JP2007216457A - Laminated film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated film which keeps oxygen-gas shielding properties even after being subjected to heat sterilization under high humidity, can stand long-term storage after sterilization, and is excellent in contents reservation properties. <P>SOLUTION: The laminated film has an ethylene-vinyl alcohol copolymer saponification product as an oxygen shielding layer and a polyamide resin in which meta-xylilenediamine units occupy at least 90 mole percent of the diamine units. Water vapor-barrier layers the water vapor permeability measured by a JIS K 7129 A method of which is 30(g/m<SP>2</SP>24 h) are formed on both sides of the oxygen shielding layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a laminated film having good oxygen gas barrier properties. More specifically, the present invention minimizes a decrease in oxygen gas barrier properties due to temperature and humidity during heat sterilization or subsequent storage environment as a packaging material for foods and beverages, and as a result, the contents are oxidized. The present invention relates to a laminated film characterized in that it can be reduced and held in a good state.

  Conventionally, in plastic packaging materials such as foods and beverages, an oxygen gas barrier layer is generally provided for the preservation of contents. As a resin having excellent oxygen gas barrier properties, a saponified ethylene vinyl alcohol copolymer (hereinafter referred to as EVOH resin), a vinylidene chloride copolymer or the like is used, and a film or a sheet in which a polyolefin resin or the like is laminated on both sides thereof is used. I came.

  As research on the alteration of contents progresses, it has become clear that the contents are altered by oxygen gas remaining inside the packaging material, and various means for improving the contents have been studied. In general, EVOH resin is often used for the purpose of an oxygen gas barrier, but it is known that EVOH resin is affected by humidity and the shielding property of oxygen gas is lowered. This tendency is more pronounced with EVOH resin with a low ethylene copolymerization ratio that has higher oxygen gas shielding properties in the dry state, and for contents that require high oxygen shielding ability after being subjected to hot water sterilization. However, there was a problem that sufficient oxygen shielding was not obtained.

  As a method for solving this drawback, various methods for adding a compound that absorbs oxygen into a film or sheet have been tried. For example, Patent Document 1 proposes an oxygen scavenger for food packaging containers that is passive when dried and becomes oxygen-philic when wet. Patent Document 2 discloses an oxygen scavenger composition obtained by stretching a thermoplastic resin film in which an oxygen scavenger composition is dispersed in a film as a film oxygen scavenger for preventing the content from being spoiled, altered or deteriorated. Containing microporous films have been proposed.

Further, Patent Document 3 discloses a sheet formed from a thermoplastic resin in which an oxygen absorbent composed of iron powder and a metal halide is dispersedly supported as a sheet or packaging container with a small decrease in oxygen absorption rate, and for packaging. Containers have been proposed. In Patent Document 4, as a plastic multilayer container excellent in oxygen permeation resistance under conditions where moisture and heat act, a resin composition in which an oxygen scavenger is blended with a gas barrier thermoplastic resin is used as an intermediate layer. A container has been proposed in which layers of moisture-resistant thermoplastic resin are provided on both sides. In Patent Document 5, as a multilayer molded container excellent in appearance characteristics in which thickness unevenness is eliminated and color unevenness is not formed on the inner surface, a layer made of an ethylene vinyl alcohol copolymer is provided between an inner layer and an outer layer made of polypropylene resin. A packaging container having a layer made of a polypropylene resin containing an iron-based oxygen scavenger has been proposed.

Further, Patent Document 6 has a three-layer structure of an oxygen gas barrier layer, a deoxidizing layer, and a breathable layer as a multilayer structure capable of actively and efficiently absorbing oxygen without performing a special treatment such as a heat treatment. Laminates have been proposed. In Patent Document 7, as a multilayer plastic container that is excellent in oxygen barrier properties and oxygen absorption, adsorbed to the inner wall of the flavor, and prevented from shifting to the inner wall of the color such as pigment, and capable of high-temperature sterilization, A multilayer plastic container composed of a laminate composed of a layer composed of a thermoplastic resin composed of carbonate ester repeating units, an olefin resin layer, a resin composition layer in which an oxygen absorbent is incorporated into an oxygen gas barrier resin, and an olefin resin layer. Proposed.

Each of these oxygen-absorbing materials has characteristics regarding oxygen-absorbing ability, but each of them has not only an oxygen-shielding property exceeding EVOH resin alone, but, for example, is required as a general packaging material for iron-based oxygen absorbers. There is a problem that transparency cannot be obtained. For oxygen scavengers that function when wet, the packaging material is kept dry until the moisture absorption over time occurs during filling and heat sterilization of the contents and long-term storage. There is a problem that it is not easy to handle such as it is necessary to keep it.
Under these circumstances, after packaging the contents, packaging materials with good preservability are still being provided, with minimal influence of reduced oxygen shielding due to temperature and humidity received from the environment during hot water sterilization and long-term storage. Not.

