EP0155021B1

EP0155021B1 - A closure cap provided with a gasket and a sealing ring from an olefin polymer

Info

Publication number: EP0155021B1
Application number: EP85200149A
Authority: EP
Inventors: Wiebren Durk Halbe Kornelis
Original assignee: Kornelis' Kunsthars Producten Industrie BV; Kornelis Kunsthars Producten Industrie BV
Current assignee: Kornelis' Kunsthars Producten Industrie BV; Kornelis Kunsthars Producten Industrie BV
Priority date: 1984-02-09
Filing date: 1985-02-07
Publication date: 1988-05-11
Anticipated expiration: 2005-02-07
Also published as: ATE34148T1; EP0155021A1; CA1292443C; ZA85865B; JP2545207B2; AU580751B2; AU3856485A; DK61285D0; DE3562601D1; JPS60204473A; DK61285A; NL8400428A; IN162719B; EP0155021B2; ES8606173A1; GR850303B; ES540171A0

Abstract

A process for making a closure cap (2) provided with a gasket (5) from a polypropylene material for a container (1), said closure cap (2) comprising an end wall and a circumferential side wall (11), in which process the gasket (5) is formed in the closure cap via a melting and a cooling operation by applying in the closure cap an amount of plastisol which is shaped therein into a gasket configuration at an elevated temperature adjusted after the plastisol addition; causing the plastisol shaped into the gasket configuration to melt completely by further energy supply and then cooling same to form the gasket, whereby starting from an integral combination of the closure cap (2) with a sealing ring (13) which is connected with the closure cap by means of a number of frangible bridges (12) capable of being broken on the first opening of the container, and, to form the gasket (5), carrying out the melting operation by heating the closure cap after addition of the plastisol to a temperature of 50 to 110 DEG C and by exposing the resulting plastisol shaped into the gasket configuration subsequently, as is known per se, to microwave energy until the plastisol has been completely molten.

