EP3965977A1

EP3965977A1 - Method for manufacturing long metal stopper caps comprising a skirt having a constant thickness

Info

Publication number: EP3965977A1
Application number: EP20723410.5A
Authority: EP
Inventors: Hervé STOPPIGLIA; Régine DEBREUX; Emilie LAE
Original assignee: Constellium Rolled Products Singen GmbH and Co KG
Current assignee: Constellium Rolled Products Singen GmbH and Co KG
Priority date: 2019-05-09
Filing date: 2020-05-06
Publication date: 2022-03-16
Also published as: MX2021012575A; US20220324010A1; JP2022531588A; WO2020225288A1

Abstract

Disclosed is a method for manufacturing metal stopper caps comprising the following sequence of steps: a) providing a strip or sheet made from aluminium alloy coated on both faces with a layer of varnish; b) a first cutting operation in order to obtain discs referred to as blanks; c) a step of stamping the blanks, in one or more passes, in order to form a stamped preform, comprising a head and a skirt; c') at least one drawing step consisting of passing the stamped preform through at least one drawing ring in order to lengthen the metal and make it thinner, so as to form a cap comprising a head preferably having a diameter of between 20 and 40 mm, and more preferably between 25 and 35 mm, a skirt preferably having a length of between 40 and 85 mm, more preferably between 40 and 83 mm, more preferably still between 40 and 80 mm, more preferably still between 40 and 70 mm, and more preferably still between 45 and 65 mm, the top of the cap being on the head side and the bottom of the cap on the side where the skirt ends, the skirt having a constant thickness of between 0.12 and 0.27 mm, and preferably between 0.15 and 0.25 mm, over at least 20% of its length starting from the bottom of the cap (and preferably up to 60% of its length starting from the bottom of the cap), and comprising a continuous and intact layer of varnish along the entire length of the skirt, on both the inside and the outside of the cap; d) an optional step of degreasing the cap; e) an optional step of printing and/or applying finishing varnish for protection and/or decoration.

Description

DESCRIPTION

Title: Method of manufacturing long metal caps comprising a skirt having a constant thickness

Field of the invention

The invention relates to the field of stopper caps comprising a metal outer shell made of aluminum alloy and in particular screw caps having a long skirt such that when the cap is unscrewed, the bottom of the skirt remains in place on the neck of the bottle. These capsules are intended for sealing containers, essentially glass bottles containing alcoholic beverages and in particular wine or spirits. The invention relates more particularly to a method of manufacturing these capsules making it possible to obtain capsules having a skirt of thickness less than the thickness of the blank and constant over its entire length, as well as a skirt having a layer of varnish. interior and exterior continuous and intact along the entire length of the skirt.

State of the art

Aluminum alloy sealing caps are typically manufactured as follows:

- A stamping press forms capsule blanks from a strip or sheet also called format, cut into blanks, varnished on both sides, with a typical thickness ranging from 0.15 to 0.25 mm without taking counts the thickness of the varnish. Depending on the height of the skirt (length of the capsule blank), one to three stamping passes may be required.

- These blanks are degreased in an oven at high temperature, typically 180 to 210 ° C, for a time ranging from 3 to 5 minutes, in order to remove the stamping lubricant.

- They are then lacquered over their entire outer surface and are passed in an oven to cook the lacquer.

- These lacquered blanks are printed on the skirt, typically by screen printing, a process known to those skilled in the art under the name of “Offset”, with final drying of the inks in an oven.

- An overprint varnish is finally applied in order to protect the printing, said varnish being dried during a passage in an oven.

- The blank thus obtained is provided with a gasket and / or an internal threaded plastic insert. It will be noted that all the aluminum alloys in question in what follows are designated, unless otherwise specified, according to the designations defined by G “Aluminum Association” in the “Registration Record Series” that it publishes regularly.

It will also be noted that all the percentages are expressed as percentages by weight, unless otherwise indicated.

