Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
2002-08-02
2003-09-16
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...
C264S176100, C264S219000, C264S330000, C359S642000, C524S127000, C525S064000, C525S067000, C525S148000, C525S462000, C525S464000, C528S196000, C528S198000, C528S480000, C528S499000, C528S50200C, C528S503000
Reexamination Certificate
active
06620906
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a polycarbonate having a low particle content and to a process for producing high-purity polycarbonate and polycarbonate of maximum purity produced therefrom as well as moulded products made from this polycarbonate.
BACKGROUND OF THE INVENTION
In order to produce polycarbonates by the so-called phase interface process, dihydroxydiarylalkanes in the form of their alkali metal salts are reacted with phosgene in heterogeneous phase in the presence of inorganic bases such as sodium hydroxide solution and of an organic solvent in which the product polycarbonate is readily soluble. During the reaction, the aqueous phase is distributed in the organic phase and after the reaction the organic, polycarbonate-containing phase is washed with an aqueous liquid, which is intended to remove inter alia electrolytes, and the washing liquid is then separated off.
Moulded products made of high-purity polycarbonates are used for optical and magneto-optical purposes, in particular in laser-readable data storage media. As the storage capacity of these media is being constantly enlarged, the demands placed on the purity of the polycarbonates used are also increasing.
DETAILED DESCRIPTION OF THE INVENTION
The object of the invention is to provide a process for removing volatile components from a polymer solution, in order to produce a high-purity polycarbonate having a particularly low particle content, which is particularly suitable as starting material for moulded products for data storage.
This object was achievable by the development and provision of the process according to the invention described in more detail below.
The invention firstly provides a process for producing polycarbonate by the phase interface process, in which the polycarbonate-containing solution is washed with an aqueous washing liquid, the washing liquid is separated off and the solvent is evaporated off and wherein the mixture of organic polycarbonate solution and residual washing liquid obtained after the separation of the washing liquid is heated by indirect heat exchange until a clear solution is attained and filtered in order to remove solid substances, wherein
A) in an initial stage, in one or more individual steps, the solution, which has a polymer content of 5 to 20 wt. %, is concentrated to 60 to 75 wt. % at a temperature of 150° C. to 250° C. in a combination of a shell-and-tube heat exchanger and a film evaporator or a coiled-tube evaporator or in a shell-and-tube heat exchanger, in each case with downstream separator, the pressure in the separator being about 0.1 to 0.4 MPa, preferably ambient pressure (i.e. about 0.1 MPa),
B) in a further stage, the solution is concentrated from 60 to 75 wt. % to at least 95 wt. %, in particular to 98 to 99.9 wt. %, at a temperature of 250° C. to 350° C., in a shell-and-tube heat exchanger with downstream separator, the shell-and-tube heat exchanger containing vertical, heated, straight tubes with or without incorporated static mixers, having an internal diameter of 5 to 30 mm, preferably of 5 to 15 mm, a length of 0.5 to 4 m, preferably of 1 to 2 m, and the throughput per heat-exchanger tube through the tubes being 0.5 to 10 kg/h, preferably 3 to 7 kg/h, based on the polymer, and the pressure in the separator being 0.5 kPa to 0.1 MPa, in particular 3 kPa to 0.1 kPa, preferably 3 kPa to 10 kPa,
C) in a further stage, the solution containing remains of solvent and/or of volatile components is concentrated to a content of solvent and/or of other volatile components of 5 to 500 ppm, at a temperature of 250° C. to 350° C., in a further shell-and-tube heat exchanger with downstream separator or in an extruder-evaporator, the shell-and-tube heat exchanger containing vertical, heated, straight tubes having an internal diameter of 5 to 30 mm, preferably of 10 to 20 mm, a length of 0.2 to 2 m, preferably of 0.5 to 1 m, and the throughput per heat-exchanger tube through the tubes being 0.5 to 10 kg/h, preferably 3 to 7 kg/h, based on the polymer, and the pressure in the separator being 0.05 kPa to 0.1 MPa, in particular 0.1 kPa to 2 kPa, and
D) the degassed polymer is subsequently isolated and optionally granulated.
