CH715816B1 - Plastic screw cap for containers, in particular plastic containers, and plastic containers provided with a plastic screw cap. - Google Patents

Abstract

The invention relates to a plastic rotary closure (1) for containers, which has an essentially cylindrical sleeve (3) which protrudes from an essentially circular disc-shaped top plate (2). The jacket (3) has an outer surface (4) and a substantially cylindrical inner surface (6) on which engagement means (7) are formed for positive interaction with corresponding fastening means for (16) a container neck (13). The jacket (3) and the head plate (2) are formed in one piece with each other and essentially consist of the same material. The jacket (3) and the head plate (2) are produced in an extrusion process from a plastic formulation which is at least 80% multimodal HDPE (high density polyethylene) with a first melt flow rate (MFR) 190°C/5 kg of a maximum of 5 g /10 min +/- 15% according to ISO 1133-1, preferably with a first melt flow rate (MFR) 190°C/5 kg of maximum 1.3 g/10 min +/- 15% according to ISO 1133-1.

Description

The invention relates to a plastic screw cap for a container, in particular a plastic container, according to the preamble of patent claim 1. The invention also relates to a plastic container provided with such a plastic screw cap.

[0002] To close containers, in particular bottles, plastic screw caps are often used, which are twisted or screwed onto a container neck provided with a pouring opening. A plastic twist-lock fastener comprises a substantially cylindrical casing which protrudes from a head plate which is substantially in the shape of a circular disk. The cylindrical shell of the plastic screw cap usually overlaps the container neck and is equipped on its inner wall with engagement means for positively locking the plastic screw cap on the container neck, which is equipped with corresponding fastening means. The engagement means for the form-fitting fixing of the plastic rotating closure are, for example, threaded sections or bayonet-like projections or depressions formed on the inner wall of the jacket. These interact in a form-fitting manner with corresponding threaded sections or bayonet-like projections or depressions formed on an outer surface of the container neck.

[0003] A so-called guarantee ring can be formed on the free end of the casing opposite the top plate of the plastic screw cap, which ring is connected to the casing by a thin, separable web of material. A snap ring formed on the container neck forms an abutment for the guarantee ring when the plastic screw cap is unscrewed by rotation, which is thereby at least partially separated from the jacket of the plastic screw cap. This shows the consumer that the container has already been opened once, even when the container is resealed.

The known plastic twist-lock closures often consist largely of a polyolefin, such as polyethylene, polypropylene or the like, and are produced in an injection molding process. The plastic used for the injection molding process must be sufficiently thin. Stress cracks can occur during the manufacture of the plastic screw caps and their assembly, and especially when they come into contact with materials that can cause stress cracks, such as surfactants, acids, etc. The plastic screw caps are usually pressed onto the neck of the container after the container has been filled. As a result of the dimensional tolerances of the container necks, the jacket of a plastic screw cap can be excessively expanded and damaged. It is immediately apparent that this is extremely undesirable and can lead to disruptions and delays in the production or bottling plant and to increased control effort.

[0005] The containers made of tinplate or non-ferrous metal, of glass or of ceramics, which have been customary in the past, are increasingly being replaced by containers made of plastic. In particular for the packaging of fluid substances, for example beverages, household products, care products, cosmetics, etc., plastic containers are now mainly used. The low weight and the lower costs certainly play a not inconsiderable role in this substitution. The use of recyclable plastic materials and the overall more favorable overall energy balance during their production also contribute to promoting the acceptance of plastic containers, in particular plastic bottles, among consumers.

[0006] Single-layer or multi-layer plastic containers are often produced in the so-called extrusion blow molding process, in particular a tubular blow molding process. The extrusion blow molding machines used for the extrusion blow molding process usually have one or more extruders for feeding in the required plastic material. The outlet of the extruder is connected to an extruder head, at whose outlet nozzle, the opening width of which can be regulated preferably, the extruded tube emerges. The extruded plastic hose can have one or more layers. The tube emerging continuously or quasi-continuously from the outlet nozzle is transferred to a blow molding tool arrangement and inflated by overpressure with the aid of a blow mandrel that is moved into the mold cavity. The inflated plastic container is then removed from the mold cavity.

