TWI811346B - Multilayer films and packaging materials - Google Patents

Abstract

The object of the present invention is to provide a multi-layer film that has good heat sealability, impact resistance, and tearability, and can be torn in one direction even after being exposed to a high temperature and high humidity environment and then to a low temperature environment. The crackability is still excellent. The present invention is a multilayer film composed of a surface layer (A) containing polypropylene resin as the main component, an intermediate layer (B) containing linear low-density polyethylene as the main component, and a cyclic polyolefin resin as the main component. The main components of the middle layer (C) and the heat sealing layer (D) are laminated in the order (A)/(B)/(C)/(D). The resin contained in the middle layer (B) The content of linear low-density polyethylene in the composition is more than 65% by mass. This multi-layer film can achieve good heat sealability, impact resistance, and tearability, and can be exposed to high temperature and high humidity environments. Suitable tearability in low temperature environments.

Description

Multilayer films and packaging materials

The present invention relates to a multilayer film used as a packaging material for food, medical supplies, etc., and more specifically, to a multilayer film capable of realizing a packaging material having good tearability.

As packaging materials for food, medical supplies, etc., from the viewpoint of protecting the contents, it is required to have good heat sealing properties and impact resistance, as well as easy opening and tearing properties to easily remove the contents when used. As a film having good heat sealability, impact resistance, and tearability, for example, a multilayer film is disclosed in which multiple layers of polyolefin-based resin without a cyclic structure are laminated at a specific thickness ratio. A layer containing a cyclic polyolefin-based resin as a main component and a layer containing a cyclic polyolefin-based resin as a main component are formed (for example, see Patent Document 1). Due to this structure, the multilayer film has both suitable heat sealing properties, impact resistance, and easy tearing properties, and has excellent straight-line cutting properties when tearing, so it has extremely good tear-opening properties. [Prior technical literature] [Patent Document]

[Patent Document 1] Japanese Patent Application Publication No. 2015-089619

[Problem to be solved by the invention]

Packaging materials, depending on their use, may be exposed to high temperature and high humidity environments due to boiling and sterilization after heat sealing, or may be exposed to low temperature environments due to refrigeration or freezing in the subsequent logistics stage. For such packaging materials, it is sought to have appropriate rupture properties even after being affected by various temperature changes.

The problem to be solved by the present invention is to provide a multi-layer film that has good heat sealability, impact resistance, and tearability, and can withstand even after being exposed to a high temperature and high humidity environment and then to a low temperature environment. The one-way tearability is still excellent. [Means to solve problems]

The present invention is a multilayer film composed of a surface layer (A) containing polypropylene resin as the main component, an intermediate layer (B) containing linear low-density polyethylene as the main component, and a cyclic polyolefin resin as the main component. The main components of the middle layer (C) and the heat sealing layer (D) are laminated in the order (A)/(B)/(C)/(D). The resin contained in the middle layer (B) The content of linear low-density polyethylene in the composition is more than 65% by mass. This multi-layer film solves the above problems. [Effects of the invention]

The multi-layer film of the present invention has good heat sealing properties, impact resistance, and easy tearing properties, and it still has one-way stability even when exposed to temperature and humidity changes such as exposure to high temperature and high humidity environments or low temperature environments. It has excellent tearing properties, so it can be suitably used in the packaging of food and medical supplies that are boiled and sterilized after heat sealing.

The multilayer film of the present invention consists of a surface layer (A) containing polypropylene resin as its main component, an intermediate layer (B) containing linear low-density polyethylene as its main component, and a cyclic polyolefin resin as its main component. The intermediate layer (C) and the heat sealing layer (D) of the components are laminated in the order (A)/(B)/(C)/(D). The resin component contained in the intermediate layer (B) The content of linear low-density polyethylene in it is more than 65% by mass.

[Surface layer (A)] The surface layer (A) of the multilayer film of the present invention is a layer containing polypropylene resin as its main component. Examples of the polypropylene-based resin include propylene homopolymers and propylene-α-olefin random copolymers, such as propylene-ethylene copolymers, propylene-but-1-ene copolymers, and propylene-ethylene-butylene copolymers. -1-ene copolymer, metallocene catalyst polypropylene, etc. These may be used individually or in combination. When these polypropylene-based resins are used as the surface layer (A), the heat resistance of the film is improved. Furthermore, when used as a single substance, this surface layer (A) becomes the surface layer of the packaging material, so that it can be used as a packaging material with gloss.

