JPS6140179B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a laminated material for thermal adhesive packaging, and more specifically, a method for manufacturing a laminated material for thermal adhesive packaging using an extrusion lamination method, which has excellent heat resistance and is suitable for use in, for example, retort pouches and small bags for boiling. Regarding. Conventionally, contents that are relatively susceptible to deterioration are sealed and packaged using a laminated material (laminate film) made by laminating a heat-adhesive film such as polyethylene, a heat-resistant synthetic resin film such as polyester or polyamide, and aluminum foil, and then heated as is. Aseptic packaging methods that enable long-term storage by sterilization are widely used, but the film used for this packaging is exposed to high temperatures along with the contents during sterilization, so it is not suitable for For example, when high-temperature processing such as retort sterilization is required, low-density polyethylene film with a low melting point cannot be used as a packaging material, and high-density polyethylene film or polypropylene with a high melting point and good heat resistance must be used. Laminated materials are used that use film as a sealant material. However, this laminated material cannot be manufactured by extrusion lamination, and after coating one side of the base film with an isocyanate adhesive solution, the solvent is evaporated in an oven.
It can only be manufactured by dry lamination, which involves drying and then pressing the sealant material onto the adhesive-coated surface, which slows down the manufacturing process and usually makes it easier to use extrusion lamination.
1/2 or less, the use of a large amount of expensive adhesive, residual solvents that leave a solvent odor in laminated materials, and isocyanate adhesives and sealant materials containing harmful substances. I have a problem. The inventors of the present invention have conducted various studies to solve the above problems, and have found that low-melting point synthetic resin films such as low-density polyethylene, which have a melting point of about 85 to 110 degrees Celsius,
Although the melting point hardly changes when irradiated with radiation at a low dose of megarad or less, this low-melting point synthetic resin film suffers from a decrease in tensile strength and delamination even at temperatures as high as 130°C. It was discovered that heat resistance, thermal adhesion, etc. were significantly improved without any problems, and this led to the present invention. That is, the present invention uses an extrusion lamination method to produce low density polyethylene, medium density polyethylene,
While heating and melting low melting point synthetic resins such as copolymers of ethylene and acrylic acid, methacrylic acid, vinyl acetate, etc., ionomer resins, or blends thereof, and extruding these films, the base material, thermal adhesive film, etc. By laminating layers to produce a laminated film at high speed, and then irradiating it with radiation at a dose of 5 megarads or less, the heat resistance of the low-melting point synthetic resin layer, such as the low-density polyethylene layer, can be improved without increasing its melting point. It also has good delamination resistance, and packaging bags made with this material can withstand high-temperature treatments such as high-temperature boil sterilization or retort sterilization. The object of the present invention is to provide a method for producing a laminated material for adhesive packaging. Hereinafter, one embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic side view showing an example of an apparatus for producing a laminated material for thermally adhesive packaging by the coextrusion lamination method used in the implementation of the present invention. In the figure, 1a and 1b are synthetic resins with different melting points, such as low density These are first and second extruders that heat and melt and extrude polyethylene and medium density polyethylene. The molten resin discharge portions of the extruders 1a and 1b are connected to a T-die 3 by adapters 2a and 2b, respectively, to form a known coextrusion laminating device. The molten resin extruded from the first and second extruders 1a and 1b is extruded into a film from a T-die 3 and laminated, and a laminated film 4 in which a low-density polyethylene film and a medium-density polyethylene film are laminated is continuously formed. Manufactured in 5 is a base material web made by winding a base material 6 made of a synthetic resin film such as polyester, polyamide, polycarbonate alone, a laminate thereof, or a laminate thereof and an aluminum foil etc. into a roll; The base material 6 fed out from the base material web 5 is coated with an isocyanate-based anchoring agent by an anchoring agent applicator 8 appropriately disposed forward in the direction of travel, dried in a hot air oven 9, and then dried in a hot air oven 9. The low-density polyethylene and medium-density polyethylene films extruded by the second extruders 1a and 1b are laminated by pressure bonding, and as shown in FIG. A laminate 11 made of the density polyethylene layer 11d is formed, and then this laminate 11 travels in a predetermined direction (direction of arrow A) and is exposed to radiation irradiation equipment 12 such as electron beams or X-rays disposed in front of the laminate 11. A laminated material 13 for thermally adhesive packaging having the medium-density polyethylene film layer as a thermally adhesive layer is manufactured by irradiating with radiation at a low dose of megarad or less. In this case, as the radiation, an electron beam is particularly preferable in view of the simplicity of the apparatus. The irradiation dose is less than 5 megarads, especially 1
