JPS6345893B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a metal container having a seam formed by thermal bonding, and more specifically to a method for efficiently and selectively heating both edges of a container material, which are engaged through an adhesive resin layer, using a high-frequency induction heating coil. The present invention relates to a method for manufacturing a metal container, which comprises forming a seam by thermal bonding. High-frequency induction heating is a heating means that is widely used for heating metal materials, and is also a heating means that is widely used for manufacturing metal containers such as adhesive cans that have seams formed by thermal bonding. However, the high-frequency magnetic field from the high-frequency induction heating coil is blocked by the metal material, so in conventional technology, the resin adhesive applied to the edge of the container material is melted by high-frequency induction heating prior to stacking. There is a method of overlapping both ends of the container material through a resin adhesive layer, and finally bumping the overlapping part while cooling to form a seam. A method is adopted in which the outside is heated by high-frequency induction, and both ends are thermally bonded by heat transfer from the outside. However, although the former method can be conveniently applied when thermal bonding is performed by pressing both ends in the overlapping direction, such as in lap side seam cans where the seam extends straight in the axial direction, , an upper body and a lower body, each consisting of a cup-shaped molded body formed by drawing or drawing-ironing a metal material, are fitted at their circumferential open ends via an adhesive to form a container. In this case, it is difficult to apply because the axial pressing force at the time of fitting causes the molten adhesive layer to protrude outside the joint or cause damage to the open end. In addition, in the latter method, the high-frequency magnetic field is blocked at the inner end of the seam and the outer end.
It is heated only by thermal conduction, and the adhesive layer interposed between the two ends has significantly poorer thermal conductivity than metal, so it takes a significantly longer time for heat bonding, and the bonding A temperature gradient is inevitably formed where the outer edge is hot and the inner edge is cold, resulting in the defect that uniform heating becomes difficult. In particular, when the metal material is a ferromagnetic material such as steel, the inner end portion is difficult to heat. Therefore, an object of the present invention is to efficiently heat both edges of a container material, which are engaged through an adhesive resin layer, simultaneously from the outer edge and the inner edge by high-frequency induction heating. The object of the present invention is to provide a method that enables efficient and selective heating. Another object of the present invention is a method for producing a metal container having a thermally bonded seam by high-frequency induction heating of the thermal adhesive located between the engaged ends to form the seam within an extremely short time. is to provide. Still another object of the present invention is to provide a method that can selectively heat both ends of a material with an adhesive layer interposed therebetween to a desired temperature. Still another object of the present invention is to provide an upper body and a lower body each consisting of a seamless cup-shaped molded body made of metal.
To provide a method in which the circumferential open ends of these are fitted together through an adhesive layer, and the adhesive layer can be efficiently and selectively heated from outside the fitted part by high-frequency induction heating. . According to the present invention, in a method for manufacturing a container that includes joining both ends of a container material containing metal through a seam formed by thermally bonding resin, the both ends are engaged through a layer of thermally adhesive resin, and At least one circumferential high-frequency induction heating coil is connected to a portion to be a joint whose ends are substantially electrically insulated locally, and the portion to be a joint is located approximately at the center of the coil, while one The width of the part where the material connected to one end of the coil and the material connected to the other end face the coil part where the direction of current is opposite and should be a joint is d, and the width of the joint width of the innermost circumference of the coil is d. When the distance is D, the distance in the longitudinal direction of the joints on the innermost circumference of the coil is L, and the distance in the radial direction between the coil and the joint is t, the following formulas 8d≧D≧d 20d≧L≧d t<D are satisfied. A method for producing a metal container, characterized in that the metal container is placed in a positional relationship such that the metal container is placed in a positional relationship, and the high-frequency induction heating coil is energized to induce an eddy current passing through each of the ends to selectively heat both ends to be a seam. is provided. As already pointed out, the present invention has an upper body and a lower body each made of a seamless cup-shaped molded body made of metal, and the circumferential open ends of the upper body and the lower body are fitted together via an adhesive layer, This adhesive layer is efficiently and selectively heated from the outside of the mating part using high-frequency induction heating.