Problem

Thus, the long capsules are obtained by a process comprising several stamping passes. However, these successive stamping passes result in a capsule whose thickness of the skirt is irregular. This irregularity can cause problems when using the capsule, for example, sometimes making it more difficult or sometimes too easy for the user to break the bridge line. The bridge line is the line along which the cap breaks when a user spins it around to open the bottle. The aim is to obtain a capsule that is more reliable on opening, for which the opening torque is less variable and more reproducible.

Some capsules can be obtained by a stamping step followed by a stretching step, but they are not long capsules and the process for obtaining them seeks to solve a particular problem:

- keep an identical shiny surface on all parts of the capsule, from the head to the skirt (see, for example, Constellium France patent application WO 2015/075324);

- keep a textured surface on the head and obtain an identical shiny surface over the entire skirt (see, for example, Constellium Neuf-Brisach patent EP 3 188 855);

- Obtain a discontinuous layer of varnish, present only at certain determined locations (see for example the Pechiney patent Food Packaging US 6,403,173).

For reasons of industrial efficiency, it is desirable that the varnish be added before the stamping and drawing steps. However, it is not certain that the varnish applied before stamping and stretching retains its integrity over the entire surface of the capsule, and in particular over the entire length of the skirt of the capsule, inside and out. the outside of the capsule.

On the other hand, it is advisable to obtain a constant thickness of the skirt but not too thin so that the skirt retains good mechanical properties and can receive the different shaping necessary for the use of the cap, in particular the molding. 1, the crimp line 3 (to hang the cap on the bottle) and the bridge line 2, as shown in Figure 1. The present invention has multiple advantages: making the thickness of the skirt uniform over its entire height by minimizing the quantity of material used, or by allowing the manufacture of taller capsules without increasing the quantity of material, while guaranteeing good mechanical properties and a continuous and intact varnish layer along the entire length of the capsule skirt.

The invention aims to solve the problem of compromise between the regularity of thickness of the skirt of the capsule while ensuring the integrity of the varnish applied before stamping and stretching over the entire length of the skirt, and while guaranteeing good mechanical properties of the skirt, by proposing a process that can be carried out under industrially economical conditions for the market for long caps for capping beverage bottles.

Object of the invention

The invention relates to a method of manufacturing metal closure caps comprising the following successive steps:

a) the supply of a strip or sheet, in aluminum alloy, preferably having a roughness Ra according to standard NF EN ISO 4287 (December 1998) of 0.2 to 0.8 μm, more preferably 0, 2 to 0.6 μm, coated on both sides with a layer of varnish;

b) a first cutting operation to obtain disks called blanks;

c) a stamping step, in one or more passes, preferably at least two passes, more preferably two or three passes, even more preferably two passes, of said blanks, preferably using a stamping lubricant , so as to form a stamped blank, comprising a head and a skirt;

c ') at least one drawing step consisting in passing the stamped blank through at least one drawing ring in order to lengthen the metal and thin it, so as to form a capsule comprising a head preferably having a diameter of 20 to 40 mm, more preferably 25 to 35 mm, a skirt preferably having a length of 40 to 85 mm, more preferably 40 to 83 mm, even more preferably 40 to 80 mm, even more preferably 40 at 70 mm, and even more preferably from 45 to 65 mm, the top of the capsule being on the side of the head and the bottom of the capsule on the side where the skirt ends, the skirt having a constant thickness of 0.12 to 0 , 27 mm, preferably 0.15 to 0.25 mm, over at least 20% of its length from the bottom of the capsule, and preferably up to 60% of its length from the bottom of the capsule , and comprising a continuous and intact layer of varnish over the entire length of the skirt, both inside and outside the capsule; d) an optional step of degreasing said capsule;

e) a possible printing and / or finishing varnishing step for protection and / or decoration.

