HK1051376A - Method of producing polycarbonates - Google Patents

Description

Method for producing polycarbonate

The invention relates to a method for producing polycarbonate, to polycarbonate substrates obtained according to said method and having a particularly high degree of purity, and to molded parts that can be produced from said polycarbonate substrates.

Polycarbonates are prepared by the so-called phase interface process, in which dihydroxydiarylalkanes in the form of their alkali metal salts are reacted in heterogeneous phase with phosgene in the presence of inorganic bases, such as caustic soda solution, and organic solvents in which the product polycarbonate is well dissolved. The aqueous phase is distributed in the organic phase during the reaction and the organic polycarbonate-containing phase is washed with an aqueous liquid after the reaction, in particular in order to remove further electrolytes, after which the washing liquid is separated off (H.Schnell "Chemistry and Physics of Polycarbonates", Polymer review, vol.IX, page 33 and below, Interscience Publishers, New York 1964).

For washing solutions containing polycarbonate, EP-A-264885 proposes stirring an aqueous washing liquid with the polycarbonate solution and centrifuging the aqueous phase.

In Japanese patent application JP-A-07196783, ｃA process for the preparation of polycarbonates is described in which the iron content of the caustic sodｃA solution used is below 2ppm in order to achieve suitable color properties.

The object of the present invention is to provide an alternative and improved method for producing pure polycarbonate or polycarbonate substrates and for producing polycarbonate moldings having a low impurity particle content (Fremdpartakelgehalt).

It has surprisingly been found that, if a special process is used, polycarbonate or polycarbonate substrates containing small amounts of foreign particles can be obtained.

The subject matter of the present application is a process for the preparation of polycarbonates by the phase interface process, in which dihydroxydiarylalkanes in the form of their alkali metal salts are reacted with phosgene in a heterogeneous phase in the presence of caustic soda solution and an organic solvent,

a) the raw materials used are depleted in iron, chromium, nickel, zinc, calcium, magnesium, aluminum or their homologues,

b) separating out the organic solvent

c) Processed polycarbonate

A depletion of the abovementioned metals or their chemical homologues in the sense of the present invention means that the starting materials used preferably contain a total metal content of not more than 2ppm, more preferably not more than 1ppm and particularly preferably not more than 0.5ppm and very particularly preferably not more than 0.2ppm, in particular the abovementioned metals and their homologues. Alkali metals are not included in this limit.

The starting caustic solution should preferably be depleted in the above-mentioned metals. In particular, the alkaline earth metal or homologues thereof content in the caustic soda solution is always not more than 1ppm, in particular not more than 0.5ppm, preferably not more than 0.3ppm, based on 100% by weight of NaOH content. In particular, the raw caustic soda solution contains no more than 1ppm, in particular no more than 0.5ppm, preferably no more than 0.1ppm, iron, based on 100% by weight of NaOH.

In the process of the invention, in particular from 20 to 55% by weight, particularly preferably from 30 to 50% by weight, of caustic soda solution are used.

The caustic soda solutions with the above-specified limits were obtained by membrane processes known from the literature.

In a preferred embodiment, in addition to the caustic solution, the starting materials bisphenol, in particular bisphenol and water, very particularly preferably bisphenol, water and organic solvent are depleted in metals, in particular in iron, chromium, nickel, zinc, calcium, magnesium and aluminum.

This also includes embodiments in which sodium bisphenolate solutions are prepared beforehand using caustic soda solutions and bisphenols.

These metal-depleted feedstocks are obtained by distilling the solvent in a preferred manner, crystallizing the bisphenol, preferably by multiple crystallization and distillation and using fully deionized water.

Fully deionized water is especially desalted, degassed and/or desilicated. For example, the conductivity can be taken as a quality criterion (overall parameter of the ion-forming species of the salts still present in trace amounts in water), wherein the completely deionized water is brought to a conductivity of 0.2. mu.S/cm (DIN 38404C 8) and SiO in the process according to the invention₂A concentration of 0.02mg/kg (VGB3.3.1.1) or always less. The dissolved oxygen content in fully deionised water is in particular less than 1ppm, preferably less than 100 ppb. Such an oxygen content is preferably adapted to all starting materials and process steps.

In a further preferred embodiment, at least the caustic soda solution, preferably also the bisphenol, particularly preferably the caustic soda solution, the bisphenol and water, very particularly preferably the caustic soda solution, the bisphenol, the water and the organic solvent of the starting material group are filtered at least once, preferably twice, very particularly preferably three times in stages before the reaction.

