JPS5955736A - Heat sealing method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-sealing method, and more particularly to a method of heat-sealing an end member to an open end of a container body by high-frequency induction heating.

Conventionally, in order to manufacture sealed containers filled with food and drink products, an end member (lid member or bottom member) is attached to the open end of the container body.
When heat-sealing, the open end is often formed into an outwardly projecting flange, and a flat end member is heat-sealed to this flange. As a result, the storage volume of the container increases, and the sharp corners of the flange portion pose a risk of injury to children's hands and fingers. Furthermore, since the end members are flat, there is a problem in that the end members are easily damaged when stacked during transportation, handling, etc.

In response to this, recently, a container has been proposed in which a rim portion having a U-shaped or V-shaped cross section and an end member having a recessed panel portion is heat-sealed to the straight cylindrical open end of the container body. has been done. This type of container solves the above-mentioned problems and has the advantage that the end member can be easily positioned when the end member is inserted into the open end. However, in the conventional heat sealing of this type of container, a heating element (for example, internally heated by an electric resistor) is inserted into the inner wall of the rim after sealing, and the rim is pressed from the outside with a pressing tool to heat the container. This was done by a sealing method.

In order to ensure the sealing performance of this type of container, the heat seal between the inner wall of the rim of the end member and the open end is important. Even when the current is turned off, it takes time for the heat-sealed part to cool and solidify due to the heat capacity of the heating element, and often, while the heat-sealed part is melting, the heating element that is tightly inserted into the inner wall is pulled out and moved around the inner wall. Therefore, the heat-sealed portion was likely to peel off, resulting in a poorly sealed container. On the other hand, when removing the heating element after the heat-sealed part has sufficiently cooled and solidified,
There was a problem that productivity decreased.

It is an object of the present invention to solve the problems of the prior art described above.

In order to achieve the above object, the present invention includes a panel portion at the open end portion of the container body, at least the inner layer of which is made of a heat-sealable resin, and an inner surface having a U-shaped or V-shaped cross section rising from the periphery of the panel portion. A high-frequency induction heating coil having a rim portion whose layer is made of a heat-sealable resin and includes a metal layer is attached to the rim portion of the end member, and the outer circumferential surface of the end member has a shape corresponding to the inner wall. are in contact or 1d opposite each other, the outer wall and the inner wall of the rim portion have a shape corresponding to the outer wall when the inner circumferential surface is in contact with the open end, and an electric current is provided to interrupt the induced circulating current. A pressing tool equipped with a plurality of suppressing members mainly made of metal and provided with an insulating layer cooperates with the heating coil to press the opening end, energizes the heating coil, and removes at least the metal on the inner wall. After the layer is heated by high-frequency induction to raise the temperature of the inner layer and the heat-sealable resin of the inner layer to a heat-sealable temperature to form a heat-sealable portion, the heating coil is deenergized and the heat-sealable portion is heated. The present invention provides a method for heat-sealing an end member to a container body, characterized in that the above-mentioned compression is released after the end member is cooled and solidified.

The present invention will be described below with reference to the drawings.

In FIG. 1, 1 is a container body, and 2 is an end member (in this case, a bottom member). As shown in FIG. 2, the container body 1 includes an outer layer 1a (heat-sealable resin, e.g., polyethylene film with a thickness of about 50 μm) and an outer intermediate layer 1b (e.g., paper material with a thickness of about 300 μm). , a central intermediate layer 1c (e.g., polyethylene film with a thickness of about 30 μm), an inner intermediate layer 1d (e.g., aluminum foil with a thickness of about 15 μm), and an inner layer 1e (heat-sealable resin 2, e.g., a polyethylene film with a thickness of about 50 μm). (Layers 1c, ld, and le are bonded by an adhesive layer (not shown) such as acid-modified polyethylene), and after rolling the blank into a cylindrical shape, a heat-sealable resin (in this case polyethylene 5) It is formed by heat-sealing the outer layer 1a and the inner layer 1e made of (Ren).

The end member 2 has a quenelle portion 3 and a rim portion 4 rising from the periphery of the panel portion, and the rim portion 4 has a roughly V-shaped cross section.
(may be in the shape of a letter) and stands up vertically 4a
, and an outer wall 4c extending obliquely downward to the outside from the upper end of the inner wall 4a via the top 4b. The outer diameter of the inner wall 4a is determined to be substantially equal to the inner diameter of the open end 1f so that the inner wall 4a can be loosely inserted into the open end 1f of the container body 1. The height of the inner wall 4a is usually about 3 to 10 mm. The radial width of the top portion 4b is determined to be substantially equal to the thickness of the open end portion 1f.

