JP2016097573A - Co-extrusion multilayer film for deep drawing molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a food package film for boil treatment having good curl inhibition property after boil and good pinhole resistance under freezing.SOLUTION: There is provided a co-extrusion multilayer film for deep drawing molding having a homopolypropylene resin layer which is a single polymer arranged on an outermost layer, a polypropylene resin layer by blended 5 mass% to 70 mass% of an ethylene-butene copolymer having the melting point of 40°C to 150°C arranged on an adjacent layer to the outermost layer, at least one layer of a polyamide resin layer arranged on an intermediate layer, a heat sealing resin layer arranged on an innermost layer and a polyethylene resin layer having density of 0.920 to 0.945 arranged on an adjacent layer to the innermost layer with total film thickness in a range of 60 μm to 250 μm, thickness ratio of the outermost layer to the total film thickness of 2% to 20% and thickness ratio of the adjacent layer to the outermost layer of 10% to 60%.SELECTED DRAWING: None

Description

  The present invention relates to a co-extrusion laminated film for deep drawing which can be suitably used as a packaging bottom material for mainly packaging block ham, raw meat, prepared foods, industrial products and the like.

  Conventionally, as a boil packaging material for boiling food, polyamide resin / adhesive resin / linear low density polyethylene resin (for example, Patent Document 1), polypropylene resin / adhesive resin / polyamide resin / adhesive resin / ethylene resin / A polyolefin resin (for example, Patent Document 2) has been used.

However, if the outer layer is a polyamide resin, there is a problem that the polyamide resin absorbs moisture during curling and curls to deteriorate the appearance.
Further, in the configuration in which the polypropylene resin is arranged in the outer layer in order to suppress the curling due to moisture absorption, the polypropylene resin has poor impact resistance at low temperatures, so that the pinhole resistance is poor, and there remains a problem in low temperature storage and transportation.
Furthermore, for various foods, the recent storage and transport conditions have changed from refrigerated to frozen, and it is necessary to combine the extremely strict requirement of pinhole resistance at freezing temperatures with curling resistance after boiling, In using packaging resin, the difficulty of the problem is increasing.

JP-A-7-1544 Japanese Patent Laid-Open No. 10-138411

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a food packaging film for boil treatment that has both good curl deterrence after boil and good pinhole resistance under freezing. And

  As a result of intensive studies on the above problems, the present invention has found that the above problems can be easily solved by adopting a specific configuration, and has completed the present invention.

  That is, the gist of the present invention is that a homopolypropylene resin layer which is a homopolymer is disposed on the outermost layer, and an ethylene-butene copolymer having a melting point of 40 ° C. or higher and 150 ° C. or lower is 5% by mass or more in the adjacent layer of the outermost layer. A polypropylene resin layer blended at a ratio of 70% by mass or less is disposed, at least one polyamide resin layer is disposed in the intermediate layer, a heat-sealable resin layer is disposed in the innermost layer, and a density of 0. A polyethylene resin layer of 920 to 0.945 is arranged, the total film thickness is in the range of 60 μm to 250 μm, the thickness ratio of the outermost layer to the total film thickness is 2 to 20%, and the thickness ratio of the adjacent layer of the outermost layer is It exists in the co-extrusion multilayer film for deep drawing characterized by being 10 to 60%.

  The co-extruded multilayer film of the present invention is curled at the seal part after boil sterilization, and thus has a good appearance shape, can be efficiently stacked, and also has impact resistance under freezing conditions. Since no tearing or perforation occurs, it is suitable as a packaging material for boiled foods, pharmaceuticals, etc., frozen storage and transporting, and can improve the hygiene safety of the contents and lengthen the storage period.

<Outermost layer>
A homopolypropylene resin that is a homopolymer is used for the outermost layer of the film of the present invention.
By disposing the homopolypropylene resin layer as the outer layer, the stiffness of the film is improved and curling due to boiling can be suppressed.
The types of polypropylene resins include random copolymers with α-olefins and block copolymers. However, when they are arranged in the outer layer, the film does not retain its elasticity and lacks curl suppression.