Furthermore, as the resin used for the surface layer (A), it is also preferable to use a propylene homopolymer and a propylene-ethylene random copolymer in combination. Propylene homopolymer is expected to improve heat resistance and rigidity; propylene-ethylene random copolymer is expected to improve gloss. By using these polypropylene resins in combination, it is easier to obtain packaging materials with heat resistance and gloss.

Furthermore, these polypropylene-based resins preferably have an MFR (melt flow rate) (230°C) of 0.5 to 30.0 g/10 minutes and a melting point of 110 to 165°C. More preferably, the MFR (230°C) is 0.5 to 30.0 g/10 minutes. 2.0～15.0g/10 minutes, melting point is 115～162℃. If the MFR and 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, and 4-methyl-pent-1-ene. , 4-methyl-hex-1-ene, etc., or two or more of these may be copolymerized simultaneously. As the copolymerization form, any of random copolymerization and block copolymerization can be used.

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

The surface layer (A) contains the above-mentioned polypropylene-based resin as a main component. Other resins that can be co-extruded may be used together in the range that does not impair the effects of the present invention. In addition, "as the main component" specifically means that 70% by mass or more of the resin component used for the surface layer (A) is a polypropylene-based resin, and preferably 80% by mass or more is a polypropylene-based resin. More preferably, 90% by mass or more is polypropylene-based resin.

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

When an olefin-based resin is used as the resin other than the above-mentioned propylene-based resin, the content is preferably 30 mass% or less of the resin component contained in the surface layer (A), more preferably 10 mass% or less, and even more preferably 5% by mass or less.

In addition, although a cyclic polyolefin-based resin can also be used as the olefin-based resin, the content of the cyclic polyolefin-based resin in the resin component contained in the surface layer (A) is preferably 10 mass % or less, more preferably In order to set it at 5 mass % or less, it is better not to use it substantially.

In the surface layer (A) used in the present invention, other resins other than those mentioned above may be used together. Examples of the other resin include thermoplastic elastomers such as polyethylene elastomers, polypropylene elastomers, and butylene elastomers; ethylene-methyl methacrylate copolymer (EMMA), and ethylene-ethyl acrylate. Copolymer (EEA), ethylene-methyl acrylate (EMA) copolymer, ethylene-ethyl acrylate-maleic anhydride copolymer (E-EA-MAH), ethylene-acrylic acid copolymer (EAA), ethylene-methacrylic acid Ethylene copolymers such as copolymer (EMAA); furthermore, ionic polymers of ethylene-acrylic acid copolymers, ionic polymers of ethylene-methacrylic acid copolymers, etc.

When the other resins mentioned above are used, their content is preferably 30% by mass or less of the resin component contained in the surface layer (A), more preferably 10% by mass or less, and still more preferably 5% by mass or less.

In the surface layer (A), in addition to the above-mentioned resin components, various additives and the like may be appropriately used in combination. As additives, for example, lubricants, anti-blocking agents, ultraviolet absorbers, light stabilizers, antistatic agents, anti-fogging agents, colorants, etc. can be appropriately used. When using these additives, it is preferable that they are used in an amount of 2 parts by mass or less, and more preferably about 0.01 to 1 part by mass relative to 100 parts by mass of the resin component used in the surface layer (A).

In particular, in order to provide processing suitability during film formation and packaging suitability in filling machines, the friction coefficient of the surface layer (A) is 0.9 or less, and preferably 0.8 or less, so a lubricant or anti-adhesive agent is appropriately added to the surface layer. (A) is also good.

