JP2018203922A - Biaxial oriented polybutylene terephthalate film having easily tearing property and flex resistance - Google Patents

Abstract

To provide a biaxial oriented polybutylene terephthalate film good in tear linear property at least along MD of the film and excellent in pinhole resistance even under a severe film manufacturing condition such as high temperature or high shear.SOLUTION: A polybutylene terephthalate resin composition containing a polybutylene terephthalate resin, a polyester-based elastomer of 1 to 30 mass% based on the polybutylene terephthalate resin, and at least one kind of reaction inhibitor selected from a group consisting of a carbodiimide compound and a phosphoric acid ester compound of 0.01 to 1.0 mass% based on total 100 mass% of the polybutylene terephthalate resin and the polyester-based elastomer, is used as a main raw material of a biaxial oriented polybutylene terephthalate film and biaxially oriented in both directions of length and width same time under a specific orientation condition.SELECTED DRAWING: None

Description

  The present invention relates to an improvement in deterioration of film properties due to a reaction between a polyester resin and an elastomer component in a film forming process in which an elastomer component is added to a polyester resin for the purpose of imparting easy tearability. More specifically, by preventing the reaction between the polyester resin and the elastomer component due to high temperature and high shear in the film forming process, the effect of adding the elastomer component even under severe film forming conditions [at least the length of the film The present invention relates to a biaxially stretched polybutylene terephthalate (hereinafter also referred to as OPBT) film capable of exhibiting good tear linearity along the direction (hereinafter also referred to as MD) and good pinhole resistance]. is there.

  Polybutylene terephthalate (hereinafter also referred to as PBT) resin is a typical resin having excellent mechanical strength, heat resistance, chemical resistance, flexibility, transparency, surface glossiness, weather resistance, low water absorption, etc. Engineering plastic. In particular, a remarkable feature of polybutylene terephthalate resin is that it has a remarkably high crystallization speed compared to other general-purpose engineering plastics. Taking advantage of this feature, injection molding applications such as various automobile parts and electrical / electronic parts In recent years, it has been widely used for the purpose of high cycleability.

In recent years, a method for producing a biaxially stretched film that has been considered difficult due to its high crystallization rate of PBT resin has been reported. In Patent Document 1, Patent Document 2, and Patent Document 3, a tubular method is reported. In the simultaneous biaxial stretching method, a method for forming an unstretched raw film having relatively low crystallinity, a method for maintaining the low crystal state until the stretching process, and optimization of various stretching conditions such as a stretching temperature and a stretching ratio. The biaxially stretched polybutylene terephthalate film having relatively high mechanical strength and low anisotropy can be obtained by using the same film forming and stretching techniques. It has been reported that it can be obtained.
However, the packaging bag made from the OPBT film obtained by the above method has poor tear openability, particularly tear linearity when opened by hand, and may cause the contents to scatter or break when opened. For this reason, it may be a fatal problem depending on the application.

  As a means of improving the tear linearity, an elastomer component that is generally phase-separated and dispersed in an island shape is added to the resin as a main raw material, and tearing is performed along the island structure. A method for expressing linearity has been proposed. For example, in Patent Documents 4 and 5, by using a polybutylene terephthalate resin composition in which a polyester-based elastomer is blended with a polybutylene terephthalate resin as a raw material, at least a film of the film is stretched simultaneously in the vertical and horizontal directions under specific stretching conditions. It has been reported that an OPBT film having good tear linearity along MD, little anisotropy, and excellent mechanical strength and transparency can be obtained. In addition, Patent Documents 6 to 11 disclose a component that is partially phase-separated and dispersed in an island shape with respect to polyethylene terephthalate resin or copolymer polyethylene terephthalate resin, for example, other polyesters such as polyester-based elastomers, polycarbonates, etc. A method has been proposed in which tearing linearity is developed along the major axis direction of the island-like structure by biaxially stretching using a raw material obtained by blending other resins with 2 to 3 components.

