EP4230544A1

EP4230544A1 - Stopper, sealing system and tin for liquids

Info

Publication number: EP4230544A1
Application number: EP23156710.8A
Authority: EP
Inventors: Fabio CEREDI
Original assignee: F Ceredi SpA
Current assignee: F Ceredi SpA
Priority date: 2022-02-16
Filing date: 2023-02-15
Publication date: 2023-08-23
Also published as: IT202200002882A1

Abstract

A tin for liquids, in particular paints, provided with a sealing system with an stopper (8) (8;) made of a polymeric material and having a diaphragm (18) configured to be torn out, in use, at the moment of the first opening; said diaphragm (18) having a removable portion (19), which is delimited laterally by at least one line of weakness (20; 201, 2011); the removable portion (19) having a gripping element (21) which is configured to be grabbed, in use, by a user; said diaphragm (18) having an incision (k) extending along a side perimeter (p1) and locally reducing the depth of the diaphragm (18); wherein a portion of said incision (k) along the perimeter (p1) constitutes a respective part of one of the lines of weakness (20; 201, 2011).

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority from Italian Patent Application No. 102022000002882 filed on February 16, 2022 , the entire disclosure of which is incorporated herein by reference.

FIELD OF THE ART

The present Patent Application for an invention relates to a stopper, a sealing system and a tin, in particular a tin for liquids.

PRIOR ART

A tin for liquids, such as paints, of the known type comprises a cup-shaped body having a longitudinal axis and an upper opening surrounded by a substantially tubular rim.
A tin for liquids of the known type also comprises a sealing system configured to seal the tin at the rim.
A sealing system of the known type comprises, in turn, a stopper and a cap.
The stopper is configured to be applied to the rim of the tin. Typically, the stopper comprises: an annular edge configured to engage by pressure with the rim of the tin; a tubular abutment configured to extend longitudinally partially into the tin; and an outer collar that protrudes longitudinally from the annular edge towards the outside of the tin. Generally, the stopper comprises a tamper-evident tear-off diaphragm which, in use, seals the tin tightly and is configured to be manually torn out by a user when first used.
The cap is configured to be applied to the outer collar of the stopper, generally the cap may be applied by screwing or press-fitting.
In the field, it is known to automatically apply a pre-assembled sealing system of the known type to the rim of a tin.

DISCLOSURE OF THE INVENTION

In the sealing systems of the known type, the diaphragm has a removable portion, which is delimited laterally by a line of weakness and is attached to a gripping element configured to be gripped, in use, by the user in such a way as to tear out, removing, both the removable portion and the entire diaphragm when the tin is first opened. The gripping element is configured to be manually gripped directly by a user, usually without using tools.
The line of weakness (also known as the half-cut) constitutes the tear path of the diaphragm. In known solutions, in order to open the diaphragm, it is necessary to apply a vertically-directed upward tearing force. This represents a problem especially in large-sized stoppers, namely stoppers with diameters greater than 70 mm. In fact, in this case, in order to be able to open the tin after grabbing the gripping element, a user must raise his arm upwards by bringing his elbow even higher than his chin. This movement is particularly uncomfortable.
In addition, in the systems of the known-type, unfavourably, the line of weakness is positioned in a substantially central portion of the diaphragm, which is the most stressed and everted zone, this being particularly relevant. In fact, in order to make tins for the transport of dangerous goods comply with the standards, in particular according to UN standards and ADR, RID, IMDG, IATA, ICAO regulations; tins must pass certain tests including: falls from height and hydraulic pressure. During these tests, the diaphragm expands by everting outwards due to internal pressure (hydraulic pressure tests) and water hammer (in falls) .
Therefore, the sealing systems of the known type, in order to pass compliance tests, must have a line of weakness with such a depth that, while ensuring the appropriate airtightness of the tin, requires the end user to apply an excessive tearing force on the diaphragm. In this regard, it should be noted that sealing systems of the type described above are made of a polymeric material, namely a material that deforms plastically. Therefore, in order to tear the diaphragm, a user must apply a breaking force such as to exceed the plastic deformation of the material at the line of weakness. A tearing force causing the diaphragm to progressively tear is transmitted by keeping on pulling the gripping element.
However, upon complete removal of the diaphragm, any excess tearing force is transmitted (due to the law of conservation of the mechanical energy) from the diaphragm to the body of the tin, substantially releasing itself in the form of a jolt of the tin itself, which can cause the leakage of material out of the tin. Together with the vertical direction of the tearing force, it results in practice in discomfort for the user and the risk of splashing.
The aim of the present invention is to provide a stopper and a sealing system that overcome the above-mentioned problems.
According to the present invention, there is provided a stopper and a sealing system according to the appended Claims.
According to the present invention, there is provided a tin according to the attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be now described with reference to the enclosed drawings, which show an exemplary non-limiting embodiment thereof, wherein:

