JP2000079669A - Biaxially stretched multilayered film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a packing film excellent in the balance of e.g. moldability, heat shrinkability, easy sealability, gas barrier properties, moisture barrier properties and flexibility, and showing excellent heat resistance especially suitable for retort sterilization. SOLUTION: A packing film comprises at least three layers wherein an intermediate layer is held between a pair of outer layers consisting of a thermoplastic resin, and the intermediate layer consists of a polyamide resin compsn. containing an aromatic diamine copolymer and an aromatic diamine polymer and at least one outer layer consisting of a polypropylene resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially oriented multilayer film having an outer layer made of a polypropylene resin, and more particularly to heat resistance, retort sterilization characteristics, easy sealing, and the like.
Packaging film with excellent balance of moldability, heat shrinkage, gas barrier properties, water vapor barrier properties, flexibility, etc. (It does not mean particularly limiting the thickness, more generally "sheet"
(The term "film" is used for the purpose of including a thickness called "film").

[0002] The biaxially stretched multilayer film of the present invention is a casing film or pillow package for filling and packaging a liquid or semi-liquid food such as sausage, a solid food such as processed meat or ham. Film and a film for deep drawing packaging.

[0003]

2. Description of the Related Art In recent years, technological innovation in the food packaging field has been remarkable, and there is a constant demand for packaging materials that are optimal for packaging, preserving, transporting, and the like of each food. In addition, automatic packaging systems have been developed for the purpose of increasing production volume and reducing costs, and packaging materials are required to have excellent suitability for automatic packaging machines.

[0004] Processed livestock products such as sausage, processed fishery products such as fish sausage, processed agricultural products such as konjac and uiro, liquid and semi-liquid food products such as cooked foods, and solid products such as processed meat and ham In the field of casing films, pillow packaging films or sheets for filling and packaging foods and the like, and deep drawing packaging films, monolayer or multilayer films made of various synthetic resins are widely used. For example, in the field of casing films, films made of a resin composition of nylon and a polyolefin-based resin, or multilayer films in which a nylon layer and a polyolefin-based resin layer are laminated are often used.

[0005] Among these, a multilayer film in which a nylon layer and a polyethylene layer are laminated (hereinafter abbreviated as "Ny / PE film") has been widely used because it has good heat sealing properties and gas barrier properties. Have been. However, this Ny / PE film has a problem that it lacks flexibility. In addition, for the Ny / PE film, it is possible to apply a heat-sealing type heat sealing method in which a polyethylene layer is used as a sealing layer (the sealing surfaces are polyethylene layers). And polyethylene layer) cannot be applied. Therefore, the Ny / PE film could not be applied to an automatic filling and packaging machine having an envelope-attached sealing mechanism.

With respect to a polyamide resin composition which satisfies various properties as a casing film by a single layer,
Several proposals have been made. For example, Japanese Patent Application Laid-Open No.
No. 2732 discloses nylon 6 and an aromatic copolyamide comprising a polycondensate of hexamethylenediamine, terephthalic acid, and isophthalic acid (hereinafter, “nylon 6I /
6T "). However, when this casing film is manufactured by the inflation method, since the internal stress of the tubular parison at the time of inflation stretching is high, the air pressure in the stretched bubble increases, and bursting of the bubble occurs frequently to perform stable inflation stretching. It was difficult. In addition, sausage is filled into the casing film by a conventional method, and after boil cooking, cooling, wrinkles occur on the surface of the product, and the dimensions of the product are difficult to stabilize. Furthermore, this casing film has high rigidity and poor workability such as shearing and filling.

In the above polyamide resin composition,
When an aromatic polyamide composed of adipic acid and meta-xylylenediamine (hereinafter abbreviated as "nylon MXD6") is used instead of nylon 6I / 6T, the above tendency becomes more remarkable. Further, a film or sheet blow-molded using nylon MXD6 is subjected to deep drawing,
The elongation from the bottom corner of the deep drawing die to the side wall is not uniform, making deep drawing difficult.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a good balance of heat resistance, retort sterilization characteristics, easy sealability, moldability, heat shrinkage, gas barrier properties, water vapor barrier properties, flexibility, and the like. An object of the present invention is to provide a biaxially oriented multilayer film suitable for use as a packaging material.

Another object of the present invention is to provide a package formed by forming a casing with the above-mentioned biaxially stretched multilayer film and containing a fluid or semi-fluid substance.

[0010]

According to the present invention, there is provided a biaxially stretched multilayer film obtained by biaxially stretching a laminated film comprising at least three layers in which an intermediate layer is sandwiched between a pair of outer layers made of a thermoplastic resin. There is provided a biaxially stretched multilayer film in which the intermediate layer is made of a polyamide resin composition containing an aromatic diamine copolymer and an aromatic diamine polymer, and at least one outer layer is made of a polypropylene resin.