In this example, the end member 2 has an outer layer 2a (for example, a thickness of about 5
Epoxy/urea baked coating of μm or thickness of approximately 1
2 μm biaxially stretched polyethylene terephthalate film), an intermediate layer 2b (metal foil 1, e.g., aluminum foil with a thickness of about 100 μm), and an inner layer 2c (heat-sealable resin 2, e.g. a polyethylene film with a thickness of about 50 μm). , (6) Each layer (if the outer layer 2a consists of a baked coating film or a printed film,
(only between the intermediate layer 2b and the inner layer 20) is bonded by an adhesive layer (not shown) such as diacid-modified polyethylene.

The end member 2 is usually formed by drawing.

Therefore, the thickness of the metal foil of the intermediate layer 2b is set to a thickness such that self-shape retention is maintained even after drawing (usually 30 to 150 μm).

6 is a high-frequency induction heating device, which includes a high-frequency induction heating coil 7 (abbreviated as a heating coil in this specification);
A magnetic core 8 having a U-shaped cross section and made of a high magnetic permeability material such as ferrite inscribed in the heating coil 7 has a peripheral edge 9a close to the lower end 7a1 of the heating coil 7 and is attached to the lower surface of the induction heating device 6. Made of a good electrical conductor (e.g. copper or aluminum), water cooled 1? It includes a magnetic flux mask sheet 9 (see FIG. 3) cooled by a tube 9b, and a support 10 made of an electrically insulating material (for example, Bakelite or epoxy resin).

The heating coil 7 includes a short cylindrical coil body 7as made of a metal sheet (usually made of a copper plate) and a coil body 7.
A water cooling pipe 7b is fixed to the inside of the upper part of the pipe a. The coil body 7a has a shape corresponding to the inner wall 4a of the rim portion 4 of the end member 2 attached to the open end 1f of the container body 1.
(so that a sound heat-sealed portion is formed between the inner wall 4a and the open end 1f).
is defined substantially equal to the inner diameter of a.

During heat sealing, the peripheral edge 3a of the panel portion 3 of the end member 2 has a smaller heat capacity (usually about 115) than the inner wall 4a that is in close contact with the open end 1f.

Therefore, if the lower end 7al of the coil body 7a is too close to the panel part 3, or if the lower end 7al is thick,
The density of magnetic flux generated at the peripheral edge 3a becomes like a dog, and the peripheral edge 3
aX, especially the inner surface layer 2c (second
The heat-sealable resin forming the layer 2a (see Fig.) melts, flows, and becomes thinner, causing the problem that the metal foil of the intermediate layer 2b is easily corroded during storage after filling and sealing the contents. Especially when heat-sealing after filling with liquid-containing contents,
If heat-sealing is performed with the liquid remaining attached to the interface area to be heat-sealed, since the permeability of water vapor in the molten resin is high, the water vapor that has permeated from the heat-sealed area will be transferred to the molten inner layer 2c of the peripheral edge 3a. Air bubbles are generated between the intermediate layer 2b, and moisture remains in the air bubbles after cooling, which tends to promote corrosion of the gold foil of the intermediate layer 2b.

In order to prevent such defects, the high-frequency induction heating device 6 should be installed during heat sealing so that the distance g between the lower end 7al of the coil body 7a and the upper surface of the panel portion 3 is one tone or more. is desirable.

Furthermore, it is desirable that the distance g be 1- or more and as small as possible within the range where the above-mentioned defects do not occur, in order to ensure the highest possible heat-sealed portion.

In addition, the lower end portion 7al is thin, preferably the thickness of the lower surface 7a'1 of the lower end portion 7a1 is 2 mm or less, and the lower surface 7a1
It is desirable that the thickness at the higher part of 1 to 92w+1 be as thin as 3 or less.

Furthermore, if the outer layer 2a of the inner wall 4a is thin, the heat of the intermediate layer 2b (metal foil) that is induction heated during heat sealing is likely to escape to the water-cooled heating coil 7, which is likely to occur.

9-. C outer layer. . . If the thickness is thinner than test 1-, use an elastic material such as a silicone comb sheet (especially when there is an overlapping part) or a fluororesin film (when there is no overlapping part), etc. on the outer surface of the coil body 7a. It is desirable to provide a thermal insulating layer (not shown) consisting of a heat insulating layer (not shown), and to set the distance between the coil main body 7a and the intermediate layer 2b to 0.1 tM1 or more and 20 tM or less.

