JPH069916B2 - Coextrusion composite film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a film material suitable for food packaging. More specifically, it relates to a coextruded composite film having excellent transparency, gas barrier property, pinhole resistance, deep drawability and interlayer adhesion.

[Conventional technology]

In recent years, single-layer or multi-layer packaging materials having an oxygen gas barrier property have been known for the long-term stable storage of foods and pharmaceuticals. In such applications, secondary molding processing such as deep drawing may be performed if necessary, or the package may be subjected to treatment in a hot atmosphere such as hot water treatment or retort treatment before being put on the market. However, the present situation is that no satisfactory packaging material has been found in the following points.

That is, ethylene-vinyl alcohol copolymer, which is known as a material with excellent gas barrier properties, shows good oxygen barrier properties under low humidity, but it does not contain oxygen under high temperature and high humidity conditions such as during retort sterilization. It has a drawback that the barrier property is lowered. In order to improve this drawback, a laminated film in which polyolefin having a low moisture permeability such as polypropylene or polyethylene is arranged in the inner and outer layers of the copolymer is used, but it is said that the moisture-proof effect at the time of retort sterilization is sufficient. It is hard to say and does not always show satisfactory performance.

For the purpose of improving the film strength, etc., an ethylene / vinyl alcohol copolymer may be laminated with an aliphatic polyamide such as nylon 6, nylon 66, etc. However, the polyamide has a large hygroscopic property, and oxygen under high humidity is used. It is insufficient in terms of improving the barrier property. Moreover, there is a drawback that the transparency is inferior, so it was difficult to say that this is a satisfactory product.

On the other hand, a partially aromatic polyamide is known as a material having excellent oxygen gas barrier properties and transparency. However, this material has a difficulty in pinhole resistance, and tends to whiten when exposed to hot water. Moreover, even if an attempt is made to coextrude with an ethylene-vinyl alcohol copolymer, a laminate having excellent interlayer adhesion cannot be obtained.

[Object of the Invention]

The present invention has been made in view of the above circumstances, and an object thereof is to have excellent oxygen gas barrier properties, particularly oxygen gas barrier properties under high humidity, and transparency, pinhole resistance, and deep drawing workability. , It is to provide a film having good resistance to hot water whitening.

[Means for solving problems]

The present invention provides a polyamide composition comprising 30 to 90% by weight of an aliphatic polyamide and 10 to 70% by weight of a partially aromatic polyamide, and a vinyl alcohol content of 40 to 85%.
The present invention relates to a composite film obtained by coextrusion with an ethylene / vinyl alcohol copolymer in the range of mol%.

In the present invention, the polyamide composition which is one of the raw materials for the co-extruded film is 30 to 90% by weight of aliphatic polyamide, preferably 45 to 80% by weight, 10 to 70% by weight of partially aromatic polyamide, and preferably 20 to 55%. % By weight (both total 100% by weight). Needless to say, a stabilizer and other commonly used additives may be added to the composition.

Here, the aliphatic polyamide refers to a polymer compound having an amide bond that does not contain an aromatic group in a substantial amount, and typical examples thereof include nylon 6, nylon 66, nylon, 610, nylon 6-66, nylon. 11, nylon 12, etc. can be mentioned. These have a molecular weight such that a film can be formed. Among these, in terms of heat resistance, toughness, pinhole resistance, etc.,
It is preferable to select from nylon 6, nylon 66 and the like.

