GB2090169A - Metal containers - Google Patents

Abstract

A can with a soldered or welded seam has an internal layer of thermoplastic tape (4) or other protective material covering the seam region. The protective material is bonded to the can body, at least partly by virtue of the heat of the welding or soldering process, in the case of a thermoplastic material. <IMAGE>

Description

SPECIFICATION Metal containers This invention relates to the production of cans and like containers, in particular for food and drinks.

The internal surfaces of such cans must have a protective coating, to prevent the contents of the can from picking up metals such as iron from the can material or lead from solder. In general, this protection is achieved by a lacquer or other protective coating applied to the sheet metal used to make the cans.

In the case of a seamed can, the seam must also be protected.

In the case of a soldered or welded seam, the metal adjacent to the seam must be left bare so that a soldered or welded joint can be produced.

The exposed metal is subsequently covered with a layer of lacquer or other material applied by spraying or by a roller. The need to apply the protective coating to the seam, and to allow the coating to dry afterwards, is inconvenient and slows down the production of cans.

It is also possible to form a seam by wrapping a thermoplastic tape around one edge of the metal, lapping the other edge over the outside of the tape, and fusing the tape by heat. The melted tape bonds the metal edges together and protects the cut edges. However, as the seam is bonded only by the fused thermoplastic material (for example nylon), this form of seam is relatively weak.

According to the present invention, a can or like container is made with a welded or soldered seam, and the region of the seam is protected by a tape or like sheet material.

The tape or other sheet material is preferably thermoplastic, so that it can be made to adhere to the internal surface of the container by the heat of the welding or soldering process.

The production of containers in this manner is quicker than when a lacquer protective coating is used, because it is no longer necessary to allow time for drying of the protective coating.

The protective material must be inert to the contents of the can and to the can material and must be stable. Polyamide plastics are particularly suitable but other thermoplastics, for example polyolefines, can be used.

Although a thermoplastic material is preferred, it is also possible to use a tape which is stuck to the inside of the can, covering the seam, by means of an adhesive.

In general, there is about 3 mm or less of bare metal on each side of the seam. A tape 10 mm wide will therefore in general provide adequate protection of this bare metal. The thickness of the tape must be sufficient to ensure that there are no imperfections even after fusing in the case of a thermoplastic tape.

The present invention is particularly advantageous in connection with welded seams.

A protective tape can be applied to the welded seams continuously immediately after the welding, using the welding heat retained in the seam to fuse the tape to the can.

The accompanying drawing illustrates one possible arrangement, based on the production of cans with welded seams by means of a Soudronic Wima welding machine.

Tin plate is shaped into a cylinder 1, with the cut edges, at the top in the drawing, overlapped by about 0.4 mm. The internal surface of the sheet metal is covered by a protective lacquer except for a strip 2 or 3 mm wide at the cut edges. The overlapped edges pass between inner and outer welding rollers 2, 3 which weld the metal edges together to form a seam.

Immediately downstream of the welding rollers, a nylon or similar tape 4 is applied to the hot seam by a pressure roller 5. The heat in the seam fuses the tape to the seam region, covering all the bare metal. To produce a perfect bond, further heat may be applied to the seam from outside.

The moving can draws the tape off a supply reel, so that fresh tape is brought into position for automatic bonding to the next can as the welded seam of the latter comes into engagement with the tape on the pressure roller 5. The cans thus are temporarily joined by the tape, which is cut off in any convenient way.

The drawing shows the seam formed at the top of the can, as in conventional equipment. It may however be preferable to form the seam at the bottom of the can so that the weight of the protective tape will cause it to lie against the seam.

For clarity, the drawing does not show the usual wire electrodes for welding, or the Z-guide for bringing the overlapping edge into the correct position for welding.

1. A method of making a can or like container of sheet metal, in which edges of the sheet metal are soldered or welded together to form a seam, and an impervious sheet material is applied to the region of the seam within the container and is secured thereto.

2. A method as claimed in claim 1 in which the sheet material is thermoplastic and is thermally bonded to the said region.

3. A method as claimed in claim 2 in which the sheet material is thermally bonded to the said region by heat arising from the welding or soldering of the seam.

