JP6875049B2 - Multilayer film for food packaging - Google Patents

Description

The present invention relates to a multi-layer film for food packaging used for packaging foods such as ham, sausage, and bacon.

For packaging processed meat products such as ham, sausage, bacon, roasted pork, and chicken, vacuum deep draw molding packaging in which the lid material and the bottom material are heat-sealed is widely used. In vacuum deep drawing and packaging, the bottom material needs to be thermoformed, so a non-stretched multilayer film produced by coextrusion is generally used as the bottom material. On the other hand, since the lid material requires printing processing and a printing layer is often interposed between the layers, a multilayer film in which each film is laminated is used as the lid material.

Further, as the material of the bottom material, polyethylene terephthalate (PET), which has relatively high rigidity and small heat shrinkage, is generally used for the outermost layer. However, in vacuum deep drawing and packaging of processed meat products, there are products that are boiled and cooked after packaging, and since the PET layer becomes cloudy in such products, polypropylene (PP) is generally used as the outermost layer. To. Therefore, in such a boiled cooking application, a multilayer film having an unstretched polypropylene (CPP) layer in the outermost layer is used as the lid material in order to balance with the outermost layer of the bottom material. Specifically, as the multilayer film having CPP on the outermost layer, a multilayer film in which a CPP layer, a PET layer, and a linear low density polyethylene (LLDPE) layer are laminated in this order is used. Further, since processed meat products are also required to have an oxygen gas barrier property, a biaxially stretched PET (VMPET) layer formed of alumina, silica or the like and having a transparent inorganic oxide vapor deposition film is widely used as the PET layer. ing.

However, when viewed as a lid material alone, such a configuration has a relatively rigid PET layer having a small heat shrinkage as an intermediate layer, and therefore has excellent printability, but has a heat shrinkage with an LLDPE layer having a large heat shrinkage. Since it is not balanced, after heat-sealing with the thermoformed bottom material, the curl to the LLDPE layer side (bottom material side) is large, causing problems such as catching on the conveyor line, printing, labels, etc., and productivity May decrease. In addition, when the packaged product is displayed at the store, the appearance (appearance) may deteriorate due to the size of the curl, and the commercial value may be impaired.

Regarding the lid material for vacuum deep draw molding packaging, Japanese Patent Application Laid-Open No. 2002-205769 (Patent Document 1) describes an outer surface having excellent dimensional stability as a lid material for a blister package for accommodating sliced ham and sliced bacon. A laminate composed of a layer, an intermediate layer having an excellent gas barrier property, and an inner surface layer having an easily peelable property is disclosed. As the intermediate layer, an ethylene-vinyl alcohol copolymer (EVOH), VMPET, and vinylidene chloride-coated cellophane (KM) are described. Specific lid materials include PET / printing / dry lamination (DL) / ethylene vinyl acetate copolymer (EVA) / EVOH / EVA (coextruded film), vinylidene chloride coated biaxially stretched polypropylene (KOP) / Printing / DL / PET / EVA, CPP / DL / VMPET / Printing / LLDPE, Biaxially Stretched Polypropylene (OPP) / DL / VMPET / Printing / EVA, CPP / DL / KM / Printing / EVA, OPP / DL / KM / Print / EVA is described.

However, even with this lid material, curling after heat sealing or boiling cooking cannot be suppressed.

Regarding packaging bags for pharmaceuticals and foods, Japanese Patent Application Laid-Open No. 2015-48094 (Patent Document 2) seals three sides of the laminated film, fills the contents from the opening, and then seals the opening. In the light-shielding packaging bag to be sealed, the laminated film has a biaxially stretched polypropylene film on the outermost layer, a film in which a barrier film and a biaxially stretched white nylon film are bonded to an intermediate layer, and a black polyethylene film on the innermost layer. However, a light-shielding packaging bag in which the outermost layer and the intermediate layer and the intermediate layer and the innermost layer are bonded by an extrusion laminating method using a polyolefin resin is disclosed. In this document, as a barrier film for the intermediate layer, films such as ethylene-vinyl acetate copolymer saponified products, polyvinylidene chloride, and polyacrylonitrile; transparent vapor-deposited layers of inorganic oxides such as silica and alumina, and polyvinylidene chloride coating are described. Biaxially stretched nylon film provided with a film layer, biaxially stretched polyethylene terephthalate (OPET) film, and OPP film are exemplified.

Further, regarding a packaging material for a photographic photosensitive material, Japanese Patent Application Laid-Open No. 2004-233517 (Patent Document 3) describes an outermost layer, an intermediate layer formed of a layer having a moisture-proof function and a layer having a light-shielding function. , A packaging material having a multi-layer structure having an innermost layer is disclosed. As the outermost layer, as a thermoplastic resin film, ethylene tetrafluoroethyl copolymer, high density polyethylene (HDPE), OPP, polystyrene, polymethylmethacrylate, biaxially stretched nylon 6, PET, polycarbonate, polyimide, polyether styrene. Is described, and in the examples, OPP is used. As the layer having a moisture-proof function, an inorganic vapor-deposited film of a metal or an inorganic oxide, a laminate of a thermoplastic resin film, or the like is described, and in the examples, the inorganic-deposited film is used. As the innermost layer, various polyolefin films are exemplified, and LLDPE is used in the examples.

However, Patent Documents 2 and 3 do not describe a lid material for vacuum deep drawing molding and packaging molding. Further, even if the packaging materials of Patent Documents 2 and 3 are used as the lid material, curl cannot be suppressed.

Japanese Unexamined Patent Publication No. 2002-205769 (paragraphs [0002] [0018] [0019]) JP-A-2015-48094 (Claim 1, paragraph [0017], Examples) Japanese Unexamined Patent Publication No. 2004-233517 (paragraphs [0036] [0050] [0053] [0057] [0059], Examples, FIG. 1)

Therefore, an object of the present invention is to provide a multilayer film for food packaging capable of suppressing the generation of curl even after heat sealing with a bottom material or heat treatment.

