JP6901214B2 - Biaxially stretched polybutylene terephthalate film with easy tearing and bending resistance - Google Patents

Description

The present invention relates to an improvement in deterioration of film physical properties due to a reaction between a polyester resin and an elastomer component in a film forming step of adding an elastomer component 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 shearing 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]. It relates to a biaxially stretched polybutylene terephthalate (hereinafter, also referred to as OPBT) film capable of exhibiting [the effect of good tear linearity and good pinhole resistance along the direction (hereinafter, also referred to as MD)]. 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, and low water absorption. Engineering plastic. In particular, a noteworthy feature of polybutylene terephthalate resin is that it has a significantly higher crystallization rate than other general-purpose engineering plastics, and by taking advantage of this feature, it is used for injection molding of various automobile parts and electrical / electronic parts. It has been widely used in recent years for the purpose of high-cycle molding.

Further, in recent years, a method for producing a biaxially stretched film, which has been considered difficult due to the fast crystallization rate of PBT resin, has been reported. In Patent Document 1, Patent Document 2, and Patent Document 3, the tubular method is used. In the simultaneous biaxial stretching method, a film forming method for unstretched raw fabric having relatively low crystallinity, a method for maintaining the low crystal state until the stretching step, and optimization of various stretching conditions such as stretching temperature and stretching ratio. By using a method for improving the biaxial stretchability of the polybutylene terephthalate resin, and further, by using the same film forming and stretching technology, a biaxially stretched polybutylene terephthalate film having relatively high mechanical strength and low anisotropy can be obtained. 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-opening property, particularly tearing linearity when opened by hand, and may cause the contents to be scattered or damaged at the time of opening. Therefore, it may be a fatal problem depending on the application.

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

Japanese Unexamined Patent Publication No. 53-79969 Japanese Unexamined Patent Publication No. 5-261809 Japanese Unexamined Patent Publication No. 5-269843 Japanese Unexamined Patent Publication No. 2013-91693 Japanese Unexamined Patent Publication No. 2016-191009 Japanese Unexamined Patent Publication No. 2006-150617 Japanese Unexamined Patent Publication No. 2006-297653 Japanese Unexamined Patent Publication No. 2004-18742 Japanese Unexamined Patent Publication No. 2002-003707 Japanese Unexamined Patent Publication No. 2006-241398 Japanese Unexamined Patent Publication No. 2006-247870

However, in the method of developing tear linearity by adding an elastomer component as described in Patent Documents 6 to 11, a polybutylene terephthalate resin is used under severe film forming conditions such as high extrusion temperature and high shear. The reaction between the resin and the polyester elastomer progresses, the compatibility changes (the phase-separated structure disappears), and there is a possibility that the conventional tear linearity is impaired. On the other hand, in order to suppress the reaction between polybutylene terephthalate and the polyester-based elastomer, the phase-separated structure can be maintained when the film is not formed at a high extrusion temperature, so that tear linearity can be obtained, but when the production rate is set to a practical level. Since high shear is applied, there is a possibility that the phase-separated structure will disappear. In addition, although the addition of the elastomer component originally improves the pinhole resistance of the biaxially stretched polybutylene terephthalate film, the reaction of the elastomer component may promote changes in the molecular structure and deteriorate the pinhole resistance. .. Therefore, when the tear linearity and pinhole resistance are improved with a mixed film of polybutylene terephthalate and a polyester-based elastomer, the reaction between such polybutylene terephthalate and the polyester-based elastomer is suppressed to form a phase-separated structure. Measures are needed to make it sustainable, but as far as we know, the problem has not yet been resolved.