Figure 1 is a perspective view of a tin comprising a sealing system according to the present invention;
Figure 2 is an exploded view of a sealing system according to the present invention;
Figures 3 and 4 are perspective views of a detail of the sealing system in Figure 2;
Figure 5 is a perspective view of a different embodiment of the detail in Figures 3 and 4;
Figure 6 is a view from below of Figure 5;
Figure 7 is a section according to the line VII-VII of Figure 6;
Figure 7A is the enlargement A of Figure 7;
Figure 8 is a view from below of a variant of the detail in Figure 5;
Figure 9 is a section according to the line IX-IX of Figure 8; and,
Figure 10 is a view from below of a further variant of the detail in Figure 5.

PREFERRED EMBODIMENT OF THE INVENTION

In Figure 1 a tin according to the present invention is globally denoted by 1. The tin 1 comprises a cup-shaped body 2 and a sealing system 3.
The cup-shaped body 2 comprises, in turn, a bottom 4, and a side wall 5 delimiting an inner cavity 6. The cavity 6 is connected to the outside through a mouth 7.
The sealing system 3 is configured to be applied to the cup-shaped body 2 in order to close the mouth 7. Preferably, the sealing system 3 is able to be opened/closed several times.
It should be noted that, hereinafter, the terms upper/lower, high/low and the like are used with reference to the tin 1 when it lies with the bottom 4 on a support plane n.
The cup-shaped body 2 has a longitudinal axis X and is axial-symmetric.
According to variants not shown, the cup-shaped body 2 may have a plurality of physical characteristics different from those shown in the example. For example, the side wall 5 may be conical and/or have countersink and/or tapering and/or convexities and/or ribs, and the like. Similarly, the bottom 4 may also have different physical characteristics, e.g. it may have: ribs and/or convexities and/or embossing, and the like. According to variants not shown, studs or rivets may be welded to the side wall 5 for mounting a handle or gripping handles.
Without losing generality and as known, the cup-shaped body 2 may be made in several pieces or in one single piece. Preferably, but not necessarily, the cup-shaped body 2 is made of sheet metal, particularly a tinplate. According to a variant not shown, the cup-shaped body 2 may be made, at least partially or completely, of another type of material. Alternatively, the cup-shaped body 2 may be made of plastic, glass, composite material, etc.
The sealing system 3 comprises, in turn, a stopper 8 and a cap 9.
The stopper 8 is configured to be applied to the mouth 7 of the cup-shaped body 2. The cap 9 is configured to be screwed onto the outer collar 14 of the stopper 8.
The stopper 8 is configured, as will be better shown hereinafter, to form a shape and interference fit with the mouth 7 of the cup-shaped body 2.
According to the examples shown, the stopper 8 has a shape that is substantially circular in plan with a central axis X'.
The stopper 8 is made of a polymeric material. The stopper 8 is made in one single piece. In particular, the stopper 8 was made by an injection moulding process.
The stopper 8 comprises: an annular edge 12 configured to engage by pressure on a rim 7' (generally made by curling the metal sheet) which delimits the mouth 7 of the cup-shaped body 2; a tubular abutment 13 configured to longitudinally extend partially inside the tin 1; and an outer collar 14 which protrudes longitudinally from the annular edge 12 towards the outside of the tin 1. According to the example shown, the collar 14 is externally threaded.
The stopper 8 also comprises a tear-off diaphragm 18 which, in use, seals an opening 15. According to the example shown, when the tin 1 is open, namely after the diaphragm 18 has been removed, the opening 15 is laterally delimited by the tubular abutment 13. The diaphragm 18 is substantially a membrane, namely a thin body configured to be torn and manually removed when it is first opened.
The diaphragm 18 has an inner surface s1 which, in use, faces inwards from the cavity 6 of the tin 1 and an outer surface s2 which faces, in use, outwards from the cavity 6 of the tin 1.
The tubular abutment 13 radially delimits the lateral perimeter p1 of the diaphragm 18 and protrudes along the central axis X' from both surfaces (inner s1 and outer s2) of the diaphragm 18. According to the example shown, the side perimeter p1 corresponds to the opening 15 when the diagram 18 has been removed. Advantageously, an incision k is present along the side perimeter p1 at the connecting section with the tubular body 13 (Figure 7A) which locally reduces the depth of the diaphragm 18 so as to facilitate the detachment of the diaphragm 18 from the tubular portion 13 along the side perimeter p1.
The side perimeter p1 has a circular shape coaxial to the central axis X'. The side perimeter p1 has a radius R1 and determines the final opening area of the tin 1 once the diaphragm 18 has been removed.
The diaphragm 18 has a removable portion 19, which is laterally delimited by at least one line of weakness 20 (also known as a half-cut). According to the example shown, the removable portion 19 is laterally delimited by two lines of weakness, hereinafter identified as 201 and 20II that are substantially parallel to each other. Therefore, the removable portion 19 substantially has a strip shape.
The diaphragm 18 comprises, in turn, a gripping element 21 which is fixed, as will be further shown hereinafter, to the removable portion 19 and is configured to be grabbed, in use, by the user so as to tear, removing, the removable portion 19 and (all of) the diaphragm 18 when the tin 1 is first opened.
The gripping element 21 is a ring configured to be hooked with a finger by a user. The gripping element 21 has a circular hole 24. According to the examples shown in Figures 2 to 8, the hole 24 is coaxial to the central axis X'. According to the example shown in Figure 10, the hole 24 is off-centred with respect to the central axis X'. The hole 24 has a radius of R5.
According to a variant not shown, the gripping element 21 is selected from a group of gripping elements differing from each other in shape and/or size. Alternatively, the gripping element may be a tab or an equivalent element configured to be grabbed and pulled manually by a user. According to a variant not shown, the line of weakness may be obtained on the side facing, in use, the outside of the tin 1.
In Figures 2 and 4 show a particular type of sealing system 3, which comprises a container 10 for an additive substance, is shown. "Additive substance" means the substance to be mixed by the user with the liquid contained in the tin 1. In this case, the sealing system 3 encloses the container 10 therein, which is interposed between the stopper 8 and the cap 9.
