WO2020203105A1 - Polyester film and production method therefor - Google Patents

Abstract

[Problem] To provide a biaxially stretched polyester film which has excellent unsusceptibility to pinhole formation and to bag breakage, is highly hygienic, and has low unevenness in machine-direction physical property. [Solution] A biaxially stretched polyester film characterized by comprising 60-95 mass% poly(butylene terephthalate) resin (A) and 5-40 mass% poly(ethylene terephthalate) resin (B) and satisfying all of the following (1) to (4). (1) To have a piercing strength, as measured in accordance with JIS Z 1707, of 0.6 N/μm or greater. (2) To have a degree of planar orientation of 0.144-0.160. (3) To have degrees of thermal shrinkage through 15-minute heating at 150°C of 0-4% for the machine direction and -1 to 3% for the transverse direction. (4) To have an antimony atom content of 7 ppm or less.

Description

Polyester film and its manufacturing method

The present invention relates to a biaxially stretched polyester film used in the packaging field of foods, pharmaceuticals, industrial products, etc., and a method for producing the same. More specifically, it not only has excellent pinhole resistance and bag breakage resistance, but also has excellent hygiene, printability, and workability, and even a long film roll with a long winding length is in the longitudinal direction. The present invention relates to a biaxially stretched polyester film having little variation in physical properties and a method for producing the same.

Packaging materials used in foods, pharmaceuticals, etc. must have the property of blocking gases such as oxygen and water vapor, that is, gas barrier properties, in order to suppress the oxidation of proteins and fats and oils, maintain the taste and freshness, and maintain the efficacy of pharmaceuticals. It has been demanded. Further, gas barrier materials used for electronic devices such as solar cells and organic ELs and electronic parts require higher gas barrier properties than packaging materials such as foods.

Conventionally, in food applications that require blocking of various gases such as water vapor and oxygen, a metal thin film made of aluminum or the like and an inorganic oxide such as silicon oxide or aluminum oxide are used on the surface of a base film layer made of plastic. A gas barrier laminated film on which an inorganic thin film is formed is generally used.

It has been known that by using a biaxially stretched nylon film as a base film layer, pinhole resistance due to the contents is improved and leakage of the contents when the bag is dropped is eliminated (for example, Patent Documents). 5). However, the biaxially stretched nylon film has a large dimensional change during moisture absorption, and has a problem that it curls due to moisture absorption during the processing process and the shape is deformed due to shrinkage when a harsh treatment such as retort sterilization is applied. was there.

On the other hand, a polyethylene terephthalate (hereinafter abbreviated as PET) film on which a thin film (inorganic thin film layer) of an inorganic oxide such as silicon oxide, aluminum oxide, or a mixture thereof is formed is transparent and the contents can be confirmed. Therefore, it is widely used. (For example, Patent Document 1 and Patent Document 2)

PET film has excellent heat resistance and dimensional stability, and can be used even when harsh treatment such as retort sterilization is applied. However, since PET film is brittle, a bag made of a laminated film using this is used. There was a problem that the bag was torn or punctured when it was dropped, and the contents packed in the bag leaked.

As a means for solving these problems, it has been studied to use a biaxially stretched polybutylene terephthalate (hereinafter abbreviated as PBT) film.

For example, in Patent Document 3, at least PBT resin or a polyester resin composition in which PET resin is blended in a range of 30% by mass or less with respect to PBT resin is 2.7 to 4.0 times simultaneously in the vertical direction and the horizontal direction. It has been known that a biaxially stretched PBT film obtained by axial stretching is used as a base film layer. According to such a technique, it is possible to obtain a packaging material for liquid filling which has bending pinhole resistance, impact resistance, and excellent aroma retention.

By the way, since a packaging film in which a polyester film is often used is expected to come into direct contact with food, it is desired that there are few foreign substances in the polyester film from the viewpoint of hygiene. In addition, since the antimony catalyst used in the process of producing (polymerizing) the polyester raw material may be carcinogenic, it is desirable that the content of antimony in the polyester film is as low as possible or not contained.

Conventionally, there are polyester raw materials that do not use an antimony catalyst, for example, as described in Patent Documents 4 and 5. However, the method for reducing the number of foreign substances in the film and the desired film characteristics are not described.

Further, even in a film obtained by stretching a polyester resin composition obtained by blending a PET resin with a PBT resin as in Patent Document 3 mentioned above, the amount of antimony contained in the film is not specified. However, there was still room for improvement in reducing the amount of antimony in the film and reducing foreign matter.

On the other hand, in the case of a film made of a polyester resin composition obtained by blending PET resin with PBT resin, it is common to mix PBT resin and other resins such as PET resin to form a film. However, since the specific gravity and the shape of the resin chip may differ between the PBT resin and other resins, the segregation of these raw material resin chips tends to cause variations in the raw material ratio in the mixing and extrusion processes, resulting in differences in physical properties in the longitudinal direction of the film. Occurs. As a result, there are cases where a product having uniform physical properties cannot be obtained in the longitudinal direction of a long product roll.

JP-A-6-278240, JP-A-11-10725 Japanese Unexamined Patent Publication No. 2017-09746 Japanese Patent No. 3461175 Japanese Patent No. 3506236

The present invention has been made against the background of the problems of the prior art.

That is, it not only has excellent pinhole resistance and bag breakage resistance, but also has excellent hygiene, printability, and workability, and even a long film roll with a long winding length has physical properties in the longitudinal direction. It is an object of the present invention to provide a biaxially stretched polyester film having little variation and a method for producing the same.

As a result of diligent studies to solve this problem, the present inventors have obtained a biaxially stretched polyester film obtained by biaxially stretching a polyester resin composition in which a PET resin is blended in a range of 40% by mass or less with respect to a PBT resin. As the PET resin used in the above, a resin produced by using a polymerization catalyst containing at least one selected from aluminum compounds and at least one selected from phosphorus-based compounds is used, and when mixing the resin chips as raw materials, , The polybutylene terephthalate resin chip is supplied to the hopper from above, and the PET resin (B) chip is supplied through a pipe (hereinafter, may be referred to as an inner pipe) having an outlet in the hopper and directly above the extruder. Then, by mixing both chips and melt-extruding them, it was found that a film having less variation in physical properties in the longitudinal direction and uniform physical properties in the longitudinal direction can be obtained, and the present invention has been completed.

That is, the present invention has the following configuration.

[1] It is characterized by containing at least 60 to 95% by mass of the polybutylene terephthalate resin (A) and 5 to 40% by mass of the polyethylene terephthalate resin (B), and simultaneously satisfying the following (1) to (4). Biaxially stretched polyester film.

(1) The puncture strength measured according to JIS Z 1707 is 0.6 N / μm or more.

(2) The degree of surface orientation of the film is 0.144 to 0.160.

(3) The heat shrinkage of the film after heating at 150 ° C. for 15 minutes is 0 to 4% in the vertical direction and -1 to 3% in the horizontal direction.

(4) The content of antimony atoms in the film is 7 ppm or less.

[2] The polyethylene terephthalate (B) is a polyester raw material containing at least one selected from aluminum compounds and at least one selected from phosphorus compounds as a polymerization catalyst. The biaxially stretched polyester film according to [1].

[3] The biaxially stretched polyester film according to [1] or [2], wherein the number of defects of 1 mm or more per 1000 square meters of the film is 1.0 or less.

[4] The maximum value of the puncture strength measured in the vertical direction from the surface layer of the film roll to the winding core every 1000 m and measured according to JIS Z 1707 is Xmax (N / μm), and the minimum value is Xmin (N / μm). ), The variation of the puncture strength represented by the following formula [1] is 20% or less when the average value is Xave, according to any one of [1] to [3]. Axial stretched polyester film.

Longitudinal variation in piercing strength (%) = 100 × (Xmax-Xmin) / Xave ... [1]

[5] The gas barrier laminated film according to any one of [1] to [4], which has an inorganic thin film layer on at least one surface of the biaxially stretched polyester film.

[6] The gas barrier laminated film according to [5], wherein an adhesive layer is provided between the polyester film and the inorganic thin film layer.

[7] The gas barrier laminated film according to [5] or [6], which has a protective layer on the surface of the inorganic thin film layer.

[8] In the melt extrusion step of the polyester raw material resin, the raw material resin chip of polybutylene terephthalate (A) is supplied to the hopper from above, and the polyethylene terephthalate (B) is passed through a pipe having an outlet in the hopper and directly above the extruder. The method for producing a biaxially stretched polyester film according to any one of [1] to [4], wherein the raw material resin chips of the above are supplied, both chips are mixed, and melt-extruded.

By using this technique, the present inventors not only have excellent pinhole resistance and bag breakage resistance, but also have excellent hygiene, printability, and workability, and use a long film roll having a long winding length. Even if there is, it has become possible to provide a biaxially stretched polyester film having little variation in physical properties in the longitudinal direction and a method for producing the same.

FIG. 1 is a schematic view for explaining an example of a method of mixing raw material resin chips for producing the biaxially stretched polyester film of the present invention. FIG. 2 is a partially enlarged view of FIG.

Hereinafter, the present invention will be described in detail.

The biaxially stretched polyester film of the present invention contains PBT resin (A) as a main component, and the content of PBT is preferably 60% by mass or more, more preferably 70% by mass or more. If it is less than 60% by mass, the piercing strength is lowered, and the film characteristics are not sufficient.

