JPH0627198B2 - Package - Google Patents

Description

TECHNICAL FIELD The present invention relates to a package for frozen storage, which is obtained by molding a crosslinked product of a mixture of two kinds of ethylene-based copolymers and has excellent cryogenic resistance and heat resistance.

2. Description of the Related Art At present, containers (for example, bottles and bags) made of glass, polyethylene, polyethylene terephthalate, polypropylene and polyvinyl chloride are widely used as medical packages. In addition, a medical bag formed by molding a laminate having low-density polyethylene as the inner and outer layers and an ethylene-vinyl acetate copolymer, an ethylene-propylene elastomer or an ethylene-butene-1 elastomer as the intermediate layer has been proposed. (Japanese Patent Laid-Open No. 54-2895), however, in recent years, transfusion of a necessary component (for example, a component of only red blood cells) is also medically preferable, and the blood or the necessary component of blood is increased due to the problem of blood supply. It is partly done to preserve the blood for a certain period and use the stocked blood or necessary components when necessary or in case of emergency.

However, long-term storage of blood is difficult at room temperature, and low-temperature storage is required, and liquefied carbonic acid (naturalization temperature -90 ° C) and liquid nitrogen (naturalization temperature -196 ° C) are used to store blood containers in these liquids. Means are taken. When using the above-mentioned various containers as blood containers used for these, glass is easy to break, and polyvinyl chloride and polypropylene are not resistant at -90 ° C and crack even with a minute impact. And it cannot be used. Further, in the case of low density or high density polyethylene and ethylene-vinyl acetate copolymer, even at a very low temperature such as in liquid nitrogen, even a minute impact causes cracking and cannot be used. In addition, although a stainless steel container is used as a frozen blood container, this container has good low temperature characteristics,
Blood is easy to leak because it is difficult to seal. Further, it has a defect that liquid nitrogen flows into the container during frozen storage, and has a defect that the state of blood is difficult to understand during use because it is not transparent.

Recently, not only storage of blood, but also storage of various organs medically, storage in liquid nitrogen, which is simple in the field of research, especially in the field of biochemistry and trial sample storage in the field of electronic materials, etc.
It is stored, and in order to preserve the freshness of raw materials such as fish, it is desired to store and store it in dry ice or at a low temperature below it, but it is inexpensive and has excellent flexibility. Is currently nonexistent.

Problems to be Solved by the Invention From the above, the present invention does not have these drawbacks (problems), that is, it has not only cryogenic resistance and good transparency, but also heavy metals and eluates. The test and acute toxicity test are also fully satisfactory, and at relatively high temperature (1
The object is to obtain a package for frozen storage that can be sterilized at 80 ° C.

Means for Solving the Problems According to the present invention, these problems include (A) “at least an ethylene unit and a group consisting of a carboxylic acid group, a dicarboxylic acid group, an anhydride group thereof and a half ester group. An ethylene-based copolymer comprising an ethylenically unsaturated compound unit having at least one selected group and having an ethylene unit content of 30 to 99.5% by weight "[hereinafter," ethylene-based copolymer (A) " ]] 1-99
% By weight and (B) "at least an ethylene unit and an ethylenically unsaturated compound unit having at least one group selected from the group consisting of a hydroxyl group, an amino group and a glycidyl group, and the content of the ethylene unit is 30 to 99.5% by weight of ethylene-based copolymer "[hereinafter referred to as" ethylene-based copolymer (B) "] 99 to 1% by weight of a mixture formed by crosslinking by heat treatment after molding.
It can be solved by a frozen storage package that is 0.01 to 2.0 mm. Hereinafter, the present invention will be specifically described.

(A) ethylene-based copolymer (A) the ethylene-based copolymer (A) used in the present invention is at least an ethylene unit, and "a group consisting of a carboxylic acid group, a dicarboxylic acid group, its anhydride group and a half ester group. An ethylene-based unsaturated compound unit having at least one group selected from "[hereinafter referred to as" second component (A) "], and an ethylene-based copolymer containing 30 to 99.5% by weight of the ethylene unit. Is.

This ethylene-based copolymer (A) is a copolymer that can be obtained by copolymerizing ethylene and the following monomers that form the second component (A), and multi-component copolymers of these and other monomers. Examples thereof include those obtained by hydrolyzing and / or alcohol-modifying the acid anhydride group in the combination and the copolymer thereof.

