JP2016210063A - Lid material film for top sealing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lid material film for top sealing which has heat resistance durable against cooling with a microwave oven as a lid material for a polypropylene-based bottom material container, and has good heat sealability preventing occurrence of stringiness and the like, and easy openability preventing occurrence of a film residue in opening after heating.SOLUTION: There is provided a film which is a coextrusion film having a base material layer, a cohesive failure layer and a heat seal layer arranged in this order so as to be adjacent to each other, where the cohesive failure layer contains one or more selected from the group of a polypropylene homopolymer, a propylene-ethylene copolymer, and linear low-density polyethylene as a main component, the heat seal layer contains 50 mass% or more of a polypropylene resin having a melting point of 155°C or higher, a tensile modulus of 1,500 MPa or more and tensile elongation of 300% or less, and a thickness of the heat seal layer is 0.5 μm or more and 10 μm or less.SELECTED DRAWING: Figure 1

Description

  The technology of the present invention relates to a lid material for a gas replacement package top seal and a package using a plastic film having heat sealability, easy peel (easy opening) property, gas barrier property and antifogging property.

In recent years, the food industry has become active in reducing food waste loss as a means of reducing environmental impact, reducing costs, and effectively using resources.
Therefore, in terms of packaging materials, we have contributed to these efforts by providing packaging materials and packaging methods that extend the shelf life of foods. For example, oxygen inflow and miscellaneous bacterial growth that cause food degradation are suppressed. The means to do is utilized.

Heat sterilization in sealed packaging and sealed packaging in an aseptic room are performed as methods for suppressing oxygen inflow and miscellaneous bacteria growth, and vacuum packaging and gas replacement packaging with gas barrier packaging materials can be used to further enhance the effect. Is used.
The form is called a top seal, as shown in FIG. 1, in which a lid material film is fused and adhered to the edge of a resin container by heat sealing.

  In addition, in these food packaging, it is required that the food can be cooked in a microwave oven together with the container, so that a relatively inexpensive and heat-resistant polypropylene resin is used as the bottom material of the packaging container, As a result, the heat sealing material of the lid material is necessarily made of polypropylene resin.

  As a conventional polypropylene film, for example, in Patent Document 1, a crystalline propylene random copolymer is used for a heat seal layer, and a crystalline propylene random copolymer, polyethylene, and an olefin copolymer rubber are used for an intermediate layer. A crystalline propylene random copolymer is laminated on the base material layer using the composition. However, in the film of Patent Document 1, although good openability is obtained, there is a problem that poor appearance such as stringing occurs in which the resin melted by heat sealing stretches into a string and adheres to the package or the packaging machine.

  In Patent Document 2, a mixture of crystalline polypropylene and propylene / 1-butene random copolymer is used for the heat seal layer, and crystalline propylene is used for the base material layer. Enables sealing. However, in the film of Patent Document 2, although heat seal strength is obtained, it is difficult to open because there is no layer having an easy-opening function. The appearance defect called the film | membrane residue which remains like a film | membrane and the deformation | transformation of a container will generate | occur | produce.

For example, in patent document 3 and patent document 4, technical disclosure is made as a lid material for containers made of polypropylene.
In Patent Document 3, a polypropylene resin polymerized using a single-site catalyst having a melting point of 120 to 140 ° C. is used for the heat seal layer, and a linear low-density polyethylene resin and amorphous ethylene-α are used for the easy-open layer. A mixture of olefin copolymers is used.
Patent Document 4 describes that a heat-seal layer uses a low-melting-point polypropylene resin having a melting point of 105 to 155 ° C. as a main component, and a cohesive failure layer contains polyethylene as an additive to the polypropylene-based resin.
However, in these films, since the low melting point polypropylene resin of the heat seal layer tends to stretch, a film residue is generated at the time of opening, which makes it difficult to give an illusion that the appearance is poor or foreign substances are mixed into the consumer. As a result, there is a growing demand for improvements from food producers.

  As described above, the conventional polypropylene heat seal film has a problem in heat sealing as in Patent Document 1, or in Patent Documents 2 to 4 in which low temperature heat sealability is aimed at, a problem occurs in opening. Yes, it was unbearable to use a top seal lid for gas replacement packaging that can be used with microwave ovens.

JP-A-62-117741 JP-A-8-238733 JP 2005-288793 JP 2008-150541 A

  In view of the above situation, the object of the present invention is to provide a heat resistant material that can withstand microwave heating cooking as a lid for a polypropylene-based bottom material container. It is an object to provide a film having easy-opening properties in which no film residue is generated at the time of opening.