It is preferable to set the dose to ~3 megarads, and by adjusting the dose within this range, the heat resistance can be improved without substantially changing the melting point of the laminated film 4 having a low melting point. The laminated material 13 manufactured in this manner is further changed in its traveling direction by the second guide roll 14 and then wound onto the winding roll 15. The heat-adhesive packaging material 13 produced by the above method is made into a bag by heat-bonding predetermined points using a suitable bag-making machine, then filled with contents, sealed by heat-bonding, and sterilized by high-temperature boiling if necessary. , retort sterilization treatment, etc. In this example, when manufacturing the laminated material, a laminated film was obtained using low-melting-point low-density polyethylene and medium-density polyethylene, and the base material was laminated on this, so a coextrusion lamination method could be adopted. As a result, the drying speed of the adhesive solvent does not determine the manufacturing rate as is the case with the dry lamination method, and the manufacturing speed is high, more than twice that of the normal dry lamination method. It is suitable for mass production. In this example, the laminate thus obtained is irradiated with radiation, and by reducing the irradiation dose to a low dose of 5 megarads or less, the melting points of the low density polyethylene layer and the medium density polyethylene layer are lowered. The heat resistance of these materials can be significantly improved with almost no increase in temperature, and when the laminated material produced in this way is used for packaging, it can withstand high temperature sterilization treatments such as retort and boiling. It is possible to reliably prevent accidents such as opening of a sealed package during the high-temperature sterilization process, and there is no peeling (delamination) between the laminated materials. In this example, a coextrusion lamination method was used as the method for producing the laminated material, but the method is not limited to this, and various extrusion lamination methods such as a film sandwich lamination method and a double lamination method may be used. It can be adopted as appropriate depending on the laminated material, and the thermal adhesive layer is not limited to medium density polyethylene, for example, low density polyethylene, copolymers of ethylene and acrylic acid, methacrylic acid, vinyl acetate, etc., ionomer resins, or It is also possible to use a blend of these materials, or to form a film by laminating heat-adhesive films made of high-density polyethylene, polypropylene, etc. in advance. Furthermore, radiation irradiation is not performed continuously in the lamination process as in this example, but after the laminate is wound up without being irradiated, it is exposed to γ-rays or X-rays using Co ⁶⁰ etc. in the wound state. Irradiation may also be performed. Accordingly, the present invention provides an extrusion lamination method in which at least one thermoplastic synthetic resin is heated and melted, extruded into a thin film, and laminated and integrated with a base material, a heat-adhesive film, etc. A laminate having at least one low melting point synthetic resin layer is manufactured by using a low melting point synthetic resin as at least one of the plastic synthetic resins, and then irradiated with radiation at a dose of 5 megarads or less. However, in this case, the extrusion lamination method is used to manufacture the laminate, so the manufacturing speed is high. By irradiating the thus produced laminate with radiation at a dose of 5 megarads or less, a laminate material with improved heat resistance can be produced while maintaining the melting point of the low-melting point synthetic resin layer almost the same as before irradiation. When used as a packaging material, it can withstand high-temperature treatments such as retort treatment and boil sterilization treatment, and does not cause problems such as delamination. Furthermore, when a low melting point synthetic resin is used as the thermal adhesive layer, its melting point hardly changes due to radiation irradiation, and since it continues to maintain its low melting point, it has the advantage that its sealing properties do not change. Further, according to the present invention, since the laminate is irradiated with radiation, the produced laminate material also has the feature of being completely sterilized. Hereinafter, the present invention will be explained in more detail with reference to Examples. Example 1 One side of a 15μ thick polyamide film was coated with an isocyanate anchoring agent, and a 20μ thick low density polyethylene layer and a 40μ thick medium density polyethylene layer were laminated thereon by coextrusion lamination. Then, this was irradiated with an electron beam of 3 megarads under irradiation conditions of 300 KV and 65 mA from the side of the medium density polyethylene layer to obtain a laminated material for thermal adhesive packaging (product of the present invention). Bags are made using this laminated material,
This is filled with meat sauce and packaged at 98℃.
Heat treatment was performed for 40 minutes. Table 1 shows the results of measuring various properties of this packaging material (laminated material). For comparison, the measurement results of packaging materials treated in the same manner as below, which were irradiated with electron beams, are also shown as comparative examples.

