FI90347B - Mold part and polymer blend for making container closure sealing elements - Google Patents

Abstract

Moulding, in particular sealing element, for mechanically sealing bottle and jar closures made of metal or plastic, consisting of a synthetic halogen-free polymer compound elastically deformable in normal conditions of use, with a styrene-butadiene-styrene-rubber (SBS-rubber) content, and containing an ester-group-free hardness modifier, whereby the Shore A hardness of the polymer compound is between 30 and 80. The polymer compound also contains an aliphatic polymer, in particular polyethylene and/or an ethylene-vinyl acetate copolymer. The polymer compound is in particular suitable as an insert for vessel closures, such as capsules and screw cups.

Description

1 90347

Mold part and polymer blend for making container sealing elements

The invention relates to a molding part, in particular a sealing element for container closures, which consists of a synthetic polymer mixture which is elastically deformable under normal conditions of use, optionally containing a filler.

The invention further relates to a polymer mixture for the production of molded parts, in particular sealing elements for container closures, which mixture is plastic, in particular thermoplastic, moldable but normally elastic under normal conditions of use and contains a synthetic polymer, hardener and possibly a blowing agent and / or filler. correspondingly a processing aid. In addition, the invention relates to a container closure, in particular a crown cap or a screw cap for a bottle with an inner seal consisting of an elastic polymeric material.

It must be possible to fit the closures to the container in a simple and nevertheless reliable manner, in which case no post-treatment is normally required and the dimensions of the opening 20 of the container and its condition and roughness (e.g. return in bottles) can be very different. For this reason, it has long been known to provide container closures, for example crown caps, with an elastic sealing element on their inner side facing the container, which, when the closure is in place, is pressed between this and the container and ensures tightness.

In the past, seals for crown caps or screw caps for bottles, respectively, were made primarily of a press cap coated with a possibly still thin plastic or aluminum foil, but for a long time the sealing element has been made entirely of a synthetic polymer blend. However, only polymer blends which are sufficiently strong and durable and at the same time have the required elasticity are suitable for this purpose.

In practice, mainly PVC is used for this purpose, but also polyethylene and mixtures of these substances with vinyl acetate or vinyl acetate-ethylene copolymers, respectively.

2 .90347

The production of container closures using such polymer blends is disclosed, for example, in DE-AS 20 33 064 and DE-OS 30 21 488.

However, these known polymer blends still have 5 significant disadvantages. The use of PVC or other halogenated plastics leads to increasing difficulties in eliminating and rendering harmless used household waste container closures. In the normal incineration of household waste, halogen plastics generate acidic gases and are hazardous to the environment. Also, the necessary addition to adjust the necessary sealing properties of small molecule plasticizers (e.g. phthalates) is not harmless to health care, as these plasticizers are again partially released from PVC and can enter the human body through the nutrient or pleasure substance contained in the container. For this reason, the proportion of plasticizer in such polymeric materials is limited by a corresponding provision upwards.

Polyethylene alone is not suitable as a sealing material 20, especially when temperature variations or damaged receptacles have to be taken into account. Polyethylene is also not suitable for CO2-containing beverages for reasons of tightness.

It is therefore an object of the invention to provide a mold part, a polymer blend for its production and a container closure of the type mentioned at the beginning, which guarantees the required tightness of the container closure in simple manufacture, does not contain harmful substances, in particular halogen-containing ingredients or small molecule ester-containing plasticizers and container closure conditions, e.g., pasteurization.

To solve this object, a mold part of the type mentioned at the beginning has the features according to claim 1 according to the invention, while the polymer compound mentioned at the beginning is provided with the features mentioned in claim 7.

Preferred embodiments are set out in the subclaims.

The polymer blend according to the invention can be prepared from readily available raw materials. It can be treated with existing 3 90347 machines, such as those manufactured by SACMI, Italy, for the treatment of comparable PVC materials. In this case, it is advantageous to add a foaming agent which, as the polymer mass emerges from the extruder, causes a certain expansion of the coil, which largely corresponds to the behavior of the PVC masses 5 under the same conditions. To improve the shear and transport behavior of the polymer blend, a small amount of highly dispersed silicic acid can be added advantageously. The plasticized polymer blend can be easily extruded, cut and then molded. It then hardens into the desired shape part 10.

This shaped part made of a polymer blend, either attached to or placed inside the container closure, has good dimensional stability and at the same time elasticity sufficient for all conventional uses of container closures to ensure tightness. The containers can be pasteurized with the closure in place without the sealing mold part suffering or becoming leakproof.

Because the polymer blend does not contain small molecule plasticizers, it is safe from food law. When it becomes 20 household waste, it cannot release any harmful acid gases in the waste incineration plant because it is halogen-free.

The container closures according to the invention correspond to the provisions set out, for example, in DIN standard 6099 for crown baskets.

It is clear that the polymer mixture according to the invention can be adapted to the respective requirements of the various applications in question, so that its composition is chosen accordingly. Thus, the elasticity can be affected by the total proportion of additives 30 that convert the starting hardness of the SBS used. The proportion of blowing agent and the degree of foaming provided by it also make it possible to adjust the material properties.

The use of the polymer blend according to the invention has the further advantage that the shaped parts produced can be lighter than the known sealing elements made of, for example, PVC. For this reason, it is possible to prepare, for example, inner seals for crown caps, which weigh only about 150 to 160 mg, from the polymer mixture according to the invention. This represents a significant material saving of 4,90347 compared to PVC inner seals.

