JP4768006B2 - Method for producing stretched multilayer film casing - Google Patents

Description

The present invention provides a casing made of a biaxially stretched multilayer film having at least three layers of an intermediate resin layer made of a polyamide-based gas barrier resin and both outer layers made of a polyolefin-based resin and having specific heat shrinkability and heat shrinkage stress. It is about the method .

  Conventionally, a casing made of biaxially stretched film is automatically filled and packaged with (semi) fluid (ie, semi-fluid or fluid) contents mainly composed of ham, sausage, stick cheese and other foods. Is widely practiced.

  The casing film preferably has good mechanical properties, extrudability, stretchability, and other good processability, transparency, and good gas barrier properties for maintaining product storage. In addition, the casing film, after filling the contents, exhibits heat shrinkability in boil sterilization, etc., not only a good appearance that prevents the occurrence of wrinkles, but also a food that has good storage stability without leaving voids, etc. It is preferable in giving the product.

  Moreover, in order to give a (semi) fluid product-filled product excellent in easy opening by automatic packaging, a heat-shrinkable biaxially stretched multi-layer film is back seam (seal that joins a pair of outer surface layers to each other) An automatic filling and packaging form in which the contents are filled and packaged after being subjected to center seam processing by a form, also referred to as “envelope sticker” is also preferable.

  Conventionally, in many cases, heat-shrinkable resin films used for packaging forms such as polyethylene resins (hereinafter sometimes abbreviated as “PE”) and polypropylene-based materials having excellent sealing properties and extrusion characteristics are used. A polyolefin resin (hereinafter abbreviated as “PO”) represented by a resin (hereinafter abbreviated as “PP”) or an ethylene-vinyl acetate copolymer (hereinafter abbreviated as “EVA”). A polyamide-based resin (hereinafter sometimes abbreviated as “Ny”) having excellent mechanical properties, stretchability, and bath barrier properties, and a vinylidene chloride resin (hereinafter referred to as “Ny”) having particularly excellent gas barrier properties. May be abbreviated as “PVDC”) or ethylene-vinyl acetate copolymer saponified resin (hereinafter abbreviated as “EVOH”), The layers of each resin and modified polyolefin-based resin (hereinafter sometimes abbreviated as "M-PO") containing Nomar resin, and is formed as a heat shrinkable multilayer film laminated with various aspects. In particular, as a typical laminated form of a multilayer film (hereinafter sometimes referred to as “polyamide multilayer film”) having a polyamide resin (Ny) excellent in mechanical properties, stretchability and gas barrier properties as an intermediate layer, When displayed from the surface layer to the inner surface layer, PO / Ny / PO, PE / Ny / PE, EVA / Ny / EVA, M-PO / Ny / EVOH / M-PO, EVA / EVOH / Ny / EVA, PP + PE / M-PO / EVOH / Ny / M-PO / PP + PE, etc. (for example, JP-B 61-53218, JP-B 3-80422, JP-A 6-210810, JP-A 8-230035, etc.) It has been known.

  However, when the above-mentioned polyamide-based multilayer film is applied to automatic filling and packaging of (semi) flowable contents including a back seam process, several problems have been found due to its inherent heat shrinkability. It was done. These problems are as follows, for example. (I) When applying (semi) fluid contents such as fish meat or livestock sausage to automatic filling packaging (for example, “KAP packaging machine” manufactured by Kureha Chemical Industry Co., Ltd.), the film shrinks during sealing. (B) A back that seals the outer layer side and inner layer side of the film. (B) The seal part is broken during the subsequent heat treatment even if it is difficult or impossible to continuously wrap off the seal bar. In the seam processing, the heat-shrinkable multilayer film shrinks, so that it is difficult to obtain a sufficient seal strength, and the processing yield is significantly reduced. Further, due to the dimensional change after processing, the width of the seamed casing is uneven, and when the content is filled with a certain amount, the product length varies and the commercial value becomes poor. The seal part is easily broken during the subsequent heat treatment. (C) The above-described problems are caused by reducing the seal width to, for example, about 0.1 to 1.5 mm in order to ensure easy opening and / or to give a beautiful appearance to the package. In particular, when back seam is performed, it tends to become particularly obvious.

Accordingly, a primary object of the present invention is to provide a method of manufacturing to solve the problems as described above, a polyamide-based multilayer film suitable for automatic packaging backseamed by the film casing or package.

  As a result of the research conducted by the inventors for the above-mentioned purpose, many of the problems of the above-described conventional film casing made of the heat-shrinkable polyamide-based multilayer film are caused by an excessive heat shrinkage ratio. Even after setting the heat shrinkage rate to an appropriate level by controlling the conditions, etc., since the gas barrier intermediate layer is made of polyamide resin, the stress (that is, heat shrinkage stress) exhibited by the multilayer film during heat shrinkage is excessive. It has been found to occur in order to become.

