JP6988082B2 - Sealant film and packaging material - Google Patents

Description

The present invention relates to a sealant film used for retort pouch packaging or the like that can be sterilized and cooked by heating or pressurizing while food or the like is packaged, and a packaging material using the sealant film.

Flexible packaging using plastic materials is used worldwide as food packaging materials, and it is showing an increasing trend as it spreads to emerging countries. Under these circumstances, retort-packed foods that have been pressurized and sterilized by heating (retort-sterilized) at high temperatures are expected to increase in demand in the food packaging market in the future due to their convenience. Retort-packed foods can be distributed at room temperature, and in addition to being easy to eat, they are also easy to handle in distribution, and are expected to expand to areas where the development of cold chains is insufficient.

In order to eat retort-packed foods, it is generally boiled in boiling water to heat them, and after heating, the film is torn from a notch provided at the upper end of the packaging bag to open the package. Therefore, the resin film used for retort packaging is required to have easy tearability. As the easily tearable retort film, for example, a propylene-based film in which a resin in which a propylene-ethylene block copolymer is mixed with a low-crystalline ethylene-based elastomer and the double refractive index is controlled in a specific range is disclosed. (See Patent Document 1).

Further, the packaging material having an easy-cut property contains a cyclic olefin resin and a linear low-density polyethylene resin as a packaging material used for a soft bag filled with a chemical solution such as physiological saline or an electrolytic solution. A packaging material having an intermediate layer and an inner layer and an outer layer of a linear low-density polyethylene resin is disclosed (see Patent Document 2).

JP 2011-162667 Patent No. 5262134

The above-mentioned propylene-based film having promoted birefringence has a decrease in tear strength due to the improvement in the rigidity of the film, but the control of the tear direction is not sufficient, and the straight-line cut property of linear tearing is observed. Was required to improve.

Further, in heavy objects for commercial use and distribution in cold regions, a packaging material using an ethylene-propylene copolymer as a sealant does not have sufficient impact resistance and may cause a bag breakage accident.

Although the packaging material used for the above soft bag has easy-cutting properties and straight-line cutting properties, it is not expected to be applied to retort-packed applications. There was a problem that the inner surfaces of the bag were fused to each other and the appearance was uneven.

An object to be solved by the present invention is to provide a sealant film and a packaging material which are excellent in easy tearing property and straight-line cutting property and which do not cause inner surface fusion and appearance unevenness of the packaging material during high temperature treatment.

Further, in the present invention, in addition to the above problems, it is an object to provide a sealant film having suitable sealing property and bag breaking resistance.

The present invention comprises a laminated film in which an outer layer (A), an intermediate layer (B) and an inner layer (C) are laminated in this order, and the outer layer (A) and the inner layer (C) contain a polyethylene-based resin, and the resin in each layer. The average density of the components is 0.940 g / cm ³ or more, the intermediate layer (B) contains a linear low-density polyethylene (b1) and a cyclic olefin resin (b2), and the linear low-density polyethylene A sealant having a density of (b1) of 0.937 g / cm ³ or more and a content of the cyclic olefin resin (b2) in the resin component contained in the intermediate layer (B) of 20 to 40% by mass. The film solves the above-mentioned problems.

Since the sealant film of the present invention has suitable easy tearing property and straight-line cutting property due to the above configuration, the packaging bag using the sealant film of the present invention has spillage of the contents at the time of opening or after the opening starts to occur. And is less likely to scatter. In addition, it is possible to realize a packaging material that does not cause inner surface fusion or uneven appearance during high-temperature treatment such as retort sterilization treatment while realizing the suitable tearability. Therefore, the sealant film of the present invention can be suitably applied to packaging materials for high temperature treatment such as retort food packaging materials that require high temperature sterilization.

Further, the sealant film of the present invention is suitable for these packaging materials because it is easy to realize suitable sealing property and bag breaking resistance.

The sealant film of the present invention is a laminated film in which an outer layer (A), an intermediate layer (B) and an inner layer (C) are laminated in this order, and the outer layer (A) and the inner layer (C) contain a polyethylene resin. The average density of the resin components in each of the outer layer (A) and the inner layer (C) is 0.940 g / cm ³ or more. The intermediate layer (B) between the outer layer (A) and the inner layer (B) contains the linear low-density polyethylene (b1) and the cyclic olefin resin (b2), and the linear low-density polyethylene (b1) is contained. A sealant film having a density of 0.937 g / cm ³ or more and a content of the cyclic olefin resin (b2) in the resin component contained in the intermediate layer (B) of 20 to 40% by mass.

