US20040241365A1

US20040241365A1 - Multi-layer packaged article

Info

Publication number: US20040241365A1
Application number: US10/844,043
Authority: US
Inventors: Kaoru Inoue; Kenji Ninomiya
Original assignee: Nippon Synthetic Chemical Industry Co Ltd
Current assignee: Nippon Synthetic Chemical Industry Co Ltd
Priority date: 2003-05-12
Filing date: 2004-05-12
Publication date: 2004-12-02
Also published as: JP2004331207A; JP4226947B2

Abstract

The present invention provides a multi-layer packaged article that is excellent in pinhole resistance and transparency. Specifically, the present invention provides a multi-layer packaged article wherein a material is packaged with a multi-layer film having a layer comprising an ethylene-vinyl alcohol copolymer and the film is irradiated by ionizing radiation of 1 to 50 kGy at 10° C. or lower. In preferable embodiments of the present invention, the multi-layer film has a layer structure comprising a layer of linear low density polyethylene placed directly or via an adhesive layer on both faces of the layer containing EVOH and is subjected to ionizing radiation under an atmosphere of −40 to 5° C. Also, the ionizing radiation is preferably γ rays.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a multi-layer packaged article wherein a material is packaged with a multi-layer film having a layer comprising an ethylene-vinyl alcohol copolymer (hereinafter referred to as EVOH). More preferably, the present invention relates to a multi-layer packaged article wherein food for chilled and frozen storage, particularly livestock meat, is packaged by packaging material that is excellent in pinhole resistance and transparency.

Usually, EVOH is excellent in transparency, gas barrier properties, aroma retaining properties, solvent resistance and oil resistance. Utilizing these properties, EVOH is used for various packaging materials such as packaging material for food, pharmaceutical products, industrial chemicals and agricultural chemicals. Particularly, EVOH is widely used as food packaging, to package food such as livestock meat, utilizing the properties of transparency and gas barrier properties.

However, EVOH is inferior in pinhole resistance compared to thermoplastic resin such as polyolefin resin and polystyrene resin.

That is, when the packaged material is shaken, for example while transporting or carrying, the EVOH layer suffers bending fatigue and pinholes develop. As a result, barrier properties decrease.

As measures to solve the above problems, suggested are the method of mixing EVOH and polyester resin (for example see JP-A-63-218352), the method of mixing EVOH, polyolefin and a specific grafted substance (for example see JP-A-3-227345), the method of mixing EVOH, nylon and an ionomer (for example see JP-A-2000-246843) and the method of mixing EVOH and nylon having a low melting point (for example see JP-A-2002-338770).

As a result of detailed studies regarding the above compositions, the compositions described in JP-A-63-218352 and JP-A-3-227345 were found to be improved in pinhole resistance. However, because compatibility of EVOH with the other resins is unfavorable and the composition takes on a sea-island structure when drawing treatment is conducted to impart shrinking property, which is necessary when using for meat packaging, gas barrier properties were found to decrease and transparency was found to decrease, as the film became white.

The compositions described in JP-A-2000-246843 and JP-2002-338770 were also found to have room for further improvement in pinhole resistance and film transparency, as compatibility of EVOH with nylon resin is too high.

Furthermore, in all of the above cases, pinhole resistance was found to decrease even further when exposed to a low temperature atmosphere such as repeated transportation in a frozen state (for example approximately −20° C.), as in the case of meat packaging.

SUMMARY OF THE INVENTION

As a result of intensive studies in light of the above, a multi-layer packaged article, wherein a material is packaged with a multi-layer film having a layer comprising an ethylene-vinyl alcohol copolymer and the film is irradiated by ionizing radiation of 1 to 50 kGy at 10° C. or lower, was found to solve the above problems. Thus, the present invention was achieved.

Furthermore, in preferable embodiments of the present invention, the multi-layer film has a layer structure comprising a layer of linear low density polyethylene placed directly or via an adhesive layer on both faces of the layer comprising EVOH and is subjected to ionizing radiation under an atmosphere of −40 to 5° C. Also, the ionizing radiation is preferably γ rays.

