DE9103212U1 - Polymer compound for the production of sealing elements for vessel closures - Google Patents

Description

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Dipl.-lng. Günther Eisenführ· Dipl.-lng. Dieter K. Speiser· Dipl.-lng. Joachim Sirasse Dr.-lng. Werner W Rabus· Dlpi.-lng. Jürgen Brügge· Dipl.-Chem. Dr. Walter MaJwaJd Patent attorney Dipl.-lng. Jürgen Klinghardt ·

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Munich

15 March 1991

DS-Chemie GmbH
Cuxhavener Strasse 42/44
Bremen-1

Polymer compound for the production
of sealing elements for vessel closures

Description

The invention relates to a polymer compound for producing sealing elements for vessel closures.

Furthermore, the invention relates to a vessel closure with such a sealing element, in particular a crown cork or screw cap, for bottles, glasses and the like, as well as such a sealing element for vessel closures, in particular bottle and glass closures made of metal or plastic.

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Vessel closures must be designed in such a way that they can be easily attached to the vessel and yet seal it reliably, while normally no secondary treatment should be required and the dimensions of the vessel opening and its condition and roughness (for example in the case of reusable bottles) can vary considerably. It has therefore been known for a long time to provide vessel closures, for example crown corks, with an elastic sealing element on their inside facing the vessel, whereby the sealing element is pressed together between this closure and the vessel when the closure is placed on it and therefore ensures tightness.

While the inserts of crown corks or bottle screw caps used to be made primarily from pressed cork, which was possibly coated with a thin plastic film or a thin aluminum foil, sealing elements have been made entirely from synthetic polymer compounds for some time now. However, only polymer compounds that are durable and resistant enough and at the same time have the necessary elasticity are suitable for this purpose.

In practice, PVC is still predominantly used in such compounds; however, polyethylene and mixtures of these substances with vinyl acetate or vinyl acetate-ethylene copolymers are already being used.

The production of vessel closures using such polymer compounds is described, for example, in German Auslegeschrift 20 33 064 and German Offenlegungsschrift 30 21 488.

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However, these known polymer compounds still have significant disadvantages. The use of PVC or other halogen-containing plastics leads to more and more problems in the disposal and neutralization of used container closures in household waste. During the usual incineration of household waste, halogenated plastics produce acidic gases, the release of which into the atmosphere is harmful. The addition of plasticizers with a low molecular weight (e.g. phthalates), which is essential for setting the required sealing properties, is also not harmless for health reasons, as these plasticizers are partially released from the PVC and enter the human body via food or drinks contained in the container. For this reason, the content of plasticizers in such polymer materials is set by appropriate regulations.

Polyethylene alone is unsuitable as a sealing material in many cases, especially when temperature fluctuations or damaged vessel openings must be taken into account. Known polyethylene seals are also unsuitable for carbonated drinks due to leak-tightness reasons.

The following requirements are placed on vessel closures, in particular crown corks, screw caps and screw lids, which are usually made of metal or plastic such as polyolefin material and in which the sealing element often takes the form of an insert glued to the inside of the closure:

Good sealing properties, especially for low-value or reusable containers. The insert must conform to a damaged surface to ensure a gas- or liquid-tight seal.

In the case of screw-on closures, the closure must have low closing and opening torques in order to enable problem-free closure in the filling plant and easy opening by the end consumer.

The product must not have any odor that could be transferred to the contents of the container.

The liner material must have good adhesion to the closure cap material, especially to olefin materials such as polypropylene or polyethylene closure caps, to ensure good retention of gases such as carbon dioxide and closure integrity. The sealing element must be fitted snugly into the closure so that it is in full contact with the opening of the vessel. It must also ensure that the integrity of the seal is maintained in the event of a tilted closure.

The insert must meet the requirements of the responsible food authority for products in direct contact with food or food products. In some countries, such sealing elements are not permitted to contain PVC or ester-containing plasticizers due to health concerns and disposal problems, particularly in the case of incineration.

The insert must be malleable during manufacture to create different profiles to suit the different sizes and shapes of the bottle or jar opening. The product must also have a good "plastic memory" for resealing the bottle.

