JPH0356663B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] Certain metal cans, such as cans for storing tea leaves, seaweed, confectionery, etc. in an airtight manner, are coated with various sealing materials on the top surface of the opening of the can body. It may be sealed tightly.

The present invention relates to a method for thermally bonding a sealing material to the periphery of the opening of a can body using a high-frequency heating coil when obtaining this type of sealed can.

[Conventional technology]

FIGS. 2 and 3 show an example of an airtight can, specifically a tea caddy, to which the present invention is directed. It consists of a cap 3 that is removably fitted to the outer periphery of the can body 1 and closes the upper end opening surface of the can body 1. An annular packing 4 is attached to the outer periphery of the upper end of the can body 1, and the gap between the can body 1 and the cap 3 placed over it is filled with the packing 4. Such a basic airtight can is known from Japanese Utility Model Application Publications No. 53-93342, No. 53-22726, No. 57-117353, and No. 58-113645, and has already been commercialized.

However, in order to maintain high airtightness during the distribution stage and reliably prevent moisture and oxidation of the contents, it is desirable to further seal the upper opening surface of the can body 1 with a sealing material 5.

As a prior art related to this sealing material 5, the present applicant has proposed that a special transparent plastic film having thermal adhesive properties is used, and this is thermally bonded to the upper opening periphery 1a of the can body 1 as shown in FIG. It has been proposed. These are Japanese Patent Application No. 59-40780 and Utility Application No. 59-30876.

In this case, the sealing material 5 is preferably formed by coating or laminating a low melting point hot melt adhesive layer 5b on one side of a film base material 5a which has good barrier properties against moisture and oxygen gas and has mechanical strength. It is formed by integrally laminating layers. As the film base material 5a, a combination of a film that provides mechanical strength and a film that provides gas barrier properties may be selected as necessary. In practice, the upper end periphery of the can body 1 is curled inward, and the periphery of the sealing material 5 is thermally bonded to this curled portion.

However, regarding this thermal bonding, the sealing material 5 is placed on the upper opening surface of the can body 1 as shown in FIG. to induction coil 6
A high frequency of about 400 kHz is passed through the can body 1 to generate an induced current i in the upper opening periphery 1a as shown by the arrow by electromagnetic induction and heat the sealing material 5 through the hot melt adhesive layer 5b. I expected it to be glued.

In addition, as a conventional technology regarding the can body 1, the can body 1
has a seam 7 running in the vertical direction as shown in Fig. 2, but there are two forms in which this seam 7 is welded butt-to-bottom, and another in which it is bonded with an adhesive having thermal adhesive properties such as nylon adhesive tape. There is,
Recently, there has been a tendency for the latter adhesive type to be frequently used.

[Problem that the invention seeks to solve]

The problem is how to effectively and reliably thermally bond the sealing material 5 to the opening peripheral edge 1a of the can body 1. Generally, the outer peripheral surface of the can body 1 is printed, and if the opening peripheral edge 1a is heated to a high temperature, the printed surface will be adversely affected by the heat. It is desired that the sealing material 5 be strongly thermally bonded to a certain extent. Insofar as this is concerned, it seems to be effective to use the aforementioned sealing material 5 having the hot-melt adhesive layer 5b to heat only the opening periphery 1a of the can body 1 using high frequency to bond the can body 1. However, the premise here is that the opening peripheral portion 1a of the can body 1 and the sealing material 5 are uniformly heated to a predetermined temperature over the entire circumference.

For this purpose, the present inventor has installed the induction coil 6 into the can body 1.
It was thought that it was a natural prerequisite that it should be annular to match the shape of the opening peripheral edge 1a, and that both 1 and 6 should be set vertically and concentrically, and the facing distance should be set uniformly.

However, it is troublesome to prepare an induction coil 6 of a shape corresponding to each change in shape of the can body 1, such as the size of the can body 1 or whether it is circular or square. In addition, the setting work of the can body 1 and the induction coil 6 had to be adjusted one by one, which made the work difficult and inefficient.