  As a result of further research, after applying biaxial stretching to the polyamide multilayer film under appropriate conditions, an appropriate heat treatment (homogeneous relaxation heat treatment performed at a relatively low temperature) is performed to obtain an appropriate heat shrinkage rate. However, it has been found that a polyamide-based multilayer film having a reduced thermal shrinkage stress is obtained, and by back seaming it, a film casing suitable for automatic filling packaging is formed. It was also found that steam or hot water having a large heat capacity is remarkably preferable as a heat treatment medium in order to perform heat treatment that exerts the effect of homogeneous relaxation heat treatment at a low temperature in an inflation process as a preferred heat treatment process. .

The stretched multilayer film casing produced by the method of the present invention is based on the above-mentioned knowledge. More specifically, the stretched multilayer film casing is composed of at least three layers of both outer layers made of the same type of polyolefin resin and gas barrier intermediate layer made of polyamide resin. A stretched multilayer film having a heat shrinkability of 2 MPa or less in both longitudinal and transverse directions at 50 ° C. and a hot water shrinkage rate of 5 to 20% at 90 ° C. is back-seamed with both outer layers. It is characterized by this.

And the manufacturing method of the extending | stretching multilayer film casing of this invention coextruded the molten at least 3 types of thermoplastic resin in the shape of a tube, the gas-barrier intermediate | middle layer which consists of polyamide-type resin, and both outer layers which consist of polyolefin-type resin Forming a tubular body composed of at least three layers, then water-cooling the tubular body to below the melting point of the main resin in each layer, and then reheating to a temperature below the melting point of the main resin in each layer of the tubular body; While putting the fluid inside the body, the tubular body is drawn vertically and stretched 2.5 to 4 times in the vertical and circumferential directions to form a biaxially stretched tubular film, which is folded and then folded inside Heat treatment at 50 ° C. is performed by heat treatment with steam or hot water at 60 to 95 ° C. from the outer surface layer (a) side of the tubular body formed again by adding fluid. Forming a biaxially stretched tubular body film having a stress of 2 MPa or less both in the longitudinal direction and the transverse direction and having a hot water shrinkage of 5 to 20% at 90 ° C., and further slitting the biaxially stretched tubular body film, It is characterized by back seam in both outer layers.

  As described above, according to the present invention, by back seaming a polyamide-based multilayer film that prevents generation of excessive heat shrinkage stress during heat shrinkage while ensuring necessary heat shrinkability, A film casing suitable for automatic filling and packaging of semi-fluid contents is provided.

The polyamide multilayer film constituting the stretched multilayer film casing according to the method of the present invention comprises at least three layers of both outer layers made of the same kind of polyolefin resin and a gas barrier intermediate layer made of polyamide resin.

Examples of the polyolefin resin forming both outer layers include a polyolefin polymerized using a single site catalyst such as a metallocene catalyst (hereinafter sometimes abbreviated as “SSC”), such as an ethylene-α-olefin copolymer, Density polyethylene (hereinafter abbreviated as “SSC-LLDPE”), linear ultra-low density polyethylene (hereinafter abbreviated as “SSC-VLDPE”), conventional ethylene-α olefin copolymer (generally “LLDPE”, “VLDPE”) These are copolymers of ethylene and one or more comonomers selected from C ₃ to C ₁₀ alpha olefins, especially C _{4 to} C ₈ alpha olefins. For example, it contains a copolymer of ethylene with butene-1, pentene-1, hexene-1, octene-1, etc.), A material selected from pyrene (hereinafter abbreviated as “PP”), a propylene-based copolymer (hereinafter abbreviated as “PP-Et”) represented by propylene-ethylene copolymer, propylene-ethylene-butene copolymer and the like. Can be used. The polyolefin resin preferably has a melting point in the range of 90 ° C. to 170 ° C., particularly 95 ° C. to 150 ° C., more preferably in the range of 100 ° C. to 140 ° C. When the melting point is larger than the upper limit value, it is difficult to stretch the film. When the melting point is smaller than the lower limit value, the seal part is easily ruptured when the package is boiled. A blend containing at least one of these polyolefin resins may be used as long as the transparency of the film is not significantly impaired.