It is particularly useful for producing pin-shaped metal containers with circumferential side seams. Therefore, the present invention will be explained below using this container as an example, but the present invention is of course not limited to this case. In FIG. 1 showing an example of a metal bottle according to the present invention, this bottle includes a lower body 1 made of a seamless cup-shaped molded body made of metal such as a tin-plated steel plate,
Upper body 2 consisting of a seamless cup-shaped molded body made of metal
These cup-shaped molded bodies are made up of
The open end portions 3 and 4 are overlapped and joined to form a circumferential side seam 5, thereby integrating the shape of the container. In this embodiment, the lower body 1 is a cup consisting of a tall thin side wall 6 formed by highly drawn and ironed metal material and a thick bottom 7 that has not been substantially ironed; On the other hand, upper body 2
This is a cup consisting of a tall thin side wall portion 8 and an upper wall 9 formed by the same molding as the lower body. The height of the side wall portion 8 of the upper body 2 is within a range that is equal to or slightly larger than the width of the joint 5. The upper wall 9 of the upper body 2 has an upwardly convex tapered surface, and a spout 10 for filling or taking out the contents is formed in the center thereof. In the specific example shown in FIG. 1, the open end 3 of the lower body 1 is narrowed to a smaller diameter than the rest of the body wall by neck-in processing in the vicinity of the open end 3. The upper body open end 4 of the diameter is inserted into the upper body open end 4 of the diameter. A thermal adhesive layer 1 is provided between the outer surface of the open end portion 3 of the lower body and the inner surface of the open end portion 4 of the upper body.
1 is provided to join and fix the lower body and the upper body. From the viewpoint of corrosion resistance, it is desirable that a portion of the adhesive 11 protrudes from the seam 5 and forms a coating layer 13 for the cut edge 12 of the metal material located inside the seam. In the metal container having the above-described structure, only an extremely small spout 10 is formed in the upper body 2, and therefore, after the upper body 2 and the lower body 1 are fitted together, this fitting is difficult. It is virtually impossible to insert a special heating mechanism etc. inside the assembly;
Therefore, it will be understood that the fitting portion can only be heated from the outside. According to the present invention, by arranging a high-frequency induction heating coil on the outside of this fitting part using a specific mechanism and energizing it, not only the open end 4 located on the outside but also the open end located on the inside can be heated. 3 can be heated efficiently and selectively, and bonding can be performed within a very short time. 2, 3 and 4 for explaining the arrangement and principle of the high frequency induction heating coil in the present invention.
In the figure, in a portion 5a that should become a seam, both ends 3 and 4 are mechanically engaged by fitting through an adhesive layer 11a, and furthermore, these ends 3 and 4 are connected by an adhesive layer 11a. There is a substantially electrically insulating relationship locally. In this specification, the term "substantially electrically insulating locally" refers not only to cases where these are in a completely electrically insulating relationship, but also to cases where an electrical short circuit occurs in some parts, as will be explained in detail later. It also includes an electrically insulating relationship such that eddy currents across both ends 3 and 4 do not occur. A high-frequency induction heating coil, generally designated 14, is arranged outside the portion 5a that is to become the seam in the positional relationship shown below. In the embodiment shown in this figure, the coil 14 has an overall spiral shape. In this coil 14, as shown in FIG. 2, current flows in the vertical direction from top to bottom at a certain point in the lower coil portion 15, while in the upper coil portion 16, current flows from bottom to top at the same point in time. The structure is such that current flows vertically. In the present invention, the portion 5a that should become a seam
is located approximately at the center of this coil 14, and the side wall portion 6 connected to the inner open end portion 3 faces the lower coil portion 15, and the outer open end portion 8 faces the upper coil portion 16, respectively. Position the coil 14. In addition, as shown in FIG.
4, the distance in the joint width direction between the innermost loops of the coil 14 is D, the distance in the joint longitudinal direction between the innermost loops of the coil 14 is L, and the radial distance between the coil 14 and the portion 5a that should be the joint is t. Then, the following formula 8d≧D≧d ………(1) Especially 4d≧D≧d ………(1a) 20d≧L≧d ………(2) Especially 10d≧L≧d ………(2a ) and t<D (3) In particular, the positional relationship should be such that t<1/2D (3a) is satisfied. In the above-mentioned positional relationship, when high-frequency current is applied to the high-frequency induction heating coil 14, the current direction in the side wall portion 6 facing the coil portion 15 is opposite to that of the coil portion, and the open end portion 3 is in the same direction. An eddy current 17 is induced that passes as follows.
Similarly, in the side wall portion 8 facing the coil portion 16, an eddy current 1 passes through the open end portion 4 in the opposite direction to the current direction in the coil portion but in the same direction.
