JP2012121241A - Biaxially-stretched polybutylene terephthalate film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably manufacture a film having characteristics suitable for a converting film, a food packaging film, and a drawing film, that is, a biaxially-stretched PBT film that has almost no anisotropy and is excellent in mechanical properties and dimensional stability.SOLUTION: A biaxially-stretched polybutylene terephthalate (PBT) film is provided such that the tensile breaking strength in all four directions is ≥200 MPa and the tensile elongation at break is ≥50% and ≤150%. The film is suitably used as a food packaging film, a drawing film, and a converting film. Such a film is stably obtained by subjecting extruded PBT resin melt to quench film-formation at a very high cooling speed of ≥200°C/second and simultaneously biaxially stretching it in the longitudinal and lateral directions respectively to 2.7-4.0 times.

Description

The present invention relates to a biaxially stretched polybutylene terephthalate (hereinafter referred to as PBT) film having good stretching process stability and productivity, little anisotropy, and excellent mechanical properties and dimensional stability.

PBT resin has characteristics such as excellent mechanical strength, heat resistance, chemical resistance, flexibility, transparency, surface gloss, weather resistance, and low water absorption. Has been used in a wide range of fields and applications. In particular, a remarkable feature of PBT resin is that it has a significantly higher crystallization speed than other general-purpose plastics. Taking advantage of this feature, it is highly cycleable in injection molding applications such as various automobile parts and electrical / electronic parts. In recent years, it has been widely used.

On the other hand, in film applications, unstretched PBT films produced by cast molding are mainly used for general sugar beet, or uniaxially stretched PBT films are used for beverage bottle shrink labels. Since there is a problem in stability, the use is limited, and in particular, it cannot be used for a converting film. In addition, the biaxially stretched PBT film is more resistant to pinholes and impacts than biaxially stretched polyethylene terephthalate (hereinafter referred to as PET) films that are commonly used as converting films for food packaging. Although superior in chemical resistance and moisture resistance compared to biaxially stretched nylon 6 (hereinafter referred to as ONY) film, it has problems in terms of film quality such as tensile rupture strength, dimensional stability, and anisotropy. However, since it is difficult to perform stable biaxial stretching due to the characteristics of the PBT resin, it has not yet been put into practical use.

As is well known, PBT resin is extremely difficult to biaxially stretch due to the effect of its high crystallization rate, and stable production is difficult just by applying biaxial stretching technology of general-purpose plastics such as PET, nylon 6, and polypropylene as they are. . In particular, it can be said that the crystallization at the time of unstretched raw film formation is suppressed as much as possible, and stretching is performed while maintaining the low crystal state, which is a big point for stably making the PBT resin a biaxially stretched film. Various methods have been proposed so far for the film-forming method of the unstretched raw material of the PBT resin, the biaxial stretching method, and the quality improvement of the biaxially stretched film. In Patent Document 1, Patent Document 2, and Patent Document 3, in the tenter method simultaneous or sequential biaxial stretching method, various stretching conditions such as stretching temperature, stretching ratio, stretching deformation rate, stretching system, or the raw fabric cooling rate, etc. A method for improving stretchability and film physical properties has been proposed by devising the unstretched raw film forming conditions. In Patent Document 3, Patent Document 4, and Patent Document 5, in the tubular method simultaneous biaxial stretching method, an unstretched raw film forming method with relatively low crystallinity and its low crystalline state are maintained until the stretching step. And a method for improving the biaxial stretchability of the PBT resin by optimizing various stretching conditions such as a stretching temperature and a stretching ratio. Furthermore, by using the film forming and stretching techniques, a biaxially stretched PBT film having relatively high mechanical strength and low anisotropy can be obtained.

