JP4232085B2 - Polyester film - Google Patents

Description

【００４３】
【発明の効果】
本発明のポリエステル系フィルムは、引張弾性率が大きいため腰感に優れ、かつ耐屈曲疲労性に優れているため、２軸延伸ポリエチレンテレフタレートフィルムと２軸延伸ナイロンフィルムの良好な特性を兼ね備えたフィルムであり、包装用フィルムとして極めて有用なフィルムといえる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polyester film. More specifically, the present invention relates to a polyester film suitable for packaging applications having excellent mechanical characteristics, thermal characteristics, and bending fatigue resistance.
[0002]
[Prior art]
Conventionally, in the field of packaging, a biaxially stretched polyethylene terephthalate film, which is a typical example of a polyester film, has been widely used because of good mechanical properties and thermal properties. However, in applications in which impact resistance and bending fatigue resistance are regarded as important, the above properties are inferior due to the hardness that is the reverse of the toughness of polyethylene terephthalate, and thus biaxially stretched nylon films have been frequently used. However, due to the essential properties of nylon polymers (the property of high moisture absorption and temperature expansion), biaxially stretched nylon films often undergo dimensional changes depending on storage conditions, and are suitable for processing such as printing and bag making. There was a drawback that it decreased. In addition, when used as a substrate for laminating, a substrate for laminating a metal or a metal oxide, there are disadvantages in that it is often restricted. In order to eliminate such drawbacks, polyester films having improved impact resistance or bending fatigue resistance have been studied.
[0003]
For example, there is a polyester film composed of a blend of linear polyester, polyethylene resin incompatible with the polyester, and ionomer resin. When the raw material blended with ionomer resin is melted in an extruder and cast from a die through a melt line, There is a drawback that the polymer is likely to stay in a molten state in the extruder or melt line, and as a result, polymer degradation products, gel-like materials, etc. are likely to be generated in the cast resin film (see, for example, Patent Document 1).
[0004]
In order to avoid such disadvantages, a polyester containing a long-chain aliphatic dicarboxylic acid having an alkylene group having 10 or more carbon atoms is biaxially oriented so that the Young's modulus is 10 to 250 kg / mm 2 and the puncture strength is 10 kg / mm or more. There is a conductive polyester film (see, for example, Patent Document 2).
[0005]
Also, the alcohol component is 40 to 99 mol% of two or more diol residues and aromatic dicarboxylic acid residues selected from HO- (CH2) 2n-OH (n: 1 to 10), long-chain aliphatic dicarboxylic acid. There exists a flexible polyester film which consists of 60-1 mol% of acid residues (for example, refer patent document 3).
[0006]
However, although these polyester films satisfy the impact resistance or bending fatigue resistance, etc., the mechanical properties (for example, tensile elastic modulus) that are characteristic of the polyester film are small, so there is a drawback that the film is weak. These films have not been satisfactory in the field of packaging for which the weight reduction (thinning) of packaging materials is strongly demanded.
[0007]
[Patent Document 1]
Japanese Examined Patent Publication No. 6-68065 [0008]
[Patent Document 2]
Japanese Examined Patent Publication No. 7-71820 [0009]
[Patent Document 3]
JP-A-3-231930
[Problems to be solved by the invention]
The object of the present invention is to solve the problems of the prior art. That is, it has a mechanical property peculiar to a polyester film, and therefore provides a polyester film that is excellent in waist feeling, can be made thin, and has excellent bending fatigue resistance.
[0011]
[Means for Solving the Problems]
The object of the present invention is 80/20 to 99/1 (% by weight) of polyester and olefin polymer mainly composed of polyethylene terephthalate and / or ethylene terephthalate having a melting point of 225 ° C. or more, and the dispersion diameter of the olefin polymer is 2 It is achieved by a polyester film comprising a polyester resin composition in the range of 10 μm.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The polyester blended in the polyester resin composition in the present invention is required to be a polyester mainly composed of polyethylene terephthalate and / or ethylene terephthalate having a melting point of 225 ° C. or higher in order to ensure mechanical properties. When a polyester mainly composed of a repeating unit other than ethylene terephthalate is used, the mechanical properties of the polyester film are often impaired, which is not preferable. Further, when a polyester mainly composed of ethylene terephthalate having a melting point of less than 225 ° C. is used, it is not preferable because the polyester film is often broken in a heat treatment step for dimensional stabilization after stretching. However, in the present invention, a polyester comprising an acid component other than terephthalic acid and / or a glycol component other than ethylene glycol can be used as long as the mechanical properties are not impaired. In particular, a polyester comprising an ethylene terephthalate unit and an ethylene isophthalate unit and having a melting point of 225 ° C. or higher is a preferable polyester for achieving the object of the present invention.