Plastic containers made of polyethylene terephthalate (PET) and similar materials, such as polyethylene furanoate (PEF), are usually manufactured in a so-called stretch blow molding process. A preform is first produced in an injection mold in an injection molding process. Recently, extrusion processes or extrusion blow molding for the production of preforms have also been proposed. The preform has an essentially elongate preform body and is closed at one longitudinal end. A neck section, which is provided with a pouring opening, adjoins the other end of the preform body. The neck section already has the later shape of the bottle neck. Threaded sections or similar projections for fixing a plastic screw cap are therefore usually already formed on the outside of the neck section. In many cases, a so-called snap ring is also provided on the neck section, which protrudes radially from the circumference. The snap ring serves as an abutment for a detachable guarantee strip of a screw-on plastic screw cap for a plastic container stretch-blown from the preform. In most of the known preforms, the preform body and the neck section are separated from one another by a so-called support ring. The support ring protrudes radially and is used to transport the preform or the plastic container produced from it and to support the preform on the mold or the plastic container when it is closed.

The preform is removed from the mold after its production and can be immediately further processed while still hot in a one-stage stretch blow molding process or, in a two-stage stretch blow molding process, can be cooled and temporarily stored on a stretch blow molding device for separate further processing in terms of space and/or time. Before further processing in the stretch blow molding device, the preform is conditioned if necessary, i.e. a temperature profile is impressed on the preform. It is then introduced into a blow mold of the stretch blow molding device. In the blow mold, the preform is finally inflated by a gas blown in at overpressure, usually air, according to the mold cavity and is additionally stretched axially with a stretching mandrel. An injection blow molding process is also already known, in which the blow molding process takes place directly after the injection molding of the preform. The preform remains on the injection core, which also forms a kind of stretch dome. The preform is in turn inflated by overpressure according to the mold cavity of a blow mold that is fed onto the injection core or vice versa, and stretched by the stretching mandrel. The finished plastic container is then demolded.

The extrusion-blown, injection-blown or stretch-blown plastic containers are usually transported to a filling plant and filled immediately after demolding. After the filling process, the plastic containers are sealed with a plastic screw cap. The plastic screw cap is usually pressed onto the neck of the container, which can lead to the stress cracks already mentioned. The forces required to unscrew the plastic screw cap can also be very high. Elderly people, but also children, can sometimes hardly apply the necessary pressing force with their fingers to generate the torque required to unscrew the closure. If pliers or the like are used, the plastic screw cap and/or the container neck can be damaged, so that the plastic container can no longer be closed securely.

The object of the present invention is therefore to remedy the disadvantages of the plastic screw caps of the prior art. Plastic twist-lock closures are to be created which, when mass-produced and assembled, have a lower rate of stress cracking. For this purpose, the unscrewing forces of the plastic screw caps are to be reduced, in particular when plastic containers are removed.

[0011] These objects are achieved according to the invention by a plastic screw cap which has the features listed in patent claim 1. Developments and/or preferred embodiment variants of the invention are the subject matter of the dependent patent claims.

The plastic screw cap for containers has a substantially cylindrical shell which protrudes from a substantially circular disk-shaped top plate. The jacket has an outer surface and a substantially cylindrical inner surface on which engagement means are formed for positive interaction with corresponding fastening means on a container neck. The casing and the top plate are formed in one piece with each other and essentially consist of the same material. The jacket and the head plate are made in an extrusion process from a plastic formulation containing at least 80% multimodal HDPE (high density polyethylene) with a first melt flow rate (MFR) 190°C/5 kg of maximum 5 g/10 min +/- 15% according to ISO 1133-1, preferably with a first melt flow rate (MFR) 190°C/5 kg of maximum 1.3 g/10 min +/- 15% according to ISO 1133-1.

By using a plastic formulation that is more viscous than the plastics usually used and the modified manufacturing process, the stress cracking problem of the plastic screw caps is taken into account both during their manufacture and during assembly on the container neck and the stress cracking rate can be reduced. This applies in particular to the rate of stress cracking as a result of environmental stress cracking (ESCR), i.e. the consequences of contact of the plastic with materials that trigger stress cracking, and with regard to relaxation, i.e. the reduction in stress due to the viscoelastic properties of the plastics used. Thus, the use of the more viscous plastic formulation according to the invention has a positive effect on the service life of the plastic screw cap. This is advantageous both from the point of view of the cap manufacturer and for the bottlers who assemble the plastic screw caps. Surprisingly, it has been found that the plastic twist-lock closures designed according to the invention also lead to reduced unscrewing forces in connection with the commonly used containers made of glass or plastic. This can ensure that older people and children can apply the necessary forces to generate the torque required to unscrew the closure.

The use of a plastic formulation that has a proportion of HDPE that is at least 90% proves to be advantageous with regard to the tasks to be solved.

The strength and resistance to stress cracking of the plastic screw cap can be improved in that the plastic formulation contains 0%-10% calcium carbonate and/or talc and/or a mixture of polymers compatible with the HDPE and suitable for the extrusion process as a filler.

In order to also meet aesthetic requirements, the plastic formulation can contain 0% to 4% of a dye in a further embodiment of the invention.