The closure and the insert must be able to withstand post-treatment such as pasteurization, hot filling, cooling, transport, etc.

The insert must not contain any surface-active substances (which, for example, impair the foam stability of beer).

- The entire closure must be able to be produced economically and at maximum speeds, currently for example up to 2500 closures per minute.

Today, there are two additional tasks for such closures:

The closures should have a valve effect in the event of excess pressure in the container, especially in the case of beer, soda and mineral water bottles;

When closed, the closures are designed to prevent substances that affect the aroma, and in particular the taste, from entering the container.

Excessive pressure in the vessel can arise, for example, if it is overheated and can cause the vessel to burst. This not only results in the loss of the contents, but also poses a very significant risk of injury, particularly from flying glass splinters. The valve effect of the closure is intended to ensure that the excess pressure (usually CO ₂ ) can escape in time and thus be rendered harmless.

Two main influences are considered responsible for the taste impairment of the contents, especially during long-term storage: firstly, oxidative aroma changes after exposure to oxygen, and secondly, taste changes due to the penetration of other, particularly aromatic substances such as benzene or phenyl ethers, for example chloroanisole. The latter are contained in objects containing wood such as pallets, boxes and the like and accumulate within packaging such as welding foil, shrink wrap and the like. These substances are suspected of being able to penetrate into the interior of containers through conventional polymer compound seals. They cause strong taste changes even in the ppm range.

To prevent oxygen from entering, sealing elements containing oxygen-binding substances (oxygen receptors) have already been proposed. These substances are intended to hold the penetrating oxygen in the sealing element so that it does not reach the contents of the container. However, oxygen receptors have not yet been approved for products that come into direct contact with food and often do not have perfect sensory properties themselves.

From DE-OS 15 44 989, sealing inserts for container closures are known that can consist of a variety of compounds. Among other things, butyl rubber/polyethylene mixtures are also described, which can also contain EVA copolymer. The composition ranges are wide; a composition in the ratio 2:2:1 is preferred for polyethylene/butyl rubber/EVA mixtures. This state of the art uses low-density polyethylene (LDPE) to ensure a particularly high degree of sealing and pressure retention over long periods at elevated temperatures. Sealing elements made from these compounds are not suitable for a pressure relief valve effect. On the other hand, LDPE compounds cannot be processed smoothly on modern machines, especially not with in-shell molding, since they smear and clump during granulation and stick to the blade after extrusion.

It is an essential object of the invention to provide polymer compounds for the production of sealing elements for vessel closures, corresponding vessel closures with such sealing elements and such sealing elements which in the closed state of the vessel closure enable a barrier effect preventing the entry of gaseous or vaporous substances such as oxygen and other taste-impairing substances into the vessel.

It is a further essential object of the invention to provide polymer compounds for the production of sealing elements for vessel closures, vessel closures with such sealing elements and corresponding sealing elements which exhibit a pressure relief valve effect at vessel internal pressures between approximately 3 and 10 bar.

In particular, it is an essential object of the invention to provide corresponding polymer compounds, vessel closures and sealing elements which exhibit both the aforementioned barrier effect and the aforementioned pressure relief valve effect.

A further object of the invention is to provide polymer compounds for producing the aforementioned vessel closures and sealing elements, which are suitable for use by in-shell molding, i.e. by mechanically shaping the unshaped, thermally plasticized polymer compound and then allowing it to solidify to form the finished elastic sealing element directly on or in the vessel closure.

A further essential object of the invention is to also meet the essential general requirements for sealing elements for vessel closures already mentioned above.

The features of the independent claims serve to solve this problem.

Advantageous embodiments are defined in the subclaims.

The polymer compound according to the invention can be produced from readily available raw materials. It can be produced using machines that are already available for further processing of comparable PVC materials and, for example, by

SACMI, Italy. To improve the cutting and transport properties of the polymer compound, a small amount of finely dispersed silica or amide wax can be advantageously included. The plasticized polymer compound can be easily extruded, cut and then molded using compression. It then hardens in the desired shape.