A further subject matter of the invention is a process for the preparation of polycarbonates by the phase interface process, in which dihydroxydiarylalkanes in the form of their alkali metal salts are reacted with phosgene in heterogeneous phase in the presence of caustic soda and an organic solvent, characterized in that,

a) the feedstock is depleted in iron-, chromium-, nickel-, zinc-, calcium-, magnesium-, aluminum-metal or homologues thereof;

d) separating off the aqueous phase formed in the reaction and washing the separated organic polycarbonate phase with an aqueous liquid; and

e) the organic polycarbonate phase which has been washed and is separated from the washing liquor, is optionally filtered and is heated and filtered at least once hot;

b) separating off the organic solvent and

c) the polycarbonate obtained is processed.

In a preferred embodiment, the reaction mixture is filtered directly after the reaction in process step d) and/or the organic polycarbonate phase obtained after the separation is filtered and/or the organic polycarbonate phase separated in process step e) is filtered.

Preferably, such filtration is carried out at least 2 times, in particular 3 times.

In a preferred embodiment, in particular in the hot filtration, at least one, preferably two, particularly preferably three, in particular stepwise, filtrations are carried out. In the case of progressive filtration, a coarser filter is used, followed by a finer filter. Preferably, the filtration of the two-phase medium in process step d) is carried out with a coarser filter.

The filters for hot filtration in method step e) use smaller pore sizes. For this purpose, it is important that the polycarbonate phase is present in as homogeneous a solution as possible. This is achieved by heating the organic polycarbonate phase which usually also contains residues of the aqueous washing liquor.

Here the wash solution is dissolved and forms a clear solution. Previously dissolved impurities, in particular dissolved alkali metal salts, precipitate out and can be filtered off.

To obtain a homogeneous solution, known freezing methods can be used in addition to the above-described method.

For the filtration of the present invention, membrane filters and sintered metal filters or bag filters are used as the filter. The filter typically has a pore size of 0.01 to 5 μm, particularly 0.02 to 1.5 μm, preferably about 0.05 to 1.0. mu.m. Such filters are commercially available, for example, from Pall GmbH, D-63363, Dreieich, and krebsb * ge GmbH, D-42477 Radevmwald (type SIKA-RCUIAS).

The combination of the methods according to the invention allows a significant increase in the service life of the filter.

Other method steps are generally known to be performed. This emulsifies the aqueous phase in the organic phase during the reaction. Where droplets of different sizes are formed. The organic phase containing the polycarbonate after the reaction is generally washed several times with an aqueous liquid and separated as far as possible from the aqueous phase after each washing process. The washing is preferably carried out with finely filtered, metal-depleted water. After washing and separation of the washing liquid, the polymer solution is generally cloudy. The wash liquid used is an aqueous liquid for separating the catalyst, a dilute mineral acid such as hydrochloric or phosphoric acid and a fully desalted water for further purification. The concentration of hydrochloric acid and phosphoric acid in the washing solution may be, for example, 0.5 to 1.0% by weight. The organic phase is preferably washed, for example, 5 times.

The phase separation apparatus used for separating the washing liquid from the organic phase is a separation vessel, phase separator, centrifuge or coalescer known in principle or a combination of these apparatuses may also be used.

To obtain a high purity polycarbonate, the solvent is evaporated. Multiple evaporator vaporizations can be performed. According to another embodiment of the invention, the solvent or a part of the solvent can be removed by spray drying. The high-purity polycarbonate is then obtained as a powder. The same applies to polycarbonates of high purity which are obtained by precipitation from organic solutions and subsequent drying of the residue. For example extrusion is a suitable means of evaporating the remaining solvent. Other processes are the rope evaporator process (Strangverdampfer technology).

Compounds which are preferably employed as starting materials are, for example, bisphenols of the general formula HO-Z-OH, where Z is an organic radical having from 6 to 30 carbon atoms which contains one or more aromatic radicals. These compounds are, for example, bisphenols belonging to the group of dihydroxydiphenyl, bis (hydroxyphenyl) alkane, indane bisphenol, bis (hydroxyphenyl) ether, bis (hydroxyphenyl) sulfone, bis (hydroxyphenyl) ketone and α, α' -bis (hydroxyphenyl) diisopropylbenzene.

