JP2001002800A - Gas barrier polyester film and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a biaxially oriented polyester film excellent in gas barrier properties and transparency without problems about sanitation, having small pearliness and excellent in appearance, and to provide a method for producing the polyester film. SOLUTION: This gas barrier film is a biaxially oriented polyester film comprising a mixture of polyethylene terephthalate (PET) with polym-xylylene adipamide (MXD6) in (60-90)/(40-10) (wt.%) ratio of the PET/MXD6 and the relative viscosity ηra of the PET and the relative viscosity ηrb of the MXD6 satisfy the following formula: formula: 11.0<=ηra×10-ηrb<=12.0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas barrier polyester film and a method for producing the same, and more particularly, to PET and MX having a specific relative viscosity.
The present invention relates to a polyester film having excellent gas barrier properties and appearance obtained by mixing D6.

[0002]

2. Description of the Related Art Polyethylene terephthalate (PET)
Is excellent in moisture resistance, mechanical strength, heat resistance and oil resistance, and is widely used in the field of food packaging and the like. Films used for food packaging are required to have high gas barrier properties in order to prevent oxidative deterioration of the contents. In such applications, polyester films coated with polyvinylidene chloride (PVDC) are preferably used. However, PVDC has a problem that dioxin is generated during incineration.

A biaxially stretched film made of an aromatic polyamide, polymethaxylylene adipamide (MXD6), has excellent gas barrier properties and MXD6 / PE
It is known that a polyamide-based biaxially stretched film having a composition of T = 99.5 to 50 / 0.5 to 50 (% by weight) is excellent in gas barrier properties and dimensional stability (Japanese Patent Publication No. 53-53).
-33618). Further, although a gas barrier property of a polyester resin composition in which MXD6 is blended with PET is excellent, transparency is remarkably reduced, so that an example in which a compatibilizer is blended is known (Japanese Patent Publication No. Hei 6-28771). Publications), when used for applications such as food packaging, there is a hygiene problem of the compatibilizer.

Further, a molten mixture of mutually incompatible resins, such as PET and MXD6, has a problem that since it takes a dispersed form of a sea-island structure, it tends to have an opaque appearance called pearl or matte. The pearl or matte tone refers to an appearance that is translucent and has fluctuations in transparency. Further, there is a problem that a phenomenon in which the film pulsates (a so-called ballistic phenomenon) often occurs when a film is formed by melt-extruding a blend of mutually incompatible resins.

[0005]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and is excellent in gas barrier properties and transparency, has no hygiene problems, and does not exhibit a pearly tone. An object of the present invention is to provide a biaxially stretched polyester film excellent in appearance and a method for producing the same.

[0006]

Means for Solving the Problems The present inventors have found that the above-mentioned problems can be solved by adopting a specific production condition using a polyester resin composition having a specific composition. The invention has been reached.

That is, the gist of the present invention is as follows. (1) PET and MXD6 are 60-90 / 40-10
(% By weight), wherein the relative viscosity ηra of PET and the relative viscosity ηrb of MXD6 satisfy the following formula. 11.0 ≦ ηra × 10−ηrb ≦ 12.0 (2) Simultaneous biaxial stretching in the longitudinal and transverse directions of an unstretched film made of a mixture of PET and MXD6 of 60 to 90/40 to 10 (% by weight) A method for producing a biaxially stretched polyester film, comprising: stretching the film.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION P used as a raw material in the present invention
ET is a known production method, that is, a transesterification method from dimethyl terephthalate and ethylene glycol, or a direct esterification method from terephthalic acid and ethylene glycol, followed by melt polymerization or further solid phase polymerization. However, other components can be copolymerized as long as the effects of the present invention are not impaired.

Other copolymerization components include isophthalic acid,
Phthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, succinic acid, adipic acid, sebacic acid, dodecane diacid, dimer acid, maleic anhydride,
Maleic acid, fumaric acid, itaconic acid, citraconic acid,
Mesaconic acid, dicarboxylic acids such as cyclohexanedicarboxylic acid, 4-hydroxybenzoic acid, ε-caprolactone, oxycarboxylic acids such as lactic acid, 1,3-propanediol, 1,6-hexanediol, glycols such as cyclohexanedimethanol, Trimellitic acid, trimesic acid, pyromellitic acid, trimethylolpropane,
Examples include polyfunctional compounds such as glycerin and pentaerythritol.

