JP7342694B2 - Laminated films and packaging materials - Google Patents

Description

The present invention relates to a laminated film used for packaging materials for foods, medical products, etc., and more particularly to a laminated film used for packaging materials with excellent impact resistance at low temperatures.

BACKGROUND ART Films mainly composed of polypropylene resins have traditionally been widely used as packaging materials for foods, medical products, etc. because they have high rigidity and high surface gloss. However, polypropylene resin alone may not provide sufficient impact resistance at low temperatures, so in applications such as frozen food packaging, a linear ethylene-α olefin copolymer layer is added to the polypropylene resin layer. Laminated films that are laminated to improve impact resistance at low temperatures are used (see Patent Document 1).

Japanese Patent Application Publication No. 2001-105468

The above laminated film has excellent impact strength at low temperatures as well as suitability for automatic packaging by laminating a polypropylene resin layer and two linear ethylene-α olefin copolymer layers having a specific density. This is a laminated film that can be suitably applied to packaging frozen foods.

In addition to packaging suitability and impact resistance, packaging materials are often required to be easy to open and tear so that the contents can be easily removed during use, especially for food and medical packaging materials. There is a high demand for straight cutting properties that allow the product to be torn in a straight line to prevent the contents from scattering or falling when the package is opened. In addition, in these applications, even if the sealing temperature fluctuates during heat sealing, appropriate heat sealing performance is required over a wide temperature range to prevent contents from leaking or outside air from entering the package. is required.

The problem to be solved by the present invention is to provide a laminated film having suitable impact resistance, particularly excellent impact resistance at low temperatures, and excellent tearability.

Furthermore, in addition to the above-mentioned problems, it is an object of the present invention to provide a laminated film that has suitable heat resistance and good suitability for automatic packaging, and can realize suitable heat sealability even in a wide temperature range.

The present invention provides a laminated film in which a surface layer (A), an intermediate layer (B), and a heat-sealing layer (C) are laminated, wherein the surface layer (A) is a layer whose main resin component is a polypropylene resin. The intermediate layer (B) is a layer containing linear low density polyethylene and a cyclic olefin resin having a glass transition temperature of 100°C or less, and the heat seal layer (C) is mainly made of linear low density polyethylene. A layer containing a resin component, the content of linear low density polyethylene in the resin component contained in the intermediate layer (B) is 65 to 85% by mass, and the content of a cyclic olefin resin having a glass transition temperature of 100 ° C. or less. The above problem is solved by a laminated film in which the amount is 15 to 35% by mass.

Since the laminated film of the present invention has suitable impact resistance, when used as a packaging material, it can suitably suppress leakage of contents due to bag breakage and entry of outside air into the inside of the package. In particular, since it has excellent impact resistance at low temperatures, it can be suitably applied to packaging frozen foods that are transported and managed at low temperatures. Furthermore, since suitable impact resistance can be achieved without bonding to a stretched base material, it is possible to reduce the cost of the packaging material. In addition to these impact resistance properties, it also has suitable tearability, especially in the width direction (straight cutability), so when applied to packaging materials, it is easy to take out the contents and open the package. Since the content is less likely to scatter or fall, it can be suitably applied to various packaging applications, especially packaging materials for food and medical products.

Furthermore, the laminated film of the present invention has good suitability for packaging machines and has suitable heat sealability over a wide temperature range, so that it can suitably package items in various temperature ranges.

The laminated film of the present invention comprises a surface layer (A) containing a polypropylene resin as the main resin component, an intermediate layer (B) containing linear low density polyethylene and a cyclic olefin resin having a glass transition temperature of 100°C or less, and It is a laminated film in which heat-sealing layers (C) containing linear low-density polyethylene as the main resin component are laminated, and the content of linear low-density polyethylene in the resin component contained in the intermediate layer (B) is 65 to 85. The content of the cyclic olefin resin having a glass transition temperature of 100° C. or less is 15 to 35% by mass.

[Surface layer (A)]
The surface layer (A) of the laminated film of the present invention is a layer containing polypropylene resin as the main resin component, and by containing the polypropylene resin as the main resin component, it achieves suitable rigidity and surface heat resistance. can. Moreover, it becomes easier to obtain a laminated film with a good appearance. As the polypropylene resin, a propylene homopolymer, a propylene-α-olefin random copolymer, a propylene-α-olefin block copolymer, etc. can be used. These may be used alone or in combination. Among these, a propylene homopolymer can be preferably used because it is easy to obtain high rigidity and transparency.

