EP3071347B1 - Method for manufacturing brilliant metal sealing caps - Google Patents

Description

Field of the invention

The invention relates to the field of closure caps comprising an outer metal shell of aluminum alloy and in particular screw caps which comprise an inner insert typically made of plastic and threaded. These capsules are intended for capping containers, mainly glass bottles containing alcoholic beverages and especially wine or spirits.

The invention relates more particularly to a method of manufacturing these capsules to obtain a substantially uniform brightness on the top, or head, and on the "vertical" wall or skirt of the outside of the capsule.

State of the art

• Une presse d'emboutissage forme des ébauches de capsules à partir d'une bande ou tôle encore appelée format, découpée en flans, vernis sur leurs deux faces, d'épaisseur typique allant de 0,15 à 0,25 mm sans prendre en compte le vernis. Selon la hauteur de la jupe (longueur de l'ébauche de capsule), une à trois passes d'emboutissage peuvent être nécessaires.

The aluminum alloy capping capsules are typically manufactured as follows:

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

• Ces ébauches sont dégraissées en étuve à haute température, typiquement de 180 à 210°C, pendant un temps allant de 3 à 5 minutes, afin d'éliminer le lubrifiant d'emboutissage.
• Elles sont ensuite laquées sur toute leur surface extérieure et sont passées en étuve afin de cuire la laque.
• Ces ébauches laquées sont imprimées sur la jupe, typiquement en sérigraphie, procédé connu de l'homme de métier sous l'appellation d' « Offset », avec un séchage final des encres en étuve.
• Un vernis de surimpression est enfin appliqué afin de protéger l'impression, ledit vernis étant séché lors d'un passage en étuve.
• L'ébauche ainsi obtenue est dotée d'un joint et/ou d'un insert plastique intérieur fileté.

The brilliant appearance of the capsule is essentially given by the quality of the varnish. In some applications, rather high-end, the glossy appearance can be obtained on the final capsule by a metallization process whose rates are generally low.

• These blanks are degreased in an oven at high temperature, typically 180 to 210 ° C, for a period of time ranging from 3 to 5 minutes, to eliminate the stamping lubricant.
• They are then lacquered on their entire outer surface and are put in an oven to cook the lacquer.
• These lacquered blanks are printed on the skirt, typically in screen printing, a method known to those skilled in the art under the name of "Offset", with a 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 seal and / or a threaded inner plastic insert.

It will be noted that all the aluminum alloys referred to below are designated, unless otherwise indicated, according to the designations defined by the "Aluminum Association" in the "Registration Record Sériés" which it publishes regularly.

Problem

The growing interest in aesthetic solutions has led the Applicant to test the use of aluminum alloy strips of known quality to those skilled in the art under the name of "brilliant" or "high gloss" is that is, having a roughness Ra, measured according to standard NF EN ISO 4287, typically less than 0.15 μm, or even 0.015 μm in the case of "high gloss", for stamping the blanks of capsules.

However, after the stamping, the quality of the glossy appearance remains substantially unchanged on the head of the blank, but is very degraded on the skirt which has a more or less matte appearance.

This problem is well known in particular from the patent EP 1 304 217 B1 of "Italcoat", whose priority request in 2001, which describes it in paragraph [0005] and proposes a relatively complex process to solve it.

• Emboutissage de métal revêtu de vernis également sur la face correspondant à l'extérieur de l'ébauche de capsule ; c'est alors la brillance du vernis qui confère la brillance finale, en général de qualité moyenne, même si le métal de base est brillant, du fait que l'aspect devenu mat de la jupe est visible par transparence.
• Métallisation sur l'extérieur de l'ébauche de capsule finale, procédé généralement mis en oeuvre pour des capsules en matière plastique et requérant une brillance exceptionnelle, mais ce procédé est lent et coûteux et de ce fait limité au domaine de l'emballage cosmétique.