  The thickness of the outermost propylene resin layer is preferably 2% or more, more preferably 3% or more, and more preferably 5% or more with respect to the total film thickness, from the viewpoint of curling of the pack appearance after boil sterilization treatment. preferable. Moreover, since it is inferior to freezing impact resistance when it is too thick, the upper limit is preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less.

<Adjacent layer of outermost layer>
The outermost adjacent layer of the film of the present invention is composed of a polypropylene resin mixed with an ethylene-butene copolymer. The ethylene ratio of the ethylene-butene copolymer is 50 mol% or more.

  Since the ethylene-butene copolymer has low crystallinity and excellent compatibility with the polypropylene resin, even if a layer mixed with the polypropylene resin is formed, the cohesiveness and transparency of the adjacent layer itself are the same as those of the outermost layer. The low-temperature impact resistance of the ethylene-butene copolymer can be reflected in the outermost layer made of polypropylene resin and its adjacent layers, and further on the entire film.

  As the product of the ethylene-butene copolymer, for example, Tafmer manufactured by Mitsui Chemicals, Engage manufactured by Dow Chemical, LUMITAC manufactured by Tosoh, LUCENE manufactured by LG Chemical, and Exact manufactured by ExxonMobil can be suitably used.

Even if a polypropylene-butene copolymer having good compatibility with the polypropylene resin is used as the mixed resin of the adjacent layer of the outermost layer, it is insufficient for the freezing impact resistance required for storage and transportation.
Further, when the composition of the adjacent layer of the outermost layer is made only of the ethylene-butene copolymer, the raw material cost increases, and the compatibility between the outermost layer and the adjacent layer or the layer interface adhesion becomes insufficient.

The lower limit of the melting point of the ethylene-butene copolymer is 40 ° C. or higher, more preferably 60 ° C. or higher, and still more preferably 80 ° C. or higher. The upper limit of the melting point is 150 ° C. or less, more preferably 135 ° C. or less, and further preferably 100 ° C. or less.
When the melting point is less than 40 ° C., crystallization proceeds at normal temperature and transparency is impaired, and when the melting point is higher than 150 ° C., flexibility is impaired and pinhole resistance is deteriorated.
The melting point can be measured according to the JIS K 7121 method.

The mixing ratio of the ethylene-butene copolymer with respect to the polypropylene resin of the adjacent layer is 5% by mass or more and 70% by mass or less with the entire layer being 100% by mass. The lower limit of the mixing ratio is more preferably 20% by mass or more, still more preferably 30% by mass or more, and the upper limit of the mixing ratio is more preferably 70% by mass or less.
When the mixing ratio is less than 5% by mass, the pinhole resistance is inferior, and when it is higher than 70% by mass, the effect of suppressing curling of the seal portion is inferior.

  The lower limit of the ratio of the thickness of the outermost adjacent layer to the total film thickness is preferably 10% or more, more preferably 15% or more. The upper limit is preferably 60% or less, more preferably 50% or less, and still more preferably 30% or less. By setting the thickness of the adjacent layer of the outermost layer to a ratio of 10% or more with respect to the total film thickness, curling of the seal portion can be suppressed, and by setting the thickness to 60% or less, deterioration of pinhole resistance at a low temperature is prevented. be able to.

<Adhesive resin layer>
The film of the present invention can be provided with an adhesive resin layer for the purpose of increasing the delamination strength of each layer. There may be one or more adhesive layers.
The adhesive resin layer is preferably composed of a polyethylene adhesive resin or a polypropylene adhesive resin. For example, when the adhesive resin layer is adjacent to a layer containing a polypropylene resin, it is preferable to use a polypropylene adhesive resin, and when adjacent to the layer containing a polyethylene resin, a polyethylene adhesive resin is preferably used.

