JP2001341201A - Shrinkable barrier film and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shrinkable barrier film which shows proper hot water shrinkage as a shrinkable film and shows excellent oxygen barrier as a barrier film. SOLUTION: A shrinkable barrier film is composed of 60 to 85 mass % of an aliphatic polyamide and 40 to 15 mass % of a xylylene-based polyamide and shows shrinkage of 15 to 40 % when it is treated in hot water at 80 deg.C for 30 min and an oxygen transmission degree of not more than 150 ml/m2.day.Mpa. The shrinkable barrier film is manufactured under a specific heat treating condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gas-barrier heat-shrinkable film (hereinafter, shrink film) and a method for producing the same. More specifically, the present invention relates to a shrink film for packaging excellent in shrinkage and gas barrier properties and suitable for shrink packaging of processed meat products such as water foods, hams and sausages, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, as a packaging material having a gas barrier property, a plastic film laminated with a polyvinylidene chloride resin has been known.
In particular, it is widely used as a packaging material for processed meat products such as aquatic foods, hams and sausages.

[0003] However, the generation of dioxins derived from chlorine-containing waste has become a social problem, and the development of so-called dechlorinated packaging materials has been awaited. A new gas barrier plastic using a chlorine-free resin or inorganic material has been awaited. Switching to film is desired.

As materials having gas barrier properties, inorganic materials such as aluminum and silicon oxide, and organic materials such as ethylene-vinyl acetate copolymer and polyacrylonitrile are known in addition to polyvinylidene chloride resin. Among them, xylylene-based polyamides have a balanced barrier property against oxygen, water vapor, and aroma components, are suitable as food packaging materials, and are known to be laminated or mixed with a base film.

[0005] However, xylylene-based polyamide resins have poor gas barrier properties, especially under high humidity, and are not always satisfactory as food packaging materials. To address these problems, it is possible to consider a method of improving the gas barrier property by applying a heat treatment at high temperature to increase the crystallinity and impart molecular orientation, but in the process of stretching and heat treating the film, High-temperature heat treatment also promotes heat setting of the film at the same time, and when using the aliphatic and xylylene-based polyamide resin as a shrink film, a certain heat shrinkage, which is a very important feature, can be sufficiently achieved. I can not secure it.

As described above, when a xylylene-based polyamide resin blend film is manufactured and used as a barrier shrink film, it is difficult to make the gas barrier properties and the heat shrink properties parallel.

[0007]

SUMMARY OF THE INVENTION The present invention provides a well-balanced barrier shrink with excellent heat shrinkability, which is an essential property for shrink packaging materials, and excellent gas barrier properties, which is an important property as a packaging material for fresh foods. The idea is to provide a film.

[0008]

Means for Solving the Problems In the production process of a film composed of a resin composition containing an aliphatic polyamide and a xylylene-based polyamide at an appropriate ratio, the present inventors have made it possible to obtain a film obtained by biaxially stretching the film. By performing low-temperature heat treatment at a low temperature, it has been found that a barrier shrink film having gas barrier properties can be produced without impairing the heat shrinkage as a shrink film,
The present invention has been reached.

That is, the gist of the present invention is as follows.

(1) It is composed of 60 to 85% by mass of an aliphatic polyamide and 40 to 15% by mass of a xylylene-based polyamide, and has a shrinkage of 15 to 15 when treated in hot water at 80 ° C. for 30 minutes.
40% and oxygen permeability of 150 ml / m ² · d
A barrier shrink film characterized by ay · MPa or less. (2) A biaxially stretched film composed of 60 to 85% by mass of an aliphatic polyamide and 40 to 15% by mass of a xylylene-based polyamide is heat-treated for at least 24 hours within a temperature range represented by the following formula (I). The method for producing a barrier shrink film according to the above (1). _{Tg A ≦ Tt ≦ Tg X ...} (I) Tg A: glass transition temperature of the aliphatic polyamide (℃) tg _X: glass transition temperature of the xylylene polyamide (℃) Tt: biaxially oriented film of the processing temperature (℃)

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

Representative examples of the aliphatic polyamide in the present invention include poly-ε-capramide (nylon 6) and polyhexamethylene adipamide (nylon 6).
6), polyhexamethylene sebacamide (nylon 61
0), polyundecamide (nylon 11), polylauramide (nylon 12), polytetramethylene adipamide (nylon 46), mixtures thereof, copolymers and the like. Of these, nylon 6 is preferable.

Representative examples of the xylylene-based polyamide used in the present invention include, for example, polymethaxylylene adipamide, polymethaxylylene sebacamide, polymethaxylylene peramide, polyparaxylylene adipamide, and polyparaxylylene adipamide. Examples thereof include a mixture and a copolymer, and among them, polymethaxylylene adipamide is preferable.