Description

The invention relates to a closure cap for a container made from an olefin polymer comprising an endwall, a circumferential side wall and a sealing ring with which the container can be sealably closed in conjunction with a locking collar disposed around the neck of the container, which sealing ring is integrally connected with the side wall of the closure cap via frangible bridges capable of being broken on the first opening of the container.
Such a closure cap is known from EP-A-34997. When applied for closing a container the sealing ring when in undamaged condition guarantees that the container has not been opened yet. As such the sealing ring is valuable as an anti-theft means. This prior closure cap including the sealing ring is in its entirety made by injection molding. The cap is not provided with a gasket.
Various types of anti-theft means in combination with a closure cap, among them the sealing ring mentioned in the preceding paragraph, are also known from a review given in an article "Verschlüsse für Getranke-ftaschen", published iri Verpackungs-Rundschau 10/1983, pages 1074-1093, neither of said closure caps comprising a gasket.
In GB-A-2 116 529 a screw closure is disclosed comprising a cap made of, for example, an olefin polymer such as polypropylene. The closure cap is provided internally with a flowed-in gasket which is also made of a plastics material which, however, is softer than the plastics material the cap is made of. The gasket may be shaped, for example, by spinning a plastisol, i.e. a dispersion of a resin (for example a vinyl resin) in a plasticiser, in a gasket receiving recess of said cap, the gasket receiving recess being annularly shaped and bordered by an outer rib and a inner rib both shaped as an outer undercut and an inner undercut, respectively, on the inner side of the cap's. The ribs are shaped as an undercut for the purpose of both to limit radially inward migration of the plastisol during formation of the gasket and to prevent detachment of the gasket.
Containing a gasket on the one hand this prior closure cap is not provided with a sealing ring of the type being integrally connected with the side wall of the closure cap through frangible bridges which are capable of being broken on the first opening of the container.
Within the framework of providing closure caps comprising a gasket, made of a plastisol material, it is observed in Dutch Patent Application nr. 80.03371 that an ideal manufacturing process is to add the plastisol material such as a vinyl resin plastisol to the closure cap and subsequently to let the plastisol flow in the closure cap until a solid gasket has been formed in situ as is normal with closure caps made of a metal. However, with a closure cap made of an olefin polymer said process is not applicable because of the difficulty that the maximum melt temperature of the olefin polymer is close to the minimum melt temperature of a plastisol material. To overcome this difficulty according to said Dutch Patent Application no. 80.93371 a closure cap often made by injection moulding from an olefin polymer, in particular a high-melting polypropylene having a melting point of approximately 165°C, after having been provided with a vinyl chloride resin plastisol, is preheated to a temperature which must be 5-35°C below the melting point of the employed olefin polymer, e.g., polypropylene, preferably 5-15°C, i.e. it must be preheated to a temperature of at least 130°C, preferably 145-160°C, followed by exposure at this temperature in an appropriate oven to microwave energy having a frequency which is not critical from a technical point of view indeed, but is effectively 300-300,000 MHz. Exposure to the microwave energy takes place at the moment when the plastisol shaped into a gasket configuration is completely liquid, i.e. completely molten, which means that the resin has been completely solvated by the plasticizer.
Preheating can be appropriately carried out in a hot air oven.
In the known process it is indicated that, in general, a temperature of the closure cap of more than 35°C below the melting temperature thereof is probably not suitable for the conventional plastisols. If there is used a plastisol having a lower melting point, then also a lower temperature of the closure cap can be maintained in the preheating step. However, if there is started from a closure cap made from an olefin polymer melting at a lower temperature, then, conversely, the temperature range to be maintained for the closure cap in the preheating step must preferably be only 5-15°C, in particular 5-10°C below the melting point of the olefin polymer. Therefore, if the closure cap is made from, e.g., polyethylene having a high density, then, accordingly, the temperature range of the closure cap in the preheating step is preferably 120-125°C.
In practice, it is assumed in the known process that, e.g., after the plastisol has been added to the closure cap, this closure cap is brought into a hot air oven having an air temperature which is 30°C, preferably 20°C, below the melting point of the olefin polymer material from which the closure cap has been made. For instance, when polypropylene is used as the olefin polymer material, the preheating step is carried out, in practice, at an air temperature of 135-160°C for 1-10 min., e.g., an air temperature of 155°C for approximately 3 minutes, followed by the procedure in a microwave oven in which the ambient temperature is likewise high enough to prevent the preheated closure cap from sustaining heavy losses of heat, and which is, e.g., at least 140°C. The duration of the microwave procedure depends on the energy supplied and is not less than approximately 1 min.
The step of shaping the plastisol in the closure cap until a gasket configuration has been obtained can be performed in the conventional manner, preferably by injecting the plastisol in liquid or semi-liquid condition into the closure cap which is advantageously arranged upside down, i.e. the end wall is positioned at the bottom side, and distributing same therein by subjecting the closure cap to a rapid rotation. There is preferably used a closure cap the end wall of which is internally provided with an inner edge, the plastisol being injected into the annular space between the inner edge and the side wall of the closure cap.
The known process is suitable for a variety of types of closure caps and containers, in particular, however, for closure caps of bottles of threaded construction or of the snap-on type, which caps can be provided with not specified anti-theft means, said caps, however, normally having a limited inner diameter of approximately 25-32 mm.