Typical examples of the monomer constituting the second component (A) include unsaturated monocarboxylic acids having at most 25 carbon atoms such as acrylic acid, methacrylic acid and ethacrylic acid, maleimidic anhydride, tetrahydrophthalic anhydride and maleoic acid. Pimaric anhydride, 4-methylcyclohexane-4-ene-
Unsaturated dicarboxylic acid anhydrides having 4 to 50 carbon atoms such as 1,2-carboxylic acid anhydride and bicyclo (2,2,1) -hept-5-ene-2,3-dicarboxylic acid anhydride can be mentioned. .

In addition, as other monomers, unsaturated such as methyl (meth) acrylate, ethyl (meth) acrylate, hydroxymethyl (meth) acrylate and diethyl fumarate having at most 30 (preferably 10 or less) carbon atoms. Examples include carboxylic acid esters and vinyl esters having at most 30 carbon atoms such as vinyl acetate and vinyl propionate.

Of the ethylene-based copolymer (A), a copolymer of ethylene and an unsaturated dicarboxylic acid anhydride or a multi-component copolymer of these and an unsaturated dicarboxylic acid ester and / or a vinyl ester is hydrolyzed and / or By modifying with an alcohol, the dicarboxylic acid anhydride group of these copolymers can be changed to a dicarboxylic acid group or a half ester group. In the present invention, an ethylene-based copolymer obtained by replacing a part or all of unsaturated dicarboxylic acid anhydride groups of the copolymer or multicomponent copolymer with a dicarboxylic acid group or a half ester group
(A) can also be used as desired.

To carry out hydrolysis, the ethylene-based copolymer (A) is used.
80 to 80% in the presence of a catalyst (eg, a tertiary amine) in an organic solvent (eg, toluene) that dissolves the copolymer.
0.5-10 hours with water at a temperature of 110 ℃ (preferably,
It can be obtained by reacting for 2 to 6 hours, preferably 3 to 6 hours, and then neutralizing with an acid.

In order to carry out the alcohol modification, the ethylene copolymer (A) can be obtained by a solution method or a kneading method described later.

The solution method is similar to the hydrolysis method in the presence or absence of the above-mentioned catalyst in an organic solvent (the reaction is slow in the absence of the catalyst) at the reflux temperature of the alcohol used for 2 minutes to 5 hours (preferably The reaction is carried out for 2 minutes to 2 hours, preferably 15 minutes to 1 hour.

On the other hand, the kneading method is usually 0.01 to 1.0 parts by weight (preferably 0.05 to 0.5 parts by weight) of tertiary amine and dicarboxylic acid in the copolymer based on 100 parts by weight of the ethylene copolymer (A). Generally 0.1 to 3.0 times by mole (preferably,
1.0 to 2.0 times mol) of saturated alcohol above the melting point of the ethylene-based copolymer (A), but below the boiling point of the alcohol used, usually used in the field of rubber and synthetic resins, Banbury mixer, extruder It is a method of reacting while kneading for several minutes to several tens of minutes (desirably 10 minutes to 30 minutes) using a kneader such as.

The saturated alcohol used in the above modification with alcohol is a linear or branched saturated alcohol having 1 to 12 carbon atoms, and examples thereof include methyl alcohol, ethyl alcohol and primary butyl alcohol.

In both cases of hydrolysis and modification with alcohol, the conversion rate to dicarboxylic acid and the half esterification rate are both 0.5 to 100%, preferably 10.0 to 100%.

The ethylene unit in this ethylene copolymer (A) is 30 to 99.
5% by weight, preferably 30-99.0% by weight, especially 35-9
9.0 wt% is preferred. The proportion of ethylenically unsaturated compound units having a carboxylic acid group, its anhydride group and half ester group in the copolymer is 0.5 to 70% by weight as their total amount, and particularly 0.5 to 60% by weight. % Is preferred. If an ethylene-based copolymer in which the proportion of ethylenically unsaturated compound units having a carboxylic acid group, its anhydride group and half ester group in this ethylene-based copolymer (A) is less than 0.5% by weight is used When heating and crosslinking with the ethylene copolymer (B) described later,
Not only is the crosslinking incomplete, but the adhesion to the metal layer is poor. On the other hand, even if it exceeds 70% by weight, the characteristics of the present invention will be exhibited, but it is not necessary to exceed 70% by weight, which is not preferable in terms of production and economy.

