KR20210008466A - Multilayer film and packaging - Google Patents

Abstract

The surface layer (A) mainly composed of polypropylene resin, the intermediate layer (B) composed mainly of linear low-density polyethylene, the intermediate layer (C) and the heat seal layer (D) composed mainly of cyclic polyolefin resin are (A)/( A multilayer film laminated in the order of B)/(C)/(D), and a multilayer film in which the content of linear low density polyethylene in the resin component contained in the intermediate layer (B) is 65% by mass or more. In addition to impact properties and tearability, it is possible to realize suitable tear properties when exposed to a low temperature environment after being exposed to a high temperature and high humidity environment.

Description

Multilayer film and packaging

The present invention relates to a multilayer film used for packaging materials such as food and medical products, and more particularly, to a multilayer film capable of realizing a packaging material having good thermal properties.

As a packaging material for food and medical products, in addition to having good heat sealability and impact resistance from the viewpoint of protection of the contents, it is easy to take out the contents when in use, easy to open and easy to tear. ) Is required. As a film having good heat sealability, impact resistance, and tear resistance, for example, a layer containing a polyolefin resin having no cyclic structure as a main component and a layer containing a cyclic polyolefin resin as a main component are plural in a specific thickness ratio. A layered multilayer film is disclosed (see, for example, Patent Document 1). This multilayer film has an extremely good tear-opening property because it has both suitable heat sealability, impact resistance, and tear resistance, and is excellent in straight cut property at the time of tearing.

Japanese Unexamined Patent Publication No. 2015-089619

Depending on the intended use, the packaging material may be exposed to a high-temperature, high-humidity environment by sterilization of boiling after heat seal or the like, or may be exposed to a low-temperature environment by refrigeration or freezing in the subsequent distribution stage. Such a packaging material is required to have suitable heat properties even after being affected by various temperature changes.

The problem to be solved by the present invention is to provide a multilayer film having excellent heat sealability, impact resistance, and tear resistance, and excellent tearability in one direction even when exposed to a low temperature environment after being exposed to a high temperature and high humidity environment.

In the present invention, the surface layer (A) containing a polypropylene resin as a main component, an intermediate layer (B) containing a linear low-density polyethylene as a main component, an intermediate layer (C) and a heat seal layer (D) containing a cyclic polyolefin resin as a main component, ( A multilayer film laminated in the order of A)/(B)/(C)/(D), wherein the content of linear low density polyethylene in the resin component contained in the intermediate layer (B) is 65% by mass or more. To solve the task.

The multilayer film of the present invention has good heat sealability, impact resistance, tear resistance, and excellent tearing property in one direction even when exposed to a high temperature, high humidity environment or low temperature environment. It can be suitably applied to packaging purposes of food and medical supplies that are sterilized.

The multilayer film of the present invention includes a surface layer (A) containing a polypropylene resin as a main component, an intermediate layer (B) containing a linear low density polyethylene as a main component, an intermediate layer (C) and a heat seal layer (D) containing a cyclic polyolefin resin as a main component. This is a multilayer film laminated in the order of (A)/(B)/(C)/(D), and the content of linear low density polyethylene in the resin component contained in the intermediate layer (B) is 65% by mass or more. .

[Surface layer (A)]

The surface layer (A) of the multilayer film of the present invention is a layer containing a polypropylene resin as a main component. Examples of the polypropylene resin include a propylene homopolymer, a propylene-α-olefin random copolymer, such as a propylene-ethylene copolymer, a propylene-butene-1 copolymer, and a propylene-ethylene-butene-1 copolymer. And metallocene catalyst-based polypropylene. These may be used individually or in combination, respectively. When these polypropylene resins are used as the surface layer (A), the heat resistance of the film is improved. Further, in the case of using as a single substance, since this surface layer (A) becomes the surface layer of the packaging material, it can be used as a gloss packaging material.

Moreover, it is also preferable to use a propylene homopolymer and a propylene-ethylene random copolymer together as a resin used for the surface layer (A). The propylene homopolymer can expect improvement in heat resistance and rigidity, and the propylene-ethylene random copolymer can expect improvement in glossiness. By using these polypropylene resins together, it becomes easy to obtain a packaging material having heat resistance and gloss.

Further, these polypropylene resins have an MFR (230°C) of 0.5 to 30.0 g/10 minutes, a melting point of 110 to 165°C, and more preferably, an MFR (230°C) of 2.0 to 15.0 g/ It is 10 minutes and the melting point is 115 to 162°C. When the MFR and the melting point are within this range, the film-forming properties of the film are improved.

Examples of the other α-olefins include ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-heptene, 4-methyl-pentene-1,4-methyl-hexene-1, etc. These may be mentioned, and two or more of these may be copolymerized at the same time. As a copolymerization form, either random copolymerization or block copolymerization can be used.