  Polyethylene adhesive resins that can be used for the adhesive resin layer include polyethylene (PE) such as low density polyethylene (LDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), and high density polyethylene (HDPE), and polypropylene. Olefin resins such as (PP), ethylene-vinyl acetate copolymer (EVA), ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl acrylate copolymer (EMA), ethylene-ethyl acrylate-maleic anhydride copolymer (E-EA-MAH), ethylene-acrylic acid copolymer (EAA), ethylene-methacrylic acid copolymer (EMMA), ethylene ionomer ( IO) and other ethylene copolymer resins That.

  Also, for example, ethylene-vinyl acetate copolymer or ethylene elastomer, monobasic unsaturated fatty acid such as acrylic acid or methacrylic acid, or anhydride of dibasic fatty acid such as maleic acid, fumaric acid or itaconic acid A modified polyolefin-based resin obtained by chemically bonding can be exemplified, and the interlayer adhesion is high and preferable.

  The type of polypropylene-based adhesive resin that can be used for the adhesive resin layer is not particularly limited, and examples thereof include an adhesive resin composed of at least one selected from the group consisting of homopolymers, random copolymers, and block copolymers. .

  When the adhesive layer is provided, the lower limit of the thickness of the adhesive layer is preferably 3 μm or more, more preferably 5 μm or more, and even more preferably 8 μm or more, from the viewpoints of workability, economy, and handleability. The upper limit is not particularly limited, but is preferably 30 μm or less, more preferably 25 μm or less, and further preferably 20 μm or less. When the thickness of the adhesive layer is 3 μm or more, the delamination strength can be improved. If the adhesive layer is too thick, the transparency is deteriorated and the total thickness of the film is increased, and the manufacturing cost is increased, so the upper limit is desirably 30 μm or less.

<Polyamide resin>
The intermediate layer of the film of the present invention is provided with at least one polyamide resin layer for the purpose of imparting pinhole resistance.

  The type of polyamide resin is not particularly limited, but specific examples include, for example, 4 nylon, 6 nylon, 7 nylon, 11 nylon, 12 nylon, 46 nylon, 66 nylon, 69 nylon, 610 nylon, 611 nylon, 6T. Nylon, 6I nylon, MXD6 nylon, 6-66 nylon, 6-610 nylon, 6-611 nylon, 6-12 nylon, 6-612 nylon, 6-6T nylon, 6-6I nylon, 6-66-610 nylon, Examples include 6-66-12 nylon, 6-66-612 nylon, 66-6T nylon, 66-6I nylon, 6T-6I nylon, 66-6T-6I nylon, and the like. Among these, it is preferable to use 6 nylon or 6-66 nylon from the viewpoint of pinhole resistance.

  Further, two or more polyamide resin layers can be provided in the intermediate layer of the film of the present invention, and in this case, each layer may be composed of different types of polyamide resins.

  The total thickness of the polyamide resin layer is not particularly limited, but as a ratio of the total film thickness, the lower limit is preferably 30% or more, and more preferably 35% or more. Further, the upper limit is preferably 70% or less, and more preferably 60% or less. By setting the lower limit of the thickness ratio of the polyamide resin layer to 30% or more, sufficient pinhole resistance can be imparted to the film, and by setting the upper limit to 70% or less, curling of the seal portion is prevented. be able to.

<Ethylene-vinyl acetate copolymer saponified resin layer>
The film of the present invention may be provided with at least one ethylene-vinyl acetate copolymer saponified resin (hereinafter sometimes abbreviated as EVOH) layer in the intermediate layer for the purpose of improving oxygen barrier properties.

The ethylene-containing molar ratio in the ethylene-vinyl acetate copolymer saponified resin layer is not particularly limited, but from the viewpoint of film formation stability, the lower limit is preferably 27 mol% or more, and 29 mol% or more. Is more preferable, and 32 mol% or more is more preferable. On the other hand, the upper limit is preferably 47 mol% or less, more preferably 44 mol% or less, and even more preferably 38 mol% or less.
The saponification degree of EVOH is preferably 90% or more, and more preferably 95% or more.