  As a result of intensive studies on the material of the heat seal layer and the layer structure of the entire film in order to solve the above problems, the present inventor has completed the following present invention.

  That is, the gist of the present invention is that in the coextruded film in which the layers are disposed adjacent to each other in the order of the base material layer, the cohesive failure layer, and the heat seal layer, the cohesive failure layer is a propylene homopolymer, propylene-ethylene copolymer. The heat seal layer is composed of 50 masses of polypropylene resin having a melting point of 155 ° C. or higher, a tensile elastic modulus of 1500 MPa or higher, and a tensile elongation of 300% or lower. %, And the heat seal layer thickness is 0.5 μm or more and 10 μm or less.

  Since the film of the present invention has good heat sealability with respect to a polypropylene-based bottom material container, it can be used as a top-sealing lid material in hermetic packaging and is useful for extending the expiry date of food. Moreover, since it has heat resistance, cooking by heating in a microwave oven is also possible. Furthermore, since a film-like film does not remain at the time of opening, it can be easily opened without causing the consumer to misunderstand it as a foreign object.

FIG. 4 illustrates a cross section of a gas replacement (gas pack) tray package.

  The film of the present invention comprises a heat seal layer, a cohesive failure layer that expresses an easy peel function, and a base material layer that holds them, and each layer will be described below.

<Base material layer>
The film of the present invention is not limited to the composition of the base material layer, but since the adhesiveness with the cohesive failure layer that expresses an easy peel (easy-opening) function is important, a polypropylene homopolymer that easily secures adhesive strength ( Homo PP), polypropylene random copolymer (random PP), and linear low density polyethylene (LLDPE) are preferably used. Among these, homo PP and random PP are preferable from the viewpoint of heat resistance, rigidity, and adhesiveness to the fracture layer.

The film of the present invention may be composed of a resin layer having various functions on the outside of the base material layer. For example, polyamide, saponified ethylene vinyl acetate copolymer (EVOH), polyethylene terephthalate (PET), olefin-based film Co-extrusion combined with an adhesive resin or the like, or composite with a stretched PET film, stretched nylon film, stretched polypropylene film or the like is possible.
Since the gas barrier property of the packaging material contributes to the extension of the food shelf life by vacuum packaging and gas replacement packaging, nylon 6, poly (metaxylylene adipamide), which has gas barrier properties outside the base material layer, It is effective to arrange a layer made of EVOH.

<Cohesive failure layer>
The film of the present invention has a cohesive failure layer constituted by mixing two or more kinds of mutually incompatible polyolefin-based resins, and can be easily opened by causing cohesive failure inside this layer at the time of opening.

The main component of the cohesive failure layer is preferably a polypropylene resin or a polyethylene resin in order to ensure coextrusion adhesion with the adjacent layer, and a propylene homopolymer, propylene-ethylene copolymer, linear low One or more selected from the group of density polyethylene (LLDPE) is used.
For the subcomponent, select one or more resins that have low compatibility with the main component and can be dispersed uniformly, and obtain a cohesive failure layer by blending two or more resins together with the main component and subcomponent. Is preferred.
For example, when the main component is a propylene homopolymer or propylene-ethylene copolymer, the subcomponent is preferably low density polyethylene (LDPE), ethylene-vinyl acetate copolymer (EVA), polybutene (PB), or the like. When the main component is LLDPE, the subcomponent is preferably PB, polystyrene (PS) or the like.
Among these, a combination of a propylene-ethylene copolymer as a main component and LDPE as a subcomponent is desirable in terms of achieving both stable opening and interlayer adhesion strength.

Regarding the mixing ratio of the main component and the subcomponent, the lower limit of the main component is 50% by mass or more, preferably 55% by mass or more, and the upper limit is less than 80% by mass, preferably less than 75% by mass, more preferably less than 70% by mass. It is. The lower limit of the subcomponent is 20% by mass or more, preferably 25% by mass or more, more preferably 30% by mass or more, and the upper limit is less than 50% by mass, preferably 45% by mass.
By adjusting the mixing ratio to the above range, it is possible to maintain good heat sealability and obtain an appropriate easy peel strength.

  The thickness of the cohesive failure layer is desirably thin, and the upper limit is preferably 15 μm or less, more preferably 12 μm or less, and even more preferably 10 μm or less. By setting the upper limit to 15 μm or less, it is possible to maintain good transparency and openability. The lower limit is 3 μm or more, and preferably mixed film formability is obtained.