Another object of the present invention is a food having excellent oxygen gas barrier property, and can suppress a decrease in oxygen gas barrier property due to cracks in the barrier layer due to damage during the packaging process or transfer, and a decrease in oxygen gas barrier property due to humidity or moisture. The purpose is to provide a multilayer film for packaging.

Still another object of the present invention is to provide a multi-layer film for food packaging which has excellent oxygen gas barrier property and can suppress curling of a flange portion as a lid material for vacuum deep drawing and packaging molding even if it is boiled after being sealed with a bottom material. To do.

Another object of the present invention is to provide a multilayer film for food packaging which is transparent, can confirm the contents, has excellent printability, and can suppress peeling between layers.

As a result of diligent studies to achieve the above problems, the present inventors include an outermost layer containing a non-stretched polypropylene resin film, an intermediate layer containing a biaxially stretched polypropylene resin film, and a non-stretched olefin resin film. We have found that the generation of curls can be suppressed even by heat treatment by combining the sealant layers in this order, and completed the present invention.

That is, the multilayer film of the present invention includes an outermost layer containing a non-stretched polypropylene-based resin film, an intermediate layer containing a biaxially stretched polypropylene-based resin film, and a sealant layer containing a non-stretched olefin-based resin film in this order. .. The intermediate layer may further contain an organic barrier film (particularly, a vinylidene chloride resin film). The non-stretched olefin resin film contained in the sealant layer may contain linear low-density polyethylene. A first adhesive layer may be interposed between the outermost layer and the intermediate layer. Further, a second adhesive layer may be interposed between the intermediate layer and the sealant layer. The first and second adhesive layers may contain a two-component curable polyether urethane-based resin. The average thickness of the intermediate layer may be 0.7 times or more the average thickness of the outermost layer. The average thickness of the sealant layer may be 0.9 times or less the average thickness of the outermost layer. The multilayer film of the present invention may be a multilayer film for food packaging (particularly, a lid material for vacuum deep draw molding packaging).

In the present invention, the outermost layer containing the unstretched polypropylene resin film, the intermediate layer containing the biaxially stretched polypropylene resin film, and the sealant layer containing the unstretched olefin resin film are combined in this order. Curling can be suppressed even after heat sealing with the bottom material or heat treatment. Further, when the intermediate layer further contains an organic barrier film, the oxygen gas barrier property can be improved, and the deterioration of the oxygen gas barrier property due to cracks in the barrier layer due to damage during packaging or transportation can be suppressed, and the organic system can be suppressed. When a vinylidene chloride-based resin film is used as the barrier film, it is possible to suppress a decrease in oxygen gas barrier property due to humidity and moisture. Therefore, even if such a multilayer film is used as a lid material for vacuum deep drawing and packaging molding and boiled after being sealed with the bottom material, the oxygen gas barrier property can be maintained and the curl of the flange portion can be suppressed. Further, the contents can be confirmed transparently, and if an adhesive layer (particularly an adhesive layer containing an ether-based adhesive) is interposed between the layers, peeling between the layers can be suppressed.

[Outermost layer]
The multilayer film of the present invention includes an outermost layer, and the outermost layer contains a non-stretched polypropylene-based resin film. In the present invention, by disposing a layer containing an unstretched polypropylene resin film to the outermost layer, it is possible to print on the back surface of the intermediate layer as viewed from the viewing side (gravure printing), crispness printed images ( For example, a multicolor printed image) can be formed.

The polypropylene-based resin constituting the unstretched polypropylene-based resin may be a propylene homopolymer (propylene homopolymer) or a propylene copolymer (propylene-based copolymer).

In the copolymer, examples of the monomer copolymerizable with propylene (copolymerizable monomer) include α-olefin (ethylene, 1-butene, 1-pentene, 1-hexene, 2-methyl-1-pentene, 3-methyl). -1-Pentene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene, 3-ethyl-1-pentene, 3-methyl-1-butene, 4-methyl-1-hexene, 4,4 -Dimethyl-1-hexene, 3-ethyl-1-hexene, 4-ethyl-1-hexene, 1-octene, 1-nonen, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene, 1-hexadecene , 1-octadecene, 1-eicosene and other α-C _2-20 olefins), alkaziene (1,4-hexadien, 1,7-octadien, 4-methyl-1,4-hexadien, 5-methyl-1,4 -Non-conjugated alkaziene such as hexadiene, conjugated alkaziene such as butadiene, isoprene), ethylene-based unsaturated carboxylic acid and its acid anhydride [(meth) acrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, crotonic acid , Isocrotonic acid, mesaconic acid, angelic acid, etc.], (meth) acrylic acid ester [(meth) acrylic acid alkyl ester, glycidyl (meth) acrylate, etc.], carboxylic acid vinyl ester (saturated carboxylic acid such as vinyl acetate and vinyl propionate) Acid vinyl ester, etc.) and the like. These monomers can be used alone or in combination of two or more. _{Of these monomers, α-C 2-6} olefins such as ethylene and 1-butene are widely used.

Examples of the form of the copolymer include block copolymerization, random copolymerization, alternating copolymerization, and graft copolymerization. Of these, usually random copolymerization and alternating copolymerization.

In the polypropylene resin, the ratio (molar ratio) of propylene (propylene unit) and copolymerizable monomer (copolymerizable monomer unit) is propylene / copolymerizable monomer = 90/10 to 100/0, preferably 95 /. It is about 5 to 100/0, more preferably about 99/1 to 100/0.

The polypropylene-based resin may be an atactic polymer, but a structure having three-dimensional regularity such as isotactic and syndiotactic is preferable from the viewpoint of improving heat resistance, and the isotactic polymer is particularly preferable.

Further, the polypropylene-based resin may be a polymer using a Ziegler catalyst or the like, but a metallocene-based resin using a metallocene catalyst is obtained because a polymer having a small amount of low-molecular-weight tack components and a narrow molecular weight distribution can be obtained. Is preferable.

