Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2002-08-05
2004-02-24
Boykin, Terressa (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C264S176100, C428S412000, C528S198000
Reexamination Certificate
active
06696542
ABSTRACT:
The invention relates to polycarbonate substrates, the preparation of which is based on 1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexanone, and their use for producing shaped articles with particularly high purity and extremely high surface brilliance and also the shaped articles which can be produced from the polycarbonate substrate.
High purity polycarbonate is required for certain shaped articles, such as in particular glazing for vehicles and headlamp diffusers for vehicle reflectors, in which high light transmission without any defects in the moulded item is of enormous importance.
Polycarbonate is prepared by the so-called phase boundary process, in which dihydroxydiarylalkanes in the form of their alkali metal salts are reacted with phosgene in the heterogeneous phase in the presence of inorganic bases such as sodium hydroxide solution and an organic solvent in which the product polycarbonate is readily soluble. During the reaction the aqueous phase is dispersed in the organic phase and after reaction the organic, polycarbonate-containing phase is washed with an aqueous liquid, wherein inter alia electrolytes are removed, and the wash liquid is then separated off.
Japanese application JP-A 07 19 67 83 describes a process for the preparation of polycarbonate in which the content of iron in the sodium hydroxide solution used should be below 2 ppm in order to achieve favourable colour properties.
The object of the present invention is the provision of an alternative and improved process for the preparation of pure polycarbonate substrates and also to provide polycarbonate shaped articles with especially high purity.
Surprisingly, it has now been found that polycarbonate shaped articles with especially high surface brilliance and purity can be obtained from polycarbonate substrates, the preparation of which is based on 1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexanone, with average molecular weights of 25,000 to 400,000 and which are prepared by a specific process.
The present application therefore provides polycarbonate substrates, the preparation of which is based on 1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexanone, with a number of defects per m
2
of fewer than 250, in particular fewer than 150, measured on a 200 &mgr;m extruded film.
The application also provides shaped articles and films, in particular glazing for vehicles and headlamp diffusers for car reflectors based on polycarbonate substrates, the preparation of which is based on 1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexanone, with a number of defects per m
2
of fewer than 250, in particular fewer than 150, measured on a 200 &mgr;m extruded film.
Polycarbonate substrates according to the invention are obtained by using a specific process.
The application therefore provides a process for the preparation of polycarbonate by the phase boundary process, wherein dihydroxydiarylalkanes in the form of their alkali metal salts are reacted with phosgene in the heterogeneous phase in the presence of sodium hydroxide solution and an organic solvent, characterised in that
a) the feedstocks are low in Fe, Cr, Ni, Zn, Ca, Mg, Al metals or their homologues
b) the organic solvent is separated off and
c) the polycarbonate obtained is worked up.
In the context of the invention, low in the metals mentioned or their chemical homologues means that the feedstocks preferably contain not more than 2 ppm, more preferably not more than 1 ppm and particularly preferably not more than 0.5 ppm and most particularly preferably not more than 0.2 ppm of total metal, in particular of the metals mentioned above and their homologues. The alkali metals are excluded from these limit values.
The feedstock sodium hydroxide solution should preferably be low in the metals mentioned. In particular, in relation to a 100 wt. % strength NaOH content, the sodium hydroxide solution should contain not more than 1 ppm, preferably not more than 0.5 ppm, more preferably not more than 0.3 ppm of an alkaline earth metal or its homologues. In particular, the feedstock sodium hydroxide solution should contain, in relation to a 100 wt. % strength NaOH content, not more than 1 ppm, preferably not more than 0.5 ppm, more preferably not more than 0.1 ppm of iron.
The sodium hydroxide solution is preferably used as a 20-55 wt. % strength, particularly preferably 30-50 wt. % strength solution in the process according to the invention.
A sodium hydroxide solution with the afore-mentioned limit values can be obtained by the membrane process known from the literature.
In a preferred embodiment, apart from the sodium hydroxide solution, the feedstock bisphenol, in particular bisphenol and water, most particularly preferably bisphenol, water and organic solvent are also low in metals, in particular low in Fe, Cr, Ni, Zn, Ca, Mg, Al.
Embodiments in which a sodium bisphenolate (solution) has previously been prepared from sodium hydroxide solution and bisphenol(s) are also included here.
These low-metal feedstocks are obtained by a procedure in which in a preferred embodiment the solvent is distilled, the bisphenol is crystallised, preferably crystallised several times or distilled, and fully deionised water is used.
The fully deionised water is preferably desalinated, degassed and/or desilicified. The electrical conductivity (sum parameter for ionogenic substances of the salt which are still present in trace amounts in the water), for instance, is used as a quality criterion, the fully deionised water in the process according to the invention being characterised by an electrical conductivity of 0.2 &mgr;S/cm (DIN 38404 C 8) and an SiO
2
concentration of 0.02 mg/kg (VGB 3.3.1.1) or in each case less.
The content of dissolved oxygen in the fully deionised water is preferably less than 1 ppm , more preferably less than 100 ppb.
In a further preferred embodiment, from among the group of feedstocks at least the sodium hydroxide solution, preferably also the bisphenol, particularly preferably the sodium hydroxide solution, the bisphenol and the water, most particularly preferably the sodium hydroxide solution, the bisphenol, the water and the organic solvent are filtered at least once, preferably twice, most particularly preferably stepwise three times, before starting the reaction.
The invention also provides a process for the preparation of polycarbonate by the phase boundary process, wherein dihydroxydiarylalkanes in the form of their alkali metal salts are reacted with phosgene in the heterogeneous phase in the presence of sodium hydroxide solution and an organic solvent, characterised in that
a) the feedstocks are low in Fe, Cr, Ni, Zn, Ca, Mg, Al metals or their homologues
b) the organic solvent is separated off and
c) the polycarbonate obtained is worked up;
d) the aqueous phase being produced during reaction is separated off and the separated organic polycarbonate phase is washed with an aqueous liquid and
e) the organic polycarbonate phase which has been washed and separated off from the wash liquid, optionally after filtration, is heated and filtered hot at least once.
In a preferred embodiment, the reaction mixture is filtered directly after reaction in process step d) and/or the organic polycarbonate phase which is obtained and separated is filtered and/or the organic polycarbonate phase obtained in process step e) is filtered.
Preferably at least two of these filtrations, in particular all three filtrations, are performed.
In a preferred embodiment, especially in the case of hot filtration, the mixture is filtered at least once, preferably twice, particularly preferably three times, in particular stepwise. In the case of stepwise filtration, coarser filters are used first and then these are replaced by finer filters. It is preferable to carry out the filtration of the two-phase media in process step d) with coarser filters.
In process step e), filters with smaller pore sizes are used for hot filtration. In this case it is important that the polycarbonate phase is present as the most homogeneous solution possible. This is achieved by heating the or
Bödiger Michael
Bruynseels Franky
de Cleyn René
Meirvenne Dirk Van
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