Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2000-06-30
2003-05-06
Kelly, Cynthia H. (Department: 1714)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S035800
Reexamination Certificate
active
06558761
ABSTRACT:
This invention concerns containers or linings for containers, particularly those which employ polymeric materials, and especially containers or linings which are intended for the transportation and storage of oxidising agents.
In recent years the distribution of solutions of oxidising agents and particularly aqueous solutions in small containers has increased dramatically. This is particularly true in the realm of disinfection and sanitisation, where the well known efficacy of microbicidal agents, combined with increasingly stringent regulations concerning health and safety in industries such as agriculture, healthcare, and food processing, has led to a greater awareness of their potential. They also find increasing usage in the home environment as for example toilet cleaners and hard surface cleaners.
On the large scale, the oxidising agents can be transported in containers such as intermediate bulk containers (IBC's) holding around 1,000 liters which can be re-used. The internal surfaces of these containers are usually specially designed and manufactured from materials which are resistant to oxidation, and which moreover do not affect the stability of the oxidising agent. Often they are formed from special grades of steel or alternatively from synthetic organic polymeric material. For many uses, particularly in the household, it is essential that the oxidising agent be provided in smaller containers, holding less than 25 liters, and often less than one liter, which are often employed for a single trip, in which case, the use of stainless steels would be both impractical and too expensive. The use of glass for small containers could be contemplated, but this would be an undesirable material for a number of both economic and practical reasons. First, glass containers are inherently fragile, and often need to be supplied surrounded by a suitable absorbent packing material which is preferably capable of not only reducing the chance of breakage but also safely taking up and holding any contents which are released accidentally. Secondly, special grades of glass would often be required to be suitably compatible with the contents. Thirdly, inner surface pre-treatment would often be necessary to prevent or reduce destabilisation of the contents. Moreover the contents would preferably be protected from damaging parts of the sun's radiation such as ultra-violet, by incorporation of a pigment or UV absorbent in the glass or by an outer wrapper. Glass is also unsuitable for squeezable containers used for household consumer products, typically squeezed to eject their contents onto a surface to be treated or into poorly accessible places such as under the rim of a conventional water closet.
In view of the known foregoing disadvantages of the listed materials, it has become commonplace for household-size containers to be made from organic polymeric compounds. These not only have the advantage of being cheaper in some instances, but in the case of thermoplastic polymers, they are capable of being moulded to any desired shape at higher temperature, and then retaining this shape on cooling. This allows them to be formed into containers that are easily handleable, and from which the contents can be poured out easily without undue inconvenience to the user. The methods of forming the containers are well known in the art, for example blow-moulding, injection moulding, thermoforming, solid-phase pressure forming or rotomoulding. The container walls can have a suitable thickness to enable the container to be rigid during normal storage, but sufficiently flexible to allow it to be deformed reversibly by hand squeezing. It also allows them to be formed into aesthetically pleasing shapes to appeal to customers, for example in a supermarket. Such materials are also easily coloured with dyes and pigments, which can be useful for product distinction.
However, there can be problems associated with such polymeric materials when they remain in contact for extended periods of time with an aggressive oxidising agent. Potentially the most dangerous of these problems is degradation of the container itself and a reduction of its mechanical properties. A loss of plasticity, often referred to hereinafter as embrittlement, can lead to rupture of the container when subjected to pressure, such as during stacking, squeezing or upon impact. It scarcely needs to be said that this is highly undesirable both from the economic perspective of product loss, but more importantly from a safety perspective, because any adjacent person, be he customer or operator, would be put at severe risk of sudden and unplanned contact with the chemical contents. The process of embrittlement can be significant in cooler climates, but is accelerated in hot climates or locations that enjoy high ambient temperatures.
To counteract adverse consequences, a number of industrial standards and specifications have been drawn up which govern the properties of polymeric materials for use with oxidising agents, and some of these have been codified into national and international laws and regulations.
It is well known that various additives can be incorporated into organic polymeric materials in order to retard or inhibit autoxidation of the polymeric chains. Such additives are usually added to the polymer prior to its being shaped into a desired form. It is not sufficient, however, in practice to consider the effect of the additives solely on the polymeric material. It is important to recognise that additives incorporated into container materials come into contact and interact with the contents of the container. Where the contents comprise oxidising agents, such additives can cause oxidising agents to decompose. This is disadvantageous, irrespective of whether the decomposition is rapid or slow. First, rapid decomposition can lead to a rapid increase in pressure inside the container which could cause its rupture and is thus unsafe. Secondly, the gradual loss of active oxidising agent is undesirable with regard to product quality and is thus economically undesirable. Thirdly, the reaction of an additive with contents leads to a lowering of the additive content in the polymeric material wall, with consequential loss of protection for the material. Consequently, the container needs protection from chemical attack to an extent that is unnecessary when the container is employed for water or other benign materials.
It is of further practical importance for at least some household applications that any additive is capable of passing current criteria with regard to food and drug regulations. This is especially relevant where the package contents are to be used directly on foodstuffs, or for sterilising or disinfecting work surfaces or medical instruments.
Several methods of preparation of the polymers employable in the current invention involve the use of a transition metal catalyst at some stage of the polymerisation process. It might be expected therefore, that incorporation into the polymer of substances which are normally regarded in the art as stabilisers for oxidants, such as peroxygens, and which are usually accepted as being effective due to their ability to chelate transition metals, would lead to stabilisation of an oxidant in contact with the polymer. It has been found surprisingly that incorporation of such a stabiliser into the polymer can result in an increased rate of loss of oxidant during storage. This is obviously undesirable because as well as stabilising the polymer towards embrittlement, it is important that any additive incorporated therein does not destabilise the container contents causing decomposition, which would have consequences as explained above.
A solution of a peracid is commercially available in a thermoplastic container which on analysis comprises a hindered phenol, which is a member of the class of materials known to act as antioxidants. The shelf-life of the container is more limited than is desired when filled with the peracid. This is an inconvenience in cold climates and is a distinct constraint on distribution
Lequeux Michel
Vandevijver Eric
Walton Michael E.
Williams Lesley A.
Ferguson Lawrence
Kelly Cynthia H.
Larson & Taylor PLC
Solvay ( Societe Anonyme)
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