JP4889075B2 - Multilayer film for deep drawing packaging and container for deep drawing packaging comprising the same - Google Patents

Description

  The present invention relates to a deep-drawing packaging container in which a difference in heat shrinkage force at a specific temperature between a bottom material made of a multilayer film and a lid material made of a multilayer film is set to a specific range, and when the deep-packed package is boil sterilized The present invention relates to a deep drawing multilayer film in which the occurrence of curling is reduced and a deep drawing packaging container comprising the same.

Various films have been proposed as deep drawing packaging films. For example, it has been proposed to use a non-shrinkable film as a bottom material, a laminated film of a non-shrinkable film and a stretched heat-setting film as a bottom material, or a shrinkable film as a bottom material and a shrinkable film or a nonshrinkable film as a lid material.
Patent Document 1 uses an unstretched composite film as a bottom material, and a heat-shrinkable composite film having a heat shrinkage rate at 95 ° C. in the range of 15 to 60% in both the vertical direction and the horizontal direction as a cover material on the bottom material. A package that can be deep-drawn and deep-drawn by heat-sealing at the edges is disclosed.
Patent Document 2 is composed of at least three layers: a surface layer (a) made of a thermoplastic resin, an intermediate layer (b) made of a polyamide-based resin, and a surface layer (c) made of a sealable resin. A multilayer film excellent in low-temperature impact resistance having an impact energy of 1.5 joules or more when converted to a thickness of 50 μm and excellent in mechanical properties such as puncture strength and pinhole resistance is disclosed.
However, these packaging bodies and multilayer films are used as multilayer films for deep drawing, and when boil processing after deep drawing packaging is performed, curling due to shrinkage between the lid material and the bottom material is caused. There is still room for further improvement in terms of generation.

JP 11-115103 A (Claim 1) JP 2003-535733 A (Claim 1 and Examples 1 to 15)

If a non-shrinkable cover material or shrinkable bottom material is used, curling may occur in the flange during boil processing, or if the vacuum secondary molding seal such as draw molding is a frame seal, vacuum pack and cover the material after boiling The bottom material shrinks even if the surface flaws (the wrinkles that occur in the unsealed part of the ears) occur due to the shrinkage difference between the bottom material and the bottom material, or the low heat shrinkable films are used for the lid and the bottom material. Because the cover is soft or the cover is soft, the cover is pulled toward the bottom, the seal line moves in the drawing direction, and the cover printing of general deep-drawn molded products is greatly displaced and difficult to see There is.
The present invention solves the above-mentioned problems when a heat-shrinkable film is used as a multilayer film for deep drawing, curling of an ear part (flange part) due to boil processing and the like after boiling of a frame-sealed package. An object of the present invention is to provide a multilayer film for deep drawing with reduced generation of comedones.

As a result of studying to solve the above problem, the flange portion is formed by using a low heat-shrinkable lid material and a low heat-shrinkable bottom material, and setting a difference in instantaneous heat-shrink force at a specific temperature between the two in a specific range. It has been found that flattening is further improved, and that the cover material bites into the bottom material side after boiling the packed product. In this case, the balance between the shrinkage characteristics of the bottom and lid materials becomes a problem, and the combination of the resin composition of the lid and bottom materials is studied, and a specific relationship between the heat shrinkage force of the lid and bottom materials is found to complete the present invention. It came to do.
That is, the first of the present invention is a multilayer film constituting the bottom material (A) and a multilayer film constituting the cover material (B) having a layer structure different from the multilayer film constituting the bottom material (A). A multilayer film for deep-drawing packaging, wherein each of the multilayer film constituting the bottom material (A) and the multilayer film constituting the lid material (B) is a surface layer (a) made of a polyester resin, and a polyamide resin An intermediate layer (b) made of and a surface layer (c) made of a sealable resin, and having a thickness of 40 to 150 μm, stretched in the machine direction (MD) and the transverse direction (TD) It is a biaxially stretched film, and each of the multilayer film constituting the bottom material (A) and the multilayer film constituting the cover material (B) has a hot water shrinkage at 90 ° C. of 5-18% in length and width, and 130 ° C. The bottom material (A) in Machine direction (MD) and transverse multi for absolute value deep or less 300 g / 20 mm width packaging difference of the instantaneous thermal contraction forces in (TD) of the multilayer film constituting the multilayer film and the lid (B) which formed Provide film.
The second aspect of the present invention is that the multilayer film constituting the bottom material (A) has a depth of 100 to 400 g / 20 mm in the instantaneous heat shrinkage force in at least one direction of the multilayer film at 130 ° C. A multilayer film for draw wrapping is provided.

The third of the present invention, the multilayer film constituting the base material (A) is an ethylene - vinyl alcohol copolymer hydrophilic gas barrier resin layer composed of a resin (d) said first or second in which further comprising A multilayer film for deep-drawing packaging of the invention is provided.
4th of this invention WHEREIN: The multilayer film which comprises a cover material (B) further contains the hydrophilic gas barrier resin layer (d) which consists of ethylene-vinyl alcohol copolymer resin , The said 1st -3rd A multilayer film for deep drawing packaging according to any of the inventions is provided.
5th of this invention provides the container for deep drawing packaging which consists of the bottom material (A) and the cover material (B) which were formed from the multilayer film for deep drawing packaging concerning the invention in any one of the said 1-4. .