The solutions known industrially are of two kinds:

• Stamping metal coated with varnish also on the face corresponding to the outside of the capsule blank; it is then the brilliance of the varnish which confers the final gloss, generally of medium quality, even if the base metal is shiny, because the matte appearance of the skirt is visible by transparency.
• Metallization on the outside of the final capsule blank, generally used for plastic capsules and requiring exceptional brilliance, but this process is slow and expensive and therefore limited to the field of cosmetic packaging.

The invention aims to solve this problem by proposing a method retaining the initial glossy appearance over the entire surface of the blank, head and skirt, under industrially economic conditions for the market of caps for capping beverage bottles.

Object of the invention

1. a) l'approvisionnement d'une bande ou tôle, en alliage d'aluminium de qualité connue de l'homme du métier sous l'appellation de « brillant » ou « grand brillant », c'est-à-dire présentant une rugosité Ra, mesurée selon la norme NF EN ISO 4287, inférieure à 0.15 µm, typiquement revêtue sur au moins l'une de ses deux faces, généralement la face destinée à l'intérieur de la capsule, d'une couche de vernis emboutissable, c'est-à-dire qui ne subit aucune détérioration au cours de l'emboutissage,
2. b) une première opération de découpage en disques appelés flans,
3. c) une étape d'emboutissage, en une ou plusieurs passes, dudit métal en flan, typiquement à l'aide d'un lubrifiant d'emboutissage, de manière à former une ébauche emboutie, comprenant une tête et une jupe, typiquement axisymétrique selon une direction axiale,
4. d) une étape de dégraissage, thermique, typiquement à une température de 180 à 210°C, pendant un temps de 3 à 5 minutes, ou chimique en milieu alcalin, de ladite ébauche emboutie, destinée à éliminer typiquement les restes de lubrifiant, pour former une ébauche dégraissée apte à être éventuellement vernie,

et caractérisé en ce qu'il comprend, après, éventuellement enchaînée directement avec l'étape d'emboutissage, au moins une étape d'étirage consistant à faire passer l'ébauche emboutie par au moins une bague d'étirage afin d'allonger le métal et l'amincir.The invention relates to a method of manufacturing metal caps for capping comprising:

1. a) the supply of a strip or sheet, of aluminum alloy of known quality to those skilled in the art under the name of "brilliant" or "high gloss", that is to say having a roughness Ra, measured according to standard NF EN ISO 4287, less than 0.15 μm, typically coated on at least one of its two faces, generally the face intended for the inside of the capsule, with a layer of lacquerable lacquer, that is to say which does not undergo any deterioration during stamping,
2. b) a first operation of cutting into discs called blanks,
3. c) a step of stamping, in one or more passes, said blank metal, typically with the aid of a drawing lubricant, so as to form a stamped blank, comprising a head and a skirt, typically axisymmetric according to an axial direction,
4. d) a step of degreasing, thermally, typically at a temperature of 180 to 210 ° C, for a time of 3 to 5 minutes, or chemical in an alkaline medium, of said stamped blank, intended to typically eliminate the residues of lubricant, for forming a defatted blank that can be varnished,

and characterized in that it comprises, after, optionally chained directly with the drawing step, at least one drawing step of passing the stamped blank through at least one drawing ring in order to lengthen the metal and thin it.

Typically, the blank has a thickness of 0.15 to 0.25 mm without taking into account the varnish.

According to the most common mode, the draw ratio (1- final thickness / initial thickness of the sheet or strip) is greater than or equal to 2.5%.

In a preferred embodiment, it is less than or equal to 30%.

According to a particular embodiment, only the face intended for the inside of the capsule is coated with a varnish before stamping and the face intended for the outside of the capsule is only after the degreasing step.

In another embodiment, the two faces for the inside and outside of the capsule are coated with a varnish before stamping.

Advantageously, the lubricant used for stamping is volatile and removed by heating.