As a result of diligent studies to solve the problem that the tear linearity and pinhole resistance are lowered due to the reaction between polybutylene terephthalate and the polyester-based elastomer due to a load such as high temperature or high shear, the present inventors have made polybutylene terephthalate. 0.01 to 1.0% by mass based on the resin, 1 to 30% by mass of the polyester-based elastomer based on the polybutylene terephthalate resin, and 100% by mass of the total of the polybutylene terephthalate resin and the polyester-based 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 phosphoric acid ester compound as a raw material and simultaneously biaxially stretching in the vertical and horizontal directions under specific stretching conditions. It was found that even under severe film forming conditions such as high temperature and high shear, OPBT film having good tear linearity at least along the MD direction of the film and excellent pinhole resistance can be obtained. , The present invention has been completed.

That is, the present invention provides the following biaxially stretched polybutylene terephthalate film. [1]
Polybutylene terephthalate resin, 1 to 30% by mass of polyester-based elastomer based on the polybutylene terephthalate resin, and 0.01 to 1.0% based on the total of 100% by mass of the polybutylene terephthalate resin and the polyester-based elastomer. It has at least longitudinal tear linearity, made using a polybutylene terephthalate resin composition containing at least one reaction inhibitor selected from the group consisting of carbodiimide compounds and phosphate ester compounds in mass%. 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-based 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-based elastomer is a polyester polyether block copolymer.
[6]
The biaxially stretched polybutylene terephthalate film has a minimum tear strength of 1.0 to less than 10.0 N / mm measured according to JIS K 7128-1, and has 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].
[7]
The biaxially stretched polybutylene terephthalate film is characterized in that the number of pinholes after being bent 1000 times is 10 or less in a gelboflex test in an environment of 5 ° C. and 40% [1] to [1] to [ 6] The biaxially stretched polybutylene terephthalate film according to any one of.
[8]
The biaxially stretched polybutylene terephthalate film is characterized in that the tensile breaking strength in all four directions (0 ° (MD), 45 °, 90 ° (TD), 135 °) is 170 MPa or more, [1] to The biaxially stretched polybutylene terephthalate film according to any one of [7].

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

FIG. 1 is a schematic view of a tubular simultaneous biaxial stretching device. FIG. 2 is a schematic view of a method for evaluating tear linearity.

Hereinafter, embodiments for carrying out the present invention will be described.
(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 containing butylene terephthalate as a main repeating unit, but specifically, 1,4-butanediol as a glycol component and a dibasic acid component. A homotype containing terephthalic acid as a main component is preferable. Further, in order to impart optimum mechanical strength characteristics, a polybutylene terephthalate resin having a melting point of 200 to 250 ° C. and an IV value in the range of 1.10 to 1.35 dl / g is preferable, and further, a melting point of 215 is preferable. Those having an IV value in the range of 1.15 to 1.30 dl / g at ~ 225 ° C. are particularly preferable.

The present invention contains a polybutylene terephthalate resin, a polyester-based elastomer that is partially phase-separated from the polybutylene terephthalate resin and dispersed in an island shape, and a carbodiimide compound and / or a phosphoric acid ester compound as a reaction inhibitor. By using a polybutylene terephthalate resin composition as a raw material and simultaneously biaxially stretching in the vertical and horizontal directions under specific stretching conditions, the phase-separated structure is maintained even under severe film-forming conditions such as high temperature and high shear. It is possible to develop tear linearity along the major axis direction of the island-like structure.

The content of the polyester-based elastomer is 1 to 30% by mass, preferably 5 to 30% by mass, and more preferably 5 to 25% by mass based on the polybutylene terephthalate resin. If the content of the polyester-based elastomer is less than 1% by mass, the tear linearity is not sufficiently exhibited, and if it exceeds 30% by mass, the mechanical strength of the OPBT film is lowered, which may cause a practical problem.

The content of at least one reaction inhibitor selected from the group consisting of the carbodiimide compound and the phosphoric acid ester compound is 0.01 to 1.0 based on a total of 100% by mass of the polybutylene terephthalate resin and the polyester-based elastomer. It is by mass, preferably 0.05 to 0.8% by mass, and more preferably 0.1 to 0.5% by 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 linearly torn by hand. If it exceeds 1.0% by mass, the effect of improving the tear linearity is unlikely to occur, and agglomerates of the reaction inhibitor may be generated as undissolved substances. As for the method of adding the reaction inhibitor, the same effect can be obtained even if it is added in the form of a compound or in the form of powder as it is.

