U.S. patent application number 10/844043 was filed with the patent office on 2004-12-02 for multi-layer packaged article.
This patent application is currently assigned to The Nippon Synthetic Chemical Industry Co., Ltd.. Invention is credited to Inoue, Kaoru, Ninomiya, Kenji.
Application Number | 20040241365 10/844043 |
Document ID | / |
Family ID | 33447132 |
Filed Date | 2004-12-02 |
United States Patent
Application |
20040241365 |
Kind Code |
A1 |
Inoue, Kaoru ; et
al. |
December 2, 2004 |
Multi-layer packaged article
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.degree. 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.degree. C. Also, the ionizing radiation is preferably .gamma.
rays.
Inventors: |
Inoue, Kaoru; (Ibaraki-shi,
JP) ; Ninomiya, Kenji; (Kurashiki-shi, JP) |
Correspondence
Address: |
WARE FRESSOLA VAN DER SLUYS &
ADOLPHSON, LLP
BRADFORD GREEN BUILDING 5
755 MAIN STREET, P O BOX 224
MONROE
CT
06468
US
|
Assignee: |
The Nippon Synthetic Chemical
Industry Co., Ltd.
|
Family ID: |
33447132 |
Appl. No.: |
10/844043 |
Filed: |
May 12, 2004 |
Current U.S.
Class: |
428/35.7 |
Current CPC
Class: |
B32B 27/30 20130101;
B65D 81/18 20130101; B32B 2439/70 20130101; B32B 27/16 20130101;
B32B 2310/0856 20130101; B32B 27/306 20130101; B32B 2323/046
20130101; Y10T 428/1352 20150115 |
Class at
Publication: |
428/035.7 |
International
Class: |
B65D 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 12, 2003 |
JP |
2003-133350 |
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.degree. 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.degree. C.
4. The multi-layer packaged article of claim 1, wherein said
ionizing radiation is .gamma. rays.
5. The multi-layer packaged article of claim 1, wherein said
material is livestock meat.
Description
BACKGROUND OF THE INVENTION
[0001] 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.
[0002] 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.
[0003] However, EVOH is inferior in pinhole resistance compared to
thermoplastic resin such as polyolefin resin and polystyrene
resin.
[0004] 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.
[0005] 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).
[0006] 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.
[0007] 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.
[0008] 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.degree. C.), as in the case of
meat packaging.
SUMMARY OF THE INVENTION
[0009] 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.degree. C. or lower, was found to solve the
above problems. Thus, the present invention was achieved.
[0010] 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.degree. C. Also, the ionizing radiation is preferably .gamma.
rays.
DETAILED DESCRIPTION
[0011] The present invention is described in detail below.
[0012] 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.
[0013] The melt flow rate (MFR) of EVOH (measured at 210.degree. 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.
[0014] 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.
[0015] 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.
[0016] 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.
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.degree.
C.
[0024] 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-.alpha.-olefin (.alpha.-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.
[0025] When the EVOH layer is represented as a (a.sub.1, a.sub.2 .
. . ) and the other substrate such as the thermoplastic resin layer
is represented as b (b.sub.1, b.sub.2 . . . ), 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,
a.sub.1/a.sub.2/b, a/b.sub.1/b.sub.2,
b.sub.2/b.sub.1/a/b.sub.1/b.sub.2 and
b.sub.2/b.sub.1/a/b.sub.1/a/b.sub.1/b.sub.2. 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.
[0026] 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.
[0027] 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 .mu.m, preferably 10 to 200 .mu.m, the
thickness of layer b is 10 to 5000 .mu.m, preferably 30 to 1000
.mu.m, and the thickness of the adhesive resin layer is 5 to 400
.mu.m, preferably 10 to 150 .mu.m.
[0028] When layer a is thinner than 5 .mu.m, 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
.mu.m, drawing properties and pinhole resistance tend to decrease
and economical efficiency decreases, thus being unfavorable. When
layer b is thinner than 10 .mu.m, rigidity is insufficient and when
the thickness is more than 5000 .mu.m, the weight becomes large and
economical efficiency decreases, thus being unfavorable. When the
adhesive resin layer is thinner than 5 .mu.m, interlayer adhesion
is insufficient and also, the thickness cannot be controlled with
stability. On the other hand, when the thickness is more than 400
.mu.m, the weight becomes large and economical efficiency
decreases, thus being unfavorable.
[0029] 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.
[0030] 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.degree. C.,
preferably 80 to 160.degree. C.
[0031] 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.degree. C.,
preferably 70 to 120.degree. C., for about 2 to 300 seconds to
thermally contract the film and obtain a tightly packaged
article.
[0032] 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.
[0033] 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.degree. 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.
[0034] Irradiation treatment is described below.
[0035] The temperature when irradiating is at most 10.degree. C.,
preferably -60 to 10.degree. C., more preferably -40 to 5.degree.
C., further preferably -25 to -5.degree. C. When the temperature is
higher than 10.degree. 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.
[0036] 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.
[0037] Examples of the ionizing radiation are .alpha.-rays,
.beta.-rays, .gamma.-rays, electron rays and neutron rays. From the
viewpoint of ease in handling, .gamma.-rays and electron rays are
preferably used and .gamma.-rays is more preferably used from the
viewpoint that even irradiation is possible.
[0038] The type of .gamma.-rays is not particularly limited and
.gamma.-rays emitted from a radiation source such as cobalt 60 and
cesium 137 are preferably used.
[0039] In this way, the multi-layer packaged article of the present
invention, which is excellent in pinhole resistance and
transparency, is obtained.
[0040] Hereinafter, the present invention is described in detail
based on Examples.
[0041] In Examples, "parts" and "%" represent weight standards
unless indicated otherwise.
EXAMPLE1
[0042] <Preparation of Multi-layer Film>
[0043] 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 .mu.m) was obtained.
[0044] <Packaging of Livestock Meat>
[0045] The multi-layer film obtained above was subjected to
simultaneous biaxial drawing at a temperature of 75.degree. 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.degree. C. for 4 seconds and then cooled in water of 5.degree.
C. for 3 minutes to obtain a multi-layer packaged article of
livestock meat.
[0046] <Ionizing Radiation Treatment>
[0047] The obtained packaged article was frozen at -20.degree. 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.degree. C. to obtain the multi-layer packaged article of the
present invention.
[0048] The multi-layer packaged article obtained above was
evaluated in the following manner.
[0049] (Pinhole Resistance)
[0050] 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.degree. 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.degree. C. and
80% RH.
[0051] (Transparency)
[0052] The haze value of the film after the above pinhole
resistance test (thickness of approximately 100 .mu.m) was measured
using "Haze Meter NDH 2000" made by Nippon Denshoku Industries Co.,
Ltd.
EXAMPLE 2
[0053] The multi-layer packaged article was obtained and evaluated
in the same manner as in Example 1, except that 25 kGy of
.gamma.-rays emitted from cobalt 60 as the radiation source were
irradiated as the ionizing radiation.
EXAMPLE 3
[0054] 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.degree.
C. by 25 kGy of .gamma.-rays emitted from cobalt 60 as the
radiation source and then frozen at -20.degree. C.
COMPARATIVE EXAMPLE 1
[0055] The multi-layer packaged article was obtained and evaluated
in the same manner as in Example 1, except that ionizing radiation
was not irradiated.
COMPARATIVE EXAMPLE 2
[0056] 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.degree.
C. and then frozen at -20.degree. C.
[0057] The evaluation results of Examples and Comparative Examples
are shown in Table 1.
1 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
[0058] 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.degree. 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.
* * * * *