The engagement means on the inner wall of the shell of the plastic screw cap are advantageously designed as threaded sections or bayonet-like projections or depressions. Such engagement means correspond to the form-fitting fastening means usually provided in plastic containers on the outer surface of the container neck.

To facilitate torque transmission when unscrewing and screwing the plastic screw cap back onto a container neck, the outer wall of the casing can be provided at least in some areas with corrugations running substantially perpendicularly to the top plate or a similar corrugated structure.

As is already known from the injection-molded plastic screw caps of the prior art, in one variant of the invention, a guarantee ring can be formed on a free end of the jacket opposite the top plate of the plastic screw cap, which ring is connected to the jacket via a thin, separable web of material is. A snap ring formed on the container neck forms an abutment for the guarantee ring when the plastic screw cap is unscrewed by rotation, which is thereby at least partially separated from the jacket of the plastic screw cap. As a result, the consumer can be shown, even when the container is resealed, that it has already been opened once.

A plastic container with a container body enclosing a cavity, at whose end opposite a container bottom a container neck with a pouring opening is connected, which container neck has an outer surface on which positive-locking fastening means are formed, is characterized by a plastic twist-lock closure according to one of the variants described. It has been shown that the plastic screw caps designed according to the invention can be unscrewed from the plastic container with reduced forces compared to the plastic screw caps known from the prior art. This means that even older people and children can generate the torque required to unscrew the cap.

The form-fitting fastening means on the outer surface of the container neck are threaded sections or bayonet-like projections or depressions and are therefore designed to correspond to the engagement means on the inner walls of the screw caps, with which they interact in a form-fitting manner.

At least the container body of the plastic container enclosing the cavity is produced in a blow molding process. In a variant that is used very frequently, the plastic container is designed as a plastic bottle. This is usually produced in a stretch blow molding process or in an injection blow molding process from a preform previously manufactured in an injection molding process. The plastic formulations used for the stretch blow molding process or the injection blow molding process include PET, PET-G, HDPE, PP, PS, PVC, PEN, copolymers of the plastics mentioned, bioplastics such as PLA or PEF, filled plastics and mixtures of the plastics mentioned.

Further advantages and features of the invention result from the following description of an embodiment with reference to the schematic drawings. In a representation that is not true to scale: FIG. 1 shows a side view of a plastic screw cap according to the invention; and FIG. 2 shows an axial section of a plastic container with a plastic screw cap.

[0024] A plastic twist-lock closure is provided with the reference numeral 1 in its entirety in FIGS. 1 and 2 . It has a substantially circular disk-shaped top plate 2, from which a substantially cylindrical jacket 3 protrudes axially. The essentially cylindrical shell 3 has an outer wall 4 which can be provided with a corrugation 5 running essentially perpendicularly to the top plate 2 . At the free end of the jacket 3 opposite the top plate 2 there can also be a guarantee ring 8 which is connected to the free end of the jacket 3 by a thin web of material 9 which can be torn open.

As can be seen from FIG. 2, the jacket 3 of the plastic screw cap 1 has a substantially cylindrical inner wall 6 in which form-fitting engagement means 7 are formed. In the illustrated embodiment, the engagement means 7 are designed as threaded sections. Alternatively, the form-fitting engagement means 7 can also be designed as bayonet-like projections or indentations.

The engagement means 7 on the inner wall 6 of the casing 3 are designed to correspond to form-fitting fastening means 16 which are arranged on an outer surface 15 of a container neck 13 equipped with a pouring opening 14 . The fastening means 16 are designed, for example, as threaded sections. Alternatively, the fastening means 16 can also be bayonet-like projections or indentations. The container neck 13 adjoins axially a container body 12, which encloses a cavity, of a container provided with the reference numeral 11 in its entirety in FIG. The container 11 can, for example, be a glass container, in particular a glass bottle. In the embodiment shown in FIG. 2, the container 11 is a plastic container, for example a plastic bottle. At least the container body 12 is manufactured in a blow molding process. The plastic container 11 shown is in particular a plastic container produced in a stretch blow molding process or in an injection blow molding process from a preform previously produced in an injection molding process. In this method, the preform neck remains largely unchanged in the subsequent blow molding process and forms the container neck 13. A so-called support ring 19, which optically separates the container neck 13 from the container body 12, also usually remains unchanged.