The lower limit of the ratio of the EVOH layer thickness to the total film thickness is preferably 3% or more, more preferably 5% or more, and further preferably 7% or more. Further, the upper limit is preferably 20% or less, more preferably 18% or less, and further preferably 15% or less.
By setting the thickness ratio of the EVOH layer to 3% or more, sufficient oxygen barrier properties can be imparted to the film, and by setting the thickness ratio to 20% or less, the pinhole resistance of the film is reduced. Manufacturing cost can be suppressed.

<Adjacent layer of innermost layer>
The adjacent layer of the innermost layer of the film of the present invention is composed of a polyethylene resin.
The type of the polyethylene resin is not particularly limited, but is preferably a linear low density polyethylene resin (hereinafter sometimes abbreviated as LLDPE). LLDPE is characterized by strong physical properties such as tensile strength, elongation, pinhole strength, and rigidity.

  The density of the polyethylene resin in the adjacent layer of the innermost layer is preferably 0.920 or more, and more preferably 0.925 or more. When the density is less than 0.920, the degree of crystallinity is low, and film contraction is likely to occur after boil sterilization, which may cause curling. When the density is 0.945 or more, the low temperature impact resistance and the deep drawability may be inferior.

As a ratio of the polyethylene resin layer thickness of the adjacent layer of the innermost layer to the total film thickness, the lower limit is preferably 20% or more, and more preferably 25% or more. Further, the upper limit is preferably 50% or less, more preferably 45% or less, and even more preferably 40% or less.
By setting the ratio of the polyethylene resin layer thickness of the adjacent innermost layer layer to the total film thickness to 20% or more, the film can have appropriate flexibility, and by setting it to 50% or less, curling of the seal portion can be achieved. Can be prevented.

<Inner layer>
A heat-sealable layer is disposed in the innermost layer of the present invention.
The type of heat-sealable resin is not particularly limited, and general polyethylene resin, cohesive failure type easy peel resin blend, delamination type easy peel resin blend, and the like can be used.

  Although it does not specifically limit as a general polyethylene-type resin layer, Low density polyethylene (LDPE), linear low density polyethylene (LLDPE), ethylene-vinyl acetate copolymer (EVA), ethylene-methyl methacrylate copolymer Polymer (EMMA), ethylene-methyl acrylate copolymer (EMA), ethylene-acrylic acid copolymer (EAA), ethylene-ethyl acrylate copolymer (EEA), ethylene-methacrylic acid copolymer (EMAA) An ionomer of ethylene-acrylic acid copolymer (EAA), an ionomer of ethylene-methacrylic acid copolymer (EMAA), and a resin composed of at least one selected from the group consisting of these ionomers. Preferably, linear low density polyethylene (LLDPE) is the main component. It is more preferable in terms of pinhole resistance is.

    When the heat seal layer is a polyethylene resin layer, the upper limit of the thickness of the innermost layer and the adjacent layer of the innermost layer is preferably 10 or more, more preferably 20% or more, more preferably 30% or more with respect to the total film thickness. More preferably. The lower limit is preferably 50% or less, and more preferably 40% or less.

When the heat seal layer has an easy peel property, it preferably exhibits an easy peel strength of 1.96 N / 15 mm width or more and 7.84 N / 15 mm width or less at 25 ° C. Moreover, it is preferable that it has cohesive failure from a viewpoint of the ease of use at the time of opening a packaging material.
When the easy peel strength is 1.96 N / 15 mm width or more, resistance to bag breakage during transportation can be obtained, and when it is 7.84 N / 15 mm width or less, good easy-openability is obtained. Can do.

  Although the resin which comprises an easy peel layer is not specifically limited, From a viewpoint of providing favorable easy peel strength and cohesive failure, it is preferable to comprise from the following resin A and resin B from which a kind differs, for example.