  When forming a multi-layer film as a bottom material and a cover material, the film is formed with a high stretch rate and a high relaxation rate, a low heat shrinkage rate, and the absolute difference in the instantaneous heat shrinkage force between the bottom material and the cover material in the vertical direction. By limiting the value to a specific range, curling and deepening of the frame seal due to the difference in shrinkage between the bottom and the lid material can be suppressed even if the deeply packed package is boiled. It became possible to give a good package. The multilayer film for deep drawing according to the present invention has a thermal shrinkage rate of preferably 5% or less, more preferably 3% or less, particularly preferably 2% or less when dry-heated (temperature 90 ° C., 5 minutes). It has a pitch printability (printing on the cover material is not greatly shifted) under conditions of a drying temperature of 80-90 ° C. for 10 seconds or less, and a seal during deep drawing (110-130 ° C., 5 seconds) However, the shrinkage force of the bottom material and the lid material balances and has dimensional stability. In addition, in the boil sterilization of the package, at 90 ° C. for 30 minutes, the hydrophilic gas barrier resin layer having rigidity of the multilayer film of the bottom material and the lid material absorbs water and softens, and then the contraction force (stress) that develops the bottom material, Since the multi-layer film of each lid material shrinks equally, curling is unlikely to occur, there is no displacement between the bottom film and the multi-layer film of the lid material, interlayer shrinkage is difficult to enter, and the transparency of the package is also good It becomes good.

  An object of the present invention is to obtain a package with extremely little occurrence of curling when the deeply drawn package is boiled or the occurrence of surface defects on the frame seal portion. This is because the hot water shrinkage rate at 90 ° C. of each of the multilayer films constituting the bottom material and the lid material is 1 to 18% in length and breadth, and the instantaneous shrinkage at a specific temperature of the multilayer film constituting the bottom material and the lid material. This can be achieved by selecting a multilayer film in which the absolute value of the difference in force (stress) falls within a specific range.

  The heat-shrinkable multilayer film constituting the bottom material (A) used in the present invention is preferably a surface layer (a) made of a thermoplastic resin, an intermediate layer (b) made of a polyamide-based resin, and a sealable resin. The surface layer (c) is composed of at least three layers.

  The thermoplastic resin constituting the surface layer (a) has appropriate stretchability in the laminated state with the intermediate layer (b) made of the polyamide-based resin, and prevents water from penetrating into the intermediate layer (b). It is necessary to use such a resin. Preferably, a thermoplastic resin having a hygroscopicity smaller than that of the polyamide resin is used. Examples of preferred thermoplastic resins include LLDPE (linear low density polyethylene), VLDPE (linear ultra-low density polyethylene), LDPE (LDPE), which have been widely used for forming laminated films of polyamide resins. Low-density polyethylene) (these polyethylenes include those polymerized with single-site catalysts (metallocene catalysts) in addition to polyethylene obtained with conventional catalysts (Ziegler-Natta catalysts)), polypropylene, propylene-ethylene copolymer Polyolefin resins such as a polymer, propylene-ethylene-butene-1 copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene methacrylic acid copolymer, ethylene-ethyl acrylate copolymer ( A relatively small amount of comonomer components other than olefin in the copolymer Less than 50% by weight)) is preferably in addition to be used, such as polyester resins are also used. Among these, the polyester-based resin is excellent in surface properties such as transparency, surface hardness, printability, and heat resistance, and is a particularly preferable surface layer (a) material for the present invention.

As the polyester resin (“PET”) constituting the surface layer (a), both an aliphatic polyester resin and an aromatic polyester resin are used.
The dicarboxylic acid component used in the polyester-based resin is not particularly limited as long as the polyester can be obtained by a normal production method. In addition to terephthalic acid and isophthalic acid, for example, dimer acid or dipic acid composed of a dimer of unsaturated fatty acids. Oxalic acid, malonic acid, succinic acid, azelaic acid, sebacic acid, phthalic acid, 5-t-butylisophthalic acid, naphthalenedicarboxylic acid, diphenyl ether dicarboxylic acid, cyclohexanedicarboxylic acid and the like. Also good. Moreover, as a diol component used for the polyester-based resin, any polyester can be obtained by a normal production method. For example, ethylene glycol, propylene glycol, tetramethylene glycol, neopentyl glycol, hexamethylene glycol, diethylene glycol, Examples include polyalkylene glycol, 1,4-cyclohexanedimethanol, 2-alkyl-1,3-propanediol, and two or more of them may be used.

  Among these, preferably an aromatic polyester-based resin containing an aromatic dicarboxylic acid component, particularly preferably a polyester of terephthalic acid as a dicarboxylic acid component and a diol having 10 or less carbon atoms, such as polyethylene terephthalate, Polybutylene terephthalate or the like is used, and a copolymerized polyester in which a part of terephthalic acid, preferably up to 30 mol%, more preferably up to 15 mol%, is replaced with another dicarboxylic acid such as isophthalic acid, or ethylene glycol, etc. A copolymer polyester resin (for example, “Kodapak PET # 9921” manufactured by Eastman Kodak Co., Ltd.) in which a part of the diol component is replaced with another diol such as 1,4-cyclohexanedimethanol is also preferably used. Further, two or more kinds of different polyester resins may be mixed and used.

  A polyester resin having an intrinsic viscosity of about 0.6 to 1.2 is preferably used. For the outer surface layer (a), for example, thermoplastic elastomers represented by thermoplastic polyurethane, and thermoplastic resins other than polyester resins such as polyolefin resins modified with acids such as maleic acid or anhydrides thereof. Up to 20% by weight.

  The surface layer (a) made of a thermoplastic resin other than the polyamide-based resin is less than the thickness of the intermediate layer (b) so as not to impair the excellent stretchability and mechanical properties of the intermediate layer (b) made of the polyamide-based resin. Is thin, and preferably has a thickness of 6% or more and less than 50%.