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'- Trill carbodiimide, N-phenyl-N'-tolyl carbodiimide, N-benzyl-N'-tolyl carbodiimide, N, N'-di-o-ethylphenyl carbodiimide, N, N'-di-p-ethylphenyl carbodiimide, N , N'-di-o-isopropylphenylcarbodiimide, N, N'-di-p-isopropylphenylcarbodiimide, 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-triisobutyl Phenylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, tert-butylisopropylcarbodiimide Examples thereof include diimide, di-β-naphthylcarbodiimide and di-tert-butylcarbodiimide.

Among the above monocarbodiimide compounds, N, N'-di-2,6-diisopropylphenylcarbodiimide is particularly preferable from the viewpoint of excellent effect of improving hydrolysis resistance and durability.

Examples of the polycarbodiimide compound include poly (p-phenylene carbodiimide), poly (m-phenylene carbodiimide), poly (methylphenylene carbodiimide), poly (diisopropylphenylene carbodiimide), poly (methyldiisopropylphenylene carbodiimide), and poly (1,3). , 5-Triisopropylphenylene carbodiimide), poly (1,3,5-triisopropylphenylene-co-1,5-diisopropylphenylene carbodiimide), poly (4,4'-diphenylmethanecarbodiimide) and other aromatic polycarbodiimides; An aliphatic polycarbodiimide such as (4,4'-dicyclohexylmethanecarbodiimide); an alicyclic polycarbodiimide such as poly (dicyclohexylmethanecarbodiimide), and the like can be mentioned.

Among the above polycarbodiimide compounds, an aliphatic polycarbodiimide is preferable, and poly (4,4'-dicyclohexylmethanecarbodiimide) is particularly preferable.
As the poly (4,4'-dicyclohexylmethanecarbodiimide), a 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 phosphoric acid ester compound used in the present invention is not particularly limited as long as it has a phosphoric acid ester structure, but an alkyl phosphoric acid ester having a melting point of 60 to 80 ° C. is preferable for developing good tear linearity. .. As the alkyl group, an alkyl group having 8 to 36 carbon atoms is preferable, an alkyl group having 10 to 30 carbon atoms is more preferable, and an alkyl group having 12 to 22 carbon atoms is particularly preferable.
Examples of such an alkyl group include an octyl group, a 2-ethylhexyl group, a secondary octyl group, a nonyl group, a secondary nonyl group, a decyl group, a secondary decyl group, an undecyl group, a secondary undecyl group and a 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 Examples thereof include a dodecyl group, a 2-octyldodecyl group, a 2-decyltetradecyl group, a 2-dodecyl hexadecyl group, a 2-hexadecyl octadecyl group and a 2-tetradecyl octadecyl group. Among them, stearyl group and isostearyl group are preferable from the viewpoint of dispersibility in polybutylene terephthalate resin.

Examples of alkyl phosphates include phosphate monooctyl ester, phosphate mono (2-ethylhexyl) ester, phosphate monodecyl ester, phosphate monolauryl ester, phosphate monostearyl ester, phosphate monobehenyl ester, and phosphate dioctyl. Examples thereof include esters, bis (2-ethylhexyl) phosphate esters, dilauryl phosphate esters and distearyl phosphate esters. These alkyl phosphates may be used alone or in combination of two or more.
Among them, 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, a commercially available product such as ADEKA STAB (registered trademark) AX-71 [manufactured by ADEKA Corporation] 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 -50, in order to maintain extremely good tear linearity and optimum mechanical strength. Those in the range of 0 ° C. are particularly preferable. When a polyester-based elastomer having a glass transition point lower than -100 ° C. is used, the compatibility with polybutylene terephthalate is significantly reduced, and the transparency and strength of the OPBT film are lowered, and the productivity due to the loss of the elastomer component is increased. 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.