JP-A-49-80178 JP 51-146572 A JP-A-53-79969 Japanese Patent Laid-Open No. 5-261809 JP-A-5-269843

However, the biaxially stretched PBT film obtained by the tenter biaxial stretching method has a large anisotropy, and the tensile breaking strength or the breaking elongation may be too low. There was a big problem in terms of suitability for secondary processing such as laminating and molding. Moreover, in the original film forming method by the casting method using the cooling drum proposed in Patent Document 3, the cooling rate of the unstretched original film can be increased only to a certain extent, and it cannot be said that it is sufficient in terms of rapid cooling film formation. It was. On the other hand, in Patent Document 5 which is a tubular method simultaneous biaxial stretching method, although the anisotropy is small, it cannot be said that the tensile breaking strength is sufficient, and the substrate breaks because it is used for a substrate film for in-mold transfer. The elongation was large, and there was room for improvement in terms of dimensional stability for packaging films and drawing. Furthermore, it is difficult to increase the cooling rate with the raw film forming method proposed in Patent Document 4, that is, with the direct water cooling on the outside and the indirect water cooling on the inside of the melt extruded into a tube shape. There is a difference in crystallinity between the inside and outside of the fabric, and as a result, it is not sufficient in terms of suppressing crystallization of the original fabric, which was one of the points for stably stretching the PBT resin, and homogenizing the total crystal of the original fabric. It was. Furthermore, from the viewpoint of the raw fabric cooling rate, the production rate is limited, and further improvement of the film forming method for the unstretched PBT raw fabric is necessary.

The present inventors have found that a polybutylene terephthalate film having a large tensile breaking strength in all four directions and a tensile breaking elongation in the range of 50 to 150% is suitable for packaging and drawing, By stretching the unstretched original fabric that has been rapidly cooled and formed at an extremely high cooling rate in the vertical and horizontal simultaneous biaxial directions, the stretching stability and productivity are good, and the mechanical properties satisfying the above conditions are low. It has been found that a biaxially stretched polybutylene terephthalate film having excellent dimensional stability can be obtained, and the present invention has been completed.

That is, the present invention provides the following items and means.
[1] Characteristically, the tensile strength at break in all four directions (0 ° (MD), 45 °, 90 ° (TD), 135 °) is 200 MPa or more, and the tensile elongation at break is 50% or more and 150% or less. Biaxially stretched polybutylene terephthalate film.
[2] The ratio between the maximum value and the minimum value among the tensile rupture strengths in four directions (0 ° (MD), 45 °, 90 ° (TD), 135 °) is 1.5 or less. The biaxially stretched polybutylene terephthalate film according to [1] above.
[3] Immediately after the polybutylene terephthalate resin is melt-extruded, the unstretched raw material obtained by rapid film formation at a cooling rate of 200 ° C./second or more is simultaneously biaxially stretched by 2.7 to 4.0 times each in length and width. The biaxially stretched polybutylene terephthalate film according to [1] or [2], obtained by
[4] The biaxially stretched polybutylene terephthalate film according to [3], wherein the cooling rate is 250 ° C./second or more.
[5] The biaxially stretched polybutylene terephthalate film according to [3], wherein the cooling rate is 350 ° C./second or more.
[6] The biaxially stretched polybutylene terephthalate according to the above [3] to [5], wherein the unstretched raw fabric has an elongation percentage of 5% or more at 40 ° C. under a load of 0.5 kg / cm. the film.
[7] The biaxially stretched polybutylene terephthalate as described in the above [3] to [5], wherein the unstretched raw fabric has an elongation of 30% or more under a load of 40 ° C. and 0.5 kg / cm. the film.
[8] The above-mentioned [3] to [7], wherein the rapid cooling film formation is performed by bringing water at 30 ° C. or less into direct contact with both surfaces of polybutylene terephthalate immediately after being melt-extruded into a film shape. Biaxially stretched polybutylene terephthalate film.
[9] The biaxially stretched polybutylene terephthalate film according to any one of [1] to [8] above, wherein the biaxially stretched polybutylene terephthalate film is used by being bonded to one or more of the following (a).
(A) Biaxially stretched nylon 6 film, biaxially stretched polypropylene film, biaxially stretched polyethylene terephthalate film, biaxially stretched ethylene-vinyl alcohol film, biaxially stretched polyethylene naphthalate film, biaxially stretched polystyrene film, biaxially stretched Aromatic polyamide film, biaxially stretched polyvinylidene chloride film, biaxially stretched polyvinyl alcohol film, various coated films, various deposited films, unstretched polyethylene film, unstretched polypropylene film, unstretched polyvinyl chloride film, ethylene-acetic acid Vinyl film, ionomer film, other ethylene copolymer film, unstretched polyvinyl alcohol film, unstretched nylon 6 film, aluminum foil, copper foil, stainless steel foil, paper, nonwoven fabric, foamed poly Styrene.
[10] The biaxially stretched polybutylene terephthalate film according to any one of [1] to [9], which is used after printing.
[11] The biaxially stretched polybutylene terephthalate film as described in [1] to [10] above, which is used as a base material for food packaging or drawing.