Among these, it is preferable that it is a copolymer with ethylene. In addition, as the content rate of other α-olefins in the copolymer, 2 to 23 mol% is preferable, and more preferably 2.5 to 15 mol%.

The surface layer (A) contains the polypropylene resin as a main component, and other resins capable of coextrusion may be used in combination within a range that does not impair the effects of the present invention. In addition, "contained as a main component" specifically refers to that 70% by mass or more of the resin component used for the surface layer (A) is a polypropylene resin, and it is preferable that 80% by mass or more is a polypropylene resin, and 90 It is more preferable that the mass% or more is a polypropylene resin.

As resins other than the polypropylene resin used for the surface layer (A), various resins used for packaging films can be used, and among them, olefin resins such as ethylene resins can be preferably used. Ethylene resins include polyethylene resins such as ultra low density polyethylene (VLDPE), linear low density polyethylene (LLDPE), low density polyethylene (LDPE), linear medium density polyethylene (LMDPE), medium density polyethylene (MDPE), and ethylene-vinyl acetate copolymer. (EVA) or the like can be used.

When an olefin resin is used as a resin other than the propylene resin, the content thereof is preferably 30% by mass or less, more preferably 10% by mass or less, and 5% by mass in the resin component contained in the surface layer (A). It is more preferable that it is below.

In addition, a cyclic polyolefin resin may be used as the olefin resin, but the content of the cyclic polyolefin resin in the resin component contained in the surface layer (A) is preferably 10% by mass or less, more preferably 5% by mass or less. It is preferable, and it is also preferable not to use it substantially.

In the surface layer (A) used in the present invention, other resins other than the above may be used in combination. Examples of the other resin include thermoplastic elastomers such as polyethylene elastomer, polypropylene elastomer, butene elastomer; Ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl acrylate (EMA) copolymer, ethylene-ethyl acrylate-maleic anhydride copolymer (E-EA- MAH), ethylene-based copolymers such as ethylene-acrylic acid copolymer (EAA), and ethylene-methacrylic acid copolymer (EMAA); Moreover, an ionomer of an ethylene-acrylic acid copolymer, an ionomer of an ethylene-methacrylic acid copolymer, etc. can be illustrated.

In the case of using the other resin, the content is preferably 30% by mass or less in the resin component contained in the surface layer (A), more preferably 30% by mass or less, and 10% by mass or less. It is more preferable and it is still more preferable that it is 5 mass% or less.

In the surface layer (A), in addition to the resin component, various additives may be suitably used in combination. As the additive, for example, a lubricant, an anti-blocking agent, an ultraviolet absorber, a light stabilizer, an anti-static agent, an anti-fogging agent, and a coloring agent can be appropriately used. When using these additives, it is preferably used in an amount of 2 parts by mass or less, more preferably about 0.01 to 1 part by mass, based on 100 parts by mass of the resin component used in the surface layer (A).

In particular, in order to impart processing suitability during film forming and packaging suitability of the filling machine, the friction coefficient of the surface layer (A) is preferably 0.9 or less, especially 0.8 or less, so that a lubricant or an anti-blocking agent is appropriately added to the surface layer (A). It is also desirable to do it.

Since the thickness ratio of the surface layer (A) to the multilayer film is easy to obtain good heat properties, particularly excellent heat properties in one direction, suitable rigidity, heat resistance, packaging machine suitability, etc., the surface layer (A) to the total thickness of the multilayer film The thickness ratio of is preferably in the range of 10 to 40%, and particularly preferably in the range of 10 to 30%.

[Intermediate layer (B)]

The first intermediate layer (B) of the multilayer film of the present invention is a layer containing linear low-density polyethylene as a main component. By laminating an intermediate layer (B) containing a linear low-density polyethylene as a main component on the intermediate layer (C) containing a cyclic polyolefin resin as a main component, it has suitable impact resistance and can be used in one direction even after exposure to a high temperature, high humidity environment or low temperature environment. It is possible to realize a multilayer film having excellent tear properties. Since the density of the linear low-density polyethylene used for the intermediate layer (B) is easy to obtain good heat resistance and impact resistance, preferably 0.930 g/cm 3 or less, more preferably 0.925 g/cm 3 or less, more preferably 0.910 to 0.920 g/cm3. Further, the average density of the resin component in the layer of the intermediate layer (B) is preferably 0.930 g/cm 3 or less, and more preferably 0.915 to 0.930 g/cm 3.

The MFR of the linear low-density polyethylene is 0.1 to 20 g/10 minutes (190° C., 21.18 N), preferably 0.3 to 10 g/10 minutes (190° C., 21.18 N), more preferably 0.5 to 5 g/10 minutes (190° C., 21.18 N). °C, 21.18N). When the MFR is within this range, it is preferable from the viewpoint of obtaining good film-forming properties.