According to another aspect of the present invention, there is provided a biaxially stretched multilayer film obtained by biaxially stretching a laminated film composed of at least three layers in which an intermediate layer is sandwiched between a pair of outer layers composed of a thermoplastic resin. And a biaxially stretched multilayer film which is corona-treated is provided, wherein the outer layer of the pair of outer layers which is in contact with the processed meat food is a resin containing 90 to 80% by weight of a polypropylene resin and 10 to 20% by weight of a polyethylene resin. You.

According to still another aspect of the present invention, there is provided a biaxially stretched multilayer film obtained by biaxially stretching a laminated film composed of at least three layers having an intermediate layer sandwiched between a pair of thermoplastic resin outer layers. The intermediate layer is made of a gas barrier resin containing an aromatic polyamide (co) polymer, and at least one outer layer is made of a polypropylene resin;
An adhesive layer between the intermediate layer and the outer layer, wherein the adhesive layer has a mixing ratio by weight of the polypropylene-based resin and the polyethylene-based resin of 80/20 to 20/80; and the polypropylene-based resin and the polyethylene-based resin A biaxially stretched multilayer film comprising a mixed resin, at least one of which contains a functional group.

According to still another aspect of the present invention, there is provided a package formed by forming a casing from the biaxially stretched multilayer film and containing a fluid or semi-fluid substance.

[0014] The present invention relates to International Publication WO98 / 292.
This corresponds to the selected invention of the invention according to No. 50.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION (Polypropylene Resin) The main feature of the biaxially stretched multilayer film of the present invention is that at least one of the pair of outer layers made of a thermoplastic resin is made of a polypropylene resin.

The polypropylene resin includes a propylene homopolymer (polypropylene) or a copolymer of propylene having a propylene content of 90% by weight or more and another olefin having a carbon number of 4 or less. The resin is used alone or in the form of a mixture of a polypropylene-based resin containing 50% by weight or more, preferably 60% by weight or more of a polypropylene-based resin and another thermoplastic resin.

Preferred examples of the polypropylene resin include a propylene / ethylene copolymer and a propylene / ethylene / butene-1 copolymer, and more preferably have a resin melting point of 130 to 155 ° C, particularly 130 to 140 ° C. Things.

(Other Thermoplastic Resins) Preferred examples of other thermoplastic resins include ethylene homopolymer (polyethylene) or ethylene having an ethylene content of 75% by weight or more, more preferably 90% by weight or more, and And a polyethylene-based resin comprising a copolymer with another olefin of 8 or less. Preferred examples of the polyethylene resin include low-density polyethylene (LDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDP).
Homopolymers such as E); linear low density polyethylene (LLDPE), very low density polyethylene (VLDPE)
Such as ethylene-α-olefin copolymers (trade names “affinity” commercially available from Dow Chemical Company, copolymers obtained using a metallocene catalyst such as “Elite”,
In particular, those having a density of 0.900 g / cm ³ or more are preferable.)
Is mentioned.

Preferred examples of other thermoplastic resins other than polyethylene resins include ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), and ethylene-methyl acrylate copolymer (EMA). ), Ethylene-methacrylic acid copolymer (EMA)
A), an ethylene-acrylic acid copolymer (EAA), an ethylene copolymer containing a polar group such as an ionomer, and the like.

(Outer layer) If the propylene content in the polypropylene resin constituting the outer layer is less than 90% by weight or the polypropylene resin content in the outer layer is less than 50% by weight,
The effect of improving the heat resistance and the suitability for retort sterilization by using a polypropylene resin for the outer layer is poor.

A particularly preferred constitution of the outer layer is to use a mixture of 95 to 70% by weight, particularly 90 to 80% by weight, of the polypropylene resin and 5 to 30% by weight, especially 10 to 20% by weight of the polyethylene resin. . Thereby, when the outer layer is subjected to corona treatment, a remarkably high improvement in meat adhesion can be obtained. In particular, corona treatment is effective for processed foods such as fish sausage, which hardly adhere to meat. When the polypropylene resin exceeds 95% by weight, the effect of corona treatment tends to be insufficient. On the other hand, when the amount of the polyethylene resin is too large, the stretchability of the intermediate layer with the polyamide resin composition is slightly lowered, and the suitability for retort tends to be insufficient.

(Other Outer Layers) A pair of outer layers may be made of a polypropylene resin or a thermoplastic resin composition containing 50% by weight or more of these resins, from the viewpoint of improving suitability for sealing in an envelope type and suitability for retort sterilization. Is preferred. However, one of the pair of outer layers may be made of a thermoplastic resin other than the polypropylene resin. As the thermoplastic resin at this time, those exemplified in the section of the above (other thermoplastic resins) are preferably used.
A polyester resin such as polyethylene terephthalate is also preferably used.

