Process for purifying polycarbonate resin solution

Details Process for purifying polycarbonate resin solution Process for purifying polycarbonate resin solution

2000-01-05

2002-05-07

Sergent, Rabon (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Treating polymer containing material or treating a solid...

C528S485000, C528S499000, C528S50200C, C210S644000, C210S767000, C210S791000, C210S799000

Reexamination Certificate

active

06384185

ABSTRACT:

BACKGROUND OF THE INVENTION
1) Field on the Invention
The present invention relates to a process for purifying a polycarbonate resin solution and more particularly to a process for purifying a polycarbonate resin solution by efficient separation between an organic solvent solution of the polycarbonate resin and an aqueous solution containing contaminations from a polycarbonate resin emulsion.
2) Prior art
Presently, as a process for producing a polycarbonate resin, a conventional process for producing a polycarbonate resin by an interfacial polycondensation method using a halogenated organic solvent such as methylene chloride is applied. In the process for producing a polycarbonate resin by the interfacial polycondensation method, a mixture of an organic solvent solution of a polycarbonate resin (hereinafter, sometimes abbreviated as “oil phase” or “O”) with an aqueous solution (hereinafter, sometimes abbreviated as “W”) is obtained at the time of the completion of the polycondensation. Since the organic phase containing a polycarbonate resin contains contaminations as by-products during the polycondensation and an alkali aqueous solution and forms an emulsion, separation between the organic solvent solution and the aqueous solution from the emulsion need to be performed.
Moreover, in order to remove a very small amount of contaminations remained in the organic solvent solution of a polycarbonate resin, a method for rinsing out the contaminations by adding an alkali aqueous solution, an acidic aqueous solution, pure water, etc., is usually applied. However, in the method, when a mixture of a polycarbonate resin solution and a rinsing liquid is vigorously stirred, an emulsion often forms.
Hitherto, in order to perform separation between the organic solvent solution and the aqueous solution from the emulsion, a liquid-liquid centrifugal separator or a settler has been used. However, when the emulsion is separated with a centrifugal separator, the centrifugal separator itself is not only expensive, but also maintenance cost of the centrifugal separator and electric power for its operation become very large. Further, unplanned stopping of the centrifugal separator has been often caused due to failure and abrasion of driving portion or rotating portion.
The separation by settling caused defects that a settler and hold-up time became large in order to ensure hold up time for separation, even if a separation plate or a baffle plate is inserted inside.
As methods to solve such problems, processes of separation by aggregation are known, for example, Japanese Patent Publication No. 46-41622 discloses a process for separation comprising passing a polycarbonate resin solution through a filtering layer having a contact angle with water of 40° or below. However, in the process, since it was comparatively difficult to separate minute water particles, it was necessary to pass repeatedly the polycarbonate resin solution through the filtering layer. Further, since contamination from a material of the filtering layer occurred and it took a time for separation after passing through the filtering layer, comparatively large settler was required.
Further, Japanese Patent Kokai (Laid-open) No. 7-309940 discloses a process of separation comprising mixing a polycarbonate resin solution with an aqueous washing liquid to form an oil droplet-in-water type emulsion and performing washing and then passing the emulsion thus washed through a filtering material. However, in the process, since a treating quantity for separation was increased, there caused problems that a large scale of instrument for separation and waste water disposal facility were required.
Japanese Patent Kokai (Laid-open) No.55-104316 discloses a process for separation between the organic solvent phase and the aqueous phase comprising passing a polycarbonate resin solution emulsified with an aqueous washing liquid of pH 2 to 14 through a fiber layer with a depth of 10 to 500 mm and an apparent density of 0.2 to 0.7 g/ml at a space velocity of 0.01 to 2 cm/second. However, the process caused defects that since the filtering layer had a large depth, pressure loss through the filtering layer due to the filler occurred, and the filtering material was flowed out and a settler was necessary.
Japanese Patent Kokai (Laid-open) No. 9-104747 discloses a process which comprises washing a crude polycarbonate solution with washing water under stirring and then performing separation between the water phase and the organic phase containing a polycarbonate resin from the crude polycarbonate resin containing the washing water by settling or centrifugal separation and filtering the organic phase containing a polycarbonate resin through a filter with pore size 20 to 180 &mgr;m at a filtering velocity of 60 to 1000 mm/min. However, in the process, although settling or centrifugal separation should be performed before filtering with a filter, it was very difficult to separate an emulsion composed of the organic solvent solution of a polycarbonate resin and the aqueous solution by settling, and even if it is possible to separate, a settler becomes very large since a long time is necessary to ensure hold-up time. Moreover, when centrifugal separation is performed, as described above, maintenance cost of centrifugal separator and electric power for its operation become very large and it is necessary to provide a spare centrifugal separator for unplanned stopping of centrifugal separator, so that operation becomes complicated.
On the other hand, in molded articles in which mixing-in of dusts need be diminished as much as possible, for example, molded articles such as compact disc, laser disc, optical card, MO disc and DVD utilized characteristics of polycarbonate including transparency, heat resistance, hydrolysis resistance and dimension stability, reduction of dusts has been required since mixing-in of dusts exerts bad influence on reading and writing of signals of submicron.
It is preferable that polycarbonate resin as an optical material contains a small quantity of “dust” as far as possible. The “dust” herein is a substance having a short diameter 0.5 &mgr;m or above derived from dusts and rubbishs in the atmosphere, contaminations contained in raw materials, floating substances remained in a solvent, metal powders due to abrasion of pneumatic pipes or instruments, etc., which causes troubles such as reading errors, writing errors by remaining in an optical disc and can be determined according to measuring equipments such as optical microscope and minute particle counter obtainable on the market.
SUMMARY OF THE INVENTION
An object of the present invention is to overcome above-mentioned defects of prior art and provide a process for purifying a polycarbonate resin solution by efficient separation between an organic solvent solution of the polycarbonate resin and an aqueous solution containing contaminations from a polycarbonate resin solution.
As a result of extensive studies to solve above-mentioned prior art problems, the inventors have found that when an water-in-oil dispersion type (W/O) emulsion composed of a mixture of an organic solvent solution with an aqueous solution and having water particles with an average diameter 1 to 100 &mgr;m in an oil is passed through a metallic filter having a filtering precision of 10 to 200 &mgr;m, a water phase in the emulsion is temporarily captured with the metallic filtering material and then the water particles are efficiently aggregated and grown on the metallic filter surface at the time of extrusion from the metallic filter and the mixture of the oil phase with the aqueous phase is passed through the metallic filter without remaining on the metallic filter, and then separation between the organic solvent solution of the polycarbonate resin and the aqueous solution containing contaminations can be readily performed by settling of the mixture of the oil phase with the aqueous phase passed through the filter for a prescribed time, thereby obtaining a polycarbonate resin solution reduced contaminations and dusts, and

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