This molded part, which is made from the polymer compound and is either adhered to the vessel closure or inserted into it, has good dimensional stability and elasticity that is suitable for ensuring tightness in all common vessel closure applications. In suitable applications, the vessels can be pasteurized with the closure in place without damaging the molded sealing part or causing it to leak.

The sealing elements according to the invention provide a pressure relief valve function between about 3 and 10 bar by elastically giving way when a certain internal pressure in the vessel is exceeded and allowing the material generating the pressure (usually carbon dioxide) to escape. As soon as the internal pressure has fallen back to the specified value at which the valve effect occurs, the sealing element closes the vessel closure again to the vessel in a completely gas-tight manner. This can prevent the container from bursting in the event of unforeseen and undesirable overpressure. The internal pressure at which the pressure relief valve function occurs can be determined by the mixture of the compound and, if necessary, additives that influence its mechanical properties.

At the same time, the sealing elements according to the invention show a pronounced barrier effect against the entry of, for example, oxygen, benzenes and chloroanisole into the container. This barrier effect lasts for very long periods of time

continues unabated and prevents the taste of beer bottles that are packaged in welded or shrink-wrapped films, or in boxes or pallets, from being altered by the ingress of such substances.

Since the polymer compound does not contain any low molecular weight plasticizers, it is harmless from the perspective of food regulations; if it ends up in household waste, it cannot give off harmful acid gases in a waste incineration plant, since it is halogen-free.

The vessel closures according to the invention meet the regulations, as laid down, for example, in DIN standard 6099 for crown corks.

It goes without saying that the polymer compound according to the invention can be adapted to the specific requirements of the various applications by a suitable choice of its composition. The elasticity can be influenced, for example, by the total proportion of additives that change the initial hardness of the components used.

The use of the polymer compound according to the invention offers the further advantage that the molded parts produced can be lighter than known sealing elements, for example made of PVC. The polymer compound according to the invention can therefore be used to produce, for example, inner inserts for crown corks with a weight of only about 150 to 160 mg, which represents a not inconsiderable saving in material compared to known inner inserts made of PVC.

It is understood that the invention can be applied without restriction to standard insert dimensions, i.e. insert weights of between approximately 150 and 250 mg for crown corks; between 220 and 320 mg for aluminum screw caps, between 250

and 400 mg for plastic screw caps and even higher weights for larger closures, as screw caps for jars etc.

It is particularly important for mechanically sealed bottle and vessel closures made of metal or plastic, such as crown corks and screw caps, that the sealing element that forms the insert is firmly attached and that its entire surface is in contact with the closure. If this is not the case, the insert can shift or twist if the vessel openings are damaged, resulting in leaks. Furthermore, if the insert does not adhere well, local shifts can cause moisture-filled bubbles that promote corrosion of metal closures. These adverse effects are effectively suppressed, in particular by the PE content of the compound.

The use of the compounds according to the invention has the advantage that the compound completely avoids any aromatic polymer content. Styrene derivatives, which are sometimes contained in similar compounds, can adversely affect the smell and taste of the packaged product.

The absence of aromatic polymers increases processing safety, especially at relatively high temperatures, by suppressing the occurrence of undesirable monomers or degradation products.

The closure with sealing element is usually manufactured using the so-called "in-shell molding" process, as used, for example, in HC industrial machines. The granulate of the compound is filled into an extruder, which melts the product and then pumps it to an opening. Outside this opening there is a rotating knife that cuts the extrudate into

a bead and throws it into the closure. This results in two important features of the new compound, namely no adhesion to the cutting edge and good spinning properties. If the spinning properties are not good, then the bead does not land in the middle of the closure, which leads to empty spaces or burrs during molding. These important factors are guaranteed by the raw materials used in the invention.

If the bead is in the middle of the closure, a stamp with a suitably selected profile presses the still molten bead together. During this process, the compound is distributed in the closure and at the same time given the required profile. Formability is also a special feature of the new sealing element formulation for the following reasons: The product must not only be easy to form, but also maintain its dimensional stability without shrinking or changing when cooling. The new composition according to the invention guarantees these essential requirements.