  As the resin A, linear low density polyethylene (LLDPE) or low density polyethylene (LDPE) whose main component is a melting point of 90 ° C. or higher, preferably 95 ° C. or higher, more preferably 100 ° C. or higher, most preferably 120 ° C. or higher. , Ethylene-vinyl acetate copolymer (EVA), ethylene-acrylic acid copolymer (EAA), ethylene-ethyl acrylate copolymer (EEA), ethylene-methacrylic acid copolymer (EMAA), ethylene-methacrylic acid At least one selected from the group consisting of a methyl copolymer (EMMA), an ethylene-methyl acrylate copolymer (EMA), and these ionomers can be used.

A higher deep drawing temperature prevents shrinkage and suppresses curling. Therefore, from the viewpoint of film heat resistance, the melting point is 120 ° C. or higher and the density is 0.915 g / cm ³ or higher and 0.945 g / A linear low density polyethylene resin (LLDPE) having a cm ³ or less is preferred.

  As the resin B, polypropylene (PP) or polybutene (PB) can be used. As the polypropylene (PP), any of random copolymers (including random copolymers obtained by metallocene catalysts), homopolymers, block copolymers and the like can be used, and among them, random copolymers can be preferably used. Examples of polybutene (PB) include 1-polybutene and 2-polybutene, and 1-polybutene can be particularly preferably used.

  The content of the resin A in the resin constituting the easy peel layer is preferably 40% by mass or more, more preferably 50% by mass or more, particularly preferably 55% by mass or more, preferably 80% by mass or less, more preferably Is preferably 70% by mass or less, particularly preferably 65% by mass or less. The content of the resin B is preferably 20% by mass or more, more preferably 30% by mass or more, particularly preferably 35% by mass or more, preferably 60% by mass or less, more preferably 50% by mass or less, and particularly preferably. Is desirably 45% by mass or less.

By making the content rates of Resin A and Resin B within the above ranges, it becomes possible to keep the easy peel strength at normal temperature and boil temperature within the preferred range, and by changing the content rates of Resin A and Resin B Easy peel strength can be adjusted.
For example, when it is desired to increase the easy peel strength, the resin A content can be increased, and when it is desired to decrease the easy peel strength, it can be achieved by decreasing the resin A content.

  When the innermost layer is an easy peel layer, 3% or more is preferable and 5% or more is more preferable with respect to the total film thickness. Moreover, as an upper limit, 20% or less is preferable and 10% or less is more preferable. By setting the lower limit to 3% or more, it is possible to give the film an appropriate opening property, and by setting the upper limit to 20% or less, stable film-forming properties can be obtained, and fluffing and film residue at the time of peeling occur. It becomes difficult to do.

<Whole film>
The total thickness of the film of the present invention is 60 to 250 μm. The lower limit of the total film thickness is preferably 60 μm or more, preferably 80 μm or more, and preferably 100 μm or more. When the total film thickness is 60 μm or less, the total film thickness is too thin, so that the impact resistance is poor. The upper limit of the total film thickness is preferably 250 μm or less, and more preferably 240 μm or less. If the total thickness of the film is 250 μm or more, the packaging material cost increases, so that it is not economical.
That is, the film of the present invention can be suitably used when the total thickness is selected in consideration of the impact and cost due to the weight and shape of the contents to be accommodated in the package.

  The film of the present invention has a hydroshot value (high speed puncture impact strength) at −20 ° C. of 50 kgf · mm or more. In the film of the present invention, the hydroshot value increases as the total thickness increases.

  The film of the present invention is an inorganic particle such as silica, talc, kaolin, calcium carbonate, or the like for the purpose of improving and adjusting various properties such as molding processability and productivity within a range that does not significantly impair the effects of the present invention. Addition of pigments such as titanium and carbon black, flame retardants, weather resistance stabilizers, heat stabilizers, antistatic agents, melt viscosity improvers, crosslinking agents, lubricants, nucleating agents, plasticizers, anti-aging agents, anti-blocking agents, etc. An agent can be appropriately added to each layer or layer interface.