Among these, SSC-LLDPE, SSC-VLDPE , LLDPE, as the VLDPE, density of 0.900 g / cm ³ or more, in particular 0.905 g / cm ³ or more ones, as the PP-Et is typified ethylene Those containing 1% by weight or more, particularly 3% by weight or more, and more preferably 5% by weight or more of the comonomer are preferably used in view of their excellent heat resistance, sealing properties, and film productivity. Particularly effective SSC-based polyolefins include those obtained by using a constrained geometric catalyst (a kind of metallocene catalyst developed by Dow Chemical Company). The ethylene-α-olefin copolymer obtained by 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 about 0.05 to about 1 substantially linear polyethylene-based resin. In the ethylene-α olefin copolymer, linear long chain branches having about 6 carbon atoms or more are selectively introduced into the molecular structure, so that excellent physical properties and good moldability are imparted to the polymer. The An example is sold by Dow Chemical under the name “Affinity” and the alpha olefin is octene-1.

  Examples of polyethylene resins obtained using other metallocene catalysts include, for example, Exact from EXXON, Umerit from Ube Industries, Evolution from Mitsui Chemicals, Kernel from Nippon Polychem, Dow Chemical There is an elite made by the company.

  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.

In order for the resulting polyamide-based multilayer film to exhibit good back seam suitability, it is necessary that the polyolefin-based resins constituting both outer layers be of the same type. Here, the “same kind” of the polyolefin resin typically means that both are polyethylene or both are propylene / ethylene copolymers. A difference of up to 8 % by weight in the content of certain components (e.g., ethylene in propylene-ethylene copolymers) is acceptable between the copolymer and the copolymer. Further, the polyolefin resin of both outer layers preferably has a melting point difference of 30 ° C. or less, particularly 10 ° C. or less.

  The above-described polyolefin-based resin can be used as an intermediate resin layer in addition to the two outer layers, if necessary. The polyolefin resin used as the intermediate layer may be the same as or different from the polyolefin resin in both outer layers. Resins other than the preferred resins described above, such as ethylene-vinyl acetate copolymer, ethylene-methacrylic acid copolymer, ethylene-methacrylic acid ester copolymer, ethylene-acrylic acid copolymer, ethylene-acrylic acid ester An ethylene copolymer such as a copolymer (for example, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer) or ionomer may be used.

  Examples of the polyamide resin (“Ny”) constituting the gas barrier intermediate layer include aliphatic polyamide polymers such as nylon 6, nylon 11, nylon 12, nylon 66, nylon 69, nylon 610, nylon 612, and nylon 6/66. And aliphatic polyamide copolymers such as nylon 6/10, nylon 6/12, nylon 6/69, and nylon 66/69. 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. For example, blends of aliphatic nylons such as nylon 66/610 / MXD6 (MXD6 is polymetaxylylene adipamide) and aromatic polyamides containing aromatic diamine units, nylon 66/69 / 6I (6I is polyhexamethylene iso Phthalamide), blends of aliphatic nylons such as nylon 6 / 6I and copolymerized aromatic polyamides containing aromatic carboxylic acid units, nylon 6I / 6T (ie, co-polymerization of isophthalic acid, terephthalic acid and hexamethylenediamine) And blends with non-crystalline aromatic polyamides having an aromatic carboxylic acid such as polyhexamethylene isophthalamide / terephthalamide), and blends with aromatic polyamides having an aromatic diamine such as nylon MXD6. . Of these polyamide resins, those having a main melting point of 160 to 210 ° C. alone or mixed are preferably used.

  The gas barrier intermediate layer can be composed of only a single layer of polyamide-based resin, but can also be used by being laminated with other gas barrier resin layers. In this case, as the other gas barrier resin, a non-chlorine resin is preferably used rather than a chlorine resin (particularly PVDC) which has excellent gas barrier properties but does not have good coextrudability with the polyamide resin layer. An example of a particularly preferable non-chlorine gas barrier resin is an ethylene-vinyl acetate copolymer saponified product (EVOH) having good moldability. Preferred laminated gas barrier intermediate layer structures include Ny / EVOH, EVOH / Ny, and Ny / EVOH / Ny. In the case of lamination, the thickness of the polyamide-based resin layer in the gas barrier resin intermediate layer is preferably 50% or more, particularly preferably in the range of 50 to 95%. If necessary, another resin layer such as an adhesive resin layer or a polyolefin resin can be inserted between the Ny layer and the EVOH layer.

  The reason why Ny / EVOH of the intermediate layer is preferable is that the coextrudability is excellent, the adhesiveness between both resins is extremely good, and it is not necessary to provide an adhesive layer in the middle. The reason why Ny / EVOH / Ny is preferable is that Ny is superior to EVOH in terms of adhesion to polyolefins of both outer layers (especially acid-modified polyolefins disposed between the polyolefin and the gas barrier intermediate layer). It is easy to suppress curling that can occur due to the difference in shrinkage behavior between Ny and EVOH, the strength of the film is strong, and even a stretched multilayer film casing in which both outer layers made of the same type of polyolefin resin are arranged has a remarkable effect. For example.