[0013]
As dicarboxylic acids other than terephthalic acid and / or isophthalic acid, aromatic dicarboxylic acids such as orthophthalic acid, naphthalenedicarboxylic acid, diphenylsulfone dicarboxylic acid, 5-sodium sulfoisophthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, Aliphatic dicarboxylic acids such as decanedicarboxylic acid, maleic acid, fumaric acid and dimer acid, oxycarboxylic acids such as p-oxybenzoic acid, and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid can be used.
[0014]
As glycol components other than ethylene glycol, aliphatic glycols such as propanediol, butanediol, pentanediol, hexanediol and neopentylglycol, alicyclic glycols such as cyclohexanedimethaneol, bisphenol A, bisphenol S and the like Aromatic glycols can be used.
[0015]
The polyester blended in the polyester resin composition according to the present invention includes an antioxidant, a heat stabilizer, an ultraviolet absorber, a plasticizer, a pigment, an antistatic agent, a lubricant, a crystal nucleating agent, inorganic or organic as necessary. You may mix | blend the lubricant etc. which consist of particle | grains.
[0016]
There is no particular limitation on the method for producing the polyester blended in the polyester resin in the present invention. That is, it can be used even if it is produced by either the transesterification method or the direct polymerization method. Further, it may be produced by a solid phase polymerization method in order to increase the molecular weight. Further, a polyester having a low oligomer content produced by a vacuum solid phase polymerization method can also be used.
[0017]
The olefin polymer blended in the polyester resin composition in the present invention is not particularly limited. Examples of olefin polymers include low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, ultrahigh molecular weight polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-butene copolymer, and other ethylene. -Α-olefin copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer, ethylene-methacrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl A methacrylate copolymer, an ethylene-vinyl alcohol copolymer, an ethylene-glycidyl acrylate copolymer, an ethylene-glycidyl methacrylate copolymer, an ethylene-maleic anhydride copolymer, or the like can be used.
[0018]
As the olefin polymer in the present invention, one kind of resin selected from the above can be used alone, but two or more kinds of resins can be used in combination, and the kind thereof is used to achieve the object of the present invention. And the addition amount can be selected suitably.
[0019]
In the present invention, it is necessary that the dispersion diameter of the olefin polymer blended in the polyester resin composition is substantially in the range of 2 to 10 μm. When the dispersion diameter of the olefin polymer is less than 2 μm, a part of the olefin polymer is apparently uniformly dissolved in the polyester and not only the effect of improving the bending fatigue resistance is saturated but also the mechanical properties of the polyester film. The properties are often impaired, and furthermore, the film-forming property is often lowered due to the deterioration of the thermal stability of the polyester resin composition, which is not preferable. On the contrary, when the dispersion diameter of the olefin polymer exceeds 10 μm, the interaction at the interface between the olefin polymer and the polyester becomes small, and the effect of improving the bending fatigue resistance of the polyester film is small, which is not preferable.
[0020]
In the polyester resin composition, an olefin polymer is dispersed in the form of islands in the polyester, and one of the selection examples of the olefin polymer for finely dispersing the dispersion diameter of the olefin polymer in the above range is a functional group. And a combination of two or more olefin-based polymers including a polyolefin containing no functional group and a polyolefin containing a functional group. By blending the olefin group having the above structure with polyester, olefin dispersed particles having a core / shell structure in which the central layer (core) is made of polyolefin and the surface layer (shell) is made of functional group-containing polyolefin are produced. It is considered to be dispersed. Specific examples include the combined use of polyethylene and ethylene- (meth) acrylic acid copolymer, and the combined use of ethylene-α-olefin copolymer and ethylene-α-olefin- (meth) acrylic acid copolymer. .
As a preferred functional group, a functional group having polarity and an effect of increasing affinity with polyester can be used. Examples thereof include a carboxyl group, a glycidyl group, and an acid anhydride group. Specific examples include ethylene-α, β-unsaturated carboxylic acid copolymers such as ethylene- (meth) acrylate copolymers and ethylene- (meth) acrylic acid ester copolymers produced by various production methods and catalysts. can do.
However, some or all of the carboxylic acid groups of the α, β-unsaturated carboxylic acid were neutralized with metal ions such as Na, K, Li, Zn, Mg, and Ca as a copolymer of vinyl monomers having functional groups. In the case of using an ionomer, it is preferable that the amount of metal ions does not exceed 200 ppm with respect to the total amount of the olefin-based polymer because foreign substances having metal particles as nuclei are likely to be generated in the melt extrusion process.