As a type of polyester-based elastomer, an aromatic polyester is used for the hard segment, a polyester polyether block copolymer using an aliphatic polyether for the soft segment, or an aromatic polyester is used for the hard segment, and the soft segment is an aliphatic polyester. A polyester-polyester block copolymer using polyester is preferable. Here, the hard segment is a polyester obtained by polycondensing an aromatic dicarboxylic acid and an alkylene glycol, and specific examples thereof include polyethylene terephthalate and polybutylene terephthalate. Further, the 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 propylene oxide block or random copolymer, ethylene oxide and tetrahydrofuran block or random copolymer and the like. Of these, block copolymers of polybutylene terephthalate and polytetramethylene glycol are 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. Examples thereof 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 a type in which various polar groups are grafted for the purpose of improving compatibility with the polybutylene terephthalate resin which is the base resin.

The polybutylene terephthalate resin composition used in the present invention contains, if necessary, a lubricant, an antiblocking agent, an inorganic bulking agent, an antioxidant, an ultraviolet absorber, an antistatic agent, a flame retardant, a plasticizer, and a colorant. , Additives such as crystallization inhibitor and crystallization accelerator may be added. Further, in order to avoid a decrease in viscosity due to hydrolysis during heating and melting, 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. It is preferable to use after performing.

(Manufacturing method of unstretched raw fabric of polybutylene terephthalate)
In order to stably produce an OPBT film, it is necessary to suppress the crystallization of the unstretched raw fabric before stretching as much as possible, and when the extruded polybutylene terephthalate melt is cooled to form a film, the polybutylene terephthalate is used. The crystallization temperature region is cooled at a certain rate or higher, that is, the raw film cooling rate is an important factor. The raw fabric cooling rate is 200 ° C./sec or higher, preferably 250 ° C./sec or higher, particularly preferably 350 ° C./sec or higher, and the unstretched raw fabric formed at a high cooling rate maintains an extremely low crystalline state. Therefore, the stability of the bubble during stretching is dramatically improved. Furthermore, since it is possible to form a film at high speed, productivity is also improved. If the cooling rate is less than 200 ° C./sec, not only the crystallinity of the obtained unstretched raw fabric becomes high and the stretchability decreases, but also in an extreme case, the stretching bubble bursts and the stretching may not continue. ..

The raw fabric film forming method is not particularly limited as long as it satisfies the raw fabric cooling rate, but the internal / external direct water cooling method is most suitable in terms of quenching film forming. The outline of the raw fabric film forming method by the internal and external direct water cooling method will be described below. First, the polybutylene terephthalate resin is melt-kneaded by an extruder set to an extrusion temperature of 280 ° C., and in the case of T-die film formation, the sheet-shaped molten resin is directly water-cooled both inside and outside by immersing it in a water tank. On the other hand, in the case of annular film forming, it is extruded downward from the annular die attached downward to the extruder to form a molten tubular thin film.

Next, the cooling water introduced from each nozzle of the cooling mandrel is guided to the cooling mandrel connected to the annular die, and is cooled by directly contacting the inside of the molten tubular thin film. At the same time, the cooling water is also flowed from the external cooling tank used in combination with the cooling mandrel, and the cooling water is directly contacted with 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 lower, and particularly preferably 20 ° C. or lower from the viewpoint of quenching film formation. If the temperature is higher than 30 ° C., whitening of the raw fabric and poor appearance of the raw fabric due to boiling of cooling water are caused, and stretching becomes gradually difficult.