  Examples of the polyamide resin ("Ny") constituting the intermediate layer (b) include nylon 6, nylon 66, nylon 11, nylon 12, nylon 69, nylon 610, nylon 612 and other aliphatic polyamide polymers, nylon 6 / 66, nylon 6/69, nylon 6/610, nylon 66/610, nylon 6/12, and other aliphatic polyamide copolymers. Among these, nylon 6/66 and nylon 6/12 are particularly preferable in terms of moldability. These aliphatic polyamide (co) polymers can be used alone or in combination of two or more. Further, blends of these aliphatic polyamide (co) polymers with aromatic polyamides as the main component are also used. Here, the aromatic polyamide means that at least a part of at least one of diamine and dicarboxylic acid has an aromatic unit, and is particularly preferably a copolyamide. Examples thereof include nylon 66/610 / MXD6 (herein, “MXD6” represents polymetaxylylene adipamide), a copolymer of an aliphatic polyamide containing an aromatic diamine unit, and nylon 66 / 69 / 6I, nylon 6 / 6I, nylon 66 / 6I, nylon 6I / 6T (where "(Nylon) 6I" is polyhexamethylene isophthalamide, "(Nylon) 6T" is polyhexamethylene terephthalamide And a copolymer of a copolymerized aromatic polyamide containing an aromatic carboxylic acid unit. These polyamide resins are preferably used singly or mixed to have a melting point of 160 to 210 ° C. The intermediate layer (b) includes an olefin resin modified with an acid such as maleic acid or an anhydride thereof, an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer, an ionomer resin, an ethylene-vinyl acetate copolymer. A thermoplastic resin other than a polyamide-based resin such as a polymer saponified product may be contained up to about 30% by weight.

  As the sealing resin constituting the surface layer (c), a polyolefin polymerized using a single site catalyst or a metallocene catalyst (hereinafter sometimes abbreviated as “SSC”), for example, linear low density polyethylene (hereinafter referred to as “SSC”). Abbreviated as “SSC-LLDPE”), linear ultra-low density polyethylene (hereinafter abbreviated as “SSC-VLDPE”); conventional ethylene-α olefin copolymer (generally referred to as “LLDPE”, “VLDPE”, etc.) ), Ethylene-vinyl acetate copolymer (hereinafter abbreviated as “EVA”), ethylene-methacrylic acid copolymer (hereinafter abbreviated as “EMAA”), ethylene-methacrylic acid-unsaturated aliphatic carboxylic acid copolymer, Low density polyethylene, ionomer (hereinafter abbreviated as “IO”) resin, ethylene-acrylic acid copolymer, ethylene-acrylic acid Thermoplastics such as ethylene copolymer (hereinafter abbreviated as “EMA”), ethylene-ethyl acrylate copolymer (hereinafter abbreviated as “EEA”), ethylene-butyl acrylate copolymer (hereinafter abbreviated as “EBA”), etc. Those selected from resins can be used. Among these, a preferable type of sealing resin is an ethylene copolymer, particularly ethylene as a main component (ie, greater than 50% by weight) and a vinyl monomer copolymerizable with ethylene as a minor component (ie, 50% by weight). %, Preferably less than 30% by weight). Examples of preferable vinyl monomers include unsaturated carboxylic acids having 8 or less carbon atoms, such as α-olefins having 3 to 8 carbon atoms, acrylic acid, methacrylic acid, acrylic acid esters, methacrylic acid esters, and vinyl acetate. Examples include esters. An acid-modified ethylene copolymer obtained by modifying these ethylene copolymers with 3% by weight or less of an unsaturated carboxylic acid is also preferably used. In addition, a thermoplastic resin such as a polypropylene resin, a polyester resin, and aliphatic nylon may be used. The sealing resin preferably has a melting point of 150 ° C. or lower, particularly 135 ° C. or lower. A blend containing at least one of these may be used as long as the transparency of the film is not impaired.

  Among these, SSC-LLDPE, SSC-VLDPE, LLDPE, VLDPE, EVA, EMAA, ethylene-methacrylic acid-unsaturated aliphatic carboxylic acid copolymer, IO resin and the like are preferably used for the surface layer (c). . In particular, effective SSC-based polyolefins include those obtained by using constrained geometric catalysts (a kind of metallocene catalyst developed by Dow Chemical Company). The ethylene-alpha olefin copolymer obtained using a constrained geometric catalyst has a long chain branching per 1000 carbon number of about 0.01 to about 3, preferably about 0.01 to about 1, more preferably from about 0.05 to about 1 substantially linear polyethylene resin. In the ethylene / α-olefin copolymer, a long chain branch having about 6 carbon atoms or more is selectively introduced in the molecular structure, so that excellent physical properties and good moldability are imparted to the polymer. The An example is sold by Dow Chemical Company under the names “Affinity” and “Elite”, and the α-olefin is 1-octene.

  Other polyethylene-based resins obtained using other metallocene catalysts include, for example, “EXACT” from EXXON, “Umerit” from Ube Industries, “Evolue” from Mitsui Chemicals, manufactured by Nippon Polychem “Kernel” and “Harmorex” of Nippon Polyolefin. The metallocene catalyst polyolefin preferably has a ratio (Mw / Mn) (polydispersity) of weight average molecular weight (Mw) to number average molecular weight (Mn) of less than 3, more preferably 1.9 to 2.2.

  The heat resistance of the surface layer (c) made of a resin that can be sealed is preferably smaller than the heat resistance of the surface layer (a) for film sealing or deep drawing. When the heat resistance of the surface layer (c) made of a resin that can be sealed is greater than the heat resistance of the surface layer (a), the conditions are met when heat is applied to the film during sealing or deep drawing. This is because the surface layer (a) may be melted on the heating plate, causing problems in sealing, suitability for packaging machinery, and deep drawing workability.

  The surface layer (c) made of a sealable resin can be provided with easy peelability, for example, in deep drawing packaging. This is accomplished, for example, by using a mixture of EMAA and polypropylene resin, or a mixture of EVA and polypropylene resin.