The same applies to the lubricant used for the drawing, which advantageously is volatile and removed by heating, typically in a passage oven or in an oven.

Moreover, the same lubricant can be used for the two stamping and drawing steps.

Advantageously, the drawing and stretching steps are chained in two integrated steps, that is to say without any intermediate step and even more advantageously, they are carried out in one and the same press stroke.

Finally, the aluminum alloy may be, but not exclusively, AA3105 or AA8011.

Description of figures

• The figure 1 is a schematic section of the capsule used for the tests, after stamping, in this case in a pass, and before stretching according to the invention. Its height h is 17.6 mm, its top or head or "high" has a radius R of 49.8 mm and is connected to the skirt or vertical wall A with a radius R of 2.8 mm
• The figure 2 schematically illustrates the embodiment of the roughness measurements according to the standard NF EN ISO 4287 in the long-to-left direction, here for a stamped capsule, and to the right in the cross-direction, here for a capsule pressed and stretched according to the invention.
• The figure 3 represents the roughness Ra in microns obtained for walls or skirts of capsule blanks, measured in the long direction from top to bottom of the wall, marked SL, or across at the top of the wall, marked ST:
  • For the capsule A, made according to the prior art from shiny metal, thus stamped and not stretched, always measured in the long direction from top to bottom of the wall, marked SL, or across at the top of the wall, marked ST,
  • For capsule B, repeat tests above,
  • For the capsule C, pressed and stretched according to the invention from glossy metal,
  • For capsule D, repeat of the tests above,
• The figure 4 represents in the same way the roughness obtained:
  • For the capsule A, stamped according to the prior art from glossy metal, on the top or top of the capsule,
  • For capsule B, repeat tests above,
  • For capsule C, pressed and stretched according to the invention from glossy metal, on the top or top of the capsule,
  • For capsule D, repeat of the tests above,
  • For the capsule E, stamped only according to the prior art from raw non-gloss rolling metal of the type known to those skilled in the art under the name "Mill Finish", (the two points SL and ST coincide),
  • For the reference F: on metal sheet metal flat brilliant starting, before stamping,
  • For reference point G: metal sheet metal flat milling mill finish "Mill Finish".
• The figure 5 represents the pattern, in graduated scale composed of optical combs, used to quantify the brightness of the capsule walls by applying the NF EN ISO 10215 standard of image sharpness characterization on anodized products to apply it to the characterization of the gloss.

Description of the invention

As previously mentioned, because of a growing market interest for aesthetic but economic caps, that is to say a cost compatible with the requirement of the market for beverage bottles and not that of products. the applicant has had the idea to test the use of aluminum alloy strips of quality known to those skilled in the art under the name of "brilliant" or "high gloss", that is to say say having a roughness Ra, measured according to standard NF EN ISO 4287, typically less than 0.15 microns, for stamping the blanks of capsules.

Alas, she found that after the stamping, if the quality of the shiny appearance remained unchanged on the head or top of the blank, it was very degraded on the skirt that had a more or less mast.

At the same time, the plaintiff had engaged in a program for reducing the thickness of said caps to minimize the amount of metal used. It has thus arrived to proceed to an additional stretching pass after the conventional stamping in one or more passes, the latter leading to a non-uniform skirt thickness which could therefore be optimized to a minimum. This type of stretching, also known as "sizing", is not used in the field of capping capsules and is used to date only in that of cans or bottles-drink.

In tests using metal of "brilliant" quality, it then unexpectedly found that the gloss was recovered at the end of said step and found on the wall or skirt of the capsule, the level of that of the top, or capsule head.

The interest of the invention was therefore multiple: uniformize the thickness of the skirt over its entire height by minimizing the amount of material used, or by allowing the manufacture of higher capsules without increasing the amount of material and finally, obtain a uniform level of gloss on the top or head and on the skirt or capsule wall.