JP-A-53-79969 Japanese Patent Laid-Open No. 5-261809 JP-A-5-269843 JP 2013-91693 A Japanese Patent Application Laid-Open No. 2006-191009 JP 2006-150617 A JP 2006-297653 A JP 2004-18742 A JP 2002-003707 A JP 2006-241398 A JP 2006-247870 A

  However, in the method of expressing tear linearity by adding an elastomer component as described in Patent Documents 6 to 11, polybutylene terephthalate resin is used under severe film forming conditions that require high extrusion temperature and high shear. There is a possibility that the reaction between the polyester elastomer and the polyester elastomer progresses and the compatibility is changed (the phase separation structure is lost), and the conventional tear linearity is impaired. On the other hand, in order to suppress the reaction between polybutylene terephthalate and polyester elastomer, if the film is not formed at a high extrusion temperature, the phase separation structure can be maintained, so that tearing linearity can be obtained, but the production rate is at a practical level. Since the high shear is applied, the phase separation structure may be lost. In addition, the addition of the elastomer component originally improves the pinhole resistance of the biaxially stretched polybutylene terephthalate film, but the reaction of the elastomer component may cause a change in the molecular structure, which may deteriorate the pinhole resistance. . Therefore, when the tear linearity and pinhole resistance are improved with a mixed film of polybutylene terephthalate and polyester elastomer, the reaction between such polybutylene terephthalate and polyester elastomer is suppressed, and the phase separation structure is improved. It is necessary to take measures to ensure that it can be maintained, but as far as we know, the problem has not yet been solved.

  As a result of intensive investigations to solve the problems of degradation of tear linearity and pinhole resistance due to the reaction between polybutylene terephthalate and a polyester-based elastomer due to a load such as high temperature and high shear, the present inventors have found that polybutylene terephthalate. 1 to 30% by weight of a polyester elastomer based on the resin, the polybutylene terephthalate resin, and 0.01 to 1.0% by weight based on a total of 100% by weight of the polybutylene terephthalate resin and the polyester elastomer. By using a polybutylene terephthalate resin composition containing at least one reaction inhibitor selected from the group consisting of a carbodiimide compound and a phosphate ester compound as a raw material, and simultaneously and longitudinally and transversely biaxially stretching under specific stretching conditions. Harsh, high temperature and high shear Also in the film conditions, at least the film along the MD direction tear linearity is good, it found to be able to obtain a OPBT film excellent pinhole resistance, and have completed the present invention.

That is, the present invention provides the following biaxially stretched polybutylene terephthalate film. [1]
0.01 to 1.0 based on polybutylene terephthalate resin, 1 to 30% by mass of polyester elastomer based on the polybutylene terephthalate resin, and 100% by mass in total of the polybutylene terephthalate resin and polyester elastomer. Made by using a polybutylene terephthalate resin composition containing at least one reaction inhibitor selected from the group consisting of a carbodiimide compound and a phosphate ester compound in mass%, and has tear linearity at least in the longitudinal direction. Biaxially stretched polybutylene terephthalate film.
[2]
The biaxially stretched polybutylene terephthalate film according to [1], wherein the carbodiimide compound is an aliphatic polycarbodiimide compound.
[3]
The biaxially stretched polybutylene terephthalate film according to [1], wherein the phosphoric acid ester compound has a melting point of 60 to 80 ° C.
[4]
The biaxially stretched polybutylene terephthalate film according to any one of [1] to [3], wherein the polyester elastomer has a glass transition point of -100 ° C to 5 ° C.
[5]
The biaxially stretched polybutylene terephthalate film according to any one of [1] to [4], wherein the polyester elastomer is a polyester polyether block copolymer.
[6]
The biaxially stretched polybutylene terephthalate film has a minimum tear strength measured in accordance with JIS K 7128-1 of less than 1.0-10.0 N / mm, and the tear linearity in the measurement direction of the minimum tear strength The biaxially stretched polybutylene terephthalate film according to any one of [1] to [5], comprising:
[7]
The biaxially stretched polybutylene terephthalate film is characterized in that, in a gelbo flex test under an environment of 5 ° C. and 40%, the number of pinholes after bending 1000 times is 10 or less, [1]-[ 6] The biaxially stretched polybutylene terephthalate film according to any one of [6].
[8]
The biaxially stretched polybutylene terephthalate film has tensile strengths in all four directions (0 ° (MD), 45 °, 90 ° (TD), 135 °) of 170 MPa or more, [1] to [7] The biaxially stretched polybutylene terephthalate film according to any one of [7].