The PBT resin (A) used as the main constituent component preferably contains terephthalic acid in an amount of 90 mol% or more, more preferably 95 mol% or more, and further preferably 98 mol% or more as a dicarboxylic acid component. Most preferably, it is 100 mol%. The glycol component of 1,4-butanediol is preferably 90 mol% or more, more preferably 95 mol% or more, still more preferably 97 mol% or more, and most preferably 1,4-butanediol at the time of polymerization. It does not contain anything other than by-products produced by the ether bond of the diol.

The lower limit of the intrinsic viscosity of the PBT resin used in the present invention is preferably 0.9 dl / g, more preferably 0.95 dl / g, and further preferably 1.0 dl / g.

When the intrinsic viscosity of the raw material PBT resin is less than 0.9 dl / g, the intrinsic viscosity of the film obtained by film formation decreases, and piercing strength, impact strength, pinhole resistance, bag breaking resistance, etc. May decrease.

The upper limit of the intrinsic viscosity of the PBT resin is preferably 1.4 dl / g. If it exceeds the above, the stress at the time of stretching becomes too high, and the film forming property may deteriorate. When PBT having a high intrinsic viscosity is used, it is necessary to raise the extrusion temperature to a high temperature because the melt viscosity of the resin becomes high, but when the PBT resin is extruded at a higher temperature, decomposition products may be easily generated.

If necessary, the PBT resin may contain conventionally known additives such as lubricants, stabilizers, colorants, antistatic agents, and ultraviolet absorbers.

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

The lower limit of the lubricant concentration is preferably 100 ppm, more preferably 500 ppm, and even more preferably 800 ppm. If it is less than the above, the slipperiness of the base film layer may decrease. The upper limit of the lubricant concentration is preferably 20000 ppm, more preferably 10000 ppm, and even more preferably 1800 ppm. If it exceeds the above, transparency may decrease.

In the biaxially stretched polyester film of the present invention, in addition to the PBT resin (A), a PET resin (B) is added for the purpose of adjusting mechanical properties and film-forming properties.

The content of PET is preferably 5% by mass or more. If it is less than 5% by mass, the film-forming property may decrease due to the crystallization of PBT.

The content of PET is preferably 40% by mass or less, more preferably 30% by mass or less. If it exceeds 40% by mass, the piercing strength is lowered, and the film characteristics are not sufficient.

Further, as the PET resin (B) used in the biaxially stretched polyester film of the present invention, a polymerization catalyst of an antimony compound such as antimony trioxide, which is conventionally used as a polymerization catalyst, is not used as much as possible. Is preferable.

By not using an antimony compound as the main polymerization catalyst in producing the PET resin (B) and using an aluminum compound described later instead, a polyester film having excellent hygiene and printability can be obtained. ..

Next, the polymerization catalyst used when producing the PET raw material (B) used in the present invention will be described. The polymerization catalyst used in the present invention is a polymerization catalyst characterized by having an ability to promote esterification. In the present invention, it is preferable not to use a polymerization catalyst of an antimony compound such as antimony trioxide which is conventionally used as described later. As such a polymerization catalyst, a polymerization catalyst containing at least one selected from aluminum compounds and at least one selected from phosphorus compounds is preferable.

A known aluminum compound can be used without limitation as the aluminum compound constituting the polymerization catalyst used when synthesizing the PET resin (B) used in the present invention.

Specific examples of the aluminum compound include organoaluminum compounds such as aluminum acetate, basic aluminum acetate, aluminum lactate, aluminum chloride, aluminum hydroxide, aluminum chloride and aluminum acetylacetonate, and aluminum oxalate, and portions thereof. Hydrolyzate and the like can be mentioned. Of these, carboxylates, inorganic acid salts and chelate compounds are preferable, and among these, aluminum acetate, basic aluminum acetate, aluminum lactate, aluminum chloride, aluminum hydroxide, aluminum hydroxide chloride and aluminum acetylacetonate are more preferable. Aluminum acetate, basic aluminum acetate, aluminum chloride, aluminum hydroxide and aluminum chloride are more preferable, and aluminum acetate and basic aluminum acetate are most preferable.

The amount of the aluminum compound used in the polymerization catalyst of the PET resin (B) used in the present invention may be 1 to 80 ppm remaining as an aluminum atom with respect to the total mass of the obtained PET resin (B). It is preferably more preferably 2 to 60 ppm, further preferably 3 to 50 ppm, particularly preferably 5 to 40 ppm, and most preferably 10 to 30 ppm.

If it is less than the above, the catalytic activity may be poor, and if it exceeds the above, aluminum-based foreign matter may be generated.

Even if the aluminum compound is placed in a reduced pressure environment during polyester polymerization, almost 100% of the used amount remains, so it can be considered that the used amount becomes the residual amount.

The phosphorus compound used in the polymerization catalyst is not particularly limited, but it is preferable to use a phosphonic acid compound or a phosphinic acid compound to greatly improve the catalytic activity, and among these, a phosphonic acid compound is used to improve the catalytic activity. Is particularly large and preferable.

Among these phosphorus compounds, a phosphorus compound having a phenol portion in the same molecule is preferable. The phosphorus compound having a phenol structure is not particularly limited, but a catalyst may be used if one or more compounds selected from the group consisting of phosphonic acid compounds and phosphinic acid compounds having a phenol moiety in the same molecule are used. The effect of improving activity is large and preferable. Among these, it is particularly preferable to use one or more phosphonic acid compounds having a phenol portion in the same molecule because the effect of improving the catalytic activity is particularly large.

In addition, examples of the phosphorus compound having a phenol portion in the same molecule include compounds represented by the following general formulas [Chemical formula 1] and [Chemical formula 2].

(In the formulas [Chemical formula 1] to [Chemical formula 2], R ¹ is a hydrocarbon group having 1 to 50 carbon atoms including a phenol portion, a hydroxyl group or a halogen group, a substituent such as an alkoxyl group or an amino group, and a carbon containing a phenol portion. Represents a hydrocarbon group of number 1 to 50. R ⁴ is a hydrocarbon having 1 to 50 carbon atoms including hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydroxyl group or a halogen group or a substituent such as an alkoxyl group or an amino group. Representing a hydrogen group. R ² and R ³ independently represent hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, and a hydrocarbon group having 1 to 50 carbon atoms including a substituent such as a hydroxyl group or an alkoxyl group. The hydrocarbon group may contain a branched structure, an alicyclic structure such as cyclohexyl, or an aromatic ring structure such as phenyl or naphthyl. The terminals of R ² and R ⁴ may be bonded to each other.)

Examples of the phosphorus compound having a phenol portion in the same molecule include p-hydroxyphenylphosphonic acid, dimethyl p-hydroxyphenylphosphonate, diethyl p-hydroxyphenylphosphonate, diphenyl p-hydroxyphenylphosphonate, and bis ( p-Hydroxyphenyl) phosphinic acid, methyl bis (p-hydroxyphenyl) phosphinate, phenyl bis (p-hydroxyphenyl) phosphinate, p-hydroxyphenylphenylphosphonate, methyl p-hydroxyphenylphenylphosphinate, p-hydroxy Examples thereof include phenyl phenylphenylphosphinate, p-hydroxyphenylphosphinic acid, methyl p-hydroxyphenylphosphinate, and phenyl p-hydroxyphenylphosphinate. In addition, a phosphorus compound represented by the following general formula [Chemical Formula 3] can be mentioned.

In the formula [Chemical Formula 3], X ₁ and X ₂ represent hydrogen, an alkyl group having 1 to 4 carbon atoms, or a metal having a valence of 1 or more, respectively.

Further, in X ₁ , the metal is divalent or higher, and X ₂ does not have to be present. Furthermore, an anion corresponding to the surplus valence of the metal may be arranged with respect to the phosphorus compound.

As the metal, Li, Na, K, Ca, Mg and Al are preferable.

By adding these phosphorus compounds having a phenol portion in the same molecule at the time of polymerization of polyester, the catalytic activity of the aluminum compound is improved and the thermal stability of the polymerized polyester resin is also improved.

Among the above, the phosphorus compound preferably used as a polycondensation catalyst is at least one phosphorus compound selected from the compounds represented by the chemical formula [Chemical Formula 4] and the chemical formula [Chemical Formula 5].

As the compound represented by the above chemical formula [Chemical Formula 4], Irganox1222 (manufactured by BAF) is commercially available. Further, as a compound represented by the chemical formula [Chemical Formula 5], Irganox 1425 (manufactured by BAF) is commercially available and can be used.

The amount of the phosphorus compound used in the polymerization catalyst of the PET raw material (B) used in the present invention is preferably 10 to 100 ppm remaining as a phosphorus atom with respect to the total mass of the obtained raw material polyester resin. It is more preferably 15 to 90 ppm, further preferably 20 to 80 ppm, particularly preferably 25 to 70 ppm, and most preferably 30 to 60 ppm.

If an amount of phosphorus atoms exceeding the above upper and lower limits remains, the polymerization activity may be lowered.

When the phosphorus compound is placed in a reduced pressure environment during polyester polymerization, about 10 to 30% of the amount used is removed from the system depending on the conditions. Therefore, in reality, it is necessary to carry out several trial experiments to determine the residual ratio of the phosphorus compound in the polyester before deciding the amount to be used.