Especially in mechanically sealing bottle or container closures made of metal or plastic, such as crown-5 caps or screw caps, it is necessary that the sealing element forming the seal adheres firmly and completely to the closure. Otherwise, if the mouth of the container is damaged, the seal may move or twist and thus leaks may occur. When the adhesion of the seal is poor, localized loosening can lead to the formation of liquid-filled bubbles which promote corrosion of the metal closures. These adverse effects are effectively prevented by the PE or EVA content of the mixture, respectively.

The use of mixtures containing PE and / or EVA has the advantage that the concentrations of aromatic polymers in the mixture are reduced or eliminated altogether. Styrene derivatives, which may be present in similar mixtures, may adversely affect the odor and taste of the packaged product.

The low concentration of aromatic polymers improves the handling safety, especially at higher temperatures, by eliminating the presence of undesired monomers or degradation products, respectively.

In filling carbonated liquids, it seems necessary in the future for the sealing element to act as a safety valve, i.e. at a given overpressure, it allows the gas to evaporate to avoid breaking the vessel. This is made possible by the plastic properties of the PE-containing mixtures according to the invention.

In the following, the invention will be explained in more detail by means of an exemplary embodiment concerning an inner seal of a crown cap.

To this end, the polymer mixture is first prepared by mixing styrene-butadiene-styrene rubber (SBS rubber) with essentially paraffinic white oil according to DAB 8 and adding 35 polyethylene (PE), ethylene-vinyl acetate copolymer (EVA) and optionally vinyl acetate-ethylene (VAE) copolymer ) and / or polystyrene. In this case, the SBS rubber having a Shore A hardness of 40 to 90 forms the main component. The content of other polymers is less than 50% by weight of the total polymer blend and is usually lower for conventional crown heights, but preferably more than 5% by weight.

In addition to these ingredients, a further 0.1% of azodicarbonamide and up to 1% by weight of high-dissociated SiO 2 are added to the polymer mixture.

The polymer mixture thus prepared is fed to a known machine, which is also used, for example, for coating crown cap capsules on the inside with PVC-containing polymeric materials.

io In this machine, the polymer mixture first enters the extruder, where it is further homogenized by thorough kneading. It exits the outlet of the extruder as a plastic coil, which is cut immediately behind the outlet into individual pieces.

These pieces, each weighing about 150 to 170 mg, are in each case transferred to the inner surface of the metal capsule, which forms the body of the crown cap. The molding press further distributes the plastic polymer mass onto this possibly pre-treated inner surface which promotes adhesion and forces it into a thin, approximately disc-shaped molding. In this case, possibly the desired ring protrusions of the shaped part can be formed, which engage when the crown cap is in place around the edge of the bottle in the region of its mouth.

After cooling and curing of the thermoplastic polymer blend, the mold part forming the inner part of the crown cap can no longer be plastically formed under normal conditions of use, but can settle elastically sealingly on the edge of the bottle when the crown cap is pressed over the bottle. Due to its elasticity, the shaped part can then compensate for unevenness (for example caused by damage) and also for the roughness required by the manufacturing tolerances of the edge of the bottle.

The polymer blend of the molding can be formed by appropriately selecting the ingredients added for hardness conversion so that it is also resistant to the elevated temperature that occurs in the pasteurization of 35 bottles.

The crown cap thus prepared is ready for use after the polymer mixture has cured and can be stored until it is used. The properties of the mold part which forms its inner seal do not change even over a relatively long period of time.

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It is clear that in addition to the use in connection with the crown caps described here, other sealing elements for container closures can also be produced, in which the corresponding shaped part is not fixedly connected to the closure body.

Claims (7)

A molding which is a sealing element for mechanical sealing of metal or plastic bottle closures and containers comprising an elastically deformable synthetic halogen-free polymer blend with a styrene-butadiene-styrene rubber (SBS rubber) containing a Shore-A, under normal conditions of use. hardness of between 40 and 90, a content of an ester group-free hardness-modifying agent and a content of an aliphatic polymer, characterized by the fact that the Shore-A hardness of the polymer blend is between 30 and 80 and that the content of polymer compounds other than SBS , particularly polyethylene and / or ethylene-vinyl acetate copolymer, does not exceed 50% by weight of the polymer blend and preferably does not exceed 5% by weight. 2. A molding according to claim 1, characterized in that the hardness-modifying agent is a mineral oil fraction, preferably a refined essentially paraffinic white oil, according to DAB 8. Molding according to claim 1 or 2, characterized in that the polymer mixture is transferred to foam. 4. A molding as claimed in any of claims 1-3, characterized in that the polymer blend contains silica SiO2, which preferably has up to a maximum of 5 wt% and preferably less than 1 wt% based on the total polymer blend. Molding according to any of claims 1-4, characterized in that its Shore-A hardness is between 40 and 70. 6. A molding as claimed in any of claims 1-5, characterized in that it is formed essentially as a circular disc-shaped inner insert for a crown cap and bottle screw closure respectively, and that it weighs between 150 and 250 mg, preferably less than 200 mg. 9 90347 7. Polymer blend for the production of sealing elements for vessel closures, which blend a) styrene-butadiene-styrene rubber (SBS rubber) with a Shore-A hardness of melan 40 and 90, b) ester group-free hardness modifier, and c) aliphatic polymer; which is substantially halogen-free, characterized in that the polymer blend is plastic, preferably thermoplastic, moldable in ordinary conditions of use for an elastic mold and its Shore-A-10 hardness is between 30 and 80 and the content of polymer compounds other than SBS, in particular polyethylene and / or ethylene-vinyl acetate copolymer, does not exceed 50% by weight of the polymer blend and preferably not less than 5% by weight.