The number average molecular weight of the polypropylene-based resin is, for example, 10,000 to 500,000, preferably 15,000 to 300,000, and more preferably about 20,000 to 100,000. In the present specification and the scope of the patent claim, the number average molecular weight of the polypropylene-based resin is measured by the GPC method at a measurement temperature of 140 ° C., using orthodichlorobenzene as a solvent and a column (Shodex GPC AD-806MS). It is a value measured by universal calibration based on polystyrene.

The melting point (or softening point) of the polypropylene-based resin is preferably higher than the melting point of the olefin-based resin contained in the sealant layer, for example, 120 to 180 ° C., preferably 130 to 175 ° C., and more preferably 150 to 173 ° C. ( In particular, it is about 160 to 170 ° C.). In the present specification and claims, the melting point of the polypropylene resin can be measured based on the melting peak temperature of the differential scanning calorimeter DSC.

In addition to polypropylene-based resins, unstretched polypropylene-based resin films include other thermoplastic resins (olefin-based resins such as polyethylene-based resins, chlorine-containing resins, styrene-based resins, petroleum resins, etc.) and conventional additives (for example, heat). Contains stabilizers, antioxidants, stabilizers such as UV absorbers, preservatives, bactericides, plastics, lubricants, colorants, viscosity modifiers, leveling agents, surfactants, antioxidants, etc.) May be good. The total ratio of the other thermoplastic resin and the additive is 50 parts by weight or less, preferably 30 parts by weight or less (for example, 0.01 to 30 parts by weight), more preferably 10 parts by weight, based on 100 parts by weight of the polypropylene resin. It is about the following (for example, 0.1 to 10 parts by weight).

The tensile strength of the unstretched polypropylene-based resin film is, for example, less than 100 MPa, preferably 10 to 90 MPa, more preferably 20 to 80 MPa (particularly 30 to 70 MPa) by a method based on JIS K7161.

The outermost layer may contain another resin film in addition to the unstretched polypropylene-based resin film, but is usually formed of the unstretched polypropylene-based resin film alone.

The average thickness of the outermost layer is, for example, 15 to 50 μm, preferably 20 to 40 μm, and more preferably about 25 to 35 μm. If the average thickness of the outermost layer is too thick, the heat shrinkage balance will be poor, curling may occur on the lid material side (outermost layer side of the lid material), and economic efficiency may be reduced. , The curl suppressing effect may be reduced.

In the present specification and claims, the average thickness is measured by using a dial gauge and measuring the thickness of 5 sheets at any 10 points of the film according to the JIS K7130 (1992) A-2 method. It can be calculated by dividing the average value of 5 sheets by 10.

[Middle layer]
The multilayer film of the present invention further includes an intermediate layer, and the intermediate layer includes a biaxially stretched polypropylene-based resin film. In the present invention, since the intermediate layer contains a biaxially stretched polypropylene-based resin film, curling due to heat treatment can be suppressed and a feeling of waist can be imparted to the multilayer film.

(Biaxially stretched polypropylene resin film)
As the polypropylene-based resin constituting the biaxially stretched polypropylene-based resin, the same polypropylene-based resin as the polypropylene-based resin constituting the non-stretched polypropylene-based resin film of the outermost layer can be used.

The biaxially stretched polypropylene-based resin film may also contain, in addition to the polypropylene-based resin, other thermoplastic resins exemplified in the section of the non-axially stretched polypropylene-based resin film, conventional additives, and the like. The total ratio of the other thermoplastic resins and additives is the same as that of the non-axially stretched polypropylene-based resin film.

The tensile strength of the biaxially stretched polypropylene-based resin film is, for example, 100 MPa or more, preferably 100 to 500 MPa, and more preferably 110 to 400 MPa (particularly 120 to 300 MPa) by a method based on JIS K7161.

In the biaxially stretched polypropylene-based resin film, the draw ratio in the film take-up direction (MD direction) is, for example, 2 to 10 times, preferably 3 to 9 times, and more preferably about 4 to 8 times. The stretch ratio in the film width direction (TD direction) is, for example, 5 to 20 times, preferably 6 to 15 times, and more preferably 7 to 13 times. If the draw ratio is too large, it may be difficult to manufacture the stretched film itself, and if it is too small, the feeling of elasticity of the film may decrease.

The biaxially stretched polypropylene-based resin film (particularly, the surface on the side that does not come into contact with the organic barrier film) may be surface-treated (for example, corona discharge treatment, flame treatment, plasma treatment, ozone or ultraviolet irradiation treatment, etc.). , It may have an easy-adhesion layer.

(Organic barrier film)
The intermediate layer may further contain an organic barrier film in addition to the biaxially stretched polypropylene-based resin film. In the present invention, by including the organic barrier film, not only the oxygen gas barrier property is improved due to the high flexibility of the barrier film, but also the oxygen gas barrier property is lowered due to cracks in the barrier layer due to damage during packaging or transportation. Can also be suppressed.

Examples of the organic barrier resin constituting the organic barrier film include vinylidene chloride resin, vinyl alcohol resin (polyvinyl alcohol, ethylene-vinyl alcohol copolymer, etc.), and water-soluble polysaccharide (water-soluble cellulose derivative, etc.). Water-soluble starch, chitosan, etc.) and the like. These organic barrier resins can be used alone or in combination of two or more. Among these organic barrier resins, vinylidene chloride-based resins are preferable because they can suppress deterioration of oxygen gas barrier properties due to humidity and moisture.

The vinylidene chloride-based resin may be a vinylidene chloride homopolymer (vinylidene chloride homopolymer) or a vinylidene chloride copolymer (vinylidene chloride-based copolymer).