When a multi-component copolymer containing the unsaturated carboxylic acid ester and / or vinyl ester is used, the total amount thereof is usually at most 70% by weight, preferably 60% by weight or less. When an ethylene-based copolymer having a copolymerization ratio of unsaturated dicarboxylic acid ester and / or vinyl ester of more than 70% by weight is used, the softening point of the copolymer becomes high, and the fluidity at a temperature of 150 ° C. or lower becomes high. Not only is it undesirable because it is impaired, it is also economically unfavorable.

(B) Ethylene copolymer (B) Further, the ethylene copolymer used in the present invention
(B) is at least an ethylene unit, "hydroxyl group,
An ethylenically unsaturated compound unit having at least one group selected from the group consisting of an amino group and a glycidyl group "(hereinafter referred to as" second component (B) "), the ethylene unit 30 to 99.5 wt% % Ethylene-based copolymer.

This ethylene-based copolymer (B) is a copolymer that can be obtained by copolymerizing ethylene with the following monomer that constitutes the second component (B), and multi-component copolymers of these and other monomers. Examples thereof include a saponified product obtained by saponifying a polymer and a copolymer of ethylene and a vinyl ester (in particular, vinyl acetate).

As the monomer constituting the second component (B), glycidyl alkyl (meth) acrylate represented by the following general formula, hydroxyalkyl (meth) acrylate (the carbon number of the alkyl group is usually 1 to 25), carbon is 3 ~ 25 α-
Alkenyl alcohol and α- with 2 to 25 carbon atoms
Amine and primary or secondary aminoalkyl (meth)
Acrylate (the carbon number of the alkyl group is usually 1 to 25) can be mentioned.

(Here, R ¹ is H or a methyl group, and R ₂ has 1 carbon atom.
~ 12 straight or branched alkyl groups. ) Typical examples of this monomer include butenetricarboxylic acid monoglycidyl ester, glycidyl methacrylate, glycidyl acrylate, glycidyl ethacrylate, itaconic acid glycidyl ester, hydroxymethyl (meth) acrylate, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate. ) Acrylate, hydroxybutyl (meth) acrylate, hydroxyhexyl (meth) acrylate, acrylic
Mention may be made of alcohols, allyl amines and aminoethyl (meth) acrylates.

Other monomers include the unsaturated carboxylic acid ester and vinyl ester.

The ethylene unit in this ethylene copolymer (B) is 30 to 99.
5% by weight, preferably 30-99.0% by weight, especially 3
5-99.0% by weight is suitable. The proportion of the ethylenically unsaturated compound unit having a hydroxyl group, an amino group and a chrysidyl group in the copolymer is 0.5 to 70% by weight for the same reason as in the case of the ethylene copolymer (A). Yes, and 0.5 to 60% by weight is particularly preferable. Furthermore, when a multi-component copolymer containing the unsaturated carboxylic acid ester and / or vinyl ester is used, the total amount thereof is generally at most 70 wt% for the same reason as in the case of the ethylene copolymer (A). %, And particularly preferably 60% by weight or less.

The ethylene-based copolymer (A) and the ethylene-based copolymer
The melt index (B) (measured according to JIS K-7210 under condition 4, hereinafter referred to as "MI") is generally 0.001.
˜1000 g / 10 min, preferably 0.05 to 500 g / 10 min, particularly preferably 0.1 to 500 g / 10 min. When these ethylene-based copolymers having an MI of less than 0.01 g / 10 min are used, it is difficult to mix these copolymers uniformly, and the moldability is not good.

Among these ethylene-based copolymers, when produced by a copolymerization method, a side chain transfer agent (for example, an organic peroxide) is usually used at a temperature of 120 to 260 ° C under a high pressure of 500 to 2500 kg / cm ² . It can be obtained by copolymerizing ethylene and the second component (A), or ethylene, the second component (B) and another component in the presence, and their production methods are well known. is there. Further, a method of producing the ethylene-based copolymer (A) by hydrolysis and / or modification with an alcohol, and the ethylene-based copolymer
Among the methods (B), the method of producing by the saponification method is also well known.

(C) Production of mixture (1) Mixing ratio In producing the mixture of the present invention, the total amount (total) of the ethylene copolymer (A) and the ethylene copolymer (B) in the obtained mixture is occupied. The mixing ratio of the ethylene-based copolymer (A) is 1 to 99% by weight [that is, the ethylene-based copolymer (B)
The mixing ratio is 99 to 1% by weight], preferably 5 to 95% by weight, and particularly preferably 10 to 99% by weight. Even if the mixing ratio of the ethylene copolymer (A) in the total amount of the ethylene copolymer (A) and the ethylene copolymer (B) is less than 1% by weight or more than 99% by weight, the mixture is a mixture. When the above-mentioned method is used for crosslinking, the crosslinking is insufficient.

