CA1335424C - Multilayered packaging materials having high gas barrier property - Google Patents

Abstract

This invention provides a gas-barrier multilayered packaging material which comprises an outer layer of a composition comprising 55-97 wt% of an EVOH and 45-3 wt% of a resin selected from the group consisting of polyamide, polyolefin, polyester and polycarbonate and an inner layer comprising a hydrophobic thermoplastic resin having a low moisture permeability. The invention further provides a gas-barrier multilayered packaging material which comprises an outer lay-er comprising a resin layer having a moisture permeability (measured at 40°C, 90% RH) of at least 40 g/m2.day, an inter-mediate layer of a composition comprising 55 to 97% by weight of an EVOH and 45 to 3% by weight of a resin selected from the group consisting of polyamide, polyolefin, polyester and polycarbonate and an inner layer comprising a hydrophobic thermoplastic resin layer having a moisture permeability lower than that of the outer layer.
Both are useful as packaging materials to be used for boil sterilization or retort sterilization.

Description

t 335424 MULTILAYERED PACKAGING MATERIALS HAVING HIGH GAS BARRIER
PROPERTY

This invention relates to multilayered packaging materials having excellent food keeping properties due to their high gas barrier properties, particularly to multi-layered packaging films, in particular lids to be used for retorting or pouches to be used for retorting, which are unparalleled with respect to excellent transparency together with high gas barrier properties. This invention also includes cup-shape or tray-shape containers having high gas --barrier properties to be used for retorting.
Laminate films consisting of aluminum foil and a polyolefin, particularly polypropylene, and metal lids for double-seaming are used as lids to be used for retorting.
Both have nearly perfect gas barrier properties but have the drawback of not being transparent, thereby rendering the contents invisible. The contents should be visible from the viewpoint of appeal to consumers, as well as the requirement that the contents not be spilled when the container is opened or when the lid is pierced with a hole before the container is heated in a microwave or the like. However, transparent lids made of plastic film are currently only in use for limited purposes due to their insufficient gas barrier properties, particularly insufficient oxygen gas barrier properties.
Polyvinylidene chloride polymer (principally vinylidene chloride-vinyl chloride copolymers, hereinafter sometimes referred to as PVDC) is an representative example of gas-barrier resins currently in use for lids, and is used in aform of lam1nated film obtained by laminating thereon a biaxially oriented nylon film (hereinafter sometimes referred to as ON) for the outer layer and a polypropylene film (hereinafter sometimes referred to as PP) for the inner ; 10 layer which is a sealing layer by dry laminating ~r a simil~r process. The oxygen gas transmission rate or oxygen permeability (hereinafter abbreviated as OTR) of PVDC is 3 to 20 cc/m2 day atm per 20 ~ . Since an OTR of about 0.8 cc/m2 day-atm is required for a packaging ~aterial to maintain food cnnt~' n~ therein in a good condition for 6 months unler norm~l circumstances, PVDC must have a thickness of at least 75 ~ .
Howev~, if F~ fi~m is 75 ~ thick, it will have a high haze and becGme yellowish. The film thickness of PVDC therefore is generally 15 to 30 ~ , and about 50 ~ only for some uses where a high barrier property is particularly required.

Thus, PVDC lids cannot be said to have sufficient food keeping performances.
Recently, films made of vinylidene chloride-ethyl acrylate copolymers are known to have particularly high gas barrier properties among PVDC-related polymers. The OTR is 1.2 cc-20~ /m2-day-atm. The polymer, however, has drawbacks of becoming opaque and increasing its OTR with retort ,.~

treatment, thereby being unsuitable for use as a transparent lid for retorting.
Among gas-barrier resins other than PVDC, there are metaxylylenediamine-adipic acid condensate (MX-nylon), polyamide, PVDC-coated polyamide and the like being used for lids. They are all of low oxygen gas barrer properties, and hence are used only for foods which have low oxidation-degradation liability or are transported and stored at low temperatures.
Pouches among packaging films for retorting are under more severe conditions. That is, while a lid is only a part ~-of a container, transparent packaging films used for pouches, skin-packs, deep-drawn packages, rocket packaging and the like constitute the whole container. Since transparent packaging films currently used for the above packagings do not have sufficient gas barrier properties, the packages after retort treatment can only be transported and stored only at low temperatures.
Ethylene-vinyl alcohol copolymer resin (hereinafter sometimes referred to as EVOH) is a thermoplastic resin having the highest gas barrier properties known today and ones exhibiting OTR's of from 0.3 (at 60 % RH) to 0.75 (80 %
RH) cc-20 /m2-day.atm are used as general-purpose brands (EVAL~ Type F, made by Kuraray Co.). EVOH is widely used as a gas-barrier material for retortable containers, e.g. cups and trays, which employ multilayered structures comprising EVOH for the intermediate layer and PP which has low .

moisture permeability as the inner and outer layers. For the purpose of further increasing food keeping performance, there is a method which comprises incorporating a drying agent in an adhesive resin layer between PP layer and EVOH layer (U.S.
Patent No. 4,407,897) or a method which comprises incorporating a drying agent in the EVOH layer itself (U.S. Patent No.
4,425,410).
Further, Japanese Patent Publication No. 24254/1986 (B.P.

2,006,108) discloses a plastic bottle to contain food, consisting of an outer layer of a polyamide, an intermediate layer of a gas-barrier resin (e.g. EVOH) and an inner layer of ~--a polyolefin or thermoplastic polyester; and also describes, as the gas-barrier resin, a blend of EVOH with 6/66 copolymer nylon in a blending ratio of 50:50 by weight. However, it has been found that if the blend of EVOH containing polyamide (nylon) in as much as 50 wt % is used, problems will occur.
Such problems include, for example, not only a decrease in the gas barrier property but also whitening when stored after retort treatment of the multilayered package. This fact is apparent from Comparative Example 6 later described herein.
Japanese Patent Publication No. 38103/1954 (B.P. 1,545,096) describes a container comprising inner and outer layers of a moisture-resistant resin or creep-resistant resin having a low moisture permeability and an intermediate layer of a 25 - composition incorporating blended therein a gas-barrier resin (e.g. EVOH/polyamide in a ratio of from 90:10 to 10:90), but it does not describe the provision of an outer layer of a resin having a comparatively high moisture permeability and an lnner layer of another resin having a low moisture permeability, or further, using a layer comprising EVOH blended with a relatively small amount of a polyamide for the intermediate layer. Nor does this patent describe a packaging material comprising an outer layer of the blended gas-barrier resin composition and an inner layer of a resin having a low moisture permeability, or the use of such packaging material for retort sterilization or boil sterilization packaging.
Japanese Patent Laid Open No. 54-78749 describes a blend of EVOH and polyamide and said blend being laminatable with ~-another thermoplastic resin, but it does not describe a packaging material comprising an outer layer of said blend and an inner layer of a resin having a low moisture permeability.
While EVOH can give superior retortable containers when used sandwiched between inner and outer layers of thick PP layers, that is, when used for rigid containers, e.g. cups and trays, it cannot provide flexible packaging films, e.g. lids and pouches which are retortable. Such packaging film must be flexible and ; 20 requires that the inner and outer resin layers be thin. This would result, during the course of retorting, in a-large amount of moisture invading the EVOH layer, thereby markedly decreasing the gas barrier property. The invasion of moisture would also create a serious problem of whitening of the EVOH layer or generation of wavy wrinkles or patterns, which makes the film suitable as a gas-barrier packaging film because of its poor appearance. Further, since EVOH melts at retorting tempera~ures ~' (about 120C), it has never been attempted to provide EVOH or blends thereof as the outer layer of packages which must contact hot water.
The present inventors assumed that the mechanism of the decrease in gas barrier property, whitening and generation of wavy wrinkle patterns through retorting is greating influenced by, in addition to the moisture absorption of EVOH layer, the condition of water in the EVOH layer just after the retorting and the behaviour of water passing from the EVOH layer through the outer layer outward and hence decreasing its amount in the film. Based on this assumption, an extensive study was made on the influence of various compositions incorporating EVOH and resins of inner and outer layers.
As a result of the study, the present inventors have found a surprising fact that should upset conventional concepts about EVOH. The fact is:
There can be obtained a packaging film which does not suffer EVOH flow of the outer layer leading to whitening or bad appearance including wavy wrinkles and patterns, and which maintains the high gas barrier property inherent to EVOH, thereby exhibiting superior performances when used for lids and pouches; by providing as an outer layer, instead of EVOH, a composition comprising of 55-97 % by weight of EVOH having an ethylene content of 20-50 mol % and 3-45 % by weight ~f a resin selected from the group consisting of polyamide resin (hereinafter sometimes referred to as PA~, polyolefin resin, polyester resin and polycarbonate resin and as an inner layer a hydrophobic thermoplastic resin, e.g. PP