In the copolymer, examples of the monomer copolymerizable with vinylidene chloride (copolymerizable monomer) include chlorine-containing monomers other than vinylidene chloride such as vinyl chloride; vinyl ester-based monomers such as vinyl acetate and vinyl propionate; butadiene and isoprene. Diene-based monomers such as (meth) acrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, crotonic acid, isocrotonic acid, mesaconic acid, angelic acid and other ethylene-based unsaturated carboxylic acids; methyl (meth) acrylic acid. , (Meta) ethyl acrylate, (meth) butyl acrylate, etc. (meth) acrylic acid alkyl ester, (meth) acrylic acid hydroxyalkyl ester, glycidyl (meth) acrylate, etc. (meth) acrylic acid ester; (meth) acrylonitrile Examples thereof include vinyl cyanide-based monomers. These copolymerizable monomers can be used alone or in combination of two or more. Among the copolymerizable monomers, vinyl chloride, vinyl acetate, (meth) acrylic acid, (meth) acrylic acid alkyl ester, (meth) acrylic acid hydroxyalkyl ester, glycidyl (meth) acrylate, (meth) acrylonitrile and the like are general-purpose. And vinyl chloride is preferred.

Examples of the form of the copolymer include block copolymerization, random copolymerization, alternating copolymerization, and graft copolymerization. Of these, usually random copolymerization and alternating copolymerization.

In vinylidene chloride-based resins, the ratio (molar ratio) of vinylidene chloride (vinylidene chloride unit) and copolymerizable monomer (copolymerizable monomer unit) is vinylidene chloride / copolymerizable monomer (particularly vinyl chloride) = 99 /. It is 1 to 5/95, preferably 97/3 to 10/90, and more preferably 95/5 to 50/50. If the proportion of vinylidene chloride is too small, the handleability (solvent solubility) may be deteriorated, and if it is too large, the oxygen gas barrier property may be deteriorated.

The number average molecular weight of the vinylidene chloride resin is, for example, 10,000 to 500,000, preferably 20,000 to 250,000, and more preferably 25,000 to 100 in terms of polystyrene in gel permeation chromatography (GPC). It may be about 000.

In addition to the organic barrier resin (particularly vinylidene chloride resin), the organic barrier film has a reactive adhesive component [isocyanate compound (tolylene diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, diphenylmethane-4, Aromatic isocyanates such as 4'-diisocyanate and derivatives thereof), imino group-containing polymers (polyethyleneimine, etc.), etc.] may be contained.

The ratio of the reactive adhesive component is 30 parts by weight or less (for example, 0.1 to 30 parts by weight), preferably 0.5 to 20 parts by weight, and more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the vinylidene chloride resin. It may be about a part.

In addition to chlorine vinylidene resins and reactive adhesive components, organic barrier films include other thermoplastic resins (olefin resins such as polyethylene resins, other chlorine-containing resins, styrene resins, petroleum resins, etc.) and shaftless. It may contain the conventional additives exemplified in the section of the stretched polypropylene-based resin film. The total ratio of the other thermoplastic resin and the additive is 50 parts by weight or less, preferably 30 parts by weight or less (for example, 0.01 to 30 parts by weight), more preferably 10 parts by weight, based on 100 parts by weight of the vinylidene chloride resin. It is about 10 parts by weight or less (for example, 0.1 to 10 parts by weight).

(Characteristics of intermediate layer)
The intermediate layer may contain another resin film in addition to the biaxially stretched polypropylene resin film and the organic barrier film, but is usually a biaxially stretched polypropylene resin film alone or a biaxially stretched polypropylene film. It is a combination of a resin film and an organic barrier film.

When the biaxially stretched polypropylene resin film and the organic barrier film are combined, the organic barrier film may be laminated on both sides of the biaxially stretched polypropylene resin film, or the biaxially stretched polypropylene resin film may be laminated on both sides of the organic barrier film. A resin film may be laminated, but usually, an organic barrier film is laminated on one surface of a biaxially stretched polypropylene-based resin film. When the organic barrier film is laminated on one surface of the biaxially stretched polypropylene resin film, the organic barrier film may be laminated on the outermost layer side or on the sealant layer side.

An adhesive layer may be interposed between the biaxially stretched polypropylene resin film and the organic barrier film, but when the organic barrier film contains a reactive adhesive component, the adhesive layer may not be interposed. .. The laminated film of the biaxially stretched polypropylene resin film and the organic barrier film without interposing an adhesive layer is a laminated film (organic barrier film) in which at least one surface of the biaxially stretched polypropylene resin film is coated with an organic barrier film. Is a laminated film, which is a coating film). A laminated film in which the organic barrier film is a coating film is also available as a commercial product.

The average thickness of the intermediate layer is, for example, 10 to 45 μm, preferably 15 to 40 μm, and more preferably about 18 to 35 μm. If the average thickness of the intermediate layer is too thick, the flexibility and economy may be lowered, and if it is too thin, the feeling of waist may be lowered.

The average thickness of the intermediate layer may be 0.5 times or more (particularly 0.7 times or more) with respect to the average thickness of the outermost layer, for example, 0.5 to 2 times, preferably 0.7 to 1. It is about 5 times, more preferably 0.8 to 1.2 times (particularly 0.9 to 1.1 times). If the thickness of the intermediate layer with respect to the outermost layer is too thin, curling may occur.

When the intermediate layer is formed of a biaxial polypropylene resin film and an organic barrier film, the average thickness ratio of the two (when each layer is a plurality of layers, the total average thickness ratio) is, for example, biaxial polypropylene. Resin film / organic barrier film = 70/1 to 5/1, preferably 60/1 to 10/1, more preferably 50/1 to 15/1 (particularly 40/1 to 20/1). If the thickness of the organic barrier film with respect to the biaxial polypropylene resin film is too thin, the oxygen gas barrier property may be lowered, and if it is too thick, curling may occur.

[Sealant layer]
The multilayer film of the present invention further includes a sealant layer, and the sealant layer contains a non-stretched olefin resin film. In the present invention, since the sealant layer contains a non-stretched olefin resin film, it has a heat-sealing property, and the multilayer film itself is heat-sealed to form a bag body, or another film or container (bottom material). Etc.) and can be heat-sealed.

The olefin resin constituting the unstretched olefin resin film is preferably an olefin resin having a lower melting point than the polypropylene resin contained in the unstretched polypropylene resin film, and may be a polypropylene resin, but polyethylene. It is preferable to contain a based resin.

The polyethylene-based resin may be an ethylene homopolymer (ethylene homopolymer) or an ethylene copolymer (ethylene copolymer).

