EP2876055B1 - Sealing cap for a container - Google Patents

Description

Technical area

The present invention relates to a plastic closure cap, of the type consisting of an upper plate extending by a peripheral skirt on the inner wall of which are formed, in relief, segments of helical threads intended to cooperate in screwing with nets corresponding made on the outer wall of the top of the neck of a container, said skirt extending at its lower free end by a tamper-evident band.

State of the art

An essential characteristic of this type of plug is the internal thread segment profile of the plug, which must be designed to facilitate the installation and the centering thereof on the neck of the container to be closed.

Thus it is known to make slopes under the threads of the cap, but under the entire length thereof.

In this field of activity, a major problem concerns the demolding of areas that are heavily undercut. The release of the nets is very sensitive and their geometric construction meets very strict rules.

• Valeur de la contre dépouille du filet, en millimètre ;
• Pente du filet ;
• Rayons de raccordement entre la pente du filet et la coque du bouchon ;
• Largeur du filet ;
• Filet continu ou non ;
• Epaisseur de paroi du bouchon ;
• Diamètre du bouchon ;
• Taille des nervures extérieures ;
• Formes des nervures extérieures ;
• Températures de la matière au niveau des zones en contre-dépouille ;
• Etat de surface des formes du filet ;
• Respect des formes lié au type d'usinage au niveau du moule.

The good ejection of the cap thread at the demolding is a function of the following parameters:

• Value of the undercut of the net, in millimeters;
• Slope of the net;
• Connecting radii between the slope of the net and the shell of the cap;
• Width of the net;
• Continuous net or not;
• Wall thickness of the plug;
• Diameter of the plug;
• Size of the outer ribs;
• Forms of outer ribs;
• Temperatures of the material at the level of undercut areas;
• Surface state of the forms of the net;
• Respect of forms related to the type of machining at the mold.

All these parameters must be clearly defined in order to obtain a quality net. The modification of only one of these parameters can degrade the release of the nets and call into question all of this precarious balance, thus degrade the complete ejection of the plug.

• Une diminution du jeu entre le filet du bouchon et celui du col du contenant ;
• Une amélioration de l'accostage entre bouchon et col, lors de sa pose sur ligne de fabrication ;
• Une rigidification du filet (amélioration du survissage).

In order to improve the technical characteristics of the plug (screwing, opening torque, etc.), an increase in the slope under the threads has already been proposed. This increase of the slope brings:

• A decrease in the clearance between the cap thread and the container neck thread;
• An improvement of the docking between the stopper and the collar, when it is laid on the production line;
• A stiffening of the net (improvement of the surviving).

• Augmentation trop importante de la masse du filet, donc de la température dans cette zone, donc il y a un risque de dégradation lors de l'éjection du bouchon au démoulage. Pour obtenir une bonne éjection du bouchon dans ce cas, cela reviendrait à dégrader le temps de cycle en l'allongeant.
• Augmentation de manière trop importante de la masse du bouchon.

But this solution presents several risks, namely:

• Too much increase in the mass of the net, therefore the temperature in this area, so there is a risk of degradation during the ejection of the cap at demolding. To obtain a good ejection of the plug in this case, it would be to degrade the cycle time by lengthening it.
• Too much increase in the mass of the stopper.

According to a first phase of the inventive step, it was sought to reconcile all the known advantages of adding a greater slope under the nets, but without the disadvantages of increasing the mass, the degradation of the demolding , deformations and cycle time. It was felt that these slopes should only be used on part of the net.

It remained to define where to place this slope. In one place in the center, in two places, make a multitude of very thin ribs or a single thicker one.

• Positionner une seule nervure au centre aurait partiellement apporté l'effet voulu, mais au risque de créer au milieu du filet un obstacle sur lequel le filet du col aurait pu venir en collision, ce qui aurait dégradé la qualité de pose du bouchon.
• Mettre une multitude de nervures très fines tel que décrit dans le document US 4 674 643 (épaisseur 0,8 mm par exemple) aurait également permis d'atteindre l'objectif partiellement car cela aurait : compliqué leur usinage au niveau du mouliste ; rendu impossible un polissage manuel (il est connu que des surfaces brutes d'érosion non polies peuvent provoquer des problèmes de démoulage) ; augmenté les surfaces de contact entre le plastique et le moule, avec un risque d'augmenter l'adhérence du plastique, et donc de dégrader le démoulage.
• Mettre une seule nervure au début du filet aurait partiellement apporté l'effet voulu car rendu dissymétrique, le filet aurait présenté un risque de déformation lié au retrait de la matière plastique lors de son refroidissement.
• Mettre une seule nervure à la fin du filet aurait partiellement apporté l'effet voulu car, rendu dissymétrique, le filet aurait présenté un risque de déformation lié au retrait de la matière plastique lors de son refroidissement. Cela aurait créé, en fin de filet, un obstacle sur lequel le filet du col aurait pu venir en collision, ce qui aurait dégradé la qualité de pose du bouchon.