Further, other polymers such as polybutylene terephthalate, polyethylene naphthalate and polycyclohexylene dimethylene terephthalate can be mixed with the raw material resin in the present invention as long as the effects of the present invention are not impaired. .

[0011] The MXD6 in the present invention may contain about 5% by weight or less of a paraxylylene adipamide component.

The polyester film of the present invention is made of PET
And MXD6 must be a mixture of 60 to 90/40 to 10 (% by weight), preferably 70 to 85/30 to 15 (% by weight). If MXD6 is less than 10% by weight, the effect of improving gas barrier properties becomes insufficient, and
When the content is more than 10% by weight, the excellent mechanical properties of PET,
Dimensional stability and transparency are reduced, and a phenomenon in which the film pulsates during extrusion (a so-called ballistic phenomenon) is likely to occur.

In the film of the present invention, it is necessary that the relative viscosity ηra of PET and the relative viscosity ηrb of MXD6 satisfy the following expression. 11.0 ≦ ηra × 10−ηrb ≦ 12.0 When ηra × 10−ηrb is larger than 12.0, MX
If the dispersion diameter of D6 is small, the pearl tone of the obtained film is strong, and if ηra × 10−ηrb is less than 11.0, a ballistic phenomenon is likely to occur during melt extrusion, and the productivity is reduced.

Further, the polyester film of the present invention comprises:
Glossiness of 100 to 200%, preferably 130 to 160
%. When the glossiness is out of this range, the pearly tone is conspicuous, the printing becomes unclear, and the commercial value decreases.

Further, the polyester film of the present invention comprises:
Oxygen permeability is 300 ml / m ² · day · MPa (equivalent to a thickness of 12 μm) or less, preferably 200 ml / m 2
²・ day ・ MPa or less, more preferably 150ml
/ M ² · day · MPa or less. Oxygen permeability is 30
When it is larger than 0 ml / m ² · day · MPa, the gas barrier properties are insufficient.

The gas barrier polyester film of the present invention can be obtained, for example, by producing it under the following conditions. That is, a raw material obtained by mixing PET and MXD6 is charged into an extruder, heated and melted, and then extruded into a sheet from a die orifice of a T-die to produce an unstretched sheet. Next, the sheet extruded from the die orifice of the T-die is tightly wound around a cooling drum using a method such as an electrostatic application casting method and cooled, and then a temperature of 80 to 1 is applied.
The film is simultaneously biaxially stretched at 40 ° C. vertically and horizontally at a magnification of 2.5 to 5.0 times, and further heat-treated at a temperature of 210 to 245 ° C. to obtain a biaxially stretched film.

When the stretching temperature is lower than 80 ° C., a uniform stretched film cannot be obtained. When the stretching temperature is higher than 140 ° C., crystallization of PET is promoted and transparency is deteriorated.
When the stretching ratio is less than 2.5 times, the strength of the obtained film is low, and when it exceeds 5.0 times, stretching becomes difficult.
If the heat treatment temperature is lower than 210 ° C., the heat shrinkage of the obtained stretched film is increased, and if it is higher than 245 ° C., the film may be blown.

In the present invention, stretching can be carried out by any of a simultaneous tenter-type biaxial stretching method, a tenter-type sequential biaxial stretching method, and a tubular method.
The tenter-type simultaneous biaxial stretching method or the tubular method is more preferable because the resulting film has excellent transparency and the film is hardly cut during stretching.

In the present invention, various additives such as a slip agent may be contained as long as the effect is not impaired. Further, the polyester film of the present invention can be subjected to a surface treatment by corona discharge treatment, surface effect treatment, plating treatment, coloring treatment, or various coating treatments.

