Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2001-06-11
2003-05-13
Boykin, Terressa M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C528S198000
Reexamination Certificate
active
06562936
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the production of a polycarbonate or the like and, more specifically, to the production of a polycarbonate or the like which is excellent in color, hydrolysis resistance, heat stability such as a reduction in molecular weight at the time of molding and color retention, and moldability such as releasability and transferability, rarely experiences residence deterioration such as coloring, crosslinking and gel formation, and has an extremely low content of foreign matter.
PRIOR ART
Polycarbonates are widely used in mechanical parts, optical moldings and auto parts, thanks to their excellent mechanical properties such as impact resistance, heat resistance and transparency.
The polycarbonates have recently been in great demand as optical moldings and widely used in optical disks, information disks, optical lenses, prisms and the like. Along with this, higher stability, releasability and transferability have been required of the polycarbonates.
Particularly, a polycarbonate having bisphenol A(2,2-bis(4-hydroxyphenyl)propane) as a recurring unit has recently been in increasingly demand mainly from optical media such as compact disks and CD-ROMs.
This polycarbonate is produced by directly reacting an aromatic dihydroxy compound (also called “aromatic diol”) such as bisphenol and phosgene (interfacial method) or by carrying out an ester exchange reaction between an aromatic dihydroxy compound and a carbonic acid diester (melting method).
Out of these, the latter method has such an advantage that the polycarbonate can be produced at a lower cost than the former interfacial method and is preferred from the viewpoint of environmental sanitation because a toxic substance such as phosgene is not used.
The polycarbonate obtained from a polycondensation reaction is generally treated by an intermeshing double-screw extruder. Particularly when the polycarbonate is supplied into an intermeshing double-screw extruder in a molten state to be treated, the coloring and crosslinking of the polycarbonate and the formation of a gel occur during this treatment and the content of foreign matter in the polycarbonate increases, thereby exerting a great influence upon the quality of a final product.
This problem is a general problem for polycarbonates. According to studies conducted by the present inventors, it has been found that this problem becomes marked particularly when a phosphorus-based compound is used as an additive to improve heat resistance or when a fatty acid ester is used as an additive to improve releasability in addition to the phosphorus-based compound.
According to studies conducted by the present inventors, it has also been found that the above problem tends to be marked when the devolatilization of a polycarbonate is carried out using water as a devolatilizing agent.
This problem is serious especially in the case of polycarbonates which have recently been used for optical application which requires high density and high accuracy, such as DVD, MO and CDR because coloring and gel formation exert a direct influence upon the optical properties such as block error rate and mechanical properties such as tension, bending and rigidity of a final product.
A polycarbonate obtained from a polycondensation reaction is generally pelletized, divided into small lots according to use purpose, remolten, mixed with additives for certain purposes and colored. A conventional polycarbonate may lack residence stability as it may be colored or its molecular weight may decrease at the time of melting. Therefore, when polycarbonate pellets are to be remolten, a heat resistant stabilizer or the like is added to improve heat stability. However, in this method, the polycarbonate is heated while it has low heat stability.
Since the water resistance of the polycarbonate may be lowered by the addition of the above heat resistant stabilizer, a molded product obtained from the polycarbonate may deteriorate in transparency during use.
JP-A 5-009286 (the term “JP-A” as used herein means an “unexamined published Japanese patent applications”) discloses a method of producing a polycarbonate by adding a phosphorus-based compound and/or a sulfur-containing acidic compound while the polycarbonate obtained from a melt polycondensation reaction is molten.
However, the publication fails to disclose a method of adding a phosphorus-based compound and/or a sulfur-containing acidic compound to the polycarbonate in a molten state and involves a problem to be solved for the continuous production of a polycarbonate having desired quality.
The above publication uses a sulfur-containing acidic compound as a catalyst neutralizer. The sulfur-containing acidic compound is added to the remaining catalyst excessively, specifically 2 times or more the molar amount of the catalyst, whereby the residual catalyst is neutralized and stabilized but an excess of the sulfur-containing acidic compound remains in the obtained polycarbonate. As a result, it cannot be said that the water resistance of the obtained polycarbonate is satisfactory, and the sulfur-containing acidic compound corrodes an aluminum film deposited on an optical disk molded product.
Therefore, the development of a polycarbonate continuous production method capable of stably producing a polycarbonate which is excellent in color and hydrolysis resistance as well as heat stability such as a reduction in molecular weight at the time of molding and color retention, and moldability such as releasability and transferability has been desired.
As for a method of producing a polycarbonate having excellent color and a low content of foreign matter by an ester exchange method, methods employing a pretreated reactor used for the production of a polymer have already been disclosed.
For example, JP-A 6-200008 discloses a method in which a reactor is cleaned with a phenol-based compound after the end of a reaction.
JP-A 6-56984 discloses a method in which polymerization is carried out after a stainless steel reactor is cleaned with a solution containing an aromatic hydroxy compound.
JP-A 9-241370 discloses a method in which a high-molecular weight polycarbonate having excellent color is obtained from a material containing substantially no FeOOH, CrOOH and NiOOH components present on the surface of a liquid contact portion. JP-A 8-277327 discloses a method in which the stainless steel of a liquid contact portion is heated.
However, all of the above publications fail to disclose or suggest a cleaning method disclosed by the present invention. The reduction of the number of foreign substances disclosed by the present invention is not taken into account in any of the above publications.
A polycarbonate for use in optical disks has recently been required to have a small error rate along with an increase in the recording density of the optical disks. A polymer having a reduced number of foreign substances which cause an error has been desired as the polycarbonate which meets the demand.
To obtain a polycarbonate having a reduced number of foreign substances, JP-A 5-239334 teaches a method of producing an optical polycarbonate having an extremely low content of foreign substances by melt polycondensing an aromatic hydroxy compound and a carbonic acid diester in the presence of a catalyst, adding and kneading additives and filtering the resulting product with a polymer filter.
JP-A 6-234845 discloses a method in which at least one filter is installed before and at the exit of the final reactor. However, the number of foreign substances formed during a reaction cannot be reduced by these methods.
JP-A 10-226723 teaches a method of obtaining a polycarbonate which is little colored and contains a small amount of fine foreign substances by transferring a polymer during or after polymerization through a pipe, wherein the flow rate of the polymer is 0.05 m/sec or more when the number average molecular weight of the molten polymer is less than 2,500 and 0.005 m/sec or more when the number average molecular weight of the molten polymer is 2,500 or more. All
Funakoshi Wataru
Hatono Kazuki
Hirata Masumi
Kaneko Hiroaki
Kiyoshige Kouji
Boykin Terressa M.
Teijin Limited
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