Further, by using the above phosphorus compound, the heat resistance of the resin can be improved. Although the cause is not clear, it is considered that the heat resistance of the polyester resin is improved by the hindered phenol portion in the phosphorus compound.

When the residual amount of the phosphorus compound is less than 10 ppm, the above-mentioned effect of improving heat resistance is diminished, and as a result, the effect of improving heat resistance and coloring of the PET raw material (B) used in the present invention may not be observed.

A metal-containing polycondensation catalyst such as an antimony compound, a titanium compound, a tin compound, and a germanium compound may be used in combination in order to further improve the catalytic activity without impairing the effect of the present invention. In that case, the antimony compound is preferably 7 ppm or less as an antimony atom with respect to the mass of the obtained copolymerized polyester resin, and the germanium compound is preferably 10 ppm or less as a germanium atom with respect to the mass of the obtained copolymerized polyester resin. The titanium compound is preferably 3 ppm or less as a titanium atom with respect to the mass of the obtained copolymer resin resin, and the tin compound is preferably 3 ppm or less as a tin atom with respect to the mass of the obtained polyester resin. For the purpose of the present invention, it is preferable not to use metal-containing polycondensation catalysts such as antimony compounds, titanium compounds, tin compounds and germanium compounds as much as possible.

In the PET raw material (B) used in the present invention, in addition to the aluminum compound, a small amount of alkali metal, alkaline earth metal, and at least one selected from the compounds may coexist as a second metal-containing component. Coexistence of such a second metal-containing component in the catalyst system is effective in improving productivity because a catalyst component having an enhanced catalytic activity and thus a higher reaction rate can be obtained in addition to the effect of suppressing the formation of diethylene glycol. .. When an alkali metal, an alkaline earth metal, or a compound thereof is added in combination, the amount used (mol%) is preferably 1 × ^{10-5 with} respect to the number of moles of the dicarboxylic acid component constituting the polyester resin. It is ~ 0.01 mol%. Alkaline metals, alkaline earth metals, or their compounds, even if they are placed in a reduced pressure environment during polyester polymerization, almost 100% of the amount used remains, so it can be considered that the amount used is the residual amount.

The polymerization catalyst according to the PET raw material (B) used in the present invention has catalytic activity not only in the polycondensation reaction but also in the esterification reaction and the transesterification reaction. The transesterification reaction between an alkyl ester of a dicarboxylic acid such as dimethyl terephthalate and a glycol such as ethylene glycol is usually carried out in the presence of a transesterification catalyst such as zinc, but the above-mentioned aluminum compound is used instead of these catalysts. You can also do it. Further, these polymerization catalysts have catalytic activity not only in melt polymerization but also in solid phase polymerization and solution polymerization.

The polymerization catalyst of the PET raw material (B) used in the present invention can be added to the reaction system at any stage of the polymerization reaction. For example, it can be added to the reaction system at any stage before and during the start of the esterification reaction or transesterification reaction, immediately before the start of the polycondensation reaction, or at any stage during the polycondensation reaction. In particular, the above-mentioned aluminum compound and phosphorus compound according to the present invention are preferably added immediately before the start of the polycondensation reaction.

The intrinsic viscosity of the PET resin (B) is preferably in the range of 0.57 to 0.76 dl / g, more preferably 0.60 to 0.73 dl / g, and further preferably 0.63 to 0.7 dl. / G. If the intrinsic viscosity is lower than 0.57 dl / g, the film tends to tear during the production of the polyester film (so-called breakage occurs), and if it is higher than 0.76 dl / g, the increase in filtration pressure becomes large and the high-precision filtration filter It tends to be difficult to extrude the resin through the resin.

The intrinsic viscosity of the resin of the biaxially stretched polyester film is preferably in the range of 0.51 to 0.70 dl / g, more preferably 0.56 to 0.68 dl / g, and further preferably 0.59. It is ~ 0.65 dl / g. When the intrinsic viscosity is lower than 0.51 dl / g, the polyester film is easily torn in the processing process such as printing, and when the intrinsic viscosity is higher than 0.76 dl / g, the effect of improving the mechanical properties becomes saturated. Prone.

Various additives may be added to the biaxially stretched polyester film of the present invention as long as its properties are not impaired. For example, a plasticizer, an ultraviolet stabilizer, a color inhibitor, a matting agent, and a deodorant may be added. Agents, flame retardants, weather resistant agents, antistatic agents, thread friction reducing agents, mold release agents, antioxidants, ion exchangers, coloring pigments and the like can be added. These additives are added in a range of 50% by mass or less with respect to the biaxially stretched polyester film.

The biaxially stretched polyester film of the present invention may contain a polyester resin other than the above (A) and (B) for the purpose of adjusting mechanical properties and the like.

As the polyester resin other than the above (A) and (B), at least one polyester resin selected from the group consisting of polyethylene naphthalate, polybutylene naphthalate and polypropylene terephthalate, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid and biphenyl. PBT resin, ethylene glycol, 1,3-propylene glycol, 1,2-propylene in which at least one dicarboxylic acid selected from the group consisting of dicarboxylic acid, cyclohexanedicarboxylic acid, adipic acid, azelaic acid and sebacic acid is copolymerized. At least one diol component selected from the group consisting of glycol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, cyclohexanediol, polyethylene glycol, polytetramethylene glycol and polycarbonate diol is copolymerized. Examples thereof include the PBT resin used.

The upper limit of the amount of the polyester resin other than the PBT resin (A) and the PET resin (B) added is preferably less than 30% by mass, more preferably 25% by mass or less. If the amount of polyester resin other than PBT resin added exceeds 30% by mass, the mechanical properties of PBT are impaired, impact strength, pinhole resistance, or bag breakage resistance becomes insufficient, and transparency and gas barrier Sexual deterioration may occur.

The lower limit of the thickness of the biaxially stretched polyester film of the present invention is preferably 3 μm, more preferably 5 μm, and even more preferably 8 μm. When it is 3 μm or more, the strength as a base film layer becomes sufficient.

The upper limit of the thickness of the biaxially stretched polyester film of the present invention is preferably 100 μm, more preferably 75 μm, and even more preferably 50 μm. When it is 100 μm or less, the processing for the purpose of the present invention becomes easier.

The upper limit of the heat shrinkage rate after heating the biaxially stretched polyester film of the present invention at 150 ° C. in the longitudinal direction for 15 minutes is preferably 4.0%, more preferably 3.0%, still more preferably 2. %. If the upper limit is exceeded, the inorganic thin film layer may crack due to the dimensional change of the base film layer that occurs in the process of forming the protective film or in the high temperature treatment such as retort sterilization treatment, and not only the gas barrier property may deteriorate, but also printing etc. Pitch deviation may occur due to dimensional changes during processing.

The upper limit of the heat shrinkage rate after heating the biaxially stretched polyester film of the present invention at 150 ° C. in the lateral direction for 15 minutes is preferably 3.0%, more preferably 2.0%, still more preferably 1%. Is. If the upper limit is exceeded, the inorganic thin film layer may crack due to the dimensional change of the base film layer that occurs in the process of forming the protective film or in the high temperature treatment such as retort sterilization treatment, and not only the gas barrier property may deteriorate, but also printing etc. Pitch deviation may occur due to dimensional changes in the width direction during processing.

The lower limit of the heat shrinkage rate after heating the biaxially stretched polyester film of the present invention at 150 ° C. in the longitudinal direction for 15 minutes is preferably 0%. Even if it is less than the above, the effect of improvement cannot be obtained any more (saturation), and it may become mechanically brittle.

The lower limit of the heat shrinkage rate after heating the biaxially stretched polyester film of the present invention at 150 ° C. in the lateral direction for 15 minutes is preferably 1.0%. Even if it is less than the above, the effect of improvement cannot be obtained any more (saturation), and it may become mechanically brittle.

The lower limit of the puncture strength of the biaxially stretched polyester film of the present invention is preferably 0.6 N / μm. If it is 0.6 N / μm or more, the strength of the bag may be insufficient when used as a bag.

In the roll of the biaxially stretched polyester film of the present invention, the maximum value of the puncture strength measured in accordance with JIS Z 1707 by sampling the film roll in the longitudinal direction from the surface layer of the film roll to the winding core every 100 m is Xmax (N). When the minimum value is Xmin (N) and the average value is Xave, the variation in the puncture strength represented by the following formula [1] is preferably 20% or less, more preferably 15% or less, and most preferably. It is preferably 10% or less.

Longitudinal variation in puncture strength (%) = 100x (Xmax-Xmin) / Xave ... [1]

If the variation in the piercing strength in the longitudinal direction of the film roll exceeds 20%, the quality of the packaging bag manufactured by secondary processing of the polyester film may vary.

The lower limit of the impact strength of the biaxially stretched polyester film of the present invention is preferably 0.05 J / μm. If it is 0.05 J / μm or more, the strength becomes sufficient when used as a bag.

The upper limit of the impact strength of the base film layer in the present invention is preferably 0.2 J / μm. Even if it is 0.2 J / μm or less, the effect of improvement may be maximized.

The lower limit of the plane orientation (ΔP) of the biaxially stretched polyester film of the present invention is preferably 0.144, more preferably 0.148, and even more preferably 0.15. If it is less than the above, the orientation is weak, so that sufficient strength cannot be obtained and the bag breaking resistance may be lowered. In addition, an inorganic thin film layer and a protective layer are provided on the base film layer to form a laminated film. In some cases, the tension and temperature applied when the protective film is formed make it easy to stretch, and the inorganic thin film layer is cracked, so that the gas barrier property may be lowered.