In particular, when dealing with a can in which the seam 7 of the can body 1 is glued in the manner described above, an experiment using an annular induction coil 6 revealed that the opening periphery 1 of the can body 1
I found that it was not possible to heat-bond the parts a uniformly, and that even the adhesive at the seam 7 melted. It is presumed that this phenomenon is caused by the induced current intensively flowing through the joint 7, which is insulated due to the adhesive, and arcing occurring at the joint.

However, in the current situation where cans in which the seam 7 of the can body 1 is glued are becoming mainstream, it is urgent to develop a system that can accommodate this, and this point led to the completion of the method of the present invention. This is Tsuta's biggest motivation.

[Purpose of the invention]

The present invention has been proposed to solve all of these conventional problems at once.

An object of the present invention is to apply the sealing material 5 to the opening peripheral edge 1a of the can body 1, not only in cans in which the seam 7 of the can body 1 is welded, but also in cans in which the seam 7 is bonded. The purpose is to make it possible to bond uniformly by heat.

Another object of the present invention is to provide a single specification induction coil 6.
The objective is to provide a product that can respond well to changes in the shape of the can body 1, such as the size of the can body 1.

Still another object of the present invention is to provide a seal material 5 without being influenced by the arrangement conditions of the can body 1 and the induction coil 6.
The object of the present invention is to provide a device that can be reliably thermally bonded and that can significantly improve workability and production efficiency.

[Means for solving problems]

The present inventor thought that the only way to solve the conventional problems was to improve the induction coil 6 side, and as an attempt, the induction coil 6 was designed to have a U-shape in plan view with a small distance between the coils. The above-mentioned sealing material (film base material 5a) is applied to the upper opening surface of the can body 1.
laminated with a hot melt adhesive layer 5b) 5
, the U-shaped part of the induction coil 6 was set horizontally just above it, and when a high frequency wave was passed through the induction coil 6, the upper end of the can body 1 was removed only in the part directly below the U-shaped part of the induction coil 6. It has been found that the sealing material 5 can be partially thermally bonded to the opening peripheral edge 1a.
In this case, the U-shaped portion of the induction coil 6 was made sufficiently larger than the diameter of the upper opening surface of the can body 1, so that the sealing material 5 could be simultaneously thermally bonded to the opposing portions.

Next, the above-mentioned U-shaped induction coil 6 is placed in a fixed position in a horizontal position, and while high-frequency waves are passed through the induction coil 6, the can body 1 with the sealing material 5 placed on the upper opening surface is held in a vertical position. When the sealing material 5 was passed across directly under the U-shaped portion of the induction coil 6,
The sealing material 5 was successively but reliably thermally bonded to the upper opening peripheral portion 1a of the can body 1 over the entire circumference. Can body 1 with surprisingly glued seam 7
Even in this case, thermal bonding was possible without any problems such as thermal melting at the joints.

The present invention was completed based on the findings from such experiments, and as shown in FIG. Coil 6 and can body 1
A high frequency wave is passed through the induction coil 9 while the
A is heated, and a sealing material 5 having thermal adhesive properties is thermally bonded to the peripheral edge 1a of the opening.

In this case, the induced current i is generated only in the opening peripheral part 1a of the can body 1 facing the U-shaped part of the induction coil 6 as shown by the arrow, and only this part is heated, but the can body 1 Since the induction coil 6 and the induction coil 6 move relative to each other, the induced current generating portion, that is, the heating portion, in the opening peripheral portion 1a gradually moves.
The opening peripheral portion 1a is uniformly heated over the entire circumference.

The same applies to the can body 1 to which the seam 7 is glued. The reason for this is not necessarily clear, but the magnitude of the induced current i is the sum of the eddy currents generated at the opening peripheral portion 1a when a high frequency is passed through the induction coil 6, and the eddy current when using this method is Since it occurs only in the portion corresponding to the U-shaped portion of the induction coil 6 in the opening peripheral portion 1a, the total sum is the same when the frequency of the high-frequency wave passed through the induction coil 6, the relative feeding speed of the can body 1, etc. are the same. If determined, it is smaller than the total sum in the conventional example, which occurs over almost the entire circumference of the opening peripheral portion 1a. Therefore, the induced current i flowing concentratedly at the joint 7
This seems to be because the arc is small and the arc does not occur.