In the present invention, the surface layer (A) contains a polypropylene resin (a1) having an MFR (230° C., 21.18N) of 12 g/10 min or less. By containing the propylene resin (a1), excellent impact resistance can be achieved even at low temperatures well below 0°C, for example, at -15°C. The MFR (230° C.) of the propylene resin (a1) is preferably 10 g/10 min or less, more preferably 8 g/10 min or less. Further, the lower limit of MFR is not particularly limited as long as it is within a range where a laminated film can be formed, but it is preferably 0.5 g/10 min or more. In particular, from the viewpoint of film formability, it is more preferably 3 g/10 min or more, and even more preferably 6 g/10 min or more.

The polypropylene resin in the surface layer (A) preferably has a melting point of 155 to 170°C, more preferably 158 to 165°C. By using polypropylene with a melting point within this range, suitable impact resistance and suitability for packaging machines can be easily achieved. In addition, suitable heat resistance can be achieved. The melting point refers to the melting peak determined by differential scanning calorimetry.

The surface layer (A) is mainly composed of the above-mentioned polypropylene resin, and other coextrudable resins may be used in combination as long as the effects of the present invention are not impaired. In addition, "main resin component" specifically means that 70% by mass or more of the resin component used for the surface layer (A) is a polypropylene resin, and 80% by mass or more is polypropylene. It is preferably a polypropylene resin, and more preferably 90% by mass or more is a polypropylene resin. It is also preferable that all the resin components in the surface layer (A) are polypropylene resins.

The content of the polypropylene resin (a1) having an MFR (230° C.) of 12 g/10 min or less in the polypropylene resin used for the surface layer (A) is preferably 70% by mass or more, and 90% by mass or more. It is more preferable that By setting the content of the polypropylene resin (a1) within the range, it becomes easier to achieve good rigidity and excellent impact resistance at low temperatures.

As the resin other than the above-mentioned 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 very low density polyethylene (VLDPE), linear low density polyethylene (LLDPE), low density polyethylene (LDPE), linear medium density polyethylene (LMDPE), and medium density polyethylene (MDPE), Ethylene-vinyl acetate copolymer (EVA) and the like can be used.

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

Further, 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, and 5% by mass. % or less, and it is also preferable that it is not used substantially.

In the surface layer (A) used in the present invention, other resins than those mentioned above may be used in combination. Examples of the other resins include thermoplastic elastomers such as polyethylene elastomers, polypropylene elastomers, and butene elastomers; ethylene-methyl methacrylate copolymers (EMMA), ethylene-ethyl acrylate copolymers (EEA), and ethylene. - Methyl acrylate (EMA) copolymer, ethylene-ethyl acrylate-maleic anhydride copolymer (E-EA-MAH), ethylene-acrylic acid copolymer (EAA), ethylene-methacrylic acid copolymer (EMAA) and ethylene-based copolymers; further examples include ionomers of ethylene-acrylic acid copolymers and ionomers of ethylene-methacrylic acid copolymers.

When using the above-mentioned other resin, it is preferable to use the content at 30% by mass or less in the resin component contained in the surface layer (A), and it is more preferable to use at 30% by mass or less, It is more preferably 10% by mass or less, and even more preferably 5% by mass or less.

In addition to the above-mentioned resin components, various additives and the like may be appropriately used in the surface layer (A). As additives, for example, lubricants, antiblocking agents, antistatic agents, antifogging agents, colorants, etc. can be used as appropriate. When these additives are used, they are 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).

The thickness ratio of the surface layer (A) to the total thickness of the laminated film is, because it is easy to obtain suitable rigidity and excellent impact resistance at low temperatures. is preferably in the range of 10 to 45%, particularly preferably in the range of 15 to 30%.

[Middle layer (B)]
The intermediate layer (B) of the laminated film of the present invention is a layer containing linear low density polyethylene and a cyclic olefin resin having a glass transition temperature of 100°C or lower, and the resin component contained in the intermediate layer (B). The content of linear low density polyethylene is 65 to 85% by mass, and the content of cyclic olefin resin is 15 to 35% by mass. By using the intermediate layer (B), suitable impact resistance at low temperatures and excellent tearability with straightness can be achieved. Moreover, it becomes easier to realize good packaging machine suitability.