The magnetic core 8 has the effect of concentrating magnetic flux on the metal layer (intermediate layer 2b and inner intermediate layer 1d) of the rim portion 4 and the open end 1f, increasing heating efficiency, and reducing leakage magnetic flux at the peripheral edge 3a. have

In the sheet 9, magnetic flux is generated in the metal layer (intermediate layer 2b) inside the peripheral edge 3a of the panel portion 30, which heats the metal layer at the core and melts the heat-sealable resin of the inner layer 2c. (10) However, depending on the working conditions, the magnetic core 8 and/or the sheet 9 may not necessarily be provided.

13, insertion of the end member 2 into the high frequency induction heating device 6;
and an air vent for easy removal. The above-mentioned components of the high-frequency induction heating device 6 are bonded to each other with an adhesive.

The support body 10 is screwed onto the frame 14.

In FIG. 4, FIG. 5, and FIG. 6, 15 is a pressing tool, which includes a plurality of (four in the figure) openable and closable pressing bodies 1.6a,
16b, 17a, and 17b. A suppressing member 18 is fixedly installed inside each suppressing body, and the inner peripheral surface 18a of the suppressing member 18 is in a closed state (the state shown in FIGS. 4 and 5).
In this case, the end member is configured to have a shape corresponding to the outer wall 4c of the end member in a state in which it is in contact with the outer surface of the open end 1f of the container body.

As shown in FIGS. 7 and 8, opposing circumferential ends 18b and 18c of each suppressing member 18 have a convex portion 19 and a concave portion 20 that engage and are slidable relative to each other in the circumferential direction. is provided. That is, each pressing member 18 is configured to be connected to each other in a telescoping manner.

As shown in FIG. 7, by pressing with the suppressing member 18, even when the rim part 4 and the opening end 1f are in contact with each other, there is a slight gap 21 between the end part 18b and the end part 18c.
a, 21. b (preferably about 0.5 or less) occurs,
A predetermined pressing force is applied between the rim portion 4 and the open end portion 1f. Since the gaps 21a and 21b are not continuous, that is, they are nested, the ends]
, 8b and 18a, no continuous gap is formed in the axial direction.

Therefore, it is desirable to use metals with high electrical conductivity (for example, aluminum alloys or brass) to avoid heat seal defects due to gaps.

In this case, a circulating induced current flowing in the circumferential direction is formed within the suppressing members 18, and the heating efficiency is significantly reduced. It is preferable to separate the above-mentioned circulating induced currents by separating them by .

The pressing bodies 16a, 16b, 17a, and 17b are made of an electrically insulating material (for example, Bakelite) having relatively high mechanical strength so as to prevent the formation of circulating induced currents.

In addition, in the case where the outer wall 4c and the opening end 1f are also heat-sealed, the thickness of the outer layer 2a of the outer wall 4C is 0.1 ttr.
When the pressure member 1 is thinner than m, for the same reason as mentioned above, the pressure member 1
A heat insulating layer (not shown) is provided on the inner circumferential surface 18a of 8, and the distance (under suppression) between the inner circumferential surface 18a and the intermediate layer 2b (metal foil) is set to 0.1 am or more and 2.0 mm or less. It is desirable to do so.

If the container body 1 has an overlapping portion, it is desirable to provide a heat insulating layer made of an elastic material such as a silicone film sheet.

The opposing pressing bodies 16a and 16b are moved in the left-right direction in the figure by an air cylinder (not shown) via piston rods 22a and 22b, respectively. A guide sylate 24 having a pair of guide surfaces 24a extending outwardly toward the suppressor 16a is fixed to the suppressor 16b.

(13) Pressing bodies 17a and 17b are pivotally supported by flanges 25a and 25b provided on both sides of the piston rod 22 a side end of the suppressing body 16a, respectively. A roller 26 is mounted on a shaft at the end of each of the pressing bodies 17a and 17b on the pressing member side, and the pressing bodies 17a and 17b are constantly pressed against the guide surface 24. a
biased to come into contact with. Therefore, as shown in FIG. 6, when the pressing members 17a and 16b retreat in the X and Y directions, respectively, the pressing members 18 move in the X and Q directions, respectively. The pressing tool 15 is brought into an open state. When the pressing bodies 16a+16b are moved forward from this open state, each roller 26 moves in a direction toward each other along the guide surface 24a, and the suppressing member is brought into the closed state as shown in FIG. I5 is configured.