JP-A-57-146651 JP-A-2-72851 Japanese Patent Laid-Open No. 4-90848 Japanese Patent Publication No. 4-60826 JP-A-7-309323 JP-A-8-72941 JP-A-9-239909

  The present invention provides a laminated film and a sheet excellent in storage stability of contents that can hardly withstand long-term storage after sterilization even when heat sterilization under high humidity is performed. It was made for the purpose.

The inventor
(1) A laminated film having a saponified ethylene vinyl alcohol copolymer and a polyamide resin in which 90 mol% or more of diamine units are metaxylylenediamine units as an oxygen shielding layer, and JIS is provided on both sides of the oxygen shielding layer. A laminated film characterized by forming a water vapor barrier layer having a water vapor permeability of 30 (g / m ² · 24 hr) or less measured by the K7129 A method;
(2) The laminated film according to (1), wherein the polyamide resin in which 90 mol% or more of the diamine units are metaxylylenediamine units is a mixed resin with an amorphous polyamide resin,
It is.

In general, EVOH resin widely used as a packaging material for processed foods causes a decrease in oxygen shielding ability during heat sterilization with heated water or steam, which increases the amount of oxygen permeation from the outside into the package. As is known, according to the laminated film of the present invention, this oxygen shielding property can be obtained by combining a polyamide resin in which 90 mol% or more of these diamine units resistant to wet heat are metaxylylenediamine units as an oxygen shielding layer. It is characterized by compensating for the decline. Further, an oxygen shielding layer comprising an EVOH resin and a polyamide resin in which 90 mol% or more of diamine units are metaxylylenediamine units has a water vapor permeability of 30 (g / m ² · 24 hr) measured by JIS K7129 A method. By having a structure in which the water vapor barrier layer is laminated on both sides of the following, it is possible to suppress the infiltration of water into the oxygen shielding layer by heated water and steam as much as possible, and good contents without causing a decrease in oxygen shielding ability It has been found that the storability is obtained.

  As the EVOH resin used in the present invention, one having an ethylene copolymerization ratio of 24 to 44 mol% can be preferably used. When the ethylene copolymerization ratio is less than 24 mol%, the processability into a container shape is inferior, or the oxygen shielding property is easily lowered due to the influence of heated water or steam. On the other hand, if the ethylene copolymerization ratio exceeds 44 mol%, the oxygen shielding ability in a dry state is not sufficient, and the contents are liable to suffer from rancidity.

  The polyamide resin in which 90 mol% or more of the diamine units used in the present invention are metaxylylenediamine units may be used alone, or 90 mol% or more of the diamine units are metaxylylenediamine units. Polyamide resin may be used as a mixed resin of amorphous polyamide resin.

Examples of the polyamide resin in which 90 mol% or more of diamine units are metaxylylenediamine units include polyamides obtained by polycondensation reaction of metaxylylenediamine and adipic acid. Such a polycondensate of metaxylylenediamine and adipic acid is also called nylon MXD6. There is no particular limitation on the method for producing the polycondensate of metaxylylenediamine and adipic acid, in addition to metaxylylenediamine and adipic acid, various derivatives such as metaxylylenediamine hydrochloride, adipic acid halide, Various derivatives such as esters can also be produced as starting materials. A polyamide resin in which 90% or more of the diamine units are metaxylylenediamine units can be copolymerized with a diamine or dicarboxylic acid other than metaxylylenediamine and adipic acid, and further an amino acid having an amino group and a carboxyl group or Lactam can also be copolymerized.

When the metaxylylenediamine unit of the polyamide resin forming the oxygen shielding layer is less than 90 mol% of the diamine unit, the oxygen shielding property is insufficient and a large amount of oxygen gas enters. In some cases, the contents may become rancid.