The density of the linear low density polyethylene used for the intermediate layer (B) is preferably 0.950 g/cm ³ or less, more preferably 0.940 g/cm ³ or less, since it is easy to obtain good impact resistance. . Further, it is preferably 0.900 g/cm ³ or more, and more preferably 0.910 g/cm ³ or more.

The MFR (190°C, 21.18N) of the linear low density polyethylene used for the intermediate layer (B) is 0.5 to 50 g/10 minutes (190°C, 21.18N), preferably 1 to 30 g/10 minutes. (190°C, 21.18N), more preferably 2 to 20 g/10 minutes (190°C, 21.18N). It is preferable that the MFR is within this range since good film formability can be obtained.

In the present invention, the content of linear low density polyethylene in the intermediate layer (B) is 65 to 85% by mass, preferably 70 to 80% by mass of the resin component contained in the intermediate layer (B). , suitable sealing properties and excellent impact resistance at low temperatures can be obtained. Further, as long as the total content is within the above range, two or more types of linear low-density polyethylenes having different densities, MFRs, etc. may be used in combination.

By containing a cyclic olefin resin having a glass transition temperature of 100° C. or lower in the intermediate layer (B), excellent tearability and straight cutability can be achieved. Examples of the cyclic olefin resin include norbornene polymers, vinyl alicyclic hydrocarbon polymers, and cyclic conjugated diene polymers. Among these, norbornene polymers are preferred. Examples of norbornene polymers include ring-opening polymers (COP) of norbornene monomers, and norbornene copolymers (COC) obtained by copolymerizing norbornene monomers with olefins such as ethylene. Also particularly preferred are hydrogenated products of COP and COC. Further, the weight average molecular weight of the cyclic olefin resin is preferably 5,000 to 500,000, more preferably 7,000 to 300,000.

The norbornene polymer and the norbornene monomer used as a raw material are alicyclic monomers having a norbornene ring. Examples of such norbornene monomers include norbornene, tetracyclododecene, ethylidenenorbornene, vinylnorbornene, ethylidetetracyclododecene, dicyclopentadiene, dimetanotetrahydrofluorene, phenylnorbornene, methoxycarbonylnorbornene, and methoxycarbonylnorbornene. Examples include carbonyltetracyclododecene. These norbornene monomers may be used alone or in combination of two or more.

The norbornene copolymer is a copolymer of the norbornene monomer and a copolymerizable olefin, and examples of such olefin include ethylene, propylene, 1-butene, etc. Examples include olefins having 2 to 20 atoms; cycloolefins such as cyclobutene, cyclopentene, and cyclohexene; and nonconjugated dienes such as 1,4-hexadiene.

The content of the cyclic olefin resin contained in the intermediate layer (B) is 15 to 35% by mass, preferably 20 to 30% by mass of the resin components contained in the intermediate layer (B), thereby improving impact resistance. Suitable tearability and straight cutability can be achieved without impairing properties.

Further, the cyclic olefin resin used in the intermediate layer (B) has a glass transition temperature of 100°C or lower, preferably 90°C or lower, and more preferably 80°C or lower. Further, the lower limit is not particularly limited, but it is preferably 50°C or higher, more preferably 60°C or higher, and even more preferably 70°C or higher. By using a cyclic olefin resin having the relevant glass transition temperature, it is easy to obtain good heat resistance and rigidity, and it is also easy to improve bag breakage resistance against dropping and the like. Moreover, it becomes easier to obtain good compatibility and to suppress unevenness in appearance. Glass transition temperature (Tg) is a value obtained by measurement by DSC.

The MFR of the cyclic olefin resin is 0.2 to 17 g/10 min (230°C, 21.18N), preferably 3 to 15 g/10 min (230°C, 21.18N), more preferably 5 to 13 g/10 min (230°C, 21.18N). When the MFR is within this range, it is preferable because it has excellent compatibility with the linear low density polyethylene (b1) and also provides good film formability in various multilayer film forming methods.

Examples of commercially available ring-opening polymers (COP) of norbornene monomers that can be used as the cyclic olefin resin used in the present invention include "ZEONOR" manufactured by Nippon Zeon Co., Ltd.; Examples of the copolymer (COC) include "APEL" manufactured by Mitsui Chemicals, Inc. and "TOPAS" manufactured by Polyplastics.

