Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1997-07-07
2000-08-29
Cain, Edward J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
4274071, C08K 338
Patent
active
06111006&
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process of preparation of polymer films and polymer coatings on substrates, to the use of certain polymer compositions for the preparation of such films and coated substrates and to certain polymer compositions. In particular the invention relates to the use of polyhydroxy-alkanoate polyesters in such method and certain compositions thereof.
Films of polymers have many uses. Free standing films of plastics materials have innumerable industrial and consumer applications. Supported films, for example, coated paper, are also widely useful, particularly for imparting the qualities of moisture resistance and heat-sealability to the coated support.
In principle, films can be prepared from polymer either by using a preparation of molten polymer or by the use of a solution of polymer in a suitable solvent. In the latter case, it is clearly necessary to match a polymer with a suitable solvent for it; for polyhydroxyalkanoate polymers, which have the merit of being biodegradable, a problem exists in that the suitable solvents are generally chlorinated and therefore environmentally detrimental. Attention has therefore diverted to attempting to prepare films of these biodegradable, and hence environmentally friendly, polymers from molten preparations of the polymer; and it is to this area that the present invention is directed.
Extrusion coating of polymer films from molten polymer has been developed for a number of plastics, in particular low density polyethylene. The standard procedure is for molten polyethylene to be extrusion coated onto a chilled roller, known in the art as a chill-roll. Low density polyethylene crystallises very quickly, and at reasonably low temperatures, so that it is adequately crystalline before it is drawn off the chill-roll, even when the roll is operating at very high line speeds, such as 700 m/min. Polyhydroxyalkanoate polymers crystallise much more slowly than low density polyethylene at typical chill-roll temperatures.
The process of polyhydroxyalkanoate crystallisation from the molten state involves growth of spherulites, which are spherical regions of crystallised material around a nucleus. Such a nucleation site may occur in the pure polymer or can be artificially introduced by the use of a nucleating agent. The optimum temperature for creating nucleating sites is considerably lower than the optimum temperature for growth of the spherulites. However the optimum temperature for crystallisation is a combination of the two parameters and usually falls between the two parameters.
It has now been found that it is possible to adapt a chill-roll process for the preparation of a polyhydroxyalkanoate film if the film formation is allowed to take place on the roll at a relatively high temperature compared to conventional extrusion coating processes, so as to improve or optimise crystallisation. The use of a high temperature chill roll allows relatively high line speeds and particularly high line speeds can be achieved using polyhydroxyalkanoate polymer with a high melt flow index (MFI).
Thus, according to a first aspect of the present invention, there is provided a process for the preparation of extruded film or extrusion coating of a polyhydroxyalkanoate polymer, the process comprising applying a layer of molten polyhydroxyalkanoate to a surface which is at a temperature in the range from 20.degree. C. above to 20.degree. C. below the optimum crystallisation temperature of the polymer, so as to form a film or coating.
Crystallisation temperature range is dependent on the co-polymer content and various additives, primarily the nucleating agent.
The molten PHA preferably has a MFI of 12 or greater, especially 18 to 35.
Therefore, in a further embodiment of the present invention there is provided a process for the preparation of extruded film or an extrusion coating of a polyhydroxyalkanoate polymer, the process comprising applying a layer of molten polyhydroxyalkanoate having a melt flow index of 12 or greater to a surface which is at a temperature in the range from
REFERENCES:
patent: 4537738 (1985-08-01), Holmes
Beusen, Esq. Jon H.
Cain Edward J.
Monsanto Company
Simon Howrey
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