, . , . ,. ~

having a low moisture permeability.
Though the resin, e.g. PA, used as an improving agent in the composition of the outer layer is distributed in the form of islands in the EVOH layer, it greatly influences prevention of the matrix of the EVOH component from flowing. This fact is completely different from the accepted concept and anticipation at the start of the study. The outer layer and inner layer herein mean the outermost layer and the innermost layer respectively.
The present inventors have further studied and found another surprising fact. That fact is:
There can be obtained a packaging film suitable for use in a variety of packaging fields, which does not create any whitening or bad appearance including wavy wrinkles and patterns, which maintains the high gas barrier property inherent to EVOH, and which does not cause blocking with the same film adjacent thereto, thereby exhibiting superior performances when used for lids and pouches, by providing as an intermediate layer, instead of EVOH, a composition comprising 55-97 % by weight of EVOH and 3-45 % by weight of a resin selected from the group consisting of PA, polyolefin, polyester and polycarbonate, an outer layer having a moisture permeability (40C, 90 % RH) of at least 40 g/m2-day, e.g.
a layer containing as a principal component at least one resin selected from the group consisting of PA, polyester and ~ polycarbonate, in particular a layer of PA having such moisture permeability, and an inner layer of thermoplastic resin, in particular PP or the like having a moisture permeability lower than that of the outer layer.
S Means and/or facts adopted finally in the invention are completely different from general recognition or anticipation conceived at the start of the study the facts are:
Though PA or like resins used as improving agents in the composition of the intermediate layer are distributed in the form of islands in EVOH layer, they greatly influence the behaviour of the matrix EVOH at retorting; and While conventional methods for producing packaging materials for retorting comprises employing as resins sandwiching EVOH layer ones having moisture permeabilities as low as possible, here, conversely, it is effective to provide as the outer layer a resin having a high moisture permeability.
Ethylene-vinyl alcohol copolymer (EVOH) is one of the resins constituting the composition of the outer layer of the first embodiment of the invention and the intermediate layer of the second embodiment of the invention and may include any polymer as long as it is obtained by hydrolyzing the vinyl acetate component of a copolymer of ethylene and vinyl acetate. As EVOH's particularly suited for the purpose of the present invention, mention may be made of those having an ethylene content of 20 to 50 mol %, particularly 27 to 40 mol %, 1 33542~
a saponification degree of the vinyl acetate component of at least 96 %, preferably at least 99 %, and a melt index (190C, 2160 g) of 0.2 to 60 g/10 min. The EVOH in the present invention may be one modified with not more than S mol %
of a copolymerizable monomer. Examples of such modifying monomer include, among others, propylene, l-butene, l-hexene, 4-methyl-1-pentene, acrylic acid esters, methacrylic acid esters, maleic acid, fumaric acid, itaconic acid, higher fatty acid vinyl esters, alkylvinyl ethers, N-(2-dimethylaminoethyl)-methacrylamide or its quaternary compound, N-vinylimidazole or its quaternary compound, N-vinylpyrrolidone, N,N-butoxymethyl-acrylamide, vinyltrimethoxysilane, vinylmethyldimethoxysilane and vinyldimethylmethoxysilane.
Examples of the polyamide resins (PA) used as one of the counterpart resins constituting the composition of the outer layer of the first embodiment of the invention or the intermediate layer of the second embodiment of the invention include, among others, polycaprolactam (nylon-6), poly-~-aminoheptanoic acid (nylon-7), poly-~-aminononanoic acid (nylon-9), polyundecaneamide (nylon-ll), polylauryl lactam (nylon-12), polyethylenediamine adipamide (nylon-2, 6), polytetramethylene adipamide (nylon-4, 6), polyhexamethylene adipamide (nylon-6, 6), polyhexamethylene sebacamide (nylon-6, 10), polyhexamethylene dodecamide (nylon-6, 12), polyoctamethylene adipamide (nylon-8, 6), polydecamethylene adipamide (nylon-10, 6) and polydodecamethylene sebacamide (nylon-10, 8); or caprolactam/lauryl lactam copolymers (nylon-6/12), caprolactam/~ -aminononAn~;c acid copolymers (nylon-6/9), caprolactam/hexamethylene diammonium adipate copoly-mers (nylon-5/6, 6), lauryl lactam/hexamethylene diammonium adi2ate copolymers (nylon-12/6, 6), hexamethylene diammonium - 5 adipate/hexamethylene diammonium sebacate copolymers (nylon-6, 6/6,10), ethylene diammonium adipate/hexamethylene diammo-nium a~ipate copolymers (nylon-2, 6~6, 5), c^-parol2ctam/hexa-; methylene diammonium adipate/hexamethylene diammonium sebacate copolymers (nylon-6/6, 6/6, 10), polyhexamethylene isophthalamide, polyhe~amethylene terephthalamide and hexamethylene isophthala~ide/terephthalamide copolymer.
Among the above mentioned PA's, caprolactom/lauryl lac-tam copolymer, that is, nylon-~/12 is the most prefer-ed in the present invention. While there are no particular limits to the ~I~c;t`ion of the 6-~c~ ,P,.~ and the 12-~ n~ in nylon-6/12, a 12-component of 5 to 60 wt~, par~icularly 10 to 50 wt~ is preferred. The relative viscosity is 2.0 to 3.6, preferably 2 to 3.2.
These PA's, particularly nylon-5/12, may be modified to polyamides containing in their polymer chain ether bonds by addition of polyetherdiamine and dic~rboxylic acid (dimeric acid or the like) in the course of the poly~n~nsAtion reaction. Also preferred are those polyamides in which the number of carboxyl end groups is reduced by addition, at the pol~condensati3n, of ~n aliphati^ amine, e.g. hexameth~l-enediamine or laurylamine or an aromatic amine, e.g.
meta~ylylenediamine or methylbenzy7amine. In this case, ., -10-~ polyamides having at least 8 x 10~5 eq./g of amino end groups and not more than 3 x 10~5 eq./g of carboxyl end groups are preferred.
It is quite unexpected that though PA in a composition distributes mostly as an island ~ nL in the EV0H
layer, it still greatly suppresses the sensitivity of EVOH against water, particularly of preventing whitening and generation of wavy patterns or stripe patterns. The mecha-nism producing such a marked efbect is not well clarified.
While PA is the best imprcving agent to be incorporated in EVOH, other resins including polyolefin, polyester and polycarbon-ate can also be used for the same purpose. It is believed, however, considering the fact that some degree of effect is : also produced by blending, instead of PA, such resins as polyolefin, polyester, polycarbonate and the like with EVOH
to prevent~ generation of wavy patterns or stripe patterns after retorting at 120-C, such effect ~ay be produced by the blending of a resin having a melting point higher than the retorting temperature. For retort sterilization at a lower temperature (e.g. 105 to 115-C) or for the purpose of boiling sterilization, blending of medium density polyethyl-ene or low density polyethylene also has an effect to some extent. However, a blend of PP, PP modified with maleic anhydride, polyethylene or polyester with EVOH has the drawbac~ that it causes poor transparency as compared with the blend of PA with EVOH. For packaging films, e.g.
lids, which end-uses emphasize transparency, blending PA

r .