[Outer layer (A)]
The polymer-based resin used for the outer layer (A) of the sealant film of the present invention includes ultra-low density polyethylene (VLDPE), linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), and linear medium-density polyethylene. (LMDPE), polyethylene resins such as medium density polyethylene (MDPE), ethylene-vinyl acetate copolymer (EVA), ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl acrylate copolymer (EEA), Ethylene-methyl acrylate (EMA) copolymer, ethylene-ethyl acrylate-maleic anhydride copolymer (E-EA-MAH), ethylene-acrylic acid copolymer (EAA), ethylene-methacrylic acid copolymer (EMAA) ) And the like; further, an ionomer of an ethylene-acrylic acid copolymer, an ionomer of an ethylene-methacrylic acid copolymer and the like can be exemplified. These polyethylene-based resins may be used alone or in combination of two or more. Among these, ultra-low density polyethylene, linear low density polyethylene, low density polyethylene, and linear medium density polyethylene can be preferably used because suitable impact resistance can be easily obtained, and linear low density polyethylene is particularly preferable. .. It is also preferable to use high density polyethylene (HDPE) in combination with these medium and low density polyethylenes.

As the linear low-density polyethylene, by a low-pressure radical polymerization method using a single-site catalyst, an ethylene monomer is used as a main component, and as comonomer, butene-1, hexene-1, octene-1, 4-methylpentene, etc. are used. It is a copolymer of α-olefin of. The comonomer content in LLDPE is preferably in the range of 0.5 to 20 mol%, more preferably in the range of 1 to 18 mol%.

Examples of the single-site catalyst include various single-site catalysts such as a metallocene catalyst system such as a combination of a metallocene compound of a Group IV or V transition metal of the Periodic Table and an organic aluminum compound and / or an ionic compound. In addition, since the single-site catalyst has a uniform active site, the molecular weight distribution of the obtained resin is sharper than that of the multi-site catalyst having a non-uniform active site, so that a low molecular weight component is formed when the film is formed on a film. It is preferable because a resin having physical properties such as less precipitation and excellent seal strength stability and impact resistance can be obtained.

Since it is easy to obtain suitable impact resistance in the outer layer (A), it is preferable to contain polyethylene-based resin in an amount of 60% by mass or more, and 80% by mass or more, based on the total amount of the resin component forming the layer. It is more preferably contained, and more preferably 90% by mass or more. Among them, it is preferable that only polyethylene-based resin is contained as a resin component, and 60% by mass or more of the resin component is linear low-density polyethylene, more preferably 80% by mass or more, and 90% by mass or more. Is more preferable.

Further, in the outer layer (A), other resins of the above polyethylene-based resin may be used in combination as long as the effect of the present invention is not impaired. Examples of other resin types that can be used in combination include polyolefin resins other than the above polyethylene resins, such as propylene homopolymers, propylene-ethylene copolymers, propylene-butene-1 copolymers, and propylene-ethylene-. Examples of polypropylene-based resins such as butene-1 copolymer and metallocene-catalyzed polypropylene can be exemplified.

When these other resins are used, it is preferably 40% by mass or less, more preferably 20% by mass or less, and 10% by mass or less in the resin component contained in the outer layer (A). Is more preferable. The lower limit is not particularly limited, but the content may be appropriately used in an amount of 1% by mass or more depending on the desired characteristics.

The outer layer (A) used for the sealant film of the present invention is a layer having an average density of resin components used in the layer of 0.940 g / cm ³ or more, preferably 0.940 to 0.945 g / cm ^3. .. By setting the average density of the resin components within the above range, uneven appearance during high-temperature treatment such as retort sterilization treatment can be suitably suppressed. The average density resin used for the layer of the resin a, resin b, and when a resin c · · ·, using the density of these resins _{d a, d b, d c} ···, in the layer When the mass of the resin is W _a , W _b , W _c ..., (d _a W _a + d _b W _b + d _c W _c ...) / (W _a + W _b + W _c ...) The calculated density.