The minimum rate of stretching is justified by the fact that the latter must at least bring the thickness of the entire skirt substantially uniformly to the value of the minimum thickness locally obtained after stamping (ie 0.203 mm in the case of the figure 1 ). The latter depends on the stamping conditions (roughness of the tool, play, clamping pressure, lubrication). This minimum rate is generally considered to be 2.5 or even 3%.

The maximum draw ratio is related to the limit of stretch before rupture, intrinsic to the alloy, which must not be exceeded during the drawing, or calibration, of the bottom of the skirt, the thickest zone (of 0.236 mm according to the figure 1 ). Its value " _max play" is given by the formula (1- _max play ₎ / (1-LIR) = e _max / e _init ) where LIR is the limit of stretchability of the metal, e _max is the maximum thickness of low skirt (0.236 mm depending on the figure 1 ) and e _init the initial thickness of the sheet (0.210 mm in the case corresponding to the figure 1 ).

In the case of an alloy of the AA3104 or 3105 type, the industrially acceptable stretching limit is 40%. A maximum draw ratio of approximately 30% is then obtained.

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

Examples of realization Stamping step

AA3105 alloy metal strips of quality known to those skilled in the art under the name "brilliant", with a Ra roughness of 0.08 μm, in a thickness of 0.210 mm (without varnish), were cut at 870 x 280 mm format.

The formats were cut into stamping blanks with a diameter of 58.70 mm using a cutting punch.

The first stamping pass was made on these unvarnished blanks with the following features:
Diameter of the punch: 34.80 mm; radius of the punch: 2.80 mm, ie a drawing ratio Re = Ø blank / punch Ø 1.69.

The diameter of the matrix was 35.30 mm and its radius 1.10 mm.

The roughness of the surface of the matrix in contact with the metal was Ra = 0.2.

The lubricant was of the type known as LAPPING OIL 67 from HENKEL.

It was deposited using an automatic device commonly used in capsule manufacturing plants.

The blanking pressure was adjusted to obtain a cup without creases.

This step made it possible to manufacture cups or capsules stamped referenced A and B as schematically represented in section at the figure 1 .

It is noted, in particular, that while the initial thickness of the metal is 0.210 mm, the minimum on said cups has increased to 0.203 mm while the maximum is 0.236 mm. This type of thickness profile is in fact characteristic of a cup obtained by stamping.

Drawing step

• Diamètre du poinçon : 34.8 mm
• Diamètre de la bague d'étirage à 10% : 35.178 mm

The second stretching pass was made on the cups previously stamped according to step 1 above, with the following features tools:

• Diameter of the punch: 34.8 mm
• Diameter of the drawing ring at 10%: 35.178 mm

jeu % étant le taux d'étirage, ici de 10 %, soit 0.1The diameter of the drawing rings corresponds to a negative clearance with respect to the initial thickness (here metal thickness = 0.210 mm) of metal between the diameters of the punch and the matrix and is calculated as follows: $$Ø\mathrm{Drawing\; ring}=Ø\mathrm{Punch}+\left(2\times \mathrm{thick}.\mathrm{metal}\times \left(1-\mathrm{Thu}\%\right)\right)$$

gambling% being the stretching ratio, here of 10%, ie 0.1

• Ainsi, pour l'épaisseur minimale de 0.203 mm, l'étirage réel est en fait de 7 %,
• Pour l'épaisseur maximale de 0.236 mm, l'étirage réel est en fait de 20 %.

In fact we saw, in step 1, that the thickness obtained in the skirt was not constant:

• Thus, for the minimum thickness of 0.203 mm, the actual drawing is in fact 7%,
• For the maximum thickness of 0.236 mm, actual stretching is actually 20%.

More generally, the minimum stretch is imposed by the minimum thickness of the skirt after stamping. In this case, for a minimum thickness of 0.203 mm, the minimum stretch to obtain a gloss recovered over the entire height of the skirt is 3.3%. This value, corresponding to the stretch necessary to obtain the minimum thickness of the skirt after stamping of 0.203 mm over its entire height, is obtained by the formula already mentioned (1- final thickness / initial thickness) where the final thickness is 0.203 mm and the initial thickness 0.210 mm.