It is preferable that the other outer layer constitutes an outer layer (outer surface layer) opposite to the outer layer (so-called inner surface layer) in contact with the contents composed of (semi) fluid substance or the like. In the outer layer, for example, a particulate lubricant composed of silica particles having a particle size of 10 μm or less is used in an amount of 1000 ppm or less, preferably 2 ppm or less.
It is also preferable to include the compound in a ratio of 00 to 800 ppm to improve the slipperiness of the obtained multilayer film and improve the suitability for pillow packaging.

(Intermediate Layer) The intermediate layer is an aromatic diamine for appropriately setting the gas barrier property at high temperature or in the retort, the stretchability, the falling or piercing of the package, or the strength at the time of shuttering. It is preferable to use a polyamide resin containing a copolymer and an aromatic diamine polymer.

(Aromatic Diamine) As the aromatic diamine, xylylenediamine is preferable, and particularly, metaxylylenediamine alone or metaxylylenediamine 60
A diamine mixture of at least 70% by weight, preferably at least 70% by weight, and at most 40% by weight of paraxylylenediamine, preferably at most 30% by weight, is preferably used.

(Aromatic Diamine Polymer) As the aromatic diamine polymer, the above-mentioned aromatic diamine and an aromatic or aliphatic dicarboxylic acid, preferably an aliphatic dicarboxylic acid, and more preferably 6 carbon atoms For example, a polyamide resin synthesized by a polycondensation reaction with an aliphatic dicarboxylic acid of No. 12 to 12, for example, adipic acid, sebacic acid, suberic acid, undecandioic acid, dodecandioic acid or the like is used. More specifically, homopolymers such as polymetaxylylene adipamide, polymetaxylylene sebacamide, polymetaxylylene veramide, metaxylylene / paraxylylene adipamide copolymer, metaxylylene / paraxylylenepi Examples thereof include a melamide copolymer, a meta-xylylene / para-xylylene azeramide copolymer, and a meta-xylylene / para-xylylene adipamide / sebacamide copolymer. Among these, polymethaxylylene adipamide (MXD6) is particularly preferred. These aromatic diamine polymers impart properties such as gas barrier properties to the biaxially oriented multilayer film of the present invention.

(Aromatic Diamine Copolymer) Examples of the aromatic diamine copolymer include a condensation unit (for example, metaxylylene adipamide) constituting the aromatic diamine polymer and another polyamide. , Preferably aliphatic polyamides such as nylon 6, nylon 11, nylon 1
2, a co-condensation polymer with one or more condensation units such as nylon 66, nylon 69, nylon 610, etc., and the aromatic diamine copolymer condensation unit content in the aromatic diamine copolymer is 4 to 40% by weight. % Is preferable. If it is less than 4% by weight, the oxygen gas barrier property of the product multilayer film is reduced, and if it exceeds 40% by weight, the rigidity of the obtained multilayer film becomes too large, and the moldability, heat shrinkability,
It tends to be less flexible. Preferred examples of the aromatic diamine copolymer include nylon 6/12 / MXD6, nylon 610 / MXD6, and nylon 66/610 / MX.
D6 and the like.

The aromatic diamine copolymer can facilitate the heating and stretching operation by slowing down the crystallization rate of the crystalline polyamide resin composition containing the aromatic diamine polymer as a main component. That is, the aromatic diamine copolymer contributes to improvement in stretchability, film-forming property, and high-frequency sealing property. In addition, the aromatic diamine copolymer improves the flexibility of the film or sheet, thereby improving the filling properties of sausage and the like, and further, is suitable for shearing, ring processing, film cutting, pillow packaging. Improves secondary workability such as machine suitability and deep drawability. This aromatic diamine copolymer improves the gas barrier properties of the film or sheet to some extent. For example, a blend of an aliphatic polyamide such as nylon 6 and an aromatic polyamide, instead of a copolymer, cannot balance these characteristics.

The polyamide-based resin composition constituting the intermediate layer comprises the above-mentioned aromatic diamine polymer in an amount of 50 to 99.
It is preferable that the aromatic diamine copolymer is mixed at a ratio of 1 to 50% by weight, particularly 5 to 40% by weight, and more preferably 60 to 95% by weight. If the compounding ratio of the aromatic diamine copolymer is too small, the effect of retarding the crystallization rate of the polyamide resin composition becomes small, and if too large, the film becomes too soft, and the casing film composed of the film becomes too soft. When filling sausage etc.
The film is stretched due to the filling pressure, the dimensions of the product are not constant, the shape is varied, and the dimensional stability and the shape stability are impaired.

(Other polyamides and the like) In the polyamide resin composition constituting the intermediate layer, in addition to the aromatic diamine polymer and the aromatic diamine copolymer, up to 20% by weight of an aliphatic polyamide, Optional components such as up to 20% by weight of amorphous polyamide and up to 30% by weight of polyolefin-based resins can be included in total up to 30% by weight.