(2) Mixing method To produce this mixture, the ethylene copolymer (A) and the ethylene copolymer (B) may be mixed uniformly. As a mixing method, dry blending may be performed using a mixer such as a Henschel mixer which is generally performed in the field of olefin polymers, and a method of melt kneading using a mixer such as Banbury, an extruder and a roll mill is used. can give. At this time, a more uniform mixture can be obtained by previously dry blending and melt-kneading the resulting mixture. When melt-kneading, it is necessary that the ethylene-based copolymer (A) and the ethylene-based copolymer (B) do not substantially undergo a cross-linking reaction (when cross-linked, the resulting mixture is molded and processed as described below. This is not preferable because it not only deteriorates the moldability, but also causes the target shape of the molded product and the heat resistance when the molded product is crosslinked). From this, the temperature of melt-kneading depends on the type and viscosity of the ethylene copolymer used, but it may range from room temperature (20 ℃) to 150 ℃.
Is preferable and 140 ° C or lower is preferable.

As a measure of this “substantially no crosslinking”, “residue having a diameter of 0.1 micron or more after extraction treatment in boiling toluene for 3 hours” (hereinafter referred to as “extraction residue”) is generally used.
It is preferably 15% by weight or less, preferably 10% by weight or less, and optimally 5% by weight or less.

(3) Manufacture of Thin Film To manufacture the mixture obtained as described above into a thin product, when manufacturing a film by T-die film method or inflation method, which is generally used in the field of thermoplastic resins. It can be obtained by extruding a film or sheet using a widely used extruder. At this time, if extrusion is carried out at a high temperature,
The ethylene copolymer (A) and the ethylene copolymer (B) are partly or wholly crosslinked to form a small lump of a gel-like product, whereby a uniform thin product cannot be obtained. For these reasons, the extrusion temperature is usually 250 ° C or lower. In particular, it is suitable to carry out in the same temperature range as in the case of the melt kneading.

In any of the above cases, after the thin product is manufactured, the thin product with good transparency is rapidly cooled in a water-cooling roll or a water tank in order to prevent the adhesion between the thin products or between the thin product and the take-up roll. can get. The thin material thus obtained has a thickness of 10 to 2000 microns (
2.0 mm), preferably 30 to 1000 microns, especially 50 to 500 microns.

It is necessary that the thin product thus obtained is not crosslinked. That is, the extraction residue is preferably 15% by weight or less, more preferably 10% by weight or less, especially 5% by weight, as described above.
The following are public.

(4) Heat treatment The thin product obtained as described above exhibits the same behavior as a normal thin product because the cross-linking hardly progresses.
In order to impart deep-chill resistance and heat resistance to the thin product at the same time,
It is important to heat-treat in the range of 100-400 ° C. When the heating temperature is 100 to 160 ° C, the average thickness is
30 seconds to 1 minute for 100 micron thin material, 5 to 30 seconds at 160 to 240 ° C, 0.1 to 20 seconds at 240 to 400 ° C (if the average thickness is thin, in a short time, and if it is thick, By heating (which requires a long time), a crosslinking reaction (condensation reaction) occurs in the resin, and the deep-chill resistance and heat resistance are significantly improved. However, until the cross-linking is started under heating, it is necessary to hold the thin product in some way so as not to lose its shape because the thin product melts. For example, there is a method (see FIG. 1) of pressing the heating roll surface kept at the crosslinking temperature. In this case, since the roll surface and the thin product adhere to each other, a good crosslinked product of the thin product can be obtained by, for example, applying Teflon processing to the roll surface. As the second method, as shown in FIG. 2, a film-like thin product formed by T-die film is used.
There is a method of passing the both ends through a furnace set to the crosslinking temperature while applying tension with rolls or the like. In addition, as a third method, nip rolls at both ends in a thin-walled product formed into a cylindrical shape by an inflation film forming machine,
There is a method of enclosing air, nitrogen, gas, etc., and passing it through a similar heating furnace (see FIG. 3). In addition, as the fourth method, the third method is further advanced, and as shown in FIG. 4, the film-like material is heated from the outside or the inside between the extrusion die and the take-up roll during inflation molding. This is a method of crosslinking. Most of these are methods in which heating and crosslinking are performed while maintaining the shape by applying tension (or pressure) to the extent that counteracts melt tension or shrinkage force to the thin material, and can be performed continuously. Described one. Besides this, a normal press,
It is possible to carry out the crosslinking treatment under pressure and heat using a rolling roll or the like, or to laminate it on a metallic material such as an aluminum foil and hold the shape to carry out the heating or crosslinking treatment. The heat-crosslinking treatment can be performed by a method other than this.