The density of each resin used for the outer layer (A) is not particularly limited as long as the average density of the resin components used is within the above range, but for polyethylene-based resins, it is preferably ^{0.880 g / cm 3 or more.} It is more preferably 0.920 g / cm ³ or more, and particularly preferably 0.940 to 0.950 g / cm ^3. Further, it is preferable to use other resins of 0.920 g / cm ^{3 or more.}

The MFR of the resin component used for the outer layer (A) is 0.1 to 20 g / 10 minutes (190 ° C., 21.18N), preferably 0.3 to 10 g / 10 minutes (190 ° C., 21.18N). It is preferably 0.5 to 5 g / 10 minutes (190 ° C., 21.18N). When the MFR is in this range, good film forming properties can be obtained in various multilayer film forming methods, which is preferable.

[Middle layer (B)]
The intermediate layer (B) of the sealant film of the present invention contains linear low-density polyethylene (b1) having ^{a density of 0.937 g / cm 3 or more.} By containing the linear low-density polyethylene, it is possible to suitably suppress fusion between inner surfaces and uneven appearance during retort sterilization treatment during high-temperature treatment, as well as suitable impact resistance. The density of the linear low-density polyethylene (b1) is preferably 0.940 g / cm ³ or more, and more preferably 0.940 to 0.945 g / cm ³ .

The MFR of the linear low density polyethylene (b1) is 0.1 to 20 g / 10 minutes (190 ° C., 21.18N), preferably 0.3 to 10 g / 10 minutes (190 ° C., 21.18N). It is preferably 0.5 to 5 g / 10 minutes (190 ° C., 21.18N). When the MFR is in this range, the compatibility with the cyclic olefin resin (b2) is excellent, and good film forming property can be obtained in various multilayer film forming methods, which is preferable.

Since the content of the linear low-density polyethylene (b1) in the intermediate layer (B) makes it easy to obtain suitable impact resistance and heat resistance during high-temperature treatment, it is included in the resin component contained in the intermediate layer (B). It is preferably 60 to 80% by mass, and more preferably 65 to 75% by mass.

By containing the cyclic olefin resin (b2) in the intermediate layer (B) of the sealant film of the present invention, excellent easy tearing property and straight-line cutting property can be realized. Examples of the cyclic olefin resin (b2) include norbornene-based polymers, vinyl alicyclic hydrocarbon polymers, and cyclic conjugated diene polymers. Among these, norbornene-based polymers are preferable. The norbornene-based polymer includes a ring-opened polymer of a norbornene-based monomer (hereinafter referred to as “COP”) and a norbornene-based copolymer obtained by copolymerizing a norbornene-based monomer and an olefin such as ethylene (hereinafter referred to as “COP”). , "COC") and the like. Also, COP and COC hydrogenated additives are particularly preferred. 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-based polymer and the norbornene-based monomer used as a raw material are alicyclic-based monomers having a norbornene ring. Examples of such norbornene-based monomers include norbornene, tetracyclododecene, etylidene norbornene, vinylnorbornene, etylidetetracyclododecene, dicyclopentadiene, dimethanotetrahydrofluorene, phenylnorbornene, methoxycarbonylnorbornene, and methoxy. Examples thereof include carbonyltetracyclododecene. These norbornene-based monomers may be used alone or in combination of two or more.

The norbornene-based copolymer is a copolymer of the norbornene-based monomer and a copolymerizable olefin, and examples of such an olefin include the number of carbon atoms of ethylene, propylene, 1-butene and the like. Examples thereof include olefins having 2 to 20 elements; cycloolefins such as cyclobutene, cyclopentene and cyclohexene; and non-conjugated diene such as 1,4-hexadiene.

The content of the cyclic olefin resin (b2) contained in the intermediate layer (B) is preferably 20 to 40% by mass, preferably 25 to 35% by mass in the resin component contained in the intermediate layer (B). It is more preferable to have. By setting the content of the cyclic olefin resin (b2) in the above range, suitable easy tearing property and straight-line cutting property can be realized without impairing the impact resistance.