It is also preferable that the intermediate layer (B) contains only the linear low-density polyethylene and cyclic olefin resin, but other resin components other than these resin components may be used as long as the effects of the present invention are not impaired. A resin may also be used in combination. Examples of other resin species that can be used in combination include polyethylene resins other than the linear low density polyethylene resins exemplified in the surface layer (A), and olefin resins such as polypropylene resins. Furthermore, thermoplastic elastomers, ethylene copolymers, ionomers, etc. may also be used.

When using these other resins, the total content of linear low density polyethylene and cyclic olefin resin should be 80% by mass or more, that is, 20% by mass or less in the resin component contained in the intermediate layer (B). The content is preferably 10% by mass or less, and more preferably 10% by mass or less. Further, the lower limit is not particularly limited, but it may be used at a content of 1% by mass or more depending on the desired characteristics.

In the intermediate layer (B), various additives and the like may be appropriately used in addition to the above-mentioned resin components. As additives, for example, lubricants, antiblocking agents, antistatic agents, antifogging agents, colorants, etc. can be used as appropriate. When these additives are used, they are 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) to the total thickness of the laminated film is preferably 50 to 80%, more preferably 65 to 75%, from the viewpoint of good packaging machine suitability and low temperature impact resistance. preferable.

The intermediate layer (B) may be composed of two or more layers, but in the case of the multi-layer composition, each layer contains linear low density polyethylene and a cyclic olefin resin, and each intermediate layer contains The effects of the present invention can be suitably achieved by setting the content of linear low density polyethylene in the included resin component to 65 to 85% by mass and the content of cyclic olefin resin to 15 to 35% by mass. In addition, when making an intermediate|middle layer into multiple layers, each layer may have the same formulation or a different formulation as long as it is the said formulation range. In addition, when the intermediate layer is composed of a plurality of layers, it is preferable that the total thickness of the intermediate layer falls within the above-mentioned thickness ratio.

[Heat seal layer (C)]
The heat-sealing layer (C) used in the laminated film of the present invention is a layer containing linear low-density polyethylene as a main resin component. By using the heat-sealing layer, good impact resistance and heat-sealability can be achieved. The density of the linear low-density polyethylene used for the heat-sealing layer (C) is preferably 0.880 to 0.940 g/cm ³ because it is easy to obtain good sealing properties and impact resistance.

The MFR of linear low density polyethylene is 0.5 to 50 g/10 min (190°C, 21.18N), preferably 1 to 30 g/10 min (190°C, 21.18 N), more preferably 2 to 20 g/10 min (190°C, 21.18 N). 10 minutes (190°C, 21.18N). It is preferable that the MFR is within this range since good film formability can be obtained.

In the present invention, by setting the content of linear low-density polyethylene in the heat-sealing layer (C) to 70% by mass or more of the resin component contained in the heat-sealing layer (C), suitable sealing properties and low-temperature properties can be achieved. It becomes easier to obtain excellent impact resistance under the conditions. The content is preferably 75% by mass or more, more preferably 80% by mass or more, and further preferably 90% by mass or more in the resin component contained in the heat seal layer (C). preferable. Furthermore, 100% by mass of the resin component contained in the heat-sealing layer (C) may be linear low-density polyethylene. Further, as long as the total content is within the above range, two or more types of linear low-density polyethylenes having different densities, MFRs, etc. may be used in combination.

In the heat-sealing layer (C), other resins than the above-mentioned linear low-density polyethylene may be used in combination without impairing the effects of the present invention. Examples of other resin species that can be used in combination include polyethylene resins other than the linear low density polyethylene resins exemplified in the surface layer (A), and olefin resins such as polypropylene resins. When an olefin resin is used as the resin other than the linear low density polyethylene, the content thereof is preferably 30% by mass or less, and 10% by mass in the resin component contained in the heat seal layer (C). It is more preferably at most 5% by mass, even more preferably at most 5% by mass.

Further, 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 heat seal layer (C) is preferably 10% by mass or less, and 5% by mass or less. It is more preferable that the amount is less than % by mass, and it is also preferable that it is not substantially used.

In addition, other resins other than those mentioned above may be used in combination in the heat-sealing layer (C), such as thermoplastic elastomers and ethylene copolymers exemplified in the surface layer (A). , ionomer, etc. When using the other resin, the content thereof is preferably 30% by mass or less in the resin component contained in the heat seal layer (C), more preferably 10% by mass or less, More preferably, it is 5% by mass or less.

In addition to the above-mentioned resin components, various additives and the like may be appropriately used in the heat-sealing layer (C). As additives, for example, lubricants, antiblocking agents, antistatic agents, antifogging agents, colorants, etc. can be used as appropriate. When these additives are used, they are 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 (C).