The subject of the invention is also a metal closure cap manufactured by the method according to the present invention, which comprises a head, a skirt, the top of the cap being on the side of the head and the bottom of the cap on the side where the skirt ends, characterized in that the thickness of its skirt is constant over at least 20% of its length starting from the bottom of the capsule (and preferably up to 60% of its length starting from the bottom of the capsule) and is 0.12 to 0.27 mm, preferably 0.15 to 0.25 mm, and in that it comprises a continuous and intact layer of varnish along the entire length of the skirt, inside as on the outside of the capsule, the head of the capsule preferably having a diameter of 20 to 40 mm, more preferably 25 to 35 mm, and the skirt of the capsule preferably having a length of 40 to 85 mm, more preferably from 40 to 83 mm, even more preferably from 40 to 80 mm, even more preferably from 40 to 70 mm, and even more preferably entirely from 45 to 65 mm.

The invention also relates to a punch for stamping and stretching an aluminum alloy blank, characterized in that it has two different diameters along its length, a first diameter DI corresponding to the part of the punch coming into contact first. with the metal to be stamped and then drawn and a second diameter D2 corresponding to the part of the punch coming into second contact with the metal to be stamped and then drawn, the two parts having different diameters being connected to each other by a conical transition part , the first diameter DI being less than the second diameter D2, the difference in diameter between DI and D2 being from 0.02 to 0.1 mm, preferably from 0.03 to 0.07 mm.

Description of figures

[Fig. 1] Figure 1 is a diagram of a long capsule. Reference 1 represents the molding, reference 2 the bridge line, reference 3 the crimping line, reference 4 the capsule, reference 5 the head of the capsule, reference 6 the skirt of the capsule, which includes a upper part (reference 7) and a lower part (reference 8).

[Fig. 2] Figure 2 is a graph illustrating the evolution of the thickness of a capsule as a function of the part of the capsule considered. The abscissa axis corresponds to the curvilinear abscissa, that is to say the distance from the center of the head of the capsule (0) to the ends of the skirt (-40 and 40), in mm. The ordinate axis corresponds to the metal thickness, in pm. The Caps.l reference corresponds to a capsule after stamping alone. References Caps. 2 and Caps.3 correspond to two capsules after stamping and stretching according to the process of the present invention.

[Fig. 3] Figure 3 shows an advantageous punch according to the present invention. The reference L represents the total length of the punch, the reference DI the first diameter and the reference D2 the second diameter, as described below. The numerical values are given by way of example. The references A and B represent section planes.

[Fig. 4] Figure 4 shows a draw ring as used in the examples. D corresponds to the diameter of the drawing rings given in the table of examples.

[Fig. 5] Figure 5 is a photo of the capsules produced according to the example.

[Fig. 6] Figure 6 is a micrograph of a section of varnished metal before stamping and drawing, as used in the example below. Reference 9 corresponds to the aluminum alloy, reference 10 to the exterior varnish of a first sample, reference 11 to the interior varnish of another sample and reference 12 to the resin in which the samples were coated.

Description of the invention

The subject of the invention is a method for manufacturing metal closure caps comprising the following successive steps:

b) a first cutting operation to obtain disks called blanks;

c ') at least one drawing step consisting in passing the stamped blank through at least one drawing ring in order to lengthen the metal and thin it, so as to form a capsule comprising a head preferably having a diameter of 20 to 40 mm, more preferably 25 to 35 mm, a skirt preferably having a length of 40 to 85 mm, more preferably 40 to 83 mm, even more preferably 40 to 80 mm, even more preferably 40 at 70 mm, and even more preferably from 45 to 65 mm, the top of the capsule being on the side of the head and the bottom of the capsule on the side where the skirt ends, the skirt having a constant thickness of 0.12 to 0 , 27 mm, preferably 0.15 to 0.25 mm, on at at least 20% of its length from the bottom of the capsule (and preferably up to 60% of its length from the bottom of the capsule), and comprising a continuous and intact layer of varnish along the entire length of the skirt , inside and outside the capsule;

d) an optional step of degreasing said capsule;

Preferably, the strip or sheet of step a) is coated on both sides with a single layer of varnish.