The cyclic olefin resin (b2) used in the intermediate layer (B) preferably has a glass transition temperature of 140 ° C. or lower, more preferably 50 to 140 ° C., and 70 to 120 ° C. It is more preferable to have. By using the cyclic olefin resin (b2) having the glass transition temperature, it is easy to obtain good heat resistance and rigidity, and it is easy to improve the bag breaking resistance against dropping and the like. In addition, it becomes easy to obtain good compatibility, and it becomes easy to suppress uneven appearance. The glass transition temperature (Tg) is a value obtained by measuring with DSC.

The MFR of the cyclic olefin resin (b2) is 0.2 to 17 g / 10 minutes (230 ° C., 21.18N), preferably 3 to 15 g / 10 minutes (230 ° C., 21.18N), and more preferably 5 to. 13 g / 10 minutes (230 ° C., 21.18 N). When the MFR is in this range, it is preferable in that the compatibility with the linear low-density polyethylene (b1) is excellent and good film forming property can be obtained in various multilayer film forming methods.

As a commercially available product that can be used as the cyclic olefin resin used in the present invention, examples of the ring-opening polymer (COP) of the norbornene-based monomer include "ZEONOR" manufactured by Nippon Zeon Co., Ltd., which are norbornene-based. Examples of the copolymer (COC) include "Appel" manufactured by Mitsui Kagaku Co., Ltd. and "TOPAS" manufactured by Polyplastics Co., Ltd.

As the resin component in the intermediate layer (B), it is preferable to contain only the linear low-density polyethylene (b1) and the cyclic olefin resin (b2), but these are within the range that does not impair the effects of the present invention. Resins other than the resin component may be used in combination. As other resin types that can be used in combination, for example, the polyethylene-based resin exemplified in the outer layer (A), the polypropylene-based resin, and the like can be exemplified.

When these other resins are used, it is preferably 20% by mass or less, and more preferably 10% by mass or less in the resin component contained in the intermediate layer (B). The lower limit is not particularly limited, but the content may be appropriately used in an amount of 1% by mass or more depending on the desired characteristics.

[Inner layer (C)]
The inner layer (C) in the sealant film of the present invention is a layer containing a polyethylene-based resin and having an average density of resin components in the layer of ^{0.940 g / cm 3 or more.} The inner layer (C) is a layer to be a heat seal layer of the sealant film.

The polyethylene-based resin used for the inner layer (C), the resin that can be used in combination with the polyethylene-based resin, and the like can be exemplified by the same ones as those of the outer layer (A), and the preferable ones are also the same. Further, regarding the content of the polyethylene-based resin and other resins, the density and the average density of the resin components in the inner layer, the same range as the outer layer (A) can be exemplified as a preferable range.

In the inner layer (C), high-density polyethylene (HDPE) is used in combination with medium- and low-density polyethylene such as ultra-low density polyethylene, linear low-density polyethylene, low-density polyethylene, and linear medium-density polyethylene. It is also preferable to do. When medium / low density polyethylene and high density polyethylene are used in combination, the content of medium / low density polyethylene in the resin component used for the inner layer (C) is 40 to 80% by mass, and the content of high density polyethylene. Is preferably 20 to 60% by mass, more preferably the content of medium / low density polyethylene is 45 to 75% by mass, and the content of high density polyethylene is 25 to 55% by mass.

[Sealant film]
The sealant film of the present invention is a laminated film in which the outer layer (A), the intermediate layer (B) and the inner layer (C) are laminated in this order. The sealant film of the present invention can realize a packaging material having suitable easy tearing property and straight-line cutting property, but which does not cause inner surface fusion or uneven appearance during high-temperature treatment such as retort sterilization treatment. In addition, it is suitable for retort packaging materials because it is easy to realize suitable sealing properties and rupture resistance.

The thickness of the sealant film of the present invention may be appropriately adjusted according to the intended use and mode, but the total thickness is 20 from the viewpoint of heat resistance in packaging applications, bag tear resistance during distribution, heat sealing properties, and the like. It is preferably ~ 150 μm, more preferably 40-100 μm.

As for the thickness ratio of each layer, the thickness ratio of the outer layer (A) is preferably in the range of 10 to 40% of the total thickness of the sealant film from the viewpoint of sealing property, easy tearing property, and laminating property. More preferably, it is ~ 30%. The thickness ratio of the inner layer (C) is preferably in the range of 10 to 40%, more preferably in the range of 15 to 30%. The thickness ratio of the intermediate layer (B) is preferably 20 to 80%, more preferably 40 to 70%.

