JP2001001399A - Gas barrier polyester film and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially stretched polyester film excellent in gas barrier properties and transparency, having no problem from an aspect of sanitation and usable for food packaging or the like. SOLUTION: A gas barrier polyester film is a biaxially stretched polyester film comprising a mixture wherein a wt. ratio of polyethylene terephthalate and polymetaxyleleneadipamide (MXD 6) is 60-90/40-10 (wt.%) and has a haze of 15% or less. In this case, the oxygen permeability of the film is 300 mol/ m2.day.MPa (in terms of a thickness of 12 μm).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gas barrier polyester film and a method for producing the same.

[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 deterioration of the contents. In such applications, polyester films coated with polyvinylidene chloride (PVDC) have been suitably used. But P
VDC 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). Gazettes), when used for applications such as food packaging, there is a hygiene problem of the compatibilizer.

[0004]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and is excellent in gas barrier properties and transparency, and has no hygiene problems, and is used for food packaging and the like. And a method for producing the same.

[0005]

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) A biaxially stretched polyester film comprising a mixture of PET and MXD6 of 60 to 90/40 to 10 (% by weight), wherein the haze is 15% or less. (2) A biaxially stretched polyester film obtained by stretching an unstretched film made of a mixture of PET and MXD6 in the range of 60 to 90/40 to 10 (% by weight) by simultaneous biaxial stretching in the longitudinal and transverse directions. Manufacturing method

[0007]

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.

[0008] 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. .

[0010] 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.

The haze of the biaxially stretched polyester film obtained by using the raw material of the present invention and using the production method of the present invention is 15% or less, and has excellent transparency.

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 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 140 ° C.
Then, the film is simultaneously biaxially stretched in the longitudinal and transverse directions 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, it is necessary to stretch using a simultaneous biaxial stretching method, and any of a tenter method and a tubular method may be used. When the sequential biaxial stretching method is used, the crystallization of the film proceeds in the first vertical or horizontal stretching step, and the film is cut at the time of stretching in the other direction of the next step, Even if the film can be stretched, the transparency of the obtained film deteriorates.

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.

[0018]

Next, the present invention will be described more specifically with reference to examples. In addition, the raw materials and measuring methods used in the evaluation of the examples are as follows. (1) Raw material PET: DH-CBR manufactured by Unitika Ltd. Relative viscosity 1.3
8 MXD6: MX Nylon 6001 manufactured by Mitsubishi Gas Chemical Company
Relative viscosity 2.1 (2) Measurement method Relative viscosity: PET: Measured at a concentration of 0.5 g / dl and a temperature of 20 ° C. using an equal weight mixture of phenol and ethane tetrachloride 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. Haze: The haze of a film having a thickness of 12 μm is determined by ASTM D
The measurement was performed according to 103-61. 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.

Example 1 A mixture of PET and MXD6 chips at a ratio of 80/20 (% by weight) was mixed at a residence time of 5 minutes and a resin temperature of 50 mmφ extruder equipped with a coat hanger type T die. 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. and stretched at a temperature of 9 ° C.
After passing through each zone adjusted to 0 ° C. and a heat treatment temperature of 225 ° C., a biaxially stretched film having a thickness of 12 μm was obtained. 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. Haze of the resulting film,
Table 1 shows the measurement results of the oxygen permeability.

Example 2 and Comparative Examples 1 and 2 A biaxially stretched film was obtained in the same manner as in Example 1 except that the mixing ratio of PET and MXD6 was changed as shown in Table 1.
Table 1 shows the results of measuring the haze and oxygen permeability of the obtained film.

Comparative Example 3 An unstretched sheet obtained in the same manner as in Example 1 was rolled 3.4 times at 90 ° C. with a roll longitudinal stretching machine and 12 times with a tenter transverse stretching machine.
After successively biaxially stretching 3.3 times at 0 ° C., it was heat-treated at 230 ° C. and subjected to a 2% relaxation treatment in the transverse direction to obtain a 12 μm thick biaxially stretched film. Haze of the resulting film,
Table 1 shows the measurement results of the oxygen permeability.

Comparative Example 4 The procedure of Comparative Example 3 was repeated except that the mixing ratio of PET and MXD6 was changed as shown in Table 1. However, the film was cut at the time of transverse stretching, and a biaxially stretched film was not obtained. .

[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 hygienic problems, and can be used for applications such as food packaging.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 77:06) B29K 67:00 77:00 B29L 7:00 F term (Reference) 3E086 BA15 BA33 BB01 BB22 BB41 BB74 CA01 4F071 AA46 AA55 AF08 AF30 AH04 BB08 BC01 4F210 AA24K AA29 AE10 AG01 AH54 QA02 QC07 QG01 QG11 QG18 4J002 CF061 CL032 GG02

Claims (3)

[Claims] 1. A biaxially stretched polyester film comprising a mixture of polyethylene terephthalate and polymethaxylylene adipamide at 60 to 90/40 to 10 (% by weight), wherein the haze is 15% or less. Gas barrier polyester film. 2. Oxygen permeability is 300 ml / m ² · day
2. The gas-barrier polyester film according to claim 1, which has a pressure of not more than MPa (converted to a thickness of 12 μm). 3. A method of stretching an unstretched film comprising a mixture of polyethylene terephthalate and polymetaxylylene adipamide in a proportion of 60 to 90/40 to 10% by weight by simultaneous biaxial stretching in the machine and transverse directions. A method for producing a biaxially stretched polyester film.