The upper limit of the plane orientation (ΔP) of the biaxially stretched polyester film of the present invention is preferably 0.160, more preferably 0.158, and even more preferably 0.156. If it exceeds the above, the orientation is too strong, and not only the film-forming property is lowered, but also the pinhole resistance may be lowered because it becomes difficult to stretch.

The upper limit of haze per thickness of the biaxially stretched polyester film of the present invention is preferably 0.66% / μm, more preferably 0.60% / μm, and even more preferably 0.53% / μm. .. When printing is applied to the base film layer having a ratio of 0.66% / μm or less, the quality of the printed characters and images is improved.

Further, the biaxially stretched polyester film of the present invention may be subjected to corona discharge treatment, glow discharge treatment, flame treatment, surface roughening treatment, as long as the object of the present invention is not impaired, and a known anchor. It may be coated, printed, decorated, etc.

The biaxially stretched polyester film of the present invention preferably has an antimony content of 7 ppm or less in the film. Since antimony is a substance of concern for carcinogenicity, the smaller the amount, the more preferable, 5 ppm is preferable, and 0 ppm is more preferable. The raw material resin antimony used in the present invention is preferably 0 ppm, but it may be mixed during production and is set to 7 ppm or less.

The biaxially stretched polyester film of the present invention preferably has one or less defects having a size of 1 mm or more per 1000 square meters (for example, per film width of 500 mm and film winding length of 2000 m). By reducing the number of defects having a size of 1 mm or more per large area of 1000 square meters to one or less in this way, the printability becomes very good. If the number of defects due to foreign matter is large, ink will be lost during printing, which is not preferable. The smaller the number of defects in the size of 1 mm or more, the more preferable, 0.5 or less is more preferable, 0.3 or less is further preferable, 0.1 or less is particularly preferable, and 0 is most preferable. In the present invention, there is a possibility that foreign matter may be mixed in when an unexpected trouble occurs, and the number is reduced to one or less.

Next, a manufacturing method for obtaining the biaxially stretched polyester film of the present invention will be specifically described. It is not limited to these.

In order to obtain the biaxially stretched polyester film of the present invention, the production method is to supply and mix the PBT resin (A) chip and the PET resin (B) chip to an extruder equipped with a hopper, and the polyester raw material from the extruder. A step of melt-extruding the resin into a sheet and cooling it on a casting drum to form an unstretched sheet, a longitudinal stretching step of stretching the molded unstretched sheet in the longitudinal direction, and a temperature at which lateral stretching is possible after the longitudinal stretching. A preheating step for preheating, a transverse stretching step for stretching in a width direction orthogonal to the longitudinal direction, a heat fixing step for heating and crystallizing the film after the longitudinal stretching and the transverse stretching, and a residual heat-fixed film. It consists of a heat relaxation step for removing the strain and a cooling step for cooling the film after the heat relaxation.

[Unstretched sheet molding process]

First, the film raw material is dried or hot air dried. Next, the raw materials are weighed, mixed, supplied to the extruder, heated and melted, and melt-casted in the form of a sheet.

Further, the molten resin sheet is brought into close contact with a cooling roll (casting roll) by an electrostatic application method to be cooled and solidified to obtain an unstretched sheet. The electrostatic application method is a method in which a voltage is applied to an electrode installed in the vicinity of a molten resin sheet in contact with a rotating metal roll and in the vicinity of a surface opposite to the surface of the resin sheet in contact with the rotating metal roll. This is a method in which the resin sheet is charged and the resin sheet and the rotary cooling roll are brought into close contact with each other.

When mixing the resin chips as raw materials, the polybutylene terephthalate resin chips are supplied to the hopper from above, and the pipe (hereinafter, may be referred to as an inner pipe) having an outlet in the hopper and directly above the extruder is used. It is preferable to supply a resin chip of polyethylene terephthalate (B), mix both chips, and melt-extrude the two chips. When a polybutylene terephthalate resin (A) chip and a polyethylene terephthalate resin (B) chip are mixed and placed in a hopper on an extruder, resin chips having different specific gravities and chip shapes can cause segregation of raw materials in the hopper. There is a high concern that raw material segregation will occur especially in places where the inner wall of the hopper is not vertical (diagonal part), but polyethylene terephthalate resin (B) is directly applied directly above the extruder in the hopper through the inner pipe. When supplied, even if the specific gravity and the chip shape are different, the bias of the raw material can be reduced, and the polyester film can be stably industrially produced.

An example of a specific mixing procedure is shown in FIG. FIG. 1 is a schematic view showing an example of the relationship between the extruder 2 provided with the hopper 1 and the inner pipe 3, and FIG. 2 is an enlarged view of a portion A of FIG.

In FIGS. 1 and 2, chips of a resin other than the polybutylene terephthalate resin (A), which is the main raw material such as the polyethylene terephthalate resin (B), are supplied through the inner pipe 3 and are the main raw material of the polybutylene terephthalate resin (A). The chips are supplied from the upper part of the hopper 1. Since the outlet 4 of the inner pipe 3 is directly above the extruder (to be exact, directly above the resin supply port 5 of the extruder 2), the polyethylene terephthalate resin (B) chips segregate in the popper over time. Since it can be prevented, the mixing ratio of the polyethylene terephthalate resin (B) can always be kept constant.

The height (H2) of the outlet 4 of the inner pipe 3 preferably satisfies the following relationship (formula a), and satisfies both the relationships (formula a) and (b). Is more preferable.

H2 <H1 (formula a)

(In the formula, H1 indicates the height of the portion where the inner wall of the hopper is vertical (see FIG. 2).

0.5 × L / tan θ <H2 (Equation b)

(In the formula, L indicates the inner diameter of the outlet 4 of the inner pipe 3 (see FIG. 2). θ is the angle of repose of another resin chip.)

By making the height of H2 larger than 0.5 × L / tan θ, the position where the resin other than the polybutylene terephthalate resin (A) chip is mixed with the polybutylene terephthalate resin chip (H3; see FIG. 2) is extruded. It can be located outside the machine and can prevent air from entering the extruder and generating bubbles.

The height H3 = H2-0.5 × L / tan θ of the mixing position of the resin other than the polybutylene terephthalate resin (A) chip is preferably higher than 0 m and less than 2 m. By setting the height above 0 m, it is possible to prevent air from entering the extruder. Further, if it is less than 2 m, the distance to the extruder can be kept short and segregation of raw materials can be prevented. The height H3 is preferably 0.3 m or more and 1.7 m or less, and more preferably 0.6 m or more and 1.4 m or less.

The lower limit of the heating and melting temperature of the resin is preferably 200 ° C., more preferably 250 ° C., and even more preferably 260 ° C. If it is less than the above, the discharge may become unstable. The upper limit of the resin melting temperature is preferably 280 ° C, more preferably 270 ° C. If it exceeds the above, the decomposition of the resin proceeds and the film becomes brittle.

When casting the molten polyester resin onto an extruded cooling roll, it is preferable to reduce the difference in crystallinity in the width direction. Specific methods for this include extruding the molten polyester resin and casting the raw materials having the same composition in multiple layers at the time of casting, and further lowering the cooling roll temperature.

The method of extruding and casting the molten polyester resin is specifically a step of melting a resin composition containing 60% by mass or more of PBT resin to form a molten fluid (1), and discharging the formed molten fluid from a die. It has at least a step (2) of contacting with a cooling roll and solidifying to form an unstretched sheet, and a step (3) of biaxially stretching the unstretched sheet.

In the step (1), the method of melting the polyester resin composition to form a molten fluid is not particularly limited, but a preferred method includes a method of heating and melting using a single-screw extruder or a twin-screw extruder. Can be done.

In step (2), the molten fluid is discharged from the die and brought into contact with the cooling roll to solidify.

The lower limit of the cooling roll temperature is preferably −10 ° C. If it is less than the above, the effect of suppressing crystallization may be saturated. The upper limit of the cooling roll temperature is preferably 40 ° C. If it exceeds the above, the crystallinity may become too high and stretching may become difficult. The upper limit of the cooling roll temperature is preferably 25 ° C. When the temperature of the cooling roll is within the above range, it is preferable to lower the humidity of the environment near the cooling roll in order to prevent dew condensation. It is preferable to reduce the temperature difference in the width direction of the cooling roll surface. At this time, the thickness of the unstretched sheet is preferably in the range of 15 to 2500 μm.

[Vertical stretching and horizontal stretching steps]

Next, the stretching method will be described. The stretching method can be either simultaneous biaxial stretching or sequential biaxial stretching, but in order to increase the puncture strength, it is necessary to increase the degree of plane orientation, and the film formation speed is high and the productivity is high. In terms of points, sequential biaxial stretching is most preferable.

The lower limit of the stretching temperature in the longitudinal stretching direction is preferably 55 ° C., more preferably 60 ° C. Breakage is unlikely to occur at 55 ° C. or higher. Further, since the vertical orientation of the film does not become too strong, the shrinkage stress during the heat fixing treatment can be suppressed, and a film with less distortion of the molecular orientation in the width direction can be obtained. The upper limit of the stretching temperature in the longitudinal stretching direction is preferably 100 ° C., more preferably 95 ° C. When the temperature is 100 ° C. or lower, the orientation of the film is not too weak and the mechanical properties of the film are not deteriorated.