The inventors of the present invention made the PBT unstretched raw film rapidly cooled and formed at an extremely high cooling rate biaxially and longitudinally and biaxially stretched stably for a long time, and increased production speed. In addition, the obtained biaxially stretched PBT film has the characteristics that the tensile strength at break is high and the elongation at break is low, and furthermore, there is little anisotropy of physical properties and it is excellent in dimensional stability. It can be suitably used for packaging, drawing, and general converting films.

It is the schematic of a tubular simultaneous biaxial stretching apparatus.

The best mode for carrying out the present invention will be described below.
(Raw Material for Biaxially Stretched PBT Film) The raw material used for the biaxially stretched PBT film is not particularly limited as long as it is a polyester having butylene terephthalate as a main repeating unit. , 4-Butanediol, or an ester-forming derivative thereof, and terephthalic acid as a dibasic acid component, or an ester-forming derivative thereof as a main component, and a homo- or copolymer-type polyester obtained by condensing them. . In order to impart optimum mechanical strength characteristics, among polybutylene terephthalate resins, those having a melting point of 200 to 250 ° C. and an IV value of 1.10 to 1.35 dl / g are preferable, and a melting point of 215 to 215 Those having a range of 225 ° C. and an IV value of 1.15 to 1.30 dl / g are particularly preferable.

Here, the copolyester mainly composed of polybutylene terephthalate replaces a part of the terephthalic acid component as the dibasic acid component with other dibasic acid components such as isophthalic acid, phthalic acid, adipic acid, and sebacic acid. And / or a part of 1,4-butanediol component as a glycol component is condensed with another glycol component such as ethylene glycol, diethylene glycol, propylene glycol, neopentyl glycol, cyclohexanedimethanol, etc. Polyester having a butylene terephthalate unit of 70% or more is preferable.

In the polybutylene terephthalate of the present invention, other polyesters such as polyethylene terephthalate, polyethylene naphthalate, polyhexamethylene terephthalate, poly (ethylene terephthalate / ethylene isophthalate), polycarbonate, and the like, as long as physical properties are not hindered. Polyamide etc. may be mixed or laminated and stretched, and if necessary, lubricant, antiblocking agent, inorganic extender, antioxidant, ultraviolet absorber, antistatic agent, flame retardant, plasticizer, Additives such as a colorant, a crystallization inhibitor, and a crystallization accelerator may be added. The PBT resin pellets are sufficiently pre-dried so that the moisture content is 0.05 wt% or less, preferably 0.02 wt% or less before heating and melting in order to avoid a decrease in viscosity due to hydrolysis during heating and melting. Is preferably used.

(Method for producing PBT unstretched raw fabric) As described above, in order to stably biaxially stretch a PBT resin, it is necessary to suppress crystallization of the unstretched raw fabric before stretching as much as possible, and an extruded PBT melt When the film is cooled to form a film, the crystallization temperature region of the polymer is cooled at a certain rate or more, that is, the raw fabric cooling rate is an important factor. The raw fabric cooling rate is 200 ° C./second or more, preferably 250 ° C./second or more, particularly preferably 350 ° C./second or more, and the unstretched raw film formed at a high cooling rate maintains an extremely low crystalline state. Therefore, the stability of the bubble at the time of stretching is dramatically improved. Furthermore, since the film can be formed at a high speed, productivity is also improved. When the cooling rate is less than 200 ° C./second, not only the crystallinity of the obtained unstretched raw fabric is increased and the stretchability is lowered, but in extreme cases, the stretched bubble may burst and stretching may not continue. .