  The heat-shrinkable multilayer film used in the bottom material (A) of the present invention is preferably a surface layer (a) made of the thermoplastic resin, an intermediate layer (b) made of a polyamide-based resin, and a surface made of a sealing resin. Although the layer (c) is included as a layer structure, other layers can be included as necessary for the purpose of improving the functionality or workability of the multilayer film. Examples of such layers include:

  Examples of the gas barrier resin constituting the hydrophilic gas barrier resin layer (d) include fragrances such as known EVOH and polymetaxylylene adipamide (“nylon MXD6”), particularly those used as an oxygen gas barrier layer. Amorphous polyamides with aromatic diamines, amorphous with aromatic carboxylic acids such as polyhexamethylene isophthalamide / terephthalamide (“nylon 6I / 6T”), which is a copolymer of isophthalic acid, terephthalic acid and hexamethylene diamine An aromatic polyamide etc. can be illustrated.

As a preferable resin constituting another layer, there is a copolymer of ethylene and at least one monomer containing an oxygen atom in the molecule. Specific examples include EVA, EMAA, ethylene / methacrylic acid / unsaturated aliphatic carboxylic acid copolymer, EMA, EAA, EBA, and IO resin. Further, a metallocene catalyst-based polyethylene having a density of less than 0.900 g / cm ³ is preferable because it has good stretchability and a multilayer film having a high thermal shrinkage can be obtained after biaxial stretching.

  The adhesive resin layer (ad) can be provided as necessary when the adhesive force between the respective layers is not sufficient. As adhesive resins, EVA, EEA, EAA, acid-modified polyolefins (reactants of olefins alone or copolymers with unsaturated carboxylic acids such as maleic acid and fumaric acid, acid anhydrides, esters or metal salts) For example, acid-modified VLDPE, acid-modified LLDPE, acid-modified EVA) and the like can be used. Preferable examples include olefinic resins modified with acids such as maleic acid or anhydrides thereof. In the above layer structure, a lubricant or an antistatic agent can be added to any layer.

  Examples of the lubricant used include hydrocarbon lubricants, fatty acid lubricants, fatty acid amide lubricants, ester lubricants, metal soaps, and the like. The lubricant may be liquid or solid. Specific examples of the hydrocarbon lubricant include liquid paraffin, natural paraffin, polyethylene wax, and micro wax. Examples of fatty acid lubricants include stearic acid and lauric acid. Fatty acid amide lubricants include stearic acid amide, palmitic acid amide, N-oleyl palmitic acid amide, behenic acid amide, erucic acid amide, arachidic acid amide, oleic acid amide, methylene bisstearamide, ethylene bisstearamide, etc. Can be given. Examples of ester lubricants include butyl stearate, hydrogenated castor oil, ethylene glycol monostearate, and stearic acid monoglyceride. The metal soap is derived from a fatty acid having 12 to 30 carbon atoms, and representative examples thereof include zinc stearate and calcium stearate. Among these lubricants, fatty acid amide lubricants and metal soaps are preferably used from the viewpoint of excellent compatibility with polyolefin resins. Preferred examples of lubricants include behenic acid amide, oleic acid amide, erucic acid amide, etc. in the form of a masterbatch. The preferable addition amount is 1 to 10% by weight based on the resin in the case of a masterbatch containing 20% by weight of lubricant.

  As the antistatic agent, a surfactant is preferably used. As the surfactant, anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants and mixtures thereof can be used. The antistatic agent is added in an amount of 0.05 to 2% by weight, more preferably 0.1 to 1% by weight, based on the resin of the layer to be added.

  The example of the preferable aspect of the laminated constitution of the multilayer film which comprises the bottom material (A) of this invention is described next. However, these are merely examples, and the present invention is not limited to these: (1) polyester resin / adhesive resin / polyamide resin / adhesive resin / sealable resin layer, (2) polyester Resin / adhesive resin / polyamide resin / gas barrier resin / adhesive resin / sealable resin layer, (3) polyester resin / adhesive resin / polyamide resin / adhesive resin / gas barrier resin / adhesive resin / seal (4) polyester resin / adhesive resin / polyamide resin / adhesive resin / gas barrier resin layer / adhesive resin / polyamide resin / adhesive resin / sealable resin layer, (5) polyester resin / Adhesive resin / polyamide resin / gas barrier resin layer / polyamide resin / adhesive resin / sealable resin layer, (6) polyolefin resin Adhesive resin / polyamide resin / adhesive resin / sealable resin layer, (7) polyolefin resin / adhesive resin / polyamide resin / gas barrier resin / adhesive resin / sealable resin layer, (8) polyolefin resin / Adhesive resin / polyamide resin / adhesive resin / gas barrier resin / adhesive resin / sealable resin layer, (9) polyolefin resin / adhesive resin / polyamide resin / adhesive resin / gas barrier resin layer / adhesiveness Resin / polyamide resin / adhesive resin / sealable resin layer, (10) polyolefin resin / adhesive resin / polyamide resin / gas barrier resin layer / polyamide resin / adhesive resin / sealable resin layer. These multilayer films can also be used as a multilayer film for the lid material (B), and the hot water shrinkage at 90 ° C. is 1 to 18%, preferably 5 to 18%, more preferably 5 to 15%. It is.

  The multilayer film constituting the bottom material (A) and the multilayer film constituting the lid material (B) have predetermined requirements, that is, the hot water shrinkage rate of the bottom material (A) and the lid material (B) at 90 ° C. is vertical. If the absolute value of the difference in instantaneous heat shrinkage force in at least one direction between the bottom material (A) and the lid material (B) at 130 ° C. is 1 to 18% in width and satisfies the width of 300 g / 20 mm or less, the same Even a multilayer film having a layer structure or a multilayer film having a different layer structure may be used.