The lower limit of the draw ratio in the longitudinal stretching direction is preferably 2.8 times, particularly preferably 3.0 times. When it is 2.8 times or more, the degree of surface orientation is increased, the piercing strength of the film is improved, and the thickness accuracy of the film is improved.

The upper limit of the draw ratio in the longitudinal stretching direction is preferably 4.3 times, more preferably 4.0 times, and particularly preferably 3.8 times. When it is 4.3 times or less, the degree of orientation of the film in the lateral direction does not become too strong, the shrinkage stress during the heat fixing process does not become too large, and the distortion of the molecular orientation in the lateral direction of the film becomes small, resulting in As a result, the vertical tearability is improved. Moreover, the effect of improving the mechanical strength and the thickness unevenness is saturated in this range.

The lower limit of the stretching temperature in the transverse stretching direction is preferably 60 ° C., and if it is 60 ° C. or higher, fracture may be less likely to occur. The upper limit of the stretching temperature in the transverse stretching direction is preferably 100 ° C., and when it is 100 ° C. or lower, the degree of orientation in the transverse stretching direction increases, so that the mechanical properties are improved.

The lower limit of the draw ratio in the transverse stretching direction is preferably 3.5 times, more preferably 3.6 times, and particularly preferably 3.7 times. If it is 3.5 times or more, the degree of orientation in the lateral direction is not too weak, and the mechanical properties and thickness unevenness are improved. The upper limit of the draw ratio in the transverse stretching direction is preferably 5 times, more preferably 4.5 times, and particularly preferably 4.0 times. If it is 5.0 times or less, the effect of improving the mechanical strength and thickness unevenness is maximized (saturated) even in this range.

[Heat fixing process]

The lower limit of the heat fixing temperature in the heat fixing step is preferably 195 ° C., more preferably 200 ° C. When the temperature is 195 ° C. or higher, the heat shrinkage rate of the film is reduced, and the inorganic thin film layer is not easily damaged even after the retort treatment, so that the gas barrier property is improved. The upper limit of the heat fixing temperature is preferably 220 ° C., and if it is 220 ° C. or lower, the base film layer does not melt and is less likely to become brittle.

[Heat relaxation section process]

The lower limit of the relaxation rate in the heat relaxation section step is preferably 0.5%. If it is 0.5% or more, breakage may be less likely to occur during heat fixing. The upper limit of the relaxation rate is preferably 10%. When it is 10% or less, the shrinkage in the longitudinal direction at the time of heat fixing becomes small, and as a result, the distortion of the molecular orientation at the edge of the film becomes small, and the straight tearability is improved. In addition, the film is less likely to sag and uneven thickness is less likely to occur.

[Inorganic thin film layer]

By providing an inorganic thin film layer on the surface of the biaxially stretched polyester film of the present invention, gas barrier properties can be imparted.

The inorganic thin film layer is a thin film made of a metal or an inorganic oxide. The material for forming the inorganic thin film layer is not particularly limited as long as it can be made into a thin film, but from the viewpoint of gas barrier properties, inorganic oxidation such as silicon oxide (silica), aluminum oxide (alumina), and a mixture of silicon oxide and aluminum oxide Things are preferred. In particular, a composite oxide of silicon oxide and aluminum oxide is preferable from the viewpoint of achieving both flexibility and denseness of the thin film layer. In this composite oxide, the mixing ratio of silicon oxide and aluminum oxide is preferably in the range of 20 to 70% by mass of Al in terms of the mass ratio of the metal content. If the Al concentration is less than 20% by mass, the water vapor barrier property may be lowered. On the other hand, if it exceeds 70% by mass, the inorganic thin film layer tends to be hard, and the film may be destroyed during secondary processing such as printing or laminating, and the gas barrier property may be lowered. The silicon oxide referred to here is various silicon oxides such as SiO and SiO ₂ or a mixture thereof, and aluminum oxide is various aluminum oxides such as AlO and Al ₂ O ₃ or a mixture thereof.

The film thickness of the inorganic thin film layer is usually 1 to 100 nm, preferably 5 to 50 nm. If the film thickness of the inorganic thin film layer is less than 1 nm, it may be difficult to obtain a satisfactory gas barrier property. On the other hand, even if the thickness exceeds 100 nm, the corresponding improvement effect of the gas barrier property can be obtained. This is not possible, and it is rather disadvantageous in terms of bending resistance and manufacturing cost.

The method for forming the inorganic thin film layer is not particularly limited, and is known, for example, a physical vapor deposition method (PVD method) such as a vacuum vapor deposition method, a sputtering method, or an ion plating method, or a chemical vapor deposition method (CVD method). The method may be adopted as appropriate. Hereinafter, a typical method for forming the inorganic thin film layer will be described by taking a silicon oxide / aluminum oxide thin film as an example. For example, when the vacuum vapor deposition method is adopted, a mixture of SiO ₂ and Al ₂ O ₃ or a mixture of SiO ₂ and Al is preferably used as the vapor deposition raw material. Particles are usually used as these vapor deposition raw materials, but at that time, it is desirable that the size of each particle is such that the pressure at the time of vapor deposition does not change, and the particle diameter is preferably 1 mm to 5 mm. For heating, methods such as resistance heating, high frequency induction heating, electron beam heating, and laser heating can be adopted. Further, it is also possible to introduce oxygen, nitrogen, hydrogen, argon, carbon dioxide gas, water vapor or the like as the reaction gas, or to adopt reactive vapor deposition using means such as ozone addition and ion assist. Further, the film forming conditions can be arbitrarily changed, such as applying a bias to the film to be deposited (laminated film to be subjected to vapor deposition) or heating or cooling the film to be deposited. Such a vapor deposition material, a reaction gas, a bias of the vapor deposition body, heating / cooling, and the like can be similarly changed when the sputtering method or the CVD method is adopted.

[Adhesive layer]

In the gas-via laminated film of the present invention, an adhesive layer can be provided between the base film layer and the inorganic thin film layer for the purpose of ensuring the gas barrier property and the lamination strength after the retort treatment.

The resin composition used for the adhesive layer provided between the base film layer and the inorganic thin film layer includes urethane-based, polyester-based, acrylic-based, titanium-based, isocyanate-based, imine-based, polybutadiene-based resins, and epoxy. Examples thereof include those to which a curing agent such as a system, an isocyanate system, or a melamine system is added. The resin composition used for these adhesive layers preferably contains a silane coupling agent having at least one type of organic functional group. Examples of the organic functional group include an alkoxy group, an amino group, an epoxy group, an isocyanate group and the like. By adding the silane coupling agent, the lamination strength after the retort treatment is further improved.

Among the resin compositions used for the adhesive layer, it is preferable to use a mixture of a resin containing an oxazoline group, an acrylic resin and a urethane resin. The oxazoline group has a high affinity with the inorganic thin film, and can react with the oxygen-deficient portion of the inorganic oxide generated during the formation of the inorganic thin film layer and the metal hydroxide, and exhibits strong adhesion to the inorganic thin film layer. .. Further, the unreacted oxazoline group existing in the adhesive layer can react with the carboxylic acid terminal generated by hydrolysis of the base film layer and the adhesive layer to form a crosslink.

The method for forming the adhesive layer is not particularly limited, and a conventionally known method such as a coating method can be adopted. Among the coating methods, the offline coating method and the in-line coating method can be mentioned as preferable methods. For example, in the case of the in-line coating method performed in the process of manufacturing the base film layer, the conditions of drying and heat treatment at the time of coating depend on the coating thickness and the conditions of the apparatus, but immediately after coating, they are fed into the stretching process in the perpendicular direction. It is preferable to dry in the preheating zone or the stretching zone of the stretching step, and in such a case, the temperature is usually preferably about 50 to 250 ° C.

Examples of the solvent (solvent) used when the coating method is used include aromatic solvents such as benzene and toluene; alcohol solvents such as methanol and ethanol; ketone solvents such as acetone and methyl ethyl ketone; ethyl acetate and butyl acetate. Etc., and examples thereof include polyhydric alcohol derivatives such as ethylene glycol monomethyl ether.

[Protective layer]

In the present invention, a protective layer is provided on the inorganic thin film layer. The metal oxide layer is not a completely dense film, but is dotted with minute defects. By applying a specific protective layer resin composition described later on the metal oxide layer to form the protective layer, the resin in the protective layer resin composition permeates the defective portion of the metal oxide layer. As a result, the effect of stabilizing the gas barrier property can be obtained. In addition, by using a material having a gas barrier property for the protective layer itself, the gas barrier performance of the gas barrier laminated film will be greatly improved.

The resin composition used for the protective layer formed on the surface of the inorganic thin film layer of the gas barrier laminated film of the present invention includes resins such as urethane-based, polyester-based, acrylic-based, titanium-based, isocyanate-based, imine-based, and polybutadiene-based resins. , Epoxy-based, isocyanate-based, melamine-based and other curing agents are added.

In the urethane resin, the polar group of the urethane bond interacts with the inorganic thin film layer and also has flexibility due to the presence of the amorphous portion, so that damage to the inorganic thin film layer is suppressed even when a bending load is applied. It is preferable because it can be used.