<Film forming method>
The multilayer film for deep drawing of the present invention can be produced using a known method. For example, an extrusion lamination method, a coextrusion inflation method, a coextrusion T-die method, or the like can be used. In particular, even when the number of film layers is large, the film forming process does not change and the thickness control is relatively easy. It is preferable to use the coextrusion T-die method.

<Example>
Examples of the present invention will be described below, but the present invention is not limited thereto.
(Production of multilayer film for deep drawing)
Using the raw materials described below, a multilayer unstretched film having the layer structure described in each Example and Table 1 was prepared by a coextrusion T-die method.
In addition, the layer order of Table 1 is from the outer layer side. Moreover, the 1st step | paragraph in a table | surface shows an abbreviation for a resin composition, and a 2nd step | paragraph shows thickness (micrometer).

(Raw material resin)
PP1: Novic PP (polypropylene homopolymer) manufactured by Nippon Polypro, density 0.900
PP2: Nippon Polypro Novatec PP (polypropylene random copolymer) mixed with 50% by mass of Mitsui Chemicals Tuffmer A (ethylene-butene copolymer, melting point 98 ° C.) PP3: Nippon Polypro Novatec PP (polypropylene random copolymer)
PP4: Nippon Polypro's Novatec PP (polypropylene random copolymer) mixed with 50% by mass of Mitsui Chemicals Toughmer XM (propylene-butene copolymer, melting point 98 ° C.)

Adhesive resin 1: Mitsubishi Chemical Modic (polypropylene resin base)
Adhesive resin 2: Mitsubishi Chemical Modic (polyethylene resin base)

Ny: DM Japan Engineering Plastic Novamid 6Ny
EVOH: Kuraray Eval Ethylene content 32mol%

LLDPE1: Nippon Polyethylene Novatec (Linear Low Density Polyethylene) Density 0.925
LLDPE2: Ube Maruzen Polyethylene Umerit (Linear Low Density Polyethylene) Density 0.918
LLDPE3: Prime polymer neozex (linear low density polyethylene) Density: 0.919
Easy peel (EP) layer: a mixture of LDPE (low density polyethylene, 60% by weight) and propylene random random copolymer (40% by weight)

Example 1
PP1 (15 μm) / PP2 (30 μm) / Adhesive resin 1 (10 μm) / Ny (25 μm) / EVOH (10 μm) / Adhesive resin 2 (10 μm) / LLDPE1 (40 μm) / LLDPE2 (10 μm)

(Example 2)
In Example 1, the layer thickness other than the second layer was increased.
PP1 (20 μm) / PP2 (30 μm) / Adhesive resin 1 (20 μm) / Ny (40 μm) / EVOH (15 μm) / Adhesive resin 2 (20 μm) / LLDPE1 (70 μm) / LLDPE2 (25 μm)

(Example 3)
In Example 1, the thicknesses of the seventh and eighth layers were changed, and the eighth layer was replaced with an easy peel layer.
PP1 (15 μm) / PP2 (30 μm) / Adhesive resin 1 (10 μm) / Ny (25 μm) / EVOH (10 μm) / Adhesive resin 2 (10 μm) / LLDPE1 (45 μm) / Easy peel layer (5 μm)

Example 4
In Example 1, the layer order of the fourth and fifth layers was changed.
PP1 (15 μm) / PP2 (30 μm) / Adhesive resin 1 (10 μm) / EVOH (10 μm) / Ny (25 μm) / Adhesive resin 2 (10 μm) / LLDPE1 (40 μm) / LLDPE2 (10 μm)