Typically the blank has a thickness of 0.15 to 0.35 mm without taking into account the varnish.

Preferably, the blank has a diameter of 80 to 96 mm. According to the present invention, the blank can have two different diameters. According to a first variant, the blank may have a diameter of 90 to 96 mm, which corresponds to what is usually practiced in the field of long capsules. This variant can make it possible to produce capsules that are longer than what is usually practiced in the field of long capsules, for example from 60 to 105 mm. The additional length can thus be cut and then recycled. The advantage of the present invention here is to make it possible not to change all the production tools while allowing recovery of the metal not used to produce capsules of the same length but having a lower thickness than what is usually practiced in the field of long capsules.

According to a second variant, the blank may have a diameter of 80 to 92 mm, which corresponds to a diameter smaller than what is usually practiced in the field of long capsules. This variant can make it possible to produce capsules of the same length as what is usually practiced in the field of long capsules, for example from 40 to 70 mm. The advantage of the present invention here is to allow a saving of metal to produce capsules of the same length but having a lower thickness than what is usually practiced in the field of long capsules.

According to a variant of the present invention, the inventors have determined a formula, which could for example serve as a tool on an industrial scale, to make it possible to determine, with a margin of error of +/- 0.1 mm, the diameter D of the starting blank as a function of the diameter B and the height H of the capsule, as well as the initial metal thickness E0, the thickness of the skirt of the capsule after stretching E and the stretching rate Red. It should be noted that the stretch ratio Red is equal to 1- (E / E0). The formula is based on the relationship saying that the volume of metal of the starting blank (E0.nD ^2/4) equals the volume of metal in the final capsule ([E0. PB ^2/4] + [H. pBE]). Note that E is equal to E0. (L-Red). The formula is then the following, after simplification:

[Formula 1]

D ^A 2 «B ^A 2 + 4 BH! I -Rod)

Where D is the diameter of the starting blank in mm, B is the diameter of the capsule in mm, H is the height of the capsule in mm and Red is the stretch ratio.

Preferably, the stamped blank is axisymmetric in an axial direction of said blank. Preferably the stamped blank has a diameter of 27 to 31 mm and / or a thickness of 0.15 to 0.35 mm.

According to the present invention, the term “constant thickness” is understood to mean when the variation in thickness over the height of the skirt is less than 5%, preferably less than 3% relative to the total thickness of the skirt without counting the varnish. . By way of comparison, the variation in thickness over the height of the skirt after stamping is generally about 20% relative to the total thickness of the skirt.

In general, in the present description, the metal thicknesses are understood to exclude the varnish.

The minimum stretching rate is justified by the fact that the latter must at least bring the thickness of the whole of the skirt substantially uniformly to the value of the minimum thickness locally obtained after stamping. The latter depends on the stamping conditions (roughness of the tool, play, pressure of the clamp, lubrication).

It should be noted that the stamping step thickens the skirt, in a non-uniform manner over the length of the skirt (see Figure 2). Therefore, the thickness of the skirt of a stamped blank, after stamping and before stretching, is variable over the length of the skirt, and generally increasing from the head of the blank to the bottom of the skirt. The thickness of the skirt of a stamped blank, regardless of the length considered, is generally greater than the initial thickness of the blank before stamping.

It should be noted that the sheet, the strip and the blank have the same thickness, that is to say the initial thickness E0.

Since the stamping step leads to thickening of the skirt, a stretch rate can be negative, equal to 0% or positive. A stretch rate of 0% means that the initial thickness of the blank is found uniformly at the level of the skirt. A negative draw ratio means that the thickness of the skirt is made uniform by the stretching step but without reducing this thickness to the same level as the initial thickness of the blank. A positive stretch rate means that the thickness of the skirt is made uniform by the stretching step by reducing this thickness to a level below the initial thickness of the blank.