The raw film forming method is not particularly limited as long as it satisfies the original film cooling rate, but the internal / external direct water cooling method is most suitable in terms of rapid cooling film forming. The outline of the raw film forming method by the internal / external direct water cooling method will be described below. First, the PBT resin is melt-kneaded by an extruder set at a temperature of 210 to 270 ° C., and in the case of T-die film formation, the sheet-like molten resin is immersed in a water tank and directly water-cooled inside and outside. On the other hand, in the case of annular film formation, the molten tubular thin film is formed by being extruded downward from an annular die attached downward to the extruder.

Next, it is led to a cooling mandrel connected to the annular die, and the cooling water introduced from each nozzle of the cooling mandrel is brought into direct contact with the inside of the molten tubular thin film to be cooled. At the same time, cooling water flows from the external cooling tank used in combination with the cooling mandrel, and the cooling water directly contacts the outside of the molten tubular thin film to be cooled. The temperature of the internal water and the external water is preferably 30 ° C. or less, and particularly preferably 20 ° C. or less from the viewpoint of rapid cooling film formation. When the temperature is higher than 30 ° C., whitening of the raw material or poor appearance of the original material due to boiling of cooling water is caused, and stretching becomes gradually difficult.

The unstretched original film formed by the above method has an elongation percentage of 5% or more at 40 ° C. under a load of 0.5 kg / cm. In terms of stretchability, it is particularly desirable that the elongation percentage is 40% or more. If the elongation is less than 5%, not only will the stretching bubble fluctuate, but the stretching itself may be difficult. The 0.5 kg / cm load is a tension approximately corresponding to the stretching stress applied to the original fabric at the stretching start point.

(Manufacturing method of biaxially stretched PBT film) The unstretched PBT raw fabric needs to be transported to a stretching zone while maintaining an atmospheric temperature of 25 ° C. or lower, preferably 20 ° C. or lower. And the crystallinity of the unstretched original fabric immediately after film formation can be maintained. Control of crystallization up to the starting point of stretching can be said to be an important point in stably performing biaxial stretching of the PBT resin together with the film forming technique of the unstretched raw material.

Examples of the simultaneous biaxial stretching method include a tubular method and a tenter method, but the tubular method is particularly preferable from the viewpoint of balance of strength in the vertical and horizontal directions. FIG. 1 is a schematic view of a tubular method simultaneous biaxial stretching apparatus. The unstretched original fabric 1 guided to the stretching zone is inserted between a pair of low-speed nip rolls 2 and then heated with a stretching heater 3 while air is being pressed into it. By blowing air more, MD by the tubular method and TD simultaneous biaxially stretched film 7 were obtained. The draw ratio may be in the range of 2.7 to 4.0 times each of MD and TD, taking into account the stretching stability and the strength properties, transparency, and thickness uniformity of the obtained biaxially stretched PBT film. preferable. When the draw ratio is less than 2.7, the tensile strength and impact strength of the obtained biaxially stretched PBT film are not preferable. In addition, when it exceeds 4.0 times, excessive molecular chain distortion occurs due to stretching, and thus breakage and puncture frequently occur during stretching, and stable production cannot be achieved. The stretching temperature is preferably in the range of 40 to 80 ° C, particularly preferably 45 to 65 ° C. Since the unstretched original fabric manufactured at the high cooling rate has low crystallinity, it can be stably stretched at a relatively low stretching temperature. In high-temperature stretching exceeding 80 ° C., stretching bubbles are vigorously shaken and large stretching unevenness occurs, and a film having good thickness accuracy cannot be obtained. On the other hand, when the stretching temperature is less than 40 ° C., excessive stretch-oriented crystallization occurs due to low-temperature stretching, leading to whitening of the film and the like. By performing the biaxial stretching process in this way, a biaxially stretched PBT film having particularly improved strength properties and little anisotropy can be obtained.

