DE19802953C2 - Process for producing a beverage can from sheet metal, in particular tinplate - Google Patents

Description

The invention relates to a method for manufacturing a beverage can made of sheet metal, in particular tinplate.

Beverage cans are usually made of tinplate or Made of aluminum. Nowadays mainly two-piece cans used, from a lower part and a lid. The lower part is in one piece and consists of a substantially cylindrical Can wall, with a can bath molded onto it. It is made by deep drawing and ironing on the manufactured in the manner described below. From a Sheet metal strip becomes a circular sheet metal disc, round blank called, cut out. By deep drawing it becomes this circular blank first pulled a bowl. This bowl must be in between the floor and cylindrical wall essential frustoconical transition, also inclined called, so that the actual can bottom in finished state has a diameter that is smaller is called the diameter of the cylindrical can wall. The Generating this bevel is great when deep drawing Problems because secondary wrinkles can occur. This Secondary folds occur to an increased extent when to Saving material and reducing weight the tin sheet with a smaller initial thickness and the same early higher strength is used. Thin sheet metal thicker and higher strengths lead to increased Secondary wrinkling. After deep-drawing the bowl by ironing the bowl height by about that Magnified three times by the cylindrical wall of the  Cups stretched in length and ent in thickness is reduced speaking. The high surface pressures in the ironing tools (stamps and rings) a coating previously applied to the sheet disturb, so that one does without the pre-painting and the interior and exterior painting only on the finished can he follows. At the end of the ironing process, the cans shaped into its final shape by the Ab stretch stamp in the can bottom and one outside the Floor tool (die) surfaced. Here, one turns towards the inside of the can domed dome, which is on its outer edge an annular setting edge merges. At this point edge then borders the finally shaped bevel on the outside on. Using air pressure on the inside of the cans floor, and / or by means of wiping fingers, it will finished lower part stripped from the ironing die. Around for cost reasons one as small as possible in diameter To be able to use the lid for its manufacture less sheet is needed, the diameter of the upper, open end of the lower part by teasing ver kleinert. Before teasing, the lower part gets on the Outside a base coat and the printing and on spray paint on the inside. After all painting drying is carried out beforehand. Ruch at water-soluble paints are solvents.

The use of beverage cans made of tinplate in damp tropical countries puts on cans for corrosion reasons floor is a problem due to scratches on the paint.  

In Japan there are also beverage cans on both sides a plastic coating made of PET (polyethylene terephthalate). The plastic coating is on a chrome-plated sheet metal strip (ECCS) in front of the cans Production applied, which is usually by laminating one prefabricated film is done. The bottom part is made by Deep drawing and further drawing with stretching, with a wall thinning of about 30 to a maximum of 50% is achieved. The plastic coating on both sides does not allow ironing because the plastic coating, especially on the outside of the can, would fail. Bare, chrome-plated sheet metal is for deep drawing and ironing are not suitable, since seizures appear on the tools. The experience with chrome-plated sheet metal Measures applied cannot be easily identified Tinplate transferred because plastic on chrome Sheet metal adheres better than tinplate.

In US 4,541,546 is a two-part beverage can made of sheet metal, e.g. B. tinplate or aluminum sheet, described ben. By deep drawing and ironing at one Embodiment of this beverage can a top herge which has a cylindrical can wall and a upper, domed end wall has. In the center of this upper end wall is one spout extending outward from the end wall, similar to a short bottle neck, molded on. The  However, making this spout requires several works Witnesses and work steps, whereby the overall manuf The cost of this beverage can is significantly more expensive become. The spout is supposed to be covered by a cap or a Plugs are closed, not described in more detail ben is how these parts look and with the grommet should work together. In addition, this is known Beverage can the upper part with the lower part by over lapping adhesive in the area of the cylindrical cans wall connected. For this purpose the lower part is in the Diameter reduced by teasing, so that it in the Upper part is insertable. To do this, the bottom margin of the upper part heated to enlarge the diameter, and the edge of the base cooled to pass through shrink knife. As a protection against corrosion the inside of the top and bottom Paint by spraying, dipping or electrostatic Coating after deep drawing and ironing applied.  