  According to the present invention, the reaction between polybutylene terephthalate and a polyester elastomer is suppressed even under severe film formation conditions such as high temperature and high shear, and the tear linearity is good at least along the MD of the film, and pinhole resistance It became possible to obtain an OPBT film having excellent properties.

FIG. 1 is a schematic view of a tubular simultaneous biaxial stretching apparatus. FIG. 2 is a schematic view of a tear linearity evaluation method.

Below, the form for implementing this invention is demonstrated.
(Raw material for OPBT film)
The main raw material used for the OPBT film is not particularly limited as long as it is a polyester having butylene terephthalate as a main repeating unit, but specifically, 1,4-butanediol as a glycol component, as a dibasic acid component A homotype mainly composed of terephthalic acid is preferred. 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. Those having a range of ˜225 ° C. and an IV value of 1.15 to 1.30 dl / g are particularly preferable.

  The present invention contains a polybutylene terephthalate resin, a polyester-based elastomer partially phase-separated from the polybutylene terephthalate resin and dispersed in an island shape, and a carbodiimide compound and / or a phosphate ester compound as a reaction inhibitor. Using the polybutylene terephthalate resin composition as a raw material, the phase-separated structure is maintained even under severe film formation conditions such as high temperature and high shear by simultaneous longitudinal and transverse biaxial stretching under specific stretching conditions. Tear linearity can be expressed along the major axis direction of the island structure.

  Content of the said polyester-type elastomer is 1-30 mass% based on polybutylene terephthalate resin, Preferably it is 5-30 mass%, More preferably, it is 5-25 mass%. If the content of the polyester-based elastomer is less than 1% by mass, the tearing linearity is not sufficiently exhibited, and if it exceeds 30% by mass, the mechanical strength of the OPBT film is lowered and there is a possibility that a practical problem may occur.

  As content of the at least 1 sort (s) of reaction inhibitor chosen from the group which consists of the said carbodiimide compound and a phosphate ester compound, 0.01-1.0 based on 100 mass% of total of polybutylene terephthalate resin and a polyester-type elastomer. It is mass%, Preferably it is 0.05-0.8 mass%, More preferably, it is 0.1-0.5 mass%. If the content of the reaction inhibitor is less than 0.01% by mass, the effect is weak, and it is difficult to develop tear linearity that can be easily and linearly torn. If it exceeds 1.0% by mass, the effect of improving the tear linearity hardly occurs, and the aggregate of the reaction inhibitor may be generated as an undissolved material. The reaction inhibitor can be added by compounding or by adding it in the form of powder as it is, and the same effect can be obtained.

Examples of the carbodiimide compound used in the present invention include a monocarbodiimide compound having one carbodiimide group in the same molecule and a polycarbodiimide compound having two or more carbodiimide groups in the same molecule.
Specific examples of the monocarbodiimide compound include N, N′-di-2,6-diisopropylphenylcarbodiimide, N, N′-di-o-tolylcarbodiimide, N, N′-diphenylcarbodiimide, N, N′-dioctyl. Decylcarbodiimide, N, N′-di-2,6-dimethylphenylcarbodiimide, N-tolyl-N′-cyclohexylcarbodiimide, N, N′-di-2,6-di-tert-butylphenylcarbodiimide, N-tolyl -N'-phenylcarbodiimide, N, N'-di-p-nitrophenylcarbodiimide, N, N'-di-p-aminophenylcarbodiimide, N, N'-di-p-hydroxyphenylcarbodiimide, N, N ' -Di-cyclohexylcarbodiimide, N, N'-di-p-tolylcarbodiimide, p-phenylene-bis -Di-o-tolylcarbodiimide, p-phenylene-bis-dicyclohexylcarbodiimide, hexamethylene-bis-dicyclohexylcarbodiimide, ethylene-bis-diphenylcarbodiimide, N, N'-benzylcarbodiimide, N-octadecyl-N'-phenylcarbodiimide, N-benzyl-N′-phenylcarbodiimide, N-octadecyl-N′-tolylcarbodiimide, N-cyclohexyl-N′-tolylcarbodiimide, N-phenyl-N′-tolylcarbodiimide, N-benzyl-N′-tolylcarbodiimide, N, N′-di-o-ethylphenylcarbodiimide, N, N′-di-p-ethylphenylcarbodiimide, N, N′-di-o-isopropylphenylcarbodiimide, N, N′-di-p-isopropylphenyl Carbo Imido, N, N′-di-o-isobutylphenylcarbodiimide, N, N′-di-p-isobutylphenylcarbodiimide, N, N′-di-2,6-diethylphenylcarbodiimide, N, N′-di- 2-ethyl-6-isopropylphenylcarbodiimide, N, N′-di-2-isobutyl-6-isopropylphenylcarbodiimide, N, N′-di-2,4,6-trimethylphenylcarbodiimide, N, N′-di -2,4,6-triisopropylphenylcarbodiimide, N, N'-di-2,4,6-triisobutylphenylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, tert-butylisopropylcarbodiimide, di- β-naphthylcarbodiimide and And di -tert- butyl carbodiimide.