In the copolymer, examples of the monomer copolymerizable with ethylene (copolymerizable monomer) include propylene, α-olefin (excluding ethylene) and alkaziene exemplified as the copolymerizable monomer of unstretched polypropylene contained in the outermost layer. , Ethylene-based unsaturated carboxylic acid and its acid anhydride, (meth) acrylic acid ester, carboxylic acid vinyl ester and the like. These copolymerizable monomers can be used alone or in combination of two or more. _{Among these monomers, α-C 3-10} olefins such as 1-butene, 1-hexane, 1-octene and 4-methyl-1-pentene are widely used, and α-C 4-8 olefins such as 1-butene are _{widely used.} Is preferable.

Examples of the form of the copolymer include block copolymerization, random copolymerization, alternating copolymerization, and graft copolymerization. Of these, usually random copolymerization and alternating copolymerization.

In the polyethylene-based resin, the ratio (molar ratio) of ethylene (ethylene unit) to the copolymerizable monomer (copolymerizable monomer unit) is ethylene / copolymerizable monomer = 50/50 to 100/0, preferably 60 /. It is about 40 to 99/1, more preferably 65/35 to 95/5 (particularly 70/30 to 90/10). If the proportion of ethylene is too small, the moldability and the like may deteriorate.

Examples of the polyethylene-based resin include low-density polyethylene (LDPE), medium-density polyethylene, high-density polyethylene (HDPE), linear (linear) low-density polyethylene (LLDPE), and the like. Of these, LLDPE is preferable from the viewpoint of heat-sealing property, and LLDPE alone may be used alone. From the viewpoint of adjusting the melting point (heat-sealing property), LLDPE and other polyolefin-based resins (particularly other polyethylene-based resins). ) May be used in combination.

When the polyolefin resin contains LLDPE, the weight ratio of LLDPE is, for example, 50% by weight or more, preferably 80 to 100% by weight, and more preferably 90 to 100% by weight or more with respect to the entire polyethylene resin.

The number average molecular weight of the olefin resin (particularly polyethylene resin) may be, for example, 10,000 to 300,000, preferably 15,000 to 200,000, and more preferably about 20,000 to 100,000. .. In the present specification and claims, the number average molecular weight of the polyolefin resin is a value measured under the same conditions as the method for measuring the number average molecular weight of the polypropylene resin contained in the outermost layer.

The melting point (or softening point) of the olefin resin (particularly polyethylene resin) is preferably lower than the melting point of the polypropylene resin contained in the outermost layer, for example, 80 to 150 ° C, preferably 90 to 140 ° C, more preferably. Is about 100 to 130 ° C. (particularly 110 to 125 ° C.). In the present specification and claims, the melting point of the olefin resin can be measured based on the melting peak temperature of the differential scanning calorimeter DSC.

The tensile strength of the unstretched olefin resin film is, for example, less than 100 MPa, preferably 10 to 90 MPa, more preferably 20 to 80 MPa (particularly 30 to 70 MPa) by a method based on JIS K7161.

In addition to the olefin resin, the sealant layer is a conventional addition exemplified in the section of other thermoplastic resins (chlorine-containing resin, styrene resin, petroleum resin, etc.) and the non-axially stretched polypropylene resin film contained in the outermost layer. It may contain an agent or the like. The total ratio of the other thermoplastic resin and the additive is 50 parts by weight or less, preferably 30 parts by weight or less (for example, 0.01 to 30 parts by weight), more preferably 10 parts by weight, based on 100 parts by weight of the olefin resin. It is about the following (for example, 0.1 to 10 parts by weight).

The sealant layer may contain another resin film in addition to the unstretched olefin resin film, but is usually formed of the unstretched olefin resin film alone.

The average thickness of the sealant layer is, for example, about 20 to 70 μm, preferably 22 to 50 μm, and more preferably 23 to 40 μm (particularly 25 to 30 μm). If the average thickness of the sealant layer is too thick, curling may occur and the economic efficiency may be reduced, and if it is too thin, the physical properties (impact resistance, piercing strength, etc.) and heat sealability may be deteriorated. ..

The average thickness of the sealant layer may be 3 times or less (particularly 0.9 times or less) with respect to the average thickness of the outermost layer, for example, 0.3 to 2 times, preferably 0.4 to 1 times, and further. It is preferably about 0.5 to 0.9 times (particularly 0.65 to 0.85 times). If the thickness of the sealant layer with respect to the outermost layer is too thick, curl may occur.

[Adhesive layer]
In the multilayer film of the present invention, a first adhesive layer may be interposed between the outermost layer and the intermediate layer, and a second adhesive layer may be interposed between the intermediate layer and the sealant layer.

As the adhesive component contained in the first and second adhesive layers, a conventional adhesive or an adhesive can be used. Examples of the adhesive include vinyl-based adhesives, polyolefin-based adhesives, polyamide-based adhesives, polyester-based adhesives, urethane-based adhesives (thermoplastic polyurethane-based adhesives, two-component curable polyurethane-based resins, etc.), cellulose. Examples include system-based adhesives and rubber-based adhesives. Examples of the pressure-sensitive adhesive include rubber-based pressure-sensitive adhesives, acrylic-based pressure-sensitive adhesives, and olefin-based pressure-sensitive adhesives (modified olefin-based pressure-sensitive adhesives, etc.).

Among these adhesive components, urethane-based adhesives are preferable from the viewpoint of having high adhesiveness and flexibility, and two-component curable polyether urethane-based resins are particularly preferable from the viewpoint of being able to highly suppress delamination between layers.

The two-component curable polyether urethane resin may be a combination of a polyether urethane having a hydroxyl group at the terminal and a curing agent.

The polyether urethane having a hydroxyl group at the terminal may be a reaction product of a polyether polyol and a polyisocyanate.

_{Examples of the polyether polyol include a single or copolymer of an oxylan compound (for example, C 2-6} alkylene oxide such as ethylene oxide, propylene oxide, butylene oxide, and tetrahydrofuran) [for example, polyethylene glycol (PEG), polypropylene glycol (for example). PPG), polytetramethylene ether glycol (PTMG), etc.] and the like. These polyether polyols can be used alone or in combination of two or more. Of these, poly C _2-4 alkylene glycol such as polypropylene glycol is preferable.