  An amorphous polyamide resin can be mixed with a polyamide resin in which 90 mol% or more of the diamine units forming the oxygen shielding layer are metaxylylenediamine units. By mixing an amorphous polyamide resin with a polyamide resin in which 90% or more of the diamine units are metaxylylenediamine units, it is possible to improve extrusion processability and laminate sheet or film molding processability. Amorphous polyamide resin is also referred to as amorphous nylon or transparent nylon, and unlike linear aliphatic nylon such as nylon 6 and nylon 66, polymer crystallization hardly occurs or crystallization rate. Is a very small special nylon. As an amorphous polyamide resin used in the present invention, for example, a polycondensate of terephthalic acid and trimethylhexamethylenediamine, a co-polymerization of 2,2-bis (p-aminocyclohexyl) propane, adipic acid and azelaic acid Condensates, copolycondensates of bis (3-methyl-4-aminocyclohexyl) methane with isophthalic acid and ω-aminododecanoic acid, copolycondensates of diphenylmethane diisocyanate with a mixture of adipic acid, azelaic acid and isophthalic acid And copolycondensates of terephthalic acid and isophthalic acid with hexamethylenediamine.

  The amorphous polyamide resin used in the present invention preferably has a melt flow rate of 8 g / 10 min or less at a test condition based on ASTM D1238, that is, a temperature of 230 ° C. and a load of 2.16 kgf, and is 6 g / 10 min or less. It is more preferable that When the melt flow rate of the amorphous polyamide resin exceeds 8 g / 10 min, the viscosity of the resin as the oxygen shielding layer becomes too low when the laminated sheet or film is formed, so that a laminated film having a stable thickness is obtained. May become difficult.

  The amorphous polyamide resin preferably has a glass transition point of 80 to 150 ° C. By using an amorphous polyamide resin having a glass transition point of 80 to 150 ° C., when forming a laminated film into a container, the occurrence of unevenness in elongation and thickness due to crystallization of the resin is prevented, and a wide range of thermoforming conditions This makes it possible to form a good container. For example, even when the sheet surface temperature in thermoforming is high or low, or when the heating time is long or short, uneven elongation and uneven thickness are less likely to occur, and the thermoforming processability of the laminated film can be improved.

  In the laminated film of the present invention, the mixing ratio of the polyamide resin in which 90 mol% or more of the diamine units are metaxylylenediamine units and the amorphous polyamide is preferably 30:70 to 80:20 (weight ratio). 40:60 to 80:20 (weight ratio) is more preferable. When the mixing ratio of the amorphous polyamide is less than 20% by weight, a sufficient improvement effect may not be obtained when the laminated film and the sheet shape are formed. If the mixing ratio of the amorphous polyamide exceeds 70% by weight, there will be a problem in the processability of the laminated film and sheet, or the properties of the polyamide resin in which 90% or more of the diamine units are metaxylylenediamine units will be impaired. There is a risk that By setting the mixing ratio of the polyamide resin in which 90 mol% or more of the diamine units are metaxylylenediamine units and the amorphous polyamide to 30:70 to 80:20 (weight ratio), the gas barrier property of the polyamide resin, In particular, it is possible to obtain a laminated film and a sheet having good thermoformability while maintaining high oxygen barrier properties when exposed to high temperature and high humidity conditions.

In the laminated film of the present invention, the water vapor barrier layer having a water vapor permeability measured by the JIS K7129 A method of 30 (g / m ² · 24 hr) or less satisfies this standard, and the contents are added to food hygiene. There is no particular limitation as long as it does not cause problems. Examples of materials that can be suitably used include various polyolefin resins such as high-density polyethylene resin, low-density polyethylene resin, and polypropylene resin, polyvinylidene chloride, fluorine resin, and polyethylene terephthalate resin. These resins may be added with a known modifier for the purpose of improving the water vapor shielding property. For example, hydrogenated terpene resins can be suitably formulated for polypropylene resins and polyethylene resins. Further, if necessary, it may be stretched or copolymerized with other components, or a pigment or the like may be formulated for the purpose of enhancing the concealability of the contents.

In the laminated film of the present invention, as an example of the constitution, a water vapor barrier layer / ethylene vinyl alcohol copolymer saponification layer / a polyamide resin layer / a water vapor barrier layer in which 90 mol% or more of diamine units are metaxylylenediamine units, Things can be considered. The method for laminating each layer is not particularly limited, and for example, it can be produced using a known laminating technique such as a coextrusion method, a coextrusion laminating method, an extrusion laminating method, or a dry laminating method.

An adhesive or an adhesive resin may be appropriately used between the water vapor barrier layer and each oxygen shielding layer. Further, depending on the resin used for the water vapor barrier layer, an adhesive or an adhesive resin may not be used.

  In the laminated film of the present invention, the thicknesses of the two layers constituting the oxygen shielding layer are not particularly specified, and can be appropriately designed according to the antioxidative properties of the food of the contents. In order to obtain the properties, the total thickness of the two oxygen shielding layers is desirably 5 μm or more.