The acid value of the urethane resin is preferably in the range of 10 to 60 mgKOH / g. It is more preferably in the range of 15 to 55 mgKOH / g, and even more preferably in the range of 20 to 50 mgKOH / g. When the acid value of the urethane resin is within the above range, the liquid stability is improved when it is made into an aqueous dispersion, and the protective layer can be uniformly deposited on the highly polar inorganic thin film, so that the coat appearance is good. It becomes.

The urethane resin preferably has a glass transition temperature (Tg) of 80 ° C. or higher, more preferably 90 ° C. or higher. By setting the Tg to 80 ° C. or higher, the swelling of the protective layer due to molecular motion in the wet heat treatment process (heating-retaining-lowering) can be reduced.

From the viewpoint of improving gas barrier properties, it is more preferable to use a urethane resin containing an aromatic or aromatic aliphatic diisocyanate component as a main component.

Among them, it is particularly preferable to contain a metaxylylene diisocyanate component. By using the above resin, the cohesive force of the urethane bond can be further enhanced by the stacking effect of the aromatic rings, and as a result, good gas barrier properties can be obtained.

In the present invention, the ratio of aromatic or aromatic aliphatic diisocyanate in the urethane resin is preferably in the range of 50 mol% or more (50 to 100 mol%) in 100 mol% of the polyisocyanate component (F). The ratio of the total amount of the aromatic or aromatic aliphatic diisocyanate is preferably 60 to 100 mol%, more preferably 70 to 100 mol%, still more preferably 80 to 100 mol%. As such a resin, the "Takelac (registered trademark) WPB" series commercially available from Mitsui Chemicals, Inc. can be preferably used. If the ratio of the total amount of aromatic or aromatic aliphatic diisocyanates is less than 50 mol%, good gas barrier properties may not be obtained.

The urethane resin preferably has a carboxylic acid group (carboxyl group) from the viewpoint of improving the affinity with the inorganic thin film layer. In order to introduce a carboxylic acid (salt) group into the urethane resin, for example, a polyol compound having a carboxylic acid group such as dimethylolpropionic acid or dimethylolbutanoic acid may be introduced as a copolymerization component as a polyol component. Further, if the carboxylic acid group-containing urethane resin is synthesized and then neutralized with a salt-forming agent, an aqueous dispersion urethane resin can be obtained. Specific examples of the salt forming agent include trialkylamines such as ammonia, trimethylamine, triethylamine, triisopropylamine, tri-n-propylamine and tri-n-butylamine, and N such as N-methylmorpholine and N-ethylmorpholine. Examples thereof include N-dialkylalkanolamines such as -alkylmorpholins, N-dimethylethanolamine and N-diethylethanolamine. These may be used alone or in combination of two or more.

Examples of the solvent (solvent) include aromatic solvents such as benzene and toluene; alcohol solvents such as methanol and ethanol; ketone solvents such as acetone and methyl ethyl ketone; ester solvents such as ethyl acetate and butyl acetate; ethylene glycol. Examples thereof include polyhydric alcohol derivatives such as monomethyl ether.

From the above, the biaxially stretched polyester film of the present invention is excellent in bag breaking resistance and bending resistance, and a wide roll is formed on the base film layer to form an inorganic thin film layer and a protective layer to form a gas barrier film. Even in the case of producing the above film, it is possible to suppress streak-like wrinkles generated during heat transfer and make the gas barrier property in the width direction uniform.

[Packaging material]

When the biaxially stretched polyester film or gas barrier laminated film of the present invention is used as a packaging material, it is preferable to form a thermosetting resin layer called a sealant. The heat-sealing resin layer is usually provided on the inorganic thin film layer, but may be provided on the outside of the base film layer (the surface opposite to the adhesive layer forming surface). The heat-sealable resin layer is usually formed by an extrusion laminating method or a dry laminating method. The thermoplastic polymer that forms the heat-sealable resin layer may be any that can sufficiently exhibit sealant adhesiveness, and is a polyethylene resin such as HDPE, LDPE, LLDPE, a polypropylene resin, or an ethylene-vinyl acetate copolymer. , Polyethylene-α-olefin random copolymer, ionomer resin and the like can be used.

Further, in the biaxially stretched polyester film or the gas barrier laminated film, a printing layer or another plastic base material and / or a paper base is provided between or outside the inorganic thin film layer or the base film layer and the heat-sealing resin layer. At least one layer or more of the material may be laminated.

As the printing ink forming the printing layer, water-based and solvent-based resin-containing printing inks can be preferably used. Examples of the resin used for the printing ink include acrylic resin, urethane resin, polyester resin, vinyl chloride resin, vinyl acetate copolymer resin, and a mixture thereof. Known printing inks include antistatic agents, light blocking agents, ultraviolet absorbers, plasticizers, lubricants, fillers, colorants, stabilizers, lubricants, defoamers, cross-linking agents, blocking agents, antioxidants, etc. Additives may be included. The printing method for providing the print layer is not particularly limited, and known printing methods such as an offset printing method, a gravure printing method, and a screen printing method can be used. For drying the solvent after printing, known drying methods such as hot air drying, hot roll drying, and infrared drying can be used.

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

[Film thickness]

It was measured using a dial gauge in accordance with JIS K7130-1999 A method.

[Film surface orientation ΔP]

About the sample The refractive index (Nx) in the longitudinal direction of the film and the refractive index (Ny) in the width direction were measured by the Abbe refractometer using sodium D line as a light source by the JIS K 7142-1996 A method, and the formula [2] was calculated. The plane orientation ΔP was calculated as described above.

Planar orientation (ΔP) = (Nx + Ny) / 2-Nz ・ ・ ・ [2]

[Heat shrinkage of film]

The heat shrinkage of the polyester film was measured by the dimensional change test method described in JIS-C-2151-2006.21, except that the test temperature was 150 ° C. and the heating time was 15 minutes. The test piece was used as described in 21.1 (a).

[Film piercing strength]

The obtained polyester film was sampled into a 5 cm square, and made into JIS Z1707 using the digital force gauge "ZTS-500N" manufactured by Imada Co., Ltd., the electric measuring stand "MX2-500N", and the piercing jig "TKS-250N". The piercing strength of the film was measured accordingly. The unit is N / μm.

[Variation of puncture strength in the longitudinal direction]

The obtained polyester film roll (width 2080 mm, winding length 30,000 m) was sampled every 100 m from the surface layer of the film roll to the winding core in the longitudinal direction.

The piercing strength of each sampled film was measured according to JIS Z 1707.

The maximum value of the obtained piercing strength was Xmax (N / μm), the minimum value was Xmin (N / μm), and the average value was Xave, and the variation in piercing strength represented by the following formula [1] was obtained. ..

Longitudinal variation in piercing strength (%) = 100 × (Xmax-Xmin) / Xave ・ ・ ・ [1]

[Impact strength of film]

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

[Contents of various atoms in polyester film]

It was quantified by the method shown below.

(A) Antimony atom

1 g of the sample was wet-decomposed with a mixed solution of sulfuric acid / hydrogen peroxide solution. Then, sodium nitrite was added to make the Sb atom Sb ^5+, and Brilliant Green was added to form a blue complex with Sb. After extracting this complex with toluene, the absorbance at a wavelength of 625 nm was measured using an absorptiometer (UV-150-02 manufactured by Shimadzu Corporation), and the amount of Sb atoms in the sample was compared from the calibration curve prepared in advance. Color quantified.

(B) Phosphorus atom

The phosphorus compound is converted to orthophosphorus by a method of dry ash decomposition in the presence of sodium carbonate or a method of wet decomposition with a mixed solution of sulfuric acid / nitric acid / perchloric acid or a mixed solution of sulfuric acid / hydrogen peroxide solution. did. Then, the molybdate was reacted in a 1 mol / L sulfuric acid solution to obtain phosphomolybdic acid, which was reduced with hydrazine sulfate to produce heteropoly blue. The absorbance at a wavelength of 830 nm was measured with an absorptiometer (UV-150-02, manufactured by Shimadzu Corporation). The amount of phosphorus atoms in the sample was quantified from the calibration curve prepared in advance.

(C) Aluminum atom

0.1 g of the sample was dissolved in a 6 M hydrochloric acid solution and left to stand for one day, and then diluted with pure water to prepare a 1.2 M hydrochloric acid measurement solution. The prepared solution sample was determined by high frequency plasma emission analysis.

[Number of defects]

A film roll having a width of 800 mm and a winding length of 10000 m (8000 square meters) was rewound using a rewinding machine. When rewinding, the number of defects was investigated using a defect detector (model FMAX MR) manufactured by FUTEC. Then, the number of defects having a size of 1 mm or more was determined in either the vertical direction or the horizontal direction. From all the defects, the number of defects per 1000 square meters was calculated by the formula [3].

Number of defects per 1000 square meters = Number of all defects ÷ 8 ... [3]

[printing]

A film roll having a defect inspection of 800 mm and a winding length of 10000 m (8000 square meters) was gravure-printed at a speed of 100 m / min and a halftone dot of 5% using a gravure printing machine (manufactured by Higashiya Iron Works Co., Ltd.). The ink used at this time was gravure printing ink (manufactured by Toyo Ink Co., Ltd .: trade name Finestar R92 ink), and was mixed with a diluting solvent (manufactured by Toyo Ink Co., Ltd .: trade name SL302) at a ratio of 77:23. .. The obtained print sample was rewound using a rewinding machine. When rewinding, the number of print omissions was investigated using a defect detector (model FMAX MR) manufactured by FUTEC. Then, the number of print omissions having a size of 1 mm or more was determined in either the vertical direction or the horizontal direction. From all the print omissions, the number of defects per 1000 square meters was calculated by [4].