According to the present invention, the degree of stretching is preferably greater than or equal to 0%, that is to say that the initial thickness of the blank is found at least. According to the most common mode, the degree of stretching (1 - final thickness E / initial thickness E0 of the sheet or of the strip or of the blank) is preferably greater than or equal to 2.5%.

The maximum stretching rate is linked to the stretch limit before breaking (of the metal and / or of the varnish), intrinsic to the aluminum alloy / varnish complex, which must not be exceeded when drawing the bottom of the skirt, the thickest area after stamping. For example, in the case of an alloy of the AA3105 type, the maximum industrially accepted stretching rate is 40%. A maximum stretching rate of approximately 30% is then obtained to take account in particular of the limits of the varnish.

According to a preferred embodiment, the stretching rate is less than or equal to 30%.

Preferably, the varnish is drawable, that is to say that it is not damaged during stamping and stretching, and that it remains present and of good quality over the entire surface of the capsule, from head to skirt. The varnish is expected to form a continuous and intact layer along the entire length of the skirt, inside and out, even after stamping and stretching.

By way of example, the interior varnish, that is to say that applied to the side of the blank which will become the interior of the capsule, can be an acrylic varnish, preferably having a basis weight of 2 to 6 mg / m ² , more preferably from 3 to 5 mg / m ² . This interior varnish should generally be suitable for food contact. It can be applied, for example, in a thickness of 1 to 6 µm, preferably 2 to 5 µm. Its color can for example be golden, silver or white.

By way of example, the exterior varnish, that is to say that applied to the side of the blank which will become the exterior of the capsule, can be a polyester varnish, preferably having a basis weight of 3 to 17 mg / m ² , more preferably from 4 to 16 mg / m ² . This outer varnish can be applied, for example, in a thickness of 4 to 12 µm, preferably 5 to 11 µm. Its color can for example be golden, silver or white.

Advantageously, a lubricant can be used for the stamping step. The lubricant is preferably volatile and removed by heating. The same applies to the lubricant used for drawing which, advantageously, is volatile and removed by heating, typically in a pass-through oven or in an oven.

Furthermore, the same lubricant can be used for both stamping and drawing stages.

Preferably, the optional degreasing step is intended to remove the lubricant remains, to form a degreased capsule capable of being optionally varnished. Degreasing can be carried out using any known method. For example, the degreasing can be thermal or chemical, preferably thermal. Thermal degreasing can for example be carried out in an oven. The temperature of the thermal degreasing is preferably 180 to 210 ° C. The duration of the thermal degreasing is preferably 3 to 5 min. This degreasing step is optional, because it is mainly useful in the case where the process comprises a printing and / or varnishing step. Also, generally, either both stages are present or both stages are absent. Preferably, the method does not include steps d) of degreasing and e) of printing and / or varnishing.

Advantageously, the stamping and drawing steps are linked without any other intermediate step. Even more advantageously, the last stamping step and the drawing step are carried out in one and the same press stroke.

Finally, the aluminum alloy can be, but not exclusively, of the type AA3105 or of the type AA8011.

The subject of the invention is also a metal closure cap manufactured by the method according to the present invention, which comprises a head and a skirt, the top of the cap being on the side of the head and the bottom of the cap on the side where the skirt ends, characterized in that the thickness of its skirt is constant over at least 20% of its length starting from the bottom of the capsule and is 0.12 to 0.27 mm, preferably 0.15 to 0 , 25 mm, and in that it comprises a continuous and intact layer of varnish over the entire length of the skirt, both inside and outside the capsule.

Preferably, the thickness of the skirt of the capsule is constant up to 60% of its length starting from the bottom of the capsule. Preferably, the diameter of the head of the capsule is 20 to 40 mm, more preferably 25 to 35 mm. Preferably, the length of the skirt of the capsule is 40 to 85 mm, more preferably 40 to 83 mm, even more preferably 40 to 80 mm, still more preferably 40 to 70 mm, and even more preferably 45 to 65 mm. The capsule according to the present invention has all the characteristics presented in connection with the process according to the present invention.

