Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
1993-12-03
2001-09-18
Dye, Rena L. (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C220S562000, C206S524900, C280S830000, C261S119100
Reexamination Certificate
active
06291042
ABSTRACT:
The present invention relates to a multilayer container made of thermoplastic material for storing hydrocarbons. This container is particularly suitable for use in automobiles.
Containers made of thermoplastic material, notably those made from polyolefins, demonstrate numerous advantages over their counterparts made of metal, notably, better impact resistance, better resistance to corrosion by exterior agents, increased weight, and greater freedom of form, etc.
However, thermoplastic materials and, particularly, polyolefins have the drawback of not being completely impermeable to a number of solvents and primarily to hydrocarbons used as motor fuel for automobiles.
Taking into account ecologic standards for limiting pollution and respecting the environment, it is thus of prime importance in the realization of such containers to provide the most effective impermeabilization treatment possible.
According to a first means which is described in European Patent Application EP-A-384,469, containers made of polyethylene, for example, may be coated to this end by means of a film of a polymer highly impermeable to solvents such as poly-omega-lactam. However, this technique makes it necessary to resort to an additional manufacturing step, namely, the deposition and polymerization of a suitable film by means of rotational molding, which is time-consuming and expensive.
According to another means described in publication WO 91/09732, such containers may be manufactured from a co-extruded parison including outer layers consisting of polyethylene and an inner layer consisting of previously sulfonated polyethylene. However, taking into account the incompatibility of polyethylene and previously sulfonated polyethylene, and in order to eliminate any subsequent risk of delamination, one is thus directed to use an adhesive intermediary layer, which will complicate the production of such containers and increase their actual cost. Another means, notably described in European Patent Application EP-A-500,166, and which until now has proved to be efficient and very economical, consists in subjecting the inner wall of such containers to a superficial treatment such as fluoration or sulfonation during or after their production.
However, stricter and stricter ecologic standards and the recent introduction of mixed fuels containing oxygenated compounds such as methanol impose higher performance fluoration or sulfonation treatments which place economic restraints on conventional containers produced, notably those made from polyolefins such as polyethylene.
In fact, the polyolefins generally used in order to realize fuel containers by blow molding must meet a number of criteria in order to be able to satisfy the specifications imposed on the final product.
Thus, these polyolefins must, among other things, demonstrate sufficient resistance to:
impact
stress-cracking
fuel
ultraviolet rays.
Moreover, these polyolefins must be economical and exhibit suitable characteristics such as good heat stability and good resistance to oxidation to facilitate their use, and the material must be virgin material or derived from reused ground material and must have suitable characteristics (viscosity, melting behavior, resilience, etc.) for use in blow molding.
Thus, it appears that these requirements make it necessary to use special polyolefins that are generally difficult to treat with superficial fluoration or sulfonation and which require a more energetic and, consequently, longer and more costly treatment.
The applicant has now realized containers of thermoplastic material permitting the simultaneous use of special high-performance resins, notably with respect to mechanical properties while ensuring effective impermeability at less cost.
The present invention relates, therefore, to a multilayer container of thermoplastic material for storing hydrocarbons, which is characterized in that the wall comprises at least a thick outer layer consisting of a thermoplastic material which imparts to it good mechanical properties and a thin inner layer of a thermoplastic material adapted to receive a surface treatment for the purpose of increasing its impermeability to hydrocarbons. The thermoplastic material adapted to receive a surface treatment consists advantageously essentially of one or a plurality of virgin polyolefins.
The container according to the present invention thus has a wall consisting of at least two associated layers and allows the use of at least two materials that specifically meet the requirements, on the one hand, for the blown piece and, on the other hand, for its surface treatment with respect to good impermeabilization.
Thus, proceeding in this manner makes it possible to choose for the material constituting the outer layer, a thermoplastic material, such as, for example, polyethylene uniquely optimized in terms of mechanical properties and having the facility to be employed in blow molding, and for the material constituting the inner layer, a thermoplastic material chosen or developed primarily with the object of easily permitting an effective superficial fluoration or sulfonation treatment. The fluoration treatment is preferred.
The thermoplastic material constituting the outer layer may be one of the thermoplastic materials exhibiting optimization of the desired properties with preference being given to polyolefins and, particularly, to high-density polyethylene (HDPE).
The outer layer may optionally contain a defined proportion of recycled polyolefins, more particularly of re-ground polyolefins provided by a recycling plant of previously used containers. This proportion of re-ground materials may, nevertheless, be chosen in such a way as not to fundamentally affect the properties of the outer layer that is produced.
The thermoplastic material constituting the inner layer may be a polyolefin such as a high-density polyethylene of a quality especially adapted to the treatment of the surface to be utilized. It may also be another thermoplastic material adapted for this type of treatment, such as other polyolefins. Or it may be a mixture of such resins, more particularly, a mixture containing HDPE.
The inner layer essentially consists of one or a plurality of virgin polyolefins. Polyethylene is preferably used as polyolefins and, particularly, a high density polyethylene (HDPE). The inner layer preferably consists essentially of a single virgin polyolefin.
Virgin polyolefin refers to an unrecycled polyolefin, i.e., one which was not subjected to any process involving high temperatures such as extrusion, injection, etc., with the possible exception of a granulation phase, as explained below. For example, polyolefin fragments obtained by grinding tubes or containers consisting of polyolefin do not meet the definition of virgin polyolefin any more than production scraps (waste) collected when polyolefins were employed for extrusion, injection, calendaring, etc.
The term “essentially consisting of” is intended to define that if one or a plurality of other thermoplastic materials (for example, a recycled polyolefin) are used in a mixture with one or a plurality of virgin polyolefins (such as defined above), the total weight of these other thermoplastic materials does not exceed 5% by weight of virgin polyolefin, preferably 1%. One or a plurality of virgin polyolefins are particularly preferred as the one material or the only thermoplastic materials present in the inner layer.
Moreover, the thermoplastic material essentially constituting the inner layer, advantageously exhibits one or a plurality of the properties below, which notably allow to improve the impermeability of superficially treated containers comprising such an inner layer.
According to a preferred modification of the invention, the inner layer is essentially free of any pigment, in contrast to common usage, which is to employ a pigment that gives it a black color.
Advantageously, the inner layer is essentially free of any additive, with the possible exception of one or a plurality of hydroxyaromatic compounds whose hydroxyl group is stearically hind
Debelle Thierry
Masson Didier
Van Schaftingen Jules-Joseph
Wouters Paul
Dye Rena L.
Schneller Marina V.
Solvay ( Societe Anonyme)
Venable
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