According to a variant not shown, the number and type of possible containers may be different from the one shown. For example, a container could be a vial or sachet (such as a sachet of sugar, oil, sauces or the like).
According to the example shown in Figures 2 to 4, the diaphragm 18 of the stopper 8 is shaped so to form a housing 33 to house the container 10. In particular, the housing 33 is coaxial to the central axis X'.
The housing 33 has a substantially truncated-cone shape. Without losing generality and according to variants not shown, the housing 33 may have shapes differing from the one shown, e.g. it may be cylindrical, parallelepipedshaped, truncated pyramid-shaped or the like.
The housing 33 is delimited by a bottom wall 34 and a side wall 35. According to the example shown, the bottom wall 34 is circular in shape. The diaphragm 18 also comprises an annular wall 36 that extends radially around the side wall 35 up to the side perimeter p1 at the intersection with the tubular abutment 13.
According to the example shown, the line of weakness 20 is made on the inner surface s1 of the diaphragm 18. According to a variant not shown, the line of weakness 20 may be obtained on the outer surface s2 of the diaphragm 18.
In the example shown in Figures 2 to 4, the removable portion 19 has a tear path t (schematised by a dotted line), running from a tear zone t0 to an opening zone tf.
The tear zone t0 is the area wherein the tear of the removable portion 19 is triggered by acting on the gripping element 21.
The opening section tf is the section where the strip of the removable portion 19, namely the lines of weakness 20I and 20II, ends, and acting on the gripping element 21 involves acting directly on the remaining part of the diaphragm 18.
The strip of the removable portion 19 is determined in such a way that once the opening section tf is reached, the diaphragm 18 detaches from the tubular abutment 13 along the lateral perimeter p1, in particular along the incision k, resulting in the complete removal of the diaphragm 18 itself and in the correct opening of the tin 1.
The gripping element 21 is fixed to the outer surface s2 of the removable portion 19 of the diaphragm 18 at the tear zone t0.
In particular, the gripping element 21 is fixed to the removable portion 19 by means of a supporting element 22 (Figure 5) which is interposed between the gripping element 21 itself and the removable portion 19. The supporting element 22 holds the gripping element 21 hanging above the outer surface s2.
According to the example shown in the Figures 2 to 4, the tear zone t0 is made on the bottom wall 34 of the housing 33 and the gripping element 21 is housed inside the housing 33 itself. The radius R5 of the hole 24 is smaller than the radius R4 of the bottom wall 34.
In the example shown in Figures 3 and 4, the tear path t comprises: a straight section t1 obtained in the bottom wall 34; a connecting section t2, in particular in the example shown in Figures 2 to 4 a section longitudinal to the side wall 35; and a semi-circular section t3, which is obtained in the annular wall 36 of the diaphragm 18.
The straight section t1 starts from the tear zone t0 and represents the starting detachment area of the removable portion 19. According to the example shown in Figures 2 to 4, the straight section t1 passes through the central area, substantially diametric, of the diaphragm 18.
The connecting section t2 is in between and connects the straight section t1 and the semi-circular section t3 with each other.
According to the example shown in Figures 2 to 4, the tear path t extends in space along a plurality of mutually incident surfaces. Specifically, the tear path t extends along the bottom wall 34, the side wall 35 and the annular wall 36. The tear path t passes through a connection c1 at the intersection between the bottom wall 34 and the side wall 35 and a connection c2 at the intersection between the side wall 35 and the annular wall 36. In this regard, it should be noted that this requires a high level of precision in the design and creation of the line of weakness 20 by means of plastic injection moulding, due to the presence of the connections c1 and c2 and, therefore, to the fact that the sections t1, t2, t3 do not lie in a single plane. Regarding the production of the mould for injection moulding, due to the above-mentioned reasons, it is difficult to manufacture and assemble the mould components in addition to the fact that it is difficult to adjust and adapt the line of weakness.
According to the example shown in Figures 2 to 4, the semi-circular section t3 is tangent to the side perimeter p1. In other words, the line of weakness 20I is in communication, namely at least incident, with the incision k of peripheral weakening. Thereby, advantageously, when tearing the removal portion 19, there is a continuous transition from the line of weakness 20II to the incision k. This advantageously results in the removal of the diaphragm 18 without having to exert force to trigger the detachment of the diaphragm 18 along the incision k. According to the example shown in Figures 2 to 4, the semi-circular section t3 has a radius R2 that is smaller than the radius R1 of the side perimeter p1.
In Figures 5 to 7 a preferred embodiment of the stopper 8 according to the present invention is shown. The components in common with the previous embodiment have the same numbering and are included therein without repeating them for the sake of brevity.
Advantageously, according to the example in Figures 5 to 7, the tear zone t0 is obtained on the annular wall 36 of the diaphragm 18. Preferably, the gripping element 21 is a ring. Advantageously, the radius R5 of the hole 24 is equal to or greater than the diameter of the housing 33, in other words it is equal to or greater than the radius R4 of the bottom wall 34. Thereby, advantageously, the housing 33 is accessible from the outside by the gripping element 21. In other words, the gripping element 21 does not affect accessibility and capacity of the housing 33.
Advantageously, the supporting element 22 is made in such a way that it is not deformed while opening the tin 1 and tearing of the removable portion 19 is facilitated. By way of illustration and not limitation, as shown in Figures 5 to 7, the supporting element 22 comprises a wedge 23 which constitutes, as will be better shown hereinafter, a stable and strong connection between the gripping element 21 and the diaphragm 18 facilitating the initial fracture of the diaphragm 18. According to a variant not shown, the supporting element 22 may comprise two or more wedges 23 placed side by side instead of a single one.
According to the example shown in detail in Figures 5 to 7, the wedge 23 comprises a prismatic body with a triangular cross-section relative to a plane perpendicular to the outer surface s2 of the diaphragm 18.
In particular, the wedge 23 has:

