ES2999272T3 - Stopper, sealing system and tin for liquids - Google Patents

Abstract

1. A can for liquids, in particular paints, provided with a sealing system with a stopper (8) (8;) made of a polymeric material and having a diaphragm (18) configured to be torn off, in use, at the time of first opening; said diaphragm (18) having a removable portion (19), which is laterally delimited by at least one line of weakness (20; 201, 2011); the removable portion (19) having a gripping element (21) which is configured to be gripped, in use, by a user; said diaphragm (18) having an incision (k) extending along a lateral 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). (Automatic translation with Google Translate, no legal value)

Description

DESCRIPTION

Cap, sealing system and can for liquids

Field of technology

This patent application for an invention relates to a cap, a sealing system and a can, in particular a can for liquids.

Prior art

A can 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 liquid can of the known type also comprises a sealing system configured to seal the can at the rim.

A sealing system of the known type comprises, in turn, a plug and a lid.

The cap is configured to be applied to the rim of the can. Typically, the cap comprises: an annular rim configured to press-fit against the rim of the can; a tubular stop configured to extend longitudinally partially within the can; and an outer collar projecting longitudinally from the annular rim toward the exterior of the can. Generally, the cap comprises a tamper-evident tearable diaphragm that, during use, hermetically seals the can and is configured to be manually torn by the user upon initial use.

The cap is configured to be applied to the outer collar of the plug, generally, the cap can be applied by screwing or by pressing.

In the field, it is known that a pre-assembled sealing system of the known type is automatically applied to the rim of a can.

In the prior art, caps, sealing systems and cans are known from documents EP 1125852 A2, US 3281 007 A, EP 2263947 A1 and EP 3162728 A1.

Disclosure of the invention

In sealing systems of the known type, the diaphragm has a removable portion, which is laterally delimited by a line of weakness and is connected to a gripping element configured to be grasped, during use, by the user so that it can be torn, removing both the removable portion and the entire diaphragm when the can is first opened. The gripping element is configured to be grasped manually directly by a user, typically without the use of 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 is particularly problematic with large caps, specifically caps with diameters greater than 70 mm. Indeed, in this case, in order to open the can after grasping the gripper, a user must raise their arm upward, bringing their elbow even higher than their chin. This movement is particularly awkward.

Additionally, in known types of systems, the line of weakness is unfavorably positioned in a substantially central portion of the diaphragm, which is the most stressed and everted area, making this particularly relevant. Indeed, in order for cans for the transport of dangerous goods to comply with standards, particularly those of the United Nations and ADR, RID, IMDG, IATA, and ICAO regulations, the cans must pass certain tests, including drops from height and hydraulic pressure. During these tests, the diaphragm expands, everting outward due to internal pressure (hydraulic pressure tests) and water hammer (during drops).

Therefore, sealing systems of the known type, in order to pass compliance tests, must have a line of weakness of such depth that, while ensuring adequate tightness of the can, it requires the end user to apply excessive tearing force to the diaphragm. In this regard, it should be noted that sealing systems of the type described above are made of a polymeric material, specifically, a material that deforms plastically. Therefore, in order to tear the diaphragm, a user must apply a breaking force that exceeds the plastic deformation of the material at the line of weakness. A tearing force that causes the diaphragm to progressively tear is transmitted by further pulling on the gripping element.

However, after the diaphragm is completely removed, any excess tearing force is transmitted (due to the law of conservation of mechanical energy) from the diaphragm to the can body, and is substantially released in the form of a jerking of the can itself, which can cause material to leak out of the can. Combined with the vertical direction of the tearing force, in practice, this results in discomfort for the user and the risk of splashing.

The objective of the present invention is to provide a plug and sealing system that overcome the problems mentioned above.

In accordance with the present invention, there is provided a cap according to any one of claims 1 to 11, a sealing system according to claim 12 and a can according to claim 13.