DE 31 05 538 A1 discloses a method for producing metal containers, at a metal blank made of electrical steel sheet by deep drawing first to one-sided open hollow body deformed with a radial flange and a cylindrical side wall becomes. By a subsequent ironing process, the side wall of the Hollow body while maintaining the wall thickness extended without the To affect the deep-drawn condition of the radial flange. It is closed in the End of the hollow body also punched out and flanged an opening. Finally, on that open end of the side wall a closure element placed, both a Deformation of the flange and the closure element edge takes place. With this known methods, however, no coated sheet metal is used and neither is Locking system inserted in the punched opening.

AT 321 694 relates to a method for producing sheet steel containers from a deep-drawn steel, in which a circular blank initially has a practically constant wall thickness is formed into a bowl by a single-stage or multi-stage deep-drawing process. By Subsequent ironing, this is reduced to the wall thickness brought desired finished height. However, this document contains no reference to special PET coatings that do not require deep drawing and subsequent ironing Survive damage.

EP 0 168 070 A1 describes a method for producing a container from sheet steel discloses, in which an opening is punched into and into an end wall Closure element is inserted.

A coated metal sheet for drawn cans is known from DE 40 29 553 A1, at a biaxially drawn polyester film under pressure on a base metal and Interposition of an adhesive layer is laminated on. The making of a Polyester film and the subsequent stretching, however, requires several operations, before the film can be laminated onto the sheet metal strip.

The object of the invention is to provide a method which is particularly cost-effective Manufacture of beverage cans from a tin coated with PET.  

This object is achieved by a method with the features of claim 1.

Advantageous procedural measures are specified in the subclaims.

With reference to the drawings, the special features and Advantages of the method explained in more detail below.

In Fig. 1, the new beverage can produced by the method according to the invention is shown partly in longitudinal section, partly in side view. It consists in wesent union from a can body 1 , a can bottom 2 and a reclosable closure system 3rd The can body 1 has a cylindrical can wall 4 and is closed at one, upper end by a one-piece with the can wall 4 consisting of an arched end part 5 , which forms the can head. In the center of the dome-shaped end part, a central opening 6 is seen before, which is formed by punching out. In this opening from the inside of the can body 1, the screw sleeve 7 is inserted, which has a radially outwardly projecting flange 7 a and a screw thread 7 b on its neck part. On this screw thread the screw cap 8 is screwed on from the outside.

The screw cap 8 has to ensure the Originali tätsschutzes a locking ring 8 a, the functions over Perfora is connected to the rest of the screw cap, Lich similarity as bottles with caps of mineral water is the case. When the screw cap 8 is closed for the first time, the locking ring snaps behind a locking shoulder 7 c not belonging to the screw thread 7 b on the screw sleeve, so that when the screw cap is opened later, the locking ring 8 a is torn or torn from the screw cap and one is torn off using the torn locking ring can recognize that the beverage can has already been opened.

The lower, initially open end of the can body 1 has to reduce the diameter D of the can wall 4 a frustoconical section 9 , which is also called indentation, and which is generated by so-called teasing. For example, B. the diameter D of the can wall 4 66 mm, then the frustoconical section 9 reduces the opening diameter D1 to 57 mm or 52 mm. This is for the purpose that a can bottom 2 with a smaller diameter can be used. This can base 2 made of sheet metal is connected to the can body 1 by flanging and folding to produce a known double fold 10 . The can can either be filled in such a way that the can body 1 , which is initially open at one end, is filled upside down with a screwed-on screw cap 8 and then the can base 2 is crimped open, or the can base can be crimped before filling the beverage can and the The can is then filled from above through the screw sleeve and then the screw cap 8 is screwed on. The former has the advantage that a higher filling speed of the beverage can can be achieved.

The screw cap 8 with locking ring 8 a and the screw sleeve 7 are preferably made of plastic, for. B. PE (polyester) or PET (polyethylene terephthalate) Herge provides. If necessary, tinplate or aluminum could also be used.

Preferably, the screw sleeve 7 with its flange 7 a is glued to the dome-shaped end part 5 because of the high internal pressures of the can or sealed using heat. The flange 7 a and also the locking ring 8 a ensure the corrosion protection of the cut edge of the opening 6 if the can body 1 consists of tinplate. Since the sealing on the bare or painted sheet would be subject to technical uncertainties, the can body 1 should have a plastic coating on the inside, which will be discussed in more detail below.