Among these anti-theft means, however, the type comprising a sealing ring produced in one piece with the closure cap and connected with the side wall of the closure cap via a number of narrow frangible bridges to be broken on the first opening of the container cannot be used within the framework of the known process. Because of the high temperature of the closure cap to be maintained in the preheating step and subsequently upon exposure to the microwave energy of only 5-35°C below the melting point of the olefin polymer material used for making the closure cap, the narrow frangible bridges and the sealing ring, respectively, will be softened and deformed, which results in that the whole construction becomes useless.
The object of the invention is to provide a closure cap made from an olefin polymer and of the type specified in the opening paragraph and further provided with a gasket of a plastisol material, which is suitable for use on a container having a wide mouth the diameter of which may be up to 90 mm and more.
The invention is characterized in that the end wall (2) is internally provided with an annular space bounded by two undercuts (3, 4), said annular space is provided with a gasket (5) made from a plastisol material and said gasket (5) is sealing on the edge of the container neck (1), said end wall (2) having a wall thickness decreased by 20-50% at the gasket (5) while the closure cap (10) is obtained starting from an integral combination of the closure cap (10) with the sealing ring (13), adding, as is known per se, an amount of the plastisol material to the annular space and, to form the gasket (5), carrying out the melting operation by heating the closure cap (10) after addition of the plastisol to a temperature of 50-110°C and by exposing the resulting plastisol shaped into the gasket configuration subsequently, as is known per se, to microwave energy until the plastisol has been completely molten.
The closure cap according to the invention may be made of a standard grade polypropylene; it is therefore not necessary to use a high-melting polypropylene material. There can also be used a normal type of plastisol, e.g., that consisting of a microsuspension of a vinyl chloride copolymer resin with 5% vinyl acetate and further comprising conventional constituents, e.g., one or more stabilizers, plasticizers, viscosity-reducing and/or torsion-reducing agents.
The starting point of a closure cap according to the invention is a cap provided with a sealing ring which is integrally connected with the side wall of the cap via the frangible bridges capable of being broken on the first opening of the container to be closed with the cap, the end wall of which is internally provided with an annular space bounded by two undercuts the outer one of which is substantially bounded by the inner periphery of the side wall of the closure cap, and into which annular space a dosed amount of plastisol is injected in the conventional manner. Moreover the closure cap according to the invention to start from is such that its end wall is thinner by 20-50% at the position where the gasket is to be formed, such as at the position of the annular space bounded by the undercuts mentioned before. This promotes the heat transfer to the plastisol in the oven, such as the hot air oven in which the preheating can be performed. Moreover, the higher flexibility of the end wall at the relevant position enhances the self-ventilating action of it when the contents of the container are pasteurized.
The plastisol disposed in situ in the closure cap is melted by preheating the combination of closure cap and plastisol to 50-110°C and then exposing the resulting gasket configuration to microwave energy which may have a frequency of 10-200 MHz.
Conveniently the melting operation is carried out by heating the closure cap after addition of the plastisol to 100°C within 15-30 sec. and completely melting the plastisol shaped into the gasket configuration by 3-15 sec. exposure to microwave energy having a frequency of 27.10-27.15 MHz. This frequency is permitted for industrial uses in the whole world.
The closure cap according to the invention is of a type comprising a homogeneous gasket, and which is further provided with an undamaged, undeformed sealing ring, and which may have such an inner diameter that it can be applied to a container having a wide mouth. For instance, according to the invention a closure cap can be obtained having an inner diameter which may be up to 90 mm or more, advantageously up to 100 mm.
The invention is particularly suitable for, although not limited to, the preparation of a closure cap with an integrally connected sealing ring the-inner side wall of which is threaded so that this container can be opened or closed by rotation of the closure cap, in conjunction with corresponding provisions made at the neck of the container.
According to a preferred embodiment the closure cap of the invention is provided with an annular space bounded by two undercuts within which the gasket is contained, the inner undercut of which is tapered in cross-section and resilient and has such a width that upon closure of the container with the closure cap the undercut partly rests on the upper surface of the container edge.
The closure cap according to the invention is the first to incorporate a combination of three properties, namely that (a) the container closed with the closure cap after filling can be closed in compression-proof and vacuum-tight condition substantially without any restriction; (b) the container can be closed again after opening so that it is completely shut off from the atmosphere, and (c) the closure of the container after the first filling is irreversibly sealable.
Because of the fact that the closure cap according to the invention can be made available with an inner diameter which may be up to 100 mm the possibility has been offered for the first time to seal containers having a wide mouth so that for the first time foodstuffs which, in practice, are packed mainly in containers having a wide mouth, e.g., a neck diameter of 90 mm, whether or not under a partial vacuum, can be offered to consumers in sealed condition with a guarantee of freshness. This ensures that the date indicating until when the product will keep, as it occurs on containers for foodstuffs, is a practically reliable date indeed. In the case of a closure without a sealing capable of being broken irreversibly such a date is actually a fiction.
The invention will be further illustrated by means of the drawing which shows an example of embodiment of the closure cap and the method of sealing it. In the drawing