As the aliphatic polyamide, for example, nylon 6, nylon 11, nylon 12, nylon 66,
Nylon 69, nylon 610, nylon 6/66, nylon 6/12 and the like can be mentioned.

The amorphous polyamide is a polyamide having an aromatic ring in a main chain and / or a side chain and having no or very poor crystallinity. Specific examples include a polycondensate of a dicarboxylic acid such as terephthalic acid or isophthalic acid with a diamine such as hexamethylene diamine, or a copolymer thereof. For example, terephthalic acid 10-5
Polyamide (nylon 6I / 6T) obtained by polycondensing a dicarboxylic acid composed of 0% by weight and 90 to 50% by weight of isophthalic acid with hexamethylenediamine is exemplified.

Examples of the polyolefin resin mixed in the intermediate layer include homopolymers of ethylene and α-olefin such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, and polypropylene; linear low-density polyethylene (LLDPE); Ultra low density polyethylene (V
LDPE) and other copolymers of ethylene and α-olefins (eg, copolymers obtained using a metallocene catalyst such as affinity); ionomer resins, polyamide-modified ionomer resins, ethylene-vinyl acetate copolymers, ethylene Ethyl acrylate copolymer, ethylene / acrylic acid copolymer, ethylene / methyl acrylate copolymer, ethylene / methyl methacrylate copolymer,
An ethylene / methacrylic acid copolymer can be used. These polyolefin resins can be used alone or in combination of two or more.

The polyolefin resin to be mixed in the polyamide resin composition is an ethylene / acrylic acid copolymer,
Ethylene-based copolymers such as ethylene-methacrylic acid copolymer and polyamide-modified ionomer resin are preferable from the viewpoint of miscibility with each polyamide component.

The polyamide-modified ionomer resin is a copolymer of ethylene and α, β-unsaturated carboxylic acid, which is prepared by adding zinc, lithium, potassium, magnesium, calcium,
A resin obtained by adding and mixing a polyamide to an ionomer ionized with a metal ion such as sodium, melt-kneading at a high temperature of 200 to 350 ° C, and modifying. As the polyamide used here, for example,
Nylon 6, nylon 66, nylon 6/66, nylon 6/10, nylon 6/12, nylon 11, nylon 12, and mixtures of two or more thereof. Among these, nylon 6 and its copolymer are preferable.

The inclusion of these polyolefin-based resins reduces the water permeability of the interlayer, and thus the product multilayer film, and reduces the weight loss of sausage and other contents through the packaging film during storage of the packaged product. It is effective in preventing. The mixing ratio of the polyolefin resin is usually 10 to 30% by weight in the polyamide resin composition.
If this compounding ratio is too small, the moisture permeability of the film becomes too large, and when packaging and storing sausages,
The loss of the contents increases. If this compounding ratio is too large, in addition to the poor stretchability, the oxygen permeability increases, and the contents are liable to rot due to oxidative deterioration.

(Polyamide-based resin composition) The polyamide-based resin composition constituting the intermediate layer can be prepared by mixing the respective components by a known method. For example, at the time of extrusion molding, a uniform composition can be obtained by mixing raw materials such as pellets, granules, and powders of each polymer. If desired, various additives such as a plasticizer, a stabilizer, a lubricant, an antioxidant, a pigment, and a dye can be added to the polyamide resin composition within a range that does not impair the properties of the film.

(Adhesive Resin Layer) The multilayer film of the present invention comprises at least the above-mentioned pair of outer layer and intermediate layer. These three layers can be simply co-extruded to form a film. With a resin layer interposed, a multilayer film having good interlayer adhesion can also be formed.

Examples of the adhesive resin include polyethylene resins (including α-olefin resins such as LLDPE and VLDPE), polypropylene, polybutene, copolymers of these monomers, ionomer resins, ethylene / acrylic acid copolymers. Polymer, a functional group obtained by graft-copolymerizing an unsaturated carboxylic acid such as maleic acid, fumaric acid, acrylic acid or an acid anhydride, or an ester to an olefin alone or a copolymer such as an ethylene-vinyl acetate copolymer. The modified polymer introduced, and a mixture of two or more thereof are exemplified.

In particular, an adhesive resin layer composed of a mixture of 20 to 80% by weight of a polypropylene resin and 80 to 20% by weight of a polyethylene resin, at least one of which has been modified with maleic acid or the like, exhibits a strong adhesive force and has a retort sterilization property. It is particularly preferably used because it shows strong heat resistance in processing and the like. If the mixing ratio of the (modified) polypropylene-based resin is too large, peeling tends to occur between the polypropylene-based resin layer and the polyamide-based resin composition layer at the fold of the casing or at the time of shearing. On the other hand, if the mixing ratio of the (modified) polyethylene resin is too large, delamination occurs during stretching, and fine cracks may occur in the polypropylene resin layer or the polyamide resin layer, which may cause rupture.