-with EVOH is preferred. For cups, trays and the like which do not require transparency blending the above-mentioned resins such as PP with EVOH can be employed.
Examples of polyolefin resins used in this invention include, among others, high density, medium density or low density polyethylene; copolymers of polyethylene with vinyl acetate, acrylic acid esters, or ~-olefins, e.g. butene, hexene, 4-methyl-1-pentene; ionomers; polypropylene~ homopolymer;
polypropylene grafted with ethylene; copolymers of propylene with ~-olefins, e.g. ethylene, hexene, 4-methyl-1-pentene and the like; poly-l-butene, poIy-4-methyl-1-pentene and the like.
Modified polyolefins, particularly modified polypropylene, are also preferably used because of their improved compatibility with EVOH. Examples of modifying agents used here are maleic acid, acrylic acid, methacrylic acid, crotonic acid, fumaric acid, itaconic acid, maleic anhydride, itaconic anhydride, citraconic anhydride, ethyl acrylate, methyl methacrylate, ethyl maleate, acrylic acid-2-ethylhexyl, acrylamide, methacrylamide, coconut oil fatty acid amides, maleimide, and the like. Such agents modify the above-mentioned polyolefins to incorporate a carbonyl group therein in concentrations of 10 to 1400 millimoles/100 g of polymer, preferably 30 to 1200 millimoles/100 g of polymer.
Examples of polyester resins (saturated polyester resins) include, among others, poly(ethylene terephthalate), poly(butylene terephthalate), poly(ethylene terephthalate/

isophthalate), poly(ethylene glycol/cyclohexanedimethanol/
terephthalate), and the like. Further the above polyesters can also be copolymerized with diols, e.g. ethylene glycol, butylene glycol, cyclohexanedimethanol, neopentylglycol, pentanediol, S etc. and dicarboxylic acids, e.g. isophthalic acid, benzo-phenonedicarboxylic acid, diphenylsulfonedicarboxylic acid, di-phenylmethanedicarboxylic acid, propylenebis(phenylcarboxylic acid), diphenyloxidedicarboxylic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid diethylsuccinic acid, etc. ~~
The composition ratio of EVOH and a counterpart resin selected from PA, polyolefin, polyester and polycarbonate which constitute the outer layer of the first embodiment of the invention or the intermediate layer of the second embodiment of the invention is 55-97 wt % : 45-3 wt %, preferably 65-85 wt % :
15-35 wt %. If the counterpart component is too small, the obtained multilayer packaging material tends to produce, upon retorting, defects in its appearance, e.g. wavy wrinkles and patterns. On the other hand if the counterpart component is too large, not only the gas barrier property will decrease but a white shade tends to remain on the multilayered packaging material stored after retort sterilization.

., , The composition of the outer layer of the first embodiment of the invention and the intermediate layer of the second embodiment of the invention may incorporate, within limits so as not to impair the purpose of the present invention, other polymers or additives, e.g. anti-oxidants, ultraviolet absorbers, plasticizers, antistatic agents, lubricants, colorants and fillers. Examples of the other polymers include polystyrene, polyvinyl chloride, acrylics, polyvinylidene chloride, polyurethanes, and the like. Among the above, copolymers of an ethylenically unsaturated momomer (e g. olefins such as ethylene and ~--propylene~ containing 2 to 25 mol~ of at least one component selected from vinyl acetate, acrylic acid esters and methacrylic acid esters or its saponified product can give, upon blending with EVOH, a flexibility to the obtained multilayered structure. Examples of the additives other than the polymers are as follows:
Stabilizers: calcium acetate, calcium stearate, hydrotal-cites, metal salts of ethylenediaminetetraacetic acid and 2~ the like.
Antioxidants: 2,5-di-t-butylhydroquinone, 2,6-di-t-butyl-p-cresol, 4,4'-thiobis-(6-t-butylphenol), 2,2'-methylene-bis(4-methyl-6-t-butylphenol), octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate, 4,4'-thiobis-(6-t-butyl-phenol) and the like.
Ultraviolet absorbers: ethyl-2-cyano-3,3-diphenylacrylate, 2-(2'-hydroxy-5'-methylphenyl~enzotriazole, 2-(2'-hydroxy-3~-t-butyl-5~-methylphenyl)-5-chlorobenzotriazole~ 2-hydroxY-1 335~
~ 4-methoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzo-- phenone, 2-hydroxy-4-octoxybenzophenone and the like.
Plasticizers,: dimethyl phthalate, diethyl phthalate, dioctyl phthalate, wax, liquid paraffin, phosphoric acid esters and the like.
Antistatic agents: pentaerythrit monostearate, sorbitan monopalmitate, oleic acid sulphate, polyethylene oxide, Carbowax* and the like.

Lubricants: ethylenebisstearoamide, butyl stearate and the like-Colorants: carbon black, phthalocyanine, quinacridone, indoline, azo-dyes, titanium oxide, Indian red and the like.
Fillers: glass fiber, asbestos, mica, ballastonite, sericite, talc, glass flake, calcium silicate, aluminum silicate, calcium carbonate and the like.
Particularly, powder selected from mica, sericite, talc and glass flake in an amount of 5 to 60 wt~ blended with 95 to 40 wt~ of the above blended resin composition is prefer-ably used for the outermost layer or the intermediate layer, paricularly for the outermost layer, since it will increase the gas barrier property. This modification is principally applicable to containers, e.g. cups and trays.