Particularly preferred diphenols belonging to the above-mentioned compounds are 2, 2-bis- (4-hydroxyphenyl) -propane (bisphenol-A/BPA), tetraalkylbisphenol-A, 4, 4- (meta-phenylenediisopropyl) diphenol (bisphenol M), 1, 1-bis- (4-hydroxyphenyl) -3, 3, 5-trimethylcyclohexanone and, if desired, mixtures thereof. Particularly preferred copolycarbonates are those based on the monomers bisphenol-A, and 1, 1-bis- (4-hydroxyphenyl) -3, 3, 5-trimethylcyclohexane. The bisphenol compounds used in the present invention are reacted with carbonic acid compounds, in particular phosgene.

Polyester carbonates are obtained by reaction of the bisphenols already mentioned, at least one aromatic dicarboxylic acid and optionally carbonic acid. Suitable aromatic dicarboxylic acids are, for example, phthalic acid, terephthalic acid, isophthalic acid, 3, 3 '-or 4, 4' -diphenyldicarboxylic acid and benzophenone-dicarboxylic acid.

Inert organic solvents used in this process are, for example, dichloromethane, the various dichloroethanes and chloropropane compounds, chlorobenzene and chlorotoluene, in particular dichloromethane and mixtures of dichloromethane and chlorobenzene.

The reaction is accelerated by catalysts, such as tertiary amines, N-alkylpiperidines or onium salts. Tributylamine, triethylamine and N-ethylpiperidine are preferably used. Monofunctional phenols, such as phenol, cumylphenol, p-tert-butylphenol or 4- (1, 1, 3, 3, -tetramethylbutyl) phenol, can be used as chain terminators and molecular weight regulators. The branching agent may employ isatin xylenol.

To prepare high-purity polycarbonates, the bisphenols are dissolved in an aqueous alkaline phase, in particular in caustic soda solution. The chain terminators required for the preparation of copolycarbonates, if appropriate, are dissolved in the aqueous alkaline phase in amounts of 1.0 to 20.0 mol% per mole of bisphenol or are added in bulk in an inert organic phase. Phosgene is subsequently passed into a mixer containing the remaining reaction components and the polymerization is carried out.

Chain terminators which may be used are not only monophenols but also monocarboxylic acids. Suitable monophenols are phenol itself, alkylphenols, such as cresol, p-tert-butylphenol, p-cumylphenol, p-n-octylphenol, p-iso-octylphenol, p-n-nonylphenol and p-iso-nonylphenol, halophenols, such as p-chlorophenol, 2, 4-dichlorophenol, p-bromophenol and 2, 4, 6-tribromophenol, and mixtures thereof.

Suitable monocarboxylic acids are benzoic acid, alkylbenzoic acids and halobenzoic acids.

Preferably, the chain terminator is a phenol of formula (I)

Wherein

R is hydrogen, tert-butyl or C, branched or unbranched₈-and/or C₉-an alkyl group.

Preferred chain terminators are phenol and p-tert-butylphenol.

The amount of chain terminators to be used is in each case 0.1 to 5 mol% based on the molar amount of diphenols used. The chain terminators may be added before, during or after the reaction with phosgene.

If appropriate, branching agents may also be added in the reaction, preferred branching agents being compounds known from polycarbonate chemistry having three or more than three functional groups, in particular compounds having 3 or more than 3 phenolic OH groups.

Branching agents are, for example, phloroglucinol, 4, 6-dimethyl-2, 4, 6-tris- (4-hydroxyphenyl) -hept-2-ene, 4, 6-dimethyl-2, 4, 6-tris- (4-hydroxyphenyl) -heptane, 1, 3, 5-tris- (4-hydroxyphenyl) -benzene, 1, 1, 1-tris (4-hydroxyphenyl) -ethane, tris- (4-hydroxyphenyl) -phenylmethane, 2, 2-bis- [4, 4-bis (4-hydroxyphenyl) cyclohexyl ] -propane, 2, 4-bis- (4-hydroxyphenyl-isopropyl) phenol, 2, 6-bis (2-hydroxy-5' -methylbenzyl) -4-methylphenol, 2- (4-hydroxy-phenyl) -2- (2, 4-dihydroxyphenyl) propane, hexa- (4- (4-hydroxyphenyl-isopropyl) -phenyl) -o-phthalate (ortotherpthalos granule), tetrakis- (4-hydroxyphenyl) -methane, tetrakis- (4- (4-hydroxyphenyl-isopropyl) -phenoxy) -methane and 1, 4-bis (4', 4 "-dihydroxytriphenyl) -methyl) -benzene as well as 2, 4-dihydroxybenzoic acid, trimesic acid, cyanuric chloride and 3, 3-bis- (3-methyl-4-hydroxyphenyl) -2-oxo-2, 3-dihydroindole.