(Other Resin Layer) In the multilayer film of the present invention, other resin layers or additional resin layers other than those described above, such as a saponified ethylene-vinyl acetate copolymer (EVOH) layer, For example, a gas barrier resin layer such as nylon MXD6 may be adjacent to the intermediate layer via an adhesive resin layer as necessary.

(Film Production) The method for producing the multilayer film of the present invention is not particularly limited, but is formed as a multilayer film by coextrusion or lamination.

The film forming method is not particularly limited, and for example, a T-die method, an inflation method and the like can be adopted. Usually, the inflation method is used. The melting temperature of the resin is usually 160 to 220 ° C., preferably 180 to 2 ° C. for the polypropylene resin constituting each layer.
00 ° C., and about 300 ° C. or less, preferably about 240 ° C. for the polyamide resin constituting the intermediate layer.
To 280 ° C, more preferably 250 to 270 ° C.
The unstretched film obtained by the T-die method is usually biaxially stretched simultaneously or sequentially by a tenter method at a stretching temperature equal to or lower than the melting point of the polypropylene resin (eg, 130 ° C. or lower). The tubular parison obtained by the inflation method is biaxially stretched by blowing air at a stretching temperature lower than the melting point of the polypropylene-based resin (for example, 130 ° C. or lower). The stretching ratio is usually 2.0 to 10.0 times, preferably 2.2 to 8.0 times, and more preferably 2.2 to 6.0 times in both the vertical and horizontal directions. By stretching, appropriate heat shrinkage and dimensional stability such as creep characteristics can be obtained.

(Laminated Structure) Through the above-mentioned production method, the biaxially stretched multilayer film of the present invention includes a single layer having the following thickness constitution including an arbitrary layer, and has a total thickness of 10 to 250 μm.
It is preferably formed as a multilayer film of 15 to 200 μm: First outer layer (outer surface layer in the case of a cylindrical state): 5 to 100 μm
m, preferably 5 to 80 μm Intermediate layer: 2 to 50 μm, preferably 2 to 20 μm Gas barrier layer (optional): 1 to 20 μm, preferably 2
Second outer layer (inner surface layer in case of cylindrical body): 5 to 100 μm
m, preferably 5 to 80 μm Adhesive resin layer (optional): 0.5 to 30 μm, preferably 1 to 20 μm

(Characteristics) In the packaging of processed meat products, from the viewpoint of product aesthetics, we do not like to produce wrinkles in packaged products such as sausages. In order to prevent the generation of wrinkles, it is necessary that the film shrinks due to heat during boil cooking or sterilization treatment to maintain a tight state. The stretched film of the present invention generally has a shrinkage (hot water shrinkage) of 5% or more, preferably 8% or more, and more preferably 10% or more, when immersed in hot water at 80 ° C.

In the casing film of the present invention, 8
If the hot water shrinkage at 0 ° C. is less than 5%, for example, after filling and cooking with a liquid or semi-liquid sausage, wrinkles occur on the product surface, which is not preferable.

As evaluation criteria for the dimensional stability of the film,
Hot water creep at 80 ° C. for 10 seconds can be employed. The hot water creep of the stretched film of the present invention is 20%
Or less, more preferably 18% or less. If the hot water creep is too large, for example, after filling and cooking sausage, the variation in product dimensions becomes too large, which is not preferable. For hot water creep, test width 2
0mm, 100mm sample length, load 1kg / m
m ² and immersed in 80 ° C warm water for 10 seconds,
It is measured as elongation relative to the original film test length.

The film of the present invention has a haze of preferably 20% or less. Due to the low haze,
The contents such as sausages can be seen from the outside of the packaging film.

The film or sheet of the present invention has a thickness of 30
Oxygen permeability measured under the conditions of ° C. and 80% RH (relative humidity) is 200 cm ³ (NTP) / m ² · day · atm or less, more preferably 135 cm ³ (NTP) / m ² · da.
y · atm or less, and the water vapor permeability measured at 40 ° C. and 90% RH is preferably 70 g / m ² · day or less. The loss of weight can be suppressed, and the flavor of the contents can be maintained.

The film of the present invention has excellent high-frequency sealing properties. Hitherto, many films made of a resin composition of a polyamide and a polyolefin resin have been proposed and used, but there is no particular mention of a high-frequency seal. The present inventors have conducted intensive studies on this sealing property, and as a result, a high-frequency sealing of a film made of a simple substance of polyamide, for example, a nylon 6 film, is performed by an automatic filling and packaging machine (automatic filling and packaging machine KAP such as sausage manufactured by Kureha Chemical Co.) Then, discharge occurred in the seal portion, and good sealing properties could not be obtained. On the other hand, the film having the outer layer made of the polypropylene-based resin of the present invention and the intermediate layer made of the polyamide-based resin composition can be discharged even when high-frequency sealing is performed using an automatic filling and packaging machine having a high-frequency sealing mechanism. No stable continuous sealing is possible. The film of the present invention has good sealing properties such as heat sealing and ultrasonic sealing as well as high frequency sealing.

