Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
2002-04-30
2004-04-13
Boykin, Terressa (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C264S211240, C264S176100, C524S151000, C524S611000, C528S196000, C528S198000
Reexamination Certificate
active
06720406
ABSTRACT:
The invention relates to a process for producing polymer pellets, in particular polycarbonate pellets, from polymer melts, in particular polycarbonate melts, by melt extruding the polymer, cooling the melt in a cooling fluid and pelletizing the solidified polymer, in which process the cooling air or ambient air coming into contact with the polymer exhibits a solids particle content of at most 10 ppm, preferably at most 5 ppm, particularly preferably at most 0.5 ppm.
High purity polycarbonates are used for optical mouldings, for example for optical and magneto-optical storage media, in particular laser-readable or -writable data storage media. Since there is a desire for these media to exhibit ever greater storage capacity, the polycarbonates used have also to exhibit increased levels of purity.
Such high purity polycarbonate is additionally used in glazing for motor vehicles and diffusers for car reflectors, in which a high level of light transmission without imperfections in the moulding is of enormous importance. Glazing of other kinds, such as for greenhouses, so-called double-wall sheets or cellular sheets or solid sheets. These mouldings are produced by injection moulding, extrusion and extrusion blow moulding using a polycarbonate with a suitable molecular weight.
To produce polycarbonates by the so-called phase interface process, dihydroxydiarylalkanes in the form of their alkali-metal salts are reacted with phosgene in the heterogeneous phase in the presence of inorganic bases such as sodium hydroxide solution and an organic solvent, in which the produced polycarbonate is readily soluble. During the reaction, the aqueous phase is dispersed in the organic phase and, after the reaction, the organic polycarbonate-containing phase is washed with an aqueous fluid intended, inter alia, to remove electrolytes and the washing fluid is then separated off. The organic solvent is then removed from the polycarbonate. In the last stage, the polycarbonate is converted into a form, e.g. pellets, which may be readily further processed.
Another possible way of producing polycarbonates is the melt transesterification process or variants thereof (three stage processes involving melt production of oligocarbonate, crystallisation, solid phase polycondensation). Here too, the polycarbonate is converted after reaction/production into a form, e.g. pellets, which may be readily further processed.
If the conventional working-up/pelletizing processes are used, the quality of the polycarbonates, in particular with respect to impurities and imperfections in the polycarbonate, is observed to be inadequate for certain uses of the polycarbonates.
The object of the invention is to provide polycarbonates and copolycarbonates having even greater purity with regard to freedom from imperfections, which are suitable for producing mouldings, in particular optical mouldings, magneto-optical and optical data storage media with particularly high data densities or a particularly low occurrence of defects and which avoid the disadvantages of the known processes.
The number of imperfections in the polycarbonate may be determined by a laser film scan test.
It has been found that the necessary polycarbonate quality may be achieved with a process of the above-stated type if working-up/pelletisation of the polycarbonate is performed under certain special conditions, according to the characterising clause of claim 1.
The invention provides a process for producing polymer pellets, in particular polycarbonate pellets, from polymer melts, in particular polycarbonate melts, by melt extruding the polymer, cooling the melt in a cooling fluid and pelletizing the solidified polymer, characterised in that the cooling air or ambient air coming into contact with the polymer exhibits a solids particle content of at most 10 ppm, preferably 5 ppm, particularly preferably 0.5 ppm.
The preferred process is characterised in that the melt extrusion, cooling of the melt and pelletisation of the polymer are performed in an enclosed room.
Pelletisation is particularly preferably performed in a room, wherein the ambient air coming into contact with the polymer material is filtered in stages, the air being preferably initially filtered through primary filters of filter classes EU 5 to EU 7, then filtered through fine filters of filter classes EU 7 to EU 9 and finally through final filters of filter classes EU 13 to EU 14 (wherein the filter classes are determined to DIN 24183 or EUROVENT 4/5, 4/4 as at August, 1999).
These polymer pellets and the mouldings produced therefrom exhibit very good results when tested using the laser film scan test, the polycarbonates produced according to the invention comprising less than 250, in particular less than 150 imperfections per m
2
of extruded film.
The invention further provides the polymer pellets which may be obtained using the process according to the invention and the use thereof to produce transparent mouldings, wherein use for producing laser-readable data storage media is particularly desirable.
The invention likewise provides transparent mouldings made from the polymer pellets according to the invention.
The polymers to be used according to the invention are, for example, polycarbonates, both homopolycarbonates and copolycarbonates and mixtures thereof. The polycarbonates may be aromatic polyester carbonates or polycarbonates which are present in a mixture with aromatic polyester carbonates. The term polycarbonate is used below to cover all the above-mentioned polymers. The polycarbonate which is preferably used is obtained in particular by the so-called phase interface process or the melt transesterification process (H. Schnell “Chemistry and Physics of Polycarbonates”, Polymerreview, Vol. IX, p. 33 ff., Interscience Publishers, New York 1964).
One of the preferred embodiments of the above-stated production process is a variant in which the feed materials are further processed according to the phase interface process,
wherein the reaction solution containing polycarbonate is optionally filtered directly after the reaction,
the aqueous phase is separated off and the polycarbonate solution obtained is optionally filtered again,
washing is performed,
the washing fluid is separated off and the solvent is evaporated,
and the mixture of organic polycarbonate solution and residual washing fluid obtained after removal of the washing fluid is optionally heated until a clear solution is obtained,
before filtration is performed again at least once, preferably twice, particularly preferably at least three times, very particularly preferably in stages to separate off the solids,
the solvent is separated off from the polycarbonate,
and the polycarbonate is worked up and pelletised under the conditions of the process according to the invention.
A preferred embodiment further provides, in addition to filtration of the cooling air or ambient air, that any cooling fluid which comes into contact with the polymer exhibits a foreign particle content of at most 2 million particles per 1 of water (particle size >0.5 &mgr;m), particularly preferably at most 1 million particles per 1 of water (particle size >0.5 &mgr;m), very particularly preferably at most 0.5 million particles per 1 of water (particle size >0.5 &mgr;m).
This may be achieved by filtration of the cooling fluid.
Filtration of the other feed materials, additives and cooling fluid medium is conveniently performed as a rule using membrane filters. The pore size of the filter materials amounts as a rule to from 0.01 to 5 &mgr;m, preferably from 0.02 to 1.5 &mgr;m, preferably from 0.05 &mgr;m to 0.6 &mgr;m. Such filter materials may be obtained commercially for example from Pall GmbH, D-63363 Dreieich and Krebsödge GmbH, D-42477 Radevormwald (SIKA-R CUIAS type).
In a preferred variant, filtration is carried out in stages with a plurality of filters, wherein coarser filters are conveniently used initially, followed by finer filters.
Another preferred polycarbonate production process is the melt polycarbonate process, in which, starting with aro
Elsner Thomas
Heuser Jürgen
Kords Christian
Kühling Steffen
Viroux Paul
Bayer Aktiengesellschaft
Boykin Terressa
Gil Joseph C.
Matz Gary F.
Preis Aron
LandOfFree
High-purity polymer granules and method for the production... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High-purity polymer granules and method for the production..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High-purity polymer granules and method for the production... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3262366