In the present invention, it is important to form the induction coil 6 into a U-shape to sequentially heat the opening peripheral portion 1a of the can body 1, and the remaining configuration may be changed as appropriate. It can be implemented by

For example, it is sufficient that at least one of the can body 1 and the induction coil 6 moves, and it does not matter whether the movement is linear or rotational.

The opening surface of the can body 1 may be covered with the sealing material 5 in advance and the sealing material 5 may be thermally bonded to the opening periphery 1a of the can body 1 using the induction coil 6. After heating the opening periphery 1a, the sealing material 5 may be thermally bonded to the opening periphery 1a.

The sealing material 5 may be cut in advance to match the shape of the opening surface of the can body 1 (circular, square, etc.), or the remaining sealing material 5 may be cut after being thermally bonded to the opening periphery 1a of the can body 1. Parts may be cut and removed. The material of the sealing material 5 may also be a paper base material, an aluminum foil laminated with a thermal adhesive film such as a nylon film, or a thermal adhesive coated on these base materials.

〔effect〕

According to the method of the present invention as described above, the opening peripheral edge 1 of the can body 1 corresponding to the U-shaped portion of the induction coil 6
Since a method is employed in which portions a are heated one after another, it is only necessary that the U-shaped portion of the induction coil 6 be placed in such a manner that it straddles at least a portion of the opening peripheral portion 1a. Preferably, all that is required is to set the length of the U-shaped portion of the induction coil 6 to be sufficiently larger than the diameter of the target can body 1, and then pass a high frequency wave of an appropriate frequency through the induction coil 6 to form the can body 1. Just by setting the relative movement speed between and the induction coil 6 to an appropriate value,
The sealing material 5 can be reliably thermally bonded to the opening peripheral portion 1a of the can body 1.

Therefore, first of all, even if there is a difference in size or planar shape of the opening surface of the can body 1, a single specification induction coil 6 will suffice, and there is no need to replace it one by one. Second, since it is not necessary to align the induction coil 6 and the can body 1 concentrically and thermally bond them under a stationary state, for example, when carrying out the seal bonding work by transporting the can body 1, Since it is not necessary to strictly adjust the position of the can body 1 with respect to the induction coil 6 which is in a stationary state, the work becomes easier, and since the can body 1 can be continuously transferred, production efficiency can also be improved. Moreover, even when moving the induction coil 6,
There is no need for troublesome work such as accurately aligning the can body 1 in the moving direction of the induction coil 6, and workability and production efficiency can be similarly improved.

Furthermore, in the present invention, even when the can body 1 to which the seam 7 is bonded is targeted, let alone the can body 1 to which the seam 7 is welded, the opening periphery of the can body 1 can be fixed without causing any inconvenience. The greatest advantage is that the sealing material 5 can be reliably thermally bonded to the portion 1a.

Embodiment 1 FIG. 1 shows a first embodiment of the present invention. First, an induction coil 6 having a U-shape in plan view was created.
The U-shaped portion of this induction coil 6 has sufficient length,
The distance between the coils at the U-shaped portions facing each other in parallel was set to about 3 mm.

As shown in FIGS. 2 and 3, the metal can used was a tin can body 1 with a bottom lid 2 wrapped around the lower end of the can body 1. Can body 1 had a true cylindrical shape, and the diameter of its upper opening was 97 mm. The length of the U-shaped portion of the induction coil 6 was made considerably larger than the diameter of the can body 1.

The sealing material 5 for closing the upper opening surface of the can body 1 is a film base material 5a made of biaxially oriented polypropylene film or biaxially oriented polyester film, and a hot melt adhesive layer made of polyamide resin, vinyl resin, etc. 5b was laminated with a transparent plastic film.