Brief description of the drawings

The invention will now be described with reference to the attached drawings, which show an embodiment as a non-limiting example thereof, wherein:

- Figure 1 is a perspective view of a can 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 of Figure 2;

- Figure 5 is a perspective view of a different embodiment of the detail of Figures 3 and 4;

- Figure 6 is a bottom view of Figure 5;

- Figure 7 is a section along line VII-VII of Figure 6;

- Figure 7A is enlargement A of Figure 7;

- Figure 8 is a bottom view of a variant, not part of the invention, of the detail of Figure 5; - Figure 9 is a section according to the line IX-IX of Figure 8; and,

- Figure 10 is a bottom view of another variant, which is not part of the invention, of the detail in Figure 5. Preferred embodiment of the invention

In Figure 1 a can according to the present invention is denoted globally by 1. The can 1 comprises a cup-shaped body 2 and a sealing system 3.

The cup-shaped body 2 comprises, in turn, a lower part 4 and a side wall 5 that delimit an interior cavity 6. The cavity 6 is connected to the exterior 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 can be opened and closed several times.

It should be noted that hereinafter the terms top/bottom, high/low and the like are used with reference to the can 1 when it meets the bottom 4 on a support plane n.

The cup-shaped body 2 has a longitudinal axis X and is axially symmetrical.

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 countersinks and/or tapers and/or convexities and/or ribs and the like. Similarly, the bottom portion 4 may also have different physical characteristics, e.g., it may have ribs and/or convexities and/or embossings and the like. According to variants not shown, bolts or rivets may be welded to the side wall 5 for mounting a grip handle or handles.

Without losing generality and as is known, the cup-shaped body 2 can be made in several pieces or in a single piece. Preferably, but not necessarily, the cup-shaped body 2 is made of sheet metal, in particular, tinplate. According to a variant not shown, the cup-shaped body 2 can be made, at least partially or completely, of another type of material. Alternatively, the cup-shaped body 2 can be made of plastic, glass, composite material, etc.

The sealing system 3 comprises, in turn, a plug 8 and a lid 9.

The plug 8 is configured to be applied to the mouth 7 of the cup-shaped body 2. The cap 9 is configured to screw onto the outer collar 14 of the plug 8.

The plug 8 is configured, as will be better shown hereinafter, to form a shape and a tight fit with the mouth 7 of the cup-shaped body 2.

According to the examples shown, the plug 8 has a shape that is substantially circular in plan with a central axis X'.

Plug 8 is made of a polymeric material. Plug 8 is manufactured in a single piece. Specifically, plug 8 was produced using an injection molding process.

The cap 8 comprises: an annular rim 12 configured to snap into a flange 7' (generally made by corrugating sheet metal) that delimits the mouth 7 of the cup-shaped body 2; a tubular stop 13 configured to extend longitudinally partially inside the can 1; and an outer collar 14 projecting longitudinally from the annular rim 12 toward the outside of the can 1. According to the example shown, the collar 14 is externally threaded.

The stopper 8 also comprises a tearable diaphragm 18 which, in use, seals an opening 15. According to the example shown, when the can 1 is open, namely after the diaphragm 18 has been removed, the opening 15 is delimited laterally by the tubular stop 13. The diaphragm 18 is substantially a membrane, namely a thin body configured to be torn and removed manually when it is first opened.

The diaphragm 18 has an inner surface s1 which, in use, faces inward from the cavity 6 of the can 1 and an outer surface s2 which, in use, faces outward from the cavity 6 of the can 1.

The tubular stop 13 radially delimits the first lateral perimeter p1 of the diaphragm 18 and projects along the central axis X' from both surfaces (inner s1 and outer s2) of the diaphragm 18. According to the example shown, the first lateral perimeter p1 corresponds to the opening 15 when the diagram 18 has been extracted. Advantageously, along the first lateral perimeter p1 in the connection section with the tubular body 13 (Figure 7A) there is an incision k 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 first lateral perimeter p1.

The first lateral perimeter p1 has a circular shape coaxial with the central axis X'. The lateral perimeter p1 has a radius R1 and determines the final opening area of the can 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 20I and 20II, which are substantially parallel to each other. Therefore, the removable portion 19 has substantially a strip shape.