Fig. 1 schematically shows an axial cross-section of a container closed with the closure cap;
Fig. 2 schematically shows an axial cross-section of a container closed with the closure cap and provided with a sealing ring, in the pre-sealed state;
Fig. 3 shows a cross-section along the line III-III in Fig. 2;
Fig. 4 shows, in cross-section, the assembly of closure cap and container according to Fig. 2 during sealing with the use of a so-called clamp; and
Fig. 5 shows a cross-section along the line V-V in Fig. 4, without the clamp and the container.

In Fig. 1 the wall of the neck of a container made of glass is indicated by 1, and 2 shows the closure cap of polypropylene. On the inside the closure cap is provided with an annular space formed by the two circumferential undercuts 3 and 4, which annular space comprises the gasket 5. The inner undercut 3 is crescent-shaped and is resilient due to the outwardly decreasing thickness of the material. The crescent-shaped construction permits the inner undercut to rest on a part of the edge of the neck opening of the container. As a result thereof a part of the higher unscrewing torsion of the gasket is absorbed and reduced by the undercut. Moreover, the crescent-shaped undercut 3 ensures that in case of pasteurization of the contents of the container the expanded air generated in that process flows out between the undercut 3, which is thereby resiliently deflicted somewhat, and the edge of the neck whereby the deflected undercut simultaneously causes an additional clamping force to be exerted on the gasket and the gasket is retained in position.
Figs. 2-5 show the closure cap of polypropylene at 10, comprising side wall 11 and sealing ring 13 which is connected with side wall 11 via a frangible bridge 12. The neck portion of the container is shown at 14, which neck portion 14 is provided with locking collar 17.
In Fi-gs. 2-5 it is shown by way of an example below a closure cap according to the invention may be sealed after closed a container with it. As shown in Fig. 2 in the state before sealing. The side wall 11 with frangible bridges 12 and sealing ring 13 is clear of the container.
Fig. 4 shows the situation in which the frangible bridge 12 with the sealing 13, which where previously exposed to the action of hot air having a temperature of 400°C for 2 sec., has been grasped by the clamp 15 moving towards the container. The frangible bridge 12 is then overstretched over and under the locking collar 17 and flattened, the sealing ring 13 also being flattened simultaneously between the clamp 15 and the neck portion 14 of the container. Fig. 5 shows, in comparison with Fig. 3, the deformation experienced by the frangible bridge 12 and the sealing ring 13, which has resulted in that the sealing ring has a diameter smaller than the largest diameter of the locking collar 17. When the closure cap is unscrewed, an axial shift of the closure cap 10 is blocked by abutment of the sealing ring 13 against the locking collar 17. When the unscrewing movement is continued, the increasing force exerted by the locking collar 17 on the combination of sealing ring 13 and frangible bridge 12 will result in that the frangible bridge 12 weakened by overstretching and flattening, which is made of the per se tough polypropylene, is broken along the line of fracture 16 (Fig. 5).

Claims

1. A closure cap (10) for a container made from an olefin polymer comprising an endwall (2), a circumferential side wall (11) and a sealing ring (13) with which the container can be sealably closed in conjunction with a locking collar (17) disposed around the neck (1) of the container, which sealing ring (13) is integrally connected with the side wall (11) of the closure cap (10) via frangible bridges (12) capable of being broken on the first opening of the container, characterized in that the end wall (2) is internally provided with an annular space bounded by two undercuts (3, 4), said annular space is provided with a gasket (5) made from a plastisol material and said gasket (5) is sealing on the edge of the container neck (1), said end wall (2) having a wall thickness decreased by 20-50% at the gasket (5) while the closure cap (10) is obtained starting from an integral combination of the closure cap (10) with the sealing ring (13), adding, as is known per se, an amount of the plastisol material to the annular space and, to form the gasket (5), carrying out the melting operation by heating the closure cap (10) after addition of the plastisol to a temperature of 50-110°C and by exposing the resulting plastisol shaped into the gasket configuration subsequently, as is known per se, to microwave energy until the plastisol has been completely molten.

2. A closure cap according to claim 1, characterized in that the inner undercut (3) is tapered in cross-section and resilient and has a largest diameter to have the sealing of the gasket (5) on the edge of the container neck (1) partly in combination with the said undercut (3).

3. A closure cap according to claims 1-2, characterized in that the inner diameter of the closure cap (10) is up to 100 mm.