4. A can or like container of sheet metal, having a welded or soldered seam, and impervious sheet material adhering to the region of the seam within the can.

5. A container as claimed in claim 4 in which the sheet material is a thermoplastic material.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Metal containers This invention relates to the production of cans and like containers, in particular for food and drinks. The internal surfaces of such cans must have a protective coating, to prevent the contents of the can from picking up metals such as iron from the can material or lead from solder. In general, this protection is achieved by a lacquer or other protective coating applied to the sheet metal used to make the cans. In the case of a seamed can, the seam must also be protected. In the case of a soldered or welded seam, the metal adjacent to the seam must be left bare so that a soldered or welded joint can be produced. The exposed metal is subsequently covered with a layer of lacquer or other material applied by spraying or by a roller. The need to apply the protective coating to the seam, and to allow the coating to dry afterwards, is inconvenient and slows down the production of cans. It is also possible to form a seam by wrapping a thermoplastic tape around one edge of the metal, lapping the other edge over the outside of the tape, and fusing the tape by heat. The melted tape bonds the metal edges together and protects the cut edges. However, as the seam is bonded only by the fused thermoplastic material (for example nylon), this form of seam is relatively weak. According to the present invention, a can or like container is made with a welded or soldered seam, and the region of the seam is protected by a tape or like sheet material. The tape or other sheet material is preferably thermoplastic, so that it can be made to adhere to the internal surface of the container by the heat of the welding or soldering process. The production of containers in this manner is quicker than when a lacquer protective coating is used, because it is no longer necessary to allow time for drying of the protective coating. The protective material must be inert to the contents of the can and to the can material and must be stable. Polyamide plastics are particularly suitable but other thermoplastics, for example polyolefines, can be used. Although a thermoplastic material is preferred, it is also possible to use a tape which is stuck to the inside of the can, covering the seam, by means of an adhesive. In general, there is about 3 mm or less of bare metal on each side of the seam. A tape 10 mm wide will therefore in general provide adequate protection of this bare metal. The thickness of the tape must be sufficient to ensure that there are no imperfections even after fusing in the case of a thermoplastic tape. The present invention is particularly advantageous in connection with welded seams. A protective tape can be applied to the welded seams continuously immediately after the welding, using the welding heat retained in the seam to fuse the tape to the can. The accompanying drawing illustrates one possible arrangement, based on the production of cans with welded seams by means of a Soudronic Wima welding machine. Tin plate is shaped into a cylinder 1, with the cut edges, at the top in the drawing, overlapped by about 0.4 mm. The internal surface of the sheet metal is covered by a protective lacquer except for a strip 2 or 3 mm wide at the cut edges. The overlapped edges pass between inner and outer welding rollers 2, 3 which weld the metal edges together to form a seam. Immediately downstream of the welding rollers, a nylon or similar tape 4 is applied to the hot seam by a pressure roller 5. The heat in the seam fuses the tape to the seam region, covering all the bare metal. To produce a perfect bond, further heat may be applied to the seam from outside. The moving can draws the tape off a supply reel, so that fresh tape is brought into position for automatic bonding to the next can as the welded seam of the latter comes into engagement with the tape on the pressure roller 5. The cans thus are temporarily joined by the tape, which is cut off in any convenient way. The drawing shows the seam formed at the top of the can, as in conventional equipment. It may however be preferable to form the seam at the bottom of the can so that the weight of the protective tape will cause it to lie against the seam. For clarity, the drawing does not show the usual wire electrodes for welding, or the Z-guide for bringing the overlapping edge into the correct position for welding. CLAIMS

1. A method of making a can or like container of sheet metal, in which edges of the sheet metal are soldered or welded together to form a seam, and an impervious sheet material is applied to the region of the seam within the container and is secured thereto.

2. A method as claimed in claim 1 in which the sheet material is thermoplastic and is thermally bonded to the said region.

3. A method as claimed in claim 2 in which the sheet material is thermally bonded to the said region by heat arising from the welding or soldering of the seam.

4. A can or like container of sheet metal, having a welded or soldered seam, and impervious sheet material adhering to the region of the seam within the can.

5. A container as claimed in claim 4 in which the sheet material is a thermoplastic material.