JPH0343121B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for manufacturing a heat-sealing container, and more specifically to a method for efficiently and smoothly heat-sealing the open end of a packaging container and a heat-sealing lid by high-frequency induction heating. Regarding improvements. Prior Art and Technical Problems of the Invention Metal cans have been used for many years as packaging containers that have almost perfect sealing properties, gas barrier properties, and excellent shape retention, but in recent years metal cans have become difficult to dispose of. This has led to the problem of so-called can pollution. As an alternative to metal cans, various three-dimensional packaging containers made of plastic have come into wide use in recent years. However, since it is difficult to seal a three-dimensional plastic container with a lid by seaming like a can, the opening end of the container and the lid are generally sealed by heat sealing. ing. It is advantageous to perform the heat-sealing operation using high-frequency induction heating in terms of shortening the heat-sealing time, preventing thermal deterioration of the resin, and improving workability. Laminated heat-sealing resin inner materials are used, but because heating cannot be performed from the open end of the container, heat-sealing still requires a relatively long time, or heat-sealing is not reliable or uniform. It has the disadvantage of lacking sex. In addition, in the case of transparent three-dimensional containers made of plastic,
The lid is also often required to be transparent.
Since it is impossible to use high-frequency induction heating to heat-seal such a transparent plastic lid, heat-sealing must be performed using a conventional heat bar, which requires a long time for heat-sealing. OBJECTS OF THE INVENTION Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks of the conventional heat sealing method, and to perform high-frequency induction heating between the open end of the container and the lid.
It is an object of the present invention to provide a method for introducing a reliable sealing structure by heat sealing within a relatively short period of time. Another object of the present invention is to maintain efficient heat generation necessary for high-frequency induction heating and excellent thermal conductivity to the heat-sealing surface at the opening end of the container to be heat-sealed or around the lid material. To provide a heat sealing method. Structure of the Invention According to the present invention, when heat-sealing a packaging container and a lid, at least one or both of the opening end of the container to be heat-sealed or the peripheral part of the lid to be heat-sealed, Using a composite of metal fiber and thermoplastic resin with an aspect ratio (l/d) of 2 or more,
There is provided a method for manufacturing a heat-sealed container, characterized in that the lid material and the open end of the packaging container are subjected to high-frequency induction heating in a superimposed state. Characteristics and Effects of the Invention The present invention is characterized in that the aspect ratio is within a certain range, that is, 2.
When the metal fibers in the above range are blended into a thermoplastic resin to form the opening end or the periphery of the lid of the packaging container to be heat-sealed, and this is used for heat-sealing by high-frequency induction heating, This is based on the knowledge that this metal fiber becomes an extremely efficient heating element during induction heating, and also provides good heat conduction to the heat sealing surface. Generally, when a conductor such as a metal is placed in an alternating electromagnetic field, a vortex current flows due to electromagnetic induction, and heat is generated due to vortex current loss. Furthermore, when the metal is a magnetic material, magnetic hysteresis loss is further added to this, resulting in even stronger heat generation. This squirt current is preferentially generated at the surface of the metal, and thus heat generation is also significant at the surface of the metal. In the present invention, since metal fibers with an aspect ratio of 2 or more are used, the surface area per unit weight and immediate specific surface area are significantly increased. There is an advantage that the heating of the opening end of the container or the surrounding area of the lid material to be heat-sealed can be significantly increased and efficiently performed. Furthermore, the electrical conductivity of a thermoplastic resin blended with metal fibers varies greatly depending on the aspect ratio of the metal fibers. That is, the larger the aspect ratio, the more contact points between metal fibers, and therefore, when compared with a constant amount of metal fibers incorporated into the resin, the electrical conductivity becomes extremely good. Therefore, when using metal fibers with a large aspect ratio, it is necessary to reduce the amount of metal fibers mixed and use high-frequency induction heating.

