Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
2001-10-04
2003-02-25
Boykin, Terressa M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C528S481000
Reexamination Certificate
active
06525171
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for producing a polycarbonate and a method of cleaning a production unit. More specifically, it relates to a process for producing a polycarbonate having excellent color and a method of cleaning a production unit for producing the above polycarbonate.
DESCRIPTION OF THE PRIOR ART
A polycarbonate resin obtained by interfacial polycondensation between bisphenol A and phosgene is widely used for various purposes, for example, electric and electronic parts, optical parts and auto parts thanks to its excellent mechanical properties and thermal properties. However, it involves a safety problem because phosgene which is toxic is used and also an environmental preservation problem because methylene chloride is used as a solvent. In addition, a chlorine component derived from methylene chloride and sodium chloride which is a by-product corrodes metallic material during the molding of a part because it remains in the polycarbonate. Then, a polycarbonate produced by an ester exchange method which eliminates use of methylene chloride and phosgene has recently been attracting much attention and polycarbonate products produced by melt polymerization have appeared on the market. However, since the polycarbonate obtained by the ester exchange method receives long-time heat history at a high temperature, it is inferior in color and therefore it is difficult to obtain a high-quality polycarbonate. Particularly, in a polycarbonate recently applied to optical uses such as DVD, DVD-RAM, MO, CD-R and CD-RW which are required to have high density and high accuracy, discoloration caused by low thermal stability and gelation caused by thermal deformation have a direct influence upon the optical properties such as block error rate and the mechanical properties such as tensile properties, flexural properties and toughness of the final product. Therefore, further improvement of color and thermal stability of the polycarbonate produced by the ester exchange method has been desired.
To suppress such discoloration, it is already known that use of an inert material as the material of a reactor is effective and there are proposed a method making use of nickel, tantalum, chromium or alloy thereof (U.S. Pat. No. 4,383,902) and a method making use of a material having an iron content of 20 wt % or less (JP-A 4-88017) (the term “JP-A” as used herein means an “unexamined published Japanese patent application”). However, reaction systems made of these materials are more expensive than reaction systems made of stainless steel and lined with glass which are used for interfacial polycondensation. The development of a reaction system which is made of an inexpensive material has been desired to prevent an increase in the cost of a polycarbonate.
One of the reaction systems made of inexpensive materials is a reaction system made of stainless steel. When a polycarbonate is produced by an ester exchange reaction using this reaction system, there arise such problems that the obtained polycarbonate is discolored, a high molecular weight polycarbonate is hardly produced and productivity is low.
To solve the above problems, a method for smoothing the surface by buffing (JP-A 4-7328) and a method for carrying out acid cleaning to remove scales on the surface and for immobilization (JP-A 4-7329) have been tried. However, with these methods, satisfactory results could not be obtained.
When production is started with a new system or when production is resumed after it is suspended, a considerably discolored polycarbonate is obtained for a long time in most cases and thus the production of articles below standards is unavoidable for a long time.
Further when a production unit is continuously used for a long time, the quality of the obtained polycarbonate deteriorates. Therefore, the production unit must be stopped, disassembled and serviced occasionally to maintain the quality. Accordingly, as the operation rate of the production unit is low and costs required for the disassembly and servicing of the system are high, there has been desired the development of an effective method of cleaning a production unit, which eliminates the need of disassembly and servicing without reducing the operation rate.
JP-A 6-56984 discloses a process for producing an aromatic polycarbonate by reacting an aromatic dihydroxy compound with a diaryl carbonate in a stainless steel reactor which has been cleaned with a solution containing an aromatic hydroxy compound.
JP-A 6-200008 discloses a process for producing a polycarbonate by reacting a carbonic acid diester with a dihydroxyaryl compound in a reactor whose reaction mixture contacting portion has been cleaned with a phenolic compound.
JP-A 9-25340 discloses a process for producing a polycarbonate through an ester exchange reaction in a reactor at least the liquid contacting portion of which has been cleaned with a carbonyl group-containing compound.
JP-A 9-124786 discloses a process for producing a polycarbonate from an aromatic dihydroxy compound and a carbonic acid diester compound in a reactor at least the liquid contacting portion of which has been cleaned with a cleaning fluid comprising a compound represented by the following formula in accordance with a melt ester exchange method:
R
01
—R
02
—OH
wherein R
01
is an alkyl group, aryl group or hydrogen atom and R
02
is an alkylene group or alkenylene group.
However, as the reaction system is not always cleaned thoroughly in the above methods, it is difficult to continuously produce a polycarbonate having excellent color for a long time.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method of cleaning a production unit for producing an aromatic polycarbonate having excellent color by an ester exchange method.
It is another object of the present invention to provide a method of cleaning an aromatic polycarbonate production unit, which enables the continuous production of an aromatic polycarbonate having excellent color for a long time when production is started with a new production unit or when production is resumed after suspension.
It is still another object of the present invention to provide a method of cleaning an aromatic polycarbonate production unit, which is capable of cleaning an aromatic polycarbonate production unit thoroughly, for example, by removing the residual polymer after the end of cleaning.
It is a further object of the present invention to provide a process for producing an aromatic polycarbonate by an ester exchange method with a production unit cleaned by the above cleaning method of the present invention.
Other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, firstly, the above objects and advantages of the present invention are attained by a method of cleaning an aromatic polycarbonate production unit, comprising cleaning the aromatic polycarbonate production unit with a carbonic acid diaryl ester at a temperature of 200 to 350° C. in an inert gas atmosphere.
According to the present invention, secondly, the above objects and advantages of the present invention are attained by a method of cleaning an aromatic polycarbonate production unit, comprising:
(1) depolymerizing an aromatic polycarbonate remaining in the production unit with a carbonate group-containing compound in the production unit to form a depolymerized product having a viscosity average molecular weight of 8,000 or less;
(2) discharging the depolymerized product from the production unit;
(3) introducing a carbonic acid diaryl ester into the production unit; and
(4) cleaning the inside of the production unit with the carbonic acid diaryl ester at a temperature of 200 to 350° C. in an inert gas atmosphere.
According to the present invention, thirdly, the above objects and advantages of the present invention are attained by a process for producing an aromatic polycarbonate, comprising carrying out an ester exchange reaction between an aromatic dihydroxy compound a
Kaneko Keiichi
Sasaki Katsushi
Sawaki Toru
Takemoto Hidemi
Boykin Terressa M.
Teijin Limited
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