a base edge h1 which is transversal to the tear path t, is in contact with the removable portion 19 and at the tear zone t0;
a proximal edge h2 which is transversal to the tear path t, is in contact with the gripping element 21; and
a distal edge h3 which is transversal to the tear path t, is in contact with the removable portion 19 and is at an intermediate position of the tear path t.

According to the example shown, the section of the wedge 23 is substantially a right-angled triangle.
The distal edge h3 is substantially perpendicular to the tear path t and has an extension substantially equal to the height 1 of the removable portion 19 (Figure 6). The height 1 refers to the extension of the removable portion 19 perpendicular to the tear path t. Advantageously, in use, the distal edge h3 acts as a fulcrum to generate an opening torque, which multiplies the breaking force exerted by the user by means of the gripping element 21 at the proximal edge h2 and base edge h3. Thus, the wedge 23 allows to reduce the breaking force which must be exerted by the user to obtain the initial detachment of the removable portion 19.
Advantageously but not exclusively, the straight section t1 of the tear path t may be limited to the area required to obtain the initial tear of the removable portion 19. In other words, the straight section t1 may substantially correspond to the distance between the base edge h1 and the distal edge h3. In other words, the straight section t1 is limited to the section required to generate the opening torque.
According to the example shown in Figures 5 to 7, the straight section t1 extends along a chord of the circumference of the side perimeter p1. In particular, the straight section t1 is radial to the side perimeter p1 of the diaphragm 18. In other words, the straight section t1 extends along a chord passing through the centre O of the diaphragm 18, namely the straight section t1 extends along the diameter of the side perimeter p1.
Advantageously, the semi-circular section t3 is coaxial to the central axis X' of the diaphragm 18 and extends along the side perimeter p1 so that a line of weakness 20 (according to the example shown the line of weakness 20II) is superimposed on (or corresponds to) the incision k. Thus, advantageously, during the detachment of the removable portion 19, the detachment of the diaphragm along the side perimeter p1 is also obtained.
According to the example shown, the semi-circular section t3 has a radius R2 given by the following relation: $R 2 = R 1 - \frac{L}{2}$
Wherein:

R1 is the radius of the side perimeter p1 of the diaphragm 18;
L is the height of the removable portion 19.