  Among the monocarbodiimide compounds, N, N′-di-2,6-diisopropylphenylcarbodiimide is particularly preferable from the viewpoint of excellent hydrolysis resistance and durability improvement effects.

  Examples of the polycarbodiimide compound include poly (p-phenylenecarbodiimide), poly (m-phenylenecarbodiimide), poly (methylphenylenecarbodiimide), poly (diisopropylphenylenecarbodiimide), poly (methyldiisopropylphenylenecarbodiimide), poly (1,3 , 5-triisopropylphenylenecarbodiimide), poly (1,3,5-triisopropylphenylene-co-1,5-diisopropylphenylenecarbodiimide), poly (4,4′-diphenylmethanecarbodiimide) and the like; poly Aliphatic polycarbodiimides such as (4,4′-dicyclohexylmethanecarbodiimide); Alicyclic polycarbodiimides such as poly (dicyclohexylmethanecarbodiimide) That.

Among the polycarbodiimide compounds, aliphatic polycarbodiimide is preferable, and poly (4,4′-dicyclohexylmethanecarbodiimide) is particularly preferable.
As the poly (4,4′-dicyclohexylmethanecarbodiimide), commercially available Carbodilite (registered trademark) LA-1 [manufactured by Nisshinbo Chemical Co., Ltd.] or the like can be used.

  These carbodiimide compounds may be used alone or in combination of two or more.

The phosphate ester compound used in the present invention is not particularly limited as long as it has a phosphate ester structure, but an alkyl phosphate having a melting point of 60 to 80 ° C. is preferable for the expression of good tear linearity. . The alkyl group is preferably an alkyl group having 8 to 36 carbon atoms, more preferably an alkyl group having 10 to 30 carbon atoms, and particularly preferably an alkyl group having 12 to 22 carbon atoms.
Examples of such an alkyl group include octyl group, 2-ethylhexyl group, secondary octyl group, nonyl group, secondary nonyl group, decyl group, secondary decyl group, undecyl group, secondary undecyl group, dodecyl group ( Lauryl group), secondary dodecyl group, tridecyl group, isotridecyl group, secondary tridecyl group, tetradecyl group, secondary tetradecyl group, hexadecyl group, secondary hexadecyl group, stearyl group, isostearyl group, eicosyl group, docosyl group (behenyl) Group), tetracosyl group, hexacosyl group, octacosyl group, triacontyl group, dotriacontyl group, tetratriacontyl group, 2-butyloctyl group, 2-butyldecyl group, 2-hexyloctyl group, 2-octyldecyl group, 2-hexyl Dodecyl group, 2-octyldodecyl group, 2-decyltetra Sill group, 2-dodecyl-hexadecyl group, 2-hexadecyl octadecyl, and 2-tetradecyl octadecyl group and the like. Of these, stearyl groups and isostearyl groups are preferred from the viewpoint of dispersibility in polybutylene terephthalate resins.

