JPH1076616A - Co-extruded composite film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a co-extruded composite film adapted to a composite film formed of a polyamide resin layer as a base material or particularly a retort packaging material having satisfactory pinholing resistance and a boiling deep drawing bottom material film having small curl occurrence. SOLUTION: The co-extruded composite film is obtained by laminating layers formed of a polypropylene resin layer (A), an ethylene-α-olefin copolymer resin layer (B) and a straight chain low-density polyethylene resin layer (C) on a base material of a polyamide resin layer, and laminating the layers in order of A, B and C from the base material side for a deep drawing bottom material and the layers in order of C, B and A from the base material side for a retort material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a multilayer film suitable for a packaging material used in the food packaging field. More specifically, the present invention relates to a co-extruded composite film suitable for a packaging material subjected to boil processing or a packaging material for retort food packaging in the field of deep drawing vacuum packaging of food.

[0002]

2. Description of the Related Art In recent years, packaging forms in the food field have been diversified due to the diversification of consumer preferences for food and the development of freezing and refrigeration distribution systems, and the packaging materials are required to have higher functions. . For example, as a retort packaging material in which food is filled into a deep-drawn bottom material, a lid material is sealed, and then retort treatment is performed under high-temperature and high-pressure conditions, polyethylene terephthalate (PET) having excellent heat resistance,
Aluminum, expanded polypropylene (OPP), 6-nylon (6-Ny), polyvinylidene chloride (PVdC)
Composite films obtained by laminating polypropylene (PP) as a seal layer on a substrate such as the above have been used. However, since these all use PP as a sealing layer,
The pinhole resistance, particularly the low-temperature pinhole resistance, was poor, and problems often occurred particularly in the packaging of solids.

On the other hand, it is known that the use of linear low-density polyethylene (LL) is effective in improving the low-temperature pinhole resistance. However, since LL has low heat resistance, it is not effective. When they are disposed in the outer layer, they cause blocking when they are retorted, and when they are disposed in the inner layer (seal layer), the sealing strength during the retort treatment is not sufficient. Further, LL has been considered to be extremely difficult to be incorporated into an inner layer having a layer structure, since the interlayer adhesion strength with PP is extremely low.

Further, as a boil packaging material for boiling a food package, polyamide resin (Ny) / adhesive resin (AD) / LL or the like has been used as a deep drawing bottom material, but the LL layer is sealed. In the case of a layer, there is a problem that the seal portion with the lid material easily curls after the boil treatment.

[0005]

SUMMARY OF THE INVENTION The present inventor has proposed that in a composite film based on a polyamide resin layer, a PP layer or a linear low-density polyethylene resin (L
As a result of intensive studies using the L) layer to provide a packaging material suitable for the purpose of use in the food field utilizing such properties as curl prevention and low-temperature pinhole resistance, a specific adhesive resin was formed between the PP layer and the LL layer. The present inventors have found that both layers can be firmly adhered to each other by interposing the layers, and arrived at the present invention.

[0006]

SUMMARY OF THE INVENTION The present invention provides a composite film having a polyamide resin layer as a base material, particularly a retort wrapping material having a good pinhole resistance, or a deep-drawing bottom material film for a boil having a small curl. The present invention provides a co-extruded composite film suitable for: a polypropylene resin layer (A), an ethylene-α-olefin copolymer resin layer (B) and a linear resin A layer composed of a low-density polyethylene-based resin layer (C) is laminated,
The present invention resides in a coextruded composite film in which the lamination order is ABC or CBA from the substrate side.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The polyamide resin constituting the substrate of the present invention has a function of imparting pinhole resistance, oxygen barrier properties, moldability for deep drawing, and the like. 6-nylon (6-Ny), called nylon, 6
6-nylon (66Ny), 6-66 nylon (6-6
MXN6 obtained by polycondensation of 6Ny), 12-nylon (12Ny), meta-xylylenediamine and adipic acid
Nylon (MXD6Ny) and blends of these can be used, and are appropriately selected from these depending on the purpose of use. For example, when deep drawing formability is required, it is preferable to use 6-Ny and 6-66Ny, and when high oxygen barrier properties are required, MX
D6Ny or a blend of MXD6Ny and 6Ny, or a saponified ethylene-vinyl acetate copolymer (EVOH) layer may be provided in addition to the polyamide resin layer. The polyamide resin layer may be a single layer made of these polyamide resins or a laminated layer according to the required quality.
Further, as the outer layer of the polyamide resin layer, another resin layer, for example, a layer of a polyethylene resin, a polypropylene resin, or the like may be laminated via an adhesive resin layer according to a desired use. By laminating a polyethylene resin layer and a polypropylene resin layer on the outer layer, the polyamide resin layer can be protected, and in particular, the pinhole resistance in a low temperature state is improved.