In the present invention, by making the content of the linear low-density polyethylene in the intermediate layer (B) 65% by mass or more in the resin component contained in the intermediate layer (B), suitable impact resistance, high temperature, high humidity environment, one direction even after exposure to a low temperature environment Can realize excellent tearing properties. The content is preferably 68% by mass or more in the resin component contained in the intermediate layer (B), more preferably 70% by mass or more, further preferably 75% by mass or more, and particularly preferably 80% by mass or more. Further, 100% by mass of the resin component contained in the intermediate layer (B) may be linear low-density polyethylene.

In the intermediate layer (B), other resins other than the linear low-density polyethylene may be used in combination as long as the effect of the present invention is not impaired. As other resin types that can be used in combination, for example, polyethylene resins other than the linear low-density polyethylene resins exemplified in the surface layer (A) and olefin resins such as polypropylene resins can be exemplified. Among them, high-density polyethylene is preferable because it is easy to improve rigidity and heat releasability. In the case of using an olefin resin as a resin other than the linear low-density polyethylene, the content is preferably 35% by mass or less, more preferably 30% by mass or less, and 20% by mass in the resin component contained in the intermediate layer (B). It is more preferable that it is below, and it is especially preferable that it is 10 mass% or less.

In addition, a cyclic polyolefin resin may be used as the olefin resin, but the content of the cyclic polyolefin resin in the resin component contained in the intermediate layer (B) is preferably 10% by mass or less, more preferably 5% by mass or less. It is preferable, and it is also preferable not to use it substantially.

In addition, in the intermediate layer (B), other resins other than the above may be used in combination, and examples of the other resins include thermoplastic elastomers, ethylene copolymers, ionomers, and the like exemplified in the surface layer (A). When using the said other resin, it is preferable to use the content in 35 mass% or less in the resin component contained in the intermediate layer (B), it is more preferable that it is 30 mass% or less, and it is more preferable that it is 20 mass% or less, It is particularly preferably 10% by mass or less.

In the intermediate layer (B), in addition to the resin component, various additives may be appropriately used in combination. As the additive, for example, a lubricant, an anti-blocking agent, an ultraviolet absorber, a light stabilizer, an anti-static agent, an anti-fogging agent, and a coloring agent can be appropriately used. When using these additives, it is preferably used in an amount of 2 parts by mass or less, more preferably about 0.01 to 1 part by mass, based on 100 parts by mass of the resin component used in the intermediate layer (B).

The thickness ratio of the intermediate layer (B) containing the polyethylene resin (b) as a main component to the multilayer film (I) is 30% or more from the viewpoint of directional releasability and other performance balance, particularly low temperature impact resistance. It is essential, and it is particularly preferably in the range of 40 to 65%.

[Intermediate layer (C)]

By containing a cyclic polyolefin resin in the second intermediate layer (C) of the multilayer film of the present invention, excellent tearability and straight cut property can be realized. Examples of the cyclic polyolefin resin include a norbornene polymer, a vinyl alicyclic hydrocarbon polymer, and a cyclic conjugated diene polymer. Among these, a norbornene-based polymer is preferable. In addition, as the norbornene-based polymer, a ring-opening polymer of a norbornene-based monomer (hereinafter referred to as ``COP''), a norbornene-based copolymer obtained by copolymerizing a norbornene-based monomer and an olefin such as ethylene (hereinafter referred to as ``COC'') ), etc. Further, hydrogenated substances of COP and COC are also particularly preferred. Further, the weight average molecular weight of the cyclic polyolefin-based resin is preferably 5,000 to 500,000, more preferably 7,000 to 300,000.

The norbornene-based polymer and the norbornene-based monomer used as a raw material are an alicyclic monomer having a norbornene ring. As such a norbornene-based monomer, for example, norbornene, tetracyclododecene, ethylidene norbornene, vinyl norbornene, ethylidene tetracyclododecene, dicyclopentadiene, dimethanotetrahydroflu Orene, phenyl norbornene, methoxycarbonyl norbornene, methoxycarbonyl tetracyclododecene, etc. are mentioned. These norbornene-based monomers may be used alone or in combination of two or more.

The norbornene-based copolymer is a copolymerization of an olefin copolymerizable with the norbornene-based monomer, and examples of such olefins are olefins having 2 to 20 carbon atoms such as ethylene, propylene and 1-butene. ; Cycloolefins such as cyclobutene, cyclopentene, and cyclohexene; Non-conjugated dienes, such as 1,4-hexadiene, etc. are mentioned.

The content of the cyclic polyolefin-based resin contained in the intermediate layer (C) is preferably 70% by mass or more, more preferably 80% by mass or more, and still more preferably 90% by mass or more in the resin component contained in the intermediate layer (C). . By setting the content of the cyclic polyolefin-based resin in the range, it becomes easy to realize suitable tear-off properties and straight cut properties without impairing impact resistance.