  The adhesive resin layer can be provided as an intermediate layer as necessary, for example, when the adhesive force between the above-mentioned respective layers is not sufficient. More preferably, as the adhesive resin, ethylene-ethyl acrylate copolymer (EAA), ethylene-acrylic acid copolymer (EAA), ethylene-methacrylic acid copolymer, ionomer resin (IO), acid-modified polyolefin ( A reaction product of an olefin or a copolymer with an unsaturated carboxylic acid such as maleic acid or fumaric acid, an unsaturated carboxylic acid anhydride, an unsaturated carboxylic acid ester or a metal salt, such as acid-modified VLDPE, Acid-modified LLDPE, acid-modified EEA, acid-modified EVA, acid-modified PP, acid-modified PP-Et) and the like can be used. Preferable examples include acid-modified polyolefins 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, aliphatic amide lubricants, ester lubricants and metal soaps. 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. Aliphatic 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, erucic acid amide, methylene bisstearamide, ethylene Examples include bisstearoamide. 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.

  Known inorganic lubricants (anti-blocking agents) such as silica and zeolite can be added to both outer layers.

  Lubricants such as aliphatic amides and silica can be added in the form of a masterbatch. The preferable addition amount is 0.1 to 10% by weight in the case of a masterbatch containing 20% by weight of lubricant.

  As the antistatic agent, a surfactant is preferably used. As the surfactant, an anionic surfactant, a cationic surfactant, a nonionic surfactant, an amphoteric surfactant and a mixture thereof can be used. The antistatic agent is preferably 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.

A preferred example of the layer structure of the polyamide-based multilayer film constituting the multilayer film of the present invention will be described below as a layer structure directed from the outer layer to the inner layer. However, these are merely examples, and the present invention is not limited to these.
(1) Polyolefin resin / Ny / Polyolefin resin (2) Polyolefin resin / Ny / EVOH / Polyolefin resin (3) Polyolefin resin / Ny / EVOH / Ny / Polyolefin resin (4) Polyolefin resin / Ny / Polyolefin resin / Ny / Polyolefin resin (5) Polyolefin resin / Adhesive resin / Ny / Adhesive resin / Polyolefin resin (6) Polyolefin resin / Adhesive resin / Ny / EVOH / Adhesive resin / Polyolefin Resin (7) polyolefin resin / adhesive resin / Ny / adhesive resin / EVOH / adhesive resin / polyolefin resin (8) polyolefin resin / adhesive resin / Ny / EVOH / Ny / adhesive resin / polyolefin Resin (9) Polyolefin resin / Ny / contact RESIN layer / polyolefin resin / adhesive resin layer / Ny / polyolefin resin (10) polyolefin resin / Ny / adhesive resin layer / EVOH / polyolefin resin

The film casing according to the method of the present invention may be composed of a single polyamide-based multilayer film, but may be composed of two or more films. When two or more sheets are stacked, if necessary, they may be stacked so that the outer surface and the inner surface are in contact with each other, may be stacked so that the outer surfaces are in contact with each other, or the inner surfaces are You may superimpose so that it may contact. The two films may be bonded together by self-adhesion of the surface layer resin, or may be bonded using a known adhesive if the self-adhesive strength is insufficient. An advantage of overlapping the films is that the uneven thickness of the film can be improved.

  The polyamide-based multilayer film is formed by laminating and stretching each of the above layers to finally form a multilayer film having a thickness in the range of 10 to 120 μm, particularly 10 to 80 μm, and further 15 to 60 μm. It is preferable to constitute a stretched multilayer film casing.

  More specifically, in the polyamide-based multilayer film, the outer surface layer made of polyolefin resin is 3 to 50 μm, particularly 5 to 30 μm, and the intermediate layer made of polyamide-based resin (or other gas barrier resin to be used arbitrarily) is individually It is preferable that the inner surface layer made of polyolefin resin has a thickness in the range of 3 to 50 μm, particularly 5 to 30 μm, in particular, 2 to 35 μm, particularly 3 to 25 μm, and in total 4 to 30 μm, particularly 6 to 30 μm. In particular, the total thickness of the outer surface layer is preferably at least 10 μm. As a result, the casing package obtained by back seaming the stretched multilayer film having a hot water shrinkage of 5 to 20% (90 ° C.) and a heat shrinkage stress of 2 MPa or less (50 ° C.) The durability to withstand heat treatment is sufficiently imparted.

  A plurality of adhesive resin layers can be provided, and the thickness is preferably in the range of 0.5 to 5 μm.

