JP2014128884A - Coextruded composite film for retort packaging - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coextruded composite film for retort packaging which has good resistance to pinhole and good impurity sealability, and suppresses the occurrence of delamination during retort processing.SOLUTION: A coextruded composite film for retort packaging comprises an outer layer, an intermediate layer and an inner layer. The outer layer is a layer made of polyamide resin, the intermediate layer is a layer made of high density polyethylene or linear low density polyethylene, and the inner layer is a heat seal layer or an easy-peel layer having cohesive failure properties.

Description

  The present invention particularly relates to a coextrusion composite film for retort that can be suitably used as a bottom material for deep drawing.

  Conventionally, a composite film mainly composed of polyamide / adhesive resin / polypropylene has been used as a deep drawing bottom film for retort.

  However, such a composite film is inferior in pinhole resistance due to the fact that the film itself is hard, and there is a problem that pinholes are likely to occur during vibration or dropping during transportation. In addition, since the polypropylene resin of the sealing layer has a higher melting point than that of the polyethylene-based resin, the sealing property is poor, and there is a problem that a sealing failure due to contaminants is likely to occur especially in the case of a package containing a large amount of liquid.

  On the other hand, it is effective to use polyethylene as the sealing layer resin in order to improve the pinhole resistance and the foreign matter sealability. However, in order to form a polyamide / adhesive resin / polyethylene film by the coextrusion method. In general, an adhesive resin based on linear low density polyethylene is used, but general linear low density polyethylene is not high in heat resistance and low in oil resistance at high temperatures exceeding 100 ° C. When a thing with a lot of oils and fats is used, there is a problem that delamination occurs between the polyamide and the adhesive resin in the retort, so that it has not been used so far.

  In order to improve pinhole resistance, Patent Document 1 proposes a film of polyamide / adhesive resin (linear low density polyethylene base) / ethylene-α-olefin copolymer / polypropylene. Because the sealing layer is polypropylene, the sealing performance is inferior, and the adhesive resin is based on linear low-density polyethylene. There is a problem that delamination occurs.

Japanese Patent Laid-Open No. 10-76616

  The present invention has been made in view of the above circumstances, and a solution to the problem is to provide a coextrusion composite film for retort that has good pinhole resistance and foreign matter sealability and does not generate delamination during retort. It is in.

  As a result of intensive studies in view of the above problems, the present inventor has found that the above problems can be easily solved by a film having a specific configuration, and has completed the present invention.

  That is, the gist of the present invention is a composite film having a configuration of an outer layer, an intermediate layer, and an inner layer, the outer layer is a layer made of a polyamide resin, and the intermediate layer is a layer made of high-density polyethylene or linear low-density polyethylene. The present invention resides in a coextruded composite film for retort, wherein the inner layer is a heat seal layer or an easy peel layer having cohesive failure.

  The co-extruded composite film of the present invention has good pinhole resistance and foreign matter sealability, does not cause delamination during retort, and is suitable for retort, and has high industrial value.

  The outer layer of the semi-invented film is a layer made of polyamide resin (PA) for the purpose of imparting pinhole resistance and deep drawability. The PA used in the outer layer is not particularly limited, but it is preferable to use a main component (50 mol% or more) of a lactam having a three-membered ring or more, a polymerizable ω-amino acid, a diamine and a dicarboxylic acid. When PA is a copolymer, the PA component is desirably contained in an amount of 80 mol% or more, preferably 85 mol% or more, and more preferably 90 mol% or more. When PA is a polymer blend, the PA component is desirably contained in an amount of 70% by mass or more, preferably 75% by mass or more, and more preferably 80% by mass or more based on the total mass of the polymer blend.