The multilayer film of the present invention can be suitably used as a casing film. The multilayer film of the present invention has good film formability and stretchability during film production, and has appropriate flexibility, hot water shrinkage, creep, toughness, gas barrier properties, dimensional stability, and automatic packaging machine suitability. Filled with processed livestock products such as ham and sausage, processed fishery products such as fish sausage, processed processed agricultural products such as konjac and uiro, and liquid / semi-fluid foods such as cooked foods. It is particularly suitable as a casing film for packaging.

In particular, prior to filling the contents consisting of processed meat products such as sausage and ham, the outer layer surface in contact with the contents is subjected to corona treatment to improve the so-called meat adhesion of the film, and to improve the film and the contents. Preventing the formation of a liquid pool at the interface is preferable from the viewpoint of maintaining not only the appearance of the package product but also the quality of the contents.

The corona treatment is generally performed using a corona generator having a high-frequency oscillator and a high-frequency power supply provided with a high-voltage transformer.
At a power of kW or less, a frequency of 5 to 120 kHz, a waveform, preferably a sinusoidal voltage and a current, a film is arranged on a processing roll (silicon coating) surface, and a corona discharge is caused between the discharge electrode and the processing roll. by processing the surface tension of the treated surface 34dyne / cm ² or more, it is preferable that the particular 36 dyne / cm ² or more.

The multilayer film of the present invention is also suitable for an embodiment in which a casing is formed by a back seal (a so-called envelope-attached seal in which the edges are overlapped so that a pair of outer layers are in contact with each other). For example, the fold width is 260 mm or less, preferably 15 to 160 m due to the back seal.
m, a cylindrical casing having a seal width of 0.1 to 15 mm is formed, and the (semi) fluid product is filled by automatic packaging after filling.
A product package is formed by sealing both ends with a heat seal.

[0055]

The present invention will be described below more specifically with reference to examples and comparative examples. In addition, each physical property measurement is as follows.

(1) Oxygen permeability According to ASTM D3985-81, MODERN C
MOCON OXTRAN-2 / 2 manufactured by ONTROL
The measurement was performed using Type 0 under conditions of 30 ° C. and 80% RH.

(2) PERMATRA made by MODERN CONTROL
Using N-W3 / 31, the measurement was performed at 40 ° C. and 90% RH according to ASTM F372-73.

(3) Interlayer adhesive strength TENSILON® manufactured by TOYO BALDWIN
Using a TM-100 type mold, prepare a test piece of the film having a test width of 15 mm and a test length of 100 mm, peel off a part of the outer layer // core layer or the inner layer // core layer with the blade of a cutter, and remove the peeled end. Using one sample, the T-peel force between the outer layer // core layer and the inner layer // core layer was measured for each sample.

(4) Shrinkage After immersing the film in hot water at 80 ° C. for 3 seconds, the shrinkage in the longitudinal and transverse directions was measured.

(5) Tensile elastic modulus TENSILON® manufactured by TOYO BALDWIN
Using a TM-100 model, a film was prepared as a test piece having a test width of 20 mm and a test length of 100 mm. At a tensile speed of 10 mm / min, the stress at 1% tensile strain was calculated, and the tensile elastic modulus in the longitudinal / lateral directions was calculated. Was measured.

(6) Meat adhesion, film peeling force Using FUDOH RHEO METER, manufactured by Leotech Co., a cut was made in the length direction of the sausage in a part of a test piece cut into a width of 3 cm at right angles to the length direction of the sausage. Then, peel the film about 2 cm in advance and chuck the part, and insert a rod-shaped shaft at the center of the circumference of the sausage, so that the sausage rotates at the time of measurement and the tensile peeling direction is always vertical at the time of film peeling measurement 6cm / mi
Peel about 3 cm long at n speed. The average value of the peeling force was defined as the film peeling force.

(7) Crystal Melting Point (Tm) The crystal melting point was measured using DSC7 manufactured by PerkinElmer. The measurement conditions weigh 5-10 mg of sample,
The resin was once melted, held at a temperature 40 ° C. higher than the melting point at that time for 2 minutes, then rapidly cooled to 0 ° C. at 200 ° C./minute and held for 2 minutes. Thereafter, the temperature was raised at 20 ° C./min, and the melting peak temperature in the process was defined as the crystal melting point.

