table 1 shows, for the biaxially stretched polyester film obtained in each of es and Comparative 195002NZ AmndSpec 19Nov2014 EHB.doc es, for example, the tear linearity, the amount of THF in the generated outgases, and the evaluation results of the oxygen permeability and the water vapor permeability after the application of the vapor deposition treatment to the film.

[Table 1] 195002NZ AmndSpec 19Nov2014 EHB.doc 21 - Modified PBT Biaxially stretched polyester film Amounts of Mixing Amounts of Oxygen permeability rater vapor permeability tution Drying conditions generated itio (mass generated outgases after vapor tion after vapor deposition outgases (^ig/g) ratio) Wg) treatment treatment content Tear of [olecula inearit^ "ime s e e @ g s g PTMG tun Modified /eight oJ Method THF BD FHF BD EG 0 0 0 0 0 0 0 0 (°C) (hr) 3BT/PET 0 0 0 0 0 0 0 0 0 (% by PTMG T—I 0 m T—I 0 0 v-1 ;N ^t- r~~ r<l ^)- t~~ mass) 1 .educed 1100 120 72 280 5 15/85 8 1 70 E E E E E E E E E ressure 1100 Leduced] 2 120 48 600 8 15/85 18 1 68 E G E E E G E E E iressure 1100 Leduced J 15 120 24 810 10 15/85 24 2 78 E G G G E G G G G iressure 4 15 1100 Iitrogen| 120 24 480 8 15/85 14 J 74 E G E E E G E E E 15 1100 Titrogenl 120 12 750 10 15/85 23 3 65 E G G E E G E E E 6 15 1100 Hot air 120 72 1200 9 15/85 36 2 72 E G G G G G G G G leduced| 7 5 1100 120 260 15/85 8 1 or 72 5 75 G E E E E E E E E n-essure less (.educed 263 5 15/85 8 1 or 8 10 1100 120 72 62 G E E E E E E E E tu )ressure less 1100 leduced| 9 120 72 302 5 15/85 9 1 or 75 G E E E E E E E E cd )ressure less p-i deduced 1 or 15 1100 120 72 280 5 5/95 3 88 E E E E E E E E E re less deduced 1 or 11 1100 120 72 280 5 10/90 6 78 E E E E E E E E E pressure less 1100 deduced 12 15 120 72 280 5 20/80 11 2 70 E G G E E G G E E pressure deduced I 13 15 600 120 72 220 6 15/85 7 2 72 G G E E E G E E E 3ressure 4000 deduced 14 15 120 72 350 5 15/85 11 1 63 G G G E E G G E E pressure 15 2000 120 72 320 5 15/85 10 1 71 G G E E E G E E E pressure u 15 1100 Hot air 120 72 1200 9 20/80 48 4 61 E G G G G G G G G 195002NZ AmndSpec 19Nov2014 EHB.doc 22 - 1 1100 deduced 120 8 1848 5 15/85 55 1 63 E A A G G p p A G pressure 2 15 1100 Nitrogen 120 6 1743 5 15/85 52 1 60 E A A G G p A G G 3 15 1100 Hot air 120 48 2236 4 15/85 67 2 68 E p A G G p p A G 4 25 1100 R-educed <u 120 72 235 4 15/85 Impossible to form film & pressure i 5 3 R-educed cd 1100 120 72 224 4 15/85 9 1 77 p E E E E E E E E pressure u 6 15 1100 d 3/97 1 or > 120 72 235 4 2 85 p E E E E E E E E 'S pressure less ^C3 7 15 1100 Reduced 120 72 208 4 25/75 14 3 60 A G G E E G G E E pressure u 8 15 500 Reduced 120 72 280 4 15/85 11 2 71 p G E E E G E E E pressure 9 15 4500 d 120 72 195 4 15/85 8 2 75 p G E E E G E E E pressure 1100 Reducec 15 120 8 1848 5 25/75 120 10 65 A p p A G p A A G pressure 195002NZ AmndSpec 19Nov2014 EHB.doc 23 - As can be seen from Table 1, in each of Examples, the amount and the molecular weight of PTMG contained in the modified PBT, the mixing ratio between the modified PBT and PET, and the amount of THF generated from the biaxially stretched polyester film satisfied the ranges specified in the present invention, and consequently, it was possible to prepare the film having ent tear linearity, being small in the amounts of the generated outgases, and being stable in the gas barrier property after the vapor deposition treatment.

