Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2000-05-08
2002-08-06
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
06429276
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for producing an aromatic polycarbonate. More particularly, the present invention is concerned with a method for producing an aromatic polycarbonate, comprising: feeding, into a polymerizer apparatus, at least one polymerizable material selected from the group consisting of a molten monomer mixture of an aromatic dihydroxy compound and a diaryl carbonate, and a molten prepolymer obtained by a process comprising reacting an aromatic dihydroxy compound with a diaryl carbonate, the polymerizer apparatus including a guide-wetting fall polymerization reaction zone which has at least one guide securely held therein and extending downwardly therethrough, and allowing the polymerizable material to fall along and in contact with the at least one guide through the guide-wetting fall polymerization reaction zone, to effect a guide-wetting fall polymerization of the polymerizable material, thereby obtaining a polymer, wherein the guide is a perforated wall-surface guide. The present invention is also concerned with a polymerizer apparatus for practicing the above-mentioned method.
The method of the present invention for producing an aromatic polycarbonate is free from the problems accompanying the conventional method: such as the problem that phenol cannot be removed efficiently; the problem that a very large motive power for agitation is needed; the problem that the molecular chain of a polymer being formed is broken by a large shearing force due to the very large motive power for agitation, resulting not only in a reduced rate of increasing molecular weight but also in a discoloration of the polymer. Also, there is the problem that the polymer is likely to suffer thermal decomposition due to a long-term thermal history, thereby inevitably causing the polymer being produced to contain thermal decomposition products, and there is the problem that the volumetric efficiency of a polymerizer is extremely low.
By the method of the present invention, an aromatic polycarbonate having a desired constant molecular weight can be stably produced at a high polymerization rate, without discoloration with respect to the polymer or generation of foreign matter. Therefore, the method of the present invention is advantageous from a commercial viewpoint.
2. Prior Art
In recent years, aromatic polycarbonates have been widely used in various fields as engineering plastics having excellent heat resistance, impact resistance and transparency. With respect to methods for producing aromatic polycarbonates, various studies have heretofore been made. Of the methods studied, a process utilizing an interfacial polycondensation between an aromatic dihydroxy compound, such as 2,2-bis(4-hydroxyphenyl)propane (hereinafter, frequently referred to as “bisphenol A”), and phosgene has been commercially practiced.
However, the interfacial polycondensation process has problems. First, it is necessary to use phosgene, which is poisonous. Second, the reaction apparatus is likely to be corroded with chlorine-containing compounds, such as hydrogen chloride and sodium chloride (which are by-produced) and methylene chloride (which is used as a solvent in a large quantity). Third, difficulties are encountered in separating and removing impurities, such as sodium chloride, and the residual methylene chloride, which adversely affect properties of a produced polymer.
With respect to a method for producing an aromatic polycarbonate from an aromatic dihydroxy compound and a diaryl carbonate, a transesterification process has conventionally been known, in which a polycarbonate is produced by performing an ester exchange reaction between bisphenol A and diphenyl carbonate in the molten state, while removing a by-produced phenolic compound (such as phenol). Unlike the interfacial polycondensation process, the transesterification process has an advantage in that a solvent need not be used. However, the transesterification process has a serious problem, namely; since the viscosity of a polymer being formed increases during the progress of the polymerization reaction, it becomes difficult to remove by-produced phenol from the polymerization reaction system efficiently, thus making it difficult to achieve a high degree of polymerization with respect to the polycarbonate produced.
Various polymerizers have been conventionally used in producing aromatic polycarbonates by the transesterification process. A vertical agitation type polymerizer vessel equipped with an agitator is widely used. The vertical agitation type polymerizer vessel equipped with an agitator is advantageous in that it exhibits high volumetric efficiency and has a simple construction, so that polymerization on a small scale can be efficiently carried out. However, the vertical agitation type polymerizer vessel has a problem in that, as mentioned above, the by-produced phenol becomes difficult to remove from the polymerization reaction system efficiently in the production of aromatic polycarbonates on a commercial scale, so that the polymerization rate becomes extremely low.
Specifically, a large-scale vertical agitation type polymerizer vessel generally has a greater ratio of liquid volume to vaporization area than a small-scale one. In other words, the depth of a reaction mixture in the polymerizer is large and, hence, the pressure in the lower part of the agitation vessel is large. In such a case, even if the degree of vacuum of the polymerization reaction zone is raised in order to achieve a high degree of polymerization in the lower part of the agitation vessel, the polymerization proceeds under virtually high pressure due to the weight of the reaction mixture, so that phenol and the like cannot be efficiently removed.
To solve the above-mentioned problem, various attempts have been made to remove phenol and the like from high viscosity polymer being formed. For example, Examined Japanese Patent Application Publication No. 50-19600 (corresponding to GB-1 007 302) discloses the use of a screw type polymerizer having a vent. Examined Japanese Patent Application Publication No. 52-36159 discloses the use of an intermeshing twin-screw extruder. Examined Japanese Patent Application Publication No. 53-5718 (corresponding to U.S. Pat. No. 3,888,826) describes a thin film evaporation type reactor, such as a screw evaporator and a centrifugal film evaporator. Further, Unexamined Japanese Patent Application Laid-Open Specification No. 2-153923 discloses a method in which a combination of a centrifugal film evaporator and a horizontal agitation type polymerizer vessel is used.
Of these polymerizers, horizontal polymerizers, such as a screw evaporator and a horizontal agitation type polymerizer vessel, are intended to increase, by rotary agitation, the surface renewal of polymer (being formed) to a level as high as possible in an attempt to remove phenol and the like efficiently. For example, Examined Japanese Patent Application Publication No. 50-19600 describes that “A relatively large, continuously renewing interface is formed between the liquid reaction system and the ambient gas or vapor, so that a volatile reaction product formed in the liquid reaction system is extremely smoothly removed.” (see page 1, right-hand column, lines 19 to 22 of the above patent document). That is, the above patent document suggests that phenol and the like can be efficiently removed by the renewal of gas-liquid interface. Further, in Examined Japanese Patent Application Publication No. 52-36159, surface renewal effect “J” is defined as a function of the screw revolution rate, the screw surface area in the reaction zone, the total screw pitch number in the reaction zone, the feed amount of raw material and the effective volume per screw pitch in the reaction zone, and it is described that it is important that the value of the surface renewal effect be in a specific range.
However, these horizontal polymerizers need rotary agitation force provided by, for example, a screw or an agitator, for increasing the s
Fukuoka Shinsuke
Komiya Kyosuke
Asahi Kasei Kabushiki Kaisha
Birch & Stewart Kolasch & Birch, LLP
Boykin Terressa M.
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