(Example 1) As a constitution of a multilayer film,
In the five-layer laminated film of outer layer / adhesive layer / core layer / adhesive layer / inner layer, nylon MXD6 (polyamide MXD6 # 6007 manufactured by Mitsubishi Chemical Corporation, melting point (Tm) = 240) was used as the core layer.
° C, glass transition point (Tg) = 75 ° C, density (d) = 1.
22) 95% by weight and nylon 66/610 / MXD6
(Mill Chemical Co., Inc., Grillon BM-18SBH, T
m = 181 ° C., Tg = 57 ° C., d = 1.12) 5% by weight
And a PP-based adhesive resin (Modick P504V, manufactured by Mitsubishi Chemical Corporation, Tm = 140) as an adhesive layer.
C, d = 0.89, MI = 4 g / 10 min, Vicat softening point (Tv) = 100 ° C.) 50% by weight and an LLDPE-based adhesive resin (Modick OM-101, T, manufactured by Mitsubishi Chemical Corporation).
m = 120 ° C., d = 0.93, MI = 3.2 g / 10 m
in, Tv = 56 ° C.) 50% by weight of a mixed resin layer, 93% by weight of propylene as an outer layer and an inner layer, ethylene
Ethylene propylene / butene-1 copolymer consisting of 2% by weight and 5% by weight of butene-1 (Sumitomo Chemical Co., Ltd., Sumitomo Noblene, FL851, Tm = 139 ° C., d = 0.9
0, MI = 6 g / 10 min, Tv = 128 ° C.) and 90% by weight of SSC-based polyethylene (manufactured by Dow Chemical Company, Elite 5100, Tm = 121 ° C., d = 0.92, MI =
0.85 g / 10 min, Tv = 107 ° C.) 10% by weight
4 extruders (outer layer, inner layer, core layer;
40φ, adhesive layer; 30φ) and 4 types and 5 layers of circular dies, co-extruded in an annular shape at a resin temperature of 250 ° C., cooled by water showering at 10 ° C., thickness 850 μm, folded width 70 mm
I got a parison. Next, the parison was reheated to a surface temperature of 150 ° C. with a far-infrared heater, stretched 4.5 / 4.5 times vertically / horizontally by an inflation method, and had a thickness of 15/2/8/2/15 μm. (Total thickness 42 μm) was obtained. Next, the surface of the stretched film was measured with an infrared thermometer and heat-treated at 140 ° C. to prepare a film of the present invention. The laminated resin and thickness configuration of the obtained multilayer film are shown below.

[0064]

(Equation 1)

The oxygen permeability, moisture permeability,
The interlayer adhesive strength, shrinkage, and tensile modulus were measured by the above methods, and are shown in Table 1 below together with the results of the following Examples and Comparative Examples.

(Examples 2 and 3) The procedure of Example 1 was repeated except that the mixing ratio of the core layer resin was changed as follows.
A biaxially stretched multilayer film of the present invention was obtained.

[0067]

(Equation 2)

Example 4 Resin Configuration PP / Ad / MXD
In a five-layer film of 6 + M-PA / Ad / PP, the adhesive resin (Ad) was used as a PP-based adhesive resin (Modick P504V, manufactured by Mitsubishi Chemical Corporation), and otherwise the same manufacturing method as in Example 1 was used to stretch a multilayer film. Tried to create.

(Example 5) Resin constitution PP / Ad / MXD
In the 6 / Ad / PP five-layer film, the adhesive resin (A
d) is replaced with a PP-based adhesive resin (Modick P50 manufactured by Mitsubishi Chemical Corporation).
4V) As a mixed resin of 50% by weight and 50% by weight of an LLDPE-based adhesive resin (Modick OM-101, manufactured by Mitsubishi Chemical Corporation), an attempt was made to produce a stretched multilayer film by the same manufacturing method as in Example 1 except for that. .

(Comparative Examples 1-2) Resin constitution PP / Ad / M
In the five-layer laminated film of XD6 / Ad / PP, the adhesive resin (Ad) was a PP-based adhesive resin (Modick P504V, manufactured by Mitsubishi Chemical Corporation) (Comparative Example 1), LLDPE
Adhesive resin (Modik OM-101, manufactured by Mitsubishi Chemical Corporation)
Otherwise (Comparative Example 2), an attempt was made to produce a stretched multilayer film by the same manufacturing method as in Example 1 except for the above.

In Comparative Example 1, a multilayer film was obtained. In Comparative Example 2, partial delamination between layers occurred during inflation stretching, and bubbles burst, so that a multilayer film was not obtained.

Table 1 shows the measured values obtained only for the film of Comparative Example 1.

[0073]

[Table 1]

(Example 6) Using the film of Example 3, paste-type beef sausage is obtained by an automatic filling and packaging machine (Kap2000, KAP2000 type) including a casing process by sticking a film on an envelope. Fill the casing, furthermore, at 120 ° C, 15 minutes, steam pressure 2
A retort sterilization treatment is performed under the condition of kg / cm ² (gauge), and a shell type sausage package (size: about 22φ ×
100 pieces of 140 mm length and weight: about 55 g / piece) were prepared. The puncture occurrence rate of the package during the retort sterilization treatment was 0%, the sausage after storage at room temperature for 2 weeks was good without rot, and the loss was 0.18%, which was a low value.