(Comparative Example 1)
In Example 1, the first layer was replaced with polyethylene resin.
LLDPE3 (15 μm) / PP2 (30 μm) / Adhesive resin 1 (10 μm) / Ny (25 μm) / EVOH (10 μm) / Adhesive resin 2 (10 μm) / LLDPE1 (40 μm) / LLDPE2 (10 μm)

(Comparative Example 2)
In Example 1, the first layer polypropylene resin was replaced with a random copolymer.
PP3 (15 μm) / PP2 (30 μm) / Adhesive resin 1 (10 μm) / Ny (25 μm) / EVOH (10 μm) / Adhesive resin 2 (10 μm) / LLDPE1 (40 μm) / LLDPE2 (10 μm)

(Comparative Example 3)
In Example 1, the resin blended in the second layer polypropylene resin was changed to a propylene-ethylene copolymer.
PP1 (15 μm) / PP4 (30 μm) / Adhesive resin 1 (10 μm) / Ny (25 μm) / EVOH (10 μm) / Adhesive resin 2 (10 μm) / LLDPE1 (40 μm) / LLDPE2 (10 μm)

(Comparative Example 4)
In Example 1, the first layer was eliminated and the thickness of the second layer was increased accordingly.
PP2 (45 μm) / Adhesive resin 1 (10 μm) / Ny (25 μm) / EVOH (10 μm) / Adhesive resin 2 (10 μm) / LLDPE1 (40 μm) / LLDPE2 (10 μm)

(Comparative Example 5)
In Example 1, the thickness of the first layer was reduced and the thickness of the seventh layer was increased accordingly.
PP1 (2 μm) / PP2 (30 μm) / Adhesive resin 1 (10 μm) / Ny (25 μm) / EVOH (10 μm) / Adhesive resin 2 (10 μm) / LLDPE1 (53 μm) / LLDPE2 (10 μm)

(Comparative Example 6)
In Comparative Example 5, the second layer was eliminated and the thickness of the seventh layer was increased accordingly.
PP1 (35 μm) / Adhesive resin 1 (10 μm) / Ny (25 μm) / EVOH (10 μm) / Adhesive resin 2 (10 μm) / LLDPE1 (50 μm) / LLDPE2 (10 μm)

(Comparative Example 7)
In Example 1, the thicknesses of the first layer and the second layer were changed.
PP1 (35 μm) / PP2 (10 μm) / Adhesive resin 1 (10 μm) / Ny (25 μm) / EVOH (10 μm) / Adhesive resin 2 (10 μm) / LLDPE1 (40 μm) / LLDPE2 (10 μm)

(Comparative Example 8)
A layer structure in which the outermost layer is nylon resin was used.
Ny (15 μm) / Adhesive resin 1 (10 μm) / Ny (40 μm) / EVOH (15 μm) / Adhesive resin 1 (15 μm) / LLDPE1 (50 μm) / LLDPE2 (10 μm)

<Preparation of evaluation sample>
The multilayer film of each example was formed at a heating temperature of 110 ° C. using a deep drawing packaging machine (FV-6300) manufactured by Omori Machine. Under the condition of molding time of 1.5 seconds, the deep drawing part has a diameter of 98mm, and the drawing depth is 20mm for the film thickness of 150μm and 40mm for the 240μm, and the bottom material is 100mm in length and 80mm in width. Was made. Thereafter, 100 g of hamburger was accommodated in the deep-drawn part for a film thickness of 150 μm, and 200 g of hamburger was accommodated for a film thickness of 240 μm.

  Next, as a cover material, a laminated film obtained by dry laminating an unstretched polypropylene film (30 μm), a 6Ny / MXDNy / 6Ny coextrusion stretched film (15 μm), and a linear low-density polyethylene film (40 μm) was used. A package was obtained by vacuum packaging over the housed bottom material.