As a specific thickness, the thickness of the outer layer (A) is preferably 2 to 60 μm, more preferably 3 to 45 μm. The thickness of the intermediate layer (B1) is preferably 4 to 120 μm, more preferably 8 to 100 μm. The thickness of the inner layer (C) is preferably 2 to 60 μm, more preferably 3 to 45 μm.

The sealant film of the present invention is a laminated film in which the outer layer (A), the intermediate layer (B) and the inner layer (C) are laminated in this order, but the gas barrier layer is between the layers as long as the effect of the present invention is not impaired. Or any other layer such as an easy-adhesion layer may be provided.

Various additives may be added to each layer of the sealant film of the present invention as long as the effects of the present invention are not impaired. Examples of the additive include antioxidants, weather-resistant stabilizers, antistatic agents, anti-fog agents, anti-blocking agents, lubricants, nucleating agents, pigments and the like.

The method for producing the sealant film of the present invention is not particularly limited, but for example, the resin used for each layer of the multilayer film (including a resin mixture containing two or more kinds of resins and additives) is extruded separately. Examples thereof include a coextrusion method in which the film is melted by heating, laminated in a molten state by a method such as a coextrusion multi-layer die method or a feed block method, and then formed into a film by an inflation method, a T-die chill roll method or the like. This coextrusion method is preferable because the thickness ratio of each layer can be adjusted relatively freely, and a film having excellent hygiene and cost effectiveness can be obtained.

[Packaging material for retort pouch]
When the sealant film of the present invention is used as a packaging material for retort pouch, another base film can be attached to the outer layer (A) side surface of the sealant film. The other base film is not particularly limited, but from the viewpoint of easily exhibiting the effects of the present invention, it is preferable to use a plastic base material, particularly a biaxially stretched resin film. Also, for applications that do not require transparency, aluminum foil can be used in combination.

Examples of the stretched resin film include biaxially stretched polyester (PET), biaxially stretched polypropylene (OPP), biaxially stretched polyamide (PA), and ethylene vinyl alcohol copolymer (EVOH) as the central layer. Examples thereof include biaxially stretched polypropylene, biaxially stretched ethylene vinyl alcohol copolymer (EVOH), alumina vapor deposition PET, silica vapor deposition PET, alumina-silica dual vapor deposition PET, silica vapor deposition PA, and alumina vapor deposition PA. These may be used alone or in combination.

Two processing methods are mainly used as a method for bonding the sealant film of the present invention and various stretched base films. One is to apply an anchor coating agent to the laminated surface of the sealant film of the present invention or the base film as necessary, and heat-melt the polymer film (polyethylene, polypropylene, etc.) based on the sealant film of the present invention. This is an extrusion laminating method in which a thin film is extruded between the laminated surfaces of a material film, pressure-bonded, and laminated. The other is a dry laminating method in which an adhesive is applied to the laminated surface of the base film, and then the sealant film of the present invention and the base film are pressure-bonded and laminated. However, when used for retort packaging, the dry laminating method is used. preferable.

Adhesives for laminating are generally cured with polyols / isocyanates, and are often used for high-performance applications such as retort applications. In the past, a combination of aluminum foil and a sealant film was generally used for bonding, but various transparent vapor-filmed films are now on the market, and due to the demand for improved visibility of the contents, the transparent vapor-deposited film is used. The number of bonded sealant films is also increasing.

Examples of the polyol used for the laminating adhesive include the polyol itself described below, a polyester polyol obtained by reacting the polyol with polycarboxylic acids described below, or ethylene glycol, diethylene glycol, triethylene glycol, and propylene glycol. Ethylene oxide, propylene oxide, butylene, starting from compounds having two active hydrogen atoms such as trimethylene glycol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, etc. Examples thereof include polyethers obtained by addition-polymerizing monomers such as oxide, styrene oxide, epichlorohydrin, tetrahydrofuran, and cyclohexylene.