Various solutions have been studied:

• Positioning a single rib in the center would have partially had the desired effect, but at the risk of creating in the middle of the net an obstacle on which the neck net could have collided, which would have degraded the quality of installation of the cap.
• Put a multitude of very thin ribs as described in the document US 4,674,643 (thickness 0.8 mm for example) would also have achieved the goal partially because it would have: complicated their machining at the level of the mold maker; rendered impossible manual polishing (it is known that unpolished rough erosion surfaces can cause mold release problems); increased the contact surfaces between the plastic and the mold, with a risk of increasing the adhesion of the plastic, and thus to degrade the demoulding.
• Put a single rib at the beginning of the net would have partially had the desired effect because made asymmetrical, the net would have presented a risk of deformation related to the withdrawal of the plastic during its cooling.
• Putting a single rib at the end of the net would have partially had the desired effect because, made asymmetrical, the net would have presented a risk of deformation related to the withdrawal of the plastic during its cooling. This would have created, at the end of the net, an obstacle on which the net of the neck could have collided, which would have degraded the quality of installation of the cap.

Description of the invention

The object of the present invention is to remedy all the drawbacks of the existing or envisaged solutions as stated above and for this purpose concerns a plastic closure plug, of the type consisting of an upper plate extending by a peripheral skirt on the inner wall of which are made, in relief, segments of helical threads intended to cooperate in screwing with corresponding threads made on the outer wall of the top of the neck of a container, said skirt extending at its end free bottom, by a tamper-evident band, characterized in that each thread segment of said cap is stiffened, locally, exclusively and discontinuously, by two reinforcing ribs, made at both ends of the net segment, along a slope of degressive angle, from the top of the latter and being connected to the inner wall of the skirt of the cap.

The present invention also relates to the features which will emerge during the following description, which should be considered in isolation or in all their possible technical combinations.

This description given by way of nonlimiting example, will better understand how the invention can be made with reference to the accompanying drawings in which:

Brief description of the figures

• The figure 1 represents, in perspective, seen from below, the plug according to the invention.
• The figure 2 represents an enlarged view, detail A according to figure 1 , representing a net segment associated with two reinforcing ribs according to the invention.
• The figure 3 is an axial sectional view of a half cap according to the invention mounted on a neck portion of a container.

detailed description

The plug 1 generally designated in the figures is constituted by an upper plate 2 extending by a peripheral skirt 3 on the inner wall 3a of which are formed, in relief, segments of helical threads 4 intended to cooperate in screwing with corresponding threads 5 made on the outer wall 6a of the top of the neck 6 of a container 7, said skirt 3 extending at its free lower end by a tamper-evident band 8.

According to the invention, each thread segment 4 of said plug 1 is stiffened, locally, exclusively and discontinuously, by two reinforcing ribs 9A, 9B, made at the two ends of the thread segment 4, along a slope of angle α degressive, from the top 4a of the latter and being connected to the inner wall 3a of the skirt 3 of the cap 1.

Preferably, the reinforcing ribs 9A, 9B of a thread segment 4 are made under it, in identical and symmetrical shapes.

This makes it possible to obtain homogeneity during the removal of the plastic material in which the stopper is produced by molding.

As clearly visible on the figure 3 , each reinforcing rib 9A, 9B of a thread segment 4 has a trapezoidal front face "a", whose small upper base "b" merges with the vertex 4a of the segment 4, and whose large lower base "c""Merges with the inner wall 3a of the skirt 3.

The width of the large base "c" is preferably 2.6 mm. Thus the machining of the thread 4 will be in one and the same step, milling with numerical control, for a gain of precision. This width will also, if necessary, perform a manual polishing in the demolding direction.

The large lower base "c" of the front face "a" of ribs 9A, 9B of each thread segment 4 is tangentially connected to the wall of the skirt, via a leave "d" of predetermined radius.

This makes it possible to obtain continuity of the slope and ribs 9A, 9B. Thus, during the docking and screwing of the cap, no shape will come to hinder abruptly the advanced net 5 neck 6.

Each reinforcing rib 9A, 9B of a thread segment 4 has side faces "h", "f", also sloping, to form a generally truncal-pyramidal block.

This makes it possible to limit as much as possible any impact with the thread 5 of the neck 6. Thus, all contact is made in the most progressive manner possible.

The periphery of the shape defined by the thread segment 4 and its two end ribs 9A, 9B form rays "d", "g", "e" with the inner wall 3a of the skirt 3 of the stopper 1.

This is to improve the demolding.