As the blending method to obtain the compositions of 2S the ~esenLinvention there is employed a methsd which comprises melt-extruding through a monoaxial or biaxial screw extruder (same directlon or different directions), an intensive mix-*Trade mark ~ er, a continuous intensive mixer or the like, and thereafter pelletizing the extruded blend under cooling.
In the multilayered packaging material of the present invention, the above composition comprising EVOH and a resin selected from the group consisting of PA, polyolefin, poly-ester and polycarbonate bearsthe role of a barrier material, the thickness of which directly affects the barrier perfor-mance. The thickness of the composition layer is selected from a range of from 5 to 250 ~ , generally from 8 to 100 1 0 ,u '~ ~
3 Hereinbelow, resinq to be used for the outer layer of the multilayered packaging material of the second embodiment will be described. Whereas the packaging material of the first embodiment sometimes causes blocking with the neighborlng same material when being retorted, the packaging material of the second embo~;m~t is free from such problems and hence is p~;clllArly usable in practice. Since the moisture permeability of the outer layer influences the appearance and the gas barrier property after retorting of the multilayered packaging material of the invention, in ~ particular those having an outer film layer, the resin used therefor must be selected carefully. While in the case where the multilayered packaging material is subiected to a sterilization treatment at 100C or below, i.e. so-called boiling sterilization, a resin having not so high thermal resistance may be used; for treatments at temperatures exceeding 100 C, particularly for retort sterilization - 1 3354`~4 ~ conducted at a temperature of from 105 to 13S-C, thermal resistance should also be taken into consideration. It has been found that in the second embodiment better results are obtained in terms of appearance a`nd gas barrier property after retorting, and so forth, the higher the moisture permeability of the outer layer. To evaluate moisture permeability, it is convenient to employ a method shown in JIS-Z-0208, which comprises mounting a specimen film onto a cup containing a moisture absorbent, fixing it to seal the cup, and thereafter allowing the cup to stand in a ~-constant-temperature-and-moisture oven conditioned at 40~C
and 90~ RH, followed by measurement of the rate of weight increase. The moisture permeability of an outer layer measured according to this method is preferably at least 40 g/m2-day, more preferabl~ at least 100 g/m2-day, most prefer-ably at least 200 g/m2 day. If the moisture permeability is less than 40 g/m2-day, the gas barrier property will restore only slowly during storage after retort sterilization.
In the present invention resins preferably used for the outer layer of the second embodim~t are polyamides, poly-esters and polycarbonates, among which PA is most preferred.
As examples of the PA mention may be made of the afore-described various PA's used for the outer layer of the firstfm~ nt or for the intermediate layer of the second ~m~;mPnt, among which preferred are nylon-6, nylon-6,6, nylon-6/6,6, and the ; like. The moisture permeabilities of the resins per thick-- ness of 10 ~ are from 900 to 1100 g/mZ-day for unoriented ~ polymers and about 390 g/m2-day for biaxially oriented polymers. The thic~ness therefore is 275 J~ or below, preferably 110 ~ or below, most preferably from 15 to 40 ~
for unoriented nylons. Biaxially oriented nylons are used with a thic~ness of 97 ~ or below, preferably 39 ~ or below, most preferably from 10 to 20 ~ . Polycarbonates, which have moisture permeabilities of from 120 to 150 g/m2-day per 10 ~ , can also be used for the outer layer and are preferably used in a thickness of from 10 to 38 ~ .
Polyester resins can also be used for the outer layer of the second embodiment. In particular, drawn films of polyethylene terephthalate resin are, having a moisture permeability of 60 g/m2-day, used in a thickness of not more than 15 ~ .
Other resins suitable for use in the outer layer in the second ~m ~ ;m~nt and their moisture permeabilities (in parentheses) are: polyetherether ketones (t43), polysulfones (490), polyethersulfones (5~0), polyetherimides (218), polyimide (208) and polyarylate (510). On the other hand, polyvinyl chloride and polystyrene are, though having high moisture permeabilities which are suited for the multilayered pac~aging material of the present invention, low in thermal resistance, thereby beingsuitable only for such limited uses as are subjected to a low-temperature sterilization.
Polypropylene has a low moisture permeability (14 to 35 g/m2 day per 10 ~ ) and can generally not be used for this purpose. Polyethylene is also low in moisture -~8-permeability and in thermal resistance, thereby being not suited for the invention.
The moisture permeability of a resin used for the outer layer is determined depending on the type of laminate as S follows: When an outer layer can be peeled off as a single-layer film, to measure its moisture permeability, from a laminate obtained by dry lamination, then the permeability thus measured will work as that of the outer layer. Adhe-sives in a laminate obtained by dry lamination have little effect on moisture permeability and are hence not taken into consideration. For a multilayered structure already laminated (a laminate or a coextruded film), the moisture permeability of a single-layer film made of the resin consti-tuting the outer layer can be used as that of the outer layer of the structure. In the case where the outer layer consists of two or more layers, the moisture permeability of the entire outer layer consisting of such number of layers can be obtained by the usual method from the moisture permeabilities of the single-layer films each made of the respective resins constituting the layers. This handling of moisture permeability can also apply in the case of the inner layer described next.
It is important that a hydrophobic thermoplastic resin layer having a low moisture permeability be used for the inner layer of the multilayered structure of the first and second embodimen~s. In particular, in the second embodiment it is important that the moisture permeability of the inner layer be lower than that of the outer layer. And depending on the purpose, further superior packaging materials can be obtained by properly selecting resins to be used for the inner layer in terms of moisture permeability, thermal resistance, heat sealability, transparency and the like.
The lower the moisture permeability of the inner layer, the higher the gas barrier property of the obtained multilayered structure will generally be. This is believed to be attributable to the fact that the relative humidity of the intermediate layer becomes lower, as the moisture permeability of the inner layeris lowered. The mois-ture permeability as defined hereinbefore of the inner layer is preferably not more than 20 g/m2-day, more preferably not more than 10 g/m2-day. For example polypropylene of 50 ~
thickness (moisture permeability 7 g/m2 day) will give a preferred result. Polypropylene is also satisfactory from the viewpoints of thermal resistance, heat sealability and transparency. While polypropylene is thus suitable for the inner layer for many end-uses, other thermoplastic resins Z0 may also be used. Examples of such resins are polyolefins other than polypropylene, polyamides, polyesters, polysty-rene, polyvinyl chloride, acrylics, polyvinylidene chloride, polyacetals, polycarbonates and the like. These resins are used sin~ly or in a laminate of more than two. In the se-cond Fmk~;m~nt, the moisture permeability of the inner layercan be made lower than that of the outer layer by either selecting a resin suited therefor or by adjusting the thickness 1 33~424 ~ ratio, etc. of the inner layer to the outer layer.
Before-mentioned additives , e.g. antioxidants, colorants and fillers,may also be incorporated in the resins used for the inner layer of the first and second ~m~;m~n~
and for the outer layer of the second embodime~.

~ The multilayered packaging materials of the first and second embodiments of the invention can be produced by the following various laminating processes: co-extrusion with or without an interlayer adhesive resin, dry lamination, sandwich lamination, extrusion lamination, co-extrusion lamination and the like. As the adhesive resin, there is used a resin comprising a polyolefin, e.g. polypropylene, polyethylene, a copolymer of ethylene with a monomer copolymerizable therewith (vinyl acetate, acrylic acid esters or the like), or the like, modified by the addition of maleic anhydride or the like.
Next, the lamination process particularly employed in the second embodiment is explained. In the co-extrusion process, when PA is used for the outer layer, sometimes an adhesive resin layer is not required between the intermediate layer, which fact is advantageous from the viewpoint of operatability. In the case where an adhesive resin layer is provided, it is preferred that the total moisture permeability of the outer layer and the adhesive Z resin layer be as high as possible, particularly at least 40 g/m2-day. For dry lamination, the process generally employed comprises bonding, with an adhesive, three or more layers of films of the outer layer, the intermediate layer and the inner layer. Commercial f`ilms can be used for the Z5 outer layer. Examples of preferred films include unoriented nylon films (CN) and biaxially oriented nylon films (ON), monoaxially oriented polyethylene terephthalate film (PET), polycarbonate films and the like. Among them, biaxially oriented films, particularly biaxially oriented nylon films can -22a-enhance the effect of the invention, and are hence most preferred. For the inner layer, besides nylon films (CN or ON), the following are preferably used,unoriented polypropylene film (CCP), biaxially oriented polypropylene film (OPP), polyethylene film, polyvinylidene film and the like, among which unoriented polypropylene film is most preferably used for the inner layer in the case where retortability and heat sealability are important. Good results can also be obtained by a method which comprises laminating the intermediate layer and the inner layer by coextrusion, and then laminating thereon by dry lamination ON, CN or the like films. ~~
The mulitlayered packaging materials of the first and the second embodiments exhibit their performance best when used as a packaging film, particularly one to be used for boil lS sterilization or retort sterilization. As uses for packaging films mention may be made of lids, pouches, vacuum packages, skin packs, deep-drawn packages, rocket packages and the like.
Lids are best used in a method which comprises tightly sealing, by heatsealing, the lid to a container principally comprising polypropylene laminated thereon with a gas-barrier material.
The lids of the present invention have a high food-keeping performance and high transparency with no yellowish shade, thereby enhancing the commercial value of the container, and further have the advantage that they can be opened while watching the contents. Pouches are used in various forms, e.g.

- 1 33542~
3-side sealing, 4-side sealing, pillows, gazettes and standing pouches, and can also be used as "bag-in-boxn. The multilayered packaging materials of the first and the second embodiments of the invention also exhibit superior performances when used as cup-shape or tray-shape containers. In this case polypropylene, high-density polyethylene, heat-resistant polyesters or the like is used for the inner layer, in a thickness of from 200 to 1200 ~, which is larger than in the case of packaging films. To form such containers employed are methods such as one which comprises co-extrusion laminating the outer layer nylon and the intermediate layer composition onto a thicker sheet of the inner layer resin, and one which comprises laminating a laminate of nylon film and the composition film tobtained by dry lamination or co-extrusion) onto a sheet of the inner layer resin by dry lamination, sandwich-laminating or the like, followed by deep drawing using a vacuum air-pressure thermoforming machine.
Containers utilizing the multilayered packaging materials of the first and the second embodiments in the forms of lids, pouches, trays and the like can be subjected to known hot-water heat treatments, e.g. retort sterilization or boil sterilization. For retort sterilization, various processes are available, for example, recovery process, substitution process, vapor process, showering process and spraying process ~,....

