This invention relates to the production of multilayer polymers structures comprising at least one layer of an alternating aliphatic polyketone and at least one comprising a polyamide having lengthy aliphatic chain segments.
Polymers of carbon monoxide and ethylenically unsaturated hydrocarbons commonly referred to as aliphatic alternating polyketones (hereafter, "polyketones") are now well known. High molecular weight alternating aliphatic polyketones are of considerable interest because they exhibit a good overall set of physical and chemical properties. The tribological and barrier properties of these materials are particularly noteworthy. This class of polymers is disclosed in numerous U.S. patents assigned to Shell Oil Company exemplified by U.S. Pat. Nos. 4,880,903 and 4,880,904 which are incorporated herein by reference.
No single polymer is known to possess properties that are optimal or even desirable for all possible polymer applications. A number of strategies are used to enhance the properties of polymers which may be useful in some respects and less desirable in others. One such approach is the formulation of polymer blends. Blending usually results in a material that has an overall property set that is the average of the materials blended. material that has an overall property set that is the average of the materials blended Another approach is to enhance a polymer's properties through the addition of certain additives. For example, certain stiff polymers may be made flexible by the addition of placticizers. Another strategy that can be used is the formation of a multilayer structure using two or more different polymers. This is frequently seen in packaging applications in which the multilayer structure is comprised of two or more polymers. For example, one polymer layer may provide the necessary chemical barrier characteristics, while benefiting from the lower cost and desired mechanical properties of another.
It would be useful to form composites or multilayer structures from the combination of one or more layers of polyamide-12 (PA-12) together with one or more layers of polyketones. PA-12 finds considerable commercial utility in applications such as industrial hoses, pipes, liners and automotive fuel lines. The barrier properties of monolithic PA-12 structures to materials such as fuels, however, could be substantially improved. This could be affected by preparing the tubing as a composite of PA-12 and polyketone. Unfortunately, PA-12 and polyketone polymers are generally considered to be insufficiently compatible or adhesive. That is, PA-12 will not readily adhere to polyketones after melt processing. Other polyamides of immediate interest which are also generally insufficiently compatible with polyketones include PA-6, PA-11, and PA-6,12.
Compatabilization of the polymer/polymer interface is a critical issue in the formation of composites. Weak interfacial bonding between the layers can result in delamination and poor overall mechanical properties. This can be overcome in some cases through the use of a tielayer between layers to be formed into the composite. Such a tielayer must be compatible or adhesive with the polymers it will join together. Another requirement of the tielayer is that it must be processible under the conditions in which the materials to be joined will be processed. Thermal degradation or crosslinking of the tielayer when exposed to the high processing heat and conditions generally required of polyketone polymers would be counterproductive in most cases. These requirements and others make it difficult to predict which materials might be useful as tielayers for any given set of polymers and make it difficult to engineer useful tielayers and composites.
U.S. Pat. No. 5,369,170 proposes a composite comprising an aminated modified polyolefin and a polyketone. The modified polyolefin can be made by reacting a modified polyolefin such as a maleic anhydride grafted polypropylene with an amine such as a diamine. The method of forming a polyketone/polyolefin layer does not address PAs.
U.S. Pat. No. 5,232,786 proposes a coextruded multilayer structure of polyketone and another layer of a cracked polybutylene or PA-6, PA-12, a copolyetherester, or a polyvinyl chloride. The multilayer structures do not use a tielayer and can consequently be readily separated when the integrity of a layer is stressed or impaired (e.g., by inducing a kink).
U.S. Pat. No. 5,300,338 proposes a coextruded laminate of polyketone and polyvinylidene flouride, PA-6,6, or phenoxy resin. The patent describes at least three different types of adhesion among various bilayer composites. The strongest adhesion was designated "interactive adhesion" and described an adhesion in which the layers could be separated only by destroying one or both of them. The weakest adhesion was designated as a "mechanical bond" in which a composition could be delaminated once the integrity of either layer was impaired. An intermediate level of adhesion was described as a "strong resistance to peel". A bilayer tubing was prepared comprising a polyketone layer and a layer of PA-6,6/PA-12 blend. The tubing displayed an intermediate level of adhesion and was not part of the inventive composition (it was prepared for comparative purposes).
None of the compositions and applications described above teach how one might effectively bond polyketone polymers with PA polymers having lengthy aliphatic chain segments (e.g., PA-12). Improvements in polyketone/PA composites would be beneficial in a number of applications. This could be most directly affected through the use of tielayers which increase the adhesion between the polymer layers.