1 to 4, 1 is an uncrosslinked thin product (sheet or film-like product), and 2 is a thin film (sheet or film-like product) that has been heated and crosslinked. Further, 3 is a heating roll, and 4 is a nip roll. Further, 5 is a heating furnace, and 6 is a cylindrical heating furnace. Further, 7 is a heating cylinder, 8 is an inflation die, and 9 is an ordinary extruder.

Further, when transparency is not particularly required, aluminum foil can be used as the outer layer. in this case,
Since the aluminum foil has good thermal conductivity, it has not only good processability and good heat-sealing property at the time of bag-making, but also the advantage that blood can be frozen and thawed uniformly in a single hour.

When a laminate with an aluminum foil is formed into a sheet or a film-like product of the uncrosslinked thin film, there is a method of laminating at the same time as extrusion using a lamination method or the like. It is also possible to pressurize and laminate when heating and crosslinking.

Examples and Comparative Examples Hereinafter, the present invention will be described in more detail with reference to Examples.

In the examples and comparative examples, dry sterilization was performed at 180 ° C.
The blood transfusion bag was exposed to the atmosphere for 2 minutes. In wet sterilization, the deterioration and damage of the bag was examined when the bag for blood transfusion was placed in a steam autoclave at 120 ° C and 2 atm for 5 minutes.

In addition, fill the obtained blood transfusion bag with red blood cells and store at -196 ° C.
A puncture test with (liquid nitrogen) was performed and a bag crushing test was performed.

A mixture of the ethylene copolymer (A) and the ethylene copolymer (B) used in the examples and comparative examples is shown below.

[(A) Ethylene Copolymer Mixture] As a mixture of the ethylene copolymer (A) and the ethylene copolymer (B), an ethylene-acrylic acid copolymer having a MI of 300 g / 10 min (density 0.954 g / cm ³ , acrylic acid copolymerization ratio
Saponified product (saponification degree) obtained by saponifying ethylene-vinyl acetate copolymer having a vinyl acetate copolymerization ratio of 20% by weight, hereinafter referred to as "EAA") and vinyl acetate of 28% by weight.
9.5%, MI 75 g / 10 min, density 0.951 g / cm ³ , hereinafter referred to as "saponified product") [mixing ratio 5
0:50 (weight ratio), hereinafter referred to as "mixture (I)"], M.
A mixture of an ethylene-methacrylic acid copolymer having an I. of 200 g / 10 minutes (density 0.950 g / cm ³ , methacrylic acid copolymerization ratio 25% by weight) and the above saponified product [mixing ratio 50:50
(Weight ratio), hereinafter "Mixture (II)", MI is 212 g
/ 10 min ethylene-ethyl acrylate-maleic anhydride terpolymer (ethyl acrylate copolymerization ratio
30.7% by weight, maleic anhydride copolymerization ratio 1.7% by weight) and MI of 123 g / 10 min. Ethylene-methyl acrylate-hydroxymethacrylate terpolymer (copolymerization ratio of methylmethacrylate 20.7% by weight, hydroxymethacrylate Copolymerization ratio 11.7% by weight) [mixing ratio 50:50 (weight ratio), hereinafter "mixture (II
I) "] and MI is 105 g / 10 min. Ethylene-methyl methacrylate-maleic anhydride terpolymer (copolymerization ratio of methyl methacrylate 20.5% by weight,
Copolymerization ratio of maleic anhydride 3.1% by weight) and terpolymer of ethylene-methyl methacrylate-glycidyl methacrylate (copolymerization ratio of methyl methacrylate 1
8.6% by weight, copolymerization ratio of glycidyl methacrylate 1
2.7% by weight) (mixing ratio 30:70 (weight ratio), hereinafter referred to as "mixture (IV)") was used. These mixtures were produced by dry blending the respective copolymers or terpolymers for 5 minutes using a Henschel mixer.