In addition, the cyclic polyolefin resin used in the intermediate layer (C) preferably has a glass transition temperature of 140°C or lower, more preferably 50 to 140°C, and still more preferably 70 to 120°C. By using the thing having the said glass transition temperature as a cyclic polyolefin resin, it becomes easy to obtain favorable heat resistance and rigidity, and it becomes easy to improve the waveband resistance against fall etc. In addition, it becomes easy to obtain good compatibility, and it becomes easy to suppress uneven appearance. The glass transition temperature (Tg) is a value obtained by measuring by DSC.

In addition, although cyclic polyolefin resins having different glass transition temperatures may be used in combination, 60% by mass or more is preferably a cyclic polyolefin resin having a glass transition point of 120°C or less from the viewpoints of extrusion suitability, cost, heat releasability, and the like.

The MFR of the cyclic polyolefin resin is 0.2 to 17 g/10 minutes (230°C, 21.18 N), preferably 3 to 15 g/10 minutes (230°C, 21.18 N), more preferably 5 to 13 g/10 minutes ( 230°C, 21.18N). When MFR is within this range, compatibility with linear low-density polyethylene is excellent, and excellent film-forming properties are obtained in various multilayer film-forming methods, which is preferable.

As a commercial item that can be used as the cyclic polyolefin-based resin used in the present invention, examples of the ring-opening polymer (COP) of a norbornene-based monomer include ``ZEONOR,'' manufactured by Nippon Xeon Corporation. As examples of the norbornene-based copolymer (COC), Mitsui Chemical Co., Ltd. "Apel", and Polyplastics Co., Ltd. "TOPAS", etc. are mentioned, for example.

As the resin component in the intermediate layer (C), it is also preferable to contain only the cyclic polyolefin resin, but other resins other than these resin components may be used in combination within the range not impairing the effects of the present invention. As other resin types that can be used in combination, for example, olefin resins having no cyclic structures other than cyclic polyolefin resins such as polyethylene resins and polypropylene resins exemplified in the surface layer (A) can be exemplified. I can. When using the olefin resin which does not have these cyclic structures, it is preferable to set it as 30 mass% or less in the resin component contained in the intermediate layer (C), it is more preferable to set it as 20 mass% or less, and 10 mass% or less It is more preferable to do it. Further, the lower limit is not particularly limited, but may be appropriately used in an amount of 1% by mass or more depending on the desired characteristics.

In the intermediate layer (C), in addition to the resin component, various additives may be appropriately used in combination. As the additive, for example, a lubricant, an anti-blocking agent, an ultraviolet absorber, a light stabilizer, an anti-static agent, an anti-fogging agent, and a coloring agent can be appropriately used. When using these additives, it is preferably used in an amount of 2 parts by mass or less, more preferably about 0.01 to 1 part by mass, based on 100 parts by mass of the resin component used in the intermediate layer (B).

In addition, as the thickness ratio of the intermediate layer (C) to the multilayer film, it is preferably 30% or less from the viewpoint of the cost surface and the film-forming property and the curling property of the film, and since the film-forming by the coextrusion lamination method described later is good, 5 It is preferably at least %.

[Heat seal layer (D)]

As the heat seal layer (D) using the multilayer film of the present invention, a heat seal layer used for various packaging films can be suitably used. Among them, since the resin layer (A), the intermediate layer (B), the intermediate layer (C) and the like are easily laminated, it is preferably a layer containing as a main component a polyolefin resin, especially a polyolefin resin having no cyclic structure. As the polyolefin-based resin, polyethylene-based resins and polypropylene-based resins exemplified in the surface layer (A) and the like can be preferably used.

Among them, from the viewpoint of strength, sealing property, and packaging machine suitability, polyethylene resin having a density of 0.916 to 0.935 g/cm 3 or polypropylene resin, a propylene-α-olefin random copolymer polymerized using a metallocene catalyst, is used. It is desirable to do. In particular, it is preferable to use a linear low-density polyethylene because it is easy to obtain a suitable sealing property without impairing the suitable straight cut property or the like. In addition, the above density range is preferable also from the suppression of adhesion of the film in the boil sterilization step.

The content of the polyolefin-based resin in the resin component contained in the heat seal layer (D) is preferably 70% by mass or more, more preferably 80% by mass or more, and still more preferably 90% by mass or more. Further, 100% by mass of the resin component contained in the heat seal layer (D) may be linear low density polyethylene.

In the intermediate layer (B), other resins other than the polyolefin-based resin may be used in combination as long as the effect of the present invention is not impaired. As the other resin, the thermoplastic elastomer or ethylene-based copolymer illustrated in the surface layer (A), An ionomer, etc. can be illustrated. In the case of using the other resin, the content is preferably 30% by mass or less in the resin component contained in the heat seal layer (D), more preferably 30% by mass or less, and 10% by mass or less. It is more preferable and it is more preferable that it is 5 mass% or less.