The packaging materials of the present invention tend to become whitish and opaque immediately after retort steri-lization. For example, a lid or pouch utili~ing the pack-aging film of the first or second ~m ~ im~nt becomes, when retorted at 120-C for 30 minutes, whitish and opaque just after the retorting. ~owever, the thus whitened container will become transparent in an hour if it is dewatered in a centrifuge and then dried in a drier to remove water adher-ing to its surface in the same manner as for conventional containers for retorting, and the OTR will also reach an equilibrium value in 12 hours. In order to make transparent ~-and restore the OTR value more surely, an accelerated drying condition is employed. For this purpose, a dry heating (generally in the air) is preferred, and preferred drying conditions are those that satisfy the following formula:

- - x + 43 ~ y ~ -x + 115 wherein x represents drying temperature (-C) and is selected from a range of 30 to 100-C, and y represents drying time (min) and is selected from a range 0.5 to 85 min. An exam-ple of the drying conditions is Z5 to 65 minutes, preferably 30 to 60 minutes, at 50-C; or 5 to 35 minutes, preferably 5 to 30 minutes at 80-C. Within limits not to impair the purpo se of the present invention, longer drying times may be adopted.
Where even such temporary opaqueness is not desired for ; the packagin~ material of the second ~m ~ ;m~nt~ it can be ~l;m;n~ted by ensuring that the m~isture pp~h;l;ty of the outer layer be 40 to 100 g/m2-day and that of the inner layer be 1 335~
-not more than 10 g/m2 day. To this end a construction comprising, for example, polyethylene terephthalate (about 12 ~) - or polycarbonate (15 to 30 ~) for the outer layer, and polypropylene (at least 50 ~) for the inner layer is suitable.
Then, a packaging film of this construction does not become whitened and opaque under normal retorting conditions (120C, 30 minutes). However, the OTR of the film of this construction tends to restore slower than in the aforementioned case where a nylon film is used for the outer layer. To accelerate restoration, a more strengthened drying condition, for example for 60 minutes at 80C, is preferred.
The multilayered packaging material of the present invention is useful principally for transparent packaging films, and, when used as a lid or a pouch for retorting, shows an excellent transparency as well as a high oxygen gas barrier property which is unparalIeled by conventional packaging materials for retorting. That is, while conventional PVDC packaging films have OTR's of 1.3 cc/m2 day atm which provide a storing capability of 4 months at longest, the transparent packaging films of the present invention readily give OTR's of from 0.2 to 0.8 cc/m2 day atm which are required for storing capability of longer than one year. This is of great benefit to retort packaging fields for food and medical supplies.
The present invention can also apply to transparent, semitransparent or untransparent retortable ~ -26-~~ containers of cup or tray shapes. In such fields there has been used EVOH, the gas barrier property of which however is known to decrease by the action of moisture invading thereinto upon retorting. To prevent the decrease, use of drying agents has been proposed. However, application of the multilayered packaging material of the present invention can well exhibit the high gas barrier property inherent to EVOH, without using a drying agent.
The above-described multilayered packaging materials of the present invention are used for food packaging as follows: It is filled with a food, and, as required, the inside is deaerated or the air inside is replaced by an inert gas, e.g. nitrogen or carbon dioxide by a known method. Then the package is tight-sealed by heatsealing or the like, and lS then subjected to a sterilization by boiling or retorting.

Foods to be packed in the multilayered packaging materials of the invention are pre-cooked foods, foods to be used as they are, or foods that are partially cooked and require only warming up before they are consumed. Examples of such foods are as follows: cooked curry, cooked hash, stewed beef, borsch, meat sauce, braised pork with sweet vinegared sauce, sukiyaki, saute and chop-suey, boiled meat & potato, Japanese hotchpotch, boiled asparagus, sweet corn, mushroom, cream-boiled tuna, soups, e.g. consomme, potage, miso-soup, pork &
vegetable soup and "Kenchin" soup, boiled rice, rice and red beans boiled, boiled-in-iron-pot rice with subsidiaries 1 335~24 (nKamameshin), roast rice, pilaf, rice-gruel, spaghetti, cooked buckwheat, vermicelli, Japanese noodles, Chinese noodles, noodles, seasonings, e.g. ones for Kamameshi and for Chinese noodles, boiled red beans, thick bean-meal soup with sugar and rice cake ("Zenzai"), boiled peas with honey and bean-jam (~Anmitsun), quenelles, hamburgers, beef steaks, roast pork, pork saute, corned beef, ham, sausage, grilled fishes, roast meat, roast fowls, roast chicken, smoked fishes, bacon, boiled fish paste, pudding, jelly, sweet jelly of beans ("Yokan") and various pet foods.
The multilayered containers of the present invention are also superior for containers or fruit, e.g. oranges, peaches, pineapples, cherries and olives; condiments, e.g. soybean sauce, sauce, vinegar, sweet sake, dressings, mayonaise, catsups, edible oil, miso and lard; bean curd; jam; butter;
margarine; fruit juices; vegetable juices; beer; cola;
lemonade; sake; distilled spirits; fruit wines; wines; whisky and brandy. Further packaging materials of the present invention can be used to contain medicines, e.g. Ringer's solution, agricultural chemicals, cosmetics, washing agents or organic liquid chemicals, e.g. benzene, toluene, xylene, acetone, methylethyl ketone, normal hexane, kerosene, petroleum benzine, thinner, grease, etc.

Other features of the invention will become apparent in the course of the following descriptions of exemplary embodiments which are given for illustration of the invention and are not intended to be limiting thereof. Hereinbelow the first embodiment of the invention is supported by Examples l-a through 18-a, and the second embodiment of the invention by Examples l through 12.

EXAMPLES
Example 1 and Comparative Examples 1 and 2 80 parts of pellets of a resin having an ethylene con-tent of 28 mol~, a saponification degree of 99.8~ and a melt index (190 C, 2160 g) of 1.2 g/10 min as EVOH and 20 parts of a PA-6/12 copolymer [weight ratio of caprolactam unit to lauryl lactam unit: 80/20, melting point: 196 C and relative viscosity: 2.5~ were dry blended and the blend was then melt-extruded through a same direction twin-screw extruder (die temperature: 230 C) to give blend pellets. After being dried, the blend pellets thus obtained were extruded through an extruder equipped with a screw of full-flight type having a diameter of 40 mm and with a coat hanger die (temperature:
230 C) of 500 mm wide into a transparent film of 50 ~ thick consisting of the composition.
Next, dry lamination was conducted with the thus obtained film of the composition as an intermediate layer, a commercial biaxially oriented nylon-6 film ~Embrem ON (trade mark)~ made by Unitica Ltd.; thickness: lS ~ and moisture permeability: 260 g/m2 day) as an outer layer and a commer-cial unoriented polypropylene film (Tohcello CP (trade mark) made by Tokyo Cellophane Ltd.; thickness: 50 ~ and moisture permeability: 7 g/m2 day} as an inner layer to obtain a transparent 3-layer film. Takelac A-385 (trade mark) (made by Takeda Chemical Industries) was used as the adhesive for the dry lamination with Takenate A-50 (trade mark) (made by Takeda Chemical Industries) as a curing agent. After the lamination, the film was left to stand for 3 days at 40C.
The film as a lid material was thermally bonded using a heat sealer, with the unoriented polypropylene layer facing inward, onto a cup-shape container made of polypropylene and filled with water. The cup was then subjected to a retort treatment using a retorting device (RCS-40RTGN, a bench high temperature and high pressure cooking sterilizing tester made by Hisaka Works) at 120C for 30 minutes.
Just after the retort treatment, the film of the lid looked whitish. Then it was dried at 80C for 5 minutes, and it became transparent again and had a good appearance with no wavy patterns.
Starting after the drying, the outside and inside of the film utilized for the lid were conditioned to 65~ RH and 100~ RH
respectively, at 20C, and the film was measured for the oxygen gas transmission rate (OTR) using OXTRAN*-10/50A (made by Mocon Co . ) .
The OTR was 1.1 cc/m2 day atm just after the drying and then rapidly decreased to 0.3 cc/m2 day atm 1.1 after 12 hours, which value proves a high oxygen gas barrier property. This oxygen gas *Trade mark v~

;
barrier property value shows that the stopper material of the present invention exhibits by far superior performance as compared with the OTR of a lid material for retort container utilizing a polyvinylidene chloride resin with a thickness of 50 ~ (Comparative Example 1) of 1.3 cc/m2 day atm, or with the OTR of a lid material of a multilayered film utilizing 2 layers of a high-barrier type polyvinylidene chloride film {SARAN-UB
(trade mark) made by Asahi Chemical Industry, thickness: 25 ~}
(Comparative Example 2) of 0.8 cc/m2 day atm after retorting.
Further the same cup as made in Example 1 was filled with cooked curry and the cup with the contents was subject to retort sterilization in the same manner as in Example 1.
Examples 2 throuqh 7 Example 1 was repeated with the exception that a thicker biaxially oriented nylon film for the outer layer (Examples 2 and 3), compositions shown in Examples 2 to 6 in Table 1 instead of the composition of EVOH and PA in Example 1, and an unoriented nylon film (Example 4) and a polyethylene terephthalate film (Example 7) were used instead of the biaxially oriented nylon film used in Example 1, to obtain various laminates.
The laminates thus obtained were subjected to retort treatments. Results of OTR measurements and evaluations of their appearances are summarized in Table 1. These Examples of the present invention all show good transparency and exhibit high oxygen gas barrier properties.