Advantageously, the semi-circular section t3 begins at a vertex F and ends at a vertex G. The vertex G coincides with the opening area tf. The vertex F coincides with the point passing between the connecting section t2 and the semi-circular section t3, namely the point at which the radius of the tear path t takes on the value R2.
The arc FG of the semi-circular section t3 has an angle at the centre α (delimited by the centre O of the circumference of the side perimeter p1) of at least 45°, preferably at least 90°. Advantageously, the angle at the centre α is at least of 135°.
According to the example shown in Figure 6, the angle at the centre α is approximately of 160°. Thus, advantageously, also taking into account the dimensions of the straight section t1 and the connecting section t2, at least half of the side perimeter p1 of the diaphragm 18 is detached from the tubular abutment 13 when the removable portion 19 is detached.
Advantageously, according to the example shown in Figures 5 to 7, an integral central portion 25 is present in the diaphragm 18. Within the central portion 25, the tear path t, tear zones t0, straight section t1, connecting section t2, semi-circular section t3 and opening section tf are not present. In other words, advantageously, in the diaphragm 18 there is a central portion 25 which has no lines of weakness 20, namely has no zones with a reduced depth. This significantly improves resistance to internal pressure and water hammer stresses.
By way of exemplary but non-limiting example, the central portion 25 is delimited by a perimeter p2 centred on the central axis X' and of radius R4. According to the example shown in Figure 6, the length of the radius R4 is at least 40% of the length of the radius R1 of the side perimeter p1.
In Figures 8 and 9 a variant of the stopper 8 shown in Figures 5 to 7 is shown. In Figures 8 and 9, the elements in common with the previous embodiment have the same numbering and are included therein without repeating them for the sake of brevity.
According to the example in Figures 8 and 9, the diaphragm 18 consists of a circular wall 38 that is substantially flat. In other words, the diaphragm 18 has no housing 33. The tear path t, the gripping element 21 and the supporting element 22 substantially correspond to what was shown above.
In Figure 10 a variant of the stopper 8 shown in Figures 8 and 9 is shown. In Figure 10, the elements in common with the previous embodiment have the same numbering and are included therein without repeating them for the sake of brevity.
In particular, according to the example shown in Figure 10, the straight section t1 is not in the radial direction with respect to the centre O of the diaphragm 18. In other words, the straight section t1 extends along any non-diameter chord of the circumferential side perimeter p1. The term "chord" of a circumference refers to a segment connecting any two points on a circumference. This makes it possible to increase the radius R3 of the connecting section t2 in order to make the user's movement to open the diaphragm 18 more ergonomic and flexible.
As shown in Figures 1 and 2, the cap 9 has a wall 30 having a perimeter in plan substantially corresponding to that of the collar 14 of the stopper 8. The cap 9 also comprises a crown 31 that protrudes axially from the perimeter of the portion 30 in such a way as to substantially form a cup-shaped body. The crown 31 is internally threaded so that it can be screwed onto the collar 14 of the stopper 8.
According to the example shown, the wall 30 of the cap 9 is circular.
In order to manufacture a tin 1 according to the present invention, the sealing system 3 of the type described above is pre-assembled and subsequently hooked to the mouth 7 of the cup shaped body 2. The operations for applying the sealing system 3 to the cup-shaped body 2 are substantially known.
In the event that the sealing system 3 comprises a container 10, the container 10, while being pre-assembled, is inserted between the cap 9 and the stopper 8 in the corresponding housing 33 and then the cap 9 is screwed.
According to a variant not shown, the sealing system 2 only comprises the stopper 8. In other words, the sealing system 3 has no cap 9.
In use, a user must unscrew the cap 9 and remove the diaphragm 18 by pulling the gripping element 21 to access the liquid contained in the tin 1.
Advantageously, by means of the diaphragm 18 according to the present invention, the tear force that the user has to apply on the gripping element 21 in order to detach the diaphragm 18 is reduced.