In the heat seal layer (D), in addition to the resin component, various additives may be appropriately used in combination. As the additive, for example, a lubricant, an anti-blocking agent, an ultraviolet absorber, a light stabilizer, an anti-static agent, an anti-fogging agent, and a coloring agent can be appropriately used. In the case of using these additives, it is preferably used in an amount of 2 parts by mass or less, more preferably about 0.01 to 1 part by mass, based on 100 parts by mass of the resin component used in the heat seal layer (D). In particular, in order to impart processability during film forming and packaging aptitude of the filling machine, the friction coefficient of the heat seal layer (D) is preferably 0.9 or less, especially 0.8 or less, so that the heat seal layer (D) includes a lubricant or an anti-blocking agent. It is also preferable to add appropriately.

In addition, especially in the case of packaging using a packaging machine alone, using a resin having a difference in melting point in the surface layer (A) of the multilayer film and the heat seal layer (D) can increase the temperature of the seal bar. , It is more preferable than the viewpoint of improving the seal strength, and specifically, it is preferable to make the melting point of the surface layer (A) higher than the melting point of the heat seal layer (D) by 10°C or more.

The thickness ratio of the heat seal layer (D) to the total thickness of the multilayer film is preferably 30% or less, more preferably 10 to 25%, since it is easy to obtain suitable heat properties and seal strength.

[Multilayer film]

In the multilayer film (I) of the present invention, the surface layer (A), the intermediate layer (B), the intermediate layer (C), and the heat seal layer (D) are in the order of (A)/(B)/(C)/(D). It is a multilayer film laminated with. The multilayer film of the present invention can achieve excellent heat sealability, impact resistance, and tear resistance, and excellent tearing properties in one direction even after exposure to a high temperature, high humidity environment or low temperature environment by the above configuration.

In the multilayer film (I) of the present invention, the thickness of the film is preferably 20 to 60 µm, more preferably 30 to 50 µm. When the thickness of the film is within this range, it becomes easy to obtain stable seal strength, packaging machine suitability, excellent pinhole resistance performance, tear-off performance, and the like.

In addition, the thickness of each layer is not particularly limited, but, for example, the thickness of the surface layer (A) is preferably 3 to 15 µm, and more preferably 5 to 12 µm. The thickness of the intermediate layer (B) is preferably 8 to 35 µm, more preferably 10 to 30 µm. The thickness of the intermediate layer (C) is preferably 1 to 15 µm, more preferably 2 to 10 µm. The thickness of the heat seal layer (D) is preferably 2 to 20 µm, more preferably 4 to 15 µm.

From the viewpoint of protection of the contents, the multilayer film of the present invention preferably has a seal strength of 5 N/15 mm or more, and more preferably 10 N/15 mm or more.

The haze of the multilayer film of the present invention is preferably 10% or less, and more preferably 8% or less, since the contents to be packaged are easily visually recognized. When the multilayer film of the present invention has such high transparency, it is easy to realize suitable packaging aptitude and suitable printing adhesion.

Although it does not specifically limit as a manufacturing method of the multilayer film (I) of this invention, For example, each resin or resin mixture used for a resin layer (A), an intermediate layer (B), an intermediate layer (C), and a seal layer (D) Are heated and melted in separate extruders, and laminated in the order of (A)/(B)/(C)/(D) in a molten state by a method such as a coextrusion multilayer die method or a feed block method, A coextrusion method in which a film is formed by inflation or a T-die chilled roll method or the like is mentioned. This coextrusion method is preferable because it is possible to relatively freely adjust the ratio of the thickness of each layer, and a multilayer film having excellent hygiene properties and excellent cost performance can be obtained. In addition, the polyethylene-based resin used in the intermediate layer (B) of the present invention has a large difference in softening point (melting point) from the high-density polyethylene or cyclic polyolefin-based resin used in other layers, so phase separation or gel may occur. have. In order to suppress the occurrence of such phase separation or gel, the T-die chilled roll method capable of performing melt extrusion at a relatively high temperature is preferable.

Since the multilayer film (I) of the present invention is obtained as a substantially non-stretched multilayer film by the above-described manufacturing method, secondary molding such as deep bridge molding by vacuum molding is also possible.

In addition, in order to improve adhesion to printing ink and lamination suitability in the case of using as a sealant film for lamination, it is preferable to perform a surface treatment on the resin layer (A). As such a surface treatment, for example, a corona treatment, a plasma treatment, a chromic acid treatment, a flame treatment, a hot air treatment, a surface oxidation treatment such as ozone/ultraviolet treatment, or a surface uneven treatment such as sand blasting may be mentioned. Is the corona treatment.

Examples of the packaging material made of the multilayer film of the present invention include a packaging stand and a packaging container used in applications such as food, pharmaceuticals, industrial parts, miscellaneous goods, and magazines.