The polyisocyanate is not particularly limited as long as it has two or more isocyanate groups in the molecule, and is, for example, an aliphatic polyisocyanate, an alicyclic polyisocyanate, an aromatic aliphatic polyisocyanate, an aromatic polyisocyanate, or a heterocyclic polyisocyanate. Isocyanates, polyisocyanates derivatives (polyisocyanate dimer, trimmer, biuret, allophanate, poly having a 2,4,6-oxadiazine trione ring which is a polymer of carbon dioxide gas and the polyisocyanate monomer. Isocyanate, carbodiimide, uretdione, etc.) and the like. These polyisocyanates can be used alone or in combination of two or more. Among these polyisocyanates, aliphatic diisocyanates such as hexamethylene diisocyanate (HDI), isophorone diisocyanates (IPDI), alicyclic diisocyanates such as hydrogenated xylylene diisocyanate (hydrogenated XDI), aromatic aliphatic diisocyanates such as XDI, Aromatic diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), and 1,5-naphthylene diisocyanate (NDI) are widely used.

As the curing agent, a conventional curing agent can be used. The conventional curing agent may be the polyisocyanate or a urethane prepolymer having an isocyanate group at the terminal.

The adhesive component contained in the first adhesive layer and the adhesive component contained in the second adhesive layer may be different adhesive components, but are usually the same adhesive component.

The first and second adhesive layers may contain the conventional additives exemplified in the section of the non-axially stretched polypropylene-based resin film contained in the outermost layer, in addition to the adhesive components, respectively. The ratio of the additive is 50 parts by weight or less, preferably 30 parts by weight or less (for example, 0.01 to 30 parts by weight), and more preferably 10 parts by weight or less (for example, 0.1 to 10 parts by weight) with respect to 100 parts by weight of the adhesive component. (Weight part).

The average thickness of the first and second adhesive layers is 0.5 to 7 μm, preferably 1 to 5 μm, and more preferably 1.4 to 4.2 μm, respectively. If the average thickness of the first and second adhesive layers is too thick, the economic efficiency may decrease, and if it is too thin, the adhesiveness between the layers may decrease.

[Print layer]
In the multilayer film of the present invention, a printing layer may be printed on the surface of any one of the intermediate layers. The print layer may be printed on the sealant layer side of the intermediate layer, but it is preferable to print on the outermost layer side from the viewpoint of visibility and the like. Further, if the intermediate layer is a combination of a base resin film and an organic barrier layer, printing layer may be printed on the surface of the base resin film, the surface of the organic barrier layer It may be printed on. As the printing layer, a conventional ink composition containing a pigment can be used. Examples of the printing method include a screen printing method, an inkjet printing method, an intaglio printing method (for example, a gravure printing method), an offset printing method, an intaglio offset printing method, and a flexo printing method. Of these methods, the gravure printing method is preferable. The average thickness of the printed layer is 0.1 to 3 μm, preferably 0.3 to 2 μm, and more preferably 0.5 to 1.5 μm, respectively.

[Multilayer film]
The multilayer film of the present invention may have an oxygen gas barrier property. When an organic barrier film is included as the intermediate layer, the oxygen gas permeability under measurement conditions of 20 ° C. and 80% RH is, for example, 5 to 200 ml / m ² · d · MPa, preferably 10 to 180 ml / according to JIS K7126. It is about m ² · d · MPa, more preferably about 15 to 150 ml / m ² · d · MPa.

The average thickness of the multilayer film of the present invention is, for example, 40 to 100 μm, preferably 50 to 90 μm, and more preferably about 60 to 80 μm. If the average thickness of the multilayer film is too thin, the feeling of waist may be lowered, and if it is too thick, the flexibility may be lowered and the economic efficiency may be lowered.

The multilayer film of the present invention is preferably used as a packaging film for heat-sealing and sealing food, and is particularly preferably used as a lid material for vacuum deep drawing and packaging of processed livestock meat products. As a bottom material to be combined with the lid material of vacuum deep drawing molding packaging, a conventional bottom material laminated with an outermost layer, an intermediate layer and a sealant layer can be used, but since curling can be suppressed, a non-stretched polypropylene resin film can be used. A bottom material having an outermost layer containing the above is preferable. The bottom material usually has a recess for accommodating the contents, and is heat-sealed with the lid material at the flange portion around the recess.

The multilayer film of the present invention can be produced by a conventional method, for example, a coextrusion molding method, a laminating method (melt extrusion laminating method, thermal laminating method or solvent-free laminating method, dry laminating method, etc.). Of these methods, the dry laminating method or the solvent-free laminating method is preferable because it has high adhesiveness between layers, is particularly excellent in heat resistance, and has high adhesiveness between layers even after heat treatment (particularly boil treatment). .. In the dry laminating method, the outermost layer, the intermediate layer, and the sealant layer can be integrated by interposing a dry laminating adhesive as an adhesive layer. In the solvent-free laminating method, the outermost layer, the intermediate layer, and the sealant layer can be integrated by interposing a solvent-free laminating adhesive as an adhesive layer.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. The characteristics of the multilayer films obtained in Examples and Comparative Examples were evaluated by the following methods.

[Ingredients used]
(Outermost layer)
Unstretched polypropylene film A (CPP30): "Pilen film-CT P1111" manufactured by Toyobo Co., Ltd., average thickness 30 μm
Unstretched polypropylene film B (CPP40): "Pilen film-CT P1111" manufactured by Toyobo Co., Ltd., average thickness 40 μm
(Middle layer)
Organic barrier coat biaxially stretched polypropylene film A (KOP20): "Senesi KOP 6050" manufactured by Daicel Value Coating Co., Ltd., average thickness 20 μm
Barrier coat biaxially stretched polypropylene film B (KOP30): "Senesi KOP 6050" manufactured by Daicel Value Coating Co., Ltd., average thickness 30 μm
Biaxially stretched polypropylene film (OPP): "Pilen film-OT P2161" manufactured by Toyobo Co., Ltd., average thickness 20 μm
Transparent thin-film polyethylene terephthalate film (VMPET): "HGMCR" manufactured by Toray Film Processing Co., Ltd., average thickness 12 μm
Organic barrier coat polyethylene terephthalate film (KET): "Senesi KET 6000" manufactured by Daicel Value Coating Co., Ltd., average thickness 12 μm
Polyethylene terephthalate film (PET): "FE2001" manufactured by Futamura Chemical Co., Ltd., average thickness 12 μm.