The thickness ratio of the heat seal layer (C) to the total thickness of the laminated film is preferably 5 to 30%, more preferably 10 to 20%, from the viewpoint of heat sealability and low temperature impact resistance. .

[Laminated film]
The laminated film of the present invention is a laminated film in which the surface layer (A), the intermediate layer (B), and the heat seal layer (C) are laminated in the order of (A)/(B)/(C). Due to this structure, the laminated film of the present invention can achieve suitable impact resistance even at low temperatures, particularly at -15°C, which is well below 0°C. It also has good film-forming properties and can achieve suitable rigidity, sealing properties, and suitability for packaging machines.

The laminated film of the present invention preferably has a film thickness of 15 to 100 μm, more preferably 30 to 50 μm. If the thickness of the film is within this range, it will be easier to obtain excellent impact resistance, rigidity, sealability, suitability for packaging machines, etc. at low temperatures.

Further, the thickness of each layer is not particularly limited, but for example, the thickness of the surface layer (A) is preferably 4 to 18 μm, more preferably 6 to 12 μm. The thickness of the intermediate layer (B) is preferably 20 to 32 μm, more preferably 26 to 28 μm. The thickness of the heat seal layer (C) is preferably 2 to 12 μm, more preferably 4 to 8 μm.

In addition, when the intermediate layer (B) has a plurality of layers, preferably, when the configuration is such as the surface layer (A)/intermediate layer (B1)/intermediate layer (B2)/heat seal layer (C), It is preferable that the total thickness of the intermediate layer is within the thickness range of the intermediate layer (B).

From the viewpoint of protecting contents, the laminated film of the present invention preferably has a sealing strength of 5 N/15 mm or more, and preferably 10 N/15 mm or more.

The laminated film of the present invention preferably has an impact strength of 0.5 J or more, more preferably 0.7 J or more, as measured by a film impact method. The impact strength is the impact strength measured after conditioning a 40 μm laminated film to −15° C.

The laminated film of the present invention preferably has a rigidity of 500 MPa or more, more preferably 530 MPa or more, since it is easy to obtain suitable packaging suitability and toughness.

In the laminated film of the present invention, the difference between the average melting point of the resin constituting the surface layer and the average melting point of the resin constituting the heat seal layer is preferably 50°C or more, more preferably 60°C or more. By using resins having the above melting point difference, it becomes easier to obtain suitable packaging suitability. The average melting point of the resin used for the surface layer and heat-sealing layer is the melting point calculated from the content and melting point of each resin component used for each layer, and the resin used for the surface layer or heat-sealing layer is a , resin b, resin c..., the melting points of these resins are Ta, Tb, Tc..., and the masses of the resins used in the layer are Wa, Wb, Wc..., It is calculated as (TaWa+TbWb+TcWc...)/(Wa+Wb+Wc...).

The method for producing the laminated film of the present invention is not particularly limited, but for example, each resin or resin mixture used for the surface layer (A), intermediate layer (B), and heat-sealing layer (C) is processed using separate extruders. After laminating (A)/(B)/(C) in the order of molten state by a method such as a coextrusion multilayer die method or a feed block method, a film is formed by an inflation method, a T-die/chill roll method, etc. For example, coextrusion method is used to mold the material. This coextrusion method is preferable because it allows the thickness ratio of each layer to be adjusted relatively freely, and a laminated film with excellent hygiene and cost performance can be obtained.

Since the laminated film of the present invention is obtained as a substantially unstretched laminated film by the above-described manufacturing method, secondary forming such as deep drawing by vacuum forming is also possible.

Furthermore, in order to improve adhesion with printing ink and suitability for lamination when used as a sealant film for lamination, it is preferable to subject the resin layer (A) to a surface treatment. Examples of such surface treatments include surface oxidation treatments such as corona treatment, plasma treatment, chromic acid treatment, flame treatment, hot air treatment, ozone/ultraviolet treatment, and surface roughening treatments such as sandblasting. Corona treatment is preferred.

Examples of the packaging material made of the laminated film of the present invention include packaging bags and packaging containers used for foods, medicines, industrial parts, miscellaneous goods, magazines, and the like.