~` Comparative Examples 3 through 5 - Example 1 was repeated except that conventional EVOH films instead of the composition film of Example 1 to obtain laminated films were used, fgllowed by retort trea~ ~ there-of. The results are shown as Comparative Examples 3 and 4 - in Table 1. Though they showed OTR's of from 0.3 to 0.4 cc/m2-day-atm, proving their high gas barrier properties, their appearances were not suited for commercial use, with wrinkles and wavy patterns over all the surfaces.
10Example 1 was again repeated except that a biaxially oriented polypropylene film (moisture permeability: 7 g/mZ-day; Comparative Example 5) was used for the outer layer, instead of the biaxially oriented nylon film, to obtain a laminate film, followed by retort treatment of the film.
- Though the film was transparent, it showed a high OTR, and was hence not suited for barrier-lids.

.

` 20 .

Table 1 Lids for Retortin,e and Their Evaluation (Retortin~ Condition: 120C, 30 min.) Intermediate Layer Composition of Intermediate Layer (thickness in ~1) Outer Moisture Inner Moisture EVOH '1 '2 PA EVOH/PA Layer'4 Permea- Layer'4 Permea- OTR'6 Appearance ratio 3 (Il) bility'5 (~) bility'Sduring storage Example I Composition (50) A D (80/20) ON (15) [260] CPP (50) [ 7] 0.3good Example 2 " (50) B D (90/10) ON (25) [156] CPP (50) [ 7] 0.2good Example 3 " (50) A E (80/20) ON (37) [105] CPP (50) [ 7] 0.4good Example 4 " (50) A E (80/20) ON (30) [300] CPP (50) [ 7] 0.4good Example 5 " (50) B D (65/35) ON (15) [260] CPP (50) [ 7] 0.7good Example 6 " (50) C D (70/30) ON (15) [260] CPP (50) [ 7] 0.5good Example 7 " (50) A D (80/20) PET (12) [ 50] CPP (50) [ 7] 1.0good -- ~p Comp. Ex. IPVDC (50) - - - ON (15) [260] CPP (50) [ 7] 1.3haze Comp. Ex. 2 SARAN-UB (50) - - - ON (15) [2603 CPP (50) [ 7] 0.8whitened Comp. Ex. 3 EVOH (50) A ON (15) [260] CPP (50) [ 7] 0.4wrinkle, wavy pattern Comp. Ex. 4 EVOH (50) B ON (15) [260] CPP (50) [ 7] 0.3wrinkle, wavy pattern Comp. Ex. 5 Composition (50) A D (80/20) OPP (20) [ 7] CPP (50) [ 7] 40transparent Comp. Ex. 6 " (50) A D (50/50) ON (15) [260] CPP (50) [ 7] 1.5whitened a little Notes: 1 335424 *1 A: ethylene content: 28 mol%, melt index: 1.2 g/10 min B: ethylene content: 33 mol%, melt index: 1.3 g/10 min C: ethylene content: 38 mol%, melt index: 1.3 g/10 min 2 D: PA-6/12, content of PA-12 unit: 20 wt%, relative viscosity: 2.5 E: PA-6/12, content of PA-6 unit: 46 wt%, relative viscosity: 2.6 '3 weight ratio 4 ON: biaxially drawn nylon film, PET: biaxially drawn polyethylene terephthalate film, CN: undrawn nylon film, OPP: biaxially drawn polypropylene film, CPP: undrawn polypropylene film '5 g/m2 day (40C, 90% RH) 6 cc 20~/m2 day- atm (after 12 hours) -33a-~` 1 335424 Example ~
The same multilayered films as used in Examples t through 7 were heatsealed into ~ouch-shapes,which were then filled with water and heatsealed at the mouths. The pouches were retorted in the same retorting oven as in Example 1 at 120C for 30 minutes. After the retorting, the surfaces of the pouches were whitish.
The pouches were then left standing in a hot-air circu-lating oven at aooc for 15 minutes. They became completely transparent and had good appearances with no wavy patterns or the li'~e.
Example ~
Example 1 was repeated except that for the outer layer a polycarbonate film {Panlite Film (trade mark), made by Teijin Ltd.; thic~ness: 20 ~ and moisture permeability:
195 g/m2 : day~ was used instead of nylon film bo obtain a 3-layer film. The thus obtained film was utilized as a stopper, and the stopper was retorted, in the same manner as in Example 1. The film after the retorting had a good appearance and showed an OTR after 12 hours of 0.7 cc/mZ-day-atm, proving its high gas barrier property.
Example 10 Dry lamination was conducted in the same manner as in Example 1 with the composition film used in Example 1 as the intermediate layer, a commercial unoriented nylon film (thickness: 450 ~ , moisture permeability: 300 g/m2 day) for the outer layer and a polypropylene sheet (thic~ness: 450 1 33542~
~ , moisture permeability: 0.78 g/m2-day) for the inner layer, to obtain a 3-layer laminated sheet. The laminate sheet thus obtained was formed into a square tray-shape container of 140 mm long, 83 mm wide and 19 mm high using a vacuum air-pressure thermoforming machine (made by Asano Laboratories). The thickness construction of the container was, from the outside, nylon (20 ~ , moisture permeability: 480 g/m2-day), the composition (33 ~ ) and polypropylene (2~6 ~ , moisture permeability: 1.2 g/m2-day). After replacement of the inside air with ni~rogen, the tray was filled with 5 ml of water and heatsealed with the lid obtained in Example 1.
Thereafter, the tray was retorted at 120-C for 30 minutes.
The tray was then taken out of the retorting oven and dried at 80-C for 15 minutes, followed by storage for 6 ; 15 months at 20-C, 65~ RH. The oxygen gas concentration in the container measured after the storage was 0.4%, a value sufficiently low to protect various foods from degradation due to oxygen.
Example 11 A co-extruded multilayered film consisting of 4 layers was prepared using feed block type co-extrusion equip-ment equipped with 4 extruders and a T die. The film con-struction was, from the outside, polyamide-6 (Novamid 10Z0 (trade mark) made by Mitsubishi Chemical Industries; thick-ness: 20 ~ }, the blend composition used in Example 1 (thick-ness: 50 ~ ), adhesive resin (Modic P-300F (trade mark) made by Mitsubishi Petrochemical Co., thickness 20 ~ } and -3~-polypropylene {Noblen MA-6 (trade mark) made by Mitsubishi Petrochemical Co., thickness: 60 ~ ~. The moisture permeabi-lity of the outer lat~er, as estimated from that of a single-layer film having the same thickness, is 450 g/m2-day. The moisture permeabilit~ of the inner layer as estimated from that measured on a 2-layer film consisting of polypropylene (60 ~ ) and the adhesive resin (20 ~ ) is 4.6 g/m2-day. The multilayered film was utili7ed as a lid in the same manner as in Example 1 and the lid was retorted at 120-C for 30 minutes, followed by hot-air drying at 80-C for S minutes.
The lid film had good transparency and had no wavy patterns. The OTR's measured 5 hours and 1 day after the retorting were 0.9 cc/m~-day-atm and 0.4 cc/m2-day-atm respectively.
Example 12 A 4-layer co-extruded multilayered sheet was prepared using the same co-extrusion equipment equipped with 4 e~trud-ers and a T die as in Example 11. The sheet construction was, from the outside, polyamide-6 ~Novamid 1020 (trade mark) made by Mitsubish- Chemical Industries, thickness: 54 ~ ), the blend composition used in Example 1 (thicXness: 135 ~ ), adhesive resin {Admer QF-500 (trade mark), thickness: 27 ~ ~
and polypropylene ~Mitsubishi Noblen X-1B (trade mark) made by Mitsubishi Petrochemical Co., thickness: 1350 ~ }. The obtained sheet was formed into a cup-shaped container with a round bottom having a radius of 33 mm and a circular top having a radius of 37 mm using a vacuum air-pressure thermo-.

forming machine (made by Asano Laboratories). The construc-tion of the cup was, from the outside, polyamide-6 (average thickness: 20 ~ ), the blend composition (50 ~ ), adhesive resin (tO ~ ) and polypropylene (500 ~ ). The moisture permeabilities of the outer and inner layers were 450 g/m2-day and 0.7 g/m2-day respectively. After replacement of inside air withnitrogen gas, the cup was filled with 5 ml of water and heatsealed with the lid shown in Example 1.
Then the cup was retorted at 120C for 30 minutes, removed from the retorting oven and hot-air dried at 80C for 15 minutes, followed by storage for 1 year at 20C, 65~ R~.
The oxygen gas concentration after the storage was 0.35~, which is sufficiently low to protect various foods from oxygen degradation.