On the other hand, a partially aromatic polyamide is a polyamide in which either a diamine component or a dicarboxylic acid component contains an aromatic component as a main component, and the other components are mainly an aliphatic component or an alicyclic component. For example, aromatic dicarboxylic acids such as terephthalic acid and / or isophthalic acid, and hexamethylenediamine, 2,2,4 and / or 2,4,4, -trimethylhexamethylenediamine, octamethylenediamine, decamethylenediamine, dodecadiene. Methylenediamine, bis-
Polyamide formed from one or more kinds of aliphatic or alicyclic diamines such as (4-aminocyclohexyl) methane, aromatic diamines such as metaxylylenediamine and / or paraxylylenediamine, and adipine Examples thereof include polyamides formed from an acid and an aliphatic dicarboxylic acid such as sebacic acid. These partially aromatic polyamides have a molecular weight such that a film can be formed. Of these, terephthalic acid and isophthalic acid are the former 10 to 40 mol% and the latter 6
It is preferable to use a polyamide of an aromatic dicarboxylic acid and an aliphatic or alicyclic diamine in a proportion of about 0 to 100 mol%.

In the polyamide composition, when the proportion of the aliphatic polyamide is more than the above range and the proportion of the partially aromatic polyamide is less than the above range, the transparency, gas barrier property and deep drawing uniformity of the composite film should be satisfied. It is not preferable because it does not reach the standard. When the proportion of the aliphatic polyamide is less than the above range and the proportion of the partially aromatic polyamide is more than the above range, the composite film is deteriorated in pinhole resistance, hot water whitening resistance, and the like.
It is not preferable because the interlaminar adhesive strength with the vinyl alcohol copolymer layer is reduced.

The ethylene / vinyl alcohol copolymer constituting one layer of the composite film of the present invention has a vinyl alcohol content of 4
It may be contained as a copolymerization component in an amount of 0 to 85 mol%, preferably 50 to 70 mol%, and another monomer of about 10 mol% or less. The most suitable method for producing such a copolymer is a method in which an ethylene-vinyl acetate copolymer having a vinyl acetate content of about 40 to 95 mol% is saponified so as to have a saponification degree of 90 to 100%. is there. If the content of vinyl alcohol in the copolymer is more than the above range, the heat resistance is poor, and if the amount is less than the above range, the gas barrier properties and mechanical properties are deteriorated, and the interlayer adhesion with the polyamide layer is also reduced. Is unfavorable because it tends to weaken. Additives that are usually added may be blended in the ethylene / vinyl alcohol copolymer.

The production of the composite film comprising the polyamide composition and the ethylene / vinyl alcohol copolymer is carried out by coextrusion under conditions such that the two come into contact with each other in the molten state. The coextrusion temperature is appropriately in the range of about 210 to 250 ° C., though it varies depending on the type and mixing ratio of each polyamide component, the type of ethylene / vinyl alcohol copolymer, and the like.

The composite film of the present invention may be a two-layer film comprising a polyamide composition layer and an ethylene / vinyl alcohol copolymer layer, or a three-layer film in which the polyamide composition layer is formed on both sides of the copolymer layer. It may be an extruded film, and various modifications are possible. For example, in addition to the above two raw materials, other materials such as polyolefin can be coextruded at the same time to form a multilayer film having three or more layers.

〔The invention's effect〕

According to the present invention, it is possible to provide a coextrusion composite film having excellent transparency, gas barrier property, pinhole resistance, deep drawing workability, and interlayer adhesion. In terms of transparency, the transparency is superior to that expected from the transparency of the composite film using the aliphatic polyamide and the partially aromatic polyamide alone. The whitening tendency is remarkably small even when contacted with hot water. In addition, the polyamide mixture system of the present invention is unexpectedly excellent also in the interlaminar adhesive strength. The composite film of the present invention has an excellent oxygen gas barrier property especially under high humidity. Taking advantage of such characteristics, the film of the present invention is suitable for food packaging, for example, meat such as raw meat and processed meat, dairy products, foods such as miso and pickles, and retort foods.

Examples 1-4 and Comparative Examples 1-2 NY-6 (Toray Amiran C
M-1021XF) as a partially aromatic polyamide, the diamine component is hexamethylenediamine and the dicarboxylic acid component is terephthalic acid / isophthalic acid = 30/70.
40% of aliphatic polyamide / partially aromatic polyamide compositions of various compositions shown in Table 1 were prepared using the polycondensate in mol%.
A polyamide composition was obtained by extruding with a φ extruder at a temperature of 220 to 240 ° C. and then cutting water-cooled strands into pellets.