The new beverage can can be made from tinplate, aluminum sheet and other metal sheets. Tinplate is preferably used, however. To produce the can body 1 , a circular sheet metal disk, called a round blank, is cut out of a sheet metal strip. The sheet thickness of the blank, also called sheet insert thickness, can be between 0.16 and 0.30 mm, preferably about 0.20 mm. The blank is thermoformed to a single, shown in Fig. 2 bowl 1 'with a height H. When using tinplate, deep drawing is carried out in one or two stages with a drawing ratio β of 1.6 to 2.4. The cup 1 thus formed 'is converted then ironed in three or four stages to that shown in Fig. 1 the can body 1, wherein the original cup height H is approximately increased by three times and produced during ironing opposite to the cup wall thinner doses wall 4. When ironing, the wall thickness of the cup, which corresponds to the original sheet metal insert thickness, is reduced to one third with a degree of deformation ϕ. The initially flat bowl bottom is formed into a dome-shaped end part and the opening 6 is punched out at the end of the ironing by stripping the can body from the ironing die by means of air pressure and using the air pressure to convert the end part of the can body into a molding tool (die) with a dome-shaped Press deepening. In principle, a later external dome generation in connection with cutting the opening is also possible. Possibly only after the can edge has been trimmed, if the outer dome interferes with the existing machines. In this case, the floor remains flat when you iron it. The can body is then reduced in diameter at its open end by teasing, so that a can base with a correspondingly smaller diameter can also be used. Optimal material utilization is achieved by ironing. The thickness of the end part, which corresponds approximately to the original sheet metal insert thickness and the thickness of the can wall, which is approximately one third of the original sheet metal insert thickness, are optimally adapted to the requirements. In the area of the open end of the can body, the wall thickness is thickened by about 60 µm compared to the rest of the can wall.

If sheet metal without art to produce the can body The can body can be coated after stretching or teasing on the inside of the can side can be spray painted. Favorable  however, it is a sheet metal for the manufacture of the can body, especially a tinplate to use, which already previously ver as a sheet metal strip with a plastic coating would see.

Because of the high pressures that exist between the stamp and the inside of the can body facing the stamp during ironing, only PET (polyethylene terephthalate) can be used as the coating plastic. In this case, the blank is then punched out of a sheet of plastic coated with PET on one side and the plastic-coated side is turned towards the deep-drawing or ironing dies during deep-drawing and ironing. After ironing, the entire inside of the can body 1 is then lined with a PET layer, as is shown enlarged in FIG. 1.

A sheet is expediently used, on which the PET layer was applied by direct extrusion. By direct extrusion of a liquid PET film a heated sheet metal strip can be a special one good adhesion of the PET layer can be achieved, what ironing is of considerable importance.

In order to ensure a high formability of the PET, the PET layer should be appropriately amorphous to be brought. This amorphous state can be caused by Reheat the coated metal strip on a Temperature above the PET melting point and on closing quick quenching achieved in a water bath become. To keep the heating-up time as short as possible, can be reheating by induction heating be effective. The reheating will also  liability improves. Thanks to the amorphous PET layer ensures that despite the high deformation bean no cracks and pores in the PET layer occur.

Trials have also shown that there is an increase the safety of avoiding pores and cracks underneath Production conditions is appropriate after deep drawing and before ironing, the preformed can body To subject (bowl) to a temperature treatment. This Temperature treatment should be at a temperature of 180 to 200 ° C for a period of 1 to 5 minutes respectively. Because tinplate is a relatively inexpensive material is for the manufacture of cans, and PET the high Resists stresses when ironing should for carrying out the method according to the invention it is advisable to use PET coated tinplate, in which the PET layer is opened by direct extrusion was brought.

Tinplate coated with PET on both sides is expediently used for the can base 2 . PET is more scratch-resistant than painting and forms a permanent corrosion protection for the can bottom on the outside at the edge 2 a. The beverage cans made entirely of tinplate can therefore also be used for subtropical countries.

It has been found that when coating a sheet a particularly good adhesion is then achieved if the sheet metal strip is in the application area of the liquid Plastic film one above the melting point of each Has plastic lying temperature. The temperature  the metal strip should be about 10 ° above the plastic melting point. However, since the melting temperatures of the different types of PET between 230 and 280 ° C lying, arise from the direct coating of tinplate Problems. The melting point of tin is allowed of 232 ° C should not be exceeded, otherwise it will an iron-tin alloy layer formation comes and also liquid tin with the pressure roller at Extrusion process would come into contact. This would the tin surface will be affected and the tin could have the required lubrication on the outside of the can do not have the effect of ironing.