• Rigidification des segments de filets 4 de bouchon 1, sans ajout de masse : ces nervures 9A,9B renforcent la résistance en flexion de chaque filet 4. Mais comme ces renforts ont été placés localement aux seuls endroits nécessaires, ils permettent, tout en assurant la rigidité voulue, un gain de masse significatif. Cette rigidification permet, lors d'un survissage du bouchon 1, de mieux résister aux efforts. Ces portions permettent donc d'obtenir un couple de survissage plus élevé.
• Gain de masse : en n'utilisant que deux portions de pente positionnées uniquement aux endroits nécessaires, cela permet de gagner en masse, point très important dans ce domaine d'activité.
• Diminution des zones chaudes : le fait qu'il y ait moins de matière plastique au niveau des filets 4 permet de diminuer les zones chaudes de la pièce. Limiter les zones chaudes dans une zone aussi sensible au démoulage que les filets permet d'améliorer l'éjection du bouchon 1. Cela permet donc de garder les caractéristiques techniques, tout en améliorant la qualité du démoulage (diminution des déformations), ainsi que la diminution du temps de cycle.
• Diminution du frottement : le fait de ne rajouter les nervures 9A,9B que par portion permet de diminuer les surfaces en contact entre le filet 5 du col 6 et le filet 4 du bouchon 1. Cette diminution du frottement permet une amélioration des conditions de vissage et facilite donc la pose du bouchon 1 sur les cols 6. Cette réduction des frottements permet également de diminuer l'effort de dévissage lors de l'ouverture du bouchon 1, ce qui est une caractéristique très recherchée de la part des utilisateurs.

The stiffening of the thread portions 4 by the end reinforcing ribs 9A, 9B provides the following advantages:

• Rigidification of thread segments 4 of plug 1, without adding mass: these ribs 9A, 9B reinforce the flexural strength of each thread 4. But as these reinforcements have been placed locally in the only necessary places, they allow, while ensuring the desired rigidity, a significant gain in mass. This stiffening makes it possible, during a survival of the stopper 1, to better withstand the forces. These portions therefore make it possible to obtain a higher oversteering torque.
• Gain mass: by using only two portions of slope positioned only in the necessary places, it allows to gain mass, very important point in this field of activity.
• Decrease in hot areas: the fact that there is less plastic in the nets 4 reduces the hot areas of the room. Limiting the hot zones in an area as sensitive to demolding as the nets improves the ejection of the plug 1. This therefore allows to keep the technical characteristics, while improving the quality of the demolding (reduced deformation), as well as the decreased cycle time.
• Reduction of the friction: the fact of not adding the ribs 9A, 9B only by portion makes it possible to reduce the surfaces in contact between the thread 5 of the neck 6 and the thread 4 of the plug 1. This reduction in friction allows an improvement of the screwing conditions and thus facilitates the installation of the plug 1 on the necks 6. This reduction in friction also reduces the effort unscrewing when opening the cap 1, which is a feature much sought after by users.

Claims (6)

1. A closure cap (1) made of plastic of the kind consisting of an upper plate (2) extended by a peripheral skirt (3), on the inner wall (3a) whereof are formed in relief segments of helical threads (4) intended to cooperate in screwing with corresponding threads (5) made on the outer wall (6a) of the top of the neck (6) of a container (7), said skirt (3) extending, at its free end, by a tamper-proof strip (8), characterized in that each segment of the thread (4) of said cap (1) is made rigid, locally, exclusively and discontinuously by two reinforcing ribs (9A, 9B) made at both ends of the thread segment (4) along a slope with a declining angle (α), arising from the peak (4a) of the latter and connecting to the inner wall (3a) of the skirt (3) of the cap (1).
2. The cap according to claim 1, characterized in that the reinforcing ribs (9A, 9B) of a thread segment (4) are made underneath it, using identical and symmetric shapes.
3. The cap according to one of claims 1 or 2, characterized in that each reinforcing rib (9A, 9B) of a thread segment (4) has a trapezoidal front face (a), the small upper base whereof (b) merges with the peak (4a) of the segment (4), and the large lower base whereof (c) merges with the inner wall (3a) of the skirt (3).
4. The cap according to claim 3, characterized in that the large lower base (c) of the front face (a) of the ribs (9A, 9B) of each thread segment (4) is connected tangentially to the wall of the skirt, through a fillet (d) of predetermined radius.
5. The cap according to one of Claims 1 to 4, characterized in that each reinforcing rib (9A, 9B) of a thread segment (4) has lateral faces (h, f), also sloping, to form a pyramidal trunk block overall.
6. The cap according to claim 5, characterized in that the periphery of the shape defined by the thread segment (4) and its two end ribs (9A, 9B) forms radii (d, g, e) with the inner wall (3a) of the skirt (3) of the cap (1).

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