The thickness ratio of the surface layer (A) relative to the multilayer film is used as a surface layer from the viewpoint of easy acquisition of good cleavability, especially excellent cleavage in one direction, appropriate rigidity, heat resistance, packaging machine suitability, etc. The thickness ratio of layer (A) to the total thickness of the multilayer film is preferably in the range of 10 to 40%, 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 its main component. By laminating an intermediate layer (B) containing linear low-density polyethylene as a main component on an intermediate layer (C) containing a cyclic polyolefin-based resin as a main component, it is possible to achieve appropriate impact resistance and achieve A multi-layer film with excellent one-way tearability even after being exposed to high temperature, high humidity or low temperature environments. The density of the linear low-density polyethylene used in the intermediate layer (B) is preferably 0.930 g/cm ³ or less, and more preferably 0.925 g/cm from the viewpoint of easily obtaining good cracking properties and impact resistance. ³ or less, more preferably 0.910 to 0.920g/cm ³ . Moreover, the average density of the resin component in the intermediate layer (B) is preferably 0.930 g/cm ³ or less, more preferably 0.915 to 0.930 g/cm ³ .

The MFR of linear low-density polyethylene is 0.1~20g/10min (190℃, 21.18N), preferably 0.3~10g/10min (190℃, 21.18N), more preferably 0.5~5g/ 10 minutes (190℃, 21.18N). If the MFR is within this range, good film-forming properties can be obtained, which is preferable.

In the present invention, by setting the linear low-density polyethylene content in the intermediate layer (B) to 65% by mass or more of the resin component contained in the intermediate layer (B), appropriate impact resistance can be achieved even if Excellent one-way tearability after exposure to high temperature, high humidity or low temperature environments. The content is preferably 68% by mass or more of the resin component contained in the intermediate layer (B), more preferably 70% by mass or more, more preferably 75% by mass or more, and particularly preferably 80% by mass or more. . Moreover, 100% by mass of the resin component contained in the intermediate layer (B) may be linear low-density polyethylene.

In the intermediate layer (B), resins other than the above-mentioned linear low-density polyethylene may be used together in a range that does not impair the effects of the present invention. Examples of other types of resins that can be used together include polyethylene resins other than the linear low-density polyethylene resins exemplified for the surface layer (A), or olefin resins such as polypropylene resins. Among them, high-density polyethylene is preferred because it is easy to increase rigidity and crackability. When an olefin-based resin is used as the resin other than the linear low-density polyethylene, the content is preferably 35 mass% or less of the resin component contained in the intermediate layer (B), and more preferably 30 mass% below, more preferably 20% by mass or less, and particularly preferably 10% by mass or less.

In addition, although a cyclic polyolefin-based resin can also be used as the olefin-based resin, the content of the cyclic polyolefin-based resin in the resin component contained in the intermediate layer (B) is preferably 10 mass % or less, more preferably In order to set it at 5 mass % or less, it is better not to use it substantially.

In addition, in the intermediate layer (B), other resins other than the above may be used together. Examples of the other resins include the thermoplastic elastomers, ethylene copolymers, ionomers, etc. exemplified in the surface layer (A). . When using this other resin, its content is preferably 35% by mass or less of the resin component contained in the intermediate layer (B), more preferably 30% by mass or less, and more preferably 20% by mass. Below, it is particularly preferable that the content is 10% by mass or less.

In the intermediate layer (B), in addition to the above-mentioned resin components, various additives and the like may be appropriately used in combination. As additives, for example, lubricants, anti-blocking agents, ultraviolet absorbers, light stabilizers, antistatic agents, anti-fogging agents, colorants, etc. can be appropriately used. When using these additives, it is preferable that they are used in an amount of 2 parts by mass or less, and more preferably about 0.01 to 1 part by mass relative to 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 determined by balancing directional ease of opening and other properties, especially low temperature impact resistance. From a sexual perspective, it must be above 30%, and the best range is between 40 and 65%.

[Middle layer (C)] By containing the cyclic polyolefin-based resin in the second intermediate layer (C) of the multilayer film of the present invention, excellent tearability and linear cutting properties can be achieved. Examples of the cyclic polyolefin-based resin include norbornene-based polymers, ethylene alicyclic hydrocarbon polymers, cyclic conjugated diene polymers, and the like. Among these, norbornene-based polymers are preferred. Examples of the norbornene-based polymer include ring-opened polymers of norbornene-based monomers (hereinafter referred to as "COP"), and copolymerization of norbornene-based monomers and olefins such as ethylene. Norbornene-based copolymers (hereinafter referred to as "COC"), etc. In addition, hydrides of COP and COC are also particularly suitable. Furthermore, 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 raw materials are alicyclic monomers having a norbornene ring. Examples of such norbornene-based monomers include norbornene, tetracyclododecene, ethylene norbornene, vinylnorbornene, ethylenetetracyclododecene, and dicyclopentadiene. Alkene, dimethyl-bridged tetrahydrofuran, phenylnorbornene, methoxycarbonylnorbornene, methoxycarbonyltetracyclododecene, etc. These norbornene-based monomers may be used alone, or two or more types may be used in combination.