Preferably, the capsule is axisymmetric in an axial direction of said capsule. Preferably, the capsule comprises a head having a thickness corresponding to the initial thickness of the blank, that is to say generally from 0.15 to 0.35 mm.

According to an advantageous embodiment, it is possible to use a punch such as that illustrated in FIG. 3, having a length L and two different diameters along its length, the diameter of the part of the punch coming into contact first with the metal to be stamped then to be drawn (= first diameter D1) being less than the diameter of the part of the punch which comes into second contact with the metal to be stamped and then to be drawn (= second diameter D2). According to this embodiment, the method according to the present invention uses a punch for the stamping / drawing step, the punch having two different diameters along its length, a first diameter D1 corresponding to the part of the punch coming into contact first. with the metal to be stamped and then drawn and a second diameter D2 corresponding to the part of the punch coming into second contact with the metal to be stamped and then drawn, the two parts having different diameters being connected together by a tapered transition part , the first diameter D1 being smaller than the second diameter D2, the difference in diameter between D1 and D2 being 0.02 to 0.1 mm, preferably 0.03 to 0.07 mm.

The first diameter D1 and the second diameter D2 are preferably 19 to 39.6 mm. The part having the diameter D1 preferably represents 25 to 35% of the height of the punch. The part having the diameter D2 is preferably 60 to 70% of the height of the punch. The transition portion is preferably 3 to 7% of the height of the punch. The length L of the punch is, in a manner known to those skilled in the art, to be adapted with respect to the length of the desired skirt. For example, D1 may be about 29.53mm, D2 about 29.58mm, and the transition portion about 5mm. The part having the diameter D1 in this case represents approximately 28.9% of the height of the punch.

This variant would make it possible to vary the thickness of the skirt of the capsule, the top of the skirt having a greater thickness than that of the bottom of the skirt. Preferably, according to this variant, the top of the skirt has a thickness of 0.15 to 0.35 mm, more preferably 0.12 to 0.27 mm, and the bottom of the skirt has a thickness of 0.12 to 0.27 mm, knowing that the thickness of the top of the skirt is greater than the thickness of the bottom of the skirt. It should be noted that the greater thickness of the upper part of the skirt would make it possible to guarantee good mechanical resistance for the realization of the possible molding, the line of bridge and the line of crimping, as well as good mechanical resistance when the bottle is opened by the end user.

The first diameter DI and the second diameter D2 are preferably 19 to 39.6 mm. The part having the diameter DI is preferably 25 to 35% of the height of the punch. The part having the diameter D2 is preferably 60 to 70% of the height of the punch. The transition portion is preferably 3 to 7% of the height of the punch. The length of the punch is, in a manner known to those skilled in the art, to be adapted with respect to the length of the desired skirt. By way of example, ID may be approximately 29.53 mm, D2 approximately 29.58 mm and the transition part approximately 5 mm, the part having as diameter ID then representing approximately 28.9% of the height of the punch.

In its details, the invention will be better understood with the aid of the examples below, which are not, however, limiting in nature.

Examples of realization

Tests have been carried out in order to demonstrate the effectiveness of the process according to the present invention for obtaining capsules having a reduced skirt thickness while maintaining an intact layer of varnish over the entire length of the skirt of the capsule. In the industrial process, it is in fact important that the varnish layer remains intact over the entire surface of the capsule, because said capsule is then generally subjected to a heat treatment, typically for 2 minutes at 160-180 ° C, and then to a print to decorate the walls of the capsule. If the varnish layer is not intact before these steps, the final capsule obtained will not meet the aesthetic criteria expected by the customer and the end user.

To check the quality of the varnish layer, and in particular the presence of this varnish layer over the entire surface of the capsule, a test is carried out using copper sulphate. This is a copper sulfate porosity test. This test is destructive and generally carried out on ten capsules by reference. The protocol is as described below. The copper sulphate solution is composed of 50 g of copper sulphate (CuSC) in the form of crystals to be dissolved in 950 g of demineralized water, to which 20 ml of 36% hydrochloric acid are added. The whole is then mixed with a stirrer.