The diaphragm 18 in turn comprises a gripping element 21 which is fixed, as will be shown further hereinafter, to the removable portion 19 and is configured to be grasped, in use, by the user so as to tear, extracting, the removable portion 19 and (all) the diaphragm 18 when the can 1 is first opened.

The gripping member 21 is a ring configured to be engaged with a finger by a user. The gripping member 21 has a circular hole 24. In accordance with the examples shown in Figures 2 to 8, the hole 24 is coaxial with the central axis X'. In accordance with the example shown in Figure 10, the hole 24 is offset 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 that differ from one another in shape and/or size. Alternatively, the gripping element may be a tab or equivalent element configured to be grasped and pulled manually by a user. According to a variant not shown, the line of weakness may be obtained on the side that faces the exterior of the can 1 during use.

A particular type of sealing system 3 is shown in Figures 2 and 4, comprising a container 10 for an additive. "Additive" means the substance that the user must mix with the liquid contained in the can 1. In this case, the sealing system 3 encloses the container 10, which is interposed between the cap 8 and the lid 9.

According to a variant not shown, the number and type of possible containers may differ from those shown. For example, a container could be a jar or bag (such as a bag for sugar, oil, sauces, or the like).

According to the example shown in Figures 2 to 4, the diaphragm 18 of the plug 8 is shaped to form a housing 33 for housing the container 10. In particular, the housing 33 is coaxial with the central axis X'.

The housing 33 has a substantially truncated conical shape. Without losing generality and according to variants not shown, the housing 33 may have shapes that differ from the one shown, e.g., it may be cylindrical, parallelepiped-shaped, truncated pyramid-shaped, or similar.

The housing 33 is delimited by a bottom wall 34 and a side wall 35. According to the example shown, the bottom wall 34 has a circular shape. The diaphragm 18 also comprises an annular wall 36 extending radially around the side wall 35 up to the first lateral perimeter p1 at the intersection with the tubular stop 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 can 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 tearing path t (schematized by a dotted line), which runs from a tearing zone t0 to an opening zone tf.

The tear zone t0 is the area where the tearing 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, specifically 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 is detached from the tubular stop 13 along the first lateral perimeter p1, in particular, along the incision k, which results in the complete extraction of the diaphragm 18 itself and the correct opening of the can 1.

The gripping element 21 is fixed to the outer surface s2 of the removable portion 19 of the diaphragm 18 in the tear zone t0.

In particular, the gripping element 21 is fixed to the removable portion 19 by means of a support element 22 (figure 5) which is interposed between the gripping element 21 itself and the removable portion 19. The support element 22 keeps the gripping element 21 hanging above the outer surface s2.

According to the example shown in figures 2 to 4, the tear zone t0 is made in the lower 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 lower wall 34.

In the example shown in Figures 3 and 4, the tearing 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 semicircular 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 initial 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, substantially diametrical area of the diaphragm 18.

The connecting section t2 is between the two and connects the straight section t1 and the semicircular section t3 to 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 molding, due to the presence of the connections c1 and c2 and therefore the fact that the sections t1, t2, t3 do not lie in a single plane. Regarding the production of injection molding molds, due to the reasons mentioned above, it is difficult to manufacture and assemble the mold 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 semicircular section t3 is tangent to the first lateral perimeter p1. In other words, the line of weakness 20I is in communication, namely, at least incident, with the peripheral weakening incision k. Thus, advantageously, when the extraction portion 19 is torn, 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 semicircular section t3 has a radius R2 that is smaller than the radius R1 of the first lateral perimeter p1.

A preferred embodiment of the plug 8 according to the present invention is shown in Figures 5 to 7. The components in common with the previous embodiment have the same numbering and are included herein without repetition for the sake of brevity.

Advantageously, according to the example of Figures 5 to 7, the tear zone t0 is obtained in 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 lower wall 34. Thus, advantageously, the housing 33 is accessible from the outside by the gripping element 21. In other words, the gripping element 21 does not affect the accessibility and capacity of the housing 33.