An extruder equipped with a T-die and an inflation die (diameter: 40 mm, die width: 30) was used to prepare the mixture (I) to (IV), EAA and saponified product obtained as described above.
The film or sheet whose thickness is shown in Table 2 was formed under the condition that the cylinder temperature is shown in Table 1 using the same. The extraction residue of the obtained film was measured. In all cases, it was 0%.

Examples 1 to 8 and Comparative Examples 1 to 4 Each of the films or sheets thus obtained was manufactured by the heating, crosslinking treatment method and temperature shown in Table 2 (Examples). 1-8).

Table 2 shows the extraction residue of the obtained film-like substance. The obtained film was used as an impulse sealer (setting 260 ° C, 5
The sheet was sealed at both ends or the periphery with a heating sheet, and a blood transfusion bag having a width of 10 cm, a length of 15 cm and a thickness shown in Table 2 was prepared. The obtained bag was subjected to a wet and dry sterilization test and a puncture test at -196 ° C.
Each bag of No. 8 had neither deterioration nor deformation of the bag, nor was it broken or broken in the piercing test.

On the other hand, the heat treatment was carried out with the mixtures shown in Comparative Examples 1 to 4 in the same manner as in the Example, but the film was melted during heating (extraction residue: 0%), and a crosslinked sheet was not obtained. .

Example 9, Comparative Example 5 In the same manner as in Example 1, the outer layer of the obtained film had a thickness of 30.
Using a film laminated with micron aluminum foil,
Crosslinking and heat treatment were carried out in the same manner as in Example 1. A blood transfusion bag was prepared in the same manner as in Example 1 so that the inner surface resins were in contact with each other.

The bag obtained was subjected to a wet and dry sterilization test and a puncture test at -196 ° C, but no deterioration or breakage was observed.

On the other hand, in Comparative Example 5, an aluminum foil was laminated on the same film as in Comparative Example 1 by the same method as in Example 9, and heating and crosslinking treatment were carried out by the same method, but the resin melted and dropped during heating. The desired crosslinked sheet was not obtained.

From the results of the above Examples and Comparative Examples, the crosslinked product of the mixture of the ethylene copolymer (A) and the ethylene copolymer (B) used in the packaging bag of the present invention is a wet or dry sterilizer. Not only can it be processed, it will not be damaged even at -196 ° C (liquid nitrogen), and it can withstand the storage of blood. In addition, the manufacturing process is inexpensive because continuous production is possible. Moreover, it is clear that a product without the conventional drawbacks can be obtained.

Effects of the Invention The crosslinked product of the mixture used for the packaging material of the present invention exhibits the following effects (features) including the manufacturing process.

(1) Since it has heat resistance and water resistance, it can be sterilized at 180 ° C and steam sterilized at 120 ° C and 2 atm.

(2) Cold resistance, especially cold cryogenic resistance of -196 ° C (liquid nitrogen) is excellent, so that cryogenic storage of blood etc. is possible.

(3) Since it is highly flexible, operations such as encapsulation of liquids are easy.

(4) Since it has good heat sealability and hygiene, is lightweight, and is inexpensive, it can be used as a frozen storage package for all things such as blood and food.

[Brief description of drawings]

1 to 4 are partial enlarged cross-sectional views of the cross-linking treatment step of the package of the present invention. 1 ... Uncrosslinked thin product (film or sheet) 2 ... Crosslinked thin product (film or sheet) 3 ... Heating roll, 4 ... Nip roll 5 ... Heating furnace, 5 ... Cylindrical heating furnace 7 ... Heating cylinder, 8 ... Inflation molding die 9 ... Extruder

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Claims (1)

[Claims] 1. From (A) ethylene simple substance and an ethylenically unsaturated compound unit having at least one group selected from the group consisting of a carboxylic acid group, a dicarboxylic acid group, an anhydride group thereof and a half ester group. And an ethylene-based copolymer having an ethylene unit content of 30 to 99.5% by weight, 1 to 99% by weight and (B) at least an ethylene unit, and a group consisting of a hydroxyl group, an amino group and a glycidyl group. Crosslinked by heat treatment after molding a mixture consisting of an ethylenically unsaturated compound unit having at least one group, and an ethylene copolymer having a content of ethylene unit of 30 to 99.5% by weight is 99 to 1% by weight. A frozen storage package having a thickness of 0.01 to 2.0 mm.