Another significant feature of the new compound is that the in-shell molding machines can now run trouble-free at maximum speed and with minimal waste. This property is due to the polymer mixture, which enables the running speeds to be increased to up to 2500 closures per minute.

At the bottling plant, the closures must be screwed onto the bottle or jar with torques of less than 0.22 kpm, preferably less than 0.17 kpm. After the bottle has been closed, which may have been hot or cold, filled or even pasteurised, the sealing element must retain its condition and shape. Most bottles are cooled to around 4 ⁰ C in refrigerators before consumption, with

no shrinkage should occur. It goes without saying that transport or storage in warm climates should not cause excessive expansion or creep, which would lead to a loss of carbon dioxide.

No foreign odor, including that from the compound, may be transferred to the bottle contents. Preventing this is another significant advantage of the invention.

The invention is described further below with reference to the embodiments which relate to an inner insert for a bottle crown cork made of metal. All data in % by weight refer, unless otherwise stated, to the total weight of the compound.

Implementation example 1:

A polymer compound is produced by mixing about 33% by weight butyl rubber (sold commercially under the name "Polysar EER 101/3" from Polysar) with about 33% by weight HDPE ("Eraclene HVSG 5215 P" from Enichem) and about 30% by weight EVA copolymer ("Evatane 2805" from ATO). The EVA copolymer has a relative VA content of about 10%. Instead of HDPE, a mixture of LDPE ("Lupolen 1800 S" from BASF AG) and PP with approximately the same Shore hardness can be used.

In addition to these components, small amounts of less than 1% by weight of finely dispersed SiO ₂ or silicone oil, pigments, stabilizers and erucic acid amide as well as 3.5% talc are added to the polymer compound. The silicon content helps to prevent the cut beads or lumps of the compound from adhering to the knife.

The polymer compound produced in this way is fed into a HC machine. In this machine, the polymer

compound first into an extruder where it is melted. It leaves the outlet opening of the extruder as a plastic extrudate, which is cut into individual lumps by a knife immediately behind the opening.

Each of these lumps, each weighing about 160 to 180 mg, is thrown onto the inner surface of a screw cap made of polypropylene (PP). The polymer compound, which is still plastic, is distributed over this inner surface by a die and pressed to form a thin, roughly disk-shaped molded part. At the same time, it is possible to form any desired ring-shaped projections on the molded part, which grip the edge of the bottle in the area of the opening when the cap is screwed on.

After the thermoplastic polymer compound has cooled and hardened, the molded part that forms the inner insert is no longer plastically deformable under normal conditions of use, but presses against the edge of the bottle with an elastic sealing effect when the cap is screwed onto the bottle. Due to its elasticity, the molded part can therefore compensate for unevenness (for example due to damage) and also the roughness of the edge of the bottle due to manufacturing tolerances.

Export example 2:

A polymer compound is produced by mixing about 48% by weight of butyl rubber with about 48% by weight of HDPE. In this case too, a mixture of approximately the same Shore hardness of LDPE with PP can be used instead of HDPE.

Less than 1% by weight of each of finely dispersed SiO ₂ or silicone oil, pigments, stabilizers and erucic acid amide as well as 3.5% talc are added to the polymer compound.

The polymer compound produced in this way is fed into an HC machine, where it first enters an extruder where it is melted. It leaves the outlet opening of the extruder as a plastic extrudate, which is cut into individual lumps by a knife immediately behind the opening.

Each of these lumps, weighing approximately 220 to 240 mg, is individually spun onto the inner surface of an aluminum capsule, which forms the body of a screw cap. The polymer compound, which is still plastic, is distributed over this inner surface by a die and pressed to form a thin, roughly disk-shaped molded part. At the same time, any desired annular projections on the molded part are formed, which grip the edge of the bottle in the area of the opening when the cap is put on.

After the thermoplastic polymer compound has cooled and hardened, the molded part that forms the inner insert of the cap is no longer plastically deformable under normal conditions of use, but presses elastically against the edge of the bottle to form a seal when the cap is screwed on. Due to its elasticity, the molded part can therefore compensate for unevenness (e.g. due to damage) and roughness due to manufacturing tolerances.