[0021]
In addition, in order to obtain the intended effect of the present invention, examples of further preferred olefinic polymers include polymers each containing a monomer component capable of forming a crosslinked structure and / or a branched structure in a range of less than 5%. can do. Examples of such a monomer include unsaturated monomers having two or more addition polymerizable reactive groups. Examples of the crosslinkable monomer include butylene diacrylate, butylene dimethacrylate, trimethylolpropane trimethacrylate, divinylbenzene, trivinylbenzene, vinyl acrylate, vinyl methacrylate and the like. Preferably, butylene diacrylate and butylene dimethacrylate can be used. Examples of the graft-bonding monomer include allyl acrylate, allyl methacrylate, diallyl maleate, diallyl fumarate, diallyl itaconate, monoallyl maleate, monoallyl fumarate, monoallyl itaconate, and the like. Preferably, allyl methacrylate and diallyl methacrylate can be used.
[0022]
As a method for obtaining a polyester resin in the present invention (a method of blending an olefin polymer with a polyester resin), a known resin mixing method can be widely used. For example, after a polyester resin and an olefin polymer are uniformly dry-blended with a blender or the like, a method of melt-kneading with a single-screw or twin-screw extruder or the like can be used.
[0023]
In the polyester resin in the present invention, the polyester and the olefin polymer are required to be 80/20 to 99/1 (% by weight). When the olefin polymer is less than 1% by weight, the effect of improving the bending fatigue resistance of the polyester film is small, which is not preferable. Conversely, when the olefin polymer exceeds 20% by weight, the mechanical properties of the polyester film are often impaired, which is not preferable.
[0024]
In the present invention, after the polyester-based resin composition is melted in a known single-screw or twin-screw extruder, the resin melted in layers from the T-die is brought into contact with a rotating cooling roll to obtain a resin film. When the molten resin is brought into contact with the cooling roll, it is preferable to employ a method of forcibly blowing air or a method of closely contacting with static electricity. Further, when the molten resin contacts the cooling roll, it is more preferable to use a measure (for example, a device such as a vacuum chamber or a vacuum box) that reduces the accompanying flow by reducing the pressure on the opposite side.
[0025]
In the present invention, the cooled and solidified resin film is stretched at least twice in the uniaxial direction at a temperature not lower than the glass transition temperature of the polyester and lower than the cold crystallization temperature, and then the melting point of the polyester −80 ° C. to the melting point of the polyester under tension. After heat treatment at a temperature of −10 ° C. for 1 to 20 seconds, and then performing relaxation treatment under heating as necessary, then cutting and removing both ends, and further performing surface treatment such as corona treatment as necessary Winding to obtain a polyester film. As the stretching method, known methods such as longitudinal uniaxial stretching by a roll method, lateral uniaxial stretching by a tenter method, sequential biaxial stretching, and simultaneous biaxial stretching (tubular method, tenter method) can be used.
[0026]
【Example】
Hereinafter, the present invention will be described based on examples.
[Evaluation methods]
(1) Melting point of polyester After heating and melting a polyester composition at 300 ° C. for 5 minutes, 10 mg of a sample obtained by quenching with liquid nitrogen and 10 ° C. using a differential scanning calorimeter (DSC) in a nitrogen stream. The peak temperature of the endothermic peak accompanying melting when the exothermic / endothermic curve (DSC curve) was measured at a rate of temperature rise per minute was defined as melting point Tm (° C.).
[0027]
(2) Average dispersion diameter of olefin polymer Polyester and olefin polymer are melt-kneaded with an extruder, and a film obtained by stretching a sheet extruded from a T-die is embedded in an epoxy resin and cured. An ultrathin section was prepared by incision with a cryomicrotome in a cross section parallel to each stretching direction. This was dyed with ruthenium oxide, held at room temperature for 10 minutes, then carbon-deposited and observed with a transmission electron microscope. The average dispersion diameter of the olefin polymer was determined by a weighted average of the long diameters using an image analyzer (V10, manufactured by Toyobo Co., Ltd.).
[0028]
(3) Tensile modulus was evaluated according to JIS K 7127.