The obtained biaxially stretched PBT film is heated in a heat roll system or a tenter system, or a heat treatment facility combining them for an arbitrary time, and heat treatment is performed at 180 to 240 ° C., particularly preferably 190 to 210 ° C. A biaxially stretched PBT film excellent in dimensional stability can be obtained. When the heat treatment temperature is higher than 220 ° C., the bowing phenomenon becomes too large and the anisotropy in the width direction increases, or the crystallinity becomes too high, resulting in a decrease in strength properties. On the other hand, when the heat treatment temperature is lower than 185 ° C., the thermal dimensional stability of the film is greatly reduced, so that the film is easily shrunk at the time of lamination or printing, which causes a practical problem.

The thickness of the biaxially stretched PBT film of the present invention is not particularly limited, but when used as a general converting film, it is 5 to 50 μm, preferably 10 to 20 μm.

The tensile strength at break in the four directions (0 ° (MD), 45 °, 90 ° (TD), 135 °) of the biaxially stretched PBT film is preferably 200 MPa or more. Properties such as impact resistance, puncture resistance, and suitability for secondary processing are significantly improved. Furthermore, in order to reduce the anisotropy, the ratio of the maximum value to the minimum value is 1. out of the tensile rupture strengths in four directions (0 ° (MD), 45 °, 90 ° (TD), 135 °). It is preferable to adjust to 5 or less, and particularly preferably 1.3 or less. On the other hand, the tensile elongation at break is from 50% to 150%, preferably from 70% to 140%, particularly preferably from 80% to 120%. If it is larger than 150% or smaller than 50%, it is not preferable because breakage or elongation of the film is likely to occur due to tension during printing or bonding to another substrate. A film having such characteristics can be stably obtained by the production method described above.

Although the biaxially stretched PBT film of the present invention can be used alone, it can be used as a converting film to be bonded to one or more other base materials. Typical examples include biaxially stretched nylon 6 film, biaxially stretched polypropylene film, biaxially stretched polyethylene terephthalate film, biaxially stretched ethylene-vinyl alcohol film, biaxially stretched polyethylene naphthalate film, biaxially stretched polystyrene film, Biaxially stretched aromatic polyamide film, biaxially stretched polyvinylidene chloride film, biaxially stretched polyvinyl alcohol film, various coat films, various vapor deposition films, unstretched polyethylene film, unstretched polypropylene film, unstretched polyvinyl chloride film, Ethylene-vinyl acetate film, ionomer film, other ethylene copolymer film, unstretched polyvinyl alcohol film, unstretched nylon 6 film, aluminum foil, copper foil, stainless steel foil, paper, Cloth, and foam polystyrene.

In addition, the biaxially stretched PBT film of the present invention can be used after being printed by a known printing method such as gravure printing, flexographic printing, or offset printing.

The biaxially stretched PBT film of the present invention is particularly suitable as a film for food packaging, a cold (room temperature) molding film for lithium ion secondary batteries, a pharmaceutical PTP, and the like, and a film for container molding and bonding of foods and the like. Can be used.

The present invention will be specifically described below with reference to examples and comparative examples.
<Example 1> (Production of biaxially stretched PBT film)
PBT resin pellets (homotype, melting point = 224 ° C., IV value = 1.26 dl / g) dried in a hot air dryer at 140 ° C. for 5 hours were melted in an extruder under conditions of cylinder and die temperatures of 210 to 260 ° C. The molten tubular thin film was extruded downward from the annular die by kneading. Subsequently, after folding through the outer diameter of the cooling mandrel with a calapsa roll, the film was drawn with a take-up nip roll at a speed of 1.2 m / min. The temperature of the cooling water in direct contact with the molten tubular thin film was 20 ° C. on both the inner side and the outer side, and the raw fabric cooling rate was 416 ° C./second. The unstretched raw material had a thickness of 130 μm and a folding diameter of 143 mm, and 1000 ppm of magnesium stearate was previously added to the PBT resin as a lubricant. The unstretched original fabric 1 formed into a film on the above conditions was conveyed to the low-speed nip roll 2 in 20 degreeC atmosphere, and the vertical and horizontal simultaneous biaxial stretching was performed with the tubular simultaneous biaxial stretching apparatus of the structure shown in FIG. The draw ratio was 3.0 times for MD and 2.8 times for TD, and the draw temperature was 60 ° C. Next, this biaxially stretched film 7 was put into a heat roll type and a tenter type heat treatment facility, respectively, and heat treated at 210 ° C. to obtain a biaxially stretched PBT film of the present invention. The biaxially stretched PBT film had a thickness of 15 μm.