[Table] From the above equation, it is clear that when metal fibers with a large aspect ratio are blended into the resin, the thermal conductivity can be significantly improved with a relatively small amount blended. Thus, according to the present invention, when the open end of the container to be heat-sealed or the periphery of the lid is formed with a resin composite containing metal fibers, the heat-sealing surface is heated from the open end side of the container by induction heating. This makes it possible to heat quickly and efficiently. Moreover, the metal fibers incorporated into the resin provide the additional benefit of increasing the stiffness, dimensional stability, and heat resistance of the formulated composition. This advantage allows
In the heat-sealed container produced by the method of the present invention, the open end, which is most important for sealing, is provided with the rigidity, dimensional stability, and heat resistance necessary to maintain the shape of the container. The present invention will be described in detail below with respect to its embodiments. Embodiments of the Invention In the present invention, as the metal fiber, a metal fiber obtained by any method known per se such as a melt spinning method, a stretching method, an extrusion method, a cutting method, a chatter vibration cutting method, etc. is used. The types of metals that make up the fibers are
It can be of any material such as steel, cast iron, stainless steel, brass, copper, aluminum, etc. and has the formula l/
d (in the formula, l is the length of the metal fiber, d is the diameter of the metal fiber)
It is important for the purpose of the present invention that the aspect ratio defined by . That is, when the amount of metal fibers to be blended is set to a constant value in a relatively low range and the aspect ratio of the metal fibers is changed, the thermal conductivity of the blended resin composition sharply increases when the aspect ratio exceeds a certain standard. shows a tendency to increase. This is thought to be because when the aspect ratio of the filled metal fibers exceeds a certain standard value, they come into almost uniform contact within the matrix, forming a stable heat conduction path. The preferred metal fiber has a diameter of 1 to 1000μ.
m, especially from 5 to 100 μm, and the stable length is from 0.1 to 1000 mm, especially from 0.5 to 100 mm. The resin in which the metal fibers are compounded may be any thermoplastic resin that is thermoformable and heat-sealable, such as low-, medium-, or high-density polyethylene, crystalline polypropylene,
Olefin resins such as crystalline ethylene-propylene copolymers, propylene-butene copolymers, and ionically crosslinked olefin copolymers; styrenic resins such as polystyrene, styrene-butadiene copolymers, and styrene-butadiene-acrylonitrile copolymers Resin; polycarbonate; polyester; polyamide; acrylic resin; polyacetal resin, etc. are used. Among these, olefin resins are preferred in terms of economy and ease of production;
Polypropylene is most desirable in terms of retort sterilization. The amount of metal fibers added to the thermoplastic resin varies depending on the aspect ratio and diameter of the metal fibers, but it is within the range of 1 to 60% by volume, especially 5 to 40% by volume based on the resin. is desirable. That is, if it falls below this range, no significant improvement in thermal conductivity can be expected, while if it exceeds the above range, the thermoformability into containers will deteriorate and the mechanical properties of the containers will also deteriorate. . The resin and the metal fibers are easily mixed by dry blending the two and, if necessary, kneading this mixture under conditions in which the resin is melted. The kneading operation may be performed using, for example, a roll, a kneader, a pelletizer, etc., or may be performed within a cylinder of an extruder, injection machine, etc. In the container body used in the method of the present invention, only the opening end to be heat-sealed may be made of a metal fiber-containing resin composite, or the entire container body including this open end may be made of a metal fiber-containing resin composite. It may be formed from a material. In the former case, the metal fiber-containing resin composite described above is provided in the form of a heat-sealing flange to a container body, which is known per se and is made of plastic, for example. Alternatively, in the case of a container having such a flange, a heat sealant layer is provided on the flange. In this case, the container body may be a container made solely of plastic, or a composite container made of plastic, paper and/or metal foil. In the latter case, the container body can be formed by any known method, except that a resin containing metal fibers is used. Furthermore, the structure of the container itself may be a single layer container made of a resin composition containing metal fibers, or a laminated container comprising a layer of a resin composition containing metal fibers, another resin layer and/or a metal foil layer. It may be. For example, the container can be formed by melt-extruding the composition into a parison shape and then blow-molding it into a bottle shape, or by directly injecting it into a mold with a container-shaped cavity. It can also be done by Furthermore, by preparing a sheet of the above composition and subjecting this sheet to vacuum forming, pressure forming, plug assist forming, stretch forming, etc., a cup-shaped flange-bottomed container can be obtained. In addition, by once forming a pipe or a bottomed preform by extrusion or injection, and subjecting this pipe or bottomed preform to axial tension stretching and circumferential expansion stretching at the resin stretching temperature, It is also possible to obtain a container in which the resin matrix has biaxial molecular orientation. Furthermore, the composition can be melt-extruded into a pipe shape and cut into a predetermined size to form a double-opening sealed container body. In the lid body used in the method of the present invention, only the peripheral portion to be heat-sealed may be formed from a metal fiber-containing resin composite, or the entire lid body may be formed from a metal fiber-containing resin composite. . When using a lid provided with a heat-sealed portion made of such a resin composite containing metal fibers, the heat-sealed portion such as the flange portion of the container body does not need to be formed from the resin composite containing metal fibers. In FIGS. 1 and 2 showing an example of a container used in the present invention, the container 1 is a cup-shaped container formed by drawing a plastic sheet,
A seamless body 2, a bottom 3 seamlessly connected to the lower end of the body, and a flange 4 provided at the upper end of the body.