DETAILED DESCRIPTION

The present invention is described in detail below. [0011]
The EVOH used in the present invention is not particularly limited. However, the ethylene content of EVOH is preferably 10 to 70% by mol, more preferably 20 to 60% by mol, further preferably 25 to 50% by mol, and the hydrolysis degree of the vinyl acetate component in EVOH is preferably at least 90% by mol, more preferably at least 95% by mol, further preferably at least 99% by mol. When the ethylene content is less than 10% by mol, gas barrier properties under high humidity and melt moldability decrease. On the other hand, when the ethylene content is more than 70% by mol, sufficient gas barrier properties are not obtained. When the hydrolysis degree of the vinyl acetate component is less than 90% by mol, gas barrier properties, thermal stability and humidity resistance decrease, thus being unfavorable. [0012]
The melt flow rate (MFR) of EVOH (measured at 210° C. under load of 2160 g, hereinafter the same) is not particularly limited, but is preferably 0.5 to 100 g/10 minutes, more preferably 1 to 50 g/10 minutes, particularly preferably 3 to 35 g/10 minutes. When the melt flow rate is lower than the above range, the inside of the extruder when molding is under high torque conditions and extrusion processing tends to become difficult. When the melt flow rate is higher than the above range, moldability decreases and the thickness precision of the layer containing EVOH in the obtained multi-layer film decreases, thus being unfavorable. [0013]
The EVOH is obtained by hydrolysis of an ethylene-vinyl acetate copolymer. The ethylene-vinyl acetate copolymer is prepared by any known polymerization method such as solution polymerization, suspension polymerization and emulsion polymerization and hydrolysis of the ethylene-vinyl acetate copolymer can be conducted by a known method. [0014]
In the present invention, a copolymerizable ethylenic unsaturated monomer can be copolymerized as long as the effects of the present invention are not inhibited. Examples of the monomer are olefins such as propylene, 1-butene and isobutene; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, (anhydrous) phthalic acid, (anhydrous) maleic acid and (anhydrous) itaconic acid, salts thereof or mono or dialkylesters thereof having 1 to 18 carbon atoms; acrylamides such as acrylamide, N-alkylacrylamide having 1 to 18 carbon atoms, N,N-dimethylacrylamide, 2-acrylamidepropane sulfonic acid, salt thereof, acrylamide propyldimethylamine, acid salt thereof and quaternary salt thereof, methacrylamides such as methacrylamide, N-alkylmethacrylamide having 1 to 18 carbon atoms, N,N-dimethylmethacrylamide, 2-methacrylamidepropane sulfonic acid, salt thereof, methacrylamide propyldimethylamine, acid salt thereof and quaternary salt thereof; N-vinylamides such as N-vinylpyrrolidone, N-vinylformamide and N-vinylacetoamide; cyanized vinyls such as acrylonitrile and methacrylonitrile; vinyl ethers such as alkylvinylether having 1 to 18 carbon atoms, hydroxyalkylvinylether and alkoxyalkylvinylether; halogenated vinyls such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride and vinyl bromide; vinyl silanes such as trimethoxyvinyl silane; allyl acetate; allyl chloride; allyl alcohol; dimethylallyl alcohol; trimethyl-(3-acrylamide-3-dimethylpropyl)-ammonium chloride and acrylamide-2-methylpropane sulfonic acid. The above monomers can be post-modified, for example, urethanized, acetalized or cyanoethylized, as long as the effects of the present invention are not lost. [0015]