The polyamide-based multilayer film constituting the film casing is produced by an inflation method according to the method of the present invention. With reference to FIG. 1, the preferable one aspect | mode is demonstrated.

  The outer surface layer composed of at least polyolefin resin, the intermediate layer composed of polyamide resin, the polyolefin resin through the annular die 2 from the number of extruders 1 (only one is shown) corresponding to the number of laminated resins constituting the multilayer film. An annular body (parison) 3 having three inner surface layers consisting of the above is coextruded and cooled to below the melting point of the main resin occupying each layer by a water bath 4 (or a known showering device), preferably below 40 ° C. While picking up with the pinch roller 5. Next, hot water having a temperature equal to or lower than the melting point of the main resin occupying each layer, for example, 80 to 95 ° C., is encapsulated in the taken-up tubular film 3a, if necessary, with an opening agent typified by soybean oil or glycerin fatty acid ester. Introduced into the bath 6, the heated tubular film 3 b is drawn upward, and a bubble-shaped tubular body 3 c is formed by the fluid air introduced between the pair of pinch rollers 7 and 8. While cooling with a ring, it is simultaneously biaxially stretched in the vertical direction (MD) and the transverse direction (TD), preferably 2 to 4 times each, more preferably 2.5 to 4 times each. If the draw ratio exceeds the upper limit value, the heat shrinkage stress of the produced film becomes excessive, or the internal pressure of the inflation bubble becomes too high, making it difficult to produce the film. If the lower limit is not reached, stretching unevenness is likely to occur, and as a result, the thickness unevenness of the produced film increases, making it difficult to obtain performance suitable for automatic (filling) packaging. The draw ratio of MD and TD may be the same or different within the above-mentioned range. Next, the stretched tubular film 3 d is drawn downward, and the bubble-shaped tubular body 3 e is formed again by the fluid air introduced between the pair of pinch rollers 9 and 10, and is held in the heat treatment cylinder 11. Then, steam is sprayed from the outlet 12 of the heat treatment cylinder 11 (or sprayed with warm water), and the biaxially stretched tubular film 3e is heated at 60 to 98 ° C, preferably 65 to 95 ° C for 1 to 20 seconds. The tubular film 3e is relaxed by 0 to 25%, preferably 5 to 20% in the vertical direction (MD) and the transverse direction (TD), preferably by heat treatment for about 1.5 to 10 seconds. The tubular body film 3 f after the heat treatment corresponds to the polyamide-based multilayer film constituting the stretched multilayer film casing of the present invention, and is wound around the winding roll 13.

  The polyamide-based multilayer film thus obtained has a hot water shrinkage rate of 90 ° C. of 5% to 20%, preferably 10% to 20% in both the vertical direction and the horizontal direction. The stress is 2.0 MPa or less, preferably 1.5 MPa or less (more preferably 1.0 MPa or less) in both the longitudinal direction and the transverse direction, and good automatic packaging suitability is imparted.

  A film having a hot water shrinkage of 90 ° C. of 5% to 20%, more preferably 10% to 20% has good mechanical suitability in an automatic filling and packaging process including a back seam processing step such as sausage and cheese, and The package obtained in the packaging has a beautiful appearance. When the hot water shrinkage rate is too large, the suitability of the packaging machine tends to be lowered. On the other hand, when the hot water shrinkage is too small, wrinkles are generated on the surface of the package due to insufficient shrinkage of the film, and the commercial value is lowered.

  The heat shrinkage stress at 50 ° C. is 2 MPa, further 1.5 MPa or less (particularly 1.0 MPa or less), so that it is excellent in packaging machine suitability and heat sealability during automatic filling and packaging, and has dimensions after processing. Changes in (especially width) are suppressed, and a packaged product having a very good appearance can be manufactured. If the heat shrinkage stress is too large, the packaging body will break or bend when the packaging machine is poorly sealed or the package filled with the contents is heat treated such as boiled or retort. May become horseshoe-shaped). When the heat shrinkage stress is small, there is almost no heat shrinkage rate, the film is wrinkled, and the appearance of the package is deteriorated.

  While maintaining excellent mechanical suitability, it has a moderate heat shrinkage rate and realizes a low heat shrinkage stress. In MD / TD, it is stretched 2 to 4 times, more preferably 2.5 to 4 times, respectively. It is extremely preferable to secure a magnification and perform low-temperature heat treatment at 60 ° C. to 98 ° C., particularly 65 ° C. to 95 ° C. with steam or hot water having a large heat capacity. At a lower draw ratio, the necessary heat shrinkability after heat treatment cannot be ensured, and the uneven thickness of the film increases, making it difficult to obtain suitability for automatic packaging machines and suitability for center seam processing. 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 60 ° C. is adopted, it is difficult to obtain the necessary effect of reducing the heat shrinkage stress, and the suitability for automatic packaging machines and center seam processing is low. It is easy to get worse and lose its commercial value due to dimensional changes of the film.