(Sealant layer)
Linear low-density polyethylene film A (LLDPE25): "TUX TCS" manufactured by Mitsui Chemicals Tohcello Co., Ltd., average thickness 25 μm
Linear low-density polyethylene film B (LLDPE30): "TUX TCS" manufactured by Mitsui Chemicals Tohcello Co., Ltd., average thickness 30 μm
Linear low-density polyethylene film C (LLDPE50): "TUX TCS" manufactured by Mitsui Chemicals Tohcello Corporation, average thickness 50 μm.

(Adhesive layer)
Polyether urethane adhesive (for dry laminating): Toyo Morton Co., Ltd. "TM-314 / CAT-14B", two-component curable dry laminating adhesive Polyester urethane adhesive (for dry laminating): Toyo Morton Co., Ltd. ) Made "TM-570 / CAT-RT37", Adhesive for two-component curable dry laminate Polyester urethane adhesive (for solvent-free laminate): Toyo Morton Co., Ltd. "EA-N373 A / B", Two-component Adhesive for curable solvent-free laminate.

(Bottom material)
Multi-layer coextruded multi-layer film for food packaging: "Sumilite CEL-4571A" manufactured by Sumitomo Bakelite Co., Ltd.

(Curling)
Using the multilayer films obtained in Examples and Comparative Examples and the multilayer coextruded multilayer film for food packaging as the bottom material, film samples cut into a size of 50 × 50 mm were overlapped so that the sealant layers were in contact with each other. The pressure was applied under the conditions of 130 ° C., 1 MPa, and 1 second. All the samples sealed after pressurization were curled toward the bottom material. Immediately after pressurization, the sample was placed on a horizontal table, the height (mm) from the horizontal position of each of the four corners was measured, and the average height was calculated. The curl property was evaluated according to the following criteria.

⊚: less than 1.0 mm ○: 1.0 mm or more and less than 2.5 mm Δ: 2.5 mm or more and less than 3.8 mm ×: 3.8 mm or more and less than 5 mm × ×: 5 mm or more.

(Oxygen barrier property)
Oxygen gas permeability (A) was measured for the multilayer films obtained in Examples and Comparative Examples under the conditions of 20 ° C. and 80% RH in accordance with JIS K7126. Further, for the film having an oxygen gas permeability of ^{less than 150 ml / m 2} · d · MPa, the oxygen gas permeability was measured after carrying out the gelboflex test shown below.

The gelboflex test was performed using a gelboflex tester (manufactured by Rikagaku Kogyo Co., Ltd.). First, the obtained film sample is cylindrically formed into a fixed head having a diameter of 8.89 cm (3.5 inches) and a movable head having the same diameter arranged in parallel at a distance of 17.78 cm (7 inches) from the fixed head. Attached to. The shaft attached to the center of the movable head controls the movement of the movable head. First, twist the movable head 440 degrees to bring it closer to the fixed head by 8.89 cm (3.5 inches), then move it horizontally to bring it closer to the fixed head by 6.35 cm (2.5 inches), and then move it in the opposite direction. It returned to the state of. This cycle was performed 50 times at a speed of 40 times / minute at 23 ° C. and 60% RH. Oxygen gas permeability (B) was also measured for the sample after the Gelboflex test.

After conducting the above tests, the oxygen barrier property was evaluated according to the following criteria.

◯: The oxygen gas permeability (A) of the sample not ^{subjected to the gelboflex test is less than 150 ml / m 2} · d · MPa, and the relationship with the oxygen gas permeability (B) after the gelboflex test is carried out. , Permeability (B) / Permeability (A) = less than 1.5 ×: Oxygen gas permeability (A) of the sample not subjected to the gelboflex test is 150 ml / m ² · d · MPa or more, or gel The relationship with the oxygen gas permeability (B) after performing the Boflex test is permeability (B) / and permeability (A) = 1.5 or more.

(Laminate strength)
The multilayer films obtained in Examples and Comparative Examples were cut into strips having a width of 15 mm to prepare test pieces, and using these test pieces, Tencilon ("RTM" manufactured by Orientec Co., Ltd.) was used in accordance with JIS K7127. -00 ") was used to measure the peel strength (laminate strength) at a tensile speed of 300 mm / min (strength between the outermost layer and the intermediate layer, strength between the intermediate layer and the sealant layer). The laminated strength of the obtained measured values was evaluated according to the following criteria.

◯: The peel strength of the outermost layer and the intermediate layer, and the peel strength of the intermediate layer and the sealant layer are both 1 N / 15 mm or more. ×: The peel strength of the outermost layer and the intermediate layer, and the intermediate layer and the sealant layer are both less than 1 N / 15 mm.

Example 1
Three films, a non-stretched polypropylene film A (CPP30) as the outermost layer, an organic barrier-coated biaxially stretched polypropylene film A (KOP20) as an intermediate layer, and a linear low-density polyethylene film B (LLDPE30) as a sealant layer, are dried. Using a laminating machine ("2DL-110TAW" manufactured by Okazaki Kikai Kogyo Co., Ltd.), line speed 150 m / min, drying temperature 1st zone: 55 ° C, 2nd zone: 65 ° C, 3rd zone: 75 ° C. The multilayer film was manufactured by dry laminating with. The organic barrier film of the intermediate layer and the sealant are opposed to each other, and a polyether urethane adhesive (for dry lamination) is used as a first adhesive layer and a second adhesive layer between the layers to have a dry thickness of 3. It was applied with a coating amount of 8 μm.