As the EVOH, at least two different kinds of EVOH can be used. In such a case, by using a mixture of EVOH wherein the ethylene contents of the compounded EVOH differ at least 5% by mol, preferably 5 to 25% by mol, more preferably 8 to 20% by mol, and/or the hydrolysis degrees differ at least 1% by mol, preferably 1 to 15% by mol, more preferably 2 to 10% by mol, and/or the ratio of MFR is at least 2, preferably 3 to 20, more preferably 4 to 15, flexibility, thermal moldability and film-forming stability are improved, while maintaining gas barrier properties. The process for preparing the EVOH (mixture) of at least two different kinds is not particularly limited. Examples are the method of mixing the paste of each ethylene-vinyl acetate copolymer before hydrolysis and then hydrolyzing, the method of mixing the alcohol or alcohol and water solution of each EVOH after hydrolysis and the method of melt kneading after mixing each EVOH. [0016]
The EVOH used in the present invention can contain acids such as acetic acid, boric acid and phosphoric acid and metal salts thereof such as alkali metal salt, alkali earth metal salt and transition metal salt. The above are preferably contained from the viewpoints that thermal stability of EVOH, long-run moldability, interlayer adhesion to the adhesive resin when made into a multi-layer film using an adhesive and thermal drawing moldability are improved. Particularly, alkali metal salt and alkali earth metal salt are preferably used, from the viewpoint of being excellent regarding the above effects. [0017]
Examples of the metal salt are metal salt such as sodium salt, potassium salt, calcium salt and magnesium salt of organic acids including acetic acid, propionic acid, butyric acid, lauric acid, stearic acid, oleic acid and behenic acid and inorganic acids including sulfuric acid, sulfurous acid, carbonic acid and phosphorous acid. Of these, acetate, phosphate and hydrogen phosphate are preferably used. The content of the metal salt is preferably 5 to 1000 ppm, more preferably 10 to 500 ppm, further preferably 20 to 300 ppm, converted to metal based on the EVOH. When the content is less than 5 ppm, the effects of adding may be insufficient and on the other hand, when the content is more than 1000 ppm, the appearance of the obtained multi-layer film becomes poor, thus being unfavorable. In the case that two or more kinds of alkali metal salt and/or alkali earth metal salt are contained, the total amount is preferably within the above range. Also, when boric acid is contained, the content is preferably 10 to 10000 ppm, more preferably 20 to 2000 ppm, further preferably 50 to 1000 ppm converted to boric acid. [0018]
The method for adding the acids or metal salts thereof to the EVOH is not particularly limited. Examples are a) the method of contacting porous precipitate of EVOH having water content of 20 to 80% by weight with an aqueous solution of the acid or metal salt thereof and then drying after the EVOH has contained the acid or salt thereof; b) the method of adding the acid or metal salt thereof to a homogenous solution of EVOH (such as water/alcohol solution), extruding in strands into a coagulation solution, cutting the obtained strands to form pellets and then drying; c) the method of mixing EVOH and the acid or salt thereof all at once and then melt kneading in an extruder; and d) the method of neutralizing the alkali (such as sodium hydroxide, potassium hydroxide) used in the hydrolysis step when preparing EVOH with an acid such as acetic acid and then adjusting the amount of the remaining acid such as acetic acid and alkali metal salt such as sodium acetate and potassium acetate that is by-produced by washing with water. In order to achieve the effects of the present invention more noticeably, the methods a), b) and d), which are excellent in dispersability of the acid or metal salt thereof, are preferably used. [0019]