<Evaluation method>
Tables 1 and 2 show the results of the following evaluation on the multilayer film and the deep-drawn package obtained in each example.
<Curl suppression evaluation>
The prepared deep-drawn package was subjected to boil sterilization at 90 ° C. for 30 minutes, and then the moisture was wiped off and stored in a refrigerator at 5 ° C. for 24 hours.
The case where the seal portion was curled by 10 mm or more from the horizontal was evaluated as “×”, and less than 10 mm was evaluated as “◯”.

<Frozen impact resistance evaluation (1)>
The prepared deep-drawn package was subjected to boil sterilization at 90 ° C. for 30 minutes, then wiped off moisture, packed in 10 cardboards, stored in a freezer at −30 ° C. for 24 hours, and immediately after that, 1.0 m high The sample was dropped 5 times and observed for the presence or absence of pinholes, and those without pinholes were evaluated as “◯” and those with pinholes as “x”.

<Frozen impact resistance evaluation (2)>
The multilayer film of each example was subjected to impact resistance under freezing using a hydroshot machine (HTM-1) manufactured by Shimadzu Corporation under the conditions of a constant temperature bath temperature of −20 ° C., a piercing speed of 3 m / sec, and a hitting core diameter of 0.5 inch. The strength (kgf · mm) was measured.

<Evaluation results>
<Curl suppression>
In Examples 1 to 4 and Comparative Examples 3, 6, and 7, curl suppression after the boil sterilization treatment was good.
On the other hand, since the outermost layer of Comparative Example 1 was made of polyethylene resin instead of homopolypropylene resin, and Comparative Example 2 was made of polypropylene random copolymer resin, curl was generated with high rigidity.
In Comparative Example 4, the homopropylene resin layer was not disposed on the outermost layer, and in Comparative Example 5, the thickness of the outermost homopropylene layer was less than 2% with respect to the total film thickness. .
In Comparative Example 8, Ny was arranged in the outer layer regardless of the total thickness of the film, and thus curl suppression was poor.

<Freezing impact resistance>
Examples 1-4 and Comparative Examples 1, 2, 4, and 5 had good impact resistance even under severe freezing conditions of −30 ° C.
Since the comparative example 3 mixed the propylene-ethylene copolymer with the polypropylene resin of the adjacent layer of the innermost layer,
Since Comparative Example 6 did not include a polypropylene resin layer containing an ethylene-based copolymer in the adjacent layer of the outermost layer, Comparative Example 7 had an outermost homopropylene layer thickness of 20% or more of the total film thickness. Because it was thick, the low temperature impact resistance was poor and pinholes were generated.

  From the above, it can be seen that Examples 1 to 4 have both good curl suppression after boil sterilization and freezing impact resistance.

  The coextruded multilayer film of the present invention has a highly rigid homopolypropylene resin layer disposed on the outermost layer, and a layer made of a mixed resin of polypropylene resin and ethylene-butene copolymer is formed adjacent to the outermost layer. , New boil treatment packaging film can be given new shape maintenance characteristics after high temperature hot water treatment and strength maintenance characteristics under freezing, food and pharmaceutical manufacturing, storage and transportation, In addition, it is possible to improve the efficiency, hygiene safety, and long-term storage in manufacturing, storage, transportation, and use for the users of these stored items.

Claims (2)

  A homopolypropylene resin layer which is a homopolymer is disposed on the outermost layer, and an ethylene-butene copolymer having a melting point of 40 ° C. or higher and 150 ° C. or lower is blended in a proportion of 5% by mass or more and 70% by mass or less in the adjacent layer of the outermost layer. A polypropylene resin layer, at least one polyamide resin layer as an intermediate layer, a heat sealable resin layer as an innermost layer, and a polyethylene resin having a density of 0.920 to 0.945 in an adjacent layer of the innermost layer The total film thickness is in the range of 60 μm to 250 μm, the thickness ratio of the outermost layer to the total film thickness is 2% to 20%, and the thickness ratio of the adjacent layer of the outermost layer is 10% to 60%. A coextruded multilayer film for deep drawing, characterized in that   A deep-drawn package using the film according to claim 1 and packaging the contents.