  The heat-shrinkable multilayer film constituting the lid material (B) used in the present invention is also composed of the surface layer (a) made of the thermoplastic resin, the intermediate layer (b) made of a polyamide-based resin, and a sealable resin. The surface layer (c) is preferably composed of at least three layers. Moreover, it is preferable that the multilayer film of a cover material (B) also includes a hydrophilic gas barrier layer (d).

  As a multilayer film of a preferred embodiment constituting the lid material (B), a coextruded multilayer film including a gas barrier resin layer (d) having hydrophilicity and a hot water shrinkage rate at 90 ° C. of preferably 5 to 18%, Preferably, 5-15% polyamide-based film is (dry) laminated, and the cover film (B) has a hot water shrinkage rate of 5-18% as a multilayer film, and is a film having essential requirements for the present invention. . Here, the polyamide film having a hot water shrinkage rate of 5 to 18% at 90 ° C. is laminated to give a predetermined hot water shrinkage rate to the multilayer film constituting the lid. Specifically, a low-shrinkage polyamide layer / ad / (MDPE / ad / Ny / EVOH / Ny / ad / LDPE) obtained by dry laminating a coextruded layer film to the low-shrinkage polyamide-based film, A multilayer film having a layer structure of (ad represents an adhesive layer) can be exemplified. In the layer structure, the parenthesis is a coextruded multilayer film, which may be shrinkable or non-shrinkable.

  Further, as another preferred embodiment of the multilayer film constituting the cover material (B), a non-shrinkage comprising a heat-shrinkable nylon film comprising a gas barrier resin layer (d) having hydrophilic gas barrier properties and a sealable polyolefin resin layer A multilayer film laminated with a conductive film can be mentioned. Specifically, a non-shrinkable film comprising a gas barrier film and a sealable polyolefin resin layer on a low-shrinkage nylon film, for example, a multilayer film of the above (MDPE / ad / Ny / EVOH / Ny / ad / PE) is dried. It is a multilayer film laminated with an adhesive by a method such as lamination. These multi-layer films for the lid material (B) are films having the essential requirements of the present invention as described above.

  The multilayer film having the heat shrinkability of the bottom material (A) and the lid material (B) according to the present invention has a final thickness of 20 to 250 μm by laminating, stretching and relaxing the above layers. Is preferably formed as a multilayer film in the range of 40 to 150 μm. For bone-wrapped meat packaging that has sharply cut bone and requires particularly high pinhole resistance, the total thickness is preferably 60 to 250 μm, particularly 90 to 150 μm.

  More specifically, the surface layer (a) made of thermoplastic resin is 0.5 to 40 μm, particularly 1 to 15 μm, and the intermediate layer (b) made of polyamide resin is 3 to 60 μm, particularly 10 to 40 μm, and a sealing resin. The surface layer (c) made of is preferably 10 to 150 μm, particularly preferably 15 to 60 μm in thickness. In particular, when the surface layer (a) is a polyester-based resin, the thickness of the layer (a) is smaller than that of the layer (b) in order to match the biaxial stretching suitability, more specifically, The former is preferably in the range of 3 to 70%, particularly 6 to 50% of the latter.

The thickness of the gas barrier resin layer (d) provided as necessary is, for example, in the range of 1 to 30 μm, preferably in the range of 2 to 15 μm. If the thickness of the gas barrier resin layer is less than 1 μm, the effect of improving the oxygen gas barrier property is poor, and if it exceeds 30 μm, it becomes difficult to extrude the layer and to stretch the multilayer film.
A plurality of adhesive resin layers can be provided, and the thickness is preferably in the range of 0.5 to 5 μm.

The multilayer film constituting the bottom material and the lid material of the present invention uses a plurality of extruders, first coextruded an unstretched film, biaxially stretched by a known method such as a tenter method, and then at least 20 in a uniaxial direction. It is also possible to form a film by performing a high relaxation heat treatment of at least%. The stretching ratio is preferably about 2.5 to 4 times in both length and width. Further, the stretched and oriented multilayer film thus formed may be bonded to another resin layer using a known laminating method.
Moreover, the film which comprises a bottom material and a lid | cover material can be obtained by dry-laminating the resin film previously extended to the co-extrusion multilayer film formed as mentioned above. When laminating a resin film (for example, a polyamide-based film) that has been stretched and oriented in advance to a coextruded multilayer film, the coextruded multilayer film is laminated with a shrinkable resin film even if the coextruded multilayer film is non-shrinkable. If the later multilayer film has a predetermined hot water shrinkage (hot water shrinkage at 90 ° C. of 2 to 15%), there is no problem.

A preferred embodiment of the method for producing a heat-shrinkable multilayer film will be described.
An outer surface layer (a) made of a thermoplastic resin through an annular die, an intermediate layer (b) made of a polyamide resin, and an extruder according to the number of laminated resin types of the multilayer film constituting the bottom material (A); A tubular body (parison) having at least three inner surface layers (c) made of a sealing resin is coextruded and cooled with a pinch roller while cooling to a temperature below the melting point of the main resin, preferably below 40 ° C. Take over. Next, it is introduced into a hot water bath of, for example, 80 to 95 ° C. below the melting point of the main resin occupying each layer while enclosing an opening agent typified by soybean oil as necessary in the tubular film taken. The heated tubular body film is drawn upward, a bubble-like tubular body is formed by the fluid air introduced between the pair of pinch rollers, and cooled with an air ring of 10 to 20 ° C. In the lateral direction, preferably 2.5 to 4 times each, more preferably 2.8 to 3.5 times each, most preferably at least 2.9 to 3.5 times in the vertical direction and at least 3 to 3 times in the lateral direction. Simultaneous biaxial stretching to 5 times. Next, the stretched tubular body film is drawn downward, a bubble-like tubular body is formed again by the fluid air introduced between the pair of pinch rollers, and held in the heat treatment cylinder. Then, steam is sprayed from the outlet of the heat treatment tube (or sprayed with warm water), and the tubular film after biaxial stretching is preferably 70 to 98 ° C, more preferably 75 ° C to 95 ° C, preferably 1 ~ 20 seconds, more preferably 1.5 to 10 seconds, and the tubular film is 15 to 40% each in the machine direction (MD) and the transverse direction (TD) (however, at least 20% in one direction) , Preferably 20-35% in each direction. The tubular film after the heat treatment corresponds to the multilayer film having the heat shrinkability of the bottom material (A) and the lid material (B) used in the present invention, and is wound around a winding roll.