The norbornene-based copolymer is obtained by copolymerizing the norbornene-based monomer and a copolymerizable olefin. Examples of such olefin include: ethylene, propylene, 1-butene, etc. having 2 Alkenes with ~20 carbon atoms; cyclic olefins such as cyclobutene, cyclopentene, cyclohexene, etc.; non-conjugated dienes such as 1,4-hexadiene, etc.

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 more preferably 70% by mass or more of the resin components contained in the intermediate layer (C). Preferably, it is above 90% by mass. By setting the content of the cyclic polyolefin-based resin within this range, impact resistance is not impaired, and appropriate tearability and straight-line cutting properties become easy to achieve.

Furthermore, the glass transition temperature of the cyclic polyolefin-based resin used in the intermediate layer (C) is preferably 140°C or lower, more preferably 50 to 140°C, and even more preferably 70 to 120°C. By using this glass transition temperature as the cyclic polyolefin-based resin, it is easy to obtain good heat resistance and rigidity, and it is also easy to improve the bag breakage resistance against falling and the like. Furthermore, it is easy to obtain good mutual solubility and suppress uneven appearance. Glass transition temperature (Tg) is a value measured by DSC (differential scanning calorimetry).

Furthermore, cyclic polyolefin-based resins with different glass transition temperatures may be used together, but from the viewpoint of extrusion suitability, cost, ease of cracking, etc., it is preferable that 60% by mass or more of the resin has a glass transition point of 120 Cyclic polyolefin-based resin below ℃.

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

As for commercially available products that can be used as the cyclic polyolefin-based resin used in the present invention, examples of ring-opened polymers (COP) of norbornene-based monomers include: Nippon Zeon Co., Ltd. "ZEONOR (ZEONOR)" manufactured by Mitsui Chemicals Co., Ltd.; examples of the norbornene-based copolymer (COC) include "APEL" manufactured by Mitsui Chemicals Co., Ltd., "TOPAS (TOPAS)" manufactured by Polyplastics Co., Ltd., and the like.

As the resin component in the intermediate layer (C), it is preferable to contain only the above-mentioned cyclic polyolefin-based resin. However, other resins other than these resin components may be used together in a range that does not impair the effects of the present invention. Examples of other types of resins that can be used together include olefin resins without a cyclic structure other than cyclic polyolefin resins such as polyethylene resins and polypropylene resins illustrated for the surface layer (A). When using these olefin-based resins without a cyclic structure, the content is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 30% by mass or less of the resin component contained in the intermediate layer (C). Set below 10% by mass. There is no particular lower limit as long as the content is 1% by mass or more according to the desired characteristics.

In the intermediate layer (C), in addition to the above-mentioned resin components, various additives and the like may be appropriately used in combination. As additives, for example, lubricants, anti-blocking agents, ultraviolet absorbers, light stabilizers, antistatic agents, anti-fogging agents, colorants, etc. can be appropriately used. When using these additives, it is preferable that they are used in an amount of 2 parts by mass or less, and more preferably about 0.01 to 1 part by mass relative to 100 parts by mass of the resin component used in the intermediate layer (C).

In addition, the thickness ratio of the intermediate layer (C) to the multilayer film is preferably 30% or less from the viewpoint of cost, film-forming properties, or film curlability; in terms of lamination by co-extrusion described below, In order to achieve good film formation by the method, it is preferably more than 5%.