1 33542~
Example l-a and Com~arative Examples l-a and 2-a 80 Parts of pellets of a resin having an ethylene content of 28 mol~, a saponification degree of 99.8~ and a melt index (190C, 2160 g) of 1.2 g/10 min as EVOH and 20 parts of a PA-6/12 copolymer [weight ratio of caprolactam unit to lauryl lactam unit: 80/20, melting point: 196C and relative viscosity: 2.5]
were dry bl-ended and the blend was then melt-extruded through a same direction twin-screw extruder (die temperature: 230C) to give blend pellets. After being dried, the blend pellets thus obtained were extruded through an extruder equipped with a full-flight type screw having a diameter of 40 mm and with a coat hanger die (temperature: 230C) of 500 mm wide into a transparent film of 50 ~ thick consisting of the composition.
Next, dry lamination was conducted with the thus obtained film of the composition as an outer layer and a commercial unoriented polypropylene film {Tohcello CP (trade mark);
thickness: 50 ~ and moisture permeability: 7 g/m2 day} as an inner layer to obtain a transparent 2-layer film. Takelac A-385 (trade mark) (made by Takeda Chemical Industries) was used as the adhesive for the dry lamination with Takenate A-50 (trade mark) (made by Takeda Chemical Industries) as a curing agent. After - the lamination, the film was left standing for 3 days at 40C.
The film as a lid material was thermally bonded using a heat sealer, with the unoriented polypropylene layer facing inward, onto a cup-shaped container made of polypropylene. The cup was .

then subjected to a retort treatment using a retorting device (RCS-40RTGN, a bench high temperature and high pressure cooking sterilizing tester made by Hisaka Works) at 120C for 30 minutes.
Just after the retort treatment, the film of the lid looked whitish. Then it was dried at 80C for 5 minutes, and it became transparent again and had a good appearance with no wavy pattern.
Starting just after the drying, the outside and the inside of the film utilized for the lid were conditioned to 65~ RH and 100~ RH, respectively, at 20C, and the film was measured for the oxygen gas transmission rate (OTR) using OXTRAN-10/50A (made by Mocon Co.) The OTR was 1.1 cc/m2 day atm just after the drying and then rapidly decreased to 0.3 cc/m2 day atm 1.1 after 4 hours, which value proves a high oxygen gas barrier property. This oxygen gas barrier property value shows that the lid material of the present invention exhibits by far superior performance as compared with the OTR of a lid material for retort container utilizing a polyvinylidene chloride resin with a thickness of 50 (Comparative Example 1-a) of 1.3 cc/m2 day atm, or with the OTR
of a lid material of a multilayered film utilizing-2 layers of a high-barrier type polyvinylidene chloride film {SARAN-UB (trade mark) made by Asahi Chemical Industry, thickness: 25 ~} (Compar-ative Example 2-a) of 0.8 cc/m2 day atm after retorting. The same cup as made in Example 1-a was filled with cooked curry and `~- rice and the cup with the contents was subjected to retort sterilization in the same manner as in Example l-a.
Examples 2-a through 6-a Examples l-a was repeated except that the outer layer compositions shown in the columns for Examples 2-a to 6-a in Table 2 were used to obtain laminate films, followed by retort treatment thereof. The OTR's measured and evaluation results of the appearances of the films are shown in Table 2. The films of these Examples of the present invention all show high transparency and high oxygen gas barrier properties.
Comparative Example 3-a Example l-a was repeated except that an EVOH film was used instead of the composition film for the outer layer to-obtain a laminate film, followed by retort treatment thereof. The surface of the film melted and the film was not suitable for practical use.

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, ~ Example 7-a The same multilayered films as used in Examples 1-a through 6-a were heatsealed into pouch-shapes, which were then filled with water and heatsealed at the mouths. The pouches were retorted in the same retorting oven as in Example l-a at 120C for 30 minutes. After the retorting, the surfaces of the pouches were whitish.
The pouches were then left standing in a hot-air circu-lating oven at ~0C for 10 minutes. They became completely transparent and had good appearances with no wavy patterns ~~
or the like.
~ Example 8-a Dry lamination was conducted in the same manner as in Example 1-a with the composition film used in Example 1-a as lS the outer layer and a polypropylene sheet (thickness: 450 - ~ , moisture permeability: 0.78 g/mZ-day) for the inner lay-er, to obtain a 2-layer laminated sheet. The laminate sheet thus obtained was formed into a square tray-shape container :
of 140 mm long, 83 mm wide and 19 mm high using a vacuum air-pressure thermoforming machine (made by Asar.o Labqratorles) The thickness construction of the container was, from theoutside, the composition (33 ~ ) and polypropylene (296 ~ , moisture permeability: 1.2 g/mZ-day). After replacement of the inside air by nitrogen, the tray was filled with 5 ml of ! 25 water and heats~alsd with the lid obtained in Example l-a.
Thereafter, the tray was retorted at 120-C for 30 minutes.
The tray was then removed from the ret~rting oven and y~

dried at 80C for 10 minutes, followed by storage for 6 months at 20C, 65% RH. The oxygen gas concentration in the container measured after the storage was 0.37~, a value sufficiently low to protect various foods from degradation due to oxygen.
Example 9-a A co-extruded multilayered film consisting of 3 layers was prepared using feed block type co-extrusion equip-ment equipped with 3 extruders and a T die. The film con-struction was, frcm the outside,the blend composition used in Example 1-a (thickness: 50 ~ ), adhesive resin ~Modic P-300F
(trade mark) made by Mitsubishi Petrochemical Co., thickness 20 ~ ) and polypropylene {Noblen MA-6 (trade mark) made by Mitsubishi Petrochemical Co., thickness: 60 ~ ~. The mois-ture permeability of the inner layer as estimated from thatmeasured on a 2-layer film consisting of polypropylene t60 ~ ) and the adhesive resin (20 ~ ) is 4.6 g/m2-day. The multilayered film was utilized as a lid in the same manner as in Example 1-a and the lid was retorted at 120C for 30 minutes, followed by hot-air drying at 80~C for 5 minutes.
The lid film had good transparency and had no wavy patterns. The OTR's measured 5 hours after the retorting were 0.4 cc/m2-day atm.
Example 10-~