In carrying out the experiment, the U-shaped part of the induction coil 6 was placed horizontally, and the can body 1 was moved in a vertical position below it at a constant speed so as to cross in a straight line as shown by the arrow. At this time, the U-shaped portion of the induction coil 6 shall completely straddle the upper end opening surface of the can body 1, and the upper end opening surface of the can body 1 shall have a circular cut out section before it passes directly under the induction coil 6. A sealing material 5 was applied.

Thus, the feeding speed of the can body 1 is 50 mm/sec, the distance between the U-shaped part of the induction coil 6 and the upper opening surface of the can body 1 is 8 mm, and the power to be supplied to the induction coil 6 is
2kw, high frequency set to 400kHz.

When carried out under the above conditions, the upper opening periphery 1a of the can body 1 was heated to 120 to 130°C, and the sealing material 5 was applied to the hot melt adhesive layer 5 on the opening periphery 1a.
It was possible to reliably heat bond the entire circumference via b.

Incidentally, when the deoxidizer 8 was put into the can body 1 together with the contents before sealing with the sealing material 5, the deoxidizer 8 adsorbed oxygen gas inside the can, creating a negative pressure inside the can, and the time Within a few days, the center of the sealing material 5 was pulled inward and deformed into a concave shape, as shown in FIG. This means that the inside of the can is completely sealed with the sealing material 5. Just to be sure, after sealing with sealant 5, compressed air is sent into the empty can.
We applied an internal pressure of about Kg/m ² and left it for a month, then checked the internal pressure with a pressure gauge, and found that the internal pressure had not dropped, confirming that it was completely sealed.

Example 2 After heating the upper end opening peripheral portion 1a of the can body 1 to 120 to 130°C using the induction coil 6 in the same manner as in Example 1, the sealing material 5 is immediately placed on the upper end opening surface of the can body 1 to open the upper end. It was thermally bonded to the peripheral edge 1a. In this case as well, sealing was achieved in the same manner as in Example 1.

Example 3 While the lower surface of the can body 1 remains open, the sealing material 5 is thermally bonded to the upper opening surface of the can body 1 in the same manner as in Example 1 or 2, and then the can body 1 is turned upside down and the contents are removed. After that, the bottom cover 2 was wound and connected to the can body 1.

Embodiment 4 A large number of can bodies 1 are arranged in several rows or in an annular shape and fixed, and the induction coil 6 is linearly moved or rotated to heat the upper opening peripheral portion 1a of each can body 1. Regarding the other points, one of the examples was selected. This embodiment is suitable when the can is small.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view illustrating a first embodiment of the method of the present invention. FIGS. 2 and 3 illustrate a metal can to which the present invention is directed, with FIG. 2 being an external perspective view and FIG. 3 being a longitudinal sectional front view. FIG. 4 is a plan view illustrating a conventional example. 1... Can body, 1a... Opening periphery of can body, 5...
...Sealing material, 5a...Film base material of sealing material,
5b...Hot melt adhesive layer of sealing material, 6...
...Induction coil, 7...Can body joint.

Claims (1)

[Claims] 1. The opening surface of the can body 1 is made to face the U-shaped induction coil 6 having a small distance between the coils, and the induction coil 6 and the can body 1 are moved relatively within the opposing surfaces. While heating, a high frequency wave is passed through the induction coil 6 to heat the opening periphery 1a of the can body 1, and the sealing material 5 having thermal adhesive properties is thermally bonded to the opening periphery 1a. Thermal bonding method. 2. The thermal bonding method according to claim 1, wherein the sealing material 5 is a transparent plastic film made by laminating a hot melt adhesive layer 5b on a film base material 5a. 3. The thermal bonding method according to claim 1, wherein the length of the U-shaped portion of the induction coil 6 is larger than the diameter of the opening surface of the can body 1. 4. The thermal bonding method according to claim 1, wherein the sealing material 5 is placed on the opening surface of the can body 1, and then the sealing material 5 is thermally bonded to the opening peripheral portion 1a of the can body 1 using an induction coil 6. 5. The thermal bonding method according to claim 1, wherein the opening periphery 1a of the can body 1 is heated by the induction coil 6, and then the sealing material 5 is thermally bonded to the opening periphery 1a.