Example 7 Using the film of Example 4,
In the same manner as in Example 6, a casing was formed, filled with meat sausage, and subjected to a retort sterilization treatment. The puncture incidence of the package was 0%, the sausage after storage at room temperature for 2 weeks was good without decay, and the weight loss was as low as 0.17%.

Example 8 Using the film of Example 5,
In the same manner as in Example 6, a casing was prepared, filled with meat sausage, and subjected to a retort sterilization treatment. The puncture occurrence rate of the package was 5%, the sausage after storage at room temperature for 2 weeks was good without decay, and the weight loss was as low as 0.17%.

Comparative Example 3 Using the film of Comparative Example 1,
In the same manner as in Example 6, a casing was prepared, filled with meat sausage, and subjected to a retort sterilization treatment. As a result of evaluating the puncture occurrence rate of the package, the puncture rate was 40%.

Example 9 Using the film of Example 3,
The surface of the sausage package that comes into contact with the sausage is subjected to corona treatment in advance, and the surface tension of the treated surface is 36 dyne / c.
An m ² film was obtained. Using this film, a casing was formed in the same manner as in Example 6, filled with fish sausage, and subjected to a retort sterilization treatment to obtain a fish sausage package. The resulting package has a puncture incidence of 0% during retort sterilization, no sausage rot after storage at room temperature for 2 weeks, a reduced amount of 0.15%, and good meat adhesion (film peeling power). 100 g / 3 cm width, peeling speed;
6 cm / min).

[0079]

As described above, according to the present invention, not only excellent balance of moldability, heat shrinkability, easy sealing property, gas barrier property, water vapor barrier property, flexibility, etc., but also particularly for retort sterilization. A biaxially stretched multilayer film exhibiting suitable excellent heat resistance can be obtained. Particularly, by using this as a casing and filling it with a (semi) fluid food such as fish meat, animal meat, or a processed product thereof, both appearance and strength can be improved. An excellent package can be obtained.

Claims (14)

[Claims] 1. A biaxially stretched multilayer film obtained by biaxially stretching a laminated film comprising at least three layers in which an intermediate layer is sandwiched between a pair of outer layers made of a thermoplastic resin, wherein the intermediate layer is made of an aromatic resin. A biaxially stretched multilayer film comprising a polyamide resin composition containing a diamine copolymer and an aromatic diamine polymer, wherein at least one outer layer is made of a polypropylene resin. 2. The biaxially stretched multilayer film according to claim 1, wherein the polyamide resin composition contains 1 to 50% by weight of an aromatic diamine copolymer and 99 to 50% by weight of an aromatic diamine polymer. 3. The biaxially stretched multilayer film according to claim 2, wherein the aromatic diamine (co) polymer is a xylylene diamine (co) polymer. 4. The biaxially stretched multilayer film according to claim 1, wherein both thermoplastic resins of the pair of outer layers are polypropylene resins. 5. The method according to claim 1, wherein at least one outer layer comprises a mixture of a polypropylene resin and a polyethylene resin.
The biaxially stretched multilayer film according to the above. 6. The biaxially stretched multilayer film according to claim 5, wherein the mixture constituting at least one outer layer contains 5 to 30% by weight of a polyethylene resin. 7. A biaxially stretched multilayer film obtained by biaxially stretching a laminated film composed of at least three layers in which an intermediate layer is sandwiched between an outer layer composed of a pair of thermoplastic resins. The outer layer in contact with the meat food has 90 to 80% by weight of the polypropylene resin and 10 to 10% of the polyethylene resin.
A biaxially oriented multilayer film which is a resin containing 20% by weight and whose outer surface is corona-treated. 8. A biaxially stretched multilayer film obtained by biaxially stretching a laminated film comprising at least three layers in which an intermediate layer is sandwiched between a pair of outer layers made of a thermoplastic resin, wherein the intermediate layer is made of an aromatic system. It is made of a gas barrier resin containing a polyamide (co) polymer, at least one outer layer is made of a polypropylene resin, and has an adhesive layer between the intermediate layer and the outer layer. The adhesive layer is made of a polypropylene resin and a polyethylene resin. The mixing ratio on a weight basis is 80/20 to 20/80.
And a biaxially stretched multilayer film comprising a mixed resin in which at least one of a polypropylene resin and a polyethylene resin contains a functional group. 9. The biaxially stretched multilayer film according to claim 1, which is heat-shrinkable. 10. A package comprising a casing formed of the biaxially stretched multilayer film according to claim 1 and containing a fluid or semi-fluid substance. 11. The package according to claim 10, wherein the casing is back-sealed. 12. The package according to claim 11, wherein both ends of the casing are sealed. 13. The package according to claim 12, wherein the fluid or semi-liquid material is automatically filled by a packaging machine. 14. The package according to claim 11, wherein the folded width of the back-sealed casing is 15 to 160 mm.