【table】

[Table] As is clear from Table 1, the product of the present invention subjected to electron beam irradiation has improved heat resistance without increasing the melting point of the low density polyethylene layer, whereas the product subjected to electron beam irradiation has improved heat resistance. The heat-sealing strength and film adhesion strength of the comparative product were reduced by heat treatment, and the appearance also deteriorated, impairing its commercial value. In addition, almost the same results were obtained when similar measurements were performed using a laminate manufactured by coextrusion. Example 2 An isocyanate-based anchoring agent was coated on the aluminum foil surface of a base material in which a 9μ-thick aluminum foil was laminated on a 12μ-thick polyethylene terephthalate film using an isocyanate-based adhesive using a dry lamination method. Thickness 20 on the face
An ethylene-acrylic acid copolymer film having a thickness of 40 μm was extruded and laminated, and a high-density polyethylene film having a thickness of 40 μm produced by an isoflation method was laminated and integrated by a film sanding method. Next, this was irradiated with an electron beam from the high-density polyethylene layer side under the same conditions as in the examples to obtain a laminated material for thermal adhesive packaging (product of the present invention). A bag was made using this laminated material, filled with curry food, and packaged, and then subjected to retort sterilization treatment at 120°C for 30 minutes. The results of various properties of this packaging material (laminated material) are shown in Table 2. For comparison, the measurement results of packaging materials treated in the same manner except for irradiation with electron beams are also shown as comparative examples.

[Table] * Membrane breakage occurred.
As is clear from Table 2, the products of the present invention subjected to electron beam irradiation can withstand retort processing well despite having a low-melting point ethylene-acrylic acid copolymer in the intermediate layer, and can be sealed after processing. While the strength and film adhesion strength were extremely good, a comparative product that had not been subjected to electron beam irradiation suffered delamination and the like due to retort treatment and was unusable. Example 3 A polyethylene terephthalate film with a thickness of 12μ was coated with an isocyanate-based anchoring agent,
A 60μ thick low-density polyethylene was laminated and integrated on this coated surface using an extrusion lamination method. Next, this was irradiated with an electron beam of 3 megarads under irradiation conditions of 300 KV and 65 mA from the low-density polyethylene layer side to obtain a laminated material for thermal adhesive packaging (product of the present invention). A bag was made using this laminated material, filled with clean cotton, and packaged, and then subjected to retort sterilization treatment at 120°C for 30 minutes. Table 3 shows the measurement results of various properties of this packaging material (laminated material). For comparison, the measurement results of a packaging material treated in the same manner except for irradiation with an electron beam are also shown as a comparative example.

[Table] As is clear from Table 3, the product of the present invention containing low density polyethylene is modified by electron beam irradiation and becomes able to withstand retort treatment at 120°C for 30 minutes. Comparative products that were not irradiated with electron beams suffered from delamination and could not withstand use. Furthermore, while the comparative product had a low-density polyethylene layer fused to the clean cotton due to retort treatment, the product of the present invention had no such problem.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view showing an example of a laminated material manufacturing apparatus used in carrying out the present invention, and FIG. 2 is an enlarged side sectional view of a laminated body manufactured by the same apparatus before radiation irradiation. 1a...First extruder, 1b...Second extruder, 3...T die, 4...Laminated film, 6...
Base material, 10... pressure roller, 11... laminate,
12...Radiation irradiation device, 13...Laminated material for thermal adhesive packaging.

Claims (1)

[Scope of Claims] 1. In an extrusion lamination method in which one or more thermoplastic synthetic resins are heated and melted and then extruded into a thin film, a base material, a thermally adhesive film, etc. are laminated and integrated. A laminate having at least one or more low-melting point synthetic resin layer is manufactured by using at least one or more of the low-melting point synthetic resin layers, and then irradiated with radiation having an irradiation dose of 5 megarads or less, A method for producing a heat-resistant laminated material for thermal adhesive packaging, in which the heat resistance of the low-melting point synthetic resin layer is improved while keeping the melting point of the layer substantially equal to that before radiation irradiation. 2. Claim 1, wherein the low melting point synthetic resin is low density polyethylene, medium density polyethylene, ethylene-vinyl acetate copolymer, ethylene-methacrylic acid copolymer, ethylene-acrylic acid copolymer, or ionomer resin. Manufacturing method described. 3. The manufacturing method according to claim 1 or 2, wherein the radiation is an electron beam.