The amount of branching agents used, if appropriate, is 0.05 to 2 mol%, also in relation to the moles of diphenols used in each case.

The branching agents can either be introduced initially into the aqueous alkaline phase with the diphenols and the chain terminators or dissolved in an organic solvent before the phosgene reaction.

A portion of up to 80 mol%, in particular from 20 to 50 mol%, of the carbonate groups in the polycarbonate may be replaced by aromatic dicarboxylic acid ester groups.

The polycarbonates according to the invention are not only homopolycarbonates but also copolycarbonates and mixtures thereof. The polycarbonates according to the invention may be aromatic polyester carbonates or polycarbonates which are present in a mixture with aromatic polyester carbonates. The polycarbonate concept represents the polycarbonate substrate obtained by the process according to the invention.

The polycarbonates have average molecular weights Mw of from 12000 to 400000, in particular from 23000 to 80000 and especially from 24000 to 40000 (calculated by determining the relative viscosity at 25 ℃ in methylene chloride at a concentration of 0.5g of polycarbonate per 100ml of methylene chloride).

The moldings of the invention prepared from the high-purity polycarbonate substrates of the invention are, in particular, optical and magneto-optical data storage media, such as compact disks, compact disks or versatile digital disks, optical prisms and prisms, glazing and headlights on motor vehicles, other types of glazing, for example greenhouse glazing, so-called double-paneled panels (stegdoppel flat) or hollow or solid panels. These moldings are produced by injection molding, extrusion and extrusion-blow molding using the polycarbonates of the invention of suitable molecular weight.

Preferred molecular weight ranges for use as data carriers are 12000 to 22000, for use as prisms and glazing are 22000 to 32000, and for use as sheets and hollow sheets are 28000 to 40000. All molecular weight data are based on weight average molar weight.

The moldings of the invention optionally have a surface treatment, such as a scratch-resistant coating.

For the production of optical prisms and films and sheets for magneto-optical data carriers, it is advantageous to use polycarbonates according to the invention having a molecular weight of 12000 to 40000, since materials having a molecular weight in this range are outstandingly thermoplastically formable. The molded article can be manufactured by an injection molding method. For this purpose, the resin is melted by heating at 300 ℃ to 400 ℃ and the mold is generally kept at 50 ℃ to 140 ℃.

For example, for the production of plate-shaped data storage materials, the high-purity polycarbonates according to the invention are suitable for this purpose using known plastic injection molding machines.

In addition to the improved filter life, a further advantage of the process according to the invention is that the polycarbonate substrates obtained are distinguished by a particularly low number of defects of less than 250, in particular less than 150, per square meter, measured on extruded films of 200 μm thickness.

The following examples serve to illustrate the invention. The invention is not limited to this embodiment.

Examples

Example 1

To prepare polycarbonates, BPA (BPA as a melt is continuously brought together with caustic soda solution) is mixed in the caustic soda solution under exclusion of oxygen. The caustic soda solutions used were of varying concentrations and purities (see table 1), and to dissolve the bisphenols, the original caustic soda solution was diluted to a 6.5% caustic soda solution with filtered, fully deionized water. The sodium bisphenolate solution is filtered (0.6 μ a filter) and charged to the polycarbonate reaction. After the reaction, the reaction solution was filtered with a 1.0 μ nom bag filter and washed.

Here washed with 0.6% hydrochloric acid and then 5 more times with filtered, fully deionized water. The organic solution was separated from the aqueous solution and, after heating the organic solution to 55 ℃, filtered first with a 0.6 μ a filter and subsequently with a 0.2 μ a filter. After isolation, poly-2, 2-bis- (4-hydroxyphenyl) -propane carbonate is obtained. The polycarbonate average molecular weight Mw is 26000.