Alkyl phosphate esters include monooctyl phosphate, mono (2-ethylhexyl) phosphate, monodecyl phosphate, monolauryl phosphate, monostearyl phosphate, monobehenyl phosphate, dioctyl phosphate Examples include esters, bis (2-ethylhexyl) phosphate, dilauryl phosphate, and distearyl phosphate. These alkyl phosphate esters may be used alone or in combination of two or more.
Among these, phosphoric acid monostearyl ester and phosphoric acid distearyl ester are preferable, and a mixture of phosphoric acid monostearyl ester and phosphoric acid distearyl ester is more preferable.
As a mixture of the phosphoric acid monostearyl ester and the phosphoric acid distearyl ester, commercially available ADK STAB (registered trademark) AX-71 [manufactured by ADEKA Corporation] and the like can be used.

  The polyester-based elastomer used in the present invention preferably has a glass transition point in the range of −100 to 5 ° C., more preferably −50 to 5 in order to maintain extremely good tear linearity and optimum mechanical strength. A range of 0 ° C. is particularly preferable. When a polyester elastomer having a glass transition point lower than −100 ° C. is used, the compatibility with polybutylene terephthalate is remarkably reduced, and the transparency and strength properties of the OPBT film are lowered and the productivity of the elastomer component is dropped. Degradation may occur. On the other hand, when the glass transition point is higher than 5 ° C., the impact resistance may be lowered or the compatibility may be too good, and sufficient tear linearity may not be exhibited.

The types of polyester elastomers are: A polyester polyether block copolymer using an aromatic polyester for the hard segment and an aliphatic polyether for the soft segment, or an aromatic polyester for the hard segment, and an aliphatic for the soft segment. A polyester polyester block copolymer using polyester is preferred. Here, the hard segment is a polyester obtained by polycondensation reaction of aromatic dicarboxylic acid and alkylene glycol, and specific examples thereof include polyethylene terephthalate and polybutylene terephthalate. Polyalkylene ether glycol used as a soft segment of the polyester polyether block copolymer is, for example, polyethylene glycol, poly (1,2 and 1,3 propylene ether) glycol, polytetramethylene glycol, polyhexamethylene ether glycol, ethylene oxide. And a block or random copolymer of propylene oxide and a block or random copolymer of ethylene oxide and tetrahydrofuran. Among these, a block copolymer of polybutylene terephthalate and polytetramethylene glycol is particularly preferable.
On the other hand, the aliphatic polyester used as the soft segment of the polyester polyester block copolymer is, for example, a polyester obtained from an aliphatic dicarboxylic acid having 2 to 12 carbon atoms and an aliphatic glycol having 2 to 10 carbon atoms, specifically, Include polyethylene adipate, polytetramethylene adipate, polyethylene sebacate, polyneopentyl sebacate, polyhexamethylene azelate, poly-ε-caprolactone, and the like. The polyester polyether block copolymer and the polyester polyester block copolymer may be of any type in which various polar groups are grafted for the purpose of improving the compatibility with the polybutylene terephthalate resin as the base resin.

  The polybutylene terephthalate resin composition used in the present invention includes a lubricant, an antiblocking agent, an inorganic extender, an antioxidant, an ultraviolet absorber, an antistatic agent, a flame retardant, a plasticizer, and a colorant as necessary. Additives such as a crystallization inhibitor and a crystallization accelerator may be added. In addition, the polyester resin pellets used are sufficiently pre-dried so that the moisture content is 0.05% by mass or less, preferably 0.01% by mass or less before heating and melting in order to avoid a decrease in viscosity due to hydrolysis during heating and melting. It is preferable to use after carrying out.

(Method for producing unstretched polybutylene terephthalate)
In order to stably produce an OPBT film, it is necessary to suppress crystallization of an unstretched raw fabric before stretching as much as possible. When the extruded polybutylene terephthalate melt is cooled to form a film, the polybutylene terephthalate The crystallization temperature region is cooled at a certain rate or higher, 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 polybutylene terephthalate resin is melt-kneaded by an extruder set at an extrusion temperature of 280 ° C. In the case of T-die film formation, the sheet-like molten resin is immersed in a water tank and directly cooled by water. 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.