Furthermore, advantageously, by means of the diaphragm 18 according to the present invention the user has to perform a semi-circular twisting movement to detach the removable portion 19. In other words, the user must exert a substantially outward arm-opening movement (not upwards as is the case with known solutions). This results in greater comfort (the elbow does not have to be lifted upwards) and greater sensitivity and precision of movement (namely better calibration of force by the user). This advantageously allows the user to remove the diaphragm 18 with greater precision, making a comfortable movement and calibrating the force without the risk of splashing when removing the diaphragm 18.
Furthermore, in the diaphragm 18 according to the present invention and as shown in Figures 5 to 10, the tear path t is realised entirely on a plane surface. This facilitates and improves the accuracy of the production process of the line of weakness 20 (half-cut) by injection moulding. It simplifies the design, manufacture and assembly of the moulds for injection moulding and of the components thereof. It simplifies the adjustment and setting of the half-cut 20. Thus, by means of the diaphragm 18 according to the present invention, in particular by means of the embodiments shown in Figures 5 to 10, it is possible to reduce the depth of the diaphragm 18 at the line of weakness 20 and a smaller depth results, in use, in a lower tear force required to obtain the detachment of the weakening portion 19.
Advantageously, according to the embodiment of the diaphragm 18 shown in Figures 5 to 10, the central portion of the diaphragm 18 itself has a depth as big as possible. In other words, the diaphragm 18 has no lines of weakness 20 at the central area. This allows to obtain a higher strength of the diaphragm 18 at the most stressed area both in case of impacts/falls and under the conditions of use for the compliance tests. Therefore, according to the embodiment shown in Figures 5 to 10, it is possible to reduce the depth of the diaphragm 18 as much as possible at the lines of weakness 20 since the latter are located in less stressed areas.

Claims

A stopper for a tin (1) for liquids, in particular for paints; wherein said stopper (8) is made in a single piece and is made of a polymeric material; said stopper (19) comprises a tubular abutment(13), which is configured to be coupled, in use, to the body (2) of a tin (1), and a diaphragm (18) configured to be torn out, in use, at the moment of the first opening; said diaphragm (18) having an incision (k) which extends along a first perimeter (p1) and reduce locally the depth of the diaphragm (18); said diaphragm (18) having one or more lines of weakness (20; 20I, 20II) which reduce locally the depth of the diaphragm (18) and delimit laterally a removable portion (19): wherein, a part of said incision (k) coincides, namely is at least incident with a respective part of one of the lines of weakness (20; 20I, 20II).
A stopper according to claim 1, wherein said removable portion (19) extends along a tear path (t) which comprises: a straight section (t1); a connecting section (t2); and a semi-circular section (t3); wherein, the connecting section (t2) is interposed between and connects the straight section (t1) and the semi-circular section (t3) ; wherein, the first perimeter (p1) of the diaphragm (18) is a circumference and has a first radius (R1) which extends from a centre (O) crossed by a central axis (X'); in particular, said semi-circular section (t3) is coaxial to said central axis (X').
A stopper according to claim 2, wherein the diaphragm (18) has a central portion (25) which is integral, namely the central portion has no depth reductions; in particular, said central portion (25) is delimited by a second perimeter (p2), which is circular and is coaxial to said central axis (X') and has a second radius (R4); in particular, said second radius (R4) has a length that is at least 40% of the length of said first radius (R1); wherein, the tear path (t) has a starting area (t0) at which the tear of the removable portion (19) is triggered; the starting area (t0) being radially arranged outside the central portion (25); wherein, said tear path (t) is entirely made on a plane surface.
A stopper according to claim 3, wherein the diaphragm (18) is shaped so as to form at least a housing (33) ; wherein, said housing is made within said central portion (25); the housing (33) is delimited by a bottom wall (34) and a side wall (35); wherein, the diaphragm (18) further comprises an annular wall (36) which extends radially around the side wall (35) between the first side perimeter (p1) and the second side perimeter (p2).
A stopper according to any one of the claims from 2 to 4, wherein the straight section (t1) extends along a chord of the circumference of the first perimeter (p1).
A stopper according to any one of the claims from 2 to 5, wherein the semi-circular section (t3) has a third radius (R2) given by the following relation: $R 2 = R 1 - \frac{L}{2}$
wherein:
R1 is the first radius of the first perimeter (p1) of the diaphragm (18);