TABLE 1

Quality of caustic soda solution
					1	2	3
％NaOH	50	50	32
				Fe(ppm)	0.7	0.46	0.02
Ca(ppm)	2.0	0.4	＜0.1
				Mg(ppm)	0.5	0.2	＜0.1
Ni(ppm)	0.2	0.2	＜0.01
				Cr(ppm)	0.4	0.25	＜0.01
Zn(ppm)	0.1	0.05	0.06
				Total number (ppm)	3.9	1.56	＜0.3

Concentration in 100% NaOH	1	2	3
				Fe(ppm)	1.4	0.9	0.06
Ca(ppm)	4.0	0.8	＜0.3
				Mg(ppm)	1.0	0.4	＜0.3
Ni(ppm)	0.4	0.4	＜0.03
				Cr(ppm)	0.8	0.5	＜0.03
Zn(ppm)	0.2	0.1	0.19
				Total number (ppm)	7.8	3.1	＜0.9

TABLE 2

	Caustic soda solution for experiments
				Filter life	1	2	3
0.6 μ a-filter before reaction	12h	10d	30d
				Post-reaction 1.0. mu.a-filter	24h	30d	＞60d
End filter 1 ═ 0.6 μ a-filter end filter 2 ═ 0.2 μ a-filter	12h	3d	21d

The polycarbonate prepared from the caustic soda solution of experiments 1 to 3 was used for the extrusion of films and the film-laser scanning tests were carried out on these films in a known manner as described below.

The extruded film had a thickness of 200 μm and a width of 60 mm. He-Ne-laser ("spot diameter" of 0.1mm) was scanned over the film at a scanning frequency of 5000Hz in the width direction and a propagation speed of 5m/s in the length direction. All of the defective portions (from 0.10mm in diameter) in which the passed laser beam was scattered were detected by an optical amplifier and counted by software. Per kilogram of polycarbonate or per m²The number of optical defects of a film is a measure of the surface quality or purity of the polycarbonate of the film.

Evaluation of extruded films by laser scanning
					PC produced from the caustic soda solution tested
Surface area per square meter	1	2	3
				0.10-0.30mm	121	64	23
＞0.30mm	148	96	35
				Total number of	269	160	58

Claims (12)

1. A process for the preparation of polycarbonates by the phase interface process, in which a bis-hydroxydiarylalkane, in the form of its alkali metal salt, is reacted with phosgene in a heterogeneous phase in the presence of caustic soda solution and an organic solvent,

a) the raw material is depleted in iron-, chromium-, nickel-, zinc-, calcium-, magnesium-, aluminium-metal or homologues thereof,

b) separating out the organic solvent

c) The polycarbonate obtained is processed.

2. A process for the preparation of polycarbonates by the phase interface process, in which dihydroxydiarylalkanes in the form of their alkali gold salts are reacted with phosgene in a heterogeneous phase in the presence of caustic soda solution and an organic solvent,

a) the feedstock is depleted in iron-, chromium-, nickel-, zinc-, calcium-, magnesium-, aluminum-metal or homologues thereof;

d) the aqueous phase formed in the reaction, if appropriate after filtration, is separated and the organic polycarbonate phase separated off, if appropriate after filtration, is washed with an aqueous liquid and

e) the organic polycarbonate phase which has been washed and has been separated off from the washing liquor is, if appropriate after filtration, heated and filtered hot at least once;

b) the organic solvent is separated out and the organic solvent is separated,

c) processing the polycarbonate obtained

3. The process as claimed in at least one of the preceding claims, characterized in that the starting material contains less than 2ppm of metals or their homologues.

4. The process as claimed in at least one of the preceding claims, characterized in that the caustic solution used has a content of alkaline earth metals or homologues thereof of not more than 0.5ppm and/or an iron content of not more than 0.5ppm, based on 100% by weight of NaOH.

5. The process as claimed in at least one of the preceding claims, characterized in that the bisphenol used as starting material is depleted in iron, chromium, nickel, zinc, calcium, magnesium, aluminum metal or homologues thereof in addition to the caustic soda solution.

6. The process as claimed in at least one of the preceding claims, characterized in that at least the caustic soda solution of the raw material group is filtered before the reaction.

7. The method as claimed in at least one of the preceding claims, characterized in that the filter pore size used in the final filtration step is less than 2 μm.

8. Polycarbonate obtainable by the process according to at least one of the preceding claims.

9. Polycarbonate characterized by a number of defective sites of less than 250 per m2, measured on a 200 μm extruded film.

10. Use of the polycarbonates as claimed in claims 9 and 10 for the production of transparent moldings.

11. Use according to claim 11, for the production of laser-readable data storage media as molded parts.

12. A molded part made from a polycarbonate as claimed in one of claims 9 and/or 10.