(Manufacturing method of OPBT film)
Polybutylene terephthalate unstretched raw fabric needs to be transported to a stretching zone while maintaining an atmospheric temperature of 25 ° C. or less, preferably 20 ° C. or less. Under the temperature control, unstretched immediately after film formation regardless of residence time. The crystallinity of the original fabric can be maintained. Control of crystallization up to the starting point of stretching is an important point for stably performing biaxial stretching of the polybutylene terephthalate resin together with the film forming technique of the unstretched raw fabric.

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 are obtained. As for the draw ratio, the MD is stretched at a stretch ratio of 3.0 times or more, preferably 3.2 times or more, and then the TD is stretched under the condition of the MD stretch ratio or less. The upper limit of the MD draw ratio is preferably 4.5 times or less, and the lower limit of the TD draw ratio is preferably 2.5 times or more. When the draw ratio of MD is less than 3.0 times and / or the draw ratio in the TD direction is less than 2.5 times, the tensile strength and impact strength are insufficient, which is not preferable. In addition, when the MD draw ratio exceeds 4.5 times, excessive molecular chain distortion occurs due to stretching, and thus breakage and puncture 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 biaxial stretching in this way, it is possible to obtain a biaxially stretched polybutylene terephthalate film having particularly improved strength properties and low anisotropy.

  The obtained OPBT film is subjected to heat treatment at 180 to 240 ° C., particularly preferably 190 to 210 ° C. for any time in a heat roll system or a tenter system, or a heat treatment facility that combines them, and thermal dimensional stability is achieved. A biaxially stretched polybutylene terephthalate film excellent in the above can be obtained. When the heat treatment temperature is higher than 240 ° C., the bowing phenomenon becomes too great 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 180 ° 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 OPBT film is not particularly limited, but when used as a general converting film, it is 5 to 50 μm, preferably 10 to 20 μm.

In the OPBT film of the present invention, the polyester-based elastomer is dispersed in the form of elongated islands in the polybutylene terephthalate resin, and linear tearing properties are developed in the direction of the major axis of the island-shaped dispersion. For all directions of the OPBT film in the present invention, JIS
The minimum value when the tear strength is measured according to K 7128-1 is 1.0 to 10.0 N / mm, preferably 3.0 to 10.0 N / mm, more preferably 4.0. 10.0 N / mm. When the minimum value of tear strength is less than 1.0 N / mm, the OPBT film may be easily broken at the time of packaging and may be difficult to handle. On the other hand, if the minimum value of the tear strength exceeds 10.0 N / mm, the tear strength is too strong and it may be difficult to open by hand.

  The tensile strength at break in the four directions (0 ° (MD), 45 °, 90 ° (TD), 135 °) of the OPBT film in the present invention is 170 MPa or more, preferably 180 MPa or more. Preferably all are 190 MPa or more, and particularly preferably all are 200 MPa or more. In the OPBT film according to the present invention, the ratio between the maximum value and the minimum value is 1.5 or less among the tensile breaking strengths in the four directions (0 ° (MD), 45 °, 90 ° (TD), 135 °). , Preferably 1.3 or less, particularly preferably 1.1 or less.