According to the invention, the term “polymer” covers polycarbonates, in fact, both homopolycarbonates and copolycarbonates and mixtures thereof. The polycarbonates according to the invention can be aromatic polyester carbonates or polycarbonates in a mixture with aromatic polyester carbonates. The term “polycarbonate” is subsequently used in place of the previously mentioned polymers.
The polycarbonate according to the invention is obtained by the so-called phase interface process (H. Schnell, “Chemistry and Physics of Polycarbonates”, Polymer Review, Vol. IXS, 22 ff., Interscience Publishers, New York 1964), in which the polycarbonate-containing solution is subsequently washed with a washing liquid, the washing liquid is separated off and the solution is evaporated off. According to the invention, this process is carried out in the stages described.
Compounds preferably used as starting compounds according to the invention are bisphenols corresponding to the general formula HO—Z—OH, wherein Z is a divalent organic group having 6 to 30 carbon atoms, which contains one or more aromatic groups. Examples of such compounds are bisphenols, which belong to the group comprising dihydroxydiphenyls, bis(hydroxyphenyl)alkanes, indane bisphenols, bis(hydroxyphenyl) ethers, bis(hydroxyphenyl) sulfones, bis(hydroxyphenyl) ketones and &agr;,&agr;′-bis(hydroxyphenyl)diisopropylbenzenes.
Particularly preferred bisphenols, which belong to the above-mentioned groups of compounds, are 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), tetraalkylbisphenol A, 4,4-(meta-phenylenediisopropyl)diphenol (bisphenol M), 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexanone as well as optionally mixtures thereof. Particularly preferred copolycarbonates are those based on the monomers bisphenol A and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexanone. The bisphenol compounds to be used according to the invention are reacted with compounds of carbonic acid, in particular phosgene.
The polyester carbonates according to the invention are obtained by reaction of the bisphenols already mentioned above, at least one aromatic dicarboxylic acid and optionally carbonic acid. Suitable aromatic dicarboxylic acids are, for example, orthophthalic acid, terephthalic acid, isophthalic acid, 3,3′- or 4,4′-diphenyldicarboxylic acid and benzophenonedicarboxylic acids.
Inert organic solvents used in the process are preferably dichloromethane or mixtures of dichloromethane and chlorobenzene.
The reaction can be accelerated by catalysts, such as tertiary amines, N-alkylpiperidines or onium salts. Preferably tributylamine, triethylamine and N-ethylpiperidine are used. A monofunctional phenol, such as phenol, cumylphenol, p-tert. butylphenol or 4-(1,1,3,3-tetramethylbutyl)phenol can be used as a chain stopper and molar mass controller. Isatinbiscresol, for example, can be used as branching agent.
To produce high-purity polycarbonates according to the invention, the bisphenols are dissolved in aqueous alkaline phase, preferably sodium hydroxide solution. The chain stoppers optionally required for the production of copolycarbonates are dissolved in quantities of 1.0 to 20.0 mol. % per mol bisphenol in the aqueous alkaline phase or added to the latter in solid form in an inert organic phase. Then phosgene is introduced into the mixer containing the other reaction components and the polymerisation is carried out.
A part, up to 80 mol. %, preferably from 20 to 50 mol. %, of the carbonate groups in the polycarbonates can be replaced by aromatic dicarboxylic ester groups.
In a further development of the invention, the thermoplastic polycarbonates have average molecular weights M
w
and a foreign particle index of less than 2.5·10
4
&mgr;m
2
/g. The sodium content is preferably less than 30 ppb, measured by atomic absorption spectroscopy.
During the reaction, the aqueou
Elsner Thomas
Heuser Jürgen
Kords Christian
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