[Heat sealing layer (D)] As the heat sealing layer (D) used in the multilayer film of the present invention, heat sealing layers used in various packaging films can be appropriately used. Among them, from the viewpoint of easy lamination with the resin layer (A), the intermediate layer (B), the intermediate layer (C), etc., it is preferable to use a polyolefin-based resin as the main component, and in particular, it is preferable to use a polyolefin-based resin that does not have a cyclic shape. The structure is composed of layers of polyolefin resin as the main component. As the polyolefin-based resin, the polyethylene-based resin or polypropylene-based resin exemplified for the above-mentioned surface layer (A) and the like can be suitably used.

Among them, from the viewpoint of strength, sealing properties, and packaging machine suitability, it is preferable to use a polyethylene resin with a density of 0.916 to 0.935 g/cm ³ or a propylene resin polymerized using a metallocene catalyst. Polypropylene resin of α-olefin random copolymer. In particular, linear low-density polyethylene is preferably used since appropriate straight-cutting properties are not impaired and appropriate sealing properties are easily obtained. Furthermore, in terms of suppressing mutual adhesion of films during the boiling sterilization step, the above-mentioned density range is also preferable.

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

In the intermediate layer (B), resins other than the above-mentioned polyolefin-based resins may be used together in the range that does not impair the effects of the present invention. Examples of the other resins include the thermoplastic elastic resins exemplified in the surface layer (A). body or vinyl copolymer, ionic polymer, etc. When using this other resin, its content is preferably 30% by mass or less of the resin component contained in the heat sealing layer (D), more preferably 10% by mass or less, and even more preferably 5% by mass or less. %the following.

In the heat sealing layer (D), in addition to the above-mentioned resin components, various additives and the like may be appropriately used in combination. As additives, for example, lubricants, anti-blocking agents, ultraviolet absorbers, light stabilizers, antistatic agents, anti-fogging agents, colorants, etc. can be appropriately used. When using these additives, it is preferable that they are used in an amount of 2 parts by mass or less, and more preferably about 0.01 to 1 part by mass relative to 100 parts by mass of the resin component used in the heat sealing layer (D). In particular, in order to provide processing suitability during film formation and packaging suitability for filling machines, the friction coefficient of the heat seal layer (D) is 0.9 or less, and preferably 0.8 or less, so a lubricant or anti-adhesive agent is appropriately added to the heat seal layer (D). Seal layer (D) is also good.

Furthermore, especially when a single body is packaged using a packaging machine, from the viewpoint that the temperature of the sealing rod can be increased and the sealing strength can be improved, the surface layer (A) and heat sealing layer (D) of the multilayer film, It is preferable to use resins with different melting points. Specifically, it is preferable that the melting point of the surface layer (A) is 10° C. or more higher than the melting point of the heat seal layer (D).

The thickness ratio of the heat sealing layer (D) to the total thickness of the multilayer film is preferably 30% or less, more preferably 10 to 25%, in order to easily obtain appropriate crackability and sealing strength.

[Multilayer film] The multilayer film (I) of the present invention is the above-mentioned surface layer (A), intermediate layer (B), intermediate layer (C), and heat sealing layer (D), with (A)/(B)/(C)/ (D) is laminated in sequence to form a multilayer film. The multilayer film of the present invention is made of this structure and can achieve good heat sealing properties, impact resistance, and easy tearing properties, and can achieve excellent one-way orientation even after being exposed to high temperature and high humidity environments or low temperature environments. Tearability.

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. If the thickness of the film is within this range, it is easy to obtain stable sealing strength, packaging mechanical suitability, excellent pinhole resistance, easy tearing performance, etc.

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, 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 sealing layer (D) is preferably 2 to 20 μm, more preferably 4 to 15 μm.

From the perspective of protecting the contents, the sealing strength of the multilayer film of the present invention is preferably 5N/15mm or more, and more preferably 10N/15mm or more.

The haze of the multi-layer film of the present invention is preferably 10% or less, and more preferably 8% or less from the perspective of easy identification of packaged contents. When the multilayer film of the present invention has such high transparency, it is easy to achieve appropriate packaging suitability and appropriate printing adhesion.