In the present invention, as long as the effects of the present invention are not lost, the layer comprising EVOH can contain saturated fatty acid amides such as stearamide; unsaturated fatty acid amides such as oleamide; bis fatty acid amides such as ethylenebis(stearamide); fatty acid metal salt such as calcium stearate, magnesium stearate and zinc stearate; lubricants such as low molecular weight polyolefin including low molecular weight polyethylene and low molecular weight polypropylene having molecular weight of approximately 500 to 10,000; inorganic salt such as hydrotalcite; plasticizers such as aliphatic polyol including ethylene glycol, glycerin and hexanediol; oxygen absorbents such as inorganic oxygen absorbents including reduced iron powder, reduced iron powder to which water-absorbing substances or electrolyte is added, aluminum powder, potassium sulfite and photocatalytic titanium oxide, organic oxygen absorbents including ascorbic acid, fatty esters and metal salts thereof, hydroquinone, gallic acid, polyphenols including phenol-aldehyde resin having a hydroxyl group, coordination compounds of nitrogen-containing compounds and transition metal including bis-salicylaldehyde-iminecobalt, tetraethylenepentaminecobalt, cobalt-Schiff base complex, porphyrins, macrocyclic polyamine complex and polyethyleneimine-cobalt complex, terpene compounds, reaction products of amino acids and reducing substances having a hydroxyl group, and triphenylmethyl compounds, and polymer oxygen absorbents such as coordinate bonded bodies of nitrogen-containing resin and transition metal including a combination of metaxylenediamine and cobalt, compositions of tertiary hydrogen-containing resin and transition metal including a combination of propylene oligomer and cobalt, compositions of oligomer having a carbon-carbon unsaturated bond and transition metal including a combination of butadiene oligomer and cobalt, anthraquinone compounds, and the above compositions to which a photoinitiator such as benzophenone, a peroxide collecting agent such as commercially available antioxidants and a deodorant such as active carbon is added; thermal stabilizers; photostabilizers; antioxidants; ultraviolet ray absorbents; colorants; antistatic agents; surfactants; antibacterial agents; antiblocking agents such as fine powder of talc; slipping agents such as amorphous silica; and fillers such as inorganic fillers. [0020]
The EVOH is preferably used in a laminate, particularly in a laminate wherein a thermoplastic resin layer is laminated on at least one face of the layer comprising EVOH. The obtained laminate has water resistance, mechanical properties and heat sealing properties and is suitable for practical use. [0021]
The multi-layer film used in the multi-layer packaged article of the present invention is a multi-layer film having a layer containing EVOH (hereinafter referred to as EVOH layer). To obtain the multi-layer film, usually, another substrate such as thermoplastic resin is laminated on one face or both faces, preferably both faces, of the EVOH layer. [0022]
Examples of the laminating method are the method of laminating by melt extruding the other substrate on the EVOH layer (film or sheet), the method of laminating by melt extruding the EVOH on the other substrate, the method of co-extruding the EVOH and the other substrate and the method of dry laminating the EVOH layer and a film or sheet of the other substrate using a known adhesive such as an organic titanium compound, an isocyanate compound, a polyester compound and a polyurethane compound. The melt molding temperature when laminating by melt extrusion or co-extrusion is usually within the range of 150 to 300° C. [0023]
As the other substrate, thermoplastic resin is useful. Specifically, examples are linear low density polyethylene; low density polyethylene; ultra low density polyethylene; medium density polyethylene; high density polyethylene; ethylene-vinyl acetate copolymer; ionomer; ethylene-propylene (block or random) copolymer; ethylene-acrylic acid copolymer; ethylene-acrylic ester copolymer; polypropylene; propylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymer; polyolefin resin in a broad sense such as homopolymer or copolymer of olefin including polybutene and polypentene and homopolymer or copolymer of these olefins that is graft-modified with unsaturated carboxylic acid or ester thereof; polyester resin, polyamide resin (including copolymerized polyamide); polyvinyl chloride; polyvinylidene chloride; acrylic resin; polystyrene; vinyl ester resin; polyester elastomer; polyurethane elastomer; chlorinated polyethylene; chlorinated polypropylene; aromatic or aliphatic polyketone; polyalcohols obtained by reducing these; and other EVOH. From the viewpoint of practicability such as properties, particularly strength, of the multi-layer film, polypropylene, ethylene-propylene (block or random) copolymer, polyamide, polyethylene, ethylene-vinyl acetate copolymer, polystyrene, polyethylene terephthalate and polyethylene naphthalate are preferably used. Of these, linear low molecular weight polyethylene is particularly preferable. [0024]