(Measuring method of raw fabric cooling rate) The raw fabric cooling rate was calculated by the following formula. The molten thin film and the raw fabric temperature were measured with a contact-type radiation thermometer. The cooling start point is the part where the molten thin film comes into contact with the cooling water or the cooling device, and the cooling end point is the part where the temperature of the unstretched original fabric reaches 30 ° C.
Raw fabric cooling rate (° C./sec)=(molten film temperature immediately before the cooling start point−raw temperature of cooling end point) (° C.) / (Distance between cooling start point to cooling end point) (m) × cooling start point ~ Raw material passage speed between cooling end points (m / sec)

(Stability of stretched bubble) The bubble stability during stretching was visually evaluated in the following four stages.
A: There is almost no shaking of the stretched bubble, excellent stability, and continuous production is also possible.
○: The stretching bubble is slightly shaken, but there is no problem in continuous productivity.
Δ: Stretched bubble is greatly shaken and continuous production for a long time is difficult.
X: The stretched bubble bursts or the film breaks in a short time.

(Evaluation method of elongation rate of unstretched raw fabric at 40 ° C. under a load of 0.5 kg / cm) Using SEX nanotechnology-EXSTAR 6220, the unstretched raw fabric immediately after film formation cooled to −20 ° C. Under a constant load of 10 mm between chucks and 1400 mN / 3 mm test width, the temperature range of 0 to 200 ° C. was increased at a pitch of 10 ° C./min, and the elongation ratio of the unstretched raw fabric at each temperature was continuously measured. The elongation at 40 ° C. determined from the temperature curve of the unstretched original fabric elongation was 43%.

(Evaluation Method of Tensile Breaking Strength and Elongation of Biaxially Stretched PBT Film) The tensile breaking strength and elongation of the biaxially stretched PBT film are made by Orientec-Tensilon (RTC-1210-A), sample width is 15 mm, chuck Measurements were made in four directions of 0 ° C. (MD) direction / 45 ° direction / 90 ° (TD) direction / 135 ° direction under the conditions of a distance of 100 mm and a tensile speed of 200 mm / min. Table 1 shows the ratio of the maximum value to the minimum value among the tensile rupture strength in each direction, the rupture elongation, and the tensile rupture strength in four directions, which were obtained based on the obtained stress-strain curve.

<Examples 2-6, Comparative Examples 1-3> In Example 1, it carried out like Example 1 except having changed the draw ratio into the conditions described in Table 1.

<Examples 7 to 9, Comparative Examples 4 to 7> In Example 1, except that the film forming method of the unstretched original fabric or the cooling rate of the original fabric was changed to the conditions described in Table 1, the same as in Example 1. went.

<Example 10, comparative example 8> In Example 1, it carried out similarly to Example 1 except having changed the internal and external cooling water temperature at the time of unstretched original film formation into the conditions described in Table 1.

As shown in Table 1, the extruded PBT resin melt was rapidly formed into a film at an extremely high cooling rate of 200 ° C./second or more, and the elongation rate at 40 ° C. under a load of 0.5 kg / cm was 5% or more. By stretching the stretched fabric biaxially and transversely by the tubular method, productivity is improved to a level where there is almost no shaking of stretched bubbles and stability is sufficient, and continuous operation is sufficiently possible. Moreover, it was found that the obtained biaxially stretched PBT film had characteristics that there was little anisotropy, high tensile breaking strength, and low tensile breaking elongation.

