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
2004-11-09
Boykin, Terressa (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C428S411100, C428S412000, C528S196000
Reexamination Certificate
active
06815524
ABSTRACT:
The invention provides polycarbonate substrates and their use for preparing moulded items with especially high purity and extremely high surface brilliance and the moulded items which can be prepared from the polycarbonate substrate.
For certain moulded items such as in particular glazing for motor vehicles and headlamps, glazing of other types such as so-called twin-wall sheets or hollow chamber sheets or solid sheets, high purity polycarbonate is required.
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 heterogeneous phase in the presence of inorganic bases such as sodium hydroxide solution and an organic solvent in which the product polycarbonate is very soluble. During reaction, the aqueous phase is distributed within 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.
In order to wash the polycarbonate-containing solution, EP-A-264 885 suggests stirring up the aqueous wash liquid with the polycarbonate solution and separating the aqueous phase by centrifuging.
Japanese application JP-A-07 19 67 83 describes a process for preparing polycarbonate in which the concentration of iron in the sodium hydroxide solution used is intended to be less than 2 ppm, in order to produce favourable colour characteristics.
The object of the present invention is the provision of an alternative and improved process for preparing pure polycarbonate substrates and the provision of polycarbonate moulded items with especially high purity and high surface brilliance.
Surprisingly, it has now been found that polycarbonate moulded items with especially high purity and high surface brilliance are obtained from polycarbonate substrates which are prepared by a special process.
Therefore, the application provides polycarbonate substrates with a low concentration of foreign particles and the polycarbonate moulded items with high surface brilliance prepared therefrom which are obtained by a process for preparing polycarbonate by the phase boundary method which is characterised in that, from the group of feedstocks, at least the feedstock sodium hydroxide solution contains very little Fe, Cr, Ni, Zn, Ca, Mg, Al or their chemical homologues.
The application therefore provides a process for preparing polycarbonate by the phase boundary process, wherein dihydroxydiarylalkanes in the form of their alkali metal salts are reacted with phosgene in heterogeneous phase in the presence of sodium hydroxide solution and an organic solvent, characterised in that
a) the feedstocks are low in the metals Fe, Cr, Ni, Zn, Ca, Mg, Al 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 preferably not more than 2 ppm, more preferably not more than 1 ppm and particularly preferably not more than 0.5 ppm and very particularly preferably not more than 0.2 ppm of total metal, in particular of the metals listed above and their homologues is contained in the feedstocks. These limiting values do not apply to the alkali metals.
It is intended that the feedstock sodium hydroxide solution should preferably be low in the metals mentioned. In particular, with reference to a 100 wt. % strength NaOH concentration, 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 alkaline earth metals or their homologues. In particular, with reference to a 100 wt. % strength NaOH concentration, the feedstock sodium hydroxide solution should contain not more than 1 ppm, advantageously not more than 0.5 ppm, preferably not more than 0.1 ppm of iron.
The sodium hydroxide solution is preferably used in the process according to the invention as a 20-55 wt. % strength, particularly preferably a 30-50 wt. % strength solution.
Sodium hydroxide solution with the limiting values mentioned above is obtainable by membrane processes known from the literature.
In a preferred embodiment, in addition to the sodium hydroxide solution, the feedstocks bisphenol, in particular bisphenol and water, very particularly preferably bisphenol, water and the organic solvent are low in metals, in particular low in Fe, Cr, Ni, Zn, Ca, Mg, Al or their chemical homologues.
Embodiments in which a sodium bisphenolate (solution) has been previously prepared from sodium hydroxide solution and bisphenol(s) are also included.
These feedstocks which are low in metal are obtained, in a preferred variant, by distilling the solvent, crystallising the bisphenol, preferably crystallising or distilling the bisphenol several times and using the water in a fully deionised quality.
The fully deionised water is preferably desalted, degassed and/or desilicified. The electrical conductivity (sum parameter for ionogenic substances from salts which are still present in trace amounts in the water) is used as a quality criterion, wherein in the process according to the invention the fully deionised water is characterised by an electrical conductivity of 0.2 &mgr;S/cm (DIN 38404 C 8) and a SiO
2
concentration of 0.02 mg/kg (VGB 3.3.1.1), or less than each of these.
The concentration of dissolved oxygen in the fully deionised water is advantageously less than 1 ppm, preferably less than 100 ppb. This oxygen concentration is preferably applied to all starting substances and process steps.
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 preferably the sodium hydroxide solution, the bisphenol, the water and the organic solvent are filtered once, preferably twice, particularly preferably three times step-wise, before the start of reaction.
The invention also provides a process for preparing polycarbonate by the phase boundary process, wherein dihydroxydiarylalkanes in the form of their alkali metal salts are reacted with phosgene in heterogeneous phase in the presence of sodium hydroxide solution and an organic solvent, characterised in that
a) the feedstocks are low in the metals Fe, Cr, Ni, Zn, Ca, Mg, Al or their homologues
b) the aqueous phase being produced during reaction is separated and the separated organic polycarbonate phase is washed with an aqueous liquid and
c) the washed, and separated from the wash liquid, organic polycarbonate phase, optionally after filtration, is heated and filtered hot at least once;
d) the organic solvent is separated off and
e) the polycarbonate obtained is worked up.
In a preferred embodiment, in process step d), the reaction mixture is filtered directly after reaction and/or the organic polycarbonate phase obtained and separated is filtered and/or the organic polycarbonate phase separated in process step e) is filtered.
Preferably at least two of these filtration procedures, in particular all three filtration procedures, are performed.
In a preferred variant, in particular in the case of hot filtration, the mixture is filtered at least once, preferably twice, particularly preferably at least three times, in particular step-wise. In the case of step-wise filtration, coarser filters are used first and then these are replaced by finer filters. The filtration procedure for the two-phase media in process step d) is preferably performed with coarse 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 organic polycarbonate phase, which generally still contains residues of aqueous wash liquid. The wash liquid then dissolves and a clear solution is produced. The previously dissolved contaminants, in particular dissolved
Bödiger Michael
Bruynseels Franky
de Cleyn René
Kühling Steffen
Meirvenne Dirk Van
Bayer Aktiengesellschaft
Boykin Terressa
Gil Joseph C.
Preis Aron
LandOfFree
Polycarbonate substrates does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Polycarbonate substrates, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polycarbonate substrates will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3363444