When the EVOH layer is represented as a (a[0025] ₁, a₂. . . ) and the other substrate such as the thermoplastic resin layer is represented as b (b₁, b₂. . . ), the layer structure of the multi-layer film is not limited to the two-layer structure of a/b and any combination is possible, such as b/a/b, a/b/a, a₁/a₂/b, a/b₁/b₂, b₂/b₁/a/b₁/b₂and b₂/b₁/a/b₁/a/b₁/b₂. Furthermore, when a regrind layer comprising a mixture of at least EVOH and thermoplastic resin is represented as R, the layer structure can be b/R/a, b/R/a/b, b/R/a/R/b, b/a/R/a/b or b/R/a/R/a/R/b.
In the above layer structure, a layer of adhesive resin is preferably formed when necessary between each layer, from the viewpoint that a multi-layer film that is excellent in drawing properties can be obtained. Various resins can be used as the adhesive resin and although the preferable type of adhesive resin depends on the type of resin b, examples are modified olefin polymers containing a carboxyl group that are obtained by chemically bonding unsaturated carboxyl acid or anhydride thereof to an olefin polymer (polyolefin resin in a broad sense described above) by addition reaction or graft reaction. Specifically, suitable examples are one or at least two compositions selected from polyethylene graft-modified with maleic anhydride, polypropylene graft-modified with maleic anhydride, ethylene-propylene (block or random) copolymer graft-modified with maleic anhydride, ethylene-ethyl acrylate copolymer graft-modified with maleic anhydride and ethylene-vinyl acetate copolymer graft-modified with maleic anhydride. The amount of unsaturated carboxylic acid or anhydride thereof that is contained in the thermoplastic resin is preferably 0.001 to 3% by weight, more preferably 0.01 to 1% by weight, further preferably 0.03 to 0.5% by weight. When the modified amount in the modified substance is small, adhesion may be insufficient and when the amount is large, crosslinking reaction occurs and moldability tends to become poor, thus being unfavorable. To the adhesive resin, EVOH, polyisobutylene, rubber elastomer components such as ethylene-propylene rubber and resin of layer b can be mixed. Particularly, mixing a polyolefin resin that is different from the matrix polyolefin resin of the adhesive resin is useful, as adhesion may be improved. [0026]
The thickness of each layer of the multi-layer film depends on the layer structure, the type of resin b, the type and shape of the livestock meat that is to be packaged, the form of packaging (container) and the desired properties. Usually, the thickness of layer a is 5 to 500 μm, preferably 10 to 200 μm, the thickness of layer b is 10 to 5000 μm, preferably 30 to 1000 μm, and the thickness of the adhesive resin layer is 5 to 400 μm, preferably 10 to 150 μm. [0027]
When layer a is thinner than 5 μm, gas barrier properties are insufficient and also, the thickness cannot be controlled with stability. On the other hand, when the thickness is more than 500 μm, drawing properties and pinhole resistance tend to decrease and economical efficiency decreases, thus being unfavorable. When layer b is thinner than 10 μm, rigidity is insufficient and when the thickness is more than 5000 μm, the weight becomes large and economical efficiency decreases, thus being unfavorable. When the adhesive resin layer is thinner than 5 μm, interlayer adhesion is insufficient and also, the thickness cannot be controlled with stability. On the other hand, when the thickness is more than 400 μm, the weight becomes large and economical efficiency decreases, thus being unfavorable. [0028]