Examples of the polyol include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, and 1,6-hexane. Dire, neopentyl glycol, methylpentanediol, dimethylbutanediol, butylethylpropanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, bishydroxyethoxybenzene, 1,4-cyclohexanediol, 1 , 4-Cyclohexanedimethanol, triethylene glycol, polycaprolactone diol, dimerdiol, bisphenol A, glycols such as hydrogenated bisphenol A, propiolactone, butyrolactone, ε-caprolactone, δ-valerolactone, β-methyl-δ -Polyesters, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, trimethylene glycol, 1,3-butanediol, 1,4-butanediol, 1 , 6-Hexanediol, neopentyl glycol and other compounds having two active hydrogen atoms were used as initiators, and monomers such as ethylene oxide, propylene oxide, butylene oxide, styrene oxide, epichlorohydrin, tetrahydrofuran and cyclohexylene were added and polymerized. Polyethers and the like can be mentioned.

Examples of the polycarboxylic acids include succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, maleic anhydride, fumaric acid, 1,3-cyclopentanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and terephthal. Acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, naphthalic acid, biphenyldicarboxylic acid, 1,2-bis (phenoxy) ethane-p , P'-dicarboxylic acid and an anhydride or ester-forming derivative of these dicarboxylic acids; p-hydroxybenzoic acid, p- (2-hydroxyethoxy) benzoic acid and ester-forming derivative of these dihydroxycarboxylic acids, dimer acid and the like. Examples include the polybasic acids of.

Examples of the polyisocyanate include organic compounds having at least two isocyanate groups in the molecule. Examples of the organic polyisocyanate include tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-methylenebis (cyclohexyl isocyanate), lysine diisocyanate, trimethylhexamethylene diisocyanate, 1 , 3- (Isocyanatomethyl) cyclohexane, 1,5-naphthalenediocyanate, triphenylmethane triisocyanate and other polyisocyanates; adducts of these polyisocyanates, bullets of these polyisocyanates, or of these polyisocyanates. Examples thereof include derivatives (modified products) of polyisocyanates such as isocyanurates.

Further, a mixture of the isocyanate and the polyol at a mixing ratio in which the isocyanate group is excessive may be used.

In the adhesive, the equivalent ratio of the hydroxyl group equivalent of the polyol to the isocyanate equivalent of the polyisocyanate is preferably 0.5 to 5.0.

In the packaging material of the present invention, the sealant film is used as a sealant, and a base film is laminated on the outer layer (A) side of the sealant film to realize good sealing property and good opening property due to suitable tearing property. can. Further, since suitable heat resistance and bag breakage resistance can be realized, fusion between inner layers (C) serving as heat seal layers and uneven appearance can be suppressed even during high temperature sterilization treatment. Therefore, the packaging material formed by laminating the sealant film of the present invention with various base materials can be suitably applied as a packaging material for retort foods.

The packaging material of the present invention can be suitably used as a packaging bag by making a bag into various shapes such as a flat bag type, a self-standing packaging bag (standing pouch) type, and a tube type. Specifically, for example, one film-shaped packaging material is folded so that the sealant layers face each other, or two film-shaped packaging materials of the present invention are laminated so that the sealant layers face each other. The peripheral end can be heat-sealed and made into a packaging bag (retort pouch) for retort foods and the like. Further, if necessary, an opening start portion such as a V notch or an I notch may be provided.

The packaging material of the present invention and a packaging bag for retort foods using the packaging material can be suitably used for packaging foods that require treatment under high temperature hot water conditions such as boiling and retort sterilization, for example, curry. It can be suitably applied to various retort food packaging applications such as stew, soup, and cooking sauce.

(Example 1)
The following resins were used as the resin components forming the outer layer, the intermediate layer, and the inner layer, respectively, to prepare a resin mixture forming each layer. These mixtures were supplied to each of the three extruders and melted at 250 ° C. The molten resin is supplied to a T-die / chill-roll method co-extrusion multilayer film manufacturing apparatus (feed block and T-die temperature: 250 ° C.) having a feed block to perform co-melt extrusion, and the layer structure of the film is changed to an outer layer. A laminated film having a three-layer structure of / intermediate layer / inner layer and having a thickness ratio of each layer of 25/50/25% and a total thickness of 50 μm was obtained.