  The easy peel strength is 23 ° C., the lower limit is 4.0 N / 15 mm width or more, preferably 6.0 N / 15 mm width or more, more preferably 8.0 N / 15 mm width or more, and the upper limit is 15.0 N / 15 mm width. Hereinafter, it is preferably 13.0 N / 15 mm width or less, more preferably 12.0 N / 15 mm width or less.

<Heat seal layer>
The heat seal layer of the film of the present invention is disposed on the surface of the inner layer of the film adjacent to the cohesive failure layer, and has a hot melt bonding function for sealing the polypropylene resin container (bottom material). Further, the heat seal layer can alleviate light scattering due to the fine irregularities of the cohesive failure layer, and improve the transparency of the entire film. Furthermore, the heat seal layer of the heat-sealed portion with the peripheral edge portion of the container breaks and peels from the lid material film at the time of opening, and remains on the container side, thereby assisting the expression of the easy peel function.

  The heat seal layer of the film of the present invention is constituted by containing 50% by mass or more of a polypropylene resin having a melting point of 155 ° C. or higher, a tensile elastic modulus of 1500 MPa or higher, and a tensile elongation of 300% or lower.

The melting point of the polypropylene resin contained in the heat seal layer of the film of the present invention by 50% by mass or more is 155 ° C. or more, and preferably 160 ° C. or more. The upper limit of the melting point of the polypropylene resin is generally about 165 ° C.
As a polypropylene resin used for heat sealing, a propylene random copolymer obtained by copolymerizing propylene with ethylene, butene or the like as a main component is usually widely used because the heat sealing processing temperature can be set low. In the film of the present invention, in comparison with them, a polypropylene resin having a high melting point range is used to achieve a good balance with easy opening.

  The lower limit of the tensile modulus of the polypropylene resin contained in the heat seal layer by 50% by mass or more is 1500 MPa or more, and preferably 1650 MPa or more. The upper limit is generally about 1800 MPa.

  The upper limit of the tensile elongation of the polypropylene resin contained in the heat seal layer by 50% by mass or more is 300% or less, preferably 250% or less, and more preferably 200% or less. The lower limit is 100% or more, and more preferably 125% or more.

If the physical properties of the polypropylene resin of the heat seal layer are outside the above range, the heat seal layer will be stretched at the time of opening, preventing easy peel properties and deteriorating the appearance and usability after opening. On the contrary, if the physical property of the homo PP is within the above range, the expansion of the heat seal layer at the time of opening is suppressed, and the heat seal layer is beautifully broken and peeled off from the lid material film and remains on the container side.
Examples of the polypropylene resin satisfying such a melting point, tensile modulus, and tensile elongation include propylene homopolymers and propylene block copolymers obtained by copolymerization of propylene, ethylene, and rubber component monomers. Propylene homopolymer can be preferably used.

The other components constituting the heat seal layer are not particularly limited, but are compatible with the polypropylene resin as the main component contained in the heat seal layer in an amount of 50% by mass or more, from the point of increasing the seal adhesion of the film. A polypropylene resin or polybutene resin having a melting point of 150 ° C. or lower is preferred.
The melting point is more preferably 130 ° C. or less, still more preferably 100 ° C. or less.
As the propylene resin, for example, a propylene-α-olefin random copolymer, a propylene homopolymer, or an elastomer obtained by modifying a propylene random copolymer can be suitably used. Although an alpha olefin is not limited, For example, ethylene and 1-butene can be mentioned.

The mixing ratio of the polypropylene resin (main component) and the other component (subcomponent) having a melting point of 155 ° C. or higher, a tensile elastic modulus of 1500 MPa or higher and a tensile elongation of 300% or lower, constituting the heat seal layer, is the lower limit of the main component 50 mass% or more, preferably 60 mass% or more, and the upper limit is less than 90 mass%, preferably less than 80 mass%. The lower limit of the subcomponent is 10% by mass or more, preferably 20% by mass or more, and the upper limit is less than 50% by mass, preferably less than 40% by mass.
By adjusting the mixing ratio to the above range, sufficient heat sealability with the bottom material container is expressed, and the easy peel function is not hindered.

  In addition, a crystal nucleating agent for polypropylene resin may be added to the heat seal layer, thereby improving the transparency, further improving the elastic modulus and decreasing the elongation, and obtaining a better opening property. .