The material that is packaged by the multi-layer film obtained in the above manner is not particularly limited. Examples are livestock meat such as beef, pork, poultry and mutton; processed meat products such as ham, sausage, salami, roast pork and roast chicken; fish paste products such as kamaboko (fish cake) and delicacies and processed agricultural products such as rice cakes, pickles, cheese and mountain vegetables. The present invention is useful as packaging for livestock meat. Use of the present invention as packaging for livestock meat is described below but the present invention is not limited thereto. [0029]
When packaging livestock meat, the multi-layer film can be used as it is, but usually, the multi-layer film is subjected to drawing treatment in order to impart thermal contraction properties and become shrink packaging. Examples of the drawing method are the roll drawing method, the tenter drawing method, the tubular drawing method, the draw blowing method, vacuum molding, pneumatic molding and vacuum pneumatic molding and of these, a method having high drawing ratio is employed. In the case of biaxial drawing, both simultaneous biaxial drawing and sequential biaxial drawing can be employed. The drawing temperature is 60 to 170° C., preferably 80 to 160° C. [0030]
The film subjected to drawing treatment is then processed into a pouch. The shape of the pouch can be determined according to the shape of the contents. After livestock meat is stored in the pouch, thermal treatment is conducted at 50 to 130° C., preferably 70 to 120° C., for about 2 to 300 seconds to thermally contract the film and obtain a tightly packaged article. [0031]
The livestock meat stored in the packaging pouch can be meat for human consumption that is bred as livestock and specific examples are beef, pork, poultry and mutton. The livestock meat can be unprocessed dressed carcass having bones or processed boneless meat divided according to each part. [0032]
The present invention is most characteristic in that the multi-layer EVOH film that constitutes the multi-layer packaged article is irradiated by ionizing radiation of 1 to 50 kGy at 10° C. or lower. The livestock meat can be packaged with the multi-layer EVOH film before irradiation or after irradiation, but in view of production efficiency, the former is preferable. [0033]
Irradiation treatment is described below. [0034]
The temperature when irradiating is at most 10° C., preferably −60 to 10° C., more preferably −40 to 5° C., further preferably −25 to −5° C. When the temperature is higher than 10° C., pinhole resistance decreases and achieving the purpose of the present invention may be difficult. The temperature can be adjusted to this range by refrigerating or by freezing. [0035]
The amount of ionizing radiation is 1 to 50 kGy, preferably 5 to 40 kGy, more preferably 15 to 30 kGy. When the amount is less than 1 kGy, the effects of the present invention may not be obtained. On the other hand, when the amount is more than 50 kGy, foul odor is generated due to decomposition of resin in the multi-layer film, thus being unsuitable. [0036]
Examples of the ionizing radiation are α-rays, β-rays, γ-rays, electron rays and neutron rays. From the viewpoint of ease in handling, γ-rays and electron rays are preferably used and γ-rays is more preferably used from the viewpoint that even irradiation is possible. [0037]
The type of γ-rays is not particularly limited and γ-rays emitted from a radiation source such as cobalt 60 and cesium 137 are preferably used. [0038]
In this way, the multi-layer packaged article of the present invention, which is excellent in pinhole resistance and transparency, is obtained. [0039]
Hereinafter, the present invention is described in detail based on Examples. [0040]
In Examples, “parts” and “%” represent weight standards unless indicated otherwise. [0041]