  Examples of the lactam having three or more members include ε-caprolactam, ω-enantolactam, ω-laurolactam, α-pyrrolidone and the like. Examples of the polymerizable ω-amino acid include ω-aminocaproic acid, ω-aminoheptanoic acid, ω-aminononanoic acid, ω-aminoundecanoic acid, and ω-aminododecanoic acid. Examples of the diamine include tetramethylene diamine, hexamethylene diamine, heptamethylene diamine, octamethylene diamine, nonamethylene diamine, decamethylene diamine, undecamethylene diamine, dodecamethylene diamine, and 2,2,4-tochimethyl hexamethylene diamine. Aliphatic amines such as 2,4,4-totimethylhexamethylenediamine, 1,3 / 1,4-bis (aminomethyl) cyclohexane, isophoronediamine, piperazine, bis (4-aminocyclohexyl) methane, 2,2 Examples include alicyclic diamines such as -bis- (4'-aminocyclohexyl) propane, and aromatic diamines such as metaxylylenediamine and paraxylylenediamine. Examples of dicarboxylic acids include aliphatic dicarboxylic acids such as glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, nonanedioic acid, decanedioic acid, undecanedioic acid, dodecanedioic acid, hexahydroterephthalic acid, Alicyclic carboxylic acids such as hexahydroisophthalic acid, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid (1,2-isomer, 1,3-isomer, 1,4-isomer, 1,5-isomer, 1,6- Body, 1,7-isomer, 1,8-isomer, 2,3-isomer, 2,6-isomer, 2,7-isomer), and aromatic dicarboxylic acids such as metal-isophthalsulfonic acid.

  In the PA layer, a PA homopolymer or copolymer derived from a lactam having three or more members, a polymerizable ω-amino acid, a diamine and a dicarboxylic acid can be used alone or as a mixture. Specifically, for example, 4 nylon, 6 nylon, 7 nylon, 11 nylon, 12 nylon, 46 nylon, 66 nylon, 69 nylon, 610 nylon, 611 nylon, 6T nylon, 6I nylon, MXD6 nylon, 6-66 Nylon, 6-610 nylon, 6-611 nylon, 6-12 nylon, 6-612 nylon, 6-6T nylon, 6-6I nylon, 6-66-610 nylon, 6-66-12 nylon, 6-66- 612 nylon, 66-6T nylon, 66-6I nylon, 6T-6I nylon, 66-6T-6I nylon and the like. These PAs may be homo resins, copolymers or mixtures thereof.

  For the PA layer, it is preferable to use a nylon resin from the viewpoint of pinhole resistance, and it is particularly preferable to use 6 nylon or 6-66 nylon. Two or more PA layers can be provided, and in this case, each layer may be formed of different types of nylon resins.

  The thickness of the PA layer is usually 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and the upper limit is usually 150 μm, preferably 120 μm, more preferably 100 μm. When the lower limit of the thickness of the PA layer is 10 μm, good pinhole resistance can be obtained, and when the upper limit is 150 μm, the cutability and thermoformability of the film can be maintained well.

  A layer made of polypropylene resin (PP) may be further provided outside the outer layer for the purpose of suppressing curling of the flange portion after retorting. Examples of PP that can be used in the PP layer include homopolymers, random copolymers with ethylene, block copolymers, and the like.

  The thickness of the PP layer is usually 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and the upper limit is usually 150 μm, preferably 120 μm, more preferably 100 μm or less. By setting the lower limit of the thickness of the PP layer to 10 μm, curling of the flange portion after retorting can be suppressed, and by setting the upper limit to 150 μm, the moldability of the film can be maintained well.

  The intermediate layer of the film of the present invention is a layer made of high density polyethylene (HDPE) or linear low density polyethylene (LLDPE).

  An adhesive layer may be provided between each layer, and the thickness thereof is usually 5 μm or more, preferably 8 μm or more, more preferably 10 μm or more from the viewpoint of workability, economy, and handleability, and the upper limit is not particularly limited. However, it is preferably 25 μm, more preferably 20 μm, and particularly preferably 15 μm. When the thickness of the adhesive layer is 5 μm or more, the delamination strength can be improved. On the other hand, if the adhesive layer is too thick, the total thickness of the film becomes thick and the manufacturing cost increases, so the upper limit is preferably 25 μm.

  As the intermediate layer, a layer made of MXD6-nylon can be further included for the purpose of improving the oxygen barrier property.

  The thickness of the MXD6-nylon layer is usually 5 μm or more, preferably 7 μm or more, more preferably 10 μm or more, and the upper limit is 50 μm, preferably 40 μm, more preferably 30 μm. By setting the lower limit of the thickness of the MXD6-nylon layer to 5 μm, good oxygen barrier properties can be obtained, and by setting the upper limit to 50 μm, the moldability of the film can be maintained well.

  The inner layer of the film of the present invention is a heat seal layer or an easy peel layer having cohesive failure, and the heat seal layer is preferably a layer made of HDPE or LLDPE. Here, having cohesive fracture property means that when the package is opened, the easy peel layer itself is broken and peeled off, and the easy peel layer after the break is the upper layer side (bottom material side) and the lower layer of the easy peel layer It means to remain on both sides (lid side). As the resin constituting the easy peel layer, for example, it can withstand retort treatment at about 120 ° C., and the easy peel strength is 1.96 N / 15 mm width (200 gf / 15 mm width) or more and 11.8 N / 15 mm width (1200 gf / 15 mm width). And a value smaller than the delamination strength of the outer layer, intermediate layer and inner layer of the film, is not particularly limited.