Examples 3 and 4

Example 2 is repeated, with 5% and 20% polyamide ("Vestamid", available from Hüls AG) being added once.

Implementation example 5

Example 2 is repeated, adding 40 wt.% polyurethane (FDA approved).

Implementation example 6

A polymer compound is prepared by mixing about 40% by weight of butyl rubber ("Polysar EER 101/3") with about 55% EVA copolymer (10% VA content, available from ATO under the designation ¹¹ EVATANE 2805").

Furthermore, 4.9% talc and 0.1% erucic acid amide are added as lubricants.

Implementation example 7

Example 6 is repeated, adding 40 wt.% polyurethane (FDA approved).

Examples 8 and 9

Example 6 is repeated, with 5 wt.% and 20 wt.% polyamide ("Vestamid" from Hüls AG) being added once.

The vessel closures produced according to the above embodiments 1-9 show both a pronounced barrier effect and valve properties.

Even over periods of several months, no penetration of oxygen, benzene or chloroanisole into the interior of the vessel is observed. If the internal pressure in the vessel is increased, the vessel closures designed according to the invention allow the excess pressure to escape before it rises to dangerous levels.

Figures 1 and 2 show the results of tests in which the barrier effect (against oxygen) was measured using an "Orbisphere" device and the valve properties were measured according to the standard delivery conditions of the brewing industry.

Fig. 1 shows the oxygen ingress over time in reusable bottles, where the crosses represent a standard PVC seal and the boxes show the data of a comparable seal according to the invention (as in Example 1). The significantly better barrier properties of the seal according to the invention are immediately apparent.

Fig. 2 shows the development of pressure tightness with increasing internal pressure, measured according to standard delivery conditions on 49 beer export bottles three weeks after their closure using a Simmonazzi machine at high speed.

As can be seen, 96% of the bottles show the desired pressure relief valve function at internal pressures between 7 and 10 bar.

By appropriately selecting the components added to modify the hardness, the polymer compound of the molded part can be designed to withstand even the increased temperature that occurs during pasteurization.

The closures produced according to the invention are ready for use after the polymer compound has hardened and can be stored until they are used; the properties of the molded part that forms the inner insert do not change even over long periods of time.

It is self-evident that - apart from the use described here in connection with crown corks and screw caps - other sealing elements for vessel closures can also be manufactured in which the corresponding molded part is firmly or loosely connected or glued to the body of the closure.

Claims (24)