On the one hand to ensure the high level of adhesion of the PET Reach layer and on the other hand the tin layer not to damage the tinplate is therefore at the production of the plastic-coated tinplate proceed in such a way that between the tin surface and the PET layer an adhesion promoter made of thermoplastic Plastic is provided, its melting temperature ≦ 210 ° C.

The PET and the adhesion promoter are expediently through Coextrusion applied to the heated tinplate strip, which is between the melting temperature of the Adhesion promoter and the melting temperature of the tin lying temperature was heated.

As a result, damage to the tin layer is avoided at a temperature of the tinplate strip in the application area of the two-layer plastic film of approximately 220.degree. C., because this temperature is below the melting temperature of the tin of 232.degree. On the other hand, however, the temperature of the tinplate tape is at least 10 ° above the melting temperature of the adhesive, so that the desired good adhesion of the adhesive is achieved on the tin surface. The adhesion promoter ensures the desired good bond between tinplate and the outside PET layer. The thickness of the PET layer should be approximately 10 to 50 μm when carrying out the method according to the invention, and that of the adhesion promoter approximately 5 to 10 μm. The tinplate used has a thickness of 0.16 to 0.30 mm. The tin coating is 1.0 to 5.0 g / m ² per strip side, preferably 2.0 to 2.8 g / m ² .

The production of a PET-coated tinplate, which is particularly suitable for the production of a beverage can according to the method according to the invention, is described below with reference to FIG. 3. A tinplate band 11 is moved in its longitudinal direction and first heated by a heating device 12 . By means of a slot die 13 , a two-layer plastic film 14 is extruded, which consists of a PET layer 14 a and an adhesive layer 14 b made of thermoplastic material. The adhesion promoter 14 b has a melting temperature that is not greater than 210 ° C. The tinplate strip 11 was previously heated in the heating device 12 to such a temperature that it had a temperature of about 220 ° C. in the application area 15 of the liquid plastic film 14 above the melting point of the coupling agent and below the melting point of the tin. The plastic film 14 is then pressed onto the tinplate strip 11 by passing it through a gap between a pressure roller 18 and a roller 17 , which is referred to as a laminator roller. The laminator roll 17 lying against the plastic film 14 is kept at a temperature which is below the melting temperature of the PET. The laminator roll 17 should expediently be kept at a temperature in the range between 20 and 80 ° C. by cooling. The laminator roll 17 is advantageously cooled by water which is passed through the laminator roll 17 . There is also a deflecting roller 19 through which the tinplate strip 11 is guided with the plastic film 14 lying against the lamina roller 17 under tension over part of the circumference of the laminator roller 17 . The pressing of the liquid plastic film 14 onto the tinplate strip 11 should take place with a force of at least 60 N / mm based on the width of the tinplate strip. While the plastic film 14 abuts on the laminator roll 17, its PET surfaces must at least be converted layer before the surface of the laminator 17 is released from the plastic film 14 by cooling in the solid state. The diameter of the laminator roll or the wrap angle with which the tinplate strip is held in contact with the plastic film 14 on the laminator roll 17 must be chosen so that at a belt speed of at least 50 m / min at least the surface layer of the PET with a cooling rate to cool from a maximum of 400 W / m ² ° C to a temperature which is at least 30 ° C below the melting point of the PET before the contact between the plastic film and the laminator roll 17 is released.

It has proven to be useful if the width of the slot die 13 is wider than that of the tinplate tape. This leads to the fact that the plastic film 14 protrudes by 20 to 30 mm on each side of the tinplate strip.

The protruding plastic film is only separated after the plastic has cooled and solidified by means of the trimming rollers 16 , which are arranged on both sides of the coated tinplate strip.

As mentioned earlier, it is important that the PET be in an amorphous state. For this purpose, the PET-coated tinplate strip is passed through an induction heating device 20 , where it is brought to a temperature above the PET melting point. Exceeding the tin melting point is not critical in this case, since the iron-tin alloy layer formation is very low due to the short heating time and the liquid tin does not come into contact with a roll. By directly introducing the tinplate strip into a water bath 21 , the tinplate strip is finally quenched to room temperature at a high cooling rate.