(Manufacturing method of OPBT film)
The polybutylene terephthalate unstretched raw fabric needs to be transported to the stretching zone while maintaining an atmospheric temperature of 25 ° C. or lower, preferably 20 ° C. or lower, and under the temperature control, unstretched immediately after film formation regardless of the residence time. The crystallinity of the raw fabric can be maintained. The control of crystallization up to the drawing start point is an important point for stably biaxially stretching the polybutylene terephthalate resin together with the film forming technology 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 in terms of vertical and horizontal strength balance. FIG. 1 is a schematic view of a tubular method simultaneous biaxial stretching device. The unstretched raw film 1 guided to the stretching zone is inserted between the pair of low-speed nip rolls 2 and then heated by the stretching heater 3 while press-fitting air into the stretched shoulder air ring 4 at the stretching end point. By blowing more air, MD and TD simultaneous biaxially stretched films 7 by the tubular method can be obtained. The stretching ratio is 3.0 times or more, preferably 3.2 times or more, and then TD is stretched under the conditions of the MD stretching ratio or less. The upper limit of the draw ratio of MD is preferably 4.5 times or less, and the lower limit of the draw ratio of TD 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. Further, when the draw ratio of MD exceeds 4.5 times, excessive strain of the molecular chain occurs due to the stretching, so that breakage or puncture occurs during the stretching process, and stable production cannot be performed. The stretching temperature is preferably in the range of 40 to 80 ° C, particularly preferably 45 to 65 ° C. Since the unstretched raw fabric produced at the high cooling rate has low crystallinity, it can be stably stretched at a stretching temperature in a relatively low temperature range. In high-temperature stretching exceeding 80 ° C., the stretching bubbles violently sway, causing large stretching unevenness, and a film with good thickness accuracy cannot be obtained. On the other hand, at a stretching temperature of less than 40 ° C., excessive stretching orientation crystallization occurs due to low temperature stretching, which causes whitening of the film and the like, and in some cases, stretching bubbles burst and it becomes difficult to continue stretching. By performing the biaxial stretching process in this way, it is possible to obtain a biaxially stretched polybutylene terephthalate film in which the strength and physical properties are dramatically improved and the anisotropy is small.

Thermal dimensional stability is obtained by putting the obtained OPBT film into a heat treatment facility using a thermal roll method, a tenter method, or a combination thereof for an arbitrary time, and performing heat treatment at 180 to 240 ° C., particularly preferably 190 to 210 ° C. An excellent biaxially stretched polybutylene terephthalate film can be obtained. When the heat treatment temperature is higher than 240 ° C., the Boeing phenomenon becomes too large and the anisotropy in the width direction increases, or the crystallinity becomes too high and the strength physical properties deteriorate. On the other hand, when the heat treatment temperature is lower than 180 ° C., the thermal dimensional stability of the film is significantly lowered, so that the film tends to shrink during laminating or printing, which causes a problem in practical use.

The thickness of the OPBT film is not particularly limited, but is 5 to 50 μm, preferably 10 to 20 μm when used as a general converting film.

In the OPBT film of the present invention, the polyester-based elastomer is dispersed in the polybutylene terephthalate resin in an elongated island shape, and linear tearability is exhibited in the major axis direction of the island-like dispersion. JIS for all directions of OPBT film in the present invention
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, and more preferably 4.0 to 4.0 N / mm. It is 10.0 N / mm. If the minimum tear strength is less than 1.0 N / mm, the OPBT film may easily break during packaging, making it difficult to handle. Further, if the minimum value of the tear strength exceeds 10.0 N / mm, the tear strength may be too strong and it may be difficult to open the package by hand.

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

The pinhole resistance of the OPBT film in the present invention can be measured using a gelboflex tester. For example, the obtained OPBT film is cut into a predetermined size (for example, 210 mm × 297 mm) to form a cylinder. After shaping and fixing to a gel body tester, the number of pinholes after bending 1000 times in a cycle of 42 times reciprocating / minute under the condition of 5 ° C. × 40% RH is measured. The OPBT film in the present invention has 10 or less pinholes, preferably 7 or less, and more preferably 5 pinholes after 1000 times of bending in a gelboflex test in an environment of 5 ° C. and 40%. The number is less than or equal to, and particularly preferably 3 or less. If the number of pinholes is larger than 10, there is a risk that cracks and pinholes will occur during transportation and processing of the OPBT film before use.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples.