Example 1; first layer: high density polyethylene resin (hereinafter referred to as HDPE) (water vapor permeability (hereinafter referred to as WVTR value) measured by JIS K7129 A method is 5 (g / m ² · 24 hr) Second layer: carboxylic acid-modified polyethylene resin (hereinafter referred to as AD), third layer: EVOH resin, fourth layer: polyamide in which 90 mol% or more of diamine units are metaxylylenediamine units Resin (hereinafter referred to as PA), 5th layer: AD, 5th layer: HDPE, and the thickness of each layer was set to HDPE / AD / EVOH / PA / AD / HDPE (30 μm / 5 μm / 5 μm / 15 μm / 5 μm / 40 μm, 100 μm in total).

A 20 cm square sample was prepared by forming a laminated film having the above-described structure by a coextrusion method. This was boiled at 90 ° C. × 30 min, and immediately after that, the oxygen shielding property was measured before and after the boil treatment in accordance with ASTM D3985 method for comparison. In addition, the oxygen permeation amount after 10 days and 30 days was also measured.
As a result of the evaluation by the above method, the oxygen shielding property was not deteriorated immediately after the boil treatment, and the oxygen permeation amount did not change even after 10 days and 30 days.

<Example 2>: The layer structure of Example 1 except that the fifth layer is low-density polyethylene (WVTR value = 15 (g / m ² · 24 hr). The resin name is hereinafter referred to as LDPE). Same as above. The thickness of each layer was HDPE / AD / EVOH / PA / AD / LDPE (30 μm / 5 μm / 5 μm / 15 μm / 5 μm / 40 μm, total 100 μm).

A 20 cm square sample was prepared by forming a laminated film having the above-described structure by a coextrusion method. This was boiled at 90 ° C. × 30 min, and immediately after that, the oxygen shielding property was measured before and after the boil treatment in accordance with ASTM D3985 method for comparison. In addition, the oxygen permeation amount after 10 days and 30 days was also measured.
As a result of the evaluation by the above method, the oxygen shielding property was not deteriorated immediately after the boil treatment, and the oxygen permeation amount did not change even after 10 days and 30 days.

<Example 3>: The layers of Example 1 except that the first layer and the fifth layer were polypropylene (WVTR value = 9 (g / m ² · 24 hr). The resin name is hereinafter referred to as PP). The configuration was the same. The thickness of each layer was PP / AD / EVOH / PA / AD / PP (30 μm / 5 μm / 5 μm / 15 μm / 5 μm / 40 μm, total 100 μm).

A 20 cm square sample was prepared by forming a laminated film having the above-described structure by a coextrusion method. This was boiled at 90 ° C. × 30 min, and immediately after that, the oxygen shielding property was measured before and after the boil treatment in accordance with ASTM D3985 method for comparison. In addition, the oxygen permeation amount after 10 days and 30 days was also measured.
As a result of the evaluation by the above method, the oxygen shielding property was not deteriorated immediately after the boil treatment, and the oxygen permeation amount did not change even after 10 days and 30 days.

<Example 4>; Example 1 except that the first layer and the fifth layer were biaxially oriented polypropylene (WVTR value = 5 (g / m ² · 24 hr). The resin name is hereinafter referred to as OPP). The same layer structure as that of No. 1 was used. The thickness of each layer was OPP / AD / EVOH / PA / AD / OPP (30 μm / 5 μm / 5 μm / 15 μm / 5 μm / 40 μm, total 100 μm).

A 20 cm square sample was prepared by forming a laminated film having the above-described structure by a coextrusion method. This was boiled at 90 ° C. × 30 min, and immediately after that, the oxygen shielding property was measured before and after the boil treatment in accordance with ASTM D3985 method for comparison. In addition, the oxygen permeation amount after 10 days and 30 days was also measured.
As a result of the evaluation by the above method, the oxygen shielding property was not deteriorated immediately after the boil treatment, and the oxygen permeation amount did not change even after 10 days and 30 days.

<Example 5>: Example 1 except that the first layer and the fifth layer were polyethylene terephthalate (WVTR value = 20 (g / m ² · 24 hr). The resin name is hereinafter referred to as PET). Same as layer structure. The thickness of each layer was set to PET / AD / EVOH / PA / AD / PET (30 μm / 5 μm / 5 μm / 15 μm / 5 μm / 40 μm, total 100 μm).