8 is induced. These eddy currents 17 and 18 are induced to have a low current density in the region of the side walls 6 and 8 and a high current density in the region of the open ends 3 and 4, respectively, so that the outer Not only the end portion 4 but also the open end portion 3 located inside is heated strongly. According to the present invention, in this case, by arranging the coil 14 and the portion 5a to be the joint so that the above-mentioned equations (1) to (3), especially the above-mentioned equations (1a) to (3a), hold true. , it becomes possible to intensively and selectively heat both open ends 3 and 4 without heating the side wall portions 6 and 8 much. Generally, in high-frequency induction heating, the stronger the degree of electromagnetic coupling between the coil and the metal material, the more the amount of induced eddy current tends to increase.From this point of view, it is recommended to increase the area of the coil 14. It is believed that the heating efficiency will be higher if it is heated. However, according to research conducted by the present inventors, although the use of such a large-area high-frequency induction heating coil certainly improves the overall heating efficiency, It has been found that portions of the side walls 6 and 8 remote from these ends are also heated considerably. On the other hand, in the present invention, the above formula (1),
As is clear from (2) and (3), the lower coil portion 15 and upper coil portion 16 of the coil 14 are placed close to the joint portion 5a to minimize the eddy current induced in the material. By making the diameter of the joint larger, it is possible to intensively and selectively heat both ends of the joint. This fact becomes clear by referring to FIGS. 5 and 6. In other words, it is made of tin and the width of the seam (d)
For a can of the shape shown in Figure 1 with a diameter of 5 mm and an outer diameter of the seam of 64 mm, in Figure 5, a high-frequency induction heating coil with D = 15 mm, L = 15 mm, and T = 3 mm, and in Figure 6, Using a high-frequency induction heating coil with D = 15 mm, L = 110 mm, and T = 3 mm, the temperature distribution downward from the inner edge of the seam is measured when heating is performed for 0.3 seconds with the high-frequency input power kept constant. show. From this result, when induction heating is performed in an arrangement outside the scope of the present invention (Fig. 6), in addition to the edges where the seams should be formed, the side walls are also heated to a higher temperature than the edges over a fairly wide area. , and at a predetermined temperature at the end (approximately
220°C), whereas induction heating with the arrangement within the scope of the present invention suppresses the temperature rise in the sidewalls to a relatively low level while heating the edges. It is understood that the heating can be focused and selectively heated rapidly. The above-mentioned tendency is observed not only in the lower part but also in the upper part, that is, the part located above the outer edge of the seam. Furthermore, the distance D in the seam width direction of the innermost circumference of the coil
Even in the case of a heating coil that is outside the scope of the present invention, there is a tendency that the side wall portion that is electromagnetically coupled to the coil portion is heated significantly, and the portion that should be the joint is difficult to heat. Furthermore, as the distance t in the radial direction between the coil and the seam increases, the electromagnetic coupling between the heating coil and the seam weakens, and the efficiency tends to decrease.
In the above case, it is recognized that the part that should become a seam will not be heated unless excessive high-frequency input power is applied. Furthermore, as the distances D and L between the innermost circumferences of the coils are brought closer to the width d of the part to be a seam, the effect of intensively and selectively rapidly heating the end part to be a seam increases. This is particularly noticeable when the material of the lower body is ferromagnetic (for example, steel) compared to non-magnetic (for example, aluminum). In the present invention, the reason why intensive and selective heating of the ends is made possible by adopting the above-described arrangement has not yet been elucidated. However, the present inventors estimate the reason for this as follows. In other words, it is recognized that the higher the current density of the eddy current induced at the overlapping ends that should become a seam, the more intensive and selective heating of the ends becomes possible. In this arrangement, the innermost loop of the coil is placed close to the joint, which increases the proportion of induced eddy current passing through the end, thereby increasing the current density at the end. The eddy currents induced by the coil include eddy currents that are induced along the coil and return through the rear end, and eddy currents that are induced along the coil and return through the end opposite the end that was induced along the coil. However, in the present invention, by setting the values of D and L to the small ranges mentioned above, the curvature of the coil becomes large, and therefore, the eddy current of the latter increases per eddy current of the former. This is thought to be due to a decrease in the eddy current ratio. This effect is more pronounced when the upper and lower body materials are ferromagnetic than when they are non-magnetic, because the inductance of the current path through the ends is ferromagnetic. This seems to be due to the fact that the current passing through the end is small because the size is large. In the present invention, the dimensions and arrangement of the coil can be defined only by the dimensions D and L of the innermost circumference of the coil for the following reason. In other words, the eddy current in the material is induced by the current in the coil, but the smaller the curvature of the coil, the smaller the curvature of the eddy current and the smaller the electrical resistance.
A larger current will be induced. Thus, even if the coil 14 is a coil that has been wound many times, such as a spiral wound coil, the innermost one acts most effectively on induction heating, and from this point of view, in the present invention, This defines the dimensions of the innermost coil. If the above-mentioned values of D and L exceed the range of the present invention, as explained with reference to FIG. 6, it tends to be difficult to intensively and selectively heat the ends.