Fields and applications in which the biaxially stretched PBT film of the present invention is used include low anisotropy, good mechanical properties and dimensional stability, and lamination or printing with one or more other substrates. Therefore, it can be used as a converting film for packaging general foods such as dried foods, marine foods, incense foods, and retort foods. In addition, it has high mechanical strength such as tensile strength, excellent cold formability such as stretch forming or deep drawing, and good moisture resistance and acid resistance, so moisture and oxygen can penetrate. It can also be used in a main base material for a battery case exterior material of a lithium ion secondary battery that uses an electrolyte solution that dislikes extremely, and other primary batteries and secondary batteries. Furthermore, it can be suitably used as a main base material for packaging materials for thermoforming that can be deep-drawn for various shapes of containers such as lunch boxes, trays, baskets and the like.

DESCRIPTION OF SYMBOLS 1 Unstretched raw fabric 2 Low speed nip roll 3 Stretching heater 4 Cooling shoulder air ring 5 Carapsa roll 6 High speed nip roll 7 Biaxially stretched film

Claims (11)

Biaxial, characterized in that all four directions (0 ° (MD), 45 °, 90 ° (TD), 135 °) have a tensile breaking strength of 200 MPa or more and a tensile breaking elongation of 50% to 150%. Stretched polybutylene terephthalate film. The ratio between the maximum value and the minimum value among the tensile rupture strengths in four directions (0 ° (MD), 45 °, 90 ° (TD), 135 °) is 1.5 or less. 2. A biaxially stretched polybutylene terephthalate film described in 1. Immediately after melt-extrusion of polybutylene terephthalate resin, it is obtained by simultaneously biaxially stretching the unstretched raw material obtained by rapid cooling and film formation at a cooling rate of 200 ° C./second or more in the longitudinal and lateral directions. The biaxially stretched polybutylene terephthalate film according to claim 1 or 2. The biaxially stretched polybutylene terephthalate film according to claim 3, wherein the cooling rate is 250 ° C./second or more. The biaxially stretched polybutylene terephthalate film according to claim 3, wherein the cooling rate is 350 ° C./second or more. The biaxially stretched polybutylene terephthalate film according to any one of claims 3 to 5, wherein an elongation percentage of the unstretched raw fabric at 40 ° C under a load of 0.5 kg / cm is 5% or more. . The biaxially stretched polybutylene terephthalate film according to any one of claims 3 to 5, wherein the elongation ratio of the unstretched raw fabric at 40 ° C under a load of 0.5 kg / cm is 30% or more. . 8. The method according to claim 3, wherein the rapid cooling film formation is performed by bringing water at 30 ° C. or less into direct contact with both surfaces of polybutylene terephthalate immediately after being melt-extruded into a film shape. Axial stretched polybutylene terephthalate film. The biaxially stretched polybutylene terephthalate film according to any one of claims 1 to 8, wherein the biaxially stretched polybutylene terephthalate film is used in combination with any one or two or more of the following (a).
(A) Biaxially stretched nylon 6 film, biaxially stretched polypropylene film, biaxially stretched polyethylene terephthalate film, biaxially stretched ethylene-vinyl alcohol film, biaxially stretched polyethylene naphthalate film, biaxially stretched polystyrene film, biaxially stretched Aromatic polyamide film, biaxially stretched polyvinylidene chloride film, biaxially stretched polyvinyl alcohol film, various coated films, various deposited films, unstretched polyethylene film, unstretched polypropylene film, unstretched polyvinyl chloride film, ethylene-acetic acid Vinyl film, ionomer film, other ethylene copolymer film, unstretched polyvinyl alcohol film, unstretched nylon 6 film, aluminum foil, copper foil, stainless steel foil, paper, nonwoven fabric, foamed poly Styrene. The biaxially stretched polybutylene terephthalate film according to any one of claims 1 to 9, which is used by printing. The biaxially stretched polybutylene terephthalate film according to any one of claims 1 to 10, which is used as a base material for food packaging or drawing.

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