Although the method for producing the multilayer film (I) of the present invention is not particularly limited, for example, a coextrusion method can be used, in which the resin layer (A), the intermediate layer (B), the intermediate layer (C), and the sealing layer ( D) Each resin or resin mixture used is heated and melted in its own extruder, and the molten state is (A)/(B)/ (C)/(D) are sequentially laminated, and then formed into a film shape by inflation or the T-die-cooling roll method. This co-extrusion method is preferable because it can relatively freely adjust the thickness ratio of each layer, so that a multi-layer film with excellent hygiene properties and excellent cost efficiency can be obtained. In addition, since the softening point (melting point) of the polyethylene resin used in the intermediate layer (B) of the present invention is greatly different from that of the high-density polyethylene or cyclic polyolefin resin used in other layers, it may There are cases where phase separation or colloidization occurs. In order to suppress the occurrence of such phase separation or colloid, a T-die-cooling roll method that can perform melt extrusion at a relatively high temperature is preferred.

Since the multilayer film (I) of the present invention can be obtained as a substantially non-stretched multilayer film by the above-mentioned manufacturing method, it can also be used for secondary forming such as deep drawing forming by vacuum forming.

Furthermore, in order to improve the adhesion with printing ink or the lamination suitability when used as a sealant film for lamination, it is preferable to perform surface treatment on the resin layer (A). Examples of such surface treatment include surface oxidation treatment such as corona treatment, plasma treatment, chromic acid treatment, flame treatment, hot air treatment, ozone-ultraviolet treatment, or surface roughening treatment such as sandblasting, but are preferably For corona treatment.

Examples of packaging materials composed of the multilayer film of the present invention include packaging bags and packaging containers used for food, pharmaceuticals, industrial parts, groceries, magazines, and the like.

This packaging bag is preferably made by using the sealing layer (D) of the multilayer film (I) of the present invention as a heat sealing layer, overlapping the sealing layers (D) with each other and heat sealing, or by laminating the resin layer (A) and The sealing layer (D) is formed by heat sealing. For example, two pieces of the multilayer film can be cut into a desired packaging bag size, overlapped and heat-sealed on three sides to form a bag shape, and then filled with the content from one side that has not yet been heat-sealed and heat-sealed to form a packaging bag. use. In addition, a packaging bag can also be formed by using an automatic packaging machine to form a roll-shaped film into a cylindrical shape, sealing the ends, and then sealing the top and bottom.

In addition, a packaging bag or container can also be formed by overlapping the sealing layer (D) and other heat-sealable films and heat-sealing them. In this case, as other films used, films such as LDPE and EVA, which have relatively weak mechanical strength, can be used. In addition, you can also use films laminated with LDPE, EVA, etc., and stretch films with relatively good tearability, such as biaxially stretched polyethylene terephthalate film (OPET), biaxially stretched polypropylene film ( Laminated film made of OPP), etc.

The multilayer film (I) of the present invention can also be used in conjunction with other substrates. Although there are no particular limitations on other base materials that can be used at this time, from the viewpoint of easily exhibiting the effects of the present invention, it is preferable to use a plastic base material with high rigidity and high gloss, especially a biaxially stretched plastic base material. resin film. In addition, when transparency is not required, aluminum foils can be used alone or in combination.

Examples of the stretched resin film include biaxially stretched polyester (PET), easily tearable biaxially stretched polyester (PET), and biaxially stretched polypropylene from the viewpoint of easy tearability. (OPP), biaxially stretched polyamide (PA), co-extruded biaxially stretched polypropylene with ethylene-vinyl alcohol copolymer (EVOH) as the central layer, biaxially stretched ethylene-vinyl alcohol copolymer (EVOH) ), co-extruded biaxially stretched polypropylene coated with polyvinylidene chloride (PVDC), etc. These can be used individually or in combination.

Examples of the lamination method when the base material is laminated on the multilayer film obtained by the above-mentioned production method as a laminate film include dry lamination, wet lamination, solvent-free lamination, Methods such as extrusion and pressing.

Examples of the adhesive used for dry lamination include polyether-polyurethane adhesives, polyester-polyurethane adhesives, and the like. Moreover, although various adhesives can be used, it is preferable to use a pressure-sensitive adhesive. Examples of the pressure-sensitive adhesive include rubber-based adhesives in which polyisobutylene rubber, butyl rubber, and mixtures thereof are dissolved in organic solvents such as benzene, toluene, xylene, and hexane; or, These rubber adhesives are blended with adhesive agents such as abietic acid rosin ester, terpene-phenol copolymer, terpene-indene copolymer, etc.; or, an organic solvent is used to dissolve 2-ethylhexyl acrylate- Acrylic adhesives made from acrylic copolymers with a glass transition point below -20°C, such as n-butyl acrylate copolymer and 2-ethylhexyl acrylate-ethyl acrylate-methyl methacrylate copolymer.