Number of missing prints per 1000 square meters = Number of all defects ÷ 8 ・ ・ ・ [4]

The details of the raw material resin and the coating liquid used in Examples and Comparative Examples are described below.

1) PBT resin (A): As the polybutylene terephthalate resin used in the production of the biaxially stretched polyester film described later, 1100-211XG (CANG CHUN PLASTICS CO., LTD., Intrinsic viscosity 1.28 dl / g) was used.

2) PET resin (B): A PET resin (B-1) polymerized with an aluminum catalyst containing no antimony catalyst and a PET resin (B-2) polymerized with an antimony catalyst were prepared by the following method.

<Preparation of polymerization catalyst solution>

(Ethylene glycol solution of phosphorus compound)

After adding 2.0 liters of ethylene glycol to a flask equipped with a nitrogen introduction tube and a cooling tube under normal temperature and pressure, while stirring at 200 rpm under a nitrogen atmosphere, Irganox1222 (BA) represented by the chemical formula (4) as a phosphorus compound. 200 g (manufactured by SF) was added. After further adding 2.0 liters of ethylene glycol, the jacket temperature was changed to 196 ° C. to raise the temperature, and the mixture was stirred under reflux for 60 minutes from the time when the internal temperature reached 185 ° C. or higher. After that, the heating was stopped, the solution was immediately removed from the heat source, and the solution was cooled to 120 ° C. or lower within 30 minutes while maintaining the nitrogen atmosphere.

(Ethylene glycol solution of aluminum compound)

After adding 5.0 liters of pure water to a flask provided with a cooling tube under normal temperature and pressure, 200 g of basic aluminum acetate (hydroxyaluminum diacetate) was added as a slurry with pure water while stirring at 200 rpm. Further, pure water was added so as to have a total volume of 10.0 liters, and the mixture was stirred at normal temperature and pressure for 12 hours. Then, the jacket temperature setting was changed to 100.5 ° C. to raise the temperature, and the mixture was stirred under reflux for 3 hours from the time when the internal temperature reached 95 ° C. or higher. Stirring was stopped and the mixture was allowed to cool to room temperature. At that time, when undissolved particles were found, the solution was filtered through a glass filter (3G) to obtain an aqueous solution of an aluminum compound.

Subsequently, 2.0 liters of the aqueous solution of the aluminum compound and 2.0 liters of ethylene glycol were charged into a flask equipped with a distillation apparatus under normal temperature and pressure, and after stirring at 200 rpm for 30 minutes, a uniform water / ethylene glycol mixed solution was prepared. Obtained. Then, the jacket temperature setting was changed to 110 ° C. to raise the temperature, and water was distilled off from the solution. When the amount of distilled water reached 2.0 liters, heating was stopped and allowed to cool to room temperature to obtain an ethylene glycol solution of an aluminum compound.

(Polymerization of PET resin (B-1))

2130 parts by mass of terephthalic acid, 1955 parts by mass of ethylene glycol, and 0.7 parts by mass of triethylamine were added to a reaction can equipped with a stirrer, a thermometer, and a cooling device for distillation, and the temperature was 220 ° C. to 250 ° C. under a pressure of 0.35 MPa. The temperature was gradually raised to, and the esterification reaction was carried out while removing the accumulated water from the system. Subsequently, as a polymerization catalyst solution, a mixed solution of the ethylene glycol solution of the phosphorus compound and the ethylene glycol solution of the aluminum compound was used as an aluminum atom with 0.047 mol% as a phosphorus atom with respect to the dicarboxylic acid component in the polyester resin. After adding to 0.021 mol%, the initial polymerization under reduced pressure was carried out to 1.3 kPa over 1 hour, the temperature rose to 270 ° C., and the late polymerization was further carried out at 0.13 kPa or less, and the intrinsic viscosity used in the present invention was obtained. Obtained 0.73 dl / g of PET resin (B-1).

(Polymerization of PET resin (B-2))

Instead of the aluminum-based catalyst, an ethylene glycol solution of Sb ₂ O ₃ of the antimony-based catalyst was prepared and added so as to have 0.084 mol% as the antimony atom, and the same production as the above-mentioned PET resin (B-1) was produced. By the method, a PET resin (B-2) having an intrinsic viscosity of 0.73 dl / g used in the comparative example of the present invention was obtained.

3) Resin having an oxazoline group (C): As a resin having an oxazoline group, a commercially available water-soluble oxazoline group-containing acrylate (“Epocross (registered trademark) WS-300” manufactured by Nippon Catalyst Co., Ltd .; solid content 10%) is prepared. did. The amount of oxazoline groups in this resin was 7.7 mmol / g.

4) Acrylic resin (D): As an acrylic resin, a 25% by mass emulsion of a commercially available acrylic acid ester copolymer (“Mobile (registered trademark) 7980” manufactured by Nichigo Vinyl Co., Ltd.” was prepared. This acrylic resin (B) The acid value (theoretical value) of was 4 mgKOH / g.

5) Urethane resin (E): As a urethane resin, a commercially available polyester urethane resin dispersion (“Takelac (registered trademark) W605” manufactured by Mitsui Chemicals, Inc .; solid content 30%) was prepared. The acid value of this urethane resin was 25 mgKOH / g, and the glass transition temperature (Tg) measured by DSC was 100 ° C. The ratio of aromatic or aromatic aliphatic diisocyanate to the total polyisocyanate component measured by 1H-NMR was 55 mol%.

6) Urethane resin (F) ;: As a urethane resin, a dispersion of a commercially available metaxylylene group-containing urethane resin (“Takelac (registered trademark) WPB341” manufactured by Mitsui Chemicals, Inc .; solid content 30%) was prepared. The acid value of this urethane resin was 25 mgKOH / g, and the glass transition temperature (Tg) measured by DSC was 130 ° C. The ratio of aromatic or aromatic aliphatic diisocyanate to the total polyisocyanate component measured by 1H-NMR was 85 mol%.

7) Coating liquid used for the adhesive layer 1

Each material was mixed at the following blending ratio to prepare a coating liquid 1 (resin composition for an adhesive layer).

Water 54.40% by mass

Isopropanol 25.00% by mass

Oxazoline group-containing resin (C) 15.00% by mass

Acrylic resin (D) 3.60% by mass

Urethane resin (E) 2.00% by mass

8) Coating liquid used for coating the protective layer 2

The following coating agents were mixed to prepare a coating liquid 2.

Water 60.00% by mass

Isopropanol 30.00% by mass

Urethane resin (F) 10.00% by mass

[Preparation of laminated laminate]

Urethane-based two-component curable adhesives (“Takelac (registered trademark) A525S” manufactured by Mitsui Chemicals, Inc. and “Takenate” are placed on the protective layer side of the gas barrier films shown in Examples 1 to 8 and Comparative Examples 1 to 4, which will be described later. A non-stretched polypropylene film with a thickness of 70 μm as a thermosetting resin layer (“P1147” manufactured by Toyo Boseki Co., Ltd.) by a dry laminating method using (registered trademark) A50 at a ratio of 13.5: 1 (mass ratio). ”) Are laminated and aged at 40 ° C. for 4 days to obtain a laminated laminate for evaluation. The thickness of the adhesive layer formed of the urethane-based two-component curable adhesive after drying was about 4 μm.

[Water vapor permeability of laminated laminate]

The above-mentioned laminated laminate was subjected to a water vapor permeability measuring device (“PERMATRAN-W1A” manufactured by MOCON) in accordance with the JIS-K7129-1992 B method under an atmosphere of a temperature of 40 ° C. and a relative humidity of 90 RH%. , The water vapor permeability under normal conditions was measured. The water vapor permeability was measured in the direction in which water vapor permeated from the base film layer side to the sealant side.

[Water vapor permeability after retort of laminated laminate]

The above-mentioned laminated laminate was subjected to a wet heat treatment of holding it in hot water at 130 ° C. for 30 minutes in a retort kettle, dried at 40 ° C. for 1 day (24 hours), and the obtained laminated laminate after the wet heat treatment. The water vapor permeability of the body was measured in the same manner as above.

The method for producing the biaxially stretched polyester film used in each Example and Comparative Example is described below. The physical properties of the following biaxially stretched polyester film are shown in Tables 1 and 2.

<Example 1>

Using a uniaxial extruder, 20% by mass of PET resin (B-1) was mixed with 80% by mass of PBT resin (A) and silica particles having an average particle size of 2.4 μm as inert particles so as to have an average particle size of 7000 ppm. The material was melted at 290 ° C. and then introduced into a melt line. However, the PET resin (B-1) was supplied using an inner pipe as shown in FIG. 1 so that segregation does not occur before entering the extruder (so that it can always be uniformly mixed with the PBT resin).

Then, it was cast from a T-die at 265 ° C. and adhered to a cooling roll at 20 ° C. by an electrostatic adhesion method to obtain an unstretched sheet.

Then, it was rolled 2.9 times in the longitudinal direction at 60 ° C., then passed through a tenter and stretched 4.0 times in the lateral direction at 90 ° C., and tension heat treatment at 200 ° C. for 3 seconds and relaxation of 9% for 1 second. After the treatment was carried out, the film was cooled by cooling at 50 ° C. for 2 seconds.