  The pinhole resistance of the OPBT film in the present invention can be measured using a gelbo flex tester. For example, the obtained OPBT film is cut into a predetermined size (for example, 210 mm × 297 mm), and a cylinder After forming into a shape and fixing to a gel bot tester, the number of pinholes after bending 1000 times with a cycle of 42 reciprocations / min under 5 ° C. × 40% RH conditions is measured. The OPBT film of the present invention has 10 or less pinholes after bending 1000 times, preferably 7 or less, more preferably 5 in a gelbo flex test at 5 ° C. and 40% environment. Or less, particularly preferably 3 or less. If the number of pinholes is larger than 10, there is a risk that the probability of occurrence of cracks or pinholes during transportation or processing of the OPBT film before use increases.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Each physical property of the film was determined by the following method.
(1) Tear linearity A4 size was cut out from the film with the MD direction of the OPBT film as the long side, and it was torn by 12 cm along the MD direction at an angle of 130 to 145 ° and a tearing speed of 500 to 1000 mm / min. The maximum deviation width between the cut line and the reference straight line along the MD direction was measured (see FIG. 2). Each sample was torn ten times, and from the results, tear linearity was evaluated according to the following criteria.
◯: 7 or more out of 10 pieces had a deviation width of less than 3 mm, and showed good tear linearity. X: Only 6 pieces out of 10 pieces had a deviation width of less than 3 mm, and the tear linearity was poor (2) Tear Strength Tear strength was measured four times per sample for each of MD and TD of the film according to JIS K 7128-1 (trouser tear method), and the average value is shown in Table 1.
(3) Impact strength The impact strength was measured 6 times per sample using an impact tester [manufactured by Toyo Seiki Seisakusho], and the average value is shown in Table 1.
(4) Bending resistance The OPBT film was sampled in A4 size with the MD direction as the long side, and bent 1000 times in an environmental test room at 5 ° C x 40% using a gelbo flex tester [manufactured by Tester Sangyo Co., Ltd.] The number of pinholes was measured four times per sample, and the average value is shown in Table 1. The test speed was 42 reciprocations / minute, the stroke distance was 152.4 mm, and the twist angle was 440 °.
(5) Tensile breaking strength Tensile breaking strength is 0 under the conditions of using a Tensilon universal testing machine (Model: RTC-1210A) manufactured by Orientec Co., Ltd., with a sample width of 15 mm, a chuck interval of 100 mm, and a tensile speed of 200 mm / min. Measurement was carried out for each of the four directions of ° C (MD) direction / 45 ° direction / 90 ° (TD) direction / 135 ° direction.

The polybutylene terephthalate resin, polyester elastomer and reaction inhibitor used in Examples, Comparative Examples and Reference Examples are as follows.
<Polybutylene terephthalate>
Toraycon (registered trademark) 1400S [manufactured by Toray Industries, Inc.]
<Polyester elastomer: Polyester polyether block copolymer>
Hytrel (registered trademark) 4777 (glass transition point: -35 ° C.) [manufactured by Toray DuPont Co., Ltd.]
Hytrel (registered trademark) 5577 (glass transition point: −20 ° C.) [manufactured by Toray DuPont Co., Ltd.]
<Carbodiimide compound>
Carbodilite (registered trademark) LA-1 [Nisshinbo Chemical Co., Ltd.]
<Phosphate compound>
ADK STAB (registered trademark) AX-71 (melting point: 71 ° C.) [manufactured by ADEKA Corporation]

<Example 1> (Production of OPBT film)
Polybutylene terephthalate resin pellets (homotype, melting point = 224 ° C., IV value = 1.26 dl / g) and 7% by mass of polyester elastomer based on polybutylene terephthalate resin pellets [Hitrel (registered by Toray DuPont) Trademark) 4777] and 0.05% by mass of carbodiimide compound [Carbodilite (registered trademark) LA-1 manufactured by Nisshinbo Chemical Co., Ltd.] based on 100% by mass of the total of polybutylene terephthalate resin pellets and polyester elastomer. To prepare a polybutylene terephthalate resin composition, which is dried in a hot air dryer at 140 ° C. for 5 hours, and melt-kneaded by an extruder set at an extrusion temperature of 280 ° C. Extruded to. 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 185 μm and a folding diameter of 143 mm, and 600 ppm of magnesium stearate was previously added as a lubricant to the polybutylene terephthalate resin composition. 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 3.2 times for MD and 3.2 times for TD, and the draw temperature was 70 ° C. Next, this biaxially stretched film 7 was put into a heat roll type and tenter type heat treatment facility, respectively, and heat treated at 210 ° C. to obtain an OPBT film of the present invention. The OPBT film had a thickness of 15 μm.

(Measurement method of raw fabric cooling rate)
The raw fabric cooling rate was calculated by the following formula. The molten tubular thin film temperature and the raw fabric temperature were measured with a contact-type radiation thermometer. The cooling start point refers to the part where the molten tubular thin film comes into contact with the cooling water or the cooling device, and the cooling end point refers to the part where the temperature of the unstretched original fabric reaches 30 ° C.
Raw fabric cooling rate (° C./second)=(melted tubular thin film temperature just before the cooling start point−raw temperature of cooling end point) (° C.) / (Distance between cooling start point to cooling end point) (m) × cooling start Speed of original fabric between point and end of cooling (m / sec)

<Examples 2 to 4>
In Example 1, it carried out like Example 1 except having changed the addition amount of the polyester-type elastomer with respect to polybutylene terephthalate and the addition amount of the reaction inhibitor into the conditions described in Table 1.