Outer layer: Ethylene-α-olefin copolymer (MFR 3.0 g / 10 minutes (190 ° C., 21.18 N), density 0.942 g / cm ³ ) (hereinafter referred to as “LLDPE (1)”) 100% by mass
Intermediate layer: LLDPE (1) 75% by mass, ring-opening polymer of norbornene-based monomer (MFR 10 g / 10 minutes (230 ° C, 21.18N), glass transition temperature (Tg) 78 ° C) (hereinafter, "COC (1)) 25% by mass)
Inner layer: LLDPE (1) 60% by mass, high-density polyethylene (MFR 8g / 10 minutes (190 ° C., 21.18N), density 0.960g / cm ³ ) (hereinafter referred to as "HDPE") 40% 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 were as follows.
Intermediate layer: LLDPE (1) 70% by mass, COC (1) 30% by mass

(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 were as follows.
Intermediate layer: LLDPE (1) 65% by mass, COC (1) 35% by mass

(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 were as follows.
Intermediate layer: LLDPE (1) 75% by mass, ring-opening polymer of norbornene-based monomer (MFR 10 g / 10 minutes (230 ° C, 21.18N), glass transition temperature (Tg) 120 ° C) (hereinafter, "COC (2)) 25% by mass.

(Example 5)
A laminated film was obtained in the same manner as in Example 2 except that the thickness ratio of the outer layer / intermediate layer / inner layer was 20/60/20%.

(Example 6)
A laminated film was obtained in the same manner as in Example 2 except that the thickness ratio of the outer layer / intermediate layer / inner layer was 15/70/15%.

(Example 7)
A laminated film was obtained in the same manner as in Example 2 except that the thickness ratio of the outer layer / intermediate layer / inner layer was 30/40/30%.

(Example 8)
A laminated film was obtained in the same manner as in Example 2 except that the resin components used for the inner layer were as follows.
Inner layer: Ethylene-α-olefin copolymer (MFR 2.5 g / 10 min (190 ° C., 21.18 N), density 0.925 g / cm ³ ) (hereinafter referred to as “LLDPE (2)”) 50% by mass, HDPE 50% by mass

(Example 9)
A laminated film was obtained in the same manner as in Example 2 except that the resin components used for the inner layer were as follows.
Inner layer: Ethylene-α-olefin copolymer (MFR 3.5 g / 10 min (190 ° C., 21.18 N), density 0.933 g / cm ³ ) (hereinafter referred to as LLDPE (3)) 70% by mass, HDPE 30 mass %

(Example 10)
A laminated film was obtained in the same manner as in Example 2 except that the thickness ratio of the outer layer / intermediate layer / inner layer was 35/30/35%.

(Example 11)
A sealant film was obtained in the same manner as in Example 2 except that the thickness ratio of the outer layer / intermediate layer / inner layer was 10/80/10%.

(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 were as follows.
Intermediate layer: LLDPE (1) 100% by mass

(Comparative Example 2)
A laminated film was obtained in the same manner as in Example 1 except that the resin components used for the inner layer were as follows.
Inner layer: LLDPE (3) 100% by mass

(Comparative Example 3)
A laminated film was obtained in the same manner as in Example 1 except that the resin components used for the outer layer and the intermediate layer were as follows.
Outer layer: LLDPE (3) 100% by mass
Intermediate layer: LLDPE (3) 75% by mass, COC (1) 25% 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 intermediate layer were as follows and the thickness ratio of the outer layer / intermediate layer / inner layer was 25/50/25%.
Intermediate layer: LLDPE (1) 85% by mass, COC (1) 15% by mass

(Comparative 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 were as follows and the thickness ratio of the outer layer / intermediate layer / inner layer was 40/20/40%.
Intermediate layer: LLDPE (1) 50% by mass, COC (1) 50% by mass

The laminated films (sealant films) obtained in the above Examples and Comparative Examples were evaluated as follows. The results obtained are shown in the table below.

(1) Tear strength The tear strength in the flow direction was measured in a constant temperature room at 23 ° C. and 50% Rh according to JIS K7128-1 (Truser method).
5N or less 〇; Excellent tearability Over 5N ×; Poor tearability