In the packaging stand, the seal layer (D) of the multilayer film (I) of the present invention is used as a heat seal layer, and the seal layers (D) are overlapped to provide a heat seal, or a resin layer (A) and a seal layer (D) are overlapped to provide heat seal. It is preferable that it is a packaging stand formed by. For example, cut the two multilayer films into the size of a desired packaging stand, overlap them, heat seal three sides to make the target, fill the contents from one side without heat seal, and seal it with heat seal. By doing so, it can be used as a packaging stand. It is also possible to form a packaging stand by sealing the end of the roll-shaped film in a cylindrical shape by an automatic packaging machine and then sealing the top and bottom.

In addition, it is also possible to form a packaging stand/container by overlapping the sealing layer (D) with another heat-sealable film and performing heat sealing. At that time, as another film to be used, a film such as LDPE or EVA, which has relatively weak mechanical strength, can be used. In addition, a laminate film in which a film such as LDPE or EVA and a stretched film having relatively good tear property, for example, a biaxially stretched polyethylene terephthalate film (OPET), a biaxially stretched polypropylene film (OPP), etc., are bonded can also be used. .

The multilayer film (I) of the present invention can be used even if it is bonded to another substrate. The other substrate that can be used at this time is not particularly limited, but from the viewpoint of easily expressing the effects of the present invention, it is preferable to use a plastic substrate having high rigidity and high gloss, particularly a biaxially stretched resin film. In addition, in the case of applications that do not require transparency, aluminum foils may be used alone or in combination.

As a stretched resin film, from the viewpoint of tearability, for example, biaxially stretched polyester (PET), heatless biaxially stretched polyester (PET), biaxially stretched polypropylene (OPP), and biaxially stretched polyamide (PA). , Coextrusion biaxially stretched polypropylene with ethylene vinyl alcohol copolymer (EVOH) as the center layer, biaxially stretched ethylene vinyl alcohol copolymer (EVOH), and coextrusion biaxially stretched polypropylene coated with polyvinylidene chloride (PVDC). Can be lifted. These may be used alone or in combination.

As a lamination method in the case of laminating the base material to the multilayer film obtained by the above-described manufacturing method to form a laminate film, for example, dry lamination, wet lamination, non-solvent lamination, extrusion lamination, and the like.

Examples of the adhesive used in the dry lamination include polyether-polyurethane-based adhesives, polyester-polyurethane-based adhesives, and the like. Moreover, although various pressure-sensitive adhesives can be used, it is preferable to use a pressure-sensitive adhesive. As a pressure-sensitive adhesive, for example, polyisobutylene rubber, butyl rubber, a rubber-based adhesive in which a mixture thereof is dissolved in an organic solvent such as benzene, toluene, xylene, or hexane, or a biethylene acid rosin in these rubber-based adhesives Compounded tackifiers such as esters, terpene/phenol copolymers, terpene/indene copolymers, or 2-ethylhexyl acrylate/n-butyl acrylate copolymer, 2-ethylhexyl acrylate/ethyl acrylate/meth And acrylic pressure-sensitive adhesives obtained by dissolving an acrylic copolymer having a glass transition point of -20°C or less, such as a methyl acrylate copolymer, with an organic solvent.

In the packaging material using the multilayer film of the present invention, in order to weaken the initial tear strength and improve the openability, it is preferable to form an arbitrary tear start portion such as V notch, I notch, perforation, microporous, etc. .

Since the multilayer film of the present invention has a directional double tear property, as a packaging form, the upper part of the package is bound with a tape, a bracket, or a resin closure, etc. It is suitable for sewing packaging with a line fastener such as a chuck or zipper that has a sewing function in the direction perpendicular to the direction (TD).

(Example 1)

As resin components for forming the respective layers of the surface layer (A), the intermediate layer (B), the intermediate layer (C), and the heat seal layer (D), the following resins were used, respectively, to prepare a resin mixture for forming each layer. The resin mixture forming each layer was supplied to each of four extruders, and the average thickness of each layer of the laminated film formed from the surface layer (A)/intermediate layer (B)/intermediate layer (C)/heat seal layer (D) was 7 μm/15. It was coextruded from the T-die at an extrusion temperature of 250°C so as to be µm/3 µm/5 µm, and cooled with a water-cooled metal cooling roll at 40°C to form a laminated film having a total thickness of 30 µm. Next, corona discharge treatment was performed on the surface layer (A) of the obtained laminated film so that the wetting tension might be 40 mN/m, and a laminated film was obtained.

Surface layer (A): 50 parts by mass of propylene homopolymer (density 0.900 g/cm 3, MFR 8.0 g/10 min) (hereinafter referred to as PP (1)), and propylene-ethylene random copolymer (density 0.900 g/cm 3, MFR 8.0 g/10min) (hereinafter referred to as PP(2)) 50 parts by mass of a mixture.

