JPH10129657A - Method for heating metal square can - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce efficiently a film fusion can which is free of sealing failure, due to insufficient film-fusion of a joined part, and a variation in quality, by heating all the joined parts of a can, including a lap part, at correct, proper temperature and satisfactorily in reproducibility when producing the film fusion can. SOLUTION: In the process of heating the side seam part 3 and rimmed part 6 of a square can 1 made of a laminated metal plate which has a film surface as the inner surface of the can, thereby welding and sealing the plastic films near the part where they are joined, the rimmed part 6 is heated as a first step and then the side seam part 3 is heated within 30min. as a second step, or the side seam part 3 is heated as a first step and as a second step the rimmed part 6 is then heated within 30min.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a metal plate having a plastic film laminated on at least one side, and the inner surface of which is covered with a plastic film.
More specifically, the present invention relates to a heating method for manufacturing a large three-piece metal square can such as a liter can, and more specifically, to fuse and seal a plastic film corresponding to a side seam portion or a winding portion, which is a joining portion of the can. Accordingly, the present invention relates to a method for heating these joints.

[0002]

2. Description of the Related Art Conventionally, a metal plate formed by laminating a corrosion-resistant plastic film is used, and a can body, a ground plate and a top plate are formed so that the film surface becomes the inner surface of the can. It has been practiced to manufacture three-piece metal square cans. In that case, can strength and can confidentiality are high,
In order to obtain a metal square can that can withstand long-term storage of corrosive substances, a side seam part that is a joint part of the can body, and a winding part that is a joint part of the can body and the top plate and the main plate are provided. Have been tried to heat and seal the plastic films near their joints and seal them.

One example is disclosed in Japanese Patent Application Laid-Open No. 54-13148.
In Japanese Patent Application Publication No. 5 (1999) -1995, a metal can coated with a polyolefin resin is proposed in which a metal plate is used in which one or both surfaces of a metal plate are coated with a polyolefin resin. However, regarding the heating method in this case, the tightened portion is heated by a burner or the like (100 to 30).
(0 ° C.), it merely states that the polyolefin resins in the tightened portion can be completely fused together by heat fusion. In Japanese Patent Publication No. 3-2744, after a plastic film is laminated on the inner surface of a can body, a side seam is formed by a rock seam method, and the side seam portion is heat-sealed. It has been proposed to use a three-layer composite film of a specific composition (three-layer composite laminate) as a laminate film in order to improve the impact resistance. Regarding the heating method in this case, in the embodiment, the joint is set to about 140.
The only thing is that the three-layer composite laminate is locally heated to about 150 ° C. to thermally melt the three-layer composite laminate, to be fused to the inner surface of the can body, and to fuse the mutually contacting parts of the three-layer composite laminate. JP-A-5-97140 and JP-A-5-13
No. 2061 discloses a resin composite steel sheet in which at least one surface of a steel sheet constituting each cut plate of a can is coated with a thermoplastic resin to a predetermined thickness, and the can body is subjected to rock seam processing, while a top plate and a main plate are wound. It has been proposed that the can be made by tightening, and then the lock seam portion and the winding portion are heated for a predetermined time at a temperature higher than the melting temperature of the thermoplastic resin to cause self-fusion on the surfaces of the thermoplastic resins. I have. As the heating conditions in this case, only the heating temperature and time are described.

[0004] As a method related to a method of heating a joint portion of a metal can, an adhesive is applied in advance to a place where a metal plate material of a three-piece can is to be joined and assembled into a can.
A technique is also known in which the joint is heated by high-frequency induction heating means to cure or fuse the adhesive. As such a technique, for example, Japanese Utility Model Application Laid-Open No. 53-39151 discloses that a high-frequency induction heating coil is laid at a position facing a passing position of a joining portion of a metal can, and the heating coil is used by the heating coil when the metal can is transported. An apparatus for heating the joint is shown. However, in this apparatus, since the relative position between the heating coil and the junction of the can to be heated is not kept constant due to shaking or dancing due to the transport vibration of the can passing through the heating section, the heating temperature is reduced. And uniform adhesive quality cannot be expected. The device described in Japanese Utility Model Publication No. 3-7054 is probably to solve the above problem. In this device, an insulator is provided on one side surface of a high-frequency induction heating coil arranged along a can transport path, and the can transport path side of the insulator is used as a sliding contact surface with a joining portion of a metal can. This is a configuration in which high-frequency induction heating is performed while a joint to be bonded is conveyed while sliding on the sliding contact surface. According to this, the distance between the joint of the metal can and the high-frequency induction heating coil is kept constant by the dimensions of the insulator.
The problem in the technique described in JP-A-3-39151 is theoretically solved. However, it is not very practical because the joining portion of the can slides on the insulator to cause rubbing or abrasion of the joining portion. Japanese Patent Publication No. Sho 62-55275 discloses a device for heating a tightened portion between a can body of a metal square can, a top plate and a main plate, which includes a horizontal frame-shaped heating coil conforming to the shape of the tightened portion to be heated. It discloses that a high-frequency induction current is applied by pressing a canned portion of the can against the heating coil with a cylinder. However, this is merely a heating device for the tightened portion, and can accurately heat the tightened portion, but does not consider heating the side seam portion, which is another important joint portion.

[0005]

As described above, in order to obtain a metal can having chemical resistance, a can is made using a laminated metal plate so that the film surface becomes the inner surface of the can. Various methods and apparatuses have been proposed or attempted as a manufacturing technique of a metal square can (hereinafter, appropriately referred to as a film-fused can) produced by heating and fusing and sealing a film at the joint. However, at present, the quality of the obtained product is not constant, and depending on the product, the leakage of the contents in the can often occurs, the strength of the can varies, and corrosive products are corroded when stored for a long time. There is a problem that there is.

Almost all places where these defects occur are multiple winding portions (hereinafter referred to as wrap portions) where the side seam portions intersect with the top plate or the main plate. Analysis of the wrapped portion where the defect occurred revealed that the film was not sufficiently fused, resulting in poor sealing resulting in fine holes. This can be for the following reasons. That is, as shown in FIG. 3, in the lap portion 7 of the metal square can, the end of the side seam portion 3 having the lock seam structure obtained by folding the goby is wrapped and fastened when the top plate 4 (or the base plate) is attached. Since it is further bent, a joining portion other than the wrap portion as shown in FIGS.
And the side seam portion 3 excluding the wrap portion 7), the metal amount is increased, and the heat capacity is correspondingly increased. Therefore, at the joint other than the wrap portion, the film 8
Is sufficiently melted, the temperature rise is relatively low in the wrap portion 7, and insufficient melting of the film 8 or insufficient flow of the film resin occurs. It is considered that sealing failure occurs. In this case, if the heating conditions are strengthened so that the film 8 is completely fused in the wrap portion 7, overheating occurs in the joints other than the wrap portion, and the film 8 may be deteriorated.

Since the above points have not been sufficiently considered, a heating method capable of efficiently producing a uniform film-fused can having a uniform quality without insufficient film fusion or poor sealing, That is, at present, a heating method suitable for manufacturing a film fusion can has not yet been established.

SUMMARY OF THE INVENTION It is an object of the present invention to enable all can joints including a lap portion to be accurately and reproducibly heated at an appropriate temperature during the production of a film-fused can. An object of the present invention is to efficiently obtain a film-fused can having no sealing failure and quality variation.

[0009]

SUMMARY OF THE INVENTION The present invention provides a so-called limited-wrap two-step heating method as a method for heating a metal square can performed at the time of manufacturing a film fusion can. That is, in the method of the present invention, as shown in FIG. 1, a side seam portion 3 which is a joining portion of a can body 2 constituting a metal square can 1; When the plastic film 4 near the joints is melted and sealed, the above-mentioned tightened parts 6 are heated as a first step by heating each of the joints 4 and the winding part 6 which is the joint with the ground plate 5. Heating the side seam portion 3 as a second stage within 30 seconds after the heating, or heating the side seam portion 3 as a first stage within 30 seconds from the heating of the side seam portion 3 as a second stage. It is characterized in that the part 6 is heated.

[0010] Specifically, after the heating of the winding portion 6 or the side seam portion 3 is completed in the first stage, the second stage heating is performed while the residual heat temperature is at least 50 ° C.
The time from the first stage heating to the second stage heating must not exceed 30 seconds to ensure the required residual heat temperature. A suitable time within that range can be determined empirically while examining the degree of fusion of the wrap portion 7 where the side seam portion 3 and the winding portion 6 intersect. Further, the ambient temperature during the transport process until the can heated at the first stage enters the heating process at the second stage affects the residual heat temperature due to the heating at the first stage. Therefore, in order to secure a required residual heat temperature, it is preferable to adjust the ambient temperature during the transfer process so as to be in the range of 5 ° C. to 50 ° C.

In the above-described two-stage heating method limited to the wrap portion, as long as the film is made of a thermoplastic resin,
Any plastic film can be used. However, it is preferable to use a single-layer or multi-layer film made of polyolefin or modified polyolefin. This kind of film has excellent chemical resistance,
This is because there is an advantage that there is no danger of causing thermal deformation in the can due to a relatively low melting temperature, and a good fusion state can be obtained because the melt viscosity is appropriate.

[0012]

[Function] In the manufacturing process of a film fusion can, a metal square can 1
When the can joint is heated in order to fuse the film at the joint of the above, the wrap portion 7 where the wound portion 6 and the side seam portion 3 intersect generally has a large amount of metal and a large heat capacity. The temperature is harder to rise than the part. However, according to the present invention, the intersection between the first-stage heating portion and the second-stage heating portion becomes the wrap portion 7. In other words, in the present invention, after heating the winding portion 6 as the first step, the second step
Heat the side seam part 3 as a step, or
After heating the side seam part 3 as the step, the winding part 6 is heated as the second step, so that in each case, each wrap part 7 is heated twice in total,
Moreover, the second-stage heating is performed within 30 seconds when the residual heat from the first-stage heating remains. Therefore, in the winding portion 6 and the side seam portion 3, the joining portion other than the wrap portion is heated only once, and the film is heated to a predetermined temperature by the one heating and is sufficiently fused, Each wrap 7 is heated twice within a predetermined period of time, and the two heatings raise the temperature to a level similar to or higher than other joints. As a result, inadequate fusion of the wrap portion 7, which often occurs in the conventional method because the temperature is less likely to rise than in other portions, is reliably eliminated, and poor sealing due to such insufficient fusion is prevented. The Rukoto.

[0013]

As described above, according to the present invention, at the time of manufacturing a film-fused can, one of the tightened portion 6 and the side seam portion 3, which are the joining portions of the metal square can 1, is heated first. Then, the other is heated within a predetermined time in which the residual heat remains, so that both the wrap portion 7 and the other joints can be heated to an appropriate temperature accurately and with good reproducibility. . In this manner, a film-fused can having no poor sealing or quality variation due to insufficient film fusion at the joint can be efficiently obtained.

[0014]

【Example】

(Embodiment 1) FIG. 2 shows a process of manufacturing a film fusion can according to an embodiment of the present invention. This manufacturing process relates to the case of manufacturing a film-fused can as shown in FIG.
A can-making process 11 for making the metal square can 1 using a material made of a laminated steel sheet, a crimping portion heating step 12 for performing high-frequency induction heating on the crimping portion 6 of the metal square can 1, And a side seam portion heating step 13 for performing high-frequency induction heating on one side seam portion 7. Then, the first conveyor 14 is used as a conveyance path for the unfused cans from the can manufacturing process 11 to the tightening portion heating step 12, and the crimping portion fusion bonding from the tightening portion heating step 12 to the side seam portion heating step 13 is performed. The second conveyor 15 is arranged as a transport path for the finished cans, and further on the downstream side of the side seam portion heating step 13,
A third conveyor 16 is arranged as a conveying path for sending out the fusion can that sends out the film fusion can after heating the winding portion 6 and the side seam portion 3 to a predetermined position.

The laminated steel sheet used as the material in the can manufacturing process 11 is made of a tin-free steel sheet having a thickness of 0.32 mm,
80μ thick made of modified polyethylene and polyethylene
m is laminated on the modified polyethylene side as an adhesive layer to a steel plate. In the can-making step 11, a normal 18-liter can (metallic square can) as shown in FIG. 1 is made with the film surface of the laminated steel plate facing the inner surface of the can. At this time, the side seam portions 3 of the body plate constituting the can body 2 are joined by a lock seam method, and the top plate 4 and the main plate 5 are attached to one end and the other end of the can body 2.
Are joined by winding. In FIG. 1, portions indicated by reference numerals 6 are winding portions.

The 18-liter can thus manufactured is sent to the winding-portion heating step 12 by the first conveyor 14. In the tightening portion heating step 12, the respective tightening portions 6 which are the joining portions between the can body 2 and the top plate 4 and the main plate 5 are brought close to a high-frequency induction heating coil (not shown) having a shape corresponding to the shape thereof. In this state, a high-frequency current is applied to the coil for 2 seconds, and the coil is heated to about 180 ° C., so that the film of the tightened portion 6 is fused. In this case, the temperature of the wrap portion 7 is about 140 ° C.

When the heating of the tightening unit 6 is completed, the can is immediately put on the second conveyor 15 and transported to the next side seam heating step 13 at a predetermined timing.
At this time, the length of the second conveyor 15 and the transfer timing are adjusted so that the temperature of the wrap portion 7 becomes approximately 200 ° C. at the time of film fusion of the side seam portion 3 described later. The time required to enter the seam portion heating step 13 was set to 22 seconds. The ambient temperature near the second conveyor 15 was about 15 ° C.

In the side seam portion heating step 13, the side seam portion 3 of the can is brought close to a linear high-frequency induction heating coil (not shown), and a high-frequency current is applied to the coil for 2 seconds, thereby obtaining a temperature of about 180 °. The film of the side seam portion 3 is fused by heating to a temperature of ° C. In this case, the temperature of the wrap portion 7 was about 200 ° C.

As described above, in the first stage, the film of the winding portion 6 is heated, and in the second stage, the film of the side seam portion 3 is heated and fused. 20 cans are randomly selected from each of them, and each can is filled with a 25% solution of sodium alkylbenzene sulfonate,
In that state, it was left at room temperature for 6 months including the summer. After the standing, each can was examined for liquid leakage and rust on the inner surface of the can. No liquid leakage occurred in all the cans, and no abnormality such as rust was observed on the inner surface of the cans.

(Comparative Example) First, an 18-liter can was made with the same specifications using the same laminated steel plate as in the above embodiment.
Next, the crimped portion of the 18-liter can was heated to about 180 ° C. by a high-frequency induction heating device similar to the high-frequency induction heating coil used in the crimped portion heating step of the embodiment of the present invention. (2 seconds) to fuse the film in the tightened portion. Thereafter, the 18-liter can was left as it is stored as appropriate, without taking into account the residual heat due to the heating of the tightening portion as conventionally performed. At this time, the film-fused portion of the winding portion is in a natural cooling state. Next, the 18-liter can that was allowed to cool naturally was heated to 180 ° C. for 2 seconds by a high-frequency induction heating device for the side seam part in another step to fuse the film in the side seam part.

According to the method of the comparative example described above, 200 film-fusing cans were prepared, and 20 cans were randomly selected from these, and each can was filled with a 25% solution of sodium alkylbenzene sulfonate. It was left at room temperature for 6 months. After this standing, each can was inspected for liquid leakage or rust on the inner surface of the can. It was confirmed that liquid leakage from the wrapping part occurred in the two cans, and that rust was generated on the inner surface of that part. Was.

[Brief description of the drawings]

FIG. 1 shows a metal square can (18) to which the heating method of the present invention is applied.
1 is an overall perspective view showing an example of a (liter can).

FIG. 2 is a process diagram showing a process for manufacturing a film-fused can according to an embodiment of the present invention.

FIG. 3 is a longitudinal sectional view of a wrap portion (multiple tightening portion) used for showing a problem when heating a metal square can.

FIG. 4 is a vertical cross-sectional view showing a portion other than a wrap portion in a tightening portion used to show a problem at the time of heating a metal square can.

FIG. 5 is a longitudinal sectional view showing a portion other than a wrap portion in a side seam portion used for showing a problem when heating a metal square can.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal square can 2 Can body 3 Side seam part 4 Top plate 5 Main plate 6 Winding part 7 Lapping part

Claims (4)

[Claims] 1. A can body 2 made of a laminated metal plate having a plastic film laminated and adhered on at least one side.
And a top plate 4 and a base plate 5 made of the same laminated metal plate joined to the upper and lower ends of the can body 2 by winding, respectively, to form a metal square can 1 having a film surface as an inner surface of the can. In the metal square can 1, a side seam portion 3 which is a joint portion of the can body 2 and a winding portion 6 which is a joint portion of the can body 2 and the top plate 4 and the base plate 5 are heated, respectively. In fusing and sealing the plastic film near the joint, the side seam portion 3 is heated as a second stage within 30 seconds after heating the wound portion 6 as a first stage, or A method for heating a metal square can, comprising heating the side seam portion 3 as a first stage within 30 seconds after heating the tightened portion 6 as a second stage. 2. The method for heating a metal square can according to claim 1, wherein the means for heating the joint of the metal square can 1 is a high-frequency induction heating coil. 3. The method for heating a metal square can according to claim 1, wherein the second-stage heating is performed in a state where the residual heat of the wound portion 6 or the side seam portion 3 heated in the first stage is 50 ° C. or more. . 4. The metal square can 1 heated in the first stage is
The method for heating a metal square can according to claim 1, wherein the atmosphere temperature in the transportation process before the stage of heating is 5 to 50C.