Furthermore, if the value of D is smaller than d, it becomes difficult to achieve the objective of the present invention, which is to heat the inner end portion to a predetermined temperature as well. The distance t between the coil 14 and the end portion 5a is related to electromagnetic coupling between the coil and the material, and this t
If the value exceeds the above range, efficient heating becomes difficult. In the present invention, the heating coil 14 may be a one-turn type instead of the spiral type shown in FIGS. 2 to 4. Further, as shown in FIG. 2, a magnetic material core 19 such as ferrite may be used to strengthen the electromagnetic coupling between the coil 14 and the material. By using the spiral-wound coil shown in Figures 2 to 4, the resonant frequency can be varied over a wide range by changing the number of turns, and by increasing the inductance, the capacitance of the capacitor used can be changed. can be made relatively small. The present invention also has the advantage of workability in that by using the coils having the dimensions and arrangement described above, high frequency induction heating operations can be performed stably without any trouble. In the method for manufacturing a container consisting of an upper body and a lower body and having a circumferential seam as described above,
Even if an electrically insulating adhesive resin is interposed between both ends, for example, the cut edges of the upper body may come into contact with the side walls of the lower body at some points, causing an electrical short circuit. In this case, if 2
When an eddy current is induced through the upper body and the lower body through two short-circuit positions, a spark discharge occurs at this short-circuit position, causing burnt paint, etc., resulting in poor appearance, and furthermore, near the spark discharge position. The disadvantage is that the temperature of the According to the present invention, the above-described configuration limits the generation area of eddy current to a relatively narrow area, so the probability of generation of eddy current passing through two short-circuit positions is suppressed to a significantly small value, resulting in stable induction heating operation. becomes possible. In the present invention, since the heating coil 14 has a relatively small dimension in the circumferential direction, a large number of heating coils 14 can be arranged in the circumferential direction of the seam to perform heating even more quickly. For example, a method in which a large number of high-frequency induction heating coils are arranged so as to substantially cover the periphery of a circumferential fitting part, and induction heating is performed while the fitted objects of the upper and lower bodies are stationary; A method of arranging several high-frequency induction heating coils and inductively heating the fitted object of the upper and lower bodies while rotating is used as appropriate. Any high frequency current used in this type of induction heating can be used as the high frequency current to be applied to the coil, and generally speaking, a high frequency of 10 KHz to 500 KHz is preferably used. The input to the heating coil varies depending on the size of the container, the required temperature and heating time, and cannot be absolutely specified, but according to the present invention, by adopting the above conditions, it can be applied in other cases. It will be clear from the description of FIG. 6 above that heating can be done in a relatively short time. According to the present invention, the outer end and the inner end can be heated to the same temperature, or they can be heated to different temperatures. In the present invention, any material that exhibits adhesive properties by being melted, softened, or activated by heat may be used as the adhesive layer, such as thermoplastic resin adhesives such as polyester, polyamide, and acid-modified polyolefin. Agents are advantageously used, but are of course not limited thereto. All materials used for containers include light metals such as aluminum, tinplate, stain-free steel, and other metal-containing materials such as various surface-treated steel plates and black plates, and these materials are coated with various paints. It doesn't matter if it's something. Further, this material may be a laminate of metal foil and plastic film, and if the plastic film exhibits heat-sealing properties, it is natural that it can be used as the adhesive layer. The present invention is suitably applied to manufacturing a container having the above-mentioned circumferential seam. For example, as shown in FIG. 22b can also be advantageously used for lock seam bonding through the adhesive layer 11,
It can also be advantageously used for heat-sealing the periphery of the lid and the flange of the body using a thermal adhesive. The invention is illustrated by the following example. Example A tin-plated steel plate with a material thickness of 0.3 mm was punched into a disc with a diameter of 120 mm, and formed into a cup shape with an inner diameter of 85 mm between a drawing punch and a drawing die according to a conventional method. Next, this cup-shaped molded product was subjected to a re-drawing process, and then ironed using a 66.10 mm diameter ironing punch and ironing die. Next, the inner and outer surfaces of this lower body were degreased and washed, then subjected to a conventional surface treatment (phosphoric acid), and the inner and outer surfaces were painted and baked with epoxy paint, followed by a netzin finish (netzin finish). Outside diameter: 63.35
mm). Next, a polyester adhesive tape (softening point: 178°C) with a thickness of 60 μm and a width of 6 mm is applied to the outer open end of the lower body using high-frequency induction heating.