The implementation of the test requires thermal degreasing. The capsules were then placed in a tank and immersed in the copper sulfate solution. The application time was 15 minutes. After this lapse of time, a simple observation with the naked eye makes it possible to see if the capsule has been attacked, each attack zone corresponding to a zone where there is no more varnish. The non-attacked areas are the same color as the original capsule, while the attacked areas are rust colored.

If there is no etched surface, then the varnish layer is present and intact over the entire surface of the capsule.

Several capsules, stamped in a single pass and then stretched, were produced according to the protocol described below. Aluminum alloy metal strips of the AA8011 type, having a roughness Ra according to standard NF EN ISO 4287 (December 1998) of 0.3 μm and an initial thickness E0 without varnish as given in Table 1 below , were cut in the format 100 mm x 300 mm. Said formats were then cut into blanks having a diameter of 64 mm using a cutting ring.

The blanks were varnished with a gold-colored varnish of the PPG-3117-3003 type for the interior of the capsules, and with a varnish as described in Table 1 below for the exterior of the capsules. The stamping step was carried out on said varnished blanks in order to obtain stamped blanks, with tools having the following characteristics (BUP 200): diameter of the punch of 33 mm and diameter of the stamping ring given in the Table 1 below.

The lubricant was of the type known under the Klüber reference Paraliq P12 (colorless paraffin-based oil). It was deposited using an automatic device commonly used in capsule manufacturing plants. The blank holder pressure was adjusted so as to obtain a stamped blank without folds.

The drawing step was carried out on the stamped blanks obtained according to the stamping step as described above, with tools having the following characteristics (BUP 200): diameter of the punch of 33 mm and diameter of the draw ring given in Table 1 below.

All the capsules tested made it possible to obtain a constant and intact layer of varnish over the entire length of the skirt following the copper sulfate test as described above. For each of the capsules, the thickness and height of the skirt were measured using a Mitutoyo brand micrometer and model 395-271-30. The thickness of the skirt of each capsule was measured at the level of dashes which can be seen in FIG. 5. Table 1 below shows the conditions of stamping and drawing as well as the results obtained.

[Table 1]

Measurements of the thickness of the skirt of the various capsules tested (such as those illustrated in Figure 2) were carried out using a Mitutoyo brand micrometer and model 395-271-30. Figure 2, and in particular the curves corresponding to Caps.2 and Caps.3 capsules obtained according to the present invention, clearly illustrates the reduction in thickness of the wall of the skirt of the capsules, by comparing with the thickness of the wall for the Caps.l capsule obtained with only one step stamping, without drawing.

Thus, the examples illustrate a possible reduction in the thickness of the skirt from 9 to 26%, while preserving the quality of the layer of varnish over the entire length of the skirt. These reductions in thickness can lead to a reduction in the quantity of metal of the order of 8 to 22%. Furthermore, various tests for manufacturing a capsule according to the present invention were carried out. They made it possible to obtain capsules whose skirt length was respectively 70 mm, 72 mm, 76.8 mm, 78.5 mm and even 78.7 mm. Regarding the thickness and quality of the varnish layer before stamping and drawing, the tested sheets were cut. Several cuts have been made. For each cut, several samples were cut and stacked on top of each other.

Regarding the thickness and quality of the varnish layer after stamping and stretching, the tested capsules were cut longitudinally. Several longitudinal sections were made.

The different samples were coated in a resin and polished, then they were observed under an optical microscope. The thickness measurements of the exterior varnish were carried out on the micrographs obtained. An example of the micrograph obtained is shown in Figure 6. Figure 6 is a sample before stamping and stretching. The micrograph in Figure 6 shows that the observation of the different layers (interior and exterior varnish, metal and resin) and the measurement of the thickness of the exterior varnish can be done easily because the different layers are clearly visible and have a clear separation.