Intermediate layer (B): 100 parts by mass of linear low-density polyethylene (density 0.918 g/cm 3, MFR 4.0 g/10 min) (hereinafter referred to as LLDPE (1)).

Intermediate layer (C): 100 parts by mass of norbornene-based copolymer (density 1.010 g/cm 3, MFR 7.0 g/10 min) (hereinafter referred to as COC (1)).

Heat seal layer (D): 100 parts by mass of linear low-density polyethylene (density 0.935/cm 3, MFR 5.0 g/10 min) (hereinafter referred to as LLDPE (2)).

(Example 2)

A laminated film was obtained in the same manner as in Example 1 except that the resin component of the resin mixture used for the intermediate layer (B) and the heat seal layer (D) was determined below.

Intermediate layer (B): A mixture of 80 parts by mass of LLDPE (1) and 20 parts by mass of high-density polyethylene (density 0.960 g/cm 3, MFR 8.0 g/10 min) (HDPE (1)).

Heat seal layer (D): 100 parts by mass of LLDPE (1).

(Example 3)

A laminated film was obtained in the same manner as in Example 2 except that the resin component of the resin mixture used for the intermediate layer (B) was determined below.

Intermediate layer (B): A mixture of 90 parts by mass of LLDPE (1) and 10 parts by mass of HDPE (1).

(Example 4)

A laminated film was obtained in the same manner as in Example 2 except that the resin component of the resin mixture used for the intermediate layer (B) was determined below.

Intermediate layer (B): 100 parts by mass of LLDPE (1).

(Example 5)

A laminated film was obtained in the same manner as in Example 4 except that the resin component of the resin mixture used for the intermediate layer (C) was determined below.

Intermediate layer (C): 100 parts by mass of norbornene-based copolymer (density 1.020 g/cm 3, MFR 8.0 g/10 min) (hereinafter referred to as COC(2)).

(Example 6)

A laminated film was obtained in the same manner as in Example 2 except that the resin component of the resin mixture used for the intermediate layer (B) was determined below.

Intermediate layer (B): 100 parts by mass of linear low density polyethylene (density 0.915 g/cm 3, MFR 3.0 g/10 min) (hereinafter referred to as LLDPE (3)).

(Example 7)

A laminated film was obtained in the same manner as in Example 5 except that the resin component of the resin mixture used for the surface layer (A) was determined below.

Surface layer (A): A mixture of 70 parts by mass of PP(1) and 30 parts by mass of PP(2).

(Example 8)

A laminated film was obtained in the same manner as in Example 4 except that the resin component of the resin mixture used for the surface layer (A) was determined below.

Surface layer (A): 50 parts by mass of PP(1) and 50 parts by mass of a propylene-α-olefin random copolymer (density 0.900 g/cm 3, MFR 7.0 g/10 min) (hereinafter referred to as PP(3)) mixture.

(Comparative Example 1)

A laminated film was obtained in the same manner as in Example 2 except that the resin component of the resin mixture used for the intermediate layer (B) was determined below.

Intermediate layer (B): A mixture of 65 parts by mass of LLDPE (1) and 35 parts by mass of HDPE (1).

(Comparative Example 2)

A laminated film was obtained in the same manner as in Example 5 except that the resin component of the resin mixture used for the intermediate layer (B) was determined below.

Intermediate layer (B): A mixture of 65 parts by mass of LLDPE (1) and 35 parts by mass of HDPE (1).

(Comparative Example 3)

A laminated film was obtained in the same manner as in Example 1 except that the resin component of the resin mixture used for the intermediate layer (B) was determined below.

Intermediate layer (B): A mixture of 65 parts by mass of LLDPE (1) and 35 parts by mass of HDPE (1).

[Visibility resistance]

The films obtained in Examples and Comparative Examples were unpacked under conditions of a center seal temperature of 160°C and an end seal temperature of 150°C with a vertical pillow stripping machine with the seal layer as the inner side, and then 180 mm in length x 150 mm in width, An umbilical cord sample having a seal width of 10 mm in each seal portion was obtained. The obtained umbilical cord sample was subjected to a heat treatment at 98° C. for 30 minutes using a boil sterilization device, and the presence or absence of a bandage of the umbilical cord sample after the heat treatment was visually evaluated. In addition, after the umbilical cord sample after the heat treatment was cooled to room temperature, the presence or absence of adhesion of the seal surface was visually evaluated.