[0020]

Next, the present invention will be described more specifically with reference to examples. In addition, the raw materials and measuring methods used in the examples are as follows. (1) Raw material PT1: Unitika's PET relative viscosity 1.38 PT2: Unitika's PET relative viscosity 1.41 PT3: Unitika's PET relative viscosity 1.48 MX1: Mitsubishi Gas Chemical's MX nylon 6001 Relative viscosity 2 .1 MX2: MX Nylon 6907 manufactured by Mitsubishi Gas Chemical Co., Ltd. Relative viscosity 2.6 MX3: MX Nylon 6121 manufactured by Mitsubishi Gas Chemical Co., Ltd. Relative viscosity 3.5 (2) Measurement method Relative viscosity; PET: phenol and ethane tetrachloride, etc. The measurement was performed at a concentration of 0.5 g / dl and a temperature of 20 ° C. using the weight mixture as a solvent. MXD6: A concentration of 1.0 g / d using 96% sulfuric acid as a solvent.
1, measured at a temperature of 25 ° C. Oxygen permeability; gas permeability measuring instrument OX-T manufactured by MOCON
The measurement was performed at a temperature of 20 ° C. and a humidity of 85% using RAN 2/20. Glossiness: Measured with a gloss meter (GM3D) manufactured by Murakami Color Research Laboratory according to ASTM D523. Productivity: The thickness of the unstretched sheet is measured at 50 points in the flow direction at 10 cm intervals, and the difference between the maximum value and the minimum value of the thickness is 10 μm.
The above items are regarded as having a ballasting effect, × 10
Those having a size of less than μm were rated as ○.

Example 1 A mixture of chips of PET and MX1 at a ratio of 80/20 (% by weight) was obtained by using a 50 mmφ extruder equipped with a coat hanger type T-die, for a residence time of 5 minutes and a resin temperature of 5 minutes. Melt extrusion was performed at 270 ° C., and an applied voltage of 7 kV was applied to a pinning wire on a cast roll adjusted to a temperature of 20 ° C., followed by rapid cooling to obtain an unstretched sheet having a thickness of 120 μm.
Next, the unstretched sheet is preheated at 100 ° C.
C. and a heat treatment temperature of 225 ° C. were passed through each zone to obtain a biaxially stretched film having a thickness of 12 μm. The stretching conditions were that the film was simultaneously biaxially stretched at a stretch ratio of 3.0 times in the longitudinal direction and 3.3 times in the transverse direction, and subjected to a 2% relaxation treatment in the transverse direction in the heat treatment zone. Glossiness of the resulting film,
Table 1 shows the results of measuring the oxygen permeability and evaluating the productivity.

Example 2, Comparative Examples 1 to 4 A biaxially stretched film was obtained in the same manner as in Example 1 except that the types and mixing ratios of PET and MXD6 were changed as shown in Table 1. Table 1 shows the results of evaluating the characteristics of the obtained film.
It was shown to.

[0023]

[Table 1]

[0024]

According to the present invention, there is provided a biaxially stretched polyester film which is excellent in gas barrier properties and transparency, has no hygiene problems, and is excellent in appearance.

Claims (4)

[Claims] 1. Polyethylene terephthalate (PET)
And polymethaxylylene adipamide (MXD6)
A biaxially oriented polyester film comprising a mixture of 90/40 to 10 (% by weight), wherein the relative viscosity η of PET is
A gas barrier polyester film, wherein the relative viscosity ηrb of ra and MXD6 satisfies the following expression. 11.0 ≦ ηra × 10−ηrb ≦ 12.0 2. The gas barrier polyester film according to claim 1, wherein the glossiness is 100 to 200%. 3. An oxygen permeability of 300 ml / m ² · day ·
The gas-barrier polyester film according to claim 1 or 2, wherein the film has a MPa (equivalent to a thickness of 12 µm) or less. 4. An unstretched film comprising a mixture of polyethylene terephthalate and polymethaxylylene adipamide of 60 to 90/40 to 10% by weight is stretched in the longitudinal and transverse directions by simultaneous biaxial stretching. A method for producing a biaxially stretched polyester film.