  Before or after stretching of the above-described method for producing a polyamide-based multilayer film, irradiation can be performed by a known method. Irradiation improves stretchability, heat resistance, mechanical strength, and the like compared to those without irradiation. In the present invention, known radiation such as α rays, β rays, electron rays, and γ rays can be used. From the viewpoint of the crosslinking effect before and after irradiation, an electron beam or γ-ray is preferable. Among them, the electron beam is advantageous in terms of handling property and high processing ability in producing a molded product.

  The aforementioned radiation irradiation conditions may be set as appropriate 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. The range of kilogray (kGy) is preferable, and in the case of γ rays, the dose rate is preferably in the range of 0.05 to 3 kGy / hour.

  Corona discharge treatment, plasma treatment, and flame treatment may be performed on the inner surface, outer surface, or both surfaces of the above-described polyamide-based multilayer film.

  The polyamide-based multilayer film thus obtained is usually cut into a width according to the dimensions of the film casing to be formed into a flat film, and then, for example, 3 to 40 mm so that both outer end portions are in contact with each other. Preferably, the film casing is overlapped with a width of 5 to 25 mm, a part of the overlapping width is sealed, and back seam processed to form a film casing, or an automatic packaging process that wraps the film casing forming process by back seam processing Provided. When the overlap width is too large, the package may be bent due to the heat shrinkage stress of the film in the overlap portion. If the overlapped portion is too small, the workability during back seam processing tends to deteriorate.

  Some examples of suitable packaging including the film casing forming process of the present invention from the polyamide-based multilayer film as described above are listed below.

  KAP manufactured by Kureha Chemical Industry Co., Ltd. is an example of an automatic filling and packaging machine used for packaging sausages and cheese. This is a flat film made into a cylinder at the homing part, and the outer surface and inner surface of the film are vertically sealed by various methods such as high frequency method, ultrasonic method, hot jet method, etc. After filling, both ends of the shell-shaped package are closed by clips or seals. Usually, after that, by immersing the package in hot water, the film shrinks, and the contents and the film are tightly fitted. The width of the flat film used for KAP is usually in the range of 40 to 450 mm. Examples of other automatic filling and packaging machines include TSA manufactured by Polyclip Co., and automatic tube packaging machines manufactured by Cartridge Pack.

  Back (center) seam processing is a process in which a flat film is formed into a cylindrical shape, and the sealing surfaces of the film are sealed with various sealing methods, preferably the outer surface and the inner surface of the film, and then wound into a roll. Shorten the length by cutting or folding the tubular film after sealing (shearing) to cut the length required for end use applications or to facilitate the work of filling the contents May be. The back seamed casing (or bag) processed in this way can be packed with contents by clipping or sealing at both ends. In general, first, one end is clipped or sealed, then the contents are filled, and then the other end is clipped or sealed to fill the contents. The package filled with the contents is usually immersed in hot water for a certain time (for example, 1 second to 7 hours) to sterilize the contents, cook, and shrink the packaging film. This hot water immersion treatment may be performed as it is in the package, or may be performed after the package is placed in a retainer. The back seamed casing or bag is characterized by less width unevenness than the seamless casing or seamless bag. In particular, a seamless casing having a small diameter is liable to have uneven width because the stretching process tends to be unstable. The width of a flat film used for back seam processing is generally 40 to 450 mm.

  The folding width of the back seamed casing is preferably 15 to 160 mm. If it is less than 15 mm, it can be done manually, but automatic packaging becomes difficult due to slipping of the film, etc., the area ratio of the overlapped portion becomes large, and the package tends to be bent. Moreover, when it exceeds 160 mm, for example, wrinkles are likely to occur in the package after heat treatment such as boil and retort treatment. In order to suppress the generation of wrinkles, packaging using a film having a large heat shrinkage stress makes it difficult to perform back seam processing, and the seal portion may be easily broken during heat treatment such as boil treatment and retort treatment.

  In general, the back seam can be formed over a seal width of 0.1 to 10 mm. However, in the case of the present invention, 0.1 to 1. It is preferable to carry out with a very reduced seal width of 5 mm. One of the very preferable characteristics of the film casing of the present invention is that even if the back seam has such a narrow seal width, it is surely sealed without breaking (puncture) of the seal portion during the subsequent heat treatment. One. As a sealing method of an automatic packaging machine, there are indirect high-frequency sealing, ultrasonic sealing, hot jet (hot air at a setting of about 300 to 350 ° C.), heat sealing, and the like.