A 20 cm square sample was prepared by forming a laminated film having the above-described structure by a coextrusion method. This was boiled at 90 ° C. × 30 min, and immediately after that, the oxygen shielding property was measured before and after the boil treatment in accordance with ASTM D3985 method for comparison. In addition, the oxygen permeation amount after 10 days and 30 days was also measured.
As a result of the evaluation by the above method, the oxygen shielding property was not deteriorated immediately after the boil treatment, and the oxygen permeation amount did not change even after 10 days and 30 days.

<Comparative Example 1>: The layer of Example 1 except that the first layer and the fifth layer were polystyrene (WVTR value = 110 (g / m ² · 24 hr). The resin name is hereinafter referred to as PS). The configuration was the same. The thickness of each layer was PS / AD / EVOH / PA / AD / PS (30 μm / 5 μm / 5 μm / 15 μm / 5 μm / 40 μm, total 100 μm).

A 20 cm square sample was prepared by forming a laminated film having the above-described structure by a coextrusion method. This was boiled at 90 ° C. × 30 min, and immediately after that, the oxygen shielding property was measured before and after the boil treatment in accordance with ASTM D3985 method for comparison. In addition, the oxygen permeation amount after 10 days and 30 days was also measured.
As a result of the evaluation by the above method, the oxygen shielding performance decreased immediately after the boil treatment, and the oxygen permeation amount was larger even after 10 days and 30 days.

<Comparative Example 2>: Same as the layer structure of Example 1 except that the PA resin of the fourth layer was eliminated. The thickness of each layer was HDPE / AD / EVOH / AD / HDPE (30 μm / 5 μm / 20 μm / 5 μm / 40 μm, total 100 μm).

A 20 cm square sample was prepared by forming a laminated film having the above-described structure by a coextrusion method. This was boiled at 90 ° C. × 30 min, and immediately after that, the oxygen shielding property was measured before and after the boil treatment in accordance with ASTM D3985 method for comparison. In addition, the oxygen permeation amount after 10 days and 30 days was also measured.
As a result of the evaluation by the above method, the oxygen shielding performance decreased immediately after the boil treatment, and the oxygen permeation amount was larger even after 10 days and 30 days.

<Comparative Example 3>: The same as the layer structure of Example 1 except that the first layer is polyvinyl chloride (WVTR value = 40 (g / m ² · 24 hr). The resin name is hereinafter referred to as PVC). It was. However, the thickness of each layer was set as follows. PVC / AD / EVOH / PA / AD / PP (30 μm / 5 μm / 5 μm / 15 μm / 5 μm / 40 μm, total 100 μm).

A 20 cm square sample was prepared by forming a laminated film having the above-described structure by a coextrusion method. This was boiled at 90 ° C. × 30 min, and immediately after that, the oxygen shielding property was measured before and after the boil treatment in accordance with ASTM D3985 method for comparison. In addition, the oxygen permeation amount after 10 days and 30 days was also measured.
As a result of the evaluation by the above method, the oxygen shielding performance decreased immediately after the boil treatment, and the oxygen permeation amount was larger even after 10 days and 30 days.

<Comparative Example 4>: Same as the layer configuration of Example 1 except that the third EVOH layer was PA. The thickness of each layer was HDPE / AD / PA / PA / AD / HDPE (30 μm / 5 μm / 5 μm / 15 μm / 5 μm / 40 μm, total 100 μm).

A 20 cm square sample was prepared by forming a laminated film having the above-described structure by a coextrusion method. This was boiled at 90 ° C. × 30 min, and immediately after that, the oxygen shielding property was measured before and after the boil treatment in accordance with ASTM D3985 method for comparison. In addition, the oxygen permeation amount after 10 days and 30 days was also measured.
As a result of the evaluation by the above method, the oxygen shielding performance decreased immediately after the boil treatment, and the oxygen permeation amount was larger even after 10 days and 30 days.

  The laminated film of the present invention can be suitably used mainly as a packaging material for food parts or industrial parts that do not like oxidation. As a production method, a known coextrusion method, dry lamination method, extrusion lamination method, or the like can be used.

Claims (2)

A saponified ethylene-vinyl alcohol copolymer as an oxygen shielding layer and a laminated film having a polyamide resin in which 90 mol% or more of diamine units are metaxylylenediamine units, JIS K7129 A method on both sides of this oxygen shielding layer A laminated film, characterized in that a water vapor barrier layer having a water vapor permeability measured by the method of 30 (g / m ² · 24 hr) or less is formed.   The laminated film according to claim 1, wherein the polyamide resin in which 90 mol% or more of the diamine units are metaxylylenediamine units comprises a mixed resin with an amorphous polyamide resin.