Claims (19)

1. A process for producing a resealable beverage can from tinplate, with the following process steps:
Stamping a round blank from a tinplate coated with PET on one side, to which the PET layer was applied by direct extrusion as follows:
a sheet of tinplate is moved and heated in its longitudinal direction,
Using a slot die, a film of molten, thermoplastic, consisting of at least a PET layer and an adhesion promoter layer, the melting point of which is at most 210 ° C., is applied directly to one side of the moving tinplate strip,
the tinplate strip is previously heated to a temperature such that it has a temperature in the application area of the liquid plastic film which is above the melting point of the adhesion promoter and below the melting point of the tin,
the plastic film is pressed against the tinplate strip by passing it through a gap between two rollers, of which the roller on the plastic film, the laminator roller, is kept below the melting temperature of the PET,
the tinplate tape is guided with the plastic film attached to the laminator roll under tension over part of the circumference of the laminator roll and held in contact with the laminator roll over a contact time or contact length which is sufficient to at least the surface layer of the tape at a tape speed of at least 50 m / min Cool the PET at a cooling rate of at most 400 W / m ² ° C to a temperature which is at least 30 ° C below the melting point of the PET before the contact between the plastic film and the laminator roll is released,
in a final aftertreatment, the coated tinplate is heated to a temperature above the melting point of the PET and the plastic film is quenched by direct introduction of the tinplate strip into a water bath at a high cooling rate to room temperature,
Shaping this round blank by deep drawing and subsequent ironing, with the PET layer facing the deep-drawing and ironing dies to form a cylindrical can body that is open on one side, with a cylindrical can wall and a can head that is domed outwards,
Punching out a central opening directly in the dome-shaped end part,
Inserting a reclosable locking system with a screw cap into the central opening,
Seal the other, open end of the can body with a separate, round can base made of sheet metal by flanging and folding to produce a double fold. 2. The method according to claim 1, characterized in that the PET layer in amorphous state. 3. The method according to claim 2, characterized in that the amorphous state by reheating the coated metal strip to a temperature above of the PET melting point and subsequent rapid quenching in a water bath is achieved. 4. The method according to any one of the preceding claims, characterized in that the can body partially preformed by deep drawing between the Deep drawing and ironing a heat treatment at one temperature from 180 to 200 ° C.   5. The method according to claim 4, characterized in that the heat treatment 1 to 5 minutes. 6. The method according to claim 1, characterized in that a plastic-coated tinplate is used, in which between the Tin surface and the PET layer an adhesion promoter from one thermoplastic is provided, whose melting temperature ≦ 210 ° C is. 7. The method according to claim 6, characterized in that the PET and the Adhesion promoter applied to the heated tinplate strip by coextrusion be, which on a between the melting temperature of the coupling agent and the melting temperature of the tin was heated. 8. The method according to any one of the preceding claims, characterized in that the can head is formed at the end of the ironing by the Stripped the can body by means of air pressure from the ironing die and the air pressure is used with the end part of the can body in a die to press dome-shaped recess. 9. The method according to any one of the preceding claims, characterized in that that the can body at its open end by teasing in diameter is shrunk before the can bottom, which has a smaller diameter has as the cylindrical can wall, is folded. 10. The method according to any one of the preceding claims, characterized in that one from a screw cap and one-sided with a flange Screw sleeve existing closure system is used that the screw sleeve from the inside of the can body through the central opening of the dome-shaped end part is inserted until its flange on the inside of the  End part rests and that on the protruding from the end part, with a Screw thread provided part of the screw sleeve the screw cap is screwed on. 11. The method according to claim 10, characterized in that a closure system is used, the screw cap and screw sleeve are made of plastic. 12. The method according to claim 10 or 11, characterized in that the Screw sleeve is glued or sealed into the end part. 13. The method according to any one of the preceding claims, characterized in that a tin base made of sheet metal is used, with plastic on both sides is coated. 14. The method according to claim 13, characterized in that for the can bottom a tinplate coated on both sides with PET is used. 15. The method according to claim 1, characterized in that the tinplate strip on such a temperature is heated that it is in the application area of the plastic film one at least 10 ° C above the melting point of the coupling agent Temperature. 16. The method according to any one of claims 1 to 15, characterized in that the Press the liquid plastic film onto the tinplate tape using the Laminator roll with a force of at least 60 N / mm, based on the width of the Tinplate tape, done. 17. The method according to any one of claims 1 to 16, characterized in that the Cooling of the laminator roll is done by water flowing through the roll is passed through.   18. The method according to claim 17, characterized in that the laminator roll is kept at a temperature in the range of 20 to 80 ° C by cooling. 19. The method according to claim 1, characterized in that the rapid cooling in the aftertreatment takes place at a cooling rate of at least 1000 W / m ² ° C to a temperature below 20 ° C.