  MD / TD is preferably 2.5 to 4 times, and more preferably 2.8 to MD / TD, in order to realize improvement of various characteristics represented by improvement of low temperature impact resistance while maintaining excellent strength. 3.5 times, most preferably, a draw ratio of 2.9 to 3.5 times in MD and 3 to 3.5 times in TD is secured, preferably 70 to 98 ° C. with steam or hot water having a large heat capacity More preferably, it is a low temperature of 75 ° C. to 95 ° C., most preferably 80 ° C. to 95 ° C., and preferably 15% to 40% (however, 20% or more in one direction), more preferably 20 in each direction. It is extremely preferable to heat-treat while relaxing 30% to 30%. At a lower draw ratio, the required film strength cannot be obtained after heat treatment, and the uneven thickness of the film also increases, making it difficult to obtain packaging suitability. On the other hand, when a medium with a small heat capacity such as heated air or a lower heat treatment temperature of less than 70 ° C. is adopted, it becomes difficult to increase the relaxation rate, and as a result, the necessary low temperature impact resistance improvement effect is obtained. It's hard to be done. On the other hand, when heat treatment is performed at a high temperature exceeding 98 ° C., the polyolefin resin as the seal layer is easily melted, and as a result, the orientation of the polyolefin layer is broken and it is difficult to obtain excellent strength. When the relaxation rate during heat treatment is less than 15%, sufficient orientation relaxation in the amorphous part represented by the desired low temperature impact resistance cannot be obtained, and when the relaxation rate during heat treatment exceeds 40%, It becomes easy to get wrinkles during film formation.

  When the multilayer film constituting the cover material (B) is laminated with a resin film having shrinkage on the coextruded multilayer film, the shrinkable or non-shrinkable coextruded multilayer film obtained as described above is shrinkable. A multilayer film for a lid material (B) having a predetermined hot water shrinkage rate can be obtained by laminating a resin film having a shrinkage property, for example, a shrinkable polyamide film with an adhesive for dry lamination.

The heat-shrinkable multi-layer film thus obtained is a bottom material as a result of the subsequent high-relaxation heat treatment while maintaining a high basic strength represented by tensile strength as a result of the high-stretching treatment of the polyamide resin layer. As the multilayer film for (A) and the lid material (B), the hot water shrinkage at 90 ° C. is 1 to 18% in length and width, preferably 5 to 18%, more preferably 5 to 15%. The absolute value of the difference in instantaneous shrinkage force (stress) in at least one direction between the multilayer film constituting the bottom material (A) and the multilayer film constituting the lid material (B) at 130 ° C. is preferably 300 g / 20 mm width or less, preferably A multilayer film having a width of 100 to 300 g / 20 mm is the multilayer film for deep drawing of the present invention. The hot water shrinkage rate in such a multilayer film is adjusted to the relaxation rate in relation to the draw ratio (however, it is maintained at 20% or more in at least one direction), thereby reducing the required low hot water shrinkage rate. It can be controlled within the range. As a result, the package that has been deep-drawn and filled with the contents is in a range in which the heat shrinkage force of the lid (B) and the bottom (A) after heat treatment such as boil sterilization is balanced, There is no occurrence of comedones due to the frame seal, and the package has a pitch printability ensured.
Here, the instantaneous heat shrinkage force is affected by the film material, the thickness of each layer, the stretch orientation and the degree of relaxation, etc. In the present invention, the multilayer film and the cover material constituting the bottom material (A) at 130 ° C. One of the requirements of the present invention is that the absolute value of the difference in instantaneous heat shrinkage force in at least one direction of the multilayer film constituting (B) is 300 g / 20 mm width or less.

  Before or after the stretching of the method for producing the heat-shrinkable multilayer film, radiation can be applied by a known method. Irradiation improves stretchability, heat resistance, mechanical strength, and the like compared to those without irradiation. Irradiation has the effect of making a film excellent in stretch film-forming property and heat resistance by its moderate crosslinking effect. In the present invention, known radiation such as α rays, β rays, electron rays, γ rays, X rays can be used. From the viewpoint of the crosslinking effect before and after irradiation, an electron beam and γ-ray are preferable, and among these, the electron beam is advantageous in terms of handleability and high processing ability in producing a molded product.

The irradiation conditions of the radiation may be appropriately set according to the intended application. For example, in the case of an electron beam, the acceleration voltage is in the range of 150 to 500 kilovolts and the irradiation dose is 10 to 200 kilo gray ( kGy) is preferable, and in the case of γ rays, it is preferable to give an irradiation dose of 10 to 200 kGy as a dose rate range of 0.05 to 3 kGy / hour.
Further, corona discharge treatment, plasma treatment, or flame treatment may be performed on the inner surface, outer surface, or both surfaces of the multilayer film.

  The multilayer film for deep drawing according to the present invention thus obtained provides a package that does not cause curling or frame seal comeback even after a secondary heat treatment such as a boil treatment. Especially, it becomes a multilayer film suitable for deep drawing packaging such as block ham, raw meat, cheese, sausage, bacon and the like.