L is the height, namely the extension perpendicular to the tear path (t), of the removable portion (19).
A stopper according to any one of the claims from 2 to 6, wherein the semi-circular section (t3) begins at a first vertex (F) and ends at a second vertex (G) so as to form an arc (FG) which has a central angle (α) of at least 45°, preferably of at least 90°; in particular of at least 135°.
A stopper according to any one of the claims from 3 to 7, wherein the stopper (19) comprises a gripping element (21) having a through-hole (24), in particular the gripping element (21) is a ring; wherein the gripping element (21)is configured to be pulled, in use, by an end user and is fixed to the removable portion (19) by means of a supporting element (22) which is interposed between the gripping element (21) and the removable portion (19); wherein, said supporting element (22) comprises one or more wedges (23); each wedge (23) having a triangular section with respect to a plane perpendicular to the external surface (s2) of the diaphragm (18) and has:
- a base edge (h1) which is transversal to the tear path (t) and is in contact with the removable portion (19) at a starting area (t0), in particular at a tear zone, of the tear path (t);

- a proximal edge (h2) which is transversal to the tear path (t) and is in contact with the gripping element (21); and

- a distal edge (h3) which: is transversal to the tear path (t), is in contact with the removable portion (19) and is at an intermediate position of the tear path (t).
A stopper according to claim 8, wherein the distal edge (h3) is substantially perpendicular to the tear path (t) and has an extension substantially equal to the height of the removable portion (19).
A stopper according to claim 8 or 9, wherein the straight section (t1) of the tear path (t) corresponds substantially to the distance between the base edge (h1) and the distal edge (h3).
A stopper according to any one of the claims from 7 to 9, wherein said hole (24) has a section of circular shape and is coaxial to said central axis (X1); in particular, the hole (24) has a third radius (R5) greater than said second radius (R4) of the central portion (25).
A stopper according to claim 2, wherein the diaphragm (18) is shaped so as to form at least a housing (33); wherein, said housing is made within said central portion (25); said housing (33) is delimited by a bottom wall (34) and a side wall (35); wherein, the diaphragm (18) further comprises an annular wall (36) extending radially around the side wall (35) to said side perimeter (p1); said straight section (t1) extending along the bottom wall (34); said connecting section (t2) extending along the side wall (35); and said semi-circular section (t3) extending on the annular wall (36).
A stopper according to claim 12, wherein said tear path (t) has a starting area (t0) at which the tear of the removable portion (19) is triggered; the starting area (t0) being arranged within the bottom wall (34).
A stopper according to claim 13, wherein the bottom wall (34) has a circular section that is coaxial to said central axis (X') and has a radius (R4); wherein the gripping element (21) is a ring and has a hole (nn) with a radius (nn) smaller than said radius (R4) of the bottom wall (34).
A sealing system for a tin for liquids, in particular paints, comprising a stopper (8) according to any one of the preceding claims and a cap (9); the stopper (8) is configured to be hooked, in use, on a cup-shaped body (2) of a tin (1); wherein, the cap (9) is configured to be coupled with said stopper (8).
A tin for liquids, in particular paints, comprising a stopper (8) according to any one of the claims from 1 to 14.