In packaging materials using the multi-layer film of the present invention, in order to weaken the initial tear strength and improve the unsealability, it is preferable to form any tear initiation such as V-shaped cuts, I-shaped cuts, perforations, micropores, etc. in the sealing part. department.

Since the multilayer film of the present invention has directional tearability, it is suitable as a packaging form for wallets in which the upper part of the package is tied with a tape, metal parts, or resin fasteners. Packaging, or resealable packaging with linear fasteners such as chucks and zippers attached with resealability in the direction (TD) perpendicular to the machine direction of the film.

(Example 1) As the resin component forming each layer of the surface layer (A), the intermediate layer (B), the intermediate layer (C) and the heat sealing layer (D), the following resins were used to prepare the resins forming each layer. mixture. The resin mixture forming each layer is supplied to four extruders respectively, so that each layer of the laminated film is formed in the surface layer (A)/intermediate layer (B)/intermediate layer (C)/heat sealing layer (D) The average thickness was 7μm/15μm/3μm/5μm. The T-die was co-extruded at an extrusion temperature of 250°C and cooled by a water-cooled metal cooling roll at 40°C. A total thickness of 30μm was formed. Laminated films. Next, the surface layer (A) of the obtained laminated film was subjected to corona discharge treatment so that the wetting tension became 40 mN/m, thereby obtaining a laminated film. 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 50 parts by mass of propylene-ethylene random A mixture of copolymers (density 0.900 g/cm ³ , MFR 8.0 g/10 min) (hereinafter referred to as PP (2)). 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 sealing layer (D): 100 parts by mass of linear low-density polyethylene (density 0.935 g/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 components of the resin mixture used for the intermediate layer (B) and the heat sealing layer (D) were changed to the following components. 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 sealing 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 changed to the following components. 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 changed to the following components. 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 changed to the following components. 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 changed to the following components. 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 changed to the following components. 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 changed to the following components. Surface layer (A): 50 parts by mass of PP (1) and 50 parts by mass of 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 changed to the following components. 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 changed to the following components. 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 changed to the following components. Intermediate layer (B): a mixture of 65 parts by mass of LLDPE (1) and 35 parts by mass of HDPE (1).

[Boiling resistance] Using a longitudinal pillow-type bag making machine, the films obtained in the Examples and Comparative Examples were used to form bags with the sealing layer as the inner side and at a central sealing temperature of 160°C and an end sealing temperature of 150°C to obtain a length of 180 mm × width. 150mm and the sealing width of each sealing part is 10mm. The obtained bag-making samples were heated at 98°C for 30 minutes using a boiling sterilization device, and the bag-making samples after the heat treatment were visually evaluated for bag breakage. In addition, after the heat-treated bag-making sample was cooled to normal temperature, whether the sealing surfaces adhered to each other was visually evaluated. ○: No bag breakage or mutual adhesion of sealing surfaces ×: The bag is broken or the sealing surface is adhered to each other.

[Transverse fissure] Using a longitudinal pillow-type bag making machine, the films obtained in Examples and Comparative Examples were used to form bags with the sealing layer as the inner side, and a bag sample having a length of 180 mm and a width of 150 mm was obtained. Cut a 5 mm incision in the center of the longitudinal sealing portion of the obtained bag-making sample, stretch both sides of the incision toward the longitudinal side in a manner that expands the incision, and unseal until the bag-making sample is longitudinally sealed. until the two transverse ends of the surface are split. The difference in distance between the splitting positions of both transverse ends and the longitudinal center positions of both transverse ends at the time of opening was measured to evaluate the selective splitting properties in the transverse direction. In addition, the rupture properties were evaluated by evaluating bag-making samples before boiling sterilization and bag-making samples that were boiled and sterilized under the same conditions as the above [boiling resistance] evaluation and then left to stand in a refrigerated environment for 4 hours. Three bag-making samples before boiling sterilization and refrigerated bag-making samples after boiling sterilization were prepared respectively, and the average value was used as the evaluation result. ○: The difference between the center position and the split position is less than 30mm at both lateral ends. △: The difference between the center position and the split position is between 30mm and 40mm at both transverse ends. ×: There are more than 1 bag-making samples that are not split to both lateral ends. [Impact resistance] The films obtained in Examples and Comparative Examples were left to stand for 4 hours in a constant temperature chamber adjusted to 0°C. After that, a BU-302 Film Impact Tester manufactured by TESTER SANGYO was used to install a 1.5-inch hammer head on the front end of the pendulum to measure the impact strength obtained by the film impact method. ○: Impact strength is 0.90 (J) or more △: Impact strength is 0.60 or more (J) to less than 0.90 (J) ×: Impact strength is less than 0.60(J)