The lower limit of the thickness of the heat seal layer is 0.5 μm or more, preferably 1.0 μm or more, more preferably 1.5 μm or more, and the upper limit is 10 μm or less, preferably 5 μm or less, more preferably 3 μm or less. It is.
When the heat seal layer is thicker than 10 μm, film residue is likely to occur even when a polypropylene resin having a melting point of 155 ° C. or higher, a tensile elastic modulus of 1500 MPa or higher, and a tensile elongation of 300% or lower is used.

  Since the film of the present invention is used as a lid for packaging that seals food, the food is put into a container by adding a food antifogging agent to one or more of the base material layer and the heat seal layer. It becomes possible to suppress fogging due to water droplets adhering to the inner surface of the lid member after being accommodated. Examples of the antifogging agent for food include polyglycerin fatty acid fatty acid esters, glycerin fatty acid esters, ethylene oxide adducts, sorbitan fatty acid esters and the like.

<Layer structure>
The layer structure of the film of the present invention is not particularly limited as long as it has at least one resin layer serving as a base material layer as an outer layer, a cohesive failure layer as an intermediate layer, and a heat seal layer as an inner layer.

  For example, a random PP layer (A), a cohesive failure layer (B), a homo PP layer (C), an LLDPE layer (D), a polyamide layer (E), an EVOH layer (F), and an adhesive resin layer (G) In this case, the following layer structure can be formed. Among them, preferred layer configurations are the following (1), (2), (4), (5), (7) or (8), and particularly preferred layer configurations are (1), (4) and (5). is there.

(1) A / B / C
(2) C / B / C
(3) D / B / C
(4) E / G / A / B / C
(5) E / G / C / B / C
(6) E / G / D / B / C
(7) F / E / G / A / B / C
(8) F / E / G / C / B / C
(9) F / E / G / D / B / C

Examples of the present invention will be described below, but the present invention is not limited thereto.
In Examples 1 to 3 and Comparative Examples 1 to 4, films having the layer structure described in each example and Table 1 were prepared by a coextrusion T-die method. In each example and the layer configuration notation in Table 1, the layer order and thickness are described from the outer layer side.
In Example 4, a film produced by a co-extrusion T-die method was produced by combining with a stretched PET film by a dry laminating method.

The following abbreviations were used to indicate the layer composition of the film in each example.
The melting point of each resin was measured according to JIS K 7121, and the tensile modulus and tensile elongation were measured according to JIS K 7161, 7162.

Ny; nylon 6
MXNy; Poly (metaxylylene diadipamide)
EVOH; Ethylene-vinyl acetate copolymer saponified product

h-PP1: Propylene homopolymer, melting point 160 ° C., tensile elastic modulus 1700 MPa, tensile elongation 100%
h-PP2: Propylene homopolymer, melting point 163 ° C., tensile modulus 1800 MPa, tensile elongation 500%
r-PP1: Propylene random copolymer, melting point 145 ° C., tensile elastic modulus 1000 MPa, tensile elongation 500%
LL1; linear low density polyethylene

EP1; cohesive failure layer (main component: propylene homopolymer, subcomponent: ethylene vinyl acetate copolymer, mixing mass% ratio 65:35)
EP2; cohesive failure layer (main component: propylene-ethylene random copolymer, accessory component: low density polyethylene, mixing mass% ratio 65:35)
EP3; cohesive failure layer (main component: linear low density polyethylene, accessory component: polybutene, mixing mass% ratio 65:35)

AD; Polypropylene adhesive resin Antifogging agent; Polyglycerin fatty acid ester TPO; Propylene thermoplastic elastomer nucleating agent; Crystal nucleating agent for polypropylene resin

In addition, when adding an antifogging agent, it formed using the masterbatch which mix | blended and kneaded 0.03 mass% of antifogging agents with respect to resin which comprises a layer.
When adding a crystal nucleating agent, 2 mass% was added with respect to resin which comprises a layer.

<Example 1>
Ny (14 μm) / AD (10 μm) / r-PP1 (20 μm) / EP1 (3 μm) / h-PP1 + r-PP1 + antifogging agent (3 μm)
The mixing mass% ratio of h-PP1 and r-PP1 in the heat seal layer is 80:20.

<Example 2>
Ny (10 μm) / MXD (5 μm) / AD (8 μm) / h-PP1 + antifogging agent (12 μm) / EP2 (3 μm) / h-PP1 + r-PP1 + antifogging agent + nucleating agent (3 μm)
The mixing mass% ratio of h-PP1 and r-PP1 in the heat seal layer is 80:20.