  The thickness of the heat seal layer is usually 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and the upper limit is usually 150 μm, preferably 120 μm, more preferably 100 μm. By setting the lower limit of the thickness of the heat seal layer to 10 μm, good pinhole resistance can be obtained, and by setting the upper limit to 150 μm, the cutability of the film can be maintained well.

  An easy peel layer can be comprised from the following resin A and resin B from which a kind differs, for example. That is, as the resin A, HDPE, LLDPE, ethylene-vinyl acetate copolymer (EVA), ethylene-acrylic acid copolymer (EAA), ethylene-ethyl acrylate copolymer (EEA), ethylene-methacrylic acid copolymer At least one selected from the group consisting of a coalescence (EMAA), an ethylene-methyl methacrylate copolymer (EMMA), an ethylene-methyl acrylate copolymer (EMA), and these ionomers can be used. On the other hand, as the resin B, PP or polybutylene (PB) can be used. As the PP of the resin B, any of homopolymer, random copolymer, block copolymer and the like can be used.

  The easy peel strength of the easy peel layer is preferably in the range of 1.96 N / 15 mm width (200 gf / 15 mm width) to 11.8 N / 15 mm width (1200 gf / 15 mm width) as described above, The numerical value is preferably smaller than the delamination strength between the intermediate layer and the inner layer. More preferably, the lower limit is 2.94 N / 15 mm width, more preferably 3.92 N / 15 mm width, and still more preferably 4 N / 15 mm width. On the other hand, the upper limit of the easy peel strength is preferably 9.8 N / 15 mm width, more preferably 7.84 N / 15 mm width. If the easy peel strength is 1.96 N / 15 mm width (200 gf / 15 mm width) or more, there is no risk of breakage during retort processing, and if it is 11.8 N / 15 mm width (1200 gf / 15 mm width) or less. , Good openability of the package can be maintained.

  The thickness of the easy peel layer is usually 3 μm or more, preferably 4 μm or more, more preferably 5 μm or more from the viewpoint of film forming properties and appearance at the time of peeling, and the upper limit is usually 15 μm, preferably 12 μm, more preferably 10 μm. To do. By setting the thickness of the easy peel layer to 3 μm or more, stable film forming properties can be obtained. On the other hand, when the thickness of the easy peel layer is 15 μm or less, the occurrence of fluffing and film residue can be suppressed when the package is opened, and a good peel appearance can be obtained.

  The total thickness of the film of the present invention is usually 300 μm or less, preferably 250 μm or less, more preferably 200 μm or less, and the lower limit is usually 70 μm, preferably 80 μm, more preferably 90 μm. If total thickness is 300 micrometers or less, while being able to maintain favorable moldability, the heating time of a shaping | molding heating process may be comparatively short, and easy openability can be maintained.

  Examples of the coextruded composite film for retort of the present invention will be shown below, but the present invention is not limited thereto.

<Evaluation method>
(1) Delamination after retorting A deep-drawing packaging machine (FV6300 manufactured by Omori Machine Industry Co., Ltd.) was used to package the fried food, and after retorting at 120 ° C. for 30 minutes, the presence or absence of delamination was evaluated. The case where delamination did not occur was evaluated as ○, and the case where delamination occurred was evaluated as ×. The results are shown in Table 1.

(2) Seal strength After packaging the deep-fried food using a deep-drawing packaging machine, the sealing surface is cut into a width of 15 mm, and the film is peeled in the direction of 180 ° C. at a tensile rate of 200 mm / min. Maximum load was measured. Evaluations were made with a circle having a width of 20 N / 15 mm or more and a circle having a width of 20 N / 15 mm or less as x. The results are shown in Table 1.

(3) Refrigeration drop test Using a deep-drawing packaging machine, hamburgers are vacuum-packed, retorted at 120 ° C for 30 minutes, frozen at -40 ° C for 24 hours, and then placed in cardboard on a concrete surface from a height of 50 cm. The film was dropped and evaluated for the presence of cracks or pinholes in the film. The case where no cracks / pinholes occurred was evaluated as “◯”, and the case where cracks / pinholes occurred was evaluated as “×”. The results are shown in Table 1.