The results obtained in terms of the thickness of the exterior varnish are reported in Table 2 below, in micrometers.

[Table 2]

For each varnish thickness value, 20 measurements were taken, at the level of the dashes that can be seen in FIG. 5. All the measurements were therefore carried out at substantially the same distance from the top of the capsule skirt. The standard deviation of the 20 measurements was 0.77 µm at most.

In addition to the thickness measurements carried out, the micrographs of the cross sections after stamping and stretching made it possible to see the continuity of the interior and exterior varnishes all along the skirt of the capsule.

Claims

1. A method of manufacturing metal caps comprising the following successive steps:

b) a first cutting operation to obtain disks called blanks;

c ') at least one drawing step consisting in passing the stamped blank through at least one drawing ring in order to elongate the metal and thin it, so as to form a capsule comprising a head and a skirt, the top of the capsule being on the side of the head and the bottom of the capsule on the side where the skirt ends, the skirt having a constant thickness of 0.12 to 0.27 mm, preferably 0.15 to 0.25 mm, over at least 20% of its length from the bottom of the capsule (and preferably up to 60% of its length from the bottom of the capsule), and comprising a continuous and intact layer of varnish over the entire length of the skirt, inside and outside of the capsule;

d) an optional step of degreasing said capsule;

2. Method according to claim 1 characterized in that the head of the capsule has a diameter of

20 to 40 mm, preferably 25 to 35 mm.

3. Method according to any one of claims 1 or 2, characterized in that the skirt of the capsule has a length of 40 to 85 mm, preferably 40 to 83 mm, more preferably 40 to 80 mm, even more preferably from 40 to 70 mm, and even more preferably from 45 to 65 mm.

4. Method according to any one of the preceding claims, characterized in that the blank has a diameter of 80 to 96 mm.

5. Method according to any one of the preceding claims, characterized in that the stretching rate (1- final thickness E / initial thickness E0) is greater than or equal to 0%, preferably greater than or equal to 2.5% .

6. Method according to any one of the preceding claims, characterized in that the stretching rate is less than or equal to 30%.

7. Method according to any one of the preceding claims, characterized in that the varnish used for the interior of the capsule is an acrylic varnish.

8. Method according to any one of the preceding claims, characterized in that the varnish used for the exterior of the capsule is a polyester varnish.

9. Method according to any one of the preceding claims, characterized in that the stamping and drawing steps are linked without any other intermediate step.

10. Method according to any one of claims 1 to 8, characterized in that the last stamping step and the drawing step are carried out in one and the same press stroke.

11. Method according to any one of the preceding claims, characterized in that a punch is used for the stamping / drawing step, the punch having two different diameters along its length, a first diameter DI corresponding to the part. of the punch coming into contact first with the metal to be stamped and then to be drawn and a second diameter D2 corresponding to the part of the punch coming into contact second with the metal to be stamped and then to be drawn, the two parts having different diameters being connected between they by a conical transition part, the first diameter DI being smaller than the second diameter D2, the difference in diameter between DI and D2 being from 0.02 to 0.1 mm, preferably from 0.03 to 0.07 mm.

12. Metal closure cap manufactured by the method according to one of claims 1 to 11, which comprises a head and a skirt, the top of the cap being on the side of the head and the bottom of the cap on the side where the skirt. ends, characterized in that the thickness of its skirt is constant over at least 20% of its length starting from the bottom of the capsule and is 0.12 to 0.27 mm, preferably 0.15 to 0, 25 mm, and in that it comprises a continuous and intact layer of varnish over the entire length of the skirt, both inside and outside the capsule, the head of the capsule preferably having a diameter of 20 40 mm, more preferably 25 to 35 mm, and the skirt of the capsule preferably having a length of 40 to 85 mm, more preferably 40 to 83 mm, even more preferably 40 to 80 mm, even more preferably of 40 to 70 mm, and even more preferably from

45 to 65 mm.