Several of the most commonly marketed lubricants have been successfully tested, including tallow, "KLÜBERFOOD NH1 16-180" and "PARALIQ P12" lubricants from "KLÜBER Lubrication".

This step made it possible to manufacture drawn stretched capsules in accordance with the invention, referenced C and D in Figures 3 and 4 .

Results of the tests:

• La rugosité de surface, cette dernière étant d'autant plus brillante que la surface est lisse donc la rugosité faible,
• La netteté d'une image réfléchie par la surface en s'appuyant sur la norme NF EN ISO 10215 relative à la caractérisation de netteté d'image sur produits anodisés.

In order to quantify the criterion of gloss, two parameters are used:

• The surface roughness, the latter being all the brighter that the surface is smooth so the low roughness,
• The sharpness of an image reflected by the surface based on the standard NF EN ISO 10215 relating to the characterization of image sharpness on anodized products.

Surface roughness Ra

The roughness of the capsule, stamped and stretched according to the invention, was compared with the roughness of the capsule only stamped (according to the prior art), and finally with the roughness initial metal strip or sheet or starting format flat, before shaping the capsule.

On the capsule itself, the roughness was measured on the wall or skirt and on the top or top, partly partly flat, in the long direction (SL), from top to bottom of the wall, and in the direction through (ST) at the top of the wall, as shown on figure 2 .

On the flat metal, the roughness was measured in the rolling direction (SL) and in the cross direction (ST).

1. A : capsule emboutie selon l'art antérieur à partir de métal brillant,
2. B : répétition des essais ci-dessus,
3. C : capsule emboutie puis étirée selon l'invention à partir de métal brillant,
4. D : répétition des essais ci-dessus,
5. E : capsule emboutie seulement, selon l'art antérieur, à partir de métal brut de laminage non brillant du type connu de l'homme de métier sous l'appellation « Mill Finish », (les deux points SL et ST sont confondus)
6. F : métal en tôle à plat brillant de départ, avant emboutissage
7. G : métal en tôle à plat brut de laminage connu sous l'appellation « Mill Finish ».

The following codes will be used:

1. A: capsule pressed according to the prior art from shiny metal,
2. B: repetition of the above tests,
3. C: capsule pressed then stretched according to the invention from glossy metal,
4. D: repetition of the above tests,
5. E: stamped capsule only, according to the prior art, from non-gloss rolling raw metal of the type known to those skilled in the art under the name "Mill Finish", (the two points SL and ST coincide)
6. F: sheet metal with glossy starting plate, before stamping
7. G: sheet metal in flat rolling mill known as "Mill Finish".

The figure 3 compares the roughness of the walls or skirts of capsules A and B of the prior art with those of capsules C and D according to the invention.

It clearly shows that the invention makes it possible to divide the roughness of the wall by a factor of three to six, and this whatever the direction of measurement (SL or ST).

In addition, the roughness of the skirts of the capsules according to the invention are very similar in the long direction and in the cross direction, which is obviously of considerable importance because of its impact on the homogeneity of the gloss all over the skirt or wall.

The figure 4 compares the roughness on the top or top of the capsules A, B, C and D as well as on the capsule E embossed only, according to the prior art, from non-gloss raw metal "Mill Finish", and on the strips or sheets starting point before stamping F, glossy sheet, and G, mill finish sheet "Mill Finish".

It clearly shows, by comparison between the capsules (A, B) and (C, D), that on the top (or top) of the capsule, the roughness is unchanged, that is to say that the invention does not change the shine of the top of the capsule. It is higher than the initial roughness of the glossy metal, but remains lower than the roughness of a mill finish metal. This point demonstrates the interest of using as a starting sheet, a shiny metal to make the most of the initial shine on the top of the capsule and obtain, by drawing, an improved shine on the whole, including the skirt or wall.