(2) Straight cutability Using a test piece having a film length of 150 mm in the flow direction and a length of 50 mm in the width direction, a notch with a width of 15 mm is made in the center of the width direction by 10 mm, and the width of the tip of the notch (W0). Is actually measured. A polyester sheet having a thickness of 0.3 mm, a width of 15 mm, and a length of 160 mm prepared in advance is attached to the tip of the notch with tape. The pasted polyester sheet is folded back in the 180 ° direction, the test piece excluding the notch on the opposite side to the tip is attached to the tensile tester, and it is torn 100 mm at a speed of 300 mm / min, and the width of the end point (W1). Is actually measured. At this time, the retention rate was calculated from the following formula and used as an index of straight-line cutability.
Retention rate [%] = W1 / W0 × 100
100 ± 20% 〇; Excellent straightness cutability Over 100 ± 30% ×; No straightness

(3) Seal strength A polyester adhesive is applied onto a biaxially stretched polyamide film having a thickness of 25 μm using a wire bar so that the coating thickness is 3.5 g / m ^2. After the adhesive was dried, a sealant film was attached and dried at 40 ° C. for 24 hours to obtain a heat seal test laminated film. Using the obtained film, a test piece heat-sealed under the conditions of 160 ° C., 0.2 MPa, and 1 second was prepared, and heat-treated at 121 ° C. for 30 minutes using an autoclave. The test piece after the heat treatment was cut into a width of 15 mm, and the seal strength was measured with a tensile tester. If it is 40 N / 15 mm or more, it can be used normally.

(4) Inner surface fusion A laminated film was obtained in the same manner as in (3). The seals of the obtained films were overlapped with each other and heat-treated at 121 ° C. for 30 minutes using an autoclave. The test piece after the heat treatment was cooled to room temperature, cut into pieces having a width of 15 mm, and the peel strength was measured with a tensile tester.
1N / 15mm or less 〇; Excellent heat resistance Over 1N / 15mm ×; Poor heat resistance

(5) Appearance unevenness A laminated film was obtained in the same manner as in (3). Using the obtained film, a bag was made so that the inner size was 100 mm × 150 mm (heat seal width 10 mm), and 200 ml of water was sealed. After retort-packing the bag-made product containing water at 121 ° C. for 30 minutes, the state of uneven appearance was visually evaluated.

As is clear from the above table, the sealant films of the present invention of Examples 1 to 11 have tear strength that is easy to tear and good straight-line cutability, and internal surface fusion and appearance unevenness occur even during high-temperature treatment. It wasn't. On the other hand, the sealant film of the comparative example did not have suitable tearability. Further, the sealant films of Comparative Examples 2 and 3 had uneven appearance, and those of Comparative Example 2 also had inner surface fusion.

Claims (9)

It is composed of a laminated film in which an outer layer (A), an intermediate layer (B) and an inner layer (C) are laminated in this order.
The outer layer (A) and the inner layer (C) contain a polyethylene-based resin, and the average density of the resin components in each layer is 0.940 g / cm ³ or more.
The intermediate layer (B) contains a linear low-density polyethylene (b1) and a cyclic olefin resin (b2).
The density of the linear low-density polyethylene (b1) is 0.937 g / cm ³ or more, and the density is 3.
A sealant film characterized in that the content of the cyclic olefin resin (b2) in the resin component contained in the intermediate layer (B) is 20 to 40% by mass. The average density of the resin components in the outer layer (A) is 0.940 g / cm. ³ Above (however, the average density is 0.945 g / cm ³ The sealant film according to claim 1 (excluding the above cases). The density of the linear low-density polyethylene (b1) is 0.937 g / cm. ³ Above (however, the average density is 0.945 g / cm ³ The sealant film according to claim 1 (excluding the above cases). The sealant film according to any one of claims 1 to 3, wherein the thickness ratio of the intermediate layer (B) is 20 to 80% of the total thickness of the sealant film. The sealant film according to any one of claims 1 to 4, wherein the thickness ratio of the outer layer (A) is 10 to 40% of the total thickness of the sealant film, and the thickness ratio of the inner layer (C) is 10 to 40%. The sealant film according to any one of claims 1 to 5 , wherein the cyclic olefin resin (b2) has a glass transition temperature of 140 ° C. or lower. The sealant film according to any one of claims 1 to 6 , which has a total thickness of 20 to 150 μm. Any of claims 1 to 7 , wherein the linear low-density polyethylene (b1) has an MFR of 0.1 to 20 g / 10 minutes, and the cyclic olefin resin (b2) has an MFR of 0.2 to 17 g / 10 minutes. The sealant film described in Crab. A packaging material using the sealant film according to any one of claims 1 to 8.