Although the total thickness of the composite film of the present invention varies depending on its use, it is generally 6 in the case of a retort packaging material.
0 to 300 μm, and about 80 to 300 μm in the case of a deep drawing bottom material film. The layer thickness of the polyamide resin in the composite film is usually 10 to 60% of the total film thickness,
Preferably, it is about 20 to 40%.

As the PP constituting the layer A of the present invention, any of propylene homopolymer, random copolymer, block copolymer and the like can be used, and it is appropriately selected according to the required characteristics of the purpose of use. For example, in a retort wrapping material, layer A is used as a sealing layer of the composite film of the present invention because of heat resistance, and a homopolymer,
Although block copolymers and the like can be used, sealing properties,
The melting point is 135 in terms of low-temperature pinhole resistance and interlayer adhesion with the ethylene-α-olefin copolymer resin layer (layer B).
It is preferred to use a random copolymer at ~ 150 ° C. In this case, the thickness of the PP layer is preferably as thin as possible in a range where the sealing strength can be exhibited, and is usually set to 40% or less, preferably 20% or less of the total thickness of the composite film.

[0010] When a deep drawing bottom material film for boiling is intended, the A layer made of PP forms an inner layer laminated on the base material layer. This is advantageous in that the effect of reducing the curl phenomenon is high.
However, the ethylene-α-olefin copolymer resin layer (B
When the interlaminar bond strength with the layer is not sufficiently obtained, it is preferable to use a random copolymer. In this case, it is desirable to arrange the PP layer thicker to secure rigidity. In a deep drawn bottom film, the layer thickness of PP is 25% of the total film thickness.
When the layer thickness is less than 25%, the rigidity is weakened, and the effect of curl improvement is not exhibited. On the other hand, when the thickness is more than 75%, the deep drawability deteriorates, which is not appropriate. .

The PP used in the present invention preferably has a melt index (MI: based on JIS K 7210) of 0.5 to 15 g / 10 min. FX4, FX6 and the like manufactured by Mitsubishi Chemical Corporation.

LL constituting C layer of composite film of the present invention
Examples thereof include polyethylene, a linear low-density copolymer of ethylene and another α-olefin, and its MI is usually in the range of 0.5 to 10 g / 10 minutes, and the specific gravity is 0.1.
94 or less, preferably 0.91 to 0.93. As the α-olefin copolymerized with ethylene,
Butene-1, hexene-1, 4-methylpentene-1,
Α-olefins having 4 or more carbon atoms, such as octene-1, may be mentioned, but a copolymer with octene-1 is preferred from the viewpoint of improving the low-temperature pinhole resistance or the interlayer adhesion strength with the B layer.

The layer thickness of the C layer formed from LL varies depending on the use of the composite film. However, in the case of a retort packaging material, in order to improve the low-temperature pinhole resistance of the film,
The thickness is preferably as large as possible, and is preferably at least 1/2 of the layer thickness of the PP layer serving as the seal layer.
It is 2 to 5 times, preferably 1.0 to 5 times. In the case of a deep drawing bottom material film, the sealing layer is selected in a range of usually 50% or less, preferably 20% or less of the total thickness of the composite film.

The ethylene-α-olefin copolymer resin constituting the layer B in the composite film of the present invention is provided for interposing the PP layer and the LL layer to firmly adhere the two layers,
As a result, in the retort film, the PP seal layer and L
The seal strength and the low-temperature pinhole resistance at the time of retort treatment of the L inner layer are compatible with each other, and in the deep drawn bottom material film, the sealing property and the curl prevention property by the LL seal layer and the PP inner layer are exhibited. Such an ethylene-α-olefin copolymer resin (hereinafter abbreviated as EAC) has a high α-olefin content, is low in crystallinity or amorphous, and has a specific gravity of 0.90 or less, preferably 0 or less. 0.88 or less, and an interlayer adhesion strength between the PP layer and the LL layer of 500 gf / 15
mm, and more preferably, a material that achieves a width of 1,000 gf / 15 mm is preferably used. This adhesive strength is 15mm
Using a tensile tester, a strip-shaped specimen
It is a value obtained by measuring the average load when peeling at 200 mm / min.

The EAC includes an ethylene-propylene copolymer resin and an ethylene-butene copolymer resin. In order to form a tight bonding layer between the PP layer and the LL layer, the ethylene-propylene copolymer resin is used. The polymer resin is more preferred because of its strong adhesive strength with the PP layer. In some cases, when sufficient adhesion cannot be achieved depending on the type of PP such as heat-resistant PP, the adhesion is improved by blending a suitable amount (up to 30% by weight) of polypropylene, preferably propylene random copolymer, with EAC. You can do it.