(4) Impact strength A test piece cut to 100 mm × 100 mm was punched at 3 m / sec with a striker having a needle diameter of 0.5 inch φ at a test temperature of −20 ° C., and the impact energy was measured. Evaluations were made as follows: の も の for 50 kgf · mm or more, ○ for 10 kgf · mm or more and less than 50 kgf · mm, and × for less than 10 kgf · mm. The results are shown in Table 1.

Example 1:
A laminated film of a bottom material and a lid material made of a laminated film having the following layer structure was produced by a coextrusion method and a dry lamination method. In the examples and comparative examples, “/” indicates that the co-extrusion method is used, and “//” indicates that the dry lamination method is used.

(Bottom material)
Ny (60 μm) / ADHDPE (10 μm) / LLDPE (50 μm)
Ny: Mitsubishi Engineering Plastic Novamid 6Ny
ADHDPE: Mitsubishi Chemical Modic LLDPE: Ube Maruzen Polyethylene Umerit High Density Type (Cover)
ONy (25 μm) // LLDPE (40 μm)
ONy: Harden film made by Toyobo LLDPE: T. U. X. Retort compatible grade

Comparative Example 1:
Except that the adhesive layer and inner layer of the bottom material and the inner layer of the lid material were changed to PP, a laminated film of the bottom material and the lid material having the following layer structure was produced in the same manner as in the examples.

(Bottom material)
Ny (60 μm) / ADPP (10 μm) / PP (50 μm)
Ny: Mitsubishi Engineering Plastic Novamid 6Ny
ADPP: Mitsubishi Chemical Modic PP: Prime Polymer Prime Polypro (cover)
ONy (25 μm) // Random copolymer CPP (40 μm)
ONy: Toyobo Harden Film Random Copolymer CPP: Toyobo Pyrene Film-CT

Comparative Example 2:
Except for changing the adhesive layer of the bottom material to LLDPE and the inner layer of the bottom material and the lid material to general-purpose LLDPE, the laminated film of the bottom material and the lid material having the following layer structure by the same method as in the examples. Produced.

(Bottom material)
Ny (60 μm) / ADLLDPE (10 μm) / LLDPE (50 μm)
Ny: Mitsubishi Engineering Plastic Novamid 6Ny
ADPP: Mitsui Chemicals Admer LLDPE: Prime Polymer MORETECH (cover material)
ONy (25 μm) // LLDPE (40 μm)
ONy: Harden film made by Toyobo LLDPE: T. U. X.

  As shown in Table 1, in Example 1, delamination due to the retort treatment did not occur. Moreover, the seal strength also showed a sufficiently strong value. Furthermore, in the drop test at a low temperature, no pinhole was generated and the impact strength was high. On the other hand, since Comparative Example 1 uses PP for the adhesive layer and inner layer of the bottom material and the inner layer of the lid material, the sealing property and the pinhole resistance were inferior. Moreover, since LLDPE was used for the adhesive layer of the base material in Comparative Example 2, the heat resistance was poor, and delamination due to retort occurred. From this, it can be seen that the coextruded composite film for retort of the present invention can improve the sealing property and the pinhole resistance without causing delamination due to the retort.

  The film of the present invention can be used as a coextruded composite film for retort that has good pinhole resistance and does not generate delamination during retort.

Claims (6)

It is a composite film having a configuration of an outer layer, an intermediate layer, and an inner layer, the outer layer is a layer made of a polyamide resin, the intermediate layer is a layer made of high-density polyethylene or linear low-density polyethylene, and the inner layer is a heat seal layer or A co-extruded composite film for retort, which is an easy peel layer having cohesive failure. The coextruded composite film for retort according to claim 1, wherein the density of polyethylene as a main component of the resin constituting the intermediate layer is 0.925 or more and the melting point is 125 ° C or more. The coextruded composite film for retort according to claim 1 or 2, wherein the heat seal layer is composed of linear low-density polyethylene having a density of 0.925 or more, or high-density polyethylene having a density of 0.930 or more. The coextruded composite film for retort according to any one of claims 1 to 3, wherein an easy peel strength of the easy peel layer is 1.96 N / 15 mm width or more and 11.8 N / 15 mm width or less at 25 ° C. The coextruded composite film for retort according to any one of claims 1 to 4, further comprising a layer made of MXD6-nylon resin as an intermediate layer. The coextruded composite film for retort according to any one of claims 1 to 5, which has a polypropylene resin outside the outer layer.