<Examples 5-7>
In Example 1, except that the type of reaction inhibitor was changed to a phosphate ester compound [ADEKA STAB (registered trademark) AX-71 manufactured by ADEKA, melting point 71 ° C.], and the addition amount described in Table 1 was changed. The same operation as in Example 1 was performed.

<Examples 8 to 10>
In Example 1, it carried out like Example 1 except having changed the kind of polyester-type elastomer into Hytrel (trademark) 5577, and having changed to the addition amount described in Table 1.

<Comparative Example 1>
In Example 1, it carried out like Example 1 except not adding a reaction inhibitor.

<Comparative Example 2>
In Example 1, it carried out like Example 1 except not adding a polyester-type elastomer and reaction inhibitor.

<Reference Example 1>
In Example 1, the reaction inhibitor was not added, and the extrusion temperature was further set at −20 ° C. than in Example 1. Other than that was carried out in the same manner as in Example 1.

<Reference Example 2>
In Example 1, the polyester-based elastomer and the reaction inhibitor were not added, and the extrusion temperature was further set at −20 ° C. than in Example 1. Other than that was carried out in the same manner as in Example 1.

As shown in Table 1, by adding at least one reaction inhibitor selected from the group consisting of a specific amount of a polyester elastomer, a carbodiimide compound and a phosphate ester compound to polybutylene terephthalate as a main raw material, polybutylene It was found that the reaction between terephthalate and the polyester-based elastomer is suppressed, and an OPBT film having tearing linearity and excellent pinhole resistance can be obtained even under severe film forming conditions.

  Since the biaxially stretched polybutylene terephthalate film of the present invention has excellent tear linearity at least along the MD direction of the film and is also excellent in pinhole resistance, the biaxially stretched polybutylene terephthalate film of the present invention Can be used as a converting film for general food packaging that requires tear opening and tearing linearity and pinhole resistance.

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 (8)

  0.01 to 1.0 based on polybutylene terephthalate resin, 1 to 30% by mass of polyester elastomer based on the polybutylene terephthalate resin, and 100% by mass in total of the polybutylene terephthalate resin and polyester elastomer. Made by using a polybutylene terephthalate resin composition containing at least one reaction inhibitor selected from the group consisting of a carbodiimide compound and a phosphate ester compound in mass%, and has tear linearity at least in the longitudinal direction. Biaxially stretched polybutylene terephthalate film.   The biaxially stretched polybutylene terephthalate film according to claim 1, wherein the carbodiimide compound is an aliphatic polycarbodiimide compound.   The biaxially stretched polybutylene terephthalate film according to claim 1, wherein the phosphoric ester compound has a melting point of 60 to 80 ° C.   The biaxially stretched polybutylene terephthalate film according to any one of claims 1 to 3, wherein the polyester-based elastomer has a glass transition point of -100 ° C to 5 ° C.   The biaxially stretched polybutylene terephthalate film according to any one of claims 1 to 4, wherein the polyester elastomer is a polyester polyether block copolymer.   The biaxially stretched polybutylene terephthalate film has a minimum tear strength measured in accordance with JIS K 7128-1 of less than 1.0-10.0 N / mm, and the tear linearity in the measurement direction of the minimum tear strength The biaxially stretched polybutylene terephthalate film according to any one of claims 1 to 5, wherein   The biaxially stretched polybutylene terephthalate film has a number of pinholes after bending 1000 times in a gelbo flex test under an environment of 5 ° C and 40%, wherein the number of pinholes is 10 or less. The biaxially stretched polybutylene terephthalate film according to any one of the above. The tensile strength at break in all four directions (0 ° (MD), 45 °, 90 ° (TD), 135 °) of the biaxially stretched polybutylene terephthalate film is 170 MPa or more. 8. The biaxially stretched polybutylene terephthalate film according to any one of 7 above.

Images