It consists of A layer 5 of a resin composition containing metal fibers is provided in a ring shape on the upper surface of the flange portion 4 for the purpose of heat sealing. This layer 5, as shown in the enlarged sectional view of FIG. 2, consists of a matrix 6 made of thermoplastic resin and metal fiber stables 7 dispersed in this matrix. In FIG. 3, which shows a lid used for sealing this container, this lid 8 has a metal foil base 9, and a suitable adhesive such as urethane adhesive (not shown) is applied to the outer surface of the metal foil base. A protective resin layer 10 such as a biaxially oriented polyester film laminated through the metal foil substrate and a heat-sealable resin inner material layer 11 such as an olefin resin film applied to the inner surface of the metal foil substrate.
It consists of Although not shown in the drawings, the lid may be provided with a known easy-to-open mechanism as shown in, for example, Japanese Unexamined Patent Publication No. 57-194958. In FIG. 4 for explaining the sealing by heat sealing between the container body 1 and the lid 8, the container body 1 is
and the lid 8 are stacked so that the metal fiber-containing resin layer 5 located at the open end of the container body 1 and the heat sealant inner surface material layer 11 of the lid 8 face each other.
The lower surface side of the flange portion 4 of the container body 1 and the peripheral edge of the lid body 8 are held under pressure by a lower support member 14 equipped with a high-frequency induction heating coil 12 and an upper pressing member 15 . Next, the high-frequency induction heating coil 12 is energized, and eddy currents are generated in the metal fibers 7 and the metal foils 9, respectively, and the resin matrix 6 and the heat-sealable resin layer 11 are efficiently heated, and as a result, , heat sealing between the container body and the lid can be efficiently performed uniformly over the entire surface and within a short time. Incidentally, the flange portion and the lid body after heat sealing can be easily cooled by blowing cold air or cold water, or by providing a cooling mechanism (not shown) in the aforementioned members 14 and 15. Instead of forming only the portion of the container body to be heat-sealed with a metal fiber-containing resin composition, the entire container is made of a metal fiber-containing resin composition 6, as shown in FIG.
It should be understood that it can be formed by In FIG. 6 showing a laminate suitable for manufacturing the container of the present invention, this laminate 16 includes a base layer 17 made of a metal fiber-containing resin composition, and a metal fiber powder compound applied to both surfaces of the base layer 17. protective resin layer 18
and 19. Protective resin layers 18 and 19
is preferably a resin that has thermal adhesion to the resin layer constituting the base layer 17, and most preferably is the same type of resin as the resin layer constituting the base layer 17. The protective resin layers 18 and 19 have a thickness of 1/100 to 1/5 of the thickness of the base layer 17, and have a thickness of 3 mm in the final container shape.
A thickness of 400 μm to 400 μm, particularly 5 to 100 μm is desirable in order to prevent metal corrosion and metal elution without impairing excellent thermal conductivity. This type of laminate can be easily formed by coextruding a resin composition containing metal fibers and a resin containing powdered metal fibers through a multilayer die, and by using this laminate, the cross section shown in FIG. A hollow-molded container such as a bottle, a pipe-shaped container body, and a cup-shaped container with a bottom are obtained. Alternatively, a laminated sheet for use in vacuum forming or the like can be easily obtained by extruding a resin melt containing metal fibers between resin films containing powdered metal fibers and by so-called Sand-German lamination. In this laminated structure container of the present invention, the exposure of metal fibers to the outer surface is effectively prevented, and significant advantages are achieved in terms of appearance characteristics and corrosion prevention, as well as surface smoothness, heat sealability, and hygiene. physical characteristics etc. are also improved. In particular, as the protective resin layers 18 and 19, titanium dioxide, iron oxide, zinc oxide, barium sulfate,
Blending a pigment such as calcium carbonate has the advantage that the metal fiber blended layer is hidden and the appearance characteristics are further improved. In FIG. 7 showing another example of the lid used in the present invention, this lid 20 is a heat-sealable lid made of a gas barrier layer 21, an outer surface protection resin layer 22, an inner surface protection resin layer 23, and a metal fiber blended resin composition. It consists of a ring 24. When using such a lid, the container body may be one in which the flange part is not provided with a ring made of a resin composition containing metal fibers, as shown in FIG. Resin layer 26, inner surface protection resin layer 2
It consists of 7. In the method of the present invention, the conditions during heat sealing may be per se known conditions. For example, the power source for high frequency induction heating is 10KHz to
A high frequency of 50MHz can be used, and the pressure during heat sealing can be in the range of 0.5 to 5Kg/ ^cm2 .