[0029]
(4) Bending fatigue resistance (number of bent pinholes)
Air was introduced into a sample film cut into a circular shape having a diameter of 150 mm from a polyester film to form a balloon-shaped bag, and attached to the tip of a glass tube of a bending machine. Air pressure and pressure (pressure: 70 kPa) are alternately supplied and exhausted (pressure reduction: 1000 hPa) with a bending machine, and expanded and contracted into a balloon-shaped bag-like film at a rate of 7.5 times / min at 23 ° C. and 65% RH. Was repeated 5000 times to give bending fatigue. The number of holes generated after 5000 times bending fatigue was visually measured as n number = 3. The number of bent pinholes was evaluated based on the minimum and maximum number of holes.
[0030]
(5) Intrinsic viscosity (IV)
It is a value (dl / g) measured at 25 ° C. in orthochlorophenol.
[0031]
[Abbreviations and contents of polyester and olefin polymer used in Examples and Comparative Examples]
(1) PET: Polyethylene terephthalate (IV: 0.75)
(2) PET-I (5): Polyethylene terephthalate / isophthalate (5 mol% repeating unit of ethyl isophthalate, IV: 0.80)
(3) PET-I (15): Polyethylene terephthalate / isophthalate (15 mol% of repeating units of ethylene isophthalate, IV: 0.79)
(4) Olefin A: Low density polyethylene (Sumitomo Chemical Co., Sumikasen G401: trade name)
(5) Olefin B: ethylene-acrylic acid copolymer (manufactured by Dow Chemical Company, Primacol 3440: trade name)
(6) Olefin C: ethylene-methacrylic acid copolymer (Mitsui DuPont Polychemical Co., Ltd., Nucrel N1108C: trade name)
(7) Olefin D: Ethylene-ethyl acrylate copolymer (Mitsui DuPont Polychemical Co., Ltd., Everflex A712: trade name)
(8) Olefin E: Ethylene-1-butene copolymer (Nippon Synthetic Rubber Co., Ltd., EBM2041P: trade name)
(9) Olefin F: Styrene-ethylene / butylene-styrene block copolymer (Asahi Kasei Corporation, Tuftec M1913: trade name)
[0032]
[Example 1]
Polyester resin with PET / olefin A / olefin B = 94.0 / 3.0 / 3.0 wt% melt extruded in a strand form at 270 ° C. using a twin screw vent type extruder, cooled in water and cut. A composition was obtained. The polyester-based resin composition was melted at 270 ° C. using a biaxial vent-type extruder, cast into a layer from a 270 ° C. T-die, and rotated on a 25 ° C. cooling roll while applying a positive charge. It was made to adhere and the resin film was obtained. Next, the film was stretched 3.3 times in the machine direction at 110 ° C., then passed through a tenter and stretched 3.6 times in the transverse direction at 110 ° C., and subjected to tension heat treatment at 228 ° C. for 3 seconds and relaxation treatment for 1 second ( 5% in the horizontal direction), and then both ends were cut and removed to obtain a polyester film having a thickness of 25 μm.
Table 1 shows the melting point of the polyester, the average dispersion diameter of the olefin polymer in the polyester resin composition, the tensile modulus of elasticity and the bending fatigue resistance of the polyester film. The polyester-based film of this example had a high feeling of waist due to its large tensile modulus, and was excellent in resistance to bending fatigue.
[0033]
[Example 2]
A polyester film having a thickness of 25 μm was obtained in the same manner as in Example 1 except that the polyester resin composition was changed to PET / olefin B / olefin E = 94.0 / 3.0 / 3.0 wt%.
Table 1 shows the melting point of the polyester, the average dispersion diameter of the olefin polymer in the polyester resin composition, the tensile modulus of elasticity and the bending fatigue resistance of the polyester film. The polyester-based film of this example had a high feeling of waist due to its large tensile modulus, and was excellent in resistance to bending fatigue.
[0034]
[Example 3]
A polyester film having a thickness of 25 μm was obtained in the same manner as in Example 1 except that the polyester resin composition was changed to PET / olefin A / olefin C = 94.0 / 3.0 / 3.0 wt%.
Table 1 shows the melting point of the polyester, the average dispersion diameter of the olefin polymer in the polyester resin composition, the tensile modulus of elasticity and the bending fatigue resistance of the polyester film. The polyester-based film of this example had a high feeling of waist due to its large tensile modulus, and was excellent in resistance to bending fatigue.
[0035]
[Example 4]
A polyester film having a thickness of 25 μm was obtained in the same manner as in Example 1 except that the polyester resin composition was changed to PET / olefin A / olefin D = 94.0 / 3.0 / 3.0 wt%.
