Process for the Production of Aerosol Dispensing and Similar Metal Cans

The invention relates to aerosol dispensing and similar metal cans adapted to contain a pressurized fluid in the form of a liquid, pulverulent or pasty product and/or a gas under pressure, of the type comprising a tubular body and a bottom fitted to the tubular body.

Aluminium aerosol dispensing cans in which the bottom is made in a single piece with the cylindrical wall of the can are known. The possibilities of shaping the upper part of such cans, intended to receive the valve and cup, are however very limited and it is notably difficult at the present to form a trunco-conical part making a distinct angle with a cylindrical lower part of the wall. Also, it is difficult to provide one-piece cans with a material other than aluminium since narrowing of a neck portion involves further difficulties. For these reasons, cans with fitted bottoms are still in great demand. However, the lower parts of known cans with fitted bottoms do not have the smooth and uniform aspect of one-piece cans, but the joint or seam forms a visible collar protruding from the periphery of the can. Such protruding seams have several disadvantages. Firstly, upon filling the cans, during which operation the cans are empty and hence light and unstable, they cannot bear against one another on a conveyor belt since the main part of their bodies are held slightly spaced apart from one another by their protruding seams. For the same reason, during transport, the cans tend to knock against one another which involves various risks, for example of damage to an outer coating or printed matter on the cans. Furthermore, since it is not possible to apply the cans against one another along their generatrices packaging several cans within a thermo-retractable envelope is practically impossible. Another drawback is that the seams form seats in which dirt can accumulate at a location liable to be contacted by the user's hand which is undesirable for example for disinfectant aerosol sprays for use by dentists or doctors. Finally, these protruding seams constitute waste space for stocking and displaying the cans by a retailer.

With a view to obviating these drawbacks, the applicant firstly proposed a reduction of the outer diameter of the seam to the outer diameter of the cylindrical part of the can body, but the seam nevertheless remained visible and still formed an objectionable seat for dirt. Secondly, the applicant has proposed pushing the seam inside the body of the can by a special process. The visible wall of the can thus obtained no longer has a discontinuity, which is an important advantage in this field where improvement of the aesthetic appearance is as important as improvements of purely mechanical characteristics.

The present invention aims not only to conceal the joint between the bottom and the side wall of the can, but to replace the conventional rolled seam type joint by a new type of joint relying mainly on a simple hooking action, and thus to simplify the manufacture.

According to the invention, there is provided an aerosol dispensing or similar metal can adapted to contain a pressurized fluid, comprising a tubular side wall and a separate bottom fitted to the side wall, wherein the side wall has an edge portion which is folded over inwardly to form with an adjacent portion of the side wall a channel, and the bottom has a peripheral skirt hookably engaged in said channel.

The invention also concerns a process for assembling such a can, comprising inserting the bottom with its peripheral skirt into an open end of the tubular side wall whereby the edge of the skirt is spaced in from the edge of the side wall, and inwardly folding over an edge portion of the side wall to form a channel in which the skirt is engaged.

The tubular side wall may be cylindrical, but not necessarily, and the same applies to the skirt which may be cylindrical, conical, pyramid-shaped or prismatic.

Preferably, the outer transverse dimensions of the skirt of the bottom, for example its diameter in the case of a bottom with a cylindrical skirt, are slightly greater than the corresponding inner dimensions of the side wall so that the bottom is force fitted in the side wall and maintains itself in the desired zone of the latter during the operation of forming the gutter.

When the can is placed under pressure, the bottom is applied by the pressure in the can in the channel of the side wall and, contrary to what could be expected, a sealing can be ensured by this contact under pressure.

It is however possible to improve sealing of the joint by using a synthetic resin or another suitable product, for example rubber. A particularly advantageous sealing process consists of employing the type of polymeric varnish with which the insides of aerosol cans are usually coated. To this end, the can and bottom are varnished and the bottom is put in place before polymerizing the varnish, this even preferably being carried out at the end of the operations, i.e. after forming the channel.

To sum up, the invention enables the bottom to be concealed inside the can body and to eliminate the seam-beading operation which is replaced by a folding operation.