The packaging bag is preferably a packaging bag formed by overlapping and heat-sealing the heat-sealing layers (C) of the laminated film of the present invention. For example, cut two sheets of the laminated film into the desired packaging bag size, stack them together and heat-seal three sides to form a bag, and then fill the contents from the one side that is not heat-sealed. By heat-sealing and sealing, it can be used as a packaging bag. Furthermore, it is also possible to form a packaging bag by sealing the ends of a roll of film into a cylindrical shape using an automatic packaging machine and then sealing the top and bottom.

It is also possible to form a packaging bag/container by overlapping and heat-sealing the heat-sealing layer (C) and another heat-sealable film. In this case, as another film to be used, a film such as LDPE or EVA, which has relatively low mechanical strength, can be used.

The laminated film of the present invention can also be used by laminating it with other base materials. Other base materials that can be used at this time are not particularly limited, but from the viewpoint of easily achieving the effects of the present invention, plastic base materials with high rigidity and high gloss, particularly biaxial It is preferable to use a stretched resin film. Furthermore, for applications that do not require transparency, aluminum foil can be used alone or in combination.

Stretched resin films include, for example, biaxially oriented polyester (PET), easily tearable biaxially oriented polyester (PET), biaxially oriented polypropylene (OPP), biaxially oriented polyamide (PA), and ethylene vinyl alcohol copolymer. Examples include coextruded biaxially oriented polypropylene having a core layer of EVOH, biaxially oriented ethylene vinyl alcohol copolymer (EVOH), and coextruded biaxially oriented polypropylene coated with polyvinylidene chloride (PVDC). These may be used alone or in combination.

Examples of the lamination method when laminating the base material to the laminated film obtained by the above manufacturing method to form a laminated film include methods such as dry lamination, wet lamination, non-solvent lamination, and extrusion lamination.

Examples of the adhesive used in the dry lamination include polyether-polyurethane adhesives, polyester-polyurethane adhesives, and the like. Although various adhesives can be used, it is preferable to use a pressure-sensitive adhesive. Examples of the pressure-sensitive adhesive include polyisobutylene rubber, butyl rubber, a rubber adhesive prepared by dissolving a mixture thereof in an organic solvent such as benzene, toluene, xylene, or hexane, or a rubber adhesive prepared by adding abiethylene rosin to these rubber adhesives. Those containing tackifiers such as ester, terpene/phenol copolymer, terpene/indene copolymer, or 2-ethylhexyl acrylate/n-butyl acrylate copolymer, 2-ethylhexyl acrylate/ethyl acrylate, etc. Examples include acrylic pressure-sensitive adhesives in which an acrylic copolymer having a glass transition point of -20° C. or lower, such as a methyl methacrylate copolymer, is dissolved in an organic solvent.

In the packaging material using the laminated film of the present invention, arbitrary tear initiation parts such as V-notches, I-notches, perforations, micropores, etc. are formed in the sealing part in order to weaken the initial tear strength and improve the ease of opening. It is preferable to do so.

Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Hereinafter, unless otherwise specified, "parts" and "%" are based on mass.

(Example 1)
The resins and resin mixtures forming each layer were prepared using the following resins as resin components forming each of the surface layer (A), intermediate layer (B), and heat seal layer (C). These resins and resin mixtures were each supplied to three extruders and melted at 250°C. The molten resin is supplied to a co-extrusion multilayer film production apparatus using a T-die/chill roll method having a feed block (feed block and T-die temperature: 250°C) to carry out co-melt extrusion, so that the layer structure of the film is A laminated film having a three-layer structure of layer (A)/intermediate layer (B)/heat-sealing layer (C) and the thickness of each layer was 8 μm/26 μm/6 μm (total 40 μm) was obtained.

Surface layer (A): Propylene homopolymer (density: 0.900 g/cm ³ , MFR (230°C, 21.18N): 8 g/10 min, melting point: 160°C) (hereinafter referred to as "HOPP"). 100 parts by mass Intermediate layer (B): Linear low density polyethylene (density: 0.925 g/cm ³ , MFR (190° C., 21.18 N): 4.1 g/10 min) (hereinafter “LLDPE (1)”) (hereinafter referred to as "COC (1)") 20 Mass part Heat seal layer (C): Linear low density polyethylene (density: 0.900 g/cm ³ , MFR (190°C, 21.18N): 4.0 g/10 min, melting point: 100°C) (hereinafter referred to as “ (referred to as “LLDPE (2)”) 100 parts by mass

(Example 2)
A laminated film was obtained in the same manner as in Example 1 except that the resin components used for the intermediate layer (B) were as follows.
Intermediate layer (B): 75 parts by mass of LLDPE (1), 25 parts by mass of COC (1)

(Example 3)
A laminated film was obtained in the same manner as in Example 2, except that the thickness of the surface layer (A)/intermediate layer (B)/heat seal layer (C) was 6 μm/19.5 μm/4.5 μm (total 30 μm). .