In contrast, in Comparative Examples, the ing unfavorable results were found.

In each of Comparative Examples 1 to 3, the amount and the molecular weight of PTMG ned in the modified PBT, and the mixing ratio between the ed PBT and PET satisfied the ranges specified in the present ion, and hence the film having tear linearity was obtained; however, the amount of generated THF exceeded the range ied in the t invention, and hence the oxygen permeability and the water vapor permeability of the vapor-deposited film were unstable.

In Comparative Example 4, the proportion of PTMG contained in the modified PBT was larger than the range specified in the present invention, and hence the film formation was difficult, and uently it was not possible to obtain a biaxially stretched polyester film.

In Comparative Example 5, the amount of generated THF specified in the present invention was satisfied, and hence the oxygen permeability and the water vapor permeability of the vapor-deposited film were ; however, the proportion of PTMG contained in the modified PBT was smaller than the range specified in the present invention, and hence it was impossible to obtain a film having a satisfactory tear linearity. 195002NZ AmndSpec 19Nov2014 EHB.doc 24 - In each of Comparative Examples 6 and 7, the amount of generated THF specified in the present ion was satisfied, and hence the oxygen permeability and the water vapor permeability of the vapor-deposited film were stable; however, the ratio between the modified PBT and PET fell outside the range specified in the present invention, and hence it was impossible to obtain a film having a satisfactory tear linearity.

In each of Comparative Examples 8 and 9, the amount of generated THF specified in the present invention was satisfied, and hence the oxygen permeability and the water vapor permeability of the vapor-deposited film were stable; however, the molecular weight of PTMG contained in the modified PBT chip fell outside the range specified in the t ion, and hence it was impossible to obtain a film having a satisfactory tear linearity.

In ative Example 10, the amount of THF generated from the biaxially stretched polyester film exceeded the range specified in the present invention, and hence the oxygen permeability and the water vapor permeability of the vapor-deposited film were unstable.

Additionally, the ratio n the ed PBT and PET fell outside the range specified in the present invention^ and hence it was impossible to obtain a film having a satisfactory tear linearity.

NZ AmndSpec 19Nov2014 EHB.doc

Claims (3)

Claims
1. [Claim 1] A biaxially stretched polyester film, being a 5 biaxially hed film comprising a modified polybutylene terephthalate (modified PBT) and polyethylene terephthalate (PET), wherein a mass ratio (modified PBT/PET) n the modified PBT and PET is 20/80 to 5/95, the modified PBT is a PBT containing 5 to 10 20% by mass of a polytetramethylene glycol unit having a molecular weight of 600 to 4,000, an amount of tetrahydrofuran (THF) generated by heat treating the biaxially stretched film in a helium gas atmosphere at 180°C for 30 minutes is 50 |J,g/g or less, and the lly 15 stretched film has tear linearity in a lengthwise direction thereof.
2. [Claim 2] A biaxially hed polyester film, wherein at 20 least on one side of the biaxially stretched polyester film according to claim 1, at least one of aluminum, aluminum oxide and silicon oxide is vapor deposited, and the biaxially stretched polyester film has a gas barrier property and tear linearity.
3. [Claim 3] A method for producing the biaxially stretched polyester film according to claim 1, wherein a modified polybutylene terephthalate ied PBT) including 5 to 30 20% by mass of a polytetramethylene glycol unit having a lar weight of 600 to 4,000 and giving an amount of tetrahydrofuran (THF), generated by heat treating in a helium gas atmosphere at 180°C for 30 minutes, of 800 |-ig/g or less and polyethylene thalate (PET) are mixed so 35 as for a mass ratio (modified PBT/PET) between the 195002NZ AmndSpec 19Nov2014 EHB.doc 26 - modified PBT and PET to be