Example 2
A multilayer film was produced by the same method as in Example 1 except that a biaxially stretched polypropylene film (OPP) was used instead of the organic barrier coated biaxially stretched polypropylene film A (KOP20) as an intermediate layer.

Example 3
A multilayer film was produced by the same method as in Example 1 except that a barrier-coated biaxially stretched polypropylene film B (KOP30) was used as the intermediate layer instead of the organic barrier-coated biaxially stretched polypropylene film A (KOP20).

Example 4
A multilayer film was produced by the same method as in Example 1 except that a linear low-density polyethylene film C (LLDPE50) was used instead of the linear low-density polyethylene film B (LLDPE30) as the sealant layer.

Example 5
A multilayer film was produced by the same method as in Example 1 except that a linear low-density polyethylene film A (LLDPE25) was used instead of the linear low-density polyethylene film B (LLDPE30) as the sealant layer.

Example 6
A multilayer film was produced by the same method as in Example 1 except that the organic barrier film of the intermediate layer and the outermost layer were opposed to each other (the intermediate layer was inverted).

Example 7
A multilayer film in the same manner as in Example 1 except that a polyester urethane adhesive (for dry laminating) is used instead of the polyether urethane adhesive (for dry laminating) as the first adhesive layer and the second adhesive layer. Manufactured.

Example 8
Three films, unstretched polypropylene film A (CPP30) as the outermost layer, organic barrier coated biaxially stretched polypropylene film A (KOP20) as the intermediate layer, and linear low-density polyethylene film B (LLDPE30) as the sealant layer, are absent. A multi-layer film was produced by solvent-free laminating under the condition of a line speed of 180 m / min using a solvent laminating machine (“L5-105” manufactured by Fuji Kikai Kogyo Co., Ltd.). The organic barrier film of the intermediate layer and the sealant are opposed to each other, and a polyether urethane adhesive (for solvent-free lamination) is used as a first adhesive layer and a second adhesive layer between the layers to have a dry thickness of 1. It was applied with a coating amount of 9.9 μm.

Comparative Example 1
A dry laminating machine (Okazaki) uses three films: unstretched polypropylene film B (CPP40) as the outermost layer, transparent vapor-deposited polyethylene terephthalate film (VMPET) as the intermediate layer, and linear low-density polyethylene film C (LLDPE50) as the sealant layer. Using "2DL-110TAW" manufactured by Kikai Kogyo Co., Ltd.), dry laminate under the conditions of line speed 150 m / min, drying temperature 1st zone: 55 ° C, 2nd zone: 75 ° C, 3rd zone: 85 ° C. , Manufactured a multilayer film. The vapor-deposited film of the intermediate layer and the outermost layer are opposed to each other, and a polyester urethane adhesive (for dry lamination) is used as a first adhesive layer and a second adhesive layer between the layers to have a dry thickness of 3.8 μm. It was applied in the coating amount that became.

Comparative Example 2
An unstretched polypropylene film A (CPP30) is used as the outermost layer, and a linear low-density polyethylene film B (LLDPE30) is used as the sealant layer instead of the linear low-density polyethylene film C (LLDPE50). A multilayer film was produced by the same method as in Comparative Example 1 except that the vapor-deposited film and the sealant layer were opposed to each other.

Comparative Example 3
A multilayer film was produced by the same method as in Comparative Example 2 except that a polyethylene terephthalate film (PET) was used instead of the transparent vapor-deposited polyethylene terephthalate film (VMPET) as the intermediate layer.

Comparative Example 4
The same method as in Comparative Example 2 except that an organic barrier-coated polyethylene terephthalate film (KET) is used as the intermediate layer instead of the transparent vapor-deposited polyethylene terephthalate film (VMPET), and the organic barrier film of the intermediate layer and the sealant layer are opposed to each other. Manufactured a multilayer film in.

Table 1 shows the evaluation results of the multilayer films obtained in Examples and Comparative Examples.

As is clear from the results in Table 1, the multilayer film of the example suppressed curling and was excellent in printability. In particular, the multilayer films of Examples 1, 3 to 6 and 8 had high oxygen barrier properties and high lamination strength. On the other hand, the multilayer films of Comparative Examples had curls, and the multilayer films of Comparative Examples 1 to 3 had low oxygen barrier properties. In particular, cracks also occurred in the multilayer films of Comparative Examples 1 and 2.

The multilayer film of the present invention can be used as a packaging film for heat-sealing and sealing food, and is suitable as a lid material for vacuum deep drawing packaging of processed livestock meat products such as ham, sausage, bacon, roasted pork, and chicken. It is particularly suitable as a lid material for vacuum deep draw molding packaging such as sausages that are boiled after being sealed.

Claims (9)

A multilayer film containing an outermost layer containing a non-stretched polypropylene resin film , an intermediate layer containing a biaxially stretched polypropylene resin film and an organic barrier film , and a sealant layer containing a non-stretched olefin resin film in this order. Organic barrier film, the multilayer film according to claim 1 wherein the vinylidene chloride-based resin layer. The multilayer film according to claim 1 or 2, wherein the non-stretched olefin resin film contained in the sealant layer contains linear low-density polyethylene. The multilayer film according to any one of claims 1 to 3, wherein a first adhesive layer is interposed between the outermost layer and the intermediate layer, and a second adhesive layer is interposed between the intermediate layer and the sealant layer. The multilayer film according to claim 4, wherein the first and second adhesive layers contain a two-component curable polyether urethane-based resin. The multilayer film according to any one of claims 1 to 5 , wherein the average thickness of the intermediate layer is 0.7 times or more the average thickness of the outermost layer. The multilayer film according to any one of claims 1 to 6 , wherein the average thickness of the sealant layer is 0.9 times or less the average thickness of the outermost layer. The multilayer film according to any one of claims 1 to 7 , which is a multilayer film for food packaging. The multilayer film according to any one of claims 1 to 8 , which is a lid material for vacuum deep drawing molding packaging.