The accompanying drawings show, by way of example, several embodiments of the invention. In the drawings:

FIG. 1 is an elevational view, half in axial cross-section, of a generally cylindrical aerosol can;

FIG. 1a is an enlarged scale view of a detail of FIG. 1; and

FIGS. 2 to 16 are schematic views of different embodiments in which means are provided for preventing a premature ripping off of the bottom after turning over thereof in the case of an overpressure.

The can shown in FIG. 1 has a generally cylindrical body formed by a cylindrical side wall 1, for example in aluminum, whose upper part 2 is trunco-conical and terminates with a rolled edge 3 adapted to receive a distributing valve, or more precisely a cup carrying this valve. The lower edge of wall 1 is folded back on itself to form a closed annular gutter or channel 4. The bottom 5 has a dished central part 5a, the concave face of which is directed outwards, and a cylindrical peripheral skirt 5b engaged in channel 4. The height of skirt 5b is greater than the height of the edge of the channel 4 so that the lower edge 5c of this skirt abuts against the bottom of the channel 4 so that a hooking of the bottom by its skirt is ensured. The pressure P in the filled can, which is of the order of 2.5 to 6.6 kg/cm.sup.2 at a temperature of 20.degree.C, acts at the lower edge 5c of skirt 5b with a pressure several times greater, this increase in pressure being proportional to the ratio of the area of the part 5a to the area of edge 5c which bears against the bottom of the channel 4. This pressure alone may, in certain cases, be sufficient to ensure a sealing of the can.

Placing and securing of the bottom takes place in the following manner:

Firstly, the bottom 5 provided with its skirt 5b is introduced into the open end of side wall 1 in such a manner that the edge 5c of the skirt is slightly spaced from the non-folded over edge of the side wall. Then the lower part of the side wall is folded inwardly and bent over to form the channel 4.

The bottom 4 is preferably initially introduced by an amount so that the edge 5c is inserted by a lesser amount than in its final position, i.e. the height of the part of the side wall extending beyond the edge 5c is less than the height of the finished channel 4. Upon forming of the channel, the bottom 5 is thus progressively axially pushed by its skirt 5b inside the tubular body, with the edge 5c of its skirt firmly abutting against the bottom of the channel 4. The fold can then be flattened by a milling or rolling operation, or left unflattened.

Aerosol cans generally have an inner coating of a polymeric varnish. Such a varnish may be used to form a fluid-tight seal of the joint. For this purpose, the inner face of wall 1 is coated with varnish 6 (FIG. 1a), then the bottom 5 is fixed in place before polymerization of the varnish. The bottom 5 may also be pre-varnished.

It is well known that the pressure inside aerosol dispensing cans increases rapidly with temperature and may reach a value of 12 kg/cm.sup.2 at a temperature of 50.degree.C. The international safety regulations stipulate that the concave bottom must turn over before the appearance of any leak. Also, it is stipulated that the pressure at which the bottom is ripped off must be equal to or greater than the pressure at which the bottom turns over. FIGS. 2 to 16 illustrate, by way of example, several embodiments of the invention adapted to increase the resistance of the turned over bottom to ripping off. One of the principles applied consists of forming a projection against which the bottom comes to abut when it turns over, the pressure of the bottom on this projection ensuring a pinching of the skirt so that an even greater pressure is necessary to cause ripping off of the bottom by deformation or unrolling of the skirt.

In FIGS. 2 to 15, the turned over bottom is shown in dashed lines.

In the embodiment shown in FIG. 2, the gutter or channel 7 of side wall 1 has an approximately circular and closed section. Upon turning over of the bottom 5 to position 5', the latter comes to press against the round upper surface of the channel at 7a. Under the effect of this pressure the edge 7b of the channel, directed approximately perpendicularly against the skirt of bottom 5, pinches this skirt and prevents bottom 5 from unrolling. The sharper the edge 7b, the more it will tend to penetrate into the material of the skirt and retain the bottom. In this case, the fold is open.

In FIG. 3, the channel has a vertical part 8a and an edge 8b bent over at right angles in the direction of the skirt of bottom 5. The effect is the same as in FIG. 2 with the difference that when the bottom 5 turns over it comes more rapidly to bear against the bent edge 8c of the channel. In this case, the fold is also open.