A polyamide resin layer as a base material and an inner layer (A
Or the C layer), a commonly used adhesive resin can be used, and examples thereof include a modified polyolefin resin such as polyethylene and polypropylene modified with an unsaturated carboxylic acid or its anhydride.

The composite film of the present invention can be produced by a co-extrusion method commonly used as a method for producing a multilayer film, and any method such as a T-die method and an inflation method can be applied.

The composite film of the present invention is useful as a packaging material in the field of foods, and the field of application is different depending on the order of layer construction. The composite film using PP as a seal layer can be applied to lids and bottom materials for deep drawing packaging by vacuum packaging, bags, pillows, and the like, but is particularly excellent for retort packaging materials. When used for deep drawing packaging lids, bags, pillows, etc. that do not involve thermoforming, dry stretching of a stretched product such as a printed polyethylene terephthalate (PET) film may be performed on this film if necessary. It is possible. Further, the composite film using LL as a seal layer is excellent as a bottom material for deep drawing. The lid material when this composite film is used as the bottom material for deep drawing is not particularly limited, but the non-stretched nylon film is less likely to shrink or deform when boiling, and if a similar component to the bottom material is used. Thus, a package excellent in curl phenomenon can be obtained.

[0019]

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

Example 1 6-Ny (trade name: Nohmitmit 1030: manufactured by Mitsubishi Chemical Corporation) as a base material, polypropylene resin (random copolymer type; trade name: FX4: manufactured by Mitsubishi Chemical Corporation) as a sealing layer (A) An ethylene copolymer (trade name: Toughmer PO) as an EAC adhesive layer (B).
680: Mitsui Petrochemical Co., Ltd.), ethylene-octene-1 copolymer resin (trade name: Moortec 0138) as inner layer (C)
N: Idemitsu Petrochemical Co., Ltd .; hereinafter abbreviated as LL-C8) and modified polyethylene resin (trade name NF505: Mitsui Petrochemical Co., Ltd .; hereinafter abbreviated as ADLL) as an adhesive layer between 6-Ny layer and C layer Using a co-extruder and a feed block, and the following five-layer five-layer film (total thickness:
100μ). The retort resistance and the low-temperature pinhole resistance of this film were measured, and the results are shown in Table 2. The methods for measuring and evaluating the retort resistance and the low-temperature pinhole resistance in this example and the following examples and comparative examples are as follows.

(1) Resistance to retort When hamburgers are vacuum-packaged using bags made by sealing three sides of each film, when a plurality of bags are retorted (120 ° C. × 30 minutes) in an autoclave, the bags are put together. Was observed to block. ：: no blocking at all and good workability ×: blocking occurs and workability is poor

(2) Low-temperature pinhole resistance Ten packages of the retort-treated package in the above (1) are packed in a cardboard box, and left standing at 0 ° C. for 24 hours.
From the height of m, the bottom was dropped 10 times. The results were evaluated as follows. ：: No pinholes were generated in all of the 10 packages. ×: Pinholes were generated even in one package.

Example 2 As substrates, 6-Ny and 6-66Ny (trade name: 2030:
Except for using Mitsubishi Chemical Co., Ltd., a composite film having the following layer structure was prepared in the same manner as in Example 1. Table 2 shows the results of measuring the retort resistance and the low-temperature pinhole resistance of this film.

Example 3 As substrates, 6-Ny and MXD6Ny (trade name: Lenny 600)
7: manufactured by Mitsubishi Gas Chemical Co., Ltd.), except that a composite film having the following layer constitution was prepared in the same manner as in Example 1. Table 2 shows the results of measuring the retort resistance and the low-temperature pinhole resistance of this film.

[0025] Example 4 seal layer (A) as a polypropylene resin (homopolymer type, trade name FL6CK: manufactured by Mitsubishi Chemical Corporation; hereinafter PP ₁
), An ethylene-butene-1 copolymer (trade name: Tuffmer A4085, manufactured by Mitsui Petrochemical Co., Ltd.) and a polypropylene resin (random copolymer type, trade name: FX4: Mitsubishi Chemical Corporation) as the EAC adhesive layer (B) Ltd., hereinafter PP ₂ as abbreviated) a mixed product (mixing weight ratio 85:15) with a reference, and, 6-Ny resin layer on the adhesive resin (trade name QF50
0: manufactured by Mitsui Petrochemical Corporation; hereinafter abbreviated as ADPP) of polypropylene resin layer (; random copolymer type tradename FX4: Mitsubishi Chemical Co., except for laminating hereinafter abbreviated as PP ₃₎ is carried out A composite film (total thickness: 100 μ) having the following layer constitution was prepared in the same manner as in Example 1. Table 2 shows the results of measuring the retort resistance and the low-temperature pinhole resistance of this film.