(Example 4)
A laminated film was obtained in the same manner as in Example 1 except that the resin components used for the intermediate layer (B) were as follows.
Intermediate layer (B): 70 parts by mass of LLDPE (1), 30 parts by mass of COC (1)

(Example 5)
A laminated film was obtained in the same manner as in Example 1 except that the resin components used for the intermediate layer (B) were as follows.
Intermediate layer (B): 75 parts by mass of LLDPE (1), cyclic olefin resin (MFR (230 ° C., 21.18 N): 5.0 g / 10 minutes, glass transition temperature: 65 ° C.) (hereinafter referred to as "COC (2) ) 25 parts by mass

(Example 6)
A laminated film was obtained in the same manner as in Example 1 except that the resin components used for the intermediate layer (B) were as follows.
Intermediate layer (B): 75 parts by mass of linear low-density polyethylene (density: 0.920 g/cm ³ , MFR (190° C., 21.18 N): 4.1 g/10 min) (hereinafter referred to as LLDPE (3)) ), COC (1) 25 parts by mass

(Comparative example 1)
A laminated film was obtained in the same manner as in Example 1 except that the resin components used for the intermediate layer (B) were as follows.
Intermediate layer (B): 90 parts by mass of LLDPE (1), 10 parts by mass of COC (1)

(Comparative example 2)
A laminated film was obtained in the same manner as in Example 1 except that the resin components used for the intermediate layer (B) were as follows.
Intermediate layer (B): 60 parts by mass of LLDPE (1), 40 parts by mass of COC (1)

(Comparative example 3)
A laminated film was obtained in the same manner as in Example 1 except that the resin components used for the intermediate layer (B) were as follows.
Intermediate layer (B): 75 parts by mass of LLDPE (1), cyclic olefin resin (MFR (230 ° C., 21.18 N): 10.0 g / 10 minutes, glass transition temperature: 110 ° C.) (hereinafter referred to as “COC (3) ) 25 parts by mass

(Comparative example 4)
A laminated film was obtained in the same manner as in Example 1 except that the resin components used for the surface layer (A) were as follows.
Surface layer (A): Linear low density polyethylene (density: 0.940 g/cm ³ , MFR (190°C, 21.18N): 2.8 g/10 min, melting point: 120°C) (hereinafter referred to as LLDPE (4) ) 100 parts by mass

(Comparative example 5)
The following resins were used as resin components to form each layer of the surface layer (A), intermediate layer (B1), intermediate layer (B2), and heat seal layer (C), and the resins forming each layer were adjusted. . These resins were each fed to four extruders and melted at 250°C. The molten resin is supplied to a co-extrusion multilayer film production apparatus using a T-die/chill roll method having a feed block (feed block and T-die temperature: 250°C) to carry out co-melt extrusion, so that the layer structure of the film is A laminated film was obtained with a four-layer configuration of layer (A)/intermediate layer (B)/intermediate layer (B2)/heat seal layer (C), and the thickness of each layer was 8 μm/20 μm/4 μm/8 μm (total 40 μm). .

Surface layer (A): 100 parts by mass of HOPP (1) Intermediate layer (B): 100 parts by mass of LLDPE (1) Intermediate layer (B2): 100 parts by mass of COC (1) Heat seal layer (C): LLDPE (2) 100 parts by mass

[Measurement of rigidity]
A 30 μm thick film cut out from the films obtained in Examples and Comparative Examples in a size of 300 mm long x 25.4 mm wide (marked line interval 200 mm) so that the longitudinal direction is the flow direction (vertical direction) of the film. was used as a test piece, and the 1% tangential modulus (unit: MPa) at 23°C was measured at a tensile speed of 500 mm/min in accordance with ASTM D-882 using a Tensilon tensile tester [manufactured by A&D Co., Ltd.] Measured using
〇: Rigidity is 500MPa or more ×: Rigidity is less than 500MPa

[Heat seal strength]
Using the films obtained in Examples and Comparative Examples, test pieces were prepared by heat-sealing them with a sealing width of 10 mm under the conditions of 130°C, 0.2 MPa, and 1 second. The seal strength was measured. Similar evaluations were conducted three times, and the average value was used as the evaluation result.
○: Heat seal strength is 5N/15mm or more ×: Heat seal strength is less than 5N/15mm