Next, the above polyamide composition was supplied to a 50 mmφ extruder of a three-kind three-layer coextrusion air-cooled inflation film molding apparatus having a 150 mmφ annular die, and an ethylene vinyl alcohol copolymer (ethylene copolymerization ratio 44 mol%) was extruded with 45 mmφ. LDPE (density 0.920 was supplied to a 40 mmφ extruder to obtain a three-layer coextrusion air-cooled inflation-molded film.

The layer structure and molding conditions of the three-layer film are as follows.

Layer composition: (outer layer) polyamide composition / ethylene vinyl alcohol copolymer / LDPE (inner layer) = 30/30 /
15 μm Molding temperature: Outer layer (polyamide composition) 250 ° C. Middle layer (ethylene vinyl alcohol copolymer) 220
Inner layer (LDPE) 180 ° C Three-layer die 230 ° C B. U. R. 1.7 Take-up speed: 8 m / min Transparency (haze) of the obtained three-layer film, interlayer adhesion strength of the polyamide composition layer / ethylene vinyl alcohol copolymer layer, under high humidity (30 ° C., 100% RH Table 1 shows the oxygen permeation amount, the pinhole resistance (pinhole generation rate), the deep drawability, and the hot water whitening resistance of the film after deep drawing.

As shown in Table 1, a three-layer film in which a polyamide composition having an aliphatic polyamide / partially aromatic polyamide composition ratio of 30/70 to 90/10 was laminated was laminated with a polyamide composition having the same composition ratio of 20/80. It is superior to interlayer film in interlayer adhesion strength, pinhole resistance, and heat-resistant water whitening method. Further, the three-layer film laminated with the polyamide composition having the same composition ratio of 30/70 to 90/10 is more transparent than the three-layer film laminated with the polyamide composition having the same composition ratio of 100/0.
Excellent deep drawing uniformity and oxygen permeability. As described above, the three-layer film obtained by laminating the polyamide composition having the same composition ratio of 30/70 to 90/10 has well-balanced physical properties and exhibits good film properties.

The physical property measurement items in the examples were carried out by the following methods.

(1) Transparency (haze) It is measured using an SM color computer manufactured by Suga Test Instruments.

(2) Interlayer adhesive strength Using an autograph manufactured by Shimadzu Corporation, after peeling off a part of the relevant interface, the peel strength of the test piece having a width of 15 mm is measured by the T peel method at a peel speed of 300 mm / min.

(3) Oxygen permeation rate 30 ° C x 100% R using MOCON OX-TRAN
Measured under H conditions.

(4) Pinhole resistance 10 ℃ using GELBO FLEX TESTER
The pinhole generation rate is determined by a method of examining the polyamide composition layer of a sample, which is bent 15 times with 30% RH condition hair, for three times, and the pinhole generation rate is determined.

(5) Uniformity of deep drawing Using a deep drawing tester manufactured by Omori Kikai Kogyo Co., Ltd., the film before drawing is marked with concentric circles at intervals of 5 mm, and the drawing temperature is 80 ° C, the drawing diameter is 100 mm, and the drawing depth is 30 mm. Measure the distance between concentric circles after deep drawing. Judgment of (uniform) ○ to △ to × (non-uniform) is made according to the uniform spacing.

(6) Heat-resistant water whitening property The deep-drawn sample was immersed in hot water at 85 ° C for 30 minutes, and the whitening state was observed to make a judgment of (whitening) × to Δ to ○ (no whitening).

Claims (1)

[Claims] 1. A polyamide composition comprising 30 to 90% by weight of an aliphatic polyamide and 10 to 70% by weight of a partially aromatic polyamide, and a vinyl alcohol content of 40 to 8.
A composite film obtained by coextrusion with an ethylene / vinyl alcohol copolymer in the range of 5 mol%.