(Example)
EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited to these Examples. In addition, the measuring method of the physical property described in this specification is as follows.
Instantaneous heat shrinkage force Fix a sample film stretched in at least one direction (for example, longitudinal direction (machine direction)) 20 mm wide and 10 cm long to the chuck part of a tensile tester, and then heated to the required temperature (130 ° C.) The applied metal block is instantaneously applied to the sample, and the contraction force generated at that time is detected by a load cell and recorded.
Instantaneous contraction force difference = | Bottom material contraction force-Lid material contraction force | (g / 20mm width)
Is the absolute value of the difference in instantaneous thermal contraction force between the multilayer film constituting the bottom material (A) and the multilayer film constituting the lid material (B) at 130 ° C., for example.
Hot water shrinkage The sample film marked at a distance of 10 cm in the machine direction (longitudinal direction) and the direction perpendicular to the machine direction (lateral direction) was immersed in hot water adjusted to 90 ° C. for 30 minutes and then taken out. Immediately cooled with water at room temperature. Thereafter, the marked distance was measured, and the ratio of the decrease from 10 cm to the original length of 10 cm was displayed as a percentage. One sample was tested five times, and the hot water shrinkage rate was displayed as an average value in each of the vertical direction (MD) and the horizontal direction (TD).
Haze
Measured according to ASTM D1003.
Curling property The deviation of the flange portion from the horizontal position of 20 mm before and after boiling the filled sample in hot water at 90 ° C. or 73 ° C. for 30 minutes was measured.
Based on the following criteria, it was judged as excellent (◯) or inferior (x).
○: Curl is less than ± 15 mm from the horizontal position,
X: The curl is ± 15 mm or more from the horizontal position,
90 ° C. hot water immersion test A deep-drawn package body filled with 400 g of a rubber plate was immersed in 90 ° C. hot water for 30 minutes, and then the presence or absence of curling of the package body and the presence or absence of wrinkles on the surface of the package body were observed.
○ has no beautiful curling on the package, no wrinkles on the surface of the package, and a beautiful appearance. X: Curling occurs, wrinkles are seen on the surface of the package, and the product value is inferior. The presence / absence of curling was determined according to the curling standard.
73 ° C. Hot Water Immersion Test A deep-drawn package body filled with 150 g of a rubber plate was immersed in 73 ° C. hot water for 30 minutes, and then the presence or absence of curling of the package body and the presence or absence of wrinkles on the surface of the package body were observed. This is mainly done when packing fillings that dislike high temperatures.
○ has no beautiful curling on the package, no wrinkles on the surface of the package, and a beautiful appearance. X: Curling occurs, wrinkles are seen on the surface of the package, and the product value is inferior.

Production example of multilayer film (Multilayer film I)
PET (3) / mod-VL (2.5) / Ny6. The thickness of the layer structure from 5 extruders through an annular die, in order from the outside to the inside, and with the thickness (μm) shown in parentheses. 66 (17) / EVOH (9) / mod-VL (2.5) / LLDPE (46), each resin was extruded to a total thickness of 80 μm, and coextruded so as to have the above layer structure And melt-bonded. The molten tubular body flowing out from the die mouth was rapidly cooled to 10 to 18 ° C. in a water bath to obtain a flat tubular body. Next, after passing the flat tubular body through a warm water bath at 92 ° C., it is converted into a bubble-shaped tubular body film by 3.1 times in the machine direction (MD) by the inflation method while being cooled with an air ring at 15 to 20 ° C. Simultaneous biaxial stretching was performed in the transverse direction (TD) at a draw ratio of 3.1 times. Next, the biaxially stretched film is introduced into a heat treatment tube to form a bubble-shaped tubular body film, heated to 90 ° C. by steam blown from the blowout port, and relaxed by 20% in the longitudinal direction and by 20% in the lateral direction. Heat treatment was performed for 2 seconds to produce a biaxially stretched film (stretch-oriented multilayer film). The folded width (flat width) of the obtained multilayer film was 490 mm and the thickness was 55 μm. The hot-water shrinkage rate at 90 ° C. of the obtained film was 7% and 8% in the longitudinal (MD) and transverse (TD) directions, respectively.

(Multilayer film II)
PET (3) / mod-VL (2.5) / Ny6 · 66 in the thickness (μm) shown in parentheses in order from the outside to the inside using the same apparatus and stretching conditions as the multilayer film I. A biaxially stretched film of (13) / EVOH (9) / mod-VL (2.5) / LLDPE (20) (total thickness was 50 μm) was obtained. The hot-water shrinkage rate at 90 ° C. of the obtained film was 11% and 12% in the longitudinal (MD) direction and the transverse (TD) direction, respectively.
(Multilayer film III)
PET (3) / mod-VL (2.5) / Ny6 · Thickness (μm) shown in parentheses in order from the outer side to the inner side through the annular die from four extruders. 66 (17) / mod-VL (2.5) / LLDPE (55) (total thickness is 80 μm) and melt-bonded. This was biaxially stretched under the same conditions as the multilayer film I to produce a stretch-oriented multilayer film. The hot water shrinkage rate of the obtained film at 90 ° C. was 10% and 11% in the longitudinal (MD) and transverse (TD) directions, respectively.

(Multilayer film IV)
ONy film (manufactured by Kojin Co., Ltd., Bonile, BN-SC580, thickness 15 μm) and (MDPE (13) / mod-VL (4) / Ny6 · 66 (2) / EVOH (6) / Ny6 · 66 ( 2) Co-extruded multilayer film of / mod-VL (4) / LDPE (19)), dry laminate adhesive (Mitsui Takeda Chemical Co., Ltd., Takelac A-315 (main agent), Takenate A-50 (cured) Agent) and a thickness of 2 μm) to dry laminate to obtain a multilayer film having a thickness of 65 μm. The hot water shrinkage rate of the obtained film at 90 ° C. was 4% and 5% in the longitudinal (MD) and transverse (TD) directions, respectively.
(Multilayer film V)
The layer structure shown in Table 1 having the thickness of 80 μm is the same as that of the multilayer film IV except that the ONy film is changed to an OPP film (manufactured by Toyobo Co., Ltd., brand pyrene, P-2161, thickness 30 μm). A multilayer film was obtained. The hot water shrinkage rate at 90 ° C. of the obtained film was 1% and 2% in the longitudinal (MD) and transverse (TD) directions, respectively.