Further, the heating temperature of the heat-sealing surface may be any temperature above the melting point of the resin and below its thermal deterioration temperature. According to the present invention, it is possible to sandwich the heat-sealing surface in between and perform efficient heating from above and below, thereby significantly shortening the heat-sealing time and increasing the production speed. It can also reduce thermal deterioration of. The invention is illustrated by the following example. Example 1 Melting point 160°C, density 0.90g/cm ³ , MI 10g/10min,
A cup container having the shape shown in Fig. 1 with an opening inner diameter of 65 mm, outer diameter of 70 mm, and height of 50 mm was fabricated using polypropylene by injection molding. Next, the polypropylene was given a density of 7.8 g/cm ³ ,
Using a composite material containing 15 vol% of steel fibers with an average diameter of 60 μm and an average length of 3 mm, the inner diameter was
A ring with a diameter of 65 mm, an outer diameter of 70 mm, and a thickness of 2 mm was molded.
This ring was heat-sealed to the flange of the polypropylene cup using a high-frequency induction heating coil similar to that shown in FIG. On the other hand, a single-layer drop lid having an outer diameter of 70 mm and a shape as shown in FIG. 3 was molded by injection molding using the polypropylene. The container body thus obtained was filled with wine jelly, and the lid material was sealed using a sealer equipped with a high-frequency induction heating coil as shown in Fig. 4 for a heating time of 0.3 seconds and a pressing time of 0.8 seconds (heating time (including 0.3 seconds) and heat sealing with a pressing force of 2 Kg/cm ² . When the obtained wine jelly filled container was subjected to hot water retort sterilization treatment at 115° C. for 30 minutes, no peeling of the seal portion was observed and the seal was complete. Comparative Example 1 In Example 1, when the ring made of steel fiber-filled polypropylene was not heat-sealed to the flange, it was impossible to perform heat sealing by high-frequency induction heating. Furthermore, when heat-sealing with a heat bar type sealer, the heating and pressing time required to obtain heat-sealing strength that does not cause peeling of the sheet part due to retort sterilization is 3 seconds, which means that heat-sealing requires a long time. did.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a molded container having a flange made of a metal fiber-containing thermoplastic resin used in the present invention, FIG. 2 is an enlarged sectional view of the flange of FIG. 1, and FIG. The figure is a sectional view of the lid body used in the present invention, FIG. 4 is an explanatory diagram for explaining the sealing by heat sealing of the present invention, and FIG. FIG. 6 is a partially enlarged cross-sectional perspective view of still another specific example of the container used in the present invention, and FIG. 7 is a partially enlarged sectional view of another specific example of the container used in the present invention. FIG. 8 is a cross-sectional view of an exemplary container of the present invention for use with the lid of FIG. 7; Reference number 1 is the container body, 2 is the seamless body, 3
4 is a bottom part, 4 is a flange part, 5 is a metal fiber blended resin composition layer, 6 is a matrix resin, 7 is a metal fiber, 8 is a lid body, 9 is a metal foil base, 10 is a protective resin layer, 11 is heat sealability 1 is a resin inner material layer, 12 is a high frequency induction heating coil, 14 is a lower support member, 1
5 is an upper pressing member, 17 is a base layer, 18 and 19
is a protective resin layer, 21 and 25 are gas barrier layers,
22 and 26 are outer protective resin layers, 23 and 27 are inner protective resin layers, and 24 is a metal fiber-containing resin ring.

Claims (1)

[Claims] 1 When heat sealing the packaging container and lid material,
The aspect ratio (l/
d) is formed from a composite of two or more metal fibers and a thermoplastic resin, and subjecting the lid material and the opening end of the packaging container to high-frequency induction heating in a state where they are overlapped. A method for producing a heat seal container characterized by: