JPH0588660B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a film cap by vacuum forming to cover the top and upper side surfaces of beverage cans having an easy-open structure such as cans and pull-tops.

[Prior Art] Canned goods generally consist of a can body, a can lid, and a can bottom, and the can body and can lid are made by rolling the periphery of the can lid around the upper edge of the can body and rolling it from the side. The top of the ridge is formed on the upper side of the can and joined.

To open this, use a can opener to cut off the lid just inside the top of the seamer ridge.Also, beverage cans such as beer and youth have a pull-top structure with a metal ring attached to the canopy. Lift the ring with your fingers and open it.

In this case, when the can is opened, the contents spill onto the can lid, or the contents are drunk by touching the rim of the can directly after opening, but the can lid and the sides around the top of the can become contaminated during the distribution process. They often have the disadvantage of being unhygienic.

Furthermore, even if there is no such contamination, consumers do not know what kind of contamination the can lid has been exposed to until after the can is manufactured and the food or drink is removed from the can, so consumers may not eat or eat the can. It has the disadvantage of making people feel anxious when drinking it.

It is sanitary to keep the can lid and its upper edge covered until just before drinking the can, and then remove the cover to take out the contents.

Based on this idea, the present inventor first shrink-wrapped the upper part of the can with a shrink film.
Although this was carried out with the idea that the purpose could be achieved easily, the problem occurred that the cans that were fixed simply by heat shrinking force would fall off the smooth surface of the can.

Further, depending on the type of canned goods, for example, canned beer, canned youth, canned mitsumame, etc., the canned goods are soaked in cooling water before being opened.

In this case, the space between the film of the can lid and the can lid was not airtight, and if the can lid was immersed in water, cooling water would enter the can lid and cause contamination.

In view of the above points, next, a film cap is created by applying an adhesive to the back side of the shrink film, or by laminating a low melting point synthetic resin film with an adhesive layer, and creating a film cap. A method was carried out in which a cap was placed over the top of the can and hot air was applied from the side to shrink the skirt portion of the film cap to the side of the top of the can and to make it adhere tightly with adhesive.

Furthermore, in order to improve the water resistance and airtightness of this film cap, the present inventor not only adhered the top side of the can by heat shrinking the shrink film, but also pressure-bonded the film cap to the top of the seamer ridge at the top of the can using an adhesive. We are developing and proposing a method to obtain higher sealing performance.

The shape of the film cap used here includes a canopy part that fits the canopy shape, a convex part that fits on the top of the seamer ridge on the upper edge of the can, and a flange-like part on the outside that is as high as the raw material film. It consists of a skirt portion that has a heat shrinkage rate.

[Problems to be Solved by the Invention] The number of beverage cans of this type currently on the market is enormous. Therefore, a huge number of film caps are required to be attached to the cans.

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel manufacturing method that can efficiently form and mass-produce adhesive film caps having the above-mentioned shape.

[Means for Solving the Problems] The present invention provides an adhesive layer on one side of a vacuum forming mold having a concave portion corresponding to the concave-convex annular shape of a film cap having a concave-convex surface that conforms to the rim and canopy surface of the can. Place the shrink film with the adhesive layer on top, and place it integrally inside the clamp frame while holding the shrink film with a clamp frame that clamps the shrink film on the vacuum forming mold. The sandwiched film is heated and softened by a heater that does not come into contact with the shrink film, which is installed in the mold, the inside of the vacuum mold is evacuated, the film is suction molded, and then the film is punched out leaving a skirt portion on the outside of the molded part. The present invention provides a method for producing film caps for canned goods.

Furthermore, in the present invention, the shape of the clamp frame is circular, and its diameter is the same as or slightly larger than the outer diameter of the concave part of the vacuum forming mold, for example, about 2 to 5 mm, so that the film outside the clamp frame is It is desirable that the heat shrinkage rate of this portion be kept approximately the same as that of the raw material film by preventing the film from being heated by the heater.

To ensure this purpose, it is desirable to cool the clamp frame with cooling water or the like, or to use the material as a heat insulator to prevent the temperature outside the clamp frame from rising.

The heater used in the present invention can also be shaped into a ring to match the molding location, and is structured to operate integrally with the clamp.

In this case, it is desirable to provide a cover on the top of the clamp to prevent heat from the heater from escaping from the top, as this allows constant and stable preheating.

If a heating plate is used as a heater, the gap between the film and the heating plate will be large when the clamp is closed.
The thickness is preferably about 0.5 to 3 mm.

If this distance is narrow and the temperature of the heating plate is high, there is a risk that the clamp will heat up before it secures the film, causing the film to shrink.

Furthermore, if they are too far apart, not only will heat be lost, but the molding cycle will become longer, reducing efficiency.

The preheating time is appropriately selected and set depending on the temperature of the heating plate, the distance between the film and the heating plate, the material and thickness of the film, and is usually about 0.5 to 5 seconds.

Although the temperature of the hot platen is higher than the softening temperature of the film used, it is better not to make it too high as much as possible, as this will give more leeway in working conditions, reduce molding loss, and improve yield.

The material of the film used in the present invention can be any thermoplastic resin, but examples include vinyl chloride resin, polyethylene, polypropylene, polystyrene, polyethylene terephthalate, polybutylene terephthalate, polyamide, etc. A heat shrinkable film having a heat shrinkage rate of 15% or more, preferably 30% or more can be used.

In the case of the present invention, it is more desirable to use a heat-shrinkable film produced by biaxial stretching since there is no anisotropy in the heat-shrinkage rate.

The thickness of the film used in the present invention is not particularly limited, but it can usually be about 10 to 200 microns.

If the film thickness is less than 10μ, there is no strength.
If it exceeds 200μ, it will be difficult to shrink by heat.

As the adhesive applied to the cover film of the present invention, any adhesive that can bond plastic film and metal can be used. For example, in addition to commercially available adhesives, a polymer film with a low softening point may be laminated to form an adhesive.

As for the adhesive used in the present invention, it is preferable to use a heat-sensitive adhesive because it is not sticky at room temperature, making it easier to perform the covering operation of the film cap, and also because it allows the annealing of the adhesive surface of the film cap to be carried out at the same time. It is also convenient because it eliminates the heat shrinkability of this part.

Examples of heat-sensitive adhesives include ethylene-vinyl acetate copolymer adhesives, copolyester adhesives, polyamide adhesives, atactic polypropylene adhesives, ethylene-ethyl acrylate copolymer adhesives, and polyurethane adhesives. A tackifier such as a petroleum resin, rosin, or pinene resin can be suitably used.

When these heat-sensitive adhesives are used, the pressure-bonding plate can be heated to melt the heat-sensitive adhesive, and after cooling, the pressure-bonding plate can be removed to complete the bonding.

[Examples] The details of the present invention will be explained below with reference to Examples shown in the drawings.

In the figure, reference numeral 1 denotes a vacuum forming mold, which has a concave shape corresponding to the shape of the film cap 2 shown in FIGS. 3 and 4. The film cap shown in FIGS. 3 and 4 is suitable for beer cans, and has a downward slope on the inside from the top 4 of the peripheral skirt portion 3, and a film cap formed on the top surface of the beer can (not shown) at the bottom. A groove 5 corresponding to the circumferential groove 5 is formed. As shown in FIG. 5, this film cap 2 has a heat-sensitive adhesive layer 7 coated on the back side of a biaxially stretched shrink film.

Therefore, the vacuum forming mold 1 has a concave shape from the top surface 8, a peripheral wall 9 corresponding to the skirt portion 3 of the film cap 2, and a ring-shaped mold forming the top portion 4 of the film cap 2 at the bottom thereof. It has a concave groove 10, and a protrusion 11 corresponding to the concave groove 5 of the film cap 2 on the inside thereof. However, in the case of a cap that does not require a groove on the top surface of a youth can, etc., the above-mentioned protrusion 11 is not necessarily necessary. A suction hole 12 for vacuum suction is provided at the bottom of the groove 10 and inside the protrusion 11.

In the figure, reference numeral 13 denotes the long shrink film part before mold forming, which consists of the shrink film 6 and the adhesive layer 7 as described above, and the vacuum forming mold 1 with the adhesive layer 7 as the upper surface.
Continuously place it on the top surface of the

A clamp frame 14 is provided to be movable up and down, and clamps the film 13 on the vacuum forming mold 1 by lowering it. A heater heating plate 15 for preheating the film 13 is provided inside the clamp frame 14, and the film 13 is preheated by the radiant heat of the heater heating plate 15, that is, without contacting the film 13. It is preferable to use, for example, an infrared lamp or the like as the heater 15, which has a good directivity of heat rays, since it is possible to prevent heat diffusion and preheat only the center of the film.

This clamp frame 14 also holds the film cap 2.
By making the clamp frame circular to match the shape of the mold and making its inner diameter match or slightly larger than the outer diameter of the concave mold, heat will not reach the flange 20 on the outer periphery of the skirt 3 of the cap 2. It is preferable that the high shrinkage rate of the raw material shrink film remains in this part as it is, and that the adhesion to the side surface of the upper end of the can can be enhanced during shrinkage.

However, if the heater 15 has a good heat ray direction, the clamp frame 14 does not necessarily have to be annular, but may be square as shown by the dotted line in FIG. 3. .

Therefore, in the method of the present invention, after the film 13 is placed on the vacuum forming mold 1 with its adhesive layer 7 facing upward, the clamp frame 14 is lowered to remove the film 1.
3 is held between vacuum molding molds, and the film 13 is preheated by a heater 15. At this time, since the adhesive layer 7 is present on the upper surface of the film 13, the heater 15 is not brought into contact with the film 13, but is preheated at a distance of, for example, 0.5 mm to 3 mm, depending on the type of heat source.

At the same time, the inside of the mold is vacuum-suctioned through the suction hole 12 to form the preheated film 13 as shown in FIG.

After molding, the film cap can be obtained by punching out the film, leaving the skirt part intact.

In this example, between the vacuum forming process and the punching process, a process is performed in which a long formed film is turned over and fed onto the can, and a film cap is bonded to the top of the seamer ridge on the top of the can. The process of punching out the skirt portion of the film cap and finally the heat shrinking process of the skirt portion can be carried out simultaneously with the method of the present invention to form the film cap of the present invention and seal the top of the can.

[Effects of the Invention] In the method of the present invention, a shrink film having an adhesive layer on one side is placed on a vacuum forming mold corresponding to the shape of the film cap with the adhesive layer facing upward, and the shrink film is placed inside the clamp frame. Since the film is preheated with a heater without coming into contact with the film and then held between the clamp frames for vacuum forming, it has the advantage that even films with an adhesive layer can be mechanically produced in large quantities. In the method of using an annular clamp frame, the heat from the heater does not reach the outside of the film clamped by the clamp frame, that is, the outer circumference of the skirt portion of the film cap, and the film in this area has a heat shrink function. This has the advantage that a film cap can be formed with a sufficient amount of residual material remaining, and a film cap with a large tightening force can be obtained.

[Brief explanation of the drawing]

The drawings show an embodiment of the method according to the invention, FIG. 1 showing the state before operation of the method according to the invention, and FIG. 2 showing the state after operation of the method according to the invention. FIG. 3 is a plan view of a film cap formed by the method of the present invention;
FIG. 4 is a sectional view, and FIG. 5 is an enlarged sectional view of the film. The symbols in the figure are: 1...Vacuum forming mold, 2...Film cap, 3...Skirt portion, 4...Cap top, 5...Cap groove, 6...Shrink film, 7...Adhesive layer , 8... Mold top surface, 9... Peripheral wall, 10... Mold groove, 12... Suction hole, 14
. . . Clamp frame, 15 . . . Heater, 20 . . . Highly shrinkable collar portion.

Claims (1)

[Claims] 1. A shrink film having an adhesive layer on one side is placed on a vacuum forming mold having a concave portion corresponding to the concave-convex annular shape of a film cap having a concave-convex surface that conforms to the rim and canopy surface of the can. The shrink film is placed on the vacuum forming mold with the adhesive layer facing upward, and the shrink film is integrally provided inside the clamp frame while the shrink film is held between the clamp frames that sandwich the shrink film on the vacuum forming mold. A film for canned goods, characterized in that the sandwiched film is heated and softened by a non-contact heater, the vacuum molding mold is evacuated to form the film by suction, and then the film is punched leaving a skirt portion outside the molded part. Cap manufacturing method. 2. The method for producing a film cap for a can according to claim 1, wherein the heater is a heating plate and the clamp also serves as a cover for the heating plate. 3 The shape of the clamp frame is circular, and its diameter is the same as or slightly larger than the outer diameter of the concave part of the vacuum forming mold, so that the film on the outside of the clamp frame is not heated by the heater, and the heat in this part is 3. The method for manufacturing a film cap for canned goods according to claim 1, wherein the shrinkage rate is maintained substantially the same as the heat shrinkage rate of the raw material film.