FIG. 4 shows a channel which has a vertical part 9a and an edge 9b bent over at right angles, but the latter is bent inwardly towards the axis of the can. It can be seen that when the bottom turns over, it comes into contact with the end of edge 9b even quicker.

The channel of FIG. 5 has a vertical part 10a whose edge is bent over to form a thickened part 10b used to pinch the skirt of the bottom when the latter turns over. The thickened part 10b may be obtained by milling or rolling the fold which is thus closed.

In the embodiment shown in FIG. 6, the channel has a vertical part 11a whose upper edge is bent inwards at 11b then outwards at 11c in a manner to combine the advantages of the embodiments according to FIGS. 3 and 4, the bottom when it turns over coming rapidly to exert a pressure on the channel, as in the case of FIG. 4 and this channel pinches the edge of the skirt as in FIG. 3.

In FIG. 7 the channel has a vertical part 12a terminated by an inwardly-directed rolled edge 12c.

The embodiment of FIG. 8 differs from that of FIG. 7 only by the fact that the rolled edge 13 is directed towards the wall 1.

In FIG. 9, the channel 14 is vertical as in FIG. 1 and the means for ensuring a pinching of the skirt 5b of the bottom are formed by an inner ring 15 fitted to the channel 14 during or after the fitting of the bottom. This ring 15 forms a projection against which the bottom comes to abut when it turns over.

FIG. 10 shows a channel with a vertical part 16a whose end 16b is bent over at an acute angle towards the wall 1. When the bottom turns over, there is, in addition to the pinching effect as described with reference to FIG. 3, a more pronounced effect of penetration of the edge of end 16b into the skirt. The skirt may also be shorter than in FIG. 3 so that the bottom comes rapidly into contact with the upper edge of the channel when it turns over.

In the embodiment of FIG. 11, the channel also has a vertical or substantially vertical part 17a terminating with a part 17b bent at an acute angle but the skirt 5b of the bottom has a peripheral undulation 5d engaged under the end of part 17b. When the bottom turns over, the skirt 5b is not only pinched but it comes to grip the part 17b by undulation 5d. In the variation shown in FIG. 11a, the undulation 5d is replaced by a peripheral fold 5e.

A gripping occuring when the bottom turns over is also provided in the embodiment shown in FIG. 12, in which the skirt 5b is folded upwardly and inwardly in a manner to come to hook under the outwardly bent edge of the channel which has a shape analogous to that of FIG. 3. The skirt 5b may be folded over prior to placing of the bottom, or simultaneously formed with the channel.

In FIG. 13, the edge of the channel has an outwardly-directed roll 18. The skirt 5b of bottom 5 is connected to the dished part 5a by a planar or substantially planar part 5g. The effect of part 5g is to increase the rigidity of the peripheral part of the bottom without preventing the dished part 5a from turning over.

In the embodiment shown in FIG. 14, the channel 19 of the side wall 1 is analogous to the channel 4 of FIG. 1, but the skirt 5b of bottom 5 is connected to the dished part 5a by a vertical or substantially vertical part 5h so that the bottom also has a channel formed by parts 5b and 5h, opposite to and engaging in channel 19. As in FIG. 13, the effect of this is to increase the rigidity of the peripheral part of the bottom whereby a higher pressure is required to rip it off.

In the embodiment of FIG. 15, the edges of channel 20 and skirt 5b are folded over one or another at 20a and 5i and are hookably engaged in one another, this hooking coming into play when there is an upward traction on skirt 5b following turning over of bottom 5. The folds can be formed by milling or rolling.

FIG. 16 is an underneath plan view of a can in which a reinforcement of channel 4 is obtained by forming vertical flutes 21 in the channel. Such flutes can be formed in any of the previously described embodiments.

Generally speaking, the operation of forming the channel may be carried out before or after printing the outer surface of the side wall. Moreover, the folded over part of the channel can also receive an imprint, such as a code, trade mark or advertising, but which will only be visible when the can is turned over.