  The multilayer film casing of the present invention formed through the back seam as described above is subjected to pre- and post-filling processing such as shearing processing for facilitating filling of the contents as necessary.

  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.

<Physical property measurement method>
1. Hot water shrinkage A film sample marked at a distance of 10 cm in the machine direction (longitudinal direction, MD) of the film and the direction perpendicular to the machine direction (transverse direction, TD) is placed in hot water adjusted to 90 ° C. for 10 seconds. After soaking, it was taken out and immediately cooled with normal temperature water. 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. The test was conducted five times for one sample, and the hot water shrinkage rate was displayed as an average value in each of the vertical and horizontal directions.

2. Method for measuring dry heat shrinkage ratio A gear oven (MOG-600, manufactured by Robert Co., Ltd.) in which a corrugated cardboard having a thickness of 3 mm is laid on a net shelf is heated to 120 ° C. Into it is placed a film sample marked at a distance of 10 cm in the machine direction (longitudinal direction, MD) of the film and in the direction perpendicular to the machine direction (transverse direction, TD). At this time, the gear oven door should be closed immediately after the sample is placed. The open time of the door shall be within 3 seconds. Close the door and leave the sample for measurement in the gear oven for 30 seconds, then take it out and let it cool naturally. 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 dry heat shrinkage was displayed as an average value in each of the vertical and horizontal directions.

3. Thermal shrinkage stress From the obtained multilayer film, two sample film bands each having a length of 250 mm and a width of 15 mm were obtained along the longitudinal direction (MD) and the transverse direction (TD), respectively , and Instron Corporation maintained at 23 ° C. The temperature is set at 200 mm between grips on an Instron universal testing machine (“5565 type”) held in a thermostat (“3119 series”), and then the thermostat is heated at a rate of 2 ° C./min. As the temperature rises, the heat shrinkage stress generated in the sample film increases, and gradually decreases when it exceeds a certain temperature (usually 50 to 120 ° C.). In the following examples and comparative examples, the value of 50 ° C. of the heat shrinkage stress value that changes with increasing temperature is displayed.

4). Measurement of crystal melting temperature Crystal melting temperature was measured using a differential scanning calorimeter DSC-7 manufactured by Perkin Elmer. In the measurement, the sample was heated from 30 ° C. to 240 ° C. at 20 ° C./min, held at 240 ° C. for 1 minute, then cooled to 30 ° C. at 20 ° C./min, and held at 30 ° C. for 1 minute. did. Thereafter, the value of the peak of the crystal melting curve when the temperature was raised to 240 ° C. under the condition of 20 ° C./min was read again as the crystal melting temperature.

<Example of film production>
Next, the manufacture example of the heat-shrinkable multilayer film by an Example and a comparative example is described. Resins used in the following production examples are summarized in Table 1 below together with their abbreviations.

Example 1
Using the apparatus shown in FIG. 1, the layer configuration is VL-1 (10) / M-PE (1.5) / NY-1 (12) in the thickness ratio shown in parentheses in order from the outside to the inside. ) / EVOH (5) / M-PE (1.5) / VL-1 (20), each resin is extruded by a plurality of extruders 1 and the molten resin is introduced into the annular die 2. Then, melt-bonding was performed so as to have the above-described layer configuration, and co-extrusion was performed. The molten tubular body 3 flowing out from the outlet of the die 2 was rapidly cooled to 10 to 18 ° C. in the water bath 4 to obtain a tubular body 3a having a flat width of 148 mm. Next, the flat tubular body 3a is passed through a warm water bath 6 at 87 ° C., and then converted into a bubble-shaped tubular body film 3c in the longitudinal direction (MD) by an inflation method while being cooled by an air ring 9 at 15 to 20 ° C. Simultaneous biaxial stretching was performed at a stretching ratio of 2.7 times and transverse direction (TD) of 2.7 times. Next, the biaxially stretched film 3d is introduced into a heat treatment tube 11 having a tube length of 2 m to form a bubble-shaped tubular film 3e, heated to 70 ° C. by steam blown from the blowing port 12, and 5% in the vertical direction. The film was heat-treated for 2 seconds while being relaxed 5% in the transverse direction and 5% in the transverse direction to produce a biaxially stretched film (polyamide multilayer film) 3f. The obtained biaxially stretched film had a flat width of 362 mm and a thickness of 49 μm.

  An outline of the layer structure and film forming (biaxial stretching) conditions of the obtained biaxially stretched film is shown in Table 2 together with those of other examples and comparative examples.