○: No sticking to the bag or seal surface

×: There is adhesion of the bag or seal surface

[Transferentiality]

The films obtained in Examples and Comparative Examples were unbundled with a vertical peeling machine with the seal layer on the inside to obtain a 180 mm long x 150 mm wide umbilical cord sample. A 5 mm slit was put in the center position of the vertical seal portion of the resulting umbilical cord sample, and both sides of the slit were stretched to the longitudinal side so that the slit would widen, and opened so as to tear up to both transverses of the vertical seal surface of the umbilical cord sample. The difference in the distance between the tear position of both transverse portions when opened and the center position in the longitudinal direction of both transverse portions was measured, and the selective thermal properties in the transverse direction were evaluated. In addition, in the evaluation of heat, the umbilical cord sample before boil sterilization and the umbilical cord sample left to stand in a refrigerated environment for 4 hours after boil sterilization under the same conditions as in the above-described [Volume resistance] evaluation were evaluated. Three umbilical cord samples before boil sterilization and refrigerated umbilical cord samples after boil sterilization were each prepared, and their average value was taken as an evaluation result.

○: The difference between the center position and the torn position is less than 30 mm in both transverses

△: The difference between the center position and the torn position is between 30 mm or more and 40 mm or less in both transverses

×: One or more umbilical cord samples that are not torn to both transverse portions

[Impact resistance]

The films obtained in Examples and Comparative Examples were allowed to stand for 4 hours in a constant temperature chamber adjusted below 0°C. Then, using a tester Sangyo-made BU-302 type film impact tester, a 1.5-inch head was attached to the tip of the pendulum, and the impact strength by the film impact method was measured.

○: Impact strength of 0.90 (J) or more

△: Impact strength of 0.60 or more (J) to less than 0.90 (J)

X: Impact strength is less than 0.60 (J)

[Measurement of stiffness]

The films obtained in Examples and Comparative Examples were measured for a 1% tangential modulus (unit: MPa) at 23° C. using a Tensillon tensile tester [manufactured by A&D Co., Ltd.] according to ASTM D-882. . The measurement was performed in the extrusion direction (hereinafter referred to as "MD") and the film width direction (hereinafter referred to as "CD") during film production.

[Seal strength]

Using the films obtained in Examples and Comparative Examples, a test piece heat-sealed with a seal width of 10 mm was prepared under conditions of 150°C, 0.2 MPa, and 1 second, cut into a width of 15 mm, and the seal strength was measured with a tensile tester. did. The same evaluation was performed 3 times, and these average values were made into the evaluation result.

○: Heat seal strength of 5N/15㎜ or more

×: Heat seal strength is less than 5N/15mm

[Transparency]

The haze of the film obtained in Examples and Comparative Examples was measured using a haze meter (manufactured by Nihon Denshoku Kogyo Co., Ltd.) according to JIS K7105 (unit: %). Transparency was evaluated based on the following criteria.

○: Haze is less than 8%

×: Haze is 8% or more

[Surface friction coefficient]

Using the films obtained in Examples and Comparative Examples, according to ASTM-D1894, under 23°C and 50% RH, the coefficient of static friction between the surface layers (A) and the coefficient of static friction between the heat seal layers (D) were determined. It was measured by the slip tester method.

○: Static friction coefficient is less than 0.8

×: static friction coefficient of 0.8 or more

The results obtained above are shown in Tables 1 to 2.

[Table 1]

[Table 2]

As is clear from the above table, the laminated films of the present invention of Examples 1 to 8 can be boil sterilized, exhibit transverse heat resistance even after exposure to a high temperature, high humidity environment or low temperature environment, and have suitable impact resistance. On the other hand, in the laminated films of Comparative Examples 1 to 3, transverse heat resistance and favorable impact resistance in a low-temperature environment after heat treatment were not obtained.

Claims (8)

The surface layer (A) mainly composed of polypropylene resin, the intermediate layer (B) composed mainly of linear low-density polyethylene, the intermediate layer (C) and the heat seal layer (D) composed mainly of cyclic polyolefin resin are (A)/( A multilayer film laminated in the order of B)/(C)/(D), wherein the content of linear low density polyethylene in the resin component contained in the intermediate layer (B) is 65% by mass or more. The method of claim 1,
A multilayer film having a density of 0.925 g/cm 3 or less of linear low density polyethylene in the intermediate layer (B). The method according to claim 1 or 2,
A multilayer film having an average density of 0.930 g/cm 3 or less in the layer of the intermediate layer (B). The method according to any one of claims 1 to 3,
The heat seal layer (D) is a multilayer film mainly composed of linear low density polyethylene. The method of claim 4,
A multilayer film having a density of 0.916 g/cm 3 or more of linear low density polyethylene in the heat seal layer (D). The method according to any one of claims 1 to 5,
A multilayer film in which 60% by mass or more of the cyclic polyolefin resin contained in the intermediate layer (C) is a cyclic polyolefin resin having a glass transition temperature of 120°C or less. The method according to any one of claims 1 to 6,
A multilayer film having a total thickness of the multilayer film in the range of 20 to 60㎛. A packaging material using the multilayer film according to any one of claims 1 to 7.