After adhering with 1.0 mm sticking out, bend the protruding part of the tape inward so as to wrap around the edge of the open end and the inner surface following this, and heat and fuse this adhesive tape to the inner and outer surfaces of the open end. Ta. On the other hand, for the upper body, a 0.23 mm thick tin-plated steel plate with epoxy paint applied on both sides was punched out into a 96 mm diameter disc, which was then formed using conventional press processing, and a spout was provided on the top wall. . (Upper body diameter 63.37mm)
Next, the lower body on which the adhesive tape was applied and the upper body were fitted with their open ends so that the overlapping portion was 5 mm, and then subjected to a high-frequency heating process using the heating coil shown below and the same process as above. A cooling process was performed at the station to melt the adhesive at the fitting portion, cool and solidify the bonding process, and produce a bonded metal container. The heating coil, heating process, and cooling process in this example will be explained in detail. The shape of the heating coil is a spiral coil as shown in Figures 2 to 4. The diameter of the conductor used in the coil is 4 mmφ, and the heating coil is electromagnetically coupled to the upper and lower bodies. The number of turns is 3 turns.
The innermost circumference D and L of the coil are 15 mm. In the heating process, the heating coil is arranged so that the distance between the heating coil and the seam in the radial direction is 3 mm, and the center of the heating coil is 2 mm above the center of the seam. While rotating as if rotating, a 150KHz high frequency oscillator
When heated for 0.3 seconds with a 4KW input, the temperature at both the outer and inner ends was 220°C.
Simultaneously with the completion of heating, in the cooling process, cooling was performed using a compressed air nozzle (original pressure 5Kg/cm ² ).
In 1.5 seconds, the temperature at the fitted part reached 140°C, the temperature at which the adhesive solidifies. Comparative Example 1 An upper body and a lower body were created in the same manner as in the example,
After fitting the upper body and lower body in the same manner as in the example,
The heating coil is arranged with either the interval D in the seam width direction of the innermost circumference of the heating coil or the radial interval T between the heating coil and the seam set outside the range of the present invention, and high-frequency heating of the fitting part is performed. I went there. Table 1 shows the high-frequency input power and time required to bring the temperature of the fitting part to 220° C. as in the example, along with the arrangement of the heating coils. Furthermore, in the example, the temperature of the fitting part was set to 220°C.
The efficiency when heated to is 100%, and the efficiency of each comparative example relative to this efficiency is also shown in Table 1. In these comparative examples, the temperature of the side wall was higher than the temperature of the mating part, and cooling was performed using a compressed air nozzle after heating, but the temperature of the mating part did not drop below the temperature at which the adhesive solidified. It took more than 5 seconds.

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 is a side sectional view showing an example of a metal bottle of the present invention, FIGS. 2 to 4 are views showing the arrangement of high frequency induction heating coils in the present invention, and FIGS. 5 and 6 are FIG. 7, a diagram showing the relationship between axial distance and heating temperature, is a diagram showing an example of application of the present invention. 1 is a lower body, 2 is an upper body, 3 and 4 are open ends, 5 is a circumferential side seam, 6 is a thin side wall, 7 is a thick bottom, 8 is a thin side wall, 9 is an upper wall, 10 1 is a spout, 11 is an adhesive layer, 12 is a cut edge of a metal material, 13 is a coating layer, 14 is a high-frequency induction heating coil, 15 is a lower coil portion, 16 is an upper coil portion, 17 and 18 are eddy currents, 22 indicates a metal material.

Claims (1)

[Scope of Claims] 1. A method for manufacturing a container that involves joining both ends of a container material containing metal through a seam formed by thermally bonding resin, wherein both ends are engaged through a layer of thermally adhesive resin. and at least one circumferential high-frequency induction heating coil with a portion to be a joint whose ends are substantially electrically insulated locally, the portion to be a joint is located approximately at the center of the coil, and one The width of the part where the material connected to one end of the coil and the material connected to the other end face the coil part where the direction of current is opposite and should be a joint is d, and the width of the joint width of the innermost circumference of the coil is d. When the interval is D, the interval in the longitudinal direction of the joint on the innermost circumference of the coil is L, and the radial interval between the coil and the joint is t, the following formulas 8d≧D≧d 20d≧L≧d t<D are satisfied. A method for manufacturing a metal container, characterized in that the metal container is placed in a positional relationship such that the metal container is placed in a positional relationship, and the high-frequency induction heating coil is energized to induce an eddy current passing through each of the ends to selectively heat both ends to be a seam. .