Advantageously, the support element 22 is made such that it is not deformed upon opening of the can 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 support element 22 comprises a wedge constituting, as will be better shown hereinafter, a stable and strong connection between the gripping element 21 and the diaphragm 18 facilitating the initial fracturing of the diaphragm 18. According to a variant not shown, the support element 22 may comprise two or more wedges placed side by side instead of a single one.

According to the example shown in detail in Figures 5 to 7, the wedge 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 has:

- a base edge h1 which is transverse to the tear path t, is in contact with the removable portion 19 and in the tear zone t0;

- a proximal edge h2 which is transverse to the tearing path t, is in contact with the gripping element 21; and

- a distal edge h3 which is transverse to the tearing path t, is in contact with the removable portion 19 and is in an intermediate position of the tearing path t.

According to the example shown, the section of the wedge is substantially a right triangle.

The distal edge h3 is substantially perpendicular to the tearing 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 tearing path t. Advantageously, during use, the distal edge h3 acts as a fulcrum for generating an opening torque, which multiplies the breaking force exerted by the user by means of the gripping element 21 on the proximal edge h2 and the base edge h3. The wedge thus makes it possible to reduce the breaking force that 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 tearing path t may be limited to the area required to obtain the initial tearing 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 first circumference of the lateral perimeter p1. In particular, the first straight section t1 is radial to the lateral perimeter p1 of the diaphragm 18. In other words, the straight section t1 extends along a chord passing through the center 0 of the diaphragm 18, specifically, the straight section t1 extends along the diameter of the first lateral perimeter p1.

Advantageously, the semicircular section t3 is coaxial with the central axis X' of the diaphragm 18 and extends along the first lateral perimeter p1 so that a line of weakness 2C (according to the example shown, the line of weakness 20II) is superimposed on (or corresponds to) the incision k. Therefore, advantageously, during the detachment of the removable portion 19, the detachment of the diaphragm is also obtained along the lateral perimeter p1.

According to the example shown, the semicircular section t3 has a radius R2 given by the following relation:

Where:

R1 is the radius of the first lateral perimeter p1 of the diaphragm 18;

L is the height of the removable portion 19.

Advantageously, the semicircular section t3 begins at a vertex F and ends at a vertex G. Vertex G coincides with the opening area tf. Vertex F coincides with the point passing between the connecting section t2 and the semicircular section t3, specifically, the point at which the tearing path radius t takes the value R2.

The arc FG of the semicircular section t3 has an angle at the center a (delimited by the center 0 of the circumference of the first lateral perimeter p1) of at least 45°, preferably at least 90°. Advantageously, the angle at the center a is at least 135°.

According to the example shown in Figure 6, the angle at the center a is approximately 160°. Therefore, advantageously, also taking into account the dimensions of the straight section t1 and the connection section t2, at least half of the first lateral perimeter p1 of the diaphragm 18 is detached from the tubular stop 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, the tear zones t0, the straight section t1, the connection section t2, the semicircular section t3 and the opening section tf are not present. In other words, advantageously, in the diaphragm 18 there is a central portion 25 that does not have lines of weakness 20, specifically, it does not have zones with a reduced depth. This significantly improves the resistance to internal pressure and water hammer stresses.

By way of example, but not limited to, the central portion 25 is delimited by a second lateral perimeter p2 centered 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 first lateral perimeter p1.

Figures 8 and 9 show a variant of the plug 8 shown in Figures 5 to 7, said variant not being part of the invention.

In Figures 8 and 9, the elements in common with the previous embodiment have the same numbering and are included without repetition for the sake of brevity.

According to the example of 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 tearing path t, the gripping element 21 and the supporting element 22 substantially correspond to what has been shown above.