Example 1
Using a deep drawing machine (manufactured by Omori Machinery Co., Ltd., FV-603) with a multilayer film I as a bottom material and a multilayer film III as a lid material, a rubber plate is filled as a simulated filling material and a deep drawing package. Got. The obtained package was observed and evaluated for the presence or absence of curling immediately after drawing and the presence or absence of surface defects on the frame seal part, and then subjected to a hot water immersion test at 90 ° C. for 30 minutes. The presence or absence of comedones was evaluated.
(Example 2)
A deep drawn package was obtained in the same manner as in Example 1 except that the multilayer film III of the lid was changed to the multilayer film IV. Evaluation similar to Example 1 was performed about the obtained package.
(Comparative Example 1)
A deep drawn package was obtained in the same manner as in Example 1 except that the multilayer film III of the lid was changed to the multilayer film V. Evaluation similar to Example 1 was performed about the obtained package.
(Example 3)
A deep drawn package was obtained in the same manner as in Example 1 except that the multilayer film I as the bottom material was changed to the multilayer film II. About the obtained package, the curl property immediately after shaping | molding, and the hot water immersion test for 73 minutes at 73 degreeC were evaluated, and the presence or absence of the curl and the presence or absence of the surface defect of a frame seal part was evaluated.

Example 4
A deep-drawn package was obtained in the same manner as in Example 1 except that the multilayer film I as the bottom material was changed to the multilayer film II and the multilayer film III as the lid was changed to the multilayer film IV. About the obtained package, the presence or absence of curl immediately after drawing and the presence or absence of surface defects on the frame seal part were observed and evaluated, and then subjected to a hot water immersion test at 90 ° C. for 30 minutes and 73 ° C. for 30 minutes. The presence or absence of curling and the presence or absence of surface defects on the frame seal portion were evaluated.
(Comparative Example 2)
A deep-drawn package was obtained in the same manner as in Example 1 except that the multilayer film I as the bottom material was changed to the multilayer film II and the multilayer film III as the lid was changed to the multilayer film V. About the obtained package, the presence or absence of curl immediately after drawing and the presence or absence of surface defects on the frame seal part were observed and evaluated, and then subjected to a hot water immersion test at 90 ° C. for 30 minutes and 73 ° C. for 30 minutes. Then, the presence or absence of curling and the presence or absence of surface defects on the frame seal part were observed and evaluated.
(Example 5)
A deep-drawn package was obtained in the same manner as in Example 1 except that the multilayer film I as the bottom material was changed to the multilayer film III and the multilayer film III as the lid was changed to the multilayer film IV. About the obtained package, the presence or absence of curl immediately after drawing and the presence or absence of surface defects on the frame seal part were observed and evaluated, and then subjected to a hot water immersion test at 90 ° C. for 30 minutes and 73 ° C. for 30 minutes. Then, the presence or absence of curling and the presence or absence of surface defects on the frame seal part were observed and evaluated.
(Example 6)
A deep drawn package was obtained in the same manner as in Example 1 except that the multilayer film III of the lid was changed to the multilayer film II. About the obtained package, the presence or absence of curl immediately after drawing and the presence or absence of surface defects on the frame seal part were observed and evaluated, and then subjected to a hot water immersion test at 90 ° C. for 30 minutes and 73 ° C. for 30 minutes. Then, the presence or absence of curling and the presence or absence of surface defects on the frame seal part were observed and evaluated. The evaluation results are shown in Table 2.

Claims (5)

A multilayer film for deep drawing packaging comprising a multilayer film constituting a bottom material (A) and a multilayer film constituting a cover material (B) having a layer structure different from the multilayer film constituting the bottom material (A). And
Each of the multilayer film constituting the bottom material (A) and the multilayer film constituting the cover material (B) is a surface layer (a) made of polyester resin, an intermediate layer (b) made of polyamide resin, and can be sealed. It is a biaxially stretched film composed of at least three surface layers (c) made of a resin and having a thickness of 40 to 150 μm, stretched in the machine direction (MD) and the transverse direction (TD) ,
Each of the multilayer film constituting the bottom material (A) and the multilayer film constituting the cover material (B) has a hot water shrinkage rate of 90% to 18% in length and width, and the bottom material (A) at 130 ° C. A multilayer for deep-drawing packaging in which the absolute value of the difference between instantaneous heat shrinkage forces in the machine direction (MD) and the transverse direction (TD) of the multilayer film constituting the cover material (B) and the width direction (TD) is 300 g / 20 mm or less the film.   The multilayer film for deep-drawing packaging according to claim 1, wherein the multilayer film constituting the bottom material (A) has an instantaneous heat shrinkage force of at least one direction of the multilayer film at 130 ° C of 100 to 400 g / 20 mm width.   The multilayer film for deep drawing according to claim 1 or 2, wherein the multilayer film constituting the bottom material (A) further comprises a hydrophilic gas barrier resin layer (d) made of an ethylene-vinyl alcohol copolymer resin.   The multilayer for deep drawing according to any one of claims 1 to 3, wherein the multilayer film constituting the cover material (B) further comprises a hydrophilic gas barrier resin layer (d) made of an ethylene-vinyl alcohol copolymer resin. the film.   A deep-drawing packaging container comprising a bottom material (A) and a lid material (B) formed from the multilayer film for deep-drawing packaging according to any one of claims 1 to 4.