<Example 3>
PP (15 μm) / AD (10 μm) / EVOH (5 μm) / AD (10 μm) / LL1 + antifogging (4 μm) / EP3 (3 μm) / h-PP1 + TPO (3 μm)
The mixing mass% ratio of h-PP1 and TPO in the heat seal layer is 90:10.

<Example 4>
Stretched PET film (12 μm) / Adhesive / EVOH (5 μm) / Ny (10 μm) / AD (10 μm) / r-PP1 (19 μm) / EP1 (3 μm) / h-PP1 + nucleating agent + antifogging agent (3 μm)

<Comparative Example 1>
Ny (14 μm) / AD (10 μm) / r-PP1 (20 μm) / EP1 (3 μm) / h-PP2 + antifogging agent (3 μm)

<Comparative example 2>
Ny (14 μm) / AD (10 μm) / r-PP1 (20 μm) / EP2 (3 μm) / r-PP1 + TPO (3 μm)

<Comparative Example 3>
Ny (14 μm) / AD (10 μm) / r-PP1 + antifogging agent (20 μm) / EP3 (3 μm) / LL1 + antifogging agent (3 μm)

<Comparative example 4>
Ny (14 μm) / AD (10 μm) / r-PP1 + antifogging agent (8 μm) / EP1 (3 μm) / h-PP1 + nucleating agent (15 μm)

<Evaluation method>
The film obtained in each example was evaluated as follows and summarized in Table 2.

<Easy peel strength>
The film obtained in each example was measured for peel strength using a tensile tester under conditions of a temperature of 23 ° C. and a peel rate of 200 mm / min.

<Easy peelability of top seal packaging>
The film obtained in each example was heat-sealed on the tray under the conditions of a top seal width of 3 mm and a seal temperature of 145 ° C. using a multi-back gas displacement tray sealer machine. A tray formed using a coextruded sheet having a PP (490 μm) / EVOH (20 μm) / PP (490 μm) structure was used.
Thereafter, 100 pieces of each test piece were manually peeled off and evaluated according to the following criteria from the appearance observation.
X: Appearance defects that can be easily found by visual inspection occur (elongation of heat seal layer is 1 mm or more and generation distance range is 10 mm or more)
△; Appearance defects caused by heat seal layer elongation that is difficult to notice visually (heat seal layer elongation is less than 1 mm and generation distance range is less than 10 mm)
○: Good appearance after peeling

As shown in Table 2, the easy peel strength of each example was suitable for practical use, but a great difference was observed in the peeled state.
In Examples 1 to 4, there was no occurrence of x evaluation, and the evaluation was good with 90% or more.
In Comparative Examples 1 and 2, since a polypropylene resin having a high elongation rate was used for the heat seal layer, it was easy to stretch, and an evaluation of x was generated. About half of the defects including Δ evaluation were observed. In Comparative Example 3, LLDPE having a lower breaking strength than polypropylene resin was used for the heat seal layer, and x evaluation did not occur, but Δ evaluation occurred 30% or more. In Comparative Example 4, the heat seal layer was as thick as 15 μm, and 90% or more was defective.

  The film of the present invention seals the heat-resistant polypropylene container with sufficient strength and seals the food to prevent contamination, and can be easily and cleanly opened after heating in a microwave oven. It can be suitably used as a top seal cover material for a gas replacement package. And since the film of this invention is easy to provide a gas barrier function, it can contribute to the prolongation of the best-before date of food, and the reduction of food waste.

DESCRIPTION OF SYMBOLS 1; Lid material film 2; Resin tray 3; Seal adhesion part of resin tray and lid material film 4; Contents, such as fresh food 5; Inert gas

Claims (3)

  In the coextruded film in which the layers are arranged adjacent to each other in the order of the base material layer, the cohesive failure layer, and the heat seal layer, the cohesive failure layer is composed of a propylene homopolymer, a propylene-ethylene copolymer, and a linear low density polyethylene. The heat seal layer is composed of 50% by mass or more of a polypropylene resin having a melting point of 155 ° C. or more, a tensile elastic modulus of 1500 MPa or more, and a tensile elongation of 300% or less. And a heat sealing layer thickness of 0.5 μm or more and 10 μm or less.   The top seal lid film according to claim 1, wherein the heat seal layer contains a propylene copolymer or a polybutene resin having a melting point of 150 ° C or lower in a range of 10% by mass to less than 50% by mass.   The packaging container produced using the film of Claim 1 or 2 for the top seal lid | cover material.

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