Each physical characteristic of the film was determined by the method shown below.
(1) Tear linearity A4 size was cut out from the film with the MD direction of the OPBT film as the long side, and 12 cm was torn and torn along the MD direction at an angle of 130 to 145 ° and a tear rate of 500 to 1000 mm / min. The maximum value of the deviation width between the cut line and the reference straight line along the MD direction was measured (see FIG. 2). Each sample was torn 10 times, and the tear linearity was evaluated from the results according to the following criteria.
〇: 7 or more out of 10 pieces had a deviation width of less than 3 mm and showed good tear linearity. ×: Only 6 out of 10 pieces had a deviation width of less than 3 mm, and the tear linearity was poor (2). Tear strength The tear strength was measured 4 times per sample for MD and TD of the film according to JIS K 7128-1 (Truser 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 Co., Ltd.], and the average value thereof 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 Gelboflex 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 round trips / minute, the stroke distance was 152.4 mm, and the twist angle was 440 °.
(5) Tensile breaking strength The tensile breaking strength is 0 under the conditions of a sample width of 15 mm, a chuck distance of 100 mm, and a tensile speed of 200 mm / min using a Tensilon universal tester (model: RTC-1210A) manufactured by Orientec Co., Ltd. Measurements were performed in 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>
Trecon (registered trademark) 1400S [manufactured by Toray Industries, Inc.]
<Polyester-based elastomer: Polyester-polyester 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 [manufactured by Nisshinbo Chemical Co., Ltd.]
<Phosphate ester compound>
ADEKA STAB (registered trademark) AX-71 (melting point: 71 ° C) [manufactured by ADEKA Corporation]

<Example 1> (Manufacturing of OPBT film)
Polybutylene terephthalate resin pellets (homotype, melting point = 224 ° C., IV value = 1.26 dl / g) and 7% by mass polyester elastomer based on polybutylene terephthalate resin pellets [Hytrel manufactured by Toray DuPont Co., Ltd. (registered) 4777] and 0.05% by mass of carbodiimide compound [Carbodilite (registered trademark) LA-1 manufactured by Nisshinbo Chemical Co., Ltd.] are mixed based on a total of 100% by mass of polybutylene terephthalate resin pellets and polyester-based elastomer. Then, a polybutylene terephthalate resin composition was prepared, dried at 140 ° C. for 5 hours in a hot air dryer, melt-kneaded by an extruder set at an extrusion temperature of 280 ° C., and a molten tubular thin film was placed below the annular die. Extruded to. Subsequently, after passing through the outer diameter of the cooling mandrel and folding with a carapsa roll, the film was taken up at a speed of 1.2 m / min by a taking-up nip roll. The temperature of the cooling water in direct contact with the molten tubular thin film was 20 ° C. on both the inside and outside, and the original fabric cooling rate was 416 ° C./sec. The thickness of the unstretched raw fabric was 185 μm, the folding diameter was 143 mm, and 600 ppm of magnesium stearate was previously added as a lubricant to the polybutylene terephthalate resin composition. The unstretched raw fabric 1 formed under the above conditions was conveyed to the low-speed nip roll 2 in an atmosphere of 20 ° C., and the tubular simultaneous biaxial stretching apparatus having the structure shown in FIG. 1 was used for simultaneous vertical and horizontal biaxial stretching. The stretching ratio was 3.2 times for MD and 3.2 times for TD, and the stretching temperature was 70 ° C. Next, the biaxially stretched film 7 was put into a thermal roll type and a tenter type heat treatment facility, respectively, and heat-treated at 210 ° C. to obtain the OPBT film of the present invention. The thickness of the OPBT film was 15 μm.