(14) Heat sealing is performed using the above apparatus as follows.

The container body 1 is placed on the lifter plate 28, and the open end 1f of the container body 1 is sealed with the rim portion 4 of the end member. Next, the lifter plate 28 is moved and stopped when it reaches directly below the high frequency induction heating device 6, and the lifter plate 28 is raised until the above-mentioned distance g reaches a predetermined value. At this point, the pressing tool 15 is in an open state. Next, an air cylinder (not shown) is operated to press the pressing body 1.
6a.

Pressing body 16a is moved by moving 16b in the closing direction.

16 b * 17 a, 17 b and the heating coil 7 cooperate to press the outer wall 4C and the inner wall 4a of the end member against the open end 1f. Almost simultaneously with the above-mentioned suppression, the heating coil 7 is energized.

In this example, the container body 1 has an outer intermediate layer 1b made of paper material.
Contains. Therefore, for example, juices can be filled using the zetsukku method (only between the inner wall and the open end).
If the outer wall 4c and the open end 1f are not heat-sealed when the container is subsequently cooled with water, water will penetrate into the paper material and the container body 1 will become soft.

It deforms and becomes a defective container. Therefore, in a case like
It is also necessary to completely heat seal between the outer wall 4c and the opening end 1f. For this purpose, it is necessary to set the frequency (fo) of the high-frequency current to be applied so low that a sufficient induced current flows through the metal foil of the intermediate layer 2b of the outer wall 4c that is in contact with the open end f.

Generally, the penetration depth 1) of high-frequency current is determined from the following equation (1).

Here, f is the frequency, and σ and μ are the electrical conductivity (in MKS units) and magnetic permeability (in MKS units) of the metal to be heated (aluminum in this example), respectively. Therefore, in this example,
It is necessary to determine the sum of the thicknesses of the aluminum foils included in the inner wall 4a, the container body 1, and the outer wall 4c as t.

The above frequency f is applied to the heating coil 7. By passing a high-frequency current through the metal foil of the inner wall 4a, opening end 1f, and outer wall 4c, the metal foil of the inner wall 4a, opening end 1f, and outer wall 4c is heated by induction, so that the polyethylene, which is a heat-sealable resin in contact with the heated metal foil portion, reaches a temperature higher than the heat-sealable temperature (melting point). In the case of polyethylene (110° C., for example, 150° C.), the temperature is raised under pressure to perform heat sealing between the inner wall 4a and the open end 1f, and between the outer wall 4c and the open end 1f.

The energization time, that is, the sheet sealing time is 0.1 to 2.
It is desirable that the time be 0 seconds. If it is shorter than 0.1 seconds, the metal layer is likely to melt or the resin layer is likely to burn out, while if it is longer than 2 seconds, the heat capacity (temperature x volume) of the heat-sealed part (including the thermal insulation layer) will decrease. This is because if the temperature is too high, the cooling time described below will become longer. Furthermore, the amount of heat absorbed by the water-cooled heating coil increases, resulting in a decrease in heating efficiency.

Since the respective suppressing members 18 are connected in a telescopic manner, the suppressing is performed substantially uniformly along the opening end 1f, and there is no risk of heat seal defects occurring due to unpressed portions.

Next, the heating coil is deenergized, and the sheet-sealing resin in the heat-sealing section (17) is heated to a solidification temperature (crystalline resin, a temperature lower than the melting point in the case of , a temperature lower than the softening point in the case of a shaped resin). ) After cooling to a very low temperature (to prevent defects such as pinholes in the heat seal part), open the suppressor 15, release the suppression, lower the lifter 28, and remove the end member from the induction heating device 6. Remove 2. water cooling/mother ifi
Since the coil main body 7a is cooled by the coil body 7a, the above cooling time is short, usually 0.2 to 2.0 seconds.

In order to shorten the cooling time in this way, it is desirable to set the energization time of the heating coil 7 and the energization interval to 1:5, for example, so that the cooling time of the coil body 7a is relatively long. In order to obtain the necessary energization impedance without reducing productivity, a turret-type heat sealing device in which a plurality of high-frequency induction heating devices 6 (for example, eight) are arranged in the circumferential direction is used. Bye.