These results are also identical for all the usual criteria for 2D or 3D roughness measurement (Rz, or Sk for example).

Reflected image sharpness:

We have here implemented the method of NF EN ISO 10215 image sharpness characterization on anodized products to apply it to the surfaces of skirts according to the invention.

Thus the graduated scale, composed of optical combs, as represented in FIG. figure 5 , and the rating, or scale of clarity, allowing a classification of the sharpness of the image, as in Table 1 below: <b> Table 1 </ b> Class 1 2 3 4 5 6 7 8 9 10 11 Width (mm) 2.0 1.75 1.5 1.25 1.0 0.75 0.5 0375 0.25 0188 0125

The test consists in placing the capsule, skirt or wall at a distance d from the optical comb pattern and evaluating the class beyond which the streaks of the pattern are no longer visible or, more precisely, are no longer visually dissociable. .

The results obtained for the capsules A and B according to the prior art as well as C and D, according to the invention, are indicated in Table 2 below: <b> Table 2 </ b> Distance from Capsules A and B (prior art) Capsules C and D (according to the invention) 0 mm 9 > 11 5 mm 8 > 11 10 mm 6 10

These results, by comparison between capsules A and B of the prior art and capsules C and D, according to the invention, show a very significant improvement in the sharpness, and therefore the corresponding gloss on the skirt of said capsules.

Claims (13)

1. Process for manufacturing metal closing caps comprising:

   a) supply of a strip or plate, made of aluminium alloy of grade known to those skilled in the art as "gloss" or "high gloss", typically coated on at least one of the two sides thereof, generally the side intended for the interior of the cap, with a layer of deep-drawable lacquer,

   b) a first cutting operation into disks referred to as blanks,

   c) a stamping operation, in one or a plurality of passes, of said metal in blank form, typically using a stamping lubricant, so as to form a stamped blank, comprising a head and a skirt, typically axisymmetric along an axial direction,

   d) a step of degreasing said stamped blank, intended to remove typically the lubricant residue, to form a degreased blank suitable for optional lacquering,

   e) an optional protective and/or decorative lacquering step,
   and characterised in that it comprises, after the stamping step, at least one drawing step consisting of passing the stamped blank through at least one drawing ring so as to elongate and thin the metal.
2. Process according to claim 1 characterised in that the blank has a thickness of 0.15 to 0.25 mm without lacquer.
3. Process according to any one of claims 1 or 2 characterised in that the drawing rate (1- final thickness/initial thickness) is greater than or equal to 2.5%.
4. Process according to any one of claims 1 to 3 characterised in that the drawing rate is less than or equal to 30%.
5. Process according to any one of claims 1 to 4 characterised in that only the side intended for the interior of the cap is coated with a lacquer prior to stamping and the side intended for the exterior of the cap is only coated after the degreasing step.
6. Process according to any one of claims 1 to 4 characterised in that both sides intended for the interior and exterior of the cap are coated with a lacquer prior to stamping.
7. Process according to any one of claims 1 to 6 characterised in that the lubricant used for stamping is volatile and removed by heating.
8. Process according to any one of claims 1 to 7 characterised in that the lubricant used for drawing is volatile and removed by heating.
9. Process according to any one of claims 1 to 8 characterised in that the same lubricant is used for the two stamping and drawing steps.
10. Process according to any one of claims 1 to 9 characterised in that the stamping and drawing steps are linked in two integrated steps, i.e. without any further intermediate step.
11. Process according to any one of claims 1 to 10 characterised in that the stamping and drawing steps are carried out in one single stroke.
12. Process according to any one of claims 1 to 11 characterised in that the aluminium alloy is type AA3105.
13. Process according to any one of claims 1 to 11 characterised in that the aluminium alloy is type AA8011.

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