(Measuring method of raw fabric cooling rate)
The original fabric cooling rate was calculated by the formula shown below. The temperature of the molten tubular thin film and the temperature of the raw fabric were measured with a contact-type radiation thermometer. The cooling start point is a portion where the molten tubular thin film is in contact with the cooling water or the cooling device, and the cooling end point is a portion where the temperature of the unstretched raw fabric reaches 30 ° C.
Raw fabric cooling rate (° C / sec) = (Temperature of molten tubular thin film immediately before the cooling start point-Primitive fabric temperature at the cooling end point) (° C) / (Distance between cooling start point and cooling end point) (m) x Cooling start Passing speed of the original fabric between the point and the cooling end point (m / sec)

<Examples 2 to 4>
In Example 1, the same procedure as in Example 1 was carried out except that the amount of the polyester elastomer added to the polybutylene terephthalate and the amount of the reaction inhibitor added were changed to the conditions shown in Table 1.

<Examples 5 to 7>
Except that in Example 1, the type of the reaction inhibitor was changed to a phosphoric acid ester compound [ADEKA STAB (registered trademark) AX-71 manufactured by ADEKA Corporation, melting point 71 ° C.], and the addition amount was changed to the amount shown in Table 1. This was done in the same manner as in Example 1.

<Examples 8 to 10>
In Example 1, the same procedure as in Example 1 was carried out except that the type of polyester elastomer was changed to Hytrel (registered trademark) 5577 and the amount added was changed to the amount shown in Table 1.

<Comparative example 1>
In Example 1, the same procedure as in Example 1 was carried out except that the reaction inhibitor was not added.

<Comparative example 2>
In Example 1, the same procedure as in Example 1 was carried out except that the polyester elastomer and the reaction inhibitor were not added.

<Reference example 1>
In Example 1, no reaction inhibitor was added, and the extrusion temperature was higher than that in Example 1 at −20 ° C. Other than that, it 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 higher than that in Example 1 at −20 ° C. Other than that, it was carried out in the same manner as in Example 1.

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

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 also has excellent pinhole resistance, the biaxially stretched polybutylene terephthalate film of the present invention has excellent pinhole resistance. Can be used as a converting film for general food packaging, which requires tear-opening property, tearing linearity, and pinhole resistance.

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 Biaxial stretching film

Claims (6)

Polybutylene terephthalate resin, 1 to 30% by mass of polyester-based elastomer based on the polybutylene terephthalate resin, and 0.01 to 1.0% based on the total of 100% by mass of the polybutylene terephthalate resin and the polyester-based elastomer. A biaxially stretched polybutylene terephthalate film having at least longitudinal tear linearity, which is produced by using a polybutylene terephthalate resin composition containing a mass% of a reaction inhibitor which is an aliphatic polycarbodiimide compound. The biaxially stretched polybutylene terephthalate film according to claim 1, wherein the polyester-based elastomer has a glass transition point of −100 ° C. to 5 ° C. The biaxially stretched polybutylene terephthalate film according to claim 1 or 2 , wherein the polyester-based elastomer is a polyester polyether block copolymer. The biaxially stretched polybutylene terephthalate film has a minimum tear strength of 1.0 to less than 10.0 N / mm measured according to JIS K 7128-1, and has 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 3, wherein the film has. Claims 1 to 4 , wherein the biaxially stretched polybutylene terephthalate film has 10 or less pinholes after being bent 1000 times in a gelboflex test in an environment of 5 ° C. and 40%. The biaxially stretched polybutylene terephthalate film according to any one of the items. Claims 1 to 1, wherein the biaxially stretched polybutylene terephthalate film has a tensile breaking strength of 170 MPa or more in all four directions (0 ° (MD), 45 °, 90 ° (TD), 135 °). The biaxially stretched polybutylene terephthalate film according to any one of 5.

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