Example 5 A printed stretched PET film was dry-laminated on a composite film of the following five types and five layers prepared in the same manner as in Example 1 to prepare a film having the following structure. Table 2 shows the results of measuring the retort resistance and the low-temperature pinhole resistance of this film.

Comparative Examples 1 to 3 The same resins as those used in Example 1 were used.
A film having the layer constitution described in 1 was prepared. Table 2 shows the results of measuring the retort resistance and the low-temperature pinhole resistance of these films.

[0028]

[Table 1]

Comparative Example 4 According to the method of Example 1, a composite film having the following layer constitution was prepared. Table 2 shows the results of measuring the retort resistance and the low-temperature pinhole resistance of this film.

[0030]

[Table 2]

Example 6 A composite film having the following layer constitution and a total thickness of 150 μm was prepared in the same manner as in Example 1. The film was evaluated for (a) curl after boiling, (b) sealability, (c) boil resistance, and (d) gloss after molding, and the results are shown in Table-3. In this example and the following examples and comparative examples, (a) curl after boiling, (b) sealability,
Evaluation methods for (c) boil resistance and (d) gloss after molding are as follows.

(A) Curling after boiling Each film was subjected to deep drawing using each film, a hamburger was stored in the obtained bottom material, and the lid material was heat-sealed and vacuum-packaged.
The cover material is a stretched Ny film (25μ) and an LL film (5
0 μ) was dry-laminated as a seal layer. However, in Comparative Example 7, since the sealing layer of the bottom material was PP,
A dry-laminated PP film (50 μ) was used as the seal layer of the lid material. The package obtained by the above method was sterilized in boil (95 ° C. × 20 minutes) and then cooled, and it was observed whether the bottom material and the cover material had curls. ○: Curling hardly occurred and there was no practical problem ×: Curling occurred and there was a practical problem

(B) Sealing properties In the above (a), when the lid is heat-sealed, the sealing strength is sufficiently high even when the sealing temperature is 150 ° C. or less (○).
When the temperature was 150 ° C. or lower, those having poor seal strength and difficult to seal were evaluated as (x).

(C) Boil resistance In (a) above, no peeling was observed between the bottom material and the lid material by boiling sterilization (o), and when peeling was observed, (x).

(D) Gloss after forming The film having good gloss on the surface of the film after deep drawing in (a) above was rated as (）), and the one with reduced gloss by deep drawing was rated as (x).

Example 7 A composite film having the following layer constitution was prepared in the same manner as in Example 6. The LL-C6 layer is made of ethylene-
It is a layer formed from hexene-1 copolymer resin (trade name: TUF2032: manufactured by Nippon Unicar Co., Ltd.). Regarding this film, (a) curl after boiling, (b) sealability, (c)
The boil resistance and (d) the gloss after molding were evaluated, and the results are shown in Table 3.

Example 8 A composite film having the following layer constitution was prepared in the same manner as in Example 6. The EVOH layer is a layer formed from a saponified ethylene-vinyl acetate copolymer (saponification degree: 44 mol%; trade name: Ezpar ER-E105: manufactured by Kuraray Co., Ltd.). The film was evaluated for (a) curl after boiling, (b) sealability, (c) boil resistance, and (d) gloss after molding, and the results are shown in Table-3.

Comparative Example 5 A composite film having the following layer constitution was prepared in the same manner as in Example 6. Regarding this film, (a)
Curling after boiling, (b) sealability, (c) boil resistance and
(d) The gloss after molding was evaluated, and the results are shown in Table-3.

Comparative Examples 6 to 8 By the same method as in Example 6, composite films having the layer constitutions shown in Table 4 below were prepared. This film was evaluated for (a) curl after boil, (b) sealability, (c) boil resistance, and (d) gloss after molding, and the results are summarized in Table-3.

[0040]

[Table 3]

[0041]

[Table 4]

[0042]

According to the coextruded composite film of the present invention, the PP layer and the LL layer provided on the polyamide resin base material are made of EAC.
Since the layers are more firmly adhered to each other, the one in which the PP layer or the LL layer is laminated as a seal layer according to the desired use is excellent in hot seal strength and low-temperature pinhole resistance in the former, and in sealability and low temperature in the latter. All of them are extremely useful as food packaging materials because of their excellent curl prevention effect.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B29L 9:00

Claims (2)

[Claims] 1. A polypropylene resin layer (A), an ethylene-α-olefin copolymer resin layer (B) and a linear low-density polyethylene resin layer (C) as seal layers on a polyamide resin layer substrate. And a laminating order of CBA from the substrate side. 2. A polypropylene resin layer (A), an ethylene-α-olefin copolymer resin layer (B) and a linear low-density polyethylene resin layer (C) as a seal layer on a polyamide resin layer base material. The laminated | stacked layer which consists of these, and the lamination order is ABC from a base material side, The co-extruded composite film characterized by the above-mentioned.