Table 1 shows the melting point of the polyester, the average dispersion diameter of the olefin polymer in the polyester resin composition, the tensile modulus of elasticity and the bending fatigue resistance of the polyester film. The polyester-based film of this example had a high feeling of waist due to its large tensile modulus, and was excellent in resistance to bending fatigue.
[0036]
[Example 5]
A polyester film having a thickness of 25 μm was obtained in the same manner as in Example 1 except that the polyester resin composition was changed to PET-I (5) / olefin A / olefin B = 94.0 / 3.0 / 3.0 wt%. Obtained.
Table 1 shows the melting point of the polyester, the average dispersion diameter of the olefin polymer in the polyester resin composition, the tensile modulus of elasticity and the bending fatigue resistance of the polyester film. The polyester-based film of this example had a high tensile elastic modulus and was excellent in low back feeling, and was excellent in bending fatigue resistance and thermal characteristics.
[0037]
[Comparative Example 1]
A polyester film having a thickness of 25 μm was obtained in the same manner as in Example 1 except that PET alone was used instead of the polyester resin composition.
Table 1 shows the melting point of the polyester, the average dispersion diameter of the olefin polymer in the polyester resin composition, the tensile modulus of elasticity and the bending fatigue resistance of the polyester film. This polyester-based film has a large tensile elastic modulus and excellent waist feeling, but is not preferable because it has poor flex fatigue resistance.
[0038]
[Comparative Example 2]
A polyester film having a thickness of 25 μm was obtained in the same manner as in Example 1 except that the polyester resin composition was changed to PET / olefin A / olefin B = 75.0 / 12.5 / 12.5 wt%.
Table 1 shows the melting point of the polyester, the average dispersion diameter of the olefin polymer in the polyester resin composition, the tensile modulus of elasticity and the bending fatigue resistance of the polyester film. This polyester-based film was excellent in bending fatigue resistance, but is not preferable because it has a small tensile elastic modulus and a slightly inferior feeling in the waist.
[0039]
[Comparative Example 3]
A polyester film having a thickness of 25 μm was obtained in the same manner as in Example 1 except that the polyester resin composition was changed to PET / olefin A = 94.0 / 6.0 wt%.
Table 1 shows the melting point of the polyester, the average dispersion diameter of the olefin polymer in the polyester resin composition, the tensile modulus of elasticity and the bending fatigue resistance of the polyester film. This polyester-based film has a large tensile elastic modulus and excellent waist feeling, but is not preferable because it has poor flex fatigue resistance.
[0040]
[Comparative Example 4]
A polyester film having a thickness of 25 μm was obtained in the same manner as in Example 1 except that the polyester resin composition was changed to PET / olefin F = 94.0 / 6.0 wt%. However, this method is not preferable because a large amount of thermally decomposable gas is generated from the extruder and the outlet of the T-die and adhesion of low molecular weight substances on the cooling roll is large.
Table 1 shows the melting point of the polyester, the average dispersion diameter of the olefin polymer in the polyester resin composition, the tensile modulus of elasticity and the bending fatigue resistance of the polyester film. This polyester-based film was excellent in bending fatigue resistance, but is not preferable because it has a small tensile elastic modulus and a slightly inferior feeling in the waist.
[0041]
[Comparative Example 5]
An attempt was made to form a film in the same manner as in Example 1 except that the polyester resin composition was PET-I (15) / olefin A / olefin B = 94.0 / 3.0 / 3.0% by weight. Since the fracture occurred in the heat treatment process from the latter half of the transverse stretching, a polyester film could not be obtained.
[0042]
[Table 1]

[0043]
【The invention's effect】
Since the polyester film of the present invention has a high tensile elastic modulus, it has excellent waist feeling and is excellent in bending fatigue resistance, and therefore has a good characteristic of a biaxially stretched polyethylene terephthalate film and a biaxially stretched nylon film. Therefore, it can be said that the film is extremely useful as a packaging film.

Claims (2)

An olefin-based polymer comprising a polyethylene terephthalate unit and an ethylene isophthalate unit and having a melting point of 225 ° C. or more, a polyethylene and an ethylene- (meth) acrylic acid copolymer, or an ethylene-α-olefin copolymer and an ethylene- An olefin polymer composed of an α- olefin- (meth) acrylic acid copolymer is blended in a ratio of 80/20 to 99/1 (% by weight), and the olefin polymer is dispersed in islands in the polyester. to become, and the olefin-based polyester film dispersion diameter which is biaxially stretched and wherein the formed of a polyester resin composition in the range of 2~10μm polymer.   The polyester film characterized by the tensile elasticity modulus of the film of Claim 1 being 2500 Mpa or more.