The content of the xylylene-based polyamide constituting the present invention must be 15 to 40% by mass. Fifteen
If the amount is less than 40% by mass, sufficient gas barrier properties cannot be obtained. If the amount exceeds 40% by mass, optical properties such as impact resistance and haze are impaired, and the quality as a food packaging material is lacking. Will be.

[0015] The barrier shrink film of the present invention comprises:
Shrinkage of 15-40 when treated in hot water at 0 ° C for 30 minutes
% Range. If the shrinkage ratio is less than 15%, it is not possible to secure a suitable shrinkage as a shrink wrapping material, and the shrink wrapping material has poor adhesion and cannot exhibit the characteristics of shrink wrapping. If it exceeds 40%, the excessive shrinkage of the film causes the packaging form to collapse, resulting in damage to the contents and breakage of the packaging material, which impairs the appearance of the product.

The oxygen permeability of the film provided by the present invention must be 150 ml / m ² · day · MPa or less. Oxygen permeability is 150ml / m ²・ day ・ M
If it exceeds Pa, the gas barrier property for preserving the packaged contents is insufficient, and is not sufficient as a barrier packaging material.

Next, a method for producing the barrier shrink film of the present invention will be described. In order to obtain a biaxially stretched film, first, for example, a mixed raw material is heated and melted by an extruder, and then an unstretched sheet is extruded from a die such as a T die or an I die, and this is air-knife cast, and electrostatically applied. A quenching film is formed by closely adhering to a rotating cooling drum by a known casting method such as a casting method.

Next, the obtained unstretched sheet is stretched 2.5 times or more in both the film advancing direction (hereinafter, MD direction) and the width direction (hereinafter, TD direction).
It is preferable to perform orientation crystallization by heat treatment. As a stretching method of the film, a method such as a flat sequential biaxial stretching method and a flat simultaneous biaxial stretching method can be applied. When the stretching ratio is less than 2.5 times, the orientation crystallization tends to be insufficient, and the mechanical strength such as impact resistance tends to decrease.
When the heat treatment temperature is lower than 120 ° C., the obtained film tends to be excessively shrunk, so that the packaging form may be broken and the contents may be damaged. If the temperature exceeds 170 ° C., on the contrary, the shrinkage decreases, so that the characteristics as a shrink wrapping material are hardly exhibited.

The film of the present invention can be obtained by subjecting the biaxially stretched film obtained through the film forming, stretching and heat treatment steps exemplified above to a heat treatment at a temperature represented by the following formula (I). Tg _A ≦ Tt ≦ Tg _X (I) Tg _A : Glass transition temperature of aliphatic polyamide (° C.) Tg _X : Glass transition temperature of xylylene-based polyamide (° C.) Tt: Processing temperature of biaxially stretched film (° C.) Heat treatment If the temperature is lower than Tg _A , sufficient gas barrier properties cannot be obtained. If the heat treatment temperature exceeds Tg _X , sufficient heat shrinkage cannot be obtained and remarkable wrinkles due to film shrinkage occur. The appearance of the product is impaired, which eventually impairs post-processing such as printing and laminating, thereby lowering the commercial value.

When poly-ε-capramide (glass transition temperature: 48 ° C.) is used as the aliphatic polyamide and polymetaxylylene adipamide (glass transition temperature: 75 ° C.) is used as the xylylene-based polyamide, the range is from 48 to 75 ° C. At 48 to 55 [deg.] C. is particularly preferable for suppressing wrinkles during unwinding of the film.

The heat treatment time needs to be 24 hours or more, and is preferably 30 to 72 hours. If the time is less than 24 hours, sufficient gas barrier properties cannot be imparted to the film.

The aliphatic polyamide and the xylylene-based polyamide constituting the present invention and the film provided by the present invention are provided within a range that does not impair the effects of the present invention.
If necessary, various additives such as an antistatic agent, an antioxidant and a lubricant can be blended.

The barrier shrink film provided by the present invention is subjected to surface activation treatment such as corona treatment, or to printing, various functional coatings, laminating, etc., to add various performances, and to use the barrier shrink film. It is possible to further increase the value.

The barrier shrink film thus obtained has suitable heat shrinkability and excellent gas barrier properties, and is suitable as a shrink film for packaging.

[0025]

EXAMPLES Next, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples. The measuring methods and evaluation methods used in the examples and comparative examples are as follows.

(1) Shrinkage ratio of hot water A piece of film having a width of 10 mm and a length of 100 mm was immersed in hot water of 80 ° C. for 30 minutes, and the dimensional change before and after the hot water treatment was measured. , Expressed as a percentage of the original length.