Expectations 1. Polymer compound for the production of sealing elements for vessel closures, which, when closed, have a barrier effect preventing the entry of gaseous or vaporous substances such as oxygen and aromatic compounds, in particular benzenes, phenyl ethers and the like into the vessel and/or have a pressure relief valve effect at vessel internal pressures of between about 3 and 10 bar and by mechanically shaping the unshaped, thermally plasticized polymer compound and subsequently allowing it to solidify to form the finished, elastic sealing element directly on or in the vessel closure wm:si Zweibrückenstrasse 17 ■ D-8OOOMünchen2 · Telephone 089-222596· FSx089-229675 -Telex522054 patd -Datex-P 4589007319 ("In-Shell Moulding"), consisting of a mixture of butyl rubber and a polymer of an a-olefinically unsaturated monomer and optionally one or more other polymer components and conventional additives such as lubricants, pigments, talc and stabilisers. 2. Polymer compound according to claim 1,
characterized in that the poly-a-olefin component consists at least partially, in particular completely, of high density polyethylene (HDPE). 3. Polymer compound according to claim 1,
characterized in that the poly-a-olefin component consists at least partially, in particular completely, of polypropylene (PP) in a mixture with polyethylene (PE), low density polyethylene (LDPE) and/or very low density polyethylene (VLDPE). 4. Polymer compound according to claim 2 or 3, characterized in that the polymer compound contains EVA copolymer as, in particular, the only, further polymer component. 5. Polymer compound according to one of claims 1 to 4, characterized in that the polymer compound has a butyl rubber content of between 20% by weight and 60% by weight, in particular between 30% by weight and 50% by weight, based on the total weight. 6. Polymer compound according to one of claims 1 to 5, characterized in that the polymer compound has a polymer content of an α-olefinically unsaturated monomer of between wt. % and 70 wt. %, in particular between 30 wt. % and 60 wt. %, based on the total weight. 7. Polymer compound according to one of claims 1 to 6, characterized in that the polymer compound contains butyl rubber and polymer of an α-olefinically unsaturated monomer in substantially equal proportions by weight, in particular in a ratio of 1:1. 8. Polymer compound according to claim 7, characterized in that the polymer compound contains the butyl rubber, the polymer and an EVA copolymer essentially in the weight ratio (1.1-1.3):(1.1-1.3):1. 9. Polymer compound according to one of claims 1 to 3, characterized in that the polymer compound contains EVA copolymer as the only polymer in addition to butyl rubber. 10. Polymer compound according to claim 9, characterized in that the polymer compound contains butyl rubber and EVA copolymer in a weight ratio of 1:(1-1.5), preferably 1:(1.3-1.4) and in particular 1:1.375. 11. Polymer compound according to one of claims 4 to 10, characterized in that the EVA copolymer contains 5 wt.% to 15 wt.%, in particular about 10 wt.% VA. 12. Polymer compound according to claim 2 or 3, characterized in that the polymer compound contains a polyamide, in particular nylon, or a polyurethane as, in particular, the only, further polymer component. 13. Polymer compound according to claim 12,
characterized in that the polymer compound contains 5 wt.% to 20 wt.% polyamide, or up to 50 wt.%, in particular about 40 wt.% polyurethane, based on total weight. 14. Polymer compound according to claim 1,
characterized in that the polymer compound contains (in percent by weight, based on total weight): Substance generally preferred particularly preferred Butyl rubber 25-40 30-35 33-34 HDPE 25-40 35-35 33-34 EVE (10% by weight VA) 25-35 28-32 29-30 and less than 0.5% by weight each of lubricant, pigment and stabilizer and less than 5% by weight of talc. 15. Polymer compound according to claim 1,
characterized in that the polymer compound contains (in percent by weight, based on total weight): Substance generally preferred particularly preferred Butyl rubber 40-60 45-52 48 HDPE 40-60 45-52 48 and less than 0.5% by weight each of lubricant, pigment and stabilizer and less than 5% by weight of talc. 16. Polymer compound according to claim 1, characterized in that the polymer compound contains (in percent by weight, based on total weight): Substance generally preferred particularly preferred Butyl rubber 30-50 35-45 40 EVE (10% by weight VA) 40-70 50-60 55 and less than 0.5% by weight each of lubricant, pigment and stabilizer and less than 5% by weight of talc. 17. A vessel closure with a sealing element, in particular a crown cork or screw cap, for bottles, glasses and the like, in which the sealing element consists of a polymer compound according to one or more of claims to 16. 18. Vessel closure according to claim 17, characterized in that the sealing element is designed as an inner insert on an inner surface of the vessel closure facing the edge of the vessel to be sealed. 19. A vessel closure according to claim 18, in the form of a crown cork, characterized in that the inner liner comprises between approximately 160 and 250 mg polymer compound. 20. A vessel closure according to claim 18, in the form of an aluminum screw cap for bottles, characterized in that the inner insert comprises between approximately 200 and 320 mg of the polymer compound. 21. A vessel closure according to claim 18, in the form of a screw closure made of plastic material for bottles, characterized in that the inner insert comprises between approximately 200 and 400 mg of the polymer compound. 22. Sealing element for vessel closures, in particular bottle and glass closures made of metal or plastic, consisting of a polymer compound according to one or more of claims 1 to 16. 23. Sealing element according to claim 22, characterized in that the sealing element is designed as an inner insert for a crown cork or a bottle screw closure in the shape of an approximately circular disk. 24. Sealing element according to claim 22, characterized in that the sealing element is designed as a sealing ring.