A variant, which is not part of the invention, of the plug 8 shown in Figures 8 and 9 is shown in Figure 10. 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 center O of the diaphragm 18. In other words, the straight section t1 extends along any non-diametric chord of the first circumferential lateral perimeter p1. The term "chord" of a circle refers to a segment connecting any two points of a circle. 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 plan perimeter substantially corresponding to that of the collar 14 of the plug 8. The cap 9 also comprises a crown 31 projecting axially from the perimeter of the portion 30 such that it substantially forms a cup-shaped body. The crown 31 is internally threaded so that it can be screwed onto the collar 14 of the plug 8.

According to the example shown, the wall 30 of the cover 9 is circular.

In order to manufacture a can 1 according to the present invention, the sealing system 3 of the type described above is pre-assembled and subsequently hooked onto 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 case where the sealing system 3 comprises a container 10, the container 10, while pre-assembled, is inserted between the lid 9 and the plug 8 in the corresponding housing 33 and then the lid 9 is screwed on.

According to a variant not shown, the sealing system 2 only comprises the plug 8. In other words, the sealing system 3 does not have a cap 9.

During 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 can 1.

Advantageously, by means of the diaphragm 18 according to the present invention, the tearing force that the user has to apply to the gripping element 21 in order to disengage the diaphragm 18 is reduced.

Moreover, advantageously, by means of the diaphragm 18 according to the present invention, the user has to carry out a semicircular twisting movement in order to disengage the removable portion 19. In other words, the user must exert an arm-opening movement substantially outwards (not upwards, as is the case with known solutions). This results in greater comfort (the elbow does not have to be raised upwards) and greater sensitivity and precision of movement (specifically, better force calibration by the user). This advantageously allows the user to extract the diaphragm 18 with greater precision, making a comfortable movement and calibrating the force without risk of splashing when extracting the diaphragm 18.

Moreover, in the diaphragm 18 according to the present invention and as shown in Figures 5 to 10, the tearing path t is entirely on a flat surface. This facilitates and improves the accuracy of the production process of the line of weakness 20 (half-cut) by injection molding. It simplifies the design, manufacture and assembly of injection molding molds and components thereof. It simplifies the adjustment and setting of the half-cut 20. Therefore, 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 tearing force required to obtain debonding 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 as great a depth as possible. In other words, the diaphragm 18 has no lines of weakness 20 in the central area. This makes it possible to obtain greater strength of the diaphragm 18 in the most stressed area both in case of impacts/drops and under the conditions of use for compliance tests. Therefore, according to the embodiment shown in Figures 5 to 10, it is possible to reduce as much as possible the depth of the diaphragm 18 at the lines of weakness 20, since the latter are located in less stressed areas.

Claims (13)