Next, the grips at both ends were cut and removed by 10% to obtain a full-width roll (hereinafter referred to as a mill roll) of a biaxially stretched polyester film having a thickness of 15 μm and a total width of 4200 mm. The obtained mill roll was slit, and two slit rolls having a roll width of 2080 mm were collected.

A gas barrier laminated film was obtained by forming an inorganic thin film layer and a protective layer on a biaxially stretched polyester film slit by the method for forming an inorganic thin film layer and a protective layer shown below.

<Formation of inorganic thin film layer>

A composite oxide layer of silicon dioxide and aluminum oxide was formed as an inorganic thin film layer on the slit film by an electron beam deposition method. Particulate SiO ₂ (purity 99.9%) and A1 ₂ O ₃ (purity 99.9%) having a thickness of about 3 mm to 5 mm were used as the vapor deposition source. Get in this way

The film thickness of the obtained film (inorganic thin layer / adhesive layer containing film) inorganic thin layer in the _(SiO 2 / _A1 2 _{O 3} composite oxide layer) was 13 nm. The composition of this composite oxide layer was SiO ₂ / A1 ₂ O ₃ (mass ratio) = 60/40.

<Formation of protective layer>

The coating liquid 2 was applied onto the inorganic thin film layer formed by the above vapor deposition by the wire bar coating method, and dried at 200 ° C. for 15 seconds to obtain a protective layer. The coating amount after drying was 0.190 g / m ² (as Dry solid content).

As described above, a gas barrier laminated film having an adhesive layer / an inorganic thin film layer / a protective layer on the base film in this order was produced.

Table 1 shows the film forming conditions, physical properties, and evaluation results of the obtained biaxially stretched polyester film and gas barrier laminated film.

<Examples 2 to 7, Comparative Examples 1 to 3>

In the film forming process of the biaxially stretched polyester films 2 to 7 and the biaxially stretched films of Comparative Examples 1 to 3, the ratio of the PBT resin (A), the type of the PET resin (B), the vertical and horizontal stretching ratio, and the relaxation rate are shown. This was carried out in the same manner as in Example 1 except that it was shown in 1 and Table 2.

<Example 8>

Using a uniaxial extruder, 80% by mass of PBT resin (A) and 20% by mass of PET resin (B-1) are mixed, and silica particles having an average particle size of 2.4 μm as inert particles are mixed as a silica concentration. A mixture prepared at 900 ppm with respect to the resin was melted at 290 ° C. and then introduced into a melt line. Then, it was cast from a T-die at 265 ° C. and adhered to a cooling roll at 20 ° C. by an electrostatic adhesion method to obtain an unstretched sheet.

Then, the resin composition for the adhesive layer (coating liquid 1) was applied by the fountain bar coating method after the vertical stretching at 60 ° C. for 2.9 times roll stretching. Then, it is guided to a tenter while drying, then passed through the tenter and stretched 4.0 times in the lateral direction at 90 ° C., subjected to tension heat treatment at 200 ° C. for 3 seconds and relaxation treatment of 9% for 1 second, and then 50. Cooling was performed at ° C. for 2 seconds.

Next, the grips at both ends were cut and removed by 10% to obtain a mill roll of a biaxially stretched polyester film having a thickness of 15 μm and a total width of 4200 mm. The obtained mill roll was slit, and two slit rolls having a width of 2080 mm were collected. In the same manner as in Example 1, an inorganic thin film layer and a protective layer were formed on the slit film to obtain a gas barrier laminated film.

Table 2 shows the film forming conditions, physical properties, and evaluation results of the obtained biaxially stretched polyester film and gas barrier laminated film.

<Comparative example 4>

Using a uniaxial extruder, 20% by mass of PET resin (B-1) was mixed with 80% by mass of PBT resin (A) and silica particles having an average particle size of 2.4 μm as inert particles so as to have an average particle size of 7000 ppm. After melting the material at 290 ° C., the melt line was introduced into a 12-element static mixer. The inner pipe was not used for mixing the PBT resin and the PET resin, and the PBT resin and the PET resin were mixed at the upper part of the hopper.

Similarly to the above, the product was cast from a T-die at 265 ° C. and adhered to a cooling roll at 20 ° C. by an electrostatic adhesion method to obtain an unstretched sheet.

Then, it was rolled 2.9 times in the longitudinal direction at 60 ° C., then passed through a tenter and stretched 4.0 times in the lateral direction at 90 ° C., tension heat treatment at 200 ° C. for 3 seconds and relaxation of 9% for 1 second. After the treatment was carried out, the film was cooled by cooling at 50 ° C. for 2 seconds.

Next, the grips at both ends were cut and removed by 10% to obtain a full-width roll (hereinafter referred to as a mill roll) of a biaxially stretched polyester film having a thickness of 15 μm and a total width of 4200 mm. The obtained mill roll was slit, and two slit rolls having a roll width of 2080 mm were collected. In the same manner as in Example 1, an inorganic thin film layer and a protective layer were formed on the slit film to obtain a gas barrier laminated film.

Table 2 shows the film forming conditions, physical properties, and evaluation results of the obtained biaxially stretched film and gas barrier laminated film.

As shown in Tables 1 and 2, the biaxial stretching of the present invention of Examples 1 to 7 is carried out by using a PET resin having a PBT ratio within the scope of the present invention and using an aluminum compound as a polymerization catalyst as a PET raw material. Compared with the case where the conventional antimony compounds shown in Comparative Examples 1 and 2 are used with the PET resin used as the polymerization catalyst, the physical properties such as strength are inferior, the pinhole resistance is excellent, and the foreign matter in the film is further improved. It was possible to obtain a biaxially stretched polyester film with less printing loss.

Further, in the biaxially stretched polyester film obtained by the present invention, the variation in the puncture strength in the longitudinal direction is small by using the inner pipe for supplying the raw material.

In Example 8, since the adhesive layer was provided between the biaxially stretched polyester film and the inorganic thin film layer, the gas barrier property after the retort treatment was good.

In Comparative Example 3, heat treatment can be performed at a high temperature in which the ratio of PET is increased, and the dimensional stability is improved, but at the same time, the ratio of PBT is reduced, so that the mechanical strength such as puncture resistance is lowered.

In Comparative Example 4, since the inner pipe was not used for supplying the raw materials and the raw material ratio fluctuated greatly in the longitudinal direction due to the segregation of the raw materials, the variation in the puncture strength in the longitudinal direction was large.

According to the present invention, not only is it excellent in pinhole resistance and bag tear resistance, but it is also excellent in hygiene, printability and workability, and even a long film roll having a long winding length is long. It has become possible to provide a biaxially stretched polyester film having little variation in physical properties in the direction and a method for producing the same. Since these films do not contain an antimony catalyst as a food packaging material, they have excellent hygiene and can be widely applied, and are expected to greatly contribute to the industrial world.

In addition to food packaging, it can be widely used in packaging of pharmaceuticals and industrial products, and in industrial applications such as solar cells, electronic paper, organic EL elements, and semiconductor elements.

Claims (8)

1. 
   Biaxial stretching containing at least 60 to 95% by mass of polybutylene terephthalate resin (A) and 5 to 40% by mass of polyethylene terephthalate resin (B) and simultaneously satisfying the following (1) to (4). Polyester film.
   
   (1) The puncture strength measured according to JIS Z 1707 is 0.6 N / μm or more.
   
   (2) The degree of surface orientation of the film is 0.144 to 0.160.
   
   (3) The heat shrinkage of the film after heating at 150 ° C. for 15 minutes is 0 to 4% in the vertical direction and -1 to 3% in the horizontal direction.
   
   (4) The content of antimony atoms in the film is 7 ppm or less.
   
2. 
   The first aspect of the present invention, wherein the polyethylene terephthalate (B) contains at least one selected from an aluminum compound and at least one selected from a phosphorus compound as a polymerization catalyst. Biaxially stretched polyester film.
   
3. 
   The biaxially stretched polyester film according to claim 1 or 2, wherein the number of defects of 1 mm or more per 1000 square meters of the film is 1.0 or less.
   
4. 
   Sampling from the surface layer of the film roll to the core in the vertical direction every 1000 m, the maximum value of the puncture strength measured according to JIS Z 1707 is Xmax (N / μm), the minimum value is Xmin (N / μm), and the average. The biaxially stretched polyester film according to any one of claims 1 to 3, wherein the variation in piercing strength represented by the following formula [1] is 20% or less when the value is Xave.
   
   Longitudinal variation in piercing strength (%) = 100 × (Xmax-Xmin) / Xave ... [1]
   
5. 
   The gas barrier laminated film according to any one of claims 1 to 4, wherein the biaxially stretched polyester film has an inorganic thin film layer on at least one surface.
   
6. 
   The gas barrier laminated film according to claim 5, wherein an adhesive layer is provided between the biaxially stretched polyester film and the inorganic thin film layer.
   
7. 
   The gas barrier laminated film according to claim 5 or 6, wherein the surface of the inorganic thin film layer has a protective layer.
   
8. 
   In the melt extrusion process of the polyester raw material resin, the raw material resin chip of polybutylene terephthalate (A) is supplied to the hopper from above, and the raw material resin of polyethylene terephthalate (B) is supplied through a pipe having an outlet directly above the extruder in the hopper. The method for producing a biaxially stretched polyester film according to any one of claims 1 to 4, wherein the chips are supplied, both chips are mixed, and melt-extruded.

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