EXAMPLE1

<Preparation of Multi-layer Film>[0042]
EVOH (ethylene content 32% by mol, hydrolysis degree 99.5% by mol, MFR 3.5 g/10 minutes), polyethylene (linear low density polyethylene, “Novatech LLUF 331” available from Japan Polychem Corporation, MFR 1.0 g/10 minutes) and adhesive resin (low density polyethylene modified with maleic anhydride, “MODIC AP L502” available from Mitsubishi Chemical Corporation) were fed to a multi-layer extruding apparatus equipped with 3 kinds of feed blocks and a multi-layer T die of five layers. Then, a multi-layer film having a layer structure of polyethylene layer/adhesive resin layer/EVOH layer/adhesive resin layer/polyethylene layer (thickness 40/10/30/10/40 μm) was obtained. [0043]
<Packaging of Livestock Meat>[0044]
The multi-layer film obtained above was subjected to simultaneous biaxial drawing at a temperature of 75° C. and a drawing rate of 50 mm/sec to three times in the TD direction and three times in the MD direction, to obtain a drawn multi-layer film. Then, using two of the above drawn multi-layer films, a pouch sealed in three directions having width of 200 mm, length of 300 mm and sealing width of 15 mm was prepared. Approximately 1 kg of dressed Boston butt (cube having length of 15 cm, width of 10 cm and height of 6 cm) was placed in the pouch and the upper area was vacuum sealed by a vacuum packaging machine. Thereafter, the packaged pouch was thermally contracted by a hot water shower of 80° C. for 4 seconds and then cooled in water of 5° C. for 3 minutes to obtain a multi-layer packaged article of livestock meat. [0045]
<Ionizing Radiation Treatment>[0046]
The obtained packaged article was frozen at −20° C. and 24 hours later, EB irradiation of acceleration voltage of 200 MeV and amount of 25 kGy was conducted in an environment of −20° C. to obtain the multi-layer packaged article of the present invention. [0047]
The multi-layer packaged article obtained above was evaluated in the following manner. [0048]
(Pinhole Resistance) [0049]
One set comprising 12 of the above multi-layer packaged articles was placed in a cardboard box in two levels with 3 pouches in the length direction and 2 pouches in the width direction. The box was stowed in the loading space of a refrigerated 2 ton truck (inside temperature −20° C.) and the truck made two round trips in one week between Yokohama and Kobe. Thereafter, the content of the two packages in the middle of the bottom level was taken out and the oxygen permeation degree of the film (average value of n=2) was measured under conditions of 23° C. and 80% RH. [0050]
(Transparency) [0051]
The haze value of the film after the above pinhole resistance test (thickness of approximately 100 μm) was measured using “Haze Meter NDH 2000” made by Nippon Denshoku Industries Co., Ltd. [0052]

EXAMPLE 2

The multi-layer packaged article was obtained and evaluated in the same manner as in Example 1, except that 25 kGy of γ-rays emitted from cobalt 60 as the radiation source were irradiated as the ionizing radiation. [0053]

EXAMPLE 3

The multi-layer packaged article was obtained and evaluated in the same manner as in Example 2, except that the packaged article was irradiated at an irradiation temperature of 5° C. by 25 kGy of γ-rays emitted from cobalt 60 as the radiation source and then frozen at −20° C. [0054]

COMPARATIVE EXAMPLE 1

The multi-layer packaged article was obtained and evaluated in the same manner as in Example 1, except that ionizing radiation was not irradiated. [0055]

COMPARATIVE EXAMPLE 2

The multi-layer packaged article was obtained and evaluated in the same manner as in Example 1, except that the packaged article was irradiated at an irradiation temperature of 20° C. and then frozen at −20° C. [0056]
The evaluation results of Examples and Comparative Examples are shown in Table 1. [0057]

TABLE 1

Transparency

Pinhole resistance (Haze value)

Ex. 1 1.8 4.2

Ex. 2 1.6 3.8

Ex. 3 2.5 4.0

Com. Ex. 1 7.0 5.5

Com. Ex. 2 6.5 4.5
The multi-layer packaged article of the present invention has excellent pinhole resistance and transparency, because the article is packaged with a multi-layer film having a layer comprising EVOH and irradiated by ionizing radiation of 1 to 50 kGy at a temperature of 5° C. or lower. Particularly, the multi-layer packaged article of the present invention is useful as a multi-layer packaged article of livestock meat for human consumption such as beef, pork, poultry and mutton. [0058]

Claims

What is claimed is:

1. A multi-layer packaged article wherein a material is packaged with a multi-layer film having a layer comprising an ethylene-vinyl alcohol copolymer; and

said film is irradiated by ionizing radiation of 1 to 50 kGy at 10° C. or lower.

2. The multi-layer packaged article of claim 1, wherein said film has a layer structure comprising a layer of linear low density polyethylene placed directly or via an adhesive layer on both faces of said layer comprising an ethylene-vinyl alcohol copolymer.

3. The multi-layer packaged article of claim 1, wherein said film is subjected to ionizing radiation in an atmosphere of −40 to 5° C.

4. The multi-layer packaged article of claim 1, wherein said ionizing radiation is γ rays.

5. The multi-layer packaged article of claim 1, wherein said material is livestock meat.