CLAIMS 1. A cap for a can (1) for liquids, in particular for paints; wherein said cap (8) is made in one piece and is made of a polymeric material; said cap (19) comprises a tubular stop (13), which is configured to be coupled, during use, to the body (2) of a can (1) and a diaphragm (18) configured to be torn, during use, at the time of the first opening; said diaphragm (18) having an incision (k) that extends along a first lateral perimeter (p1) and locally reduces the depth of the diaphragm (18); said diaphragm (18) having one or more lines of weakness (20; 20I, 20II) that locally reduce the depth of the diaphragm (18) and laterally delimit 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); wherein said removable portion (19) extends along a tearing path (t) comprising: a straight section (t1); a connecting section (t2); and a semicircular section (t3); wherein, the connecting section (t2) is interposed between and connects the straight section (t1) and the semicircular section (t3); wherein, the first lateral perimeter (p1) of the diaphragm (18) is a circumference and has a first radius (R1) extending from a center (O) crossed by a central axis (X'); In particular, said semicircular section (t3) is coaxial with said central axis (X'); wherein the diaphragm (18) has an integral central portion (25), specifically, the central portion has no depth reductions; said central portion (25) is delimited by a second lateral perimeter (p2), which is circular and coaxial with 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 tearing path (t) has a starting area (t0) in which the tearing of the removable portion (19) is triggered; wherein said tearing path (t) is made entirely on a flat surface; said plug being characterized in that: the diaphragm (18) is shaped so as to form at least one 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); the diaphragm (18) further comprises an annular wall (36) extending radially around the side wall (35) between the first side perimeter (p1) and the second side perimeter (p2); the starting area (t0) being arranged radially outside the central portion (25). 2. A stopper according to claim 1, wherein the straight section (t1) extends along a chord of the circumference of the first lateral perimeter (p1). 3. A plug according to claim 1 or 2, wherein the semicircular section (t3) has a third radius (R2) given by the following relationship: where: R1 is the first radius of the first lateral perimeter (p1) of the diaphragm (18); L is the height, specifically, the extension perpendicular to the tearing path (t), of the removable portion (19). 4. A plug according to any one of the preceding claims, wherein the semicircular section (t3) begins at a first vertex (F) and ends at a second vertex (G) so as to form an arc (FG) having a central angle (a) of at least 45°, preferably at least 90°; in particular, at least 135°. 5. A cap according to any one of the preceding claims, wherein the cap (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, during use, by an end user and is fixed to the removable portion (19) by means of a support element (22) interposed between the gripping element (21) and the removable portion (19); wherein, said support element (22) comprises one or more wedges; each wedge 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) that is transverse to the tearing path (t) and is in contact with the removable portion (19) in a starting area (t0), in particular, in a tearing zone, of the tearing path (t); - a proximal edge (h2) that is transverse to the tearing path (t) and is in contact with the gripping element (21); and - a distal edge (h3) that: is transverse to the tearing path (t), is in contact with the removable portion (19), and is in an intermediate position along the tearing path (t). 6. A plug according to claim 5, wherein the distal edge (h3) is substantially perpendicular to the tearing path (t) and has an extension substantially equal to the height of the removable portion (19). 7. A plug according to claim 5 or 6, wherein the straight section (t1) of the tear path (t) substantially corresponds to the distance between the base edge (h1) and the distal edge (h3). 8. A plug according to claim 5 or claim 6, wherein said through hole (24) has a circular cross-section and is coaxial with said central axis (X1); in particular, the through hole (24) has a third radius (R5) larger than said second radius (R4) of the central portion (25). 9. A stopper for a can (1) for liquids, in particular for paints; said stopper (8) being made in one piece and being made of a polymeric material; said stopper (19) comprising a tubular stopper (13), which is configured to be coupled, in use, to the body (2) of a can (1) and a diaphragm (18) configured to be torn, in use, at the time of first opening; said diaphragm (18) having an incision (k) extending along a first lateral perimeter (p1) and locally reducing the depth of the diaphragm (18); said diaphragm (18) having one or more lines of weakness (20; 20I, 20II) that locally reduce the depth of the diaphragm (18) and laterally delimit 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); wherein said removable portion (19) extends along a tearing path (t) comprising: a straight section (t1); a connecting section (t2); and a semicircular section (t3); wherein, the connecting section (t2) is interposed between and connects the straight section (t1) and the semicircular section (t3); wherein, the first lateral perimeter (p1) of the diaphragm (18) is a circumference and has a first radius (R1) extending from a center (O) crossed by a central axis (X'); In particular, said semicircular section (t3) is coaxial with said central axis (X'); said plug being characterized in that: the diaphragm (18) is shaped so as to form at least one housing (33); wherein said housing is made within a 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) up to said first 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 semicircular section (t3) extending into the annular wall (36). 10. A stopper according to claim 9, wherein said tearing path (t) has a starting area (t0) at which tearing of the removable portion (19) is triggered; the starting area (t0) being disposed within the bottom wall (34). 11. A stopper according to claim 10, wherein the bottom wall (34) has a circular section that is coaxial with 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). 12. A sealing system for a can for liquids, particularly paints, comprising a cap (8) according to any one of the preceding claims and a lid (9); the cap (8) is configured to engage, in use, a cup-shaped body (2) of a can (1); the lid (9) is configured to engage said cap (8). 13. A can for liquids, in particular paints, comprising a stopper (8) according to any one of claims 1 to 11.