A 3-layer co-extruded multilayered sheet was prepared using the same co-extrusion equipment equipped with 3 ext_ud-ers and a T die as in Example 9-a. The sheet construction was, from the outside, the blend composi~onused in Example l-a (thickness: 135 ~ ), adhesive resin ~Admer QF-500 ttrade mark), thickness: 27 ~ ~ and polypropylene ~Mitsubishi Noblen X-1B (trade mark) made by Mitsubishi Petrochemical Co., thickness: 1350 ~ }. The obtained sheet was formed into a cup-shaped container with a round bottom having a radius Oc 33 mm and a circular top ha~ing a radius of 37 mm using a vacuum air-pressure thermoforming machine (made by Asano Laboratories). The construction of the cup was, from the outside, the blend o~s;tion (50 ~ ), ~dhesive resin (10 ~ ) and polypropylene (S00 ~ ). The moisture permeability of the inner layer was 0.7 g/m2 day. AfterreplA~mPnt of the inside air with nitrogen gas, the cup was filled with 5 ml of water and heatsealed with the lid shown in Example l-a.
Then the cup was retorted at 120C for 30 minutes, removed from the retorting o~en and hot-air dried at 80C for 15 minutes, followed by storage for 1 year at-20-C, 65% RH.
The oxygen gas concentration after the storage was 0.32%, which value corresponds to a weight of oxygen gas permeated of 1.19 cc-STP, which in turn corr~sp~ to an ~ unt of 4 ppm of oxygen absorbed by an aqueous food whenthe container is filled with food. The concentration is sufficiently low to protect various foods from oxygen degradation.
Examples 11-a through 16-a A kneaded blend composition (Composition-a) was prepar-ed from 70 parts of the same blend composition as used in Example 1-a and 30 parts of mica (mascobite mica, flake dia-~It -- .
meter: 30 ~ , aspect ratio: 30) using a same direction twin-screw extruder-kneader. This operation was repeated using sericite (flake diameter: 13 ~ , aspect ratio: 20), talc (fla~e diameter: 10 ~ , aspect ratio: ~) and glass flake (flake diameter: 50 ~ , aspect ratio: 25) to obtain Composi-tions-b, -c and -d, respectively.
- Separately, two pelletized blends were prepared; i.e.
Composition-e from 85 parts of a resin pellet, as EVOH, hav-ing an ethyiene content of 33 mol%, a saponification degree t0 of 99.8~ and a melt index (190~C, 2160 g) of 1.3 g/10 min -~ and 15 parts of a polyethylene terephthalate/isophthalate having an isophthalic acid component in the acid component of 6 mol~ and an intrinsic viscosity of 0.84 dl/g), (flake diameter: 10 ~ ), and Composition-f from 85 parts of the above EVO~ and 15 parts of a polycarbonate ~Upiron E-2000 (trade mark) made by Mitsubishi Gas Chemical).
' Then cup-shaped containers were prepared in the same manner as in Example 10-a except that the above 6 composi-tions (C~m~s;tion-a through C~s;tion-f) were used instead of the blend composition used in Example 10-a. The cups were re-torted, then stored for 1 year, and thereafter measured for the oxygen concentrations therein (Examples ll-a through 16-a). The concentration values measured were, in alphabetical sequence of the compositions, 0.25 %, 0.29 %, 0.30 %, 0.26 ~, 0.33 % and 0.35 ~. All of the values are sufficiently low to protect various foods from oxygen degradation.

; -45-Example 17-a The same multilayered film as used in Example l-a was, with an unoriented polypropylene layer as the inner layer, heatsealed into a square pouch of 10 cm x 10 cm. The pouch was filled with 40 g of stewed beef, then, after deaerating the inside, the pouch was tight sealed by heatsealing. The food package thus obtained was retorted in a retorting oven at 120C for 15 minutes. The package was then removed from the retorting oven, water adhered thereto was removed in a centrifuge, and dried in a drier at 80C for 18 minutes.
The contents of the food package could be seen through the film. The contents showed, after storage for 6 months at room temperature, no change in color shade or taste.
Example 18-a lS Dry lamination similar to that in Example l-a was conducted to obtain a transparent 3-layer film having an outer layer of the composition used in Example l-a, an intermediate layer of a commercial PVDC film {Kflex (trade mark) made by Kureha Chemical Industries: thickness: 15 ~} and an inner layer of a commercial unoriented polypropylene film {Tohcello CP (trade mark), thickness: 50 ~}. The thus obtained film was superior particularly in food keeping properties when used as retortable pouches or lids.

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Claims (24)

1. A gas-barrier multilayered packaging material which comprises an outer layer of a composition comprising 55 to 97%
by weight of an ethylene-vinyl alcohol copolymer having an ethylene content of 20 to 50 mol% and 45 to 3% by weight of a resin selected from the group consisting of polyamide resin, polyolefin resin, polyester resin and polycarbonate resin and an inner layer of a hydrophobic thermoplastic resin having a low moisture permeability.

2. A multilayered packaging material as defined in Claim 1, wherein said moisture permeability (measured at 40°C, 90% RH) of the inner layer is not higher than 20 g/m2.day.

3. A multilayered packaging material as defined in Claim 1, wherein said composition of the outer layer comprises an ethylene-vinyl alcohol copolymer and a polyamide resin.

4. A multilayered packaging material as defined in Claim 3, wherein said polyamide resin is caprolactam-lauryl lactam copolymer.

5. A multilayered packaging material as defined in Claim 1, wherein said hydrophobic thermoplastic resin having a low moisture permeability is polypropylene resin.

6. A multilayered packaging film for boil sterilization or retort sterilization comprising the multilayered packaging material according to Claim 1.

7. A container lid for boil sterilization or retort sterilization comprising the multilayered packaging material according to Claim 1.

8. A pouch for boil sterilization or retort sterilization comprising the multilayered packaging material according to Claim 1.

9. A cup-shaped or tray-shaped container for boil sterilization or retort sterilization comprising the multilayered packaging material according to Claim 1.

10. A food package obtained by filling a food in the multi-layered packaging material according to Claim 1 and then boil or retort sterilizing the package containing the food.

11. A process for producing a food package, which comprises filling a food in the multilayerd packaging material according to Claim 1, retorting the package containing the food, and then drying it under the condition which satisfies the following formula:

wherein x represents drying temperature (°C) and is selected from a range of 30 to 100°C, and y represents drying time (min) and is selected from a range of 0.5 to 85 minutes.

12. A gas-barrier multilayered packaging material comprising an outer layer which comprises a resin layer having a moisture permeability (measured at 40°C, 90 % RH) of at least 40 g/m2.day, an intermediate layer which comprises a composition comprising 55 to 97 % by weight of an ethylene-vinyl alcohol copolymer resin having an ethylene content of 20 to 50 mol % and 45 to 3 % by weight of a resin selected from the group consisting of polyamide resin, poly-olefin resin, polyester resin and polycarbonate resin, and an inner layer which comprises a hydrophobic thermoplastic resin layer having a moisture permeability lower than that of the outer layer.

13. A multilayered packaging material as defined in Claim 12, wherein said moisture permeability of the inner layer is not higher than 20 g/m2.day.

14. A multilayered packaging material as defined in Claim 12, wherein said resin utilized for the outer layer comprises as a principal component at least one member selected from the group consisting of polyamide, polyester and polycarbonate.

15. A multilayered packaging material as defined in Claim 12, wherein said resin utilized for the outer layer comprises as a principal component at least one member selected from the group consisting of polycapramide and poly(hexamethylene diammonium adipate) and caprolactam/hexamethylene diammonium adipate) copolymer.

16. A multilayered packaging material as defined in Claim 12, wherein said composition of the intermediate layer comprises an ethylene-vinyl alcohol copolymer and a polyamide.

17. A multilayered packaging material as defined in Claim 16, wherein said polyamide resin is caprolactam-lauryl lactam copolymer.

18. A multilayered packaging material as defined in Claim 12, wherein said resin utilized for the inner layer is polypropylene resin.

19. A multilayered packaging film for boil sterilization or retort sterilization comprising the multilayered packaging material according to Claim 12.

20. A lid for containers for boil sterilization or retort sterilization comprising the multilayered packaging material according to Claim 12.

21. A pouch for boil sterilization or retort sterilization comprising the multilayered packaging material according to Claim 12.

22. A cup-shaped or tray-shaped container for boil sterilization or retort sterilization comprising the multilayered packaging material according to Claim 12.

23. A food package obtained by filling a food in the multilayered packaging material according to Claim 12 and then boil or retort sterilizing the package containing the food.

24. A process for producing a food package, which comprises filling a food in the multilayered packaging material according to Claim 12, retorting the package containing the food, and then drying it under the condition which satisfies the following formula:

-x + 43 ? y ? -x + 115 wherein x represents drying temperature (°C) and is selected from a range of 30 to 100°C, and y represents drying time (min) and is selected from a range of 0.5 to 85 min.