It can be seen from Fig. 2 that the engagement means 7, in particular the threaded sections, on the inner wall 6 of the jacket 3 of the plastic screw cap 1 interact in a form-fitting manner with the fastening means 16, in particular the threaded sections, on the outer surface 15 of the container neck 13 and thereby Fix the plastic screw cap 1 on the container neck 13. As indicated in FIG. 2, a circumferential sealing cone 10 can protrude from the top plate 2 of the plastic screw cap 1 inside the casing 3 and forms a seal with respect to an inner surface 18 of the container neck 13 in the area of the pouring opening 14 . 2 also shows a snap ring 17 formed on the container neck 13, which is arranged in the area of the thin, tearable web of material 9 with which the guarantee ring 8 is connected to the free end of the jacket 3. The snap ring 17 forms an abutment against an inwardly projecting section of the guarantee ring 8 when the plastic screw cap 1 is unscrewed from the plastic container and causes the thin web of material 9 to tear open. This shows the consumer, even when the container is closed again, that it has already been opened once is.

The shell 3 and the top plate 2 of the plastic screw cap 1 are formed in one piece with each other and consist essentially of the same material. The jacket 3 and the head plate 2 are produced in an extrusion process from a plastic formulation which is at least 80% multimodal HDPE (high density polyethylene) with a first melt flow rate (MFR) 190° C./5 kg of a maximum of 5 g/10 min +/- 15% according to ISO 1133-1, preferably with a first melt flow rate (MFR) 190°C/5 kg of maximum 1.3 g/10 min +/- 15% according to ISO 1133-1.

The plastic container 11 is usually produced in a stretch blow molding process or in an injection blow molding process from a preform previously manufactured in an injection molding process. The plastic formulations used for the stretch blow molding process or the injection blow molding process include PET, PET-G, HDPE, PP, PS, PVC, PEN, copolymers of the plastics mentioned, bioplastics such as PLA or PEF, filled plastics and mixtures of the plastics mentioned.

The invention has been described using the example of a specific embodiment. The foregoing description is only illustrative of the invention and is not to be taken as limiting. Rather, the invention is defined by the patent claims and the equivalents that are apparent to a person skilled in the art and are encompassed by the general idea of the invention.

Claims (12)

1. Plastic twist-lock closure for containers with a substantially cylindrical shell which protrudes from a substantially circular disc-shaped top plate, which shell has an outer surface and a substantially cylindrical inner surface on which engagement means for positive interaction with corresponding fastening means on a container neck are formed, as a result characterized in that the shell and the head plate are integrally formed with each other, consist essentially of the same material and are extruded from a plastic formulation which is at least 80% multimodal HDPE, i.e. high density polyethylene, with a first melt flow rate, i.e. MFR, 190°C/5 kg of maximum 5 g/10 min +/- 15% according to ISO 1133-1, preferably with a first melt flow rate, i.e. MFR, 190°C/5 kg of maximum 1.3 g/10 min +/- 15% according to ISO 1133-1. 2. Plastic screw cap according to claim 1, characterized in that the plastic formulation has a proportion of HDPE which is at least 90%. 3. Plastic screw cap according to claim 1 or 2, characterized in that the plastic formulation contains 0% - 10% calcium carbonate and/or talc and/or a mixture of polymers compatible with the HDPE and suitable for the extrusion process as a filler. 4. Plastic screw cap according to one of the preceding claims, characterized in that the plastic formulation contains 0% to 4% of a dye. 5. Plastic screw cap according to one of the preceding claims, characterized in that the engagement means are formed on the inner wall of the jacket threaded sections or bayonet-like projections or depressions. 6. Plastic twist-lock fastener according to one of the preceding claims, characterized in that the outer wall of the jacket is provided at least in regions with a corrugation or ribbed structure running substantially perpendicularly to the top plate. 7. Plastic screw cap according to one of the preceding claims, characterized in that a guarantee ring is formed on one of the top plate of the plastic screw cap opposite the free end of the shell, which is connected to the shell via a thin, separable web of material. 8. Plastic container with a container body enclosing a cavity, at the end of which opposite a container bottom a container neck with a pouring opening is connected, which container neck has an outer surface on which form-fitting fastening means are formed, characterized in that the plastic container has a plastic screw cap according to one of the preceding claims . 9. Plastic container according to claim 8, characterized in that the form-fitting fastening means on the outer surface of the container neck are designed as threaded sections or bayonet-like projections or depressions. 10. Plastic container according to claim 8 or 9, characterized in that at least the container body enclosing the cavity is produced in a blow molding process. 11. Plastic container according to one of claims 8 to 10, characterized in that it is produced in a stretch blow molding process or in an injection blow molding process from a preform previously manufactured in an injection molding process. 12. Plastic container according to one of claims 8 to 11, characterized in that it PET, PET-G, HDPE, PP, PS, PVC, PEN, copolymers of the plastics mentioned, bioplastics such as PLA or PEF, filled plastics and mixtures of the above includes plastics.