(Examples 2-9, Comparative Examples 1-3)
Various biaxially stretched films were prepared in the same manner as in Example 1 except that the layer structure and film forming (biaxial stretching) conditions were changed as shown in Table 2, and the relaxation and heat treatment conditions were changed as shown in Table 2, respectively. Obtained.

(Comparative Example 4)
Toppero unstretched polypropylene film CPP GHC (thickness 20 μm) is used as nylon 6 film, Bonile SC (thickness 15 μm) of Mitsubishi Chemical Kojin Pax Co., Ltd. A laminate film was produced. The thickness of the adhesive layer (represented by //) between CPP and Ny6 was 2 μm, and a known polyester adhesive was used.

  The various biaxially stretched films obtained in the above Examples and Comparative Examples were each subjected to the above physical property measurement and the following performance evaluation test. The results are summarized and shown in Table 3 below.

<Performance evaluation test>
1. Automatic Sausage Filling Test After slitting the manufactured tubular film to a width of 85 mm, using the automatic filling and packaging machine KAP-500 manufactured by Kureha Chemical Industry Co., Ltd., the sealing method is the hot jet method (method of blowing heated air onto the film) ), And a back seam to form a casing under the conditions of an air temperature of 260 ° C., a blowing air pressure of 0.8 kg / cm ³ , a film feed speed of 10 m / min, and a seal width of about 1.3 mm. An automatic filling test of sausage was performed, in which sausage was filled.

  The folded width of the film casing after sealing (the width when the tubular film was flattened) was 37 mm, the distance between the clips was 200 mm, and the weight after filling was about 65 g.

The package was boiled in hot water at 80 ° C. for 60 minutes and immediately cooled in cooling water at 5 to 10 ° C. for 30 minutes. Thereafter, the sufficiently cooled package was immersed in hot water at 90 ° C. for 5 seconds and cooled. The appearance of the package after cooling was evaluated according to the following criteria.
A: There was no problem in sealing performance, and automatic filling and packaging could be performed continuously. In addition, no wrinkles were observed in the package after filling, and a good appearance was shown.
B: Although automatic filling and packaging were possible without any problem in sealing properties, wrinkles were observed in the package after filling, and the package did not have commercial value.
C: When hot jet sealing was performed, it was impossible to continuously perform automatic filling and packaging by contacting the forming portion or the like due to shrinkage of the film.

2. Back seam test After slitting the manufactured tubular film to a width of 145 mm, using a back seam machine S-70 (sealing method: high frequency seal) manufactured by Kureha Chemical Co., Ltd., 48 shots per minute, film feed A mechanical suitability test of a back seam having a seal width of about 1.0 mm was performed under conditions of a speed of 14 m / min and a seal portion current of 230 mA.
The folding width of the film after the back seam (width in the state where the tubular film was flattened) was 65 mm.
After filling the resulting back seamed casing with pork sausage raw material with a margin of about 5% (so that the volume of the content is 95 with respect to the volume of the casing 100), both ends are made of metal clips And was immersed in hot water at 80 ° C. for 60 minutes to obtain a package. The center seam processability and the appearance of the package were evaluated according to the following criteria.
A: Continuous back seam processing was possible, and the width unevenness of the back seamed casing was 2 mm or less. The resulting package was free of wrinkles and had a beautiful appearance.
B: Continuous center seam processing was possible, but the width unevenness of the back seamed casing was 2 mm or less. The resulting package had wrinkles and the package had no commercial value.
C: Continuous back seam processing is impossible.

The schematic of the apparatus system suitable for implementing the manufacturing method of the polyamide-type multilayer film for film casings by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Extruder 2 Annular die 3 Molten tubular body (3c: during inflation, 3e: during heat treatment)
6 Hot water bath 9 Cold air ring 11 Heat treatment cylinder

Claims (1)

At least three types of molten thermoplastic resins are coextruded into a tube to form a tubular body composed of at least three layers of a gas barrier intermediate layer composed of a polyamide-based resin and both outer layers composed of a polyolefin-based resin. The body is cooled with water below the melting point of the main resin occupying each layer, and then reheated to a temperature below the melting point of the main resin occupying each layer of the tubular body. The outer surface layer side of the tubular body formed by stretching the biaxially stretched tubular film by drawing 2.5 to 4 times each in the vertical direction and the circumferential direction while being drawn out, folding it, and then forming the fluid therein Heat treatment with steam or hot water at 60 to 98 ° C. and cooling, the heat shrinkage stress at 50 ° C. is 2 MPa or less in both the vertical and horizontal directions, and 90 ° C. A biaxially stretched tubular body film having a hot water shrinkage of 5 to 20% is formed, and the biaxially stretched tubular body film is slit, and then back seamed with both outer layers. Method.

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