[Straight cutting performance]
The films obtained in the Examples and Comparative Examples were tested in the width direction by making 10 mm incisions at intervals of 50 mm in the width direction using a test piece with a length of 297 mm in the width direction and a length of 210 mm in the machine direction. The straight cutting properties were evaluated by tearing by hand. The test was conducted three times.
The films obtained in the Examples and Comparative Examples were cut into a size of 250 mm in the width direction and 250 mm in the machine direction to obtain test pieces. On one side of the obtained test piece in the flow direction, four 10 mm incisions were made in the direction perpendicular to the flow direction (parallel to the width direction) at intervals of 50 mm from one end of the side. The center part of the cut piece on the side where the cut was made and the center part of the adjacent cut piece were held, and the test piece was torn in the 180° width direction to the end to evaluate the straight cutability. Similar evaluations were made for all cuts using three test pieces. The evaluation criteria are as follows.
〇: In all tests, the deviation between the tear start part and the tear end end is within ±5 mm ×: In one or more tests, the deviation between the tear start part and the tear end end is ±5 mm or more

[Horizontal tearability]
The films obtained in the Examples and Comparative Examples were used as test pieces with a length in the width direction of 297 mm and a length in the machine direction of 210 mm, and a test piece with a length in the width direction of 210 mm and a length in the machine direction of Using a 297 mm test piece, 10 mm incisions were made at intervals of 50 mm in the width direction and machine direction, and the crosswise tearability was evaluated by tearing by hand in the width direction and machine direction. The test was conducted three times.
Six test pieces each having a length of 250 mm in the width direction and a length of 250 mm in the machine direction were cut out from the films obtained in Examples and Comparative Examples. Regarding the three test pieces, a tearing test in the width direction was conducted in the same manner as the straight cutability test described above.
In each of the other three test pieces, four 10 mm incisions were made on one side in the width direction in a direction perpendicular to the width direction (parallel to the flow direction) at intervals of 50 mm from one end of the side. The test piece was held at the center of the cut piece on the side where the cut was made and the center part of the adjacent cut piece, and was torn to the end in a direction of 180° in the flow direction. Similar evaluations were made for all cuts using three test pieces. The evaluation criteria are as follows.

〇: Can be easily torn by hand in all tear tests in the width direction, and resistance to tearing occurs or cannot be torn in all tear tests in the machine direction ×: One or more tear tests in the width direction or can be easily broken by hand in one or more tear tests in the machine direction.

[Shock resistance]
A test piece was prepared in which the films obtained in Examples and Comparative Examples were left undisturbed for 4 hours in a constant temperature room adjusted to -15°C, and a test piece was left undisturbed for 4 hours in a constant temperature room adjusted to -15°C. . For each test piece, the impact strength was measured by the film impact method using a BU-302 film impact tester manufactured by Tester Sangyo, with a 1.0-inch head attached to the tip of a pendulum.
○: Impact strength is 0.70 (J) or more ×: Impact strength is less than 0.70 (J)

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

As is clear from the above table, the laminated films of the present invention of Examples 1 to 6 have suitable rigidity and excellent impact resistance at very low temperatures of -15°C, as well as suitable tearability. Met. On the other hand, the laminated films of Comparative Examples 1 to 5 did not have suitable rigidity, impact resistance, and tearability.

Claims (4)

A laminated film in which a surface layer (A), an intermediate layer (B) and a heat seal layer (C) are laminated,
The surface layer (A) is a layer containing polypropylene resin as the main resin component,
The intermediate layer (B) is a layer containing linear low density polyethylene and a cyclic olefin resin having a glass transition temperature of 100° C. or less,
The heat seal layer (C) is a layer containing linear low density polyethylene as a main resin component,
The content of linear low density polyethylene in the resin component contained in the intermediate layer (B) is 65 to 85% by mass, and the content of cyclic olefin resin having a glass transition temperature of 100 ° C. or less is 15 to 35% by mass. A laminated film characterized by: The laminated film according to claim 1, wherein the total thickness of the laminated film is in the range of 20 to 60 μm. The laminated film according to claim 1 or 2, wherein the laminated film has an impact strength of 0.7 J or more at -15°C. A packaging material using the laminated film according to any one of claims 1 to 3.