[Measurement of rigidity] The 1% tangent modulus (unit: MPa) of the films obtained in Examples and Comparative Examples at 23° C. was measured in accordance with ASTM D-882 using a TENSILON tensile testing machine [manufactured by A&D Co., Ltd.]. The measurement is carried out in the extrusion direction (hereinafter referred to as "MD") and the transverse direction of the film (hereinafter referred to as "CD") during film production.

[Seal strength] Using the films obtained in the Examples and Comparative Examples, test pieces were heat-sealed with a sealing width of 10 mm under conditions of 150°C, 0.2 MPa, and 1 second, cut into 15 mm wide, and measured on a tensile testing machine. Seal strength. The same evaluation is performed three times, and the average value is used as the evaluation result. ○: Heat sealing strength is 5N/15mm or more ×: Heat sealing strength does not reach 5N/15mm

[Transparency] The haze (unit: %) of the films obtained in Examples and Comparative Examples was measured using a haze meter (manufactured by Nippon Denshin Industry Co., Ltd.) in accordance with JIS K7105. Transparency is assessed against the following benchmarks. ○: Haze less than 8% ×: Haze is 8% or more

[Skin friction coefficient] According to ASTM-D1894, the static friction coefficient of the surface layers (A) and the static friction of the heat sealing layers (D) were measured using the slip tester method at 23°C and 50% RH using the films obtained in the Examples and Comparative Examples. coefficient. ○: Static friction coefficient does not reach 0.8 ×: Static friction coefficient is 0.8 or more

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

[Table 1]

[Table 2]

As can be clearly seen from the above table, the laminated films of the present invention in Examples 1 to 8 can be boiled and sterilized, and still show transverse cracking properties even after being exposed to high temperature and high humidity environments or low temperature environments, and have appropriate resistance. Impact strength. On the other hand, the laminated films of Comparative Examples 1 to 3 did not obtain transverse crack resistance in a low-temperature environment after heat treatment and appropriate impact resistance.

Claims (8)

A multi-layer film characterized by: It consists of a surface layer (A) with polypropylene resin as its main component, an intermediate layer (B) with linear low-density polyethylene as its main component, and an intermediate layer (C) with cyclic polyolefin resin as its main component. , and the heat sealing layer (D) are laminated in the order of (A)/(B)/(C)/(D), and the resin component contained in the intermediate layer (B) is linear low-density polyethylene. The content is more than 65% by mass. The multilayer film of claim 1, wherein the linear low-density polyethylene in the intermediate layer (B) has a density of 0.925g/ ^cm3 or less. The multilayer film of claim 1 or 2, wherein the average density in the middle layer (B) is 0.930g/cm ³ or less. The multilayer film of claim 1 or 2, wherein the heat sealing layer (D) contains linear low-density polyethylene as its main component. The multilayer film of claim 4, wherein the linear low-density polyethylene in the heat sealing layer (D) has a density of 0.916g/cm ³ or more. The multilayer film of claim 1 or 2, wherein at least 60% by mass of the cyclic polyolefin resin contained in the intermediate layer (C) is a cyclic polyolefin resin with a glass transition temperature of 120°C or less. The multilayer film of claim 1 or 2, wherein the total thickness of the multilayer film is in the range of 20 to 60 μm. A packaging material using the multi-layer film according to any one of claims 1 to 7.