As described above, a container is formed in which the bottom member is heat-sealed to the container body. After filling the container with the contents, the lid member is heat-sealed (18) in the same manner to form a sealed container. Manufactured.

The invention is not limited to the above examples. For example, the container body may be made of only plastic (including a plastic laminate; in this case, a seamless container body may be formed by an extruder), or plastic and metal, without any paper material. It may also be a laminate of foils. In this case, there is no risk of softening due to water penetration, so heat sealing of only the inner wall may be sufficient. However, in the case of heat-sealing the lid member, it is desirable to heat-seal the outer wall at the same time, since there is a risk that moisture from the contents may adhere to the inner surface of the opening end and cause pinholes or the like to occur in the heat-sealed portion. Further, the container body can have an appropriate shape such as a rounded corner cylindrical shape.

Further, the metal layer may be exposed on the outer surface of the end member. However, in this case, it is necessary to cover the outer circumferential surface of the coil body 7a with an electrically and thermally insulating film in order to prevent discharge due to a short circuit and to prevent the above-mentioned panel portion peripheral portion 3a from overheating. When heat-sealing a small outer wall 4c as well, it is necessary to cover the inner circumferential surface of the suppressing member 18 with an electrically and thermally insulating film for the same reason.

Note that the number of suppressors 16 is preferably three or more. In the case of two, it is not possible to apply a sufficient radially inward pressing force near the circumferential end of the suppressing member 18, and heat seal defects are likely to occur near the circumferential end.

Further, as in the heating coil 7' shown in FIG. 9, the coil body 77a may be formed by laminating and winding thin metal sheets. Also in the case of 7'a1, the lower end of the coil body
It is desirable that the thickness be within the above-mentioned range.

According to the present invention, the end member having the rim portion having a roughly U-shaped or V-shaped cross section is heat-sealed to the container body by high-frequency induction heating, and the suppression is released after the sealed portion is cooled and solidified. Therefore, it is possible to form a sound heat-sealed portion in a very short time.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of a main part of an example of an apparatus for carrying out the method of the present invention, FIG. 2 is an enlarged vertical cross-sectional view of part A in FIG. 1, and FIG.
The figure is an enlarged longitudinal sectional view showing the state of part B in Fig. 1 under pressure, Fig. 4 is a plan view showing the press tool used in Fig. 1 in the closed state, and Fig. 5 is the Fig. 6 is a plan view showing the pressing tool in the open state in Fig. 4, Fig. 7 is a longitudinal sectional view taken along line - V in Fig. FIG. 6 is a vertical cross-sectional view taken along the line 1--1 in FIG. 6, and FIG. 9 is a vertical cross-sectional view of a main part showing another example of a heating coil used for carrying out the present invention. DESCRIPTION OF SYMBOLS 1... Container body, 1f... Opening end, 1e... Inner layer (layer made of heat-sealable resin), 2... End member, 2b... Intermediate layer (layer made of metal foil) ), 2C...
Inner layer (heat-sealable resin layer), 3...
Nogunnel part, 4... Rim part, 4a... Inner wall, 4C.
...Outer wall, 7°7'...Heating coil, 15...Press tool, 18...Press member. (21) Fig. 1 14 0 b4 b q 16, 40 91332 687 1B□, 8.616a JP-A-59-55736 (7) Fig. 2 Fig. 3〉i JP-A-59-55736 (8)

Claims (1)

[Claims] (1) At least the inner layer of the container body is made of a heat-sealable resin, and the inner layer is heat-sealed to the open end of the container body, the panel portion and the inner layer having a U-shaped or V-shaped cross section rising from the periphery of the channel portion. The rim part of the end member is made of plastic resin and includes a metal layer, and a high-frequency induction heating coil having an outer peripheral surface having a shape corresponding to the inner wall is brought into contact with the inner wall of the rim part, or The outer wall and the inner wall of the rim portion are opposed to each other, and the inner circumferential surface has a shape corresponding to the outer wall in contact with the open end, and an electrically insulating layer is provided for blocking induced circulating current. A pressing tool having a plurality of pressing members mainly made of metal cooperates with the heating coil to press the opening end and energize the heating coil to at least remove the metal layer on the inner wall. After high-frequency induction heating is performed to raise the temperature of the heat-sealable resin of the inner layer and the inner layer to a heat-sealable temperature to form a heat-sealed portion, the heating coil is deenergized, and the heat-sealed portion is cooled. A method of heat-sealing an end member to a container body, the method comprising releasing the above-mentioned compression after solidification.