(2) Oxygen permeability Using an OX-TRAN 2/20 type oxygen permeability measuring device manufactured by Modern Control Co., the measurement was carried out at 20 ° C. and a relative humidity of 85%.

(3) Haze The film before hot water treatment was measured according to JIS-K-6714.

(4) Film Wrinkle The appearance of a wrinkle in the film roll having a width of 500 mm was visually judged immediately after the heat treatment and when the film was unwound from the roll at a speed of 30 m / min. The scale was evaluated according to the following criteria. ：: No wrinkles were observed. Δ: Yori wrinkles are observed. X: Bent wrinkles are observed.

Example 1 Poly-polyester having a relative viscosity of 3.0 (25 ° C., 95% by weight sulfuric acid)
65% by mass of ε-capramide (nylon 6) and polymethaxylylene adipamide (MXD6) 3 having a relative viscosity of 3.5
5 mass% was mixed and melted at 270 ° C., extruded into a sheet using a T-die, and then air-knife cast.
Quickly cool by contacting with a 5 ° C. rotating drum, 150 μm thick
Was obtained. Subsequently, this unstretched film is
2. longitudinally on a metal roll heated to 50-70 ° C.
The film was stretched 0 times to obtain a uniaxially stretched film. Next, the film was stretched 3.3 times in the width direction at 90 ° C. by a tenter type transverse stretching machine,
After heat treatment at 0 ° C. for 10 seconds, the film was cooled and wound up to obtain a biaxially stretched film having a thickness of 15 μm. Subsequently, the wound film roll was heat-treated with a stocker kept at 50 ° C. for 40 hours.
Table 1 shows the results of measuring the hot water shrinkage, oxygen permeability and haze of the obtained film and observing wrinkles of the film roll.

Examples 2 to 5 Table 1 shows the mixing mass ratio of nylon 6 and MXD6 and the heat treatment temperature.
A film was obtained in the same procedure as in Example 1, except that the content was changed to the content shown in (1). Table 1 shows the results of evaluation of the film according to the above procedure.

Comparative Example 1 A film was obtained in the same procedure as in Example 1 except that MXD6 was not blended. Table 1 shows the results of evaluation of the film according to the above procedure.

Comparative Examples 2-3 The mixing mass ratio of nylon 6 and MXD6 was changed to the contents shown in Table 1, and the biaxially stretched film roll was heated at 20 ° C.
A film was obtained in the same procedure as in Example 1 except that the film was stored for a time. Table 1 shows the results of evaluation of the film according to the above procedure.

Comparative Examples 4 to 6 Table 1 shows the mixing mass ratio of nylon 6 and MXD6 and the heat treatment temperature.
The heat-treated film was obtained in the same procedure as in Example 1 except that the content was changed to that shown in (1). Table 1 shows the results of evaluation of the film according to the above procedure.

[0035]

[Table 1]

[0036]

According to the present invention, it is possible to provide a packaging film having a suitable hot water shrinkage as a shrink packaging material and having excellent gas barrier properties under high humidity. Further, the barrier shrink film of the present invention is extremely useful in heavy packaging applications such as water food products and processed meat products.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) // B29K 77:00 B29K 77:00 B29L 7:00 B29L 7:00 F term (reference) 3E067 AA11 AB01 AB05 AB06 BB14A BB18A BC03A CA01 CA05 CA06 EE48 FA01 FB01 FC01 GD01 4F071 AA54 AA55 AF61 AG28 BB06 BB07 BC01 BC17 4F073 AA00 AA17 AA29 BA29 BB01 GA01 HA04 4F210 AA29K AA30 AG01 AR06 AR11 QA02 QA03 CL05 Q1 CL05 Q01 CL03

Claims (2)

[Claims] 1. An 80% by weight aliphatic polyamide and 40 to 15% by weight xylylene-based polyamide,
The shrinkage when treated in hot water for 30 minutes is 15 to 40%, and the oxygen permeability is 150 ml / m ² · day · M.
A barrier shrink film characterized by being at most Pa. 2. A biaxially stretched film comprising 60 to 85% by mass of an aliphatic polyamide and 40 to 15% by mass of a xylylene-based polyamide is heat-treated at a temperature represented by the following formula (I) for 24 hours or more. The method for producing a barrier shrink film according to claim 1. _{Tg A ≦ Tt ≦ Tg X ...} (I) Tg A: glass transition temperature of the aliphatic polyamide (℃) tg _X: glass transition temperature of the xylylene polyamide (℃) Tt: biaxially oriented film of the processing temperature (℃)